Control of prehension for the transradial prosthesis: Natural-like image recognition system

We describe the hardware and software for the control of prehension for a dexterous transradial prosthesis. The prehension process comprises hand orientation (three degrees of freedom) and the opening of the hand in a manner that is appropriate for the shape and size of the object. The hardware consists of a standard web camera, accelerometer, ultrasound distance sensor, laser pointer and an LED illumination system. Software operating in real time estimates the shape and size of the object as well as the relative orientation of the hand with respect to the object. Based on this data, the controller generates signals that are sent to the three-dimensional (3D) wrist rotator, and drives which control fingers and thumb of the transradial prosthesis, thereby preparing the hand for palmar, lateral, or precision (2-digit or 3-digit) grasps. The choice of the grasp follows heuristics captured from healthy humans when grasping and expressed in the form of IF-THEN rules.