Transcript PowerPoint at Reading

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 neurorehabilitation 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   (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
SAII Ruffini
>10 <8
RA=Rapid adapting
SA=Slow adapting
60
Vibration, Tickle
Stretch, Tension
Golgi Tendon Organ/Muscle spindle, limited by joint dynamics
0-13 Hz
Temperature receptors (free nerve endings)
Pain receptors
Vestibular system
Exploratory procedures (S. Lederman)
Lateral motion
(texture)
Pressure
(hardness)
Contour following
(global shape)
Static contact
Enclosure
Unsupported holding
(temperature)
(global shape)
(weight)
Also specific function testing (eg glove), and self motion tests (eg scissors)
Haptics are two-way and multimodal
•
Vision dominates
–
•
Wolperts open loop
–
•
•
•
•
Rock & Victor, McGirk
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
 f  mx
• Grounded haptic interface
allows perception of
weight
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
•
•
•
Not possible to convey
perception of weight
Cybergrasp and
feelspace
Haptic and visual spaces
• Co-located haptics and vision
– Implies stereo graphics (e.g.
shutter glasses)
• Closely associated haptics
and vision
16
Non co-located spaces with
scaling
• Scaled and displaced haptic and visual spaces
17
Visual dominance
• Rock, Harris and Victor
• Ernst, Gepshtein and Banks – visually difficult tasks
gain greater assistance from haptic
18
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)
Z hcl  Z d  Z h
• Assumes all torque at joints transfers to the tip of the robot
• MIT manus
Phantom Sensable
(Backdrivable)
Impedance (Carignan and Cleary 2000)
1
Zhcl  Zd  ( I  KF ) Zh
• 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
HapticMaster (Admittance
control)
Encounter
• Encounter haptics used in therapy by Erlandson 1995
Passive
• Neater eater
• Can calculate passivity measures as sum of energy
into and out of all the terminals (ports) that interact
with humans or the environment.
• Passive if total energy is decreasing.
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
Work of Dragoljub Surdilovic,
Fraunhoffer IPK, Berlin
Difference Between 2-Arm Cobot and
Corresponding Robot-Manipulator
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
(mm)
(N/mm)
(N)
Tooth size
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/L8hapticdesig
ns.html