JP2013238838A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus for equalizing a density of a toner image.SOLUTION: The image forming apparatus includes: a bias voltage application section 260 for applying a first bias voltage to a magnetic roller 130 and applying a second bias voltage to a developing roller 150; a density detection section for detecting a density of a toner image; a determination section 272 for determining whether or not a density of a rear end part of the toner image is more dense than a density of a center part and a front end part on the basis of the density of the toner image detected by the density detection section; a voltage control section 273 for controlling the bias voltage application section 260 to adjust the first bias voltage and the second bias voltage when the determination section 272 determines that the density of the toner image is dense; and a light control section 274 for controlling a laser scanner unit 4a to adjust a quantity of light emitted after the voltage control section 273 controls the bias voltage application section 260.

Description

  The present invention relates to an image forming apparatus capable of forming an image on an image forming medium using toner.

  Some image forming apparatuses such as copiers, multifunction machines, and printers form an image on an image forming medium (paper) using toner. The image forming apparatus includes a photosensitive drum and a developing device. The image forming apparatus develops the electrostatic latent image formed on the photosensitive drum with the toner supplied from the developing device, and forms a toner image on the surface of the photosensitive drum.

  The developing device includes a touch-down developing type developing device. The touchdown development type developing device includes a magnetic roller and a developing roller. The developing device supplies the two-component developer including toner and carrier to the magnetic roller, then supplies the toner from the magnetic roller to the developing roller, and further causes the toner to fly from the developing roller to the photosensitive drum. Thus, toner is supplied to the photosensitive drum.

  By the way, when the image forming apparatus is provided with a touch-down developing type developing device, there is a possibility that a so-called “rear end pool” may occur in the toner image formed on the photosensitive drum. The rear end pool is a phenomenon in which the density of the rear end portion of the toner image is higher than the density of the front end portion and the central portion of the toner image. The trailing edge pool occurs because the toner does not fly straight from the developing roller to the photosensitive drum, and the flying destination of the toner concentrates on the trailing edge of the toner image.

  For this reason, some image forming apparatuses detect the degree of edge enhancement of a toner image formed on a photosensitive drum. That is, the image forming apparatus develops the reference latent image formed on the photosensitive drum to form a reference visible image, and the degree of edge density of the reference visible image becomes higher than the density at the center (edge). The degree of emphasis) is detected. Then, the image forming apparatus increases the peak-to-peak voltage of the AC component of the developing bias voltage in order to reduce or prevent edge enhancement (see Patent Document 1).

JP-A-5-66654

  As described above, the image forming apparatus described in Patent Document 1 relaxes or prevents the degree of edge enhancement by increasing the peak-to-peak voltage. However, the peak-to-peak voltage is a parameter for obtaining the basic performance of the image forming apparatus such as the image density and uniformity of the reference visible image. For this reason, in the invention described in Patent Document 1, there is a risk that the basic performance of the image forming apparatus is sacrificed in order to reduce or prevent the degree of edge enhancement.

  An object of the present invention is to provide an image forming apparatus that equalizes the density of a toner image.

  According to the present invention, a developer containing a magnetic carrier and a toner is carried by a magnetic force so that a developer layer is formed on the surface of the developer carrying rotator, and the developer carrying rotator is disposed opposite to the developer carrying rotator. A toner-carrying rotator having a toner layer formed on the surface by toner moved from the developer-carrying rotator, a light source that emits light, and the toner-carrying rotator and the light source that are disposed opposite to each other and emitted from the light source An electrostatic latent image is formed on the surface by the generated light, and the electrostatic latent image is developed by the toner moved from the toner-carrying rotator to form a toner image on the surface; A bias voltage applying unit that applies a first bias voltage to the developer-carrying rotator and a second bias voltage to the toner-carrying rotator, and a density that detects the density of the toner image When the first toner image as a toner image is formed on the knowledge unit and the image carrier, the first toner image is based on the density detected by the density detection unit for the first toner image. A determination unit configured to determine whether or not a part of the image includes a darker part than the other part of the first toner image except the part; and the first toner image is determined by the determination unit. A voltage control unit that controls the bias voltage application unit to adjust the first bias voltage and the second bias voltage when it is determined that a portion having a high density exists in the part, and the voltage control And an optical control unit that controls the light source so as to adjust the amount of emitted light after the bias voltage application unit is controlled by the unit.

  According to the present invention, it is possible to provide an image forming apparatus that equalizes the density of a toner image.

It is a figure for demonstrating arrangement | positioning of each component of a copier. It is a figure which shows the image development apparatus and photosensitive drum of 1st Embodiment. It is a figure which shows a mode that the toner layer of predetermined thickness is formed on the surface of a developing roller. It is a figure which shows the relationship between the output voltage of a density sensor, and the measurement time by a density sensor. FIG. 4 is a diagram illustrating a relationship between a toner image density and a voltage difference between a first bias voltage and a second bias voltage. FIG. 6 is a diagram illustrating a relationship between a density difference between a density at a front end portion and a central portion and a density at a rear end portion in a toner image and a second bias voltage. FIG. 4 is a diagram illustrating a relationship between a toner image density and a light amount. 5 is a flowchart for explaining the operation of the copier in the first embodiment. It is a figure which shows the image development apparatus and photosensitive drum of 2nd Embodiment. 6 is a graph showing a relationship between a density of a toner image and a second bias voltage V2. 10 is a flowchart for explaining the operation of the copier in the second embodiment.

Hereinafter, embodiments of an image forming apparatus of the present invention will be described with reference to the drawings.
[First Embodiment]
With reference to FIG. 1, the overall structure of a copier 1 as an image forming apparatus in the first 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 transfer 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. Details of the reading unit 301 will be described later.

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, a 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 conveyance 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, the charging by the charging units 10a, 10b, 10c, and 10d, the laser scanner unit 4a, the charging unit 10a, 10b, 10c, and 10d in order from the upstream side to the downstream side along the surface of each of the photosensitive drums 2a, 2b, 2c, and 2d. 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 Is eliminated, and cleaning is performed 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 disposed so as to face a developing roller 150 described later and laser scanner units 4a, 4b, 4c, and 4d described later. Each of the photosensitive drums 2a, 2b, 2c, and 2d forms an electrostatic latent image on the surface by the light emitted from the laser scanner units 4a, 4b, 4c, and 4d. Further, each of the photosensitive drums 2 a, 2 b, 2 c, and 2 d develops an electrostatic latent image with toner moved from the developing roller 150, thereby forming a toner image on the surface.

  That is, 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.

  The laser scanner units 4a, 4b, 4c, and 4d (corresponding to the “light source” of the present invention) emit light (laser light). That is, 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 the 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. Each of the developing devices 16a, 16b, 16c, and 16d includes a developing roller that is disposed to face the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, a stirring roller for stirring the toner, and the like. 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).

  The toner images of the respective colors formed on the photosensitive drums 2a, 2b, 2c, and 2d are sequentially primary-transferred onto the intermediate transfer belt 7 (corresponding to the “intermediate transfer member” of the present invention). The intermediate transfer belt 7 is stretched around a driven roller 35, a counter roller 18 that is 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.

  The 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.

  The primary transfer rollers 37a, 37b, 37c, and 37d are respectively supplied with the respective color toner images formed on the photosensitive drums 2a, 2b, 2c, and 2d on the intermediate transfer belt 7 by a primary transfer bias applying unit (not shown). A primary transfer bias for transferring 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 a 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 separation position where the secondary transfer roller 8 is separated from the intermediate transfer belt 7. Specifically, the secondary transfer roller 8 is disposed at a 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. It is arranged at a separated position.

  On the opposite side of the intermediate transfer belt 7 from the secondary transfer roller 8, a counter roller 18 is disposed. 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 secondary transfer roller 8 and the opposing roller 18. 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 presses each color toner constituting the toner image secondarily transferred onto the paper T to fix it 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. By transporting the paper T while 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 pressurized. The

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 the paper T are arranged in a stacked manner. 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 double feed prevention mechanism including 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. Prepare.

  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 forms part of the right side surface of the apparatus main body M in the closed state, and a paper feed roller 66. The 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 T is placed on the open manual feed tray 65. The paper feed roller 66 feeds the paper T placed on the open manual feed tray 65 to the manual feed path La.

  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 apparatus (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 skew (oblique paper feeding) of the paper T In addition, a registration roller pair 80 is arranged to synchronize with the timing of toner image formation 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 for forming a toner image on the opposite surface (non-printing surface) to the surface already printed when performing double-sided printing on the paper T. According to the return transport path Lb, the paper T transported from the first branching section Q1 to the paper discharge section 50 is turned upside down and returned to the first transport path L1, and is disposed upstream of the secondary transfer roller 8. It can be conveyed upstream of the registration roller pair 80. A predetermined toner image is transferred onto the non-printing surface at the secondary transfer nip N2 on the paper T that has been turned 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 sheet detection sensor is disposed at a predetermined position in 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 (left side in FIG. 1) of the apparatus main body M, 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.
Further, 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 a 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 according to the first embodiment includes the cover body 40 having such a configuration. When a paper jam (JAM) occurs in the main transport paths L1 to L3, the cover body 40 is shown in FIG. By rotating from the closed position to the 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, the developing device of the first embodiment will be described in detail with reference to FIGS. As described above, the copying machine 1 includes the four developing devices 16a, 16b, 16c, and 16d. Since each has the same configuration, the developing device 16a will be described below as a representative.
FIG. 2 is a diagram illustrating the developing device 16a and the photosensitive drum 2a. FIG. 3 is a diagram illustrating a state where 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 according to the first embodiment is disposed inside the developing container 110 and a developing container 110 that contains a two-component developer 190 including a toner 192 and a magnetic carrier 191. Stirring rollers 120a and 120b, a magnetic roller 130 (corresponding to the “developer carrying rotor” of the present invention) disposed above the stirring roller 120a in the vertical direction, and a side of the magnetic roller 130 (left side in FIG. 2) ) In the vicinity of the magnetic roller 130, a cover member 141 disposed above the layer thickness regulating blade 140 in the vertical direction, and a developing roller disposed opposite the magnetic roller 130. 150 (corresponding to the “toner carrying rotator” of the present invention), a bias voltage applying unit 260, and a control unit 270. .

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 accommodated 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 in the first embodiment, the toner 192 is positively charged. Further, the toner 192 adheres to the magnetic carrier 191 due to electrostatic force.

The magnetic roller 130 carries the two-component developer 190 including the magnetic carrier 191 and the toner 192 by a magnetic force. Thereby, a developer layer 194 is formed on the surface of the magnetic roller 130.
That is, the magnetic roller 130 includes a magnetic sleeve 131 that can rotate in a predetermined direction and constitutes 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 FIG. A predetermined first bias voltage V <b> 1 is applied to the magnetic sleeve 131 by a bias voltage application unit 260 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 first 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 first magnetic roller magnetic pole member 132 is disposed such 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 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 cover member 141 is a member that constitutes a part of the case body of the developing device 16a. The 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 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 194 whose layer thickness is regulated by the layer thickness regulating blade 140 to form a toner layer 193 on the surface of the developing roller 150. The developing roller 150 includes a developing sleeve 151 that constitutes 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 developing sleeve 151 is rotationally driven 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 FIG. 2) at a position facing the developing sleeve 151 and the magnetic sleeve 131. Is done. Here, a predetermined second bias voltage V <b> 2 is applied to the developing sleeve 151 by a bias voltage application unit 260 described later.

The developing roller magnetic pole member 152 is fixedly disposed facing the first magnetic roller magnetic pole member 132 inside the developing sleeve 151. The developing roller magnetic pole member 152 is disposed corresponding to the portion of the developing roller 150 that is 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 south 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 inside the magnetic roller 130 and the developing roller magnetic pole member 152 disposed inside 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 the developing roller. 150.

  As shown in FIG. 2, the bias voltage application unit 260 applies the first bias voltage V <b> 1 to the magnetic roller 130 based on the control of the voltage control unit 273 described later. The bias voltage application unit 260 applies the second bias voltage V <b> 2 to the developing roller 150 based on the control of the voltage control unit 273 described later. An electric field that moves the toner 192 between the magnetic roller 130 and the developing roller 150 due to a 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). Occurs. Here, the voltage difference (relation between the second bias voltage V2 and the first bias voltage V1) is a voltage difference between the second bias voltage V2 and the first bias voltage V1 when the second bias voltage V2 is used as a reference. is there.

The copier 1 further includes a density sensor 280 and a control unit 270.
The density sensor 280 is disposed to face each of the photosensitive drums 2a, 2b, 2c, and 2d. In FIG. 2, only the density sensor 280a facing the photosensitive drum 2a is shown. The density sensor 280a includes, for example, a light emitting unit (not shown) that irradiates light to the photosensitive drum 2a and a light receiving unit (not shown) that receives light reflected by the photosensitive drum 2a. The density sensor 280a measures the density of the toner image formed on the photosensitive drum 2a based on the reflected light received by the light receiving unit. The density sensor 280a supplies the measured density as a voltage signal to a density processing unit 271 described later.
The position where the density sensor 280 is disposed is not limited to the above example. For example, the density sensor 280 may be disposed to face the intermediate transfer belt 7 (intermediate transfer member).

The control unit 270 includes a density processing unit 271, a determination unit 272, a voltage control unit 273, and a light control unit 274.
The density processor 271 constitutes a density detector that detects the density of the toner image formed on the photosensitive drum 2a or the intermediate transfer belt 7 together with the density sensor 280a. That is, when the density processing unit 271 receives the voltage signal output from each density sensor 280, the density processing unit 271 acquires the density based on the voltage value of the voltage signal.

When the first toner image as the toner image is formed on the photosensitive drum 2a, the determination unit 272 detects the density detected by the density detection unit for the first toner image (the density acquired by the density processing unit 271). ) To determine whether or not a part of the first toner image has a darker part than other parts except for a part of the first toner image. Here, the first toner image is a solid image. The part of the first toner image is a rear end portion of the first toner image when the rotation direction of the photosensitive drum 2a is the front side.
Here, for example, the photosensitive drum 2a has a diameter of 30 mm, the photosensitive drum 2a has a linear velocity of 200 mm / sec, the developing roller 150 has a diameter of 20 mm, the developing roller 150 has a linear velocity of 350 mm / sec, and the photosensitive drum 2a When the distance to the developing roller 150 is 100 μm, the length of the dark portion at the trailing edge of the toner image is about 0.5 to 2.0 mm.
Therefore, the determination unit 272 determines whether the density of the rear end portion is higher than that of each of the central portion and the front end portion in the first toner image formed on the photosensitive drum 2a.

  Here, FIG. 4 is a diagram showing the relationship between the output voltage of the density sensor 280a and the measurement time by the density sensor 280a. Here, FIG. 4A shows a case where the density of the rear end of the first toner image is higher than the density of the central portion and the front end (a state where a so-called “rear end pool” occurs). . FIG. 4B shows a case where the density of the first toner image is uniform (a state in which a so-called “rear end pool” has not occurred).

  As shown in FIG. 4A, the measurement result (output voltage) of the density sensor 280a decreases at the portion where the first toner image is formed, based on the density of the surface of the photosensitive drum 2a. Further, when a so-called “rear end pool” is generated in the first toner image, the measurement result (output voltage) of the density sensor 280a is rearward compared to the central portion and the front end portion of the first toner image. It further decreases at the end (see range D shown in FIG. 4). As a result of the measurement by the density sensor 280a, the determination unit 272 determines that the difference between the center portion and the front end portion and the rear end portion of the first toner image is, for example, 0.02 V or more, preferably 0.05 V or more. In this case, in the first toner image formed on the photosensitive drum 2a, it is determined that the density at the rear end is higher than the density at the center and the front end (there is a “rear end pool”). To do.

  On the other hand, as shown in FIG. 4B, in the measurement result (output voltage) of the density sensor 280a, a voltage corresponding to the first toner image is, for example, 0.02V or more, preferably 0.05V or more. If there is no difference, the determination unit 272 determines that the density of the first toner image formed on the photosensitive drum 2a is uniform (no “rear end pool”).

  When the determination unit 272 determines that a dark portion exists in a part of the first toner image, the voltage control unit 273 determines the first bias voltage (DC component), the second bias voltage (DC component), and the like. The bias voltage application unit 260 is controlled so as to adjust. The voltage control unit 273 adjusts the first bias voltage and the second bias voltage for each of the developing devices 16a, 16b, 16c, and 16d.

  Specifically, the voltage control unit 273 determines that the dark portion exists in a part of the first toner image by the determination unit 272, that is, the rear end of the first toner image by the determination unit 272. When it is determined that the density of the part is higher than the density of the center part and the front end part, the following control is performed. The voltage control unit 273 controls the bias voltage application unit 260 so as to decrease the respective voltage values of the first bias voltage and the second bias voltage while maintaining the voltage difference between the first bias voltage and the second bias voltage. .

Here, FIG. 5 is a diagram illustrating the relationship between the density of the toner image and the voltage difference between the first bias voltage and the second bias voltage. FIG. 5A shows a case where the toner image is a solid image. FIG. 5B shows a case where the toner image is a half image (non-solid image).
As shown in FIG. 5A, when the toner image is a solid image, the density of the toner image and the voltage difference between the first bias voltage and the second bias voltage are substantially proportional. On the other hand, as shown in FIG. 5B, when the toner image is a half image, the density of the toner image is substantially constant regardless of the voltage difference between the first bias voltage and the second bias voltage.

  FIG. 6 is a diagram showing the relationship between the density difference between the density at the front end and the center and the density at the rear end in the toner image and the second bias voltage. As shown in FIG. 6, when the voltage value of the second bias voltage is lowered, the toner image density difference (so-called “rear end pool”) disappears.

  Accordingly, the voltage control unit 273 controls the bias voltage application unit 260 so as not to change the voltage difference between the first bias voltage and the second bias voltage, thereby appropriately adjusting the density of the toner image formed on the photosensitive drum 2a. Maintain a proper concentration. Further, the voltage control unit 273 eliminates the difference between the density of the rear end portion and the density of the central portion and the front end portion of the toner image by lowering the voltage values of the first bias voltage and the second bias voltage. As a result, a so-called “rear end pool” does not occur in the toner image formed on the photosensitive drum 2a.

  Here, the voltage control unit 273 refers to the first toner image formed on the photosensitive drum 2a when the determination unit 272 determines that a portion having a high density exists in a part of the first toner image. The bias voltage application unit 260 is controlled based on the density (density acquired by the density processing unit 271) detected by the density detection unit for different second toner images. The second toner image is a solid image. That is, when the control unit 270 (the copy machine 1) decreases the voltage values of the first bias voltage and the second bias voltage while maintaining the voltage difference between the first bias voltage and the second bias voltage, And forming the second toner image on the photosensitive drum 2a, and the respective voltages of the second bias voltage and the first bias voltage based on the density of the second toner image acquired by the density processing unit 271. Repeat with lowering the value. The control unit 270 (the copying machine 1) prevents the so-called “rear end pool” from occurring in the second toner image through such repetition.

  The light control unit 274 controls the laser scanner unit 4a to adjust the amount of emitted light after the bias voltage application unit 260 is controlled by the voltage control unit 273. The light control unit 274 adjusts the amount of light for each of the laser scanner units 4a, 4b, 4c, and 4d. Specifically, the light control unit 274 is different from the first toner image and the second toner image formed on the photosensitive drum 2a after the bias voltage application unit 260 is controlled by the voltage control unit 273. The laser scanner unit 4a is controlled based on the density (density acquired by the density processing unit 271) detected by the density detection unit for the third toner image. The third toner image is a non-solid image.

An example of a non-solid image is a half image. As a more specific example, the non-solid image is a half image having a density of 50% or less, and more preferably a half image having a density of 30%.
When the voltage value of the second bias voltage is adjusted (lowered) by the voltage control unit 273, the density of the half image changes. Therefore, the density of the half image is adjusted by adjusting the amount of light emitted from the laser scanner unit 4a to the photosensitive drum 2a.

FIG. 7 is a diagram illustrating the relationship between the density of the toner image and the amount of light. FIG. 7A shows a case where the toner image is a solid image. FIG. 7B shows a case where the toner image is a half image.
As shown in FIG. 7A, when the toner image is a solid image, the density of the toner image is almost constant regardless of the amount of light. On the other hand, as shown in FIG. 7B, when the toner image is a half image (non-solid image), the density of the toner image and the amount of light are in a substantially proportional relationship.
Therefore, the light control unit 274 acquires the density of the toner image formed on the photosensitive drum 2a by the density processing unit 271, and the photosensitive drum 2a is irradiated from the laser scanner unit 4a based on the acquired density. The adjustment of the density of the toner image (half image) is repeated by adjusting the amount of light to be emitted. As a result, the density of the half image is adjusted while the density of the solid image remains constant.

  Next, the operation of the copy machine 1 in the first embodiment will be described. FIG. 8 is a flowchart for explaining the operation of the copier 1 in the first embodiment.

  In step ST1, the copying machine 1 forms a solid image (first toner image) on the photosensitive drum 2a.

  In step ST2, the control unit 270 (density processing unit 271) determines whether or not the density of the solid image formed in step ST1 is equal to or higher than a predetermined first density. Here, the predetermined first concentration is a concentration set as appropriate. If the density of the solid image is not equal to or higher than the predetermined first density (NO), the process proceeds to step ST3. If the density of the solid image is equal to or higher than the predetermined first density (YES), the process proceeds to step ST4.

  In step ST3, the control unit 270 (voltage control unit 273) increases the voltage difference between the first bias voltage V1 and the second bias voltage V2 by controlling the bias voltage application unit 260. After step ST3, the process returns to step ST1. In step ST1 after step ST3, the copier 1 forms a solid image on the photosensitive drum 2a based on the voltage value increased in step ST3.

  In step ST4, the control unit 270 (determination unit 272) determines whether the rear end portion of the solid image is darker than the central portion and the front end portion based on the density of the solid image acquired by the density processing unit 271 ( Whether there is a “rear end pool” or not. That is, when the determination in step ST4 is made after step ST2, the control unit 270 (determination unit 272) determines whether or not “rear end pool” exists in the solid image formed in step ST1. If there is a rear end pool (YES), the process proceeds to step ST5. If there is no rear end pool (NO), the process proceeds to step ST7.

  In step ST5, the control unit 270 (voltage control unit 273) controls the bias voltage application unit 260 to maintain the voltage difference between the first bias voltage V1 and the second bias voltage V2 (keep constant). ), The respective voltage values of the first bias voltage V1 and the second bias voltage V2 are lowered.

  In step ST6, the copier 1 forms a solid image (second toner image) on the photosensitive drum 2a based on the voltage value lowered in step ST5. After step ST6, the process returns to step ST4. When the determination in step ST4 is performed after step ST6, in step ST4, the control unit 270 (determination unit 272) determines whether or not “rear end pool” exists in the solid image formed in step ST6. .

  In step ST7 after step ST4, the copier 1 forms a half image (third toner image) on the photosensitive drum 2a.

  In step ST8, the control unit 270 (density processing unit 271) determines whether or not the density of the half image formed in step ST7 is equal to or higher than a predetermined second density. Here, the predetermined second concentration is a concentration set as appropriate. If the half density is not equal to or higher than the predetermined second density (NO), the process proceeds to step ST9. If the density of the half image is equal to or higher than the predetermined second density (YES), the process ends.

  In step ST9, the control unit 270 (light control unit 274) controls the laser scanner unit 4a so as to increase the amount of emitted light. After step ST9, the process returns to step ST7. In step ST7 after step ST9, the copier 1 forms a half image on the photosensitive drum 2a based on the light amount adjusted in step ST9.

As described above, according to the copying machine 1 of the first embodiment, the following effects are produced.
That is, when the determination unit 272 determines that the density of the rear end portion of the first toner image (solid image) is higher than the densities of the center portion and the front end portion, the copier 1 of the first embodiment The voltage controller 273 adjusts the first bias voltage and the second bias voltage, and the light controller 274 adjusts the amount of light emitted from the laser scanner unit 4a. Thereby, the copying machine 1 can make the density of the toner image uniform.

  Further, in the copier 1, the voltage control unit 273 lowers the voltage values of the first bias voltage and the second bias voltage while maintaining the voltage difference between the first bias voltage and the second bias voltage. The copier 1 maintains the density of the toner image formed on the photosensitive drum 2a at a desired density by maintaining (making constant) the voltage difference between the first bias voltage and the second bias voltage. Can do. That is, the copying machine 1 can avoid deterioration in basic performance for forming a toner image. Further, the copier 1 can make the density of the toner image uniform by lowering the voltage values of the first bias voltage and the second bias voltage.

  Further, the copier 1 adjusts the first bias voltage and the second bias voltage based on the density of the second toner image (solid image) formed on the photosensitive drum 2a. In other words, the copier 1 repeats the formation of the second toner image, the measurement of the density of the second toner image, and the adjustment of the first bias voltage and the second bias voltage to make the density of the toner image uniform. . Therefore, the copying machine 1 can avoid the “rear end pool”.

  The copier 1 also controls the laser scanner unit 4a based on the density of the third toner image (half image) formed on the photosensitive drum 2a. That is, the copying machine 1 repeats the formation of the third toner image, the measurement of the density of the third toner image, and the adjustment of the light amount of the light emitted from the laser scanner unit 4a, thereby adjusting the density of the half image. Set to an appropriate concentration. Therefore, the copier 1 can avoid the deterioration of the basic performance of forming the toner image by setting the density of the half image to an appropriate density.

[Second Embodiment]
FIG. 9 is a diagram illustrating the developing device 16a and the photosensitive drum 2a according to the second embodiment.
A copier 1 as an image forming apparatus in the second embodiment has the same configuration as the copier 1 shown in FIG. Further, the developing device of the second embodiment shown in FIG. 9 has substantially the same configuration as the developing device shown in FIGS. The developing device of the second embodiment is different from the developing device shown in FIGS. 2 and 3 in that the control unit 270 includes a supply / discharge control unit 275. Although the copying machine 1 includes four developing devices 16a, 16b, 16c, and 16d, each has the same configuration, and therefore, the developing device 16a will be described below as a representative.

  The density processing unit 271 and the density sensor 280a as the density detection unit detect the density of the toner image as described above. Therefore, the density processing unit 271 and the density sensor 280a detect the density of a toner image (solid image) formed after the bias voltage application unit 260 is controlled by the voltage control unit 273.

  The supply / discharge control unit 275 performs control for toner supply and control for toner discharge. Specifically, the supply / discharge control unit 275 supplies toner from the toner cartridge 5a to the developing container 110. Further, the supply / discharge control unit 275 forcibly discharges the toner already stored in the developing container 110. For example, the developing device 16 a is provided with a cleaning device 290 for collecting toner adhering to the surface of the developing roller 150. The supply / discharge control unit 275 controls the magnetic roller 130, the developing roller 150, and the cleaning device 290 to discharge the toner stored in the developing container 110 by the cleaning device 290.

The supply / discharge control unit 275 discharges the toner and supplies the toner when the density of the toner image based on the detection by the density detection unit (the density sensor 280a and the density processing unit 271) is less than a predetermined density.
That is, when the flying property (developability) of the toner stored in the developing container 110 is lowered, the potential difference between the first bias voltage V1 and the second bias voltage V2 is maintained as in the first embodiment. If the voltage values of the first bias voltage V1 and the second bias voltage V2 are lowered, the density of the solid image may not be maintained within a desired density range. Therefore, the developing device 16a replaces the toner stored in the developing container 110 by consuming (discharging) the toner at the supply interval (between sheets) of the paper T in order to restore the developing property of the toner.

FIG. 10 is a graph showing the relationship between the density of the toner image and the second bias voltage V2.
With the toner (deteriorated toner) already stored in the developing container 110, when the second bias voltage V2 is about 50 [V] or less, the density of the toner image decreases. On the other hand, with toner that has not deteriorated (new toner), when the second bias voltage V2 is about 30 [V] or less, the density of the toner image decreases. From the relationship shown in FIG. 10, it can be understood that the density of the toner image can be maintained when the new toner is used even if the second bias voltage V2 is further lowered.

  Therefore, the copying machine 1 according to the second embodiment has the toner (deterioration) in the developing container 110 when the density of the toner image based on the detection by the density detection unit (the density sensor 280a and the density processing unit 271) is less than a predetermined density. By discharging the toner) and supplying the toner (new toner) from the toner cartridge 5a to the developing container 110, the density of the toner image is made uniform and the density of the toner image is prevented from being lowered.

  Here, the amount of toner consumed (discharged) between sheets is generally set according to the print rate of the output image, the use environment, and the like. However, it is difficult to set an appropriate consumed toner amount according to various usage situations. In this embodiment, toner image formation, toner image density detection, and toner discharge and supply based on the density detection result are repeated, so that a minimum amount of toner is consumed to obtain an optimum image quality. Can do.

  Next, the operation of the copy machine 1 in the second embodiment will be described. FIG. 11 is a flowchart for explaining the operation of the copier 1 in the second embodiment.

  The processing from step ST11 to step ST16 is the same as the processing from step ST1 to step ST6 of the first embodiment. For this reason, the description from step ST11 to step ST16 is omitted.

  Step ST17 is executed after the process of step ST16. In step ST17, the control unit 270 (density processing unit 271) determines whether or not the density of the solid image formed in step ST16 is equal to or higher than a predetermined third density. Here, the third concentration is, for example, a lower limit value of the above-described desired concentration range, and is a concentration that is set as appropriate. If the density of the solid image formed in step ST16 is equal to or higher than the predetermined third density (YES), the process returns to step ST14. If the density of the solid image formed in step ST16 is not equal to or higher than the predetermined third density (NO), the process proceeds to step ST18.

  In step ST18, the control unit 270 (supply / discharge control unit 275) discharges the toner stored in the developing container 110 from the developing container 110 and supplies the toner stored in the toner cartridge 5a to the developing container 110. Here, the toner discharge amount and the toner supply amount may be set in accordance with the density detected in step ST17. After step ST18, the process returns to step ST11.

  Step ST19 is a process performed when “NO” is determined in step ST14. The processing from step ST19 to step ST21 is the same as the processing from step ST7 to step ST9 of the first embodiment. For this reason, the description from step ST19 to step ST21 is omitted.

  Note that the processing in steps ST17 and ST18 discharges and supplies toner according to the density of the solid image. However, the control unit 270, when the difference between the second bias voltage V21 when the density of the solid image is lower than the third density and the second bias voltage V22 when the trailing edge pool does not occur is less than 10V, The developability may be restored by consuming the toner between the sheets.

As described above, according to the copying machine 1 of the second embodiment, the following effects are produced.
That is, the copying machine 1 according to the second embodiment uses the supply / discharge control unit 275 to develop the toner image when the density of the toner image based on the detection by the density detection unit (the density sensor 280a and the density processing unit 271) is less than a predetermined density. The toner is discharged from the container 110 and the toner is supplied to the developing container 110. As a result, the copying machine 1 can make the density of the toner image uniform and obtain an optimum image quality (image density).

In addition, this invention is not limited to embodiment mentioned above, It can implement with a various form.
The copying machine 1 of the above-described embodiment is a color copying machine, but is not limited to this mode, and may be a monochrome copying machine.
In the copying machine 1 according to the above-described embodiment, the toner image is transferred onto the paper T via the intermediate transfer belt 48 (indirect transfer method). The formed toner image may be directly transferred to the paper T (direct transfer method).

Further, the image forming apparatus of the present invention is not limited to the copying machine 1 described above. In other words, the image forming apparatus of the present invention may be a multi-function machine having a copy function, a facsimile function, a printer function, and a scanner function, or may be a facsimile or a printer.
The transfer material on which the toner image is fixed by the image forming apparatus of the present invention is not limited to the paper T, and may be a film sheet such as an OHP (overhead projector) sheet.

DESCRIPTION OF SYMBOLS 1 ... Copy machine (image forming apparatus), 4a, 4b, 4c, 4d ... Laser scanner unit (light source), 130 ... Magnetic roller (developer carrying rotary body), 150 ... Developing roller (toner carrying rotary body), 260 ... Bias voltage application unit, 271 ... concentration processing unit, 272 ... determination unit, 273 ... voltage control unit, 274 ... light control unit

Claims (9)

A developer-carrying rotating body in which a developer layer is formed on the surface by carrying a developer containing a magnetic carrier and toner by a magnetic force;
A toner-carrying rotator that is disposed opposite to the developer-carrying rotator and has a toner layer formed on the surface by toner moved from the developer-carrying rotator;
A light source that emits light;
An electrostatic latent image is formed on the surface by the light emitted from the light source and disposed opposite to the toner carrying rotator and the light source, and the electrostatic latent image is formed by the toner moved from the toner carrying rotator. An image carrier on which a toner image is formed by developing the toner image;
A bias voltage applying unit for applying a first bias voltage to the developer carrying rotator and applying a second bias voltage to the toner carrying rotator;
A density detector for detecting the density of the toner image;
When a first toner image as a toner image is formed on the image carrier, a part of the first toner image is based on the density detected by the density detector for the first toner image. A determination unit for determining whether or not there is a darker part than the other part except the part of the first toner image;
The bias voltage application unit is configured to adjust the first bias voltage and the second bias voltage when the determination unit determines that a portion having a high density exists in the part of the first toner image. A voltage controller to control;
A light control unit that controls the light source to adjust the amount of light emitted after the bias voltage application unit is controlled by the voltage control unit;
An image forming apparatus comprising: The voltage control unit calculates a voltage difference between the first bias voltage and the second bias voltage when the determination unit determines that a portion having a high density exists in the part of the first toner image. 2. The image forming apparatus according to claim 1, wherein the bias voltage application unit is controlled to decrease the voltage values of the first bias voltage and the second bias voltage while maintaining the voltage. When the determination unit determines that a portion having a high density exists in the part of the first toner image, the voltage control unit defines the first toner image formed on the image carrier. The image forming apparatus according to claim 1, wherein the bias voltage application unit is controlled based on a density detected by the density detection unit for different second toner images. The image forming apparatus according to claim 3, wherein the second toner image is a solid image. The light control unit, based on the density detected by the density detection unit for the third toner image formed on the image carrier after the bias voltage application unit is controlled by the voltage control unit, The image forming apparatus according to claim 1, wherein the image forming apparatus controls a light source. The image forming apparatus according to claim 5, wherein the third toner image is a non-solid image. The image forming apparatus according to claim 1, wherein the density detection unit detects a density of a toner image formed on the image carrier. An intermediate transfer member to which a toner image formed on the image carrier is transferred;
The image forming apparatus according to claim 1, wherein the density detection unit detects a density of a toner image transferred to the intermediate transfer member. A supply / discharge control unit that performs control for toner supply and performs control for toner discharge;
The density detector detects a density of a toner image formed after the bias voltage application unit is controlled by the voltage controller;
The supply / discharge control unit discharges the toner and supplies the toner when the density of the toner image based on the detection is less than a predetermined density;
The image forming apparatus according to claim 1.

Images