JP2010128016A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress latent-image deterioration in a developing process. <P>SOLUTION: A control unit 10 sets a developing bias potential so that a first potential difference may change to 0 V, 50 V, ..., and 400 V, calculates a second potential difference for every setting of the developing bias potential and stores each pair of the first potential difference and the second potential difference in a storage part 20. The control unit 10 collates each stored pair of first potential difference and second potential difference with potential difference data 201 previously stored in the storage part 20 and specifies the developing state according to each pair. Thereafter, the control unit 10 reads out a control condition corresponding to the specified developing state from a control condition table 202 previously stored in the storage part 20, and then, starts to control the image forming apparatus 100 based on the read control condition. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  In an electrophotographic image forming apparatus, the surface of a photoreceptor is charged and then exposed to form an electrostatic latent image. An electrostatic latent image is a latent image formed by the difference between the potential of an exposed area and the potential of an unexposed area. In this type of image forming apparatus in which this electrostatic latent image is developed with a two-component developer containing toner and carrier and transferred to paper, the amount of change in the amount of toner in the developer becomes longer as the development process lasts longer. May become larger. In addition, the residual potential of the photosensitive member may increase due to temperature, humidity, charging fatigue due to charging, or exposure fatigue due to exposure, the sensitivity may decrease, and the initial potential may decrease. If the amount of toner in the developer or the state of the photoconductor changes, the image quality of the image may change.

As a technique for maintaining good image quality, Patent Document 1 describes an image forming apparatus that measures the resistance of a developer and adjusts the developer replenishment amount and trickle discharge amount from the measurement results. Patent Document 2 describes an image forming apparatus that measures the resistance of a developer and corrects the developing bias AC component when the measured value exceeds a threshold value. In Patent Document 3, the electrode member is placed in contact with the magnetic brush on the surface of the developing roller, and when a developing bias voltage is applied to the developing roller, a change in the current flowing through the electrode member via the carrier is indicated. There is described an image forming apparatus that detects an ammeter and changes a developing bias voltage based on a detection result. Patent Document 4 describes an image forming apparatus that measures a transfer output condition of a transfer device by measuring a potential after development and predicting a charge amount of fog toner.
JP-A-7-79218 JP 2007-057618 A JP-A-10-232539 JP 2005-17770 A

  In the electrostatic latent image, when the difference between the potential of the exposed area and the potential of the unexposed area becomes small, the electrostatic latent image is deteriorated, and the image quality is deteriorated. An object of the present invention is to suppress deterioration of an electrostatic latent image during a development process.

  In order to solve the above-described problem, an image forming apparatus according to a first aspect of the present invention is an image forming unit that forms an image according to a control condition, and charges the surface of the image carrier to a first potential. The surface of the image carrier is exposed, the second potential is set as a development potential, the exposed area is developed, and an image is formed, and the image is held after the image is formed by the image forming unit. In the body, a measuring means for measuring a third potential which is a potential of an area other than the exposed area, the control condition followed by the image forming means, and a potential difference between the first potential and the second potential An acquisition unit that acquires a plurality of correspondence information, which represents a correspondence relationship between a first potential difference that is a first potential difference and a second potential difference that is a potential difference between the first potential and the third potential; The first potential in the means, and Based on the third potential measured by the measuring unit, the second potential difference is calculated, and the plurality of correspondence information acquired by the acquiring unit is used to calculate the second potential difference in the image forming unit. The control condition corresponding to the first potential difference, which is the difference between the potential of 1 and the second potential, and the second potential difference calculated by the calculation means is specified, and the specified control condition Control means for controlling the image forming means.

  An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, wherein the calculating means includes a plurality of the first potential in the image forming means and a plurality of exposed areas on the image carrier. The plurality of second potential differences are calculated from the plurality of third potentials measured by the measuring means when developed at the second potential, respectively, and the control means is obtained by the obtaining means. The control conditions corresponding to the plurality of first potential differences in the image forming unit and the plurality of second potential differences calculated by the calculation unit are specified based on the plurality of correspondence relationship information. The image forming unit is controlled according to the specified control condition.

  An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the first aspect, wherein the image forming means uses the second potential obtained by superimposing an alternating voltage on a direct current voltage as a developing potential, and performs the control. The condition is a condition for at least one of an amplitude and a frequency of the AC voltage.

  An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the third aspect, wherein the calculating means is at least one of the first potential in the image forming means and the amplitude and frequency of the AC voltage. A plurality of second potential differences are calculated from the plurality of third potentials measured by the measuring means when the change occurs, and the control means obtains the plurality of correspondences obtained by the obtaining means. Based on the relationship information, the control conditions corresponding to the plurality of first potential differences in the image forming unit and the plurality of second potential differences calculated by the calculation unit are specified, and the specified control conditions And controlling the image forming means.

  An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to any one of the first to fourth aspects, wherein the image forming apparatus is close to or separate from the image holding body and close to the image holding pair. A transfer unit that transfers the image formed by the image forming unit to a transfer target, and the measurement unit is configured to move the image holding member closer to the image holding member than a position where the transfer unit is close to the image holding member. When the transfer unit is arranged on the downstream side of the moving direction of the surface and the transfer unit is separated from the image carrier, the third potential is measured, and the transfer unit transfers the image. , And measuring the potential of the image carrier after the transfer.

  An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to the first aspect, wherein the control conditions include the first potential in the image forming means, the second potential in the image forming means, Conditions regarding at least one of exposure intensity when the image forming unit exposes the surface of the image carrier, a replenishment amount of toner contained in the developer used by the image forming unit for development, and a discharge amount of the developer It is characterized by being.

  The image forming apparatus according to claim 7 of the present invention is an image forming unit that forms an image according to a control condition, and charges the surface of the image carrier, and exposes the charged surface of the image carrier, An image forming unit that develops an exposed area and forms an image; a measurement unit that measures a potential of an area other than the exposed area in the image carrier after an image is formed by the image forming unit; When the potential difference between the surface potential of the image carrier charged by the image forming unit and the potential measured by the measuring unit exceeds a threshold value, the control condition is changed so as to reduce the potential difference. And control means for controlling the image forming means.

According to the image forming apparatus of the first aspect of the present invention, it is possible to suppress the deterioration of the latent image during the development process.
According to the image forming apparatus of the second aspect of the present invention, the state of the developing device is more accurately determined than in the case where this configuration is not used, and the latent image in the developing process is determined according to the state. Deterioration can be suppressed.
According to the image forming apparatus of the third aspect of the present invention, in the developing device to which an AC voltage is applied, it is possible to suppress the deterioration of the latent image during the developing process.
According to the image forming apparatus of the fourth aspect of the present invention, in the developing device to which an AC voltage is applied, the state of the developing device is more accurately determined as compared with the case where this configuration is not used, and the state Accordingly, it is possible to suppress the deterioration of the latent image during the development process.
According to the image forming apparatus of the fifth aspect of the present invention, the measuring unit that measures the potential of the region other than the exposed region on the image holding member after the image is formed by the image forming unit is transferred by the transfer unit. It can also serve as a measuring means for measuring the potential of the image carrier after being recorded.
According to the image forming apparatus of the sixth aspect of the present invention, it is possible to suppress the deterioration of the latent image during the development process.
According to the image forming apparatus of the seventh aspect of the present invention, it is possible to suppress the deterioration of the latent image during the development process.

Embodiments according to the present invention will be described below.
Here, an electrophotographic printer (image forming apparatus) including an intermediate transfer belt and a so-called tandem engine will be described as an embodiment of the present invention. However, the present invention is limited to this embodiment. is not.

[A. Constitution]
[A-1. Overall configuration of image forming apparatus]
FIG. 1 is a schematic diagram illustrating an overall configuration of an image forming apparatus 100 according to an embodiment of the present invention. As shown in the figure, the image forming apparatus 100 includes a control unit 10, a storage unit 20, a communication unit 30, an operation unit 40, an image forming unit 50, and a potential measuring unit 60.

The control unit 10 is an arithmetic device including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and the like (none of which are shown). The control unit 10 controls the operation of each unit of the image forming apparatus 100 by reading a program stored in the ROM into the RAM and executing the program.
The storage unit 20 is a storage device such as an HDD (Hard Disk Drive), and stores various data used for image formation, a maximum value, a minimum value, a step size, and the like of a first potential difference (ΔV _S0 ) described later. The storage unit 20 stores the potential difference data 201 obtained by experiments or the like for the correspondence between the measured potential difference at a predetermined portion in the image forming unit 50 and the development state of the image forming unit 50 (hereinafter referred to as a development state). A control condition table 202 describing the control conditions for each development state is stored. Details of the potential difference data 201 and the control condition table 202 will be described later.
The communication unit 30 is an interface device for exchanging image data with external devices such as a digital still camera, a personal computer, and a scanner.
The operation unit 40 is an input device provided with a touch panel, displays various information related to image formation, and outputs instruction information in response to instructions from the user.

The potential measuring unit 60 is an electrometer controlled by the control unit 10. The potential measurement unit 60 includes a measurement sensor 601, converts the potential measured by the measurement sensor 601 into a signal, and outputs the signal to the control unit 10.
The image forming unit 50 forms an image based on the image data input via the communication unit 30 on a sheet-like recording material (hereinafter referred to as “recording paper”). The recording paper includes so-called plain paper, paper having a surface coated with a resin or the like, and recording materials other than paper. Specifically, the image forming unit 50 has the following configuration.

[A-2. Configuration of image forming unit]
FIG. 2 is a diagram illustrating a configuration of the image forming unit 50. In the figure, the alternate long and two short dashes line indicates the conveyance path of the recording paper. The image forming unit 50 includes a plurality of paper feed trays 501, a plurality of paper transport rollers 502, an exposure device 503, transfer units 504 Y, 504 M, 504 C, and 504 K, an intermediate transfer belt 505, and a plurality of belt transport rollers 506. A secondary transfer roll 507, a backup roll 508, a fixing device 509, a discharge port 510, and a discharge sheet receiver 511.

  Each of the paper feed trays 501 stores recording paper having a predetermined type and size, and supplies the recording paper at a timing instructed by the control unit 10. A paper transport roll 502 transports the recording paper supplied from the paper feed tray 501 to a nip region formed by the secondary transfer roll 507 and the backup roll 508. The exposure device 503 includes a laser light source, a polygon mirror, and the like (none of which are shown), and irradiates laser light corresponding to image data toward the transfer units 504Y, 504M, 504C, and 504K.

  The transfer units 504Y, 504M, 504C, and 504K form images using yellow (Y), magenta (M), cyan (C), and black (K) color toners, respectively, on the intermediate transfer belt 505. Transcript. The transfer units 504Y, 504M, 504C, and 504K differ only in the toner used, and there is no significant difference in the configuration. Hereinafter, when it is not necessary to distinguish between them, the alphabet at the end of the code indicating the color of the toner is omitted and referred to as “transfer unit 504”.

[A-3. Configuration of transfer unit]
FIG. 3 is a diagram showing the configuration of the transfer unit 504. As shown in the figure, the transfer unit 504 includes a photosensitive drum 5041, a roller charger 5042, a developing device 5043, a primary transfer roll 5044, a drum cleaner 5045, and a charge eliminating device 5046, and a photosensitive drum 5041. A measurement sensor 601 of the potential measurement unit 60 is arranged along the surface of the electrode. The photosensitive drum 5041 is an image carrier having a charge generation layer and a charge transport layer, and is rotated in the direction of arrow A in the drawing by a driving unit (not shown). A roller charger 5042 charges the surface of the photosensitive drum 5041. Here, the measurement sensor 601 is disposed downstream of the developing device 5043 and upstream of the primary transfer roll 5044 in the rotation direction of the photosensitive drum 5041 (arrow A).

FIG. 4 is a conceptual diagram for explaining the state of the surface potential of the photosensitive drum 5041. Here, for convenience of explanation, it is assumed that the toner charge is plus (+), and the roller charger 5042 charges the surface of the photosensitive drum 5041 to a plus potential having the same sign as the toner charge. To do. The sign of toner charge and charging of the photosensitive drum 5041 by the roller charger 5042 may not be plus but may be minus (−). The roller charger 5042 shown in FIG. 3 charges the surface potential (V _dev ) of the photosensitive drum 5041 to a predetermined potential. Hereinafter, this potential is referred to as an initial potential (V _S0 ). Then, as shown in FIG. 4A, a part of the surface of the photosensitive drum 5041 is exposed by the exposure device 503 to remove the charge, and the surface potential is the latent image low portion potential (V _L0 ). Become. Further, it is assumed that the potential of the other portion, that is, the portion not exposed by the exposure apparatus 503 remains unchanged at the initial potential (V _S0 ). FIG. 4A shows the surface potential of the photosensitive drum 5041 after being exposed by the exposure device 503. The exposed portion becomes an image line portion, and the unexposed portion becomes a non-image line (background) portion, whereby an electrostatic latent image is formed on the surface of the photosensitive drum 5041.

The developing device 5043 contains a two-component developer containing toner of any one of Y, M, C, and K and a magnetic carrier such as ferrite powder. In addition, a magnet roller to which a voltage is applied so that the potential of the developing device 5043 becomes a predetermined potential (V _b : hereinafter referred to as a developing bias potential) is provided. Here, the potential of the developing device 5043 is a potential when the voltage applied to the developing device 5043 is a DC voltage, and the voltage applied to the developing device 5043 is a voltage obtained by superimposing the AC voltage on the DC voltage. In this case, it means the average potential. Here, a case where the voltage applied to the developing device 5043 is a voltage obtained by superimposing an AC voltage on a DC voltage will be described. The developing bias potential (V _b ) is a potential smaller than the initial potential (V _S0 ) when the toner charge is plus (+), and is lower than the latent image lower potential (V _L0 ). A large potential is chosen. That is, when the toner charge is positive (+), the magnitude relationship between these potentials is V _S0 > V _b > V _L0 .

A nonmagnetic sleeve that can rotate is provided on the magnet roller, and a magnetic carrier is connected to the sleeve surface by the magnetic force of the magnet roller, thereby forming a magnetic brush. When the tip of the magnetic brush comes into contact with the surface of the photosensitive drum 5041, the toner adheres to the portion exposed on the surface of the photosensitive drum 5041 by the exposure device 503, that is, the image line portion of the electrostatic latent image. An image is formed (developed) on the surface of the drum 5041. More specifically, since the toner has a positive (+) charge as described above, when the potential of the developing device 5043 is larger than the surface potential of the photosensitive drum 5041 (that is, on the positive side). Then, it moves from the developing device 5043 to the surface of the photosensitive drum 5041. Accordingly, in the non-image area, since the developing bias potential (V _b ) of the developing device 5043 is smaller than the initial potential (V _S0 ) of the photosensitive drum 5041, the toner does not move while In this case, since the developing bias potential (V _b ) of the developing device 5043 is larger than the latent image low potential (V _L0 ) of the photosensitive drum 5041, the toner moves.

During development by the developing unit 5043, a leak current flows due to a potential difference between the developing unit 5043 and the photosensitive drum 5041. Specifically, the latent image low potential (V _L0 ), which is the potential of the image line portion, is positively charged and becomes a low potential (V _L ) after development. On the other hand, since the initial potential (V _S0 ) that is the potential of the non-image area is larger than the development bias potential (V _b ), a current flows conversely to become the non-image area potential (V _S ) after development. When the surface potential of the photosensitive drum 5041 after the development is measured, the post-development non-image area potential (V _S ) is measured in the non-image area. On the other hand, in the image area, the post-development image area potential (V _H ) that is increased by the toner layer potential is measured due to the charge of the adhered toner. FIG. 4B shows the surface potential of the photosensitive drum 5041 after being developed by the developing unit 5043.

  Returning to FIG. 3, the description will be continued. The primary transfer roll 5044 generates a predetermined potential difference at a position where the intermediate transfer belt 505 faces the photosensitive drum 5041, and the image is transferred to the intermediate transfer belt 505 by this potential difference. The drum cleaner 5045 removes untransferred toner remaining on the surface of the photosensitive drum 5041 after image transfer. The neutralization device 5046 neutralizes the surface of the photosensitive drum 5041. In other words, the drum cleaner 5045 and the charge eliminating device 5046 remove unnecessary toner and charges from the photosensitive drum 5041 in preparation for the next image formation.

  The intermediate transfer belt 505 is an endless belt member, and the belt conveyance roll 506 stretches the intermediate transfer belt 505 (see FIG. 2). At least one of the belt conveyance rolls 506 is provided with a drive unit (not shown), and moves the intermediate transfer belt 505 in the direction of arrow B in the drawing. Note that the belt conveyance roll 506 that does not have a drive unit rotates following the movement of the intermediate transfer belt 505. As the intermediate transfer belt 505 moves and rotates in the direction of arrow B in the figure, the image transferred by the transfer unit 504 is moved to a nip region formed by the secondary transfer roll 507 and the backup roll 508.

  The secondary transfer roll 507 and the backup roll 508 generate a predetermined potential difference at a position where the intermediate transfer belt 505 faces the recording sheet, and the image is transferred to the recording sheet by the potential difference. The fixing device 509 includes a heating roll 5091 and a pressure roll 5092. The recording sheet is heated and pressed by these roll members to fix the image transferred to the recording sheet. The recording paper on which the image is fixed is guided to the discharge port 510 by the paper transport roll 502 and is stacked on the discharge paper receiver 511.

[A-4. Configuration of potential difference data]
Next, the potential difference data 201 stored in the storage unit 20 will be described. As shown in FIG. 4, after development, the initial potential (V _S0 ) of the non-image area becomes the non-image area potential (V _S ) after development. Here, the potential difference between the initial potential (V _S0 ) and the developing bias potential (V _b ) is the first potential difference (ΔV
_S0 ), and the potential difference between the initial potential (V _S0 ) and the post-development non-image area potential (V _S ) is called the second potential difference (ΔV _S ).
The correspondence relationship between the first potential difference (ΔV _S0 ) and the second potential difference (ΔV _S ) varies depending on the development state. In each development state, the second potential difference (ΔV _S ) increases as the first potential difference (ΔV _S0 ) increases. I know it will grow. However, it is known that this correspondence is not a proportional relationship. The potential difference data 201 is data that associates the correspondence between the first potential difference (ΔV _S0 ) and the second potential difference (ΔV _S ) for each of a plurality of development states.
After development, the latent image low portion potential (V _L0 ) of the image area becomes the low potential (V _L ) after development. However, since toner adheres to the image area, it is measured by the potential measuring section 60. What can be done is the post-development image area potential (V _H ) and not the post-development low area potential (V _L ). Further, the potential difference between the latent image low potential (V _L0 ) and the post-development low potential (V _L ) is affected not only by the first potential difference (ΔV _S0 ) but also by the amount of attached toner. Therefore, in the present invention, the measurement value for calculating the second potential difference (ΔV _S ), that is, the post-development non-image area potential (V _S ) is used. Specifically, the control unit 10 determines whether or not the part measured by the measurement sensor 601 of the potential measurement unit 60 is an image line unit based on the rotational movement distance of the photosensitive drum 5041 and the control status of the exposure apparatus 503. The measured value when this part is a non-image area is used as the post-development non-image area potential (V _S ).
Note that the control unit 10 may determine whether or not the measured part is between pages, and determine whether or not this part is an image line part. Further, such a determination may be omitted by arranging the measurement sensor 601 at a position corresponding to the margin in advance. In this case, the measurement sensor 601 measures only the non-image portion.

  FIG. 5 is a diagram in which the potential difference data 201 stored in the storage unit 20 is plotted on a graph. Factors that affect the function of the transfer unit 504 include environmental factors such as temperature and humidity, and equipment factors such as toner material and toner ratio in the developer. These factors are combined to develop the transfer unit 504. This development state is distinguished from each other depending on whether or not it easily affects the image.

The potential difference data 201 shown in FIG. 5 includes a plurality of first potential differences (ΔV _S0 ) in each of three different development states “CASE I”, “CASE II”, and “CASE III” of the transfer unit 504. , Combinations of the second potential differences (ΔV _S ) corresponding to these are included. As shown in FIG. 5, in any development state, when the first potential difference (ΔV _S0 ) indicated by the horizontal axis in the figure is relatively small, the second potential difference (ΔV _S ) indicated by the vertical axis.
Although the slope of is small, when the first potential difference (ΔV _S0 ) increases to a certain level, the slope of the second potential difference (ΔV _S ) tends to suddenly increase. This is because when the first potential difference (ΔV _S0 ) exceeds the threshold value, dielectric breakdown occurs between the developing device 5043 and the photosensitive drum 5041, and discharge occurs.

When this discharge occurs, a phenomenon called so-called carrier fog (BCO: Bead Carrier Over) occurs in which the magnetic carrier in the developer flies to the photosensitive drum 5041, and the image is disturbed, so that the image quality of the image is significantly deteriorated. In particular, when the magnetic brush method is employed, since the brush density is generally coarse (for example, 5.5 lines / mm ² ), the graininess and line reproducibility of the image deteriorate due to the discharge from each brush tip. . However, if the first potential difference (ΔV _S0 ) is too small, the non-image area potential (V _{S0 to} V _S ) of the photosensitive drum 5041 becomes the development bias potential (V _b ) or the post-development image area potential (V _H). ), The toner may directly adhere to the non-image area from the developing unit 5043 during development, and the image quality of the image may deteriorate. Further, since the edge effect is enhanced, a phenomenon called so-called background fogging occurs in which toner adheres from the image line portion of the image formed on the photosensitive drum 5041 to the non-image line portion after development, and the image quality of the image may deteriorate. is there. Therefore, the first potential difference (ΔV _{S0 is} not large enough to cause significant carrier fog.
) Should be set large.

FIG. 6 is a diagram showing the influence on the carrier fog by the second potential difference (ΔV _S ). In FIG. 6, the horizontal axis represents the second potential difference (ΔV _S ), and the vertical axis represents the number of carrier fog (unit: pieces / cm
² ) Plotting. Here, if the allowable threshold value for the number of carrier fog is “1000”, the number of carrier fog can be reduced below this threshold by setting the second potential difference (ΔV _S ) to 24 V or less in all development states. You can see that you can. Therefore, in order to make the number of carrier fogs below the threshold, the first potential difference (ΔV _S0 ) is about 330 V or less for “CASE I” and about 260 V for “CASE II”, as shown in FIG.
In the following, it is understood that “CASE III” must be set to about 240 V or less. That is, it can be seen that these development states are easily discharged in the order of “CASE I” → “CASE II” → “CASE III”. Of these development states, the first potential difference (ΔV _S0 ) can be set to the largest in “CASE I”, which is hard to discharge.

[A-5. Control Condition Table Configuration]
FIG. 7 is a diagram illustrating an example of the control condition table 202. As shown in FIG. 7, the control condition table 202 describes control conditions for controlling the transfer unit 504 for each of a plurality of development states included in the potential difference data 201. As described above, the developing state is easily discharged in the order of “CASE I” → “CASE II” → “CASE III”. Each control condition described in the control condition table 202 is set to a value such that the second potential difference (ΔV _S ) becomes smaller as the developing state easily discharges. For example, the initial potential (V _S0 ) is set in the order of high → middle → low as the developing state is easily discharged. This order is, for example, the order in which the first potential difference (ΔV _S0 ) decreases under the condition that the development bias potential (V _b ) is a fixed value, and as a result, the second potential difference (ΔV
_S ) is a smaller order. Here, the developing bias potential (V _b ) is also set in the order of high → middle → low as the developing state easily discharges. However, the initial potential (V _S0 ) is the developing bias potential (V _S0 ). Even if it changes with V _b ), the respective setting conditions are set so that the second potential difference (ΔV _S ) becomes smaller as the developing state easily discharges.

The control condition table 202 includes an AC component amplitude (V _pp ) and an AC component frequency in addition to the initial potential (V _S0 ), the developing bias potential (V _b ), and the latent image low potential (V _L0 ) described above. (F) is defined as a control condition. As described above, here, a voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing device 5043, and an average potential thereof becomes a developing bias potential (V _b ). The amplitude of the AC voltage is the AC component amplitude (V _pp ), and the frequency of the AC voltage is the AC component frequency (f).

Further, the control condition table 202, the toner supply amount W _f is the amount for replenishing the toner to the developing device 5043 per unit time, the amount of discharge is the developer discharge the developer from the developing device 5043 per unit time The quantity W _d is determined as a control condition. The developer used here is a two-component developer containing a toner and a magnetic carrier, but the impedance of the developer decreases due to a decrease in toner concentration in the developer due to toner consumption and environmental changes. If the contrast of the electrostatic latent image is lowered due to a decrease in the impedance of the developer, the graininess, highlight portion tone reproduction, carrier fog, etc. may occur, and the image quality of the image may deteriorate. Therefore, the control unit 10 by controlling the toner supply amount W _f and the developer discharge amount W _d, compensate for this change. The control condition table 202 may describe the type of toner to be supplied.
The control unit 10 refers to the above-described potential difference data 201 and the control condition table 202, so that the correspondence relationship between the control condition followed by the transfer unit 504 (image forming unit) and the first potential difference and the second potential difference is determined. It functions as an acquisition means for acquiring a plurality of correspondence information.

[B. Operation]
FIG. 8 is a flowchart showing the operation of the image forming apparatus 100 according to the embodiment of the present invention. When a user performs an operation for instructing activation of the apparatus via the operation unit 40 of the image forming apparatus 100, the control unit 10 of the image forming apparatus 100 initializes a control condition for controlling the transfer unit 504 ( Step S101). Next, the control unit 10 reads the maximum value, minimum value, and step size of the first potential difference (ΔV _S0 ) stored in advance in the storage unit 20 (step S102).
The development bias potential (V _b ) is set so that the first potential difference (ΔV _S0 ) becomes the read minimum value (step S103). Here, the maximum value is 400 V, the minimum value is 0 V, and the step size is 50 V. Therefore, in step S103, the first potential difference (ΔV _S0 ) is 0V.
Set to

Then, the control unit 10 determines whether or not the first potential difference (ΔV _S0 ) exceeds the read maximum value (step S104). If it is determined that the first potential difference (ΔV _S0 ) does not exceed the maximum value (step S104; NO), the control unit 10 uses the measurement sensor 601 of the potential measurement unit 60 to develop a non-image area potential (V _S ) after development. Is measured (step S105), and a second potential difference (ΔV _S ) that is a potential difference between the initial potential (V _S0 ) and the measured non-image area potential (V _S ) after development is calculated. The information is stored in the storage unit 20 in association with the first potential difference (ΔV _S0 ) (step S106). When the first potential difference (ΔV _S0 ) and the second potential difference (ΔV _S ) are stored in association with each other,
The controller 10 sets the developing bias potential (V _b ) so that the first potential difference (ΔV _S0 ) increases by the step size read in step S102 (step S107), and returns the process to step S104. Therefore, the control unit 10 determines that the first potential difference (ΔV _S0 ) is 0V, 50V, 100
The development bias potential (V _b ) is set so as to change to V,..., 350 V, 400 V, the second potential difference (ΔV _S ) is calculated for each setting, and the first potential difference (ΔV _S0 ) and the second potential difference are calculated. (ΔV
Each set of _S ) is stored in the storage unit 20. That is, the control unit 10 sets the initial potential (first potential) in the transfer unit 504 (image forming unit) and the exposed area on the photosensitive drum 5041 (image holding member) to a plurality of development bias potentials (second potential). ), A plurality of second potential differences (second potential differences) are calculated from a plurality of post-development non-image area potentials (third potentials) measured by the potential measuring unit 60 (measuring means) in the case of each development. It is an example of the calculation means to do.

On the other hand, if it is determined that the first potential difference (ΔV _S0 ) exceeds the maximum value (step S104;
YES), the control unit 10 collates each set of the first potential difference (ΔV _S0 ) and the second potential difference (ΔV _S ) stored in Step S106 with the potential difference data 201 stored in the storage unit 20 (Step S106). S108), the development state corresponding to each set is specified (step S109). Specifically, for example, the absolute value of the error between the potential difference data 201 and each set described above is summed for each development state, and the development state having the smallest total value is specified as the corresponding development state. . Thereafter, the control unit 10 reads out the control condition corresponding to the specified development state from the control condition table 202 stored in the storage unit 20 (step S110), and starts control of the transfer unit 504 based on the read control condition. (Step S111).

As described above, the image forming apparatus 100 determines whether or not the development state tends to deteriorate the image quality of the image by measuring the post-development non-image area potential (V _S ), and according to the determination result. To select one of the predetermined control conditions. Accordingly, the function of the image forming apparatus 100 is controlled under optimal control conditions corresponding to the development state.

[C. Modified example]
The above-described embodiment may be modified as follows. Moreover, you may combine the aspect deform | transformed as follows.
(Modification 1) In the above-described embodiment, the development bias potential (V _b ) is set so that the first potential difference (ΔV _S0 ) increases from the minimum value to the maximum value for each step size. The non-image area potential (V _S ) after development was measured to calculate the second potential difference (ΔV _S ). That is,
Had calculated a second potential difference ([Delta] V _S) corresponding to the plurality of first electrical potential difference (ΔV _S0), first potential corresponding to the second potential difference calculating (ΔV _S) (ΔV _S0) can be one . In this case, for example, the control unit 10 causes the first potential difference (ΔV _S0 ) to be a value stored in advance in the storage unit 20 or a currently used value stored in the RAM of the control unit 10. Is set with a developing bias potential (V _b ), a second potential difference (ΔV _S ) at this time is calculated, and a first potential difference (ΔV _S0 ) is calculated.
And the second potential difference (ΔV _S ) may be stored in the storage unit 20. Then, the control unit 10 collates this set with the potential difference data 201 stored in the storage unit 20, specifies the development state corresponding to this set, and controls the control conditions corresponding to the specified development state. What is necessary is just to start control of the transfer unit 504 according to the control conditions read from the condition table 202 and read. In short, the control unit 10 has an initial potential (first potential) in the transfer unit 504 (image forming unit) and a post-development non-image portion potential (third potential) measured by the potential measuring unit 60 (measurement unit). ) To calculate a second potential difference (second potential difference).

(Modification 2) In the above-described embodiment, the voltage applied to the developing device 5043 is a voltage obtained by superimposing an AC voltage on a DC voltage. However, the voltage applied to the developing device 5043 may be only a DC voltage. . Further, the control unit 10 changes the amplitude (V _pp ) and frequency (f) of the AC component of the voltage applied to the developing device 5043 to change the post-development non-image portion potential (V _S ) after the change. The development state may be specified by measuring and calculating the second potential difference (ΔV _S ). In this case, the control unit 10 detects the potential measurement unit 60 (measurement unit) when at least one of the initial potential (first potential) in the transfer unit 504 (image forming unit) and the amplitude or frequency of the AC voltage changes. It functions as a calculation means for calculating a plurality of second potential differences (second potential differences) from the plurality of post-development non-image area potentials (third potential) measured by the above.
FIG. 9 is a diagram for explaining the influence on the potential difference data 201 by superimposing an AC voltage on a DC voltage. FIG. 9A shows the first potential difference (ΔV _S0 ) on the horizontal axis and the second potential difference (ΔV
It is a conceptual diagram at the time of plotting _S ) on a vertical axis | shaft. As shown in this figure, as compared with the case where only the DC voltage is applied and the potential of the developing device 5043 is set to the developing bias potential (V _b ), a voltage obtained by superimposing the AC voltage on the DC voltage is applied. When the potential is the developing bias potential (V _b ), the graph moves in the direction of the arrow. That is, when the AC voltage is superimposed, the second potential difference (Δ
V _S ) increases. On the other hand, FIG. 9B is a conceptual diagram in the case where the second potential difference (ΔV _S ) is plotted on the horizontal axis and the number of carrier fog (unit: pieces / cm ² ) is plotted on the vertical axis. At this time, when the AC voltage is superimposed, the graph moves in the direction of the arrow as compared with the case of only the DC voltage. That is, when the AC voltage is superimposed, the number of carrier fog (BCO) decreases. Then, it is known that the amount of increase in the second potential difference (ΔV _S ) in FIG. 9A and the amount of decrease in BCO in FIG. 9B cancel each other. That is, the number of carrier fogs depends only on the DC component of the voltage applied to the developing device 5043.

On the other hand, FIG. 9C shows the second potential difference (ΔV _S ) on the horizontal axis and the second potential difference (ΔV corresponding to the vertical axis).
V _S) Evaluation of graininess of the image when the calculated (hereinafter, a conceptual diagram when plotting the granularity evaluation). At this time, the granularity evaluation hardly changes between the case of only the DC voltage and the case where the AC voltage is superimposed. That is, it is known that the granularity evaluation is determined by the second potential difference (ΔV _S ) regardless of whether the voltage applied to the developing device 5043 is only a DC component or an AC component is superimposed.
Accordingly, when only the DC voltage is applied to the developing device 5043 in calculating the second potential difference (ΔV _S ) by changing the control condition, the first potential difference (ΔV _S0 ) − shown in FIG.
Each of the graph of the second potential difference (ΔV _S ) and the graph of the second potential difference (ΔV _S ) −number of carrier fogs shown in FIG. 9B includes a region where the slope increases steeply. It becomes. In the region where the slope increases sharply, the amount of change on the horizontal axis (definition region) is small compared to other regions even if the amount of change on the vertical axis (value region) is large. The effect of the error is less likely to appear in the corresponding value on the horizontal axis. Here, the second potential difference (ΔV _S ) corresponding to a certain number determined as the number of carrier fogs is specified from FIG.
Since the first potential difference (ΔV _S0 ) corresponding to V _S ) is obtained, it is preferable to apply only a DC voltage to the developing device 5043 from the viewpoint of accuracy.
On the other hand, when the second potential difference (ΔV _S ) corresponding to the graininess evaluation is specified, there is no cancellation as described above. Therefore, the graininess evaluation does not depend only on the DC component of the voltage applied to the developing device 5043. . That is, if the second potential difference (ΔV _S ) is calculated by changing only the DC voltage without superimposing the AC voltage on the developing device 5043, the degree of influence by the AC component cannot be obtained.
Therefore, when calculating the second potential difference (ΔV _S ), it is desirable to perform both the case where the voltage applied to the developing device 5043 is a DC voltage and the case where the AC voltage is superimposed.

(Modification 3) In the above-described embodiment, the control unit 10 calculates the second potential difference for each changed setting, stores each set of the first potential difference and the second potential difference in the storage unit 20, and The development state is identified by collating the set with the potential difference data 201 stored in advance in the storage unit 20, and the control conditions corresponding to the identified development state are read out, but without identifying the development state, The control conditions may be determined directly. In this case, the potential difference data 201 and the control condition table 202 are not necessary. For example, the control unit 10 calculates the second potential difference for each changed setting, plots each set of the first potential difference and the second potential difference, and when the predetermined second potential difference exceeds the threshold, It is only necessary to reset at least one of the initial potential and the developing bias potential so as to reduce the difference between the two potentials.

(Modification 4) In the above-described embodiment, the measurement sensor 601 of the potential measurement unit 60 is disposed downstream of the developing device 5043 and upstream of the primary transfer roll 5044 in the rotation direction of the photosensitive drum 5041. The measurement sensor 601 may be disposed downstream of the primary transfer roll 5044. In this case, it is desirable that the primary transfer roll 5044 be configured to be close to or away from the photosensitive drum 5041. As indicated by a broken line in FIG. 3, when the primary transfer roll 5044 is close to the photosensitive drum 5041, that is, when the primary transfer roll 5044 transfers an image, the measurement sensor 601A has been transferred. The surface potential of the subsequent photosensitive drum 5041 is measured. On the other hand, when the primary transfer roll 5044 is separated from the photosensitive drum 5041, the measurement sensor 601A is similar to the above-described measurement sensor 601, and the surface potential of the photosensitive drum 5041 after being developed by the developing device 5043. That is, in the non-image area, the post-development non-image area potential (V _S ) is measured. Thereby, the measurement sensor 601A measures both the surface potentials of the photosensitive drum 5041 before and after the transfer.

  In the above-described embodiment, a predetermined value is used as the initial potential. However, as shown in FIG. 3, the potential measurement unit 60 includes an initial potential measurement sensor 602 that measures the initial potential. Also good. This is because the initial potential may fluctuate even with the same applied voltage depending on the state of the photosensitive drum 5041, and the photosensitive drum 5041 may not be charged as set by the control unit 10. As described above, by providing the initial potential measurement sensor 602, the control unit 10 performs feedback control and the like to set the surface potential of the photosensitive drum 5041 to the initial potential as set.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. 2 is a diagram illustrating a configuration of an image forming unit. FIG. FIG. 3 is a diagram illustrating a configuration of a transfer unit. It is a conceptual diagram for demonstrating the state of the surface potential of a photoconductor drum. It is the figure which plotted the potential difference data memorize | stored in the memory | storage part on the graph. It is a figure which shows the influence on the carrier fog by a 2nd electric potential difference. It is a figure which shows an example of a control condition table. FIG. 5 is a flowchart showing the operation of the image forming apparatus according to the embodiment of the present invention. It is a figure explaining the influence on potential difference data by superimposing an alternating voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Control part, 100 ... Image forming apparatus, 20 ... Memory | storage part, 201 ... Potential difference data, 202 ... Control condition table, 30 ... Communication part, 40 ... Operation part, 50 ... Image forming part, 501 ... Paper feed tray, 502 ... paper transport roll, 503 ... exposure device, 504 ... transfer unit, 5041 ... photosensitive drum, 5042 ... roller charger, 5043 ... developer, 5044 ... primary transfer roll, 5045 ... drum cleaner, 5046 ... static elimination device, 505 ... Intermediate transfer belt, 506... Belt transport roll, 507 .. secondary transfer roll, 508 .. backup roll, 509 .. fixing device, 5091... Heating roll, 5092. ... potential measurement unit, 601 ... measurement sensor.

Claims (7)

An image forming means for forming an image according to a control condition, wherein the surface of an image carrier is charged to a first potential, the charged surface of the image carrier is exposed, and the second potential is used as a development potential. Image forming means for developing the developed area and forming an image;
A measurement unit that measures a third potential that is a potential of a region other than the exposed region in the image carrier after the image is formed by the image forming unit;
The control condition followed by the image forming means, a first potential difference that is a potential difference between the first potential and the second potential, and a potential difference between the first potential and the third potential. An acquisition means for acquiring a plurality of pieces of correspondence information representing a correspondence relationship between the two potential differences;
A calculating means for calculating the second potential difference from the first potential in the image forming means and the third potential measured by the measuring means;
Based on the plurality of correspondence information acquired by the acquisition unit, the first potential difference that is a difference between the first potential and the second potential in the image forming unit, and the calculation unit An image forming apparatus comprising: a control unit that specifies the control condition corresponding to the calculated second potential difference and controls the image forming unit according to the specified control condition. The calculation means includes a plurality of the first potentials measured by the measurement means when the first potential in the image forming means and the exposed area on the image carrier are developed with the plurality of second potentials, respectively. A plurality of the second potential differences from the potential of 3;
The control unit is configured to control the plurality of first potential differences in the image forming unit based on the plurality of correspondence information acquired by the acquisition unit and the plurality of second potentials calculated by the calculation unit. The image forming apparatus according to claim 1, wherein the control condition corresponding to the potential difference is specified, and the image forming unit is controlled based on the specified control condition. The image forming unit uses the second potential obtained by superimposing an AC voltage on a DC voltage as a development potential,
The image forming apparatus according to claim 1, wherein the control condition is a condition for at least one of an amplitude and a frequency of the AC voltage. The calculating means includes the first potential in the image forming means and the plurality of third potentials measured by the measuring means when at least one of the amplitude and frequency of the AC voltage changes. Calculating a plurality of the second potential differences;
The control unit is configured to control the plurality of first potential differences in the image forming unit based on the plurality of correspondence information acquired by the acquisition unit and the plurality of second potentials calculated by the calculation unit. The image forming apparatus according to claim 3, wherein the control condition corresponding to the potential difference is specified, and the image forming unit is controlled based on the specified control condition. A transfer unit that is close to or separate from the image holding member and that transfers an image formed by the image forming unit to a transfer member when close to the image holding pair;
The measuring means is arranged on the downstream side of the surface of the image carrier in the moving direction from the position where the transfer means is close to the image carrier, and the transfer means is separated from the image carrier. 5. The method according to claim 1, wherein the third potential is measured, and when the transfer unit transfers the image, the potential of the image holding member after the transfer is measured. The image forming apparatus according to any one of the above. The control conditions include the first potential in the image forming unit, the second potential in the image forming unit, the exposure intensity when the image forming unit exposes the surface of the image carrier, and the image forming unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is a condition for at least one of a replenishment amount of toner contained in the developer used for development and a discharge amount of the developer. Image forming means for forming an image according to control conditions, the image forming means for charging the surface of the image carrier, exposing the charged surface of the image carrier, developing the exposed area, and forming an image ,
In the image carrier after the image is formed by the image forming unit, a measuring unit that measures a potential of a region other than the exposed region;
When the potential difference between the surface potential of the image carrier charged by the image forming unit and the potential measured by the measuring unit exceeds a threshold, the control condition is changed so as to reduce the potential difference. An image forming apparatus comprising: a control unit that controls the image forming unit.

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