Image forming apparatus

Abstract

To provide an image forming device with which it is possible to smoothly convey a waste developer in a collection path for collecting a waste developer and suppress toner clogging in the collection path.SOLUTION: An image forming device comprises a photoreceptor drum, a developing unit, a cleaning unit, a collection unit 11, and a control unit. The collection unit 11 includes a collection path 111a where a developer disposal path 112a in which a waste developer from the ejection unit of the developing unit is conveyed and toner disposal paths 113a, 114a in which a waste toner from the cleaning unit is conveyed join together, and collects a waste developer that includes a waster toner and a waste carrier. The collection path 111a has at least in part a point where flow resistance is large. When the weight ratio of the waste carrier to the waste toner of the waste developer in the collection path 111a is less than a prescribed value, the control unit executes a carrier ejection process of moving the carrier from the developing unit to the photoreceptor drum and removing it by the cleaning unit to eject.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] In electrophotographic image forming apparatuses such as copiers and printers, a toner image to be transferred onto a recording medium such as paper is formed by attaching toner to an electrostatic latent image formed on the surface of an image carrier such as a photoreceptor drum and then developing it. In the developing unit, in order to continuously form a uniform image, a developer containing toner accommodated in a developing container is conveyed while being agitated in the developing container.

[0003] For example, a conventional image forming apparatus disclosed in Patent Document 1 includes a developing unit having a stirring member that replenishes a developer containing toner and a carrier, supplies the developer to a developing roller, and changes the amount of the developer discharged to the outside according to the rotation speed. This image forming apparatus switches the rotation speed of the stirring member from a second speed lower than the first speed to the first speed and rotates the stirring member for a predetermined time based on the increased amount of the developer when the stirring member rotates at the second speed. Thereby, even if the rotation speed of the stirring member is switched, the amount of the developer in the developing unit can be stabilized.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the case of the prior art, if the developing unit continues to be driven at a low speed, the developer is not discharged from the developing unit. For example, when there is a recovery path for transporting and recovering by merging the waste developer discharged from the developing unit and the waste toner remaining on the surface of the image carrier and removed, if the developer is not discharged from the developing unit, the weight ratio of the waste carrier to the waste toner of the waste developer in the recovery path may decrease. As a result, the fluidity of the waste developer in the recovery path is significantly reduced. For example, when there is a location on the recovery path where the flow resistance is greater than that of the toner disposal path, there is a problem that toner clogging occurs at that location.

[0006] The present invention has been made in view of the above points, and an object thereof is to provide an image forming apparatus capable of smoothly transporting a waste developer in a recovery path for recovering the waste developer and suppressing toner clogging on the recovery path.

Means for Solving the Problems

[0007] To solve the above problems, an image forming apparatus according to the present invention includes an image carrier, a developing unit, a cleaning unit, a recovery unit, and a control unit. The image carrier carries a toner image on its surface. The developing unit includes a developing container that houses a two-component developer containing toner and a carrier, a developer carrier that carries the developer in the developing container, and a discharge unit that discharges excess developer from the developing container, and develops an electrostatic latent image formed on the surface of the image carrier with the toner to form the toner image. The cleaning unit removes the toner remaining on the surface of the image carrier. The recovery unit has a recovery path that merges and conveys a developer waste path through which waste developer discharged from the discharge unit is conveyed and a toner waste path through which waste toner removed by the cleaning unit is conveyed, and recovers the waste developer including the waste toner and the waste carrier through the recovery path. The control unit controls the operations of the image carrier, the developing unit, the cleaning unit, and the recovery unit. The recovery path has a portion where the flow resistance is greater than that of the toner waste path at least in part. When the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path is less than a predetermined value, the control unit moves the carrier from the developing unit to the surface of the image carrier during non-image formation, and executes a carrier discharge process of removing and discharging the carrier from the surface of the image carrier by the cleaning unit.

Advantages of the Invention

[0008] According to the configuration of the present invention, by discharging the carrier through the image carrier and the cleaning unit, the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path can be increased, and the fluidity of the waste developer can be suitably maintained. Thereby, the waste developer can be smoothly conveyed in the recovery path, and toner clogging on the recovery path can be suppressed.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the following content.

[0011] FIG. 1 is a schematic vertical cross-sectional front view of the image forming apparatus 1 of the embodiment. FIG. 2 is a block diagram showing the configuration of the image forming apparatus 1 of FIG. 1. FIG. 3 is a schematic vertical cross-sectional front view around the image forming section 20 of the image forming apparatus 1 of FIG. 1. As an example of the image forming apparatus 1 of the present embodiment, it is a tandem type color printer that transfers a toner image to a sheet S using an intermediate transfer belt 31. The image forming apparatus 1 may be a so-called multifunction machine having functions such as printing, scanning (image reading), and facsimile transmission.

[0012] As shown in FIGS. 1, 2, and 3, the image forming apparatus 1 includes a paper feeding section 3, a paper conveyance section 4, an exposure section 5, an image forming section 20, a transfer section 30, a fixing section 6, a paper discharge section 7, and a control section 8 provided in its main body 2.

[0013] The paper feeding section 3 accommodates a plurality of sheets S and separates and feeds out the sheets S one by one during printing. The paper conveyance section 4 conveys the sheet S sent out from the paper feeding section 3 to the secondary transfer section 33 and the fixing section 6, and further discharges the sheet S after fixing from the paper discharge port 4a to the paper discharge section 7. When double-sided printing is performed, the paper conveyance section 4 diverts the sheet S after fixing on the first side to the reverse conveyance section 4c by the branching section 4b, and conveys the sheet S to the secondary transfer section 33 and the fixing section 6 again. The exposure section 5 irradiates the image forming section 20 with laser light controlled based on image data.

[0014] The image forming unit 20 is disposed below the intermediate transfer belt 31. The image forming unit 20 includes a yellow image forming unit 20Y, a cyan image forming unit 20C, a magenta image forming unit 20M, and a black image forming unit 20B. These four image forming units 20 have the same basic configuration. Accordingly, in the following description, the identification symbols "Y", "C", "M", and "B" representing each color may be omitted unless particularly limited.

[0015] The image forming unit 20 includes a photosensitive drum (image carrier) 21 rotatably supported in a predetermined direction (clockwise in FIGS. 1 and 3). The image forming unit 20 further includes a charging unit 22, a developing unit 40, and a drum cleaning unit 23 disposed around the photosensitive drum 21 along its rotation direction. Note that a primary transfer unit 32 is disposed between the developing unit 40 and the drum cleaning unit 23.

[0016] The photosensitive drum 21 has a photosensitive layer on its outer peripheral surface. The charging unit 22 charges the surface of the photosensitive drum 21 to a predetermined potential. The exposure unit 5 exposes the surface of the photosensitive drum 21 charged by the charging unit 22 to form an electrostatic latent image of the document image. The developing unit 40 supplies toner to the electrostatic latent image for development to form a toner image. Thereby, the photosensitive drum 21 carries the toner image on its surface. Each of the four image forming units 20 forms a toner image of a different color. The drum cleaning unit 23 removes and cleans the toner and the like remaining on the surface of the photosensitive drum 21 after the toner image is primarily transferred to the surface of the intermediate transfer belt 31. In this way, the image forming unit 20 forms an image on the sheet S.

[0017] As shown in FIG. 1, the transfer unit 30 includes an intermediate transfer belt (image carrier) 31, primary transfer units 32Y, 32C, 32M, 32B, a secondary transfer unit 33, and a belt cleaning unit 34. The intermediate transfer belt 31 is disposed above the four image forming units 20. The intermediate transfer belt 31 is rotatably supported in a predetermined direction (counterclockwise in FIG. 1). The intermediate transfer belt 31 is an intermediate transfer member on which toner images carried on the surfaces of the photosensitive drums 21 of the four image forming units 20 are sequentially superimposed and primarily transferred. The four image forming units 20 are arranged in a so-called tandem arrangement in a row from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 31.

[0018] The primary transfer units 32Y, 32C, 32M, 32B are disposed above the image forming units 20Y, 20C, 20M, 20B of each color with the intermediate transfer belt 31 interposed therebetween. The secondary transfer unit 33 is disposed on the upstream side of the fixing unit 6 in the paper conveyance direction of the paper conveyance unit 4 and on the downstream side of the intermediate transfer belt 31 in the rotation direction with respect to the image forming units 20Y, 20C, 20M, 20B of each color in the transfer unit 30. The belt cleaning unit 34 is disposed on the upstream side of the intermediate transfer belt 31 in the rotation direction with respect to the image forming units 20Y, 20C, 20M, 20B of each color.

[0019] The toner images are primarily transferred onto the surface of the intermediate transfer belt 31 by the primary transfer units 32Y, 32C, 32M, 32B of each color. Then, as the intermediate transfer belt 31 rotates, the toner images of the four image forming units 20 are continuously superimposed and transferred onto the intermediate transfer belt 31 at a predetermined timing, whereby a color toner image in which yellow, cyan, magenta, and black toner images are superimposed is formed on the surface of the intermediate transfer belt 31.

[0020] The color toner image on the surface of the intermediate transfer belt 31 is transferred onto the paper S sent in synchronization by the paper conveyance unit 4 at a secondary transfer nip portion formed in the secondary transfer unit 33. The belt cleaning unit 34 removes and cleans toner and the like remaining on the surface of the intermediate transfer belt 31 after secondary transfer.

[0021] The fixing unit 6 is disposed above the secondary transfer unit 33. The fixing unit 6 heats and presses the sheet S onto which the toner image has been transferred to fix the toner image on the sheet S.

[0022] The sheet discharge unit 7 is disposed above the transfer unit 30. The sheet S on which the toner image has been fixed and the printing has been completed is conveyed to the sheet discharge unit 7.

[0023] The control unit 8 includes a CPU, an image processing unit, a storage unit, and other electronic circuits and electronic components (all not shown). The CPU controls the operations of the respective components provided in the image forming apparatus 1 based on programs and data for control stored in the storage unit, and performs processes related to the functions of the image forming apparatus 1. Each of the paper feed unit 3, the paper conveyance unit 4, the exposure unit 5, the image forming unit 20, the transfer unit 30, and the fixing unit 6 receives an individual command from the control unit 8 and cooperates to perform printing on the sheet S. The storage unit is composed of a combination of a non-volatile storage device such as a program ROM (Read Only Memory), a data ROM, etc., and a volatile storage device such as a RAM (Random Access Memory).

[0024] Subsequently, the configuration around the image forming unit 20 will be described with reference to FIGS. 4 and 5 in addition to FIGS. 2 and 3. FIG. 4 is a plan view of a horizontal cross section of the developing unit 40 of the image forming unit 20 in FIG. 3. FIG. 5 is a schematic vertical cross-sectional rear view of the recovery unit 11 of the image forming apparatus 1 in FIG. 1.

[0025] The developing unit 40 supplies toner to the surface of the photosensitive drum 21. The developing unit 40 includes a developing container 41, a first conveying member 42, a second conveying member 43, a developing roller (developer carrier) 44, a regulating blade 45, and a discharge unit 46.

[0026] The developing container 41 has an elongated shape extending along the axial direction of the photosensitive drum 21 (the depth direction of the paper surface in FIG. 3), and is arranged with its longitudinal direction horizontal. The developing container 41 accommodates a two-component developer containing, for example, toner and a magnetic carrier as the developer to be supplied to the photosensitive drum 21.

[0027] The developing container 41 has a partition portion 411, a first conveyance chamber 412, a second conveyance chamber 413, a first communication portion 414, and a second communication portion 415.

[0028] The partition portion 411 is provided at the lower part inside the developing container 41. The partition portion 411 is disposed at a substantially central portion in the direction intersecting the longitudinal direction of the developing container 41 (the left - right horizontal direction in FIG. 3, the up - down direction in FIG. 4). The partition portion 411 is formed in a substantially plate shape extending in the longitudinal direction and the up - down direction of the developing container 41. The partition portion 411 divides the inside of the developing container 41 in the direction intersecting the longitudinal direction.

[0029] The first conveyance chamber 412 and the second conveyance chamber 413 are provided inside the developing container 41. The first conveyance chamber 412 and the second conveyance chamber 413 are formed by the inside of the developing container 41 being divided by the partition portion 411 and are juxtaposed at substantially the same height.

[0030] The second conveyance chamber 413 is disposed adjacent to and below the arrangement region of the developing roller 44 in the developing container 41. That is, the second conveyance chamber 413 faces the developing roller 44. The first conveyance chamber 412 is disposed in a region in the developing container 41 that is farther from the developing roller 44 than the second conveyance chamber 413. The developing agent supply port 412a of the first conveyance chamber 412 is open, and the developing agent is supplied through the developing agent supply port 412a.

[0031] The first communication portion 414 and the second communication portion 415 are respectively disposed outside both end portions in the longitudinal direction of the partition portion 411. The first communication portion 414 and the second communication portion 415 communicate the first conveyance chamber 412 and the second conveyance chamber 413 in the direction intersecting the longitudinal direction of the partition portion 411 (the left - right horizontal direction in FIG. 3, the up - down direction in FIG. 4), that is, in the thickness direction of the partition portion 411 having a substantially plate shape. In other words, the first conveyance chamber 412 and the second conveyance chamber 413 communicate with each other at both end portions in the longitudinal direction.

[0032] The first conveying member 42 is disposed in the first conveying chamber 412. The second conveying member 43 is disposed in the second conveying chamber 413. The second conveying member 43 extends parallel and close to the developing roller 44. The first conveying member 42 and the second conveying member 43 are rotatably supported by the developing container 41 about an axis extending horizontally in parallel with the developing roller 44. The basic configurations of the first conveying member 42 and the second conveying member 43 are the same. The first conveying member 42 has spiral first conveying blades 42b on the outer peripheral portion of a rotating shaft 42a extending along the longitudinal direction of the developing container 41. The second conveying member 43 has spiral second conveying blades 43b on the outer peripheral portion of a rotating shaft 43a extending along the longitudinal direction of the developing container 41.

[0033] The first conveying member 42 conveys the developer while stirring it in the first direction f1 from the first communication portion 414 side toward the second communication portion 415 side along the axial direction of rotation in the first conveying chamber 412. The second conveying member 43 conveys the developer while stirring it in the second direction f2 from the second communication portion 415 side toward the first communication portion 414 side along the axial direction of rotation in the second conveying chamber 413. The second direction f2 is opposite to the first direction f1.

[0034] The first communication portion 414 communicates the downstream end in the second direction f2 of the second conveying chamber 413 with the upstream end in the first direction f1 of the first conveying chamber 412. The first communication portion 414 conveys the developer from the second conveying chamber 413 side toward the first conveying chamber 412 side. The second communication portion 415 communicates the downstream end in the first direction f1 of the first conveying chamber 412 with the upstream end in the second direction f2 of the second conveying chamber 413. The second communication portion 415 conveys the developer from the first conveying chamber 412 side toward the second conveying chamber 413 side.

[0035] The developing roller 44 is disposed above the second conveyance chamber 413 within the developing container 41. A part of the surface of the developing roller 44 is exposed from the developing container 41 and is disposed to face the photoreceptor drum 21. The developing roller 44 is rotatably supported by the developing container 41 about an axis extending parallel to the axis of the photoreceptor drum 21. The developing roller 44 carries the developer within the second conveyance chamber 413. The developing roller 44 supplies the toner within the developing container 41 to the surface of the photoreceptor drum 21 in the facing region with the photoreceptor drum 21, develops the electrostatic latent image, and forms a toner image.

[0036] The regulating blade 45 is disposed on the upstream side in the rotation direction of the developing roller 44 in the facing region between the developing roller 44 and the photoreceptor drum 21. The regulating blade 45 faces the developing roller 44 in proximity thereto, and is disposed with a predetermined interval provided between the tip thereof and the surface of the developing roller 44. The regulating blade 45 extends over the entire axial direction of the developing roller 44. The regulating blade 45 regulates the layer thickness of the developer (toner) carried on the surface of the developing roller 44 passing through the gap between the tip of the regulating blade 45 and the surface of the developing roller 44.

[0037] The developer within the developing container 41 circulates in a predetermined circulation direction between the first conveyance chamber 412 and the second conveyance chamber 413 through the first communication portion 414 and the second communication portion 415 by the rotation of the first conveyance member 42 and the second conveyance member 43. At this time, the toner within the developing container 41 is agitated, charged, and carried on the surface of the developing roller 44. The toner carried on the surface of the developing roller 44 is conveyed to the facing region between the developing roller 44 and the photoreceptor drum 21 by the rotation of the developing roller 44 after the layer thickness thereof is regulated by the regulating blade 45. When a predetermined developing voltage is applied to the developing roller 44, due to the potential difference with the potential of the surface of the photoreceptor drum 21, the toner carried on the surface of the developing roller 44 moves to the surface of the photoreceptor drum 21 in the facing region with the photoreceptor drum 21. In this way, the electrostatic latent image on the surface of the photoreceptor drum 21 is developed with toner.

[0038] The discharge unit 46 is provided further downstream than the downstream end of the second transport chamber 413 in the second direction f2. The discharge unit 46 is connected to the second transport chamber 413. The interiors of the discharge unit 46 and the second transport chamber 413 communicate with each other. The discharge unit 46 has a developer discharge port 46a and a discharge blade 461.

[0039] Note that the rotation shaft 43a of the second transport member 43 extends continuously into the discharge unit 46. One end in the axial direction of the rotation shaft 43a is rotatably supported by the developing container 41 at the downstream end of the discharge unit 46 with respect to the second direction f2 of the second transport chamber 413.

[0040] The developer discharge port 46a is disposed at the downstream end of the discharge unit 46 with respect to the second direction f2 of the second transport chamber 413. The developer discharge port 46a opens, for example, below the rotation shaft 43a of the second transport member 43. The excess developer in the developing container 41 is discharged from the developer discharge port 46a. That is, in the discharge unit 46, the excess developer in the second transport chamber 413 is conveyed toward the developer discharge port 46a.

[0041] The discharge blade 461 extends spirally along the axial direction on the outer peripheral portion of the rotation shaft 43a of the second transport member 43. The discharge blade 461 is provided integrally with the rotation shaft 43a in the same manner as the second transport blade 43b. The discharge blade 461 has the same winding direction as the second transport blade 43b. That is, the conveyance direction of the developer in the discharge unit 46 is the same as the second direction f2 of the second transport chamber 413. Thereby, the discharge blade 461 conveys the excess developer in the discharge unit 46 toward the developer discharge port 46a. Note that the discharge blade 461 has a smaller pitch and a smaller outer diameter than the second transport blade 43b, for example.

[0042] Further, the second transport member 43 includes a regulating portion 43c in addition to the second transport blade 43b. The regulating portion 43c is provided integrally with the rotation shaft 43a in the same manner as the second transport blade 43b.

[0043] The regulating part 43c is arranged on the downstream side of the second conveying blades 43b of the second conveying member 43 with respect to the second direction f2 of the second conveying chamber 413. The regulating part 43c faces the connection part between the second conveying chamber 413 and the discharging part 46 in the axial direction of the rotating shaft 43a.

[0044] The regulating part 43c is formed in a blade shape that spirally extends along the axial direction on the outer peripheral part of the rotating shaft 43a. That is, the regulating part 43c is formed on the second conveying member 43 in the second conveying chamber 413. The winding direction of the regulating part 43c is opposite to that of the second conveying blades 43b. Thereby, the regulating part 43c blocks the developer conveyed to the vicinity of the downstream end in the second conveying chamber 413 and restricts the movement of the developer toward the discharging part 46 side. The regulating part 43c has a smaller pitch than the second conveying blades 43b.

[0045] The outer peripheral part of the regulating part 43c has a predetermined interval (clearance) from the inner surface of the developing container 41. The developer that has reached a predetermined amount or more in the second conveying chamber 413 is conveyed as surplus developer from the gap between the outer peripheral part of the regulating part 43c and the inner surface of the developing container 41 toward the discharging part 46.

[0046] The drum cleaning part 23 removes the toner remaining on the surface of the photosensitive drum 21 after primary transfer. The drum cleaning part 23 includes a cleaning roller 231, a cleaning blade 232, and a discharging member 233.

[0047] The cleaning roller 231 contacts the surface of the photosensitive drum 21 with a predetermined pressure and rotates in a direction in which the contact area with the photosensitive drum 21 moves in the same direction as the photosensitive drum 21 by a driving part (not shown). The cleaning blade 232 contacts the surface of the photosensitive drum 21 with a predetermined pressure. The cleaning roller 231 and the cleaning blade 232 remove and clean the toner and the like remaining on the surface of the photosensitive drum 21 after primary transfer. The discharging member 233 has spiral blades and discharges the waste toner removed from the surface of the photosensitive drum 21 toward a recovery part 11, which will be described later, provided outside the drum cleaning part 23.

[0048] Note that the belt cleaning unit 34 also has the same structure as the drum cleaning unit 23. After secondary transfer, the belt cleaning unit 34 removes the toner remaining on the surface of the intermediate transfer belt 31 and discharges it toward a recovery unit 11 provided outside the belt cleaning unit 34, which will be described later.

[0049] As shown in FIGS. 1, 2, and 5, the image forming apparatus 1 further includes a recovery unit 11. The recovery unit 11 is disposed, for example, on the front side or the back side of the image forming unit 20 and the transfer unit 30. The recovery unit 11 includes a housing 111, a developer waste pipe 112, a first toner waste pipe 113, a second toner waste pipe 114, and a recovery member 115.

[0050] The housing 111 has an elongated shape extending in the direction (the left - right horizontal direction in FIG. 1) and the vertical direction in which four image forming units 20 are juxtaposed. The developer waste pipe 112, the first toner waste pipe 113, and the second toner waste pipe 114 are connected and communicate with each other at the upper part of the housing 111. The housing 111 accommodates the waste developer discharged from the discharge part 46 of the developing unit 40 and the waste toner removed by the drum cleaning unit 23 and the belt cleaning unit 34.

[0051] The recovery unit 11 has four developer waste pipes 112 extending individually from the discharge parts 46 of the four developing units 40. Further, the recovery unit 11 has four first toner waste pipes 113 extending individually from the four drum cleaning units 23. The second toner waste pipe 114 extends from the belt cleaning unit 34. That is, the recovery unit 11 includes a developer waste path 112a through which waste developer is conveyed from the developing unit 40, a first toner waste path 113a through which waste toner is conveyed from the drum cleaning unit 23, and a second toner waste path 114a through which waste toner is conveyed from the belt cleaning unit 34.

[0052] At the bottom inside the housing 111, a recovery path 111a is provided. The recovery path 111a is where the developer waste path 112a, the first toner waste path 113a, and the second toner waste path 114a merge. The recovery path 111a extends along the direction in which the four image forming units 20 are juxtaposed. At one end of the bottom of the housing 111 in the direction in which the recovery path 111a extends, a waste developer discharge port 111b that opens downward is provided.

[0053] The recovery member 115 is at the bottom inside the housing 111 and is disposed on the recovery path 111a. The recovery member 115 is supported by the housing 111 so as to be rotatable about an axis extending along the direction in which the four image forming units 20 are juxtaposed. The recovery member 115 has spiral recovery blades 115b on the outer peripheral portion of a rotary shaft 115a extending along the longitudinal direction of the housing 111. The recovery member 115 conveys the waste developer and waste toner that have fallen onto the recovery path 111a at the inner bottom of the housing 111 toward the waste developer discharge port 111b.

[0054] Note that a connection pipe 111c is attached below the waste developer discharge port 111b. A waste tank (not shown) is connected to the lower end of the connection pipe 111c. The recovery path 111a includes the waste developer discharge port 111b and the connection pipe 111c. The waste developer discharge port 111b and the connection pipe 111c have a greater flow resistance than the first toner waste path 113a and the second toner waste path 114a, for example, due to reasons such as a small flow path diameter and being bent. That is, the recovery path 111a has a portion where the flow resistance is greater than that of the toner waste path at least in part.

[0055] With the above configuration, the recovery unit 11 recovers the waste developer containing waste toner and waste carrier via the recovery path 111a. Further, the image forming apparatus 1 includes a photosensitive drum 21 and an intermediate transfer belt 31 as image carriers, and includes a drum cleaning unit 23 and a belt cleaning unit 34 as cleaning units. Since the recovery unit 11 includes a developer waste path 112a, a first toner waste path 113a, a second toner waste path 114a, and a recovery path 111a, the waste developer containing waste toner and waste carrier can be collected together and easily recovered.

[0056] Note that the operations of the photosensitive drum 21, the developing unit 40, the drum cleaning unit 23, the belt cleaning unit 34, and the recovery unit 11 are controlled by the control unit 8.

[0057] Next, the relationship between the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a and the occurrence of toner clogging at the waste developer discharge port 111b or the connecting pipe 111c on the recovery path 111a was evaluated. The results are shown in Table 1.

[0058]

Table 1

[0059] Table 1 shows the evaluation results of the relationship between the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a and the occurrence of toner clogging at the waste developer discharge port 111b or the connecting pipe 111c on the recovery path 111a for two samples each of the waste developers of yellow, cyan, magenta, and black colors. The weights of the waste toner and waste carrier in the waste developer were calculated by measuring the weight of the waste carrier obtained by sucking the waste developer through a 795-mesh screen after measuring the weight of the waste developer (waste toner and waste carrier).

[0060] According to Table 1, when the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a is 5% or more, it can be seen that there is no toner clogging on the recovery path 111a. Therefore, when the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a is less than a predetermined value, the control unit 8 of the image forming apparatus 1 of the present embodiment moves the carrier from the developing unit 40 to the surface of the photosensitive drum 21 during non-image formation, and the carrier is removed from the surface of the photosensitive drum 21 by the drum cleaning unit 23 and discharged, and executes a carrier discharge process.

[0061] According to the above configuration, by discharging the carrier through the photosensitive drum 21 and the drum cleaning unit 23, the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a can be increased, and the fluidity of the waste developer can be suitably maintained. Thereby, the waste developer can be smoothly conveyed in the recovery path 111a, and it is possible to suppress toner clogging on the recovery path 111a.

[0062] In particular, based on the evaluation results shown in Table 1, the control unit 8 of the image forming apparatus 1 of the present embodiment executes a carrier discharge process when the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a is less than 5%. According to this configuration, the carrier discharge process can be executed at an appropriate timing. That is, it is possible to suppress the carrier discharge process from being executed more than necessary, and it is possible to improve the productivity related to image formation and suppress the consumption of the developer.

[0063] As a method of moving the carrier from the developing unit 40 to the surface of the photosensitive drum 21, for example, (1) a method of increasing the developing current flowing between the developing roller 44 and the photosensitive drum 21 to reduce the carrier resistance, and (2) a method of widening the potential difference between the photosensitive drum 21 and the developing unit 40 between sheets are effective.

[0064] Alternatively, in the carrier discharge process, the carrier may be moved from the developing unit 40 to the surface of the photoreceptor drum 21, further moved to the surface of the intermediate transfer belt 31, and then removed from the surface of the intermediate transfer belt 31 by the belt cleaning unit 34 and discharged.

[0065] Subsequently, the execution conditions of the carrier discharge process will be described. In this description, as the configuration and operating conditions of the image forming apparatus 1, the filling rate of the magnetic carrier in the container (not shown) that supplies the developer to the developing container 41 is 10%, the toner consumption per sheet of A4 size paper at a printing rate of 1% is 3 mg, the transfer efficiency is 80%, the initial amount of developer in the developing container 41 is 300 g, the amount of developer in the developing container 41 at the stable state is 350 g, and the toner charge amount at the stable state is 30 μC / g.

[0066] When the amount of developer is stable, the amount of carrier discharged from the discharge portion 46 of the developing unit 40 is the same as the amount of carrier supplied from the container. For example, when the printing rate is 5%, the toner consumption is 15 mg per sheet of A4 size paper (3 mg × 5%), so the amount of toner supplied from the container is also 15 mg. Since the carrier filling rate in the container is 10%, the amount of waste carrier is 1.5 mg.

[0067] The amount of waste toner is the amount of toner remaining on the surfaces of the photoreceptor drum 21 and the intermediate transfer belt 31 without being transferred. If the transfer efficiency is 80%, the amount of waste toner is 3 mg with respect to 15 mg of toner consumed per sheet of A4 size paper.

[0068] Therefore, the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a is 50% (1.5 mg / 3 mg). In the case of this condition, according to Table 1, there is little possibility of toner clogging occurring on the recovery path 111a, and it is considered that the carrier discharge process does not need to be executed.

[0069] When the weight ratio of the waste developer to the waste toner in the recovery path 111a is less than a predetermined value, it is when the period during which the developer (carrier) is not discharged from the developing container 41 continues for a long time. When the period during which the developer (carrier) is not discharged from the developing container 41 continues for a long time, for example, (1) the period from the start of use of the image forming apparatus 1 until the amount of the developer stabilizes, and (2) when the toner charge amount in the developing container 41 becomes less than a predetermined value, correspond thereto.

[0070] In these cases, in any case, the amount of the developer in the developing container 41 is in a state below the stable bulk, and the carrier is not discharged from the developing container 41 due to the mechanism. Therefore, in these cases, it is necessary to forcibly discharge the carrier through the photosensitive drum 21 and the drum cleaning unit 23 to increase the fluidity of the waste developer and suppress toner clogging on the recovery path 111a.

[0071] For this reason, for example, regarding the period from the start of use of the image forming apparatus 1 until the amount of the developer stabilizes, the control unit 8 executes a carrier discharge process every time a predetermined period has elapsed since the start of use of the image forming apparatus 1. The period until the amount of the developer stabilizes is calculated by calculating the amount of the carrier replenished to the developing container 41 from the amount of toner calculated from the integrated printing rate, and discharging an amount of the carrier less than the replenished carrier amount through the photosensitive drum 21 and the drum cleaning unit 23 in a timely manner, whereby toner clogging on the recovery path 111a can be suppressed.

[0072] For example, when the toner consumption per sheet of paper at a printing rate of 1% is 3 mg, if the printing rate is 5%, 1.5 mg of carrier per sheet of paper is supplied to the developing container 41. Thus, if the carrier of more than 0.15 mg and less than 1.5 mg per sheet of paper is discharged through the photosensitive drum 21 and the drum cleaning unit 23, toner clogging on the recovery path 111a can be suppressed. Therefore, it is possible to avoid a long period during which the developer (carrier) is not discharged from the developing container 41 from the start of use of the image forming apparatus 1 until the amount of the developer stabilizes. And the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a can be increased, and the fluidity of the waste developer can be suitably maintained.

[0073] Also, for example, regarding the case where the toner charge amount in the developing container 41 becomes less than a predetermined value, the control unit 8 measures the toner charge amount in the developing container 41, and when the toner charge amount is less than the predetermined value, executes a carrier discharge process.

[0074] Regarding the measurement of the toner charge amount, as shown in FIG. 2, the image forming apparatus 1 further includes a voltage application unit 12, a current detection unit 13, and a density detection unit 14.

[0075] The voltage application unit 12 includes, for example, a power supply unit and a control circuit (both not shown). The voltage application unit 12 is electrically connected to the developing roller 44 of the developing unit 40. The voltage application unit 12 applies a developing voltage to the developing roller 44. Specifically, the voltage application unit 12 applies a developing voltage obtained by superimposing a DC voltage and an AC voltage during development to the developing roller 44. The control unit 8 controls the application timing, voltage value, polarity, application time, etc. of the developing voltage to the developing roller 44 via the voltage application unit 12.

[0076] The current detection unit 13 detects the developing current flowing between the developing roller 44 and the photosensitive drum 21 when a developing voltage is applied to the developing roller 44. The control unit 8 receives information related to the amount of current flowing into the developing roller 44 detected by the current detection unit 13. By integrating the developing current i detected by the current detection unit 13 over the application time during development, the total charge amount Q of the developed toner image can be obtained. The control unit 8 can measure the total charge amount Q of the toner image based on the developing current i detected by the current detection unit 13.

[0077] The density detection unit 14 is disposed opposite to the surface of the photosensitive drum 21. The density detection unit 14 includes, for example, a light emitting unit including a light emitting element such as an LED (Light Emitting Diode), and a light receiving unit including a light receiving element such as a photodiode, and is provided with a reflection type optical sensor (both are not shown). The light emitting unit irradiates detection light at a predetermined angle toward the toner image transferred to the surface of the photosensitive drum 21. The light receiving unit receives the detection light irradiated by the light emitting unit toward the toner image and reflected by the toner image.

[0078] The light receiving unit includes a specular reflection light receiving unit that receives specularly reflected light and a diffuse reflection light receiving unit that receives diffusely reflected light among the detection light reflected by the toner image. When there is no toner on the surface of the photosensitive drum 21, the detection light irradiated from the light emitting unit is specularly reflected without being diffusely reflected by the toner and is incident more on the specular reflection light receiving unit. And as the amount of toner on the surface of the photosensitive drum 21 increases, more light is diffusely reflected by the toner, and gradually the incident amount of the diffuse reflection light receiving unit increases. In this way, the density detection unit 14 irradiates detection light from the light emitting unit toward the toner image, reflects it with the toner image, and detects the density of the toner image formed on the surface of the photosensitive drum 21 based on the detection light received by the light receiving unit (specular reflection light receiving unit and diffuse reflection light receiving unit).

[0079] Note that the density detection unit 14 may be configured to be disposed opposite to the surface of the intermediate transfer belt 31 and detect the density of the toner image primarily transferred to the surface of the intermediate transfer belt 31.

[0080] The toner weight M of the toner image formed on the surface of the photoreceptor drum 21 can be estimated by detecting the density of the toner image by the density detection unit 14 and converting it into weight. For example, by previously storing in a storage unit or the like a predetermined table or the like showing the relationship between the output value of the density detection unit 14 and the toner weight M and using the same, the control unit 8 can measure the toner weight M of the toner image based on the density of the toner image formed on the surface of the photoreceptor drum 21 detected by the density detection unit 14.

[0081] Then, the control unit 8 can measure the toner charge amount Q / M in the developing container 41 based on the total charge amount Q and the toner weight M of the toner image.

[0082] When the toner charge amount in the developing container 41 is less than a predetermined value, that is, when the toner charge amount in the developing container 41 is lower than the toner charge amount at the time of stability, it becomes difficult to discharge the carrier from the developing container 41. For example, as described above, when the toner charge amount at the time of stability is 30 μC / g and the toner charge amount in the developing container 41 is less than 30 μC / g, it becomes difficult to discharge the carrier from the developing container 41.

[0083] Thereby, for example, when the toner consumption per sheet of paper at a printing rate of 1% is 3 mg, if the printing rate is 5%, by discharging 0.15 mg or more and less than 1.5 mg of the carrier per sheet of paper through the photoreceptor drum 21 and the drum cleaning unit 23, toner clogging on the recovery path 111a can be suppressed. Therefore, when the toner charge amount in the developing container 41 becomes less than a predetermined value, it is possible to avoid a long period during which the developer (carrier) is not discharged from the developing container 41. And, the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a can be increased, and the fluidity of the waste developer can be suitably maintained.

[0084] Also, by using the current detection unit 13 and the density detection unit 14 as described above, it becomes possible to easily measure the toner charge amount in the developing container 41.

[0085] Also, when performing the above carrier discharge process, it is more preferable that the carrier current value of the developer is 8 μA or more and 80 μA or less. According to this configuration, the developer used for forming the toner image in the developing unit 40 has the characteristic of having a lower carrier resistance than the developer generally used in an image forming apparatus. As a result, the carrier easily moves to the photosensitive drum 21. Therefore, the carrier can be efficiently discharged through the photosensitive drum 21 and the drum cleaning unit 23. That is, the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path 111a can be increased, and the fluidity of the waste developer can be suitably maintained.

[0086] As described above, the embodiments of the present invention have been described. However, the scope of the present invention is not limited thereto, and various modifications can be made without departing from the gist of the invention.

[0087] For example, in the above embodiment, the image forming apparatus 1 is a so-called tandem type color printing image forming apparatus that sequentially forms a plurality of color images. However, the present invention is not limited to such a model. The image forming apparatus may be a color printing image forming apparatus that is not of the tandem type or a monochrome printing image forming apparatus, and may also be an image forming apparatus that does not use an intermediate transfer belt.

Industrial Applicability

[0088] The present invention can be used in an image forming apparatus.

Explanation of Reference Numerals

[0089] 1 Image forming apparatus 8 Control unit 11 Recovery unit 12 Voltage application unit 13 Current detection unit 14 Density detection unit 20 Image forming unit 21 Photosensitive drum (image carrier) 23 Drum cleaning unit 30 Transfer unit 31 Intermediate transfer belt (image carrier) 34 Belt cleaning section 40 Developing section 41 Developing container 42 First conveying member 43 Second conveying member 43c Regulation section 44 Developing roller (developer carrier) 46 Discharge section 46a Developer discharge port 111 Housing 111a Recovery path 111b Spent developer discharge port 112 Developer disposal pipe 112a Developer disposal path 113 First toner disposal pipe 113a First toner disposal path 114 Second toner disposal pipe 114a Second toner disposal path 115 Recovery member 412 First conveyance chamber 412a Developer supply port 413 Second conveyance chamber 414 First communication section 415 Second communication section 461 Discharge vane f1 First direction f2 Second direction S Sheet

Claims

1. An image carrier that carries a toner image on its surface, a developing container that houses a two-component developer containing toner and a carrier, a developer carrier that carries the developer in the developing container, and a discharge unit that discharges excess developer from the developing container, and a developing unit that develops an electrostatic latent image formed on the surface of the image carrier with the toner to form the toner image, a cleaning unit that removes the toner remaining on the surface of the image carrier, a recovery path that combines and conveys a developer waste path through which waste developer discharged from the discharge unit is conveyed and a toner waste path through which waste toner removed by the cleaning unit is conveyed, and a recovery unit that recovers the waste developer including the waste toner and the waste carrier through the recovery path, a control unit that controls operations of the image carrier, the developing unit, the cleaning unit, and the recovery unit, comprising: at least a part of the recovery path has a portion with a greater flow resistance than the toner waste path, when the weight ratio of the waste carrier to the waste toner in the waste developer in the recovery path is less than a predetermined value, the control unit moves the carrier from the developing unit to the surface of the image carrier during non-image formation, and executes a carrier discharge process of removing and discharging the carrier from the surface of the image carrier by the cleaning unit, the control unit measures the charge amount of the toner in the developing container, and when the charge amount of the toner is less than a predetermined value, executes the carrier discharge process, and an image forming apparatus characterized by this.

2. a current detection unit that detects a developing current flowing between the developer carrier and the image carrier when a developing voltage is applied to the developer carrier, a density detection unit that detects the density of the toner image formed on the surface of the image carrier, comprising: the control unit measures the total charge amount of the toner image based on the developing current detected by the current detection unit, measures the toner weight of the toner image based on the density of the toner image detected by the density detection unit, and measures the toner charge amount based on the total charge amount and the toner weight of the toner image, and the image forming apparatus according to Claim 1, characterized by this.

3. The control unit executes the carrier discharge process every time a predetermined period has elapsed since the start of use of the image forming apparatus, and the image forming apparatus according to Claim 1 or Claim 2, characterized by this.

4. The control unit executes the carrier discharge process when the weight ratio of the waste carrier to the waste toner of the waste developer in the recovery path is less than 5%. The image forming apparatus according to any one of claims 1 to 3.

5. The image carrier includes a photosensitive drum that carries the toner image formed by the developing unit on its surface, an intermediate transfer belt onto which the toner image carried by the photosensitive drum is primarily transferred, and includes The cleaning unit includes a drum cleaning unit that removes the toner remaining on the surface of the photosensitive drum, a belt cleaning unit that removes the toner remaining on the surface of the intermediate transfer belt, and includes The recovery unit includes a developer waste path that extends from the discharge unit of the developing unit and through which the waste developer is conveyed, a first toner waste path that extends from the drum cleaning unit and through which the waste toner is conveyed, a second toner waste path that extends from the belt cleaning unit and through which the waste toner is conveyed, and a recovery path where the developer waste path, the first toner waste path, and the second toner waste path merge, The image forming apparatus according to any one of claims 1 to 4, characterized by including.

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