A comparison of tracking control methods in multi-legged robots

In this paper, a hexapod robot that consists of its body and six legs is considered. The leg mechanism is a 1-UP&2-UPS (U-universal joint, P-prismatic joint and S-spherical joint) parallel mechanism with three degree-of-freedoms (DOFs). A comparative investigation of tracking control methods in the hexapod robot with parallel legs is presented. The methods include standard PID control, position-velocity loops cascade control, and hybrid sliding mode control. It is difficult to get the accurate model of the parallel legs due to the nonlinear uncertainties, therefore this paper applies decentralized control strategy to design the controllers. The inverse kinematics of one leg is derived for mathematic model, based on which three control methods are examined. The results are shown to identify the difference of them and prove the effectiveness and applicability of hybrid sliding mode control.