Projector, and projection display control method

Abstract

To suppress decrease in light flux value of display light when performing derating of a laser diode as a light source in a projector.SOLUTION: A projector has a light source part 62, a light source drive part 50, and a display control device 42 including a control part 44. The control part performs normal control mode for adjusting each light output so as to satisfy white balance when a temperature of a red laser diode can be suppressed to an allowable temperature or less, and when the temperature cannot be suppressed to the allowable temperature or less, performs derating for the red laser diode, and increases drive current value of green and blue laser diodes or a green laser diode and increases light output so as to suppress decrease in light flux value of display light due to decrease in light output of the red laser diode, thereby performing light flux maintenance control mode that prioritizes maintenance of the light flux value of the display light over maintenance of white balance.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a projector mounted on a vehicle such as an automobile, a projection display control method, and the like. [Background technology]

[0002]

[0034] to

[0036] of Patent Document 1 discloses that "in a display device such as a head-up display, when the temperature of each of the red (R), green (G), and blue (B) laser diodes (LD) exceeds a predetermined temperature, a current limit (derating) of the drive current is implemented."

[0003] Furthermore, in

[0044] Figure 8 of the same document states that "for example, when the optical output Pr (in other words, the supply current Ir) of a red (R) laser diode is limited, the optical output Pg (drive current Ig) of the green (G) laser diode and the optical power Pb (drive current Ir) of the blue (B) laser diode are set so as to maintain white balance (WB) for the limited optical output Pr (current Ir)." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-037531 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, when a red (R), green (G), or blue (B) laser diode (hereinafter sometimes referred to as LD) exceeds a predetermined temperature, a current limit (derating) of the optical output (drive current) is implemented to suppress the temperature rise of the LD. At this time, in Patent Document 1, the optical outputs (drive currents) of LDs of other colors are also limited so that white balance (WB) is maintained for the limited optical outputs (drive currents). In other words, in Patent Document 1, when derating is performed on LDs of one color, derating is also performed on LDs of other colors in order to maintain white balance (WB). In this case, it is undeniable that the luminous flux value (in other words, "brightness") of the display light obtained by combining the lights of the respective colors will decrease.

[0006] Here, we consider a case where a projector (outdoor projector) is mounted on a vehicle and projects and displays an image onto the road surface or the like, and the light output of red (R), green (G), and blue (B) LDs is synthesized to obtain display light so as to obtain a desired white balance (WB). For example, with an outdoor projector, an image is projected directly onto the road surface, etc., and is therefore directly affected by sunlight, etc. Therefore, when the intensity of external light such as sunlight is high, the visibility of the image projected onto the road surface, etc. is reduced. Images displayed on road surfaces, etc., include navigation information related to safe vehicle driving, so it is conceivable that a decrease in image visibility could have a direct impact on the safe operation of a vehicle. Therefore, if the luminous flux value (brightness) of the display light is reduced by uniformly derating the red (R), green (G), and blue (B) light as in Patent Document 1, it is not possible to meet the demand in the projector field of maintaining the visibility of the image.

[0007] Furthermore, in projectors (outdoor projectors), a high-output light source is required to maintain the desired visibility of the image, so the temperature rise in the LDs of each color is often rapid, and it can be expected that the temperature rise in the LDs of each color will be even more rapid when the ambient temperature is high. Therefore, in projectors (outdoor projectors), it is particularly important to protect the LD by derating (suppressing a decrease in lifespan), and furthermore, a forced cooling mechanism using a Peltier element (or fan) is required, but in this case, it is undeniable that the projector (outdoor projector) will become larger. On the other hand, when a projector (outdoor projector) is mounted on a vehicle, there is a limit to the space available for mounting the projector on a vehicle, so it is also important to prevent the projector from becoming too large.

[0008] Patent Document 1 does not mention such issues specific to projectors, nor does it mention any solutions to them.

[0009] One object of the present invention is to suppress a decrease in the luminous flux value of the display light (in other words, the brightness of the image) when derating is performed on a laser diode serving as a light source in a projector.

[0010] Other objects of the present invention will become apparent to those skilled in the art by referring to the following exemplary aspects and best modes, as well as the accompanying drawings. [Means for solving the problem]

[0011] In order to facilitate an understanding of the outline of the present invention, the following examples are given of embodiments according to the present invention.

[0012] In a first aspect, the projector is mounted on a vehicle and displays an image by projecting display light onto an object outside the vehicle, and includes a light source unit including red, green, and blue laser diodes, a light source drive unit capable of changing the light output of the red, green, and blue laser diodes by adjusting drive current values ​​of the red, green, and blue laser diodes, and a display control device including a control unit that controls the light source drive unit, and the control unit controls the light output of each of the red, green, and blue laser diodes when the temperature of the red laser diode can be suppressed to an allowable temperature or lower for the red laser diode during operation of the light source unit. A normal control mode is implemented in which each light output is adjusted so that the output satisfies the desired white balance, and if the temperature of the red laser diode cannot be suppressed to below the allowable temperature for the red laser diode, the drive current value of the red laser diode is reduced to perform derating, and the drive current value of the green and blue laser diodes or the green laser diode is increased to increase the light output so as to suppress a decrease in the luminous flux value of the display light due to a decrease in the light output of the red laser diode, thereby implementing a luminous flux maintenance control mode in which maintaining the luminous flux value of the display light takes priority over maintaining the white balance.

[0013] In the first aspect, attention is paid to the fact that in a high-temperature environment, the heat resistance of a red (R) LD is lower than that of LDs of other colors (green, blue), and that when used at a temperature exceeding the allowable temperature (predetermined temperature), inconveniences such as an inability to maintain the desired oscillation wavelength or a shortened lifespan can occur. Therefore, for the red (R) LD, current limitation (derating) of the drive current is implemented in a high-temperature environment to suppress the temperature rise of the red (R) LD. However, when the optical output of the red (R) LD decreases, the light intensity of the display light itself decreases, and the brightness of the image displayed by the projector on, for example, the road surface decreases. In this case, the visibility of the image displayed on the road surface decreases uniformly, and if the decrease in visibility is significant, it can be expected that, for example, images important for vehicle operation may become difficult to see. Taking this into consideration, in the first aspect, when derating is performed on the red (R) LD, the drive current is increased for each of the green (G) and blue (B) LDs, or for the green (G) LD, to increase the light output, thereby compensating for the decrease in the luminous flux value (brightness) of the display light caused by the decrease in the light output of the red (R) LD, and suppressing the decrease in the luminous flux value of the display light. When the luminous flux maintenance mode is adopted, it is undeniable that the white balance will be disrupted. However, as mentioned above, with projectors (especially outdoor projectors that display images on outdoor objects), it is more important to maintain the visibility of the image and clearly present the necessary information to the viewer (driver, etc.) as a vehicle occupant than to maintain the quality of the image by maintaining the white balance. Therefore, in this embodiment, by adopting a new mode (luminous flux maintenance mode) that prioritizes maintaining the brightness of the displayed image, the convenience of the projector is improved, which also contributes to the safe operation of the vehicle.

[0014] In a second aspect dependent on the first aspect, the light source unit may have a cooling mechanism that forcibly cools the light source unit, and the control unit may implement the luminous flux maintenance mode when the temperature of the red laser diode cannot be kept below the allowable temperature even when the cooling mechanism is operated, and after implementing the luminous flux maintenance mode, when the cooling mechanism is able to keep the temperature of the red laser diode below the allowable temperature, the control unit may switch the luminous flux maintenance control mode to the normal control mode.

[0015] In the second aspect, an example of a preferred control procedure is illustrated. In this aspect, a cooling mechanism is used to suppress the temperature rise of the red (R) LD, and if the operation of the cooling mechanism cannot suppress the temperature of the red (R) LD below the allowable temperature, the luminous flux maintenance mode is implemented. Furthermore, after the luminous flux maintenance mode is implemented, if the cooling mechanism is able to suppress the temperature of the red (R) LD below the allowable temperature, the luminous flux maintenance control mode is automatically switched to the normal control mode. In the second aspect, the temperature rise of the red (R) LD is suppressed by cooling using a cooling mechanism and derating, while the luminous flux value of the display light (display image) is complemented by an enhancement process for the light output of the green (G) and blue (B) or green (G) LD, thereby automatically suppressing a decrease in brightness. Furthermore, after the luminous flux maintenance mode is implemented, when the cooling mechanism returns to a state where the temperature rise of the red (R) LD can be suppressed, the luminous flux maintenance control mode is released and the normal control mode is automatically restored. According to this aspect, since the vehicle occupants (viewers such as the driver) do not need to operate the equipment, even if the temperature of the LD cannot be kept below the allowable temperature when, for example, the intensity of external light such as sunlight is strong or when a high-brightness image is continuously displayed, the visibility of the displayed image can be maintained without increasing the burden on the occupants, thereby improving the convenience of the projector.

[0016] In a third aspect dependent on the second aspect, the cooling mechanism may have an electrical cooling unit consisting of a Peltier element or a cooling fan, and the electrical cooling unit may be provided only for the red laser diode.

[0017] In the third aspect, an electrical cooling unit is provided to electrically cool the temperature of the LD. The electrical cooling unit is realized by, for example, a Peltier element or a cooling fan. By providing the electrical cooling unit, the cooling operation of the LD can be started at a desired timing. In this embodiment, this electrical cooling unit is provided only for the red (R) LD, and is not provided for the green (G) and blue (B) LDs. From a mechanical standpoint, this simplifies the structure for electrical cooling, which contributes to simplifying the internal configuration of the projector and making the projector more compact. On the other hand, from an electrical perspective, since the electrical cooling unit is provided only in the red (R) LD, the control of the electrical cooling unit by the control unit is simplified, which has the advantage of reducing the burden on the control unit.

[0018] In a fourth aspect dependent on any one of the first to third aspects, when switching from the normal control mode to the luminous flux maintenance control mode, the control unit may perform the derating by maintaining the current upper limit value of the drive voltage waveform of the red laser diode and reducing the pulse width of the drive voltage waveform, and may variably control the upper limit values ​​of the drive voltage waveforms of the green and blue laser diodes or the green laser diode to be increased from the current value, or may maintain the current value and increase the pulse width of the drive voltage waveform, thereby suppressing a decrease in the luminous flux value of the display light due to a decrease in the light output of the red laser diode.

[0019] According to the fourth aspect, by combining the control of the upper limit value of the drive voltage waveform of each color LD and the control of the pulse width (duty) of the drive voltage waveform, a more accurate and finer "luminous flux maintenance control mode" can be realized.

[0020] In a fifth aspect dependent on any one of the first to fourth aspects, when switching from the normal control mode to the luminous flux maintenance control mode, the control unit may implement a transition control mode in which the drive current of at least one of the red, green, and blue laser diodes is changed continuously or gradually over multiple stages over time.

[0021] In the fifth aspect, in addition to the "normal control mode" and the "luminous flux value maintenance control mode", a "transition control mode" is provided. In the luminous flux maintenance control mode, the brightness of the display light (display image) is maintained, but the white balance is lost, and in particular, since derating is performed on the red (R) LD, the displayed image becomes an image lacking in red. Therefore, if the "normal control mode" is suddenly switched to the "luminous flux maintenance control mode" at a certain point in time, the display quality of the displayed image (especially the display quality related to color) may suddenly deteriorate, which may cause discomfort to the vehicle occupants (viewers such as the driver). Taking this into consideration, in this embodiment, when switching from the normal control mode to the luminous flux maintenance control mode, a transition control mode is implemented in which the driving current (optical output) of the laser diode is changed continuously or gradually over multiple stages over time. This prevents a sudden drop in the display quality of the displayed image, and effectively prevents the vehicle occupants from feeling uncomfortable.

[0022] In a sixth aspect, a projection display control method is a projection display control method for a projector that is mounted on a vehicle and displays an image by projecting display light onto an object outside the vehicle, and includes: a first step of implementing a normal control mode in which, when a temperature of the red laser diode can be suppressed to an allowable temperature for the red laser diode or below, the light output of each of the red, green, and blue laser diodes is adjusted so that the light output of each of the red, green, and blue laser diodes satisfies a desired white balance, if the temperature of the red laser diode cannot be suppressed to an allowable temperature for the red laser diode or below, a second step of implementing a luminous flux maintenance control mode in which, when the temperature of the red laser diode cannot be suppressed to an allowable temperature for the red laser diode or below, the drive current value of the red laser diode is reduced to perform derating, and the drive current value of the green and blue laser diodes or the green laser diode is increased to increase the light output so as to suppress a decrease in the luminous flux value of the display light due to a decrease in the light output of the red laser diode, thereby prioritizing maintenance of the luminous flux value of the display light over maintenance of the white balance.

[0023] According to the sixth aspect, a projection display control method can be realized that can effectively suppress a decrease in the luminous flux value of the display light (in other words, the brightness of the image) when derating of a laser diode as a light source in a projector is performed.

[0024] Those skilled in the art will easily understand that the exemplified embodiments according to the present invention can be further modified without departing from the spirit of the present invention. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a diagram showing an example of a display by a vehicle-mounted projector (outdoor projector). [Figure 2] FIG. 2 is a diagram illustrating an example of a system configuration of a projector. [Figure 3] Figure 3(A) is a diagram showing an example of a characteristic line (derating characteristic line) showing the characteristics of light output versus temperature for a red LD, and characteristic lines showing the characteristics of light output versus temperature for green and blue LDs when the luminous flux maintenance control mode is not used. Figure 3(B) is a diagram showing an example of a characteristic line (derating characteristic line) showing the characteristics of light output versus temperature for a red LD, and characteristic lines showing the characteristics of light output versus temperature for green and blue LDs when the luminous flux maintenance control mode is used. [Figure 4] FIG. 4 is a diagram showing an example of the internal configuration of the LD module in the projector. [Figure 5] Figure 5 shows an example of the duty, light output, and temperature change of the control voltage (drive signal for the red LD) of the red LD when there is no derating control of the red LD (when the red LD is in normal control mode), as well as an example of the duty, light output, and temperature change of the control voltage (drive signal for the red LD) of the red LD when there is derating control of the red LD. [Figure 6] Figure 6 shows an example of the duty, light output, and temperature change of the control voltage (driving signal for the green LD) of the green LD when there is no derating control of the red LD (when the red LD is in normal control mode), as well as an example of the duty, light output, and temperature change of the control voltage (driving signal for the green LD) when there is derating control of the red LD (when the luminous flux maintenance control mode). [Figure 7]FIG. 7 is a diagram showing an example of control in which, when switching from the normal control mode to the luminous flux maintenance control mode, a transition control mode is implemented in which the drive currents (operating states) of the red, green, and blue LDs are changed continuously or gradually over multiple stages over time. [Figure 8] FIG. 8 is a flowchart showing an example of a control procedure for a method of driving a light source (a method of controlling projection display). DETAILED DESCRIPTION OF THE INVENTION

[0026] The best mode described below is used to facilitate understanding of the present invention, and therefore, those skilled in the art should be aware that the present invention is not unduly limited by the embodiments described below.

[0027] (First embodiment) Please refer to Fig. 1. Fig. 1 is a diagram showing an example of a display by a vehicle-mounted projector (outdoor projector).

[0028] Although each display example is independent, for the sake of convenience, a plurality of displays are shown together in FIG.

[0029] Also, in Figure 1, the fan-shaped area indicated by the dashed line shows an example of the display area of ​​each projector (here, an outdoor projector as a road surface projection display device that projects an image onto the road surface) mounted on vehicle 1 (in other words, fixed integrally to vehicle 1).

[0030] In the example of FIG. 1, six projectors 10a to 10f are mounted on the vehicle 1. The number of projectors is not limited to this example. The projectors may be projectors having individual lamp bodies (lamp fixtures), or may be projectors that use, for example, headlights 2 as a light source. In the example of FIG. 1, each of the six projectors 10a to 10f is a projector having an individual lamp body (lamp fixture).

[0031] In Figure 1, a projector 10a mounted on the front right end of a vehicle 1 displays an image 12 of a stop line (e.g., a white line) on the road surface to prompt a person 8 to stop temporarily and prevent them from entering the road 4.

[0032] In addition, projector 10b attached to the right door of vehicle 1 displays a welcome image (an image of the word "Welcome") on the road surface 4 to welcome the arrival of vehicle 1 at its destination.

[0033] In addition, when the vehicle 1 is reversed onto a road (e.g., a sidewalk) 6, the projector 10c mounted on the right end at the rear of the vehicle 1 displays an image 16 of an arrow on the road surface 4 to indicate to a bicycle or the like approaching from behind that the vehicle 1 is reversing onto the road 6.

[0034] Furthermore, a projector 10f mounted on the front end of the vehicle 1 displays an image 13 of an arrow indicating a left turn on the road surface 4 as a navigation display while the vehicle 1 is traveling on a road.

[0035] Note that the display example in Figure 1 is just an example and is not limited to this. The projector (outdoor projector) can display various images on outdoor objects such as the road surface or wall (or the outer surface of the door or window of the vehicle).

[0036] Next, reference will be made to Fig. 2. Fig. 2 is a diagram showing an example of the system configuration of a projector.

[0037] The projector 10 has a display control device 42 (including a control unit 44), an RGB light generation unit 60 that generates and outputs light of each color of red (R), green (G), and blue (B) required to display an image, a mirror unit 110 that has dichroic mirrors 111 to 113 that are provided corresponding to the light of each color of red (R), green (G), and blue (B), a speckle reduction unit 120 (including a diffuser 121) that reduces speckle noise, and a projection unit 71 that projects the display light onto the road surface, etc.

[0038] The control unit 44 of the display control device 42 has a normal control unit 45 that performs "normal control" before the derating of the red (R) LD starts, and a luminous flux maintenance control unit 47 that performs "luminous flux maintenance control" after the derating starts, which compensates for the decrease in luminous flux (light output) of the red (R) LD due to derating by increasing the light output of LDs of other colors, thereby suppressing the decrease in brightness of the display light.

[0039] The RGB light generating unit 60 has a light source unit 62 including LDs 61a, 61b, and 61c of each color, red (R), green (G), and blue (B), a cooling unit 63 including a Peltier element 65 as an electrical cooling mechanism and a heat sink 66 as a natural cooling mechanism, a Peltier element driving unit 51, and a light source driving unit 50.

[0040] The projection unit 71 has a focusing optical system 81 (equipped with a collimator lens 131, a fly's eye lens 132, and a condenser lens 133), an optical modulation unit (here, a digital micromirror device) 82, an optical path changing unit 83, a display element driving unit 86 that drives the minute mirrors (display elements) that make up the digital micromirror device, and a projection optical system 84.

[0041] Next, reference will be made to Fig. 3. Fig. 3(A) is a diagram showing an example of a characteristic line (derating characteristic line) indicating the characteristics of light output versus temperature for a red LD, and characteristic lines indicating the characteristics of light output versus temperature for green and blue LDs when the luminous flux maintenance mode is not used, and Fig. 3(B) is a diagram showing an example of a characteristic line (derating characteristic line) indicating the characteristics of light output versus temperature for a red LD, and characteristic lines indicating the characteristics of light output versus temperature for green and blue LDs when the luminous flux maintenance mode is used.

[0042] In the following explanation, regarding white balance (WB), as an example, we will consider white balance (WB) to be achieved when the ratio of the light output of the LDs of red (R), green (G), and blue (B) is approximately 4:2:1.

[0043] In this embodiment, when the ambient temperature (environmental temperature) of the projector 10 is not high (normal temperature), the drive current and light output of the LDs 61a to 61c of each color are kept so as not to exceed the maximum rated current value and maximum rated light output by control (software-based control) by the control unit 44 of the display control device 42, and at this time, the brightness of the display light can be maintained at, for example, 500 lumens.

[0044] However, if the ambient temperature of the projector 10 rises and becomes a high-temperature environment, for example, the drive current of the red (R) LD 61a, which has the lowest heat resistance, may exceed the maximum rated current, causing problems such as a shortened lifespan of the red (R) LD 61a, making it inoperable.

[0045] Specifically, in the normal control mode of the projector 10, the brightness of the display light obtained by combining the light emitted from the red (R), green (G), and blue (B) LDs 61a to 61D is controlled to be maintained at, for example, 500 lumens, and it is assumed here that the "environmental temperature" rises to 25°C to 60°C.

[0046] Even in this case (when the temperature continues to rise as described above), by operating (turning on) the Peltier element 65 as the electrical cooling mechanism (electrical cooling element) shown in Figure 2 above to perform forced cooling, the "light source temperature," which is the temperature of the red (R) LD 61a itself, can be kept below, for example, 40°C, which is the upper limit of the allowable temperature, and in this case the brightness of the display light can be maintained at 500 lumens.

[0047] However, if the "ambient temperature" exceeds, for example, 60°C, the cooling performance of the Peltier element 65 will not be sufficient, and if this continues, it is expected that the "light source temperature" of the red (R) LD 61a will exceed the upper limit of the allowable temperature of 40°C, increasing the possibility that the red (R) LD 61a will become a bottleneck.

[0048] Therefore, in this embodiment, in order to prevent the drive current (or optical output) of the red (R) LD 61a from exceeding the maximum rated current (or maximum rated optical output), the red (R) LD 61a is derated to reduce the brightness of the red (R) light and suppress an increase in the "light source temperature" of the red (R) LD 61a.

[0049] On the other hand, the green (G) and blue (B) LDs 61b and 61c have better heat resistance than the red (R) LD 61a, so forced cooling by a Peltier element 65 as an electrical cooling mechanism (cooling element) is not performed, and the light output of the green (G) and blue (B) LDs 61b and 61c, or only the green (G) LD, is increased to compensate for the decrease in brightness of the display light due to the derating of the red (R) LD 61a.

[0050] Furthermore, green (G) light has a higher relative luminosity factor than the other two colors and has a large impact on the visibility of images, so effectively increasing the green (G) light makes it easier to maintain the luminous flux value of the display light.

[0051] Furthermore, the red (R) LD 61a becomes inoperable if the ambient temperature exceeds 85°C, for example, but the green (G) and blue (B) LDs 61b and 61c can operate even if the ambient temperature exceeds 85°C, just like LEDs (light-emitting diodes), and it is the red (R) LD 61a that becomes the bottleneck. In this embodiment, taking into consideration the heat resistance of the LDs 61a to 61c of each color, a clear distinction is made between the "red (R) LD 61a, which becomes a bottleneck," and the "green (G) and blue (B) LDs 61b and 61c, which have excellent heat resistance," and control is implemented to focus derating, and in a preferred example, forced cooling, on the red (R) LD 61a. On the other hand, the light output of the green (G) and blue (B) LDs 61b and 61c is increased so as to suppress a decrease in the luminous flux value of the display light. As a result, the white balance of the display light of the projector 10 deviates from the desired value, but the luminous flux value is controlled to approach the desired value (to be maintained at the desired value). In other words, in this embodiment, a new control mode called "luminous flux maintenance control mode" is implemented.

[0052] When the "luminous flux maintenance mode" is adopted, it is undeniable that the white balance (WB) will be disrupted. However, as described above, in projector 10 (especially an outdoor projector that displays an image on an outdoor object), it is more important to maintain the visibility of the image and clearly present the necessary information to the viewer (driver, etc.) as a passenger of vehicle 1 than to maintain the quality of the image by maintaining the white balance (WB). Therefore, by adopting a new mode (luminous flux maintenance mode) that prioritizes maintaining the brightness of the displayed image, the convenience of projector 10 is improved, which also contributes to the safe operation of vehicle 1.

[0053] Fig. 3(A) shows an example of control when the luminous flux maintenance control mode is not implemented (however, derating of the red (R) LD 61a is implemented). In Fig. 3(A), the characteristics of the light output (relative value) of each of the red (R), green (G), and blue (B) LEDs 61a to 61c versus the ambient temperature are shown by characteristic lines RL, GL, and BL.

[0054] For the red (R) LD 61a, when the ambient temperature exceeds 60° C., derating begins and the light output is reduced at a predetermined rate, and this reduction continues until the ambient temperature reaches 80° C. When the ambient temperature reaches 80° C., the light output from the red (R) LD 61a is stopped.

[0055] As shown by the characteristic lines GL and BL, the green (G) and blue (B) LDs 61b and 61c maintain a predetermined light output until the ambient temperature reaches 60°C. When the ambient temperature exceeds 60°C, the light output of the red (R) LD 61a is reduced by derating, as described above. At this time, in order to ensure white balance, the light outputs of the green (G) and blue (B) LDs 61b and 61c also gradually reduce over time in response to the reduction in the light output of the red (R) LD 61a.

[0056] Fig. 3(B) shows an example of control when the luminous flux maintenance control mode is implemented. In Fig. 3(B), the characteristics of light output (relative value) versus ambient temperature for each of the red (R), green (G), and blue (B) LEDs 61a to 61c are shown by characteristic lines RL', GL', and BL'.

[0057] The characteristic line RL' for the red (R) LD 61a is the same as the characteristic line RL in FIG.

[0058] As shown by characteristic lines GL' and BL', the green (G) and blue (B) LDs 61b and 61c maintain a predetermined light output up to an ambient temperature of 60°C, but once the ambient temperature exceeds 60°C, the light output of the green (G) and blue (B) LDs 61b and 61c increases in accordance with the degree of derating of the red (R) LD 61a or in synchronization with the derating in order to maintain the brightness of the display light. This compensates for the decrease in the luminous flux of the display light and maintains the brightness.

[0059] Next, reference will be made to Fig. 4. Fig. 4 is a diagram showing an example of the internal configuration of an LD module in a projector. In Fig. 4, parts that are common to the previous figures are given the same reference numerals.

[0060] The projector 10 mounted on the vehicle 1 includes an LD module 100. The LD module 100 includes a drive unit 50 and an outdoor display control device .

[0061] The display control device 42 and the RGB light generation unit 60 are included.

[0062] The display control device 42 has a control unit 44, which has a duty determination unit 91, a control voltage generation unit 92, a normal control unit 44, a luminous flux maintenance control unit 47, a light source temperature determination unit 95, and a cooling unit state determination unit 97.

[0063] Based on the temperature detected by the light source temperature sensor 64, the light source temperature determination unit 95 determines (estimates) the temperature of the red (R) LD 61a (and similarly for the LDs 61b and 61c of the other colors) that is the light source.

[0064] Furthermore, cooling unit state determination unit 97 determines the state of cooling unit 63 based on information indicating the driving status of Peltier element driving unit 51 (such as the driving current of the Peltier element).

[0065] The RGB light generating unit 60 includes a duty setting unit 55, a variable voltage source 56, a voltage comparator 57 configured using an operational amplifier, a collector-grounded NPN bipolar transistor (emitter follower) 58 whose base is driven by the output voltage of the voltage comparator 57 and which supplies a drive current (on-current) IL to an LD 61 (here, a red (R) LD 61a) included in a light source unit 62, a cooling unit 63 including a Peltier element 65 connected to the bottom of the red (R) LD 61a and a submount (preferably serving also as a heat sink) 66, a resistor R (in other words, a load resistor of the LD 61; hereinafter, sometimes simply referred to as a "resistor") for monitoring the current of the LD 61 (here, the red (R) LD 61a), a light source temperature sensor 64, and a Peltier element driving unit (cooling unit driving unit) 51 that drives the Peltier element 65 as an electric cooling mechanism (electrical cooling element).

[0066] Variable voltage source 56 is a voltage source (for example, a variable output voltage regulator) that has two control terminals (an output voltage control terminal VC and an output enable terminal EN) and is capable of variably controlling the output voltage. Note that the terminal marked GND in the figure is a ground terminal.

[0067] In this variable voltage source 56, the voltage level of the output voltage Vout output from the voltage output terminal VO (hereinafter sometimes referred to as the "VO terminal") is variably controlled by the control voltage V applied to the output voltage control terminal VC (hereinafter sometimes referred to as the "VC terminal").

[0068] Furthermore, during a period when an active level (e.g., H level) voltage is applied to the output enable terminal EN (hereinafter sometimes referred to as the "EN terminal") of the variable voltage source 56, voltage output from the VO terminal is permitted, whereas during a period when an inactive level (e.g., L level) voltage is applied, voltage output from the VO terminal is prohibited.

[0069] Therefore, by the duty setting unit 55 applying a voltage signal (duty setting voltage) VD of a predetermined period and a predetermined duty to the EN terminal, the duty of the output voltage Vout output from the VO terminal of the variable voltage source 56 can be variably controlled.

[0070] Furthermore, a negative feedback control system is formed by the variable voltage source 56, voltage comparator 57, NPN bipolar transistor (emitter follower) 58, light source unit 62, and resistor R, and this negative feedback control system forms an APC circuit (automatic power control circuit).

[0071] In other words, the amount of drive current IL is automatically adjusted by negative feedback control so that the output voltage Vout output from the VO terminal of the variable voltage source 56 is the same as the voltage corresponding to the voltage drop across resistor R (determined by the product of the resistance value of resistor R and the drive current IL of the LD).

[0072] Therefore, by adjusting the voltage level of at least one of the voltage (control voltage) V applied to the VC terminal of the variable voltage source 56 and the duty setting voltage VD applied to the EN terminal, the voltage value (voltage amplitude) and duty of the output voltage Vout output from the VO terminal are set to predetermined values, and the drive current IL of the red (R) LD 61a, which is the light source, is uniquely determined in accordance with this predetermined value.

[0073] Next, reference will be made to Fig. 5. Fig. 5 is a diagram showing an example of the duty, optical output, and temperature change of the control voltage (drive signal for the red LD) of the red LD when there is no derating control of the red LD (when the red LD is in normal control mode), and an example of the duty, optical output, and temperature change of the control voltage (drive signal for the red LD) of the red LD when there is derating control of the red LD.

[0074] In the figure, "Ts1" indicates a first temperature reference value, and "Ts2" indicates a second temperature reference value, which is the upper limit of the allowable temperature. When the temperature of the light source (LD 61 (61a to 61c)) is near the first temperature reference value Ts1, it can be determined that the temperature is low, and when it is near the second temperature reference value (upper limit of the allowable temperature) Ts2, it can be determined that the temperature is high.

[0075] A-1 in FIG. 5 shows a control example in the normal control mode of the red LD 61a (in other words, without derating of the red LD 61a).

[0076] 5, a control voltage V1 with a duty of 100% is supplied to the VC terminal of the variable voltage source 56. In this case, the optical output of the red (R) LD 61a is maintained at P1. Note that the red LD 61a may be pulse-driven with a duty of less than 100% in the normal control mode.

[0077] The temperature of the red (R) LD 61a rises over time as shown by the characteristic line QT1. However, since the Peltier element 65 is turned on at time tq1, the temperature of the red (R) LD 61a does not exceed the second temperature reference value (upper limit of allowable temperature) Ts2 (in other words, it is kept below Ts2).

[0078] A-2 in FIG. 5 shows a control example when dithering is performed for a red LD. In A-2 of FIG. 5, a control voltage V2 is applied to the VC terminal of the variable voltage source 56, and a duty setting voltage VD applied to the EN terminal sets, for example, a duty of 50%. As a result, an output voltage V2 with a duty of 50% is output from the VO terminal of the variable voltage source 56. In this case, the optical output of the red (R) LD61a becomes P2 (P2 < P1) in the time average during the period from time t1 to t8, and the optical output (drive current) is reduced.

[0079] The temperature of the red (R) LD61a rises, for example, during the period TB1 from time t1 to t2, and the light source temperature drops during the period TB2 (cooling period) from time t2 to t3 because the optical output is stopped. Hereinafter, the same operation is repeated until time t8. However, since the time width of the pulse drive is short, the change in the light source temperature is substantially smoothed without following the above-mentioned rise and fall, and as shown by the characteristic line QT2, the light source temperature does not exceed the second temperature reference value (allowable temperature upper limit value) Ts2 (in other words, it is suppressed to Ts2 or less).

[0080] Next, refer to FIG. 6. FIG. 6 shows an example of the duty, optical output, and temperature change of the control voltage (drive signal of the green LD) of the green LD when there is no dithering control of the red LD (in the normal control mode of the red LD), and an example of the duty, optical output, and temperature change of the control voltage (drive signal of the green LD) of the green LD when there is dithering control of the red LD (in the light flux maintenance control mode).

[0081] In A-1 of FIG. 6, a control voltage V3 is applied to the VC terminal of the variable voltage source 56, and a duty setting voltage VD applied to the EN terminal sets, for example, a duty of 50%. As a result, an output voltage V3 with a duty of 50% is output from the VO terminal of the variable voltage source 56. In this case, the optical output of the green (G) LD61b becomes P3 in the time average during the period from time t1' to t8'.

[0082] For example, the temperature of the green (G) LD 61b rises during a period TB1' from time t1' to t2', and then drops during a period TB2' (cooling period) from time t2' to t3', because light output is stopped. Similar operations are repeated until time t8'. However, because the pulse drive duration is short, the change in the light source temperature is smoothed out without actually following the above-mentioned rise and fall, and as shown by characteristic line QT3, the light source temperature does not exceed the second temperature reference value (upper limit of allowable temperature) Ts2 (in other words, it is kept below Ts2).

[0083] 6A-2, a control voltage V3 is applied to the VC terminal of the variable voltage source 56. In other words, the voltage amplitude of the control voltage itself is the same as that in A-1 of FIG. On the other hand, a duty of, for example, 70% (a duty greater than 50% at A-1 in FIG. 6) is set by the duty setting voltage VD applied to the EN terminal. As a result, an output voltage V3 with a duty of 70% is output from the VO terminal of variable voltage source 56. Here, the above duty of 70% is just an example, and it can be changed to various appropriate values. However, considering that the duty is set to 50% in A-1 of Fig. 6, in order to increase the optical output, it is necessary to set a duty greater than 50% in A-2 of Fig. 6. 6A-2, the optical output of the green (G) LD 61b becomes P4 (P4>P3) on a time average over the period from time t1'' to t8'' because the duty of the output voltage V3 output from the variable voltage source 56 is increased. This compensates for the decrease in brightness of the display light due to the derating of the red LD 61a, and the luminous flux value is maintained.

[0084] The temperature of the green (G) LD 61b rises, for example, during a period TB1'' from time t1'' to t2'', and during a period TB2'' (cooling period) from time t2'' to t3'', the light output is stopped, so the light source temperature drops. Thereafter, the same operation is repeated until time t8''.

[0085] However, because the time width of the pulse drive is short, the change in the light source temperature is essentially smoothed out without following the above-mentioned rise and fall, and as shown by characteristic line QT4, the light source temperature does not exceed the second temperature reference value (upper limit of allowable temperature) Ts2 (in other words, it is kept below Ts2).

[0086] As described above, in the control example of FIG. 6, when switching from the normal control mode to the luminous flux maintenance control mode, derating is performed for the red (R) LD 61a by reducing the pulse width of the drive voltage waveform, and the upper limit value (upper limit voltage value) of the drive voltage waveform of the green and blue LDs 61b, 61c, or the green (G) LD 61b is either increased from the current state or maintained at the current state, and the pulse width of the drive voltage waveform (in other words, the voltage waveform of the output voltage Vout of the variable voltage source 56) is increased, thereby variably controlling to suppress a decrease in the luminous flux value of the display light due to a decrease in the optical output of the red laser diode.

[0087] According to this control, by combining the control of the upper limit value of the drive voltage waveform of LDs 61a to 61c of each color with the control of the pulse width (duty) of the drive voltage waveform, a more accurate and finer "luminous flux maintenance control mode" can be realized.

[0088] (Second embodiment) Next, reference is made to Fig. 7. Fig. 7 is a diagram showing an example of control in which a transition control mode is implemented in which the drive currents (operating states) of the red, green, and blue LDs are changed continuously or gradually over multiple stages over time when switching from the normal control mode to the luminous flux maintenance control mode.

[0089] In this embodiment, in addition to the "normal control mode" and the "luminous flux value maintenance control mode," a "transition control mode" is provided.

[0090] In the "luminous flux maintenance control mode," the brightness of the display light (display image) is maintained, but the white balance is disrupted, and in particular, since derating is performed on the red (R) LD, the displayed image becomes an image lacking in red.

[0091] Therefore, if the "normal control mode" is suddenly switched to the "luminous flux maintenance control mode" at a certain point in time, the display quality of the displayed image (especially the display quality related to color) may suddenly deteriorate, which may cause discomfort to the vehicle occupants (viewers such as the driver).

[0092] Taking this into consideration, in the control example of Fig. 7, when switching from the "normal control mode" to the "luminous flux maintenance control mode," a "transition control mode" is implemented in which the drive current (optical output) of at least one laser diode is changed continuously or gradually over multiple stages over time. This prevents a sudden drop in the display quality of the displayed image, and effectively prevents the vehicle occupants from feeling uncomfortable.

[0093] In the control example of Figure 7, switching from "normal control mode" to "luminous flux maintenance control mode" begins at time t10. During this switching, "transition control mode" is implemented at times t20, t30, etc., and the switching to "luminous flux maintenance control mode" is completed at time t40.

[0094] (Third embodiment) Next, reference is made to Fig. 8. Fig. 8 is a flowchart showing an example of a control procedure for a method of driving a light source (a method of controlling projection display).

[0095] In step S1, normal control is performed.

[0096] In step S2, it is determined whether derating of the red LD is necessary. If the answer is No, the process returns to step S1, and if the answer is Yes, the process proceeds to step S3.

[0097] In step S3, derating control of the red LD and light output enhancement control (luminous flux maintenance control) of the green and blue LDs or the green LD are performed.

[0098] In step S4, it is determined whether or not it is necessary to continue derating the red LD. If the answer is No, the process returns to step S3, and if the answer is Yes, the process proceeds to step S5.

[0099] In step S5, it is determined whether or not the control should be ended. If N, the process returns to step S1 (automatic return), and if Y, the process ends.

[0100] As described above, according to the embodiment of the present invention, in a projector, it is possible to suppress a decrease in the luminous flux value of display light when derating of a laser diode as a light source is performed.

[0101] The present invention is not limited to the above-described exemplary embodiments, and those skilled in the art will be able to easily modify the above-described exemplary embodiments to the extent that they fall within the scope of the claims. [Explanation of symbols]

[0102] 1 vehicle, 2 headlight, 4, 6 road, 8 person (pedestrian, etc.), 10 (10a to 10f) projector (e.g., outdoor projector), 12 stop line (white line, etc.) image, 13 navigation arrow image, 14 welcome effect image, 16 arrow image, 42 display control device, 44 control unit, 45 normal control unit, 47 luminous flux maintenance control unit, 50 light source drive unit, 51 Peltier element drive unit, 55 duty setting unit, 56 variable voltage source, 57 voltage comparator, 58 collector-grounded NPN bipolar transistor (emitter follower), 60 RGB light generation unit, 61 laser diode (LD) , 61a to 61c... Red, green, and blue laser diodes (LDs), 63... Cooling unit, 64... Light source temperature sensor, 65... Peltier element, 66... ​​Submount (heat sink or stem), 81... Light collection optical system, 82... Light modulation unit (digital micromirror device or the like), 83... Light path changing unit, 84... Projection optical system, 91... Duty determination unit, 92... Control voltage generation unit, 95... Light source temperature determination unit, 97... Cooling unit state determination unit, 110... Mirror unit, 111 to 113... Dichroic mirror, 120... Speckle reduction unit, 121... Diffuser, 131... Collimator lens, 132... Fly's eye lens, 133... Condenser lens.

Claims

1. A projector that is mounted on a vehicle and displays an image by projecting display light onto an object outside the vehicle, a light source unit including red, green, and blue laser diodes; a light source driver capable of changing the optical output of the red, green, and blue laser diodes by adjusting the drive current values ​​of the laser diodes; a display control device including a control unit that controls the light source drive unit; and The control unit During operation of the light source unit, If the temperature of the red laser diode can be suppressed to a temperature equal to or lower than the allowable temperature for the red laser diode, a normal control mode is implemented in which the light output of each of the red, green, and blue laser diodes is adjusted so that the light output of each of the red, green, and blue laser diodes satisfies a desired white balance; If the temperature of the red laser diode cannot be suppressed to the allowable temperature or lower for the red laser diode, Derating is performed by reducing the drive current value of the red laser diode, and increasing a drive current value of the green and blue laser diodes or the green laser diode to increase light output so as to suppress a decrease in the luminous flux value of the display light due to a decrease in the light output of the red laser diode; This allows a luminous flux maintenance control mode to be implemented in which maintaining the luminous flux value of the display light takes priority over maintaining the white balance. Projector.

2. a cooling mechanism for forcibly cooling the light source unit; The control unit When the temperature of the red laser diode cannot be suppressed to the allowable temperature or less even if the cooling mechanism is operated, the luminous flux maintenance mode is implemented; after the luminous flux maintenance mode is implemented, if the cooling mechanism is able to suppress the temperature of the red laser diode to the allowable temperature or lower, the luminous flux maintenance control mode is switched to the normal control mode; 2. The projector according to claim 1.

3. the cooling mechanism has an electric cooling unit made of a Peltier element or a cooling fan, The electrical cooling unit is provided only for the red laser diode.

3. The projector according to claim 2.

4. The control unit When switching from the normal control mode to the lumen maintenance control mode, The upper limit of the driving voltage waveform of the red laser diode is maintained at the current level, and the derating is performed by reducing the pulse width of the driving voltage waveform, The upper limit value of the drive voltage waveform of the green and blue laser diodes or the green laser diode is increased from the current state, or the current state is maintained and the pulse width of the drive voltage waveform is increased, thereby variably controlling the upper limit value of the drive voltage waveform of the green and blue laser diodes or the green laser diode to suppress a decrease in the luminous flux value of the display light due to a decrease in the optical output of the red laser diode.

2. The projector according to claim 1.

5. The control unit When switching from the normal control mode to the lumen maintenance control mode, 2. The projector according to claim 1, wherein a transition control mode is implemented in which the drive current of at least one of the red, green, and blue laser diodes is changed over time continuously or gradually through multiple steps.

6. 1. A projection display control method for a projector that is mounted on a vehicle and displays an image by projecting display light onto an object outside the vehicle, comprising: During operation of the light source unit, which includes red, green, and blue laser diodes, a first step of implementing a normal control mode in which, if the temperature of the red laser diode can be suppressed to a temperature equal to or lower than an allowable temperature for the red laser diode, the light output of each of the red, green, and blue laser diodes is adjusted so that the light output of each of the red, green, and blue laser diodes satisfies a desired white balance; a second step of implementing a luminous flux maintenance control mode in which, when the temperature of the red laser diode cannot be suppressed to the allowable temperature or lower for the red laser diode, a drive current value of the red laser diode is reduced to perform derating, and a drive current value of the green and blue laser diodes or the green laser diode is increased to increase light output so as to suppress a decrease in the luminous flux value of the display light due to a decrease in the light output of the red laser diode, thereby prioritizing maintenance of the luminous flux value of the display light over maintenance of the white balance; A projection display control method comprising:

Images