Mechatronic Design and Experimental Research on a Precision Testing Platform for Secondary Encoders in Industrial Robots *

The application of industrial robots in machining has attracted growing attention. However, the flexibility of their serial joints limits the absolute positioning accuracy of the robot end-effector, preventing it from meeting the precision requirements of machining tasks. To improve the end-effector’s positioning accuracy, a secondary encoder is proposed at the joint end of the robot, working in tandem with the motor-end encoder. This paper presents the design and development of an integrated mechatronic testing platform for evaluating several common high-precision optical encoders, including grating scale and circular grating. This platform integrates multi-axis motion controllers, servo drives, industrial PC, autocollimator, and mechanical components. It simultaneously acquires real-time angle data from various optical encoders and autocollimator via host-computer software. The angle measurement accuracy of different optical encoders is evaluated based on autocollimator accuracy standards. Additionally, a least-squares optimization algorithm is employed to fit the radius of grating scale optical encoders based on graduation error definitions. The platform successfully enables the installation and testing of multiple optical encoders. The angle measurement accuracy of multiple optical encoders is verified using the autocollimator measurement method. Experimental results demonstrate that these encoders offer high measurement accuracy and are suitable for use as secondary encoders in industrial robots. This research not only offers solutions for implementing secondary encoders in industrial robots but also establishes a theoretical foundation for designing and enhancing high-precision robotic control systems.