Abstract: As the torso is critical to the coordinated movement and flexibility of vertebrates, a 6-(Degree of Freedom) DOF bionic parallel torso with noteworthy motion space was designed in our previous work. To improve the compliance of the parallel mechanism, a pair of virtual muscle models is constructed on both sides of the rotating joints of each link of the mechanism, and a bionic muscle control algorithm is introduced. By analyzing the control parameters of the muscle model, dynamic characteristics similar to those of biological muscle are obtained. An adaptive stiffness control is proposed to adaptively adjust the stiffness coefficient with the change in the external load of the parallel mechanism. The attitude closed-loop control can effectively keep the attitude angle unchanged when the position of the moving platform changes. The simulations and experiments are undertaken to validate compliant movements and the flexibility and adaptability of the parallel mechanism.

Key words: Bionic mechanism , · Compliance control , · Muscle model , · Stifiness adaptation , · Dura-rate integral learning