Head-up display device
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- NIPPON SEIKI CO LTD
- Filing Date
- 2024-11-26
- Publication Date
- 2026-06-05
Smart Images
Figure 2026092319000001_ABST
Abstract
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 having 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, The system comprises a rotational drive unit that rotates the first polarizer, which is positioned at a distance from the liquid crystal cell, A head-up display device that receives the illumination light and emits display light from the liquid crystal display element onto the windshield, The display light emitted from the liquid crystal display element is linearly polarized along the transmission axis of the first polarizer. The rotation drive unit is capable of switching the first polarizer to a first rotation position and a second rotation position in which the transmission axes are oriented in different directions. From the first polarizer at the first rotation position, the S-polarized display light is emitted toward the reflective surface of the windshield. From the first polarizer at the second rotation position, the display light with P polarization is emitted toward the reflective surface. The liquid crystal display element inverts the color tone of the image represented by the display light when the first polarizer is in the second rotation position compared to when the first polarizer is in the first rotation position. [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] Furthermore, the direction of vibration of the light rays contained in the display light L relative to the reflective surface 3a may change slightly depending on the position where they enter the windshield 3. Therefore, the expressions S-polarization or P-polarization used below do not necessarily mean that all of the display light L is perfectly S-polarized or P-polarized, but rather that the optical component in question is adjusted to emit S-polarized or P-polarized light relative to the windshield 3. Also, the display light L that reaches the user 4 after being reflected by the windshield 3 as a result of the display unit 5 emitting S-polarized display light L only needs to mainly contain an S-polarized component. Similarly, the display light L that reaches the user 4 after being reflected by the windshield 3 as a result of the display unit 5 emitting P-polarized display light L only needs to mainly contain a P-polarized component.
[0014] As shown in Figure 3, the display unit 5 comprises an illumination unit 6, a liquid crystal display element 7 having a liquid crystal cell 10, a first polarizer 21 and a second polarizer 22, a rotation drive unit 8, and a control unit 9.
[0015] The illumination unit 6 is configured to emit illumination light C toward the liquid crystal display element 7. The configuration of the illumination unit 6 is arbitrary, but for example, the illumination unit 6 is configured to include a plurality of LEDs (Light Emitting Diodes), a condenser lens, a lenticular lens, a light diffuser plate, etc., mounted on a light source substrate in order from furthest from the liquid crystal display element 7. Furthermore, as the illumination unit 6, known configurations such as the configuration described in Japanese Patent Application Publication No. 2020-160293 can be appropriately adopted.
[0016] The liquid crystal display element 7 emits display light L that represents an image upon receiving illumination light C. The liquid crystal cell 10 is, for example, a TFT (Thin Film Transistor) liquid crystal of an active matrix driving method. The liquid crystal cell 10 includes 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 positioned on the side of the first polarizer 21. The pair of substrates 11 and 12 are each formed transparently from glass, plastic, or the like. 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 process according to the type of the liquid crystal cell 10.
[0017] 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 IPS, which will be 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).
[0018] 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 accordingly, the liquid crystal display element 7 displays an image by the combination of each pixel in a transmitted or non-transmitted state. How the liquid crystal display element 7 displays an image varies according to the type of the liquid crystal cell 10.
[0019] As the type of the liquid crystal cell 10, any type such as TN (Twisted Nematic), VA (Vertical Alignment), IPS (In-Plane Switching), etc. can be adopted, and the type is not limited.
[0020] The first polarizer 21 and the second polarizer 22 face each other across the liquid crystal cell 10. The first polarizer 21 is positioned at a distance from the liquid crystal cell 10. The first polarizer 21 is a well-known polarizing film (also called a polarizing plate), and emits light incident from one side as linearly polarized light along a transmission axis 21a (see Figure 4) perpendicular to the absorption axis from the other side. The first polarizer 21 is held by a holding member (not shown) and is rotatable about a rotation center line parallel to the optical axis passing through the first polarizer 21. This rotation center line may coincide with the optical axis. The first polarizer 21 is rotationally driven by a rotation drive unit 8.
[0021] 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.
[0022] The rotation drive unit 8 includes a motor, gear mechanism, etc., and rotates the first polarizer 21 under the control of the control unit 9. The rotation drive unit 8 can switch the first polarizer 21 between a first rotation position and a second rotation position, in which the transmission axis 21a faces 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 first polarizer 21 in which the transmission axis 21a is aligned with S polarization, and (ii) the second rotation position is the rotation position of the first polarizer 21 in which the transmission axis 21a is aligned with P polarization. In other words, the first rotation position and the second rotation position in this embodiment are 90° apart from each other around the rotation center line.
[0023] In this embodiment, the second polarizer 22 is positioned in a crossed nicol configuration with respect to the first polarizer 21 in the first rotation position. A crossed nicol configuration means that the transmission axis 21a of the first polarizer 21 and the transmission axis (not shown) of the second polarizer 22 are orthogonal. On the other hand, the second polarizer 22 is in a parallel nicol configuration with respect to the first polarizer 21 in the second rotation position. A parallel nicol configuration means that the transmission axis 21a of the first polarizer 21 and the transmission axis (not shown) of the second polarizer 22 are parallel. 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] When the first polarizer 21 is in the first rotation position (i.e., when the first polarizer 21 and the second polarizer 22 are crossed nicols), the liquid crystal display element 7 displays the image in the following ways: (i) when the type of liquid crystal cell 10 is TN, (ii) when the type of liquid crystal cell 10 is VA, and (iii) when the type of liquid crystal cell 10 is IPS. On the other hand, when the first polarizer 21 is in the second rotation position (i.e., when the first polarizer 21 and the second polarizer 22 are parallel nicols), if no countermeasures are taken, the display mode will be reversed compared to when the first polarizer 21 is in the first rotation position. In this embodiment, as described later, this problem is solved by reversing the color tone (gradation) of the image represented by the display light L when the first polarizer 21 is in the second rotation position compared to when the first polarizer 21 is in the first rotation position.
[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, S-polarized display light L is emitted from the first polarizer 21 at the first rotation position, and P-polarized display light L is emitted from the first polarizer 21 at the second rotation position.
[0026] In the following, the state in which the first polarizer 21 is in the first rotation position may be referred to as the first state, and the state in which the first polarizer 21 is in the second rotation position may be referred to as the second state.
[0027] Figure 4 is a diagram illustrating the control of the polarization state of the display light L emitted from the first polarizer 21. 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. The light that receives illumination light C, passes through the second polarizer 22 to become linearly polarized, and passes through the liquid crystal cell 10 becomes control light Lc, which is controlled to be either S-polarized or P-polarized depending on the liquid crystal state of the liquid crystal layer 13. The polarization state of the control light Lc is controlled to be either S-polarized or P-polarized for each region of the liquid crystal layer 13 corresponding to a pixel by applying a voltage through the transparent electrode of the liquid crystal cell 10. For example, when the display mode is NB mode when the first polarizer 21 is in the first rotation position, in the region of the liquid crystal layer 13 corresponding to a pixel, the control light Lc is P-polarized when the voltage is off, and the control light Lc is S-polarized when the voltage is on. Furthermore, when the display mode is NW mode with the first polarizer 21 in the first rotation position, in the region of the liquid crystal layer 13 corresponding to the pixel, the control light Lc becomes S-polarized when the voltage is off, and the control light Lc becomes P-polarized when the voltage is on.
[0028] The left-hand diagram in Figure 4 represents the first state (i.e., the state where the first polarizer 21 is in the first rotation position). In this case, only the S-polarized component of the control light Lc that has passed through the liquid crystal cell 10 passes through the transmission axis 21a of the first polarizer 21, and as a result, S-polarized display light L is emitted from the first polarizer 21. In other words, in the first state, S-polarized display light L is emitted from the display unit 5.
[0029] The right-hand diagram in Figure 4 represents the second state (i.e., the state where the first polarizer 21 is in the second rotation position). In this case, only the P-polarized component of the control light Lc that has passed through the liquid crystal cell 10 passes through the transmission axis 21a of the first polarizer 21, and as a result, the first polarizer 21 emits P-polarized display light L. In other words, in the second state, the display unit 5 emits P-polarized display light L.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] Furthermore, the control unit 9 communicates with input devices (not shown) mounted on the vehicle, such as a touch panel and steering wheel switches, 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 first polarizer 21 from one of the first state and the second state to the other state (that is, switches the first polarizer 21 from one of the first rotation position and the second rotation position to the other position).
[0034] 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 first polarizer 21 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 first polarizer 21 to the second state. In other words, the control unit 9 switches the first polarizer 21 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 first polarizer 21 from one of the first rotation position and the second rotation position to the other position).
[0035] Furthermore, the control unit 9 may control the brightness of the illumination light C emitted by the illumination unit 6 to be lower when the first polarizer 21 is in the first rotation position (i.e., the first state suitable when the user 4 is not wearing polarized sunglasses) than when the first polarizer 21 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.
[0036] Furthermore, the control unit 9 controls the operation of the liquid crystal display element 7 so that when the first polarizer 21 is in the second rotation position (second state) compared to when it is in the first rotation position (first state), the color tone (gradation) of the image represented by the display light L is reversed.
[0037] Here, if the color specifications of the liquid crystal display element 7 are such that the R (red), G (green), and B (blue) subpixels are each represented by 8 bits, then the RGB subpixels are each represented by 256 gradations from 0 to 255. In other words, if the color tone of any pixel that makes up the image is represented as R(x), G(y), and B(z), then x, y, and z each represent values from 0 to 255. In this case, if we denote the maximum value of the color tone, 255, as M, then color inversion means converting the color tone of the pixel in question to R(Mx), G(My), and B(Mz). For example, if the control unit 9 controls the color tone of any pixel constituting the image with R(200), G(0), B(50) in the first state, then in the second state, it controls the color tone of that pixel with R(255-200), G(255-0), B(255-50) (i.e., it controls it with R(55), G(255), B(205)).
[0038] As a result, when the liquid crystal display element 7 is in the second rotation position compared to the first rotation position, the color tone (gradation) of the image represented by the display light L is inverted. This prevents the color tone of the image represented by the display light L, as seen by the user 4, from being inverted between the first and second states, and suppresses any sense of unnaturalness for the user 4 when transitioning from one state to the other. The color tone inversion method is the same as above even when each of the R, G, and B subpixels is represented by something other than 8 bits (for example, 10 bits, 12 bits). In other words, when x, y, and z are each represented from 0 to M (where M is the maximum value of the color tone), color tone inversion means converting R(x), G(y), B(z) to R(Mx), G(My), B(Mz).
[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 represented by the display light L can be considered as the image in the region where the transmission and opacity of light can be controlled within the liquid crystal display element 7. When the image is monochrome, color inversion means reversing the brightness and darkness (white and black).
[0042] The second polarizer 22 may be positioned in parallel with the first polarizer 21 at the first rotation position. In this case, the display mode is reversed compared to the above embodiment, but the fact that S-polarized display light L is emitted from the first polarizer 21 at the first rotation position and P-polarized display light L is emitted from the first polarizer 21 at the second rotation position remains unchanged.
[0043] In the above explanation, explanations of publicly known technical matters have been omitted where appropriate to facilitate understanding of this disclosure.
[0044] 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]
[0045] 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, 21a...transmission axis 22…Second polarizer C…Illumination light Lc...Control 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, The system comprises a rotational drive unit that rotates the first polarizer, which is positioned at a distance from the liquid crystal cell, A head-up display device that receives the illumination light and emits display light from the liquid crystal display element onto the windshield, The display light emitted from the liquid crystal display element is linearly polarized along the transmission axis of the first polarizer. The rotation drive unit is capable of switching the first polarizer to a first rotation position and a second rotation position in which the transmission axes are oriented in different directions. From the first polarizer at the first rotation position, the S-polarized display light is emitted toward the reflective surface of the windshield. From the first polarizer at the second rotation position, the display light with P polarization is emitted toward the reflective surface. The liquid crystal display element inverts the color tone of the image represented by the display light when the first polarizer is in the second rotation position compared to when the first polarizer is in the first rotation position. Head-up display device.
2. The brightness of the illumination light emitted by the illumination unit is lower when the first polarizer is in the first rotation position than when the first polarizer 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 rotation 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 first polarizer 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.