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ALE glossary

Send mail to: sales@appliedlaser.co.uk with questions or comments about this web site. Copyright Applied Laser Engineering Ltd 2002

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Eccentricity, out-of-level and droop tolerant system

When a graphical pattern is engraved onto a cylinder which is not mounted perfectly concentrically to the axis of rotation, or is not mounted perfectly level, or suffers from droop, the positioning and/or size of the graphical features can become distorted in the significantly circumferential direction.  This can be particularly problematic if a roll is to be engraved more than once in register or if it is to be used in register with another roll.  Furthermore it can be difficult to set the concentricity of a roll to a tolerance smaller than the required feature positioning required.  A system can be provided to substantially correct for the mis-positioning of the engraved features due to mounting eccentricity.  This may consist of a distance measuring device mounted directly below the belly of the roll travelling axially with the engraving head.  The engraved data is shifted vertically at the side engraving position by a magnitude and direction to correct for the measured vertical distance variation.

Laser Beam Loci, Form and Function.

ALE laser engraving machines can be made up of a rotating roller with the meansto progress a focused laser beam along the axis of the roller. The circumferential direction around the Roller Being Engraved is considered to be the Y axis. The X axis is the axis parallel to the axis of the Roller Being Engraved (RBE). ALE laser engraving machines can equally be supplied as an X/Y engraving platform. For simplicity's sake, we consider a roller to be flat, therefore X/Y and roller engraving are considered to be identical processes. The following descriptionsights rollers but is equally applicable to X/Y engraving platforms.

Helical Engraving Locus (HEL).

 

This is the most elementary beam locus and the foundation of nearly all other beam loci. This beam locus is achieved by a laser beam being focused onto the surface of a rotating roller, at the same time as the focused beam is being mechanically moved along the axis of the roller. Alternatively, this locus can be achieved by a laser being focused onto the surface of a roller that is simultaneously rotating, as well as moving along its own axis, past the focused laser beam. The distance along the X axis between two adjoining convolutions of this locus is called the Engraving Pitch Rate (EPR).

It is worth noting there are four possible ways to produce the engraving helices. The roller can rotate clockwise or anti clockwise and the axial movement can be right to left or left to right. For simplicity, we call these four engraving helices: E0, E1, E2, E3. Subtle engraving asymmetries are often engraving direction sensitive.

This is why the Laminar Sequence of Engraving command, LSEQ, is available to define any sequence of engraving helices, in order to produce highly symmetric engraving.

ALE engraving machines are often equipped with high speed beam deflectors, in order to move the beam rapidly in the circumferential and the axial directions. By adding positive or negative, circumferential and/or axial deflection components to the elementary helices: E0, E1, E2, E3, a myriad of beam loci can be formed.

These two components are called Delta Y and Delta X respectively, for brevity sake DY and DX.

Software controlled beam and data sequencing allow ALE customers to define their own beam loci. In the Anilox marketplace wavy structures have become very popular. However there are many pre-defined beam loci, that can either be used without alteration or they can be automatically added together , or they can be end user modified to suit the needs of a particular application.

Cylindrical Engraving Mode (CEM).

This beam locus is formed by subtracting DX from the HEL, where DX takes the form of a saw-tooth waveform, having a period equal to the time taken for one rotation of the RBE and an amplitude of EPR. The function of this locus is to

produce an engraving that is orthogonal to the X axis and parallel to the Y axis.

Axial Jump And Dwell Engraving JADE Mode.

This beam locus is formed by adding DX to the HEL, where DX takes the form of a

staircase waveform. See JADE for the function of this locus.

Circumferential Jump And Dwell Engraving JADE Mode .

This beam locus is formed by adding DY to the HEL, where DY takes the form of a saw-tooth waveform. See JADE for the function of this locus.

Hop And Drop Engraving HADE Mode .

This beam locus is formed by adding a DY and a DX to the HEL repetitively and cumulatively. Typical incremental values for DY would be one Y pixel, this is the Drop. Typical incremental values for DX would be ten X pixels, this is the Hop. The accumulation of DY and DX would typically last for four Hops. Thus a total Hop of forty X pixels would have occurred, as well as a total Drop of four Y pixels. It is important to note, that in the case of this example, once the process restarts, the first pixel to be engraved with zero Hop and zero Drop will be four pixels in Y, after the last pixel was engraved with zero Hop and zero Drop. This amounts to a Y Hop of four pixels. So, the Hop and Drop is hopping pixels in X and Y.

The functional advantages of this mode are, not only do you obtain a wide X separation of temporally adjoined laser pulses, but you also obtain wide temporal separation for spatially adjoining pixels in the Y axis. As a result, all pixels are

either widely spatially separated or widely temporally separated

Multi Beam Engraving Mode

This beam locus is formed by adding a DX to the HEL repetitively and cumulatively.

Typical incremental values for DX would be ten X pixels. This would be typically four accumulations of DX. Thus, in this example, a total of forty X pixels would have occurred before the process restarts. It is important to note that, in the case of this example, once the process restarts, the first pixel to be engraved with zero DX will be one Y pixel offset from the last pixel engraved with DX equal to zero.

The functional advantage of this mode is, you obtain a wide X separation of temporally adjoined laser pulses. However, when you return to DX zero no additional Y separation is gained and only a modest temporal gain is achieved.

Multi Graphic Channels.

 

ALE laser engraving machines receive multiple graphic channels of real time data.

This data can be used to define laser power, laser set up parameter sets, laser focus position, move focused beam in X and move focused beam in Y. All of this data can be changed dynamically, or at the start of each of the layers of a multilayer engraving. As a result, within one engraving, different laser powers can be used. Different laser parameters sets can be used; eg. pulse length, pulse energy and pulse repetition rate. Within an engraving, the laser beam focus can be changed. The focused laser spot can also be dynamically moved, in X and Y, in real time.

 

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ALE GLOSSARY - Page 5