Biomechanical Upper Limb Model for Postural Tremor Absorber Design

The current work promotes the use of non-invasive devices for reducing involuntary tremor of human upper limb. It concentrates on building up an upper limb model used to reflect the measured tremor signal and is suitable for the design of a passive vibration controller. A dynamic model of the upper limb is excited by the measured electromyography signal scaled to reach the wrist joint angular displacement measured by an inertial measurement unit for a patient with postural tremor. A passive tuned-mass-damper (TMD) placed on the hand is designed as a stainless-steel beam with a length of 91 mm and a cross-sectional diameter of 0.79 mm, holding a mass of 14.13 g. The damping ratio and mass position of the TMD are optimized numerically. The fundamental frequency of the TMD is derived and validated experimentally through measurements for different mass positions, with a relative error of 0.65%. The modal damping ratio of the beam is identified experimentally as 0.14% and increases to 0.26-0.46% after adding the mass at different positions. The optimized three TMDs reduce 97.4% of the critical amplitude of the power spectral density at the wrist joint.