Application of Vision System in Dimension Measurement of Automobile Parts

1 Introduction

As the foundation of the automotive industry, automotive parts are an essential factor in supporting the sustainable and healthy development of the automotive industry. The current automotive industry is vigorously carrying out independent development and innovation, and it needs a strong parts system to support it. What follows are the safety and reliability of automotive parts. The size detection of automotive parts has become an indispensable choice.

There are many ways to measure automotive parts on the market. However, considering the detection efficiency and detection accuracy, the measurement method based on machine vision is increasingly favored by the majority of parts manufacturers for its convenient and accurate detection advantages.

Delta DMV machine vision system has high-speed precision, multi-task computing processing capabilities and intelligent and user-friendly operation interface. It can be widely used in the fields of identification, confirmation, coordinate positioning, measurement counting, defect detection, etc. in the food, beverage, medicine and packaging industries.

In this solution, the customer needs to measure several dimensional parameters of a certain part on the car, as shown in Figure 1.

Figure 1 Required measurement dimensions

2 Specific inspection requirements

Machine vision needs to detect the size of the red mark in the part of Figure 1 - the height of the left and right pins, and at the same time detect the position and verticality of the two PINs; the position is obtained by measuring the offset of the left and right PIN feet from the standard position, and the measurement accuracy is 0.2mm.

According to the requirements put forward by the customer, considering all the inspection points, two cameras are required to "watch" from two directions respectively to fully inspect, so the overall solution requires a Delta one-to-two DMV machine vision system to implement.

Figure 2: On-site equipment and camera installation diagram

Figure 3 System overall scheme diagram

As shown in Figure 3, the lower camera is used to detect the verticality of the part and the height of the left and right pins, and the upper camera is used to detect the position of the part (i.e., the offset between the position of the two PIN pins and the standard position).

3 Detection principle

In Figure 3, the lower camera illuminates the PIN of the part through the circular upper light source. Because the tops of the two PIN pins of the part are relatively smooth, two bright spots will appear after being illuminated by the light source (as shown in Figure 4). Then, the "spot" tool is selected from the DMV controller algorithm library to analyze the positions of the two bright spots respectively, so that the two coordinate values ​​are compared with the standard position coordinate values ​​to calculate the offsets DL and DR of the two PIN pins, which are the position.

Figure 4 The effect of the camera below

In Figure 3, the upper camera uses backlighting to clearly show the outline of the part, and then uses the "edge position" tool to extract each feature point, and calculates the height HL and HR of the left and right needles through the function, as shown in Figure 5. [page]

Figure 5 Left and right needle height diagram

4. Analysis of the detection scheme

Since this case involves high-precision dimensional measurement, the equipment must be calibrated before each formal measurement. That is, the DMV first runs the calibration program (manual operation by the operator), takes pictures of the standard sample (the sample with the most standard size), and stores the parameters obtained by calculation and analysis into the DMV detection system to improve the system detection accuracy.

4.1

The main purpose of the calibration program is to calculate the proportional relationship between pixels and actual size. At the same time, the coordinate values ​​of the left and right needles of the standard sample are also stored in the memory as reference points for the subsequent detection program calculation.

Run the calibration program and obtain a screenshot of the standard sample as shown in Figure 6.

Figure 6 Screenshot of standard sample

In Figure 6, because the photos taken by the camera are measured in pixels instead of millimeters in reality, the calibration program is required to convert the two and calculate the proportional relationship K value. (Note: Because the field of view of the upper camera and the lower camera in this case are different, the proportional relationship K value will also be different.) The calculation

formula for K is as follows: K value = actual size of the object being measured (mm) / number of pixels measured by the camera (Pixle).

According to the proportional relationship between the pixel values ​​measured by the two cameras and the actual size of the parts, the calculation results of K1 and K2 values ​​are as follows:

K1=16.72mm/452pixel=0.03mm/pixel (one pixel value represents 0.03mm);

K2=2.54mm/278pixel=0.01mm/pixel (one pixel value represents 0.01mm);

In this solution, the calibration program will also store the standard position coordinate values ​​(X1, Y1) and (X2, Y2) of the left and right needles of the standard part into the DMV memory as a reference point for the subsequent position calculation.

4.2 Detection Program

After the system calibration is completed, run the detection program to start the detection.

Figure 7 Camera screenshot of the detection program running

First, the lower camera determines the offset of the PIN pin, and the "DIST()" function in the DMV function library calculates the deviation of the left and right PIN pins from the standard position point: DL = DIST (X1, Y1, X1', Y1') / K1, DR = DIST (X2, Y2, X2', Y2') / K2, and then calculates the left and right pin heights according to the upper camera.

4.3 Acceptance data

The measurement accuracy of DMV is analyzed through the following 10 sets of acceptance data, and it is concluded that the solution can fully meet the customer's requirement of 0.2mm detection accuracy, and the actual measurement error of DMV is only 0.02mm.

Table 1 Acceptance data (unit: mm)

Table 2 System Configuration

5 Conclusion

In the application field of component size measurement, Delta DMV visual inspection system provides the best inspection solutions for some manufacturers pursuing high efficiency and high quality, meeting customers' needs for faster, more convenient and more accurate measurements, and solving another bottleneck technology in the development of the manufacturing industry. (end)