Euron Winter Meeting in Rehabilitation Robotics March 30th – April 4th 2008

Haptics in Rehabilitation

William Harwin

University of Reading

http://www.isrg.reading.ac.uk or http://www.reading.ac.uk/~shshawin/LN (follow the euron2008 link)

Abstract

• There are ideas in haptic technologies and haptic perception that are relevant to robot mediated rehabilitation. The technologies can inform the design of new, reliable, safe and (relatively) low cost devices and systems for assistive and rehabilitation technologies. A classic example of this approach is the use of the HapticMaster for neuro-rehabilitation. Haptic perception is concerned with giving convincing feedback to the individual that complies with the expectations of the interaction. This principle may also be relevant in ensuring and testing the hypothesis that any new neuro-rehabilitation technique might actually work.

What is haptics

• when we speak of ‘the world of touch’, or ‘tactile æsthetics’, we are referring to the data provided by an intimate combination of them both and for this sense Prof. Révész uses the adjective ‘haptic’. How does Prof. Révész find out whether the blind have tactile æsthetic experiences? – Mind XLVII 1939 cited in Oxford English

Dictionary

Haptic perception

Definition of haptic• haptik (M. Dessoir 1892) the study of touch and tactile sensations, esp. as a

means of communication • from the Greek φή (Haphe), able to come into contact with, able to touch• 'the sensibility of the individual to the world adjacent to his body by the use of his

body' [Gibson 1966]

Information capacity

• Receptive finger spelling– Human signer = 600

characters per minute

– Ralph finger spelling hand = 180 characters per minute

• Tadoma– Speaking speeds (C.

100 words per minute)

Extending physiological proprioception/ Active touch

• EPP – D.C. Simpsons (1972) explains rapid learning curve for cable drive prosthetics– The basis for tool use– Information synthesis

• Cutaneous– Temperature (heat flow)– Pain– Skin vibration (texture, slip

friction)– Skin stretch

• Proprioceptive– Joint speed, muscle tension

and length

Proprioceptors and Skin receptors

Receptor Sensor Field Frequency Threshold Sensed Correlate

Diameter

(mm) (Hz) (um)

RAI Meissner 3-4 8-64 30 Tickle, Vibration, Tap

SAI Merkel 3-4 2-32 15 Pressure

RAII Pacinian >20 >64 1 Vibration, Tickle

SAII Ruffini >10 <8 60 Stretch, Tension

RA=Rapid adaptingSA=Slow adapting

Golgi Tendon Organ/Muscle spindle, limited by joint dynamics0-13 Hz

Temperature receptors (free nerve endings) Pain receptorsVestibular system

Exploratory procedures (S. Lederman)

Lateral motion(texture)

Pressure(hardness)

Contour following(global shape)

Unsupported holding(weight)

Enclosure(global shape)

Static contact(temperature)

Also specific function testing (eg glove), and self motion tests (eg scissors)

Haptics are two-way and multimodal

• Vision dominates– Rock & Victor, McGirk

• Wolperts open loop– Most predictions are accurate enough

(Size weight illusion)

• Haptic perception is usually a component of a multisensory input

• Motor plan for haptic perception also available to change the local environment

• Haptics may serve to confirm where visual cues are insufficient.

• Gepshtein and Banks, Visually easy allow angle discrimination, visually difficult tasks rely on stereo vision and haptics

So what are haptic interfaces

Hapkit: First experiments in a haptic drum kit• Feels and sounds (almost) like a

real drum• Normal drumming techniques

can be applied• Play multiple drums in the same

location• Suspend large ‘virtual’ drums

upside-down, create new types of drum

Cave Navigation via a shopping trolley

Haptic interface principles

• Ideal Freespace– Frobot=0– Mass=0– Large hand accelerations

possible

• Ideal Hard contact– Fhuman=Frobot– Fhuman=K displacement

• For a steel cube 1 cm3 displacement =1um

• Grounded haptic interface allows perception of weight xmf

Technical challenge

• Actuators saturate• Setting Factuator=0 problematic, especially

as frequency increases– Back drivable system design on this

assumption (90% of devices)– Impedance systems attempt to reduce both

Factuator (during freespace) and effective proof mass

• Measurement of transition from Freespace to hard contact is noisy, quantised and delayed

– Resulting in limit cycles and low device stiffness

• Workspace of device seldom matches human

• PLAY STOAT VIDEO

U.Washington Biorobotics Laboratory exoskeleton

Ungrounded and vibrotactile

• Cybergrasp and• feelspace

• Not possible to convey perception of weight

Why is haptics relevant to rehabilitation?

Because they are designed to work with humans at multiple levels.

Safety

Low inertia implies low energy at (relatively) high speeds.

Compliance implies time for energy to dissipate (see Zinn et al. 2004)

Control architectures

• Impedance

• Admittance

• Backdrivable

• Encounter

• Passive

• Cobots

Backdriveable (Carignan and Cleary 2000)

hdhcl ZZZ

• Assumes all torque at joints transfers to the tip of the robot

• MIT manus

Impedance (Carignan and Cleary 2000)

• Simpler form of admittance control (see also Carignan 2000)• Requires a force torque sensor at wrist• Gentle/S, Gentle/G, Gentle/G hand assist are all admittance

hFdhcl ZKIZZ 1)(

Encounter

• Encounter haptics used in therapy by Erlandson 1995

Passive

• Neater eater

Passive

• Energy going into device greater than energy coming out.

• Suitable for technologies such as ER and MR Fluids

• Example shown is the Oxford Magpie (Evens)

Passive Neater eater

Cobots

H: Pamaid

• Now known as the guido, available from haptica.com

• A linkage based cobot developed by D. Surdilovic et al (2003) at Fraunhofer IPK, Berlin

Scaling demand: Comparison of devices

Device Price Workspace Stiffness Force max/cont

Tooth size

(mm) (N/mm) (N)

Omega £8,540 160x160x 120

14.5 12/12 3.5x

Phantom Desktop

£6,530 160x120x 120

3.16 7.9/1.7 14x

Omni £1,205 160x120x 70 1.53 3.3/0.88 33x

Premium 1.5 £13,820 381x257x 191

3.5 8.5/1.4 14x

Novint Falcon euro 250 101x101x 101

~8 9.0/? 6x

HapticMaster (Surrogate for othodont)

euro ~20,000

400x360x ~460

50 100 1

Conclusion

• Haptics provides an excellent working framework for many rehabilitation applications where there is a need for direct contact between the human and the machine

• The forces are well controlled and a range of stiffnesses and impedances can be set by high level controllers.

• http://www.reading.ac.uk/~shshawin/LN/L8hapticdesigns.html