Patent Description:
The virtual image display device of <CIT> includes an illumination light source, an image member, a first lens, and a second lens. The illumination light source provides illumination light. The image member blocks at least a part of the illumination light to form an image on the display screen. The first lens is a single-surface lens having a single refractive surface on the surface on both sides. The second lens is a lens array having an array structure in which a plurality of lens units are arrayed. The single-surface lens and the lens array are provided as separate components, and the illumination performance is enhanced by a combination of these lenses.

<CIT> discloses a lighting system with a plurality of light emitting diodes mounted in a predetermined range on a surface of a wiring board and a lens array composed by forming lens parts for refracting illumination light emitted from the light emitting diodes by making them correspond to the respective light emitting diodes. The lens parts formed on the outside are so mounted as to tilt the center axis x of each lens part with respect to the optical axis y of the corresponding light emitting diodes, and each light emitting diode is so mounted as to be positioned on a focal point of the corresponding lens part or in the vicinity of the focal point.

<CIT> relates to a directed Fresnel lens which has an angular field of view which is not centered on the direction perpendicular to the lens. This type of lens has a field of view which can be centered on a non-vanishing angle of incidence. Another Fresnel lens is known from <CIT>.

In <CIT> and in <CIT>, however, there is a concern that the build of a virtual image display device becomes large.

An object of the disclosure is to provide a virtual image display device in which enlargement of the build is suppressed while achieving high illumination performance.

The object is solved by the subject-matter of claim <NUM>. Advantageous further developments are indicated in the dependent claims.

According to one mode discloses herein, a virtual image display device displays a virtual image by projecting light of an image onto a projection portion. The virtual image display device includes:.

An overall reference axis line is defined as a virtual center line of the array structure that passes through the array structure, and an individual center axis line is defined as a center line of the individual area that is parallel to the overall reference axis line and passes through the individual area.

Each of the plurality of Fresnel lens units includes a plurality of divided lens surfaces. The plurality of divided lens surfaces curve convexly or the plurality of divided lens surfaces curve concavely.

The array structure includes a plurality of eccentric Fresnel lens units as the plurality of Fresnel lens units. The plurality of divided lens surfaces of each of the plurality of eccentric Fresnel lens units have curvature centers that are offset from the individual center axis line toward an overall reference axis side of the individual center axis line that is close to the overall reference axis line or an opposite side of the individual center axis line that is away from the overall reference axis line.

The curvature center of each divided lens surface belonging to the same eccentric Fresnel lens unit is offset from the individual center axis line by a specific offset amount that is set every eccentric Fresnel lens units. An inter-axis distance is defined as a distance between the overall reference axis line and the individual center axis line. The specific offset amount of the eccentric Fresnel lens units having a larger value of the inter-axis distance is greater than the specific offset amount of the eccentric Fresnel lens units having a smaller value of the inter-axis distance.

According to such a mode, the Fresnel lens array having the array structure in which the plurality of Fresnel lens units are arrayed is provided between the illumination light source and the image member. Each of the plurality of Fresnel lens units includes a plurality of divided lens surfaces that curve convexly or concavely in the individual area. A local refraction action as if each individual center axis line is the optical axis is exhibited by the common curved shape while enlargement of the build of the lens array due to bulging out of the lens surface by division is suppressed.

Since the illumination light passing through the position away from the overall reference axis line receives a larger deflection action, the overall refracting function as if the overall reference axis line is the optical axis can be further exhibited by the assembly of the plurality of eccentric Fresnel lens units.

Since the same array structure exhibits both the local refracting function and the overall refracting function, an increase in the number of components is suppressed. As described above, enlargement in the build of the virtual image display device can be suppressed while achieving high illumination performance.

Note that the reference signs in parentheses in the Claims exemplarily indicate a correspondence relationship with the portions of the embodiments to be described later, and are not intended to limit the technical scope.

Hereinafter, a plurality of embodiments will be described with reference to the drawings. Note that the same reference numerals are given to corresponding components in each embodiment, and redundant description may be omitted. When only a part of the configuration is described in each embodiment, the configuration of the other embodiment described above can be applied to other parts of the configuration. In addition, not only a combination of configurations explicitly described in the description of each embodiment but also configurations of a plurality of embodiments can be partially combined even if not explicitly described as long as there is no particular problem in the combination.

As illustrated in <FIG>, a virtual image display device according to a first embodiment of the present disclosure is a head-up display (hereinafter, HUD) <NUM> used in a vehicle <NUM> and configured to be mounted on the vehicle <NUM>. The HUD <NUM> is installed on an instrument panel <NUM> of the vehicle <NUM>. The HUD <NUM> projects light toward a projection portion 3a provided on a windshield <NUM> of the vehicle <NUM>. The light reflected by the projection portion 3a reaches a viewing region EB set in the interior of the vehicle <NUM>. In this way, the HUD <NUM> displays a virtual image VRI visually recognizable from the viewing region EB in an exterior space on a side opposite to the viewing region EB with the windshield <NUM> in between.

Therefore, an occupant serving as a viewer who located an eye point EP in the viewing region EB can recognize various types of information displayed in the virtual image VRI. The various types of information to be displayed include, for example, information indicating the state of the vehicle <NUM> such as a vehicle speed, view aiding information, road information, and the like.

Hereinafter, unless otherwise specified, each direction indicated by front, back, up, down, left, and right is described with reference to the vehicle <NUM> on a horizontal plane HP.

The windshield <NUM> of the vehicle <NUM> is a transmissive member formed in a translucent plate shape using, for example, glass or synthetic resin. The windshield <NUM> is disposed above the instrument panel <NUM>. The windshield <NUM> is disposed so as to be inclined such that a spacing between the windshield <NUM> and the instrument panel <NUM> increases from the front toward the back. The windshield <NUM> forms the projection portion 3a on which light is projected from the HUD <NUM> in a smooth concave surface shape or planar shape. The projection portion 3a is configured to surface-reflect light from the HUD <NUM>.

Note that the projection portion 3a may be configured to reflect light toward the viewing region EB by diffractive reflection by the interference fringes instead of surface-reflection by providing a reflection type holographic optical element on the windshield <NUM>. Further, the projection portion 3a may not be provided on the windshield <NUM>. For example, a combiner separate from the vehicle <NUM> may be installed in the interior of the vehicle <NUM>, and the projection portion 3a may be provided in the combiner.

The viewing region EB is a space region where the virtual image VRI displayed by the HUD <NUM> can be visually recognized so as to satisfy predetermined visibility (e.g., so that the entire virtual image VRI has predetermined luminance or more), and is also referred to as an eye box. The viewing region EB is set in the interior space of the vehicle <NUM>. The viewing region EB is typically disposed so as to overlap with an eyellipse set in the vehicle <NUM>. The eyellipse is set, for example, in the vicinity of the headrest of the driver's seat. The eyellipse is set for each of both eyes, and is set as an ellipsoidal virtual space based on an eye range statistically representing a spatial distribution of the eye point EP of the occupant (see also JISD0021: <NUM> for details). The viewing region EB is arranged so as to include, for example, both of a pair of eyellipse corresponding to both eyes.

A specific configuration of the HUD <NUM> will be described below. The HUD <NUM> includes a housing <NUM>, a light guide unit <NUM>, a display <NUM>, and the like.

The housing <NUM> is formed of, for example, synthetic resin or metal to have a light shielding property, and is installed in the instrument panel <NUM> of the vehicle <NUM>. The housing <NUM> has a hollow shape that accommodates the light guide unit <NUM>, the display <NUM>, the control unit, and the like. The housing <NUM> has a window portion <NUM> that opens optically on an upper surface portion facing the projection portion 3a. The window portion <NUM> is covered with, for example, a dustproof sheet <NUM> capable of transmitting light formed as a virtual image VRI.

The light guide unit <NUM> guides the light emitted from the display <NUM> to the viewing region EB via the projection portion 3a. The light guide unit <NUM> includes, for example, a plane mirror <NUM> and a concave mirror <NUM>. The plane mirror <NUM> has a reflecting surface <NUM> by, for example, forming a metal film of aluminum or the like by vapor deposition on a surface of a base material made of synthetic resin or glass. The reflecting surface <NUM> of the plane mirror <NUM> is formed in a smooth planar shape. The light entering the plane mirror <NUM> from the display <NUM> is reflected by the reflecting surface <NUM> toward the concave mirror <NUM>.

The concave mirror <NUM> has a reflecting surface <NUM> by, for example, forming a metal film of aluminum or the like by vapor deposition on a surface of a base material made of synthetic resin or glass. The reflecting surface <NUM> of the concave mirror <NUM> is formed in a smooth concave surface shape by being curved to a concave shape. The light entering the concave mirror <NUM> from the plane mirror <NUM> is reflected by the reflecting surface <NUM> toward the projection portion 3a. Here, the size of the virtual image VRI is enlarged with respect to the size of the image on a display screen <NUM> of the display <NUM> by the reflecting surface <NUM> of the concave mirror <NUM> having positive optical power.

The light reflected by the concave mirror <NUM> is transmitted through the dustproof sheet <NUM> and emitted to the outside of HUD <NUM>, and enters the projection portion 3a of windshield <NUM>. When the light reflected by the projection portion 3a reaches the viewing region EB, the virtual image VRI can be viewed from the viewing region EB. Here, since the projection portion 3a is provided on the windshield <NUM> as a transmissive member, the virtual image VRI can be visually recognized while being superimposed on a scene exterior to the vehicle <NUM> visually recognized through the windshield <NUM>.

The concave mirror <NUM> is turnable about a rotation shaft 24a extending in the left-right direction in accordance with driving of the actuator. By such turning, the display position of the virtual image VRI and the position of the viewing region EB can be adjusted to be displaced in the vertical direction.

The display <NUM> displays an image on a rectangular display screen <NUM>, and emits light for forming an image as the virtual image VRI toward the light guide unit <NUM>. As illustrated in <FIG>, the display <NUM> of the present embodiment is a liquid crystal display. The display <NUM> includes a casing <NUM>, a light source unit <NUM>, a first lens member <NUM>, a second lens member <NUM>, a diffusion plate <NUM>, an image member <NUM>, and the like.

The casing <NUM> is formed in a box shape or a tubular shape having a light shielding property from, for example, synthetic resin or metal. A casing <NUM> interiorly accommodates the light source unit <NUM>, the first lens member <NUM>, the second lens member <NUM>, and the diffusion plate <NUM>. Accompanying therewith, in the casing <NUM>, an opening window is formed at a position facing the plane mirror <NUM>, and the image member <NUM> is arranged so as to close the opening window. The light source unit <NUM>, the first lens member <NUM>, the second lens member <NUM>, and the diffusion plate <NUM> constitute a backlight for the image member <NUM>.

The light source unit <NUM> is formed by mounting a plurality of illumination light sources <NUM> on a light source circuit substrate <NUM>. The light source circuit substrate <NUM> is, for example, a flat plate-shaped rigid substrate using a synthetic resin such as glass epoxy resin as a base material. For the illumination light source <NUM> of the present embodiment, for example, a light emitting diode (LED) light source serving as a point light source is adopted.

Each illumination light source <NUM> is electrically connected to a power supply through a wiring pattern on the light source circuit substrate <NUM>. Each illumination light source <NUM> is formed by sealing a chip-shaped blue light emitting diode with a yellow fluorescent body obtained by mixing a yellow fluorescent agent with a synthetic resin having light projecting property. The yellow fluorescent body is excited by the blue light emitted from the blue light emitting diode with the light emission intensity corresponding to the amount of current, and yellow light is emitted. Mixing of the blue light and the yellow light results in emission of white (more specifically, pseudo-white) illumination light from each illumination light source <NUM>.

Here, each illumination light source <NUM> emits illumination light in a radiation angle distribution in which the light emission intensity relatively decreases as it is angularly diverged from a light emission peak direction PD in which the light emission intensity becomes maximum. The light emission peak directions PD of the respective illumination light sources <NUM> are directions common to each other and are perpendicular to the surface of the light source circuit substrate <NUM>. As described above, the surface of the light source circuit substrate <NUM> is a planar light source arrangement surface LP on which each illumination light source <NUM> is arranged.

On the light source arrangement surface LP, the plurality of illumination light sources <NUM> are arranged side by side so as to be shifted at least in the longitudinal corresponding direction RLD out of the short corresponding direction RSD and the longitudinal corresponding direction RLD. In particular, in the present embodiment, the plurality of illumination light sources <NUM> are arrayed in a line at a predetermined array pitch along the longitudinal corresponding direction RLD.

Here, the short corresponding direction RSD means a direction in which a vector indicating the short direction SD of the display screen <NUM> is indicated by a vector projected onto the light source arrangement surface LP when the display screen <NUM> is projected onto the light source arrangement surface LP along the opposite direction of the light emission peak direction PD. Here, the longitudinal corresponding direction RLD means a direction in which a vector indicating the longitudinal direction LD of the display screen <NUM> is indicated by a vector projected onto the light source arrangement surface LP when the display screen <NUM> is projected onto the light source arrangement surface LP along the opposite direction of the light emission peak direction PD. If the display screen <NUM> is parallel to the light source arrangement surface LP, the short corresponding direction RSD coincides with the short direction SD, and the longitudinal corresponding direction RLD coincides with the longitudinal direction LD.

The first lens member <NUM> is disposed between the light source unit <NUM> and the second lens member <NUM> on the optical path between the light source unit <NUM> and the image member <NUM>. The first lens member <NUM> is formed to have translucency by, for example, synthetic resin or glass. The first lens member <NUM> is a convex lens array in which convex lens elements <NUM> individually provided in one-to-one correspondence with the illumination light sources <NUM> are arrayed in accordance with the arrangement of the illumination light sources <NUM> on the light source arrangement surface LP.

In the present embodiment, the plurality of illumination light sources <NUM> are arrayed in a line along the longitudinal corresponding direction RLD. In correspondence therewith, the same number of convex lens elements <NUM> are provided so as to form a pair with the illumination light source <NUM>. The plurality of convex lens elements <NUM> are arrayed in a line at a predetermined array pitch along the longitudinal corresponding direction RLD. The spacing between the convex lens element <NUM> and the illumination light source <NUM> that form a pair is set to be the same spacing for each pair.

Each convex lens element <NUM> is disposed to face the individually corresponding illumination light source <NUM>, and collects the illumination light emitted from each illumination light source <NUM>. Each convex lens element <NUM> has an incident side lens surface facing the illumination light source <NUM> side formed into a common smooth planar shape by the first lens member <NUM>. On the other hand, in each convex lens element <NUM>, the emission side lens surface facing the second lens member <NUM> side is an individual lens surface for each convex lens element <NUM> and is formed into a smooth convex surface shape curved convexly.

For example, in the present embodiment, the array pitch of the illumination light sources <NUM> and the array pitch of the convex lens elements <NUM> are set to the same pitch as each other. The optical axis of each convex lens element <NUM> is set along the light emission peak direction PD, and is set to pass through the individually corresponding illumination light source <NUM>. Therefore, the illumination light emitted from each illumination light source <NUM> efficiently enters each individually corresponding convex lens element <NUM>, and is refracted and collected.

The second lens member <NUM> is disposed between the first lens member <NUM> and the diffusion plate <NUM> on the optical path between the light source unit <NUM> and the image member <NUM>. The second lens member <NUM> is formed to have translucency by, for example, synthetic resin or glass. The second lens member <NUM> has a macroscopically flat plate-shaped outer appearance shape. The second lens member <NUM> is disposed, for example, along the parallel direction of the light source arrangement surface LP.

As illustrated in an enlarged manner in <FIG>, the second lens member <NUM> is a Fresnel lens array having an array structure <NUM> in which a plurality of (e.g., odd number, seven) Fresnel lens units <NUM> are arrayed. The second lens member <NUM> has an incident side lens surface <NUM> facing the first lens member <NUM> side formed into a common smooth planar shape between the Fresnel lens units <NUM>. In the second lens member <NUM>, the emission side lens surface <NUM> facing the diffusion plate <NUM> and the image member <NUM> side is formed in a composite surface shape including a plurality of divided surfaces. In this way, the array structure <NUM> is formed on the emission side lens surface <NUM> of the second lens member <NUM>.

As will be described later, the second lens member <NUM> has a light collecting function of collecting the illumination light in the short corresponding direction RSD out of the short corresponding direction RSD and the longitudinal corresponding direction RLD. The second lens member <NUM> has an overall reference axis line AX1 that is defined as a virtual center line of the array structure <NUM> that passes through the array structure. The overall reference axis line AX1 is a virtual center line with respect to the entire array structure <NUM>. The overall reference axis line AX1 is an axis corresponding to the optical axis of the second lens member <NUM> or the entire array structure <NUM>. The overall reference axis line AX1 can be defined to lie along the light emission peak direction PD on a cross section in which the second lens member <NUM> exhibits a light collecting function, that is, a cross section including the center of the display screen <NUM>, the short direction SD, and the short corresponding direction RSD. In the array structure <NUM> formed by the emission side lens surface <NUM> of the second lens member <NUM>, both side parts sandwiching the overall reference axis line AX1 are formed in a linearly symmetric shape with the overall reference axis line AX1 as a symmetry axis.

On this cross section, the overall reference axis line AX1 is further disposed so as to pass through the center of the display screen <NUM>. In addition, the overall reference axis line AX1 is arranged such that there is no shift in the short corresponding direction RSD with respect to the optical axis of each convex lens element <NUM>, and the coordinates in the short corresponding direction RSD coincide with each other.

For example, in the present embodiment, the plurality of Fresnel lens units <NUM> are arrayed along a short corresponding direction RSD perpendicular to the longitudinal corresponding direction RLD in which the illumination light source <NUM> and the convex lens element <NUM> are arrayed. Each Fresnel lens unit <NUM> occupies an individual area IA as a region individually corresponding to each Fresnel lens unit in the array structure <NUM>. In the present embodiment, each individual area IA is formed in an elongated stripe having a width in the short corresponding direction RSD and extending in the longitudinal corresponding direction RLD.

Each Fresnel lens unit <NUM> has a divided lens surface <NUM> dividedly formed in plurals (e.g., four). The divided lens surface <NUM> is divided to reduce a coordinate difference in a direction along the overall reference axis line AX1 due to a maximum sag amount and a minimum sag amount in each Fresnel lens unit <NUM>. The spacing at which the divided lens surface <NUM> is divided along the perpendicular direction of the overall reference axis line AX1 may be an equal spacing or a spacing corresponding to the sag.

Each divided lens surface <NUM> is arranged such that, for example, the thickness of the second lens member <NUM> in the maximum sag amount portion in the individual area IA is substantially the same between the divided lens surfaces <NUM>. Note that each divided lens surface <NUM> may be arranged such that, for example, the thickness of the second lens member <NUM> in the minimum sag amount portion in the individual area IA is substantially the same between the divided lens surfaces <NUM>.

Here, the thickness at each portion of the second lens member <NUM> is defined as a distance from the incident side lens surface <NUM> to the emission side lens surface <NUM> along the perpendicular direction of the incident side lens surface <NUM>. In this way, a step is formed between the divided lens surfaces <NUM> adjacent to each other.

In particular, in the present embodiment, the divided lens surface <NUM> is divided in the short corresponding direction RSD that exhibits a light collecting function. Therefore, each of the divided lens surfaces <NUM> is formed in stripes having a width narrower than that of each of the individual areas IA. Each of the Fresnel lens units <NUM> of the present embodiment can be said to be a linear Fresnel lens, and the second lens member <NUM> can be said to be a linear Fresnel lens array.

Each divided lens surface <NUM> in each Fresnel lens units <NUM> has a common curved shape out of a convex surface shape curved convexly or a concave surface shape curved concavely. In the present embodiment, as the common curved shape, a cylindrical surface having a convex surface shape curved convexly and having a curvature in the short corresponding direction RSD is adopted. The cylindrical surface referred to herein includes not only an authentic cylindrical surface having a constant curvature at each portion but also an aspherical cylindrical surface obtained by composing a correcting shape by an aspherical coefficient with the authentic cylindrical surface. However, in the present embodiment, an authentic cylindrical surface is adopted. Note that the curvature center CC of the divided lens surface <NUM> to be described later can be defined by approximating the curved shape to an arc when the curved shape is aspherical. The least squares method is used for approximation to the arc.

Each Fresnel lens unit <NUM> has its own individual center axis line AX2. The individual center axis line AX2 is an axis penetrating the center that equally divides the dimension of the individual area IA in the width direction (in other words, the short corresponding direction RSD) on the cross section, and can be defined as an axis parallel to the overall reference axis line AX1.

Among the odd-numbered Fresnel lens units <NUM> arrayed with each other, the paraxial Fresnel lens unit 44N arranged at the center has a mode in which the individual center axis line AX2 substantially coincides with the overall reference axis line AX1, as illustrated in <FIG>. In the paraxial Fresnel lens unit 44N, both side parts sandwiching the individual center axis line AX2 in the width direction are formed in a linearly symmetric shape with the individual center axis line AX2 as a symmetry axis. The curvature center CCN of each divided lens surface 45N belonging to the paraxial Fresnel lens unit 44N is arranged on the overall reference axis line AX1 and the individual center axis line AX2. The curvature center CCN is shifted in the direction along the overall reference axis line AX1 and the individual center axis line AX2 between the respective divided lens surfaces 45N by a step formed between the divided lens surfaces 45N.

Among the odd-numbered Fresnel lens units <NUM>, a plurality of (e.g., six) eccentric Fresnel lens units 44E excluding the paraxial Fresnel lens unit 44N have a mode in which the individual center axis line AX2 is shifted with respect to the overall reference axis line AX1. The plurality of eccentric Fresnel lens units 44E are arrayed in an arrangement of sandwiching the paraxial Fresnel lens unit 44N from both sides. In the eccentric Fresnel lens unit 44E, both side parts sandwiching the individual center axis line AX2 are formed in an asymmetric shape. As illustrated in <FIG> and <FIG>, the curvature center CCE of each divided lens surface <NUM> belonging to the eccentric Fresnel lens unit 44E is eccentric to the same side that is an overall reference axis side AS of the individual center axis line AX2 that is close to the overall reference axis line AX1 or an opposite side OS of the individual center axis line AX2 that is away from the overall reference axis line AX1.

Here, the same side is commonly set with respect to all the divided lens surfaces 45N belonging to all the eccentric Fresnel lens units 44E. In the present embodiment, the overall reference axis side AS is adopted as the same side. Therefore, as illustrated in <FIG>, in each eccentric Fresnel lens units 44ER arranged at one side SL of the overall reference axis line AX1 in the array structure <NUM>, the curvature center CCE is offset from the respective individual center axis line AX2 toward the overall reference axis side AS, that is, toward the other side SR of the overall reference axis line AX1. As illustrated in <FIG>, in each eccentric Fresnel lens unit 44EL arranged at the other side SR of the overall reference axis line AX1 in the second lens member <NUM>, the curvature center CCE is offset from the respective individual center axis line AX2 toward the overall reference axis side AS, that is, toward the one side SL of the overall reference axis line AX1.

The curvature center CCE of each divided lens surface 45E belonging to the same eccentric Fresnel lens unit 44E is offset from the individual center axis line AX2 to the same side by a specific offset amount EA that is set every eccentric Fresnel lens units 44E, and is arranged on an eccentric axis AXE parallel to the individual center axis line AX2. The curvature center CCE is shifted in the direction along the eccentric axis AXE between the divided lens surfaces 45E by a step formed between the divided lens surfaces 45E.

The specific offset amount EA of the eccentric Fresnel lens units having a larger value of the inter-axis distance is greater than the specific offset amount of the eccentric Fresnel lens unis having a smaller value of the inter-axis distance. More preferably, the specific offset amount EA is set to be substantially proportional to the inter-axis distance AD.

Such an array structure <NUM> will be further described using a virtual base curved surface to become a base of the array structure <NUM>. The array structure <NUM> of the present embodiment is a structure based on the composite of the convex array lens surface B1p illustrated in <FIG> and the single-convex lens surface B2p illustrated in <FIG>. The convex array lens surface B1p is a base curved surface in which a plurality of small convex lens surfaces Bsp having optical axes corresponding to the individual center axis line AX2 are arranged on a straight line. The single convex lens surface B2p is configured by a single convex lens surface having an optical axis corresponding to the overall reference axis line AX1. The curvature radius of the small convex lens surface Bsp is set to be sufficiently smaller than the curvature radius of the single convex lens surface B2p. This is because a shorter focal length is usually expected to be set for the array-like lens.

As illustrated in <FIG>, a composite lens surface B3pp obtained by simply composing the convex array lens surface B1p and the single convex lens surface B2p has a shape in which the small convex lens surfaces Bsp arrayed on a straight line in the convex array lens surface B1p are re-arrayed on a curve of the single convex lens surface B2p. Each small convex lens surface Bsp is in a state in which both side parts sandwiching the optical axis specific to the small convex lens surface Bsp are formed in an asymmetric shape by lying along the single convex lens surface B2p. In each small convex lens surface Bsp, the curvature center is eccentric toward the optical axis side of the original single convex lens surface B2p with respect to the respective optical axis.

However, in the composite lens surface B3pp, since the plurality of small convex lens surfaces Bsp having a short focal length move back and forth in the direction along the optical axis, the focal positions of the plurality of small convex lens surfaces Bsp also move back and forth in the direction along the optical axis. If a lens member in which the composite lens surface B3pp is appeared as it is adopted with respect to the planar light source arrangement surface LP, the focal position of each of the small convex lens surfaces Bsp has a non-uniform positional relationship with respect to the light source arrangement surface LP. Therefore, the local light collecting function of the illumination light expected on each of the small convex lens surfaces Bsp of the original convex array lens surface B1p cannot be uniformly exhibited on a light receiving surface <NUM> and a display screen <NUM> of the image member <NUM>.

Therefore, in the present embodiment, as illustrated in <FIG>, the entire composite lens surface B3pp is formed into a Fresnel lens to form the macroscopically flat-plate shaped second lens member <NUM> described above. That is, the continuous composite lens surface B3pp appears in the array structure <NUM> in a mode in which its partial shape is copied and divided into the divided lens surfaces <NUM>. Each small convex lens surface Bsp in the base curved surface (synthetic lens surface B3pp) corresponds to each Fresnel lens unit <NUM> of the array structure <NUM>.

Each of the Fresnel lens units <NUM> has a configuration in which each of the divided lens surfaces <NUM> is arranged along a reference plane RP commonly set among the Fresnel lens units <NUM> so to as lie along the parallel direction of the light source arrangement surface LP. Since each focal point that can be defined in each Fresnel lens unit <NUM> is adjusted in the direction along the overall reference axis line AX1, the local light collecting function of the illumination light can be more uniformly realized in accordance with the planar light source arrangement surface LP.

Then, each small convex lens surface Bsp is extracted in a mode of being divided into each divided lens surface <NUM> in each Fresnel lens unit <NUM> while maintaining the above-described asymmetric shape. As a result, the overall light collecting function expected on the original single convex lens surface B2p can be simultaneously exhibited.

As illustrated in <FIG>, the diffusion plate <NUM> is disposed between the second lens member <NUM> and the image member <NUM> on the optical path between the light source unit <NUM> and the image member <NUM>. The diffusion plate <NUM> is formed in a flat plate shape by dispersing diffusion particles such as microbeads in a base material made of, for example, a translucent synthetic resin. For example, the diffusion plate <NUM> is disposed along the parallel direction of the image member <NUM> so as to keep a constant spacing from the light receiving surface <NUM> of the image member <NUM>. In other words, the diffusion plate <NUM> is disposed to be inclined with respect to the light source arrangement surface LP. The diffusion plate <NUM> appropriately diffuses the illumination light subjected to the local light collecting action immediately before the image member <NUM>.

The image member <NUM> is formed into a panel shape (flat plate shape). The image member <NUM> is a transmissive TFT liquid crystal panel using a thin film transistor (Thin Film Transistor, TFT), and is, for example, an active matrix liquid crystal panel in which a plurality of liquid crystal pixels arrayed in a two-dimensional array are formed.

The image member <NUM> is formed with an optical opening that is formed to be able to transmit light and is optically opened. The optical opening is formed in a square shape having the longitudinal direction LD and the short direction SD, that is, a rectangular shape in a mode in which the liquid crystal pixels are arranged as described above.

A surface facing the light guide unit <NUM> side in the optical opening is a display screen <NUM> that displays an image. On the other hand, a surface facing the light source unit <NUM> side in the optical opening is a light receiving surface <NUM> that receives the illumination light.

The entire surface of the optical opening is closed by stacking a pair of polarizing plates, a liquid crystal layer sandwiched between the pair of polarizing plates, and the like. Each polarizing plate has a transmission axis and an absorption axis orthogonal to each other. Each polarizing plate has a property of transmitting light polarized in the transmission axis direction and absorbing light polarized in the absorption axis direction. The pair of polarizing plates are arranged to be respectively orthogonal to the transmission axis. The liquid crystal layer can rotate the polarization direction of the light entering the liquid crystal layer according to the applied voltage by applying the voltage for every liquid crystal pixel. In this way, the image member <NUM> can change the ratio of light transmitting through the polarizing plate on the light guide unit <NUM> side by the rotation of the polarization direction, that is, the transmittance for every liquid crystal pixel.

Therefore, the image member <NUM> can form an image on the display screen <NUM> by shielding at least a part of the illumination light emitted from the light source unit <NUM> and received by the light receiving surface <NUM>. Adjacent liquid crystal pixels are provided with color filters of different colors (e.g., red, green and blue), and various colors are reproduced by a combination thereof.

In the present embodiment, the display screen <NUM> and the light receiving surface <NUM> of the image member <NUM> are arranged to be inclined with respect to the surface of the light source circuit substrate <NUM>, in other words, the light source arrangement surface LP. Specifically, the image member <NUM> is arranged in an inclined posture in which the display screen <NUM> and the light receiving surface <NUM> are rotated by an inclination angle of about <NUM> to <NUM> degrees around a virtual rotation axis that lies along the longitudinal direction LD of the display screen <NUM> and passes through the center of the display screen <NUM> from a virtual parallel posture that lies along the parallel direction of the light source arrangement surface LP. Therefore, in the present embodiment, the longitudinal corresponding direction RLD substantially coincides with the longitudinal direction LD, and the short corresponding direction RSD forms the same angle as this inclination angle with the short direction SD.

The operation and effect according to the first embodiment described above will be described again below.

According to the first embodiment, the second lens member <NUM> serving as a Fresnel lens array having the array structure <NUM> in which the plurality of Fresnel lens units <NUM> are arrayed is provided between the illumination light source <NUM> and the image member <NUM>. Each Fresnel lens unit <NUM> dividedly forms a plurality of divided lens surfaces <NUM> having a common curved shape in its individual area IA. A local refraction action as if each individual center axis line AX2 is the optical axis is exhibited by the common curved shape while enlargement of the build of the lens member <NUM> due to bulging out of the lens surface by division is suppressed.

The Fresnel lens unit <NUM> includes a plurality of eccentric Fresnel lens units 44E. Each eccentric Fresnel lens units 44E has, as an eccentricity amount eccentric to the same side (e.g., the overall reference axis side AS), an offset amount EA that gradually increases as the inter-axis distance AD between the individual center axis line AX2 and the overall reference axis line AX1 increases. That is, since the illumination light passing through the position away from the overall reference axis line AX1 receives a larger deflection action, the overall refracting function as if the overall reference axis line AX1 is the optical axis can be further exhibited by the assembly of the plurality of eccentric Fresnel lens units 44E.

Since the same array structure <NUM> exhibits both the local refracting function and the overall refracting function, an increase in the number of components is suppressed. As described above, the build of the HUD <NUM> serving as the virtual image display device can be suppressed while achieving high illumination performance.

According to the first embodiment, the Fresnel lens unit <NUM> further includes one paraxial Fresnel lens unit 44N. The paraxial Fresnel lens unit 44N coincides the individual center axis line AX2 with the overall reference axis line AX1, and locates the curvature center CCN on the individual center axis line AX2. The paraxial portion in the overall refracting function based on the overall reference axis line AX1 appears as a paraxial Fresnel lens unit 44N. When the paraxial portion exhibits a refracting function in a favorable state, the generated amount of aberration outside a lens axis is reduced, and the illumination performance is further enhanced.

Furthermore, according to the first embodiment, the paraxial Fresnel lens unit 44N has a symmetric shape with the individual center axis line AX2 as a symmetry axis, and each eccentric Fresnel lens unit 44E has an asymmetric shape with respect to the corresponding individual center axis line AX2. The overall refracting function having the overall reference axis line AX1 as the pseudo optical axis can be easily realized by combining the Fresnel lens unit 44N having a symmetric shape and the Fresnel lens unit 44E having an asymmetric shape.

Furthermore, according to the first embodiment, each Fresnel lens units <NUM> has a configuration in which the divided lens surface <NUM> is arranged along the reference plane RP commonly set among the Fresnel lens units <NUM> so to as lie along the parallel direction of the light source arrangement surface LP. Then, the positional relationship between the planar light source arrangement surface LP and the focal position of each Fresnel lens unit <NUM> can be made uniform over the entire illumination system. Therefore, a more uniform illumination to the image member <NUM> can be realized.

According to the first embodiment, the common curved shape of each Fresnel lens unit <NUM> is a convex surface shape curved convexly, and the same side is the overall reference axis side AS. Such an array structure <NUM> can realize a local light collecting function corresponding to each individual center axis line AX2 and an overall light collecting function corresponding to the overall reference axis line AX1. The local light collecting function enhances the efficiency of illumination from the illumination light source <NUM> to the image member <NUM>, and raises the luminance of the virtual image VRI. Since the illumination light is concentrated on the viewing region EB by the overall light collecting function, the luminance of the virtual image VRI visually recognized from the viewing region EB can be further increased. As described above, high illumination performance can be achieved with a configuration in which the increase in build due to the increase in the number of components is suppressed.

As illustrated in <FIG> and <FIG>, the second embodiment is a modification of the first embodiment. The second embodiment will be described focusing on differences from the first embodiment.

An array structure <NUM> in the second embodiment is a structure based on the composite of the convex array lens surface B1p illustrated in <FIG> and the single-concave lens surface B2m illustrated in <FIG>. The convex array lens surface B1p is similar to that of the first embodiment. The single concave lens surface B2m is configured by a single concave lens surface having an optical axis corresponding to the overall reference axis line AX1.

As illustrated in <FIG>, a composite lens surface B3pm obtained by simply composing the convex array lens surface B1p and the single concave lens surface B2m has a shape in which the small convex lens surfaces Bsp arrayed on a straight line in the convex array lens surface B1p are re-arrayed in a curve of the single concave lens surface B2m. Each small convex lens surface Bsp is in a state in which both side parts sandwiching the optical axis of the small convex lens surface Bsp are formed in an asymmetric shape by lying along the single concave lens surface B2m. In each small convex lens surface Bsp, the curvature center is eccentric toward the side opposite to the optical axis side of the original single concave lens surface B2m with respect to the respective optical axis.

The entire composite lens surface B3pm described above is formed into a Fresnel lens as illustrated in <FIG>, thereby forming an array structure <NUM> in which a plurality of Fresnel lens units <NUM> having a plurality of divided lens surfaces <NUM> are arranged in the second embodiment.

As illustrated in <FIG>, in the array structure <NUM>, the paraxial Fresnel lens unit 44N has a structure similar to that of the first embodiment.

As illustrated in <FIG> and <FIG>, the curvature center CCE of each divided lens surface 245E belonging to the eccentric Fresnel lens unit 244E is eccentric to the same side of the overall reference axis side AS and the opposite side OS thereof with respect to the individual center axis line AX2.

However, the second embodiment is different from the first embodiment in that the opposite side OS to the overall reference axis line AX1 is adopted as the same side. In each eccentric Fresnel lens unit 244EL arranged at the one side SL of the overall reference axis line AX1 in the array structure <NUM>, the curvature center CCE is offset from the respective individual center axis line AX2 toward the opposite side OS opposite to the overall reference axis line AX1, that is, toward the side away from the other side SR of the overall reference axis line AX1. In each eccentric Fresnel lens unit 244ER arranged at the other side SR of the overall reference axis line AX1 in the array structure <NUM>, the curvature center CCE is offset from the respective individual center axis line AX2 toward the opposite side OS opposite to the overall reference axis line AX1, that is, toward the side away from the one side SL of the overall reference axis line AX1.

The offset amount EA specific to each eccentric Fresnel lens unit 244E is set so as to gradually increase as the inter-axis distance AD increases. More preferably, the specific offset amount EA is set to be substantially proportional to the inter-axis distance AD.

According to the second embodiment described above, the array structure <NUM> can realize a local light collecting function corresponding to each individual center axis line AX2 and an overall diverging function corresponding to the overall reference axis line AX1. The local light collecting function enhances the efficiency of illumination from the illumination light source <NUM> to the image member <NUM>, and raises the luminance of the virtual image VRI. Since the illumination light can widely reach the viewing region EB by the overall diverging function, luminance unevenness of the virtual image VRI felt by the viewer when the head is moved can be suppressed. As described above, high illumination performance can be achieved with a configuration in which the increase in build due to the increase in the number of components is suppressed.

Although a plurality of embodiments have been described above, the present disclosure is not to be construed as being limited to these embodiments, and can be applied to various embodiments and combinations within a scope covered by the claims.

Specifically, as a first modification, the plurality of Fresnel lens units <NUM>, <NUM> in the array structure <NUM>, <NUM> may be arrayed along the longitudinal corresponding direction RLD. In addition, the convex array lens surface B1p in the base curved surface can be expanded to a shape in which the small convex lens surfaces Bsp are two-dimensionally arrayed. In this case, the plurality of Fresnel lens units <NUM>, <NUM> in the array structure <NUM>, <NUM> may be two-dimensionally arrayed.

As a second modification, the plurality of Fresnel lens units <NUM>, <NUM> may be arranged concentrically centered on the overall reference axis line AX1 to exhibit a refracting function in both the short corresponding direction RSD and the longitudinal corresponding direction RLD. The concentric circle herein may be a perfect circle or an ellipse as long as it is a circle centered on the overall reference axis line AX1.

As a third modification, the paraxial Fresnel lens unit 44N may not be provided. For example, when an even number of Fresnel lens units <NUM>, <NUM> are provided and the overall reference axis line AX1 is set so as to pass through the boundary between the Fresnel lens units <NUM>, <NUM> adjacent to each other at the center, all the Fresnel lens units <NUM>, <NUM> correspond to the eccentric Fresnel lens units 44E, 244E.

As a fourth modification, the array structure <NUM>, <NUM> may be formed on the incident side lens surface <NUM>.

As a fifth modification, the array structure <NUM>, <NUM> may be a structure based on composite of the concave array lens surface and the single convex lens surface B2p or the single concave lens surface B2m. In this case, the curved shape common to the plurality of divided lens surfaces 45N, 45E, and 245E is, for example, a concave surface shape curved to a concave shape such as a concave cylindrical surface or a concave spherical surface. Then, a diverging function is exhibited as a local refracting function.

As a sixth modification, the curved shape common to the plurality of divided lens surfaces 45N and 45E may be made aspherical by composing the correcting shapes by the aspherical coefficient. In this case, the curvature center CCN of the divided lens surface 45N may deviate from the overall reference axis line AX1 and the individual center axis line AX2. The curvature centers CCE of the divided lens surfaces 45E, 245E may not be located on the same eccentric axis AXE. When the eccentricity amount differs between the divided lens surfaces 45E, 245E belonging to the same Fresnel lens unit 44E and 244E, the offset amount EA specific to the Fresnel lens units 44E, 244E may be defined using the average value of the individual eccentricity amount with respect to the divided lens surfaces 45E, 245E as a representative value.

As a seventh modification, each illumination light source <NUM> forming a pair facing each convex lens element <NUM> may have a configuration that mainly includes an assembly of a plurality of light emitting diodes instead of one light emitting diode. The assembly may be configured to be regarded as a planar light source by assembling the point light sources.

As an eighth modification, the array pitch of the convex lens elements <NUM> in the first lens member <NUM> may be set to be larger than the array pitch of the illumination light sources <NUM>. The convex lens element <NUM> on the outer side may be slightly shifted with respect to the paired illumination light source <NUM>.

As a ninth modification, a configuration in which only one illumination light source <NUM> is provided may be adopted. In this case, one illumination light source <NUM> may be a planar light source or regarded as a planar light source to constitute the planar light source arrangement surface LP.

In a tenth modification, as the lens member disposed between the light source unit <NUM> and the image member <NUM>, the convex lens array such as the first lens member <NUM> may not be provided and only the Fresnel lens array such as the second lens member <NUM> may be provided. In this case, the plurality of Fresnel lens units <NUM>, <NUM> in the array structure <NUM>, <NUM> of the Fresnel lens array may be provided as many as the illumination light sources <NUM>, and each Fresnel lens unit <NUM>, <NUM> may be paired with the individually corresponding illumination light source <NUM>. In this case, the individual region ID of each Fresnel lens unit <NUM>, <NUM> may be arranged to face the corresponding illumination light source <NUM>.

As an eleventh modification, as a lens member disposed between the light source unit <NUM> and the image member <NUM>, a lens member different from the first lens member <NUM> and the second lens member <NUM> may be added.

As a twelfth modification, the diffusion plate <NUM> may be disposed to be inclined with respect to image member <NUM>. For example, the diffusion plate <NUM> may be disposed along a parallel direction of the light source arrangement surface LP and the reference plane RP. Further, the diffusion plate <NUM> itself may not be provided.

As a thirteenth modification, the image member <NUM> may be arranged in a parallel posture along the parallel direction of the light source arrangement surface LP and the reference plane RP.

As a fourteenth modification, the light guide unit <NUM> may have a configuration including a convex surface mirror having a reflecting surface of convex surface shape instead of the plane mirror <NUM>. The light guide unit <NUM> may have a configuration including a lens, a prism, a holographic optical element, and the like.

Claim 1:
A virtual image display device that displays a virtual image by projecting light of an image onto a projection portion (3a), the virtual image display device comprising:
a light source (<NUM>) that emits light;
an image member (<NUM>) that forms the image by partially shielding the light; and
a Fresnel lens array (<NUM>) arranged in an optical path between the light source and the image member and having an array structure (<NUM>, <NUM>) in which a plurality of Fresnel lens units (<NUM>, <NUM>) are arrayed, each of the plurality of Fresnel lens units having an individual area (IA), wherein
an overall reference axis line (AX1) is defined as a virtual center line of the array structure that passes through the array structure,
an individual center axis line (AX2) is defined as a center line of the individual area that is parallel to the overall reference axis line and passes through the individual area,
each of the plurality of Fresnel lens units includes a plurality of divided lens surfaces (<NUM>, <NUM>), the plurality of divided lens surfaces curving convexly or the plurality of divided lens surfaces curving concavely,
the array structure includes a plurality of eccentric Fresnel lens units (44E, 244E) as the plurality of Fresnel lens units,
the plurality of divided lens surfaces (45E, 245E) of each of the plurality of eccentric Fresnel lens units have curvature centers (CC, CCE) that are offset from the individual center axis line toward a same side of the individual center axis line, the same side being an overall reference axis side (AS) of the individual center axis line that is close to the overall reference axis line or an opposite side (OS) of the individual center axis line that is away from the overall reference axis line,
the curvature center (CCE) of each divided lens surface (45E) belonging to the same eccentric Fresnel lens unit (44E) is offset from the individual center axis line (AX2) by a specific offset amount (EA) that is set every eccentric Fresnel lens units (44E),
an inter-axis distance (AD) is defined as a distance between the overall reference axis line and the individual center axis line, and
the specific offset amount (EA) of the eccentric Fresnel lens units having a larger value of the inter-axis distance (AD) is greater than the specific offset amount of the eccentric Fresnel lens units having a smaller value of the inter-axis distance (EA).