JP2014137532A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing rear end thickening from being noticeable even after duration of use.SOLUTION: An image forming apparatus comprises: a developer carrier 130; a toner carrier 150; an image carrier 2a; a measurement unit; and a bias control unit 272. The bias control unit 272 controls, at a predetermined timing, a bias application unit to vary a voltage to be applied respectively to the developer carrier 130 and the toner carrier 150 in order to adjust the amount of toner supplied to the image carrier 2a from the toner carrier 150, and forms a plurality of toner images according to the varied voltage. The bias control unit 272 acquires a saturated toner amount on the basis of a value related to the toner regarding the plurality of toner images, and adjusts developing bias conditions between the image carrier 2a and the toner carrier 150 on the basis of the saturated toner amount and an initial saturated toner amount as an initial value.

Description

  The present invention relates to an image forming apparatus capable of forming an image on a transfer material using toner.

  Some image forming apparatuses such as copiers, multifunction machines, and printers form an image on a transfer material (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 rear end pool is generated when the toner is excessively supplied to the rear end portion of the toner image because the linear velocity of the developing roller is higher than the linear velocity of the photosensitive drum.

  For this reason, the image forming apparatus detects the degree of edge enhancement of the toner image formed on the photosensitive drum and 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

  In the conventional image forming apparatus, the density of the trailing edge pool in the toner image formed after the endurance sometimes becomes higher than the density of the trailing edge pool in the toner image formed initially. FIG. 9 is a diagram illustrating the relationship between the electrostatic latent image contrast, the saturated toner amount, and the toner supply amount in the initial stage, and the relationship between the electrostatic latent image contrast, the saturated toner amount, and the toner supply amount after the endurance. FIG. 9A shows the initial stage. FIG. 9B shows the state after endurance. Arrows D1 and D2 in FIG. 9 indicate the latent image contrast. The latent image contrast is a potential difference between the image portion and the non-image portion. The latent image contrast varies depending on the electrostatic capacity of the photosensitive drum. In addition, when toner is supplied from the developing roller to the photosensitive drum, the electric field between the photosensitive drum and the developing roller is weakened by the charge of the toner, and finally the development stops. The saturated toner amount is a toner amount when development is stopped. The toner supply amount is an amount of toner that can be supplied from the developing roller to the photosensitive drum. The toner supply amount is determined based on the toner amount per unit area in the developing roller and the ratio between the linear velocity of the developing roller and the linear velocity of the photosensitive drum. The front end shown in FIG. 9 is the front end of the toner image formed on the photosensitive drum. The trailing edge is the trailing edge of the toner image formed on the photosensitive drum. Here, the rotation direction of the photosensitive drum is a forward direction.

In the rear end portion shown in FIG. 9A, since more toner is supplied than in the front end portion or the central portion, development is performed until the saturated toner amount is reached, and a rear end pool (see arrow E1) occurs. .
After the endurance, since the film thickness of the photosensitive drum becomes thin, the capacitance of the photosensitive drum changes compared to the initial stage. As a result, as shown in FIG. 9B, the electrostatic contrast after the endurance (see arrow D2) becomes higher than the initial electrostatic contrast (see arrow D1). Further, the saturated toner amount becomes higher than the initial value as the electrostatic contrast becomes higher. For this reason, the toner can be supplied up to the saturated toner amount as the upper limit, so that the density of the rear end pool (see arrow E2) after endurance is higher than the initial rear end pool (see arrow E1). That is, after the endurance, the rear end pool becomes prominent.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can prevent the rear end pool from becoming prominent even after durability.

  The image forming apparatus includes a developer carrier, a toner carrier, an image carrier, a measurement unit, and a bias control unit. The developer carrying member carries a two-component developer containing toner and carrier. The toner carrier is supplied with toner from the developer carrier and carries the toner. An electrostatic latent image is formed on the surface of the image carrier, and the electrostatic latent image is developed with toner supplied from the toner carrier to form a toner image. The measurement unit measures a value related to toner in a toner image. The bias applying unit applies a voltage to each of the developer carrier and the toner carrier. The bias control unit controls the bias application unit. The bias control unit adjusts a voltage applied to each of the developer carrier and the toner carrier in order to adjust the amount of toner supplied from the toner carrier to the image carrier at a predetermined timing. The bias applying unit is controlled to be variable, and a plurality of toner images are formed according to the variable voltage. The bias control unit obtains a saturated toner amount based on the value relating to the toner for the plurality of toner images measured by the measurement unit, and uses the saturated toner amount and an initial saturated toner amount as an initial value. Based on this, a developing bias condition between the image carrier and the toner carrier is adjusted.

  According to the present invention, it is possible to suppress the rear end pool from becoming prominent even after endurance.

It is a figure for demonstrating arrangement | positioning of each component of a copier. It is a figure which shows a developing device and a photoconductor drum. It is a figure which shows a mode that the toner layer of predetermined thickness is formed on the surface of a developing roller. 6 is a first graph showing a relationship between toner density and voltage difference. 6 is a second graph showing the relationship between toner density and voltage difference. It is a graph which shows the relationship between the DC voltage applied to a developing roller, and a 1st variation | change_quantity. It is a graph which shows the relationship between the amount of correction | amendment, and 2nd variation | change_quantity. It is a graph which shows the relationship between a film thickness and the number of printed sheets. It is a figure which shows the relationship between the electrostatic latent image contrast in the initial stage, the amount of saturated toner, and the amount of toner supply, and the relationship between the electrostatic latent image contrast, the amount of saturated toner, and the amount of toner supply after durability.

  Hereinafter, an embodiment of the present invention will be described. First, referring to FIG. 1, the overall structure of a copier 1 as an example of an image forming apparatus according to 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 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.

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 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 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 to face a developing roller 150 (to be described later) and laser scanner units 4a, 4b, 4c, and 4d (to be 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 2a, 2b, 2c, and 2d develops an electrostatic latent image with toner supplied 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 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 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 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 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 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 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, the developing device of this 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.

The developing device 16a of this embodiment contains a two-component developer 190 composed of a toner 192 and a magnetic carrier 191. The developing device 16a develops the electrostatic latent image by supplying toner 192 to the photosensitive drum 2a to form a toner image.
Specifically, as illustrated in FIGS. 2 and 3, the developing device 16 a is disposed inside the developing container 110 and a developing container 110 that stores a two-component developer 190 including a toner 192 and a magnetic carrier 191. Stirring rollers 120a and 120b, a magnetic roller 130 disposed above the stirring roller 120a in the vertical direction, and a layer thickness restriction disposed near the magnetic roller 130 on the side (left side in FIG. 2) of the magnetic roller 130 A blade 140, a cover member 141 disposed above the layer thickness regulating blade 140 in the vertical direction, a developing roller 150 disposed opposite to the magnetic roller 130, a bias applying unit 260, and a control unit 270. Prepare. The magnetic roller 130 corresponds to an embodiment of the “developer carrier” of the present invention. The developing roller 150 corresponds to an embodiment of the “toner carrier” of the present invention.

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 120 a and 120 b 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 this 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 applying 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. The developing roller 150 is supplied with the toner 192 from the magnetic roller 130 and carries the toner 192. 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 applying 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 developing device 16 a includes a density sensor 280 and a control unit 270. The control unit 270 includes a density processing unit 271, a bias application unit 260, and a bias control unit 272.

The density sensor 280 and the density processing unit 271 constitute the “measurement unit” of the present invention. The density sensor 280 and the density processing unit 271 (measurement unit) measure values related to toner in the toner image. The value relating to the toner is, for example, the toner density in the toner image or the toner amount (paste amount) in the toner image. 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.
Upon receiving the voltage signal output from each density sensor 280, the density processing unit 271 acquires the toner density in the toner image based on the voltage value of the voltage signal.

  The bias applying unit 260 applies a voltage to each of the magnetic roller 130 and the developing roller 150. That is, the bias application unit 260 applies the predetermined first bias voltage V1 to the magnetic sleeve 131 (magnetic roller 130) as described above. As described above, the bias applying unit 260 applies the predetermined second bias voltage V2 to the developing sleeve 151 (the developing roller 150). A DC voltage and an AC voltage are superimposed on each of the first bias voltage V1 and the second bias voltage V2.

  The bias control unit 272 controls the bias application unit 260. The bias controller 272 biases the voltage applied to each of the magnetic roller 130 and the developing roller 150 to vary in order to adjust the amount of toner supplied from the developing roller 150 to the photosensitive drum 2a at a predetermined timing. The application unit 260 is controlled to form a plurality of toner images according to the variable voltage.

  The predetermined timing is determined based on the cumulative driving time of the photosensitive drum 2a. Since the predetermined timing is determined based on the cumulative driving time of the photosensitive drum 2a regardless of the size of the paper T, an appropriate timing can be set. As an example, when the initial film thickness of the photosensitive drum 2a is 30 μm, the film thickness of the photosensitive drum 2a after printing 100,000 sheets is 25 μm, and the photosensitive drum 2a after printing 200,000 sheets. The film thickness is 20 μm. For this reason, the predetermined timing may be, for example, every time 50,000 sheets are printed.

  FIG. 4 is a first graph showing the relationship between toner density and voltage difference. FIG. 5 is a second graph showing the relationship between toner density and voltage difference. The second graph is a graph obtained by enlarging a part of the first graph. FIG. 6 is a graph showing the relationship between the DC voltage applied to the developing roller 150 and the first change amount. FIG. 7 is a graph showing the relationship between the correction amount and the second change amount. FIG. 8 is a graph showing the relationship between the film thickness and the number of printed sheets.

  The graphs of FIGS. 4 to 8 are obtained in the following example. The photosensitive drums 2a, 2b, 2c, and 2d have a linear velocity of 250 mm / sec, the photosensitive drums 2a, 2b, 2c, and 2d have an outer diameter of 30 mm, the developing roller 150 has an outer diameter of 20 mm, and the developing roller 150 and the photosensitive drum. The distance between 2a, 2b, 2c and 2d is 0.1 mm, the dark potential of the photosensitive drums 2a, 2b, 2c and 2d is 500V, the bright potential of the photosensitive drums 2a, 2b, 2c and 2d is 80V, and development The DC voltage applied to the roller 150 is 140V (initial), the initial film thickness of the photosensitive drums 2a, 2b, 2c, and 2d is 30 μm, and the desired density of the toner image is 1.2.

  The bias control unit 272 described above controls the bias application unit 260 to thereby provide a voltage difference ΔV between the first bias voltage V1 applied to the magnetic roller 130 and the second bias voltage V2 applied to the developing roller 150. Is variable. In the example illustrated in FIGS. 4 and 5, the bias control unit 272 controls the bias application unit 260 so that the voltage difference ΔV is 200V, 300V, 350V, 400V, 450V, 500V, and 550V. Then, the bias controller 272 forms a toner image based on each voltage difference ΔV. As an example, the bias controller 272 forms a toner image when the voltage difference ΔV is 550V.

  Further, the bias control unit 272 acquires the saturated toner amount based on the toner-related values for the plurality of toner images measured by the measurement unit, and based on the saturated toner amount and the initial saturated toner amount as an initial value. The developing bias condition between the photosensitive drum 2a and the developing roller 150 is adjusted. The density sensor 280 and the density processing unit 271 (measurement unit) measure the density of the toner image formed based on each of the plurality of voltage differences ΔV. The bias control unit 272 acquires the saturated toner amount based on the density of the plurality of toner images. The saturated toner amount is the maximum toner concentration among a plurality of toner concentrations measured by the density sensor 280 and the density processing unit 271 (measurement unit). For example, the saturated toner amount is a toner amount (toner concentration) corresponding to a portion where the graph is saturated when a graph showing the relationship between the toner concentration and the voltage difference is drawn as shown in FIGS. In the case illustrated in FIG. 5, the saturated toner amount (toner amount) becomes 1.5 (after endurance). The initial saturated toner amount is the saturated toner amount in the initial stage. The initial saturated toner amount is obtained in the same manner as the saturated toner amount after endurance. In the case illustrated in FIG. 5, the initial saturated toner amount (initial toner amount) is 1.4.

The bias controller 272 adjusts the development bias condition based on the amount of change between the initial saturated toner amount and the saturated toner amount after the endurance. More specifically, the development bias condition is adjusted based on the first change amount and the second change amount.
The first change amount is a change amount between the initial saturated toner amount and the saturated toner amount after durability. In the case illustrated in FIGS. 4 and 5, the first change amount (ΔTD) is 0.1 (= 1.5−1.4). When the first change amount 0.1 is applied to the relationship between the DC voltage applied to the developing roller 150 and the first change amount (see FIG. 6), the DC voltage becomes 100V. Here, the relationship shown in FIG. 6 is preset.

  The second change amount is a change amount of a voltage difference between the voltage applied to the magnetic roller 130 and the voltage applied to the developing roller 150 when a toner image having a predetermined density is obtained. That is, the second change amount is a change amount between the initial voltage difference and the voltage difference after endurance when a predetermined density is obtained as the toner density of the toner image. In the case illustrated in FIG. 4, 1.2 (predetermined density) is obtained as the toner density of the toner image when the voltage difference ΔV is 394 V in the initial stage. In the case illustrated in FIG. 4, after the endurance, when the voltage difference ΔV is 344 V, a toner image density of 1.2 (predetermined density) is obtained. Therefore, in the case illustrated in FIG. 4, the second change amount is 50 V (= 394 V to 344 V).

  Then, when the second change amount 50V is applied to the relationship between the correction amount and the second change amount (see FIG. 7), the correction amount becomes 8V. The correction amount is an amount for correcting the value of the DC voltage obtained based on the relationship illustrated in FIG. Here, the relationship shown in FIG. 7 is preset.

  The bias controller 272 adjusts the DC voltage applied to the developing roller 150. For example, the bias control unit 272 obtains the DC voltage 108V to be applied to the developing roller 150 by adding the DC voltage 100V obtained based on FIG. 6 and the correction amount 8V obtained based on FIG. The bias control unit 272 controls the bias application unit 260 so as to apply the DC voltage 108V to the developing roller 150 when forming an image. In addition, the bias controller 272 controls the bias applying unit 260 to apply a DC voltage of 452 V (= 108 V + 344 V) to the magnetic roller 130 in order to maintain a voltage difference 344 V for obtaining a predetermined toner density.

  The above configuration (operation) is particularly effective when a single-layer organic photosensitive drum is used as the photosensitive drums 2a, 2b, 2c, and 2d. When a discharge product or the like adheres to the surface of a single-layer organic photosensitive drum, the discharge product is removed by scraping the surface of the drum. That is, when a single-layer organic photosensitive drum is used as the photosensitive drums 2a, 2b, 2c, and 2d, film scraping on the photosensitive drums 2a, 2b, 2c, and 2d becomes remarkable. Therefore, in the present embodiment, even when the film thickness of the photosensitive drums 2a, 2b, 2c, and 2d is changed, the rear end accumulation is suppressed by having the above configuration.

As described above, according to the copying machine 1 of the present embodiment, the following effects are produced.
In other words, the copier 1 of the present embodiment has the magnetic roller 130 and the developing roller 150 to adjust the amount of toner supplied from the developing roller 150 to the photosensitive drums 2a, 2b, 2c, and 2d at a predetermined timing. The bias application unit 260 is controlled so as to vary the voltage applied to each, and a plurality of toner images are formed according to the varied voltage. Further, the copier 1 acquires the saturated toner amount based on the toner density for the plurality of toner images measured by the density sensor 280 and the density processing unit 271, and acquires the saturated toner amount and the initial saturated toner amount as an initial value. Based on the above, the developing bias conditions between the photosensitive drums 2a, 2b, 2c, and 2d and the developing roller 150 are adjusted. As a result, the copying machine 1 can suppress the rear end accumulation from becoming prominent even after endurance. That is, the copying machine 1 can make the density of the rear end pool after endurance the same as that of the initial rear end pool in the solid image. Further, since the copying machine 1 does not develop toner more than intended, it can suppress an increase in toner consumption.

  The adjustment of the developing bias condition is to adjust the DC voltage applied to the developing roller 150. Thereby, the copying machine 1 can change the developing bias condition between the photosensitive drum 2 a and the developing roller 150.

  The development bias condition is adjusted based on the first change amount and the second change amount. The first change amount is a change amount between the initial saturated toner amount and the saturated toner amount after durability. The second change amount is a change amount of a voltage difference between the voltage applied to the magnetic roller 130 and the voltage applied to the developing roller 150 when a toner image having a predetermined density is obtained. Since the copier 1 considers the second change amount, the DC voltage applied to the developing roller 150 can be corrected according to the change in developability with time.

  The predetermined timing is determined based on the cumulative driving time of the photosensitive drums 2a, 2b, 2c, and 2d. As a result, the copier 1 can set the timing according to the actual operation even when an image is formed on the paper T having a different length (size) for each job.

In addition, this invention is not limited to embodiment mentioned above, It can implement with a various form.
The copier 1 of the present embodiment suppresses deterioration of the trailing edge pool generated in the toner image after endurance compared to the initial stage. However, the application of the present embodiment is not limited to suppressing the deterioration of the rear end pool.

The copier 1 of the present embodiment is a color copier, but is not limited to this form and may be a monochrome copier.
In the copying machine 1 of the present embodiment, the toner image is transferred to the paper T via the intermediate transfer belt 7 (indirect transfer method). However, the present invention is not limited to this form, and is formed on the photosensitive drum. The transferred toner image may be directly transferred to the paper T (direct transfer method).
The copier 1 of the present embodiment is configured to print both sides of the paper T, but is not limited to this, and may be configured to print one side of the paper.

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), 2a, 2b, 2c, 2d ... Photosensitive drum (image carrier), 130 ... Magnetic roller (developer carrier), 150 ... Developing roller (toner carrier), 260 ... Bias application unit, 271... Density processing unit (measurement unit), 272... Bias control unit, 280... Density sensor (measurement unit)

Claims (4)

A developer carrying member carrying a two-component developer containing toner and carrier;
A toner carrier that is supplied with toner from the developer carrier and carries the toner;
An electrostatic latent image is formed on the surface, and the electrostatic latent image is developed by the toner supplied from the toner carrier to form a toner image; and
A measurement unit for measuring a value related to toner in the toner image;
A bias applying section for applying a voltage to each of the developer carrier and the toner carrier;
A bias control unit for controlling the bias application unit,
The bias control unit includes:
In order to adjust the amount of toner supplied from the toner carrier to the image carrier at a predetermined timing, the bias is applied to vary the voltage applied to the developer carrier and the toner carrier. A plurality of toner images according to the variable voltage by controlling the unit,
A saturated toner amount is acquired based on a value related to the toner for the plurality of toner images measured by the measuring unit, and the image holding is performed based on the saturated toner amount and an initial saturated toner amount as an initial value. An image forming apparatus for adjusting a developing bias condition between a body and a toner carrier. The image forming apparatus according to claim 1, wherein the adjustment of the developing bias condition is to adjust a DC voltage applied to the toner carrier. The adjustment of the developing bias condition is as follows:
The amount of change between the initial saturated toner amount and the saturated toner amount;
A change amount of a voltage difference between a voltage applied to the developer carrier and a voltage applied to the toner carrier when obtaining a toner image of a predetermined density;
The image forming apparatus according to claim 1, wherein the adjustment is performed based on the image quality. The image forming apparatus according to claim 1, wherein the predetermined timing is determined based on a cumulative driving time of the image carrier.

Images