An indirect method for non-contact sensing of robot joint angles using accelerometers with automatic in-situ calibration

Abstract

An indirect, self-calibrating, easy to install, and robust joint angle sensing method is presented in this thesis. The approach is based on the use of a pair of accelerometers placed on each link near the joint axis. Two different methods are described for automatic, in-situ, integrated calibration of the accelerometers, which significantly improve joint angle estimation accuracy. The angle sensing method is suitable for harsh environments and applications where traditional contact-type angle sensors cannot be deployed, or problems are associated with their use. It is believed joint angle sensing in heavy-duty hydraulic manipulators is one of the best applications for this method. A Takeuchi TB035 mini-excavator in the Robotics and Control Laboratory of the University of British Columbia is used in this thesis to evaluate the performance of the developed system. This machine is equipped with digital resolvers at each joint. The outputs of the resolvers are compared to the estimated joint angles in various conditions. According to the experimental results presented in this thesis, the achieved accuracy with the accelerometer-based system is ±1.33% of the full-scale angle (±1.6° in 120°). The performance of the proposed method is also evaluated in position control of the machine and dynamic measuring of its payload. It is shown that the performance of this method is comparable to the performance of the digital resolvers in both tasks.