Piston inspection system prevents engine failures

An automatic vision inspection system to read the alphanumeric product identifiers cast into pistons has been developed by Olmec-UK Ltd for an automotive engine manufacturer. The pistons must be checked immediately prior to engine testing to ensure that the correct ones are used. Starting an engine with incorrect pistons fitted results in catastrophic failure with the entire engine having to be scrapped.

Automatic reading of the alphanumeric identifiers posed a huge challenge for the vision system because the characters were never intended for machine reading. Although the characters stand raised from the background material, there is very little contrast between them and the background and this is made even worse because the material is very reflective. In addition, pistons are produced from a variety of different moulds, so there is significant variation in the quality of the characters from batch to batch.

The vision solution featured the use of 4 individual cameras, each equipped with their own ringlights to image each of the pistons simultaneously. Using red illumination optimises contrast and minimises noise in the resultant images. The system is controlled using Olmec’s VP2-CR system which features character recognition software that takes into account different fonts, quality, scale, skew and slant of the characters. The system features a simple, graphical user interface using a touch screen controller, and is also configured to allow for the different working distances that occur when different engine types are inspected.

The engines arrive at the vision inspection station on a conveyor. The conveyor is stopped and the vision system inspects all 4 pistons. If any piston fails the inspection, the process is stopped to allow an operator to make an additional visual assessment. Since the vision system has been introduced, there have been no engine failures due to fitting of incorrect pistons, saving the manufacturer a considerable amount of money.