JP2812532B2 - Sheet conveying device using photoreceptor belt - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transport device for holding and transporting a sheet member such as a transfer sheet and a copy original of an electrostatic recording device by electrostatically adsorbing it to an endless belt-shaped transport member.

Prior art As a color copier using the electrostatographic process,
A color copying machine of a color separation image superimposing transfer system in which toner images of different colors sequentially formed on one photoreceptor are superimposed and transferred on the same transfer paper while being aligned and fixed to obtain a color copy. It has been known. In a color copying machine of this type, the transfer sheet is reciprocated and transported a plurality of times at a transfer section in contact with one photoconductor, or the transfer sheet is wrapped around a transfer drum and is rotated multiple times. In addition, the toner images of different colors are formed on a plurality of photoconductors at different timings, the transfer sections of the respective photoconductors are arranged in a straight line, and the transfer paper is conveyed so as to sequentially contact the transfer sections of the respective photoconductors. Also, a method of superimposing and transferring by superposition is known.

In the case where the transfer paper is reciprocated by passing through the transfer section of one photoconductor or the transfer paper is linearly transported by sequentially passing through the transfer sections of a plurality of photoconductors, the unfixed toner is transferred onto the transfer paper. Since the image is on the sheet, the sheet cannot be conveyed while being nipped by the conveying roller pair.

Not only color copiers but also black-and-white monochrome copiers, facsimile machines, electrostatic printers, etc., have a heater in the fixing device, so that the heat is transferred to the photoconductor to prevent deterioration. There is a considerable distance between the transfer position and the fixing device along which the transfer paper carrying the unfixed toner image must be transported.

As a transporting means of the transfer paper carrying the unfixed toner image as described above, a belt which moves and holds the transfer paper on the surface of a circulating endless belt so that the back surface of the toner image carrying surface does not come in close contact with and displaces. The method of transporting the transfer paper by entrainment is widely used.

As a method of holding and transporting a sheet such as a transfer sheet so as not to be in close contact with an endless belt, the following method has conventionally been adopted.

(A) Air suction system The endless belt is provided with a number of holes or is composed of a plurality of belts, and suctions air from a gap between adjacent belts into a suction box provided inside the belt, thereby seating the sheet on the belt surface. To hold and transport.

In this method, an air pump and an air passage are required for sucking air, and there is a disadvantage that the device becomes large.

(B) Grip method A gripper is provided on a belt, and the leading end of a fed sheet is gripped by the gripper to hold and convey the sheet.

In this method, the operation time of the grip is required, and it is difficult to continuously convey the sheet at a high speed.
There is a problem that a conveyance jam occurs due to a gripper grip error.

In an electrostatic recording apparatus, a sheet is conveyed by using an endless belt. In addition to the above-described transfer sheet conveying belt, an original is automatically fed onto a contact glass of a transfer machine or an original reading apparatus. Automatic Document Feeder (Automatic Docu
ment Feeder: ADF) conveyor belt.

Currently used ADF transport belts include:
A rubber belt with a high coefficient of friction that is driven while the original is pressed against the surface of the contact glass is used,
When a document is conveyed while being pressed against a contact glass surface using a transfer belt made of a rubber-based material, there is a disadvantage that the surface is easily stained by contact with the document and the contact glass, and dirt is not easily removed from the belt surface. Furthermore, if the original is a highly translucent tracing paper or thin paper, the dirt pattern is read and exposed, and the quality of the copied image and the reproduced image is degraded. Has become.

Therefore, it has been proposed to mix an antifouling agent into the material of the belt, apply an antifouling oil, or contact a cleaning blade in order to make the belt less likely to become dirty. The fact is that the effect is low and the durability is lacking.

For the purpose of solving the above-mentioned drawbacks, there have been proposed some devices that use an electrostatic attraction force as a means for transporting a sheet such as a transfer sheet or a document on a transport belt without shifting the sheet.

For example, JP-A-53-116825 discloses that as an ADF transport belt, an electrode pattern is embedded in an insulator belt, a voltage is applied between the electrodes to create an electric field corresponding to the electrode pattern, and the electrostatic force is applied. 2. Description of the Related Art There has been proposed an apparatus that sucks and conveys a conveyed sheet. A device that embeds an electrode pattern on a sheet suction surface and suctions a sheet by applying a voltage is often used in a flatbed type pen plotter or the like because a stable suction force can be obtained. However, the endless belt in which the electrode pattern is embedded has a complicated structure of means for applying a high voltage to the rotating part, which not only increases the cost, but also causes the electrode pattern to be disconnected or fed due to bending at the roller winding part. There is a problem in durability such as abrasion of parts.

Japanese Patent Application Laid-Open No. 63-288844 discloses that the surface of a conveyor belt in contact with a member to be conveyed is a film forming layer surface of an amorphous silicon photoreceptor, and the surface has a coefficient of friction, difficulty in adhering dirt, and cleaning of dirt. Utilizing characteristics such as ease of cleaning, it prevents contamination on the surface of the conveyor belt and provides a means for applying a voltage to the surface to charge the amorphous silicon layer surface, and electrostatically attracts the member to be transferred. There has been proposed a conveyor belt device which conveys the photosensitive member and reduces the potential with time by the dark current of the photoreceptor to remove the charge.

However, this method has a drawback that it is necessary to form a belt by depositing amorphous silicon on a conductive substrate, and the belt itself is expensive because the film formation speed is low.

In addition, a device that uniformly charges the surface of the photoreceptor and suctions a dielectric sheet such as paper has a lower suction force than a device that embeds the above-described electrode pattern and forms an uneven electric field to suction. It is small, is easily affected by changes in environmental conditions such as temperature and humidity, and has the disadvantage that the sheet may not be reliably sucked depending on conditions such as high temperature and high humidity.

In view of the above-mentioned problems of various sheet holding / conveying systems using a conventional electrostatic attraction belt, the present applicant has previously proposed a simple configuration using Japanese Patent Application No. 1-327,324 (filed on December 19, 1989). Proposed a low cost, compact, and highly durable sheet holding / conveying device that can securely hold and convey sheets and the like.

In order to solve the above-mentioned problems, the sheet conveying device applies an alternating voltage to the dielectric endless belt-shaped holding / conveying member such as polyester via a conductive blade or a roller, thereby applying a voltage to the surface of the holding / conveying member. An alternating charge density pattern is formed, and a position at which the sheet is supplied to the holding and conveying member is set in a range in contact with a support roller serving as a counter electrode of the voltage applying unit.

Due to the alternating charge density pattern formed on the surface of the endless belt-shaped holding and conveying member, an uneven electric field is formed near the surface of the holding and conveying member. The sheet material such as transfer paper, which is a dielectric, is supplied to the holding / transporting member in a range in contact with the counter electrode of the voltage applying means, and is attracted by a strong suction force, and is attracted to the holding / transporting member by the uneven electric field. The sheet is held so as not to be displaced, and is conveyed while being carried by the holding / conveying member.

However, this method requires a high-voltage AC power supply to form an alternating charge density pattern.Especially, when a high-frequency power supply is required, it is affected by stray capacitance, reactive current flows, and the power supply becomes larger. There is a disadvantage of doing so. or,
Since the conductive blade or the conductive roller is provided in a direction perpendicular to the belt running direction, the charge density pattern is limited to a stripe pattern having an equal interval or a preset unequal interval orthogonal to the belt running direction.

Therefore, the present applicant separately requires, without using an AC power supply as a means for forming an alternating charge density pattern on the transport belt, the sheet transport belt at least on the outer surface of the base material whose outermost layer is a conductive layer or a semiconductor layer. A charging unit configured to provide a photoreceptor layer, charging the photoreceptor layer around the sheet conveying belt in the running direction, a flashable discharging unit for discharging the charged photoreceptor storage layer by light irradiation, The present invention has proposed a sheet conveying apparatus in which a conveying sheet supply position is provided, the photosensitive layer is uniformly charged by the charging unit, and an alternating charge density pattern is formed by blinking a light removing unit at a predetermined timing. This proposal eliminates the need for large AC or alternating power supplies, and is low cost, long life,
In addition, it has become possible to realize a transport belt device capable of obtaining stable transport performance. As the above charging means,
A corona discharger type charger similar to the charging means of the photoreceptor as the latent image carrier can be used, and contact charging by a conductive roller can also be employed. The latter case is advantageous in that ozone is not generated by corona discharge as in the former case.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances of a conventional sheet conveying apparatus using an endless belt, and takes advantage of the characteristics of an apparatus using a photosensitive belt as an endless belt to more stably hold and convey a sheet. It is an object of the present invention to provide a sheet conveying device that can perform the above-described operations.

Means for Solving the Problems In order to solve the above-mentioned problems, a first invention of the present invention is a sheet conveying apparatus using a photosensitive belt having the above-mentioned configuration separately proposed by the present applicant. Means for detecting the size of the sheet to be detected. Based on the size information of the sheet detected by the size detecting means, a desired portion of the photoreceptor belt is selectively uniformized by the charging means and the light eliminating means. By performing static elimination, formation of a coarse uniform pattern, formation of a dense uniform pattern or uniform charging, a weak electrostatic attraction force is obtained in a region corresponding to the leading end of the conveyed sheet, and at least a part of a region thereafter. It is characterized in that the blinking control of the light removing means is performed so that a stronger electrostatic attraction force can be obtained than at the tip.

In this case, the above-mentioned light discharging means is constituted by a plurality of light emitting elements which are arranged in a straight line substantially in the direction perpendicular to the circumferential direction of the endless photoreceptor belt over the entire width of the photoreceptor belt, and which can blink individually. It is further desirable that the control is performed so that the electric charge in the area corresponding to the outside of the sheet is removed by the light discharging means based on the sheet width information detected by the sheet size detecting means.

According to a second aspect of the present invention, there is provided a sheet conveying apparatus using a photosensitive belt having the above-described configuration, which is separately proposed by the present applicant. It comprises a plurality of light-emitting elements which are arranged in a straight line substantially in the right angle direction substantially over the entire width of the photoreceptor belt, and can be individually turned on and off, and have means for detecting the size of a sheet introduced into the sheet conveying device, Based on the size information of the sheet detected by the size detecting means, a predetermined portion of the photoreceptor belt is selectively and uniformly discharged by the charging means and the light discharging means, forming a coarse uniform pattern, and a dense uniform pattern. Or uniform charging, so that at least in the area corresponding to the leading end of the sheet to be conveyed, the electrostatic attraction force at the center is stronger than the electrostatic attraction at both ends. Wherein the flashing control the light-emitting element of the optical charge removing means.

With the configuration described above, in the first invention, a weak electrostatic attraction force is obtained in a region corresponding to the leading end of the conveyed sheet of the photoreceptor belt, and at least a part of the subsequent region is obtained. Stronger electrostatic attraction than the tip can be obtained.

As a result, during conveyance of the sheet, the sheet is reliably conveyed without being displaced or bent by the photoreceptor belt due to the strong suction force after the leading end. When the leading edge of the sheet reaches the separating section due to the curvature, the attraction force between the leading edge of the sheet and the photoreceptor belt is weak, so that the sheet is easily peeled off due to its own waist, and the separation is reliably performed.

In order to weaken the suction force at the leading edge of the sheet and increase the suction force after that, a desired portion of the photoreceptor belt uniformly charged by the charging unit is selectively uniformly discharged by the light discharging unit, and the light source blinks Thus, formation of a coarse uniform pattern, formation of a dense uniform pattern, or maintenance of a uniform charging state due to non-operation of the light removing means.

The order of the strength of the adsorption force is, in order from the strongest one, a pattern having a high density → a pattern having a low density → uniform charging → equal charge removal. The reason why the attraction force can be changed depending on the pattern density will be described with reference to FIG.

FIG. 4 is a diagram showing a difference in lines of electric force formed by a potential difference between patterns due to the density of an electrostatic pattern formed on an endless photoreceptor belt.

The upper part of the figure shows a negatively-charged potential profile, and below it shows the lines of electric force correspondingly formed on the surface of the photoreceptor belt. The lines of electric force are formed in a direction indicated by an arrow in the drawing from a place having a high potential to a place having a low potential. The intensity of the electric field becomes strong at the edge of the potential pattern where the density of the electric flux lines is high.

In areas where the density of the electrostatic pattern is low, the distance between the charges remaining on the photoreceptor belt increases, so the electric field generated by the potential difference between the remaining charge and the remaining charge forms a greater distance. Is done. At the same time, the potential gradient is high at the edge portion of the charge pattern. Therefore, when the pattern density is low, the density of the portion having the high potential gradient is low, and the suction force on the sucked sheet is low. That is, a suction force is exerted on a sheet at a position distant from the photosensitive belt, but the suction force on the sucked sheet is small. On the other hand, in a region where the density of the electrostatic pattern is high, the suction force at a distant position is small, but the suction force at the sucked sheet is large.

It is considered that the uniformly charged portion has a very low pattern density because the pattern density is considered to be very coarse, and it is not necessary to explain that the attraction portion has a further lower attractive force.

When the electrostatic pattern is a striped pattern extending in the width direction of the photoreceptor, the light source of the light removing unit may be a single rod-shaped light source.

However, the electrostatic pattern is not limited to the striped pattern, and the light source of the light removing unit may be a plurality of light emitting elements arranged in the width direction of the photoconductor, and may be a checkered electrostatic pattern.

Further, by eliminating charges on the outer portion of the sheet carrier of the photoreceptor belt based on the size information of the sheet size detecting means, it is possible to prevent the photoreceptor belt from electrostatically attracting fine dust and becoming dirty. Can be prevented. In this case, it is necessary to continuously turn on the light source of the light removing unit according to the width of the sheet outside the width of the sheet and blink within the range of the width to form a uniform pattern. It is necessary to be composed of a plurality of light emitting elements which are arranged in a straight line over the entire width of the photoreceptor belt in a direction perpendicular to the circumferential direction of the body belt and which can blink solidly.

In the configuration of the second invention, the sheet can slide in the plane of the belt by adsorbing and holding the central portion in the width direction of the sheet with a strong adsorption force and the both end portions with a low adsorption force. Even if the sheet is distorted when guided by the belt, the distortion can be eliminated, and wrinkling hardly occurs when the sheet is fed to the fixing roller and fixed between the rollers as in the embodiment described later.

Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a view showing an example of a two-color laser printer provided with a sheet conveying device using a photosensitive belt according to the present invention.

This printer has two sets of laser writing optical systems sharing a rotary polygon mirror 3 as a deflector for optical scanning.
The writing optical system includes a first laser oscillator 1, a rotary polygon mirror 3,
The first f-θ lens 4 and the mirrors 5, 5 ', 5 "
The laser beam 2 carrying the image information to be developed in a color, for example, black, passes through the first writing optical system to the first directly above the photosensitive drum 7 uniformly charged by the charging charger 6.
The writing position is irradiated and scanned to form a first latent image. The first latent image is stored in a first latent image provided next to the first writing position.
The developing device 8 develops the first color (black in this example).

On the other hand, the second writing optical system includes a second laser oscillation device 9, a rotary polygon mirror 3, a second f-θ lens 11, and mirrors 12 and 12 ', and has a second color (for example, a chromatic color such as red or blue). The laser beam 10 carrying image information to be developed in the first and second developing optical systems is irradiated and scanned via the second writing optical system at a second writing position provided at a position following the first developing device 8. 2 are formed. The second latent image is developed into a second color by a second developing device 13 provided downstream of the second writing position. Since the latent image developed with the first color is not completely recovered by the development and the latent image remains, the threshold value of the development potential is set so that the latent image is developed by the second developing device 13 so that color mixing does not occur. Are set appropriately, and appropriate developing bias is applied.

The two-color toner images formed in the same image forming area of the photoreceptor 7 are transferred onto the transfer paper fed from the paper feeder 14 under the action of the transfer charger 15, and the present invention is applied thereto. The sheet is conveyed to a fixing device 17 by a sheet conveying device 16 using a photosensitive belt, and is fixed and discharged.

After the transfer, the toner remaining on the photosensitive drum 7 is cleaned by the cleaning device 18 and the charge is removed to prepare for the next image formation.

As shown in FIG. 2, the conveying device 16 using the photoreceptor belt includes a photoreceptor endless belt 24 supported by a driving roller 22 and a driven roller 23 and circulating in the direction of the arrow, and a charger 20 for charging the photoreceptor belt. The charged photoreceptor belt 24 comprises a light eliminator 21 for irradiating light while blinking and erasing light to form an electrostatic pattern, and the charging charger 20 and the light eliminator 21 are moved with respect to the circumferential direction of the photoreceptor belt 24. They are provided in this order and upstream of the transfer paper introduction position.

The light removing device 21 is linearly arranged in a direction perpendicular to the circumferential direction of the photoreceptor belt 24 and substantially over the entire width of the belt, and is formed as an array of a large number of light-emitting elements that can be turned on and off individually. . Although not shown in the figure, the high-voltage power supply connected to the charging charger 20, the light erasing device 21 blinks, the high-voltage power supply is turned on / off, and the belt drive is turned on / off.
A control device is provided for controlling the turning off together with the sequence of the printer, image forming conditions, and the like. The individual blinking of each light-emitting element of the optical charge removing device 21 and the blinking control as a whole are performed by a size detection signal of the transfer sheet fed from the sheet feeding device 14 as described later.

The transfer paper fed from the paper feeding device 14, the toner image transferred by the transfer / separation device 15, and separated from the photosensitive drum 7 is guided to the sheet conveying device 16. The driving of the transporting device is started so that the leading end of the transfer paper reaches the sheet transporting device, and the charging charger 20 and the light neutralizing device 21 are driven. a)
(E), the transfer paper formed on the photoreceptor belt 24 as shown in FIG. 6 and FIG. When the transfer paper reaches the position, the transfer paper is separated from the photoconductor belt 24 by the curvature of the photoconductor belt 24 and the waist of the transfer paper, separated and conveyed to the fixing device.

In addition to the above basic configuration, a cleaning device for the photoreceptor belt 24 after the transfer paper is separated, or a static eliminator for initializing by performing static elimination prior to the next charging by the charging charger 20 may be provided. it can. Further, at the end of printing or in an area where it is not necessary to adsorb the transfer paper, the power supply of the charger may be turned off, or the light removing means 21 may be continuously turned on to remove the charge of the photosensitive belt 24 over the entire area.

FIG. 3 is a view showing a sheet conveying device using a photosensitive belt using a conductive roller 20 'instead of a corona discharger type charger as a charging means. Members having the same functions as those in FIG. The same reference numerals are given. The use of a conductive roller as the charging means has the advantage of eliminating the generation of ozone.

In FIGS. 5 (a), (b),... (E), a weak electrostatic attraction force is obtained in the area corresponding to the leading end of the sheet, and at least a part of the area thereafter is stronger than the leading end. Various modes of decharging the photoreceptor belt that can obtain an electroadhesive force will be described. These are based on the order of high-density pattern → low-density pattern → uniform charging → uniform static elimination in the order of strong electrostatic attraction.

(A) The tip is erased and thereafter uniformly charged to a predetermined voltage. (B) The tip is erased and a predetermined uniform electrostatic pattern thereafter. (C) The tip is uniformly charged and thereafter a predetermined electrostatic pattern. Uniform electrostatic pattern (d) A rough pattern at the front end, a predetermined uniform pattern at the subsequent part, and the subsequent charge is erased. (E) A charge erasure area at the rear end in (a), (b) and (c). Formation ((e) shows an example in which a leading edge erasure, a uniform pattern, and a charge erasing part are provided subsequently thereto). In addition, the density of the pattern is gradually changed from the leading edge to the trailing edge. It is also possible.

In each example shown in FIG. 5, the electrostatic pattern is a stripe pattern extending in the width direction of the photoreceptor, so that a single rod-like light source can be used as the light source of the light removing unit.

6 (a), (b),..., (E) show examples in which electric charges are erased from the portion outside the sheet carrying portion of the photosensitive belt based on the size information of the sheet size detecting means. Sixth
(A), (b),..., (E) are examples in which the charge is erased outside the sheet width in the example of FIG. 5 (a), (b),. . In this charge erasing, the light source of the light removing means is formed of a large number of light emitting elements arranged linearly over substantially the entire width in the width direction of the photoreceptor belt, and the light sources outside the sheet are continuously turned on. This is achieved by:

FIG. 7 is a view showing an example of a charged state of a photosensitive belt in which a sheet is attracted with a strong suction force at a center portion in the width direction of the sheet and a weak suction force is applied at both ends thereof. A low density electrostatic pattern is formed at both ends of the pattern. The high-density pattern is alternately turned on and off once for each light emitting element of the light removing means as one unit, and the low-density pattern is turned on and off every two scans for two adjacent light emitting elements as one unit. Is repeated to form a high-density and low-density checkerboard pattern. In the drawing, the level of the potential is shown in black and white. Note that such a pattern need not necessarily be formed over a region corresponding to the entire length of the sheet, and it is effective to form the pattern at least in a region corresponding to the leading end of the sheet.

Effects As described above, according to the first aspect, the attraction force of the sheet front end portion is weak, the curvature separation is reliably performed, and the sheet is securely adsorbed by the strong suction force after the front end portion.

Further, according to the second aspect, only the central portion of the sheet is strongly attracted, so that when the sheet is guided by the belt, the distortion can be eliminated even if the sheet is subjected to distortion.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing an overall schematic structure of an example of an image forming apparatus provided with a sheet conveying device according to the present invention, and FIG. 2 shows a structure of an embodiment of the sheet conveying device of the present invention provided in the device. FIG. 3 is a cross-sectional view showing the configuration of the modified embodiment, FIG. 4 is a schematic diagram showing the difference in electric lines of force formed due to the density of an electrostatic pattern formed on a sheet conveying belt, 5 (a), (b),..., (E) and FIGS. 6 (a), (b),..., (E) show the electrostatic force formed on the sheet conveying belt by the first invention. FIG. 7 is a plan view showing an example of a pattern, and FIG. 7 is a plan view showing an example of an electrostatic pattern formed on a sheet conveying belt according to the second invention. 16 ... Sheet conveying device by photoreceptor belt 20, 20 '... Charging means 21 ... Light eliminating means 22 ... Drive roller 23 ... Driving roller 24 ... Photoreceptor belt

Claims (3)

(57) [Claims] 1. An endless photoreceptor belt having a photoreceptor layer formed on a substrate having at least an outermost layer being a conductive layer or a semiconductor layer, and arranged around the endless photoreceptor belt in the circumferential direction. Charging means for charging the photoreceptor layer, blinking light discharging means for discharging the charged photoreceptor layer by light irradiation, and means for introducing a conveyed sheet into the endless belt. A sheet conveying device for electrostatically adsorbing a conveyed sheet to the surface of an endless photoreceptor belt, and conveying the sheet, the unit having a unit for detecting a size of a sheet introduced into the sheet conveying device, Based on the size information of the sheet, the above-mentioned charging unit and the above-mentioned light discharging unit selectively selectively remove a desired portion of the photoreceptor belt uniformly, form a coarse uniform pattern, form a dense uniform pattern or form uniform charging. go,
The blinking control of the light removing unit is performed so that a weak electrostatic attraction force is obtained in a region corresponding to the leading end of the conveyed sheet, and a stronger electrostatic attraction force is obtained in at least a part of the subsequent region. A sheet conveying device, characterized in that: 2. The method according to claim 1, wherein the light removing means is arranged linearly in a direction perpendicular to the circumferential direction of the endless photoreceptor belt and substantially over the entire width of the photoreceptor belt, and includes a plurality of light emitting elements which can blink individually. 2. The image forming apparatus according to claim 1, wherein the control is performed such that the electric charge in an area corresponding to the outside of the sheet is removed by the light removing unit based on the sheet width information detected by the sheet size detecting unit. The sheet conveying device as described in the above. 3. An endless photoreceptor belt in which a photoreceptor layer is formed on a base material having at least an outermost layer being a conductive layer or a semiconductor layer, and arranged around the endless photoreceptor belt in the circumferential direction thereof. Charging means for charging the photoreceptor layer, blinking light discharging means for discharging the charged photoreceptor layer by light irradiation, and means for introducing a conveyed sheet into the endless belt. In the sheet conveying apparatus which conveys the conveyed sheet by electrostatically adsorbing the surface of the endless belt, the above-mentioned light discharging means is linear in a direction perpendicular to a circumferential direction of the endless photoreceptor belt and substantially over the entire width of the belt. And a means for detecting the size of a sheet to be introduced into the sheet conveying device, comprising a plurality of light-emitting elements which can be individually flashed, based on the size information of the sheet detected by the size detecting means. The above-mentioned charging means and the above-mentioned light discharging means selectively perform uniform charge elimination on a required portion, formation of a coarse uniform pattern, formation of a dense uniform pattern or uniform charging, at least on the leading end of the conveyed sheet. A sheet conveying device, characterized in that the light emitting element of the light removing means is turned on and off so as to obtain a stronger electrostatic attraction force at the center than at both ends in a corresponding area.