Abstract: Given the current situation where a fully functional steel ball appearance inspection machine has not yet been manufactured in China, we designed a steel ball appearance inspection control system based on a programmable logic controller (PLC). This paper proposes measures to prevent electromagnetic interference in the PLC control system, analyzes and calculates the timing properties and inspection time of the inspection system, and describes the method of generating control timing using a PLC. Keywords : PLC; steel ball appearance inspection; electromagnetic interference; timing 1 Introduction Rolling bearings are important basic components in the national machinery industry, and the quality of steel balls, as the rolling elements of bearings, plays a decisive role in the performance and safety of rolling bearings. Only the Czech Republic manufactures fully functional steel ball visual inspection machines globally. Previously, these machines used cam-controlled switches with timing determined by an internal gearbox, resulting in high noise levels. Electrical sparks at the switches and surge currents from load power outages could cause interference. In 1990, China first imported a Czech steel ball visual inspection machine, largely controlled by analog circuits. Due to technological monopoly, China has relied entirely on Czech products for steel ball inspection ever since. This design uses a PLC to achieve accurate timing control and signal processing to meet inspection requirements. 2. Overview of the Inspection Control System 2.1 The overall structure of the steel ball visual inspection system and the functions performed by the PLC can be divided into four parts: (1) Feeding system: hopper, diameter sorter, supply channel. (2) Unfolding system: unfolding mechanical system, isolator, ball counter, feeder, feeding mechanical fingers. (3) Inspection system: photoelectric detector, vibration detector, eddy current detector. (4) Control device: programmable controller, touch screen. After the steel balls are processed from the hopper to the inspection and sorting, the PLC must completely control the movement state of the steel balls, complete the closed-loop control of the entire inspection, and communicate with the touch screen and the detection device in real time. The PLC configured in the system is the Mitsubishi FX1n model. The touch screen is connected to the PLC through the RS485 interface. Communication parameter settings: data bits: 7 bits; stop bits: 1 bit; parity bits: even parity; baud rate: 9600bps; timeout constant is 3 seconds. [align=center] Figure 1 Block diagram of the entire control system[/align] 2.2 PLC input and output signal analysis: (1) Isolator signal: The signal emitted when the steel balls accumulate, which is a square wave with an indefinite period. The PLC determines whether the square wave is valid by judging the high level of the square wave. (2) Ball counter signal: Analyzed and calculated from the isolator signal. (3) Debugging signal of the unfolding mechanism: The PLC controls the debugging motor in the unfolding mechanism. This debugging motor is also the main drive motor for the machine. This signal carries a feedback signal with a certain frequency. The change in the frequency of this signal determines whether the drive of the unfolding mechanism is normal. The signal line uses aviation shielded cable. (4) Photoelectric detection, vibration detection signal, eddy current detection signal: rectangular pulse, rising edge triggers PLC. (5) Output point is connected to different models of solid-state relays. 3 Software Design 3.1 Time Delay Consideration: The time delay considered in this program is as follows: (1) Input and output delay of solid-state relay (within 2ms). (2) Input filtering delay of PLC (within 10ms), output response time (within 1ms). (3) PLC timing error (lower deviation is 1ms, 10ms, 100ms; upper deviation is one scan cycle). (4) Response time of actuator (within 3ms). (5) Execution cycle of this program; interrupt mode is used between the touch screen and PLC, and the delay is ignored. 3.2 Inspection Time Determination: The steel ball must be placed on the unfolding mechanism for a sufficient time. The following is an analysis of the steel ball unfolding time. In the diagram below, the axis of the control roller is on the straight line CJ, and the center of the steel ball is at point O. The steel ball rotates at a constant speed on the control roller of the unfolding mechanism and revolves at a constant speed around the control roller. Now, the coordinate system is established as follows: [align=center] Figure 2 Schematic diagram of steel ball unfolding[/align] We get: The control roller rotates around the axis, ω0=ωz. During the normal unfolding process, when the control roller interacts with the steel ball on a contact line (only one side of the control roller is discussed), and the steel ball has a small rotation angle ∠OJB (let's call it α) in the YZ plane, since AB⊥AJ; BC⊥CJ, we have the following relationship: We get. The two triangles △AJB and △BJC share a side, so the two triangles are congruent. Let ∠AJB = ∠BJC = , ∠AJC = 2α. When the steel ball rotates by an angle α on the Y-Z plane, it rotates by an angle 2α relative to the rotation. The control rollers control the rotation of the steel ball around the x-axis for each revolution around the z-axis. If the effective detection area of ​​the sensor is a circular region with a diameter σ, taking a certain overlap factor, then 2σ/3 = φR, from which the half-bandwidth can be obtained. A steel ball with an unfolding radius of r needs to rotate around the z-axis for 3 revolutions. The entire unfolding time is [not specified]. Different control rollers should be used for unfolding steel balls of different diameters. For a steel ball with a diameter of 5.5562 mm, it needs to rotate 36 times, with an inspection time (ms). Since the FX1n PLC only has four 1ms timers, it cannot meet the needs of all diameter groups. If a 1ms timer is needed, the MOV instruction can be used to transmit the inspection time of the group. To some extent, this can relatively increase the inspection speed of the inspection machine, but a very strict design is required in the timer reset and MOV instruction execution order and exception handling protection, which greatly increases the number of program steps. When a PLC provides a large number of 10ms timers, using a 10ms timer is relatively concise, greatly reducing the number of program steps. Since the number of program steps provided by the PLC is limited, this greatly facilitates the expansion of other functions. Using a 1ms timer on the feeder to complete the duty cycle timing can reduce program timing errors. The inspection instrument uses a last-on-first-off (LIFO) approach to ensure reliable signal transmission. The feeder's operating cycle includes the time for the ball's free fall, the time for feeding the steel ball to the meridian wheel (loading time), and the opening time for the unfolding mechanism to release the steel ball (unloading time). The calculation of loading and unloading times must consider the action delay of the actuators and other related errors (mainly the timer's timing error, which may be 10ms less than the timing setpoint). The sum of the loading and unloading times is 43ms, a fixed value. Loading and unloading time (t) = Guaranteed completion time of the feeding mechanical finger action (29ms) + Reserved time for the steel ball's unstable state (8ms) + Guaranteed execution time of the sorter (6ms). The program setting time for a 5.5562 mm steel ball is T' = T + t = 273. 3.3 Touchscreen Interface Design: We designed several main interfaces: diameter selection interface; debugging interface; encryption interface; inspection status information display interface; alarm interface. The operation is intuitive and easy to understand. 4 Conclusions and Innovative Viewpoints: The following is the control timing waveform verification for the inspection of a 5.5562 mm diameter steel ball; the execution cycle is T' = 273 ms. [align=center] Figure 3 Waveform diagram of 5.5562 mm diameter inspection[/align] It can be seen from the figure that it completely matches the program setting value. Channel 1 is the cycle of the feeding mechanical finger; Channel 2 is the cycle of the feeder; other waveform verifications are omitted. The steel ball inspection rate is consistent with that of the Czech Republic. Using PLC to complete the design of a steel ball appearance inspection system is a design unprecedented globally. This design makes the system easy to operate, highly stable, and has been debugged and run on-site, meeting the requirements. The inspection results are accurate and reliable. It can be shut down at a time and in a quantitative manner, and 15 groups of different sizes of steel balls can be selected, reaching the international first-class level. The algorithm for calculating the inspection time of steel balls is unique, and the method of using scalar representation to represent the motion vector of the steel ball is innovative. It has played a significant role in promoting the steel ball inspection technology in China. References: [1] Huang Kunrong. Application of PLC and touch screen control system in sterilizer [J]. Microcomputer Information. 2005, 2: 5 [2] Kim, Chouikha. Attenuation characteristics of high rate home-networking PLC signals [J]. Power Delivery. IEEE Transactions on. 2002. Volume 17. Issue 4. [3] Zhao Gang, Ma Songxuan, et al. Theoretical analysis of the meridional unfolding mechanism in A viko K-type steel ball appearance inspection machine [J]. Journal of Sichuan University. Sichuan University Press. 1997