A Lightweight Redundant Manipulator with High Stable Wireless Communication and Compliance Control

Abstract

For traditional manipulators, there is a large number of electrical cables between the motion controller and the joint servo controllers. It is very inconvenient for maintenance, update, and safe operation. In this paper, we develop a lightweight redundant manipulator with high stable wireless communication link and compliance control. The motion controller, servo controller, and communication link are taken as a whole system to be optimized. The manipulator body and the motion controller are physically separated. It is very helpful for building distributed networked-manufacturing system or intelligent manufacturing system for Industry 4.0. The control system can be quickly updated by changing the object's identification without reconnect the communication cables. The mechanical part of the manipulator contains modular joints and links. Each joint is integrated with hall sensors, an incremental magnetic encoder, an absolute magnetic encoder and current sensors. The electrical part includes a central controller, seven joint servo controllers, and a wireless communication module based on ZigBee. By designing the application layer protocol, the communication stability is improved. In order to achieve the force control requirements in fine operation like assembly. A wireless compliance control frame is then designed. The compliance control method is realized on the central controller, by which the generated control commands are sent to the joint servo controllers through a wireless link. The problems caused by large electrical cables are then solved. Finally, the prototype and the experimental system are developed. Some experiments are carried out, including wireless communication test, trajectory tracking experiments, load carrying experiments, and wireless impedance control experiments. Results verify the functions and performance of the developed 7-DOF manipulator.