Integrated machine-vision system inspects automotive electronic connectors
Automotive antibrake systems (ABSs) and protective airbags are two examples of systems that must not fail. Buried inside the ABS and airbag systems are wire terminations and connections. Fast-con, crimp, or lug wire terminators come in a nearly endless variety of shapes and sizes and are used extensively in the automotive and other electronics markets.
As more intelligence is designed into automobiles, the number of fast-con connectors continues to increase—as can the ramifications of a defective termination. In the past, manufacturers inspected fast-con connectors off-line by pulling samples from final reels. These reels could contain anywhere from 1000 to 10,000 parts each. A quality inspector would cut a sample of the parts and run them through a number of visual and physical tests, such as force gauges to measure insertion forces, and various physical and visual checks, which can be time-consuming and ineffective because of the nature of the stamping process.
In each type of connector, a female connector accepts a male terminal connected to a bus, electrical component, or another wire to complete a circuit. These female and male terminals measure a few millimeters on each side and are typically stamped out of tin- or gold-plated copper strips at a rate of 600 per minute before being packaged on a cardboard reel for shipping.
While many manufacturers still quality check these connectors by off-line sampling using a variety of manual and automated test equipment, buyers are showing impatience with perceived defects by returning entire batches when they come across a single defective connector. The result is a push for fast-con connector manufacturers to move toward 100% automated inspection of these connectors.
Using a pair of PPT Vision 5200 IMPACT cameras with tethered C40 processors, photoeye trigger, telecentric optics, mirrors, machined metal supports, and Rockwell Automation Micrologix PLC to supervise the operation, easycontrol has created the Visikron fast-con inspection system to provide 100% inspection of electronic connectors in a compact system footprint that uses a vertical design to maximize manufacturing floor space (see Fig. 1).
The stamping room
Strips of metal are often fed into an enclosed stamping room because of the amount of debris thrown off by the stamping machine. Operators typically stand outside the safety enclosure with a roll-feeder, feeding the stamping machine. Technicians remove the set of reels after they are filled—about every 15 minutes—and do not come into contact with the hydraulic stamping system unless a problem arises.
This arrangement virtually guarantees that adding an inspection station will encounter manufacturing space challenges, since most safety enclosures or manufacturing rooms are not spacious, but efficient. Tackling the inspection challenge, easycontrol built a system that stacks elements: processing power in the base of the inspection, followed by machine guides and supports, and then a pair of tethered cameras and lights (see Fig. 2).
A rigid strip of stamped parts, reminiscent of a bandolier, is pushed into the easycontrol inspection station by the stamping station in the fast-con inspection application, however, the system can be internally powered with a servo to pull the stamped parts into the inspection station or in a flow-through configuration if the reeler provides the impetus for connector movement.
Optics keep system tight
In one fast-con application at a connector-manufacturing facility in Spain, the stamped parts are pushed into the inspection station. A pair of guide rollers with spring-tension setting help feed the rigid strip to a carbon-coated machined guide designed by easycontrol and built by Barcelona, Spain, machine shop Mecánica Busquets. The guides are carbon coated to protect them from abrasion caused by the metal connectors. This application used a fixed set of guides; however, Mecánica Busquets makes an adjustable stage for easycontrol that can accommodate any connector strip up to 25 mm across and 7 mm high.
As each connector enters the inspection window for the first camera, it interrupts an IR beam, and a trigger signal is issued from a Keyence photoeye to a Rockwell Micrologix PLC mounted in the processing cabinet in the base of the system. Rafael Soto, easycontrol general manager, said his designers use the Micrologix PLC because of its speed, reliability, and global technical support.
The 24-V trigger signal is sent from the PLC to an optoisolated port on two IMPACT C40 vision processors. The C40 uses onboard field-programmable gate arrays to handle communication, including Ethernet, and 24-V I/O, plus a 1-GHz PowerPC microprocessor to run the IMPACT software suite, including the Vision Program Manager for image processing, and Control Program Manager for the graphic user interface.
Image capture
The C40 initiates an image acquisition and transfer from a tethered 640 × 480-pixel camera across a proprietary PPT cable and protocol based on Cypress Semiconductor HotLink chipset. To accommodate a variety of defects, fields of view, and connector sizes, easycontrol uses TLM telecentric lenses from Edmund Optics for increased depth of focus with minimal distortion. PPT 661-0113-SC red LEDs with cross collimators and diffuser provide directed illumination of the part in backlight configuration (see Fig. 3).
The first camera is mounted directly above the guide channel, looking down on the connectors. The second camera is offset to the side, is also perpendicular to the guide, and images the side of the connector via an Edmund Optics gold-plated mirror mounted to the side of inspection window 2. The use of the mirror allows the camera to be mounted above the connector rather than to the side, reducing the width of the inspection station by approximately 50%.
“We initially used a standard mirror, but went with a high-quality, gold-plated mirror to limit distortion in the acquired image and to limit mirror degradation from the caustic industrial atmosphere interacting with the mirror’s surface,” explains Soto. The mirror is mounted on a precision mount from EKSPLA.
Each image is fed into a dedicated PPT C40 processing unit, where edge detection, blob analysis, and comparison of the imaged shape against a stored template provide accurate variance measurements. This information is then passed on to a Dell PC in the system’s base and displayed on the Visikron’s TFT color monitor (see Fig. 4).
Because the 5200 cameras have their own processing, and the Micrologix PLC provides a hub for trigger and alarm signals, as well as stop/go communication with the upstream stamper and downstream reeler, the PC’s main function is to store images; the C40 has 256 Mbytes of on-board memory for image buffer and storage and displays the system’s user interface. Because of this distributed processing architecture, easycontrol’s Girón says they only require an entry-level PC to operate the system.
Features, advantages, benefits
“Small pieces of cutting debris can move into and out of the stamping die where the parts are formed,” says easycontrol director of international operations Juan Girón. “This debris causes intermittent parts to be out of specification. The problem could happen anywhere within a reel of parts and not reveal itself to the human eye as a gross defect.
“Usually, it will throw just one critical dimension out, such as the internal gap between the spring and housing of the connector itself. Similar random defects can be caused by oil aquaplaning. But if a random defect makes it through to the customer, the standard response is to send the entire lot back. This forces the manufacturer to manually inspect hundreds of thousands of individual pieces or write off the entire lot. To address this problem, we developed the Visikron.”
