JP5549569B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying apparatus, a facsimile machine, a printer, a plotter, a multifunction peripheral, and a printing apparatus.

  The developer (carrier, toner) in the developer container is agitated, and the toner is transported to a developing region (development nip portion) facing the image carrier such as a photoconductor to form a latent image formed on the image carrier. 2. Description of the Related Art There is an image forming apparatus having a developing device of a type that develops toner that has not been used for development in a developing area, and returns the toner to a developer container, and replenishes toner in the developer container as needed. In addition, there is an image forming apparatus having an image area storage unit that stores an image area and a calculation unit that calculates an image area ratio.

  As an example of the developing device, a developer carrier having a plurality of magnetic poles formed opposite to the image carrier, and a developer regulating member for regulating the amount of developer carried on the developer carrier. Two conveying members that convey the developer contained in the developing device in the longitudinal direction to form a circulation path, and the conveying member are disposed substantially opposite to the developer carrying member, A first conveying member that supplies the developer to the developer carrying member while conveying the developer in the longitudinal direction, and a second conveying member that conveys the developer that is opposed to the developer carrying member and separated from the developer carrying member. In addition, there is a type that includes communication ports that are disposed at both ends of the first and second transport members and transfer the developer between the transport members.

  In such a development method called a one-way circulation development method in which development is performed in the process of circulating the developer in one direction, a deviation occurs in the developer volume upstream and downstream of the conveying member. If there is a deviation in the developer volume on the upstream and downstream of the transport member, the developer bulk deviation tends to cause a pumping failure that does not occur on the developer carrier on the first transport member side, and the second transport member side. In this case, the developer detached from the developer carrying member cannot be collected and a follow-up image that re-adheres to the developer carrying member is likely to be generated.

In addition, poor pumping and rotation are particularly likely to occur when printing with a low image area continues. This is because the fluidity of the developer is lowered due to the embedding and detachment of the additive adhering to the toner surface. Such a state of the developer is called deterioration and causes an abnormal image.
The following technologies are considered to be related to countermeasures for such problems.

(1): When the developer in the developer container is agitated in a state where the toner consumption is low, such as outputting many images with a low image area ratio, background stains, image blurring, density fluctuations, background stains of replenishing toner, etc. It is known that various problems occur, and the cause is estimated to be developer deterioration due to developer agitation, for example, charging abnormality due to embedding of additives in the toner, change in charging characteristics due to change in toner average particle diameter, etc. It is said.

  As a countermeasure, an area ratio of an image to be formed is detected in an image forming apparatus that forms an electrostatic latent image on an image carrier and develops the electrostatic latent image by a developing device using a developer. The image area ratio detecting means for detecting the development area and the development driving time detecting means for detecting the development driving time of the developing device are improved by forcibly consuming the developer according to the image area ratio per unit driving time of development. (See, for example, Patent Document 1).

  However, the technique of Patent Document 1 does not provide a solution for the deterioration of the developer and the abnormal image due to the deviation in the developer volume in the upstream and downstream of the conveying member in the unidirectional circulation development.

(2): a two-component developing type biaxial transport type developing device, a toner collecting mechanism for collecting only toner from the developer carried on the developer carrying member even after passing through the developing region, a developer supply path, and a partition A collected toner conveying path having a collected toner conveying means for conveying the toner collected by the toner collecting mechanism, and the collected toner conveying path and the developer supply path near the end of the collected toner conveying direction in the collected toner conveying direction. It has been proposed that the undeveloped toner can be circulated by communicating with each other (see, for example, Patent Document 2). In this method, it is considered that the deterioration of the developer is small because the deteriorated toner can be collected accurately, but the configuration of the developing device is complicated and is not suitable for downsizing.

(3): a toner image forming unit that has a photoconductor and forms a toner image on the surface of the photoconductor; a transfer fixing unit that prints an image by transferring and fixing the toner image on the surface of the photoconductor to a transfer material; And a control device for controlling the toner image forming unit and the transfer fixing unit. The control device uses a developing bias voltage applied in the developing operation when the bulk of the two-component developer in the developing device rises above a predetermined value. The toner discharging operation for moving the toner in the two-component developer onto the photosensitive member and the toner discharging operation are completed by operating the photosensitive member and the developing roller for a predetermined time while applying a lower developing bias voltage to the developing roller. The toner image forming unit is controlled so that a toner replenishing operation for replenishing toner from the toner replenishing device into the developing device until a predetermined density is performed at the time. Image forming apparatus has been proposed that (for example, see Patent Document 3).
However, although this conventional technique is suitable as a method for uniformly consuming toner from the developing roller, it is not suitable when there is a place where toner is to be consumed and a place where toner is not desired to be consumed.

  In view of the above problems, the present invention ensures the necessary fluidity of the developer even under conditions where the developer is deteriorated (for example, when printing with a low image area continues), It is an object to provide a stable image by preventing the occurrence of an abnormal image due to a defect.

In order to achieve the object, the present invention has the following configuration.
(1): a developing device that contains a developer containing a carrier and toner and develops a latent image formed on the image carrier with the developer, an image area storage means for storing an image area, and an image area ratio Having a computing means for computing,
The developing device includes a developer carrying body that is opposed to the image carrying body and has a plurality of magnetic poles formed around it, a developer regulating member that regulates the amount of developer carried on the developer carrying body,
Two transport members that transport the developer contained in the developing device in the longitudinal direction to form a circulation path;
The transport member is disposed substantially opposite to the developer carrier, and a first transport member that supplies the developer to the developer carrier while transporting the developer in the longitudinal direction;
A second transporting member that faces the developer carrying member and conveys the developer detached from the developer carrying member;
In the image forming apparatus provided with communication ports that are disposed at both ends of the first and second transport members and transfer the developer between the transport members,
When the image area ratio calculated from the image area stored in the image area storage means is less than or equal to a predetermined image area ratio, the amount of toner consumed with a deviation in the longitudinal direction of the developer carrier The toner forcible consumption operation for forcibly consuming the toner from the developer carrying member is performed (claim 1).
In the developing device according to the present invention, there is a deviation in the volume of the developer in the longitudinal direction of the developer carrier within the transport path of the developing device. In an image forming apparatus using this developing device, when an image with a low image area is continuous, an abnormal image due to poor rotation or pumping occurs due to a decrease in the fluidity of the developer. By uniformly forcibly consuming toner with respect to the amount of developer in the direction, the fluidity aimed at the developer can be maintained, so that a stable image free from defective pumping and abnormal images due to rotation is provided. be able to.
(2): In the image forming apparatus described in (1),
The deviation of the toner consumption amount in the longitudinal direction of the developer carrying member due to the forced toner consumption operation is approximately the same ratio as the deviation of the developer amount in the longitudinal direction in the transport path of the developing device.
Due to the characteristic that deviation of the developer amount occurs in the transport path, toner consumption from the developer in the transport path cannot be consumed in the same ratio when toner is uniformly consumed in the longitudinal direction of the developer carrier. For this reason, unevenness occurs in the state of the developer in the developer transport path. Therefore, the same amount of toner can be forcibly consumed per unit developer amount with respect to the developer amount in the longitudinal direction in the transport path, and the developer deterioration state with no deviation in the longitudinal direction of the developer carrier can be obtained. Since it can be made uniform, it is possible to provide a stable image free from abnormal images due to poor pumping or rotation.
(3): In the image forming apparatus according to (1) or (2), the forced toner consumption operation forms a latent image on the uniformly charged image carrier by writing means, and a developer carrier. The operation is to develop the toner amount necessary for the forced toner consumption amount.
By executing the forced toner consumption by developing the latent image formed on the photoconductor so that the toner consumption varies in the longitudinal direction of the developer carrier, the toner consumption corresponding to the longitudinal direction of the developer carrier is achieved. Therefore, it is possible to provide a stable image free from abnormal images due to poor pumping and accompanying rotation.
(4): In the image forming apparatus according to any one of (1) to (3), the toner forced consumption operation is performed during a non-printing operation of the image forming apparatus.
By performing the toner forced consumption operation during non-printing, it is possible to provide a stable image without extending the printing time due to the toner consumption operation and the cleaning time of the transfer means.
(5): In the image forming apparatus according to any one of (1) to (4), the shape factor SF-1 of the toner is in the range of 100 to 180, and the shape factor SF-2 is 100 to 180. (Claim 5).
A developer capable of securing fluidity can be provided, and a stable image free from abnormal images due to poor pumping or accompanying rotation can be provided.
(6): In the image forming apparatus according to any one of (1) to (5), a plurality of the developing devices may be provided.
(7): In the image forming apparatus according to any one of (1) to (6), the developing device includes at least one selected from a photoconductor as the image carrier, a charging unit, and a cleaning unit. It can be configured as a part of a process cartridge that is integrally supported and detachable from the main body of the image forming apparatus.
(8) In the image forming apparatus described in (7), a plurality of the process cartridges can be provided.

  According to the present invention, the fluidity aimed at the developer can be maintained, so that it is possible to provide a stable image having no abnormal image due to poor pumping or accompanying rotation.

1 is a configuration diagram illustrating a printer as an image forming apparatus. FIG. FIG. 2 is an enlarged view showing a printer image forming unit shown in FIG. 1. FIG. 3 is a cross-sectional view of the developing device as viewed from the axial direction of the developer carrier. FIG. 3 is an external perspective view of a process cartridge including a developing device. FIG. 3 is an external perspective view of the developing device when viewed from an obliquely upper side of the developing device toward the photosensitive drum. It is sectional drawing of a developing device. FIG. 6 is a diagram illustrating a developer circulation path in the developing device when viewed from the photosensitive drum side toward the developing device. FIG. 4 is a diagram illustrating a developer circulation path in the developing device and an image pattern for forced toner consumption corresponding to the circulation path when viewed from the photosensitive drum side toward the developing device. 6 is a graph showing the developer height in the developing roller in the longitudinal direction. FIG. 6 is a schematic diagram for explaining a shape factor of toner.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

[Configuration and operation of image forming apparatus]
1 to 7, an embodiment of the present invention will be described in detail. First, the configuration and operation of the entire image forming apparatus will be described with reference to FIGS. FIG. 1 is a block diagram showing a printer as an image forming apparatus, and FIG. 2 is an enlarged view showing an image forming unit thereof.

  As shown in FIG. 1, image forming portions 6Y, 6M, 6C, and 6BK corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 8 of the intermediate transfer unit 10. Yes. The four image forming units 6Y, 6M, 6C, and 6BK installed in the apparatus main body 100 have substantially the same structure except that the toner colors used in the image forming process are different. 6, the alphabet (Y, M, C, BK) of the reference numerals in the photosensitive drum 1, the photosensitive drum 1, and the primary transfer bias roller 9 is omitted.

  Referring to FIG. 2, the image forming unit 6 includes a photosensitive drum 1 as an image carrier, a charging unit 4 disposed around the photosensitive drum 1, a developing device 5 as a developing unit, and a cleaning unit 2. (Only the developing device 5 is shown in FIG. 1). An image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the photosensitive drum 1, and a desired toner image is formed on the photosensitive drum 1.

  The photosensitive drum 1, the charging unit 4 by the charging unit, the developing device 5, and the cleaning unit 2 by the cleaning unit that constitute the image forming unit 6 are each detachably installed on the image forming apparatus main body 100 as a single unit. Configured to be able to. Alternatively, these constituting the image forming unit 6 may be integrated to form a process cartridge that is detachable from the image forming apparatus main body 100. The process cartridge may be configured to integrally support at least one selected from the photosensitive drum 1, the charging unit 4, and the cleaning unit 2 and the developing device 5. A plurality of process cartridges are provided corresponding to each color (yellow, magenta, cyan, black). The photosensitive drum 1, the charging unit 4, the cleaning unit 2, and the developing device 5 constituting the image forming unit 6 are replaced with new ones when they reach the end of their lives. Since the process cartridge is integrated, the workability when performing maintenance of the image forming unit 6 is improved.

  Referring to FIG. 2, the photosensitive drum 1 is rotationally driven in a clockwise direction in FIG. 2 by a drive unit (not shown). Then, the surface of the photosensitive drum 1 is uniformly charged at the position of the charging unit 4 (charging process).

  Thereafter, the surface of the photosensitive drum 1 reaches an irradiation position of a laser beam L emitted from an exposure unit (not shown), and an electrostatic latent image is formed by exposure scanning at this position (exposure process).

  Thereafter, the surface of the photosensitive drum 1 reaches a developing nip portion 5a that is a position facing the developing device 5, and the electrostatic latent image is developed at this position to form a desired toner image (developing step). .

  Thereafter, the surface of the photosensitive drum 1 reaches a position facing the intermediate transfer belt 8 and the first transfer bias roller 9 (9Y, 9M, 9C, and 9BK in FIG. 1), and on the photosensitive drum 1 at this position. The toner image is transferred onto the intermediate transfer belt 8 (primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drum 1.

  Thereafter, the transferred surface of the photosensitive member 1 reaches a position facing the cleaning unit 2, passes through the lubricant application roller 7, and then untransferred toner remaining on the photosensitive drum 1 is collected by the cleaning blade 2 a. (Cleaning process).

  Finally, the surface of the photosensitive drum 1 reaches a position facing a neutralization unit (not shown), and the residual potential on the photosensitive drum 1 is removed at this position. Thus, a series of image forming processes performed on the photosensitive drum 1 is completed.

  Note that the above-described image forming process is performed by each of the four image forming units 6Y, 6M, 6C, and 6BK. That is, referring to FIG. 1, laser light L based on image information is emitted from exposure units (not shown) arranged below the image forming units 6Y, 6M, 6C, and 6BK. Irradiation is directed onto the photosensitive drum 1 of 6M, 6C, 6BK. Specifically, the exposure unit emits a laser beam L from a light source, and irradiates the latent image by irradiating the photosensitive drum 1 via a plurality of optical elements while scanning the laser beam L with a polygon mirror that is rotationally driven. Form. Thereafter, the latent image is developed with toner through a developing step. Each color toner image formed on each photosensitive drum 1 is transferred onto the intermediate transfer belt 8 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 8.

  As shown also in FIG. 1, the four primary transfer bias rollers 9Y, 9M, 9C, and 9BK respectively sandwich the intermediate transfer belt 8 between the photosensitive drums 1Y, 1M, 1C, and 1BK, and perform primary transfer. A nip is formed. Then, a transfer bias having a polarity opposite to the polarity of the toner is applied to the primary transfer bias rollers 9Y, 9M, 9C, and 9BK.

  The intermediate transfer belt 8 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 9Y, 9M, 9C, and 9BK. In this way, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1BK are primarily transferred while being superimposed on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 19. At this position, the secondary transfer backup roller 12 sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip 19N. The color toner image formed on the intermediate transfer belt 8 is transferred onto a transfer material P such as transfer paper conveyed to the position of the secondary transfer nip 19N. At this time, the untransferred toner that has not been transferred to the transfer material P remains on the intermediate transfer belt 8. Untransferred toner remaining on the intermediate transfer belt 8 is removed by a cleaning unit (not shown) to return to the initial state.
Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.

  Here, the transfer material P, which is a recording medium conveyed to the position of the secondary transfer nip 19N, is fed from a paper feed unit 26 disposed below the apparatus main body 100 to a paper feed roller 27, a registration roller pair 28, and the like. It was conveyed via.

  Specifically, a plurality of transfer materials P such as transfer paper are stored in the paper supply unit 26 in a stacked manner. When the paper feed roller 27 is driven to rotate counterclockwise in FIG. 1, the uppermost transfer material P is fed between the rollers of the registration roller pair 28.

  The transfer material P conveyed to the registration roller pair 28 is temporarily stopped at the position of the roller nip of the registration roller pair 28 that has stopped rotating. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the transfer material P is conveyed toward the secondary transfer nip 19N. In this way, a desired color image is transferred onto the transfer material P.

  Thereafter, the transfer material P on which the color image is transferred at the position of the secondary transfer nip 19N is conveyed to the position of the fixing unit 20. At this position, the color image transferred to the surface is fixed on the transfer material P by heat and pressure generated by the fixing roller and the pressure roller.

  Thereafter, the transfer material P is discharged out of the apparatus through the rollers of the discharge roller pair 29. The transferred P discharged from the apparatus main body 100 by the discharge roller pair 29 is sequentially stacked on the stack unit 30 as an output image. Thus, a series of image forming processes in the image forming apparatus is completed.

  The present invention is applied to such an image forming apparatus having an image area storage unit for storing an image area and a calculation unit for calculating the area.

[Configuration and operation of developing device]
3 to 7, the configuration and operation of the developing device 5 in the image forming unit 6 will be described in more detail.

  The developing device 5 includes a developing roller 51 as a developer carrying member facing the photosensitive drum 1, a doctor blade 52 as a developer regulating member installed below the developing roller 51, and developer containing portions 58 and 59. In order to detect the toner concentration in the developer G, a two-component developer G composed of a carrier and toner is provided in the developer accommodating portions 58 and 59. The toner density sensor is accommodated.

  The doctor blade 52 is a member that regulates the amount of developer carried on the developing roller 51. The developer accommodating portions 58 and 59 are partitioned by a collection guide (separation plate) 57, and the leading end of the collection guide 57 constitutes the outer peripheral portion of the developing roller 51 and faces the developing sleeve 51a that rotates with a predetermined interval. ing.

  As shown in FIG. 3, the developing roller 51 is composed of a magnet fixed inside, a developing sleeve 51a that rotates around the magnet, and the like, and is in close proximity to the photosensitive drum 1 as shown in FIG. Are arranged. The magnet of the developing roller 51 is formed with five magnetic poles, P1 to P5. Then, when the developing sleeve 51a rotates around the magnet on which these five magnetic poles are formed, the developer G moves on the developing sleeve 51a along with the rotation. In addition, the radial line attached | subjected to the developing roller 51 of FIG. 3 shows the position where each magnetic force of P1 pole-P5 pole becomes a peak.

(Configuration of representative example)
In FIG. 3, the developing device 5 includes a developing roller 51, a doctor blade 52, a supply transport screw 53, and a recovery transport screw 54 as a rotating unit. A fixed amount of a developer in which toner (5.8 μm) containing a polyester resin as a main component and a carrier (35 μm) as magnetic fine particles are uniformly mixed to 7 wt% is filled, and is arranged in parallel along the longitudinal direction of the developing roller 51. By rotating the supply screw 53 and the collection screw 54 arranged at 600 to 800 rpm, the toner is stirred and conveyed after replenishment to the developing roller 51 at the same time, and the toner and carrier are uniformly mixed and charged.

  The uniformly mixed developer develops an outer peripheral portion of the developing roller 51 by the P4 and P5 magnetic forces of the mag roller 55 contained in the developing roller 51 from the supply conveying screw 53 provided in parallel with the developing roller 51 in parallel. The sleeve 51a is conveyed to the outer peripheral surface of the sleeve 51a, and is conveyed to the developing nip portion 51N, which is a developing region formed by the photosensitive member 1 and the sleeve, by rotating the sleeve 51a as indicated by an arrow in the drawing. The toner develops the latent image on the photoconductive drum 1 by forming. The developed developer is collected by the collection conveying screw 54 via the collection guide (separation plate) 57 as the sleeve 51a rotates.

  The supply conveyance screw 53 and the collection conveyance screw 54 convey the developer accommodated in the developing device in the longitudinal direction to constitute a circulation path. The supply conveying screw 53 supplies the developer to the developing roller 51 while conveying the developer in the longitudinal direction. The collection conveying screw 54 faces the developing roller 51 and conveys the developer separated from the developing roller 51.

  FIG. 4 is a front view of the developing device, a plan view projected from above (in the direction of arrow A in FIG. 5) (a state in which the upper wall of the developing container is removed), and a cross-sectional view of the screw conveying unit. The flow of the developer (flow between the screws and from the developing roller to the collecting screw) is shown.

  In the screw end regions a and b, the agitation / conveying chamber by the upper collecting conveying screw 54 and the lower supplying conveying screw 53 constitutes a communicating port in the vertical direction. In the section, the developer is delivered and conveyed from the lower stage to the upper stage. As for the shape of the screw in the communication portion, a paddle or a reverse-wound screw is provided, and the conveying ability in the direction perpendicular to the conveying direction is given.

  FIG. 6 is a schematic view showing a state of developer deposition in the developing device. The white arrow in the figure indicates the moving direction of the developer. Since the developer is supplied to the developing sleeve 51 a while being agitated and transported by the supply transport screw 53 and is completely recovered by the recovery transport screw 54, the developer accumulation state in the developer accommodating portion 58 is indicated by a broken line. It becomes slanted as shown in. As shown in the figure, the amount of developer in the supply transport screw 53 decreases in the downstream direction in the transport direction indicated by the arrow.

  The developer is uniformly developed when the relationship between the developer conveying capacity: Wm and the developer conveying amount on the developing sleeve 51: Ws is Wm> Ws, which is obtained from the diameter, pitch and rotation speed of the supply conveying screw 53. It is conveyed onto the sleeve 51a. If this condition is not satisfied, the developer is insufficient on the downstream side of the supply conveying screw 53, and it becomes impossible to supply the developer to the developing sleeve 51a.

  Similarly, as indicated by an arrow G1 in FIGS. 3 and 7, the developer is recovered from the developing sleeve 51a to the recovery conveying screw 54, but the developer that is not recovered due to the increase in the bulk is separated from the separation plate 57 and the developing. As shown by the arrow G2 from the gap of the sleeve 51 to the supply screw side, it is supplied again to the developing nip 51N without being sufficiently stirred by the supply conveying screw 53. That is, it is necessary to set the rotational speed of the supply and recovery transport screws 53 and 54 to exceed the developer transport amount on the developing sleeve 51, and the screw is inevitably set to a high speed.

(Explanation of claim 1):
The image forming apparatus according to the present invention is premised on having an image area storage unit and a calculation unit that calculates an image area ratio from the image area stored in the image area storage unit.
In FIG. 6, the bulk of the developer in the first transport path T1 increases from the communication port U1 side to the communication port U2 side, and the developer amount varies within the transport path T1. Have If the height of the developer on the communication port U1 side which is one end side of the transport path T1 is h1, and the height of the developer on the communication port U2 side is h2, h1 <h2.

(Description of defects when printing low image area):
The developing device of the present invention was mounted on an image forming apparatus (trade name: imagio MP C5000 modified machine), and images of each image area ratio were printed, and the occurrence of abnormal images was confirmed every 1000 sheets. The method for confirming the abnormal image was performed by printing halftone and solid images on the entire A3 vertical area every 1000 sheets. Table 1 shows the abnormal image occurrence status. In the table, “◯” indicates that there is no abnormal image, and “X” indicates that an abnormal image is generated due to rotation or pumping failure.

  Thus, as the image area ratio is lower, the number of printed sheets until the occurrence of an abnormal image becomes smaller, and an abnormal image becomes faster. At least in this embodiment, when the image area ratio is 2% or less, a follow-up operation due to a decrease in fluidity due to the deterioration of the developer or an abnormal image due to poor pumping occurs, so a fluidity improvement operation is required. In addition, since the occurrence of abnormal images can be suppressed by making the developer in an image area ratio of 2% or more, even when many images with a low image area ratio are printed, the image area ratio is 2%. The fluidity of the developer can be improved by forcibly consuming the deteriorated toner in the developer so as to reach a level.

Example 1:
The developing device of the present invention was installed in an image forming apparatus (trade name: imagio MP C5000 modified machine), and the forced toner consumption operation was performed once every 20 predetermined sheets when the image area ratio was 0.5% continuously. (Assuming that the average image area of the most recent specified number of images is calculated, and when the average image area ratio falls below a threshold value set in advance in the image forming apparatus, a flag is set for control and a forced toner consumption operation is performed. In the embodiment, an example in which the specified number of sheets is 20 and the average image area ratio of the 20 sheets is 0.5% is shown.) The method for confirming the abnormal image was performed by printing halftone and solid images on the entire A3 vertical area every 1000 sheets.

As the forced toner consumption operation, a trapezoidal solid image was printed as a toner forced consumption image, as shown in FIG. The image area of the trapezoid is as follows: developing device communication port U2 side (upper bottom): 14.28 cm, developing device communication port U1 side (lower bottom): 7.14 cm, longitudinal direction (height): 29.0 cm. Since there is, it becomes 311 cm ² .

FIG. 8 shows the relationship between the developing device and the toner forced consumption image. If the toner adhesion amount on the photosensitive drum 1 is 0.5 mg / cm ² , 155.5 mg of toner is consumed. By making the image for forced toner consumption trapezoidal, a deviation can be given to the amount of toner consumed in the longitudinal direction of the developing roller, and more toner can be consumed on the communication port U2 side. Therefore, as shown in Table 2, when printing with a low image area continues, it is possible to prevent the occurrence of an abnormal image by performing toner forced consumption.

  As a comparative example, when forced printing is performed with an image area ratio of 0.5%, there is no forced toner consumption (Comparative Example 1), and a forced toner consumption operation with no toner consumption deviation in the longitudinal direction is performed once every 20 sheets. Table 2 shows the state of occurrence of abnormal images in the case of the comparison (Comparative Example 2) (printing paper passing direction: 10.7 cm × longitudinal direction: 29.0 cm as forced toner consumption at this time). In the table, “◯” indicates that there is no abnormal image, and “X” indicates that an abnormal image is generated due to rotation or pumping failure.

  In the case where there was no forced toner consumption, density unevenness images occurred due to rotation after 2000 sheets. In addition, since the toner in the developer is deteriorated, the solid image is blurred.

  Also, when the toner is forcibly consumed once for 20 sheets as in the first embodiment (when the toner is forcibly consumed, a sheet passing direction: 10.7 cm × longitudinal direction: 29.0 cm is printed), a halftone image is also displayed. The density unevenness due to the rotation occurs at 5000 sheets. The occurrence position of the abnormal image is on the right side of the image, so in the developing device, it is on the communication port U2 side, which is the side where the developer amount is large. This is probably because the deteriorated toner stays on the side with a lot of developer due to insufficient toner forced consumption. Therefore, in the embodiment of the present invention, it is preferable that the forced toner consumption during low image area continuous printing has a forced toner consumption deviation according to the amount of developer in the developer transport path.

(Explanation of claim 2):
Next, the deviation amount of the forced toner consumption will be described. Since it is desirable that there is no toner density unevenness in the developer with respect to the image density unevenness, when the toner is forcibly consumed, it is desirable to uniformly consume the toner from the developer in the transport path. Therefore, it is desirable to set the toner forced consumption amount proportional to the developer amount in the developer conveyance path. As described in the second embodiment, the deviation of the toner consumption amount in the longitudinal direction of the developing roller 51 due to the forced toner consumption operation should be approximately the same as the deviation of the developer amount in the longitudinal direction in the conveyance path of the developing device.

  FIG. 9 shows the position in the first developer transport path T1 in the developing device and the bulk of the developer. In FIG. 9, the volume of the developer in the first developer transport path T1 is pumped up to the developing roller 51 by a certain amount, so that the developer amount decreases toward the downstream and decreases almost linearly. Yes. In this embodiment, the developer height h1 on the communication port U1 side was 6 mm, and the developer height h2 on the communication port U2 side was 12 mm.

Example 2:
The developing device of the present invention is mounted on an image forming apparatus (trade name: imagio MP C5000 modified machine). Here, a trapezoidal solid is used as a toner consuming operation once every 20 sheets when printing an image area ratio of 0.5%. The image was printed. Here, evaluation was performed by changing the length of the left side of the image (upper base of the trapezoid). The method for confirming the abnormal image was performed by printing a halftone and solid image on the entire A3 vertical area every 1000 sheets.

As the forced toner consumption operation, a trapezoidal solid image was printed as a toner forced consumption image. The developing device communication port U2 side (upper base): 14 so that the trapezoidal image area of the forced toner consumption pattern is the same as the height ratio of the developer, the upper base and the lower base are 2: 1. .28 cm, developing device communication port U1 side (bottom bottom): 7.14 cm, longitudinal direction (height): 29.0 cm = 311 cm ² .

Further, as a comparative example, the trapezoidal area for forced toner consumption is as follows: developing device communication port U2 side (upper bottom): 7.14 cm, developing device communication port U1 side (lower bottom): 7.14 cm, longitudinal direction (height ): 29.0 cm = 207 cm ² (Comparative Example 3), trapezoidal area of developing device communication port U2 side (upper bottom): 28.56 cm, developing device communication port U1 side (lower bottom): 7.14 cm, longitudinal Direction (height): 29.0 cm = 518 cm ² (Comparative Example 4).
Table 3 shows the occurrence status of abnormal images at this time.

  In Table 3, “◯” indicates that there is no abnormal image, and “×” indicates that an abnormal image is generated due to a follow-up or pumping failure.

  In Example 2, even when printing with a low image area was continued, an abnormal image due to revolving or poor pumping did not occur. However, in Comparative Example 3, an abnormal image was generated due to rotation or pumping failure from 2000 sheets. Also, in Example 3, abnormal images were not generated due to rotation or pumping failure, but because the toner consumption on the left side of the image was too much, a deviation in the toner concentration occurred, and the image density was slightly reduced, and the image density was slightly reduced. This causes an image density deviation. From the above results, the trapezoidal shape corresponding to the volume of the developer in the first developer transport path T1 of the developing device 5 generates the most abnormal image.

(Explanation of claim 3)
The forced toner consumption operation is performed by forming and developing a latent image of a forced toner consumption pattern on the photosensitive member of the uniformly charged photosensitive drum 1 by a writing unit. The toner image developed on the photoconductor of the photoconductor drum 1 may be collected by the photoconductor cleaning unit 2 with the bias of the transfer unit 10 turned off, or transferred to the transfer unit 10 and used as a transfer unit cleaning unit. It may be collected. Further, the cleaning may be performed by both the photosensitive drum 1 and the transfer unit 10, and at that time, the bias to the transfer unit 10 may be changed to change the toner cleaning distribution amount.

(Explanation of claim 4)
Since the toner forced consumption operation is performed by developing toner on the photosensitive member from the developing device, the toner adheres to the photosensitive member, the intermediate transfer unit, and the transfer unit. In particular, if toner adheres to the transfer means, the back side of the transfer material may be soiled. Therefore, if the forced toner consumption operation is performed during printing, a cleaning operation for the photosensitive member, the intermediate transfer member, and the transfer unit is required, and the printing operation itself becomes longer. Therefore, if it is determined that the forced toner consumption operation is necessary based on the average image area ratio accumulated in the image area storage means, the forced toner consumption operation is performed during the non-printing operation, for example, before the printing operation is completed. As a result, the forced toner consumption operation can be performed without extending the printing operation.

(Explanation of claim 5)

  The toner shape factor SF-1 is preferably in the range of 100 to 180, and the shape factor SF-2 is preferably in the range of 100 to 180. FIG. 10A is a diagram schematically illustrating the shape of the toner in order to explain the shape factor SF-1, and FIG. 10B is a diagram illustrating the shape factor SF-2. The shape factor SF-1 indicates the ratio of the roundness of the toner shape, and is represented by the following formula (1). This is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4.

SF-1 = {(MXLNG) ² / AREA} × (100π / 4) Expression (1)

  When the value of SF-1 is 100, the shape of the toner is a true sphere, and becomes larger as the value of SF-1 increases. The shape factor SF-2 indicates the ratio of the unevenness of the toner shape, and is represented by the following formula (2). A value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner onto the two-dimensional plane by the figure area AREA and multiplying by 100 / 4π.

SF-2 = {(PERI) ² / AREA} × (100 / 4π) (2)

  When the SF-2 value is 100, the unevenness on the toner surface does not exist, and as the SF-2 value increases, the unevenness on the toner surface becomes more prominent. Specifically, the shape factor is measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX 3: manufactured by Nireco) and analyzing it. Calculated.

  When the shape of the toner is close to a spherical shape, the contact state between the toner and the toner or the toner and the photoconductor becomes a point contact, so that the adsorbing force between the toners becomes weak and the fluidity increases, and the toner and the photoconductor The attraction force becomes weaker and the transfer rate becomes higher. If either of the shape factors SF-1 or SF-2 exceeds 180, the transfer rate is lowered, which is not preferable.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Cleaning part 2a Cleaning blade 4 Charging part 5 Developing device 5a Developing nip part 6Y, 6M, 6C, 6BK Image forming part 7 Lubricant application roller 8 Intermediate transfer belt 9 First transfer bias roller 10 Intermediate transfer unit 19 Secondary transfer roller 19N Secondary transfer nip 20 Fixing section 26 Paper feed section 27 Paper feed roller 28 Registration roller pair 29 Paper discharge roller pair 30 Stack section 51 Development roller 51a Development sleeve 51N Development nip section 52 Doctor blades 53, 54 Conveying screw 57 Collection guide (separation plate)
55 Mag rollers 58 and 59 Developer container 100 Main body a, b Region G Developer G1 Arrow L Laser light P Transferred material T1 First transport path U1, U2 Communication port

JP 2003-76079 A JP 2009-230114 A JP 2009-222918 A

Claims (8)

A developing device that contains a developer having a carrier and toner and develops a latent image formed on the image carrier with the developer, an image area storage unit that stores an image area, and an arithmetic unit that calculates an image area ratio Have
The developing device includes a developer carrying body that is opposed to the image carrying body and has a plurality of magnetic poles formed around it, a developer regulating member that regulates the amount of developer carried on the developer carrying body,
Two transport members that transport the developer contained in the developing device in the longitudinal direction to form a circulation path;
The conveying member is disposed opposite to the developer carrying member, and supplies a developer to the developer carrying member while conveying the developer in the longitudinal direction;
A second transporting member that faces the developer carrying member and conveys the developer detached from the developer carrying member;
In the image forming apparatus provided with communication ports that are disposed at both ends of the first and second transport members and transfer the developer between the transport members,
When the image area ratio calculated from the image area stored in the image area storage means is less than or equal to a predetermined image area ratio, the amount of toner consumed with a deviation in the longitudinal direction of the developer carrier An image forming apparatus for performing a forced toner consumption operation for forcibly consuming the toner from the developer carrying member. The image forming apparatus according to claim 1.
2. An image forming apparatus according to claim 1, wherein the deviation of the toner consumption in the longitudinal direction of the developer carrying member due to the forced toner consumption operation is approximately the same ratio as the deviation of the developer amount in the longitudinal direction in the transport path of the developing device. The image forming apparatus according to claim 1, wherein
The forced toner consumption operation is an operation in which a latent image is formed on the uniformly charged image carrier by a writing unit, and a toner amount necessary for the forced toner consumption is developed by a developer carrier. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the toner forcible consumption operation is performed during a non-printing operation of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 4, wherein:
An image forming apparatus, wherein the toner has a shape factor SF-1 in the range of 100 to 180, and a shape factor SF-2 in the range of 100 to 180. The image forming apparatus according to any one of claims 1 to 5,
An image forming apparatus comprising a plurality of the developing devices. The image forming apparatus according to any one of claims 1 to 6,
The developing device is integrally supported together with at least one selected from a photoconductor as the image carrier, a charging unit, and a cleaning unit, and is configured as a part of a process cartridge that is detachable from the image forming apparatus main body. An image forming apparatus. The image forming apparatus according to claim 7.
An image forming apparatus comprising a plurality of the process cartridges.

Images