Design of a Passive Lower Limb Exoskeleton with Cable-driven Remote Gravity Compensation Mechansims

This paper presents a passive lower limb exoskeleton with hip and knee joints for walking assistance. At the waist frame of the exoskeleton, a gravity balancing mechanism consisting of a cam and a compression spring is designed. The compression spring acts on the cam through a follower and connects the hip and knee joints by means of a rope drive to provide gravity compensation to the human lower limbs. By designing the gravity balancing mechanism at the waist, the weight of the lower limb exoskeleton can be reduced. This improves the acceptability and safety of lower limb exoskeletons. This paper introduces the working principle of the gravity balancing mechanism, describes the design method of the cam and establishes a dynamics simulation model to verify the rationality of the design. The simulation results prove that the design can reduce the root mean square torque values of the hip and knee joints by 54.8% and 52.8% respectively under gait cycle, which helps maintain the gravity balance and achieves the design purpose.