Synchronized LED image projection device with progressive lighting control

Abstract

Synchronized LED Image Projection Device with Progressive Lighting Control Such a device, comprising an electrically powered LED arranged to illuminate an image to be projected, and an image-changing module for replacing the image to be projected with another image, the device being configured to operate, alternatively: in an image display mode (S1), in which the image present in the path of the lighting beam is held in position and in which the electric current varies over time (t) with a first duty cycle (R1), and; in an image-changing mode (S2), in which the electric current varies with a second duty cycle (R2), and in which the image present in the path of the light beam is replaced by another image;the device further comprising an electrical control circuit equipped with a controllable current source having a common input pin for a pulse-width modulation dimming signal and for switching the circuit on or off, the electrical control circuit being configured to allow gradual illumination of the LED before the display of a first image in image display mode (S1). Figure to be published with the abbreviation: Figure 7;

Description

Title of the invention: Synchronized LED image projection device with progressive lighting control Technical field

[0001] The technical field of the invention is that of image projection devices and more particularly those equipping motor vehicles and allowing the projection of images onto the ground. TECHNOLOGICAL BACKGROUND

[0002] Today there are such devices, sometimes called "dynamic carpet projectors" in English (modular ground projectors), allowing images to be projected onto the ground when a door is opened or unlocked, or when approaching it, when the driver brings a key or an opening badge close to the vehicle.

[0003] Such a device uses, for example, a disc 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 disc. To project a particular image from the disc, an electric motor drives the disc to rotate it, so as to cause the image to be projected onto the path of the illuminating light beam (in practice, opposite the illumination lens). The device also comprises an optical projection system, located opposite the source, on the other side of the disc. This system comprises at least one lens, and makes it possible to project the image that has been placed in the light beam onto the ground.

[0004] In such a device, the LED (according to the English acronym for "Light Emitting Diode", i.e. light-emitting diode or DEL) is generally powered by an electric current which varies over time, with a variation in square waves.

[0005] It is desirable that this square wave variation meets certain criteria. In particular, it is desirable that its variation frequency be quite high, for example of the order of fifty Hz or more, to avoid flickering or a fluctuation in brightness being 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 square wave pulses. If the frequency of the square wave signal is low, this repeated extinction of the LED may be perceived by an individual, due to the limited retinal persistence of the human eye, and give rise to a visual impression of undesirable flickering.

[0006] It is also desirable, in general, to employ a moderate duty cycle, for, between two square pulses, leave a sufficient lapse of time to be able to pass from one image to the other (by rotating the disc) while the LED is off. This allows you to pass from one image to the other without smearing or overlapping between images, or masking parts of the image.

[0007] The duty cycle is then chosen so as to satisfy a compromise between: on the one hand, a fairly long extinction between two pulses, to allow a change of image, and on the other hand, an extinction that is not too long, so that it is not perceptible to the eye, in order to avoid a sensation of flickering of the projected images. This compromise most often leads to a fairly low duty cycle, of the order of 10 to 30% for example.

[0008] This type of projection device makes it possible to improve the visibility of the vehicle access area, to create visual effects in its vicinity, or to communicate information to a user of the vehicle in an easily understandable manner, when he approaches the vehicle. Known projection devices are generally satisfactory in terms of size, robustness and visual rendering of the projected images.

[0009] Such a device generally comprises an electrical control circuit, connected to the LED and to the actuator of the image change disk, and capable of controlling the electrical current flowing in the LED as a function of a dimming frequency in pulse width modulation. The electrical control circuit then comprises a control module (typically in the form of a microcontroller) and a controllable current source (also called a "driver" in English) connected on the one hand to the control module and on the other hand to the LED to supply it with electricity.According to a constraint of economic realization of the controllable current source, the latter can comprise, in addition to a positive voltage input pin, a common input pin of a dimming signal in pulse width modulation and of standby or wake-up of the circuit, the dimming signal in pulse width modulation (at the dimming frequency) being emitted by the control module. In order to reduce the energy consumption, the electrical control circuit is generally configured to go into standby after a predetermined duration without signal on the common pin (this duration being called subsequently “time of extinction of the controllable current source”, typically a duration of the order of 10 ms for certain controllable current sources).

[0010] However, in an image display mode, when the electrical control circuit controls the electrical current flowing in the LED as a function of a dimming frequency in pulse width modulation whose corresponding period is greater than the extinction time of the controllable current source (this period must in fact remain sufficiently high to leave a sufficient lapse of time for be able to switch from one image to another), the duty cycle must be chosen accordingly as sufficiently high to prevent the electrical circuit from going into standby (typically a duty cycle of around 30% for a dimming frequency in pulse width modulation of around 70 Hz). However, such a choice of value for the duty cycle does not allow a progressive and "soft" appearance of the image projected on the ground (in other words a luminous appearance in progressive fading, pleasant for the visual perception of the user). Such a progressive and "soft" appearance of the image projected on the ground is in fact particularly useful and appreciable when the user approaches the vehicle, for example when his keys are detected.Using low brightness is therefore important for achieving a pleasant gradual switching on because the perception of brightness by the human eye follows a logarithmic law, with variations around the smallest lighting values ​​being perceived as much greater than variations around higher values. Without this, the external observer has a much less satisfactory perception of a sudden switching on of the lighting function.

[0011] It is therefore desirable to propose an image projection device allowing a progressive and “soft” appearance of the images, while retaining an inexpensive electrical control circuit and maintaining the performance of the device in terms of display, that is to say in terms of visual rendering. SUMMARY

[0012] In this context, the present technology relates to a method of controlling an image projection device, the device comprising: • at least one LED, which emits a beam of light when powered by an electric current, • an image change module comprising different images to be projected mounted or engraved on a mobile element coupled to an electromechanical actuator, configured to place on the path of the lighting light beam, selectively, on command, one or other of the images to be projected, and • an electrical control circuit, connected to the LED and to the actuator of the image change module, and capable of controlling the electrical current flowing in the LED as a function of a dimming frequency in pulse width modulation, the electrical control circuit comprising a control module and a controllable current source connected on the one hand to the control module and on the other hand to the LED to electrically power it, the control module being configured to emit a dimming signal in pulse width modulation having said dimming frequency in pulse width modulation, the controllable current source comprising a positive voltage input pin and a common pin for inputting the dimming signal in pulse width modulation and for putting the circuit into standby or waking up, the electrical control circuit being configured to go into standby after a predetermined duration without a signal on said common pin, the method comprising the following modes: - in an image display mode: the image present on the path of the lighting beam is maintained in position and the electric current which supplies the LED varies over time with a first duty cycle, and - in an image change mode: the electric current which powers the LED varies over time with a second duty cycle, and the actuator sets the mobile element in motion to replace the image present on the path of the beam with another of said images, the method comprising a phase of displaying a first image, during which the electrical circuit controls the electrical current flowing in the LED as a function of a first dimming frequency in pulse width modulation, the electrical current varying over time with the first duty cycle, said predetermined duration of the electrical control circuit (8) being less than the period corresponding to said first dimming frequency in pulse width modulation, the method further comprises, before the phase of displaying a first image, an initial step during which: - the electrical circuit controls the electric current flowing in the LED according to a second dimming frequency in pulse width modulation, the second dimming frequency being greater than the first dimming frequency, such that said predetermined duration of the electrical control circuit is greater than or equal to the period corresponding to said second dimming frequency in pulse width modulation, - and the electrical circuit controls the pulse width modulation of the electric current flowing in the LED so that the duty cycle of the variation of the electric current goes from a zero value to the value of the first duty cycle.

[0013] In the image display mode, the electrical circuit controls the electric current flowing in the LED as a function of the first pulse width modulation dimming frequency, the electric current varying over time with the first duty cycle. The value of the first pulse width modulation dimming frequency is chosen such that its period corresponds The value of the first duty cycle is then chosen to be high enough to prevent the electrical circuit from going into standby mode.

[0014] In the image change mode, the time interval during which the LED is off is large (by choosing a suitable second duty cycle), which makes it possible to change the image while the LED is off.

[0015] Thanks to the initial step during which the electrical circuit controls the electric current flowing in the LED according to the second dimming frequency in pulse width modulation, the second dimming frequency being higher than the first dimming frequency, it is possible to control the switching on of the electric current flowing in the LED (via pulse width modulation) with a duty cycle of the electric current gradually changing from a zero value to the value of the first duty cycle, thus generating a progressive, pleasant and “soft” lighting of the LED.

[0016] Indeed, by increasing the dimming frequency in pulse width modulation during this initial stage, it is possible to achieve much lower current duty cycles than in the display and image change modes, without risking the electrical circuit going into standby and without having to change the electrical control circuit.

[0017] In addition to the characteristics mentioned above, the method which has just been presented may have one or more of the following optional characteristics, considered individually or according to all technically conceivable combinations: • the second duty cycle is less than or equal to the first duty cycle (a second duty cycle less than the first duty cycle making it possible, in image change mode, to have sufficient extinction time to change image, while controlling the LED with a high duty cycle and a low peak current in image display mode, therefore with high energy efficiency and few losses. This therefore makes it possible to reduce the energy consumption of the device while retaining the same characteristics in terms of display and visual rendering). • in the image change mode: the electric current has a square wave variation, the current being equal to a maximum current value during a power-up interval and being substantially zero during an extinction interval, and the actuator is controlled so as to replace the image present on the beam path during said extinction interval; • the first duty cycle and / or the second duty cycle is substantially equal to 30%; • the first dimming frequency in pulse width modulation is substantially equal to 70 Hz; • the second dimming frequency in pulse width modulation is between 100 Hz and 400 Hz, preferably substantially equal to 100 Hz (which makes it possible to avoid, within the controllable current source, problems linked to the rise and fall times of the pulse width modulation square waves, in relation to the total duration of the square wave, problems which occur at high frequencies); • during the initial stage, the electrical circuit commands the device to operate in a transition mode, during which the electrical current flowing in the LED has a time variation in a slot, with an intermediate duty cycle, between the zero value and the value of the first duty cycle; • in the transition mode, the electric current flowing in the LED varies in a slot by presenting several successive slots whose duty cycle varies gradually and monotonically, from one slot to another; • the peak current of the electric current which powers the LED is a function of the temperature.

[0018] The present technology also relates to an image projection device, the device comprising: • at least one LED, which emits a beam of light when powered by an electric current, • an image change module comprising different images to be projected mounted or engraved on a mobile element coupled to an electromechanical actuator, configured to place on the path of the lighting light beam, selectively, on command, one or other of the images to be projected, and • an electrical control circuit, connected to the LED and to the actuator of the image change module, and capable of controlling the electrical current flowing in the LED as a function of a dimming frequency in pulse width modulation, the electrical control circuit comprising a control module and a controllable current source connected on the one hand to the control module and on the other hand to the LED to electrically power it, the control module being configured to emit a dimming signal in pulse width modulation having said dimming frequency in pulse width modulation, the source of controllable current comprising a positive voltage input pin and a common input pin for the dimming signal in pulse width modulation and for putting the circuit into standby or waking up, the electrical control circuit being configured to go into standby after a predetermined duration without a signal on said common pin, the electrical control circuit being configured so that: • in an image display mode: the image present on the path of the lighting beam is maintained in position and the electric current which supplies the LED varies over time with a first duty cycle, and the electrical circuit is configured to control the electric current flowing in the LED according to a first dimming frequency in pulse width modulation, said predetermined duration of the electrical control circuit being less than the period corresponding to said first dimming frequency in pulse width modulation, • in an image change mode: the electric current which powers the LED varies over time with a second duty cycle, and the actuator sets the mobile element in motion to replace the image present on the path of the beam with another of said images, the electrical control circuit being further configured to: • control the electric current flowing in the LED according to a second dimming frequency in pulse width modulation, the second dimming frequency being greater than the first dimming frequency, such that said predetermined duration of the electrical control circuit is greater than or equal to the period corresponding to said second dimming frequency in pulse width modulation, and • control the pulse width modulation of the electric current flowing in the LED so that the duty cycle of the variation of the electric current goes from a zero value to the value of the first duty cycle.

[0019] In addition to the characteristics mentioned above, the device which has just been presented may have one or more of the following optional characteristics, considered individually or according to all technically conceivable combinations: • the device further comprises an optical projection system arranged to project onto the ground, from a motor vehicle, the image placed in the path of the light beam; • the electrical control circuit is configured to: • receive a signal to open or unlock an opening from the vehicle, and for • in response to said signal, command a switch from image display mode to image change mode; • the controllable current source is a direct current to direct current converter, configured to control the electric current flowing in the LED according to the dimming frequency in pulse width modulation; • the controllable current source is a synchronous regulator.

[0020] The optional characteristics presented above in terms of method can also be applied to the device which has just been described.

[0021] The present technology and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0022] The figures are presented for information purposes only and are not limiting.

[0023] [Fig.l] schematically represents a vehicle equipped with an image projection device implementing the present technology, seen from the side.

[0024] [Fig.2] schematically represents the image projection device, seen in perspective.

[0025] [Fig.3] schematically represents a disk of the device of [Fig.2].

[0026] [Fig.4] represents elements of the device of [Fig.2], in the form of functional blocks tionals.

[0027] [Fig.5] represents an electrical control circuit of the device of [Fig.4] in the form of functional blocks, the electrical control circuit comprising a control module and a controllable current source.

[0028] [Fig.6] schematically represents the controllable current source of [Fig.5], according to a particular embodiment.

[0029] [Fig.7] is a diagram representing different phases of a method of controlling an image projection device according to the present technology, and illustrating more precisely the evolution over time of the duty cycle of the driving current of an LED of the image projection device.

[0030] [Fig.8] is a diagram representing the same of the control method of the image projection device according to the present technology, illustrating more precisely the evolution over time of the dimming frequency in pulse width modulation of the driving current of the LED. DETAILED DESCRIPTION

[0031] [Fig.l] represents a motor vehicle 1 equipped with an image projection device, 2, allowing the projection of an image 3 onto the ground. As will be seen later bottom, the device 2 can be controlled by the opening of a front or rear door 10, or another opening such as the trunk 11.

[0032] 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 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 30cm from the ground), for example 4 to 10 cm on each side.

[0033] The image projection device 2 comprises at least one LED 60 (possibly several) which serves as a light source. This LED emits an illumination 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 as a 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 (Iml, in [Fig.2]). The device 2 also comprises 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 the LED 60, on the other side of a disc 5 which carries the image to be projected. 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 Iml, with a very high magnification, and, in general, an expansion effect. Indeed, the image 3 formed on the ground has at least 0.5 m on each side, and can even occupy an area 1 m long by 1 m wide or more, and the ground is illuminated grazingly by the projection device.

[0034] The projection device 2 also comprises an image change module 7, which comprises different images Iml, Im2, Im3,... to be projected, mounted or engraved on a mobile element, here a disc 5. The disc 5 is coupled to an electromechanical actuator, here an electric motor 4, by a shaft 40. It will be noted that a mobile element other than a disc could be used to support and move the images, as a variant. In any case, the image change module 7 is configured to place on the path of the illumination light beam F, selectively (i.e. one image at a time), on command, one or other of the images to be projected. For this, the motor 4, typically a stepping motor, rotates the disc 5 to bring the image to be projected to the ground in the light beam F, in front of the optical projection system 21.

[0035] The images Iml, Im2, Im3,... of the change module are each formed on an image support, for example made of glass, which is essentially transparent (i.e. allowing the majority of the incident light power to pass through). These images can be engraved (possibly by laser), glued or even lithographed on the image supports in question. The images hnl, Im2, Im3,... are distributed in a circle on the disc 5 ([Fig.3]), here on the periphery of the disc, over its entire circumference, for example with a constant angular distance between images.

[0036] The projection device 2 also comprises an electrical control circuit 8, connected to the LED 60 and to the motor 4 ([Fig.4]). The electrical control circuit 8 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). As illustrated in [Fig.5], the electrical control circuit 8 comprises: • a controllable current source 12, of the driver type, connected to the LED 60 to supply it electrically, • an amplifier stage (not shown), of the driver type, to control motor 4 (unless this driver is included in the motor), and • a control module 14, for example of the programmable circuit or microcontroller type, to control the current source 12 of the LED and the motor driver.

[0037] The control module 14 also comprises reception means (not shown), for example a communication interface, wired or wireless, for receiving a signal s, coming from another electronic unit of the vehicle, the electronic control circuit 8 being configured to control the LED 60 and the motor 4 as a function of the signal s received (as explained in detail below). Alternatively or additionally, the reception means of the electronic control circuit 14 could be configured to directly receive this signal from a remote control device of the vehicle, such as a mobile phone or a “plip” key.

[0038] The electrical control circuit 8 is configured to control the LED 60 and the motor 4 in a synchronized manner, in particular, to control the motor to change the image during a period of time during which the LED is kept off. The electrical control circuit 8 is capable of controlling the electrical current flowing in the LED as a function of a dimming frequency in pulse width modulation.

[0039] The control module 14 is configured to output a pulse width modulation dimming signal Sg, this signal having a frequency equal to the pulse width modulation dimming frequency. As illustrated in [Fig.6], the controllable current source 12 comprises a positive voltage input pin 16 and a common pin 18 for inputting the pulse width modulation dimming signal Sg and for putting the circuit 8 into standby or waking up. The electrical control circuit 8 is configured to go into standby after a predetermined duration without a signal on the common pin 18 (also called duration extinction), typically a duration of extinction of the controllable current source 12 of the order of 10 ms. Preferably, as illustrated in [Fig. 6], the controllable current source 12 also comprises an electronic component 19 integrating one or more controllable power transistors of the insulated gate field effect transistor (MOSFET) type, a diagnostic pin 20, two pins 22A, 22B for circulating a current for driving the LED 60, a set of capacitors C1, C2, C3, C4, an inductance L1, and a set of resistors R1, R2, R3, R4, two of these resistors R3, R4 of which are mounted in a voltage divider bridge on pin 22B of the electronic component 19. In the particular embodiment illustrated in [Fig.6], the controllable current source 12 thus forms a DC to DC converter as well as a synchronous regulator, configured to control the electric current flowing in the LED 60 (via the pins 22A, 22B), as a function of the dimming frequency in pulse width modulation. The pin 22B acts as a feedback input for the electric current flowing in the LED 60. Indeed, thanks to the voltage divider bridge R3, R4, the electronic component 19 is able to measure the value of the intensity of this electric current, and thus to be able to control the current as a function of the dimming frequency in pulse width modulation contained in the dimming signal Sg in pulse width modulation.The driving current of the LED 60, which has a frequency equal to the dimming frequency in pulse width modulation, thus leaves the electronic component via pin 22A, then flows into the LED 60, and finally returns to the electronic component 19 via pin 22B. The peak current of the driving current which supplies the LED 60 is for example a function of the temperature (using for example, to do this, a thermal resistance for at least one of the resistors R3, R4 of the voltage divider bridge).

[0040] Remarkably, the electrical control circuit 8 is configured to control the projection device to operate alternately, according to: • an image display mode, in which the image present on the path of the lighting beam is maintained in position, and • an image change mode, • LED 60 being powered with identical or different duty cycles, in the image display mode and in the image change mode.

[0041] In this case, in the image display mode, which corresponds to phase SI in FIGS. 7 and 8, the electrical control circuit 8 controls the electrical current flowing in the LED 60 as a function of a first dimming frequency in pulse width modulation Fl, and the electrical current which supplies the LED 60 varies over time t with a first duty cycle RI. The first dimming frequency in pulse width modulation Fl is for example substantially equal to 70 Hz, and the first duty cycle RI is for example substantially equal to 30%. The extinction duration of the controllable current source 12 is less than the period corresponding to the first dimming frequency in pulse width modulation FL In the chosen embodiment, the extinction duration of the controllable current source 12 is 10 ms and is in fact less than 14.3 ms = (1 / 70 Hz).

[0042] In the image change mode (phase S2, in FIGS. 7 and 8), the electrical control circuit 8 controls the electric current flowing in the LED 60 as a function of the first dimming frequency in pulse width modulation F1, and the electric current which supplies the LED 60 varies over the time t with a second duty cycle R2. In FIGS. 7 and 8, the second duty cycle R2 is equal to the first duty cycle RL. In a variant not illustrated, the second duty cycle R2 may be less than the first duty cycle RL. It is in this image change mode that the motor 4 sets the disc 5 in motion to replace the image (Iml for example) present on the path of the light beam F, with another of the images of the disc (Im2 for example).

[0043] Without this being limiting within the scope of the present invention, the switching from the image display mode to the image change mode can for example be triggered following the reception of a signal s for opening the opening 10, 11 by the electrical control circuit 8.

[0044] The switching from the static display mode to the image change mode could be triggered following the reception, directly by the electrical control circuit, of an opening control signal emitted by a remote control device of the vehicle with transmitter, such as a mobile telephone or a “plip” key.

[0045] Alternatively, the switching from the display mode to the image change mode can be triggered by the reception, by the electrical control circuit 8, of a signal s, transmitted by another electrical unit of the vehicle 1 (for example via a CAN network or equivalent), this other unit being in charge of the centralized control of the openings, or of the standby exit control of the vehicle, for example. In this case, the signal s received by the electrical control circuit 8, and according to which a change of projected image is triggered, is a signal for opening the opening 10, 11 of the vehicle. This signal s can be produced following the reception, by the electronic unit in question, of an opening command coming from a plip key or equivalent. The signal s can be emitted by the electronic unit in question (responsible for centralized opening) when it detects that an authorized user is at proximity of the vehicle, for example by detecting the proximity of a vehicle user identification badge (possibly a passive electronic badge), or a vehicle opening badge, an authorized mobile phone, or another identifiable electronic device.

[0046] The electric current I which supplies the LED 60 has a square wave variation here. That is to say, it varies by alternately presenting: • during a supply time interval, a constant intensity, called maximum peak current, then • during an extinction interval, a zero or substantially zero intensity (i.e. less than one tenth of the peak current, or even less), • then, again, a constant intensity, then zero, and so on.

[0047] The duty cycle of this square wave variation, denoted R, is equal to the duration of the power-on interval, divided by the sum of the duration of the power-on interval and the duration of the off interval. Thus, when R=10%, the LED is on for only 10% of the time period of the square wave signal (it is then on for 9 times less time than it is off, during this period).

[0048] Alternatively, the electric current could have a variation which is not exactly in a slot (for example with a slight variation in intensity during the supply interval), but nevertheless with, as previously: • a supply time interval, during which the current has a non-negligible intensity, for example greater at each instant than 1 / 10 of the maximum intensity of the current (again called peak current); then • an extinction time interval, during which the current has zero intensity or at least substantially zero (less than 1 / 10 of the peak current, or even less); • then again a power-on interval, then a power-off interval, and so on...

[0049] In this case, the duty cycle remains defined as indicated above (duration of the power-on interval, divided by the sum of the duration of the power-on interval and the duration of the power-off interval).

[0050] In the image change mode, the electric current therefore has a current slot, during the power supply time interval, then a zero or almost zero current during the extinction interval already mentioned. During the extinction interval, the electric control circuit 8 commands the motor 4 to rotate the disc 5 to replace the image present on the illuminating light beam with another image on the disc.

[0051] The duration of the extinction interval is at least equal to a replacement time of the image change module 7. This image replacement time, which is a kind of mechanical response time of this module, is equal to (or possibly even slightly greater than) the time required for the motor to rotate the disc from a first angular position, in which one of the images Iml, Im2, Im3, ... is in the light beam F, to a second angular position in which another of these images is located, entirely, in the light beams (with immobilization in this second angular position).

[0052] According to the invention, the method for controlling the image projection device 2 comprises, before the phase S1 of displaying a first image, an initial step (denoted S0 in FIGS. 7 and 8) during which the electrical circuit 8 controls the electric current flowing in the LED 60 as a function of a second dimming frequency in pulse width modulation F2. The second dimming frequency F2 is greater than the first dimming frequency F1, such that the duration of extinction of the controllable current source 12 is greater than or equal to the period corresponding to the second dimming frequency in pulse width modulation F2. The second dimming frequency in pulse width modulation F2 is preferably between 100 Hz and 400 Hz, for example substantially equal to 100 Hz.When the second dimming frequency in pulse width modulation F2 is equal to 100 Hz, and the extinction duration of the controllable current source 12 is equal to 10 ms, we have the extinction duration of the controllable current source 12 which is equal to the period corresponding to this second dimming frequency in pulse width modulation F2 (10 ms = 1 / 100 Hz).

[0053] During this same initial step S0, and as illustrated in [Fig.7], the electrical circuit 8 controls the pulse width modulation of the electric current flowing in the LED 60 (via the controllable current source 12) so that the duty cycle R of the variation of the electric current goes from a zero value to the value of the first duty cycle RI (this evolution of the duty cycle R being shown diagrammatically by the curve El in [Fig.7]). This makes it possible to obtain progressive, pleasant and “soft” lighting of the LED 60, and therefore of the projected image. Indeed, by increasing the dimming frequency in pulse width modulation to the value F2 during this initial step, it is possible to achieve much lower duty cycles of the current than in the display and image change modes, without risking that the electrical circuit 8 goes into standby and without having to change this electrical control circuit 8.The performance of the image projection device 2 in terms of display, i.e. in terms of visual rendering, is furthermore maintained.

[0054] Preferably, during this initial step S0, the electrical circuit 8 controls to the device 2 to operate according to a transition mode, during which the electric current flowing in the LED 60 has a time variation in slots, with an intermediate duty cycle, between the zero value and the value of the first duty cycle RI. The electric current flowing in the LED 60 then varies in slots by presenting several successive slots whose duty cycle R increases gradually and monotonically, from one slot to the next. During this transition mode, the duty cycle thus increases gradually from one slot to the next, to gradually pass from the zero value to the value of the first duty cycle RL

[0055] This gradual variation of the LED power parameters, and therefore of the lighting parameters of the projected image, makes it possible to make the initial transition to the display mode as "smooth" as possible for a user from a visual point of view.

[0056] In the transition mode, the successive values ​​of the duty cycle, corresponding to the successive electric current slots, can for example be equally distributed, between the zero value and the value of the first duty cycle RL. Other distributions (non-equal distribution) are nevertheless possible.

[0057] Although this is not shown in the figures, it should be noted that the method for controlling the image projection device 2 according to the invention may comprise a final step during which the electrical circuit 8 controls the electric current flowing in the LED 60 as a function of the second dimming frequency in pulse width modulation F2. During this final step, the electrical circuit 8 controls the pulse width modulation of the electric current flowing in the LED 60 (via the controllable current source 12) such that the duty cycle R of the variation of the electric current changes from the value of the first duty cycle RI to the zero value. This makes it possible to obtain a progressive, pleasant and “soft” extinction of the LED 60, and therefore of the projected image.

[0058] Preferably, during this final step, the electrical circuit 8 controls the device 2 to operate according to a second transition mode, during which the electric current flowing in the LED 60 has a time variation in square waves, with an intermediate duty cycle, between the value of the first duty cycle RI and the zero value. The electric current flowing in the LED 60 then varies in square waves by presenting several successive square waves whose duty cycle R decreases gradually and monotonically, from one square wave to the next. During this transition mode, the duty cycle thus gradually decreases from one square wave to the next, to gradually pass the value of the first duty cycle RI to the zero value.

[0059] In this second transition mode, the successive values ​​of the duty cycle, cor corresponding to successive electric current slots can for example be equally distributed, between the value of the first duty cycle RI and the zero value. Other distributions (non-equal distribution) are nevertheless possible.

Claims

1. Claims Method for controlling an image projection device (2), the device comprising: - at least one LED (60), which emits a light beam (F) for illumination when it is powered by an electric current, - an image change module (7) comprising different images (Iml, Im2, Im3) to be projected mounted or engraved on a mobile element (5) coupled to an electromechanical actuator (4), configured to place on the path of the light beam (F) for illumination, selectively, on command, one or other of the images to be projected, and - an electrical control circuit (8), connected to the LED (60) and to the actuator (4) of the image change module, and capable of controlling the electric current flowing in the LED as a function of a pulse width modulation dimming frequency (f), the electrical control circuit (8) comprising a control module (14) and a controllable current source (12) connected on the one hand to the control module (14) and on the other hand to the LED (60) to electrically power it, the control module (14) being configured to emit a pulse width modulation dimming signal (Sg) having said pulse width modulation dimming frequency (f), the controllable current source (12) comprising a positive voltage input pin (16) and a common pin (18) for inputting the pulse width modulation dimming signal (Sg) and for putting the circuit into standby or waking up (8),the electrical control circuit (8) being configured to go into standby mode after a predetermined period without a signal on said common pin (18), the method comprising the following modes: - in an image display mode (ID): the image present on the path of the lighting beam is maintained in position and the electric current which supplies the LED (60) varies over time with a first duty cycle (RD), and in an image change mode (S2): the electric current which supplies the LED (60) varies over time with a second duty cycle (R2), and the actuator sets the mobile element (5) in motion to replace the image present on the path of the beam with another of said images, the method comprising a phase (SI) of displaying a first image, during which the electrical circuit (8) controls the electric current flowing in the LED (60) as a function of a first frequency (Fl) of dimming in pulse width modulation, the electric current varying over time with the first duty cycle (RI), said predetermined duration of the electrical control circuit (8) being less than the period corresponding to said first frequency (Fl) of dimming in pulse width modulation, characterized in that the method further comprises, before the phase (SI) of displaying a first image, an initial step (S0) during which: the electrical circuit (8) controls the electric current flowing in the LED (60) according to a second dimming frequency (F2) in pulse width modulation, the second dimming frequency (F2) being greater than the first dimming frequency (F1), such that said predetermined duration of the electrical control circuit (8) is greater than or equal to the period corresponding to said second dimming frequency (F2) in pulse width modulation, and the electrical circuit (8) controls the pulse width modulation of the electric current flowing in the LED (60) such that the duty cycle (R) of the variation of the electric current goes from a zero value to the value of the first duty cycle (RI).

2.

3. The method of claim 1, wherein the second duty cycle (R2) is less than or equal to the first duty cycle (RI). A method according to claim 1 or 2, wherein, in the embodiment of image change (S2): the electric current has a square wave variation, the current being equal to a maximum current value during a feed interval and being substantially zero during an extinction interval, and wherein the actuator (4) is controlled so as to replace the image present in the beam path during said extinction interval.

4. A method according to any preceding claim, wherein the first duty cycle (RI) and / or the second duty cycle (R2) is substantially equal to 30%.

5. A method according to any preceding claim, wherein the first pulse width modulation dimming frequency (F1) is substantially equal to 70 Hz.

6. Method according to any one of the preceding claims, in which the second frequency (F2) of dimming in pulse width modulation is between 100 Hz and 400 Hz, preferably substantially equal to 100 Hz.

7. Method according to any one of the preceding claims, in which, during the initial step (S0), the electrical circuit (8) controls the device (2) to operate according to a transition mode, during which the electric current flowing in the LED has a time variation in a slot, with an intermediate duty cycle (R), between the zero value and the value of the first duty cycle (RI).

8. Method according to claim 7, in which, in the transition mode, the electric current flowing in the LED varies in a slot by presenting several successive slots whose duty cycle (R) varies gradually and monotonically, from one slot to another.

9. A method according to any preceding claim, wherein the peak current of the electric current supplying the LED (60) is a function of temperature.

10. Image projection device (2) comprising: - at least one LED (60), which emits a light beam (F) for illumination when it is powered by an electric current (I), - an image change module (7) comprising different images (Iml, Im2, Im3) to be projected mounted or engraved on a mobile element (5) coupled to an electromechanical actuator (4), configured to place on the path of the light beam (F) for illumination, selectively, on command, one (Iml) or the other (Im2) of the images to be projected, and - an electrical control circuit (8), connected to the LED (60) and to the actuator (4) of the image change module, and capable of controlling the electric current flowing in the LED as a function of a pulse width modulation dimming frequency (f), the electrical control circuit (8) comprising a control module (14) and a controllable current source (12) connected on the one hand to the control module (14) and on the other hand to the LED (60) to electrically power it, the control module (14) being configured to emit a pulse width modulation dimming signal (Sg) having said pulse width modulation dimming frequency (f), the controllable current source (12) comprising a positive voltage input pin (16) and a common pin (18) for inputting the pulse width modulation dimming signal (Sg) and for putting the circuit into standby or waking up (8),the electrical control circuit (8) being configured to go into standby mode after a predetermined period without a signal on said common pin (18), the electrical control circuit (8) being configured so that: - in an image display mode (SI): the image present on the path of the lighting beam is maintained in position and the electric current which supplies the LED (60) varies over time with a first duty cycle (RI), and the electrical circuit (8) is configured to control the electric current flowing in the LED (60) as a function of a first dimming frequency (Fl) in pulse width modulation, said predetermined duration of the electrical control circuit (8) being less than the period corresponding to said first dimming frequency (Fl) in pulse width modulation, - in an image change mode (S2): the electric current which supplies the LED (60) varies over time with a second duty cycle (R2), and the actuator (4) sets the mobile element (5) in motion to replace

11.

12.

13. the image present on the path of the beam by another of said images, the device (2) being characterized in that the electrical control circuit (8) is further configured to: controlling the electric current flowing in the LED (60) as a function of a second dimming frequency (F2) in pulse width modulation, the second dimming frequency (F2) being greater than the first dimming frequency (F1), such that said predetermined duration of the electrical control circuit (8) is greater than or equal to the period corresponding to said second dimming frequency (F2) in pulse width modulation, and controlling the pulse width modulation of the electric current flowing in the LED (60) such that the duty cycle (R) of the variation of the electric current changes from a zero value to the value of the first duty cycle (RI). Device (2) according to claim 10, further comprising a system projection optics (21) arranged to project onto the ground, from a motor vehicle (1), the image (Iml) placed on the path of the light beam (F). Device (2) according to the preceding claim, in which the electrical control circuit (8) is configured to: receive a signal(s) for opening or unlocking an opening (10, 11) of the vehicle (1), and for in response to said signal, commanding a switch from the image display mode (SI) to the image change mode (S2). Device (2) according to any one of claims 10 to 12, in wherein the controllable current source (12) is a direct current to direct current converter, configured to control the electric current flowing in the LED (60) as a function of the dimming frequency (f) in pulse width modulation.

14. Device (2) according to any one of claims 10 to 13, wherein the controllable current source (12) is a synchronous regulator.

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