Abstract : This paper presents a measurement and control system utilizing the combined operation of a microcomputer and a programmable logic controller (PLC). This system fully leverages the advantages of the microcomputer's strong data acquisition and processing capabilities, while also taking advantage of the PLC's high reliability and suitability for switch control, achieving optimal testing results. This system overcomes the inconvenience of using an industrial computer alone for durability testing, and also overcomes the difficulty of data processing when using a PLC alone. Application results demonstrate that this system can effectively perform performance and durability tests on clutches. 1. Introduction With increasing demands on vehicles, their safety has become a major concern. The quality of the clutch directly affects the quality of the vehicle and the smoothness of driving. Clutch bench testing is an important means of verifying clutch quality, and the performance of the clutch test bench measurement and control system directly affects the test results. This article introduces a new vehicle clutch test bench we developed. Adhering to the requirements of the Chinese industry standard QC/T66-93, it fully utilizes the advanced means provided by the development of computer and modern measurement and control technologies for testing the comprehensive performance parameters of clutches. Utilizing a microcomputer-based test bench, it has the following characteristics: ① The test system adopts an advanced and reasonable bench type—inertial drive; ② The system has good human-machine interface and is highly adaptable to multiple products and standards; ③ The system has strong resistance to vibration and electromagnetic interference; ④ The system's testing and control strictly comply with the provisions of the testing standards. Unreasonable or non-compliant operations will not be responded to and will be accompanied by a warning signal; ⑤ It has certain redundancy measures to allow for manual operation in case of sudden computer failure or other emergencies. Due to the adoption of a combined microcomputer and programmable logic controller (PLC) control scheme, the system's testing accuracy, reliability, and ease of use are greatly improved. The system software is written in VC++, with a user-friendly human-machine interface. It has functions such as automatic testing, automatic control, automatic data processing, automatic printing, and plotting. Experiments show that this system is highly responsive, has high measurement accuracy, and excellent detection and control effects. It also features low cost, ease of operation, and high reliability. The use of this system has improved the level of clutch testing. 2. Microcomputer and PLC Combined Control System Common computer-controlled measurement and control systems fall into two categories: those using microcomputers and those using programmable logic controllers (PLCs). Microcomputers offer greater flexibility and data processing capabilities, while PLCs offer high reliability and are suitable for switch control. Considering the requirements of this system—including high-precision testing, numerous test items, and durability testing—using only a microcomputer for durability testing is insufficient in terms of reliability; while using only a PLC lacks flexibility in data processing. Therefore, the system's measurement and control adopts a combined microcomputer and PLC scheme, which improves the measurement accuracy, flexibility, and reliability of the control system. The overall structure of the measurement and control system is shown in Figure 1. Analog signal acquisition and data processing are handled by a PC. Switch input and solenoid valve control can be handled by the PLC, or the PC can send commands to the PLC via RS232 bus to read the switch status or issue control instructions. All switching operations are driven by the PLC. During performance testing, the PC acts as the overall controller, controlling the solenoid valves via the PLC and simultaneously acquiring and processing various data. During durability testing, the PC can be offline, with the PLC controlling simpler actions independently. This combined computer and programmable controller approach fully leverages the computer's strong data acquisition and processing capabilities while utilizing the programmable controller's high reliability and suitability for switching control, achieving optimal testing results and effectively completing clutch performance and durability tests. 3. Composition of the Clutch Test Bench The clutch test bench system, using a combined microcomputer and PLC control, mainly consists of an inertial test bench, hydraulic cylinders, a frequency converter, a PLC control module, a microcomputer control console, and a data acquisition system. 1) Inertial Test Bench. The bench structure is shown in Figure 2, providing the required driving force and speed for the system. The bench is powered by a 30kW AC variable-speed motor, capable of reaching a speed of 8000 r/min and a maximum torque of 60 N•m. The inertia flywheel stores energy, simulating the inertia value of the total mass of the unit converted to the clutch shaft during start-up. The oil heating device is mainly used to simulate the oil temperature changes of a motorcycle under operating conditions. It also includes a clutch mounting mechanism and an inertia block simulating the rotational inertia of the clutch driven shaft. The loading system uses a hydraulic loading method and consists of a loading brake, a stop brake, and the clutch operating system under test. The loading brake provides resistance torque on the driven shaft, the stop brake stops the driven shaft, and the clutch operating device under test uses a double-acting cylinder, a resistance torque application device, a brake, and a clutch disengagement and engagement mechanism. 2) Hydraulic cylinder. Provides power for clutch disengagement, engagement, braking, and loading. 3) Frequency converter (VVVF). Primarily used to cause changes in the speed of the drive motor to simulate the speed changes of a motorcycle under all operating conditions. 4) PLC control module. It provides control of various motors such as the main unit and fan, and sends 0/1 signals to the PLC control port via RS232 to control the active motor, eddy current dynamometer, axial hydraulic cylinder, low-speed motor, brake hydraulic cylinder, electromagnetic clutch, oil heater, and hydraulic station motor to produce corresponding actions. 5) Microcomputer control console. The industrial control computer acts as the main unit. The base plate slot and transition board have multiple switch I/O channels and drive circuits for panel indicators and alarms, as well as timer programmable speed measurement circuits and analog input channels. 6) Data acquisition system. Includes conditioning circuits for temperature, torque, and speed signals. The signals are acquired and sent to the microcomputer data channel. 4 PLC control module A major feature of this system is the use of a measurement and control scheme that combines a microcomputer and a programmable logic controller (PLC). The PLC circuit mainly plays the role of logic switch control in this system. The programmable logic controller MK-120S is selected for switch control. The structural diagram is shown in Figure 3. This system has the following three applications: 1) Controlling the on/off state of the test equipment. It mainly controls the on/off state of components including centrifugal fan, oil pump relay, frequency converter, hydraulic cylinder, hydraulic station, low-speed motor, oil heater, and electromagnetic clutch by sending 0/1 signals to various ports of the PLC via RS-232. 2) Protection of test equipment. When the hydraulic station malfunctions or overloads, the centrifugal fan malfunctions or overloads, the slide table motor slides out of range, or an emergency occurs during the test, the test and test equipment will automatically shut down. 3) Self-diagnostic function. The software periodically checks the external environment of the test. Once an abnormality occurs, the CPU immediately takes measures to prevent the fault from escalating and stores the fault information in the memory. The PLC port settings are as follows: ①COM2 is connected to RS-232; ②P40～P47 ports are connected to contactor KM2, solenoid valve, and relay respectively to control motor, hydraulic cylinder, heater, and clutch, etc. Other port settings are shown in Figure 3. In addition to control via PLC, the system also monitors the connection status of each hardware device in real time on-site through an RS-232 serial communication monitoring and tracking program. Due to the high reliability, strong anti-interference capability, rich I/O interface modules, simple programming, easy installation, and convenient maintenance of PLCs, the structure of this system is simplified and its performance is optimized. 5 Other Hardware Circuit Boards Other hardware circuit boards include: a timer/counter board for measuring speed and torque; a data acquisition board for data acquisition, waveform analysis, and processing; and a D/A board for constructing analog voltage/current outputs and digital inputs/outputs. 5.1 Timer/Counter Board The timer/counter board is an isolated, programmable, multi-functional timer/counter module compatible with the AT bus. It provides 8 channels of 16-bit counters/timers, 8 channels of digital inputs/outputs, and also provides 8 levels of interrupt management for the 8 timer/counters. The three 8253 programmable timer chips on the board provide 9 independent 16-bit counters/timers, one of which is used as an on-board clock divider circuit, and the remaining 8 channels are for user use. Each input/output channel is isolated from field signals or equipment using optocouplers, effectively blocking ground loops between the field computer system and the local area computer system. The technical specifications are as follows: 1) Number of digital I/O channels: 8 (isolated) inputs / 8 (isolated) outputs; 2) Digital signal input frequency: 10kHz (square wave); 3) Number of timer/counter channels: 8 independent counters/timers (isolated); 4) Counter length: 16 bits; 5) Input frequency range: 0～10kHz (square wave); 6) Internal clock range: 40Hz～2MHz; 7) Duty cycle: 0～100%. 5.2 Data Acquisition Board The data acquisition board is an AT bus compatible multi-functional data acquisition board, integrating A/D, D/A, digital I/O, and timer/counter functions. The programmable gain can be selected as 1, 2, 4, 8 or 1, 10, 100, 1000. The A/D converter supports three A/D circuit start-up modes: software trigger, timer trigger, and external trigger. It supports 8-bit DMA, software polling, and interrupt-driven data transfer modes. The A/D conversion circuit has three triggering methods: software triggering, timed triggering, and external triggering. 5.3 D/A Board The D/A board is an AT bus compatible 8-channel D/A board. It uses a 12-bit resolution high-speed D/A converter, providing 8 D/A analog output channels. Each D/A output channel is independent, with a voltage output accuracy of ±1LSB. The analog output voltage range can be set to ±5V, 0～5V, ±10V, 0～10V, 1～5V via jumpers, and the output analog current range is 0～10mA, 4～20mA. It also provides 16 digital input channels and 16 digital output channels, which can be used for digital signal status monitoring and digital output control actuator on/off switching. 6 Software This system is developed using VC language tools and has a user-friendly human-machine interface. The test bench has functions such as automatic testing, automatic control, automatic data processing, automatic printing, and plotting. Test control can be performed not only through menus and the interface but also through command lines. The overall software block diagram is shown in Figure 4. Due to the poor electromagnetic environment and strong interference, in addition to a series of electromagnetic compatibility protection measures in the hardware structure, in order to ensure the reliability of the measurement data, the Grubbs criterion is adopted in the data processing. The criterion is that if the residual Ei corresponding to a certain measured value Xi satisfies the equation (1), the data should be discarded. In the software, n is set to a fixed value of 15, and the significance level a = 0.05 is taken. In this way, abnormal data in a set of data can be eliminated by the algorithm, so that the measured parameters of the test are more accurate and reliable. 7 Conclusion This paper introduces a clutch test system using a computer and a programmable controller for joint control. It is suitable for various performance and durability tests of clutches of various types in vehicles. Due to the joint control of the computer and the programmable controller, the measurement and control level of the test bench is improved. Fault judgment and automatic shutdown alarm can be performed, thereby realizing unattended operation of the test process. The PLC programmable controller is reliable, compact in structure, flexible in use, and energy-saving. The test system has been debugged and is actually running. The test results of various parameters are reliable, real-time, and highly accurate. While the microcomputer and PLC combined control system described in this paper has achieved good results in application, further research in the following areas will greatly advance the improvement of system performance: 1) Based on the characteristics of the controlled object and combined with the control features of the PLC, optimize the system design to fully utilize system resources. This will enable the following system functions: short-to-medium distance measurement, monitoring, and alarm during the experimental process; and real-time monitoring and alarm of digital and analog signal states. 2) Conduct in-depth research on control strategies and parameter measurement to find better control strategies and parameter measurement methods, resulting in more stable and accurate measured parameters.