VPC: A time-efficient control method for a hexapod wheel-legged robot based on velocity planning

Abstract Aiming at the problem that control methods of wheel-legged robot for future Mars exploration missions are too complex, a time-efficient control method based on velocity planning for a hexapod wheel-legged robot is proposed in this paper, which is named as velocity planning control. When foot end or wheel at knee contacts ground, the desired velocity of foot end or knee is transformed according to the velocity transformation of rigid body from the desired velocity of torso which is obtained by the deviation of torso position and posture. Furthermore, the torques of joints can be obtained by impedance control. When suspended, the leg is regarded as a system consisted of a virtual spring and a virtual damper to realize control of legs in the swing phase. Besides, leg sequences of switching motion between wheeled configuration and legged configuration are planned. According to complexity analysis, velocity planning control has lower time complexity and less times of multiplication and addition compared with virtual model control. Besides, simulations show that velocity planning control can realize stable periodic gait motion, wheel-leg switching motion and wheeled motion and the operation time of velocity planning control is about 33.89% less than that of virtual model control, which promises a great prospect for velocity planning control in future planetary exploration mission.