JP2012173340A - Developing device and image forming apparatus - Google Patents

Abstract

A developing device capable of suppressing toner consumption and image density reduction is provided.
A toner carrier that forms a toner layer with toner supplied from a developer carrier, a first voltage applying unit that applies a first bias voltage to the developer carrier, and a toner carrier. The first voltage application unit 261 and the second voltage application unit 262 apply a second bias voltage V2 to the body 150, and the voltage difference at which a toner layer having a predetermined thickness is formed on the toner carrier 150. An applied voltage control unit 271 that controls the voltage application unit 262, a temperature / humidity measurement unit 252, an environmental temperature and humidity measured by the temperature / humidity measurement unit 252, and a toner carrier based on a preset printing rate A toner diameter calculation unit 272 that calculates the toner diameter of the toner layer formed on 150, and a voltage difference is adjusted based on the toner diameter calculated by the toner diameter calculation unit 272 Comprising a voltage difference adjustment unit 273 instructs the applied voltage control unit 271, a.
[Selection] Figure 2

Description

  The present invention relates to a developing device for developing an electrostatic latent image formed by an electrophotographic method, and an image forming apparatus including the developing device.

  In recent years, a two-component developer containing at least a carrier and a toner is held by a magnetic force to form a magnetic brush with a carrier contained in the two-component developer on the surface of the developer carrier, and the magnetic brush supplies the toner carrier. A toner layer is formed on the surface of the toner carrier by the toner to be developed, and the electrostatic latent image on the surface of the image carrier is developed as a toner image by flying the toner from the toner layer to the image carrier. Down type (also referred to as hybrid type) developing devices are attracting attention.

  By the way, the large-diameter toner has high chargeability and low adhesion force to the toner carrier, and therefore has good developability. For this reason, in a touch-down developing device, selective development in which large-diameter toner is selectively developed on the image carrier is likely to occur. Therefore, when continuous printing (printing) is performed, small-diameter toner accumulates (remains) on the toner carrier, resulting in a decrease in image density.

  In order to suppress a decrease in image density due to selective development as described above, the difference (voltage difference) between the bias voltage applied to the developer carrying member and the bias voltage applied to the toner carrying member is set to a constant period. In this way, a process for correcting and maintaining the density of the image, so-called calibration, is performed. However, the calibration execution cycle is generally performed about once every several hundreds of prints in order to suppress a decrease in development efficiency (productivity). A decrease in the concentration of is inevitable.

  Therefore, the relationship between the bias voltages applied to the toner carrier and the developer carrier during non-printing is determined according to the relationship between the biased voltages applied to the toner carrier and the small diameter toner remaining on the toner carrier to the developer carrier. Proposal of a developing device that controls the difference in the recovered voltage so that the toner layer formed on the surface of the toner carrier is kept stable and suppresses density reduction and density unevenness due to selective development. (For example, refer to Patent Document 1).

  In addition, by controlling the bias voltage applied to the toner carrier and the developer carrier during non-printing to generate a specific potential difference between the two carriers, a specific toner layer including a small-diameter toner having poor developability is formed. The toner density is accumulated on the surface of the toner carrier, and then the toner carrier is stopped, the toner on the surface of the toner carrier is peeled off, discharged to the image carrier, and discarded. A developing device that suppresses the reduction has also been proposed (see, for example, Patent Document 2).

JP 2005-55840 A JP 2005-99663 A

  However, in the developing device described in Patent Document 1, since the small-diameter toner that has been peeled off to the developer carrier side is collected in the device, the proportion of the small-diameter toner in the two-component developer in the device gradually increases. . In particular, immediately before new toner is replenished in the apparatus, the ratio of the small-diameter toner becomes very large, and the density decreases greatly during that time.

  Further, in the developing device described in Patent Document 2, the toner including the small-diameter toner peeled off from the surface of the toner carrier is discharged to the image carrier side and discarded. As the amount of toner increases, the wasted amount of toner must be replenished, resulting in an increase in running cost.

An object of the present invention is to provide a developing device capable of suppressing a decrease in image density due to selective development in which small-diameter toner accumulates while suppressing an increase in running cost due to wasteful consumption of toner.
Another object of the present invention is to provide an image forming apparatus including the developing device.

  According to the present invention, a developer carrier that forms a magnetic brush by a carrier contained in a two-component developer on a surface by holding a two-component developer including at least a carrier and a toner by a magnetic force, and opposed to the developer carrier. A toner carrier that is disposed and forms a toner layer on the surface with toner supplied from the developer carrier; a first voltage applying unit that applies a first bias voltage to the developer carrier; and the toner carrier. The relationship between the second voltage applying unit for applying the second bias voltage to the first bias voltage applied by the first voltage applying unit and the second bias voltage applied by the second voltage applying unit is as follows. An applied voltage control unit for controlling the first voltage application unit and the second voltage application unit, an environmental temperature and a humidity so as to obtain a voltage difference at which a toner layer having a predetermined thickness is formed on the surface of the toner carrier; A temperature / humidity measuring unit to be measured, and the toner carrier on the basis of an environmental temperature and humidity measured by the temperature / humidity measuring unit and a preset printing rate at the time of non-development after a predetermined number of times of development. Instructing the applied voltage control unit to adjust the voltage difference based on the toner diameter calculated by the toner diameter calculating unit and a toner diameter calculating unit that calculates the toner diameter of the toner layer formed on the surface of the toner layer And a voltage difference adjusting unit.

  Further, the adjustment value of the voltage difference by the voltage difference adjustment unit is preferably obtained by an expression of a predetermined coefficient × (standard toner diameter−toner diameter calculated by the toner diameter calculation unit).

  In addition, the image forming apparatus further includes a developing density detecting unit that detects a developing density by the developing device, and the voltage difference adjusting unit is configured to adjust the voltage difference based on the toner diameter before the development, when the predetermined number of times of development is completed. Preferably, the applied voltage control unit is instructed to feedback-correct the voltage difference to a predetermined development density based on the development density detected by the development density detection unit.

  The voltage difference adjustment unit starts development with a voltage difference feedback-corrected based on the development density detected by the development density detection unit, and based on the toner diameter when the number of developments exceeds a predetermined number. It is preferable to perform adjustment of the voltage difference.

  According to the present invention, an electrostatic latent image is formed on the surface of the developing device, and a toner image is formed on the electrostatic latent image by receiving toner from the toner layer of the developing device. A plurality of image carriers, a transfer unit that directly or indirectly transfers a toner image formed on the image carrier to a sheet-like transfer material, and the transferred toner image on a sheet-like transfer material The present invention relates to an image forming apparatus including a fixing unit for fixing.

According to the present invention, it is possible to provide a developing device capable of suppressing a decrease in image density due to selective development in which small-diameter toner accumulates while suppressing an increase in running cost due to wasteful consumption of toner.
In addition, according to the present invention, an image forming apparatus including the developing device can be provided.

FIG. 3 is a diagram for explaining an arrangement of each component of the copier 1 according to the embodiment of the present invention. FIG. 3 is a cross-sectional view for explaining a configuration of a developing device 16a and a photosensitive drum 2a in the copier according to the present embodiment. 4 is a partially enlarged view showing a state in which a toner layer 193 having a predetermined thickness is formed on the surface of the developing roller 150. FIG. 4 is a partially enlarged view showing a state in which a toner layer 193 having a predetermined thickness is formed on the surface of the developing roller 150. FIG. It is a flowchart which shows operation | movement of the image development apparatus 16a of this embodiment. 6 is a graph showing the relationship between the amount of adhesion and the applied voltage (adjustment value) Vs in toner of each particle size used in the experiment. 5 is a graph showing the relationship between applied voltage (adjustment value) Vs and density ID for toner of each diameter used in the experiment. It is a graph which shows the relationship between the adhesion amount and density | concentration ID of the toner of each diameter used for experiment. It is a graph which shows the change of density ID by the time of continuous development.

Hereinafter, an embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.
With reference to FIG. 1, the overall structure of a copier 1 as an image forming apparatus in the present embodiment will be described. FIG. 1 is a diagram for explaining the arrangement of each component of the copier 1.

As shown in FIG. 1, a copier 1 as an image forming apparatus is disposed on an upper side in the vertical direction Z of the copier 1 and on a lower side of the copier 1 in the vertical direction Z. An apparatus main body M that forms a toner image on a sheet T as a sheet-like image forming material based on image information read by the image reading apparatus 300.
In the description of the copying machine 1, the sub-scanning direction X is also referred to as “left-right direction” of the copying machine 1, and the main scanning direction Y (direction passing through FIG. 1) is also referred to as “front-back direction” of the copying machine 1. The vertical direction Z of the copier 1 is orthogonal to the sub-scanning direction X and the main scanning direction Y.

First, the image reading apparatus 300 will be described.
As shown in FIG. 1, the image reading apparatus 300 includes a lid member 70 and a reading unit 301 that reads an image of a document G.
The lid member 70 is connected to the reading unit 301 so as to be opened and closed by a connecting unit (not shown). The lid member 70 has a function of protecting a reading surface 302A described later.

  The reading unit 301 includes a housing 306 and a reading surface 302 </ b> A disposed on the upper side of the housing 306. The reading unit 301 includes an illumination unit 340 including a light source, a plurality of mirrors 321, 322, and 323, and a first frame 311 and a second frame that move in the sub-scanning direction X in an internal space 304 of the housing 306. A body 312, an imaging lens 357, a CCD 358 as a reading device, and a CCD substrate 361 that performs predetermined processing on image information read by the CCD 358 and outputs the image information to the apparatus body M side. Prepare. The illumination unit 340 and the first mirror 321 are accommodated in the first frame 311. The second mirror 322 and the third mirror 323 are accommodated in the second frame 312.

  The reading surface 302A extends in a direction perpendicular to the sub-scanning direction X and the main scanning direction Y, and extends over most of the sub-scanning direction X in the reading unit 301. The document G is placed on the reading surface 302A. Each of the first frame 311 and the second frame 312 moves in the sub-scanning direction X while keeping the length of an optical path H (optical path length) to be described later constant. Thereby, the image of the original G placed on the reading surface 302A is read.

  In the internal space 304 of the housing 306, the plurality of mirrors 321, 322, and 323 form an optical path H for allowing light from the original G to enter the imaging lens 357. In addition, the first frame 311 moves at a constant speed A in the sub-scanning direction X, and the second frame 312 moves at a constant speed A / 2 in the sub-scanning direction X. The length of H is kept constant. As a result, the image of the original G placed on the reading surface 302A is read on the reading surface 302A.

Next, the apparatus main body M will be described.
The main body M of the apparatus forms an image forming unit GK that forms a predetermined toner image on the paper T based on predetermined image information, and feeds the paper T to the image forming unit GK and discharges the paper T on which the toner image is formed. A paper supply / discharge unit KH for paper.
The outer shape of the apparatus main body M is configured by a case body BD as a casing.

  As shown in FIG. 1, the image forming unit GK includes photosensitive drums 2a, 2b, 2c, and 2d as image carriers (photosensitive members), charging units 10a, 10b, 10c, and 10d, and a laser as an exposure unit. Scanner units 4a, 4b, 4c, 4d, developing devices 16a, 16b, 16c, 16d, toner cartridges 5a, 5b, 5c, 5d, toner supply units 6a, 6b, 6c, 6d, drum cleaning unit 11a, 11b, 11c, 11d, static eliminators 12a, 12b, 12c, 12d, intermediate transfer belt 7, primary transfer rollers 37a, 37b, 37c, 37d, secondary transfer roller 8, counter roller 18, fixing Part 9.

  As shown in FIG. 1, the paper feed / discharge unit KH includes a paper feed cassette 52, a manual paper feed unit 64, a transport path L for paper T, a registration roller pair 80, a first paper discharge unit 50a, 2 paper discharge unit 50b. As will be described later, the transport path L includes a first transport path L1, a second transport path L2, a third transport path L3, a manual transport path La, a return transport path Lb, and a post-processing transport path Lc. Is a collection of

Hereinafter, each configuration of the image forming unit GK and the paper supply / discharge unit KH will be described in detail.
First, the image forming unit GK will be described.
In the image forming unit GK, charging by the charging units 10a, 10b, 10c, and 10d in order from the upstream side to the downstream side along the respective surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, and the laser scanner units 4a, 4b, 4c, 4d exposure, development devices 16a, 16b, 16c, 16d development, intermediate transfer belt 7 and primary transfer rollers 37a, 37b, 37c, 37d primary transfer, static eliminators 12a, 12b, 12c, 12d And cleaning by the drum cleaning units 11a, 11b, 11c, and 11d.
Further, in the image forming unit GK, secondary transfer by the intermediate transfer belt 7, the secondary transfer roller 8 and the counter roller 18, and fixing by the fixing unit 9 are performed.

  Each of the photosensitive drums 2a, 2b, 2c, and 2d is formed of a cylindrical member and functions as a photosensitive member or an image carrier. Each of the photosensitive drums 2 a, 2 b, 2 c, and 2 d is disposed so as to be rotatable in the direction of an arrow about an axis that extends in a direction orthogonal to the traveling direction of the intermediate transfer belt 7. An electrostatic latent image can be formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d.

  Each of the charging units 10a, 10b, 10c, and 10d is disposed to face the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the charging units 10a, 10b, 10c, and 10d uniformly charges the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d negatively (minus polarity) or positively (plus polarity).

  The laser scanner units 4a, 4b, 4c, and 4d function as exposure units, and are spaced apart from the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the laser scanner units 4a, 4b, 4c, and 4d includes a laser light source (not shown), a polygon mirror, a polygon mirror driving motor, and the like.

  Each of the laser scanner units 4a, 4b, 4c, and 4d scans and exposes the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d based on image information related to the image read by the reading unit 301. The scanning exposure is performed by each of the laser scanner units 4a, 4b, 4c, and 4d, thereby removing the charges on the exposed portions of the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Thereby, electrostatic latent images are formed on the respective surfaces of the photosensitive drums 2a, 2b, 2c, and 2d.

  The developing devices 16a, 16b, 16c, and 16d are provided corresponding to the photosensitive drums 2a, 2b, 2c, and 2d, respectively, and are disposed to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d. Each of the developing devices 16a, 16b, 16c, and 16d attaches toner of each color to the electrostatic latent image formed on the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d, and transfers a color toner image to the photosensitive drum. 2a, 2b, 2c and 2d are formed on the respective surfaces. Each of the developing devices 16a, 16b, 16c, and 16d corresponds to four colors of yellow, cyan, magenta, and black. Details of the developing devices 16a, 16b, 16c, and 16d will be described later.

  The toner cartridges 5a, 5b, 5c, and 5d are provided corresponding to the developing devices 16a, 16b, 16c, and 16d, respectively, and the toners of the respective colors supplied to the developing devices 16a, 16b, 16c, and 16d, respectively. To accommodate. Each of the toner cartridges 5a, 5b, 5c, and 5d accommodates yellow toner, cyan toner, magenta toner, and black toner.

  The toner supply units 6a, 6b, 6c, and 6d are provided corresponding to the toner cartridges 5a, 5b, 5c, and 5d and the developing devices 16a, 16b, 16c, and 16d, respectively. The toners of the respective colors accommodated in 5d are supplied to the developing devices 16a, 16b, 16c, and 16d, respectively. Each of the toner supply units 6a, 6b, 6c, and 6d is connected to each of the developing devices 16a, 16b, 16c, and 16d by a toner supply path (not shown).

  To the intermediate transfer belt 7, the toner images of the respective colors formed on the photosensitive drums 2a, 2b, 2c, and 2d are sequentially primary-transferred. The intermediate transfer belt 7 is stretched around a driven roller 35, a counter roller 18 including a driving roller, a tension roller 36, and the like. Since the tension roller 36 biases the intermediate transfer belt 7 from the inside to the outside, a predetermined tension is applied to the intermediate transfer belt 7.

  Primary transfer rollers 37a, 37b, 37c, and 37d are arranged to face each other on the side opposite to the photosensitive drums 2a, 2b, 2c, and 2d with the intermediate transfer belt 7 interposed therebetween.

  A predetermined portion of the intermediate transfer belt 7 is sandwiched between the primary transfer rollers 37a, 37b, 37c, and 37d and the photosensitive drums 2a, 2b, 2c, and 2d, respectively. The predetermined portion thus sandwiched is pressed against the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d. Primary transfer nips N1a, N1b, N1c, and N1d are formed between the photosensitive drums 2a, 2b, 2c, and 2d and the primary transfer rollers 37a, 37b, 37c, and 37d, respectively. In each of the primary transfer nips N1a, N1b, N1c, and N1d, the toner images of the respective colors developed on the photosensitive drums 2a, 2b, 2c, and 2d are sequentially primary-transferred onto the intermediate transfer belt 7, respectively. As a result, a full-color toner image is formed on the intermediate transfer belt 7.

  To the primary transfer rollers 37a, 37b, 37c, and 37d, toner images of the respective colors formed on the photosensitive drums 2a, 2b, 2c, and 2d are respectively transferred to the intermediate transfer belt 7 by a primary transfer bias applying unit (not shown). A primary transfer bias for transferring the toner image is applied.

  The static eliminators 12a, 12b, 12c, and 12d are arranged to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively. The static eliminators 12a, 12b, 12c, and 12d respectively irradiate the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d to irradiate light, and the photosensitive drums 2a, 2b, and 2c after primary transfer is performed. 2d, each surface is neutralized (charge is removed).

  The drum cleaning units 11a, 11b, 11c, and 11d are disposed to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, respectively. Each of the drum cleaning units 11a, 11b, 11c, and 11d removes toner and adhering matter remaining on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, and conveys the removed toner to a predetermined recovery mechanism. And collect it.

  The secondary transfer roller 8 secondarily transfers the full-color toner image primarily transferred to the intermediate transfer belt 7 onto the paper T. A secondary transfer bias for transferring the full color toner image formed on the intermediate transfer belt 7 to the paper T is applied to the secondary transfer roller 8 by a secondary transfer bias applying unit (not shown).

  The secondary transfer roller 8 contacts or separates from the intermediate transfer belt 7. Specifically, the secondary transfer roller 8 is configured to be movable between a contact position where the secondary transfer roller 8 is in contact with the intermediate transfer belt 7 and a spaced position where the secondary transfer roller 8 is separated from the intermediate transfer belt 7. Specifically, the secondary transfer roller 8 is disposed at the contact position when the full-color toner image primarily transferred onto the surface of the intermediate transfer belt 7 is secondarily transferred to the paper T, and in other cases. Are arranged at spaced positions.

  A counter roller 18 is disposed on the opposite side of the intermediate transfer belt 7 from the secondary transfer roller 8. A predetermined portion of the intermediate transfer belt 7 is sandwiched between the secondary transfer roller 8 and the opposing roller 18. Then, the paper T is pressed against the outer surface of the intermediate transfer belt 7 (the surface on which the toner image is primarily transferred). A secondary transfer nip N <b> 2 is formed between the intermediate transfer belt 7 and the secondary transfer roller 8. In the secondary transfer nip N2, the full-color toner image primarily transferred to the intermediate transfer belt 7 is secondarily transferred to the paper T.

  The fixing unit 9 melts and heats the toner of each color constituting the toner image secondarily transferred onto the paper T and fixes the toner on the paper T. The fixing unit 9 includes a heating rotator 9a heated by a heater and a pressure rotator 9b pressed against the heating rotator 9a. The heating rotator 9a and the pressure rotator 9b sandwich and pressurize the paper T onto which the toner image has been secondarily transferred, and convey the paper T. When the paper T is conveyed in a state of being sandwiched between the heating rotator 9a and the pressure rotator 9b, the toner transferred to the paper T is fixed to the paper T by being melted and pressed. Is done.

Next, the paper supply / discharge unit KH will be described.
As shown in FIG. 1, in the lower part of the apparatus main body M, two paper feed cassettes 52 that store paper T are arranged in an up-down direction. The paper feed cassette 52 is configured to be pulled out from the housing of the apparatus main body M in the horizontal direction. In the paper feed cassette 52, a placement plate 60 on which the paper T is placed is disposed. In the paper feed cassette 52, the paper T is stored in a state of being stacked on the placement plate 60. The paper T placed on the placement plate 60 is sent out to the transport path L by the cassette paper feed unit 51 arranged at the end of the paper feed cassette 52 on the paper feed side (the left end in FIG. 1). The cassette paper feed unit 51 includes a forward feed roller 61 for taking out the paper T on the placement plate 60 and a paper feed roller pair 63 for feeding the paper T one by one to the transport path L. Is provided.

  A manual paper feed unit 64 is provided on the right side surface (right side in FIG. 1) of the apparatus main body M. The manual paper feed unit 64 is provided mainly for supplying the apparatus main body M with a paper T of a size and type different from the paper T set in the paper feed cassette 52. The manual paper feed unit 64 includes a manual feed tray 65 that constitutes a part of the right side surface of the apparatus main body M in the closed state, and a paper feed roller 66 as a feed roller. The manual feed tray 65 functions as a placement portion on which one or a plurality of sheets T can be placed in the open state, and a lower end of the manual feed tray 65 is attached to the vicinity of the paper feed roller 66 so as to be rotatable (openable and closable). The paper feed roller 66 sends out (feeds) the paper T placed on the open manual feed tray 65 toward the manual feed path La inside the housing 306.

  A first paper discharge unit 50 a and a second paper discharge unit 50 b are provided on the upper side of the apparatus main body M. The first paper discharge unit 50a and the second paper discharge unit 50b discharge the paper T to the outside of the apparatus main body M. Details of the first paper discharge unit 50a and the second paper discharge unit 50b will be described later.

  The conveyance path L for conveying the paper T includes a first conveyance path L1 from the cassette paper feeding unit 51 to the secondary transfer nip N2, a second conveyance path L2 from the secondary transfer nip N2 to the fixing unit 9, and a fixing unit. 9 to the first paper discharge section 50a, the manual conveyance path La for joining the paper supplied from the manual paper feed section 64 to the first conveyance path L1, and the third conveyance path L3 on the upstream side. The paper transported from the upstream side to the downstream side is reversed and returned to the first transport path L1, and the paper transporting the third transport path L3 from the upstream side to the downstream side is connected to the second paper discharge unit 50b. And a post-processing transport path Lc for transporting to a post-processing device (not shown).

Moreover, the 1st junction part P1 and the 2nd junction part P2 are provided in the middle of the 1st conveyance path L1. A first branch portion Q1 is provided in the middle of the third transport path L3.
The first joining part P1 is a joining part where the manual feed path La joins the first transport path L1. The second junction P2 is a junction where the return conveyance path Lb merges with the first conveyance path L1.
The first branch portion Q1 is a branch portion where the post-processing transport path Lc branches from the third transport path L3. A rectifying member 58 is provided in the first branch portion Q1. The rectifying member 58 rectifies the transport direction of the paper T carried out from the fixing unit 9 to the third transport path L3 toward the first paper discharge section 50a or the post-processing transport path Lc toward the second paper discharge section 50b ( Switch).

  In the middle of the first transport path L1 (specifically, between the second joining portion P2 and the secondary transfer roller 8), a sensor for detecting the paper T and correction of the skew (oblique paper feeding) of the paper T In addition, a registration roller pair 80 is arranged for matching the timing with the formation of the toner image in the image forming unit GK. The sensor is disposed immediately before the registration roller pair 80 in the transport direction of the paper T (upstream in the transport direction). The registration roller pair 80 conveys the paper T by performing the above-described correction and timing adjustment based on detection signal information from the sensor.

  The return conveyance path Lb is a conveyance path that is provided to make the opposite surface (unprinted surface) opposite to the already printed surface to the intermediate transfer belt 7 when performing duplex printing on the paper T. According to the return conveyance path Lb, the sheet T conveyed from the first branching section Q1 to the first sheet discharge section 50a is turned upside down and returned to the first conveyance path L1 to the upstream side of the secondary transfer roller 8. It can be conveyed upstream of the registered registration roller pair 80. A predetermined toner image is transferred onto the unprinted surface in the secondary transfer nip N2 on the paper T that is reversed upside down by the return conveyance path Lb.

  A first paper discharge unit 50a is formed at the end of the third transport path L3. The first paper discharge unit 50 a is disposed on the upper side of the apparatus main body M. The first paper discharge unit 50a is open toward the right side surface of the apparatus main body M (the right side in FIG. 1, the manual paper feed unit 64 side). The first paper discharge unit 50a discharges the paper T transported through the third transport path L3 to the outside of the apparatus main body M.

  On the opening side of the first paper discharge section 50a, a paper discharge stacking section M1 is formed. The paper discharge stacking unit M1 is formed on the upper surface (outer surface) of the apparatus main body M. The paper discharge stacking unit M1 is a part formed by the upper surface of the apparatus main body M being depressed downward. The bottom surface of the paper discharge stacking unit M1 constitutes a part of the top surface of the apparatus main body M. In the paper discharge stacking unit M1, sheets T formed with a predetermined toner image and discharged from the first paper discharge unit 50a are stacked and stacked.

A second paper discharge unit 50b is formed at the end of the post-processing conveyance path Lc. The second paper discharge unit 50b is disposed on the upper side of the apparatus main body M. The second paper discharge section 50b opens toward the left side of the apparatus main body M (left side in FIG. 1, the side to which the post-processing apparatus is connected). The second paper discharge unit 50b discharges the paper T conveyed through the post-processing conveyance path Lc to the outside of the apparatus main body M.
A post-processing device (not shown) is connected to the opening side of the second paper discharge unit 50b. The post-processing device performs post-processing (stapling, punching, etc.) of paper ejected from the image forming apparatus (copy machine 1).
A paper detection sensor is disposed at a predetermined position on each conveyance path.

Next, a paper jam (JAM) in the main transport path L1 to L3 (the first transport path L1, the second transport path L2, and the third transport path L3 are collectively referred to as “main transport path” hereinafter) and the return transport path Lb. A structure for eliminating the problem will be briefly described.
As shown in FIG. 1, on the left side surface of the apparatus main body M (left side in FIG. 1), main conveyance paths L1 to L3 and a return conveyance path Lb are arranged in parallel so as to mainly extend in the vertical direction. A cover body 40 is provided on the left side of the apparatus body M (left side in FIG. 1) so as to form a part of the side surface of the apparatus body M. The cover body 40 is connected to the apparatus main body M via a fulcrum shaft 43 at the lower end thereof. The fulcrum shaft 43 is disposed along the direction in which the axial direction crosses the main transport paths L1 to L3 and the return transport path Lb. The cover body 40 is configured to be rotatable between a closed position (position shown in FIG. 1) and an open position (not shown) with the fulcrum shaft 43 as a center.

  The cover body 40 includes a first cover portion 41 that is rotatably connected to the apparatus main body M by a fulcrum shaft 43, and a second cover portion 42 that is rotatably connected to the apparatus main body M by the same fulcrum shaft 43. It consists of and. The first cover portion 41 is located on the outer side (side surface side) of the apparatus main body M than the second cover portion 42. In FIG. 1, the hatched portion with the left-down dashed line is the first cover portion 41, and the hatched portion with the right-down dashed line is the second cover portion 42.

In the state where the cover body 40 is located at the closed position, the outer surface side of the first cover portion 41 forms a part of the outer surface (side surface) of the apparatus main body M.
In the state where the cover body 40 is located at the closed position, the inner surface side (the apparatus main body M side) of the second cover portion 42 forms part of the main transport paths L1 to L3.
Further, in a state where the cover body 40 is located at the closed position, the inner surface side of the first cover portion 41 and the outer surface side of the second cover portion 42 form at least a part of the return conveyance path Lb. That is, the return conveyance path Lb is formed between the first cover part 41 and the second cover part 42.

  The copying machine 1 of the present embodiment includes the cover body 40 having such a configuration, so that when a paper jam (JAM) occurs in the main transport paths L1 to L3, the cover body 40 is closed as shown in FIG. By rotating from the position to an open position (not shown) to open the main transport paths L1 to L3, it is possible to process paper jammed in the main transport paths L1 to L3. On the other hand, when a paper jam occurs in the return conveyance path Lb, the cover body 40 is rotated to the open position, and then the second cover portion 42 is moved to the apparatus main body M side (right side in FIG. ) To open the return conveyance path Lb, the paper jammed in the return conveyance path Lb can be processed.

  Next, a configuration related to the developing devices 16a, 16b, 16c, and 16d, which is a characteristic part of the copier 1 of the present embodiment, will be described with reference to FIGS. As described above, the copying machine 1 includes the four developing devices 16a, 16b, 16c, and 16d. Since the copier 1 has the same configuration, the developing device 16a is described as a representative here. To do.

  FIG. 2 is a cross-sectional view for explaining the configuration of the developing device 16a and the photosensitive drum 2a in the copier of the present embodiment. FIG. 3 is a partially enlarged view showing a state in which a toner layer 193 having a predetermined thickness is formed on the surface of the developing roller 150. FIG. 4 is a partially enlarged view showing a state in which a toner layer 193 having a predetermined thickness is formed on the surface of the developing roller 150.

  As shown in FIGS. 2 and 3, the developing device 16 a of this embodiment includes a developing container 110 that contains a two-component developer including at least a magnetic carrier and toner, and an agitation roller 120 a that is disposed inside the developing container 110. , 120b, a magnetic roller 130 as a developer carrying member disposed above the one stirring roller 120a in the vertical direction, and a side of the magnetic roller 130 (on the left side in FIG. 2) close to the magnetic roller 130. A layer thickness regulating blade 140, a toner scattering prevention cover member 141 disposed above the layer thickness regulating blade 140 in the vertical direction, and a developing roller 150 as a toner carrier disposed facing the magnetic roller 130. , Rotation detection unit 251, development density detection unit 291, first voltage application unit 261, second voltage application unit 262, environmental temperature And a temperature and humidity measuring unit 252 for measuring the humidity, and the control unit 270, a storage unit 280, a.

To the developing container 110, the toner 192 is supplied from the toner cartridge 5a (see FIG. 1) via the toner supply unit 6a (see FIG. 1).
The stirring rollers 120a and 120b stir the two-component developer 190 stored in the developing container 110. In the stirred two-component developer 190, static electricity is generated by friction, the magnetic carrier 191 is negatively charged, and the toner 192 is positively charged. Further, the toner 192 adheres to the magnetic carrier 191 due to electrostatic force.

The magnetic roller 130 includes a magnetic sleeve 131 that can rotate in a predetermined direction and forms the surface of the magnetic roller 130, and a plurality of magnetic roller magnetic pole members 132 to 137 disposed inside the magnetic sleeve 131.
The magnetic sleeve 131 has a cylindrical shape and is made of a nonmagnetic member. The magnetic sleeve 131 is rotationally driven in the direction of arrow B shown in FIGS. A predetermined first bias voltage V1 is applied to the magnetic sleeve 131 by a first voltage application unit 261 described later.

As shown in FIGS. 2 and 3, the plurality of magnetic roller magnetic pole members 132 to 137 are fixed inside the magnetic sleeve 131 at predetermined intervals in the circumferential direction.
The magnetic roller magnetic pole member 132 is disposed corresponding to a portion of the magnetic roller 130 that is closest to a developing sleeve 151 described later. The magnetic roller magnetic pole member 132 is disposed so that the N pole is located on the outer side (the peripheral surface side of the magnetic sleeve 131).

  As shown in FIG. 3, a part of the two-component developer 190 accommodated in the developing container 110 is held on the surface of the magnetic sleeve 131 by the magnetic force of the magnetic roller magnetic pole members 132 to 137. A part of the two-component developer 190 held on the surface of the magnetic roller 130 forms a developer layer (magnetic brush) 194.

  The layer thickness regulating blade 140 regulates the layer thickness of the developer layer 194 formed on the surface of the magnetic roller 130. That is, the layer thickness regulating blade 140 regulates the layer thickness (height) of the developer layer 194 formed by the two-component developer 190 held by the magnetic roller 130 and passes through the layer thickness regulating blade 140. The layer thickness of the developer layer 194 is kept constant. The layer thickness regulating blade 140 is made of a plate-like member, and is arranged so that the tip portion 142 side faces and is close to the surface of the magnetic sleeve 131. A predetermined gap (gap) is formed between the tip 142 of the layer thickness regulating blade 140 and the surface of the magnetic sleeve 131.

  The toner scattering prevention cover member 141 is a member constituting a part of the case body of the developing device 16a. The toner scattering prevention cover member 141 is disposed above the layer thickness regulating blade 140 in the vertical direction and on the side of the magnetic roller 130 (left side in FIG. 2). The toner scattering prevention cover member 141 prevents the toner 192 from scattering outside the developing device 16a.

  The developing roller 150 is disposed to face the magnetic roller 130. A toner layer 193 is formed on the surface of the developing roller 150 by the toner 192 moved from the magnetic roller 130. Specifically, the toner layer 193 is formed on the surface of the developing roller 150 by moving the toner 192 from the developer layer (magnetic brush) 194 whose layer thickness is regulated by the layer thickness regulating blade 140. The developing roller 150 includes a developing sleeve 151 that forms the surface of the developing roller 150, and a developing roller magnetic pole member 152 that is disposed inside the developing sleeve 151.

  The developing sleeve 151 has a cylindrical shape and is made of a nonmagnetic member. The surface of the developing sleeve 151 is covered with a resin layer (not shown) containing a resistance adjusting agent. The developing sleeve 151 rotates at a position facing the magnetic sleeve 131 so that the moving direction of the developing sleeve 151 is opposite to the moving direction of the magnetic sleeve 131 (the direction of the arrow C shown in FIGS. 2 and 3). Driven. Here, a predetermined second bias voltage V <b> 2 is applied to the developing sleeve 151 by a second voltage applying unit 262 described later.

  The developing roller magnetic pole member 152 is disposed in the developing sleeve 151 so as to face the first magnetic roller magnetic pole member 132. The developing roller magnetic pole member 152 is disposed corresponding to the portion of the developing roller 150 closest to the magnetic sleeve 131. In other words, the developing roller magnetic pole member 152 and the first magnetic roller magnetic pole member 132 are disposed to face each other across the region where the developing sleeve 151 and the magnetic sleeve 131 are closest to each other.

  The developing roller magnetic pole member 152 has a polarity different from the outer polarity of the first magnetic roller magnetic pole member 132 at the end facing the first magnetic roller magnetic pole member 132. That is, the developing roller magnetic pole member 152 is disposed so that the S pole is located on the outer side (the peripheral surface side of the developing sleeve 151). A magnetic field 171 is formed between the first magnetic roller magnetic pole member 132 disposed in the magnetic roller 130 and the developing roller magnetic pole member 152 disposed in the developing roller 150. In the region where the magnetic field 171 is formed between the magnetic roller 130 and the developing roller 150, the developer layer 194 rises from the surface of the magnetic roller 130 under the influence of the magnetic field 171, forms a magnetic brush, and develops. Contact the roller 150.

Next, a configuration related to control in the developing device 16a of the present embodiment will be described in detail.
As shown in FIG. 2, the first voltage application unit 261 receives the control signal output from the application voltage control unit 271 described later, and applies the first bias voltage V <b> 1 to the magnetic roller 130.
The second voltage application unit 262 applies a second bias voltage V2 to the developing roller 150 in response to a control signal output from an application voltage control unit 271 described later.
Due to the voltage difference (bias voltage difference VB) between the first bias voltage V1 applied to the magnetic roller 130 and the second bias voltage V2 applied to the developing roller 150, the magnetic roller 130 and the developing roller 150 are An electric field for moving the toner 192 is generated. The bias voltage difference VB is a voltage difference between the first bias voltage V1 and the second bias voltage V2 when the first bias voltage V1 is used as a reference.

  As shown in FIG. 2, the rotation detector 251 detects the rotation of the developing roller 150. The rotation detection unit 251 detects that the developing roller 150 has started to rotate, and outputs a detection signal to the control unit 270.

  As shown in FIG. 2, the temperature / humidity measurement unit 252 measures the environmental temperature and humidity in the developing device 16 a and outputs a measurement signal to the toner diameter calculation unit 272.

  As shown in FIG. 2, the development density detector 291 detects the density of the patch 292 attached to the surface of the photosensitive drum 2 a and outputs a density detection signal to the controller 270.

  As shown in FIG. 2, the control unit 270 includes an applied voltage control unit 271, a toner diameter calculation unit 272, a voltage difference adjustment unit 273, a counter 274, a continuous development (printing) determination unit 275, and a normal mode control. Part 276.

  The counter 274 receives the detection signal from the rotation detection unit 251, counts the number of developments (number of printed sheets), and outputs the count signal to the continuous development (printing) determination unit 275.

  The continuous development (printing) determination unit 275 determines whether there is an instruction for continuous development (printing) to the copier 1.

  The normal mode control unit 276 outputs a control signal to the application voltage control unit 271 to instruct the application voltage control unit 271 so that the bias voltage difference VB is the first voltage difference VB1 in the normal development mode.

  The toner diameter calculation unit 272 is set in advance with the environmental temperature and humidity measured by the temperature / humidity measurement unit 252 during non-development (non-printing) after a predetermined number of developments (predetermined number of prints) has been completed. Based on the printing rate (development rate) stored in the storage unit 280, the toner diameter in the toner layer 193 formed on the surface of the developing roller 150 is calculated, and a calculation signal is output to the voltage difference adjustment unit 273.

The voltage difference adjustment unit 273 is detected by the development density detection unit 291 before adjusting the voltage difference based on the toner diameter at the time of non-development (non-printing) after a predetermined number of developments (printing a predetermined number of sheets). Based on the developing density, the applied voltage control unit 271 is instructed to feedback-correct the voltage difference to a predetermined developing density. More specifically, the voltage difference adjustment unit 273 receives the density detection signal from the development density detection unit 291 and adjusts the bias voltage difference VB before adjusting the voltage difference based on the toner diameter during non-development (non-printing). A control signal is output to the applied voltage control unit 271 so that the second voltage difference VB2 is set, and the applied voltage control unit 271 is instructed.
Further, the voltage difference adjustment unit 273 receives the calculation signal output from the toner diameter calculation unit 272 (based on the toner diameter calculated by the toner diameter calculation unit 272), and changes the bias voltage difference VB to the third voltage difference VB3. The control signal is output to the applied voltage control unit 271 so that the applied voltage control unit 271 is instructed.

  Further, the voltage difference adjustment unit 273 starts development with the second voltage difference VB2 that is feedback-corrected based on the development density detected by the development density detection unit 291, and the number of developments (number of prints) is a predetermined number of times (predetermined printing). When the number exceeds the number of sheets), the voltage difference is adjusted to obtain the third voltage difference VB3 based on the toner diameter calculated by the toner diameter calculating unit 272. The predetermined number of development times (number of printed sheets) is, for example, about 10 to 15 times (10 to 15 sheets).

The voltage difference adjustment value Vs for obtaining the third voltage difference VB3 in the voltage difference adjustment unit 273 is obtained by the following equation (1).
Vs = K × (standard toner diameter−toner diameter calculated by toner diameter calculator 272) (1)
Note that K is a predetermined coefficient, and K will be described in detail in an embodiment described later.

  The applied voltage control unit 271 receives the control signal output from the normal mode control unit 276 and the control signal output from the voltage difference adjustment unit 273, and controls the first voltage application unit 261 and the second voltage application unit 262. Is output.

When the bias voltage difference VB is the first voltage difference VB1, an electric field for moving a predetermined amount of toner 192 from the magnetic roller 130 toward the developing roller 150 is generated between the magnetic roller 130 and the developing roller 150. .
In the case where the bias voltage difference VB is adjusted to the second voltage difference VB2, a larger amount between the magnetic roller 130 and the developing roller 150 from the magnetic roller 130 toward the developing roller 150 than in the case of the first voltage difference VB1. An electric field for moving the amount of toner 192 is generated, and feedback (feedback) correction is performed so that the development density (print density) becomes a predetermined density.
When the bias voltage difference VB is adjusted to the third voltage difference VB3, the transition of density change during development after the completion of the predetermined number of developments is predicted so that the feedback corrected development density does not fall below a certain level. Next, feed forward (sequence) correction is performed.

  As shown in FIG. 4, after a lapse of a predetermined time when the bias voltage difference VB is set to the first voltage difference VB1, the movement of the toner 192 is in an equilibrium state where the toner 192 does not move between the magnetic roller 130 and the developing roller 150. That is, the equilibrium state of the movement of the toner 192 balances the movement of the toner 192 in the direction from the magnetic roller 130 toward the developing roller 150 and the movement of the toner 192 in the direction from the developing roller 150 toward the magnetic roller 130. It is in a state.

  When the bias voltage difference VB changes from this equilibrium state, the toner 192 can move from the magnetic roller 130 to the developing roller 150 or from the developing roller 150 to the magnetic roller 130. For example, when the equilibrium state in the first voltage difference VB1 is changed to the bias voltage difference VB larger than the first voltage difference VB1, the positively charged toner 192 is moved from the developing roller 150 to the magnetic roller 130. When the bias voltage difference VB smaller than the first voltage difference VB1 is changed from the equilibrium state in the first voltage difference VB1, the positively charged toner 192 is moved from the magnetic roller 130 to the developing roller 150.

As illustrated in FIG. 2, the storage unit 280 includes a bias voltage difference storage unit 281 and a development rate (printing rate) storage unit 282.
The bias voltage difference storage unit 281 stores voltage information related to the first bias voltage V1 and the second bias voltage V2 for setting the bias voltage difference VB to the first voltage difference VB1, the second voltage difference VB2, or the third voltage difference VB3. It is remembered.
The development rate (print rate) storage unit 282 stores a development rate (print rate) set by the user prior to the start of development (image formation start).

  Next, a specific operation of the developing device 16a of the present embodiment will be described with reference to FIGS. FIG. 5 is a flowchart showing the operation of the developing device 16a of this embodiment.

  First, as shown in FIG. 5, when the power of the copier 1 is turned on by the user in step ST1, the process proceeds to step ST2.

  Next, in step ST2, the normal mode control unit 276 outputs a control signal to the applied voltage control unit 271 so that the bias voltage difference VB between the magnetic roller 130 and the developing roller 150 is the first voltage difference VB1. Then instruct.

  In step ST2, as shown in FIGS. 2 and 3, the two-component developer 190 is first stirred by the stirring rollers 120a and 120b. Accordingly, static electricity due to friction is generated in the stirred two-component developer 190. The magnetic carrier 191 is negatively charged, and the toner 192 is positively charged. Further, the toner 192 adheres to the magnetic carrier 191 due to electrostatic force.

As shown in FIG. 3, the two-component developer 190 is held on the surface of the magnetic roller 130 that rotates in the rotation direction B by the magnetic force of the magnetic roller magnetic pole members 132 to 137 disposed inside the magnetic sleeve 131. A developer layer (magnetic carrier) 194 is formed on the surface of the magnetic roller 130 by the magnetic force of the magnetic roller magnetic pole members 134 to 137.
The developer layer 194 formed on the surface of the magnetic roller 130 rotates with the rotation of the magnetic sleeve 131, contacts the layer thickness regulating blade 140, and is regulated to a predetermined layer thickness.

  The developer layer 194 regulated to a predetermined layer thickness by the layer thickness regulating blade 140 moves to the vicinity of the position where the magnetic roller 130 and the developing roller 150 face each other, and is located in the region where the magnetic field 171 is formed. In this region, the developer layer 194 rises under the influence of the magnetic field 171, forms a magnetic brush, and contacts the developing roller 150.

  As a result, as shown in FIGS. 2 to 4, most of the positively charged toner 192 out of the two-component developer 190 held on the surface of the magnetic roller 130 has an electric field caused by the first voltage difference VB1. Under the influence, it is transferred to the developing roller 150 side. As a result, a toner layer 193 is formed on the surface of the developing roller 150. Thereafter, the process proceeds to step ST3.

  In step ST3, the user instructs the copier 1 to form (print) an image on the paper T. In response to an instruction to print an image on the paper T in step ST3, an operation for printing an image on the paper T by the copying machine 1 is started. Thereby, a process progresses to step ST4.

  As shown in FIGS. 4 and 5, in step ST4, the developing device 16a develops the electrostatic latent image formed on the photosensitive drum 2a with the toner layer 193 formed on the developing roller. Specifically, the surface of the developing roller 150 on which the toner layer 193 is formed faces the surface of the photosensitive drum 2a. The electrostatic latent image is developed by the potential difference between the developing roller 150 and the photosensitive drum 2a. That is, an electrostatic latent image is formed on the surface of the photosensitive drum 2a, and a toner image is formed on the electrostatic latent image upon receiving toner from the toner layer 193 of the developing device 16a.

As shown in FIG. 1, the toner images developed on the photosensitive drum 2 a are sequentially primary transferred onto the intermediate transfer belt 7. The toner image primarily transferred to the intermediate transfer belt 7 is secondarily transferred to the paper T by the secondary transfer roller 8. The toner image secondarily transferred onto the paper T is conveyed to the fixing unit 9 and fixed on the paper T by the fixing unit 9.
Thereafter, the paper T is transported to the first paper discharge unit 50a through the third transport path L3, and is discharged from the first paper discharge unit 50a to the paper discharge stacking unit M1. In this way, printing of the paper T by the copying machine 1 is completed.

Next, as shown in FIG. 5, in step ST <b> 5, the continuous development (printing) determination unit 275 determines whether or not the predetermined number of developments (predetermined number of printings) has been completed based on the count value counted by the counter 274. Determine. When the continuous development (printing) determination unit 275 determines that the predetermined number of developments (predetermined number of printings) has been completed (ST5: YES), the development density detection unit 291 is placed on the surface of the photosensitive drum 2a. The density detection signal of the pasted patch 292 is output to the control unit 270. Thereby, a process progresses to step ST6.
On the other hand, when the continuous development (printing) determination unit 275 determines that the predetermined number of times of development (predetermined number of prints) has not been completed in step ST5 (ST5: NO), the process returns to step ST2.

  In step ST6, the voltage difference adjustment unit 273 of the control unit 270 determines the bias voltage difference VB between the magnetic roller 130 and the development roller 150 based on the density detection signal from the development density detection unit 291 as the bias of the storage unit 280. The applied voltage control unit 271 is instructed to set the second voltage difference VB2 stored in the voltage difference storage unit 281. By this instruction, the development density is feedback corrected to a predetermined density set in advance. Thereafter, the process proceeds to step ST7.

  In step ST7, development by the developing device 16a is started in the state of the second voltage difference VB2 in which the development density is feedback-corrected. Thereafter, the process proceeds to step ST8.

  In step ST8, the environmental temperature and humidity measured by the temperature / humidity measuring unit 252 and the developing rate (printing rate) stored in the developing rate (printing rate) storage unit 282 of the storage unit 280 are the toner diameter calculating unit. 272 is read.

  The toner diameter calculation unit 272 calculates the toner diameter of the toner layer 193 formed on the surface of the developing roller 150 based on the read environmental temperature and humidity and the development rate (printing rate), and adjusts the voltage difference between the calculation signals. To the unit 273.

  Next, as shown in FIG. 5, in step ST <b> 9, the continuous development (printing) determination unit 275 determines whether or not the number of times of development (number of printed sheets) at the second voltage difference VB <b> 2 has exceeded a predetermined number of times (predetermined number of sheets). judge. If the continuous development (printing) determination unit 275 determines that the number of times of development (number of printed sheets) has exceeded the predetermined number of times (predetermined number of sheets) (ST9: YES), the process proceeds to step ST10. On the other hand, when the continuous development (printing) determination unit 275 determines that the number of development times (number of printed sheets) does not exceed the predetermined number of times (predetermined number of sheets) (ST9: NO), the process returns to step ST7.

In step ST10, the voltage difference adjustment unit 273 adjusts the voltage difference so that the bias voltage difference VB becomes the third voltage difference VB3 based on the toner diameter calculated by the toner diameter calculation unit 272. The voltage difference adjustment value Vs for obtaining the third voltage difference VB3 by the voltage difference adjustment unit 273 is obtained by the above-described equation (1).
As a result, the development density is feedforward adjusted (corrected) so that the development of the density change during the development after the completion of the predetermined number of developments (end of the predetermined number of prints) is predicted and the development density does not decrease below a certain level. Will be.

  After that, in step ST11, the continuous development (printing) determination unit 275 determines whether or not there is an instruction for continuous development (printing) for a predetermined number of times (predetermined number of sheets) or more. If the continuous development (printing) determination unit 275 determines that there is an instruction for development (printing) that continues for a predetermined number of times (predetermined number) (ST11: YES), the process returns to step ST7. When the continuous development (printing) determination unit 275 determines that the copying machine 1 has not been instructed to perform development (printing) for a predetermined number of times (predetermined number of sheets) or more (ST11: NO), the photosensitive drum by the developing device 16a. The toner image is not continuously formed on 2a, and the process proceeds to step ST12.

  As shown in FIG. 5, in step ST12, the normal development mode ends, and the process returns to step ST2.

  As described above, according to the present embodiment, the magnetic roller based on the density detection signal of the patch 292 attached to the surface of the photosensitive drum 2a when the predetermined number of developments (predetermined number of printings) is completed. A bias voltage difference VB between 130 and the developing roller 150 is a second voltage difference VB2. As a result, according to the present embodiment, it is possible to feedback-correct the development density that has decreased with the previous development (printing) to a predetermined density.

  In addition, after the development density is feedback-corrected, the toner diameter of the toner layer 193 formed on the surface of the developing roller 150 is calculated based on the environmental temperature, humidity, and printing rate, and based on the calculated toner diameter. Thus, by executing adjustment of the voltage difference so that the bias voltage difference VB becomes the third voltage difference VB3, the transition of density change during development after the completion of the predetermined number of times of development (end of the predetermined number of prints) is predicted. Thus, even after the completion of the predetermined number of developments (end of the predetermined number of printings), the feedforward adjustment (correction) can be performed so that the development density after feedback correction does not decrease below a certain level.

  As a result, it is possible to suppress a decrease in development density due to selective development in which small-diameter toner having strong adhesion is accumulated, and to maintain a stable development density even during continuous development.

According to the developing device 16a in the copier 1 of the present embodiment, for example, the following effects are exhibited.
In the present embodiment, the relationship between the first bias voltage V1 applied to the magnetic roller 130 and the second bias voltage V2 applied to the developing roller 150 indicates that the toner layer 193 having a predetermined thickness is formed on the surface of the developing roller 150. An applied voltage control unit 271 that controls the first voltage application unit 261 and the second voltage application unit 262, a temperature / humidity measurement unit 252 that measures environmental temperature and humidity, and a predetermined number of times so that a voltage difference is formed. The toner diameter of the toner layer 193 formed on the surface of the developing roller 150 based on the environmental temperature and humidity measured by the temperature / humidity measuring unit 252 and a preset printing rate at the time of non-development after the development of the toner is completed. The toner diameter calculation unit 272 that calculates the voltage and the applied voltage control unit 271 so as to adjust the voltage difference based on the toner diameter calculated by the toner diameter calculation unit 272. Comprising a voltage difference adjustment unit 273 instructs the.

Therefore, according to the present embodiment, the bias voltage difference is adjusted based on the toner temperature calculated based on the environmental temperature and humidity, and the printing rate, so that after a predetermined number of developments (a predetermined number of printings are completed) Feedforward adjustment (correction) is performed so that the development of density change during the subsequent development is predicted, and the development density does not decrease below a certain level even after development of a predetermined number of times (end of printing of a predetermined number of sheets). It can be carried out.
Thereby, while suppressing an increase in running cost due to wasteful consumption of toner, it is possible to suppress a decrease in development density due to selective development in which small-diameter toner having strong adhesion is accumulated, and to maintain a stable development density.

In this embodiment, the voltage difference adjustment unit 273 feedback corrects the voltage difference to a predetermined development density based on the development density detected by the development density detection unit 291 before adjusting the voltage difference based on the toner diameter. The applied voltage control unit 271 is instructed to do so.
Therefore, in the present embodiment, after completion of a predetermined number of developments (end of a predetermined number of prints), the density that has decreased with the development so far can be feedback-corrected (primary correction) to a predetermined development density. Further, in the present embodiment, by performing the feedforward adjustment (secondary correction) described above, the transition prediction of density change during development after the completion of the predetermined number of developments (end of the predetermined number of printings) is performed. It can be done more accurately. Thereby, even during continuous development over a long period of time, a change in density can be suppressed to a minimum.

As mentioned above, although preferred embodiment of this invention was described, this invention can be implemented with a various form, without being limited to embodiment mentioned above.
For example, in the above-described embodiment, the case where the toner 192 is positively charged has been described. However, the present invention is not limited to this. The toner 192 may be negatively charged. Specifically, in the above-described embodiment, the case where the positively charged toner 192 is used has been described. As described above, when the positively charged toner 192 is used, the first voltage difference VB1 is a bias voltage difference VB larger than the second voltage difference VB2.

On the other hand, when the negatively charged toner 192 is used, the first voltage difference VB1 is set to a bias voltage difference VB smaller than the second voltage difference VB2. Accordingly, even when the negatively charged toner 192 is used, the same effect as that of the above-described embodiment can be obtained.
Except for this point, the configuration, operation, and effect when using the negatively charged toner 192 are the same as those when using the positively charged toner 192.

  In the above-described embodiment, the image forming apparatus is a color indirect transfer type that uses the intermediate transfer belt 7 to transfer a plurality of color toner images onto the paper T, but is not limited thereto. The type of the image forming apparatus is not limited to this, and may be a direct transfer type image forming apparatus that does not use an intermediate transfer belt or an image forming apparatus for monochrome printing.

The type of the image forming apparatus of the present invention is not particularly limited, and may be a color copier, a printer, a facsimile, or a complex machine thereof.
The sheet-shaped transfer material is not limited to the paper T, and may be a film sheet, for example.

Next, examples and comparative examples of the present invention will be described based on experiments with reference to FIGS. However, the present invention is not limited to the following examples.
FIG. 6 is a graph showing the relationship between the amount of adhesion and the applied voltage (adjustment value) Vs in the toner of each particle size used in the experiment. FIG. 7 is a graph showing the relationship between the applied voltage (adjustment value) Vs and the density ID for toner of each diameter used in the experiment. FIG. 8 is a graph showing the relationship between the adhesion amount of toner of each diameter used in the experiment and the density ID. FIG. 9 is a graph showing changes in density ID during continuous development.

[Method and purpose of experiment]
When the developing rate (printing rate) was changed in an environment with different developability and temperature / humidity due to the difference in toner diameter, the average diameter of the toner in the toner layer formed on the surface of the developing roller was examined. Here, the number of printed sheets was set to 10 sheets each.
In addition, a change in density between the case where the above-described primary correction and secondary correction were performed and the case where these were not performed was examined.

[Conditions for experiment]
Developing roller diameter: 25 mm
Development roller rotation speed: 400 mm / sec
Magnetic roller diameter: 25mm
Magnetic roller rotation speed: 600 mm / sec
Gap between the layer thickness regulating blade and the magnetic roller: 0.50 mm
Applied voltage: 100 to 300V
Peak voltage: 1000V
Toner diameter: 4, 5, 6, 7, 8 μmφ

[Experimental results and discussion]
As is apparent from the graphs shown in FIGS. 6 to 8, the smaller the toner diameter, the smaller the amount of adhesion and the higher the density. From this result, for example, in order to obtain a target density of 1.4 using toner of 7 μmφ, an applied voltage of 200 V is required, whereas a target density of 1 is used using 4 μmφ toner. .4, an applied voltage of 290V is required. From these tendencies, it can be seen that when the toner diameter changes by 1 μmφ, a difference of about 30 V occurs in the applied voltage.
Further, if small diameter toner is accumulated on the developing roller, the toner is charged up and the toner layer becomes thin. If development is performed in this state, there is a concern that the density may be lowered. However, as shown in FIG. 8, the smaller the toner diameter, the higher the density of the toner with a small amount of adhesion. Therefore, it was confirmed that the decrease in density due to the accumulation of the small diameter toner is not a problem.

  Further, when the developing rate (printing rate) is changed under an environment where the temperature and humidity are different, the average diameter of the toner in the toner layer formed on the surface of the developing roller is examined. The result was obtained. Here, toner of 7 μmφ was used.

  As is apparent from Tables 1 to 3, the lower the outside air temperature and humidity, the smaller the toner diameter of the toner layer formed on the surface of the developing roller, and the developing rate (printing rate). It can be seen that the toner diameter of the toner layer formed on the surface of the developing roller becomes smaller as the value of) decreases.

As described above, as shown in FIG. 7, when the toner diameter changes by 1 μmφ, a difference of about 30 V is generated in the applied voltage, so that the voltage difference adjustment value Vs for the secondary correction by the voltage difference adjustment unit 273 is taken into consideration. For example, the coefficient K in the equation (1) for obtaining the value is “30”. Therefore, the adjustment value Vs of the voltage difference for the secondary correction is
Adjustment value Vs = 30 × (standard toner diameter−toner diameter calculated by toner diameter calculating section) (1)

For example, when the toner diameter is 7 μmφ, the development rate (printing rate) is 5%, the outside air temperature is 37 ° C., the humidity is 40%, and the applied voltage for primary correction is 200V,
Adjustment value Vs = 30 × {7− (6.5)} = 15V.
Therefore, the adjustment value of the voltage difference for the primary correction + the adjustment value of the voltage difference for the secondary correction = 200V + 15V = 215V
It becomes.

In addition, when the voltage difference adjustment value 15V for secondary correction is applied and printing durability (endurance continuous development) is performed, and when the voltage difference adjustment value is not applied and printing durability (endurance continuous development) is performed When the change in concentration was examined, the results shown in FIG. 9 were obtained.
As is apparent from the graph shown in FIG. 9, when 15V is applied as the adjustment value of the voltage difference, even if the number of printing durability (number of times of development) exceeds 100 (100 times), there is almost no decrease in density. It was confirmed that stable density printing (development) could be maintained.

DESCRIPTION OF SYMBOLS 1 ... Copy machine (image forming apparatus), 2a, 2b, 2c, 2d ... Photosensitive drum (image carrier), 16a, 16b, 16c, 16d ... Developing device, 130 ... Magnetic roller (Developer carrying) 150) developing roller (toner carrier), 190 ... two-component developer, 191 ... magnetic carrier, 192 ... toner, 193 ... toner layer, 194 ... developer layer (magnetic brush), 261 ... First voltage application unit, 262 ... Second voltage application unit, 271 ... Application voltage control unit, 272 ... Toner diameter calculation unit, 273 ... Voltage difference adjustment unit, 291 ... Development density detection unit, 300 ... Temperature / humidity measuring unit, T ... paper (transfer material), V1 ... first bias voltage, V2 ... second bias voltage, Vs ... adjusted value of voltage difference

Claims (5)

A developer carrying member that holds a two-component developer containing at least a carrier and a toner by a magnetic force and forms a magnetic brush by a carrier contained in the two-component developer on the surface;
A toner carrier that is disposed opposite to the developer carrier and forms a toner layer on the surface with toner supplied from the developer carrier;
A first voltage applying unit for applying a first bias voltage to the developer carrier;
A second voltage application unit for applying a second bias voltage to the toner carrier;
A relationship between the first bias voltage applied by the first voltage application unit and the second bias voltage applied by the second voltage application unit is such that a toner layer having a predetermined thickness is formed on the surface of the toner carrier. An applied voltage control unit that controls the first voltage application unit and the second voltage application unit so as to obtain a voltage difference of
A temperature / humidity measurement unit that measures environmental temperature and humidity;
At the time of non-development after a predetermined number of times of development, the toner layer formed on the surface of the toner carrier based on the environmental temperature and humidity measured by the temperature / humidity measurement unit and a preset printing rate A toner diameter calculator for calculating the toner diameter;
And a voltage difference adjusting unit that instructs the applied voltage control unit to adjust the voltage difference based on the toner diameter calculated by the toner diameter calculating unit. The adjustment value of the voltage difference by the voltage difference adjustment unit is:
The developing device according to claim 1, wherein the developing device is obtained by an expression of a predetermined coefficient × (standard toner diameter−toner diameter calculated by the toner diameter calculating unit). A development density detector for detecting the development density of the developing device;
The voltage difference adjustment unit is configured to perform the voltage difference based on the development density detected by the development density detection unit before adjusting the voltage difference based on the toner diameter during non-development after a predetermined number of developments. The developing device according to claim 1, wherein the applied voltage control unit is instructed to feedback-correct the image to a predetermined development density. The voltage difference adjustment unit starts development with a voltage difference that is feedback-corrected based on the development density detected by the development density detection unit, and the voltage difference based on the toner diameter when the number of developments exceeds a predetermined number. The developing device according to claim 3, wherein the adjustment is performed. A developing device according to any one of claims 1 to 4,
One or more image carriers on which an electrostatic latent image is formed and a toner image is formed on the electrostatic latent image upon receipt of toner from the toner layer of the developing device;
A transfer unit that directly or indirectly transfers the toner image formed on the image carrier to a sheet-like transfer material;
An image forming apparatus comprising: a fixing unit that fixes a transferred toner image to a sheet-like transfer material.

Images