SLIP-Model-Based Dynamic Motion Transition Between Different Fixed Points in One Stride in a Leg-Wheel Transformable Robot

Abstract

We report on the development of a motion generation strategy that allows the robot to transit from one stable running motion to another in one stride by actively changing leg stiffness in real time. Stable motion of the robot is generated based on the stable fixed-point trajectories of the spring-loaded inverted pendulum (SLIP) model. While the transition of the ordinary SLIP model with fixed parameters gradually converges if stable, a robot that uses force control to simulate the passive spring of the SLIP can actively modulate leg-spring stiffness. This enables the robot to switch instantly to another fixed-point trajectory of the SLIP model without going through multi-stride transition. The proposed method is implemented on a leg-wheel transformable robot, TurboQuad, and is evaluated experimentally. The results confirm that the robot can successfully transit between different fixed-point trajectories.