Design of laser-assisted width measurement system based on area array CCD width measurement technology

1 Introduction

In industrial sites, structured light is widely used in high-precision measurements due to its unique advantages. Point structured light is mostly used in measurement systems based on triangulation principles, while multi-line structured light and grid structured light are mostly used in three-dimensional modeling and artificial intelligence. With the development of detection and sensor, electronic information, computers, communications and other technologies, steel plate width gauges have experienced the development of several types of width gauges, including optical-mechanical scanning, active CCD photoelectric, passive CCD photoelectric and laser-assisted CCD photoelectric. In terms of methods, there are roughly mechanical contact width measurement methods, television measurement methods, linear array CCD width measurement methods, laser width measurement methods, etc. However, they have low accuracy, high labor intensity, complicated technical implementation, and some even cause a certain amount of radiation. . A simple and easy solution is proposed here to implement a width measurement system based on area array CCD and laser assistance.

2 Measurement system implementation

The system implements steps such as camera calibration, image acquisition, median filtering, threshold transformation, laser breakpoint extraction, and steel plate width calculation, as shown in Figure 1.

The details of camera calibration and image processing are as follows: first, the laser is irradiated on the steel plate, the photo is taken by the Gigabit network camera, and the image is input to the computer through the Gigabit network card. After image processing, the two image coordinates of the laser breakpoint are obtained. The spatial coordinates of the laser breakpoint are obtained from the calibrated mathematical model. According to the Pythagorean theorem, the length of the line segment between the two points is calculated. If there is a groove on the site and the steel plate is fixed, the inclination of the steel plate does not need to be considered. The length of the line segment is the width of the steel plate. Figure 2 is the schematic diagram of the width measurement system.

2.1 Camera calibration

Camera calibration refers to deriving the camera matrix from the calibration points in the world coordinate system and the corresponding image pixel coordinates, and estimating the internal parameters of the camera. Because no matter how the thickness of the steel plate changes, the steel plate always has an intersection line with the laser surface, that is, the width direction of the steel plate. It has nothing to do with the z-axis direction, so plane calibration is used, as shown in Figure 3. Place the calibration plate (Figure 4) on the laser surface, take the direction perpendicular to the calibration plate as the z-axis, and establish a plane rectangular coordinate system on the calibration plate with directions parallel and perpendicular to the width of the steel plate. Select the center of the circle as the calibration point. The distance between the centers of two adjacent circles is 16 mm. According to the selected coordinate system, the positions of these calibration points on the laser surface are known. The camera is determined by obtaining its corresponding image coordinates. 12 internal and external parameters to complete the calibration work.