JP2002189205A - Light control device and driving method therefor, and image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the performance, image quality, and reliability of a light control device and an image pickup device b always smoothly raising the variation of liquid crystal alignment of relaxation thereof and shortening a response time of light transmissivity even if a cell gap varies according to manufacturing conditions when a liquid crystal element for light control is driven in a halftone. SOLUTION: A light control device provided with a liquid crystal element, a detection means for detecting the cell gap of the liquid crystal element 12 such as a CCD image pickup element 55c and a pulse control part 62 (further 64) for pre-inserting a control driving pulse corresponding to the minimum transmissivity or the maximum transmissivity based on the control according to the cell gap judged by a cell gap judging circuit 65 before a driving pulse corresponding to at least the target transmissivity is given, when the transmissivity of light emitted from the liquid crystal element 12 is varied from the current transmissivity to the target transmissivity. Moreover, the driving method for driving the light control device by using the driving pulse for control, and the image pickup device wherein the light control device is arranged in the optical path of an image pickup system.

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, a driving method thereof, and an imaging device using the light control device.

[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 cell and guest-host (GH
(GuestHost) type liquid crystal cells are used.

FIG. 17 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. Although not shown, the GH cell 2 is sealed between two glass substrates and has an operating electrode and a liquid crystal alignment film (the same applies hereinafter). In the GH cell 2, liquid crystal molecules 3 and dichroic dye molecules 4 are sealed.

The dichroic dye molecules 4 have anisotropy in light absorption, for example, a positive type (p) absorbing light in the longitudinal direction of the molecule.
Type) dye molecules. The liquid crystal molecules 3 are of a positive type (positive type) having a positive dielectric anisotropy, for example.

FIG. 17A shows a state of the GH cell 2 when no voltage is applied (no voltage is applied). Incident light 5
Are linearly polarized by transmitting through the polarizing plate 1. In FIG. 17A, since the direction of polarization coincides with the direction of the major axis of the dichroic dye molecules 4, light is emitted from the dichroic dye molecules 4.
And the light transmittance of the GH cell 2 decreases.

[0006] Then, as shown in FIG.
When a voltage is applied to the cell 2, the direction of the major axis of the dichroic dye molecules 4 becomes perpendicular to the direction of linearly polarized light as the liquid crystal molecules 3 are oriented in the direction of the electric field. Therefore, the incident light 5 is transmitted by the GH cell 2 without being absorbed.

In the GH cell 2 shown in FIG. 17, as shown in FIG. 18, the average light transmittance of visible light (in air; a polarizing plate is added in addition to the liquid crystal cell) with the application of the operating voltage. The light transmittance at that time was referred to (= 100%):
Similarly, the maximum light transmittance when the voltage is increased to 10 V is about 60%, and the change in the light transmittance is gradual.

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. 17, 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 dimmer that is configured only with the GH cell 2 without using the polarizing plate 1.

[0010]

In the operation of the above-described light control device, when the light transmittance is changed, the driving pulse is changed in a stepwise manner. Response when the light transmittance is slightly changed in halftone as compared with a large step response from (maximum light transmittance) to light blocking (minimum light transmittance) or a large step response from light blocking to transparent The time could be significantly longer, which was a problem.

That is, the above-mentioned optical density ratio of the light control device is:
Depending on the distance between two opposing substrates such as two glass substrates constituting a GH cell (hereinafter referred to as a cell gap), the larger the cell gap (the thicker the liquid crystal layer), the more transparent The difference in light transmittance between the light-shielding and light-shielding times increases, and the optical density ratio can be increased. However, the light transmittance in the transparent state decreases. When the cell gap changes, GH
The transient response speed as a light control device using a cell also changes. When the gap increases, the response speed tends to surely decrease as the number of liquid crystal molecules existing in the effective optical path length increases.

Accordingly, an object of the present invention is to provide a liquid crystal element for dimming operation in a halftone mode, in which even if the cell gap fluctuates due to manufacturing conditions, the change in the orientation of the liquid crystal or its relaxation is always smoothly started. Therefore, the response time (transient response speed) of the light transmittance is significantly and appropriately shortened, and the performance, image quality, and reliability of the light control device and the imaging device are improved.

[0013]

That is, the present invention relates to a liquid crystal element; a detecting means for detecting a cell gap of the liquid crystal element; and a transmittance of light emitted from the liquid crystal element is calculated from a current light transmittance. When changing to the target light transmittance, at least before giving a drive pulse corresponding to the target light transmittance,
A pulse control unit that inserts a control drive pulse corresponding to the minimum light transmittance or the maximum light transmittance in advance in accordance with the cell gap. A driving method of driving using a driving pulse,
In addition, the present invention relates to an imaging device in which the light control device is disposed in an optical path of an imaging system.

According to the present invention, when slightly changing the light transmittance of the liquid crystal element from the current light transmittance to the target light transmittance in a halftone, before giving a drive pulse corresponding to the target light transmittance, A control drive pulse corresponding to complete light blocking (minimum light transmittance) or complete transparency (maximum light transmittance) is appropriately inserted in advance, and the control drive pulse is used to determine the actual cell gap value that affects the response speed. Therefore, compared to the case where the driving pulse corresponding to the target light transmittance is simply given in a step shape and driven, the change in the orientation of the liquid crystal or the relaxation thereof rises more smoothly, and the target light transmittance is reduced. The response time to reach can be significantly and appropriately reduced.

Before inventing the present invention, the inventor of the present invention disclosed in Japanese Patent Application No. 2000-31501, when slightly changing the light transmittance of a liquid crystal element from a current transmittance to a target transmittance in a halftone, Before the drive pulse corresponding to the target transmittance is given, a control drive pulse corresponding to the time of complete light shielding (minimum transmittance) or the time of complete transparency (maximum transmittance) is appropriately inserted in advance, so that the target transmittance is simply obtained. The liquid crystal alignment change (or its relaxation) rises more smoothly than when driving is performed by applying a drive pulse corresponding to the step shape, and the response time until reaching the target transmittance can be greatly reduced. (Hereinafter, this is referred to as a prior invention).

As a result of further studies by the present inventor on the prior invention, the transient response speed of the liquid crystal light control device is greatly increased by the distance (cell gap) between the two glass substrates constituting the liquid crystal cell to be used. The optimum value of the control drive pulse insertion time differs depending on the cell gap even in the case of performing two-stage modulation drive with the control drive pulse according to the prior application inserted for the purpose of achieving a high-speed response at halftone depending on the cell gap. There was found.

The present inventor has provided a mechanism for automatically recognizing the cell gap of a mounted liquid crystal element,
The present inventors have found that, by adding an optimum control pulse corresponding to the cell gap, the liquid crystal optical element can be driven at a higher speed in a form suited to the characteristics of each liquid crystal element, and arrived at the present invention.

For example, if the correlation between the light transmittance when the liquid crystal element is transparent and / or when the light is shielded and the cell gap (which is almost uniquely determined by the constituent material of the liquid crystal cell) is input in advance, the manufacturing process can be performed. Even if the finished cell gap varies due to the above-mentioned variation, a more accurate cell gap can be grasped from the light transmittance of the actual cell mounted.

When slightly changing the light transmittance of the liquid crystal element from the current transmittance to the target transmittance in a halftone,
Before applying the drive pulse corresponding to the target transmittance, completely shaded (minimum transmittance) or completely transparent (maximum transmittance)
The control drive pulses corresponding to the above are appropriately inserted in advance by the number of pulses corresponding to the cell gap, so that the alignment change of the liquid crystal (or the relaxation thereof) can be optimally adjusted to the characteristics of each liquid crystal cell. This makes it possible to start up more smoothly and to significantly reduce the transient response time required to reach the target transmittance.

[0020]

In the present invention, the light transmittance of the liquid crystal element when it is transparent and / or when it is shielded from light is preferably detected in advance, and the cell gap is determined from the detected value.

Further, the control driving pulse has at least a controlled pulse voltage and / or pulse number, and the pulse voltage is equal to the pulse voltage that causes the minimum light transmittance or the maximum light transmittance. Alternatively, it may be a value between the pulse voltage and the pulse voltage that produces the target light transmittance.

The control driving pulse has a controlled pulse width and / or pulse number, and the pulse width is equal to the pulse width that causes the minimum light transmittance or the maximum light transmittance. Alternatively, a value between this pulse width and a pulse width that produces the target light transmittance is good.

The control drive pulse can be controlled not only by the above-described pulse voltage or pulse width, but also by pulse density and further by using both of them.

The liquid crystal element is preferably a guest-host type liquid crystal element using negative liquid crystal as a host material and a dichroic dye as a guest material.

Such a liquid crystal element is based on the prior invention of Japanese Patent Application No. 11-322186 already filed by the present applicant. According to this prior invention, a liquid crystal device and a polarizing plate arranged in the optical path of light incident on the liquid crystal device constitute a dimmer, and further, a guest-host type using a negative type liquid crystal as a host material. By using liquid crystal, the ratio of the absorbance between when no voltage is applied and when a voltage is applied (that is, the ratio between optical densities) is improved, the contrast ratio of the light control device is increased, and the light control operation is performed from a bright place to a dark place. Can be performed normally.

In the guest-host type liquid crystal cell (GH cell) 2 shown in FIG. 17, a positive type liquid crystal having a positive dielectric anisotropy (Δε) is used as a host material 3 and a guest material 4 is used.
A positive dye 4 having a positive dichroic light absorption anisotropy (ΔA) is used, and a polarizing plate 1 is disposed on the incident side of the GH cell 2;
When the change in the light transmittance when the operating voltage is applied is measured using a rectangular wave as a drive waveform, as shown in FIG. 18, the average light transmittance of visible light (in air; in addition to the liquid crystal cell, Refer to the transmittance when a polarizing plate is added (= 100
%): The same applies hereinafter), but the voltage is increased to 10 V
The maximum light transmittance when raised to about 60% is about 60%, and the change in light transmittance is 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 if a voltage is applied, the director of the director is not affected. The orientation does not change (or
It is considered that liquid crystal molecules remain (which hardly change).

On the other hand, in the prior invention, as shown in FIG. 9, in the guest-host type liquid crystal cell (GH cell) 12, as the host material 13, a negative type having a negative dielectric anisotropy (Δε) was used. Merck MLC-66 liquid crystal
08 is used as an example, and the guest material 4 is a positive type dye having dichroism D5 (manufactured by BDH) as an example, so that the polarizing plate 11 is disposed on the incident side of the GH cell 12, and a rectangular wave is formed. When the change in the light transmittance when the operating voltage was applied was measured as a drive waveform, as shown in FIG. 10, the average light transmittance of visible light (in air) was reduced to about the maximum light transmittance with the application of the operating voltage. It decreases from 75% to several%, and the change in light transmittance becomes relatively steep.

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

As described above, in the present invention, when the GH cell is formed by using the negative type host material, the light transmittance (particularly when transparent) is improved, and the position of the GH cell is fixed in the imaging optical system as it is. This makes it possible to realize a compact light control device that can be used as a light control device. In this case, by arranging a polarizing plate in the optical path of the incident light to the liquid crystal element, the ratio of the absorbance between when no voltage is applied and when a voltage is applied (that is, the ratio of the optical density) is further improved,
The contrast ratio of the light control device is further increased, and the light control operation can be performed more normally from a bright place to a dark place.

In the present invention, the dielectric anisotropy of the negative liquid crystal of the liquid crystal element is preferably negative, but the guest material is made of a positive or negative dichroic dye molecule. May be. The host material is preferably a negative type, but may be a positive type.

In the present invention, the negative (or positive) host material and the positive (or negative) guest material can be selected from known materials. However, in the case of actual use, a composition which is selected and blended so as to exhibit nematicity in an actual use temperature range may be used.

The light control device 2 comprising the GH cell 12 described above
The lens 3 is disposed between a front lens group 15 and a rear lens group 16 including a plurality of lenses such as a zoom lens, as shown in FIG. 11, for example. The light transmitted through the front lens group 15 is linearly polarized through the polarizing plate 11, and then 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 enter and exit the effective optical path of the light incident on the GH cell 12 in the same manner as in the above-mentioned prior invention by the present applicant. 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 means for taking the polarizing plate 11 in and out, FIG.
A mechanical iris as shown in FIG. 2 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. 12, the iris blades 18 and 19 are partially overlapped, and when this 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 by the polarizing plate 11.

FIG. 13 is a partially enlarged view of the 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. 13A, 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, FIG.
As shown in (b), the polarizing plate 11 moves on the effective optical path 20 and gradually covers the opening 22. Iris feather 18, 1
When the overlapping of the components 9 becomes large, the polarizing plate 11 covers the entire opening 20 as shown in FIG.

Next, the light control operation of the light control device 23 using the mechanical iris will be described.

As the subject, not shown, becomes brighter, the iris blades 18, 19, which have been opened in the vertical direction, are driven by a motor, not shown, and begin to overlap, as shown in FIG. Thus, 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. 13B).

At this time, the GH cell 12 is in a state of not absorbing light (because of thermal fluctuation or surface reflection, etc.).
There is some absorption by the GH cell 12. ). For this reason,
The light passing through the polarizing plate 11 and the light passing through the opening 22 are
The intensity distributions are almost equal.

Thereafter, the polarizing plate 11 is completely opened.
Is covered (FIG. 13C). Further, when the brightness of the object increases, the voltage to the GH cell 12 is increased, and the 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, the iris blade 18 is moved downward by driving a motor (not shown).
Further, the iris blade 19 is moved upward. Thus,
The polarizing plate 11 is moved out of the effective optical path 20 (FIG. 13).
(A)).

Further, as shown in FIGS. 11 to 13, the polarizing plate 11 (transmittance, for example, 40% to 50%) can go out of the effective optical path 20 of the light. Not absorbed. Therefore, the maximum transmittance of the light control device can be increased to, for example, twice or more. Specifically, this light control device is combined with a conventional fixedly installed polarizing plate and GH.
The maximum transmittance is, for example, about twice as large as that of a dimmer including cells. Note that the minimum transmittance is the same for both.

Further, since the polarizing plate 11 is moved in and out by using a mechanical iris which is put into practical use in a digital still camera or the like, a light control device can be easily realized. Further, since the GH cell 12 is used, in addition to dimming by the polarizing plate 11, dimming can be performed by absorbing the light by the GH cell 12 itself.

In this way, the light control device can increase the contrast ratio between light and dark and can maintain the light amount distribution substantially uniform.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 First, an example of a light control device using a guest-host type liquid crystal (GH) cell will be described.

This light control device has a G
It comprises an H cell 12 and a polarizing plate 11. The GH cell 12 is provided between two glass substrates (both not shown) each having a transparent electrode and an alignment film formed thereon, and a negative liquid crystal molecule (host material) and a positive or negative two-color liquid crystal molecule. A mixture with a chromatic dye molecule (guest material) is enclosed.

As the liquid crystal molecules, for example, MLC-6608 manufactured by Merck, which is a negative type liquid crystal having a negative dielectric anisotropy, is used as an example. The dichroic dye molecules 4 have anisotropic light absorption. For example, D5 manufactured by BDH, which is a positive dye that absorbs light in the molecular long axis direction, is used as an example.
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 12.

The light control device 23 comprising the GH cell 12
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, as shown in FIG. 11, for example. The light transmitted through the front lens group 15 is linearly polarized through the polarizing plate 11, and then 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 has the same structure as the above-mentioned prior application by the present applicant.
The light can enter and exit the effective optical path of the 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. 12 may be used.

When a rectangular wave was input as a driving waveform into the GH cell 12 and the change in light transmittance when an operating voltage was applied was measured (FIG. 9), as shown in FIG. As a result, the average light transmittance (in air) of visible light was reduced from the maximum light transmittance of about 75% to several percent. Depending on the liquid crystal cell structure and constituent materials used, the GH cell 12
Reached almost the minimum light transmittance when a pulse voltage of ± 5 V (1 kHz) or more was applied.

However, when the state is changed from the transparent state to the completely light-shielded state or from the completely light-shielded state to the transparent state as in the case of 0V → ± 5V and ± 5 → 0V, the light transmittance responds at a somewhat high speed. However, when trying to slightly change the light transmittance in a halftone, a response time several times as long as the case may be required.

For example, as shown in FIG. 1A, a GH cell having a cell gap of 4.12 μm at room temperature of 25 ° C.
When a drive pulse voltage change of 0V → ± 5V is given, when the light transmittance responds at 23.4 ms, as shown in FIG. 1B, when the halftone drive is performed at ± 2V → ± 3V, the response becomes The time has deteriorated to about 87.4 ms.

The transient response speed is further affected by the cell gap of the liquid crystal element. As the cell gap increases, the number of liquid crystal molecules existing in the effective optical path length increases. To increase. Conversely, the shorter the cell gap, the shorter the response time.

For example, in the case of a liquid crystal optical element having a cell gap of 3.04 μm and the same material as described above, 0 → ± 5V
In response to the change in the driving pulse voltage, the response time of the light transmittance is as fast as 7.8 ms, and the response time is as fast as about 20.0 ms even if the half-tone driving is performed at ± 2 → ± 3 V.

When an image pickup apparatus is to be realized by using a liquid crystal cell as a light control element, a change in response speed fluctuated due to a variation in cell gap, particularly a decrease in response speed when the cell gap is large, is caused by automatic exposure adjustment. And so on.

In order to solve this problem, the inventor of the present invention has made intensive studies and found that the cell gap of the mounted liquid crystal optical element is accurately grasped in advance from the value of the light transmittance in the transparent state or in the light-shielded state. In the case of driving in halftone, first, the control drive waveform corresponding to the complete light shielding state (minimum transmittance)
It has been found that the response time can be significantly reduced by inserting an appropriate number of pulses according to the cell gap of the liquid crystal element before the drive waveform for providing the target transmittance.

For example, as shown in FIG. 1C, for a liquid crystal optical element having a cell gap of 4.12 μm, ± 2 → ±
In the case of driving at 3 V, first, a ± 5 V rectangular wave corresponding to a completely light-shielded state (minimum transmittance) is generated by ± 3 V for 12 ms.
When inserted before the drive waveform of V, the response time of the light transmittance could be significantly reduced from 87.4 ms to 11.0 ms.

Similarly, when the liquid crystal optical element having a cell gap of 4.12 μm is driven at ± 3 → ± 2 V,
First, a control drive waveform of 0 V corresponding to a completely transparent state (maximum transmittance) was inserted by 18 ms before a drive waveform of ± 2 V. As shown in FIG. Could be reduced from 51.4 ms to 18.8 ms.

In the present embodiment, the time width and voltage of the control drive pulse to be inserted in the middle can be freely selected to some extent so as to be easily controlled. However, there is an optimum value for the time width of the control pulse to be interposed according to the cell gap of the liquid crystal element, and the setting is such that the transient response of the light transmittance overshoots the target value (FIG. 3C). Is not preferred.

For example, in the case of the above-mentioned liquid crystal optical element having a cell gap of 3.04 μm, when driving at ± 2 → ± 3 V, a rectangle of ± 5 V corresponding to a completely light-shielded state (minimum transmittance) first. When the wave was inserted for 3 ms before the driving waveform of ± 3 V, the response time of the light transmittance was 20.0 m
From s to 3.0 ms, it was able to be further reduced significantly.

Similarly, when a liquid crystal optical element having a cell gap of 3.04 μm is driven at ± 3 → ± 2 V, a driving waveform of 0 V corresponding to a completely transparent state (maximum transmittance) is first applied for 10 ms. , ± 2 V, the response time of the light transmittance was 20.0 ms to 7.0.
ms.

FIG. 5 shows that ± 2 → ± 3V and ± 3 → ± 2V
The optimum time width of the intermediate insertion control pulse obtained as a result of studying the improvement of the transient response speed when the liquid crystal element is driven in the halftone of FIG.

By grasping this relationship, even if the cell gap varies in the manufacturing process, the light transmittance in the transparent or light-shielded state is detected in advance, and the cell gap of the mounted liquid crystal optical element is accurately recognized from this. In advance (FIG. 4), by inserting a control drive pulse intermediately with an optimum time width corresponding to this (FIG. 5), as shown in FIGS. 6 and 7, an optimum form suitable for each liquid crystal cell is obtained. Thus, it has become possible to greatly improve the transient response speed of halftone driving.

Embodiment 2 In this embodiment, the driving method of the liquid crystal cell is changed from pulse voltage modulation (PHM) described in Embodiment 1 to pulse width modulation (PWM).

For example, if the basic pulse generation cycle is 100
By controlling the pulse width within this basic period as μs, as shown in FIG.
Similar to the pulse voltage modulation described above, the average light transmittance (in air) of visible light was reduced from a maximum light transmittance of about 75% to several percent.

Then, the pulse peak value is fixed at 5 V, and the pulse width is controlled so that 0 μs → 100 μs, 100 μs →
When changing from a transparent state to a completely light-shielded state or from a completely light-shielded state to a transparent state as in 0 μs, the light transmittance responds to a certain high-speed, but slightly changes the light transmittance in a halftone. In this case, several times as much response time was required.

For example, at a room temperature of 25 ° C., the cell gap 4
In the GH cell of μm, when the light transmittance responds to the change of the drive pulse width from 0 μs to 100 μs at the light transmittance of about 20 ms, when the halftone driving is performed from 20 μs to 40 μs, the response time deteriorates to about 90 ms.

The transient response speed when driven by pulse width modulation is greatly affected by the cell gap of the liquid crystal element. As the cell gap increases, the number of liquid crystal molecules existing in the effective optical path length increases. The time required for the transient response increases. Conversely, as the cell gap becomes smaller,
Response time is shorter.

For example, in the case of a liquid crystal optical element having a cell gap of 3 μm and made of the same material as described above, the response time of the light transmittance is about 1 with respect to a change in the drive pulse width from 0 to 100 μs.
The response time is reduced to about 20 ms even if halftone driving is performed from 20 to 40 μs.

When an image pickup apparatus is to be realized by using a liquid crystal cell as a light control element, a change in the response speed fluctuated due to a variation in the cell gap, particularly a decrease in the response speed when the cell gap is large, is caused by automatic exposure adjustment. And so on.

In order to solve this problem, the inventor of the present invention has intensively studied and found that even in the case of halftone driving by pulse width modulation (PWM), the mounting is determined in advance from the value of the light transmittance at the time of transparent or light shielding. In the case of driving in a half tone, the control drive waveform corresponding to the completely light-shielded state (minimum transmittance) is first determined by the control waveform corresponding to the target transmittance. Previously, it has been found that the response time can be significantly reduced by inserting a suitable number of pulses according to the cell gap of the liquid crystal element.

For example, when a liquid crystal optical element having a cell gap of 4 μm is driven with a pulse width change of 20 → 40 μs, first, a rectangular wave having a pulse width of 100 μs corresponding to a completely shielded state (minimum transmittance) is applied. 12ms, 40
When inserted before the driving waveform having a pulse width of μs, the response time of the light transmittance could be significantly reduced from about 90 ms to about 10 ms.

Similarly, when driving a liquid crystal optical element having a cell gap of 4 μm with a pulse width change of 40 → 20 μs, a control drive waveform of 0 μs corresponding to a completely transparent state (maximum transmittance) is first applied. When inserted by 18 ms before the drive waveform having a pulse width of 20 μs, the response time of the light transmittance was able to be reduced from about 55 ms to about 20 ms.

In this embodiment as well, the time width and voltage of the control drive pulse to be inserted in the middle can be freely selected to some extent so as to facilitate control. However, the time width of the control pulse that is interposed in accordance with the cell gap of the liquid crystal element includes:
A setting in which there is an optimum value and the transient response of the light transmittance overshoots the target value is still not preferable.

For example, in the case of the above-mentioned liquid crystal optical element having a cell gap of 3 μm, when driving with a pulse width change of 20 → 40 μs, a completely light-shielded state (minimum transmittance) is initially set.
When a rectangular wave having a pulse width of 100 μs corresponding to the above was inserted by 3 ms before the drive waveform having a pulse width of 40 μs, the response time of the light transmittance was able to be reduced from about 20 ms to about 3 ms. .

Similarly, when a liquid crystal optical element having a cell gap of 3 μm is driven by a pulse width change of 40 → 20 μs, first, a liquid crystal optical element corresponding to a completely transparent state (maximum transmittance) is set to 0.
When the control drive waveform of μs was inserted by 10 ms before the drive waveform of the pulse width of 20 μs, the response time of the light transmittance was able to be reduced from about 20 ms to about 7 ms.

Further, in this embodiment, since the driving is performed by using the pulse width modulation, the threshold voltage is lower than that of the pulse voltage modulation of the first embodiment, and the characteristics are shifted to the lower voltage side as a whole. Therefore, control at a low voltage is possible, and power consumption can be reduced. Further, since the change in light transmittance is relatively gradual, the transmittance can be easily controlled by the voltage, and the gradation is improved.

Embodiment 3 FIG. 14 shows that the dimming device 23 according to the above embodiment is 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 are arranged along the optical axis indicated by the chain line. Corresponding third-group lens 53 and fourth-group lens (for focusing) 54, and CCD package 55 are arranged in this order at appropriate intervals, and the CCD package 55 has an infrared cut filter 55a, an optical low-pass filter system 55b. , A CCD image sensor 55c.

Between the second lens group 52 and the third lens group 53, the G lens according to the present invention described above is disposed near the third lens group 53.
A light control device 23 including the H cell 12 and the polarizing plate 11 is mounted on the same optical path for light amount adjustment (light amount stop). The fourth lens group 54 for focusing is disposed so as to be movable between the third lens group 53 and the CCD package 55 along the optical path by a linear motor 57, and the second lens group 52 for zooming is disposed in the optical path. Along the first lens group 51 and the light control device 23, it is movably disposed.

FIG. 15 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 lenses 52 and 3
Since the dimming device 23 according to the present invention is provided between the group lenses 53, the amount of light can be adjusted by applying an electric field as described above, the system can be reduced in size, and the size of the optical path can be substantially reduced. 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.

FIG. 16 is a block diagram of a driving circuit of the above-mentioned CCD camera. According to this, 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 CCD image sensor 55c is processed by the Y / C signal processing unit 61, and GH is output as luminance information (Y signal).
The drive pulse whose pulse voltage or pulse width is controlled as described above is generated in synchronism with the basic clock of the drive circuit unit 60 by the control signal from the control circuit unit which is fed back to the cell drive control circuit unit 62. Circuit section 63
From. The control circuit unit 62 and the pulse generation circuit unit 63 constitute a GH liquid crystal drive control unit 64 for controlling a pulse voltage or a pulse width.

Before the cell gap is determined, the light transmittance of the mounted light control device 23 when it is transparent and / or when it is shielded is detected by the CCD image sensor 55c.
The cell gap determination circuit 6 uses this detection information as luminance information.
Put in 5. As a result, the pulse voltage, the pulse number or the pulse width, and the pulse number corresponding to the automatically (self) recognized cell gap are generated from the pulse generation circuit 63.
It is controlled by the control circuit unit 62.

In a system different from this 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 unit 62 and the GH is output. In synchronization with a clock of a cell drive circuit unit (not shown), a drive pulse whose pulse voltage or pulse width is controlled can be obtained from the pulse generation circuit unit.

Although the present invention has been described with reference to the embodiments and examples, the above examples can be variously modified based on the technical idea of the present invention.

For example, the structure and material of the liquid crystal element and the light control device, the drive mechanism thereof, the drive circuit, and the configuration of the control circuit can be variously changed. The driving waveform can be any of a rectangular wave, a trapezoidal wave, a triangular wave, and a sine wave. The inclination of the liquid crystal molecules changes according to the potential difference between the two electrodes, and the light transmittance is controlled. The method for detecting the cell gap and the method for controlling the driving pulse based on the cell gap are not limited to those described above.

The light control device and the image pickup device of the present invention are suitable when the drive electrode of the liquid crystal optical element is formed at least over the entire area of the effective light transmitting portion. By controlling the drive pulse, batch control of the light transmittance over the entire effective optical path width can be performed with high accuracy.

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.

Further, 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 stuck to the iris blade 18, it may be stuck 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. 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.

Further, 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 also 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 diaphragm and the filter.

[0099]

According to the present invention, when the light transmittance of the liquid crystal element is slightly changed in halftone from the current light transmittance to the target light transmittance, the driving pulse corresponding to the target light transmittance is changed. Before application, a control drive pulse corresponding to complete light shielding (minimum light transmittance) or complete transparency (maximum light transmittance) is appropriately inserted in advance, and the control drive pulse is inserted according to the cell gap. Therefore, compared to the case where the driving pulse corresponding to the target light transmittance is simply applied in a step-like manner, the change in the orientation of the liquid crystal or the relaxation thereof rises more smoothly, and the response until the target light transmittance is reached is obtained. Time can be reduced significantly and appropriately.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of an improvement result of a halftone response speed according to an embodiment of the present invention.

FIG. 2 is a graph showing another example of the result of improving the response speed of the halftone.

FIG. 3 is a graph showing an example of drive pulse control for improving a halftone response speed.

FIG. 4 is a graph showing a change in transmittance depending on a cell gap in a transparent state and a light-shielded state.

FIG. 5 is a graph showing a relationship between a cell gap and an appropriate pulse insertion time.

FIG. 6 is a graph showing a change in response time due to a cell gap at the time of rising.

FIG. 7 is a graph showing a change in response time due to a cell gap at the time of falling.

FIG. 8 is a graph and a driving pulse waveform diagram showing a relationship between a light transmittance and a pulse width of a driving pulse of a light control device according to another embodiment of the present invention.

FIG. 9 is a schematic diagram showing the operation principle of an example of the light control device according to the present invention.

FIG. 10 is a graph showing the relationship between the light transmittance of the light control device and the drive applied voltage.

FIG. 11 is a schematic side view of the light control device using the liquid crystal optical element.

FIG. 12 is a front view of a mechanical iris of the light control device.

FIG. 13 is a schematic partial enlarged view showing an operation of a mechanical iris near an effective optical path of the light control device.

FIG. 14 is a schematic sectional view of a camera system incorporating the light control device.

FIG. 15 shows an algorithm of light transmittance control in the camera system.

FIG. 16 is a block diagram of a camera system including a drive circuit.

FIG. 17 is a schematic view showing the operation principle of a conventional light control device.

FIG. 18 is a graph showing the relationship between the light transmittance of the light control device and the drive applied voltage.

[Explanation of symbols]

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 blades, 20 ... Effective optical path (cell middle or center), 22 ... Opening, 23 ... Dimming device, 24 ... Cell peripheral, 31A, 31B ... Glass substrate, 32A, 32B ... Transparent (operating) electrode , 33A, 33B: alignment film, 34: liquid crystal material, 35: sealing material, 36: spherical spacer, 37: columnar spacer, 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 image sensor, 60
... CCD drive circuit section, 61 ... Y / C signal processing section, 62 ...
Control circuit section, 63 ... Pulse generation circuit section, 64 ... Pulse voltage or pulse width control section (GH liquid crystal drive control device), 6
5. Cell gap determination circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H088 EA37 EA38 GA02 GA13 HA06 JA06 KA02 MA10 2H093 NA01 NA53 NA56 NC52 NC65 ND06 ND32 ND60 NF06 NG07 5C006 AA15 AA16 AA17 AF45 AF46 AF51 BA19 BB11 BF39 EC21 FA05 FA20 FA20 FA20 EE29 FF07 JJ02 JJ04 JJ05 JJ06 JJ07 KK52

Claims (21)

[Claims] A liquid crystal element; a detecting means for detecting a cell gap of the liquid crystal element; and when changing a transmittance of light emitted from the liquid crystal element from a current light transmittance to a target light transmittance, A pulse control unit that inserts a control drive pulse corresponding to the minimum light transmittance or the maximum light transmittance in advance according to the cell gap before giving a drive pulse corresponding to at least the target light transmittance. Dimmer. 2. The light control device according to claim 1, wherein a light transmittance of the liquid crystal element when it is transparent and / or when light is shielded is detected in advance, and the cell gap is determined from the detected value. 3. The control drive pulse has at least a controlled pulse voltage and / or number of pulses.
The light control device according to claim 1. 4. The pulse voltage of the control drive pulse is:
4. The light control device according to claim 3, wherein the light control device has a pulse voltage that is equivalent to the minimum light transmittance or the maximum light transmittance, or a value between the pulse voltage and the pulse voltage that generates the target light transmittance. 5. 5. The light control device according to claim 1, wherein the control drive pulse has at least a controlled pulse width and / or pulse number. 6. The pulse width of the control drive pulse is equal to the pulse width that produces the minimum light transmittance or the maximum light transmittance, or is between this pulse width and the pulse width that produces the target light transmittance. The light control device according to claim 5, which is a value. 7. The light control device according to claim 1, wherein the liquid crystal element is a guest-host type liquid crystal element using negative liquid crystal as a host material and a dichroic dye as a guest material. 8. A method of driving a light control device including a liquid crystal element, wherein a cell gap of the liquid crystal element is detected in advance, and a transmittance of light emitted from the liquid crystal element is determined based on a current light transmittance and a target light transmittance. When changing to a rate, at least before giving a drive pulse corresponding to the target light transmittance, a control drive pulse corresponding to the minimum light transmittance or the maximum light transmittance is inserted in advance according to the cell gap, Driving method of light control device. 9. The method according to claim 8, wherein a light transmittance of the liquid crystal element when it is transparent and / or when light is shielded is detected in advance, and the cell gap is determined from the detected value. 10. The method according to claim 8, wherein the control drive pulse is controlled by at least a pulse voltage and / or the number of pulses. 11. The pulse voltage of the control drive pulse is equal to the pulse voltage that produces the minimum light transmittance or the maximum light transmittance, or is between this pulse voltage and the pulse voltage that produces the target light transmittance. The method of driving a light control device according to claim 10, wherein the value is a value. 12. The control driving pulse is controlled by at least a pulse width and / or the number of pulses.
The driving method of the light control device described in 1 above. 13. The pulse width of the control drive pulse is:
The driving of the light control device according to claim 12, wherein the pulse width that generates the minimum light transmittance or the maximum light transmittance is equal to or a value between this pulse width and the pulse width that generates the target light transmittance. Method. 14. A liquid crystal device comprising a negative liquid crystal as a host material and a dichroic dye as a guest material.
The method for driving a light control device according to claim 8, wherein a host-type liquid crystal element is used. 15. An image pickup device in which a light control device including a liquid crystal element is arranged in an optical path of an image pickup system, wherein the light control device detects a cell gap of the liquid crystal device; When changing the transmittance of light emitted from the liquid crystal element from the current light transmittance to the target light transmittance, at least before giving a drive pulse corresponding to the target light transmittance, the minimum light transmittance or the maximum light transmittance An imaging apparatus comprising: a pulse control unit that inserts a control drive pulse corresponding to a rate in advance in accordance with the cell gap. 16. The light control device according to claim 15, wherein a light transmittance of the liquid crystal element when it is transparent and / or when light is shielded is detected in advance, and the cell gap is determined from the detected value. 17. The imaging device according to claim 15, wherein the control drive pulse has at least a controlled pulse voltage and / or pulse number. 18. The pulse voltage of the control drive pulse is equal to the pulse voltage that produces the minimum light transmittance or the maximum light transmittance, or is between this pulse voltage and the pulse voltage that produces the target light transmittance. The imaging device according to claim 17, which is a value. 19. The control drive pulse has at least a controlled pulse width and / or number of pulses.
The imaging device according to claim 15. 20. A pulse width of the control drive pulse,
20. The imaging apparatus according to claim 19, wherein the pulse width is equal to the pulse width that causes the minimum light transmittance or the maximum light transmittance, or a value between the pulse width and the pulse width that causes the target light transmittance. 21. The imaging device according to claim 15, wherein the liquid crystal element is a guest-host type liquid crystal element using negative liquid crystal as a host material and a dichroic dye as a guest material.