A new absolute angle detection system and its application for angle measurement of ACRO-DD

Abstract

In this paper, we propose a new absolute angle detection system with two absolute encoders. Recently, an active-caster with dual-wheels has been developed for driving mobile platforms for robots, personal mobiles, and electric wheelchairs, etc. The active-caster has two actuators for driving wheel axis and steering axis independently. By cooperative control of these motors, the active-caster can generate velocity with an arbitral direction and magnitude. Detecting the absolute angle of a steering shaft is necessary for controlling the active-caster. If the control system cannot measure the angle of steering shaft at the startup time, it is impossible to derive reference velocities for motors. In our previous work, we designed a new type of active-caster robotic drive with dual-wheel and a differential mechanism (ACRO-DD). Its steering mechanism has no room around its center to attach an absolute encoder to measure the steering angle. Therefore a unique absolute angle detection system was developed with two potentiometers and gears for ACRO-DD. However, this method has two problems. First, it is easy to be affected by noise. Second, the potentiometer has an insensitive area. In this research, the new angle detection system is proposed to overcome these problems. We change the potentiometers to the absolute encoders, and propose a high resolution angle detection system. The absolute encoder is robust to noise, and does not have an insensitive area. By using this method, resolution is improved, and rounding error does not occur.