ADAPTIVE SLIDING-MODE CONTROL OF SPHERICAL ROBOT WITH ESTIMATED ROLLING RESISTANCE

摘要

A spherical robot will inevitably be affected by rolling resistance from the ground when it is used in an unstructured exploration environment. Because of the complex contact condition between the robot and the ground, it is very difficult to obtain the information about the rolling resistance correctly. This fact decreases the movement performances of spherical robots greatly. In this study, dynamic models of the sphere subsystem and the inner suspension subsystem are derived. By Lyapunov theorem, the sliding surface with integral element is applied to construct a new sliding-mode control scheme to track the desired velocity of the spherical robot. In the proposed controller, the sgn(x) function is replaced by the tanh(x) function, in order to reduce the inherent chattering phenomena of the sliding-mode algorithm. Because the rolling resistance is uncertain, an adaptive control scheme is applied to estimate the uncertain rolling resistance dynamically, which makes the robot more sensitive and adaptive in unstructured exploration. The simulation results demonstrate the validity of the proposed schemes.