Patent Publication Number: US-2022221717-A1

Title: Projection device and head-up display

Description:
TECHNICAL FIELD 
     The present disclosure relates to a projection device mounted on a vehicle and a head-up display including the projection device. 
     BACKGROUND ART 
     In recent years, a head-up display has been developed that displays, for a passenger of a vehicle, an image including information about the vehicle by, for example, a virtual image. Such a head-up display has a problem of reducing luminance unevenness of a virtual image to be displayed. 
     Under these circumstances, Patent Literature 1 discloses a head-up display in which a plurality of light source elements, a first lens, a second lens, a diffusion member, and a spatial modulation element are arranged in this order, and the first lens changes an optical path of light emitted from each light source element such that the light emitted from each light source element reaches the same region on an incident surface of the spatial modulation element. 
     In addition, a head-up display mounted on a vehicle is required to be made compact in order to avoid interference with other in-vehicle components. Under these circumstances, Patent Literature 2 discloses a vehicle display device in which a reflector having a predetermined opening angle with a liquid crystal display element is arranged on a back surface side of the liquid crystal display element so as to face the liquid crystal display element, and a light source is arranged in an opening portion having an opening angle with the reflector and the liquid crystal display element. 
     Meanwhile, in a head-up display mounted on a vehicle, them is an increasing need to increase a size of a virtual image. For this purpose, it is necessary to increase a size of a spatial modulation element. Consequently, it is also necessary to increase a thickness of a lens provided between the spatial modulation element and a light source while ensuring an optical path length between the spatial modulation element and the light source. As a result, in a backlight unit from a back surface of the spatial modulation element to the light source, an amount of protrusion in a normal direction of the spatial modulation element increases, and mountability of the head-up display on a vehicle deteriorates. 
     In Patent Literature 1, since the plurality of light sources, the first lens, the second lens, the diffusion member, and the spatial modulation element are arranged in series in this order, when the size of the spatial modulation element is increased, the amount of the backlight unit protruding in the normal direction of the spatial modulation element is increased. Therefore, mountability of the head-up display of Patent Literature 1 on a vehicle deteriorates. 
     In Patent Literature 2, since the reflector is merely arranged to face the liquid crystal display at a predetermined angle, luminance unevenness cannot be suppressed. 
     CITATION LIST 
     Patent Literatures 
     
         
         Patent Literature 1: Japanese Patent Application Laid-Open No. 2016-126314 
         Patent Literature 2: Japanese Patent No. 6078798 
       
    
     SUMMARY OF INVENTION 
     The present disclosure has been made to solve the above problems, and an object of the present disclosure is to improve mountability on a vehicle while suppressing luminance unevenness of an image emitted by a spatial modulation element. 
     A projection device according to one aspect of the present disclosure is a projection device mounted on a vehicle, the projection device including: a plurality of light sources arranged in a first direction; a spatial modulation element that modulates incident light into image information and emits the image information; a lens that changes an optical path of light emitted from each of the plurality of light sources such that the light emitted from each light source reaches substantially the same region of an incident surface of the spatial modulation element; and a first reflective optical member that deflects the light emitted from the lens toward the spatial modulation element, the first reflective optical member having a shape that deflects light emitted from the lens so as to be incident on an arbitrary point on the incident surface of the spatial modulation element at a predetermined reference incident angle. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating an example of a configuration of a head-up display according to an embodiment. 
         FIG. 2  is a diagram illustrating an example of a configuration of a projection device. 
         FIG. 3  is a perspective view of the projection device illustrated in  FIG. 2 . 
         FIG. 4  is a diagram illustrating an example of a casing of a head-up display according to a modification of the present disclosure. 
         FIG. 5  is a diagram illustrating an example of arrangement of a plurality of light sources according to the modification of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are examples embodying the present invention and do not limit the technical scope of the present invention. 
     Hereinafter, the embodiments will be described with reference to the accompanying drawings.  FIG. 1  is a diagram illustrating an example of a configuration of a head-up display  10  according to the embodiment. The head-up display  10  is mounted on a vehicle  100 . The vehicle  100  is, for example, a moving body such as a four-wheeled automobile. However, this is an example, and the vehicle  100  may be a railway vehicle, a motorcycle, an aircraft, a helicopter, a ship, and various devices that carry persons. 
     The vehicle  100  includes a windshield  14 . The windshield  14  is, for example, a windshield provided in front of a cockpit of the vehicle  100 . The head-up display  10  includes a projection device  11 , a reflective optical member  12  (an example of a second reflective optical member), and a casing  13 . 
     The head-up display  10  is a device that projects, onto the windshield  14 , an image for allowing an observer  101  to visually recognize a virtual image  15 . 
     The projection device  11  includes a backlight unit  20  and a spatial modulation element  24 . The backlight unit  20  illuminates the spatial modulation element  24 . The spatial modulation element  24  is, for example, a liquid crystal panel. The spatial modulation element  24  modulates light emitted from the backlight unit  20  according to a video signal input from a display control circuit (not illustrated). The modulated light is emitted from the spatial modulation element  24  as transmitted light. 
     The spatial modulation element  24  displays an image indicating a state of the vehicle  100 , for example, an image indicating a speed meter or an image indicating a speed of the vehicle  100 . The transmitted light which has been emitted from the spatial modulation element  24  is guided into an eye box  102  of the observer  101  via the reflective optical member  12  and the windshield  14 . Consequently, the observer  101  visually recognizes the virtual image  15 . The virtual image  15  displays the state of the vehicle  100  such as speed. Therefore, the observer  101  can check the state of the vehicle  100  through the virtual image  15 . The eye box  102  is a region where the observer  101  can visually recognize the virtual image  15  without omission. 
     The reflective optical member  12  includes a first mirror  121  and a second mirror  122 . The first mirror  121  reflects light emitted from the spatial modulation element  24  toward the second mirror  122 . The second mirror  122  reflects the light from the first mirror  121  toward the windshield  14 . A reflective surface of the second mirror  122  has a concave shape. Although the reflective optical member  12  includes two mirrors of the first mirror  121  and the second mirror  122 , this is an example, and the reflective optical member may include one mirror or three or more mirrors. In addition, a refractive optical system such as a lens may be further arranged on an optical path of the reflective optical member  12 . 
     The casing  13  houses the projection device  11  and the reflective optical member  12 . The casing  13  is, for example, a substantially rectangular parallelepiped. The casing  13  has, on an upper surface thereof, an opening portion  13   a  through which light from the reflective optical member  12  is emitted. The opening portion  13   a  may be provided with a transparent cover. 
       FIG. 2  is a diagram illustrating an example of a configuration of the projection device  11 . The projection device  11  includes a plurality of light sources  21  (see  FIG. 3 ), a lens  22 , a reflective optical member  23  (an example of a first reflective optical member), and the spatial modulation element  24 . A diffusion member may be further arranged on an incident surface  22   a  side of the spatial modulation element  24 , so that light distribution characteristics of lights from the plurality of light sources  21  can be smoothed. The plurality of light sources  21 , the lens  22 , and the reflective optical member  23  constitute the backlight unit  20 . The spatial modulation element  24  includes an incident surface  24   a  which light enters and an emission surface  24   b  from which light is emitted. The incident surface  24   a  and the emission surface  24   b  have the same shape. As illustrated in  FIG. 3 , the incident surface  24   a  and the emission surface  24   b  have, for example, a rectangular shape including a short side  241  and a long side  242 . 
     Note that in the following description, a three-dimensional orthogonal coordinate system including three axes of an X axis, a Y axis, and a Z axis orthogonal to each other is set in the drawings. The X axis is parallel to the short side  241  of the spatial modulation element  24 . The Y axis is parallel to the long side  242  of the spatial modulation element  24 . The Z axis is parallel to a normal line of the spatial modulation element  24 . Note that a Y axis direction (a longitudinal direction) is an example of a first direction. A Z axis direction is an example of a second direction orthogonal to the first direction. 
       FIG. 3  is a perspective view of the projection device  11  illustrated in  FIG. 2 . As illustrated in  FIG. 3 , the plurality of light sources  21  are arranged in a line in the Y axis direction, for example, at fixed intervals. However, this is an example, and the light sources may be arranged at unequal intervals. Thus, luminance unevenness can be suppressed. Each of the plurality of light sources  21  includes a light emission surface  21   a . The plurality of light sources  21  are arranged such that a normal line of the emission surface  21   a  is parallel to the X axis. The plurality of light sources  21  are, for example, light emitting diodes (LED). However, this is an example, and the plurality of light sources  21  may be, for example, laser diodes or organic light emitting diodes. Note that although in  FIG. 3 , four light sources  21  are illustrated as the plurality of light sources  21 , this is merely an example, and the number of the plurality of light sources  21  can take any value of two or more. 
     Furthermore, the plurality of light sources  21  are arranged such that the normal line of the emission surface  21   a  intersects the normal line of the spatial modulation element  24 . In  FIG. 2 , the normal line of the emission surface  21   a  faces an X axis direction, and the normal line of the spatial modulation element  24  faces the Z axis direction. Therefore, the normal line of the spatial modulation element  24  and the normal line of the emission surface  21   a  are orthogonal to each other, this is an example. For example, angles of both the normal lines can be any angle as long as it is an angle other than 180 degrees, and can be, for example, an angle of 10 degrees or more and 90 degrees or less, an angle of 20 degrees or more and 80 degrees or less, and an angle of 30 degrees or more and 70 degrees or less. 
     The lens  22  changes an optical path of light emitted from each of the plurality of light sources  21  such that the light emitted from each light source  21  reaches substantially the same region of the incident surface  24   a  of the spatial modulation element  24 . Substantially the same region is intended to allow a slight deviation for a region reached by light emitted from each of the plurality of light sources  21 . Specifically, the lens  22  is arranged close to the plurality of light sources  21 . The lens  22  has a longitudinal direction parallel to the Y axis direction. The lens  22  includes the incident surface  22   a  which lights emitted from the plurality of light sources  21  enter. The lens  22  includes an emission surface  22   b  that deflects diverging lights of the plurality of light sources  21  in the Z axis direction into substantially parallel lights and emits the substantially parallel lights. The incident surface  22   a  faces the emission surfaces  21   a  of the plurality of light sources  21 . One lens  22  is arranged for the plurality of light sources  21 . However, this is an example, and two, or three or more lenses may be arranged for the plurality of light sources  21 . 
     At least one of the incident surface  22   a  and the emission surface  22   b  of the lens  22  has a convex shape in order to give the lens  22  positive refractive power. The convex shape of at least one of the incident surface  22   a  and the emission surface  22   b  of the lens  22  is rotationally symmetric with respect to an optical axis. However, this is an example, and at least one of the incident surface  22   a  and the emission surface  22   b  of the lens  22  may have a toroidal shape having different curvatures in the Y axis direction and the Z axis direction or a free-form surface shape. A total internal reflection (TIR) lens can be also used as the incident surface  22   a  of the lens  22 . This enables the light from the light source  21  to be efficiently emitted to the reflective optical member  23 , resulting in improving light use efficiency. In the present embodiment, the lens  22  is a plano-convex lens in which only the emission surface  22   b  has a convex shape. 
     The emission surface  22   b  of the lens  22  has a convex shape with an aspherical form in which curvatures in the Y axis direction and the Z axis direction are different from each other. Specifically, the emission surface  22   b  has a curvature in the Z axis direction larger than a curvature in the Y axis direction. The reason why the curvature in the Z axis direction is made larger than the curvature in the Y axis direction is to narrow down a light beam and guide a parallel light toward the short side  241  of the spatial modulation element  24 . On the other hand, the reason why the curvature in the Y axis direction is made smaller than the curvature in the Z axis direction is that the light from each light source  21  is guided over the entire long side  242 . Therefore, in the spatial modulation element  24  having the Y axis direction as a longitudinal direction and the X axis direction as a lateral direction, the lens  22  is allowed to constitute a lens suitable for light emitted from each of the plurality of light sources  21  to reach the same region of the incident surface  24   a  of the spatial modulation element  24 . 
     Furthermore, the emission surface  22   b  has a shape in the Y axis direction, for example, in which the curvature decreases from the center to the edge so that an illuminance distribution, of the light emitted from the plurality of light sources  21 , on the incident surface  24   a  of the spatial modulation element  24  becomes uniform. However, a free-form surface shape may be provided in order to reduce the luminance unevenness, and the shape is not limited thereto. In addition, the emission surface  22   b  has a shape in the Z axis direction, for example, in which the curvature decreases from the center to the edge so that the illuminance distribution on the incident surface  24   a  becomes uniform. However, a free-form surface shape may be provided in order to reduce the luminance unevenness, and the shape is not limited thereto. 
     The lens  22  is made of a transparent material having a predetermined refractive index. The refractive index of the transparent material is, for example, about 1.4 to 1.6. As the transparent material, a resin such as an epoxy resin, a silicon resin, an acrylic resin, or polycarbonate can be used. In the present embodiment, the lens  22  is made from, for example, polycarbonate in consideration of heat resistance. 
     Reference is made to  FIG. 2 . The reflective optical member  23  includes a reflective surface that deflects the light emitted from the lens  22  toward the spatial modulation element  24 . The reflective optical member  23  has a shape that deflects light emitted from the lens  22  so as to be incident on an arbitrary position P on the incident surface  24   a  of the spatial modulation element  24  at a predetermined reference incident angle. Specifically, the reflective optical member  23  has a free-form surface shape. The arbitrary position P represents a plurality of positions on the incident surface  24   a . The reflective optical member  23  is, for example, a mirror. 
     In the head-up display  10 , the position, the shape, and the like of the reflective optical member  12  are determined such that the virtual image  15  of a target size is displayed at a target display position, and a reference incident angle at each of the plurality of positions on the incident surface  24   a  of the spatial modulation element  24  is determined based on the determined position and shape of the reflective optical member  12 . Therefore, a shape, of the reflective optical member  23 , at a position P 1  as a position where a light beam L 1  is deflected toward the position P, has a shape that causes the light beam L 1  to be incident on the position P at the reference incident angle. 
     The reference incident angle includes a first component viewed from the long side  242  of the spatial modulation element  24 , i.e., from the X axis direction, and a second component viewed from the short side  241 , i.e., from the Y axis direction. Therefore, the shape at the position P 1  is a shape which causes the light beam L 1  to enter the position P with the first component and the second component of the reference incident angle. Accordingly, the reflective optical member  23  has a free-form surface shape in which each position P 1  causes the light beam L 1  to be incident on the corresponding position P on the incident surface  24   a  with the first component and the second component of the reference incident angle. As illustrated in  FIG. 3 , at the position P 1 , a curvature C 1  obtained when the reflective optical member  23  is cut along an X-Y plane is, for example, larger than a curvature C 2  obtained when the reflective optical member  23  is cut along a Z-X plane. Accordingly, as a whole, a degree of inclination of the reflective optical member  23  when viewed from the Z axis direction is larger than a degree of inclination when viewed from the Y axis direction. 
     Although the reflective optical member  12  has been here described as having a free-form surface shape, the present disclosure is not limited thereto. As a result of determining the shape at each position P 1  of the reflective optical member  23  such that light enters the position P at the reference incident angle, the reflective optical member  12  may have a flat plate shape or a spherical shape. In this case, the reflective optical member  23  can have a planar shape or a spherical shape. 
     As described above, according to the present embodiment, the reflective optical member  23  deflects the light beam emitted from the lens  22  and guides the light beam to the spatial modulation element  24 . This brings the plurality of light sources  21  to be arranged such that the normal line of the emission surface  21   a  intersects the normal line of the spatial modulation element  24 . As a result, when the size of the spatial modulation element  24  is increased, an amount by which the backlight unit  20  protrudes in the normal direction of the spatial modulation element  24  can be suppressed. As a result, the present embodiment enables improvement of mountability of the head-up display  10  on the vehicle  100 . 
     In addition, the lens  22  changes an optical path of light emitted from each of the plurality of light sources  21  such that the light emitted from each light source reaches the same region of the incident surface  24   a  of the spatial modulation element  24 . Furthermore, the reflective optical member  23  has a shape that deflects light emitted from the lens  22  so as to be incident on an arbitrary point P on the incident surface of the spatial modulation element  24  at a reference incident angle. Therefore, the present embodiment enables luminance unevenness of an image emitted by the spatial modulation element  24  to be suppressed. 
     Further, as illustrated in  FIG. 3 , the plurality of light sources  21  are arranged in parallel with the long side  242  of the spatial modulation element  24 . Therefore, the size of the projection device  11  can be reduced as a whole as compared with a case where the plurality of light sources  21  are arranged in parallel with the short side  241  of the spatial modulation element  24 . This enables further improvement of mountability of the head-up display  10  on the vehicle  100 . 
     Note that the present disclosure is allowed to adopt the following modification. 
     (1)  FIG. 4  is a diagram illustrating an example of the casing  13  of the head-up display  10  according to the modification of the present disclosure. In  FIG. 4 , the casing  13  includes an attachment portion  131  to which the projection device  11  is attached. The attachment portion  131  is a bottomed hole extending obliquely from an opening portion  133  in a bottom surface  132  of the casing  13 . A cross section of the attachment portion  131  has the same shape as a cross section of the projection device. Therefore, the projection device  11  is fitted into the attachment portion  131  by insertion into the casing  13  in an arrow direction. A bottom surface  134  of the attachment portion  131  is open. Accordingly, the light emitted from the spatial modulation element  24  is taken into the casing  13  and guided to the windshield  14  via the reflective optical member  12  and an opening portion  13   a  illustrated in  FIG. 1 . 
     (2) Although in the modification (1), the spatial modulation element  24  is provided inside a casing  11   a  of the projection device  11 , this is an example. The spatial modulation element  24  may be provided on the bottom surface  134  of the attachment portion  131 . 
     (3) Although in the example of  FIG. 3 , the plurality of light sources  21  are arranged in a line in the Y axis direction, this is an example.  FIG. 5  is a diagram illustrating an example of arrangement of the plurality of light sources  21  according to the modification of the present disclosure. As illustrated in  FIG. 5 , the plurality of light sources  21  may be arranged in a matrix of predetermined rows×predetermined columns in the Y axis direction and the Z axis direction. As a result, an image having sufficient luminance can be obtained in a case where the spatial modulation element  24  is enlarged. 
     (4) Although in the example of  FIG. 1 , the head-up display  10  displays the virtual image  15 , the present disclosure is not limited thereto, and an image may be displayed on a part (for example, a console box or the like) of the vehicle  100 . 
     A projection device according to one aspect of the present disclosure is a projection device mounted on a vehicle, the projection device including: a plurality of light sources arranged in a first direction; a spatial modulation element that modulates incident light into image information and emits the image information; a lens that changes an optical path of light emitted from each of the plurality of light sources such that the light emitted from each light source reaches substantially the same region of an incident surface of the spatial modulation element; and a first reflective optical member that deflects the light emitted from the lens toward the spatial modulation element, the first reflective optical member having a shape that deflects light emitted from the lens so as to be incident on an arbitrary point on the incident surface of the spatial modulation element at a predetermined reference incident angle. 
     According to this configuration, the first reflective optical member deflects light emitted from the lens and guides the light to the spatial modulation element. Accordingly, this configuration allows the plurality of light sources to be arranged such that a normal line of an emission surface intersects a normal line of the spatial modulation element. As a result, when the size of the spatial modulation element is increased, this configuration enables suppression of an amount by which a backlight unit from the light source to the spatial modulation element protrudes in the normal direction of the spatial modulation element. As a result, this configuration enables improvement of mountability of the head-up display on a vehicle. 
     In addition, the lens changes the optical path of the light emitted from each of the plurality of light sources such that the light emitted from each light source reaches the same region of the incident surface of the spatial modulation element. Furthermore, the first reflective optical member has a shape that deflects light emitted from the lens so as to be incident on an arbitrary point on the incident surface of the spatial modulation element at the reference incident angle. Therefore, this configuration enables luminance unevenness of an image emitted by the spatial modulation element to be suppressed. 
     In the above aspect, the first reflective optical member may have a free-form surface shape. 
     According to this configuration, since the first reflective optical member has the free-form surface shape, it is possible to easily make light emitted from the lens be incident on an arbitrary point on the incident surface of the spatial modulation element at the reference incident angle. 
     In the above aspect, the plurality of light sources may be arranged such that a normal line of an emission surface intersects a normal line of the spatial modulation element. 
     According to this configuration, since the plurality of light sources are arranged such that the normal line of the emission surface intersects the normal line of the spatial modulation element, an amount by which a backlight unit from the light source to the spatial modulation element protrudes in the normal direction of the spatial modulation element can be more reliably suppressed. As a result, this configuration enables further improvement of mountability of the head-up display on a vehicle. 
     In the above aspect, the first direction may be parallel to a longitudinal direction of the spatial modulation element. 
     According to this configuration, since the plurality of light sources are arranged in parallel to the longitudinal direction of the spatial modulation element, the projection device can be downsized as compared with a case where the plurality of light sources are arranged in parallel to a lateral direction of the spatial modulation element. 
     In the above aspect, the lens may have a convex surface at least as the emission surface. 
     According to this configuration, it is possible to easily realize a lens that changes an optical path of light emitted from each of the plurality of light sources such that the light emitted from each light source reaches the same region of the incident surface of the spatial modulation element. 
     In the above aspect, the emission surface of the lens may have a larger curvature in a second direction than a curvature in the first direction, the second direction being orthogonal to the first direction. 
     According to this configuration, since in the spatial modulation element having the first direction as a longitudinal direction and the second direction as a lateral direction, a lens can be configured which is suitable for light emitted from each of the plurality of light sources to reach the same region of the incident surface of the spatial modulation element. 
     In the above aspect, the plurality of light sources may be arranged in a matrix in the first direction and the second direction orthogonal to the first direction. 
     According to this configuration, an image having sufficient luminance can be obtained in a case where the spatial modulation element is enlarged. 
     A head-up display according to another aspect of the present disclosure includes the above-described projection device; and a second reflective optical member for projecting light emitted from the spatial modulation element onto a reflective member provided on the vehicle. 
     According to the present configuration, it is possible to provide a head-up display having improved mountability on a vehicle while suppressing luminance unevenness of an image emitted from the spatial modulation element. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to a device that is mounted on a vehicle and displays video such as a virtual image.