FR2569865A1 - Device for drawing graphics on a screen using a laser beam - Google Patents

Abstract

The device allows graphics to be drawn on a screen 5 using a laser beam by blocking from the projection certain lines of the path. It comprises at least one laser source 1 and two so-called tracing optical deflectors 2, 3 disposed on the light path 4 in order to deflect the radiation along two orthogonal axes controlled by a computer. According to the invention it also comprises at least one other so-called blocking optical deflector 10, also disposed on the optical path 4, but controlled by the computer to occupy only two fixed positions, a passive position pp in order to allow the two tracing deflectors 2, 3 to scan the field of the screen and an active position pa to send the beam out of this field.

Description

Device for drawing a laser beam graphic on a screen La

  the present invention relates to a device for

  draw a graphic - such as a writing, a pattern for decoration

  advertising or other - by laser beam on a screen which can be any medium, opaque, translucent or even transparent, or

  even created by smoke emission or otherwise.

  As shown in the schematic perspective, illustrated by FIG. 1, such a device includes at least one laser source 1 such as a tube for example and two optical tracing deflectors 2,3 positioned on the light path of ray 4 from this tube and directed to

  a screen 5, for deflecting this radius along two orthogonal axes x, y.

  Generally, these deflectors are galvanometers, known in the trade as "scanners", the respective coils of which cause, when excited, the rotation of small mirror-holding shafts 6.1, 6.2 extending along the axes x, y; this rotation takes place at an angle which is a function of the voltage applied to the winding considered by a computer; thus, the computer generates, by acting on the deflector 2 only, a horizontal scan X of the laser beam and by intervening on the deflector 3 only, a vertical scan Y. Therefore, that this computer delivers between 18 and 25 times per second to deflectors 2 and 3 of the voltages which correspond to precise preprogrammed positions of the light point on the screen and which these positions are explored in the same order very quickly, the eye keeps the memory of the course

  and, by retinal persistence, sees a graphic.

  To see a square 7 (FIG. 2), it suffices for the computer to define on the screen 5, suitably exciting the deflectors 2, 3, four equidistant points p. 1 to p. 4 and continuously explores them in the direction of the arrows F1 to F4 at the

high frequency mentioned above.

  To see the letter A (figure 3), it suffices that the computer defines on the screen the five angular points p. 5 to p. 9 and continuously explores them in the direction of the arrows F5

to F8 at the above frequency.

  To see the letter B (figure 4), it suffices that the computer defines on the screen the four angular points and intermediate points of the contour p. 10 to p. 21 and continuously explores them in the direction of the arrows F9 to F14 at the

above frequency (Figure 5).

  To see the letters A and B (Figures 4 to 6), the computer must then define the points p on the screen. 5 to p. 21

  and explores them at the above frequency always in the same order.

  This order can be that emerging from FIG. 5 and according to which the exploration of the letter A (arrows F5 to F8) is followed by that of the letter B (arrows F9 to F14) by connecting them

  by path from point p. 6 in point p. 10 following arrow F1.

  We then see on the screen the letters A and B connected by a line

oblique 8 (Figure 5).

  But the order of exploration may be different to place the connecting line of the letters elsewhere. Thus and as shown in FIG. 6, the exploration of the letter A is carried out in the order p. 5, p. 6, p. 7, p. 8, p. 9, p. 8, p. 6, p. 8, p. 9 following the arrows F5 F F7, F8, F'8, F 'and the connection to the letter B explored as before is carried out by tracking point p. 9 to point p. 12 following arrow F2. We then see

  on the screen the letters A and B linked by a basic line 9.

  The exploration according to FIG. 6 makes it possible to obtain a group of letters that is more readable than that obtained by the exploration according to FIG. 5, but obliges to "retrace one's steps" (arrows F'8

and F'7).

  The main object of the invention is to delete from the composition, whether it is a writing such as AB or a drawing or any other representation, the unnecessary connecting lines reduce the good readability of the image and that without

  modify the selection and exploration of points by the computer.

  This object is already achieved by a known device which interrupts scanning while the laser beam travels from the last point of a pattern to the first point of the next pattern, in other words

  along the connecting line to be deleted.

  This device then comprises a shutter constituted by a galvanometer or "scanner" similar to that of the two deflectors

  aforementioned optics 2 and 3, but the shaft of which carries a shutter

  ration. In the unexcited state, the galvanometer places the shutter out of the space scanned by the laser beam; on the other hand, in the excited state that the computer controls between the extreme points of the lines to be erased, the galvanometer puts the shutter across this space to

  intercept the laser beam and prevent it from reaching the screen 5.

  Since the deflection angle of the "scanner" is

  very low (around 30), the shutter must be rela-

  tively long, which implies a mass of inertia incompatible with the frequency of the computer-controlled exploration cycles. Indeed, the response time of the "scanner" depends on the moment of inertia of the mass which it must animate and experience shows that the command frequency is slowed down so that the image obtained is not rigorously stabilized. In addition, the effectiveness of the shutter is limited, since the erasure of the connecting lines

  is imperfect and the boundaries thereof are imprecise.

  To remedy this defect_ the computer emits signals with steep edges, very fast and very powerful which have the drawback of operating the "scanner" very noisily and also of damaging it after a few hundred hours of operation. This results in relatively costly maintenance and detrimental immobilization of the equipment without however achieving the desired perfection of the erasure of the links.

between patterns.

  The object of the present invention is to

  erasure, but by remedying the disadvantages of this provision

known sitive.

  According to the invention, the improved device comprises, in addition to the two so-called tracing optical deflectors, at least one other so-called erasing optical deflector, also arranged on the optical path of the laser beam between the laser tube and the screen, but computer controlled to occupy only two fixed positions, one passive pp to allow the two other deflectors X and Y to explore the screen field and the other active pa to send back

the radius outside this field.

  Several erasing optical deflectors can be connected in series so that their respective deflection angles are added in order to divide the frequency response by as much.

the whole deviator.

  The erasing optical deflector (s) may cooperate with a fixed diaphragm 13, such as a plate, of

  preferably adjustable, delimiting a hole 14 or a slot.

  Given the extremely small size of the mirrors of the optical tracing deviators (which makes it possible to reduce their mass and increase the frequency of scanning) and also given the very small distance between the mirror of the optical erasing deflector and the most close to the other aforementioned mirrors,

  just a very small angular deviation of the effraction mirror

  cement so that the laser beam reflected by it leaves the field of the following tracing mirror, which leads to the same result

  only a shutter due to the absence of a ray on the screen.

  As a result, the erasure of the connecting lines can be obtained without reducing the scanning frequency and without premature wear of the device, with exceptional image quality as regards the precision of its tracing, the accuracy of the

  erasures and the stability of the projection.

  Various other features and benefits of

  the invention will moreover emerge from the detailed description which follows.

  An embodiment and variants of the subject of the invention are shown, by way of nonlimiting examples, in FIGS. 7 to 9 of the appended drawing which further comprises the

Figures 1 to 6 above.

  In this drawing: - Figure 7 is a schematic perspective showing an embodiment of the device according to the invention, - Figures 8 and 9 are views similar to the

Figure 1, illustrating variants.

  In these various embodiments we find the laser tube 1, the two optical tracing deviators 2, 3 and the screen 5 on which the laser beam 4 reflected by the mirrors 6.2 and 6.3 with horizontal scans X and respectively vertical Y. embodiment shown schematically in Figure 7, the device further comprises an optical erasure deflector 10 whose shaft carries a mirror 6.10. This erasing deflector is a "scanner" similar to the previous one, but whose mirror is not capable of occupying, under the control of

  the computer, that two extreme positions.

  In the so-called passive "pp" position of non-excitation of the winding of the "scanner" 10, a position which is shown in solid lines in FIG. 7, the mirror 6.10 is disposed between the laser tube 1 and the "scanner" 2 being oriented in such a way that the laser beam 4 reflected by this mirror 6.10 can explore the field of the mirror 6.2 and by reflection that of the mirror 6.3. As soon as this condition is met, the orientation of the "scanner" 10 does not matter. In the so-called active position "pa" for excitation of the winding of the "scanner" 10, a position which is shown in phantom in FIG. 7, the mirror 6, 10 is angularly offset with respect to the previous position by a very weak, but sufficient to return the laser beam outside the aforementioned field of the mirror 6.2. Thus, in this position, the device does not return any laser beam to the screen 5 and the image is then free of

  trace as long as the change of position is active.

  - This way of proceeding makes it possible to obtain a

very precise rage from the zero point.

  However, the so-called passive position according to which the laser beam explores the field can be obtained by excitation of the

  winding of the scanner 10 and the so-called active position allowing the

  cement, by non-excitation of this winding.

  According to the variant illustrated in FIG. 8, several

  Erasing optical deflectors can be connected in series.

  In the example shown, there are two of them designated by the references 11 and 12. This particular arrangement makes it possible to reduce the overall response time since each of the mirrors 6.11 and 6.12 of these "scanners" 11 and 12 need only pivot by half the angle scanned by the mirror 6.10 of the "scanner" 10 (Figure 7) to deflect the laser beam 4 outside the field of the mirror 6.2 of the first

  tracing "scanner" 2 which presents itself.

  According to the variant shown diagrammatically in FIG. 9, the erasure "scanners" or 10 or 11 and 12 cooperate with a diaphragm 13 intercepting the laser beam 4 coming from the mirror (s) 6.10 or 6.11 and 6.12, which makes it possible inter alia to reduce computer-controlled angular travel. This diaphragm is preferably a plate delimiting a hole 14 or a slot

orthogonal to the pivot axis.

Claims (4)

  1. Device for drawing in a fixed or animated fashion a graphic design such as a writing, a decorative, advertising motif   or other by laser beam on a screen (5) by erasing from the   jection all the features of the path which connect the elements of the composition and which should not appear, this device comprising at least one laser tube (1) and two deflectors   so-called tracing optics (2, 3), preferably of the galvano- type   metric, arranged on the light path (4) to deflect the ray along two orthogonal axes and controlled by a computer delivering, according to the displayed program, voltages which are a function of the deflection angles and which follow each other according to an adjustable cycle and frequency , characterized in that it comprises at least one other so-called erasing optical deflector (10; 11, 12), also arranged on the aforementioned optical path (4), but controlled by the computer to occupy only two positions fixed, one passive (pp) to allow the two other deflectors (X and Y) to explore the screen field and the other active (pa), to return the beam out of this field.   2. Device according to claim 1, characterized in that the passive position (pp) is obtained by de-excitation of the   so-called erasing optical deflector (10; 11, 12).   3. Device according to claim 1 or 2, characterized in that several optical erasure deflectors (11, 12) are connected in series so that their respective angles of deflection are added in order to divide by as much the frequency response of the whole deviator.   4. Device according to any one of the claims.   1 to 3, characterized in that the optical deflection deflector (s) (10; 11, 12) cooperate with a fixed diaphragm (13), such as a plate, preferably adjustable, delimiting a hole (14) or a slot.