JP4873540B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device installed in an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a process cartridge and an image forming apparatus including the developing device It is.

Conventionally, in an image forming apparatus such as a copying machine or a printer, a developing device containing a two-component developer composed of a non-magnetic toner and a magnetic carrier (including a case where an external additive or the like is added) is often used. ing.
In such a two-component developing system developing device, a developer housed in the device using a stirring member in which a plurality of ellipsoidal plates inclined with respect to the rotating shaft are arranged at intervals in the rotating shaft direction. Is known in the art (see, for example, Patent Document 1).

  Specifically, the developing device includes a developer carrying member (developing roller), a supply member (paddle roller) for transporting and supplying the developer toward the developing roller, and stirring for stirring the developer in the rotation axis direction (longitudinal direction). A member (agitating paddle), a detecting means (toner concentration sensor) for detecting the toner concentration of the developer accommodated in the apparatus, and the like are installed.

  In the developing device configured as described above, toner is appropriately supplied into the device from a toner supply port provided in the developing device in accordance with the toner density detected by the toner density sensor. The replenished toner is agitated and mixed in the longitudinal direction and a direction orthogonal to the longitudinal direction by a stirring member, a paddle roller, and the like together with the developer in the developing device. Then, the toner that is frictionally charged and adsorbed on the carrier is supplied to the developing roller together with the carrier by the paddle roller, and the developer is carried on the developing roller. After the developer carried on the developing roller is regulated to an appropriate amount by the doctor blade, the toner in the developer adheres to the latent image on the photosensitive drum at a position facing the photosensitive drum (image carrier). . Here, the toner concentration sensor is often disposed at a position facing the stirring member in order to increase the detection accuracy.

JP-A-7-199615

  In the conventional developing device described above, when the rotation speed of the stirring member is increased as the speed of the image forming apparatus increases, the unevenness of the elliptic plate pitch (the interval between the elliptic plates provided on the stirring member) appears on the output image. An image sometimes occurred. This is because, as the stirring member is rotated at a higher speed, the stirring property in the rotation axis direction by the stirring member becomes too large, and a large height difference of an elliptical plate pitch occurs on the developer surface of the developer in the apparatus. .

In order to avoid such a phenomenon, a method of optimizing the stirring property in the rotation axis direction by the stirring member by increasing the inclination angle of the elliptical plate provided on the stirring member (the inclination angle with respect to the rotation axis). Can be considered.
However, when the inclination angle of the elliptical plate is increased, the developer flow in the vicinity of the toner concentration sensor (detecting means) facing the stirring member becomes stagnant, and the detection accuracy by the toner concentration sensor decreases. (Followability of the toner density sensor is deteriorated). When the detection accuracy of the toner density sensor is lowered, the toner is excessively replenished in the developing device and becomes higher than the target toner density, and background stains (toner adhesion is scheduled on the output image and the image carrier). This is a phenomenon in which toner adheres to a non-existing area.) Or toner is scattered from the developing device.

  The phenomenon in which the detection accuracy of the toner density sensor is reduced in this way is particularly during idling when the toner from the developing device is hardly consumed (when the developing device is driven without performing the developing step). It appears prominently. Such idling rotation of the developing device is an image forming apparatus in which a recording medium conveyance path is set long (for example, an image forming apparatus provided with a post-processing apparatus such as a finisher or a conveyance path for double-sided printing. Etc.), the above-mentioned problems are not particularly negligible.

  The present invention has been made to solve the above-described problems. Even when the speed of the apparatus is increased, a pitch-like uneven image is not generated on the output image, and the toner density is reduced. An object of the present invention is to provide a developing device, a process cartridge, and an image forming apparatus in which the detection accuracy of the detection means for detecting is highly accurate and stable, and does not cause background contamination or toner scattering.

According to a first aspect of the present invention, there is provided a developing device for developing a latent image formed on an image carrier while containing a developer composed of toner and a carrier, and having a rotating shaft as a developing device. A plurality of elliptical plates that are inclined with respect to the rotation axis direction are disposed at intervals, and a stirring member that stirs the developer in the rotation axis direction, and is opposed to the stirring member and has a toner concentration in the developer. comprising a detection means for detecting that the said stirring member, the stirring projections facing a portion of the detection surface of the detection means as viewed in the rotation axis direction with projecting the detection means side with respect to the rotation diameter Two are provided so as to be shifted by 180 degrees in the rotation direction of the member, and one of the two protrusions is disposed so as to be opposed from the center of the detection surface of the detection means to one end when viewed in the rotation axis direction. The two The other projecting portion of the output portion is one which is arranged so as to face toward the other end from the center of the detection surface of the detection means as viewed in the rotation axis direction.

The developing device according to a second aspect of the present invention is the developing device according to the first aspect, wherein the stirring member includes a plurality of rib portions in the rotation direction that connect outer peripheral portions of the plurality of elliptic plates in the rotation axis direction. And the protrusion is disposed on the rib portion.

According to a third aspect of the present invention, there is provided the developing device according to the second aspect , wherein the stirring member is configured such that the rib portion on which the protruding portion is disposed is inclined with respect to the rotation shaft. It is formed.

According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects , the length of the protruding portion is detected by the detecting means when viewed in the direction of the rotation axis. It is formed so as to be shorter than the length of the surface.

A developing device according to a fifth aspect of the present invention is the developing device according to any one of the first to fourth aspects, further comprising: a variable unit that varies the number of rotations of the stirring member. The rotation speed of the agitating member when the apparatus is driven to perform a developing process for developing the latent image formed on the image carrier when the apparatus is driven without performing the developing process. Control is performed so as to be higher than the rotational speed of the stirring member.

The developing device according to claim 6 is the developing device according to any one of claims 1 to 5, wherein the stirring member has an inclination angle of the elliptical plate with respect to the rotation axis of 60 ± 15. The interval between the plurality of elliptical plates in the direction of the rotation axis is 15 ± 10 mm.

A developing device according to a seventh aspect of the invention is the developing device according to any one of the first to sixth aspects, wherein the detection means is a magnetic sensor.

A process cartridge according to an eighth aspect of the present invention is a process cartridge that is detachably installed on the main body of the image forming apparatus, and includes the developing device according to any one of the first to seventh aspects. It is a thing.

An image forming apparatus according to a ninth aspect of the invention includes the developing device according to any one of the first to seventh aspects.

  In the present application, the “process cartridge” refers to a charging unit that charges the image carrier, a developing device (developing unit) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. It is defined as a unit in which at least one of the cleaning unit and the image carrier are integrated and configured to be detachable from the image forming apparatus main body.

  Since the present invention has a plurality of protrusions protruding in the rotation direction of the stirring member and projecting toward the detection means side and facing a part of the detection surface of the detection means, the detection means The fluidity of the nearby developer can be improved efficiently. As a result, even when the speed of the apparatus is increased, a pitch-like uneven image is not generated on the output image, and the detection accuracy of the detection means for detecting the toner density is improved and stabilized. It is possible to provide a developing device, a process cartridge, and an image forming apparatus that are free from dirt and toner scattering.

Embodiment.
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.

First, referring to FIG. 1, the configuration and operation of the entire image forming apparatus according to the present embodiment will be described.
In FIG. 1, 50 is a main body of a digital copying machine as an image forming apparatus, 51 is a document conveying unit that conveys a set document D to a document reading unit 52, and 52 is a document that optically reads image information of the document D. A reading unit 53 is an exposure unit that irradiates the photosensitive drum 54 with exposure light L based on image information read by the document reading unit 52, 54 is a photosensitive drum as an image carrier, and 55 is a photosensitive drum 54. 58 is a transfer unit that transfers the toner image formed on the photosensitive drum 54 to the recording medium P, 59 is a cleaning unit that collects untransferred toner on the photosensitive drum 54, and 61 to 64 are A paper feeding unit storing a recording medium P such as transfer paper, 65 is a fixing unit for fixing unfixed toner on the recording medium P, 70 is an intake device for sucking gas in the developing device 80, and 80 is a photosensitive drum. Shape on 54 A developing device (developing unit) that develops the electrostatic latent image, 120 a toner bank in which a plurality of toner bottles 121 are installed, and 122 a waste toner that stores waste toner collected by the cleaning unit 59 and the transfer unit 58 Show the bottle.

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, the document D is conveyed from the document table in the direction of the arrow in the drawing by the conveyance roller of the document conveyance unit 51 and passes over the document reading unit 52. At this time, the document reading unit 52 optically reads the image information of the document D passing above.
Then, the optical image information read by the document reading unit 52 is converted into an electric signal and then transmitted to the exposure unit 53 (writing unit). Then, the exposure unit 53 emits exposure light L such as laser light based on the image information of the electrical signal toward the photosensitive drum 54.

  On the other hand, the photosensitive drum 54 rotates in the clockwise direction in the drawing, and first, the surface thereof is uniformly charged at a position facing the charging unit 55. Then, the surface of the photosensitive drum 54 charged by the charging unit 55 reaches the irradiation position of the exposure light L. At this position, an electrostatic latent image corresponding to the image information of the document D is formed.

Thereafter, the surface of the photosensitive drum 54 on which the latent image is formed reaches a position facing the developing device 80. Then, the latent image on the photosensitive drum 54 is developed by the developing device 80.
Here, the toner in the developing device 80 is mixed with the carrier together with the toner supplied from the toner replenishing unit by a paddle roller or the like. The frictionally charged toner is supplied onto the developing roller together with the carrier. The toner in the toner replenishing unit is appropriately supplied into the developing device 80 as the toner in the developing device 80 is consumed. Consumption of the toner in the developing device 80 is detected by a toner density sensor installed in the developing device 80. Further, the toner in the toner replenishing unit is appropriately replenished from a toner bank 120 in which a plurality of toner bottles 121 are detachably installed.

  Thereafter, the surface of the photosensitive drum 54 developed by the developing device 80 reaches a position facing the transfer unit 58. At this position, the toner image on the photosensitive drum 54 is transferred onto the recording medium P. At this time, a small amount of untransferred toner that is not transferred to the recording medium P remains on the photosensitive drum 54.

Thereafter, the surface of the photosensitive drum 54 having untransferred toner that has passed through the transfer unit 58 reaches a position facing the cleaning unit 59. Then, the untransferred toner is collected in the cleaning unit 59 by the cleaning blade in contact with the photosensitive drum 54. The toner collected by the cleaning unit 59 is conveyed as waste toner toward the waste toner bottle 122 through a waste toner conveyance path (not shown).
Thereafter, the surface of the photosensitive drum 54 that has passed through the cleaning unit 59 reaches a static elimination unit (not shown). Then, the potential on the surface of the photosensitive drum 54 is eliminated, and a series of image forming processes is completed.

On the other hand, the recording medium P conveyed to the transfer unit 58 operates as follows.
First, one of the plurality of paper feeding units 61 to 64 is automatically or manually selected (for example, the upper paper feeding unit 61 is selected).
Then, one of the recording media P stored in the paper feeding unit 61 is conveyed toward the position of the conveyance path K.

Thereafter, the recording medium P that has passed through the conveyance path K reaches the position of the registration roller. Then, the recording medium P that has reached the position of the registration roller is timed to align with the toner image formed on the photosensitive drum 54, and is transferred to the transfer position (the transfer portion 58 and the photosensitive drum 54). It is conveyed toward the opposite position).
Then, the recording medium P after the transfer process passes through the position of the transfer unit 58 and then reaches the fixing unit 65 through the conveyance path. At this position, the unfixed toner image on the recording medium P is fixed by heat and pressure. Thereafter, the recording medium P after the fixing process is discharged from the apparatus main body 1 as an output image.
Thus, a series of image forming processes is completed.
The image forming apparatus in the present embodiment is a high-speed machine, and the conveyance speed of the recording medium P (or the linear speed on the outer peripheral surface of the photosensitive drum 54) is set to about 630 mm / second.

Here, referring to FIG. 1, the intake device 70 mainly includes a duct 75, an intake tube 71, an air pump 72 (diaphragm type air pump), an exhaust tube 73, a recovery tank 74, and the like.
The duct 75 is detachably connected to the opening of the developing device 80 so as to communicate with the developing device 80. The exhaust tube 71 is formed of a flexible material, and conveys air sucked from the duct 75 (the toner floating in the developing device 80 is also sucked simultaneously) to the air pump 72.

The air pump 72 includes a pump body having an intake valve and an exhaust valve, a rubber material covered in a recess of the pump body, a drive unit that moves the rubber material to change the internal volume of the pump body, and the like. .
The exhaust tube 73 is formed of a flexible material and conveys the air discharged from the air pump 72 (toner is also discharged simultaneously) to the collection tank 74.

  The collection tank 74 is disposed in the vicinity of the paper feeding units 61 to 64 and is detachable from the apparatus main body 1. The recovery tank 74 is provided with an opening communicating with the outside of the apparatus main body 1, and a filter 74 a is covered with the opening. The filter 74a is formed by stretching PTFE (polytetrafluoroethylene). The filter 74a has a fine continuous porous structure and collects toner through air.

  In the intake device 70 configured as described above, the air pump 72 operates to suck in the developing device 80 during the image process described above. As a result, a suction air flow from the outside of the developing device 80 into the developing device 80 is generated at the opening 86 (see FIG. 2) of the developing device 80 where the developing rollers 81 and 82 facing the photosensitive drum 54 are installed. Thus, toner scattering from the opening 86 is reduced.

  The air in the developing device 80 sucked from the duct 75 passes through the intake tube 71, the air pump 72, and the exhaust tube 73 and is conveyed into the collection tank 74. At this time, the toner floating in the developing device 80 together with the air in the developing device 80 is also transported to the recovery tank 74. The air conveyed to the collection tank 74 passes through the filter 74a and is discharged out of the apparatus main body 1. The toner conveyed to the collection tank 74 is collected by the filter 74 a and accumulated in the collection tank 74.

Next, the configuration and operation of the developing device 80 will be described in more detail with reference to FIG.
Referring to FIG. 2, 81 is a first developing roller as a developer carrying member facing the photosensitive drum 54, 82 is a second developing roller as a developer carrying member facing the photosensitive drum 54, and 83 is a first developing roller. A paddle roller as a supply member for supplying developer to one developing roller 81, 84 is a stirring roller as a stirring member having a plurality of elliptical plates 84 a in the rotation axis direction (longitudinal direction), and 85 is a front end of the first developing roller 81. Doctor blades 86 disposed so as to face each other, 86 is an opening through which the first developing roller 81 and the second developing roller 82 are exposed, 87 is an inlet seal that protrudes and contacts the photosensitive drum 54, and 88 is a developer Stirring plate for agitating the developer in the longitudinal direction, 89 is a conveying screw for agitating the developer in the longitudinal direction, and 100 is a test for detecting the toner concentration of the developer contained in the developing device 80. Toner density sensor as a means (a magnetic sensor) shows.
In the developing device 80, a developer (two-component developer) having a carrier (magnetic carrier) as a magnetic material and a toner (non-magnetic toner) is accommodated.

  The two developing rollers 81 and 82 rotate in the direction of the arrow in FIG. The developer is uniformly agitated and mixed in the direction of the rotation axis (longitudinal direction) by the agitation roller 84, the conveying screw 89, and the agitation plate 88 that rotate in the direction of the arrow. Then, the toner that is frictionally charged and adsorbed on the carrier is supplied to the first developing roller 81 together with the carrier by the paddle roller 83 (supply member), and the developer is carried on the first developing roller 81.

At this time, the toner accommodated in the toner replenishing portion 90 is transported by the transporting member 91 to the position of the replenishing roller 92 (saw tooth roller), and from the replenishing roller 92 through a plurality of holes formed in the slit plate 93. Thus, the toner is appropriately supplied into the developing device 80. It should be noted that the toner in the toner replenishing section 90 is appropriately stored in the developing device 80 based on the detection result of the toner concentration sensor 100 that detects the toner concentration in the developing device 80 (the ratio of the toner in the developer). To be replenished.
Here, the toner concentration sensor 100 as a detection means is a magnetic sensor that detects the magnetic permeability of the developer flowing in the vicinity of the detection surface 100a and converts it into a voltage. Specifically, when the toner concentration of the developer is low, the sensor output (output voltage) of the toner concentration sensor 100 increases as the magnetic permeability increases, and when the toner concentration of the developer is high, the magnetic permeability decreases. As a result, the sensor output (output voltage) of the toner density sensor 100 is lowered.

Thereafter, the amount of developer carried on the first developing roller 81 is adjusted to an appropriate amount at the position of the doctor blade 85, and then reaches a position facing the photosensitive drum 54 (which is the first developing area). Further, the developer that has passed through the facing position moves from the first developing roller 81 to the second developing roller 82 and then reaches a position facing the photosensitive drum 54 (which is a second developing area). The toner in the developer adheres to the electrostatic latent image formed on the surface of the photosensitive drum 54 at the facing position. Thus, the developing process by the developing device 80 is completed.
Note that the developer on the second developing roller 82 after the developing process is separated from the second developing roller 82 and then conveyed to the position of the stirring roller 84 by the paddle roller 83. The developer separated from the first developing roller 81 at the position of the doctor blade 85 is agitated in the longitudinal direction by the agitating plate 88 and the conveying screw 89 and then conveyed to the position of the agitating roller 84.

Next, the configuration and operation of the stirring roller 84, which is characteristic in the present embodiment, will be described in detail.
FIG. 3 is a perspective view showing a stirring roller 84 (elliptical plate roller) as a stirring member installed in the developing device. FIG. 4 is a side view showing a main part of the stirring roller 84 (near the position where the toner density sensor 100 is disposed).

  3 and 4, the stirring roller 84 has a plurality of elliptical plates 84a inclined with respect to the rotation shaft 84b (shaft portion) in the rotation axis direction (the direction perpendicular to the paper surface of FIG. 2). Left and right direction). The stirring roller 84 configured in this manner rotates about the rotation shaft 84b, whereby the developer is stirred and mixed in the direction of the rotation shaft, and the toner density of the developer stored in the developing device 80 rotates. Uniform in the axial direction.

Here, in the present embodiment, the stirring roller 84 has an inclination angle of the elliptical plate 84a with respect to the rotation shaft 84b set to 60 degrees, and the interval (elliptical plate pitch) in the rotation axis direction of the plurality of elliptical plates 84a is set. It is set to 15 mm. In the high-speed image forming apparatus as in the present embodiment, the inclination angle of the elliptical plate 84a is set to 60 ± 15 in order to suppress the generation of the uneven image of the elliptical plate pitch accompanying the high-speed rotation of the elliptical roller 84. As the degree, it is preferable that the elliptical plate pitch is 15 ± 10 mm.
The outer diameter of the elliptical plate 84a is set to 34 mm, and the thickness of the elliptical plate 84a is set to 2 mm. Furthermore, the rotation speed of the stirring roller 84 is set to 300 to 460 rpm.

  With reference to FIGS. 3 and 4, the stirring roller 84 in the present embodiment has a plurality of rib portions 84c (vertical conveying means) connecting the outer peripheral portions of the plurality of elliptic plates 84a in the rotation axis direction in the rotation direction. (4 are provided at intervals of 90 degrees in the rotation direction). By providing the rib portion 84c on the stirring roller 84 in this way, in addition to the stirring ability (lateral stirring ability) in the rotation axis direction by the elliptical plate 84a, the carrying ability (vertical carrying ability) in the direction of the paddle roller 83 is obtained. It will be. That is, the developer is stirred in the direction of the rotation axis by the stirring roller 84, and the developer is positively conveyed toward the paddle roller 83 serving as a supply member.

  Referring to FIGS. 2 and 4, toner density sensor 100 is disposed at a position facing the agitation roller 84 and substantially at the center in the rotation axis direction. In this embodiment, the toner concentration sensor 100 is disposed below the stirring roller 84. However, the toner concentration sensor 100 is obliquely below the stirring roller 84 (for example, the center of the stirring roller 84 and the detection surface 100a are connected to each other). It is also possible to dispose the virtual line segment at a position inclined by 20 degrees with respect to the vertical line.

  Referring to FIG. 4, the stirring roller 84 in the present embodiment protrudes toward the toner density sensor 100 side (outside the outer periphery of the elliptical plate 84a) with respect to the rotation diameter, and in the direction of the rotation axis. As a result, a plurality of protrusions 84d facing a part of the detection surface 100a of the toner density sensor 100 are provided in the rotation direction.

Specifically, the stirring roller 84 is provided with two protruding portions 84d so as to be shifted by 180 degrees in the rotation direction. One of the two protrusions 84d (the protrusion 84d at the lower side in FIG. 4) extends from the center Y of the detection surface 100a to one end (the left end in FIG. 4) when viewed in the rotation axis direction. It arrange | positions so that it may oppose. On the other hand, of the two protrusions 84d, the other protrusion (the protrusion 84d on the upper side in FIG. 4) is the other end (in FIG. 4) from the center Y of the detection surface 100a when viewed in the rotation axis direction. (It is the right end.)
The protruding portion 84d is integrally formed on the rib portion 84c1, and is formed so that the length thereof is shorter than the length of the detection surface 100a in the rotation axis direction. The gap G between the protruding portion 84d and the detection surface 100a is set to about 0.7 mm.

  When the protrusion 84d of the stirring roller 84 configured in this way has a large inclination angle of the elliptical plate 84a in order to suppress the generation of uneven images of the elliptical plate pitch accompanying the high-speed rotation of the elliptical roller 84. Even so, the flowability of the developer in the vicinity of the toner concentration sensor 100 can be improved efficiently. In particular, the protrusion 84d is disposed so as to face only a part of the detection surface 100a, but not the entire detection surface 100a, and the protrusion 84d is disposed at an interval in the rotation direction, whereby the toner concentration sensor 100 is disposed. As a result, an appropriate developer fluidity necessary for detecting the toner density with high accuracy can be obtained.

Here, as shown in FIG. 4, the stirring roller 84 has an area (opening area) of a space surrounded by the rib portion 84c1 provided with the protruding portion 84d, the two elliptical plates 84a adjacent to the rotating shaft 84b. However, it is preferable to form it so that it is smaller than the area (opening area) of the space surrounded by the two elliptical plates 84a adjacent to the rib portion 84c where the protruding portion 84d is not disposed and the rotating shaft 84b. . Thereby, the fluidity of the developer in the vicinity of the toner density sensor 100 can be more efficiently improved.
Furthermore, the circumferential linear speed of the rotation diameter of the stirring roller 84 (the outer diameter portion of the elliptical plate 84a) is set to the circumferential linear speed of the rotation diameter of the paddle roller 83 (the outer diameter portion of the paddle roller 83). Therefore, it is preferable to set it to 1/2 or less. Thereby, the fluidity of the developer in the vicinity of the toner density sensor 100 can be improved while maintaining the horizontal stirring ability and the vertical conveying ability by the stirring roller 84.

  In the present embodiment, as shown in FIG. 4, a rectangular protruding portion 84d is provided on a rib portion 84c1 that is installed in parallel to the rotating shaft 84b. On the other hand, as shown in FIG. 5, it is also possible to provide a protruding portion 84d on the rib portion 84c1 that is installed so as to be inclined with respect to the rotating shaft 84b. Even with the agitation roller 84 (projection portion 84d and rib portion 84c1) configured in this way, it is necessary to detect the toner concentration with high accuracy by the toner concentration sensor 100, as in the present embodiment. An appropriate developer fluidity can be obtained.

FIG. 6 is a graph showing the sensitivity of the toner density sensor 100 (detection means), which is an experimental confirmation of the effects of the present embodiment described above.
In FIG. 6, the horizontal axis indicates the toner concentration of the developer accommodated in the developing device 80, and the vertical axis indicates the sensor output of the toner concentration sensor 100. In FIG. 6, a solid line R1 indicates that the opening area in the vicinity of the rib portion 84c1 where the protruding portion 84d is provided in the stirring roller 84 in the present embodiment is equal to the opening area in the vicinity of the rib portion 84c1 where the protruding portion 84d is not provided. 6 is a graph showing the sensitivity of the toner density sensor 100 when the toner density sensor 100 is used. A solid line R2 is a graph showing the sensitivity of the toner density sensor 100 when the agitation roller 84 (as in FIG. 4) in the present embodiment is used. A solid line R3 indicates the toner density sensor 100 when the rotation speed is further reduced (about 78%) using the agitation roller 84 (in FIG. 4) in the present embodiment. It is a graph which shows a sensitivity. As the slope of the graph in FIG. 6 is larger, the sensitivity (following performance) of the toner density sensor 100 is higher, and the toner density can be detected with higher accuracy.

As shown in FIG. 6, it can be seen that sufficient sensitivity (trackability) of the toner density sensor 100 can be obtained by using the elliptical roller 84 in the present embodiment. In particular, comparing the solid line R1 and the solid line R2, the opening area in the vicinity of the rib part 84c1 provided with the protruding part 84d is smaller than the opening area in the vicinity of the rib part 84c1 in which the protruding part 84d is not provided. It can be seen that the sensitivity of the toner density sensor 100 is increased. Further, comparing the solid line R2 and the solid line R3, it can be seen that the sensitivity of the toner density sensor 100 increases when the number of revolutions of the stirring roller 84 is slightly lowered.
In the experiment relating to the solid lines R1 to R3 described above, there was no occurrence of an uneven image of the elliptic plate pitch due to the high speed rotation of the elliptic roller 84 on the output image.

Further, in the above experiment, when the sensitivity of the toner density sensor 100 was confirmed using the stirring roller 84 not provided with the protruding portion 84d, the runaway of the toner density control (followability of the toner density sensor 100 was reduced, This is a phenomenon in which the toner density is controlled to be extremely higher than the target.
Furthermore, in the above experiment, when the image quality of the output image was confirmed using the stirring roller 84 in which the inclination angle of the elliptical plate 84a was 45 degrees and the elliptical plate pitch was set to 26 mm, the elliptical plate pitch (about 26 mm pitch) )) Has occurred.

The runaway of toner density control described above is particularly noticeable during idle rotation (when the developing device 80 is driven without performing the developing process) when the toner from the developing device 80 is hardly consumed. Specifically, when the double-sided print mode, the intermittent print mode, or the like is performed, the ratio at which the developing device 80 is idly rotated increases, so that the toner density control is likely to run away.
In consideration of such a phenomenon, a variable means for changing the rotation speed of the stirring roller 84 is provided, and when the developing process is not performed (during idle rotation), the rotation speed of the stirring roller 84 is normal. It can also be controlled to be lower than the number of rotations (when the developing process is performed). This makes it possible to control toner density with higher accuracy.

  As described above, in this embodiment, the toner protrudes toward the toner density sensor 100 (detecting means) with respect to the rotation diameter of the stirring roller 84 (stirring member) and is formed on a part of the detection surface 100a of the toner density sensor 100. Since a plurality of opposing protruding portions 84d are provided in the rotation direction of the stirring roller 84, the flowability of the developer in the vicinity of the toner concentration sensor 100 can be improved efficiently. Thereby, even when the image forming apparatus is speeded up, a pitch-like uneven image is not generated on the output image, and the detection accuracy of the toner concentration sensor 100 for detecting the toner concentration is increased and It is possible to stabilize and prevent the occurrence of background dirt and toner scattering.

  In the present embodiment, the developing device 80 is a unit that can be attached to and detached from the apparatus main body 1 independently. On the other hand, the developing device 80, the photosensitive drum 54, the charging unit 55, and the cleaning unit 59 can be integrated to form a process cartridge. Also in this case, the same effect as this embodiment can be obtained.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that the present embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a developing device and its vicinity in the image forming apparatus of FIG. 1. It is a perspective view which shows the stirring member installed in the developing device of FIG. It is a side view which shows the principal part of a stirring member. It is a side view which shows the principal part of another stirring member. It is a graph which shows the sensitivity of a toner density sensor.

Explanation of symbols

50 Image forming apparatus body (apparatus body),
54 photosensitive drum (image carrier), 58 transfer section,
80 developing device (developing part), 81 first developing roller, 82 second developing roller,
83 Paddle roller (supply member),
84 Stirring roller (stirring member),
84a elliptical plate, 84b rotation axis,
84c rib part, 84c1 rib part (rib part of sensor position),
84d protrusion,
85 doctor blade,
86 opening, 87 inlet seal, 88 stirring plate,
89 conveying screw, 91 conveying member,
92 Supply roller, 93 Slit plate 100 Toner density sensor (detection means, magnetic sensor), 100a Detection surface.

Claims (9)

A developing device that stores a developer composed of toner and a carrier and develops a latent image formed on an image carrier,
A plurality of elliptical plates inclined with respect to the rotation axis are disposed at intervals in the rotation axis direction and a stirring member for stirring the developer in the rotation axis direction;
A detecting unit facing the stirring member and detecting a toner concentration of the developer;
With
The stirring member protrudes toward the detection means with respect to the rotation diameter, and a protruding portion facing a part of the detection surface of the detection means in the rotation axis direction is shifted by 180 degrees in the rotation direction of the stirring member. Two in preparation,
One of the two protrusions is disposed so as to face one end from the center of the detection surface of the detection means when viewed in the rotation axis direction, and the other protrusion of the two protrusions is the rotation shaft. A developing device, wherein the developing device is arranged so as to face from the center of the detection surface of the detection means to the other end when viewed in the direction . The stirring member includes a plurality of rib portions in the rotation direction connecting the outer peripheral portions of the plurality of elliptic plates in the rotation axis direction,
The developing device according to claim 1, wherein the protruding portion is disposed on the rib portion. The developing device according to claim 2, wherein the stirring member is formed such that the rib portion on which the protruding portion is disposed is inclined with respect to the rotation shaft. The development according to claim 1, wherein the protrusion is formed so that a length thereof is shorter than a length of a detection surface of the detection unit when viewed in a rotation axis direction. apparatus. Comprising variable means for varying the rotational speed of the stirring member,
The variable means is configured to drive the apparatus without rotating the stirring member during the developing process when the apparatus is driven to perform the developing process of developing the latent image formed on the image carrier. 5. The developing device according to claim 1, wherein the developing device is controlled so as to be higher than a rotational speed of the stirring member during the operation. The stirring member is formed such that an inclination angle of the elliptic plate with respect to the rotation axis is 60 ± 15 degrees, and an interval in a rotation axis direction of the plurality of elliptic plates is 15 ± 10 mm. The developing device according to claim 1. The developing device according to claim 1, wherein the detection unit is a magnetic sensor. A process cartridge that is detachably attached to the image forming apparatus main body,
A process cartridge comprising the developing device according to claim 1. An image forming apparatus comprising the developing device according to claim 1.

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