Nonlinear inverse dynamic control of an omnidirectional robot using slip rolling modes

Abstract

Omnidirectional mechanisms are characterized by their ability to enable motion without being constrained by the non-holonomic constraints of a conventional differential drive based mobile robot platform, allowing the development of highly maneuverable robot platforms. The effective utilization of an omnidirectional robot, such as the OmniBot presented in this thesis, in highly dynamic environments such as robot-soccer, requires an effective control strategy. This thesis presents a nonlinear inverse dynamic control strategy for the control of an omnidirectional robot, utilizing steady-state slip rolling modes. A nonlinear wheel slip model approximating the traction forces at work on the wheel, is incorporated into the dynamics of the system and the resulting equations of motion are derived using the Euler-Lagrange formulation. They are then transformed to slip-space where the slip dynamics are analyzed and steady-state slip modes are derived. Based on the steady-state slip mode analysis, an assumption is made of linear correspondence between slip and applied torque, in steady state. This assumption is utilized to develop the proposed Steady-state Slip rolling mode Inverse Dynamic Control (SSIDC) strategy. The performance of the proposed controller is verified through detailed simulations as well as real experiments on the OmniBot, and is compared with that of an Ideal Rolling mode Inverse Dynamic Control (IRIDC) strategy, which is based on the conventional ideal-rolling assumption, for various motion tasks. The results indicate that the proposed SSIDC control strategy is effective for the task of high performance control of omnidirectional robots.