Myoelectrically Controlled NYU-Hosmer Prehension Actuator and Michigan Hook

D. S. CHILDRESS, PHD*Chicago, Illinois


The New York University-Hosmer Prehension Actuator (PA) and the Michigan Hook are both powered prosthetic components that operate by means of an electric motor providing torque to wrap a flexible cable around a pulley, thereby providing a pulling force in the cable. With the Michigan Hook, this action opens the 10X hook against an elastic band. The PA is a more versatile and more powerful version of this mechanism in which the action can be used to replace the body-powered cable pulling required by various voluntary-opening terminal devices. The PA and Michigan Hook require only single-site control and one electrical switch to turn the drive motor on and off. Simplicity of control complements the simplicity of the mechanisms and the simplicity of their application.

A new myoelectric controller has been developed for the Michigan Hook and the PA mechanism. A myoelectric signal from the amputee actuates a metal-oxide semiconductor field-effect transistor that supplies voltage to the drive motor. The power transistor functions as a switch. When the myoelectric signal exceeds a threshold voltage, the motor is turned on and the Michigan Hook or the device connected to the PA opens against elastic bands. When the signal is below the threshold, the motor is turned off and the elastic bands close the terminal device at a controlled rate determined by a damping resistor across the motor terminals.

The PA is particularly effective in applications for above-elbow and higher level amputees who use body-powered cable-driven systems and who have difficulty in operating the terminal device when the elbow is flexed. Myoelectric control permits subtle, simple, and effective operation of the PA. The myoelectric controller permits easy operation of the Michigan Hook in various applications.

*Northwestern University, 345 Superior Street, Chicago, IL 60611