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Design and Analysis of a Spatial Four-DOF Lower Limb Rehabilitation Robot

Aiming at the existing problem that the majority of lower limb rehabilitation robots can only realize patient's leg to move in the sagittal plane, cannot achieve the patient's leg to move in coronal plane, a spatial four-DOF multi-pose lower limb rehabilitation robot is proposed. The robot could also realize the sitting training posture, the lying training posture and the standing training posture. The robot includes seat, left mechanical leg and right mechanical leg. Each mechanical leg with series-parallel mechanism includes the hip joint with two DOFs, knee joint with one DOF and ankle joint with one DOF which correspond to the hip joint, knee joint and ankle joint of human. This paper describes the mechanical design and kinematic analysis of the rehabilitation robot. The coordinate system of the lower limb rehabilitation robot is established, and the degree of freedom of the spatial leg mechanism is calculated. The inverse kinematics of the single leg mechanism and the forward kinematics of the lower limb rehabilitation robot are analyzed. The workspace of the leg mechanism was calculated. The kinematics analysis of the leg mechanism lays a theoretical base for the future controlling of the robot prototype.