Qinghong Guo, Chris J.B. Macnab, and Jeff K. Pieper
Hopping robots, running robots, nonlinear control, robust control, sliding mode control
This paper presents a control algorithm to achieve hopping with a single rigid-link articulated leg with foot, robust to model uncertainty and bounded disturbances. A gait generator, based on previous work, supplies desired trajectories for the joints in flight and stance phases. In the underactuated flight phase, a gain-scheduled LQR control keeps the joint trajectories close to the pre-planned path. Due to uncertainties and disturbances, the touch-down configuration will not generally be known with certainty. In the stance phase a terminal sliding mode provides a path back to the desired trajectory. A finite-time control ensures the joints follow the terminal sliding mode. These methods avoid the reaching phase and discontinuous signals found in standard sliding modes. The proposed control achieves robustness while avoiding excessive torques and torque chatter. In simulation the robot achieves periodic hopping, which is robust to a significant unknown payload.
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