An integrated force feedback system for a prosthetic hand

Abstract

Touch feedback has been found to aid upper limb amputees in their experience with their prosthetic device, and feedforward of a signal representing the commanded force extracted from the surface electromyography (sEMG) signals can also help the subject to verify force intention. This work seeks to combine these two ideas into an integrated force feedback system which can be included with a sEMG controlled prosthetic hand, to improve the amputee’s ability to control and to interpret the forces applied. The physical haptic forces that act against the closing motion of each of the fingers of the prosthetic hand are measured by force sensitive resistors located within the actuation drive trains of the device, while the intended magnitude of the grasping force is measured from the intensity of the motion control sEMG signals that are read from the amputee’s residual limb prior to the application of the force. The force intention measurement is supplied to the subject as a feedforward signal for a short period of time, allowing the subject to choose and intuitively correct the force to be applied prior to its actuation, while the actual force feedback signal from each finger is supplied whenever there is a force applied to the drive train, even when the finger motor is turned off. During the grasping process, both the single feedforward and the multiple feedback signals are conveyed to the subject through haptic vibration motors that can be placed strategically in the socket of the device to convey the force information to the user.