Method for controlling optical components, and blind spot assist system

Abstract

This invention provides a control method for an optical element and a blind spot assist system that can suppress the reduction in visibility caused by response time when viewing a scene through a dimmable element that can switch between a transparent state and a reflective state. [Solution] The optical member 1 comprises a dimming member 3 having multiple regions that can be switched between a transparent state and a reflective state, and a reflective member 2 positioned opposite the dimming member 3 and reflecting the light reflected by the dimming member 3 back towards the dimming member 3. The dimming member 3 is composed of a cholesteric liquid crystal panel 4, in which at least one region is in a transparent state and the other regions are in a reflective state, and dimming control is performed in which the regions that are set to be transparent are sequentially switched. In the blind spot assist system having the optical member 1, the switching time from the reflective state to the transparent state is set to a predetermined or lower by controlling the voltage applied to the cholesteric liquid crystal panel 4, and the switching time from the transparent state to the reflective state is set to a predetermined or lower by controlling the temperature of the panel.

Description

[Technical Field]

[0001] This disclosure relates to a control method for an optical element having a component that can switch between a transparent state and a reflective state, and to a blind spot assist system. [Background technology]

[0002] Conventionally, an optical component having a component that can switch between a transparent state and a reflective state is, for example, the one described in Patent Document 1. The optical component described in Patent Document 1 comprises a reflective component that reflects visible light and a dimming component having multiple regions that can switch between a transparent state and a reflective state. This optical component is used, for example, as a blind spot assist device, in which one of the multiple regions is made transparent and the remaining regions are made reflective, and dimming control is performed to sequentially switch the regions that become transparent, thereby allowing the user to see the scene in the blind spot region. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-22908 [Overview of the project] [Problems that the invention aims to solve]

[0004] The optical component described above has an electrochromic light-adjusting element. While electrochromic elements can switch between transparent and reflective states by applying voltage, this involves ion movement, making it difficult to reduce the time required for this switching (hereinafter referred to as "response time") to less than 1 second. When viewing an object moving in a blind spot area through a light-adjusting element with a response time greater than 1 second, the movement of the object appears to the human eye as stop-motion, resulting in reduced visibility.

[0005] In view of the above, this disclosure aims to provide a control method for an optical element and a blind spot assistance system that can suppress the reduction in visibility caused by response time when viewing a scene through a dimming element that can switch between a transparent state and a reflective state. [Means for solving the problem]

[0006] According to one aspect of this disclosure, a method for controlling an optical element comprising: a reflective member (2) that reflects visible light; a dimming member (3) composed of a cholesteric liquid crystal panel (4) positioned opposite the reflective member, having N regions (31 to 3N) (N: an integer of 2 or more) that can switch between a transparent state with a visible light transmittance of 60% or more and a reflective state with a visible light reflectance of 60% or more; This includes performing dimming control by sequentially repeating the following steps: switching at least one of N reflective regions to a transparent state by applying a voltage to the cholesteric liquid crystal panel, leaving the remaining regions reflective, then switching the transparent regions back to a reflective state, and finally switching at least one of the other reflective regions back to a transparent state. In switching at least one region to a transparent state, the time required for the change from a reflective state to a transparent state is reduced to below a predetermined level by controlling the voltage applied to the cholesteric liquid crystal panel. In switching from a transparent state to a reflective state, the time required for the change from transparent to reflective state is kept below a predetermined level by controlling the temperature of the cholesteric liquid crystal panel.

[0007] This control method for an optical component involves controlling the voltage and temperature applied to a cholesteric liquid crystal panel in an optical component having a dimming element with multiple regions that can switch between a transparent state and a reflective state. The control method uses voltage control to reduce the time required to switch from the reflective state to the transparent state to a predetermined level, and uses temperature control to reduce the time required to switch from the transparent state to the reflective state to a predetermined level. As a result, the response time of the optical component having the dimming element becomes 1 second or less, making this a control method for an optical component that can suppress the decrease in visibility caused by the response time.

[0008] From another perspective of this disclosure, a blind spot assistance system, A reflective member (2) that reflects visible light, A dimming member (3) is composed of a cholesteric liquid crystal panel (4) positioned opposite a reflective member and has N regions (31 to 3N) (N: an integer of 2 or more) that can switch between a transparent state with a visible light transmittance of 60% or more and a reflective state with a visible light reflectance of 60% or more. A temperature sensor (7) for measuring the temperature of the cholesteric liquid crystal panel, The system includes a control unit (6) that controls the voltage applied to the cholesteric liquid crystal panel and controls the temperature of the cholesteric liquid crystal panel based on temperature information measured by a temperature sensor, The control unit is The dimming control is performed by sequentially repeating the following steps: switching at least one of the N reflective regions to a transparent state by voltage control, leaving the remaining regions reflective, then switching the transparent region back to a reflective state, and finally switching at least one of the other reflective regions back to a transparent state. Voltage control is used to keep the time required to change from a reflective state to a transparent state below a predetermined level, and temperature control is used to keep the time required to change from a transparent state to a reflective state below a predetermined level.

[0009] This blind spot assistance system comprises a dimming member having multiple regions that can be switched between a transparent state and a reflective state, and a control unit that performs voltage control and temperature control applied to the cholesteric liquid crystal panel. The control unit also controls the time required to switch from the reflective state to the transparent state to a predetermined level or less by voltage control, and controls the time required to switch from the transparent state to the reflective state to a predetermined level or less by temperature control. As a result, the response time of the dimming member becomes 1 second or less, making it a blind spot assistance system that can suppress the reduction in visibility caused by response time.

[0010] The reference numerals in parentheses attached to each component indicate an example of the correspondence between that component and the specific components described in the embodiments described later. [Brief explanation of the drawing]

[0011] [Figure 1] This is a cross-sectional view showing an optical component according to an embodiment. [Figure 2] This figure shows an example of the connection between the partitioned areas and the control unit of the dimming component. [Figure 3] This diagram shows the configuration of a cholesteric liquid crystal panel. [Figure 4] This is an explanatory diagram showing the case where the first region of the dimming component is transparent. [Figure 5] This is an explanatory diagram illustrating the case where the Nth region of the dimming component is transparent. [Figure 6] This figure shows the measurement results of the changes in transmittance and reflectance when the voltage applied to a cholesteric liquid crystal panel is switched from off to on. [Figure 7] This figure shows the measurement results of the changes in transmittance and reflectance when the voltage applied to a cholesteric liquid crystal panel is switched from on to off. [Figure 8] This figure shows the measurement results of the change in transmittance of a cholesteric liquid crystal panel when the applied voltage is increased. [Figure 9] This figure shows the relationship between the time it takes for the transparent state to become functional and the applied voltage. [Figure 10] It is a diagram showing the measurement results of the change in reflectance of a cholesteric liquid crystal panel when the temperature is increased. [Figure 11] It is a diagram showing the relationship between the function manifestation time in the reflective state and the reciprocal of the absolute temperature. [Figure 12] It is a diagram showing the results of measuring the changes in capacitance and resistance values when the frequency of the applied voltage to the cholesteric liquid crystal panel is changed. [Figure 13] It is a diagram showing the circuit configuration in perspective view formed by the cholesteric liquid crystal panel and the power supply in FIG. 12. [Figure 14] It is a diagram showing the relationship between the frequency of the driving voltage of the cholesteric liquid crystal panel and the panel temperature. [Figure 15] It is an explanatory diagram of an example of frequency control of the driving voltage according to the temperature of the cholesteric liquid crystal panel. [Figure 16] It is a diagram showing an example of the circuit configuration when the transparent electrode of the cholesteric liquid crystal panel functions as a heater. [Figure 17] It is a time chart showing an example of voltage application for driving by the first power supply and voltage application for heating by the second power supply in the circuit configuration of FIG. 16. [Figure 18] It is an explanatory diagram of a modification example of the voltage application for driving by the first power supply in the circuit configuration of FIG. 16. [Figure 19] It is a diagram showing another shape example of the transparent electrode of the cholesteric liquid crystal panel.

Embodiments for Carrying Out the Invention

[0012] The embodiments of this disclosure will be described below with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be denoted by the same reference numerals. Furthermore, if only a part of a component is described in an embodiment, the other parts of the component can be replaced with components described in a previous embodiment. The following embodiments can be partially combined with each other, even if not explicitly stated, as long as it does not hinder the combination.

[0013] (Embodiment) A blind spot assistance system according to an embodiment will now be described. The blind spot assistance system of this embodiment includes an optical member 1 that is attached to, for example, a member or obstacle that obstructs the user's field of view and creates a blind spot, and allows the user to see the scenery in the blind spot area. In the case of an in-vehicle application, for example, the optical member 1 is attached to the pillar of the vehicle on which it is mounted, and guides ambient light from the area that becomes a blind spot due to the pillar towards the user, allowing the user to see the scenery in the blind spot area.

[0014] The optical component 1 includes, for example, a reflective member 2 having a reflective surface 2a that reflects visible light, as shown in Figure 1, and a dimming member 3 positioned opposite to the reflective surface 2a so as to be substantially parallel to it, and capable of switching between a transparent state that transmits visible light and a reflective state that reflects light. "Subjectively parallel" includes not only a state where they are perfectly parallel, but also a state where they are slightly tilted to the extent that it does not interfere with the guidance of ambient light due to the influence of dimensional errors or mounting accuracy of a housing or holding member (not shown). The optical component 1 has the reflective member 2 and the dimming member 3 attached to a housing or holding member (not shown), and these members are held in a substantially parallel state. When ambient light is incident on the dimming member 3 side from behind the reflective member 2, a portion of the ambient light is repeatedly reflected by the reflective region of the dimming member 3 and the reflective surface 2a of the reflective member 2, while a portion of the ambient light is emitted from the transparent region of the dimming member 3. As a result, the optical component 1 guides ambient light incident from a blind spot area blocked by an obstacle (not shown) located behind the reflective component 2 between the reflective component 2 and the dimming component 3, and emits this ambient light to the outside over a wide area of ​​the dimming component 3, thereby allowing the user to see the ambient view in the blind spot area.

[0015] In this embodiment, the reflective member 2 is a member having a reflective surface 2a with a visible light reflectivity of a predetermined value or higher (for example, 80% or more, though not limited to this value). The reflective member 2 is formed by laminating a thin metal film made of a metallic material such as Al (aluminum) and a transparent protective film made of silicon in that order on a substrate made of any material such as glass, ceramic, or resin. The reflective member 2 is held in a housing or the like (not shown) with its reflective surface 2a facing the dimming member 3, and acts as a mirror that reflects the light reflected by the dimming member 3 back towards the dimming member 3.

[0016] The dimming member 3, as shown in Figure 2 for example, has a plurality of partitioned regions 31 to 3N (N: an integer of 2 or more), and is a member that can switch between a transparent state that transmits visible light and a reflective state that reflects visible light for each of the regions 31 to 3N. The dimming member 3 may also be called a "dimming mirror". The dimming member 3 is composed of one or more cholesteric liquid crystal panels 4.

[0017] The cholesteric liquid crystal panel 4, as shown in Figure 3 for example, has two transparent substrates 41 and 45 arranged opposite each other, two transparent electrodes 42 and 44 formed on the opposing surfaces of the transparent substrates 41 and 45, and a cholesteric liquid crystal layer 43 sandwiched between the transparent electrodes 42 and 44. The transparent substrates 41 and 45 are made of any translucent material, such as glass. The transparent electrodes 42 and 44 are made of any translucent conductive material, such as ITO (Indium-Tin Oxide).

[0018] The cholesteric liquid crystal layer 43 is, for example, a layered structure in which rod-shaped liquid crystal molecules are stacked in multiple layers, and is obtained by adding a chiral material to a nematic liquid crystal. In Figure 3, the boundaries of the multiple stacked liquid crystal layers constituting the cholesteric liquid crystal layer 43 are shown by dashed lines, but the number of layers is not limited to that shown in Figure 3. In the cholesteric liquid crystal layer 43, the wavelength of reflected light is λ, the pitch in the thickness direction of the stacked liquid crystal layers is P, and the average refractive index of the liquid crystal layers is n. a Let λ = n a The equation ×P holds true. Furthermore, if Δn is the difference in refractive index between the transverse and vertical directions of the liquid crystal layer, then Δλ = Δn × P, which is typically 40 to 60 nm. In the cholesteric liquid crystal layer 43, when no voltage is applied, the liquid crystal molecules are able to rotate in directions intersecting the thickness direction. Liquid crystal layers with a large pitch P reflect long-wavelength light, while liquid crystal layers with a small pitch P reflect short-wavelength light. For example, when λ is in the visible light wavelength range of 450 nm to 750 nm, the cholesteric liquid crystal layer 43 is configured by stacking 5 to 10 liquid crystal layers with continuously changing pitch P, thereby enabling the reflection of light in the above wavelength range.

[0019] When an AC voltage is applied to the transparent electrodes 42 and 44 of the cholesteric liquid crystal panel 4, the arrangement of liquid crystal molecules in each liquid crystal layer constituting the cholesteric liquid crystal layer 43, which is in a mirror-like (reflective) state, changes to align along the thickness direction, resulting in a transparent state in which visible light is transmitted with almost no reflection. In other words, the cholesteric liquid crystal panel 4 can be switched between a transparent state and a reflective state depending on whether or not a voltage is applied. The voltage applied to the cholesteric liquid crystal panel 4 and the temperature of the panel are controlled by the control unit 6, which will be described later, so that the time required to switch between the transparent state and the reflective state, i.e., the response time, is 1 second or less. Details of this will be described later. The cholesteric liquid crystal panel 4 constitutes, for example, one region of the dimming member 3, and the number of regions is the same as the number of regions. Alternatively, the cholesteric liquid crystal panel 4 may be divided into N regions, for example, by the transparent electrodes 42 and 44, and constitute multiple regions 31 to 3N of the dimming member 3. Note that the transparent state refers to a state in which 60% or more of visible light is transmitted. Furthermore, a reflective state refers to a state in which, for example, 60% or more of visible light is reflected.

[0020] For the sake of explanation, the surface of the dimming member 3 that faces the reflective surface 2a of the reflective member 2 will be referred to as the "opposing surface 3a," and the surface opposite to the opposing surface 3a will be referred to as the "emitting surface 3b." Furthermore, the planar direction along the opposing surface 3a, which is the direction in which ambient light is guided by reflection from the opposing surface 3a and the reflective surface 2a, will be referred to as the "light guidance direction." In addition, of the two ends of the dimming member 3 in the light guidance direction, the end on the side where light is first incident will be referred to as the "incident end," the end on the opposite side of the incident end will be referred to as the "end end," and the incident end side of the outer edge of the dimming member 3 will be referred to as the "incident end side 3A."

[0021] Furthermore, as shown in Figure 2, the N regions constituting the dimming member 3 are referred to as the first region 31, second region 32, third region 33, fourth region 34, ..., the (N-1)th region 3(N-1), and the Nth region 3N, in order from the incident end to the terminal end. Note that the dashed lines in Figure 2 are convenient boundaries between regions 31 to 3N of the dimming member 3 and are not actually visible to the user.

[0022] The dimming member 3 has, for example, a plurality of regions 31 to 3N that are partitioned so as to be arranged parallel to the incident edge 3A. In Figure 2, a representative example is shown in plan view in which the outer shape of the dimming member 3 is rectangular and the outer shapes of the plurality of regions 31 to 3N are rectangular, but it is not limited to this. The outer shapes of the dimming member 3 and the plurality of regions 31 to 3N can be changed as appropriate. The dimming member 3 is connected to the transparent electrodes 42 and 44 of the cholesteric liquid crystal panel 4 by wiring 5 such as an FPC, and is connected to the control unit 6 via the wiring 5. The dimming member 3 performs dimming control in which at least one of the plurality of regions 31 to 3N is made transparent, the remaining other regions are kept in a reflective state, and the regions that become transparent are sequentially switched.

[0023] Specifically, when no voltage is applied, the dimming member 3 is in a reflective state where all regions 31 to 3N mainly reflect visible light. As shown in Figure 4, for example, when a voltage is applied to the first region 31 of regions 31 to 3N, the first region 31 becomes transparent, allowing ambient light L1 to pass through, while the other regions 32 to 3N, to which no voltage is applied, remain in a reflective state, reflecting ambient light L1. The dimming member 3 then sequentially switches the transparent region from the first region to the second region 32, from the second region 32 to the third region 33, and so on, until finally, as shown in Figure 5, for example, the Nth region 3N becomes transparent. After regions 31 to 3N are each made transparent, the same dimming control is repeated.

[0024] The control unit 6 has a configuration as a microcomputer equipped with a CPU, RAM, ROM, and non-volatile rewritable memory (not shown) on a circuit board with circuit wiring (not shown). CPU, RAM, and ROM are abbreviations for Central Processing Unit, Random Access Memory, and Read Only Memory, respectively. The control unit 6 reads and executes a computer program stored in the ROM or non-volatile rewritable memory, which are non-transitional physical recording media. When this computer program is executed, a method corresponding to the computer program is performed. That is, the control unit 6 acquires temperature information of the dimming member 3 from the temperature sensor 7 and performs various control processes such as controlling the drive voltage of the dimming member 3 and controlling the temperature of the cholesteric liquid crystal panel 4 according to the computer program. The control unit 6 is connected to a power supply for driving the dimming member 3 and is positioned behind the reflective member 2, i.e., on the opposite side of the reflective surface 2a.

[0025] The temperature sensor 7 is, for example, positioned at the end of the light-emitting surface 3b of the dimming member 3 and outputs a signal corresponding to the temperature of the dimming member 3. The temperature sensor 7 is, for example, a thermocouple and inputs a signal to the control unit 6 via wiring (not shown). The number and arrangement of the temperature sensors 7 may be changed as appropriate.

[0026] The above describes the basic configuration of the blind spot assistance system of this embodiment.

[0027] [Response time in dimming control and its reduction] Next, the response time in dimming control of the dimming component 3 will be explained.

[0028] When attempting to allow the user to perceive a scene of moving objects via the dimming element 3, the response time must be below a predetermined level, i.e., the frame rate must be above a predetermined level. If the frame rate is below the predetermined level, the human eye will perceive the scene of moving objects as a stop-motion animation, resulting in reduced visibility. For example, a frame rate of 24Hz or higher is considered acceptable for human perception of video.

[0029] For example, if the number of regions of the dimming element 3 is N=2, then switching between the transparent state and the reflective state in the first region 31 and the second region 32 is required twice. In this case, when switching on and off at a frame rate of 24Hz or higher to suppress a decrease in visibility, the response time in one region must be 1 / (24×2) ≈ 20 msec or less. Note that if the number of regions is N, then when the frame rate is 24Hz or higher, the response time in one region must be 1 / (24×N) seconds or less.

[0030] In the case of electrochromic panels, ion movement is involved when switching from a reflective state to a transparent state by applying voltage, making it difficult to keep the response time under 1 second. In contrast, the cholesteric liquid crystal panel 4 can keep the response time under 1 second.

[0031] Here, Figures 6 and 7 show the results of measuring the changes in transmittance and reflectance of light with wavelengths of 450 nm to 750 nm when the applied voltage was switched on and off in the cholesteric liquid crystal panel 4. The results shown in Figures 6 and 7 were obtained by applying a voltage with a square wave of 200 Hz, ±170 V, and a duty cycle of 1:1, and measuring the transmittance and reflectance at room temperature (25°C). Furthermore, the reflectance measurement was performed using two cholesteric liquid crystal panels 4 with left and right polarization stacked on top of each other.

[0032] For the sake of explanation, the following will refer to the change in the cholesteric liquid crystal panel 4 from a transparent state to a reflective state, or from a reflective state to a transparent state, where the transmittance or reflectance after the change is 60% or higher, as "function manifestation."

[0033] When the voltage application was switched from off to on, i.e., when the voltage was on, the cholesteric liquid crystal panel 4 showed that the time it took for the reflective function to disappear was 7 msec, while the time it took for the transparent function to emerge was 90 msec, which was significantly later than the time it took for the reflective function to disappear, as shown in Figure 6. The function emergence time is the time required from the moment the voltage application is switched on / off until the function emerges. Hereinafter, the function emergence time for the transparent state will be referred to as the "transparency emergence time," and the function emergence time for the reflective state will be referred to as the "reflection emergence time."

[0034] On the other hand, when the applied voltage was switched from on to off, i.e., when the voltage was off, the cholesteric liquid crystal panel 4, as shown in Figure 7, lost its transparent function in 7 msec, while the reflection activation time was 240 msec, which was significantly later than the loss of the transparent function. Thus, the cholesteric liquid crystal panel 4 had a response time of less than 1 second in both the voltage-on and voltage-off states, meaning that the time required for the function to disappear was short, while the function activation time was relatively long.

[0035] Here, when the number of regions of the dimming element 3 is N=2, if the frame rate is to be 24Hz or higher, the response time required for the activation and deactivation of the cholesteric liquid crystal panel 4 must be 1 / 24 × 2 ≈ 20 msec or less. However, while the time required for the deactivation of the function is 20 msec or less, the transparency activation time and reflection activation time significantly exceed 20 msec. For example, when the voltage is turned on, the reflection function disappears in less than 20 msec, while the activation of the transparency function is significantly delayed, exceeding 20 msec. As a result, when users view moving scenes through the dimming element 3, they perceive them as stop-motion. Therefore, when using the cholesteric liquid crystal panel 4, it is necessary to shorten the transparency activation time and reflection activation time in order to suppress the decrease in visibility.

[0036] Next, we will explain how to shorten the functional activation time within the response time. As a result of our diligent research, we have found that the transparency activation time can be shortened by controlling the applied voltage, and the reflection activation time can be shortened by controlling the temperature.

[0037] For example, as shown in Figure 8, when a square wave with a frequency of 200 Hz, ±200 V, and a duty cycle of 1:1 was applied, the transparency emergence time was 13 msec, and this was significantly shortened by increasing the driving voltage. Then, using the two data points for transparency emergence time when driving with a square wave at ±170 V and ±200 V as described above, a plot of applied voltage and transparency emergence time was taken, yielding the results shown in Figure 9. The dashed line in Figure 9 connects the two data points at ±170 V and ±200 V, assuming that the response time changes exponentially with respect to the applied voltage because the liquid crystal molecules arranged in a spiral within the cholesteric liquid crystal panel 4 align in the direction of the applied voltage. According to the approximate straight line shown by the dashed line in Figure 9, for example, an applied voltage of 195 V is required to achieve a transparency emergence time of 20 msec. Thus, the transparency emergence time of the cholesteric liquid crystal panel 4 can be shortened by increasing the applied voltage for driving, and the driving voltage can be appropriately determined according to the target transparency emergence time.

[0038] On the other hand, the functional manifestation of the reflective state in the cholesteric liquid crystal panel 4 occurs when the voltage is off, and no driving force is acting on it. Therefore, focusing on the fact that the fluidity of liquid crystal molecules increases with temperature, the temperature of the cholesteric liquid crystal panel 4 was set to 60°C, and the change in reflectivity when the voltage was turned on to off was measured, yielding the results shown in Figure 10. Hereafter, for the sake of simplicity, the temperature of the cholesteric liquid crystal panel 4, i.e., the temperature of the dimming member 3, will simply be referred to as the "panel temperature". Note that the results shown in Figure 10 are from when the voltage was turned off from a square wave drive with a frequency of 200 Hz, ±170 V, and a duty cycle of 1:1. As shown in Figure 10, the reflection manifestation time at a temperature of 60°C was 13 msec, which was significantly shorter than at 20°C. Here, using the three data points of reflection manifestation time at 20°C, 40°C, and 60°C respectively, the reciprocal of the absolute temperature 1 / T(K)-1 When an Arrhenius plot was taken between the temperature and the reflection onset time, a nearly linear relationship was obtained, as shown in Figure 11. The reflection onset time of the cholesteric liquid crystal panel 4 decreased as the panel temperature increased, such as at 20°C, 40°C, and 60°C. By working backward from the equation of the approximate straight line based on the data at the three points of 20°C, 40°C, and 60°C, it can be calculated that the panel temperature should be 57°C to achieve a reflection onset time of 20 msec. Thus, the reflection onset time of the cholesteric liquid crystal panel 4 can be shortened by increasing the panel temperature, and temperature control can be appropriately performed according to the target reflection onset time.

[0039] Furthermore, increasing the panel temperature causes the pitch P of the liquid crystal layers within the cholesteric liquid crystal layer 43 to fluctuate, altering the wavelength range of reflected light, i.e., the reflection band. Therefore, it is preferable that the cholesteric liquid crystal layer 43 be designed with a number of layers and a pitch P that allows the reflection band to be wider than the visible light range while obtaining the necessary reflection band within the operating temperature range, taking into account the reflection onset time and temperature range required to suppress the decrease in visibility.

[0040] [Temperature control of cholesteric liquid crystal panels] The panel temperature can be increased, for example, by controlling the frequency of the drive voltage applied between the transparent electrodes 42 and 44 when driving the cholesteric liquid crystal layer 43.

[0041] Figure 12 shows the results of measuring the capacitance and resistance values ​​when the frequency of the ±1V voltage applied to the cholesteric liquid crystal panel 4 was varied in the range of 20Hz to 100kHz. The results shown in Figure 12 were measured using a cholesteric liquid crystal panel of approximately 10cm square size, treating the cholesteric liquid crystal panel as a resistor and capacitor, and measuring them as a circuit connected in parallel with an AC power supply, as shown in Figure 13.

[0042] As shown in Figure 12, the capacitance of a cholesteric liquid crystal panel is approximately 1.5 × 10⁻¹⁰ at a frequency of 20 Hz. -9 F, at a frequency of 100Hz, is approximately 1.2 × 10⁻⁶ -9F. At frequencies from 10 kHz to 100 kHz, it was approximately 1.0×10 -9 F, and it was almost constant within the above frequency range. Since the capacitance of the cholesteric liquid crystal panel hardly changed even when the frequency of the applied voltage was changed, almost no change in the transmittance and reflectance was observed even when the frequency of the driving voltage was changed.

[0043] As shown in Fig. 12, the resistance value of the cholesteric liquid crystal panel was approximately 6.2×10 5 Ω at 20 Hz, approximately 6.1×10 5 Ω at 100 Hz, approximately 3.0×10 5 Ω at 10 kHz, and almost 0 Ω at 100 kHz. The resistance value of the cholesteric liquid crystal panel hardly changed in the range of 20 Hz to 100 Hz, but decreased gently when exceeding 100 Hz and decreased more rapidly when exceeding 10 kHz. From this result, it can be understood that by increasing the frequency of the driving voltage of the cholesteric liquid crystal panel, the cholesteric liquid crystal panel can generate heat and raise the temperature. Note that since the amount of heat generation increases rapidly when the frequency exceeds 10 kHz and temperature control becomes difficult, the frequency of the driving voltage is preferably 10 kHz or less. Also, since the capacitance increases and the rate of decrease in transmittance may slow down when the frequency is less than 100 Hz, the frequency of the driving voltage is preferably 100 Hz or more.

[0044] For example, when a cholesteric liquid crystal panel was placed in an environment at room temperature of 25°C, and the drive voltage was set to ±200V, with a 1:1 duty cycle square wave, the panel temperature was measured using a thermocouple while the frequency was varied, and the results shown in Figure 14 were obtained. The cholesteric liquid crystal panel remained almost unchanged at 25°C at a frequency of 20Hz, reached 37°C at 100Hz, and 45°C at 200Hz, showing that the temperature increased as the frequency increased. Therefore, when adjusting the temperature of a cholesteric liquid crystal panel by controlling the frequency of the drive voltage, for example, as shown in Figure 15, if the temperature is lower than the target temperature (e.g., 57°C), the frequency should be set higher. Furthermore, once the temperature of the cholesteric liquid crystal panel reaches the target temperature, the panel temperature can be maintained at the target temperature by gradually lowering the frequency of the drive voltage to prevent the panel temperature from excessively exceeding the target temperature, and finally setting it to a constant frequency.

[0045] Furthermore, the panel temperature can also be increased by applying a DC voltage separate from the drive voltage to each of the transparent electrodes 42 and 44, causing the transparent electrodes 42 and 44 to function as heaters. In this case, as shown in Figure 16, for example, the cholesteric liquid crystal panel 4 has a first power supply V1 that applies an AC voltage for driving and a second power supply V2 that applies a DC voltage for heating, both connected to the transparent electrodes 42 and 44. Hereafter, for convenience of explanation, the AC voltage for driving may simply be referred to as the "drive voltage," and the DC voltage for heating may be referred to as the "heating voltage."

[0046] Note that the circuit shown in Figure 16 is for the case where one cholesteric liquid crystal panel 4 constitutes one region of the dimming element 3. If the number of regions of the dimming element 3 is N, the blind spot assist system will have N circuits of the one shown in Figure 16. Also, in Figure 16, in order to make the circuit configuration easier to understand, the transparent electrodes 42 and 44 of the cholesteric liquid crystal panel 4 are simplified and hatched, and the transparent substrates 41 and 45 and the cholesteric liquid crystal layer 43 are omitted.

[0047] The drive circuit, which applies a drive voltage between the transparent electrodes 42 and 44 from the first power supply V1, has a switch S1, for example, composed of a transistor, and the timing of the application of the drive voltage can be controlled by the on / off control of switch S1 by the control unit 6. The first power supply V1 is an AC power supply that can apply a voltage of ±195V or more at a frequency of 100Hz in a square wave with a duty cycle of 1:1, as shown in Figure 16, for example, and the frequency and voltage can be changed as appropriate.

[0048] The heating circuit, which applies a heating voltage to the transparent electrodes 42 and 44 individually from the second power supply V2, is configured such that, for example, the High side and Low side each branch into two, with one branch connected to the transparent electrode 42 and the other to the transparent electrode 44, so that the polarities of the transparent electrodes 42 and 44 match. In the heating circuit, for example, switch S2 is placed on one branch on the High side and switch S3 on the other, and switch S4 is placed on one branch on the Low side and switch S5 on the other. In the heating circuit, the timing of the application of the heating voltage to the transparent electrodes 42 and 44 can be controlled by the control unit 6 by controlling the on / off state of switches S2 to S5, which are composed of, for example, transistors. Switches S2 to S5 can be, for example, simultaneously on or off. The second power supply V2 is, for example, a battery of 12V or less, and is independent of the drive circuit in order to suppress the occurrence of crosstalk while preventing DC voltage from being applied between the transparent electrodes 42 and 44 of the cholesteric liquid crystal panel 4. The second power supply V2 can be any independent power supply that does not interfere with the first power supply V1, and instead of a battery, it may be a DC power supply with adjustable voltage.

[0049] The on / off timings of the drive circuit switch S1 and the heating circuit switches S2-S5 are staggered, for example, as shown in Figure 17, to prevent the drive voltage and heating voltage from being applied to the transparent electrodes 42 and 44 simultaneously. The control of voltage application to the cholesteric liquid crystal panel 4 is not limited to the above example, as long as the timing of application of the drive voltage to the transparent electrodes 42 and 44 and the timing of application of the heating voltage do not overlap. For example, from the viewpoint of preventing the heating voltage from interfering with the waveform of the drive voltage, it is preferable to include a timing for turning off all switches S1-S5 between the timing of turning on switch S1 and the timing of turning on switches S2-S5. Thus, the control of the application timing of the drive voltage and heating voltage may be changed as appropriate.

[0050] The above describes control of panel temperature by frequency control of the drive voltage or by applying a heating voltage, but these may be used in combination. When used in combination, for example, the control unit 6 acquires panel temperature information from the temperature sensor 7 and is configured to increase the frequency of the first power supply V1, increase the voltage of the second power supply V2, or both, if the panel temperature is lower than the target temperature. Then, for example, if the panel temperature is above the target temperature, the control unit 6 can control at least one of the frequency of the first power supply V1 and the voltage of the second power supply V2 so that the panel temperature does not fluctuate. Note that if the panel temperature becomes too high, the state of the liquid crystal molecules in the cholesteric liquid crystal layer 43 may change, so it is preferable that the cholesteric liquid crystal panel 4 be dimmed to 100°C or below.

[0051] According to this embodiment, the blind spot assistance system comprises a dimming member 3 composed of a cholesteric liquid crystal panel 4 and having multiple regions that can be switched between a transparent state and a reflective state, and a control unit 6 that performs voltage control and temperature control applied to the cholesteric liquid crystal panel 4. The control unit 6 performs dimming control that sequentially repeats the process of setting at least one of the multiple regions 31 to 3N of the dimming member 3 to a transparent state and the other regions to a reflective state, then changing the transparent region to a reflective state, and switching at least one of the other reflective regions to a transparent state. The control unit 6 then controls the driving voltage in the cholesteric liquid crystal panel 4 to reduce the time required to switch from the reflective state to a predetermined level or less, and controls the panel temperature to reduce the time required to switch from the transparent state to a predetermined level or less. As a result, the response time of the dimming member 3 in the blind spot assistance system becomes 1 second or less, and the reduction in visibility caused by the response time can be suppressed.

[0052] In other words, the blind spot assistance system can be said to perform the following control method for the optical element 1 by, for example, the control unit 6. The control method for the optical element 1 includes dimming control of the dimming element 3, and when switching to the transparent state, the transparency appearance time is set to a predetermined level or less by controlling the drive voltage, and when switching to the reflective state, the reflection appearance time is set to a predetermined level or less by controlling the panel temperature. As a result, when a moving scene is made visible to the user via the dimming element 3, the frame rate of switching between the transparent state and the reflective state in the dimming element 3 is set to a predetermined level or higher, and the decrease in visibility caused by response time is suppressed.

[0053] (Other embodiments) This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence range. In addition, various combinations and forms, as well as other combinations and forms including one, more, or less of those elements, fall within the scope and concept of this disclosure.

[0054] (1) In the above embodiment, an example was described in which the transparent electrodes 42 and 44 of the cholesteric liquid crystal panel 4 function as heaters, but the invention is not limited to this, and a light-transmitting heater separate from the cholesteric liquid crystal panel 4 may be placed on both sides of the panel.

[0055] (2) In the above embodiment, an example was described in which a constant drive voltage is applied between the transparent electrodes 42 and 44 of the cholesteric liquid crystal panel 4 for a predetermined time using the first power supply V1, but the invention is not limited to this. For example, as shown in Figure 18, the voltage applied at the last timing of each predetermined time when the switch S1 of the drive circuit is turned on may be made larger than the voltage applied at other timings, thereby increasing the rate of increase in transmittance. This ensures sufficient light in the transparent state and improves the visibility of the scene viewed by the user through the dimming member 3. Thus, the control of the drive voltage of the cholesteric liquid crystal panel 4 in the expression of the transparent state can be changed as appropriate.

[0056] (3) In the above embodiment, an example was described in which the transparent electrodes 42 and 44 of the cholesteric liquid crystal panel 4 are each in a rectangular solid shape, but the invention is not limited to this. The transparent electrode 44 may have a pattern shape with multiple slits along the direction in which the voltage is applied by the second power supply V2 of the heating circuit, for example, as shown in Figure 19. The same applies to the transparent electrode 42. In this case, the transparent electrodes 42 and 44 are each made up of a pattern shape with slits, and are configured so that the slits do not face each other in the thickness direction of the cholesteric liquid crystal panel 4. As a result, the cholesteric liquid crystal panel 4 is configured so that the heating voltage is applied to the transparent electrodes 42 and 44 in a linear direction along the slits, functioning as an efficient heater, and also allowing the application of a driving voltage to the cholesteric liquid crystal layer 43. Note that in Figure 19, for ease of viewing, the configuration of the driving circuit and the part of the heating circuit connected to the transparent electrode 42 has been omitted.

[0057] (4) It goes without saying that, in each of the above embodiments, the elements constituting the embodiment are not necessarily essential unless explicitly stated to be particularly essential or unless they are clearly considered essential in principle. Also, in each of the above embodiments, when numerical values ​​such as the number, numerical values, quantities, or ranges of the components of the embodiment are mentioned, the embodiment is not limited to those specific numbers unless explicitly stated to be particularly essential or unless it is clearly limited to a specific number in principle. Also, in each of the above embodiments, when the shape, positional relationship, etc. of the components are mentioned, the embodiment is not limited to those shapes, positional relationships, etc. unless explicitly stated or unless it is clearly limited to a specific shape, positional relationship, etc. in principle. [Explanation of Symbols]

[0058] 2…Reflective member, 3…Dimming member, 3a…Opposite surface, 3b…Emitting surface, 31~3N…Region of dimming member, 4…Cholesteric liquid crystal panel, 42, 44…Transparent electrode, 43…Cholesteric liquid crystal layer, 6…Control unit, 7…Temperature sensor

Claims

1. A control method for an optical element comprising: a reflective member (2) that reflects visible light; a cholesteric liquid crystal panel (4) positioned opposite the reflective member; and a dimming member (3) having N regions (N: an integer of 2 or more) (31 to 3N) that can switch between a transparent state with a visible light transmittance of 60% or more and a reflective state with a visible light reflectance of 60% or more; The dimming control includes sequentially repeating the following steps: switching at least one of the N regions in the reflective state to the transparent state by applying a voltage to the cholesteric liquid crystal panel, leaving the remaining regions in the reflective state, then switching the transparent region back to the reflective state, and finally switching at least one of the other reflective regions back to the transparent state. In switching at least one of the aforementioned regions to the transparent state, the time required for the change from the reflective state to the transparent state is reduced to a predetermined value by controlling the voltage applied to the cholesteric liquid crystal panel. A method for controlling an optical element, wherein, in switching the transparent region to the reflective state, the time required for the change from the transparent state to the reflective state is controlled by controlling the temperature of the cholesteric liquid crystal panel to make it less than or equal to a predetermined time.

2. In switching the region from the reflective state to the transparent state, a voltage is applied to at least one of the regions such that the time from the reflective state to the transparent state is 1 / (24 × N) seconds or less. The method for controlling an optical member according to claim 1, wherein, in switching the transparent region to the reflective state, the temperature of the cholesteric liquid crystal panel is controlled such that the time it takes to switch from the transparent state to the reflective state is 1 / (24 × N) seconds or less.

3. The method for controlling an optical member according to claim 2, wherein, in switching the transparent region to the reflective state, the temperature of the cholesteric liquid crystal panel is controlled by frequency control of the voltage applied to the cholesteric liquid crystal panel.

4. In switching the transparent region to the reflective state, the surface of the cholesteric liquid crystal panel facing the reflective member is designated as the opposing surface (3a), and the surface opposite the opposing surface is designated as the emission surface (3b), and heating is performed on both the opposing surface and the emission surface to control the temperature of the cholesteric liquid crystal panel, as described in claim 2.

5. In switching the transparent region to the reflective state, By applying a voltage to the two transparent electrodes (42, 44) that sandwich the cholesteric liquid crystal layer (43) of the cholesteric liquid crystal panel, they function as heaters, thereby controlling the temperature of the cholesteric liquid crystal panel. A method for controlling an optical member according to claim 2, wherein the voltage applied to the transparent electrode is defined as a driving voltage, the voltage used to change the electrode from a reflective state to a transparent state is defined as a heating voltage, and the driving voltage is not applied when the heating voltage is applied.

6. The method for controlling an optical member according to claim 5, wherein, in applying the heating voltage, a DC voltage is applied individually to the two transparent electrodes.

7. The method for controlling an optical member according to claim 6, wherein, when applying the heating voltage, a power source independent of the power source for applying the drive voltage is used.

8. In switching the region from the reflective state to the transparent state, an AC voltage is applied to at least one of the regions for a predetermined time. The method for controlling an optical member according to any one of claims 1 to 7, wherein, when applying the AC voltage, the voltage applied last during the predetermined time is made greater than the voltage applied at other timings.

9. It is a blind spot assistance system, A reflective member (2) that reflects visible light, A dimming member (3) is composed of a cholesteric liquid crystal panel (4) positioned opposite the reflective member, and has N regions (31 to 3N) (N: an integer of 2 or more) that can switch between a transparent state with a visible light transmittance of 60% or more and a reflective state with a visible light reflectance of 60% or more. A temperature sensor (7) for measuring the temperature of the cholesteric liquid crystal panel, The system includes a control unit (6) that controls the voltage applied to the cholesteric liquid crystal panel and controls the temperature of the cholesteric liquid crystal panel based on temperature information measured by the temperature sensor, The control unit, The dimming control is performed by sequentially repeating the following steps: switching at least one of the N regions in the reflective state to the transparent state by voltage control, leaving the remaining regions in the reflective state, then switching the transparent region back to the reflective state, and finally switching at least one of the other reflective regions back to the transparent state. A blind spot assistance system that uses voltage control to reduce the time required for the state to change from the reflective state to the transparent state to a predetermined level or less, and uses temperature control to reduce the time required for the state to change from the transparent state to the reflective state to a predetermined level or less.

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