WO2023175138A1

WO2023175138A1 - Image projection device with optimised image change

Info

Publication number: WO2023175138A1
Application number: PCT/EP2023/056877
Authority: WO
Inventors: Rabih TALEB
Original assignee: Valeo Vision
Priority date: 2022-03-18
Filing date: 2023-03-17
Publication date: 2023-09-21
Also published as: FR3133573B1; FR3133573A1

Abstract

The invention relates to an image projection device comprising: at least one LED that emits an illumination light beam, and at least one image change module comprising different images to be projected, said images being mounted on a disc coupled to a stepper motor. The device comprises an electrical control circuit configured to control the motor so as to rotate the disc in order to change the projected image, by controlling the motor with a step-change control frequency (f) which is greater than or equal to a given target frequency (fc) during a main phase (Pp), and then decreases gradually down to zero during a controlled deceleration phase (Pd).

Description

DESCRIPTION

TITLE: Image projection device with optimized image change

TECHNICAL AREA

[0001] The technical field of the invention is that of image projection devices and more particularly those fitted to motor vehicles and allowing the projection of images on the ground.

TECHNOLOGICAL BACKGROUND

[0002] There are today such devices, sometimes called "dynamic carpet projectors" in English (modular floor projectors), making it possible to project images on the ground when a door is opened or unlocked, or when approaching it, when the driver approaches a key or a vehicle opening badge.

[0003] Such a device uses, for example, a disk on which images are placed. This device comprises a light source, generally an LED, which produces an illuminating light beam, shaped by an illumination or collimation lens placed downstream of the source, between the source and the disk. To project this or that image from the disc, an electric motor activates the disc to make it rotate, so as to bring the image to be projected onto the path of the lighting light beam (in practice, in front of the illumination lens ). The device also includes an optical projection system, located opposite the source, on the other side of the disc. This system includes at least one lens, and allows the image that has been placed in the light beam to be projected onto the ground.

[0004] In such a device, the LED (according to the Anglo-Saxon acronym for “Light Emitting Diode”, that is to say light emitting diode or LED) is generally powered by an electric current which varies over the course of the time, with a niche variation.

[0005] It is desirable that this slot variation respects certain criteria.

[0006] It is particularly desirable that its variation frequency and/or its duty cycle be high enough, to prevent flickering or fluctuation brightness is not perceived by an individual. Indeed, from an electrical point of view, the response time of an LED is generally very short so that the LED stops emitting light as soon as it is no longer electrically powered, between two pulses in niche. If the frequency of the square signal is low (or if the duty cycle is low), this repeated extinction of the LED can be perceived by an individual, due to the limited retinal persistence of the human eye, and give rise to an impression visual of unwanted flickering. In Figure 1, which represents possible operating points in the LED current variation frequency / duty cycle R plane, the curve Cv1 shows the limit above which it is desirable to work, to avoid that an individual does not perceive a flicker or a fluctuation in light intensity of the image formed on the ground (in this case in the case of a generally white floor, in a bright environment - not in the dark). The hatched area located under the Cv1 curve therefore corresponds to an area to be avoided if possible, in the LED - R plane.

[0007] But it is also desirable, in general, to use a duty cycle and/or a variation frequency that is not too high, in order, between two current pulses (in slot), to leave a sufficient period of time to be able to pass from one image to another (by rotating the disc) while the LED is off. This allows you to move from one image to another without blurring or overlapping between images, or masking of image parts. In Figure 1, the curve Cv2' shows the limit below which it is desirable to work, to have sufficient time to change image during the LED extinction interval, between two current slots . The dotted hatched area, located above the Cv2' curve, thus corresponds to an area to be avoided if possible, in the LED - R plane. The position of this curve in the LED/R plane is fixed by the time of response of the disk-motor assembly, that is to say by the time necessary to go from one image to the other disk, with a stop in the final position (in the case of figure 1, this time response time is 10 ms).

[0008] Finally, the inventors have noticed that the use of a low duty cycle R is unfavorable in terms of energy efficiency Eff of the LED. Indeed, to obtain the same average brightness, when we reduce the duty cycle R, we must in return increase the peak current, which reduces the energy efficiency of the LED, as explained below (with reference to Figure 12) . In Figure 1, the Cv3 curve thus corresponds to a duty cycle limit, above which it is preferable to work, for efficiency reasons (this curve corresponds to a target brightness, and to a given maximum acceptable electrical consumption).

[0009] In Figure 1, the unhatched zone Z' then corresponds to the zone in which the LED frequency and the duty cycle R are chosen to satisfy these different criteria. As we can see, this zone is not very extensive, in the fLED - R plane, even though these curves correspond to a very efficient LED (of the “bichip” type, that is to say with a double substrate), and a motor-disc assembly that is also very efficient in terms of response time.

[0010] It is therefore desirable to increase the extent of the zone of the LED - R plane in which these different operating criteria are satisfied, in order to give more freedom in the choice of the operating point of the device or in the choice of components of the projection device.

SUMMARY

[0011] To remedy at least in part the limitations of the prior art, the present technology then concerns an image projection device comprising: at least one LED emitting a lighting light beam, an image changing module comprising different images to be projected mounted on a disk coupled to a stepper motor, and an electrical control circuit, connected to the stepper motor and configured to control the motor in accordance with a given control sequence, so as to rotate the disk : from a first angular position, in which a first of said images is present on the path of the light beam, to a second angular position, in which a second of said images is present on the path of the light beam, with stop in the second angular position, the electrical control circuit being configured to, during the control sequence, control the motor with a step change control frequency which, during a main phase, is greater than or equal to a given target frequency, then during a phase of controlled deceleration, gradually decreases to zero.

[0012] In the projection devices of the prior art, the movement of the disk is most often stopped instantly, the pitch change control signal passing instantly (at time t3', in Figure 3) from a non-zero control frequency fo, at a zero frequency. This instantaneous stop, which corresponds to “pull-in” type operation of the stepper motor, makes it possible to reduce to a minimum the duration during which the disk is driven. But, after the movement, the sudden stopping of the rotation of the disk causes an oscillation phenomenon whose duration turns out to be long in practice, sometimes as long as the movement itself (see figure 3). Now it is desirable that the image, placed on the path of the lighting beam, has stopped oscillating (angularly), or that the oscillation falls below a certain threshold, which can be angular, for example 0 .1 degree or 0.01 degree, before turning the LED back on, to avoid forming a flickering image on the ground. In practice, it is therefore desirable that the LED remains off for the duration of drive by the motor, and also for this duration of oscillation (i.e.: until these oscillations are damped). The mechanical reaction time to consider is therefore t3'+ t'ose, which, in the case of Figure 3, is worth 10ms, as for Figure 1 (while the duration t3' of the movement itself is 5ms only).

On the contrary, in the device conforming to the present technology, when passing from one image to another, the motor is controlled according to the following sequence: main phase (main movement phase), during which the frequency of command is greater than or equal to the target frequency (for example constant, and equal to this target frequency), then controlled deceleration phase.

The addition of this controlled deceleration phase extends the total duration of the control sequence, compared to an instantaneous stop of the rotation. But in counterpart, this substantially reduces the duration of the transient oscillation regime which follows the stopping of the motor (see Figure 7 for example). And it turns out in practice that the reduction in oscillation duration thus obtained is greater than the loss of time due to the addition of the deceleration phase. The addition of this progressive deceleration phase therefore ultimately makes it possible to reduce the total mechanical response time of the motor-disc system, and thus to increase the extent of the working zone Z, in the LED - R plane (see the Figure 1 1, for example, which corresponds to a response time of 7ms, instead of 10 ms for Figure 1).

[0015] The fact of introducing this progressive deceleration phase also makes it possible, during the main movement phase, to use a step change control frequency value greater than the operating limits in pull-in mode of the motor ( a reminder of the definition of the operating limit in pull-in mode is given below), which leads to a significant angular speed, higher than in pull-in mode, without risking missing signal steps control when stopping. This ability to use a high angular speed (without risking missing steps) also helps to reduce the total time needed to replace one image with the next, thus increasing the extent of the working area Z.

[0016] In the projection device which has just been described, it may be desirable to angularly offset the first image and the second image quite significantly (for example with a difference greater than or equal to 45 degrees, or even greater than or equal to 60 degrees). Indeed, the deceleration phase (possibly combined with the use of a target frequency value greater than the pull-in limits) makes it possible to reduce the mechanical response time, but on the other hand increases the angular distance to be covered or which must be traversed by the disk (during the command sequence). Depending on the type of engine used, it may then be necessary to substantially separate the first and second images, to be projected successively.

[0017] To obtain a notable difference between the first and second images, it can then be provided that the first image and the second image are not consecutive, on the disk, at least one other of said images being interposed between the first image and the second picture. This makes it possible to separate these two images angularly, without losing space on the disk, since the interval between the two images is then used to place another image. This makes it possible to maintain a high total number of images on the disk, while having a significant angular difference between two images projected successively (ie: projected one immediately after the other).

The projection device can in particular be configured (in particular its electrical control circuit 8) to project the images of the disk successively, according to a pre-established projection sequence. For example, the image Im1, then Im2, then Im3, then Im4, then Im5, then Im6, then Im7, then Im8, then Im9, then lm10, then Im1 1, then Im12 if the disc has 12 images, Im1 to Im12. The images in question are then positioned on the disk in such a way that, for each pair of two images in this sequence which immediately follow one another in the sequence (for example for the pair Im5, Im6), the two images in question are not not consecutive on the disk, at least one other of said images being interposed between these two images. To successively display all the images in the sequence, the motor then rotates the disc so that, at each image change, it skips the interspersed image or images, without projecting them.

[0019] To display all of the images on the disk, the disk then rotates more than one revolution, in practice almost two complete revolutions, if an interposed image is inserted each time (or almost every time) between two images. successive in the sequence. Indeed, during a first revolution of the disc, one image out of two will be projected, and in the following revolution, it is the “intercalated” images, not projected during the first revolution, which will be projected (see figure 9). And if two interposed images are inserted each time (or almost at the same time) between two successive images of the sequence, then the disc will make almost three complete revolutions to project the entire sequence (see Figure 1 1).

[0020] In addition to the characteristics mentioned above, the device which has just been presented may include one or more of the following optional characteristics, considered individually or according to all technically possible combinations: the number of images interposed between the first image and the second image is less than or equal to four; this also ensures that the distance to be covered between the first and second images is not increased too much, which would end up increasing the time needed to move from one of these two images to the other; the control sequence comprises, before the main phase, a controlled acceleration phase, during which the pitch change command frequency increases progressively (in practice from zero) until reaching said target frequency; during the control sequence, the motor exerts a given motor torque, and in which the electrical control circuit is configured so that said target frequency is greater than a pull-in frequency of the motor, the pull-in frequency being a limiting frequency beyond which the motor misses certain steps of the control signal, if it is commanded to pass from a first stopping position to a second stopping position at a constant angular speed corresponding to said frequency of step change control and exerting said motor torque; the electrical control circuit is configured so that said target frequency is lower than a pull-out frequency of the motor, the pull-out frequency being a limiting frequency for which, when the motor exerts said motor torque and the motor is already rotating at an angular speed corresponding to said step change control frequency, then, if the control frequency is increased beyond the pull-out frequency, the motor misses certain steps of the control signal; the first angular position and the second angular position are angularly offset relative to each other by at least 45 degrees, or even by at least 60 degrees; the first angular position and the second angular position are angularly offset relative to each other by less than 120 degrees, or even less than 90 degrees; the device further comprising an optical projection system arranged to project onto the ground, from a motor vehicle, the image placed on the path of the light beam; the electrical control circuit is configured to: receive a signal for opening or unlocking a door of the vehicle, and in response to said signal, control the motor in accordance with said control sequence.

[0021] The present technology also relates to a method of controlling an image projection device as described above, the method comprising a control sequence during which the electrical control circuit controls the motor so as to rotating the disk: from a first angular position, in which a first of said images is present on the path of the light beam, to a second angular position, in which a second of said images is present on the path of the light beam, with stopping in the second angular position, and, during the control sequence, the electrical control circuit controls the motor with a step change control frequency which, during a main phase, is greater than or equal to a given target frequency , then during a controlled deceleration phase, gradually decreases to zero.

The optional characteristics presented above in terms of device can also be applied to the process which has just been described.

[0023] This technology and its various applications will be better understood on reading the following description and examining the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

[0024] The figures are presented for information purposes only and are in no way limiting. [0025] [Fig. 1] schematically represents a work zone Z' respecting certain criteria, in a variation frequency plane - cyclic ratio of an electric current supplying an LED of a projection device.

[0026] [Fig. 2] schematically represents a disk of an image projection device of the prior art.

[0027] [Fig. 3] schematically represents the evolution over time of an angular position of the disk of Figure 2, during a change of image to be projected, for an image projection device of the prior art.

[0028] [Fig. 4] schematically represents a vehicle equipped with an image projection device implementing the present technology, seen from the side.

[0029] [Fig. 5] schematically represents the image projection device of the vehicle of Figure 4, seen in perspective.

[0030] [Fig. 6] represents elements of the device of Figure 5, in the form of functional blocks.

[0031] [Fig. 7] schematically represents the evolution over time of an angular position of a disk of the device of Figure 5, during a change of image to be projected, as well as the corresponding evolution, over time, a step change control frequency controlling a stepper motor coupled to this disk.

[0032] [Fig. 8] schematically represents an operating point of the stepper motor, in a control frequency - exerted torque plane.

[0033] [Fig. 9] schematically represents the disk of the device of Figure 5.

[0034] [Fig. 10] schematically represents another disk that can be fitted to the device of Figure 5.

[0035] [Fig. 11] schematically represents a work zone Z respecting certain criteria, in a variation frequency plane - cyclic ratio of an electric current supplying LEDs of the projection device of Figure 5.

[0036] [Fig. 12] schematically represents a current-voltage characteristic of an LED of the device of Figure 5. DETAILED DESCRIPTION

[0037] Figure 4 represents a motor vehicle 1 equipped with an image projection device, 2, allowing the projection of an image 3 on the ground. As will be seen below, the device 2 can be controlled by opening a front or rear door 10, or another opening such as the trunk 11.

The device 2 is placed at the bottom of the body, for example just under the vehicle where the height is limited and the environment is aggressive (water splashes, risk of impact with elements on the road, etc.) . It is therefore protected by a box, of limited size (since the device is 20cm to 30 cm from the ground), for example 4 to 10 cm on each side.

The image projection device 2 comprises at least one LED 60 (possibly several) which serves as a light source. This LED emits a lighting light beam, F, when it is powered by an electric current, I. The device 2 also comprises an illumination lens 20 (more generally, an optical system comprising at least one lens), serving of condenser. This lens makes it possible to shape the light beam emitted by the LED, in particular by making it less divergent. The illumination lens 20 is placed downstream of the LED 60, between the LED and the image to be projected (Im1, in Figure 2). The device 2 also includes an optical projection system 21 arranged to project the image to be projected onto the ground, from the motor vehicle 1. The optical projection system 21 is located on the path of the light beam F, downstream of the image to be projected. Here, it is located opposite LED 60, on the other side of a disk 5 which carries the image to be projected, as well as other images. The optical projection system 21 comprises one or more lenses or mirrors. It forms on the ground an image 3 of the image to be projected Im1, with very significant magnification, and, in general, a dilation effect. Indeed, the image 3 formed on the ground has at least 0.5 m side, and can even occupy an area 1 m long by 1 m wide or more, and the ground is illuminated in a grazing manner by the device. projection.

[0040] The projection device 2 also includes an electric motor 4, step by step, coupled to the disk 5 by a shaft 40. Several images Im1, Im2, Im3,..., Im12 are mounted on the disk (12 images in everything, in the example shown; see Figure 9). The images Im1, Im2, Im3,... are distributed in a circle on the disk 5, here at the periphery of the disk, over its entire circumference, for example with a constant angular distance 5 between consecutive images, on the disk (here, this deviation is 30 degrees). To replace the projected image with another image, the motor 4 rotates the disk 5 to bring this other image into the light beam F, facing the optical projection system 21, in place of the previous image .

The images Im1, Im2, Im3, etc. of disk 5 are each formed on an image support, for example made of glass, essentially transparent (that is to say allowing most of the power to pass through). incident light). These images can be engraved (possibly by laser), glued or even lithographed on the image supports in question.

The projection device 2 also comprises an electrical control circuit 8, connected to the motor 4 (Figure 6). The electrical control circuit 8 is also connected to the LED 60. It can be produced in whole or in part on a printed circuit 6 located in the housing of the projection device (and on which the LED 60 is soldered). Certain elements of the electrical control circuit can be integrated into the motor housing. The electrical control circuit comprises for example: a controllable current source (delivering a pulsed current), connected to the LED 60 to power it electrically, an amplifier stage, of the driver type, to control the motor 4, and a module control, for example of the programmable circuit type, to control the motor (more precisely, to control the motor driver, here; as well as to control the current source of the LED).

[0044] The control module also comprises reception means, for example a wired or wireless communication interface, for receiving a signal s, coming from another electronic unit of the vehicle, the electronic control circuit 8 being configured to control the LED and the motor according to the signal s received (as explained in detail later), in particular to trigger an image change according to this signal. Alternatively or in addition, the reception means of the electronic control circuit could be configured to directly receive this signal from a vehicle remote control device, such as a mobile telephone or a “plip” key.

The electrical control circuit 8 is configured here to control the LED 60 and the motor 4 in a synchronized manner, in particular, to control the motor an image change for a period of time during which the LED is kept off.

The electrical control circuit 8 is configured to power the LED with a square electric current having a duty cycle R, and an LED variation frequency. The duty cycle in question is equal to the duration of the current slot (current pulse), divided by the total period of the periodic variation in slots.

[0047] The electrical control circuit 8 is also configured to control the motor 4 in accordance with a given control sequence Sc (FIG. 7), so as to rotate the disk 5: from a first angular position a1, in which a first of said images (for example Im1) is present in the lighting light beam F, up to a second angular position a2, in which a second of said images (for example Im2) is present in the light beam F, with stop in the second angular position, to replace the projected image (Im1) with another (Im2).

Remarkably, the electrical control circuit 8 is configured to, during the control sequence Sc, control the motor 4 with a step change control frequency, f, which, during a main phase Pp ( main phase of movement), is greater than or equal to a given target frequency fc, then during a controlled deceleration phase, Pd, gradually decreases to zero.

[0049] As explained in detail in the “summary” section, this controlled deceleration phase makes it possible to reduce the total mechanical response time of the motor-disc system, compared to a sudden stopping of the rotation, because it makes it possible to reduce the duration of the transient oscillation regime which follows the stopping of the motor (i.e.: its stopping at a given step).

[0050] The step change control frequency, f, is the frequency of the control signal, in square, which controls the movements of the stepper motor. step 4. The motor can for example be configured to rotate by one step in response to a slot (one step) of the control signal (or, possibly, in response to a given number of slots of this signal, for example in response in two successive slots). The angular speed at which the motor rotates is therefore directly proportional to this step change control frequency.

[0051] During the main phase Pp, the control frequency f can, as here, be constant, equal to the target frequency fc. Alternatively, it could, however, vary during this period (for example with a slight increase then linear decrease, or with a bell-shaped variation). During the deceleration phase Pd, the step change control frequency f can, as here, successively present at least two, or even at least four successive values distributed, for example equally distributed between fc and zero. The controlled deceleration phase Pd has, for example, a duration of less than 2ms.

[0052] The electrical control circuit 8 is also configured so that the control sequence Sc also includes, before the main phase Pp, a controlled acceleration phase Pa during which the step change control frequency f gradually increases. , from zero, until reaching said target frequency fc. As for the controlled deceleration phase, the acceleration phase Pa can, as here, successively present at least two, or even at least four successive values distributed, for example equally distributed between zero and fc. The controlled acceleration phase Pa, for example, has a duration of less than 2 ms.

[0053] This progressive acceleration phase, as well as the controlled deceleration phase make it possible, during the main phase, to control the motor with a control frequency fc greater than the pull-in limit of the motor, without however risking miss steps of the motor control signal, which contributes, through a high angular speed, to reducing the total mechanical response time of the device.

[0054] Figure 8 illustrates this movement, beyond the pull-in limits of the motor 4. This figure shows, in the plane f - C, where C is the torque exerted by the motor, the CPI limit of a operation in “pull-in” mode, for the motor considered.

[0055] As is known in the field of stepper motors, operation in pull-in mode corresponds to movement from a first stopping position (stationary shaft) to a second stopping position. , at speed angular (and therefore at constant control frequency), as in the example of Figure 3 for example. For such a mode of movement, at a given control frequency f, if the torque C exerted on the motor shaft becomes greater than the limit Cpi(f), then the motor will miss certain steps of the control signal (ie: does not will not move, for certain slots of the control signal), in any case with a high probability. Likewise, for a given torque CM exerted by the motor, for such a mode of movement (of the stop-displacement-stop type), if the control frequency f is greater than a frequency called pull-in frequency fpi, then the motor will miss some steps of the control signal (at least with a high probability).

[0056] Figure 8 also shows a curve, CPO, corresponding to the so-called pull-out limit. When the motor is controlled with a given control frequency f, and is rotating at an angular speed corresponding to this control frequency, if the torque C exerted on the motor shaft becomes greater than the limit Cpo(f), then the motor will miss some steps of the control signal (at least with a high probability). Likewise, for a given torque CM exerted by the motor, when the motor is already rotating, at a constant angular speed corresponding to the control frequency f considered, if the frequency becomes greater than a frequency called pull-out frequency fpo, then the motor will miss some steps of the control signal (at least with a high probability).

[0057] Here, the target frequency fc used during the main phase Pp is greater than the pull-in frequency fpi corresponding to the torque CM to be exerted by the motor during the control sequence Sc. As can be seen in the figure 8, this makes it possible to use a control frequency almost 4 times greater than for a pull-in type movement mode, such as that of Figure 3. The frequency fc is also lower than the pull-out frequency fpo corresponding to this CM torque (so as not to risk missing steps of the motor control signal). The torque CM exerted by the motor during the control sequence Sc can correspond to an average torque exerted during this sequence. This torque can be measured beforehand during tests (to adequately choose the frequency fc to use), or be estimated on the basis of the inertia of the disc, the expected angular acceleration and a possible friction torque. . [0058] The controlled acceleration phase, the controlled deceleration phase, and the use of a target frequency value fc greater than the pull-in limits each make it possible to usefully reduce the duration between the departure of the disk, and its immobilization without residual oscillation, during an image change. But this on the other hand increases the angular distance traveled by the disk during this phase change.

[0059] Also, it is provided here, on disk 5, to angularly shift the images which are intended to be projected successively (one immediately after the other, for example the images Im1 and Im2), with an angular deviation between them important, greater than or equal to 45 degrees, and even here, greater than or equal to 60 degrees. This angular difference can, however, remain less than 120 degrees (or even 90 degrees), so as not to increase the distance to be covered too much, which would end up increasing the time necessary to go from one image to another.

[0060] Two images, intended to be projected successively, are thus separated angularly more than on a disk of the prior art such as disk 5.0 in Figure 2 (where two such images are separated by 30 degrees).

[0061] The space available between these two images can then be left free, without any other image (with for example an image every 60 degrees, or every 90 degrees - i.e. 4 images in total on the disk - for example). But this reduces the total number of different images present on the disk.

The space available between two images to be projected successively (for example Im1, and Im2) can also, as here, be used to place another image to be projected (Im7, in the example of Figure 9), which will be projected later, at another moment in a projection sequence planned for device 2. This makes it possible to angularly separate these two images, while maintaining a high total number of images, on disk 5.

[0063] The electrical control circuit 8 is thus configured to (for example, its control module is programmed to) control the motor 4 so as to project the images of the disk 5 successively, according to a preestablished projection sequence, here, according to the sequence Im1, then Im2, then Im3, then Im4, then Im5, then Im6, then Im7, then Im8, then Im9, then lm10, then Im1 1, then Im12. And the images in question are positioned on disk 5 in such a way that, for each couple of two images of this sequence which immediately follow each other in the sequence (for example for the pair Im5, Im6), the two images in question are not consecutive on the disk, at least one other of said images (Im1 to Im12) being interposed between these two images. It will be noted that this arrangement is implemented for the disk 5, but also for the disk 5' of Figure 10, which, as a variant, could be used in place of the disk 5, in the image projection device 2 . As a further variation, other distributions of the images, conforming to the arrangement described in this paragraph, could be used.

[0064] To successively display all the images of the projection sequence, the motor 4 then rotates the disk 5 so as, at each image change, to skip the “interspersed” image or images, without project them.

[0065] Figure 9 shows the arrangement of figures Im1,..., Im12, on disk 5. Disk 5 has 12 images in total, distributed with a constant angular difference 5 of 30 degrees between two consecutive images on the disk. Motor 4 is a stepper motor whose number of steps (here 48) is a multiple of the total number of images. On the periphery of the disk, the images are distributed in the following order (order, in terms of geometric position, on the disk): Im1, then Im7, then Im2, then Im8, then Im3, then Im 9, then Im4, then lm10, then Im5, then Im1 1, then Im6, then Im12; and then, again, Im1. In this example, there is therefore each time an “interspersed” image, between two images to be projected successively.

[0066] The successive movements of the disk, carried out to project the images Im1,..., Im12 in accordance with the projection sequence mentioned above, are represented by the arrows "step 1", "step 2", etc. ., in Figure 9. The first five movements of the motor, to successively project the images Im1 to Im6, correspond to rotations of 2x5 each time (i.e. 60 degrees), since the number of "interposed" images is 1, here. To then move to image Im7, the disk performs a rotation of 3x5 (i.e. 90 degrees), then resumes rotations of 2x5 (60 degrees) until the end of the sequence (image Im12).

[0067] To project all of the images Im1 to Im2, disk 5 rotates almost two revolutions (in this case, 690 degrees). During the first round, images Im1 to Im6 are projected. Then, during the second round, images Im7 to Im12 (interspersed between images Im1 to Im6) are projected. [0068] On the disk 5' of Figure 10, a similar distribution of images is used, but each time with two images "interspersed" (instead of one), between two images intended to be projected successively. successively. The 12 images of the 5' disk are therefore distributed in the following order on the periphery of the disk: Im1, then Im5, then Im9, then Im2, then Im6, then Im 10, then Im3, then Im7, then Im1 1, then Im4, then Im8, then Im12; and then, again, Im1. These images are again distributed with a constant angular difference of 30 degrees between two consecutive images on the disk.

[0069] The successive movements of the disk, carried out to project the images Im1,..., Im12 in accordance with the projection sequence mentioned above, are represented by the arrows "step 1", "step 2", etc. ., in Figure 10. The first four movements of the motor, to successively project the images Im1 to Im4, correspond to rotations of 3x5 each time (i.e. 90 degrees), since the number of "interposed" images is two, on the 5' disc. To then move to image Im5, the disk performs a rotation of 4x5 (i.e. 120 degrees), then resumes rotations of 3x5 (90 degrees) until image Im8, then performs a rotation of 4x5 to move to image image Im9, and then resumes rotations of 3x5 (90 degrees) until the end of the sequence (image Im12). To project all of the images Im1 to Im2, the 5' disc then rotates almost three revolutions.

[0070] As already indicated, the controlled deceleration phase Pd, as well as, here, the controlled acceleration phase Pa and the use of a high target frequency value fc (greater than the pull-in limit) allow to reduce the total mechanical reaction time of device 2, to approximately 7 ms in the example presented. For comparison, for the same device, controlled with a constant command frequency fo throughout the entire movement (without acceleration/deceleration ramp), and a total movement of 30 degrees (see disk 5.0 in Figure 2), the total mechanical response time is approximately 10 ms.

[0071] Figure 1 1 illustrates the effect of such a reduction in mechanical response time, on the extent of the working zone Z. Figure 1 1 in fact corresponds to a total mechanical response time of 7 ms, instead of 10 ms. This figure is identical to Figure 1, except that the limit curve Cv2' is replaced by the curve Cv2, which corresponds to this reduced response time. As we can see, this reduction in response time significantly increases the extent of the zone of work Z, in which the three criteria presented in the background part are satisfied. Note in particular that this larger working area makes it possible to use a higher duty cycle.

[0072] However, a higher duty cycle makes it possible to improve the energy efficiency of the LED 60. Indeed, as illustrated in Figure 12 (which represents the current-voltage characteristic of the LED 60), an increase in the electric current d The power supply I is accompanied by an increase in the supply voltage U (due to the non-zero internal resistance of the LED), and therefore an increase in the electrical power consumed. Thus, for example, with a duty cycle R1 of 90% and a peak current 11, the average electrical power consumed will be P1 =0.9x11 XU(I1). While with a duty cycle R2 of 10% and a peak current 12=9x11, the average light power produced will be the same (or almost the same), while the average electrical power consumed will be P2=0.1 XI2XU(I2 )=0.9XI1 xU(9xl1), which is therefore significantly greater than P1, since U increases with I, for the LED (this drop in efficiency, when the peak current is increased, is explained by the losses in the internal resistance , non-zero, of the LED).

[0073] Increasing the extent of the working zone Z therefore makes it possible to reduce the energy consumption of the LED, among other things. More generally, this increases the freedom of design of the device 2, and possibly makes it possible to select less efficient, and therefore less expensive, components (for example, a “monochip” LED, that is to say with a single substrate, at instead of a “bichip” LED), while maintaining the same final performance for the device.

[0074] Here, the image change control sequence, Sc, (intended for example to replace the initial image with one more suited to a door opening context) is triggered by reception, by the electrical circuit control 8, of a signal s, transmitted by another electrical unit of the vehicle 1 (for example using a CAN network or equivalent). This other unit is for example in charge of the centralized control of the openings, or the vehicle wake-up control. Here, the signal s received by the electrical control circuit 8, and according to which an image change is triggered, is an opening signal for the door 10, 11 of the vehicle. This signal can be produced following receipt, by the electronic unit in question, of an opening command coming from a plip key or equivalent. The signal s can also be emitted by the electronic unit in question (responsible for centralized opening) when it detects that an authorized user is near the vehicle, for example by detecting the proximity of an identification badge of the vehicle user (possibly a passive electric badge), or a vehicle opening badge, an authorized mobile phone, or another identifiable electronic device.

[0075] Alternatively, the image change control sequence could also be triggered following receipt, directly by the electrical control circuit (rather than by another electronic unit of the vehicle), of a control signal d opening of the opening emitted by a vehicle remote control device with transmitter, such as a mobile phone or a “plip” key.

[0076] As emerges from the description above, the electrical control circuit 8 of the projection device is configured to control this device 2 in accordance with a control method comprising a control sequence Sc during which the electrical circuit of control 8 controls the motor 4 so as to rotate the disk 5: from a first angular position a1, in which a first of the images of the disk Im1 is present on the path of the light beam F, to a second angular position a2, in which a second of said images Im2 is present on the path of the light beam F, with stop in the second angular position, the electrical control circuit 8 controlling the motor 4, during the control sequence Sc, with a control frequency f step change which: during the main phase Pp, is greater than or equal to the target frequency fc mentioned above, then during a controlled deceleration phase Pd, gradually decreases to zero.

Claims

[Claim 1] Device (2) for projecting images comprising:

- at least one LED (60) emitting a lighting light beam (F),

- an image changing module (7) comprising different images (Im1, Im2, Im3, Im12) to be projected mounted on a disk (5) coupled to a stepper motor (4), and

- an electrical control circuit (8), connected to the stepper motor (4) and configured to control the motor (4) in accordance with a given control sequence (Sc), so as to rotate the disk (5): o from a first angular position (ccl), in which a first of said images (Im1) is present on the path of the light beam (F), o to a second angular position (a2), in which a second of said images ( Im2) is present on the path of the light beam (F), with stop in the second angular position,

- characterized in that the electrical control circuit (8) is configured to, during the control sequence (Sc), control the motor (4) with a step change control frequency (f) which, o during a main phase (Pp), is greater than or equal to a given target frequency (fc), then o during a controlled deceleration phase (Pd), gradually decreases to zero.

[Claim 2] Device (2) according to claim 1, in which the first image (Im1) and the second image (Im2) are not consecutive, on the disk (5), at least one other of said images (Im7; Im5 , Im9) being interposed between the first image (Im1) and the second image (Im2).

[Claim 3] Device (2) according to claim 2, in which the number of images interposed between the first image (Im1) and the second image (Im2) is less than or equal to four. [Claim 4] Device (2) according to claim 2 or 3, in which the electrical control circuit (8) is configured to control the motor

(4) so as to successively project the images (Im1, Im2, Im3, Im12) from the disk (5) in accordance with a preestablished projection sequence, said images being distributed on the disk so that, for each pair grouping two of said images (Im1, Im2) which immediately follow each other in the projection sequence, the two images (Im1, Im2) of the pair are non-consecutive on the disk, at least one other of said images (Im7; Im5, Im9) being interposed between the two images of the couple.

[Claim 5] Device (2) according to the preceding claim, in which the disk (5) rotates more than one revolution, or even more than one and a half revolutions to successively project said images (Im1, Im2, Im3, Im12 ) in accordance with said projection sequence.

[Claim 6] Device (2) according to one of the preceding claims, in which the control sequence (Sc) comprises, before the main phase (Pp), a controlled acceleration phase (Pa), during which the step change control frequency (f) gradually increases (from zero) until said target frequency (fc) is reached.

[Claim 7] Device (2) according to one of the preceding claims, in which, during the control sequence (Sc), the motor (4) exerts a given motor torque (CM), and in which the electrical circuit control (8) is configured so that said target frequency (fc) is greater than a pull-in frequency (fpi) of the motor, the pull-in frequency (fpi) being a limiting frequency beyond which the motor (4) misses certain steps of the control signal, if it is commanded to move from a first stopping position to a second stopping position at a constant angular speed corresponding to said control frequency (f) of change of step and exerting said motor torque (CM).

[Claim 8] Device (2) according to the preceding claim, in which the electrical control circuit (8) is configured so that said target frequency (fc) is lower than a pull-out frequency (fpo) of the motor , the pull-out frequency (fpo) being a limiting frequency for which, when the motor exerts said motor torque (CM) and the motor is already rotating at an angular speed corresponding to said step change control frequency (f), then, if the control frequency is increased beyond the pull-out frequency (fpo), the motor misses certain steps of the control signal.

[Claim 9] Device (2) according to one of the preceding claims, in which the first angular position (a1) and the second angular position (a2) are angularly offset relative to each other by at least 45 degrees, or even at least 60 degrees.

[Claim 10] Device (2) according to one of the preceding claims, in which the first angular position (a1) and the second angular position (a2) are angularly offset relative to each other by less than 120 degrees , or even less than 90 degrees.

[Claim 1 1] Device (2) according to one of the preceding claims, further comprising an optical projection system (21) arranged to project onto the ground, from a motor vehicle (1), the image (Im1) placed on the path of the light beam (F).

[Claim 12] Device (2) according to the preceding claim, in which the electrical control circuit (8) is configured to:

- receive a signal(s) of opening or unlocking of an opening (10, 1 1) of the vehicle (1), and to

- in response to said signal, control the motor (4) in accordance with said control sequence (Sc).

[Claim 13] Method for controlling an image projection device (2) which comprises: at least one LED (60) emitting a lighting light beam (F), an image changing module (7) comprising different images (Im1, Im2, Im3, Im12) to be projected mounted on a disk (5) coupled to a stepper motor (4), and an electrical control circuit (8) connected to the stepper motor (4), the method comprising a control sequence (Sc) during which the electrical control circuit (8) controls the motor (4) so as to rotate the disk (5): o from a first angular position (a1), in which a first of said images (Im1) is present on the path of the light beam (F), o to a second angular position (a2), in which a second of said images ( Im2) is present on the path of the light beam (F), with stop in the second angular position,

- the method being characterized in that, during the control sequence (Sc), the electrical control circuit (8) controls the motor (4) with a step change control frequency (f) which, o during a main phase (Pp), is greater than or equal to a given target frequency (fc), then o during a controlled deceleration phase (Pd), gradually decreases to zero.