A SELF-LEVELLING HIGHER ORDER SLIDING MODE CONTROLLER FOR A LEG-WHEELED ROBOT WITH EXPERIMENTS

Farbod Fahimi, Swaroop Kotike, and Rahul Rameshbabu

Keywords

Leg-wheeled robots, self-levelling, prismatic legs, nonlinear control, sliding mode control

Abstract

The problem of levelling a leg-wheeled robot is treated as a closed- loop robust control problem. A robot with four prismatic legs is considered. The rates of leg extension/contraction are the control inputs. The roll and pitch angle of the robot’s body are the control outputs, whose desired values are zero. The slope of the terrain and its rate of change are considered as (bounded) disturbances to the system. A Higher-Order Sliding Mode control law is derived that determines the rates of leg extension/contraction in real-time, which keep the robot’s body level despite the (bounded) changes in terrain slope. The results of the experimental closed-loop levelling are presented and discussed.

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