Load distribution and skid compensation control of omni-directional vehicle with independent driving modules

Abstract

The demand for robots in various application fields has been increasing in recent years. Robots are becoming active in a greater variety of environments, so there is a growing need for higher robot mobility that ensures safe and smooth movement. That need has drawn attention to the omnidirectional vehicle (ODV). ODV's can move forward and backward and turn to the left and right, but they can also move directly sideways and diagonally, and rotate in a fixed position. This high mobility enables an ODV to change direction in a small space, to parallel park easily, and perform other adaptive movements that are suitable to the vehicle environment. Omni-directional mobility has previously required special mechanisms that have been associated with problems of durability and stability. To address those problems, we have developed a nonholonomic ODV that uses two-wheel modules equipped with ordinary tires. However, the stability and smooth motion of the vehicle is usually affected by the load from the road surface, so a control system that distributes that load appropriately over all the motors is needed. Another problem is that there may be a loss of total driving force and vehicle speed under conditions in which the tires spin freely without traction. To maintain total driving force, a torque compensation system for each of the wheels is important. Here, we propose a method for load distribution control and a method for skid compensation control and present test results that show the effectiveness of the proposed methods.