Optical: systems and elements – Deflection using a moving element – By moving a reflective element
Patent
1994-07-01
1997-02-04
Phan, James
Optical: systems and elements
Deflection using a moving element
By moving a reflective element
359201, 359212, 359224, 347260, G02B 2608
Patent
active
056004788
DESCRIPTION:
BRIEF SUMMARY
This invention relates to lasers and, more particularly, to laser dot-matrix marking and printing, hereinafter referred to as "marking".
Laser marking is well known in the art and in one such laser marking arrangement a pulsed laser beam is directed through an optical system including a laser beam deflecting means, the beam deflecting means is controlled by a computer and a programme in the computer controls the deflecting means to cause the path of the laser beam to be traversed through a fixed angle, thus to sweep or "scan" a target.
For most such arrangements the laser beam is caused to scan in one plane and the target is displaced in a direction at right angles to the said plane of laser beam displacement whereupon the scan of the laser beam in combination with the target displacement, allows marking over an area of the target.
The computer further controls the firing of the laser, in pre-programmed positions along the scan path of the laser beam over each or selected scans, whereupon a desired dot-matrix marking over an area of the target is obtained.
Such an arrangement, comprising a computer controlled laser with a laser beam deflecting means arranged to direct the laser beam to scan a target in one plane is, hereinafter referred to as "a laser marking system of the type defined".
The target area may comprise a laminate, the external layer of which is burnt away or vaporized by the laser beam to expose the second layer which is differently coloured from the surface layer, or the heat generated by the beam may cause a distinctive discoloration of the target surface or the beam may etch the surface of the target.
Any given target surface to be marked by a laser beam requires a minimum energy density of the beam over a predetermined dwell period to produce a satisfactory marking of the surface. The length of the laser pulse required for a given target surface is inversely proportional to the available laser power and proportional to the area of the target surface in the path of the laser beam when the laser is pulsed.
A problem exists with prior art laser marking systems of the type defined in that currently proposed beam deflecting means are relatively slow to operate or are very expensive and inefficient.
By way of one example, the United Kingdom Patent Publication No. 2133352 discloses a laser marking system of the type defined wherein the output beam of an RF excited wave guide or non-wave guide CO2 laser is directed through an acousto-optic deflector, electronic control means synchronized with the laser drive means drive the acousto-optic deflector so as to selectively deflect the laser pulses in space to produce a one-dimension array of pulses, and an optical system focuses the pulses in said array onto an article to be marked. Acousto-optic deflectors are relatively expensive, as also is the optical system provided to receive the output beam from the acousto-optic deflector to focus said beam and to give an acceptable scan dimensions for the focussed beam.
In other embodiments disclosed in the United Kingdom Patent Publication No 2133352 the acousto-optic deflector is replaced by a mirror arrangement, which may include a multi-faceted spinning mirror or a two mirror system in which one mirror is fixed and the other mirror is displaced by an electronic device, such as a piezoelectric transducer.
An object of the present invention is to provide a laser beam deflecting means of relatively cheap construction which affords a relatively wide range of scan, which affords a high degree of accuracy for the direction of the beam and which, in practise, offers a relatively fast rate of operation.
According to the present invention there is provided a laser marking arrangement wherein a laser beam deflecting means causes the path of a laser beam to scan in one plane, a target is displaced in a direction at right angles to the plane of scan and a computer controls the firing of the laser at pre-programmed positions along the scan path, over each or selected scans, whereupon a desired dot-matrix marking over
REFERENCES:
patent: 4233612 (1980-11-01), Hirayama et al.
patent: 4307930 (1981-12-01), Saito
patent: 4791591 (1988-12-01), Asanuma et al.
patent: 4971413 (1990-11-01), Inoue
Drucker William A.
Imaje (SA)
Phan James
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