The manufacturing process of electronic connectors generally starts with punching pins. Electronic connectors (pins) are stamped from thin metal strips using large, high-speed stamping machines. One end of the large roll of metal strip is sent to the front end of the punching machine, and the other end passes through the hydraulic worktable of the punching machine and is wound into the take-up wheel.
After the connector pins are stamped, they should be sent to the electroplating section. At this stage, the electrical contact surfaces of the connector are plated with various metallic coatings. A similar class of problems as in the stamping stage, such as twisted, chipped or deformed pins, also occurs when the stamped pins are fed into the plating equipment. Such quality defects are easily detected by the techniques described in this paper.
However, for most machine vision system suppliers, many quality defects in the electroplating process still belong to the "forbidden zone" of the inspection system. Manufacturers of electronic connectors wanted inspection systems that could detect a variety of inconsistent defects such as fine scratches and pinholes on the plating surface of connector pins. Although these defects are easy to identify for other products (such as aluminum can bottoms or other relatively flat surfaces); due to the irregular and angled surface design of most electronic connectors, visual inspection systems are difficult to obtain. Enough to identify the images needed for these subtle defects.
Because certain types of pins are coated with multiple layers of metal, manufacturers also want the inspection system to be able to distinguish the various metal coatings in order to verify their presence and proportions. This is a very difficult task for a vision system using a monochrome camera, since the gray levels of the image are practically the same for different metal coatings. Although the camera of the color vision system can successfully distinguish these different metal coatings, the problem of lighting difficulties still exists due to the irregular angles and reflection effects of the coating surface.
3. Injection molding
The plastic box seat of the electronic connector is made in the injection molding stage. The usual process is to inject molten plastic into the metal film, and then rapidly cool it into shape. A so-called "leakage" occurs when the molten plastic fails to fill the caul completely. This is a typical defect that needs to be detected during the injection molding stage. Other defects include filled or partially blocked receptacles (these receptacles must be kept clean and free to properly mate with the pins during final assembly). Since the backlight can be used to easily identify the leakage of the box seat and the blockage of the socket, the machine vision system used for quality inspection after injection molding is relatively simple and easy to implement.
The final stage of electronic connector manufacturing is finished product assembly. There are two ways to connect the electroplated pins to the injection molded box seat: single mating or combined mating. Single mating refers to inserting one pin at a time; combined mating means connecting multiple pins to the box seat at the same time. No matter what kind of plug-in method is adopted, the manufacturer requires to detect whether all pins are missing and positioned correctly during the assembly stage; another type of routine detection task is related to the measurement of the spacing on the mating surface of the connector.
Like the stamping stage, the assembly of the connector also poses a challenge to the automatic inspection system in terms of inspection speed. While most assembly lines clock in at one to two pieces per second, vision systems often have to complete several different inspections for each connector that passes the camera. Therefore, detection speed has once again become an important system performance indicator.
After the assembly is completed, the external dimensions of the connector are much larger than the dimensional tolerance allowed by a single pin in orders of magnitude. This also brings another problem to the visual inspection system. For example: Some connector boxes have a size of more than one foot and have hundreds of pins. The detection accuracy of each pin position must be within a few thousandths of an inch. Obviously, the detection of a one-foot-long connector cannot be completed on one image, and the visual inspection system can only detect the quality of a limited number of pins in a small field of view each time. There are two ways to complete the inspection of the entire connector: use multiple cameras (increasing system cost); or continuously trigger the camera when the connector passes in front of a lens, and the vision system will "stitch" the single-frame images taken continuously , to judge whether the quality of the entire connector is qualified. The latter method is the detection method usually adopted by the PPT visual inspection system after the connector assembly is completed.
The detection of "actual position" is another requirement of the detection system for connector assembly. This "actual position" is the distance from the tip of each pin to a specified design reference line. Vision inspection systems must draw this imaginary baseline on the inspection image to measure the "actual position" of each pin apex and determine whether it meets quality standards. However, the reference point used to delineate this reference line is often not visible on the actual connector, or sometimes appears on another plane and cannot be seen at the same moment in the same shot. In some cases it was even necessary to grind away the plastic on the connector housing to locate this reference line.