Research on the roundness digital system of the in

Research on the digital system of the roundness of the inner ring of rolling bearings

this paper designs an intelligent detection system for the roundness of the inner ring of bearings. The system adopts photoelectric encoder and other angle sampling, digital display, and is connected with the upper computer, which overcomes the shortcomings of the traditional roundness test system, such as unable to prevent reverse rotation, difficult reading, easy to receive and waste by mistake, and no data processing function

keyword: bearing detection; Displacement sensor; singlechip; Photoelectric encoder: roundness meter

rolling bearing is a standard component with high interchangeability. It has the advantages of low friction, easy to start, simple lubrication and easy replacement. It is an important supporting part for transmitting motion and bearing load in all kinds of machinery, and it is almost an indispensable component in mechanical structure. With the development of industry, higher requirements are put forward for the performance, service life and reliability of bearings. The performance, service life and reliability of rolling bearings depend on their design, manufacturing and testing processes. Detection is an important link to improve the performance of bearings

the inner ring of the bearing is a component in close contact with the shaft, which has not only dimensional errors, but also roundness errors, roughness errors, waviness errors, etc. In this paper, displacement sensor is used to measure the roundness of bearing inner ring, photoelectric encoder control system is used for equal angle sampling, and 8-bit w78e52 single chip microcomputer is used for control and data processing unit. The data is transmitted to the upper computer through the serial port, which is convenient for centralized analysis of data. Connected with LED, the result of data processing can be displayed, and the reading is convenient, so as to realize the intellectualization and digitization of the roundness detection of rolling bearings

1 overall design of the system

the system is mainly composed of three parts: detection part, signal acquisition and processing part, input and output part. The overall structure is shown in Figure 1. The detection part includes sensor, photoelectric encoder, amplification and filtering The signal acquisition and processing part is responsible for AD conversion, system control and storage of sampling data The input and output part is composed of LED and keyboard (as shown in Figure 1)

Figure 1 overall block diagram of the system

the inner ring of the bearing is fixed on one floating probe and two fixed probes. The displacement sensor is connected with the floating probe through a mechanical device. The photoelectric encoder controls the equal angle sampling of the sensor, and the signal of the sensor is amplified and filtered into a DC. The signal from ADC is processed and stored by MCU. The inner ring of the bearing rotates for one cycle, and the data collection is completed. Finally, the MCU finds out the maximum and minimum values in the 3 data, calculates the travel value, and displays it through LED. The relationship between the maximum reading difference F and roundness error F of one cycle of workpiece rotation is

in the formula k - reflection coefficient, which is checked by GBT [1], that is, the difference divided by the reflection coefficient is roundness error

2 detection part

2.1 selection of sensor

according to the roundness instrument standard jb/t 10028 1999, in the instrument error class A, the linear error of the measurement system is not greater than 2% of the full scale, and the sensitive valve of the measurement system is not greater than 0.02 μ m[2]。

the system adopts the contact measurement method, so the differential transformer inductive sensor with the advantages of good stability, simple and reliable structure and strong anti-interference is selected as the displacement sensor

the e-dt-80sb sensor of the primary measurer selected in this system has the advantages of high measurement accuracy, high sensitivity, easy clamping and positioning, and meets the roundness instrument standard jb/t 10028 1999. Although its dynamic response frequency is not high, it can fully meet the speed response requirements (sampling points) in roundness measurement. The performance is as follows:

total stroke (mm): 3

measurement range (mm): ± 0.5

linear error: ± 0.5%

repeatability error（ μ m) : 0.2

2.2 measuring circuit of differential transformer displacement sensor

the output of differential transformer sensor is AC voltage. If measured with AC voltmeter, it can only reflect the magnitude of armature displacement, not the direction of movement, and its measured value will include zero residual voltage. Therefore, phase sensitive detection circuit and differential rectification circuit are usually used in actual measurement. The phase sensitive detection circuit needs to use the primary excitation voltage as the phase reference to determine the polarity of the output voltage, which requires an excitation signal source with constant amplitude and frequency, and it needs to compensate the phase offset of the primary and secondary of the differential transformer and the errors caused by temperature and frequency fluctuations. The differential rectification circuit does not need to consider the phase problem, and the circuit is relatively simple. In this paper, the differential rectifier circuit is selected for post-processing of the output signal of the differential transformer (as shown in figure 2.1[3])

figure the engineer immediately replied. 2.1 full wave differential rectification circuit diagram

2.3 signal amplification

the signal from the sensor is generally weak. Experimental method: usually only a few millivolts to tens of millivolts. The output signal range of this sensor is 0.028mv ~ 100mV, while the a/d converter requires a full-scale input of ± 5V. Therefore, it is necessary to amplify to improve the resolution and reduce the noise, and make the maximum value of the conditioned signal equal to the maximum input value of a/d, so as to improve the conversion accuracy. For this topic, there is only one channel signal input. In order not to cause the amplified maximum signal to exceed the full range of ADC, its amplification factor

that is, the signal amplification circuit adopts gain k=50

2.4 filter circuit

in roundness measurement, due to the influence of various noise signals, the measurement data is not credible. Therefore, the original measurement data must be filtered to filter unnecessary high-frequency signals and obtain signals of a specific frequency band. The second-order RC active low-pass filter is used in this system (as shown in Figure 2.2)

2.5 counting circuit

the counting method can be realized by software or hardware. Although the circuit of counting with pure software is simple, the counting speed is slow and easy to make mistakes. Although the method of using external counting chip is fast, the hardware circuit is complex and the cost is high. Combining these two methods, this paper adopts a combination of software and hardware, that is, the counter inside the single chip microcomputer to count

rotate the inner ring of the bearing manually, and the speed will not be too fast or too slow. For the resolution of the photoelectric encoder, the maximum response frequency and the allowable maximum speed are not high; The photoelectric encoder does not bear great external force, so the mechanical performance requirements are not high. Considering the working environment, this paper selects the optical rotary encoder trd-2e a to complete the system design. Its performance specifications are as follows:

item: trd-2e a

resolution: 1024 pulses/revolution

output signal form: a · B two-phase

maximum response frequency: 200kHz

allowable maximum speed: 5000rpm

starting torque ≤ 0.001N · m

Figure 2.2 second-order voltage controlled voltage source low-pass filter circuit

Table 1 is not determined to be high or low level

terminate the counting pulse a of the photoelectric encoder to D.D end of trigger and external interrupt in of MCU T1 end, the B end of the photoelectric encoder is connected to the CLK end of the D trigger, and the pulse after the D trigger, namely the direction control pulse (DIR), is connected to the external interrupt INT1 end of the MCU (as shown in Figure 2.3 [4]). Open the corresponding interrupt and set the gate of T1 to 1. At this time, in addition to setting Tr1 to 1, it is also necessary to make the INT1 pin high level before starting the counter. It can be seen from table 1 that only when dir is high level and a is positive or negative jump, the inner ring of the bearing rotates forward. Therefore, when the inner ring forward rotation condition is met, the sensor reads and counts. The inner ring of the bearing rotates for one cycle, enters the interruption program, sends the collected data to the PC, and calculates the travel value to obtain the roundness

figure 2.3 counting circuit wiring diagram

this circuit does not collect data when the bearing inner ring is reversed and does not rotate. Thus, the accuracy of the data is ensured, and the inaccuracy caused by the inner loop inversion caused by the operator's jitter is eliminated

3. Selection of a/d converter

for the selection of a/d converter, conversion rate and resolution are two important parameters. Its design is as follows [5]:

3.1 Selection of conversion rate

in the system, the photoelectric encoder controls the sampling of ADC. The photoelectric encoder rotates for one cycle, and the ADC samples 1024 times. Manually rotating the photoelectric encoder for one cycle takes at least 0.8 seconds, that is, the maximum sampling rate of photoelectric encoder is 1.25, so the conversion rate of ADC is greater than the sampling rate of photoelectric encoder of 1.25

3.2 selection of resolution

sensor measurement range ± 0.5mm, measurement accuracy 1 μ m。 Through actual measurement, the maximum output signal of the sensor is 1.25V, that is, the maximum measured displacement of the sensor is ± 0.5mm, when the probe moves 1 μ m. The output signal voltage of the sensor is u, that is, u is the minimum output signal of the sensor. According to the resolution formula 4.1

the ADC resolution of the system is actually selected as n=10. If n is larger, the a/d conversion accuracy is improved, but the price is expensive and not economical. In practice, the output signal of the sensor is too weak and needs to be amplified by the amplification circuit. The resolution of a/d can be reduced when the amplified signal is sent to a/d, so n=10 bits is selected

to sum up all the calculation results, combined with the actual working conditions, combined with the economic conditions, we decided to adopt a double integral a/d converter MC14433 produced by Motorola Company, which is based on CMOS manufacturing process and has a high degree of automation in the experimental process. Its working performance is as follows:

3 (1/2) bit double integral ADC

the working voltage range is: dual power supply 4 5.

a/d conversion accuracy is 0.05% (11 bit binary number),

corresponds to kHz clock frequency, and the conversion rate is t/s (greater than the conversion rate of photoelectric encoder)

4. Conclusion the rolling bearing roundness meter introduced in this paper can accurately measure the roundness of bearings, and has the advantages of simple circuit, stability and reliability. The photoelectric encoder is used for equal angle sampling to prevent the error caused by jitter (reversal) and improve the measurement accuracy. The LED display avoids the problems of difficult reading and high labor intensity of the traditional bearing inner ring roundness measuring instrument. The sampling data is sent to PC through serial port, which is convenient for centralized analysis of bearing data, and makes up for the lack of data processing in traditional detectors. The roundness meter has simple and reliable structure, high measurement accuracy, good stability and economy, and has a good application prospect