Authors: Zhang Xudong, Guan Jifu, Gu Liang
The active suspension bench test measurement and control system based on the PXI platform described in this paper, the system hardware is easy to configure, with a PXI chassis As the foundation, with different PXI boards, you can achieve a variety of functions, low cost, comprehensive functions, scalability, and upgradeability It has the advantages of high test accuracy and high reliability. “
With the continuous improvement of people’s requirements for the smoothness and handling stability of vehicles, it is hoped that when the vehicle load, driving speed, road condition There is a growing need for active vehicle suspension as the vehicle automatically adjusts the stiffness of the suspension system as driving conditions change Increase. At the same time, the industry’s research on active suspension systems has also become more in-depth and extensive. For active suspension systems, there are many types of actuators that generate active power, and the active control algorithms are also different. Therefore, , a flexible and convenient active suspension bench test measurement and control system that has good compatibility with various mechanical structures and control algorithms. necessary.
According to actual needs, this paper establishes an active suspension bench test host computer monitoring and control system. Using this system, the comprehensive performance of various active suspension systems can be fully tested, and the host computer system can be used for comprehensive testing. Apply various control algorithms written by the user to the active suspension to verify the control effect and find the best control scheme for the active suspension The development and refinement of the rack system provides the means for design and verification.
1. System Platform Overview
The hardware part of the measurement and control platform of this active suspension system is built on the basis of the PXI system. PXI (PCI eXtensions for Instrumentation, PCI extensions for instrumentation systems) technology was developed in 1997 and officially launched in 1998 to An open industry standard introduced to meet the increasing demand for complex instrumentation systems.
PXI is a rugged PC-based measurement and automation platform. PXI combines the electrical bus features of PCI with the rugged, modular and Eurocard mechanical packaging features of CompactPCI, and adds A dedicated sync bus and key software features are included. This makes it a high-performance, low-cost carrier platform for measurement and automation systems. These systems can be used in a variety of fields such as manufacturing test, military and aerospace, machine measurement and control, automotive production, and industrial test.
2. The hardware structure and characteristics of the measurement and control system platform
The hardware is mainly composed of six parts: host computer, signal preprocessing module, sensor, hydraulic test bench, active suspension system, PXI chassis and signal acquisition and output boards. The host computer is used to measure and control the simulation process, analyze and save the simulation results, run the algorithm model, and output control signals to execute the The signal preprocessing module is used to provide a constant current source for the sensor, eliminate the Voltage offset, and increase the control signal. Drive capability; sensors include pressure sensors, displacement sensors, acceleration sensors, and temperature sensors to obtain data required by control algorithms; hydraulic test bench Provide an excitation source for the active suspension to simulate actual road conditions; the active suspension system is equivalent to the actuator of the control algorithm, including components such as shock absorbers, oil and gas suspensions, hydraulic pumps, and various proportional valves and on-off valves that control the on-off of hydraulic pipelines; The above-mentioned links are organically combined into a complete closed-loop system. The structural framework of the measurement and control platform is shown in the figure below:
Figure 1. Structural framework of measurement and control platform
The upper computer and the controller are connected through a network cable, and the measurement and control of the simulation process by the upper computer is realized by sharing variables.
The monitoring system can centrally configure each equipment involved in the test, and can start, stop and adjust all equipment at the upper level. It is completed on the machine, which makes the operation of the test personnel easy and convenient, reduces the labor intensity of the test, and improves the efficiency of the test. Through the computer Display screen, the test personnel can understand the temperature, pressure, Acceleration and motion travel and other data, and perform related measurement and analysis, based on which to judge the performance of the suspension system and the vibration reduction effect, and at any time Human intervention is possible.
The host computer is the core of the entire measurement and control system, with a good human-computer interaction interface, and it is also the carrier of the measurement and control software. NI’s PXI chassis, controllers and application software developed based on LabVIEW constitute a virtual instrument measurement and control platform. It has the functions of fully digital acquisition, test and analysis, rich hardware and software resources, strong scalability, automatic test process, high test accuracy, It has the advantages of good repeatability, convenient operation and high cost performance.
A temperature sensor and a pressure sensor are installed in the oil and gas suspension and shock absorber cylinder, and the unsprung mass shaft head and An accelerometer is installed on the sprung mass, and a pull-wire displacement sensor is installed between the unsprung and sprung masses .The signal collected by the sensor eliminates the offset through the signal conditioning module, and transmits it to the analog signal interface of the PXI board. After conversion, transmit to the host computer
The connection relationship of the active suspension measurement and control system bench test hardware part is shown in the figure below
The control signal output by the active suspension bench test measurement and control system is divided into two types: 3 PWM signals and 1 switching signal. . The PWM signal is used to: 1) drive the motor, drive the hydraulic pump, and provide the power source for the entire active suspension system; 2) adjust the ratio Adjust the opening of the relief valve to control the pressure value in the hydraulic pipeline; 3) Adjust the opening of the damping valve, Realize the adjustment of the damping ratio to achieve the purpose of adjusting the damping force. 1-way switch signal is used to adjust the on/off of the 2/2-way valve to realize the on/off function of the active suspension. The control signal output by the PXI board first increases the driving capability of the signal through the signal preprocessing module, and then connects to the Control component.
Figure 2 The connection relationship of the active suspension measurement and control system
Figure 3 The connection relationship of the bench test hardware part of the active suspension measurement and control system
3. Measurement and control system platform software design and application method
The host computer monitoring program can realize the collection, recording, analysis, calculation and other functions of the bench test data, and can Record data, analyze results, and graphs to generate test reports. The debugging, measurement and control of the test system are all automated, with high reliability, and the operation interface is friendly and convenient, easy to use Use.The main functions of the detection software are shown in the table below
Table 1 Software function table
3.1 Operation interface
The software part of the bench test measurement and control system is written based on the LabVIEW virtual instrument development environment, which can realize multi-channel signal acquisition, measurement, and analysis , control signal output, test data saving, reading and other functions, can fully cope with various active or semi-active suspension bench tests The operation interface is similar to the oscilloscope commonly used in the laboratory, and it is easy to use
3.2 Data collection and analysis functions
The measurement and control system uniformly measures and analyzes the parameters required by the active suspension control algorithm, following the connections shown in Figure 1.3. The relationship between the temperature, pressure, acceleration, displacement and other sensors to measure the signal through the signal conditioning 0~5V standard signal to the PXI system , and displayed on the measurement and control interface.
Figure 4 The main interface of the host computer monitoring program operation
The operation interface, in the form of tabs, divides the system into waveform browsing/setting, waveform measurement, FFT spectrum, and waveform playback. Five functions of analysis of amplitude and frequency characteristics, in addition, the system can also adjust the X and Y axes of the waveform according to the actual needs of the operator Coordinate range, real-time capture of waveform graph, current waveform and save as .dmp file, editing experiment name, experimenter and file name, etc. function. Before starting the system, you should first set the sampling rate. After the system is running, you can perform corresponding operations according to actual needs to achieve Browse, measure, analyze, and record acquired data. The main operation interface of the system is shown in the figure below.
Figure 5. Host computer program filter options
The measurement and control platform provides a variety of measurement analysis and data processing options for the measured data:
A. Filter settings
The measurement and control platform provides a wealth of filtering methods, which can be set according to different situations, including Bessel, Butterworth, 5 filter topologies such as Chebyshev, Inverse Chebyshev, and Ellipse, high-pass, low-pass, band-pass, band-stop, smooth, etc. 5 filter types, and can set the filter high and low cutoff frequency, filter order, and IIR/FIR selection accordingly.
The measurement and control platform can measure any sensor signal of the bench test system. The content of the test interface agent is shown in the figure below.
C. FFT spectrum
The measurement and control platform can perform FFT amplitude (root mean square), FFT amplitude (peak), power Spectral and Power Spectral Density measurements, and Display the measurement results as waveforms.
D. Amplitude-frequency characteristic analysis
The measurement and control platform calculates the amplitude-frequency characteristics of the vehicle body acceleration and the amplitude-frequency characteristics of the moving stroke according to the signals measured by the acceleration sensor and the displacement sensor. .
3.3 Waveform recording and playback functions
The test system needs to collect 7 channels of data at the same time. When debugging the algorithm, the test cycle is often very long, and the Requires multiple experiments with an algorithm or product. Therefore, the original experimental data saving and playback functions are designed in the experimental program. This function provides a convenient and simple operation for saving test data, and at the same time, avoids the test caused by human factors as much as possible. Inconsistent parameter settings, or omission of experimental data, ensured the consistency of repeated experiments.
The data measured during the experiment and some other information during the experiment, such as the name of each measurement channel, the total number of samples collected, the sampling The interval, experiment operator name, experiment date, etc., will all be saved in the file.The file name and save path of the test data file can be customized and edited by the test operator according to personal habits
The test data playback interface is shown in the figure below. In order to facilitate the test personnel to analyze and compare the previous test data, the measurement and control system provides a data playback function, which can Import the raw data into the system to obtain the time domain signal corresponding to the data, the power spectral density of the acceleration signal, and the amplitude-frequency characteristics of the vehicle acceleration. Graph and Amplitude-Frequency Characteristic Graph of Body Moving Stroke. The waveform data playback interface is shown in the figure below.
Figure 9 PC program waveform data playback interface
3.4 Measurement and control system platform application method
1) System initialization: After entering the test system, the first step is to initialize the system, mainly for the sensor calibration module, The signal acquisition module, the control signal output module, the measurement and control system monitoring module, and the control algorithm import module are initialized. Report an error to the abnormal situation, and make necessary preparations for the operation of the measurement and control system.
2) Set corresponding test parameters and test information: including sampling information, test time, tester, test remarks, etc.
3) Sensor calibration: Any sensor will have errors at the beginning of use or after a period of use. To ensure test accuracy, the sensor must be calibrated to obtain a new calibration value. The method of calibration is to measure 5 or more points within the valid test range, enter the corresponding parameter values, and calculate According to the input value, the computer uses the method of linear regression to calculate, and obtains the regression equation, the maximum calibration value, the maximum voltage value, the absolute error relative error, etc., and store these values in the appropriate file.
4) Import the control algorithm into the active suspension bench test measurement and control system, and establish the corresponding relationship between the algorithm parameters and the hardware interface: first Compile the control algorithm file into a dynamic link library file, and then import the compiled dynamic link library file into the measurement and control system , select the communication rate between the model and the hardware and the hardware I/O port to use in the system, establish the port and A mapping of algorithm parameters.
5) Run the active suspension bench test measurement and control system: until the set test content is completed, the system stops working, and the error occurs during the start test. The system automatically shuts down or man-made emergency stop caused by system abnormality.
6) Real-time acquisition, processing and analysis of measured data: This system includes signal filtering topology, filtering type, and low cutoff Frequency, high cutoff frequency, order, filter function settings such as IIR/FIR, max, min, rms for all signals Value, Fundamental Frequency, DC Value, Period Average, Rise Time, Fall Time, and can calculate acceleration and displacement signals Amplitude spectrum, RMS spectrum, power spectrum, and power spectral density can calculate the amplitude-frequency characteristics of vehicle sprung mass acceleration, Amplitude-frequency characteristics of moving stroke.
7) Real-time storage of measurement data: mainly store the collected signals on the local hard disk in the LabVIEW-specific .tdms file format , or store the data in a database for later analysis or processing.
8) Real-time display and playback of the measured data: mainly to carry out the collected signals in the time domain and frequency domain Real-time display; can also re-read the saved .tdms file and display it on the host computer terminal. Through the comparison of the results of many experiments, it is easy to know the advantages and disadvantages of each control algorithm, so as to choose the appropriate control algorithm. Provide a basis.
9) After the test is completed, the test results can be printed according to different report formats, and the control effect of the control algorithm can be comprehensively evaluated.
The design described in this article provides a test system that not only meets the test requirements of active suspension systems, but is also fully compatible with semi-active And passive suspension test, the test process is automated, high precision, good repeatability, and compared with foreign equipment with the same function, the price is low , the hardware configuration is simple, and the scalability is strong.