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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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3D Scanning

Non-contact scanning of surfaces can be a very useful process sometime combined with a laser engraving process.  It can be used to digitise the texture of an object in order to create input data to the laser engraving process, such as a Maestro, anilox or BEF  engraving.  It can also be useful as feedback to the results of an engraved surface to optimise focus control.

Beam delivery

Many configurations of beam delivery can be useful.  It is often useful to externally modulate lasers separately to the internal control of the laser.  It is often necessary to deflect a laser beam in one or more axes to allow the focussed spot position to be accurately controlled at potentially high speed.  Examples of both these techniques are used in the ALE Thermalase, MBAnilox and MBGraphic systems.

 

Multiple laser beams can be delivered to the workpiece either via separate focussing lenses or they can be combined optically before or at the final focussing lens to give one or more focussed spots.  The choice of system depends on many factors including the range of wavelengths and powers being employed, the means of registering the various lasers as well as the type of engraving required.  These methods have been used variously in ALE Gemini and Delta Gemini systems.  ALE systems combining different wavelengths have been utilised in ALE Hybrid systems.

Beam quality beam shape

The size, shape and cross-sectional profile of the focussed laser spot can have a dramatic effect on the engraved result.  For high quality, high resolution engravings often a high quality beam is preferred, with M2 in the region 1.1-2, where M2=1 is the highest theoretical beam quality giving the smallest theoretical focussed spot with a Gaussian profile.  For some engravings however, it is preferred to have a different cross-section of power within the focussed spot such as a top-hat profile.

Clunk-clunk multi-hit

This mode of multi-hit anilox engraving stops the motion of the main machine carriage for the duration of the number of roll rotations required to engrave the number of hits per cell in a given column of cells.  When they are complete the laser pulsing onto the roll is stopped, the carriage is moved along one column width to the next column of cells and the cycle repeats.  The name comes from the audible stop-start of the machine carriage.  Advantages can be the minimal equipment upgrade required; disadvantages include exposure of machine linear axis mechanical deficiencies and the relatively long time taken between columns for the move.

Dry-ice blasting

This is a cleaning method related to snow jet cleaning.  This process cleans by blasting small particles of frozen CO2 at the substrate within a jet of dry compressed air.  The parameters are adjusted so that the particles have a slightly abrasive impact followed by an ‘explosive’ effect as the solid state sublimes to the gas phase thereby dislodging the debris.  A number of systems are commercially available.

Electro-polishing

This process cleans by electrolytic dissolving of protruding details of the engraved surface such as burrs and roughness.  The workpiece is suspended as the anode in a bath of suitable electrolyte.

External beam deflection

The main axes of the scan of the focussed spot on the workpiece are created by the rotation of the roll about its own axis and the traverse of the engraving carriage along the axis of the roll, either by movement of the engraving carriage and/or the roll.  Due to the masses involved these axes have limited bandwidth of movements possible.  It is therefore desirable to add further means of deflecting the focussed spot on the surface of the roll.  Two examples of such techniques are an acousto-optic deflector or an ALE wobbler device.  The acousto-optic deflector can rapidly vary the angle of incidence of the laser beam with respect to the lens and hence vary the position of the focussed spot.  An acousto-optic deflector can often simultaneously provide the function of an acousto-optic modulator.  The ALE Wobbler uses a high speed translation device to rapidly control the position of the focussing lens.  Examples of both are utilised in the ALE MBAnilox and MBGraphic systems.  For some types of engraving it may be preferred to add a galvo scanner or similar.  This device typically utilises one or more mirrors rotated by galvanometers to scan the laser beam(s) in one or more axes.  A further alternative means of deflecting or scanning laser beam(s) is a polygon mirror.  The galvo scanner and polygon mirror generally have the advantage of larger scan angles and higher laser powers, but have the disadvantage of reduced scan control.

External beam deflection can also be utilised to move the beam around in such a way that the laser beam(s) are not being affected by the plasma or debris created by the effect of preceding laser interaction at adjacent sites.

 

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ALE GLOSSARY  - 1 2 3 4 5 6