A new wearable power assist device for lower back support is proposed in this paper. The waist power assist suit is designed to relieve lower back pain and it is equipped with four pushrods to realize the three-dimensional rotation around the waist joint. The mathematical model of the device including the kinematics and the dynamics is presented on the basis of the freedom analysis. The model of the pushrod considering friction described in modified lugre model is given in the third part. A

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... of lumbar rehabilitation movement is put forward. To ensure the coordination work of the four motors, an improved mean deviation coupling control strategy is proposed. Displacement tracking controller based on robust adaptive integral backstepping control is adopted to deal with friction. To demonstrate the effectiveness of the proposed synchronous control strategy, simulation is carried out in Matlab/Simulink and the simulation results show better performances when compared to deviation coupling cooperative control. At last, simulation has been carried out using the Anybody software in order to prove the availability of the mechanism.