DE102021209454A1 - Method for controlling a laser diode and a digital micromirror device of an imaging unit in a holographic head-up display - Google Patents

Abstract

A method for controlling a light source and a digital micromirror device (DMD) having an imaging unit, wherein a light beam from the light source is directed onto a number of micromirrors of the DMD, with the help of which an image can be generated and output depending on the respective mirror positions : operating the DMD by means of pulse width modulation in a scheme of bit segments that follow one another within an update time; activating at least one micro-mirror to set a first mirror position (ON) within a first sub-interval of the update time comprising one or more pulses, the pulses corresponding to the bit segments, such that the light beam portion incident on the micro-mirror is emitted; and providing a power supplied to the light source for at least the period of time of the first sub-interval to cause the light source to emit a predetermined amount of light therein. In a first mode of operation, the light source is powered within a second sub-interval of the same update time, in which the at least one micro-mirror of the digital micro-mirror device assumes a second mirror position (OFF) so that the light beam fraction incident on the micro-mirror is not output from the imaging unit . A time-average value of the power in the second sub-interval is increased compared to a time-average value of the power within the first sub-interval in order to counteract cooling of the light source in the case of a small amount of light intended for output from the image-forming unit.

Description

technical field

Aspects of the invention presented here relate to a method for controlling at least one light source and a digital micromirror device of an imaging unit, with a light beam being directed from the light source onto a number of micromirrors of the digital micromirror device, with the aid of which an image is generated by the imaging unit depending on the respective mirror positions unit can be generated and output. These or other aspects also relate in particular to an augmented reality (AR) head-up display, which has the imaging unit.

State of the art

Applications from the areas of augmented reality ("augmented reality", AR, often also referred to as "true AR") have increasingly found their way into the field of head-up displays in recent years. Here, e.g. by means of the head-up display, the vehicle driver is shown two or three-dimensional information in a holographic manner in his field of vision through a window of the vehicle (in particular the windshield) or the field of vision with objects detected therein is superimposed with this information. This can be done via a holographic optical element (HOE) integrated into the window (or into a transparent plate placed in front of it), which - also referred to as a so-called combiner - is irradiated in a suitable manner by an imaging matrix with a light wave front, with the Utilization of the effects of the implemented in the holographic optical element hologram highly coherent light is required, which can therefore preferably come from one or more laser modules in which laser diodes or laser diode arrays are installed.

Such head-up displays usually include an imaging or image-generating unit (PGU) with a light source, an optics module and the combiner or the HOE element as a projection surface. The imaging unit usually has a digital micromirror device (DMD) whose micromirrors can be individually controlled in a known manner in an “ON” or “OFF” position in order to generate and project a desired image when the Radiation from the light source is directed onto the digital micromirror device. Light intensities are often generated via pulse width modulation during operation of the micromirror. Such a system is, for example, in D. Doherty, G. Hewlett: "Phased Reset Timing for Improved Digital Micromirror Device Brightness", in SID International Symposium 1998, published by Society for Information Display, Santa Ana, CA, ISSN0098-0966X/98/ 2901 (hereinafter: Doherty et al. (1998)) or in WO 94/09472 A1 described. In particular, an amplitude modulated video signal is converted into a digital representation of the pulse width modulation. This means that the individual micromirrors are set to the "ON" or "OFF" position in a fixed time frame with division into sequences of bits in order to generate a specific brightness amplitude. The time frame specified in each case for the micromirrors corresponds to an update time (total refresh period) of the micromirror in question. This is divided into bits, each with a specified time period. The bit with the least significant bit (LSB, least significant bit) comprises a fraction 1/(2 ⁿ −1) of the total time of the time frame, where n is the total number of bits provided, for example n=5 in the publication cited. The next higher bit includes twice the fraction or twice the time duration, etc. In order to split up those bits that are consequently assigned longer time durations and thus improve the integration of the light by the human eye, so-called bit splitting is also used , so that within each individual time frame, the "ON" and "OFF" positions assigned to the individual bits are evenly distributed. The most significant bit (MSB, most significant bit), within which the mirror position is either only "ON" or only "OFF", could otherwise - depending on the duration of the time frame (or the total refresh period) and the selected number n of bits - have a length that can already be perceived by the human eye.

In a holographic AR head-up display, e.g. in the case of a motor vehicle, a laser with a very narrow wavelength spectrum is required as the light source for the holographic optical element (HOE) in the windshield, which is why semiconductor lasers are particularly suitable. However, the wavelength of semiconductor lasers is temperature-dependent, which is why the relevant laser diodes generally have to be kept at a substantially constant temperature during operation. More precisely, there is a need to keep the junction temperature of the semiconductor components of the laser diodes constant. Although a certain stabilization against temperature fluctuations can be achieved by considering external cavities (resonators) in the laser diodes with the aid of, for example, volume Bragg gratings (VBG), a further improvement is definitely desirable.

At the same time, however, considerable differences in brightness should also be possible in an AR head-up display. This can apply, for example, in motor vehicles for night-time driving conditions, in particular when the brightness in the AR head-up display has to be adjusted when the backlight from oncoming vehicles fluctuates greatly. However, it may also be necessary to quickly adjust the brightness in daytime driving conditions, for example when entering or exiting tunnels, etc.

For this brightness adjustment, the current or the power and/or the duration of the laser pulses must also be adjusted with which the laser diode(s) in the AR head-up display are operated. If the average power of a relevant laser diode is reduced, the junction temperature is then also reduced as a result, which in turn can lead to a wavelength drift and/or line broadening of the radiation emitted by the laser.

In order to prevent the wavelength drift and/or line broadening, a Peltier element (thermoelectric cooler, TEC) could be provided in order to achieve a responsive temperature control with only a small delay. It is known to arrange Peltier elements adjacent to components (packages with chip and housing), such as laser diodes, in order, for example, to bring about a cooling or heating effect in order to compensate for temperature fluctuations in a targeted manner. However, the effect of such a structure is too sluggish in time to meet the above requirements in a head-up display.

In the publication KR 10-2020-0040408 A it was proposed to mount the semiconductor component (i.e. the chip) in a laser diode package including the housing directly on this Peltier element. However, such retrofitted laser diodes (as laser packages) for red, green, blue (RGB) and with sufficient power for use in AR head-up displays are currently not available.

There is therefore a problem of how, e.g. even with a comparatively sluggish temperature control by means of a Peltier element provided only outside the laser package, rapid brightness adjustments can nevertheless be made possible without the wavelength of the laser changing. It should be noted that similar problems can also exist with other optical elements that are strongly dependent on wavelength, such as the diffraction gratings mentioned above. Such are also used, for example, in head-up displays with fiber optic technology.

In the pamphlet DE 10 2006 036 112 A1 describes a method for operating a lighting system with a high-pressure discharge lamp, the emitted radiation of which is also supplied to an electronic micromirror device. Colors are generated in a known manner by means of a color wheel through which the radiation is passed, defining a plurality of sequential color segments. The commutating lamp current has half-waves to which the color segments are assigned, with each half-wave being assigned a number of color segments. At the end of each half-wave, a so-called maintenance pulse is emitted, which stabilizes the discharge of the lamp. This maintenance pulse increases the lamp current for a short time and is in an intermediate phase in which the output of the radiation reflected by the micromirror device for the purpose of projection is suppressed. This stabilizes an electrode temperature of the high-pressure discharge lamp, which has a positive effect on the discharge. The effect of the lamp current during the color segments of a half-cycle and the maintenance pulse of the same half-cycle on the electrode temperature at the time of the commutation following the half-cycle is balanced in such a way that the discharge is stabilized even if the color temperature is changed during operation. For this purpose, the amplitude of the lamp current in the color segments is compensated for by changing the lamp current in the intermediate phase, for example by changing the duration of the maintenance pulse or by changing the amplitude of the same.

Presentation of Aspects of the Invention

Some of the aspects described below are based on the object of enabling rapid brightness adjustments in an imaging unit with a light source, even with great dynamics, without the parameters of the light source changing in the process, in particular the wavelength in the case of a laser used.

The object is achieved by a method for controlling at least one light source and an imaging unit having a digital micromirror device with the features of patent claim 1. Advantageous refinements and developments are specified in the dependent claims.

The starting point is a corresponding method in which a light beam from the light source is directed onto a number of micromirrors of the digital micromirror device (DMD), with the help of which an image is generated by the imaging unit (PGU) depending on the respective mirror positions and can be issued. The light source can preferably be one or more laser modules.

Such a method comprises, for example, steps in which the digital micromirror device is operated by means of pulse width modulation in a scheme of bit segments of a predetermined time duration which follow one another within an update time or a time frame. In particular, this means that - as described at the beginning - the individual micromirrors are switched to the "ON" positions separately and independently of one another in a fixed time frame (frame or total refresh period), which can correspond to the update time, with division into sequences of bits. or "OFF" can be set in order to generate a certain brightness amplitude, which is specified, for example, and/or can correspond to a video signal. The time frame specified in each case for the micromirror can correspond to an update time (total refresh period) of the micromirror in question. This is divided into bits, each with a specified time period. The update time is defined as the smallest unit of time on the basis of which the brightness of the radiation reflected by the micromirrors (e.g. for a laser module of a specific color) is controlled for since the assignment of ON'' or "OFF" to the bits only gives this value in an integrated manner.

The scheme of bit sequences can also be used, for example, as described in Doherty et al. (1998): the least significant bit (LSB) comprises, for example, a fraction 1/(2 ⁿ -1) of the total time of the time frame, where n is the total number of bits provided. The next higher bit comprises twice the fraction or time duration, etc. up to the most significant bit (MSB), which has the longest time duration, namely the fraction 2 ^n-1 /(2 ⁿ -1).

The respective bit segment within the time frame or the update time of the micromirrors can now have the time duration assigned to the corresponding bit. This does not have to be done “in one go”. Rather, as above with reference to, for example, Doherty et al. (1998) additionally described within the update time, ie split up. This means that within each individual time frame, the "ON" and "OFF" positions assigned to the individual bits are divided and, for example, divided into segments with approximately the same length of time. Each bit segment described here with the "ON" or "OFF" position assigned to it can therefore be the duration of the entire bit (e.g. fractions of 1/(2 ⁿ -1) to 2 ^n-1 /(2 ⁿ -1) of the update time) or - in the case of bit splitting - of the divided segments (fractions purely as an example as in Doherty et al. (1998): 1/(2 ⁿ -1) for bit 0, and 2/(2 ⁿ -1) for all other, especially split bits 1,...,n-1, with n=number of bits).

It should be noted here that, according to aspects of the invention, other or modified schemes are also possible in principle. The invention is not limited to the specific configuration of the representation of the pulse widths in bits in order to achieve a specific integrated brightness. It is also possible to control the micromirrors with continuously varying pulse widths.

The method proposed here also comprises the steps of activating at least one micromirror of the digital micromirror device in order to, within a first partial interval of the update time comprising one or more pulses, wherein the pulse(s) correspond to the bit segment(s), a set the first mirror position (e.g. "ON") in such a way that the portion of the light beam falling on the micromirror is output from the imaging unit. In other words, as described above, the micromirrors are set to "ON" bit by bit or bit segment by bit - depending on the desired brightness - in order to emit light. These bits or bit segments together form a first interval that is not necessarily contiguous in the time frame. Alternatively, only each individual pulse width can be considered, which then combines exclusively contiguous bit segments or possibly even just a single "ON" switched, isolated bit segment to form the first sub-interval. It should be noted that the chosen designation "ON" for a mirror position, where the beam is reflected in such a way that it is output from the imaging device, is purely subjective and does not reflect whether the micromirror in question is in that position with power or voltage is supplied or not.

Further steps are providing power to the light source for at least the duration of the first sub-interval to cause the light source to emit a predetermined amount of light therein. This can mean that the respective micromirror is supplied with essentially constant power within the first partial interval and correspondingly also emits essentially constant light power. This can also be reduced in amplitude. However, it can also mean in particular that the individual bit segments are not provided with a constant power supply within their intended time period, or even with a power supply that is only provided at times or in sections in order to control the average light output.

Individual aspects of the invention now provide a first operating mode in which the light source assumes a second mirror position (OFF) within a second sub-interval of the update time, which is complementary to the first sub-interval, in which the at least one micro-mirror of the digital micro-mirror device assumes a second mirror position (OFF), so that the light falling on the micro-mirror Light beam portion is not output from the imaging unit is supplied with a power. In other words, the light source also radiates when the relevant micromirror reflects the radiation in such a way that it does not leave the imaging unit as useful radiation. One possibility is that the reflected light beam is directed into a light sink (eg light-absorbing screen, etc.) in this mirror position.

The light yield (power of the useful light over the entire time frame depending on the power used in the light source) is of course reduced by this control. However, independent of the respective pulse widths, a power that is essentially more balanced over time is implemented in the light source, in particular a laser module. As a result, the heat input in the light source tends to be decoupled from the currently requested light requirement.

Like the first sub-interval, the complementary second sub-interval can comprise one or more bit segments, which also do not necessarily have to be contiguous. However, the second sub-interval can also only be the sub-interval that follows (or respectively precedes) the individual pulse of the first sub-interval, until a new pulse of a subsequent bit segment begins.

It should be noted that “complementary” here designates a second time interval that is different from the first interval and that fills the time frame, but only to the extent that activation of the micromirrors is possible at all. In the case of color rendering with RGB, the colors are activated regularly and sequentially, which means that the update time is tripled, for example. Nevertheless, according to embodiments, the complementary second time interval is limited to the time that the respective color is activated. Since three laser modules are controlled in the same way but with different bit values, in this case three first time intervals and three associated, complementary second time intervals occur within the one higher-level update time. The colors must not overlap in time. An embodiment is described in detail below. The update time, as it is used here in the narrower sense, therefore corresponds to the duration of the time frame defined for a color or the sum of the time durations of the bits or bit segments contained therein.

Furthermore, according to the present aspects, in this control, a time-average value of the power in the complementary second sub-interval is increased compared to a time-average value of the power within the first sub-interval. This power control can be used to counteract a cooling of the light source even more effectively in the case of a small amount of light that is intended or requested for output from the imaging unit.

This measure is particularly effective when the amount of light is regulated so far, e.g. due to low external requirements, that in the scheme of consecutive bit segments within an update time with a constant amplitude of the power supply, the average radiated light power is no longer limited by a " ON" switched least significant bit (LSB) can be represented. Rather, according to configurations, the amplitude within the bit segments can be further reduced by additional measures in order to thus achieve a high dynamic range of the light output. i.e. a large ratio between maximum and minimum light output. Such measures are described, among other things, in "Enabling the Next Generation of Automotive Head-Up Display Systems", Application Report DLPA043A (Oct. 2013, revised version Nov. 2017) from Texas Instruments.

By compensating for the very low power in this case within the first sub-interval with a higher power or increased power in the second sub-interval, the total power consumption remains constant regardless of the light requirement or the light yield and the heat input also remains constant as a result. This effectively prevents a disadvantageous change in the laser properties during operation, in particular a wavelength drift, etc.

Such an operating mode can be particularly useful in those situations where high dynamics are required in a short adaptation time, for example with a head-up display installed in the vehicle in a situation in which the vehicle enters tunnels, underpasses, multi-storey car parks or underground car parks during the day - or departing, or in the case of an aircraft that enters dense clouds separated from each other by free sunlit areas. These transitions happen suddenly. For example, a lower brightness requirement after entering the tunnel would lead to a drop in performance, which in turn would result in a temperature change in the laser module. This could come from conventionally, as described, affect the quality of the radiation emitted by the laser module, for example a wavelength drift, which has an adverse effect on the holographic representation. The drop in power and amplitude is now compensated for by an increase in the amplitude in the second sub-interval, in which no light is emitted. The temperature of the laser module and in particular of the barrier layer relevant for the generation of radiation and any Bragg grating remains constant as a result, as does the wavelength of the radiation. At the same time, however, a rapid brightness adjustment can take place in this operating mode in that the average power in the second sub-interval is immediately adapted to the power adjustment in the first sub-interval.

In general, it can be said that the proposed control method for one or more light sources and an imaging unit having a DMD enables laser dimming over a high dynamic range of powers, in which impairments are caused by a lower heat input in the light source due to a drop in the power supply, in particular in the area very low power can be avoided. The method can therefore be used to advantage wherever a DMD is operated with laser radiation over a high dynamic range.

This aspect can advantageously be combined with a further development of the method, according to which a second operating mode is provided, into which there is an optional switchover from the first operating mode. In this case, the light source is supplied with power within the second sub-interval of the update time (time frame with the number of bits, total refresh period, "bytes"), which is complementary to the first sub-interval, with a time-average value of the power within the first sub-interval being essentially the same as a time-average value of the power within the second sub-interval. This operating mode corresponds e.g.

In other words, the mean power in the first partial interval is still comparatively high in the second operating mode, because the amplitude of the current with which the laser module is supplied is consistently high. Although the second sub-interval is also supplied with power, but only with the same mean power, so as not to cause any change in power overall when the lighting conditions change, there is no compensation for any reduced current amplitude in the first sub-interval. In a simple case, a current with an overall constant current level flows through the laser module.

The second operating mode can be described as conventional, but the combination with the first operating mode is particularly advantageous because it is possible to switch smoothly from one operating mode to the other. For example, during normal daytime driving when entering a tunnel, the brightness requirement can drop sharply, more than is still possible with the bit representation (high dynamics). Here, as described, the amplitude within the pulse can be reduced. Switched to the first operating mode (“tunnel mode”) from the second operating mode (“daytime driving mode”), this can be compensated for by an increased average power in the second sub-interval.

According to a further development of the method, the increased time average value of the power in the second sub-interval is dimensioned in the first operating mode in such a way that it compensates for the low time average value of the power within the first sub-interval, so that a resulting time average value of the power is based on the entire bit -Segment in the first mode of operation is substantially equal to the corresponding time average value of the power in the second mode of operation. In other words, the average power converted over an update time is the same between the first operating mode and the second operating mode. The advantage is that you can switch between the two modes without affecting the heat generation in the light source. In practice, the proportion of useful light in the first operating mode will be significantly lower than in the second operating mode.

According to a development of the method, a third operating mode is provided, into which it is possible to switch from the first (and in particular also from the second) operating mode. In this case, the light source is not supplied with power within the second sub-interval of the update time, which is complementary to the first sub-interval. In the case of vehicles, in particular motor vehicles, this operating mode can be particularly suitable for driving at night, at least in an operation that lasts longer than, for example, only a short passage through a tunnel or the like. Because only light remains within the period of the "ON" position of the relevant Micromirror is emitted, and no longer in the second sub-interval, here of course there is an advantage of a high proportion of useful light with simultaneous power savings. Since here, depending on the required brightness, different amounts of light are emitted per time frame or update time, and since, in particular, If a potentially significant drop in performance is to be expected when switching from one of the other two operating modes to the third operating mode, further measures can be provided here in order to compensate for or prevent the varying heat input. For example, the temperature-dependent cooling can be provided with the aid of a Peltier element. This optional aspect is described further below. However, because such measures require a reaction time (e.g. from the measurement of a temperature change with the help of a sensor, via the controller to the insertion of the heat conduction into the barrier layer), i.e. there is a certain inertia, this operating mode is less suitable for fast (laser) Suitable dimming applications as described above with reference to the first mode of operation.

1. (a) eine für das Bit-Segment bzw. die Bit-Segmente (die ja ggf. das erste Teilintervall ausmachen) bestimmte Lichtmenge, die von der Lichtquelle abhängig von der Leistung und der Zeitdauer des ersten Teilintervalls emittiert wird, einen vorgegebenen ersten Schwellwert unterschreitet; und
2. (b) bestimmt wird, dass eine voraussichtliche Dauer, in welcher die für das jeweilige Bit-Segment bestimmte Lichtmenge in dem genannten Bereich liegt, mehr als ein zweiter Schwellwert beträgt.

According to further developments of the method, criteria for switching between the operating modes are provided. For example, the third mode of operation can be selected for switching when

1. (a) a quantity of light, determined for the bit segment or bit segments (which may make up the first sub-interval), which is emitted by the light source depending on the power and the duration of the first sub-interval, falls below a predetermined first threshold value ; and
2. (b) it is determined that an expected duration in which the quantity of light determined for the respective bit segment is in the said range is more than a second threshold value.

The expected period of time mentioned is the planned duration of the activation of the third operating mode.

1. (a) eine für das Bit-Segment bzw. die Bit-Segmente bestimmte Lichtmenge, die von der Lichtquelle abhängig von der Leistung und der Zeitdauer des ersten Teilintervalls emittiert wird, einen vorgegebenen ersten Schwellwert unterschreitet; und
2. (b) bestimmt wird, dass eine voraussichtliche Dauer, in welcher die für das jeweilige Bit-Segment bestimmte Lichtmenge in dem genannten Bereich liegt, weniger als ein zweiter Schwellwert beträgt.

According to another embodiment, the first mode of operation is selected when

1. (a) a quantity of light which is determined for the bit segment or the bit segments and which is emitted by the light source as a function of the power and the duration of the first sub-interval falls below a predetermined first threshold value; and
2. (b) it is determined that an expected duration, in which the amount of light determined for the respective bit segment is in the said range, is less than a second threshold value.

Here, too, the anticipated period of time mentioned is the planned duration of the activation of the first operating mode here.

According to a further exemplary embodiment, the second operating mode is selected and switched to when a certain amount of light for the bit segment, which is emitted by the light source depending on the power and the duration of the first sub-interval, exceeds a predetermined first threshold value. In the example of the daytime driving mode, this is easy to understand, since the display requires a minimum brightness that is adapted to the ambient light.

According to exemplary embodiments, the first threshold value can be 20% or less of a maximum value of an amount of light that can be emitted within the bit segment, which is dependent on a nominal power of the light source, preferably 15% or less, more preferably 10% or less, more preferably 5% or less, most preferably 1% or less.

According to further exemplary embodiments of the method, the second threshold value can optionally be between 10 minutes and 60 minutes, for example 10, 20, 30, 40, 50 or 60 minutes, or intermediate values. This exemplary information can relate to the operation of head-up displays in motor vehicles. Other threshold times may be useful in other vehicles or applications and the aspects described herein are not limited thereto.

According to a development of the method, the light source is a semiconductor light source, preferably a laser diode or a laser diode array. As described, in this case the control of the power with regard to the generation and development of heat in the semiconductor barrier layer is particularly critical, so that the proposed aspects unfold particular advantages here.

According to a further development of the method already indicated above, a junction temperature in the semiconductor light source can be readjusted in the first, second and/or third operating mode with the aid of a Peltier element assigned to the semiconductor light source. According to special embodiments, the Peltier control can also be permanently activated or operated, i.e. in all 3 operating modes. A temperature sensor can, for example, measure the temperature of the relevant laser diode housing and the Peltier control then keeps this comparatively constant, even if the ambient temperature of the entire module changes. This control can be sluggish due to the heat conduction. The temperature of the laser diode housing can also change when switching to the third operating mode due to the changed power loss of the diode, with the Peltier element being able to slowly readjust.

According to a further development of the method, at least in the first, possibly also in the second and / or third operating mode, the power with which the light source is supplied over the first and second sub-interval or over the respective complete bit segment or selectively maintained substantially constant in a continuous mode, or controlled in a discontinuous mode, over a portion thereof. For example, continuous mode and discontinuous mode are in US 2014/0085731 A1 or in "Enabling the Next Generation of Automotive Head-Up Display Systems", Application Report DLPA043A (Oct. 2013, revised version Nov. 2017) by Texas Instruments, and stand for the high dynamic range concept proposed therein. The concept is explained below in connection with the detailed description of exemplary embodiments.

According to a further development of the method, the light source and the imaging unit are part of an AR head-up display, with the light beam emitted by the imaging unit being directed via optics onto a combiner, which is formed by a holographic optical element. As described, the application in an AR head-up display offers special advantages and meets the special requirements there for a permanent and permanent holographic display.

Another aspect of the present invention relates to a device, in particular an AR head-up display, comprising an imaging unit and at least one light source, comprising a control device for carrying out the method steps according to one or more of the aspects, developments and exemplary embodiments mentioned above is set up. The same advantages result as described above.

In the possible uses of laser modules in vehicles described above, a laser diode is often used as a standard component, which consists of the actual laser diode, namely a laser chip, a substrate carrying the laser chip, electrical lines with optional electronic components such as a photodiode, two or three contact lugs or pins, and is formed from a protective housing with a decoupling window for these components. The laser chip can be an edge emitter. The housings with the base made of substrate and contact pins are standardized in terms of size, e.g. they can be TO 38, TO 56 or TO 90 housings, etc. In the present application, “laser diode” can also refer to the entire module with housing and base and not just the actual laser chip.

Further advantages, features and details of the invention result from the claims, the following description of preferred embodiments and with reference to the drawings. In the figures, the same reference symbols designate the same features and functions.

character list

• 1 in schematischer Darstellung einen Überblick über den Aufbau eines AR-HUD-Systems, in welchem Ausführungsbeispiele der Erfindung implementiert sein können;
• 2 in schematischer Darstellung den Aufbau einer Lichtquelle für das AR-HUD-System aus 1 mit jeweils einem Lasermodul für die RGB-Farben;
• 3 in etwas größerem Detail, aber auch schematisch dargestellt, ein Lasermodul aus 2 mit Peltierelement;
• 4 den Aufbau bzw. die Aufteilung eines Zeitrahmens oder der Aktualisierungszeit für die aufeinander abgestimmte Steuerung eines DMD und der Lichtquelle durch Bits, sowie darunter zwei Beispiele für das Setzen von Bits zum Erzielen von Helligkeitswerten;
• 5 den Aufbau bzw. die Aufteilung eines Zeitrahmens oder der Aktualisierungszeit wie in 4, wobei aber einzelne Bits durch Bit-Splitting in voneinander zeitlich getrennte Bit-Segmente aufgeteilt werden;
• 6 in diagrammartiger Darstellung die Steuerung der Helligkeit innerhalb eines Bit-Segments (aufgetragen gegen die Zeit) in dem kontinuierlichen Modus, um den dynamischen Bereich zu vergrößern;
• 7 in diagrammartiger Darstellung die Steuerung der Helligkeit innerhalb eines Bit-Segments (aufgetragen gegen die Zeit) ähnlich wie in 6, aber in dem diskontinuierlichen Modus, um den dynamischen Bereich noch weiter zu vergrößern;
• 8 in einem Diagramm in schematischer Weise die Steuerung einer optischen Bilderzeugungsvorrichtung in dem dritten Betriebsmodus (Nachtfahrmodus);
• 9 in einem Diagramm wie in 8 in schematischer Weise die Steuerung einer optischen Bilderzeugungsvorrichtung, aber in dem zweiten Betriebsmodus (Tag- oder Normalfahrtmodus);
• 10 in einem Diagramm wie in 8 oder 9 in schematischer Weise die Steuerung einer optischen Bilderzeugungsvorrichtung, aber in dem ersten Betriebsmodus (Tunnelfahrtmodus).

Show it:

• 1 a schematic representation of an overview of the structure of an AR-HUD system in which exemplary embodiments of the invention can be implemented;
• 2 in a schematic representation of the structure of a light source for the AR-HUD system 1 each with a laser module for the RGB colors;
• 3 a laser module in somewhat greater detail, but also shown schematically 2 with Peltier element;
• 4 the construction or the division of a time frame or the update time for the coordinated control of a DMD and the light source by bits, as well as below two examples for the setting of bits to achieve brightness values;
• 5 the structure or division of a time frame or the update time as in 4 , but individual bits are divided into time-separated bit segments by bit-splitting;
• 6 diagrammatically controlling brightness within a bit segment (plotted versus time) in continuous mode to increase dynamic range;
• 7 in a diagrammatic representation the control of the brightness within a bit segment (plotted against time) similar to in 6 , but in the discontinuous mode to increase the dynamic range even further;
• 8th in a diagram in a schematic way the control of an optical imaging device in the third operating mode (night driving mode);
• 9 in a diagram like in 8th in a schematic way the control of an optical imaging device, but in the second operating mode (day or normal driving mode);
• 10 in a diagram like in 8th or 9 schematically shows the control of an optical imaging device, but in the first mode of operation (tunneling mode).

In the following description of preferred exemplary embodiments, it must be taken into account that the present disclosure of the various aspects is not limited to the details of the construction and the arrangement of the components, as they are illustrated in the following description and in the figures. The example embodiments may be practiced or carried out in various ways. It is further to be understood that the phraseology and terminology used herein are used for the purpose of specific description only and should not be construed as such in a limiting manner by those skilled in the art.

Some of the aspects and exemplary embodiments of the invention are or can be compatible with an application, for example with regard to some of the DLP chip sets for AR-HUD technologies presented by Texas Instruments Inc. Dallas, Texas, and the associated high dynamic range concept build on. In particular, exemplary embodiments of the proposed control method can be implemented in terms of programming and/or by adapting/supplementing the hardware in a control device 10 of an AR-HUD system 1, as is shown in 1 is shown, which very roughly and simplistic reflects the architecture of the Texas Instruments proposal.

As in 1 As can be seen, the AR-HUD system 1 comprises, as main components, a control device 10, an imaging optical device 20, a projection optics 30, and a holographic optical element integrated in the window (windshield of an automobile) or in a transparent plate placed in front of it 40 (HOE), which acts as a combiner. External elements are the on-board communication system 2 of the motor vehicle with a host processor 4. The information to be displayed holographically and, for example, dimming commands can be transmitted to the control device 10 from this system via RGB video signal lines 5 and other lines 6 for instructions etc. The information to be displayed holographically can in particular be ADAS messages (ADAS: advanced driver assistance system), physical data about the motor vehicle during the current journey or navigation data.

The control device 10 can include the actual DMD controller 12 , a laser module controller 14 and a power supply unit 16 . The optical imaging device 20 has the micromirror device 22 and light sources 24 that are set up to direct the radiation they emit selectively onto the individual mirrors of the micromirror device 22 . The DMD controller 12 controls the micro-mirror device 22, or selectively places each micro-mirror in an “ON” or “OFF” position. In the "ON" position, the radiation impinging on the respective micromirror is directed into the projection optics 30, while in the "OFF" position it is directed, for example, into a light sink such as an absorption screen.

The micromirrors are controlled by the DMD controller 12 in a time-coordinated manner in a scheme of bit sequences which, when put together, result in individual bits of a time frame of a predetermined time duration, as will be described in greater detail below. The time frame corresponds to the update time (frame refresh priod) of the micro mirrors. Due to the bit-by-bit representation within the time frame of fixed duration, the respective brightnesses to be displayed are represented digitally.

The control of the light sources 24, which can be, for example, three laser modules representing the colors RGB, is carried out by the laser module controller 14 in a coordinated manner with the control of the micromirrors by the DMD controller 12. In other words, the light sources 24 are also Bit-wise or bit-segment-wise controlled, the individual bits between the control of the micromirror and the control of the laser modules essentially match in terms of time.

The projection optics 30 can, as in 1 is shown schematically, a number of collimating lenses 31, 33 and a deflection mirror 32 include. The control device 10, the optical image generating device 20 and the projection optics 30 together form an image generating unit 8 (PGU—picture generating unit). In practice, the imaging unit 8 of the AR-HUD system 1 is located within the dashboard of a motor vehicle and the radiation it emits impinges on the holographic optical element 40 upwardly out of the dashboard. The inclination and alignment of the holographic optical element 40 and the projection optics 30 are coordinated with one another such that the driver 46 of the motor vehicle perceives the holographic image 42 in the desired manner and in high quality within a space 44 referred to as an “eye box”.

Regarding 2 an exemplary structure of the light sources 24 is described. There can be one laser module 24a, 24b, 24c for the colors R, G and B can be provided, the light beam of which hits semi-transparent mirrors in such a way that their beam path diverges at the exit of the light source (in 2 schematically represented by a collimating lens) superimposed geometrically. Simultaneous emission of radiation is possible, but the bit-by-bit control regularly provides for consecutive time frames to be reserved for the individual colors.

Regarding 3 is a single the in 2 shown laser module 24a-c shown in more detail, which serves as the light source 24. The laser module 24a-c includes a heat sink 25, on which a Peltier element 26 is attached, and a base plate 27 for the laser diode, which in turn is arranged on the Peltier element 26. A bracket 202 (stem), to which a submount 204 is fastened, extends vertically from the base plate 27 . A laser chip 204, which is designed as a vertical edge emitter, is attached to this. The laser chip 204 can be supplied with power through contact pins 201 . The power supply is controlled by the laser module controller 14 as described above. The Peltier element 26 can also be gradually controlled by the laser module controller 14 (separately from the power supply of the laser chip 204) in order to bring about cooling of the laser module that is desired in each case. The laser module 24a-c also includes a protective cap 205 for the package, which may be a conventional TO 38, TO 56, TO 90, etc. package.

Again 2 can be found (not in 3 shown), the laser module 24a-c can each have (for example still inside the housing) a collimation lens and a VBG grating, which together with the laser chip 204 form a resonator.

Figures four and five show the setup or structure of a time frame that can be used to control the digital micromirrors as well as the light sources. The representations shown correspond roughly to those in Doherty et al. (1998) proposed setup for operating DMDs.

In 4 a division of a single time frame with a predetermined time duration P into, for example, five bits 0, 1, 2, 3, and 4 is shown at the top along a time axis t. The time frame can also be divided into fewer or more bits. The least significant bit 0 (LSB) is assigned a shortest time period. For each subsequent bit, the allocated time doubles. In the illustration shown, the time frame is divided with a resolution of 1/31 (least significant bit).

On the second and third lines in 4 Two arbitrary examples of bits being set by the DMD controller 12 are shown in the middle and below. A set bit corresponds to an "ON" position of a micromirror, an unset bit corresponds to an "OFF" position. A set bit is in 4 represented by hatching. For the bar in the middle, the bit sequence is 01101, which corresponds to 13/31 of the total duration of the time frame. Consequently, about 42% of the maximum brightness can be represented by this bit sequence. At the beam below in 4 the image sequence is 10110, which corresponds to 22/31 of the total duration of the time frame. Consequently, about 71% of the maximum brightness can be represented by this bit sequence.

Set bits or the durations of contiguously set bits are referred to below as the first sub-interval T1 of the time frame and unset bits or the durations of contiguously not set bits are referred to below as the second sub-interval T2 of the time frame.

This in 4 The basic principle of the digital control of the micromirrors shown by bit-by-bit setting of the “ON” or “OFF” positions of a relevant micromirror by the DMD controller 12 can be refined by the above-mentioned bit splitting. the to 4 analog bars are in 5 shown. The upper bar shows the same time frame of a specified time period P, but the individual bits apart from the first bit 0 and the second bit 1 within the time frame are divided into individual bit segments B0 to B14 and separated in time from one another. It should be noted that in the present disclosure, non-split bits, namely those bits 0 and 1, are also construed as bit segments. This also applies to the in 4 shown simple structure, so that the bit segments B0 to B4 arise there. Both structures (such in 4 as well as in 5 ) are covered by exemplary embodiments of the control method according to the invention.

In the 5 Bars (time frames) shown in the middle and below indicate the same bit sequence as in 4 in the middle and below the time sequence for the bit segments B0 to B14 is shown as an example again (bit sequences 01101 and 10110). There is clearly a fine distribution of "ON" or "OFF" positions over the time frame, which further prevents the human eye from perceiving artifacts.

The 6 and 7 point to US 2014/0085731 A1 and "Enabling the Next Generation of Automotive Head-Up Display Systems", Application Report DLPA043A, describe two ways in which the dynamic range of the light output can be further improved. In 6 is above a single bit segment (e.g. B0 - B14) is shown, with the horizontal axis representing the time axis and the vertical axis representing the supply current or light output. This is a bit segment whose associated bit is set. Accordingly, the maximum current flows over the entire duration of the bit segment (eg 50 µs). If, for example, a lower brightness is to be generated over the time frame than can be represented by the least significant bit, it is proposed here that the light output provided by the light source 24 be reduced by the laser module controller 14 when the micromirror is set to "ON" or the duration , in which radiation is emitted, compared to the time provided for the bit segment (see 6 below). Because there is still constant power supply within the pulse, such operation is called continuous mode. This enables a dynamic range of 100:1 to be achieved.

The in goes even further 7 pulse control shown. In discontinuous mode, one or more short flow pulses are generated. Both the switch-on and the switch-off time of each flux pulse are controlled by alternately switching on and then switching off a current shunt from an energy store (eg capacitor) to ground. The flow pulse size is controlled by detecting when the flow pulse has reached a predetermined setpoint. Turning on the power shunt can abruptly shut off power to the selected laser module. As in 7 indicated schematically, a dynamic range of 5000:1 can be achieved.

Exemplary embodiments and aspects are based on the previous control principles for the in 1 The AR-HUD system 1 shown operates with three scenarios, each of which is represented by operating modes between which it is possible to switch, for example. The operating modes are in the 8th until 10 shown.

If, for example, it is foreseeable that only a low level of brightness is required for the driver for a longer period of time, for example a period of time that exceeds a threshold value of 30 minutes, as can be the case when driving at night, the host processor can, for example the in 8th operating mode shown (“third operating mode”) can be activated. It can here in particular in the 6 and 7 methods shown for pulse control within a bit segment can be performed in continuous or discontinuous mode.

In the 8th until 10 show the curves R, G and B - plotted against time t - the successive activation of the respective laser module 24a, 24b, 24c (from top to bottom). That is, this period of time is available for emission from the optical imaging device 20 in R, G, or B, respectively. The activation time (which defines the individual time frame for each color) can be seen for R, G and B (see high level). The sum of these three color segments forms the refresh time P or the superordinate time frame. For the sake of simplicity are in the 8th until 10 only pulses of the same duration are shown for all colors, and only one pulse per time frame. As in 4 and 5 shown, but multiple bit segments can be set per time frame.

Fourth and fifth place in 8th until 10 the mirror position "ON/OFF" and the power supply (or power supply) R_L of the laser module with the laser diode emitting light in the red wavelength range are listed. The power supply of the laser modules, which emit green or blue light, is analog and is not shown separately.

The "ON" mirror position corresponds to the activation of a respective micro-mirror of the digital micro-mirror device. The one pulse shown represents a first partial interval of the update time P (or the activation time). A first mirror position “ON” is set over the pulse width shown or the bit segment shown (high level) in such a way that the light beam component incident on the micromirror is output from the imaging unit 8 . In night driving mode, power is supplied as in 8th shown only at the same time as the mirror position "ON", i.e. at the same time as the first time interval. In a complementary time interval of the update time P, which is available for activating the laser module of the relevant color (activation time: level R, G, B high), there is no power supply (the figures only show the integrated update time across all colors, not the color-related update time, which forms the sum of the two sub-intervals).

It is essential here with reference to 8th (night drive or third operating mode) that the average laser power P _ℓ (of the red laser) is significantly reduced compared to the laser power at full brightness if the curve R_L in 8th with the appropriate in 9 compares, which shows the "second" operating mode for day or normal driving. This reduces the temperature of the laser chip (especially in the barrier layer), which, as described, is undesirable because of the wavelength shift. In the exemplary embodiment, this is achieved by readjustment using the Peltier element 26 balanced. Due to the thermal capacity of the entire laser package, however, this regulation takes several seconds (typically 5 - 30 s). It also takes the same amount of time to switch back to high brightness.

The operating mode for high brightness (normal or daytime driving) is in 9 shown. Each laser diode or each laser module 24a-c remains switched on continuously for the respective color segment (ie only during the activation of the colors R, G, B within the update time), specifically with a constant laser power P _con , and the brightness is only adjusted through the DMD mirrors. The junction temperature also remains constant in this case. This mode of operation corresponds to the brightness control with a high-pressure discharge lamp as the light source.

In 10 the principle for the first operating mode is shown. This is activated when a quick and strong adjustment of the brightness is required.

During the "ON" time of the DMD micromirrors (first time interval), the laser power P _r is reduced as well as in 8th with reference to the third mode of operation to achieve the high brightness dynamics. Also particularly short pulses as in 7 shown are possible. However, during the "OFF" time, ie within the second time interval, the mirror for the respective color is now supplied with power to the relevant laser module 24a-c, if possible even with an increased laser power P _h , by the same average power P _m as in 9 (Normal or daytime driving) via the update time or the time frame. As a result, an approximately the same average junction temperature is also achieved. As a result, the wavelength also remains constant. When increasing the laser power, however, the permitted maximum currents of the relevant laser diode must be taken into account. But even if the laser power cannot be increased beyond P _h due to the limitation, the average power will not deviate greatly from P _h and only a small change in wavelength will result. Since the in the 2 and 3 shown wavelength-stabilized laser diodes can be operated stably in a temperature range of about 5 °, this is quite tolerable. Typical bit segment durations are 50 µs, so there is no problem in switching the laser fast enough.

For the decision as to whether to switch between the second and third operating modes, further information from the outside is required, for example from the on-board computer system 2 of the motor vehicle. Depending on the time, position and season, it can be determined whether it is a night drive. This also applies to the decision as to whether to switch between the second and the first operating mode. If this information is not available, operation can also be carried out using only the first and second operating modes. In this case, however, an increased energy consumption occurs because the laser diodes are heated unnecessarily. In the exemplary embodiment, the Peltier element 26 is advantageously regulated across all operating modes.

One benefit of operating in the night drive mode, or third mode of operation, at night is that the laser module 24 on may result in some background light with the mirrors in the "OFF" position.

For a holographic AR HUD with fast brightness control and high dynamics, it is necessary that the junction temperature of the laser diode changes little. This problem is solved by the present exemplary embodiments of standard laser diodes in TO56 or TO90 packages, etc. This results in a much more cost-effective solution than if, for example, diodes were developed in new packages with an integrated Peltier element and then had to be time-consuming to qualify them for automotive applications.

Reference List

1

AR HUD system

2

onboard communication system

4

host processor

8th

Imaging / Image Generating Unit (PGU)

10

control device

12

DMD controller

14

laser module control

16

power management system

20

optical imaging device

22

DMD, Micromirror Device

24

light source(s)

24a - c

Laser modules, laser diodes

25

heatsink

26

Peltier element

27

base plate (of the housing)

201

contact pins

202

bracket

203

submount

204

laser chip

205

cap

30

projection optics

31, 33

collimating lenses

32

deflection mirror

40

holographic optical element (HOE, combiner)

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 9409472 A1 [0003]
• DE 102006036112 A1 [0010]
• US20140085731 A1 [0043, 0065]

Claims (14)

Method for controlling at least one light source (24) and an imaging unit (8) having a digital micromirror device (22), a light beam being directed from the light source (24) onto a number of micromirrors of the digital micromirror device (22), with the aid of which an image can be generated and output by the imaging unit (8) depending on the respective mirror positions, comprising: operating the digital micromirror device (22) by means of pulse width modulation in a scheme of bit segments (B0-B14) that follow one another within an update time (P) predetermined period of time; activating at least one micro-mirror of the digital micro-mirror device (22) to achieve a first mirror position (ON) within a first sub-interval (T1) of the update time comprising one or more pulses, the pulse or pulses corresponding to the bit segment(s). set so that the portion of the light beam incident on the micromirror is output from the imaging unit (8); providing power to the light source for at least the duration of the first sub-interval (T1) to cause the light source (24) to emit a predetermined amount of light therein; characterized in that in a first operating mode the light source (24) within a second subinterval (T2) complementary to the first subinterval (T1) of the same update time (P) in which the at least one micromirror of the digital micromirror device (22) has a second mirror position (OFF ) occupies, so that the portion of the light beam incident on the micromirror is not output from the image-forming unit (8), is powered, with a time-average value (P _h ) of the power in the complementary second sub-interval (T2) compared to a time-average value (P _r ) the power is increased within the first sub-interval (T1) in order to counteract a cooling of the light source (24) in the case of a small amount of light intended for output from the imaging unit (8). procedure according to claim 1 , wherein in a second operating mode, into which the first operating mode is optionally switched, the light source (24) is supplied with power within the second sub-interval (T2) of the update time (P), which is complementary to the first sub-interval (T1), wherein in the second operating mode a time average value (P _con ) of power within the first sub-interval (T1) is substantially equal to a time average value (P _con ) of power within the second sub-interval (T2). procedure according to claim 2 , wherein in the first operating mode the increased time-average value (P _h ) of the power in the second sub-interval (T2) is dimensioned such that it compensates for the low time-average value (P _r ) of the power within the first sub-interval (T1), so that a resulting time-average (P _m ) of power relative to the total update time (P) in the first mode of operation is substantially equal to the corresponding time-average (P _con ) of power in the second mode of operation. procedure according to claim 2 or 3 , wherein in a third operating mode, into which the first operating mode is selectively switched, the light source (24) is not supplied with power within the second sub-interval (T2) of the update time (P) complementary to the first sub-interval (T1). procedure according to claim 4 , wherein the third operating mode for switching is selected when (a) a specific quantity of light for the relevant bit segment(s) (B0-B14) is emitted by the light source (24) as a function of the power and the duration of the first sub-interval (T1 ) is emitted falls below a predetermined first threshold value; and (b) it is determined that an expected duration in which the amount of light determined for the respective bit segment (B0-B14) lies in the said range is greater than a second threshold value. Method according to one of Claims 1 until 5 , wherein the first operating mode is selected if (a) a certain quantity of light for the relevant bit segment (B0-B14) is emitted by the light source depending on the power and the duration of the first sub-interval (T1), a falls below a predetermined first threshold value; and (b) it is determined that an expected duration in which the amount of light determined for the respective bit segment (Bo-B14) lies in the said range is less than a second threshold value. Method according to one of claims 2 or 3 until 6 , as far as related to claim 2 , Wherein the second operating mode is selected and switched to when a certain amount of light for the bit segment (B0-B14) is emitted by the light source (24) as a function of the power and the duration of the first partial inter valls (T1) is emitted exceeds a or the predetermined first threshold value. Method according to one of Claims 5 , 6 , or 7, if referred back to claim 5 or 6 , wherein the first threshold value is 20% or less of a maximum value of an amount of light that can be emitted within the bit segment, which is dependent on a nominal power of the light source (24), preferably 15% or less, more preferably 10% or less, more preferably 5% or less, most preferably 1% or less. Method according to one of Claims 5 or 6 , where the second threshold is between 10 minutes and 60 minutes. Method according to one of Claims 1 until 9 , wherein the light source (24) is a semiconductor light source, preferably a laser diode or a laser diode array. procedure according to claim 10 , wherein in the first and/or second operating mode a junction temperature in the semiconductor light source is readjusted with the aid of a Peltier element (26) assigned to the semiconductor light source. Method according to one of Claims 1 until 11 , wherein at least in the first operating mode the power with which the light source (24) is supplied, over the first sub-interval (T1) and second sub-interval (T2) or over the complete bit segment, optionally in a continuous mode substantially held constant or controlled in a discontinuous mode. Method according to one of the preceding claims, wherein the light source (24) and the imaging unit (8) are part of an AR head-up display, the light beam emitted by the imaging unit (8) being transmitted via an optic (30 - 33) is directed to a combiner (40) formed by a holographic optical element. Device, in particular an AR head-up display, comprising an image-generating unit (8) with a digital micromirror device (22) and at least one light source (24), comprising a control device (10, 12, 14) for carrying out the method steps according to one of the Claims 1 until 13 is set up.

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