The way in which the beam is directed and focused to the marking/cutting point.
The beam is directed by reflection off of mirrors then delivered and focused through a lens. The lens truncates the beam to the smallest possible focused spot. The lens is Plano-convex: curved on top, flat on the bottom.
Plotter based laser system lenses are calibrated by focal length. The focal length is the distance from the bottom (flat) of the lens to the point where the beam is at its smallest truncated diameter. For a 38mm CO2 lens this spot size is approximately 0.076mmØ. Differing lenses are suitable for differing effects. Lenses with longer focal lengths have larger spot sizes and offer a greater tolerance for defocus.
The motion system itself is a custom designed X-Y plotter mechanism driven by highly accurate (within 0.025mm), very fast servomotors. There are two mirrors to direct the beam in an X-Y manner, covering the working field, which is rectangular in shape.
The motion system functions in two ways (modes):
In this mode the lens carriage scans from left to right (X-axis) applying laser energy as a series of dots. By stepping the Y-axis at the end of the X-axis travel an image is built up by a combination of these dotted lines. The principle works similar to that of a common office desktop printer. The amount of Y-axis steps is variable through several pre-defined calibrations.
The lens carriage is fixed to a bearing pack, which is mounted to a rigid rail fitted with a very high tolerance. This design reduces vibration and/or wobble – which is common to systems with older motion system designs like hard plastic, spring adjusted bearing sets - and allows the X-axis to work to speeds of 3.55m/sec producing a good quality image very fast.
In this mode it is quite easy to produce images to photographic detail as well as engrave in 2D, 2.5D, relief and multiple layer effect.
This mode is always used when the system is cutting but can also be used to add some interesting effects to engraving, like highlighting the outside edge of text characters.
Vector mode drives the plotter in a simple X-Y manner to guide the laser beam along the cutting path.
Evolution systems can be commanded to vector from any graphics package, however, they also have the capacity to be driven directly by HPGL code, which can often provide superior quality paths.
The laser beam passes through a reducing device called an aperture. This increases beam quality but also effects the power level and the final focused spot size. The user, to suit the application at hand, can adjust the aperture setting.
The beam is then expanded to protect the directional mirrors. This also allows the beam to be condensed by the final optic to a usable size. These mirrors are mounted to galvanometers (galvos); motors that vibrate at very high speed. One of these galvos operates through the X-axis the other through the Y-axis.
The beam is steered by the galvos and projected onto the top of the lens. Evolution Galvo laser lenses differ greatly from the Plano-convex versions used within our plotter type laser systems.
They are F-Theta Ronar: very complex devices with at least four elements and are reasonably valuable.
The function of the lens is to deliver the beam at the correct angle and position plus to a focused spot size. Spot sizes vary depending on the lens used and also on the application at hand. Galvo type laser lenses are not calibrated in focal length as the focal length actually differs somewhat depending on the application at hand. Galvo laser lenses are calibrated by diameter; that is the effective marking field that the lens will function within. This field is always circular. The laser is controlled by custom software. Basically, the variables are the speed of the motion system (5m/sec max), power of laser in percentage and frequency. As well as being pulsed, the laser of YAG based Galvo systems can be driven in a Constant Wave (C/W) mode.
The motion system is essentially a vector device. Text and other variables can be entered directly, even automatically - such as serialisation. Images are created in a graphics package, such as CorelDraw, for importation to the system software. Once imported the image is scaled and positioned. It can be processed in outline only or it can be filled within the application software of the laser by a multitude of different configurations all giving different effects and production rates.
By careful combination of the variable settings the system can function to an almost limitless range of different effects. The beam can be used to mark the surface only, mark subsurface, discolour without material removal or remove material completely (engrave).