JP2006154193A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the unevenness of image density by sufficiently supplying developer from a supply screw to a developing roller and stably conveying the developer on the developing roller. <P>SOLUTION: In the developing device, the revolving speed Y of the supply screw for supplying the developer to the developing roller is expressed by an expression: Y≥a×G-b×R/r+C. In the expression, Y means the revolving speed of the supply screw (rotation/minute), G means a gap (mm) between the developing roller and the supply screw, R means the diameter (mm) of the supply screw, and r means the diameter (mm) of the developing roller, then coefficients (a) and (b) and a constant C are numerical values obtained by investigating an exhaustion limit (g) in terms of the specification of a developer supply part and a developer stirring part constituting the developing device, the diameter of the supply screw, and the gap G. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier such as a photosensitive member to form a toner image, and an electrophotographic system or an electrostatic recording system that includes the developing device. The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.

Conventionally known image forming apparatuses charge and expose an image carrier to form an electrostatic latent image, and a latent image formed on the image carrier forms a toner image and an image by a developing device. Then, the image is transferred onto a sheet by a transfer unit and then thermally fixed by a fixing device to form an image.
In a color image forming apparatus having a plurality of developing devices each having a two-component developer composed of a toner and a carrier, color toners of different colors are transferred onto an image carrier, and a color toner image of a plurality of colors is transferred to a sheet or an intermediate Transfer onto the transfer body.

  The developing device is disposed to face the image carrier on which the electrostatic latent image is carried, and is disposed in close proximity to the developer carrier that carries the two-component developer and the developer carrier. A developer layer thickness regulating member that regulates the layer thickness of the two-component developer carried on the body, a developer supply stirring and conveying means, and the like are provided.

The two-component developer on the developer carrying member is formed into a thin layer by a developer layer thickness regulating member and is transported to a developing area facing the image carrying member to develop the electrostatic latent image on the image carrying member. (For example, see Patent Documents 1 and 2)
Further, there has been proposed a developing device for an electrophotographic image forming apparatus using a two-component developer so that uniform development can be performed over the entire image surface. (For example, see Patent Document 3)
JP 2002-91157 A JP 2002-148921 A JP 2002-31948 A

  However, since the toner and carrier have been reduced in particle size for the purpose of improving image quality and uniformity, and the flowability of the developer has been reduced accordingly, the developer used for development is surely removed from the developing roller, In addition, it has become difficult to supply a developer sufficiently mixed with toner to the developing roller. Further, in the color machine, since the toner consumption rate per page is large, there is a problem of ensuring uniformity within a page or between pages.

  In response to the above problem, stirring and mixing have become possible by increasing the diameter and pitch of the supply and stirring screw and further setting the rotational speed of the screw high, but with the downsizing of the developing device, The problem of uniformity has occurred because the developer has been transported directly from the supply screw without using a cross paddle or the like to transport the developer to the developing roller.

  The present invention has been made in view of the above situation, and a developing device capable of ensuring image uniformity without causing a developer conveyance failure on the developing roller even when the developer is directly supplied from the supply screw to the developing roller. I will provide a.

The above object is achieved by the following configuration.
(Claim 1)
A developing roller for conveying and carrying a developer to a developing position for developing the electrostatic latent image on the image carrier;
Opposing to the developing roller, supplying the developer onto the developing roller while rotating, and facing the supplying screw and the supplying screw for conveying the developer in the rotation axis direction, stirring the developer while rotating, In a developing device having a developer agitation supply unit comprising a stirring screw that conveys the developer in the direction of the rotation axis opposite to the supply screw via the partition plate and supplies the developer to the supply screw,
A developing device characterized in that the number of rotations of the supply screw is set to a condition of the following formula.
Y ≧ a × G−b × R / r + C
In the formula, Y is the number of rotations of the supply screw (rotations / minute), G is the gap length (mm) between the developing roller and the supply screw, R is the diameter of the supply screw (mm), and r is the diameter of the developing roller (mm). Show.
The coefficients a and b and the constant C are functions of the screw rotation speed at an inflection point at which the depletion limit does not decrease even if the screw rotation speed in the developing device is increased.
(Claim 2)
The developing device according to claim 1, wherein the driving unit that drives the developing roller and the driving unit that drives the supply screw are independently transmitted to each other.
(Claim 3)
A charging unit for charging the image carrier, an exposure unit for exposing the charged image carrier, a developing device for developing the exposed image carrier to form a toner image, and a toner image on the image carrier. 3. An image forming apparatus having a transfer means for transferring to a recording paper and a fixing means for fixing a toner image formed on the recording paper, wherein the developing device is the developing device according to claim 1 or 2. Image forming apparatus.

  According to the first aspect of the present invention, in supplying the developer to the developing roller, the developer such as a cross paddle disposed between the developing roller and the supplying screw and having a function of delivering the developer from the supplying screw to the developing roller. In the configuration in which the developer is directly transferred from the supply screw to the developing roller without using the intermediate conveying means, the developer can be sufficiently supplied, and the developer conveyance failure on the developing roller is eliminated, and the uniformity of the image density is improved. It can be secured.

  According to the second aspect of the present invention, in addition to the effect of the first aspect of the invention, the rotation speed of the supply screw is set regardless of the change in the rotation speed of the developing roller due to the speed control of the developing device system. As a result, the developer conveyance failure on the developing roller is eliminated, and the uniformity of the image density can be ensured.

  According to the third aspect of the present invention, the image density of each color in the color image forming apparatus can be kept uniform, and a high-quality color image can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is an overall configuration diagram of a color copying machine including an image forming apparatus 100 on which a plurality of sets of developing devices according to the present invention are mounted and an image reading apparatus 200.

  The image forming apparatus 100 is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-shaped intermediate transfer member 6, a sheet feeding and conveying unit, and a fixing device 24. Consists of.

  The image forming unit 10Y that forms a yellow image includes a charging unit 2Y, an exposure unit 3Y, a developing device 4Y, and a cleaning unit 8Y disposed around the image carrier 1Y. The image forming unit 10M that forms a magenta image includes an image carrier 1M, a charging unit 2M, an exposure unit 3M, a developing device 4M, and a cleaning unit 8M. The image forming unit 10C that forms a cyan image includes an image carrier 1C, a charging unit 2C, an exposure unit 3C, a developing device 4C, and a cleaning unit 8C. The image forming unit 10K that forms a black image includes an image carrier 1K, a charging unit 2K, an exposure unit 3K, a developing device 4K, and a cleaning unit 8K. Hereinafter, the image carriers 1Y, 1M, 1C, and 1K are referred to as image carriers 1 as representatives.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported. Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred (primary transfer) by the transfer means 7Y, 7M, 7C, and 7K onto the rotating intermediate transfer body 6 and synthesized. A color image is formed. The paper P stored in the paper feeding cassette 20 is fed by the paper feeding means 21 and is conveyed to the transfer means 7A through the paper feeding rollers 22A, 22B, 22C, the registration rollers 23, and the like. The image is transferred (secondary transfer). The sheet P on which the color image has been transferred is subjected to fixing processing by the fixing device 24, is sandwiched between the sheet discharge rollers 25, and is placed on the sheet discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the paper P by the transfer means 7A, the residual toner is removed by the cleaning means 8A from the intermediate transfer body 6 from which the paper P is separated by curvature.

  Reference numerals 5Y, 5M, 5C, and 5K denote toner replenishing units that replenish new toner to the developing devices 4Y, 4M, 4C, and 4K, respectively.

  An image reading device 200 including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of the image forming apparatus 100.

  Details of the developing devices 4Y, 4M, 4C, and 4K in FIG. 1 will be described with reference to FIGS.

  2 is a central sectional view of the developing device according to the present invention, and FIG. 3 is a plan view of a lower mechanism of the developing device. In the following description, the developing devices 4Y, 4M, 4C, and 4K in FIG.

  The developing device 4 includes a developing device main body 40, a developing roller 41, a developer regulating member (bread cutting plate) 42, a supply screw 43, a stirring screw 44, a toner concentration sensor (toner concentration detecting means) 47, and the like.

  The developing device main body 40 includes a lower main body 40A that supports the developing roller 41, the supply screw 43, and the stirring screw 44, and an upper lid 40B.

  The lower main body 40 </ b> A includes a developer supply unit 401 that stores the supply screw 43 and a developer stirring unit 402 that stores the stirring screw 44. The developer supply unit 401 and the developer stirring unit 402 are formed on both sides with the first partition 404 standing upright from the bottom of the lower main body 40A.

  A developing roller 41 comprising a developing sleeve 41A and a magnetic field generating means (magnet roll) 41B is disposed to face the image carrier 1 shown in FIG. 1 carrying an electrostatic latent image, and the developing sleeve 41A is rotatably supported. ing.

  The magnetic field generating means 41B is arranged inside the developing sleeve 41A and has a plurality of magnetic poles N1, N2, N3, S1, S2, S3, S4. The developer stripping magnetic pole S1 strips off the developer on the developing roller 41 and scatters it. The developer receiving magnetic pole S <b> 2 sucks the developer supplied by the supply screw 43 and attaches it to the developing roller 41.

  The supply screw 43 conveys the developer conveyed from the stirring screw 44 while stirring, and supplies the developer uniformly to the developing roller 41.

  The stirring screw 44 is arranged in parallel to the supply screw 43, mixes the new toner replenished from the toner replenishing means 5 of FIG. To do.

  The developer released from the surface of the developing roller 41 is collected by the developer supplying unit 401 by the magnetic pole S1 for removing the developer from the developing roller 41.

  A toner concentration sensor 47 provided at the bottom of the developer supply unit 401 on the downstream side of the developer conveyance detects the toner concentration of the developer conveyed. In response to the toner density detection signal, the control means (not shown) drives the toner replenishing means 5 in FIG. 1 to replenish new toner to the toner replenishing opening 409 provided near the developer transport upstream side of the developer stirring part 402. . The toner replenishing means 5 can also optically detect the image density after the development processing and perform toner replenishment control according to the detection result of the image density.

  As shown in FIG. 3, each of the supply screw 43 and the agitation screw 44 is a spiral screw-like member, and conveys the developer in the direction of the rotation axis and releases the developer in a direction substantially perpendicular to the rotation axis.

  The developer conveyance downstream side of the developer supply unit 401 and the developer conveyance upstream side of the developer agitation unit 402 communicate with each other through a second opening 407 formed in the vicinity of one end of the first partition 404. Yes.

  The developer transport downstream side of the developer agitating unit 402 and the developer transport upstream side of the developer supply unit 401 communicate with each other through a third opening 408 formed in the vicinity of the other end of the first partition 404. Yes.

  The developer in the developer supply unit 401 is returned to the upstream side of the developer conveyance in the developer stirring unit 402 from the second opening 407 formed in one end of the first partition 404 by the supply screw 43. The

  The developer refluxed into the developer agitating unit 402 is conveyed by the agitating screw 44 while mixing and stirring the new toner replenished from the toner replenishing opening 409 and the developer. Is discharged from the third opening 408 formed in the end of the toner and is conveyed into the developer supply unit 401. In the developer supply unit 401, the supply screw 43 radiates and supplies the developer to the developing roller 41 while being conveyed in the axial direction.

  Returning to FIG. 2, the rotation direction of the stirring screw 44 (arrow x44) is the supply direction so that the rotation direction of the supply screw 43 (arrow x43) is opposite to the rotation direction of the developing roller 41 (arrow x41). By configuring the screw 43 in the direction opposite to the rotation direction, not only the efficiency of the developer supply to the developing roller 41 is achieved, but also a stable developer supply is possible, and a good image is obtained. be able to.

In the developer, the magnetic carrier has a magnetization amount in a magnetic field of 79 kA / m in the range of ^{20 to} 70 A · m ² / kg, the magnetic carrier has a magnetic carrier in the range of 30 to 80 μm, and a particle size of A two-component developer having a non-magnetic toner in the range of 3 to 8 μm, and applying a developing bias with an alternating electric field superimposed on the developing roller 41, the image carrier 1 having an electrostatic latent image is applied with the non-magnetic toner. Develop with magnetic toner.

The developing roller (not shown) and the driving means for the supply and stirring screw are independent of each other. Regardless of the control of the rotation speed of the developing roller, the rotation speed of the supply screw can be set.
Further, the development roller drive and the supply screw drive are separated, and the development roller rotation is controlled by setting the rotation speed of the supply screw to the above condition regardless of the control of the rotation speed of the development roller (when controlling the speed of the image forming apparatus). Even when the number of rotations is changed, the developer conveyance failure on the developing roller can be prevented, and the uniformity of the image density can be ensured.

  Specifically, as the developing device becomes smaller, it becomes difficult to dispose a supply paddle in the developing device, and even when the developer is supplied from the supply screw to the developing roller as shown in FIG. In addition, it is possible to prevent a developer conveyance failure on the developing roller.

Further, in a developing device having a collecting unit provided with a collecting roller for separating and collecting a developer (not shown) that is separated from the developer supplying unit above the developer supplying unit as in the prior art, the rotation of the developing roller The direction is clockwise as opposed to the rotational direction shown in FIG. 2, the developer receiving magnetic pole is at the lower part of the developing roller (near the developing roller magnetic pole S1 in FIG. 2), and the developer stripping magnetic pole is at the upper right of the developing roller ( In the vicinity of the developing roller magnetic pole N2 in FIG. 2, the developer can be received and peeled off reliably.
However, when it is difficult to dispose the developer collecting unit independently in a small developing device as in the present invention, the developing roller is rotated counterclockwise as shown in FIG. 2 in order to ensure developer peeling. It is necessary to rotate it, peel it off with the stripping magnetic pole S1, and collect it directly to the developer supply unit. For this reason, the receiving pole is at the S2 position. The position of the receiving pole S2 is close to the developer supply section, that is, the lower right side of the developing roller is preferable for receiving the developer. However, when the stripping pole S1 and the receiving pole S2 approach each other, the developer stripped by the stripping pole S1 is removed. There is a problem in that it is received by the receiving pole S2 again without being stirred by the supply screw. In order to prevent this problem, it is necessary to increase the distance between the stripping pole S1 and the receiving pole S2, but the position of the receiving pole S2 is shown in FIG. 2 contrary to the position of the receiving pole S2 that is preferable for receiving the developer. Thus, the developing roller is on the upper right side.
Even if the position of the receiving pole S2 is arranged at the position shown in FIG. 2, the developer can be sufficiently supplied by setting the rotational speed of the supply screw to the condition derived from the equation (3). A developer conveyance failure can be prevented.

  The developer circulation in the developing device according to the present invention will be described with reference to FIG. FIG. 4 is a schematic diagram showing the circulation of the developer in the developing device 4.

  The developer in the developing device 4 circulates as described in the following (1) to (5).

  (1) On the upstream side 402a of the developer stirring section 402, the developer refluxed from the developer supply section 401 and the new toner carried from the toner replenishing means 5 are stirred and mixed by the stirring screw 44, and the arrow The developer is conveyed in the developer moving direction indicated by V1.

  (2) The mixed developer passes through the third opening 408 on the downstream side of the developer stirring unit 402 and is introduced to the upstream side of the developer supply unit 401. In the developer supply unit 401, the developer is discharged to the developing roller 41 as indicated by an arrow V4 while being conveyed in the developer moving direction indicated by the arrow V2 by the supply screw 43.

  (3) The developer on the developing roller 41 is developed in the developer area facing the image carrier 1. The developer whose toner density has decreased after the development processing is peeled off from the developer carrying member 41 by the peeling magnetic pole S1 and moved as indicated by an arrow V5.

  (4) The developer collected in the developer supply unit 401 is transported as indicated by an arrow V6, and after the toner concentration is detected by the toner concentration sensor 47, the developer passes through the second opening 407, and then the arrow V7. As shown in FIG. 4, the developer is introduced upstream of the developer stirring unit 402.

  (5) In the developer agitation unit 402, toner replenishment is performed by the toner replenishment means 5 based on the toner density detection signal of the toner density sensor 47, and the developer merges in the arrow V1.

  Although the developer is conveyed in the circulation system as described above, a part of the developer is circulated between the developer supply unit 401 and the developer stirring unit 402 as indicated by arrows V1, V2, V6, and V7.

  The operating conditions of the supply screw according to the present invention will be described with reference to FIGS.

  Regarding the number of rotations of the supply screw, the present inventor investigated the occurrence of developer conveyance failure on the developing roller because the developer conveyance failure on the developing roller hinders uniformity of image density and causes image failure. Thus, the influence of the rotational speed of the supply screw on the amount of developer in the developing device was found, and the rotational speed condition of the supply screw was set.

  FIG. 5 is a graph showing the relationship between the rotation speed (rotation / min) of the supply screw 43 and the depletion limit (g) of the developing device 4. The depletion limit (g) represents the minimum mass (g) of the developer held in the developing device 4 at which the developer conveyance failure does not occur on the developing roller 41. When the developer amount in the developing device is less than the depletion limit, a developer conveyance failure occurs on the developing roller 41, and when the developer amount exceeds the depletion limit, the developer conveyance failure does not occur on the development roller 41. The determination of the developer conveyance failure is to visually confirm whether or not screw pitch developer unevenness is generated on the developing roller 41.

  In FIG. 5, the depletion limit does not change at a certain rotational speed or higher as the screw rotational speed is increased. The region where the depletion limit does not change is the limit at which the supply performance of the developing device system can be obtained most. By using the screw rotation speed in this region, the supply performance can be utilized to the maximum. From the above, the supply screw rotation speed Sp at the inflection point P at which the depletion limit does not decrease even when the supply screw rotation speed is increased can be set as the lower limit of the screw rotation speed at which the developer supply performance is maximized.

  FIG. 6 illustrates the relationship between the gap (G) (mm) between the developing roller 41 and the supply screw 43 and the supply screw rotation speed Sp at the inflection point P. From FIG. 6, it can be seen that the supply screw speed Sp at the inflection point P is substantially proportional to the gap between the developing roller 41 and the supply screw 43, and the following equation (1) can be derived by the method of least squares.

Y = a × G + α (1) Formula FIG. 7 illustrates the relationship between (the diameter R of the supply screw 43) / (the diameter r of the developing roller 41) and the supply screw speed Sp at the inflection point P. Is. From FIG. 7, it can be seen that the inflection screw rotation speed Sp is substantially proportional to R / r, and that α in the equation (1) depends on R / r. From the above, the following equation (2) can be derived by the method of least squares.

α = −b × R / r + C (2) From the above results, a, b, and C can be derived, and the rotation speed Y of the supply screw 43 satisfies the following conditions to supply the developer. Performance can be ensured and good development performance can be obtained.

Y ≧ a × G−b × R / r + C
However, Y is the rotation speed (rotation / min) of the supply screw, G is the gap (mm) between the developing roller and the supply screw, R is the supply screw diameter (mm), and r is the developing roller diameter (mm).

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

<Survey example>
In this investigation example, evaluation was performed using an image forming apparatus provided with the developing device 4 shown in FIGS. 1 and 2.
The main configuration of the image forming apparatus shown in FIG. 1 is as follows, and is common to the investigation example and Examples 1 to 4.
[Image carrier (photosensitive member) potential]
-Charging potential: -250V to -900V variable, set to -600V-Image formation surface potential during exposure: -40V to -150V variable, set to -50 to -100V [Developing device]
・ Developing roller diameter 30mm,
・ Developing roller rotation speed: 200 to 500 rotation / minute variable, set to 400 rotation / minute ・ Supply and stirring screw rotation speed variable from 0 to 600 rotation / minute ・ Development bias applying means DC bias: −200 V to −700 V variable , Set to -500 V AC bias: 0.5 kvpp to 2.0 kvpp, 2 kHz to 7 kHz variable, set to 1 kv and 2 kHz respectively, developing sleeve potential: -500 V
[Two-component developer]
Carrier: average particle size 45 μm, polymerization toner: average particle size 6.5 μm
(Investigation method)
In the investigation, the depletion limit when the supply screw diameter was set to 30 mm, 27 mm, and 24 mm and the gap between the development roller and the supply screw was set to 3 mm, 5 mm, and 7 mm, respectively, in a developing device having a developing roller diameter of 30 mm was performed.
The survey was conducted as follows.
(1) Keep the supply screw rotation speed, the supply screw diameter, and the gap between the development roller and the supply screw constant, and first estimate the amount of developer that would cause a developer conveyance failure on the development roller, A test was performed with the amount of the developer, and it was confirmed that a developer conveyance failure occurred. Thereafter, the developer amount was added in increments of 10 g, and data on the depletion limit at which no developer conveyance failure occurred was collected.
(2) The test of (1) was performed at each rotation speed by changing the rotation speed of the supply screw by 50 rotations / minute in the supply screw diameter and the gap between the developing roller and the supply screw.
(3) The above measurements (1) and (2) were performed for each combination of the supply screw diameter, the developing roller and the supply screw gap.

(Determination method for developer conveyance failure)
The presence or absence of screw pitch-like developer unevenness on the developing roller was visually confirmed. The developer unevenness was evaluated as good.

(Investigation result)
FIGS. 8A, 8B and 8C illustrate the results.
From FIGS. 8A, 8B, and 8C, the depletion limit does not change at a certain rotational speed or higher as the screw rotational speed is increased. The region where the depletion limit does not change is the limit at which the supply performance of the developing device system can be obtained most. By using the screw rotation speed in this region, the supply performance can be utilized to the maximum. Based on the above, in each measurement, the supply screw rotation speed at the inflection point at which the depletion limit does not decrease even when the supply screw rotation speed is increased is set as the lower limit of the supply screw rotation speed at which the developer supply performance is maximized. Can do.
FIG. 9 is based on FIGS. 8A, 8B, and 8C, and the gap between the developing roller and the supply screw and the depletion limit are reduced when the supply screw diameter is 30 mm, 27 mm, and 24 mm. The relationship between the rotation speed of the supply screw at the intersection of the region and the region that does not change is illustrated. FIG. 9 shows that the screw rotation number is proportional to the gap between the developing roller and the supply screw, and the average of the proportionality constant a is 18.697 from FIG. From the above, the supply screw rotation speed Y can be expressed by the following equation.

Y = 18.697 × G + α (1) Expression FIG. 10 is obtained by connecting the points shown in FIG. 9 for each supply screw diameter. From FIG. 10, it can be seen that α in the equation (1) depends on the supply screw diameter because the supply screw rotation speed varies depending on the supply screw diameter. Since the developing roller diameter is constant at 30 mm, it can be seen from FIG. 10 that the supply screw rotation speed is proportional to the supply screw diameter.

The term related to the supply screw diameter is related to the developing roller diameter, and is represented by the ratio of the supply screw diameter to the developing roller diameter.
FIG. 11 shows the relationship between the ratio α in the formula (1) and the ratio of supply screw diameter (R) / developing roller diameter (r). From FIG. 11, α can be expressed by the following equation.

α = −584.72 × R / r + 804.04 (2) From the result of the above equation (2), from the equations (1) and (2), a = 18.697, b = −584.72, C804.04 The rotation speed of the supply screw can be expressed by the following formula.

Y = 18.697 × G−584.72 × R / r + 804.04 (3) If the supply screw speed is equal to or higher than the expression (3), the developer is supplied to the developing roller from the supply screw. In this system, a sufficient supply of the developer can be obtained, the developer conveyance failure on the developing roller can be prevented, and the uniformity of the image density can be secured.

<Example 1>
In the investigation example, the supply screw diameter was 30 mm, the gap between the developing roller and the supply screw was 5 mm, and the stirring screw diameter was 30 mm, and the supply screw rotation speed was derived 312 based on the supply screw rotation speed calculation formula according to the result of the investigation example. An image was formed under the same conditions as in the investigation example except that the rotation speed was set to 8 rpm.
(Evaluation methods)
On the formed image, the presence or absence of unevenness of the supply screw pitch was visually confirmed, and the absence of unevenness was accepted.
(result)
There was no problem with the developer conveyance on the developing roller, and an image having a uniform density was obtained.

<Example 2>
In the investigation example, the supply screw diameter was 27 mm, the gap between the developing roller and the supply screw was 7 mm, and the stirring screw diameter was 27 mm, and the supply screw rotation speed was derived based on the supply screw rotation speed calculation formula based on the result of the investigation example 408. An image was formed under the same conditions as in the investigation example except that the rotation speed was set to 7 rotations / minute.

The evaluation method is based on Example 1.
(result)
There was no problem with the developer conveyance on the developing roller, and an image having a uniform density was obtained.
<Example 3>
In the first embodiment, the rotation speed of the supply screw is set to the rotation speed of the condition based on the above-described investigation example regardless of the control of the rotation speed of the developing roller (when controlling the speed of the image forming apparatus).
Supply screw diameter: 30 mm, gap between developing roller and supply screw: 5 mm, stirring screw diameter: 30 mm, supply and stirring screw rotation speed: 312.8 revolutions / minute, common to Example 1.
In addition to the above settings, images were formed by switching the number of rotations of the developing roller in two stages.
Development roller rotation speed:
1/1 speed: 400 rotations / minute 1/2 speed: 200 rotations / minute The evaluation method is based on Example 1.
(result)
Even when the rotation speed of the developing roller was 1/1 or 1/2, there was no problem in the developer conveyance on the developing roller, and an image having a uniform density was obtained.
<Example 4>
In Example 3, the change was made only by making the rotation speed of the supply screw interlock with the rotation speed of the developing roller. Accordingly, the rotation speed of the supply and agitation screw varies according to the control of the rotation speed of the developing roller (when controlling the speed of the image forming apparatus).
1/1 speed: Development roller rotation speed, supply and stirring screw rotation speed are both 400 rotations / minute 1/2 speed: Development roller rotation speed, supply and stirring screw rotation speed are both 200 rotations / minute (result)
At 1/1 speed, the rotation speed of the supply screw is 400 rotations / minute, which is more than 312.8 rotations / minute, which is the setting of Example 3, and there is no problem in the developer conveyance on the developing roller, and an image with a uniform density is obtained. Obtained.
At 1/2 foot, the supply screw rotation speed was 200 rotations / minute, which was less than 312.8 rotations / minute, which was the setting in Example 3, so that a developer conveyance failure on the developing roller occurred and the image density was Unevenness and variation occurred.

Overall configuration diagram of a color copying machine composed of an image forming apparatus and an image reading apparatus 1 is a central sectional view of a developing device according to the present invention. The top view of the lower mechanism of a developing device. FIG. 4 is a schematic diagram showing circulation of a developer in the developing device. The characteristic diagram of a supply screw rotation speed (rev / min) and a depletion limit (g). The characteristic diagram of the gap (mm) between a developing roller and a supply screw, and the supply screw rotation speed Sp (rotation / min) of the inflection point P at which the depletion limit is constant. The characteristic diagram of supply screw rotation speed Sp (rotation / minute) and (supply screw diameter / developing roller diameter) R / r at an inflection point P at which the depletion limit becomes constant. FIG. 8A is a characteristic diagram of the supply screw rotation speed (rotation / min) and the depletion limit (g) at a supply screw diameter of 30 mm and a gap of 3, 5 and 7 mm, and FIG. FIG. 8 is a characteristic diagram of the supply screw rotation speed (rotation / min) and the depletion limit (g) at gaps 3, 5, and 7 mm, and FIG. 8C shows the supply screw diameter at 24 mm and supply screw rotation speed at gaps 3, 5, and 7 mm. It is a characteristic view of (rotation / min) and a depletion limit (g). Based on FIGS. 8 (a), (b), and (c), the gap (mm) between the developing roller and the supply screw, and the supply screw speed Sp (rotation / min) at the inflection point P at which the depletion limit is constant. Characteristic diagram. The characteristic diagram which tied FIG. 9 for every supply screw diameter. The characteristic diagram of coefficient α and (supply screw diameter / developing roller diameter).

Explanation of symbols

1, 1Y, 1M, 1C, 1K Image carrier 4, 4Y, 4M, 4C, 4K Developing device 10Y, 10M, 10C, 10K Image forming unit 100 Image forming device 40 Developing device body 40A Lower body 40B Upper lid 401 Developer supply Section 402 Developer stirring section 41 Developing roller 43 Supply screw 44 Stirring screw 47 Toner density sensor (toner density detection means)

Claims (3)

A developing roller for conveying and carrying a developer to a developing position for developing the electrostatic latent image on the image carrier;
Opposing to the developing roller, supplying the developer onto the developing roller while rotating, and facing the supplying screw and the supplying screw for conveying the developer in the rotation axis direction, stirring the developer while rotating, In a developing device having a developer agitation supply unit comprising a stirring screw that conveys the developer in the direction of the rotation axis opposite to the supply screw via the partition plate and supplies the developer to the supply screw,
A developing device characterized in that the number of rotations of the supply screw is set to a condition of the following formula.
Y ≧ a × G−b × R / r + C
In the formula, Y is the number of rotations of the supply screw (rotations / minute), G is the gap length (mm) between the developing roller and the supply screw, R is the diameter of the supply screw (mm), and r is the diameter of the developing roller (mm). Show.
The coefficients a and b and the constant C are functions of the screw rotation speed at an inflection point at which the depletion limit does not decrease even if the screw rotation speed in the developing device is increased. The developing device according to claim 1, wherein the driving unit that drives the developing roller and the driving unit that drives the supply screw are independently transmitted to each other. A charging unit for charging the image carrier, an exposure unit for exposing the charged image carrier, a developing device for developing the exposed image carrier to form a toner image, and a toner image on the image carrier. 3. An image forming apparatus having a transfer means for transferring to a recording paper and a fixing means for fixing a toner image formed on the recording paper, wherein the developing device is the developing device according to claim 1 or 2. Image forming apparatus.

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