Adaptive Admittance Control for an Ankle Exoskeleton Using an EMG-Driven Musculoskeletal Model

Various rehabilitation robots have been employed to recover the motor function of stroke patients. To improve the effect of rehabilitation, robots should promote patient participation and provide compliant assistance. This paper proposes an adaptive admittance control scheme (AACS) consisting of an admittance filter, inner position controller, and electromyography (EMG)-driven musculoskeletal model (EDMM). The admittance filter generates the subject's intended motion according to the joint torque estimated by the EDMM. The inner position controller tracks the intended motion, and its parameters are adjusted according to the estimated joint stiffness. Eight healthy subjects were instructed to wear the ankle exoskeleton robot, and they completed a series of sinusoidal tracking tasks involving ankle dorsiflexion and plantarflexion. The robot was controlled by the AACS and a non-adaptive admittance control scheme (NAACS) at four fixed parameter levels. The tracking performance was evaluated using the jerk value, position error, interaction torque, and EMG levels of the tibialis anterior (TA) and gastrocnemius (GAS). For the NAACS, the jerk value and position error increased with the parameter levels, and the interaction torque and EMG levels of the TA tended to decrease. In contrast, the AACS could maintain a moderate jerk value, position error, interaction torque, and TA EMG level. These results demonstrate that the AACS achieves a good tradeoff between accurate tracking and compliant assistance because it can produce a real-time response to stiffness changes in the ankle joint. The AACS can alleviate the conflict between accurate tracking and compliant assistance and has potential for application in robot-assisted rehabilitation.

THE THREE-DIMENSIONAL MOVEMENT CORRELATIONS BETWEEN ELBOW AND WRIST JOINT AND ANTHROPOMETRIC DETERMINANTS

This study aimed to investigate three-dimensional (3D) kinematic characteristics of elbow and wrist motions, the relationship between them, and the anthropometric factors affecting them. Using motion capture system, this study measured and calculated the 3D angles of elbow flexion/extension, elbow pronation/supination, wrist flexion/extension, and wrist adduction/abduction of 40 healthy young adults. The study measured nine anthropometric variables and used unpaired [Formula: see text]-tests to assess gender difference. Also, bivariate correlation tests and step-wise multiple regression analyses were performed between joint ranges and anthropometric variables, as well as different joint motions. Results showed two opposite patterns occurred during elbow flexion/extension. The study found a correlation between the range of elbow flexion/extension and the range of elbow pronation/supination that occurred during elbow flexion/extension. Additionally, the study tested joint correlations between the four joint motions. Finally, the study established bivariate and multiple regression relationships between range of elbow motions and anthropometric factors. This research presented an unrecognized pattern of 3D elbow flexion/extension, and associations between various anthropometric factors and different joint motions. These findings can contribute to the design of orthosis of upper extremities and the rehabilitation of joint mobility.