An automatic control system was designed to suppress pathological tremor on wrist joint with two degrees of freedom (DoF) using functional electrical stimulation (FES). The tremor occurring in the wrist flexion-extension and adduction-abduction was expected to be suppressed. A musculoskeletal model of wrist joint was developed to serve as the control plant, which covered four main muscles (extensor carpi radialis longus, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris). A second-order mechanical impedance model was used to describe the wrist skeletal dynamics. The core work was to design the controller and a hybrid control strategy was proposed, which combined inverse model based on feed forward control and linear quadratic regulator (LQR) optimal control. Performance of the system was tested under different input conditions (step signal, sinusoidal signal, and real data of a patient). The results indicated that the proposed hybrid controller could attenuate over 94% of the tremor amplitude on multi-DoF wrist joint.
