JPH0715555B2 - Automatic exposure adjustment device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an automatic exposure adjustment device, and more particularly to an automatic exposure adjustment device that changes an exposure amount by a liquid crystal shutter provided on an exposure optical path.

<Prior Art> Conventionally, in an image reading apparatus, an exposure amount for exposing a document is set by changing a voltage applied to a light source. However, when a fluorescent lamp is used as the light source, there is a problem that the exposure amount cannot be changed even if the applied voltage is changed.

In view of these problems, a copying machine has been invented as disclosed in Japanese Patent Laid-Open No. 57-78058, which performs exposure adjustment by using an exposure illuminance correcting liquid crystal plate. The exposure illuminance correction liquid crystal plate used in this copying machine has a plurality of illuminance control segments juxtaposed in the longitudinal direction, and these illuminance control segments can be controlled independently of each other. Alternatively, the exposure amount of the original document by the light source can be adjusted in whole or in part by changing the reflection ratio. However, in the copying machine having this configuration, the light transmission ratio of each illuminance control segment of the exposure illuminance correction liquid crystal plate is adjusted in advance so that the charge distribution on the photoconductor is made uniform according to the type of light source and the type of optical system. Alternatively, the reflection ratio is set, and only the optimum exposure adjustment can be performed for each copying machine, and the density of characters, lines, etc. on the original document during the scanning exposure operation of the original document, or the original paper sheet. The exposure cannot be automatically adjusted according to the lightness and darkness of itself, and only the copying operation with the preset exposure amount can be performed by the manual operation. Therefore, there is a problem in that it is not possible to obtain an optimum copy image for each original.

<Purpose> The present invention has been made in view of the above problems,
An object of the present invention is to provide an automatic exposure adjustment device capable of performing optimum exposure adjustment corresponding to the light and shade of each part of a document while performing an image reading operation.

<Structure> The automatic exposure adjusting device of the present invention for achieving the above object has a structure in which an original is operated and exposed by light from a light source, and an electrostatic latent image is formed on a photosensitive member by reflected light from the original. A device that is applied to an image reading device and adjusts the exposure amount when the above-mentioned document is exposed. The device is provided in an exposure optical path from the light source to the photoconductor and has a large number of segments in the length direction and the width direction. And a drive circuit that drives each segment of the liquid crystal shutter to change the shutter shape, and a sensor that detects the document density near the exposure position by detecting the reflected light from the document. By controlling the drive circuit based on the output of the sensor in the process of scanning and exposing the document by the light from the light source, the exposure amount is variably controlled according to the shading of each part of the document. It is characterized in that it comprises a control means.

<Operation> According to the above configuration, the sensor detects the document density near the exposure position in the process of scanning and exposing the document. By controlling the drive circuit based on the sensor output, the shutter shape of the liquid crystal shutter is controlled according to the shading of each part of the document. As a result, in the process of scanning and exposing the document, the exposure amount is variably controlled according to the shading of each part of the document.

<Example> Hereinafter, detailed description will be given with reference to the accompanying drawings illustrating an example.

FIG. 1 is a schematic view showing the internal mechanism of a copying machine equipped with the automatic exposure adjusting device of the present invention.

(1) is a main body of a copying machine, and an original placing table (11) having an original pressing plate is provided on the upper surface, and two cassettes (12) and (13) for feeding sheets are removed from the lower right side surface. The tray (14) is mounted so that it can be mounted, and a tray (14) for supporting the copy paper (P) that has completed copying is provided at a predetermined position on the left side surface. By providing the partition plate (15) at a predetermined internal position, the upper chamber (16) and the lower chamber (17) are formed, and the reciprocable optical system (2) is provided in the upper chamber (16). A copy processing section (4) and a copy paper transport section (3) are provided in the lower chamber (17).

The optical system (2) comprises a light source (21), a first reflecting mirror (22) having a curved reflecting surface, a second reflecting mirror (23), a third reflecting mirror (24) and a fourth reflecting mirror (25). , Lens (26), and fifth
It consists of a reflector (27), of which the light source (21)
The first reflecting mirror (22) reciprocates once for each copying operation, whereby the original document on the original document table (11) can be sequentially scanned and exposed, and the reflected light from the original document is reflected by the light source (21). ) And the second reflecting mirror (23) to the fourth reflecting mirror (25), the lens (26), and the fifth reflecting mirror (23) that follow the movement of the first reflecting mirror (22).
The surface of a photosensitive drum (41) described later is irradiated with light through a reflecting mirror (27) and a slit (28) formed at a predetermined position of the partition plate (15).

The copy paper transport unit (3) takes out one copy paper (P) from each of the cassettes (12) and (13) and sends it to the registration roller (3).
3) Paper feed rollers (31) and (32) for feeding to (34), and a conveyance roller (35) for feeding the copy paper (P) from the registration roller (34) to the copy processing section (4). A belt (36) for conveying the copy paper (P) separated from the copy processing section (4), a heat fixing roller (37) for heating and fixing the toner image on the copy paper (P), and heating and fixing Later copy paper (P)
And a carry-out roller (38) for sending the sheet toward the tray (14), and by selectively driving the paper feed rollers (31) (32), the desired cassette (12) or (13) is formed.
One copy sheet (P) can be delivered.

The copy processing section (4) is provided with a photosensitive drum (41) which is provided substantially in the center of the lower chamber (17) and rotates in one direction (direction of arrow A1 in the figure) for each copy operation. Along with the photoconductor drum (41), a charger (42), a developing device (43), a transfer charger (44), and a peeling charger (4)
5) and a cleaner (46) are provided in this order. Therefore, the charging charger (42) causes the photoconductor drum (4
After uniformly charging the photoreceptor layer in 1), slit (28)
An electrostatic latent image corresponding to the original is formed by the light radiated through the developing device (43), toner is adsorbed by the developing device (43) to form a toner image, and then the transfer charger (44) sends it from the conveying roller (35). The toner image is transferred onto the supplied copy paper (P), the copy paper (P) is separated from the photosensitive drum (41) by the separation charger (45), and finally the cleaner (4
The toner remaining on the photoconductor drum (41) is collected by 6).

FIG. 2 is a block diagram showing an automatic exposure adjusting device of the present invention, in which a liquid crystal shutter (55) is provided at the light irradiation part of the light source (21).
Is provided, and the light transmitted through the half mirror (25 ') (identified as corresponding to the fourth reflecting mirror (25) in FIG. 1) among the reflected light from the original (18) is a lens. Each segment (56) of the liquid crystal shutter (55) is focused by (51) and received by the CCD area sensor (52), and the output signal of the CCD area sensor (52) is passed through the control circuit (53) and the drive circuit (54). A feedback control system is configured by applying the voltage to the light source so that the exposure adjustment corresponding to the type of the document (18) can be performed.

The light reflected by the half mirror (25 ') is focused by the lens (26) and received by the CCD line sensor (61), and the output signal of the CCD line sensor (61) is converted by the binarization circuit (62). It can be binarized and applied to the memory (63).

FIG. 3 shows a segment (56) of a liquid crystal shutter (55), which has a cell (5) having transparent electrodes (57) (57) on both sides.
Liquid crystal (59) is enclosed in 8) and transparent electrodes (57) (57)
A segment (56) is composed of a liquid crystal (59) that changes from a transparent state to a reflective state by applying an operating voltage between them, or vice versa. As shown in the figure, the liquid crystal shutter (55) is configured by arranging a plurality of dot matrix shapes in the longitudinal direction and the width direction. However, the cell (5
8) is formed into one and many pairs of transparent electrodes (5
7) It is also possible to form a liquid crystal shutter by forming (57) (see FIG. 5).

Therefore, by driving the segments (56) independently of each other through the control circuit (53) and the drive circuit (54), the liquid crystal shutter (55) corresponds to the output signal of each part of the CCD area sensor (52). It is possible to obtain the optimum exposure state corresponding to the light and shade of the document (18) by controlling the light-shear region and the light-transmissive region of the shape.

More specifically, the CCD line sensor (61) is
It receives only the reflected light corresponding to the original area that is extremely narrow in the scanning exposure direction of 8). For example, if a black line is drawn over the main scanning line of the original (18), the CCD line is drawn. The sensor (61) outputs a signal indicating that the whole is black, and if a white line is drawn over the main scanning line of the document (18), the CCD line sensor (61) is a signal indicating that the whole is white. Is output. CCD area sensor (5
2) receives reflected light corresponding to a wider original area than the CCD line sensor (61),
For example, even if a black line is drawn on the entire area of a specific main scanning line of the document (18), if there is a white area around the black line, a signal corresponding to the average illuminance as a whole is output. In other words, the CCD area sensor (52) detects the reflected light from the document to detect the document density near the exposure position.

Therefore, by receiving the reflected light from a considerably wide area of the document (18) and driving the liquid crystal shutter (55),
The original exposure amount can always be kept at an optimum value, and the reflected light from a specific narrow range is received and binarized.
It is possible to develop the electrostatic latent image in an optimum state.

However, by providing the CCD line sensor at a position deviated from the image forming position of the lens (51), the same operation as the CCD area sensor can be performed.

FIG. 6 is a block diagram showing an exposure adjustment device that corrects the light source. The liquid crystal shutter (5
5) is provided, and the reflected light from the reference plate (19) of a predetermined color such as white formed at the position preceding the scanning exposure of the document (18) is reflected by the reflecting mirror (25 ″) (first It is grasped as corresponding to the fourth reflecting mirror (25) in the figure) and led to the CCD sensor (64) through the lens (26), and C
The output signal of the CD sensor (64) is applied to each segment (56) of the liquid crystal shutter (55) through the control circuit (53 ') and the drive circuit (54'). Further, the output signal of the CCD sensor (64) is also applied to the binarization circuit (62), and the binarized signal is applied to the memory (63) or the like.

More specifically, in this embodiment, the manuscript (18)
The reference plate (19) is exposed prior to the scanning exposure of, the reflected light is detected by the CCD sensor (64), and a feedback signal is sent to the liquid crystal shutter (55) through the control circuit (53 ′) and the drive circuit (54 ′). Since it is applied to each segment (56) of the document, the light source (2
Not only is it possible to correct the illuminance pattern in the length direction (shading correction) for 1), but it is also possible to effectively compensate for changes over time, environmental changes such as temperature, and changes in the voltage applied to the light source. In addition, if the constant of the control circuit (53) is changed by an external operation, it is possible to make a part or the whole area of the copied image bright and dark. Furthermore, a fluorescent lamp is used as the light source (21) to change the applied voltage. Even when only a constant illuminance is obtained, the liquid crystal shutter (55) can perform shading correction and the like.

Therefore, by receiving the reflected light from a considerably wide area of the document (18) and driving the liquid crystal shutter (55),
The original exposure amount can always be kept at an optimum value, and the reflected light from a specific narrow range is received and binarized.
It is possible to develop the electrostatic latent image in an optimum state.

In particular, the exposure adjustment apparatus shown in FIG. 6 performs shading correction, temporal change of the light source (21), environmental changes such as temperature, and applied voltage change during the prescan, and then the exposure adjustment apparatus shown in FIG. Thus, if the exposure amount is adjusted in accordance with the lightness and darkness of each part of the document during the operation exposure operation of the document, an optimum copy image can be obtained, which is the most preferable implementation.

The present invention is not limited to the above-described embodiments, and for example, instead of using a liquid crystal shutter having a structure for changing the light transmission characteristics, a liquid crystal shutter having a structure for changing the light reflection characteristics can be used. , A photodiode array or the like can be used as the sensor instead of the CCD sensor, and can be applied to various image reading devices such as a facsimile in addition to the copying machine, and the scope of the invention is not changed. It is possible to make various design changes within.

<Effect> As described above, according to the present invention, in the process of scanning and exposing a document, the sensor detects the document density near the exposure position,
The shutter shape of the liquid crystal shutter is controlled based on the output of this sensor. As a result, in the process of scanning and exposing the document, the exposure amount is variably controlled according to the density of each part of the document. As a result, the optimum exposure amount can be set in each part of the document, and the optimum image reading operation can be realized.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing the internal mechanism of a copying machine, FIG. 2 is a block diagram showing an automatic exposure adjusting device, FIG. 3 is a vertical sectional view of a liquid crystal shutter, FIG. 4 is a front view of the same, and FIG. Is a longitudinal sectional view showing another embodiment of the liquid crystal shutter, and FIG. 6 is a block diagram showing an exposure adjusting device. (18) ... manuscript, (21) ... light source, (52) ... CCD area sensor as sensor, (54) ... drive circuit, (55)
…… LCD shutter, (56) …… Segment.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-58-153958 (JP, A) JP-A-54-47648 (JP, A) JP-A-57-157272 (JP, A)

Claims (3)

[Claims] 1. An exposure amount when an original is exposed by scanning an original with light from a light source and forming an electrostatic latent image on a photoconductor by reflected light from the original. A liquid crystal shutter having a large number of segments arranged in parallel in the length direction and the width direction, which is interposed in the exposure optical path from the light source to the photoconductor, and drives each segment of the liquid crystal shutter. A drive circuit for changing the shape of the shutter, a sensor for detecting the density of the document near the exposure position by detecting the reflected light from the document, and the sensor for scanning the document with the light from the light source. An automatic exposure adjusting device, comprising: a control unit that variably controls the exposure amount according to the shading of each portion of the document by controlling the drive circuit based on the output of the above. 2. The liquid crystal shutter according to claim 1, wherein the segments of the liquid crystal shutter are arranged in a dot matrix.
The automatic exposure adjustment device according to the item. 3. The automatic exposure adjustment apparatus according to claim 1 or 2, wherein the sensor is a CCD sensor and outputs a signal corresponding to each segment of the liquid crystal shutter.