1 hardware system Automatic detection of thread parameters based on PC architecture, mainly by the lighting system, CCD camera and optical imaging system, image acquisition card, image processing systems, mechanical detection systems and electronic control systems and other components.
At the time of measurement, after illumination by the lighting system, the screw thread image of the fastener is collected by the CCD camera and the optical path imaging system, and then the digital image is transmitted to the computer through the image acquisition card. The computer then processes the digital image according to the corresponding algorithm. The parameters such as profile angle, pitch, and median diameter of the thread are compared with the standard to calculate the deviation.
Screws
2 software system The software system that the thread parameter automatically detects mainly includes the system control module image processing module and so on.
System control module: Initialization; complete the initial configuration of the system image interface card and standard parameters. Image manipulation; Capture and save 8-bit gray images and capture images into memory.
Image processing module: The image processing module includes an image preprocessing algorithm for reducing noise, highlighting the edge information of the thread profile, an edge detection and extraction algorithm for detecting and extracting the edge information of the outline, a system calibration algorithm for measuring the actual size of the digital image, and a calculation thread The parameters of the algorithm.
Machine vision technology was used to design the automatic measurement system of thread parameter measurement, and the parameters such as thread angle, pitch and middle diameter of standard thread samples were measured. The measurement results show that the thread parameters are within the specified error range. Due to the high efficiency and reliability of visual inspection, after further investigation, it is considered that it can be used in production practice.
In the section through the screw thread axis, the outline shape of the thread is called a tooth profile. The angle between two adjacent flank faces is called the angle of the tooth. The common thread has a triangular shape and a tooth angle of 60°.
Measurement methods
1 thread angle measurement
The thread angle is also called the tooth angle. The measurement of the angle of the thread can be achieved by measuring the flank angle, which is the angle between the flanks of the thread and the vertical plane of the thread axis. The approximate profile of the thread teeth is sampled in straight sections on both sides of the thread, and a linear least-squares fit is applied to the sample points.
2 pitch measurement
The pitch is the distance between a point on the thread and the corresponding point on the adjacent thread. The measurement must be parallel to the thread axis.
3 thread diameter measurement
The middle diameter of the thread is the distance from the middle diameter line perpendicular to the axis, and the middle diameter line is an imaginary line.