Vitronics Soltec has incorporated two vision-system options into the mySelective system. PCB positioning accuracy relative to the solder waves can vary when adjustable pallet grippers are used. Tolerances add up very quickly. But the robot system can be used to compensate for deviations in positioning when linked to a vision system using fiducial recognition. Two areas of the PCB are designated as fiducials. Those two points on the PCB (at opposite corners) are utilized by the teaching system to identify the exact position of the PCB in relation to the robot/soldering stations. The robot calculates the deviation in XY-directions, automatically compensates for it, then checks the rotational angle and automatically adjusts that parameter if needed, and re-checks the XY-parameters for perfect alignment. Occasionally, extreme accuracy is needed. Fluctuations in temperature within the soldering machine may compromise accuracy and have to be compensated. This often occurs, for example, when a number of screens are located on a single MultiWave plate (for low product mix, high volume). In this instance, fiducial correction for thermal variances is mandatory. Fiducials located close to the solder waves are checked by a camera installed in the Z-axis looking downward. Correction can be performed in 3 different ways: when machine temperature changes (value is user-adjustable), after a given number of PCBs have been processes (selectable), or as a combination of both. The Z-axis mounted camera travels to each solderpot during a correction cycle. When compensation is needed, it is done by making an offset to the machine reference point of each solderpot. Measurement cycle time is approximately 2s; vision-system accuracy is 1/10 of a pixel or approximately 0.01mm.
EPP EUROPE 428
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