Abstract : This paper specifically explores the application of PLC and stepping motor on the Train Wheel Photograph system. The control system is designed and the hardware structure and software implementation method of the control system are described. Key words : PLC, stepping motor, wheel photograph, pulse controlling This necessitates enhanced monitoring of bearing temperature rise. When a train passes by, it continuously radiates infrared heat energy, creating a temperature field on its surface. Thermal imagers installed on both sides of the rails absorb this infrared radiation energy emitted by the wheels, displaying the thermal image on a fluorescent screen. This allows for accurate assessment of the surface temperature distribution and real-time alarms for axles with excessive temperature rise, preventing train derailments or overturning due to axle overheating. This paper uses a PLC-controlled stepper motor to drive the thermal imager for detecting wheel axle temperature. 2 System Design Modern motion control methods mainly include DC servo drives, AC servo drives, and stepper servo drives. Among them, AC servo drives offer the best performance but are more expensive. With the rapid development of stepper servo drive control technology, the microstepping accuracy of stepper servo drives has been continuously improved, and the shortcomings of oscillation and step loss have been gradually overcome, significantly improving their cost-effectiveness. Stepper motors can be directly controlled by digital signals, operate in open-loop mode without feedback, have no cumulative positioning error, and offer high control accuracy. Therefore, they are widely used in precision positioning control systems such as digital control and computer control. A Programmable Logic Controller (PLC) is a technology platform suitable for industrial field control. PLCs integrate computer technology, automatic control technology, and communication technology. Using a simple, process-oriented, and user-friendly programming language, users can design and implement various complex logic controls through software. PLCs have good real-time refresh capabilities, can generate pulse signals of a certain frequency, and have high-power transistor output interfaces that can meet the voltage and current requirements of stepper motor windings. Therefore, this system uses a programmable logic controller (PLC) as the control core, a stepper motor as the actuator, and sensors as the detection elements to achieve temperature rise detection. The system structure is shown in Figure 1. When a train approaches, the sensor sends the detected speed pulse signal to the PLC interface X0. The PLC calculates the corresponding train speed based on this pulse signal and outputs a corresponding speed pulse signal to the stepper motor driver. The driver controls the stepper motor to drive the thermal imager in a semi-circular motion. When the thermal imager's speed is the same as or close to the train's speed, it tracks and photographs the train wheels, thereby determining the wheel axle temperature. Infrared detectors are arranged along the railway tracks; the thermal imager is mounted on a frame approximately 1 meter away from the tracks. The angular displacement of the stepper motor is proportional to the number of input pulses; the rotational speed is proportional to the pulse frequency; and the direction of rotation is related to the phase sequence of the pulses distributed to the windings of the stepper motor. Therefore, a PLC can generate control pulses of a certain period to shift the shift register, generating a corresponding timing sequence. A ring distributor then sequentially activates the output relays to drive the stepper motor, and a counter controls the number of pulses, allowing the stepper motor to rotate at a certain speed and angle. Based on functional requirements and considering the performance of the stepper motor, a two-phase hybrid stepper motor 2S42Q-03848 with a step angle, phase current of 1.2A, and holding torque of 0.32Nm is selected to drive the thermal imager. The stepper motor driver is a 2M412 with a DC power supply voltage of 18V-36V, which implements pulse and direction control of the motor according to the PLC's control instructions. There are two ways for a PLC to control a motor: one is pulse + direction control (Y0 and Y2 output pulses, Y1 and Y3 output direction), and the other is forward and reverse pulse output (Y0 outputs CW pulses, Y1 outputs CCW pulses). We use the first method. 3. Implementation of the Control System In this system, it is crucial that the PLC calculates the train's speed based on the pulse width. We selected a Delta PLC DVPl6EH00T with 8 input points (X0-X7) and 8 output points (Y0-Y7) to control the stepper motor's operating state and speed. Besides general logic control and arithmetic functions, and direct PLSY pulse output, its most important feature is its SPD pulse speed detection function, which can be conveniently used to measure train speed. SPD control format: When the control signal is ON, D1 calculates the high-speed pulse input from X0. After 40ms, the calculation automatically stops, and the result is stored in D0. When the 40ms count is complete, the content of D1 is cleared to 0. When the control signal is ON again, D1 starts counting again. The main purpose of the sPD instruction is to calculate the proportional value of the rotational speed. The measured D0 result is proportional to the rotational speed, and the motor speed is obtained by the following formula [sup][2][/sup]. Where: N: rotational speed; n: number of pulses generated by the rotating equipment in one revolution; t: detection time (ms). The system control wiring diagram is shown in Figure 2, and the I/O ports and their functions are shown in Table 1. [align=center] [/align] 4 System Software Design Stepper motors go through a process of acceleration → high speed → deceleration → low speed → stop. Its pulse frequency characteristics are shown in Figure 3. Among them, segment 0a is the acceleration stage, accelerating from 0 to fl; segment ab is the high-speed (uniform speed) operation stage; segment bc is the deceleration operation stage, decelerating from fl to f2; segment cd is the low-speed operation stage, until stopping at point d. The PLSR instruction is a pulse output instruction with additional deceleration function. By setting the maximum frequency value of the pulse output, the total number of pulses of all pulse outputs, and the acceleration and deceleration time, the speed and direction of the stepper motor are controlled. The number of acceleration and deceleration segments of this instruction is fixed at l 0 segments. When outputting, the output pulse starts at a frequency that increases by S 1/1 0 each time, and the time of each frequency output pulse is fixed at S 3/9. Figure 4 is the flowchart of the control software program designed according to the electrical control principle, combined with the PLC programming method and production process requirements. 5 Conclusion This paper designs a control system based on programmable controller and stepper motor for the detection of train wheel axle temperature. It realizes the automatic photography of train wheel bearings and has the advantages of simple control, stable and reliable operation and short development cycle. It is a practical stepper motor control scheme. References : [1] Zhou Fenglei. Application of PLC and stepper motor in the transformation of combing machine. PLC & FA, 2005 (4): 100-101, 136 [2] Delta PLC User Manual [3] Song Jian, Yuan Chi et al. Application of PLC control of stepper motor in milling machine for agricultural vehicle gear processing. Agricultural Mechanization Research, 2003, 4(2): 221-222 [4] Chen Yifei, Xue Yingcheng. PLC fuzzy neural network variable frequency speed control system. Electrical Drive Automation, 2004, 26(1): 36-38, 47 [5] Wang Binsheng, Sun Jing. Application of PLC in stepper motor drive system. Machine Tool Electrical, 2001(2) Author Introduction Pan Zi Male Engineer Research direction: software and hardware design of control system.