Head-up display and head-up display design method

Abstract

In order to increase the display quality of a head-up display, the head-up display according to the present invention is configured so as to comprise a display element 1 that emits display light PL indicating vehicle information, a case C that accommodates the display element 1 and has an emission port from which the display light PL is emitted to the outside, an optical element 3 including a translucent dust cover 33 that covers the emission port, and a phase element 2 that is constituted from a plurality of phase difference plates 21-23 having different polarization characteristics and is disposed at a prescribed inclination θ with respect to the principal ray of the display light PL. The phase element 2 is designed by a first step S1 for setting a light propagation characteristic of the optical element 3, and a second step S2 for setting a target value of emission light of the optical element 3 and calculating the polarization characteristics of each of the plurality of phase difference plates and the inclination θ serving as an approximate solution for the target value.

Description

[Technical Field]

[0001] The present disclosure relates to a head-up display mounted in a vehicle. [Background technology]

[0002] A head-up display is disclosed in Patent Document 1. In this head-up display, display light emitted from a liquid crystal display is reflected by multiple reflecting mirrors, passes through a light-transmitting dustproof cover that covers the light outlet, and is further reflected by the vehicle windshield, causing a virtual image of the display light to be visible to the driver's eyes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-14153 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inventors of the present disclosure have discovered that in the process of passing through or reflecting off each optical element, such as a reflecting mirror, a translucent dustproof cover, or a windshield, unintended polarization or a decrease in brightness occurs in the display light due to the influence of the arrangement of each optical element, etc.

[0005] In view of the above-mentioned problems, the present disclosure aims to improve the display quality of a head-up display. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the head-up display of the present disclosure includes: an indicator that emits an indicator light that indicates vehicle information; a case that houses the indicator and has an outlet that emits the indicator light to the outside; an optical element including a light-transmitting dustproof cover covering the light exit opening; The polarizer is made up of a plurality of retardation plates with different polarization characteristics and is disposed at a predetermined inclination with respect to the principal ray of the display light.

[0007] In order to solve the above-described problems, the design method of the head-up display of the present disclosure includes: A design method for a head-up display in which display light emitted by a display element is visually recognized through an optical element and a phase shifter, the retarder is composed of a plurality of retardation plates having different polarization characteristics, and is disposed on an optical path of the display light at a predetermined inclination with respect to a principal ray of the display light, a first step of setting the optical propagation characteristics of the optical element; and a second step of setting a target value of the emitted light of the optical element, and calculating the inclination and the polarization characteristics of each of the plurality of retardation plates that are an approximate solution to the target value. [Effects of the Invention]

[0008] According to the present disclosure, the display quality of the virtual image displayed by the head-up display is improved. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic diagram of head-up display configuration [Figure 2] Diagram showing light propagation in a head-up display [Figure 3] Diagram showing the arrangement of the retarder [Figure 4] Diagram showing the design procedure for the phase shifter DETAILED DESCRIPTION OF THE INVENTION

[0010] The head-up display (HUD) of the present disclosure will be described with reference to the accompanying drawings.

[0011] See Figures 1 and 2. The head-up display HUD is mounted in the instrument panel of a vehicle and projects display light PL toward the windshield WS of the vehicle, which is located in front of the eyes of a passenger (mainly the driver) P. The display light PL is reflected by the windshield WS, allowing the passenger P to see a virtual image V of the display light PL in front of the windshield WS.

[0012] The head-up display HUD has a display element 1, a phase shifter 2, a first reflecting mirror 31, a second reflecting mirror 32, a control unit 4, and a case C having an exit port covered with a translucent dustproof cover 33.

[0013] The indicator 1 emits display light that displays vehicle information. Of this display light, a reference ray that passes through the center of the indicator 1 is defined as a principal ray PL. The indicator 1 is, for example, a liquid crystal display, and includes a light source 11 and a liquid crystal panel 12. Note that the indicator 1 may be an organic EL display, a projector, or the like, in addition to a liquid crystal display.

[0014] The light source 11 is a backlight that illuminates the liquid crystal panel 12. The light source 11 is, for example, an LED that emits white light. Although not shown, various lenses such as a collimator lens that converts the light emitted by the light source 11 into uniform parallel light are arranged between the light source 11 and the liquid crystal panel 12.

[0015] The liquid crystal panel 12 is, for example, a TFT (Thin Film Transistor) active matrix panel. The liquid crystal panel 12 has a liquid crystal cell composed of a pair of transparent substrates and a liquid crystal layer sealed between the substrates, and polarizing filters facing each other across the liquid crystal cell. When a driving voltage is applied to the liquid crystal layer under the control of the control unit 4, the liquid crystal panel 12 controls the orientation of the liquid crystal molecules in the liquid crystal layer, thereby switching between a transmissive state and a non-transmissive state for each pixel arranged in a matrix. Because unpolarized light from the light source 11 passing through a pixel in the transmissive state is polarized to linearly polarized light and passes through, the liquid crystal panel 12 can also be defined as a polarizer.

[0016] The liquid crystal panel 12 is controlled by the control unit 4 to switch between a transparent state and a non-transparent state for each pixel to display a predetermined image. This image may be, for example, figures or numbers representing vehicle information such as the vehicle's traveling speed, vehicle warnings, and route guidance information.

[0017] The retarder 2 is a laminated retardation plate in which retardation films that generate a plurality of different retardations are laminated. Different retardations refer to, for example, different azimuth angles or ellipticity angles for specific wavelengths. The retarder 2 is disposed on the optical path through which the display light PL passes, tilted by θ degrees with respect to the principal ray of the display light PL emitted by the display element 2. As shown in FIG. 3 , in this embodiment, the retarder 2 is disposed between the display element 1 and the optical element 3. The retarder 2 is formed by laminating three retardation films, namely, retardation films 21, 22, and 23 made of resin. The tilt θ of the retarder 2 and the characteristics of each of the retardation films 21 to 23 will be described in detail in the "Design Procedure for Retarder 2" section below.

[0018] An optical element that reflects or transmits the display light PL on the optical path from the display light PL to the eyes of the passenger P is defined as an optician 3. In this embodiment, the optician 3 corresponds to the first reflecting mirror 31, the second reflecting mirror 32, the light-transmitting dustproof cover 33, and the windshield WS. Here, the optician provided in the head-up display HUD is defined as an internal optician. The internal optician corresponds to the first reflecting mirror 31, the second reflecting mirror 32, and the light-transmitting dustproof cover 33. Furthermore, an optician that is not an internal optician but is outside the head-up display HUD is defined as an external optician. The external optician corresponds to the windshield WS.

[0019] The first reflecting mirror 31 is a reflecting mirror that reflects the display light PL that has passed through the phase shifter 2 toward the second reflecting mirror 32. The first reflecting mirror 31 is, for example, a plane mirror.

[0020] The second reflecting mirror 32 is a reflecting mirror that reflects the display light PL reflected by the first reflecting mirror 31 toward the light exit port of the case C. The second reflecting mirror 32 is, for example, a concave mirror.

[0021] The light-transmitting dustproof cover 33 is a transparent resin film made of acrylic resin, polycarbonate resin, etc. The light-transmitting dustproof cover 33 covers the light exit opening formed in the case C, and is curved along the light exit opening.

[0022] The control unit 4 is a circuit board having a microcontroller that controls the display element 1.

[0023] The case C is a case made of black resin or metal with light blocking properties, and houses the display element 1, the phase shifter 2, the first reflecting mirror 31, the second reflecting mirror 32, and the control unit 4.

[0024] (Design procedure for phase shifter 2) The design procedure for the retarder 2 will be described below with reference to Fig. 4. The following design procedure will obtain optimal values ​​(approximate solutions) for the characteristics and arrangement of the three retardation films 21, 22, and 23.

[0025] (Process S1) In step S1, quantitative evaluation values ​​of the incident light and the outgoing light of each optical element 3 at the three wavelengths of red, green, and blue light are measured, and the light propagation characteristics of each optical element 3 are calculated from these quantitative evaluation values. Note that this measurement is performed in the absence of the phase shifter 2. After performing step S1, step S2 is performed.

[0026] In this embodiment, the wavelength of the red light is, for example, 488 nm. The wavelength of the green light is, for example, 532 nm. The wavelength of the blue light is, for example, 632 nm. The optical elements 3 are the first reflecting mirror 31, the second reflecting mirror 32, the light-transmitting dustproof cover 33, and the windshield WS. Here, the measurement of the quantitative evaluation value of the incident light on the first reflecting mirror 31, which is located at the forefront, is in a state where the phase shifter 2 is not present, and therefore is also the quantitative evaluation value of the emitted light from the display element 1.

[0027] The measurement of the quantitative evaluation values ​​of the incident light and the emitted light of the optical element 3 refers to, for example, the Stokes parameters. As a specific example, the Stokes parameters of incident light a(λ) of one optical element 3 at wavelength λ are measured as four Stokes parameters Sa0(λ), Sa1(λ), ​​Sa2(λ), and Sa3(λ).Furthermore, the Stokes parameters of output light b(λ) of one optical element 3 at wavelength λ are measured as four Stokes parameters Sb0(λ), Sb1(λ), ​​Sb2(λ), and Sb3(λ).

[0028] The propagation characteristics of the light of the optical element 3 are, for example, the amplitude ratio angle and the phase difference. These amplitude ratio angle and the phase difference can be derived from the above-mentioned Stokes parameters.

[0029] (Process S2) In step S2, a target value of the output light b(λ) at wavelength λ of the final-stage optical element 3 is set, and the polarization characteristics and arrangement of the retarder 2 that satisfy (or approximate) this target value are calculated. An optimal solution (approximate solution) for the polarization characteristics and arrangement of the retarder 2 is calculated using a genetic algorithm. The detailed procedure of step S2 of this genetic algorithm is shown in the following steps S21 to S27, and step S21 is executed first.

[0030] (Step S21) In step S21, various condition values ​​for the genetic algorithm are set. After step S21 is executed, step S22 is executed.

[0031] Specific examples of the various condition values ​​in step S22 are as follows. This example is for obtaining a phase shifter 2 that has the highest display luminance efficiency when a passenger P views the virtual image V with the naked eye without wearing polarized sunglasses. The initial genes of the phase shifter 2 have no polarization characteristics or tilt, and are in a state that has no effect on the display light PL. (1) Initial value of phase shifter 2 (initial gene) (1A) The tilt of the entire phase shifter 2 is θ=0 (1B) No polarization characteristics of retardation films 21 to 23 (2) Evaluation function: S-polarized component of the light emitted from the last optical element 3 at each wavelength of the discretized number of spectra (3) Crossover method: 1 point crossover (4) Crossover rate: 90% (5) Mutation rate: 10% (6) Selection method: Elite selection (20% selection) (7) Initial population: 100 individuals (8) Initial group selection method: random selection (9) Number of generations: 1000 (10) Polarization analysis method: Jones matrix method (11) Refractive index dispersion of the material: Use the phase difference measured by the Senarmont method and the ratio of each wavelength

[0032] (Step S22) In step S22, one gene is selected from the current generation population and set as the setting value of the phase shifter 2, and light propagation is simulated. This simulation simulates the propagation of display light PL emitted by the display element 1 as it passes through the phase shifter 2 and each optical element 3. This simulation calculates quantitative evaluation values ​​of the incident light and emitted light of each optical element 3. After step S22 is performed, step S23 is performed.

[0033] (Step S23) In step S23, an evaluation value is calculated based on the evaluation function. This evaluation value becomes the evaluation value of the setting value (gene) of the phase shifter 2. After step S23 is executed, step S24 is executed.

[0034] (Step S24) In step S24, it is determined whether there are any unselected genes in the current generation population. If there are no unselected genes, step S25 is executed. If there are unselected genes, one gene is selected from the unselected genes and step S22 is executed again.

[0035] (Step S25) In step S25, genes in the current generation population are selected. In this embodiment, genes in the current generation population are selected by elite selection (20% selection). After step S25 is performed, step S26 is performed.

[0036] (Step S26) In step S26, crossover and mutation are performed based on the genes of the current generation population to create the next generation population. In this embodiment, the crossover method is one-point crossover, and the mutation rate is set to 10%. After step S26 is performed, step S27 is performed.

[0037] (Step S27) In step S27, it is determined whether the selection of the next generation is unnecessary. If the current generation has reached the number of generations set in step S22, it is determined that the selection of the next generation is unnecessary, and step S3 is executed. If the current generation has not reached the number of generations set in step S22, the next-generation population created in step S26 is selected as the current-generation population, and step S22 is executed again.

[0038] (Process S3) In step S3, the gene with the highest evaluation value is selected from the genes obtained in the above-mentioned step S2 (steps S21 to S27).

[0039] In this embodiment, the phase shifter 2 with the genes obtained in step S3 as the set value was found to have the following characteristics when the following phase difference films 21 to 23 were arranged at an inclination θ of 46°.

[0040] (Characteristics of the retardation film 21) The retardation film 21 has an azimuth angle of −88° and an ellipticity angle of 2.2° for a wavelength of 488 nm, an azimuth angle of −88° and an ellipticity angle of 15° for a wavelength of 532 nm, and an azimuth angle of −87° and an ellipticity angle of 33° for a wavelength of 632 nm.

[0041] (Characteristics of the retardation film 22) The retardation film 22 has an azimuth angle of −42° and an ellipticity angle of 4.4° for a wavelength of 488 nm, an azimuth angle of 39° and an ellipticity angle of −12° for a wavelength of 532 nm, and an azimuth angle of −29° and an ellipticity angle of 20° for a wavelength of 632 nm.

[0042] (Characteristics of retardation film 23) The retardation film 23 has an azimuth angle of −34° and an ellipticity angle of −34° for a wavelength of 488 nm, an azimuth angle of −20° and an ellipticity angle of 32° for a wavelength of 532 nm, and an azimuth angle of −7.9° and an ellipticity angle of 26° for a wavelength of 632 nm.

[0043] As described above, the multiple retardation films 21-23 of the retarder 2 obtained by the optimal solution (approximate solution) are designed to offset adverse effects such as accumulated minute polarization due to the arrangement of each optical element 3, and are designed based on a concept completely different from that of a wave plate such as a λ / 4 plate that simply converts linearly polarized light emitted from the display element 1 into circularly polarized light. In particular, by using the multiple retardation films 21-23, the effects of the multiple optical elements 3 can be widely offset.

[0044] The above is the design procedure for the phase shifter 2.

[0045] In the above-described embodiment, the retarder 2 is configured with three retardation films 21 to 23, but is not limited to this. At least two retardation films are sufficient, and for example, five or seven retardation films may be used. In a preferred embodiment, the number of retardation films in the retarder 2 is set so as to correspond to each optical element 3. In this case, since each retardation film can be designed to cancel out the corresponding optical element 3, when there is a change in the components of the head-up display, the change can be accommodated by adding a retardation film corresponding to the optical element at the change point to the retarder 2, which makes the design easier.

[0046] In the above-described embodiment, it is preferable to place the phase shifter 2 between the display element 1 and the optical element 3, but this is not limiting. The phase shifter 2 may be placed anywhere between the display element 1 and the external optical element (windshield WS). For example, the phase shifter 2 may be placed between the second reflecting mirror 32 and the light-transmitting dustproof cover 33 of the internal optical element (first reflecting mirror 31, second reflecting mirror 32, and light-transmitting dustproof cover 33).

[0047] In the above-described embodiment, the phase shifter 2 is designed by evaluating the light emitted from the windshield WS of the external optical element, which is the optical element 3 at the final stage. However, the present invention is not limited to this. When evaluating the head-up display HUD alone, the light emitted from the light-transmitting dustproof cover 33 at the final stage of the internal optical element may be evaluated. Alternatively, the light emitted from any optical element 3 may be evaluated.

[0048] In the above-described embodiment, an example has been shown in which the phase shifter 2 is designed to be optimal for the case in which the passenger P views the virtual image V with the naked eye without wearing polarized sunglasses, but the present disclosure is not limited to this. The present disclosure is suitable for obtaining a phase shifter 2 that offsets adverse effects due to the arrangement of the optical element 3, etc., in order to obtain desired output light.

[0049] For example, when designing an optimal phase shifter 2 for when a passenger P is wearing polarized sunglasses and viewing a virtual image V, this can be achieved by setting an evaluation function that evaluates "the intensity of the P-polarized component of the light emitted from the last-stage optical element 3 at each wavelength of the discretized number of spectra."

[0050] Furthermore, when designing a phase shifter 2 that provides uniform display quality regardless of whether passenger P is wearing polarized sunglasses, this can be achieved by setting an evaluation function that evaluates the "difference in intensity between the S-polarized component and the P-polarized component of the light emitted from the final-stage optical element 3 at each wavelength of the discretized number of spectra." Alternatively, this can be achieved by designing a phase shifter 2 that is closest to circularly polarized light using an evaluation function that evaluates the "flattening of the polarized component of the light emitted from the final-stage optical element 3."

[0051] In the above-described embodiment, the initial genes of the retarder 2 are set to have no polarization characteristics or tilt and to have no effect on the display light PL, but the present invention is not limited to this. In order to easily obtain an optimal solution (approximate value) of the genetic algorithm, it is preferable to set predetermined values ​​of polarization characteristics and tilt.

[0052] As described above, the head-up display of the present disclosure is configured to include a display element 1 that emits display light PL that displays vehicle information, a case C that houses the display element 1 and has an outlet through which the display light PL is emitted to the outside, an optical element 3 that includes a light-transmitting dustproof cover 33 that covers the outlet, and a phase shifter 2 that is composed of a plurality of retardation plates 21 to 23 with different polarization characteristics and is positioned at a predetermined inclination θ with respect to the principal ray of the display light PL. With this configuration, the adverse effect on the display light PL caused by the arrangement of the display element 1 and the optical element 3 can be offset by the phase shifter 2, thereby suppressing degradation of the display quality. In other words, the inventors of the present disclosure have discovered that the problem of adverse effects such as polarization caused by differences in the incident angles of the display light PL on the first reflecting mirror 31, the second reflecting mirror 32, and the translucent dustproof cover 33 can be solved by providing a phase shifter 2 that offsets the adverse effects caused by the optical element 3.

[0053] The head-up display design method of the present disclosure is a design method for a head-up display in which display light PL emitted by a display element 1 is viewed via an optical element 3 and a retarder 2. This design method is such that the retarder 2 is composed of a plurality of retardation plates 21 to 23 having different polarization characteristics, and is arranged on the optical path of the display light PL at a predetermined inclination θ with respect to the principal ray of the display light PL. The design method includes a first step S1 of setting the light propagation characteristics of the optical element 3, and a second step S2 of setting a target value for the light emitted from the optical element 3 and calculating the inclination θ and the polarization characteristics of each of the plurality of retardation plates, which are approximate solutions to the target value. By configuring in this way, it is possible to design a phase shifter 2 that offsets the adverse effect on the display light PL caused by the arrangement of the display element 1 and the optical element 3. [Explanation of symbols]

[0054] 1: Indicator 11:Light source 12: LCD panel (polarizer) 2: Phaser 21: Phase difference film (phase difference plate) 22: Phase difference film (phase difference plate) 23: Phase difference film (phase difference plate) 3: Optical element (internal optical element) 31: 1st reflector 32:Second reflector 33: Translucent dustproof cover 4: Control section WS: Windshield (external optics) HUD: Head-up display PL:Display light

Claims

1. an indicator that emits an indicator light that indicates vehicle information; a case that houses the indicator and has an outlet that emits the indicator light to the outside; an optical element including a light-transmitting dustproof cover covering the light exit opening; a phase shifter that is composed of a plurality of phase difference plates having different polarization characteristics and that is disposed at a predetermined inclination with respect to a principal ray of the display light; A head-up display comprising: The phase shifter does not have a reflecting portion that reflects the display light and changes the optical path through which the display light passes, but allows the display light to pass through.

2. The plurality of retardation plates are stacked. The head-up display according to claim 1 .

3. The phase shifter is disposed between the display element and the optical element. The head-up display according to claim 1 or 2.

4. A design method for a head-up display in which display light emitted by a display element is visually recognized through an optical element and a phase shifter, the retarder is composed of a plurality of retardation plates having different polarization characteristics, and is disposed on an optical path of the display light at a predetermined inclination with respect to a principal ray of the display light, a first step of setting the optical propagation characteristics of the optical element; a second step of setting a target value of the output light of the optical element, and calculating the inclination and the polarization characteristics of each of the plurality of retardation plates that are an approximate solution to the target value; A method for designing a head-up display comprising:

5. the first step deriving the propagation characteristics from a measurement value of a quantitative evaluation value of the optical element in a state where the phase shifter is not present; the second step searches for the approximate solution using a genetic algorithm; The method for designing a head-up display according to claim 4.

6. the evaluation function of the genetic algorithm evaluates the intensity of S-polarized light or P-polarized light at at least three wavelengths of the output light of the optical element; The method for designing a head-up display according to claim 5.

7. the evaluation function of the genetic algorithm evaluates the flattening of polarization components of polarized light at at least three wavelengths of the output light of the optical element; The method for designing a head-up display according to claim 5.

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