JP2016045305A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an image lag by optimally controlling the amount of discharging light and suppress the optical fatigue and the deterioration of a photosensitive body, to prolong the life of the photosensitive body.SOLUTION: An image forming apparatus includes a discharging ability adjustment mode. In this mode, a solid patch part and a blank part are formed in the first round of a photosensitive body 3K, and a halftone patch part is formed in the second round. The potential difference between a first surface potential at a place in the halftone patch part, which has been the solid patch part, and a second surface potential at a place in the halftone patch part, which has been the blank part is detected. When the potential difference is beyond a prescribed value, the amount of light of a discharging lamp 22K is increased until the potential difference is the prescribed value or less, and then a printing operation is started. In the same manner, a discharging ability adjustment mode can also be executed on the basis of the difference in amount of attachment of toner on an intermediate transfer belt 41.SELECTED DRAWING: Figure 7A

Description

The present invention relates to an electrophotographic image forming apparatus and an image forming method used for copying, printers, and the like, and in particular, a ghost image (positive afterimage / negative afterimage) due to a difference in surface potential or toner adhesion amount of an image carrier. The present invention relates to an image forming apparatus and an image forming method having a function of correcting image forming conditions so as to prevent the occurrence of image formation.

In an electrophotographic image forming apparatus, an image is generally formed by the following process. That is, first, an electrostatic latent image is formed on an image carrier such as a photosensitive member uniformly charged by a charging device by optical scanning or the like, and the electrostatic latent image is developed by a developing device. To do. Next, the toner image obtained by development is transferred from the image carrier to a transfer member such as a recording paper or an intermediate transfer member. Residual charges exist on the image carrier after the transfer process, but the residual charges are removed by a charge eliminating means such as a charge eliminating lamp (see Patent Documents 1 to 4).

Such a light source or the like irradiates the photosensitive member with light by providing a transfer process, a static elimination process, a cleaning process, or a pre-exposure process using light irradiation in addition to the process shown in FIG.

The reason why the image carrier is neutralized by the neutralizing means is as follows. That is, the image bearing member after the transfer process has a history of electrostatic latent images. In the state where the history of the electrostatic latent image exists, even if the uniform charging process is performed by the charging unit, the potential of the image carrier is hardly uniform.

When a subsequent image is formed on an image carrier that is not at a uniform potential while the history of the electrostatic latent image remains, an afterimage of the previous image is generated in the solid portion of the image. . In order to avoid the occurrence of such an afterimage, the image carrier after the transfer process is neutralized and returned to the initial state.

As described above, the conventional image forming apparatus erases the history of the electrostatic latent image by the static elimination lamp or the like, but an afterimage at the previous printing may be printed depending on the print contents. That is, for example, when a low gradation image such as a halftone image is printed immediately after a high gradation image such as a solid image is formed, an afterimage of the high gradation image at the previous printing may remain in the low gradation image. there were.

The inventions described in Patent Documents 1 to 4 take various measures so that such an afterimage does not occur, but it has not yet been possible to effectively suppress the afterimage regardless of the printing contents. For example, Patent Document 5 and Patent Document 6 are known as techniques relating to afterimage suppression and charging unevenness prevention. Patent Document 5 suppresses afterimages by reducing the afterimage potential difference by increasing the amount of charge removal light. Patent Document 6 corrects image forming conditions by detecting the occurrence of a ghost (afterimage) due to charging unevenness in halftone.

However, when the amount of charge removal light is increased in the invention of Patent Document 5, the charge removal light causes light fatigue and deterioration of the photosensitive member, leading to shortening of its life. Further, Patent Document 6 corrects image forming conditions, but it is not easy to optimally correct a plurality of image forming conditions. In addition, a method of directly irradiating the charging unit with the neutralizing light as in Patent Document 7 (0020 stage) is also known. However, it is difficult to control the amount of the neutralizing light. There was a fear.

The present invention has been made in view of such a situation, and an object of the present invention is to effectively suppress afterimages regardless of the printing contents by optimally controlling the light amount of the static elimination light, and to perform photosensitivity by the static elimination light. An object of the present invention is to provide an image forming apparatus capable of suppressing the light fatigue and deterioration of a body and extending its life.

In order to solve the above problems, an image forming apparatus according to the present invention includes:
An image carrier that carries a latent image and is rotatable, a charging unit that uniformly charges the circumferential surface of the image carrier, and the latent image is exposed on the circumferential surface by exposing the circumferential surface of the image carrier. Writing means for writing; developing means for developing the latent image as a toner image with toner; transfer means for transferring the toner image to a recording medium directly or via an intermediate transfer member; A neutralizing unit that neutralizes the peripheral surface of the body at a position of a charging portion between the charging unit and the image carrier; and a write unit and a developing unit that are disposed between the writing unit and the developing unit. In an image forming apparatus having a surface potential detecting means for detecting a surface potential and a control means for controlling increase / decrease in the charge removal capability of the charge removing means,
Before starting the printing operation of the image forming apparatus, the writing unit forms a full patch solid patch portion and a non-exposed blank portion on the first circumferential surface of the image carrier, and the transfer unit. Forming a halftone patch portion overlaid on the portion where the solid patch portion and the blank portion were formed on the peripheral surface of the second circumference of the image carrier after being transferred by the charging means and charged by the charging means,
The surface potential detecting means detects a potential difference between a first surface potential of a portion that was the solid patch portion in the halftone patch portion and a second surface potential of a portion that was the blank portion,
When the potential difference exceeds a predetermined value, the control unit has a neutralization capability adjustment mode for starting a printing operation after increasing the neutralization capability of the neutralization unit until the potential difference becomes a predetermined value or less. The image forming apparatus is characterized.

  Instead of increasing the charge removal capability of the charge removal unit until the potential difference becomes a predetermined value or less, the charge removal capability of the charge removal unit may be increased until the difference in the toner adhesion amount of the intermediate transfer member becomes a predetermined value or less.

According to the present invention, a halftone patch portion is formed in the solid patch portion formed in the first turn of the image carrier and the blank portion in the second turn, and based on the potential difference between the solid patch portion and the blank portion in the halftone patch portion. The presence or absence of afterimage generation can be detected. And, by optimally controlling the amount of neutralizing light so that the potential difference is less than or equal to a predetermined value, afterimages are always effectively suppressed regardless of the content of printing, and light fatigue and deterioration of the photoreceptor due to static elimination light are suppressed. Thus, the lifetime can be extended. In addition, by detecting the difference in the amount of toner attached to the intermediate transfer member, it is possible to control the amount of static electricity more appropriately, and more reliably suppress afterimages, more reliably suppress photoconductor fatigue and deterioration, and extend the life. Can do.

1 is a schematic configuration diagram illustrating an overall configuration of a printer as an image forming apparatus according to an embodiment of the present invention. It is a schematic side view of an image forming unit used in the image forming apparatus. It is a schematic side view of an image forming unit used in the image forming apparatus. It is a schematic side view of an image forming unit used in the image forming apparatus. It is a figure which shows a static elimination process. It is a figure which shows the change of the residual potential of a photoreceptor with respect to the travel distance of a photoreceptor. FIG. 4 is a diagram of a solid patch and a halftone patch formed on a photoconductor. FIG. 3 is a diagram of a solid patch and a halftone patch formed on an intermediate transfer belt. It is a figure which shows the relationship between the rotation speed of a photoreceptor, and the surface potential of a photoreceptor. FIG. 4 is a diagram illustrating a relationship between the number of rotations of a photoconductor and the amount of toner attached on an intermediate transfer belt. It is a flowchart which shows control of the static elimination light quantity based on the residual potential difference on a photoconductor. It is a figure which shows the correction coefficient for controlling the static elimination light quantity according to developing capability. FIG. 7B is a flow diagram in which control of the amount of charge to be removed according to the developing ability is added to the flow of FIG. 7A. FIG. 6 is a flowchart illustrating control of a charge removal amount based on a difference in toner adhesion amount on an intermediate transfer belt. FIG. 6 is a diagram illustrating an example in which a plurality of toner adhesion amount detection sensors are arranged in the main scanning direction of the intermediate transfer belt. It is a figure which shows the example of a digital halftone image pattern. It is a figure which shows the example of the digital halftone image pattern of a real image.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. As described above, the present invention is characterized in the adjustment of the charge removal capability (charge removal light amount) in the charge removal capability adjustment mode. That is, according to the detection result of the residual potential difference of the photosensitive member detected by the surface potential detection unit or the detection result of the difference in toner adhesion amount on the intermediate transfer body (intermediate transfer belt) detected by the toner adhesion amount difference detection unit, Irradiate the charging nip with a neutralizing light amount increased to an appropriate light amount. Thus, the afterimage is always effectively suppressed regardless of the printed content, and the photo-fatigue (electrostatic fatigue) and deterioration of the photosensitive member due to the charge-removing light are suppressed, thereby extending its life.

The first embodiment uses the detection result of the residual potential difference of the photoconductor, and the second embodiment uses the detection result of the toner adhesion amount difference on the intermediate transfer belt. Since the first embodiment and the second embodiment have many common parts, in the following description, the two embodiments will be described in parallel.

(Image forming device)
FIG. 1 is a schematic configuration diagram illustrating an overall configuration of a printer which is an example of an image forming apparatus according to an embodiment of the present invention. 2A, 2B, and 2C are schematic configuration diagrams illustrating a configuration example of a black image forming unit 1K used in the printer.

However, FIG. 2A shows a conventional image forming unit 1K, and FIGS. 2B and 2C show an image forming unit 1K used in the embodiment of the present invention. The differences between the image forming units 1K are the position of the static elimination lamp 22K, the configuration of the drum cleaning device 15K, and the arrangement of the surface potential detection sensor 76. Other configurations are common to the three image forming units 1K.

The printer shown in FIG. 1 includes four image forming units 1Y, 1C, 1M, and 1K for generating yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K) toner images. . These image forming units use Y toner, C toner, M toner, and K toner of different colors as image forming substances for forming an image, but the other configurations are the same.

Taking an image forming unit 1K for generating a K toner image as an example, as shown in FIGS. 2A, 2B, and 2C, the image forming unit 1K includes a photosensitive drum 3K as an image carrier. And a developing unit 7K as developing means for developing the latent image on the photosensitive member 3K.

The photosensitive unit 2K and the developing unit 7K are detachably attached to the printer main body integrally as the image forming unit 1K. However, the developing unit 7K can be attached to and detached from the photosensitive unit 2K in a state where it is detached from the printer main body.

Below the image forming units 1Y, 1C, 1M, and 1K in the drawing, an optical writing unit 20 as a latent image forming unit is disposed. The optical writing unit 20 as writing means irradiates the photoconductors 3Y, 3C, 3M, 3K after uniform charging of the image forming units 1Y, 1C, 1M, 1K with the laser light L based on the image information. .

Thereby, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 3Y, 3C, 3M, and 3K. In the optical writing unit 20, the laser light L emitted from the light source is deflected by the polygon mirror 21 that is rotationally driven by a motor, and the photoreceptors 3Y, 3C, 3M, and 3K are passed through a plurality of optical lenses and mirrors. Is irradiated. Instead of such a configuration, it is also possible to employ one that performs optical scanning with an LED array.

In FIG. 1, below the optical writing unit 20, a first paper feed cassette 31 and a second paper feed cassette 32 that supply recording paper P as a recording medium are arranged so as to overlap in the vertical direction. In each of these paper feed cassettes, a plurality of recording papers P as recording media are accommodated in a state of recording paper bundles. A first paper feed roller 31a and a second paper feed roller 32a are in contact with the uppermost recording paper P, respectively.

When the first paper feed roller 31a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the first paper feed cassette 31 is vertical on the right side of the cassette in the figure. The paper is discharged toward a paper feed path 33 arranged to extend in the direction.

When the second paper feed roller 32a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the second paper feed cassette 32 is directed toward the paper feed path 33. Discharged. A plurality of transport roller pairs 34 are arranged in the paper feed path 33, and the recording paper P fed into the paper feed path 33 is sandwiched between the rollers of the transport roller pair 34 while being fed between the paper feed paths 33. 33 is conveyed from the lower side to the upper side in the figure.

A timing roller pair 35 is disposed at the end of the paper feed path 33. The timing roller pair 35 temporarily stops the rotation of both rollers as soon as the recording paper P sent from the transport roller pair 34 is sandwiched between the rollers. Then, the recording paper P is sent out to a secondary transfer nip described later at an appropriate timing.

Above each of the image forming units 1Y, 1C, 1M, and 1K, a transfer unit 40 is disposed as a transfer unit that is endlessly moved counterclockwise in the drawing while stretching an intermediate transfer belt 41 as an intermediate transfer member. It is installed. In addition to the intermediate transfer belt 41, the transfer unit 40 includes a belt cleaning unit 42, a first bracket 43, a second bracket 44, and the like.

Also provided are four primary transfer rollers 45Y, 45C, 45M, 45K, a secondary transfer backup roller 46, a drive roller 47, an auxiliary roller 48, a tension roller 49, and the like. The intermediate transfer belt 41 is endlessly moved in the counterclockwise direction in the figure by the rotational drive of the drive roller 47 while being stretched around these eight rollers.

The four primary transfer rollers 45Y, 45C, 45M, and 45K sandwich the intermediate transfer belt 41 that moves endlessly between the photoreceptors 3Y, 3C, 3M, and 3K to form primary transfer nips. Then, a transfer bias having a polarity opposite to that of the toner (for example, plus) is applied to the back surface (loop inner peripheral surface) of the intermediate transfer belt 41.

The intermediate transfer belt 41 passes through the primary transfer nips for each of the colors Y, C, M, and K in accordance with the endless movement of the intermediate transfer belt 41, and on the photoreceptor 3Y, 3C, 3M, 3K on the front surface. The Y toner image, the C toner image, the M toner image, and the K toner image are primarily transferred so as to overlap each other. As a result, a four-color superimposed toner image (hereinafter referred to as “four-color toner image”) is formed on the intermediate transfer belt 41.

The secondary transfer backup roller 46 constituting the secondary transfer means sandwiches the intermediate transfer belt 41 with the secondary transfer roller 50 disposed outside the loop of the intermediate transfer belt 41 to form a secondary transfer nip. ing. The timing roller pair 35 feeds the recording paper P sandwiched between the rollers toward the secondary transfer nip at a timing to synchronize with the four-color toner image on the intermediate transfer belt 41.

The four-color toner image on the intermediate transfer belt 41 is affected by the secondary transfer electric field formed between the secondary transfer roller 50 to which the secondary transfer bias is applied and the secondary transfer backup roller 46, and the influence of the nip pressure. Then, the secondary transfer is collectively performed on the recording paper P in the secondary transfer nip. Then, combined with the white color of the recording paper P, a full color toner image is obtained.

The residual transfer toner remaining on the intermediate transfer belt 41 without being transferred to the recording paper P even after passing through the secondary transfer nip is cleaned by the belt cleaning unit 42. The belt cleaning unit 42 makes the cleaning blade 42a abut against the front surface of the intermediate transfer belt 41, thereby scraping off and removing the transfer residual toner on the belt.

A fixing unit 60 as a fixing unit for fixing the toner image on the recording paper P is disposed above the secondary transfer nip in the figure. The fixing unit 60 includes a pressure heating roller 61 that includes a heat source such as a halogen lamp, and a fixing belt unit 62.

The fixing belt unit 62 includes a fixing belt 64 as a fixing member, a heating roller 63 containing a heat source 63a such as a halogen lamp, a tension roller 65, a driving roller 66, and the like. Then, the endless fixing belt 64 is endlessly moved in the counterclockwise direction in the drawing while being stretched by the heating roller 63, the tension roller 65, and the driving roller 66.

In the process of endless movement, the fixing belt 64 is heated from the back side by the heating roller 63. A pressure heating roller 61 that is driven to rotate in the clockwise direction in the drawing is in contact with the surface of the fixing belt 64 that has been heated in this manner. Thereby, a fixing nip where the pressure heating roller 61 and the fixing belt 64 abut is formed.

Outside the loop of the fixing belt 64, a temperature sensor (not shown) is disposed so as to face the front surface of the fixing belt 64 with a predetermined gap, and the fixing belt 64 just before entering the fixing nip. Detect the surface temperature of. The detection result is sent to a fixing power supply circuit (not shown).

The fixing power supply circuit performs on / off control of power supply to the heat source 63 a included in the heating roller 63 and the heat source 61 a included in the pressure heating roller 61 based on the detection result by the temperature sensor. Thereby, the surface temperature of the fixing belt 64 is maintained at about 140 ° C., for example.

The recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 41 and then fed into the fixing unit 60. The recording paper P is heated and pressed by the fixing belt 64 and the pressure heating roller 61 in the process of being conveyed from the lower side to the upper side in the figure while being sandwiched between the fixing nips in the fixing unit 60. The full color toner image is fixed on the recording paper P.

The recording paper P subjected to the fixing process in this manner is discharged outside the apparatus after passing between the rollers of the paper discharge roller pair 67. A stack unit 68 is formed on the upper surface of the housing of the printer main body, and the recording paper P discharged to the outside by the discharge roller pair 67 is sequentially stacked on the stack unit 68.

Above the transfer unit 40, four toner cartridges 100Y, 100C, 100M, and 100K that store Y toner, C toner, M toner, and K toner are disposed. Each color toner in the toner cartridges 100Y, 100C, 100M, and 100K is appropriately supplied to the developing devices 7Y, 7C, 7M, and 7K of the image forming units 1Y, 1C, 1M, and 1K. The toner cartridges 100Y, 100C, 100M, and 100K are detachable from the printer main body independently of the image forming units 1Y, 1C, 1M, and 1K.

(Image forming unit)
The image forming unit is configured as shown in FIGS. 2A, 2B, and 2C. FIG. 2A shows a conventional image forming unit, which is shown in order to clarify the features of the image forming unit used in the embodiment of the present invention shown in FIGS. 2B and 2C. As described above, the difference between the image forming units 1K is the position of the charge removal lamp 22K, the configuration of the drum cleaning device 15K, and the arrangement of the surface potential detection sensor 76. Other configurations are common to the three image forming units 1K.

(Photoreceptor unit)
In FIG. 2A showing a conventional image forming unit, a photoconductor unit 2K includes a photoconductor 3K, a drum cleaning device 15K, a static elimination lamp 22K as a static elimination means, a charging device 23K as a charging means for charging the surface of the photoconductor 3K, and the like. have.

The photoreceptor 3K is obtained by sequentially laminating an organic photosensitive layer and a surface layer on a peripheral surface of a drum-shaped conductive support. The organic photosensitive layer includes a charge generation layer and a charge transport layer. The thickness of the charge transport layer is appropriately selected in accordance with desired photoreceptor characteristics within a range of 10 to 40 [μm]. In addition, an undercoat layer is formed between the conductive support and the organic photosensitive layer in the photoreceptor 3K as necessary.

Note that the photoreceptor 3K may be formed of a single-layer photoreceptor that includes both the charge generation material and the charge transport material in the same layer. Further, an intermediate layer may be provided between the undercoat layer and the photosensitive layer. In addition, other types of photosensitive layers such as an amorphous silicon photosensitive film may be used in addition to the organic photoreceptor.

The drum cleaning device 15K includes an application brush roller 17K, a cleaning blade 18K, a solid lubricant 19K, a recovery coil 20K, and the like.

The application brush roller 17K has a metal rotating shaft member and a brush roller portion made of a plurality of conductive fibers standing on the peripheral surface thereof. The application brush roller 17K scrapes off the lubricant from the solid lubricant 19K in accordance with the rotation and applies it to the surface of the photoreceptor 3K.

By applying the lubricant, a film made of a lubricant powder is formed on the surface of the photosensitive member 3K, and the adhesion between the photosensitive member 3K and the toner is weakened to improve the cleaning property. The life of the photosensitive member 3K is extended by weakening the rubbing force with various members in contact with the photosensitive member 3K.

As solid lubricant 19K, zinc stearate, barium stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, magnesium stearate, zinc oleate, cobalt oleate, Examples include fatty acid metal salts such as magnesium oleate and zinc palmitate, natural waxes such as carnauba wax, and fluororesins such as polytetrafluoroethylene.

The neutralizing lamp 22K may be a general luminescent material such as a fluorescent lamp, a tungsten lamp, a halogen lamp, a mercury lamp, a sodium lamp, a light emitting diode (LED), a semiconductor laser (LD), or an electroluminescence (EL).

In order to irradiate only light in a desired wavelength range, various filters such as a sharp cut filter, a band pass filter, a near infrared cut filter, a dichroic filter, an interference filter, and a color temperature conversion filter are used for the static elimination lamp 22K. You can also

The charging device 23K includes a roller charging type charging roller 231K and a cleaning brush roller 232K. The charging roller 231K uniformly charges the surface of the photoreceptor 3K that is driven to rotate in the clockwise direction in the drawing by a driving unit (not shown).

The charging roller 231K is composed of a cored bar which is a conductive support (not shown), a roller part coated on the peripheral surface of the central part in the longitudinal direction, and abutment rollers fixed to both ends in the longitudinal direction of the cored bar. Has been. A charging bias is applied to the cored bar by a power source (not shown). Then, a discharge is generated between the conductive roller portion and the photoconductor 3K through the charging gap, so that the photoconductor 3K is uniformly charged.

In the configuration example of FIG. 2A, the charging roller 231K that is driven to rotate counterclockwise in the drawing is brought close to the photosensitive member 3K while a charging bias is applied by a power source (not shown), thereby uniformly charging the photosensitive member 3K. . Instead of the charging roller 231K, a charging brush may be brought into contact with the photoreceptor 3K.

Further, a device that uniformly charges the photosensitive member 3K, such as a corona charging type scorotron charger, may be used. The surface of the photoreceptor 3K that is uniformly charged by the charging device 23K is exposed and scanned by a laser beam emitted from the optical writing unit 20 to carry an electrostatic latent image for K.

The cleaning brush roller 232K includes a metal cored bar and a brush roller unit made of a plurality of conductive fibers electrostatically flocked on the peripheral surface of the cored bar. Then, the toner is scraped off from the peripheral surface of the charging roller 231K by being rotated along with the rotation of the charging roller 231K while being in contact with the roller portion of the charging roller 231K.

The developing unit 7K includes a screw roller 8K, a toner concentration sensor 10K including a magnetic permeability sensor as a toner concentration detecting unit, a developing roller 12K, a doctor blade 14K as a developer regulating member, and the like. The developing unit 7K contains a K developer (not shown) having a magnetic carrier and negatively chargeable K toner.

The screw roller 8K is rotationally driven by a driving unit (not shown) and conveys the K developer in the developing unit 7K in a direction perpendicular to the paper surface. The toner density of the K developer in the middle of conveyance is detected by the toner density sensor 10K.

A developing roller 12K is disposed above the developing unit 7K. The developing roller 12K includes a magnet roller 13K in a developing sleeve made of a non-magnetic pipe that is driven to rotate counterclockwise in the drawing. A part of the K developer is pumped up to the surface of the developing roller 12K by the magnetic force generated by the magnet roller 16K.

Then, after the developer layer thickness is regulated by the doctor blade 14K disposed so as to maintain a predetermined gap with the developing roller 12K as the developer carrying member, the developer is developed opposite to the photoreceptor 3K. The toner is conveyed to the area, and K toner is attached to the electrostatic latent image for K on the photoreceptor 3K. By this toner adhesion, a K toner image is formed on the photoreceptor 3K. The K developer that has consumed the K toner by the development is returned to the developing unit 7K as the developing roller 12K rotates.

The K toner image formed on the photoreceptor 3K is intermediately transferred to the intermediate transfer belt 41. The drum cleaning device 15K removes the toner remaining on the surface of the photoreceptor 3K after the intermediate transfer process. As a result, the surface of the photoreceptor 3K that has been subjected to the cleaning process is neutralized by the neutralizing light emitted from the neutralizing lamp 22K. By this charge removal, the surface of the photoreceptor 3K is initialized and prepared for the next image formation.

In FIG. 1, in the image forming units 1Y, 1C, and 1M for other colors, Y toner images, C toner images, and M toner images are similarly formed on the photoreceptors 3Y, 3C, and 3M, and the intermediate transfer belt 41 is formed. Intermediate transfer is performed on the top.

The above is the outline of the conventional image forming unit 1K. In the conventional image forming unit 1K of FIG. 2A, a static elimination lamp 22K is disposed on the upstream side of the drum cleaning device 15K, and irradiates the peripheral surface of the photoreceptor 3K immediately after primary transfer with static elimination light. However, it was found that the neutralization effect was low when the neutralization light was irradiated earlier than the charging timing. Therefore, in the image forming unit 1K shown in FIGS. 2B and 2C, the discharge light L ′ from the discharge lamp 22K is irradiated toward the charging nip of the charging roller 231K.

The static elimination lamp 22K can be combined with any optical filter. As the optical filter, any one of a sharp cut filter, a band pass filter, a near infrared cut filter, a dichroic filter, an interference filter, and a color temperature conversion filter can be used.

2A includes an application brush roller 17K, a cleaning blade 18K, a solid lubricant 19K, a recovery coil 20K, and the like. However, the application brush roller 17K and the solid lubricant 19K as the lubricant application mechanism are not indispensable for the image forming apparatus.

Therefore, in the image forming unit 1K shown in FIGS. 2B and 2C, the drum brushing device 15K having only the cleaning blade 18K is used by omitting the coating brush roller 17K and the solid lubricant 19K for cost reduction.

In the image forming unit 1K shown in FIGS. 2A and 2B, a surface potential detection sensor 76 for detecting the potential of the peripheral surface of the photoreceptor 3K is disposed between the charging roller 231K and the developing roller 12K. In contrast, the image forming unit 1K in FIG. 2C eliminates the surface potential detection sensor 76 in FIG. 2B.

In the image forming unit 1K of FIG. 2C, a toner adhesion amount detection sensor 77 is arranged on the immediate upstream side of the secondary transfer roller 50 as shown in FIG. 1, instead of the surface potential detection sensor. That is, it can be said that the surface potential on the photosensitive member 3K is detected from the toner adhesion amount on the intermediate transfer belt 41.

The toner adhesion amount detection sensor 77 detects the regular reflection light or diffuse reflection light of the detection toner pattern (toner patch) transferred from the photosensitive member 3K to the intermediate transfer belt 41 by using an optical sensor, and thereby detects the toner adhesion amount detection sensor 77 on the intermediate transfer belt 41. The toner adhesion amount is detected.

As the toner adhesion amount detection sensor 77, an optical sensor having a light emitting element such as an LED and a light receiving element such as a phototransistor can be used. The reflected light of the light emitting element irradiated toward the toner patch on the intermediate transfer belt is detected by the light receiving element, and the toner adhesion amount of the toner patch is detected from the amount of the reflected light.

In general, the optical sensor can detect the low adhesion side with a relatively high sensitivity, but if the high adhesion side has a high adhesion of a certain level or more, it cannot be detected with a high sensitivity due to the detection sensitivity of the light receiving element. That is, the optical sensor has a predetermined detection range in which the toner patch can be detected with high sensitivity.

Therefore, in order to accurately determine the toner adhesion amount (or development γ), the toner adhesion amounts of a plurality of toner patches constituting the gradation pattern are within a toner adhesion amount detection range that can be detected with high sensitivity by an optical sensor. Therefore, it is desirable to distribute at equal intervals from the low adhesion side to the high adhesion side.

The above is the outline of the photoreceptor unit 2K including the charging device 23K. On the surface of the photoreceptor 3K uniformly charged by the charging device 23K, an electrostatic latent image is formed by optical scanning with the laser beam L, and enters a developing region which is a position facing the developing unit 7K. The developing unit 7K develops the latent image using a two-component developer (hereinafter simply referred to as a developer) containing a magnetic carrier and a non-magnetic toner (not shown).

(Development unit)
The developing unit 7K includes a screw roller 8K that conveys the developer contained in the developing unit 7K in the axial direction while stirring the developer, and a stirring roller 9K that conveys the developer while stirring. Further, the developing unit 7K includes a developing sleeve 12K that faces the photosensitive member 3K through an opening provided in the casing, a doctor blade 14K having a tip approaching the developing sleeve 12K, and the like.

The developing sleeve 12K includes a magnet roller 13K that is arranged concentrically with the developing sleeve 12K and transfers toner in the developer carried on the surface of the developing sleeve 12K to the photoreceptor 3K. The magnet roller 13K has a plurality of magnetic poles sequentially arranged in the rotation direction of the developing sleeve 12K.

Each of these magnetic poles applies a magnetic force to the developer on the sleeve at a predetermined position in the rotational direction. As a result, the developer sent from the stirring roller 9K is attracted and carried on the surface of the developing sleeve 12K, and a magnetic brush is formed along the magnetic field lines on the surface of the developing sleeve 12K.

The image forming unit 1K is configured as described above, and the photosensitive member 3K having a K toner image formed on the surface by development by the developing unit 7K enters a K primary transfer nip described later with rotation. In the primary transfer nip, the K toner image on the photoreceptor 3K is primarily transferred onto the front surface of the intermediate transfer belt.

The surface of the photoreceptor 3K after passing through the primary transfer nip is discharged by the discharging lamp 22K and then enters a cleaning position by the drum cleaning device 15K.

When the peripheral surface of the photoreceptor 3K enters the cleaning position, the transfer residual toner on the peripheral surface of the photoreceptor 3K is scraped off by the cleaning blade 18K. The transfer residual toner thus scraped off is conveyed to the end portion in the direction orthogonal to the paper surface of the drawing by the recovery coil 20K. Then, it is discharged outside the drum cleaning device 15K and collected in a waste toner bottle (not shown).

(Mechanism of afterimage generation)
FIG. 3 is a diagram showing a static elimination process. FIGS. 3A to 3C show the afterimage generation mechanism when the charge removal process is not performed. FIGS. 3D to 3F show the afterimage suppressing action in the case of performing the charge removal process using the charge removal light.

FIG. 3A shows immediately after the exposure process. The charged charge remains almost as it is in the non-image portion (blank portion) on the surface of the photoreceptor, whereas most of the charged charge is neutralized and lost by exposure in the central image portion (solid patch portion). For this reason, the surface potential of the photoconductor as the image carrier is the exposure potential Vl in the image portion and the charging potential Vd in the non-image portion.

FIG. 3B shows the transfer process. In this transfer step, the photosensitive member surface potential remains Vl in the solid portion of the image where the toner is moved. On the other hand, in the non-image area, a positive charge is injected into the photoconductor due to the transfer bias applied in the transfer process, so the photoconductor surface potential of the non-image area is positively charged.

In the state of FIG. 3B, when the next image charging process is started without the neutralizing light irradiation, as shown in FIG. 3C, the surface of the photoreceptor injected in the previous image transfer process in the non-image portion of the previous image. Due to the positive charge, the absolute value of the charging potential is lower than Vd by ΔVd (afterimage potential) (first surface potential). On the other hand, in the image portion of the previous image, since there is no positive charge on the surface of the photoreceptor, the charged potential Vd (second surface potential).

When the next image including the solid portion is formed on the photosensitive member 3K in which the history of the electrostatic latent image remains, an afterimage corresponding to the magnitude of the afterimage potential difference ΔVd is generated in the solid portion. Resulting in. That is, in the case of FIG. 3C, a negative afterimage with a low image density is generated in the solid portion of the next image corresponding to the afterimage potential difference ΔVd.

Note that the amount of positive charge injected in the transfer process increases as the transfer current value increases, so that the afterimage potential difference ΔVd increases corresponding to the transfer current value, and the afterimage tends to become worse. Also, the lower the charging potential Vd (the smaller the absolute value), the larger the afterimage potential difference ΔVd, and the afterimage tends to be further deteriorated.

(Afterimage suppression effect by static elimination light)
Next, the afterimage suppression action by the charge removal light will be described with reference to FIGS. FIG. 3D shows a state immediately after the photosensitive member is irradiated with static elimination light. As shown in the figure, when charge removal light is irradiated, negative charges (electrons) and positive charges (holes) are uniformly generated in the charge generation layer (CGL layer).

As shown in FIG. 3D, positive charges due to a transfer bias are injected into the surface of the non-image portion of the photoreceptor in the transfer process of the previous image. For this reason, the charged potential of the non-image portion is lowered by the positive charge, and the electric field is weakened. Accordingly, the positive charge generated from the charge generation layer (CGL layer) is difficult to move to the photosensitive member surface side in the non-image portion.

On the other hand, the positive charge due to the transfer bias is not injected into the surface of the image portion of the photoconductor in the transfer process of the previous image. For this reason, the electric field is strong in the image portion, and the positive charges generated by the irradiation of the static elimination light are easily moved to the surface of the photoreceptor.

Next, let us consider a case where charging and neutralizing light irradiation are simultaneously performed on the photosensitive member in the charging step. FIG. 3 (e) shows a state immediately after the start of this charging and neutralizing light irradiation. As shown in the figure, the positive charge generated in the charge generation layer (CGL layer) by the neutralizing light irradiation passes through the charge transfer layer (CTL layer) due to the electric field generated by the negative charge on the surface of the photoreceptor due to charging. Trying to move to the body surface side.

FIG. 3F shows a state after the positive charge generated in the charge generation layer (CGL layer) by the discharge of static electricity has moved to the surface of the photoreceptor. In the case where there is no neutralizing light irradiation in FIG. 3C or in comparison with FIG. 3E just before FIG. 3F, the potential difference ΔVd ′ between the image portion and the non-image portion becomes small (ΔVd ′ <ΔVd). It can be seen that the afterimage improves more efficiently.

As shown in FIG. 2A, even if the charge removal light L ′ is irradiated on the front side of the charging nip where no charging bias is applied, no electric field is applied. Therefore, the positive charge generated by the charge removal light hardly moves to the surface of the photoreceptor. The afterimage improvement effect is small. Further, since the positive charge generated in the charge generation layer by the charge removal light disappears over time, it is effective for reducing the afterimage to irradiate the charge nip portion where the electric field is applied.

In other words, as shown in FIG. 2A, the conventional image forming unit 1K that does not irradiate the charging nip portion with the charge eliminating light has no or very little effect on eliminating the afterimage. On the other hand, the irradiation of the charge nip to the charging nip is also effective for negative afterimages.

As described above, afterimage generation can be suppressed by increasing the charge removal light amount L ′. However, increasing the charge removal light amount L ′ accelerates deterioration of the photoreceptor due to electrostatic fatigue and shortens the life of the photoreceptor. There's a problem. In the conventional image forming apparatus, as shown in FIG. 2A, since the irradiation position of the charge removal light is away from the charging nip portion, the positive charge generated by the charge removal light cannot be effectively used for reducing the afterimage potential difference.

Further, in the case of an image forming unit that does not have a lubricant application mechanism as shown in FIGS. 2B and 2C, the film thickness variation of the charge generation layer (usually 0.05 to 2 μm) is larger than that of an image forming unit that has a lubricant application mechanism ( Therefore, it is necessary to irradiate the charge removal amount corresponding to the film thickness. However, it is not easy to change the amount of charge removal (increased light amount) in response to the decrease in the film thickness of the photoconductor.

(Irradiation light irradiation to the charging nip)
Therefore, as shown in FIG. 2B and FIG. 2C, the neutralizing light irradiation by the neutralizing lamp is performed aiming at the charging nip portion as the neutralizing light L′ 1. The static elimination light L′ 1 irradiated toward the charging nip portion is controlled to an appropriate static elimination light amount that does not cause an afterimage according to the detection result of the potential difference of the residual potential detected by the potential difference detection control.

(Transition of residual potential)
FIG. 4 shows the transition of the residual potential on the photoreceptor 3K according to the conventional example and the embodiment of the present invention. Since the embodiment of the present invention can provide a more appropriate amount of charge removal than in the past, the residual potential difference can be kept small over time with the same amount of charge removal, and deterioration of the photoreceptor 3K due to charge removal over time can be suppressed. It can be seen that it is.

(Solid patch and halftone patch)
5A and 5B show the solid patch portion and the halftone patch portion of the first embodiment and the second embodiment, respectively. In FIG. 5A, a solid patch portion and a halftone patch portion are sequentially formed in the rotation direction on the circumferential surface of the photoreceptor 3K. The white background other than both patch portions is a blank portion (blank portion).

The solid patch portion is located on the front side in the rotational direction, and the halftone patch portion is located on the rear side in the rotational direction. The interval between the solid patch portion and the halftone patch portion is a distance corresponding to one cycle (one circumference) of the photoreceptor 3K. The reason why the distance corresponding to one period (one round length) is increased is to confirm the presence or absence of the afterimage by overlapping the solid patch and the halftone patch.

Further, as shown in FIG. 5A, the surface potential detection sensor 76 is arranged at the center in the main scanning direction of the photoreceptor 3K, and the toner adhesion amount detection sensor 77 is arranged at the center in the width direction of the intermediate transfer belt 41 as shown in FIG. . Note that the surface potential detection sensor 76 and the toner adhesion amount detection sensor 77 may be arranged not only at one place but also at a plurality of places. For example, the toner adhesion amount detection sensor 77 may be disposed at three positions in the width direction of the intermediate transfer belt 41 as will be described later with reference to FIG.

Here, the “solid patch” refers to a rectangular patch having a predetermined size obtained by fully exposing a photoconductor to form a single-color image having a uniform density. The “halftone patch” refers to a rectangular patch having a predetermined size obtained by exposing a photoconductor with a light amount smaller than full exposure in order to form a monochromatic image having a uniform density. In FIG. 5A, both of the patches are “latent image patches”, and in FIG. 5B, both of the patches are “toner patches”.

The halftone patch can be formed as an “analog halftone patch” or a “digital halftone patch”. Here, an analog halftone patch is formed.

(Detection of surface potential difference and toner adhesion amount difference that causes afterimage)
FIG. 6A shows the relationship between the number of rotations (circulation) of the photoreceptor 3K and the surface potential of the photoreceptor 3K. FIG. 6B shows the relationship between the number of rotations (circulation) of the photosensitive member 3K and the toner adhesion amount of the intermediate transfer member.

The black solid patch portion and the blank portion of FIG. 5A and FIG. 5B are formed in the region including [1] [2] on the first round of the photoreceptor 3K, and FIG. 5A is illustrated in the region including [3] [4] on the second round. 5B is formed as a black halftone patch portion.

6A and 6B, an afterimage of the first round solid patch portion is generated in the second halftone patch portion of the photoreceptor 3K by the afterimage generation mechanism described above with reference to FIG. That is, as shown in FIG. 6A, the history of the portion where the potential drops at [1] [2] in the pattern of the first round of the photoreceptor 3K remains at the next image formation. As a result of the history appearing as a surface potential difference, an afterimage having a toner adhesion amount (0.10 mg / cm ² ) thinner than a predetermined toner adhesion amount (0.15 mg / cm ² ) as shown in [3] and [4] in FIG. 6B. Is generated.

Note that the surface potential varies with respect to the toner adhesion amount shown in FIG. 6B even when the amount of writing light decreases as in the case of a solid image. However, since a difference in toner adhesion amount due to development is less likely to occur, an afterimage does not appear. On the other hand, in the halftone image, since the sensitivity of the toner adhesion amount is high with respect to the surface potential difference, the afterimage is generated due to the difference in the adhesion amount when developed.

The extent of the afterimage depends on the potential difference (ΔVl ₃ , ΔVl ₄ ) to the toner adhesion amount difference (ΔM / A ₁ , ΔM /
Proportional to A ₂ ). Here, the surface potential can be measured using, for example, a Trek surface potential meter Model 344. The toner adhesion amount can be measured by an optical sensor. In this way, by detecting a potential difference or a toner adhesion amount difference with a surface electrometer or an optical sensor, it is possible to detect the presence or absence of afterimage generation before printing. Note that under this condition, the amount of adhesion of the portion corresponding to the solid portion on the second circumference of the photoconductor is small, but the amount of adhesion may increase when the image forming conditions are different.

(Static removal capacity adjustment mode)
As described above, the presence or absence of afterimage generation can be detected based on the potential difference between the solid patch portion and the halftone patch portion or the difference in toner adhesion amount. FIG. 7A, FIG. 7C, and FIG. 7D show a flow (static removal capability adjustment mode) in which the amount of discharge light is controlled before printing of the image forming apparatus using this fact. This flow is executed by a control means (not shown) for increasing / decreasing the charge removal capability of the charge removal lamp 22K as the charge removal means.

FIG. 7A and FIG. 7C show the charge removal light amount control based on the surface potential difference, and FIG. 7D shows the charge removal light amount control based on the toner adhesion amount difference. FIG. 7C is a flowchart in which control of the amount of charge to be removed according to the developing ability is added to the flow of FIG. 7A (S′1, S′2). Steps S′1 and S′2 in FIG. 7C are for calculating the target potential difference S in consideration of a correction coefficient in FIG. 7B described later.

In FIG. 7A, FIG. 7C, and FIG. 7D, the charge removal light amount is first turned off, and the charge removal light amount is increased so as to satisfy ΔVl ≦ S or ΔM / A ≦ S. As another method, first, the charge removal light amount is set to the previous value, and the charge removal light amount is increased or decreased to obtain ΔVl = S or ΔM / A.
However, it may be set to an optimal value such that = S.

Here, if the potential difference of the residual potential indicated by ΔVl in FIG. 6A is a predetermined value (for example, 5V) or more, the light amount L′ 1 is increased in step S5 of FIG. 7A and step S′7 of FIG. Potential difference detection control is performed and repeated until the value of ΔVl in FIG. 6A becomes a predetermined value S (for example, 5 V) or less.

Further, the toner adhesion amount difference indicated by ΔM / A in FIG. 6B is a predetermined value S (for example, 0.05 mg /
If it is equal to or greater than cm ² ), the amount of light L′ 1 is increased in step S5 of FIG. 7D, toner adhesion detection control is performed, and this is repeated until the value of ΔM / A in FIG.

When an image is formed using the light quantity L′ 1 set based on this result, the image formed by the residual potential on the photoreceptor 3K does not deteriorate, and a high-quality image can be provided. As described above, in the present invention, the output of the surface potential detection sensor 76 is detected, and the amount of static elimination light of the light amount L′ 1 is controlled, so that the occurrence of an afterimage in halftone can be suppressed.

If the potential difference between the residual potentials is equal to or smaller than a predetermined value S (for example, 5 V), the light amount L′ 1 may be maintained without changing the light amount L′ 1. If the predetermined value S is decreased, the degree of afterimage generation is improved, but the amount of light is increased by the amount by which the predetermined value S is decreased. Therefore, the predetermined value S can be changed, and the necessary increase / decrease change amount of the predetermined value S can be determined after confirming the degree of afterimage generation.

(Control of the amount of static elimination according to the development capacity)
FIG. 7B shows a correction coefficient in the case where the amount of static elimination light is controlled according to the size of the development γ. Depending on the environment in which the machine is placed and the travel distance of the developer, the developing ability of the toner during the printing operation (toner adhesion amount per development potential: development γ, unit: mg / cm ² / kV) always varies.

Here, the development γ is a parameter indicating a correspondence relationship between the development potential and the toner adhesion amount. The development potential indicates a potential difference between the exposed portion potential on the photosensitive member and the development bias. As the development potential increases, the toner adhesion amount to the one-dot electrostatic latent image increases and the image density increases.

Even if the potential difference ΔVl of the residual potential detected by the surface potential detection sensor 76 is the same, the toner adhesion amount difference varies depending on the developing ability (development γ). For this reason, the degree of occurrence of afterimages on the image varies depending on the development γ. Since the toner adhesion amount difference is proportional to the product of the potential difference ΔVl and the development γ, the toner adhesion amount difference becomes large and the afterimage deteriorates when the developing ability is high, and the toner adhesion amount difference becomes small when the developing ability is low. The afterimage improves.

Therefore, the predetermined value S of the potential difference of the residual potential is corrected according to the developing ability (development γ), and the intensity of the static elimination light L′ 1 is changed. FIG. 7B shows an example of a list of correction coefficients by development γ. In order to determine the optimum image forming conditions, the image forming apparatus periodically performs process control and measures the developing ability.

By correcting the predetermined value S of the potential difference of the residual potential in accordance with the developing capability immediately before executing the neutralizing capability adjustment mode, it is possible to set an optimal neutralizing light amount considering the developing capability. Note that the value of the correction coefficient varies depending on the characteristics of the photoreceptor 3K and the system configuration, and thus detailed description thereof is omitted. Of course, the predetermined value S of the potential difference may be continuously corrected so that the amount of charge removal is inversely proportional to the development γ.

(Execution time of static elimination capacity adjustment mode)
In the charge removal capability adjustment mode, it is necessary to perform an image forming operation in order to detect the toner adhesion amount. When the neutralization capacity adjustment mode is executed every time before printing, toner adhesion amount control is frequently performed. Then, it takes time for the user to wait, and printing cannot be performed immediately even in a hurry.

In addition, since the image forming unit is moved for detecting the toner adhesion amount, if the toner adhesion amount control is frequently performed, the travel distance of the photoconductor is unnecessarily increased, and the replacement frequency of the image forming unit is reduced. It will increase. Therefore, it is desirable to execute the neutralization capability adjustment mode only when the number of printed sheets of the image forming apparatus exceeds a certain threshold number. The threshold number of sheets is determined by the photosensitive member travel distance that is assumed that the thickness of the photosensitive layer of the photosensitive member 3K has been cut by a predetermined amount or more. The threshold number can be changed depending on the system.

In the case of a system that does not apply the lubricant to the photoreceptor 3K, the neutralization capability adjustment mode is entered once every several thousand sheets. Also, when it is detected that the photoconductor has been replaced, the static elimination capability adjustment mode is executed. In this way, by periodically executing the static elimination capability adjustment mode or by executing the static elimination capability adjustment mode during the adjustment operation such as process control, it is possible to reduce the convenience for the user and reduce the travel distance for a long time. Thus, the occurrence of afterimages can be suppressed.

Therefore, the image forming apparatus according to the embodiment of the present invention can achieve both a reduction in the residual image and a reduction in the electrostatic fatigue of the photosensitive member as compared with the conventional image forming apparatus, and can suppress the generation of the residual image over a long period of time.

(Multiple arrangement of toner adhesion detection sensors)
FIG. 8 is an embodiment in which a plurality of toner adhesion amount detection sensors 77 are arranged in the main scanning direction of the intermediate transfer belt 41. In FIG. 8, toner adhesion amount detection sensors 77 are arranged at three locations on the front side (Front), the center (Center), and the rear side (Rear) of the intermediate transfer belt 41.

Due to variations in charging parts and differences in transfer pressure between the front side, the center of the intermediate transfer belt 41, and the rear side (hereinafter abbreviated as “FCR”), the toner adhesion amount difference changes in the main scanning direction. May change. In such a case, if the amount of charge removal is determined and corrected at a certain point, the amount of charge removal is not sufficient in the worst part, and an afterimage may occur.

Therefore, in order to stabilize the image, the toner adhesion amount detection sensor 77 for detecting the toner adhesion amount on the intermediate transfer belt is detected at, for example, three points of FCR as shown in FIG. The toner adhesion amount detection sensor 77 detects the toner adhesion amount at three points of the FCR in the main scanning direction, and corrects the amount of static electricity suitable for each location according to the flowchart shown in FIG. 7D.

In this way, by correcting the amount of static elimination at the three points of the FCR, it is possible to suppress the afterimage generation without variation even in the main scanning direction. In this embodiment, the number of toner adhesion amount detection sensors 77 is three, but it is needless to say that the number of sensors in the main scanning direction is not limited to three.

As described above, by arranging an arbitrary plurality of toner adhesion amount detection sensors 77 and using the plurality of sensors to determine the correction amount of the charge removal amount in the main scanning direction, the afterimage can be suppressed over the entire image.

(Halftone image)
An analog halftone image is used in the above-described potential difference detection control. However, in an actual image of a digital printer, an analog halftone with a low write light amount is unstable. For this reason, afterimages cannot be sufficiently suppressed even after controlling the amount of charge to be discharged to the charging nip according to the detection result of the potential difference of the residual potential using an analog halftone image. However, the amount of light is too strong than necessary, and electrostatic fatigue of the photoreceptor 3K may be promoted.

Therefore, instead of the analog halftone, a dot is shot with a solid writing light amount, and a halftone image is formed by changing the area ratio. That is, a digital halftone image as shown in FIGS. 9A (a) and 9 (b) is used. By using such a digital halftone image, afterimage generation is suppressed as compared with the case of using an analog halftone, and an optimal charge removal amount with less electrostatic fatigue can be set.

7A, 7C, and 7D, the same control as described above may be performed by changing the image pattern of the halftone patch portion of FIGS. 5A and 5B to a digital halftone image pattern.

By the way, various dither patterns are used for the actual image of the digital printer. In the dither pattern, gray gradation is expressed by small dots in a halftone pattern, and the difference in density is expressed by changing the size and density of the halftone dots.

However, the extent and appearance of afterimages differ for each type of dither pattern. For this reason, there may be a case where the afterimage cannot be sufficiently suppressed even if the amount of charge removal applied to the charging nip is controlled according to the detection result of the potential difference of the residual potential using a predetermined digital halftone image. On the other hand, even if the afterimage can be suppressed, the amount of light is too strong than necessary, and electrostatic fatigue of the photoreceptor may be promoted.

Therefore, in such a case, it is preferable to use a digital halftone image that is a real image having a high output frequency after adjustment, as shown in FIGS. By using a digital halftone image of a real image with high output frequency after such adjustment, afterimage generation is suppressed and less static fatigue is achieved than when a predetermined digital halftone image is used. The amount of light can be set.

Also in this case, with respect to the detection pattern imaging method of FIGS. 7A, 7C, and 7D, the image pattern of the halftone patch part of FIGS. A halftone image pattern may be used to perform the same control as described above.

  Although the present invention has been specifically described above based on the embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the technical idea described in the claims. Needless to say. For example, although the two-component developer is used in the above-described embodiment, a magnetic or non-magnetic one-component developer can be used instead of the two-component developer. These developers may be either negative developers or positive developers.

Further, the charge eliminating means is not limited to a charge eliminating lamp. The neutralization unit may be any unit that can apply a neutralization bias to the image carrier. Such a static elimination means can be appropriately selected from known static eliminators.

1Y, 1C, 1M, 1K: Image forming units 2Y, 2C, 2M, 2K: Photoconductor units 3Y, 3C, 3M, 3K: Photoconductors 7Y, 7C, 7M, 7K: Development units 8K: Screw rollers 9K: Stirring rollers 10K: toner density sensor 12K: developing roller 13K: magnet roller 14K: doctor blade 15K: drum cleaning device 16K: magnet roller 17K: coating brush roller 18K: cleaning blade 19K: solid lubricant 20: optical writing unit 20K: recovery coil 21: Polygon mirror 22K: Static elimination lamp 23K: Charging device 231K: Charging roller 232K: Cleaning brush roller 31: First paper feeding cassette 31a: First paper feeding roller 32: Second paper feeding cassette 32a: Second paper feeding roller 33 : Paper feed path 34: Feed roller pair 35: Timing roller pair 40: Transfer unit 41: Intermediate transfer belt 42: Belt cleaning unit 42a: Cleaning blade 43: First bracket 44: Second bracket 45Y, 45C, 45M, 45K: Primary transfer roller 46: Two Next transfer backup roller 47: Driving roller 48: Auxiliary roller 49: Tension roller 50: Secondary transfer roller 60: Fixing unit 61: Pressure heating roller 61a: Heat source 62: Fixing belt unit 63: Heating roller 63a: Heat source 64 : Fixing belt 65: Tension roller 66: Drive roller 67: Paper discharge roller pair 68: Stack unit 76: Surface potential detection sensor 77: Toner adhesion amount detection sensor 100Y, 100C, 100M, 100K: Toner cartridge

Japanese Patent No. 2618009 JP 2000-181159 A JP 2000-66552 A JP 2008-122440 A JP 2007-79168 A JP 2008-122440 A JP-A-8-76559

Claims (10)

An image carrier that carries a latent image and is rotatable, a charging unit that uniformly charges the circumferential surface of the image carrier, and the latent image is exposed on the circumferential surface by exposing the circumferential surface of the image carrier. Writing means for writing; developing means for developing the latent image as a toner image with toner; transfer means for transferring the toner image to a recording medium directly or via an intermediate transfer member; A neutralizing unit that neutralizes the peripheral surface of the body at a position of a charging portion between the charging unit and the image carrier; and a write unit and a developing unit that are disposed between the writing unit and the developing unit. In an image forming apparatus having a surface potential detecting means for detecting a surface potential and a control means for controlling increase / decrease in the charge removal capability of the charge removing means,
Before starting the printing operation of the image forming apparatus, the writing unit forms a full patch solid patch portion and a non-exposed blank portion on the first circumferential surface of the image carrier, and the transfer unit. Forming a halftone patch portion overlaid on the portion where the solid patch portion and the blank portion were formed on the peripheral surface of the second circumference of the image carrier after being transferred by the charging means and charged by the charging means,
The surface potential detecting means detects a potential difference between a first surface potential of a portion that was the solid patch portion in the halftone patch portion and a second surface potential of a portion that was the blank portion,
When the potential difference exceeds a predetermined value, the control unit has a neutralization capability adjustment mode for starting a printing operation after increasing the neutralization capability of the neutralization unit until the potential difference becomes a predetermined value or less. An image forming apparatus. An image carrier that carries a latent image and is rotatable, a charging unit that uniformly charges the circumferential surface of the image carrier, and the latent image is exposed on the circumferential surface by exposing the circumferential surface of the image carrier. Writing means for writing; developing means for developing the latent image as a toner image with toner; transfer means for transferring the toner image to a recording medium directly or via an intermediate transfer member; A neutralizing unit that neutralizes a peripheral surface of the body at a position of a charging unit between the charging unit and the image carrier, and a toner adhesion amount of the intermediate transfer body immediately before secondary transfer from the intermediate transfer body to a recording medium In an image forming apparatus, comprising: a toner adhesion amount detecting means for detecting the amount of charge;
Before starting the printing operation of the image forming apparatus, the writing unit forms a full patch solid patch portion and a non-exposed blank portion on the first circumferential surface of the image carrier, and the transfer unit. Forming a halftone patch portion overlaid on the portion where the solid patch portion and the blank portion were formed on the peripheral surface of the second circumference of the image carrier after being transferred by the charging means and charged by the charging means,
The toner adhesion amount detection means detects a difference between a first toner adhesion amount at a portion that was the solid patch portion and a second toner adhesion amount at a location that was the blank portion in the halftone patch portion. When the adhesion amount difference exceeds a predetermined value, the control unit increases the charge removal capability of the charge removal unit until the adhesion amount difference becomes equal to or less than the predetermined amount, and then the neutralization capability adjustment mode is started to start the printing operation. An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the neutralizing unit includes a neutralizing lamp that emits neutralizing light.   3. The image forming apparatus according to claim 1, wherein the charging unit is a roller charging system or a corona charging system.   The image forming apparatus according to claim 1, wherein the halftone patch is an analog halftone patch or a digital halftone patch.   3. The image forming apparatus according to claim 1, wherein the neutralization capability adjustment mode is executed every predetermined number of prints of the recording medium.   2. An image according to claim 1, wherein a plurality of said surface potential detection means are provided in the main scanning direction of said image carrier, and the charge removal capability of said charge removal means can be increased or decreased in the main scanning direction of said image carrier. Forming equipment.   3. The toner adhering amount detection means is provided in a plurality in the main scanning direction of the intermediate transfer body, and the charge removal capability of the charge removal means can be increased or decreased in the main scanning direction of the intermediate transfer body. Image forming apparatus. 9. The neutralization capability adjustment mode is executed when the image carrier is composed of a photosensitive member having a photosensitive layer, and the photosensitive layer of the photosensitive member is worn by a predetermined amount or more. 1. An image forming apparatus according to item 1. 10. The image forming apparatus according to claim 1, wherein the neutralization capability adjustment mode is executed when the image carrier is replaced. 11.