Possibility of using a continuum master device to control a continuum surgical robot

Ho Man Ng

Imperial College Biomedical Engineering (BEng)

About Me

• 3rd Year Imperial College student, biomedical engineering• Summer internship in CUHK• Interested in clinical medical research in the future

Winner of the best poster in 2nd Year Group Project – developing a horse riding simulator for physiotherapy

What is the problem?

• ESD robotic surgery using endoscope (developed by CUHK)

• Surgeons’ feedback about viewpoint (at PWH)– Hard to measure distance in endoscope– Two arms covering each other– Not easy to predict and cut the submucosal tissue

• ESD surgery is technically challenging for beginners, high learning curve and many complications for beginners, so haptic feedback useful for learning [1]

1. Anthony Yuen Bun Teoh et al. "Difficulties and Outcomes in Starting Endoscopic Submucosal Dissection - Springer." (n.d.): n. pag. Difficulties and Outcomes in Starting Endoscopic Submucosal Dissection - Springer. 01 May 2010. Web. 15 Aug. 2014.

What is a continuum robot?

• Worked for narrow environments• Hyper-redundant design

A section of a continuum robot, pulled by strings (in blue)The orange part is the primary backbone

Background information

• Many existing commercial haptic devices

Novint Falcon [2]

HapticMaster [3]

2. "Novint Falcon." Novint Falcon. Novint, 14 Aug. 2014. Web. 14 Aug. 2014.3. Der Linde, Van, R.Q et al. FCS Control Systems, The Netherlands (n.d.): n. pag.The HapticMaster, a New High-

performance Haptic Interface. Universiteit Twente, 15 Aug. 2014. Web. 15 Aug. 2014.

Prior Work

• Work has been done to do haptic feedback in simulation of Minimal Invasive Surgery [4]

– Force feedback is usually the main method in haptic feedback– Done for training surgeons for Minimal Invasive Surgery– Prerecorded data of specific tissues in different organs would be

transferred to the master– Difficulties include real time rendering and the difficulties to

simulate realistic tool-tissue interactions

4. Cagatay Basdogan et al. "Haptics in Minimally Invasive Surgical Simulation and Training." IEEE Computer Graphics and Applications. N.p., Mar.-Apr. 2004. Web. 15 Aug. 2014.

Prior Work

• Research has also been done to provide haptic feedback to users with robotic surgical systems [5]

– Experiments have been done using Da Vinci System– Focused on providing force feedback– Surgeons typically uses sense of touch to puncture tissue, pull

suture through and tie knots– It was found that force feedback reduces the number of errors by

a factor of three (although data is not conclusive)

5. Okamura, Allison M. " Methods for haptic feedback in teleoperated robot-assisted surgery." National Center for Biotechnology Information. U.S. National Library of Medicine, 29 June 2005. Web. 15 Aug. 2014.

Design of master for haptic movement• Continuum robot is hard to map to existing haptic devices

and not ergonomic• Design of a continuum master device solves mapping

problems and is easier for surgeons to predict the right movement

Design of master for haptic movement

Theory – Impedance Control

• Classical feedback loop methods are not suitable for controlling the haptic device

• Instead, using relation between force and position as a control parameter [6][7]

6. Hogan, Neville. "Impedance Control: An Approach to Manipulation: Part I—Theory." Journal of Dynamic Systems, Measurement, and Control 107.1 (1985): 1. Web.7. Hogan, Neville. "Impedance Control: An Approach to Manipulation: Part II—Implementation." Journal of Dynamic Systems, Measurement, and Control 107.1 (1985): 8. Web.

Classic algorithm for rendering with an impedance-type device[8]

1. Read the position of the user from the haptic display

2. See if there is any collision with the objects in the real environment

3. Calculate forces if there is any collision

4. Send corresponding torque commands to the motor

8. Allison M. Okamura. "Lecture 4: Kinesthetic Haptic Devices: Rendering." ME 327: Design and Control of Haptic Systems Spring 2014. Stanford University, 2014. Web. 15 Aug. 2014.

Static rigid body interaction

• With impedance control, nothing is perfectly rigid: F=kx

If xuser= xwall , F=k(xwall - xwall)

Stiffness k>0

Damping for obstacles

• Adding a dissipative term, where b is the damping coefficient

• The term would only work when going into the wall• Also creates vibrations at impact point

Modeling for friction?

(a) Viscous damping; (b) coulomb model; (c) Coulomb and viscous; (d) “stiction”; (e) Karnopp’s model; (f) the Stribeck effect

9. Richard, C., Cutkosky, M. R., & MacLean, K. (1999). Friction identification for haptic display. Proc. of Haptic Interfaces for Virtual Environments and Teleoperator Systems (HAPTICS). 19 Aug 2014

Another method: admittance control

[3]

• Inverse of impedance control• i.e.: viewed from the haptic device, it is force in,

displacement out• Backlash and tip inertia eliminated• Impedance control: Performance lacking in higher forces,

high mass and high stiffness[10]

• Admittance control: high stiffness and minimal friction• Intrinsically register forces encountered

10. Adams, R.j., and B. Hannaford. "Control Law Design for Haptic Interfaces to Virtual Reality." IEEE Transactions on Control Systems Technology 10.1 (2002): 3-13. Web.

Admittance control algorithm

Experiments that can be done

• Building a impedance controlled continuum master device and test if it is useful for controlling the continuum robot

• Test and build the relationship of different tissue and its stiffness and damping value

• Possibility of using admittance control to do a haptic feedback system on the continuum master device

Difficulties faced (for experiment 1)

• Controller issues:– Faulhaber motion controller (RS232) is designed to deliver

precise position and can return voltage and current– Can create elasticity but there isn’t a way to control the stiffness

due to the internal feedback loop in the motion controller– Not found away to get around it yet– Faulhaber do not have a force/voltage input, which makes

controlling the force directly difficult

Difficulties faced (for experiment 1)

• Passivity issues:– If the energy feedback from the robot is larger than the original

force, the system would be unstable– Oscillation may occur as well if the feedback force factor wasn’t

chosen well– Hard to choose the right force due to the difficulty to change the

force control with the controller used

Possible solutions

• Use Arduino with a motor controller to directly control the voltage to the motor, which is analogue to the force– Separate the position sensor from the motor– Use a simple motor

• Use admittance control and map the PVA vector through force input– Preferably force sensor close to hand

The way forward

• Haptic feedback is a difficult topic with some of its theory already well researched

• However, continuum robots is a relatively new concept• A demand in haptic feedback in surgery – force sensing

technique through continuum robot is viable[11]

• Useful to integrate into existing ESD surgical robot in the future

11. Xu, K., & Simaan, N. (2008). An investigation of the intrinsic force sensing capabilities of continuum robots. Robotics, IEEE Transactions on, 24(3), 576-587.

The way forward

• Other methods to increase the user experience of surgeons can be done

• Augmented reality with the opportunity to detect tumour locations is one of the directions– Using our own camera, there is an opportunity to work on such a

system in the future– Replacing the need to have a haptic feedback by the visual cues

On another note

• Other work: Capsule Solidworks

On another note

• Visiting MISSC and help setting up and performing experiments

Acknowledgements

• Prof. Carmen Poon• Hu Yang, Kachun and Esther in the lab• Prof. Yam in MAE Dept• Prof. Chiu, Dr. Chung and many other doctors in MISSC

centre

© Faculty of Medicine The Chinese University of Hong Kong

Thank You!