Computer simulation of the dynamics of a human arm and orthosis linkage mechanism

This paper describes the use of computer modelling and simulation during the design and development of a motorized upper limb orthotic system to be used to aid the dysfunctional human arm. The orthosis consisted of a three-degree-of-freedom shoulder module and a lower arm module providing movements at the elbow and wrist. Simulation software has been used to model the mechanism created by the connection of the orthosis and the arm. With this model it has been possible to analyse the kinematics and kinetics of both the arm and orthosis during a variety of dynamic loading conditions. In particular, the power requirements of the orthotic joints during the execution of specific tasks have been determined and these data have been used to specify the motors of a working prototype. The effect of misalignment between real and orthotic shoulder joints has also been investigated and a potentially hazardous situation has been highlighted prior to testing of the prototype by a volunteer in the laboratory.