FR2499718A1 - METHOD AND DEVICE FOR DETECTING SURFACE DEFECTS OF MECHANICAL PARTS, PARTICULARLY CURVED SURFACE PARTS - Google Patents

Abstract

THIS PROCESS IS OF THE TYPE WHICH OPERATES BY ANALYSIS OF THE LUMINOUS DIFFRACTION GENERATED BY DEFECTS IN THE PARTS TO BE EXAMINED. IT CONSISTS OF LIGHTING THE SURFACE S OF THE PART TO EXAMINE WITH NON-COHERENT LUMINOUS RADIATION, FORMING A FLAT IMAGE OF THIS SURFACE S IN A TRANSPARENT PHOTOSENSITIVE MEDIUM 16 IN WHICH THE SPATIAL DISTRIBUTION OF INTENSITY OF THE NON-COHERENT LUMINOUS RADIATION SURFACE S PRODUCES A CORRESPONDING AND PROPORTIONAL SPATIAL DISTRIBUTION OF THE REFRACTION INDEX VALUES, TO ILLUMINATE THIS TRANSPARENT PHOTOSENSITIVE MEAN 16 FOLLOWING AN ORDERED SCAN BY ELEMENTARY ZONES WITH A COHERENT LUMINOUS RADIATION POLARIZATION OF THE LINEARIZATION VARIATION AND PENDING AT LEAST ONE OF THE POLARIZATION COMPONENTS OF THE LUMINOUS RADIATION COHERENT AFTER THE LATTER HAS CROSSED THE TRANSPARENT PHOTOSENSITIVE MEDIUM 16. THE INVENTION ALSO RELATES TO A DEVICE FOR IMPLEMENTING THE PROCESS AND WHICH INCLUDES A SPATIAL LIGHT MODULATOR 14 .

Description

The present invention relates generally to a method of

  detection of surface defects of mechanical parts, especially mechanical parts

i curved surface.

  The invention relates in particular to a method based on the analysis of the light diffraction generated

  by possible surface defects, this analysis is

  operating by observing the ateration of the characters--

  of a coherent electromagnetic wave in

  the spatial frequency plane or Fourier plane.

  The analysis of light diffraction generates

  drée by surface defects is a technique cons

  naked and commonly used for detection and identification

  identification of surface defects (crevices, cracks,

  cracks, cuts, scratches and the like)

  caniques. Normally, this analysis is done in light-

  rant the surface to be examined with a plane and coherent light radiation and then detecting the distribution

  spatial intensity of the radiation reflected by the over-

face examined.

  According to a common form of implementation, the analysis of the light diffraction generated by surface defects is carried out by means of a device.

  which comprises a first optical system, or emission system

  sion, intended to send a plane and coherent light radiation on the surface to be examined and a second optical system or reception system, for example, a display screen or a matrix of photoelectric sensors arranged in a position symmetrical to that of the first optical system relative to the direction normal to the surface to be examined and intended to provide indications

  on the spatial distribution of the intensity of the ray-

  reflected by the surface to be examined.

  The theoretical foundations of this type of analysis

  spnt amply exposedq along with some examples

  ples of possible applications, in chapters 4 and 7 of the text "Introduction to Fourier Optices" by Joseph

  W. Goodman - Editions Mc. Graw-Hil-, 1968.

  The analysis of light diffraction generates

  drée by surface defects implementation -confor-

  mement to the processes described above sees its application limited to the control of plane mechanical parts and it is not suitable for the quality control of parts with a curved surface, in particular parts whose

  the surface does not admit at least one direction of cancellation

  curvature (double curvature surfaces).

  Indeed, in these pieces, we can observe, depending on the part examined, a continuous variation of the

  direction normal to the surface, which results in a

  continuous riation of the direction of propagation of the ray-

  onformation reflected by the surface to be examined. For

  see the analysis of the light diffraction generated by surface defects of mechanical parts

  of this type by known methods, it is therefore necessary to

  re to follow in space the radiation reflected by

  the part while ensuring, however, that the analysis device

  lysis is continuously placed correctly at a dis-

  predetermined fixed tance of the surface to be checked.

  These operating conditions prove to be practically impracticable outside the laboratory and

  they are entirely inapplicable to quality control

  tative of industrial processes, especially when it must

  be performed on all parts produced.

  In addition, when the parts to be inspected are

  have large dimensions, for example, in the case of motor vehicle bodies or parts of such bodies which are subjected to paint treatments or surface protection,

  the need to explore all of the

  face of the room makes it virtually impossible to

  quality control at compatible rates

  with the times of industrial production.

  The object of the present invention is to provide a method which makes it possible to carry out in a rapid and precise manner the control of the quality of surface finish of mechanical parts having curved surfaces and / or of large dimensions. The subject of the invention is a method for detecting possible surface defects of mechanical parts, in

  particularly mechanical parts with curved surfaces,

  rant by analysis of the light diffraction generated by these surface defects, and characterized in that it comprises the phases consisting in:

  a) illuminate the surface of the room which it has

  git to detect faults with non-coherent light radiation, b) to form a planar image of said surface in

  a transparent photosensitive means in which the distribution

  spatial increase in intensity of light radiation no

  coherent reflected by said surface produces a distribution

  corresponding and proportional spatial tion of values of the refractive index, c) illuminating the transparent photosensitive means according to a scanning ordered by elementary zones with a coherent linearly polarized light radiation, d) detecting during the scanning operation the

  variations of at least one of the polarization components

  tion of coherent light radiation after the ray-

  luminous passage through said photosensitive means

parent,

  e) deduce from these variations an indication of

  possible surface defects of the part.

  In the method described above, the analysis of the light diffraction generated by the surface defects of a mechanical part is carried out by examining a planar image of the surface to be checked, which eliminates the

  disadvantages described above, which manifest themselves in

  that the part to be tested has a curved surface in

particular double curvature.

  The invention further relates to a device for

  the implementation of the process described above including the

  main feature is that it includes

take:

  a) means for lighting with a ray-

  non-coherent light emanation of the surface of the room whose faults are to be detected, b) a spatial light modulator comprising

  at least one layer of a transparent photosensitive material

  rent in which a spatial intensity distribution

  of non-coherent light radiation produces a

  corresponding and proportional spatial increase in value

  their refractive index, c) an optical system interposed between the surface of the part whose defects are to be detected and the spatial light modulator, this optical system being capable of forming a planar image of this surface on said layer of transparent photosensitive material, d) a source of coherent light radiation

linearly polarized.

  e) means for moving in motion

  relating the spatial light modulator and said ray-

  coherent light so that this radiation

  illuminates said layer of transparent photosensitive material

  te according to a sweeping ordered by elementary zones, and f) detector means intended to detect during the scanning operation the variations of at least

  one of the polarization components of the radiation

  coherent mineral after this radiation has passed through said

  layer of transparent photosensitive material.

  The device according to the invention further comprises electronic calculating means connected to the

  detector means and intended to deduce from said varia-

  tions of at least one of the polarization components of the coherent light radiation an indication of possible

surface defects of the part.

  The theoretical foundations will be explained below

of the invention.

  The spatial light modulator ("Spatial Light Nlodulator" - SLUI - or, according to another expression usually used in the technique "Light Valve") is a device of great interest for the development "in

  real time "of optical signals. It is generally cons-

  formed by a flat support on which a layer is placed

  cho transparent of a material which is likely to

  to trust its characteristics of transmission of the electric waves

  tromagnetics, in particular its refractive index, as a function of the intensity of a non-luminous radiation

coherent falling on its surface.

  The local variation in the value of the refractive index can result from the manifestation of different

  physical phenomena. In a first class of disposi-

  tifs, known in the art under the name of "PROM Pockels Rlead-out Optical Modulator", a layer of

  photoconductive material is interposed between two electro

  flat transparent trodes to which a voltage of pola-

  risatior, is applied by an external generator. Under these conditions, the variation in conductivity as a function

  of the intensity of a light radiation that we make

  ber on lo device causes, due to the effect con-

  naked under the designation of linear electro-optical effect or Poclcels effect, a proportional variation of the index of refraction of the matter, variation which is thus likely to modify the phase, and therefore polarization, characteristics of a radiation coherent bright which

  spreads inside the material.

  In particular, when the light radiation

  falling on the device has a spatial distribution

  the non-uniform intensity, the corresponding and proportional spatial distribution of the values of the refractive index constitutes an image, generally of the high definition type, of the source of non-coherent light radiation which can also be constituted by an object partially reflective illuminated by a normal, incandescent or fluorescent source. We can read this image in a non-destructive way by dropping

  on the device a coherent light radiation pola-

  laughed linearly and detecting the variation of the charac-

  polarization teristics of this light radiation

  coherent after it has crossed the layer of pho-

  tosensitive. The reading operation can be carried out with an ordered scanning of the layer of photosensitive material by elementary zones (for example by lines) according to the

  criteria commonly used in receiving devices

  television. The spatial light modulator is therefore an optical-optical converter, capable of operating a conversion of optical information of the type

  non-coherent into optical information of the coherent type.

  You can delete the image stored in the d spo-

  by reversing the bias voltage applied to the two transparent electrodes between which is

  interposed the photosensitive layer. Alternatively, the erase-

  can be obtained by illuminating the layer of photosensitive material with a non-coherent light radiation of high intensity and spatially uniform (of the designated type

  commonly by the English expression "flood light").

  In other spatial light modulators,

  different from the PROMs described above, we obtain the

  the refractive index by causing the

  festation of electro-optical effects in materials such as

  that liquid crystal (SLM), photodi-

  chemical and ferroelectric. In addition, there are

  positive spatial light modulators in which the image is stored in the form of a deformation of the layer of photosensitive material, which has the effect of modifying the length of the optical path and consequently

  polarization of coherent linear polarized radiation-

  ment used for the read operation.

  There are other indications on the foundations

  theoretical elements and the criteria for using modu-

  spatial light readers in the article "Spatial Light Modulators" by D. Casasent-Proceedings of the IEEE, volume 659 no. 1, January 1977, pages 143 - 157 and, moreover, in

  the article "Realtime Spatial Light Modulators" by B. Schnee-

  berger, F. Laeri, T. Tschudi and F. Mast, Optics Communi-

  cations, volume 31, no. 1, October 1979, pages 13 - 15.

  Other features and advantages of the

  vention will be better understood on reading the description

  tion which will follow from an exemplary embodiment and with reference to the accompanying drawings on which

  Figure 1 is a schematic view of an arrangement

  sitive for the implementation of the process according to the invention

  tion; and Figure 2 is a schematic representation

  of the structure of a spatial light modulator used

dried in the device.

  In Figure 1, we have indicated in S the surface

  of a part to be checked, for example a part of the

bodywork of a motor vehicle.

  In 10, a normal light source is indicated, for example a tungsten lamp, intended to illuminate by non-coherent light radiation the surface S of the part to be controlled. An optical system 12 has the function of forming on a spatial modulator of light 14 an image of the

  surface to be checked S. The optical system 12 is advantageous

  sement constituted by an objective capable of forming on the spatial light modulator 14 a reduced image of the

  surface S, thus making the qualitative control of pi

  these large dimensions possible and even easy to achieve

  ser. The objective is preferably of the deep type.

  field of view, i.e. a lens with a low ratio between focal length and diagonal of the image format, which eliminates the effects exerted

  on the precision of the control by the differences in

  tance between the device and the different points of a

  same part From the different controlled parts success-

  sively. The spatial light modulator 14, which is of a type known per se, preferably of the type PROM described

  above, is constructed in accordance with the structure re-

  shown schematically in FIG. 2. This spatial light modulator 14 essentially comprises:

  a) a layer 16 of trans-photosensitive material

  parent in which a spatial intensity distribution

  of non-coherent light radiation induces a distribution

  corresponding and proportional spatial tion of values of the refractive index, b) a first planar electrode 18, t ansparent to the non-coherent radiation reflected by the surface S of the part to be checked,

  c) a plane and semi-transparent dielectric mirror

  rent 209 interposed between the photosensitive material layer

  ble 16 and the first planar electrode 18, the surface

  bending of this dielectric mirror being directed towards the layer of transparent photosensitive material 16, d) a second transparent planar electrode 22

  which faces the surface of the photo material layer

  transparent sensitive 16 which is opposite to the plane dielectric mirror 20, and

  e) a supply unit 24 intended to apply

  quer at least two different voltage levels between the first and second transparent electrodes 18, 22 respectively.

  The first voltage level corresponds to the con-

  editions in which, according to the methods described above, the manifestation of the photoconductivity characteristics of the layer of transparent photosensitive material 16 is observed while the second voltage level is that which causes the erasure of the image stored in this layer of transparent photosensitive material 16. The supply unit 24 controls the functions for storing and erasing the image formed on the

  layer of photosensitive material 16, allowing effect

  successively kill the examination of different distributions

  spatial luminous intensity which correspond to the ima-

  management of surfaces of mechanical parts that are framed

successively by objective 12.

  In 26 a source of linearly polarized coherent light radiation, of known type (laser), has been indicated. The light radiation produced by the source 26 is sent to the spatial light modulator 14 via an optical system which makes it possible to move this radiation relative to the modulator 14. This optical system comprises:

  a) a first mirror 28 intended to deflect the ray-

  coherent light produced by the source 26, b) a second mirror 30 intended to intercept

  the radiation deflected by the first mirror 28 and at the

  veer in a direction substantially perpendicular to the surface of the photosensitive layer 16 of the spatial light modulator 14, d) a cylindrical lens 32 interposed between the first mirror 28 and the second mirror 30 and which has its focus F at the point of the first mirror 28 which is struck by the radiation produced by the source 26,

  e) a first actuator 34 used to make the oscillation

  the first mirror 28 around an axis -A orthogonal to the

  focal line L of the cylindrical lens 32 and in the direction

  tion of the light radiation emitted by the source 26 and which also passes through the focal point F of the lens 32, and

  f) a second actuator 36 used to make os-

  blink the second mirror 30 around an axis B which intersects the focal line L of the cylindrical lens 32 and which lies in a plane orthogonal to the axis A. The coherent linear polarized light radiation

  the air is deflected by the second mirror 30 towards the mo-

  spatial light dulator 14 so that, after passing through the second transparent electrode 22, the ray-

  falling on the layer of transparent photosensitive material

  parent 16 in a substantially perpendicular direction

on the surface of this layer 16.

  After passing through layer 16, it

  coherent light is reflected by the semi-mirror

  transparent 20, crosses layer 16 again and leaves

  of the spatial light modulator 14. Coherent radiation

  rent coming out of the spatial modulator 14 is reflected by a semitransparent mirror 38 interposed between the spatial light modulator 14 and the second mirror 30 and it is diverted towards a normal optical analyzer 4-0 constituted, by

example by a polarizer.

  At 42, there is shown schematically a matrix of photoelectric converter arranged in cascade with respect to the analyzer 40 and intended to produce at the output of each of the converters an electrical signal indicative of the intensity of the light radiation falling on this

  converter 42. Between the optical analyzer 40 and the ma-

  converter.photoelectrica42 is interposed

  a lens 44 intended to send onto the contact matrix

  photo-electric vertisseurs42 the light radiation which

comes out of the analyzer 40.

  In 46, a calculated electronic circuit has been indicated.

  lator powered by the matrix output signals

  photo-6lectrical converters 42. Circuit 46 is capable of

  ble to provide a corresponding digital value distribution

  corresponding to the spatial distribution of intensity of the ray-

  luminous light falling on the matrix of converters

photoelectric 42.

  The assembly formed by the optical analyzer 40, the matrix of photo-6electric converters42, the lens 44 and the electronic calculating circuit 46 constitutes an apparatus capable of detecting, during the scanning operation by elementary zones of the layer of material.

  photosensitive transparent 16, the variations in intensity

  luminous tee which appear according to the direction of

  one of the polarization components of cohesive radiation

  rent after the latter has crossed this layer of ma-

  transparent photosensitive 16.

  Dans.ne simplified form of implementation of the device, which is not shown in the drawings,

  the matrix of photo-electric converters b 42 and the circuit

  cooked electronic calculator 46 can be replaced

  by a normal frosted screen, which allows to observe the

  spatial distribution of light intensity

  coherent leaving the optical analyzer 40.

  In the embodiment shown in FIG. 1, the device according to the invention further comprises a logic control unit 48, connected to the electronic computer circuit 469 to the actuators 34 and 36, and

  to the power supply unit 24 of the spatial light modulator

  era 14. This logic control unit 48 is preferably

  this constituted by a microprocessor device which is also able to ensure the functions of the circuit

electronic calculator 46.

  We will now describe the operation of this device.

  When the surface S to be checked has been correct-

  mentally framed and developed by the lens 12, the logic control unit 48 acts on the power supply unit 24 of the spatial light modulator 14 so as to allow the image of the surface to be checked to be memorized S

  in the layer of transparent photosensitive material 16.

  Simultaneously, or after a predetermined period of time has elapsed, the logic control unit 48 activates the actuators 34 and 36 to cause the first mirror 28 and the second mirror 30 to oscillate, thereby switching on.

  the scanning operation by elementary areas of the

  che of transparent photosensitive material 16.

* When, during the scanning operation, the

  coherent light radiation passes through key areas

  the transparent photosensitive material layer

  16 which correspond to parts of the surface to be contr8-

  ler which are free from defect (phew possibly, which

  correspond to the surface of an example sample piece

  te of faults), it falls on the matrix of converters

  photoelectric42 a light radiation whose

  spatial intensity contribution is taken as reference data. For example, in the case of subject areas

  to a paint treatment (parts of bodies of other

  tomobiles), the reference distribution can be likened to a light peak (! 'spot') located in the center of the matrix of photoelectric converters42, which corresponds to the origin of the plane of spatial frequencies (Fourier plane) represented by the surface of the matrix of photoelectric converters42.

  The presence of a defect on the surface to be

  tr8ler S produces a variation in the spatial distribution

  the intensity of the light radiation incident on the matrix of photoelectric converters 42, conferring

  to this distribution of elongated or irregular geometries

  eras or, in any way different from that which was taken as a reference. This variation is detected by

  the electronic circuit 46 and signaled to the

  control logic unit 48 which, being connected to the means

  scanning (mirrors 28, 30 and actuators 34, 36) identi-

  fie the elementary area of the photosensitive material layer

  ble 16 and, therefore, the portion of the surface to be con-

  tr8ler S o was found the presence of a defect, in

  emitting a corresponding alarm signal.

  The electronic calculator circuit 48 is further capable of identifying, on the basis of known type algorithms, the type of faults (scratches, holes, cracks

  etc.) observed from the spatial distribution by-

  the intensity of the light radiation falling on the matrix of photo-electric converters

presence of fault.

  At the end of the scanning operation, the logic control unit 48 performs, via

  the power supply unit 24, erasing the memo image

  risde in the spatial light modulator 14, as a signal

  at the same time availability for the execution of a

new type of control.

  The new control cycle can be executed

  on a mechanical part different from that pre-checked

  cedent, or on another part of the piece

  tr1lée laying the previous cycle when, as in the case of quality control of a vehicle body

  automobile treated by painting, the dimensions of the pi-

  species to control are important and, anyway, such

  them that it is not possible to frame them entirely

within the scope of objective 12.

  In this case, the device can be usefully

  associated with an automatic displacement device

  tif of the device itself with respect to the room to be con

  tr8ler, making the process fully automatic

of the verification operation.

  Of course, various modifications can be made by those skilled in the art to the device which has just been described solely by way of nonlimiting example.

  without departing from the scope of the invention.

1 4

Claims (9)

R E V E N D I C A T i 0 N S   1 - Method for detecting surface faults   this mechanical parts, especially mechanical parts   curved surfaces, operating by diffraction analysis   tion of light caused by these surface defects and   characterized in that it comprises the phases consisting in: a) illuminating the surface (S) of the part in question   detect faults with non-co-   inherent, b) form a plane image of said surface in   a transparent photosensitive means (16) in which the   spatial distribution of intensity of light radiation no   coherent reflected by said surface (S) produces a dis-   corresponding and proportional spatial contribution of   their refractive index, c) illuminate the medium pho--   transparent tosensib3e (16) according to an orderly scanning by elementary zones with a coherent linearly polarized light radiation, d) detecting during the scanning operation the variations of at least one of the components of polarization of the coherent light radiation after   the light radiation having passed through said photosensitive means   2m transparent ble (16), and e) deduce from these variations an indication of possible surface defects of the surface examined.   2 - Device for detecting surface faults   this mechanical parts, in particular surface parts   this curve, operating by light diffraction analysis in-   generated by these surface defects and characterized in that it comprises: a) means (10) serving to illuminate with non-coherent light radiation the surface (S) of the   part for which faults are to be detected, b) a modu-   ! space light generator (14) comprising at least one   che of a transparent photosensitive material (16) in the   which a spatial distribution of non-coherent light intensity produces a corresponding and proportional spatial distribution of values of the refractive index, c) an optical system (12) interposed between the surface (S) of the part in question acts to detect   faults and the spatial light modulator (14), this system   optical teme being capable of forming a planar image of this surface (S) on said layer of photosensitive material   ble transparent (16), d) a source of light radiation   coherent linearly polarized waves (26), e) means (28, 30; 34t 36) for moving in relative movement the spatial light modulator (14) and said radiation   coherent light so that this light shines   said layer of transparent photosensitive material (16) is   lon an orderly scanning by elementary areas, and f) detector means (40, 44, 42) intended to detect during the scanning operation the variations of at least one of the   polarization components of cohesive light radiation   rent after this radiation has passed through said layer of   transparent photosensitive material (16).   3 - Device according to claim 2, charac-   terized in that it further comprises calculating means   electronic sensors (46) connected to the detector means (42) and intended to deduce from said variations of at least one of the polarization components of the light radiation an indication of possible surface defects of the surface examined (S).   4 - Device according to one of claims   2 and 3, characterized in that the spatial light modulator   material (14) provided with said layer of transparent photosensitive material (16) comprises, in a manner known per se: a)   a first planar electrode (18) transparent to the ray-   non-coherent reflection from the surface to be examined (S), b) a plane and serni-transparent dielectric mirror (20)   interposed between the layer of photosensitive material trans-   parent (16) and the first planar electrode (18), the surface   that of this mirror being directed towards the layer of transparent photosensitive material (16), c) a second planar electrode (22) transparent to coherent light radiation,   which faces the surface of the photo material layer   transparent sensitive (16) which is opposite the planar dielectric mirror (20), and d) a power supply unit   (24) intended to apply at least two levels of tension   different between the first and. the second electro- transparencies (18, 22).   - Device according to any one of claims 2 to 4, characterized in that said optical system comprises a lens with a large depth of chaimp (12).   6 - Device according to any one of the   vendications 2 to 5, characterized in that the means   before moving the spatial light modulator and said   coherent light radiation in relative motion   nent: a) a first mirror (28) intended to deflect the ray-   ment produced by the source (26) of coherent light radiation, b) a second mirror (30) intended to deflect the   radiation deflected by the first mirror (28) in a di-   substantially normal rection at the surface of the pho-   transparent tosensitive (16) of the spatial light modulator   era (14), d) a cylindrical lens (32) interposed in   be the first mirror (28) and the second mirror (30) and which has its focus (F) at the point of the first mirror (28) which   is struck by the radiation produced by the ray source-   coherent luminous element (26), e) actuator means (34) used to oscillate the first mirror (28) around   an axis (A) orthogonal to the focal line (L) of the lens   the cylinder as (32) and to the direction of incidence of the ray-   coherent luminous action which passes through the focal point of this cylindrical lens (32), and f) actuator means (36) used to oscillate the second mirror (30) around an axis (B) which cuts the line focal length (L) of the cylindrical lens and which lies in a plane orthogonal to the axis   (A) around which said first mirror (28) is made to oscillate.   7 - Device according to claim 6, ca-   characterized in that said detector means comprise   a) an optical analyzer (40), b) a first optical system   that (38) interposed between the second mirror (30) and the mo-   spatial light dulator (14) and intended to deflect towards   said optical analyzer (40) the coherent radiation exits   both of the spatial modulator (14), c) a conversion matrix   photoelectric weavers (42) intended to produce at the exit   tie of each converter an electrical signal indicative of the value of the intensity of the light radiation which   falls on this optical converter (40); and d) a second-   optical system (44) for directing light radiation from the optical analyzer (40) to the matrix   photoelectric converters (42).   8 - Device according to claim 7, ca-   characterized in that the optical analyzer is a polarizer.   9 - Device according to claim 7, ca-   characterized in that said first optical system (38) is   constituted by a semi-transparent mirror.   - Device according to claims 3 and   7, characterized in that said electronic calculating means   tronic (46) include an electronic circuit supplied   ted by signals coming out of the converter matrix   photoelectric (42) and intended to form a distribution   tion of numerical values corresponding to the spatial intensity distribution of the light radiation falling on   * 25 the matrix of photo-electric converter (42).   11 - Device according to any one of the claims   ticns 2 to 10, characterized in that it further comprises me nity logiqoue   control (48) connected to the electronic calculator means   ques (46), said actuator means (34, 36) for oscillating the first mirror (28) and the second mirror (30) and the power supply unit (24) of the spatial modulator of light (14).