“Anti-fatigue” control for over-actuated bionic arm with muscle force constraints

In this paper, we propose an “anti-fatigue” control method for bionic actuated systems. Specifically, the proposed method is illustrated on an over-actuated bionic arm. Our control method consists of two steps. In the first step, a set of linear equations is derived by connecting the acceleration description in both joint and muscle space. The pseudo inverse solution to these equations provides an initial optimal muscle force distribution. As a second step, we derive a gradient direction for muscle force redistribution. This allows the muscles to satisfy force constraints and generate an even distribution of forces throughout all the muscles (i.e. towards "anti-fatigue"). The overall proposed method is tested for a bending-stretching movement. We used two models (bionic arm with 6 and 10 muscles) to verify the method. The force distribution analysis verifies the “anti-fatigue” property of the computed muscle force. The efficiency comparison shows that the computational time does not increase significantly with the increase of muscle number. The tracking error statistics of the two models show the validity of the method.