Display device and control method for display device

Abstract

This display device (1) comprises an image displayer (10) that has a display function layer (11), a first projector (20) that irradiates the image displayer (10) with ultraviolet light, a second projector (40) that irradiates an irradiation region (10c) on the image displayer (10), in which the light scattering properties of the display function layer (11) are increased, with visible light having an arbitrarily defined wavelength so as to display a visible light image (60), a temperature measurement unit (70) that measures the ambient temperature, and a control unit (50) that controls the ultraviolet light radiation and the visible light radiation, wherein: in the display function layer (11), the rate of increase in the light scattering intensity due to the reception of ultraviolet light having a constant intensity differs depending on the ambient temperature; and when the ambient temperature satisfies an alignment temperature condition, the control unit (50) determines the length of the radiation time of the ultraviolet light on the basis of the ambient temperature and controls the ultraviolet light radiation on the basis of the length of the radiation time such that the light scattering intensity in the irradiation region (10c) is constant.

Description

Display device and control method for display device

[0001] This disclosure relates to a display device and a method for controlling the display device.

[0002] In recent years, display devices have been developed that use technology to display images on transparent glass such as car windshields and building windows. Patent Document 1 discloses a display device that has a display functional layer whose light scattering properties increase when exposed to ultraviolet light, which is then projected onto the image display body to create a screen (make it opaque), and then projected onto the image display body to display an image related to the visible light (visible light image).

[0003] Patent No. 7063081

[0004] The display function layer of an image display unit has the property that the intensity of light scattering (light scattering intensity) when receiving ultraviolet light (when screened) changes depending on the temperature of the operating environment of the display unit (for example, the location where the image display unit is installed). Therefore, there is a risk that the brightness of the visible light image displayed on the image display unit will fluctuate due to changes in the temperature of the operating environment. However, the display unit of Patent Document 1 does not take into consideration keeping the brightness of the visible light image displayed on the image display unit constant.

[0005] Therefore, the purpose of this disclosure is to provide a technology that can keep the brightness of a visible light image displayed on an image display device constant even when temperature changes occur in the operating environment.

[0006] A display device according to one aspect of the present disclosure includes: an image display body having a display function layer whose light scattering intensity increases when it receives ultraviolet light under predetermined temperature conditions and decreases when it receives visible light in a specific wavelength range; an ultraviolet light irradiation unit that irradiates the image display body with ultraviolet light; a visible light irradiation unit that irradiates an irradiated area on the image display body, where the light scattering intensity of the display function layer has increased due to the irradiation of ultraviolet light, with visible light of an arbitrary wavelength to display a visible light image in the irradiated area; a temperature measuring unit that measures the ambient temperature indicating the temperature of the environment in which the image display body is used; and a control unit that controls the irradiation of ultraviolet light from the ultraviolet light irradiation unit and the irradiation of visible light from the visible light irradiation unit, wherein the rate of increase in light scattering intensity due to the reception of ultraviolet light of a constant intensity in the display function layer differs depending on the ambient temperature, and the control unit determines the irradiation time of ultraviolet light by the ultraviolet light irradiation unit based on the ambient temperature when the ambient temperature satisfies the temperature conditions, and controls the irradiation of ultraviolet light based on the irradiation time so that the light scattering intensity in the irradiated area remains constant.

[0007] Furthermore, a display device in another aspect of the present disclosure includes an image display body having a display function layer whose light scattering intensity increases when exposed to ultraviolet light under predetermined temperature conditions and decreases when exposed to visible light in a specific wavelength range; an ultraviolet light irradiation unit that irradiates the image display body with ultraviolet light; a visible light irradiation unit that irradiates an irradiated area on the image display body, where the light scattering intensity of the display function layer has increased due to the irradiation of ultraviolet light, with visible light of an arbitrary wavelength to display a visible light image on the image display body; a temperature measuring unit that measures the ambient temperature indicating the temperature of the environment in which the image display body is used; and a control unit that controls the irradiation of ultraviolet light from the ultraviolet light irradiation unit and the irradiation of visible light from the visible light irradiation unit, wherein the rate of increase in the light scattering intensity of the irradiated area due to the reception of ultraviolet light of a certain intensity varies depending on the ambient temperature, and the control unit controls the irradiation of visible light such that the visible light illuminance in the irradiated area where the visible light image is displayed increases as the ambient temperature decreases within a temperature range that satisfies the temperature conditions.

[0008] Furthermore, a control method for a display device according to one aspect of the present disclosure is a control method for a display device that irradiates an image display body having a display function layer whose light scattering intensity increases when it receives ultraviolet light under predetermined temperature conditions and whose light scattering intensity decreases when it receives visible light in a specific wavelength range with ultraviolet light, and irradiates an irradiated area on the image display body where the light scattering intensity of the display function layer has increased due to the irradiation of ultraviolet light with visible light of an arbitrary wavelength to display a visible light image on the image display body, wherein the rate of increase in the light scattering intensity of the irradiated area due to the reception of ultraviolet light of a constant intensity differs depending on the ambient temperature, which indicates the temperature of the environment in which the image display body is used, and when the ambient temperature satisfies the temperature conditions, the length of the irradiation time of ultraviolet light to the irradiated area of ​​the image display body is determined based on the ambient temperature, and the irradiation of ultraviolet light to the irradiated area is controlled based on the irradiation time length so that the light scattering intensity of the irradiated area remains constant.

[0009] Furthermore, a control method for a display device in another aspect of the present disclosure is a control method for a display device in which ultraviolet light is irradiated onto an image display body having a display function layer whose light scattering intensity increases when it receives ultraviolet light under predetermined temperature conditions and decreases when it receives visible light in a specific wavelength range, visible light of an arbitrary wavelength is irradiated onto an irradiated area on the image display body where the light scattering intensity of the display function layer has increased due to the irradiation of ultraviolet light, and a visible light image is displayed on the image display body, wherein the rate of increase in the light scattering intensity of the irradiated area due to the reception of ultraviolet light of a certain intensity differs depending on the ambient temperature, which indicates the temperature of the environment in which the image display body is used, and after irradiating the irradiated area with ultraviolet light for a certain irradiation time and with a certain ultraviolet light intensity, the visible light image is displayed on the image display body by irradiating with visible light, and the irradiation of visible light to the irradiated area is controlled such that the lower the ambient temperature is within the temperature range that satisfies the temperature conditions, the higher the visible light illuminance in the irradiated area where the visible light image is displayed.

[0010] According to this disclosure, it becomes possible to keep the brightness of the visible light image displayed on the image display device constant even when temperature changes occur in the operating environment.

[0011] This is a perspective view showing the schematic configuration of a display device according to the first embodiment of this disclosure. This is a cross-sectional view showing the schematic configuration of the image display body shown in Figure 1. This is a cross-sectional view showing the schematic configuration of the display function layer in a transparent state. This is a cross-sectional view showing the schematic configuration of the display function layer in an opaque state. This is a graph illustrating an example of the behavior of increasing light scattering intensity due to orientation temperature conditions and ultraviolet light irradiation. This is a block diagram showing an example of the hardware and functional configuration of the control unit. This is a graph illustrating an example of the correspondence between ultraviolet light irradiation time and light scattering intensity. This is a flowchart showing an example of a control method for a display device according to the first embodiment of this disclosure. This is a graph showing an example of the change in light scattering intensity value due to the passage of ultraviolet light irradiation time for each condition of ambient temperature and ultraviolet light irradiation intensity. This is a flowchart showing an example of a control method for a display device according to a first modification of the first embodiment of this disclosure. This is a block diagram showing an example of the hardware and functional configuration of the control unit in a display device according to the second embodiment of this disclosure. This is a flowchart showing an example of a control method for a display device according to the second embodiment of this disclosure. This is a perspective view showing the schematic configuration of a display device according to the third embodiment of this disclosure.

[0012] Embodiments of the present invention will be described below with reference to the drawings. Note that the drawings are schematic and may differ from actual ones. Furthermore, the embodiments of the present invention described below are illustrative examples of devices and methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited to the structure, arrangement, etc., of the components described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims.

[0013] 1. Figure 1 of the first embodiment is a perspective view showing the schematic configuration of a display device 1 according to the first embodiment of the present invention. The display device 1 of this embodiment includes an image display body 10, a first projector (an example of an ultraviolet light emitting unit) 20, a second projector (an example of a visible light emitting unit) 40, a control unit 50, and a temperature measuring unit 70.

[0014] The image display body 10 is a thin plate-shaped member whose optical state changes between a transparent state and an opaque state, and has a front surface 10a facing the first projector 20 and the second projector 40, and a back surface 10b opposite the front surface 10a. The image display body 10 changes from a transparent state (non-screen state) to an opaque state (screen state) when it receives ultraviolet light, and changes from an opaque state to a transparent state when it receives visible light in a specific wavelength range. The image display body 10 may be attached, for example, to the windshield of an automobile. A detailed description of the image display body 10 will be given later.

[0015] The first projector 20 is a projector that emits ultraviolet light and has an arbitrary ultraviolet light source (UV light source), and is positioned opposite the front surface 10a of the image display unit 10. The first projector 20 is an ultraviolet light emitting unit that projects ultraviolet light onto the image display unit 10, and for example, emits ultraviolet light with a wavelength of around 365 nm. The first projector 20 projects ultraviolet light onto the front surface 10a of the image display unit 10, changing the ultraviolet light irradiated area 10c on the image display unit 10 from a transparent state to an opaque state (screen state).

[0016] The second projector 40 is a color projector and is positioned opposite the front surface 10a of the image display unit 10. The second projector 40 has any visible light source such as a laser, mercury lamp, or LED, and emits visible light for image projection as a visible light projection unit, which is light of one of three colors: blue (for example, a wavelength of around 450 nm), green (for example, a wavelength of around 530 nm), and red (for example, a wavelength of around 630 nm), or light of a combination of two or more colors. The second projector 40 projects visible light onto the illumination area 10c of the first projector 20 of the image display unit 10, thereby displaying a visible light image 60 of any color and shape on the non-transparent image display unit 10. In other words, the second projector 40 is a visible light projection unit that projects visible light of an arbitrary wavelength onto the illumination area 10c on the image display body 10, which has been made opaque (screen state) by the projection of ultraviolet light, and displays a visible light image 60 with arbitrary shape and color components within the illumination area 10c.

[0017] The control unit 50 controls the operation of the first projector 20 and the second projector 40. The control unit 50 communicates with a higher-level control device (not shown) and switches the first projector 20 and the second projector 40 between emitting light and not emitting light. The control unit 50 communicates with the higher-level control device and sends a predetermined signal or command to the first projector 20 to instruct it to emit ultraviolet light. As a result, under the instruction of the control unit 50, ultraviolet light is emitted onto the front surface 10a of the image display unit 10, making the illumination area 10c opaque (screened). The control unit 50 also communicates with the higher-level control device and sends image information to the second projector 40. As a result, under the instruction of the control unit 50, visible light is emitted onto the illumination area 10c and the visible light image 60 is displayed.

[0018] The control unit 50 is connected to each projector of the display device 1 and to a higher-level control device (not shown) so as to be able to communicate with information. When the image display unit 10 is installed inside a car (for example, on the windshield), the control unit 50 may be installed inside the car (on the dashboard, etc.). However, it is not limited to this, and the control unit 50 may be a portable information terminal device for the user. Furthermore, the control unit 50 may be able to communicate with a higher-level control device (not shown) that serves as an image (video) source, such as a video recorder or a personal computer, and may be able to receive video signals, computer signals, etc., as image (video) signals. The detailed configuration of the control unit 50 will be described later.

[0019] In the display device 1, the first projector 20 and the second projector 40 emit ultraviolet light and visible light for projecting the visible light image 60, respectively, based on the control of the control unit 50, so that the visible light image 60 displayed on the image display unit 10 is contained within the ultraviolet light irradiation area 10c on the image display unit 10.

[0020] The temperature measuring unit 70 is equipped with a temperature sensor and measures the temperature of the environment in which the display device 1 is used (ambient temperature). The environment in which the display device 1 is used may be, for example, the location where the image display unit 10 is installed. The temperature measuring unit 70 is connected to the control unit 50 so as to be able to transmit information and may be installed in any location indoors where the image display unit 10 is installed and in which the ambient temperature can be measured. The temperature measuring unit 70 may be provided on the image display unit 10, for example, or on the first projector 20 or the second projector 40. However, it is preferable to provide the temperature measuring unit 70 on the image display unit 10 in order to more accurately capture the change in the response speed of the liquid crystal molecules 91 in response to the ambient temperature. When the image display unit 10 is installed inside a car (for example, on the windshield), the temperature measuring unit 70 may be installed in any location inside the car (for example, on the dashboard). The temperature measuring unit 70 transmits a signal indicating the ambient temperature (temperature signal) to the control unit 50.

[0021] Next, with reference to Figure 2, the image display body 10 of the display device 1 will be described in detail. Figure 2 is a cross-sectional view showing the schematic configuration of the image display body 10. The image display body 10 of this embodiment includes a display function layer 11 and an ultraviolet light shielding layer 12. The display function layer 11 is arranged on the side of the transparent substrate 101 that forms the front surface 10a of the image display body 10, and the ultraviolet light shielding layer 12 is arranged on the side of the transparent substrate 102 that forms the back surface 10b of the image display body 10. In other words, the image display body 10 may be configured in which the display function layer 11 and the ultraviolet light shielding layer 12 are stacked in this order from the transparent substrate 101 side toward the transparent substrate 102 side. Note that the image display body 10 only needs to include at least the transparent substrates 101, 102 and the display function layer 11.

[0022] The display function layer 11 is a film material whose optical state changes between a transparent state and an opaque state. The display function layer 11 has optical properties in which the intensity of light scattering (light scattering intensity) increases when it receives ultraviolet light, and decreases when it receives visible light. When the display function layer 11 receives ultraviolet light, it becomes opaque due to the increase in light scattering, and when it receives visible light, it returns to a transparent state due to the decrease in light scattering. As a result, the image display body 10 can reversibly change between a transparent state (non-screen state) and an opaque state (screen state). As will be described in more detail later, the light scattering of the display function layer 11 decreases when it receives visible light in a specific wavelength range. The display function layer 11 in this embodiment is a liquid crystal film containing host liquid crystal molecules 91 and azobenzene molecules 92.

[0023] The ultraviolet light shielding layer 12 is a transparent film member that shields ultraviolet light. The ultraviolet light shielding layer 12 is formed of a transparent resin containing an ultraviolet light reflector or ultraviolet light absorber, and shields light in the wavelength region near ultraviolet light by reflecting or absorbing it. The ultraviolet light shielding layer 12 is positioned on the transparent substrate 102 side that forms the back surface 10b of the image display body 10, and prevents ultraviolet light from entering the display function layer 11 from the back surface 10b of the image display body 10. Therefore, for example, when the image display body 10 is attached to the windshield of a car, it is possible to prevent the image display body 10 from becoming opaque due to sunlight or headlights.

[0024] The transparent substrate 101 forms the front surface 10a of the image display unit 10. The transparent substrate 102 forms the back surface 10b of the image display unit 10. The transparent substrates 101 and 102 are protective substrates that protect the display function layer 11 and the ultraviolet light shielding layer 12. The transparent substrates 101 and 102 only need to have transparency that does not hinder the visibility of the visible light image 60 projected onto the opaque image display unit 10, and may be, for example, glass substrates. Alternatively, the transparent substrates 101 and 102 may be transparent resin substrates formed from transparent resin. Furthermore, the transparent substrate 102 may also have the role of preventing ultraviolet light entering from the outside from reaching the display function layer 11, in place of the ultraviolet light shielding layer 12. In this case, the transparent substrate 102 may be formed from a material that shields ultraviolet light, or an ultraviolet light shielding film may be attached to it.

[0025] Next, the display function layer 11 of the image display unit 10 will be described in detail with reference to Figures 3A and 3B. Figure 3A is a cross-sectional view showing the schematic configuration of the display function layer 11 in a transparent state together with the transparent substrates 101 and 102, and Figure 3B is a cross-sectional view showing the schematic configuration of the display function layer 11 in a non-transparent state together with the transparent substrates 101 and 102.

[0026] As described above, the display functional layer 11 in this embodiment is a liquid crystal film containing host liquid crystal molecules (hereinafter referred to as liquid crystal molecules 91) and azobenzene molecules 92. The liquid crystal film is sandwiched between transparent substrates 101 and 102 and has a polymer network structure in which liquid crystal molecules 91 and azobenzene molecules 92 are present. When azobenzene molecules 92 receive ultraviolet light, their structure changes from the trans form 92a to the cis form 92b, and when they receive visible light in a specific wavelength range, their structure changes from the cis form 92b to the trans form 92a. When azobenzene molecules 92 change to the cis form 92b, they bend and disrupt the arrangement (orientation) of the liquid crystal molecules 91. Therefore, if ultraviolet light is projected onto the display function layer 11 in an arrangement state where the liquid crystal molecules 91 are aligned approximately perpendicular to the thickness direction of the display function layer 11 (see Figure 3A) and the liquid crystal phase is in the nematic phase, the liquid crystal molecules 91 change to a focal conic state and their arrangement is disrupted, changing to a scattering state (see Figure 3B), and the intensity of light scattering (light scattering intensity) increases. In other words, the transmittance of visible light decreases. On the other hand, if visible light in a specific wavelength range is projected onto the display function layer 11 in a scattering state (see Figure 3B) and the liquid crystal molecules 91 are in a focal conic state, the liquid crystal molecules 91 change to an arrangement state (see Figure 3A) and the liquid crystal phase changes to the nematic phase, and the light scattering intensity decreases. In other words, the transmittance of visible light increases.

[0027] The visible light in a specific wavelength range that reduces the light scattering intensity of the display functional layer 11 (hereinafter also referred to as "specific visible light") is the visible light in the absorption wavelength range of the azobenzene molecule 92 that has been converted to the cis isomer 92b upon reception of ultraviolet light. The azobenzene molecule 92 that has been converted to the cis isomer 92b has a high absorbance of visible light in the wavelength range of approximately 400 nm to 570 nm. In other words, the visible light in the wavelength range of approximately 400 nm to 570 nm, which is the absorption wavelength range of the azobenzene molecule 92 that has been converted to the cis isomer 92b, corresponds to the specific visible light. That is, when the display functional layer 11 contains azobenzene molecule 92 as a light scattering material, visible light with a color component corresponding to blue or green becomes the specific visible light that reduces the light scattering intensity of the display functional layer 11. When the azobenzene molecule 92 receives blue or green visible light as the specific visible light, its structure changes from the cis isomer 92b to the trans isomer 92a, and the light scattering intensity of the display functional layer 11 decreases. Therefore, the image display unit 10 in this example changes from an opaque state (screen state) to a transparent state (non-screen state) when it receives blue or green visible light.

[0028] Based on the above properties of the display function layer 11, the light scattering intensity of the display function layer 11 can be reduced by irradiation with specific visible light, thereby erasing the visible light image displayed on the image display body 10. Specifically, in the display device 1, when erasing a visible light image, with the first projector 20 stopped emitting ultraviolet light, the second projector 40, under the control of the control unit 50, emits specific visible light (for example, blue light with a wavelength of around 450 nm) onto the front surface 10a of the image display body 10, thereby changing the ultraviolet light-irradiated area 10c on the image display body 10 from an opaque state to a transparent state. This allows, for example, when the image display body 10 is installed on the windshield of a car, visibility from inside the vehicle can be quickly secured. Furthermore, if ultraviolet light projection is stopped, the light scattering properties of the display function layer 11 decrease over time due to specific visible light contained in sunlight or white illumination (in this example, blue or green visible light), and the image display body 10 gradually becomes transparent (non-screen state), causing the visible light image 60 within the illumination area 10c to be erased.

[0029] Furthermore, the liquid crystal molecules 91 in the display functional layer 11 have the property that their orientation (arrangement) is more easily disrupted as their viscosity decreases. The viscosity of the liquid crystal molecules 91 decreases with increasing temperature. When the viscosity is reduced, the orientation of the liquid crystal molecules 91 is disrupted even when the proportion of azobenzene molecules 92 that have been photoisomerized to the cis form is small. As a result, the rate of increase in light scattering intensity of the display functional layer 11 increases with increasing temperature, making it more likely to become opaque. On the other hand, the viscosity of the liquid crystal molecules 91 increases with decreasing temperature. When the viscosity is increased, the orientation of the liquid crystal molecules 91 is less likely to be disrupted. As a result, the rate of increase in light scattering intensity of the display functional layer 11 decreases with decreasing temperature, making it less likely to become opaque.

[0030] Thus, the orientation state of the liquid crystal molecules 91 contained in the display function layer 11 is affected not only by ultraviolet light but also by changes in ambient temperature (rise and fall). However, if the ambient temperature deviates from a predetermined temperature range, it becomes difficult to control the orientation by ultraviolet light irradiation. In other words, the display function layer 11 increases in light scattering intensity when exposed to ultraviolet light under predetermined temperature conditions (orientation temperature conditions) that do not deviate from the above temperature range, and decreases in light scattering intensity when exposed to visible light in a specific wavelength range under the orientation temperature conditions. The orientation temperature conditions indicate the temperature range (orientation temperature range) in which the orientation of the liquid crystal molecules 91 can be controlled, and temperatures within the orientation temperature range are temperatures that satisfy the orientation temperature conditions. When the ambient temperature is below the lowest temperature within the orientation temperature range (a low-temperature environment that does not satisfy the orientation temperature conditions), the liquid crystal molecules 91 crystallize and their viscosity increases, causing them to lose fluidity, making it difficult to make the display function layer 11 opaque by ultraviolet light irradiation. Furthermore, if the ambient temperature exceeds the maximum temperature within the orientation temperature range (i.e., a high-temperature environment that does not meet the orientation temperature conditions), the liquid crystal molecules 91 undergo a phase transition to an isotropic phase, and are unable to change the display functional layer 11 to an opaque state.

[0031] Figure 3C is a graph illustrating an example of the behavior of increasing light scattering intensity under orientation temperature conditions and ultraviolet light irradiation. In Figure 3C, the light scattering intensity of the display functional layer 11 is shown on the vertical axis, and the ultraviolet light irradiation time (seconds) is shown on the horizontal axis. In this example, the display functional layer 11 is sandwiched between two transparent substrates and consists of liquid crystal molecules 91, which are liquid crystal compounds, at least one polymerizable compound, and two chiral compounds including azobenzene. More specifically, it consists of chiral azobenzene and a non-photoresponsive chiral compound. The ultraviolet light irradiation intensity is set to a constant value (20 mW / cm²). ２ The orientation temperature range was set from 20°C (minimum temperature) to 40°C (maximum temperature). In Figure 3C, for ease of understanding, the behavior of the increase in light scattering intensity of the display functional layer 11 is shown in the cases where the ambient temperature is the maximum and minimum temperature within the orientation temperature range.

[0032] As shown in Figure 3C, when the ambient temperature is the lowest temperature within the orientation temperature range (20°C), the light scattering intensity value is 67 36 seconds after the start of ultraviolet light irradiation. In contrast, when the ambient temperature is the highest temperature within the orientation temperature range (40°C), the light scattering intensity rises to 79 36 seconds after the start of ultraviolet light irradiation. In other words, even when ultraviolet light is irradiated with the same irradiation intensity and duration, the light scattering intensity of the display function layer 11 is greater at higher ambient temperatures. Specifically, in a high-temperature environment (40°C in this example), the light scattering intensity of the display function layer 11 increases rapidly from the start of ultraviolet light reception, and opacification progresses faster compared to a low-temperature environment (20°C in this example). On the other hand, in a low-temperature environment (20°C in this example), the increase in light scattering intensity in the display function layer 11 is gradual, and the progress of opacification from the start of ultraviolet light reception is slower compared to a high-temperature environment (40°C in this example).

[0033] Thus, the display function layer 11 in the image display unit 10 has the characteristic that the rate of increase in light scattering intensity due to reception of ultraviolet light of a constant intensity differs depending on the ambient temperature. Therefore, even if the intensity of ultraviolet light irradiated onto the image display unit 10 is the same, the time it takes for the light scattering intensity value of the display function layer 11 to reach a predetermined value suitable for displaying a visible light image and for screening to be completed will differ depending on the ambient temperature. For this reason, if ultraviolet light is irradiated onto the image display unit 10 with the same intensity and irradiation time regardless of the ambient temperature, the strength of the light scattering properties (light scattering intensity) of the display function layer 11 will change depending on the ambient temperature, resulting in differences in the degree of opacity (screening) progress. As a result, the brightness of the visible light image 60 displayed on the image display unit 10 will also fluctuate. In detail, the higher the light scattering intensity, the higher the brightness (visibility) of the visible light image 60 displayed on the image display unit 10 (irradiated area 10c).

[0034] Therefore, in the display device 1 according to this embodiment, the control unit 50 controls the irradiation of ultraviolet light to the image display body 10 so that the light scattering intensity of the display function layer 11 in the image display body 10 remains constant even when the ambient temperature changes. Specifically, the control unit 50 determines the irradiation time of ultraviolet light from the first projector 20 based on the ambient temperature. This makes it possible to keep the brightness of the visible light image displayed in the irradiation area 10c constant. The control unit 50 of the display device 1 according to this embodiment will be described in detail below with reference to Figures 4A and 4B.

[0035] As shown in Figure 4A, the control unit 50 is an electronic control device that controls the operation (e.g., light irradiation) of each projector (first projector 20, second projector 40) in the display device 1, and comprises a processor 50a and a storage device 50b. The control unit 50 may be a microcomputer, single-board computer, etc., that reads a program from the storage device 50b using the processor 50a and executes processing according to the program to realize control and various functions in the display device 1.

[0036] The processor 50a may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage device 50b may include memory such as ROM (Read Only Memory) or RAM (Random Access Memory) used as main memory, as well as non-transitory tangible storage media such as memory registers and cache memory. The storage device 50b stores a database as a data storage module 51. The data storage module 51 holds guaranteed temperature data 511 and characteristic data 512.

[0037] The guaranteed temperature data 511 is data indicating the orientation temperature conditions described above. For example, the guaranteed temperature data 511 may include the highest and lowest temperatures at which the orientation of the liquid crystal molecules 91 can be controlled by ultraviolet light irradiation. This allows the guaranteed temperature data 511 to indicate the temperature range (orientation temperature range) at which the orientation of the liquid crystal molecules 91 can be controlled. If the ambient temperature deviates from the orientation temperature range and the orientation of the liquid crystal molecules 91 becomes difficult to control, the image display body 10 cannot be made into a screen state (non-transparent state), and the display of the visible light image 60 itself becomes difficult. Therefore, the orientation temperature conditions indicated by the guaranteed temperature data 511 are also data indicating the temperature range (operational guaranteed temperature range) at which the operation of the display device 1 is guaranteed. The guaranteed temperature data 511 may also include the lowest temperature and the difference in temperature from the lowest temperature to the highest temperature. For example, if the orientation temperature range is from 15°C to 40°C, it may include the lowest temperature (15°C) and the difference from the lowest temperature to the highest temperature (25°C). Similarly, it may also include the highest temperature and the difference in temperature from the highest temperature to the lowest temperature.

[0038] The characteristic data 512 is data that associates the irradiation time length of ultraviolet light to the irradiation region 10c of the image display body 10 with the value of the light scattering intensity of the display functional layer 11 in the irradiation region 10c obtained by ultraviolet light irradiation at the irradiation time length. The irradiation time length of ultraviolet light to the irradiation region 10c indicates, that is, the irradiation time length of ultraviolet light at a constant irradiation intensity from the first projector 20 to the irradiation region 10c of the image display body 10, and the light scattering intensity of the irradiation region 10c is, that is, the light scattering intensity of the display functional layer 11 corresponding to the irradiation region 10c. The irradiation time length of ultraviolet light in the characteristic data 512 may be set so as not to exceed a predetermined maximum irradiation time.

[0039] The data storage module 51 holds characteristic data for each temperature that satisfies the alignment temperature condition. That is, the storage device 50b stores the characteristic data 512 for each predetermined temperature that satisfies the alignment temperature condition (for example, for each 1°C). Therefore, the characteristic data 512 is data indicating the change in the correspondence relationship between the irradiation time length of ultraviolet light and the light scattering intensity accompanying the temperature change, and indicates the characteristics of the liquid crystal molecules 91 related to the light scattering intensity of the display functional layer 11 (the change in the alignment order degree of the liquid crystal molecules 91 according to the ambient temperature). Note that the temperature interval (storage temperature interval) at which the storage device 50b (data storage module 51) stores the characteristic data 512 is not particularly limited, and the characteristic data 512 may be held at a predetermined temperature interval of 1°C or more, or the characteristic data 512 may be held at an interval of less than 1°C (for example, for each 0.5°C).

[0040] The characteristic data 512 only needs to be data that can specify the association between the irradiation time length of ultraviolet light and the value of the light scattering intensity for each temperature that satisfies the alignment temperature condition (temperature within the alignment temperature range), and the data format is not particularly limited. The data storage module 51 may hold the characteristic data 512 in a table format that associates the value of the temperature that satisfies the alignment temperature condition with, for example, the combination of the irradiation time length and the light scattering intensity.

[0041] Here, a specific example of characteristic data 512 will be explained using Figure 4B. Figure 4B is a diagram showing an example of characteristic data held in the data storage module 51, where the light scattering intensity of the display function layer 11 in the irradiation area 10c is shown on the vertical axis, and the irradiation time (seconds) of ultraviolet light from the first projector 20 is shown on the horizontal axis. In this example, the display function layer 11 has the same configuration as the example shown in Figure 3C, and the orientation temperature range is set to 20°C to 40°C. In this example, the data storage module 51 holds characteristic data at 1°C intervals within the orientation temperature range of 20°C to 40°C, and Figure 4B shows extracted data from the characteristic data corresponding to the highest temperature of 40°C and the lowest temperature of 20°C. In this example, the irradiation intensity of ultraviolet light from the first projector 20 is 20 mW / cm². ２ The numerical values ​​shown in Figure 4B are examples only and do not limit the configuration of this disclosure.

[0042] As shown in Figure 4B, the characteristic data 512 shows the correspondence between the value of the light scattering intensity of the display function layer 11 and the irradiation time during a predetermined maximum irradiation time of ultraviolet light (80 seconds in this example). In other words, the characteristic data 512 shows the change in the value of the light scattering intensity within the maximum irradiation time for each temperature. In this example, the characteristic data 512 associates the value of the light scattering intensity every second within the 80-second ultraviolet light irradiation time. That is, multiple (80 in this example) characteristic data 512 are linked to one temperature within the orientation temperature range. Note that the characteristic data 512 at each temperature only needs to show the change in the light scattering intensity value at predetermined time intervals within the maximum irradiation time, and these intervals may be 1 second or longer, or less than 1 second (e.g., 0.5 seconds).

[0043] In this example, in the characteristic data 512 associated with an environmental temperature of 20 °C (the lowest temperature), for an irradiation time length of "72 (seconds)", a light scattering intensity of "79" is associated. At an environmental temperature of 20 °C, when the light scattering intensity reaches "79", the light scattering intensity does not increase thereafter. That is, in this example, the light scattering intensity of "79" corresponds to the maximum value of the light scattering intensity at the lowest temperature within the temperature range (within the alignment temperature range) that satisfies the alignment temperature conditions of this example. The maximum value of the light scattering intensity at the lowest temperature is referred to as the "required intensity value". The required intensity value indicates the value of the light scattering intensity of the irradiation region 10c required for displaying the visible light image 60 in the image display body 10. The display device 1 according to the present embodiment can display the visible light image 60 on the image display body 10 with a brightness that provides good visibility from the user by setting the value of the light scattering intensity of the display function layer 11 in the irradiation region 10c to be not less than the required intensity value. Note that the required intensity value varies depending on the composition of the display function layer 11 (for example, the types and characteristics of the liquid crystal molecules 91 and azobenzene molecules 92), and is not limited to "79", which is the required intensity value in this example.

[0044] Thus, the characteristic data 512 includes the required intensity value. The characteristic data 512 corresponding to the required intensity value is data indicating the conditions (display conditions) required for displaying the visible light image 60 in the image display body 10. That is, the characteristic data 512 includes data indicating the display conditions of the visible light image 60. Therefore, in the display device 1 according to the present embodiment, the storage device 50b (data storage module 51) stores the required intensity value as the display condition of the visible light image 60. More specifically, the data storage module 51 stores, as the above display condition, the required intensity value and the irradiation time length of ultraviolet light at which the light scattering intensity corresponding to the required intensity value can be obtained in the irradiation region 10c among the characteristic data 512.

[0045] In this example, the characteristic data 512 associated with an ambient temperature of 40°C (maximum temperature) shows a faster rate of increase in light scattering intensity compared to an ambient temperature of 20°C (minimum temperature). As a result, a light scattering intensity value of "83," which is greater than the light scattering intensity value (required intensity value) at an ambient temperature of 20°C, is associated with an irradiation time of "72 seconds." In other words, for the same irradiation time of "72 seconds," there is a difference in the light scattering intensity value between the characteristic data 512 for an ambient temperature of 20°C and the characteristic data for an ambient temperature of 40°C. On the other hand, in the characteristic data 512 associated with an ambient temperature of 40°C, a light scattering intensity value of "79," which corresponds to the required intensity value, is associated with an irradiation time of "36 seconds." In other words, characteristic data 512 indicates that at an ambient temperature of 40°C, by shortening the ultraviolet light irradiation time to "36 seconds" compared to an ambient temperature of 20°C, the light scattering intensity value of the irradiation area 10c becomes equivalent to the required intensity value. As described above, within the orientation temperature range, the rate of increase in the light scattering intensity in the irradiated area 10c due to the reception of ultraviolet light increases as the ambient temperature rises. Therefore, in the characteristic data 512, the longer the ultraviolet light irradiation time required to obtain a light scattering intensity value equivalent to the required intensity value, the higher the temperature of the data corresponding to the temperature. Note that the light scattering intensity of the display function layer 11 in the irradiated area 10c may be simply described as "light scattering intensity in the irradiated area 10c".

[0046] As will be described in more detail later, the control unit 50 determines the irradiation time of ultraviolet light from the first projector 20 using the ambient temperature and characteristic data 512, and controls the irradiation of ultraviolet light by the first projector 20 based on the irradiation time, thereby making the light scattering intensity of the irradiation area 10c a constant value. As a result, the brightness of the visible light image 60 can be kept constant when the ambient temperature is within the orientation temperature range.

[0047] The data storage module 51 only needs to store, as characteristic data 512, the required intensity value and the irradiation time of ultraviolet light that yields a light scattering intensity equivalent to the required intensity value for each temperature within the temperature range. For example, in the example shown in Figure 4B, it is sufficient to store, for each 1°C interval within the orientation temperature range of 20°C to 40°C, the required intensity value "79" and the irradiation time of ultraviolet light that yields a light scattering intensity equivalent to the required intensity value (for example, "36 (seconds)" at 40°C).

[0048] The storage device 50b also stores programs for implementing control modules such as the data acquisition module 52 and the irradiation control module 53. The processor 50a executes these programs to realize the functions of the control unit 50. The data acquisition module 52 acquires data related to the control of ultraviolet light irradiation and visible light irradiation from each device that can communicate with the control unit 50 and outputs it to the irradiation control module 53. For example, the data acquisition module 52 acquires a temperature signal from the temperature measurement unit 70 indicating the temperature of the operating environment (ambient temperature) of the display device 1 and outputs it to the irradiation control module 53.

[0049] The data acquisition module 52 also acquires data (guaranteed temperature data 511 and characteristic data 512) held by the data storage module 51 and outputs it to the irradiation control module 53. For example, the data acquisition module 52 may acquire guaranteed temperature data 511 from the data storage module 51 and output it to the irradiation control module 53 along with the temperature signal. Alternatively, the data acquisition module 52 may acquire specific data from the characteristic data 512 held by the data storage module 51 based on instructions from the irradiation control module 53 and output it to the irradiation control module 53. Furthermore, the data acquisition module 52 may acquire an image signal sent from a higher-level control device (not shown) and output it to the irradiation control module 53.

[0050] The irradiation control module 53 controls the irradiation of ultraviolet light by the first projector 20 and the irradiation of visible light by the second projector 40 based on various data output from the data acquisition module 52.

[0051] First, the control of ultraviolet light irradiation (screening of the image display unit 10) by the irradiation control module 53 will be explained. When the ambient temperature of the display device 1 satisfies the orientation temperature condition, the irradiation control module 53 in the control unit 50 determines the irradiation time of ultraviolet light from the first projector 20 based on the ambient temperature, and controls the ultraviolet light irradiation so that the light scattering intensity of the display function layer 11 in the irradiation area 10c of the image display unit 10 remains constant based on the irradiation time. More specifically, the irradiation control module 53 sets the light scattering intensity of the display function layer 11 in the irradiation area 10c to a value corresponding to the required intensity value described above, based on the determined irradiation time. This makes it possible to keep the brightness of the visible light image 60 displayed on the image display unit 10 constant even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature condition). Furthermore, by setting the light scattering intensity of the irradiation area 10c to a value corresponding to the required intensity value described above, the brightness of the visible light image 60 can be kept constant in a state where visibility to the user is good. The value corresponding to the required intensity value may include a light scattering intensity value that matches the required intensity value, and a light scattering intensity value that is close to the required intensity value and within an error range in which the user does not perceive a difference in the brightness of the visible light image 60.

[0052] Specifically, the irradiation control module 53 reads characteristic data 512 from the data storage module 51 and determines the irradiation time of ultraviolet light by the first projector 20 based on the read characteristic data 512. The irradiation control module 53 determines whether the ambient temperature satisfies the orientation temperature conditions based on the ambient temperature and guaranteed temperature data 511 output by the data acquisition module 52. If the ambient temperature is within the orientation temperature range indicated by the guaranteed temperature data 511, the irradiation control module 53 may determine that the ambient temperature satisfies the orientation temperature conditions and read the characteristic data 512 based on the ambient temperature.

[0053] The irradiation control module 53 identifies the data representing the maximum value of light scattering intensity (required intensity value) from the characteristic data 512 corresponding to the lowest temperature within the orientation temperature range (e.g., 20°C), and acquires the characteristic data 512 containing the required intensity value via the data acquisition module 52. The irradiation control module 53 also identifies the data from the characteristic data 512 corresponding to the ambient temperature whose light scattering intensity value corresponds to the required intensity value, and acquires this data via the data acquisition module 52. If there is no characteristic data 512 that matches the ambient temperature, the irradiation control module 53 may acquire the characteristic data 512 corresponding to the temperature closest to the ambient temperature. Furthermore, if there is no data in the characteristic data 512 corresponding to the ambient temperature whose light scattering intensity value matches the required intensity value, the irradiation control module 53 may acquire the characteristic data 512 whose light scattering intensity value is closest to the required intensity value.

[0054] When the irradiation control module 53 acquires characteristic data 512 that corresponds to the ambient temperature and the light scattering intensity value corresponds to the required intensity value, it determines the ultraviolet light irradiation time indicated by the data as the ultraviolet light irradiation time of the first projector 20 to the image display unit 10. The irradiation control module 53 sends the determined irradiation time to the first projector 20. As a result, the first projector 20, under the control of the control unit 50 (irradiation control module 53), can irradiate with ultraviolet light so that the light scattering intensity value in the irradiation area 10c remains constant (required intensity value) based on the irradiation time according to the ambient temperature. As a result, the brightness of the visible light image 60 displayed on the image display unit 10 can be easily kept constant regardless of temperature changes in the operating environment.

[0055] In this manner, the irradiation control module 53 acquires the ultraviolet light irradiation time length indicated by the characteristic data 512 corresponding to the ambient temperature when the ambient temperature satisfies the orientation temperature condition, and controls the irradiation of ultraviolet light by the first projector 20 based on the irradiation time length. As a result, when displaying the visible light image 60, the light scattering intensity of the irradiation area 10c of the image display body 10 is controlled to be constant regardless of changes in the ambient temperature, and the visible light image 60 can be displayed at a constant brightness. In other words, regardless of changes in the ambient temperature, the image display body 10 can be made into a screen state (non-transparent state) that allows the visible light image 60 to be displayed at a constant brightness. In this embodiment of the display device 1, the irradiation intensity of the ultraviolet light irradiated by the first projector 20 is constant. For this reason, the irradiation control module 53 may send the determined irradiation time length along with the constant irradiation intensity to the first projector 20, or the first projector 20 may be configured to irradiate ultraviolet light at a constant irradiation intensity in response to the irradiation time length sent from the irradiation control module 53.

[0056] As mentioned above, the higher the temperature in the characteristic data 512, the shorter the irradiation time of ultraviolet light required to obtain a light scattering intensity value equivalent to the required intensity value. Therefore, the irradiation time of ultraviolet light by the first projector 20, determined by the irradiation control module 53 in the control unit 50, becomes shorter as the ambient temperature increases. This makes it possible to more reliably set the light scattering intensity value of the irradiation area 10c to the required intensity value by determining the irradiation time according to the ambient temperature, and to more reliably display the visible light image 60 with a constant brightness.

[0057] Next, the control of visible light irradiation by the irradiation control module 53 will be described. The irradiation control module 53 may acquire an image signal sent from a higher-level control device via the data acquisition module 52, generate image information for displaying a visible light image 60 corresponding to the image signal, and send it to the second projector 40. The image information may include image color information indicating the color components of each pixel of the visible light image 60. The irradiation control module 53 should send the image information to the second projector 40 after the screenization of the image display body 10 by ultraviolet light irradiation from the first projector 20 is completed. The second projector 40 irradiates the image display body 10 with visible light in the wavelength range corresponding to the image information sent by the irradiation control module 53. As a result, the light scattering intensity of the irradiation area 10c is controlled to a value corresponding to the required intensity value, and visible light is irradiated onto the image display body 10, which has become a screen state (non-transparent state) suitable for image display. Therefore, the visible light image 60 can be displayed at a constant brightness regardless of temperature changes in the operating environment. In this embodiment, the intensity of visible light emitted from the second projector 40, that is, the amount of light incident on the irradiation area 10c (illuminance on the surface (front surface 10a) of the irradiation area 10c), is constant.

[0058] Next, an example of a control method for the display device 1 will be described with reference to Figure 5. Figure 5 is a flowchart showing an example of the control flow related to ultraviolet light irradiation (screening of the image display body 10) and the display of a visible light image, which are performed by the control unit 50 in the display device 1. For example, the control unit 50 may start control related to ultraviolet light irradiation (screening) based on the receipt of an image signal indicating a visible light image 60 from a higher-level control device (not shown).

[0059] As shown in Figure 5, the control unit 50 acquires the ambient temperature of the operating environment of the display device 1 (S1). Specifically, the irradiation control module 53 acquires the ambient temperature measured by the temperature measurement unit 70 via the data acquisition module 52. Next, the control unit 50 determines whether the ambient temperature satisfies the orientation temperature conditions (S2). Specifically, the irradiation control module 53 acquires guaranteed temperature data 511 from the data storage module 51 via the data acquisition module 52 and determines whether the ambient temperature satisfies the orientation temperature conditions. If the ambient temperature is within the orientation temperature range indicated by the guaranteed temperature data 511, the irradiation control module 53 determines that the ambient temperature satisfies the orientation temperature conditions (S2:Y) ​​and acquires the light scattering intensity value (required intensity value) required for displaying the visible light image 60 (S3). Specifically, the irradiation control module 53 acquires data from the data storage module 51 via the data acquisition module 52 that has the maximum light scattering intensity value (required intensity value) among the characteristic data 512 corresponding to the lowest temperature within the orientation temperature range.

[0060] Next, the control unit 50 extracts characteristic data 512 corresponding to the operating environment temperature (ambient temperature) (S4), and identifies data from the extracted characteristic data 512 that shows the light scattering intensity corresponding to the required intensity value (S5). Specifically, the irradiation control module 53 extracts characteristic data 512 corresponding to the ambient temperature from the data storage module 51 via the data acquisition module 52, and identifies data from the extracted multiple characteristic data 512 that shows the light scattering intensity value that corresponds to (or is equivalent to) the required intensity value. Here, the light scattering intensity value that corresponds to (or is equivalent to) the required intensity value may be a value that matches the required intensity value or a value that is closest to the required intensity value.

[0061] Next, the control unit 50 determines the irradiation time of ultraviolet light by the first projector 20 based on the identified characteristic data 512 (S6), and screens (makes opaque) the image display unit 10 by irradiating it with ultraviolet light for the specified irradiation time (S7). Specifically, the irradiation control module 53 obtains the irradiation time of ultraviolet light contained in the data identified from the characteristic data 512 corresponding to the ambient temperature (characteristic data 512 where the light scattering intensity value corresponds to the required intensity value), determines this irradiation time as the irradiation time of ultraviolet light in the first projector 20, and sends this irradiation time to the first projector 20. As a result, the control unit 50 (irradiation control module 53) emits ultraviolet light from the ultraviolet light source of the first projector 20 and irradiates the image display body 10 (irradiation area 10c) having a display function layer 11 with ultraviolet light for the duration of the irradiation time, thereby screening (making opaque) the image display body 10 so that the light scattering intensity value of the irradiation area 10c corresponds to the required intensity value.

[0062] Next, the control unit 50 causes the image display unit 10 to display a visible light image 60 by irradiating it with visible light (S8). For example, after the image display unit 10 has been screened by ultraviolet light irradiation, the irradiation control module 53 sends image information indicating the shape of the visible light image 60 and the color components of each pixel to the second projector 40. As a result, visible light with a wavelength corresponding to the color components of the visible light image indicated by the image information is irradiated from the second projector 40 onto the image display unit 10 (irradiation area 10c) that has been screened by the ultraviolet light irradiation described above, and the visible light image 60 is displayed.

[0063] On the other hand, if the control unit 50 (irradiation control module 53) determines that the ambient temperature is not within the orientation temperature range indicated by the guaranteed temperature data 511 (i.e., it deviates from the orientation temperature range) (S2:N), it terminates the control of ultraviolet light irradiation and visible light irradiation because the ambient temperature does not meet the orientation temperature conditions and the light scattering intensity value in the display function layer 11 of the image display body 10 cannot be controlled by ultraviolet light irradiation. This suppresses the implementation of unnecessary ultraviolet light irradiation. The irradiation control module 53 may wait for a certain period of time or until the ambient temperature comes within the orientation temperature range if the ambient temperature deviates from the orientation temperature range.

[0064] As described above, in this embodiment, the control method of the display device 1 by the control unit 50 determines the irradiation time of ultraviolet light to the irradiation area 10c of the image display body 10 based on the ambient temperature when the ambient temperature satisfies the orientation temperature condition (S4 to S6), and controls the irradiation of ultraviolet light to the irradiation area based on the irradiation time so that the light scattering intensity of the irradiation area 10c remains constant (S7). As a result, even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature condition), it is possible to keep the brightness of the visible light image 60 displayed on the image display body 10 constant.

[0065] 1-1. First Modification In the above embodiment, the ultraviolet light irradiation intensity of the first projector 20 in the display device 1 is constant, and the irradiation time of ultraviolet light irradiation is determined according to the ambient temperature, thereby controlling the ultraviolet light irradiation so that the light scattering intensity value of the image display body 10 (irradiated area 10c) is constant, and the brightness of the visible light image 60 is kept constant. However, the disclosure is not limited to this. For example, the control unit 50 may determine the ultraviolet light irradiation intensity and the ultraviolet light irradiation time of the first projector 20 according to the ambient temperature, and control the ultraviolet light irradiation so that the light scattering intensity value of the image display body 10 (irradiated area 10c) is kept constant.

[0066] When the display device 1 is used in a high-temperature environment, the cooling efficiency of each projector (first projector 20, second projector 40) that makes up the display device 1 decreases compared to when it is used in a low-temperature environment, which may necessitate larger cooling components. However, if the cooling components become larger, the suitability of the display device 1 as an in-vehicle device will decrease. Therefore, it is necessary to reduce the amount of heat generated from the light source of the projector when used in a high-temperature environment.

[0067] In this modified version, the display device 1 determines the ultraviolet light irradiation intensity and irradiation duration according to the ambient temperature. Specifically, in this modified version, the control unit 50 sets the irradiation intensity to a lower value as the ambient temperature increases. This reduces the amount of heat generated from the ultraviolet light source of the first projector 20, making it possible to suppress the enlargement or miniaturization of cooling components such as heat sinks and fans. Therefore, the display device 1 according to this modified version has improved suitability as an in-vehicle device and also provides energy-saving effects.

[0068] The ultraviolet light control in this modified example will be explained in detail below using Figure 6. Figure 6 is a graph showing an example of the change in light scattering intensity value over time of ultraviolet light irradiation for each condition of ambient temperature and ultraviolet light irradiation intensity. In Figure 6, the light scattering intensity of the display function layer 11 in the irradiation area 10c is shown on the vertical axis, and the irradiation time (seconds) of ultraviolet light by the first projector 20 is shown on the horizontal axis. In this example, the orientation temperature range is from 20°C to 40°C. In this example, the predetermined irradiation time was set to "50 seconds" and the required intensity value was set to "59". The display function layer 11 in this example is sandwiched between two transparent substrates and has a configuration that includes liquid crystal molecules 91, which are a different type of liquid crystal compound from the examples shown in Figures 3C and 4B, at least one polymerizable compound, and two types of chiral compounds including azobenzene. More specifically, it has a configuration that includes chiral azobenzene and a non-photoresponsive chiral compound. As shown in Figure 6, in this example, when the ambient temperature is the lowest temperature in the orientation temperature range (20°C), the irradiation intensity is 20 mW / cm². ２ When ultraviolet light is irradiated using this method, the irradiation time for ultraviolet light that yields the required intensity value of "59" in the display functional layer 11 is "50 seconds".

[0069] Figure 6 shows the relationship between the ultraviolet light irradiation time and the light scattering intensity value in the display functional layer 11 when the ultraviolet light irradiation intensity at the highest temperature in the orientation temperature range is lower than the irradiation intensity at the lowest temperature. In the example shown in Figure 6, when the ambient temperature is the highest temperature in the orientation temperature range (40°C), the ultraviolet light irradiation intensity is set to 5 to 20 mW / cm². ２The value was varied within this range. As shown in Figure 6, even at the same ambient temperature of 40°C, the rate of increase in the light scattering intensity value in the display functional layer 11 (rate of increase in light scattering intensity) slows down as the ultraviolet light irradiation intensity decreases. For example, when the irradiation intensity is 5 mW / cm² ２ In this case, even after the predetermined maximum irradiation time (50 seconds in this example) has elapsed, the light scattering intensity value does not reach the required intensity value, making it unsuitable for controlling the irradiation of ultraviolet light to keep the light scattering intensity value of the display function layer 11 constant.

[0070] In contrast, the irradiation intensity was 10 mW / cm². ２ In this case, the irradiation intensity is reduced compared to when ultraviolet light is irradiated at the lowest temperature, and the required intensity value of "59" can be obtained with an irradiation time of "32 seconds," which is shorter than the predetermined maximum irradiation time (50 seconds in this example). Therefore, the amount of heat generated from the ultraviolet light source of the first projector 20 can be reduced while keeping the light scattering intensity value of the display functional layer 11 constant during ultraviolet light irradiation. For reference, the irradiation intensity is 20 mW / cm². ２ In this case, the irradiation time for ultraviolet light required to obtain the required intensity value of "59" in the display function layer 11 is "20 seconds". Although the irradiation time is significantly shortened, the amount of heat generated from the ultraviolet light source of the first projector 20 cannot be reduced.

[0071] Based on the above, in this modified example, the control unit 50 only needs to determine the ultraviolet light irradiation intensity in the first projector 20 to be such that, when the ambient temperature within the orientation temperature range is higher than the minimum temperature, the required intensity value can be obtained by ultraviolet light irradiation with an irradiation time that does not exceed the maximum irradiation time.

[0072] Specifically, in this modified example, the characteristic data 512 stored in the storage device 50b (data storage module 51) may indicate the association between the irradiation time length of ultraviolet light to the irradiation region 10c of the image display body 10, the value of the light scattering intensity within the irradiation region 10c obtained by ultraviolet light irradiation for the irradiation time length, and the ultraviolet light intensity in the ultraviolet light irradiation. Also, the ultraviolet light intensity indicated by the characteristic data 512 stored in the data storage module 51 may be set to a smaller value as the corresponding temperature (temperature within the alignment temperature range) is higher. In the example shown in FIG. 6, the ultraviolet light intensity in the characteristic data 512 corresponding to the lowest temperature (20°C) is set to " ２ 20 mW / cm ２ ", and the ultraviolet light intensity in the characteristic data 512 corresponding to the highest temperature (40°C) may be set to "

[0073] 10 mW / cm

[0074] ". Also, for the characteristic data 512 corresponding to temperatures exceeding the lowest temperature among the characteristic data 512, it may be set such that the ultraviolet light intensity decreases as it approaches the highest temperature. Note that the ultraviolet light intensity in the characteristic data 512 may have the ultraviolet light intensity in the characteristic data 512 corresponding to the lowest temperature as the maximum value and the ultraviolet light intensity in the characteristic data 512 corresponding to the highest temperature as the minimum value. Also, the control unit 50 (irradiation control module 53) may send the irradiation time length and the ultraviolet light intensity indicated by the data (data corresponding to the required intensity value) specified from the characteristic data 512 corresponding to the environmental temperature to the first projector 20 to control the light scattering intensity within the irradiation region 10c of the image display body 10 to the required intensity value. Thereby, in the display device 1 in this modified example, even if a temperature change occurs in the usage environment (an environment where the environmental temperature satisfies the alignment temperature condition), the brightness of the visible light image 60 displayed on the image display body 10 can be made constant. Also, by reducing the irradiation intensity of ultraviolet light as the environmental temperature is higher, it is possible to suppress a reduction in the cooling efficiency of the first projector 20, so that it is possible to suppress an increase in the size of the cooling device (or miniaturize the cooling device), improve the suitability of the display device 1 as an in-vehicle device, and achieve an energy-saving effect.In this modified example, the irradiation control module 53 of the control unit 50 extracts characteristic data 512 corresponding to the ambient temperature via the data acquisition module 52, identifies the data corresponding to the required intensity value from the extracted characteristic data 512, acquires the ultraviolet light intensity (ultraviolet light irradiation intensity) and irradiation time indicated by the data, and sends it to the first projector 20.

[0075] More specifically, in this modified example, if the characteristic data 512 includes ultraviolet light intensity as described above, the irradiation control module 53 may identify data from the characteristic data 512 corresponding to the ambient temperature where the light scattering intensity corresponds to the required intensity value under the above-described display conditions and the irradiation time does not exceed a predetermined maximum irradiation time, and send the irradiation time and ultraviolet light intensity (ultraviolet light irradiation intensity) indicated by the identified data to the first projector 20. This makes it possible to control ultraviolet light irradiation in such a way that the brightness of the visible light image 60 displayed on the image display unit 10 is kept more reliably constant while reducing the ultraviolet light irradiation intensity in the first projector 20. Note that the characteristic data 512 may also be configured not to include data where the irradiation time exceeds the maximum irradiation time. This makes it possible for the irradiation control module 53 to easily acquire characteristic data 512 that does not exceed the maximum irradiation time. Alternatively, the characteristic data 512 may also be configured to include characteristic data 512 that exceeds the current maximum irradiation time. In this case, the characteristic data 512 becomes versatile data that can accommodate extensions of the maximum irradiation time, etc.

[0076] Figure 7 is a flowchart showing an example of the control method for the display device 1 in this modified example. In this modified example, the control unit 50 (irradiation control module 53) extracts characteristic data 512 corresponding to the temperature of the operating environment (ambient temperature) in the same manner as in step S4 above (S14), identifies data from the extracted characteristic data 512 that shows the value of the light scattering intensity corresponding to the required intensity value (S15), and determines the irradiation time and irradiation intensity of ultraviolet light in the first projector 20 based on the identified characteristic data 512 (S16). As described above, the ultraviolet light intensity shown by the characteristic data 512 in this modified example is set to a smaller value as the corresponding temperature increases. Therefore, the irradiation control module 53 can reduce the ultraviolet light irradiation intensity in the first projector 20 according to the ambient temperature by determining the ultraviolet light irradiation intensity shown by the characteristic data 512 corresponding to the required intensity value as the ultraviolet light irradiation intensity.

[0077] The control unit 50 (irradiation control module 53) sends the determined ultraviolet light irradiation time and irradiation intensity to the second projector 40, and screens (makes opaque) the irradiation area 10c of the image display body 10 by ultraviolet light irradiation (S17). Specifically, the irradiation control module 53 sends the determined ultraviolet light irradiation time and irradiation intensity to the first projector 20. As a result, the control unit 50 (irradiation control module 53) emits ultraviolet light from the ultraviolet light source of the first projector 20 according to the irradiation intensity, and irradiates the image display body 10 (irradiation area 10c) having the display function layer 11 with ultraviolet light for the irradiation time, and screens (makes opaque) the image display body 10 so that the light scattering intensity value of the irradiation area 10c corresponds to the required intensity value.

[0078] Next, the control unit 50 displays the visible light image 60 on the image display unit 10 by irradiating it with visible light, similar to step S8 (S18). As a result, visible light with a wavelength corresponding to the color component of the visible light image indicated by the image information is irradiated from the second projector 40 onto the image display unit 10 (irradiation area 10c) that has been screened by the ultraviolet light irradiation described above, and the visible light image 60 is displayed. Steps S11, S12, and S13 in Figure 7 are equivalent to steps S1, S2, and S3 shown in Figure 5, so their explanation is omitted.

[0079] As described above, in this modified example, the control method of the display device 1 by the control unit 50 determines the irradiation time and irradiation intensity of ultraviolet light to the irradiation area 10c of the image display unit 10 based on characteristic data 512 corresponding to the ambient temperature when the ambient temperature satisfies the orientation temperature condition (S14 to S16), and controls the irradiation of ultraviolet light to the irradiation area 10c based on the irradiation time and irradiation intensity so that the light scattering intensity of the irradiation area 10c remains constant (S17). This makes it possible to keep the brightness of the visible light image 60 displayed on the image display unit 10 constant even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature condition). Furthermore, by reducing the irradiation intensity of ultraviolet light as the ambient temperature increases, the reduction in the cooling efficiency of the first projector 20 can be suppressed, thereby suppressing (or miniaturizing) the size of the cooling device, improving the suitability of the display device 1 as an in-vehicle device, and achieving energy saving effects.

[0080] 2. Second Embodiment Next, a second embodiment of the present disclosure will be described with reference to Figure 8. In the first embodiment described above, an embodiment was described in which the brightness of the visible light image 60 is controlled to a constant level by the value of the light scattering intensity of the irradiation area 10c in the image display body 10, but the present disclosure is not limited thereto. In this embodiment, an embodiment will be described in which the irradiation conditions (irradiation intensity, irradiation time) for the screening of the image display body 10 are kept constant, and the brightness of the visible light image 60 displayed on the image display body 10 is controlled to a constant level by the visible light illuminance on the surface of the irradiation area 10c (the amount of light irradiated from the second projector 40 and incident on the surface). The visible light illuminance on the surface (front surface 10a) of the irradiation area 10c may be simply referred to as "visible light illuminance in the irradiation area 10c" below.

[0081] Figure 8 is a block diagram showing an example of the hardware and functional configuration of the control unit 500 included in the display device 1 according to the embodiment. The display device 1 according to the second embodiment is the same as the display device 1 according to the first embodiment, except that it includes the control unit 500. In Figure 8, the same reference numerals are used for components of the control unit 500 that are equivalent to those of the control unit 50 in the first embodiment, and detailed explanations are omitted.

[0082] The control unit 500 differs from the control unit 50 of the first embodiment in that it controls the visible light irradiation by the second projector 40 so that the visible light illuminance in the irradiation area 10c of the image display unit 10 remains constant, thereby keeping the brightness of the visible light image 60 constant. As will be described in detail later, the control unit 500 controls the visible light irradiation by the second projector 40 so that the lower the ambient temperature is within the temperature range that satisfies the orientation temperature conditions, the higher the visible light illuminance in the irradiation area 10c of the image display unit 10 on which the visible light image 60 is displayed. As a result, even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature conditions), the brightness of the visible light image 60 on the image display unit 10 can be kept constant.

[0083] As shown in Figure 8, in the control unit 500, the storage device 50b stores a database which serves as a data storage module 510. The data storage module 510 differs from the data storage module 51 according to the first embodiment in that it holds illuminance data 513.

[0084] The illuminance data 513 is data indicating the illuminance (lx) of visible light on the surface of the illumination area 10c of the image display body 10, which is irradiated from the second projector 40, and is used for controlling visible light irradiation in the control unit 500. The data storage module 510 may store the illuminance data 513 for each temperature that satisfies the orientation temperature condition. In other words, the storage device 50b may store the illuminance data 513 for each predetermined temperature that satisfies the orientation temperature condition (for example, every 1°C). The temperature interval (storage temperature interval) for which the storage device 50b (data storage module 510) stores the illuminance data 513 is not particularly limited, and characteristic data may be stored at predetermined temperature intervals of 1°C or more, or at intervals of less than 1°C (for example, every 0.5°C).

[0085] Visible light irradiation for displaying the visible light image 60 by the second projector 40 is performed after ultraviolet light irradiation (screening of the image display unit 10) by the first projector 20 at a constant irradiation intensity and duration. As described above, the rate of increase in light scattering intensity due to the reception of ultraviolet light of a constant intensity in the display function layer 11 of the image display unit 10 differs depending on the ambient temperature. Therefore, the light scattering intensity value (post-irradiation intensity value) in the display function layer 11 of the image display unit 10 (irradiated area 10c) after ultraviolet light irradiation with a constant irradiation duration and constant ultraviolet light intensity will differ depending on the ambient temperature.

[0086] The illuminance data 513 is data for controlling visible light irradiation so that the lower the ambient temperature (the lower the light scattering intensity value of the irradiation area 10c after screening), the higher the visible light illuminance on the surface of the irradiation area 10c of the image display body 10 is, taking into account the difference in post-irradiation intensity values ​​due to ambient temperature. In other words, the visible light illuminance shown by the illuminance data 513 becomes larger as the corresponding temperature decreases. As a result, the lower the ambient temperature and the smaller the post-irradiation intensity value of the irradiation area 10c, the greater the amount of light incident on the surface of the irradiation area 10c, and the amount of visible light when displaying the visible light image 60 that is visible to the user is kept constant regardless of the ambient temperature. That is, the brightness of the visible light image 60 can be kept constant.

[0087] In this embodiment, the visible light illuminance (illuminance in the irradiation area 10c) for each temperature shown in the illuminance data 513 is calculated based on the light scattering intensity value (post-irradiation intensity value) of the image display body 10 (irradiation area 10c) after ultraviolet light irradiation (screening) with a constant irradiation time and a constant ultraviolet light intensity. Specifically, the illuminance data 513 corresponding to each temperature that satisfies the orientation temperature conditions, that is, the visible light illuminance in the irradiation area 10c corresponding to each temperature, is calculated based on the following formula (1).

[0088] In equation (1), the post-irradiation intensity value at the highest temperature among those that satisfy the orientation temperature condition is denoted as "a," and the visible light illuminance (lx) in the irradiation area 10c at the highest temperature is denoted as "A." Furthermore, the post-irradiation intensity value at temperatures below the highest temperature among those that satisfy the orientation temperature condition is denoted as "b," and the visible light illuminance (lx) in the irradiation area 10c at that temperature is denoted as "B." B = A × a / b ... Equation (1)

[0089] Here, with reference to Figure 3C, a specific example of the illuminance data 513 calculated by the above formula (1) will be explained. As shown in Figure 3C, a constant irradiation time (36 seconds) and a constant ultraviolet light intensity (20 mW / cm² in this example) are applied to the image display unit 10. ２ The light scattering intensity value (post-irradiation intensity value) of the display function layer 11 in the image display body 10 (irradiation area 10c) after ultraviolet light irradiation by ) differs depending on the ambient temperature. In this example, the orientation temperature range was from 20°C to 40°C, and the post-irradiation intensity value was "67" at an ambient temperature of 20°C (lowest temperature), and the post-irradiation intensity value was "79" at an ambient temperature of 40°C (highest temperature).

[0090] In the example shown in Figure 3C, assuming that the visible light illuminance in the irradiation area 10c at the highest temperature is "10000 (lx)", the visible light illuminance in the irradiation area 10c at the lowest temperature (20°C) will be "11791 (lx) (= 10000 (lx) × 79 / 67)". Therefore, the visible light illuminance in the irradiation area 10c at the lowest temperature (20°C) is higher than the visible light illuminance at the highest temperature. In other words, the intensity of the visible light irradiated from the second projector 40 increases, and the amount of light incident on the surface of the irradiation area 10c increases.

[0091] Furthermore, in this embodiment, the visible light illuminance shown by the illuminance data 513 is calculated based on the above formula (1), so that the product of the visible light illuminance value in the irradiated area 10c while the visible light image 60 is being displayed (while visible light is being irradiated from the second projector 40) and the post-irradiation intensity value is the same whether the ambient temperature corresponds to the highest temperature within the orientation temperature range or to a temperature lower than the highest temperature (the lowest temperature in this example). Here, "the same" includes a small error value (for example, 5 or less).

[0092] In the example shown in Figure 3, the product of the visible light illuminance value shown in the illuminance data 513 corresponding to the lowest temperature (20°C) and the post-irradiation intensity value is "789997 (= 11791 (lx) × 67)", and the product of the visible light illuminance value shown in the illuminance data 513 corresponding to the highest temperature (40°C) and the post-irradiation intensity value is "790000 (= 10000 (lx) × 79)", with a difference of "3". In other words, at the lowest and highest temperatures among the temperatures that satisfy the orientation temperature conditions, the product of the visible light illuminance value shown in the illuminance data 513 and the post-irradiation intensity value is the same. As a result, regardless of temperature changes in the operating environment, visible light is scattered on the surface of the image display body 10 (irradiation area 10c) after screening, and the amount of visible light reaching the user's eyes can be controlled to be more reliably constant. That is, the brightness of the visible light image 60 can be made more reliably constant.

[0093] Thus, the illuminance data 513 represents the visible light illuminance in the irradiation area 10c corresponding to each temperature that satisfies the orientation temperature condition, that is, the visible light illuminance calculated by the above formula (1). Note that the illuminance data 513 corresponding to the highest temperature, that is, the visible light illuminance in the irradiation area 10c at the highest temperature, is a predetermined fixed value that serves as the basis for calculating the illuminance data 513 for each temperature below the highest temperature (reference illuminance).

[0094] In this embodiment, the irradiation time for ultraviolet light irradiation when the image display unit 10 is screened may be the time until the light scattering intensity value of the irradiation area 10c reaches the required intensity value by ultraviolet light irradiation at a predetermined irradiation intensity at the highest temperature within the orientation temperature range. This ensures that the post-irradiation intensity value at the highest temperature in formula (1) corresponds to the required intensity value. Furthermore, the reference illuminance at the highest temperature may be a visible light illuminance that allows the visible light image 60 to be displayed at a brightness that provides good visibility to the user when the light scattering intensity value of the irradiation area 10c corresponds to the required intensity value. This ensures that the brightness of the visible light image 60 displayed on the image display unit 10 remains more reliable and constant even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature conditions).

[0095] Next, the irradiation control module 530 of the control unit 500 will be described. Based on various data output from the data acquisition module 52, the irradiation control module 530 controls the irradiation of ultraviolet light by the first projector 20 and the irradiation of visible light by the second projector 40.

[0096] In this embodiment, as described above, the irradiation control module 530 controls the irradiation of the image display body 10 with ultraviolet light by the first projector 20 (screening of the image display body 10) based on a fixed irradiation time and a fixed ultraviolet light intensity. The irradiation control module 530 sends a predetermined irradiation time and ultraviolet light intensity to the first projector 20. For example, the irradiation control module 530 may send an irradiation intensity and irradiation time to the first projector 20 that allows the light scattering intensity of the irradiation area 10c to be controlled to a value equivalent to the required intensity value at the highest temperature within the orientation temperature range, regardless of the ambient temperature. As a result, the first projector 20, under the control of the control unit 500 (irradiation control module 530), emits ultraviolet light from the ultraviolet light source based on a fixed irradiation intensity and a fixed irradiation time, and irradiates the irradiation area 10c of the image display body 10 with ultraviolet light.

[0097] In this embodiment, the irradiation time of ultraviolet light in the first projector 20 is constant, and as described above, the irradiation time is adjusted to the high-temperature environment (the highest temperature within the orientation temperature range). Therefore, the irradiation time is not extended in response to a decrease in ambient temperature. Consequently, the time required to start displaying the visible light image 60 (the time required to screen the image display unit 10) can be shortened regardless of the ambient temperature.

[0098] The constant irradiation intensity and irradiation time sent to the first projector 20 may be stored in the data storage module 510. In this case, the irradiation control module 530 can acquire the irradiation intensity and irradiation time via the data acquisition module 52. The irradiation control module 530 can perform control to irradiate with ultraviolet light by the first projector 20 when the ambient temperature satisfies the orientation temperature condition. Similar to the irradiation control module 53 in the first embodiment, the irradiation control module 530 can determine whether the ambient temperature satisfies the orientation temperature condition based on the ambient temperature (temperature measured by the temperature measurement unit 70) and guaranteed temperature data 511 output by the data acquisition module 52, and if the orientation temperature condition is met, it can send the irradiation intensity and irradiation time length to the first projector 20.

[0099] Next, the control of visible light irradiation by the irradiation control module 530 of the control unit 500 will be described in detail. The irradiation control module 530 controls the visible light irradiation by the second projector 40 so that the lower the ambient temperature is within the temperature range (orientation temperature range) that satisfies the orientation temperature conditions, the higher the visible light illuminance in the irradiation area 10c where the visible light image 60 is displayed. This shortens the time required to start displaying the visible light image 60, and makes it possible to keep the brightness of the visible light image 60 displayed on the image display unit 10 constant even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature conditions).

[0100] More specifically, the irradiation control module 530 controls the visible light irradiation by the second projector 40 so that the product of the visible light illuminance value in the irradiation area 10c while the visible light image 60 is being displayed and the post-irradiation intensity value are equal, regardless of whether the ambient temperature corresponds to the highest temperature within the orientation temperature range or to the ambient temperature being lower than the highest temperature. This ensures that the amount of visible light when the visible light image 60 is displayed, as seen by the user, remains constant regardless of the ambient temperature, and the brightness of the visible light image 60 can be kept more reliably constant.

[0101] Specifically, the irradiation control module 530 reads illuminance data 513 from the data storage module 510 and controls the visible light irradiation from the second projector 40 based on the visible light illuminance indicated by the read illuminance data 513. The irradiation control module 530 may read illuminance data 513 corresponding to the ambient temperature via the data acquisition module 52 if the ambient temperature is within the orientation temperature range indicated by the guaranteed temperature data 511. If there is no illuminance data 513 that matches the ambient temperature, the irradiation control module 530 may acquire illuminance data 513 corresponding to the temperature closest to the ambient temperature.

[0102] As described above, since the illuminance data 513 is calculated based on the above formula (1), the product of the visible light illuminance and the post-irradiation intensity value shown in the illuminance data 513 corresponding to a temperature below the highest temperature within the orientation temperature range is equivalent to the product of the visible light illuminance and the post-irradiation intensity value shown in the illuminance data 513 corresponding to the highest temperature. The irradiation control module 530 sends the visible light illuminance shown in the acquired illuminance data 513 along with the image information to the second projector 40. As a result, the second projector 40, under the control of the control unit 500, can irradiate with visible light (display of the visible light image 60) so that the visible light illuminance in the irradiation area 10c of the image display body 10 becomes the value shown in the illuminance data 513. As a result, the visible light from the second projector 40 is scattered on the surface of the image display body 10 (irradiation area 10c) after screening, and the amount of visible light that the user can see can be controlled to be more reliably constant. In other words, the brightness of the visible light image 60 can be made more reliably constant.

[0103] Figure 9 is a flowchart showing an example of a control method for the display device 1 according to this embodiment. In this embodiment, the control unit 500 (irradiation control module 530) acquires the ambient temperature in the same manner as in step S1 above (S21), and determines whether the acquired ambient temperature satisfies the orientation temperature conditions (S22). If the ambient temperature is within the orientation temperature range indicated by the guaranteed temperature data 511, the irradiation control module 530 determines that the ambient temperature satisfies the orientation temperature conditions (S22:Y), and sends a predetermined constant irradiation intensity and irradiation time to the first projector 20 to screen the image display body 10 by irradiating it with ultraviolet light at the irradiation intensity and irradiation time (S23).

[0104] Next, the control unit 500 (irradiation control module 530) acquires illuminance data 513 from the data storage module 510 based on the ambient temperature (S24), and displays a visible light image 60 on the image display unit 10 (irradiation area 10c) by visible light irradiation based on the visible light illuminance indicated by the illuminance data 513 (S25). Specifically, the irradiation control module 530 sends image information and the visible light illuminance indicated by the illuminance data 513 to the second projector 40. As a result, visible light with a wavelength corresponding to the color component of the visible light image indicated by the image information is irradiated from the second projector 40 onto the image display unit 10 with an intensity corresponding to the visible light illuminance indicated by the illuminance data 513, and the visible light image 60 is displayed.

[0105] As described above, the visible light illuminance indicated by the illuminance data 513 increases as the ambient temperature decreases. Therefore, as the ambient temperature decreases, the amount of light incident on the irradiation area 10c by visible light irradiation based on the visible light illuminance, i.e., the visible light illuminance in the irradiation area 10c, increases. Accordingly, by controlling visible light irradiation based on the visible light illuminance indicated by the illuminance data 513, the control unit 500 (irradiation control module 530) can control the irradiation of visible light to the irradiation area 10c such that the visible light illuminance in the irradiation area 10c where the visible light image 60 is displayed increases as the ambient temperature decreases within the temperature range that satisfies the orientation temperature condition. As a result, even if the light scattering intensity (intensity value after irradiation) in the irradiation area 10c after screening differs, the amount of visible light that the user can see can be kept constant. In other words, even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature condition), the brightness of the visible light image 60 displayed on the image display unit 10 can be kept constant.

[0106] In this embodiment, the display device 1 is configured such that the data storage module 51 stores illuminance data 513 calculated based on the above formula (1), but the disclosure is not limited thereto. For example, when the irradiation control module 530 performs visible light irradiation control, the display device 1 may calculate the visible light illuminance in the irradiation area 10c according to the ambient temperature each time based on the above formula (1). In this case, the data storage module 51 only needs to store the reference illuminance and post-irradiation intensity value (required intensity value) at the highest temperature within the orientation temperature range, and the post-irradiation intensity value corresponding to each temperature within the orientation temperature range.

[0107] 3. Third Embodiment Next, a third embodiment of the present disclosure will be described with reference to Figure 10. This embodiment is an embodiment in which the display device 1 is equipped with a third projector 30 that emits visible light (specific visible light) for erasing a visible light image displayed on an image display body 10. The third projector 30 is a projector that emits specific visible light and is positioned opposite the front surface 10a of the image display body 10. As a specific visible light emitting unit, the third projector 30 emits specific visible light (blue light) with a wavelength of approximately 450 nm, for example. The third projector 30 emits specific visible light onto the image display body 10, which is in an opaque state, to change the ultraviolet light irradiation area 10c on the image display body 10 from an opaque state to a transparent state.

[0108] As described above, the display function layer 11 becomes cloudy due to increased light scattering when it receives ultraviolet light, and returns to a transparent state when it receives specific visible light, as its light scattering decreases. Therefore, by emitting specific visible light (blue light) from the third projector 30, the ultraviolet light-irradiated area 10c on the image display body 10 can be made transparent (non-screen state), and the display of the visible light image can be terminated. According to the configuration of this embodiment, by providing a dedicated projector that emits visible light to erase the visible light image, the visible light image can be reliably erased, and the control by the control unit 50 can be simplified, reducing the processing load.

[0109] (Effects of the Embodiment) (1) In the display device 1 according to the first embodiment of this disclosure, the rate of increase in the light scattering intensity of the display function layer 11 due to the reception of ultraviolet light of a constant intensity differs depending on the ambient temperature. When the ambient temperature satisfies the orientation temperature condition, the control unit 50 determines the irradiation time of ultraviolet light by the first projector 20 based on the ambient temperature, and controls the irradiation of ultraviolet light based on the irradiation time so that the light scattering intensity of the display function layer in the irradiation area 10c becomes constant. The display device 1, under the control of the control unit 50, determines the irradiation time of ultraviolet light by the first projector 20 based on the ambient temperature when the ambient temperature satisfies the orientation temperature condition, and controls the irradiation of ultraviolet light based on the irradiation time so that the light scattering intensity of the display function layer in the irradiation area 10c becomes constant. With this configuration, the light scattering intensity of the display function layer 11 in the irradiation area 10c can be set to a constant value by ultraviolet light irradiation when the image display body 10 is screened. Therefore, even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature conditions), the brightness of the visible light image 60 displayed on the image display unit 10 can be kept constant.

[0110] (2) The display device 1 includes a data storage module 51 that stores the above-mentioned required intensity value as a display condition for the visible light image 60 on the image display body 10. The required intensity value is the maximum value of the light scattering intensity of the irradiation area 10c at the lowest temperature within the temperature range that satisfies the orientation temperature condition. The control unit 50 may determine the irradiation time of ultraviolet light by the first projector 20 based on the ambient temperature when the ambient temperature satisfies the orientation temperature condition, and control the first projector 20 based on the irradiation time to set the light scattering intensity of the irradiation area 10c to a value corresponding to the required intensity value. With this configuration, by setting the light scattering intensity of the irradiation area 10c to the required intensity value, the brightness of the visible light image 60 can be kept constant in a state that is easily visible to the user. (3) In the display device 1, the data storage module 51 stores the above-mentioned required intensity value and the irradiation time of ultraviolet light that yields a light scattering intensity equivalent to the required intensity value in the irradiation area 10c as display conditions, and the display function layer 11 determines that the rate of increase in the light scattering intensity in the irradiation area 10c due to the reception of ultraviolet light increases as the ambient temperature increases, and the irradiation time of ultraviolet light determined by the control unit 50 may become shorter as the ambient temperature increases. With this configuration, by determining the irradiation time according to the ambient temperature, the light scattering intensity value of the irradiation area 10c can be more reliably set to the required intensity value, and the visible light image 60 can be displayed more reliably with a constant brightness.

[0111] (4) In the display device 1, the data storage module 51 stores characteristic data 512 for each predetermined temperature that satisfies the orientation temperature condition, which associates the length of ultraviolet light irradiation time of the irradiation area 10c of the image display body 10 with the value of the light scattering intensity of the irradiation area 10c obtained by ultraviolet light irradiation at the said irradiation time. The characteristic data 512 includes data indicating the above-mentioned display conditions. The control unit 50 may identify data from the characteristic data corresponding to the ambient temperature that indicates the value of the light scattering intensity corresponding to the above-mentioned required intensity value, and determine the ultraviolet light irradiation time indicated by this data as the irradiation time of ultraviolet light by the first projector 20. With this configuration, the brightness of the visible light image 60 displayed on the image display body 10 can be easily kept constant regardless of temperature changes in the operating environment. (5) In the display device 1 according to the first modified example of the first embodiment described above, the characteristic data 512 indicates the correspondence between the irradiation time of ultraviolet light to the irradiation area 10c of the image display body 10, the value of the light scattering intensity within the irradiation area 10c obtained by ultraviolet light irradiation for the irradiation time, and the ultraviolet light intensity during ultraviolet light irradiation. The ultraviolet light intensity indicated by the characteristic data 512 stored in the data storage module 51 is set to a smaller value as the corresponding temperature increases. The control unit 50 may send the irradiation time and ultraviolet light intensity indicated by the data identified from the characteristic data 512 corresponding to the ambient temperature to the first projector 20 and control the light scattering intensity within the irradiation area 10c to the required intensity value indicated by the display conditions described above. With this configuration, even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature conditions), the brightness of the visible light image 60 displayed on the image display unit 10 can be kept constant. Furthermore, the reduction in the cooling efficiency of the first projector 20 is suppressed, making it possible to suppress the enlargement of the cooling device (or miniaturize the cooling device), thereby improving the suitability of the display device 1 as an in-vehicle device and achieving energy-saving effects.

[0112] (6) In the display device 1 according to the first modified example described above, when the characteristic data 512 includes ultraviolet light intensity as described in (5) above, the control unit 50 may identify data from the characteristic data corresponding to the ambient temperature in which the light scattering intensity corresponds to the required intensity value in the display conditions and the irradiation time does not exceed a predetermined maximum irradiation time, and send the irradiation time and ultraviolet light intensity indicated by the identified data to the ultraviolet light irradiation unit. With this configuration, ultraviolet light irradiation can be controlled in such a way that the brightness of the visible light image 60 displayed on the image display unit 10 is kept more reliably constant while reducing the ultraviolet light irradiation intensity in the first projector 20.

[0113] (7) In the display device 1 according to the second embodiment described above, the rate of increase in light scattering intensity due to reception of ultraviolet light of a constant intensity in the display function layer 11 differs depending on the ambient temperature, and the control unit 500 controls the irradiation of visible light by the second projector 40 so that the lower the ambient temperature, within the temperature range that satisfies the orientation temperature condition, the higher the visible light illuminance in the irradiation area 10c where the visible light image 60 is displayed. The display device 1 according to the second embodiment, under the control of the control unit 500, irradiates the irradiation area 10c with ultraviolet light for a constant irradiation time and with a constant ultraviolet light intensity, and then displays the visible light image 60 on the image display body by irradiating with visible light, and controls the irradiation of visible light by the second projector 40 to the irradiation area 10c so that the lower the ambient temperature, within the temperature range that satisfies the orientation temperature condition, the higher the visible light illuminance in the irradiation area 10c where the visible light image 60 is displayed. With this configuration, even if temperature changes occur in the operating environment (an environment where the ambient temperature satisfies the orientation temperature conditions) and the light scattering intensity value of the display function layer 11 differs in the irradiated area 10c after ultraviolet light irradiation, the brightness of the visible light image 60 displayed on the image display body 10 can be kept constant by controlling the visible light illuminance in the irradiated area 10c. (8) In the display device 1 according to the configuration of (7) above, the value of the light scattering intensity in the irradiated area 10c of the image display body 10 after ultraviolet light irradiation with a certain irradiation time and a certain ultraviolet light intensity is defined as the post-irradiation intensity value, and the control unit 500 controls ultraviolet light irradiation by the first projector 20 based on a certain irradiation time and a certain ultraviolet light intensity, and the visible light irradiation by the second projector 40 may be controlled so that the product of the visible light illuminance value in the irradiated area 10c while the visible light image 60 is displayed and the post-irradiation intensity value is the same when the ambient temperature corresponds to the highest temperature within the orientation temperature range and when the ambient temperature is lower than the highest temperature. With this configuration, regardless of temperature changes in the operating environment, visible light is scattered on the surface of the image display body 10 (irradiation area 10c) after screen formation, allowing for more reliable and consistent control of the amount of visible light reaching the user's eyes. In other words, the brightness of the visible light image 60 can be more reliably kept constant.

[0114] 1 Display device 10 Image display unit 10a Front 10b Back 10c Irradiation area 11 Display function layer 12 Ultraviolet light shielding layer 101, 102 Transparent substrate 20 First projector 40 Second projector (example of visible light projection unit) 50, 500 Control unit 50a Processor 50b Storage device 51, 510 Data storage module 511 Guaranteed temperature data 512 Characteristic data 513 Illuminance data 52 Data acquisition module 53, 530 Irradiation control module 60 Visible light image 70 Temperature measurement unit

Claims

1. A display device comprising: an image display body having a display function layer whose light scattering intensity increases when it receives ultraviolet light under predetermined temperature conditions and decreases when it receives visible light in a specific wavelength range; an ultraviolet light irradiation unit that irradiates the image display body with ultraviolet light; a visible light irradiation unit that irradiates an irradiated area on the image display body where the light scattering intensity of the display function layer has increased due to irradiation with ultraviolet light, with visible light of an arbitrary wavelength, to display a visible light image within the irradiated area; a temperature measuring unit that measures the ambient temperature indicating the temperature of the environment in which the image display body is used; and a control unit that controls the irradiation of ultraviolet light from the ultraviolet light irradiation unit and the irradiation of visible light from the visible light irradiation unit, wherein the rate of increase in the light scattering intensity due to the reception of ultraviolet light of a constant intensity in the display function layer differs depending on the ambient temperature; and the control unit, when the ambient temperature satisfies the temperature conditions, determines the irradiation time of ultraviolet light by the ultraviolet light irradiation unit based on the ambient temperature and controls the irradiation of ultraviolet light based on the irradiation time so that the light scattering intensity of the display function layer in the irradiated area remains constant.

2. The display device according to claim 1, comprising a storage unit that stores a required intensity value indicating the value of the light scattering intensity of the irradiation area required for displaying the visible light image as a display condition for the visible light image, wherein the required intensity value in the display condition is the maximum value of the light scattering intensity of the irradiation area at the lowest temperature within a temperature range that satisfies the temperature condition, and the control unit determines the irradiation time of ultraviolet light by the ultraviolet light irradiation unit based on the ambient temperature when the ambient temperature satisfies the temperature condition, and controls the ultraviolet light irradiation based on the irradiation time to set the light scattering intensity of the irradiation area to a value corresponding to the required intensity value.

3. The display device according to claim 2, wherein the storage unit stores the required intensity value and the irradiation time of ultraviolet light that yields a light scattering intensity equivalent to the required intensity value in the irradiation area as the display conditions, the rate of increase in the light scattering intensity in the irradiation area due to the reception of ultraviolet light increases as the ambient temperature increases, and the irradiation time of ultraviolet light determined by the control unit becomes shorter as the ambient temperature increases.

4. The display device according to claim 3, wherein the storage unit stores characteristic data relating the length of ultraviolet light irradiation time of the irradiation area of ​​the image display body to the value of the light scattering intensity of the irradiation area obtained by ultraviolet light irradiation at the irradiation length, for each predetermined temperature that satisfies the temperature conditions, the characteristic data includes data indicating the display conditions, and the control unit identifies data indicating the value of the light scattering intensity corresponding to the required intensity value from among the characteristic data corresponding to the ambient temperature, and determines the length of ultraviolet light irradiation time indicated by the data to be the length of ultraviolet light irradiation time by the ultraviolet light irradiation unit.

5. The display device according to claim 4, wherein the characteristic data indicates the correspondence between the irradiation time of ultraviolet light to the irradiation area of ​​the image display body, the value of the light scattering intensity within the irradiation area obtained by the ultraviolet light irradiation at the irradiation time, and the ultraviolet light intensity during the ultraviolet light irradiation, the ultraviolet light intensity indicated by the characteristic data stored in the storage unit is set to a smaller value as the corresponding temperature increases, and the control unit sends the irradiation time and ultraviolet light intensity indicated by the data identified from the characteristic data corresponding to the ambient temperature to the ultraviolet light irradiation unit, thereby controlling the light scattering intensity within the irradiation area to the required intensity value indicated by the display conditions.

6. The display device according to claim 5, wherein the control unit identifies data from the characteristic data corresponding to the ambient temperature in which the light scattering intensity corresponds to the required intensity value in the display conditions and the irradiation time does not exceed a predetermined maximum irradiation time, and sends the irradiation time and ultraviolet light intensity indicated by the identified data to the ultraviolet light irradiation unit.

7. A display device comprising: an image display body having a display function layer whose light scattering intensity increases when it receives ultraviolet light under predetermined temperature conditions and decreases when it receives visible light in a specific wavelength range; an ultraviolet light irradiation unit for irradiating the image display body with ultraviolet light; a visible light irradiation unit for irradiating an irradiated area on the image display body where the light scattering intensity of the display function layer has increased due to irradiation with ultraviolet light, with visible light of an arbitrary wavelength to display a visible light image on the image display body; a temperature measuring unit for measuring the ambient temperature indicating the temperature of the environment in which the image display body is used; and a control unit for controlling the irradiation of ultraviolet light from the ultraviolet light irradiation unit and the irradiation of visible light from the visible light irradiation unit, wherein the rate of increase in light scattering intensity due to the reception of ultraviolet light of a certain intensity of the display function layer differs depending on the ambient temperature, and the control unit controls the irradiation of visible light such that the visible light illuminance in the irradiated area where the visible light image is displayed increases as the ambient temperature decreases within a temperature range that satisfies the temperature conditions.

8. The display device according to claim 7, wherein the value of the light scattering intensity in the irradiated area of ​​the image display body after performing ultraviolet light irradiation with a fixed irradiation time and a fixed ultraviolet light intensity is defined as the post-irradiation intensity value, the control unit controls the ultraviolet light irradiation based on the fixed irradiation time and the fixed ultraviolet light intensity, and controls the visible light irradiation so that the product of the visible light illuminance value in the irradiated area while the visible light image is displayed and the post-irradiation intensity value is equal when the ambient temperature corresponds to the highest temperature within the temperature range and when the ambient temperature is lower than the highest temperature.

9. A control method for a display device, comprising: irradiating an image display body having a display function layer whose light scattering intensity increases when it receives ultraviolet light under predetermined temperature conditions and decreases when it receives visible light in a specific wavelength range with ultraviolet light; irradiating an irradiated area on the image display body where the light scattering intensity of the display function layer has increased due to the irradiation of ultraviolet light with visible light of an arbitrary wavelength to display a visible light image on the image display body, wherein the rate of increase in light scattering intensity due to the reception of ultraviolet light of a constant intensity of the display function layer differs depending on the ambient temperature, which indicates the temperature of the environment in which the image display body is used; determining the irradiation time of ultraviolet light to the irradiated area of ​​the image display body based on the ambient temperature when the ambient temperature satisfies the temperature conditions; and controlling the irradiation of ultraviolet light to the irradiated area based on the irradiation time so that the light scattering intensity of the display function layer in the irradiated area remains constant.

10. A control method for a display device, comprising: irradiating an image display body having a display function layer whose light scattering intensity increases when it receives ultraviolet light under predetermined temperature conditions and decreases when it receives visible light in a specific wavelength range with ultraviolet light; irradiating an irradiated area on the image display body where the light scattering intensity of the display function layer has increased due to the irradiation of ultraviolet light with visible light of an arbitrary wavelength to display a visible light image on the image display body, wherein the rate of increase in the light scattering intensity of the irradiated area due to the reception of ultraviolet light of a constant intensity varies depending on the ambient temperature, which indicates the temperature of the environment in which the image display body is used; displaying the visible light image on the image display body by irradiating visible light after irradiating the irradiated area with ultraviolet light for a constant irradiation time and with a constant ultraviolet light intensity; and controlling the irradiation of visible light to the irradiated area such that the visible light illuminance in the irradiated area where the visible light image is displayed increases as the ambient temperature decreases within a temperature range that satisfies the temperature conditions.

Images