JP2966499B2 - Developing device in image forming apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a developing device in an image forming apparatus such as a copying machine, and more particularly, to a toner supply control device.

(Prior Art) As is well known, in an image forming apparatus such as a copying machine or a printer, a two-component developer obtained by mixing an electrostatic latent image formed on a photoreceptor with, for example, a toner and a carrier is used. , A visible image is processed, and the visible image is transferred onto copy paper and then fixed to obtain a copy.

One of the above-described image forming apparatuses is a color copying machine that obtains a color image by superimposing images of different colors on the same copying paper. The schematic configuration of the copying machine will now be described with reference to FIG. .

That is, the color copier includes a scanner unit 21 for reading a document, an image processing unit 22 for electrically processing an image signal output as a digital signal from the scanner unit 21, and each color from the image processing unit 22. And a printer unit 23 for forming an image on copy paper based on the image recording information.

The above-described scanner unit 21 includes a lamp 25 that illuminates the original placed on the original placing table 24 while moving the original in the scanning direction.
A mirror 26, 27, 28 for setting the optical path of the reflected light from the original illuminated by the lamp 25; an image forming lens 29 arranged in this optical path to form an image on the dichroic prism 30; And a light receiver 31 that separates the reflected light from the light and receives the light for each wavelength. Scanner section mentioned above
In 21, in the dichroic prism 30, for example, a light receiver that receives reflected light from a document separated into three kinds of colors of red R, green G, and blue B, that is, image light, receives colors of respective wavelengths, That is, the light enters the red CCD 31R, the green CCD 31G, and the blue CCD 31B, and is converted into a digital signal in the light receiver.

The above-described digital signal is output to the image processing unit 22,
The same processing unit 22 performs processing necessary for image forming exposure, which will be described later, to record information of each color, for example, black (hereinafter, abbreviated as Bk), yellow (the same, Y), magenta (the same, M), The signals are converted into recording and forming signals of cyan (same as C).

FIG. 5 shows a case where the above four colors of Bk, Y, M, and C are formed, but the number of colors is not limited to this.

On the other hand, a signal from the image processing unit 22 is input to the printer unit 23, and is used for operation control of the image exposure laser light emitting devices 32Bk, 32C, 32M, and 32Y according to each color.

The above-described printer unit 23 is a part for exposing image light from a document onto a photoreceptor, processing the electrostatic latent image formed by the exposure into a visible image with a developer, and transferring the processed image onto copy paper. It is.

That is, in the illustrated example, the printer unit 23 is provided with four sets of recording devices 33Bk, 33C, 33M, and 33Y arranged side by side.

Since each of the recording devices described above has the same configuration,
For the sake of simplicity, the recording apparatus for C (cyan) will now be described, and the description of the other colors will be omitted.
Note that components having the same function for each color have the same reference numerals, and a reference numeral indicating each color is added to the reference numeral to distinguish the configuration of each color.

That is, in the recording device 33C for C (cyan), the photosensitive member 34C on the drum is arranged in the optical path from the laser light emitting device 32C, and the image forming is performed around the photosensitive member 34C along the rotation direction. A charging device 35C, a developing device 36C, a transfer device 37C, and the like for performing the processing are provided similarly to a known copying machine.

Then, the photosensitive member 34C uniformly charged by the charging device 35C
A latent image of a cyan image is formed by exposure by the laser light emitting device 32C, and the latent image is processed into a visible image by the developing device 36C.

On the other hand, the printer unit 23 is provided with a paper feed unit for copying paper, and from this paper feeding unit, for example, one of two kinds of sizes is selected by a paper feed roller 38. The copy paper is conveyed to the conveyance belt 41 passing through the transfer position of the photoreceptor 34C after its leading end is aligned with the leading end of the image by the registration roller 40.

Then, the copy paper carried on the transport belt 41 and transported to the transfer position of the photoconductor 34C is sequentially transported toward the photoconductors 34Bk, 34C, 34M, and 34Y, each of which has been subjected to visible image processing, and After the visible image of each color is electrostatically transferred by the action of the transfer device 37 provided opposite to the transfer belt 37, the visible image of each color is transferred to the fixing roller 42 from the transfer belt 41 to receive the fixing, and is discharged out of the apparatus by the discharge roller 43. Is discharged. The transfer belt 41 described above electrostatically attracts the copy paper carried thereon,
The belt is conveyed at a moving speed without displacement.

By the way, in the above-described developing device, for example, when a two-component developer in which a resin toner and a magnetic carrier such as iron powder are mixed is used, an amount of toner corresponding to the amount of the consumed toner is supplied. There is a need to maintain a constant concentration.

For this reason, conventionally, a reference density pattern is developed on a photoreceptor, the ratio of the density of this pattern to the density of the background portion of the photoreceptor is calculated, and the toner is developed on the developing device side so that the ratio becomes constant. A structure in which a fixed amount of replenishment is performed (for example, JP-A-63-210873 and JP-A-63-27868),
At this stage, the image density on the photoreceptor is measured, and when the density is not at the predetermined density, the operation state of the replenishing member in the toner replenishing unit so as to correct the density, for example, the rotational speed of the replenishment roller, Structure for controlling the rotation speed (for example,
No. 56542, JP-A-60-165465, JP-A-63-101
No. 970), or to control the bias applied to the replenishing member based on the difference between the image density of the photoreceptor and the reference density, or to control the operating state of the replenishing member described above. (See, for example,
-221798, JP-A-63-146081).

(Problems to be Solved by the Invention) However, in the above-described toner supply control, the toner supply may be performed during the development of the photoconductor. , And density unevenness may occur in a developed image, resulting in extremely poor image characteristics as a copy.

In addition, due to environmental changes (charge-up) of the developer,
Poor toner replenishment or excessive replenishment may occur.

For this reason, for example, by counting how many times replenishment is performed during a predetermined number of copies such as every eight sheets, a predetermined standard replenishment potential, that is, a bias (V _B ) and standard supply bias (V _BO )
A method of stabilizing the image density by changing the replenishing potential in accordance with the number of replenishments as shown in the following table with a focus on the difference between the replenishment frequency and the number of replenishments has been proposed. ).

However, when replenishing the developer by the above-described replenishment control, in the process of using the developer, the sixth
As shown in the figure, even with the same replenishment potential, the replenishment amount is reduced, the replenishment potential fluctuates, and the image density may become unstable. In FIG. 6, a plurality of lines represent the results of detection at a plurality of locations in the axial direction of the developing sleeve, respectively.
In FIG. 6, a diagram indicated by reference numeral (A) indicates a case where a new developer is used, and a diagram indicated by reference numeral (B) indicates a development diagram which is collected and replenished several times. Each shows the case where an agent was used.

This is mainly due to the fact that the acceptor of the carrier decreases with the deterioration of the developer and the toner adheres to the developing sleeve, so that the sleeve is easily stained,
It is probable that sufficient replenishment potential could not be obtained.

Accordingly, an object of the present invention is to provide a developing device capable of replenishing toner, which can stabilize the image density evenly when the replenishment is started during development, in view of the above-described problem in the toner replenishment control.

(Means for Solving the Problems) In order to achieve this object, the present invention provides a developing device having a replenishing unit for supplying toner from a replenishing tank to a magnetic brush developing sleeve, and a unit for applying a bias to the toner replenishing unit. In the apparatus, a control unit is connected to an output side of the replenishment toner bias setting circuit, and an input side is connected to an optical detection element for detecting a reflection density from a density reference pattern formed on a photoreceptor. The control unit counts the number of toner replenishments within the number of copies when a predetermined number of copies are made, and applies the toner to the developing sleeve so that the target replenishment number is reached in accordance with the number. above that bias (V _B) and by selecting the bias applied to the replenishing means a difference of (V _B -V _H0) as the center value of the standard replenishing bias (V _H0) applied to said toner supplying means Output to the bias setting circuit, and the difference (V _B
−V _H0 ) is corrected.

(Operation) According to the present invention, based on the number of toner replenishments performed within a preset number of copies, if the number of replenishments tends to be large, the bias applied to the toner replenishing means and the developing bias The bias potential is set in a direction to increase the difference between the bias and the developing bias. In contrast, when the number of replenishments tends to be small, the difference between the bias applied to the toner replenishing unit and the developing bias is reduced. By setting the bias potential, the toner supply amount can be stabilized.

(Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS.

FIG. 1 is a schematic sectional view showing the overall configuration of a developing device according to an embodiment of the present invention.

That is, in FIG. 1, the developing device 1 includes a developing tank 3 provided with a developing sleeve 2 therein, and a replenishing tank 4 containing replenished toner.

The above-described developing tank 3 has an opening at a position facing the photoconductor 5, and a part of the peripheral surface of the developing sleeve 2 is exposed from this opening. The rotation direction of the developing sleeve 2 is set so that the developing sleeve 2 can move in the same direction as the tangential direction with respect to the photoreceptor 5. By magnet group 6,
A magnetic brush is formed on the surface so that the magnetic brush can correspond to the photoconductor 5.

On the other hand, a supply roller 7 is located at a supply toner outlet in the supply tank 4, and the supply roller 7 is in contact with a supply roller 8 that is close to the developing sleeve 2. A blade 9 is brought into contact with the supply roller 8 together with the supply roller 7, and the supply toner supplied by being rubbed by the supply roller 7 is thinned by the blade 9 and carried on the surface. It is designed to be transported toward.

The replenishing roller 8 includes a clutch 10 that is driven via a control unit described later. When the replenishing roller 8 is turned on when replenishing toner, replenishment of toner toward the developing sleeve 2 is possible. You can rotate in the direction. In FIG. 1, reference numeral 11 denotes a developer collecting screw, reference numeral 12 denotes a supply screw for returning the collected developer to the developing sleeve 2 again, and reference numeral
Reference numeral 13 denotes a seal plate.

The above-mentioned developing sleeve 2, supply roller 7, supply roller 8 and blade 9 are provided with bias circuits 14 and 15, respectively.
Each of the bias circuits 14 and 15 has a bias circuit 15 for the supply roller 7, the supply roller 8 and the blade 9 in the supply tank 4 whose operation is controlled by a toner supply control unit 16 described later. .

That is, as shown in FIG. 2, the toner replenishment control unit 16 includes, for example, a microcomputer 16A as a main part, and the microcomputer 16A stores a basic program and basic data necessary for arithmetic control processing. And a RAM 16 for taking in data, and signals are exchanged with external devices such as the above-described bias circuit 15 and supply roller clutch 10 via an input / output device (I / O interface) 16D. .

The input port of the input / output device 16D has a copy start switch 17, a numeric keypad 18 for setting the number of copies, and a density of a reference density pattern 5A (see FIG. 1) formed on the photoreceptor 5. Photo sensors 19 to be detected are respectively connected.

The clutch 10 is connected to the output port of the input / output device 16D.
Drive circuit 10A and the above-described bias circuit 15 are connected.

The toner replenishment control unit 16 controls the toner replenishment roller 8 for correcting the toner replenishment amount in accordance with the number of toner replenishments for a predetermined number of copies (the last eight in the present embodiment).
Specifically, as shown in FIG. 3, a polarity and a potential in a direction for eliminating a difference from a charge amount at a target image density are set. ing. The above-described counting of the number of times of replenishment is performed, for example, based on the reference density pattern formed on the photoconductor 5.
The ratio (V _SP / V _SG ) between the reflected light output from 5A (A _SP ) and the reflected light output from the background surface of the photoconductor 5 (V _SG ) is larger than a reference value corresponding to the target image density. The case, that is, the case where the amount of reflected light is large is counted as the time of replenishment.

That is, in the case of the present embodiment, the charging polarity of the toner is set to (−)
As shown in Table 1, the number of replenishments for the past eight cards is counted, and the change amount of the replenishment potential ΔV _HB and the center of the replenishment potential are set so that the number of replenishments becomes four (/ 8). The amount of change ΔV _HB is selected to set the bias applied to the supply roller 8. Here, the center value of the supply potential V _B -V _HO (However, V _B: a developing bias, V _HO: Standard supply bias), the replenishment times, for example, in eight, when it once, the supply roller 8 The applied bias potential (V _H ) is expressed as V _H = V _HO + ΔV _HB + ΔV _HB . Therefore, if the number of replenishments is small, centering on the number of replenishments (4 times / 8 sheets), the amount of one replenishment is large, so the replenishment potential is reduced accordingly. If the number of replenishments is large, one replenishment is performed. Since the amount is small, the supply potential is increased.

However, as the initial value of the center value _{(V B + V HO),} B K, M: 50V Y, C: is set to 100 V. (However, V _B : developing bias, V _HO : standard replenishing bias) Since the present embodiment has the above-described structure, the third embodiment will be described below.
The operation will be described based on a flowchart for explaining the operation of the toner supply control unit 16 shown in the figure.

That is, when the copy start switch 17 is turned on, the control process of the toner replenishment control unit 16 is started. The toner replenishment control unit 16 copies the replenishment data for the past seven sheets, and replenishes the replenishment data based on a signal from the photo sensor 19. The presence / absence is discriminated, the total of the number of replenishments is determined, and the replenishment bias potential is selected from this total based on Table 1 and output to the bias circuit 15.

Therefore, the toner on the supply roller 8 is supplied to the bias circuit 15.
The toner is supplied toward the developing sleeve 2 by the bias from.

(Effects of the Invention) As described above, according to the present invention, the number of times toner is supplied in a predetermined number of copies is counted, and the supply potential and the central value of the supply potential are changed. , The image density can be stabilized.

Further, according to the present invention, by performing the above-described change, it is possible to cope with a replenishment defect due to the deterioration of the developer and a replenishment defect due to sleeve contamination. By taking measures, replenishment control for stabilizing the image density can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the overall configuration of a developing device according to an embodiment of the present invention, FIG. 2 is a block diagram for explaining a main part of the developing device shown in FIG. 1, and FIG. FIG. 2 is a diagram for explaining the characteristics of the main part shown in FIG. 2, FIG. 4 is a flowchart for explaining the operation of the main part shown in FIG. 2, and FIG. 5 is an arrangement showing an example of the image forming apparatus. FIG. 6 and FIG. 6 are diagrams for explaining problems in the conventional structure. 1 ... developing device, 2 ... developing sleeve, 3 ... developing tank,
4 replenishment tank, 5 photoreceptor, 7 supply roller, 8
... supply roller, 9 ... blade, 15 ... bias circuit,
16 control unit, 17 copy start switch, 18 numeric keypad, 19 photosensor.

Claims (1)

(57) [Claims] 1. A developing device comprising: a replenishing means for supplying toner from a replenishing tank to a magnetic brush developing sleeve; and a means for applying a bias to the toner replenishing means, wherein the replenishment toner bias setting circuit is connected to an output side. The input side includes a toner replenishing device having a control unit connected to an optical detection element for detecting a reflection density from a density reference pattern formed on the photoreceptor. Is performed, the number of toner replenishments within that number is counted, and a bias (V _B ) applied to the developing sleeve and a bias (V _B ) applied to the toner replenishing means are set so as to reach the target number of replenishments in accordance with the number. that by selecting the standard replenishment bias bias applied to the replenishing means a difference of (V _B -V _H0) as the center value of (V _H0) is output to the bias setting circuit, further, the replenishment count Flip the difference (V _B -
A developing device for an image forming apparatus, which corrects the center value of V _H0 ).