Developing device and image forming apparatus

Abstract

To prevent over time the occurrence of a density difference between an upstream side and a downstream side along a conveyance direction of developer supply means that conveys and supplies developer along an axial direction of a developer holding body.SOLUTION: A developing device comprises: a developer holding body that holds developer and develops a latent image on an image holding body; developer supply means that conveys developer along an axial direction of the developer holding body and supplies the developer to the developer holding body; and gap adjustment means that sets a gap between the developer holding body and the image holding body to be larger on an upstream side than a downstream side in a conveyance direction of the developer supply means, and adjusts over time the gap to be equal on the upstream side and the downstream side in the conveyance direction of the developer supply means.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present invention relates to a developing device and an image forming apparatus. [Background technology]

[0002] Conventionally, techniques relating to developing devices have already been proposed, for example, as disclosed in Patent Document 1.

[0003] Patent Document 1 uses a two-component developer consisting of a magnetic carrier and toner, and has an agitation section that circulates the developer using two screws arranged parallel to a developer holder, and the developer held on the developer holder is agitated while being replaced by the developer on the screw side close to the developer holder, and toner is replenished to the screw side away from the developer holder, and is configured so that if the gap on the upstream side of the circulating developer on the developer holder side is Gp1 and the gap on the downstream side is Gp2, the relationship Gp1 > Gp2 is satisfied. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-17774 A Summary of the Invention [Problem to be solved by the invention]

[0005] The object of this invention is to suppress the occurrence of a concentration difference over time between the upstream and downstream sides in the transport direction of a developer supplying means that transports and supplies developer along the axial direction of a developer carrier. [Means for solving the problem]

[0006] The invention described in claim 1 includes a developer holder that holds a developer and develops a latent image on an image holder; a developer supplying means for supplying the developer to the developer carrier while transporting the developer in an axial direction of the developer carrier; a gap adjusting means for adjusting a gap between the developer carrier and the image carrier; A developing device comprising: The gap adjusting unit adjusts the gap from a state in which the gap on the upstream side in the transport direction of the developer supplying unit is larger than the gap on the downstream side in the initial operation of the developing device to a state in which the gap on the upstream side in the transport direction of the developer supplying unit is larger than the gap on the downstream side in the initial operation of the developing device. As it increases The gap on the upstream side is adjusted so that the gap on the upstream side and the gap on the downstream side are equal. This is a developing device.

[0007] In the invention described in claim 2, the gap adjustment means has two gap setting rotors that are rotatably arranged in contact with a surface of the image carrier at both ends in the axial direction of the developer supply means, The gap setting rotor disposed on the upstream side in the transport direction of the developer supply means has an outer diameter larger than that of the gap setting rotor disposed on the downstream side during the initial operation of the developing device, and the outer diameter of the gap setting rotor disposed on the downstream side is larger than that of the gap setting rotor disposed on the upstream side in the transport direction of the developer supply means. As it increases 2. The developing device according to claim 1, wherein the outer diameter is reduced.

[0008] In the invention described in claim 3, the two gap setting rotors are biased by biasing means so as to come into contact with the surface of the image carrier, 3. The developing device according to claim 2, wherein the gap setting rotor arranged upstream in the transport direction of the developer supply means is made of a material that is more easily worn than the gap setting rotor arranged downstream.

[0009] The invention described in claim 4 is a developing device described in claim 3, in which the biasing force of the biasing means for biasing the two gap setting rotors is set to be greater on the upstream side along the transport direction of the developer supply means than on the downstream side.

[0010] The invention described in claim 5 is a developing device described in claim 2, in which the upstream end of the image carrier in the transport direction of the developer supply means has a surface roughness set to be greater than that of the downstream end.

[0011] The invention described in claim 6 further comprises a transfer means for transferring the developed image of the image carrier onto a recording medium; a fixing unit for fixing the developed image on the image carrier onto the recording medium; Equipped with The developing device according to any one of claims 1 to 5 is used in an image forming apparatus. Effect of the Invention

[0012] According to the invention described in claim 1, it is possible to suppress the occurrence of concentration differences over time between the upstream and downstream sides in the transport direction of the developer supplying means, which transports and supplies developer along the axial direction of the developer holder.

[0013] According to the invention described in claim 2, the gap setting rotor arranged upstream in the transport direction of the developer supply means can suppress concentration differences along the transport direction compared to a case in which the outer diameter is initially set equal to that of the gap setting rotor arranged downstream.

[0014] According to the invention described in claim 3, the gap-setting rotor arranged upstream in the transport direction of the developer supply means can suppress the occurrence of concentration differences along the transport direction over time, compared to when the gap-setting rotor arranged downstream is made of a material having the same wear resistance.

[0015] According to the invention described in claim 4, wear of the gap-setting rotor located upstream can be promoted compared to a case in which the biasing forces of the biasing means for biasing the two gap-setting rotors are equal.

[0016] According to the invention described in claim 5, it is possible to promote wear of the gap-setting rotor located on the upstream side, compared to a case in which the surface roughness of the upstream and downstream ends of the image carrier in the transport direction of the developer supply means are equal.

[0017] According to the invention described in claim 6, compared to a case in which a developing device described in any of claims 1 to 5 is not used as the developing means, it is possible to suppress the occurrence of concentration differences over time between the upstream and downstream sides in the transport direction of the developer supplying means, which transports and supplies the developer along the axial direction of the developer holder. [Brief description of the drawings]

[0018] [Figure 1] 1 is an overall configuration diagram showing an image forming apparatus to which a developing device according to a first embodiment of the present invention is applied; [Diagram 2] FIG. 1 is a configuration diagram showing a process cartridge to which a developing device according to a first embodiment of the present invention is applied. [Diagram 3] FIG. 1 is a cross-sectional view showing a developing device according to a first embodiment of the present invention. [Figure 4] 11 is a graph showing a decrease in the amount of developer due to a reduction in the size of a developing device. [Diagram 5] FIG. 4 is an explanatory diagram illustrating the operation of the developing device. [Figure 6] FIG. 1 is a diagram showing the main configuration of a conventional developing device. [Figure 7] 4 is a graph showing characteristics of a conventional developing device. [Figure 8] FIG. 4 is an explanatory diagram showing the development characteristics of a photosensitive drum. [Figure 9] FIG. 1 is a diagram showing the main configuration of a conventional developing device. [Figure 10] 1 is a configuration diagram showing a main part of a developing device according to a first embodiment of the present invention; [Figure 11] 4 is a graph showing deterioration of toner over time. [Figure 12] 1 is a graph showing the relationship between the difference in the gap (so-called DRS) between the photosensitive drum and the developing roll at both ends in the axial direction of the developing roll and the difference in the amount of development. [Figure 13] FIG. 11 is a schematic diagram showing a main part of a developing device according to a second embodiment of the present invention. [Figure 14] FIG. 11 is a schematic diagram showing a main portion of a developing device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] [Embodiment 1] FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus to which a developing device according to a first embodiment of the present invention is applied, and FIG. 2 is a schematic diagram showing an image forming device of the image forming apparatus.

[0021] <Overall configuration of image forming apparatus> The image forming apparatus 1 according to the first embodiment is configured as, for example, a color printer. As shown in Fig. 1, the image forming apparatus 1 includes a plurality of image forming devices 10 that form toner images developed with toner constituting a developer, an intermediate transfer device 20 that holds the toner images formed by each image forming device 10 and transports them to a secondary transfer position where the toner images are finally secondarily transferred onto a recording paper 5 as an example of a recording medium, a paper feed device 30 that stores and transports the required recording paper 5 to be supplied to the secondary transfer position of the intermediate transfer device 20, and a fixing device 40 that fixes the toner image on the recording paper 5 that has been secondarily transferred by the intermediate transfer device 20. In addition, 1a in the figure indicates the device body of the image forming apparatus 1. This device body 1a is formed of a support structure member, an exterior cover, etc.

[0022] The imaging device 10 is composed of four imaging devices 10Y, 10M, 10C, and 10K that are dedicated to forming toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K), respectively. These four imaging devices 10 (Y, M, C, and K) are arranged in a line at an angle in the internal space of the device main body 1a.

[0023] The black imaging device 10K is disposed at the most downstream side along the moving direction B of the intermediate transfer belt 21 of the intermediate transfer device 20. The image forming device 1 has, as image forming modes, a full-color mode in which the color imaging devices 10 (Y, M, C) and the black (K) imaging device 10K are operated to form a full-color image, and a black and white mode in which only the black (K) imaging device 10K is operated to form a black and white (monochrome) image.

[0024] Each of the image forming devices 10 (Y, M, C, K) includes a rotating photoconductor drum 11 as an example of an image carrier, as shown in Fig. 2. Around the photoconductor drum 11, the following devices as an example of a toner image forming means are mainly arranged. The main devices are a charging device 12 that charges the image-forming peripheral surface (image bearing surface) of the photosensitive drum 11 to a required potential, an exposure device 13 that irradiates the charged peripheral surface of the photosensitive drum 11 with light based on image information (signal) to form an electrostatic latent image (for each color) with a potential difference, developing devices 14 (Y, M, C, K) as an example of a developing means that develops the electrostatic latent image with developer toner of the corresponding color (Y, M, C, K) to form a toner image, primary transfer devices 15 (Y, M, C, K) as an example of a primary transfer means that transfers each toner image to the intermediate transfer device 20, and drum cleaning devices 16 (Y, M, C, K) that remove and clean toner and other deposits that remain on and adhere to the image bearing surface of the photosensitive drum 11 after the primary transfer.

[0025] The photoconductor drum 11 has an image bearing surface formed on the circumferential surface of a grounded cylindrical or columnar substrate 111. The image bearing surface has a photoconductive layer (photosensitive layer) 112 made of a photosensitive material such as an organic photoconductive material (OPC). The photoconductor drum 11 is supported so as to rotate in the direction indicated by arrow A by power transmitted from a drive device (not shown).

[0026] The charging device 12 is composed of a contact-type charging roll arranged in contact with the photosensitive drum 11. A charging voltage is supplied to the charging device 12. When the developing device 14 performs reversal development, the charging voltage is a voltage or current of the same polarity as the charging polarity of the toner supplied from the developing device 14. A cleaning roll 121 that cleans the surface of the charging device 12 is arranged to be in contact with the rear side of the charging device 12. Note that the charging device 12 may be a non-contact charging device such as a scorotron arranged in a non-contact state with the surface of the photosensitive drum 11.

[0027] The exposure device 13 forms an electrostatic latent image by deflecting and scanning a laser beam LB configured according to image information along the axial direction of the photoconductor drum 11 of each of the image forming devices 10 (Y, M, C, K) for yellow (Y), magenta (M), cyan (C), and black (K). Note that the exposure device 13 may be an LED print head that forms an electrostatic latent image by irradiating the photoconductor drum 11 with light according to image information using LEDs (Light Emitting Diodes) as a plurality of light emitting elements arranged along the axial direction of each photoconductor drum 11.

[0028] Each of the developing devices 14 (Y, M, C, K) is configured by arranging a developing roll 141 that holds the developer and transports it to a development area facing the photosensitive drum 11 inside a device housing 140 in which an opening and a developer storage chamber are formed, a supply transport member 142 and a stirring transport member 143 such as two screw augers that transport the developer while stirring it so that it passes through the developing roll 141, and a layer thickness regulating member 144 that regulates the amount (layer thickness) of the developer held on the developing roll 141. In this developing device 14, a development voltage is supplied between the developing roll 141 and the photosensitive drum 11 from a power supply device (not shown). In addition, the developing roll 141, the supply transport member 142, and the stirring transport member 143 are rotated in the required direction by power transmitted from a drive device (not shown). Furthermore, a two-component developer containing a non-magnetic toner and a magnetic carrier is used as the above-mentioned four color developers 4 (Y, M, C, K). The developing device 14 will be described in detail later.

[0029] The primary transfer device 15 (Y, M, C, K) is a contact type transfer device equipped with a primary transfer roll that rotates in contact with the periphery of the photosensitive drum 11 via the intermediate transfer belt 21 and is supplied with a primary transfer voltage. As the primary transfer voltage, a DC voltage showing a polarity opposite to the charging polarity of the toner is supplied from a power supply device (not shown).

[0030] The drum cleaning device 16 is composed of a container-shaped main body 16a with an opening in one portion, a cleaning plate 16b that is arranged so as to come into contact with the peripheral surface of the photosensitive drum 11 after primary transfer with a required pressure and removes and cleans any remaining toner and other adhering matter, and a delivery member 16c such as a screw auger that collects the toner and other adhering matter removed by the cleaning plate 16b and transports it to a recovery system (not shown).

[0031] The intermediate transfer device 20 is disposed so as to be located above each of the image forming devices 10 (Y, M, C, K) as shown in Fig. 1. As shown in Fig. 1, the intermediate transfer device 20 is mainly composed of an intermediate transfer belt 21 that rotates in the direction indicated by the arrow B while passing through a primary transfer position between the photosensitive drum 11 and the primary transfer device 15 (primary transfer roll), a plurality of belt support rolls 22-25 that support the intermediate transfer belt 21 in a desired state from its inner surface and rotatably support it, a secondary transfer device 26 as an example of a secondary transfer means that is disposed on the outer peripheral surface (image bearing surface) side of the intermediate transfer belt 21 supported by the belt support roll 22 and secondarily transfers the toner image on the intermediate transfer belt 21 to the recording paper 5, and a belt cleaning device 27 that removes and cleans toner, paper powder, and other deposits that remain and adhere to the outer peripheral surface of the intermediate transfer belt 21 after passing through the secondary transfer device 26.

[0032] The intermediate transfer belt 21 is an endless belt made of a material in which a resistance adjusting agent such as carbon black is dispersed in a synthetic resin such as polyimide resin or polyamide resin. The belt support roll 22 is configured as a back support roll for secondary transfer, the belt support roll 23 is configured as a drive roll that is rotated by a drive device (not shown), the belt support roll 24 is configured as a surface finishing roll that forms the image forming surface of the intermediate transfer belt 21, and the belt support roll 25 is configured as a tension applying roll that applies tension to the intermediate transfer belt 21. The belt support roll 23 also serves as an opposing roll that faces the belt cleaning device 27.

[0033] The secondary transfer device 26 is a contact type transfer device including a secondary transfer roll that rotates in contact with the circumferential surface of the intermediate transfer belt 21 and is supplied with a secondary transfer voltage at a secondary transfer position, which is the outer circumferential surface portion of the intermediate transfer belt 21 supported by the belt support roll 22 in the intermediate transfer device 20. A DC voltage having the same polarity as or opposite to the charge polarity of the toner is supplied as a secondary transfer voltage from a power supply device (not shown) to the secondary transfer roll 26 or the belt support roll 22 of the intermediate transfer device 20.

[0034] 1, the fixing device 40 is configured by disposing, inside a housing (not shown) in which an inlet and an outlet for the recording paper 5 are formed, a heating rotator 41 in the form of a roll or belt that rotates in the direction indicated by the arrow and is heated by a heating means so that the surface temperature is maintained at a predetermined temperature, and a pressure rotator 42 in the form of a roll or belt that rotates in contact with the heating rotator 41 at a predetermined pressure substantially along the axial direction of the heating rotator 41. In the fixing device 40, the contact area where the heating rotator 41 and the pressure rotator 42 come into contact with each other becomes a fixing processing section that performs the required fixing process (heating and pressurization).

[0035] The paper feeder 30 is disposed so as to be located below the imaging devices 10 (Y, M, C, K). This paper feeder 30 is mainly composed of one (or more) paper containers 31 that contain stacks of recording paper 5 of desired sizes, types, etc., and a feeder 32 that feeds the recording paper 5 one sheet at a time from the paper container 31. The paper container 31 is attached so that it can be pulled out, for example, from the front side (left side in the drawing), which is the side that a user of the device main body 1a faces during operation.

[0036] Examples of the recording paper 5 include thin paper such as plain paper or tracing paper used in electrophotographic copiers and printers, or OHP sheets, etc. In order to further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper 5 is as smooth as possible, and for example, coated paper in which the surface of plain paper is coated with a resin or the like, or so-called thick paper with a relatively large basis weight such as art paper for printing can be suitably used.

[0037] Between the paper feed device 30 and the secondary transfer device 26, there is provided a paper feed conveying path 34 consisting of one or more paper conveying roll pairs 33 and conveying guides (not shown) that convey the recording paper 5 sent out from the paper feed device 30 to the secondary transfer position. The paper conveying roll pair 33 arranged at a position immediately before the secondary transfer position in the paper feed conveying path 34 is configured as, for example, a roll (registration roll) that adjusts the conveying timing of the recording paper 5. In addition, between the secondary transfer device 26 and the fixing device 40, there is provided a paper conveying path 35 for conveying the recording paper 5 sent out from the secondary transfer device 26 after the secondary transfer to the fixing device 40. Furthermore, in a portion near the discharge port for the recording paper 5 formed in the device main body 1a, there is provided an ejection conveying path 38 equipped with a paper ejection roll pair 37 for ejecting the recording paper 5 sent out from the fixing device 40 after the fixing to a paper ejection section 36 provided at the top of the device main body 1a.

[0038] Between the fixing device 40 and the paper discharge roll pair 37, a switching gate (not shown) for switching the paper transport path is provided. The paper discharge roll pair 37 is configured so that its rotation direction can be switched between a forward direction (discharge direction) and a reverse direction. When forming images on both sides of the recording paper 5, the rotation direction of the paper discharge roll pair 37 is switched from the forward direction (discharge direction) to a reverse direction after the rear end of the recording paper 5 with an image formed on one side passes through the switching gate. The recording paper 5 transported in the reverse direction by the paper discharge roll pair 37 has its transport path switched by the switching gate, and is transported to a double-sided transport path 39 formed in a substantially vertical direction along the back surface of the device main body 1a. The double-sided transport path 39 includes a paper transport roll pair 39a for transporting the recording paper 5 to the paper transport roll pair 33 in an inverted state, a transport guide, and the like.

[0039] Moreover, in this embodiment 1, a manual feed tray 50 is provided on the front side of the device main body 1a so as to be openable and closable around a fulcrum 51. Recording paper 5 fed from the manual feed tray 50 is separated one by one by an auxiliary feed device 52 and conveyed to the feed device 32 along a manual feed conveying path 53.

[0040] 1, reference numerals 145 (Y, M, C, K) denote toner cartridges arranged in a direction perpendicular to the paper surface, each cartridge containing developer including at least toner to be supplied to a corresponding developing device 14 (Y, M, C, K). The toner cartridges 145 (Y, M, C, K) supply toner of each color to the corresponding developing device 14 (Y, M, C, K) via a toner supply device (not shown).

[0041] 1 indicates a control device that comprehensively controls the operation of the image forming apparatus 1. The control device 100 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), or a bus for connecting the CPU, the ROM, etc., a communication interface, etc. (not shown).

[0042] <Operation of the image forming device> Hereinafter, a basic image forming operation by the image forming apparatus 1 will be described.

[0043] Here, the operation in a full-color mode in which the four image forming devices 10 (Y, M, C, K) are used to form a full-color image composed of a combination of toner images of four colors (Y, M, C, K) will be described.

[0044] When the image forming apparatus 1 receives command information requesting a full-color image forming operation (printing) from a user interface or printer driver (not shown), the four image creating devices 10 (Y, M, C, K), the intermediate transfer device 20, the secondary transfer device 26, the fixing device 40, etc. start up.

[0045] 1 and 2, in each imaging device 10 (Y, M, C, K), first, each photoconductor drum 11 rotates in the direction indicated by the arrow A, and each charging device 12 charges the surface of each photoconductor drum 11 to a required polarity (negative polarity in the first embodiment) and potential. Next, the exposure device 13 irradiates the surface of the charged photoconductor drum 11 with laser light LB based on an image signal obtained by converting image information input to the image forming device 1 into each color component (Y, M, C, K), and forms an electrostatic latent image of each color component composed of a required potential difference on the surface.

[0046] Next, each image forming device 10 (Y, M, C, K) develops the electrostatic latent image of each color component formed on the photoconductor drum 11 by supplying toner of the corresponding color (Y, M, C, K) charged to the required polarity (negative polarity) from the developing roll 141 and electrostatically attaching it to the electrostatic latent image of each color component. Through this development, the electrostatic latent image of each color component formed on each photoconductor drum 11 is visualized as a toner image of four colors (Y, M, C, K) developed with the toner of the corresponding color.

[0047] Next, when the toner images of each color formed on the photosensitive drum 11 of each image creating device 10 (Y, M, C, K) are transported to the primary transfer position, the primary transfer device 15 (Y, M, C, K) performs primary transfer of the toner images of each color in such a manner that they are superimposed in order onto the intermediate transfer belt 21 rotating in the direction indicated by arrow B of the intermediate transfer device 20.

[0048] In addition, in each of the imaging devices 10 (Y, M, C, K) where the primary transfer has been completed, the drum cleaning device 16 scrapes off any adhering matter to clean the surface of the photosensitive drum 11. This makes each of the imaging devices 10 (Y, M, C, K) ready for the next image formation operation.

[0049] Next, the intermediate transfer device 20 conveys the primary transferred toner image to the secondary transfer position by the rotation of the intermediate transfer belt 21. Meanwhile, the paper feeder 30 sends out the required recording paper 5 to the paper feed path 34 in accordance with the image creation operation. In the paper feed path 34, a pair of paper feed rolls 33 as registration rolls feeds and supplies the recording paper 5 to the secondary transfer position in accordance with the transfer timing.

[0050] At the secondary transfer position, the secondary transfer device 26 performs secondary transfer of the toner images on the intermediate transfer belt 21 all at once onto the recording paper 5. After the secondary transfer is completed in the intermediate transfer device 20, the belt cleaning device 27 removes and cleans the surface of the intermediate transfer belt 21 to remove any toner or other deposits remaining thereon after the secondary transfer.

[0051] Next, the recording paper 5 onto which the toner image has been secondarily transferred is peeled off from the intermediate transfer belt 21 and then transported to the fixing device 40 via a paper transport path 35. In the fixing device 40, the recording paper 5 after the secondary transfer is introduced and passed through a contact portion between a rotating heating rotator 41 and a pressing rotator 42, thereby performing the necessary fixing process (heating and pressing) to fix the unfixed toner image onto the recording paper 5. Finally, in the case of an image forming operation in which an image is only formed on one side of the recording paper 5 after fixing, the recording paper 5 after fixing is discharged by a paper discharge roll pair 37 to a paper discharge section 36 installed at the top of the device main body 1a.

[0052] By the above operation, the recording paper 5 is outputted on which a full-color image formed by combining four color toner images is formed.

[0053] By operating only the black (K) image forming device 10K, the recording paper 5 on which a monochrome image is formed is output.

[0054] <Process cartridge configuration> In this embodiment, the image forming members consisting of the photosensitive drum 11, the charging device 12 arranged around the photosensitive drum 11, the developing device 14, and the drum cleaning device 16 are assembled into an integrated unit to form a process cartridge 80 (Y, M, C, K) as an example of an image forming unit.

[0055] FIG. 2 is a cross-sectional view showing the process cartridge 80. As shown in FIG.

[0056] 2, the process cartridge 80 includes a process cartridge main body as an example of an image forming unit main body in which the photosensitive drum 11, the charging device 12, the developing device 14, and the drum cleaning device 16 are mounted as an integrated unit. In the illustrated embodiment, the process cartridge main body is made up of a device housing 140 of the developing device 14, a main body 16a of the drum cleaning device 16, and further frame members (not shown) disposed at the front and rear ends along the mounting direction of the process cartridge 80.

[0057] The photosensitive drum 11 is rotatably mounted on a frame member (not shown) of the process cartridge body. On the other hand, the developing device 14 is mounted on the process cartridge body so as to be able to swing about a swing fulcrum 146 in a direction in which the developing roll 141 approaches and separates from the photosensitive drum 11, as shown in FIG. 3. The developing device 14 has tracking rolls 161 and 162 as gap setting members arranged at both ends along the axial direction of the developing roll 141, which are stirring and conveying members, by an elastic member (not shown), such as a coil spring, stretched between the device housing 140 of the developing device 14 and the frame member of the process cartridge body to which the photosensitive drum 11 is rotatably mounted. Although the tracking rolls are not shown in FIG. 3, the tracking rolls are configured to abut against the surface of the photosensitive drum 11. By configuring in this way, the gap (so-called DRS) between the photosensitive drum 11 and the developing roll 141 is set to a required value with high accuracy.

[0058] <Configuration of the developing device> 2 and 3 are cross-sectional configuration diagrams showing the developing device according to the first embodiment.

[0059] As shown in FIG. 2 and FIG. 3, the developing device 14 includes a device housing 140 as an example of a developing device main body. The device housing 140 is roughly divided into a lower housing 140a arranged at the lower part of the developing device 14 and an upper housing 140b arranged at the upper part of the developing device 14. The lower housing 140a and the upper housing 140b are airtightly joined, and inside the device housing 140, as shown in FIG. 2, a developer storage chamber 150 that stores a two-component developer 4 is formed. An opening 151 is provided in an area of ​​the device housing 140 facing the photosensitive drum 11. In addition, inside the device housing 140, a developing roll 141 as an example of a developer holder is arranged rotatably along the arrow direction C so that a part of the developing roll 141 is exposed to the opening 151. The developing roll 141 has a magnet roll 141a as an example of a magnetic field generating means that is fixedly disposed inside and has magnetic poles of required polarity disposed at required positions along the circumferential direction, and a cylindrical developing sleeve 141b as an example of a developer transport member that is rotatably disposed on the outer periphery of the magnet roll 141a at a required rotation speed along the direction of arrow C. The developing sleeve 141b is formed into a cylindrical shape from a non-magnetic material such as aluminum or non-magnetic stainless steel.

[0060] In this embodiment 1, the rotation direction of the developing sleeve 141b is set to be opposite to the rotation direction of the photosensitive drum 11. That is, the rotation direction A of the photosensitive drum 11 is set to be clockwise as shown in FIG. 2, whereas the rotation direction C of the developing sleeve 141b is set to be counterclockwise. As a result, the outer peripheral surface of the developing sleeve 141b moves in the same direction as the movement direction of the surface of the photosensitive drum 11 in the development region facing the photosensitive drum 11. The rotation direction of the developing sleeve 141b may be set to be the same as the rotation direction A of the photosensitive drum 11.

[0061] The rotation speed of the developing sleeve 141b is determined according to the productivity of the image forming apparatus 1, which is determined by the rotation speed (process speed) of the photoconductor drum 11. The productivity of the image forming apparatus 1 is represented, for example, by the number of A4 size SEF recording papers 5 on which images can be formed per unit time.

[0062] The magnet roll 141a is a development area facing the photosensitive drum 11, and is provided with a development pole S1 disposed at a position slightly displaced upstream in the rotation direction of the photosensitive drum 11 from the closest position, a transport pole N1 disposed at the downstream end in the rotation direction of the developing sleeve 141b at the opening 151 of the device housing 140 and adjacent to the downstream side of the development pole S1 in the rotation direction of the developing sleeve 141b, and transports the developer 4 used for development into the device housing 140, and a transport pole N2 disposed downstream of the transport pole N1 in the rotation direction of the developing sleeve 141b, and transports the developer 4 used for development into the device housing 140. The developer roller 141a includes a pick-off pole S2, which also functions as a transport pole for transporting the developer 4 to the inside of the device housing 140 together with the pole N1 and peels off the developer 4 from the surface of the developing sleeve 141b, a pickup pole S3, which is disposed downstream of the pick-off pole S2 in the rotation direction of the developing sleeve 141b and causes new developer 4 supplied while being stirred by the supply transport member 142 to be attracted to the surface of the developing sleeve 141b, and a trimming pole N2, which is disposed downstream of the pickup pole S3 in the rotation direction of the developing sleeve 141b and works with a layer thickness regulating member 144 to make the developer layer uniform. At a position facing the trimming pole N2 of the magnet roll 141a, a layer thickness regulating member 144 is disposed to regulate the amount (layer thickness) of the developer 4 held on the surface of the developing sleeve 141b. The layer thickness regulating member 144 is made of a magnetic material formed in a cylindrical shape and regulates the layer thickness of the developer 4 to a required value when the magnetic force of the trimming pole N2 acts on the developer 4. The developer 4 is formed in a magnetic brush-like layer on the surface of the developing sleeve 141b, and is attracted to and transported by the magnetic poles of the magnet roll 141a. The layer thickness regulating member 144 may be made of a non-magnetic material such as SUS.

[0063] Inside the device housing 140, a supply transport member 142 as an example of a developer supply means, such as a screw auger (supply auger) that scoops up the developer 4 contained in the developer storage chamber 150 and supplies it to the developing roll 141, is disposed obliquely below the developing roll 141 along the vertical direction. The supply transport member 142 is rotated counterclockwise by a drive device (not shown). Inside the device housing 140, a stirring transport member 143 as an example of a developer transport means, such as a screw auger (admix auger) that stirs and transports the developer 4 supplied to the device housing 140, is disposed on the back side of the supply transport member 142. The stirring transport member 143 is also rotated clockwise by a drive device (not shown).

[0064] The lower housing 140a is provided with a first storage section 147 and a second storage section 148 each having a substantially semi-cylindrical cross section to store the supply transport member 142 and the stirring transport member 143. The first storage section 147 and the second storage section 148 are separated by a partition wall 152 provided in the lower housing 140a. The upper housing 140b is provided with a third storage section 153 which stores the developer 4 together with the first storage section 147 of the lower housing 140a and supplies it to the developing roll 141.

[0065] 3, first and second passages 154, 155 are provided at both ends along the longitudinal direction of the partition wall 152, respectively, for transferring the developer 4 between the supply transport member 142 and the agitation transport member 143. The end of the agitation transport member 143 on the inner side along the axial direction is extended so as to protrude toward the rear side of the device housing 140. A substantially cylindrical supply section 156 is provided at the extended portion of the agitation transport member 143. The cylindrical supply section 156 is provided with a supply port 157 through which the toner of the corresponding color is supplied from the toner cartridge 145 (Y, M, C, K). The supply port 157 is covered by a shutter member (not shown) so as to be freely opened and closed.

[0066] In recent years, the developing device 14 configured as described above has tended to be significantly smaller in size in accordance with the miniaturization of the image forming device 1. Naturally, the miniaturized developing device 14 also has a smaller device housing 140 itself, and the amount of developer 4 accommodated in the first accommodating portion 147 and the second accommodating portion 148 in the device housing 140 also becomes smaller.

[0067] 4, the amount of developer 4 contained inside the developing device 14 is significantly reduced as the developing device 14 becomes smaller, for example, from 200 g in a large developing device 14 to 50 g in a small developing device 14. In this case, if the toner concentration of the developer 4 inside the developing device 14 is 10% (weight ratio), the toner amount of the large developing device 14 is 20 g, while the toner amount of the small developing device 14 is extremely small at 5 g.

[0068] Therefore, in the developing device 14 which has been made small in size in accordance with the miniaturization of the image forming apparatus 1, when an image with high image density such as a solid image (100% density) is developed, the following technical problem occurs.

[0069] That is, when an image with high image density such as a solid image is developed in a compact developing device 14, the developer 4 supplied to the developing roll 141 on the upstream side along the conveying direction of the supplying and conveying member 142 consumes toner by developing the high density image, as shown in FIG. 5. At this time, the amount of developer 4 conveyed by the supplying and conveying member 142 and supplied to the developing roll 141 in the compact developing device 14 is smaller than that in the large developing device 14. Therefore, on the downstream side along the conveying direction of the supplying and conveying member 142, the developer 4 with reduced toner density due to toner consumption in developing the high density image is supplied to the developing roll 141, resulting in a technical problem in that the density of the image developed by the developing roll 141 is reduced.

[0070] Therefore, in order to solve this technical problem, in the developing device 14, instead of setting the upstream value Gp1 of the gap DRS between the photosensitive drum 11 and the developing roll 141 in the transport direction of the supply and transport member 142 equal to the downstream value Gp2 as shown in FIG. 6(a), initially setting the upstream value Gp1 of the gap DRS between the photosensitive drum 11 and the developing roll 141 in the transport direction of the supply and transport member 142 larger than the downstream value Gp2 (Gp1>Gp2) as shown in FIG. 6(b), and configuring the development concentration of the developing roll 141 in the transport direction of the supply and transport member 142 to be equal on the upstream and downstream sides as shown in FIG. 7, thereby eliminating the concentration difference between the upstream and downstream sides in the transport direction of the supply and transport member 142.

[0071] In the developing device 14, the toner in the developer 4 held on the surface of the developing roll 141 migrates to and adheres to the surface of the photoconductor drum 11, thereby developing the electrostatic latent image formed on the surface of the photoconductor drum 11. At that time, the developer 4 forms a magnetic brush on the surface of the developing roll 141, and is transferred from the surface of the developing roll 141 to the surface of the photoconductor drum 11 by electrostatic force (Coulomb force) acting on the toner in the developer 4 due to the potential difference between the surface potential of the photoconductor drum 11 and the development bias potential applied to the developing roll 141, and is developed.

[0072] At this time, in the developing device 14, as shown in FIG. 8, when toner T, which is a charged particle, is present in the electric field E caused by the potential difference between the photosensitive drum 11 and the developing roll 141, an electrostatic force (Coulomb force) F, as shown in the following formula, acts on the toner T. F=e·E Here, e is the amount of charge that the toner T has.

[0073] Moreover, the electric field E is given by the following formula: E = (V L -V B ) / (s / ε s +s / ε D ) Here, V L is the surface potential on the photoconductor drum 11, VB is the DC component of the developing bias applied to the developing roll 141, ε s is the relative dielectric constant of the photosensitive layer 112 of the photosensitive drum 11, ε D indicates the relative dielectric constant of the developer layer.

[0074] The surface of the photosensitive drum 11 is charged to a desired surface potential V H After being charged to , the image area is exposed by the exposure device 13 to an exposed area potential V L At that time, the DC component V of the developing bias is applied to the developing roll 141 facing the photosensitive drum 11. B is applied to the toner T, and the toner T is attracted to the surface potential V L and the developing bias potential V of the developing roll 141 B The development is performed at a development potential determined by the potential difference between the

[0075] The toner T is agitated with the carrier and transported inside the device housing 140 of the developing device 14, and is frictionally charged to a negative polarity. Meanwhile, the surface of the photoconductor drum 11 is charged to a required negative surface potential V H After being charged to , the image area is exposed by the exposure device 13 to an exposed area potential V L The potential decreases (negative polarity).

[0076] Therefore, the toner T is attracted to the surface potential V H and the surface potential V L and the developing bias potential V applied to the developing roll 141. B This causes reversal development.

[0077] In the developing device 14, as described above, by setting the value Gp1 of the gap DRS between the photoconductor drum 11 and the developing roll 141 on the upstream side in the transport direction of the supply transport member 142 to be larger than the value Gp2 on the downstream side (Gp1>Gp2), the developing electric field E becomes larger on the downstream side than on the upstream side in the transport direction of the supply transport member 142. As a result, in the developing device 14, the difference in development concentration between the upstream side and the downstream side in the transport direction of the supply transport member 142 is eliminated as shown in FIG.

[0078] However, if the DRS, which is the gap between the photosensitive drum 11 and the developing roll 141 in the developing device 14, is initially set larger on the upstream side along the transport direction of the supply and transport member 142 than on the downstream side, as shown in Figure 9, then over time, as the developer 4 in the developing device 14 deteriorates and the developing performance decreases, a new technical problem arises in that the image density decreases on the upstream side along the transport direction of the supply and transport member 142, where the DRS is relatively larger, compared to the downstream side.

[0079] Therefore, the developing device 14 according to this embodiment 1 is configured to include a gap adjustment means that initially sets the gap between the developer carrier and the image carrier so that it is larger on the upstream side in the transport direction of the developer supply means than on the downstream side, and adjusts it over time so that the upstream and downstream sides in the transport direction of the developer supply means become equal.

[0080] That is, in the developing device 14 according to the first embodiment, as shown in FIG. 10, tracking rolls 161 and 162 are rotatably mounted as an example of a gap setting means for setting the gap DRS between the photosensitive drum 11 and the developing roll 141 when the developing roll 141 rotates. The tracking rolls 161 and 162 are rotatably mounted on rotation shafts 163 and 164 that rotatably support the developing sleeve 141b of the developing roll 141. The tracking rolls 161 and 162 are formed in a disk shape having a required outer diameter by a synthetic resin such as POM. The tracking rolls 161 and 162 are mounted between the developing device 14 and the photosensitive drum 11 and are configured to contact the surface of the photosensitive drum 11 with a required pressing force by coil springs 165 and 166 as an example of a biasing means. The tracking rolls 161 and 162 also function as a gap adjustment means together with the coil springs 165 and 166.

[0081] The photosensitive drum 11 does not have a photosensitive layer 112 at either end along its axial direction, and a base material (blank tube) 111 made of aluminum, stainless steel, or the like is exposed. The tracking rolls 161, 162 contact (abut) the base material 111 located at either end along the axial direction of the photosensitive drum 11.

[0082] In this embodiment 1, as shown in FIG. 10, the outer diameters of the tracking rolls 161, 162, which are respectively arranged at both ends along the axial direction of the developing roll 141, are set so as to be larger on the upstream side than on the downstream side along the transport direction of the supply and transport member 142.

[0083] As a result, the gap (DRS) between the photoconductor drum 11 and the developing roll 141 is set such that a value Gp1 on the upstream side along the transport direction of the supply transport member 142 is larger than a value Gp2 on the downstream side.

[0084] Also, in this embodiment 1, as shown in FIG. 10, the spring constant k1 of the coil spring 165 that biases the upstream side of the supply and conveying member 142 along the conveying direction is set to be equal to the spring constant k2 of the coil spring 166 that biases the downstream side of the supply and conveying member 142 along the conveying direction (k1=k2) or greater than the spring constant k2 of the coil spring 166 that biases the downstream side of the supply and conveying member 142 along the conveying direction (k1>k2).

[0085] The tracking rolls 161 and 162 made of synthetic resin come into contact with both ends along the axial direction of the photosensitive drum 11 made of a metal tube, and as a result wear over time, the outside diameter gradually becomes smaller.

[0086] The outer diameter of the tracking rolls 161, 162 arranged at both ends in the axial direction of the developing roll 141 is set to be larger on the upstream side than on the downstream side along the transport direction of the supply transport member 142. Therefore, when the spring constants k1, k2 of the coil springs that urge the tracking rolls 161, 162 toward the photosensitive drum 11 are equal, or when the spring constant k1 of the coil spring 165 that urges the upstream side along the transport direction of the supply transport member 142 is set to be larger than the spring constant k2 of the coil spring 166 that urges the downstream side (k1>k2), of the pressing forces F at which the tracking rolls 161, 162 contact (abut) against the surface of the photosensitive drum 11, the pressing force F1 on the upstream side along the transport direction of the supply transport member 142 becomes larger than the pressing force F2 on the downstream side (F1>F2).

[0087] As a result, the difference between the outer diameters of the tracking rolls 161, 162 on the upstream side and the downstream side along the transport direction of the supply transport member 142 decreases over time, and the two values ​​converge to approximately the same value. The gap (DRS) between the photoconductor drum 11 and the developing roll 141 is configured such that the upstream value Gp1 and the downstream value Gp2 along the transport direction of the supply transport member 142 are approximately equal (Gp1 ≈ Gp2).

[0088] In this way, the tracking rolls 161, 162, which are respectively arranged at both ends along the axial direction of the developing roll 141, gradually wear (over time) as they rotate in contact with the photosensitive drum 11, and the initially set difference in outer diameter between the tracking rolls 161 and 162 is eliminated, and over time the values ​​Gp1 ≒ Gp2 become approximately equal.

[0089] Incidentally, the developing device 14 develops the electrostatic latent image formed on the surface of the photosensitive drum 11, and as a result, the toner in the developer 4 contained inside the device housing 140 is consumed.

[0090] The developing devices 14 of the imaging devices 10 (Y, M, C, K) for yellow (Y), magenta (M), cyan (C) and black (K) are supplied with toner of the corresponding color from toner cartridges 145 (Y, M, C, K) as shown in FIG. 1.

[0091] 3, in the developing device 14, toner supplied from a toner cartridge 145 is transported by an agitating and transporting member 143 along the axial direction of the agitating and transporting member 143. Then, while the toner supplied inside the developing device 14 is transported along the axial direction by the agitating and transporting member 143, the toner is agitated with the carrier in the developer 4 contained inside the device housing 140 and is frictionally charged to a negative polarity.

[0092] The developer 4 transported to the end along the axial direction by the agitating transport member 143 is transported to the supply transport member 142 via the second passage portion 155. The developer 4 transported to the supply transport member 142 is transported along the axial direction by the supply transport member 142 and is supplied to the developing roll 141 by the supply transport member 142.

[0093] The developing roll 141 develops the electrostatic latent image formed on the surface of the photoconductor drum 11, thereby consuming the toner in the developer 4. After the developer 4 supplied to the developing roll 141 develops the electrostatic latent image formed on the surface of the photoconductor drum 11, the developer 4 is once peeled off from the surface of the developing roll 141 as shown in FIG. 2, and new developer 4 is supplied to the surface of the developing roll 141 by the supply and transport member 142.

[0094] The developer 4 transported to the end in the axial direction by the supply transport member 142 is delivered to the agitating transport member 143 via the first passage portion 154.

[0095] <Function of the developing device> In the developing device 14 according to this embodiment 1, it is possible to suppress the occurrence of a concentration difference over time between the upstream and downstream sides along the transport direction of the developer supplying means, which transports and supplies the developer along the axial direction of the developer holder, as follows.

[0096] That is, as shown in FIG. 2, the developing device 14 according to the first embodiment is miniaturized, and the device housing 140 of the developing device 14 is formed small (small capacity).

[0097] Therefore, when the developing device 14 initially develops an image with a high image density, such as a solid image (100% density), as shown in FIG. 5, the developer 4 supplied to the developing roll 141 on the upstream side along the transport direction of the supply and transport member 142 develops the high-density image and the toner is consumed, whereas on the downstream side along the transport direction of the supply and transport member 142, the developer 4 with the toner concentration reduced due to the toner consumption is supplied to the developing roll 141.

[0098] Therefore, in the developing device 14, the development density tends to be higher on the upstream side in the transport direction of the supply transport member 142 than on the downstream side initially.

[0099] 10, in the developing device 14 according to the first embodiment, the outer diameter of the tracking roll 161 arranged at one end along the axial direction of the developing roll 141 is set to be larger than the outer diameter of the tracking roll 162 arranged at the other end. Therefore, the developing roll 141 has a lower development concentration initially on the upstream side along the transport direction of the supply transport member 142 than on the downstream side.

[0100] Therefore, in the developing device 14, as shown in FIG. 12, due to the miniaturization of the developing device 14, the development concentration tends to be higher on the upstream side along the transport direction of the supply and transport member 142 than on the downstream side. In addition, the gap between the photosensitive drum 11 and the developing roll 141 is set larger on the upstream side along the transport direction of the supply and transport member 142 than on the downstream side, so that the development concentration tends to be lower on the upstream side along the transport direction of the supply and transport member 142 than on the downstream side. As a result, the development concentration on the upstream side and downstream side along the transport direction of the supply and transport member 142 is approximately equal.

[0101] On the other hand, in the developing device 14, the developer 4 contained inside the device housing 140 deteriorates over time, and the charge control agent and the like added to the toner T becomes embedded inside the toner T or detaches from the surface of the toner T, reducing the charging performance of the toner. In addition, the charge control agent detaches from the surface of the toner T and adheres to the surface of the carrier, causing the developer 4 to deteriorate.

[0102] In the developing device 14, when the developer 4 deteriorates, as shown in FIG. 11, the charge amount of the toner that should be charged negatively decreases, or a portion of the toner becomes charged positively, which is the opposite polarity to the original negative charging polarity.

[0103] 12, when the developer 4 in the developing device 14 deteriorates over time, the difference in the development concentration (development amount) caused by the difference in the gap between the photoconductor drum 11 and the developing roll 141 between the upstream side and the downstream side along the transport direction of the supply transport member 142 decreases. As a result, in the developing device 14, the difference in the development amount between the upstream side and the downstream side along the transport direction of the supply transport member 142 is eliminated, and when the gap between the upstream side and the downstream side along the transport direction of the supply transport member 142 is equal, the development amount also changes to be approximately equal.

[0104] In the developing device 14 according to this embodiment 1, as shown in FIG. 10, initially, the gap between the photosensitive drum 11 and the developing roll 141 is set to be larger on the upstream side along the transport direction of the supply transport member 142 than on the downstream side.

[0105] Therefore, as shown in Figure 10, in the developing device 14, the tracking roll 161 arranged upstream along the transport direction of the supply and transport member 142 contacts the surface of the photosensitive drum 11 with a contact force F greater than that of the tracking roll 162 arranged downstream.

[0106] Therefore, as shown in FIG. 10(b), in the developing device 14, the tracking roll 161 arranged on the upstream side along the transport direction of the supply and transport member 142 is more susceptible to wear than the tracking roll 162 arranged on the downstream side, and over time, the outer diameter of the tracking roll 161 arranged on the upstream side along the transport direction of the supply and transport member 142 becomes approximately equal to the outer diameter of the tracking roll 162 arranged on the downstream side.

[0107] As a result, in the developing device 14, when the gap between the photosensitive drum 11 and the developing roll 141 becomes approximately equal on the upstream and downstream sides along the transport direction of the supply and transport member 142, the developer 4 contained inside the device housing 140 deteriorates, and the amount of developer on the upstream and downstream sides along the transport direction of the supply and transport member 142 becomes approximately equal.

[0108] In this way, in the developing device 14 of the above-mentioned embodiment 1, the amount of development becomes approximately equal on the upstream and downstream sides along the transport direction of the supply and transport member 142 over time, thereby preventing or suppressing differences in image density.

[0109] [Embodiment 2] Second Embodiment FIG. 13 is a structural view showing a developing device according to a second embodiment of the present invention.

[0110] In the developing device of this embodiment 2, the two gap-setting rotors are each urged by a urging means so as to contact the surface of the image carrier, and the gap-setting rotor located upstream in the transport direction of the developer supply means is formed from a material that is more susceptible to wear than the gap-setting rotor located downstream.

[0111] That is, in the developing device 14 according to the second embodiment, as shown in FIG. 13, the tracking roll 162 disposed on the downstream side is made of, for example, polyoxymethylene (POM) or polyacetal (PA).

[0112] On the other hand, the tracking roll 161 arranged on the upstream side is formed of, for example, polypropylene (PP), polystyrene (PS), polyethylene (PE), elastomer or other synthetic resin, which is softer and more susceptible to wear than the tracking roll 162 arranged on the downstream side.

[0113] At this time, the spring constant k1 of the coil spring 165 arranged at one end along the axial direction of the developing roll 141 is set to be equal to (k1=k2) or larger than (k1>k2) the spring constant k2 of the coil spring 166 arranged at the other end.

[0114] Thus, in the developing device 14 according to the above-mentioned embodiment 2, as shown in FIG. 13, the tracking roll 161 arranged on the upstream side along the transport direction of the supply and transport member 142 is made of a material that is softer and more susceptible to wear than the tracking roll 162 arranged on the downstream side.

[0115] As a result, over time, in the developing device 14, the tracking roll 161 arranged on the upstream side along the transport direction of the supply and transport member 142 is more likely to wear than the tracking roll 162 arranged on the downstream side, and the tracking roll 161 arranged on the upstream side along the transport direction of the supply and transport member 142 wears and becomes smaller in outer diameter.

[0116] Therefore, in the developing device 14, the difference in outer diameter between the tracking roll 161 arranged on the upstream side along the transport direction of the supply and transport member 142 and the tracking roll 162 arranged on the downstream side decreases over time and becomes approximately equal in value.

[0117] Therefore, the developing device 14 according to the above-mentioned second embodiment is capable of adjusting, over time, the difference in outer diameter between the tracking roll 161 arranged upstream along the transport direction of the supply and transport member 142 and the tracking roll 162 arranged downstream so that they become approximately equal with even greater certainty.

[0118] The other configurations and operations are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0119] [Embodiment 3] Third Embodiment FIG. 14 is a structural view showing a developing device according to a third embodiment of the present invention.

[0120] In the developing device 14 according to the third embodiment, the upstream end of the image carrier in the transport direction of the developer supplying means is set to have a larger surface roughness than the downstream end.

[0121] That is, in the image forming apparatus 1 according to this embodiment 3, as shown in FIG. 14, among the ends along the axial direction of the photosensitive drum 11, the end corresponding to the upstream side along the transport direction of the supply transport member 142 is formed with a rough surface by blasting processing or the like.

[0122] The photosensitive drum 11 has no photosensitive layer 112 formed in non-image areas, which are both ends along the axial direction, and a base material (base tube) 111 made of a metal such as aluminum or stainless steel is exposed.

[0123] The substrate (bare tube) 11a exposed at the end corresponding to the upstream side along the transport direction of the supply and transport member 142 of the photosensitive drum 11 has its surface subjected to a blasting process or the like so that its surface roughness is rougher than that of the substrate 11b on the downstream side along the transport direction of the supply and transport member 142.

[0124] As a result, over time, the developing device 14 will wear out early as the tracking roll 161, which is located upstream in the transport direction of the supply and transport member 142, comes into contact with the base material (bare tube) 11a, which corresponds to the upstream in the transport direction of the supply and transport member 142 of the photosensitive drum 11 and has a rough surface.

[0125] Therefore, the developing device 14 according to the above-mentioned embodiment 3 is capable of adjusting, over time, the difference in outer diameter between the tracking roll 161 arranged upstream along the transport direction of the supply and transport member 142 and the tracking roll 162 arranged downstream so that they are more reliably approximately equal.

[0126] The other configurations and operations are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0127] In the above embodiment, an image forming apparatus that forms a full-color image has been described as an example of an image forming apparatus, but the present invention is not limited to this, and it goes without saying that the image forming apparatus may also be one that forms a monochrome image. [Explanation of symbols]

[0128] 1...Image forming device 11...Photoconductor drum 14...Developing device 140...Device housing 141...Developing roll 142...Supply and transport member 143...Agitating and conveying member 161...Tracking roll 162...Tracking roll 165…Coil spring 166…Coil spring

Claims

1. a developer carrier that holds a developer and develops the latent image on the image carrier; a developer supplying means for supplying the developer to the developer holder while transporting the developer in an axial direction of the developer holder; a gap adjusting means for adjusting a gap between the developer carrier and the image carrier; A developing device comprising: The gap adjusting means adjusts the gap on the upstream side so that the gap on the upstream side and the gap on the downstream side become equal as the usage time of the developing device increases from a state in which the gap on the upstream side in the transport direction of the developer supplying means is larger than the gap on the downstream side during an initial operation of the developing device. Developing device.

2. the gap adjustment means has two gap setting rotors that are rotatably arranged in contact with a surface of the image carrier at both ends of the developer supply means in the axial direction, 2. The developing device according to claim 1, wherein the gap setting rotor arranged upstream along the transport direction of the developer supply means has an outer diameter larger than that of the gap setting rotor arranged downstream during the initial operation of the developing device, and the outer diameter becomes smaller as the usage time of the developing device increases.

3. the two gap setting rotors are biased by biasing means so as to come into contact with the surface of the image carrier, 3. The developing device according to claim 2, wherein the gap setting rotor arranged on the upstream side in the transport direction of the developer supplying means is made of a material that is more easily worn than the gap setting rotor arranged on the downstream side.

4. 4. The developing device according to claim 3, wherein the biasing force of the biasing means for biasing the two gap setting rotors is set to be greater on the upstream side in the transport direction of the developer supply means than on the downstream side.

5. 3. The developing device according to claim 2, wherein the surface roughness of the upstream end of the image carrier in the transport direction of the developer supplying means is set to be greater than that of the downstream end of the image carrier.

6. a transfer means for transferring the developed image on the image carrier to a recording medium; a fixing unit for fixing the developed image on the image carrier onto the recording medium; Equipped with 6. An image forming apparatus using the developing device according to claim 1.

Images