JP2006243116A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of outputting an image having high image quality over a long term by decreasing the stress of developer arised in a developing device. <P>SOLUTION: A developer supply roller 44 supplying the developer to a developing roller 41 comprises a rotating sleeve and a magnet body arranged inside the sleeve, and is constituted to move to a plurality of stop positions by rotating the magnet body in the inner periphery direction of the sleeve. The image forming apparatus controls so that the developer may be supplied to the developing roller through the supply roller from a developer stirring part in the developing device by setting the magnet body inside the supply roller to the 1st stop position for a time equivalent to the inside of an image forming area in an image forming mode, and the amount of the developer supplied to the developing roller 41 may be made small by setting the magnet body inside the supply roller to the 2nd stop position for the time equivalent to the outside of the image forming area. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus including a developing device that is used in a copying machine, a printer, a facsimile, an image forming apparatus having a composite function, and the like and develops an electrostatic latent image on an image carrier.

In recent years, electrophotographic image forming apparatuses are also required to have the same high image quality and high durability as offset printing. The key to achieving high durability is the life of the developer.

  In an electrophotographic image forming apparatus, it is generally more advantageous in terms of image quality to use a two-component developer composed of a toner and a carrier than a one-component developer. However, in order to extend the life of the two-component developer, it is important how to reduce the stress applied to the developer. The stress on the developer is applied everywhere in the developing device (or developing system). Among them, typical places are (1) a developer layer forming portion and (2) an image forming area (image carrier). And the opposite portion).

  As a conventional technique for reducing the stress on the developer, there is a technique in which the rotation of the developing roller is stopped except during the development, as can be seen in Patent Document 1.

In the case of this prior art, although (1) developer stress in the developer layer forming portion can be avoided among the stressed locations (1) and (2), (2) the developer is not used in the image forming area. Since the image carrier and the developing roller have a speed difference while being carried, they are stressed. Therefore, the developer stress reduction technique is incomplete.
JP-A-2-125273

  An object of the present invention is to provide an image forming apparatus capable of outputting a high-quality image over a long period of time by minimizing the stress applied to the developer. That is, the present invention provides a developing device that reduces developer stress in the developer layer forming section and the image forming area as much as possible by supplying the developer to the developing roller only when it is necessary for image formation such as in the image forming area. It is intended to provide.

  According to a first aspect of the present invention, there is provided an image having a developing device that forms a toner image by developing an electrostatic latent image formed on an image carrier with a magnetic developer containing toner carried on a developing roller. In the forming apparatus, the developing device includes a developing roller having a rotating developing sleeve and a magnetic field generating means having at least a top magnetic pole disposed therein, a developer supplying roller for supplying the developer to the developing roller, and developing A developer stirring member that stirs the agent and conveys the developer to the developer supply roller, and the developer supply roller includes a rotating sleeve and a magnet body disposed inside the sleeve, The magnet body is configured to be movable to a plurality of stop positions by rotating in the inner circumferential direction of the sleeve, and during the time corresponding to the image forming area in the image forming mode, the developer supply roller By setting the magnet body inside the roller to the first stop position, the developer is supplied to the developing roller from the developer stirring unit in the developing device via the developer supplying roller, and corresponds to the outside of the image forming area. In the image forming apparatus, the time is controlled so that the amount of developer supplied to the developing roller is reduced by setting the magnet body inside the developer supplying roller to a second stop position.

  According to a second aspect of the present invention, in the first aspect, when a specific image forming mode different from the normal image forming mode is selected in the operation unit of the image forming apparatus, the time corresponding to the image forming area is set. By setting the stop position of the magnet in the developer supply roller at a third stop position different from the first stop position in the normal image forming mode, the development supplied to the developing roller The image forming apparatus is characterized in that the amount of the agent is controlled to be smaller than that in a normal image forming mode.

  According to a third aspect of the present invention, in the first or second aspect, the developing roller and the developer supply roller have their surfaces moved in opposite directions at opposite portions of the two rollers to supply the developer. An image forming apparatus characterized by the above.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, a straight line connecting a rotation axis center of the developing roller and a rotation axis center of the developer stirring member close to the developing roller is a horizontal line. An image forming apparatus characterized in that an included angle is set to be less than 30 °.

  According to the first aspect of the present invention, the developer supplying member for supplying the developer to the developing roller is used, the phase of the magnet body arranged inside the developer supplying member is changed, and the image forming area and the image forming are changed. Switching control is performed according to the time corresponding to outside the area. As a result, the developer can be pumped and transported on the developing roller only for a necessary time (a time corresponding to the image forming area), and the stress received by the developer in the developer layer forming unit and the image forming apparatus unit can be increased. Since it can be reduced, there is an effect of extending the developer life.

  In addition, problems such as a decrease in image density that occurs during continuous mass printing and high-speed printing are solved, and a high-quality printed image can be output. Further, 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.

  According to the invention of claim 2, when the specific image forming mode different from the normal image forming mode is selected in the operation unit of the image forming apparatus, the amount of developer supplied to the developing roller is set to the normal image forming mode. The toner spent can be reduced by controlling the amount to be less.

  According to the third aspect of the present invention, the developing roller and the developer supply roller develop the toner from the developer supply roller by supplying the developer with the respective surfaces moving in opposite directions at the opposing portions of the rollers. The developer is efficiently conveyed to the roller.

  According to the fourth aspect of the present invention, the development angle is set so that the angle formed by the straight line connecting the rotation axis center of the developing roller and the rotation axis center of the developer stirring member closest to the developing roller to the horizontal line is less than 30 °. It is possible to form a thin device with a reduced height of the apparatus, and the upper layer of the developer stirred by the developer stirring member is arranged at a position closer to the lower side than the horizontal line position of the developing roller. The developer pumped up by the agent stirring member can be stably conveyed to the upper magnetic pole of the developing roller via the developer supply roller.

  Embodiments of the present invention will be described below. The description in this column does not limit the technical scope of the claims or the meaning of terms.

[Image forming apparatus]
FIG. 1 is a configuration diagram of an image forming apparatus including an image forming apparatus main body A, an image reading apparatus SC, and an automatic document feeder DF.

  The illustrated image forming apparatus main body A includes an image carrier (photosensitive drum) 1, a charging unit 2, an image exposure unit (image writing unit) 3, a developing unit 4, a transfer unit 5, a charge eliminating unit 6, a separation claw 7, The image forming unit includes a cleaning unit 8 and the like, a fixing unit 9, and a paper transport system.

  The paper transport system includes a first transport unit including a paper feed cassette 10, a first paper feed unit 11, a second paper feed unit 12, a transport unit 13, a paper discharge unit 14, and a manual paper feed unit 15; It is composed of a circulation refeeding section that circulates and refeeds paper.

  The paper feed cassette 10 and the first paper feed means 11 are formed by a plurality of paper feed means (three stages in the figure), and accommodate and feed a plurality of types of paper P. The paper size is input by manual setting by the operation unit 21 or automatic paper size setting by the paper size detecting means.

  The paper P that has passed through the conveying means 13 and has been fixed by the fixing means 9 is conveyed by a conveying path switching means 16 to a straight discharge path conveying path r1, a reverse discharging path conveying path r2, and a double-sided circulation path conveying path. One of r3 is selected and conveyed.

  The paper P passing through the transport path r1 is discharged with the image forming surface facing up (face up). The paper P passing through the transport path r2 advances to the transport paths r3 and r4 of the double-sided circulation path, and is then transported in reverse, passes through the transport path r2, and is discharged with the image forming surface facing down (face down). .

  The second transport unit branches the paper P on which the image has been formed by the image forming unit, before the paper discharge unit 14 by the transport path switching unit 16, transports the paper P along the circulation refeeding path, and recirculates the paper. The paper P is reversed by the reverse conveying roller 17 in the middle of the paper path, and then fed again to the image forming unit via the second paper feeding unit 12.

  The document d placed on the document table of the automatic document feeder DF is transported by the paper feeding means, and one or both side images of the document d are read by the optical system of the image reading device SC and read by the image sensor CCD. It is. The analog signal photoelectrically converted by the image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in the image processing unit 20 and then sent to the image exposure means 3.

  In the image exposure means 3, the output light from the semiconductor laser is applied to the image carrier 1 of the image forming unit to form a latent image. In the image forming unit, processes such as charging, exposure, development, transfer, separation, and cleaning are performed. An image is transferred by the transfer means 5 on the paper P fed from the paper feed cassette 10 and the manual paper feed means 15. The paper P carrying the image is fixed by the fixing unit 9 and discharged from the paper discharge unit 14.

  Alternatively, the single-sided image processed paper P sent to the circulation refeed unit by the conveyance path switching unit 16 is reversed by the reverse conveyance roller 17 and then subjected to double-sided image processing in the image forming unit, and then fixed by the fixing unit 9. The paper is processed and discharged by the paper discharge means 14.

[Developer configuration]
FIG. 2 is a sectional view showing an embodiment of the developing device 4 according to the present invention, and FIG. 3 is a plan view of a lower mechanism of the developing device 4.

  The housing of the developing device 4 has a two-part configuration including a lower lower casing 40 and an upper upper casing 50, and can be opened and closed.

  In the lower casing 40, a developing roller 41, a first developer stirring member (hereinafter referred to as a first stirring screw) 42, a second developer stirring member (hereinafter referred to as a second stirring screw) 43, a developer supply A roller (hereinafter referred to as a supply roller) 44 and the like are disposed.

  The lower casing 40 includes a developer supply chamber 401 that houses the first stirring screw 42 and a developer stirring chamber 402 that houses the second stirring screw 43. The developer supply chamber 401 and the developer stirring chamber 402 are formed on both sides with a partition wall 403 standing upright from the bottom of the lower casing 40.

  A developer amount regulating member 51 and a support member 52 that supports the developer amount regulating member 51 are disposed in the upper casing 50 that covers the upper portion of the lower casing 40. The developer amount regulating member 51 regulates the thickness of the developer layer on the photosensitive drum 1.

  The developing roller 41 includes a rotatable developing sleeve 41A and a fixed magnetic field generating means (magnet roll) 41B.

  In a region where the developing sleeve 41A and the first stirring screw 42 face each other, the developing sleeve 41A rotates from below to above, and the first stirring screw 42 rotates from above to below.

  The developing roller 41 is disposed to face the photosensitive drum 1 carrying the electrostatic latent image, and is driven to rotate by a driving source (not shown). On the developing sleeve 41A, an AC voltage from the AC power source E1 and a DC voltage from the DC power source E2 are superimposed as a developing bias.

  The magnetic field generating means 41B is disposed inside the developing sleeve 41A and has five magnetic poles N1, N2, N3, S1, and S2. The magnetic pole S1 is a main magnetic pole facing the photosensitive drum 1, the magnetic pole N1 is a stripped magnetic pole, and the magnetic pole N2 is a top magnetic pole. The tip of the developer amount regulating member 51 is disposed in the vicinity of the magnetic pole S2 of the magnetic field generating means 41B.

  Two magnetic poles N1 and N2 adjacent to each other among the plurality of magnetic poles of the magnetic field generating means 41B are arranged in the same polarity to form a repulsive magnetic field. The stripping magnetic pole N1 for stripping off the developer strips off and disperses the developer on the developing sleeve 41A. The developer receiving upper magnetic pole N2 draws up the developer supplied by the first stirring screw 42 and attaches it to the developing sleeve 41A.

  The first agitating screw 42 agitates and conveys the developer conveyed from the second agitating screw 43 and supplies it uniformly to the developing roller 41. The first stirring screw 42 and the second stirring screw 43 are both helical screw members.

  The second agitating screw 43 is arranged in parallel to the first agitating screw 42, and mixes and agitates the new toner replenished from the toner replenishing means 47 (see FIG. 3) and the developer refluxed from the developing sleeve 41A to a first agitation. It is conveyed to the upstream part of the stirring screw 42.

  The first stirring screw 42 conveys the developer in the direction of the rotation axis and releases the developer in a direction substantially perpendicular to the rotation axis.

  By setting an angle θ1 formed by a straight line connecting the rotation axis center R1 of the developing roller 41 and the rotation axis center R2 of the first stirring screw 42 close to the developing roller 41 to be a horizontal line, the first stirring screw 42 is set to less than 30 °. The upper layer of the developer agitated by the above is disposed in the vicinity below the horizontal line position of the developing roller 41, and the developer can be pumped stably by the upper magnetic pole N2 and the supply roller 44.

[Developer]
The developer is a two-component developer composed of a magnetic carrier and a nonmagnetic polymer toner. The amount of magnetization in 1 kilo Oersted of the magnetic carrier is in the range of 20 to 70 emu / g, and the particle size of the magnetic carrier is 50 μm or less. The particle size of the nonmagnetic polymer toner is 7.5 μm or less.

[Circulating developer transport]
FIG. 4 is a schematic diagram showing the circulation of the developer in the developing device 4. Hereinafter, the circulation of the developer will be described.

  (1) On the upstream side of the developer stirring chamber 402, the developer refluxed from the developer supply chamber 401 and the new toner replenished from the toner replenishing means 47 are carried in and stirred and mixed by the second stirring screw 43. Then, the developer is conveyed in the developer moving direction indicated by an arrow V1.

  (2) The mixed developer passes through the first opening 404 on the downstream side of the developer agitating chamber 402, is conveyed as indicated by the arrow V2, and is introduced upstream of the developer supply chamber 401. . In the developer supply chamber 401, the developer is conveyed as indicated by an arrow V3 while being conveyed in the developer moving direction by the first stirring screw 42.

  (3) The first stirring screw 42 discharges the developer to the supply roller 44 as indicated by an arrow V4 while conveying the developer in the direction of the rotation axis.

  (4) The developer carried on the rotating supply roller 44 is discharged and adhered to the rotating developing sleeve 41A, and the developer layer thickness is regulated by the developer amount regulating member 51, and passes through the arrow V5. Conveyed as shown.

  (6) The developer carried on the developing sleeve 41 </ b> A is developed in the developer area facing the photosensitive drum 1. The developer whose toner concentration has decreased after the development processing is peeled off from the developing roller 41 by the peeling magnetic pole N1.

  (7) The removed developer is carried into the developer supply chamber 401 as indicated by an arrow V6.

  (8) The developer conveyed into the developer supply chamber 401 is conveyed by the first agitating screw 42 as indicated by an arrow V7, passes through the second opening 405, and as indicated by an arrow V8. It is introduced upstream of the stirring chamber 402.

  (9) In the developer stirring chamber 402, toner supply by the toner supply means 47 is performed by a toner concentration detection signal of a toner concentration sensor (not shown), and the developer joins the arrow V1.

  The developer is conveyed in the circulation system as described above, but a part of the developer is indicated by arrows V1, V2, V3, V6, V7, and V8 between the developer supply chamber 401 and the developer stirring chamber 402. Circulate.

[Supply roller and control means]
FIG. 5 is a cross-sectional view showing driving of the magnet body disposed in the supply roller 44. FIG. 6 is a block diagram showing the control of the supply roller 44.

  The supply roller 44 includes a rotating sleeve 44A and a magnet body 44B disposed therein. The magnet body 44B having the upper magnetic pole S3 and the magnetic poles S4 and N4 is configured to be movable to a plurality of stop positions by rotating in the inner circumferential direction of the sleeve 44A.

  Hereinafter, an example of the stop position control of the magnet body 44B of the supply roller 44 will be described.

  FIG. 5A shows a state where the phase of the magnet body 44B in the normal image forming mode is set to the first stop position. The first stop position is indicated by an angle φ1 from the lowest point of the magnet body 44B. The angle φ1 of the first stop position is set within a range of 0 ° to 30 °.

  In a time corresponding to the image forming area in the normal image forming mode, it is necessary to draw up a sufficient amount of developer onto the developing roller 41 for development. At this time, a first stop position that opposes the first agitating screw 42 so that the scooping magnetic pole S3 of the magnetic poles S3, S4, N4 of the magnet body 44B of the supply roller 44 can easily draw the developer from the first agitating screw 42. I'm in.

  FIG. 5B shows a state in which the phase of the magnet body 44B in the normal image forming mode is set to the second stop position. The second stop position is indicated by an angle φ2 from the lowest point of the magnet body 44B. The angle φ2 of the second stop position is set within a range of 40 ° to 90 °.

  Since it is not necessary to perform development outside the image forming area (between sheets or at the start or end of the image forming sequence), it is not necessary to form a developer layer on the developing roller 41. Alternatively, the developer transport amount may be set small. Therefore, it is not necessary to pump up the developer on the developing roller 41. Or the pumping amount may be reduced. At this time, the pumping magnetic pole S3 of the magnet body 44B of the supply roller 44 is not directed downward so as to reduce the developer pumping amount. Therefore, the magnet body 44B is rotated from the time phase (first stop position) in the image forming area and set to another phase (second stop position).

  FIG. 5C shows a state in which the phase of the magnet body 44B in the specific image forming mode is set to the third stop position. The third stop position is indicated by an angle φ3 from the lowest point of the magnet body 44B. In the third stop position, the angle φ3 is set within a range of 20 ° to 40 °.

  Regarding the timing of switching the stop position of the magnet body 44B of the supply roller 44 at the boundary between the inside and outside of the image forming area, the first time is about 10 to 20 mm before the start of image forming in consideration of the temporal stability of the conveyance amount. It is realistic to set it so that it enters the stop position area, and keep it as the first stop position area until about 10 mm after the end of image formation. The actual timing of switching the stop position of the magnet body 44B of the supply roller 44 is set in consideration of the fact that the supply roller 44 is upstream of the developing nip in the rotation direction of the developing roller 41.

  Further, when a specific image forming mode such as a so-called “character mode”, which is set only for a character image that does not require an accurate image density, is selected, the developer conveyance on the developing roller 41 is performed. A small amount may be set. In this case, the third stop position (in the image forming area) different from the first stop position (in the image forming area) of the magnet body 44B of the supply roller 44 in the normal image forming mode is set. Outside the image forming area, there is no problem at the same second stop position as in the normal image forming mode. Of course, different stop positions may be set. It is realistic to set the third stop position in a region between the first stop position and the second stop position.

  As described above, by controlling the switching of the stop position of the magnet body 44B of the supply roller 44, it is possible to further reduce the developer stress at the developer amount regulating member 51 and the development nip portion.

  The developing device 4 of the present invention is a type in which the height difference between the developing roller 41 and the first stirring screw 42 is small, and the rotation axis center of the developing roller 41 and the rotation axis center of the first stirring screw 42 closest to the developing roller 41 are The angle between the straight line connecting the lines and the horizontal line is less than 30 °. Accordingly, the rotation direction of the supply roller 44 is set to the counter direction with respect to the developing roller 41 in order to prevent a ghost image from being generated due to a poor replacement of the developer on the developing roller 41.

[Common conditions]
Image forming device: A4 size paper, 75 sheets per minute processing machine (digital monochrome machine shown in Fig. 1)
Process speed: 420mm / sec
Image forming area: non-image forming area = 62.5: 37.5
Diameter of the photosensitive drum 1: 80 mm
Charge voltage V0 of the photoreceptor 1: -700V
Potential Va of the developing roller 41: −500V
Photoconductor solid exposure potential Vi: -50V
Development bias AC component: 1.0 kVp-p (rectangular wave, 5 kHz)
Image exposure means 3: Semiconductor laser (wavelength 780 nm)
Diameter of developing roller 41: 30 mm / Number of magnetic poles: 5 poles Number of magnetic poles of developing roller 41: 5 poles Length of magnetized portion of developing roller 41 in longitudinal direction: 330 mm
Surface distance from the surface of the photosensitive drum 1 to the developing roller 41: about 0.3 mm
Developer conveyance amount on the developing roller 41: about 250 g / m ² (in the image forming area in the normal mode)
Moving speed / process speed of developing roller 41: 2.0
Diameter of supply roller 44: 25 mm
Number of magnetic poles of supply roller 44: 3 poles Distance between supply roller 44 surface and developing roller 41 surface: about 3 mm
The moving speed of the sleeve 44B of the supply roller 44: The moving speed of the developing sleeve 41A of the developing roller 41 is equal to the moving speed of the developing roller 41. The angle θ2 of the straight line connecting the rotation axis center R3 of 44 and the horizontal line: 5.0 °
Phase of magnet body 44B of supply roller 44:
In the case of the first stop position, the upper magnetic pole S3 is 20 ° downstream from the lowest point in the rotation direction.
In the case of the second stop position, the upper magnetic pole S3 is 70 ° downstream from the lowest point in the rotation direction.
In the case of the third stop position, the upper magnetic pole S3 is 40 ° downstream from the lowest point in the rotation direction.
Outer diameter of the first stirring screw 42 and the second stirring screw 43: 20 mm
An angle θ1: 20 ° formed by a straight line connecting a rotation axis center R1 of the developing roller 41 and a rotation axis center R2 of the first stirring screw 42 close to the developing roller 41 with a horizontal line.
Toner: Polymerized toner with a volume average particle size of 4.5 μm (black)
Carrier: volume average particle size 25 μm / magnetization strength 60 emu / g
Toner concentration: 6%
[Example 1]
Example 1 satisfies the requirements of claim 1.

  The phase of the magnet body 44B disposed inside the supply roller 44 is switched corresponding to the inside and outside of the image forming area. That is, during the time corresponding to the image forming area, the phase of the magnet body 44B is set to the first stop position shown in FIG. 5A so that a sufficient amount of developer can be pumped up. The upper magnetic pole S3 is directed downward and is set at a position close to the first stirring screw 42.

  During the time corresponding to the outside of the image forming area, the phase of the magnet body 44B is set to the second stop position shown in FIG. 5B in order to minimize the pumping of the developer.

The developer transport amount on the developing roller 41 when set to the first stop position is about 250 g / m ² , and the developer transport amount is 0 when set to the second stop position. The phase (stop position) of the magnet body 44B in the image forming area for a considerable time is not switched by two types of image patterns (A, B) described later.

[Example 2]
The second embodiment satisfies the requirements of claim 2.

  When a specific image forming mode different from the normal image forming mode is selected in the operation unit 21 of the image forming apparatus, the stop position of the magnet body 44B in the supply roller 44 at the time corresponding to the image forming area is set. By setting the third stop position different from the first stop position in the normal image forming mode, the amount of developer supplied to the developing roller 41 is controlled to be smaller than that in the normal image forming mode. To do.

  In addition to the conditions of the first embodiment, the phase (stop position) of the magnet body 44B in a corresponding time within the image forming area is switched by two types of image patterns (A, B) described later.

The phase of the magnetic body 44B and the developer conveyance amount are about 250 g / m ² at the first stop position for the image A, and about 150 g / m ² at the third stop position for the image B.

[Comparative example]
As in Patent Document 1, in the type in which the rotation of the developing roller is stopped outside the image forming area (there is no supply roller), the rotation shaft center of the developing roller is connected to the rotation shaft center of the supply screw closest to the developing roller. The included angle between the straight line and the horizontal line is 25 °. The upper magnetic pole of the developing roller is a normal fixed magnet. The developer conveyance amount is about 250 g / m ² .

[Performance comparison in each example / comparative example]
FIG. 7 is a timing chart of an embodiment of the phase switching control of the supply roller 44 and a comparative example. In the examples and comparative examples, three A4 size sheets are continuously printed.

  In the first and second embodiments, the developing roller 41 is continuously rotated during image formation, and the phase of the supply roller 44 is switched to either the first stop position or the second stop position. In the comparative example, the developing roller is on / off controlled.

  In each of the above examples / comparative examples, a live-action test was performed to compare developer deterioration states.

[Test content]
Print pattern: Monochrome image with an average print rate of 6%
Number ratio of two types of image patterns (A, B) = (60%, 40%)
Image A: Solid image for 3% printing rate + Character image for 3% printing rate
Image B: Character image for a printing rate of 6% Printing mode: A4 size paper, continuous printing 100,000 sheets printing Environment: General environment (20 ° C, 50%)
Confirmation of developer deterioration state: Collect developer for every 10,000 prints and measure toner spent.

Toner spent measuring method: The transmittance of a solution obtained by dissolving 5 g of a carrier in 100 ml of a solvent methyl ethyl ketone (MEK) was measured. If 100,000 sheets are printed and the transmittance is 85% or more, the developer durability is OK.
[test results]
The test results are shown in FIG. FIG. 8 is a characteristic diagram showing the number of prints and the transmittance of toner spent.

  In the case of Example 1 and Example 2 that satisfy the requirements of the present invention, the transmittance of the toner spent exceeds 85% even after the completion of printing 100,000 sheets, and it can be said that the degree of developer deterioration is small. In particular, in the case of Example 2 in which the phase (stop position) of the magnet body 44B inside the supply roller 44 is switched by using two types of image patterns (A, B), good results are shown.

  On the other hand, in the case of Comparative Example 1 in which the supply roller 44 is not installed and the developing roller 41 is merely stopped outside the image forming area, the developer deterioration proceeds rapidly and the transmittance of the toner spent at the end of printing 100,000 sheets. Is 80%.

  FIG. 9 is a characteristic diagram showing an example of the magnetic pole angle of the supply roller 44 and the developer conveyance amount.

  The horizontal axis indicates the angle φ from the lowest point of the upper magnetic pole S3 of the magnet body 44B arranged in the supply roller 44, and the vertical axis indicates the developer conveyance amount.

  As the angle φ from the lowest point of the upper magnetic pole S3 increases, the developer conveyance amount decreases. In the first stop position, the angle φ1 is set within a range of 0 ° to 20 °. In the second stop position, the angle φ2 is set within a range of 40 ° to 50 °. In the third stop position, the angle φ3 is set within a range of 20 ° to 40 °. Thus, the developer conveyance amount can be easily controlled by changing the angle φ.

  When the operator selects a specific image forming mode different from the normal image forming mode in the operation unit 21 of the image forming apparatus main body A, for example, when the toner save mode is set in the operation unit 21. The control means sets the angle φ corresponding to the time in the image forming area to an angle φ3 larger than the angle φ1 in the normal image forming mode. The toner save mode is set when, for example, an image with only characters, an image with a large margin, or a case where the image density is intentionally lowered so that the image can be read.

1 is a configuration diagram of an image forming apparatus including an image forming apparatus main body, an image reading apparatus, and an automatic document feeder. 1 is a cross-sectional view showing an embodiment 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. Sectional drawing which shows the drive of the magnet body arrange | positioned in a supply roller. The block diagram which shows control of a supply roller. The timing chart of the Example and comparative example of phase switching control of a supply roller. FIG. 6 is a characteristic diagram showing the number of prints and the transmittance of toner spent. FIG. 6 is a characteristic diagram illustrating an example of a magnetic pole angle of a supply roller and a developer conveyance amount.

Explanation of symbols

1 Image carrier (photosensitive drum)
4 Developing Device 21 Operation Unit 40 Lower Casing 41 Developing Roller 41A Developing Sleeve 41B Magnetic Field Generating Unit (Magnet Roll)
42 First developer stirring member (first stirring screw)
43 Second developer stirring member (second stirring screw)
44 Developer supply roller (supply roller)
44A Sleeve 44B Magnet body 50 Upper casing 51 Developer amount regulating member A Image forming apparatus main body N1 Stripped magnetic pole N2, S3 Floating magnetic pole S1 Main magnetic pole S2, N3, S4, N4 Magnetic pole P Paper θ1, θ2 Depression angle φ, φ1, φ2 , Φ3 angle

Claims (4)

In an image forming apparatus having a developing device for developing an electrostatic latent image formed on an image carrier with a magnetic developer containing toner carried on a developing roller to form a toner image.
The developing device comprises a developing roller having a rotating developing sleeve and a magnetic field generating means having at least a top magnetic pole disposed therein;
A developer supply roller for supplying a developer to the developing roller;
A developer stirring member that stirs the developer and conveys it to the developer supply roller,
The developer supply roller includes a rotating sleeve and a magnet body arranged inside the sleeve, and is configured to be movable to a plurality of stop positions by rotating the magnet body in the inner circumferential direction of the sleeve. And
During the time corresponding to the image forming area in the image forming mode, the magnet body inside the developer supply roller is set to the first stop position so that the developer agitating unit in the developing device passes through the developer supply roller. Supply developer to the developing roller,
In the time corresponding to the time outside the image forming area, the amount of the developer supplied to the developing roller is controlled by setting the magnet body inside the developer supplying roller to the second stop position. Image forming apparatus. When the specific image forming mode different from the normal image forming mode is selected in the operation unit of the image forming apparatus, the stop position of the magnet body in the developer supply roller at the time corresponding to the image forming area Is set to a third stop position different from the first stop position in the normal image forming mode, so that the amount of developer supplied to the developing roller is smaller than that in the normal image forming mode. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled. 3. The image forming apparatus according to claim 1, wherein the developing roller and the developer supply roller supply the developer by moving surfaces of the developing roller and the developer supply roller in opposite directions at opposite portions thereof. . 4. The depression angle between a straight line connecting a rotation axis center of the developing roller and a rotation axis center of the developer stirring member close to the developing roller and a horizontal line is set to be less than 30 °. The image forming apparatus according to claim 1.

Images