Pontiac Coil manufactures electrical coils, solenoids, and electromechanical devices for automotive, trucking, mobile equipment, medical, information technology and telecommunications applications. In building a fuel stator for a diesel engine, the company has long manually inspected every part to ensure that the lead tower cap had been attached with pins or screws and that the lead towers have been soldered. The company is monetarily penalized for any defect on this part. Pontiac Coil asked a vision systems distributor if they could provide a more cost-effective solutionthan their existing one.
The Vision Traceability Group (VTG), a certified solutions provider of machine vision solutions that is a division of McNaughton-McKay Electric Company, proposed using a Cognex vision system. Rob Osgood, Manufacturing Engineer for Pontiac Coil, developed the application using the vision sensor’s graphical user interface in one week and installed it on the line in only 90 minutes. “The In-Sight vision system has demonstrated its ability to flawlessly inspect several different part numbers,” Osgood said. “In its first full week of operation, it detected two defects, more than paying for itself.”
Manufacturing fuel injection stators
Quality assurance and process control are the foundation of manufacturing at Pontiac Coil. Customers include Delphi, Eaton, Visteon, Cummins, American Axle, Behr, Honeywell, Husco, Teleflex, Bosch, Usui and Ogura. Pontiac Coil is headquartered in Clarkston, MI, with additional manufacturing facilities in Searcy, AR, and Nottingham, UK.
Most diesel engines use fuel injectors to deliver an atomized fuel charge to the engine cylinders. An electronic timing circuit delivers precisely timed electrical pulses for operation of the fuel injector. These pulses are delivered to a solenoid stator assembly which generates magnetic forces to actuate a solenoid plunger mounted in the fuel injector that controls the injection of fuel into each engine cylinder. The housing of the solenoid stator assembly protects the internal electrical components and locates them precisely in relation to the reciprocating solenoid plunger.
Pontiac Coil builds several types of stators for diesel engines used on heavy trucks. These stators are inspected on a dial machine that checks for high potential (hipot) conditions by applying a high voltage and making sure it does not penetrate the shell. The machine also performs leak testing and laser inspection of threads inside the body. Parts that pass all tests are then laser etched with a unique serial number. The dial machine is manually loaded and unloaded. In the past, the only manual inspection operation was to check the fasteners on the stator.
Two different types of fasteners—pins and star head screws—are used on the two different types of stators inspected on this line and the company needs to ensure that the correct screw is present. Each terminal also needs to be coated with solder so that it makes a good connection with the housing. Also, there are lobes located on the housing to the left and right of a cavity that could potentially be broken off, so the stators also need to be inspected for their presence. Pontiac Coil has used a number of costly vision systems in similar applications and consultants are typically needed to configure these complex systems.
Tim McLennan, sales engineer for VTG, visited Pontiac Coil and examined the application. He performed a study to evaluating the feasibility of using a much less expensive Cognex vision solution to inspect the part. McLennan brought sample parts back to the company’s vision lab and Jim Witherspoon, Application Engineer for VTG, performed the feasibility study. After experimenting with the application in the lab, Witherspoon concluded that lighting is the key to this application. “Various direct ring lights can be attempted but the CCS High Intensity ring light makes this application very robust,” Witherspoon’s report concluded. “If there is a solder then the tips glow a bright white. If the solder is missing then the tips remain dark. The pins and screw verification also works very well with the prescribed lighting.”
Witherspoon recommended the Cognex In-Sight vision system because it provides both EasyBuilder® and spreadsheet application development interfaces. Cognex In-Sight Micro vision systems enable powerful vision applications using a small self-contained package available at an economical cost. Additionally, In-Sight vision systems feature the EasyBuilder interface that walks the user through the process of configuring the vision application step by step. The In-Sight enclosure is only 30mm x 30mm x 60mm and provides 640 x 480 (VGA) resolution.
In-Sight vision systems are the size of a remote-head camera so they are ideal for mounting in very tight spaces on robots, production lines and machinery. In addition to their small size, they provide flexible mounting capability with a unique non-linear calibration tool that enables mounting at angles of up to 45-degrees for hard-to-reach applications. They also offer an Ethernet output that simplifies the task of interfacing the vision system and, in some applications, eliminates the expense of a programmable logic controller (PLC) by communicating directly with the production system.
Developing the vision application
The feasibility study demonstrated that the In-Sight vision system could identify good parts from bad parts,” said Rob Osgood, Manufacturing Engineer for Pontiac Coil. “I took on the task of developing the application and integrating the vision system into our production system.” Osgood started off by mounting the vision system and connecting it by an Ethernet cable to the network switch. The vision system is powered by a Power over Ethernet (PoE) adaptor. He used the lighting and the lens recommended by VTG. Osgood configured the vision system with an IP address on the network that was immediately recognized by the Allen Bradley PLC that controls the production system PLC. The EasyBuilder interface automatically generates the Allen Bradley ControlLogix commands needed to communicate with the PLC.
Osgood used the spreadsheet functionality to perform several filtering operations, including binarization and stretching, for each screw position. He used a series of contrast tools to search for each of the fasteners that should be present in the stator housing. The contrast tools measure the number of light pixels relative to the dark pixels within each area where each of the five screws and two lobes are supposed to be located. The next step after verifying the presence of the screws or lobes is the use of pattern tools to check the type of each fastener on the stator.
The presence of solder is inspected simply by binarizing the image of each terminal and measuring the grey scale. Osgood identified the lobes by searching for the plastic circle on each lobe and verifying its diameter. He used EasyBuilder’s point-and-click communications setup to configure the vision system to send inspection results to the PLC after each inspection. In the deployment mode, color tools graphics, a results table and a filmstrip enable to the operator and maintenance staff to review images in order to verify the identification of bad parts and troubleshoot the application.
“The vision application has helped us improve quality while reducing manpower on the inspection line,” Osgood concluded. “The vision system’s relatively low cost was easy to justify since we are penalized for any defect. The vision system has operated for six months and in this time, it has never passed a bad part nor failed a good part. The result is that we have been able to free up a manual inspector on the line for a more proactive assignment and run the inspection system without operators except for loading and unloading parts. The programmability of the vision system means that we can easily modify the program to compensate for design or process changes. Most important of all, we are confident that we have no fastener-related defects.”