Pre-scan and post-scan refer to the sequence of focusing and scanning.Pre-scan is focused before scan and post-scan is focused after scan.The common galvanoscope marking machine adopts the post-scan mode.
In the large-format laser marking machine with dynamic focusing, a long focal length dynamic focusing device is used before the galvanometer scanning.The laser spot is focused by the dynamic focusing lens, and the focusing focal length is greater than the distance from the dynamic focusing lens to the galvanometer.That is, scanning the beam as it comes into focus.In the process of plane scanning, the distance between the workpiece plane and the focus lens is constantly changing, so if the focal length of the focus lens is fixed, it is hard to carve marks on the workpiece plane.This is why dynamic focusing is used.The focal length of the focusing lens is changed according to the distance from each point on the workpiece plane to the focusing lens, so that all points of light after focusing are concentrated in the plane where the workpiece is.Dynamic focusing galvanometer scanning method is the best solution for large format high-speed scanning because it can lengthen the focal length and increase the scanning area.This mode is a typical galvanoscopic pre-scan.This dynamic focusing method is much faster than the traditional way, about 1000point/second.However, the dynamic focusing lens used in this way is expensive and the control software is complex, so it is rarely used in the general marking machine.The advantage is that the size of each spot in the scanning plane can be guaranteed to be the same.
The common galvanometer laser marking machines use a post-scan method.The beam output by the laser is first scanned by the galvanometer, and then focused on the scanning plane through the f-theta lens.This method is easy to control, but the scanning area is limited by the f-theta lens, and the size of each point of light in the scanning plane is different.The center is smaller, the surrounding area is larger,and it is easy to produce pincushion and waist distortion.The advantage of this method is that the control software is easy to realize, the cost is lower, the speed is faster, so it is used for most of the galvanometer scanning laser marking machine.
