Head-up displays and display devices

Abstract

To provide a head-up display suppressing deterioration in visibility of a virtual image generated when reflected light from the outside overlaps with the virtual image.SOLUTION: A head-up display 1 comprises a light source 20, a liquid crystal panel 40 for transmitting light from the light source 20 to project an image, and a prism sheet 50 for refracting the light transmitted through the liquid crystal panel 40. The prism sheet 50 includes a sheet surface 51 parallel to a plate surface of the liquid crystal display panel 40, and a plurality of prisms 52 facing the plate surface of the liquid crystal display panel 40 on the opposite side of the sheet surface 51 and disposed in parallel. Each of the plurality of prisms 52 is formed into a square cross section by a first prism surface 52a inclined to the sheet surface 51 and a second prism surface 52b inclined to the sheet surface 51 and whose angle formed with the sheet surface 51 is larger than that of the first prism surface 52a, where an angle formed by the first prism surface 52a and the sheet surface 51 is 35° or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a head-up display and a display device.

Background Art

[0002] There is known a display device applied to a vehicle head-up display device that projects an image onto a light-transmitting body such as a windshield to allow a user to visually recognize a virtual image (for example, Patent Document 1). The display device includes a backlight, a liquid crystal display panel that transmits light from the backlight and projects an image, a prism sheet that refracts the light transmitted through the liquid crystal display panel, and a housing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the display device of Patent Document 1, when light from the outside such as sunlight is reflected by a prism sheet or the like and the reflected light overlaps with the virtual image, the visibility of the virtual image may be reduced.

[0005] The present disclosure has been made in view of the above problems, and an object thereof is to suppress a decrease in the visibility of a virtual image caused by the reflected light from the outside overlapping with the virtual image in a head-up display and a display device.

Means for Solving the Problems

[0006] The head-up display of the present disclosure includes a light source, a liquid crystal panel that transmits light from the light source and projects an image, and a prism sheet that is inclined with respect to the plate surface of the liquid crystal panel and refracts the light transmitted through the liquid crystal panel.

[0007] Furthermore, the display device of this disclosure comprises a light source, a liquid crystal panel that transmits light from the light source and projects an image, and a prism sheet that is inclined with respect to the surface of the liquid crystal panel and refracts the light that has passed through the liquid crystal panel. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram of a head-up display according to an embodiment. [Figure 2] Figure 2 is a schematic diagram of the light source and image output unit. [Figure 3] Figure 3 is an enlarged side view of the prism sheet. [Figure 4] Figure 4 shows the propagation and reflection of external light in the image output section. [Figure 5] Figure 5 shows an example of the simulation results for reflected light. [Figure 6] Figure 6 is a schematic diagram of an image output unit according to a modified embodiment. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below. Furthermore, the components described below include those that are readily conceivable to those skilled in the art, and those that are substantially the same. In addition, the components described below can be combined as appropriate.

[0010] Furthermore, the disclosure is merely an example, and modifications that a person skilled in the art could easily conceive of while maintaining the spirit of the invention are naturally included within the scope of this disclosure. In addition, the drawings may schematically represent the width, thickness, shape, etc. of each part in order to clarify the explanation, but these are merely examples and do not limit the interpretation of this disclosure. In addition, in this specification and each drawing, elements similar to those described above in previously shown drawings are denoted by the same reference numerals, and detailed explanations may be omitted as appropriate.

[0011] In the drawings, the Dx direction is the height direction of the head-up display 1, the Dy direction is the width direction of the head-up display 1, and the Dz direction is the depth direction of the head-up display 1. Note that the directions Dx, Dy, and Dz are examples, and this disclosure is not limited to these directions.

[0012] Figure 1 is a schematic diagram of a head-up display 1 according to an embodiment. The head-up display (hereinafter referred to as HUD) 1 is an example of a display device that projects an image onto a translucent body 2 to allow the user U to view a virtual image VG. The translucent body 2 is, for example, a windshield, but is not limited to this; any configuration on which the image of the HUD 1 is projected is acceptable.

[0013] The HUD1 comprises a housing 10, a light source 20, an image output unit 30, and an optical element 70. The housing 10 is box-shaped and includes the light source 20, the image output unit 30, and the optical element 70.

[0014] Figure 2 is a schematic diagram of the light source 20 and the image output unit 30. The light source 20 has a light-emitting element (not shown), such as an LED (Light Emitting Diode), inside a rectangular parallelepiped case. The light source 20 irradiates the image output unit 30 with light. The optical axis of the light emitted from the light source 20 is perpendicular to the light source emission surface 21 of the light source 20. The light source emission surface 21 is parallel to the Dy direction and is inclined around an axis parallel to the Dy direction with respect to the output axis Vz (hereinafter referred to as the Dy axis). The output axis Vz is the axis along which the optical axis of the emitted light Lc, which will be described later, emitted from the image output unit 30 is aligned. Specifically, the output axis Vz is parallel to the Dz direction and extends from the image output unit 30 toward the optical element 70.

[0015] The angle between the perpendicular V1 of the light source emission surface 21 and the output axis Vz is called the first inclination angle θ1. The first inclination angle θ1 is acute. The light source emission surface 21 may be perpendicular to the output axis Vz, rather than being inclined. In this case, the first inclination angle θ1 is zero.

[0016] Light emitted from the light source 20 is incident on the image output unit 30 as incident light La. The optical axis of the incident light La is parallel to the perpendicular V1. The image output unit 30 transmits and refracts the incident light La and emits output light Lc along the output axis Vz. The image output unit 30 comprises a liquid crystal panel 40, a prism sheet 50, and a support 60.

[0017] The liquid crystal panel 40 projects an image by transmitting light from the light source 20. The liquid crystal panel 40 is a transmissive liquid crystal display panel. The liquid crystal panel 40 has a panel incident surface 41 facing the light source 20, to which light from the light source 20 enters as incident light La, and a panel exit surface 42 to which the incident light La is emitted as transmitted light after passing through the liquid crystal panel 40.

[0018] The panel incident surface 41 and the panel exit surface 42 are parallel to each other. Also, the panel incident surface 41 and the panel exit surface 42 are inclined about the Dy axis with respect to the light source exit surface 21. The angle formed by the perpendicular V2 to the panel incident surface 41 and the output axis Vz is referred to as the second inclination angle θ2. The second inclination angle θ2 is an acute angle and is larger than the first inclination angle θ1. Incidentally, the second inclination angle θ2 may be the same angle as the first inclination angle θ1.

[0019] The liquid crystal panel 40 has a plurality of pixels driven by an active matrix system. The plurality of pixels are two-dimensionally arranged along the plate surface of the liquid crystal panel 40. In an image output region (not shown) where the plurality of pixels are arranged, a light transmission pattern corresponding to an image projected as a virtual image VG is formed by individually controlling the plurality of pixels. Thereby, when the incident light La passes through the image output region, the amount of light is adjusted and emitted as transmitted light. The optical axis of the incident light La and the optical axis of the transmitted light are parallel to each other.

[0020] The prism sheet 50 refracts the light that has passed through the liquid crystal panel 40. Specifically, the prism sheet 50 refracts the transmitted light emitted from the panel exit surface 42 and emits it as the emitted light Lc along the output axis Vz. That is, the optical axis of the emitted light Lc is inclined with respect to the optical axis of the incident light La that is parallel to the optical axis of the transmitted light. The prism sheet 50 emits the emitted light Lc toward the optical member 70. The prism sheet 50 is inclined with respect to the plate surface of the liquid crystal panel 40. The prism sheet 50 has a sheet surface 51 and a plurality of prisms 52.

[0021] The sheet surface 51 is inclined with respect to the plate surface of the liquid crystal panel 40. Specifically, the sheet surface 51 is inclined about the Dy axis with respect to the panel exit surface 42 of the liquid crystal panel 40. The angle formed by the perpendicular V3 to the sheet surface 51 and the output axis Vz is referred to as the third inclination angle θ3.

[0022] The third inclination angle θ3 corresponds to the emission angle of the emitted light Lc emitted from the sheet surface 51. The third inclination angle θ3 is an acute angle. The details of the relationship between the second inclination angle θ2 and the third inclination angle θ3 will be described later.

[0023] The multiple prisms 52 face the surface of the liquid crystal panel 40 on the side opposite to the sheet surface 51. Specifically, the multiple prisms 52 face the panel emission surface 42 of the liquid crystal panel 40.

[0024] Figure 3 is an enlarged side view of the prism sheet 50. The multiple prisms 52 are arranged on a plane S parallel to the sheet surface 51. Each of the multiple prisms 52 is formed in a rectangular cross-section by a first prism surface 52a and a second prism surface 52b.

[0025] The first prism surface 52a and the second prism surface 52b are inclined with respect to the sheet surface 51 around the Dy axis. The angle between the second prism surface 52b and the sheet surface 51 is greater than that between the first prism surface 52a and the sheet surface 51. In other words, the first prism angle α of the first prism surface 52a with respect to the sheet surface 51 is smaller than the second prism angle β of the second prism surface 52b with respect to the sheet surface 51. The first prism angle α and the second prism angle β are determined so that transmitted light along the perpendicular V2 is refracted and emitted as output light Lc along the output axis Vz.

[0026] Furthermore, the multiple prisms 52 are arranged in parallel. Specifically, the edges R formed by the first prism surface 52a and the second prism surface 52b of each of the multiple prisms 52 are arranged along the Dy axis. In other words, the multiple prisms 52 are arranged so that their respective edges R are parallel to each other.

[0027] Furthermore, in two adjacent prisms 52 among the multiple prisms 52, the first prism surface 52a of one prism 52 and the second prism surface 52b of the other prism 52 are formed continuously. In other words, the plane S is not exposed.

[0028] As shown in Figure 2, the support 60 supports the liquid crystal panel 40 and the prism sheet 50. The support 60 comprises a first support portion 61 and a second support portion 62. The first support portion 61 supports the liquid crystal panel 40. Specifically, the first support portion 61 supports the peripheral edge of the panel incident surface 41 and is bonded to the peripheral edge of the panel incident surface 41 by adhesive or the like. The first support portion 61 also supports the second support portion 62. The second support portion 62 supports the prism sheet 50 at an angle to the liquid crystal panel 40. Specifically, the second support portion 62 supports the peripheral edge of the sheet surface 51 and is bonded to the peripheral edge of the sheet surface 51 by adhesive or the like.

[0029] As shown by the dashed arrow in Figure 1, the optical member 70 guides the emitted light Lc to the light-transmitting body 2 through the opening 11 of the housing 10. Specifically, the optical member 70 is a concave mirror. The optical member 70 may also be composed of multiple concave mirrors and reflecting mirrors.

[0030] The emitted light Lc guided by the optical element 70 is projected onto the translucent body 2. User U, who directs their gaze towards the emitted light Lc projected onto the translucent body 2, sees the virtual image VG.

[0031] As described above, the emitted light Lc from the image output unit 30 is emitted along the output axis Vz, and the panel output surface 42 of the liquid crystal panel 40 is inclined around the Dy axis with respect to the output axis Vz. As a result, the user U can perceive the virtual image VG as having a three-dimensional effect in the Dz direction.

[0032] Furthermore, as described above, the light source emission surface 21 of the light source 20 is inclined around the Dy axis with respect to the output axis Vz. In this case, compared to the case where the light source emission surface 21 is perpendicular to the output axis Vz, the incident angle of the incident light La emitted from the light source emission surface 21 and incident on the panel incident surface 41 becomes smaller. This makes it possible to suppress the decrease in brightness of the light that forms the virtual image VG and the contrast of the virtual image VG.

[0033] Next, the relationship between the second tilt angle θ2 and the third tilt angle θ3 will be explained in detail. In the HUD1, external light such as sunlight (hereinafter referred to as external light) Lg enters the housing 10 through the opening 11, travels along the output axis Vz in the opposite direction to the direction of propagation of the emitted light Lc, and may be reflected by the prism sheet 50, etc. When this reflected light overlaps with the virtual image VG, the visibility of the virtual image VG decreases.

[0034] The relationship between the second tilt angle θ2 and the third tilt angle θ3 is determined to be an angle that suppresses the overlap of reflected light with the virtual image VG. Specifically, the difference between the second tilt angle θ2 and the third tilt angle θ3 is determined based on the reflection angle of the reflected light shown below. The difference between the second tilt angle θ2 and the third tilt angle θ3 corresponds to the angle (hereinafter referred to as the relative angle θs) between the sheet surface 51 and the plate surface (panel emission surface 42) of the liquid crystal panel 40, as shown in Figure 2.

[0035] Figure 4 shows the propagation and reflected light of external light Lg in the image output unit 30. In Figure 4, the propagation of external light Lg is shown by a dashed line. The reflected light is the light that is reflected from the external light Lg by the prism sheet 50 and the panel output surface 42, etc. The reflection angle of the reflected light is defined as the angle between the optical axis of the reflected light and the output axis Vz.

[0036] In Figure 4, the second inclination angle θ2 of the panel emission surface 42 is 45°, and the third inclination angle θ3 of the sheet surface 51 is 35°. In other words, this shows the case where the relative angle θs is 10°. It also shows the case where the first prism angle α is 40° and the second prism angle β is 90°.

[0037] The external light Lg travels along the output axis Vz and reaches point A on the sheet surface 51. A portion of the external light Lg that reaches point A is reflected at point A on the sheet surface 51. The external light Lg reflected at point A is called the first reflected light Lr1, and the angle between the optical axis of the first reflected light Lr1 and the output axis Vz is called the first reflection angle θr1. The first reflected light Lr1 is reflected once at point A on the sheet surface 51.

[0038] Furthermore, external light Lg that is not reflected at point A on the sheet surface 51 is refracted at point A and enters the prism sheet 50, and is refracted at point B on the first prism surface 52a and exits from the prism sheet 50. The angle at which the external light Lg is refracted depends on the relative refractive index of the material of the prism sheet 50 and the air outside the prism sheet 50.

[0039] A portion of the external light Lg emitted from point B on the first prism surface 52a is reflected at point C on the second prism surface 52b, and further reflected at point D on the panel emission surface 42. The external light Lg reflected at point D is refracted at point E on the first prism surface 52a and enters the prism sheet 50, and is refracted at point F on the sheet surface 51 and exits from the prism sheet 50. The external light Lg emitted from point F is called the second reflected light Lr2, and the angle between the optical axis of the second reflected light Lr2 and the output axis Vz is called the second reflection angle θr2.

[0040] The second reflected light Lr2 is reflected a total of two times at point C on the second prism surface 52b and at point D on the panel emission surface 42. The prism sheet 50 and the liquid crystal panel 40 have a specific reflectivity (e.g., 8%) based on their materials. Therefore, the more times there are reflections, the lower the light intensity. Thus, the second reflected light Lr2 is reflected more times than the first reflected light Lr1, and the light intensity of the second reflected light Lr2 is lower than that of the first reflected light Lr1.

[0041] On the other hand, the external light Lg that was not reflected at point C on the second prism surface 52b is refracted at point C and incident on the prism sheet 50, and is refracted at point G on the first prism surface 52a and exits from the prism sheet 50. The external light Lg that exits from point G on the first prism surface 52a is reflected at point H on the panel exit surface 42, and is further refracted at point I on the second prism surface 52b and incident on the prism sheet 50, and is refracted at point J on the sheet surface 51 and exits from the prism sheet 50. The external light Lg that exits from point J is called the third reflected light Lr3, and the angle between the optical axis of the third reflected light Lr3 and the output axis Vz is called the third reflection angle θr3.

[0042] The third reflected light Lr3 is reflected once at point H on the panel emission surface 42. Therefore, the second reflected light Lr2 is reflected more times than the third reflected light Lr3, and the light intensity of the second reflected light Lr2 is less than that of the third reflected light Lr3. When the light intensity of the reflected light is relatively small, as in the case of the second reflected light Lr2, the visibility of the virtual image VG does not decrease even if the reflected light overlaps with the virtual image VG.

[0043] Furthermore, if the reflected light is tilted significantly with respect to the output axis Vz, the reflected light does not overlap with the virtual image VG, and the decrease in the visibility of the virtual image VG is suppressed. Therefore, the difference between the second tilt angle θ2 and the third tilt angle θ3, i.e., the relative angle θs, is determined so that the reflected light with one reflection is tilted relatively significantly with respect to the output axis Vz. In other words, the relative angle θs is determined so that the first reflection angle θr1 and the third reflection angle θr3 are relatively large. It is also desirable that the second reflection angle θr2 of the second reflected light Lr2 with two reflections be relatively large.

[0044] Figure 4 illustrates the propagation of external light Lg when it reaches point A on the prism sheet 50. However, external light Lg may also reach points other than point A on the prism sheet 50, resulting in reflected light with a different reflection angle from the first reflected light Lr1, second reflected light Lr2, and third reflected light Lr3 shown in Figure 4. Therefore, when determining the relative angle θs, a simulation is performed to derive the reflection angle of the reflected light based on multiple external light Lg beams that enter the prism sheet 50 at different positions.

[0045] Figure 5 shows an example of the simulation results for reflected light. In Figure 5, the second inclination angle θ2 of the panel emission surface 42 is 45°, and the third inclination angle θ3 of the sheet surface 51 is 35°. That is, the relative angle θs is 10°. Also, the first prism angle α is 30°, and the second prism angle β is 70°. 100 light rays, representing external light Lg, are incident on the sheet surface 51 from different positions.

[0046] External light Lg incident on the sheet surface 51 is reflected and refracted by the sheet surface 51 and the prism 52 as described above, and is emitted from the sheet surface 51 as multiple reflected rays Lr. In this simulation, the number of reflections is limited to two. However, total internal reflection is not counted as a reflection.

[0047] Table 1 shows an example of the simulation results for reflected light Lr. Table 1 shows the smallest reflection angle among the multiple reflected light Lr that have been reflected only once, for each case where the second tilt angle θ2 of the panel exit surface 42 is 45°, the first prism angle α is 30°, and the second prism angle β is 70°, and the third tilt angle θ3 of the sheet surface 51 is changed in 5° increments from 25° to 45°, that is, when the relative angle θs is changed in 5° increments from 0° to 20°.

[0048] The larger the reflection angle of the reflected light Lr, the more the reflected light Lr is tilted with respect to the output axis Vz, and the less it overlaps with the virtual image VG. In other words, a larger reflection angle indicates better results.

[0049] In Table 1, when the relative angle θs is between 10° and 15°, the reflection angle is relatively large. In other words, it is preferable that the relative angle θs is between 10° and 15°.

[0050] [Table 1]

[0051] Furthermore, if the relative angle θs is greater than 20°, the prism sheet 50 cannot refract the transmitted light and emit the outgoing light Lc along the output axis Vz. Therefore, in the simulation, the relative angle θs is set to a range of 0° to 20°.

[0052] Furthermore, in the above simulation, the first prism angle α is 30°, the second prism angle β is 70°, and the second tilt angle θ2 of the panel emission surface 42 is 45°. However, in simulations where the first prism angle α is in the range of 30±5°, the second prism angle β is in the range of 70±5°, and the second tilt angle θ2 is different from 45°, the reflection angle is relatively large and good results are obtained, similar to the results of the above simulation, when the relative angle θs between the sheet surface 51 and the plate surface (panel emission surface 42) of the liquid crystal panel 40 is between 10° and 15°. When the second tilt angle θ2 is between 35° and 45°, good results similar to those when the second tilt angle θ2 is 45° are obtained.

[0053] Furthermore, any other effects and benefits brought about by the embodiments described above that are obvious from this specification or that can be appropriately conceived by a person skilled in the art are naturally provided by this disclosure.

[0054] Figure 6 is a schematic diagram of an image output unit 30 according to a modified embodiment. The modified image output unit 30 further includes a diffuser plate 180 between the liquid crystal panel 40 and the prism sheet 50. The diffuser plate 180 is attached to the panel emission surface 42. The diffuser plate 180 diffuses and transmits the incident light. The diffuser plate 180 can suppress the occurrence of moiré patterns. In addition, the diffuser plate 180 suppresses the amount of reflected light Lr that is reflected by the panel emission surface 42 and emitted from the sheet surface 51. Therefore, the diffuser plate 180 can suppress a decrease in the visibility of the virtual image VG.

[0055] Furthermore, in the modified image output unit 30 support 160, the second support portion 162 supports the peripheral edge of the diffuser plate 180. The support 160 also further comprises a third support portion 163. The third support portion 163 is positioned on the second support portion 162 and supports the prism sheet 50 such that the plate surface (panel emission surface 42) of the liquid crystal panel 40 is inclined with respect to the sheet surface 51. The third support portion 163 supports the peripheral edge of the prism sheet 50 from both the sheet surface 51 side and the side of the multiple prisms 52.

[0056] Furthermore, this disclosure is also applicable to display devices other than HUD1, such as navigation systems, smartphones, tablets, and VR (Virtual Reality) goggles. [Explanation of Symbols]

[0057] 1. Head-up display 20 light source 30 Image output section 40 LCD panels 42 Panel ejection surface (the surface of the LCD panel) 50 prism sheets 51 Seat surface 52 Prisms 52a First prism surface 52b Second prism surface

Claims

1. Light source and A liquid crystal panel that transmits light from the aforementioned light source and projects an image, The system comprises a prism sheet that is inclined with respect to the surface of the liquid crystal panel and refracts light transmitted through the liquid crystal panel, The prism sheet is A sheet surface that is inclined with respect to the surface of the aforementioned liquid crystal panel, It has a plurality of prisms facing the surface of the liquid crystal panel on the opposite side of the sheet surface, The angle between the sheet surface and the surface of the liquid crystal panel is 10° or more and 15° or less. Head-up display.

2. Each of the multiple prisms is formed in a cross-sectional angular shape by a first prism surface inclined with respect to the sheet surface and a second prism surface inclined with respect to the sheet surface and having an angle with respect to the sheet surface that is greater than that of the first prism surface, and is arranged in parallel. The head-up display according to claim 1.

3. In two adjacent prisms, the first prism surface of one prism and the second prism surface of the other prism are formed continuously. The head-up display according to claim 2.

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