Variable Center of Mass Control for Omni-Directional Cart with Power-Assist Function

This paper proposes an admittance control with a variable center of mass ( COM) for a power-assisted omnidirectional cart. This power-assist system works by an admittance control using operation forces measured by the force-sensing handle consisting of load cells. To realize the admittance control, the virtual mass/inertia is defined with dynamic parameters such as mass, inertia, damping coefficients, and the location information. The behavior of the virtual mass/inertia is determined by the relative position between the force-applied point and the location of the virtual mass/inertia. Therefore, we propose a variable COM control method in which the optimal position of COM is determined automatically depending on the operation mode for improving the maneuverability of the omnidirectional cart. To evaluate the proposed control method, a series of experiments were conducted by using the prototype of an omnidirectional cart with active caster drive mechanisms. From the results of the experiments, the optimal COMs for pulling, pushing forward, pushing lateral, turning on the spot, and pushing in a curve were determined independently. Finally, running experiments were performed by the control system with the running pattern detection and automatic COM switching function. It was confirmed that the proposed control system was successfully installed on the prototype cart and its maneuverability was improved.