Head-up display device

Abstract

This invention provides a head-up display device that allows users wearing polarized sunglasses to see the display light while also offering efficient use of the display light. [Solution] The head-up display device comprises a liquid crystal display element 7 having a first polarizer 21 and a second polarizer 22 facing each other with a liquid crystal cell 10 in between, a half-wave plate 40 through which display light Lp emitted from the liquid crystal display element 7 in response to illumination light C passes, and a rotation drive unit 8 that rotates the half-wave plate 40. The rotation drive unit 8 can switch the half-wave plate 40 between a first rotation position and a second rotation position. From the half-wave plate 40 in the first rotation position, S-polarized display light L is emitted toward the reflective surface of the windshield, and from the half-wave plate 40 in the second rotation position, P-polarized display light L is emitted toward the reflective surface.

Description

Technical Field

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

Background Art

[0002] Patent Document 1 describes a head-up display device that allows a user to visually recognize display light (specifically, an image represented by the display light) reflected by a vehicle windshield. The device described in Patent Document 1 includes a polarization unit that emits the display light as P-polarized light, so that a user wearing polarized sunglasses can also visually recognize the image. This is because the polarized sunglasses are configured to cut S-polarized light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, the reflectance of S-polarized light on the windshield is higher than that of P-polarized light. However, in the configuration described in Patent Document 1, since the display light is fixed to P-polarized light, the luminance of the display light reaching the user is lower than in the case where the display light contains more S-polarized light than P-polarized light. That is, with this configuration, there is a risk that the luminance of the display light for a user not wearing polarized sunglasses will be sacrificed, and there is room for improvement in terms of the utilization efficiency of the display light.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a head-up display device that allows a user wearing polarized sunglasses to visually recognize display light while achieving good utilization efficiency of the display light.

Means for Solving the Problems

[0006] To achieve the above objectives, the head-up display device relating to this disclosure is A liquid crystal cell, and a liquid crystal display element having a first polarizer and a second polarizer facing each other across the liquid crystal cell, An illumination unit that emits illumination light toward the liquid crystal display element, A half-wave plate through which the display light emitted from the liquid crystal display element in response to the illumination light passes, The system includes a rotational drive unit for rotating the half-wave plate, A head-up display device that irradiates the display light that has passed through the half-wave plate onto a windshield, The first polarizer is located between the half-wave plate and the liquid crystal cell. The display light emitted from the liquid crystal display element is directed toward the half-wave plate as linearly polarized light along the transmission axis of the first polarizer. The rotational drive unit is capable of switching the half-wave plate to a first rotational position and a second rotational position in which the optical axes of the half-wave plate face in opposite directions. From the half-wave plate at the first rotational position, the S-polarized indicator light is emitted toward the reflective surface of the windshield. From the half-wave plate at the second rotational position, the display light with P polarization is emitted relative to the reflective surface. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a head-up display device that allows users wearing polarized sunglasses to see the display light while also having good utilization efficiency of the display light. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic diagram of a head-up display device according to one embodiment of the present disclosure. [Figure 2] A diagram illustrating S-polarization and P-polarization according to the same embodiment. [Figure 3] A schematic diagram of the display unit according to the same embodiment. [Figure 4] A diagram illustrating the control of the polarization state of the display light according to the same embodiment. [Modes for carrying out the invention]

[0009] One embodiment of this disclosure will be described with reference to the drawings.

[0010] The head-up display device 1 (hereinafter also referred to as HUD device 1) shown in Figure 1 is installed in the vehicle's dashboard 2 and projects display light L representing an image onto the vehicle's windshield 3. The display light L reflected by the windshield 3 displays a virtual image V of the image. The user 4 (mainly the vehicle's driver) views the virtual image V through the windshield 3. Hereafter, this act of the user 4 viewing the virtual image V may be referred to as the user 4 viewing the display light L.

[0011] The HUD device 1 comprises a display unit 5 that emits display light L, a plane mirror 1a, and a concave mirror 1b. The display light L emitted by the display unit 5 is reflected by the plane mirror 1a and then the concave mirror 1b, before heading towards the windshield 3. In this way, the display light L emitted from the HUD device 1 enters the windshield 3 and is reflected by the reflective surface 3a of the windshield 3.

[0012] Referring to Figure 2, S-polarized and P-polarized light for the windshield 3 will be explained. Here, the incident plane P with respect to the reflective surface 3a of the windshield 3 is defined in optics as a plane perpendicular to the reflective surface 3a and containing the incident and reflected rays. Note that the indicator light L shown in Figure 2 represents a representative ray of the indicator light L. S-polarized light for the windshield 3 is polarization that vibrates perpendicular to the incident plane P (i.e., vibrates in the out-of-plane direction Dv of the incident plane P). On the other hand, P-polarized light for the windshield 3 is polarization that vibrates parallel to the incident plane P (i.e., vibrates in the in-plane direction Dp of the incident plane P). The terms S-polarized and P-polarized light used below refer to polarization as described above.

[0013] Note that the direction of vibration of the light rays included in the display light L may change slightly depending on the position where the display light L is incident on the windshield 3. Therefore, the expressions S-polarized light or P-polarized light used below mean that the target optical member is adjusted to emit S-polarized light or P-polarized light with respect to the windshield 3, and it does not necessarily mean that all of the display light L is perfectly S-polarized light or P-polarized light. Also, as a result of the display unit 5 emitting S-polarized display light L, the display light L that is reflected by the windshield 3 and reaches the user 4 only needs to mainly contain an S-polarized component. Similarly, as a result of the display unit 5 emitting P-polarized display light L, the display light L that is reflected by the windshield 3 and reaches the user 4 only needs to mainly contain a P-polarized component.

[0014] As shown in FIG. 3, the display unit 5 includes a lighting unit 6, a liquid crystal display element 7 having a liquid crystal cell 10, a first polarizer 21, and a second polarizer 22, a half-wave plate 40, a rotation drive unit 8, and a control unit 9.

[0015] The lighting unit 6 is configured to emit illumination light C toward the liquid crystal display element 7. The configuration of the lighting unit 6 is arbitrary. For example, the lighting unit 6 includes, in order from the farthest from the liquid crystal display element 7, a plurality of LEDs (Light Emitting Diodes) mounted on a light source substrate, a condenser lens, a lenticular lens, a light diffusion plate, etc. Further, as the lighting unit 6, for example, a known configuration such as the configuration described in Japanese Patent Application Laid-Open No. 2020-160293 can be appropriately adopted.

[0016] The liquid crystal display element 7 receives the illumination light C and displays an image toward the half-wave plate 40. The liquid crystal display element 7 emits display light Lp representing the image toward the half-wave plate 40. Hereinafter, in order to distinguish this display light Lp from the display light L emitted from the half-wave plate 40 as described later, it is called the original display light Lp. The display light L emitted from the half-wave plate 40 is also the same as the original display light Lp in that it represents the image, but it is called in this way in order to distinguish from which configuration the light is emitted.

[0017] The liquid crystal cell 10 is, for example, a TFT (Thin Film Transistor) liquid crystal of the active matrix driving method. The liquid crystal cell 10 is configured to include a pair of substrates 11 and 12 and a liquid crystal layer 13 encapsulated between the pair of substrates 11 and 12. The substrate 11 is located on the side of the half-wave plate 40. The pair of substrates 11 and 12 are each formed transparently from glass, plastic, etc. On the surface of each of the pair of substrates 11 and 12 facing the liquid crystal layer 13, a transparent electrode (not shown) and an alignment film (not shown) covering the transparent electrode are formed. That is, the liquid crystal cell 10 is provided with a pair of transparent electrodes and a pair of alignment films. The pair of alignment films are subjected to a rubbing treatment according to the type of the liquid crystal cell 10.

[0018] For example, the transparent electrode formed on the substrate 11 is configured as a common electrode, and the transparent electrode formed on the substrate 12 is configured as a pixel electrode (including sub-pixel electrodes). When the type of the liquid crystal cell 10 is the IPS described later, transparent electrodes constituting the common electrode and the pixel electrode are formed on the substrate 12. Further, the substrate 11 is provided with a color filter layer (not shown) formed by arranging color filters of each color of R (red), G (green), and B (blue).

[0019] The liquid crystal display element 7 displays an image by a combination of pixels (including sub-pixels). Specifically, under the control of the control unit 9, it is selected whether to apply an on voltage to the portion corresponding to each pixel of the liquid crystal layer 13 through the pair of transparent electrodes, and the liquid crystal display element 7 displays an image by the combination of each pixel that becomes a transmission or non-transmission state accordingly. How the liquid crystal display element 7 displays an image differs according to the type of the liquid crystal cell 10.

[0020] Any type of liquid crystal cell 10 can be used, such as TN (Twisted Nematic), VA (Vertical Alignment), or IPS (In-Plane Switching), and the type is not limited. In any case, regardless of which liquid crystal type is used, the first polarizer 21 in this embodiment is provided such that the transmission axis of the first polarizer 21 is aligned with S polarization.

[0021] The first polarizer 21 and the second polarizer 22 face each other across the liquid crystal cell 10. The first polarizer 21 is located between the half-wave plate 40 and the liquid crystal cell 10 and is, for example, bonded to the substrate 11. The first polarizer 21 is a well-known polarizing film (also called a polarizing plate) that emits light incident from one side as linearly polarized light along a transmission axis perpendicular to the absorption axis from the other side.

[0022] The second polarizer 22 is located between the illumination unit 6 and the liquid crystal cell 10 and is, for example, bonded to the substrate 12. The second polarizer 22, like the first polarizer 21, is a well-known polarizing film and emits light incident from one side as linearly polarized light along a transmission axis perpendicular to the absorption axis from the other side. Unpolarized illumination light C emitted from the illumination unit 6 is incident on the liquid crystal cell 10 as linearly polarized light along the transmission axis of the second polarizer 22.

[0023] In this embodiment, the second polarizer 22 is arranged in a crossed nicol configuration with respect to the first polarizer 21. A crossed nicol configuration means that the transmission axes of the first polarizer 21 and the second polarizer 22 are orthogonal to each other. Note that a configuration where the transmission axes of the first polarizer 21 and the second polarizer 22 are parallel to each other is called a parallel nicol configuration. The display mode of the liquid crystal display element 7 is either NB (normally black) mode or NW (normally white) mode. In NB mode, a dark display (black display) is achieved when the applied voltage is off. On the other hand, in NW mode, a bright display (white display) is achieved when the applied voltage is off.

[0024] The liquid crystal display element 7, in which the first polarizer 21 and the second polarizer 22 are arranged in a crossed nicol relationship, displays an image in NW mode when the type of liquid crystal cell 10 is TN, displays an image in NB mode when the type of liquid crystal cell 10 is VA, and displays an image in NB mode when the type of liquid crystal cell 10 is IPS. Alternatively, the display mode of the liquid crystal display element 7 may be reversed with respect to the above display modes (i) to (iii) by arranging the first polarizer 21 and the second polarizer 22 in parallel nicols.

[0025] In this embodiment, regardless of the combination of the display mode of the liquid crystal display element 7 and the type of liquid crystal cell 10, the original display light Lp emitted from the liquid crystal display element 7 of this embodiment is directed toward the half-wave plate 40 as linearly polarized light (i.e., S-polarized light) along the transmission axis of the first polarizer 21.

[0026] The half-wave plate 40 is a well-known configuration also called a half-λ plate. When light vibrating at a 45° angle is incident on the optical axis 40a shown in Figure 4, it is emitted as light with its vibration direction rotated by 90°. The optical axis 40a of the half-wave plate 40 is either a speed axis or a slow axis that are orthogonal to each other. The half-wave plate 40 is held by a holding member (not shown) and is rotatable around a rotation centerline parallel to the optical axis that passes through the half-wave plate 40. This rotation centerline may coincide with the optical axis. The half-wave plate 40 is rotationally driven by a rotation drive unit 8.

[0027] The rotation drive unit 8 includes a motor, gear mechanism, etc., and rotates the half-wave plate 40 under the control of the control unit 9. The rotation drive unit 8 can switch the half-wave plate 40 between a first rotation position and a second rotation position, where the optical axis 40a is oriented in different directions. The first rotation position and the second rotation position are different from each other and are rotation positions around the aforementioned rotation center line. In this embodiment, (i) the first rotation position is the rotation position of the half-wave plate 40 where the optical axis 40a is parallel to or perpendicular to the vibration direction of the original display light Lp, which is S-polarized, and (ii) the second rotation position is the rotation position of the half-wave plate 40 where the optical axis 40a is oriented at a 45° angle to the vibration direction of the original display light Lp, which is S-polarized. In other words, the first rotation position and the second rotation position in this embodiment are 45° apart from each other around the rotation center line (i.e., θ as shown in Figure 4 is 45°).

[0028] In this embodiment, regardless of the combination of the display mode of the liquid crystal display element 7 and the type of liquid crystal cell 10, S-polarized display light L is emitted from the half-wave plate 40 at the first rotation position, and P-polarized display light L is emitted from the half-wave plate 40 at the second rotation position.

[0029] In the following, the state in which the half-wave plate 40 is in the first rotation position will be referred to as the first state, and the state in which the half-wave plate 40 is in the second rotation position will be referred to as the second state.

[0030] Figure 4 is a diagram illustrating the control of the polarization state of the display light L emitted from the half-wave plate 40. In this figure, a mark with a horizontally extending arrow in a circle represents S polarization, and a mark with a vertically extending arrow in a circle represents P polarization.

[0031] The left-hand diagram in Figure 4 represents the first state (i.e., the state where the half-wave plate 40 is in the first rotation position). In this case, the original display light Lp emitted from the liquid crystal display element 7, which is S-polarized, passes through the half-wave plate 40 while retaining its S-polarization, and as a result, S-polarized display light L is emitted from the half-wave plate 40. In other words, in the first state, S-polarized display light L is emitted from the display unit 5.

[0032] The right-hand diagram in Figure 4 represents the second state (i.e., the state where the half-wave plate 40 is in the second rotation position). In this case, the original display light Lp emitted from the liquid crystal display element 7, which is S-polarized, is converted to P-polarized light by the half-wave plate 40, and as a result, P-polarized display light L is emitted from the half-wave plate 40. In other words, in the second state, P-polarized display light L is emitted from the display unit 5. Note that in Figure 4, the planar shape of the half-wave plate 40 is represented as a rectangle to facilitate understanding of the rotation position, but the planar shape of the half-wave plate 40 is arbitrary as long as it can cover the image display area of ​​the liquid crystal display element 7 in both the first and second rotation positions.

[0033] As mentioned above, polarized sunglasses are configured to cut S-polarized light. Therefore, the second state, in which P-polarized display light L is emitted from the display unit 5 and as a result reaches the user 4, is suitable when the user 4 is wearing polarized sunglasses. On the other hand, the first state, in which S-polarized display light L is emitted from the display unit 5 and as a result reaches the user 4, is suitable when the user 4 is not wearing polarized sunglasses.

[0034] Thus, the HUD device 1 emits P-polarized display light L in the second state, allowing users wearing polarized sunglasses to see the display light L, while in the first state, it emits S-polarized display light L, which has a higher reflectivity on the windshield 3 than P-polarized light. Therefore, the HUD device 1 has good utilization efficiency of the display light L.

[0035] The control unit 9 is composed of a microcontroller, various drive circuits, etc., and controls the operation of the lighting unit 6, the liquid crystal display element 7, and the rotary drive unit 8. For example, the control unit 9 communicates with the vehicle's ECU (Electronic Control Unit) and other equipment to display various vehicle-related information on the liquid crystal display element 7.

[0036] Furthermore, the control unit 9 communicates with input devices (not shown) such as a touch panel and steering wheel switches mounted on the vehicle and receives instructions from the user 4 via the input devices. In this embodiment, the control unit 9 receives a first trigger signal T1 from the input device as an instruction from the user 4 via the input device, which indicates a switch from one of the first state and the second state to the other state. In response to the first trigger signal T1, the control unit 9 switches the half-wave plate 40 from one of the first state and the second state to the other state (that is, switches the half-wave plate 40 from one of the first rotation position and the second rotation position to the other position).

[0037] Furthermore, the control unit 9 is located inside the vehicle and includes a camera that images the user 4, and communicates with a sensor (not shown) that detects whether the user 4 is wearing polarized sunglasses. The control unit 9 receives a second trigger signal T2 from the sensor, which is a detection signal indicating whether the user 4 is wearing polarized sunglasses. If the second trigger signal T2 indicates that the user 4 is not wearing polarized sunglasses, the control unit 9 controls the half-wave plate 40 to the first state, and if the second trigger signal T2 indicates that the user is wearing polarized sunglasses, the control unit 9 controls the half-wave plate 40 to the second state. In other words, the control unit 9 switches the half-wave plate 40 from one of the first and second states to the other state in response to the second trigger signal T2 (that is, it switches the half-wave plate 40 from one of the first rotation position and the second rotation position to the other position).

[0038] Furthermore, the control unit 9 may control the brightness of the illumination light C emitted by the illumination unit 6 so that it is lower when the half-wave plate 40 is in the first rotation position (i.e., the first state suitable when the user 4 is not wearing polarized sunglasses) than when the half-wave plate 40 is in the second rotation position (i.e., the second state suitable when the user 4 is wearing polarized sunglasses). In other words, the control unit 9 may relatively increase the brightness of the illumination light C in the second state compared to the first state. Here, the reflectivity at the windshield 3 is significantly lower for P-polarized light than for S-polarized light. Therefore, if the brightness of the illumination light C is not changed between the first and second states, the image viewed by user 4 wearing polarized sunglasses in the second state will be unnecessarily darker than the image viewed by user 4 wearing polarized sunglasses in the first state. However, by controlling the brightness of the illumination light C as described above, it is possible to prevent the image viewed by user 4 wearing polarized sunglasses in the second state from becoming unnecessarily dark.

[0039] The present invention is not limited by the embodiments and drawings described above. Modifications (including the deletion of components) can be made as appropriate without altering the essence of the invention.

[0040] The HUD device 1 may be mounted on a vehicle other than a vehicle and may be configured to emit display light L toward the windshield of the vehicle.

[0041] The liquid crystal display element 7 is not limited to an active drive system, but may also be a passive drive system. Furthermore, the liquid crystal display element 7 is not limited to one that displays an image using a matrix of pixels, but may also be a monochrome liquid crystal display element that performs segment display. In the case of a liquid crystal display element 7 that performs segment display, the image in the region where the transmission and opacity of light can be controlled in the liquid crystal display element 7 can be considered as the image represented by the original display light Lp and the display light L.

[0042] In the liquid crystal display element 7, the first polarizer 21 may be provided such that its transmission axis aligns with the P-polarization. In this way, when the liquid crystal display element 7 emits the original P-polarized display light Lp, the half-wave plate 40 may convert the original P-polarized display light Lp into S-polarized display light L at the first rotation position and emit it, and at the second rotation position, emit the original P-polarized display light Lp as is, as P-polarized display light L. In this case, the orientation of the optical axis 40a of the half-wave plate 40 is reversed between the first and second rotation positions compared to the above embodiment.

[0043] The liquid crystal display element 7 may be a reflective liquid crystal display element used in LCOS (Liquid Crystal On Silicon) (also called a reflective liquid crystal projector). In this case, three liquid crystal display elements 7 are provided, corresponding to each of the R, G, and B colors, and the illumination unit 6 emits illumination light C of each of the R, G, and B colors toward each liquid crystal display element 7 (a well-known configuration having a light source, a mirror, and a dichroic mirror). The half-wave plate 40 should be positioned so that the combined display light L emitted from each liquid crystal display element 7 passes through it.

[0044] In the above explanation, explanations of publicly known technical matters have been omitted where appropriate to facilitate understanding of this disclosure.

[0045] This invention allows for various embodiments and modifications without departing from the broad spirit and scope of the invention. Furthermore, the embodiments described above are for illustrative purposes only and do not limit the scope of the invention. In other words, the scope of this invention is indicated not by the embodiments, but by the claims. Various modifications made within the scope of the claims and the equivalent scope of the meaning of the invention are considered to be within the scope of this invention. [Explanation of Symbols]

[0046] 1. Head-up display device (HUD device) 1a...Plane mirror, 1b...Concave mirror 2… Dashboard 3...windshield, 3a...reflective surface 4…User 5…Display unit 6…Lighting Department 7… LCD display element 8…Rotating drive unit 9... Control Unit 10...Liquid crystal cell, 11,12...Substrate, 13...Liquid crystal layer 21…First polarizer 22…Second polarizer 40...1 / 2 wavelength plate, 40a...optical axis C…Illumination light Lp…Display light (original display light) L...display light, V...virtual image P...Incidence plane, Dv...Out-of-plane direction, Dp...In-plane direction T1…First trigger signal, T2…Second trigger signal

Claims

1. A liquid crystal cell, and a liquid crystal display element having a first polarizer and a second polarizer facing each other across the liquid crystal cell, An illumination unit that emits illumination light toward the liquid crystal display element, A half-wave plate through which the display light emitted from the liquid crystal display element in response to the illumination light passes, The system includes a rotational drive unit for rotating the half-wave plate, A head-up display device that irradiates the display light that has passed through the half-wave plate onto a windshield, The first polarizer is located between the half-wave plate and the liquid crystal cell. The display light emitted from the liquid crystal display element is directed toward the half-wave plate as linearly polarized light along the transmission axis of the first polarizer. The rotation drive unit is capable of switching the half-wave plate to a first rotation position and a second rotation position in which the optical axes of the half-wave plate face in opposite directions. From the half-wave plate at the first rotational position, the S-polarized indicator light is emitted toward the reflective surface of the windshield. From the half-wave plate at the second rotational position, the display light with P polarization is emitted relative to the reflective surface. Head-up display device.

2. The brightness of the illumination light emitted by the illumination unit is lower when the half-wave plate is in the first rotation position than when it is in the second rotation position. The head-up display device according to claim 1.

3. The system further includes a control unit that controls the operation of the rotary drive unit, The control unit controls the operation of the rotary drive unit in accordance with at least one of the user's instructions via the input device and a detection signal from a sensor that detects whether the user is wearing polarized sunglasses, and switches the half-wave plate from one of the first rotation position and the second rotation position to the other position. The head-up display device according to claim 1 or 2.

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