Optical system comprising a laser emitter and at least one variable focal length projection lens

Abstract

TITLE: Optical system comprising a laser emitter and at least one variable focal length projection lens. Optical projection system, particularly for motor vehicles, comprising a laser emitter, an oscillating mirror device (4) and an optical projection device (5) comprising at least one projection lens (51) having a variable focal length, the optical system (1) comprising a control unit (52) capable of changing the focal length of at least one projection lens (51) as a function of a position of the oscillating mirror device (4). Figure for the abstract: Figure 1a

Description

Title of the invention: Optical system comprising a laser transmitter and at least one variable focal length projection lens

[0001] The invention relates to an optical system comprising a laser emitter and at least one variable focal length projection lens. The invention also relates to a motor vehicle equipped with an optical system according to the invention. Finally, it relates to a method of using such an optical system.

[0002] In the automotive industry, it is known to equip motor vehicles with various optical systems. In particular, these may be included in a headlight, in particular a front headlight, of the vehicle, or in a side skirt, or even in a rearview mirror so as to implement lighting and / or the projection of specific information onto a projection surface defined on the roadway in front of or around the vehicle. In such application examples, the light beam is grazing and the projection surface is particularly inclined relative to at least one part of the optical system and is extended so that it can, for example, extend up to 3 meters in front of the vehicle. As a result, different portions of the projection surface are separated from the optical system by more or less significant distances.

[0003] The projection of information onto a surface inclined relative to the optical system is thus accompanied by a variation in the sharpness and size of the projected image within the projection surface. Consequently, the sharpness of the image is not uniform across the entire projection surface, certain areas of the projection surface having reduced sharpness, unsuitable for the projection of information, and deformations of the shape of the image are observed.

[0004] The invention falls within this context and aims to propose an alternative to known optical systems allowing the projection of images, in particular by means of laser light sources, onto inclined surfaces so as to obtain an image of suitable quality, in particular having uniform sharpness.

[0005] To this end, the invention relates to an optical projection system, in particular for a motor vehicle, comprising: - a laser transmitter configured to emit at least one light beam; - an oscillating mirror device configured to reflect the at least one light beam towards a projection surface; and - an optical projection device arranged downstream of the oscillating mirror device in a direction of propagation of the at least one light beam and comprising at least one projection lens.

[0006] In particular, the at least one projection lens comprises a variable focal length and in that the optical system comprises a control unit capable of modifying the focal length of the at least one projection lens as a function of a position of the oscillating mirror device and / or as a function of a position of the at least one light beam in the projection surface.

[0007] In particular, the at least one projection lens comprises an electromagnetic element and a liquid portion, the control unit being configured to circulate an electric current through the electromagnetic element and to vary a voltage of said electric current so as to vary the focal length of the at least one projection lens.

[0008] Optionally, the control unit is configured to vary an intensity of the at least one light beam emitted by the laser transmitter as a function of the position of the oscillating mirror device and / or as a function of a position of the at least one light beam in the projection surface so as to ensure uniformity of illumination within the projection surface.

[0009] According to an exemplary embodiment, the optical device comprises a first optical assembly, a second optical assembly and a translucent screen, interposed between the first optical assembly and the second optical assembly: - the translucent screen comprising an input face facing the first optical assembly and an output face, opposite the input face, and facing the second optical assembly; - an image focus of the first optical assembly being arranged on the output face of the translucent screen, such that the first optical assembly is configured to form an intermediate image on the output face of the translucent screen; and - the second optical assembly being configured to project onto a projection surface an image of the intermediate image and the second optical assembly comprising at least one variable focal length projection lens.

[0010] For example, the translucent screen is defined by an optical blur greater than or equal to 15% and a transmission coefficient greater than or equal to 80%.

[0011] In particular, the oscillating mirror device comprises a mobile scanning mirror and a mechanical drive means: - the oscillating mirror device being configured to implement a “raster” type scan, the control unit being configured to vary the focal length of the at least one projection lens as a function of the movement of the scanning mirror along a defined axis and / or as a function of the movement of the light beam along a defined direction; or - the oscillating mirror device being configured to implement a vector type scan, the control unit being configured to vary the focal length of the at least one projection lens depending on the movement of the scanning mirror capable of moving the beam the light beam along at least one defined direction.

[0012] In particular, the laser transmitter comprises a plurality of RGB type laser light sources comprising red, green and blue laser light sources capable of projecting the at least one combined light beam onto the oscillating mirror device.

[0013] The invention also relates to a vehicle comprising an optical projection system according to the invention.

[0014] The invention finally extends to a method of projecting a light beam onto a projection surface by means of an optical system according to the invention, comprising varying the focal length of the at least one projection lens as a function of a position of the oscillating mirror device and / or as a function of a position of the at least one light beam in the projection surface.

[0015] In particular, the variation of the focal length of the at least one projection lens is carried out: - according to a progression that is at least partly linear; and / or - according to a progression by level(s) including at least one phase of focal stability.

[0016] Other details, characteristics and advantages will emerge more clearly on reading the detailed description given below, for informational and non-limiting purposes, in relation to the various exemplary embodiments illustrated in the following figures:

[0017] [Fig.1a] is a general schematic representation of an optical system comprising an adaptive projection lens in a vehicle projecting a light beam into a first position onto a projection surface.

[0018] [Fig.lb] is a general schematic representation of the optical system projecting the light beam into a second position on the projection surface.

[0019] [Fig.2] is a schematic representation of an example of variation of the focal length of an adaptive projection lens of the optical system.

[0020] [Fig. 3] is a schematic representation of a scan performed by a raster-type oscillating mirror device.

[0021] [Fig.4] is a schematic representation of a scan performed by a vector type oscillating mirror device.

[0022] [Fig.5a] is a schematic representation of a first example embodiment of the optical system comprising a translucent screen.

[0023] [Fig.5b] is a schematic representation of a second exemplary embodiment of the optical system comprising a translucent screen.

[0024] Figures 1 to 5b schematically illustrate exemplary embodiments of an optical system 1 according to the invention configured to project at least one beam luminous Fx on a projection surface 2. In particular, the optical system 1 is included in a motor vehicle 10. According to a non-limiting exemplary embodiment, the optical system 1 is included in a projector of the vehicle, in particular a front projector, so as to implement lighting and / or the projection of specific information on a projection surface 2 defined on the roadway. According to alternative exemplary embodiments, the optical system 1 is included in a rearview mirror, or side mirror, of the vehicle or at the level of a rocker panel of the vehicle so as to implement lighting and / or the projection of specific information on a portion of the roadway.

[0025] By convention in the description below, the direction in which the motor vehicle 1 moves in a straight line is defined as being the longitudinal direction X, the axis representing the longitudinal direction X being oriented, in a conventional manner, from front to rear. The direction perpendicular to the longitudinal direction and located in a plane parallel to the ground is called the transverse direction Y. The direction perpendicular to the directions X and Y, orthogonal to the ground on which the vehicle 1 rests, is called the vertical direction Z. This defines a direct reference XYZ represented in the figures requiring it. The terms “first” and “second” or “primary” and “secondary” are intended to distinguish similar elements and not to define a hierarchy within said elements. Also, the terms “upstream” and “downstream” refer to a direction of propagation of a light beam Fx considered.

[0026] In the illustrated example, the projection surface 2 is located, in a non-limiting manner, in front of the vehicle 1. In particular, the projection surface 2 has an inclined position relative to the optical system 1, that is to say relative to the headlight or the rearview mirror, such that distances Dx separating a point of the optical system 1 from different points of the projection surface 2 located at the level of the ground on which the vehicle rests are not equal. In particular, the optical system 1 is configured to project at least one grazing light beam Fx onto the projection surface 2. “Grazing” is understood to mean in particular a light beam Fx not projected perpendicular to the optical system 1.

[0027] The projection surface 2 considered may be more or less extensive. For example, the projection surface 2 extends over all or part of a possible projection zone of which a proximal limit Lp is, for example, located 15 cm, or even 30 cm, from the optical system 1 or the front of the vehicle 1 along a defined projection direction 500 and a distal limit Ld is located 1.5 m, or even 3 m from the optical system 1, the projection surface 2 being between the proximal limit Lp and the distal limit Ld. The proximal limit Lp thus corresponds to the limit of the projection surface closest to the optical system 1 or the front of the vehicle 1 while the distal limit Ld is the most distant limit. In particular, the projection direction 500 extends parallel, or substantially parallel, to the longitudinal direction X. The projection surface 2 is, according to a preferred embodiment, rectangular or substantially rectangular and is defined along a first direction 100, parallel to the projection direction 500 and extending between the proximal limit Lp and the distal limit Ld, and a second direction 200 perpendicular to the first direction 100.

[0028] Generally speaking, the optical system 1 according to the invention comprises a laser transmitter 3, an oscillating mirror device 4 and an optical device 5 comprising at least one variable focal length projection lens 51, also referred to as an adaptive projection lens 51 or “focus tunable lense” in English. Here, the term “variable focal length projection lens” means a projection lens whose focal length can be modified without mechanical movement of said lens within the optical system 1.

[0029] The laser transmitter 3 is configured to emit the at least one light beam Fx towards the oscillating mirror device 4 and through the optical device 5. The laser transmitter 3 bringing the at least one light beam Fx is not shown here in Figures 1a and 1b for the purpose of simplifying the representation of different projection positions of the at least one light beam Fx on the projection surface 2, it is nevertheless shown in [Fig. 5a] or [Fig. 5b], said representations applying mutatis mutandis to the examples shown in Figures 1a and 1b. Optionally but preferably, the laser transmitter 3 comprises a plurality of laser light sources. For example, said sources comprise red, green and / or blue laser light sources.In the case where the laser transmitter 3 comprises at least one red laser light source, one green laser light source and one blue laser light source, the laser transmitter 3 is then an “RGB laser transmitter”, making it possible to emit a light beam Fx of the desired color. Each laser light source of the laser transmitter 3 then emits a primary light beam Fx, and these primary light beams are combined to form the light beam Fx. The light beam Fx is then directed towards a reflective surface of the oscillating mirror device 4. In particular, the different laser light sources are controlled independently of each other. In particular, each of the light sources can be activated or deactivated independently of the activation or deactivation of the other light sources.

[0030] The oscillating mirror device 4 is configured to reflect the at least one light beam Fx emitted by the laser transmitter 3 towards the optical device 5 in order to form a final image Ifx on the projection surface 2. The at least one light beam Fx thus forms a light spot Tx on a reflective surface of the oscillating mirror device 4 which is then reflected.

[0031] The oscillating mirror device 4 comprises in particular, in a conventional manner, a mobile scanning mirror 41, which reflects the at least one light beam Fx as a function of an angle of rotation in which it is arranged, and a mechanical device 42 for oscillating the mirror. The scanning mirror 41 may be of any known type and driven according to conventional drive methods. As further described below, the scanning mirror 41 is moved within a defined scanning zone so as to move the at least one light beam Fx in the defined projection surface 2. Thus, for each position of the scanning mirror 41 the light beam Fx is returned in a given direction on the projection surface 2, i.e. between the proximal limit Lp and the distal limit Ld, and forms a primary image at a given instant. Each position of the scanning mirror 41 of the oscillating mirror device 4 thus forms a primary image.The superposition of the different primary images resulting from the different positions of the oscillating mirror device 4 forms the final image Ifx perceived by a user on the projection surface 2. Indeed, due to the retinal persistence of the observer, the latter does not distinguish the primary images, but perceives the image resulting from their superposition.

[0032] For example, the oscillating mirror device 4 is of the MEMS type, from the English “Micro Electro Mechanical Systems” meaning “micro-electromechanical system”, making it possible to orient each of the incident light beams according to a plurality of angular orientations over time.

[0033] According to an exemplary embodiment, the oscillating mirror device 4 is configured to implement a sequential two-dimensional scanning along lines to form an image on the projection surface 2, also known as "raster scan" or "raster scanning". The mechanical device 42 of the oscillating mirror device 4 makes it possible to oscillate the scanning mirror 41 around a pivot point within a scanning zone defined along a first axis and a second axis, orthogonal to each other. The movement of the oscillating mirror device 4 along the first axis, for example parallel to a vertical direction, is configured to allow a movement of the at least one light beam Fx along the first direction 100, visible in [Fig. 3], within the projection surface 2, that is to say here between the proximal limit Lp and the distal limit Ld.The movement of the oscillating mirror device 4 along the second axis, for example parallel to the horizontal direction, is configured to allow a movement of the at least one light beam along the second direction 200 of the projection surface 2 between two extreme edges B1, B2 here delimiting a width of the projection surface 2.

[0034] Particularly, in the case of a “raster” type scan, an oscillation speed along the first direction 100 is strictly less than an oscillation speed along the second direction 200. The second axis thus corresponds to a fast axis along which the oscillating mirror device 4 is in resonance while the first axis corresponds to a slow axis of mechanical detachment of the oscillating mirror device 4. The oscillating mirror device 4 is thus configured to take a plurality of different angular orientations and to pass from one to the other of these angular orientations at very high frequency.

[0035] For example, a scan along the second axis, i.e. between the extreme edges B1, B2 of the projection surface 2, oscillates at a frequency of the order of 1 KHz while the scan along the first axis, i.e. here between the proximal limit Lp and the distal limit Ld of the projection surface 2, is carried out at a frequency of the order of 50 Hz.

[0036] Optionally, additionally or alternatively, a scanning time of the oscillating mirror device 4 along the first axis, i.e. along the slow axis, and allowing projection at different points along the first direction 100 is strictly greater than 1 ms, or even strictly greater than 10 ms. In particular, a scanning time of the oscillating mirror device 4 along the first axis is of the order of 16 ms. Conversely, a scanning time of the oscillating mirror device 4 along the second axis, corresponding to the fast axis, so as to allow projection of the light beam Fx along the second direction 200 is strictly less than 1 ms, or even 100 ps. In particular, a scanning time of the oscillating mirror device 4 along the second axis is of the order of 28 ps.

[0037] In particular, the orientation of the oscillating mirror device 4 and the scanning speed thereof along the first direction 100 and the second direction 200 are adapted and defined as a function of a reaction time of the at least one adaptive projection lens 51, as further detailed below. Conventionally, adaptive projection lenses have a reaction time of the order of 1 ms. Also, for example, a scanning time of the oscillating mirror device 4 along the first axis and of projection of the light beam along the first direction 100 is strictly greater than the reaction time of the at least one adaptive projection lens 51, i.e. 1 ms.Conversely, for example, a scanning time of the oscillating mirror device 4 along the second axis so as to allow a projection of the light beam Fx along the second direction 200 is strictly less than the reaction time of the at least one adaptive projection lens 51, i.e. strictly less than 1 ms.

[0038] According to an alternative embodiment, the oscillating mirror device 4 is configured to implement a “vector” type scan in order to form the final image Ifx on the projection surface 2. Similar to what has been explained above, the mechanical device 42 of the oscillating mirror device 4 makes it possible to oscillate the scanning mirror 41 within the scanning area so as to move the at least one light beam Fx. In particular, vector scanning allows the movement of the light beam Fx along a path directly tracing the shapes and contours of a pattern or information to be projected onto the projection surface 2. The path thus traced varies depending on the pattern or information to be projected. The movement of the oscillating mirror device 4 allows the free movement of the light beam Fx within the projection surface 2, that is to say in the entire dimension defined along the first direction 100 and in the entire dimension defined along the second direction 200. Also, in such an alternative, the movements of the scanning mirror 41 are not limited along axes defined as explained above. In particular, such scanning is devoid of fast or slow axes and is not carried out in resonance.

[0039] For example, as further explained below, a scanning duration of the oscillating mirror device 4 between two distinct positions of the oscillating mirror device 4, corresponding to the projection of two successive primary images, is strictly greater than 1 ms, or even 10 ms. In particular, such a scanning duration between two distinct positions of the oscillating mirror device 4 is of the order of 16 ms.

[0040] Independently of the type of oscillating mirror device 4 implemented, the laser transmitter 3 is, optionally but preferably, capable of varying an intensity of the light beam Fx over the course of the scanning carried out in order to define the pattern or information to be projected as a function of the position of the oscillating mirror device 4.

[0041] The optical projection device 5 is arranged downstream of the oscillating mirror device 4 in a direction of propagation of the at least one light beam Fx. In general, the optical projection device 5 comprises the at least one projection lens 51 and a control unit 52. As detailed further below, the control unit 52 is advantageously capable of modifying the focal length of the at least one projection lens 51 as a function of a position of the oscillating mirror device 4.

[0042] Optionally, as illustrated in [Fig.2], the at least one projection lens 51 comprises an electromagnetic element 53 and a liquid portion 54. The electromagnetic element 53 forms a frame surrounding the liquid portion 54 continuously. For example, the electromagnetic element 53 is made of an electrically conductive metallic material such as copper or aluminum. The liquid portion 54 is arranged in a casing 55, in particular made of electroactive polymer, and comprises a transparent liquid material such as water, oil, an organic solution, a liquid polymer or a mixture of liquid polymers.

[0043] The control unit 52 is configured to circulate an electric current through the electromagnetic element 53, thereby generating an electric field then exerting pressure on the liquid portion 54, in particular on the envelope 55 surrounding it. The control unit 52 is also configured to vary a voltage of the electric current so as to vary characteristics of the liquid portion 54 and thus modify the focal length of the at least one projection lens 51 as a function of the position of the oscillating mirror device 4. In particular, the variation of the voltage of the electric current results in a variation of the shape of the liquid portion 54 and particularly of the shape of a curve of a diopter of the liquid portion 54. The term "diopter" means the interface between the liquid portion 54 and the air surrounding the at least one projection lens 51. The focal length of the at least one projection lens 51 can then be modified as a function of the refractive index of the liquid portion 54 and of the electric current flowing through the electromagnetic element 53.

[0044] According to known alternative examples, not detailed, the at least one projection lens 51 is a liquid lens actuated by electrowetting or with a piezoelectric actuator.

[0045] As indicated above, in a conventional manner, the reaction time of the at least one adaptive projection lens 51 to change shape following the transmission of an instruction by the control unit 52 is of the order of 1 ms.

[0046] Figures 3 and 4 illustrate an example of the path of the light beam Fx within the projection surface 2 as a function of successive positions of the oscillating mirror device 4 for a “raster” type scan and for a vector type scan respectively.

[0047] In the example illustrated, in [Fig. 3], representative of the “raster” type scan, the path considered begins at the top, to the left of the projection zone, at the initial point PL. The oscillating mirror device 4 is controlled so that the light beam Fx is moved along a first line L1 extending parallel to the second direction 200, between the extreme edges B1, B2 of the projection surface 2, that is to say here along a width of the projection surface 2. In particular, according to the example illustrated, the light beam Fx is moved along the first line L1 from a first extreme edge B1 and towards an opposite second extreme edge B2.The control unit 52 is configured to vary the focal length of the at least one projection lens 51 as a function of the movement of the scanning mirror 41 along the first axis and therefore as a function of the movement of the light beam Fx along the first direction 100, that is to say as a function of the position, along the first direction 100, of a line traveled within the projection surface 2. In particular, an electric current is applied continuously through the at least one projection lens 51, the voltage of said current being modulated by the control unit 52 in order to vary the focal length as a function of the position of the device. oscillating mirror 4, particularly of the position of the light beam Fx along the first direction 100.

[0048] At the same time, the laser transmitter 3 is in operation as long as the light beam Fx is moved between the extreme edges Bl, B2 of the projection surface 2.

[0049] When the light beam Fx reaches one of the extreme edges B1, B2, here the second extreme edge B2, the laser transmitter 3 is interrupted in order to allow the movement of the oscillating mirror device 4 along the first axis so as to move the position of the light beam Fx along the first direction 100, in anticipation of its movement along a second line L2, distinct from the first line L1 and extending parallel to the second direction 200 and to the first line L1. On the other hand, the electric current flowing through the at least one projection lens 51 is maintained when the oscillating mirror device 4 is moved between the different projection lines along the first direction 100.

[0050] Then, the laser transmitter 3 is put back into operation in order to allow the movement of the light beam Fx along the second line L2 between the extreme edges B1, B2, in particular here from the second extreme edge B2 and towards the first extreme edge B1. Again, when the light beam Fx reaches the limit of the projection surface 2, here the first extreme edge B1, the laser transmitter 3 is interrupted in order to allow the movement of the oscillating mirror device 4 along the first axis in order to move the position of the light beam along the first direction 100, here in anticipation of its movement along a third line L3, distinct from the first line L1 and the second line L2 and extending parallel to them and to the second direction 200.

[0051] Such a principle is repeated for a plurality of lines extending parallel to the second direction 200 and each having a different position along the first direction 100, i.e. a different proximity relative to the proximal limit Lp and to the distal limit Ld, up to a final position of the light beam Fx, here for example represented by the end point Pf. The laser transmitter 3 is thus kept in operation for the time of the movement of the light beam Fx along each line considered, corresponding to a movement of the light beam Fx from the first extreme edge B1 towards the second extreme edge B2, here in the case of lines of odd number, or vice versa in the case of lines of even number.The operation of the laser transmitter 3 is interrupted each time the light beam Fx reaches one of the edges of the projection surface 2 in order to allow the execution of a displacement of the oscillating mirror device 4 along the first axis and the transition from a line n to an adjacent line n+1. When the light beam Fx reaches the end point Pf, the laser transmitter 3 is switched off and the device . oscillating mirror 4 is moved to return to its initial, or nominal, position configured to allow the projection of the beam, as illustrated in [Fig.3] by the solid line plot. Advantageously, a time required for the movement of the oscillating mirror device 4 from the end point Pf to the initial point PI is strictly greater than the reaction time of P at least one projection lens 51.

[0052] At the same time, the electric current applied to the at least one adaptive projection lens 51 is applied continuously between the time when the light beam Fx is arranged at the initial point PI of the scan and the time when the light beam Fx is arranged at the end point Pf of the scan. Such a principle makes it possible to preserve the integrity of the electromagnetic element 53 by limiting the interruption of the electric current. Similarly, during the movement of the oscillating mirror device 4 from the end point Pf to the initial point PI, the electric current applied to the at least one adaptive projection lens 51 is maintained and the voltage value can be adjusted as required, the duration necessary for such a movement being adapted to allow said lens to apply such a setpoint.For example, during such a movement, the voltage of the electric current is raised to a predefined highest value, in particular corresponding to the voltage value to be applied to the initial point PI and, as the oscillating mirror 4 moves along the first direction 100, i.e. along the different lines considered, the voltage of the electric current is lowered until it reaches a predefined lowest value, in particular corresponding to the voltage value to be applied to the final point Pf. Indeed, a low voltage will result in obtaining a low curvature of the at least one projection lens 51 and therefore a lower optical power, i.e. here a long focal length adapted for greater proximity to the distal limit Ld.Conversely, a higher voltage results in a greater curvature of the at least one projection lens 51 and therefore a higher optical power, i.e. a short focal length adapted for greater proximity to the proximal limit Lp.

[0053] The control unit 52 continuously applies an electric current to the at least one adaptive projection lens 51 during the movement of the oscillating mirror device 4 along the first direction 100 so as to modulate the focal length of the at least one projection lens 51 as needed depending on the position, along the first direction 100, of the line traveled by the light beam Fx at a given instant. In particular, the control unit 52 is configured to vary the focal length of the at least one projection lens 51 depending on the proximity of the at least one light beam Fx to the distal limit Ld and / or the proximal limit Lp of the projection surface 2. In other words, the control unit 52 is configured to vary the focal length of the at least one projection lens 51 depending on the distance Dx separating the optical system 1, in particular the at least one adaptive projection lens 51, from a point of the projection surface 2 to the ground onto which a primary image is projected at a given instant in order to obtain the final image Ifx. Such a distance Dx is in particular determined along an axis perpendicular to the at least one projection lens 51 passing through the point considered, as illustrated schematically in [Fig.la] or 1b.

[0054] For example, the greater the proximity of the light beam Fx to the distal limit Ld of the projection surface 2, the greater the focal length. In particular, the greater the focal length, the lower the voltage of the applied electric current. In other words, the greater the distance Dx separating the optical system 1 from the point of the projection surface 2 onto which a primary image is projected at a given instant in order to obtain the final image Ifx, the greater the focal length and the lower the voltage of the electric current.

[0055] The variation of the focal length of the at least one projection lens 51 is thus synchronized with the movement of the oscillating mirror device 4, particularly with its movement along the first axis so as to allow the movement of the light beam along the first direction 100, here between the different lines. The orientation of the oscillating mirror device 4 is advantageously defined so that the speed of movement of the oscillating mirror device 4 along the first axis, and by extension the speed of movement of the light beam Fx along the first direction 100, is adapted to the reaction time of the at least one projection lens 51 for each of said lines.The positioning of the oscillating mirror device 4 so that the first direction 100 extends parallel to, or substantially to, the projection direction 500 of the projection surface 2 makes it possible to adjust the focal length of the at least one projection lens 51 as the oscillating mirror device 4 moves over the parts of the projection surface 2 furthest from the optical system 1 and the vehicle 10 most likely to have reduced sharpness in the optical systems of the prior art, i.e. here as a function of the movement of the oscillating mirror 4 from one line to the other.

[0056] As further explained below, with reference to the method according to the invention, the variation of the focal length of the at least one projection lens 51 and / or of the voltage of the electric current applied thereto can evolve in a continuous linear manner or in a continuous manner in stages.

[0057] In the example illustrated in [Fig. 4], representative of vector type scanning, the path considered begins at an initial point PI specific to a pattern or information to be projected, to be distinguished from a nominal point PO, corresponding to the position of the light beam Fx when the oscillating mirror device 4 is in a nominal, or rest, position. In such an exemplary embodiment, the laser transmitter 3 is, for example, in operation as long as the light beam Fx is moved between the initial point PI and the end point Pf of the pattern or information to be projected. When a continuous pattern is traced, the laser emitter 3 is switched on throughout the tracing of the pattern. Conversely, when the pattern to be traced is discontinuous, the laser emitter 3 can be switched off during the tracing. Note that the initial point PI of the pattern can be located in a part of the projection surface 2 distinct from the nominal point PO. Also, the laser emitter 3 can be switched off during a movement of the oscillating mirror device 4 between a nominal position, allowing the light beam Fx to be projected at the nominal point PO, and an initial position, allowing the light beam Fx to be projected at the initial point PI of the pattern or information considered. The laser emitter 3 is also switched off to allow the oscillating mirror device 4 to return to the nominal position when the end point Pf of the pattern or information is distinct from the nominal point PO.

[0058] The oscillating mirror device 4 is controlled so as to direct the light beam Fx along a contour defining said pattern or said information within the projection surface 2. The oscillating mirror device 4 can thus move in a less restrictive manner than in the case of a raster-type oscillating mirror device 4. Similar to what has been explained previously, the control unit 52 is configured to vary the focal length of the at least one adaptive projection lens 51 as a function of the position of the oscillating mirror device 4. Thus, an electric current is applied to the at least one projection lens 51 and maintained continuously when the oscillating mirror device 4 is moved and the voltage of the electric current exerted is adapted as a function of the position of the light beam Fx device in the projection surface 2.

[0059] The oscillating mirror device 4 here having a movement slower than the reaction speed of the at least one adaptive projection lens 51, the variation of the focal length of the at least one projection lens 51 is synchronized with the movement of the oscillating mirror device 4 so as to move the light beam Fx along the first direction 100 and / or the second direction 200. Note that, between two positions of the oscillating mirror device 4, the speed of movement of the latter may be caused to vary between a low speed limit and a high speed limit. Also, the vector type oscillating mirror device 4 tends to have a lower movement speed than the “raster” type oscillating mirror device 4 described previously.For example, the vector-type oscillating mirror device 4 has a maximum speed of the order of 5 KHz, such a speed being able to vary according to the movements made between two positions. For example, such a speed is of the order of 1 Hz in the case of a turn.

[0060] According to a non-limiting example, the variation of the focal length of the at least one projection lens 51 depends on the proximity of the light beam Fx with the distal limit Ld. and the proximal limit Lp of the projection surface 2, in other words, it is a function of the distance separating an illuminated point of the oscillating mirror device 4 from a point of the projection surface 2 similarly to what has been described previously.

[0061] For example, the greater the proximity to the distal limit Ld of the projection surface 2, the greater the focal length must be and the lower the voltage of the applied electric current, as described above.

[0062] In other words, the control unit 52 is configured to vary the focal length of the at least one projection lens 51 as a function of the distance Dx separating the optical system 1, in particular the at least one adaptive projection lens 51, from a point of the projection surface 2 onto which a primary image is projected at a given instant in order to obtain the final image Ifx.

[0063] Optionally, independently of the type of movement of the oscillating mirror device 4 implemented, the control unit 52 is configured to vary an intensity of the at least one light beam Fx emitted by the laser emitter 3, in particular of at least one laser light source, in order to ensure suitable and homogeneous illumination of the final image Ifx perceived on the projection surface 2. Indeed, the illumination of an area of ​​the final image Ifx projected on the projection surface 2 depends on the light intensity and the projection distance. Conventionally, for a constant light intensity, the illumination decreases with the projection distance. Here, for example, the term "projection distance" is understood to mean the distance separating the pivot point of the oscillating mirror device 4 and a point on the projection surface 2 onto which the light beam Fx is projected at a given instant.Indeed, due to the grazing effect and due to the movement of the oscillating mirror device 4, the projection distance is caused to change. Also, according to a preferred example, in order to ensure uniformity of illumination within the projection surface 2, the light intensity of the at least one light beam Fx emitted by the laser transmitter 3 increases proportionally to the projection distance as a function of the position of the oscillating mirror device 4 at a given instant.

[0064] It should be noted that, optionally but preferably, the light beam Fx arrives collimated on the oscillating mirror device 4 while the optical projection device 5 is capable of converging rays of said beam, here particularly at a given distance corresponding to the projection distance.

[0065] According to a particular, optional exemplary embodiment, the optical device 5 comprises a first optical assembly 6, a second optical assembly 7 and a translucent screen 8, interposed between the first optical assembly 6 and the second optical assembly 7, the second optical assembly 7 comprising the at least one adaptive projection lens 51 described previously.

[0066] In particular, the translucent screen 8 is arranged so that an input face 81 of said screen is turned towards the first optical assembly 6 while an output face 82 of said screen, opposite the input face 81, is turned towards the second optical assembly 7.

[0067] Preferably, the first optical assembly 6 comprises a primary projection lens or a plurality of primary projection lenses. The first optical assembly 6 is interposed between the oscillating mirror device 4 and the translucent screen 8 so that it is configured to form an intermediate image Ix of the light spot Tx, projected onto the oscillating mirror device 4, on the output face 82 of the translucent screen 8.

[0068] The second optical assembly 7 is configured to project, or image, the intermediate image Ix onto the projection surface 2 so as to form the final image Ifx there. As explained above, according to non-limiting exemplary embodiments, the projection surface 2 is an inclined surface, in particular relative to the second optical assembly 7 and / or relative to the translucent screen 8.

[0069] The translucent screen 8 is arranged within the optical device 5 so as to be interposed between the first optical assembly 6 and the second optical assembly 7. Consequently, the translucent screen 8 is interposed between the second optical assembly 7, particularly the at least one adaptive projection lens 51, and the oscillating mirror device 4. In this way, when the eye of an observer observes the optical system 1 according to the invention, it perceives the at least one light beam Fx at the second optical assembly 7 and / or the intermediate image Ix projected at the translucent screen 8 instead of directly perceiving the light spot Tx projected at the oscillating mirror device 4, regardless of whether the eye is at rest or in the accommodation phase, also referred to as focusing. Such a principle thus advantageously makes it possible to optimize the ocular safety of an observer located in the vicinity of the optical system 1 or the vehicle.

[0070] In particular, the translucent screen 8 is arranged so that an image focus Fli of the first optical assembly 6 is arranged on the output face 82 of the translucent screen 8 or substantially on the output face 82. Here, the term “substantially” means that the position of the image focus Fli of the first optical assembly 6 is located at ±1.00 mm, or even at ±500 pm or even ±300 pm from the output face 82 of the translucent screen 8.

[0071] Optionally, the translucent screen 8 is arranged so that an object focus F2o of the second optical assembly 7 is arranged at the exit face 82 of the translucent screen 8, in particular so as to be merged with the image focus Fli of the first optical assembly 6. Such a principle can in particular be implemented when the at least one light beam Fx is collimated. Rays forming the at least one light beam Fx exiting from the second optical assembly 7 extend then parallel or substantially parallel to each other. In particular, the optical device 5 is then afocal.

[0072] Alternatively, the translucent screen 8 is arranged so that the object focus F2o of the second optical assembly 7 extends between the exit face 82 of the translucent screen 8 and the second optical assembly 7. More particularly, the object focus F2o of the second optical assembly 7 is arranged between the image focus Fli of the first optical assembly 6 and the second optical assembly 7. Such a principle can in particular be implemented in the case of a non-collimated light beam Fx converging downstream of the exit face 82 of the translucent screen 8 in the direction of propagation of the at least one light beam Fx. Such a principle is in particular implemented in the case of projection of information onto a projection surface 2 located at a given, predefined projection distance. Rays of the at least one light beam Fx exiting from the second optical assembly 7 then converge towards each other.Such a principle makes it possible to minimize the size of the intermediate image Ix projected onto the intermediate screen in order to optimize its resolution and sharpness while ensuring the ocular safety of an observer due to the presence of the translucent screen 8 by preventing the accommodation of the eye on the oscillating mirror device 4.

[0073] Thus, for example, the object focus F2o of the second optical assembly 7 is separated from the image focus Fli of the first optical assembly 6 by a distance less than or equal to 1.00 mm, or even less than or equal to 300 pm, such a distance being zero when said foci are merged, as indicated above, and not zero when said foci are distinct.

[0074] In particular, a distance separating the output face 82 of the translucent screen 8 from the second optical assembly 7, for example from a surface of the at least one adaptive projection lens 51, is defined by the following relation: De_opt2 — Qpj - c|f2 )

[0075] Where: De_opt2 is the distance separating the output face 82 of the translucent screen 8 from the second optical assembly 7; df2 is the focal length of the second optical assembly 7, in particular of the at least one adaptive projection lens 51; dpj is the distance between the second optical assembly 7, for example at the surface of the at least one adaptive projection lens 51, and the projection surface 2.

[0076] The translucent screen 8 has in particular the function of a diffuser, that is to say that it partly allows the light beam Fx to be diffused or split and to modify, in particular increase, the angular size and the size of the retinal image of the final image Ifx relative to the size of the light spot Tx projected onto the oscillating mirror device 4. For an external observer, the intermediate image Ix projected onto the translucent screen 8 is then the image of the projected source and thus becomes the point of accommodation of the observer's eye, for accommodation at infinity of the eye or for the eye at rest, instead of the light spot Tx projected onto the oscillating mirror device 4, even in the event of failure or blockage of the oscillating mirror device 4.

[0077] Thus, the first optical assembly 6 creates, on the translucent screen 8, an intermediate image Ix of the light spot Tx projected onto the oscillating mirror device 4 while the second optical assembly 7 reproduces the intermediate image Ix on the projection surface 2. Advantageously, the second optical assembly 7 makes it possible to increase the dimension of the final image Ifx, projected onto the target projection surface 2 relative to a dimension of the intermediate image Ix. The size of at least one light beam Fx is thus greater at the output of the optical system 1, i.e. downstream of the second optical assembly 7, than at the input thereof, i.e. upstream of the oscillating mirror device 4.

[0078] In the absence of the translucent screen 8, the observer's eye directly perceives the light spot Tx projected onto the oscillating mirror device 4 and the apparent angle of the projected image, and consequently the retinal image, is smaller. It is therefore necessary to limit the brightness, in other words, the light illumination, of the laser emitter 3 in order to ensure the ocular safety of any observer present. The integration of the translucent screen 8 advantageously makes it possible to overcome such a limitation since the observer can no longer directly perceive the light spot Tx formed by the laser emitter 3 on the oscillating mirror device 4.

[0079] In such an exemplary embodiment, the oscillation frequency of the oscillating mirror device 4 is thus not limited as a function of the brightness of the laser emitter 3. For example, such an oscillation frequency may be of the order of 25 KHz for at least one of the axes. According to a particular, non-limiting example, the oscillation frequency is between 10 Hz and 200 Hz, in particular of the order of 50 Hz, along the slow axis, that is to say here for a scan along the first axis and a light beam Fx moving along the first direction 100, and of the order of 5 to 60 KHz along the fast axis, that is to say here for a scan along the second axis and a light beam Fx moving along the second direction 200.

[0080] According to exemplary embodiments, the translucent screen 8 is made of a material selected from glass, plastic, such as polycarbonate or even ceramic. For example, the translucent screen 8 is obtained by injection, overmolding and / or photolithography. It is, for example, sized so as to have a surface greater than or equal to a surface of the first optical assembly 6, for example of the primary projection lens, and / or greater than or equal to a reflective surface of the oscillating mirror device 4.

[0081] Preferably, the translucent screen 8 has a transmission coefficient greater than or equal to 80%. In particular, the transmission coefficient is measured in a conventional manner by flux measurement with an integrating sphere and without passing through the translucent screen 8.

[0082] The translucent screen 8 also has an at least partial obstruction function by preventing direct visibility of the oscillating mirror device 4, and particularly of the light spot Tx projected onto it. In particular, preferably, the translucent screen 8 is defined by a level of optical blur greater than or equal to 15%. The term "optical blur" means a veil, also referred to as reflection mist or "haze" in English. The term "level of optical blur" means the percentage of light dispersed outside a cone of 2.5° centered on an optical axis of the optical system 1. In this way, the at least one light beam Fx is able to propagate through the translucent screen 8 but the accommodation of the eye of an observer on the oscillating mirror device 4 is not possible.

[0083] According to exemplary embodiments, the translucent screen 8 has an optical blur of the surface, volume or holographic type.

[0084] A translucent screen 8 of surface type has a mist at least arranged on one of the faces of the translucent screen 8, in particular at least on the exit face 82 thereof. Preferably, such a translucent screen 8 has a level of optical blur greater than or equal to 15%.

[0085] A translucent screen 8 of the volume type has a haze over all or part of a thickness of the translucent screen 8, corresponding to the dimension between the entry face 81 and the exit face 82. Preferably, the translucent screen 8 then has a level of optical blur greater than or equal to 20%, or even 22%.

[0086] A translucent screen 8 of holographic type comprises patterns or microstructures, optionally combined with a mist, in particular at the exit face 82. In particular, said patterns or microstructures have a regular periodicity. Said patterns are of the order of a micrometer and are arranged so as to diffuse the at least one light beam Fx in a privileged field of vision. Preferably, the translucent screen 8 then has a level of optical blur greater than or equal to 25%, or even 27%.

[0087] Optionally, all or part of the thickness of the translucent screen 8, between the entry face 81 and the exit face 82, has a heterogeneous structure.

[0088] In particular, the heterogeneous structure of the translucent screen 8 comprises a plurality of microstructures selected from: - heterogeneous graining arranged at the level of all or part of the output face 82 82; and / or - a plurality of microscopic prisms; and / or - an irregular heterogeneous holographic pattern.

[0089] The heterogeneous structure of the translucent screen 8 thus depends on the texturing thereof.

[0090] The term “graining” means that the translucent screen 8, in particular the exit face 82, comprises a plurality of grains. The heterogeneity of the structure is then obtained by heterogeneity of shapes, dimensions, refractive index of said grains and / or heterogeneity of distribution, or density, of said grains within the translucent screen 8. For example, the grains have dimensions of the order of 1 to 10 μm.

[0091] By “microscopic prisms” is meant that the translucent screen 8, in particular the exit face 82, comprises a plurality of polyhedra whose dimensions may be of the order of 1 to 10 μm. The heterogeneity of the structure is then obtained by heterogeneity of shapes, dimensions, refractive index, and / or distribution, or density, of said prisms within the translucent screen 8.

[0092] The term “holographic pattern” means that the translucent screen 8, in particular the output face 82, comprises a plurality of holograms corresponding to microstructures with regular periods. The heterogeneity of the structure is then obtained by heterogeneity of shapes, dimensions, inclination, refractive index, and / or distribution, or density, of said holograms within the translucent screen 8.

[0093] The invention also extends to a method of projecting a light beam Fx onto a projection surface 2 by means of an optical system 1 according to the invention. Such a method can also be described as a method of controlling an optical system 1 according to the invention or as a method of operating a vehicle being equipped with such an optical system 1. It is understood that the above description, relating to the optical system 1, applies here mutatis mutandis to the method and vice versa.

[0094] The method comprises the projection of at least one light beam Fx onto the projection surface 2 comprising the variation of the focal length of the at least one projection lens 51 as a function of a position of the oscillating mirror device 4 between different instants tx considered. As described previously, the variation of the focal length of the at least one adaptive projection lens 51 is, for example, carried out by applying an electric current through at least a portion of said lens and by varying a voltage of said electric current. It is understood that the alternatives described above apply here mutatis mutandis.

[0095] In particular, as explained above with reference to the optical system 1, the method is executed so that the projection of the at least one light beam Fx is put implemented by a sequential two-dimensional scan along lines to form an image on the projection surface 2, also called a “raster” type scan, or by a free scan following a path representative of an outline of a pattern or information to be projected, i.e. a vector type scan, as described above.

[0096] In particular, when the method implements raster type scanning, the control unit 52 is configured to vary the focal length of the at least one projection lens 51 as a function of the movement of the scanning mirror 41 along at least one direction, in particular along the first axis so as to allow the movement of the light beam Fx along the first direction 100.

[0097] Optionally but preferably, independently of the type of scanning implemented, the control unit 52 is configured to vary the focal length of the at least one projection lens 5 by varying the voltage of the electric current exerted at the level of the at least one projection lens 51, as a function of the position of the oscillating mirror device 4 and, consequently, as a function of the position of the at least one light beam Fx in the projection surface 2.In particular, such a variation is carried out as a function of a proximity of the light beam Fx to the proximal limit Lp of the projection surface 2, corresponding to the limit of said surface closest to the at least one projection lens 51, and / or as a function of a proximity of the light beam Fx to the distal limit Ld of the projection surface 2, corresponding to the limit of said surface furthest from the at least one projection lens 51 while evolving along the first direction 100. For example, the greater the proximity to the distal limit Ld of the projection surface 2, the greater the focal length and, in particular, the lower the voltage of the electric current exerted.

[0098] In other words, in the case of a projection surface 2 inclined relative to the optical system 1, in particular relative to the at least one projection lens 51, the control unit 52 is configured to vary the focal length of the at least one projection lens 51 as a function of the distance Dx separating the at least one adaptive projection lens 51 from a point on the ground of the projection surface 2 onto which a primary image is projected at a given instant in order to obtain the final image Ifx.

[0099] According to alternative embodiments, the variation of the focal length of the at least one adaptive projection lens 51 is carried out: - according to an at least partly linear progression; or - according to a progression in stages.

[0100] Here, a linear progression is understood to mean that the focal length of the at least one projection lens 51 and / or the voltage of the electric current applied to it evolves continuously along a linear line defined as a function of the position of the oscillating mirror device 4. In particular, the position of the oscillating mirror device 4 is defined as a function of position coordinates of the light beam Fx at a given instant along the first direction 100 and / or as a function of a proximity of the at least one light beam Fx projected onto the projection surface 2 for the position considered relative to the proximal limit Lp and / or to the distal limit Ld of the projection surface 2. Alternatively again, the linear progression of the focal length of the at least one projection lens 51 and / or of the voltage of the electric current applied thereto evolves continuously as a function of the distance Dx separating the optical system 1, in particular the at least one adaptive projection lens 51, from a point of the projection surface 2 onto which a primary image is projected at a given instant in order to obtain the final image Ifx.

[0101] Such a principle allows a progressive and continuous evolution of the voltage value so as to maintain optimal sharpness of the final image Ifx over the entire projection surface 2, in particular along the first direction 100.

[0102] A stepwise progression is understood to mean that the variation of the focal length of the at least one projection lens 51 and / or of the voltage of the electric current applied thereto comprises intermediate phases of stability in its evolution. Thus, for example, a first focal length value of the at least one projection lens 51 and / or of the voltage of the electric current is applied for any position of the oscillating mirror device 4 lower than a first position threshold within the scanning zone, that is to say any position for which the light beam is between the proximal limit Lp of the projection surface 2 and an intermediate limit corresponding to a position of the light beam Fx when the oscillating mirror device 4 is in the position of the first threshold.In particular, the position of the oscillating mirror device 4 is defined as a function of position coordinates of the light beam Fx along the first direction 100, the first position threshold then corresponding to a position coordinate limit threshold along the first direction 100. Alternatively or additionally the position threshold is defined as a function of a proximity of the at least one light beam Fx projected onto the projection surface 2 relative to the proximal limit Lp and / or the distal limit Ld of the projection surface 2. Such a principle can be repeated for a plurality of position thresholds and associated focal length values.

[0103] Alternatively, the progression by stages of the focal length of the at least one projection lens 51 and / or of the voltage of the electric current applied to it applies mutatis mutandis to an evolution defined as a function of the distance separating the optical system 1, in particular the at least one adaptive projection lens 51, from a point on the ground of the projection surface 2 onto which a primary image is projected at a given instant in order to obtain the final image Ifx.

[0104] The optical system 1 and the method according to the invention thus advantageously make it possible to adapt the focal length of the at least one adaptive lens as a function of the distance at which the image is projected and / or as a function of the position of the oscillating mirror device 4. The invention is adapted to the reaction time necessary for said lens to adapt its focal length and allows simple control thereof.

[0105] Such a principle makes it possible to maintain the level of sharpness of the final image Ifx at a level higher than a minimum acceptable sharpness threshold over the entire projection surface 2, in particular along the first direction 100, while minimizing the focal length variations of the at least one projection lens 51.

[0106] The invention thus advantageously makes it possible to optimize the quality of the final image projected onto various projection surfaces by ensuring a level of sharpness adapted to projection onto large projection surfaces, in particular by means of a grazing light beam. The invention also advantageously makes it possible to optimize the illumination of the final image so as to ensure its homogeneity.

[0107] The present invention cannot, however, be limited to the means and configurations described and illustrated here and it also extends to any equivalent means or configuration and to any technically operative combination of such means insofar as they ultimately fulfill the functionalities described and illustrated in the present document.

Claims

Claims

1. Optical projection system (1), in particular for a motor vehicle (10), comprising: - a laser transmitter (3) configured to emit at least one light beam (Fx); - an oscillating mirror device (4) configured to reflect the at least one light beam (Fx) towards a projection surface (2); and - an optical projection device (5) arranged downstream of the oscillating mirror device (4) in a direction of propagation of the at least one light beam (Fx) and comprising at least one projection lens (51); characterized in that the at least one projection lens (51) comprises a variable focal length and in that the optical system (1) comprises a control unit (52) capable of modifying the focal length of the at least one projection lens (51) as a function of a position of the oscillating mirror device (4) and / or as a function of a position of the at least one light beam (Fx) in the projection surface (2).

2. Optical projection system (1) according to the preceding claim, wherein the at least one projection lens (51) comprises an electromagnetic element (53) and a liquid portion (54), the control unit (52) being configured to circulate an electric current through the electromagnetic element (53) and to vary a voltage of said electric current so as to vary the focal length of the at least one projection lens (51).

3. Optical projection system (1) according to one of the preceding claims, wherein the control unit (52) is configured to vary an intensity of the at least one light beam (Fx) emitted by the laser transmitter (3) as a function of the position of the oscillating mirror device (4) and / or as a function of a position of the at least one light beam (Fx) in the projection surface (2) so as to ensure uniformity of illumination within the projection surface (2).

4. Optical projection system (1) according to one of the preceding claims, in which the optical device (5) comprises a first optical assembly (6), a second optical assembly (7) and

5.

6.

7. a translucent screen (8), interposed between the first optical assembly (6) and the second optical assembly (7): - the translucent screen (8) comprising an entry face (81) facing the first optical assembly (6) and an exit face (82), opposite the entry face, and facing the second optical assembly (7); - an image focus (Fli) of the first optical assembly (6) being arranged on the output face (82) of the translucent screen (8), so that the first optical assembly (6) is configured to form an intermediate image (Ix) on the output face (82) of the translucent screen (8); and - the second optical assembly (7) being configured to project onto a projection surface (2) an image of the intermediate image (Ix) and the second optical assembly (7) comprising at least one projection lens (51) with variable focal length. Optical projection system (1) according to the preceding claim, in which the translucent screen (8) is defined by an optical blur greater than or equal to 15% and a transmission coefficient greater than or equal to 80%. Optical projection system (1) according to one of the preceding claims, in which the oscillating mirror device (4) comprises a movable scanning mirror (41) and mechanical drive means: - the oscillating mirror device (4) being configured to implement a "raster" type scan, the control unit (52) being configured to vary the focal length of the at least one projection lens (51) as a function of the movement of the scanning mirror (41) along a defined axis and / or as a function of the movement of the light beam (Fx) along a defined direction; Or - the oscillating mirror device (4) being configured to implement a vector type scan, the control unit (52) being configured to vary the focal length of the at least one projection lens (51) as a function of the movement of the scanning mirror (41) capable of moving the light beam (Fx) along at least one defined direction. Optical projection system (1) according to one of the preceding claims, in which the laser emitter (3) comprises a plurality of RGB type laser light sources comprising red, green and blue laser light sources capable of projecting the at least one combined light beam (Fx) onto the oscillating mirror device (4).

8. Vehicle comprising an optical projection system (1) according to one of the preceding claims.

9. A method of projecting a light beam (Fx) onto a projection surface (2) by means of an optical system (1) according to one of claims 1 to 7, comprising varying the focal length of the at least one projection lens (51) as a function of a position of the oscillating mirror device (4) and / or as a function of a position of the at least one light beam (Fx) in the projection surface (2).

10. Method for projecting a light beam (Fx) according to the preceding claim, in which the variation of the focal length of the at least one projection lens (51) is carried out: - according to an at least partly linear progression; and / or - according to a progression by step(s) comprising at least one phase of stability of the focal length.

Images