Image forming apparatus

Abstract

To prevent local density unevenness while reducing downtime.SOLUTION: A control unit can execute a mode for controlling a first driving unit that drives to rotate a first conveying screw and a second conveying screw so that the ratio of the rotation speed (Vsc) of the first conveying screw and the second conveying screw to the rotation speed (Vsl) of a developer carrier in a non-image forming period (Vsc / Vsl) becomes smaller than Vsc / Vsl in an image forming period, and controlling a second driving unit that drives to rotate the developer carrier and a third conveying screw. In the mode, the ratio of the rotation speed (Vsc3) of the third conveying screw to Vsl in the non-image forming period (Vsc3 / Vsl) is equal to Vsc3 / Vsl in the image forming period.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus including a developing device that develops an electrostatic image formed on an image carrier with a developer containing toner and carrier. [Background technology]

[0002] The developing device includes a developing sleeve as a rotatable developer carrier that carries and transports a two-component developer (hereinafter simply called developer) containing toner and carrier to a development area where an electrostatic image formed on an image carrier is developed. Inside the developing sleeve, a magnet is fixedly arranged so as not to rotate and has multiple magnetic poles that generate a magnetic field for carrying the developer on the surface of the developing sleeve.

[0003] In addition, a regulating blade serving as a developer regulating member for regulating the amount of developer carried on the developing sleeve is disposed opposite the developing sleeve. The regulating blade is disposed opposite one of a plurality of magnetic poles of the magnet. This allows a developer pool to be formed upstream of the regulating blade in the surface movement direction of the developing sleeve, and a constant amount of developer can be secured immediately upstream of the regulating blade, making it possible to stably supply developer to the developing sleeve.

[0004] However, a non-moving layer of developer may be formed upstream of the regulating blade in the surface movement direction of the developing sleeve. Since the developer in the non-moving layer is not replaced, the developer in the non-moving layer maintains the same toner concentration and does not become further triboelectrically charged. The developer in the non-moving layer will continue to have a lower toner charge amount over a long period of time. As a result, a difference occurs between the toner charge amount of the developer in the moving layer and the toner charge amount of the developer in the non-moving layer upstream of the regulating blade in the surface movement direction of the developing sleeve.

[0005] On the other hand, due to the influence of changes in the fluidity of the developer in the moving layer or irregular vibrations caused by the operation of the image forming apparatus, a part of the developer in the non-moving layer at the boundary with the moving layer may collapse and be taken into the moving layer. In this case, the greater the difference between the toner charge amount of the developer in the moving layer and the toner charge amount of the developer in the non-moving layer, the more likely it is that localized density unevenness will occur when the developer in the non-moving layer that has been taken into the moving layer is transported to the development area.

[0006] Therefore, the driving source for driving the conveying screw and the driving source for driving the developing sleeve are driven independently. Then, when the ratio of the rotation speed Vsc of the conveying screw to the rotation speed Vsl of the developing sleeve is Vsc / Vsl, a mode (hereinafter referred to as toner layer movement control) is executed in which Vsc / Vsl during non-image formation is made smaller than Vsc / Vsl during image formation. This is known as a technology for breaking down the immobile layer formed upstream of the regulating blade in the surface movement direction of the developing sleeve (see Patent Document 1).

[0007] On the other hand, the developing device described in Patent Document 1 is a so-called function-separated developing device in which the function of supplying developer containing toner and carrier to the developing sleeve and the function of recovering developer from the developing sleeve are separate. The function-separated developing device has a supply chamber that supplies developer to the developing sleeve, and a recovery chamber (also called a stirring chamber) that recovers developer that has passed through a development area facing an image carrier from the developing sleeve. In addition, in the function-separated developing device, it is possible to recover developer that has passed through the development area from the developing sleeve in the recovery chamber without passing through the supply chamber.

[0008] In a function-separated developing device, the developer is transported from the upstream side to the downstream side in the developer transport direction in the supply chamber, and the developer in the supply chamber is supplied to the developing sleeve, so the amount of developer in the supply chamber tends to be smaller on the downstream side in the developer transport direction than on the upstream side. Also, in a function-separated developing device, the developer is transported from the upstream side to the downstream side in the developer transport direction in the recovery chamber, and the developer is recovered from the developing sleeve, so the amount of developer in the recovery chamber tends to be larger on the downstream side in the developer transport direction than on the upstream side. Therefore, in a function-separated developing device, the height of the developer surface on the downstream side in the developer transport direction in the recovery chamber tends to be higher than the height of the developer surface on the upstream side in the developer transport direction in the recovery chamber.

[0009] In such a function-separated developing device, when toner layer movement control is performed, the distribution of developer in the recovery chamber tends to be uneven. Therefore, depending on the distribution of developer in the developing container, when toner layer movement control is performed, there is a risk that the developer on the developing sleeve cannot be collected in the recovery chamber and overflows. This is because when the rotation speed of the conveying screw is slowed down in the toner layer movement control, the developer stagnates in the recovery chamber, and the recovery chamber does not have enough space to collect the developer.

[0010] Therefore, in a function-separated developing device, during non-image formation, a period is provided in which only the conveying screw is driven while the driving of the developing sleeve is stopped, prior to the toner layer movement control. In this way, a technology is known in which a space for recovering the developer on the developing sleeve is secured in advance and developer overflow is suppressed by executing control to drive only the conveying screw while the driving of the developing sleeve is stopped (see Patent Document 2). [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2011-53451 A [Patent Document 2] JP 2015-222396 A Summary of the Invention [Problem to be solved by the invention]

[0012] However, in the configuration of Patent Document 2, when no image is being formed, a period must be set in which only the conveying screw is driven with the development sleeve stopped prior to toner layer movement control, resulting in downtime.

[0013] The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing localized density unevenness while suppressing downtime. [Means for solving the problem]

[0014] In order to achieve the above object, an image forming apparatus according to one aspect of the present invention has the following configuration: That is, the image forming apparatus is capable of performing an image forming operation for forming an image on a recording material, and includes an image carrier, a rotatable developer carrier that carries and transports a developer containing toner and a carrier to a development area where an electrostatic image formed on the image carrier is developed, a regulating member that is disposed opposite the developer carrier and that regulates the amount of developer carried on the developer carrier, a first chamber that supplies the developer to the developer carrier, and a second chamber that is disposed opposite the developer carrier and that collects the developer that has passed through the development area from the developer carrier. a developing device including: a partition wall that separates the first chamber from the second chamber; a first transport screw that is disposed in the first chamber and transports the developer in a first direction; a second transport screw that is disposed in a first region of the second chamber and transports the developer in a second direction opposite to the first direction; and a third transport screw that is disposed in a second region of the second chamber horizontally adjacent to the first region of the second chamber and transports the developer in a third direction opposite to the second direction; a first drive unit that drives the developer carrier and the third conveying screw, a second drive unit that rotationally drives the developer carrier and the third conveying screw, and a control unit that controls the first drive unit to rotationally drive the first conveying screw and the second conveying screw, and controls the second drive unit to rotationally drive the developer carrier and the third conveying screw, wherein a ratio of a rotation speed (Vsc) of the first conveying screw and the second conveying screw when the first drive unit rotates and drives the first conveying screw and the second conveying screw to a rotation speed (Vsl) of the developer carrier when the second drive unit rotates and drives the developer carrier by is defined as Vsc / Vsl, and a rotation speed (Vsc3) of the third conveying screw when the second drive unit rotates and drives the third conveying screw by is defined as Vsc3 / Vsl to a rotation speed (Vsl) of the developer carrier when the second drive unit rotates and drives the developer carrier byA mode can be executed in which the first driving unit and the second driving unit are controlled so that Vsc3 / Vsl during the non-image formation period is smaller than Vsc / Vsl during the image formation period in which the image formation operation is being performed, and in the mode, Vsc3 / Vsl during the non-image formation period is equal to Vsc3 / Vsl during the image formation period. Effect of the Invention

[0015] According to the present invention, it is possible to suppress downtime and localized density unevenness. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram for explaining a configuration of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of a developing device according to the first embodiment. [Diagram 3] FIG. 2 is a diagram illustrating a configuration of a developing device according to the first embodiment. [Figure 4] FIG. 2 is a diagram for explaining a configuration of a recovery chamber in the first embodiment. [Diagram 5] 1 is a graph showing the relationship between the rotation speed (Vsc) of the first conveying screw and the second conveying screw, the rotation speed (Vsl) of the developing sleeve, and the rotation speed (Vsc3) of the third conveying screw in the first embodiment. [Figure 6] 4 is a flowchart for explaining control in the first embodiment. [Figure 7] 13 is a graph showing the relationship between the rotation speed (Vsc) of the first conveying screw and the second conveying screw, the rotation speed (Vsl) of the developing sleeve, and the rotation speed (Vsc3) of the third conveying screw in the second embodiment. [Figure 8] 10 is a flowchart for explaining a control in the second embodiment (a control in the third embodiment). [Figure 9] 13 is a diagram illustrating a configuration of a developing device according to a third embodiment. FIG. [Figure 10]13 is a graph showing the rotation speed (Vsc) of the first conveying screw and the second conveying screw, the rotation speed (Vsl) of the developing sleeve, and the rotation speed (Vsc3) of the third conveying screw in the third embodiment. [Figure 11] 13 is a flowchart illustrating a control in the fourth embodiment. [Figure 12] FIG. 11 is a diagram illustrating a configuration of a developing device according to another embodiment. [Figure 13] FIG. 4 is a diagram for explaining the configuration of a developing device in a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <First embodiment> The first embodiment will be described with reference to Figures 1 to 6. First, the schematic configuration of an image forming apparatus will be described with reference to Figure 1.

[0018] [Configuration of image forming device] In electrophotographic image forming devices such as copiers, printers, facsimiles, and multifunction machines that have multiple functions, a developing device supplies charged toner to an electrostatic image (electrostatic latent image) formed on an image carrier, and visualizes the image as a toner image. The visualized toner image is then transferred to a recording material (transfer material), and the toner image is fixed to the recording material by applying heat and pressure, and the image is output.

[0019] As shown in Fig. 1, an image forming apparatus 100 according to the first embodiment is capable of performing an image forming operation for forming an image on a recording material. The image forming apparatus 100 has four image forming stations Y, M, C, and K, each of which includes a photosensitive drum 1Y, 1M, 1C, and 1K as an image carrier, in an image forming apparatus main body 101. The photosensitive drums 1Y, 1M, 1C, and 1K are each a cylindrical photosensitive body. An intermediate transfer device is disposed below each image forming station. The intermediate transfer device is configured such that an intermediate transfer belt 51 as an intermediate transfer body is stretched around rollers 53, 55, and 56 and runs in the direction of the arrow.

[0020] In the first embodiment, the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K are charged by primary charging devices 2Y, 2M, 2C, and 2K of a corona charging type, which is a non-contact charging method. The charged surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K are exposed to laser light by exposure devices 3Y, 3M, 3C, and 3K, each of which is driven by a laser driver, to form electrostatic latent images corresponding to the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1K. The electrostatic latent images are developed with a developer by developing devices 4Y, 4M, 4C, and 4K to form toner images of yellow, magenta, cyan, and black, respectively.

[0021] The toner images formed at each image forming station are transferred and superimposed on intermediate transfer belt 51 by a transfer bias of transfer rollers 52Y, 52M, 52C, and 52K serving as primary transfer means. The four-color toner image formed on intermediate transfer belt 51 is transferred onto a recording material by secondary transfer roller 54 serving as secondary transfer means disposed opposite roller 53. Toner remaining on intermediate transfer belt 51 without being transferred to the recording material is removed by intermediate transfer belt cleaner 8. The recording material is, for example, a sheet material such as paper or a plastic sheet.

[0022] The recording material onto which the toner image has been transferred is pressurized and heated by a fixing device 7 equipped with a fixing roller. This fixes the toner image onto the recording material. Furthermore, primary transfer residual toner remaining on the photosensitive drums 1Y, 1M, 1C, and 1K after the primary transfer is removed by cleaners 6Y, 6M, 6C, and 6K in preparation for the next image formation. Furthermore, an LED is lit in the cleaner 6 to reduce potential unevenness that occurs during the image formation operation in preparation for the next image formation.

[0023] In the first embodiment, a drum-shaped photoconductor (photosensitive drum) is used as the image carrier, but a belt-shaped photoconductor can also be used. The charging method, transfer method, cleaning method, and fixing method are not limited to the above methods. The image forming stations described above basically have the same configuration, except for the developing color. For this reason, the following description will omit the suffixes Y, M, C, and K that indicate the configuration of each station. Since there are multiple process speeds required for the transfer and fixing processes according to the paper type, there are multiple driving speeds for the developing device.

[0024] [Developing device configuration] Next, the developing device 4 will be described with reference to Figs. 2 to 4. The developing device 4 is disposed in the image forming apparatus main body 101, and develops an electrostatic latent image formed on an image carrier with a developer containing toner and a carrier. The developing device 4 has a developing container 40 that contains a developer. The developer in the first embodiment is a so-called two-component developer containing non-magnetic toner and a carrier having magnetism. A developing sleeve 41 as a developer carrier is rotatably supported in the developing container 40. The developing sleeve 41 is disposed parallel to the direction of the rotation axis of the photosensitive drum 1, and develops an electrostatic latent image on the surface of the photosensitive drum 1 with a developer.

[0025] The developing container 40 is also provided with a regulating blade 43 (developer regulating member) that regulates the layer thickness of the developer carried on the developing sleeve 41. The developing sleeve 41 carries and transports the developer supplied from a developing chamber 401 (described later) on its surface. Each developing sleeve 41 is formed in a cylindrical shape, and a magnetic roller 42 is disposed therein in a non-rotating manner. The developing sleeve 41 is driven to rotate in the direction of the arrow shown in FIG. 2, and carries and transports the developer by the magnetic attraction force of the magnetic roller 42.

[0026] The developing container 40 is partitioned by a partition wall 48 into an upper developing chamber (developer transport path) 401 as a first chamber, and an agitating chamber (developer transport path) 402 as a second chamber, which is disposed below the developing chamber 401. The developing chamber 401 is a functional chamber that supplies developer to the developing sleeve 41. The agitating chamber 402 is a functional chamber that receives and agitates recovered developer recovered from the developing sleeve 41, excess developer that was not supplied to the developing sleeve 41 in the developing chamber 401, and replenishment developer replenished from outside the developing device 4.

[0027] That is, the developing device 4 of the first embodiment is a so-called function-separated developing device in which the function of supplying developer containing toner and carrier to the developing sleeve 41 is separated from the function of recovering the developer from the developing sleeve 41. The function-separated developing device has a supply chamber that supplies developer to the developing sleeve 41, and a recovery chamber (agitation chamber 402) that recovers the developer that has passed through the development area A facing the photosensitive drum 1 from the developing sleeve 41. In addition, in the function-separated developing device, the developer that has passed through the development area A can be recovered from the developing sleeve 41 in the recovery chamber (agitation chamber 402) without passing through the supply chamber (development chamber 401).

[0028] A first transport screw 44 as a first transport member and a second transport screw 45 as a second transport member are provided in the developing chamber 401 and the stirring chamber 402, respectively. The first transport screw 44 and the second transport screw 45 are both screw members having helical blades on a rotation axis arranged approximately parallel to the rotation axis direction (longitudinal direction) of the developing sleeve 41.

[0029] In the developing device 4 (function-separated developing device) of the first embodiment, as shown in the cross-sectional view of FIG. 2, the bottom 401b of the supply chamber (developing chamber 401) is located vertically above the bottom 402b of the recovery chamber (agitation chamber 402). The rotation center of the first conveying screw 44 is located vertically above the rotation center of the developing sleeve 41. The regulating blade 43 is located vertically above the rotation center of the developing sleeve 41.

[0030] 3, a first communication portion 404 and a second communication portion 405 are provided at both longitudinal end sides of the partition wall 48 as transfer portions (developer transport paths) that transport the developer between the developing chamber 401 and the stirring chamber 402. The first communication portion 404 has an opening formed therein that allows the developer to move from the stirring chamber 402 to the developing chamber 401. The second communication portion 405 has an opening formed therein that allows the developer to move from the developing chamber 401 to the stirring chamber 402.

[0031] The first transport screw 44 is disposed opposite the developing sleeve 41, and supplies the developer to the developing sleeve 41 while rotating to stir and transport the developer in a first direction from the first communicating portion 404 toward the second communicating portion 405. The second transport screw 45 rotates to stir and transport the developer in a second direction from the second communicating portion 405 toward the first communicating portion 404. The second transport screw 45 is disposed below the first transport screw 44 with respect to the direction of gravity, and the second direction is opposite to the first direction. The rotation of the first transport screw 44 and the second transport screw 45 circulates the developer in the developing container 40 while stirring and transporting it.

[0032] The developing device 4 is provided with a third transport screw 46 as a third transport member (agitation member). The third transport screw 46 is disposed below the developing sleeve 41 and adjacent to the second transport screw 45, and collects the developer from the developing sleeve 41 and agitates and transports the developer in the opposite direction to the second transport screw 45. The third transport screw 46 is a screw member having a spiral blade provided on a rotation axis disposed approximately parallel to the rotation axis direction of the developing sleeve 41.

[0033] In the developing device 4, the developing sleeve 41 rotates in the direction of the arrow in FIG. 2 (clockwise) during development, and developer is supplied from the developing chamber 401, and the two-component developer is carried, the layer thickness of which is regulated by the cutting of the magnetic brush by the regulating blade 43. The developer is then transported to the developing area A facing the photosensitive drum 1, where the developer is supplied to the electrostatic latent image formed on the photosensitive drum 1 to develop the latent image. Thereafter, the developer that contributed to the development is collected and transported from the developing sleeve 41 by the third transport screw 46, and is transferred to the second transport screw 45.

[0034] Here, the toner and carrier, which are components of the developer used in the first embodiment, will be described. The toner has a base made of a binder resin containing a colorant, and additives added to the base. In the first embodiment, a negatively charged polyester resin is used as the resin of the toner. The volume average particle diameter is preferably 4 μm or more and 10 μm or less, and in the first embodiment, a toner with a volume average particle diameter of 7 μm is used. If the particle diameter of the toner is too small, it becomes difficult to rub against the carrier, making it difficult to control the charge amount, and if the particle diameter is too large, a fine toner image cannot be formed.

[0035] The carrier may be surface-oxidized or unoxidized metals such as iron, nickel, cobalt, manganese, chromium, rare earth metals, alloys thereof, or oxide ferrite, and in the first embodiment, a ferrite carrier with an average volume particle size of 40 μm was used. If the particle size of the carrier is too small, there is a problem that the carrier adheres to the latent image carrier during development, and if it is too large, there is a problem that the carrier disturbs the toner image during development.

[0036] In the first embodiment, the developer container 40 contains 300 g of developer, the developer has a toner to carrier weight ratio of 1:9 when installed, and the toner concentration is 10% by weight. The average charge amount of the toner at a toner concentration of 10% in a 23°C, 50% environment is 40 μC / g.

[0037] Next, a cross-sectional configuration of the developing device 4 will be described. In the first embodiment, the developing container 40 has an opening at a position corresponding to the developing area A facing the photosensitive drum 1, and the developing sleeve 41 is rotatably disposed so as to be partially exposed in the direction of the photosensitive drum 1 at this opening. As described above, the magnet roller 42 contained in the developing sleeve 41 is fixed so as not to rotate.

[0038] Here, the flow of developer in a cross section will be described. First, as the first transport screw 44 transports the developer, the developer jumps up and is supplied to the developing sleeve 41. Since the developer contains magnetic carriers, it is bound by the magnetic force generated by the magnet roller 42 in the developing sleeve 41, and as the developing sleeve 41 rotates, the developer on the developing sleeve 41 passes through the regulating blade 43 and is regulated to a predetermined amount. The developer regulated to a predetermined amount is transported to the developing area A facing the photosensitive drum 1, and the toner is supplied to the electrostatic latent image. The developer that has passed through the developing area A is collected by the third transport screw 46 in the developing container. The collected developer is transported in the transport direction of the third transport screw 46 and merges upstream of the second transport screw 45.

[0039] 2, the drive system of the developing device 4 according to the first embodiment has a drive source for driving the first conveying screw 44 and the second conveying screw 45 and a drive source for driving the developing sleeve 41 and the third conveying screw 46, which are driven independently. That is, the developing sleeve 41 and the third conveying screw 46 are rotated by a first motor M1 (first drive section, first drive device). On the other hand, the first conveying screw 24 and the second conveying screw 25 are rotated by a second motor M2 (second drive section, second drive device). Both of these two motors (first motor M1, second motor M2) use DC motors and are driven at a rotation speed corresponding to the conveying speed of the recording material during the image forming operation (i.e., the peripheral speed of the intermediate transfer belt 51, the process speed).

[0040] Next, details of the developing sleeve 41 will be described. The developing sleeve 41 is rotatably attached to the developing container 40, and the rotation shaft of the developing sleeve 41 is rotated by a driving force supplied from a first motor M1, thereby conveying the developer to the photosensitive drum 1. In the first embodiment, the developing sleeve 41 is made of aluminum, and has a diameter of 20 mm in cross section at the portion facing the photosensitive drum 1.

[0041] The surface properties of the developing sleeve 41 and the transport properties of the developer will be described. First, when the surface of the developing sleeve 41 is as smooth as a mirror, the friction between the developer and the surface of the developing sleeve 41 is extremely small, so that the developer is hardly transported even when the developing sleeve 41 rotates. Therefore, by providing appropriate irregularities on the surface of the developing sleeve 41 and creating friction between the surface of the developing sleeve 41 and the developer, the developer will follow the rotation of the developing sleeve 41. In the first embodiment, the surface of the developing sleeve 41 is subjected to a blasting process to provide irregularities with a surface roughness of about 15 μm.

[0042] The blasting process is a processing method in which particles such as abrasive powder or glass beads having a predetermined particle size distribution are sprayed at high pressure. Hereinafter, the blasted portion is referred to as the blasted region, and the end portion not subjected to the blasting process is referred to as the non-blasted region. Since the developing sleeve 41 transports the developer in the blasted region, the blasted region needs to be provided in a range slightly wider than the image forming region. In the first embodiment, the range in which the blasted developer transport capacity is achieved is 330 mm. In addition to the example of performing the blasting process on the surface of the developing sleeve 41 as a means for providing the surface of the developing sleeve 41 with developer transportability, a modified example in which a process of forming grooves or recesses is performed on the surface of the developing sleeve 41 may be used.

[0043] The magnet roller 42 will be described with reference to Fig. 2. The magnet roller 42, which is a roller-shaped magnetic field generating means contained within the developing sleeve 41, is fixedly disposed in the developing container 40. The magnet roller 42 has a developing magnetic pole S1 at a position facing the developing area A. The magnetic field of the S1 pole formed in the developing area A causes the developer to form a magnetic brush, and while this magnetic brush comes into contact with the photosensitive drum 1 rotating in the developing area A, it develops the electrostatic latent image into a toner image by electrostatic force of the charged toner.

[0044] In addition to the S1 pole, the magnet roller 42 has a total of five poles: N1, N2, N3, and S2 poles. The role of each magnetic pole of the magnet roller 42 and the flow of developer in cross section will be explained. First, as the first transport screw 44 transports the developer, the developer jumps up and is supplied to the developing sleeve 41. The developer is constrained by the N2 pole because it contains magnetic carrier. Next, as the developing sleeve 41 rotates, the developer passes through the S2 pole facing the regulating blade 43, and the developer is regulated to a predetermined amount.

[0045] The regulated developer passes through the N1 pole and is supplied to the S1 pole facing the photosensitive drum 1. The developer that has passed through the development area A and consumed toner for the electrostatic latent image is released from the magnetic binding force of the magnetic poles between the N3 and N2 poles and is collected by the third transport screw 46. Note that in a configuration in which the pole between the S2 pole facing the regulating blade 43 and the development pole S1 (the N1 pole in the first embodiment) is omitted, developer transport becomes unstable, which may cause density unevenness.

[0046] Next, the regulating blade 43 will be described in detail. The regulating blade 43 is disposed so as to face the developing sleeve 41 upstream of the developing region in the rotation direction of the developing sleeve 41 in order to adjust the amount of developer carried on the developing sleeve 41 and supplied to the electrostatic latent image to a predetermined amount. The regulating blade 43 also defines the interval through which the developer on the developing sleeve 41 can pass from the developing container 40 toward the photosensitive drum 1.

[0047] In the first embodiment, a plate-shaped regulating blade 43 extending along the rotation axis direction of the developing sleeve 41 is used as a regulating member for regulating the amount of developer. Aluminum is used as the material of the regulating blade 43. The regulating blade 43 is disposed on the developer container 40 side, upstream of the photosensitive drum 1 in the rotation direction of the developing sleeve 41, so that the tip of the regulating blade 43 faces the center of the developing sleeve 41. As the developing sleeve 41 rotates, the developer on the developing sleeve 41 passes between the tip of the regulating blade 43 and the developing sleeve 41 and is sent to the developing area A. Therefore, by adjusting the gap between the regulating blade 43 and the surface of the developing sleeve 41, the amount of developer carried on the developing sleeve 41 and transported to the developing area can be adjusted.

[0048] Incidentally, if the gap between the regulating blade 43 and the developing sleeve 41 is too narrow, it is undesirable because foreign matter in the developer and toner aggregates are likely to clog the gap. Also, if the mass per unit area of ​​the developer transported on the developing sleeve 41 is too large, problems such as the developer clogging in the vicinity of the position facing the photosensitive drum 1 and carrier adhesion to the photosensitive drum 1 occur. On the other hand, if the mass per unit area of ​​the developer transported on the developing sleeve 41 is too small, a desired toner image cannot be developed, and a problem of reduced image density occurs. In the first embodiment, the developer transport amount is 30 mg / cm when the toner concentration is 10% after installation of the developing device 4 (initial state when no developer is used). 2 In order to achieve this, the gap (SB gap) between the regulating blade 43 and the developing sleeve 41 was set to 400 μm.

[0049] In the first embodiment, the diameter of the developing sleeve 41 is 20 mm, the diameter of the photosensitive drum 1 is 80 mm, and the closest area between the developing sleeve 41 and the photosensitive drum 1 is set to 400 μm. With this configuration, development is performed in a state where the developer transported to the development area A is in contact with the photosensitive drum 1. The developing sleeve 41 is made of non-magnetic aluminum, and a magnetic roller 42 serving as a magnetic field generating means is installed inside the developing sleeve 41 in a non-rotating state, so that in the development area, the developer forms a magnetic brush due to the magnetic field of the S1 pole located at a position facing the photosensitive drum 1.

[0050] In the above-described configuration, the developing sleeve 41 rotates in the direction of the arrow as shown in FIG. 2 during development, and conveys the developer, which is appropriately regulated by the regulating blade 43, to the developing area A facing the photosensitive drum 1. In the developing area, the developer forms a magnetic brush by the magnetic field of the magnet roller 42, and supplies toner to the electrostatic latent image formed on the photosensitive drum 1 to obtain a toner image. At this time, a developing bias voltage, which is a superimposed DC voltage and AC voltage, is applied to the developing sleeve 41 from a power source (not shown). In the first embodiment, a DC voltage of -500V and an AC voltage with a square wave peak-to-peak voltage Vpp of 1500V and a frequency f of 12kHz are used. However, the DC voltage value and the AC voltage waveform are not limited to these. In the developing area, the non-image forming portion on the photosensitive drum 1 is charged to -600V, and an electrostatic latent image is formed by a laser so that the potential of the electrostatic latent image forming portion increases according to the density of the output image.

[0051] In the development area A, the developing sleeve 41 moves in the same direction as the movement direction of the photosensitive drum 1. The peripheral speed ratio between the developing sleeve 41 and the photosensitive drum 1 is set to 1.5 times. The larger the peripheral speed ratio, the more toner is supplied, but if it is too large, problems such as toner scattering occur, so it is usually set between 1 and 2 times.

[0052] In the first embodiment, there are multiple speeds depending on the paper type, and at speed 1, the photosensitive drum 1 is driven at a peripheral speed of 320 mm / s and the developing sleeve 41 is driven at a peripheral speed of 480 mm / s, and at speed 2, the photosensitive drum 1 is driven at a peripheral speed of 160 mm / s and the developing sleeve 41 is driven at a peripheral speed of 240 mm / s. The toner consumption at the maximum density portion is 0.5 mg / cm 2 When the maximum amount of toner is consumed for A4 size, 0.31 g is used.

[0053] The developer that is regulated by the regulating blade 43 and passes through the development area is collected in the developing container 40 by the take-in section 47, so the amount of developer that can pass through the take-in section 47 is considerably larger than the amount of developer regulated by the regulating blade 43. This is to enable the take-in section 47 to take in the developer even if the shape of the regulating blade 43, the gap between the regulating blade 43 and the developing sleeve 41, the magnetic force of the magnet roller 42, developer characteristics, etc. vary due to mass production, or the developer deteriorates with use, increasing the transport amount. In the first embodiment, the developer transport amount of the developing sleeve 41 is 30 mg / cm. 2 60mg / cm 2 A gap is provided between the developing sleeve 41 and the container so that the developer can be taken in as described above.

[0054] Here, the configuration of the developing device 4 in the longitudinal direction (the direction of the rotation axis of the developing sleeve 41) will be described with reference to Fig. 3. The inside of the developing container 40 is vertically divided at approximately the center thereof into a developing chamber (also called a supply chamber) 401 and an agitating chamber (also called a recovery chamber) 402 by a partition wall 48. The developer D is contained in the developing chamber 401 and the agitating chamber 402.

[0055] The developing chamber 401 and the stirring chamber 402 are respectively provided with a first conveying screw 44 and a second conveying screw 45, which are conveying members serving as developer stirring and conveying means. The first conveying screw 44 is disposed at the bottom of the developing chamber 401 along the axial direction of the developing sleeve 41. The first conveying screw 44 is rotated by the driving force supplied from the second motor M2 (second driving device), thereby conveying the developer in the developing chamber 401 along the axial direction and supplying the developer to the developing sleeve 41. The second conveying screw 45 is disposed at the bottom of the stirring chamber 402 along the rotation axis direction of the developing sleeve 41. The second conveying screw 45 is rotated by the driving force supplied from the second motor M2 (second driving device), thereby conveying the developer in the stirring chamber 402 in the rotation axis direction opposite to that of the first conveying screw 44.

[0056] The developing chamber 401 and the stirring chamber 402 are communicated with each other through a first communication portion 404 and a second communication portion 405. The second communication portion 405 is a communication portion (also called a pumping portion) that pumps up the developer recovered from the developing sleeve 41 and the developer pumped down from the developing chamber 401 to the stirring chamber 402 by the second conveying screw 45. The developer is circulated between the developing chamber 401 and the stirring chamber 402 through the first communication portion 404 and the second communication portion 405, which are communication portions at both ends of the partition wall 48, by conveyance caused by the rotation of the first conveying screw 44 and the second conveying screw 45.

[0057] As shown in the cross-sectional view of Fig. 4, the stirring chamber (recovery chamber) 402 is composed of two parts: a first region 402a in which the second conveying screw 45 is disposed, and a second region 403 in which the third conveying screw 46 is disposed. As shown in the cross-sectional view of Fig. 2, the second region 403 of the stirring chamber (recovery chamber) 402 is a region adjacent to the first region 402a of the stirring chamber (recovery chamber) 402 in the horizontal direction.

[0058] In the second region 403, the developer is transported in the axial direction opposite to that of the second transport screw 45, and is transported upstream of the second chamber. In the first embodiment, no partition is provided between the first region 402a and the second region 403 of the stirring chamber (recovery chamber) 402. For this reason, the developer may be splashed up by the second transport screw 45, and the developer transported by the second transport screw 45 and the developer transported by the third transport screw 46 may be partly mixed together.

[0059] Next, the transport path of the developer will be described. The developer is stirred and transported through a first route (route that does not contribute to development) from the supply chamber (first chamber) 401 to the pumping section 405 to the recovery chamber (second chamber) 402 to the pumping section 404 to the supply chamber (first chamber) 401. In addition, the developer is transported by the first transport screw 44 in the supply chamber (first chamber) 401 to the developing sleeve 41 to the recovery chamber 403 to the third transport screw 46 to the recovery chamber 403 to the second transport screw 45 to the pumping section 404 to the supply chamber (first chamber) 401. The second route contributes to development and then passes through the pumping section 404. In addition, in the longitudinal direction of the recovery chamber 402, the developer recovered from the developing sleeve 41 flows toward the pumping section 404, so the amount of developer tends to increase downstream of the recovery chamber 402, and the amount of developer near the pumping section 404 increases.

[0060] Next, the toner concentration control will be described. The pumping unit 404 of the developing device 4 is provided with a toner concentration sensor (inductance sensor) that detects the magnetic permeability of the developer at a certain volume near the sensor surface and calculates the ratio of toner and carrier (toner concentration). Then, the supply amount is adjusted so that the toner concentration calculated by the toner concentration sensor becomes the target toner concentration. In other words, when deviation from the target toner concentration occurs, the toner supply amount is corrected and controlled to match the target value. The toner that is supplied according to the detection result of this toner concentration sensor is Si. If the target toner concentration is Tt and the detected current toner concentration is Ts, if Tt-Ts is negative, Si is positive, and if Tt-Ts is positive, Si is negative. In addition, since there is an appropriate range for the toner concentration, upper and lower limits are usually set for the target toner concentration. In the first embodiment, a range of 6 to 12% is used.

[0061] 2, the regulating blade 43 serving as a developer regulating member for regulating the amount of developer carried on the developing sleeve 41 is disposed opposite the developing sleeve 41. The regulating blade 43 is disposed opposite one of a plurality of magnetic poles (pole S2) of the magnet 42. As a result, a developer pool is formed upstream of the regulating blade 43 in the surface movement direction of the developing sleeve 41, and a constant amount of developer can be secured immediately upstream of the regulating blade 43, making it possible to stably supply developer to the developing sleeve 41.

[0062] However, a non-moving layer of developer may be formed upstream of the regulating blade 43 in the surface movement direction of the developing sleeve 41. Since the developer in the non-moving layer is not replaced, the developer in the non-moving layer maintains the same toner concentration and does not become further triboelectrically charged. The toner charge amount of the developer in the non-moving layer will decrease over a further long period of time. As a result, a difference occurs between the toner charge amount of the developer in the moving layer and the toner charge amount of the developer in the non-moving layer upstream of the regulating blade 43 in the surface movement direction of the developing sleeve 41.

[0063] On the other hand, due to the influence of changes in the fluidity of the developer in the moving layer or irregular vibrations caused by the operation of the image forming apparatus, a part of the developer in the non-moving layer at the boundary with the moving layer may collapse and be taken into the moving layer. In this case, the greater the difference between the toner charge amount of the developer in the moving layer and the toner charge amount of the developer in the non-moving layer, the more likely it is that localized density unevenness will occur when the developer in the non-moving layer that has been taken into the moving layer is transported to the development area.

[0064] Therefore, the drive source for driving the first and second conveying screws 44 and 45 and the drive source for driving the developing sleeve 41 are driven independently. The ratio of the rotation speed (Vsc) of the first and second conveying screws 44 and 45 to the rotation speed (Vsl) of the developing sleeve 41 is set to Vsc / Vsl. In this case, a mode (hereinafter referred to as toner layer movement control) is executed in which Vsc / Vsl during non-image formation is made smaller than Vsc / Vsl during image formation. This breaks up the immobile layer formed upstream of the regulating blade 43 in the surface movement direction of the developing sleeve 41.

[0065] However, in a function-separated developing device, when toner layer movement control is performed, the distribution of developer in the recovery chamber (stirring chamber 402) tends to be biased. For this reason, depending on the distribution of developer in the developing container 40, when toner layer movement control is performed, there is a risk that the developer on the developing sleeve 41 will not be able to be collected in the recovery chamber (stirring chamber 402) and will overflow. This is because when the rotation speed (Vsc) of the first conveying screw 44 and the second conveying screw 45 is slowed down in the toner layer movement control, the developer stagnates in the recovery chamber (stirring chamber 402), and the space in the recovery chamber (stirring chamber 402) for collecting the developer becomes insufficient.

[0066] This is a significant problem in a developing device (developing device 4000 in a comparative example shown in FIG. 13) in which the third conveying screw 46 is not provided in the recovery chamber (agitation chamber 402). Also, this is a significant problem in a developing device in which the drive of the first conveying screw 44, the second conveying screw 45, and the third conveying screw 46 is separate from the drive of the developing sleeve 41. This is because, in the longitudinal direction of the recovery chamber (agitation chamber 402), the developer recovered from the developing sleeve flows toward the pumping section 404, so that the amount of developer tends to increase toward the downstream of the recovery chamber (agitation chamber 402). As a result, the amount of developer increases near the pumping section 404, and there is a risk of the developer overflowing downstream of the recovery chamber (agitation chamber 402).

[0067] In contrast to this, in the developing device 4 of the first embodiment, in addition to the second conveying screw 45, a third conveying screw 46 is provided in the recovery chamber (agitation chamber 402). Moreover, in the developing device 4 of the first embodiment, the driving of the first conveying screw 44 and the second conveying screw 45 is separate from the driving of the third conveying screw 46 and the developing sleeve 41. The details will be described below.

[0068] [Characteristic configuration of the invention according to the first embodiment] In the first embodiment, during toner layer movement control, the third conveying screw 46 is driven so that its rotation speed is faster than the rotation speeds of the first conveying screw 44 and the second conveying screw 45.

[0069] In the first embodiment, when toner layer movement control is performed during non-image formation, the rotational speed of the first conveying screw 44 and the second conveying screw 45 is Vsc, the rotational speed of the developing sleeve 41 is Vsl, and the rotational speed of the third conveying screw 46 is Vsc3.

[0070] The ratio of the rotation speed (Vsc) of the first conveying screw 44 and the second conveying screw 45 to the rotation speed (Vsl) of the developing sleeve 41 is defined as Vsc / Vsl. In this case, the screws are driven so that Vsc / Vsl during the toner layer movement control is smaller than Vsc / Vsl during the image forming operation. Also, the ratio of the rotation speed (Vsc3) of the third conveying screw 46 to the rotation speed (Vsl) of the developing sleeve 41 is defined as Vsc3 / Vsl. In this case, the screws are driven so that Vsc / Vsl during the toner layer movement control is equal to Vsc3 / Vsl during the image forming operation.

[0071] In this way, Vsc3 / Vsl during toner layer movement control is driven to be equal to Vsc3 / Vsl during image formation operation. As a result, the developer on the downstream side of the recovery chamber (mixing chamber 402) where the amount of developer is large is transported to the upstream side of the recovery chamber by the third transport screw 46, thereby preventing developer overflow.

[0072] [Control in the first embodiment] In the first embodiment, during an image forming period in which an image is formed on a recording material, the first conveying screw 44 and the second conveying screw 45 are driven at a rotation speed of 800 rpm, and the third conveying screw 46 and the developing sleeve 41 are driven at a rotation speed of 600 rpm.

[0073] During a non-image forming period when the image forming operation is not being performed, the driving of the first conveying screw 44 and the second conveying screw 45 is stopped (i.e., the rotation speeds of the first conveying screw 44 and the second conveying screw 45 are set to zero) as the toner layer movement control. Also, during the non-image forming period, the developing sleeve 41 and the third conveying screw 46 are driven at 600 rpm for one second.

[0074] FIG. 5 is a graph showing the rotation speeds of the first conveying screw 44 and the second conveying screw 45, and the rotation speeds of the developing sleeve 41 and the third conveying screw 46. As shown in FIG.

[0075] In the first embodiment, the CPU 20 (control unit) controls the first motor M1 so as to change the rotation speeds of the first conveying screw 44 and the second conveying screw 45. Moreover, the CPU 20 controls the second motor M2 so as to change the rotation speeds of the developing sleeve 41 and the third conveying screw 46. The CPU 20 also controls an accumulating memory for counting the number of times N that the toner layer movement control has not been executed, to determine the execution timing of the toner layer movement control.

[0076] It is necessary to execute the control in the first embodiment before the toner layer obstructs the gap (SB gap) between the regulating blade 43 and the developing sleeve 41. In the first embodiment, the earliest the toner layer is formed and obstructs the transport is when the toner consumption rate is 1% and the temperature inside the developing device 4 rises to 45°C, which occurs after a driving time equivalent to 5,500 sheets of A4 size paper is passed. For this reason, the control in the first embodiment is executed when the driving time reaches 5,000 sheets. In other words, the CPU 20 executes the toner layer movement control every time an image is formed on a predetermined number of recording materials in the image forming operation.

[0077] FIG. 6 is a flowchart illustrating the control in the first embodiment.

[0078] 6 is executed by the CPU 20 reading out a control program stored in the memory 30 and controlling various devices. The control in Fig. 6 starts a flow after the image forming apparatus 100 receives an instruction to start an image forming operation (an instruction to execute a print job) (after printing starts).

[0079] After printing starts, the CPU 20 reads out from the memory 30 various high voltages and rotation speeds that are predetermined in accordance with the process speed, controls the CPU 20, applies and drives various drive systems including the first motor M1 and the second motor M2, and starts the image formation operation (S101).

[0080] Next, the CPU 20 calculates the number m of images output by the image forming operation converted into an A4 size (S102).

[0081] Next, the CPU 20 adds the converted number of sheets m to the number of times N that the toner layer movement control has not been performed (S103), and determines whether N is equal to or greater than a threshold value of 5000 (S104). If N is equal to or greater than the threshold value of 5000 (S104: yes), the CPU 20 suspends the image forming operation and executes the toner layer movement control during the non-image forming period (S105). On the other hand, if N is less than the threshold value of 5000 (S104: no), the process returns to S101 and the image forming operation continues.

[0082] When performing the toner layer movement control during non-image formation, the rotation speed of the first conveying screw 44 and the second conveying screw 45 is Vsc, the rotation speed of the developing sleeve 41 is Vsl, and the rotation speed of the third conveying screw 46 is Vsc3. The ratio of the rotation speed (Vsc) of the first conveying screw 44 and the second conveying screw 45 to the rotation speed (Vsl) of the developing sleeve 41 is Vsc / Vsl. In this case, in the toner layer movement control, the screws are driven so that Vsc / Vsl during the toner layer movement control is smaller than Vsc / Vsl during the image forming operation. In addition, in the toner layer movement control, the ratio of the rotation speed (Vsc3) of the third conveying screw 46 to the rotation speed (Vsl) of the developing sleeve 41 is Vsc3 / Vsl. In this case, the screws are driven so that Vsc / Vsl during the toner layer movement control is equal to Vsc3 / Vsl during the image forming operation. Then, when the toner layer movement control in S105 is completed, the series of controls related to FIG. 6 is completed.

[0083] In the first embodiment, the number of rotations of the developing sleeve 41 for driving A4 size paper is set as one sheet, and when the number of rotations of the developing sleeve 41 for driving differs depending on the size of the paper, the conversion is based on the number of rotations. For example, A3 size is twice as long as A4 size, so it is counted as two sheets.

[0084] In this way, in the first embodiment, the toner layer movement control is executed every time an image is formed on a predetermined number of sheets of recording material during the image forming operation. That is, the toner layer movement control is driven so that Vsc3 / Vsl during the toner layer movement control is equal to Vsc3 / Vsl during the image forming operation. As a result, the developer on the downstream side of the recovery chamber (mixing chamber 402) where the developer amount is large is transported to the upstream side of the recovery chamber by the third transport screw 46, so that developer overflow can be suppressed.

[0085] <Second embodiment> If the distribution of developer in the developing container 40 is disrupted as a result of performing toner layer movement control as in the first embodiment, there is a possibility that developer cannot be temporarily supplied to a part of the developing sleeve 41, resulting in a part of the developed toner image being missing. This is because when toner layer movement control is performed, developer distribution differs from that during image forming operation, and developer is biased to a certain part. For this reason, when image forming operation is performed immediately after performing toner layer movement control, developer cannot be supplied to the developing sleeve 41, and the amount of developer carried on the developing sleeve 41 decreases.

[0086] Therefore, in the second embodiment, in the non-image forming period, after the toner layer movement control is performed, developer circulation control is performed to drive the developing sleeve 41, the third conveying screw 46, the first conveying screw 44, and the second conveying screw 45. Then, after the developer circulation control is performed, the image forming operation is performed.

[0087] The rotation speeds of the developing sleeve 41 and the third conveying screw 46 during developer circulation control are set to be the same as the rotation speeds of the developing sleeve 41 and the third conveying screw 46 during image formation. Also, the rotation speeds of the first conveying screw 44 and the second conveying screw 45 during developer circulation control are set to be the same as the rotation speeds of the developing sleeve 41 and the third conveying screw 46 during image formation.

[0088] In addition, the driving time during developer circulation control is preferably such that the developer circulates at least one revolution, and in the second embodiment, the driving is performed for 5 seconds. Note that in the second embodiment, the driving is stopped once between the developer circulation control and the image formation control, but the image formation operation may be resumed without stopping the driving after the developer circulation control. If the image formation operation is resumed without stopping the driving after the developer circulation control, the downtime is reduced.

[0089] In the second embodiment, the developer circulation control is the same as in the first embodiment, except for the rotational driving of the first conveying screw 44 and the second conveying screw 45. During the image formation period, the first conveying screw 44 and the second conveying screw 45 are rotated at a speed of 800 rpm, and the third conveying screw 46 and the developing sleeve 41 are rotated at a speed of 600 rpm.

[0090] FIG. 7 is a graph showing the rotation speeds of the first conveying screw 44 and the second conveying screw 45, and the rotation speeds of the developing sleeve 41 and the third conveying screw 46 in the second embodiment.

[0091] During the non-image formation period, as toner layer movement control, the driving of the first conveying screw 44 and the second conveying screw 45 is stopped, and the developing sleeve 41 and the third conveying screw 46 are driven at 600 rpm for 1 second. Then, before the image formation operation, as developer circulation control, the first conveying screw 44 and the second conveying screw 45 are driven at a rotation speed of 800 rpm, and the third conveying screw 46 and the developing sleeve 41 are driven at a rotation speed of 600 rpm for 5 seconds.

[0092] FIG. 8 is a flowchart illustrating the control in the second embodiment.

[0093] 8 is executed by CPU 20 reading out a control program stored in memory 30 and controlling various devices. Also, the flow of the control in Fig. 8 is started after image forming apparatus 100 receives an instruction to start an image forming operation (an instruction to execute a print job) (after printing starts).

[0094] After printing starts, the CPU 20 reads out from the memory 30 various high voltages and rotation speeds that are predetermined in accordance with the process speed, controls the CPU 20, applies and drives various drive systems including the first motor M1 and the second motor M2, and starts the image formation operation (S201).

[0095] Next, the CPU 20 calculates the number m of images output by the image forming operation converted into an A4 size (S202).

[0096] Next, the CPU 20 adds the converted number of sheets m to the number of times N that the toner layer movement control has not been performed (S203), and determines whether N is equal to or greater than a threshold value of 5000 (S204). If N is equal to or greater than the threshold value of 5000 (S204: yes), the CPU 20 suspends the image forming operation and executes the toner layer movement control during the non-image forming period (S205). On the other hand, if N is less than the threshold value of 5000 (S204: no), the process returns to S201 and the image forming operation continues.

[0097] When the toner layer movement control in S205 is completed, the CPU 20 executes the developer circulation control (S206). Before the image forming operation, the first conveying screw 44 and the second conveying screw 45 are driven at a rotation speed of 800 rpm, and the third conveying screw 46 and the developing sleeve 41 are driven at a rotation speed of 600 rpm for 5 seconds as the developer circulation control. The rotation speeds of the developing sleeve 41 and the third conveying screw 46 during the developer circulation control are set to the same as the rotation speeds of the developing sleeve 41 and the third conveying screw 46 during the image forming operation. In addition, the rotation speeds of the first conveying screw 44 and the second conveying screw 45 during the developer circulation control are set to the same as the rotation speeds of the developing sleeve 41 and the third conveying screw 46 during the image forming operation. Then, when the developer circulation control in S206 is completed, the series of controls related to FIG. 8 are terminated.

[0098] In the second embodiment, the number of rotations of the developing sleeve 41 for driving A4 size paper is set as one sheet, and when the number of rotations of the developing sleeve 41 for driving differs depending on the size of the paper, the conversion is based on the number of rotations. For example, A3 size is twice as long as A4 size, so it is counted as two sheets.

[0099] In this way, in the second embodiment, in the non-image formation period, after performing the toner layer movement control, the developer circulation control is performed to drive the developing sleeve 41, the third conveying screw 46, the first conveying screw 44, and the second conveying screw 45. Then, after performing the developer circulation control, the image formation operation is performed. This makes it possible to suppress a situation in which the developer cannot be temporarily supplied to a part of the developing sleeve 41 during the image formation operation after performing the toner layer movement control, resulting in a part of the toner image to be developed being missing.

[0100] <Third embodiment> The image forming apparatus 100 and the developing device 4 in the third embodiment have the same configuration as those in the first embodiment, except for the replenishment agent S and the developer discharge port 406 provided in the developing device 4, and a description of the same parts will be omitted. In the third embodiment, the configuration is such that the carrier with reduced charging ability is discharged together with the developer from the developer discharge port 406, while a replenishment agent having carrier and toner is replenished, thereby maintaining the charging ability of the carrier in the developing device 4 and maintaining the charge amount of the toner. In the case of such a configuration, if the amount of carrier discharged is large compared to the amount of carrier replenished in image formation, the developer gradually decreases and the developing device 4 cannot function, so certain restrictions are required for the toner layer movement control and developer circulation control that discharge the developer.

[0101] In the third embodiment, carrier C is replenished to the developing device 4 together with toner T as replenishment agent S. This is to deal with the decrease in the charge amount of the carrier accompanying the image forming operation, and by replenishing new carrier into the developing device 4, the charge ability of the carrier is maintained and the charge amount of the toner is kept within an appropriate range. In the third embodiment, a mixture of toner T and carrier C in a weight ratio of 9:1 is used as the replenishment agent S. However, the invention according to the third embodiment can be applied even when the weight ratio is different or when the toner and carrier are replenished separately.

[0102] To prevent excess carrier from accumulating in the developing device 4 when the replenishment agent containing carrier is replenished and the developer from overflowing from the developing device 4, the developing device 4 is usually provided with a developer discharge port 406 for discharging the excess carrier together with the developer. When the developing device 4 is provided with the developer discharge port 406, the amount of developer in the developing device 4 remains within a substantially constant range.

[0103] The configuration of the developing device 4 in the third embodiment is shown in the cross-sectional view of Fig. 9. The developer discharge port 406 is provided downstream of a supply portion that faces the developing sleeve 41 and supplies the developer so that excess developer after being supplied to the developing sleeve 41 can be discharged. The developer discharge port 406 is also provided upstream of the supply port so that the replenishment agent is not discharged immediately after replenishment. As described above, it is preferable to provide the supply port downstream of the opposing region of the developing sleeve 41 in the supply chamber 401 so that the replenishment agent is not supplied to the developing sleeve 41 without being sufficiently mixed with the developer in the developing device 4.

[0104] In the configuration of the third embodiment, when toner layer movement control is performed as in the first embodiment, the distribution of developer is disrupted, and then, when the developer in the developing device 4 is excessively discharged as in the first and second embodiments, the developer becomes insufficient. When the developer becomes insufficient, the developer cannot be supplied to a part of the developing sleeve 41, and there is a possibility that a part of the developed toner image will be missing.

[0105] This is because when the toner layer movement control is executed, the developer is biased to one area, unlike the developer distribution during image formation operation, and the biased developer is excessively discharged when passing near the developer discharge port 406 during normal driving. When the rotation speeds of the developing sleeve 41 and the third conveying screw 46 are made relatively faster than those of the first conveying screw 44 and the second conveying screw 45 as in the third embodiment, more developer than usual accumulates on the upstream side of the recovery chamber 402. Then, normal driving causes the developer to be excessively discharged.

[0106] If the amount of carrier replenished is small relative to the amount of carrier discharged after the toner layer movement control, the image forming operation continues, and the developer gradually decreases each time the toner layer movement control is executed, making it impossible to supply developer to the developing sleeve 41.

[0107] In the third embodiment, in a non-image forming period, after executing the toner layer movement control, the developing sleeve 41, the first conveying screw 44, and the second conveying screw 45 are driven to be slower than during the image forming operation. At this time, the ratio (Vsc / Vsl) of the rotation speed (Vsc) of the first conveying screw 44 and the second conveying screw 45 to the rotation speed (Vsl) of the developing sleeve 41 is made smaller than during the image forming operation, thereby reducing the discharge amount from the developer discharge port 406.

[0108] In the third embodiment, the first conveying screw 44 and the second conveying screw 45 are driven at a slower speed than during the image forming operation while the driving of the developing sleeve 41 is stopped. This reduces the vertical vibration applied to the developer, thereby reducing the bulk of the developer, and also reduces the amount of developer passing through the developer discharge port 406, thereby suppressing the discharge of the developer.

[0109] FIG. 10 is a graph showing the rotation speeds of the first conveying screw 44 and the second conveying screw 45, and the rotation speeds of the developing sleeve 41 and the third conveying screw 46 in the third embodiment.

[0110] In the third embodiment, the developer circulation control is the same as in the second embodiment, except for the rotational driving of the first transport screw 44 and the second transport screw 45. In the developer circulation control, the developing sleeve 41 and the third transport screw 46 are driven at 300 rpm, and the first transport screw 44 and the second transport screw 45 are driven at 400 rpm for 10 seconds each. It is preferable that the driving time is the time until the developer that has accumulated since the image forming operation passes through the developer discharge port 406.

[0111] The flow chart for explaining the control in the third embodiment is the same as FIG. 8 described above in the second embodiment. In the configuration of the third embodiment, the rotation speed of the first conveying screw 44 and the second conveying screw 45 is suppressed, so that the developer overflow can be suppressed while the developer discharge can be suppressed. Specifically, when the control described above in the second embodiment is executed, the amount of developer discharged is 1 g. In contrast, when the control in the third embodiment is executed, the amount of developer discharged is suppressed to 0.3 g.

[0112] <Fourth embodiment> The image forming apparatus 100 and the developing device 4 in the fourth embodiment have the same configuration as those in the first embodiment, except that they have a toner characteristic detection means and a temperature detection means (temperature sensor).

[0113] The driving time required for the toner layer to be formed varies depending on the state of the developer during driving. For example, if the temperature of the developer is high, the toner layer will form in a shorter driving time than if the temperature is low. Also, if the average toner residence time is long (which occurs when the toner in the developing device 4 is subjected to a large load and the toner characteristics change, causing image formation with a low printing rate to continue for a long period of time), the toner layer will form more quickly than if the average toner residence time is short.

[0114] In the first embodiment, the control is executed at an earlier timing than the timing when the developer transport failure occurs most quickly. Therefore, depending on the state of the developer, the control may be executed earlier than necessary, which may cause downtime.

[0115] It is sufficient to execute the toner layer movement control before a developer transport failure occurs. Therefore, the execution timing of the toner layer movement control can be optimized according to the state of the developer, and downtime due to the execution of the toner layer movement control can be reduced. In the fourth embodiment, the change in the toner characteristics is estimated using the average printing rate of the past 1,000 sheets. The detection result of the temperature sensor in the developing device 4 is used as the developer temperature. The CPU 20 determines the execution timing of the toner layer movement control based on the calculation result by the average printing rate calculation means, the detection result by the temperature sensor in the developing device 4, and the unexecuted index Ni.

[0116] Since the toner layer's obstruction of developer transport varies depending on the toner characteristics and developer temperature, a weighted number m of sheets is added to the unimplemented index Ni according to the developer condition and the rotation time of the developing sleeve 41. In the fourth embodiment, the earliest transport failure is calculated as 1, and the case where it takes twice as long is calculated as 0.5. (See Table 1, which shows the weighting of the unimplemented index Ni according to the developer condition.)

[0117] [Table 1]

[0118] The number of output sheets and the unexecuted index Ni of the toner layer movement control are updated for each image formation. The unexecuted index Ni is calculated by accumulating indexes determined by the temperature during image formation, the average print rate of the past 1000 sheets, and the paper size. For example, if the temperature when A4 size paper is passed is 42°C and the average print rate of the past 1000 sheets is 10%, 0.8 is added to the unexecuted index Ni. The execution flow of the toner layer movement control replaces the unexecuted number N of the first embodiment with the unexecuted index Ni.

[0119] FIG. 8 is a flowchart illustrating the control in the fourth embodiment.

[0120] 11 is executed by the CPU 20 reading out a control program stored in the memory 30 and controlling various devices. The control in Fig. 11 starts a flow after the image forming apparatus 100 receives an instruction to start an image forming operation (an instruction to execute a print job) (after printing starts).

[0121] After printing starts, the CPU 20 reads out from the memory 30 various high voltages and rotation speeds that are predetermined in accordance with the process speed, controls the CPU 20, applies and drives various drive systems including the first motor M1 and the second motor M2, and starts the image formation operation (S401).

[0122] Next, the CPU 20 calculates the number m of images output by the image forming operation converted into an A4 size (S402).

[0123] Next, the CPU 20 acquires the temperature of the developing device 4 from a temperature sensor in the developing device 4, acquires the image DUTY (print rate) (S403), and adds the unexecuted index Ni (S404). Next, the CPU 20 determines whether the unexecuted index Ni is equal to or greater than a threshold value of 5000 (S405). If it is equal to or greater than the threshold value of 5000 (S405: yes), the CPU 20 interrupts the image forming operation and executes toner layer movement control during the non-image formation period (S406). On the other hand, if it is less than the threshold value of 5000 (S405: no), the process returns to S401 and the image forming operation continues.

[0124] In the fourth embodiment, the number of rotations of the developing sleeve 41 for driving A4 size paper is set as one sheet, and when the number of rotations of the developing sleeve 41 for driving differs depending on the size of the paper, the conversion is based on the number of rotations. For example, A3 size is twice as long as A4 size, so it is counted as two sheets.

[0125] In the fourth embodiment, when the developer temperature is 39° and the image duty is 10%, the weighting index is 0.5 (see Table 1), so that the toner layer movement control needs to be performed only half as frequently as in the first embodiment, thereby reducing downtime.

[0126] (Other embodiments) The present invention is not limited to the above-described embodiments, and various modifications (including organic combinations of the respective embodiments) are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0127] In the above-mentioned first to fourth embodiments, the developing device has one developing sleeve 41, but it may have a configuration having a plurality of developing sleeves 41. A cross-sectional view of a developing device (a function-separated developing device) having two developing sleeves 41 is shown in FIG. 12. In this case, in the developing device 400 shown in FIG. 12, the upstream developing sleeve 41a transfers the developer that has passed through the regulating blade 43 to the downstream developing sleeve 41b. The developing device 400 is a function-separated developing device in which a supply chamber (developing chamber 401) that supplies the developer to the upstream developing sleeve 41a and a recovery chamber (agitation chamber 402) that recovers the developer from the downstream developing sleeve 41b are separately provided. In the developing device 400, the first conveying screw 44 and the second conveying screw 45 are rotated by the first motor M1. The upstream developing sleeve 41a, the downstream developing sleeve 41b, and the third conveying screw 46 are rotated by the second motor M2.

[0128] In the above embodiment, as shown in Fig. 1, the image forming apparatus 100 is configured to use the intermediate transfer belt 51, but the present invention is not limited to this. It is also possible to apply the present invention to an image forming apparatus configured to transfer the recording material by directly contacting the photosensitive drum 1 in sequence. [Explanation of symbols]

[0129] 1 Photosensitive drum 4. Developing device 20 CPU 41 Developing sleeve 43 Regulatory Blade 44 First conveying screw 45 Second conveying screw 46 Third conveying screw 48 Bulkhead 100 Image forming device 401 Developing Room 402 Stirring chamber M1 First motor M2 Second motor

Claims

1. An image forming apparatus capable of performing an image forming operation for forming an image on a recording material, an image carrier, a rotatable developer carrier that carries and conveys a developer containing toner and a carrier to a developing area for developing an electrostatic image formed on the image carrier, a regulating member disposed opposite to the developer carrier and regulating the amount of the developer carried by the developer carrier, a first chamber for supplying the developer to the developer carrier, a second chamber disposed opposite to the developer carrier and recovering the developer that has passed through the developing area from the developer carrier, a partition wall partitioning the first chamber and the second chamber, a first conveying screw disposed in the first chamber and conveying the developer in a first direction, a second conveying screw disposed in a first region of the second chamber and conveying the developer in a second direction opposite to the first direction, and a third conveying screw disposed in a second region of the second chamber horizontally adjacent to the first region of the second chamber and conveying the developer in a third direction opposite to the second direction, and a developing device having the same, a first driving unit that rotationally drives the first conveying screw and the second conveying screw, a second driving unit that rotationally drives the developer carrier and the third conveying screw, a control unit that controls the first driving unit to rotationally drive the first conveying screw and the second conveying screw, and controls the second driving unit to rotationally drive the developer carrier and the third conveying screw, comprising, when the ratio of the rotational speed (Vsc) of the first conveying screw and the second conveying screw when the first driving unit rotationally drives the first conveying screw and the second conveying screw to the rotational speed (Vsl) of the developer carrier when the second driving unit rotationally drives the developer carrier is defined as Vsc / Vsl, and the rotational speed (Vsc3) of the third conveying screw when the second driving unit rotationally drives the third conveying screw is defined as Vsc3 / Vsl with respect to the rotational speed (Vsl) of the developer carrier when the second driving unit rotationally drives the developer carrier, The control unit is capable of executing a mode in which Vsc / Vsl during a non-image formation period in which the image formation operation is not being performed is made smaller than Vsc / Vsl during an image formation period in which the image formation operation is being performed, and in the mode, Vsc3 / Vsl during the non-image formation period is equal to Vsc3 / Vsl during the image formation period An image forming apparatus characterized by this.

2. In the mode, the rotational speeds of the first conveyance screw and the second conveyance screw during the non-image formation period are slower than the rotational speeds of the first conveyance screw and the second conveyance screw during the image formation period The image forming apparatus according to claim 1, characterized by this.

3. In the mode, the rotational speeds of the first conveyance screw and the second conveyance screw during the non-image formation period are zero The image forming apparatus according to claim 1, characterized by this.

4. The control unit is capable of executing the mode each time an image is formed on a predetermined number of recording materials in the image formation operation The image forming apparatus according to any one of claims 1 to 3, characterized by this.

5. The image forming apparatus further includes a temperature sensor that detects the temperature inside the developing device, and the control unit when the temperature inside the developing device detected by the temperature sensor is a first temperature, is capable of executing the mode each time an image is formed on a first number of recording materials in the image formation operation, and when the temperature inside the developing device detected by the temperature sensor is a second temperature higher than the first temperature, is capable of executing the mode each time an image is formed on a second number of recording materials less than the first number in the image formation operation The image forming apparatus according to any one of claims 1 to 4, characterized by this.

6. The control unit when the average printing rate is a first ratio, is capable of executing the mode each time an image is formed on a first number of recording materials in the image formation operation, and when the average printing rate is a second ratio lower than the first ratio, is capable of executing the mode each time an image is formed on a second number of recording materials less than the first number in the image formation operation The image forming apparatus according to any one of claims 1 to 4, characterized by this.

7. The first driving unit is a first motor for rotationally driving the first conveying screw and the second conveying screw. The second driving unit is a second motor for rotationally driving the developer carrier and the third conveying screw. The image forming apparatus according to any one of claims 1 to 6, characterized in that.

8. The regulating member is located vertically above the rotation center of the developer carrier. The image forming apparatus according to any one of claims 1 to 7, characterized in that.

9. The rotation center of the first conveying screw is located vertically above the rotation center of the developer carrier. The image forming apparatus according to any one of claims 1 to 8, characterized in that.

10. The bottom of the first chamber is located vertically above the bottom of the second chamber. The image forming apparatus according to any one of claims 1 to 9, characterized in that.

11. An image forming apparatus capable of executing an image forming operation for forming an image on a recording material, an image carrier, a rotatable first developer carrier that carries and conveys a developer containing toner and a carrier to a first developing region for developing an electrostatic image formed on the image carrier, and a second developer carrier that carries and conveys the developer to a second developing region for developing the electrostatic image formed on the image carrier. The second developer carrier is disposed opposite to the first developer carrier, and the developer that has passed through the first developing region is transferred from the first developer carrier. A regulating member disposed opposite to the first developer carrier and regulating the amount of developer carried on the first developer carrier, a first chamber for supplying the developer to the first developer carrier, a second chamber disposed opposite to the second developer carrier and recovering the developer that has passed through the second developing region from the second developer carrier, a partition wall partitioning the first chamber and the second chamber, a first conveying screw disposed in the first chamber and conveying the developer in a first direction, and a second conveying screw disposed in a first region of the second chamber and conveying the developer in a second direction opposite to the first direction. And a third conveying screw disposed in a second region of the second chamber horizontally adjacent to the first region of the second chamber and conveying the developer in a third direction opposite to the second direction. A developing device having: a first driving unit for rotationally driving the first conveying screw and the second conveying screw; a second driving unit that rotationally drives the first developer carrier, the second developer carrier, and the third transport screw; a control unit that controls the first driving unit to rotationally drive the first transport screw and the second transport screw, and controls the second driving unit to rotationally drive the first developer carrier, the second developer carrier, and the third transport screw; and includes when the ratio of the rotational speed (Vsc) of the first transport screw and the second transport screw when the first driving unit rotationally drives the first transport screw and the second transport screw to the rotational speed (Vsl) of the first developer carrier and the second developer carrier when the second driving unit rotationally drives the first developer carrier and the second developer carrier is defined as Vsc / Vsl, and the rotational speed (Vsc3) of the third transport screw when the second driving unit rotationally drives the third transport screw to the rotational speed (Vsl) of the first developer carrier and the second developer carrier when the second driving unit rotationally drives the first developer carrier and the second developer carrier is defined as Vsc3 / Vsl, the control unit is capable of executing a mode of controlling the first driving unit and the second driving unit such that Vsc / Vsl in a non-image forming period when the image forming operation is not being performed is smaller than Vsc / Vsl in an image forming period when the image forming operation is being performed, and in the mode, Vsc3 / Vsl in the non-image forming period is equal to Vsc3 / Vsl in the image forming period An image forming apparatus characterized by this.

12. In the mode, the rotational speeds of the first transport screw and the second transport screw in the non-image forming period are slower than the rotational speeds of the first transport screw and the second transport screw in the image forming period The image forming apparatus according to claim 11, characterized by this.

13. In the mode, the rotational speeds of the first transport screw and the second transport screw in the non-image forming period are zero The image forming apparatus according to claim 11, characterized by this.

14. The control unit is capable of executing the mode each time an image is formed on a predetermined number of recording materials in the image forming operation The image forming apparatus according to any one of claims 11 to 13, characterized by this.

15. The image forming apparatus further comprises a temperature sensor for detecting the temperature inside the developing device, wherein the control unit, when the temperature inside the developing device detected by the temperature sensor is a first temperature, the mode can be executed each time an image is formed on a first number of recording materials in the image forming operation, when the temperature inside the developing device detected by the temperature sensor is a second temperature higher than the first temperature, the mode can be executed each time an image is formed on a second number of recording materials less than the first number in the image forming operation The image forming apparatus according to any one of claims 11 to 14, characterized in that.

16. The control unit, when the average printing rate is a first ratio, the mode can be executed each time an image is formed on a first number of recording materials in the image forming operation, when the average printing rate is a second ratio lower than the first ratio, the mode can be executed each time an image is formed on a second number of recording materials less than the first number in the image forming operation The image forming apparatus according to any one of claims 11 to 14, characterized in that.

17. The first driving unit is a first motor for rotationally driving the first conveying screw and the second conveying screw, The second driving unit is a second motor for rotationally driving the developer carrier and the third conveying screw The image forming apparatus according to any one of claims 11 to 16, characterized in that.

18. The regulating member is located vertically above the rotation center of the developer carrier The image forming apparatus according to any one of claims 11 to 17, characterized in that.

19. The rotation center of the first conveying screw is located vertically above the rotation center of the developer carrier The image forming apparatus according to any one of claims 11 to 18, characterized in that.

20. The bottom of the first chamber is located vertically above the bottom of the second chamber The image forming apparatus according to any one of claims 11 to 19, characterized in that.

Images