JP4591113B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a developing device in an electrophotographic image forming apparatus.

  Conventionally used developing devices will be described with reference to FIG.

  The developing device is partitioned into a supply chamber A for supplying developer to the developing sleeve GS and an agitating chamber B for stirring the developer. The supply chamber A includes a rotation direction conveying member K called a paddle and a screw. A conveying member HK1 is provided, and a stirring / conveying member member HK2 made of a screw is provided in the stirring chamber B.

  The rotation direction conveying member K is a plate in which a plate parallel to the rotation axis direction is radially fixed to the axis, and has a conveyance force in the rotation direction, but does not have a conveyance force in the rotation axis direction. The agitating / conveying members HK1 and HK2 have a conveying force in the direction of the rotation axis, and convey the developer in the direction of the rotation axis while agitating, so that the toner concentration in the developer and the toner charge amount are made uniform.

  The developer is stirred in the stirring chamber B by the stirring / conveying member HK2, and the toner is uniformly mixed in the developer and charged, and then sent to the supply chamber A.

  In the supply chamber A, the developer is conveyed by the agitating / conveying member HK1, and is agitated by the agitating / conveying member HK1 and the rotation direction conveying member K, and the toner density and the toner charge amount are further uniformized. Supplied to the sleeve GS.

  Thus, as described above, the rotation direction conveying member K conveys the developer in the rotation direction and supplies the developer to the developing sleeve GS, but has no conveyance force in the rotation axis direction. The developer received from the agitating / conveying member HK1 is supplied to the developing sleeve GS at the receiving position without being moved in the rotation axis direction. Therefore, if the developer supplied from the stirring chamber B is non-uniform in terms of toner concentration and toner charge amount, the developer on the developing sleeve GS may become non-uniform.

  As electrophotographic image forming apparatuses are used in the field of printing or are used as color image forming apparatuses, there is an increasing need for high image quality and high speed.

  Among the techniques for dealing with such high image quality and high speed, the development technique has a problem of deterioration in image quality due to the uneven developer as described above. In particular, a technique for quickly increasing the charge amount of toner supplied to the developing device to a predetermined level is required.

  Technologies aimed at satisfying this condition have been developed.

  That is, in Patent Document 1, a developing device that drops toner from above and supplies it to the developing device, and rotates them so that the two developer agitating units move from top to bottom at the toner replenishment position. It is disclosed.

  In Patent Document 2, it has two developer agitating means, one developer agitating means is constituted by one having a conveying function in the axial direction, and the other is constituted by one having no conveying function in the axial direction, There is disclosed a developing device that rotates two developer agitating units so as to move from top to bottom at a replenishment position where the replenishment toner drops.

  In Patent Document 3, two developer agitation units are provided for the developer supply and recovery unit, and one developer agitation unit conveys the developer in the same direction as the developer supply agitation unit, and the other developer agitation unit. The developer agitating means is configured so that the means conveys the developer in the direction opposite to the developer supply / recovery means, and the conveying ability of the other developer agitating means is equal to the conveying ability of the developer supply / collecting means A developing device is disclosed that is equal to the sum of the conveying ability of one developer stirring means.

In Patent Documents 1 to 3, after two agitation means are provided in the agitation chamber and agitated, the developer is supplied to the supply and recovery chamber, whereby the developer with uniform toner density and charge amount is supplied to the developing sleeve. is doing.
JP 2004-326033 A JP 2004-326034 A JP 2004-326035 A

  In the developing techniques described in Patent Documents 1 to 3, since the developer is sent to the supply chamber after the developer is stirred by the two developer stirring means, the stirring of the developer in the stirring chamber is strengthened, Developer mixing and toner charging are enhanced.

  As a result, the toner can be uniformly mixed in the developer within a short time and the toner can be charged within the short time, but the stress on the developer is strengthened, and the deterioration of the developer due to the stress becomes a problem. .

  The strengthening of the developer agitation is mainly effective in an image forming process in which the toner consumption is large and the toner replenishment ratio is high. On the other hand, in the image forming process in which the toner consumption is small, that is, in the image forming process for forming an image with a low printing rate, there is a problem that the image quality is deteriorated due to the deterioration of the developer as a result of the strengthening of the stirring. .

  An object of the present invention is to provide an image forming apparatus that forms a high-quality image by preventing deterioration of the developer due to stress in the developing device with enhanced stirring performance and deterioration of image quality due to deterioration.

The object is achieved by the following invention.
(Claim 1)
A developer carrier that conveys the developer to the development area by rotation;
Supply means for supplying the developer to the developer carrier while conveying the developer in a first direction along the rotation axis by rotation;
Stirring / conveying means for conveying the developer in a second direction opposite to the first direction while stirring the developer by rotation; and
In an image forming apparatus having a developing unit having a stirring unit having an inclined stirring blade formed around an axis, the stirring unit stirring the developer transported by the stirring / transporting unit,
Depending on the printing ratio it has a control means for controlling the amount of rotation of the stirring means per unit operating time of the stirring and conveying means,
The control means continuously rotates the stirring means in image formation of an image having a printing rate equal to or higher than a predetermined value, and repeatedly stops and rotates the stirring means in image formation of an image lower than the predetermined value. An image forming apparatus that is intermittently driven .

According to the first aspect of the present invention, it is possible to improve the stirring force of the developer and to prevent the image quality from being deteriorated due to toner deterioration that is likely to occur in a developing device capable of high-speed development, and to be influenced by the properties of the image to be formed. Thus, an image forming apparatus that always forms an image with high image quality is realized.

Further , the control range of the stirring of the developer by the stirring means is widened, and the stirring means can be controlled with higher accuracy.

Hereinafter, the present invention will be described by way of examples. However, the present invention is not limited to the embodiments described below.
<Image forming apparatus>
FIG. 2 is an overall view of a color image forming apparatus having a developing device according to an embodiment of the present invention.

  As shown in FIG. 2, the color image forming apparatus includes an image forming apparatus main body GH and an image reading apparatus SC provided on the upper portion of the image forming apparatus main body GH.

  The image forming apparatus main body GH is a so-called tandem color image forming apparatus, and forms images of monochromatic toner images of yellow, magenta, cyan, and black along the moving direction of an intermediate transfer body that is an example of a transfer body. Forming portions Y, M, C, and Bk are arranged, and a single color toner image formed on the image carrier of each of the image forming portions Y, M, C, and Bk is multiply transferred onto the intermediate transfer member and superposed to perform intermediate transfer. After a multicolor toner image is formed on the body, it is collectively transferred onto a recording material.

  In the figure, an analog signal scanned and exposed by an optical system on a document image placed on the image reading device SC, read into a line image sensor CCD, and photoelectrically converted by the line image sensor CCD is converted into an analog signal by an image processing unit. After being digitized after processing, A / D conversion, shading correction, image compression processing, etc., it is used as a control signal for the exposure apparatus 3.

  In the figure, an image forming portion for forming yellow (Y), magenta (M), cyan (C) and black (Bk) single color toner images on the peripheral portion of the intermediate transfer member 20 which is an example of a transfer member. Y, M, C, and Bk are arranged in a column in order.

  The image forming units Y, M, C, and Bk all have a common structure. The image forming unit Y includes a photoreceptor drum 1Y as an image carrier, a charging device 2Y, an exposure device 3Y, a developing device 4Y, a transfer device 5Y, and a photoreceptor cleaning device 6Y.

  The image forming unit M includes a photoreceptor drum 1M as an image carrier, a charging device 2M, an exposure device 3M, a developing device 4M, a transfer device 5M, and a photoreceptor cleaning device 6M.

  The image forming unit C includes a photoreceptor drum 1C as an image carrier, a charging device 2C, an exposure device 3C, a developing device 4C, a transfer device 5C, and a photoreceptor cleaning device 6C.

  The image forming unit Bk includes a photosensitive drum 1Bk as an image carrier, a charging device 2Bk, an exposure device 3Bk, a developing device 4Bk, a transfer device 5Bk, and a photosensitive member cleaning device 6Bk.

  The photoconductive drums 1Y, 1M, 1C, and 1Bk have a layer thickness (film thickness) as a photoconductive layer on the outer periphery of a cylindrical base formed of a metallic member such as aluminum having an outer diameter of about 40 to 100 mm. A photoconductive layer of an organic photoreceptor layer (OPC) of about 20 to 40 μm is formed, or rotates in the direction indicated by the arrow.

  The charging devices 2Y, 2M, 2C, and 2Bk are attached close to a direction perpendicular to the moving direction of the photosensitive drums 1Y, 1M, 1C, and 1Bk (a direction perpendicular to the drawing in the drawing). For the charging devices 2Y, 2M, 2C, and 2Bk, a corotron, a scorotron, a charging roller, or the like is used.

  The exposure devices 3Y, 3M, 3C, and 3Bk rotate and scan laser light emitted from a semiconductor laser (LD) light source (not shown) in the main scanning direction by a rotating polygon mirror (no symbol), and an fθ lens (no symbol). Then, exposure (image writing) is performed on the photosensitive drum 1 through an electric signal corresponding to an image signal through a reflecting mirror (not shown), and a static image corresponding to an original image is formed on the photosensitive layer on the surface of the photosensitive drum 1. An electrostatic latent image is formed. In addition to the laser, an LED array, liquid crystal, plasma, or the like can be used for the exposure devices 3Y, 3M, 3C, and 3Bk, and dot exposure based on image data is performed.

  The charging device 2Y and the exposure device 3Y, the charging device 2M and the exposure device 3M, the charging device 2C and the exposure device 3C, and the charging device 2Bk and the exposure device 3Bk respectively constitute latent image forming means.

  The developing devices 4Y, 4M, 4C, and 4Bk use a developing device that performs development using a two-component developer mainly composed of toner and carrier, and uses toner charged to the same polarity as that of the photosensitive member. A reversal developing type developing device that performs development is preferably used.

  For the transfer devices 5Y, 5M, 5C, and 5Bk, for example, a transfer roller, corotron, or scorotron using foamed rubber such as silicon or urethane is used. A conductive roller is used as the transfer roller, and a transfer voltage is applied to the conductive roller.

  The photoreceptor cleaning devices 6Y, 6M, 6C, and 6Bk clean the photoreceptors 1Y, 1M, 1C, and 1Bk after transfer. For the cleaning devices 6Y, 6M, 6C and 6Bk, a blade cleaning device using a rubber blade is preferably used.

The intermediate transfer body 20 uses a semiconductive endless (seamless) resin belt member having a volume resistivity of about 10 ⁷ to 10 ⁹ Ω · cm and a surface resistivity of about 10 ¹⁰ to 10 ¹² Ω / □. It is done. The intermediate transfer member 20 is wound around a plurality of roller members including tension rollers, and circulates and moves as indicated by arrows.

  For the transfer device 5A, for example, a transfer roller, corotron, or scorotron using foamed rubber such as silicon or urethane is used. A conductive roller is used as the transfer roller, and a transfer voltage is applied to the conductive roller.

  6A is an intermediate transfer member cleaning device as an intermediate transfer member cleaning means, and a blade cleaning device using a rubber blade is preferably used as the intermediate transfer member cleaning device 6A.

  The image forming process (image forming process) will be described below.

  At the start of image recording, the photoreceptors 1Y, 1M, 1C, and 1Bk and the intermediate transfer member 20 operate as indicated by arrows, respectively, so that a yellow toner image is formed in the image forming unit Y and a magenta toner image is formed in the image forming unit M. Then, a cyan toner image is formed in the image forming unit C, and a black toner image is formed in the image forming unit Bk. These toner images are transferred to the intermediate transfer body 20 in the transfer devices 5Y, 5M, 5C, and 5Bk. A multicolor toner image is formed on the intermediate transfer member 20 by being superimposed on the transfer member 20.

  The photoreceptors 1Y, 1M, 1C, and 1Bk after the transfer are cleaned by the photoreceptor cleaning devices 6Y, 6M, 6C, and 6Bk.

  On the other hand, the recording material P accommodated in the paper feed cassettes 20A, 20B, and 20C is fed by the feed roller 21 and the paper feed roller 22A provided in the paper feed cassettes 20A, 20B, and 20C, respectively, and the transport rollers 22B and 22C. , 22D, in synchronization with the writing timing of the exposure device, and conveyed by the registration roller 23. In the transfer area of the transfer device 5A as a secondary transfer unit to which a voltage having a polarity opposite to that of the toner is applied, the intermediate transfer member 20 is transferred. The superimposed multicolor toner images formed on the upper surface are transferred together.

  The recording material P to which the color image has been transferred is subjected to fixing processing by the fixing device 7 and further conveyed and discharged by the first conveying means 18.

Further, after the color image is transferred onto the recording material P by the transfer device 5A, the intermediate transfer member 20 is cleaned by the intermediate transfer member cleaning device 6A.
<Developing device>
The developing device develops the electrostatic latent image using a two-component developer mainly composed of toner and carrier.

  The toner constituting the two-component developer is preferably a small particle size toner having a volume average particle size of 3 μm to 6 μm. With such a small particle size toner, it is possible to form a high-resolution image with high resolution and excellent fine line reproducibility.

  As the carrier constituting the two-component developer, a coating carrier in which a magnetic core is resin-coated is preferable, and a carrier having a volume average particle diameter of 20 μm to 50 μm is preferable. Even when a toner having a small particle diameter is used with such a carrier, the antistatic property to the toner can be improved, fogging and toner scattering can be reliably prevented, and carrier adhesion can be reliably prevented.

  As the developing bias, reverse development in which a bias voltage having the same polarity as the charging polarity of the photosensitive member is applied is preferable, and a developing bias in which alternating current is superimposed on direct current is preferable.

  FIG. 3 shows an example of the developing device according to the embodiment of the present invention, and is a view seen from above with the lid 41 removed. FIG. 4 is a front sectional view.

  The developing device 4 is formed in a ridge in which an opening for forming a developing region G is formed by the housing 40 and the lid 41.

  A developing sleeve 42 as a developer carrier is disposed in the developing region G, and a magnet roll 43 having a plurality of magnetic poles including a developing pole is disposed inside the developing sleeve 42.

  A screw 45 as a supply unit, a screw 46 as a stirring / carrying unit, and a stirring member 47 as a stirring unit are provided in order from the side closer to the developing sleeve 42.

  Reference numeral 44 denotes a regulating member that regulates the amount of the developer conveyed by the developing sleeve 42 and forms a uniform developer layer on the developing sleeve 42, and includes a blade.

  The interior of the developing device is partitioned by a partition 40a provided in the housing 40 into a supply / recovery chamber 4r1 in which a screw 45 serving as a supply means is disposed and a stirring chamber 4r2 in which a screw 46 and a stirring member 47 are disposed.

  The developing sleeve 42, the screws 45 and 46, and the stirring member 47 are rotated as indicated by arrows in FIG.

  The flow of the developer at the time of development is as shown in FIG. 3, and the developer is conveyed from the left to the right in FIG. 3 by the screw 46 as shown by the arrow W2 which is the second direction in the stirring chamber 4r2. It passes through the opening 40a1 provided in the partition 40a as indicated by an arrow W3 and is supplied to the supply and recovery chamber 4r1, and the inside of the supply and recovery chamber 4r1 is indicated by an arrow W1 that is the first direction from right to left in FIG. To move.

  In the moving process indicated by the arrow W1, the developer is transferred from the screw 45 to the developing sleeve 42, and the developer is supplied to the developing sleeve 42.

  The developed developer passes under the developing sleeve 42 and is collected by the screw 45. The developed developer is collected by the screw 45, passes through the opening 40a2 provided in the partition 40a as indicated by the arrow W4, and circulates in the stirring chamber 4r2.

  By the illustrated rotation of each of the rotating bodies 42, 45, 46, and 47 shown in FIG. 4, a developer flow indicated by arrows W1 to W4 in FIG. 3 is formed, the developer circulates, and development is continuously performed. .

  The toner that replenishes the amount consumed by development is replenished from above (upper in FIG. 4) at the left end 4c of the stirring chamber 4r2 in FIG.

  FIG. 5 shows the overall arrangement of the screw 45, the screw 46 and the stirring member 47, and FIG. 6 shows a partial structure of the screw 45, 46 and the stirring member 47.

  As described above, the screw 45 conveys the developer in the direction of the rotation axis while stirring the developer, supplies the developer to the developing sleeve 42, and collects the developer from the developing sleeve 42. As shown in FIG. 6A, the screw 45 is a stirring / conveying member in which a spiral rib RB is formed on the axis AX. As shown in FIG. 5, the screw 45 spirals over a length corresponding to the entire length of the developing sleeve 42. Shaped ribs RB are formed.

  Therefore, the screw 45 conveys the developer with a substantially uniform axial conveying force over its entire length by the rotation, and stirs the developer in the conveying process.

  At the left end portion of the screw 45 in FIG. As shown in FIG. 6C, the rotation direction conveyance unit 45a is composed of a rotation member called a paddle parallel to the axis, in which a plurality of flat plates PD are radially formed on the axis AX, and has conveyance force in the rotation direction. Does not have a conveying force in the direction of the rotation axis. The developer is sent from the supply / recovery chamber 4r1 to the stirring chamber 4r2 through the hole 4r12 by the rotation direction conveyance unit 45a.

  As shown in FIG. 6A, the screw 46 is also formed with a spiral rib RB over substantially the entire length, and a rotation direction conveying portion 46a is provided at the right end in FIG. As shown in FIG. 6C, the rotation direction conveyance unit 46a is composed of a rotation member called a paddle parallel to the axis and having a plurality of flat plates PD formed radially on the axis AX, and has a conveyance force in the rotation direction. Does not have a conveying force in the direction of the rotation axis. The developer is sent from the stirring chamber 4r2 to the supply / recovery chamber 4r1 through the hole 4r11 by the rotation direction conveyance unit 46a.

  As shown in FIG. 6B, the stirring member 47 is a stirring member provided with a large number of stirring blades CP made of an elliptical flat plate inclined to the axis AX and has a stirring function, but has a conveying force in the direction of the axis AX. do not do.

  Due to the rotation of the screw 46 and the rotation of the stirring member 47, the developer is subjected to the stirring action by the screw 46 and the stirring member 47 during the axial conveyance process by the screw 46, so that the stirring function in the stirring chamber 4r2 is strengthened. The developer sent from the chamber 4r2 to the supply / recovery chamber 4r1 is sufficiently mixed, so that the toner has a sufficient charge amount.

  Therefore, the developer supplied to the developing sleeve 42 is sufficiently uniform in toner density and charge amount, and the toner is supplied to the developing sleeve 42 in a state having a sufficient charge amount.

  FIG. 7 is a block diagram of a control system of the image forming apparatus according to the embodiment of the present invention.

  The control means CR calculates the printing rate based on the image size information and the image data.

  The image size information is the size information set by the operator in the operation unit OP or the size information included in the image formation command received from the outside by the communication unit IF, and the image data is image data acquired by image reading or This is image data output as data for driving the light source of the exposure apparatus by the image processing unit GP based on image data received from the outside via the communication unit IF.

  The control means CR adds up the total area of the image from the image size information for every predetermined number of sheets, and calculates the printing rate by adding up the image data formed in the total area.

  In the image formation, the control means CR calculates a printing rate for every predetermined number of sheets, and controls the clutch CL according to the printing rate. The clutch CL is provided in the drive system of the stirring member 47 in the drive system that drives the screws 45 and 46 and the stirring member 47, and drives and stops the stirring member 47 while continuously driving the screws 45 and 46. Allows control.

  When the printing rate is equal to or higher than a predetermined threshold, the control means CR turns on the clutch CL and continuously rotates the stirring member 47 together with the screws 45 and 46. When the printing rate is less than the predetermined value, the control means CR intermittently turns on / off the clutch CL and intermittently drives the stirring member 47 to rotate.

  It is also possible to use a motor as the driving means for the stirring member 47 and perform control different from that of the screws 45 and 46 to control the speed of the motor for driving the stirring means in accordance with the printing rate.

  By such control, the stirring / conveying means (screw 46) rotates continuously, whereas the stirring means (stirring member 47) rotates intermittently, so the rotation of the stirring means per unit operating time of the stirring / conveying means Since the amount decreases, when an image with a low printing rate is formed, the stirring action of the developer in the developing device is lowered, and the stress applied to the developer is reduced. As a result, the deterioration of the toner, which is likely to occur during the formation of an image with a low printing ratio, and the fogging, character scattering, density unevenness, toner scattering, and the like due to toner deterioration are prevented. Further, in the low printing rate image formation, since the amount of toner to be replenished is small, the toner is sufficiently mixed in the developer and sufficiently charged by the lowered stirring action.

<Process conditions>
A negatively chargeable OPC photoconductor is used using the color image forming apparatus shown in FIG. 1. Process speed (moving speed of photoconductor and intermediate transfer member): 400 mm / s, number of output sheets: 65 sheets per minute (A4 size) )
・ Development bias: DC + AC
AC bias: voltage Vac = 1 kV (peak-to-peak), frequency f = 5 kHz, waveform: rectangular wave
DC bias: Vdc-VL = -500V
However, Vdc is the developing sleeve potential, and VL is the maximum exposed portion of the photoreceptor.
Vdc−VL is a value controlled by feedback control based on detection of the surface of the photoreceptor.
・ Photoconductor surface potential
Maximum exposure area potential (VL): -50V to -100V
Charging potential (unexposed portion potential VH): VH−Vdc = −150V so that the control / development gap (shortest distance between the photosensitive member and the developing sleeve) is 0.3 mm in accordance with Vdc: 0.3 mm
Developer transport amount: 25 ± 2 mg / cm ²
-Toner adhesion amount on the photoreceptor (toner adhesion amount M at the maximum exposed portion): 0.4 mg / cm ²
(Photoconductor toner adhesion amount control by controlling the rotation speed of the developing sleeve)
<Developing sleeve 42>
・ Outer diameter: 30mm
-Length in rotation axis direction (excluding shaft part): 330 mm (magnet roll length: 320 mm)
・ Surface: Rz = 10μm by blasting
・ Rotation direction: Opposite direction to photoconductor in development area ・ Magnetic pole: 7
Magnetic flux density of developing magnetic pole (N1): 120mT
Magnetic flux density of layer forming magnetic pole (N2): 50 mT
Magnetic flux density of pumping pole (S2): 60mT
Repulsive magnetic field angle θ: 90 °
For the configuration of the magnet roll 43, see FIG. 8. Developing sleeve rotation speed: 210 to 280 times per minute (control so that the toner adhesion amount becomes a predetermined value)
<Screw 45>
・ Outer diameter: 24mm
・ Shaft diameter: 6mm
・ Helix pitch: 30mm
-Spiral rib thickness: 1mm
・ Rotational axis length (excluding shaft): 440mm
End shape: A disc (flange) with an outer diameter of 24 mm is provided at both ends, and a paddle is provided at the downstream end in the developer transport direction. Spacing with the developing sleeve (the shortest distance between the outer circumferences): 4 mm
-Arrangement with respect to the developing sleeve: Arrange the screw so that the straight line connecting the rotation center of the developing sleeve and the rotation center of the screw passes through the center (45 ° position) between the repulsive magnetic poles.-Gap with the housing: 1.5 mm
・ Rotational direction: Moves in the opposite direction to the developing sleeve at a position facing the developing sleeve. ・ Rotating speed: 400 times per minute <Screw 46>
・ Shape, outer diameter, shaft diameter, pitch, spiral rib thickness, axial length, and end shape are the same as the screw 45, but the paddle position is opposite <stirring member 47>
・ Outer diameter: 24mm
・ Shaft diameter: 6mm
・ Agitating blade: Elliptical plate ・ Agitating blade mounting angle: 45 ° to the rotation axis
・ Agitating blade pitch: 25 mm
・ Rotational axis length (excluding shaft): 440mm
-End shape: Discs (flange) with outer diameter of 24 mm are installed at both ends.-Gap with supply screw: 2.5 mm
・ Gap between casing: 1.5 mm
Rotation direction: opposite to the screw 46 (the screw 46 and the stirring member 47 move in the opposite direction at the opposite position)
・ Rotation speed: 400 times per minute or 0
400 times per minute when the printing rate is 3% or more, 0% when the printing rate is less than 3%
However, if the printing rate is less than 3%, every 50 sheets of images are rotated at a speed of 400 times / min for 3 seconds. <Developer>
・ Toner: Only magenta toner and cyan toner consisting of polymerized toner are used.
Toner is externally added with large diameter silica, small diameter silica, large diameter titania, small diameter titania, and calcium stearate.
Volume average particle size: 5.5 μm
Particle size distribution CV value: = 18 ± 2%
・ Carrier: Coated carrier with ferrite core coated with acrylic resin
Volume average particle size: 25 μm
Saturation magnetization: 7.5 wb · m / kg
-Toner concentration and charge amount:
Before image output (both magenta toner and cyan toner) 7% by mass, 40 ± 2 μC / g
After image output (both magenta toner and cyan toner) 7% by mass, 40 ± 3 μC / g
-Developer amount in the developing device: 1100 g
<Toner supply>
Replenishment position: Dropped from above between the screw 46 and the stirring / conveying member 47 to replenish. Toner replenishment speed: 30 g / min at maximum
Toner replenishment control: Uses a toner concentration sensor that detects the toner concentration by measuring the magnetic permeability, and controls the replenishment motor based on the output of the toner sensor <image output>
(1) Cyan monochromatic character pattern (printing rate 1%) is output continuously 200 pages (2) Cyan monochromatic character / line pattern (printing rate 7%) is output continuously 200 pages (3) Magenta monochromatic character pattern (printing rate 1%) Continuous 200 sheet output (4) Magenta monochrome character / line pattern (printing rate 7%) Continuous 200 sheet output The above image output is repeated 10 times to form an A4 size 8000 image, and the above (1) to (4) Each of the images was evaluated for fogging, character scattering, and density unevenness every 800 sheets. Further, in-machine contamination was evaluated at the stage when all image formation tests were completed.

  Further, as a comparative example, the image formations (1) to (4) were performed by rotating the stirring member 47 at 400 times / min regardless of the printing rate.

  The results are shown in Table 1.

  In Table 1, “◯” indicates that the evaluation items of fogging, character scattering, and uneven density stains were sufficiently suppressed and a high-quality image was formed. “Δ” indicates that fogging, letter scattering, density unevenness, or in-machine contamination occurred slightly.

  As is apparent from Table 1, in the comparative example, there was a decrease in image quality due to toner deterioration, but in the examples, there was no decrease in image quality and a high quality image was formed.

It is a figure which shows the conventional developing device. 1 is an overall view of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows an example of the image development apparatus in embodiment of this invention. FIG. 4 is a front sectional view of the developing device shown in FIG. 3. It is a figure which shows the whole arrangement | positioning of the screws 45 and 46 and the stirring member 47. FIG. FIG. 4 is a diagram showing a partial structure of screws 45 and 46 and a stirring member 47. 2 is a block diagram of a control system of the image forming apparatus according to the embodiment of the present invention. FIG. It is a figure which shows a magnet roll.

Explanation of symbols

4, 4Y, 4M, 3C, 4Bk Developing device 42 Developing sleeve 45, 46 Screw 47 Stirring member

Claims (1)

A developer carrier that conveys the developer to the development area by rotation;
Supply means for supplying the developer to the developer carrier while conveying the developer in a first direction along the rotation axis by rotation;
Stirring / conveying means for conveying the developer in a second direction opposite to the first direction while stirring the developer by rotation; and
In an image forming apparatus having a developing unit having a stirring unit having an inclined stirring blade formed around an axis, the stirring unit stirring the developer transported by the stirring / transporting unit,
Depending on the printing ratio it has a control means for controlling the amount of rotation of the stirring means per unit operating time of the stirring and conveying means,
The control means continuously rotates the stirring means in image formation of an image having a printing rate equal to or higher than a predetermined value, and repeatedly stops and rotates the stirring means in image formation of an image lower than the predetermined value. An image forming apparatus that is intermittently driven .

Images