Currently, the vast majority of testing equipment for automotive safety components is imported from countries with developed automotive manufacturing industries, especially functional testing equipment for ABS (Anti-lock Braking System) sensors. Therefore, it is necessary to independently develop a fast, stable, and universal testing device suitable for the production environment to meet the requirement of a mandatory inspection step in the production process. This design uses the NI PCI-6220 multifunction data acquisition card and LabVIEW 7.1 development software to develop a testing system that meets the requirements based on Volkswagen's ABS sensor functional testing standards. This system is fast, reliable, and capable of data acquisition, analysis, and storage, and has already been put into use on the production line. The working principle of ABS: The most important function of ABS is not to shorten the braking distance, but to maintain the directional stability of the vehicle during braking. When ABS is activated, the friction between the wheels and the road surface is rolling friction. It fully utilizes the maximum adhesion between the wheels and the road surface for braking, thereby increasing braking acceleration and shortening the braking distance, but most importantly, ensuring the directional stability of the vehicle. ABS working is equivalent to applying intermittent braking at a very high frequency. Therefore, in an emergency, if the brake pedal is fully depressed, you will definitely feel the brake pedal vibrate and hear a "clicking" sound from the master cylinder, indicating that the ABS is working normally. The master cylinder continuously adjusts the braking pressure, thus generating continuous feedback force on the brake pedal. The test principle is shown in Figure 1. During the test, the ABS rotation system is driven by the drive system to rotate at a constant speed in any direction. For the MK60 ABS sensor, this means rotating at a constant speed of 139.5 r/m without braking force. As shown in Figure 2, voltages of 12Vdc and 3.3Vdc are applied to the sensor between contacts ① and ② (UB), respectively. Two tests are performed continuously during rotation, ensuring a complete revolution in each test. When the ABS sensor senses the trigger plate, it generates a square wave peak; otherwise, it generates a trough. The voltage US is obtained using a 115Ω high-precision resistor R. When UB is 12V, the frequency of the square wave, the maximum and minimum values ​​of the peak current IH, the maximum and minimum values ​​of the trough current IL, and the duty cycle of the signal are calculated based on the measured voltage value. As shown in Figure 3, when UB is 3.3V, the number of pole pairs and the pole gap are calculated based on the measured voltage value. If these values ​​are within the permissible range, the ABS sensor can be deemed qualified. [align=center] Figure 1 Schematic diagram of ABS sensor test system Figure 2 ABS circuit diagram Figure 3 ABS square wave[/align] To ensure a complete test cycle and to determine if the number of pole pairs of the ABS sensor is correct, a reference pulse generator is required. For this purpose, a toothed disk with 45 teeth was made, because the number of pole pairs of the workpiece is normally 43, so the number of teeth on the disk is close to that. The tooth gap ratio of the disk is 1:1, and it rotates with the workpiece under test. The number of teeth on the reference disk is detected by a photoelectric switch. Only when the signal of 45 photoelectric switches is detected can it be ensured that the ABS has completed a complete test cycle. The photoelectric switch generates a sequence of pulses from 0 to 24V, but after photoelectric isolation by the interface board, it is converted into a sequence of pulses from 0 to 5V, hereinafter referred to as REF signal. When selecting this photoelectric switch, it should be noted that the response frequency should be greater than 45 × 139.5 ÷ 60 = 105Hz. The control principle utilizes an NI PCI-6220 multifunction data acquisition card. The ABS and REF signals are connected as analog voltage inputs to channels 0 and 1 of the card via differential input. To ensure testing accuracy, the analog sampling rate is set to 25 kS/s, and the buffer size for each channel is set to 500 kS to reliably store the test data. The number of read points per channel is set to 250s. The test condition judgment signal and the test conclusion value are output as digital signals to the DIO. To achieve the switching of test voltages and the input/output of analog and digital signals, an interface board was designed and developed, the block diagram of which is shown in Figure 4. The interface board contains two DC/DC modules, used to convert 24Vdc to 5Vdc and 12Vdc respectively. The 5Vdc is used for the DIO of the multifunction data acquisition card. To protect the NI PCI-6220 multifunction data acquisition card, bidirectional input opto-isolation and NPN/PNP input selection switches are used for digital inputs, dividing the 24 digital values ​​into 16 inputs and 8 outputs. The output section uses a Darlington driver module to drive relay outputs. The required test voltage accuracy is 12±0.1V and 3.3±0.1V, using two voltage regulators and potentiometers to ensure that the test voltage is adjusted to 12V and 3.3V. Yaskawa SGMGH series servo motors and SGDM series servo controllers are selected to maintain constant speed. The servo motor uses a 17-bit encoder and applies internal speed control, eliminating the need for other control modules to achieve constant speed testing. [align=center]Figure 4 Interface Board Structure Diagram[/align] Figure 5 is the test program flowchart, and Figure 6 is the overall equipment diagram. The specific test steps are as follows: [align=center]Figure 5 Test Program Flowchart Figure 6 Overall Equipment Diagram[/align] 1. Power on and run the program. First, the program is initialized, including reading parameter setting values ​​and initializing arrays and clusters. 2. The test program scans the "test command" pulse signal every 50ms, and this pulse signal is maintained for at least 200ms. Once the "test command" pulse signal is scanned, the test begins. 3. The previous test results must be cleared first. 4. Relays K1 and K13 on the interface board are powered on and connected to the ABS sensor. A 12V voltage is applied to perform the first test, and the test value is calculated. 5. Relay K13 on the interface board remains connected to the ABS sensor, K1 is disconnected, and the voltage is switched to 3.3V to perform the second test, and the test value is calculated. 6. Summarize the calculation results and draw a conclusion. 7. Output the calculation results and test conclusions, and send them to the PLC as I/O signals indicating test completion and pass/fail status; display the calculation results and test conclusions on the main interface of the test software; save the calculation results along with the time, date, and barcode. 8. Wait for feedback signals from the PLC. If a "result received" signal is received from the PLC within 3 seconds, return to step 2 and wait for the "test instruction" pulse signal to prepare for the next test; otherwise, issue an alarm. The program design uses the standard LabVIEW state machine as a template, with a total of 19 boxes. Four clusters are established as data highways: ABS and REF sequential comparison, parameter setting, calculation results, and measured data. A total of 15 subroutines are called to complete functions such as testing, parameter setting, and hardware testing. The display screen can switch between four interfaces: "View Data," "First Waveform," "Second Waveform," and "Parameter Setting and Hardware Testing." The default screen is "View Data," which is also the main interface, as shown in Figure 7. The default screen displays the calculated values ​​of the required test items, the test results, the number of tests performed after this program run, the number of qualified tests, and the pass rate. During the test, the test progress is displayed. The ABS and REF signal waveforms of two consecutive tests are shown in the "First Waveform" and "Second Waveform" screens. Figure 8 shows the waveform of the first test. Authorized users can set parameters in the "Parameter Settings and Hardware Test" screen. Hardware tests can be performed when system debugging is required. Data log files are generated daily with the date as the file prefix, such as "2006-6-3_ABS". [align=center] Figure 7 Main Interface Figure 8 First Test Waveform[/align] The test data is prepended with the date, time, and barcode of the tested component and saved accordingly. A new row is added after each test, and the data is stored simultaneously on both the C and D drives, each with 80GB capacity, to ensure data security and facilitate data traceability. The log files can be viewed using Excel software. Because the acquisition speed is very fast, although theoretically the rising and falling edges of a square wave signal are considered to be abrupt transitions, such as from 0V to 5V, if this transition process is amplified many times, the intermediate value between 0V and 5V can be captured, which could be 2.7V, 3.5V, etc. This is a value within such a transition process, representing the peak or trough exceeding the limit. Analysis of the acquired data reveals that, based on the required sampling rate and square wave frequency, at most one intermediate value can be generated during the transition process. Therefore, identifying and filtering this intermediate value in the program avoids false or unqualified data from being included in the calculation. Furthermore, although macroscopically: if the ABS sensor is qualified, and the reference signal has 45 teeth, the ABS should have 43 teeth, analysis of the paper model reveals that at the instant sampling begins, the relative states of the ABS or the reference signal (REF) are different, resulting in different calculated values. That is, if the pulse sequence judgment result is REF before ABS, then using REF as the reference, ABS=43 is correct when REF=46; if the pulse sequence judgment result is ABS before REF, then using ABS as the reference, REF=45 is correct when ABS=44; if the pulse sequence judgment result is ABS and REF arrive simultaneously, then using ABS as the reference, REF=45 is correct when ABS=43. [align=center] Figure 9 LabVIEW Block Diagram Program[/align] Conclusion Practice has proven that LabVIEW 7.1's graphical programming is easy to read and understand. The rich examples in the software are extremely useful for beginners, and practical decorative components can create beautiful and practical interfaces. Figure 9 is a LabVIEW block diagram program. Currently, this ABS functional testing system has been delivered and put into use. The system is technically reliable, runs stably, and can guarantee measurement accuracy. Compared to similar imported equipment, although the sampling rate of the acquisition card is 250kS/s, the A/D conversion resolution of the imported equipment is 12 bits, while the conversion resolution of the NI PCI-6220 is 16 bits. In addition, the price of the imported equipment is 3 to 4 times that of this system. The success of this system has also saved users equipment investment.