Design of an underactuated prosthesis arm

Abstract

In motion design of a prosthesis arm, number of actuators is considered the most crucial part. The higher number of actuator allows us to have many degree of freedom while results in the heavy weight of the device. In the past, motors and pneumatic systems are commonly used as actuators for prosthesis devices. Albeit easy to control and fast response, motors have limitation that single motor can only control one degree of freedom for full performance of motion. Hence, seven degrees of freedom arm requires a large number of actuators. For application like prosthesis arm, the heavy and bulky size of the prosthesis mechanism is therefore not practical for daily usage. In order to reduce the number of actuator and the weight of prosthesis, we propose a design of an underactuated system for a prosthesis arm with three degrees of freedom motion. The design focuses on the case of shoulder disarticulation. The prosthesis arm has 2 degrees of freedom at shoulder and 1 degree of freedom at the elbow. The mechanism consists of gearboxes and a pulley for force transmission. The mechanism was controlled through a closed loop position control. The prosthesis was made of PLA and aluminum and the total weight is 1.7 kg. The designed prosthesis is capable for posture such as eating, drinking and carrying object of weight not exceed of 1 kg. The range of motion showed that angles of arm can be moved +/− 87° in up and down rotation+/−37° in forward and backward rotation, and the elbow can rotate+/− 40°.