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Vision assess quartz packaging in watches

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Micro Crystal in Switzerland, part of the Swatch Group and a manufacturer of quartz crystals for clocks and mobile telephones, among other things, has strict quality assurance requirements in the production process for watch components. Optimised packaging is also of great importance for customer satisfaction and Micro Crystal has implemented the Cognex In-Sight 5401 to inspect the packaging of ceramic surface-mounted devices (SMDs), which houses the oscillating quartz. These high-frequency mini tuning forks (32,768 vibrations per minute) ensure constant frequencies and time information in products all over the world.

Since mid-2007, the company has been using an Optical Tape End-Controller with an In-Sight 5401 to provide high packaging quality. A roll of uninspected SMD tape is guided over a worktable on which the In-Sight 5401 subjects the individual miniature packages, measuring only millimetres and containing the quartz, to an automatic optical inspection. The system assess whether there is an SMD in the package, if it is in the correct position, and whether the batch number is correctly imprinted onto the ceramic housing.

The In-Sight 5401 is supported by Cognex PatMax, which uses pattern-matching technology to locate objects reliably even if they are of different sizes, differently aligned, or partly covered. Using PatMax, the detection of the laser marked batch numbers, which are not sharply contoured 100 per cent of the time, is completely reliable.

PatMax uses geometric measurement instead of a pixel matrix to identify the most important individual features in the image of the object. It then sets the spatial relationships between the central features of the taught image in relation to the real-time image. By analysing the geometrical information, PatMax is able to determine the position of the object clearly.

Identifying the batch number is not a simple task. According to the packaging specifications of Micro Crystal, the gold contact surfaces of the ceramic housing must always be on the side facing away from the camera, and therefore should be invisible to the vision system. If the Cognex system detects fluctuations in brightness triggered by the gold areas on the grey ceramic surface, the Optical Tape End-Controller registers this. The faulty section is then moved to a pre-determined processing point and removed by hand.

From 2008, In-Sight and PatMax are to be used a step earlier, for packaging the SMD itself. In this way, Micro Crystal aims to detect and eliminate faults as early as the packaging process.

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