Analysis of subway wheel detection system

Rail transit, as a convenient and fast way of travel, is occupying an increasingly important position in the increasingly busy urban transportation network. At present, the parameter testing for wheels mainly includes: wheel set size, wheel tread shape, tread defect and internal flaw detection.

The detection of most wheelset parameters in the maintenance of subway vehicles in China is still in the manual stage. In actual measurement, the workload is large and the efficiency is low. At the same time, human factors will inevitably interfere, which will directly affect the accuracy of the measurement. Wheel overhaul and analysis of wheel parameters have a great impact.

This article introduces a high-precision metro wheel diameter detection device that directly measures the wheel diameter, avoids human factors, is compatible with the measurement range and measurement accuracy, and meets the needs of wheel parameter analysis and wheel repair.

1 Structure and principle of wheel diameter detection device

For wheel diameter measurement, the measurement range of the diameter is required to be 500mm to 900mm, and the measurement accuracy is required to be 0.005mm. According to the method of indirect measurement, the accuracy of the measurement does not meet the requirements. To ensure accuracy, direct measurement methods are used. According to the measurement requirements, a high-precision wheel diameter measuring device is designed. The wheel diameter measuring device includes a sliding probe, a scale, a base, a linear guide, a square tube, a V-shaped iron, a base frame and a fixed probe.

Because the measurement range is relatively large, direct measurement must be used to measure it in sections, otherwise it does not meet the accuracy requirements. Using the principle of separate measurement of large and small numbers, the diameter measurement is divided into four segments of 500mm ～ 600mm, 600mm ～ 700mm, 700mm ～ 800mm, 800mm ～ 900mm. A grating ruler with a range of 100mm and a resolution of 0.0005mm is selected. Set the measurement benchmark, set the initial values of the four sections to 500mm, 600mm, 700mm, and 800mm respectively and calibrate them with a stick. The base frame is composed of aluminum alloy profiles, and the connection angle between the aluminum alloy profiles can be twisted, which can be easily disassembled and relatively moved, and the square tube is kept fixed relative to the base frame. When measuring, adjust the base frame to a suitable position for calibration. The V-shaped iron can be mounted on the wheel during measurement and used for longitudinal positioning. The electromagnet can be attached to the side of the wheel and used for lateral positioning.

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The base includes a scale, a backing plate, a linear guide, a linear bearing, a sleeve, a fixed seat and a probe. The linear guide is fixed to the base plate of the base. The sleeve is fixed to the linear bearing through a fixing seat. The linear bearing is fixed in the sleeve by a bolt. The scale ruler moves. During calibration, the probe is fixed relative to the linear guide. The fixed base can slide along the linear guide. The standard measuring rod is placed between the fixed probe and the sliding probe.

In the measurement, after the calibration is completed, the fixed base is fixed relative to the linear guide. When the sliding probe is pressed by the wheel tread, the spring on the probe will deform, and the sliding probe slides to a certain position in the linear guide. The probe will simultaneously drive the scale and vice ruler to move at the same time. This is the principle of measuring large numbers and decimals. At this time, the display of the scale is the decimal part of the measurement, and the specification of the measuring rod is the large part of the measurement. The auxiliary probe, the probe and the wheel can contact at three points to ensure the reliability of the measurement.

For the wheel diameter to be directly measured, the longest chord of the wheel must be used, otherwise the measurement results will be affected. Therefore, when designing the wheel diameter measuring device, one end of the probe at both ends can be fixed, and the other end can slide the probe to swing along the wheel tread, and swing the probe along the wheel tread. The square tube includes a slide seat, a ball screw, a coupling and a motor fixing plate. The stepper motor is connected to the ball screw through a coupling. The nut of the ball screw is connected to the slide. The slide can slide in the aluminum alloy square tube. The slide is fixed to the base plate. It can move the base up and down during measurement.

At the time of calibration, the stepper motor drives the ball screw to raise the base and move the sliding probe to the same centerline. The two ends of the measuring rod are in contact with the center of the measuring probe, which can facilitate the calibration of the measuring rod. During the measurement, the base is moved up and down along the square tube by the stepping motor driven by the stepping motor, the scale, and the linear guide. During the up and down movement, the sliding probe is always in close contact with the wheel tread under the action of the spring.

Because the outer contour of the wheel tread will exert pressure on the sliding probe, with the up and down scanning of the sliding probe, due to the change of the contour of the wheel tread, the sliding probe will also move the scale in the linear bearing. During the dynamic swing scanning of the sliding probe, the measuring scale outputs the chord length of the probe across the points of the wheel in real time. The maximum value is the wheel diameter.

During the scanning of the probe along the curve, the measuring scale will measure the length of each point swept by the probe, and send all the chord length values collected by the measuring scale to the PC. The PC saves and displays all measurement data. And compare the data before and after, find its turning point is the wheel diameter.

In order to ensure the reliability of the measurement, the three-point contact is adopted, and the fixed probe and the sliding probe are in point contact with the wheel, and the auxiliary probe is close to the wheel tread. To avoid the influence of human factors, during the measurement, the “V” iron height is adjusted to be mounted on the wheel, the electromagnet is adsorbed on the inner side of the wheel, and the stepping motor drives the probe to swing up and down to complete the measurement.

2 Calibration process of wheel diameter detection device

(1) According to the size of the wheel, move the base frame to a suitable position and fix it. Use appropriate standard measuring rods of 500mm, 600mm, 700mm, and 800mm. The stepper motor base moves the sliding probe and the fixed probe in the same straight line and moves. Linear guide, the standard measuring rod is fixed between the fixed probe and the sliding probe, and the calibration length is the length of the standard measuring rod.

(2) Adjust the "V" iron height mounted on the wheel, the electromagnet is adsorbed on the inner side of the wheel, the fixed probe is close to the wheel tread of one side, the sliding probe and the auxiliary probe are close to the wheel tread of the other side, The compression spring of the sliding probe moves the scale ruler back.

(3) The stepping motor in the square tube drives the base to move along the wheel tread at a constant speed. The sliding probe scans and scans on the wheel tread. Under the action of the spring force and the pressure of the wheel tread, the sliding probe moves forward and backward to measure the scale Output a series of data to the PC, where the maximum inflection point is the wheel diameter.

3 Experiment

The standard wheel set with a diameter of 753.905mm is known as the tested wheel. The detection device is calibrated with a standard measuring rod of 700mm. After calibration, the wheel diameter detection device is mounted on the tested wheel. The stepper motor drives the base to slide the probe. And the fixed probe moves 20mm up and down the center line. When the probe scans the wheel tread to sample the chord length of each point, the largest chord length of 53.904mm is the diameter, and the diameter of the tested wheel is 753.904mm. The wheel diameter measuring device is compatible with measurement range and measurement accuracy, and meets the needs of wheel parameter analysis and wheel repair. In the subway wheelset diameter test, every link from the mechanical system to the experimental field test affects the measurement results. The errors mainly include the following sources.

(1) Manufacturing error: The machining of mechanical parts will greatly affect the accuracy of the measuring device, and the machining accuracy of mechanical parts will bring systematic errors.

(2) Mechanical assembly error: In the mechanical structure of the wheel diameter measuring device, the assembly accuracy of mechanical parts also brings system errors. Mechanical structure assembly accuracy, such as the assembly accuracy of the probe and the shaft sleeve, the installation accuracy of the aluminum alloy profile support bracket of the wheel diameter measuring device will introduce errors

(3) Errors will also be introduced during the experimental test. For example, errors will occur during the calibration process, and the sampling frequency will also introduce system systematic errors. Under the condition of ensuring the sampling performance, the sampling frequency can be appropriately increased.

Conclusion

This topic presents a stepped standard wheel diameter measurement scheme. Through the design of a high-precision wheel diameter measurement device, the wheel wheel-to-wheel diameter measurement efficiency and accuracy are further improved, human error is reduced, and wheel repair Provide theoretical basis.

(Source: Equipment Management Network)