Development of a Capacitive Force/Torque Sensor for Lower Limb Rehabilitation Robots for Spasm Detection

Abstract

The presence of abnormal muscle retraction and contraction during the rehabilitation training poses significant challenges for patients with lower limb dysfunction caused by stroke, as it hinders their ability to regain lower limb function. Therefore, it is vital to detect spasm force during the training to adjust the force generated by rehabilitation robots. This paper presents the design and development of a capacitive force/torque sensor for lower limb rehabilitation to detect muscle spasm. The double differential measurement method and a decoupling structure with built-in crossed roller bearing were adopted achieve high sensitivity and high accuracy. Calibration tests were conducted with a commercial torque and rotational speed sensor to verify the design and accuracy of capacitive force/torque sensor. Results show that the proposed sensor exhibits a linearity of 1.04%, a resolution of 0.05N·m and a maximum measurement error of approximately 2.07%. Lastly, experiments were conducted to assess spasm detection capabilities in a lower limb rehabilitation robot which has capacitive force/torque sensors installed on knee and hip joints.