JP2010039383A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is able to uniformize the degree of stresses of the toner in developer, regardless of the image area, without having to provide a discharge mode for deteriorated toner and to able to suppress faults, such as, scattered toner and soiled base. <P>SOLUTION: A developing device 4 includes: a toner recovery roller 46 for recovering toner from developer on a developing roller 43; and a recovered toner conveying means 49 for resupplying the recovered toner to the conveying path of the conveying screw 44b of a developer stir conveyance means 44. The recovered toner conveying means 49 is provided with a toner-recovering screw 48. At a low image area output, a fresh toner is supplied, while toner that has received stress is accumulated in the recovered toner conveying means 49; and when a high image area is output, the toner that has already received stress is recovered during the low image area output is used first for development, thereby decreasing the total weight of the toner. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, and a multifunction machine provided with at least one of these, and more particularly to an image forming apparatus that performs development with a two-component developer.

As a dry two-component developing method used in a conventional color image forming apparatus, a biaxial transport type developing device is shown in FIG.
The developing device of the biaxial transport type includes two transports: an auger 104 and a supply / collection transport path 105 for supplying and collecting the developer to the developing roller 103, and a transport agitation auger 101 and a stirring transport transport path 102 after toner replenishment. It consists of an auger and two transport paths, and is juxtaposed in the horizontal direction below the developing roller 103.
In this conventional two-component developing device, when an image having a low image area is continuously output, the same developer continues to rotate around the developing device without leaving the developing device. As a result, problems such as burying of external additives and charge-up occur.
On the other hand, when image output of a high image area continues, the replenished new toner is used for development with little stirring. At this time, although the stress received by the toner is small, the toner does not sufficiently start up charging, and problems such as scattering and background contamination occur.
As described above, the toner agitation time greatly deviates from an appropriate range in accordance with the output image area, thereby causing many problems.

  For example, in the image forming apparatus described in Patent Document 1, when a low image area ratio continues to be output, a countermeasure is taken in which the deteriorated toner is forcibly discharged and replaced with new toner.

Japanese Patent Laid-Open No. 2003-076079

However, this discharge mode causes a decrease in toner yield (consumption efficiency).
The above problems and the decrease in toner yield are derived from the following inefficiencies of the conventional two-component developer.
While the image in the low image area is being output, the toner in the developing device is in a state of receiving a lot of stress as described above, but the toner is hardly used for development and is a new toner that is replenished during the image output of the high image area Since there is almost no stress of toner in the developing device, it is often used for development.
In other words, the conventional two-component developer is a wasteful system in which toner that is hardly subjected to stress is preferentially used for development.

  According to the present invention, the level of toner stress in the developer can be made uniform regardless of the image area without providing a discharge mode for the deteriorated toner, and the occurrence of problems such as toner scattering and scumming can be suppressed. An object of the present invention is to provide an image forming apparatus.

In order to achieve the above object, the present invention is provided with a means for separating and collecting the toner from the developer on the developing roller and a means for storing the collected toner, and the total amount of toner circulating in the developing device is determined. The method is variable.
That is, when outputting a low image area, new toner is replenished while storing stressed toner, and the total weight of the developer is increased to lower the toner stress in the developer. Conversely, when outputting a high image area, the low image area is low. It was decided to reduce the total weight by preferentially using the already stressed toner collected at times for development.
As a result, even if the discharge mode is not provided, the degree of toner stress in the developer can be made uniform regardless of the image area.

  Specifically, in the first aspect of the invention, an image carrier, a charging device that charges the image carrier, and an exposure device that forms an electrostatic latent image by exposing the charged surface of the image carrier. A developer carrying member that carries a developer including toner and a carrier and visualizes the electrostatic latent image with the toner contained in the developer; and stirring the developer on the developer carrying member. A toner that collects toner from the developer on the developer carrying member in an image forming apparatus having a developer agitating and conveying means to be supplied and a new toner conveying path for supplying new toner to the developer agitating and conveying means A collecting member, and a collecting toner conveying unit for re-supplying the collected toner to the developer stirring and conveying unit, and the collecting toner according to a toner amount a [g] used for image formation per unit time. Toner in transport means And wherein the increasing or decreasing the amount w [g].

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, when the Max value [g] of the amount of collected toner entering the collected toner conveying means is W and the reference value for control is A, the collection is performed. When the toner weight in the toner conveying means is in the range of 0 ≦ w <W and the toner amount a [g] used for development per unit time is small (a ≦ A [g]), the recovery is performed. The toner weight in the toner conveying means is increased.
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the amount of toner collected by the collected toner conveying unit per unit time by the toner collecting member is Aa [g] or more. It is characterized by.

According to a fourth aspect of the present invention, in the image forming apparatus according to the second or third aspect, all of the toner is supplied to the developer agitating / conveying means from the new toner conveying path.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the toner weight in the collected toner conveying means is in the range of 0 <w ≦ W, and the amount of toner used for development per unit time When a [g] is large (a> A [g]), the weight of toner in the collected toner conveying means is reduced.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the amount of toner collected by the collected toner conveying means per unit time by the toner collecting member is 0 [g]. .
According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, the supply of toner to the developer agitating / conveying means is all performed from the collected toner conveying means.

According to an eighth aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, the supply of the toner to the developer agitating / conveying means is performed by performing A [g] per unit time from the new toner conveying path. Minutes from the collected toner conveying means.
According to a ninth aspect of the present invention, in the image forming apparatus according to the first aspect, the toner weight in the collected toner conveying means is w = W, and the toner amount a used for development per unit time is small (a In the case of ≦ A), the toner weight in the collected toner conveying means does not change.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, the toner consumption [g] of a single solid image is x, the unit time [s] is T, and the continuous image When the time [t] required to print one image at the time of output is t, the control reference value A [g] is
0.02 · x · T / t ≦ A ≦ 0.07 · x · T / t
It is characterized by satisfying.
According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first to tenth aspects, the collected toner conveying means has a toner conveying screw, and the increase / decrease in the toner weight in the collected toner conveying means This is performed by controlling the rotation of the toner conveying screw.

According to the present invention, it is possible to equalize the degree of stress of the toner in the developer regardless of the image image area without providing the discharge mode.
When outputting a low image area, it is possible to prevent the same toner from continuing to circulate in the developing device by separating the toner from the developer, accumulating the toner in the collected toner conveying means, and supplying new toner accordingly. .
By collecting the difference of the amount used for development to the collected toner conveying means, it is possible to always separate a certain amount of toner from the carrier even when outputting a low image area.
Even when outputting an image having a low image area, a predetermined amount or more of new toner can be replenished in a unit time.
At the time of outputting a large image area, toner scattering and background contamination can be suppressed by replenishing already collected toner that has been stirred to some extent instead of new toner.
In addition, by replenishing collected toner that has already been subjected to light stress stored at a low image area and at a high image area that consumes a lot of toner, the stressed developer can be preferentially used for development. Good.
When outputting an image with a large image area, a certain amount or more of toner is used for development, so there is no need to collect it separately.
By supplying the collected toner with the highest priority when outputting an image with a large image area, the stressed toner can be used efficiently for development.
Even when an image with a low image area is output, only when the toner has accumulated to the full capacity, the recovered toner transport means replenishes the recovered toner instead of the new toner, so that the toner is recovered from the recovered toner transport means. It can prevent overflow.
By setting the control reference value to the average output image area ratio of the user, the toner can be circulated efficiently without waste.
By controlling the number of rotations of the toner collection screw, it is possible to easily control the increase / decrease in the toner weight of the collected toner conveying means.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a sectional view of an image forming portion of the image forming apparatus according to the present embodiment, FIG. 2 is a sectional view of the developing device, and FIG. 3 is a top view (plan view) of the developing device.
As shown in FIG. 1, the image forming apparatus according to this embodiment includes a developing device 4 for each of a plurality of photoconductors arranged in parallel, and forms a single-color toner image on each photoconductor. This is a so-called tandem type color image forming apparatus in which monochromatic toner images are sequentially transferred onto an intermediate transfer belt, and finally a combined color image is transferred onto a sheet and recorded. FIG. The figure is shown.

  Explaining the configuration, a latent image is optically formed by the exposure device 3 on the photoconductors 1a to 1d as image carriers uniformly charged by the charging devices (charging rollers 2a to d in the figure) (writing position). 3a to d) and the developing devices 4a to d form visible toner images. The toner images formed on the photoreceptors 1a to 1d are once transferred onto the intermediate transfer belt 5 by intermediate transfer belt transfer means (primary transfer rollers) 12a to 12d, and conveyed at a predetermined timing through a pair of registration rollers 6. The toner image on the intermediate transfer belt 5 is transferred onto the transfer paper by the paper transfer means (secondary transfer roller 7) onto the transfer paper. The toner image transferred to the transfer paper is conveyed to the fixing device 8, and the toner image on the transfer paper is fixed by heat and discharged. The arrows in the figure indicate the paper conveyance path.

Untransferred toner that has not been transferred to the intermediate transfer belt 5 on the photosensitive member is scraped off from the photosensitive member by the photosensitive member cleaning devices 9a to 9d. Residual charges on the photosensitive member are discharged by a discharging unit (not shown) to prepare for the next image forming operation.
Untransferred toner scraped off by the cleaning devices 9a to 9d passes through a waste toner conveyance path (not shown), and untransferred toner on the intermediate transfer belt 5 and a pattern image for process control are transferred by the intermediate transfer cleaning device 13. The toner is scraped off from the intermediate transfer belt 5 and stored in a waste toner storage container (not shown) through the waste toner transport path.
The new toner filled in the toner cartridges 10a to 10d is supplied to the developing devices 4a to 4d through the toner replenishing devices 11a to 11d.

Next, the developing device will be described in detail with reference to FIGS.
The developing roller 43 as a developer carrying member includes a magnet roller in which a plurality of magnetic poles are magnetized in a roller in which a nonmagnetic material is formed in a cylindrical shape.
The two-component developer that is mixed and stirred while being circulated by the developer stirring and conveying means 44 is magnetically attracted by the magnetic force of the magnet in the developing roller 43, and on the surface of the developing roller 43 as the developing roller 43 rotates. It is conveyed by the provided unevenness not shown.
The developer agitating / conveying means 44 includes a conveying screw 44a as a developer supplying member that supplies the developer to the developing roller 43 while agitating and conveying the developer, and a conveying screw as a developer agitating member that delivers the developer to the conveying screw 44a. 44b. Openings (not shown) for delivering the developer are formed on the front and back sides in the longitudinal direction of the conveying screws 44a and 44b, and the developer circulates in the casing.

The transported developer is made to have a uniform layer thickness by a regulating member 45 (hereinafter referred to as “developing doctor”) that regulates the amount of developer on the developing roller 43 to a certain fixed amount, and is opposed to the photoreceptor 1 ( Development is performed on the photoreceptor 1 in the development area.
Here, only the toner adheres to the photosensitive member 1, and the toner that has not been developed and the carrier that has transported the toner face the toner collecting roller 46 as a toner collecting member as the developing roller 43 rotates. To.
A voltage is applied to the toner collection roller 46, and the toner collection roller 46 collects only the toner uniformly in the longitudinal direction. The toner is collected by attracting and peeling the toner on the developing roller 43 with an electrostatic force.
The toner that has not been recovered by the toner recovery roller 46 and the carrier that has transported the toner are further transported to the agent separation position facing the transport screw 44a of the developer stirring and transporting means 44 as the developing roller 43 further rotates. Is peeled off from the surface of the developing roller 43 by the repulsive pole, and falls on the conveying screw 44a and stirred.

The toner collected on the toner collecting roller 46 is peeled off from the toner collecting roller 46 by a toner removing mechanism (here, a blade) 47 as the toner collecting roller 46 rotates, and a toner collecting screw 48 serving as a toner conveying screw is contained therein. To the collected toner conveying means 49.
The toner collection roller 46 will be described in detail. The toner recovery roller 46 is in contact with the magnetic carrier and is disposed in the vicinity of the developing roller 43 including the magnet roller, so that the material is an aluminum tube which is a nonmagnetic material. Further, the installation position of the toner collection roller 46 is set such that the clearance with the developing roller 43 arranged in parallel is 0.2 to 0.4 mm which is equivalent to the clearance between the photosensitive member 1 and the developing roller 43. The toner recovery in this embodiment is performed electrostatically with respect to the developer after passing through the photoreceptor.
The principle is the same as the toner supply by electrostatic force performed from the developing devices 4a to 4d to the photosensitive member 1 described above.

The toner adhesion amount per area on the toner collecting roller 46 increases in proportion to the difference between the bias applied to the toner collecting roller 46 and the bias applied to the developing roller 43 of the developing device 4 (hereinafter referred to as “developing bias”). To do. FIG. 7 shows the relationship with the toner adhesion amount when the toner collection roller 46 is rotated in the forward direction at about twice the peripheral speed of the developing roller 43 and the bias applied to the toner collection roller 46 is changed.
The slope of the straight line in FIG. 7 can take various values depending on combinations such as carrier type, toner type, and surface property of the toner collecting roller. By changing the applied bias, the toner weight desired to be collected per unit time can be changed. In this embodiment, the developer A shown in FIG. 7 was used.
In this embodiment, the two toner recovery rollers 46 and the developing roller 43 are recovered with a speed difference in the forward direction. However, there is a method in which the toner recovery roller 46 is rotated in the counter direction for recovery. .
In this embodiment, the mechanism 47 for removing the toner attached to the surface of the toner recovery roller 46 is shown as scraping with a blade brought into contact with the edge. However, it is physically scraped with a brush roller or a scraper. Examples include a mechanism or a mechanism for changing the bias applied to the toner collection roller 46 and changing the electrostatic attraction force to peel off and collect the toner.

As shown in FIG. 3, the toner collected by the collected toner conveying means 49 is conveyed in the direction of arrow R by the toner collecting screw 48, and is replenished to the conveying path of the conveying screw 44b by gravity. The replenishment position is the same as the replenishment position of new toner from the new toner transport path 11.
By controlling the rotation amount of the toner collection screw 48, the replenishment amount of the collected toner (the discharge amount of the collected toner that has already been stressed from the collected toner conveying means 49) can be adjusted.
In this embodiment, the collected toner conveying means 49 is provided inside the developing device 4, but it may be installed outside the developing device 4. In that case, a replenishment of recovered toner may be performed using a MONO pump or the like.

Next, toner collection / replenishment control will be described with reference to FIG.
Consider a case where control is performed in a unit time T [s] cycle. When the accumulated toner consumption during T [s] at a certain point was _a n [g], depending on the value, T toner recovery amount per _{[s] b n [g]} , the new toner (NEW Toner) replenishment amount c _n [g] and recovered toner replenishment amount d _n [g] were determined as follows.
[A _n ≦ A When toner consumed in development is small (low image area)]
b _n = A−a _n + α
c _n = A
d _n = α
α is an arbitrary value of 0 or more. In this experiment, α = 0.
Therefore, in the collected toner conveying means, the toner of Δw = b _n −d _n = A−a _n [g] per unit time increases.
[A _n > A When a lot of toner is consumed in development (high image area)]
b _n = β
c _n = γ
d _n = a _n −γ + β
β and γ are arbitrary values of 0 or more. In this experiment, β = 0.
γ was made variable according to the toner weight in the collected toner conveying means. Γ = A when the toner weight is small, and new toner is periodically replenished in the developer, and γ = 0 when the toner weight is large, so that the toner does not collect too much in the collected toner conveying means 49. did. Recovery so that the toner of Δw per unit time _{= d n -b n = a n} -γ [g] content is reduced from conveying means.

Here, A is assumed to be the average of the toner weight consumed in development during T [s].
From the statistical result of the image area ratio output by the user (FIG. 5), it can be seen that the image area ratio has a peak in the vicinity of 3 to 7%.
When the image area ratio is y%, the toner weight consumed per T [s] is y · x · T / t [g].
It is.
Here, x is the toner consumption [g] of a single solid image, and t is the time [t] required to print one image during continuous image output.
Since the image area ratio to be output varies depending on the purpose of use of the user (such as images with a large image area are likely to be output on a high-speed machine), a width of 0.03 · x · T / t ≦ A ≦ 0.07・ X ・ T / t
A is determined within the range of
This time, the experiment was conducted with a copying machine with 30 sheets / min at A4 horizontal and a deposit amount of 0.45 mg / cm 2 per unit area at all solids. The control period was the time required to output 10 images, and A was determined as follows.
t = 2 [s], x = 0.45.20.29 = 0.26 [g], T = 20 [s], y = 5 [%]
A = 0.05 · 0.26 · 20/2 = 0.13 [g]
method of detecting a _n have now went from the image area ratio.
a _n = (sum of image area ratios output during unit time Ts) · x / 2
It was calculated from the following formula.

In addition to the above method, a method in which the toner concentration is detected by a toner concentration sensor and the toner consumption amount is calculated may be used.
The above is the control when there is sufficient recovered toner in the recovered toner conveying means.
When there was no recovered toner, all of the replenishing toner was of course fresh.
[A _n ≦ A When toner consumed in development is small (low image area)]
b _n = A−a _n + α
c _n = A + α
d _n = 0
[A _n > A When a lot of toner is consumed in development (high image area)]
b _n = β
c _n = a _n + β
d _n = 0

Conversely, if the transport path is full of collected toner,
[A _n ≦ A When toner consumed in development is small (low image area)]
b _n = A−a _n + α
c _n = 0
d _n = A + α
[A _n > A When a lot of toner is consumed in development (high image area)]
b _n = β
c _n = 0
d _n = a _n + β
Replenishment / recovery control was performed according to
Detection of the amount of collected toner in the collected toner conveying means was performed using two optical sensors with different mounting heights for full detection and empty detection.

FIG. 6 shows the change over time in the toner charge amount distribution when 2K (K = 1000) images with an image area ratio of 1% and 20 solid images were continuously printed. The charge distribution was measured using an E-spart analyzer manufactured by Hosokawa Micron.
FIG. 6A shows the result of the comparative example (conventional biaxial developing device), and FIG. 6B shows the result of this embodiment.
In the comparative example, the charge amount distribution is shifted to the strong charge or weak charge side by the image with the stirring time, whereas in this example, the toner charge amount distribution is stable, and the toner deterioration reduction effect is recognized. It is done.

1 is a cross-sectional view of a main part of an image forming apparatus according to an embodiment of the present invention. It is a schematic sectional drawing of a developing device. It is a schematic plan view of a developing device. 6 is a timing chart for explaining toner collection / replenishment control. It is a graph which shows the statistical result of the image area rate which a user outputs. 2 is a graph showing a change in toner charge amount distribution over time, (a) is a comparative example, and (b) is a graph of the present invention. 6 is a graph showing a change in toner adhesion amount with respect to a difference between a developing bias and a bias applied to a collecting roller. It is a general | schematic sectional view of the conventional biaxial conveyance type developing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor as image carrier 2 Charging device 3 Exposure device 11 New toner conveyance path 43 Developing roller as developer carrier 44 Developer stirring and conveying means 46 Toner collecting roller as toner collecting member 49 Collected toner conveying means 48 Toner Toner recovery screw as a transport screw

Claims (11)

An image carrier, a charging device that charges the image carrier, an exposure device that exposes a charged surface of the image carrier to form an electrostatic latent image, and a developer containing toner and a carrier and the developer A developer carrying member that visualizes an electrostatic latent image with toner contained in the developer, developer stirring and conveying means for feeding the developer while stirring the developer carrying member; In an image forming apparatus having a new toner conveyance path for supplying the developer agitating and conveying means,
A toner collecting member for collecting toner from the developer on the developer carrying member, and a collected toner conveying means for re-supplying the collected toner to the developer stirring and conveying means,
An image forming apparatus, wherein the toner weight w [g] in the collected toner conveying means is increased or decreased according to a toner amount a [g] used for image formation per unit time. The image forming apparatus according to claim 1.
When the Max value [g] of the collected toner amount entering the collected toner conveying means is W and the control reference value is A,
When the toner weight in the collected toner conveying means is in the range of 0 ≦ w <W and the amount of toner a [g] used for development per unit time is small (a ≦ A [g]), An image forming apparatus characterized in that the toner weight in the collected toner conveying means increases. The image forming apparatus according to claim 2.
An image forming apparatus, wherein the amount of toner collected by the toner collecting member per unit time by the toner collecting member is Aa [g] or more. The image forming apparatus according to claim 2 or 3,
2. An image forming apparatus according to claim 1, wherein all of the toner is supplied to the developer agitating / conveying means from the new toner conveying path. The image forming apparatus according to claim 1.
When the toner weight in the collected toner conveying means is in the range of 0 <w ≦ W and the toner amount a [g] used for development per unit time is large (a> A [g]) An image forming apparatus characterized in that the toner weight in the collected toner conveying means is reduced. The image forming apparatus according to claim 5.
2. An image forming apparatus according to claim 1, wherein the amount of toner collected by the toner collecting member per unit time is 0 [g]. The image forming apparatus according to claim 5 or 6,
2. An image forming apparatus according to claim 1, wherein all of the toner is supplied to the developer agitating / conveying means from the collected toner conveying means. The image forming apparatus according to claim 5 or 6,
The image forming apparatus according to claim 1, wherein the toner is supplied to the developer agitating / conveying means by performing A [g] per unit time from the new toner conveying path and performing the shortage from the recovered toner conveying means. The image forming apparatus according to claim 1.
When the toner weight in the collected toner conveying means is w = W and the toner amount a used for development per unit time is small (a ≦ A), the toner weight in the collected toner conveying means changes. An image forming apparatus characterized by not. The image forming apparatus according to claim 1,
Reference value for control when toner consumption [g] of a single solid image is x, unit time [s] is T, and time [t] required to print one image during continuous image output is t A [g] is
0.02 · x · T / t ≦ A ≦ 0.07 · x · T / t
An image forming apparatus characterized by satisfying the above. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the collected toner conveying unit includes a toner conveying screw, and the toner weight in the collected toner conveying unit is increased or decreased by controlling rotation of the toner conveying screw.

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