PCB boards can be found in virtually every electronic device on the market. With the help of Adaptive Vision software, engineers from Otes Elektronik designed a laser marking machine for PCB assembly lines which eliminates the need to use paper labels. Seeing that the size of the target area on some PCBs can be very limited, the laser marking process requires very high precision so that the marking is positioned exactly at the required place. This requirement is especially crucial due to the fact that the PCBs can be placed on the conveyor in a wrong way.
The position under the laser head changes for every single PCB and, as a result, the marking position is also different. Correcting it can be done in two ways: one, through mechanical fixing and second, through checking the position using a camera. In our design we have decided to combine both methods. The width of the PCB is mechanically fixed so thet the positioning in Y axis is always precise. Then the X axis deviation is checked by our camera application - we are checking the position deviation of the PCB edge in the X axis and then add this deviation as position offset to the laser head. Finally, the marking field's position is translated according to this measured value. Our device uses a 5MP mono camera and can achieve up to 0,05mm measuring accuracy, which is perfect for this kind of application.
Apart from the above mentioned positioning correction mechanism, we have also developed another algorithm for the PCB rotation offset. In the electronics industry this is referred to as “fiducial correction” of the PCB. It employs 2 diagonal fiducial correction points as well as predefined shapes. The camera is positioned over the first point and checks the position deviation from defined position. Then the second point is measured and using this data gathered at two different positions, we are able to find rotation offset and also position deviation in the PCB. Thus, we are able to ascertain if there were any manufacturing quality problems present during bare PCB manufacturing.
Another key element for this project was the software used. Adaptive Vision Studio provided us not only with flexible and easy-to-use macrofilters that allowed us to obtain successful results in a very short time, but also the possibility to quickly export them to DLL files, which could be integrated with our own machine control software. The Studio's DLL generator was very easy to use, worked straight out of the box and helped us to save time, as we did not need to develop this part on our own.