JP2001142048A - Light control device, imaging device, and driving method thereof - Google Patents

Abstract

[PROBLEMS] To provide a light control device and a light control device capable of easily and accurately performing transmittance control, lowering the threshold value, improving the number of gradations, simplifying the drive circuit, and reducing the cost. To provide an imaging device used and a driving method thereof. A light control device includes a GH cell (12) and a polarizing plate (11).
A driving pulse generation circuit 63 for driving the GH cell 12 and a pulse width control unit 64 for modulating the pulse width of the driving pulse for controlling the transmittance of light incident on the GH cell 12. Light control device 23 provided, and CCD camera 5 provided with this light control device in the optical path of the imaging system
Imaging device such as 0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control device for adjusting the amount of incident light and emitting the light, an image pickup device using the same, and a method for driving these devices.

[0002]

2. Description of the Related Art Generally, a light control device using a liquid crystal cell includes:
A polarizing plate is used. In this liquid crystal cell, for example, TN
(Twisted Nematic) type liquid crystal cells and guest-host type liquid crystal cells (GH (Guest Host) cells) are used.

FIG. 20 is a schematic diagram showing the operation principle of a conventional light control device. This dimmer mainly includes a polarizing plate 1 and a GH
And cell 2. The GH cell 2 is sealed between two glass substrates (not shown), and an operating electrode and a liquid crystal alignment film are not shown (the same applies hereinafter). In the GH cell 2,
Liquid crystal molecules 3 and dichroic dye molecules 4 are enclosed. The dichroic dye molecules 4 have anisotropy in light absorption, and are, for example, positive (p-type) dye molecules that absorb light in the molecular long axis direction. The liquid crystal molecules 3 are of a positive type (positive type) having a positive dielectric anisotropy.

FIG. 20A shows a state of the GH cell 2 when no voltage is applied (no voltage is applied). Incident light 5
Is converted into linearly polarized light by transmitting through the polarizing plate 1.
In FIG. 20A, since the polarization direction coincides with the molecular long axis direction of the dichroic dye molecules 4, light is absorbed by the dichroic dye molecules 4 and the transmittance of the GH cell 2 decreases. .

[0005] Then, as shown in FIG.
When a voltage is applied to the cell 2, the direction of the long axis of the dichroic dye molecules 4 is perpendicular to the direction of linearly polarized light. Therefore, light is transmitted by the GH cell 2 without being absorbed.

When a negative (n-type) dichroic dye molecule that absorbs light in the direction of the minor axis of the molecule is used, the operation is the reverse of the case of the positive dichroic dye molecule 4 described above. When the voltage is applied, the light is not absorbed, and when the voltage is applied, the light is absorbed.

In the light control device shown in FIG. 20, the ratio of the absorbance between when a voltage is applied and when no voltage is applied, that is, the ratio of the optical density is about 10. This has about twice the optical density ratio as compared with a light control device which does not use the polarizing plate 1 but includes only the GH cell.

[0008]

In order to drive the above-mentioned conventional light control device, the transmittance is controlled by modulating the voltage intensity by applying a DC (direct current) voltage and applying an alternating voltage.

However, in a consumer-level product, it is difficult to perform voltage control with high accuracy, and it is not easy to obtain a low-threshold characteristic, and the number of gradations of the transmittance level is limited. D / A conversion is required for voltage control based on transmitted light intensity, and circuit cost increases.

The present invention has been made in consideration of the above circumstances, and has as its object to easily and accurately control the transmittance, reduce the threshold value, improve the number of gradations, and simplify the driving circuit. It is an object of the present invention to provide a dimming device capable of achieving cost reduction and cost reduction, an imaging device using the same, and a driving method thereof.

[0011]

That is, the present invention provides a liquid crystal device, a driving pulse generator for driving the liquid crystal device, and the driving device for controlling the transmittance of light incident on the liquid crystal device. The present invention relates to a light control device including a pulse width control unit that modulates a pulse width of a pulse, and an image pickup device in which the light control device is disposed in an optical path of an image pickup system.

According to the light control device and the image pickup device of the present invention,
Since the light transmittance is controlled by modulating the pulse width of the driving pulse of the liquid crystal element for dimming, the pulse width modulation is easier and the transmittance can be more accurately controlled by the clock than the voltage intensity modulation. In addition to being able to control, the transmittance change due to the pulse width is possible at a low threshold, and the change is relatively gradual, making the transmittance control easy and accurate,
The number of gradations can be increased, and D / A conversion is not required, so that the circuit cost can be reduced. In particular, for products at the consumer level, pulse width modulation is advantageous because of its accuracy and simplicity. In addition, even when the above-described device is implemented in recent digitally controlled products, the time axis is controlled as in pulse width control. Control can be expected to achieve high-precision control at low cost.

As described above, according to the present invention, a pulse width modulation method is applied to a liquid crystal light control device, and a drive waveform is selected to improve the device optical characteristics and its stability. It was taken.

Further, the present invention provides a method of driving the light control device and the image pickup device of the present invention with good controllability by controlling the transmittance of light incident on the liquid crystal element when driving the liquid crystal element. Another object of the present invention is to provide a method of driving a light control device and an image pickup device, which modulates a pulse width of a drive pulse of a liquid crystal element.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A light control device and an image pickup device according to the present invention,
In these driving methods, it is desirable that the pulse voltage of the driving pulse by the pulse width modulation is constant. Further, it is desirable that the time average of the voltage applied between the drive electrodes of the liquid crystal element at the time of the modulation of the pulse width is substantially zero in order to eliminate a bias effect due to a DC component which causes flicker.

Further, the pulse width modulation is performed so that the driving pulse waveform exists within the period of the fundamental frequency. In this case, the fundamental frequency and the modulation width of the pulse width modulation are controlled so that flicker does not occur in steady driving. Is preferably adjusted, and the pulse of the drive waveform is preferably taken out in synchronization with the clock of the drive circuit unit.

The luminance information of the emitted light is fed back to the control circuit, and the pulse width modulated drive pulse is obtained in synchronization with the clock of the drive circuit by the control signal from the control circuit. Or the drive circuit unit is a drive circuit unit of an image sensor arranged on the light emission side of the light control device, and an output signal of the image sensor is fed back to the control circuit unit as luminance information. The pulse width-modulated drive pulse may be obtained in synchronization with a clock of the drive circuit unit by a control signal from a control circuit unit.

The light control device and the image pickup device of the present invention are:
It is preferable that the drive electrode of the liquid crystal element is formed at least over the entire area of the effective light transmitting portion, and by controlling the drive pulse width to the drive electrode formed as described above, over the entire effective optical path width. Batch control of transmittance can be performed with high accuracy.

Further, the liquid crystal element is a guest-host type liquid crystal element, that is, the host material of the liquid crystal element is a negative or positive liquid crystal having a negative or positive dielectric anisotropy; The guest material of the liquid crystal element is preferably made of positive or negative dichroic dye molecules having positive or negative light absorption anisotropy.

In particular, when a negative type liquid crystal (ie, having a negative dielectric anisotropy (Δε)) is used as a host material, a positive type (ie, a negative type liquid crystal) is used.
The light transmittance at the time of light transmission (especially transparent) is improved as compared with the case of using a liquid crystal having a positive Δε, and the position can be fixed as it is in the imaging optical system.

When a polarizing plate is arranged in the optical path of the light incident on the liquid crystal element, the ratio of the absorbance between when no voltage is applied and when a voltage is applied (ie, the ratio of the optical density) is improved, and The contrast ratio increases, and light control can be normally performed from a bright place to a dark place.

Preferably, the polarizing plate is disposed on a movable portion of a mechanical iris so that the polarizing plate can be moved in and out of the optical path.

Hereinafter, the present invention will be described with reference to a liquid crystal ND (neutral densit
y) Preferred embodiments applied to filters and camera systems are described with reference to the drawings.

First, the light transmittance of the light control device and its optical arrangement First, the guest-host type liquid crystal cell (GH) shown in FIG.
In the cell 2, MLC-6849 manufactured by Merck, which is a positive general-purpose liquid crystal having a positive dielectric anisotropy (Δε), is used as the host material 3, and the guest material 4 has dichroic light absorption. B which is a positive type dye having a positive anisotropy (ΔA)
Using D5 manufactured by DH, the polarizing plate 1 was arranged on the incident side of the GH cell 2, and a change in light transmittance when an operating voltage was applied was measured using a rectangular wave as a driving waveform.

As a result, as shown in FIG. 4, the average light transmittance of visible light (in air; see the transmittance when a polarizing plate is added in addition to the liquid crystal cell) with the application of the operating voltage (=) 10
0%): The same applies hereinafter. ) Increases, but the voltage is increased by 2
It was found that when the voltage was increased to 0 V, the maximum transmittance was about 60%, and the change in light transmittance was gradual.

This is because, when a positive type host material is used, the interaction of liquid crystal molecules at the interface with the liquid crystal alignment film of the liquid crystal cell is strong when no voltage is applied, so that even when a voltage is applied, the director of the director is not affected. This is probably because liquid crystal molecules whose orientation does not change (or hardly changes) remain.

On the other hand, as shown in FIG.
In the host type liquid crystal cell (GH cell) 12, MLC-6608 manufactured by Merck, which is a negative type liquid crystal having a negative dielectric anisotropy (Δε), is used as the host material 13, and the guest material 4 has two colors. The polarizing plate 11 is made of GH cell 1 using D5 manufactured by BDH, which is the same positive type dye having the above-mentioned properties.
2, and the change in light transmittance when an operating voltage was applied was measured using a rectangular wave as a drive waveform. The light transmittance in this case is opposite to that in FIG. 9 and is transmitted when no voltage is applied, but becomes non-transmitted with the voltage applied.

As a result, as shown in FIG. 3, the average light transmittance (in air) of visible light decreases from the maximum transmittance of about 75% to several percent with the application of the operating voltage, and the light transmission It was found that the change in the rate became steep.

This is because, when a negative type host material is used, the interaction of liquid crystal molecules at the interface with the liquid crystal alignment film of the liquid crystal cell when no voltage is applied is very weak.
This is considered to be because light is easily transmitted when no voltage is applied, and the direction of the director of the liquid crystal molecule is easily changed with the application of the voltage.

As described above, in the GH cell 12 using the negative type host material, the light transmittance is improved, and it is possible to design in a region having a high light transmittance. Further, since the change in light transmittance is steep, a light control device capable of controlling the light transmittance by operating voltage uniquely can be provided.

In the above GH cell, the combination of the host material and the guest material may be various, such as a negative type (Δε <0) -positive type (ΔA> 0) and a negative type (Δε <0).
0) -negative type (ΔA <0), positive type (Δε> 0) -positive type (ΔA> 0), positive type (Δε> 0) -negative type (ΔA <
0).

In the above-mentioned GH cell, a drive electrode, for example, an ITO (indium oxide: tin-doped) electrode is adhered on the substrate surface. A system or a matrix system may be used.

In the light control device according to the present invention,
Negative-type host materials having a negative dielectric anisotropy (Δε) that can be used are exemplified below. However, in the case of actual use, a composition selected from the following compounds and blended is used so as to exhibit nematicity in an actual use temperature range.

[0034]

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[0035]

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[0036]

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[0037]

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[0038]

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[0039]

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[0040]

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[0041]

(Equation 1)

[0042]

(Equation 2)

[0043]

(Equation 3)

[0044]

(Equation 4)

In the light control device according to the present invention,
Usable positive type host materials having a positive dielectric anisotropy include the following.

<Exemplary Compounds>

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[0047]

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[0048]

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[0049]

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[0050]

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[0051]

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[0052]

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[0053]

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[0054]

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[0055]

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[0056]

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[0057]

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[0058]

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[0059]

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[0060]

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[0061]

[0062]

(Equation 5)

[0063]

(Equation 6)

[0064]

(Equation 7)

[0065]

(Equation 8)

[0066]

(Equation 9)

[0067]

(Equation 10)

[0068]

[Equation 11]

[0069]

(Equation 12)

[0070]

(Equation 13)

[0071]

[Equation 14]

[0072]

(Equation 15)

[0073]

(Equation 16)

[0074]

[Equation 17]

[0075]

(Equation 18)

In the light control device according to the present invention,
The dichroic dye molecules that can be used are exemplified below.

[0077]

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[0078]

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[0079]

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Basic drive waveform of rectangular wave and flicker of light control device As shown in FIG. 2, for example, the drive waveform of the GH cell 12 is a rectangular wave, but can be driven by either a trapezoidal wave or a sine wave. The inclination of the director of the liquid crystal changes according to the potential difference between the electrodes, and the light transmittance is controlled. Therefore, normally, transmittance control is performed by this peak value (pulse voltage).

However, such control of the peak value is as follows.
Basically, D / A conversion that is performed by replacing the analog signal with an analog signal is required. In addition, it is difficult to control the voltage with high accuracy, which causes an increase in circuit cost.

On the other hand, the electro-optical response of a nematic liquid crystal material is milliseconds even at a high speed, and several hundred milliseconds at a slow speed. Here, the present inventor studied what is appropriate as a frequency when the drive pulse width modulation method is applied to a material system having such a response characteristic.

For example, as shown in FIG.
Each drive pulse was applied in the order of 0V → −5V → 0V. The change in transmittance due to changing the width of the pulse (especially the pause pulse 0 V) was observed.

As a result, it was found that when the pause pulse period was 300 μs or longer, flicker was observed in the transmittance, and optical stability was lacking. It was found that in the rest period of 200 μs or less, no flicker of the transmittance was observed.

Therefore, in the case of this light control device, it can be seen that the idle period may be set not to be longer than 200 μs during the driving by the pulse width modulation. Since the response speed of the liquid crystal changes depending on the type of the liquid crystal or the environmental temperature, it is necessary to select a setting free from flicker within the use conditions. Controlling the pulse width by feeding back the ambient temperature is also effective for obtaining stable element optical characteristics.

Pulse width modulation From the above examination results, the basic pulse generation period is set to 10
The pulse width (PW) was controlled within this basic period with 0 μs. FIG. 1 shows a case where the pulse peak value is constant at 5 V and 10 V.

In each case, the transmittance could be easily controlled by controlling the pulse width (the transmittance including the polarizing plate when the applied voltage was zero was 100%). This is because the direction of the director of the liquid crystal molecules is changed by the electric field energy corresponding to the width of the pulse voltage, and the alignment is controlled.
Also, by combining the pulse crest value and pulse width,
It can be seen that the transmittance can be freely controlled. This means
As for the gradation limitation by the minimum clock limit, the resolution of the gradation control is increased by controlling the voltage digitally to the lower bits and adding pulse width modulation as the upper bits (the upper and lower bits may be set in reverse order). Possible). Also, from the viewpoint of cost, there is an advantage in using a waveform created by processing a clock of a peripheral circuit on which the dimming element is mounted.

FIG. 6 shows two forms (A) and (B) of the waveform at the time of pulse width modulation. In the waveform of (A), a pulse is inserted at the start of the basic period, while in (B), This is an example in which a pulse is applied after a fixed delay time from the start of the basic cycle, and the effect is the same as in the case of (A). The pulse application after such a delay time may be performed for each basic cycle,
Any combination with the waveform shown in FIG. The required number of drive pulses may be applied within the basic period.
(C) shows pulse density modulation for modulating the number density of pulses.

FIG. 7 shows a liquid crystal relaxation process when a negative type liquid crystal is used as a host material as in the GH cell shown in FIG. According to this, it is understood that the relaxation time after voltage application → off changes depending on the magnitude of the pulse voltage, and the relaxation time becomes longer as the voltage is applied higher.

FIG. 8 shows the transmitted light intensity (A) of the light control element and its variation (B) in the relaxation process similar to FIG.
(C) shows the region where relaxation occurs linearly (0-5 m
Comparison of the variations in s) revealed the following.

In order to make the fluctuation within 1%, an off time of 300 μs or less is required. To make the fluctuation within 2%, 42
Off time of 0 μs or less is required.

This fact corresponds to the condition for eliminating the transmittance flicker as shown in FIG. 5, and the above basic period is set under the condition that the variation of 2% or less is allowed (for example, 100 μs and 100 μs). can do.

The meaning of the fluctuation within 2% is based on the fact that it is equivalent to an imaging specification of a CCD which is currently used and described later.

The CCD image pickup is actually an average of the amount of light received accumulated within the field period, so it is expected that it will not appear as flicker during normal operation, but the dynamic range of transmittance control is small. Will drop. Further, when a shutter function or the like is used, the relationship between the shutter open time and the amount of light is not linear, which is a problem in control. Therefore, it is considered that the above-mentioned variation within 2% is desirable.

If a basic period exceeding the field period is used, an image is taken as flicker, and setting the basic period within the field period is a limit basic period in pulse width control.

Comparison between Pulse Width Modulation and Pulse Voltage Modulation FIG. 9 shows a comparison between the characteristics of the conventional pulse voltage modulation (PHM) and the pulse width modulation (PWM) according to the present invention (the horizontal axis in this figure). Is the time average of the absolute value of the potential difference applied between the electrodes, which was expressed as a corresponding voltage).

As a result, the pulse width modulation has a lower threshold voltage and shifts to a lower voltage side as a whole, so that low voltage control is possible and power consumption can be reduced. In addition, since the transmittance changes relatively slowly, the transmittance can be easily controlled by the voltage, and the gradation can be improved.

As described above, the pulse width modulation has the following advantages. (1) Low threshold characteristics can be obtained by driving pulse width modulation. (2) The number of gradations of the transmittance level can be increased, and highly accurate transmittance control is possible. (3) Since D / A conversion is not performed, circuit cost can be reduced.

Pulse width modulation and pulse density modulation Instead of modulating the peak value (voltage) of the pulse, the pulse density is modulated (PDM), and the pulse width modulation (PWM) is performed.
And compared. The pulse density modulation is to change the number of pulses generated within a certain unit time, and one pulse width is very short and contains many high frequency components.

As shown in FIG. 10, the driving characteristics of PWM and PDM are similar to each other. However, considering the low power consumption, in the pulse density modulation, the charge / discharge current to the liquid crystal cell per unit time is large, and it can be seen that the pulse width modulation is more advantageous. From the viewpoint of impedance matching, pulse width modulation is more advantageous.

Influence by Number of Pulses When driving using a pulse width modulation waveform, driving is performed so that the time average of the potential difference applied between the electrodes becomes substantially zero (in other words, the DC component becomes 0 V). By
This eliminates the bias of polarization of ions and the like in the light control element, and enables highly accurate transmittance control.

That is, as shown in FIG. 11, when the positive and negative polarities are alternately applied to the drive waveform of (A) by two pulses each as shown in (B), the number of pulses of both positive and negative polarities is obtained. , The same transmittance driving characteristics could always be obtained when the time averages were the same.

Also, as shown in (C), the number of positive and negative pulses was measured with m = 1, 2,...
There was no change in the illustrated transmittance vs. pulse width characteristics.

Further, even if the order of pulse generation is different as in (D), if the number of positive and negative pulses is the same, the same characteristics are exhibited. Further, it can be expected that there is no problem if the time width of the pulse is individually modulated as long as the time average is equivalent.

On the other hand, when the number of positive and negative pulses is different (when the negative pulse is k times larger than the positive pulse), the transmittance at the time of k = 1 is the transmittance in the symmetric drive.
When k becomes large and the asymmetry increases, the transmittance becomes larger than a predetermined transmittance as shown in FIG. 12, making controllability difficult. It does not depend on the value of m and shows a similar variation for k.

Further, when the asymmetric polarity is instantaneously inverted, the transmittance temporarily decreases and returns to the immediately preceding transmittance within a few seconds (observed as a long-period flicker). This transient fluctuation on the order of seconds is considered to be due to the bias of mobile ions in the liquid crystal cell caused by the bias voltage on the time average.

For the above reasons, the symmetry of the pulse number (the number of positive and negative bipolar pulses is the same) is more desirable for the stable driving than the asymmetry of the pulse number.

When a positive liquid crystal is used Unlike the above-described example, in FIG. 2, a positive liquid crystal (MLC-6849 manufactured by Merck) is used as a host material.
And a GH cell was fabricated in the same manner as described above except for the above.

As a result, as shown in FIG. 13, the transmitted light intensity change is larger in the case of pulse width modulation (B) than in the case of voltage modulation of the rectangular wave having the same fundamental frequency and applied (A). Since it is relatively gentle, controllability and gradation are improved, and the same transmitted light intensity can be obtained with a lower threshold value from the comparison of (C).

Specific Example of Light Control Device Next, an example of a light control device using, for example, the GH cell 12 among the GH cells described above will be described with reference to FIGS.

As shown in FIG. 14, the dimmer 23 includes the GH cell 12 and the polarizing plate 11a. The GH cell 12 is sealed between two glass substrates (not shown).
The GH cell 12 contains a negative liquid crystal molecule (host material) and a positive or negative dichroic dye molecule (guest material). Liquid crystal molecules have, for example, a negative dielectric anisotropy, and dichroic dye molecules have anisotropy in light absorption, and are, for example, p-type, which absorbs light in the molecular major axis direction. The light absorption axis of the polarizing plate 11 was orthogonal to the light absorption axis when a voltage was applied to the GH cell.

The light control device 23 is disposed between a front lens group 15 and a rear lens group 16 composed of a plurality of lenses such as a zoom lens. The light transmitted through the front lens group 15 is linearly polarized through the polarizing plate 11, and then
The light enters the GH cell 12. The light transmitted through the GH cell 12 is condensed by the rear lens group 16 and projected on the imaging surface 17 as an image.

The polarizing plate 11 constituting the light control device 23
Can be moved in and out of an effective optical path of light incident on the GH cell 12. Specifically, by moving the polarizing plate 11 to a position indicated by a virtual line, the light can be emitted out of the effective optical path. As a means for taking the polarizing plate 11 in and out, a mechanical iris shown in FIG. 15 may be used.

This mechanical iris is a mechanical diaphragm device generally used for digital still cameras, video cameras and the like, and mainly includes two iris blades 18 and 19,
The polarizing plate 11 is attached to the iris blade 18.
The iris blades 18, 19 can be moved up and down. The iris blades 18 and 19 are relatively moved using a drive motor (not shown) in the direction indicated by the arrow 21.

As a result, as shown in FIG. 15, the iris blades 18 and 19 are partially overlapped with each other. When the overlap increases, the opening 22 on the effective optical path 20 located near the center of the iris blades 18 and 19 is formed. Is covered with the polarizing plate 11.

FIG. 16 is a partially enlarged view showing a mechanical iris near the effective optical path 20. At the same time as the iris blade 18 moves downward, the iris blade 19 moves upward. Along with this, as shown in FIG. 16A, the polarizing plate 11 attached to the iris blade 18 also moves out of the effective optical path 20. Conversely, by moving the iris blade 18 upward and the iris blade 19 downward, the iris blades 18 and 19 overlap each other. Accordingly, as shown in FIG. 16B, the polarizing plate 11 moves on the effective optical path 20 and gradually covers the opening 22. Iris feather 1
8 and 19, when the mutual overlap becomes large, FIG.
As shown in (2), the polarizing plate 11 covers the opening 20.

Next, the dimming operation of the dimmer 23 using the mechanical iris will be described.

As the subject (not shown) becomes brighter, the iris blades 18 and 19 opened upward are driven by a motor (not shown) as shown in FIG.
Begin to overlap. As a result, the polarizing plate 11 attached to the iris blade 18 starts to enter the effective optical path 20 and covers a part of the opening 22 (FIG. 16B).

At this time, the GH cell 12 is in a state of not absorbing light (there is some absorption by the GH cell 12 due to thermal fluctuation, surface reflection, or the like). For this reason, the light having passed through the polarizing plate 11 and the light having passed through the opening 22 have substantially the same intensity distribution.

After that, the polarizing plate 11 is completely opened.
(FIG. 16 (c)). Further, when the brightness of the subject increases, the voltage to the GH cell 12 is increased, and light is adjusted by absorbing the light with the GH cell 12.

On the contrary, when the subject becomes dark,
First, by reducing or not applying a voltage to the GH cell 12, the light absorbing effect of the GH cell 12 is eliminated. Further, when the subject becomes dark, a motor (not shown) is driven to move the iris blade 18 downward and the iris blade 19 upward. Thus, the polarizing plate 11 is moved out of the effective optical path 20 (FIG. 1).
6 (a)).

According to this embodiment, since the polarizing plate 11 (transmittance, for example, 40% to 50%) can be taken out of the effective optical path 20 for light, the light is not absorbed by the polarizing plate 11. Therefore, the maximum transmittance of the light control device can be increased to, for example, twice or more. Specifically, when this light control device is compared with a conventional light control device including a fixedly installed polarizing plate and a GH cell, the maximum transmittance is, for example, about twice. Note that the minimum transmittance is the same for both.

Further, since the polarizing plate 11 is moved in and out using a mechanical iris which is put into practical use in a digital still camera or the like, a dimming device can be easily realized.

Since the GH cell 12 is used, dimming can be performed by absorbing the light by the GH cell 12 in addition to dimming by the polarizing plate 11.

As described above, the light control device according to the present invention has the following features.
The contrast ratio between light and dark can be increased, and the light amount distribution can be kept substantially uniform.

As the GH cell 12 used in this embodiment, a negative (n-type) dichroic dye molecule is used under the condition that the dielectric anisotropy of liquid crystal molecules is negative. You may.

In the conventional light control device as shown in FIG. 20, the polarizing plate 1 is always fixed and installed in the effective optical path of light. Therefore, for example, 50% of the light is always absorbed by the polarizing plate, and there is also an influence such as surface reflection of the polarizing plate. For this reason, the maximum transmittance of the light transmitted through the polarizing plate cannot exceed, for example, 50%, and the amount of light significantly decreases. This decrease in light quantity is one of the factors that make it difficult to commercialize a light control device using a liquid crystal cell.

On the other hand, various light control devices not using a polarizing plate have been proposed. As an example of a light control device that does not use a polarizing plate, a two-layer GH cell may be used. In this GH cell, the first layer absorbs a polarized light component in the same direction as a certain polarized light, and the second layer absorbs a polarized light component in a direction perpendicular to the polarized light. Further, there is a device that utilizes a phase transition of a cholesteric-nematic liquid crystal cell. Furthermore, there is a polymer scattering type that utilizes the scattering of liquid crystal.

However, in these light control devices that do not use a polarizing plate, the ratio of the absorbance between when no voltage is applied and when a voltage is applied, that is, the ratio between the optical densities is only about 5, as described above. For this reason, the contrast ratio of the light control device is small, and it is insufficient for normal light control from a bright place to a dark place. Further, in the polymer scattering type light control device, the imaging performance of the image pickup optical system is significantly deteriorated.

In addition, depending on the liquid crystal system to be used, the light transmittance in a transparent state may be dark. Therefore, when imaging with such a light amount, it is necessary to remove the dimmer from the imaging optical system.

On the other hand, in the present embodiment, the polarizing plate 1
1, which can be moved in and out of the effective optical path, it is possible to increase the light amount, increase the contrast ratio, and keep the light amount uniform.

Specific Example of Camera System FIG. 17 shows that the light control device 23 according to the embodiment is connected to a CCD (Ch).
5 shows an example in which the camera is incorporated into an (arge coupled device) camera.

That is, in the CCD camera 50, the first lens group 51 and the second lens group (for zoom) 52 corresponding to the front lens group 15 and the rear lens group 16 correspond to the lens front group 15 along the optical axis indicated by the one-dot chain line. A third lens group 53, a fourth lens group (for focusing) 54, and a CCD package 55 are arranged in this order at appropriate intervals. The CCD package 55 includes an infrared cut filter 55a, an optical low-pass filter system 55b, a CCD The image sensor 55c is housed. The distance between the second group lens 52 and the third group lens 53 is 3
Near the group lens 53, the light control device 23 including the GH cell 12 and the polarizing plate 11 according to the present invention is mounted on the same optical path for light amount adjustment (light amount stop). Note that the focusing fourth group lens 54 includes a linear motor 5.
7 movably disposed between the third lens group 53 and the CCD package 55 along the optical path.
The group lens 52 is disposed so as to be movable between the first group lens 51 and the light control device 23 along the optical path.

FIG. 18 shows an algorithm of a light transmittance control sequence by the light control device 23 in this camera system.

According to this embodiment, the second group lens 52
Since the light control device 23 according to the present invention set between the lens and the third group lens 53 can adjust the light amount by applying the electric field as described above, the system can be downsized, and the effective range of the optical path is substantially large. It can be downsized. Therefore, CC
It is possible to reduce the size of the D camera. Also,
Since the amount of light can be appropriately controlled by the magnitude of the voltage applied to the patterned electrodes, the conventional diffraction phenomenon can be prevented, a sufficient amount of light can be made incident on the image sensor, and the blur of the image can be eliminated.

Driving Circuit of Camera System FIG. 19 is a block diagram of a driving circuit of the above-mentioned CCD camera. According to this, it has the drive circuit unit 60 of the CCD image sensor 55c arranged on the light emission side of the light control device 23,
The output signal of the D imaging element 55c is processed by the Y / C signal processing unit 61, and is fed back as luminance information (Y signal) to the GH cell drive control circuit unit 62. The drive circuit unit receives a control signal from the control circuit unit. In synchronization with the 60 basic clocks, a drive pulse whose pulse width has been modulated as described above is obtained from the pulse generation circuit section 63. The control circuit section 62 and the pulse generation circuit section 63 constitute a GH liquid crystal drive control section 64 for pulse width control.

In a system different from the camera system, the light emitted from the light control device 23 is received by a photodetector (or photomultiplier), and the luminance information of the emitted light is fed back to the control circuit 62 to provide a GH signal. In synchronization with a clock of a cell drive circuit unit (not shown), a drive pulse whose pulse width is controlled can be obtained from the pulse generation circuit unit.

As described above, the present invention has been described in accordance with the preferred embodiments. However, the above-described embodiments can be variously modified based on the technical idea of the present invention.

For example, the structure and material of the above-described liquid crystal element and the polarizing plate, the driving mechanism thereof, and the configuration of the driving circuit and the control circuit can be variously changed. The driving waveform is a square wave,
It can be driven by either a trapezoidal wave or a sine wave, and the tilt of the liquid crystal changes according to the potential difference between the two electrodes, and the light transmittance is controlled.

As the GH cell, a GH cell having a two-layer structure or the like can be used in addition to the above-described one. Polarizing plate 1
The position of one GH cell 12 with respect to the front lens group 15 and the rear lens group 16 is not limited to this arrangement, but may be any position that is optimal from the setting conditions of the imaging lens. That is, unless an optical element such as a retardation film that changes the polarization state is used, the polarizing plate 11
It can be placed at any position on the subject side or the image sensor side, such as between the lens and the rear lens group 16. Furthermore, polarizing plate 1
1 may be arranged before or after a single lens (single lens) instead of the front lens group 15 or the rear lens group 16.

The number of iris blades 18 and 19 is not limited to two, and a larger number may be used.
Conversely, one sheet may be used. Also, the iris blades 18 and 19
Although they are overlapped by moving in the vertical direction, they may move in other directions, or may be narrowed down from the periphery toward the center.

Although the polarizing plate 11 is attached to the iris blade 18, it may be attached to the iris blade 19.

Further, as the subject becomes brighter, the light is adjusted by moving the polarizing plate 11 in and out, and then the light is absorbed by the GH cell 12. On the contrary, the light is absorbed by the GH cell 12 first. Dimming may be performed.
In this case, after the transmittance of the GH cell 12 has decreased to a predetermined value, light adjustment is performed by taking the polarizing plate 11 in and out.

Although a mechanical iris is used as a means for moving the polarizing plate 11 in and out of the effective optical path 20, the present invention is not limited to this. For example, by directly installing the film on which the polarizing plate 11 is stuck on the drive motor, the polarizing plate 1
1 may be taken in and out.

In the above example, the polarizing plate 11 is moved in and out of the effective optical path 20, but it is of course possible to fix the position in the effective optical path.

The light control device of the present invention can be used in combination with other known filter materials (for example, organic electrochromic materials, liquid crystals, electroluminescent materials, etc.).

Further, the dimming device of the present invention has the CC
In addition to the optical diaphragm of an imaging device such as a D camera, it can be widely applied to various optical systems, for example, for adjusting the amount of light in an electrophotographic copying machine or an optical communication device. Further, the light control device of the present invention can be applied to various image display elements for displaying characters and images, in addition to the optical filters.

[0148]

According to the light control device and the image pickup device of the present invention, the light transmittance is controlled by modulating the pulse width of the drive pulse of the liquid crystal device for light control. In comparison with pulse width modulation, it is easy to perform transmittance control with high accuracy by using a clock, and it is possible to change transmittance with a low threshold by a pulse width, and the change is relatively gradual. The transmittance control becomes easy and highly accurate, the number of gradations can be increased, and the D / A conversion is unnecessary, and the circuit cost can be reduced. In particular, for products at the consumer level, pulse width modulation is advantageous because of its accuracy and simplicity. In addition, even when the above-described device is implemented in recent digitally controlled products, the time axis is controlled as in pulse width control. Control can be expected to achieve high-precision control at low cost.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a light transmittance and a pulse width of a driving pulse of a light control device according to an embodiment of the present invention, and a driving pulse waveform diagram.

FIG. 2 is a schematic diagram showing an operation principle of the light control device.

FIG. 3 shows the relationship between the light transmittance and the applied voltage of a light control device using a negative type liquid crystal, which is 0 to 10 V (A) and 0 to 20 V.
It is a graph shown in the range of (B).

FIG. 4 shows the relationship between the light transmittance and the applied voltage of a light control device using a positive type liquid crystal, which is 0 to 10 V (A) and 0 to 20 V.
It is a graph shown in the range of (B).

FIG. 5 is a waveform chart showing the relationship between the waveform of a drive pulse of the light control device and the transmittance flicker at various pulse pause times.

FIG. 6 is a waveform chart showing various modulations of a driving pulse of the light control device.

FIG. 7 is a graph and a table for explaining a relaxation process of a negative liquid crystal system of the light control device.

FIG. 8 is a graph showing a response characteristic of the light control device using the negative liquid crystal.

FIG. 9 is a graph showing a comparison between a light transmittance and a voltage in pulse width modulation and pulse voltage modulation of a drive pulse of the light control device.

FIG. 10 is a graph showing a comparison between a light transmittance and a duty ratio in pulse width modulation and pulse density modulation of a drive pulse of the light control device.

FIG. 11 is a diagram showing various pulse waveforms and a light transmittance characteristic diagram in pulse width modulation of a driving pulse of the light control device.

FIG. 12 is a light transmittance characteristic diagram according to the number of positive and negative pulses of a driving pulse of the light control device.

FIG. 13 is a graph showing a comparison between changes in transmitted light intensity in pulse voltage modulation and pulse width modulation of a driving pulse of a light control device using a positive type liquid crystal.

FIG. 14 is a schematic side view of the light control device.

FIG. 15 is a front view of a mechanical iris of the light control device.

FIG. 16 is a schematic partial enlarged view showing an operation of a mechanical iris near an effective optical path of the dimmer.

FIG. 17 is a schematic sectional view of a camera system incorporating the light control device.

FIG. 18 shows an algorithm of light transmittance control in the camera system.

FIG. 19 is a block diagram of a camera system including a drive circuit.

FIG. 20 is a schematic diagram illustrating the operation principle of a conventional light control device.

[Explanation of symbols]

Reference numerals 1, 11: polarizing plate, 2, 12: GH cell, 3: positive liquid crystal, 4: positive dye molecule, 5: incident light, 13: negative liquid crystal, 15, 16: lens group, 17: imaging surface, 18, 19
... Iris blade, 20 ... Effective optical path, 22 ... Aperture, 23
... dimmer, 50 ... CCD camera, 51 ... 1 group lens,
52: 2 group lens, 53: 3 group lens, 54: 4 group lens, 55: CCD package, 55b: Optical low-pass filter, 55c: CCD imaging device, 60: CCD drive circuit unit, 61: Y / C signal processing unit , 62 ... control circuit section, 6
3 pulse generator, 64 pulse width controller (GH liquid crystal drive controller)

Continued on front page F term (reference) 2H088 EA33 GA13 HA06 HA24 JA06 KA26 KA27 MA13 2H093 NA56 NB02 NC49 NC54 ND07 ND10 NE06 NF06 NG20 5C022 AA01 AA11 AB14 AB15 AC42 AC55

Claims (56)

[Claims] 1. A liquid crystal element, a driving pulse generator for driving the liquid crystal element, and pulse width control for modulating a pulse width of the driving pulse to control a transmittance of light incident on the liquid crystal element. Light control device comprising: 2. The light control device according to claim 1, wherein a pulse voltage of the drive pulse by the pulse width modulation is constant. 3. The light control device according to claim 1, wherein the time average of the voltage applied between the drive electrodes of the liquid crystal element during the modulation of the pulse width is substantially zero. 4. The pulse width modulation according to claim 1, wherein the pulse width modulation is performed such that a driving pulse waveform exists within a period of a fundamental frequency.
The light control device described in 1 above. 5. The light control device according to claim 4, wherein a modulation width of the fundamental frequency and the pulse width modulation is adjusted so that flicker does not occur in the steady driving. 6. The light control device according to claim 4, wherein the pulse having the drive waveform is extracted in synchronization with a clock of a drive circuit unit. 7. The luminance information of the emitted light is fed back to a control circuit unit, and a control signal from the control circuit unit
7. The light control device according to claim 6, wherein the pulse width modulated drive pulse is obtained in synchronization with a clock of the drive circuit unit. 8. The light control device according to claim 1, wherein the liquid crystal element is a guest-host type liquid crystal element. 9. The light control device according to claim 8, wherein the host material of the liquid crystal element is a negative or positive liquid crystal having a negative or positive dielectric anisotropy. 10. The light control device according to claim 8, wherein the guest material of the liquid crystal element is made of a positive or negative dichroic dye molecule having positive or negative light absorption anisotropy. 11. The light control device according to claim 1, wherein a polarizing plate is disposed in an optical path of light incident on the liquid crystal element. 12. The light control device according to claim 11, wherein the polarizing plate is disposed so as to be able to be taken in and out of the optical path. 13. The light control device according to claim 12, wherein the polarizing plate is disposed in a movable portion of a mechanical iris so that the light can be moved in and out of the optical path. 14. The liquid crystal device according to claim 1, wherein the drive electrode is formed over at least the entire area of the effective light transmitting portion.
The light control device described in 1 above. 15. A liquid crystal element, a driving pulse generator for driving the liquid crystal element, and pulse width control for modulating a pulse width of the driving pulse to control transmittance of light incident on the liquid crystal element. An imaging apparatus in which a dimming device including a unit is disposed in an optical path of an imaging system. 16. The imaging device according to claim 15, wherein a pulse voltage of the drive pulse based on the pulse width modulation is constant. 17. The imaging device according to claim 15, wherein a time average of a voltage applied between drive electrodes of the liquid crystal element at the time of modulation of the pulse width is substantially zero. 18. The imaging apparatus according to claim 15, wherein the pulse width modulation is performed so that a driving pulse waveform exists within a period of a fundamental frequency. 19. The imaging apparatus according to claim 18, wherein the fundamental frequency and the modulation width of the pulse width modulation are adjusted so that flicker does not occur in the steady driving. 20. The imaging device according to claim 18, wherein the pulse of the driving waveform is taken out in synchronization with a clock of a driving circuit unit. 21. The drive circuit section, wherein the drive circuit section is a drive circuit section of an image sensor arranged on the light emitting side of the dimmer, and an output signal of the image sensor is fed back to the control circuit section as luminance information. By the control signal from the control circuit part,
20. The pulse width-modulated drive pulse is obtained in synchronization with a clock of the drive circuit unit.
An imaging device according to item 1. 22. The imaging device according to claim 15, wherein the liquid crystal element is a guest-host type liquid crystal element. 23. The imaging device according to claim 22, wherein the host material of the liquid crystal element is a negative or positive liquid crystal having a negative or positive dielectric anisotropy. 24. The imaging device according to claim 22, wherein the guest material of the liquid crystal element is made of a positive or negative dichroic dye molecule having positive or negative light absorption anisotropy. 25. The imaging device according to claim 15, wherein a polarizing plate is provided in an optical path of light incident on the liquid crystal element. 26. The imaging device according to claim 25, wherein the polarizing plate is disposed so as to be able to be taken in and out of the optical path. 27. The imaging device according to claim 26, wherein the polarizing plate is disposed on a movable portion of a mechanical iris so that the polarizing plate can be moved in and out of the optical path. 28. The liquid crystal device according to claim 1, wherein the drive electrode is formed over at least the entire area of the effective light transmitting portion.
5. The imaging device according to 5. 29. A method for driving a light control device, comprising: when driving a liquid crystal element, modulating a pulse width of a driving pulse of the liquid crystal element in order to control a transmittance of light incident on the liquid crystal element. 30. The driving method of a light control device according to claim 29, wherein a pulse voltage of the driving pulse by the pulse width modulation is fixed. 31. The driving method of a light control device according to claim 29, wherein a time average of a voltage applied between driving electrodes of the liquid crystal element at the time of modulating the pulse width is substantially zero. 32. The method according to claim 29, wherein the pulse width modulation is performed so that a driving pulse waveform exists within a period of a fundamental frequency.
The driving method of the light control device described in 1 above. 33. The method according to claim 32, wherein the fundamental frequency and the modulation width of the pulse width modulation are adjusted so that flicker does not occur in the steady driving. 34. The driving method of a light control device according to claim 32, wherein the pulse of the driving waveform is taken out in synchronization with a clock of a driving circuit unit. 35. The luminance information of the outgoing light is fed back to the control circuit unit, and a control signal from the control circuit unit
35. The driving method of a light control device according to claim 34, wherein the pulse width-modulated drive pulse is obtained in synchronization with a clock of the drive circuit unit. 36. The driving method of the light control device according to claim 29, wherein a guest-host type liquid crystal element is used as the liquid crystal element. 37. The method of driving a light control device according to claim 36, wherein a negative or positive liquid crystal having a negative or positive dielectric anisotropy is used as a host material of the liquid crystal element. 38. The method of driving a light control device according to claim 36, wherein a positive or negative dichroic dye molecule having positive or negative light absorption anisotropy is used as a guest material of the liquid crystal element. 39. The driving method of a light control device according to claim 29, wherein a polarizing plate is disposed in an optical path of light incident on the liquid crystal element. 40. The driving method of a light control device according to claim 39, wherein the polarizing plate is disposed so as to be able to be taken in and out of the optical path. 41. The driving method of a light control device according to claim 40, wherein the polarizing plate is disposed on a movable portion of a mechanical iris so that the polarizing plate can be moved in and out of the optical path. 42. The driving method of a light control device according to claim 29, wherein the light control device in which a drive electrode of a liquid crystal element is formed at least over an entire area of an effective light transmitting portion is used. 43. When driving an image pickup device having a liquid crystal element arranged in an optical path of an image pickup system, a pulse width of a drive pulse of the liquid crystal element is modulated in order to control a transmittance of light incident on the liquid crystal element. , A driving method of an imaging device. 44. The driving method of an imaging device according to claim 43, wherein a pulse voltage of the driving pulse by the pulse width modulation is constant. 45. The method according to claim 43, wherein the time average of the voltage applied between the drive electrodes of the liquid crystal element during the modulation of the pulse width is substantially zero. 46. The apparatus according to claim 43, wherein the pulse width modulation is performed such that the driving pulse waveform exists within the period of the fundamental frequency.
The driving method of the imaging device described in 1 above. 47. The method according to claim 46, wherein the fundamental frequency and the modulation width of the pulse width modulation are adjusted so that flicker does not occur in the steady driving. 48. The driving method of an imaging device according to claim 46, wherein the driving waveform pulse is extracted in synchronization with a clock of a driving circuit unit. 49. The driving circuit section is a driving circuit section of an image sensor arranged on the light emission side of the dimmer, and an output signal of the image sensor is fed back to the control circuit section as luminance information, and 49. The driving method of an imaging device according to claim 48, wherein the pulse width-modulated drive pulse is obtained in synchronization with a clock of the drive circuit unit by a control signal from a circuit unit. 50. The method according to claim 43, wherein a guest-host type liquid crystal element is used as the liquid crystal element. 51. The method according to claim 50, wherein a negative or positive liquid crystal having a negative or positive dielectric anisotropy is used as a host material of the liquid crystal element. 52. The method according to claim 50, wherein a positive or negative dichroic dye molecule having positive or negative light absorption anisotropy is used as a guest material of the liquid crystal element. 53. The method according to claim 43, wherein a polarizing plate is disposed in an optical path of light incident on the liquid crystal element. 54. The driving method of an imaging device according to claim 53, wherein the polarizing plate can be moved in and out of the optical path. 55. The driving method of an imaging device according to claim 54, wherein the polarizing plate is disposed on a movable portion of a mechanical iris so that the polarizing plate can be moved in and out of the optical path. 56. The driving method of an imaging device according to claim 43, wherein the dimming device in which a driving electrode of the liquid crystal element is formed at least over an entire effective light transmitting portion is used.