Compact Cooler Chills Compact Detector

Daniel C. McCarthy, News Editor

Robots offer speed and precision to many manufacturing processes, such as the application of paint on automobiles. However, optical components facilitating this precision need to be compact to easily mount on the robot's arm and rugged to endure the rigors of industrial environments.
OptiSense GmbH of Bochum, Germany, manufactures the PaintChecker system, which uses an infrared detector to measure the thickness of a fresh layer of paint within milliseconds at an accuracy of about 1.0 µm -- an industrial applications story by itself (see EuroPhotonics, April/May 1999, pp. 30-31). More notably, a very compact and rugged cryogenic cooler from Hymatic Engineering chills the detector.
EG&G Optoelectronics and Laser Components GmbH collaborated on the detector assembly and selected Hymatic's Stirling Cryocooler. The system calculates the thickness of the paint layer by firing a short laser pulse on the coated part and registering how quickly the heat is absorbed and radiated from the paint. The detector operates between 8 and 12 µm, which enables use of moderate laser power to prevent damage to the paint layer. To achieve this sensitivity, Hymatic's cooler maintains detector temperature at 80 K. It weighs 1.25 lb and measures 6 in. long with a 2-in. diameter.
The system's designers evaluated several coolers before settling on Hymatic's product. According to Johannes Kunsch of Laser Components, many competitive devices failed to comply with the stringent size, weight and lifetime specifications enabling them to be mounted on a robot and to perform reliably in an industrial environment.
Hymatic's cooler not only is compact, but also has a 20,000-hour warranty. The cooler was designed to perform several times longer without maintenance, according to Martin Bailey, a sales representative for Hymatic. Some of the bulkier coolers had a mean time to failure of 4000 hours, which is less than six months of operation. "This is far out of any acceptance at automotive industries, where plants work in three shifts six days a week," Kunsch said.