JP2010113030A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which supplied toner is quickly conveyed to a developing device when much toner is consumed, and which does not cause deterioration in image density and fogging even when images which require little toner consumption are consecutively printed on many sheets. <P>SOLUTION: The image forming apparatus 100 includes: the developing device including a first conveying member 112 conveying developer in a predetermined direction by rotating, and a second conveying member 113 conveying the developer in a direction reverse to the predetermined direction by rotating; a toner supply device supplying the toner in an amount in accordance with the toner consumption in the developing device to the developing device; and a conveying member drive motor controller 120 controlling rotational speed of the first conveying member 112 and the second conveying member 113 based on feature quantities corresponding to the toner consumption or the supply amount of toner supplied to the developing device from the toner supply device. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that visualizes an electrostatic latent image using an electrophotographic system.

  2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses such as copying machines, printers, and facsimiles are known. An electrophotographic image forming apparatus forms an electrostatic latent image on the surface of a photosensitive drum (toner image carrier), and develops the electrostatic latent image by supplying toner to the photosensitive drum by a developing device. The toner image formed on the photosensitive drum by development is transferred to a sheet such as paper, and the toner image is fixed on the sheet by a fixing device.

  In recent years, two-component developers that are excellent in toner charging stability are often used in image forming apparatuses that support full color and high image quality.

  The two-component developer is composed of toner and carrier, and the toner and the carrier are rubbed by stirring them in the developing device, and a properly charged toner is obtained by this friction.

  In the developing device, the charged toner is supplied to the surface of the developing roller, for example, and moves to an electrostatic latent image formed on the photosensitive drum by electrostatic attraction. As a result, a toner image based on the electrostatic latent image is formed on the photosensitive drum.

  Further, recently, there has been a demand for speeding up and downsizing of an image forming apparatus, and there is a need to quickly and sufficiently charge the two-component developer and to carry the two-component developer quickly.

  In view of this, in the image forming apparatus, a circulation type developing device is employed in order to instantly disperse the replenished toner in the two-component developer and impart an appropriate charge amount. The circulation type developing device includes a two-component developer conveyance path that is a path through which the two-component developer is circulated and a two-component developer conveyance that conveys the two-component developer while stirring in the two-component developer conveyance path. And a member.

For example, Patent Document 1 discloses that a supply toner can be immediately dispersed in a developer without applying an excessive force to the developer, and an appropriate charge amount can be applied. A developing device having a high ability to uniformize the toner density of the developer in the section is described. That is, a developer conveying path for circulating the developer is provided in the developer accommodating portion for accommodating the two-component developer in which the toner and the carrier are mixed, and a feed screw-like shape is provided in the developer conveying path. A developer conveying member having a plurality of wing bodies is provided, and a mesh screen member is attached between the wing bodies. By rotating the developer conveying member, the developer is conveyed, and the developer passes through the mesh-like screen member a plurality of times, and the developer is stirred, and appropriate charging is performed by friction between the toner and the carrier. It is.
Japanese Patent Laid-Open No. 10-63081 (published March 6, 1998)

  However, in the above-described circulation type developing device, when a large number of images having a low printing rate are continuously printed, the two-component developer continues to be circulated and conveyed for a long time without supplying new toner. In this case, there is a problem that the flowability of the two-component developer is extremely lowered by embedding the external additive of the toner in the toner, and the image density is lowered (hereinafter also referred to as a “debemoco phenomenon”). . This problem is particularly noticeable in color toners that use soft binder resins.

  On the other hand, when a large amount of toner is consumed, it is necessary to quickly transport the toner to the development area.

  The present invention has been made in view of the above-described conventional problems. When a large amount of toner is consumed, the replenished toner can be quickly conveyed to the developing device, and an image with low toner consumption can be obtained. An object of the present invention is to provide an image forming apparatus free from a decrease in image density and fog when a large number of sheets are printed continuously.

  In order to solve the above problems, an image forming apparatus of the present invention includes a developing tank in which first and second transport paths for transporting a developer containing toner and a carrier are formed, and a first transport path. A first conveyance member that is provided and rotates to convey the developer in a predetermined direction; and a second conveyance member that is provided in the second conveyance path and conveys the developer in a direction opposite to the predetermined direction by rotation. And a developer carrying member that carries the developer in the second conveyance path and supplies toner contained in the developer to the photoreceptor, and the developer tank communicates the first and second conveyance paths. A developing device having a first communication path, a second communication path formed on the opposite side of the first communication path and communicating with the first and second transport paths, and A toner supply amount corresponding to the toner consumption amount is supplied to the developing device. -Rotational speed of the first conveying member and the second conveying member based on a characteristic amount corresponding to the replenishing device and the toner consumption amount or the toner replenishing amount replenished from the toner replenishing device to the developing device. A conveyance member rotation control unit for controlling the rotation.

  According to the above configuration, the rotational speeds of the first transport member and the second transport member are controlled based on the feature amount corresponding to the toner consumption amount in the developing device or the toner replenishment amount replenished to the developing device. be able to. Here, the toner replenishing device replenishes the developing device with an amount of toner corresponding to the toner consumption. That is, the toner replenishment amount varies according to the toner consumption amount. Therefore, the rotation speeds of the first transport member and the second transport member can be changed to a speed that is optimal for the toner replenishment amount. As a result, when a large amount of toner is consumed, the replenished toner can be quickly conveyed to the developing device, and even when a large number of images with low toner consumption are continuously printed, image density is reduced or fogged. It is possible to provide an image forming apparatus having no image.

  For example, it can be controlled to increase the rotation speed as the feature amount increases. That is, when the feature amount is relatively large (that is, when the toner replenishment amount is relatively large), the rotational speeds of the first transport member and the second transport member are relatively increased, and the feature amount is relatively If it is small (that is, when the toner replenishment amount is relatively small), the rotational speeds of the first transport member and the second transport member can be made relatively slow. Thus, when a large amount of toner is consumed and a large amount of toner is replenished, the rotational speed of the first transport member and the second transport member is increased, so that the replenished toner can be transported to the developing device quickly. it can. On the other hand, when the toner is transported for a long time with a small amount (or zero) of toner replenishment, such as printing a large number of images with low toner consumption, the first transport member and the second transport member Since the rotation speed becomes slow, it is possible to prevent a decrease in toner fluidity, and as a result, it is possible to suppress a decrease in image density and fogging.

  Further, in the image forming apparatus of the present invention, the toner replenishing device includes a toner storage container in which a toner discharge port is formed, and a screw auger disposed in the toner storage container and transporting the toner to the toner discharge port. It is preferable that the conveyance member rotation control unit uses a rotation number of the toner discharge member as the feature amount.

  According to the above configuration, the toner replenishing device can discharge the toner only by rotating the toner discharging member that is a screw auger. Further, the amount of toner replenished from the toner replenishing device is proportional to the rotation speed of the toner discharging member. Therefore, the rotation speed of the toner discharge member is one of the feature amounts corresponding to the toner replenishment amount, and the conveyance member rotation control unit uses the rotation speed of the toner discharge member as the feature amount. By using the rotation speed of the toner discharge member, the rotation speeds of the first conveyance member and the second conveyance member can be changed to optimum values at the timing when the toner is replenished from the toner replenishing device. Further, since the rotation speed of the toner discharge member is proportional to the toner replenishment amount, even in process control where the toner consumption amount and the toner replenishment amount are not exactly equal, the first conveyance member and the second conveyance member are The toner can be rotated at a rotation speed optimum for the toner replenishment amount.

  Further, in the image forming apparatus of the present invention, the developing device includes a toner concentration detecting member that detects a toner concentration in the developing tank, and the conveying member rotation control unit uses a predetermined threshold as the feature amount. It is preferable to use a value obtained by subtracting the toner density value measured by the toner density detecting member.

  According to the above configuration, the conveyance member rotation control unit uses a value obtained by subtracting the toner density value measured by the toner density detecting member from the predetermined threshold value as the feature amount. Here, a value obtained by subtracting the toner density value measured by the toner density detecting member from the predetermined threshold corresponds to the toner consumption amount in the developing device. Since the toner replenishing device replenishes the developing device with an amount of toner corresponding to the toner consumption amount, the value obtained by subtracting the toner density value measured by the toner density detecting member from the predetermined threshold value indirectly determines the toner replenishing amount. Corresponding. Therefore, the first transport member and the second transport member can be rotated at a rotation speed that is optimal for the toner replenishment amount. By using the feature amount, there is no need to provide a component for detecting the toner replenishment amount.

  Furthermore, the image forming apparatus of the present invention further includes a pixel count unit that obtains the number of print dots from the image data to be printed, and the transport member rotation control unit uses the print dot obtained by the pixel count unit as the feature amount. It is preferable to use a number.

  According to said structure, a conveyance member rotation control part uses the number of printing dots as said feature-value. Here, the number of print dots means the number of pixels to which toner is attached, and corresponds to the amount of toner consumed in the developing device. Then, since the toner replenishing device replenishes the developing device with an amount of toner corresponding to the toner consumption, the number of print dots indirectly corresponds to the toner replenishing amount. Therefore, the first transport member and the second transport member can be rotated at a rotation speed that is optimal for the toner replenishment amount. By using the feature amount, there is no need to provide a component for detecting the toner replenishment amount.

  Furthermore, in the image forming apparatus of the present invention, the carrier is a magnetic carrier, and the developing tank has a toner replenishing port for receiving the toner replenished by the toner replenishing device in the first transport path. The developing device includes an electromagnet for forming a magnetic brush made of the magnetic carrier on the first transport path on the first transport path on the predetermined direction side of the toner supply port. It is preferable to provide an electromagnet control unit that supplies current to the electromagnet at a timing when toner is replenished by the replenishing device.

  According to the above configuration, the replenished toner is captured by the magnetic brush and sufficiently mixed with the remaining developer. Further, the magnetic brush is formed at a timing when toner is supplied, and is not formed when toner is not supplied. Therefore, the developer is not unnecessarily stressed by the magnetic brush.

  Furthermore, in the image forming apparatus of the present invention, it is preferable that the first transport member and the second transport member are screw augers.

  According to the above configuration, even if the rotation speeds of the first transport member and the second transport member are increased, the developer can be transported with a relatively small stress, and the developer is hardly worn or deteriorated.

  Furthermore, in the image forming apparatus of the present invention, the transport member rotation control unit is configured so that the ratio between the maximum rotation speed and the minimum rotation speed of the first and second transport members is 1.5 or more and 3 or less. It is preferable to control the rotation speeds of the first transport member and the second transport member.

  According to the above configuration, by setting the ratio between the maximum rotation speed and the minimum rotation speed to 1.5 or more, a large number of images with low toner consumption are continuously generated while suppressing the wear and deterioration of the developer more effectively. Thus, even when printing is performed, it is possible to more effectively suppress image density reduction and fogging. In addition, by setting the ratio of the maximum rotation speed and the minimum rotation speed to 3 or less, a change in toner charge amount can be reduced, and the occurrence of uneven image density can be more effectively prevented.

  According to the present invention, the rotation speeds of the first transport member and the second transport member can be changed to a speed optimal for the toner replenishment amount. As a result, when a large amount of toner is consumed, the replenished toner can be quickly conveyed to the developing device, and even when a large number of images with low toner consumption are continuously printed, image density is reduced or fogged. It is possible to provide an image forming apparatus having no image.

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

(Overall configuration of image forming apparatus)
First, an image forming apparatus according to the present invention will be described.

  FIG. 3 is an explanatory diagram showing the overall configuration of the embodiment of the image forming apparatus 100 according to the present invention.

  The image forming apparatus 100 converts a multicolor or monochromatic image as a visible image on a predetermined sheet (recording paper) based on image data included in an input command such as image data transmitted from the outside via a communication network or the like. To form. As shown in FIG. 3, the image forming apparatus 100 according to the present embodiment charges the surfaces of the photosensitive drums 3a to 3d and the photosensitive drums 3a to 3d corresponding to the image carrier on which a latent image is formed. Charger (charging roller) 5a to 5d, exposure unit (exposure device) 1 for forming an electrostatic latent image on the surface of photoreceptor drums 3a to 3d, and supply of toner to the electrostatic latent image on the surface of photoreceptor drums 3a to 3d Developing devices 2a to 2d for forming toner images, toner replenishing devices 22a to 22d for supplying toner to the developing devices 2a to 2d, and intermediate transfer belts for transferring the toner images on the surfaces of the photosensitive drums 3a to 3d to a recording medium. A unit (transfer device) 8; a fixing unit (fixing device) 12 for fixing a toner image on a recording medium; cleaner units 4a to 4d for removing and collecting toner; paper transport paths S and S1, and a paper feeding cassette 1 , Manual paper feed tray 20, a paper discharge tray 15 or the like. A scanner or the like may be provided above the image forming apparatus 100.

  The image data of the color image handled in the image forming apparatus 100 of the present embodiment is image data corresponding to the four hues of black (K), cyan (C), magenta (M), and yellow (Y). A visible image is formed using a color image corresponding to a color image using each color. Accordingly, the developing devices 2a to 2d, the photosensitive drums 3a to 3d, the charging rollers 5a to 5d, and the cleaner units 4a to 4d are provided in each of four units so as to form four types of latent images corresponding to the respective colors. Yes. In other words, four image forming stations (image forming units) each including a developing device, a photosensitive drum, a charger, and a cleaner unit are provided. The four image forming stations are arranged in a line in the order of four colors along the moving direction of the intermediate transfer belt 7 (see arrow B in FIG. 3). The symbols a to d correspond to a for black, b for cyan, c for magenta, and d for yellow.

  The photosensitive drums 3a to 3d are substantially cylindrical image carriers, and are controlled to rotate in a predetermined direction by a driving unit and a control unit (not shown). The photoconductive drums 3a to 3d are configured by forming a photoconductive layer on a base material. For example, a metal drum made of aluminum or the like is used as a base material, and a photoconductive layer such as amorphous silicon (a-Si), selenium (Se), or an organic photo semiconductor (OPC) is formed in a thin film on the outer peripheral surface thereof. ing. Note that the configuration of the photosensitive drums 3a to 3d is not particularly limited to the above-described configuration.

  The charging rollers 5a to 5d are contact type chargers that uniformly charge the surfaces of the photosensitive drums 3a to 3d to a predetermined potential. In this embodiment, as shown in FIG. 3, a contact type roller type is used as the charging device, but instead of the charging rollers 5a to 5d, a contact brush type charger or a non-contact charger is used. A type charger may also be used.

  The exposure unit 1 is a laser scanning unit (LSU) that is disposed below the photosensitive drums 3a to 3d and includes a laser irradiation unit and a reflection mirror. However, in addition to the laser scanning unit, the exposure unit 1 may be an EL (electroluminescence) in which light emitting elements are arranged in an array or an LED writing head. The exposure unit 1 exposes the charged photosensitive drums 3a to 3d according to the input image data, thereby forming electrostatic latent images corresponding to the image data on the surfaces of the photosensitive drums 3a to 3d.

  The developing devices 2a to 2d are for developing (developing) the electrostatic latent images formed on the photosensitive drums 3a to 3d with toner. Each of the developing devices 2a to 2d contains toner of each hue of black, cyan, magenta, and yellow, and an electrostatic latent image of each hue formed on each of the photosensitive drums 3a to 3d is black. The toner images are visualized as cyan, magenta, and yellow toner images. Above the developing devices 2a to 2d, toner transfer mechanisms 102a to 102d and toner replenishing devices 22a to 22d are respectively arranged correspondingly.

  The toner replenishing devices 22a to 22d are arranged above the developing devices 2a to 2d and store unused toner (powder toner) (details will be described later).

  The intermediate transfer belt unit 8 is disposed above the photosensitive drums 3a to 3d, and includes intermediate transfer rollers 6a to 6d, an intermediate transfer belt 7, an intermediate transfer belt driving roller 71, an intermediate transfer belt driven roller 72, and an intermediate transfer belt tension. A mechanism 73, an intermediate transfer belt cleaning unit 9, and a transfer roller 11 are provided. The intermediate transfer belt 6, the intermediate transfer belt drive roller 71, the intermediate transfer belt driven roller 72, and the intermediate transfer belt tension mechanism 73 stretch the intermediate transfer belt 7 and rotationally drive the intermediate transfer belt 7 in the direction of arrow B in FIG. It is something to be made.

  The intermediate transfer roller 6 is rotatably supported by an intermediate transfer roller mounting portion in the intermediate transfer belt tension mechanism 73 of the intermediate transfer belt unit 8. The intermediate transfer roller 6 is applied with a transfer bias having a polarity opposite to the charging polarity of the toner in order to transfer the toner images carried on the surfaces of the photosensitive drums 3 a to 3 d onto the intermediate transfer belt 7. As a result, the toner images of the respective colors formed on the photosensitive drums 3 a to 3 d are sequentially transferred onto the outer peripheral surface of the intermediate transfer belt 7, and a full-color toner image is formed on the outer peripheral surface of the intermediate transfer belt 7. .

  The intermediate transfer roller 6 is formed with a metal (for example, stainless steel) shaft having a diameter of, for example, 8 to 10 mm as a base, and the surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, the intermediate transfer roller 6 can uniformly apply a high voltage to the intermediate transfer belt 7. In this embodiment, a roller-shaped transfer electrode (intermediate transfer roller 6) is used as the transfer electrode, but a brush or the like can also be used.

  The intermediate transfer belt 7 is provided so as to be in contact with each of the photosensitive drums 3a to 3d. A color toner image (multicolor toner image) is formed on the intermediate transfer belt 7 by sequentially superimposing and transferring the toner images of the respective color components formed on the photosensitive drums 3a to 3d. The intermediate transfer belt 7 is formed in an endless shape using a film having a thickness of, for example, about 100 μm to 150 μm.

  Transfer of the toner image from the photosensitive drums 3 a to 3 d to the intermediate transfer belt 7 is performed by the intermediate transfer roller 6 in contact with the back side of the intermediate transfer belt 7. A high voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 6 in order to transfer the toner image.

  As described above, the electrostatic latent images on the respective photosensitive drums 3a to 3d are visualized with toners corresponding to the color components to be respectively toner images, and these toner images are superimposed and laminated on the intermediate transfer belt 7. The As described above, the stacked toner images are moved to a contact position (transfer portion) between the conveyed paper and the intermediate transfer belt 7 by the rotation of the intermediate transfer belt 7, and the transfer roller disposed at this position is moved. 11 is transferred onto the paper. In this case, the intermediate transfer belt 7 and the transfer roller 11 are pressed against each other at a predetermined nip, and a voltage for transferring the toner image onto the sheet is applied to the transfer roller 11. This voltage is a high voltage having a polarity (+) opposite to the charging polarity (−) of the toner.

  In order to obtain the nip constantly, either the transfer roller 11 or the intermediate transfer belt drive roller 71 is made of a hard material such as metal, and the other is a soft material such as an elastic roller (elastic rubber roller or foamable resin roller). Etc.).

  The toner adhering to the intermediate transfer belt 7 due to the contact between the intermediate transfer belt 7 and the photosensitive drum 3 and the toner image remaining on the intermediate transfer belt 7 without being transferred when the toner image is transferred from the intermediate transfer belt 7 to the sheet. The toner is removed and collected by the intermediate transfer belt cleaning unit 9 because it causes toner color mixing in the next step.

  The cleaner unit 4 removes and collects the toner remaining on the surfaces of the photosensitive drums 3a to 3d with a lubricant or the like after the development and image transfer processes.

  The intermediate transfer belt cleaning unit 9 is provided with a cleaning blade (cleaning member) that contacts the intermediate transfer belt 7. The portion of the intermediate transfer belt 7 that is in contact with the cleaning blade is supported by the intermediate transfer belt driven roller 72 from the back side.

  The paper feed cassette 10 is for accumulating sheets (for example, recording paper) used for image formation, and is provided below the image forming unit and the exposure unit 1. On the other hand, a paper discharge tray 15 provided in the upper part of the image forming apparatus 100 is for placing printed sheets face down.

  When the paper fed from the paper feed cassette 10 or the manual paper feed tray 20 passes between the transfer roller 11 and the intermediate transfer belt 11, the charge polarity (−) of the toner on the transfer roller 11 is opposite to that of the toner. A high voltage (+) is applied. As described above, the electrostatic latent images on the respective photosensitive drums 3 a to 3 d are visualized with toners corresponding to the respective hues to become toner images, and these toner images are stacked on the intermediate transfer belt 7. The Thereafter, the laminated toner images are moved to a contact position between the conveyed paper and the intermediate transfer belt 7 by the rotation of the intermediate transfer belt 7, and the intermediate transfer belt 11 is moved by the transfer roller 11 disposed at this position. A toner image is transferred from the outer peripheral surface of the belt 7 onto the sheet.

  Further, the image forming apparatus 100 is provided with a sheet conveyance path S for guiding the sheet of the paper feed tray 10 and the sheet of the manual feed tray 20 to the paper discharge tray 15 via the transfer unit and the fixing unit 12. . The transfer unit is located between the intermediate transfer belt driving roller 71 and the transfer roller 11.

  In the sheet conveyance path S, pickup rollers 16a and 16b, a registration roller 14, a transfer unit, a fixing unit 12, conveyance rollers 25a to 25h, and the like are arranged.

  The pickup roller 16 a is a pull-in roller that is provided at the end of the paper feed tray 10 and supplies sheets one by one from the paper feed tray 10 to the sheet conveyance path S. The pickup roller 16 b is a drawing roller that is provided near the manual feed tray 20 and supplies sheets from the manual feed tray 20 to the sheet conveyance path S one by one. The conveyance roller 25 is a small roller for promoting and assisting conveyance of the sheet, and is provided along the sheet conveyance path S.

  The fixing unit 12 includes a heat roller 81, a pressure roller 82, and the like. The heat roller 81 and the pressure roller 82 rotate with the sheet interposed therebetween. The heat roller 81 is controlled by a control unit (not shown) so as to have a predetermined fixing temperature. This control unit controls the temperature of the heat roller 81 based on a detection signal from a temperature detector (not shown).

  The heat roller 81 heat-presses the sheet together with the pressure roller 82 to melt, mix, and press the color toner images transferred to the sheet, and heat-fix the sheet. The sheet on which the multicolor toner image (each color toner image) is fixed is conveyed to the reverse sheet discharge path of the sheet conveyance path S by the plurality of conveyance rollers 25 and is reversed (the multicolor toner image is on the lower side). Are discharged onto the paper discharge tray 15.

  The registration roller 14 temporarily holds the sheet fed from the sheet feeding cassette 10 or the manual sheet feeding tray 20 used when printing a small number of sheets and is transported through the sheet transport path S1, or the sheet. The sheet conveyed via the conveyance path S is guided between the transfer roller 11 and the intermediate transfer belt 7 at a timing synchronized with the rotation of the intermediate transfer belt 7. Therefore, the registration roller 14 stops rotating when the operation of the photosensitive drum and the intermediate transfer belt 7 is started, and the sheet fed or conveyed prior to the rotation of the intermediate transfer belt 7 has the front end at the registration roller 14. 14, the movement in the paper transport path S is stopped. Thereafter, the registration roller 14 starts rotating at a timing at which the front end portion of the sheet and the front end portion of the toner image formed on the intermediate transfer belt 7 face each other at a position where the transfer roller 11 and the intermediate transfer belt 7 are in pressure contact with each other. To do.

  Here, in the case of single-sided printing, the sheet transport path S is a path for transporting a sheet of paper from the paper feed cassette 10 or the manual paper feed tray 20 to the paper discharge tray 15, and the sheet transport path S1 is a double-sided sheet. In the case of printing, this is a route through which the back side of the paper printed on one side is printed.

  More specifically, in the case of single-sided printing, the sheet conveyed from the paper feed tray 10 is conveyed to the registration roller 14 by the conveyance roller 25a in the sheet conveyance path S, and the leading edge of the sheet and the intermediate transfer belt 7 are conveyed by the registration roller 14. The toner image is conveyed to a transfer portion (a contact position between the transfer roller 11 and the intermediate transfer belt 7) at a timing when the leading end of the stacked toner images is aligned. In the transfer portion, a toner image is transferred onto the sheet, and this toner image is fixed on the sheet by the fixing unit 12. Thereafter, the sheet is discharged onto the discharge tray 15 from the discharge roller 25c via the conveyance roller 25b.

  Further, the sheet conveyed from the manual feed tray 20 is conveyed to the registration roller 14 by a plurality of conveying rollers 25 (25f, 25e, 25d). Subsequent sheet conveyance operations are discharged to the sheet discharge tray 15 through a process similar to that for the sheets supplied from the sheet feed tray 10 described above.

  On the other hand, in the case of double-sided printing, the trailing edge of the sheet that has completed single-sided printing and passed through the fixing unit 12 as described above is chucked by the paper discharge roller 25c. Next, the sheet is guided to the conveying rollers 25g and 25h by the reverse rotation of the paper discharge roller 25c, and after the printing on the back surface is again performed through the registration roller 14, it is discharged to the paper discharge tray 15.

(Structure of toner supply device)
Hereinafter, the structure of toner replenishing devices 22a to 22d (hereinafter denoted by reference numeral 22) according to the embodiment of the present invention will be described with reference to FIGS.

  The toner replenishing device 22 is disposed on the upper side of the developing devices 2a to 2d (refer to FIG. 3 and denoted by reference numeral 2 below), and stores unused toner (powder toner).

  FIG. 4 is a cross-sectional view showing the configuration of the toner replenishing device 22 shown in FIG. As shown in FIG. 4, the toner replenishing device 22 includes a toner container 121, a toner discharge member 122 and a toner stirring member 125 disposed in the toner container 121.

  The toner storage container 121 is a substantially semi-cylindrical container member having an internal space for storing toner, and rotatably supports a toner stirring member 125 and a toner discharge member 122 disposed therein. Yes. In the toner container 121, a toner discharge port 123 is formed below the toner discharge member 122, and the toner is disposed between the inside of the toner container 121 in which the toner stirring member 125 is disposed and the toner discharge member 122. A discharge member partition wall 124 is provided.

  The toner discharge member partition wall 124 allows the toner pumped up by the toner stirring member 125 to be held in an appropriate amount around the toner discharge member 122.

  The toner discharge port 123 is a substantially rectangular opening provided from the central portion in the axial direction, and is disposed at a position facing the upper portion of the toner transfer mechanisms 102a to 102d (see FIG. 3 and denoted by reference numeral 102 below). . In order to transport the toner collected around the toner discharge member 122 to the toner discharge port 123 more quickly, the toner discharge port 123 is preferably formed below the center of the toner discharge member 122.

  FIG. 5 is a cross-sectional view of the toner discharge member 122 shown in FIG. The toner discharge member 122 is rotated to discharge the toner in the toner container 121 from the toner discharge port 123 and supply the toner to the developing device 2 via the toner transfer mechanism 102.

  As shown in FIG. 5, the toner discharge member 122 includes a first toner transfer blade 122a and a second toner transfer blade 122b, and a toner discharge member that rotates integrally with the first toner transfer blade 122a and the second toner transfer blade 122b. The toner discharging member rotating shaft 122c is configured to be driven to rotate by a toner discharging member driving motor 129. The screw auger includes a rotating shaft 122c. Here, the first toner conveying blade 122a and the second toner conveying blade 122b are wound in opposite directions, and the rotation of the toner discharging member rotating shaft 122c is controlled by the toner discharging member driving motor 129. The toner can be conveyed from both ends in the axial direction of the toner discharge member 122 toward the toner discharge port 123.

  The structure of the toner discharge member 122 is determined by the position where the toner discharge port 123 is formed. For example, when the toner discharge port 123 is formed below or near the center of the toner discharge member 122, the toner discharge member 122 is wound in the opposite direction with the toner discharge port 123 as a boundary as shown in FIG. It is preferable to employ a screw auger having blades. When the toner discharge port 123 is formed below either end of the toner discharge member 122, it is preferable to use a screw auger having blades wound in the same direction.

  The toner discharge member 122 that is a screw auger has a larger amount of toner discharge per unit time than, for example, a sponge roller. Therefore, a large amount of toner can be discharged in a short time.

  Further, the amount of toner discharged from the toner discharge port 123 changes according to the number of rotations of the toner discharge member 122. That is, the toner discharge amount when the toner discharge member 122 is rotated three times is approximately three times the toner discharge amount when the toner discharge member 122 is rotated once. Therefore, the toner discharge amount can be controlled by controlling the rotation speed of the toner discharge member 122.

  The toner stirring member 125 rotates around the toner stirring member rotating shaft 125 a to pump up the toner in the toner storage container 121 and stir the toner stored in the toner storage container 121 to the toner discharge member 122. It is a plate-like member to be conveyed, and is provided with a toner scooping member 125b at the tip. The toner pumping member 125 b is made of a flexible polyethylene terephthalate (PET) sheet and is attached to both ends of the toner stirring member 125.

  In FIG. 4, the toner stirring member 125 rotates in the arrow direction R, whereby the toner is stirred and pumped up toward the toner discharge member 122. At this time, the toner pumping member 125 b rotates while sliding and deforming the inner wall 121 a of the toner container 121 due to its flexibility, and supplies the toner to the toner discharge member 122. Then, the toner discharge member 122 guides the supplied toner to the toner discharge port 123 by its rotation.

  Further, as shown in FIG. 5, the toner replenishing device 22 includes a toner discharge member rotation speed detection unit 118 that detects the rotation speed of the toner discharge member 122. Specifically, on the toner discharge member rotation shaft 122c of the toner discharge member 122, a reflection portion that reflects light and a non-reflection portion that does not reflect light are alternately provided. The number of rotations of the toner discharging member 122 is detected by irradiating the axis with light and detecting the reflected light.

  The toner discharge member rotation speed detection unit 118 starts rotation speed detection at a predetermined timing, counts and outputs the rotation speed until the rotation is stopped.

  Note that the toner discharge member rotation speed detection unit 118 may detect the rotation speed of the toner discharge member 122 based on signal data for driving the toner discharge member drive motor 129.

(Developer structure)
Next, the structure of the developing device 2 according to the embodiment of the present invention will be described in detail with reference to FIGS.

  6 is a cross-sectional view showing the configuration of the developing device 2, and FIG. 7 is a cross-sectional view taken along the line A-A 'of FIG.

  6 and 7, the developing device 2 includes a developing tank 111 (111a to 111d in FIG. 3), a first conveying member 112 and a second conveying member 113 installed in the developing tank 111, a developing roller 114, A developer tank cover 115 in which a toner supply port 115 a is formed, a doctor blade 116, a partition plate (partition wall) 117 provided between the first transport member 112 and the second transport member 113, and a toner concentration detection sensor 110. It has.

  The developing tank 111 is a tank for storing a two-component developer including toner received from the toner replenishing device 22 and a carrier (in this embodiment, a magnetic carrier having magnetism), and is disposed in the first tank. The first conveying member 112 and the second conveying member 113 are rotatably supported. The developing tank 111 circulates and conveys the two-component developer therein, and as shown in FIG. 6, the two conveying paths P and Q are separated by a partition plate 117 parallel to the axial direction of the developing roller 114. Is formed. A first transport member 112 is installed in the transport path P, and a second transport member 113 is installed in the transport path Q.

  The developing tank cover 115 is a cover that covers the top of the developing tank 111, and a toner replenishing port 115a for receiving toner on the upper surface near the one end of the conveying path P where the first conveying member 112 is installed. Is formed.

  The first transport member 112 and the second transport member 113 are members for circulating and transporting the toner received from the toner supply port 115 a in the developing tank 111.

  As shown in FIG. 7, the 1st conveyance member 112 is comprised by the screw auger which consists of the 1st rotating shaft 112b which rotates integrally with the helical 1st conveyance blade 112a and the 1st conveyance blade 112a. By controlling the rotation of the first rotating shaft 112b by the first conveying member drive motor 119a connected to one end of the first rotating shaft 112b, the two-component developer is transferred from one end of the first rotating shaft 112b to the other end. It can be conveyed while stirring.

  The 2nd conveyance member 113 is comprised by the screw auger which consists of the 2nd rotating shaft 113b rotated integrally with the helical 2nd conveyance blade 113a and the 2nd conveyance blade 113a. By controlling the rotation of the second rotating shaft 113b by the second conveying member drive motor 119b connected to one end of the second rotating shaft 113b, the two-component developer is stirred from one end of the second rotating shaft 113b to the other end. It can be transported.

  In this embodiment, the 1st conveyance blade 112a and the 2nd conveyance blade 113a are wound by the same shape, and the 1st rotating shaft 112b and the 2nd rotation are carried out by the 1st conveyance member drive motor 119a and the 2nd conveyance member drive motor 119b, respectively. By controlling the rotation direction of the shaft 113b in the reverse direction, the toner can be conveyed in a predetermined direction. That is, the first transport member 112 and the second transport member 113 transport the two-component developer in the opposite directions while stirring.

  Of course, even if the first conveying blade 112a and the second conveying blade 113a are wound in opposite directions, the rotational directions of the first rotating shaft 112b and the second rotating shaft 113b are controlled in the same direction, so that The same effect is obtained.

  Here, for easy understanding of the explanation, in FIG. 7, the developing tank 111 is formed substantially parallel to the axial direction of the first rotating shaft 112b on the side where the first conveying member 112 is disposed. The wall is the developing tank wall 111a, and the wall on the side where the second conveying member 113 is disposed is formed substantially parallel to the axial direction of the second rotating shaft 113c, that is, the wall facing the developing tank wall 111a. Is defined as a developing tank wall 111b. Further, a wall formed close to the first transport member drive motor 119a and the second transport member drive motor 119b, that is, a wall formed substantially perpendicular to the axial direction of the first rotation shaft 112b and the second rotation shaft 113b is formed in the developing tank. The wall 111c is defined as a developing tank wall 111d. The wall formed on the opposite side of the developing tank wall 111c and facing the developing tank wall 111c is referred to as a developing tank wall 111d.

  As shown in FIG. 7, between the first conveying member 112 and the second conveying member 113, both the shafts (the first rotating shaft 112 b and the second rotating shaft 113 b) are extended, and both ends are One partition plate 117 spaced from the developing tank wall 111c and the developing tank wall 111d by a predetermined distance is disposed. Accordingly, in the developing tank 111, the first communicating path a formed on the developing tank wall 111c side and formed by a gap between the developing tank wall 111c side and the partition plate 117, and the developing tank wall 111d side is formed. A second communication path b formed by a gap between the wall 111d side and the partition plate 117 is formed. In addition, the 1st conveyance member 112 and the 2nd conveyance member 113 are mutually parallel so that the mutual peripheral surfaces may oppose through the partition plate 117 arrange | positioned between both. So that they are parallel.

  Further, when the two-component developer is transported in the developing tank 111, the two-component developer is stirred and transported by the first transport member 112 and the second transport member 113. The direction of conveyance from the second communication path b to the first communication path a by the first conveyance member 112 is indicated by an arrow X, which is opposite to the direction of the arrow X. The direction of conveyance to the communication path b will be described with an arrow Y.

  More specifically, the transport path of the two-component developer in the developing tank 111 is as follows.

  That is, the toner received from the toner replenishing port 115a is mixed and stirred with the carrier in the developing tank 111 by the first conveying member 112 to become a two-component developer. The two-component developer reaches the first communication path a via the conveyance path P along the direction of the arrow X, passes through the first communication path a, and is stirred and conveyed along the conveyance path Q along the direction of the arrow Y. Is done. Then, the two-component developer reaches the second communication path b, passes through the second communication path b, and is conveyed again by the conveyance path P.

  Therefore, in the developing tank 111, the two-component developer is transferred between the transport path P, the first communication path a, the transport path Q, and the second communication path b, and the transport path P → the first communication path a → the transport path Q →. A path for circulating and conveying is formed in the order of the second communication path b → the conveying path P.

  The developing roller 114 is a magnet roller that is disposed in the developing tank 111 and is driven to rotate about an axis by a driving unit (not shown), and conveys the two-component developer in the developing tank 111 to the photosensitive drum 3. Is for. The developing roller 114 is provided so as to face the photosensitive drum 3 and be separated from the photosensitive drum 3 with a gap. The two-component developer conveyed by the developing roller 114 comes into contact with the photosensitive drum 3 at the closest portion, and develops (develops) the electrostatic latent image formed on the surface of the photosensitive drum 3. A contact area between the developing roller 114 and the photosensitive drum 3 is a developing nip portion. In the developing nip portion, a developing bias voltage is applied to the developing roller 114 from a power source (not shown) connected to the developing roller 114, and the developing roller The toner is supplied from the two-component developer on the surface 114 to the electrostatic latent image on the surface of the photosensitive drum 3.

  Then, while the two-component developer is being conveyed via the conveyance path Q, the developing roller 114 rotates and is carried on the surface of the two-component developer, and the toner in the two-component developer thus pumped is exposed to light. It moves to the body drum 3 and is consumed sequentially.

  The doctor blade 116 is a plate-like member that extends parallel to the axial direction of the developing roller 114. One end in the short direction is supported by the developing tank 111 and the other end is the developing roller below the developing roller 114 in the vertical direction. 114 is provided to be separated from the surface with a gap. As the material of the doctor blade 116, stainless steel can be used, but aluminum or synthetic resin can also be used.

  When the position of the transport path P corresponding to the toner replenishing port 115a is set at the beginning of the toner circulation transport path, the toner density detection sensor 110 is attached to the final end of the transport path. That is, as shown in FIG. 7, when the toner supply port 115 a is formed at the end of the transport path P on the second communication path b side, the toner concentration detection sensor 110 is the center of the second transport member 113. Is attached to the bottom surface of the developing tank 111 below the second conveying member 113 on the second communication path b side from the vertical direction.

  This is because the toner density on the final end side is the lowest in the two-component developer circulation conveyance path. By arranging the toner density detection sensor at this position, the toner density decreases in each circulation path. This is because it can be detected immediately.

  The toner concentration detection sensor 110 is provided such that its sensor surface is exposed inside the developing tank 111.

  The toner concentration detection sensor 110 outputs a detected toner concentration measurement value of the circulating conveyance path of the toner every predetermined time (for example, 0.5 to 1 second).

  Note that a general toner concentration detection sensor can be used as the toner concentration detection sensor 110, and examples thereof include a transmitted light detection sensor, a reflected light detection sensor, and a magnetic permeability detection sensor. Among these, a magnetic permeability detection sensor is preferable.

  A power supply (not shown) is connected to the magnetic permeability detection sensor. The power supply applies a drive voltage for driving the magnetic permeability detection sensor and a control voltage for outputting the detection result of the toner density to the control means. Application of a voltage to the magnetic permeability detection sensor by the power source is controlled by the control means. The permeability detection sensor is a type of sensor that receives the control voltage and outputs the toner density detection result as an output voltage value. Basically, the sensitivity near the median value of the output voltage is good. It is used by applying a control voltage to obtain a voltage. Such type of magnetic permeability detection sensors are commercially available, and examples thereof include TS-L, TS-A, TS-K (all are trade names, manufactured by TDK Corporation) and the like.

  In the above-described embodiment, it has been described that the rotation speed of the toner discharge member 122 is detected by the toner discharge member rotation speed detection unit 118 formed in the developing device 2. You may form in the replenishment apparatus 22. FIG. Alternatively, a detection device such as a sensor can be attached to the toner discharge member 122 to directly detect the rotation speed of the toner discharge member 122.

  Further, as shown in FIGS. 6 and 7, a magnetic field is applied to the transport path P on the outer surface of the developing tank 111 in the side wall 111 a of the developing tank forming the transport path P among the walls of the developing tank 111. An electromagnet 130 for forming is attached. The electromagnet 130 is disposed on the X direction side from the toner supply port 115a, and forms a magnetic brush 130 ′ made of a carrier in the conveyance path P by forming a magnetic field in the conveyance path P. It is.

  In the present embodiment, the magnetic brush 130 ′ is formed on the inner surface of the developing tank 111 on the X direction side of the toner supply port 115a in the transport path P, and the formation position of the magnetic brush 130 ′ is close to the toner supply port 115a. The more preferable. This is because as the magnetic brush 130 'is formed closer to the toner supply port 115a, the toner supplied from the toner supply port 115a can be mixed with the developer immediately after the supply.

  The newly supplied unused toner enters the conveyance path P from the toner supply port 115a, and is preferably conveyed by the first conveyance member 112 while sufficiently agitating the developer in the conveyance path P. The magnetic brush 130 ′ has a function of suppressing the fluidity of the developer and the toner lump in the conveyance path P. More specifically, the developer and the toner mass are temporarily blocked by the magnetic brush 130 ′ at the interface between the developer and the toner mass. The toner lump of toner is captured by the magnetic brush 130 ′ until mixed with the developer. As a result, it is possible to suppress the situation where the replenished toner is transported in the transport path P as a lump, and the replenished toner and the developer can be sufficiently mixed. Sufficiently charged toner can be supplied to the developing roller 114. Therefore, problems such as image fogging and toner scattering can be reduced.

  For this reason, in order to sufficiently mix the replenished toner and the developer existing in the past, it is preferable to attach an electromagnet 130 for forming a magnetic field in the transport path P.

  In order to form the magnetic brush 130 ′ in the portion of the side wall 111 a that is in contact with the upper surface of the developer, the electromagnet 130 is attached to the outer wall surface of the side wall 111 a as in the above embodiment, or the partition member 113. It is preferable to attach a magnet to the wall surface.

  Further, as shown in FIG. 6B, the electromagnet 130 can be attached to the surface of the developing tank cover 115 (the outer surface of the developing tank 111). As a result, in the developing device 2, the magnetic brush 130 ′ is moved from the back surface of the developing tank cover 115 (the inner surface of the developing tank 111) to the upper surface of the developer in the transport path P (interface between the developer and the space). It is supposed to be formed. Accordingly, when the developer in the developing tank 111 is replaced, the carrier attached to the developing tank cover 115 can be easily removed when the developing tank cover 115 is removed and the developer is extracted. Therefore, compared with the case where a magnet is provided on the side wall 111a of the developing tank 111 or the partition plate 113, the developer replacement workability is significantly improved.

  The electromagnet 130 is supplied with a current at a timing when toner supply is performed by a toner supply controller described later. Thereby, the magnetic brush is not formed except when the toner is replenished, and the stress of the two-component developer can be suppressed.

(Rotation control of toner discharge member and transport member)
Hereinafter, with reference to FIGS. 1 and 2, rotation control of the toner discharging member 122 of the toner replenishing device 22 and the first conveying member 112 and the second conveying member 113 of the developing device 2 will be described.

  FIG. 1 shows a configuration for controlling the rotation of the toner discharging member 122 of the toner replenishing device 22 and the rotation of the first conveying member 112 and the second conveying member 113 of the developing device 22 in the image forming apparatus 100 according to the present embodiment. FIG.

  As shown in FIG. 1, the image forming apparatus 100 includes a toner replenishment control unit 128 and a conveyance member drive motor control unit 120.

  The toner replenishment control unit 128 is for controlling the toner supply from the toner replenishing device 22 and the toner replenishment amount based on the toner concentration measurement value received from the toner concentration detection sensor 110. That is, the toner replenishment control unit 128 acquires a toner concentration measurement value from the toner concentration detection sensor 110 every predetermined time (for example, 0.5 to 1 second), and the value and a predetermined toner concentration setting value. Make a comparison. If there is a comparison result that the measured toner density is lower than the toner density setting value, the toner discharge that drives and rotates the rotating shaft 122b of the toner discharge member 122 so that the toner is supplied from the toner replenishing device 22 into the developing tank 111. A control signal is sent to the member drive motor 129 to rotate the toner discharge member 122.

  At this time, the toner replenishment control unit 128 determines the toner replenishment amount based on the comparison result between the toner density measurement value received from the toner density detection sensor 110 and the toner density setting value, and controls the rotation speed of the toner discharge member drive motor 129. Thus, the amount of toner supplied from the toner replenishing device 22 to the developing device 2 can be adjusted.

  For example, when the difference between the toner density measurement value received from the toner density detection sensor 110 and the toner density setting value is large, a large amount of toner replenishment is required, and the rotation speed of the toner discharge member drive motor 129 is set large. Thus, a large amount of toner is replenished. Note that the rotation speed is set so that the time required to rotate the set number of rotations falls within the predetermined time (for example, 0.5 to 1 second). That is, the amount of toner replenished within a predetermined time is increased.

  On the contrary, when the difference between the toner density measurement value received from the toner density detection sensor 110 and the toner density setting value is small, a small amount of toner replenishment amount is required, and the rotation speed of the toner discharge member drive motor 129 is set small. By doing so, a small amount of toner is replenished. Also in this case, the rotation speed of the toner discharge member drive motor 129 is set so that the time required for rotation by the set number of rotations falls within the predetermined time (for example, 0.5 to 1 second). . That is, the amount of toner replenished within a predetermined time is reduced.

  The toner replenishment control unit 128 stores a relational expression or table indicating the correspondence between the difference between the toner density measurement value and the toner density setting value and the rotation speed of the toner discharge member drive motor 129. The number of rotations of the toner discharge member drive motor 129 is set based on the equation or the table. That is, the relational expression or table is determined in advance so as to show a correspondence relation in which the rotation speed of the toner discharge member driving motor 129 increases as the difference between the measured toner density value and the toner density setting value increases. .

  When the toner replenishment control unit 128 rotates the set number of rotations, it sends a drive stop signal to the toner discharge member drive motor 129 to stop the rotation of the toner discharge member drive motor 129 and the toner discharge member 122.

  In addition, the toner replenishment control unit 128 controls the toner discharge member drive motor 129 to cause the current to flow through the electromagnet 130 at the timing of rotating the toner discharge member 122, and the magnetic brush 130 on the downstream side of the toner supply port 115 a of the conveyance path P. Let's form. Then, the toner replenishment control unit 128 stops applying the current to the electromagnet 130 at a timing at which the rotation driving of the toner discharge member 122 is stopped or at a timing after a certain time has elapsed from the stop. Thus, the magnetic brush 130 'is formed only when the toner is replenished, and the replenished toner can be prevented from becoming a lump, and the magnetic brush 130' is not formed except during the toner replenishment. Can reduce stress on

  The conveyance member drive motor control unit 120 is configured to output the first conveyance member drive motor 119a (the first conveyance member 112) based on the rotation number of the toner discharge member 122 output from the toner discharge member rotation number detection unit 118 of the toner supply device 22. ) And the second conveying member drive motor 119b (second conveying member 113).

  In addition, as a detection cycle by the toner discharge member rotation speed detection unit 118, a predetermined time that is the same cycle as the toner concentration measurement cycle by the toner concentration detection sensor 110 is adopted, for example, every 0.5 to 1 second. The rotation speed of the member drive motor 129 can be detected and sent to the conveying member drive motor control unit 120. In this case, the toner discharge member rotation speed detection unit 118 sets a timing later than the start of detection by the toner density detection sensor 110 as a delay time until the rotation of the toner discharge member drive motor 129 to start rotation. . The toner discharge member rotation speed detection unit 118 counts and outputs the rotation speed from the start of the detection until the rotation is stopped.

  Alternatively, the rotation number of the toner discharge member drive motor 129 is detected and conveyed only when the toner discharge member drive motor 129 is rotated based on the comparison result of the toner supply control unit 128 based on the detection value of the toner density detection sensor 110. It can also be sent to the member drive motor controller 120.

  The conveyance member drive mode control unit 120 stores a relational expression or table indicating a correspondence relationship between the rotation speed of the toner discharge member 122 and the rotation speeds of the first conveyance member 112 and the second conveyance member 113. Based on the relational expression or the table, the rotational speed corresponding to the rotational speed detected by the toner discharge member rotational speed detector 118 is determined. Here, in the relation shown by the relational expression or the table, the rotation speed of the toner discharging member 122 and the rotation of the conveying members 112 and 113 suitable when the toner supply amount corresponding to the rotation speed is supplied. The speeds are associated with each other, and the rotational speeds of the conveying members 112 and 113 are set to increase as the rotational speed of the toner discharging member 122 increases. Then, the transport member drive mode control unit 120 drives the first transport member 112 and the second transport member 113 at the determined rotational speed.

  Next, the flow of the rotation driving process for the first transport member 112 and the second transport member 113 will be described. FIG. 2 is a flowchart showing the flow of the rotation driving process of the first transport member 112 and the second transport member 113.

  First, the toner replenishment control unit 128 acquires the toner density measurement value detected by the toner density detection sensor 110 at predetermined time intervals, and the toner discharge member drive motor 129 is obtained based on the comparison result between the toner density setting value and the toner density measurement value. And the toner discharge member 122 is rotated by the set number of rotations.

  Then, the toner discharge member rotation number detection unit 118 counts the rotation number C of the toner discharge member 122 from when the toner discharge member 122 starts to rotate until the rotation of the toner discharge member 122 is stopped. The rotation number C is sent to the conveying member drive motor control unit 120 (S1).

  Next, the conveyance member drive motor control unit 120 determines the rotation speed P of the first conveyance member 112 and the second conveyance member 113 based on the rotation number C input from the toner discharge member rotation number detection unit 118. For example, the conveyance member drive motor control unit 120 calculates the rotation speed P by the following formula (1) (S2).

P = R (1 + αC) (1)
Here, R is the reference rotational speed of the first transport member drive motor 119a and the second transport member drive motor 119b when the toner replenishment amount from the toner replenishing device 22 is zero. The minimum rotation speed at which the toner can be charged to a desired charge is set in advance as the reference rotation speed.

The coefficient α is a real number larger than zero. As described above, the toner replenishment control unit 128 stores a relational expression or table indicating the correspondence between the difference between the toner density measurement value and the toner density setting value and the rotation speed of the toner discharge member drive motor 129. . Therefore, the range of values that can be taken by the rotation speed of the toner discharge member drive motor 129 is determined from the above relational expression or table. On the other hand, if the rotational speeds of the first transport member 112 and the second transport member 113 are made too fast, the temperature of the two-component developer rises and tends to deteriorate. Further, it is conceivable that the developer is transported too quickly and the toner is transported to the developing region without being sufficiently charged due to insufficient stirring, causing problems such as background fogging and toner scattering. From these viewpoints, the upper limit of the rotational speed of the first transport member 112 and the second transport member 113 is determined in advance in order to prevent deterioration and wear of the two-component developer, background fogging, toner scattering, and the like. Then, when the maximum value of the rotational speed of the toner discharger drive motor 129 can take the C _2, P _{2 = R} as the rotational speed indicated by (1 + αC ₂₎ is below the upper limit, the coefficient α is preset Has been.

  For example, when the number of rotations detected by the toner discharge member rotation number detection unit 118 is high, that is, when the amount of toner replenishment within a predetermined time is large, the conveyance member drive motor control unit 120 displays the first conveyance member drive motor. The rotational speed of 119a and the 2nd conveyance member drive motor 119b is set to a rotational speed faster than the reference rotational speed R.

  Alternatively, when the rotation number detected by the toner discharge member rotation number detection unit 118 is low, that is, when the amount of toner replenishment within a predetermined time is small, the conveyance member drive motor control unit 120 is connected to the first conveyance member drive motor 119a. The rotational speed with respect to the second conveying member drive motor 119b is set to a value that is higher than the reference rotational speed R but lower than when the amount of toner replenishment is large.

  Then, the conveyance member drive motor control unit 120 calculates the rotation speed at which the rotation speeds of the first conveyance member 112 and the second conveyance member 113 are calculated via the first conveyance member drive motor 119a and the second conveyance member drive motor 119b. Both are rotationally driven so as to be P (S3).

  According to the above configuration, the rotation speeds of the first transport member 112 and the second transport member 113 can be changed according to the toner replenishment amount. Specifically, when a high printing rate image is printed, a large amount of toner is consumed, and a large amount of toner is replenished, the first conveying member 112 and the second conveying member 113 are rotated at high speed. The replenished toner can be transported to the development area earlier. As a result, poor image formation due to toner shortage can be prevented. In addition, when a plurality of images with a low printing rate are printed and the toner is not replenished, the first conveying member 112 and the second conveying member 113 are rotated at a low speed, so that the toner consumption is small and the toner is long. Even if transported in a time-circulated manner, it is possible to prevent the fluidity of the two-component developer from being lowered and to suppress the image density from being lowered.

The ratio of the present embodiment, the maximum rotation speed P ₂ of the first conveying member 112 and the second conveying member 113, (the rotational speed when the toner supply amount is zero, i.e. the minimum speed) reference rotational speed and R P ₂ / R is preferably controlled to 1.5 or more and 3 or less.

  When the ratio between the maximum rotation speed and the minimum rotation speed is 1.5 or more, when many images with low toner consumption are printed continuously while suppressing wear and deterioration of the two-component developer more effectively In this case, it is possible to more effectively suppress image density reduction and fogging. In addition, by setting the ratio of the maximum rotation speed and the minimum rotation speed to 3 or less, a change in toner charge amount can be reduced, and the occurrence of uneven image density can be more effectively prevented.

(Modification 1)
In the embodiment described above, the toner supply amount is adjusted by controlling the rotation speed of the toner discharge member 122 based on the toner density value of the toner circulation conveyance path by the toner density detection sensor 110, and the toner discharge member rotation speed detection unit 118 controls the toner. It has been described that the rotation speeds of the conveying members 112 and 113 are adjusted by detecting the rotation speed (toner replenishment amount) of the discharge member. However, the adjustment of the rotation speed of the conveying members 112 and 113 is not limited to this.

  For example, as shown in FIG. 9, the first value is based on the toner density measurement value detected by the toner density detection sensor 110 instead of the rotation speed of the toner discharge member 122 detected by the toner discharge member rotation speed detection unit 118. The rotational speeds of the transport member 112 and the second transport member 113 can also be controlled.

  That is, the toner density measurement value detected by the toner density detection sensor 110 is sent to the toner replenishment control unit 128 and also sent to the conveying member drive motor control unit 120. Then, the conveyance member drive motor control unit 120 controls the rotation speeds of the first conveyance member 112 and the second conveyance member 113 based on the comparison result between the detected toner density measurement value and the toner density setting value.

  As described above, the toner replenishment control unit 128 determines the difference between the toner density measurement value and the toner density setting value (however, the toner density measurement value <the toner density setting value is satisfied) and the rotation speed of the toner discharge member drive motor 129. The number of rotations of the toner discharging member 122 is set based on a relational expression or a table indicating the corresponding relationship. The rotational speed of the toner discharge member 122 is proportional to the toner replenishment amount. Therefore, the difference between the toner density measurement value and the toner density setting value can be said to be one of the parameters corresponding to the toner replenishment amount.

  Therefore, the conveyance member drive motor control unit 120 stores a relational expression or table indicating the correspondence between the difference between the measured toner density value and the toner density setting value and the rotation speed of the conveyance members 112 and 113. Based on the relational expression or the table, the rotational speed corresponding to the difference between the toner density measurement value detected by the toner density detection sensor 110 and the toner density setting value is determined. In the correspondence relationship shown in the relational expression or the table, the toner density measurement value corresponds to the rotation speed of the conveying members 112 and 113 suitable when the toner supply amount corresponding to the toner density measurement value is supplied. As the difference between the toner density measurement value and the toner density setting value (however, the toner density measurement value <the toner density setting value is satisfied) increases, the rotation speed of the conveying members 112 and 113 also increases. Has been. Then, the transport member drive motor control unit 120 controls the first transport member drive motor 119a and the second transport member drive motor 119b so that the transport members 112 and 113 rotate at the determined rotational speed.

  Specifically, when the difference between the toner density measurement value detected by the toner density detection sensor 110 and the toner density setting value is large, a large amount of toner is replenished, and thus the first conveyance member 112 and the second conveyance member 113. Is rotated faster than the reference rotation speed R.

  Conversely, when the difference between the measured toner density value and the toner density setting value is small, only a small amount of toner is replenished, so that the first conveying member 112 and the second conveying member 113 are rotated slightly faster than the reference rotation speed R. You can do it.

  However, when the toner density measurement value is equal to or higher than the toner density setting value, toner replenishment is not performed, and thus the first conveyance member 112 and the second conveyance member 113 are rotated at the reference rotation speed R.

  Also according to such a modification, the rotation speeds of the first conveyance member 112 and the second conveyance member 113 can be changed according to the toner replenishment amount. That is, when a high printing rate image is printed, a large amount of toner is consumed, and a large amount of toner is replenished, the first conveying member 112 and the second conveying member 113 are rotated at a high speed. Image formation defects can be prevented. In addition, when a plurality of images with a low printing rate are printed and the toner is not replenished, the first conveying member 112 and the second conveying member 113 are rotated at a low speed, which reduces the fluidity of the two-component developer. It is possible to prevent the decrease in image density.

(Modification 2)
As another modification, the rotation speeds of the first conveyance member 112 and the second conveyance member 113 may be set based on the number of print dots (number of print pixels) of the image. The number of print dots is the number of pixels to which toner is attached, and corresponds to the amount of toner consumed. Since it is necessary to replenish only the consumed toner amount, the number of print dots also corresponds to the toner replenishment amount to be replenished. That is, it can be said that the number of printed dots is one of the parameters corresponding to the toner replenishment amount.

  The image forming apparatus according to this modification includes a pixel count unit that calculates the number of print dots from image data to be printed.

  In the image forming apparatus according to the present modification, the toner replenishment control unit 128 may determine the number of rotations of the toner discharge member 122 based on the number of printed dots obtained by the pixel count unit. By multiplying the number of printing dots by the amount of toner per printing dot, the toner consumption can be easily obtained. Therefore, the toner replenishment amount to be replenished can be easily obtained from the number of print dots. In this case, the toner replenishment control unit 128 stores in advance a relational expression or table indicating the correspondence between the number of printed dots and the rotational speed of the toner discharging member 122, and the rotational speed is determined based on the relational expression or table. Can be set. In the correspondence relationship shown in the relational expression or the table, the number of print dots is associated with the number of rotations of the toner discharging member 122 in the case of replenishing only the toner amount obtained by multiplying the print dot number by the toner amount per print dot. It has been.

Further, in the image forming apparatus according to this modification, the conveyance member drive motor control unit 120 controls the rotation speeds of the first conveyance member 112 and the second conveyance member 113 based on the number of print dots obtained by the pixel count unit. To do. Specifically, the conveyance member drive motor control unit 120 stores a relational expression or table indicating a correspondence relationship between the number of print dots and the rotation speed of the conveyance members 112 and 113, and based on the relational expression or table. Thus, the rotational speed corresponding to the number of print dots is determined. In the correspondence relationship shown in the relational expression or the table, the rotation speeds of the conveying members 112 and 113 suitable when the number of printing dots and the toner amount obtained by multiplying the number of printing dots by the toner amount per printing dot are replenished. And the rotation speed of the conveying members 112 and 113 is set to increase as the number of printed dots increases.
The transport member drive motor control unit 120 controls the first transport member drive motor 119a and the second transport member drive motor 119b so that the transport members 112 and 113 rotate at the determined rotational speed.

  Also, after the toner is replenished each time, it is preferable to clear the count value of the pixel count unit and set the next time to start counting.

  Note that the number of rotations of the toner discharge member 122 (that is, the amount of toner replenishment) can be controlled based on the number of print dots counted by the pixel count unit, and the conveyance member drive motor control unit 120 can control the toner discharge member 122. The rotational speeds of the first transport member 112 and the second transport member 113 may be controlled according to the number of rotations.

  In addition, the image forming apparatus according to the present modification may include a calculation unit that calculates a toner consumption amount or a toner supply amount according to the number of print dots counted by the pixel count unit. Then, the toner replenishment control unit 128 may control the rotation speed of the toner discharge member 122 based on the calculation result. Further, the conveyance member drive motor control unit 120 may control the rotation speed of the conveyance members 112 and 113 based on the calculation result by the calculation unit.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The present invention can form a high-quality image without image density reduction or fog even when a large number of images with low toner consumption are continuously printed while suppressing wear and deterioration of the two-component developer. The present invention can be applied to image forming apparatuses such as multifunction machines, printers, and facsimile machines.

FIG. 6 is an explanatory diagram illustrating an example of a method for controlling rotation of a toner discharge member of a toner replenishing device of an image forming apparatus and rotation of a conveyance member of a developing device according to an embodiment of the present invention. 4 is a flowchart illustrating a method for controlling rotation of a conveyance member of a developing device according to an embodiment of the present invention. 1 is a cross-sectional view of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a main configuration of a toner supply device according to an embodiment of the present invention. FIG. 5 is a cross-sectional view taken along arrow C-C ′ in FIG. 4. (A) is sectional drawing which shows the principal part structure of the toner replenishing apparatus which concerns on embodiment of this invention, (b) is sectional drawing which shows the principal part structure of the toner replenishing apparatus which concerns on other embodiment of this invention. is there. It is A-A 'arrow sectional drawing of Fig.6 (a). It is B-B 'arrow sectional drawing of Fig.6 (a). FIG. 10 is an explanatory diagram showing another example of a method for controlling rotation of the toner discharge member of the toner replenishing device of the image forming apparatus and rotation of the conveying member of the developing device according to the embodiment of the present invention.

Explanation of symbols

2 Developing device 22 Toner replenishing device 110 Toner concentration detection sensor (toner concentration detection member)
111 Developing tank 112 First conveying member 113 Second conveying member 115 Developing tank cover 115a Toner replenishment port 117 Partition plate 118 Toner discharge member rotation speed detection unit 119a, 119b Conveying member driving motor 120 Conveying member driving motor controller (conveying member rotation motor) Control part)
122 Toner discharging member 123 Toner discharging port 124 Toner discharging member partition 125 Toner stirring member 128 Toner replenishment control unit 129 Toner discharging member rotation speed detecting unit

Claims (7)

A developer tank having first and second transport paths for transporting a developer containing toner and a carrier, and a first tank that is provided in the first transport path and rotates to transport the developer in a predetermined direction. A first conveying member, a second conveying member that is provided in the second conveying path and conveys the developer in a direction opposite to the predetermined direction by rotating; A developer carrying member for supplying toner contained in the developer to the photosensitive member, wherein the developer tank communicates with the first and second transport paths, and the reverse side of the first communication path. A developing device having a second communication path formed through the first communication path and communicating with the first and second transport paths;
A toner replenishing device that replenishes the developing device with an amount of toner corresponding to a toner consumption amount in the developing device;
A transport member that controls the rotation speeds of the first transport member and the second transport member based on a feature amount corresponding to the toner consumption amount or the toner replenishment amount replenished from the toner replenishing device to the developing device. An image forming apparatus comprising: a rotation control unit. The toner replenishing device includes a toner container having a toner discharge port, and a toner discharge member that is a screw auger disposed in the toner container and transports the toner to the toner discharge port.
The image forming apparatus according to claim 1, wherein the conveyance member rotation control unit uses a rotation number of the toner discharge member as the feature amount. The developing device includes a toner concentration detecting member that detects a toner concentration in the developing tank,
The image forming apparatus according to claim 1, wherein the conveyance member rotation control unit uses a value obtained by subtracting a toner density value measured by the toner density detection member from a predetermined threshold value as the feature amount. It has a pixel count unit that calculates the number of print dots from image data to be printed,
The image forming apparatus according to claim 1, wherein the conveyance member rotation control unit uses the number of print dots obtained by the pixel count unit as the feature amount. The carrier is a magnetic carrier;
The developing tank has a toner supply port for receiving toner supplied by the toner supply device in the first transport path,
The developing device includes an electromagnet for forming, in the first conveyance path, a magnetic brush made of the magnetic carrier on the first conveyance path on the predetermined direction side of the toner supply port.
5. The image forming apparatus according to claim 1, further comprising an electromagnet control unit configured to supply a current to the electromagnet at a timing when the toner is replenished by the toner replenishing device.   The image forming apparatus according to claim 1, wherein the first transport member and the second transport member are screw augers.   The conveyance member rotation control unit is configured to control the first conveyance member and the second conveyance member so that a ratio between the maximum rotation speed and the minimum rotation speed of the first and second conveyance members is 1.5 or more and 3 or less. The image forming apparatus according to claim 1, wherein the rotation speed is controlled.

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