JP2022017636A - Light source device, control method for light emission, and program - Google Patents

Abstract

To provide a light source device in which the flicker phenomenon can be suppressed, a control method for light emission, and a program.SOLUTION: A light source device in which the flicker phenomenon can be suppressed, a control method for light emission, and a program are provided. A light source device 10 according to one embodiment includes a plurality of light sources 11a and 11b, and a light emission control unit 13 that controls the light sources 11a and 11b individually to perform light emission. The light emission control unit 13 controls so that at least one of the light sources 11a and 11b emits light randomly over time.SELECTED DRAWING: Figure 4

Description

The present invention relates to a light source device, a light emission control method and a program.

In the field of displays, it is required to make the displayed image finer by appropriately controlling the light emitting state (for example, brightness).

For example, Patent Document 1 describes a technique for correcting the emission luminance of a light emitting element of a liquid crystal display device. Specifically, in a liquid crystal display device, when correcting the emission brightness of a predetermined block in a certain area, only the block to be corrected is turned on in the area, and all the other blocks are turned off. Therefore, a method of causing a light receiving element to receive light is disclosed. This is intended to measure the brightness of the block to be corrected with high accuracy.

Japanese Unexamined Patent Publication No. 2008-268642

In expanding the dynamic range of a display, particularly a display using an LED (Light Emitting Diode), control in the case of emitting light with a minute amount of light emission becomes a particular problem. Specifically, since the width of the LED emission pulse in a minute emission amount is narrow and the emission interval is wide, there is a problem that a person who sees the LED emission in a minute emission amount recognizes the flicker phenomenon. rice field. The technique described in Patent Document 1 does not consider such a problem.

An object of the present disclosure is to solve such a problem, and an object of the present invention is to provide a light source device capable of suppressing a flicker phenomenon, a light emission control method, and a program.

The light source device according to one aspect of the present disclosure includes a plurality of light sources and a light emission control unit that individually controls the plurality of light sources to emit light, and the light emission control unit includes at least one of the plurality of light sources. It is controlled to emit light randomly over time.

The light emission control method according to one aspect of the present disclosure includes a step of controlling the plurality of light sources to emit light so that at least one of the plurality of light sources emits light randomly over time, and the plurality of light sources. It includes a step of individually controlling and emitting light.

The program according to one aspect of the present disclosure is a program for causing a computer to execute a method for controlling a light source, and the method for controlling a light source is such that at least one of a plurality of light sources is randomly emitted over time. The present invention includes a step of controlling the plurality of light sources to emit light, and a step of individually controlling the plurality of light sources to emit light.

In the light source device, the light emission control method, and the program described above, at least one of the plurality of light sources is randomly emitted, so that the flicker recognized by the user is compared with the case where the light sources are periodically emitted. The phenomenon can be suppressed.

INDUSTRIAL APPLICABILITY According to the present disclosure, it is possible to provide a light source device capable of suppressing a flicker phenomenon, a light emission control method, and a program.

It is sectional drawing of the display 90 which concerns on a related technique. It is a top view of the LED board 91 which concerns on a related technique. It is a graph which shows the control method of the LED element 92 which concerns on a related technique. It is a block diagram of the light source apparatus 10 which concerns on Embodiment 1. FIG. It is a top view which shows the arrangement example of the light emitting part 14 which concerns on Embodiment 1. FIG. It is a graph which shows the light emission control example which concerns on Embodiment 1. FIG. It is a top view which shows the other arrangement example of the light emitting part 14 which concerns on Embodiment 1. FIG. It is a top view which shows the other arrangement example of the light emitting part 14 which concerns on Embodiment 1. FIG. It is a block diagram of the light source apparatus 20 which concerns on Embodiment 2. FIG. It is a top view of the LED board 24 which concerns on Embodiment 2. FIG. It is a graph which shows the 1st example of the light emission control which concerns on Embodiment 2. FIG. It is a graph which shows the example of the light emission control in the ultra-low luminance state which concerns on Embodiment 2. It is a top view of the LED board 24 which concerns on Embodiment 2. FIG. It is a graph which shows the 2nd example of the light emission control which concerns on Embodiment 2. FIG. It is a graph which shows the light emission control example which concerns on Embodiment 4. It is a graph which shows the example of the monitor waveform of the light receiving element which concerns on Embodiment 4. FIG. It is a graph which shows the example of the light emission pattern in the region (i) which concerns on Embodiment 4. FIG. It is a figure which shows the variation of the LED board 24 which concerns on Embodiment 5. It is a figure which shows the variation of the LED board 24 which concerns on Embodiment 5. It is sectional drawing of the display 50 which concerns on Embodiment 5. FIG. It is a block diagram which shows the internal circuit 60 of the light source apparatus which concerns on Embodiment 6. It is a block diagram which shows the hardware configuration example of a computer.

(Related technology)
Prior to explaining embodiments of the present disclosure, related techniques will be described. FIG. 1 is a cross-sectional view of a display 90 according to a related technique. The display 90 includes an LED substrate 91, a lens L, a luminance increasing film F, and a liquid crystal panel P.

The LED substrate 91 irradiates light from a plurality of LED elements 92 provided on the substrate. The irradiated light is incident on the lens L, refracted, and reaches the luminance increasing film F. The luminance increasing film F passes only the (coherent) light polarized in a predetermined direction among the incident light through the liquid crystal panel P, and the other incident light is reflected and returned to the lens L side. For example, DBEF (Dual Brightness Enhancement Film) can be applied to the brightness increasing film F.

The incident light returned to the lens side reaches the lens and the LED substrate 91 in order, is reflected by the LED substrate 91, and reaches the luminance increasing film F again. At this time, among the incident light that has reached the luminance increasing film F again, the incident light polarized in a predetermined direction is passed through the liquid crystal panel P, and the other light is reflected and returned to the lens side. By this mechanism, light polarized in a predetermined direction is incident on the liquid crystal panel P without waste. When the user visually recognizes the liquid crystal panel P, the user can see the image.

FIG. 2 is a top view of the LED substrate 91. The LED substrate 91 includes a plurality of LED elements 92 each having an LED chip 93, and a substrate main body 94. The plurality of LED elements 92 are arranged on the LED substrate 91 in a square grid pattern. The light emission of the LED element 92 is individually controlled by a control unit (not shown) by PWM (Pulse Width Modulation) dimming. Specifically, when the LED element 92 emits light with a large emission amount, the emission pulse width used for emission control is lengthened, and when the LED element 92 emits light with a small emission amount, the emission pulse width is shortened. ..

In the following description, "luminance" means the peak value in the emission pulse, and "emission amount" means the emission amount within a predetermined time due to the continuation of the emission pulse. The "emission amount" can also be expressed as a value obtained by multiplying the luminance value by the duration of the emission pulse, which is the pulse width.

FIG. 3 shows a control method of the LED element 92. As shown in FIGS. 3 (1) to 3 (3), the LED element 92 emits light based on a periodic emission pulse based on the pulse of the synchronization signal Sync. The pulse of the synchronization signal Sync is generated at t1, t2, and t3, and the emission pulse of (1) to (3) is generated by the pulse.

The pulse width Tw of each emission pulse in (1) to (3) is variable and changes according to the image to be displayed. However, the emission pulses in (1) to (3) are all generated at the same timing.

Since the light emission timings of all the LED elements 92 are the same, it is not possible to detect the brightness value of each LED element 92 in the light receiving element. Therefore, the brightness difference between the LED elements 92 cannot be adjusted, and the uniformity in the image of the display 90 deteriorates. Further, since the current is supplied to all the LED elements 92 at the same timing, the change in the current consumption becomes large. Attempting to make the power supply circuit compatible with this will lead to an increase in cost.

Further, as the amount of light emitted becomes smaller, the light emitting time width of the light emitting pulse becomes narrower, and the interval between the light emitting pulses (timing from the light emission ON to the next light emission ON) becomes longer. This ON-OFF of light emission is perceived by the user as a flicker phenomenon. In particular, when the light emission is periodic, it is easily recognized as a flicker phenomenon.

Further, since the LED element 92 generates heat by causing the LED element 92 to emit light, the brightness of the LED element 92 may change and uneven brightness may occur. In particular, in light emission at low brightness, whether or not the LED element 92 emits light is unstable, so that the change in brightness due to temperature becomes large. There is a limit to eliminating this luminance unevenness only by controlling the amount of current flowing through the LED element 92, and it is considered necessary to actually detect the light emitting state to eliminate it.

In view of the above description, the present disclosure relates to a technique for controlling the light emission of an LED so that the user does not recognize the flicker phenomenon. Hereinafter, embodiments of the present invention will be described with reference to the drawings. Needless to say, the embodiments described below and the individual technical features described therein can be used in any combination.

(Embodiment 1)
The first embodiment describes the outline of the technique of the present disclosure. FIG. 4 is a block diagram of the light source device 10 according to the first embodiment. The light source device 10 includes light sources 11a and 11b, a photodetector 12, and a light emission control unit 13. The light sources 11a and 11b and the photodetector 12 are included in the light emitting unit 14.

The light source 11a (first light source) and the light source 11b (second light source) are light emitting elements such as LEDs, and their light emission is controlled by the light emission control unit 13.

The photodetector 12 (photodetector) detects the light emission of each of the light sources 11a and 11b, and is, for example, a light receiving element such as a photodiode, a phototransistor (illuminance sensor), or a photoresistor using the photoelectric effect. Is also good. The photodetector 12 outputs a signal corresponding to the detected light emission to the light emission control unit 13.

The light emission control unit 13 outputs a control signal to the light sources 11a and 11b based on the signal from the photodetector 12 (light emission detection result), thereby individually controlling the light sources 11a and 11b to emit light. For example, the light emission control unit 13 changes the light emission amount of the light sources 11a and 11b by changing at least one of the brightness (height of the light emission pulse), the width or the interval (duty ratio) of the light sources 11a and 11b. Is also good.

The light emission control unit 13 makes at least one of the light sources 11a and 11b emit light at random over time, and the light sources 11a and 11b do not overlap the timing at which the photodetector 12 detects the light sources of the light sources 11a and 11b. Is controlled to emit light.

Here, "to make the light source emit light randomly over time" (hereinafter, simply referred to as "to make the light source emit light randomly") means that the light source does not emit light periodically and within a predetermined elapsed time as a sample. , It means that there is a significantly different period (not an error) in the light emission interval. As a result, it is possible to suppress the flicker phenomenon recognized by the user as compared with the case where the light source emits light periodically. The light emission control unit 13 may make only one of the light sources 11a and 11b emit light at random, or may make both of them emit light at random. However, by causing both to emit light at random, the flicker phenomenon recognized by the user can be suppressed more effectively.

Further, as an additional feature, the photodetector 12 is provided in the light source device 10, the photodetector 12 individually detects the light emission of the light sources 11a and 11b, and the light emission control unit 13 determines the detection result of the light detector 12. Based on this, light sources 11a and 11b may be individually controlled to emit light. As a result, even if the brightness of the light source changes due to the temperature change of the light sources 11a and 11b, the photodetector 12 detects the change in brightness and feeds it back to the light emission control unit 13, so that the light emission control unit 13 determines the brightness of the light source. Changes can be suppressed.

Further, by controlling the light emission of the light sources 11a and 11b so that the timings of detection by the photodetector 12 do not overlap, the photodetector 12 distinguishes (separates) the light emission of the light source 11a and the light emission of the light source 11b. ) Can be detected. Therefore, the light emission control unit 13 controls the light emission of the light source 11a based on the light emission state of the detected light source 11a, and controls the light emission of the light source 11b based on the light emission state of the detected light source 11b. The light emission of the light sources 11a and 11b can be controlled individually.

A specific example of the timing at which the light emission control unit 13 causes the light sources 11a and 11b to emit light will be described so that the timings at which the photodetector 12 detects the light sources of the light sources 11a and 11b do not overlap.

FIG. 5 shows an arrangement example of the light sources 11a and 11b and the photodetector 12 in the light emitting unit 14. In FIG. 5, the photodetector 12 is located at approximately equal distances from the light source 11a and the light source 11b, respectively.

FIG. 6 shows control of the light emission timing of the light sources 11a and 11b executed by the light emission control unit 13 in the light emission unit 14 shown in FIG. The solid line in FIG. 6 shows the emission pulses of the light sources 11a and 11b generated by the emission control unit 13.

The light emission control unit 13 shifts the light emission timing of the light source 11b by tx from the light emission timing of the light source 11a so that the light emission detection timings of the light sources 11a and 11b do not overlap. It is preferable to make tx larger than the light emission period tp of one light emission pulse of the light source 11a in that the light emission detection timings of the light sources 11a and 11b do not overlap with each other.

The photodetector 12 does not have to be located at approximately equal distances from the light source 11a and the light source 11b, respectively. For example, as shown in FIG. 7, the light source 11a may be arranged closer to the photodetector 12 as compared with the light source 11b, or as shown in FIG. 8, the light source 11b may be light as compared with the light source 11a. It may be located near the detector 12. Even in this way, since the difference in detection timing caused by the difference in distance from each light source to the photodetector 12 is small, the same control as that shown in FIG. 6 is possible.

In the above description, the method of shifting the light emission timing of the light source 11b after the light emission timing of the light source 11a has been described, but the same control can be executed even when the light emission timing of the light source 11a is shifted after the light emission timing of the light source 11b. ..

Further, the light source included in the light emitting unit 14 may be a light source other than the light sources 11a and 11b. For example, in the light emitting unit 14, a plurality of light sources may be arranged in a grid pattern, and the light sources 11a and 11b may be adjacent (closest) light sources among them, or may be distant light sources. Is also good.

Further, as a light detector, a first photodetector corresponding to the light source 11a and a second photodetector corresponding to the light source 11b are individually provided, and each photodetector emits light of the light sources 11a and 11b, respectively. You may adopt the configuration which detects. In this case, even if the light emission timings of the light sources 11a and 11b overlap (simultaneously), the photodetector 12 can individually acquire the light emission of the light sources 11a and 11b. Therefore, the light emission of the light sources 11a and 11b can be controlled individually. Even in this case, the flicker phenomenon can be suppressed by causing at least one of the light sources 11a and 11b to emit light at random.

By providing the photodetectors 12 individually in this way, it is possible to make the process executed by control easier. However, in the configuration shown in FIG. 5, there is an advantage that the number of photodetectors 12 can be reduced.

The photodetector 12 is not essential in the light source device 10, and the light emission control unit 13 does not use the detection result of the photodetector 12, but based on the correspondence between the brightness of the light source and the control signal set in advance, the light source. 11a and 11b can be controlled to have a desired brightness. Even with such a configuration, the flicker phenomenon can be suppressed by causing at least one of the light sources 11a and 11b to emit light at random.

The light source device described above can be applied to a backlight light source of a head-up display (hereinafter referred to as HUD). The applied HUD is realized by, for example, a TFT (Thin Film Transistor) method. For example, in addition to the light source device 10 described in this embodiment, the HUD includes a lens L, a luminance increasing film F, and a liquid crystal panel P as shown in FIG.

The HUD is used in various fields such as airplane operation, automobile driving, medical treatment, and computer games. For example, in the field of automobiles, the HUD is used to support safe driving of a car by displaying an arrow or the like indicating the speed or the traveling direction of the car. In recent years, augmented reality (AR) HUD technology, which matches and projects displays on actual driving landscapes, has also attracted attention.

The HUD is required to improve the visibility of the displayed content by expanding the viewing angle, increasing the brightness and increasing the definition, and to make the display form and display position of the image user-friendly. Further, the HUD has problems such as suppression of postcard effect, uniformity of screen brightness, and high contrast.

Further, the brightness of the image projected by the HUD needs to be adjusted to the driving situation of the automobile. For example, when traveling on a snowy road in fine weather, high brightness (for example, 10,000 nits or more) is required for the HUD display. If the HUD display becomes dark in this state, the driver may not be able to recognize the HUD display. On the other hand, while traveling in the dark, the HUD display is required to have a considerably low brightness (for example, about several nits). If the HUD is displayed with high brightness in this state, the driver can recognize the HUD display, but may not be able to sufficiently recognize the scenery outside the vehicle when driving. From the above, a wide dynamic range is required for the light source used for the HUD.

As a means for solving such a problem, a local dimming technique for a light source that individually controls the brightness or the amount of light emitted from a plurality of LED elements is assumed. In particular, if a large number of LED elements can be controlled with high accuracy, it will greatly contribute to solving the above-mentioned problems.

Due to the characteristics of the LED element used by HUD, in order to control the light emission of the LED element stably over a wide dynamic range, not only DC dimming that controls the applied voltage to the LED element to realize a large amount of light emission but also DC dimming PWM dimming is also required to realize a minute amount of light emission. However, as described above, in a minute light emission state, the light emission time width of the light emission pulse becomes narrow and the interval between the light emission pulses becomes long, so that the flicker phenomenon is likely to occur. Therefore, when the driver recognizes the HUD display as a flickering phenomenon while driving in the dark, there is a possibility that the display cannot be recognized accurately and fatigue may be accumulated.

As described above, the light source device 10 according to the first embodiment can suppress the flicker phenomenon recognized by the user by causing the light source to emit light at random. Therefore, it is possible to display the HUD in which the flicker phenomenon is suppressed even in a minute light emitting state. Therefore, safe driving, which is the biggest problem in automobiles, can be realized more reliably. It can be said that this is an effect that cannot be imagined from a general display used for a television or the like.

Further, by making it possible to distinguish and detect the light emission of a plurality of light sources (for example, LED elements), it is possible to accurately control the light emission of each light source. Then, even when the temperature changes inside the light source device and the brightness of the light source changes, the light emission control unit can control the brightness of the light source according to the situation such as the scenery outside the vehicle. As a result, it is resistant to temperature changes and has the effects of highly accurate local dimming and contrast improvement (wide dynamic range).

However, the light source device 10 according to the first embodiment can also be mounted as a light source device for a general display.

(Embodiment 2)
The second embodiment describes a more detailed example of the technique of the present disclosure. FIG. 9 is a block diagram of the light source device 20 according to the second embodiment. The light source device 20 functions as a backlight light source for a display, and includes an LED element 21 as a light source, a light receiving element 22 as a photodetector, and a light emission control unit 23. The LED element 21 and the light receiving element 22 are included in the LED substrate 24.

FIG. 10 is a top view of the LED substrate 24. On the substrate body 25 of the LED substrate 24, 18 LED elements 21 and 10 light receiving elements 22 are arranged in a square grid pattern, respectively. Each LED element 21 has an LED chip 26. Here, one light receiving element 22 is arranged in the center of the four LED elements 21 arranged in a square grid pattern. Therefore, the distance between the one light receiving element 22 and the four LED elements 21 is substantially equidistant. Above the LED substrate 24, a lens L, a luminance increasing film F, and a liquid crystal panel P as shown in FIG. 1 are provided. The light source device 20, the lens L, the luminance increasing film F, and the liquid crystal panel P constitute a display (display device).

The light emission control unit 23 outputs a control signal by DC (Direct Current) dimming or PWM dimming to each LED element 21 based on the signal (light emission detection result) from each light receiving element 22 to output each LED. The element 21 is individually controlled to emit light. Here, the light emission control unit 23 makes each LED element 21 emit light at random, and causes each LED element 21 to emit light so that the timing at which each light receiving element 22 detects the light emission of the LED element 21 does not overlap. Control. Hereinafter, a specific control example will be described.

(First example)
FIG. 11 is a first example showing control of the light emission timing of the LED element 21. In FIG. 11, the light emission timings for four of (a) to (d) in FIG. 10, which are a part of the 18 LED elements 21, are shown. The emission timings of (a) to (d) shown in FIG. 11 are random rather than periodic.

Further, the (adjacent) (a) and (b) that are in close contact with each other are sequentially emitted by shifting the emission timings of the respective LED elements 21 so as not to overlap. Therefore, in FIG. 10, the light receiving element 22 (e) located at substantially equidistant distances from (a) and (b) can detect the light emission of (a) and the light emission of (b) separately. Similarly, the emission timings of (b) and (c) and (c) and (d) adjacent to each other are shifted so as not to overlap. Therefore, in FIG. 10, the light receiving element 22 (f) located at substantially equidistant distances from (b) and (c) can detect the light emission of (b) and the light emission of (c) separately, and can be detected with (c). The light receiving element 22 (g) located substantially equidistant from (d) can detect the light emission of (c) and the light emission of (d) separately.

As described above, the smaller the amount of light emission, the narrower the light emission time width of the light emission pulse, and the longer the interval (timing from the light emission ON to the next light emission ON) of the light emission pulse. This ON-OFF of light emission is perceived by the user as a flicker phenomenon. However, as shown in FIG. 11, the light emission control unit 23 eliminates the periodicity of the light emission pulses of each LED element 21 and generates the light emission pulse intervals so as to be random over time, which causes a flicker phenomenon for the user. Is hard to see.

FIG. 12 shows a control example of the light emission timing when the light emission amount is further reduced (in the case of so-called ultra-low brightness, which is a light emission amount equal to or less than a predetermined threshold value) from the light emission timing control example shown in FIG. In (a) to (d) in FIG. 12, a part of the plurality of light emission timings is masked (thinned out) to suppress the light emission, so that the total light emission amount is reduced. In FIG. 12, in each of (a) to (d), the timing of masking is random over time. This can suppress the flicker phenomenon more than the masking is performed periodically. The LED element 21 for mask control may be any one or more of the LED elements 21 (a) to (d).

In the above example, the light emission control of the LED elements 21 (a) to (d) in FIG. 10 is illustrated, but the same light emission control can be applied to the 14 LED elements 21 other than the LED elements 21 (a) to (d). It is possible. Further, in the LED element 21, only one of the following is generated so that the light emission timing is not periodic but random over time, or the timing for masking the light emission timing is random over time. May be controlled. Further, the control target may be one or more arbitrary number of LED elements 21. By executing such control, the flicker phenomenon can be further suppressed.

(Second example)
FIG. 13 is a top view of the LED substrate 24 for explaining the second example. The 18 LED elements 21 arranged on the LED substrate 24 are divided into four categories (p) to (s). (P) to (s) are categories for controlling the light emission timing as described below.

FIG. 14 is a second example showing control of the light emission timing of the LED element 21. In FIG. 14, the light emission timings for the four patterns (p) to (s) are shown. Here, (p) to (s) are controlled so that the emission timings do not overlap with each other. Specifically, in (p), emission pulses are generated at times t1, t2, and t3 in synchronization with the rising edge of the synchronization signal SYNC, and emission timings are reached as (q), (r), and (s). Shifts to slow down. This is because one light receiving element 22 located at approximately equal distances from the four LED elements 21 (p) to (s) individually and sequentially receives the four LED elements 21. With the above control, the light emission of the four LED elements 21 can be individually detected by one light receiving element 22 in the entire LED substrate 24, so that the brightness emitted by all the LED elements 21 can be monitored.

Further, the emission timings for the four patterns of each (p) to (s) shown in FIG. 14 are originally periodic timings. However, in (p) to (s), by performing masking at random timings, (p) to (s) are controlled to emit light at random. By this mask control, the flicker phenomenon can be suppressed. This control can be executed when the amount of light emitted is equal to or less than a predetermined threshold value.

In the second example described above, since the four patterns shown in (p) to (s) are sufficient for both the light emission timing and the mask control, the light emission control unit 23 is compared with the first example. Can reduce the number of patterns generated for light emission control.

Then, in the first and second examples, the detection value (light emission peak value) received by each light receiving element 22, the light emitting time of the known light emitting pulse, and each light receiving element 22 and its light receiving element 22 are in close contact with each other. The brightness value of each LED element 21 can be calculated individually by using the distances from the four LED elements 21. By controlling the calculated brightness value to match the target brightness value of each LED element 21, individual brightness control of each LED element 21 becomes possible. Further, by this luminance control, it is possible to make the display luminance of the entire light source device 20 uniform and suppress the luminance change due to the temperature change. In this luminance control, the light receiving element 22 may also detect the light emission of the LED element 21 that is not in close contact with the light receiving element 22. However, it is very easy for those skilled in the art to set the emission luminance so that the detected value becomes a negligible level, or to correct the detected value as a mixture noise in advance.

(Third example)
In FIG. 13, two light receiving elements 22 (first and second light) are provided at substantially equidistant distance (and closest contact distance) from any LED element 21 except the LED element 21 provided at the four corners of the LED substrate 24. There is a detector). When the LED element 21 emits light, these two light receiving elements 22 simultaneously detect the detection value. If the sensitivities of these two light receiving elements 22 are the same, the detected values of the two light receiving elements 22 will be the same value, but this is not the case if the sensitivities vary. In that case, calibration for the sensitivity variation of the two light receiving elements 22 can be easily performed based on the detection value detected by each light receiving element 22. Since the LED elements 21 provided at the four corners of the LED substrate 24 have one light receiving element 22 capable of detecting light emission, it is not necessary to emit light in this calibration.

Further, the two light receiving elements 22 to be calibrated do not have to be at substantially equidistant distance from the specific LED element 21 to be light emitted. However, there is an advantage that the comparison between the two detection values can be performed more easily when the two detection values are approximately equidistant.

By controlling the light source device 20 as described above, it is possible to suppress the flicker phenomenon even in a minute light emitting state and display an image on the display with good visibility. Further, it is possible to perform control (highly accurate local dimming) in which the brightness of each LED element 21 is accurately detected. Therefore, even if there is a temperature change due to the driving of the LED element 21 and other parts, it is possible to suppress the luminance unevenness of the LED element 21 or improve the contrast of the image.

In particular, the second embodiment has the following effects.
(1) Since the light emitting pulses of the adjacent LED elements 21 do not overlap (do not overlap), it is not necessary to provide the light receiving element 22 in a one-to-one correspondence with the LED element 21, and the number of light receiving elements 22 is smaller. The brightness value of each LED element 21 can be grasped periodically. Therefore, the uniformity of the image can be improved.
(2) Since the sensitivity variation between the light receiving elements 22 can be corrected, the uniformity can be further improved.
(3) By supplying the current to the LED element 21 at different timings, the change in the current consumption can be reduced. Therefore, the load of the LED drive power supply can be reduced, and the electromagnetic wave emitted by the light source device 20 can be suppressed, which is effective from the viewpoint of EMC (Electromagnetic Compatibility).

Further, the light source device 20 described in the second embodiment can be mounted as a light source device for the entire display as in the light source device 10 described in the first embodiment, but can be applied to a backlight light source of the HUD. And it is even more effective. Further, by using the light source device 20 according to the second embodiment, the sensitivity difference between the light receiving elements 22 can be calibrated, so that the uniformity of the entire screen can be further improved.

(Embodiment 3)
The third embodiment describes a method in which the light source device 20 according to the second embodiment can accurately detect the light emission amount of the LED element 21 even if the resolution of the light emission amount of the light receiving element 22 is lowered.

Improving the dynamic range of an image is an important issue in a light source device applied to a display. For example, the luminance ratio in the image displayed by the HUD is about 1: 3000 to 4000. In order to accurately detect light in this large dynamic range with a light receiving element, a resolution of 12 bits (4096 steps) is insufficient, and a circuit having a resolution of 13 to 14 bits is required.

The third embodiment is for simplifying the circuit or reducing the cost in view of this problem. FIG. 15 is a graph showing an example of a light emission control method of an LED element according to the brightness displayed on the HUD. The vertical axis of FIG. 15 is the amount of light emitted, and the horizontal axis is the DC current value flowing through the LED element.

In FIG. 15, the region where the DC current value is I1 or more and the light emission amount is N1 or more (i), and the region where the DC current value is less than I1 and I2 or more and the light emission amount is N1 or more and N2 or more is (ii). , The region where the DC current value is less than I2 and the amount of light emitted is N2 is defined as (iii). The DC current value and the luminance value have a linear relationship, and I1> I2 and N1> N2. Further, as described above, the light emission amount is a value represented by a value obtained by multiplying the luminance value by the duration of the light emission pulse which is the pulse width.

In the region (i), control by DC dimming is performed, in the region (ii), control by PWM dimming is performed, and in the region (iii), PWM dimming and control to mask the emission pulse are performed. The technique of masking the emission pulse is as described in the second embodiment.

In the light emission control, the relationship between the HUD light emission amount (luminance value) and the DC current value in the region (i), the relationship between the HUD light emission amount in the region (ii) and the Duty ratio at the time of PWM dimming, and ( The relationship between the light emission amount of HUD and the amount of masking the light emission pulse in the region of iii) is known. Further, in the region (i), the relationship between the luminance value detected by the light receiving element at the time of DC dimming and the actual luminance value of the LED is also known.

FIG. 16 is an example of the monitor waveform of the light receiving element when each of the control methods shown in (i) to (iii) is executed. Referring to FIG. 16, when light is emitted in the region (i) in which the light emission amount is a large light emission amount of N1 or more, the current flowing through the LED element becomes variable by DC dimming, so that the brightness of the LED element is increased. The peak value (height in the graph of FIG. 16) of is variable. This peak value can be raised to the peak value corresponding to the maximum brightness.

In FIG. 16, in the regions (ii) and (iii) where the light emission amount is a small light emission amount less than N1, the peak value in one light emission pulse of the LED element does not change in either case. Therefore, the waveform peak value monitored by the light receiving element does not change in the regions (ii) and (iii).

In the region (ii), the pulse width (emission time) of one emission pulse becomes variable by PWM dimming. That is, the duty ratio changes. As a result, the amount of light emitted by the light receiving element also changes.

On the other hand, in the region (iii), the pulse width of one emission pulse is the minimum, and the pulse width cannot be further narrowed. Therefore, by masking a part of the emission pulses, the number of emission pulses within a predetermined time is changed to change the emission amount.

From the above, in the regions (ii) and (iii), the amount of light emitted can be calculated by multiplying the peak value of the light emitting pulse detected by the light receiving element by the light emitting period and converting per unit time. Therefore, as shown below, the detection dynamic range of the light receiving element can be lowered.

For example, the maximum brightness in DC dimming is A (nit), the maximum current value in the maximum brightness is B (mA), and the current value that is the limit of light emission control in DC dimming is 1 (mA). At this time, the brightness at a current value of 1 (mA) in DC dimming is A / B (nit). Therefore, the luminance A to A / B (nit) is controlled by DC dimming. When the luminance is less than A / B (nit), the control is performed by (ii) or (iii).

Therefore, the ratio of the maximum brightness to the brightness that is the threshold value for control is A: A / B = B: 1. For example, if B is about several tens to several hundreds, the resolution required for the light receiving element to realize the above-mentioned light emission control is about 8 to 9 bits (256 to 512 Steps), and the resolution of 13 to 14 bits is unnecessary. .. That is, the detection dynamic range required for the light receiving element becomes smaller. Therefore, the circuit of the light receiving element can be made considerably inexpensive.

As described above, in the HUD, it is desired to control the luminance in a wide dynamic range using a large number of LED elements. Therefore, reducing the detection dynamic range required for the light receiving element is particularly effective in the field of HUD.

FIG. 17 is a graph showing an example of a light emission pattern. (P) to (s) show light emission patterns of a plurality of LED elements as shown in FIG. In FIG. 17, the section before time t1 is a section in which each LED element is made to emit light by a light emitting pulse having a constant peak value, pulse width and interval (duty ratio) of the light emitting pulse, and the light emission brightness of each LED element is monitored. (Brightness value detection section). In the luminance value detection section, the peak value and the Duty ratio of the reference emission pulse are determined, and the luminance value predicted to be obtained by the emission pulse is compared with the actually detected luminance value to obtain the desired luminance. Obtain the luminance value-emission pulse relationship to obtain the value.

As shown in FIG. 17, in the luminance value detection section, the emission timings of (a) to (d) do not overlap and are offset from each other. Since the control described in the first and second embodiments is possible in the luminance value detection section, the emission luminance of the LED element can be individually controlled by individually detecting the emission luminance of the LED element by the light receiving element. can.

The section from time t1 to t2 is a section (dimming section) in which the amount of light emitted is controlled by dimming. In this dimming section, dimming is performed to emit light with a desired amount of light emission using the relationship between the brightness value and the light emission pulse adjusted in the above-mentioned brightness value detection section. In the dimming section, dimming control may be performed in any region (i) to (iii) of FIG. Further, in the dimming section, the light receiving element does not detect the light emission of the LED element.

After time t2, the luminance value detection section is set again, and even if the relationship between the luminance value and the emission pulse changes due to a temperature change or the like in the dimming section from time t1 to t2, the correct luminance value-emission pulse Relationships can be calculated. In this way, the brightness value detection section (calibration section) is periodically provided in the dimming section, and the brightness value of the LED element is acquired by acquiring the relationship between the brightness value of the LED element and the light emitting pulse in the brightness value detection section. Can be controlled more accurately.

(Embodiment 4)
(Variation 1)
The fourth embodiment shows variations of the LED substrate 24 according to the second embodiment. FIG. 18 is an example in which one light receiving element 32 is arranged near the center of the LED substrate 34. In this case, by individually and sequentially emitting light from the LED elements 21 shown in FIG. 18, the light receiving element 32 can individually detect the light emitting pulse of each LED element 21. The period during which the LED elements 21 emit light in order is, for example, the luminance value detection section shown in FIG.

Further, the LED element 21 which is farther from the light receiving element 32 may emit light so that the brightness value becomes higher. For example, in FIG. 18, the LED element 21 (t) is in close contact with the light receiving element 32, and the LED element 21 (u), the LED element 21 (v), and the LED element 21 (w) are connected to the light receiving element 32 in this order. It is installed in a close position. At this time, the luminance value in the light emission control can be increased in the order of the LED element 21 (w), the LED element 21 (v), the LED element 21 (u), and the LED element 21 (t). As a result, the light receiving element 32 can detect light emission with the same accuracy as the near LED element 21 even if it is a distant LED element 21.

(Variation 2)
Next, another variation of the LED substrate 24 according to the second embodiment will be shown. FIG. 19 is an example in which one light receiving element 42 for measuring the emission luminance of the LED element 21 is arranged in the vicinity of each LED element 21 on the LED substrate 44. The LED elements 21 are arranged in a square grid pattern. In this variation, the distance between the LED elements 21 is wide, and for the light receiving element 42, light emission from an LED element other than the nearby LED element 21 to be detected does not have a particular effect on the brightness measurement of the light receiving element 42. Is assumed.

Further, for the light receiving element 42, the return light from the LED element 21 to be detected (light that does not directly enter the light receiving element 42 but is reflected by the surface of another component and is incident on the light receiving element 42) is also the light receiving element 42. It has no particular effect on brightness measurement. FIG. 20 is a cross-sectional view of the display 50 including the LED substrate 24. The display 50 includes an LED substrate 24, a lens L, and a liquid crystal panel P. The lens L and the liquid crystal panel P are the same as those shown in FIG. 1, and the description thereof will be omitted. The light receiving element 42 can detect the directly incident light from the LED element 21 more strongly by directing the light receiving surface toward the LED element 21 to be detected.

In FIG. 20, it is shown that the light from the LED element 21 is reflected by the liquid crystal panel P and becomes incident light (broken line in FIG. 20) on the light receiving element 42. However, since the incident light has a considerably lower intensity than the light directly incident on the light receiving element 42, it does not have a particular influence on the luminance measurement of the light receiving element 42.

As described above, the components other than the directly incident light from the LED element 21 to be detected emit light so that the detected value is negligible in comparison with the detected value of the directly incident light to be detected. It is possible to set the brightness or correct it as noise.

In this variation 2, each LED element 21 can have the same light emission timing. This point is different from the variation 1 in which it is necessary to change the light emission timing of each LED element 21. As a result, the number of control signals for the LED element 21 in the light source device can be reduced (that is, the scale of the control circuit for the LED can be reduced). Further, since the light emitted from the LED elements other than the LED element 21 to be detected does not have a particular influence on the luminance measurement of the light receiving element 42, there is no limitation on the duty width at the time of dimming by PWM control. That is, since the amount of light emitted during light emission can be increased as compared with variation 1, the detection and control of light emission becomes easier.

However, in the configuration of FIG. 19, it is not necessary to set the light emission timings of all the LED elements 21 to the same timing. For example, in FIG. 19, the light emission control may be performed so that the light emission timings of the closest LED elements 21 are different timings and the light emission timings of the second closest LED elements 21 are the same.

In both variations 1 and 2, the flicker phenomenon can be suppressed by causing each LED element 21 to emit light at random.

(Embodiment 5)
In the embodiment of the second embodiment, a sampling signal for the light receiving element 22 to monitor the detected value according to the four types of emission classifications (a) to (d) or (p) to (s) is required. .. In the fifth embodiment, means for reducing the generation of sampling signals is shown.

FIG. 21 is a block diagram showing an internal circuit 60 in the light source device. The internal circuit 60 includes a light receiving element 61, a current-voltage conversion amplifier 62 (hereinafter referred to as an amplifier 62), an LPF (Low-Pass Filter) 63, and an A / D converter 64 (hereinafter referred to as a converter 64).

The amplifier 62 converts the current output by the light receiving element 61 into a voltage and outputs the voltage. Further, the amplifier 62 has a circuit for switching the gain in order to relax the dynamic range detected by the light receiving element 61. For example, the output terminal of the amplifier 62 and the resistance R are connected via a switch, and the gain can be controlled by switching the switch on and off. As such a configuration, a general photodiode I / V amplifier can be applied.

For example, in the example shown in the third embodiment, the gain A is used in the region (i) where the DC dimming is performed, and the PWM dimming or the region where the PWM dimming and the light emission pulse are masked is controlled (ii). ), (Iii), a gain B different from the gain A can be used. However, it goes without saying that the gains that can be used are not limited to these two patterns, and that further gain patterns can be added. By increasing the gain pattern, it is possible to improve the detection accuracy of light emission and reduce the resolution of the A / D converter.

For example, it is assumed that the I-Vamp outputs at each of the above gains A and B are as follows.
Gain A; X ₁ (nit) -Y ₁ (mV) to X ₂ (nit) -Y ₂ (mV)
Gain B; X ₁ (nit) -Y ₁ (mV) to X ₃ (nit) -Y ₃ (mV)
However, X ₂ > X ₁ > X ₃ and Y ₂ > Y ₁ > Y ₃ .

At this time, the resolution required for the A / D converter 64 is such that both the ratio X ₂ / X ₁ (or Y ₂ / Y ₁ ) and X ₁ / X ₃ (or Y ₁ / Y ₃ ) can be discriminated. Is fine. If there is only one gain, the required resolution must be able to discriminate the ratio X ₂ / X ₃ (or Y ₂ / Y ₃ ), and the resolution needs to be high, but there are two types. When using gain, it is not necessary to increase the resolution. For example, depending on the values of X ₂ / X ₁ and X ₁ / X ₃ , the A / D converter 64 may have a resolution capability of about 12 bits.

Returning to FIG. 21, the description will be continued. The LPF 63 improves the reading accuracy of the converter 64 by smoothing the pulsed detection value converted into a voltage by the amplifier 62 at the time of PWM dimming. Parameters such as the order of LPF63 and the cutoff frequency can be freely adjusted because they can be applied to a system having arbitrary characteristics.

The converter 64 is composed of a microcontroller and A / D-converts the output value from the LPF 63. As described above, the resolution required for conversion does not need to be set to a high value by switching the gain of the amplifier 62.

With the circuit configuration as described above, A / D conversion can be performed without increasing the resolution without generating a sampling signal for monitoring the detection value of the light receiving element. Therefore, the internal circuit configuration in the light source device can be simplified. Further, even when the dynamic range is expanded in the HUD, it is not necessary to increase the resolution according to the dynamic range.

(Embodiment 6)
In the first and second embodiments, it is also possible to mount the temperature sensor on the light source device. The light emission control unit corrects the detection value of the light receiving element according to the temperature characteristics of the light receiving element (photodetector) based on the temperature measured by the temperature sensor. Since the detection value of the light receiving element may be affected by the ambient temperature thereof, it is possible to detect the brightness more accurately by performing correction processing on the detected value. A known technique can be appropriately used for this correction process.

If the temperature sensor is provided in the vicinity of the light receiving element, the temperature detected by the temperature sensor may be regarded as the ambient temperature of the light receiving element. Further, if the temperature sensor is separated from the light receiving element by a predetermined distance, the temperature obtained by adding a predetermined correction to the temperature detected by the temperature sensor may be regarded as the ambient temperature of the light receiving element.

(Other embodiments)
In the second embodiment, in the light source device, a plurality of LED elements are arranged on the substrate in a square grid pattern. However, the method of arranging the LED elements is not limited to this, and an arrangement along a square grid other than a square grid, or any other type of polygonal grid may be used.

Further, the light emission control process described in each of the above embodiments can be executed by a computer. For example, when the light source device is mounted on the HUD, the computer of the automobile can execute the control process. FIG. 22 is a block diagram showing a hardware configuration example of such a computer. Referring to FIG. 22, the computer 100 includes a processor 101 and a memory 102.

The processor 101 reads software (computer program) from the memory 102 and executes it to perform the light emission control process described in the above-described embodiment. The processor 101 includes a CPU (Central Processing Unit), MPU (Microprocessor), MCU (Micro-Control Unit), FPGA (Field-Programmable Gate Array), DSP (Demand-Side Platform), and ASIC (Application Specific Integrated Circuit). One of the above may be used, or a plurality of them may be used in parallel.

The memory 102 is composed of a volatile memory, a non-volatile memory, or a combination thereof. The memory 102 may include storage located away from the processor 101. In this case, the processor 101 may access the memory 102 via an I / O (Input / Output) interface (not shown).

In the example of FIG. 22, the memory 102 is used to store the software module group. The processor 101 can perform the processing described in the above-described embodiment by reading these software modules from the memory 102 and executing the software modules.

As described above, one or more processors of a computer execute one or more programs including a set of instructions for causing the computer to perform the algorithm described with reference to the drawings. By this process, the light emission control process (step) described in the above-described embodiment can be realized.

Programs can be stored and supplied to a computer using various types of non-transitory computer readable medium. Non-temporary computer-readable media include various types of tangible storage media. Examples of non-temporary computer-readable media include magnetic recording media (eg, flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (eg, magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs. Includes CD-R / W, semiconductor memory (eg, mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (random access memory)). The program may also be supplied to the computer by various types of transient computer readable medium. Examples of temporary computer readable media include electrical, optical, and electromagnetic waves. The temporary computer-readable medium can supply the program to the computer via a wired communication path such as an electric wire and an optical fiber, or a wireless communication path.

Although this disclosure has been described above with reference to the embodiments, the disclosure is not limited to the above. Various changes that can be understood by those skilled in the art can be made to the structure and details of this disclosure within the scope of the disclosure.

10 Light source device 11a, 11b Light source 12 Light detector 13 Light emission control unit 20 Light source device 21 LED element 22, 32, 42 Light receiving element 23 Light emitting control unit 24, 34, 44 LED board 25 Board body 26 LED chip 60 Internal circuit 61 Light receiving Element 62 Current-voltage conversion amplifier 63 LPF
64 A / D converter

Claims (14)

With multiple light sources
A light emission control unit for individually controlling the plurality of light sources to emit light is provided.
The light emission control unit controls at least one of the plurality of light sources to emit light at random over time.
Light source device. When the light emission control unit emits light at least one of the plurality of light sources with a light emission amount equal to or less than a predetermined threshold value, the light emission control unit is used to control the light emission of the light source to emit light with a light emission amount equal to or less than the predetermined threshold value. By executing a control for masking a part of the light source and setting the masking timing in the control to be random over time, the light source is made to emit light randomly over time.
The light source device according to claim 1. When at least one of the plurality of light sources emits light with a light emission amount equal to or less than a predetermined threshold value, the light emission control unit emits a light emission pulse used for controlling light emission of the light source to emit light with a light emission amount equal to or less than the predetermined threshold value. By generating the light source so that the interval is random over time, the light source is made to emit light at random over time.
The light source device according to claim 1 or 2. Further, a photodetector for detecting the light emission of each of the plurality of light sources is provided.
The light emission control unit individually controls and emits light from the plurality of light sources based on the detection result of the light detection unit.
The light source device according to any one of claims 1 to 3. The light emission control unit randomly emits light at least one of the plurality of light sources over time, and controls the light emission timings of the plurality of light sources so as not to overlap.
The light source device according to claim 4. The light emission control unit determines the light emission peak value of the plurality of light sources detected by the light detection unit, the distance between the light detection unit and the plurality of light sources, and the light emission time in one light emission of the plurality of light sources. The brightness values of the plurality of light sources are calculated individually by using.
The light source device according to claim 4 or 5. The light emission control unit individually controls the luminance values of the plurality of light sources based on the calculated luminance values of the plurality of light sources.
The light source device according to claim 6. The photodetector includes a first photodetector and a second photodetector that detect the light emission of at least a specific light source among the plurality of light sources.
The light emission control unit is based on the detection result of the light emission of the specific light source in the first photodetector and the detection result of the light emission of the specific light source in the second photodetector. Correcting the variation in sensitivity between the photodetector and the second photodetector,
The light source device according to any one of claims 4 to 7. The distance between the first photodetector and the specific light source is substantially equal to the distance between the second photodetector and the specific light source.
The light source device according to claim 8. The photodetector detects the light emission of at least the first light source and the second light source among the plurality of light sources.
The distance between the first light source and the photodetector is farther than the distance between the second light source and the photodetector.
The light emission control unit controls the first light source to emit light with higher brightness than the second light source.
The light source device according to any one of claims 4 to 9. The light source device further includes a temperature sensor that measures the temperature of the photodetector.
The light emission control unit corrects the detection result of the light detection unit based on the temperature measured by the temperature sensor.
The light source device according to any one of claims 4 to 10. The plurality of light sources are LEDs.
A head-up display comprising the light source device according to any one of claims 1 to 11. A step of controlling the plurality of light sources to emit light so that at least one of the plurality of light sources emits light at random over time.
The step of individually controlling the plurality of light sources to emit light,
A method of controlling light emission. A program that causes a computer to execute a light source control method.
The method of controlling the light source is as follows.
A step of controlling the plurality of light sources to emit light so that at least one of the plurality of light sources emits light at random over time.
The step of individually controlling the plurality of light sources to emit light,
Program with.

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