CA2168662A1

CA2168662A1 - Laser marker system

Info

Publication number: CA2168662A1
Application number: CA002168662A
Authority: CA
Inventors: Joseph James Stone
Original assignee: Individual
Current assignee: General Electric Co PLC
Priority date: 1993-08-03
Filing date: 1994-08-03
Publication date: 1995-02-09
Also published as: EP0712517A1; USRE35446E; JPH09503885A; WO1995004326A1; AU7271394A; US5294774A

Abstract

A laser marker system for marking indicia onto a substrate (146) includes an exit lens (140) having a focal length and a single laser source (120). The surface of the substrate (146) to be marked is positioned generally at the focal plane of the lens (140). The single laser source (120) is arranged so that its energy output beams are oriented in a generally parallel relationship. The single laser source includes segmented reflecting means (131) for generating a plurality of output energy beams (139) to create a column of spots on the substrate (146) with a higher resolution. The segmented reflecting means (131) is comprised of a back-reflecting mirror which is formed of a plurality of different mirror segments (131a-131n). A device is provided for moving each of the plurality of different mirror segments between a lasing position (148) and a non-lasing position (150) to vary the number of output energy beams and thus the number of spots on the substrate (146).

Description

WO 95/04326 PCT/Gs94/0l707 ~ 8~ 6 ~

LASER MARKER SYSTEM
This invention relates generally to an apparatus for m~rking moving objects or substrates and more particularly, it relates to an improved laser marker system for suitably coding paper labels, other substrates, printed m~t~ri~l, plastic, painted surfaces and the like in which the number of dot positions in a vertical column is increased, thereby producing a higher resolution than has been traditionally available.

In U.S. Patent No. 4,652,722 issued on March 24, 1987, there is disclosed a laser m~rking ~pa ~us which utilizes seven lasers for generating a 7-dot high character matrix and is ~signed to the same assignee as the present invention. In particular, the laser beam from each source is directed by fixed mirrors through a single exit lens and then onto the surface to be m~rk-d Individual laser mirrors each corresponding with one of the lasers are not movable and remain stationary during normal operation of the a~ us, even though they are adjustable for initial system ~lignment. The surface to be marked is positioned on a conventional conveyor or other device adapted to move the objects along a linear path ~dj~cent the laser output head.

Each laser defines an esse-nti~lly collim~t~d energy source which is focused, by the exit lens, into a dot of a predetermined small size for precision m~rking of article surfaces as they pass the output head substantially in the focal plane thereof. The incident angle of each of the seven laser sources onto the exit lens is initially adjusted to provide a plurality of closely spaced and focused dots which define a vertical column of seven energy dots from which the character matrix can be obtained by modulation of the dots as the article or ~1686 6 ~
Dru~k~xerr~piar substrate is moved past the exit lens.

In order to produce a higher printing quality for the character matrix and increase the number of types of the character matrix that can be printed, there is needed to generate a higher number of spots or dots for each vertical column. Simply increasing the number of the present seven lasers in US-A~652722 is impractical since the system costs would increase dramatically due to the increased components used. For example, if it was desired to provide a vertical column of 21 dots so as to improve the resolution by a factor of three, then there would be required an additional 14 lasers and associated components therefor. Also, it has been envisioned that the laser mirror 24 of US-A-4652722 used to reflect the bearns from the respective milrors 36a-36g via the delivery tube 18 to the exit lens 26 through the delivery tube 20 could be simply rotated so as to move the seven dots up or down to produce the 21 dots.
However, this technique would require that the ~ mPt~.r of the exit lens 26 be increased by appr~ ximately two inches, thereby increasing subst~nti~lly the system costs.

Accordingly, there has arisen a need for an improved laser marker system which has a higher resolution but without increasing 5nbst~ntiAlly its cost and complexity. The present invention represents an improvement over US-A-4652722.

Accordingly, it is a general obJect of the present invention to provide an improved laser marker system which is relatively simple and economical to mAnufA~lre and assemble.

.

It is an object of the present invention to provide a laser marker system for m~rking indicia onto a substrate in which the number of dot positions is increased, thereby producing ~E~ E~ EE~

a higher resolution than has been traditionally available.

According to the invention there is provided a laser marker system for m~rkinE indicia onto a substrate, comprising: a single laser source having segm~nte~ reflecting means for generating a plurality of output energy beams arranged in a generaUy parallel relationship; and an exit lens spaced from the laser source and onto which said energy beams are directed for focusing onto the ~ ul~slldl~ positioned generally at the focal plane of the lens to create a plurality of spots on the ~iub~ lld~e.

This allows a lugher resolution to be attained.

Preferably the segm~--nted refl~cting means is compri ce~ of a back-reffecting mirror which is formed of a plurality of dirrclcll~ mirror segmPntc Preferably the system incl~des means for moving each of the plurality of dirrt;~ mirror segments between a lasing position and a non-lasing position to vary the number of output energy beams and ~us the number of spots on the :iUIJ~iLLd~C.

The inventlon will now be descnbed fnrther by way of exarnple wlth reference to the '' .

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accompanying drawings in which:

Figure 1 is an elevational diagrammatical representation of a laser marker appa.~tus of the prior art;

Figure 2 is an elevational diagrammatical representation of a laser marker system, constructed in accordance with the principles of the present invention;

Figure 3 is an enlarged schematic representation of the single laser source 120 in Figure 2; ~

Figure 4 is a side elevational view of the back reflecting mirror 130 in Figure 3;

Figure 5 is a front plan view of the back-reflecting rrurror in Figure 3;

Figure 6 is a schematic elevational view of the laser optical relationships for the n laser beams from the single laser source 120 onto the focal plane via a focusing lens;

Figures 7 and 8 are schematic representations, illustrating how the back-reflecting mirrors are changed from a lasing position to a non-lasing position;

Figure 9 is a schematic representation of a second :~ltern~te embodiment for the single laser source 120 of Figure 3;

~ WO 95/04326 2 ~ ~ ~6 6 2 pcT/Gs94lol7o7 Figure 10 is a schematic representation of a third ~It~rn:~te embodiment for the single laser source being formed in a multi-cavity block;

Figure 11 is a partial view, similar to Figure 3, but illustrating an alternate embodiment of how the back-reflecting mirrors are changed from a lasing position to a non-lasing position;

Figure 12 is a view, similar to Figure 10, but illustrating a fourth alternate embodiment for the single laser source being formed in a tapered multi-cavity block; and Figure 13 is a sch~-m~tic representation of a rotating device for the individual mirror segment 149.

Refelling now in detail to the drawings, there is shown in Figure 1 a dia~.. ~i.lical representation of a laser marker a~p~dlus 10 of the prior art. The laser marker apparatus of the prior art is adapted to mark or inscribe alphanumeric characters or other symbols definable within a matrix of precl~t~ number of dot rows onto the surface of movable articles, such as product p~ck~gin~, beverage containers, bottle closures, labels, ~ub~lldles and the like.

The laser al,pa dlus 10 includes a housing or cabinet 12 mounted on a support stand structure 14 and being adapted to receive a source of power via an A.C. wall-plug 16 and a power conditioning unit 18.

The cabinet 12 is used to house a plurality of lasers 20a-20g, a corresponding number of RF laser excitation sources 22 over the respective lasers, a plurality of turning mirrors 24a-WO 95/04326 ~ 6 6 2 PCT/GB94/01707 24g, an interior directing mirror 26, and a rnicroprocessor controller 28. A laser head unit30 is mounted exteriorally of the upper end portion of the cabinet 12 via a mounting flange 32. The head unit is comprised of a horizontal beam delivery tube 34, an exterior directing mirror 36, a vertical beam delivery tube 38, and an exit lens 40. The directing mirror 36 is located at the intersection of the horizontal and vertical delivery tubes 34, 38. The exit lens 40 is prefeldbly arranged at the lower end of the vertical lens tube which is movable telescopingly in the delivery tube 38 so as to permit focusing.

The laser apparatus 10 is described with reference to the cooldi,,ales X, Y, and Z of the orthogonal coordinate system illustrated in the drawings. In the p~ "lc;d embodiment, the seven lasers 20a-20g are forrned of a water cooled CO2 gas laser type and arranged vertically in the Y-direction within the cabinet 12, as illnctr~ted in Figure 1. The energy output beams from these lasers are passed through their respective output ends 44 in the X-direction and then impinge upon corresponding seven turning mirrors 24a-24g. The seven lasers 20a-20g direct substantially collim~ted energy beams, which have a divergence of approximately 4 milliradians, into the corresponding seven turning mirrors 24a-24g. The turning mirrors reflect the beams off the directing mirror 26, through the delivery tube 34, and into the directing mirror 36. Thereafter, the beams are passed through the delivery tube 38 and into optical contact with the exit lens 40.

The path of the energy beam from one of the lasers (i.e., laser 20a) to a m~rking article 46 includes the directing mirrors 26 and 36 and the exit lens 40. In this manner, the laser beams from the lasers 20a-20g are focused as seven discrete spots or dots onto the surface of the article 46. These seven discrete dots extend preferably along a line in the X-~ 6 ~g ~

direction which is transverse to the direction of the article movement (which is the Z-direction, that is, perpendicular to the plane of the drawing). This line in the X-direction defines a single column of the characters or symbols for m~rking As the article to be marked passes the laser head umt, each laser describes a track or line on the article surface which defines a corresponding row of the characters m~rk~tl In the prior art embodiment, the seven discrete dots are uniformly spaced thereby forming evenly spaced parallel character rows.

The turning mirrors 24a-24g are rigidly mounted and do not move during normal m~rking operations. However, the turning mirrors are separately adJustable for initial system ~lignm~nt to provide the ne~çcs~ry angular separation between ~ ent beams but do not generally require fur~er movement thereafter. This is achieved by the lateral positioning of the turning rnirrors along thé X direction. In this prior art embodiment, the directing mirrors 26 and 36 are also fixedly mounted about an axis ext~n~iin~ in the Z-direction.

Even though the energy output beam from the laser 20a is highly c~ llim~t~, it is not absolutely parallel but rather diverges at a known small angle ~ which is approximately 4 milliradians. Accordingly, the energy from the laser 20a does not focus to a point of infinittocim~l size, but to a finite dot or spot of visible proportions The ~ mPt.~I of each dot is determined by the well-known relationship that the dot ~ m~.ter is the product of the beam divergence /~ ~ and the focal length F as follows:

Dot Diameter = F . A ~ =

For example, with a typical focal length of 10.16cm (four inches) and a beam divel~,ellce of 4 milliradians, the dot ~ m~otlo~r is calculated to be:

~MENDE~ SH~ET

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.

Dot Diameter = 10.16cm x .004 radians = 0.04064 cm .

As is known to those skilled in the art, the spot separation of ~ cent dots on the surface .,~: . .
to be marked within each group is det~rmined by the angular dirr~;lellce ~ in the angular path between adjacent beams times the focal length. Thus, there is given:

Spot Separation = F . l~ ~

The turning mirrors are spaced laterally in the X-direction so as to provide the angular difference ~ ~ in the angular path between ~ c~nt beams. For the noImal 4 mil~iradians beam, the angle A~ is typically made to be equal to 4 rnilliradians so as to produce dots that are tangential to each other.

.
Although the laser m~rkinp~ a~ Lus shown in the prior art embo-lim~ont of Figure 1 , provides a highly s~si~f~tory laser .,.~,ki.,p system, it has not been found to be free from all problems. In particular, in order to further generate increased nllmher of dots for each vertical . ....................................................... .
column so as to produce higher quality images or to print simnlt~n~ously ~ itit~n~l lines in each colurnn, there would be required the use of a larger number of lasers as well as RFexcitation , sources. As a result, there would be a substantial increase in t'ne total ~y~.~ell s costs thereby making this approach impractical.

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There is shown in Figure 2 a dia~ ~lical representation of a laser marker system 110 ~=
constructed in accordance with the principles of the present invention. The laser marker system 110 represents a significant improvement over the laser marker a~a-~us 10 of Figure 1. The laser system 110 includes a housing or cabinet 112 mounted on a support stand structure 114 and ~ .
being adapted to receive a source of power via an A.C. wall plug 116 and a power conditioning unit 118.

The cabinet 112 is used to house a single laser source 120, a corresponding single R.F.
laser excitation source 122 for the laser source, a focusing lens 142, an interior directing mirror 126, and a microprocessor controller 128. A laser head unit 130 is mounted exterIorly of.the upper end of the cabinet 112 via a mounting flange 132. The head unit is compri~e~l of a horizontal bearn delivery tube 134, an exterior directing mirror 136, a vertical delivery tube 138, and an exit lens 140. The directing mirror 136 is located at the intersection of the horizontal and vertical delivery tubes 134 and 138. The exit lens 140 is preferably arranged at the lower end of a vertical lens tube which is movable telescopingly in the delivery tube 138 so as to permit focusing.

The laser marker system 110 is described with reference to the same coordinates X, Y, - and Z of the orthogonal coordill~e system illustrated in Figure 1. In the embodiment of the present invention, the single laser source 120 is arranged so as ~o extend vertically in the Y-direction in the cabinet 112, as illustrated in Figure 2. The multiple energy output beams 139 from the single laser source are passed through its output end 137 in the Y-direction and impinge upon the focusing lens 142. The focusing lens 142 receives the multiple energy output beams 139 consisting of incident parallel energy beams and directs them onto the J;E~'`E~ S~

WO 95l04326 ~ PCT/GB94/01707 ~8S6~

directing rnirror 126. This redirection establishes a small angular dir~elellce between beams similar to that produced by the turning mirrors in the prior example. The directing mirror reflects the beams through the delivery tube 134 and into the directing mirror 136.
Thereafter, the beams are passed through the delivery tube 138 and into optical contact with t'ne exit lens 140.

In Figure 3, there is shown a more detailed schematic represçnt~tion of the single laser source 120 of Figure 2. Unlike the conve~llional lasers 20a-20g which is designed so that each generates a single laser beam, the single laser source 120 is of a unique construction so as to produce multiple laser beams. The laser 120 is preferably a low pressure CO2 gas type and is comprised of a rectangularly-shaped housing or enclosure 123 having a ceramic tube 125 forrned therein so as to define a gas-filled chamber 127.

The gas-filled chamber 127 is o~ldliv~ly connected to ends of a pair of exciting electrodes 129a and 129b whose other ends are connectible to a pulse source of RF energy (not shown) in order to directly excite the laser into energy emission. The excited gas chamber is provided with a rear or back-reflecting mirror 131 located at its one end 133. An output-beam receiving mirror 135 is located at the other end 137 of the gas chamber 127.
The mirror 135 is preferably formed as a partially reflecting mirror so that part of the IR
energy beam is passed out of the gas chamber in the enclosure 123 and defines an output energy beam 139 (three of which are shown) which is to be used for m~rking an article. This output energy beam is used to form the image to be printed on the article. A focusing lens 142 receives the output energy beam 139 and directs the incident parallel energy beams onto the directing mirrors 126 and 136 and then onto the exit lens 140.

~ WO 9!;/04326 PCT/GB94/01707 ~68~62 Instead of a one-piece back-reflecting mirror like those in the conventional lasers 20a-20g, the back-reflecting mirror 131 of the present invention is divided into a plurality of different mirror segments 131a, 131b, ...131n interconnected by thin portions 143. This can be best seen from Figures 4 and 5. This construction permits each of the mirror segments 131a-131n to be bent so that they can be moved from a lasing position to a non-lasing position. It will be noted that each of the mirror segm~nt.~ 131a-131n must be precisely aligned with the sharod common output-beam receiving mirror 135 so that a plurality of corresponding output energy beams 139a-139n will be generated. In other words, output energy beams will only be generated for those mirror segments in the lasing position and no output energy beam will 't,e formed for those mirror segments in the non-lasing position.

The use of the plurality of dirr~ t mirror segm~nt~e 131a-131n permits the selection of higher resolutions to be produced by the m~rking device. Further, since neither of the directing rnirrors 126 or 136 are required to bend (which tends to slow down the rate at which the items to be marked can be moved past the laser head), the laser marker systern of the present invention has a much faster speed of operation.

In this manner, each of the energy beams may be caused to be operative or inoperative by controlling the position or ~lignm.ont of the mirror segments 131a-131n. Assuming that certain ones of the mirror segments are fully aligned, there is illustrated in Figure 6 a column of parallel, selected output energy beams 147a-147d being generated which can be passed through the focusing lens 142. As a result, there is created a column of corresponding selected dots 148a-148d on the surface 144 of the article 146 to be marked. When it is desired to obtain a higher resolution, the number of segments in the back-reflecting mirror WO 95/04326 ~ l ~ 8 ~ ~ 2 PCT/GB94/01707 ~

131 is increased.

In Figure 7, there is shown a schematic representation of how one individual segment 149 of the mirror segments may be flexed or bent so as to create a small movement of the back-reflecting mirror in order to cause a mi~lignmto~t As a consequence, the segment 149 will be changed from the lasing position shown in the solid line 148 to the non-lasing position shown in the dotted line 150.

The individual mirror segment 149 can be rotated about a point P at or near its center.
One method of doing this is to use a piezo-electric bimorph element that is rigidly mounted at one end and is coupled to the mirror segm~nt 149 a distance R beyond the point P as shown in Figure 13. When the voltage is applied to the bimorph, it will be caused to bend, rotating the mirror segment 149 about a point P. The actual values being determined by the type of piezo-electric device actually employed for the required mirror displacement.
Examples of piezo.-electric devices suitable for present purposes include those devices manufactured by the VellliL,on Division of Morgan Matroc, Inc., Bedford, Ohio.

A second method of rotating the mirror segment 149 is to employ the well-known galvanometer method. This method is not as fast as a piezo-electric device, but may be s~ti~f~ctorily used for smaller mirrors and slower m~rking devices. Such an arrangement employs permanent magnets disposed on either side of the mirror segment which is mounted for rotation and which carries a coil. A current passing through the coil causes the mirror segment to reflect in a direction and by an amount proportional to the magnitude and polarity of the current. Other suitable techniques for rotating the mirror segment include magneto-WO 95/04326 ~ 6 ~ 6 6 ~ pcTlGs94lol7o7 13strictive elements and for some applications, servo-mech~nisms.

In Figure 8, there is shown a bimorph element which is used to rotate the mirror segrnent 152 from the lasing position (solid line 154) to the non-lasing position (dotted line 156). In the lasing position, it will be noted that the surface of the mirror segmPnt 152 has sukst~nti~lly a flat or slight concave configuration. In the non-læing position, the surface of the mirror segment 1'2 is changed to a convex configuration.

In Figure 9, there is shown a second ~ItP.rn~tP, embodiment for the single laser source 120 in Figure 2. It can be seen that the laser 220 is quite similar in its construction to the laser 120 of Figure 3, except that the back-reflecting mirror 230 formed of mirror segrnents 230a-230n are located outside of the enclosure 222. Further, the end 232 of the enclosure is closed by an IR window 234. As a result, the mirror segments 230a-230n are more convenient to assemble and to control since they are located on the outside of the enclosure 222 thereby making them more easily ~ce~sihle. Except for these dirrt;,ences, the operation of the laser 220 is identical to the laser 120 of Figure 3.

In Figure 10, there is shown a third ~ltern~te embodiment for the single laser source 120 which is configured to provide a multiple, low pressure laser system. The multiple laser system includes a rectangularly-shaped ceramic block 310 having a plurality of cavities 312a-312n defining multiple laser ch~nn~ls All of the channels are excited by a cornmon RF

excitation source of energy. It should be understood to those skilled in the art that the number of cavities or channels correspond to the number of mirror segments. Thus, the output energy beams will be in the lasing position or non-lasing position dependent upon the WO 95/04326 PcT/Gss4/01707 ~

~lignm~nt of the mirror segments associated with the corresponding channels. While it is not necessa;y to separate the individual channels from each other so that the gas mixture is allowed to flow between the ch~nnel~, a plurality of barriers 320 may be formed in which each is disposed between adjacent channels so as to reduce interaction of one energy beam with another one.

In Figure ll, ~here is illustrated another ~ltt~.rn~te embodiment of how the back-reflecting mirrors are changed from the lasing position to the non-lasing position. It can be seen that the laser 420 is quite similar in its construction to the laser 120 of Figure 3, except that there has been added a Q switch 422 which is located in front of the back-reflecting mirror 424 formed of mirror segments 424a-424n. The Q switch is preferably comprised of a plurality of liquid crystal gates 422a422n (Figure 11). These may consist of a suitable liquid crystal m~t~-ri~l between transparent, electrically conductive plates. When no voltage is applied between the plates, across the liquid crystal m~t~.ri~l, the crystals are in a diverse orientation and the assembly is opaque. When sufficient voltage is applied, the crystals align and the element becomes transparent. In this state, the Q switch is on and the element of the laser system in which it is located will lase. As a result, the number of corresponding output energy beams from the associated mirror segments 424a-424n are controlled by selectively turning on certain ones of the liquid crystal energy gates. Except for these differences, the operation of the laser 420 is identical to the laser 120 of Figure 3.

In Figure 12, there is depicted a fourth altt-.rn~te embodiment for the single laser r source which is configured to provide a multiple, low pressure laser system. It can be seen that the multiple laser system of Figure 12 is quite similar in its construction to the laser ~ WO 95/04326 PCT/GB94/01707 ~ 662 system of Figure 10, except the plurality of barriers 520 used to form the plurality of cavities ~12a-512n are made to taper inwardly from its front end to its rear end. In this manner, the output energy beams in each corresponding channel will be caused to impinge upon the directing mirror 126 of Figure 2 without the n~eesity of the focusing lens 142.

From the foregoing detailed description, it can thus be seen that the present invention provides an improve~ laser marker system for m~rking indicia to a substrate in which the number of dot positions in a vertical column is increased. The present laser marker system includes a single laser source having segmented reflecting means for generating a plurality of output energy beams to create a column of spots on a ~ubsL~le. The segm~nte~ reflecting means consists of a back-reflecting mirror which is formed of a plurality of dirrclcllt mirror segm~-nte. Further, there is provided a device for moving each of the plurality of dirr~lcll~
mirror segm~-nt.e between a lasing position and a non-lasing position to vary the number of output energy beams and thus the number of spots on the ~ub~ lc.

Claims

1. A laser marker system for marking indicia onto a substrate, comprising: a single laser source (120) having segmented reflecting means (131) for generating a plurality of output energy beams (139) arranged in a generally parallel relationship; and an exit lens (140) spaced from the laser source (120) and onto which said energy beams are directed for focusing onto the substrate (146) positioned generally at the focal plane of the lens to create a plurality of spots on the substrate (146).

2. A laser marker system as claimed in Claim 1, wherein said segmented reflecting means (131) is comprised of a back-reflecting mirror which is formed of a plurality of different mirror segments (131a-131n).

3. A laser marker system as claimed in Claim 2, further comprising means for moving each of said plurality of different mirror segments (131a-131n) between a lasing position (148, 154) and a non-lasing position (150, 156) to vary the number of output energy beams and thus the number of spots on the substrate (146).

4. A laser marker system as claimed in Claim 2, wherein said plurality of mirror segments (131a-131n) are located on an end of an enclosure (123) containing a gas-filled chamber (127).

5. A laser marker system as claimed in Claim 2, wherein said plurality of mirror segments (131a-131n) are located outside of an enclosure (123) containing a gas-filled chamber (127).

6. A laser marker system as claimed in Claim 5, wherein an IR window is positioned on the end of the enclosure (123) containing the gas-filled chamber (127).

7. A laser marker system as claimed in Claim 1, wherein said single laser source (120) is formed in a multi-cavity block (312a-312n) so as to define the multiple laser channels.

8. A laser marker system as claimed in Claim 7, further comprising a plurality of barriers (520) in which each is disposed between adjacent channels (512a-512n) so as to reduce interaction of one energy beam with another one.

9. A laser marker system as claimed in Claim 3, wherein said means for moving each of said plurality of different mirror segments (31a-31n) includes means for rotating said mirror segments.

10. A laser marker system as claimed in Claim 3, wherein said means for moving each of said plurality of different mirror segments (31a-31n) includes means for flexing said mirror segments.

11. A laser marker system as claimed in Claim 1 including a delivery tube (134, 138) through which the output beam (139) travel towards the exit lens (140).