Method for controlling a light scanner in a headlamp for vehicles

Abstract

The invention relates to a method for controlling a light scanner (7) in a headlight for vehicles, wherein the laser beam of at least one modulated laser light source (1) is directed in a scanning manner, by way of the light scanner, onto a light conversion means (8) so as to generate a light image (11) thereon, which is projected via an imaging system (12) as a light image (11) onto the roadway, a micromirror (10) of the light scanner is pivoted according to defined characteristic control curves in at least one coordinate direction, the desired light image (11) is divided into a pixel set having n rows and/or m columns, the horizontal and/or vertical characteristic control curves for the micromirror (10) are adapted to at least one selected row and/or column in terms of the required optical power of the pixels, and the adapted horizontal and/or vertical characteristic control curves are used to control the micromirror.

Claims

1. A method for controlling a light scanner (7) in a headlight for vehicles, the method comprising: directing a laser beam of at least one modulated laser light source (1) in a scanning manner, by way of the light scanner, onto a light conversion means (8) so as to generate a light image (11) thereon, which is projected via an imaging system (12) as a light image (11) onto a roadway; and pivoting a micromirror (10) of the light scanner according to defined characteristic control curves in at least one coordinate direction, wherein: the desired light image (11) is divided into a pixel set having n rows and/or m columns; horizontal and/or vertical characteristic control curves for the micromirror (10) are adapted to at least one selected row and/or column in terms of the required optical power of the pixels; and the adapted horizontal and/or vertical characteristic control curves are used to control the micromirror.

2. The method according to claim 1, wherein the selected row and/or column is that in which, in total across the n pixels thereof, the maximum illumination intensity is required.

3. The method according to claim 1, wherein: the desired light image is divided into a pixel set having n rows and m columns; in a first step, for optimizing the characteristic control curves according to the desired light distribution for every pixel of the pixel set, the required illumination intensity E.sub.ij is defined; in a second step (v12), the column (r)/row selected is that in which, in total across the n pixels thereof, the maximum illumination intensity, namely the total illumination intensity of this column c2/row, is required; in a third step (v22), it is calculated, proceeding from this total illumination intensity, what unit of time per illumination intensity t.sub.lx is available on average in this column (c2)/row, namely t.sub.slx=T.sub.s/E.sub.c2ges., wherein T.sub.s denotes half the period duration of the column period/row period, and E.sub.c2 ges. denotes the sum of all predefined illumination intensity values per pixel which is required in this half period duration of the column period; in a fourth step (v32), the illumination intensities (E.sub.c2n) of the column (c2)/row, which are present in a series, are used to create a new series, wherein the illumination intensity E.sub.c2n of every element of the new series is E.sub.c2n=E.sub.c2j; in a fifth step (v32), every element of the new series is multiplied by the unit of time per illumination intensity t.sub.slx so as to obtain a new time series that, by way of the deflection angle v=.sub.Vmax/n available for each pixel, is defined as a new optimized characteristic control curve, and every element of the time series is multiplied by the deflection angle =.sub.max/n available for every pixel, whereby a deflection, and thus an optimized characteristic control curve, is obtained for every pixel of the column/row; and in a sixth step (v52,) this characteristic control curve is used to control the micromirror for each column/row.

4. The method according to claim 3, wherein the remaining axis is controlled using a defined, non-optimized characteristic control curve.

5. The method according to claim 3, wherein: in a seventh step (v62), the utilization of the laser power per pixel is evaluated, and the row/column having the best utilization .sub.max is ascertained; in an eighth step (v72), the column having optimal utilization of the installed laser power is selected and used for the optimization of the characteristic control curve of the remaining axis, and thereafter the procedure follows steps analogously to the first (v11), second (v22), third (v32) and fourth (v42) steps, proceeding from the utilization of the installed laser power per pixel, wherein all utilizations of the installed laser power in the respective pixel are added up in the row (r2) in which the previously ascertained highest utilization of the installed laser power was able to be delivered; in a ninth step (v82), it is subsequently calculated, proceeding from the utilization .sub.r2 ges, what unit of time per utilization t.sub.Z is available in this row (r2),
t.sub.Z=T.sub.Z/.sub.r2 ges. wherein T.sub.Z is half the period duration of the row period, and .sub.r2 ges. is the sum of all calculated or measured utilizations of the installed laser power per pixel which is required in this half period duration of the row period; in a tenth step (v92), the respective utilization values of the row (r2) are used to create a new series, wherein the illumination intensity .sub.r2m of every element of the new series is .sub.r2m=.sub.j=1.sup.m .sub.r2j; and in an eleventh step (v102), the elements of the new series are multiplied by the unit of time per utilization t.sub.Z and, by way of the deflection angle .sub.H=.sub.Hmax/m available for every pixel, are defined as a new optimized horizontal/vertical characteristic control curve.

6. The method according to claim 5, wherein in a twelfth step (v112), the optimized characteristic control curve is used for the vertical/horizontal axis and the horizontal/vertical axis and, analogously to the seventh step (v62), the utilization of the installed laser power per pixel is ascertained.

7. The method according to claim 3, wherein the optimization of the characteristic control curves is carried out step by step (steps v11 through v111) in reverse order with respect to the rows and columns, or axes, so as to obtain furthermore two optimized characteristic control lines.

8. The method according to claim 1, wherein a selection from all the resulting optimized characteristic control curves takes place as a function of the desired light image, wherein the most favorable combination is used to control the light scanner.

9. A headlight for vehicles, comprising: a light scanner (7) comprising a micromirror (10); a light conversion means (8); an imaging system (12); a laser control unit (3) and a processing unit (2) associated therewith; and at least one modulated laser light source (1), the laser beam of which can be directed in a scanning manner, by way of the light scanner (7), onto the light conversion means (8) so as to generate a light image (11) thereon, which is projected via the imaging system (12) as a light image (11) onto a roadway, wherein the micromirror (10) of the light scanner is pivotable according to defined characteristic control curves in at least one coordinate direction, and wherein the processing unit (4) is configured to carry out the method of claim 1.

Description

(1) The invention, along with further advantages, will be described in greater detail hereafter based on exemplary embodiments, which are illustrated in the drawings. In the drawings:

(2) FIG. 1 schematically shows the components of a headlight essential for the invention, and the relationship thereof.

(3) FIG. 2 shows the power distribution based on a light image generated by a scanning laser beam, which is deflected by a conventional mirror oscillating about two axes;

(4) FIG. 3 shows a desirable, exemplary light distribution for a headlight;

(5) FIG. 4 shows the division of a light image into rows and columns;

(6) FIGS. 5a and 5b show flow charts of two variants of the method according to the invention;

(7) FIG. 6 shows a desirable starting light image;

(8) FIG. 7 shows an optimized characteristic control curve;

(9) FIG. 8 shows a diagram illustrating the utilization of the installed laser power after carrying out an optimization method;

(10) FIG. 9 shows a further optimized characteristic control curve;

(11) FIG. 10 shows a diagram illustrating the utilization of the installed laser power after carrying out a further optimization method; and

(12) FIG. 11 shows another diagram illustrating the utilization of the installed laser power after carrying out a further optimization method.

(13) Referencing FIG. 1, one exemplary embodiment of the invention will now be described in greater detail. In particular, the parts important for a headlight according to the invention are shown, wherein it is clear that a motor vehicle headlight also contains a number of other parts that allow useful use of the headlight in a motor vehicle, such as in particular a passenger car or motorcycle. The lighting-related starting point of the headlight is a laser light source 1, which emits a laser beam 2 and which is associated with a laser control unit 3, wherein this control unit 3 is used for power supply purposes and for monitoring the laser emission or, for example, for controlling the temperature, and is also configured to modulate the intensity of the emitted laser beam. Modulating in the context of the present invention is understood to mean that the intensity of the laser light source can be altered, either continuously or in a pulsed manner, within the meaning of switching on and off. What is essential is that the light output can analogously be dynamically altered, depending on the angular position of a mirror, which will be described later. Additionally, there is also the option of switching on and off for a certain period of time so as not to illuminate or to suppress defined areas. One example of a dynamic control concept for generating an image by way of a scanning laser beam is described, for example, in document A 514633 by the applicant.

(14) In practice, the laser light source often comprises multiple laser diodes, for example six, each being 1 watt, so as to achieve the desired power or the required luminous flux. The control signal of the laser light source 1 is denoted by U.sub.s.

(15) The laser control unit 3, in turn, receives signals from a central processing unit 4, which can be supplied sensor signals s.sub.1 . . . s.sub.i . . . s.sub.n. These signals can be switching commands for switching from high-beam light to low-beam light, for example, or signals recorded, for example, by sensors S.sub.1 . . . S.sub.n, such as cameras, which pick up the lighting conditions, environmental conditions and/or objects on the roadway. The signals can also stem from vehicle-to-vehicle communication information. The processing unit 4 shown here schematically in the form of a block can be included entirely or partially in the headlight and is used, in particular, to carry out the method of the invention described hereafter.

(16) The laser light source 1 emits blue or UV light, for example, wherein a collimation optical system 5 and a focusing optical system 6 are connected downstream of the laser light source. The configuration of the optical systems depends, among other things, on the type, number and spatial arrangement of the laser diodes used, the required beam quality, and the desired laser spot size on the light conversion means.

(17) The focused or shaped laser beam 2 arrives at a light scanner 7 and is reflected by a micromirror 10 onto a light conversion means 8 designed as a luminous area in the present example, which comprises a phosphor for light conversion, for example, in the known manner. The phosphor converts blue or UV light into white light, for example. Phosphor in the context of the present invention is generally understood to mean a substance or a substance mixture that converts light having one wavelength into light having a different wavelength or a wavelength mixture, and in particular into white light, which can be subsumed under the term wavelength conversion.

(18) Luminescence dyes are used, wherein the starting wavelength is generally shorter, and thus higher in energy, than the emitted wavelength mixture. The desired white light impression is created by additive color mixing. White light is understood to mean light having a spectral composition that evokes a white color impression in humans. Naturally, the term light is not limited to radiation visible to the human eye. Optical ceramics, for example, may be used for the light conversion means, which are transparent ceramics such as YAG-Ce (cerium-doped yttrium aluminum garnet).

(19) It shall be noted at this point that the drawing shows the light conversion means as a phosphor surface, on which the scanning laser beam generates, or scanning laser beams generate, an image that is projected proceeding from this side of the phosphor. However, it is also possible to use a translucent phosphor, in which the laser beam, coming from the side facing away from the projection lens, generates an image, wherein, however, the emitting side is located on the side of the light conversion means facing the projection lens. In this way, both reflective and transmissive beam paths are possible, wherein ultimately a mixture of reflective and transmissive beam paths is not excluded either.

(20) The micromirror 10 oscillating about two axes in the present example is controlled by a mirror control unit 9 with the aid of driver signals a.sub.x, a.sub.y and, for example, is deflected in two directions x, y that are orthogonal to one another. The mirror control unit 9 is also controlled by the processing unit 4 so as to be able to set the oscillation amplitudes of the micromirror 10 and the instantaneous angular speed thereof, wherein asymmetric oscillations about the respective axis may also be settable. The control of micromirrors is known and can take place in a variety of ways, such as electrostatically, electromagnetically or electrodynamically. In tried and tested embodiments of the invention, the micromirror 10 pivots in the x direction about a first rotational axis 10x, and in the y direction about a second rotational axis 10y, and the maximum amplitude, as a function of the control thereof, results in deflections in the resulting light image of, for example, +/35 in the x direction and 12 to +6 in the y direction, wherein the mirror deflections are half of these values.

(21) The position of the micromirror 10 is advantageously reported back to the mirror control unit 9 and/or to the processing unit 4 with the aid of a position signal p.sub.r. It shall be noted that other beam deflection means, such as movable prisms, may be used, even though the use of a micromirror is preferred.

(22) The laser beam 2 thus scans across the light conversion means 8, which is generally planar, but does not have to be planar, and generates a light image 11 having a predefined light distribution. This light image 11 is now projected onto the roadway 13 as a light image 11 by way of an imaging system 12. The laser light source is pulsed at high frequency or continuously controlled in this process, so that, corresponding to the position of the micromirror, arbitrary light distributions can not only be set, such as high-beam light/low-beam light, but can also be rapidly altered when a particular terrain or roadway situation requires, for example when pedestrians or oncoming vehicles are detected by one or more of the sensors S.sub.1 . . . S.sub.n and, accordingly, a change in the geometry and/or intensity of the light image 11 of the roadway illumination is desirable. The imaging system 12 is illustrated simplified here as a lens.

(23) The term roadway is used for simplified illustration here since, of course, it depends on the local circumstances whether the light image 11 is in fact located on the roadway or also extends beyond it. In principle, the image 11 corresponds to a projection onto a vertical surface area in accordance with the relevant standards that refer to motor vehicle lighting technology.

(24) Exemplary embodiments of the method according to the invention will be described hereafter in greater detail. Initially, the desired light image is divided into a pixel set having n rows and m columns, wherein in the grid shown in FIG. 4 m=30 and n=60 applies, which is to say 30 rows and 60 columns are present. It should be clear that any arbitrary, technologically reasonable other resolution may be selected here. In the illustrated example, in any case 30*60=1800 pixel fields are present.

(25) It is now ascertained in which column and in which row the pixel is located for which the highest optical power must be delivered, wherein this optical power for each pixel depends on the desired light distribution, or on the desired intensity in the respective pixel. The corresponding specifications are defined for each pixel as a particular illumination intensity in 1, and these values are used to calculate the required optical power in watt per pixel, taking the efficiency of the optical system of the headlight and, where necessary, the efficiency of a light conversion means into consideration.

(26) The invention now provides that the horizontal and/or vertical characteristic control curves for the micromirror are adapted to a selected row and/or column in terms of the required optical power of the pixels, and the adapted horizontal and/or vertical characteristic control curves are used to control the micromirror. The most general case is one in which the micromirror is controlled linearly with respect to the two axes, and thus no resonant operation is selected. However, it should be clear that the invention can also be applied only to control with respect to one axis, namely when scanning takes place only in one axis, for example using a wide light spot or multiple micromirrors, which scan a spot on top of or next to one another.

(27) Subsequent to the aforementioned definition of the n rows and m columns, the definition of the required illumination intensity E.sub.ij per pixel, and the ascertainment of the maximum required power per pixel, either the horizontal or the vertical characteristic control curve is adapted, which is to say optimized, whereby two variants are obtained. First, one variant of the invention is described in which the vertical characteristic control curve is optimized, which is that which relates to the columns and is referred to as Variant 2, wherein reference is made to FIGS. 5a and 5b.

(28) Step v12:

(29) In this step, the column in which the previously ascertained highest optical power must be delivered is defined as column c2, and the total illumination intensity of this column c2 is calculated. FIG. 6 shows the desired light image in which the column c2 was ascertained with the maximum illumination intensity.

(30) The total illumination intensity is denoted by E.sub.c2 ges.

(31) Step v22:

(32) In this subsequent step, proceeding from this total illumination intensity, it is calculated what unit of time per illumination intensity t.sub.slx is available in this column c2.
t.sub.slx=T.sub.S/E.sub.c2 ges.

(33) Here, T.sub.S denotes half the period duration of the column period, and E.sub.c2 ges. denotes the sum of all predefined illumination intensity values per pixel which is required in this half period duration of the column period. A column period shall be understood to mean the duration that the mirror requires when pivoting about a (horizontal) axis for scanning in the vertical direction, which is to say in the column direction.

(34) Step v23:

(35) Thereafter, the respective illumination intensities of the column c2 E.sub.c2n, which are present in a series, are used to create a new series, wherein the illumination intensity E.sub.c2n of every element of the new series is E.sub.c2n=.sub.j=1.sup.n E.sub.c2j.

(36) Step v42:

(37) In this subsequent step, the elements of the new series are multiplied by the unit of time per illumination intensity t.sub.slx, and they are defined by way of the deflection angle .sub.V=.sub.Vmax/n available for every pixel as a new optimized characteristic control curve, which is shown in solid form for one example in FIG. 7 where also the deviation from the dotted linear control is apparent. T.sub.s denotes half the period duration of the column period. The x-axis in FIG. 7 represents the time, and the deflection takes place across the entire column period and thus T.sub.s corresponds to half this time.

(38) Step v52:

(39) The optimized characteristic control curve is now applied, and linear, and thus not optimized, control is used for the remaining axis.

(40) Step v62:

(41) In this step, the utilization is evaluated (such as in % of the laser power per pixel), and the row having the best utilization .sub.max is ascertained:

(42) The evaluation can take place either by way of calculation or by way of measurement.

(43) If the evaluation is to take place by way of measurement, a corresponding headlight system is set up, and the utilization of the installed laser power is back-calculated for every pixel via the luminous flux in the created light image. It is possible, for example, to measure the luminous flux for every pixel, and back-calculate it to watt per pixel via the efficiency of the light conversion means (phosphor).

(44) From a calculation point of view, one must proceed from the possible deliverable optical power of a laser diode in the light image. For example, a laser diode delivers 1 W of optical power, which is to be divided among the 6030 pixels, for example, due to the scanning process.

(45) With a linear control curve, optical power of 0.556 mW could be delivered in each pixel in this example.

(46) With the optimized control curve, this power of 1 W, however, is no longer divided evenly, but is distributed at varying speeds across the pixels according to the optimized control curve.

(47) The optical power distribution, resulting from the use of the optimized control curve, using a laser diode of one watt, for example, can then be used to calculate the number of laser diodes needed for every pixel, namely as the required optical power per pixel P.sub.m,n divided by the deliverable optical power per pixel P.sub.m,n by way of the optimized characteristic control curve, using a laser diode having 1 W optical power, for example.

(48) In this way, the number of laser diodes needed for the respective pixels is obtained, wherein, of course, rounding is necessary if the result of the division is not an integer.

(49) The utilization of the installed laser for every pixel P.sub.m,n is then obtained by the dividing the required optical power in pixels P.sub.m,n by the product of the deliverable power of a laser diode in pixels P.sub.m,n and the maximum number of required laser diodes in all pixels.

(50) FIG. 8 shows the utilization of the installed laser power in every pixel calculated or measured for a representative example, wherein a higher utilization corresponds to a higher density of dots in the drawing.

(51) Step v72:

(52) Now, the column having optimal utilization of the installed laser power is selected and used for the optimization of the characteristic control curve of the remaining axis (the horizontal characteristic control curve in this example).

(53) The procedure is, in principle, the same as with the optimization of the vertical characteristic control unit in method steps v12, v22, v32, v43; however, here one does not proceed from the illumination intensity, but from the utilization of the installed laser power per pixel.

(54) For this purpose, the row in which the previously ascertained highest utilization of the installed laser power was able to be delivered is defined as row r2, and all utilizations of the installed laser power in the respective pixel are added up. See also step v82.

(55) Step v82:

(56) Thereafter, proceeding from the utilization .sub.r2 ges., namely the sum of the utilizations from step v72, it is calculated what unit of time per illumination t.sub.Z is available in this row r2.
t.sub.Z=T.sub.Z/.sub.r2 ges.

(57) wherein T.sub.Z is half the period duration of the row period, and .sub.r2 ges. is the sum of all calculated or measured utilizations of the installed laser power per pixel which is required in this half period duration of the row period.

(58) Step v92:

(59) In this step, the respective utilization values of the row r2 are used to create a new series, wherein the illumination intensity .sub.r2m of every element of the new series is .sub.r2m=.sub.j=1.sup.m .sub.r2j.

(60) Step v102:

(61) Now, the elements of the new series are multiplied by the unit of time per utilization t.sub.Z and are defined via the deflection angle .sub.H=.sub.Hmax/m available for every pixel as a new optimized characteristic control curve for the horizontal control of the micromirror. For the considered example, this characteristic curve is shown as a solid curve in FIG. 9, while the dotted line again corresponds to linear control without optimization, wherein it is apparent that the deviation of the optimized horizontal characteristic control curve from the linear progression is now only minor.

(62) Step v112:

(63) A usable optimized characteristic control curve has now been obtained for both the vertical and the horizontal axis of the microscanner or micromirror. In this application, analogously to step v62, the utilization of the installed laser power is either calculated or measured in a test set-up. This utilization is shown in FIG. 10 in a representation comparable to FIG. 8.

(64) Analogously, the optimization of the characteristic control curves of the respective axes takes place in reverse order, which resulted in one variant of the invention in which the horizontal characteristic control curve is optimized, which is that which relates to the rows and is referred to as Variant 1. The flow charts in FIGS. 5a and 5b show this in steps v11 through v111, wherein no separate explanation is required here since only the rows and columns, or horizontal and vertical, have been swapped here compared to the second variant. The row r1 having the maximum illumination intensity in the desired light image is apparent in FIG. 6, which was already mentioned above.

(65) Thus, first the optimization of the horizontal characteristic control curve takes place, this is then applied in step v51 and subsequently evaluated in step v61 so as to optimize the remaining vertical characteristic control curve in the subsequent steps v71 through v101. The utilization when employing the method according to variant 1 is represented in FIG. 11, wherein in this figure, deviating from the representations according to FIGS. 8 and 10, the percentage of the utilization for every pixel is entered in numbers. For the sake of a clear illustration, FIG. 11 only shows the left half of the light image; the right half would have to be added laterally reversed for the entire light image.

(66) Regardless of whether variant 1 or 2 is employed, utilizations of the laser power close to 100% are achieved in the important regions of the light image.

(67) When the above-described methods are employed, a variety of characteristic control curves are obtained, which result in different utilizations of the installed laser power. More precisely, both an optimized horizontal characteristic control line and an optimized vertical characteristic control line are obtained for each variant. Which variant is better depends on the desired light image, the resolution, and the desired intensity in the respective pixels, so that a comparison of the results is recommended, which can be carried out in the step Compare utilization. Typically, however, the optimized horizontal characteristic control curve and the optimized vertical characteristic control curve of the respective variant fit together the best in the spirit of a best-possible overall utilization.

(68) When looking at the method shown in FIGS. 5a and 5b, it is apparent that different combinations or simplifications are possible. It is possible, for example, to employ the optimized horizontal characteristic control curve obtained in variant 1 with the optimized vertical characteristic control curve obtained in variant 2, and vice versa, and to determine, in a comparison, the combination of characteristic control curves which is the most favorable for the specific case, so as to then use this combination for controlling the micromirror.

(69) In many cases, it will not be necessary to employ the aforementioned comparison, which is to say only one variant of the method is then carried out, and the result obtained is employed without further verification. As was already mentioned above, the optimization, by nature, is only carried out in this single axis for a headlight scanning only in one axial direction, corresponding to steps v61 through v101 of variant 1, for example.