Design and Analysis of a Hybrid-Driven Ankle Joint for Lower Extremity Exoskeleton Robots

In order to improve the safety and comfort of human-machine interaction and its adaptability to complex unstructured environments, a new type of ankle joint based on series of elastic drive and rigid drive hybrid was designed between the motor and exoskeleton robot. Linear spring groups were introduced to achieve flexible driving and absorb the ground reaction force and other impact vibration. At the same time, a disk brake device was designed to retain the rigid drive function to quickly and accurately respond to the motion of the human ankle joint and reduce human-machine movement deviation. The dynamic model of the ankle joint was established. The stability of the hybrid driver under different parameters were obtained through frequency domain analysis. Through simulation experiments, the accuracy and effectiveness of the model were verified. Introduction With the advent of twenty-first Century, the number of patients with cerebrovascular diseases such as stroke has increased dramatically in the world, especially in developed countries. Many countries have increased research and development of exoskeleton robots and developed various prototypes of exoskeleton robots with different functions and capabilities[1], such as BLEEX (Berkeley Lower Extremity Exoskeleton) of Berkeley, HAL(Hybrid Assist Legs) of Japan’s Tsukuba University and ReWalk of Israeli company Argo medical Technology[2]. Since Pratt[3] and others of Massachusetts Institute of Technology introduce series elastic actuation to biped walking robots, the application of compliant SEA drive is becoming more and more extensive. Leach designed discretely coupled linear multi-mode driver. Lauria[4] has applied high performance differential series elastic actuator. Haeufle[5] applied the clutch and spring parallel actuators to the lower extremities exoskeleton robots. Elliott J. Rouse [6] designed a detachable series elastic actuator for the knee joint prosthesis. In this paper, we designed a new hybrid compliant driver for the ankle joint of a lower limb exoskeleton robot. The compliant drive is realized by introducing a number of linear springs, and the rigid driving is kept by disc brakes, thus the hybrid compliant drive of the lower limb exoskeleton robot is realized. Design of the Ankle Joint Hybrid Compliance Driving Combined with theory of human biomechanics and ankle joint movement analysis, the joint power and torque and the range of ankle joint can be obtained. The gait of lower extremities is periodic, and gait cycle usually refers to time spent on the heel during walking. Each gait cycle can be divided into support stage (Stance Phase) and swing stage (Swing Phase). The supporting stage is the instant from heel touching ground to tip of foot leaving ground, which accounts for about 3/5 of the gait cycle. The swing phase is the instant from tip of foot leaving ground to the moment when heel touches ground, which accounts for about 2/5 of the gait cycle. The movement of ankle joint has three degrees of freedom, which is flexion / extension movement around coronal axis in sagittal plane, adduction / abduction movement around sagittal axis in coronal plane, and internal rotation / external rotation around vertical axis in transverse section. The lower extremity biomechanics experimental data of