http://www.hi.mce.uec.ac.jp/yklab/
Developing a man-machine integrated
system and research on basic system
technologies
Hiroshi YOKOI Laboratory
Summary of Research
Study of an Innovative Machine/Human Interface for Reproducing
Motion and Sensory Function by Connecting Humans and Machines
Hiroshi YOKOI
The Yokoi laboratory primarily pursues studies on two themes associated with the application of human interface technologies to medicine and welfare. The first theme is
the study of “substitution” technologies for motor functions, such as artificial hands
and feet for individuals who have lost their limbs. The second involves assistance and
recovery technologies for those who have lost some of their motor functions due to
partial paralysis or other conditions.
Study of Substitution Technologies and Myoelectric Prosthetic Hand
We are developing a prosthetic hand capable of reproducing the motions of the human hand based on EMG measurements. This work involves collecting three-channel
EMG data to determine the intended movement, then activating the motors to produce this movement. We have succeeded in reproducing 15 patterns of movement,
including closing and opening the hand, gripping, and wrist movements. Together,
these allow users to play the rock-paper-scissor game, reach for objects in narrow
spaces, write text, and turn doorknobs. The functions made possible by these movements account for 61% of the actions performed by the hand in normal household
settings. Our use of tactile feedback contributes to the success of this system. For
example, the motions involved in
pouring water are quite similar to
those for pouring oil, but humans can
detect the difference in the sensations
triggered by the two actions. Our
myoelectric prosthetic hands incorporate eight patterns of active sensing
to render them capable of distinguishing such tactile differences.
Keywords
Myoelectric prosthetic hand; myoelectric
sensor; cybernetics; cyborgs; tactile
feedback; brain science; brain function
assessment; biofeedback; powerassisting devices; brain-machine
interface; rehabilitation; robotics
Japan Society of Mechanical
Engineers; Japan Society for
Affiliations Precision Engineering; Society of
Instrument and Control Engineers;
Robotics Society of Japan
Member
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Hiroshi Yokoi, Professor
The decision-making process underlying actual motions is complex. For
example, the action of slipping your
hand into a glove requires a passive element of exerting just enough
force to keep the fingers extended.
Developing a mechanism for such
delicate motion control is among our
key future research themes. Another
theme is that 200 tactile stimulus
points are required to reproduce the
tactile sensations experienced at the
fingertips, however, in actual use,
the number of tactile feedback pads
cannot be increased to stimulate 200
points. Having identified an approach
based on signal processing techniques that takes advantage of hallucinatory motion to reproduce tactile
sensations using fewer pads, we are
proceeding with research in this area.
Alongside our studies on myoelectric
prosthetic hands, we are analyzing
the effects of myoelectric prosthetic
hands on brain function, as shown by
fMRI (functional magnetic resonance
Prosthetic hand for able-bodied persons for EMG measurements
Fastening the prosthetic hand for able-bodied persons
Life Sciences
imaging). We have investigated differences in the reaction of
the brain triggered by the use of myoelectric prosthetic hands
with and without tactile feedback, finding, in the latter case,
that the activity in both the motor and visual cortexes is high
and closely coupled to the movement of the hands and eyes,
while the former case is associated with less brain activity.
We made a curious discovery during this investigation: Due to
the instruments available at our facility, the prosthetic hand had
been attached to the right-hand side of the subject, thereby returning the tactile feedback to the area of the brain that typically processes information for the left side of the body. However,
the brain still responded as though the right hand was present.
That is, the brain correctly registered the presence of the right
hand and immediately switched to the area required to process
the associated signals. Based on this discovery, we concluded
that even when brain function is partially lost, as with a stroke,
it may be possible to recruit another part of the brain to assume
the functions using this flexible capacity of the brain.
Study of Assistance and Recovery and Power-Assisting
Devices
In the area of assistance and recovery, we are seeking to create a power-assisting device not just for use in assisting the
handicapped, but for use in rehabilitation programs. In cases
involving paralysis of the arm, the muscles in the hand normally
become fixed in the closed position. Rehabilitative procedures
to prevent such muscle contracture involve exercises to stretch
and flex the fingers. Our research applies our power-assisting
devices to such procedures to enhance the effectiveness and
efficiency of rehabilitation.
Our study revealed that even paralyzed hands emit myogenic
signals, although weak. By applying the abovementioned technologies of the myoelectric prosthetic hands, it may be possible
to develop a power-assisting device that can move a paralyzed
hand at will.
Advantages
Approaching Natural Human Hand Motion
Through Biofeedback
A prototype myoelectric prosthetic hand, almost ready for practical use
The system for the prosthetic hands being developed at our
laboratory relays myoelectric signals to the prosthetic hands
while relaying information on the actions of the hand/machine.
This crucial biofeedback allows us to reproduce finger motions
in ways previous systems could not.
We have also developed a unique algorithm for the action of
turning a doorknob, which is realized through two successive
decisions: gripping the knob and rotating the wrist, performed
in combination with a complex movement of the fingers. Our
laboratory prides ourselves in having devised one of the most
advanced technologies for reproducing such actions that involve the simultaneous execution of multiple motions. The sensors, methodology, software, and even the myoelectric sensors
we use were all created at our laboratory; the methodology and
software for estimating the movements of the fingers based on
myoelectric signals were also developed here. The technologies we have developed make it possible to build devices and
address the entire research process. This is the greatest advantage offered by our laboratory.
Future Prospects
Six servomotors that control the motions of the prosthetic hand
only ten or so people across Japan actually use myoelectric
prosthetic hands; the rest have access only to cosmetic prosthetics that provide no function, only the appearance of having
a hand.
Making a Myoelectric Prosthetic Hand Available at
the Cost of Cosmetic Prosthetics
Based on our conviction that we can create a myoelectric prosthetic hand in the same price range as cosmetic prosthetics,
we have succeeded in producing models that approach the
targeted price range.
The ultimate goal of Professor Yokoi is to produce an affordable, practical myoelectric prosthetic hand. Currently, even the
simplest myoelectric prosthetic hands capable of executing the
opening/closing motion of the hands cost as much as a new
car. The national government provides financial aid for such
prosthetics only to those who have lost both arms, and even
this aid falls woefully short of actual costs. It is no surprise that
Every one of us has experienced societal pressures related to
our appearance. Professor Yokoi hopes to help us move toward a society in which people are free to identify what is truly
important, that which is found inside, and to express pride and
hope in who they are. Through his studies, he hopes to change
society by eliminating the sense of inadequacy that so often
accompanies morphological or functional differences.
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