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Summary of Research

Study of an Innovative Machine/Human Interface for Reproducing Motion and Sensory Function by Connecting Humans and Machines

The Yokoi laboratory primarily pursues studies on two themes associated with the ap-plication 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 HandWe are developing a prosthetic hand capable of reproducing the motions of the hu-man hand based on EMG measurements. This work involves collecting three-channel EMG data to determine the intended movement, then activating the motors to pro-duce 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 move-ments 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 incorpo-rate eight patterns of active sensing to render them capable of distinguish-ing such tactile differences.The decision-making process under-lying actual motions is complex. For example, the action of slipping your hand into a glove requires a pas-sive 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 tech-niques that takes advantage of hal-lucinatory 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

Developing a man-machine integrated system and research on basic system technologies

Hiroshi YOKOI Laboratory

Hiroshi YOKOI

http://www.hi.mce.uec.ac.jp/yklab/

Myoelectric prosthetic hand; myoelectric sensor; cybernetics; cyborgs; tactile feedback; brain science; brain function assessment; biofeedback; power-assisting devices; brain-machine interface; rehabilitation; robotics

Affiliations

Japan Society of Mechanical Engineers; Japan Society for Precision Engineering; Society of Instrument and Control Engineers; Robotics Society of Japan

Member Hiroshi Yokoi, Professor

KeywordsProsthetic hand for able-bodied persons for EMG measurements

Fastening the prosthetic hand for able-bodied persons

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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 re-turning the tactile feedback to the area of the brain that typical-ly 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 DevicesIn the area of assistance and recovery, we are seeking to cre-ate 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 tech-nologies 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

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 in-volve the simultaneous execution of multiple motions. The sen-sors, 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 technolo-gies we have developed make it possible to build devices and address the entire research process. This is the greatest advan-tage offered by our laboratory.

Future Prospects

Making a Myoelectric Prosthetic Hand Available at the Cost of Cosmetic Prosthetics

The ultimate goal of Professor Yokoi is to produce an afford-able, 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

Life Sciences

A prototype myoelectric prosthetic hand, almost ready for practical use

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 pros-thetics that provide no function, only the appearance of having a hand.Based on our conviction that we can create a myoelectric pros-thetic hand in the same price range as cosmetic prosthetics, we have succeeded in producing models that approach the targeted price range.Every one of us has experienced societal pressures related to our appearance. Professor Yokoi hopes to help us move to-ward 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.