JP5492803B2 - Developing device and image forming apparatus - Google Patents

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 toner is carried on the surface of a developer carrying member to form a magnetic brush, and the toner supplied from the magnetic brush to the toner carrying member is used to form a toner on the surface of the toner carrying member. A so-called touch-down method (also referred to as a hybrid method) in which an electrostatic latent image on the surface of the image carrier is developed as a toner image by forming a layer and causing toner to fly from the toner layer to the image carrier. Development devices are attracting attention.

  In the case of a touch-down developing device, if the developer contains a large amount of fine powder, external additives, and the like that do not contribute to development, it may cause a decrease in developability. Therefore, in order to improve developability, measures are taken such as reducing the interval between the toner carrier and the image carrier or increasing the alternating current (AC) peak voltage (Vpp). However, when such measures are taken, leakage of the applied voltage tends to occur between the toner carrier and the image carrier. As a result, the touch-down operation of moving only the sufficiently charged toner to the toner carrier without moving the carrier of the two-component developer does not function sufficiently.

Therefore, an aluminum base tube is used as a constituent material of the toner carrier, and the surface of the aluminum base tube is subjected to an aluminum oxide film treatment of 5 μm or more, and the toner carrier subjected to the aluminum oxide film treatment and the image carrier A developing device has been proposed in which the interval is set within a predetermined range in which leakage of an applied voltage does not occur (see, for example, Patent Document 1).
Further, by forming a resin coating layer on the surface of the toner carrier, and adjusting the volume resistance and surface resistance of the surface of the toner carrier by containing a resistance adjusting agent such as carbon black in the resin coating layer, A developing device that suppresses leakage of applied voltage between the toner carrier and the image carrier has also been proposed (see, for example, Patent Document 2).

JP 2004-318092 A Japanese Patent Laid-Open No. 11-249414

  However, in the developing device described in Patent Document 1, because of toner aging, the toner is easily triboelectrically charged on the aluminum oxide film, and a so-called charge-up phenomenon occurs in which the surface charge of the toner increases. In addition, the toner tends to adhere to the surface of the toner carrier. In particular, when a toner having a small particle size is used to improve the image quality, the toner adheres more easily to the surface of the toner carrier due to the charge-up phenomenon.

  On the other hand, in the developing device described in Patent Document 2, the occurrence of charge-up phenomenon is suppressed by the resin coating layer on the surface of the toner carrier, the toner is prevented from sticking to the surface of the toner carrier, and the resistance adjuster This makes it possible to adjust the volume resistance and surface resistance of the surface of the toner carrier, and is effective in suppressing leakage of the applied voltage.

However, in the developing device described in Patent Document 2, when further high-speed development is performed, the development performance tends to be lowered due to the reduction of the toner transfer time from the toner carrier to the image carrier. In order to suppress such a decrease in development performance, it is necessary to apply a higher AC peak voltage. In order to suppress leakage when a high AC peak voltage is applied, it is effective to increase the resistance by the resistance adjusting agent contained in the resin coating layer. However, if the resistance is increased, during continuous development (printing) Electric charges accumulate on the surface of the toner carrier, and the half density of the toner image gradually increases, while the solid density gradually decreases.
On the other hand, in order to suppress such a change in the density of the toner image within an allowable range, it is necessary to take a long time until the start of development. A decline is inevitable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that can suppress a decrease in developing performance and developing efficiency and can suppress a change in density of a toner image.
Another object of the present invention is to provide an image forming apparatus including the developing device.

  The present invention carries a two-component developer containing at least a carrier and a toner, a developer carrier on which a magnetic brush is formed on the surface by a carrier contained in the two-component developer, and an electrostatic latent image is formed on the surface A toner carrier that is disposed opposite to the image carrier and carries toner supplied from the developer carrier and forms a toner layer with the magnetic brush; and from the toner carrier to the surface of the image carrier. A voltage application unit for applying a voltage to the toner carrier so as to form a potential difference between the toner carrier and the image carrier for developing an electrostatic latent image as a toner image; The present invention relates to a developing device comprising: an applied voltage control unit that controls the voltage application unit so that a voltage before starting development is higher than a saturation voltage at the time of development.

  The surface of the toner carrier is preferably covered with a resin layer containing a resistance adjusting agent.

  Further, the applied voltage control unit is configured so that the surface potential of the toner carrier due to the applied voltage is within a range of ± 3 V of the saturation voltage during development, with respect to the applied voltage to the toner carrier before the start of development. It is preferable to control the voltage application unit.

  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 developing performance and developing efficiency and suppressing a change in density of a toner image.
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. 2 is a cross-sectional view for explaining a configuration of a developing device 16a and a photosensitive drum 2a in the copier of 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 voltage control timing chart showing timing of control of a second bias voltage V2 by a second voltage application unit 262. 6 is a graph showing changes with time in the potential of the developing sleeve 151 in a comparative example in which a voltage applied to the developing roller 150 is fixed and an example in which the voltage is controlled to be changed.

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 “back-and-forth 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 and each of the developing devices 16a, 16b, 16c, and 16d are connected 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 the 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 carrier disposed above the one stirring roller 120a in the vertical direction, a layer thickness regulating blade 140 disposed in the vicinity of the magnetic roller 130, and a layer thickness regulating blade 140 is a toner scattering prevention cover member 141 disposed above the vertical direction of 140, a developing roller 150 as a toner carrier disposed opposite to the magnetic roller 130, and a rotation detection unit 251 that detects the rotation of the developing roller 150. A first voltage application unit 261, a second voltage application unit (voltage application unit) 262, a control unit 270, and a storage unit 280. , Comprising 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. The agitated two-component developer 190 generates static electricity due to friction, and in this embodiment, the magnetic carrier (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 disposed so that the tip end side faces and is close to the surface of the magnetic sleeve 131. A predetermined gap (gap) is formed between the tip 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 192 is moved from the developer layer (magnetic brush) whose layer thickness is regulated by the layer thickness regulating blade 140 to the surface of the developing roller 150 to form the toner layer 193. 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 153 containing a resistance adjusting agent. The developing sleeve 151 rotates at a position facing the magnetic sleeve 131 such that the moving direction of the developing sleeve 151 is opposite to the moving direction of the magnetic sleeve 131 (the direction of arrow C shown in FIGS. 2 and 3). Driven. A predetermined second bias voltage V2 is applied to the developing sleeve 151 by a second voltage applying unit 262 described later.

The developing roller magnetic pole member 152 is fixedly disposed inside 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 and forms a magnetic brush to form the developing roller. 150.

As shown in FIG. 2, the first voltage application unit 261 receives a control signal S4 output from an application voltage control unit 271 described later, and applies a first bias voltage V1 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 S4 output from an application voltage control unit 271 described later.
The toner 192 is moved between the magnetic roller 130 and the developing roller 150 by a bias voltage difference (related to the first bias voltage V1 applied to the magnetic roller 130 and the second bias voltage V2 applied to the developing roller 150) VB. An electric field 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. Specifically, the rotation detection unit 251 detects that the developing roller 150 has started to rotate and outputs a detection signal S1.

  As shown in FIG. 2, the control unit 270 includes an applied voltage control unit 271, a pre-development control unit 272, a development time control unit 273, a mode setting unit 274, a timer 275, and a continuous print determination unit 276. Have.

  The applied voltage control unit 271 receives a control signal S3 output from the pre-development control unit 272 described later or a control signal S2 output from the development control unit 273 described later, and receives the first voltage application unit 261 and the second voltage. A control signal S4 is output to the application unit 262.

The timer 275 receives the detection signal S1 from the rotation detection unit 251 and measures the elapsed time in the pre-development start mode.
The continuous printing determination unit 276 determines whether there is a continuous printing instruction to the copier 1.

The mode setting unit 274 selectively sets (switches) a normal development mode or a pre-development start mode.
The normal development mode is a mode in which a toner layer 193 having a predetermined thickness is formed on the surface of the developing roller 150 when development by the developing device 16a is performed. The pre-development mode is a mode in which the toner layer 193 is formed on the surface of the developing roller 150 before the development by the developing device 16a is started. Specifically, the mode setting unit 274 sets the pre-development mode for a predetermined time when the copier 1 is powered on. The mode setting unit 274 switches from the pre-development start mode to the normal development mode when the pre-development start mode for a predetermined time is completed.

The pre-development control unit 272 instructs the application voltage control unit 27 to set the bias voltage difference VB to the first voltage difference VB1 in the pre-development start mode. The development control unit 273 instructs the application voltage control unit 271 to set the bias voltage difference VB to the second voltage difference VB2 in the normal development mode.
By setting the bias voltage difference VB to the first voltage difference VB1, an electric field that moves a large amount of toner 192 between the magnetic roller 130 and the developing roller 150 is moved between the magnetic roller 130 and the developing roller 150. Arise. In addition, by setting the bias voltage difference VB to the second voltage difference VB2, the magnetic roller 130 and the developing roller 150 are more between the magnetic roller 130 and the developing roller 150 than the first voltage difference VB1. An electric field is generated that moves a small amount of toner 192.

  As shown in FIG. 4, after a predetermined time has elapsed when the bias voltage difference VB is set to the second voltage difference VB2, the movement of the movable toner 192 is in an equilibrium state in which the toner does not move between the magnetic roller 130 and the developing roller 150. Become. That is, the balanced state of movement of the toner 192 is a state in which 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 are balanced. It is.

  When the bias voltage difference VB is changed 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 second voltage difference VB2 is changed to the bias voltage difference VB larger than the second voltage difference VB2, the positively charged toner 192 is moved from the developing roller 150 to the magnetic roller 130. In addition, when the bias voltage difference VB smaller than the second voltage difference VB2 is changed from the equilibrium state in the second voltage difference VB2, the positively charged toner 192 is moved from the magnetic roller 130 to the developing roller 150.

  As illustrated in FIG. 2, the development control unit 273 refers to a storage unit 280 described later, and acquires voltage information related to the second voltage difference VB2 stored in the storage unit 280. The development control unit 273 instructs the applied voltage control unit 271 based on the voltage information stored in the storage unit 280. Specifically, the development control unit 273 instructs the bias voltage difference VB to be the second voltage difference VB2 by outputting a control signal S2 to the applied voltage control unit 271 during normal development. As a result, a toner layer 193 having a predetermined thickness is formed on the surface of the developing roller 150.

  As shown in FIG. 2, the pre-development control unit 272 instructs the applied voltage control unit 271 to set the bias voltage difference VB to the first voltage difference VB1 in the pre-development start mode.

  The pre-development control unit 272 acquires voltage information related to the first voltage difference VB1 stored in the storage unit 280 with reference to the storage unit 280 described later. The pre-development control unit 272 receives the detection signal S1 output from the rotation detection unit 251 and instructs the applied voltage control unit 271 to set the bias voltage difference VB to the first voltage difference VB1.

  Specifically, the pre-development control unit 272 performs the first rotation in the pre-development start mode on the basis of the detection signal S1 output from the rotation detection unit 251 and the voltage information stored in the storage unit 280. A control signal S3 is output to the applied voltage control unit 271 so that the difference VB becomes the first voltage difference VB1. Then, in the final rotation, the control signal S2 is output from the development control unit 273 to the applied voltage control unit 271 so that the bias voltage difference VB becomes the second voltage difference VB2.

  The first voltage difference VB1 is a bias voltage difference VB that generates an electric field in which a large amount of toner moves from the magnetic roller 130 to the developing roller 150. The second voltage difference VB2 is a bias voltage difference VB that generates an electric field in which a smaller amount of toner moves from the magnetic roller 130 to the developing roller 150 than in the case of the first voltage difference VB1.

As illustrated in FIG. 2, the storage unit 280 includes a bias voltage difference storage unit 281.
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 and the second voltage difference VB2.

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. FIG. 6 is a voltage control timing chart showing the control timing of the second bias voltage V2 by the second voltage application unit 262.
First, as shown in FIG. 5, in step ST1, the power of the copier 1 is turned on by a user operation.

  Next, in step ST2, the mode setting unit 274 sets the pre-development mode. The pre-development mode is a mode in which a large amount of toner 192 is transferred to the surface of the developing roller 150 when development is performed by the developing device 16a.

  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. Static electricity due to friction is generated in the stirred two-component developer 190. As a result, 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. Thereafter, the processing proceeds to step ST3.

  As shown in FIG. 5, in step ST3, the pre-development control unit 272 applies the applied voltage control unit so that the bias voltage difference VB between the magnetic roller 130 and the development roller 150 is the first voltage difference VB1. The control signal S3 is output to 271. With this output, as shown in FIG. 6, a constant voltage V <b> 1 is applied to the magnetic roller 130. On the other hand, a voltage V3 higher than the saturation voltage V2 at the time of development is applied to the developing roller 150. Specifically, the applied voltage V3 to the developing roller 150 before the start of development can be controlled so that the potential of the developing sleeve 151 that rises by the applied voltage V3 falls within the range of ± 3 V of the saturation voltage V2 at the time of development. , V2 = DC 330V, and V3 = DC 430V.

  As a result, as shown in FIGS. 2 to 4, the positively charged toner 192 constituting the two-component developer 190 held on the surface of the magnetic roller 130 has a first voltage difference as the bias voltage difference VB. It is affected by the electric field due to VB1. A large amount of toner 192 is transferred to the developing roller 150 side. As a result, a thick toner layer 193 is formed on the surface of the developing roller 150. Thereafter, the processing proceeds to step ST4.

  In step ST4, it is determined whether or not the pre-development start mode time counted by the timer 275 has passed a predetermined time t. If it is determined that the pre-development start mode time has not passed the predetermined time t (NO), the process returns to step ST3 and the pre-development start mode state is continued. On the other hand, if it is determined that the pre-development start mode time has passed the predetermined time t (YES), the process proceeds to step ST5.

  In step ST5, the mode setting unit 274 switches from the pre-development start mode to the normal development mode. The development mode is a mode in which an appropriate amount of toner 192 in the developer layer 194 formed on the surface of the magnetic roller 130 with a predetermined layer thickness is transferred to the development roller 150 side. Specifically, the mode setting unit 274 can switch from the pre-development start mode to the normal development mode while the toner image is not formed on the photosensitive drum 2a by the developing device 16a. Thereafter, the processing proceeds to step ST6.

  As shown in FIGS. 2 and 5, in step ST <b> 6, the development control unit 273 performs the first rotation of the developing roller 150 based on the acquired voltage information of the storage unit 280 and the magnetic roller 130 and the developing roller 150. The control signal S2 is output to the applied voltage control unit 271 so that the bias voltage difference VB between the first voltage difference VB1 and the second voltage difference VB2 is changed. With this output, as shown in FIG. 6, the voltage applied to the developing roller 150 is switched from the high voltage V3 = DC 430V before development to the saturation voltage V2 = DC 330V during development.

  As a result, the positively charged toner 192 constituting the two-component developer 190 held on the surface of the magnetic roller 130 has the second voltage as the bias voltage difference VB as shown in FIGS. It is affected by the electric field due to the difference VB2. Therefore, a smaller amount of toner 192 than in the pre-development start mode is transferred to the developing roller 150 by the magnetic brush. As a result, a toner layer 193 having a predetermined thickness is formed on the surface of the developing roller 150.

As shown in FIG. 5, in step ST7, the user instructs the copier 1 to form (print) an image on the paper T. The user's instruction to print to the copier 1 may be an instruction to print an image on one sheet of paper T, or an instruction to print an image on a plurality of sheets of paper T.
In response to an instruction to print an image on the paper T in Step ST7, an operation for printing an image on the paper T by the copying machine 1 is started. Thereafter, the processing proceeds to step ST8.

As shown in FIGS. 4 and 5, in step ST8, 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. In other words, 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 by 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 to the paper T is conveyed to the fixing unit 9, and the toner is fixed to 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 illustrated in FIG. 5, in step ST <b> 9, the continuous printing determination unit 276 determines whether there is a continuous printing instruction to the copier 1. If the continuous printing determination unit 276 determines that there is an instruction for continuous printing (YES), the toner image is continuously formed on the photosensitive drum 2a by the developing device 16a. And the process returns to step ST8. On the other hand, when the continuous printing determination unit 276 determines that there is no instruction for continuous printing (NO), the toner image is not continuously formed on the photosensitive drum 2a by the developing device 16a. Advances to step ST10.

  As shown in FIG. 5, in step ST10, the normal development mode ends, and the process returns to step ST2.

As described above, according to the present embodiment, the voltage applied from the second voltage applying unit 262 to the developing roller 150, that is, the bias voltage difference VB between the magnetic roller 130 and the developing roller 150 is normally set before the start of development. By controlling to the first voltage difference VB1 higher than the second voltage difference VB2 at the time of development, it is possible to shorten the rising time until the charge accumulation on the surface of the developing roller 150 reaches saturation.
Therefore, according to the present embodiment, it is possible to suppress a change in density of the toner image due to charge accumulation during continuous development without reducing the development efficiency of the developing device 16a.

According to the developing device 16a in the copier 1 of the present embodiment, for example, the following effects are exhibited.
In this embodiment, the magnetic brush 194 by the carrier 191 included in the two-component developer 190 carries the toner 192 supplied from the magnetic roller 130 formed on the surface, and the developing roller 150 that forms the toner layer 193 is supported. With respect to the applied voltage, an applied voltage control unit 271 that controls the applied voltage control unit 271 is provided so that the voltage before the start of development is higher than the saturation voltage during development.

  Therefore, the time required for the developing roller 150 to reach the saturation potential and form a toner layer having a predetermined thickness on the surface of the developing roller 150 can be shortened. As a result, the developing efficiency of the developing device 16a and, in turn, the productivity (first copy time) of the image forming apparatus can be improved, and a decrease in density at the initial stage of development can be suppressed.

  In the development mode, by controlling the voltage applied to the developing roller 150 to the saturation voltage at the time of development, accumulation of charges on the surface of the developing roller 150 can be suppressed. Thereby, a change in image density due to charge accumulation during continuous development can also be suppressed. Therefore, when developing at high speed and continuously, it is possible to perform development at a stable density in a long range from the initial development to the completion of development.

In this embodiment, the surface of the developing sleeve 151 in the developing roller 150 is covered with a resin layer 153 containing a resistance adjusting agent. Therefore, the occurrence of a charge-up phenomenon due to frictional charging between the surface of the developing sleeve 151 and the toner 192 and the adhesion of the toner 192 to the surface of the developing sleeve 151 due to the charge-up can be suppressed. Further, by adjusting the volume resistance and surface resistance of the surface of the developing sleeve 151 by the resistance adjusting agent, it is possible to suppress leakage of applied voltage between the developing roller 150 and the photosensitive drum.
Therefore, even when a high voltage is applied in the early stage of development, the effect of suppressing a leak and moving a large amount of toner 192 to the developing roller 150 can be sufficiently functioned.

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 case where the DC voltage Vdc is changed as means for changing the voltage applied to the developing roller 150 has been described. Instead, the duty ratio of the AC voltage is changed. Also good.

  The above-described embodiment is a color indirect transfer type image forming apparatus that transfers a plurality of color toner images onto the paper T using the intermediate transfer belt 7, but the type of the image forming apparatus is not limited to this, The image forming apparatus may be a direct transfer type 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 with reference to FIG. However, the present invention is not limited to the following examples. FIG. 7 is a graph showing the change with time of the potential of the developing sleeve 151 in the comparative example in which the voltage applied to the developing roller 150 is fixed and the example in which the voltage is controlled to be changed.

Common conditions in the examples and comparative examples subjected to the experiment are as follows.
Linear velocity of the surface of the photosensitive drum: 250 mm / sec
Photoconductor drum dark potential: 250V, Photoconductor drum light potential: 20V
The outer diameter of the photosensitive drum: φ30 mm, the outer diameter of the developing roller φ16 mm, the distance (interval) between the developing roller and the photosensitive drum: 0.1 mm
Toner amount in developer: 25 μC / g, toner particle size (average particle size): 7.0 μm
An aluminum oxide film is formed on the surface of the developing roller, and the surface of the oxide film is coated with a urethane resin containing carbon as a resistance adjusting agent. The thickness of this surface coating material was 15 μm.

  In the case of the comparative example, a constant DC voltage Vdc 1330 V is always applied to the developing roller 150. On the other hand, in the case of the example, the DC voltage Vdc 430V was applied for 2.5 seconds from the start of application, and thereafter, control was performed to change the DC voltage Vdc to 330V.

  When the above experiment was performed, the potential of the developing sleeve 151 showed a change with time as shown in FIG. Looking at the time variation of the potential, in the case of the comparative example, the time from the start of voltage application until the developing sleeve 151 reaches the saturation potential and the toner layer having a predetermined thickness is formed on the surface is 5.0. A time t1 of more than a second was required. On the other hand, in the case of the embodiment, only a time t2 of 2.0 seconds is required from the start of voltage application until the developing sleeve 151 reaches the saturation potential and forms a toner layer with a predetermined thickness on the surface. It was confirmed that there was no. These times t1 and t2 are waiting times for image formation.

DESCRIPTION OF SYMBOLS 1 ... Copy machine (image forming apparatus), 2a, 2b, 2c, 2d ... Photosensitive drum (image carrier), 7 ... Intermediate transfer belt (transfer part), 8 ... Secondary transfer roller (transfer part) ), 9... Fixing portion, 16 a, 16 b, 16 c, 16 d... Developing device, 130... Magnetic roller (developer carrier), 150 .. developing roller (toner carrier), 153. ... two-component developer, 191 ... magnetic carrier (carrier), 192 ... toner, 193 ... toner layer, 194 ... developer layer (magnetic brush), 261 ... first voltage application unit, 262 ... Second voltage application unit (voltage application unit), 271... Applied voltage control unit, T... Paper (transfer material), V1... First bias voltage, V2.

Claims (3)

A developer carrying member that carries a two-component developer containing at least a carrier and a toner, and on which a magnetic brush is formed by a carrier contained in the two-component developer;
A toner carrier that is disposed opposite to an image carrier on which an electrostatic latent image is formed, carries toner supplied from the developer carrier, and forms a toner layer with the magnetic brush;
In order to develop an electrostatic latent image on the surface of the image carrier from the toner carrier as a toner image, a voltage is applied to the toner carrier so as to form a potential difference between the toner carrier and the image carrier. A voltage applying unit for applying
An applied voltage control unit that controls the voltage application unit so that a voltage before the start of development is higher than a saturation voltage at the time of development, with respect to the voltage applied from the voltage application unit to the toner carrier ,
The applied voltage control unit is configured to apply the voltage applied to the toner carrier before the start of development so that the surface potential of the toner carrier due to the applied voltage is within a range of ± 3 V of a saturation voltage during development. that controls the application unit developing device. The developing device according to claim 1, wherein a surface of the toner carrier is covered with a resin layer containing a resistance adjusting agent. A developing device according to claim 1 or 2 ,
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