Compliance control of an ultrasonic motor powered prosthetic forearm

The capability of a prosthetic device to mimic the response of the actual limb with respect to voluntary motor commands and to environmental loads should be addressed. This paper discusses the compliance control of an ultrasonic motor powered prosthetic forearm which utilizes cutaneously measured electromyogram (EMG) signals sensed with electrodes over the muscles as means of detecting motor commands sent by the central nervous system (CNS). Compliance control of the artificial limb was studied by implementing the bilinear model of the forearm and hand. This model emphasizes the role of the visco-elastic properties of the musculo-skeletal system of the actual limb in controlling its net configuration and movement. The flexor and extensor muscles extending over a joint influence the overall joint impedance and determines the equilibrium position of the joint. Relaxing both flexor and extensor muscles makes the joint compliant to external forces, while activating both muscles increases the impedance of the joint