As shown in Fig. 5a and Fig. 5c, link 1 (the LBB) is a human limb with a revolute joint A. The RRP chain and the LBB form an inverted crank-slider mechanism. Pulley 2 is fixedly connected to link 2, and pulley 1 is articulated to link 3 and fixed to the SG. Pulley 1 and Pulley 2 are connected by a timing belt. Through this connection, the rotation angle θ of the LBB is transmitted to the SG which drives the PGCU to compress the spring, and then the PGCU generates the anti-gravity torque which is transmitted to the LBB through the TBM to achieve gravity balance.