CA1295690C - Method and devices for incribing images by means of a laser - Google Patents

Abstract

The invention relates to a method for the registration of images by laser, as well as its means of implementation. The device (10) on which the image is written comprises: - a first layer of a material (2) than ink, arranged in parallel columns (C), and covered with a second layer (3), capable of absorbing laser radiation; - a laser beam (F) capable of a double movement relative to the device (10), a first rapid movement along the columns (C) and a second slow movement relative to the first, along an axis (OX) perpendicular to the bands. - Means (M) for modulating the power of the laser beam (F) as a function of the information to be entered, in synchronism with the above movements. The laser beam describes the zone (ZI) where the image must be formed according to the columns, with or without destroying the absorbent layer (3), thus making the first layer (2) appear or not depending on the power of the beam. and therefore information to be entered. Figure 2.

Description

gROC1 ~ 13TH FOR IMAG REGISTRATION: ¢ P ~
: [~ SER, AND I) ISPOSITI ~ æ D ~ MISE ~ N OEUVRE
OF THE PROCESS

The object of the present invention is a method for laser image registration, as well as its means of implementation artwork - In the present description, we generally mean 5 per image, both graphics and text, photography .....

For some applications, it is necessary to form an image on a support that is difficult falsifiable or liable to be infringed.
. ~ 10 Different methods are known for this purpose. Among these, we can add the impression of the bank note type, ; `who uses a chemical transfer process; different special provisions make this process possible cii: Hardly falsifiable ~ but, for certain uses, its 15 contr ~ eaçon remains insufficiently difficult.
Other techniques, such as those which are . ~ used for the manufacture of optical digital disks, . use a layer ablation mechanism chosen to absorb incident radiation; ] .a absorbent layer a ~

2 0 times removed by radiation, lets appear polluting the support, thus forming an image. These processes do not however make it possible to obtain a "rendering", that is to say a quality (definition of the image, contrast...), equivalent to images produced by printing.
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The problem which the present invention aims to solve ;; is therefore the realization of an image whose renc} u is comparable to that of the imaginative ~, clui so.:it lf3 pl.us difEicile possib] .e at falsiflel and pl ~ di: fEicile possihle ~ i cont: re: eairf; ~, such ~) roced ~ i from: renllsatiorl Findallt notarnment:
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its application in the production of senior documents security, like identity documents for example.

I, e process according to the invelltioIt allows to answer these goal s using - 5 - a first layer of a material, deposited on a support, forming two areas, an image area and a key area reading, and covered only on the image area of a second layer, capable of absorbing laser radiation;
- a laser beam capable of double movement relative to the previous material:
a first rapid movement, along a first axis;
~ 'a second movement, slow compared to the firstJ according to a second axis, for example perpendicular to the first;
means of modulating the power of the laser beam according to the information to be entered in synchronism with the first movement above.
In this way, the laser beam gulded using the reading area describes the ~ one image where the image should be formed in strips parallel to the first axis, with or without destroying the absorbent layer, thus making the first appear or not layer in function of the beam power and therefore of the information to be entered. The reading ~ one used to guide registration is deleted at the end of the operation.

Other objects, features and results of The invention will become apparent from the following description, illustrated by the appended figures, which represent:
- Figures la and lb, different modes of realization image support station;
- Figure 2, an embodiment of means

3 0 image registration optics ;, ~ - Figures 3a, 3b and 3c, sché1nas expllcatifs du operation of the arrangement according to the invention . ~
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_ Figure 4, an embodiment of means control of the optical means of the ~ igure 2, for implementing the method according to the invention.
In these different figures, the same references are 5 relate to the same elements.

Figure la represents a first embodiment image support according to the invention.
On c ~ tte figurc, there is therefore shown a support 1, for example in paper, cardboard or plastic, SUI which we have defined two zones: a ZI irnage zone and a reading zone ZLJ separated by a ZZ axis, parallel to the OX axis of lm reference orthonormal OXY. On the image zone ZI 'we have deposited a first material 2 along strips 20 parallel to the OY axis, thus forming columns, marked C1, C2, C3 ...
Ci .... This material 2 is for example an ink deposited by a gravure printing, intaglio, ofPset type process On the image area ~ Z1 is deposited a layer ~ of ~
-` second material which is chosen to absorb radiation preset, such as ~ laser radiation. Preferably, this 2 omaterial 3 is characterized by a low melting temperature.
It may however be preferable, for certain applications, ,.
that this temperature is not too low, for example around 200C, to stay above temperatures which are usually operated the plastlfications of 2 5 supports. Layer 3 is for example organic metal.
It can be of low thickness, SOII absorption being determined, for a given radiation, by its composition and ,.
its thick ~ eur. For example, a layer of Tellurium about 200 A is suitable.
In the part of the support corresponding to the area of reading Z [, we also deposited tapes of the first material (2) according to the same columns C1, C2 .... Ci. Ces bands can be continuous or not; they are represented for example on ln eigure la erl two patterns, marked 41 and '.

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42, also aligned according to columns C. It should be noted that the material constituting the necks ~ nnes or the patterns of the ZL reading may be different from material 2.
For clarity of the figure, the surfaces of the bands 20 and reasons 41 and 42 It has been pointed out.

FIG. 1b represents an alternative embodiment of the previous figure, differing in that the bands 20 of the image zone ZI are now produced in discreet form by microsurPaces 21, aligned according to C columns like previously. For example, the microsurl ~ aces can be squares of 20, um aside.
To simplify the figure, layer 3 of the maltériau absorbent has not been shown.
,, 'Figure 2 shows an embodiment of the l 5 optical means of image registration SIII 'support previous.
In this figure, we find by way of example the device described in FIG. 1, generally referenced 10, ; ~ cGmportant the reading zone ZL and the image zone ZI) this the latter being covered by the absorbent material 3.
The registration device comprises a laser L, ! ~ 'emitting a light beam F towards Ull modulator M. Ce last is cormnande by a signal 1 ?, this command ~ allowing to modulate 1A laser power L as a function of ; ~ 25 information to write on device 10. Leaving modulator M, the light energy is directed towards a mirror vihrant Mv, through the medium of separation S. Le mirror M is likely to oscillate around an axis zz, parallel to the OX axis. The mirror M flies the laser beam 3 0 to device 10 on which ll Eorme Im spot SL.
: you may also have, if necessary, means (not shown) of EocalisntloIl clu ~ aisceau ~ on the device 10.

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As a function of the beam power controlled by the previous signal P, the device operates one of the two ways:
:. - the first operating mode: ionnemerlt corresponds to the case 5 where the light power is low, for example between 1 mW and 3 mW;
- the second operating mode corresponds to significant light pulsation, for example a few tens of miUiwatts, allowing local ablation of the l 0 layer 3 and thus showing the material 2.
All of the zones in which the material 2 appears as the desired image.
The control of the movement of the mirror M around the zz axis allows the spot SI of the laser beam to describe a l 5 colonn ~ C of the ~ one image ZI In addition,] e device 10 is driven along the OX axis by a translational movement by relative to the optical device, so as to allow the beam '~ laser to go from one column to the next. This movement can be either discontinuous, limited to the time available between the ;; ~ 20 spot sweep movements along the OY axis, ie contiml etlent with respect to the scan along OY, so as to allow a writing in parallel columns.
So, by the command (P) of the module ~ 3ur M, we inscribe an image on the zonQ ZI ~ whose quality depends 2 5 of the parameters selected in particular for the control of the beam power F and spot scanning speeds SL.
In an alternative embodiment, the support 1 is of a different color from the banks 20 or the microsurfaces 21, 3 o in order to make any falsification more difficult: indeed, an attempt to falsify alOI'S U11 ~ 3 high probability of ea.ire nppa: raître: SUppOl't instead of material. 2.

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Regarding the order of the IEaiscQau laser, different variants are possible and are illustrated on the Figures 3a to 3c.
The light pulses can be of width 5 constant according to a constant frequency, the inscription being then of binary type.
In an alternative embodiment, the pulses ~ `bright can be of variable width so as to make appear a more or less extensive pattern. That is iUustrated in Figure 3a.
In this last figure, the power P of the laser beam F as a function of time. The power P evolves between a minimum level Pm and a level maximum PM, with variable pulse width (L1, L2) ~ Figure 3b shows a partial section of device 10, produced according to a column when the latter `~ receives the ~ las0r aisceau modulated as shown in Figure 3a.
On this section, we represent ~ the substrate `~ 2o partially covered with a strip 20: in fact, this remains when the laser power is at minimum level Pm and on the contrary ea was deleted by the laser beam on - widths corresponding to the pulse widths L1 and : 2 5 In the case where the columns are formed of ? ~ microsurfaces as described in figure lb, the pulses must be synchronized with these microsurPaces.
In a variant of reallsation, the power of laser beam no longer evolves binary between two levels 30 Pm and PM, as shown in Figure 3a, mnis changes from Variable amount between these two levels, which allows detr ~ has more or less largely the absorbent layer 3 and, alnsl, de Palre appait aître moti ~ s for example sensitk3ment triangular. This is shown as an example on the figu: re 3c, where we see the trace of two bands 20 and where ;

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, triangular patterns 31 and 32, of different shapes, appear. For the sake of clarity, only the ~ ones where the material 2 apparalt were dotted.
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The laser beam F is then partially reflected.
(Figure 2) by the device 10 to the vibrating mirror Mv then referred, by means of separation S, to Ime cell phots ~ sensitive C where it forms a light spot T. I, a cell C
provides an electrical detection signal D.
This last signal is used, as shown below Figure 4, for the synchronization of the scanning of the device 10 by the SL spot with the information constituting the image, formank the signal P.
~; ~ this effect, the SL spot scans the total ~ head of each . column C, including the part located in the reading area ZL The pattern (s) (41, 42 in Figures 1) of the area of ZL reading allow recognition (identification) of the beginning of a column. Indeed, the nature of the patterns 41, ~ 12 ( - more or less supporting the beam than the support 1) and their possible thickness (causing in case of excess thickness a decentering of spot T on cell C) cause variations in amplitude of the detection signal D, variations characteristics of a column start. It should be noted that this marking cannot be done directly on the C columns of the image zone Zl ~ the layers 20 or 21 then being covered 2 5 by the absorbent layer 3.
In an alternative embodiment, the motlfs 41, 42 i ~ can be variable from one column to another, thus allowing further identification of each column.

FIG. 4 represents an embodiment of the electronic means for controlling the device according to the invention.

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L0 electric detection signal D is, after amplification in an amplifier 40, transmitted to a circuit 43 of recognition of the start of the column.
Under the control of a timing device 45, including a clock and counters, 10 circuits 43 delivers a signnl corresponding to the instant To d0 start of column of zon0 image Z; I ~ for ex0mpl0 the passage of a binary signal in state O. Cs signal 0st delivered to the int0ntion of a logic circuit 46 of the AND gate type, itself providing the modulator command signal P ~ (~ vl, Figure 2). I) years this realization, the signal indicating the instant To pass0, a ~ ant to be transmitted to gate ET 46, in a clrcuit d0 determination of the instant Tl at the end of the column. S ~ ette determination is carried out from time Tol by addition of a constant duration corresponding to the scanning time of the column by the Eaisceau l ?; in this example the signal .i indicating the instant Tl is constituted by the same signal logic going to state 1. Circuit 44 is controlled by the timing circuit 45.
2 O In the variant embodiment represented on the ; FIG. 10 device also includes a comparator 47, comparing the detection signal from amplifier 40 to a threshold; c01a detects a possible exit from the spot SL laser outside sl'0 band 20: indeed, in this case, the 2 5 difference in reflectivity between material 2 and support 1 causes un0 varlation (for exampleQ un0 d: lminution) the amplitude of signal n. I, e comparator output signal 47 is also connected to the AND gate 46. The latter receives still the information I to write on the device 10, in 3o synchronism with the instants To and T1, using a buffer memory pa: r example.
The ET 4ff gate also has the function of authorizing the Information I passags when the SI spot is in the area ZI image (between 10s instants To and Tl) and, if applicable, only when it is well aligned on a column (by action -, ~, . : ~:

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: 9 of comparator 47). Enin, the chronometry device 45 controls the movement of the mirror Mv.

We have thus described a device on which it is possible to register an image using a laser beam 5 electrically directed by a signal, binary or not, represented image, allowing excellent rendering, difficult to counterfeit and whose falsification can also be made difficult .
Note that the reading area (ZL) part of the 10 device is not necessarily carried out on the same support as the image area (~ I); in all cases, e11e is separated from the latter after registration of the image, in order to make it impossible to locate columns C.
It should also be noted that it is possible to register '! i 5 a color image, subject to placing in the image areas of the microsurfaces 21 (figure lb) of different colors according to a predefined arrangement (for example in squares with four colors: blue, yellow, red and black) and order the laser beam accordingly.
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2 0 The description given above was understood of course non-limiting example and variants are possible: 1bles which fall within the scope of the invention. For example, ple that it is possible to deposit an additional layer on the absorbent layer 3, this additional layer being 25 transparent, having a thickness of the order of half the length wave of laser radiation and has the function of achieving unf3 adaptation between air and layer 3, thus limiting 1 reflections on the surface of] a layer 3. It is also so that it has been described (eigu: re 2) a movement of the device read by 3 0 with respect to the optical means which are bad, of course, relatie movement, the optical means can also be = n movement, the available ~ itlE 10 can Evrntue11ement be Eixe.

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Claims (6)

1. Method for registering an image on a device support using a laser beam, characterized by the fact that the support device comprises:
- a first material (2) arranged in columns on the support and forming two areas, an image area and a reading area;
- a second material (3), absorbent, susceptible to be destroyed by the laser beam, placed on the first material on the image area only;
the laser beam being capable of a double relative movement with respect to the support device:
- a first rapid movement, along a first axis (OY);
- a second movement, slow compared to the first, along a second axis (OX);
the laser beam being guided on the columns by means of the reading area and the power of the laser beam being modulated depending on the image in synchronism with the first movement so as to destroy or not destroy the second material, thus making the first material appear or not, the areas of the image area where the first material appears forming the image, the reading area being deleted after registration. 2. Device for registration according to the claim 1 of an image on a support device, characterized by the fact that it comprises:
- means (L) for producing the laser beam (F);
- means (M) for modulating the power of the laser beam by a signal representative of the image to to register ;

- means (Mv) ensuring the scanning by the support device laser beam along the first axis (OY);
means for guiding the laser beam on the support device columns (10);
means for synchronizing the position of the laser beam with the signal representative of the image to to register. 3. Support device for the registration of an image to using a laser beam by the method of claim 1, characterized in that it comprises:
- a first material (2 3, arranged in columns on the support and forming two zones, the image zone and the zone reading;
- a second absorbent material (3), deposited on the image area of the first material, the ablation of the second material being likely to reveal the first material according to a configuration forming the image;
the reading area being capable of being separated from the area image after registration of the image. 4. Support device according to claim 3, characterized in that the first material (2) is arranged on the support material (1) in continuous columns (C). 5. Support device according to claim 3, characterized in that the first material (2) is arranged on the support material (1) according to microsurfaces, (21) aligned according to the columns (C). 6. Support device according to claim 5, characterized in that the microsurfaces (21) are of different colors, allowing image registration in color.