Automated Inspection Made Easy with Machine Vision
When product margins are very low, cost is critical in every step of the manufacturing process, but the consequences of shipping a bad part to the customer are becoming greater. In the auto industry, some original equipment manufacturers (OEMs) specify that any supplier that ships one bad part must hire third-party inspectors to sort every part it produces for a specified period of time.
To avoid this profit-killing cost, one automotive supplier installed an automated inspection solution using machine vision. The supplier was able to implement a very low-cost temperature control valve inspection system using one Cognex In-Sight Micro 1100 vision system for three inspections:
- The right brass core is being used;
- The right spring is in place; and
- Installation of a washer and retainer clip.
Before the automation, an operator checked the assembly before the pressing operation, and incorrect assemblies were common.
Simpler programming is key
The supplier called in Kerry Whitt, area manager for Kirby Risk, the distributor of Cognex machine vision products in Indiana. Whitt said this would not have been possible before. “The cost of purchasing the hardware and programming the vision system would have run well into the tens of thousands of dollars," he says.
A new generation of vision systems has simplified the programming to the point that it can now be done by engineers who are familiar with the inspection application but not necessarily with machine vision. In this case, one camera inspected the part three times.
Whitt says, “I picked the Cognex Micro 1100 vision system because it is small and inexpensive yet provides access to a wide array of vision tools. For example, the PatMax pattern matching tool makes it easy to distinguish one type of part from another.”
The vision system follows assembly steps with the operator.
First, place the brass core in the fixture and press a button connected to a PLC that indicates the part is ready for inspection. The vision system acquires an image and the Cognex sequencer tool executes the proper algorithms for the assembly step.
The PatMax tool was programmed by acquiring an image that included the core and teaching the proper area of interest. It recognizes the core even if it is in a different position, as long as it is within the confines of the search area. The vision system sends a pass or fail to the PLC. Red and green lights at the station indicate failed or passed inspections.
Step two, install the spring and push the button again. The system acquires a second image to check for the correct spring. While the springs look very similar to the naked eye, the algorithm easily detects the difference between the two. The search area allows rotation of the spring without causing false rejects. Again the vision system activates a pass or fail output based on the inspection results with a red or green light.
Step three, put on the retainer ring and trigger the press to fix the retainer ring onto the assembly. The vision system acquires a third image, which is used to locate the top of the part (the right-most box in the image in Figure 5). Then a series of four line-to-line-distance tools measures the diameter of the assembly at cross-sections whose locations are relative to the top of the assembly.
Algorithms check for the presence of the spring, washer and retainer. The fourth distance tool verifies the absence of a second retainer. For the part to pass, the spring, washer, and retainer must all be present, and there must be one retainer only. A green light indicates a correct assembly.
Easy quality, low cost
The only hardware consisted of the vision system and a backlight. Programming took four hours and was accomplished by someone familiar with the application and the Easybuilder interface.
The supplier’s plant personnel will be able to modify the program easily if the part changes or add new programs to inspect additional parts without incurring consulting expenses. The application shows how inexpensive and easy-to-program vision systems are helping manufacturers ensure quality at a low cost.
Information provided by Cognex.
Fig. 1: PatMax tool inspects for correct brass core. Fig. 2: Incorrect brass core detected by vision system. Fig. 3: PatMax tool inspects for correct spring. Fig. 4: Incorrect spring detected by vision system. Fig. 5: Line tools inspect for presence of three parts.