JP2011053394A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming proper images for a long period by suppressing excessive deterioration of a developer, even when a low-coverage continuous printing state continues for a long period. <P>SOLUTION: The image forming apparatus includes a developing device to which a fixed amount of carrier is supplied at intervals of a fixed time and to which, at intervals of a fixed set time, the amount of toner corresponding to a deficiency for a prescribed value of a toner concentration is supplied, when the toner concentration being in a toner deficient region A where the toner concentration is lower than the prescribed value, with a fixed amount of toner being supplied, in response to transition of the toner concentration from the toner deficient region A to an appropriate concentration region B where the toner concentration is equal to or higher than the prescribed value and is lower than an allowable limit value higher than the prescribed value, only carrier is supplied, in response to transition of the toner concentration to the appropriate concentration region B from a toner excessive region C where the toner concentration is equal to or higher than the allowed limiting value, and only the carrier is supplied, when the toner concentration is in the toner excess region C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus that performs development using a two-component developer.

Conventionally, as an electrophotographic image forming apparatus, a two-component developer (hereinafter also simply referred to as “developer”) composed of a toner and a carrier is used. A developing device that forms a toner image by adhering the toner to an electrostatic latent image formed on an image bearing member, and replenishing new toner and carrier continuously or intermittently. There is known an image forming apparatus equipped with a so-called trickle developing type developing device that gradually discards used developer.
In general, a two-component developer is stressed by an agitating operation, and an external additive such as a lubricant added to the surface of toner particles constituting the toner is detached from the toner particles, or conversely buried in the toner particles. As a result, the chargeability of the developer decreases and the charge amount of the toner becomes low, or the fluidity of the developer decreases and the coefficient of friction between the carrier and the toner becomes high. When the carrier contamination phenomenon occurs where the toner adheres to the carrier, new toner is replenished continuously or intermittently by using this trickle development method, thereby supplying both external additives. Therefore, excessive deterioration of the developer is suppressed. Even if the external additive alone is replenished into the developing device, it is difficult to bring the toner and carrier into uniform contact.
In a general trickle developing type developing device, a predetermined amount of carrier is put in a toner bottle or toner cartridge in which toner for replenishment is stored, so that the carrier is also supplied when the toner is replenished. The composition to be replenished is adopted.

  However, in such a trickle development type developing device, a state in which a document having a low printing rate (coverage) such as a character document is continuously printed (hereinafter also referred to as “low coverage continuous printing state”) is long. When the toner is used for image formation, the toner density in the developing device is hardly lowered due to a very small amount of toner. As a result, the developer is excessively deteriorated without replenishment of new toner, As a result, there is a problem that image fogging or toner scattering due to a decrease in chargeability and fluidity of the developer occurs in the formed visible image.

  In order to solve such a problem, for example, Patent Document 1 discloses that a low-coverage continuous print state is long by continuously supplying a constant amount of toner even when the toner density in the developing device reaches a specified value. A method for suppressing excessive deterioration of the developer over time is disclosed.

  However, even with such a method, if the toner density in the developing device becomes so high as to hinder image formation, the toner supply must be stopped, and eventually the excessive deterioration of the developer can be suppressed. become unable.

Japanese Patent No. 4122816

  The present invention has been made based on the above circumstances, and an object of the present invention is to suppress excessive deterioration of the developer even when the low-coverage continuous printing state continues for a long time, and to prevent image fogging and toner over a long period of time. An object of the present invention is to provide an image forming apparatus capable of forming a good image without scattering.

An image forming apparatus according to the present invention includes a developer accommodating portion that accommodates a two-component developer composed of a toner and a carrier for developing an electrostatic latent image carried on an image carrier,
A toner replenishing mechanism having toner replenishing means for replenishing toner to the developer containing portion; and a carrier replenishing mechanism for supplying carrier to the developer containing portion;
Surplus developer discharging means for discharging surplus two-component developer from the developer containing portion;
In an image forming apparatus comprising a developing device having a toner concentration detecting means for detecting a toner concentration of a two-component developer in the developer containing portion,
In the developer supply mechanism,
A certain amount of carrier is replenished at certain time intervals,
The toner density detected by the toner density detection means at a fixed set time interval is a toner shortage area A that is less than a specified value, and is less than an allowable limit value greater than the specified value and greater than the specified value. When a certain density area is an appropriate density area B and a density area that is equal to or greater than the allowable limit value is an excessive toner area C,
For each predetermined set time interval,
When the toner density detected by the toner density detecting means is in the toner shortage region A, an amount of toner corresponding to the shortage with respect to the specified value of the toner density is replenished,
When the toner density detected by the toner density detecting means is in the proper density area B, when the proper density area B is shifted from the toner shortage area A, a certain amount of toner is replenished, and the proper density area B Is transferred from the excessive toner area C, only the carrier is replenished,
When the toner density detected by the toner density detecting means is in the excessive toner area C, only the carrier is replenished.

In the image forming apparatus of the present invention, in the developer replenishing mechanism, when the toner density detected by the toner density detecting means is in the appropriate density area B shifted from the toner insufficient area A, a certain amount of toner is supplied. Along with the carrier,
It is preferable that the amount of the carrier to be replenished is controlled so as to become smaller as the toner density approaches the specified value.

  In the image forming apparatus of the present invention, in the developer replenishing mechanism, the amount of carrier replenished when the toner concentration detected by the toner concentration detecting means is in the excessive toner region C is the toner concentration. It is preferable to control so that the amount becomes smaller as the value approaches the allowable limit value.

  According to the image forming apparatus of the present invention, in the trickle developing type developing device, the replenishment of the toner is continued even when the toner density reaches the specified value or more, and the allowable limit value where the toner density is larger than the specified value. In this case, since the carrier is replenished until the toner density drops to the specified value, the deterioration of the developer is suppressed over a long period regardless of the amount of toner consumed by the development. Therefore, even when the low coverage continuous print state continues for a long time, the developer is prevented from excessive deterioration, and as a result, good chargeability is obtained over a long period of time, and a good image without image fogging or toner scattering is obtained. Can be formed.

It is explanatory drawing which shows an example of a structure of the image forming apparatus of this invention. FIG. 2 is an explanatory diagram illustrating an example of a configuration of a developing device in the image forming apparatus of FIG. 1. FIG. 3 is a plan view schematically showing a part of a developing roller and a developer container in the developing device of FIG. 2. FIG. 6 is a control flow diagram illustrating an example of a developer supply operation for adjustment in the image forming apparatus of the present invention. FIG. 10 is a control flow diagram illustrating another example of an adjustment developer replenishment operation in the image forming apparatus of the present invention. 6 is a graph showing a change in toner concentration in the developer accommodating portions according to Examples 1 and 2 and Comparative Examples 1 and 2. 6 is a graph showing a transition of a charge amount of toner in a developer container according to Examples 1 and 2 and Comparative Examples 1 and 2.

  Hereinafter, the present invention will be specifically described.

<First Embodiment>
The image forming apparatus of the present invention includes a developing device having a developer replenishing mechanism described in detail below.

  Specifically, the image forming apparatus of the present invention is configured such that, for example, four sets of image forming units 100Y, 100M, 100C, and 100K are arranged in the vertical direction along the intermediate transfer belt 17 that is an intermediate transfer member. Tandem color image forming apparatus.

  Each of the image forming units 100Y, 100M, 100C, and 100K is stretched around the rollers 17a to 17i, and is driven by an intermediate transfer belt 17 that circulates in a direction indicated by an arrow by a drive source (not shown), and is grounded. In this state, the photosensitive drums 10Y, 10M, 10C, and 10K that are image carriers that are rotated counterclockwise and parallel to the rotational axes of the photosensitive drums 10Y, 10M, 10C, and 10K that include the scorotron charger. And charging means 11Y, 11M, 11C, and 11K that apply a uniform potential to the surfaces of the photosensitive drums 10Y, 10M, 10C, and 10K by corona discharge having the same polarity as the toner, and a polygon mirror, for example. The photoconductive drums 10Y, 10M, 10C, and 10K that are scanned in parallel with the rotation axes of the photoconductive drums 10Y, 10M, 10C, and 10K are uniformly charged. Exposure means 12Y, 12M, 12C, and 12K for forming an electrostatic latent image by performing image exposure on the surface of 0M, 10C, and 10K, and toner, and photosensitive drums 10Y, 10M, 10C, and 10K. Development devices 20Y, 20M, 20C, and 20K having a developer replenishment mechanism according to the present invention that are conveyed to the surface of the toner and visualize the electrostatic latent image.

  The photoconductor drums 10Y, 10M, 10C, and 10K are obtained by forming an organic photoconductor layer (OPC) provided with an overcoat layer (protective layer) on the outer peripheral surface of a cylindrical metal base made of an aluminum material. For example, the outer diameter is 100 mm.

  In FIG. 1, 16Y, 16M, 16C, and 16K are cleaning units that collect residual toner remaining on the photosensitive drums 10Y, 10M, 10C, and 10K after the primary transfer.

  Here, the image forming unit 100Y forms a yellow toner image, the image forming unit 100M forms a magenta toner image, and the image forming unit 100C forms a cyan toner image. According to the unit 100K, a black toner image is formed.

  In such an image forming apparatus, the toner images of the respective colors formed on the photosensitive drums 10Y, 10M, 10C, and 10K of the image forming units 100Y, 100M, 100C, and 100K are circulated on the intermediate transfer belt 17. Further, for example, a color toner image is formed by being sequentially transferred and superimposed by primary transfer means 14Y, 14M, 14C, and 14K made of, for example, a transfer roller. In the secondary transfer means 18 made of, for example, a transfer roller, a paper feed tray is formed. The recording material P transferred from (not shown) is collectively transferred, fixed by a fixing device (not shown), and then discharged outside the apparatus.

  Specific examples of the recording material P include plain paper from thin paper to thick paper, high-quality paper, coated printing paper such as art paper or coated paper, commercially available Japanese paper or postcard paper, and plastic film for OHP. Various kinds of cloth and the like can be mentioned, but the invention is not limited to these.

[Development equipment]
The developing devices 20Y, 20M, 20C, and 20K having the developer replenishment mechanism provided in the image forming apparatus of the present invention have the same configuration except that the colors of the toners to be filled are different from each other. In the following, the developing device 20Y will be described as a representative.
FIG. 2 is an explanatory diagram showing an example of the configuration of the developing device in the image forming apparatus of the present invention.
In the developing device 20Y, the toner and the carrier are replenished continuously or intermittently, and a part of the developer in the developing device 20Y is continuously or intermittently discharged little by little and is developed while being discarded. The trickle development method.

  As shown in FIGS. 2 and 3, the developing device 20Y contains a two-component developer composed of a toner and a carrier for developing the electrostatic latent image carried on the photosensitive drum 10Y as an image carrier. Developer accommodating portion 21, toner replenishing means (not shown) for replenishing toner to the developer accommodating portion 21, and carrier replenishing means (not shown) for replenishing carrier to the developer accommodating portion 21. A developer replenishment mechanism, surplus developer discharging means (not shown) for discharging excess developer from the developer containing portion 21, and toner concentration detection for detecting the toner concentration of the developer in the developer containing portion 21. And means 25.

Specifically, the developing device 20Y is opposed to the photosensitive drum 10Y via the developing region R and is counterclockwise as indicated by an arrow so that the developing device 20Y is moved in the opposite direction to the photosensitive drum 10Y in the developing region R. A developing roller 22 rotated in the direction, and a supply collecting member 24 that rotates counterclockwise and supplies developer to the developing roller 22 on the upper side and collects developer returned from the developing roller 22 on the lower side. The agitating members 23 that are rotated in the opposite direction to the supply and recovery member 24 and mix and agitate while circulating and conveying the developer extend in the axial direction (perpendicular to the paper surface in FIG. 2) and are parallel to each other. The developer accommodating portion 21 is arranged in this order in the front-rear direction (left-right direction in FIG. 2), and is arranged in the supply / recovery area 21y and the agitation area 21x respectively partitioned by the partition walls 29. It is provided to.
Reference numeral 28 denotes, for example, a rod-like or plate disposed with a predetermined gap from the developing roller 22 for regulating the thickness of the developer layer to be formed on the outer peripheral surface of the developing roller 22 to a predetermined size. It is a developer layer thickness regulating member made of a magnetic material.

The toner concentration detection means 25 is not particularly limited, and various known ones can be used. For example, a so-called magnetic type that detects a current value that changes according to the magnetic permeability by applying a voltage to the coil. A sensor can be used. When such a magnetic sensor is used, this magnetic sensor is disposed at a position facing the bottom of the agitating member 23 of the developer accommodating portion 21, for example.
Further, as the toner density detection means 25, for example, a system that indirectly detects the toner density by detecting the toner adhesion amount based on the reflection density of the patch image formed on the photosensitive drum 10Y may be used. it can.

The developing roller 22 is, for example, a cylindrical developing sleeve made of a nonmagnetic material such as aluminum, which is rotatably provided, and a fixing roller 22 that is fixed inside the developing sleeve so as to be separated in the circumferential direction. And a cylindrical magnet body having magnetic poles. The outer diameter of the developing roller 22 is, for example, φ30 mm.
The stirring member 23 and the supply / recovery member 24 are, for example, screw-shaped having spiral blades formed so as to extend spirally at a pitch of a uniform size in the axial direction over the entire outer periphery of the cylindrical shaft member. Can be.
The outer diameters of the stirring member 23 and the supply / recovery member 24 are each, for example, φ27 mm.

In the developing device 20Y, a developer agitation circuit is formed by the agitation zone 21x and the supply / recovery zone 21y of the developer accommodating portion 21, and the agitating member 23 in the roof plate 21a of the developer accommodating portion 21 is installed. On the stirring area 21x and on the upstream side (left side in FIG. 3) in the transport direction, along the transport direction, in the toner replenishing means, a toner transport member (for example, a screw) is formed from a toner storage portion (not shown). For example, a toner supply port 27a for supplying new toner (hereinafter also referred to as “new toner”) into the developer storage unit 21 by the carrier supply unit (not shown) from the carrier storage unit (not shown), for example. A new unused carrier (hereinafter also referred to as “new carrier”) is formed by a carrier conveying member (not shown) made of a screw. Carrier supply opening 27b for replenishing the developer accommodating section 21 is formed side by side in this order.
By providing the toner replenishing port 27a and the carrier replenishing port 27b on the upstream side in the transport direction on the agitation zone 21x, the replenished new toner and the new carrier are not sufficiently agitated with the already-stored developer, and the developing roller 22 is prevented from being supplied.

Further, the position immediately upstream of the position where the toner supply port 27a and the carrier supply port 27b are formed in the developer agitation circulation path, that is, the supply / recovery area 21y where the supply / recovery member 24 is installed in the developer container 21. A developer discharge port 26 for discharging excess developer is formed at the most downstream position.
Since the developer discharge port 26 is provided at a position immediately upstream of the position where the toner supply port 27a and the carrier supply port 27b are formed, before the new toner and the new carrier are mixed with the already stored developer. It is suppressed that it is discharged immediately.
The developer discharging method is not particularly limited and various methods can be adopted. Specifically, for example, the height of the wall surface of the developer containing portion 21 is set only at the portion of the developer discharging port 26. By keeping the fixed amount low, the excess developer in the agitation circuit is automatically overflowed, or, for example, a spiral blade is partially reversed as the supply / recovery member 24 or the agitation member 23 For example, a method in which the developer is prevented from being transported by using and the surplus developer in the stirring circulation path is automatically overflowed from the wall surface of the developer container 21.

  The amount of developer relating to yellow that is accommodated in the developer accommodating portion 21 of the developing device 20Y is, for example, 600 g.

In the developing device 20Y as described above, the developing operation is performed as follows.
That is, the two-component developer filled in the developer accommodating portion 21 is mixed, agitated, and supplied as described in detail below, and conveyed to the outer peripheral surface of the developing roller 22 by the supply and recovery member 24. Thereafter, the developer is adhered to the outer peripheral surface of the developing roller 22 by a magnetic force, and the developer layer thickness regulating member 28 regulates the thickness thereof to form a developer layer by a magnetic brush, which is conveyed to the developing region R, and the developing region In R, reversal development is performed by applying a development bias voltage in which an alternating current (AC) voltage is superimposed on a direct current (DC) voltage as necessary between the developing roller 22 and the photosensitive drum 10Y. The electrostatic latent image on the photosensitive drum 10Y is visualized.
On the other hand, the two-component developer that has not visualized the electrostatic latent image is peeled off from the developing roller 22 by the action of the repulsive magnetic field of the magnet body, recovered by the supply recovery member 24, and mixed, stirred, and supplied again. To be served.

The mixing / stirring / feeding operation is performed as follows.
That is, the developer is mixed, stirred and frictionally charged while being transported in one direction along the axial direction by the stirring member 23 in the stirring area 21x, and is transported by the stirring member 23 by the supply and recovery member 24 in the supply and recovery section 21y. The toner is frictionally charged by being mixed and stirred while being conveyed in the same size in the opposite direction and supplied to the developing roller 22. The developer is circulated and conveyed in the stirring zone 21x and the supply / recovery zone 21y.

In the image forming apparatus of the present invention, the following developer replenishment operation is performed in the developer replenishment mechanism.
That is, (1) a certain amount of carrier is replenished to the developer accommodating portion 21 from the toner replenishing port 27a and / or the carrier replenishing port 27b at regular time intervals, and (2) in addition to this, the toner The toner density detected by the density detection means 25 at a fixed set time interval is less than the specified value in the toner shortage area A, and is less than the allowable limit value that is greater than the specified value and greater than the specified value. When the density area is the appropriate density area B and the density area equal to or higher than the allowable limit value is the toner excess area C, (2-a) toner detected by the toner density detection means 25 at every predetermined set time interval. When the density is in the toner shortage area A, an amount of new toner corresponding to the shortage with respect to the specified value of the toner density is replenished, and (2-b) the toner density detection means 25 When the detected toner density is in the proper density area B, (2-b-i) when the proper density area B is shifted from the toner shortage area A, a certain amount of new toner is supplied, and (2- b-ii) When the appropriate density area B is shifted from the excessive toner area C, only new carriers are replenished. (2-c) The toner density detected by the toner density detecting means 25 is in the excessive toner area C. Only new carriers will be replenished.

  The above (1) is steady carrier replenishment. For example, 10 to 50 mg, preferably 20 mg of new carrier is replenished every 30 seconds. By such regular carrier replenishment, trickle development is basically performed and excessive deterioration of the carrier can be suppressed. On the other hand, if there are too many new carriers to be replenished as regular carrier replenishment, an unnecessarily large amount of new carriers will be used, resulting in high use costs and new carriers replenished as regular carrier replenishment. If the amount is too small, the replacement of the carrier in the two-component developer becomes insufficient, and the effect of the trickle development method cannot be obtained sufficiently.

  The above (2) is developer supply for adjustment. Specifically, as shown in FIG. 4, first, the toner density in the developer container 21 is measured, and the detected toner density is determined. When the toner density is less than the specified value, the above (2-a) is performed until the toner density becomes equal to or higher than the specified value, and the amount of toner corresponding to the shortage is supplied, and the detected toner density exceeds the specified value. When the toner concentration reaches the allowable limit value, the above (2-b-i) is performed to supply a constant amount of toner, and the detected toner concentration exceeds the allowable limit value. The toner supply is stopped and the above (2-b-ii) or (2-c) is performed until the toner density becomes less than the specified value, so that only the carrier is supplied.

  The predetermined set time interval for detecting the toner density by the toner density detecting means 25 is, for example, every 0.5 to 10 seconds, preferably every 1 second.

The specified value serving as an index for toner and carrier replenishment is the lower limit of the toner density range in which the desired image density can be obtained, for example, 4 to 8%, and particularly preferably 6%.
The allowable limit value is a value larger than a specified value, and is an upper limit value of a toner density range that does not cause problems such as image fogging and toner scattering in a visible image. Although it varies depending on the configuration and the state of use of the developer, it is preferably 6 to 12%, for example, and particularly preferably 8% when the specified value is 6%.

The carrier replenishment amount in the case where the toner density is in the excessive toner area C and very close to the allowable limit value and in the proper density area B shifted from the excessive toner area C is 1.0 × per second. It is preferable to control the amount to be 10 ⁻⁵ Mc or more and 1.0 × 10 ⁻⁴ Mc or less (where Mc is the amount of carrier to be accommodated in the developer accommodating portion 21).
The case where the toner concentration is extremely close to the allowable limit value is, for example, a case where the specified value is a toner concentration of 6% and the allowable limit value is a toner concentration of 8%, for example, a case where the toner concentration is less than 8.09%. it can.
For example, when the developer amount in the developer accommodating portion 21 is 600 g and the specified value of the toner density is 6%, the carrier amount Mc is 564 g. Therefore, the toner excess region C is extremely close to the allowable limit value. In this case, and in the case of the proper density region B shifted from the excessive toner region C, the replenishment amount of the carrier can be set to 10 mg, for example.
When the amount of carrier replenishment is too small, the speed until the toner density reaches the specified value becomes low. On the other hand, when the replenishment amount of the carrier is excessive, a large amount of the carrier is replenished at a time, and the replenished carrier is difficult to be mixed with the already stored developer, which may cause a problem.

In the following, an example of control of developer replenishment for adjustment in the developer replenishment operation in which the specified value is the toner concentration 6% and the allowable limit value is the toner concentration 8% will be described in detail with reference to Table 1 below. Note that the specific amounts of new toner and new carrier to be replenished vary depending on the specific configurations of the image forming apparatus and the developing apparatus and the usage state of the developer.
First, in the case where the toner density is shifted in the order of the toner shortage area A, the appropriate density area B, and the toner excess area C, the amount of toner corresponding to the shortage amount up to the specified value replenished in the toner shortage area A Is controlled as shown in the area A of Table 1 below, the amount of a constant amount of toner replenished in the appropriate density area B is 3.3 mg, and the amount of carrier replenished in the excessive toner area C is 10 mg.
Next, when the toner density is shifted in the order of the excessive toner area C, the appropriate density area B, and the insufficient toner area A, the amount of carrier replenished in the excessive toner area C and the appropriate density area B is both 10 mg.
In this example, when the output value of the toner density detection means is larger than 2.02V, the toner density is less than 6%, and when the output value of the toner density detection means is 1.8V or less, it is converted to the toner density. 8% or more.

  The control in the developing device 20Y described above is similarly performed in each of the developing devices 20Y, 20M, 20C, and 20K of the image forming units 100Y, 100M, 100C, and 100K. Control in each of these developing devices 20Y, 20M, 20C, and 20K is performed independently.

[Two-component developer]
The toner constituting the two-component developer used in the image forming apparatus of the present invention is not particularly limited, and various known toners can be used. For example, the volume-based median diameter is 3 to 9 μm. It is preferable to use a so-called polymerized toner obtained by a polymerization method. By using the polymerized toner, high resolution and stable image density can be obtained in the formed visible image, and the occurrence of image fog is extremely suppressed.

  Further, the carrier constituting the two-component developer used in the image forming apparatus of the present invention is not particularly limited, and various known ones can be used. For example, the volume-based median diameter is 30 to 65 μm. And a ferrite carrier made of magnetic particles having a magnetization of 20 to 70 emu / g is preferable. When a carrier with a volume-based median diameter of less than 30 μm is used, carrier adhesion may occur and a white-out image may be generated. When a carrier with a volume-based median diameter of greater than 65 μm is used, There may occur a case where an image having a uniform image density is not formed.

  According to the image forming apparatus as described above, replenishment of new toner is continued even when the toner density reaches a specified value or more in the trickle developing type developing device 20Y, and the toner density is higher than the specified value. When the toner concentration exceeds the allowable limit value, the new carrier is replenished until the toner concentration drops to the specified value. Therefore, the developer is deteriorated over a long period regardless of the amount of toner consumed by the development. Therefore, even when the low coverage continuous printing state continues for a long time, excessive deterioration of the developer is suppressed, and a good image free from image fogging and toner scattering can be formed over a long period of time.

<Second Embodiment>
As shown in FIG. 5, the second example of the image forming apparatus of the present invention is a toner concentration in which the developer concentration for adjustment in the developer replenishing operation by the developer replenishing mechanism is detected by the toner concentration detecting means 25. When the toner density is in the proper density area B transferred from the toner shortage area A, control is performed so that a fixed amount of toner and a controlled amount of carrier are supplied so that the toner density decreases as the toner density approaches a specified value. Other than that, the image forming apparatus has the same configuration as that of the first embodiment.
In the control relating to the carrier replenishment in the appropriate density area B shifted from the toner shortage area A, it is preferable that the carrier replenishment amount be set to 0 when the toner density is very close to the specified value. The case where the toner density is very close to the specified value can be, for example, the case where the specified value is 6% toner density and the allowable limit value is 8% toner density, for example, the case where the toner density is less than 6.09%. .

In the following, an example of control of developer replenishment for adjustment in the developer replenishment operation in which the specified value is the toner density 6% and the allowable limit value is the toner density 8% will be described in detail with reference to Table 2 below. Note that the specific amounts of new toner and new carrier to be replenished vary depending on the specific configurations of the image forming apparatus and the developing apparatus and the usage state of the developer.
First, in the case where the toner density is shifted in the order of the toner shortage area A, the appropriate density area B, and the toner excess area C, the amount of toner corresponding to the shortage amount up to the specified value replenished in the toner shortage area A Is controlled as shown in area A in Table 2 below, the amount of toner supplied in the appropriate density area B is 3.3 mg, and the amount of carrier replenished in the appropriate density area B is The amount of the carrier that is controlled in the area B 2 and is replenished in the excessive toner area C is 10 mg.
Next, when the toner density is shifted in the order of the excessive toner area C, the appropriate density area B, and the insufficient toner area A, the amount of carrier replenished in the excessive toner area C and the appropriate density area B is both 10 mg.
In this example, when the output value of the toner density detection means is larger than 2.02V, the toner density is less than 6%, and when the output value of the toner density detection means is 1.8V or less, it is converted to the toner density. 8% or more.

  According to the image forming apparatus as described above, in addition to the same effects as those of the image forming apparatus of the first embodiment, an increase in toner density from the specified value is suppressed, and an unnecessarily large amount of carriers are loaded. Replenishment is prevented.

<Third Embodiment>
In the third example of the image forming apparatus of the present invention, when the developer supply for adjustment in the developer supply operation by the developer supply mechanism is in the toner excess region C, the toner concentration detected by the toner concentration detection means 25 is The configuration of the image forming apparatus according to the first embodiment is the same as that of the image forming apparatus according to the first embodiment, except that the amount of the carrier replenished in step S1 is controlled so as to become smaller as the toner density approaches the allowable limit value. Is.
In the control related to the carrier replenishment in the excessive toner region C, it is preferable that the carrier replenishment amount be set to 0 when the toner density is extremely close to the allowable limit value. The case where the toner concentration is extremely close to the allowable limit value is, for example, a case where the specified value is a toner concentration of 6% and the allowable limit value is a toner concentration of 8%, for example, a case where the toner concentration is less than 8.09%. it can.

In the following, an example of control of developer replenishment for adjustment in a developer replenishment operation in which the specified value is a toner concentration of 6% and the allowable limit value is a toner concentration of 8% will be described in detail with reference to Table 3 below. Note that the specific amounts of new toner and new carrier to be replenished vary depending on the specific configurations of the image forming apparatus and the developing apparatus and the usage state of the developer.
First, in the case where the toner density is shifted in the order of the toner shortage area A, the appropriate density area B, and the toner excess area C, the amount of toner corresponding to the shortage amount up to the specified value replenished in the toner shortage area A Is controlled as shown in region A in Table 3 below, the amount of a constant amount of toner replenished in the appropriate density region B is 3.3 mg, and the amount of carrier replenished in the excessive toner region C is 3 is controlled as in region C.
Next, when the toner density is shifted in the order of the excessive toner area C, the proper density area B, and the insufficient toner area A, the amount of carrier replenished in the excessive toner area C is the area C in Table 3 below. Thus, the amount of carrier replenished in the appropriate concentration region B is 10 mg.
In this example, when the output value of the toner density detection means is larger than 2.02V, the toner density is less than 6%, and when the output value of the toner density detection means is 1.8V or less, it is converted to the toner density. 8% or more.

  According to the image forming apparatus as described above, in addition to the effects similar to those of the image forming apparatus of the first embodiment, since the toner concentration is rapidly lowered to the specified value, the developer can be more reliably extended over a long period of time. Is suppressed, and an unnecessarily large amount of carriers is prevented from being replenished.

<Fourth embodiment>
In the fourth example of the image forming apparatus of the present invention, the developer concentration for adjustment in the developer replenishing operation by the developer replenishing mechanism is transferred from the toner shortage region A when the toner concentration detected by the toner concentration detecting means 25 is shifted. When the toner density is in the appropriate density area B, the toner is controlled to be supplied together with a constant amount of toner, and a controlled amount of carrier so that the toner density becomes smaller as the toner density approaches a specified value. In this case, the amount of the replenished carrier is controlled so as to become smaller as the toner density approaches the allowable limit value. It has a configuration.
In the control relating to the carrier replenishment in the appropriate density area B shifted from the toner shortage area A, it is preferable that the carrier replenishment amount be set to 0 when the toner density is very close to the specified value. The case where the toner density is very close to the specified value can be, for example, the case where the specified value is 6% toner density and the allowable limit value is 8% toner density, for example, the case where the toner density is less than 6.09%. .
In the control related to the carrier replenishment in the excessive toner region C, it is preferable that the carrier replenishment amount be set to 0 when the toner density is extremely close to the allowable limit value. The case where the toner concentration is extremely close to the allowable limit value is, for example, a case where the specified value is a toner concentration of 6% and the allowable limit value is a toner concentration of 8%, for example, a case where the toner concentration is less than 8.09%. it can.

In the following, an example of control of developer replenishment for adjustment in the developer replenishment operation in which the specified value is the toner concentration 6% and the allowable limit value is the toner concentration 8% will be described in detail with reference to Table 4 below. Note that the specific amounts of new toner and new carrier to be replenished vary depending on the specific configurations of the image forming apparatus and the developing apparatus and the usage state of the developer.
First, in the case where the toner density is shifted in the order of the toner shortage area A, the appropriate density area B, and the toner excess area C, the amount of toner corresponding to the shortage amount up to the specified value replenished in the toner shortage area A Is controlled as shown in the area A of Table 4 below, the amount of a constant amount of toner replenished in the appropriate density area B is 3.3 mg, and the amount of carrier replenished in the appropriate density area B is 4 and the amount of carrier replenished in the excessive toner area C is controlled as shown in area C of Table 4 below.
Next, when the toner density is shifted in the order of the excessive toner area C, the proper density area B, and the insufficient toner area A, the amount of carrier replenished in the excessive toner area C is the area C in Table 4 below. Thus, the amount of carrier replenished in the appropriate concentration region B is 10 mg.
In this example, when the output value of the toner density detection means is larger than 2.02V, the toner density is less than 6%, and when the output value of the toner density detection means is 1.8V or less, it is converted to the toner density. 8% or more.

  According to the image forming apparatus as described above, in addition to the same effects as those of the image forming apparatus according to the first embodiment, in the appropriate density area B shifted from the toner insufficient area A, the toner density rises from the specified value. In the excessive toner area C, the toner density is rapidly lowered to the specified value, so that the deterioration of the developer over a long period of time can be suppressed more reliably, and a large amount of carrier can be replenished unnecessarily. Is prevented.

  Although the image forming apparatus of the present invention has been described above, the present invention is not limited to the above-described configuration, and various changes can be made.

  For example, in the developing device, the new toner and the new carrier are not limited to being replenished independently. For example, in the developer replenishment mechanism, the new toner and the new carrier are conveyed from the toner accommodating portion and the carrier accommodating portion. Once mixed and stirred in the intermediate tank, the developer container may be replenished as a new developer.

  Further, for example, the image forming apparatus of the present invention is not limited to being configured as a color image forming apparatus, and may be a monochrome image forming apparatus.

  Specific examples of the present invention will be described below, but the present invention is not limited to these examples.

<Example 1>
Using the image forming apparatus having the configuration shown in FIG. 1, in the developer replenishment mechanism, 20 mg of new carrier is replenished every 30 seconds as a regular carrier replenishment, and Table 1 above as a developer replenishment for adjustment every second. According to the above, while replenishing new toner and new carrier, 360,000 copies were printed continuously with a 0.1% coverage document, and the occurrence of toner scattering and image fogging was observed. In particular, toner scattering and image fogging occurred. There wasn't. FIG. 6 shows the transition of the toner concentration in the developer container, and FIG. 7 shows the transition of the toner charge amount. In FIGS. 6 and 7, it is indicated by a line (1).
In the following, the toner shortage area A is a case where the output value of the toner density detecting means is larger than 2.02 V, and this is a case where the toner density is less than 6% in terms of toner density. The proper density region B is a case where the output value of the toner density detecting means is larger than 1.8V and not larger than 2.02V. The excessive toner area C is when the output value of the toner density detection means is 1.8 V or less, which is 8% or more when converted to toner density. The toner concentration was detected by the toner concentration detecting means every second.

<Example 2>
As in the case of Example 1 except that new toner and new carrier were replenished according to the above Table 4 every second as a developer supply for adjustment, the occurrence of toner scattering and image fogging was observed. Neither scattering nor image fogging occurred. FIG. 6 shows the transition of the toner concentration in the developer container, and FIG. 7 shows the transition of the toner charge amount. In FIGS. 6 and 7, it is indicated by a line (2).

<Comparative Example 1>
As a developer replenishment for adjustment, new toner is replenished every second in accordance with Table 1 in the toner shortage region A, and new toner other than the steady carrier replenishment in the proper density region B and the excessive toner region C. Except that the toner and the new carrier were not replenished, the toner scattering and the image fogging were observed in the same manner as in Example 1. As a result, when the 5,000 sheets were printed, the toner scattering occurred and 25,000. Image fogging occurred when the sheets were printed. FIG. 6 shows the transition of the toner concentration in the developer container, and FIG. 7 shows the transition of the toner charge amount. In FIGS. 6 and 7, this is indicated by line (3).

<Comparative Example 2>
As a developer replenishment for adjustment, an amount of new toner according to Table 1 above is replenished in the toner shortage area A and 3.3 mg of new toner is replenished in the appropriate density area B every second. In the excess region C, toner scattering and image fogging were observed in the same manner as in Example 1 except that new toner and new carrier were not replenished except for regular carrier replenishment. When 10,000 sheets were printed, In this case, toner scattering occurred, but no image fogging occurred. FIG. 6 shows the transition of the toner concentration in the developer container, and FIG. 7 shows the transition of the toner charge amount. In FIGS. 6 and 7, it is indicated by a line (4).

As described above, in the first and second embodiments, toner scattering and image fog do not occur, and a higher charge amount can be obtained over a longer period than that in FIG. 7. Therefore, according to the image forming apparatus of the present invention, It was found that the deterioration of the developer contained in the toner was suppressed.
Further, in Example 2, since the increase in the toner density accompanying the replenishment of new toner is suppressed over a longer period than in FIG. 7 and a high charge amount is obtained from beginning to end, the developer contained in the developer containing portion is removed. It has been found that deterioration is more reliably suppressed. In Example 2, the toner concentration detected by the toner concentration detecting means did not exceed the allowable limit value.
On the other hand, in Comparative Example 1, since the low-coverage continuous printing state lasts for a long time and the toner density changes in the vicinity of 6%, the new toner is hardly replenished, and as a result, the developer deteriorates. It was confirmed that gradually higher charge amounts could not be obtained.
In Comparative Example 2, a constant amount of toner was supplied up to 6,000 sheets even when the toner density exceeded the specified value, so that a high charge amount was obtained up to 6,000 sheets. After exceeding the number of sheets, it was confirmed that new toner was hardly replenished, so that the deterioration of the developer progressed and a gradually higher charge amount could not be obtained.

10Y, 10M, 10C, 10K Photosensitive drums 11Y, 11M, 11C, 11K Charging means 12Y, 12M, 12C, 12K Exposure means 14Y, 14M, 14C, 14K Primary transfer means 16Y, 16M, 16C, 16K Cleaning means 17 Intermediate transfer Belts 17a to 17i Roller 18 Secondary transfer means 20Y, 20M, 20C, 20K Developing device 21 Developer container 21a Roof plate 21x Stirring area 21y Supply / recovery area 22 Developing roller 23 Stirring member 24 Supply / recovery member 25 Toner density detecting means 26 Developer discharge port 27a Toner supply port 27b Carrier supply port 28 Developer layer thickness regulating member 29 Partition 100Y, 100M, 100C, 100K Image forming unit P Recording material R Development area

Claims (3)

A developer containing portion containing a two-component developer comprising a toner and a carrier for developing an electrostatic latent image carried on the image carrier;
A toner replenishing mechanism having toner replenishing means for replenishing toner to the developer containing portion; and a carrier replenishing mechanism for supplying carrier to the developer containing portion;
Surplus developer discharging means for discharging surplus two-component developer from the developer containing portion;
In an image forming apparatus comprising a developing device having a toner concentration detecting means for detecting a toner concentration of a two-component developer in the developer containing portion,
In the developer supply mechanism,
A certain amount of carrier is replenished at certain time intervals,
The toner density detected by the toner density detection means at a fixed set time interval is a toner shortage area A that is less than a specified value, and is less than an allowable limit value greater than the specified value and greater than the specified value. When a certain density area is an appropriate density area B and a density area that is equal to or greater than the allowable limit value is an excessive toner area C,
For each predetermined set time interval,
When the toner density detected by the toner density detecting means is in the toner shortage region A, an amount of toner corresponding to the shortage with respect to the specified value of the toner density is replenished,
When the toner density detected by the toner density detecting means is in the proper density area B, when the proper density area B is shifted from the toner shortage area A, a certain amount of toner is replenished, and the proper density area B Is transferred from the excessive toner area C, only the carrier is replenished,
2. An image forming apparatus according to claim 1, wherein when the toner concentration detected by the toner concentration detecting means is in the excessive toner area C, only the carrier is replenished. In the developer replenishing mechanism, when the toner density detected by the toner density detecting means is in the proper density area B transferred from the toner shortage area A, the carrier is replenished with a certain amount of toner,
The image forming apparatus according to claim 1, wherein the amount of the replenished carrier is controlled so as to decrease as the toner density approaches a specified value. In the developer replenishing mechanism, when the toner concentration detected by the toner concentration detecting means is in the excessive toner region C, the amount of carrier replenished becomes smaller as the toner concentration approaches the allowable limit value. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled as follows.