JP2009300488A - Developing device, image forming apparatus equipped with the same and developer replenishing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine an appropriate replenishment amount of a developer by accurately recognizing the total amount of the developer even employing a trickle system. <P>SOLUTION: A developing device includes: a developer detecting means 22 that changes an output voltage in accordance with a difference of toner concentration in the developer stored in a developer container 11; a developer supply means 20 for supplying the developer to the developer container 11; and a developer replenishment control means 5 that calculates the total amount of the developer stored in the developer container 11 based on the amplitude value of the detection voltage output from the developer detecting means 22, calculates the toner concentration based on the mean value of the detection voltages, and controls the amount of the developer to be replenished by the developer supply means 20 so that the desired toner concentration can be obtained, based on the total amount of the developer and the toner concentration obtained by the calculations. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing device, an image forming apparatus including the developing device, and a developer replenishing method.

  Conventionally, as an image forming apparatus, first information corresponding to a toner concentration of a two-component developer including toner and carrier particles is detected by a first sensor, and second information corresponding to the density of the two-component developer is second It is known that the toner supply to the two-component developer is controlled using the output of the first sensor and the output of the second sensor detected by a sensor (see, for example, Patent Document 1).

JP-A-5-341654

  However, since the conventional image forming apparatus employs a so-called trickle system that supplies and discharges the developer, it is difficult to accurately grasp the total amount of the developer. For this reason, there has been a problem that the amount of developer replenishment that can achieve a desired toner concentration cannot be determined appropriately.

  Accordingly, the present invention provides a developing device capable of determining the appropriate developer replenishment amount by grasping the total amount of developer and toner density, and an image forming apparatus equipped with the developing device, even in the trickle system It is another object of the present invention to provide a developer replenishing method.

As a means for solving the above problems, the present invention provides:
Developing device
A developing device that stirs a developer containing toner and a carrier contained in a developer container and supplies the developer to an image carrier,
Developer detecting means for changing an output voltage according to a difference in toner concentration of the developer contained in the developer containing container;
Developer supplying means for supplying a developer to the developing means;
Based on the amplitude value of the detection voltage output from the developer detection means, the total amount of developer accommodated in the development means is calculated, and the toner density is calculated based on the average value of the detection voltages. And a developer replenishment control unit that controls the amount of developer replenishment by the developer supply unit based on the total amount of developer and the toner concentration.

  The developer detection means includes various detection means for detecting the toner density, such as a magnetic type that detects a change in the magnetic permeability of the developer, or an optical type that detects a change in the reflected light amount of the developer. Can be used.

  With the above-described configuration, it is possible to easily grasp the total amount of developer simply by obtaining the amplitude value of the detection voltage in spite of the trickle system. Further, the toner density can be easily grasped only by obtaining the average value of the detection voltages. Since the developer replenishment amount is controlled in consideration of not only the calculated toner concentration but also the calculated total amount of developer, a desired toner concentration can be obtained accurately. . Further, since the amplitude value and the average value of the detection voltage are used, it is only necessary to provide a single detection means, and the production can be made at low cost.

The developer replenishment control means may calculate the total amount of developer according to the following equation based on the amplitude value of the detection voltage output from the detection unit of the developer detection means.
M = −a × V1 + b
M: total amount of developer V1: amplitude value of detection voltage output from developer detection means a, b: constant

The developer replenishment control means may calculate the toner density according to the following equation based on the average value of the detection voltages output from the developer detection means.
Tc = −c × V2 + d
Tc: toner density V2: average value of detection voltage output from developer detection means c, d: constant

The developer replenishment control means may determine the developer replenishment amount according to the following equation.
m = (− e × Tc / 100 + f) × M
m: developer replenishment amount e, f: constant

The developer storage container is divided into a first storage portion and a second storage portion that are juxtaposed and extend from one end side to the other end side. The first storage portion has a replenishment portion formed on one end side, and a second storage portion. The accommodating portion is formed with a discharge portion on one end side, and the first accommodating portion and the second accommodating portion are communicated with each other via the communicating portions at both ends, and the first accommodating portion is replenished from the replenishing portion on the one end side. A first conveying means for conveying the developer while stirring toward the communicating portion on the other end side is disposed, and the developer supplied from the first accommodating portion to the second accommodating portion via the communicating portion is discharged to the second accommodating portion. A second conveying means for conveying while stirring toward the
It is preferable that the toner density detecting unit is disposed at the most downstream portion of the first conveying unit located on the opposite side to the replenishing unit.

  With this configuration, the developer transported by the first transport unit is likely to stay and the toner concentration detection unit can be disposed in a region where the pressure by the developer is high, and the trickle system is relatively stable. Output characteristics can be obtained.

Further, the present invention provides a means for solving the above-described problems,
How to replenish the developer
A step of detecting a difference in toner concentration between the toner contained in the developer containing container and the developer containing the carrier by the developer detecting means and outputting as a detection voltage;
Calculating the total amount of developer accommodated in the developer accommodating container based on the amplitude value of the output detection voltage, and calculating the toner density based on the average value;
Calculating a replenishment amount of developer to be replenished to the developer container based on the calculated total amount of developer and toner concentration;
And a step of replenishing the developer container with the developer based on the calculated replenishment amount of the developer.

  Further, according to the present invention, as means for solving the above-described problems, the image forming apparatus includes a developing device having any one of the above-described configurations.

  According to the present invention, the total amount of developer is calculated based on the amplitude value of the detection voltage in the developer detection means, the toner concentration is calculated based on the average value of the detection voltage, and the total amount of developer thus obtained is calculated. In addition, since the developer replenishment amount is determined based on the toner concentration so as to obtain a desired toner concentration, appropriate replenishment control can be performed.

  Embodiments according to the present invention will be described below with reference to the accompanying drawings. In the following description, terms indicating specific directions and positions (for example, terms including “upper”, “lower”, “one end”, “other end”, etc.) are used as necessary. Is used to facilitate understanding of the invention with reference to the drawings, and the technical scope of the present invention is not limited by the meaning of these terms.

(Constitution)
FIG. 1 shows a trickle type image forming apparatus in which not only toner but also developer is replenished among electrophotographic systems using a two-component developer. The image forming apparatus generally includes an image forming unit 1, a transfer unit 2, an exposure unit 3, a paper feeding unit 4, a cleaning unit 5, a control unit 6 (see FIG. 4), and the like.

  As shown in FIG. 2, the image forming unit 1 includes a charging device 8, a developing device 9, a cleaning device 10, and the like around the photosensitive drum 7. As shown in FIG. 1, the image forming unit 1 is arranged at four locations along the intermediate transfer belt 27 of the transfer unit 2, and yellow (Y), magenta (M), cyan (C), By performing black (Bk) image formation, a color image is formed on the surface of the intermediate transfer belt 27.

  The charging device 8 forms a predetermined surface potential on the surface of the photosensitive drum 7. This surface potential becomes an electrostatic latent image when exposed by the exposure unit 3.

  As shown in FIGS. 2 and 3, the developing device 9 contains a stirring screw 12, a supply screw 13, and a developing roller 14 in a developer container 11.

  As shown in FIG. 3, the developer storage container 11 has a long box shape extending from one end side to the other end side, and the inside is partitioned by the partition wall 15 and the first storage portion 16 and the second storage portion along the longitudinal direction. It is divided into two parts. However, both end sides of the first accommodating portion 16 and the second accommodating portion 17 are communicated by communicating portions 18a and 18b, respectively, and the accommodated developer circulates while being stirred.

  A developer replenishing port 19 is formed on one end side of the first accommodating portion 16, and the developer is replenished from the corresponding cartridge 20. Here, a two-component developer containing toner and carrier is used as the developer. However, an external additive or the like may be further included in the developer. Note that the toner concentration of the developer stored in the developer container 11 in advance is 7%, and the toner concentration of the developer replenished from the cartridge 20 is 80% (carrier concentration is 20%, usually 10 to 20%).

  On the other hand, a developer discharge port 21 is formed on one end side of the second storage portion 17 so that the carrier deteriorated by discharging the developer appropriately does not remain in the developer storage container 11 for a long period of time. ing. Note that the total amount of the developer in the developer container 11 varies by about ± 20% due to the supply and discharge of the developer.

  The stirring screw 12 is arranged in the first housing portion 16 with a configuration including a spiral blade 12b around the rotation shaft 12a. The agitation screw 12 is agitated while transporting the developer from one end side to the other end side by being rotationally driven.

  At the most downstream portion of the stirring screw 12, a magnetic permeability sensor 22 that is a developer detecting means is disposed. The magnetic permeability of the developer depends on the toner concentration, and decreases as the toner concentration increases and increases as the toner concentration decreases. Therefore, the magnetic permeability sensor 22 outputs the difference in the magnetic permeability of the developer located in the detection region as a detection voltage, and calculates the toner density based on this detection voltage as described later. Here, the initial adjustment is made so that the output voltage becomes about 2.6 V at a desired toner concentration (7%). In the example of FIG. 3, the sensitivity per 1% toner density is about −0.5 V /% in an area having linear sensitivity (toner density about 4 to 10%). Therefore, for example, if the detection voltage is 2.1 V, the toner density is 8%, and if it is 3.1 V, the toner density is 6%.

  Similarly to the stirring screw 12, the supply screw 13 has a configuration in which a spiral blade 13b is provided around the rotation shaft 13a and is disposed in the second accommodating portion 17. The supply screw 13 is driven to rotate, thereby transferring the developer from the communication portion 18 a side to the communication portion 18 b side and supplying the developer to the developing roller 14.

  As shown in FIG. 2, the developing roller 14 has a plurality of permanent magnets 24 accommodated in a cylindrical sleeve 23 (here, five permanent magnets S2, N2, S1, N1, and S3 are connected to the developing roller 14). In order and clockwise.) The sleeve 23 is configured to rotate forward and backward in the circumferential direction by a sleeve driving means (not shown).

  In addition, a regulating member 25 that is opposed to the outer peripheral surface of the developing roller 14 is attached to the developer container 11. The regulating member 25 scrapes off excess toner adhering to the developing roller 14 and regulates the amount of toner supplied to the photosensitive drum 7. Further, each of the screws 12, 13 may be provided with a flat paddle (not shown) separately from the blades 12b, 13b, so as to improve the stirring performance. In particular, when the paddle is provided in the vicinity of the communication portion 18a or 18b, the developer can be smoothly conveyed from the first storage portion 16 to the second storage portion 17 or from the second storage portion 17 to the first storage portion 16. It is preferable in that it can be made.

  As shown in FIG. 1, the cleaning device 10 cleans the toner remaining on the surface after the transfer to the surface of the photosensitive drum 7.

  The transfer unit 2 spans an intermediate transfer belt 27 between a pair of support rollers 26, drives the support roller 26 by a driving means (not shown), and circulates the intermediate transfer belt 27 in an arrow direction. A transfer unit 28 and a secondary transfer unit 29 are provided.

  The exposure unit 3 irradiates the photosensitive drum 7 with laser light to form an electrostatic latent image corresponding to image data read by a scanner (not shown).

  The paper feeding unit 4 sequentially conveys the recording medium 31 stored in the cassette 30 to the secondary transfer unit 29 via the conveyance roller 32. A toner image is transferred to the recording medium 31 conveyed to the secondary transfer unit 29, and the toner image transferred by the fixing unit 33 is fixed, and then is carried out to the discharge tray 34.

  The cleaning unit 5 can come into contact with and separate from the intermediate transfer belt 27, and can collect toner remaining on the intermediate transfer belt 27 by approaching the cleaning unit 5.

  The control unit 6 estimates the toner concentration and the total amount of the developer stored in the developer storage container 11 based on the detection voltage input from the magnetic permeability sensor 22 as will be described later. A supply amount of developer to be supplied to the developer container 11 is calculated.

(Operation)
Next, the operation of the image forming apparatus having the above configuration will be described.

  At the time of image formation, color print data obtained by reading an image or image data output from a personal computer or the like is subjected to predetermined signal processing, and then yellow (Y), magenta (M), cyan (C ) And black (Bk) image signals of the respective colors are supplied to the image forming units 1.

  In each image forming unit 1, a laser beam modulated by an image signal is projected onto each photosensitive drum 7 to form an image latent image. Then, toner is supplied from the developing device 9 to the photosensitive drum 7.

  In the developing device 9, the developer stored in the developer container 11 is circulated while being stirred by rotationally driving the stirring screw 12 and the supply screw 13. Then, the toner is supplied from the supply screw 13 to the developing roller 14, scraped off by the regulating member 25 to be a fixed amount, and then conveyed to the photosensitive drum 7.

  As a result, yellow, magenta, cyan, and black toner images are formed on each photosensitive drum 7. The formed yellow, magenta, cyan, and black toner images are primary-transferred by the primary transfer unit 28 while sequentially superposed on the moving intermediate transfer belt 27. The superimposed toner image formed on the intermediate transfer belt 27 in this way moves to the secondary transfer unit 29 as the intermediate transfer belt 27 moves.

  A recording medium 31 is supplied from the paper supply unit 4. The supplied recording medium 31 is conveyed between the secondary transfer unit 29 and the intermediate transfer belt 27 by the conveyance roller 32, and the toner image formed on the intermediate transfer belt 27 is transferred. The recording medium 31 to which the toner image has been transferred is further conveyed to a fixing device, where the transferred toner image is fixed and then discharged to the discharge tray 34.

  By the way, in the developing device 9, supplying toner to the photosensitive drum 7 reduces the toner concentration of the stored developer, and the carrier deteriorates due to long-term use. Drain and replenish. In replenishment of developer, the control unit 6 executes a replenishment amount determination process for determining the replenishment amount as follows.

In the replenishment amount determination process, as shown in FIG. 5, first, the detection voltage output from the magnetic permeability sensor 22 is read for a predetermined time (step S1). FIG. 6 is a graph showing changes in the read detection voltage. Then, the average value of the detected detection voltages is calculated (step S2), and the average value of the detection voltages is converted into the toner density according to the following equation (step S3). In the graph shown in FIG. 6, the average value of the detection voltages is 2.3V.
Tc = −c × V2 + d
Tc: Toner concentration V2: Average value of detection voltage output from magnetic permeability sensor 22 c, d: Constant

  Here, the constant c is based on how the average value of the detection voltage changes with respect to the total amount of the developer in the developer container 11 being increased by 20% and decreased by 20% of the target value. , D was obtained. That is, the relationship between the detection voltage and the toner concentration is 4% which is the minimum value of the toner density and 10% which is the maximum value in the linear region where the relationship between the detection voltage and the toner concentration in the magnetic permeability sensor 22 changes linearly. Based on how the detection voltage changes with respect to 7%, which is an appropriate value,%, a single mathematical expression that changes linearly was obtained. FIG. 7 shows the relationship between the change in the average value of the detection voltage and the toner density when the total amount of the developer is increased or decreased by 20% of the target value, and the average value of the detected voltage obtained as a result. And a toner density. As a result, 9.5946 was obtained for the constant c and 31.455 for the constant d. However, the relationship between the detection voltage and the toner density may be determined based on a straight line (here, two straight lines) connecting the average values of the detection voltages due to the difference in toner density. Absent.

  As described above, since the toner density is calculated based on the calculated average value of the detection voltages, the detection accuracy can be improved. In addition, the magnetic permeability sensor 22 is disposed at the most downstream portion of the stirring screw 12, where the developer tends to stay and the pressure is high. Therefore, it is possible to accurately detect the toner concentration regardless of the difference in the total amount of developer in the developer container 11.

Subsequently, the average value of the amplitude values of the read detection voltages is calculated (step S4), and the total amount of developer stored in the developer storage container 11 is estimated according to the following equation (step S5).
M = −a × V1 + b
M: total amount of developer V1: amplitude value of detection voltage output from magnetic permeability sensor 22 a, b: constant

  Here, the total amount of developer in the developer container 11 is based on how the amplitude value of the detection voltage changes with respect to a plurality of values including a 20% increase and a 20% decrease of the target value. Constants a and b were obtained. FIG. 8 is a graph showing the obtained mathematical formula. As a result, 107.14 was obtained for the constant a and 396.33 was obtained for the constant b.

  As described above, the total amount of the developer stored in the developer storage container 11 can be easily calculated based on the amplitude value of the detection voltage from the magnetic permeability sensor 22 without providing a special sensor. Can do.

Thereafter, based on the toner density and the total amount of developer obtained by the above formula, the replenishment amount of the developer is calculated according to the following formula (step S6).
m = (− e × Tc / 100 + f) × M
m: developer replenishment amount e, f: constant

  Here, as shown in FIG. 9, the carrier concentration of the developer to be replenished is 20%, the target toner concentration is 7%, and the detected toner concentration is changed to any of 4, 5 and 6%, Constants e and f were obtained by predicting that the estimated total amount of developer would be any of 190 to 270 g (9 data in 10 g units). FIG. 10 is a graph of the mathematical formulas obtained for each toner concentration (4, 5, 6%). For example, when the toner density is 6%, the constant e is 1.37 and the constant f is 0.0959. In this case, if the estimated total amount of the developer is 230 g, the replenishment amount of the developer is 3.15 g by inputting the obtained constants and these values into the above formula. On the other hand, even if the detected toner density is the same 6%, when the estimated total amount of developer is 250 g, the developer replenishment amount is 3.24 g.

  In this way, in calculating the replenishment amount, not only the toner concentration but also the total amount of developer accommodated in the developer accommodating container 11 is taken into consideration, so that the toner concentration obtained after replenishment can be accurately determined. Value. Therefore, a desired toner density cannot be obtained, and an image such as streak noise (noise consisting of a plurality of streak patterns generated when black level correction is performed on image data in units of lines), fog, density unevenness, etc. Problems such as noise can be prevented. In particular, when the total amount of developer accommodated in the developer accommodating container 11 decreases with the downsizing of the image forming apparatus, the toner concentration is greatly affected by the amount of developer replenishment, and thus the effect thereof is It will be huge.

(Other embodiments)
Note that the present invention is not limited to the configuration described in the embodiment, and various modifications can be made.

  As a sensor for detecting the total amount of developer and toner concentration in the developer container 11, another sensor can be used instead of the magnetic permeability sensor 22. For example, an optical sensor that irradiates light to the developer and detects the amount of reflected light may be used, and the detection voltage may be used.

  Further, both a magnetic sensor and an optical sensor may be provided, a magnetic sensor may be used for toner density detection, and an optical sensor may be used for detection of the total amount of developer. Conversely, an optical sensor may be used to detect the toner density, and a magnetic sensor may be used to detect the total amount of developer. However, as described above, if only the magnetic permeability sensor 22 is provided, the configuration is simplified and it is preferable in that it can be manufactured at low cost.

  However, an optical sensor cannot be used with a developer composed of a black toner using a carbon block as a coloring material and a carrier because the optical density characteristic hardly changes due to a difference in toner density.

  When the magnetic permeability sensor 22 is provided at the lowest position of the stirring screw 12 and at the lowest position of the developer container 11, the pressure acting on the developer can be further increased to stabilize the output characteristics. It becomes possible. Further, by partially increasing the outer diameter of the rotating shaft of the agitating screw 12 at the most downstream portion, the same effect can be obtained even if the channel cross-sectional area is reduced.

1 is a schematic front view of an image forming apparatus according to an embodiment. FIG. 2 is a schematic longitudinal sectional view showing the developing device of FIG. 1. (A) is a schematic longitudinal cross-sectional view of the developer container of FIG. 2, (b) is the side view. It is a block diagram of FIG. It is a flowchart which shows the content of the replenishment amount determination process performed with the control unit of FIG. It is a graph which shows the change of the detection voltage read by the control unit of FIG. 2 is a graph showing a relationship between an average value of detection voltages read by the control unit of FIG. 1 and toner density. 2 is a graph showing a relationship between an amplitude value of a detection voltage read by the control unit of FIG. 1 and a total amount of developer stored in a developer storage container. 6 is a table showing a relationship between a detected toner density and a total amount of developer when a developer is replenished and the like. FIG. 10 is a graph showing the relationship between the total amount of developer and the replenishment amount in FIG. 9 for each toner density difference.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming unit 2 ... Transfer unit 3 ... Exposure unit 4 ... Paper feed unit 5 ... Cleaning unit 6 ... Control unit (developer supply control means)
7 ... photosensitive drum 8 ... charging device 9 ... developing device (developing means)
DESCRIPTION OF SYMBOLS 10 ... Cleaning apparatus 11 ... Developer container 12 ... Agitation screw (1st conveyance means)
12a ... Rotating shaft 12b ... Blade 13 ... Supply screw (second conveying means)
DESCRIPTION OF SYMBOLS 13a ... Rotary shaft 13b ... Blade | wing 14 ... Developing roller 15 ... Partition wall 16 ... 1st accommodating part 17 ... 2nd accommodating part 18 ... Communication part 19 ... Developer supply port (replenishment part)
20 ... cartridge (developer supply means)
21 ... Developer discharge port (discharge unit)
22 ... Magnetic permeability sensor (developer detection means)
DESCRIPTION OF SYMBOLS 23 ... Sleeve 24 ... Permanent magnet 25 ... Restriction member 26 ... Support roller 27 ... Intermediate transfer belt 28 ... Primary transfer part 29 ... Secondary transfer part 30 ... Cassette 31 ... Recording medium 32 ... Conveyance roller 33 ... Fixing unit 34 ... Ejection tray

Claims (7)

A developing device that stirs a developer containing toner and a carrier contained in a developer container and supplies the developer to an image carrier,
Developer detecting means for changing an output voltage according to a difference in toner concentration of the developer contained in the developer containing container;
Developer supply means for supplying a developer to the developer container;
Based on the amplitude value of the detection voltage output from the developer detection means, the total amount of developer stored in the developer storage container is calculated, and the toner concentration is calculated based on the average value of the detection voltage. And a developer replenishment control means for controlling the amount of developer replenishment by the developer supply means so that a desired toner concentration is obtained based on the total amount of developer and the toner concentration. A developing device. The developing device according to claim 1, wherein the developer replenishment control unit calculates a total amount of developer according to the following equation based on an amplitude value of a detection voltage output from the developer detection unit.
M = −a × V1 + b
M: total amount of developer V1: amplitude value of detection voltage output from developer detection means a, b: constant 3. The developer supply control unit according to claim 1, wherein the developer replenishment control unit calculates a toner density according to the following expression based on an average value of detection voltages output from a detection unit of the developer detection unit. Development device.
Tc = −c × V2 + d
Tc: toner density V2: average value of detection voltage output from developer detection means c, d: constant The developing device according to claim 1, wherein the developer replenishment control unit determines a replenishment amount of the developer according to the following formula.
m = (− e × Tc / 100 + f) × M
m: developer replenishment amount e, f: constant The developer storage container is divided into a first storage portion and a second storage portion that are juxtaposed and extend from one end side to the other end side. The first storage portion has a replenishment portion formed on one end side, and a second storage portion. The accommodating portion is formed with a discharge portion on one end side, and the first accommodating portion and the second accommodating portion are communicated with each other via the communicating portions at both ends, and the first accommodating portion is replenished from the replenishing portion on the one end side. A first conveying means for conveying the developer while stirring toward the communicating portion on the other end side is disposed, and the developer supplied from the first accommodating portion to the second accommodating portion via the communicating portion is discharged to the second accommodating portion. A second conveying means for conveying while stirring toward the
5. The developing device according to claim 1, wherein the toner density detection unit is arranged at a most downstream portion of a first transport unit located on a side opposite to the supply unit.   An image forming apparatus comprising the developing device according to claim 1. A step of detecting a difference in toner concentration between the toner contained in the developer containing container and the developer containing the carrier by the developer detecting means and outputting as a detection voltage;
Calculating the total amount of developer accommodated in the developer accommodating container based on the amplitude value of the output detection voltage, and calculating the toner density based on the average value;
Calculating a replenishment amount of developer to be replenished to the developer container based on the calculated total amount of developer and toner concentration;
And a step of replenishing the developer containing container with a developer so as to obtain a desired toner density based on the calculated replenishment amount of the developer.

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