Reducer manufacturers explain torque measurement for high-precision industrial robot reducers.

　　 High-Precision Torque Measurement for Industrial Robot Reducers

　　Torque testing is critical for enhancing the quality of high‑precision reducers—key components of industrial robots. This paper presents a novel torque‑measurement system for a vertical‑type tester, which minimizes the distance between the torque sensor and the robot’s reducer, thereby ensuring the shortest possible measurement chain. A symmetrical system architecture improves overall stiffness and facilitates error compensation. The characteristics of torque‑measurement errors arising from shaft bending and torsional deformation are analyzed. A torque calibrator comprising two high‑accuracy torque‑output systems is employed to calibrate the torque sensors in the measurement setup. Furthermore, a practical and robust compensation model based on a backpropagation neural network is developed to accurately determine the input and output torques of the reducer. With a torque‑measurement accuracy of 0.1% across the entire torque range, this instrument is well suited for precise measurement of both input and output torques in robotic reducers.

　　 Introduction

　　Currently, industrial robots are widely used across numerous sectors, and the performance requirements for their reducers are becoming increasingly complex. Consequently, comprehensive testing of the overall performance of precision reducers plays a crucial role in advancing robotic technology. Many researchers and experts have conducted extensive studies on manufacturing errors in the internal components of reducers, and significant progress has been made in evaluating the performance of precision reducers. Key performance parameters of reducers typically include torsional stiffness, transmission error, backlash, no‑load rotation, and transmission efficiency. Among these, torque is a primary variable in the definitions of these parameters; given that torque exhibits time‑dependent characteristics, it is essential to measure the input and output shaft torques of the reducer under test in real time.

　　The measurement module incorporates a torque sensor to measure the input and output torques of the reducer. Depending on the testing requirements, the drive and load systems are selected as integral components of the instrument. In terms of layout, the horizontal configuration is the predominant design. The sensor, drive unit, and other connecting elements are supported by cantilevers and mounted in series on guide rails or a horizontal base, making it one of the common configurations for robotic reducer testers. It is well suited for long-term, multi-parameter monitoring.

　　 One of the common configurations of reducer testing equipment

　　To facilitate the installation and removal of various types of gear reducers, the aforementioned instrument requires components to be mounted on guide rails. This design significantly compromises the instrument’s overall torsional stiffness. Moreover, additional torques arising from shaft bending and torsional deformation are incorporated into the measurement results. Non-uniform friction and misalignment errors caused by component deformation further induce torque fluctuations. These issues inevitably interfere with accurate torque measurement.

　　The contribution of this paper lies in proposing a torque‑measurement method based on a backpropagation (BP) neural network, which is applied to a vertical precision robot reducer tester. This approach addresses several limitations of existing solutions and achieves high‑accuracy torque measurement across the entire measurement range.

　　 Overview of Torque Measurement Systems

　　To measure the input and output torques of a reducer, a torque measurement system for both the input and output sides was designed based on a novel vertical precision robot reducer tester. The instrument comprises two torque measurement modules: the reducer input-side torque measurement module (TMMISR) and the reducer output-side torque measurement module (TMMOSR). Each module consists of an electric motor, a torque sensor, a test-mode switching component, and associated connecting parts. In Figure 2, the red portion represents the test assembly (TA), within which the robot reducer is mounted. The TA facilitates rapid installation of different types of reducers and employs a standardized interface for connection to the vertical precision robot reducer tester.