A machine vision system ensures that temperature controllers meet high quality standards.




InterControl (Nuremburg, Germany) manufactures thermostats, thermal links and temperature limiters used to control and monitor temperatures in household appliances and HVAC systems.

Recently, the company decided that one of the temperature controllers it makes for use in appliances needed to undergo a 100 percent quality inspection to ensure reliability. Comprised of a ceramic base with a bimetal mechanism and a number of different connection and fastening options, the controller is manufactured via a fully automated assembly process. Although it manufactures some 50 million of the controllers each year, InterControl wanted to ensure that every one of them was assembled correctly and that every ceramic base was crack-free.

The resulting inspection station employs a compact In-Sight 5400 machine vision camera from Cognex Corp. (Natick, MA) that processes approximately 80 assemblies per minute. Each individual temperature controller is inspected for a host of different defects, including ceramic separation, cracks and contact angles. The system also checks each base’s lateral supports; the geometry of its electrical connections; base plate hole diameters; flange type; and color. Total image-processing cycle time is approximately 0.3 second.

Critical to the success of the new inspection station is the ability to accommodate approximately 150 different controller types all being built by the same automated system. In some cases identical base plates are paired with different ceramic bases and mounted with different contacts. In others, different models use the same contacts, but have the contacts connected at different angles.

“At one point, someone mentioned 17 solutions being on the table,” says InterControl operations manager Peter Wild, illustrating the complexity of the problem. “None of them, however, could hold up in series production.”

Ultimately, the company opted to use an object-oriented inspection approach, in which the base plate is first scanned and then the correct test program run accordingly. This not only simplifies test program administration, but reduces costs, and improves the transparency, safety and flexibility of the actual work.

In operation, the parameters of the dozens of different controller variants are all stored directly within the In-Sight camera, where they can be automatically called up as needed. The camera operates as a fully autonomous unit within the assembly line, and is equipped with robust and accurate vision algorithms that ensure system reliability. The user interface is easy to operate and enables the machine personnel to easily program in new variants.

Initially, discoloration caused by dripping oil would sometimes cause false alarms, registering a part as being defective when it wasn’t. To fix this problem, the machine now stops automatically whenever it registers three faulty parts in succession. All fault sources are statistically recorded and analyzed so that operators can easily pinpoint and quickly rectify any production problems that might crop up.

Since installing the inspection station, InterControl’s already low fault rate of 25 to 50 defective products per million has fallen even further, to the point where complaints and return deliveries have disappeared almost completely.

For more on vision inspection, visit www.cognex.com or call 508-650-3000.