WO2020080001A1

WO2020080001A1 - Display apparatus, display system, and mobile object

Info

Publication number: WO2020080001A1
Application number: PCT/JP2019/035930
Authority: WO
Inventors: Takayuki Shitomi
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2018-10-19
Filing date: 2019-09-12
Publication date: 2020-04-23
Anticipated expiration: 2021-04-19
Also published as: JP2020067459A

Abstract

A display apparatus includes a light source device including a light source element and configured to emit laser light that is output in response to the light source element supplied with current and turned on, a scanner configured to display an image with scanning light that is the laser light scanned in two dimensions, and a photodetector configured to receive the scanning light. The display apparatus performs time control in which intensity of light received by the photodetector is controlled based on a time period during which the light source element is turned on in a state where a predetermined amount of current is supplied to the light source element, and the time period when the photodetector is scanned differs depending on the intensity of light.

Description

DISPLAY APPARATUS, DISPLAY SYSTEM, AND MOBILE OBJECT

Embodiments of the present disclosure relate to a display apparatus, a display system, and a mobile object.

In a mobile object such as a vehicle, a display apparatus such as a head-up display (HUD) is used as an application for allowing a driver (viewer) to visually recognize various types of information (vehicle information, warning information, navigation information, etc.) with a slight shift of their eyes.

For example, PTL 1 describes a laser light source drive apparatus including a light source that emits light when current is supplied and that lases when current equal to or larger than a threshold current value is supplied; a light source control means for supplying current to the light source on the basis of a light intensity characteristic to drive the light source; and an outside light detecting means for detecting the intensity of the outside light. The light intensity characteristic is represented by a straight line that indicates a relation between the current supplied to the light source and the light intensity of the light source, and includes a first straight line that includes a current value smaller than the threshold current value and a second straight line that includes a current value equal to or larger than the threshold current value. In a case where the intensity of the outside light detected by the outside light detecting means is lower than a predetermined value, the light source control means sets an initial current value to zero and supplies a driving current corresponding to a required light intensity to the light source on the basis of the first straight line or the second straight line.

Japanese Patent Application Publication No. 2015-162526

According to the present disclosure, it is possible to provide a display apparatus capable of appropriately detecting scanning light.

A display apparatus a light source device including a light source element and configured to emit laser light that is output in response to the light source element supplied with current and turned on, a scanner configured to display an image with scanning light that is the laser light scanned in two dimensions, and a photodetector configured to receive the scanning light. The display apparatus performs time control in which intensity of light received by the photodetector is controlled based on a time period during which the light source element is turned on in a state where a predetermined amount of current is supplied to the light source element, and the time period when the photodetector is scanned differs depending on the intensity of light.

According to one aspect of the present disclosure, it is possible to provide a display apparatus capable of appropriately detecting scanning light.

The accompanying drawings are intended to depict example embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.
Fig. 1 is a diagram illustrating a configuration of a display system according to a first embodiment of the present disclosure. Fig. 2 is a diagram illustrating a hardware configuration of a display apparatus according to the first embodiment of the present disclosure. Fig. 3 is a diagram illustrating a functional configuration of a control device according to the first embodiment of the present disclosure. Fig. 4 is a diagram illustrating a specific configuration of a light source device according to the first embodiment of the present disclosure. Fig. 5 is a diagram illustrating a specific configuration of a light deflection device according to the first embodiment of the present disclosure. Fig. 6 is a diagram illustrating a specific configuration of a screen according to the first embodiment of the present disclosure. Fig. 7A is a diagram illustrating the effect that differs depending on the magnitude relation between an incident ray bundle diameter and a lens diameter in a micro-lens array (MLA), according to an embodiment of the present disclosure. Fig. 7B is a diagram illustrating the effect that differs depending on the magnitude relation between an incident ray bundle diameter and a lens diameter in an MLA, according to an embodiment of the present disclosure. Fig. 8A is a diagram illustrating a specific configuration of a light-intensity adjuster according to the first embodiment of the present disclosure. Fig. 8B is a diagram illustrating a specific configuration of the light-intensity adjuster according to the first embodiment of the present disclosure. Fig. 8C is a diagram illustrating a specific configuration of the light-intensity adjuster according to the first embodiment of the present disclosure. Fig. 9 is a diagram illustrating the correspondence between a mirror of the light deflection device and a scan area, according to an embodiment of the present disclosure. Fig. 10 is a diagram illustrating a scan line path at the time of a two-dimensional scan, according to an embodiment of the present disclosure. Fig. 11A is a diagram illustrating a specific configuration of a photodetector according to an embodiment of the present disclosure. Fig. 11B is a diagram illustrating a specific configuration of a photodetector according to an embodiment of the present disclosure. Fig. 12A is a diagram illustrating a synchronizing signal output from a photodetector, according to an embodiment of the present disclosure. Fig. 12B is a diagram illustrating a synchronizing signal output from a photodetector, according to an embodiment of the present disclosure. Fig. 13A is a diagram illustrating the relation between the radiation intensity of an laser beam incident on a photodetector and a shift in the timing of a synchronizing signal, according to an embodiment of the present disclosure. Fig. 13B is a diagram illustrating the relation between the radiation intensity of a laser beam incident on a photodetector and a shift in the timings of synchronizing signals, according to an embodiment of the present disclosure. Fig. 14 is a graph illustrating the the input-output characteristics (driving current-output characteristics) of a laser beam, according to an embodiment of the present disclosure. Fig. 15 is a graph illustrating the relation between a driving current for a laser beam and the radiation intensity of a laser beam incident on a photodetector, according to an embodiment of the present disclosure. Fig. 16A is a diagram illustrating how the time intervals in which laser beams are driven are determined based on the radiation intensity of the incident laser beam, according to an embodiment of the present disclosure. Fig. 16B is a diagram illustrating how the time interval in which laser beams are driven are determined based on the radiation intensity of an incident laser beam, according to an embodiment of the present disclosure. Fig. 16C is a diagram illustrating how the time intervals at which laser beams are driven are determined based on the radiation intensity of the incident laser beam, according to an embodiment of the present disclosure. Fig. 17A is a graph illustrating how the radiation intensity of light is controlled according to the first embodiment of the present disclosure. Fig. 17B is a graph illustrating how the radiation intensity of light is controlled according to the first embodiment embodiment of the present disclosure. Fig. 18A is a diagram illustrating the setting of the time period based on a time constant, according to an embodiment of the present disclosure. Fig. 18B is a diagram illustrating the setting of the time period based on a time constant, according to an embodiment of the present disclosure. Fig. 19A is a graph illustrating how the radiation intensity of light is controlled according to a second embodiment of the present disclosure. Fig. 19B is a graph illustrating how the radiation intensity of light is controlled according to the second embodiment of the present disclosure. Fig. 20 is a flowchart of a radiation-intensity of light controlling flow, according to an embodiment of the present disclosure.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.

Embodiments of the present disclosure are described below with reference to the accompanying drawings. In the description of the drawings, like reference signs denote like elements, and overlapping descriptions are omitted.

Embodiments

System Configuration

Fig. 1 is a diagram illustrating a system configuration of a display system according to a first embodiment of the present disclosure. Fig. 1 illustrates a display system 1 that allows a viewer 3 to visually recognize an image (virtual image 45) having a favorable luminance distribution while suppressing a decrease in luminance in an edge portion of the image visually recognized by the viewer 3 and a decrease in luminance when the viewpoint of the viewer moves.

In the display system 1, projection light from a display apparatus 10 is projected onto a transmitting-reflecting member to allow the viewer 3 to visually recognize a display image. The display image is an image that is superimposed on the field of vision of the viewer 3 and displayed as the virtual image 45. The display system 1 is installed in, for example, a mobile object, such as a vehicle, an aircraft, or a vessel, or an immobile object, such as a drive simulation system or a home theater system. In the present embodiment, a case where the display system 1 is installed in an automobile, which is an example of the mobile object, is described. The use of the display system 1 is not limited to this case.

The display system 1 allows the viewer 3 (driver) to, for example, visually recognize through a windshield 50 navigation information used in driving the vehicle, the navigation information including, for example, the speed of the vehicle, route information, the distance to the destination, the name of the current location, the presence or absence and the position of an object (target object) ahead of the vehicle, signs indicating the speed limit, etc., congestion information, and so on. In this case, the windshield 50 functions as the transmitting-reflecting member that transmits part of incident light and that reflects at least part of the remaining part. The distance from the position of the eyes of the viewer 3 to the windshield 50 is about several tens of centimeters to one meter.

The display system 1 includes the display apparatus 10, an outside light sensor 20, a free-form surface mirror 30, and the windshield 50. The display apparatus 10 is, for example, an HUD apparatus that is mounted in the automobile, which is an example of the mobile object. The display apparatus 10 is disposed at any position by taking into consideration the interior design of the automobile. The display apparatus 10 may be, for example, disposed below the dashboard of the automobile or embedded in the dashboard.

The display apparatus 10 includes a light source device 11, a light deflection device 13, a screen 15, and a light-intensity adjuster 16. The light source device 11 is a device that emits laser light from a light source to the outside of the device. The light source device 11 may emit laser light that is, for example, a combination of laser rays in three colors of red (R), green (G), and blue (B). The outside light sensor 20 is a sensing device that is provided to sense the outside light intensity, namely, for example, the illuminance, in the display system 1. As illustrated in Fig. 1, the outside light sensor 20 is placed, for example, near the windshield 50.

The laser light emitted from the light source device 11 is incident on the light-intensity adjuster 16. The light-intensity adjuster 16 adjusts the radiation intensity of the incident laser light. The laser light that passes through the light-intensity adjuster 16 is guided to a reflecting surface of the light deflection device 13.

The light deflection device 13, which is an example of a light deflection unit, is a device that changes the direction of travel of the laser light with, for example, micro-electromechanical systems (MEMS). The light deflection device 13 includes, for example, a mirror-type scan means formed of a single very small MEMS mirror that swings about two axes orthogonal to each other or two MEMS mirrors that swing or rotate about one axis. The laser light deflected by the light deflection device 13 is scanned over the screen 15. The light deflection device 13 need not include a MEMS mirror and may include a polygon mirror, etc.

The screen 15 is a divergent member having a function of diverging laser light at a predetermined angle of divergence. The screen 15 includes, for example, a transmitting optical element, such as an MLA 200 (see Fig. 6) or a diffusion plate, having a light diffusing effect as a form of an exit-pupil expander (EPE). The screen 15 may include a reflecting optical element, such as a micro-mirror array, having a light diffusing effect. When the laser light deflected by the light deflection device 13 is scanned over the screen 15, an intermediate image 40, which is a two-dimensional image, is formed on the screen 15.

The light-intensity adjuster 16 has predetermined light transmittance, is disposed on the optical path of the laser light, and changes the radiation intensity of light that passes through the light-intensity adjuster 16. As a result, the brightness of the intermediate image 40 and that of the virtual image 45 are adjusted. The light-intensity adjuster 16 increases the transmittance to decrease the radiation intensity of light that passes therethrough when outside light is dark on the basis of the result of sensing by the outside light sensor 20, thereby making a formed image darker. The light-intensity adjuster 16 decreases the transmittance to increase the radiation intensity of light that passes therethrough when outside light is bright, thereby making a formed image brighter.

As the projection system of the display apparatus 10, a panel system may be adopted in which the intermediate image 40 is formed by an imaging device such as a liquid crystal panel, a digital mirror device (DMD) panel, or a vacuum fluorescent display (VFD). Alternatively, a laser scanning system may be adopted in which the intermediate image 40 is formed by scanning a laser beam emitted from the light source device 11.

The display apparatus 10 according to the first embodiment employs the laser scanning system. In the laser scanning system, light emission or non-light emission can be specified for each pixel. Accordingly, a high-contrast image can be generally formed. As the projection system, the display apparatus 10 may use the panel system.

The virtual image 45, which is projected onto the free-form surface mirror 30 and the windshield 50 with the laser light (ray bundle) exiting from the screen 15, is displayed as an enlarged image of the intermediate image 40. The free-form surface mirror 30 is designed and disposed so as to compensate for inclination, deformation, displacement, etc. of the image due to the curved form of the windshield 50. The free-form surface mirror 30 may be placed so as to be rotatable about a predetermined rotating shaft. Accordingly, the free-form surface mirror 30 can adjust the reflection direction of the laser light (ray bundle) exiting from the screen 15 and change the display position of the virtual image 45.

Here, the free-form surface mirror 30 is designed based on existing optical design simulation software so that the image formation position of the virtual image 45 is at a desired position and so that a certain light concentration power is obtained. In the display apparatus 10, the light concentration power of the free-form surface mirror 30 is set so that the virtual image 45 is displayed at a position (depth position), for example, 1 m or more and 30 m or less (preferably, 10 m or less) distant from the position of the eyes of the viewer 3. The free-form surface mirror 30 may be a concave mirror or a curved mirror. The free-form surface mirror 30 is an example of an image formation optical system.

The windshield 50 is the transmitting-reflecting member having a function (partial reflection function) of transmitting part of laser light (ray bundle) and reflecting at least part of the remaining part. The windshield 50 functions as a semi-transmitting mirror that allows the viewer 3 to visually recognize the front scene and the virtual image 45. The virtual image 45 is image information for allowing the viewer 3 to visually recognize, for example, vehicle information (speed, travel distance, etc.), navigation information (route guidance, traffic information, etc.), and warning information (collision warning, etc.). The transmitting-reflecting member may be, for example, a front windshield provided separately from the windshield 50. The windshield 50 is an example of a reflecting member.

The virtual image 45 may be displayed so as to be superimposed on the scene ahead of the windshield 50. The windshield 50 is not flat but is curved. Accordingly, the image formation position of the virtual image 45 is determined on the basis of the curved surface of the free-form surface mirror 30 and that of the windshield 50. As the windshield 50, a semi-transmitting mirror (combiner) that has a partial reflection function and functions as a separate transmitting-reflecting member may be used.

With the above-described configuration, laser light (ray bundle) exiting from the screen 15 is projected toward the free-form surface mirror 30 and reflected by the windshield 50. The viewer 3 is able to visually recognize the virtual image 45 that is an enlarged image of the intermediate image 40 formed on the screen 15 with the light reflected by the windshield 50.

Hardware Configuration

Fig. 2 is a diagram illustrating a hardware configuration of the display apparatus according to the first embodiment of the present disclosure. The hardware configuration in each embodiment may be the same as the hardware configuration illustrated in Fig. 2, or a constituent element may be added to or deleted from the hardware configuration in each embodiment.

The display apparatus 10 includes a control device 17 for controlling operations of the display apparatus 10. The control device 17 is a controller for, for example, a substrate or an integrated circuit (IC) chip mounted in the display apparatus 10. The control device 17 includes a field-programmable gate array (FPGA) 1001, a central processing unit (CPU) 1002, a read-only memory (ROM) 1003, a random access memory (RAM) 1004, an interface (I/F) 1005, a bus line 1006, a laser diode (LD) driver 1008, a MEMS controller 1010, a motor driver 1012, and a motor driver 1014.

The FPGA 1001 is an IC for which the configuration can be changed by a designer of the display apparatus 10. The LD driver 1008, the MEMS controller 1010, the motor driver 1012, and the motor driver 1014 generate driving signals in accordance with control signals from the FPGA 1001. The CPU 1002 is an IC that performs processing for controlling the display apparatus 10 as a whole. The ROM 1003 is a storage device that stores a program for controlling the CPU 1002. The RAM 1004 is a storage device that functions as a work area of the CPU 1002. The I/F 1005 in an interface for communicating with an external apparatus. The I/F 1005 is connected to, for example, a controller area network (CAN) of the automobile.

An LD 1007 is, for example, a semiconductor light-emitting device that constitutes part of the light source device 11. The LD driver 1008 is a circuit that generates a driving signal for driving the LD 1007. A MEMS 1009 constitutes part of the light deflection device 13 and is a device that displaces a scan mirror. The MEMS controller 1010 is a circuit that generates a driving signal for driving the MEMS 1009. A motor 1011 is an electric motor that rotates the rotating shaft of the free-form surface mirror 30. The motor driver 1012 is a circuit that generates a driving signal for driving the motor 1011. A filter driving motor 1013 is an electric motor that moves a filter unit transmitting light emitted from the light source device 11. The motor driver 1014 is a circuit that generates a driving signal for driving the filter driving motor 1013.

Functional Configuration

Fig. 3 is a diagram illustrating a functional configuration of the control device according to the first embodiment of the present disclosure. Functions implemented by the control device 17 include a vehicle information reception unit 171, an external information reception unit 172, an image generation unit 173, an image display unit 174, a storing-reading unit 178, and a storage unit 179.

The vehicle information reception unit 171 has a function of receiving information about the automobile (information about the speed, travel distance, etc.) from the CAN, etc. The vehicle information reception unit 171 is implemented by the I/F 1005 and the CPU 1002 illustrated in Fig. 2 performing processing and by a program, etc. stored in the ROM 1003.

The external information reception unit 172 has a function of receiving, from an external network, information about the outside of the automobile (position information from a global positioning system (GPS), route information or traffic information from a navigation system, etc.). The external information reception unit 172 is implemented by the I/F 1005 and the CPU 1002 illustrated in Fig. 2 performing processing and by a program, etc. stored in the ROM 1003.

The image generation unit 173 has a function of generating image information for displaying the intermediate image 40 and the virtual image 45 on the basis of information input from the vehicle information reception unit 171 and the external information reception unit 172. The image generation unit 173 is implemented by the CPU 1002 illustrated in Fig. 2 performing processing and by a program, etc. stored in the ROM 1003.

The image display unit 174 has a function of forming the intermediate image 40 on the screen 15 on the basis of display information generated by the image generation unit 173 and projecting laser light (ray bundle) that forms the intermediate image 40 toward the windshield 50 to display the virtual image 45. The image display unit 174 is implemented by the CPU 1002, the FPGA 1001, the LD driver 1008, the MEMS controller 1010, the motor driver 1012, and the motor driver 1014 illustrated in Fig. 2 performing processing and by a program, etc. stored in the ROM 1003.

The image display unit 174 includes a control unit 175, an intermediate image forming unit 176, and a projection unit 177. The control unit 175 generates control signals for controlling operations of the light source device 11 and the light deflection device 13 in order to form the intermediate image 40. The control unit 175 generates a control signal for controlling operations of the free-form surface mirror 30 in order to display the virtual image 45 at a predetermined position.

The intermediate image forming unit 176 forms the intermediate image 40 on the screen 15 on the basis of a control signal generated by the control unit 175. The projection unit 177 projects laser light that forms the intermediate image 40 onto a transmitting-reflecting member (for example, the windshield 50) in order to form the virtual image 45 that is to be visually recognized by the viewer 3.

The storing-reading unit 178 has a function of storing various types of data in the storage unit 179 and reading various types of data from the storage unit 179. In the storage unit 179, for example, data of various conditions to be used in controlling the display system 1 is stored in advance.

Light Source Device

Fig. 4 is a diagram illustrating a specific configuration of the light source device according to the first embodiment of the present disclosure. The light source device 11 includes

light source elements

111R, 111G, and 111B (hereinafter referred to as light source elements 111 when the elements need not be distinguished from one another),

coupling lenses

112R, 112G, and 112B, apertures 113R, 113G, and 113B, combining

elements

114, 115, and 116, a light splitting element 117, a lens 118, and a photodetector 119.

Each of the

light source elements

111R, 111G, and 111B in three colors (R, G, and B) is, for example, an LD having a single light-emitting point or a plurality of light-emitting points. Each of the

light source elements

111R, 111G, and 111B radiates a laser beam of a radiation intensity that corresponds to a change in a driving current supplied to the light source element. The

light source elements

111R, 111G, and 111B radiate laser light (ray bundles) having different wavelengths λR, λG, and λB (for example, λR = 640 nm, λG = 530 nm, and λB = 445 nm) respectively.

The laser light (ray bundles) radiating from the

light source elements

111R, 111G, and 111B is coupled by the

coupling lenses

112R, 112G, and 112B respectively. The laser light (ray bundles) coupled by the

coupling lenses

112R, 112G, and 112B is shaped by the apertures 113R, 113G, and 113B respectively. The apertures 113R, 113G, and 113B have a shape (for example, a circle shape, an oval shape, a rectangular shape, a square shape, etc.) that corresponds to a predetermined condition, such as the angle of divergence of the laser light (ray bundles).

The laser light (ray bundles) shaped by the apertures 113R, 113G, and 113B is combined by the three combining

elements

114, 115, and 116. Each of the combining

elements

114, 115, and 116 is a plate-shaped or prism-shaped dichroic mirror, and reflects or transmits the laser light (ray bundle) in accordance with the wavelength, so that the laser light (ray bundles) is combined into one ray bundle. The combined ray bundle is incident on the light splitting element 117.

Part of the incident light incident on the light splitting element 117 passes through the light splitting element 117 and the remaining part is reflected by the light splitting element 117. That is, the combined ray bundle is split by the light splitting element 117 into transmitting light and reflected light.

The transmitting light passes through the lens 118, is emitted to the light deflection device 13, and is used to draw an image on the screen 15 and to display a virtual image. That is, the transmitting light is used as image light.

The reflected light is incident on the photodetector 119. The photodetector 119 outputs an electric signal corresponding to the intensity of the incident laser light. The output electric signal is, for example, output to the FPGA 1001 and can be used to control the display system 1. Accordingly, the reflected light is used as monitor light for adjusting the intensity of laser light and as monitor light for adjusting the color and luminance of a virtual image that is consequently displayed.

Light Deflection Device

Fig. 5 is a diagram illustrating a specific configuration of the light deflection device according to the first embodiment of the present disclosure. The light deflection device 13 is a MEMS mirror manufactured through a semiconductor process and includes a mirror 130, meander beam parts 132, a frame member 134, and a piezoelectric member 136. The light deflection device 13 is an example of a scanner.

The mirror 130 has a reflecting surface that reflects laser light emitted from the light source device 11 toward the screen 15. In the light deflection device 13, the pair of meander beam parts 132 is formed with the mirror 130 therebetween. The meander beam parts 132 include a plurality of folded parts. The folded parts each include a first beam part 132a and a second beam part 132b that are alternately disposed. The meander beam parts 132 are supported by the frame member 134. The piezoelectric member 136 is disposed so as to connect the first beam part 132a and the second beam part 132b adjacent to each other. The piezoelectric member 136 applies different voltages to the first beam part 132a and the second beam part 132b to make the first beam part 132a and the second beam part 132b warp.

Accordingly, the first beam part 132a and the second beam part 132b adjacent to each other are bent in different directions. The bending is accumulated, and the mirror 130 rotates in the vertical direction about an axis that extends in the right-left direction. With such a configuration, the light deflection device 13 is able to perform an optical scan in the vertical direction at a low voltage. An optical scan in the horizontal direction centered about an axis that extends in the up-down direction is performed by resonance using, for example, a torsion bar connected to the mirror 130.

Screen

Fig. 6 is a diagram illustrating a specific configuration of the screen according to the first embodiment of the present disclosure. On the screen 15, laser light emitted from the LD 1007 that constitutes part of the light source device 11 is focused. The screen 15 is a divergent member for diverging the laser light at a predetermined angle of divergence. The screen 15 illustrated in Fig. 6 has an MLA structure in which a plurality of micro-lenses 150 having a hexagonal shape are closely arranged. The width (the distance between two sides opposite to each other) of the micro-lenses 150 is about 200 μm. The screen 15 includes the micro-lenses 150 having a hexagonal shape. Accordingly, the plurality of micro-lenses 150 can be arranged with high density.

The shape of the micro-lenses 150 is not limited to a hexagonal shape and may be, for example, a quadrilateral shape or a triangular shape. Although the structure in which the plurality of micro-lenses 150 are regularly arranged is illustrated, the arrangement of the micro-lenses 150 is not limited to this. For example, the center of each micro-lens 150 may be displaced from the center of the other micro-lenses 150 to make the arrangement irregular. In a case where such a decentered arrangement is employed, the micro-lenses 150 have different shapes.

Figs. 7A and 7B are diagrams illustrating the effect that differs depending on the magnitude relation between the incident ray bundle diameter and the lens diameter in the MLA. In Fig. 7A, the screen 15 includes an optical plate 151 in which the micro-lenses 150 are aligned and disposed. In a case where incident light 152 is scanned over the optical plate 151, the incident light 152 is diverged by the micro-lenses 150 and becomes diverged light 153. In the screen 15, the incident light 152 can be diverged at a desired angle of divergence 154 with the structure of the micro-lenses 150. The micro-lenses 150 are designed so as to be arranged at intervals 155 larger than the diameter 156a of the incident light 152. Accordingly, in the screen 15, interference does not occur between the lenses, and speckles (speckle noise) are not produced.

Fig. 7B illustrates the optical path of the diverged light in a case where the diameter 156b of the incident light 152 is twice as large as the interval 155 of the micro-lenses 150. The incident light 152 is incident on two micro-lenses 150a and 150b from which diverged

light rays

157 and 158 are produced. At this time, in a region 159, the two diverged light rays are present, which may cause light interference. In a case where the interference light enters the eyes of the viewer, the interference light is visually recognized as speckles.

Taking into consideration the above, the interval 155 of the micro-lenses 150 are designed so as to be larger than the diameter 156 of the incident light in order to reduce speckles. Although the description has been given with reference to Fig. 7A and Fig. 7B in which the lenses are convex lenses, a similar effect is expected in a case of concave lenses.

Fig. 8A, Fig. 8B, and Fig. 8C are diagrams illustrating a specific configuration of the light-intensity adjuster according to the first embodiment of the present disclosure. The light-intensity adjuster 16 is provided so that at least part thereof is placed on the optical path of laser light emitted from the light source device 11. The reference character "L" in Figs. 8A to 8C indicates laser light emitted to the light-intensity adjuster 16.

The light-intensity adjuster 16 includes a filter unit 161. The filter unit 161 is made of a material having desired light transmittance. In the present embodiment, the filter unit 161 includes three neutral density (ND) filters 1611, 1612, and 1613 each having different transmittance. In the present embodiment, a description is given under the assumption that, for example, the transmittance of the

filters

1611, 1612, and 1613 is 100%, 50%, and 10%, respectively. The filter unit 161 is driven by the filter driving motor 1013 and is slid in the right-left direction of Figs. 8A to 8C. Consequently, the light-intensity adjuster 16 performs switching so as to allow the laser light to pass through the

filter

1611, 1612, or 1613. That is, in a case of Fig. 8A, the transmittance of the filter 1611, that is, 100%, is the transmittance of the light-intensity adjuster 16. In a case of Fig. 8B, the transmittance of the filter 1612, that is, 50%, is the transmittance of the light-intensity adjuster 16. In a case of Fig. 8C, the transmittance of the filter 1613, that is, 10%, is the transmittance of the light-intensity adjuster 16. Accordingly, when switching between the plurality of filters each having different transmittance is performed to select a filter, the light transmittance of the light-intensity adjuster 16 can be switched and selected.

Although the case has been described where three ND filters each having different transmittance are used as the light-intensity adjuster 16, the light-intensity adjuster 16 is not limited to this, and a configuration may be applied in which a gradation-type filter having transmittance that continuously changes is used or a configuration may be applied in which the radiation intensity of the light is adjusted by adjusting the polarization angle. Alternatively, the filter unit 161 may include one filter, and the transmittance of the light-intensity adjuster 16 can be changed by switching between the presence and the absence of the filter on the optical path.

As described above, the light-intensity adjuster 16 adjusts the radiation intensity of laser light passing through the light-intensity adjuster 16. When the radiation intensity of the laser light is adjusted by the light-intensity adjuster 16, the light intensity of the intermediate image 40 and that of the virtual image 45 displayed by the display system 1 are also adjusted. As a result, the brightness of the virtual image 45 perceived by the viewer 3 is changed.

Fig. 9 is a diagram illustrating the relation between the mirror of the light deflection device and a scan area. The light emission intensity, the lighting timing, and the light waveform in each of the light source elements 111 of the light source device 11 are controlled by the FPGA 1001. Each of the light source elements 111 of the light source device 11 is driven by the LD driver 1008 to emit laser light. The laser light emitted from each of the light source elements 111 and combined on the optical path is deflected by the mirror 130 of the light deflection device 13 about the α axis and the β axis in two dimensions and is incident on the screen 15 from the mirror 130 as scanning light, as illustrated in Fig. 9. That is, the screen 15 is scanned in two dimensions by a main scan and a sub-scan by the light deflection device 13. At this time, the laser light emitted from the light source device 11 passes through the light-intensity adjuster 16, and thereafter, is incident on the light deflection device 13. Accordingly, the radiation intensity of the scanning light deflected by the light deflection device 13 has been adjusted by the light-intensity adjuster 16.

The scan area is the entire area that can be scanned by the light deflection device 13. The scanning light is swung and scanned (reciprocally scanned) in the main scan direction (X-axis direction) at a high frequency of about 20000 to 40000 Hz over the scan area of the screen 15 and is scanned in one way in the sub-scan direction (Y-axis direction) at a low frequency of about several tens of hertz. That is, the light deflection device 13 performs a raster scan over the screen 15. In this case, the display apparatus 10 controls light emission of each of the light source elements 111 in accordance with the scan position (the position of the scanning light), thereby enabling drawing or display of a virtual image on a per pixel basis.

The cycle of the sub-scan is about several tens of hertz as described above. Accordingly, the time taken to draw one screen, that is, the scan time (one cycle of the two-dimensional scan) for one frame, is about several tens of milliseconds. For example, in a case where the main scan cycle is 20000 Hz and the sub-scan cycle is 50 Hz, the scan time for one frame is 20 msec.

Fig. 10 is a diagram illustrating a scan line path at the time when two-dimensional scanning is performed. As illustrated in Fig. 10, the screen 15 includes an image region R1 (active scan area) in which the intermediate image 40 is drawn (that is irradiated with light modulated based on image data) and a non-image region R2 other than the image region R1. The non-image region R2 is, for example, a frame-like region that surrounds the image region R1.

The scan area is an area that is a combination of the image region R1 and part of the non-image region R2 (a part near the outer edge of the image region R1) on the screen 15. In Fig. 10, the scan line path in the scan area is represented by a zigzag line. In Fig. 10, the number of scan lines is smaller than the actual number for convenience sake.

As described above, the screen 15 includes the transmitting optical element, which is the MLA 200, having a light diffusing effect. The image region R1 need not have a rectangular shape or need not be a flat region, and may have a polygonal shape or may be a curved region. The screen 15 may include, for example, a reflecting optical element, such as a micro-mirror array, having a light diffusing effect. The following description is given under the assumption that the screen 15 includes the MLA 200.

The screen 15 includes a photosensor 60, which is a photodetector, in a peripheral region of the image region R1 (part of the non-image region R2) in the scan area. The photosensor 60 receives scanning light and detects the light intensity of the received scanning light. In Fig. 10, the photosensor 60 is disposed in the corner on the －X side and the ＋Y side of the image region R1. The photosensor 60 detects an operation of the light deflection device 13 by detecting the radiation intensity of the received scanning light and outputs, to the FPGA 1001, a synchronizing signal for determining the scan start timing and the scan end timing.

Figs. 11A and 11B are diagrams illustrating a specific configuration of the photodetector according to the first embodiment of the present disclosure. The photosensor 60, which is an example of the photodetector, includes a photodiode (PD) 61 for converting received laser light into an electric signal and an integrated circuit (IC) 62 that functions as an electric circuit. The IC 62 includes a current amplifier 621 for amplifying a weak electric signal obtained as a result of conversion, a gain resistor 622 that transforms the voltage of the output current from the current amplifier 621, and a comparator 623 that compares the signal subjected to voltage transformation with a reference voltage (hereinafter referred to as Vref) and outputs a synchronizing signal on the basis of the result of comparison. Although Fig. 11B illustrates an example where the output destination of the synchronizing signal is the FPGA 1001, the output destination is not limited to this and may be, for example, the light source device 11.

Figs. 12A and 12B are diagrams illustrating the the synchronizing signal output from the photodetector. When the light receiving surface of the PD 61 is scanned with laser light, a voltage-transformed signal corresponding to the intensity of the received light is input to the comparator 623. In a case where the value of the input voltage-transformed signal is higher than the predetermined voltage value Vref, a Low signal is output from the comparator 623. In a case where the value of the input voltage-transformed signal is lower than the predetermined voltage value Vref, a High signal is output from the comparator 623. The output signal from the comparator 623 is output to the FPGA 1001. When the timing at which the output signal from the comparator 623 is changed from High to Low is monitored, the FPGA 1001 can know the timing at which laser light, which is the scanning light, is scanned over the photosensor 60. Accordingly, the output signal can be used as a synchronizing signal for detecting an operation of the light deflection device 13, determining the scan start timing and the scan end timing, and synchronizing the operation of the light deflection device 13 with operations of the other devices.

Figs. 13A and 13B are diagrams illustrating the relations between the radiation intensity of a laser beam incident on a photodetector and a shift in the timings of synchronizing signals. Fig. 13B illustrates comparator input signals when the light intensity of the light received per unit time is first light intensity, second light intensity, and third light intensity, and a first synchronizing signal, a second synchronizing signal, and a third synchronizing signal that are output when the light intensity of the light received per unit time is the first light intensity, the second light intensity, and the third light intensity respectively. In a case where laser light having the largest first light intensity and laser light having the smallest third light intensity are scanned, the input signal to the comparator changes, and a shift (ΔT) in the timing at which the signal is changed from the High signal to the Low signal, that is, the timing at which the synchronizing signal is output, occurs. That is, even if the timing of a scan by the light deflection device 13 remains unchanged, the timing at which the photosensor 60 outputs a synchronization detecting signal changes based on the amount of laser light received by the PD 61. This shift in the timing results in a shift in a display image. Accordingly, the radiation intensity of a laser beam that is received by the photosensor 60 needs to be highly accurate.

Fig. 14 is a diagram illustrating the input-output characteristics of a laser beam (i.e., the input-output characteristics of a laser beam in relation to the amount of laser driving current). A laser typically has input-output characteristics as illustrated in Fig. 14. Accordingly, when the amount of driving current to be supplied to the light source elements 111 is adjusted, the radiation intensity of laser light emitted from the light source device 11 is adjusted. As a consequence, the radiation intensity of the light received by the photosensor 60 can be controlled. In the display apparatus 10, for example, the light intensity can be controlled by controlling the amount of current to be supplied to the light source elements 111 based on the image display unit 174. Note that such control may be referred to as current control.

As illustrated in Fig. 14, there exist a first region (hereinafter referred to as a light-emitting diode (LED) region) in which the output intensity of light gradually changes relative to changes in the amount of driving current, a second region (hereinafter referred to as an LD region) in which the output intensity of light rapidly changes, and a change point (hereinafter referred to as Ith) between the first region and the second region. Ith is affected (is changed) by the temperature. Accordingly, when the amount of driving current within a range in which the amount of driving current may be equal to Ith (Ith region) is used, it is difficult to control the light intensity of the light received by the photosensor 60 with high accuracy. Accordingly, it is preferable not to use current within the Ith region for the photosensor 60 that needs to output a synchronizing signal with high accuracy. In the following descriptions of graphs, the Ith region may be omitted.

Fig. 15 is a diagram illustrating the relation between the driving current for a laser and the radiation intensity of the incident laser beam of the photodetector. Fig. 15 illustrates the radiation intensity of the incident laser beam of the photosensor 60 in a case where the transmittance of the light-intensity adjuster 16 is 10%, 50%, and 100% when the laser has the output characteristics as illustrated in Fig. 14.

As described with reference to Fig. 13B, changes in the radiation intensity of the incident laser beam of the photosensor 60, that is, changes in the light intensity of the light received by the photosensor 60, may cause a shift in a display image. Accordingly, in order to suppress a shift in a display image, the radiation intensity of the incident laser beam needs to be within a predetermined range. This predetermined range is illustrated as an allowable fluctuation range for radiation intensity of incident light in Fig. 15. The first light intensity corresponds to the upper limit of the allowable fluctuation range for radiation intensity of incident light, and the third light intensity corresponds to the lower limit of the allowable fluctuation range for radiation intensity of incident light. To perform synchronization detection of scanning light on the basis of the radiation intensity of the incident laser beam of the photosensor 60, the target value of the radiation intensity of the incident laser beam of the photosensor 60 is to be within the allowable fluctuation range for radiation intensity of incident light. As illustrated in Fig. 15, with the amount of driving current in the LED region, an output below the allowable fluctuation range for radiation intensity of incident light is obtained. Accordingly, it is preferable to use the amount of driving current in the LD region. As described with reference to Fig. 14, in order to control the laser light amount with high accuracy, it is preferable not to use, as the amount of driving current of the laser driving current, the amount of driving current in the Ith region in which the characteristic may change due to, for example, the temperature.

In that regard, in a case where the transmittance is 10% and 50%, the radiation intensity of the incident laser beam within the allowable fluctuation range for radiation intensity of incident light can be achieved with a current amount in the LD region without using the amount of driving current in the Ith region. On the other hand, in a case where the transmittance is 100%, the radiation intensity of the incident laser beam of laser light that passes through the light-intensity adjuster 16 decreases to a small degree. Accordingly, the radiation intensity of the incident laser beam of the photosensor 60 increases. As a result, in order to make the radiation intensity of the incident laser beam be within the allowable fluctuation range for radiation intensity of incident light, a smaller amount of driving current is used, and the amount of driving current that is used is in the Ith region accordingly. In other words, in a case where the radiation intensity of the incident laser beam of the photosensor 60 changes to a large degree for a reason other than the driving current, that is, for example, the light amount adjustment by the light-intensity adjuster 16 described above, an attempt to make the radiation intensity of the incident laser beam equal to a predetermined light intensity of received light only with the current control requires use of the Ith region.

Focusing on the slopes in Fig. 15, as the slope of the radiation intensity of the incident laser beam relative to the driving current increases, the control resolution of the radiation intensity of the incident laser beam decreases. Accordingly, the control resolution of the radiation intensity of the incident laser beam is highest when the transmittance is 10%, second highest when the transmittance is 50%, and third highest when the transmittance is 100%. Accordingly, although the current control can be performed to make the radiation intensity of the incident laser beam be within the allowable fluctuation range for radiation intensity of incident light with the amount of driving current that is not in the Ith region in the case where the transmittance is 10% and 50%, the transmittance of 10% is advantageous from the perspective of control resolution of the radiation intensity of the incident laser beam.

As described with reference to Fig. 15, when the radiation intensity of the light incident on the photosensor 60, that is, the light intensity of the light received by the photosensor 60, is made equal to a predetermined amount, it might not be possible to cope with a light reduction method for a wide range only with the control of the amount of driving current.

Figs. 16A to 16C are diagrams illustrating the setting of the time period of a laser driving time based on the radiation intensity of the incident laser beam.

Each one of Figs. 16A, Fig. 16B, and Fig. 16C indicates the radiation intensity of a laser beam incident on the photosensor 60. In other words, the radiation intensity P1, P2 and P3 of the light that is received by the photosensor 60 per unit time in a case where the filter 1613 having the lowest transmittance is selected and the transmittance of the light-intensity adjuster 16 is 10%, in a case where the filter 1612 is selected and the transmittance of the light-intensity adjuster 16 is 50%, and in a case where the filter 1611 is selected and the transmittance of the light-intensity adjuster 16 is 100% are illustrated in Fig. 16A, Fig. 16B, and Fig. 16C, respectively. Figs. 16A, 16B, and 16C further illustrate comparator input signals and synchronizing signals in the respective cases. As the conversion process from an optical signal to an electric signal performed by the photosensor 60 takes a certain time, an input signal to the comparator can be considered to be the integrated radiation intensity of laser light incident on the PD 61.

When time control is performed such that the duty ratio, which corresponds to the time period, is made different depending on the radiation intensity P1, P2, or P3 of the light received per unit time, the integrated light intensity of light received by the photosensor 60 can be controlled. In Figs. 16A to 16C, the time intervals are set based on the radiation intensity P1, P2, and P3, respectively, so that the integrated radiation intensity received by the photosensor 60 is substantially the same. The radiation intensity is determined based on the radiation intensity of the incident laser beam. For this reason, time control based on the radiation intensity can be regarded as time control based on the radiation intensity of the incident laser beam. The radiation intensity of the incident laser beam is determined on the basis of the transmittance of the light-intensity adjuster 16. Accordingly, time control based on the radiation intensity can be regarded as time control based on the transmittance of the light-intensity adjuster 16.

Figs. 17A and 17B are diagrams illustrating how the radiation intensity of light is controlled according to the first embodiment of the present disclosure. Fig. 17A indicates the radiation intensity of the light received by the photosensor 60 per unit time relative to the amount of driving current in a case where pulsed lighting with a duty ratio of 10% is applied when the ND filter having transmittance of 100% is used and in a case where pulsed lighting with a duty ratio of 20% is applied when the ND filter having transmittance of 50% is used. Fig. 17B indicates the integrated radiation intensity of the received light relative to the amount of driving current in the case where pulsed lighting with a duty ratio of 10% is applied when the ND filter having transmittance of 100% is used and in the case where pulsed lighting with a duty ratio of 20% is applied when the ND filter having transmittance of 50% is used.

Fig. 17A indicates that, at the time of a scan with pulsed lighting with a duty ratio of 20% and with the radiation intensity (P2) when the transmittance is 50% as illustrated in Fig. 16B, when compared to a scan with continuous lighting with the radiation intensity P1 when the transmittance is 10% as illustrated in Fig. 16A, the radiation intensity P2 is five times the radiation intensity P1. Fig. 17A further indicates that, at the time of a scan with pulsed lighting with a duty ratio of 10% and with the radiation intensity (P3) when the transmittance is 100% as illustrated in Fig. 16C, the radiation intensity P3 is ten times the radiation intensity P1. In the display apparatus 10, for example, radiation-intensity of light controlling processes using the time period during which the light source elements 111 are turned on in a state where a predetermined amount of current is supplied by the image display unit 174 to the light source elements 111 (hereinafter sometimes referred to as time control) can be performed. The time control described here may be generally referred to as, for example, pulse width modulation (PWM) control or duty control.

The solid line in Fig. 17B indicates that, when a current value for which the integrated radiation intensity of the received light is within an allowable light amount change range when the transmittance is 10% is assumed to be a reference current value Ip0, in a state where the reference current value Ip0 is used when the transmittance is 50% and when the transmittance is 100%, the time period in the time control is set so that the integrated radiation intensity of the received light is within the allowable light amount change range for the radiation intensity.

In Fig. 17B, comparative examples are represented by the two-dot chain lines. That is, in a case where the radiation intensity is P1, P2, and P3 for the same current value Ip0 as illustrated in Fig. 17A, both in a case where continuous lighting is performed when the transmittance is 100% and the radiation intensity is P3 and in a case where continuous lighting is performed when the transmittance is 50% and the radiation intensity is P2, current within the Ith region is to be used in order to make the integrated radiation intensity of the received light be within the allowable light amount change range, that is, the control is unstable.

When the time control in which the unit received-light amount is made different, such as P1, P2, or P3 for the same current value Ip0 as illustrated in Fig. 17A and the duty ratio, which corresponds to the time period, is made different depending on the radiation intensity P1, P2, or P3 of the light received per unit time as represented by the solid line in Fig. 17B, the integrated radiation intensity of the received light of the photosensor 60 can be controlled.

As described with reference to Figs. 16A to 16C and Figs. 17A and 17B, in all cases of Figs. 16A, 16B, and 16C, control is performed so that the integrated radiation intensity of the received light is within a predetermined range and is more preferably is the same. As a result, even in a case where the range of the radiation intensity of the light received by the photosensor 60 per unit time changes to a large degree, such as in a case where, for example, the amount of light that reaches the screen 15 is adjusted by the light-intensity adjuster 16, the timing of a synchronizing signal does not shift.

In the present embodiment, the reference current value is determined, the reference current value being a value of the current for which the integrated radiation intensity of the received light is within the predetermined range when the filter having the lowest transmittance of 10% is used among the plurality of filters. In a case of selecting a filter having the other transmittance, the time period is set so that the integrated radiation intensity of the received light is within the predetermined range in a state where the reference current value is used. This is because the slope relative to the driving current is gradual when a filter having low transmittance is used as illustrated in Fig. 17B, that is, the control resolution of the received-light amount is high. When the time period is thus set, control in which the control resolution of the received-light amount is high can be performed.

Although an ideal operation state in the present embodiment has been described, the responsivity of the laser and that of the IC in an actual operation differ from those in the ideal state. For this reason, fine adjustments need to be made to the amount of light emitted from the light source device 11, the received-light amount of the photosensor 60, and the time period in the time control. For example, in a case of performing the time control using a duty ratio corresponding to each received-light amount, the received-light amount might not be ideally constant. For this reason, the current control for making each received-light amount be within a predetermined range may be performed in addition to the time control.

Figs. 18A and 18B are diagrams illustrating the relation between the time period at the time of the time control and a time constant of the photosensor.

In a case where the photosensor 60 includes, for example, an electric circuit, such as the IC 62, the electric circuit has a specific response speed, and the response speed is represented by a time constant, a cutoff frequency, etc. Fig. 18A illustrates a case where the off time at the time of pulsed lighting, in other words, the time period, is made smaller than the time constant (cutoff frequency), and Fig. 18B illustrates a case where the off time is made larger than the time constant (cutoff frequency).

In Fig. 18A, the pulsed lighting off time of the laser is shorter than the time constant of the circuit. Accordingly, changes (ripples) in the comparator input waveform after conversion to an electric signal by the IC 62 are small, and the wave form is substantially equivalent to that at the time of continuous lighting.

In Fig. 18B, the pulsed lighting off time of the laser is longer than the time constant of the circuit. Accordingly, changes (ripples) in the comparator input waveform after conversion to an electric signal by the IC 62 are large. As a result, a timing shift or an erroneous detection occurs.

As described above, the pulsed lighting off time, in other words, the time period in the time control, is made shorter than the time constant (cutoff frequency) of the electric circuit included in the photosensor 60, as illustrated in Fig. 18A, so that the output waveform of the photosensor 60 can be made stable.

Figs. 19A and 19B are diagrams illustrating how the radiation intensity of light is controlled according to a second embodiment of the present disclosure. Figs. 19A and 19B illustrate the relation between the radiation intensity of light received per unit time and the integrated radiation intensity of received light in a case where pulsed lighting is performed with a duty ratio of 50% when the transmittance is 100% and when the transmittance is 50%. In the present embodiment, the configuration described with reference to Fig. 1 to Fig. 15 is employed in common with the first embodiment, and the description thereof will be omitted.

As described with reference to Fig. 18B, the pulsed lighting off time of the laser longer than the time constant of the circuit may cause a timing shift or an erroneous detection. Depending on the time constant of the photosensor 60 used in the display apparatus 10, there are some cases in which control cannot be performed with stable waveform of a synchronizing signal is stable when the pulsed lighting is performed with a short time period such as when the duty ratio is 10% or 20%. In the present embodiment, pulsed lighting with a duty ratio of 50%, which corresponds to a time period with which the waveform of a synchronizing signal from the photosensor 60 becomes stable, is applied when the transmittance is 100%. Accordingly, when the transmittance is 50%, synchronization control can be performed with a small timing shift and with a high control resolution, and when the transmittance is 100%, synchronization control with a small timing shift can be performed. A specific description will be given below.

Fig. 19A indicates that, for a scan with continuous lighting with radiation intensity P4 when the transmittance of the light-intensity adjuster 16 is 10%, radiation intensity P5 when the transmittance is 50% and the radiation intensity P5 when the transmittance is 100% are set. In this case, driving currents Ip1, Ip2, and Ip3 are set so that the radiation intensity P5 is twice the radiation intensity P4.

Fig. 19B indicates the integrated received-light amount relative to the driving current in a case where pulsed lighting with a duty ratio of 50% is applied when the ND filter having transmittance of 100% is used and in a case where pulsed lighting with a duty ratio of 50% is applied when the ND filter having transmittance of 50% is used.

The conversion process from an optical signal to an electric signal performed by the photosensor 60 takes a certain time. Accordingly, an input signal to the comparator can be considered to be the integrated received-light amount of the PD 61. Accordingly, when a current value Ip1 is set as a driving current for which the integrated received-light amount when the transmittance is 10% is within the allowable light amount change range as illustrated in Fig. 19B, it is possible to perform control with which the integrated received-light amount is within the allowable light amount change range when the radiation intensity is P5 for a driving current Ip2 when the transmittance is 50%, and when the radiation intensity is P5 for a driving current Ip3 when the transmittance is 100%.

As described above, in the second embodiment, even in a case where it is not possible to perform control using a short time period because of a relation with the time constant of the photosensor 60, synchronization control with a small timing shift can be performed when the transmittance of the light-intensity adjuster 16 is 100%. When the transmittance is 50%, control can be performed with a gradual slope of the integrated received-light amount relative to the driving current compared to that when the transmittance is 100%. Accordingly, when the transmittance is 50%, synchronization control can be performed with a small timing shift and with a high control resolution for the received-light amount.

In the first embodiment, control is performed in which the time period is made different, that is, continuous lighting, a duty ratio of 20%, or a duty ratio of 10% is used, for the different radiation intensity of P1, P2, and P3, so that the integrated received-light amount, which is the integral of the radiation intensity for a predetermined time, is within a predetermined range. In the present embodiment, control is performed in which the time period is made different, that is, continuous lighting is used for the radiation intensity P4 and a duty ratio of 50% is used for the radiation intensity P5, so that the integrated received-light amount is within the predetermined range.

Also in the present embodiment, when control is performed so that the integrated received-light amount is within a predetermined range and is more preferably is the same, even in a case where the range of the radiation intensity of the light received by the photosensor 60 per unit time changes to a large degree as a result of, for example, the light-intensity adjuster 16 adjusting the amount of light that reaches the screen 15, the timing of a synchronizing signal does not shift.

Further, the present embodiment is applied to a case where the time period for obtaining a stable control waveform is limited due to a relation with the time constant of the photosensor 60, that is, a case where a short time period, such as a duty ratio of 10% or a duty ratio of 20%, used in the first embodiment is not used. When the driving current is made different depending on the transmittance of the light-intensity adjuster 16, the integrated received-light amount can be within a predetermined range even if the time period that can be used is limited.

Although an ideal operation state in the present embodiment has been described, the responsivity of the laser and that of the IC in an actual operation differ from those in the ideal state. Accordingly, fine adjustments need to be made to the amount of light emitted from the light source device 11, the received-light amount of the photosensor 60, and the time period in the time control. For example, in a case of performing the time control using a duty ratio corresponding to each received-light amount, the received-light amount might not be ideally constant. Accordingly, the current control for making each received-light amount be within a predetermined range may be performed in addition to the time control.

Although the number of filters each having different transmittance is three in both the first embodiment and the second embodiment, the number is not limited to three, and any appropriate number may be set in accordance with the use form of the display apparatus 10. Although the driving currents to be supplied to the light source elements 111 are Ip0 in common for all the filters in the first embodiment, and the driving currents to be supplied to the light source elements 111 are different from one another and Ip1, Ip2, and Ip3 for the respective filters in the second embodiment, the driving currents are not limited to these. That is, in one display apparatus, when some of the different filters are used, a common driving current may be supplied, and when some of the different filters are used, different driving currents may be supplied.

Fig. 20 is a flowchart of a radiation-intensity of light controlling flow, according to an embodiment of the present disclosure. This flow starts in response to, for example, the start of an optical scan by the light deflection device 13. The flow is applicable to both the first embodiment and the second embodiment.

First, the control unit 175 sets the initial value of the driving current for the laser (S101). As the initial value of the driving current, a current value that is at least not equal to Ith needs to be stored in advance in the storage unit 179. The control unit 175 performs current control so that the integrated received-light amount is controlled so as to be equal to a predetermined integrated received-light amount but does not perform the time control (S102). The predetermined integrated received-light amount corresponds to, for example, an allowable light amount change range. The initial value of the driving current and the allowable light amount change range need to be stored in advance in the storage unit 179.

Next, the control unit 175 determines whether the integrated received-light amount of the photosensor 60 is equal to the predetermined integrated received-light amount without using current in the Ith region (S103). In a case where the integrated received-light amount is equal to the predetermined integrated received-light amount (in a case of YES), the control in step S102 is continued. That is, for example, even if the transmittance of the light-intensity adjuster 16 is changed, the control unit 175 continues control so that the integrated received-light amount is within the allowable light amount change range only with the current control. On the other hand, in a case where the control unit 175 determines in step S103 that the integrated received-light amount is not equal to the predetermined integrated received-light amount (in a case of NO), the control unit 175 performs the current control and the time control as described with reference to Figs. 16A to 16C through Figs. 19A and 19B (S104).

As described above, with control using only the current control, in order to control the integrated received-light amount so as to be within a predetermined range, the driving current decreases as the transmittance of the light-intensity adjuster 16 increases. In this flow, in a state where only the current control is performed, it is determined whether the driving current decreases to the Ith region, which is a region in which the driving current is lower than that in the LD region (step S103). In a case where the driving current decreases to the Ith region or is highly likely to decrease to the Ith region, the time control is started. That is, the driving current is controlled to be a predetermined current, in the LD region, not equal to the Ith current to increase the output luminance of the light source, which is a laser, and switching to pulsed lighting corresponding to the received-light amount of the photosensor 60 when the driving current is the predetermined current is performed. When control is performed based on only the current control in a case where the transmittance of the light-intensity adjuster 16 is low and by using also the time control in a case where the transmittance is high, the integrated light amount of the photosensor 60 can be kept constant.

The current control is more accurate than the time control. Accordingly, when the current control is firstly performed as in step S101, the current control, which is highly accurate control, can be performed on a priority basis in the control of the radiation intensity of the light received by the photosensor 60. The flow for performing the current control on a priority basis is not limited to the flow in Fig. 20. As a flow that is executed in a state where both the current control and the time control are performed, the control unit 175 may monitor the transmittance of the light-intensity adjuster 16 and may change the control in which both the current control and the time control are performed to control in which only the current control is performed. For example, such change is performed when transmittance with which the integrated radiation intensity of received light is controlled within an allowable fluctuation range with the current control. For example, such change is performed when the smallest transmittance is used in the display apparatus 10.

As described with reference to the first embodiment and the second embodiment as examples, even for a display apparatus in which, for example, a plurality of filters each having different transmittance are used and that has a wide dynamic range of the luminance, when the two types of control, that is, the current control and the time control, are performed in accordance with the transmittance of the light-intensity adjuster 16, scanning light can be appropriately detected.

Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the disclosure of the present disclosure may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims.

The present disclosure can be implemented in any convenient form, for example using dedicated hardware, or a mixture of dedicated hardware and software. The present disclosure may be implemented as computer software implemented by one or more networked processing apparatuses. The processing apparatuses can compromise any suitably programmed apparatuses such as a general purpose computer, personal digital assistant, mobile telephone (such as a WAP or 3G-compliant phone) and so on. Since the present disclosure can be implemented as software, each and every aspect of the present disclosure thus encompasses computer software implementable on a programmable device. The computer software can be provided to the programmable device using any conventional carrier medium (carrier means). The carrier medium can compromise a transient carrier medium such as an electrical, optical, microwave, acoustic or radio frequency signal carrying the computer code. An example of such a transient medium is a TCP/IP signal carrying computer code over an IP network, such as the Internet. The carrier medium can also comprise a storage medium for storing processor readable code such as a floppy disk, hard disk, CD ROM, magnetic tape device or solid state memory device.

Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions.

This patent application is based on and claims priority pursuant to 35 U.S.C. §119(a) to Japanese Patent Application No. 2018-197947, filed on October 19, 2018, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

Reference Sings List

1 Display system
10 Display device
11 Light-source device (an example of a light source)
13 Light deflector
15 Screen (an example of an optical element)
16 Light-intensity adjuster (an example of a light amount adjustment unit)
161 Filter unit
1611, 1612, 1613 Filter
30 Free-form surface mirror
50 Front windshield (an example of a reflector)
61 Photodiode
62 Integrated circuit

Claims

A display apparatus comprising:
a light source device including a light source element and configured to emit laser light that is output in response to the light source element supplied with current and turned on;
a scanner configured to display an image with scanning light that is the laser light scanned in two dimensions; and
a photodetector configured to receive the scanning light,
wherein the display apparatus performs time control in which intensity of light received by the photodetector is controlled based on a time period during which the light source element is turned on in a state where a predetermined amount of current is supplied to the light source element, and
wherein the time period when the photodetector is scanned differs depending on the intensity of light.
The display apparatus according to Claim 1, wherein
the display apparatus performs current control in which the intensity of light is controlled based on an amount of current to be supplied to the light source element, and
at least the amount of current when the photodetector is scanned is changed in the current control.
The display apparatus according to Claim 1 or 2, wherein
the time period when the photodetector is scanned differs depending on intensity of light received per unit time, and
the time period is controlled so that integrated light intensity of received light that is an integral of the unit received-light amount for a predetermined time is within a predetermined range.
The display apparatus according to Claim 3, wherein
in a case where the integrated light intensity of received light is within the predetermined range in a state where the display apparatus performs the current control but does not perform the time control, the display apparatus does not perform the time control.
The display apparatus according to any one of Claims 1 to 4, wherein
a region scanned by the scanner includes an image region irradiated with light corresponding to image data and a non-image region other than the image region, and
the photodetector is configured to receive the scanning light in the non-image region.
The display apparatus according to Claim 3, further comprising
a filter configured to transmit light between the light source element and the photodetector and to change a light amount of the transmitted light, wherein
the time period differs depending on transmittance of the light passing through the filter.
The display apparatus according to Claim 6, wherein
the filter includes a plurality of filters each having different transmittance, and
the display apparatus switches one of the plurality of filters that is placed between the light source element and the photodetector.
The display apparatus according to Claim 7, wherein
a value of the predetermined amount of current for which the integrated light intensity of received light is within the predetermined range when one of the plurality of filters having smallest transmittance is selected is set as a reference current value, and
in a case where one of the plurality of filters having transmittance other than the smallest transmittance is selected, the time period is set so that the integrated light intensity of received light is within the predetermined range in a state where the reference current value is used.
The display apparatus according to any one of Claims 1 to 5, further comprising
a filter configured to transmit light between the light source element and the photodetector and to change a light amount of the transmitted light,
wherein the amount of current to be supplied to the light source element differs depending on transmittance of the light passing through the filter.
The display apparatus according to any one of Claims 1 to 9, wherein the time period is set based on a response speed of the photodetector.
The display apparatus according to Claim 10, wherein
the photodetector includes an electric circuit, and
the response speed is a time constant of the electric circuit.
A display system comprising:
the display apparatus according to any one of Claims 1 to 11;
a divergent member scanned with the scanning light and configured to diverge the scanning light; and
a reflecting member configured to reflect the diverged light.
A mobile object comprising
the display system according to Claim 12,
wherein the reflecting member is a windshield configured to reflect the diverged light.