LIQUID CRYSTAL DIMMER AND METHOD FOR LIQUID CRYSTAL DIMMERING

Description

Technical Field

[0001] The present invention relates to a liquid crystal optical modulation device and a liquid crystal light modulation method, particularly suitable for performing gradation control of a liquid crystal panel particularly using PHM (pulse height modulation) in the form of a rectangular wave.Background Art

[0002] In a known technology that has been proposed (e.g., Patent Literature 1), the ratio of a non-operating state to an operating state of polymer dispersed-type liquid crystal is reduced compared to a case in which an AC voltage from a commercial power source is applied directly to a transparent electrode, so that high transparency can be achieved. Further, Patent Literature 2 discloses a power supply circuit for a liquid crystal welding lens or shutter providing a consistent and stable regulated power signal for driving or powering the liquid crystal shutter for maintaining stable performance over the life of the power supply and a battery level indicator feature to provide advance warning of degraded device performance. In addition, Patent Literature 3 discloses a driving method for a liquid crystal light modulating device using a liquid crystal composition that contains liquid crystals that exhibit a scattered focal conic phase state and a transparent nematic phase state depending on the applied voltage. In addition, Patent Literature 4 discloses a power supply circuit for a shutter, configured to apply an AC drive voltage to the shutter wherein a frequency of the AC drive voltage is inversely proportional to the magnitude of the drive voltage, in order to minimize power required for driving the shutter as well as an amount of perceivable flicker.[CITATION LIST][PATENT LITELATURE]

[0003] Patent Literature 1: Jpn. Pat. Appln. KOKAI Publication No. 2013-072895 Patent Literature 2: US 5 751 258 A Patent Literature 3: US 2007 / 195033 A1 Patent Literature 4: WO9313397 A1. Disclosure of Invention[TECHNICAL PROBLEM]

[0004] FIGS. 7A and 7B illustrate a general configuration in which a polymer dispersed-type liquid crystal panel is applied to a window glass 10 having a simple blind function.

[0005] FIG. 7A shows the power off state. The polymer dispersed liquid crystal 17 is sealed and filled in an inside defined by transparent electrodes 13 and 14 on inner surface sides of two parallel plate glasses 11 and 12 as substrates, and spacers 15 and 16. A commercial power source 18 and a switch 19 are connected to the transparent electrodes 13 and 14.

[0006] Here, because the switch 19 is off, no voltage from the commercial power source 18 is applied to the polymer dispersed liquid crystal 17 between the transparent electrodes 13 and 14. In the polymer dispersed liquid crystal 17, as shown in the figure, a large number of liquid crystal molecules along mesh-like polymer fibers inside are irregularly arranged, so that light cannot be transmitted through the two glass plates 11 and 12 and is scattered. Since the window glass 10 of this state scatters light as in the case of frosted glass and cannot transmit most of the light, the whole glass becomes white when seen from the indoor side. Therefore, for example, even if a tree is present outside the window glass 10, a silhouette of the tree will appear only vaguely.

[0007] FIG. 7B shows a state in which the switch 19 is turned on. A voltage is applied to the polymer dispersed liquid crystal 17 between the transparent electrodes 13 and 14 to form an electric field, and liquid crystal molecules in the polymer dispersed liquid crystal 17 are aligned with their major axes in the direction orthogonal to the glass surface. Accordingly, the two glass plates 11 and 12 transmit the light and become transparent. The whole of the window glass 10 in this state looks transparent when seen from the indoor side, and a tree present outside the window glass 10 is clearly visible.

[0008] FIGS. 7A and 7B show how the window glass 10 looks in the off state and the on state; however, in this type of window glass 10, it is possible to perform halftone driving, thereby performing light control driving for steplessly adjusting a semi-transparent condition between the scattering and the transmission.

[0009] FIG. 8A shows a voltage applied between the transparent electrodes 13 and 14 in the power-off state shown in FIG. 7A. As shown in the figure, since the switch 19 is turned off, 0 (zero) [V] is maintained.

[0010] FIG. 8B illustrates a voltage applied between the transparent electrodes 13 and 14 in the power-on state shown in FIG. 7B. Here, the figure shows a state where a 30 [Hz] rectangular wave is amplified between a wave peak value +40 [V] / -40 [V]. Assuming that an effective voltage value at that time is denoted by Vc, an effective current value Ic is expressed by the following equation when resistance components are ignored. Ic = 2 π fCVc

[0011] Where f: frequency, and C: capacitance of liquid crystal.

[0012] That is, it can be seen that the current consumption of this type of liquid crystal panel depends on the drive frequency, and the current consumption can be reduced by lowering the drive frequency.

[0013] For example, when the frequency f is set to 1 [Hz], no particular problem is caused in a state where light is scattered or transmissive, i.e., in a complete power-off state or a power-on state where a full voltage is applied, as shown in FIGS. 7A and 7B, or 8A and 8B; however, in the case of halftone driving using an intermediate voltage value, apparent flicker is visually recognized, causing a failure as a blind function.

[0014] Also in the above-mentioned patent document, in order to obtain high transparency, a technique is proposed in which a rectangular wave voltage is applied instead of a sinusoidal voltage of a commercial power supply to a liquid crystal optical modulation device having a liquid crystal layer using a polymer dispersed liquid crystal. However, the document describes a point of still causing flicker (flickering).

[0015] The appearing of flicker becomes more noticeably the lower the drive frequency and drive voltage are, which is contrary to the above described desire to lower the current consumption.

[0016] The present invention has been made in view of the actual situation described above, and an object of the present invention is to provide a liquid crystal optical modulation device and a liquid crystal optical modulation method which can realize control of the optical modulation of a liquid crystal panel with lower power consumption while suppressing the appearance of flicker.[SOLUTION TO PROBLEM]

[0017] According to one aspect of the present invention, there is provided a liquid crystal optical modulation device according to claim 1.[ADVANTAGEOUS EFFECTS OF INVENTION]

[0018] According to the present invention, it is possible to realize control of optical modulation of a liquid crystal panel with lower power consumption, while suppressing the appearance of flicker.Brief Description of Drawings

[0019] FIG. 1 is a block diagram showing a circuit configuration in a control circuit section according to an embodiment of the present invention. FIG. 2 is a diagram illustrating the relationship between a voltage applied to a liquid crystal panel related to a first operation example, which does not form part of the claimed subject-matter, and a transmittance through a liquid crystal panel. FIG. 3 is a diagram illustrating how flicker is seen when the liquid crystal panel according to the first operation example is sequentially driven with respective voltage values while changing the frequency of a rectangular wave. FIG. 4 is a diagram illustrating the relationship between a voltage applied to the liquid crystal panel for each drive frequency and a transmittance of the liquid crystal panel, which is the basis of the control contents according to the first operation example shown in FIG. 2. FIG. 5 is a diagram illustrating the relationship between a voltage applied to the liquid crystal panel related to a second operation example, which forms part of the claimed subject-matter, and a transmittance of the liquid crystal panel. FIG. 6 is a diagram illustrating the relationship between a voltage applied for each drive frequency to a reverse mode liquid crystal panel according to a further operation example, that does not form part of the claimed subject-matter, and a transmittance of the liquid crystal panel. FIG. 7A is a diagram showing a structure of a window glass using a general polymer dispersed liquid crystal and a light-controlled state (at a power-off state). FIG. 7B is a diagram showing a structure of a window glass using a general polymer dispersed liquid crystal and a light-controlled state (at a power-on state). FIG. 8A is a diagram illustrating a waveform of a drive voltage of the polymer dispersed liquid crystal related to FIG. 7A. FIG. 8B is a diagram illustrating a waveform of a driving voltage of the polymer dispersed liquid crystal related to FIG. 7B.

[0020] Mode for Carrying Out the Invention Hereinafter, an embodiment of the present invention will be described in detail.[Configuration]

[0021] First, the configuration of the present embodiment will be described.

[0022] A liquid crystal optical modulation device according to the present invention can be realized, in the configuration shown in FIGS. 7A and 7B, by interposing a control section (optical modulation control section) 20 instead of a switch 19 between two lines connecting transparent electrodes 13, 14 and a commercial power supply 18.

[0023] FIG. 1 is a block diagram showing a circuit configuration of the control section 20. In the same figure, alternating-current power of 100 [V] to 240 [V] from the commercial power supply 18 is supplied to an AC / DC converter portion 21 of the control section 20. The AC / DC converter portion 21 includes two AC / DC converters 21A and 21B.

[0024] The AC / DC converter 21A is a variable output type AC / DC converter, rectifies the alternating-current power of 100 [V] to 240 [V] supplied from the commercial power supply 18 and reduces the voltage, in response to a control signal from a microcomputer 23 to be described later, converts the alternating-current power into direct-current power of 5 [V] to 75 [V], and outputs the direct-current power to a switching circuit 22.

[0025] Another AC / DC converter 21B is a fixed output AC / DC converter, rectifies the alternating-current power of 100 [V] to 240 [V] supplied from the commercial power supply 18 and reduces the voltage, converts the alternating-current power to direct-current power of a fixed value of 5 [V], and outputs the direct-current power to the microcomputer 23.

[0026] The microcomputer 23 operates with direct-current power of 5 [V] supplied from the AC / DC converter 21B, receives an operation via an operation unit (not shown), e.g., a dial switch, and performs a control operation in the control section 20, specifically, outputs control signals to the AC / DC converter 21A and the switching circuit 22.

[0027] That is, the microcomputer 23 outputs a control signal for controlling the direct-current voltage value output from the AC / DC converter 21A to the AC / DC converter 21A, using, for example, a PWM (pulse width) signal, etc.

[0028] Furthermore, the microcomputer 23 controls, for the switching circuit 22, a frequency of the alternating-current power output from the switching circuit 22, using, for example, a drive control signal based on a switching pulse.

[0029] The switching circuit 22 is an inverter circuit, and oscillates the direct-current power of a variable voltage supplied from the AC / DC converter 21A so as to have a drive frequency in accordance with the drive control signal from the microcomputer 23, and converts it into alternating-current power, and then supplies the alternating-current power to a liquid crystal panel serving as a load, such as the window glass 10.[First Operation Example, not forming part of the claimed subject-matter]

[0030] FIG. 2 is a diagram illustrating the relationship between a voltage applied to the liquid crystal panel serving as a load and the transmittance of the liquid crystal panel, in the control section 20. If the same figure is explained assuming that the applied voltage is controlled in units of 1 [V], the frequency of a rectangular wave at a voltage of 0 (zero) [V] to 25 [V] applied to the liquid crystal panel is set to 100 [Hz]; the frequency of a rectangular wave at a voltage of 26 [V] to 30 [V] is set to 60 Hz; the frequency of a rectangular wave at a voltage of 31 [V] to 35 [V] is set to 30 [Hz]; and the frequency of a rectangular wave at a voltage of 36 [V] to 50 [V] is set to 1 [Hz].

[0031] From when the applied voltage exceeds about 20 [V], the degree of increase in transmittance corresponding to the increase in voltage starts to change gradually and largely, and the degree of increase in transmittance corresponding to the increase in voltage greatly and largely changes in the range of the applied voltage of 25 [V] to 35 [V].

[0032] Then, at the applied voltage of 35 [V] to about 40 [V], the change in the degree of increase in transmittance corresponding to the increase in voltage has decreased as necessary, and has exhibited an S-shaped transmittance change characteristic as a whole.

[0033] FIG. 3 illustrates how flicker appears when the above-mentioned liquid crystal panel is sequentially driven at each voltage value while changing the frequency of the rectangular wave. In the same figure, the case where no flicker has been seen is indicated by "A", and the case where flicker has been seen is indicated by "B".

[0034] As described above, it can be understood that flicker appears more noticeably the lower drive frequency and drive voltage are.

[0035] In addition, in the same figure, the consumption current value at a drive voltage of 40 [V] is also described in the case where the same value at a drive frequency of 1 [Hz] is regarded as a unit "1", and as is shown by the above equation (1), it can be understood that the current consumption value increases in proportion to the drive frequency.

[0036] FIG. 4 is a diagram illustrating the relationship between the voltage applied to the liquid crystal panel for each drive frequency and the transmittance of the liquid crystal panel, which is the basis of the control contents in the control section 20 shown in FIG. 2.

[0037] From the same figure, it can be understood that the lower the drive frequency, the higher the degree of increase in transmittance in accordance with the increase in drive voltage. If the appearance of flicker is not taken into account, it can be understood that it is advantageous to set a lower drive frequency also in terms of the consumption current.

[0038] However, in reality, flicker appears and the degree of visual recognition also varies depending on individual differences, so the results of selecting a frequency in accordance with the range of each drive voltage are as per the contents shown in FIG. 2.

[0039] As described above, it is possible to realize the control of the optical modulation of a liquid crystal panel with lower power consumption while suppressing the appearance of flicker.[Second Operation Example, forming part of the claimed subject-matter]

[0040] FIG. 5 is a diagram illustrating the relationship between the voltage applied to the liquid crystal panel serving as a load and the transmittance of the liquid crystal panel, in the control section 20. If the same figure is explained assuming that the applied voltage is controlled in the units of 1 [V], the frequency of a rectangular wave at a voltage of 0 (zero) [V] to 30 [V] applied to the liquid crystal panel is set to 60 [Hz], and the frequency of a rectangular wave at a voltage of 31 [V] to 50 [V] is set to 30 [Hz].

[0041] Compared to the control contents shown in FIG. 2 described above, the drive voltage is divided into two half ranges, and the drive frequency is switched and controlled with a single threshold "30 [V]" interposed between the two half ranges.

[0042] As a result, it is possible to prevent the appearance of flicker assuredly and suppress the power consumption to a certain extent, and reduce the manufacturing cost of the device by further simplifying the configuration and control of the control section, particularly the configurations and control of the microcomputer 23 and the switching circuit 22.[Other Operation Example not forming part of the claimed subject-matter]

[0043] In the above embodiment, the case of using a polymer dispersed liquid crystal in the normal mode is illustrated, in which light is in an opaque diffusion state in the condition where no voltage is applied, and the transparency is increased as necessary by increasing the voltage value under a condition where a voltage is applied; however, another operation example is applied to a liquid crystal panel in a reverse mode, which has a characteristic opposite to the characteristic described above.

[0044] The driving contents of a polymer dispersed liquid crystal element itself in the reverse mode will be described below based on the assumption that the technique the reverse mode polymer dispersed liquid crystal element itself is obvious to those skilled in the art.

[0045] FIG. 6 illustrates the relationship between the voltage applied to the liquid crystal panel for each drive frequency and the transmittance of the liquid crystal panel, which is the basis of the control contents when the liquid crystal panel in the reverse mode is driven and controlled using the control section 20 in this embodiment.

[0046] From the same figure, it can be understood that the lower the drive frequency, the less the fall in transmittance, unless the drive voltage is set higher, and in particular, that the fall in transmittance is extremely slow particularly at the lowest drive frequency 1 Hz.

[0047] Here, if the same figure is explained assuming that the applied voltage is controlled in units of 1 [V], it can be considered that it is possible to realize, even in a polymer dispersed liquid crystal element in the reverse mode, control of optical modulation of a liquid crystal panel with lower power consumption while suppressing the appearance of flicker, by setting, for example, the frequency of a rectangular wave at a voltage of 0 (zero) [V] to 5 [V] applied to the liquid crystal panel to 100 [Hz], the frequency of a rectangular wave at a voltage of 6 [V] to 10 [V] to 60 [Hz], the frequency of a rectangular wave at a voltage of 11 [V] to 20 [V] to 30 [Hz], and the frequency of a rectangular wave at a voltage of 21 [V] to 50 [V] to 1 [Hz].

[0048] In each of the above-described operating examples, a liquid crystal element (optical modulation device) using a polymer dispersed liquid crystal as an object to be driven is illustrated, but the present invention is not limited thereto. The liquid crystal element may have a configuration in which a polarizing plate and an alignment film are disposed at both ends of a liquid crystal layer, and a TN (Twisted Nematic) method, a VA (Vertical Alignment) method, an IPS (In-Plane Switching) method, etc. can be used. In addition to the liquid crystal elements, various types of electro-optical elements in which the refractive index changes depending on a voltage can be used as an optical modulation element serving as a load.

[0049] The present invention is not limited to the above embodiments, and can be variously modified in the implementation stage without departing from the scope of the appended claims.

Claims

1. A liquid crystal optical modulation device configured to perform light control drive of a liquid crystal panel that is in an opaque and diffused state when no voltage is applied thereto, the device comprising: an optical modulation control section (20) configured to switch and set a frequency of a drive voltage in the form of a rectangular wave which is to be applied to the liquid crystal panel, in accordance with a first range and a second range, higher than the first range, of the drive voltage, wherein the optical modulation control section (20) is configured to switch and set the frequency of the drive voltage so as to be decreased in conjunction with an increase of the drive voltage from the first range to the second range; wherein the device is configured to compare the drive voltage and a preset threshold separating the first range and the second range of the drive voltage, wherein the optical modulation control section (20) is configured to switch and set the frequency of the drive voltage to a first fixed value of the frequency associated with the first range or to a second fixed value associated with the second range in accordance with a comparison result between the drive voltage and the preset threshold, wherein the first fixed value is higher than the second fixed value.

2. A method of operating the liquid crystal optical modulation device of claim 1 for performing light control drive of a liquid crystal panel that is in an opaque and diffused state when no voltage is applied thereto, the method comprising, by the liquid crystal optical modulation device: controlling light of the liquid crystal panel by switching and driving a frequency of a drive voltage in the form of a rectangular wave, which is to be applied to the liquid crystal panel, in accordance with a first range and a second range, higher than the first range, of the drive voltage, wherein the controlling the light of the liquid crystal panel comprises switching and setting the frequency of the drive voltage so as to be decreased in conjunction with an increase of the drive voltage from the first range to the second range, further comprising comparing the drive voltage and a preset threshold separating the first range and the second range of the drive voltage, wherein the controlling the light of the liquid crystal panel further comprises switching and setting the frequency of the drive voltage to a first fixed value of the frequency associated with the first range or to a second fixed value associated with the second range in accordance with a comparison result between the drive voltage and the preset threshold, wherein the first fixed value is higher than the second fixed value.