Display device

Abstract

The present invention provides a display device that can remove speckle appropriately even at low brightness. A display device 1 comprises a light source 2 that emits laser light, a diffusion member 31 which is disposed on the light path of the laser light emitted by the light source 2 and which diffuses the laser light, a rotary motor 32 that rotates diffusion member 31, and a control unit 7 that controls the light source 2 and the rotary motor 32, wherein the control unit 7 is provided with a brightness control means that controls the brightness of the laser light on the basis of PWM driving and a rotation number control means that increases the number of rotations of the diffusion member 31 in response to a decrease in the duty ratio of the PWM driving.

Description

[Technical Field]

[0001] The present disclosure relates to display devices such as head-up displays. [Background technology]

[0002] In display devices that use laser light as a light source, in order to achieve image stability at low brightness, the light source unit is driven in a current band where the light output is stable by extending the off time using PWM drive, thereby reducing the brightness.

[0003] Furthermore, in display devices that use laser light as a light source, a phenomenon called speckle is known, in which the content of an originally uniform surface brightness becomes non-uniform due to the coherence of the laser light. To remove this speckle, a method of spatially or temporally multiplexing the laser light is used. For example, a technique for removing speckle by rotating or oscillating a diffusion member provided on the optical path of the laser light is known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-25466 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when controlling the brightness of laser light using PWM drive, the lighting time is shortened on the low brightness side, making it impossible to ensure the number of multiplexings required to ensure image quality per unit time (speckle removal), and as a result, there is a risk that speckles will become apparent due to the coherence of the laser light.

[0006] Therefore, an object of the present disclosure is to provide a display device that can appropriately remove speckles even at low brightness. [Means for solving the problem]

[0007] In one aspect, the following solution is provided.

[0008] (1) a light source unit that emits laser light; a diffusing member disposed on an optical path of the laser light emitted by the light source unit and diffusing the laser light; a diffusion member rotating unit that rotates the diffusion member; a control unit that controls the light source unit and the diffusion member rotation unit, a diffusion member moving unit that moves an incident position of the laser light on the diffusion member in a radial direction of the diffusion member, The control unit a brightness control means for controlling the brightness of the laser light based on PWM driving; The diffusion member The incident position of the laser beam is moved to the outer periphery. and a control means.

[0009] (2) In the configuration of (1) above, The control unit The diffusion member Increase the rotation speed of Control means moreover It is characterized by being equipped with:

[0011] ( 3 ) the above( 1 ) or ( 2 ) in the configuration of The diffusion member has a concave-convex pattern in which the pitch of the concave-convex portions becomes narrower toward the outer periphery.

[0012] ( 4 ) From (1) above ( 3 ) in any of the configurations The diffusing member is disposed between the light source unit and a lens group that refracts the laser light. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to appropriately remove speckles even at low luminance levels. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing a schematic configuration of a display device according to an embodiment of the present invention; [Figure 2] FIG. 4 is a schematic diagram showing the pitch of projections and recesses of a diffusion member. [Figure 3] 10 is a graph showing the current-light output characteristics of a light source unit. [Figure 4] FIG. 4 is a diagram showing a PWM control waveform of a light source unit. [Figure 5] 10 is a graph showing the relationship between PWM duty and the rotation speed of the diffusion member. [Figure 6] 10 is a graph showing the relationship between the PWM duty and the laser incident radius of the diffusion member. DETAILED DESCRIPTION OF THE INVENTION

[0015] Each embodiment will be described in detail below with reference to the accompanying drawings.

[0016] [Display device] FIG. 1 is a diagram showing a schematic configuration of a display device according to one embodiment of the present invention.

[0017] The display device 1 shown in FIG. 1 is incorporated into a vehicle head-up display that uses laser light as a light source. Display light emitted from the display device 1 is projected onto a light-transmitting member (e.g., a vehicle windshield or combiner), and a virtual image of the display light is displayed in front of the light-transmitting member. The virtual image displayed may be numbers, letters, or figures representing instrument information such as the vehicle's traveling speed, vehicle warnings, the operating status of vehicle functions such as various surrounding sensors, and route guidance. The display device 1 includes a light source unit 2 that emits laser light (red laser light R, green laser light G, and blue laser light B), a rotating diffusion unit 3 that diffuses the laser light emitted from the light source unit 2, a lens group 4 that refracts the laser light that has passed through the rotating diffusion unit 3, a diffusion plate 5 that diffuses the laser light that has passed through the lens group 4, a liquid crystal panel 6 that forms an image using the laser light that has passed through the diffusion plate 5 as backlight, and a control unit 7 that controls the light source unit 2, the rotating diffusion unit 3, and the liquid crystal panel 6.

[0018] The lens group 4 in this embodiment includes a collimator lens 41, a fly-eye lens 42, a condenser lens 43, and a field lens 44, but the configuration of the lens group 4 is not limited to this. Furthermore, although the liquid crystal panel 6 that forms an image using laser light as a backlight has been exemplified as the image forming unit, a MEMS system that uses a micromirror device based on MEMS technology, an LCOS system that uses a reflective liquid crystal panel, a DMD system that uses a digital micromirror device, or the like may also be used.

[0019] [Rotating diffusion section] As shown in Figure 1, the rotating diffusion unit 3 includes a disk-shaped diffusion member 31, a rotary motor 32 (diffusion member rotation unit) that rotates the diffusion member 31 around the circular center of the diffusion member 31 as the rotation axis, and a moving motor 33 (diffusion member moving unit) that moves the incident position of the laser light on the diffusion member 31 in the radial direction of the diffusion member 31 by moving the diffusion member 31 and the rotary motor 32 in a direction perpendicular to the optical path of the laser light.

[0020] Any motor can be used as the rotary motor 32 as long as its rotation speed can be controlled. The movement motor 33 can be configured using a servo motor that moves the rotary motor 32 forward and backward in accordance with the rotation of the feed screw 33a. For example, the movement position of the rotary motor 32 can be detected by a stroke sensor and fed back to the control unit 7, thereby enabling precise control of the positions of the rotary motor 32 and the diffusion member 31. A stepping motor may also be used as the movement motor 33, and the movement distance may be precisely set by the number of drive steps.

[0021] Fig. 2 is a schematic diagram showing the concave-convex pitch of the diffusing member. In Fig. 2, 200 indicates a plan view of the diffusing member 31, and 202 indicates a cross-sectional view along the radial direction of the diffusing member 31. In the cross-sectional view indicated by 202, the X1 side in the X direction corresponds to the inner circumferential side, and the X2 side corresponds to the outer circumferential side.

[0022] 2, the diffusion member 31 has an uneven pattern including many uneven surfaces on at least one surface. This uneven pattern is formed so that the uneven pitch is large on the inner circumferential side (smaller rotation radius side) and small on the outer circumferential side (larger rotation radius side).

[0023] Such diffusing member 31 diffuses the incident laser light even when it is not rotating, but when it is rotating due to the rotation motor 32, the laser light is multiplexed to achieve a speckle reduction effect. Furthermore, when the number of rotations of diffusing member 31 is increased, the number of times the laser light crosses the irregularities (number of times per unit time) increases, so the number of multiplexing can be increased, thereby enhancing the speckle reduction effect.

[0024] Furthermore, if the incident position of the laser light onto the rotating diffusing member 31 is moved toward the outer periphery of the diffusing member 31, the circumferential distance of the laser light incident position increases, and the number of times the laser light crosses the asperities during one rotation of the diffusing member 31 increases, so the multiplexing number can be increased and the speckle reduction effect can be further enhanced. Furthermore, if the incident position of the laser light onto the rotating diffusing member 31 is moved toward the outer periphery of the diffusing member 31, the asperity pitch of the laser light incident position becomes smaller and the number of times the laser light crosses the asperities increases, so the multiplexing number can be increased and the speckle reduction effect can be further enhanced.

[0025] [Control Unit] The control unit 7 has functional configurations realized by cooperation between hardware and software, including a brightness control means for controlling the brightness of the laser light emitted by the light source unit 2, a rotation speed control means for controlling the rotation speed of the diffusion member 31, and an incident position control means for controlling the incident position of the laser light relative to the diffusion member 31.

[0026] Fig. 3 is a graph showing the current-light output characteristics of the light source unit. In Fig. 3, the horizontal axis represents current I and the vertical axis represents light output L, and the curve relating to the current-light output characteristics of the light source unit 2 is shown by a solid line. In Fig. 3, current bands A and B are shown within dotted lines.

[0027] As shown in Figure 3, when looking at the current I-light output L characteristics of the light source unit 2, there is a current band A where the light output L becomes unstable below a certain current value. If current control is performed in this area, the amount of light becomes unstable, resulting in flicker and a deterioration in color balance, so low brightness control using current band A cannot be performed.

[0028] However, in a head-up display for a vehicle incorporating the display device 1, when displaying a virtual image at night when the surrounding environment is dark, it is necessary to stably display the image at a low light intensity corresponding to the current band A in which the light output L in Figure 3 becomes unstable. Fig. 4 is a diagram showing PWM control waveforms of the light source unit. In Fig. 4, time-series waveform 400 corresponds to the case where PWM duty = 100% and integrated light intensity = 100%, time-series waveform 401 corresponds to the case where PWM duty = 75% and integrated light intensity = 75%, time-series waveform 402 corresponds to the case where PWM duty = 50% and integrated light intensity = 50%, and time-series waveform 403 corresponds to the case where PWM duty = 25% and integrated light intensity = 25%.

[0029] As shown in FIG. 4, the brightness control means increases the time that the PWM drive is turned off, thereby avoiding current band A and achieving stable low brightness by using current band B, which provides stable light output L. In other words, the brightness control means reduces the duty ratio of PWM drive, thereby achieving stable low brightness by using current band B, which provides stable light output L. However, when controlling the brightness of the light source unit 2 using this PWM drive, the lighting time of the laser light-emitting element is shortened at low brightness, which reduces the number of multiplexes by the diffusing member 31. Therefore, in this embodiment, by using the configuration described below, stable low brightness is achieved by using current band B, which provides stable light output L, without significantly reducing the number of multiplexes by the diffusing member 31.

[0030] Fig. 5 is a graph showing the relationship between PWM duty and the rotation speed of the diffusion member 31. In Fig. 5, the horizontal axis represents the duty ratio of PWM drive (denoted as "Duty") and the vertical axis represents the rotation speed (rpm), and the curve showing the relationship between PWM duty and the rotation speed of the diffusion member 31 is shown.

[0031] 5, the rotation speed control means increases the rotation speed of the diffusing member 31 in response to a decrease in the duty ratio of the PWM drive. With such a rotation speed control means, as the brightness decreases, the angular velocity ω of the linear velocity V=rω (r: radius, ω: angular velocity) at the laser light incident position on the diffusing member 31 increases and the linear velocity V increases, thereby increasing the number of times the laser light crosses the unevenness of the diffusing member 31 and making it possible to increase the number of multiplexes.

[0032] Fig. 6 is a graph showing the relationship between PWM duty and the laser incident radius of the diffusing member. In Fig. 6, the horizontal axis represents the duty ratio of PWM drive (denoted as "Duty") and the vertical axis represents the incident position r, and the curve showing the relationship between PWM duty and the laser incident radius of the diffusing member (incident position r) is shown.

[0033] As shown in Fig. 6, the incident position control means shifts the incident position of the laser beam relative to the diffusing member 31 toward the outer periphery in response to a decrease in the duty ratio of the PWM drive. In other words, by shifting the position of the diffusing member 31 so that the rotation radius r of the diffusing member 31, which is the incident position of the laser beam, increases as the brightness decreases. This increases the linear velocity V=rω (r: radius, ω: angular velocity) at the laser beam incident position of the diffusing member 31, thereby increasing the radius r and linear velocity V. This increases the number of times the laser beam crosses the irregularities of the diffusing member 31, thereby further increasing the number of multiplexing. Furthermore, the diffusing member 31 is formed so that the average irregularity pitch becomes narrower toward the outer periphery. Therefore, even at the same linear velocity V, which increases the number of times the laser beam crosses the irregularities of the diffusing member 31, the narrower the irregularity pitch of the diffusing member 31, thereby further increasing the number of times the laser beam crosses the irregularities of the diffusing member 31.

[0034] The display device 1 of this embodiment optimally combines the above-mentioned characteristic configurations (rotation speed control means, incident position control means, and unevenness pitch of the diffusion member 31), thereby enabling image representation with less speckle visibility, stable color balance, and flicker even at low brightness.

[0035] [Effects of the embodiment] According to this embodiment, the display device 1 includes a light source unit 2 that emits laser light, a diffusion member 31 that is arranged on the optical path of the laser light emitted by the light source unit 2 and diffuses the laser light, a rotary motor 32 that rotates the diffusion member 31, and a control unit 7 that controls the light source unit 2 and the rotary motor 32. The control unit 7 includes a brightness control means that controls the brightness of the laser light based on PWM drive, and a rotation speed control means that increases the rotation speed of the diffusion member 31 in response to a decrease in the duty ratio of the PWM drive, so that the multiplexing number can be increased and speckles can be appropriately removed even at low brightness.

[0036] In addition, the display device 1 further includes a movement motor 33 that moves the incident position of the laser light relative to the diffusion member 31 in the radial direction of the diffusion member 31, and the control unit 7 includes an incident position control means that moves the incident position of the laser light relative to the diffusion member 31 toward the outer periphery in accordance with a decrease in the duty ratio of the PWM drive, so that the number of multiplexes can be further increased even at low brightness, thereby making it possible to appropriately remove speckles.

[0037] Furthermore, since the diffusion member 31 has an uneven pattern in which the uneven pitch becomes narrower toward the outer periphery, the multiplexing number can be further increased at low brightness to appropriately remove speckles.

[0038] Furthermore, since the diffusion member 31 is disposed between the light source unit 2 and the lens group 4 that refracts the laser light, the incident area of ​​the laser light onto the diffusion member 31 is reduced, and the diffusion member 31 and the rotating diffusion unit 3 can be prevented from becoming large.

[0039] Although each embodiment has been described in detail above, it is not limited to the specific embodiment, and various modifications and changes are possible within the scope of the claims. It is also possible to combine all or a plurality of components of the above-described embodiments.

[0040] (Variation 1) The head-up display for a vehicle incorporating the display device 1 may include a light sensor (external light detection unit) that detects the brightness of the surrounding environment. Alternatively, the head-up display for a vehicle incorporating the display device 1 may be configured to obtain the brightness of the surrounding environment from an external source.

[0041] Furthermore, when the brightness of the surrounding environment is brighter than a predetermined value, the control unit 7 may control the brightness of the laser light by fixing the PWM duty ratio to 100 and reducing the current value, and only when the brightness of the surrounding environment is darker than a predetermined value, by increasing the time that the brightness control means is turned off via PWM drive, so that current band A is avoided and a stable low brightness is output using current band B, which provides a stable light output L.

[0042] By configuring in this manner, speckles are appropriately removed even at low brightness, particularly in a head-up display for a vehicle, and the quality of the virtual image display at night is improved. [Explanation of symbols]

[0043] 1 Display device 2 Light source section 3 Rotating diffusion section 31 Diffusion element 32 Rotational Motor 33 Travel motor 33a lead screw 4 lens groups 41 Collimator lens 42 Fly-eye lens 43 Condenser Lens 44 Field Lens 5 Diffuser 6 LCD panel 7 Control Unit

Claims

1. a light source unit that emits laser light; a diffusing member disposed on an optical path of the laser light emitted by the light source unit and diffusing the laser light; a diffusion member rotating unit that rotates the diffusion member; a control unit that controls the light source unit and the diffusion member rotation unit, a diffusion member moving unit that moves an incident position of the laser light on the diffusion member in a radial direction of the diffusion member, The control unit a brightness control means for controlling the brightness of the laser light based on PWM driving; an incident position control means for moving the incident position of the laser light relative to the diffusion member toward the outer periphery in accordance with a decrease in the duty ratio of the PWM drive.

2. The control unit 2. The display device according to claim 1, further comprising a rotation speed control means for increasing the rotation speed of said diffusion member in response to a decrease in the duty ratio of PWM drive.

3. The display device according to claim 1 , wherein the diffusion member has a concave-convex pattern in which the pitch of the concave-convex portions becomes narrower toward the outer periphery.

4. The display device according to claim 1 , wherein the diffusion member is disposed between the light source unit and a lens group that refracts laser light.

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