Abstract: This paper introduces a new design scheme for a multifunctional transmission test bench, which significantly improves the accuracy, automation level, ability to simulate actual working conditions, and applicability of the transmission test bench.
Keywords: Mechanical transmission | Multifunctional test bench | Digital control
introduction
With the development of the machinery industry and the continuous improvement of scientific research, higher requirements are being placed on the experimental and testing methods for mechanical transmission products. For a long time, the development of transmission test benches in my country has remained largely at the level of traditional manual methods. The main types are closed-loop test benches using mechanical or hydraulic force for power flow and closed-loop test benches using generators as loads for electrical power. These test benches, while possessing unique features due to their energy-saving or loading characteristics, all share a common drawback: low automation. They are difficult to conduct tests according to pre-designed procedures and cannot simulate the impact of actual working conditions on various mechanical transmission products. Therefore, the test results inevitably deviate significantly from the actual situation, which greatly affects the direct guiding role of test data in the design and production of mechanical transmission products. Most transmission test platforms are operated manually, making the monitoring of the test process and the collection and processing of test data cumbersome and inaccurate, and hindering the implementation of multi-parameter automatic control and failure determination.
To address the aforementioned shortcomings, we propose a novel approach—based on a mechanically enclosed experimental platform, driven by an AC motor, employing an AC variable frequency speed control system for stepless speed regulation, and a digital hydraulic loading control system for stepless loading and load spectrum simulation. The control system utilizes object-oriented programming techniques and a layered design philosophy, integrating multiple control and data processing algorithms to provide a user-friendly human-machine interface and visualize the data acquired by the computer.
Composition and working principle of the multi-functional test bench
Based on the different power transfer principles and loading methods of the test bench, test benches can be divided into three main categories: open power flow type, closed power flow type, and electric power flow closed type. Mechanically closed power flow test benches (as shown in Figure 1) are widely used because they can perform large power tests with small-power prime movers and low power consumption, offering advantages such as not requiring energy-consuming devices and energy saving. In a closed system, power flows out at one end and in at the other, forming a closed-loop flow. Therefore, only a small amount of energy input from the outside is needed to maintain system operation. The energy supplied by the motor mainly compensates for the frictional power loss of various components in the closed system during operation, and its value is approximately 10% to 15% of the closed power value.
2 System Solution
The test bench control device should be able to control the changes in speed and load online in real time, with fast response speed and strong anti-interference ability; the data acquisition and processing should meet the requirements of wide sampling range, be able to sample at different frequencies, automatically process and analyze data, obtain analysis results, and have a convenient and easy-to-control operating interface.
2.1 Hardware Solution
The hardware approach primarily utilizes dedicated integrated circuits and specially designed hardware circuit boards to acquire, convert, average, amplify, count, and filter torque and speed signals. This method is complex, requiring various regulated power supplies such as ±24V, 10V, and 5V. It suffers from a complex structure, low reliability, and limited functionality, only providing instantaneous values and lacking the ability to store, display, or print data.
2.2 Software Solution
This system is built on the Windows 2000 platform and developed using VC++. It abstracts frequency converters, motors, load cells, sensors, data acquisition cards, etc., into classes, modularizing the equipment. The system allows for expansion, modification, addition, and combination of classes to accommodate changes in test specimens and equipment, enabling various experiments and greatly improving 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 its core, equipped with a microcontroller system, to control the motor speed control system and the hydraulic loading system respectively. The industrial control computer is not only a controller, but also functions as a recorder, oscilloscope, and dynamic signal analyzer. It can also easily set different alarm parameters such as speed, torque, and temperature, as well as 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 acquisition and testing
After configuring the parameters of the CB2000 cassette torque meter and the PCL-812PG multifunction data acquisition card, performance parameter testing is performed using a JC2B torque-speed sensor (as shown in Figure 3) and the matching CB2000 cassette torque meter. Data acquisition, processing, and control are completed by a computer. The system operates via a human-machine interface. Depending on the task, tests can be conducted using standard or non-standard methods. Test results can be displayed digitally or graphically on the screen, output to a printer, or stored in a database.
3.2 Load and speed control
Voltage signals are sent to the frequency converter and digital valve through the analog output port of the PC812-PG to control the speed and load.
4. Design features and applications of the test bench
This design organically combines a traditional mechanical transmission test bench with emerging computer technology. The computer enables digital control of speed and load, resulting in sensitive speed and load responses. It effectively simulates actual working conditions and achieves accurate, online, real-time, and high-speed acquisition and processing of torque and speed signals from the test bench. The use of a frequency converter allows for constant torque and constant power speed regulation, eliminating the inconvenience of traditional control cabinets. This test bench also has strong development potential; through continuous software upgrades and minor hardware improvements, its applicability can be continuously expanded.
Applicable mechanical transmission devices include cylindrical gear reducers, gearboxes, bevel gears, automotive drive axles, worm gear reducers, planetary gear reducers, chain drives, and other transmission devices.
Below are 1k data points (Figures 4 and 5) of the speed signal acquired when the load is constant at M = 130 N•m and the input speed of the subtractor is N = 1000 r/min. Fourier transform or wavelet transform (details omitted) can be performed to analyze the system and diagnose faults. Figure 6 shows the transmission efficiency curves under different speeds and loads. The input speeds, from top to bottom, are 600 r/min, 800 r/min, 1000 r/min, 1200 r/min, and 1600 r/min.
When the experimental platform rotates, it consumes a portion of the motor's power, which varies only with the speed of the transmission shaft. The main factors causing this power loss include friction in the transmission components during rotation, increased friction due to machining and assembly errors, oil churning, air resistance, and other dynamic loads. As the rotational speed increases, the transmission efficiency decreases under the same load due to increased power loss. Figure 6 shows that under the same load, the higher the rotational speed, the lower the efficiency, indicating that the experimental platform's test results are consistent with the theory. The experimental platform uses a 9-stage precision closed cylindrical gear transmission, whose theoretical transmission efficiency should be around 96%. However, due to friction in the motor, loader, transmission, bearings, etc., oil loss, assembly errors, and measurement errors, the calculated transmission efficiency is lower than the theoretical value.
5. Conclusion
This novel multifunctional mechanical transmission test bench is based on a closed-loop mechanical transmission test bench with a computer as its core. It employs a frequency converter and an AC motor as the speed control system, and a hydraulic pump station and loader to form the loading system to simulate actual working conditions. Torque and speed sensors are used to acquire torque and speed data, and together with a cylindrical gear reducer, it constitutes a closed-loop mechanical transmission test bench with a power flow. The entire test bench uses a computer as the control and processing center, and this design fully demonstrates the flexible application of computer resources and digital technology. The test bench developed in this paper has been successfully used to test system transmission power and the load-bearing capacity of mechanical products. Multiple tests have shown that compared with other existing similar test benches, this test bench has a significantly higher degree of automation and a markedly enhanced ability to simulate actual working conditions.
References
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