Image display device

The image display device includes a light source, screens on which images are formed by being irradiated with light from the light source, a scanning unit that scans the screens by using the light from the light source, an optical system that generates a virtual image by using light from the screens, and a drive unit that includes a holder for integrally supporting the screens and moves the screens together with the holder The screens are aligned in a direction perpendicular to a movement direction of the holder caused by the drive unit, and are installed at positions that are shifted from each other by a certain distance in the movement direction.

BACKGROUND

1. Technical Field

The present disclosure relates to an image display device. For example, the present disclosure relates to an image display device suitable for being mounted on a moving body such as a passenger vehicle.

2. Description of the Related Art

In recent years, an image display device called a head-up display has been developed, and the head-up display concerned has been mounted on a moving body such as a passenger vehicle. In the head-up display mounted on the passenger vehicle, light modulated by image information is projected toward a windshield (windscreen), and the light reflected by the windshield is applied to driver's eyes. In this way, the driver can view a virtual image of an image in front of the windshield. For example, a vehicle speed or an outside air temperature is displayed as the virtual image. Recently, it is also considered to display, as a virtual image, a navigation image and an image for calling the attention on passengers to the driver.

In the above head-up display, a laser light source such as a semiconductor laser can be used as a light source to generate a virtual image. In this configuration, laser light scans a screen while being modulated depending on a video signal. The screen diffuses the laser light to broaden a region in which the light is radiated to the driver's eyes. This arrangement prevents the driver's eyes from getting out of the irradiated region even if the driver moves his or her head to some extent, and the driver thus can view the image (virtual image) satisfactorily and stably.

PTL 1 below discloses a configuration in which a screen is moved in an optical axis direction to vary an image-forming position of a virtual image in a front-back direction. In this configuration, the screen is driven by using a motor, a feed screw, and a rack.

CITATION LIST

Patent Literature

SUMMARY

A series of images are drawn on a screen while varying a position of the screen in an optical axis direction at a high speed. This enables display of an image whose sight distance varies in a depth direction (hereafter, referred to as a “depth image”). With this configuration, a depth image such as an arrow indicating a traveling direction of a vehicle can be displayed while being superimposed on a road on an intersection, for example.

Furthermore, an image is drawn while fixing the position of the screen. This enables display of an image whose sight distance is constant (hereafter, referred to as a “fixed image”) at a position with a predetermined sight distance as a virtual image. With this configuration, information such as a vehicle speed or an outside air temperature can be displayed. In this case, a sight distance of the fixed image is set remarkably shorter than a sight distance of depth image. For example, the sight distance of the depth image is set to about 10 m to about 100 m, and the sight distance of the fixed image is set to about 3 m. When a range of the sight distance of the fixed image largely differs from a range of the sight distance of the depth image in such a manner, if one screen is caused to display both the depth image and the fixed image, a movement range of the screen is remarkably extended. This makes it difficult to stably move the screen at a high speed.

To solve such a problem, a configuration in which a screen for the depth image and a screen for the fixed image are independently disposed can be used. This configuration can reduce a movement range of the screen for the depth image, and can stably move the screen at a high speed.

However, in the configuration in which the screen for the depth image is independently driven, the screen for the depth image is moved relative to the screen for the fixed image. Therefore, a gap needs to be disposed between a holder for supporting the screen for the depth image and an installation mechanism of the screen for the fixed image. Hence, when both the screens are viewed from a light irradiating side, a gap is generated between both the screens. A virtual image of a source of light scanning the screens is visually recognized by a driver through this gap, which is a problem.

In terms of such a problem, an object of the present disclosure is to provide an image display device capable of independently displaying images on a plurality of screens, while preventing a virtual image of a source of light scanning the screens from being visually recognized by a driver.

An image display device according to a primary aspect of the present disclosure includes a light source, a first screen, a second screen, a scanning unit, an optical system, a holder, and a drive unit. The first screen is irradiated with light from the light source to form an image on the first screen. The second screen is irradiated with the light from the light source to form an image on the second screen. The scanning unit scans the first screen and the second screen using the light from the light source. The optical system forms a virtual image by using light from the first screen and the second screen. The holder integrally supports the optical system and the first and second screens. The drive unit moves the first and second screens together with the holder. Herein, the first screen and the second screen are aligned perpendicular to a movement direction of the holder caused by the drive unit, and are installed at positions that are shifted from each other by a certain distance in the movement direction.

According to the image display device of this aspect, the first screen and the second screen are integrally supported by the holder and are simultaneously driven. Therefore, a gap as in a case where only the first screen is independently driven does not need to be disposed. Hence, when both the screens are viewed from a light irradiating side, a gap between both the screens can be prevented from being generated. This can prevent a virtual image of a light emitting source of light scanning the screens from being visually recognized by the driver, through this gap. As described above, the image display device according to this aspect can independently display the images on the plurality of screens, while preventing the virtual image of the light emitting source of light scanning the screens from being visually recognized by the driver.

An image display device according to another aspect of the present disclosure includes a light source, a screen, an optical system, a holder, a drive unit, and a light shield member. The screen is irradiated with light from the light source to form an image on the screen. The optical system forms a virtual image by using the light from the screen. The holder supports the screen. The drive unit moves the screen together with the holder. The light shield member covers a periphery of the screen. Herein the holder has a protuberance that supports a peripheral edge of the screen. The light shield member is installed on the holder such that an inner peripheral edge of the light shield overlaps an upper surface of the peripheral edge of the screen supported by the protuberance through a heat resistant member.

According to the image display device of this aspect, stray light that such as natural light goes backward through the optical system and approaches a portion of the holder around the screen is blocked by the light shield member. Therefore this portion of the holder is prevented from becoming high in temperature by the stray light. Accordingly the screen can be prevented from receiving damage by heat from the holder, the heat being generated by the stray light. Further, the heat resistant member is interposed between the light shield member and an upper surface of the screen. Therefore, even when the light shield member becomes high in temperature by the stray light, heat propagation from the light shield member to the screen can be prevented. Accordingly, the screen can be prevented from being damaged by the heat from the light shield member. Furthermore the screen is installed on the holder such that the peripheral edge of the screen is supported by a protuberance. Therefore even when the stray light enters a position of the holder right below the peripheral edge of the screen from around an inner peripheral edge of the light shield member and this position right below the peripheral edge of the screen becomes high in temperature, heat at this position right below the peripheral edge of the screen does not directly propagate to the screen. Hence the screen can be prevented from being damaged by heat from this position right below the peripheral edge of the screen. In this way, according to the image display device of this aspect, the screen can be prevented from being damaged by heat owing to the stray light that goes backward through the optical system and approaches the holder.

As described above, the present disclosure can provide an image display device capable of independently displaying images on a plurality of screens, while preventing a virtual image of a light emitting source of light scanning the screens from being visually recognized by a driver.

Effects or meanings of the present disclosure will be further clarified in the following description of the exemplary embodiment. However, the exemplary embodiment described below is merely an example of implementing the present disclosure, and the present disclosure is not at all limited to the example described in the following exemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, an exemplary embodiment of the present disclosure will be described with reference to the accompanying drawings. X, Y, and Z-axes perpendicular to one another are added to respective drawings. In this exemplary embodiment, the present disclosure is applied to an on-vehicle head-up display.

Note that, in the exemplary embodiment described below, screen108corresponds to a “first screen” described in the claims, and screen109corresponds to a “second screen” described in the claims. Light shield member364corresponds to a “first light shield member” described in the claims, and light shield member365corresponds to a “second light shield member” described in the claims. Further, protuberance361ecorresponds to a “first protuberance” described in the claims, and protuberance361icorresponds to a “second protuberance” described in the claims. However, those correspondence relationships do not limit at all significances of respective terms described in the claims.

FIGS. 1A and 1Bare views schematically illustrating a usage form of image display device20.FIG. 1Ais a view schematically illustrating, in a see-through manner, an inside of passenger vehicle1as seen from the side of passenger vehicle1, andFIG. 1Bis a view of a front of passenger vehicle1in a driving direction as seen from the inside of passenger vehicle1.

As illustrated inFIG. 1A, image display device20is installed inside dashboard11of passenger vehicle1.

As illustrated inFIG. 1AandFIG. 1B, image display device20projects laser light, which is modulated by a video signal, onto projection region13near a driver's seat on a lower side of windshield12. The laser light is reflected by projection region13, and is applied to an oblong region (eyebox region) around a position of driver2's eyes. In this way, predetermined image30is displayed as a virtual image in a viewing field in front of driver2.

Therefore, driver2can view image30, which is the virtual image, superimposed on a scene in front of windshield12. In other words, image display device20forms image30, which is the virtual image, in a space in front of projection region13of windshield12.

FIG. 1Cis a view schematically illustrating a configuration of image display device20.

Image display device20includes irradiation light generator21and mirror22. Irradiation light generator21emits light modulated by the video signal. Mirror22has a curved reflecting surface, and reflects the light, which is emitted from irradiation light generator21, toward windshield12. The light reflected by windshield12is applied to eye2aof driver2. An optical system of irradiation light generator21and mirror22are designed such that image30as the virtual image can be displayed in a predetermined size in front of windshield12.

Mirror22constitutes an optical system for generating the virtual image by using light from screens108,109to be described later. This optical system does not necessarily have to be constituted only with mirror22. For example, this optical system may include a plurality of mirrors, and may include a lens or other components.

FIG. 2is a diagram illustrating a configuration of irradiation light generator21in image display device20and a circuit configuration used for irradiation light generator21.

Light source101includes three laser light sources101ato101c. Laser light sources101ato101crespectively emit a laser beam in a red wavelength band, a laser beam in a green wavelength band, and a laser beam in a blue wavelength band. In this exemplary embodiment, in order to display a color image as image30, light source101includes three laser light sources101ato101c. In cases where a monochrome image is displayed as image30, light source101may include only one laser light source corresponding to a color of the image. Laser light sources101ato101care configured with semiconductor lasers, for example.

Laser beams emitted from laser light sources101ato101care respectively converted into parallel light by collimator lenses102ato102c. At this time, the laser beam emitted from each of laser light sources101ato101cis shaped into a circular beam shape by an aperture (not illustrated). Note that, in place of collimator lenses102ato102c, shaping lenses may be used, each of which shapes the laser beam into a circular beam shape and collimates the laser beam. In such a case, the aperture can be omitted.

Then, with respect to the laser beams of the respective colors emitted from laser light sources101ato101c, optical axes of the laser beams are aligned with one another by mirror103and two dichroic mirrors104,105. Mirror103totally reflects the red laser beam transmitted through collimator lens102a. Dichroic mirror104reflects the green laser beam transmitted through collimator lens102b, and transmits the red laser beam reflected by mirror103. Dichroic mirror105reflects the blue laser beam transmitted through collimator lens102c, and transmits the red laser beam and the green laser beam, which have passed through dichroic mirror104. Mirror103and two dichroic mirrors104,105are disposed so as to align the optical axes of the laser beams of the respective colors with one another, the laser beams being emitted from laser light sources101ato101c.

Scanning unit106reflects the laser beams of the respective colors that have passed through dichroic mirror105. Scanning unit106is made of, for example, a micro electro mechanical system (MEMS) mirror. The scanning unit106includes a configuration to rotate mirror106a, onto which the laser beams of the respective colors having passed through dichroic mirror105is made incident, around an axis parallel to the Y-axis and an axis perpendicular to the Y-axis in response to a drive signal. Mirror106ais rotated as described above, whereby a reflecting direction of the laser beam changes in an in-plane direction of an X-Z plane and in an in-plane direction of a Y-Z plane. In this way, as will be described later, screens108,109are scanned by the laser beams of the respective colors.

Note that, although scanning unit106is configured with the MEMS mirror of such a two-axis driving system here, scanning unit106may have another configuration. For example, scanning unit106may be configured with a combination of a mirror rotationally driven around the axis parallel to the Y-axis and a mirror rotationally driven around the axis perpendicular to the Y-axis.

Correction lens107is designed to direct the laser beams of the respective colors in a positive direction of the Z-axis regardless of a swing angle of the laser beams deflected by scanning unit106. Screens108,109are scanned by the laser beams to form images, and screens108,109diffuse the incident laser beams to a region (eyebox region) around a position of eye2aof driver2. Each of screens108,109is made of a transparent resin such as polyethylene terephthalate (PET).

Screen108is used to display a depth image whose sight distance changes in a depth direction, and screen109is used to display a fixed image whose sight distance is constant. For example, an arrow for guiding a driving direction of a vehicle is displayed as the depth image, and characters indicating a vehicle speed or an outside air temperature are displayed as the fixed image.

Drive unit300reciprocates screens108,109in a direction (Z-axis direction) parallel to a traveling direction of the laser beam. A configuration of drive unit300will be described later with reference toFIG. 4AtoFIG. 14B.

Image processing circuit201includes an arithmetic processing unit such as a central processing unit (CPU) and a memory, processes a video signal, which is input thereto, and controls laser drive circuit202, mirror drive circuit203, and screen drive circuit204. Laser drive circuit202varies emission intensity of laser light sources101ato101cin response to a control signal from image processing circuit201. Mirror drive circuit203drives mirror106aof scanning unit106in response to a control signal from image processing circuit201. Screen drive circuit204drives screens108,109in response to a control signal from image processing circuit201. Control in image processing circuit201at the time of an image display operation will be described later with reference toFIG. 16A.

FIG. 3Ais a perspective view schematically illustrating a configuration of screen108.FIG. 3Bis a view schematically illustrating a scanning method of the laser beam with respect to screen108.

As illustrated inFIG. 3A, a plurality of first lens units108afor diverging the laser beam in the X-axis direction are formed on a surface on a laser beam incident side of screen108(that is, a surface on a negative side of the Z-axis) so as to be arrayed in the X-axis direction. A shape of first lens units108aas viewed in the Y-axis direction is a substantially circular arc shape. A width in the X-axis direction of each of first lens units108ais, for example, 50 μm.

Further, a plurality of second lens units108bfor diverging the laser beam in the Y-axis direction are formed on a surface on a laser beam emission side of screen108(that is, a surface on a positive side of the Z-axis) so as to be arrayed in the Y-axis direction. A shape of second lens units108bas viewed in the X-axis direction is a substantially circular arc shape. A width in the Y-axis direction of each of second lens units108bis, for example, 70 μm.

An incident surface (a surface on the negative side of the Z-axis) of screen108having the above-described configuration is scanned, as illustrated inFIG. 3B, in the positive direction of the X-axis by beam B1in which the laser beams of the respective colors are superimposed on one another. On the incident surface of screen108, scanning lines L1to Lk through which beam B1passes are set beforehand at constant intervals in the Y-axis direction. Start positions of scanning lines L1to Lk coincide with one another in the X-axis direction, and end positions of scanning lines L1to Lk coincide with one another in the X-axis direction. A diameter of beam B1is set to approximately 50 μm, for example.

Scanning lines L1to Lk are scanned by high frequency beam B1in which the laser beams of the respective colors are modulated by the video signal, thereby forming an image. The image thus constituted is projected onto the region (eyebox) around the position of eye2aof driver2via screen108, mirror22, and windshield12(refer toFIG. 1C). In this way, driver2visually recognizes image30as the virtual image in a space in front of windshield12.

Screen109also has a configuration similar to that of screen108. In the Y-axis direction, a width of screen109is set smaller than a width of screen108. Screen109is also scanned by beam B1in the X-axis direction, similar to screen108. A number of scanning lines for screen109is smaller than a number of scanning lines for screen108.

In this exemplary embodiment, screens108,109are integrally supported, and are driven by drive unit300. When the depth image is displayed, screen108is scanned by beam B1while being moved in an optical axis direction (Z-axis direction) together with screen109. When the fixed image is displayed, screen109is stopped at a predetermined position together with screen108, and is scanned by beam B1.

Next, a configuration of drive unit300will be described.

FIG. 4Ais a perspective view illustrating the configuration of drive unit300, andFIG. 4Bis a perspective view illustrating the configuration of drive unit300when light shield cover302is detached.FIG. 5Ais a perspective view illustrating the configuration of drive unit300when light shield cover302, magnetic cover308, and structure body301are detached.FIGS. 4A, 4B, and 5Aillustrate drive unit300supported by support base306and fixed base310.

Note that in the following, the configuration will be described, defining directions by X, Y, and Z-axes, and in addition, assuming that a side closer to a center of drive unit300and a side farther from the center of drive unit300in a plan view are respectively referred to as an inside and an outside, for the sake of convenience.

As illustrated inFIGS. 4A and 4B, screens108,109are integrally supported by structure body301so as to incline in the same direction with each other. Two screens108,109are aligned in a direction (Y-axis direction) perpendicular to a movement direction (Z-axis direction) caused by drive unit300, and are installed at positions that are mutually shifted by a predetermined distance in the movement direction (Z-axis direction). Light shield cover302is installed so as to cover a periphery of structure body301. Light shield cover302is installed on an upper surface of magnetic cover308to cover slits308bof magnetic cover308illustrated inFIG. 4B.

Structure body301installed with screens108,109is installed to inner frame303aof support member303illustrated inFIG. 5A. Support member303is supported, movably in the Z-axis direction, by two support units305aligned in the Y-axis direction via four suspensions304. Support units305are installed to support base306. Each support unit305includes gel covers305aon a positive side and a negative side of the X-axis, respectively, and gels are filled in those gel covers305afor dumping.

In this way, screens108,109are supported, movably in the Z-axis direction, by support base306via structure body301, support member303, suspensions304, and support units305. Configurations of support member303and suspensions304will be described later with reference toFIGS. 8A to 8C. Further, a configuration of support base306will be described later with reference toFIG. 5B.

Magnetic circuit307is further installed on support base306. Magnetic circuit307is used to apply a magnetic field to coil341(refer toFIG. 8A) mounted on support member303. When a drive signal (current) is applied to coil341, electromagnetic force in the Z-axis direction is excited in coil341. With this configuration, support member303and coil341are driven in the Z-axis direction. Thus, screens108,109move in the Z-axis direction. A configuration of magnetic circuit307will be described later with reference toFIGS. 6A and 6B.

Magnetic cover308is put on an upper surface of magnetic circuit307. Magnetic cover308is made of a magnetic material and functions as a yoke of magnetic circuit307. When magnetic cover308is put on the upper surface of magnetic circuit307, magnetic cover308is attracted to magnetic circuit307. Magnetic cover308is thus installed on drive unit300. As illustrated inFIG. 4B, magnetic cover308is provided with opening308ato let structure body301pass through, and slits308bto let corresponding beams303c(refer toFIG. 8A) of support member303pass through.

Support base306is installed on fixed base310through damper units309. Damper units309support the support base306while keeping support base306in suspension in the positive direction of the Z-axis with respect to fixed base310. Damper units309absorb the vibration generated in association with the driving of support member303before the vibration is transmitted from support base306to fixed base310. Configurations of damper units309and fixed base310will be described later with reference toFIG. 7.

On fixed base310, position detection unit400is further installed. Position detection unit400includes printed board401facing a side surface of support member303on the positive side of the X-axis. An encoder (not illustrated) is disposed on a surface of printed board401on the negative side of the X-axis. This encoder detects a position of support member303in the Z-axis direction. A method for detecting the position of support member303with the encoder will be described later with reference toFIG. 8A.

FIG. 5Bis a perspective view illustrating a configuration of support base306when viewed from the positive side of the Z-axis.

As illustrated inFIG. 5B, support base306has an rectangular shape in a plan view. Support base306is made of a highly rigid metal material. Opening311is formed at a center of support base306to let laser light pass through. In addition, on each of four corners of support base306, circular hole313for installing each of damper units309is formed.

Further, at a central position in the X-axis direction in each of an end part on a positive side of the Y-axis and an end part on a negative side of the Y-axis of support base306, opening312for receiving support unit305is formed. In addition, on an upper surface (a surface on the positive side of the Z-axis) of support base306, a plurality of bosses314for positioning magnetic circuit307and support units305is formed.

FIGS. 6A and 6Bare perspective views each showing a configuration of magnetic circuit307.

Magnetic circuit307is equipped with two yokes321aligned in the Y-axis direction. Yokes321have a U-shape when viewed from the X-axis direction. Inner walls321bof each of two yokes321are separated in two pieces. On an inner side of outer wall321aof each of yokes321, magnet322is installed. Further, on an outer side of two walls321bon an inner side of each of yokes321, magnet323to face magnet322is installed. Between magnet322and magnet323facing each other, a gap into which coil341(refer toFIG. 8A) to be described later is inserted is created.

Magnetic circuit307is further equipped with two yokes324aligned in the X-axis direction. Yokes324have a U-shape when viewed from the Y-axis direction. Outer wall324aof each of two yokes324is separated in two pieces, and inner wall324bof each of two yokes324is also separated in two pieces. On an inner side of each of two walls324aon an outer side of each of yokes324, magnet325is installed. Further, on an outer side of each of two walls324bon an inner side of each of yokes324, magnet326to face magnet325is installed. Between magnet325and magnet326facing each other, a gap into which coil341(refer toFIG. 8A) to be described later is inserted is created. An end of each of magnets326in the Y-axis direction overlaps a side surface of inner wall321bof adjacent yoke321.

On each of lower surfaces of two yokes321and each of lower surfaces of two yokes324, holes (not illustrated) are formed at positions into which bosses314of support base306illustrated inFIG. 5Bare fitted. Yokes321,324are installed on an upper surface of support base306such that bosses314are fitted into the holes formed in the lower surfaces of yokes321,324. As illustrated inFIG. 6B, magnetic circuit307is thus installed on the upper surface of support base306.

FIG. 7is an exploded perspective view illustrating an assembly step of support base306and fixed base310.

As illustrated inFIG. 7, each of damper units309includes damper309a, washer309b, and screw309c. Fixed base310includes: opening331to let laser light pass through; screw holes332into which screws309care screwed; opening333in which position detection unit400is installed; and bosses334with which position detection unit400is positioned. Fixed base310is integrally formed of a highly rigid metal material.

Dampers309aare integrally formed of a material excellent in damping property. Dampers309aare formed of, for example, a material with high viscous damping such as αGEL or rubber. A sleeve in a cylindrical shape is fitted into a hole formed at a center of each of dampers309a. Each of dampers309ais fitted into hole313formed at each of four corners of support base306. In this state, washers309bare put on the upper surfaces of dampers309a. Further, screws309care inserted into washers309band screwed in screw holes332of fixed base310. By this step, support base306is supported by fixed base310via dampers309a.

FIG. 8Ais a perspective view illustrating a configuration of support member303and suspensions304when support member303and suspensions304are assembled.

As illustrated inFIG. 8A, support member303has a frame shape. Support member303is formed of a lightweight and highly rigid material. In this exemplary embodiment, support member303is formed of a liquid crystal polymer in which a carbon filler is mixed. Support member303is equipped with inner frame303aand outer frame303bboth in an approximately rectangular shape in a plan view. Inner frame303aand outer frame303bare connected to each other with four beams303csuch that a center of inner frame303aand a center of outer frame303bcoincide with each other in a plan view. Inner frame303ais elevated at a position shifted upward (the positive direction of the Z-axis) from outer frame303b.

Structure body301is installed on an upper surface of inner frame303a. In addition, coil341is mounted on a lower surface of outer frame303b. Coil341turns around along the lower surface of outer frame303bso as to form a shape in which corners of a rectangle are rounded.

Radially extending connection members303dare respectively formed at four corners of outer frame303b. Each of these connection members303dhas a flange on an upper end and a lower end. On an upper surface of the flange on an upper side of each of connection members303d, an end of upper suspension304is fixed with fixing member303e. Further, on a lower surface of the flange on a lower side of each of connection members303d, an end of lower suspension304is fixed with fixing member303e. In this manner, suspensions304are mounted on support member303.

Further, support member303includes bridges303feach connecting connection members303dthat are neighboring to each other in the Y-axis direction. A part of each bridge303fexcept both ends in the Y-axis direction extends parallel to the Y-axis direction, and at a center of the part, installing surface303gparallel to a Y-Z plane is provided. A scale is installed on installing surface303gof bridge303f, on the positive side of the X-axis, of support member303.

Two suspensions304on the positive side of the Y-axis and two suspensions304on the negative side of the Y-axis are mounted on support units305as illustrated inFIG. 5A. In this step, coil341mounted on the lower surface of outer frame303bis inserted into the gap between the mutually facing magnets of magnetic circuit307illustrated inFIG. 6B. Further, the scale installed on installing surface303gof bridge303f, on the positive side of the X-axis, of support member303faces the encoder installed on printed board401of position detection unit400.

The encoder of position detection unit400includes an optical sensor that radiates light to the scale and receives light reflected from the scale, and the optical sensor optically detects movement of the scale in the Z-axis direction. On the basis of a detected signal from the encoder, a position of support member303and screens108,109in the Z-axis direction is detected.

Driving of screens108,109are thus controlled.

Note that magnetic poles of magnets322,323,325, and326of magnetic circuit307illustrated inFIG. 6AandFIG. 6Bare adjusted such that a drive signal (current) applied to coil341causes coil341to generate driving force in one direction parallel to the Z-axis direction.

Each ofFIG. 8BandFIG. 8Cis a plan view illustrating a configuration of suspension304.

In this exemplary embodiment, a shape of suspension304on an upper side (the positive side of the Z-axis) and a shape of suspension304on a lower side (the negative side of the Z-axis) illustrated inFIG. 8Aare different from each other. Herein suspension304on the upper side is referred to as suspension304-1, and suspension304on the lower side is referred to as suspension304-2, for the sake of convenience.

Suspensions304-1,304-2are thin plate-shaped members and are each integrally formed of a conductive and flexible metal material. Suspensions304-1,304-2are made of a beryllium copper alloy, for example. Suspensions304-1,304-2each have a symmetrical shape with respect to a central position in the X-axis direction. Suspensions304-1,304-2each have three holes304a, at the central position in the X-axis direction, for mounting suspension304-1,304-2on support unit305. Further, suspensions304-1,304-2each have extensible structures304bhaving a crank shape on both sides of three holes304a.

Furthermore, suspensions304-1,304-2each have a pair of flanges304cprotruding in the positive direction of the Y-axis. In addition, suspensions304-1,304-2each have a pair of arms304dextending in the X-axis direction, and have holes304eat respective ends of those arms304d. Furthermore, suspensions304-1,304-2each have a pair of flanges304fprotruding from the respective ends of arms304din the negative direction of the Y-axis. Furthermore, suspensions304-1,304-2each have a pair of hooks304gon respective end sides of extensible structures304b. When screens108,109are reciprocated in the Z-axis direction, suspensions304-1,304-2are deformed into an S-shape, in the Z-axis direction. Hooks304gare disposed in each of suspensions304-1,304-2so as to be positioned at respective inflection points of the deformation. As illustrated inFIG. 4A, hooks304gare housed in gel covers305a. Hooks304gare provided to enhance a damping effect caused by the gel.

Extensible structures304bof suspensions304-1,304-2are different in shape from each other. In other words, each of extensible structures304bof suspension304-1is formed by providing cutouts C1and C2from the negative and positive sides of the Y-axis, respectively. In contrast, each of extensible structures304bof suspension304-2is formed by providing cutout C3only from the negative side of the Y-axis. Structures of suspensions304-1,304-2other than the shapes of extensible structures304bare the same with each other.

Providing extensible structures304ballows suspensions304-1,304-2to easily warp in the Z-axis direction. This configuration allows support member303supporting structure body301and screens108,109to be moved at a high speed in the Z-axis direction.

Further, since extensible structure304bof upper suspension304-1is different from extensible structure304bof lower suspension304-2, buckling rigidity of suspension304-1can be different from buckling rigidity of suspension304-2. The buckling rigidity herein indicates a degree of hardness in deformation of suspensions304-1,304-2against external force (compression or tension) in the positive or negative direction of the X-axis, and can be denoted by (load/deformation quantity).

The buckling rigidity of upper suspension304-1is made different from the buckling rigidity of lower suspension304-2in this manner. Therefore, when support member303supporting structure body301and screens108,109is reciprocated at a high frequency in the Z-axis direction, generation of excessive amplitude owing to a resonance mode can be suppressed.

Note that further effects exerted by suspensions304-1,304-2will be described below in more detail with reference toFIGS. 18A to 19B.

Note that, in this exemplary embodiment, suspensions304-1,304-2are shared as a feeding path of the drive signal for coil341. In this exemplary embodiment, as described above, support member303is formed of the liquid crystal polymer in which the carbon filler is mixed, and therefore has conductivity. Accordingly, when suspensions304-1,304-2are shared for feeding electricity, an attachment structure of suspensions304-1,304-2to support member303needs to be electrically insulated.

Each ofFIG. 9AandFIG. 9Bis an exploded perspective view of the attachment structure of suspension304-1to support member303.

As illustrated inFIG. 9A, fixing member303eincludes screw351and two plate-shaped clampers352. Upper and lower surfaces of each of two clampers352are subjected to an oxidation treatment. A hole is provided at a center of clamper352. A diameter of a shaft of screw351is smaller than a diameter of the hole of clamper352and a diameter of hole304eof suspension304-1. Further, the diameter of hole304eof suspension304-1is made larger than the diameter of the hole of clamper352, and therefore screw351is not brought in contact with suspension304-1.

While causing hole304eof suspension304-1and the hole of clamper352to coincide with each other, the end of suspension304-1is interposed between two clampers352. In this state, the end of suspension304-1is placed on an upper surface of connection member303dof support member303, and screw351is screwed into screw hole303hof connection member303d. This configuration allows the end of suspension304-1to be fixed to the upper surface of connection member303dof support member303, as illustrated inFIG. 9B. Similarly, lower suspension304-2is also fixed to a lower surface of connection member303d.

Since the upper and lower surfaces of each of two clampers352are electrically insulated, even if the ends of suspensions304-1,304-2are screwed in this manner, suspensions304-1,304-2are not electrically conducted with support member303. Therefore, suspensions304-1,304-2can appropriately be used as the feeding path for coil341.

After suspensions304-1,304-2are thus mounted on support member303, an end of coil341(refer toFIG. 8A) mounted on outer frame303bof support member303is connected to flange304fformed on the end of suspension304-1or suspension304-2by soldering. A lead wire for supplying the drive signal to coil341is connected to flange304cof suspension304-1or suspension304-2by soldering. The drive signal is thus supplied to coil341through suspension304-1or suspension304-2.

Next, a configuration of structure body301will be described with reference toFIGS. 10A to 14B.

FIG. 10Ais a perspective view of a configuration of holder361viewed from above, andFIG. 10Bis a perspective view of the configuration of holder361viewed from below.FIG. 11is a plan view of holder361viewed from above. InFIG. 11, hatching is applied to regions of protuberances361eand361i, for the sake of convenience.

Holder361is formed of a frame-shaped member. Holder361is formed of a lightweight and highly rigid material. In this exemplary embodiment, holder361is integrally molded with a magnesium alloy. A shape of holder361is symmetry with respect to the X-axis direction.

Holder361has lower frame361afor supporting screen108for the depth image, and upper frame361bfor supporting screen109for the fixed image.

Lower frame361ahas opening361chaving a rectangular shape in a plan view. Further, three walls361dprotruding upward are disposed at an edge portion of the positive side of the Y-axis on an upper surface of lower frame361a. Also, walls361dare respectively disposed at edge portions of the positive and negative sides of the X-axis on the upper surface of lower frame361a. Protuberance361eprotruding upward is disposed between those walls361dand opening361c. Protuberance361eis continuously formed so as to extend along a peripheral edge of opening361c. Protuberance361eis lower than walls361d. Four hooks361fprotruding in the Z-axis direction are disposed at positions on outer sides of walls361don the upper surface of lower frame361a.

Upper frame361bhas opening361ghaving a rectangular shape in a plan view. Further, three walls361hprotruding upward are disposed at an edge portion of the negative side of the Y-axis on an upper surface of upper frame361b. Also, walls361hare respectively disposed at edge portions of the positive and negative sides of the X-axis on the upper surface of upper frame361b. Protuberance361iprotruding upward is disposed between those walls361hand opening361g. Protuberance361iis continuously formed so as to extend along a peripheral edge of opening361g. Protuberance361iis lower than walls361h. Four hooks361jprotruding in the Z-axis direction are disposed at positions on outer sides of walls361hon the upper surface of upper frame361b.

A step between lower frame361aand upper frame361bis closed by wall361k. An upper surface of wall361kis made lower by one stage, by being dug downward (the negative direction of the Z-axis). Furthermore, on a lower surface of holder361, ten protrusive pieces361lprotruding downward from an inner side of the lower surface are provided as illustrated inFIG. 10B. A contour of the lower surface of holder361coincides with a contour of inner frame303aof support member303illustrated inFIG. 5A. When holder361is placed on inner frame303a, ten protrusive pieces361lof holder361are tightly fitted to an inner side of inner frame303a. Holder361is thus positioned on support member303.

Screen108for the depth image is placed on protuberance361eof lower frame361a, and is supported by holder361. At this time, an end of screen108on the negative side of the Y-axis goes into a lower side of wall361k. Protuberance361eis formed so as to continuously extend along three sides of screen108, when screen108is placed on protuberance361e. In this state, screen108is housed in an inner part of five walls361d, and a slight gap is produced between an outer periphery of screen108and walls361d.

Screen109for the fixed image is placed on protuberance361iof upper frame361b, and is supported by holder361. At this time, an end of screen109on the positive side of the Y-axis overlaps an upper side of wall361k. Protuberance361iis formed so as to continuously extend along three sides of screen109, when screen109is placed on protuberance361i. In this state, screen109is housed in an inner part of five walls361h, and a slight gap is produced between an outer periphery of screen109and walls361h.

FIG. 12is an exploded perspective view illustrating an attachment step of light shield members364,365to holder361.FIG. 13is a perspective view illustrating a configuration of structure body301when screens108,109and light shield members364,365are attached to holder361.FIG. 14Ais a plan view illustrating a configuration of structure body301before light shield members364,365are mounted on structure body301.FIG. 14Bis a plan view illustrating the configuration of structure body301after light shield members364,365are mounted on structure body301.

As illustrated inFIG. 12andFIG. 14A, heat resistant members (hereafter, referred to as “heat resistant packing members”)362,363are stuck on upper surfaces of screens108,109, respectively. Heat resistant packing members362,363are respectively installed near edges of three sides of screens108,109so as to be respectively positioned substantially right above protuberances361e,361iillustrated inFIG. 10A. Heat resistant packing members362,363may be respectively stuck on screens108,109before screens108,109are respectively placed on protuberances361e,361i.

Heat resistant packing members362,363are configured with an elastically deformable material excellent in heat resistance and heat insulation. Heat resistant packing members362,363are formed of heat resistant silicon rubber, for example. Each of heat resistant packing members362,363is a stick-shaped member having a square section. When screens108,109are set to holder361as illustrated inFIG. 12, an upper surface of heat resistant packing member362is higher than the upper surface of wall361d, and similarly an upper surface of heat resistant packing member363is higher than the upper surface of wall361h.

As illustrated inFIG. 12, light shield members364,365are made of a thin plate member. A thickness of each of light shield members364,365is about 0.2 mm, for example. Light shield members364,365are configured with a lightweight material excellent in heat resistance and light shielding property. Light shield members364,365are formed of a magnesium alloy, for example.

Light shield member364has a shape in which a rectangular portion is cut out from a rectangle on the negative side of the Y-axis of the rectangle.

Light shield member364has holes364aeach of which is engaged with corresponding hook361fof holder361. Light shield member364has rectangular cutout364bon the negative side of the Y-axis.

Light shield member365has a shape in which a rectangular portion is cut out from a rectangle on the positive side of the Y-axis of the rectangle.

Light shield member365has holes365aeach of which is engaged with corresponding hook361jof holder361. Light shield member365has rectangular cutout365bon the positive side of the Y-axis.

Four holes364aare respectively engaged with corresponding hooks36if, thereby mounting light shield member364on lower frame361aof holder361. Similarly, four holes365aare respectively engaged with corresponding hooks361j, thereby mounting light shield member365on upper frame361bof holder361. At this time, heat resistant packing members362,363are compressed in the Z-axis direction while generating reaction force. This reaction force secures engagement between hooks361f,361jand holes364a,365a, respectively, without loosening.

As illustrated inFIG. 13,FIG. 14AandFIG. 14B, assembly of structure body301is thus completed. In this state, a peripheral edge of light shield member364on an inner peripheral side overlaps an upper surface of a peripheral edge of screen108supported by protuberance361ethrough heat resistant packing members362. Further, a peripheral edge of light shield member365on an inner peripheral side overlaps an upper surface of a peripheral edge of screen109supported by protuberance361ithrough heat resistant packing members363. Screens108,109are exposed upward respectively through cutouts364b,365bof light shield members364,365.

Structure body301thus assembled is placed on inner frame303aof support member303illustrated inFIG. 5Ato be bonded and fixed. At this time, protrusive pieces361l(refer toFIG. 10B) on the lower surface of holder361are tightly fitted to the inner side of inner frame303a. Attachment of structure body301to support member303is thus completed.

Subsequently, a positional relationship between screens108,109and a display operation using screens108,109will be described.

FIG. 15Ais a view schematically illustrating the positional relationship between screens108,109.

As described above, in this exemplary embodiment, screens108,109are integrally supported by holder361. Therefore, when screen108for the depth image is moved in the optical axis direction (Z-axis direction), screen109for the fixed image is simultaneously moved in the optical axis direction (Z-axis direction). For example, when screen108is moved within range W1from position Ps0to position Ps1to generate the depth image, screen109for the fixed image is moved within range W10from position Ps10to position Ps11upon generating the depth image. Herein a distance of range W1and a distance of range W10are equal to each other. Further distance D1of a position shift between screen108and screen109is always constant during movement of screens108,109.

Note that a sight distance from driver2with respect to the image (virtual image) is made longer, as screens108,109distant from mirror22inFIG. 1Cmore. In other words, position Ps0is a boundary position of screen108on a farther sight-distance side, and position Ps1is a boundary position of screen108on a nearer sight-distance side. Screen109is located at a position displaced on the positive side of the Z-axis from screen108by distance D1. Therefore an image (virtual image) displayed by screen109is displayed on the nearer sight-distance side than an image (virtual image) displayed by screen108is.

In this exemplary embodiment, position Ps11is defined as a fixed position where screen109is fixed to display the fixed image. More specifically, the positional relationship (distance D1of the position shift) between screens108,109is set such that, when screen108for the depth image is positioned at the boundary position (position Ps1) on the nearer sight-distance side within the movement range (range W1) where screen108is moved to display the depth image, screen109for the fixed image is positioned at the fixed position (position Ps11) to display the fixed image. Screens108,109are installed on holder361while keeping this positional relationship.

When the positional relationship between screens108,109is set in this way, the depth image is displayed while moving screen108from position Ps0to position Ps1, and then the fixed image can successively be displayed while stopping screen109. In other words, when screen108for the depth image is moved to position Ps1that is a terminating position of a display process of the depth image, screen109for the fixed image is positioned at the fixed position (position Ps11) to display the fixed image. Hence, after screen108for the depth image is moved to position Ps1, screen109for the fixed image needs not to be moved to the fixed position to display the fixed image while further driving holder361. Thus, the display of the depth image and the display of the fixed image can be performed smoothly and stably through a series of operations.

FIG. 15Bis a view schematically illustrating a scanning method of the laser beam with respect to screens108,109.

In an image display operation, screen108is first scanned by the laser beam. Screen108is sequentially scanned from scan line L1set on the most positive side of the Y-axis to scan line Lk. During this scanning, holder361is moved to the positive side of the Z-axis, and screen108is moved from position Ps0to position Ps1. In this process, the depth image is displayed. Holder361is then stopped, and screen109is fixed at position Ps11. In this state, screen109is sequentially scanned from scan line Lk+1 to scan line Lk. In this process, the fixed image is displayed.

Note that, in this exemplary embodiment, after the display operation of the fixed image is completed, an image whose sight distance is not varied (hereafter, referred to as a “vertical image”) is displayed using screen108in a process in which screens108,109are returned to positions Ps0, Ps10, respectively. The vertical image is an image for marking a pedestrian, for example, and is displayed being superimposed on the pedestrian at a position with a sight distance of the pedestrian. In this process, screen108is sequentially scanned from scan line Lk to scan line L1.

FIG. 16Ais a graph illustrating a drive example of screen108when an image illustrated inFIG. 16Bis displayed in region S1. In this exemplary embodiment, screen109is moved according to the movement of screen108.

Screen108is repeatedly moved taking a period from time t0to time t5as one cycle. During a period from time t0to time t1, screen108is moved from position Ps0(farthest position) to position Ps1(nearest position), and during a period from time t2to time t5, screen108is returned from position Ps1(nearest position) to position Ps0(farthest position). During a period from time t1to time t2, screen108is stopped at position Ps1(nearest position). A movement cycle of screen108, that is, the period from time t0to time t5is 1/60 seconds, for example. Screen108is moved as illustrated inFIG. 16Aby changing a current applied to coil341described above while monitoring an output of the encoder in position detection unit400.

InFIG. 16B, the period from time t0to time t1is a period for displaying depth image M1extending in the depth direction, and the period from time t2to time t5is a period for displaying vertical image M2extending in the vertical direction. InFIG. 16B, the period from time t1to time t2is a period for displaying fixed image M3in region S2.

During the period from time t0to time t1, laser light sources101ato101care caused to emit light at timing corresponding to depth image M1on scan lines corresponding to depth image M1while screen108is linearly moved from position Ps0to position PS1. Therefore, depth image M1as illustrated inFIG. 16Bis displayed in region S1as a virtual image.

During the period from time t1to time t2, screen108is stopped at position Ps1. Accordingly, screen109for the fixed image is stopped at position Ps11that is the display position for fixed image M3. During this period, laser light sources101ato101care caused to emit light at timing corresponding to fixed image M3on scan lines corresponding to fixed image M3. Therefore fixed image M3is displayed in region S2ahead of projection region13.

Further, during the period from time t2to time t5, screen108is returned to position Ps0. At this time, screen108is stopped at position Ps2during a period from time t3to time t4. During this period, laser light sources101ato101care caused to emit light at timing corresponding to vertical image M2on scan lines corresponding to vertical image M2.

Therefore vertical image M2as illustrated inFIG. 16Bis displayed ahead of projection region13of windshield12.

The above-described control is performed by image processing circuit201illustrated inFIG. 2. With this control, depth image M1and vertical image M2are displayed in region S1as virtual images, and fixed image M3is further displayed in region S2as a virtual image, during the period from time t0to time t5. In the above-described control, display timing of depth image M1, vertical image M2, and fixed image M3includes a time shift, but the shifted time is extremely short. Then driver2recognizes an image on which depth image M1, vertical image M2, and fixed image M3are superimposed.

In this manner, driver2can view an image based on the video signal (depth image M1, vertical image M2, and fixed image M3) while superimposing the image on a scene including road R1and pedestrian H1.

Note that, in the example ofFIG. 16B, one vertical image M2is defined, and therefore one stop position (position Ps2) of screen108is set in the process ofFIG. 16A. However, if a plurality of vertical images M2is defined, a plurality of stop positions is set according to the plurality of vertical images M2in the process ofFIG. 16A. Note that, in the process ofFIG. 16A, the period from time t0to time t5is constant, and time t5is unchanged. Therefore the movement speed of screen108(slope of a waveform inFIG. 16A) before and after the stop positions is modified in response to increasing or decreasing of the number of stop positions.

According to the above-described exemplary embodiment, the following effects are exerted.

Screen108and screen109are integrally supported by holder361and are simultaneously driven. Therefore generation of a gap between screens108,109can be prevented, when viewed in a projection direction of light. Hence, it is possible to prevent a virtual image of the light emitting source of the light scanning screens108,109from being visually recognized by the driver, through the gap between screens108,109. Accordingly, the images can be independently displayed by screens108,109while preventing the virtual image of the light emitting source of light scanning screens108,109from being visually recognized by the driver.

FIG. 17Ais a view describing this effect.FIG. 17Aillustrates a section of structure body301taken in a plane parallel to the Y-Z plane. InFIG. 17A, a broken line arrow indicates a ray of laser light that has been reflected by mirror106aof scanning unit106and reaches near a boundary between screens108,109.

When viewed from the positive side of the Z-axis, the gap generated between screens108,109leaks laser light that has been reflected by mirror106aof scanning unit106, and this leaked laser light enters eyes of driver2. Thus, a virtual image of the light taking a reflection point of the laser light on mirror106aas the light emission source is visually recognized by driver2.

In contrast, in this exemplary embodiment, screens108,109are installed on holder361. Therefore, as illustrated inFIG. 17A, an end of screen108on the negative side of the Y-axis and an end of screen109on the positive side of the Y-axis can be overlapped each other in the Z-axis direction. Therefore, in this exemplary embodiment, no gap is generated between screens108,109, when viewed from the positive side of the Z-axis. This configuration can prevent the virtual image of light taking the reflection point on mirror106aas the light emission source from being visually recognized by driver2.

Furthermore, in this exemplary embodiment, wall361kis formed in holder361to close the step between an end of screen108facing screen109and an end of screen109facing screen108as illustrated inFIG. 17A. This configuration can securely prevent leakage of light of the light emission source from a boundary portion between screen108and screen109. For example, even when the laser light reflected by mirror106ais slightly diffused and enters a portion of the step between screens108,109, this laser light is blocked by wall361k, thereby prohibiting leakage from the portion of the step. Hence, it is possible to more securely prevent the virtual image of the light emitting source of the light scanning screens108,109from being visually recognized by the driver.

As described with reference toFIG. 15A, screen108and screen109are installed on holder361such that, when screen108is positioned at one boundary position (position Ps1) within the movement range in which screen108is moved to display the depth image, screen109is positioned at the fixed position (position Ps11) to display the fixed image. With this configuration, screen108is moved from position Ps0to position Ps1to display the depth image, and then the fixed image can successively be displayed while stopping screen109. Thus, the display of the depth image and the display of the fixed image can be performed smoothly and stably through a series of operations.

Note that, in this exemplary embodiment, the positional relationship between screen108and screen109is set such that, when screen108is positioned at a boundary position (position Ps1) on the nearer sight-distance side within the movement range (range W1), screen109is positioned at the fixed position (position Ps11). Otherwise, the positional relationship between screen108and screen109may be set such that, when screen108is positioned at a boundary position (position Ps0) on the farther sight-distance side within the movement range (range W1), screen109is positioned at the fixed position (position Ps11). In this case, the depth image is displayed while screen108is moved from position Ps1to position Ps0, and then screen108is stopped at position Ps0and the fixed image is displayed by screen109.

However, when the positional relationship between screens108,109is set in this manner, the distance between screens108,109in the optical axis direction (Z-axis direction) is increased. Therefore holder361is increased in size in the optical axis direction (Z-axis direction). In contrast, as in the above-described exemplary embodiment, the positional relationship between screens108,109is set such that, when screen108is positioned at the boundary position (position Ps1) on the nearer sight-distance side within the movement range (range W1), screen109is positioned at the fixed position (position Ps11). This configuration can suppress the distance between screens108,109to be small and can achieve downsizing of holder361. Then holder361can be decreased in weight, and screens108,109can accurately be driven more stably.

Note that, in this exemplary embodiment, the stray light including natural light can be taken in from the outside and can be introduced into image display device20. In this case, since the stray light is condensed to peripheries of screens108,109by mirror22, stray light with high intensity is irradiated to the peripheries of screens108,109. This possibly causes holder361to become considerably high in temperature.

To solve this problem, in this exemplary embodiment, screens108,109are respectively covered by light shield member364,365through heat resistant packing members362,363while being respectively placed on protuberances361e,361iillustrated inFIG. 10A, as illustrated inFIG. 12. This configuration allows the stray light that goes backward through mirror22and approaches a portion of holder361around screens108,109to be blocked by light shield members364,365. Therefore this portion of holder361is prevented from becoming high in temperature by the stray light. Accordingly, screens108,109can be prevented from receiving damage by heat from holder361.

Further heat resistant packing members362,363are respectively interposed between light shield members364,365and upper surfaces of screens108,109. Therefore, even when light shield members364,365become high in temperature by the stray light, heat propagation from light shield members364,365to screens108,109can be prevented. Accordingly, damage of screens108,109due to the heat from light shield members364,365can be prevented.

Furthermore screens108,109are installed on holder361such that peripheral edges of screens108,109are respectively supported by protuberances361e,361i. Therefore even when the stray light enters positions of holder361right below the peripheral edges of screens108,109from around inner peripheral edges of light shield members364,365, and those positions right below the peripheral edges of screens108,109become high in temperature, heat at those positions right below the peripheral edges of screens108,109does not directly propagate to screens108,109. Therefore screens108,109can be prevented from being damaged by heat from those positions right below the peripheral edges of screens108,109.

FIG. 17Bis a view for describing the above-described effect.FIG. 17Billustrates a section of an end of holder361on the positive side of the Y-axis taken in a plane parallel to the Y-Z plane. InFIG. 17B, broken line arrows indicate the stray light.

As illustrated inFIG. 17B, the majority of light approaching an upper surface of holder361is blocked by light shield member364. However, a part of the stray light enters region A10of holder361passing through an inner side of light shield member364. Region A10becomes considerably high in temperature owing to irradiation of the stray light. However, since the peripheral edge of screen108is placed on protuberance361e, a gap is generated between screen108and region A10and therefore heat in region A10does not directly propagate to screen108. Accordingly, screen108can be prevented from being damaged by heat generated in region A10.

Note that the heat generated in region A10spreads to the inside of holder361, and a part of the heat propagates to protuberance361e. However the heat disperses before propagating to protuberance361e, and therefore protuberance361edoes not become so high in temperature. Accordingly, even when protuberance361eis brought in contact with screen108, screen108is not damaged by heat from protuberance361e. Similarly, other parts of the peripheral edge of screen108are prevented from being damaged by heat owing to protuberance361eextending along the periphery edge. Screen109is also prevented from being damaged by heat owing to protuberance361e.

As illustrated inFIG. 10A,FIG. 10B, andFIG. 11, protuberances361e,361iare continuously provided along three sides of screen108and three sides of screen109, respectively. Screens108,109each have a rectangular contour. This allows screens108,109to be stably supported by protuberances361e,361i, respectively. Protuberances361e,361imay discontinuously be disposed along the three sides of screen108and the three sides of screen109, respectively.

Note that protuberances361e,361ido not necessarily have to be formed integrally with holder361. Protuberances361e,361imay be configured by installing other members on holder361. However, when protuberances361eand361iare integrally formed with holder361in advance as in the above-described exemplary embodiment, a procedure for installing the other members configuring protuberances361e,361ion holder361can be omitted. This can simplify an assembly procedure of structure body301more.

According to suspensions304-1,304-2in the above-described exemplary embodiment, the following effect can further be exerted.

FIG. 18Ais a graph illustrating fatigue characteristics of beryllium-copper alloy 25 used for suspensions304-1,304-2.

InFIG. 18A, a vertical axis indicates the maximum stress given to this metal, and a horizontal axis indicates a repeat count until the metal is broken when bending is iteratively repeated with the stress indicated by the vertical axis. The fatigue characteristics inFIG. 18Aare verified by the inventor of the present disclosure.

With reference toFIG. 18A, it can be understood that, when the maximum stress is suppressed to about 300 MPa, the repeat count of breaking limit can extended up to 1010times or more.

FIG. 18Bis a graph illustrating characteristics of suspensions304-1,304-2used in the above-described exemplary embodiment.

FIG. 18Bincludes a graph indicating a load necessary to displace a center position of each of suspensions304-1,304-2by a displacement amount indicated by a horizontal axis, and a graph indicating the maximum stress generated in suspensions304-1,304-2when the center position of each of suspensions304-1,304-2is displaced by the displacement amount indicated by the horizontal axis. Since spring constants of suspensions304-1,304-2are equal to each other, the graph of the load is common for suspensions304-1,304-2. Each graph inFIG. 18Bis obtained from simulation performed by the inventor of the present disclosure.

Herein each of suspensions304-1,304-2has 71.4 mm in total length and has 0.3 mm in thickness. Each of suspensions304-1,304-2is made of beryllium-copper alloy 25. Effective lengths of two portions of each of suspensions304-1,304-2excluding a center portion (fixed portion) and ends (support portions) are 29.1 mm.

With reference toFIG. 18B, a load necessary to reciprocate a center position of each of suspensions304-1,304-2with a range of ±1.5 mm in the Z-axis direction is about 4 N. Furthermore, when the center position of each of suspensions304-1,304-2is reciprocated with the range of ±1.5 mm in the Z-axis direction, the maximum stress generated in each of suspensions304-1,304-2slightly exceeds 300 MPa. In contrast, with reference toFIG. 18A, the repeat count of breaking limit when the maximum stress slightly exceeds 300 MPa is 1010times or more. Accordingly, by using suspensions304-1,304-2, screens108,109can be reciprocated 1010times or more, that is, semipermanently.

FIG. 19Ais a plan view illustrating configurations of suspensions (Type 1, 2, and 3) according to a comparative example.

In the suspension of Type 1, no extensible structure is provided between a center portion and arms A1. In the suspension of Type 2, extensible structures B11are provided by providing cutouts C11between a center portion and arms A1. Similarly, in the suspension of Type 3, extensible structures B12are provided by providing cutouts C12between a center portion and arms A1. However, shapes of extensible structures B11, B12are different from shapes of extensible structures304bof suspensions304-1,304-2(refer toFIG. 8BandFIG. 8C). Further, widths of arms A1of the suspensions of Type 1 to Type 3 are set broader than those of suspensions304-1,304-2.

FIG. 19Bis a graph indicating a relationship between a displacement amount and a stress of each of the suspensions according to the comparative example (Type 1, 2, and 3).

Herein each of the suspensions of Type 1 to Type 3 has 72.8 mm in total length and has 0.2 mm in thickness. Each of the suspensions of Type 1 to Type 3 is made of beryllium-copper alloy 25. Effective lengths of two portions of each of the suspensions of Type 1 to Type 3 excluding a center portion (fixed portion) and ends (support portions) are 29.1 mm. Thicknesses of the suspensions of Type 2 and Type 3 are set large, to set spring constants of the suspensions of Type 2 and Type 3 to be equal to spring constants of suspensions304-1,304-2.

When the center position of each of suspensions of Type 2 and Type 3 is reciprocated with the range of ±1.5 mm in the Z-axis direction, the maximum stress generated in each of those suspensions slightly exceeds 400 MPa. In contrast, with reference toFIG. 18A, the repeat count of breaking limit when the maximum stress slightly exceeds 400 MPa is about 108times. Accordingly, the repeat count of breaking limit when the suspensions of Type 2 and Type 3 are used is considerably reduced, in comparison with a case where suspensions304-1,304-2in the above-described exemplary embodiment are used.

Note that, in the suspension of Type 1, no extensible structure is provided, and therefore its maximum stress is suppressed to about 300 MPa, similar to suspensions304-1,304-2in the above-described exemplary embodiment. However, the suspension of Type 1 is provided with no extensible structure, and therefore the suspension of Type 1 is hardly warped in the Z-axis direction. Accordingly, a load necessary for reciprocating the center of the suspension with the range of ±1.5 mm is remarkably increased.

As studied in the above-described verification, use of suspensions304-1,304-2in the above-described exemplary embodiment can remarkably improve life time of suspensions304-1,304-2while suppressing the load, when the center of each of suspensions304-1,304-2is reciprocated with the range of ±1.5 mm. Note that, when such an effect is not needed, the shapes of suspensions304-1,304-2may not necessarily be the shapes illustrated inFIG. 8B,FIG. 8C, respectively, but the suspensions illustrated inFIG. 19Amay be used, for example. Also in this case, the buckling rigidity of the upper suspension is preferably set different from the buckling rigidity of the lower suspension.

Modification Example

Although the exemplary embodiment of the present disclosure has been described above, the present disclosure is not limited to the exemplary embodiment described above, and moreover, a variety of modifications can be applied to application examples according to the present disclosure besides the exemplary embodiment described above.

For example, in the above-described exemplary embodiment, although two screens108,109are installed on holder361, a number of screens to be installed on holder361is not limited to two. For example, two screens for the fixed image may be disposed at positions whose sight distances are different from each other, together with the screen for displaying the depth image. In this case, when the screen for the depth image is positioned at the boundary position within the movement range, the two screens for the fixed image may be positioned at positions to display the fixed images with respective sight distances. A plurality of screens for the depth image may be disposed.

Furthermore, in the above-described exemplary embodiment, the image is displayed by screen109in a state in which screen109is stopped. However the image may be displayed by screen109while moving screen109.

Furthermore, in the above-described exemplary embodiment, screens108,109are installed on structure body301while being inclined with respect to a state vertical to the Z-axis by substantially identical angles. However inclined angles of screens108,109may be different from each other. Alternatively both of or one of screens108,109may be installed on structure body301in the state vertical to the Z-axis. Further, shapes and sizes of screens108,109are also not limited to those described in the above-described exemplary embodiment.

Furthermore, in the above-described exemplary embodiment, the head-up display to be mounted on passenger vehicle1is exemplified. However the present disclosure is not limited to the on-vehicle application, and is applicable to other types of image display devices.

Moreover, the configurations of image display device20and irradiation generator21are not limited to those illustrated inFIG. 1CandFIG. 2, and can be modified as appropriate. In addition, the configuration of drive unit300for moving screens108,109is not limited to one described in the exemplary embodiment, and can be modified as appropriate. For example, a configuration in which a drive unit of a piezoelectric type or an electrostatic type drives screens108,109may be used.

The exemplary embodiment of the present disclosure is modifiable in various ways as appropriate within the scope of the technical idea disclosed in the claims.