Trajectory Control of Snake-Like Robots in Operational Space Using a Double Layer Sliding Mode Controller

This paper presents operational space control of snake-like robots for tracking designated paths using a double layer sliding mode control algorithm. The snake robot has n links with assumed lateral sliding that leads to n+2 degrees-of-freedom (DOF) while it has only n-1 actuator at joints and therefore it is underactuated. Kinematic constraints were determined which describe the geometric relationship between the position of links’ mass center and the joints’ relative angle. The outer layer (loop) of the controller was designed to modulate the parameters of the serpenoid curve using the kinematic constraints in order to the mass center of links follow different designated paths. The inner layer of sliding mode controller was developed to guarantee tracking of the modulated serpenoidal pattern by the snake robot’s joints. In this work, Kane’s method was used to model the robot dynamics with a Coulomb friction for interaction with ground. Uncertainty with an upper bound was considered for the model parameters. To demonstrate the effectiveness of the designed controller in presence of uncertainties, the double layer controller was examined on a four links snake-like robot with uncertain model parameters in tracking of a straight line and a circular path. Simulation results are presented in support of the proposed idea.