Type Synthesis of Adaptive Lower Limb Exoskeleton Mechanisms for Knee Joint Unloading

Abstract Exoskeleton robots play an important role in assisting human locomotion and healthcare services. This study focuses on the type synthesis issue of a class of unloading exoskeleton mechanisms that reduce the load on the joints of the lower limbs by supporting the body weight. First, four unloading scenarios are proposed to address the unloading needs of the knee joint. The osteokinematic model of the knee–ankle–subtalar joint was established. To avoid the problem of human–exoskeleton mismatch, an exoskeleton configuration synthesis method based on the linear correlation of screws is proposed to synthesize the exoskeleton chains that can self-adapt to the knee and ankle–subtalar joint motions, and the adaptive exoskeleton configurations corresponding to the four unloading scenarios are obtained by combining these chains. A case study is conducted on the RRR exoskeleton, and the kinematic model and Jacobian of the human–exoskeleton closed-loop mechanism are derived. Through simulation, the working mechanism of the RRR exoskeleton for adapting to and supporting the knee joint is validated. The exoskeleton configurations proposed in this article provide alternative configurations for lower limb assistive exoskeleton, unloading exoskeleton, or rehabilitation exoskeleton design.