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Georgia Institute of Technology | Milwaukee School of Engineering | North Carolina A&T State University | Purdue University

University of Illinois, Urbana-Champaign | University of Minnesota | Vanderbilt University

Test Bed 6-Human Assist Devices

(Fluid-powered ankle-foot-orthoses)

Liz Hsiao-Wecksler (UIUC) Will Durfee (UM) Geza Kogler (GT)Zongliang Jiang (NCAT)Doug Cook (MSOE)Vito Gervasi (MSOE)Tom Chase (UM)David Kittelson (UM)Eric Barth (Vanderbilt)

Yifan David Li(UIUC) Morgan Boes (UIUC)Mazhar Islam (UIUC)Jicheng Xia (UM)Nebiyu Fikru (UM)Lei Tian (UM)Mark Hofacker (Vanderbilt)Dan Cramer (Vanderbilt)Davorin Stajsic (NCAT)

Faculty Students

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Motivation Test Bed 6 Timeline Progress on Pneumatic AFO Progress on Hydraulic AFO TB6 Affiliated Projects Future Work

Overview

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Do energy-to-weight and power-to-weight advantages of fluid power (FP) continue to hold for tiny, mobile FP systems (10-100 W)? Drive development of enabling FP technologies Create new portable, wearable, FP assist devices

TB6 Product Platform: Ankle-Foot Orthosis Numerous pathologies / injuries create below the knee muscle

weakness and impair gait Currently no portable powered ankle-foot orthosis avalible for treatment

Stroke (4.7M*) Polio (1M*) Multiple sclerosis (400K*)

Spinal cord injuries (200K*) Cerebral palsy (100K*) Trauma

* Number of people in US that would benefit from an active lower limb orthosis [Dollar and Herr, IEEE Trans Robotics, 24(1): 144-158, 2008]

Major question being answered

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Potential applications

• Rehabilitation of lower leg muscles (possible from the patient’s personal residence instead of restricted to clinic)

• Assistance in walking (including flexibility to walk outside)

• General use for public commercial applications where large amounts of walking are required

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TB6 Development Timeline

ca 2007

ca 2008

ca 2010Passive

pneumatic power- harvesting AFO for motion

control (Untethered)

Powered pneumatic

AFO for both motion

control and assistance (Tethered)

Portable Powered pneumatic AFO for both motion

control and assistance

(Untethered)

Multiple Design Versions Started with motion control and progressed to powered actuation

Pneumatic AFO

Custom integrated (Untethered)

CCEFP affil. proj.50-150 psi6-20 Nm

Light-weightSafer

Off-the-shelf components

Hydraulic AFO

ca 2012

IMU

• IMU based mode recognition• Functional energy efficiency

analysis

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Setup for Pneumatic AFO

Power: Engine or CO2

Electronics: Sensors and

driving electronics

Actuation: Valves,

Regulators, Actuator

The world’s lightest, most compact, untethered, pneumatically powered AFO

Structure:Shell, lines, integration

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Actuation for LEVEL GROUND

Level: Dorsiflexion, create clearance for limb advancementStair Descent: Plantarflexion, prepare for next landing

Different Functional Need for Stair Descent

IMU

Inertial Sensor Based Gait Mode Recognition and Actuation ControlGoal: recognize different gait modes (stairs and ramps) and control the actuation accordingly

Actuation for Stair Descent• Mode recognized by IMU• Plantarflexor (0-20GC and 60-100GC)

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Number of Subjects: 5 (male) Weight: average 82.0kg (70-97kg)Age: average 23.4 (20-27) Height: average 178.6cm (166-191cm)

Experimental ProtocolThree gait mode conditions:1.Outdoor stairs, one step traverse2.Outdoor stairs, two step traverse3.Indoor stairs, two step traverseLevel ground was assessed during approach for ascent and descent the stairsThree PPAFO actuation algorithms:a.Passive: no actuation providedb.Mode Controller: level controller except stair descent (plantarflexor torque during swing)c.Level Controller: actuation provided using original level ground walking mode controller for all gait modesOnly (c) tested for gait mode conditions 2-4.

Subject

IndoorTwo

StairsMode Ctrl

OutdoorTwo

StairsMode Ctrl

OutdoorOne StairMode Ctrl

1 98 92.5 98.1

2 92.1 71.5 78.2

3 90.5 88.9 96.4

4 96.7 97.2 95.5

5 92.8 92.9 91.5

Avg 94.0 88.6 91.5

Inertial Sensor Based Gait Mode Recognition and Actuation Control

Stair and ramp modes can be recognized by tracking the vertical position differences and foot angle for each step

TB6 Team Meeting, 02/22/2013 9

Goal: Compare fuel consumption and work output between different control algorithms

CO2 Bottle

Wireless Data Logging

Micro Controller

Computer

Data Logging Receiver

Force, Angle, Pressure

Procedure Notes:

•Four healthy subjects (22-30 y.o.)

•3 minute trials of walking, ~150Hz sampling

•CO2 bottles were weighed before and after each trial for fuel consumption

•Each bottle was warmed to room temperature in a water bath before use

• 4 bottles were rotated for use to allow warming

Control Mode Condition

Direct Event

State Estimation – no recycling

State Estimation – with recycling

Functional Efficiency Analysis

TB6 Team Meeting, 02/22/2013 10

Control Mode Condition Average Fuel consumption

(per 3 min trial)

Average NetWork output

(per step)

Direct Event (DE) 57.5 g 4.7 J

State Estimation – no recycling (SE) 61.0 g 3.5 J

State Estimation – with recycling (SER) 50.5 g 3.3J

Results

•SE took on average 6% more fuel than DE.

•SER saves 17.5% of fuel compared to the fuel consumption of SE.

•The DE scheme did more work than SE or SER.

•SE and SER did approximately the same amount of work per gait cycle

Results on fuel consumption and net work output for different controllers

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Hydraulic Ankle Foot Orthosis: First Platform

Torque: 90 N-m(600 lbs force for a 3cm moment arm)

Small packaging space

Weight: < 1 kg

Portability: untethered

Longevity: 10,000 steps

Peak power: 250 W

Artist rendering

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Pump Conduits ActuatorsBatteryElectric Motor

Linear?orRotary?

Long?orShort?

Piston?or

Vane?

Gearhead?or

Not?

Many System Level Questions Need to Be Answered Before Specifying Each Component

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0 200 400 600 800 10000

20

40

60

80

100

Gear ratio

Gea

rhea

d ef

ficie

ncy

(%)

1 2 3 4 5 6 7 8 9 1040

50

60

70

80

90

Pump displacement (cc/rev)

Pu

mp

effi

cie

ncy

(%

)

The Efficiency and Weight of Each Component Can Be Modeled Analytically

Electric DC Motor Weight

Gear-head Efficiency

Hydraulic Cylinder Weight

Axial-Piston Pump Efficiency

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The Established Efficiency and Weight Models Can Identify the AFO Configuration

Power Pack

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2pp

outoutth P

TV

Pump displacement (cc/rev):

tan2

p

thp Rz

VAPump piston area (m^2):

pp Ad 4

Pump piston bore (m):

z

pR

Num. of pistons

Pitch radius

Swash-plate angle

),,,( pppthp PdVf Pump efficiency:

Design Variables Can Be Expressed by Known Parameters*

* Key pump design variable: pump displacement, pump piston bore and pump efficiency. To simplify the design problem, other pump parameters were adopted from the three-piston Oildyne pump.

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100

100

100

120

120

120

120

140

140

140140

160

160

160

160

180

180

180

200

200

200

220

220

220

240

240

240

260

280

10

10

10

10

15

15

1515

20

2020

252525

303035

0.5

0.5

0.5

0.5

1

11

11.5

1.5 1.5222

2.52.5

33 3.544.55

15 15 15

20 20 20

25 25 2530 30 30

35 35 3540 40 40

240

260

260

260

260

280280

280

280

280

280280300 300

300

300300

300

320 320320

320320

320

340 340360 360380400

Pump shaft speed (rpm)

Pu

mp

ou

tlet

pre

ssu

re (

MP

a)

1200 1400 1600 1800 2000 2200 2400 2600 2800 3000

5

10

15

20 Desired DC motor T (mNm)Pump cylinder bore (mm)Pump displacement (cc/rev)Cylinder bore (mm)Battery weight (g)

Design Variables Can Be Plotted on P-n Plot

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Component Part Number Wt (g) Dia (mm) Len (mm)

Actuator Package

PF Cylinder Custom part 165 17.2 100

DF Cylinder Custom part 23 7 100

Joint Pulley Custom part TBD 60 NA

Total 188 72 130

Power Source

Valves TBD

Pump Custom part 190 32 53

Gear Head Maxon 166930 118 32 27

DC Motor Maxon 397172 141 45 27

Total 449 45 107

Energy Source

Battery TP2700-6SPL25 465 50 x 34 x 102

The Hydraulic AFO Components Can Be Specified Based on the Design Map

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1. System level analyses are necessary to identify the design guidelines for the hydraulic AFO.

2. The analytical efficiency and weight models for the system level analyses are achievable.

3. For the hydraulic AFO, the actuators would better be separated from the power source, similar to an excavator.

4. The analytical efficiency and weight models are also needed to specify each component in the hydraulic AFO system.

Conclusions

Goal : Create an efficient MEMS based proportional valve for controlling air flow in pneumatic systems

Targets High flow rate (40 slpm at 6 → 5 bar) Compact (< 4 cm3)Low power usage (< 1 mW)

ProgressPort plate with array of orifices successfully fabricated and tested for flow and pressure

Displacement sensor integrated to meso-scaleprototype valve

Fabrication of MEMS unimorph actuator nearing completion

Next StepsComplete and test MEMS unimorph actuatorDemonstrate proportional control on meso-scale valve

Fabricate MEMS bimorph PZT actuator

Affiliated Projects: 2F MEMS Valve (Nebiyu Fikru, UMN)

Electrical

ActuatorPort plate

contact

pallet

Spring 2013 plans• NCAT will continue to work on Quanser and

XNA integration, and further game and GUI development. Currently there are some XNA and Quanser API incompatibilies that need to be resolved.

• Plan on doing experimental research using CybexNorm system (shown) to emulate a game therapy session in order to test the effects of different factors that may have an impact on game performance (social interaction among patients, leg dexterity, different seating positions, etc.)

• This experiment will help with further development of the game with features that ensure patient improvement, and a game therapy that is effective on a more diverse patient population.

Affiliated ProjectsClinician Centered AFO Interface (Davorin Stajsic, NCAT)

• Passive HCCI thermal-management – Successful testing w/ surrogate source– http://utwired.engr.utexas.edu/lff/symposium/proceeding

sArchive/pubs/Manuscripts/2012/2012-09-Cook.pdf

• Currently not funded by CCEFP• Developing high-efficiency pneumatic actuation

system– >60% ηthermodynamic using <15g fuel/hr– CCEFP rejected 2011 proposal– Proposal submitted to NSF National Robotics Institute

• Co-robotics applications – legged robots, assisting humans

Affiliated Projects – 2D MSOE

Goal : Create a gravimetrically and volumetrically efficient strain accumulator for pneumatic systems

•Targets • Pressures 7-10 bar • Max volume of 34 ml

•Progress• Accumulator operating below 7 bar fitted

•Next Steps• Fabricate accumulator for use with pressures up to 150 psi• Evaluate gravimetric and volumetric efficiencies

Affiliated ProjectsElastomeric Accumulator (Dan Cramer, Vanderbilt)

Goal : Create a compact, near silent, pneumatic power source with low amounts of vibration

Targets 20 Watts80 psigMounted on ankle-foot orthosis

ProgressCompleted dynamic model of thermocompressorConstructed single stage prototype

Novel take on Stirling cycle device Piston controlled directly by brushless DC

motor and reciprocating lead screw Developed method of achieving high rates of

heat transfer in compact device In process of patenting

High Temperature/High Efficiency Enabled by use of fused quartz and

machinable ceramic

Next Steps Instrument and test prototypeRefine modelBuild multistage compressor capable of high pressure

Pressure Transducer

Fused Quartz Cylinder

Stainless Steel Heater Head

Macor Machinable Ceramic

Reciprocating Lead Screw

DC Motor

Affiliated Projects: 2B.4 Controlled Stirling Thermocompressor (Eric Barth, Vanderbilt)