Method for controlling a lighting system

Abstract

Method for controlling a lighting system. The invention relates to a method for controlling a lighting system (1), said lighting system (1) comprising a light emission means (2) emitting a light beam (FL) from at least one laser source (3, 4, 5), said light beam (FL) being emitted towards at least one mirror (7) of a microelectromechanical device (8) of the lighting system (1), the mirror (7) being configured to oscillate from a first position (A) to a second position (B) in order to reflect the light beam (FL) towards a projection area (10) by causing a sweep of the light beam (FL) over the projection area (10), the method comprising: - A step of determining an oscillation frequency of the mirror (7), - A step of adapting the energy emission intensity or switching off the at least one laser source (3, 4, 5) as a function of the oscillation frequency of the mirror (7). (Figure 1)

Description

Title of the invention: Method for controlling a lighting system

[0001] The present invention relates to the field of optoelectronics and finds particular application in the automotive industry. More specifically, it relates to lighting systems integrated into vehicles for the performance of signaling and / or decorative lighting functions.

[0002] These lighting systems, used both inside and outside vehicles, project light onto various surfaces to form patterns, warnings, or logos. Outside, they can be used for safety signaling, for example, by projecting open door warnings or parking guidelines onto the ground. Inside, these lighting systems can be implemented to enhance the vehicle's aesthetics and generate purely decorative patterns, but they can also contribute to safety, for example, by projecting pictograms representing a risky driving situation into the driver's field of vision.

[0003] Lighting systems for projecting pictograms, signage patterns, or decorative motifs onto a given projection surface can, for example, be based on the use of an RGB (Red, Green, Blue) light emission means composed of three laser sources. A light beam corresponding to one of these colors can then be combined with the other light beams to form a light beam, thus creating a wide range of colors. These lighting systems also include one or more mirrors onto which the light beam corresponding to the combination of the laser beams is directed. These mirrors are configured to direct said light beam toward a targeted projection area by oscillating from a first position to a second position, thus allowing the projection surface to be scanned at a speed high enough to give the user the impression that the projected image is stationary.

[0004] This light beam can, however, pose a danger to eye health. Indeed, when viewed, the light beam creates a retinal image which, depending on the beam's power, can cause eye damage. The greater the beam's power and the longer the exposure time on the retina, the greater the potential damage.

[0005] Under normal conditions, when the mirror oscillates, the exposure time is short, and the retinal image is formed only briefly. Thus, when the transit time is less than 5 microseconds, the thermal effect on the eye is minimal, thereby limiting the risk of eye damage, even with high light powers.

[0006] However, in the event of a failure of the mirror, for example a failure of a micro-electromechanical device controlling the mirror, resulting in a slowing down or a stoppage of the oscillation, the exposure time may increase, thus increasing the risk of eye damage by thermal effect depending on the power of the light beam.

[0007] This hazard necessitates a limitation on the power of the laser sources. Indeed, the various safety standards take into account both the normal operating conditions of the mirror and potential malfunctions. The power used in the RGB system is therefore limited by these standards, which reduces the maximum brightness that can be achieved by a projected image.

[0008] There is therefore a need for a method and / or a lighting system that allows the use of high powers in order to achieve high brightness of the projected image, while reducing the potential danger to the eyes.

[0009] The objective of the invention described in this document is therefore to overcome the drawbacks of the prior art by presenting a method for controlling a lighting system, said lighting system comprising a light emission means emitting a light beam from at least one laser source, said light beam being emitted towards at least one mirror of a microelectromechanical device of the lighting system, the mirror being configured to oscillate from a first position to a second position in order to reflect the light beam towards a projection area by causing a sweep of the light beam over the projection area, the method comprising:

[0010] - A step of determining an oscillation frequency of the mirror,

[0011] - A step of adapting the intensity of energy emission or stopping the minus a laser source depending on the oscillation frequency of the mirror.

[0012] Preferably, the light emission means emits a light beam composed of rays from several laser sources, for example an RGB system comprising a blue laser source, a red laser source and a green laser source.

[0013] In embodiments of the invention where the lighting system comprises several laser sources, the light-emitting means may include a mixing means, for example composed of dichroic mirrors, which combines the light rays from the laser sources into a single light beam. The light beam is then directed onto the mirror. It is therefore understood that, depending on whether each laser source is activated or deactivated at a given moment, the light beam projected onto the mirror has a specific color.

[0014] The light beam is then reflected by the mirror towards the projection area. The oscillation of the mirror is controlled by a microelectromechanical device. This oscillating movement allows the mirror to tilt from the first position to The second method allows the light beam to scan the entire projection area, thus creating a fixed image for the observer thanks to the effect of retinal persistence. It should be noted that everything that applies to a single mirror connected to the microelectromechanical device also applies, in the rest of the description, to a plurality of mirrors.

[0015] To obtain this retinal persistence effect, the mirror must oscillate at a certain oscillation frequency. It should be noted that this frequency is the inverse of the mirror's oscillation period, that is, the inverse of the time required for the mirror to move from the first position to the second position.

[0016] According to the invention, the aim is to avoid eye risks for observers when a malfunction of the device means that the effect of retinal persistence is lost, with the appearance of a luminous point instead of a line, thus increasing the luminous intensity at that point.

[0017] To this end, in the determination step, the method determines the oscillation frequency to check whether there is a stopping or a slowing down of the mirror's oscillation. For this purpose, the oscillation period is determined, and then the oscillation frequency is deduced from it. Commercially available microelectromechanical devices can be used to measure this oscillation period, and then the oscillation frequency is calculated from the measured period, possibly by a control element such as a PCB.

[0018] Alternatively, the method could simply determine the oscillation period without converting it into a frequency. In this case, the subsequent matching step is based on the oscillation period rather than the oscillation frequency.

[0019] Regarding the adaptation or shutdown step, this consists of adjusting or stopping at least one of the laser sources. More precisely, depending on the frequency or oscillation period determined during the determination step, the system can modulate or stop at least one of the laser sources. By modulating the energy emission intensity, or by stopping one of the laser sources while leaving at least one on when there are several, the method reduces the risk of eye injury by decreasing the energy emission intensity of the light beam, while maintaining a luminous function. By stopping all the laser sources, or the single source if there is only one, it completely eliminates this risk.

[0020] It should be noted that the choice of completely stopping the emission of the light beam or simply modulating its energy emission intensity may depend on the function of the projected image. Thus, if the projected image has a purely decorative function, it is not detrimental to program the stopping of the light beam emission in the event of a detected risk. On the other hand, when the projected image is associated with a safety function, it is preferable to provide the possibility of modulating the intensity. energy emission from the light beam, to continue to provide this safety function in a degraded version.

[0021] The control method thus makes it possible to use higher energy emission intensities within the lighting system, enabling the projection of a brighter image. In the event of a malfunction in the mirror's oscillation, the energy emission intensity is adjusted or completely stopped, thereby preventing eye hazards and allowing the safe use of a laser source capable of generating a higher energy emission intensity.

[0022] According to an optional feature of the invention, during the adaptation or shutdown step, at least one laser source is stopped when the oscillation frequency is below a shutdown threshold.

[0023] It is understood that when the lighting system comprises only one laser source, and if the oscillation frequency determined during the determination step is lower than the cutoff frequency, then this laser source is stopped. Thus, the light beam ceases to be emitted, interrupting the projection onto the projection area, thereby preventing potential eye problems due to an excessively low oscillation frequency.

[0024] It should be noted that, when the light system includes several laser sources, if the oscillation frequency is lower than the cutoff threshold frequency, all the laser sources are stopped, which makes it possible to completely interrupt the light beam.

[0025] Alternatively, the stopping threshold can be expressed in terms of oscillation period. In this case, at least one laser source, or all the sources if the light system has several, is stopped when the oscillation period determined during the determination step is greater than the stopping threshold period.

[0026] According to an optional feature of the invention, the light system comprises several laser sources and, during the adaptation step, at least one of the laser sources is stopped and at least one of the laser sources is kept active when the oscillation frequency is between a modulation threshold and the stopping threshold.

[0027] The use of an additional threshold, namely the modulation threshold, in addition to the stopping threshold, makes it possible to anticipate an intermediate state where the projection of the light beam can continue if the conditions do not appear too dangerous for the observer. This modulation threshold offers additional flexibility, allowing the system to maintain projection in situations where the risk to the eyes is deemed acceptable.

[0028] It should be noted that when the modulation threshold and the cutoff threshold are expressed in terms of frequency, the determined oscillation frequency must be lower than the modulation threshold frequency and higher than the cutoff threshold frequency. Conversely, when the modulation threshold and the cutoff threshold are expressed in terms of period, the determined oscillation period must be greater than the modulation threshold period and less than the cutoff threshold period.

[0029] When the oscillation frequency determined during the determination step lies between the modulation threshold frequency and the cutoff threshold frequency, one or more laser sources are switched off, but at least one source remains on; the energy emission intensity of the light beam is then reduced. Thus, when the modulation threshold frequency is reached, the projected image becomes less bright, and it disappears completely if the cutoff threshold frequency is reached.

[0030] By way of example, in an RGB system with three laser sources—blue, red, and green—one or two of the laser sources can be switched off when the oscillation frequency is between the modulation threshold frequency and the cutoff threshold frequency. If the oscillation frequency falls below the cutoff threshold frequency, all three sources are switched off. It is therefore understood that when the modulation threshold frequency is reached, there is a decrease in the energy output intensity of the light beam. However, a change in the color of the beam can also occur, since one or more colors disappear from the light beam when the corresponding sources are switched off.

[0031] According to an alternative of the invention, the light system comprises several laser sources and, during the adaptation step, the energy emission intensity of at least one of the laser sources is decreased when the oscillation frequency is between a modulation threshold and the stopping threshold.

[0032] The modulation threshold and the cutoff threshold, whether expressed in frequency or period, are based on the same principle as previously described. However, in this alternative, if the frequency or period lies between these thresholds, it is the energy emission intensity of at least one of the laser sources that is reduced, rather than switching off one or more laser sources.

[0033] Thus, when this reduction in the energy emission intensity of the laser sources is uniform between the laser sources, the energy emission intensity of the light beam decreases, which reduces the brightness of the projected image without changing its color.

[0034] According to an optional feature of the invention, the energy emission intensity of at least one laser source is decreased by modulating an electric current supplying energy to said laser source.

[0035] To modulate the electric current supplied to the laser source, the control method may in particular use the previously mentioned control element, which adjusts the electric current supplied and, consequently, influences the energy emission intensity of each of the laser sources.

[0036] According to an optional feature of the invention, the laser sources consist of a blue laser source, a green laser source, and a red laser source, with at least one laser source that is switched off or whose energy emission intensity is reduced being preferably the red or blue laser source. This constitutes an RGB system. According to the invention, when it is necessary to switch off one or more laser sources without switching off all the sources, the aim is to switch off the red or blue laser source. Indeed, in RGB systems, the red light beam represents approximately 50% of the energy emission intensity of the light beam, while the blue light beam represents approximately 25%. In comparison, the contribution of the green light beam is negligible.Thus, stopping the red or blue laser source has a much more significant impact on the energy emission intensity of the light beam than stopping the green laser source.

[0037] It should be noted that the process can modulate the energy emission intensity of only certain laser sources, such as blue or red, without necessarily stopping them completely.

[0038] According to an optional feature of the invention, the cutoff threshold frequency and the modulation threshold frequency are greater than the frequency of an eye danger threshold.

[0039] The eye hazard threshold corresponds to a theoretically calculated oscillation frequency above which the light beam, depending on its energy emission intensity and exposure time, can cause serious effects on the eyes. Therefore, the cutoff and modulation thresholds must be set at frequencies higher than this hazard threshold, since a lower frequency could pose a risk to the eyes.

[0040] Alternatively, when these thresholds are expressed in periods, the stopping threshold and the modulation threshold must be lower than the ocular danger threshold, because a longer oscillation period corresponds to a longer exposure time on the eye, increasing the ocular risk.

[0041] According to an optional feature of the invention, the frequency of the stopping threshold is between the frequency of the modulation threshold and the frequency of the eye danger threshold.

[0042] Indeed, when the oscillation frequency falls below the modulation threshold frequency, the energy emission intensity of the light beam decreases, which reduces the brightness of the projected image. When the frequency falls further and reaches the cutoff threshold frequency, the image projection ceases completely, thus eliminating the eye hazard, since the energy emission intensity of the light beam is reduced to zero. Thus, if the oscillation frequency reaches the frequency of the eye danger threshold, there is no risk to the eyes since the laser sources are deactivated.

[0043] Alternatively, when these thresholds are expressed in oscillation period, the period of the ocular danger threshold is higher than that of the stopping threshold, and the period of the modulation threshold is lower than that of the stopping threshold.

[0044] According to an optional feature of the invention, the system includes a control element controlling the laser sources and the oscillation frequency is calculated by the control element on the basis of information on an oscillation period of the mirror, the oscillation period being measured by the micro-electromechanical device.

[0045] The invention also relates to a lighting system enabling, in particular, the implementation of a method as previously mentioned. More specifically, according to the invention, a lighting system comprises a light emission means configured to emit a light beam towards a mirror of a microelectromechanical device, the light emission means comprising at least one laser source, the mirror being configured to tilt from a first to a second position in order to reflect the light beam, causing a sweep of said beam over a projection area, characterized in that the lighting system implements the control method as previously described.

[0046] Other features, details and advantages of the invention will become clearer upon reading the following description on the one hand, and the illustrative and non-limiting examples of embodiments given with reference to the accompanying drawings on the other hand, in which:

[0047] [Fig.1] is a schematic diagram of a lighting system within the meaning of the invention;

[0048] [Fig.2] is a flowchart of a first embodiment of an adaptation step of an energy emission intensity or stopping power of at least one laser source;

[0049] [Fig.3] is a logic diagram of a second embodiment of a step of adapting an energy emission intensity or stopping at least one laser source.

[0050] The features and variants of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of the features described below, isolated from the other described features, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0051] In the figures, the elements common to several figures retain the same reference.

[0052] The [Fig.1] is a schematic diagram of a lighting system 1 within the meaning of the invention.

[0053] The lighting system 1 includes a light emission means 2 emitting a light beam FL. This light emission means 2 includes at least one laser source, here three laser sources and more particularly a blue laser source 3, a green laser source 4 and a red laser source 5. It is therefore understood that the light emission means 2 uses in this embodiment a so-called RGB technology.

[0054] Each of these laser sources produces a light beam of a certain color. The red laser source 5 thus produces a red light beam RR which is then directed to a mixing means 6 of the light-emitting means 2. Similarly, the blue laser source 3 and the green laser source 4 produce respectively a blue light beam RB and a green light beam RV, which are also directed to the mixing means 6 of the light-emitting means 2.

[0055] The mixing means 6 here consists of a plurality of dichroic mirrors. It should be noted that other mixing technologies, different from dichroic mirrors, can also be used as long as they are capable of efficiently combining the three light rays into a single light beam FL, while directing them in a specific direction.

[0056] In this embodiment, the mixing means 6 comprises a blue dichroic mirror 61, a green dichroic mirror 62, and a red mirror 63. The blue dichroic mirror 61, the green dichroic mirror 62, and the red mirror 63 are positioned to intercept the light rays emitted respectively by the blue laser source 3, the green laser source 4, and the red laser source 5. Dichroic mirrors have the characteristic of selectively reflecting certain wavelengths while allowing others to pass through. Thus, they make it possible to select and combine the desired wavelengths, creating a light beam FL resulting from the combination of the three light rays emitted by the blue laser source 3, the green laser source 4, and the red laser source 5.

[0057] In the arrangement shown in [Fig. 1], the blue dichroic mirror 61 and the green dichroic mirror 62 are necessarily dichroic because they must reflect blue light and green light respectively, while allowing other wavelengths to pass through, but it should be noted that the red mirror 63 would not need to exhibit this dichroic property, because it only has to reflect red light and is not traversed by any other light ray.

[0058] In other embodiments of the invention, the red mirror 63 may, by way of non-limiting example, be positioned so that blue and green light pass through it. In this case, the red mirror 63 must be dichroic in order to allow these wavelengths to pass through while reflecting the red light. It should be noted that this positioning is particularly relevant in the generation of white light. Indeed, in this context, red light generally constitutes approximately 50% of the total energy emission intensity of the FL light beam, making it the limiting component in the production of white light. Positioning the red mirror 63 so that blue and green light pass through it prevents red light from passing through other dichroic mirrors, thus minimizing light intensity losses by eliminating any attenuation due to transmission through the blue dichroic mirror 61 and the green dichroic mirror 62.

[0059] In this embodiment, the laser sources are controlled by a control element 9. This control element 9 controls each laser source and allows one or all of the laser sources to be switched off, or the energy emission intensity of one or all of the laser sources to be modulated. It is thus understood that the control element 9 can adjust, by its action on the laser sources, the energy emission intensity of the light beam FL produced by the light emission means 2.

[0060] The light beam FL, after being combined by the mixing means 6, is directed towards a mirror 7. This mirror 7 can oscillate between a first position A and a second position B. To do this, it can pivot about one or more axes, so as to be able to oscillate between the two positions A, B. It should be noted that everything that applies and is described for a single mirror 7 can be applied to a plurality of mirrors 7.

[0061] In the first position A, the mirror 7 reflects the light beam FL onto a projection area 10 at a first location within that projection area 10. When the mirror 7 is positioned in the second position B, it reflects the light beam FL to a second location within the projection area 10. Thus, it is understood that when the mirror 7 moves from the first position A to the second position B and vice versa, the light beam FL moves from the first location within the projection area 10 to the second location within the projection area 10 and vice versa. The oscillation of the mirror 7 between these two positions A and B is rapid, so that when this movement occurs, the human eye perceives a line on the projection area 10 between the first and second locations within the projection area 10, due to the phenomenon of retinal persistence.

[0062] In order to allow the oscillation of the mirror 7, it is connected to a micro-electromechanical device 8. This micro-electromechanical device 8 provides the necessary energy and controls the oscillation of the mirror 7 from the first position A to the second position B.

[0063] The assembly formed by the microelectromechanical device 8 connected to the mirror 7 is generally called a MEMS mirror. In this context, the microelectromechanical device 8 is a microsystem made from semi-solid materials conductors, which includes one or more mechanical elements, notably to oscillate the mirror 7.

[0064] By way of non-limiting example, the mirror 7 oscillates between the first position A and the second position B with an oscillation period of between 24 and 300 ms for a light beam power FL of between 650 and 700 mW. It is thus understood that, in a light system 1 with a light beam power FL of between 650 and 700 mW, the oscillation frequency is between 3 and 35 kHz.

[0065] In rare cases, the oscillation of mirror 7 may slow down or stop. This has the effect of increasing the oscillation period, thus reducing the oscillation frequency. In these situations, the oscillation period and frequency may no longer correspond to the aforementioned values.

[0066] Various causes can lead to a slowing or stopping of the oscillation of the mirror 7. For example, malfunctions can occur due to damaged connections that transmit signals between the mirror 7 and the microelectronic device 8, thus preventing the mirror 7 from receiving the commands necessary to change position. In addition, an interruption of the power supply to the microelectromechanical device 8 can prevent the mirror 7 from operating. Furthermore, the mirror 7 can also be mechanically blocked.

[0067] In the event of a malfunction, the oscillation frequency of the mirror 7 may decrease, and in such cases, the mirror 7 may stop oscillating altogether. To prevent any impact of the light beam on the health of an observer in such situations, the invention therefore proposes a control method to be implemented in the lighting system 1 as described above.

[0068] This control method is specifically designed to regulate the energy emission intensity of the light beam FL from the light-emitting means 2. More precisely, it allows this energy emission intensity to be modulated according to the oscillation frequency or the oscillation period of the mirror 7. Thus, if the oscillation frequency decreases and the oscillation period increases, the method reduces the energy emission intensity of the light beam FL or stops it completely. This makes it possible to use a high-power light source, which, at full power, allows for the generation of high-intensity light beams while avoiding the eye risks associated with a malfunction in the oscillation of the mirror 7.

[0069] It should be noted that the method can be based either on the oscillation period of the mirror 7, or on the oscillation frequency of the mirror 7. When it is based on the oscillation frequency, the method uses the oscillation period to calculate the oscillation frequency, whereas when it is based on the oscillation period, the method retains the oscillation period as such.

[0070] The method thus includes a step of determining the oscillation frequency or the oscillation period of the mirror 7. To do this, the microelectromechanical device 8 may include elements capable of measuring the oscillation period and extracting information relating to the oscillation period. Commercially available microelectromechanical devices 8 generally possess this capability.

[0071] Regardless of whether the process operates based on oscillation period or oscillation frequency, the information relating to the measured oscillation period is transmitted to the control unit 9, as illustrated by line I in [Fig. 1]. When the process is based on the oscillation frequency, the control unit 9 calculates the frequency from the measured oscillation period. Conversely, when the process is based on the oscillation period, the control unit 9 does not calculate the oscillation frequency and directly uses the oscillation period as a parameter.

[0072] The determination step therefore makes it possible to check if the frequency or period of oscillation is correct and to detect any possible malfunction of the oscillation of the mirror 7.

[0073] The method then includes a step of adapting the intensity of energy emission or stopping at least one of the laser sources as a function of the oscillation frequency of the mirror 7 or the oscillation period of the mirror 7.

[0074] Figure 2 is a flowchart of a first embodiment of the step of adapting the energy emission intensity or stopping at least one laser source. It should be noted that in this figure, the oscillation frequency of mirror 7 is represented by the letter "F" and its oscillation period by the letter "P".

[0075] In this embodiment, the control method implements a stop step without the possibility of adapting the energy emission intensity of the laser sources.

[0076] During this step, the process therefore stops the operation of the entire light-emitting means 2 in order to interrupt the projection of the light beam FL. Thus, when only one laser source is used in the light-emitting means 2, it is switched off, and when several laser sources are present, they are all switched off, thereby preventing any projection of the light beam FL.

[0077] The control unit 9, based on the frequency or oscillation period determined during the determination step, decides and controls the shutdown of the laser source(s) in order to cease the emission of the light beam FL. To this end, the method determines in a first step SI the oscillation frequency F or the oscillation period P of the mirror 7, and then compares it in a second step S2 with respect to a defined threshold, namely the shutdown threshold SA.

[0078] This SA stopping threshold is itself defined in relation to another threshold, namely the eye hazard threshold SD. The eye hazard threshold SD represents a frequency of mirror oscillation 7 dangerous for the eyes or a period of mirror oscillation 7 dangerous for the eyes.

[0079] It is thus understood that when the process operates in frequency mode, if the oscillation frequency F of the mirror 7 is lower than the danger threshold frequency SD, there is an eye risk. Similarly, when the process operates in period mode, if the oscillation period P is greater than the danger threshold period SD, there is also an eye risk.

[0080] The cutoff threshold SA corresponds to the threshold at which the laser sources are switched off in order to completely stop the emission of the light beam FL. The cutoff threshold SA is positioned relative to the eye hazard threshold SD. It must therefore be positioned sufficiently far from this hazard threshold SD so that, in the event of a rapid decrease in the oscillation frequency F of the mirror 7, and thus a rapid increase in the oscillation period P, the method can stop the emission of the light beam before the eye hazard threshold SD is reached.

[0081] It is therefore understood that, when the process operates in frequency mode, the frequency of the stopping threshold SA is higher than that of the eye hazard threshold SD. Conversely, when the process operates in period mode, the period of the stopping threshold SA is lower than that of the eye hazard threshold SD.

[0082] Thus, when the process operates in frequency mode, if the oscillation frequency F of the mirror 7, determined during the determination step, is lower than the cutoff threshold frequency SA, the control process implements a third step S3 in which the control element 9 shuts down the laser source(s) to completely cease the emission of the light beam FL. Similarly, when the process operates in period mode, if the oscillation period P of the mirror 7 exceeds the cutoff threshold period SA, the laser source(s) are also switched off by the control element 9 to completely interrupt the emission of the light beam FL in a corresponding third step S3.

[0083] Conversely, when the oscillation frequency F of mirror 7 is greater than the stopping threshold frequency SA or when the oscillation period P of mirror 7 is less than the stopping threshold period SA, the control method implements a fourth step S4 during which normal operation is maintained, without intervention from the control unit and therefore without altering the energy emission intensity of the light beam. Of course, at the output of the third step S3 or the fourth step S4, selectively implemented depending on the result of the comparison performed in the second step S2, the first step can be cyclically reactivated to ensure continuous monitoring over time and, if necessary, to allow a return to normal operation should the malfunction be resolved.

[0084] It should be noted that the eye hazard threshold SD can vary depending on the energy emission intensity of the light beam FL. Indeed, a high energy emission intensity increases the risk of eye hazard, thus requiring a stricter eye hazard threshold SD, with a higher frequency and a shorter period. The stopping threshold SA therefore also depends on the energy emission intensity of the light beam FL, since it is determined based on the eye hazard threshold SD.

[0085] Fig. 3 is a flowchart of a second embodiment of the step of adapting the intensity of energy emission or stopping at least one laser source.

[0086] In this second embodiment, the control method considers, in addition to the stopping threshold SA during the second step S2, which can always lead to a third step S3 of stopping the function, a modulation threshold SM. This modulation threshold SM, like the stopping threshold SA, is set at a higher frequency than that of the eye hazard threshold SD when expressed as an oscillation frequency, and at a shorter period than that of the eye hazard threshold SD when expressed as an oscillation period.

[0087] Furthermore, when the process operates in frequency mode, the modulation threshold SM is set at a higher frequency than the cutoff threshold SA, such that the cutoff threshold frequency SA lies between the modulation threshold frequency SM and the eye hazard threshold SD. Similarly, when the process operates in period mode, the period of the modulation threshold SM is shorter than the cutoff threshold SA, so that the cutoff threshold period SA lies between the modulation threshold period SM and the eye hazard threshold SD.

[0088] It follows that the fourth step S4 of the embodiment described above is implemented, if necessary, only following a first additional step S5 which consists of a step of comparing the oscillation frequency F or the oscillation period P with respect to the corresponding modulation threshold SM.

[0089] Following this first additional step S5 of the second embodiment, when the process operates in frequency mode, if the determined oscillation frequency F of the mirror 7 is lower than that of the modulation threshold SM but higher than that of the stopping threshold SA, the energy emission intensity of the light beam FL is modulated in a second additional step S6. Similarly, when the process operates in period mode, if the oscillation period P of the mirror 7 is higher than that of the modulation threshold SM but lower than that of the stopping threshold SA, the energy emission intensity of the light beam FL is also modulated in this second additional step S6.

[0090] As before, if the result of the comparison is favorable, the control process implements the fourth step S4 during which normal operation is perpetuated, without intervention of the control unit and therefore without alteration of the energy emission intensity of the light beam.

[0091] Thus, between the modulation threshold SM and the cutoff threshold SA, the energy emission intensity of the light beam FL is modulated, while between the cutoff threshold SA and the danger threshold SD, the light beam FL is completely switched off. This allows a light signal to continue to be displayed even if the oscillation frequency of the mirror 7 slows down, and without endangering the user.

[0092] Several solutions exist for modulating the energy emission intensity of the light beam FL. One solution consists of adjusting the energy emission intensity of the laser source when there is only one within the light emission means 2, or of at least one of the laser sources when there are several, which has the effect of reducing the energy emission intensity of the light beam FL. To this end, the control element 9 controls the energy emission intensity of the laser source(s) by modulating the electrical current supplied to these laser sources, in order to manage their respective energy emission intensity.

[0093] When several laser sources are present, it is possible to modulate the energy emission intensity of all the laser sources or only some of them. Typically, in this embodiment, the energy emission intensity of all the laser sources, that is, of the three laser sources, is modulated simultaneously to adjust the energy emission intensity of the light beam FL. Thus, when the energy emission intensity of the light beam FL is modulated in this way, the color of the emitted light signal does not change, because the proportion of each light ray in the light beam FL remains constant.

[0094] Alternatively, it is possible to reduce the energy emission intensity of a single laser source while maintaining the energy emission intensity of at least one other laser source. In this case, the color of the FL light beam will change, resulting in a light signal of a different color. Preferably, if the energy emission intensity of all laser sources is not modulated, the energy emission intensity of the red laser source 5 or the blue laser source 3 is modulated, as they contribute most significantly to the overall energy emission intensity of the FL light beam. For example, the red light beam RR can represent up to 50% of the total energy emission intensity of the FL light beam.

[0095] A second solution for modulating the energy emission intensity of the light beam FL, in the case where the light emission means 2 contains several laser sources, is to completely switch off at least one of the laser sources while at unless another remains in operation. In the case of an RGB system, as described previously, it is therefore possible to turn off one or two of the laser sources.

[0096] Preferably, in an RGB system, it is the red laser source 5 that is switched off, since the red light beam RR generally represents about 50% of the light beam FL. The switched-off laser source can also be the blue laser source 3, or the red laser sources 5 and blue laser sources 3, since blue is the second most prevalent color in the light beam FL. The green component, on the other hand, contributes little to the total power of the light beam FL. In this context, it is therefore generally less relevant to switch it off, although this is possible with the method described in the invention.

[0097] As described above, the present invention achieves its objective by providing a method for controlling at least one laser source in a lighting system, based on the oscillation frequency or period of a mirror reflecting a light beam from a light-emitting means containing this laser source. This control method avoids eye risks due to a malfunction in the mirror's oscillation, because in the event of a malfunction, the energy output of the light beam is adjusted to prevent any problems.

[0098] The present invention is not limited to the means and configurations described and illustrated herein and also extends to any equivalent means and configuration as well as to any technically operative combination of such means.

Claims

Demands

1. Method for controlling a light system (1), said light system (1) comprising a light emission means (2) emitting a light beam (FL) from at least one laser source (3, 4, 5), said light beam (FL) being emitted towards at least one mirror (7) of a micro-electromechanical device (8) of the light system (1), the mirror (7) being configured to oscillate from a first position (A) to a second position (B) in order to reflect the light beam (FL) towards a projection area (10) causing a sweep of the light beam (FL) over the projection area (10), the method comprising: - a step of determining an oscillation frequency of the mirror (7), - a step of adapting the intensity of energy emission or stopping of the at least one laser source (3, 4, 5) as a function of the oscillation frequency of the mirror (7).

2. A control method according to claim 1, wherein during the adaptation or shutdown step, at least one laser source (3, 4, 5) is stopped when the oscillation frequency is below a shutdown threshold (SA).

3. A control method according to claim 2, wherein the light system (1) comprises several laser sources (3, 4, 5) and wherein, during the adaptation step, at least one of the laser sources (3, 4, 5) is stopped and at least one of the laser sources (3, 4, 5) is kept active when the oscillation frequency is between a modulation threshold (SM) and the stopping threshold (SA).

4. A control method according to claim 2, wherein the light system (1) comprises several laser sources (3, 4, 5) and wherein, during the adaptation step, the energy emission intensity of at least one of the laser sources (3, 4, 5) is decreased when the oscillation frequency is between a modulation threshold (SM) and the stopping threshold (SA).

5. A control method according to claim 4, wherein the energy emission intensity of at least one laser source (3, 4, 5) is decreased by modulating an electric current supplying energy to said laser source (3, 4, 5).

6. A control method according to any one of claims 3 to 5, wherein the laser sources (3, 4, 5) consist of a blue laser source (3), a green laser source (4) and a red laser source (5), at least one laser source (3, 4, 5) which is stopped or whose energy emission intensity is reduced being preferably the red laser source (5) or blue (3).

7. A control method according to any one of claims 3 to 6, wherein the cutoff threshold frequency (SA) and the modulation threshold frequency (SM) are greater than the frequency of an eye hazard threshold (SD).

8. A control method according to claim 7, wherein the cutoff threshold frequency (SA) is between the modulation threshold frequency (SM) and the eye hazard threshold frequency (SD).

9. A control method according to any one of claims 1 to 8, wherein the light system (1) comprises a control member (9) controlling the laser sources (3, 4, 5) and wherein the oscillation frequency is calculated by the control member (9) on the basis of information on an oscillation period of the mirror (7), the oscillation period being measured by the microelectromechanical device (8).

10. A lighting system (1) comprising a light emission means (2) configured to emit a light beam (FL) towards a mirror (7) of a micro-electromechanical device (8), the light emission means (2) comprising at least one laser source (3, 4, 5), the mirror (7) being configured to tilt from a first position (A) to a second position (B) in order to reflect the light beam (FL) causing a sweep of said beam (FL) over a projection area (10), characterized in that the lighting system (1) implements the control method according to any one of claims 1 to 9.

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