Abstract: This paper introduces an opto-mechatronics integrated automatic detection system for train wheelsets. The system employs several new technologies, including high-precision laser displacement measurement and high-speed synchronous sampling. The measurement algorithm utilizes various data processing methods such as digital filtering and curve fitting. The system boasts high reliability, strong anti-interference capability, and high measurement accuracy, making it highly valuable for practical applications. Keywords: Automatic detection, laser displacement measurement, synchronous sampling, digital filtering, freight car wheelset. In recent years, due to the increasing speed of trains, the development of train bearing systems, and the demand for railway information management, traditional manual wheelset measurement devices are no longer sufficient due to their low efficiency, high error rate, and inconvenience for information management. Simultaneously, the development of trains towards high-speed and heavy-load operation has accelerated wheelset wear, shortened maintenance cycles, and increased workload for various vehicle maintenance sections. Therefore, timely and accurate monitoring of wheelset wear is crucial. Researching corresponding detection technologies can provide practical detection devices for railway departments and also offer practical detection methods for the study of wheel-rail relationships in high-speed railways. This paper addresses key technical issues in wheelset inspection and proposes a mechatronics-integrated train wheelset inspection and diagnostic system. This system utilizes advanced technologies such as CCD cameras, large-range high-precision laser displacement sensors, high-speed synchronous sampling, digital filtering, and curve fitting, encompassing both control and mechanical assemblies. This system can not only rapidly detect the wheelset's external parameters but also solve the most critical problem of tread parameter detection. Following the process standards outlined in the "Rules for Assembly and Maintenance of Railway Freight Car Wheelsets and Rolling Bearings of the Ministry of Railways of the People's Republic of China," the system can perform non-contact, rapid, and automatic measurement of relevant dimensional parameters of train wheelsets with or without bearings installed during maintenance. Its application will undoubtedly provide a fully automated, high-precision, and high-efficiency inspection method for train wheelset measurement and maintenance. 1. Measurement System Overview This system is a device capable of fully automatically measuring the geometric parameters of railway vehicle wheelsets and achieving automated computer management. The inspection system employs high-precision laser sensors (LK501) and high-speed synchronous sampling, ensuring that the designed system can quickly and accurately complete the detection of wheelset-related parameters. The electrical control part of the entire detection system mainly consists of an upper control computer and interface, a lower computer (which completes the motion control of the measuring head, synchronous data acquisition, and uploading of the acquired data), a servo motor controller, a wheelset motion control part, and a signboard image input part. The upper computer software has a user-friendly interface and rich functions, with certain animation display functions. It can complete the display and storage of measurement data, and the detection results can be automatically printed on the vehicle system 51-C card. 1.1 Basic Components of the System This system consists of two main parts: a mechanical system and an electrical control system. The mechanical system is the actuator for wheelset control, which mainly completes the motion functions of the wheelset, such as wheel entry, buffering, lifting, wheel rotation, wheel drop, and wheel exit. Its actuators are solenoid valves and cylinders. This paper mainly studies the design and implementation of the electrical control system, so the electrical control system will be introduced in detail below. The electrical control system consists of two parts: (1) a measurement control circuit; (2) a follow-up actuator. The composition of the system is shown in Figure 1. 1.2 System Working Principle Overview 1.2.1 The mechanical transmission mechanism, consisting of a helical ball screw and a precision linear sliding guide, is mounted on a servo motor, while the laser sensor is mounted on a slide. When the motor moves according to a predetermined operating mode, it drives the laser sensor to scan the wheelset. 1.2.2 The measurement control circuit drives the wheelset control actuator through the control output unit of the lower-level computer, causing the wheelset to reach a predetermined position. Simultaneously, the servo motor starts scanning and measurement. At the start of measurement, the distance between the workpiece and the laser sensor is a set value (this set value corresponds to the zero point of the linear measurement segment of the laser sensor). During the measurement process, the laser sensor moves along the sliding guide. When the size of the workpiece changes, the distance between the laser sensor and the workpiece also changes, and its output voltage signal changes accordingly. After sampling by the A/D conversion unit, it is sent to the lower-level computer; this is the radial (Y) data of the wheelset. Simultaneously, the lower-level computer synchronously counts the number of feedback pulses from the servo motor controller. The microcontroller uses this to calculate the displacement of the laser sensor along the sliding guide; this is the axial data of the wheelset. The servo motor operates at a set speed, while the motor controller sends feedback pulses of a certain frequency output from the photoelectric encoder on the motor to the lower-level computer. The lower-level computer counts these pulses, sampling the measurement output data of the laser sensor every 20 count pulses (corresponding to 0.1 mm in the axial direction) via an A/D converter. This achieves synchronous sampling. The lower-level computer transmits the data to the upper-level computer at high speed through a serial interface based on the RS422A standard. After fusing the radial and axial data, the upper-level computer can draw a two-dimensional image of the measured workpiece and calculate the relevant wheelset geometry parameters. 2 System Detection and Management Software 2.1 Software System Overview The system detection and management software mainly processes the measurement data and calculates various geometric parameters of the wheelset to obtain the detection results. The software is developed using C++ Builder 5.0 and adopts a multi-tasking and multi-threaded modular design. It mainly includes a main interface display module, a measurement information processing module, a serial communication module, a database management module, an image input and display module, and a wheelset information printing module. Based on the specific characteristics and requirements of this testing system, the overall software system block diagram is shown in Figure 2. 2.2 Software Modules and Functional Monitoring Module: This is the core of the software, mainly including the main interface display module, measurement information processing module, and database management module. 2.2.1 Main Interface Display Module: This module displays measurement information during the testing of train wheelsets, including wheelset motion control and animation display, camera capture of the wheelset axle end markings, wheelset shape geometric parameters, and the shape diagram of the tested wheelset. 2.2.2 Measurement Information Processing Module: This module is used for the analysis and processing of measurement data uploaded by the lower-level computer, mainly including digital filtering, curve fitting, and calculation of relevant parameters. This module is the key component of the upper-level computer software; the quality of its data processing algorithm directly affects the final measurement accuracy of this testing system. 2.2.3 Database Management Module: This module stores operator management information and all information about the tested train wheelsets. This information cannot be modified arbitrarily; the module provides password protection, and only the system administrator can access it. It also features database query and statistical functions, allowing users to query historical testing records by operator and testing date. Management personnel can also analyze recent workload to plan for future work. The serial communication sub-thread is primarily responsible for information exchange between the host computer and the slave computer. It is a relatively independent thread relative to the main thread, running in the background and constantly monitoring the serial port. This thread employs a dual serial port coordination mechanism to ensure high-speed synchronous measurement. Image input utilizes a USB-based camera to meet the requirements of high-speed, high-quality image transmission. Using the aforementioned hardware and software design methods, this high-precision laser wheel pair detection system exhibits high reliability, strong anti-interference capabilities, and all performance indicators meet the system's measurement accuracy requirements, demonstrating significant practical application value. The system's measurement accuracy is shown in Table 1.