Patent Description:
In a known technology that has been proposed (e.g., Patent Literature <NUM>), 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 <NUM> 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 <NUM> 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 <NUM> 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.

<FIG> illustrate a general configuration in which a polymer dispersed-type liquid crystal panel is applied to a window glass <NUM> having a simple blind function.

<FIG> shows the power off state. The polymer dispersed liquid crystal <NUM> is sealed and filled in an inside defined by transparent electrodes <NUM> and <NUM> on inner surface sides of two parallel plate glasses <NUM> and <NUM> as substrates, and spacers <NUM> and <NUM>. A commercial power source <NUM> and a switch <NUM> are connected to the transparent electrodes <NUM> and <NUM>.

Here, because the switch <NUM> is off, no voltage from the commercial power source <NUM> is applied to the polymer dispersed liquid crystal <NUM> between the transparent electrodes <NUM> and <NUM>. In the polymer dispersed liquid crystal <NUM>, 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 <NUM> and <NUM> and is scattered. Since the window glass <NUM> 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 <NUM>, a silhouette of the tree will appear only vaguely.

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

<FIG> show how the window glass <NUM> looks in the off state and the on state; however, in this type of window glass <NUM>, 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.

<FIG> shows a voltage applied between the transparent electrodes <NUM> and <NUM> in the power-off state shown in <FIG>. As shown in the figure, since the switch <NUM> is turned off, <NUM> (zero) [V] is maintained.

<FIG> illustrates a voltage applied between the transparent electrodes <NUM> and <NUM> in the power-on state shown in <FIG>. Here, the figure shows a state where a <NUM> [Hz] rectangular wave is amplified between a wave peak value +<NUM> [V]/-<NUM> [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.

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

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.

For example, when the frequency f is set to <NUM> [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 <FIG>, or <FIG> and <FIG>; however, in the case of halftone driving using an intermediate voltage value, apparent flicker is visually recognized, causing a failure as a blind function.

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).

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.

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.

According to one aspect of the present invention, there is provided a liquid crystal optical modulation device according to claim <NUM>.

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.

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

First, the configuration of the present embodiment will be described.

A liquid crystal optical modulation device according to the present invention can be realized, in the configuration shown in <FIG>, by interposing a control section (optical modulation control section) <NUM> instead of a switch <NUM> between two lines connecting transparent electrodes <NUM>, <NUM> and a commercial power supply <NUM>.

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

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

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

The microcomputer <NUM> operates with direct-current power of <NUM> [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 <NUM>, specifically, outputs control signals to the AC/DC converter 21A and the switching circuit <NUM>.

That is, the microcomputer <NUM> 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..

Furthermore, the microcomputer <NUM> controls, for the switching circuit <NUM>, a frequency of the alternating-current power output from the switching circuit <NUM>, using, for example, a drive control signal based on a switching pulse.

The switching circuit <NUM> 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 <NUM>, 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 <NUM>.

<FIG> 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 <NUM>. If the same figure is explained assuming that the applied voltage is controlled in units of <NUM> [V], the frequency of a rectangular wave at a voltage of <NUM> (zero) [V] to <NUM> [V] applied to the liquid crystal panel is set to <NUM> [Hz]; the frequency of a rectangular wave at a voltage of <NUM> [V] to <NUM> [V] is set to <NUM>; the frequency of a rectangular wave at a voltage of <NUM> [V] to <NUM> [V] is set to <NUM> [Hz]; and the frequency of a rectangular wave at a voltage of <NUM> [V] to <NUM> [V] is set to <NUM> [Hz].

From when the applied voltage exceeds about <NUM> [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 <NUM> [V] to <NUM> [V].

Then, at the applied voltage of <NUM> [V] to about <NUM> [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.

<FIG> 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".

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

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

<FIG> 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 <NUM> shown in <FIG>.

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.

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>.

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.

<FIG> 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 <NUM>. If the same figure is explained assuming that the applied voltage is controlled in the units of <NUM> [V], the frequency of a rectangular wave at a voltage of <NUM> (zero) [V] to <NUM> [V] applied to the liquid crystal panel is set to <NUM> [Hz], and the frequency of a rectangular wave at a voltage of <NUM> [V] to <NUM> [V] is set to <NUM> [Hz].

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

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 <NUM> and the switching circuit <NUM>.

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.

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.

<FIG> 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 <NUM> in this embodiment.

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 <NUM>.

Here, if the same figure is explained assuming that the applied voltage is controlled in units of <NUM> [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 <NUM> (zero) [V] to <NUM> [V] applied to the liquid crystal panel to <NUM> [Hz], the frequency of a rectangular wave at a voltage of <NUM> [V] to <NUM> [V] to <NUM> [Hz], the frequency of a rectangular wave at a voltage of <NUM> [V] to <NUM> [V] to <NUM> [Hz], and the frequency of a rectangular wave at a voltage of <NUM> [V] to <NUM> [V] to <NUM> [Hz].

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.

Claim 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 (<NUM>) 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 (<NUM>) 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 (<NUM>) 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.