“With the development of the machinery industry and the continuous improvement of the scientific research level, higher requirements have been continuously put forward for the experimental and testing methods of mechanical transmission products. For a long time, the development of transmission test benches in my country has basically remained at the level of traditional manual methods. The main types are mechanical power flow closed test benches with mechanical force or hydraulic pressure and electric power closed test benches with generators as loads. .
Authors: Wen Hu, Xiang Zhongfan, Yao Hong
With the development of the machinery industry and the continuous improvement of the scientific research level, higher requirements have been continuously put forward for the experimental and testing methods of mechanical transmission products. For a long time, the development of transmission test benches in my country has basically remained at the level of traditional manual methods. The main types are mechanical power flow closed test benches with mechanical force or hydraulic pressure and electric power closed test benches with generators as loads. . These test benches have their own characteristics due to energy saving or loading, and they all have a common disadvantage, but the degree of automation is low, it is difficult to carry out the test according to the pre-designed test process, and it is impossible to simulate the actual working conditions for various mechanical transmission products. Therefore, there is always a considerable distance between the test results and the actual situation, which greatly affects the direct guiding role of the test data on the design and production of mechanical transmission products. Most of the transmission test platforms use manual operation, and the monitoring of the test process and the collection and processing of test data are cumbersome and low in accuracy, and it is difficult to realize automatic multi-parameter control and failure determination.
In order to make up for the above deficiencies, we put forward a new scheme – based on a mechanically enclosed mechanical transmission test bench, driven by an AC motor, using an AC variable frequency speed regulation system to achieve stepless speed regulation, and a digital hydraulic loading control system to achieve no Simulation of stage loading and load spectrum. The control system adopts object-oriented programming technology and layered design idea, integrates various control algorithms and data processing algorithms, provides a friendly human-computer interaction interface, and visualizes the data collected by the computer.
1 The composition and working principle of the multifunctional test bench
According to the power transfer principle and loading method of the test bench, the test bench can be divided into three categories: open power flow, closed power flow and electric power flow closed. The mechanically enclosed power flow test bench (as shown in Figure 1) is widely used because it can perform large power tests with low power prime movers and low power consumption, and has the advantages of not needing to install energy-consuming devices and saving energy. In a closed system, power flows out from one end and flows from the other end, forming a closed loop flow, so as long as a small amount of energy is input from the outside world, the system can be kept running. The energy supplied by the motor is mainly to compensate the frictional power loss of each component in the closed system during operation, and its value is about 10% to 15% of the closed power value.
2 system solutions
The control device of the test bench should be able to control the changes of speed and load in real time online, with fast response speed and strong anti-interference ability; data collection and processing should meet the needs of a wide sampling range, can realize sampling at different frequencies, and automatically process and analyze data to obtain The analysis results are displayed, and the operation interface is convenient and easy to control.
2.1 Hardware solution
The method of using hardware mainly adopts the special integrated circuit and specially designed hardware circuit board to complete the acquisition, conversion, averaging and amplification, counting, filtering and so on of the torque speed signal. The hardware circuit is complex, and only the power supply needs to provide various regulated power supplies such as positive and negative 24V, 10V, 5V, etc. The structure is complex, the reliability is low, and the function is single. Various index values can only be obtained instantaneously, but cannot be stored, displayed or printed. Wait.
2.2 Software solution
The system is built on Windows2000 platform, compiled with VC++ language. The Inverter, motor, carrier, sensor, data acquisition card, etc. are abstracted into classes, and the equipment is modularized. The system can be expanded, modified, added, and combined for the replacement of test bench specimens and equipment to achieve multiple It can greatly improve the applicability of the test bench and its control system.
2.3 Design scheme
The test bench uses a high-end industrial control computer as the core, and is equipped with a single-chip microcomputer system to control the motor speed control system and the hydraulic loading system respectively. The industrial computer is not only a controller, but also has functions such as a recorder, an oscilloscope, and a dynamic signal analyzer. It can also easily set different alarm parameters such as rotational speed, torque, temperature, and failure judgment indicators according to the needs of different experiments. Its overall design scheme is shown in Figure 2.
3 Computer data acquisition, testing and control
3.1 Computer data collection and testing
After configuring the parameters of the CB2000 card torque meter and the PCL-812PG multi-function data acquisition card, the performance parameter test is performed by using the JC2B torque and speed sensor (as shown in Figure 3) and the matching CB2000 card torque meter. The data acquisition, processing and control tasks are completed by the computer. It is operated in the form of man-machine dialogue. According to different tasks, it can be tested according to standard or non-standard test methods. The test results can be displayed on the screen in the form of numbers or curves, or output to the printer, and can also be saved. in the database.
3.2 Load and Speed Control
Through the analog output port of PC812-PG, the voltage signal is sent to the frequency converter and the digital valve respectively to realize the control of the speed and load.
4 Design features and uses of the test bench
The design scheme organically combines the traditional mechanical transmission test bench with the emerging computer technology. The computer realizes the digital control of the speed and load, which makes the speed and load sensitive, and can better simulate the actual working conditions. Accurate, online, real-time, high-speed acquisition and processing of torque and speed signals. The use of frequency converters can realize constant torque speed regulation and constant power speed regulation, eliminating the inconvenience of using control cabinets in the past. The test bench also has strong development potential, and the application scope of the test bench can be continuously increased through the continuous upgrade of the software version and a small amount of hardware improvement.
Applicable mechanical transmission devices include cylindrical gear reducer, transmission, bevel gear, automobile drive axle, worm reducer, planetary gear reducer, chain belt drive, transmission and other devices.
The following is the acquisition load is always M=130N? m, the 1k data of the rotational speed signal at the input end of the subtractor N=1000r/min (as shown in Figure 4 and Figure 5), perform Fourier transform or wavelet transform (omitted) to analyze and diagnose the system. Figure 6 is a graph of transmission efficiency at different speeds and loads. The input speeds from top to bottom in the graph are 600r/min, 800r/min, 1000r/min, 1200r/min, and 1600r/min, respectively.
When the test bench rotates, it consumes part of the power of the motor, which only changes with the speed of the transmission shaft. The main factors that cause this power loss are the friction of the transmission parts during rotation, the increased friction due to machining and assembly errors, as well as oil churning, air resistance and other dynamic loads. As the speed increases, the transmission efficiency will decrease under the same load due to the increase in power loss. It can be seen from Figure 6 that under the same load, the higher the rotational speed, the lower the efficiency, which also shows that the test results of the experimental bench are consistent with the theory. The experimental bench is a 9-level precision closed cylindrical gear transmission, and the theoretical value of its transmission efficiency should be about 96%. The calculated transmission efficiency is lower than the theoretical value.
The new multi-functional mechanical transmission test bench is based on the mechanical power flow closed mechanical transmission test bench, takes the computer as the core, adopts the frequency converter and the AC motor as the speed control system, and uses the hydraulic pump station and the loader to form the loading system to simulate the actual work. In this case, the torque and speed data are obtained by the torque and speed sensor, and together with the cylindrical gear reducer, it constitutes a mechanical transmission test bench with a closed power flow. The entire test bench uses a computer as the control and processing center, and the design scheme fully reflects the flexible use of computer resources and digital technology. The test bench developed in this paper has been successfully used to test the transmission power of the system and the load of mechanical products. Several tests have shown that compared with other existing test rigs of the same kind, the automation degree of the test bench is greatly improved, and the ability to simulate actual working conditions is significantly enhanced.