JP5365533B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make nonuniform image density (streak) in a half-tone portion inconspicuous and to prevent cleaning failure due to imbalance of lubrication of a cleaning blade, in an image forming apparatus that has a separation pawl for preventing an image from being roughened due to a decrease in the toner-charging capability when a toner image is formed between images and when printing is continuously performed at a low printing rate. <P>SOLUTION: The image forming apparatus has an inter-image toner image formation control portion for forming a toner image between images so as to reduce the degree of change in the surface of a photoreceptor drum in the direction of the rotation shaft of the photoreceptor drum after image formation and removal are performed more than once. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a developing type image forming apparatus using a developer composed of a toner and a carrier.

  In an electrophotographic image forming apparatus such as a copying machine or a printer, a developing method (two-component developing method) using a developer (two-component developer) composed of toner and a carrier is often used.

  In a two-component development type image forming apparatus, image information is written by an image writing unit on a uniformly charged photosensitive member, for example, a photosensitive drum that is driven to rotate about a rotation axis, and a latent image is formed on the surface. Then, the toner is attached to the electrostatic latent image by a developing device to form a toner image, and the toner image is transferred to a transfer material, for example, recording paper.

  The recording paper to which the toner image has been transferred is separated from the photosensitive drum, fixed by a fixing device, and discharged.

  The photosensitive drum on which the toner image is transferred to the recording paper is subjected to charging to form a new latent image after the toner remaining on the surface is removed by the toner removing means. The toner removing unit rubs the surface of the rotating photosensitive drum with a member such as a cleaning blade, for example, and peels off the toner remaining on the surface. In order to smoothly perform the rubbing of the cleaning blade, a technique for forming a toner image on a photosensitive drum using a toner containing a specific amount of a lubricant such as zinc stearate is disclosed (Patent Document). 1).

  In the two-component development method, the toner and carrier in the developer are stirred in a stirring tank attached to the developing device, and the toner is charged from the carrier by frictional charging and electrostatically attached to the outer surface of the carrier. Become. The carrier to which the toner is attached, that is, the developer, is conveyed to a developing region that is a portion facing the photosensitive drum by a developer conveying member such as a developing sleeve containing a magnetic roll. In the developing area, the toner in the developer leaves the carrier and adheres to the electrostatic latent image portion of the photosensitive drum, forming a toner image.

  In the two-component development method, the toner in the agitation tank is consumed and reduced by repeating the development operation. Usually, fresh toner corresponding to the reduced toner is supplied and replenished. The amount of developer and the toner concentration in the tank are kept within a predetermined range.

  By the way, in image formation, the amount of image data for forming a toner image within the unit area of the formed image may be expressed by a printing rate. For example, when the image is formed by toner images and blank portions of the same amount, the printing rate is 50%.

  When a large amount of image formation with a low printing rate is performed, the amount of toner transferred to the photosensitive drum due to development is small, so that a large amount of toner remains in the stirring tank without being developed. The toner that remains in the agitation tank without being developed becomes longer in the circulation time in the developing device, and the charging ability is reduced by the stress that is agitated for a long time. A decrease in toner charging ability deteriorates transfer efficiency and causes image defects such as image defects.

  In order to prevent such image defects, the printing rate in the formed image is measured, and when image formation is performed at a low printing rate, it is applied to a transfer material such as recording paper formed on the photosensitive drum. A toner image having a predetermined density and pattern that is not transferred to a transfer material is formed between an image to be transferred (hereinafter referred to as a transfer target image) and a subsequent transfer target image (Patent Document). 2). The toner in the developing device is discharged by forming a toner image between the transfer target image to be transferred to a transfer material such as recording paper on the photosensitive drum and the subsequent transfer target image, and the fresh toner is developed. Since the apparatus is replenished, the developer in the developing apparatus can be maintained in a preferable state even when a large amount of image formation with a low printing rate is performed.

  A toner image formed between images to be transferred (hereinafter referred to as an inter-image toner image) is not transferred onto a transfer material such as recording paper, but is removed from the surface of the photosensitive drum by a toner removing unit. The formation of the inter-image toner image and the removal by the toner removing unit are performed whenever necessary according to the printing rate in the image formation performed by the image forming apparatus.

  By the way, in order to reliably separate the paper on which the toner image is transferred from the photosensitive drum, a separation claw is disposed (see Patent Document 3).

  A plurality of separation claws are usually arranged along the direction of the rotation axis of the surface of the photosensitive drum, and each of the separation claws is arranged in contact with the surface of the photosensitive drum. Then, the front end portion is hooked on the surface of the rotating photosensitive drum and the end face of the paper that is in close contact with the photosensitive drum, and the paper is separated from the photosensitive drum.

  If the separation claw is in contact with the same part of the photosensitive drum that is driven to rotate, the surface of the photosensitive drum may be scratched. It is also made not to contact (see Patent Document 4).

  If the above-described inter-image toner image is formed at a position where the separation claw faces and contacts the photosensitive drum, the inter-image toner image is not transferred to a transfer material such as recording paper. The inter-image toner image is conveyed to the contact position of the separation claw.

  The inter-image toner image conveyed to the contact position of the separation claw is scraped off by the separation claw that is in contact with the photosensitive drum. The toner scraped off by the separation claws may be scattered around and cause contamination inside the image forming apparatus. For this reason, a technique for forming an inter-image toner image while avoiding the position where the separation claw on the photosensitive drum contacts is disclosed (see Patent Document 5).

  FIG. 11 is a diagram illustrating an example of an inter-image toner image according to the related art.

Inter-image toner image P in the prior art along a straight line L _p which is in contact with the surface of the photosensitive drum 31 in parallel to the rotation axis CL ₃₁ of the photosensitive drum 31 as shown in FIG. 11 (a), the separation pawl 38L and separation The claw 38 </ b> R is formed so as to avoid a portion where it contacts the photosensitive drum 31. The inter-image toner image P includes toner adhering portions T ₁ , T ₂ , T _{3 to} which toner of a constant density is adhered, and blank portions B ₁ , B ₂ to which toner is not adhered. The blank portion _B 1, _{B 2} along the straight line _{L P} parallel to the rotational axis _{CL 31} of the photosensitive drum 31, the separation claw 38L and separation pawl 38R is formed in contact with the site to the photosensitive drum 31.

  The inter-image toner image P is removed from the surface of the photosensitive drum 31 when the photosensitive drum 31 rotating in the direction of the arrow in the drawing is rubbed against the cleaning blade 371.

  The formation and removal of the inter-image toner image P on the photosensitive drum 31 is performed whenever necessary according to the printing rate in the image formation performed by the image forming apparatus. Since the inter-image toner image P is formed between the transfer target images of the rotating photosensitive drum 31, the circumferential position to be formed is determined and fluctuated by the position of the transfer target image.

On the other hand, the direction and position along the rotational axis CL ₃₁ of the photosensitive drum 31 to image between the toner image P is formed is constant. In the prior art, the image patterns of the formed inter-image toner image P (the shapes and arrangement positions of the toner adhering portion and the blank portion) are the same.

FIG. 11B is a diagram in which the inter-image toner images P formed multiple times (three times in the drawing) on the photosensitive drum in the prior art are arranged side by side. In FIG. 11 (b) three of the photoreceptor drum 31 by the image between the toner image P is formed, respectively, shown side by side along the end in a straight line L _0.

As shown in the figure, the inter-image toner images P ₁ , P ₂ , and P ₃ formed three times are formed at a fixed position from the end of the photosensitive drum 31. Then each image pattern in the image between the toner images _{P 1,} P 2, _{P 3} are the same, each of the toner adhesion portion of the image between the toner images _{P 1, P 2, P 3} T 1, T 2, T 3, In addition, the shape of the blank portions B ₁ and B ₂ and the position at which each of the blank portions B ₁ and B ₂ is formed are constant along the rotational axis of the photosensitive drum 31.

Accordingly, each of the toner adhesion portion T ₁ of the image between the toner images P _1, P _2, P ₃ are formed at the same position from the end portion of the photosensitive drum 31, each of the illustrated left end along the straight line L _1, each illustrated right end portion is formed along a straight line L _2. Similarly toner adhesion portion T ₂ are formed on the same position from the end portion of the photosensitive drum 31, shown left end along the straight line L _3, illustrated right end portion is formed along a straight line L _4. The toner adhesion portion T ₃ is formed at the same position from the end portion of the photosensitive drum 31, each of the illustrated left end along the straight line L _5, illustrated right end portion is formed along a straight line L _6.

Japanese Patent Laid-Open No. 11-184340 JP 2003-76079 A Japanese Patent Laid-Open No. 7-92819 JP-A-6-43780 JP 2009-162977 A

The toner in the inter-image toner image is removed from the surface of the photosensitive drum 31 when the photosensitive drum 31 is rubbed against the cleaning blade 371. However, as shown in FIG. 11, an inter-image toner image composed of toner adhering portions T ₁ , T ₂ , T 3 to which toner adheres and blank portions B ₁ , B ₂ to which no toner adheres is obtained by a cleaning blade 371. Even if the toner is removed, an imbalance may occur between the portion where the toner is attached to the surface of the photosensitive drum and the portion where the toner is not attached.

  For example, when a toner containing a lubricant (for example, zinc stearate) is used, even if the inter-image toner image is removed from the photosensitive drum 31 by the cleaning blade 371, the toner adheres to the photosensitive drum 31. A small amount of the lubricant contained in the toner remains at the site where the toner has been removed. On the other hand, no lubricant remains in the blank portion.

  The formation and removal of the inter-image toner image P on the photosensitive drum 31 is performed whenever necessary according to the printing rate in the image formation performed by the image forming apparatus. When a plurality of times of image formation, particularly image formation with a low printing rate is performed many times, formation and removal of the inter-image toner image P are also performed many times, and toner adheres to a plurality of locations on the peripheral surface of the photosensitive drum 31. The toner lubricant removed from the portion remains. On the other hand, the lubricant does not adhere to the blank portion where the toner has not adhered. Therefore, when the formation and removal of the inter-image toner image P is performed many times, a portion where the lubricant adheres to the circumferential portion of the surface of the photosensitive drum (the portion where the toner attachment portion is formed and removed), Parts where the lubricant does not adhere (blank portions corresponding to parts where the separation claws face each other) are formed adjacent to each other in the axial direction of the photosensitive drum 31.

FIG. 12 is a diagram illustrating a portion where the lubricant formed on the surface of the photosensitive drum in the conventional technique adheres and a portion where the lubricant does not adhere. FIG. 12 is a diagram illustrating the photosensitive drum 31 after the formation and removal of the inter-image toner image P described in FIG. 11 is repeated. As illustrated in FIG. 12A, the surface of the photosensitive drum 31 is illustrated. Sites Y ₁ , Y ₂ , Y ₃ where the lubricant remains and adheres along the circumferential direction and sites Z ₁ , Z ₂ where the lubricant does not adhere are formed adjacent to each other in the axial direction. Sites Y ₁ , Y ₂ , Y ₃ where the lubricant remains adhered are sites where formation and removal of the toner adhesion portions T ₁ , T ₂ , T ₃ are repeated, respectively, and sites Z ₁ , where the lubricant does not adhere Z ₂ is a portion corresponding to the blank portions B ₁ and B ₂ . Boundary between the region Z1 lubricant does not adhere site Y ₁ and the lubricating agent remaining attached is a position corresponding to the straight line L ₂ which shown in FIG. 11 (b) in the photosensitive drum 31. Likewise boundary between sites _{Z 1} and site _{Y 2,} the boundary between the part _{Y 2} and site _{Z 2,} the boundary between the region _{Z 2} and part _{Y 3,} respectively, shown in FIG. 11 (b) in the photosensitive drum 31 The positions corresponding to the straight lines L ₃ , L ₄ , L ₅ .

  FIG. 12B is a conceptual diagram showing a cross-section of the surface portion of the photosensitive drum 31, and the thickness of the lubricant adhering portion is expressed exaggeratingly than the actual thickness.

As shown in the drawing, the thickness of the lubricant in the portions Y ₁ , Y ₂ , and Y _{3 where} the lubricant remains adhered increases rapidly from the portions Z ₁ and Z ₂ where the adjacent lubricant does not adhere.

  The amount of lubricant in the part where the lubricant on the surface of the photosensitive drum adheres and remains is adjacent to the part where the lubricant does not remain, and the amount of lubricant attached abruptly changes at the boundary, That is, the rapid change in the surface of the photosensitive drum in the direction of the rotation axis is an imbalance in the surface condition provided to the photosensitive drum, and causes the following problems.

Image Density Unevenness A difference in potential occurs between the part where the lubricant on the photosensitive drum adheres and remains, and the part where it does not remain. In particular, when a halftone image is formed, there may be a problem that the boundary portion where the amount of lubricant that adheres and remains suddenly changes looks streaks.

Unsatisfactory cleaning Since the adhesion state of the lubricant in the direction of the rotation axis of the photosensitive drum is not uniform, the cleaning blade is not lubricated, and the cleaning blade that slides on the photosensitive drum is partially pulled differently. For this reason, the rubbing of the surface of the photosensitive drum and the scraping off of the residual toner are not uniform, which causes a cleaning failure.

  The present invention has been made in view of the background as described above. In an image forming apparatus having a separation claw, it is possible to prevent image deterioration due to a decrease in toner charging ability when continuous printing at a low printing rate is performed. Another object of the present invention is to provide an image forming apparatus that performs image density unevenness (streaks) in a halftone portion without conspicuous and without causing a cleaning failure due to an unbalanced lubrication of the cleaning blade.

  The above problem is solved by the following means.

1. An image writing unit;
A photosensitive drum that is driven to rotate about a rotation axis and forms and carries a latent image based on image information written by the image writing unit;
A developing device for converting a latent image carried on the photosensitive drum with toner containing a lubricating component into a toner image;
A separation claw for separating the recording paper onto which the toner image on the photosensitive drum has been transferred from the photosensitive drum;
A cleaning unit for removing toner remaining on the photosensitive drum,
In addition to performing the transfer target image forming operation for transferring the toner image on the photosensitive drum to the recording paper, the toner image to be transferred to the recording paper formed on the photosensitive drum and the subsequent recording paper An inter-image toner image having a plurality of toner adhering portions facing each other with a blank portion avoiding the separation claw sandwiched between the subsequent toner image transferred to the toner image and discharging a part of the toner from the developing device In the image forming apparatus for removing the inter-image toner image by the cleaning unit,
An inter-image toner image formation control unit that controls the operation of the image writing unit to write an inter-image toner image in which the toner adhesion amount of the toner adhesion unit gradually decreases toward the blank portion. An image forming apparatus.

2 . 2. The image forming apparatus according to 1 , wherein a dimension of the toner adhering portion in a direction along a circumference of the photosensitive drum gradually decreases toward the blank portion.

3 . An image writing unit;
A photosensitive drum that is driven to rotate about a rotation axis and forms and carries a latent image based on image information written by the image writing unit;
A developing device for converting a latent image carried on the photosensitive drum with toner containing a lubricating component into a toner image;
A separation claw for separating the recording paper onto which the toner image on the photosensitive drum has been transferred from the photosensitive drum;
A cleaning unit for removing toner remaining on the photosensitive drum,
In addition to performing the transfer target image forming operation for transferring the toner image on the photosensitive drum to the recording paper, the toner image to be transferred to the recording paper formed on the photosensitive drum and the subsequent recording paper An inter-image toner image having a plurality of toner adhering portions facing each other with a blank portion avoiding the separation claw sandwiched between the subsequent toner image transferred to the toner image and discharging a part of the toner from the developing device In the image forming apparatus for removing the inter-image toner image by the cleaning unit,
An inter-image toner image formation control unit that controls the operation of the image writing unit to write an inter-image toner image in which the density of toner adhering to the toner adhering unit gradually decreases toward the blank portion ; An image forming apparatus.

4 . An image writing unit;
A photosensitive drum that is driven to rotate about a rotation axis and forms and carries a latent image based on image information written by the image writing unit;
A developing device for converting a latent image carried on the photosensitive drum with toner containing a lubricating component into a toner image;
A separation claw for separating the recording paper onto which the toner image on the photosensitive drum has been transferred from the photosensitive drum;
A cleaning unit for removing toner remaining on the photosensitive drum,
In addition to performing the transfer target image forming operation for transferring the toner image on the photosensitive drum to the recording paper, the toner image to be transferred to the recording paper formed on the photosensitive drum and the subsequent recording paper An inter-image toner image having a plurality of toner adhering portions facing each other with a blank portion avoiding the separation claw sandwiched between the subsequent toner image transferred to the toner image and discharging a part of the toner from the developing device In the image forming apparatus for removing the inter-image toner image by the cleaning unit,
Wherein by controlling the operation of the image writing unit, every time the formation of the inter-image toner image, the image between images between the toner image to perform writing of the toner image boundary position between the blank portion in the toner adhesion portion varies An image forming apparatus having a formation control unit .

5 . A separation claw moving mechanism for moving the separation claw along the rotation axis direction of the photosensitive drum;
5. The image forming apparatus according to claim 1 , 3 , or 4 , wherein the blank portion in the inter-image toner image is formed at a position of the separation claw to be moved.

  According to the present invention, image density unevenness (streaks) can be prevented in a halftone portion by preventing image blur due to a decrease in toner charging ability when low printing rate printing is continuously performed in an image forming apparatus having a separation claw. It is possible to provide an image forming apparatus that does not stand up and that does not cause a cleaning failure due to an imbalance in the lubrication of the cleaning blade.

1 is a conceptual diagram of an image forming apparatus G according to an embodiment of the present invention. 3 is a block diagram illustrating a control relationship of the image forming apparatus G. FIG. 2 is a conceptual diagram illustrating a configuration of an image forming unit 3 of an image forming apparatus G. FIG. FIG. 6 is a diagram illustrating an inter-image toner image formed by the image forming apparatus G of the present embodiment. FIG. 6 is a diagram illustrating an example of an inter-image toner image in which a toner adhesion amount of a toner adhesion portion gradually decreases toward a blank portion. FIG. 6 is a diagram illustrating an example of an inter-image toner image in which a boundary position between a toner adhering portion and a blank portion varies every time an inter-image toner image is formed a plurality of times. It is a schematic block diagram explaining the mechanism which reciprocates a separation nail. FIG. 6 is a diagram illustrating a state where an inter-image toner image formation position is conveyed to a position where separation claws 38L and 38R face each other as the photosensitive drum 31 rotates. It is a figure which shows the state which formed the inter-image toner image P which arranged the blank part in the position which opposes the separation claws 38L and 38R to be moved several times corresponding to the movement of the separation claws 38L and 38R. 5 is a flowchart for explaining timing for forming an inter-image toner image P. It is a figure which shows an example of the toner image between images in a prior art. It is a figure explaining the site | part to which the lubricant formed in the surface of the photoreceptor drum in the prior art adheres, and the site | part which a lubricant does not adhere.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a conceptual diagram of an image forming apparatus G according to an embodiment of the present invention.

  The image forming apparatus G includes an image reading unit 1, an image writing unit 2, an image forming unit 3, a paper feeding / conveying unit 5, an operation display unit 6, a fixing unit 7, a control unit 9, and the like. Further, the image forming apparatus G has an automatic document feeder 8 at the top of the main body. The image forming apparatus G performs an image forming operation for forming and discharging a toner image on a sheet based on job information input from the operation display unit 6 under the control of the control unit 9.

  The automatic document feeder 8 feeds the documents placed on the document placing table 81 one by one by the document separating means 82 and discharges them to the document discharge table 85. The document image is read by a slit 11 provided in the document conveyance path, which is a document image reading position of the image reading unit 1.

  The image reading unit 1 captures a document image, which is light-irradiated by the lamp 12 at the position of the slit 11, as a linear CCD by a first mirror unit 13, a second mirror unit 14, and an imaging lens 15. An image is formed on the element 16. The signal output from the image sensor 16 is A / D converted in the image processing unit of the control unit 9, subjected to processing such as shading correction and image compression, and stored as image data in the RAM 93 of the control unit 9.

  The image writing unit 2 rotates at a constant speed of the image forming unit 3 by the laser beam and the polygon mirror based on the image data called from the RAM 93, and is uniformly charged by the charging unit 32. The electrostatic latent image corresponding to the original image is formed on the surface of the photosensitive drum 31 by scanning the surface.

  The electrostatic latent image formed on the photosensitive drum 31 is reversely developed by the developing unit 34 of the image forming unit 3 to become a toner image.

  Corresponding to the timing of toner image formation, the sheet S is fed from the sheet feeding / conveying unit 5 having manual sheet feeding means or a tray that accommodates the sheet S as a transfer material, and is conveyed by the conveying roller 51. The timing roller 52 synchronizes the toner image formed on the photosensitive drum 31 with the toner image and sends it to the transfer area.

  In the transfer area, the toner image (transfer target image) formed on the surface of the photosensitive drum 31 is transferred to the paper S by the action of the transfer unit 35.

  The sheet S carrying the toner image is separated from the surface of the photosensitive drum 31 by the action of the separation unit 36 and sent to the fixing unit 7. Reference numeral 38 </ b> R denotes a separation claw, and the front end of the separation claw faces and comes into contact with the photosensitive drum 31 to ensure separation of the sheet S from the photosensitive drum 31. In the present embodiment, another separation claw 38L (not shown) is arranged on the illustrated back side of the illustrated separation claw 38R.

  In the fixing unit 7, the sheet S carrying the toner image is conveyed while being heated and pressurized by the heating roller 71 and the pressure roller 72, the toner image is fixed on the sheet S, and is discharged to the outside by the discharge roller 53. Discharged.

  When the paper S is turned upside down and sent out, the switching guide 54 guides the paper S to the paper discharge / refeed unit 55, switches back the paper S, and sends it to the discharge roller 53.

  In addition, when forming an image on both sides of the sheet S, the sheet S that has been fixed on the first side is led to the reversing unit 56 of the paper discharge / refeed unit 55 by the switching guide 54 and reversed. Thereafter, the image is sent to the image forming unit 3 via the conveyance path 57 and used for image formation on the second surface.

  On the other hand, the surface of the photosensitive drum 31 after the transfer of the toner image onto the paper S is prepared for the next image formation after the residual toner is removed by the cleaning unit 37.

  FIG. 2 is a block diagram illustrating a control relationship of the image forming apparatus G.

  The control unit 9 is a computer system having a CPU 91 as a central processing element, a ROM 92 and a RAM 93 as memories, and an arithmetic unit, an I / O port, a communication interface, etc. (not shown). It is connected to each part via.

  Control of each unit is performed by the CPU 91 executing a program corresponding to the job stored in the ROM 92. In addition to the program for operating the CPU 91, the ROM 92 stores inter-image toner image data, which will be described later, and predetermined constants (threshold values, etc.). The RAM 93 functions as a storage unit capable of storing and reading a plurality of pieces of information, and also functions as a counter for adding and storing quantities.

  The CPU 91 also functions as an inter-image toner image formation control unit. The image writing unit 2 performs writing based on the inter-image toner image data between the transfer target images under the control of the CPU 91, thereby forming an inter-image toner image on the photosensitive drum 31.

  In addition, about the block which is not directly related to description of embodiment of this invention, description in a figure is abbreviate | omitted.

  FIG. 3 is a conceptual diagram illustrating the configuration of the image forming unit 3 of the image forming apparatus G.

  The image forming unit 3 includes a photosensitive drum 31 that is a drum-shaped image carrier, and a charging unit 32, a developing unit 34, a transfer unit 35, a separating unit 36, a cleaning unit 37, and the like arranged along the peripheral surface thereof. Become.

  The arrow a in the figure indicates the optical path of the laser beam of the image writing unit 2 that scans and exposes the peripheral surface, which is the photosensitive surface of the photosensitive drum 31, and the arrow b indicates the path of the paper S before the toner image is transferred. , Arrow c indicates the path of the sheet S carrying the transferred toner image.

  An arrow r indicates the rotation direction of the photosensitive drum 31.

  The photosensitive drum 31 uniformly charged by corona discharge of the charging unit 32 is subjected to scanning exposure with the beam light carrying the image information by the image writing unit 2, so that a latent image is formed on the photosensitive drum 31. Is formed. The formed latent image is conveyed to a position facing the developing unit 34 by the rotation of the photosensitive drum 31, and is developed by the developing unit 34 to become a toner image.

  Corresponding to the position of the developed image, the sheet S is sent out by the timing roller 52, and the toner image (transfer target image) on the photosensitive drum 31 is transferred to the sheet S by the action of the transfer unit 35.

  The sheet S carrying the toner image is separated from the photosensitive drum 31 by the action of the separation unit 36 and proceeds to the fixing unit 7 provided in the direction of the arrow c. The separation claw 38R and the separation claw 38L (not shown) arranged on the back side thereof are arranged with their tips abutting against the surface of the photosensitive drum 31, and the separation of the sheet S from the photosensitive drum 31. Make sure.

  When images are continuously formed, it is necessary to provide a predetermined interval (between sheets) between the sheets conveyed continuously by the transfer unit 35. Therefore, the transfer target image on the photosensitive drum 31 transferred to the sheet is also formed with an image interval (inter-sheet interval) corresponding to the interval of the conveyed sheet.

  The inter-image toner image P (details will be described later) is formed between the images to be transferred (between sheets) transferred onto the sheet on the photosensitive drum 31.

  Under the control of the CPU 91 that also functions as an inter-image toner image formation control unit, the image writing unit 2 uses a laser beam that carries image information (image pattern information) of the inter-image toner image P with the photosensitive drum 31. A scanning exposure is performed between the images to be transferred (paper interval), and a latent image of the inter-image toner image is formed on the photosensitive drum 31. The latent image of the inter-image toner image P formed on the photosensitive drum 31 is developed by the developing unit 34 and becomes an inter-image toner image P to which toner is attached. Since this inter-image toner image P is not transferred onto the paper, it is carried on the photosensitive drum 31 as it is and conveyed to the cleaning unit 37.

  The cleaning unit 37 includes a cleaning blade 371.

  The cleaning blade 371 is generally made of an elastic resin, for example, a polyurethane resin, and rubs the surface of the photosensitive drum 31 whose tip is rotationally driven to remove toner remaining on the surface of the photosensitive drum 31. To do.

  In order to smoothly perform the rubbing between the cleaning blade 371 and the photosensitive drum 31, the image forming apparatus G uses a lubricant containing a specific amount of lubricant, in this embodiment, zinc stearate. .

FIG. 4 is a diagram illustrating an inter-image toner image formed by the image forming apparatus G according to the present embodiment. Reference numeral 31 shown in the figure is a flat developed outer peripheral surface of a cylindrical photosensitive drum 31. I ₁ and I ₂ represent transfer target images formed on the outer periphery of the photosensitive drum 31, I ₁ is a transfer target image formed in advance, and I ₂ is a transfer formed after I _1. This is the target image. An arrow x is a direction in which the image is moved by the rotation of the photosensitive drum 31.

As illustrated, the inter-image toner image P is formed between the transfer target images I ₁ and I ₂ (between sheets) under the control of the CPU 91 that also functions as an inter-image toner image formation control unit. .

  The inter-image toner image is a belt-like image extending along the rotation axis direction of the photosensitive drum 31 and is formed on the peripheral surface of the photosensitive drum 31 with a blank portion without toner adhesion at a position facing the separation claw. Is done.

The image forming apparatus in the present embodiment has two separation claws (separation claws 38L and 38R), and the inter-image toner image P has two blank portions B _{1 at} positions facing the separation claws 38L and 38R, respectively. , and _{B 2,} toner adhesion portion _T 1, _{T 2} across the blank portion _{B 1} is composed of a toner adhesion portion _T 2, _{T 3} Prefecture across the blank portion _{B 2.}

The image pattern of the inter-image toner image P, that is, the inter-image toner constituted by the toner adhering portion T ₁ , the blank portion B ₁ , the toner adhering portion T ₂ , the blank portion B ₂ , and the toner adhering portion T ₃ . In the image P, the toner adhesion portions T ₁ , T ₂ , T ₃ , the shape and size of the blank portions B ₁ , B ₂ , the formation position on the photosensitive drum 31, and the toner adhesion portions T ₁ , T ₂ , T ₃ The toner density is stored in the ROM 92 of the control unit 9 as inter-image toner image data.

The inter-image toner image P is formed by using the inter-image toner image data stored in the ROM 92 as a transfer target image (I ₁ ) formed in advance on the photosensitive drum 31 by the image writing unit 2, and A latent image is formed by writing between subsequent transfer target images (I ₂ ) (between sheets), and developed by the developing unit 34.

  In this way, by forming the inter-image toner image P, the toner of the developing unit 34 is consumed, and fresh toner is replenished to the developing device. Therefore, even when a large amount of image formation with a low printing rate is performed, development is performed. The toner in the portion 34 can be kept in a preferable state.

  The inter-image toner image P is removed by the cleaning unit 37 as described above without being transferred to the paper.

  As described above, in the image forming apparatus G of the present embodiment, toner containing a specific amount of lubricant (zinc stearate) is used.

Even if the inter-image toner image composed of the toner adhesion portions T ₁ , T ₂ , T _{3 to} which the toner adheres and the blank portions B ₁ , B ₂ to which the toner is not adhered is removed by the cleaning blade 371 of the cleaning portion 37, A small amount of lubricant remains in the portion of the photosensitive drum 31 where the toner is removed from the toner adhesion portion T, but no lubricant remains in the blank portion where no toner is adhered.

  Accordingly, when the formation and removal of the inter-image toner image P is executed many times, the portion where the lubricant adheres to the circumferential portion of the surface of the photosensitive drum 31 (the portion where the toner attachment portion T is formed and removed). And the site | part (part corresponding to a blank part) to which a lubricant does not adhere is alternately formed along the axial direction of the photosensitive drum.

  There is a potential difference between the portion on the photosensitive drum where the lubricant remains attached and the portion where the lubricant does not remain. Therefore, even if the same exposure is made, there is a difference in image density, and if the lubricant thickness of the portion where the lubricant remains is suddenly increased from the portion where the lubricant does not adhere, especially when a halftone image is formed, There may be a problem that the boundary portion between the portion where the agent remains and the portion where the lubricant does not adhere appears streak. Further, the portion of the photosensitive drum on which the lubricant remains adhered and the portion where it does not remain are partially different in the manner in which the cleaning blade that slides on the photosensitive drum is pulled. For this reason, the rubbing of the surface of the photosensitive drum and the scraping off of the residual toner are not uniform, which causes a cleaning failure.

  In the image forming apparatus G of the present embodiment, even when the formation and removal of the inter-image toner image P are executed many times, the boundary between the part where the lubricant remains on the photosensitive drum and the part where the lubricant does not remain is obtained. It is configured to form an inter-image toner image P in which the change in the thickness of the lubricant is gradual, that is, the degree of change in the surface of the photosensitive drum in the rotation axis direction is gradual.

Hereinafter, the content of the inter-image toner image P in which the change in the thickness of the lubricant at the boundary between the portion where the lubricant remains on the photosensitive drum and the portion where the lubricant does not remain will be described.
<First Embodiment of Inter-Image Toner Image P>
In the first embodiment, the toner adhesion amount of the toner adhesion part in the inter-image toner image gradually decreases toward the blank part.

  FIG. 5 is a diagram illustrating an example of an inter-image toner image in which the toner adhesion amount of the toner adhesion portion gradually decreases toward the blank portion.

To gradually reduce the toner adhesion amount of the toner adhesion part in the inter-image toner image toward the blank part is realized by gradually reducing the circumferential dimension of the photosensitive drum of the toner adhesion part toward the blank part. FIG. 5A is a diagram showing an inter-image toner image P in which toner adhering portions T ₁ , T ₂ , and T ₃ are arranged by gradually reducing the circumferential dimension of the photosensitive drum toward the blank portion.

As shown in the figure, the toner adhering portions T ₁ , T ₂ , T ₃ are formed to have an M portion having a shape in which the circumferential dimension of the photosensitive drum gradually decreases toward the blank portion.

  Data for forming the inter-image toner image P shown in FIG. 5A is stored in the ROM 92 as the inter-image toner image data, and the image writing unit 2 uses the inter-image toner image data to store the data on the photosensitive drum 31. Writing is performed between images to be transferred.

  Calling of the inter-image toner image data from the ROM 92 and writing by the image writing unit 2 using the called inter-image toner image data are performed under the control of the CPU 91. The CPU 91 calls the inter-image toner image data and performs writing using the inter-image toner image data at a predetermined timing, so that the image shown in FIG. An inter-image toner image P shown in a) is formed.

In addition, gradually decreasing the toner adhesion amount of the toner adhesion part in the toner image between the images toward the blank part gradually reduces the image density of the toner adhesion part (the density of the toner adhered to the toner adhesion part) toward the blank part. This is also realized. FIG. 5B is a diagram illustrating an inter-image toner image P in which toner adhesion portions T ₁ , T ₂ , and T _{3 in} which the image density of the toner adhesion portion is gradually decreased toward the blank portion are arranged.

As shown in the drawing, the toner adhesion portions T ₁ , T ₂ , and T ₃ are formed to have an N portion where the image density gradually decreases toward the blank portion.

  Data for forming the inter-image toner image P shown in FIG. 5B is stored in the ROM 92 as inter-image toner image data, and the image writing unit 2 uses the inter-image toner image data to store the data on the photosensitive drum 31. Writing is performed between images to be transferred.

  Calling of the inter-image toner image data from the ROM 92 and writing by the image writing unit 2 using the called inter-image toner image data are performed under the control of the CPU 91. The CPU 91 calls the inter-image toner image data and performs writing using the inter-image toner image data at a predetermined timing, so that the image shown in FIG. An inter-image toner image P shown in b) is formed.

As shown in FIG. 5A, the inter-image toner image P in which the toner adhesion portions T ₁ , T ₂ and T ₃ are arranged, or the toner adhesion portions T ₁ and T ₂ as shown in FIG. 5B. inter-image toner image P which arranged T _3, when the formation and removal was performed multiple times, the thickness of the lubricant at the boundary of the site where the lubricant on the photosensitive drum are attached remains, a site that does not remain Is an inter-image toner image in which the change of the surface of the photosensitive drum can be made gentle, that is, the degree of change of the surface in the rotation axis direction of the photosensitive drum can be made gentle.

  FIG. 5C shows the thickness of the lubricant remaining on the surface of the photosensitive drum when the formation and removal of the inter-image toner image P as shown in FIGS. 5A and 5B is performed a plurality of times. FIG. FIG. 5C is a conceptual diagram showing a cross-section of the surface portion of the photosensitive drum 31, and the thickness of the lubricant adhering portion is expressed exaggerated than the actual thickness.

As shown, the thickness of the lubricant P _A at the portion Y _1, Y _2, Y ₃ the lubricant remains deposited on the surface of the photosensitive drum 31, part Z ₁ adjacent lubricant does not adhere, has been gradually increased from Z _2, when forming a halftone image, the boundary portion between the portion not adhered site and lubricant lubricant remains suppressing problems or visible to streaky, a cleaning failure be able to.
<Embodiment 2 of Inter-Image Toner Image P>
In the second embodiment, the boundary position between the toner adhesion portion and the blank portion is changed every time the inter-image toner image is formed a plurality of times.

  FIG. 6 is a diagram illustrating an example of an inter-image toner image in which the boundary position between the toner adhering portion and the blank portion changes every time the inter-image toner image is formed a plurality of times.

  The boundary position between the toner adhering portion and the blank portion is changed, for example, by sequentially forming a plurality of inter-image toner images P having different boundary positions between the toner adhering portion and the blank portion.

In the present embodiment, three types of image patterns shown in FIG. 6A having different boundary positions with the blank portion of the toner adhesion portion are represented by the inter-image toner images P _A , P _B , P _C , and P _B. The sequential formation between the transfer target images on the photosensitive drum is sequentially repeated as one cycle.

Here, the image between the toner image P _A, the blank portion is formed at a position where the peripheral surface of the photosensitive drum 31 faces the separation claw 38.

The axial length of the photosensitive drum 31 in the blank portion of the image between the toner image P _B, that is, the width is wider than the rotation axis direction of the width of the photosensitive drum 31 in the blank portion of the image between the toner image P _A, and configured such blank portion of the image between the toner image P images between the toner image P _a in the region of the blank portion of the _B is included. Similarly, the width of the blank portion of the image between the toner image P _C is wider than the width of the blank portion of the image between the toner image P _B, and an image between the toner image P _B in the region of the blank portion of the image between the toner image P _C The blank part is configured to be included.

The data for forming the inter-image toner images P _A , P _B , and P _C shown in FIG. 6A are the inter-image toner image data A, the inter-image toner image data B, and the inter-image toner image data C, respectively. The image writing unit 2 writes between the images to be transferred on the photosensitive drum 31 using the inter-image toner image data A, B, and C.

  The calling of the inter-image toner image data from the ROM 92 and the writing by the image writing unit 2 using the called inter-image toner image data are performed under the control of the control unit 9.

Control unit 9 first call inter-image toner image data A at a predetermined timing, and to perform the writing using the inter-image toner image data A call inter-image toner image P _A between the transfer target image Subsequently, the inter-image toner image data B is called and the inter-image toner image data A is first used to form the inter-image toner image P _A between the transfer target images that follow. Writing is performed using the inter-image toner image data _B to form an inter-image toner image P _B. The formation of the inter-image toner images P _A , P _B , P _C , and P _B in this order between the transfer target images on the photosensitive drum is sequentially repeated as one cycle.

FIG. 6B shows one cycle formed between the transfer target images of the photosensitive drum 31 in order of the inter-image toner images P _A , P _B , P _C , and P _B. is a diagram for explaining a state to form a toner image P _a and P _B between two images of the first in the cycle following thereafter.

As described above, the width of the blank portion of the image between the toner image P _B is wider than the width of the blank portion of the image between the toner image P _A, and, the inter-image toner images in the region of the blank portion of the image between the toner image P _B is configured to include a blank portion of the P _a, the width of the blank portion of the image between the toner image P _C is wider than the width of the blank portion of the image between the toner image P _B, and, and, the inter-image toner image P _C The blank portion of the inter-image toner image P _B is included in the blank portion region. With this configuration, along the photosensitive drum 31 to the image formed between the toner image P _A, P _B, in the axial direction of the photosensitive drum 31 at the boundary between the toner adhesion portion and a blank portion in each of the P _C The position changes every time an inter-image toner image is formed. Therefore, after such an inter-image toner image is formed and removed repeatedly, the change in the thickness of the lubricant at the boundary between the portion where the lubricant adheres and remains on the photosensitive drum does not occur. It can be made gentle, that is, the degree of change of the surface of the photosensitive drum in the rotation axis direction is gentle.
<Third Embodiment of Inter-Image Toner Image P>
The inter-image toner image P in the first and second embodiments described above has a blank portion facing the separation claws 38L and 38R whose axial positions facing the peripheral surface of the photosensitive drum 31 are constant. However, the inter-image toner image in the third embodiment moves in conjunction with the separation claw in which the blank portion moves along the rotation axis direction of the photosensitive drum.

  By moving the separation claw along the direction of the rotation axis of the photosensitive drum, the portion where the separation claw contacts the photosensitive drum is not fixed at the same location, so that the life of the photosensitive drum can be extended.

  By using the configuration of the separation claw reciprocating unit 4 according to the present invention, the life of the rotating body 5 can be extended.

  Further, the change in the thickness of the lubricant at the boundary between the portion where the lubricant remains on the photosensitive drum and the portion where the lubricant does not remain can be made gentle.

  FIG. 7 is a schematic configuration diagram illustrating the separation claw reciprocating unit 4 that reciprocates the separation claw, and is a view of the photosensitive drum 31 and the separation claw 38R (38L) illustrated in FIG. 1 as viewed from above.

  The separation claw reciprocating unit 4 is disposed on a substrate 41 fixed to the image forming apparatus, on a reciprocating shaft 42, a slope cam 43, a cam rotating shaft 43s, an urging spring 44, a driving motor KM1, a motor shaft KMa, and a driving gear G1. And a cam rotation gear G2. Two separation claws 38L and 38R are fixed to a reciprocating movement shaft 42, and the reciprocating movement of the reciprocating movement axis 42 in the horizontal direction in the figure swings the separation claw 38L and the separation claw 38R in the horizontal direction in the figure. Reference numeral 46 denotes a line sensor, which is arranged in parallel to the rotation axis of the photosensitive drum 31, and detects the position of the separation claw 38L.

  The reciprocating shaft 42 is fitted and held in the holes (not shown) of the holding portions 42a and 42b fixed to the substrate 41 so as to be slidable in the axial direction. The cam rotation shaft 43s is rotatably supported in a hole (not shown) of the holding portion 43a fixed to the substrate 41. The separation claw 38L and the separation claw 38R are fixed to the reciprocating movement shaft 42 with their tips abutting against the photosensitive drum 31, respectively. f is the distance between the tips of the separation claw 38L and the separation claw 38R fixed to the reciprocating shaft 42.

  The drive motor KM1 disposed on the substrate 41 rotates in a constant direction at a constant rotational speed. Then, the cam rotation gear G2 is rotated via the motor shaft KMa and the drive gear G1, and the cam rotation shaft 43s and the slope cam 43 fixed to the cam rotation gear G2 are rotated. The inclined cam 43 is formed such that the surface facing the reciprocating movement shaft 42 has a predetermined inclination (cam surface) with respect to a plane perpendicular to the cam rotating shaft 43s.

  The reciprocating shaft 42 is arranged such that the shaft center is eccentric from the shaft center of the cam rotation shaft 43 s and the left end in the drawing is in contact with the cam surface of the inclined cam 43.

  The urging spring 44 is wound around the outer periphery of the reciprocating shaft 42 between the holding portion 42b and the adjacent separation claw 38R, and urges the reciprocating shaft 42 in the direction of the inclined surface of the inclined cam 43.

  Therefore, when the slope cam 43 is rotated, the reciprocating shaft 42 that is biased by the biasing spring 44 and abuts against the cam surface of the slope cam 43 is swung in the left-right direction in the drawing for each rotation of the slope cam 43. The In the figure, h is a moving amount by which the reciprocating shaft 42 moved by the rotation of the slope cam 43 is moved from the leftmost position in the figure to the rightmost position in the figure, and is determined by the cam surface shape of the slope cam 43.

  With the above configuration, when the drive motor KM1 rotates, the inclined cam 43 rotates, and the reciprocating shaft 42 that contacts the cam surface of the inclined cam 43 reciprocates left and right in the drawing. Therefore, the separation claw 38L and the separation claw 38R fixed to the reciprocating movement shaft 42 are reciprocated by a movement amount h in the direction of the rotation axis of the photosensitive drum 31 with the distance f between the tips thereof as the drive motor KM1 rotates. repeat.

  Reference numeral 46 denotes a line sensor, which is disposed in parallel to the rotation axis of the photosensitive drum 31. The line sensor 46 detects the position of the separation claw 38L that is reciprocated.

  The positions of the separation claw 38L and the separation claw 38R with respect to the photosensitive drum 31 are determined by the rotational speed (a) of the drive motor KM1 rotating in a certain direction and the gear ratio between the drive gear G1 and the cam rotation gear G2 ( The rotational direction and rotational speed of the slope cam 43 determined from b), the cam surface shape (c) of the slope cam 43, the position (d) of the cam surface with which the reciprocating shaft 42 abuts, the separation claw 38L and the separation claw 38R It is determined by the arrangement position (e) on the reciprocating shaft 42. Among these conditions, (a), (b), (c), and (e) are conditions determined by design and are constant.

  As the inclined cam 43 rotates, the position of the reciprocating shaft 42 in contact with the cam surface in the left-right direction in the figure changes.

  The degree of change in the position when the reciprocating shaft 42 is moved from the leftmost position to the rightmost position with the change in the rotational position (rotational angle) of the slope cam 43, and the reciprocating shaft 42 is moved from the rightmost position. The degree of position change when returning to the leftmost position is determined by the cam surface shape of the slope cam 43.

  Since the slope cam 43 is rotated at a constant speed, the position of the reciprocation shaft 42 in the cycle until the reciprocation shaft 42 is moved from the leftmost position to the rightmost position and returns to the leftmost position is determined by the rotational speed of the slope cam 43. It is determined by the cam surface shape of the slope cam 43. The reciprocating shaft 42 contacting the inclined cam 43 rotated at a constant speed repeats the cycle from the leftmost position to the rightmost position and returning to the leftmost position at a constant cycle.

  Therefore, the line sensor 46 detects the position of the separation claw 38L from the position of the separation claw 38L detected by the line sensor 46 and the design conditions (a), (b), (c), and (e). It is possible to calculate the position after the elapse of time, that is, the positions of the separation claw 38L and the separation claw 38R after an arbitrary time elapses from the time when the line sensor 46 detects the position of the separation claw 38L.

  In this embodiment, when the interval between the sheets of the photosensitive drum reaches the position where scanning exposure is performed by the writing beam light from the image writing unit 2, the latent image of the inter-image toner image formed by writing is developed. When the toner image is transferred to the position where the separation claws 38L and 38R are arranged, the light beam carrying the inter-image toner image information is irradiated so that the blank portion comes to the position where the separation claws 38L and 38R that move are opposed to each other.

  FIG. 8 is a diagram illustrating a state where the formation position of the inter-image toner image is conveyed to a position where the separation claws 38L and 38R face each other as the photosensitive drum 31 rotates. The latent image of the inter-image toner image formed on the peripheral surface of the photosensitive drum 31 formed by the irradiation of the beam light indicated by the arrow a is conveyed to a position facing the developing unit 34 by the rotation of the photosensitive drum 31 and the toner image. And is conveyed to a position where the separation claws 38L and 38R face each other. In the illustrated angle θ, the latent image of the inter-image toner image formed by the irradiation of the beam light becomes the inter-image toner image P, and the photosensitive drum 31 is conveyed to the position where the separation claws 38L and 38R face each other. Rotation angle. The rotational speed of the photosensitive drum 31 is constant. If the rotational angular speed is ω, the time t required for the photosensitive drum 31 rotating at the rotational angular speed ω to be rotated by the angle θ is calculated by t = θ / ω. .

  On the other hand, as described above, the line sensor 46 determines the position of the separation claw 38L from the position of the separation claw 38L detected by the line sensor 46 and the design conditions of (a), (b), (c), and (e). It is possible to calculate the position after the elapse of an arbitrary time from the detected time point, that is, the positions of the separation claw 38L and the separation claw 38R with respect to the photosensitive drum 31 after the elapse of the arbitrary time.

  In the present embodiment, the separation detected by the line sensor 46 when the interval between the transfer target images formed on the photosensitive drum reaches the position where scanning exposure is performed by the writing beam light from the image writing unit 2. Based on the position of the claw 38L and the design conditions (a), (b), (c), and (e), the position of the separation claw 38L and the separation claw 38R after the time t calculated from t = θ / ω has elapsed. And the beam light carrying the inter-image toner image information is irradiated so that the blank portion comes to the calculated position. The latent image of the inter-image toner image formed by the irradiation of the beam light is conveyed by the rotation of the photosensitive drum 31 and becomes the inter-image toner image P which is a toner image in the developing unit 34, and the separation claws 38L and 38R are It is transported to the opposite position.

  The elapsed time until the inter-image toner image P formed from the irradiation of the beam light carrying the inter-image toner image information is conveyed to the position where the separation claws 38L and 38R face each other is t (= θ / ω). The separation claws 38L and 38R are moved to positions where time t (= θ / ω) has elapsed from the irradiation time of the beam light carrying the inter-image toner image information. The positions of the separation claws 38L and 38R when the time t has elapsed from the irradiation time of the beam light carrying the inter-image toner image information are calculated, and blank portions corresponding to the separation claws 38L and 38R at the calculated positions are calculated. Since the arranged inter-image toner image P is formed, the toner of the inter-image toner image P is not scraped off by the separation claws 38L and 38R and scattered around, thereby causing contamination inside the image forming apparatus. .

  FIG. 9 is a diagram showing a state in which an inter-image toner image P in which a blank portion is arranged at a position facing the moved separation claws 38L and 38R is formed a plurality of times corresponding to the movement of the separation claws 38L and 38R. .

As shown in the figure, the inter-image toner images P ₁ , P ₂ , P ₃ ,... Are formed with blank portions disposed at positions facing the separation claws 38L and 38R to be moved. And the position of the boundary between the blank portion and the toner adhesion portion in each of the formed inter-image toner images P ₁ , P ₂ , P ₃ ,... Fluctuates and is not fixed.

  Thus, by forming the blank part at a position facing the separation claw to be moved, the change in the thickness of the lubricant at the boundary between the part where the lubricant remains on the photosensitive drum and the part where it does not remain Can be made gentle, that is, the degree of change of the surface of the photosensitive drum in the rotation axis direction can be made gentle.

  Although the number of separation claws in the present embodiment described above is two, the number of separation claws is not limited to two, and may be three or more, for example.

  The inter-image toner image P is formed when a transfer target image having a low printing rate is formed. An example of setting the execution timing and the number of times of forming the inter-image toner image P will be described.

  The inter-image toner image P is formed under the control of the CPU 91 in the image forming apparatus G.

The CPU 91 measures the printing rate of the transfer target image in the image forming operation performed by the image forming apparatus G, and when the transfer target image having a printing rate lower than a predetermined printing rate is continuously formed, the inter-image toner image P To form. Specifically, the inter-image toner image when the average value of the printing rate of each of the transfer target image when executing the formation of the transfer target image m consecutive times (average printing rate r _m) is lower than the threshold value r _k P is formed. Threshold r _k is a constant which has been stored in ROM92 with predetermined, which is the lower limit of the printing ratio the developer in the developing unit is kept to a preferred state.

Then, it is determined that transfer imaging threshold smaller average printing ratio r _m is performed m times, the threshold r _k and the average printing ratio difference transfer imaging times m the value of m times of transfer object multiplied by the r _m As the shortage of the amount of toner to be consumed in image formation, the number of formations of the inter-image toner image P that compensates for this is calculated.

When the numerical value obtained by replacing the amount of toner discharged by forming the inter-image toner image P once with the printing rate is r _P and the number of inter-image toner images is formed x,
r _P · x = (r _k −r _m ) · m
Since the following equation holds,
The number x of inter-image toner images can be calculated by x = (r _k −r _m ) m / r _P.

Note r _P is a predetermined value calculated from the amount of toner to be attached to the area and toner adhesion of the toner attachment (density) in the image between the toner image P, it is housed in advance ROM 92.

By forming the inter-image toner image P of the number of times x calculated by the calculation formula x = (r _k −r _m ) m / r _{P, the} toner consumption is insufficient due to the formation of the transfer target image m times. The toner for supplementing the amount can be discharged, and the developer in the developing section 34 can be kept in a preferable state.

  FIG. 10 is a flowchart for explaining the timing of forming the inter-image toner image P.

The CPU 91 measures the respective printing ratios r when the transfer target image P is formed a predetermined number of times (m times) (step S1), and the predetermined number of times (m times) is made at step S2. thereby calculating an average printing rate r _m of the transfer target image.

In step S3, the average printing ratio r _m that calculated to confirm whether the threshold r _k is less than or. Proceeds to step S4 when the average printing ratio _{r m} is smaller than the threshold value _{r k} (step S3 Yes), when the average printing ratio _{r m} is not smaller than the threshold value _{r k} in (Step S3 No) the process proceeds to step S9 .

  In step S4, the CPU 91 calculates the number of times x of forming the inter-image toner image. The number of times x is calculated using the following calculation formula stored in the memory.

x = (r _k −r _m ) m / r _P
When the number of times x for forming the inter-image toner image is calculated, the counter number n, which is the number stored in the RAM 93 functioning as a counter, is reset and n = 0 is set (step S5). The counter number n can be reset or added under the instruction of the CPU 91.

  In step S6, an inter-image toner image is formed between images to be transferred (between sheets), and in the subsequent step S7, the counter number n is incremented to n = n + 1. If the inter-image toner image formed in step S6 is the first inter-image toner image, n = 0 + 1 = 1.

  In step S8, it is confirmed whether or not the counter number n is equal to or greater than the number of times x of forming an inter-image toner image. When the counter number n is equal to or greater than the number of times of forming an inter-image toner image x (step S Yes), the process proceeds to step S9. On the other hand, when the counter number n is not equal to or greater than the number of times of forming the inter-image toner image x (No in step S6), the process returns to step S6, and the inter-image toner image is formed between the transfer target images in step S6 The incrementing of the counter number n in S7 is repeated until it is confirmed in step S8 that the counter number n is equal to or greater than the number x of inter-image toner images. When the counter number n is equal to or greater than the number of times of forming the inter-image toner image x (step S Yes), the process proceeds to step S9 without forming a new inter-image toner image.

  In step S9, it is confirmed whether or not the job for forming the transfer target image is completed. When the job for forming the transfer target image is not completed (No in step S9), the process returns to step S1, and steps S1 to S9 are performed. The series of operations up to are repeated until the job for forming the transfer target image is completed. When the job for forming the transfer target image is completed (No in step S9), the formation of the transfer target image is ended.

Thus, by forming the inter-image toner image P with the number of times x calculated by the calculation formula x = (r _k −r _m ) m / r _P, the toner consumption amount in forming the transfer target image m times. The toner that compensates for the shortage can be discharged, and the developer in the developing section 34 can be kept in a preferable state.

DESCRIPTION OF SYMBOLS 1 Image reading part 2 Image writing part 3 Image forming part 31 Photosensitive drum 32 Charging part 34 Developing part 35 Transfer part 36 Separating part 37 Cleaning part 371 Cleaning blade 38L, 38R Separation claw 4 Separation claw reciprocating movement part 41 Substrate 42 Reciprocation moving shaft 43 with slant cam 44 urging spring 46 the line sensor 5 sheet feeding and conveying section 6 the operation display unit 7 fixing unit 8 automatic document feeder 9 control unit P-picture between the toner images B _{1, B 2} blank portion T _{1, T 2} , T ₃ toner adhesion part S paper

Claims (5)

An image writing unit;
A photosensitive drum that is driven to rotate about a rotation axis and forms and carries a latent image based on image information written by the image writing unit;
A developing device for converting a latent image carried on the photosensitive drum with toner containing a lubricating component into a toner image;
A separation claw for separating the recording paper onto which the toner image on the photosensitive drum has been transferred from the photosensitive drum;
A cleaning unit for removing toner remaining on the photosensitive drum,
In addition to performing the transfer target image forming operation for transferring the toner image on the photosensitive drum to the recording paper, the toner image to be transferred to the recording paper formed on the photosensitive drum and the subsequent recording paper An inter-image toner image having a plurality of toner adhering portions facing each other with a blank portion avoiding the separation claw sandwiched between the subsequent toner image transferred to the toner image and discharging a part of the toner from the developing device In the image forming apparatus for removing the inter-image toner image by the cleaning unit,
An inter-image toner image formation control unit that controls the operation of the image writing unit to write an inter-image toner image in which the toner adhesion amount of the toner adhesion unit gradually decreases toward the blank portion. An image forming apparatus. The image forming apparatus according to claim 1 , wherein a dimension of the toner adhering portion in a direction along a circumference of the photosensitive drum gradually decreases toward the blank portion. An image writing unit;
A photosensitive drum that is driven to rotate about a rotation axis and forms and carries a latent image based on image information written by the image writing unit;
A developing device for converting a latent image carried on the photosensitive drum with toner containing a lubricating component into a toner image;
A separation claw for separating the recording paper onto which the toner image on the photosensitive drum has been transferred from the photosensitive drum;
A cleaning unit for removing toner remaining on the photosensitive drum,
In addition to performing the transfer target image forming operation for transferring the toner image on the photosensitive drum to the recording paper, the toner image to be transferred to the recording paper formed on the photosensitive drum and the subsequent recording paper An inter-image toner image having a plurality of toner adhering portions facing each other with a blank portion avoiding the separation claw sandwiched between the subsequent toner image transferred to the toner image and discharging a part of the toner from the developing device In the image forming apparatus for removing the inter-image toner image by the cleaning unit,
An inter-image toner image formation control unit that controls the operation of the image writing unit to write an inter-image toner image in which the density of toner adhering to the toner adhering unit gradually decreases toward the blank portion ; An image forming apparatus. An image writing unit;
A photosensitive drum that is driven to rotate about a rotation axis and forms and carries a latent image based on image information written by the image writing unit;
A developing device for converting a latent image carried on the photosensitive drum with toner containing a lubricating component into a toner image;
A separation claw for separating the recording paper onto which the toner image on the photosensitive drum has been transferred from the photosensitive drum;
A cleaning unit for removing toner remaining on the photosensitive drum,
In addition to performing the transfer target image forming operation for transferring the toner image on the photosensitive drum to the recording paper, the toner image to be transferred to the recording paper formed on the photosensitive drum and the subsequent recording paper An inter-image toner image having a plurality of toner adhering portions facing each other with a blank portion avoiding the separation claw sandwiched between the subsequent toner image transferred to the toner image and discharging a part of the toner from the developing device In the image forming apparatus for removing the inter-image toner image by the cleaning unit,
Wherein by controlling the operation of the image writing unit, every time the formation of the inter-image toner image, the image between images between the toner image to perform writing of the toner image boundary position between the blank portion in the toner adhesion portion varies An image forming apparatus having a formation control unit . A separation claw moving mechanism for moving the separation claw along the rotation axis direction of the photosensitive drum;
5. The image forming apparatus according to claim 1 , wherein the blank portion in the inter-image toner image is formed at a position of the separation claw to be moved.

Images