High precision measurement of CD drive components
In the production of plates for CD drives, a total of eight pins are pressed into four punched plates and welded with lasers. The plates are transported into the stations for processing and inspection on workpiece holders. The length of the pins as far as the groove applied is vital for compliance with the axial clearance of the rollers mounted on them. To ensure this length is obtained, all eight pins need to be exactly measured to ±0.005mm using machine vision.
To perform the length measurements, contact with the plate bases must be ensured. The arrangement of the components and the curvature of the bases mean that this cannot be done optically. Therefore, a sleeve with measurement windows is positioned over each pin. The length is then determined in relative terms from the distance between the groove and the lower edge of the window. This means that a very small trimming can be selected to achieve exceptionally accurate measurements. Due to space constraints, specially designed tiny transmitted light units consisting of an LED are used, and are passed over the pin along with the measuring sleeve for each inspection. The eight cameras with telecentric lenses are operated using the CV-600 machine vision system and controlled using an intuitive user interface. The repetition accuracy of the machine vision system supplied is ±0.002mm and the absolute accuracy of the entire system is better than ±0.005mm. A further CV-600 system including five cameras is used to inspect the welding points.
The 100% inspection regime means that no defective parts can progress along the production chain. Downtime and production stoppages are prevented and expensive complaints avoided.