The accuracy of component placement should be consistent within the mounting area of the SMT placement machine. In order to achieve this consistency, some placement machine manufacturers use the transmission coordinate accuracy deviation distribution of the mapping and mounting table, count the number of component samples defined by each network intersection, and measure the coordinate position relative to the network. The maximum placement area is built with a deviation table and measures for compensation. This method can reduce the influence of the mechanical component defects on the distribution accuracy of the PCB carrying platform and the placement head, but it cannot reduce the random mechanical variation or the instability of the servo system and the amount of digital conversion.
Another effective method is to measure the coordinate motion position of each drive shaft by using a laser interferometer. The servo system drives each drive shaft to translate to each test point of the network, and the measurement should be as close as possible to the placement position of the PCB mounting surface. This will achieve the maximum measurement accuracy. The laser interferometer has a sub-micron resolution. When the components are mounted, the deviation of each drive shaft is compensated, and the deviation of the positioning accuracy can be less than 10 μm.