JPH10116006A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the defect of image quality such as the rupture of toner and toner scattering by providing an electric field shielding member shielding a function member for controlling image forming operation from the electric field of a precleaning electrifying means. SOLUTION: A corotron 51 is disposed between the transfer point A of a photoreceptor drum 20 and a cleaning device 53. The function parts such as a density detecting sensor 54 and a post-transfer jam sensor 55 are arranged in the vicinity of the point A. Then, the electric field shielding member 60 is also provided. A sensor holder 60 functioning as the electric field shielding member to which the sensor 55 is attached allows transfer paper 24 carried on a transfer drum 23 to be influenced by the electric field E formed by the electrifying action by the corotron 51 and shields the sensor 55 from the electric field E.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for multiplexing a plurality of toner images of different colors on a transfer material supporting member such as a transfer drum or a transfer belt made of an insulating film. The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a printer that forms a color image by transferring.

[0002]

2. Description of the Related Art Conventionally, a transfer sheet is electrostatically attracted to a transfer material carrier such as a transfer drum or a transfer belt made of an insulating film of this kind, and toner images of different colors are multiplexed on the transfer sheet. In an image forming apparatus that forms a color image by transferring, as shown in FIG.
A plurality of toner images having different colors such as black, yellow, magenta, and cyan are sequentially formed on the transfer drum 101, and the plurality of toner images formed on the photosensitive drum 100 are transferred onto a transfer sheet 101 held on a transfer drum 101. The cleaning device 1 including a cleaning blade 103 and the like removes the toner remaining on the photosensitive drum 100 after the multiple transfer to the photosensitive drum 100.
04 to facilitate cleaning.
A pre-cleaning corotron 105 is provided for removing the toner remaining on the toner image. In this image forming apparatus, the unfixed toner image transferred onto the transfer sheet 102 is simultaneously discharged by the pre-cleaning corotron 105 so that the unfixed toner image immediately after being transferred onto the transfer sheet 102 is discharged. To prevent the transfer paper 1 from being charged in a low humidity environment.
23, a discharge is generated between the unfixed toner image on the transfer paper 102 and another member arranged near the separation position of the photosensitive drum 100, and the toner image transferred onto the transfer paper 102 is changed as shown in FIG. It is configured to prevent the occurrence of an image quality defect called "toner burst" which scatters in a round stamp pattern.

In the vicinity of a transfer point A where the photosensitive drum 100 and the transfer drum 101 are close to each other,
Functions such as a jam sensor 106 for detecting a jam in which the transfer paper 102 onto which the toner image has been transferred from the photosensitive drum 100 is wound around the photosensitive drum 100, and a synthetic resin holder 107 for holding the jam sensor 106 A member is arranged. Therefore, in a low humidity environment, especially when the height (pile height) of the toner image is high and the resistance value of the transfer paper 102 is high, or when the transfer paper 102 having a high resistance value is used, the jam sensor 106 is used.
Corotron 1 before cleaning
The toner immediately after being charged by the electric discharge of 05 and transferred onto the transfer paper 102 of the same polarity is repelled, and a streak of cyan or the like may be generated along the process direction as shown in FIG.

In such an image forming apparatus, the post-transfer jam sensor 106 is located at a position close to the transfer point A.
Is disposed, the abnormality that the transfer paper 102 that has passed the transfer point A peels off from the transfer drum 101 and winds around the photosensitive drum 100 is detected early, and the photosensitive drum 100 is stopped in a short time. This is because it is necessary.

[0005]

However, the prior art described above has the following problems. That is, in the image forming apparatus configured as described above, FIG.
As shown in FIG. 2, since the post-transfer jam sensor 106 needs to be disposed at a position close to the transfer point A, the edge of the post-transfer jam sensor 106 is charged by the influence of the discharge of the corotron 105 before cleaning. become. For this reason, in the image forming apparatus, when the unfixed toner immediately after being transferred onto the transfer sheet 102 is excessively discharged by the pre-cleaning corotron 106, the transfer sheet 102 is conveyed by the transfer drum 101 during the transfer.
There is a problem that an image quality defect occurs in which toner is scattered on members arranged around the transfer drum 101.

In order to solve this problem, the applicant of the present invention disclosed in Japanese Patent Application Laid-Open No. HEI 8-171318, an electric charge having the same polarity as the toner generated from the pre-cleaning static eliminator is carried on the transfer material. There has already been proposed an image forming apparatus configured so as to have a charge adhesion suppressing means for restricting adhesion to a recording sheet on a body.

However, in the case of the image forming apparatus according to this proposal, as described above, the pre-cleaning corotron 1 is used.
Since a functional member such as the post-transfer jam sensor 106 is further provided near the transfer point A where the cleaning roller 05 is disposed, the problem becomes complicated, and the pre-cleaning corotron 10 is used.
5 is transferred to the transfer drum 10
Is provided with the charge adhesion suppressing means for restricting the adhesion to the transfer paper 102 on the
Due to 05, there is a problem that the effect of removing the unfixed toner image transferred on the transfer paper 102 cannot be obtained, and the image quality defect called "toner burst" as described above occurs again. On the other hand, in the above-mentioned image forming apparatus, in order to prevent the image quality defect called “toner rupture”, the unfixed toner immediately after being transferred onto the transfer paper 102 is excessively discharged by the pre-cleaning corotron 105. In this case, the post-transfer jam sensor 106 is charged by the discharge from the pre-cleaning corotron 105, and the toner image is charged by the discharge of the pre-cleaning corotron 105, and the transfer paper 102 having the same polarity as the charged post-transfer jam sensor 106. There is a trade-off problem that an image quality defect occurs in which the toner immediately after being transferred onto the upper surface repels and toner streaks occur in the process direction.

The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a post-transfer jam sensor near a transfer point where a pre-cleaning charging unit is disposed. It is possible to prevent any image quality defects such as "toner rupture" and toner scattering from occurring, and to obtain a good image even when the functional members such as To provide a simple image forming apparatus.

[0009]

That is, according to the first aspect of the present invention, toner images of different colors are sequentially formed on an image carrier, and the toner images of different colors formed on the image carrier are formed. Is transferred onto the transfer material carried on the transfer material carrier in a multiplex manner for each color to form an image, and the image is formed on the image carrier near the downstream side of the transfer position of the image carrier. And a functional member for controlling an image forming operation is disposed between the pre-cleaning charging unit and the transfer position. An electric field shield that shields the electric field of the pre-cleaning charging unit from reaching the functional member, while allowing the electric field formed by the charging unit to extend to the transfer material carried on the transfer material carrier. It is configured to provide a wood.

The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the electric field shielding member is disposed between the pre-cleaning charging unit and the functional member. . The invention according to claim 3 is the image forming apparatus according to claim 1, wherein the electric field shielding member is disposed between the functional member and the transfer material carrier.

Further, according to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the electric field shielding member is formed of an insulating material so as not to concentrate an electric field. Device.

Further, in the invention described in claim 5, the electric field shielding member is formed in a shape in which an electric field is not concentrated by a grounded conductive material. An image forming apparatus according to any one of the preceding claims.

Further, the invention according to claim 6 is the image forming apparatus according to claim 1 or 2, wherein the electric field shielding member is disposed on a functional member in a stacked state.

[0014] Still further, the invention described in claim 7 is as follows.
7. The electric field shielding member is an insulating sheet material, and an amount of protrusion to the functional member is appropriately set according to a volume resistance value of the electric field shielding member to be used.
An image forming apparatus according to (1).

Further, according to the present invention, a toner image having a different color is sequentially formed on an image carrier, and the toner images having different colors formed on the image carrier are transferred to a transfer material carrier. A cleaning operation for forming an image by sequentially and multiplexly transferring each color on the transfer material carried thereon, and removing the toner remaining on the image carrier near the downstream side of the transfer position of the image carrier. In an image forming apparatus having a pre-charging unit and a functional member for controlling an image forming operation between the pre-cleaning charging unit and a transfer position, an edge of the functional member is cleaned by the cleaning. An image forming apparatus characterized in that the pre-charging means has a gentle shape in which an electric field formed by a discharging action is not concentrated on a part.

According to a ninth aspect of the present invention, the electric field shielding member has a two-layer structure in which a grounded conductive member and an insulating member are bonded to each other, and the edge of the insulating member is made of a conductive material. The image forming apparatus according to claim 1, wherein the image forming apparatus protrudes by 1 mm or more from an edge of the member.

Further, the invention described in claim 19 is:
The electric field shielding member includes a holding member made of a synthetic resin having a frame for holding a functional member, and an insulating sheet material disposed on an upper surface of the frame of the holding member. Item 2. An image forming apparatus according to Item 1.

[0018]

In the image forming apparatus according to the first aspect of the present invention, the electric field formed by the charging means before cleaning is allowed to extend to the transfer material carried on the transfer material carrier. Since the electric field shielding member for shielding the electric field of the pre-cleaning charging means from reaching the functional member is provided, the toner transferred to the transfer material on the transfer material carrier by the pre-cleaning charging means is provided. Since the image is neutralized and the potential of the toner image immediately after being transferred onto the transfer material can be appropriately reduced, it is possible to prevent image quality defects such as toner rupture from occurring.

In the image forming apparatus according to the first aspect of the present invention, the functional member for controlling an image forming operation disposed between the pre-cleaning charging means and the transfer position includes a pre-cleaning member. Since the electric field of the charging unit is configured to be blocked by the electric field shielding member, the functional member can be prevented from being charged by the discharge from the pre-cleaning charging unit by the electric field shielding member. The functional member is charged by the discharge from the pre-cleaning charging unit, and the edge portion of the toner image is charged by the discharge of the pre-cleaning charging unit, and the toner immediately after being transferred onto the transfer material having the same polarity as the charged functional member. Can be prevented, and image quality defects such as generation of toner streaks along the process direction can be prevented.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

FIG. 3 shows an embodiment of a multi-transfer digital color copying apparatus as an image forming apparatus according to the present invention.

In FIG. 3, reference numeral 1 denotes a main body of the digital color copying apparatus, and an image reading apparatus 3 (Image Input Terminator) for reading an image of an original 2 is provided at an upper end in the main body 1 of the digital color copying apparatus.
l) is arranged. The image reading device 3 illuminates the image of the document 2 placed on the platen glass 4 while being pressed by the platen cover 5 with the light source 6,
The reflected light image of the original 2 is scanned and exposed to the CCD sensor 10 via the first and second scanning mirrors 7 and 8 and the imaging lens 9, and the color sensor reflected light image of the original 2 is predetermined by the CCD sensor 10. Dot density (for example, 16 dots / mm)
To read in.

The color material reflected light image of the original 2 read by the image reading device 3 is, for example, original reflectance data of three colors of red (R), green (G), and blue (B) (8 bits each). As the image processing device 12 (Image Process)
The image processing apparatus 12 transmits the reflectance data of the document 2 to the shading correction, the position shift correction, the lightness / color space conversion, the gamma correction, the frame erasure, the color / movement editing, and the like. Predetermined image processing is performed.

The image data subjected to the predetermined image processing by the image processing device 12 as described above includes black (K), yellow (Y), magenta (M), and cyan (C) (each 8 bi).
t) is converted into original color material gradation data of four colors and ROS1
5 (Raster Output Scanner), and the ROS 15 performs image exposure with laser light in accordance with the original color material gradation data.

As shown in FIG. 3, the ROS 15 modulates the semiconductor laser 16 in accordance with the original color material gradation data, and emits laser light LB from the semiconductor laser 16 in accordance with the gradation data. The laser beam LB emitted from the semiconductor laser 16 is deflected and scanned by a rotary polygon mirror 17 and is scanned and exposed on a photosensitive drum 20 as an image carrier via a reflection mirror 18.

The photosensitive drum 20 on which the laser beam LB is scanned and exposed by the ROS 15 is driven to rotate at a predetermined speed in a direction indicated by an arrow by a driving means (not shown). The surface of the photosensitive drum 20 is
After being charged to a predetermined potential by the charging corotron 21 in advance, an electrostatic latent image is formed by scanning and exposing a laser beam LB in accordance with document color material gradation data. The electrostatic latent images formed on the photoreceptor drum 20 include four color developing units 22K, 22Y, 22M, 22C of black (K), yellow (Y), magenta (M), and cyan (C).
Are sequentially developed by a rotary type developing device 22 provided with a toner image having a predetermined color.

The toner image formed on the photosensitive drum 20 is transferred to a transfer sheet 2 as a transfer material held on a transfer drum 23 disposed adjacent to the photosensitive drum 20.
4 is sequentially transferred by the charging of the transfer corotron 25. As shown in FIG. 3, the transfer paper 24 includes a plurality of paper feed cassettes 2
8, 29, and 30 can be fed by a paper feed roll 31, or can also be fed from a manual feed tray 38 arranged on a side surface outside the copying apparatus main body 1. The sheet is conveyed to the surface of the transfer drum 23 by the plurality of conveying rollers 32 and the registration rollers 33. Then, the transfer paper 24 is electrostatically attracted to the surface of the transfer drum 23 by the charging of the transfer corotron 25 which also serves as a charger for electrostatic attraction, and the transfer drum 23
Held on the surface. The manual feed tray 38 can also feed a transparent OHP sheet for an overhead projector or the like in addition to a transfer sheet of a non-standard size such as a postcard, so that an image can be formed on the OHP sheet or the like. ing. Further, from the manual feed tray 38, the transfer paper 24 on which an image is formed on one side is fed upside down, so that double-sided copying is possible.

The transfer paper 24 on which the toner image of a predetermined number of colors has been transferred from the photosensitive drum 20 is separated from the surface of the transfer drum 23 by the discharge of the separation corotron 34, and then conveyed to the fixing device 35. And the fixing device 3
5, a toner image is formed on the transfer paper 24 by heat and pressure.
The color image is fixed on the sheet and discharged onto the sheet discharge tray 36, thereby completing the color image copying process.

In FIG. 3, reference numeral 37 denotes a charge removing corotron pair for removing charge from the transfer drum 23.

FIG. 2 is a block diagram showing the image forming unit of the digital color copying apparatus of the multiple transfer system.

In FIG. 2, reference numeral 20 denotes the photosensitive drum, and a transfer drum 23 as a transfer material carrier is provided so as to be in contact with or close to the surface of the photosensitive drum 20. The transfer drum 23 is driven to rotate at the same speed as the peripheral speed of the photosensitive drum 20 by a drive mechanism (not shown). As shown in FIG.
As shown in FIG. 5, a drum having a pair of ring members 40, 40 as annular members disposed at both ends in the axial direction, and a tie bar plate 41 as a connecting member connecting these ring members 40, 40 to each other. With a frame-like body,
A circumferential edge 42a of a transfer film 42 made of a dielectric film such as polyethylene terephthalate or polyvinylidene fluoride is fixed to the tie bar plate 41, and both side edges are made to extend along the outer peripheral surfaces of the ring members 40, 40. The transfer film 42 is fixed to a tie bar plate 41 at the rear end 42b in the circumferential direction of the transfer film 42 so as to be formed in a hollow cylindrical shape as described later.

As described above, the transfer drum 24 is supplied with the transfer paper 24 from one of the plurality of paper feed cassettes 28, 29, and 30, and the transfer paper 24 is transferred by the registration roll 33. Drum 23
And is charged by the transfer corotron 25 from the back side of the transfer drum 23, and is electrostatically attracted onto the transfer film 42 of the transfer drum 23. On the transfer paper 24 adsorbed on the transfer drum 23, black (K), yellow (Y), magenta (M), and cyan (C) toner images sequentially formed on the photosensitive drum 20 are provided.
The transfer is performed by charging the transfer corotron 25.

The transfer paper 24 on which the toner image of a predetermined number of colors has been transferred from the photosensitive drum 20 is discharged by a peeling corotron 34 as shown in FIG. After being separated from the surface of the fixing device 35, the toner image is conveyed to the fixing device 35 via the conveyance guide 45, and the toner image is fixed on the transfer sheet 24 by heat and pressure by the fixing roller 35a and the pressure roller 35b of the fixing device 35 The sheet is discharged onto a discharge tray 36 outside the apparatus by a fuser outlet roll 46.

Further, in this embodiment, a pre-cleaning charging unit for removing the toner remaining on the image carrier is disposed near the downstream side of the transfer position of the image carrier. In an image forming apparatus in which a functional member for controlling an image forming operation is arranged between the transfer position and the transfer position, an electric field formed by a charging action of the pre-cleaning charging unit is transferred on a transfer material carrier. An electric field shielding member for shielding the electric field of the pre-cleaning charging unit from reaching the functional member while allowing the electric field to reach the material is provided. The electric field shielding member is disposed, for example, between the pre-cleaning charging unit and the functional member. Further, the electric field shielding member is formed of, for example, an insulating material in a shape in which an electric field is not concentrated.

That is, in the above-described digital color copying apparatus, as shown in FIGS. 1 and 2, the toner image formed on the photosensitive drum 20 is transferred to the transfer paper 24 held on the transfer drum 23. The toner 50 remaining on the photoconductor drum 20 is weakened in adhesion to the photoconductor drum 20 by a discharge having a polarity opposite to the charging polarity of the toner from the corotron 51 before cleaning, and the cleaning blade 52 and a brush (not shown) The photosensitive drum 2 is mechanically mechanically moved by the cleaning device 53 including
0 is configured to be removed from the surface. The pre-cleaning corotron 51 has functions of "prevention of the trailing edge of the sheet" and "prevention of toner rupture (circle stamp)", in addition to the charge removal operation of the photosensitive drum 20 before the cleaning.

As shown in FIG. 5, the "paper trailing edge line" means that the trailing edge of the transfer
At the moment when the sheet is moved out of the transfer position between the transfer drum 24 and the transfer drum 23, a remarkable electric discharge occurs between the rear end of the transfer paper 24 and the photosensitive drum 20, and an electrostatic history remains on the photosensitive drum 20. This is a phenomenon in which the charge history appears as a streak in the next image. Therefore, the pre-cleaning corotron 51 is
The electrostatic history at the moment when the rear end of the transfer sheet 24 comes out of the transfer position is prevented by removing the surface of the photosensitive drum 20 from the charge. As described above, “toner rupture” means that the charged toner transferred to the surface of the transfer sheet 24 past the transfer point A, particularly at low humidity, comes close to the charge before being discharged by the discharge corotron 34, as described above. This is a phenomenon in which a discharge occurs between an edge of an object (regardless of a conductor or an insulator) and the toner image is scattered like a burst as shown in FIG. For this reason, the pre-cleaning corotron 51
Prevents the toner from bursting by appropriately discharging the charged toner transferred to the surface of the transfer sheet 24 past the transfer point A.

As described above, the pre-cleaning corotron 51 is used to effectively perform functions such as “paper trailing edge streak” and “toner rupture” in addition to the charge removal action of the photosensitive drum 20. The cleaning device 53 is provided between the transfer point A of the drum 20 and the cleaning device 53.

However, in the vicinity of the transfer point A between the transfer point A of the photosensitive drum 20 and the cleaning device 53, several other functional parts other than the pre-cleaning corotron 51 are arranged as necessary. Have been. In other words, in the vicinity of the transfer point A, for example, as shown in FIGS. 1 and 2, in order to appropriately control the toner density of the image formed on the photosensitive drum 20, A density detection sensor 54 for detecting a toner patch for density detection to be performed, and optical detection of the presence or absence of the transfer paper 24 on the transfer drum 23 at a point in time when a predetermined time has elapsed after the transfer of the toner image. 6
As shown in FIG. 5, a functional component such as a post-transfer jam sensor 55 for detecting whether or not the transfer paper 24 is wound around the photosensitive drum 20 is disposed. Among these functional components, the above-mentioned post-transfer jam sensor 55 detects the jam such that the transfer paper 24 separates from the transfer drum 23 and wraps around the photoconductor drum 20, and detects the jam immediately to detect the jam. As shown in FIGS. 1 and 2, the body drum 20 is disposed as close to the transfer point A as possible so that the body drum 20 can be stopped.

Further, in this embodiment, as shown in FIG. 1, the electric field E formed by the pre-cleaning corotron 51 by the charging action is allowed to reach the transfer paper 24 carried on the transfer drum 23. An electric field shielding member 60 that shields the electric field E of the pre-cleaning corotron 51 from reaching functional components such as the post-transfer jam sensor 55 and the density detection sensor 54 is provided.

That is, in this embodiment, as shown in FIG. 1 and FIGS.
The shield plate 66 located above the sensor 55 of the sensor holder 60 as an electric field shielding member to which the sensor 5 is attached is configured to protrude. This is because the post-transfer jam sensor 55 is not charged near the transfer point A under the influence of the electric field of the pre-cleaning corotron 51, and the unfixed toner transferred onto the transfer paper 24 is discharged from the pre-cleaning corotron 51. This is to prevent the static electricity from being appropriately removed.

As shown in FIG. 7, the sensor holder 60 is made of a synthetic resin such as ABS, and is formed in a substantially rectangular flat plate shape. One end of the sensor holder 60 rotates the transfer drum 23 as shown in FIG. A support shaft 62 that allows the transfer drum unit 61 that is rotatably supported to be tiltable so that the transfer drum unit 61 can be separated from the photosensitive drum 20 when a jam or the like occurs.
And is fixedly attached. For this reason, as shown in FIG. 7, the sensor holder 60 is provided with a mounting portion 63 at one end in the width direction for mounting to the support shaft 62. The sensor holder 60 has a flat plate portion 64 having a large area disposed substantially horizontally toward the photosensitive drum 20 side, and an end portion of the flat plate portion 64 on the photosensitive drum 20 side is provided. As shown in FIG. 1, a shielding plate 66 that shields the upper side of the post-transfer jam sensor 55 via a rising wall 65 for attaching the post-transfer jam sensor 55 by screwing or the like, is connected to the photosensitive drum 20 side. It extends substantially horizontally toward. As shown in FIG. 7, one end 67 in the longitudinal direction of the shielding plate 66 is formed in a curved shape so that it is difficult to be charged by the discharge of the corotron 51 before cleaning, and the other end 68 is a corner. Is an R-shaped inclined portion 69
Through the upper flat plate portion 70 projecting slightly above the flat plate portion 64. Since the upper flat plate portion 70 is located below the shielding plate portion 66 of the post-transfer jam sensor 55, the discharge of the pre-cleaning corotron 51 reaches the transfer paper 24 side on the transfer drum 23, and the density is detected. Even when the sensor 54 is charged, the sensor 54 also has an effect of blocking the influence of the charge appearing on the toner image on the transfer paper 24.

The shielding plate 66 of the sensor holder 60
The amount of protrusion from the end of the post-transfer jam sensor 55 is, for example, 0.5 to 2.0 mm from the end face of the sensor 55 as shown in FIG.
Is set to 7.5 mm from the corotron wire 71.
Also, the height of the shielding plate 66 of the sensor holder 60 is
For example, as shown in FIG. 9, it is set at a position 7.9 mm from the corotron wire 71 of the corotron 51 before cleaning.

Further, as shown in FIG. 8, the sensor holder 60 to which the post-transfer jam sensor 55 is attached is moved relative to the density detection sensor 54 disposed between the sensor holder 60 and the pre-cleaning corotron 51. Even if the density detecting sensor 54 is charged by the discharge of the pre-cleaning corotron 51, the effect of the electric field does not affect the unfixed toner transferred onto the transfer sheet 24, and the unfixed toner image on the sheet surface is discharged. It is configured to be slightly retracted with respect to the end of the density detection sensor 54 so as to be able to operate. The above sensor holder 60
Is set to 4.0 to 5.0 mm from the end face of the sensor 54 and 4.0 mm from the corotron wire 71 of the pre-cleaning corotron 51, for example. The height of the upper end surface 70 of the sensor holder 60 located below the density detection sensor 54 is, for example, as shown in FIG.
It is set at a position of 2 mm. As described above, since the density detection sensor 54 is different from the post-transfer jam sensor 55 in the position / height / thickness, the post-transfer jam sensor 5
The protrusion amount is set to be different from 5.

Further, as shown in FIG. 7, the sensor holder 60 is provided with a plurality of shielding plate portions 66 as protrusions.
And the upper flat plate portion 70 is connected by a gentle curve. This is because if the sensor holder 60 has a protrusion such as a corner, the electric charge of the pre-cleaning corotron 51 is prevented from being concentrated and charged at that portion.

As described above, in the above embodiment,
As shown in FIG. 1, the electric field E of the pre-cleaning corotron 51 is controlled by the pre-cleaning corotron 51 while allowing the electric field E formed by the charging action of the pre-cleaning corotron 51 to reach the transfer paper 24 carried on the transfer drum 23. Since the sensor holder 60 is provided as an electric field shielding member for shielding the functional components such as the jam sensor 55 after the transfer, the transfer is performed by the pre-cleaning corotron 51 onto the transfer paper 24 on the transfer drum 23. Since the toner image can be neutralized and the potential of the toner image immediately after being transferred onto the transfer paper 24 can be appropriately reduced, it is possible to prevent image quality defects such as toner rupture from occurring.

Further, in the above embodiment, it is assumed that the electric field of the pre-cleaning corotron 51 reaches the post-transfer jam sensor 55 and the density detection sensor 54 disposed between the pre-cleaning corotron 51 and the transfer position. As shown in FIGS. 1 and 7, since the sensor holder 60 is configured to be shielded by the shield plate 66 and the upper flat plate 70, the post-transfer jam sensor is discharged by the discharge from the corotron 51 before cleaning by the sensor holder 60. Since the charging of the toner image 55 can be prevented, the post-transfer jam sensor 55 is charged by the discharge from the pre-cleaning corotron 51, and the edge portion of the toner image is charged by the discharge of the pre-cleaning corotron 51. Transfer paper of the same polarity as the rear jam sensor 55 4 and the toner immediately after being transferred repel on, toner muscles along the process direction can be prevented from image quality defect occurs such occurs.

Second Embodiment FIG. 11 shows a second embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals. The electric field shielding member is disposed on the functional member in a stacked state, and the electric field shielding member is an insulating sheet material, and the amount of protrusion with respect to the functional member is determined according to the volume resistance of the electric field shielding member used. It is configured to be set appropriately.

That is, in Embodiment 2, FIG.
As shown in FIG. 5, an insulating sheet material 75 such as Mylar (trade name) is attached to the upper surface of the jam sensor 55 after the transfer, and the shape of the insulating sheet material 75 is such that the edge portion is hardly charged. It has a gentle shape. However, since the insulating sheet material 75 itself does not have the rigidity to support the functional components such as the post-transfer jam sensor 55, the functional components such as the post-transfer jam sensor 55 include:
It needs to be attached to other members.

In the second embodiment, since each of the functional parts to be charged can be arranged with the amount of protrusion determined in advance by experiment, there is considerable flexibility. When the protrusion amount of the insulating sheet material 75 is set to the same 2 mm and the volume resistance value is changed to compare the degree of image quality defect occurrence, as shown in FIG.
The larger the volume resistance value of the sheet material 75 is, the more advantageous it is in preventing the generation of the trailing edge streaks, but conversely, the more easily the toner bursts. This is because when the volume resistance value is large, the insulating sheet material 8
It is considered that this is because the electrostatic capacity of 0 increases, and the electric charge of the pre-cleaning corotron 51 is excessively accumulated in the sheet material 80, and the charge elimination of the toner on the surface of the transfer paper 24 is insufficient. According to an experiment, when the protrusion amount of the sheet material 75 with respect to the sensor 55 is 2 mm, by using a member having a volume resistance value larger than 10 ¹⁴ Ω and smaller than 10 ¹⁷ Ω, both “streak / toner rupture” can be reduced. Not generated. In a member having a volume resistance value higher than 10 ¹⁷ Ω,
By setting the amount of protrusion to 1 mm, "streak / toner rupture"
It has been confirmed by the experiments of the present inventors that no generation occurs.

As described above, the second embodiment is simpler than the configuration in which the protrusion is provided in the sensor holder 60, and is very effective if the sensor 55 or the like is attached to another member having rigidity. Means.

The other configuration and operation are the same as those of the first embodiment, and the description thereof will be omitted.

Third Embodiment FIGS. 13 to 15 show a third embodiment of the present invention. The same parts as those of the above-described embodiment are denoted by the same reference numerals and will be described. In 3, the electric field shielding member includes a holding member made of a synthetic resin having a frame for holding a functional component, and an insulating sheet material disposed on an upper surface of the frame of the holding member. Have been.

That is, the third embodiment is a combination of the first embodiment and the second embodiment. In the third embodiment, the post-transfer jam sensor 55
In order to prevent the sheet from being charged, an insulating sheet material 7 is provided above the post-transfer jam sensor 55, which is the most effective method.
As shown in FIG. 15, the post-transfer jam sensor 55 is attached to the upright portion 65 of the sensor holder 60 as shown in FIG. It is fixed by means such as screwing. In order to dispose an insulating sheet material 75 on the upper surface of the post-transfer jam sensor 55, the shielding plate 66 of the sensor holder 60 has
As shown in FIG. 15 to FIG. 15, a frame portion 77 is formed by providing an opening 76 larger than the outer shape of the sensor holder 60. As a result, the insulating sheet material 75
Is not directly adhered to the upper surface of the jam sensor 55 after the transfer,
7 is affixed to the upper surface by double-sided tape or the like.

By doing so, the rigidity for mounting the jam sensor 55 after transfer is obtained to some extent,
Compared to the first embodiment in which the electric field shielding member is formed only from the synthetic resin sensor holder 60, a wider latitude can be obtained by the amount of protrusion of the shielding plate portion 66 of the sensor holder 60, and design freedom. The degree increases by that amount. That is, in the third embodiment, even if the amount of protrusion of the shielding portion 66 of the sensor holder 60 is smaller than that in the first embodiment, it is possible to effectively prevent the jam sensor 55 from being charged after the transfer.

The other configuration and operation are the same as those of the above-described embodiment, and the description thereof will be omitted.

Fourth Embodiment FIG. 16 shows a fourth embodiment of the present invention. The same parts as those of the above embodiment are denoted by the same reference numerals and described. The electric field shielding member,
The electric field shielding member is arranged between the pre-cleaning charging unit and the functional member, and is formed in a shape in which an electric field is not concentrated by a grounded conductive material.

That is, in the fourth embodiment, FIG.
17, and as shown in FIG.
A conductive shield plate 80 made of a grounded metal thin plate or the like is provided between the first shield and the density detection sensor 54. The end portion 81 of the conductive shielding plate 80 on the photosensitive drum 20 side has a gentle curved shape that changes in the axial direction, and the optimum curved shape is determined by an experiment. Since this can be disposed in a place where the eyes of an ordinary operator do not touch, it can be an effective electric field shielding means even if it is formed of a thin sheet metal having low rigidity.

The shape of the end portion 81 of the conductive shielding plate 80 is, for example, as shown in FIG.
It is formed in a large curved shape of not less than mm. By forming the conductive shielding plate 80 in this manner, for example, FIG.
As shown in FIG. 8, the end portion 81 of the conductive shielding plate 80 is simply compared with a case where R is added at the intersection of the straight portion and the straight portion.
It is possible to prevent the electric field from the pre-cleaning corotron 51 from being concentrated on the edge of the conductive shielding plate 80,
It is possible to effectively prevent image quality defects from occurring.

In the fourth embodiment, as shown in FIG. 17, even if the edge of the post-transfer jam sensor 55 and the like slightly protrudes from the end 81 of the conductive shielding plate 80 toward the photosensitive drum 20, the cleaning is performed. The electric field from the front corotron 51 can be guided to the grounded conductive shielding plate 80, and the post-transfer jam sensor 55 etc.
It can be effectively prevented from being charged under the influence of the electric field from the first.

The other configuration and operation are the same as those of the first embodiment, and the description thereof will be omitted.

Fifth Embodiment FIG. 19 shows a fifth embodiment of the present invention. The same parts as those of the above embodiment are denoted by the same reference numerals and described. The edge portion of the functional member is configured to have a gentle shape in which an electric field formed by the charging action by the pre-cleaning charging unit does not concentrate on a part.

That is, in the fifth embodiment, instead of newly providing an electric field shielding member as in the above-described embodiment, as shown in FIG. 19, a density detecting sensor 54 and a post-transfer jam sensor 55 are provided. The functional member itself has a shape in which the electric field is hardly concentrated. For example, as shown in FIG. 19, the edge portion of the post-transfer jam sensor 55 is formed into a spherical shape having a large radius of curvature R so that electric charges are not accumulated. This method is effective when there is a degree of freedom in the shape of the sensor because this method is the simplest and has little effect on other components.

The other configuration and operation are the same as those of the above-described embodiment, and the description thereof will be omitted.

Sixth Embodiment FIG. 20 shows a sixth embodiment of the present invention. The same parts as those of the above embodiment are denoted by the same reference numerals and described. The electric field shielding member,
2 where a grounded conductive member and an insulating member are bonded together
It has a layer structure, and is configured such that the edge of the insulating member protrudes 1 mm or more from the edge of the conductive member.

That is, in the sixth embodiment, FIG.
21. As shown in FIG. 21, the electric field shielding member 90 is composed of an insulating member 91 and a grounded conductive member 92. Both the conductive member 91 and the insulating member 92 are formed in a gentle shape so that the electric field does not concentrate on the edge portion. The edge of the insulating member 91 is set to be shifted at least 1 mm outward from the edge of the conductive member 92. This electric field shielding member 90
Is disposed at the same position as the conductive shielding plate 80 of the fourth embodiment, for example, but is not limited thereto.
As shown in FIG. 3, the sensor holder 60 may be arranged on the upper horizontal plate 70.

The other configuration and operation are the same as those of the above-described embodiment, and the description thereof will be omitted.

[0067]

According to the present invention, there is provided the above-described structure and operation, in which functional members such as a post-transfer jam sensor and a density detection sensor are disposed near the transfer point where the pre-cleaning corotron is disposed. Even if it is not possible, it is possible to prevent the occurrence of image quality defects such as "toner burst" and toner scattering, and to provide an image forming apparatus capable of obtaining a good image.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a main part of a digital color copying apparatus as an image forming apparatus according to a first embodiment of the present invention;

FIG. 2 is a configuration diagram illustrating an image forming unit of the digital color copying apparatus as the image forming apparatus according to the first embodiment of the present invention;

FIG. 3 is a configuration diagram illustrating a digital color copying apparatus as an image forming apparatus according to a first embodiment of the present invention;

FIG. 4 is a perspective view showing a transfer drum.

FIG. 5 is an explanatory diagram showing the principle of generation of the posterior muscle.

FIG. 6 is a configuration diagram showing a paper jam.

FIG. 7 is a perspective view showing a sensor holder.

FIG. 8 is an explanatory plan view showing a positional relationship between a sensor holder and a sensor.

FIG. 9 is an explanatory front view showing a positional relationship between a sensor holder and a sensor.

FIG. 10 is a perspective view showing an image forming section of a digital color copying machine as Embodiment 1 of the image forming apparatus according to the present invention.

FIG. 11 is a perspective view showing a main part of a digital color copying apparatus as an image forming apparatus according to a second embodiment of the present invention.

FIG. 12 is a graph showing a relationship between a volume resistance value of a sheet material and an image quality defect.

FIG. 13 is a perspective view showing a sensor holder which is a main part of a digital color copying apparatus as Embodiment 3 of the image forming apparatus according to the present invention.

FIG. 14 is a plan view of a main part of FIG.

FIG. 15 is a sectional view of a main part of FIG.

FIG. 16 is a configuration diagram showing a main part of a digital color copying apparatus as Embodiment 4 of the image forming apparatus according to the present invention.

FIG. 17 is a plan view showing a conductive shielding member.

FIG. 18 is a plan view showing a comparative example of a conductive shielding member.

19 (a), 19 (b) and 19 (c) are configuration diagrams respectively showing main parts of a digital color copying apparatus as an image forming apparatus according to Embodiment 5 of the present invention.

FIG. 20 is a plan view showing an electric field shielding member which is a main part of a digital color copying apparatus as Embodiment 6 of the image forming apparatus according to the present invention.

FIG. 21 is a front view of FIG. 20;

FIG. 22 is a configuration diagram showing an image forming unit of a conventional digital color copying apparatus.

FIG. 23 is an explanatory diagram showing an image quality defect due to toner rupture.

FIG. 24 is an explanatory diagram showing image quality defects due to streak generation in the process direction.

[Explanation of symbols]

Reference Signs List 20 photosensitive drum, 23 transfer drum, 24 transfer paper, 51 corotron before cleaning, 52 cleaning blade, 54 density detection sensor, 55 jam sensor after transfer, 60 sensor holder (electric field shielding member).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuya Fujita 2274 Hongo, Fuji Xerox Co., Ltd., Ebina-shi, Kanagawa Prefecture (72) Inventor Keiji Yamamoto 2274 Hongo, Ebina-shi, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Masaaki Tokunaga, 2274 Hongo, Fuji Xerox Co., Ltd., Ebina-shi, Kanagawa Prefecture

Claims (10)

[Claims] 1. A toner image of a different color is sequentially formed on an image carrier, and the toner images of different colors formed on the image carrier are transferred onto a transfer material carried on a transfer material carrier. An image is formed by sequentially and multiplexly transferring each image, and a pre-cleaning charging unit for removing the toner remaining on the image carrier is disposed near the downstream side of the transfer position of the image carrier. In an image forming apparatus including a functional member for controlling an image forming operation between a pre-charging unit and a transfer position, an electric field formed by the charging unit by the pre-cleaning charging unit is formed on a transfer material carrier. An image forming apparatus, comprising: an electric field shielding member that shields the electric field of the pre-cleaning charging unit from reaching the functional member while allowing the electric field to reach the carried transfer material. 2. The image forming apparatus according to claim 1, wherein the electric field shielding member is disposed between the pre-cleaning charging unit and the functional member. 3. The image forming apparatus according to claim 1, wherein the electric field shielding member is disposed between the functional member and the transfer material carrier. 4. The image forming apparatus according to claim 1, wherein the electric field shielding member is formed of an insulating material in a shape in which an electric field is not concentrated. 5. The image forming apparatus according to claim 1, wherein the electric field shielding member is formed of a grounded conductive material in a shape in which an electric field is not concentrated. 6. The image forming apparatus according to claim 1, wherein the electric field shielding member is disposed on the functional member in a stacked state. 7. The electric field shielding member according to claim 6, wherein the electric field shielding member is an insulating sheet material, and an amount of protrusion to the functional member is appropriately set according to a volume resistance value of the electric field shielding member to be used. Image forming apparatus. 8. A toner image of a different color is sequentially formed on an image carrier, and the toner images of different colors formed on the image carrier are transferred onto a transfer material carried on a transfer material carrier. An image is formed by sequentially and multiplexly transferring each image, and a pre-cleaning charging unit for removing the toner remaining on the image carrier is disposed near the downstream side of the transfer position of the image carrier. An image forming apparatus comprising a functional member for controlling an image forming operation disposed between a pre-charging unit and a transfer position, wherein an electric field formed by the pre-cleaning charging unit by a discharging action on an edge portion of the functional member. An image forming apparatus characterized by having a gentle shape that does not concentrate on a part. 9. The electric field shielding member has a two-layer structure in which a grounded conductive member and an insulating member are bonded to each other,
2. The image forming apparatus according to claim 1, wherein the edge of the insulating member protrudes by 1 mm or more from the edge of the conductive member. 10. The electric field shielding member includes a holding member made of a synthetic resin having a frame for holding a functional member, and an insulating sheet material disposed on an upper surface of the frame of the holding member. The image forming apparatus according to claim 1, wherein: