JPH04124613A - Liquid crystal shutter - Google Patents

Abstract

PURPOSE:To offer the liquid crystal shutter which can switch a normally white mode and a normal black mode by moving at least one of two polarizing plates to a 1st position where their polarizing directions are parallel and a 2nd position where the polarizing directions cross each other at right angles. CONSTITUTION:The liquid crystal shutter 7 is constituted by sandwiching a TN type liquid crystal optical modulating element 31 between the two polarizing plates 32 and 33, one polarizing plate 32 and TN type liquid crystal optical modulating element 31 are arranged nearly in the center of a liquid crystal printer 1, and the other polarizing plate 33 is supported rotatably by a couple of holders 34 and 35 right below it. The latter polarizing plate 33 is formed in a disk shape and its outer peripheral part engages a gear 36a fitted onto the driving shaft of a driving motor 36. When an image contains much bright data, the liquid crystal shutter 7 is switched to the normal white mode and when the image contains much dark data, the liquid crystal shutter 7 is switched to the normally black mode. Consequently, a print result of high picture quality is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal shutter that switches between light transmission and light blocking.

[Prior Art] Conventionally, this type of liquid crystal shutter uses, for example, a twisted nematic type liquid crystal light modulation element (hereinafter referred to as a TN type liquid crystal light modulation element). This TN type liquid crystal light modulation element is
When the liquid crystal is sandwiched between two transparent electrode substrates (outside) and two alignment films with uniform linear grooves (inside), and no voltage is applied between the transparent electrodes, the liquid crystal molecules takes a specific alignment state according to the force regulated by the grooves of the alignment film, but since the groove directions of the two alignment films mentioned above are shifted by 90 degrees from each other, the liquid crystal molecules have a twisted structure in the long axis direction of the molecules. The orientation of the liquid crystal molecules is twisted by 90 degrees in the re-alignment film. As shown in FIG. 4, the liquid crystal shutter 60 is constructed by sandwiching the TN type liquid crystal light modulating element 61 in this state between two polarizing plates 62 and 63 whose polarization directions are perpendicular to each other.

A light beam 64 is transmitted through one polarizing plate 62 of this liquid crystal shutter 60.
, the light ray 64 becomes linearly polarized by the first polarizing plate 62. While this linearly polarized light travels through the liquid crystal,
Due to the birefringence of liquid crystal molecules and the above-mentioned 90 degree twisted alignment structure, the polarization direction becomes linearly polarized light rotated by 90 degrees. As a result, as shown in FIG. 4(a), the polarization direction of the linearly polarized light matches the polarization direction of the other polarizing plate 63, and the linearly polarized light is emitted as is. However, when a voltage is applied between the transparent electrodes, the liquid crystal molecules are forcibly aligned in the direction of the electric field, so the above-mentioned 90 degree twisted alignment structure is not formed, and as shown in Figure 4(b), the incident linearly polarized light is The linearly polarized light reaches another polarizing plate without rotation of the polarization direction, and the polarization direction of the linearly polarized light and the polarization direction of the other polarizing plate 63 are perpendicular to each other at the time of output, and the light is blocked. The liquid crystal shutter 60 that blocks incident light by applying a voltage in this manner is called a normally white mode liquid crystal shutter.

Further, as shown in FIG. 5, a TN type liquid crystal light modulation element 61
A liquid crystal shutter 65 is also known in which the light is sandwiched between two polarizing plates 62 and 66 whose polarization directions are parallel. In this liquid crystal shutter 65, as shown in FIG. 5(a), when no voltage is applied, the polarization direction of the incident light polarized by the liquid crystal and the polarization direction of the target polarizing plate 66 are perpendicular to each other. , the incident light is blocked. However, when the voltage is applied, the fifth
As shown in Figure (b), the incident light reaches the other polarizing plate 66 without being polarized, the polarization direction of the incident light matches the polarization direction of the other polarizing plate 66, and is transmitted. The liquid crystal shutter 65, which transmits incident light by applying a voltage, is normally
It is called a black mode liquid crystal shutter. In addition, in FIGS. 4 and 5, the polarization directions of the polarizing plates 62, 63, and 66 are shown by thin lines so that the directions of polarization can be easily understood.

[Problems to be Solved by the Invention] However, since conventional liquid crystal shutters are fixed to either normally white mode or normally black mode, there is a problem that it is not possible to obtain both modes with one liquid crystal shutter. There is. Therefore, in an image forming apparatus using this liquid crystal shutter, if a normally black mode liquid crystal shutter is used, if there is a lot of dark data in the image data, the amount of light transmitted will be reduced and the formed image will be On the other hand, if you use a normally white mode liquid crystal shutter, the amount of light transmitted will increase if the image data contains a lot of bright data, and the resulting image will become too bright overall. .

The present invention has been made to solve the above-mentioned problems, and has two positions: a first position where the polarization directions of the two polarizing plates constituting the liquid crystal shutter are parallel, and a second position where the polarization directions are orthogonal to each other. Another object of the present invention is to provide a liquid crystal shutter that can be switched between normally white mode and normally black mode by moving at least one of both polarizing plates.

[Means for Solving the Problems] In order to achieve this object, the liquid crystal shutter of the present invention has the following features:
A moving means is provided for moving at least one of the polarizing plates to a first position where the polarization directions of the two polarizing plates are parallel to each other and a second position where the polarization directions are orthogonal to each other.

[Function] The liquid crystal shutter having the above configuration becomes normally black mode when one of the at least two polarizing plates is moved by the moving means to the first position where the polarization directions of both polarization plates are parallel, and the polarization direction is changed. When they are moved to second positions perpendicular to each other, the normally white mode is entered.

[Example] Hereinafter, an example embodying the present invention will be described with reference to FIGS. 1 to 3.

FIG. 2 shows a schematic configuration of a liquid crystal printer 1 using the liquid crystal shutter 7 of this embodiment. This liquid crystal printer 1 uses a photosensitive recording medium consisting of a photosensitive pressure sensitive paper 11 (hereinafter referred to as microcapsule paper) and a color developing paper 14. The surface of the support of the microcapsule paper 11 is coated with microcapsules, and the microcapsules contain a dye precursor that reacts with a color developer. A color developer is coated on the surface of the support of the color developer paper 14 and develops color by reacting with a dye precursor.
It is described in SP4399209, etc., and is omitted here.

A halogen lamp 3 as an exposure light source is disposed at the center above the liquid crystal printer 1, and a beam flap 2 is disposed above the halogen lamp 3. Further, a condenser lens 4 is arranged below the halogen lamp 3, and an infrared cut filter 5 is further arranged below it. Below the infrared cut filter 5, there is a red filter 6R and a green filter 6.
A filter unit 6 including a blue filter 6B is movably arranged, and below it a liquid crystal shutter 7 (hereinafter referred to as LCD) and an imaging lens 8 are arranged.

A light-shielding cartridge 9 is disposed in the lower part of the interior of the liquid crystal printer 1, and an unexposed microcapsule paper 11 is wound around a cartridge shaft 10 inside the cartridge 9. The microcapsule paper 11 stands still at the position where the image is formed by the imaging lens 5d on the right side of the cartridge 9, and is exposed in this state to form a latent image. Microcapsule paper 1
1 is superimposed on a developer paper 14 (described later), passes between pressure rollers 12a and 12b arranged to the right of the image forming position, and is wound up on a winding shaft 13.

A plurality of sheets of color developer paper 14 are stacked above the winding shaft 13, a half-moon roller 15 is provided above the color developer paper 14, and a paper feed roller 16 and a paper feed guide (
(not shown) are provided. Further, a heat fixing device 1 is provided below the developer paper 14 and to the right of the pressure rollers 12a and 12b.
A heater 18 and a conveyor belt 1 are installed inside the heater 18.
9 are arranged.

Next, the structure of the liquid crystal shutter 7 will be explained with reference to FIG.

As shown in FIG. 1, the liquid crystal shutter 7 is sandwiched between a TN type liquid crystal light modulation element 31 and two polarizing plates 32 and 33. One of the polarizing plates 32 and the TN type liquid crystal light modulation element 31 is As shown in FIG. 1, the polarizing plate 33 is disposed approximately at the center of the liquid crystal printer 1, and the other polarizing plate 33 is rotatably supported by a pair of holders 34 and 35 directly below it. The other polarizing plate 33 is formed into a disk shape, and its outer circumferential portion engages with a gear 36a fitted onto the drive shaft of the drive motor 36. Then, the drive motor 36 moves the polarizing plate 33 to a first position where the polarizing directions of the polarizing plate 32 and the polarizing plate 33 are parallel, and a second position where the polarizing directions of the polarizing plate 32 and the polarizing plate 33 are perpendicular. is rotated.

The liquid crystal shutter 7 is in a normally black mode when the polarizing plate 33 is placed in the first position, and is in a normally white mode when the polarizing plate 33 is placed in the second position. This drive motor 36 is a Norms motor and constitutes a moving means. Further, a strut hole 33a is formed protruding from a part of the outer peripheral portion of the other polarizing plate 33,
When this strike 7/<33a engages with the holder 34, the polarization directions of the polarizing plates 32 and 33 become parallel.

It should be noted that the polarization directions of both polarizing plates 32 and 33 are shown by thin lines to make it easier to understand. Further, since the TN type liquid crystal light modulation element 31 is the same as the conventional one, its explanation will be omitted.

The transparent electrode substrate of the TN type liquid crystal light modulation element 31 is connected to the liquid crystal shutter control section 23.

This liquid crystal shutter control section 23 is connected to the RAM 22,
An image is displayed on a liquid crystal display screen based on the image data stored in the RAM 22. Incidentally, the liquid crystal shutter control section 23 is composed of a microcomputer 1. R
The AM 22 is connected to the interface 20 via the A/D controller 21, and stores the video signal input to the liquid crystal printer 1 or image data converted into a digital signal.

The operation of the liquid crystal printer 1 configured as above will be explained with reference to FIG. 3.

When the power is turned on, the memory content of the RAM 22 is erased as an initial setting, and the drive motor 36 is moved to the polarizing plate 33.
Rotate clockwise in Figure 1.

Due to this rotation, the stopper 33a comes into contact with the holder 34,
Thereafter, the drive motor 36 loses synchronization and stops rotating.

In this state, the polarizing plate 33 is placed at a first position where its polarizing direction is parallel to the polarizing direction of the polarizing plate 32, and the liquid crystal shutter 7 is in the normally black mode. Along with that,
The internal flag of the liquid crystal shutter control section 23 is set to "0".

Here, when a print start key (not shown) is pressed, the video signal input from the interface 20 is converted into a digital signal by the A/D converter, and the image data for red (hereinafter referred to as R image data) is converted into a digital signal. ,
The image data for green (hereinafter referred to as 0 image data) and the image data for blue (hereinafter referred to as 8 image data) are divided and stored in the RAM.

In this state, the mode switching routine shown in FIG. 3 is executed. Note that 5i (i is a natural number) indicates each step of the mode switching routine. The brightness of the entire image is calculated from the logical product of each image data (S1), and the calculated value is compared with an intermediate value stored in advance in the liquid crystal shutter control section 23 (S2). If the calculated value is larger than the intermediate value (S2: Y
ES), the entire image is determined to be bright, and it is determined whether the internal flag of the liquid crystal shutter control unit 23 is rOJ (S
3). If the power has just been turned on, the internal flag is rOJ (S3: YES), so the drive motor 36 rotates the polarizing plate 33 in the counterclockwise direction in FIG. It is placed at a second position perpendicular to the direction (S4).

That is, the liquid crystal shutter 7 is switched to normally white mode. Then, the internal flag is changed to "1" and this routine ends.

On the other hand, if the mode immediately before this routine is executed is the normally white mode, the internal flag is "1" (S3: No), so the mode will not change.
This routine ends.

If the calculated value is equal to or less than the intermediate value in S2 (S2: No), it is determined that the entire image is dark, and it is determined whether the internal flag is "1" (S6). If the power has just been turned on, the internal flag is "0" (S6: NO), so the liquid crystal shutter 7 is already in the normal state.
Since the mode has been switched to black mode, this routine ends without switching the mode. On the other hand, if the mode immediately before this routine is executed is the normally white mode, since the internal flag is "1" (S6: YES), the drive motor 36 drives the polarizing plate 3.
3 is rotated clockwise in FIG. 1 and placed in a first position where its polarization direction is parallel to the polarization direction of the polarizing plate 32 (S7). That is, the liquid crystal shutter 7 is switched to the normally black mode. Then, the internal flag is r
It is changed to OJ (S8), and this routine ends.

When the above mode switching routine is completed, the liquid crystal shutter control section 23 reads the R image data from the RAM 22,
An image corresponding to the data is displayed on a liquid crystal display screen.

Next, the halogen lamp 3 is turned on, and the light is efficiently condensed by the deflector 2 and the condensing lens 4 into parallel light, which is then irradiated onto the liquid crystal shutter 7 via the infrared cut filter 5 and the red filter 6R. A red image to be recorded is formed on the stationary microcapsule paper 11 by the imaging lens 8 and exposed.

When the red exposure is completed, the halogen lamp 3 is turned off, the red filter 6R is replaced with the green filter 6G, and the liquid crystal shutter control unit 23 reads six image data from the RAM 22, and displays an image according to the data on the liquid crystal shutter 7. let Then, exposure is started in the same manner as above. Thereafter, the green filter 6G is replaced with the blue filter 6B, and the liquid crystal shutter control section 23 reads out eight image data from the RAM 22, and displays an image corresponding to the data on the liquid crystal screen. Then, exposure is started in the same manner as above. When the exposure of each image data is completed, a color latent image is formed on the microcapsule paper 11. Next, the microcapsule paper 11 is sent toward the pressure rollers 12a and 12b by the driving force of the take-up roller 13. On the other hand, developer paper 1
4 is fed one by one by a half-moon roller 15, passes through a paper feed guide, and is transferred to pressure rollers 12a and L2 by a paper feed roller 16.
Sent to b. The pressure roller 1 is moved in a state where the exposed surface of the microcapsule paper 11 and the color developer coated surface of the color developer paper 14 face each other.
2a and 12b, and the image is transferred to the developer paper 14. The color developing paper 14 is further conveyed by a conveyor belt 19, and color development is promoted by a heat fixing device 17 having a heater 18, and the color is outputted as an image.

As described in detail above, the liquid crystal printer 1 of this embodiment switches the liquid crystal shutter 7 to the normally white mode or normally black mode depending on the brightness of the entire input image, that is, the liquid crystal printer 1 switches the liquid crystal shutter 7 to the normally white mode or normally black mode depending on the brightness of the entire input image. When there is a lot of bright data, the liquid crystal shutter 7 is switched to normally white mode, and when there is a lot of dark data, the liquid crystal shutter 7 is switched to normally black mode, so that high quality printing results can be obtained.

The present invention is not limited to the one embodiment described above, and various changes can be made without departing from the spirit thereof. For example, although a halogen lamp is used as the light source in this embodiment, a metal halide lamp may also be used.

Furthermore, the order in which the color filters are replaced is not limited to R-G-B.

[Effects of the Invention] As is clear from the above detailed description, according to the present invention, the polarization directions of the two polarizing plates are at the first position where they are parallel to each other, and at the second position where the polarization directions are orthogonal to each other. By moving at least one of both polarizing plates, it is possible to provide a liquid crystal shutter that can be switched between a normally white mode and a normally black mode.

[Brief explanation of drawings]

1 to 3 show an embodiment embodying the present invention, FIG. 1(a) is a perspective view showing a liquid crystal shutter as an embodiment, and FIG. 1(b) is an exploded view of the liquid crystal shutter. Perspective view, 2nd
The figure is a schematic configuration diagram showing the configuration of a liquid crystal printer using the liquid crystal shutter, and FIG. 3 is a flowchart showing mode switching of the liquid crystal shutter. FIG. 4 is a diagram showing the optical path when the liquid crystal shutter is set in the normally black mode, and FIG. 5 is a diagram showing the optical path when the liquid crystal shutter is set in the normally white mode. In the figure, 7 is a liquid crystal shutter, 31 is a liquid crystal light conversion element, and 32
．． 33 is a polarizing plate, and 36 is a drive motor (moving means).

Claims (1)

[Scope of Claims] A liquid crystal shutter in which a liquid crystal light modulating element is sandwiched between one or two polarizing plates, comprising: a first position where the polarization directions of both the polarizing plates are parallel, and a second position where the polarization directions are orthogonal to each other. A liquid crystal shutter comprising a moving means for moving at least one of the polarizing plates to two positions.