Driving-Stepping Locomotion Control for Wheel-Legged Robots

In the study of trot gait locomotion in traditional quadruped robots, it has been observed that the robot’s body is prone to flip around the diagonal line of the body. A wheel-legged quadruped robot without shoulder abduction joints is introduced in this paper, and an innovative solution to the problem of body flipping during trot gait is achieved by introducing a novel wheel controller. First, according to the robot configuration, posture kinematics and dynamics of legs have been analyzed, and then optimized ground reaction forces are solved based on single rigid body dynamics, virtual model control and quadratic program optimization. With the optimization of ground reaction forces and well-controlled wheels, the wheel-legged robot can exhibit driving-stepping locomotion stably, which applies trot gait with rotating wheels simultaneously, making the robot looks like skating. The driving-stepping locomotion controller decouples desired forward velocity into velocity contributed by stepping and driving with wheels, and both contributions can be controlled independently. The simulation results indicate that the wheel-legged robot achieves stable driving-stepping locomotion with minimal body oscillation, facilitated by the introduced driving-stepping locomotion controller.