JPH0219954B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a slit exposure type variable magnification copying machine that changes the magnification of projecting an original image onto a photoreceptor by moving a lens.

Generally, in a full-size copying machine, when adjusting the amount of exposure to the photoconductor depending on the type of document, variations in the light source, or changes in the sensitivity of the photoconductor, the light amount is changed by adjusting the voltage applied to the document illumination lamp. Measures such as changing the aperture amount in the lens or changing the aperture width of an exposure slit provided near the original or the photoreceptor have been taken.

In a full-size copying machine, in addition to adjusting the exposure amount as in the above-mentioned full-size copying machine, the amount of light irradiated to the photoreceptor per unit area changes greatly by changing the magnification.
In order to obtain an image with a density that the operator has set in advance according to his/her preference before changing the magnification, the exposure amount must be adjusted significantly each time the magnification is changed.

Conventionally, this type of adjustment device uses a lens diaphragm to change the aperture amount for each magnification conversion, changes the aperture width of an exposure slit to adjust the amount of light irradiated to the photoreceptor, or adjusts the amount of light irradiated to the photoreceptor according to the magnification conversion. Measures have been taken to change the amount of light by adjusting the voltage applied to the document illumination lamp. However, in the method of changing the lens diaphragm or the exposure slit aperture width, the operator must be able to change it manually and also automatically change the lens diaphragm etc. according to the selected magnification. However, since the driving means and their control mechanism are complicated, and the exposure amount adjustment is approximate, there is a problem in terms of accuracy. On the other hand, in the method of changing the light intensity of the illumination lamp, the illuminance of the photoreceptor is not a linear function of the magnification ratio, as will be explained later.
It is extremely difficult to set the lamp light intensity to correspond to a preset magnification ratio, and as it becomes an approximation, there is a problem in terms of accuracy as described above.
Moreover, the color temperature changes, which is not preferable. In particular, in the case of enlarged and variable magnification copying, the illuminance of the photoreceptor is reduced compared to full-size copying, so in this case the amount of lamp light must be increased, but from the perspective of normal copying machine use, it is difficult to make full-size copies. From the standpoint of energy saving, it is undesirable to prepare a high illumination lamp in preparation for enlarged and variable magnification copying, which is less frequent than the conventional method.

The present invention has been made in view of the above-mentioned conventional problems, and is particularly applicable to a slit exposure variable magnification copying machine that can select enlarged copying in addition to full-size copying. It is an object of the present invention to provide a slit exposure type variable magnification copying machine capable of stably and accurately adjusting the amount of exposure to a photoreceptor without using an illumination lamp.

That is, the present invention includes a scanning means for scanning an original, and an optical system having a lens and a slit disposed near the photoreceptor, which projects an image of the original scanned by the scanning means onto a photoreceptor. In a slit exposure type variable magnification copying machine that can select between copying at a first magnification and copying at a second magnification larger than the first magnification by moving the lens, When copying, the photoreceptor is moved at a slower speed than when copying at the first magnification, and the scanning means is also moved at a slower speed than when copying at the first magnification. The speed V _(n) and the moving speed U _(n) of the scanning means are V _(n) = 4/(1+m) ²・V ₍₁₎ U _(n) = 4/m (1+m) ²・V ₍₁₎ (However, V ₍₁₎ is the circumferential speed of the photoreceptor when copying at the same magnification.) This is a slit exposure type variable magnification copying machine that satisfies the following.

Further, the present invention includes a scanning means for scanning an original, a lens for projecting an image of the original scanned by the scanning means onto a photoreceptor, and a slit disposed near the original placing means for placing the original. A slit exposure variable magnification copying machine is equipped with an optical system, and can select between copying at a first magnification and copying at a second magnification larger than the first magnification by moving the lens. When copying at the second magnification, the photoreceptor is moved at a slower speed than when copying at the first magnification, and the scanning means is also moved at a slower speed than when copying at the first magnification. The circumferential speed of the photoreceptor V _(n) and the moving speed of the scanning means U _(n) when m is V _(n) = 4 m / (1 + m) ²・V ₍₁₎ U _(n) = 4 / (1 + m) This is a slit exposure type variable magnification copying machine that satisfies the following: ^2.V ₍₁₎ (where V ₍₁₎ is the circumferential speed of the photoreceptor when copying at the same magnification).

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a transparent document table, on which a document 0 is placed. Lighting lamp 2 and 1st
The mirror 3 is attached to one support member,
The first mirror 3 and the second mirror 4 move in the direction of the arrow at a speed ratio of 1:1/2 to optically scan the document 0 from the bottom surface. The original image light is transmitted through the imaging lens 5 and the third lens.
The photoreceptor 10 provided on the outer peripheral surface of a drum 9 rotating in the direction of the arrow is exposed through the four mirrors 6 and 7 and the exposure slit 8. Above exposure slit 8
is arranged near the photoreceptor 10, and its aperture width is always constant even if the copying magnification changes. However, in order to obtain the image density desired by the operator, the aperture width may be adjusted at any time using a density adjustment dial or the like. However, this aperture width cannot be changed by changing the magnification. Incidentally, this also applies to the slit 8 in FIG. Note that various image forming process elements are provided around the photoreceptor, as will be described later.

In the above optical system, the imaging lens 5 and the third,
Variable-magnification copying is performed by moving the four mirrors 6 and 7 from the position shown by the solid line, where the same-sized copy is performed, to the position shown by the chain line. In this case, the third and fourth mirrors 6 and 7
is attached to one support member to reduce the number of movable members and facilitate optical adjustment.

The imaging lens 5 is located at the position 5a, and the third,
When the fourth mirrors 6 and 7 are at positions 6a and 7a, respectively, the imaging lens 5 is at position 5b during reduction/magnification copying, and the third and fourth mirrors 6 and 7 are at positions 6b and 7b, respectively. In some cases, this occurs when enlarging and changing the size of the copy. If the reduction ratio is the reciprocal of the enlargement ratio, each lens position 5a, 5b is at exactly the same distance from the lens position at the same magnification, and is at a symmetrical position with the imaging lens 5 as a boundary. The same applies to each of the mirrors 6 and 7.

In the above optical system, even if the copying magnification changes, the light intensity of the illumination lamp and the illumination angle of the lamp relative to the document do not change, so the illuminance on the surface of the document remains constant. Further, the opening amount of the exposure slit 8 is always constant, and the aperture amount of the imaging lens 5, which is adjusted by the operator to obtain the desired image density, is also set so as not to change due to the magnification changing operation. .

Here, the magnification is m (however, m = 1 is the same magnification, m < 1
is the reduction, m > 1 is the expansion), the illuminance E _(n) on the photoconductor
is expressed as E _(n) = A/(1+m) ² ...(1). A lamp brightness, document type,
This is a constant determined by the transmittance of the imaging lens, etc.

If the illuminance on the photoconductor during copying at the same size is E ₍₁₎ , then E _(n) /E ₍₁₎ =A/(1+m) ² /A/(1+m) ² =4/(1+m) ² ... The relationship (2) holds true.

On the other hand, since the amount of light exposure on the photoreceptor needs to be constant during both full-size and variable-magnification copying, the width of light irradiation onto the photoconductor is W _(n) for variable-magnification copying and W (n) for full-size copying. ₍₁₎ , and the circumferential speed of the photoreceptor is V _(n) during variable-magnification copying and V ₍₁₎ during full-size copying, then E _(n)・W _(n) /V _(n) = E ₍ The relationship ₁₎・W ₍₁₎ /V ₍₁₎ ...(3) holds true.

By the way, in the above optical system, the exposure slit 8 is arranged near the photoreceptor, and its opening amount is always constant, so W _(n) = W ₍₁₎ ...(4), and formula (2) ), (4) into (3) to find the circumferential speed V _(n) of the photoreceptor during variable magnification copying, V _(n) = E _(n) / E ₍₁₎・W _(n) /W ₍₁₎・V ₍₁₎ =4/(1+m) ²・V ₍₁₎ ...(5) That is, when the magnification is m, if the photoreceptor is rotated at a circumferential speed that is 4/(1+m) ^twice the circumferential speed of the photoreceptor during full-size copying, the same amount of exposure as during full-size copying can be obtained. .

In order to set the magnification of the image in the rotational direction of the photoreceptor to m, the first mirror 3 must move at a speed of 1/m of the circumferential speed of the photoreceptor during variable-magnification copying with a magnification of m. If the moving speed of the mirror (in other words, the scanning speed of the document) is U _(n) , then U _(n) = 1/m・V _(n) = 4/m (1+m) ²・V ₍₁₎ ……( 6) becomes.

As is clear from equations (5) and (6) above, the exposure amount during variable-magnification copying can be controlled to be the same as that during full-size copying by simply changing the circumferential speed of the photoreceptor. Then, there are no approximation factors at all, and the exposure amount can be adjusted accurately. Especially m≧1
The effect is remarkable in a copying machine that can perform both full-size and enlarged variable-size copies. That is, since copying machines normally perform copying at the same size in overwhelmingly many cases, the light intensity of the illumination lamp, the circumferential speed of the photoreceptor, and other charging conditions are set to provide optimal conditions for copying at the same size. However, in general, the slower the circumferential speed of the photoreceptor, the greater the margin of process conditions such as charging and developing conditions, so even if the process conditions vary slightly, the image quality is hardly affected. Therefore, as is clear from equation (5), V _(n)
<V ₍₁₎ , and the circumferential speed of the photoreceptor is slower than that during full-size copying, so that very stable image quality can be obtained during enlarged and variable-magnification copying. In this case, if a potential control means, which will be described later, is used in combination, the image quality during enlarging and variable-magnification copying can be controlled to be substantially the same as that during full-size copying.

FIG. 2 shows another embodiment in which the same exposure slit 8 as in FIG. 1 is disposed near the original 0 (therefore, the image of the slit 8 is projected onto the photoreceptor by the lens). The exposure slit 8 is attached to the same support member as the first mirror 3, and moves in the same direction as the first mirror 3.

In this example, the magnification is m, and the illuminance on the photoreceptor is
Assuming E _(n) , the following relationship holds true as in Equation (1) above: E _(n) = A/(1+m) ² ... (1'). A is the same constant as above.

Also, if the illuminance on the photoconductor at the same magnification is E ₍₁₎ ,
Similar to equation (2) above, the following relationship holds: E _(n) /E ₍₁₎ = 4/(1+m) ² ... (2').

In this embodiment, since the exposure slit 8 is arranged near the original, the width of light irradiation on the photoreceptor changes depending on the magnification m.

That is, as shown in FIG. 3, since the opening amount of the exposure slit 8 is constant regardless of the value of the magnification m,
The light irradiation area for the original is constant during both 1x and variable magnification copying, and when the imaging lens 5 is at the 1x copying position, the light irradiation area A of the photoreceptor and that of the original are as shown by the chain line A'. However, when the imaging lens is at the variable magnification copying position, there will be a difference between the two light irradiation areas A'' and A.

Here, the light irradiation width of the original when the magnification is m is W ₍₁₎ ,
Letting that of the photoreceptor be W _(n) , W _(n) = m・W ₍₁₎ ... (3').

On the other hand, since the amount of exposure onto the photoreceptor needs to be constant during both full-size and variable-magnification copying, the circumferential speed of the photoconductor during variable-magnification copying is V _(n) , and that during full-size copying is V _{( 1)} , the following relationship holds: E _(n)・W _(n) /V _(n) = E ₍₁₎・W ₍₁₎ /V ₍₁₎ ……(4′).

Substituting the above equations (2') and (3') into (4') to find the circumferential speed V _(n) of the photoreceptor during variable magnification copying, V _(n) = E _(n) /E _{( 1)}・E _(n) /W ₍₁₎・V ₍₁₎ =4m/(1+m) ²・V ₍₁₎ ……(5′) That is, when the magnification is m, if the photoreceptor is rotated at a circumferential speed of 4 m/(1+m) ^twice the circumferential speed of the photoreceptor during full-size copying, the same exposure amount as during full-size copying can be obtained.

If the moving speed of the first mirror 3 is U _(n) , then U _(n) = 1/m·V _(n) = 4/(1+m) ² ·V ₍₁₎ as above.

In the optical system shown in Figure 2, as is clear from equation (5'), 4m/(1+m) ² ≦1 (where m>0). Therefore, the circumferential speed of the photoconductor V _(n) is V _(n) ≦V ₍₁₎ regardless of the magnification, and the circumferential speed of the photoconductor is slower in enlargement/reduction copying than in the case of full-size copying. By using the electric potential control procedure described later in combination, it is possible to obtain the same extremely stable image quality during variable-magnification copying as during full-size copying.

FIG. 4 shows the circumferential speed conversion mechanism of the photoreceptor 10, in which the driving force of the drive motor 11 is transferred to the drum 9, the transfer paper conveying roller system 14, and the first and second The signal is transmitted to the pulley 15 for moving the mirrors 3 and 4. During variable-magnification copying, the clutches 12 and 13 are disengaged, and the other clutch 16 and 17 is engaged, so that the driving force of the drive motor 11 is transferred to the drum 9 via the variable speed gear train 18.
etc.

In the above example of the mechanism, one variable-magnification copying case has been described, but it is possible to cope with multiple magnifications by arranging variable speed gear trains and clutches in multiple stages, which are set according to the magnification.

FIG. 5 shows a copying machine equipped with various image forming process elements, in which a drum 9 is rotatably supported by a shaft 19 on the main body (not shown), and rotated in the direction of the arrow by the drive motor 11. do. A photoreceptor 10 consisting of a conductive base layer, a photoconductive layer, and a transparent surface insulating layer is provided on the circumferential surface of the photoreceptor drum.
The photoreceptor 10 is first erased of residual charges by a corona discharger 20, and then is uniformly and primarily charged by a DC corona discharger 21, and then the image of the original 0 is slit-exposed by the optical system. At the same time, it is subjected to corona discharge by an alternating current for static elimination or a direct current corona discharger 22 for static elimination having a polarity opposite to that of the above-mentioned charging. This discharger 22 is provided with a slit opening to allow the speed of light to pass therethrough. Thereafter, the entire surface of the photoreceptor 10 is uniformly illuminated by the lamp 23, and a high-contrast electrostatic latent image corresponding to the original image is formed. This electrostatic latent image is visualized as a toner image by a developing device 24 such as a magnetic brush type, and then the toner image is conveyed to the circumferential surface of the photoconductor P at the same speed as the circumferential speed of the photoconductor 10. The toner is transferred by applying a corona discharge with a polarity opposite to that of the toner charge by the corona discharger 25. The transfer paper P after the transfer is separated from the circumferential surface of the photoreceptor in a separating section 26 and then guided to a fixing device 27 having heating and pressure rollers, etc., where the toner image is fixed. On the other hand, the peripheral surface of the photoconductor after transfer is cleaned by a cleaning device 28 such as a rubber blade.
The residual toner image is removed by the printer and the copying machine is ready for the next copying operation. The transfer paper P is conveyed from a paper feed cassette (not shown) toward the circumferential surface of the photoreceptor for one sheet.

Copying machines equipped with the exposure amount adjusting device as described above are capable of controlling the brightness of the electrostatic latent image formed on the photoconductor even if the circumferential speed of the photoconductor changes between full-size copying and variable-magnification copying. Means is provided for controlling the surface potential of the photoreceptor so that the partial potential and the dark potential of the same original become the same standard value both during full-size copying and variable-magnification copying. In other words, by changing the electric field intensity between the corona dischargers 21 and 22 and the photoreceptor in FIG. 5 to an intensity corresponding to the selected photoreceptor peripheral speed, and controlling the corona discharge applied to the photoreceptor. ,
Even if the circumferential speed of the photoreceptor is changed, that is, even if the process speed is changed, a good copy image of the same quality is always obtained.

As the means and method for controlling the surface potential of the photoreceptor, those already disclosed in detail in Japanese Patent Application No. 103038/1988 can be used, so only a brief explanation will be given here. This control method uses a surface potential sensor 29 to measure the surface potential of the photoreceptor 10 during the previous rotation of the drum, feeds it back, and corrects it to maintain a constant surface potential of the drum when the original image is exposed. This is a method to keep it within the standards. Here, the pre-rotation of the drum 9 means that when copying a desired number of sheets from a desired original, the drum 9 is rotated before scanning the original and projecting the image onto the photoreceptor.
After this pre-rotation is completed, the document is scanned a set number of times, and the image thereof is exposed on the photoreceptor to obtain the desired number of copies.

Now, in FIG. 5, while the photoreceptor 10 is rotated forward at a circumferential speed corresponding to the selected copying magnification, a reference current is applied to each of the primary charging corona discharger 21 and the static eliminator corona discharger 22, and the photoreceptor is rotated. The bright and dark potentials of the surface are alternately measured by the sensor 29. Blank exposure lamp 3 when measuring bright area potential
0 is lit and turned off when dark area potential is measured. Signals of bright potential and dark potential detected by sensor 29 are amplified by amplifier circuit 31 and input to arithmetic control circuit 32 . The arithmetic control circuit 32 compares a preset target potential constant signal generation means 33 with the signal detected by the sensor 29, calculates the difference, and calculates a correction current according to a preset correction formula. is added to the reference current, and the added current is applied to the primary charging corona discharger 21 and the static elimination corona discharger 22 via the primary high voltage power supply 34 and the static elimination corona discharger power supply 35, respectively. In this way, of the reference current plus the correction current, one corresponding to the dark potential is applied to the primary charging corona discharger 21, and one corresponding to the bright potential is applied to the static elimination corona discharger 22. The reference current plus the correction current becomes the reference current for the next control (the next time the drum front rotates). After the above-described control is repeated during the pre-rotation of the drum, the surface potential of the photoreceptor 10 finally comes to fall within a predetermined standard. After this state is reached, scanning of the original and projection of its image onto the photoreceptor at the selected magnification is started.

Target potential constant signal generation means 33 in the above control device.
The signal is converted according to the copy magnification. That is,
As mentioned above, this signal is transmitted to the corona dischargers 21 and 22 during variable magnification copying when the circumferential speed of the photoreceptor is slow.
The voltage applied to the image is converted so as to be reduced by a value corresponding to the magnification ratio compared to when copying at the same size.

In this way, both when copying at the same size and when copying at variable magnification, the bright area potential of the latent image for the same original is the bright area potential, and the dark area potential is within the specified standard range, so that good copies are always obtained. An image is obtained.

Furthermore, if a variety of signals are provided for the target potential constant signal generating means 33, the present invention can be applied directly to a copying machine having a multi-stage magnification ratio.

Note that the present invention is not limited to the above-mentioned optical system; in addition to optical systems consisting of a mirror and a zoom lens, or a mirror and an in-mirror lens, the present invention is also applicable to optical systems consisting of a mirror and an in-mirror lens, in which the lenses have completely different focal lengths. It can also be applied to known variable magnification optical systems such as optical systems that replace lenses and change only the conjugate length. Furthermore, the present invention can also be applied to a copying machine that uses a moving document table and a slit exposure method instead of a moving optical system.

According to the present invention, in the case of enlarged copying, where the amount of exposure on the photoreceptor has conventionally tended to decrease, the photoreceptor moving speed is changed to a slower speed than when copying at the same size, and the document scanning speed is also changed when copying at the same size. Since the speed has been changed to a lower speed than the previous one, it is possible to suppress the drop in the exposure amount on the photoconductor, and therefore keep the exposure amount on the photoconductor stable and constant without using a special high-intensity document illumination lamp. becomes possible.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of one embodiment of the optical system, Fig. 2 is the same diagram as above of another embodiment of the optical system, Fig. 3 is an explanatory diagram showing the projection area of the optical system in Fig. 2, and Fig. 4 is a schematic diagram of an embodiment of the optical system. FIG. 5 is a schematic diagram of an embodiment of a circumferential speed conversion mechanism of a photoreceptor, and FIG. 5 is a schematic diagram of a copying machine equipped with various image forming process elements. 0 is the original, 2 is the illumination lamp, 3 is the first mirror,
4 is a second mirror, 5 is an imaging lens, 6 is a third mirror, 7 is a fourth mirror, 8 is an exposure slit, 9 is a drum, 10 is a photoreceptor, 11 is a transmission gear train, 16,
17 is a gear shifting clutch.

Claims (1)

[Scope of Claims] 1. A scanning means for scanning an original, and an image of the original scanned by the scanning means is projected onto a photoreceptor.
an optical system having a lens and a slit disposed near the photoconductor, and by moving the lens, copying at a first magnification and copying at a second magnification larger than the first magnification are performed. In a selectable slit exposure variable magnification copying machine, when copying at the second magnification, the photoreceptor is moved at a slower speed than when copying at the first magnification, and the scanning means also moves at the first magnification. The circumferential speed of the photoreceptor V _(n) and the moving speed of the scanning means U _(n) when the magnification is m are V _(n) = 4/(1+m) ²・V ₍₁₎ Slit exposure variable magnification characterized by satisfying U _(n) = 4/m (1 + m) ²・V ₍₁₎ (where V ₍₁₎ is the circumferential speed of the photoreceptor during copying at the same size) Copy machine. 2. A scanning means for scanning an original, and projecting an image of the original scanned by the scanning means onto a photoreceptor;
The optical system includes a lens and an optical system having a slit disposed near the document placement means for placing the document, and by moving the lens, copying at a first magnification and copying at a second magnification larger than the first magnification are performed. In a slit exposure type variable magnification copying machine that allows copying at two magnifications to be selected, when copying at the second magnification, the photoreceptor is moved at a slower speed than when copying at the first magnification, and The scanning means is also moved at a slower speed than when copying at the first magnification, and the circumferential speed of the photoreceptor V _(n) and the moving speed of the scanning means U _(n) at the magnification m are V _(n) = 4 m. /(1+m) ²・V ₍₁₎ U _(n) = 4/(1+m) ²・V ₍₁₎ (where, V ₍₁₎ is the circumferential speed of the photoconductor during copying at the same magnification). Slit exposure variable magnification copying machine.