JP2014235367A - Bearing structure and developing device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of aggregates by smoothly circulating the flow of powder such as a developer around a shaft end part.SOLUTION: In a bearing structure, the end of the shaft part 281a of a rotation member 281 is inserted into a bearing recessed part 283a cylindrically recessed, to freely rotatably support the rotation member 281. A circulation space 285 is formed between the opening peripheral edge part of the bearing recessed part 283a and the shaft part 281a.

Description

  The present invention relates to a bearing structure and a developing device using the same.

  For example, image forming apparatuses such as copying machines and printers are provided with a large number of rotating members that rotate around an axis, such as a photosensitive drum, a developing roller, a cleaning roller, a fixing roller, a toner conveying screw, and a sheet conveying roller. . For this reason, a bearing structure is formed at the end of the shaft portion of the rotating member to support the rotating member so as to be rotatable about the axis. In the bearing structure, a concave portion is provided in a wall portion of a housing, and the concave portion is rotatably inserted so as to receive an end portion of a shaft portion in the concave portion (for example, see Patent Document 1).

  The image forming apparatus also includes a developing device that develops an electrostatic latent image formed on the surface of the photosensitive drum with each color toner (developer) to form a toner image. As shown in FIG. 7, this developing device includes a screw shaft 1281 for stirring the developer in a housing 1280. The screw shaft 1281 has a bearing structure in which the shaft end portion of the screw shaft 1281 is inserted into the bearing recess 1283 of the housing 1280 and the opening of the bearing recess 1283 is often covered with a rubber seal GS. In this way, by sealing the bearing recess 1283 with the rubber seal GS, the developer is prevented from entering the bearing recess 1283.

JP 2010-2578

  When the bearing recess 1283 is sealed with the rubber seal GS, as shown in FIG. 8, the rubber seal GS deteriorates and the sealing performance becomes weak, and a gap is formed between the screw shaft 1281. For this reason, the developer enters the inside of the rubber seal GS from the gap between the rubber seal GS and the screw shaft 1281. . The developer accumulated in the bearing recess 1283 easily aggregates due to heat from the outside and heat from rotation of the screw shaft 1281. Further, when the runout of the screw shaft 1281 is large, the surface in contact with the bearing 1283 becomes large, and the degree of aggregation of the developer also becomes high. When the aggregated developer remains in the bearing recess 1283, the developer adheres to the screw shaft 1281 and the inner surface of the bearing recess 1283. Such fixing of the developer increases the rotational torque of the screw shaft 1281 and increases the risk of shaft breakage.

  In order to solve the above-described problems, it is desirable to remove the rubber seal GS in order to constantly circulate the developer so that it does not accumulate in the bearing recess 1283, which is advantageous in terms of cost. However, in order to remove the rubber seal GS, even when the developer has entered the bearing recess 1283, the developer does not stay and returns to the housing immediately, and it is necessary to suppress the occurrence of aggregation.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a bearing structure that can smoothly circulate a flow of powder such as a developer around a shaft end and suppress the generation of aggregates, and a developing device using the same. And

  The present invention is a bearing structure in which an end portion of a shaft portion of a rotating member is inserted into a bearing recess recessed in a cylindrical shape to rotatably support the rotating member, and the opening peripheral edge of the bearing recess and the A distribution space is formed between the shaft portion and the shaft portion. Here, the distribution space is larger than a gap (space) generated in the bearing portion between the bearing recess and the shaft portion in order to exert a bearing function, and a powder such as a developer entering the bearing recess flows. An easily set space.

  The present invention lies in that a groove is formed on the outer periphery of the shaft portion facing the opening periphery of the bearing recess, and a flow space is formed between the opening periphery of the bearing recess and the shaft.

  In the present invention, an inclined surface that is reduced in diameter toward the center in the axial direction of the shaft portion is formed in a portion of the shaft portion that faces the opening periphery of the bearing recess, and the opening periphery of the bearing recess and the shaft This is because a distribution space is formed between the two parts.

  In the present invention, an inclined surface whose diameter increases toward the center in the axial direction of the shaft portion is formed at the opening peripheral portion of the bearing concave portion, and a flow space is provided between the opening peripheral portion of the bearing concave portion and the shaft portion. It is in having formed.

  As described above, since a flow space is formed between the peripheral edge of the bearing recess and the shaft, powder such as developer that tends to stay in the bearing recess is likely to go out of the bearing recess. At the same time, the friction between the bearing and the rotating member can be reduced to reduce the agglomerates in the bearing portion.

  In the developing device of the present invention, the bearing structure is used for a bearing of a screw member that stirs the developer. In the developing device of the present invention, developer powder aggregates in the bearing portion are reduced, and therefore white spots generated when the aggregates are mixed into the developer are also reduced.

  The present invention can smoothly circulate powders such as developer accumulated in the bearing without stagnation, and can suppress the generation of aggregates.

1 is an overall configuration diagram of a color printer that is an example of an image forming apparatus according to an embodiment of the present disclosure. FIG. 2 is a schematic diagram of a developing device according to an embodiment of the present invention. It is a schematic sectional drawing which shows the bearing structure of the developing device which has a groove | channel in an axial end part. It is a schematic sectional drawing which shows the bearing structure of the developing device which has a taper surface in a bearing. FIG. 5 is a schematic cross-sectional view showing a bearing structure of a developing device having a groove at a shaft end portion and a tapered surface at a bearing. It is a schematic sectional drawing which shows the bearing structure of the developing device which has a taper surface in an axial end part. It is a schematic sectional drawing which shows the bearing structure of the conventional developing device. It is a schematic sectional drawing which shows the bearing structure of the conventional developing device.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of a tandem type digital color printer (hereinafter simply referred to as “printer”) 10 which is an example of an image forming apparatus. The printer 10 includes an intermediate transfer belt 12 at substantially the center of the inside thereof. The intermediate transfer belt 12 is made of a semiconductive material, is supported on the outer peripheral portions of the three rollers 14, 16, and 18 and is driven to rotate in the direction of arrow A.

  Below the lower horizontal portion of the intermediate transfer belt 12, four image forming units (image forming means) 20Y respectively corresponding to yellow (Y), magenta (M), cyan (C), and black (K) toners. , 20M, 20C, and 20K are arranged side by side along the intermediate transfer belt 12.

  Each of the image forming units 20Y, 20M, 20C, and 20K has a photosensitive drum 22Y, 22M, 22C, and 22K, respectively. Around the photosensitive drums 22Y, 22M, 22C, and 22K, chargers 24Y, 24M, 24C, and 24K for uniformly charging the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K in order along the rotation direction. Print head portions 26Y, 26M, 26C, and 26K that form an electrostatic latent image by exposing the surface of the uniformly charged photoconductive drum according to each color image data, and electrostatic formed on the surface of the photoconductive drum. Intermediate transfer belts at positions facing the photosensitive drums 22Y, 22M, 22C, and 22K with the intermediate transfer belt 12 sandwiched between the developing devices 28Y, 28M, 28C, and 28K that develop the latent images with toners of the respective colors to form toner images. -Next transfer for primarily transferring the toner image formed on the surface of the photosensitive drum, which is provided in contact with the inside of the photosensitive drum 12, onto the intermediate transfer belt 12. Over La (primary transfer member) 30Y, 30M, 30C, 30K and cleaner for cleaning and collecting toner remaining on the photosensitive drum surface after the primary transfer 32Y, 32M, 32C, and a 32K are arranged respectively. The print head portions 26Y, 26M, 26C, and 26K are composed of a large number of LEDs arranged in the main scanning direction parallel to the axial direction of the photosensitive drum.

  A secondary transfer roller (secondary transfer member) 34 is pressed against the outside of the portion of the intermediate transfer belt 12 supported by the roller 18. A contact area between the secondary transfer roller 34 and the intermediate transfer belt 12 is a transfer area 36. The secondary transfer roller 34 can be retracted to a position where it is not in contact with the intermediate transfer belt 12 by a retracting mechanism (not shown).

  A primary transfer voltage V1 is applied to the primary transfer roller 30Y by a power source (not shown). Similarly, the primary transfer voltage V1 is applied to the other primary transfer rollers 30M, 30C, and 30K. Due to the action of the primary transfer voltage V1, the color toner images formed on the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K of the image forming units 20Y, 20M, 20C, and 20K are electrostatically attracted to each other. Primary transfer is performed on the transfer belt 12.

  A secondary transfer voltage V2 is applied to the secondary transfer roller 34 by a power source, and the support roller 18 of the intermediate transfer belt 12 is grounded. The toner image formed on the intermediate transfer belt 12 by the action of the secondary transfer voltage V2 is electrostatically attracted to the paper conveyed to the transfer area 36 and is secondarily transferred as described later. It has become.

  A cleaning brush 41 is pressed against the portion of the intermediate transfer belt 12 supported by the roller 16. The cleaning brush 41 scrapes and collects the toner remaining on the intermediate transfer belt 12 after the secondary transfer into the waste toner box 40. As with the secondary transfer roller 34, the cleaning brush 41 can also be retracted to a position where it is not in contact with the intermediate transfer belt 12 by a retracting mechanism (not shown). A paper feed cassette 42 is detachably disposed at the bottom of the printer 10. The sheets S stacked and accommodated in the sheet feeding cassette 42 are sent out one by one from the uppermost one to the conveying path 46 by the rotation of the sheet feeding roller 44.

  The conveyance path 46 extends from the paper feed cassette 42 to the paper discharge tray 11 through the nip portion of the timing roller pair 48, the secondary transfer region 36, and the fixing unit 50. The timing roller pair 48 is for feeding the paper S sent from the paper feed cassette 42 to the transfer area 36 in synchronization with the image on the intermediate transfer belt 12.

  A timing sensor 52 is disposed in the vicinity of the timing roller pair 48. The timing sensor 52 is for detecting that the leading edge of the paper S sent from the paper feed cassette 42 to the transport path 46 is nipped by the timing roller pair 48. When the leading edge of the paper S is detected by the paper feed sensor 52, the timing roller pair 48 temporarily stops its rotation, and then the paper S is conveyed to the transfer area 36 in synchronization with the toner image on the intermediate transfer belt 12. To do.

  In addition, a paper thickness sensor 54 is disposed to face one roller 48a of the timing roller pair 48. The paper thickness sensor 54 detects the amount of movement of the roller 48a when the leading edge of the paper is nipped by the timing roller pair 48, whereby the paper is plain paper, thick paper or OHP sheet. Can be determined.

  The fixing unit 50 is supported by a pair of rollers 56 and 58 and is driven to rotate in the direction of arrow B, and a fixing roller 62 that is pressed against the roller 56 via the fixing belt 60 and is driven to rotate in the direction of the arrow. The fixing region 64 is a nip portion between the fixing belt 60 and the fixing roller 62 through which the sheet on which the toner image is secondarily transferred passes. The fixing belt 60 is heated by a heater (not shown).

  The developing devices 28Y, 28M, 28C, and 28K are developing devices provided with two screws 281 and 282 in a housing 283. FIG. 2 shows a schematic diagram of the developing device. Since the basic configurations of the developing devices 28Y, 28M, 28C, and 28K are generally well-known examples, a detailed description thereof will be omitted. The developing devices 28Y, 28M, 28C, and 28K are arranged around the photosensitive drums 22Y, 22M, 22C, and 22K, and components such as the developing roller 280, the agitation screw 281 and the supply screw 282 are included in the housing 283. It is held by. A developer (two-component developer containing toner and carrier) is accommodated in the housing 283.

  The developing roller 280 rotates while carrying the developer on the surface thereof, supplies the developer to the electrostatic latent image on the photosensitive drum at the development position, and visualizes the electrostatic latent image. The stirring screw 281 is a screw member in which a spiral blade 281b is formed around a rotating shaft 281a as a shaft portion. The supply screw 282 is a screw member in which a spiral blade 282b is formed around the rotation shaft 282a, and supplies the developer to the surface of the developing roller 280. In FIG. 2, the flow of the developer is indicated by an arrow.

  Both ends of the stirring screw 281 and the supply screw 282 are rotatably supported by the housing 283. Power for rotation is transmitted to one end of the stirring screw 281 and the supply screw 282. The other end portions of the stirring screw 281 and the supply screw 282 are rotatably supported by the housing 283 via a bearing. FIG. 3 is a schematic sectional view showing the bearing structure of the stirring screw 281. In addition, since the bearing structure of the supply screw 282 is the same as that of the stirring screw 281, the description of the supply screw 282 is omitted.

  The wall surface of the housing 283 includes a bearing recess 283a. The bearing recess 283a is formed in a circular cylindrical shape that is recessed from the wall surface, and the end of the rotating shaft 281a of the stirring screw 281 is rotatably inserted. A slight gap with a predetermined tolerance is formed between the rotating shaft 281a and the bearing recess 283a.

  A groove 281c is continuously formed in the axial circumferential direction on the outer periphery of the rotary shaft 281a. The length dimension L in the axial longitudinal direction of the groove 281c is set to a predetermined length dimension, and the opening peripheral edge 283b of the bearing recess 283a is positioned at the center of the groove 281c. That is, by forming a groove 281c on the outer periphery of the rotating shaft 281a opposite to the opening peripheral portion of 283a, an annular flow for facilitating the flow of the developer between the opening peripheral portion of the bearing recess 283a and the rotating shaft 281a. A space 285 is formed. The opening area of the distribution space 285 can be set as appropriate depending on the type of developer.

  Next, the operation of the printer 10 having the above configuration will be described. When an image signal is input from an external device (for example, a personal computer) to an image signal processing unit (not shown) of the printer 10, the image signal processing unit digitally converts the image signal into yellow, cyan, magenta, and black. A signal is generated and transmitted to the LED drive circuit for the print head.

  This drive circuit performs exposure by causing the print head portions 26Y, 26M, 26C, and 26K of the image forming units 20Y, 20M, 20C, and 20K to emit light based on the input digital signals. This exposure is performed with a time difference in the order of the print head units 26Y, 26M, 26C, and 26K. Thereby, electrostatic latent images for the respective colors are formed on the surfaces of the respective photosensitive drums 22Y, 22M, 22C, and 22K.

The electrostatic latent images formed on the photosensitive drums 22Y, 22M, 22C, and 22K are developed by the developing devices 28Y, 28M, 28C, and 28K, respectively, and become toner images of the respective colors.
The toner images of the respective colors are sequentially superimposed on the intermediate transfer belt 12 that moves in the direction of arrow A by the action of the primary transfer rollers 30Y, 30M, 30C, and 30K to which a positive primary transfer voltage is applied. Transcribed.

  The superimposed toner images formed on the intermediate transfer belt 12 in this way reach the transfer area 36 as the intermediate transfer belt 12 moves. Then, the superimposed color toner images are sent out from the paper feed cassette 42 to the conveyance path 46 by the action of the secondary transfer roller 34 to which a secondary transfer voltage having the same polarity as the primary transfer voltage is applied, and a timing roller pair 48. The second transfer is collectively performed on the sheet S passing through the transfer region 36 by the above driving. The toner remaining on the intermediate transfer belt 12 after the secondary transfer is collected by the waste toner box 40 by the action of the cleaning brush 41 to which a positive cleaning current is applied.

  The sheet S on which the toner image is secondarily transferred is sent to the fixing unit 50 through the conveyance path 46, and passes through the fixing region 64 where the toner image is heat-fixed on the sheet S. Then, the paper S is discharged to the paper discharge tray 11.

  The color image forming operation is performed as described above. In the case of a monochrome image, only the image forming unit 20K operates based on the input monochrome image data, and a black toner image is formed on the intermediate transfer belt 12. Thereafter, similarly, the black toner image is secondarily transferred to the paper S in the transfer region 36, heated and fixed by the fixing unit 50, and the paper S is discharged to the paper discharge tray 11.

  In the developing devices 28Y, 28M, 28C, and 28K, the stirring screw 281 and the supply screw 282 stir and transport the developer while rotating. At this time, the developer passes through the flow space 285 and enters the bearing recesses 283a that support the stirring screw 281 and the supply screw 282, respectively. Since the circulation space 285 is provided between the bearing recess 283a and both the screws 281 and 282, the developer entering the circulation space 285 is easy to move. As a result, the developer can easily come out of the bearing recess 283a without staying through the circulation space 285, and the stay of the developer can be prevented.

  Further, since the retention of the developer can be prevented, the aggregation of the developer can also be suppressed. In addition, it becomes difficult for the developer to be fixed in the bearing recess 283a, and the flow space 285 also plays a role of reducing friction between the screw shaft 281 and the bearing 283 that causes agglomeration. Can also prevent danger. Further, when aggregates are generated, the aggregates are mixed in the developer, so that there is a problem that white spots are generated in the image. Since the present embodiment suppresses the generation of aggregates, it is possible to prevent the occurrence of white spots.

  FIG. 4 is a schematic cross-sectional view showing a bearing structure of a stirring screw 281 having a tapered surface 283c on the bearing. In the bearing structure shown in FIG. 4, a tapered surface (inclined surface) 283c is formed on the peripheral edge of the opening of the bearing recess 283a without forming a groove in the shaft portion (rotating shaft 281a). The tapered surface 283c is formed by chamfering the peripheral edge of the opening, and the diameter of the developer is increased toward the direction (axial center) where the developer exits from the bearing recess 283a. In this manner, by forming the tapered surface 283c whose diameter increases toward the axial center of the rotating shaft 281a at the opening peripheral portion of the bearing concave portion 283a, between the opening peripheral portion of the bearing concave portion 283a and the rotating shaft 281a. A distribution space 285 is formed. Therefore, the developer that has entered the bearing recess 283a easily exits from the bearing recess 283a without staying through the circulation space 285, and the developer can be prevented from staying.

  FIG. 5 is a schematic cross-sectional view showing a bearing structure of a stirring screw 281 having a groove 281c at the shaft end and a tapered surface 283c at the bearing. In the bearing structure shown in FIG. 5, a groove 281c is formed in the rotating shaft 281a, and a tapered surface 283c is formed in the bearing recess 283a. Thus, the distribution space 285 is provided by providing both the groove 281c and the tapered surface 283c. Therefore, the developer that has entered the bearing recess 283a easily exits from the bearing recess 283a without staying through the circulation space 285, and the developer can be prevented from staying.

  FIG. 6 is a schematic cross-sectional view showing a bearing structure of a stirring screw 281 having a tapered surface 281d at the shaft end. The bearing structure shown in FIG. 6 has a tapered surface 281d formed on the rotating shaft 281a. The tapered surface 281d is provided over the inside and outside of the bearing recess 283a, and the diameter of the developer is reduced toward the direction of exiting the bearing recess 283a. In this way, by forming the tapered surface 281d having a diameter reduced toward the center in the axial direction of the rotation shaft 281a at the portion facing the opening periphery of the bearing recess 283a in the rotation shaft 281a, the opening periphery of the bearing recess 283a. A circulation space 285 is provided between the rotary shaft 281a and the rotary shaft 281a. Therefore, the developer that has entered the bearing recess 283a easily exits from the bearing recess 283a without staying through the circulation space 285, and the developer can be prevented from staying.

  The present invention is not limited to these embodiments. For example, the groove 281c of the rotating shaft 281a, the tapered surface 283c of the bearing recess 283a, and the tapered surface 281d of the rotating shaft 281a can be provided intermittently in the axial direction other than the case where they are continuous in the axial direction. is there. In the present embodiment, the bearing structure is used for the developing devices 28Y, 28M, 28C, and 28K. However, the shaft portion of the component device (including the device device other than the image forming device) such as the cleaning brush 41 is illustrated. It is also possible to employ this type of bearing.

  By using the printer shown in FIG. 1 equipped with the developing device having the bearing structure shown in FIG. 5, the depth of the groove 281c formed in the rotating shaft 281a is changed, and whether or not the output image has a cloudy point is determined. It was observed visually. Under high-temperature and high-humidity environment, 7000 sheets of A4 size sample image with 1% printing rate were printed, and for every 1000 sheets, a cyan solid image was output to make it easy to observe the presence or absence of cloudy spots. I investigated. Then, after printing 7000 sheets, a cyan solid image and a green solid image in which cyan and yellow were mixed at the start of image formation on the next day were output, and the number of cloudy spots was examined. When the number of clouding points was 0, “◯”, 4 or less were “Δ”, and 5 or more were “x”. Table 1 shows the results. The rotation shaft 281a is a resin rotation shaft having a diameter of 6 mm, and the width of the groove 281c is 10 mm.

  As apparent from Table 1, when the depth of the groove is 1 mm, the white cloud point is 4 or less until 1000 sheets of printing durability, and there was no problem in practical use. The above clouding point was generated. When the depth of the groove was 1.2 mm, the cloudiness point was 4 or less up to 5000 sheets of printing durability, and there was no problem in practical use. When the depth of the groove was 1.4 mm, 1.5 mm, 1.6 mm, and 1.7 mm, the cloudiness point was 4 or less even on 7000 printing plates. From the above results, it is considered that the effect of suppressing the occurrence of white clouding point is higher when the depth of the groove formed on the rotating shaft is deeper. In addition, since the strength of the rotating shaft is reduced when the groove is deepened, it is desirable to appropriately determine the depth of the groove in consideration of the diameter and material of the rotating shaft.

10 Printer 20 Imaging unit (imaging means)
22 Photosensitive drum 28 Developing device 41 Cleaning brush 280 Developing roller 281 Stirring screw (rotating member, screw member)
281a Rotating shaft (shaft)
281c Groove 281d Tapered surface (inclined surface)
282 Supply screw (rotary member, screw member)
283a Bearing recess 283c Tapered surface (inclined surface)
285 distribution space

Claims (5)

A bearing structure in which an end portion of a shaft portion of the rotating member is inserted into a bearing recess recessed in a cylindrical shape to rotatably support the rotating member,
A bearing structure characterized in that a flow space is formed between an opening peripheral edge of the bearing recess and the shaft portion.   The bearing structure according to claim 1, wherein a groove is formed on an outer periphery of the shaft portion facing the opening peripheral portion of the bearing concave portion, and a flow space is formed between the opening peripheral portion of the bearing concave portion and the shaft portion.   An inclined surface having a diameter reduced toward the axial center of the shaft portion is formed in a portion of the shaft portion facing the opening peripheral portion of the bearing concave portion, and between the opening peripheral portion of the bearing concave portion and the shaft portion. The bearing structure according to claim 1, wherein a circulation space is formed.   An inclined surface having a diameter increasing toward an axial center of the shaft portion is formed at an opening peripheral portion of the bearing concave portion, and a flow space is formed between the opening peripheral portion of the bearing concave portion and the shaft portion. The bearing structure in any one of 1-3.   5. A developing device, wherein the bearing structure according to claim 1 is used for a bearing of a screw member that stirs a developer.