Designing of a hand rehabilitation robotic device for the ... · All the robotic system may use 2...

SCHOOL OF INDUSTRIAL AND

INFORMATION ENGINEERING

Master of Science in Biomedical Engineering

Designing of a hand rehabilitation

robotic device for the post-stroke

patients with flaccidity

supervisor: prof. Carlo Albino FRIGO

Paweł Leszek Michalec

893315

Academic Year 18/19

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Table of Contents

Summary .........................................................................................................................2

Sommario ........................................................................................................................ 7

1. Introduction ........................................................................................................... 13

1.1. Stroke ............................................................................................................... 13

1.2. Defining the scope of thesis ............................................................................. 15

1.3. Outline ............................................................................................................. 16

2. Theory section ........................................................................................................ 17

2.1. Natural and flaccid paralysis hand motion ..................................................... 17

2.2. Hand rehabilitation devices ............................................................................ 19

3. Method section ....................................................................................................... 25

3.1. Project assumptions ........................................................................................ 25

3.2. Concept ........................................................................................................... 28

3.3. Data collecting, calculations, and element selection ..................................... 32

3.4. Prototype ......................................................................................................... 46

3.5. Control ............................................................................................................ 50

3.6. Analysis of the prototype ................................................................................. 52

4. Discussion .............................................................................................................. 57

5. Conclusion .............................................................................................................. 59

References ..................................................................................................................... 61

2

Summary

Prolonged lifetime brings a big number of various diseases and health cases in old

age. One of the major problems is the stroke, that has a huge impact on people quality

of life. Almost 70% of the post-stroke patients suffer from some disabilities connected

to it. Stroke, occurs whenever there is a blood or a clot blocking the blood flow

to the brain, what leads to death of the brain cells. It can cause some minor

disabilities, partial paralyze, and leads even to death.

The major treatment after the stroke is rehabilitation. It starts in the very first

days of hospitalization to recover as many muscles function as it is possible.

In the first weeks after the stroke, the patient suffers from the flaccidity,

that is caused by the muscles weakness. Later, antagonist muscles start to voluntary

tense, what leads to the spasticity.

At the beginning, rehabilitation focuses on stabilization of the hip

and shoulder joint. In the next step, therapy tries to recover functionality of the limbs

during everyday tasks. Physiotherapists help patients to function independently.

The ability of grasping and moving objects is essential for the normal life,

however, rehabilitation of the hand is not always sufficient, what leads to poor

recovery of it. The aim of this thesis is to design a robotic device for a hand

rehabilitation of the post-stroke patients suffering from flaccidity.

Due to the complexity of the subject, first the theoretical studies about stroke

and flaccidity were done. They gave better look on the difference between the affected

and the healthy hand movement. A hand has 21 degrees of freedom (DoF) thanks

to the big number of joint and muscles. The importance of the hand is also visible

in the big size of the area of the brain, that represents a hand motions and sensation.

The advantage of the robotic rehabilitation is huge compared to the traditional

one. It gives feedback of the recovery process, what can be used in the future

development of guidelines for rehabilitation. Moreover, the time of each training can

be extended, while maintaining a low cost of it.

All the robotic system may use 2 types of a control. The Continuous Passive

Motion (CPM) is used in almost all types of the robots. The device constantly moves

affected joints between established range of motion. However, the muscles of the

hand of the patient do not work during this type of exercise. This technique helps

with restoring proper nerve signal flow, nevertheless there is only small recovery

occurring.

The second type of the control is an active system. The robot follows intentions

of the patient, so the movement is not influenced by the robot. Whenever, there

is a need of help, the robot starts to move. The signal can be process in different ways.

It can use strain gauges, force sensors or biological signals like surface

electromyography (sEMG).

3

Analysis of existing rehabilitation robots was made. Gloreha, that uses

hydraulic system connected to the soft glove, achieves the movement of all the fingers

by pulling and pushing them from the dorsal side of the hand. There was reported

better blood flow and increased of a grip strength of the patient that were using this

robot. However, this robot is limited only to flexion and extension of the fingers

to the grip position with no division to specific finger joint.

The next robot, Amadeo, has 5 DoF and it has a shape of a board on which

there are 5 sliders. Physiotherapist connects the arm of the patient to the board,

and each finger to the slider. Thanks to the device, patient may achieve grip and

extension position. It works with kids and adults. However, not all the range of finger

motion is covered by this robot.

Hand of Hope is a glove shaped robot, that uses electric micro motors

to achieve movement. The electromyography (EMG) and electroencephalography

(EEG) signals are used to activate motors. This device has 4 different modes

of training: CPM, EMG triggered movement, EMG based movement, and active

system. Unfortunately, this robot has only 5 DoF and it is limited to the gripping

movement.

The highest prospecting soft actuator robot, developed by Polygerinos, uses

material, that change its shape by fluid flow. Thanks to that, the patient can execute

very complex tasks. Nevertheless, not many researches of using this robot was made.

All the devices improve grip strength, but usually they are not handy

and transportable. They strongly simplify the movement of the fingers, and only some

of them, the patient can wear without supervision of physiotherapist. It seems

the soft glove made by Polygerinos gives the most complex movement and meets

the biggest number of assumptions for the rehabilitation device. However, this

research also proves, there is not enough products to help patient to fully recover

their ability of hand movement after the stroke.

Based on the given knowledge, guidelines of the project were identified.

The major assumption is to design the robot, that can be used at home. Because

of the high occupancy of physiotherapists, the traditional rehabilitation may not be

enough to recover the hand motion. Home therapy brings, economic advantages

and rehabilitation progress because of the higher involvement of the patient

in the therapy.

However, it is crucial to make device save to use by the patient without

supervision of the physiotherapist. Moreover, if it is too expensive it will not be

borrowed or bought by the patient. It has to be transportable and simple, to make

the post-stroke patients able to use it safely. The last technical factor is to use

the source of the energy, that is accessible at home. The power should be focused

on the electricity.

An executed movement of the device should replicate kinematic movement

of the fingers, what will lead to proper recovery. Even with lower number of DoF,

compared to the biological hand, the movement can still be healthy for the patient,

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as all the rehabilitation robots works. Also the position of the joints of the device

should be the same as the position of the biological joints. Otherwise the patient

could be injured.

The range of motion should cover all the possible movements of the hand,

and the device should use a force of 15 N, that is not exceed during daily living

activities. The frequency of the task execution should oscillate around 30 cycles

per minute.

The control should give a possibility of choosing between active and passive

system, as this is a norm for the rehabilitation robots.

With necessary background, a concept of the device was created and the 3D

model was designed. The designed device is aimed at rehabilitation of flexion

and extension movement of the metacarpophalangeal joint (MP joint)

and the proximal interphalangeal joint (PIP joint) of 4 fingers: index, middle, ring,

and pinkie. The design was focused on using the device at home without supervision

of physiotherapist.

The patient puts the affected hand inside the ABS 3D printed wrist holder, that

has a soft glove with 2 C-rings on each finger. C-rings are placed between the MP

and the PIP joint and between the PIP and the distal interphalangeal (DIP) joint.

Each C-ring is connected to the motor and the spring by wire. The motors pulls

the wires and position each joint in the extension position. From the bottom,

whenever the motors release wires, springs pull the fingers to the flexion position.

A direction of the movement of the wires is changed by the wheel systems placed

on the wrist holder and the frame. Thanks to them, the motor and the spring system

was placed on the front of the device. The concept with listed elements is shown

in figures 0.1 and 0.2.

Figure 0.1 - wearable part of a device [38]

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Figure 0.2 - interior of the device with open side cover [38]

The motor system is placed inside the motor box. Moreover, the motor box

contains a power board, a microcontroller, an electric lock, and the Wheatstone

bridges. The wires are attached to the plate with strain gauges on it. The strain gauge

collects information of the occurring tension on the wire, and sends the signal

to the microcontroller. Based on this signal, control was made. The concept with

listed elements is shown in figure 0.3.

Figure 0.3 - interior of the motor box [38]

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The whole interior of the device is fixed to the telescopic slides, that can be

slide out from the frame for easier installation of the hand. The magnetic sensors

where used to check if everything is in the right position before a training starts.

The force on each joint was measured. The maximal force, that can be created

by the springs was set. For the MP joint it was 27 N and for the PIP joint it was 18 N.

The distance of the movement between end positions was 50 mm and 100mm. Based

on that springs, Vanel U.092.080.0500.IX and T.087.070.0380.A, were selected.

Next, servo motors were selected. Needed torque to overcome the springs

and additional 15 N was calculated. This value was taken as a maximal force created

during everyday life activities. Chosen servo motors were Hitec HS-5645MG

for the MP joint and Hitec HS805 for the PIP joint.

The minimal thickness of 3D printed elements was calculated. All thicknesses

of the sections of the wrist holder were set at 5 mm. The dimension of the aluminum

alloy shaft of the wheel system was 6mm and the wires dimension 1,07 mm.

The used force sensors were 5 kg Micro load cells by Phidgets with dedicated

Wheatstone Bridges 1046-0B. The magnetic sensors were Schmersal BNS 250.

Everything was connected to the microcontroller STM32F411E Discovery. The device

starts by clicking RobotShop Rocker Switch. The power supply for all the 5V

instrumentation was Botland PMT 5V50W1AA. Moreover, because of the movement

of the interior part, e-chain Igus 0.26m E2i.10.06.018.0 + E2.100.06.12PZ.A1

was used.

In the last part, the prototype, that was based on the 3D model, was built

and ran with dedicated software to primary validate functionality of the robot.

However, the prototype was designed only for 1 finger control, what is enough

to validate functionality of it. Moreover, no telescopic slides were used. They do not

affect the functionality of the robot.

The created software sends the pulse width modulation (PWM) signal

to the motors, collects data from the strain gauges and runs the device in 4 different

modes: passive, active, resistive, and test. The test mode was created to manually

control motors and to collect data for calibration and analysis of the functionality.

Moreover, there were created 4 tasks to execute. The application was created

in C# language.

To properly run the device all the task position were found. Next, the change

of voltage of strain gauges was analysis, and based on it, the influence of the spring

was found and the thresholds set. At the end, all the created functions of the program

were validated with a positive result. The software gives a possibility of using 3 modes

of the training.

The biggest advantage of the designed robot, comparing to other existing

solutions, is the possibility of using it at home. Even if it does not cover the whole

range of hand motion, it still provides possibility of separate movement of the MP

and the PIP joint.

7

The closed palm design does not allow using the device as a portable glove

in everyday life activities. Moreover, there is no thumb rehabilitation, what should

be added in the future development.

The prototype demonstrated the functionality of the device and gave a good

prospect for the future development and use of the robot as an additional tool

in the traditional rehabilitation.

Sommario

Il prolungamento della durata della vita comporta il verificarsi di numerosi disturbi

e patologie in età avanzata. Uno dei maggiori problemi è l'ictus, che ha un impatto

enorme sulla qualità della vita delle persone.

Circa il 70% dei pazienti che hanno subito ictus soffre di alcune disabilità

ad esso collegate. L’Ictus può verificarsiquando un coagulo di sangue blocca il flusso

sanguigno al cervello, determinando la morte delle cellule cerebrali e causando

alcune disabilità minori, paralisi parziali e persino la morte.

Il trattamento principale dopo l'ictus è la riabilitazione. Essa comincia nei

primissimi giorni di ricovero in ospedale per recuperare quante più funzioni

muscolari possibile. Nelle prime settimane dopo l'ictus, il paziente soffre di flaccidità,

causata dalla debolezza muscolare. Successivamente, i muscoli antagonisti iniziano

a contrarsi volontariamente, portando alla spasticità.

Inizialmente, la riabilitazione si concentra sulla stabilizzazione dell'anca e della

spalla. Il passaggio successivo della terapia è volta a ripristinare la funzionalità degli

arti durante le attività quotidiane. I fisioterapisti aiutano i pazienti a muoversi

in modo indipendente.

La capacità di afferrare e spostare oggetti è essenziale per la vita ordinaria,

tuttavia, la riabilitazione della mano non è sempre sufficiente e comporta uno scarso

recupero delle sue funzionalità. L’obiettivodella presente tesi è progettare

un dispositivo robotico per la riabilitazione della mano dei pazienti che hanno subito

ictus e che soffrono di flaccidità.

Data la complessità dell’argomento, in primo luogo è stato condotto uno studio

teoretico sull’ictus e sulla problematica della flaccidità. Uno degli aspetti evidenziati

è la differenza tra il movimento della mano colpita dalla patologia e quella sana.

La mano possiede 21 gradi di libertà (GdL) permessi dal gran numero di articolazioni

e muscoli. L'importanza della mano si rispecchia anche nelle grandi dimensioni

dell'area del cervello dedicata al suo movimento e percezione tattile.

Il vantaggio della riabilitazione robotica è enorme rispetto a quello tradizionale: essa

fornisce feedback sul processo di recupero, i quali possono essere utili

nel futuro sviluppo di linee guida per la riabilitazione. Inoltre, la durata di ciascun

allenamento può essere prolungata, pur mantenendo un costo contenuto.

Tutti i sistemi robotici possono utilizzare due tipi di controllo. Il movimento

passivo continuo (CPM) è utilizzato in quasi tutti i robot. Il dispositivo muove

costantemente le articolazioni interessate nel range di movimento stabilito. Tuttavia,

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i muscoli della mano del paziente non lavorano durante questo tipo di esercizio.

Questa tecnica aiuta a ripristinare il corretto flusso del segnale nervoso, mail

recupero che ne consegue è basso.

Il secondo tipo di controllo è il sistema attivo. Il robot segue le intenzioni

del paziente, quindi il movimento non è stabilito dal robot. Ogni volta che c'è bisogno

di aiuto, il robot inizia a muoversi. Il segnale può essere elaborato in diversi modi.

Possono essere utilizzati estensimetri, sensori di forza o segnali biologici come

l'elettromiografia di superficie (sEMG).

È stata effettuata l'analisi dei robot per la riabilitazione attualmente esistenti.

Gloreha, che utilizza un sistema idraulico collegato ad un guanto, permette

il movimento di tutte le dita tirandole e spingendole verso il lato dorsale della mano.

I pazienti che hanno utilizzato questo robot hanno riportato un miglioramento

del flusso sanguino e della forza di presa. Tuttavia, questo robot si limita solo

alla flessione e all'estensione delle dita nella posizione di presa senza suddividere

il movimento per ogni articolazione specifica delle dita.

Il secondo robot, Amadeo, possiede 5 GdL ed è costituito da una piattaforma

in cui vi sono 5 cursori. Il fisioterapista collega il braccio del paziente alla piattaforma

e ogni dito a ciascun cursore. Grazie al dispositivo, il paziente può effettuare

la posizione di presa ed estensione.

Il robot può essere utilizzatosia con bambini che con adulti. Purtroppo, anche

in questo caso l’ampiezza del movimento delle dita è limitata.

Hand of Hope è un guanto robotico che utilizza micro-motori elettrici per

effettuareil movimento. I segnali ottenuti dall’elettromiografia (EMG)

e dall'elettroencefalografia (EEG) vengono utilizzati per attivare i motori. Questo

dispositivo ha quattro diverse modalità di allenamento: CPM, movimento attivato

da EMG, movimento basato su EMG e sistema attivo. Sfortunatamente, questo robot

ha solo 5 GdL ed è limitato al movimento di presa.

Il robot ad attuatori flessibilipiù promettente è stato sviluppato da Polygerinos,

caratterizzato dall’utilizzo di un materiale che cambia forma grazie al flusso

di un fluido che scorre al suo interno. Grazie a questo meccanismo il paziente può

eseguire compiti molto complessi. Eppure, non sono ancora stati effettuati sufficienti

studi sui risultati dell’utilizzo di questo dispositivo.

Tutti questi dispositivi migliorano la forza di presa, ma non sono di semplice

utilizzoo trasportabili, semplificano eccessivamente il movimento delle dita e solo

alcuni di essi possono essere indossati dal paziente senza la supervisione

del fisioterapista. Sembra che il guanto flessibile realizzato da Polygerinos permetta

il movimento più realistico e soddisfi il maggior numero di requisiti per i dispositivi

di riabilitazione. Questa ricerca dimostra che non ci sono abbastanza dispositivi

in commercio per aiutare il paziente a recuperare completamente la propria capacità

di movimento della mano a seguito di un ictus.

Sulla base delle conoscenze ottenute, sono state definite le linee guida

del progetto. Il requisito principale è la possibilità dell’uso domestico del robot.

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La riabilitazione tradizionale potrebbe non essere sufficiente per recuperare

il movimento della mano, a causa delle tempistiche ospedaliere. La terapia

domiciliare porta vantaggi economici e progressi nella riabilitazione grazie

al maggiore coinvolgimento del paziente nella terapia.

Per l’utilizzo domestico è fondamentale rendere sicuro il dispositivo

per il paziente senza la supervisione del fisioterapista. Deve essere trasportabile

e semplice, per consentire ai pazienti post-ictus di utilizzarlo in sicurezza.

Un ulteriore requisito tecnico riguarda la fonte di energia impiegata, che deve essere

accessibile da casa, come ad esempio l’energia elettrica.

Ogni movimento eseguito del robot dovrebbe replicare la cinematica fisiologica

delle dita per ottenere un corretto recupero. Anche se con un numero di GdL inferiore

rispetto a quelli permessi da una mano in salute, il movimento può ancora portare

beneficio al paziente, come dimostrano i robot attualmente disponibile. Le posizioni

articolari assunte dal dispositivo dovrebbero rispecchiare quelle fisiologiche, per non

recare danno al paziente.

Il dispositivo dovrebbeincludere tutti i possibili movimenti della mano,

impiegando una forza massima di 15 N, da non superare durante le attività

quotidiane. La frequenza di esecuzione delle attività dovrebbe oscillare intorno

a 30 cicli al minuto.

Come è di norma per i robot di riabilitazione, dovrebbe essere data

la possibilità di scelta tra sistema di controllo attivo o passivo.

Alla luce delle conoscenze necessarie sono state definite le specifiche

di progetto del dispositivo e un corrispondente modello 3D. Il robot è finalizzato

alla riabilitazione della flessione e del movimento di estensione dell'articolazione

metacarpo-falangea (articolazione MP) e dell'articolazione interfalangea prossimale

(articolazione PIP) di 4 dita: indice, medio, anello e mignolo. Il design

si è concentrato sull'utilizzo del dispositivo in casa senza la supervisione

del fisioterapista.

Il paziente posiziona la mano interessata all'interno del supporto per il polso

realizzato in ABS tramite stampante 3D, dotato di un guanto flessibile con 2 anelli a C

su ciascun dito. Gli anelli a C sono posizionati tra l’articolazione MP e l'articolazione

PIP e tra la PIP e l'articolazione interfalangea distale (DIP). Ogni anello a C

è collegato al motore e alla molla tramite uncavo. I motori tirano i cavi e posizionano

ciascuna articolazione nella posizione di estensione. Ogni volta che i motori rilasciano

i cavi, le molle posizionate in basso tirano le dita nella posizione di flessione.

La direzione del movimento dei cavi viene modificata dai sistemi di ruote posizionati

sul supporto del polso e sul telaio. In tal modo è stato possibile posizionare motore

e il sistema a molla sulla parte anteriore del dispositivo. Il disegno del prototipo

con l’elenco dei diversi elementi è mostrato nelle figure 0.1 e 0.2.

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Figura 0.1 - parte indossabile del dispositivo [38]

Figura 0.2 - interno del dispositivo con coperchio laterale aperto [38]

Il sistema motorizzato è localizzato dentro la scatola motore, la quale dotato

di una scheda di potenza, un microcontrollore, una serratura elettrica e dei ponti

di Wheatstone. I cavi sono fissati alla piastra con degli estensimetri. L'estensimetro

trasduce la tensione del cavo in un segnale elettrico utilizzato dal microcontrollore.

Il controllo è stato effettuato sulla base di questo segnale. Il disegno del prototipo

con l’elenco dei diversi elementi è mostrato nella figura 0.3.

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Figura 0.3 - interno della scatola motore [38]

L’interno del dispositivo è fissato alle guide telescopiche, che possono essere

estratte dal telaio per facilitare l'inserimento della mano. I sensori magnetici hanno

lo scopo di verificare la corretta posizione prima dell'inizio di un allenamento.

Le molle Vanel U.092.080.0500.IX e T.087.070.0380.A. sono state

selezionate in base alle misure di forza su ogni articolazione e alla forza massima

impostata. Per l'articolazione MP si è ottenuto 27 N e per l'articolazione PIP, 18 N.

L’ampiezza del movimento risultante è data dalla differenza tra le posizioni finali

di 50 mm e 100 mm.

Successivamente, i servo motori sono stati selezionati calcolando la coppia

necessaria per vincere la forzadalle molle con 15 N aggiuntivi. Questo valore è stato

preso come forza massima impiegata durante le attività della vita quotidiana.

I servomotori scelti per le articolazioni MP e PIP sono Hitec HS-5645MG e Hitec

HS805 rispettivamente.

Lo spessore delle sezioni del supporto per polso stampato 3D è stato fissato

a 5 mm. La dimensione dell'albero in lega di alluminiodel sistema a ruotaè di 6 mm

e la lunghezza dei cavidi 1,07 mm.

I sensori di forza utilizzati sono celle di carico Micro da 5 kg di Phidgets

con ponti di Wheatstone 1046-0B. I sensori magnetici sono iSchmersal BNS 250.

Gli elementi sono collegati al microcontrollore STM32F411E Discovery.

Il dispositivo si avvia attivando l’interruttore RobotShop Rocker. Per tutta

la strumentazione a 5v è stato utilizzato l’alimentatore Botland PMT 5V50W1AA.

12

Inoltre, per evitare movimenti all’interno del dispositivo è stata utilizzata

la e-chain Igus 0,26m E2i.10.06.018.0 + E2.100.06.12PZ.A1.

In fine, il prototipobasato sul modello 3D è stato realizzato e gestito con

un software creato appositamente per la convalida primaria della funzionalità

del robot, per la quale è stato sufficiente progettare il prototipo solamente

per il controllo di un dito. Non sono state utilizzate guide telescopiche poiché

non influiscono sulla funzionalità del robot.

Il software creato invia il segnale di Pulse Width Modulation (PWM) ai motori,

raccoglie i dati dagli estensimetri e permette il funzionamento del dispositivo

in 4 diverse modalità: passivo, attivo, resistivo e test. La modalità test è stata creata

per poter controllare manualmente i motori e per raccogliere dati per la calibrazione

e l'analisi della funzionalità. In totale sono state create 4 attività da eseguire.

Per la programmazione è stato impiegato il linguaggio C#.

Per eseguire correttamente il dispositivo sono state calcolate tutte le posizioni

dell'attività. Successivamente, è stata analizzata la variazione di tensione degli

estensimetri e, sulla base di quest’ultima, è stata calcolata l’azione della molla e sono

state fissate le soglie. In fine, tutte le funzioni create del programma sono state

validate ottenendo un risultato positivo. Il software offre la possibilità di utilizzare

3 modalità di allenamento.

Il più grande vantaggio del robot progettato, rispetto ad altre soluzioni

esistenti, è la possibilità di utilizzarlo comodamente in casa. Anche se non copre

l'intera gamma di movimenti possibili della mano, offre comunque la possibilità

di un movimento separato dell’articolazione MP e dell'articolazione PIP.

Il design a palmo chiuso non consente tuttavia l'utilizzo del dispositivo come

guanto portatile nelle attività quotidiane e la riabilitazione del pollice non è permessa.

Il prototipo ha dimostrato la piena funzionalità del dispositivo e ha fornito una buona

prospettiva per il futuro sviluppo e l’utilizzo del robot come strumento aggiuntivo

nella riabilitazione tradizionale.

13

1. Introduction

1.1. Stroke

The progress of medicine has a huge influence on people's health and length of their

life. In Europe the life expectancy at birth is 80,6 years (data from 2015), while

in 1990 it was 75 years. Because of expanding of the life time, there is more and more

people over 65 years old. In the World in 2016 the group of elderly was 19,2%

of population, and now it keeps increasing. However, due to the populations ageing,

the number of various diseases and health cases affecting them also increases [1,2].

In recent years in Europe smaller percentage of people having a stroke was

observed. However, with increasing number of older people, the number of strokes

is higher and keeps growing through the years. Chart 1.1 shows an increasing number

of discharges of post-stroke patients from the hospitals over 20 years. These numbers

were growing through the years [1,3].

Chart 1.1 - Rates of hospital discharges for stroke (1990 - 2010) in Europe and Europe Union [3]

In 2015 the number of recorded stroke incidences in Europe was 1 555 365.

In this group female were majority - around 56,5%. The forecasts predicts that

the number of recorded stroke incidence will increase by 34% before 2035 [3].

Data shows that at the end of 2015 there were almost 1200 post-stroke people

per 100 000 people living in Europe. In each country the percentage of post-stroke

people who get a health care was different. This numbers are between 10% to 80%.

Moreover, rehabilitation care in Europe is not everywhere developed properly, while

it is one of the main processes, which helps to recover correct functionality

of the body [1].

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Stroke is one of the major cause of the death and the biggest cause of disability

of adults. There can be distinguish two most common types of stroke. First one

is ischaemic stroke which covers 85% of all strokes incidence and have place when

blood flow is blocked by a clot and it does not go to the brain. Haemorrhagic stroke

occurs when there is a burst of blood vessel. Both types lead to death of the brain

cells, hence depending on the time of the stroke it can lead to small disabilities which

may be fully recovered, or to paralysis or even to death. More than 2/3 post-stroke

patients suffer from some disabilities [1,4].

When the stroke occurs, the opposite side of the body to the side of a brain

where stroke took place is paralyzed. Paralysis can affect up to the half of the body.

Moreover, stroke can cause lower motor functionality, problems with speaking

and understanding, loss of vision or delusions. It is important to make an immediate

diagnosis because any delay brings a bigger damage of a brain. Patient with diagnosis

of stroke are immediately transferred for a surgical treatment to remove a cause

of the stroke - blood or a clot. After successful surgery the patient stays on a drug

therapy to decrease probability of another stroke. The rehabilitation process

is initiated in the first few days [4,5].

The rehabilitation process helps patients to fully or partly recover of their

motor functionality, which is necessary in almost all daily activities.

Early mobilization benefits the patients. There is a focus on lower limb to make able

the patient to walk safety. Moreover, it is important to protect the shoulder.

Because of the flaccidity, muscle tone is lower and the shoulder joint is not stable.

Then minor paresis are under care. With a proper rehabilitation process some stages

of recovery can be distinguished [5,8].

In the first period after stroke, flaccid paralysis occurs, that means there

is a lack of voluntary movements, hence a patient cannot contract the muscles.

Flaccid paralysis take place due to the nerve damage, which affects a proper signal

connection in the way brain-muscles. Subsequently muscles loss occurs.

The antagonist muscles stay tensed. This unbalance situation, after few months,

leads to the second stage [8].

During the second stage, in some muscles redevelopment of limb synergies

begins, what leads to a small spasticity, pain, and uncontrollable muscle movements.

Also a small voluntary movements occur. Between 25% to 43% of patients suffer

spasticity in the first year after stroke. Due to the time, there is an increase

of the spasticity [8].

Post stroke hand, during a wrist drop exercise, acts differently than a healthy

hand. For a flaccidity, a flexion is exacerbated while in spasticity involuntary

extension occurs. Difference in behavior of the wrist during the wrist drop for spastic

and flaccid paresis is shown in figure 1.2.

15

Figure 1.2 - Wrist drop (B) - flaccid paresis (C) - spastic paresis [28]

However, with a proper rehabilitation care, effects of stroke can decrease

or fully disappear and increase control over the muscles. With time the complex

movements may be performed up to full recovery. Nowadays the rehabilitation

process is a golden standard to treat post-stroke patients [8,9].

1.2. Defining the scope of thesis

The most common post stroke issue is motor impairment. Almost 80% of patient

who had a stroke suffer from it. A patient who needs an acute rehabilitation in 32%

during first 3 months suffer from upper limb spasticity. Only a small group

of patients fully recover their upper limb functionality. That leads to the problems

in daily life activities which very often requires use of hands [9,10].

The researches show that the fastest recovery process happens in first 4 weeks.

In next 3-6 months the progress slows down. Rehabilitation acts positively

on mechanism of plasticity and brings short and long term gains in motor control.

Passive mobilization activates a motor network and promotes motor recovery.

Moreover, in the hemiparesis stage the immobilized bones of joints have a tendency

to decrease their density what may lead to pain or fracture [11,12,13,16].

It is important to perform rehabilitation in all post-stroke stages and focus on

all joints and muscles not to lead to any complications. However, 4 physiotherapists

from Poland, in the interview for the purpose of this paper, have said that the hand

rehabilitation is very often overlooked because of the lack of time with individual

patient and long recovery process with no visible results in the short period of time.

Physiotherapists are more focused on the lower limb rehabilitation and recovery

of the shoulder and elbow joint which have a bigger impact on a daily life activities

than precise movement of the wrist and fingers.

Robotic therapy brings a lot of advantages. There are highly repetitive,

the training may be more intense and more frequent, what decreases load of work

16

of physiotherapist. Also the movement of any task is finished and precise.

Moreover, it gives recovery data from the session which can be analyzed and used

in the future studies. Although the robots are used worldwide, it is not clearly

understood what are exact advantages of this kind of therapy in post-stroke care.

Nowadays the golden standard is to use robots therapy in parallel to the conventional

therapy, what seems to give the highest progress [9,17].

Home-based rehabilitation is also an expected way of treatment.

From the economic point of view it reduces the cost of rehabilitation process

by decreasing time spent in the health care institution. From the rehabilitation point

of view it brings to the patient an additional motivation while spending time

with family. Patients are more satisfied with this kind of therapy. However,

there are some issues with safety of the patient and lack of specific equipment

in the home environment. Also the researches in the area of potential hazard

or negative effects of home-based rehabilitation are limited [9].

Researches already showed that home-based therapy combined with regular

rehabilitation care, increases patients independence. Cochrane Collaboration review

showed that there is a bigger improvement in actives of daily living (ADL) for home

rehabilitated patients than treated in the conventional way [18].

This work will try to solve a problem of insufficient help in post-stroke patients

life and possibility of higher progress in hand recovery. The goal is to design

and preliminary test a robotic device for recovery of precision movements

of the fingers for post-stroke patients with flaccidity. The device should

be transportable and useable in home environment without direct supervision

of physiotherapist. The device should support the rehabilitation process in the first

4 weeks after stroke when there is the biggest impact on recovery process.

1.3. Outline

The purpose of this work is to design a hand rehabilitation robotic device

for the post-stroke patients with flaccidity, which can be used in home environment.

This system can give better outcome of rehabilitation therapy and a bigger amount

of training hours. This device could enable patients with acute stroke, flaccid

paralysis, muscle weakness and spine injuries, to perform rehabilitation task which

will lead to faster recovery of the hand motion and higher skills in the daily life

activities. This device will be inexpensive to be lent beyond the clinic or bought

by patient for personal use. Moreover, it will be safe to use by a patient without direct

supervision of the medical care staff.

This paper compares already existing solutions of the robotic devices

for a hand rehabilitation and lists their advantages and limitations. Thesis shows

the design of the hand rehabilitation robotic device with all necessary calculation

and assumption. Moreover, the paper explains control strategy for the rehabilitation

tasks and also describes future direction in which the project can go.

17

For the purpose of the thesis, two prototypes were built and the analyze

of the tasks execution by the robotic device was made.

2. Theory section

2.1. Natural and flaccid paralysis hand motion

The hand is composed from 27 bones divided into 3 types called: carpals, metacarpals

and phalanges. 8 carpals create a wrist and give a various of possible movement

to the hand. Palm, the middle part of the hand between wrist and fingers, is built

from 5 metacarpals. Fourteen phalanges are divided into proximal, medial and distal

and build human's fingers. There are 3 of them in each finger and 2 in the thumb.

This bones construction gives 21 degrees of freedom (DOF) to the hand. There are

4 DOF in each finger. Metacarpophalangeal joint (MP) has 2 DOF and proximal

interphalangeal joint (PIP) and distal interphalangeal joint (DIP) have 1 DOF.

The thumb has only interphalangeal and metacarpophalangeal joint with 1 DOF.

The palm joint of the thumb has 3 DOF. The anatomy of the hand is shown in

figure 2.1 [24, 25].

Figure 2.1 - Bones and joints of the hand and the wrist [26]

18

The normal adult hand has following ranges of motion. In MP joints

the adduction / abduction movement ranges from -20° to 20° and bending motion

from 20° to 90°. In PIP joints the bending motion is from 0° to 110° and in DIP joints

from 0° to 70° [24].

There are mainly 2 groups of muscles: extrinsic and intrinsic muscles.

Extrinsic muscles lie in the forearm narrowing into tendons and go to ligamentous

or bony part of the hand. Extrinsic muscles mostly assist in flexion-extension of the

wrist and finger, while intrinsic muscles are responsible for adduction-abduction and

cooperate with the extrinsic muscles to produce the opposition patterns like

in spherical grasp [25, 26].

Big number of joints and muscles in a hand obviously gives a possibility

of a large number of patterns of movement. Flexor and extensor muscles along

the proximal-distal axis gives some main flexion and extension patterns in fingers

and the attachments provides independent movements of fingers. From the other

hand a thumb is more versatile. It is due to the flexion-extension rotary plane

of the carpometacarpal joint. Besides that, another major fact is a big area

in the brain responsible for the hand control and sensation. The area representing

the hand is almost equal to the area covered by movement of arms, trunk, and legs.

Almost equally big is the area responsible for sensing of the hands.

This representation of the hand in brain shows how advanced and how important this

system is [26].

There are some main prehension movements distinguished in a hand

functionality, for example fixation movement. While grabbing an object the forces

from the muscles are equalized by the object itself, but when the hand is empty

or the object is delicate the hand maintains a position by co-contraction of groups

of muscles opposite to each other. Post-stroke patient cannot maintain this position,

and this is a big issue in the ADL [26].

After stroke due to actual denervation or disruption of signal in CNS

the muscle tonus may result in a flaccidity or paralysis. The bundles of muscles may

be affected only partly, but even while stimulating, this muscles may not sustain

the movement. However, acquisition and retrieval of information are similar

in the healthy brain and in the post-stroke one. The flaccidity of muscle groups causes

lower tension on antagonist muscle groups and leads to plastic reorganization which

catabolize antagonist muscle groups and increase weakness and flaccidity [11, 27].

Moreover, flaccidity creates a problem of joint instability. In the highest risk

is the glenohumeral joint which is placed in human shoulders. It is important

to stabilize and train the shoulder in order to prevent joint luxation and not cause any

injury [27].

When the flaccid side of the body in not loaded it becomes affected by

spasticity, which distorts or prevents the recovery of normal movement of the limb.

In fact muscles tension increases abnormally as a consequence of any stretch applied

19

to the muscle, what leads to resistance to movements imposed by external forces

and also to movements produced by the agonist muscles [27].

2.2. Hand rehabilitation devices

Traditional rehabilitation therapy for upper limb recovery have some limitation.

First of all this kind of therapy has to be individual with physiotherapist what is more

expensive and brings a problem of availability. Also there are no proper guidelines

for recovery of hand and therapists do not have feedback of the recovery process,

what leads to lower effectiveness of the therapy [24].

Compared to the traditional therapy, robotic rehabilitation units have a lot

to offer. They give a feedback of the recovery process and data about motion.

Moreover, the moves are repetitive and precise. Also they decrease the costs

of a therapy and occupancy of therapists. However, a lot of researches and proper

guidelines must be done [24].

The basic principal of the rehabilitation process with use of robotic devices

is application of the Continuous Passive Motion (CPM) what leads to restoring

of the motor functions of the affected limb. This technique is based on having

a passive constrained limb, while joints are constantly moved by a robot between

established range of motion [24].

The other idea is to use a robot as an active mechanism. The exercise thus will

be actively produced by the patient and the mechanism gives some constant

resistance to the movement of a joint while moving. Combining these two kind of

exercises, CPM and active system, gives the best results in recovery of the movement

and proprioception of a joint [29, 30].

The robotic devices should meet some criteria and follow specific guidelines.

The movement provided by robot should be healthy and safe for a patient. The finger

should move on its kinematic biological trajectory. The length between joints

of the device and patient's joints should be accurate, not to create an external torque

on the bones, what can lead to fracture. The force does not necessarily need

to be as high as a grasping force of the patient, however it should be high enough

to maintain the rehabilitation tasks. The frequency of movement should be around 30

cycles/minute for a single task to make a device effective. The wearable part

of the robot should be as light as possible and comfortable to the patient. It does not

have to be made from soft materials, although it is advisable.

Most of the hand movement are coordinate action between fingers and wrist.

It is recommended that the robot reproduces some of these movements,

and the rehabilitation tasks are not only focused on a single finger or just a wrist, but

covers both movements in the same time. This treatment can train a complex

movement as writing or using a fork. It would improve faster recovery of the patients

quality of life [31].

20

The robotic rehabilitation devices should meet all guidelines mentioned above.

It is important to support recovery process with a proper device not to make any kind

of harm to patient and to make this process effective.

There are already some robotic rehabilitation devices for upper limb recovery

used in the health care. One of these projects is Gloreha which was invented

and started in Lumezzane in Italy by a group of Small and Medium Enterprises

(SMEs) in industrial area. Gloreha is a soft exoskeleton in the shape of glove, which

is mounted on the dorsal side of the hand and strapped around the wrist.

This solution leaves the palm side open, hence the patient can grab objects during

task executing.

Gloreha motor functions are achieved by hydraulic system connected

to the fingers by wires. The hydraulic system is placed in the transportable box.

This solution gives an individual passive mobilization of each finger. The whole

device is connected to the computer and controlled by a software. The example

of Gloreha is shown in figure 2.1 [19].

Figure 2.2 - Gloreha robot Source: http://trends.medicalexpo.com/idrogenet/project-74722-415129.html

The studies made by the group of Luciano Bissolotti showed that after ten

sessions of treatment on the post-stroke patients the spasticity was decreased

in the area of the hand. There was also better blood flow in the region that was

moving. However, this research had a small sample size and no control group, what

could lead to some not controlled study bias. The further study should be done [19].

Clinical results showed that after 10 session Gloreha treatment the patients

that were up to 3 weeks after stroke, increased their grip strength by 113,29% while

control group had increased it by 13,87% in the same period. Also there was small

21

difference in pinch trial in benefit for Gloreha. Moreover, this treatment significantly

improved coordination of mono and bi-manual tasks. Also the patients in the chronic

phase after 1 week of sessions had visible decrease of spasticity [20].

However, despites of its advantages there are some crucial problems with this

device. First of all the movement is simple, there is only flexion and extension

of the fingers without division into metacarpophalangeal, proximal interphalangeal,

and distal interphalangeal joint. Also there is no abduction and adduction control.

Moreover, the whole equipment is big and expensive. There is no possibility to use

it at home, but only in the rehabilitation centers.

Another robotic device for upper limb rehabilitation is Amadeo. It is a device

with 5 degrees of freedom with possibility of moving each finger. Fingers

are connected to the slider by a rotational joint what allows to do a gripping

movement. However, not all the workspace of the finger is covered by this solution.

The wrist is fixed by straps. This device is universal and can be equipped by adults

and children as well as it can be used for right and left hand rehabilitation.

The example of the Amadeo robot is shown in figure 2.2 [21].

Figure 2.3 - Amadeo robot Source: https://products.iisartonline.org/productinfo.php?go=33

Amadeo can be use for passive and active rehabilitation. Active rehabilitation

may work with surface electromyography (sEMG) signal taken from the extensor

and flexor muscles of the forearm. Device is connected to the screen where data

22

is shown in conjunction with rehabilitation progress. Moreover, the software

has games which increase patients motivation [21].

The clinical use proves that using Amadeo improves gripping and pinching

of the affected arm and increases its strength. However, the patient needs

an assistance of the physiotherapist to connect fingers to the joints and electrodes

to the muscles. The machine is also big what reduces its use to the rehabilitation

centers. Once again the movement is limited to the grasp. There is no abduction

and adduction movements and no joint specify movements [22].

University of technology in Hong Kong created manipulator called Hand

of Hope (HOH). It is a devise which works on neuromuscular rehabilitation

of the hand. It is a biofeedback device using EMG and EEG signal to activate a desire

movement of the patient's hand. Signals are projected on the screen so the patient

can see responses and the training session is engaging. The hand in the hand brace

is placed on the dorsal side leaving the palm free. The device has 5 degrees of freedom

and uses electric micro motors to initiate movement. The device, with a hand in it,

is placed on the special pad to constrain a hand (figure 2.3) [23,24].

Figure 2.4 - Hand of Hope

Source: https://products.iisartonline.org

The training session of HOH can be done in 4 different modes. First mode

is the CPM movement, which is basic for this kind of devices,. Second and third

are based on the EMG signal. Either EMG signal can be a trigger for CPM movement,

or the movement occurs while EMG signal occurs. The last type of training

is a completely independent movement of patient's fingers while device works

23

as an active mechanism, which creates a torque to resist the movement of the fingers

and strengthen muscles [24].

HOH helps to post-stroke patients initiate and maintain voluntary movements

and motor learning by biofeedback. It has various number of possible training modes.

The whole device is small and transportable, however, it needs an assist of medical

care to install electrodes on the surface of forearm. Also there is a need to have a set

for each hand, right or left. Moreover, it is limited only to a gripping with

no abduction and adduction movement. The instrument is portable, so the patient

can wear it to support simple grasping movement in daily activities [23, 24].

Maref in Korea developed Reliver RL-100 instrument for hand rehabilitation.

It is a soft hand device which works with gas chambers which moves fingers

and wrist. It is used for fingers and wrist paralysis training. It improves brain

plasticity and acts on blood vessels. The device is comfortable to wear for patient

and its movement is soft. With this instrument it is possible to maintain abduction

and adduction movement of the fingers as well as flexion and extension, however

range of motion in each movement is limited. Moreover, device is complex

and it needs outer gas source to work. There was no research found proving benefits

of this device [24].

Figure 2.5 - Reliver RL-100

Source: https://cn.diytrade.com/china/pd/6407902/气动式手康复装置.html

Panagiotis Polygerinos from Harvard University developed robotic hand that

uses a soft actuator, a thin rectangular bladder from elastomeric fiber-reinforced

material, that can be bended, extended, and twisted. While the fluid is injected

24

the actuator starts to extend, bend or twist as is shown in figure 2.6. This actuators

have low resistance while not pressurized what gives a free, unloaded movement

of a hand. Meanwhile, when it is pressurized it produces a force to move an individual

finger [31].

Figure 2.6 - Soft actuator (A) - exploded view of unpressurized segments (B) - pressurized view with

combination of motions [31]

Each actuator is adjusted to individual finger and covers all 3 joints. This gives

precise control over the finger movement. There is a tube which goes from one end

of the actuator and injects or outlets pressure from it. It works in closed loop control.

The glove is wear only on one side and leaves a palm free, what can be use

with catching objects. Moreover, all the pumps and controllers are mounted

in a small box which can be placed next to the patient. The intention of movement is

taken from the signal from the force sensors placed on the dorsal side of the fingers.

There are 4 sensors which are placed between each joint. The scheme of the glove (A)

and example of the possible training task (B) is shown in figure 2.7 [31].

Figure 2.7 - Soft rehabilitation glove (A) - scheme (B) - example of motion [31]

25

This glove gives a complex movement which is similar to a biological

movement of the hand. It gives a possibility to perform very challenging tasks like

finger opposition movement with a thumb. This complex movement may highly

increase a recovery process of the hand [24, 31].

The position of the joints is read from GUI system and the glove

is personalized to the individual patient. This gives a healthy movement of the joints.

Moreover, there is no high weight placed on the hand, the glove weight less than 0,5

kg. All other elements are placed in the box. These parameters and also the open

palm design gives an extra freedom which leads to a possibility of using this glove

as a portable device in daily life activities. However, the box may be annoying

for the patient to move around. Also this glove does not have a good feedback

of finger position. Moreover, there is not many research done with the use of this

rehabilitation glove, hence its effectiveness is unknown [24, 31].

All listed devices improve grip of the post-stroke patients, however only two

of them are handy and transportable. The soft glove made by Polygerinos and Reliver

RL-100. Moreover, there is no data about using them at home while this process gives

a big profit to recovery. Also almost all devices strongly simplify the movement

of the fingers, only Polygerinos's soft glove gives the complex movement close

to the biological one. The other have no division into metacarpophalangeal, proximal

interphalangeal and distal interphalangeal joint movement and no abduction

and adduction movement. In some devices the range of the movement is limited what

decrease efficiency of use. Most of the precision movement of the hand are due

to coordinate action between fingers and wrist and in all the previous examples

the wrist was fixated and motionless, hence there is no rehabilitation process on it.

From all the listed devices, it seems, soft glove made by Polygerinos gives

the most complex movement and meets the most of assumptions for the robotic hand

rehabilitation. However, it still needs a bigger number of researches on the use

on patients to have an objective comparison. Also there is no feedback from this

product, so physiotherapist may not follow the telemedicine progress of the patient

when the rehabilitation is done.

This research shows there is still not enough products to help post-stroke

patients in full recovery of their hand motor function. Moreover, it proves that even

existing solutions need further improvement. Also the process of hand rehabilitation

needs more accurate guidelines for future robotic devices.

3. Method section

3.1. Project assumptions

From the knowledge of previous chapters some requirements for future projects were

made. The projects should meet them in number as high as possible. The hand

robotic device is aimed to support rehabilitation process of the post-stroke patient

in a stage of flaccid paralysis or weak spasticity.

26

Because of the high occupancy of physiotherapists, their time with patients

is limited, hence the rehabilitation process may be negligence. A conversation

with some therapists explained that a traditional rehabilitation is mostly focused

on walking, position stabilization, and shoulder stabilization first, while hand

recovery stays as a minor problem. A perfect solution to problem of insufficient

rehabilitation could be a robotic device. From already existing devices one can find

few main ways of designing this types of robots.

The robot can be stationary, what means that it is used in the rehabilitation

center. Mostly this kind of robots need support of physiotherapist. Very often the help

is only limited to setting up the device or putting some elements on patient's hand,

while the rehabilitation tasks are done individually by patient. Hence, it leads only

to small decrease of work load on the health care stuff as long as they still need

to supervise the patient. Moreover, the patient has to stay in the rehabilitation center

or arrive to it.

Home therapy brings both, economic advantages and rehabilitation progress.

It is cheaper for patient or a health found, if patient stays at home instead of spending

a time in the rehabilitation center. Because of spending time at home, patient has

higher motivation to perform rehabilitation what gives better results in the recovery

process. The other idea is to use the device at patient's home with telemedicine

support. In this case physiotherapist develops patient's training and explains how

to use the device. The rehabilitation is done at patient's home and the results

are saved and send to rehabilitation center. Thanks to this the supervisor can see

patient's progress. Home rehabilitation gives benefits to both, the patient

and the physiotherapist.

However, while rehabilitation is done at home there are some important issues

to be solved. First of all there is a safety factor which is crucial as long as patient uses

the device on his own without supervision. It is significant to make a device safe

and free from all possible failures leading to occurring danger for patient's health.

Secondly, there is an economic factor. If the device is too expensive, patient may not

afford it or rehabilitation center would not want to lend it. The third factor is size

of the device. It is important to make the rehabilitation device compact

and transportable. If it is too big, there can be problems with delivery to the patient's

house and placing it there. It would also make transport more expensive. The last

thing is to design this device as a home device. It has to use technologies and source

of energy which are common in houses, and if it use any other technology it should

be delivered with a device. Gas and fluid driven devices require pumps which are not

commonly use at home. Use of this kind of technologies may be problematic

for the patient. Moreover, that could lead to another problem which is a noise created

by it. Loud work could make it unusable in home environment. Another solution

is a use of electric elements instead of gas or fluid ones. Electricity is a norm

for all houses. Moreover, electric motors and cylinders are very quiet what would not

be disturbing for people around.

27

To achieve a healthy movement in hand rehabilitation, a trained movement

should replicate kinematic movement of the fingers. The perfect solution would have

21 degrees of freedom, however by decreasing number of DOF the movement may

still be healthy and effective during rehabilitation as long as it tracks kinematic

motion of biological hand. Nevertheless, lower number of DOF decrease complexity

of movement which can be achieved by the device.

The length of joints of the device should be in the same position and work

in the same plane as the biological ones. Any deviation may harm patient or make

some pathological changes in motion. Moreover, joints of patients with flaccid hand

are not well attached, so there is a risk of prolapse. There should be a compressive

force acting on joints. Patients that suffer from flaccidity may not feel properly their

fingers because of low stress in the joints, which is due to slow fluid flow. External

forces may give them a sensation of fingers and provides better nutrition

in the fingers, what is necessary to rebuild muscle tissue and increase effectiveness

of a recovery process [14, 27].

The grasping force of the healthy hand can achieve high values, however

in daily living activities this force does not exceed 15N. Moreover, people

with flaccidity have their grasping force reduced or cannot strain their muscles.

The actuators do not need to generate the maximum grasping force, it is enough

if they cover usable force of daily living activities. Moreover, device should not affect

natural movement of fingers, cause injuries, or discomfort to the patient who wears

it [31].

There is an increase in efficiency of training when it is repeated few time

per day in blocks of 20 minutes. Moreover, the series of extending or flexing task

should occur with a frequency of 30 cycles per minute [11, 31].

A wearable part of a robot should not be heavier than 0,5 kg. However,

it is important to have it as light as possible to not fatigue patient by wearing a device

itself. Besides, it is advisable to use soft materials, which give comfort to the patient

while wearing it. Moreover, soft materials weight less than conventional materials.

The patients can have some limitations in their body movement what can

be inconvenient while setting up a device with no additional help. As long as

a devices may be used at home this help may not be accessible. Some patient may

have clenched hand because of occurring spasticity, while the others may have totally

flaccid hand. Hence, device should be design in the way to be easy to set up for

patient with different types of limitation and with use of one hand.

Besides mechanical factors, there are guidelines about control and data

collecting. There are few ideas of the control. Robot can execute a task itself with

a passive patient's hand inside. However, this is very limiting solution with low

effectiveness. The other solution is to create a system for active exercises. Whenever

the task is executed correctly, robot stays passive, but if there are any errors of the

trajectory or patient cannot perform the movement, the robot switches to the passive

mode and gives a push till the proper movement occurs. Next control system adds

28

some constant resistance, during task executing, to improve and strengthen

the movement.

Moreover, data can be collected from finger motions by EMG,

or any other signal from which it is possible to read a desired movement. In this case

the most important factor is accuracy and time of data processing, rather than a way

of collecting it.

It is recommended that robot can process some additional data which can

be useful for physiotherapists and patient in seeing the progress of the therapy.

This kind of feedback increases effectiveness of recovery process. Patient have extra

motivation because all progresses are measured.

Not all the guidelines are obligatory to meet, however the high number

of them is advisable. With all this information in mind, the concept device was

designed and built.

3.2. Concept

A main aspect of designing robotic device for hand rehabilitation of post-stroke

patients is possibility of using it in home environment. It is due to the fact, there

is a lack of this kind instrumentation. It can be a great additional help in the

rehabilitation therapies. The concept of the device is shown in figures 3.1 - 3.3.

Figure 3.1 - interior of the device with open side cover [38]

29

Figure 3.2 - interior of the motor box [38]

Figure 3.3 - wearable part of the device [38]

The rehabilitation robot uses a soft material glove (1) which is worn by the

patient. There is only an upper and a side part of the glove what gives possibility

of wearing it without necessity of sliding a hand inside it. This task could be

problematic for the patients with flaccidity. On the glove there is 3D-printed wrist

holder (2) made from polycarbonate which has high stiffness and strength, what gives

the possibility of lowering a mass of elements while good mechanical properties

are still achieved. Nowadays, 3D printing brings good quality and low production cost

30

of elements, what can be crucial, as an economic factor, in home use devices.

The wrist holder main function is keeping the hand steady in a natural position

during the training. The hand is fixed inside the wrist holder by two velcro fasteners

(3) placed under the wrist and around the palm.

On the fingers, just above proximal interphalangeal and distal interphalangeal

joints there are placed 3D printed C-rings (4) which are also fasten by velcro.

The C-shape of them makes the setting up process easier for patient. The C-rings can

be applied from the side on the fingers. To each ring two wires (5) are attached,

one from the dorsal side and the other one from the palmar side of the hand.

Moreover, the wires from motors to distal C-rings go through the proximal C-rings.

This is due to applying the force in the same direction for different position

of the hand. The wires transport force to the C-rings which act on fingers flexion

and extension. Some part of the force compresses joints. The robot uses biological

joints of patient to achieve movement of fingers. Thanks to this solution some small

compressive force is created. Acting on the joints attachment prevents prolapse

of them.

The upper wires go through the wrist holder on the top of the hand

and connect to the motor system (6) inside the motor box (7). The bottom wires go

to the palm side through the wheel system (9) on the wrist holder to the spring

system (8). The way of the wires is defined by different types of wheel systems.

On the top of the wrist holder there is the tenon (10) with a lock hole

in the middle of the surface. After sliding the tenon inside the dock (11), the lock (12)

stops further movement of the hand in the operating position. This system can be

used to change the glove between right and left hand. Also, in some cases it can be

used by the patient with a high level disability to install the device on the hand.

The motor box covers all electric and moving parts from the patient. Besides

the motor system, inside the box there is the electric lock (13), microcontroller (14),

Wheatstone bridges (15) and power board (16).

The frame (17) is build from aluminum profiles which are stiff and light while

the price of them is low. The rehabilitation process takes place inside the frame.

The size of the device should be as small as possible to transport it and place it

on a table or a desk. The interior of the device is hanged on the telescopic slides (18)

so it can be slide out from the frame. However, to maintain proper work during

sliding in and out the cables must be routed. For this task E-chain (19) was used.

Device should be connected to the computer by USB wire and ran

with a dedicated software. The results will show on the screen. Moreover, patient can

play games while executing tasks. This help with their bigger involvement into

rehabilitation process. The software can offer telemedicine and can send results

to physiotherapist for proper care over patient. However, the whole system is ran

from the microcontroller inside the device. Outer computer only receives data

and trigger tasks and actions.

31

The device should be connected to the regular electric socket and transform

the voltage to 5 V to power all the motors and sensors. This is why the power board is

used. It converts high voltage into lower, used by instruments.

When the patient wants to install the hand inside the device, the electric lock

opens and the interior of the device slides out from the frame. There is an easy access

to the wrist holder. Patient pulls up the lock (20) on the spring system to release

springs and remove tension from the wires. Spring system is presented in figure 3.4.

Next, patient slides in the hand to the wrist holder and straps it. Afterwards patient

installs two C-rings on each finger and straps them. Now the springs inside the spring

system can be pushed back to their operating position. The sensor (21) informs

if the springs are in the right position. In the end the patient slides back the telescopic

slide to the box and the lock gets blocked. After proper installation information

from the second sensor (22) occurs. The device is ready to use. The installation

position is shown in figure 3.5.

Figure 3.4 - 1: the spring system; 2: interior of the spring system, by unlocking, truck releases and moves on the rails. The springs are not stretched anymore [38]

32

Figure 3.5 - Device in installation position [38]

The task execution is achieved thanks to cooperation between motors

and springs. From the top, the servo motors can rotate by 180 degrees and pull

the wire. On each wire there is a plate with strain gauge (23) which collects

information about tension on the wire. From the bottom, wires go from C-ring

to spring system and each goes to the individual spring. The spring causes a tension

from the other side keeping the finger in stable position. Moreover, whenever motor

moves and slacks upper wire, the spring pulls it back. In that way all the wires

are tight in any moment.

When the rehabilitation exercises are finished, the lock opens and patient can

slide out the wrist holder and free patient's hand the same way as in the installation

process.

To verify the concept, a first prototype was made. It uses the same principle

of working. Two wires go to each C-ring, from the top a motor is placed,

and from the bottom a spring. However, there was no calculation or element selection

made, the prototype was built to prove the idea of working.

3.3. Data collecting, calculations, and element selection

The first step of designing was to prepare a hand model. From the research

the dimensions of the hand were found and presented [32]. A model of the hand

was downloaded from the GrabCAD library [33]. Figure 3.6 shows schematic view

of dimensions and their naming. Figure 3.7 presents the model of the hand used

in designing of robotic device.

33

Figure 3.6 - Schematic view of the measured dimensions [32]

Figure 3.7 - Model of a human left hand from GrabCAD [33]

All dimensions were compared to research results and presented in table 3.8.

The difference in dimensions were small and they were oscillating around 3%

for 50th percentile of male's left hand. Only the difference in dimension of breadth

of first joint of digit 1 was bigger (6%). The results were good for further use

and the hand was chosen as a model around which the rehabilitation device

was designed.

34

Dimension name Research value (mm) Model value (mm) Difference (%)

Hand length 192,98 196,84 2

Palm length 110,89 112,42 1

Hand breadth at thumb 101,95 104,32 2

Hand breadth at metacarpal 86,25 87,33 1

Fingertip to root digit 1 56,51 54,95 3





Breadth of first joint of digit 1 21,50 22,81 6





First joint to root digit 2 47,07 46,57 1




Second joint to root digit 1 22,74 22,65 0





Table 3.8 - Comparison of dimensions of the left hand for 50th percentile and 3D model [32]

Further, a range of motion was established. The maximum range of motions

for the MP (metacarpophalangeal) joints are from 0° to 90°. In the presented

solution abduction and adduction movements were neglected. The PIP (proximal

interphalangeal) joints move from 0° to 110°, however in the solution the range of

their motion may not occur fully. The PIP joints may bend to 90° whenever the MP

joints are bend to 90°. In other positions the range of motion of the PIP joints is

higher. It is due to design of the device. The DIP (distal interphalangeal) joints

movement was also neglected due to lower importance of use compared to other kind

of movements. Both end positions are shown in figure 3.9.

35

Figure 3.9 - 1: hand in full stretch; 2: hand in a grip position [38]

Strength of the fingers was roughly estimated experimentally. To this task the

first prototype was used. A hand scale was mounted to the finger at the end of the

wire. By flexing the finger, the hand scale showed created force in kilograms. The

measurement was made for each finger and each joint. All the results are shown in

table 3.10.

36

Finger Force on MP joint [N] Force on PIP joint [N]

Index 32 21

Middle 36 24

Ring 29 20

Pinkie 27 18

Table 3.10 - Fingers joints force [38]

Nevertheless, the weight is a very poor sensor with large measurement error,

the result may be used as a guide value of magnitude of force needed to flex finger.

The force of the spring should not create maximal value of the finger force

not to cause any injury to the patient. Moreover, patient with flaccid hand can create

only a small tension in their muscles, hence the force should be only a part

of the maximal force. However, due to the strength of the grip, results may be various

between different patients. It should be optimized in clinic trials.

The maximal value of force created by the springs was set at 27 N for the MP

joints and 18 N for the PIP joint. These numbers correspond to the pinkie finger

strength, which is the lowest from all the fingers.

Next, the length of movement of wires was measured on a prototype

for the MP and the PIP joint of the middle finger where the wire has the longest way

to travel between the two end positions. For the MP joint required length was 91 mm.

The PIP joint movement was 46 mm. However, to have some extra length the values

were set accordingly at 50 mm for the PIP joint and 100 mm for the MP joint.

The spring has to create a minimal force enough to hold the finger stably.

In the full extension, force of the spring cannot exceed the maximal strength

of the finger. It is important not to cause a harm to the patient by creating too high

force.

For the PIP joint movement the spring Vanel U.092.080.0500.IX was selected.

Its elongation is from 50 mm to 199 mm. The maximal force created by it is 20 N.

However, the force in working area values between 11,2 N to 19 N.

The MP joint spring is Vanel T.087.070.0380.A. This spring is shorter

and elongations goes from 38 mm to 148,5mm. Its maximal force is 22 N

and the force in the working area oscillates between 9,9 N to 21,3 N.

As it was mentioned before, the device is fully electric. To produce the action

of wire movements electric motors are used. Rotation of the motors takes less place

than linear movement, hence the servo motors are used. They create

a high torque while maintaining small dimensions thanks to the internal gear.

As an arm of a servo motor rotates by 180°, to cover full range of motion

of the finer, the length of arm has to be equal, or bigger, than a half of the way

of movement between the end positions. The lengths of arms are 𝑅1 = 50 𝑚𝑚 for the

37

PIP joint and 𝑅2 = 25 𝑚𝑚 for the MP joint. The scheme of servo motor arms is shown

in figure 3.11.

Figure 3.11 - Scheme of servo motors arms [38]

Servo motor has to create a force higher than the maximal force of the spring,

to spread it easily. Moreover, the small resistance from the finger may occur, that

is why servo motor torque has to be big enough to move all the load. Required force

was set at 15 N more than the minimal force needed to overcome springs. 15 N

is the maximal force created during daily life activities. By knowing length of the arm

and needed force, torque created by servo motor on the MP and the PIP joint

was calculated.

𝑀 = (𝐹𝑠𝑝𝑟𝑖𝑛𝑔 + 15 𝑁) ∙ 𝑅 (3.1)

𝑀1 = 19 𝑁 + 15 𝑁 ∙ 50 𝑚𝑚 = 1700 𝑁𝑚𝑚 ≈ 17,33 𝑘𝑔/𝑐𝑚

𝑀2 = 21,3 𝑁 + 15 𝑁 ∙ 25 𝑚𝑚 = 907,5 𝑁𝑚𝑚 ≈ 9,25 𝑘𝑔/𝑐𝑚

For the MP joint movement, Hitec HS805 servo motors, 1 for each finger,

was chosen. The maximum torque of them is 19,8 kg/cm. The operating voltage range

is from 4,8V to 6.0V. The weight is 152 grams.

The second type of servo motors, used on the PIP joints, is Hitec HS-5645MG,

and the torque in 5V is 11 kg/cm. It weights 110 grams. Four motors were used.

Nylon was chosen as the material for the wires because it shows a low

elongation properties and low thermal effect on its length. It is important to have

38

a material with low elongation to precisely control position of the finger. Nylon's

tensile strength is 𝑘𝑡 = 80 𝑀𝑃𝑎 [34]. The maximal force working on the wires is

43,1 N, and it is generated by Hitec HS-5645MG servo motor. The wire works

on tensile. The minimal diameter d of nylon string was calculated.

𝜎 =𝐹

𝑆≤𝑘𝑡𝑋𝑡

(3.2)

where: 𝜎 - tensile stress

F - force of tensile

𝑠 = 𝜋𝑑2

4 - surface area

𝑋𝑡 = 1,5 - safety factor

𝑑 ≥ 4 ∙ 𝐹

𝜋 ∙ 𝑘𝑡

𝑑 ≥ 4 ∙ 43,1 𝑁

𝜋 ∙ 80 𝑀𝑃𝑎

𝑑 ≥ 1,02 [𝑚𝑚]

The chosen wire is a guitar string, size .042, what is around 1,07 mm

of diameter.

To measure the tension and to have a feedback from the device, strain gauges

were used and attached to the wires. Selected strain gauges are 5 kg Micro load cell

by Phidgets, which cover the maximal force occurring on the wires, 43,1 N. The device

uses 8 sensors to control all the motors. To amplify signal Phidgets 1046-0B

Wheatstone Bridges were used. These W-bridges are fully compatible with the chosen

strain gauges and has 4 inputs to control independently 4 sensors in the same time.

To collect signals from all the strain gauges, two W-bridges were used.

For all 3D printed elements ABS material was selected, which is one

of the most common used materials for 3D printing nowadays. Elements printed

from ABS are tough and durable, while mass and the cost of them is low. Moreover,

it withstands long time period without big structural changes, what prevent element

against failure.

The wrist holder is the most loaded 3D printed element in the device. It has a

shape of a half ring with extended side of it as It is shown in figure 3.12. It has to hold

steady the wrist during training session without failure or deformation. To calculate

thickness of it, it was divided for 3 segments and the moment of inertia for each

segment was calculated. This is due to complex shape of it, and normalized inertia

moment cannot be used in this case.

39

Figure 3.12 - auxiliary drawing; d, e, f - distance from section coordinate system to main coordinate system; g - thickness of wrist holder [38]

𝐼𝑥 = 𝐼𝑢 + 𝐴𝑢 ∙ 𝑃𝑢2

𝑢

(3.3)

𝐼𝑥 𝑠𝑞𝑢𝑎𝑟𝑒 =𝑏 ∙ 𝑕3

3

(3.4)

𝐼𝑥 𝑕𝑎𝑙𝑓 𝑐𝑖𝑟𝑐𝑙𝑒 =𝜋 ∙ 𝑅4

8 (3.5)

𝐼1 =𝜋 ∙ (17,5 + 𝑔 − 17,5)4

8=𝜋 ∙ 𝑔4

8

𝐼2 =35 ∙ 𝑔3

3

𝐼3 =20 ∙ 𝑔3

3

𝐼𝑥 = 𝐼1 + 𝐴1 ∙ 𝑃12 + 𝐼2 + 𝐴2 ∙ 𝑃2

2 + 𝐼3 + 𝐴3 ∙ 𝑃32

40

where: 𝑃1 = 𝑃2 = 𝑃3 = 6;

𝐴1 =𝜋 ∙ (35 + 𝑔)2

2−𝜋 ∙ 352

2=𝜋 ∙ (70𝑔 + 𝑔2)

2

𝐴2 = 35 ∙ 𝑔

𝐴3 = 20 ∙ 𝑔

𝐼𝑥 =𝜋𝑔4

8+

55𝑔3

3+ 18𝜋𝑔2 + (1260𝜋 + 1980)𝑔

Next, there was derived equation to calculate a minimal thickness of the wrist

holder.

𝑊𝑥 =𝐼𝑥𝑦∗

(3.6)

Where: 𝑦∗ = 𝑔 + 17,5;

𝜎 =𝑀𝑏

𝑊𝑥≤𝑘𝑏𝑋

(3.7)

Where: 𝑀𝑏 - bending moment, 𝑘𝑏 - flexural strength, X = 3 - safety factor

The research shows that for a healthy man the torque of wrist during flexion

goes up to 15 Nm = 15000 Nmm [35]. This value was set as a minimal value that

the wrist holder has to withstand. The flexural strength was set at 30 MPa. This value

is lower than a nominal value for ABS, because the element is 3D printed.

This process has an impact on the material properties of created elements.

Because the value of flexural strength strongly depends on the quality of 3D printing,

the safety factor was set at 3 to ensure no failure even when quality of a part is lower.

𝐼𝑥 −𝑋 ∙ 𝑀𝑏

𝑘𝑏∙ 𝑦∗ ≥ 0

𝜋𝑔4

8+

55𝑔3

3+ 18𝜋𝑔2 + (1260𝜋 + 1980)𝑔 −

3 ∙ 15000

30∙ 𝑔 + 17,5 ≥ 0

𝜋𝑔4

8+

55𝑔3

3+ 18𝜋𝑔2 + 1260𝜋 + 480 𝑔 − 26000 ≥ 0

𝑔 ≈ 4,98 [𝑚𝑚]

The designed thickness was set at 5 mm.

Next, the thickness of tenon was calculated. The force that tenon

has to withstand is a weight of the arm. For the male, the weight is around 4,3 kg

[36]. However, there is a possibility that the user may lean on the arm and create

bigger pressure. The final value was set at 300 N. The tenon in the dock is stretched.

41

The weakest segment of it, is the base. The length of the base was set at 10 mm. The

thickness was calculated. Figure 3.13 presents auxiliary drawing for the calculations.

Figure 3.13 - auxiliary drawing; b - thickness of tenon [38]

𝐹

𝐴≤𝑘𝑡𝑋

(3.8)

where 𝐴 = 10 𝑚𝑚 ∙ 𝑏

𝑏 ≥𝑋 ∙ 𝐹

10 𝑚𝑚 ∙ 𝑘𝑡

𝑏 ≥3 ∙ 140𝑁

10𝑚𝑚 ∙ 28,5 𝑀𝑃𝑎

𝑏 ≥ 3,2 𝑚𝑚

The value of thickness was set at 5 mm as the rest of the wrist holder.

This change was made to reduce a chance of failing of this segment.

The shaft of the wheel system was made from aluminum alloy 3.3315, which

has good mechanical properties and low weight. This alloy was used for all other

metallic elements. The most loaded shaft is the one on the dock (figure 3.14).

42

Figure 3.14 - Wheel system on the dock [38]

A calculation of the highest loaded profile was made. The maximal force F

is a sum of two forces from each pair of wheels. However, this is just a theoretical

force caused by motors in a hypothetical situation when wheels does not rotate

and motors pull the shaft. The real value of load should be significantly lower.

Each pair of wheels was treated as one. Scheme of the shaft is shown in figure 3.15.

Based on that calculations and diagrams were made.

𝐹 = 43,1 𝑁 + 38,3 𝑁 = 81,4 𝑁

Figure 3.15 - Scheme of the shaft with diagram of shear and moment [38]

43

𝑆 = 0 𝑎𝑛𝑑 𝑀 = 0 (3.9)

𝑆 = 𝑅𝑎 − 4 ∙ 𝐹 + 𝑅𝑏

𝑀𝑎 = −14,5 ∙ 𝐹 − 33,5 ∙ 𝐹 − 52,5 ∙ 𝐹 − 72,5 ∙ 𝐹 + 93 ∙ 𝑅𝑏 = 93 ∙ 𝑅𝑏 − 173 ∙ 𝐹

𝑅𝑏 =

173

93𝐹 ≈ 151,5 𝑁

𝑅𝑎 =199

93𝐹 ≈ 174,2 𝑁

1) 0 ≤ 𝑥 < 14,5

𝑀1 = 𝑅𝑎 ∙ 𝑥

𝑆1 = 𝑅𝑎

2) 14,5 ≤ 𝑥 < 33,5

𝑀2 = 𝑅𝑎 ∙ 𝑥 − 𝐹(𝑥 − 14,5)

𝑆2 = 𝑅𝑎 − 𝐹

3) 33,5 ≤ 𝑥 < 52,5

𝑀3 = 𝑅𝑎 ∙ 𝑥 − 𝐹(𝑥 − 14,5) − 𝐹(𝑥 − 32,5)

𝑆3 = 𝑅𝑎 − 2 ∙ 𝐹

4) 52,5 ≤ 𝑥 < 72,5

𝑀4 = 𝑅𝑎 ∙ 𝑥 − 𝐹(𝑥 − 14,5) − 𝐹(𝑥 − 32,5) − 𝐹(𝑥 − 52,5)

𝑆4 = 𝑅𝑎 − 3 ∙ 𝐹

5) 72,5 ≤ 𝑥 < 93

𝑀5 = 𝑅𝑎 ∙ 𝑥 − 𝐹(𝑥 − 14,5) − 𝐹(𝑥 − 32,5) − 𝐹(𝑥 − 52,5)− 𝐹(𝑥 − 72,5)

𝑆5 = 𝑅𝑎 − 4 ∙ 𝐹

The maximal value of the torque occurs for 𝑥 = 52,5 𝑚𝑚 , and has a value

of 𝑀𝑚𝑎𝑥 ≈ 4505 𝑁𝑚𝑚. Next, the minimal diameter of the shaft was calculated.

𝜎𝑏 =𝑀𝑏

𝑊𝑧≤ 𝑘𝑏 (3.10)

where: 𝑊𝑧 =𝜋𝑑3

16

𝑑 ≥ 16 ∙ 𝑀𝑚𝑎𝑥

𝜋 ∙ 𝑘𝑏

3

For the 3.3315 aluminum alloy tensile strength is 𝑅𝑒 = 230 𝑀𝑃𝑎. The value

of flexural strength is 𝑘𝑏 = 0,6 ∙ 𝑅𝑒 = 138 𝑀𝑃𝑎.

44

𝑑 ≥ 16 ∙ 4505 𝑁𝑚𝑚

𝜋 ∙ 138 𝑀𝑃𝑎

3

𝑑 ≥ 5,5 𝑚𝑚

The final diameter was set at 6 mm. However, there is also shear stress acting

on the shaft. To check if the diameter is big enough to withstand loads the Huber's

equation (3.11) was used. Shear in the position of maximal moment is S = 70 N.

𝜎𝑟𝑒𝑑 = 𝜎2 + 3(𝜏2) (3.11)

𝜎𝑟𝑒𝑑 = 𝑀𝑚𝑎𝑥

𝑊𝑧

2

+ 3((𝑆

𝐴)2) ≤ 𝑘𝑟𝑒𝑑

where: 𝐴 = 𝜋𝑑2; 𝑘𝑟𝑒𝑑 = 0,55 ∙ 𝑅𝑒 ≈ 126 𝑀𝑃𝑎

𝜎𝑟𝑒𝑑 = (4505 𝑁𝑚𝑚)

𝜋 ∙ (6 𝑚𝑚)3

16

2

+ 3((70 𝑁

𝜋 ∙ (6 𝑚𝑚)2)2) = 106 𝑀𝑃𝑎 ≤ 126 𝑀𝑃𝑎

The 6 mm shaft is big enough to stand all the occurring loads.

The telescopic slides were used to slide out the interior of the device from

the frame. By designing a complete device the length of movement of 300 mm was

chosen. The sliders were used to have a possibility to install the hand inside the wrist

holder with not limited access to it by the frame. The load capacity of the sliders has

to be big enough to support the weight of the arm and the weight of the components

of the device. The total mass should be lower than 10 kg, however the safety factor

was set at 3. To execute this task Kipp K0540 telescopic slides with load capacity

of 35 kg and range of 300 mm were selected. Moreover, the spring module locates

at the bottom of the device, the second pair of sliders was used to support it. In this

case, because of the low mass of the spring module, Kipp K0536 was selected.

This is the smallest telescopic slide available with 300 mm range of extension.

The load capacity of it is 15 kg.

Before any movement of motors start, there is a need to check if all

the elements are in the working positions. For this task inductive safety sensors were

used. The selected sensors are Schmersal BNS 250 with 2 mm detecting range. One

sensor is attached to the frame and the other one to the motor box. Whenever user

moves back the interior part of the device to the working position, the signal

from the sensor is send to the electric lock, Junson JS-303, and closes it.

The second sensor is attached to the spring module. Before device initiates its

work, the spring module has to be in its working position and the locker has to be

45

closed. When both sensors send a positive signal, the motor may start moving.

However, if there is a break in signal sending from the sensors, the whole device stops

immediately.

To start the device, 5 V RobotShop Rocker Switch has to be clicked, what sends

a power to all electric elements.

The system is controlled by microcontroller STM32F411E Discovery. It works

on 5 V voltage. It has an USB exit, so after connecting it to the computer there is

communication between the software and the device. It has 180 MHz processor,

which is enough to run PWM signal for 8 motors. Each motor needs only 5 Hz PWM

signal to run properly.

Because the device is connected to the 240 V AC, there is a need to use power

board to convert the input voltage to 5V DC on output, as all listed electrical elements

use it. Each motor needs 800 mA of current, for 8 motors it is 6,4 A. All other electric

devices use less than 1 A of current. That leads to selecting a power board that can

stand around 7,5 A current. Selected power board is Botland PMT 5V50W1AA which

converts 240 V AC to 5 V DC and have the output current of 10 A. This is fair reserve

to use the device safety and not to cause any high heating.

There is a need to use an electric chain for cables to maintain a smooth

movement of the sliders when the interior of the device is slide in and out. There are

3 cables which goes into the motor box. First one transfers 240 V AC from the electric

socket to the power board. This cable has 12 mm diameter. Second one, a 5 V DC,

goes from the power board to the Rocker Switch. It's diameter is 2,1 mm. The third

one is an USB cable also 2,1mm diameter. The interior of the e-chain has to fit all the

cables. The selected e-chain is Igus 0.26m E2i.10.06.018.0 + E2.100.06.12PZ.A1.

The travel range of it is 310 mm, what is 10 mm more than the range of the telescopic

slides.

The frame is build from 20 mm aluminum square profiles V-Slot 2020. These

are the smallest normalized aluminum profiles available on the market. They have

fast connection system based on the T-slots. The telescopic slides, that carries the rest

of the elements are connected to the frame. The frame is covered with ABS plates

to protect interior of the device from the dust. Moreover, there is no access

to the moving elements, hence no harm to the user should be done.

The locker of the spring module and the wrist holder is indexing plunger

Elesa-Ganter GN 817-4-6-B.

To safely place the device on the table leveling feet Elesa-Ganter

LX.25-SW13-M6x24 were used. They have rubber endings which keeps the device

motionless on the surface of the table.

The whole device weights 8,2 kg and has a cuboid shape of dimensions:

344 mm width, 383 mm height, and 401 mm length.

The 3D model of the rehabilitation device was designed in SolidWorks.

Figures 3.16 and 3.17 show model of the device with all selected elements marked and

listed.

46

Figure 3.16 - Scheme with listed elements [38]

Figure 3.17 - Scheme with listed elements that are inside the motor box [38]

3.4. Prototype

The first prototype was made to validate the basic concept of work, and to measure

the forces needed for the finger movement. The second prototype, was based

47

on the designed 3D model and it uses the same or similar elements,

as in the model. However, this prototype works only with one finger, what

is representative for all the fingers. The device was made to analys the precision

of the movement and functionality of the code in all 3 types of control loop.

The aluminum frame was built as in the 3D model. Nevertheless, it is 80mm

more narrow compare to 3D modeled. This change was done because the prototype

works only with 1 finger, hence there are only two motors. Moreover, the telescopic

slides were not used. It does not affect the work of the instrument. All the parts were

fixed to the frame. The wrist holder was made from the wrist brace and attached to

the metal plate. Wrist brace was used to orientate and hold the hand in one position.

The C-rings were glued to the glove's index finger and connected to the wires made

from a guitar nylon string. Just above and below the wrist brace, there are 2 plates

with wheels on it to change direction of the wire. That gives the possibility of placing

both motors in front of the device. On the top, the wires go to the Phidgets strain

gauges, and next to the servo motors. In this prototype, both motors were

Hitec HS805. To have similar force on the MP joint as in calculations, in both motors

50 mm reaction arms were used. Because of the high current, that motors need,

a separate power source was created. It converts 230V from the electric socket to 5V

on the output. The motors and the microcontroller is connected to the power supply.

The W-Bridge and second input of microcontroller is connected to the computer.

The program collects data from the W-bridge and sends it back to the

microcontroller. The control wire of the motor was connected to the microcontroller

STM32F411E Discovery. On the bottom of the device there are 2 springs. Because

of high cost of production single spring, instead of the Vanel springs other, less

expensive, springs were used. They were validated experimentally. For this use, the

force created by them is from 8 N to 19 N, what is similar to the original values of

Vanel springs.

Besides the prototype, a mechanical flaccid finger was made. It uses hinges

as the PIP and the MP joint. Moreover, it has mechanical limitations, that make

the finger move as a biological one. The finger was fixed to the frame, and placed

inside the glove. The device was tested with it inside to imitate a flaccid finger.

The prototype with mounted mechanical flaccid finger inside is shown

in figures 3.18 - 3.20.

48

Figure 3.18 - The prototype with mechanical flaccid finger [38]

Figure 3.19 - Top view of the prototype. To remove mechanical finger, demount first plate from the left [38]

49

Figure 3.20 - Close up to the working area [38]

This prototype gives a better look on how modeled device functions, and shows

if there are any problems with it. The prototype with elements description is shown

in figure 3.21.

Figure 3.21 - The prototype with elements listed [38]

50

3.5. Control

The program that provides reading of voltage from the strain gauges was created.

Thanks to the W-Bridge with microcontroller inside, the task was to communicate

the computer with the W-Bridge and to collect information from two ports, that

are connected to the strain gauges. The program uses Phidget22 library and it is

based on the guideline from the official website.

The servo motors use pulse width modulation (PWM) signal of value 3V

and frequency of 50 Hz to control their position. The STM microcontroller provides

this kind of voltage on PE5 and PA2 ports. Positions of the motors have the PWM

pulse duration between 0,9 ms to 2,1 ms. This values match both end positions

of the servo motor.

The control system of the rehabilitation device uses signal from the strain

gauges and the programmed information about the task, that has to be achieved.

There are three main modes of task execution:

passive - if the patient is unable to move the fingers, the robot device moves

them repetitively without any involvement of the patient.

active - whenever the patient moves the fingers correctly, the device follows

the movement. If there is any longer pause in the movement, the robotic

device switches to passive mode. However, if the user starts the proper

movement, device switches back to the active mode.

resistive - the device keeps the constant resistance to the movement.

The patient needs to overcome it during the movement.

All three modes were programmed based on the signal from the strain gauges

and saturation of the PWM signal. The passive mode executes the task, by rotating

the motor till reaching the setpoint, which is set depending on the given task.

However, if the signal from the strain gauges is higher than the safety threshold, the

motors stop and go to the starting position. The values of maximal force were tested

and verified.

The active mode follows the movement of the user by keeping the value from

the sensor on the same level dependent on the position of the spring. In each

position, the spring creates different force according to Hooke's law. This mean that

the threshold in the task execution was set individually for each position. However, if

the position of the motor does not change during a short period of time the control

switches to the passive mode. This time period was set at 2 sec. Moreover, if the user

starts to move the finger in the wrong direction, the motor does not allow for it. At

the moment, the patient starts to move the finger properly, the value on the strain

gauge changes, and the motor switches back to the active mode. The value change

depending on the direction of the movement and the spring extension.

The resistive mode keeps the value of the strain gauge on the set level, taking

into account the spring extension. The value of the resistance may be set between

0,1 kg and 0,9 kg. This is due to the minimal force created by the spring. However,

51

in the prototype the resistance was set permanently. The way the resistive mode

works is similar to the active mode. Only the thresholds are shifted.

Because of the lack of encoders, the motor position is known indirectly from

the saturation of PWM signal. In each move, saturation changes by the known value

of the step. Based on that, the control of the position for each mode was made, while

the strain gauges signal was a trigger for further movement and the safety threshold.

During running the program, a menu window with possible modes of training

to choose appears. After clicking each button, a choice of different tasks is given:

1) flexing the finger to the grip position

2) full extension of the finger

3) flexing the MP joint to 90° position

4) flexing the PIP joint to 90° position.

Moreover, a test mode was created. This mode is used to control the motors

manually and save the reading from the strain gauges in each position. Thanks to

that, setup of thresholds and steps was done. In the prototype there is no temperature

compensation, the test mode may be used when the prototype is placed in a different

environment, to reset the values of thresholds. A different temperature can have

an impact on the strain gauge reading.

The whole control system was programmed in C# language in Microsoft Visual

Studio. The prototype was ran and controlled from the computer. Microcontroller

collects information about saturation of the PWM signal from the computer and

controls both motors. The interface of written application is shown in figure 3.22.

Figure 3.22 - The interface of the application [38]

When the program starts, it rotates the motors till the tense on the wires

occurs, what is the starting position. At the beginning, there is no tense, so the user

may easily install a glove. By clicking the task button, the program starts to execute it

in the chosen mode. Until the task is not finished or an error occurs, other tasks

52

cannot be chosen. After successfully executing a task, a message box pops up. Next,

another task can be chosen. The MP and the PIP joint exercise first moves the finger

to the extension position, and next the task is executed.

Lower buttons are locked unless the test button is clicked. In the test mode,

user can move each joint up and down manually. In each position data from the

strain gauges is saved in the file. Moreover, tasks buttons still work, but now, the data

is collected while the motors are moving.

If there is a high tense on the wire, motors go to the installation position

and the error message box pops up.

After clicking the exit button, motors moves to the installation position.

3.6. Analysis of the prototype

Firstly, calibration of all variables was done. This task was achieved in the test mode.

At the beginning, exact positions for each tasks were found manually. The saturations

for each position were listed in table 3.23.

Motor MP Motor PIP

Grip 1,95 1,72

Extenion 2,46 1,27

MP joint 90° 2,01 1,72

PIP joint 90° 2,46 1,45

Table 3.23 - Saturation in ms. The PWM signal has frequency of 50 Hz, what is 20 ms [38]

Further, the step value was found. The movement suppose to take around 2s.

The value of the PWM signal change in each step was set at 0,02 ms. However,

because of a fast change of saturation in the microcontroller, the motor was moving

very fast. To solve this problem, a delay was added to the loop of program. After few

trials, the delay of 100 ms was found that matches the best and gives a smooth

movement of motors and set the task executing time around 2 s.

After setting the motors, the voltage values of the strain gauges for each

position were found. The values of position between grip and extension position were

used to find a pattern of voltage change caused by the springs. In the first trial,

the change was measured in static positions, which means that the motor was

stopped in some position and data was taken. The value changes for both strain

gauges caused by the springs are shown on chart 3.24 and 3.25

53

Chart 3.24 - Behavior of the MP spring; static test [38]

Chart 3.25 - Behavior of the PIP spring; static test [38]

There can be noticed a linear trend of the characteristics. It should be pointed

out, that in both the charts the value of voltage increases while the spring is extended.

However, it has some deviation. One of the reasons is, while flexing the finger,

the wire from the springs and from the motors transfers the loads in different angle

to the finger. In some positions, bigger amount of the force compresses joints than

in others. That leads to not perfectly linear characteristic. Moreover, some errors

of the reader occurs. Mostly, the error oscillates between ±0,02 mV. Based

on the charts, impact of the springs in each step was found.

Next, few values of threshold for the active mode was set. However, with its

low value motors were not stable, and there was a lot of twitches. With higher value,

there was some resistance, that was used later in the resistive mode. In the next step,

a safety value was set. Whenever any strain gauge sends a value higher than the safety

-0,039-0,038-0,037-0,036-0,035-0,034-0,033-0,032-0,031

-0,03

1,95 2,06 2,12 2,19 2,26 2,33 2,39 2,46

Vo

ltag

e in

mV

Saturation in ms

MP joint

0,0670

0,0680

0,0690

0,0700

0,0710

0,0720

1,72 1,68 1,61 1,54 1,48 1,41 1,34 1,27

Vo

ltag

e in

mV

Saturation in ms

PIP joint

54

value, the program switches to the error mode, and releases motors and informs

about the error occurring. All the values of voltage are listed in table 3.26.

MP Voltage PIP voltage

Grip -0,031 0,069

Extension -0,029 0,072

Spring step 0,0009 0,0015

Active threshold 0,002 0,002

Resistive threshold 0,005 0,005

Safety threshold (grip) 0,01 0,01

Table 3.26 - Voltage variables in mV [38]

A difference in voltage between MP and PIP strain gauge does not correspond

to different load, but to starting value of measurement. The measured value is not

important. The control works based on the change of the value of voltage.

Finally, a test of all the movements and modes was done. First, on the

mechanical flaccid finger, then on the healthy person finger. The range of motion

goes to 90° for the MP joint, and around 60° for the PIP joint. A low value of flexing

the PIP joint is caused by big dimensions of the C-rings, that are bigger than

in the 3D model. During flexing, both C-rings obstruct to each other and prevent

further movement.

This test was not fully successful. In some position, the active mode was

activated without finger movement. Moreover, in the active and resistive mode the

required force to start movement was not always constant. All other modes worked

sufficiently.

The unsatisfying results of the device functionary were caused by the incorrect

data measurement. The signal was taken during static test, while during dynamic

movement the tension on the wires is different. Hence, the program was rearranged.

In the second measurement, the voltage values of the strain gauges were save

during movement of motors. This test was repeated several times to see the

measurement repeatability. Despite the threshold estimation, by repeating this test

for different values of the step and time delay, the smoothest movement was

identified. The results are shown on charts 3.27 - 3.32.

55

Chart 3.27 - Behavior of the MP spring; dynamic test A:

MP step = 0,02 ms; PIP step = 0,02 ms; time delay = 100 ms [38]

Chart 3.28 - Behavior of the PIP spring; dynamic test A:


Chart 3.29 - Behavior of the MP spring; dynamic test B:


-0,050

-0,040

-0,030

-0,020

-0,010

-

2,0

1

2,1

9

2,3

7

2,3

5

2,1

7

1,9

9

2,1

2

2,3

0

2,4

1

2,2

4

2,0

6

2,0

8

2,2

6

2,4

4

2,2

8

2,1

0

2,0

3

2,2

1

2,3

9

2,3

3

2,1

5

2,1

7

2,3

5

2,3

7

2,1

9

2,0

1

Vo

ltag

e in

mV

Saturation in ms

MP joint

0,065 0,066 0,067 0,068 0,069 0,070 0,071 0,072 0,073

1,6

1

1,4

3

1,3

6

1,5

4

1,5

0

1,3

2

1,3

0

1,4

8

1,5

4

1,3

6

1,4

3

1,6

1

1,5

9

1,4

1

1,3

9

1,5

7

1,4

5

1,2

7

1,3

4

1,5

2

Vo

ltag

e in

mV

Saturation in ms

PIP joint

-0,045 -0,040 -0,035 -0,030 -0,025 -0,020 -0,015 -0,010 -0,005

-

2,0

1

2,1

7

2,3

3

2,4

1

2,2

6

2,1

0

2,0

1

2,1

7

2,3

3

2,4

1

2,2

6

2,1

0

2,0

1

2,1

7

2,3

3

2,4

1

2,2

6

2,1

0

2,0

1

2,1

7

2,3

3

2,4

1

2,2

6

2,1

0

1,9

9

Vo

ltag

e in

mV

Saturation in ms

MP joint

56

Chart 3.30 - Behavior of the PIP spring; dynamic test B:


Chart 3.31 - Behavior of the MP spring; dynamic test C:


Chart 3.32 - Behavior of the PIP spring; dynamic test C:


0,065 0,066 0,067 0,068 0,069 0,070 0,071 0,072 0,073

1,6

1

1,4

5

1,3

0

1,3

0

1,4

5

1,6

1

1,6

1

1,4

5

1,3

0

1,3

0

1,4

5

1,6

1

1,6

1

1,4

5

1,3

0

1,3

0

1,4

5

1,6

1

1,6

1

1,4

5

1,3

0

1,3

0

1,4

5

1,6

1

Vo

ltag

e in

mV

Saturation in ms

PIP joint

-0,040

-0,035

-0,030

-0,025

-0,020

-0,015

-0,010

-0,005

-

2,0

1

2,1

2

2,2

4

2,3

5

2,3

9

2,2

8

2,1

7

2,0

6

2,0

6

2,1

7

2,2

8

2,3

9

2,3

5

2,2

4

2,1

2

2,0

1

2,1

0

2,2

1

2,3

3

2,4

4

2,4

1

2,3

0

2,1

9

Vo

ltag

e in

mV

Saturation in ms

MP joint

0,066

0,067

0,068

0,069

0,070

0,071

0,072

0,073

1,6

2

1,5

2

1,4

3

1,3

3

1,2

9

1,3

8

1,4

8

1,5

7

1,6

2

1,5

2

1,4

3

1,3

3

1,2

9

1,3

8

1,4

8

1,5

7

1,6

2

1,5

2

1,4

3

1,3

3

1,2

9

1,3

8

1,4

8

1,5

7

Vo

ltag

e in

mV

Saturation in ms

PIP joint

57

By comparing the test A (MP step = 0,02 ms; PIP step = 0,02 ms;

time delay = 100 ms) to the test B (MP step = 0,02 ms; PIP step = 0,02 ms;

time delay = 50 ms) it is noticeable the smoother effect of the spring on the MP joint

during faster movement. In this test, the slope is more stable and has smaller

distortion in the bottom part of the chart, that shows flexion. Moreover, during

flexion it was expected to have constantly decreasing voltage. In the test A and B, this

assumption was not met.

In the test C (MP step = 0,014 ms; PIP step = 0,02 ms; time delay = 100 ms),

the voltage during extension was constantly increasing and during flexion decreasing

as it was anticipated. Moreover, from all the tests, for the MP joint, the highest

repeatedly has the test C. In all listed examples there is a drop of the voltage before

flexion occurs. It is due to short pause between another task, hence no motor

movement affected the measurement.

In all the tests, data from the PIP joint shows a small jump at the end of the

extension. For the test B, there is a drop of the voltage in the mentioned area. In all

the tests the data is constant between each repetition. However, the smoothest

voltage change is in the test C.

Based on this results, the prototype was recalibrate to use data from the test C.

Moreover, the program was changed to save and use collected data instead of

previously chosen constant spring step. All listed thresholds stayed untouched.

With new calibration, all modes worked properly and all the tasks were

achieved. However, there were some motor twitching while moving. It is probably

caused by occurring high torque. The device was noisy, when the motors were loaded.

Moreover, as expected there was a force compressing joints together. This force did

not give an unpleasant sensation to the user.

The wrist holder, made from the wrist brace, did not stabilized the hand

in one position. There was a possibility of small rotation of the hand. It was caused

by the soft material from which the brace was made. However, in the 3D model

it should not be a problem, because there is used 3D printed ABS wrist holder, which

should keep the hand fixed.

The device can be easily placed on the table and training may be done

in a sitting position. Because of the flaccidity which occurs in the whole limb, there

could be a need for using some arm support for the patient.

4. Discussion

By comparing existing solutions of the hand rehabilitation robotic devices, it was

discovered that this area of device is new and still needs further improvements.

Thanks to researches and analysis of existing solutions, the guide for designing

of rehabilitation devices was delineated. Accordingly, a 3D model of a hand

rehabilitation robotic device for a home usage was designed. Based on it,

58

the prototype was built, tested, and analyzed. This process has permitted to get

a better look on pros and cons of the presented solution.

The biggest advantage of the tested device, comparing to other solutions, is the

possibility of using the device at home. From the beginning, the design was focused

on potential condition of usage. The developed instrument is cheap and easy to set

up, so it can be bought by the patient or lent from the rehabilitation center. This gives

an opportunity to train the affected limb for longer time compared to conventional

therapy, where the time with physiotherapist is limited.

The patient does not feel weight of the device, because his hand hangs inside it.

It is very important for the patient to relax his arm. However, this leads to the

limitation, that the device is not portable. The concept does not have an open palm

design, what does not leave a place for the future improvement of the device

as a portable one. Moreover, the device may use a software which can provide

entertaining games, however the limitation of not using the device during a regular

day activity will not be replaced by the games.

In contrast to other solutions, this device moves two joints, MP and PIP.

The skipped DIP joint does not have as important function as the other two

in everyday activities. However, as in many solution, there is no abduction

and adduction movement. There is no thumb leading and the wrist is fixated inside

the wrist holder.

The device loads the joints by compressing them together. Patients

with flaccidity very often do not feel their fingers well and compressing the joints

together might produce a better fluids flow in the fingers and restore sensation of

touch. However, this compressive force is different in different position, because of a

linear behavior of springs.

From one hand, the device does not allow to achieve a full range of motion

of the hand, mostly, because some parts of it are moving on the proximal side

of the hand. However, because of separate movements of fingers and joint, the area

of motion may be bigger than in most of existing solutions.

The device is small and light, which is good for transportation. However, it

has to be extended with a different sizes of gloves for different patients, and different

sets depending on which hand is affected, left or right.

The device uses only electric elements, which are possible to use at home.

Moreover, the device offers 3 types of task executing: active, passive, and resistive.

The rehabilitation may be more specific for individual patient.

The motors work loudly, what can be annoying for some patients. However,

with shorter arm of rotation, this noise should disappear. The prototype proved

working of the concept and opens a path to future analysis.

The studies were only limited to the test on the healthy person and the model

of the flaccid finger. There is a need of expanding them to post-stroke patients.

Moreover, there was only basic safety test and theoretical analysis of safety done

on it.

59

The system should be expanded with a software, that can collect data

and analyze it. Moreover, there should be a possibility of connecting the patient

and physiotherapist account, so that a telemedicine scheme can be implemented.

Telemedicine could lead to better feedback than in traditional rehabilitation. The

software may be expanded by regular games and VR system, what could lead to

higher involvement in the rehabilitation process. The thumb system should be added

to rehabilitation.

All mentioned improvements are possible to be added in the future works.

5. Conclusion

The main objective of this thesis was to design the robotic device for a hand

rehabilitation of the post-stroke patients. The device should be useable at home

without direct supervision of physiotherapist.

In the first part of the work, the aftermaths of stroke were presented. It was

proven that the hand rehabilitation is very often neglected, what leads to spasticity,

while the proper rehabilitated flaccidity in the first 4 weeks may increase recovery

of normal functioning of the hand. Next, the healthy hand movement was discussed

and compared to flaccid one. It is worth reminding, that post-stroke patient very

often struggle with joint instability, which is consequence of low tension

in the muscles. This aspect was taken into consideration in the designing process.

Some existing solutions of the robotic device for a hand rehabilitation were

presented and deeply analyzed. Almost all listed devices had a common issue

of strongly simplified movement of the fingers. Only the solution developed

by Polygerinos recreates movement of the fingers similar to the biological one.

All the devices help in a grip strength recovery, but only two of them, in theory, could

be used at home. Unfortunately, no research have been done yet in this area of usage.

Next, the guidelines for designing of a robotic device were defined. This part

helps to understand how the rehabilitation device should work, to give the best effect

on recovery process. Firstly, the main focus was put on creating a device that could be

used by the patient at home. Then, some mechanical factors as a range of motion,

frequency of movement, and forces acting on the finger were characterized.

With all collected knowledge, the concept of the rehabilitation device was

created and a first prototype was built. This prototype was used to verify work

of the concept. The concept was verified with a positive results and the 3D model

of the device was designed. The device has a shape of the box, that can be placed

on a table. Interior of the device has a glove with wires connected, that are pulled

by the servo motors and the springs. By controlling movements of the motors, fingers

are forced to flex and extend. For data collection, strain gauges were used.

All necessary calculations were done and proper element selection was made.

Based on the designed model, a prototype was built. It is limited to two joints

on the index finger, what is enough to test the control system and the task execution

of the prototype. For checking the control, three modes of control were created:

60

passive, active and resistive. For the motor control the PWM signal generator was set.

Moreover, a program to read values of the strain gauges was created.

The last task was to test and study the work of the device, and verify the quality

of task execution. Firstly, the device was calibrated, starting from the range

of movement. Then thresholds of strain gauges were set. After full calibration,

all modes were tested with use of the mechanical flaccid finger and a healthy hand.

The results of this work were satisfying. The aim of this thesis was to cover

the niche in home-use devices for rehabilitation. However, further researches

in the area of rehabilitation devices should take into account moving rehabilitation

process from the rehabilitation centers to the patients home. Nevertheless,

the created device is not free of defects, however with future development it can

be improved.

From all the listed examples the soft glove made by Polygerinos seems to have

the biggest potential to become major device used in the hand rehabilitation.

However, solution presented in this work, thanks to the adaptation to home

environment and a possibility of giving proper feedback of recovery process, can

be a great alternative for the traditional rehabilitation and represent a meaningful

step in the future design of the robotic rehabilitation devices, by showing potential

of a home therapy.

61

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