Measurement and analysis of structural dynamics properties of robotic joint transmission system

Abstract

Abstract The flexibility of a robotic manipulator is considered an important factor, especially the joint compliance for improving the accuracy and operating speed of a robot application. In this article, two methods are employed to identify the structural dynamic characteristics of each joint transmission system of an ITRI‐U type robot. The driving system of each joint is modeled as a mass‐spring‐damper mechanism that has a second‐order dynamic mathematical equation. Then, the response experiments of hammer impact excitation and motor driving actuation are done and the difference between them compared. Those are used to simulate two different operation situations, the robot colliding with the environment and the discontinuing dynamic operation impacts. The system's parameters of each joint axis are obtained by the system identification technique. From the experimental results, the angular error of the motor shaft can be compensated by the control gain of the motor controller. However, the small damping ratio of the robotic mechanism limits the magnitude of servo gain. If the servo gain increases, the robot arm has oscillation phenomenon during dynamic operation. In addition, the error due to joint elasticity cannot be overcome by the current industrial robotic controller. Therefore, a suitable controller should be designed to compensate the dynamic effects of joint compliance with the identified parameters.