Estimation of Dynamic Impedance of Human Wrist Joint in F/E with a Novel Instrument

Thanks to its significances in human daily life and suggesting valuable clues to wearable robotic devices, studying on the dynamic characteristics of human wrist joint has been recently aroused increasing interests. Despite great successes and breakthroughs, the biomechanical properties, especially the impedance characteristics, of human wrist joint have not been fully or deeply investigated. In order to study the passive and active impedance characteristics of human wrist joint, this paper firstly develops a wrist joint impedance measurement instrument (WriJIMI) based on the principle of series elasticity. Then, a reliable and accurate estimation method is adopted to describe the dynamics of wrist joint. Afterwards, the accuracy and reliability of the developed device are verified via experimental tests. Finally, some other experimental tests are conducted over 8 subjects to investigate the passive and active impedance characteristics of human wrist joint. In terms of studying the characteristics of impedance, a real-time feedback training method is also designed to guide subjects to control their degrees of forearm muscles co-contraction. The experimental results reveal that there are no obvious relationship between inertial parameters and forearm muscle activation, whereas the damping and stiffness parameters gradually increase as human wrist muscle activations increase. Moreover, passive impedance of wrist joint estimated in this paper is consistent with current research results.