JP2019056789A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can prevent the occurrence of dirt on the back side of a recording medium resulting from a first image, compared with a case where when executing a first image forming operation, the image forming apparatus forms the first image in a portion of an image formable range of image holding means corresponding to a range from the leading end to the rear end of the recording medium during its conveyance.SOLUTION: An image forming apparatus comprises control means that forms a first image TG with developing means by attaching a developer to a surface at least outside an image quality guarantee range 212 and within an image formable range 210 of image holding means 21, and executes a first image forming operation of transferring the image to a recording medium 9B with transfer means. In the first image forming operation, the control means forms the first image TG in a portion corresponding to a range from a position Ps inside the leading end 9a of the recording medium 9B during its conveyance to a position Pe inside the rear end 9b during its conveyance within the image formable range 210 of the image holding means 21.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an image forming apparatus.

  Conventionally, as an image forming apparatus having a function of estimating the cause of occurrence of an abnormal image, for example, those described in the following patent documents are known.

  First, in Patent Document 1, a sample image is output as an image that is not output by normal image processing, and the sample image is read by an image input device to determine whether an abnormal image has occurred. There is shown an image forming apparatus in which a sign of occurrence of an abnormal image is found before an abnormality occurs and an action is taken at an early stage. Further, Patent Document 1 exemplifies that the abnormality is that the fixing roller and the pressure roller of the fixing device are deformed and that the photosensitive drum has a lot of moisture.

  Japanese Patent Application Laid-Open No. 2004-228561 calculates a shift amount of image data with respect to a normal state, determines whether or not the state is abnormal based on the shift amount, and identifies an abnormal portion from the state of the image forming apparatus. When it is determined that there is an abnormality by the abnormal part identification unit and the state determination unit, it is determined that there is an abnormality by the image processing unit that performs image processing for abnormality according to the output of the abnormal part identification unit and the state determination unit In this case, an image forming apparatus including serviceman call output means for outputting a serviceman call signal is shown.

  Patent Document 3 discloses an image input unit, an image forming unit that forms an output image on a recording medium based on the input image data, a discharge unit that discharges the recording medium on which the image is recorded, and a discharge unit. An image reading unit that outputs a read image obtained by reading the recorded recording medium, an abnormality detection image generation unit that outputs image data for abnormality detection that is likely to generate an abnormal image due to the charging unit of the image forming unit, and the abnormality Comparing means for comparing the output data from the image reading means that has read the recording medium on which the output image is formed based on the detection image data and the input image data for abnormality detection, and outputting a determination result; An image forming apparatus having a determination unit capable of detecting the presence or absence of abnormality of the charging unit based on the determination result of the comparison unit is shown.

Further, in Patent Document 4, a patch image is formed at each stage while changing and setting density control factors that affect the image density in multiple stages, the image density of each patch image is detected, and based on the detection result. In an image forming apparatus that performs image density control by adjusting a density control factor, at least one of the patch images is used as an abnormality determination patch image, and a density detection result and a predetermined reference value for the abnormality determination patch image An image forming apparatus that compares the above and determines whether there is an abnormality in the apparatus based on the result is shown.
In Patent Document 4, a patch image in which the development bias that is a density control factor is changed and two patch images developed with the maximum development bias are used as abnormality determination patch images, and these density detection results are used as a predetermined reference. An embodiment is shown in which an abnormality of the apparatus is determined by comparison with the concentration.

JP 2004-133081 A JP 2007-334269 A JP 2008-170549 A JP 2004-341233 A

  The present invention forms a first image in which a developer is adhered to a surface that is at least outside the image quality guarantee range and within the image formable range when the electrostatic latent image of the image holding unit is not formed. When the first image forming operation of transferring the image onto the recording medium by the transfer unit is executed, the portion corresponding to the range from the leading end to the trailing end of the recording medium in the image forming range of the image holding unit. The present invention provides an image forming apparatus capable of preventing the backside contamination of the recording medium due to the first image as compared with the case of forming the image on the surface.

The image forming apparatus of the present invention (A1)
Image holding means having an image quality guarantee range set to a surface image formable range;
Charging means for charging the surface of the image holding means in an image formable range;
Developing means to which a developing bias voltage is supplied and which develops an electrostatic latent image formed in at least the image quality guarantee range of the image holding means with a developer to form a developer image;
Transfer means for transferring the developer image to a recording medium directly or via an intermediate transfer member;
A first image formed by adhering developer by the developing means is formed on the surface of the image holding means that is at least outside the image quality guarantee range and within the image formable range, and is transferred to a recording medium by the transfer means. A control means for executing one image forming operation;
With
In the first image forming operation, the control unit moves the first image from a position on the inner side of the image forming range of the image holding unit when the recording medium is transported from a rear end thereof. Is formed in a portion corresponding to the range up to the inner position.

In the image forming apparatus of the invention (A2), in the image forming apparatus of the invention A1, the control means sets the image forming range of the image holding means to a charging potential applied when forming an electrostatic latent image by the charging means. The first image forming operation is executed after the charged state and the developing bias voltage are maintained at the developing potential applied when forming the electrostatic latent image.
In the image forming apparatus of the invention (A3), in the image forming apparatus of the invention A1, the control unit puts the image forming range of the image holding unit into a state where it is not charged by the charging unit and The first image forming operation is executed after the development bias voltage is not supplied.

The image forming apparatus according to the present invention (A4) is the image forming apparatus according to the above-described invention A2, in which the control means performs the development in accordance with the time when the first image should be formed during the first image forming operation. An operation of changing the bias voltage from a developing potential applied at the time of forming the electrostatic latent image to a special developing potential at which the first image is formed and an operation of returning to the developing potential applied at the time of forming the electrostatic latent image are performed.
The image forming apparatus according to the present invention (A5) is the image forming apparatus according to the above-described invention A2, in which the control means performs the charging in accordance with the time when the first image should be formed during the first image forming operation. The charging voltage supplied to the means is changed from the charging potential applied at the time of forming the electrostatic latent image to the special charging potential at which the first image is formed, and the operation is returned to the charging potential applied at the time of forming the electrostatic latent image. Is.
The image forming apparatus according to the present invention (A6) is the image forming apparatus according to the above-described invention A3, wherein the control means performs the first image in accordance with the time when the first image is to be formed during the first image forming operation. An operation of supplying a developing bias voltage at a special developing potential for forming one image to the developing means and an operation of stopping the supply are performed.

In the image forming apparatus of the invention (A7), in the image forming apparatus of the invention A4, the control means performs an operation of changing the developing bias voltage to the special developing potential. The timing when it coincides with the charging potential applied at the time of forming the latent image is after the time corresponding to the leading edge when the recording medium is conveyed.
In the image forming apparatus of the invention (A8), in the image forming apparatus of the invention A4 or A7, the control means returns the developing bias voltage from the special developing potential to the developing potential applied when forming the electrostatic latent image. The operation is performed so that the timing when the potential during the returning process coincides with the charging potential applied at the time of forming the electrostatic latent image is before the time corresponding to the trailing edge during conveyance of the recording medium.
In the image forming apparatus of the invention (A9), in the image forming apparatus of the invention A5, the control means performs the operation of changing the charging voltage to the special charging potential. The timing when it coincides with the developing potential applied at the time of image formation is performed after the time corresponding to the leading edge when the recording medium is conveyed.
In the image forming apparatus according to the invention (A10), in the image forming apparatus according to the invention A5 or A9, the control means returns the charging voltage from the special charging potential to a charging potential applied when forming an electrostatic latent image. Is performed so that the time when the potential in the returning process coincides with the developing potential applied at the time of forming the electrostatic latent image is before the time corresponding to the rear end of the conveyance of the recording medium.
In the image forming apparatus of the invention (A11), in the image forming apparatus of the invention A6, the control means performs an operation of supplying a developing bias voltage that becomes the special developing potential. The timing when it coincides with the adhesion start potential when the adhesion of the developer to the image holding means starts is after the time corresponding to the leading edge when the recording medium is conveyed.
In the image forming apparatus of the invention (A12), in the image forming apparatus of the invention A6 or A11, the control means performs the operation of stopping the supply of the developing bias voltage, and the potential during the supply stop process is the image holding. The timing when it coincides with the adhesion end potential when the adhesion of the developer to the means is completed is before the time corresponding to the rear end when the recording medium is conveyed.

The image forming apparatus of the invention (A13) is the image forming apparatus of the invention A4, wherein the control means forms the special developing potential and the electrostatic latent image as the special developing potential in the first image forming operation. A potential that falls within a numerical range smaller than a contrast potential, which is a potential difference between a developing potential applied during electrostatic latent image formation and a latent image potential, is used.
The image forming apparatus of the invention (A14) is the image forming apparatus of the invention A5, wherein the control means forms the special charging potential and the electrostatic latent image as the special charging potential in the first image forming operation. The potential difference between the developing potential applied at times and the developing potential applied at the time of electrostatic latent image formation falls within a numerical range smaller than the contrast potential, which is the potential difference between the latent image potential and the latent image potential.
The image forming apparatus of the invention (A15) is the image forming apparatus of the invention A6, in which the control means uses the special developing potential and the image holding means as the special developing potential in the first image forming operation. A potential that falls within a numerical range in which the potential difference from the surface potential when not charged is smaller than the contrast potential, which is the potential difference between the developing potential and the latent image potential applied during electrostatic latent image formation, is used.

The image forming apparatus according to the present invention (A16) is the image forming apparatus according to any one of the inventions A1 to A15, wherein the image holding means is a rotating member, and the control means is the first image forming operation. In this case, an image having a length equal to or longer than one rotation of the image holding means is formed as the first image and transferred to a recording medium.
The image forming apparatus according to the present invention (A17) is the image forming apparatus according to the above-described invention A16, wherein, when the first image forming operation is performed, the control means serves as the first image more than two rotations of the image holding means. Is formed and transferred onto one or a plurality of recording media.
The image forming apparatus according to the present invention (A18) is the image forming apparatus according to any one of the inventions A1 to A17, wherein the control means is configured to place an electrostatic latent image on the image holding means during the first image forming operation. Is not performed.

  According to the image forming apparatus of the invention A1, the developer is adhered to the surface of the image holding unit that is at least outside the image quality guarantee range when the electrostatic latent image is not formed and is within the image formable range. When the first image forming operation is performed in which the first image is formed and transferred to the recording medium by the transfer unit, the first image is transferred from the leading end to the trailing end of the image holding unit when the recording medium is conveyed. As compared with the case where the recording medium is formed in a portion corresponding to the above range, it is possible to prevent the back surface of the recording medium from being stained due to the first image.

In the image forming apparatus according to the invention A2, it is possible to know a sign that the end portion of the image quality guarantee range of the image holding means is worn and the occurrence of an abnormality in the charging means.
In the image forming apparatus according to the invention A3, it is possible to know a sign that the end portion of the image quality guarantee range of the image holding means is worn and the occurrence of an abnormality in a portion other than the end portion of the image quality guarantee range of the image holding means.

In the image forming apparatus of the invention A4, it is possible to easily prevent the recording medium from being stained on the back surface due to the first image by changing the developing bias voltage.
In the image forming apparatus according to the invention A5, it is possible to easily prevent the recording medium from being stained due to the first image due to the change in the charging voltage.
In the image forming apparatus according to the invention A6, it is possible to easily prevent the backside of the recording medium from being stained due to the first image by supplying and stopping the supply of the developing bias voltage without charging the image holding unit.
In the image forming apparatuses of the inventions A7, A9, and A11, in addition to being able to accurately prevent the backside contamination of the recording medium due to the first image, the first image is positioned at least near the front end of the recording medium. Therefore, it is possible to know the sign of abnormality or the occurrence of abnormality in the image holding means or the like.
In the image forming apparatuses according to the inventions A8, A10, and A12, in addition to accurately preventing the occurrence of backside contamination of the recording medium due to the first image, the first image is close to at least the rear end of the recording medium. It is possible to know the sign of abnormality or the occurrence of abnormality in the image holding means or the like by transferring it to the position.
In the image forming apparatuses according to the inventions A13, A14, and A15, it is possible to form a first image in which a sign of abnormality or occurrence of abnormality in the image holding unit or the like can be easily visually recognized.

In the image forming apparatus according to the invention A16, it becomes easier to know a periodic abnormality sign or occurrence of abnormality in the image holding means or the like.
In the image forming apparatus according to the invention A17, it is possible to reliably know a sign of a periodic abnormality or the occurrence of abnormality in the image holding unit or the like.
In the image forming apparatus of the invention A18, it is possible to form the first image that is not affected by the exposure unit that forms the electrostatic latent image.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to Embodiment 1 and the like. FIG. 2 is an enlarged schematic diagram illustrating a configuration of an image forming apparatus in the image forming apparatus of FIG. 1. FIG. 2 is a block diagram showing a configuration of a part of a control system (mainly a control system related to a first image forming operation) in the image forming apparatus of FIG. 1. FIG. 2 is a schematic diagram illustrating a configuration of each part in a photosensitive drum. (A) is a conceptual diagram showing a potential relationship on the photosensitive drum when a normal image is formed, and (b) is a conceptual diagram showing a potential relationship on the photosensitive drum when the first image forming operation is executed. . It is a conceptual diagram which shows the operation time etc. in a 1st image formation operation | movement. It is a schematic diagram which shows an example of the result obtained by 1st image formation operation | movement. (A) is a schematic diagram showing a state of the first image formed by the first image forming operation at the secondary transfer position, and (b) is a first image formed by the first image forming operation and its first image. FIG. 3 is a schematic diagram illustrating a relationship with a recording sheet on which one image is finally formed. It is a graph which shows the result of the test which supports the suitable conditions of special development potential. FIG. 10 is a conceptual diagram illustrating a potential relationship on a photosensitive drum when a first image forming operation is performed by the image forming apparatus according to the second embodiment. It is a conceptual diagram which shows the operation time etc. in a 1st image formation operation | movement. FIG. 10 is a conceptual diagram illustrating a potential relationship on a photosensitive drum when a first image forming operation by an image forming apparatus according to Embodiment 3 is executed. It is a conceptual diagram which shows the operation time etc. in a 1st image formation operation | movement. It is a schematic diagram which shows an example of the result obtained by 1st image formation operation | movement. FIG. 12 is a schematic diagram illustrating another example of a result obtained by the first image forming operation in the first and second embodiments. It is a conceptual diagram which shows the structure regarding the length of the 1st image formed by each 1st image formation operation | movement. It is a conceptual diagram which shows the other structure regarding the length of the 1st image formed by each 1st image forming operation | movement, (a) shows the example which forms a 1st image on 1 sheet of recording paper, (b) Shows an example in which the first image is formed on two recording sheets. (A) is a schematic diagram showing a state at a secondary transfer position of a first image formed by the first image forming operation as a comparative example, and (b) is formed by the first image forming operation of (a). FIG. 6 is a conceptual diagram illustrating an example of a backside stain on a recording sheet that is generated due to the first image.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

[Embodiment 1]
1 to 3 show an image forming apparatus 1 according to the first embodiment. 1 shows the configuration of the image forming apparatus 1, FIG. 2 shows the configuration of the image forming apparatus in the image forming apparatus 1, and FIG. 3 shows the configuration of a part of the control system in the image forming apparatus 1. .

<Overall Configuration of Image Forming Apparatus>
The image forming apparatus 1 employs an electrophotographic method, and finally forms an image composed of a developer on recording paper 9 as an example of a recording medium based on image information including characters, photographs, figures, and the like. It is.

As shown in FIG. 1, the image forming apparatus 1 includes a casing 10 having a box-like appearance as a whole, and the casing 10 is configured with toner as a developer. An image forming device 20 that forms a toner image that is an example of a developer image, and a toner image formed by the image forming device 20 is held by primary transfer and then transported to a secondary transfer position where it is secondarily transferred to a recording sheet 9. The intermediate transfer device 30, the recording paper 9 supplied to the secondary transfer position of the intermediate transfer device 30, and the paper supply device 40 for supplying and supplying the toner image secondarily transferred by the intermediate transfer device 30 to the recording paper 9 A fixing device 50 for fixing is disposed.
The housing 10 is formed with a support structure portion and an exterior portion using materials such as a support member and an exterior material, for example. A one-dot chain line shown in FIG. 1 is a main conveyance path of the recording paper 9 inside the housing 10.

In addition, the image forming apparatus 1 includes an operation display device 14 having an input unit 14a for inputting instructions, conditions, and the like regarding the operation of the image forming apparatus 1 and a display unit 14b for displaying various information such as the conditions and states of the operation. A central control device 60 and the like that control the overall operation of the entire image forming apparatus 1 (the above-described devices and the like) are also arranged.
Further, as will be described later, the image forming apparatus 1 has a function of estimating (predicting) that some parts are abnormal.

The image forming device 20 includes four image forming devices 20Y, 20M, 20M, 20M, 20M, 20M, 20M, 20M, 20M, 20M, and 20D respectively forming developer (toner) images of four colors of yellow (Y), magenta (M), cyan (C), and black (K). 20C and 20K are used.
Each of the image forming devices 20 (Y, M, C, K) includes a photosensitive drum 21 that is rotationally driven in a required direction, as shown in FIGS. 1 and 2, and each of the photosensitive drums. A charging device 22, an exposure device 23, a developing device 24, a primary transfer device 25, a drum cleaning device 26, a static eliminator 27, and the like are disposed around the area 21, respectively.

Among these, the photosensitive drum 21 forms, for example, an image forming surface (image forming range) having a photo-dielectric layer (photosensitive layer) made of a photosensitive material on the peripheral surface of a cylindrical or columnar conductive substrate to be grounded. 2 is a drum-shaped photoconductor as an example of the image holding unit. The photosensitive drum 21 is provided so as to be driven to rotate in a direction indicated by an arrow A by receiving power from a rotation driving device (not shown).
The charging device 22 is, for example, a contact-type charging device that includes a charging roll 221 that is disposed in a state of rotating in contact with the image forming surface of the photosensitive drum 21 and is supplied with a required charging voltage.

The exposure device 23 is an example of an exposure unit, and is configured using, for example, a non-scanning exposure device configured using a light emitting diode and an optical component, or an optical component such as a semiconductor laser and a polygon mirror. A scanning type exposure apparatus is applied. The exposure device 23 receives image information input from the outside through a communication means, a reading device, etc., and image information stored in an internal storage unit after each image component (not shown) has undergone a required process, and each color component ( Y, M, C, and K) are input as image signals that have been decomposed. The exposure device 23 performs exposure according to the input image signal.
The developing device 24 is an example of a developing unit. For example, the developing device 24 (Y) that uses a two-component developer including toner of any one of the four colors (Y, M, C, and K) and a magnetic carrier. , M, C, K) apply. Further, the developing device 24 (Y, M, C, K) is used, for example, to perform reversal development by charging the toner to a negative polarity. Further, the developing device 24 (Y, M, C, K) holds a two-component developer housed in the housing and rotates a developing roll 241 etc. that rotates so as to be conveyed to a developing region facing the photosensitive drum 21. I have. For example, a developing bias voltage in which an AC component is superimposed on a DC component is supplied to the developing roll 241 between the photosensitive drum 21 and the developing roll 241.

The primary transfer device 25 is an example of a transfer unit, and is, for example, disposed so as to be driven and rotated in contact with an image forming surface portion as a primary transfer position of the photosensitive drum 21 (via an intermediate transfer belt 31 described later). In addition, a contact type transfer device including a primary transfer roll to which a required primary transfer voltage is supplied is applied.
The drum cleaning device 26 is disposed so as to contact at least the image forming surface portion after the primary transfer of the photosensitive drum 21 in the cleaning work opening of the housing, and scrapes unnecessary materials such as residual toner on the image forming surface. A cleaning member such as an elastic plate to be removed is provided.
For example, the static eliminator 27 neutralizes (dissipates charges) the image forming surface of the photosensitive drum 21 by exposure or the like so that the surface potential becomes almost zero.

The intermediate transfer device 30 is disposed at a position below the four image forming devices 20 (Y, M, C, K).
The intermediate transfer device 30 is an example of a transfer unit, and is indicated by an arrow B while passing through primary transfer positions facing the primary transfer device 25 of the photosensitive drum 21 in the image forming device 20 (Y, M, C, K). An intermediate transfer belt 31 is arranged to rotate in the direction.
The intermediate transfer belt 31 is formed into an endless belt shape having a required thickness and electric resistance value using a material obtained by dispersing a resistance adjusting agent such as carbon on a base material such as polyimide resin or polyamide resin. is there.
The intermediate transfer belt 31 is supported around a plurality of support rolls 32a to 32e so as to be rotatable. The support roll 32a serves as a drive roll, the support roll 32b cooperates with the drive roll 32a as a driven roll that holds the intermediate transfer belt 31 so that the primary transfer surface is formed, and the support roll 32c applies tension to the intermediate transfer belt 31. The support roll 32d is configured as a secondary transfer backup roll, and the support roll 32e is configured as a cleaning backup roll, as a tension applying and meandering correction roll that applies and corrects meandering of the intermediate transfer belt 31.

The intermediate transfer device 30 includes a secondary transfer device 35 that is an example of a transfer unit that secondarily transfers the toner image transferred onto the intermediate transfer belt 31 to the recording paper 9, and an image on the outer peripheral surface of the intermediate transfer belt 31. A belt cleaning device 36 that removes and removes unnecessary materials such as toner that stays on the holding surface and adheres thereto is provided.
The secondary transfer device 35 includes, for example, a contact member such as a secondary transfer roll disposed so as to contact and rotate the image holding surface portion supported by the secondary transfer backup roll 32d of the intermediate transfer belt 31. A contact type transfer device is employed. In the secondary transfer device 35, a contact member such as a secondary transfer roll is grounded, and a required secondary transfer voltage is supplied to the secondary transfer backup roll 32d.
The belt cleaning device 36 is disposed in contact with at least the image holding surface portion after the secondary transfer of the intermediate transfer belt 31 in the cleaning work opening of the housing, and an unnecessary object such as residual toner on the image holding surface. A cleaning member such as an elastic plate for scraping and cleaning is provided.

The paper feeding device 40 is arranged at a position below the intermediate transfer device 30.
The sheet feeding device 40 is detachably attached to the housing 10 and accommodates a recording body 9 in a state in which recording sheets 9 having a desired size and type are stacked on a stacking plate (not shown). A delivery device 42 that feeds the recording paper 9 from the container 41 toward the supply conveyance path one by one is provided. The number of containers 41 and delivery devices 42 is increased or decreased as necessary.
Further, the sheet feeding device 40 supplies the recording paper 9 from a sheet feeding tray (not shown) used in the state opened to the outside of the housing 10 so as to join a middle portion of a supply conveyance path (Rt1) described later. A paper feed mechanism is provided.
The recording paper 9 can be applied as long as it is a recording medium that can be transported by a transport path in the housing 10 and can transfer and fix a toner image. For example, the recording paper 9 is cut into a predetermined size. In addition to paper, special media such as postcards and special media such as envelopes can also be used.

The fixing device 50 is disposed at a position below the intermediate transfer device 30.
In the fixing device 50, a heating rotator 52, a pressurizing rotator 53, and the like are installed inside a casing 51 in which an inlet 51a and an outlet 51b of the recording paper 9 are formed. The heating rotator 52 is a structure having a form such as a roll, a belt, or a belt / pat that rotates in a direction indicated by an arrow and is heated by heating means so that the surface temperature is maintained at a predetermined temperature. The pressurizing rotator 53 is a structure having a roll, a belt, a belt / pat, or the like that is driven to rotate in contact with a predetermined pressure in a state substantially along the axial direction of the heating rotator 52. Further, in the fixing device 50, a fixing process in which the recording sheet 9 holding the toner image is introduced and the fixing process (heating and pressurizing) is performed at a portion where the heating rotator 52 and the pressing rotator 53 are in contact with each other. It is configured as a part.

Further, the image forming apparatus 1 includes a supply conveyance path Rt1 that connects between the sheet feeding apparatus 40 and the intermediate transfer apparatus 30 as a main sheet conveyance path inside the housing 10, and a secondary transfer position of the intermediate transfer apparatus 30. A relay conveyance path Rt2 that connects between the fixing device 50 and the sheet discharge port 11 between the fixing apparatus 50 and the housing 10 is provided.
The supply conveyance path Rt1 is a conveyance path that conveys and supplies the recording paper 9 delivered from the paper feeding device 40 to the secondary transfer position of the intermediate transfer device 30, and is not shown as a plurality of paper conveyance roll pairs 45a to 45d and the like. It is composed of a plurality of paper guide members and the like. The sheet transport roll pair 45d is configured as a so-called registration roll pair that adjusts the timing when the recording sheet 9 is supplied to the secondary transfer position. The relay conveyance path Rt2 is a conveyance path that conveys the recording paper 9 after the secondary transfer to the fixing device 50, and includes, for example, a suction belt conveyance device 46. The paper discharge transport path Rt3 is a transport path for transporting the recording paper 9 on which an image has been formed after fixing so as to be discharged to the discharge accommodating portion 12, and includes a plurality of discharge roll pairs 47a and 47b and a paper guide member (not shown). It is configured.

<Image Forming Operation of Image Forming Apparatus>
In the image forming apparatus 1, a basic image forming operation described below is performed. Here, an operation in the case of forming a full-color image configured by combining toner images of four colors (Y, M, C, K) will be described as an example.

First, in the image forming apparatus 1, when the central controller 60 receives a request command for an image forming operation from the outside or the like, in each of the four image forming apparatuses 20 (Y, M, C, and K), each photosensitive drum 21 is moved to an arrow A. Each charging device 22 is supplied with a charging voltage to generate a contact discharge. As a result, the image forming surface of each photosensitive drum 21 is charged to a required polarity (for example, negative polarity) and potential.
Subsequently, each exposure device 23 performs exposure according to the image signal that has been separated into each color component (Y, M, C, K) on the image forming surface of each photosensitive drum 21 after charging. Thereby, an electrostatic latent image of each color component having a predetermined potential is formed on the image forming surface of each photosensitive drum 21.

Subsequently, each developing device 24 (Y, M, C, K) supplies toner of a color (Y, M, C, K) charged to a predetermined polarity (minus polarity) from the developing roll, A developing electric field formed between the developing roll 241 and the photosensitive drum 21 in response to the development bias voltage is electrostatically attached to the electrostatic latent image portion of each color component on the image forming surface of the photosensitive drum 21. . As a result, toner images of corresponding colors among the four colors (Y, M, C, K) are individually formed on the image forming surface of each photosensitive drum 21.
Subsequently, each primary transfer device 25 is supplied with a primary transfer voltage to form a primary transfer electric field between the primary transfer device 25 and the photosensitive drum 21, whereby the toner image on each photosensitive drum 21 is transferred to the intermediate transfer belt in the intermediate transfer device 30. Primary transfer is performed in order (Y, M, C, K) on the 31 image holding surfaces. The drum cleaning device 26 cleans the image forming surface of each photosensitive drum 21 after the primary transfer or the like. Further, the static eliminator 27 neutralizes the image forming surface of each photosensitive drum 21 after the primary transfer or the like to prepare for the next image forming operation on each photosensitive drum 21.

  Next, in the intermediate transfer device 30, the intermediate transfer belt 31 rotates in the direction indicated by the arrow B, whereby the unfixed toner image that is primarily transferred and held on the image holding surface faces the secondary transfer device 35. Transport to the next transfer position. On the other hand, in the paper feeding device 40, the delivery device 42 sends the required recording paper 9 from the container 41 to the supply conveyance path Rt 1, and then sends it to the secondary transfer position of the intermediate transfer device 30 via the supply conveyance path Rt 1. Supply. At the secondary transfer position, the secondary transfer device 35 receives the supply of the secondary transfer voltage and forms a secondary transfer electric field between the secondary transfer device 31 and the four colors on the intermediate transfer belt 31. The toner image is secondarily transferred to one side of the recording paper 9.

Next, the recording sheet 9 on which the unfixed toner image is secondarily transferred is separated from the intermediate transfer belt 31 and then conveyed so as to be sent to the fixing device 50 via the relay conveyance path Rt2. In the fixing device 50, the recording paper 9 is heated and pressurized when it is introduced into and passed through the fixing processing section which is a contact portion between the heating rotator 52 and the pressing rotator 53. As a result, the toner constituting the toner image on the recording paper 9 is melted under pressure, and the toner image is fixed on the recording paper 9.
Subsequently, the recording sheet 9 on which the toner image has been fixed is discharged from the inside of the casing 51 of the fixing device 50 and then conveyed through the sheet discharge conveyance path Rt3, and finally passes through the sheet discharge port 11. By being discharged to the outside of the housing 10, it is accommodated in the discharge accommodating portion 12.

  By performing the above operation, one recording sheet 9 on which a full-color image is formed on one side is output. When a request command for a plurality of image forming operations is received, the image forming operation is repeated in the same manner for the number of sheets.

  In addition, the image forming apparatus 1 forms a monochrome image by operating any one of the four image forming apparatuses 20 (Y, M, C, K) in the image forming operation. It is also possible to form a color image other than a full-color image by operating two or three of the image forming devices 20 (Y, M, C, K) in combination.

<Parts abnormality estimation function>
The image forming apparatus 1 has the following configuration as a function of estimating that an abnormality occurs in some parts such as the photosensitive drum 21.
That is, as shown in FIGS. 3, 6, 7, and the like, the image forming apparatus 1 has at least a surface of the photosensitive drum 21 outside the image quality guarantee range 212 and within the image formable range 210 by the developing device 24. A control unit 61 that executes a “first image forming operation” in which a first image TG formed by adhering a developer is formed and transferred to the recording paper 9 by the intermediate transfer device 30 (finally the transfer device 25); The control means 61 includes the first image TG in the first image forming operation on the inner side of the leading end 9a when the recording paper 9 (9B) is conveyed in the image formable range 210 of the photosensitive drum 21. A portion LE corresponding to a range from the position Ps to the position Pe inside the rear end 9b at the time of conveyance is formed.

Here, the image formable range 210 of the photosensitive drum 21 is a range excluding both end portions (image non-formable portions) where the image cannot be formed in the axial direction D of the photosensitive drum 21 as illustrated in FIG. More specifically, it is a portion of the image forming surface of the photosensitive drum 21 on which the photosensitive layer is formed, and is a range in which an image forming operation can be performed by charging, exposing (latent image forming) and developing processes. As shown in FIG. 4, the range in which the developer is held on the developing roll 241 and development is possible (developable range) is substantially the same as the range in the axial direction D of the image formable range 210 of the photosensitive drum 21.
The image quality guarantee range 212 of the photosensitive drum 21 is a range set inside the image formable range 210 excluding both end portions in the axial direction D of the photosensitive drum 21, and is actually a normal image (a borderless image). Is included in the range in which the image is formed. Further, the image quality guarantee range 212 is a range having a width in the axial direction D substantially corresponding to the dimension of the feed width of the recording sheet having the maximum feed width among the recording sheets 9 usable in the image forming apparatus 1. .
Further, the end portions 215 and 216 outside the image quality guarantee range 212 in the image formable range 210 exclude the image quality guarantee range 212 in the axial direction D of the image formable range 210 as illustrated in FIG. 4 and the like. It is a part that exists at both ends. The end portions 215 and 216 in the image formable range 210 correspond to the surface outside the image quality guarantee range 212 of the photosensitive drum 21 and within the image formable range 210.

  The control means 61 includes an arithmetic processing device, a storage element, an input / output device, an external storage device, and the like. Further, the control means 61 executes a required control operation based on, for example, a program and data stored in the storage element (ROM or the like). In particular, in the first embodiment, at least the first An image forming operation can be executed. The control unit 61 is configured as a part that performs a part of the control function of the central control device 60, but may be configured as an independent control unit different from the central control device 60.

As shown in FIG. 3, the control means 61 is connected to the power supply means 15, the exposure drive unit 16 that drives the exposure device 23, the rotation drive unit 17, the display unit 14b of the operation display device 14, and the like. A control signal necessary for one image forming operation is transmitted.
The power supply unit 15 supplies a charging voltage to the charging roll 221 of the charging device 22, a developing bias voltage to the developing roll 241 of the developing device 24, a primary transfer voltage to the primary transfer device 25, and a secondary transfer voltage to the secondary transfer device 35. Is a means that can supply a heating voltage to the heating means in the heating roll 52 of the fixing device 40 in a required magnitude at a required time. The rotation driving unit 17 is a rotating member such as a photosensitive drum 21 and a developing device 24 in the image forming device 20 (Y, M, C, and K), a rotating member such as a driving roll in the intermediate transfer device 30, and a feeding in the paper feeding device 40. This means includes an electric motor that generates and transmits rotational power to a rotating member such as the device 42, a rotating member such as the heating roll 52 of the fixing device 50, and a rotation transmission mechanism.

In addition, the control unit 61 includes a communication unit 19 that communicates information with an external device, the input unit 14a of the operation display device 14, and a reference signal acquisition unit 18 that acquires a reference signal that is a start time of an image forming operation. Thus, information necessary for the control operation is obtained.
The reference signal acquisition unit 18 includes, for example, a reading device 72 installed so as to optically read a reference mark formed at one end or both ends of the intermediate transfer belt 31 in the intermediate transfer device 30.
The control means 61 calculates and grasps in advance the start time and end time of each related operation on the basis of the reference mark acquisition timing (t0) acquired by the reference signal acquisition means 18, and the recording paper 9 The transport arrival time and passage time are calculated and grasped.

In the first image forming operation, since the first image TG is also formed on the surface of the photosensitive drum 21 that becomes at least the end portions 215 and 216 outside the image quality guarantee range, the first image TG formed on the end portions 215 and 216 is formed. Since the image TG also needs to be transferred to the recording paper, the feeding width (dimension in the width direction when transported) of the recording paper is almost the same as the dimension along the axial direction D of the image formable range 210 on the photosensitive drum 21. Special recording paper (paper for confirmation) 9B having the same dimensions is used (FIG. 7).
The special recording paper 9B is accommodated in the paper feeding device 40 and supplied to the secondary transfer position of the intermediate transfer device 30, or is accommodated in a manual tray in a manual paper feeding mechanism (not shown) and then supplied and transported path Rt1. Then, the toner is fed so as to be joined in the middle of the toner and supplied to the secondary transfer position of the intermediate transfer device 30.

The first image forming operation is executed, for example, when a service engineer (serviceman) selects and instructs the execution mode of the first image forming operation from the input unit 14a of the operation display device 14. Has been.
In this case, for example, the execution mode related to the first image forming operation is displayed on the display unit 14b of the operation display device 14 as a selection instruction screen and is arbitrarily selected and executed. Further, it is preferable that the first image forming operation is performed periodically according to the usage frequency progress state based on information such as the number of formed images.

  In the case of the image forming apparatus 1 including a plurality of image forming apparatuses 20 including the photosensitive drum 21, the charging device 22, the developing device 24, and the like, the first image forming operation is performed using the plurality of image forming apparatuses 20 (Y , M, C, K), each one is performed separately.

<First image forming operation>
In the image forming apparatus 1, when an execution mode related to the first image forming operation is selected and instructed by the service engineer from the input unit 14a of the operation display device 14, the first image forming by the control means 61 described below is performed. The action is executed.

  The first image forming operation at this time is performed a total of four times while operating the four image forming devices 20 (Y, M, C, K) one by one. Here, as a representative example, the first image forming operation when the black color K image forming device 20K is operated will be described.

  First, when the control unit 61 receives a start command (st) related to the first image forming operation, the image forming device 20, the intermediate transfer device 30, the paper feeding device 40, and the fixing device 50 necessary for the first image forming operation are received. A required voltage starts to be supplied from the power supply means 15 to the power supply unit 15 and a required rotational power starts to be transmitted from the rotation drive unit 17.

  At this time, as shown in FIG. 5B and FIG. 6, the control unit 61 sets the image forming range 212 of the photosensitive drum 21 that starts rotating in the image forming device 20 </ b> K when the electrostatic latent image is formed by the charging device 22. The first image forming operation is performed after the charging potential Vh1 is applied and the developing bias voltage supplied to the developing device 24K is maintained at the developing potential Vd1 applied when forming the electrostatic latent image. Migrate to

Here, the charging potential Vh1 and the development potential Vd1 applied at the time of forming the electrostatic latent image are set and used when performing a normal image forming operation based on image information input to the image forming apparatus 1. The charging potential and the developing potential (both are potentials corresponding to the value of the DC component). Hereinafter, the charging potential Vh1 and the developing potential Vd1 at this time are referred to as “normal charging potential Vh1” and “normal developing potential Vd1”.
Incidentally, FIG. 5A illustrates the relationship of each potential and the like in the case of performing the normal image formation. 5A indicates the potential of the electrostatic latent image formed by exposure of the exposure device 23 with respect to the image quality guarantee range 212 of the photosensitive drum 21 after being charged.

  Subsequently, the control unit 61 receives the start command (st) relating to the first image forming operation, and after the required time has elapsed, the control unit 61 applies the intermediate transfer belt 31 to which the reading device 72 serving as the reference signal acquisition unit 18 rotates. When a certain reference mark is read as a reference signal, the timing of each operation relating to the first image forming operation, the conveyance timing of the recording paper 9B, etc. are ascertained with reference to the time (t0) when the reference signal is acquired. Start executing the image forming operation.

  In the first image forming operation at this time, as shown in FIG. 7, the developing bias voltage supplied to the developing device 24K is normally set in accordance with the time when the first image TG is to be formed, as shown in FIG. The operation for changing the development potential Vd1 to the special development potential Vd2 for forming the first image TG and the operation for returning the changed special development potential Vd2 to the normal development potential Vd1 are performed. .

  The special developing potential Vd2 is a black developer that supplies at least the ends 215 and 216 outside the image quality guarantee range 212 of the photosensitive drum 21 from the developing device 24K with reference to the normal charging potential Vh1 that is fixed. This is a potential that generates a potential difference Δα that can be developed with (toner) (a developer can be electrostatically attached). The potential difference Δα at this time is expressed as a difference (absolute value | Vh1−Vd2 |) between the normal charging potential Vh1 and the special development potential Vd2.

  As the special development potential Vd2 that generates such a potential difference Δα, for example, as shown in FIG. 5B, a potential having a magnitude exceeding the normal charging potential Vh1 in absolute value is employed. The special development potential Vd2 can be obtained in advance by, for example, conducting an experiment for examining a development bias voltage suitable for performing the development. Note that both the development potential Vd1 and the development potential Vd2 can be set by the voltage of the DC component.

  In the first image forming operation, first, in the image forming device 20K, the image forming range 210 of the rotating photosensitive drum 21 is charged by the charging device 22 so as to have the normal charging potential Vh1, and then the exposure device 23. Then, it passes through the developing device 24K supplied with the developing bias voltage changed.

At this time, the operation for changing the developing bias voltage to the special developing potential Vd2 is performed when the potential in the changing process coincides with the normal charging potential Vh1, as exemplified in FIG. The timing (t12) is performed after the time point (t2) corresponding to the leading end 9a when the recording paper 9B is conveyed.
The time point (t2) corresponding to the leading edge 9a of the recording paper 9B at this time is grasped as the time point when the elapsed time (Ts) calculated in advance from the reference signal acquisition time point (t0) has elapsed. The calculated elapsed time (Ts) is calculated from, for example, a position assumed on the photosensitive drum 21 and a set value such as a process speed by back-calculating from a scheduled time when the leading edge 9a of the recording paper 9B reaches the secondary transfer position. It is a calculated time.
At this time, the time point (t11) when the development bias voltage is changed from the normal development potential Vd1 to the special development potential Vd2 is as shown in FIG. 6 from the time point (t0) when the reference signal is acquired. The time when the required time selected from the viewpoint of satisfying the condition (t12> t2) has elapsed.

As a result, in the image forming device 20K, the developer (toner) does not adhere to the photosensitive drum 21 while the developing bias voltage having the normal developing potential Vd1 is supplied to the developing device 24K. When the bias voltage is changed to the special development potential Vd2, the developer (toner) starts to adhere to the photosensitive drum 21.
Strictly speaking, the toner starts to adhere at this time from the time when the development potential in the changing process reaches a potential (minimum developable potential) Vdm slightly exceeding the normal charging potential Vh1, as shown in FIG. It is. Further, the development bias voltage at this time is completely changed to the special development potential Vd2 when the required time (t13-t11) elapses from the start time (t11) of the change to the special development potential Vd2. The

  At this time, as shown in FIG. 5B, the photosensitive drum 21 in the image forming device 20K is charged so that the image formable range 210 has a normal charging potential Vh1 having a negative polarity, for example. Thus, the developing roller 241 of the developing device 24K to which a developing bias voltage that is changed to a special developing potential Vd2 having a magnitude exceeding the charging potential Vh1 and having a negative polarity, for example, is supplied is opposed.

As a result, a potential difference Δα1 (= | Vd2−Vh1 |) is generated between the photosensitive drum 21 and the developing roll 241 to develop the end portions 215 and 216 outside the image quality guarantee range 212 of the photosensitive drum 21. For example, when “−550V” is applied as the normal charging potential Vh1 and “−600V” is applied as the special development potential Vd2, the potential difference Δα1 is “50V” in absolute value.
As a result, the photosensitive drum 21 in the image forming device 20K is developed by the attachment of black toner charged to the negative polarity in the entire image formable range 210 including the end portions 215 and 216 outside the image quality guarantee range 212. One image TG starts to be formed.
That is, the first image TG at this time starts to be formed from a position corresponding to a position on the photosensitive drum 21 that is inside the leading end 9a of the special recording paper 9B.

Further, the operation for returning the developing bias voltage in the first image forming operation from the special developing potential Vd2 to the normal developing potential Vd1 is performed by the control means 61 as shown in FIG. Is performed before the time point (t3) corresponding to the rear end 9b when the recording paper 9B is conveyed.
At this time, the time (t3) corresponding to the rear end 9b of the recording paper 9B is obtained by adding the required time calculated in advance from the length and the conveyance speed of the recording paper 9B to the time (t2) corresponding to the leading end 9a. The elapsed time (Te) is grasped as the time when the reference signal is acquired (t0).
At this time, the time point (t14) at which the development bias voltage starts to return from the special development potential Vd2 to the normal development potential Vd1 is as shown in FIG. 6 from the time point (t0) when the reference signal is acquired. The time when a required time selected from the viewpoint of satisfying the condition (t15 <t3) has elapsed.

As a result, in the image forming device 20K, the developing bias voltage of the normal developing potential Vd1 is supplied to the developing device 24K, so that the developer (toner) adheres to the photosensitive drum 21 from the developing device 24K. finish.
Strictly speaking, at this time, the adhesion of the toner is finished when the developing potential in the returning process exceeds the minimum developable potential Vdm close to the charging potential Vh1, as shown in FIG. Further, the development bias voltage at this time is completely returned to the normal development potential Vd1 at the time (t16) when the required time (t16-t14) has elapsed from the start time (t14) to return to the normal development potential Vd1. .

  At this time, the photosensitive drum 21 in the image forming device 20K faces the developing roll 241 of the developing device 24K to which the developing bias voltage returned to the normal developing potential Vd1 is supplied.

As a result, the photosensitive drum 21 in the image forming device 20K may have black toner charged with a negative polarity attached to the entire image formable range 210 including the end portions 215 and 216 outside the image quality guarantee range 212. The formation of the first image TG ends.
That is, the first image TG at this time is formed and ended up to a position corresponding to a position on the photosensitive drum 21 that is inside the rear end 9b of the special recording paper 9B.

Subsequently, the first image TG made of the black toner formed on the photosensitive drum 21 by the first image forming operation is primarily transferred to the intermediate transfer belt 31 of the intermediate transfer device 30 and then conveyed, and then FIG. As shown in a), the toner image is secondarily transferred to a special recording sheet 9B at the secondary transfer position.
Finally, the unfixed first image TG is fixed on one side of the special recording paper 9B by the fixing device 50 as shown in FIG. 8B, and then recorded on the special recording paper 9B. It is output to the discharge container 12 in a state.

Thus, the first image forming operation by the operation of the image forming device 20K is completed.
In the first image forming operation, after the operation process by the operation of the black image forming device 20K is completed, the remaining color image forming devices 20 (Y, M, C) are operated independently. Sequentially executed in the same manner.

<Result of first image forming operation>
When the first image forming operation is executed, as shown in FIG. 6, the first image TG is transferred from the leading end 9a of the recording sheet 9B in the image formable range 210 of the photosensitive drum 21 during the transfer. It is formed in a portion LE corresponding to a range existing inside the maximum range in the length direction during conveyance up to the rear end 9b.
As a result, in the first image forming operation, as illustrated in FIG. 7 and FIG. 8B, the first image TG is located on the inside of the special recording paper 9B with respect to the leading end 9a during the conveyance. It is formed so as to fall within the range from the position Ps to the position Pe inside the rear end 9b during the conveyance. An arrow indicated by a symbol E in FIG. 7 and the like is a direction when the recording paper 9 (9B) is conveyed.

  For reference, the first image TG in the first image forming operation is a length from the leading end 9a of the recording sheet 9B during conveyance to the trailing end 9b during conveyance of the image forming range 210 of the photosensitive drum 21. When the first image TGX that exists in a portion corresponding to an excessive range that protrudes outside the same range as the maximum range in the vertical direction or beyond that in the transport direction is formed (comparative example), the following problem occurs. To do.

  That is, when the first image TGX in this comparative example is secondarily transferred from the intermediate transfer belt 31 to the special recording paper 9B at the secondary transfer position in the intermediate transfer device 30, as illustrated in FIG. Of the first image TGX, the image portion TGXn at the end of the leading end 9a and the trailing end 9b of the recording paper 9B or protruding from one or both of the leading end 9a and the trailing end 9b is the secondary transfer roll of the secondary transfer device 35. Will be transferred to. When the surface of the secondary transfer roll is formed of an elastic layer, the transferred image portion TGXn (toner) is particularly likely to remain. The protruding image portion TGXn transferred to the secondary transfer roll of the secondary transfer device 35 is illustrated in FIG. 18B in a normal image forming operation performed after the first image forming operation is completed. As a result, it may adhere to the back surface of the recording paper 9 passing through the secondary transfer position and induce back surface contamination.

In this regard, in the first image forming operation by the image forming apparatus 1, the first image TG extends from the leading end 9a of the recording paper 9B to the trailing end 9b in the image formable range 210 of the photosensitive drum 21 as described above. It is formed in a portion LE corresponding to a range existing inside the maximum range in the length direction during conveyance (FIG. 6).
Therefore, when the first image TG is secondarily transferred from the intermediate transfer belt 31 to the special recording paper 9B at the secondary transfer position in the intermediate transfer device 30, as illustrated in FIG. In the first image TG, the leading end 9a and the trailing end 9b of the recording paper 9B and the image portion (toner) protruding from them are not generated, and the protruding image portion is secondary transferred by the secondary transfer device 35. There is no transfer to the roll.
Therefore, in the image forming apparatus 1, the back surface of the recording paper 9 due to the first image TG does not occur.

  In the image forming apparatus 1, when the first image forming operation is executed, for example, a service engineer looks at the image of the first image TG obtained by being output to the special recording paper 9B. Thus, the service engineer can know whether or not there is a sign that at least the end of the image quality guarantee range 212 in the photosensitive drum 21 is worn (end wear).

That is, on the special recording paper 9B output at this time, as illustrated in FIG. 7, an image composed of the first image TG in which the toner is substantially uniformly adhered to the entire area of one side is formed. .
At this time, it appears to extend in the vicinity of the left and right ends of the width direction W substantially perpendicular to the conveyance direction E of the special recording paper 9B after output, for example, along the conveyance direction E as illustrated in FIG. It may be confirmed that the image portions K1 and K2 having high density exist. In this case, it can be known (estimated) that there is a sign that end wear of the photosensitive drum 21 occurs. Note that the left and right ends of the special recording paper 9 </ b> B appearing with the image portions K <b> 1 and K <b> 2 appear corresponding to the ends 215 and 216 outside the image quality guarantee range 212 of the photosensitive drum 21.
On the other hand, in the vicinity of the left and right end portions of the special recording paper 9B after output, the presence of the dark image portions K1 and K2 that appear to be streaks may not be confirmed. In this case, it can be known that there is no sign that end wear of the photosensitive drum 21 occurs.

  In addition, in the first image forming operation, the first image TG is transferred from the position Ps close to at least the front end 9a of the special recording paper 9B to know the sign of abnormality or the occurrence of abnormality in the photosensitive drum 21 or the like. it can. Further, in the first image forming operation, the first image TG is transferred to a position Pe at least near the rear end 9b of the special recording paper 9B to know a sign of abnormality or occurrence of abnormality in the photosensitive drum 21 or the like. it can.

Incidentally, the reason why dark image portions K1 and K2 that appear to be streaks appear in the first image TG output by the first image forming operation is as follows.
In other words, if there is a wear part in the image formable range 210 of the photosensitive drum 21, the film thickness of the photosensitive layer corresponding to the wear part decreases, the dark attenuation level increases, and the dark attenuation level increases. Correspondingly, the rate at which the potential when the photosensitive drum 21 is charged is increased correspondingly, and as a result, a larger amount of toner is attached to the worn portion in the developing process. It is visualized as a portion where the concentration is higher than that of the normal portion.
If there are dark image portions K1 and K2 that look like streaks at the left and right end portions of the special recording paper 9B, the wear portions in front of the image quality guarantee range 212 that develop into the original end wear. Therefore, the existence of the image portions K1 and K2 can be regarded as a sign of end wear. In addition, when end wear occurs in the image formable range 210 of the photosensitive drum 21, when a normal image is formed, a streak image defect due to end wear occurs in the image. End up.

In the first image forming operation, as a special development potential for changing the development bias voltage, a configuration example in which the potential is larger than the normal charging potential Vh1 by an absolute value to the extent that the potential difference Δα1 is obtained (see FIG. 5 (b)).
However, as the special development potential, as long as a potential difference that can develop the end portions 215 and 216 outside the image quality guarantee range 212 of the photosensitive drum 21 can be obtained, a two-dot chain line in FIG. As illustrated, a potential having an absolute value smaller than the normal charging potential Vh1 can be applied as the special developing potential Vd3. The potential difference at this time is Δα2 as shown in FIG.
If such a special development potential Vd3 is adopted when the level of dark decay of the worn portion on the photosensitive drum 21 is relatively large, the developed portion (potential difference Δα2) can be developed even with respect to the worn portion. is there.

In the first image forming operation, as the special development potential Vd2 (Vd3), the potential difference Δα1 (Δα2) between the special development potential Vd2 (Vd3) and the normal charging potential Vh1 is the normal development potential Vd1. It is preferable to use a potential (Δα <Vc) that falls within a numerical range smaller than the contrast potential Vc, which is a potential difference between the image potential and the latent image potential Vi.
When the potential difference Δα1 (Δα2) with the normal charging potential Vh1 is larger than the contrast potential Vc as the special development potential Vd2 (Vd3), for example, due to an abnormality occurring in the photosensitive drum 21 or the like. Thus, it is difficult to reveal an abnormal image that can be formed by the first image forming operation in the first embodiment, and there is a problem that the sensitivity of detecting a sign of abnormality or occurrence of abnormality is lowered.

  As a numerical value range in which the potential difference Δα1 (Δα2) is smaller than the contrast potential Vc, for example, a range of 10 to 40% is preferable, and a range of 20 to 30% is more preferable.

Here, FIG. 9 shows the result of examining the relationship between the contrast potential Vc and the density.
FIG. 9 is a graph showing the results when a test for confirming the relationship between the contrast potential and the development density for proper density reproduction is performed. Further, the “contrast potential” on the horizontal axis of the graph of FIG. 9 is the contrast potential Vc when the contrast potential applied to obtain an image having an image area ratio of 100% (so-called solid image) is 100%. Indicates a percentage (percentage). The “density” on the vertical axis indicates the development density when the density of each developer image when developed at each contrast potential is measured with a spectral densitometer or the like.
In FIG. 9, when the contrast potential applied at the time of normal electrostatic latent image formation is 100%, the detection sensitivity related to the variation in the latent image potential is high when the density is 50%. Therefore, when the most preferable density setting value is set in a range of 50 ± 5%, the contrast potential corresponding to the density setting value is in a range of about 18 to 27% so as to be sandwiched between two-dot chain lines. In this case, the contrast potential may be set in a range of 20 to 30%, for example.
On the other hand, when the concentration is in the range of 50 ± 20%, at least the potential unevenness caused by a physical abnormality such as a scratch can be detected. Therefore, when this density range is allowed, the contrast potential can be set to a range of about 10 to 40%.
According to the research of the inventors of the present invention, when the concentration exceeds 80%, the above detection cannot be performed, and therefore the contrast potential cannot be set to a range of 50% or more from the result shown in FIG. Has been confirmed.

  Furthermore, as for the time point (t2) corresponding to the leading end 9a of the recording paper 9 in the first image forming operation, if it is in time for changing the developing bias voltage (t11, t13), the actually conveyed recording is performed. The passage of the leading end 9a of the sheet 9 can be grasped based on a signal detected by a detecting means such as a sensor.

[Embodiment 2]
10 and 11 show the main part (configuration of the first image forming operation) of the image forming apparatus according to the second embodiment.
The image forming apparatus according to the second embodiment has the same configuration as the image forming apparatus 1 according to the first embodiment except that a part of the first image forming operation by the control unit 61 is changed.

<First image forming operation>
In the first image forming operation in the second embodiment, as shown in FIG. 10 and FIG. 11, the charging device 22 (charging roll) is controlled in accordance with the timing when the first image TG is to be formed. 221) an operation for changing the charging voltage supplied from the normal charging potential Vh1 to a special charging potential Vh2 for forming the first image TG, and an operation for returning the changed special charging potential Vh2 to the normal charging potential Vh1. And come to do.

As shown in FIG. 11, the special charging potential Vh2 has at least the end portions 215 and 216 outside the image quality guarantee range 212 of the photosensitive drum 21 with reference to the fixed normal development potential Vd1 as the developing device 24K. Is a potential that generates a potential difference Δβ that can be developed with a black developer (toner) supplied from the toner. The potential difference Δβ at this time is expressed as a difference (absolute value | Vd1−Vh2 |) between the normal development potential Vd1 and the special charging potential Vh2.
As the special charging potential Vh2 for generating such a potential difference Δβ, for example, as shown in FIG. 10, a potential having a magnitude lower than the normal development potential Vd1 by an absolute value is employed. The special charging potential Vh2 is also obtained in advance by, for example, conducting an experiment for examining a charging potential suitable for performing the development. When a voltage in which alternating current is superimposed on direct current is supplied as the charging voltage, the charging potentials Vh1 and Vh2 may be set by the voltage of the direct current component.

  In the first image forming operation, first, in the image forming device 20K, the image forming range 210 of the rotating photosensitive drum 21 is charged by the charging device 22 so as to have the normal charging potential Vh1, and then the special charging is performed. After being recharged at the potential Vh2, it passes through without being exposed to the exposure device 23, and then passes through the developing device 24K to which the developing bias voltage of the normal developing potential Vd1 is supplied.

At this time, the operation for changing the charging voltage to the special charging potential Vh2 is performed by the control means 61 when the potential in the changing process coincides with the normal development potential Vd1, as illustrated in FIG. (T22) is performed after the time point (t2) corresponding to the leading end 9a when the recording paper 9B is conveyed (t22> t2).
The time point (t2) corresponding to the leading edge 9a of the recording paper 9B at this time is the time point when the elapsed time (Ts) calculated in advance from the reference signal acquisition time point (t0) has passed, as in the first embodiment. As grasped.
At this time, the time point (t21) when the charging voltage is changed from the normal charging potential Vh1 to the special charging potential Vh2 is the above time from the time point (t0) when the reference signal is acquired, as shown in FIG. This is the time when the required time selected from the viewpoint of satisfying the target condition (t22> t2) has elapsed.

As a result, in the image forming device 20K, the developer (developer (Vd1) is supplied with a developing bias voltage which is set to the normal developing potential Vd1 while the charging device 22 is charged with the normal charging potential Vh1. However, when the charging voltage is changed to the special charging potential Vh2, the developer (toner) adheres to the surface portion of the photosensitive drum 21 charged with the special charging potential Vh2. start.
Strictly speaking, the toner starts to adhere at this time, as shown in FIG. 11, when the charging potential in the changing process reaches a potential (minimum developable potential) Vdm slightly lower than the normal development potential Vd1. From the point in time. Further, the charging voltage at this time is completely changed to the special charging potential Vh2 at the time (t23) when the required time (t23-t21) elapses from the start time (t21) of changing to the special charging potential Vh2. .

  At this time, as shown in FIG. 10, the photosensitive drum 21 in the image forming device 20K is charged so that its image formable range 210 becomes a special charging potential Vh2 having a negative polarity, for example, while the normal drum 21 It faces the developing roll 241 of the developing device 24K to which the developing bias voltage at the developing potential Vd1 is supplied.

As a result, a potential difference Δβ (= | Vd1−Vh2 |) is generated between the photosensitive drum 21 and the developing roller 241 to develop the end portions 215 and 216 outside the image quality guarantee range 212 of the photosensitive drum 21. For example, when “−550V” is applied as the normal charging potential Vh1, “−490V” is applied as the special charging potential Vh2, and “−520V” is applied as the normal development potential Vd1, the potential difference Δβ is “30V” in absolute value. Become.
As a result, the photosensitive drum 21 in the image forming device 20K is developed with black toner charged with negative polarity in the entire image formable range 210 including the end portions 215 and 216 outside the image quality guarantee range 212, and developed. The first image TG starts to be formed.
That is, the first image TG at this time starts to be formed from a position corresponding to a position on the photosensitive drum 21 that is inside the leading end 9a of the special recording paper 9B.

Further, the operation for returning the charging voltage in the first image forming operation from the special charging potential Vh2 to the normal charging potential Vh1 is performed by the control means 61 as shown in FIG. The time (t25) when it coincides with the developing potential Vd1 is before the time (t3) corresponding to the rear end 9b when the recording paper 9B is conveyed (t25 <t3).
At this time, the time point (t24) at which the charging voltage starts to return from the special charging potential Vh2 to the normal charging potential Vh1, as shown in FIG. 11, is from the timing condition described above from the time point (t0) when the reference signal is acquired. The time when a required time selected from the viewpoint of satisfying (t25 <t3) has elapsed.

As a result, in the image forming device 20K, the charging voltage to be the normal charging potential Vh1 is supplied to the charging device 22, so that the image formable range 210 of the photosensitive drum 21 is charged with the normal charging potential Vh1. Thus, the attachment of the developer (toner) from the developing device 24K to the photosensitive drum 21 is completed.
Strictly speaking, at this time, the adhesion of the toner ends as shown in FIG. 11 in which the charging potential in the returning process exceeds the minimum developable potential Vdm close to the normal development potential Vd1. It is from the time. Further, the charging voltage at this time is completely returned to the normal charging potential Vh1 at the time (t26) when the required time (t26-t24) has elapsed from the start time (t24) to return to the normal charging potential Vh1.

  At this time, the photosensitive drum 21 in the image forming device 20K is supplied with a developing bias voltage of the normal developing potential Vd1 in a state where the image formable range 210 is charged to the normal charging potential Vh1. It faces the developing roll 241.

As a result, the photosensitive drum 21 in the image forming device 20K may have black toner charged with a negative polarity attached to the entire image formable range 210 including the end portions 215 and 216 outside the image quality guarantee range 212. The formation of the first image TG ends.
That is, the first image TG at this time is formed up to a position corresponding to a position on the photosensitive drum 21 that is inside the rear end 9b of the special recording paper 9B.

Subsequently, the first image TG made of black toner formed on the photosensitive drum 21 by the first image forming operation is primarily transferred to the intermediate transfer belt 31 of the intermediate transfer device 30 and conveyed, and then the secondary image TG is transferred to the secondary image. Secondary transfer is performed on a special recording sheet 9B at the transfer position.
Finally, the unfixed first image TG is fixed on one side of the special recording paper 9B by the fixing device 50, and then output to the discharge container 12 while being recorded on the special recording paper 9B.

Thus, the first image forming operation by the operation of the image forming device 20K is completed.
Also, in the first image forming operation, after the operation process by the operation of the black image forming device 20K is completed, the remaining color image forming devices 20 (Y, M, C) are individually operated. However, it is executed in the same manner sequentially.

<Result of first image forming operation>
When this first image forming operation is executed, as in the case of the first image forming operation in the first embodiment, the first image TG is an image of the photosensitive drum 21 as shown in FIG. In the formable range 210, the recording paper 9B is formed in a portion LE corresponding to a range existing inside the maximum range in the length direction during conveyance from the leading end 9a during conveyance to the rear end 9b during conveyance. Will be.
As a result, in this first image forming operation, as in the case of the first image forming operation in the first embodiment, as illustrated in FIG. 7 and FIG. The special recording sheet 9B is formed so as to fall within a range from a position Ps inside the leading end 9a during conveyance to a position Pe inside the trailing end 9b during conveyance.

  Also in the image forming apparatus according to the second embodiment, the first image TG formed by the first image forming operation is caused by almost the same reason as that of the first image forming operation in the first embodiment. The back side of the recording paper 9 is not stained.

  Further, in the image forming apparatus according to the second embodiment, when the first image forming operation is executed, for example, a service engineer looks at the image of the first image TG obtained by being output to the special recording sheet 9B. I will investigate. Thus, the service engineer can know whether or not there is a sign that at least the end of the image quality guarantee range 212 in the photosensitive drum 21 is worn (end wear).

In the first image forming operation in the second embodiment, as the special charging potential Vh2, the potential difference Δβ between the special charging potential Vh2 and the normal development potential Vd1 is the normal development potential Vd1 and the latent image potential Vi. It is preferable to use a potential (Δβ <Vc) that falls within a numerical range smaller than the contrast potential Vc (FIG. 5A) that is a potential difference between the first and second potentials.
When a potential at which the potential difference Δβ with respect to the normal development potential Vd1 is equal to or higher than the contrast potential Vc is used as the special charging potential Vh2, for example, due to an abnormality occurring in the photosensitive drum 21 or the like, It is difficult to reveal an abnormal image that can be formed by one image forming operation, and there is a problem that sensitivity for detecting a sign of abnormality or occurrence of abnormality is lowered.

  The numerical range in which the potential difference Δβ is smaller than the contrast potential Vc is, for example, preferably in the range of 10 to 40%, more preferably in the range of 20 to 30%, similarly to the reason described in the first embodiment (FIG. 9). It is a range.

[Embodiment 3]
12 and 13 show the main part (configuration of the first image forming operation) of the image forming apparatus according to the third embodiment.
The image forming apparatus according to the third embodiment has the same configuration as the image forming apparatus 1 according to the first embodiment except that a part of the first image forming operation by the control unit 61 is changed.

<First image forming operation>
In the first image forming operation in the third embodiment, when the control unit 61 receives a start command (st) related to the first image forming operation, the first image forming operation is performed as in the case of the first embodiment. While the required voltage starts to be supplied from the power supply means 15 to the necessary image forming device 20, intermediate transfer device 30, paper feeding device 40, fixing device 50, etc., the required rotational power starts to be transmitted from the rotation drive unit 17. The configuration at the start stage is as follows.

  That is, in this first image forming operation, as shown in FIG. 13, the control means 61 puts the image forming range 212 of the photosensitive drum 21 that starts rotating in the image forming apparatus 20K into a state where it is not charged by the charging device 22. In addition, after the developing bias voltage is not supplied to the developing device 24K, the first image forming operation is started.

  Subsequently, when the control signal 61 receives the start command (st) relating to the first image forming operation and the required time has elapsed and the reference signal acquisition unit 18 reads the reference mark as the reference signal, the reference signal The timing of each operation related to the first image forming operation, the conveyance timing of the recording paper 9B, and the like are grasped with reference to the time (t0) when the first image forming operation is acquired, and the first image forming operation is started.

  In the first image forming operation at this time, the first image TG is formed in accordance with the time when the first image TG should be formed, as shown in FIGS. An operation of changing the developing bias voltage to be a special developing potential Vd4 to the developing device 24K and an operation of stopping the supply of the developing bias voltage are performed.

As shown in FIG. 12, the special development potential Vd4 is a surface potential (approximately 0 V) of the image forming range 210 of the photosensitive drum 21 that is not charged by the charging device 22 (after passing through the static eliminator 27). ) As a reference, at least the end portions 215 and 216 outside the image quality guarantee range 212 of the photosensitive drum 21 are generated with a potential difference Δγ that can be developed with black developer (toner) supplied from the developing device 24K. It is a potential. The potential difference Δγ at this time is expressed as a difference (| Vd4−0 |) between the surface potential (approximately 0 V) of the uncharged photosensitive drum 21 and the special developing potential Vd4.
The special development potential Vd4 that generates such a potential difference Δγ is also obtained in advance by, for example, conducting an experiment for examining a development potential suitable for performing the development.

  In the first image forming operation, first, in the image forming device 20K, the image forming range 210 of the rotating photosensitive drum 21 passes through the charge eliminator 27 and is not charged by the charging device 22. In this state, the light passes through the exposure device 23 without being exposed to light, and then passes through the development device 24K to which a development bias voltage having a special development potential Vh4 is supplied.

At this time, the operation for supplying the developing bias voltage to the above-described special developing potential Vd4 is such that the developing potential in the supply start process can form an image on the photosensitive drum 21 by the control means 61 as illustrated in FIG. After the time point (t2) when the timing (t32) when it coincides with the adhesion start potential (Vds) when the adhesion of the developer (toner) to the range 210 starts corresponds to the leading edge 9a during conveyance of the recording paper 9B. (T32> t2).
The time point (t2) corresponding to the leading edge 9a of the recording paper 9B at this time is the time point when the elapsed time (Ts) calculated in advance from the reference signal acquisition time point (t0) has passed, as in the first embodiment. As grasped.
Further, at this time, the time point (t31) at which the supply of the developing bias voltage at the special developing potential Vd4 is started is as shown in FIG. 13 from the time point (t0) when the reference signal is acquired (t32). > It is the time when the required time selected from the viewpoint of satisfying t2) has elapsed.

Thus, in the image forming device 20K, the developer (toner) does not adhere to the photosensitive drum 21 from the developing device 24K while charging by the charging device 22 and supply of the developing bias voltage to the developing device 24K are not performed. However, when a developing bias voltage having a special developing potential Vd4 is supplied to the developing device 24K, the developer (toner) starts to adhere to the uncharged surface portion of the photosensitive drum 21 from the developing device 24K.
Strictly speaking, the toner starts to adhere at this time from the time when the development potential generated by the development bias voltage that has started to be supplied reaches the adhesion start potential (Vds), as shown in FIG. . The developing bias voltage at this time reaches the special developing potential Vd4 completely at the time (t33) when the required time (t33-t31) elapses from the time (t31) when the supply is started.

  At this time, as shown in FIG. 12, the photosensitive drum 21 in the image forming device 20K is not charged, and the surface potential of the photosensitive drum 21 is kept at a surface potential of approximately 0 V, while a special developing potential is maintained. It faces the developing roll 241 of the developing device 24K to which the developing bias voltage of Vd4 is supplied.

As a result, a potential difference Δγ (= | Vd4−0 |) is generated between the photosensitive drum 21 and the developing roll 241 to develop the end portions 215 and 216 outside the image quality guarantee range 212 of the photosensitive drum 21. For example, when “−30 V” is applied as the special development potential Vd4, the potential difference Δβ1 is “30 V” in absolute value.
As a result, the photosensitive drum 21 in the image forming device 20K is developed with black toner charged with negative polarity in the entire image formable range 210 including the end portions 215 and 216 outside the image quality guarantee range 212, and developed. The first image TG starts to be formed.
That is, the first image TG at this time starts to be formed from a position corresponding to a position on the photosensitive drum 21 that is inside the leading end 9a of the special recording paper 9B.

In addition, the operation of stopping the supply of the developing bias voltage at the above-described special developing potential Vd4 in the first image forming operation is performed by the control means 61, as illustrated in FIG. The rear end 9b when the recording paper 9B is conveyed is the time (t35) when it coincides with the adhesion end potential (Vde) when the adhesion of the developer (toner) to the image formable range 210 of the photosensitive drum 21 is completed. (T35 <t3) before the time point (t3) corresponding to.
At this time, the time point (t34) at which the supply of the developing bias voltage starts to be stopped, as shown in FIG. 13, is a point of view that satisfies the above timing condition (t35 <t3) from the time point (t0) when the reference signal is acquired. When the required time selected in elapses.

As a result, the image forming device 20K is returned to the state where the charging by the charging device 22 and the supply of the developing bias voltage to the developing device 24K are not performed, so that the developer (toner) from the developing device 24K to the photosensitive drum 21 is restored. ) Is finished.
Strictly speaking, the attachment of the toner at this time ends when the developing potential becomes a small magnitude exceeding the attachment end potential (Vde) as shown in FIG. Further, the development bias voltage at this time is completely stopped when a required time (t36-t34) elapses from the time (t34) when the supply is stopped.

  At this time, the photosensitive drum 21 in the image forming device 20K faces the developing roll 241 of the developing device 24K to which the developing bias voltage is not supplied while the image forming range 210 is not charged. Become.

As a result, the photosensitive drum 21 in the image forming device 20K may have black toner charged with a negative polarity attached to the entire image formable range 210 including the end portions 215 and 216 outside the image quality guarantee range 212. The formation of the first image TG ends.
That is, the first image TG at this time is formed and ended up to a position corresponding to a position on the photosensitive drum 21 that is inside the rear end 9b of the special recording paper 9B.

  Subsequently, the first image TG made of black toner formed on the photosensitive drum 21 by the first image forming operation is primarily transferred to the intermediate transfer belt 31 of the intermediate transfer device 30 and conveyed, and then the secondary image TG is transferred to the secondary image. Secondary transfer is performed on a special recording sheet 9B at the transfer position. Finally, the unfixed first image TG is fixed on one side of the special recording paper 9B by the fixing device 50, and then output to the discharge container 12 while being recorded on the special recording paper 9B. .

Thus, the first image forming operation by the operation of the image forming device 20K is completed.
Also, in the first image forming operation, after the operation process by the operation of the black image forming device 20K is completed, the remaining color image forming devices 20 (Y, M, C) are individually operated. However, it is executed in the same manner sequentially.

<Result of first image forming operation>
When this first image forming operation is executed, as in the case of the first image forming operation in the first embodiment, the first image TG is an image of the photosensitive drum 21 as shown in FIG. In the formable range 210, the recording paper 9B is formed in a portion LE corresponding to a range existing inside the maximum range in the length direction during conveyance from the leading end 9a during conveyance to the rear end 9b during conveyance. Will be.
As a result, in the first image forming operation, as illustrated in FIGS. 14, 7, 8 (b) and the like, as in the case of the first image forming operation in the first embodiment, One image TG is formed on a special recording sheet 9B so as to fall within a range from a position Ps inside the leading end 9a during conveyance to a position Pe inside the trailing end 9b during conveyance. .

  Also in the image forming apparatus according to the second embodiment, the first image TG formed by the first image forming operation is caused by almost the same reason as that of the first image forming operation in the first embodiment. The back side of the recording paper 9 is not stained.

  Furthermore, also in the image forming apparatus according to the third embodiment, when the first image forming operation is executed, for example, a service engineer looks at the image of the first image TG obtained by being output to the special recording sheet 9B. I will investigate. Thus, the service engineer can know whether or not there is a sign that at least the end of the image quality guarantee range 212 in the photosensitive drum 21 is worn (end wear).

  The first image TG illustrated in FIG. 14 includes the result of the first image forming operation in the first and second embodiments near the end in the width direction W substantially perpendicular to the conveyance direction E of the special recording paper 9B. Similarly, there may be dark image portions K1, K2 that appear to extend in a streak pattern along the transport direction E. In this case, similar to the result of the first image forming operation in the first and second embodiments, it can be known that there is a sign that end wear of the photosensitive drum 21 occurs.

  Further, in the first image TG illustrated in FIG. 14, a dark image portion K4 having a different density from the image portions K1 and K2 exists in a portion corresponding to the image quality guarantee range 212 of the special recording paper 9B. Is shown. In this case, it is difficult to determine that there is a sign of another abnormality other than end wear in the photosensitive drum 21 only by the presence of the image portion K4.

However, there may be a case where the image portion K4 periodically exists at substantially the same interval along the conveyance direction E of the recording paper 9B, for example.
In this case, when the interval between the image portions K4 is substantially the same as the outer peripheral length (circumference) of the photosensitive drum 21, for example, the image portion K4 is in the circumferential direction within the image quality guarantee range 212 of the photosensitive drum 21. It can be inferred that this is a result obtained by damage occurring at approximately the same interval or a part having deteriorated function. That is, in this case, it is possible to determine that there is a sign of another abnormality other than end wear in the photosensitive drum 21.

Furthermore, when the special recording paper 9B on which the first image TG as illustrated in FIG. 15 is obtained as a result of performing the first image forming operation in the first and second embodiments, the implementation is performed thereafter. When the first image forming operation in Embodiment 3 is performed, as a result, for example, a special recording sheet 9B on which the first image TG illustrated in FIG. 14 is formed may be obtained.
Here, the first image TG illustrated in FIG. 15 further includes a dark image portion K4 having a different density from the image portions K1 and K2 in a portion corresponding to the image quality guarantee range 212 of the special recording paper 9B. The first image TG illustrated in FIG. 14 illustrating the result of performing the first image forming operation in the third embodiment, whereas the image portion K3 having a different density exists, the image portions K1, K2 The image portion K4 is present in the same manner, but the image portion K3 is not present.

In this case, it is considered that the image portion K3 has disappeared in connection with the fact that charging by the charging device 22 which is a peculiar configuration of the first image forming operation in the third embodiment is not performed. It can be known that there is a sign of abnormality such as damage or functional deterioration that causes the image portion K3 to be formed in part.
At this time, if the period (interval) of the image portion K3 is a dimension corresponding to the length (circumference) of the outer periphery of the charging roll 221, the image portion K3 is damaged or functions in part of the charging roll 221. The possibility that the information is a sign of an abnormality of deterioration is further increased.

In the first image forming operation in the third embodiment, as the special development potential Vd4, the potential difference Δγ between the special development potential Vd4 and the surface potential of the image forming range 210 of the photosensitive drum 21 when not charged is obtained. It is preferable to use a potential (Δβ <Vc) that falls within a numerical range smaller than the contrast potential Vc (FIG. 5A), which is a potential difference between the normal development potential Vd1 and the latent image potential Vi.
When a potential at which the potential difference Δγ with respect to the normal development potential Vd1 is equal to or higher than the contrast potential Vc is used as the special charging potential Vd4, for example, due to an abnormality occurring in the photosensitive drum 21, the charging roll 221 or the like, There is a problem such that it becomes difficult to reveal an abnormal image that can be formed by the first image forming operation in the third mode, and the sensitivity to detect the sign of abnormality or the occurrence of abnormality decreases.

  The numerical range in which the potential difference Δγ is smaller than the contrast potential Vc is, for example, preferably in the range of 10 to 40%, more preferably in the range of 20 to 30%, similarly to the reason described in the first embodiment (FIG. 9). It is a range.

[Other embodiments]
In the first to third embodiments, when each first image forming operation is executed, as illustrated in FIG. 16, the first image TG has a length equal to or longer than one rotation (CL1) of the photosensitive drum 21. It is preferable that an image composed of the above is formed and transferred to a special recording sheet 9B.

In this case, it is necessary to apply a special recording sheet 9B having a length L1 in the transport direction E that is longer than the length of one rotation (CL1) of the photosensitive drum 21 or more. Reference sign LE in FIG. 16 and the like is a length (range) in the rotation direction of the first image TG formed on the photosensitive drum 21.
As described above in the third embodiment, when the first image TG is formed by forming an image having a length equal to or longer than one rotation (CL1) of the photosensitive drum 21 as the first image TG. This makes it easier to know the signs of periodic abnormalities and the occurrence of abnormalities in the photosensitive drum 21 and the charging roll 221.

  In the first to third embodiments, when each first image forming operation is executed, as illustrated in FIG. 17, the first image TG is equal to or more than two rotations (CL2) of the photosensitive drum 21. It is preferable that an image having a length of 1 mm is formed and transferred to one or a plurality of special recording sheets 9B.

In this case, whether to use one sheet or a plurality of sheets as the special recording sheet 9B depends on the relationship between the length L1 of the recording sheet 9B and the length of one rotation (CL1) of the photosensitive drum 21. Selected based on. FIG. 17A illustrates a case where the first image TG having a length equal to or longer than two rotations (CL2) is formed on one special recording sheet 9B, and FIG. CL2) The case where the first image TG having the above length is formed on two special recording sheets 9B1 and 9B2. In the case of the configuration example shown in FIG. 5B, the first image TG formed on the two special recording sheets 9B1 and 9B2 is a first image TG having a length equal to or longer than one rotation (CL1) of the photosensitive drum 21. It is necessary to form two 1-image TGs.
As described in the third embodiment, when the first image TG is formed by forming an image having a length equal to or longer than two rotations (CL2) of the photosensitive drum 21 as the first image TG as described above. A sign of a periodic abnormality in the photosensitive drum 21 and the charging roll 221 and the occurrence of the abnormality can be found from one image TG having a length equal to or longer than two rotations (CL2) of the photosensitive drum 21. , More surely easier to know.

  In addition, as for the image forming apparatus, as long as the image forming apparatus includes an image holding unit such as a photoconductor, a contact or non-contact type charging unit, a developing unit, a transfer unit, and a fixing unit, the first embodiment and the like. The image forming apparatus 1 is not limited to the image forming apparatus 1 that employs the intermediate transfer method (intermediate transfer apparatus 30) exemplified in the above, and other types of image forming apparatuses may be used. As another type of image forming apparatus, for example, an image forming apparatus of a type that directly transfers from the photosensitive drum 21 of the image forming apparatus 20 to the recording paper 9 without adopting the intermediate transfer system can be cited.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 9 ... Recording paper (an example of a recording medium)
9B: Special recording paper (an example of a recording medium)
9a ... leading end 9b during conveyance ... rear end 21 during conveyance ... photosensitive drum (an example of image holding means)
22: Charging device (an example of charging means)
24. Developing device (an example of developing means)
25. Primary transfer device (an example of transfer means)
31 ... Intermediate transfer member 35 ... Secondary transfer device (an example of transfer means)
61 ... Control unit 210 ... image formable range 212 ... image quality guarantee range 215,216 ... end Ps outside image quality guarantee range ... position Pe inside the leading edge during conveyance Pe ... position LE inside the trailing edge during conveyance ... Range Vd1 from the inner position Ps to the inner position Pe ... Normal development potential (development potential applied during electrostatic latent image formation)
Vd2, Vd4 ... Special charging potential Vh1 ... Normal charging potential (charging potential applied during electrostatic latent image formation)
Vh2 ... Special charging potential Vi ... Latent image potential Vc ... Contrast potential

Claims (18)

Image holding means having an image quality guarantee range set to a surface image formable range;
Charging means for charging the surface of the image holding means in an image formable range;
Developing means to which a developing bias voltage is supplied and which develops an electrostatic latent image formed in at least the image quality guarantee range of the image holding means with a developer to form a developer image;
Transfer means for transferring the developer image to a recording medium directly or via an intermediate transfer member;
A first image formed by adhering developer by the developing means is formed on the surface of the image holding means that is at least outside the image quality guarantee range and within the image formable range, and is transferred to a recording medium by the transfer means. A control means for executing one image forming operation;
With
In the first image forming operation, the control unit moves the first image from a position on the inner side of the image forming range of the image holding unit when the recording medium is transported from a rear end thereof. An image forming apparatus that forms a portion corresponding to a range up to the inner position.   The control unit causes the image forming range of the image holding unit to be charged to a charging potential applied when forming an electrostatic latent image by the charging unit, and applies the developing bias voltage when forming the electrostatic latent image. The image forming apparatus according to claim 1, wherein the first image forming operation is executed after the development potential is maintained.   The control unit executes the first image forming operation after setting the image formable range of the image holding unit to a state in which the image forming unit is not charged by the charging unit and not supplying the developing bias voltage to the developing unit. The image forming apparatus according to claim 1.   In the first image forming operation, the control means forms a first image from a developing potential that applies the developing bias voltage at the time of forming the electrostatic latent image in accordance with the time when the first image should be formed. 3. The image forming apparatus according to claim 2, wherein an operation for changing to a special developing potential and an operation for returning to a developing potential applied at the time of forming an electrostatic latent image are performed.   In the first image forming operation, the control means applies the charging voltage supplied to the charging means in accordance with the timing at which the first image should be formed from the charging potential applied at the time of forming the electrostatic latent image. The image forming apparatus according to claim 2, wherein an operation for changing to a special charging potential for forming one image and an operation for returning to a charging potential applied when forming an electrostatic latent image are performed.   In the first image forming operation, the control unit applies a developing bias voltage to the developing unit so as to have a special developing potential at which the first image is formed in accordance with a timing at which the first image is to be formed. The image forming apparatus according to claim 3, wherein an operation of supplying and an operation of stopping the supply are performed.   The control means performs the operation of changing the developing bias voltage to the special developing potential, and the timing when the potential during the changing process coincides with the charging potential applied at the time of forming the electrostatic latent image is conveyed to the recording medium. The image forming apparatus according to claim 4, wherein the image forming apparatus is performed after a time corresponding to a leading edge of time.   The control means returns the developing bias voltage from the special developing potential to the developing potential applied when forming the electrostatic latent image, and the potential in the returning process coincides with the charging potential applied when forming the electrostatic latent image. The image forming apparatus according to claim 4, wherein the time when the recording is performed is before a time corresponding to a rear end when the recording medium is conveyed.   The control means performs the operation of changing the charging voltage to the special charging potential, and the timing when the potential during the changing process coincides with the developing potential applied at the time of forming the electrostatic latent image is when the recording medium is transported. The image forming apparatus according to claim 5, wherein the image forming apparatus is performed after a time corresponding to the tip of the image forming apparatus.   The control means performs an operation of returning the charging voltage from the special charging potential to a charging potential applied at the time of electrostatic latent image formation, and the potential at the time of the return process coincides with a developing potential applied at the time of electrostatic latent image formation. The image forming apparatus according to claim 5, wherein the time is set to be before a time corresponding to a rear end of the recording medium transport.   The control means performs an operation of supplying a developing bias voltage at the special developing potential, and the potential at the time of starting the supply coincides with the adhesion start potential when the adhesion of the developer to the image holding means starts. The image forming apparatus according to claim 6, wherein the timing is at or after a time corresponding to a leading edge when the recording medium is conveyed.   The control means performs an operation of stopping the supply of the development bias voltage, and the timing when the potential during the supply stop process coincides with the adhesion end potential when the adhesion of the developer to the image holding means ends. The image forming apparatus according to claim 6, wherein the image forming apparatus is performed before a time corresponding to a rear end when the recording medium is conveyed.   The control means is configured such that a potential difference between the special development potential and a charging potential applied at the time of forming the electrostatic latent image is a development potential applied at the time of forming the electrostatic latent image as a special development potential in the first image forming operation. The image forming apparatus according to claim 4, wherein a potential that falls within a numerical range smaller than a contrast potential, which is a potential difference between a potential and a latent image potential, is used.   The control means determines, as a special charging potential in the first image forming operation, a potential difference between the special charging potential and a development potential applied at the time of forming the electrostatic latent image is a development potential applied at the time of forming the electrostatic latent image. The image forming apparatus according to claim 5, wherein a potential that falls within a numerical range smaller than a contrast potential, which is a potential difference between a potential and a latent image potential, is used.   The control means develops a special development potential in the first image forming operation, in which a potential difference between the special development potential and the surface potential when the image holding means is not charged is applied when an electrostatic latent image is formed. The image forming apparatus according to claim 6, wherein a potential that falls within a numerical range smaller than a contrast potential that is a potential difference between the potential and the latent image potential is used. The image holding means is a rotating member,
16. The control unit according to claim 1, wherein the control unit forms an image having a length equal to or longer than one rotation of the image holding unit as the first image during the first image forming operation and transfers the image to a recording medium. The image forming apparatus according to any one of the above.   In the first image forming operation, the control unit forms an image having a length equal to or longer than two rotations of the image holding unit as the first image, and transfers the image to one or a plurality of recording media. Item 17. The image forming apparatus according to Item 16.   The image forming apparatus according to claim 1, wherein the control unit does not perform an operation of forming an electrostatic latent image on the image holding unit during the first image forming operation.

Images