JP4806180B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a developing device using a two-component developer and an image forming apparatus such as a facsimile, a printer, an electrophotographic copying apparatus, and a plotter equipped with the developing device.

  2. Description of the Related Art Conventionally, an image forming apparatus including a developing device that uses a two-component developer including a toner and a carrier is known. In this image forming apparatus, the toner supplied from the toner supply unit is mixed by a stirring member such as a screw and a paddle and then supplied to the image forming unit, and the developer that has consumed the toner in the image forming unit is again the toner supply unit. Then, mixing with toner, stirring, and conveyance are repeated.

  The ratio between the toner and the carrier in the two-component developer is detected by a toner density sensor, and the toner is replenished from the toner replenishing unit according to the toner consumption. However, since the toner density changes depending on the volume of the developer and the detection position, as a technique for correcting these, a technique for detecting the density by following a change in the volume of the developer by arranging a toner density sensor in the vertical direction of the transport unit. For example, in “Patent Document 1”, a technique for detecting a density fluctuation in the longitudinal direction by arranging a plurality of toner density sensors at a location away from the agitating and conveying unit is disclosed in, for example, “Patent Document 2”. A technique for detecting a density fluctuation in the longitudinal direction by arranging a plurality of toner density sensors at a predetermined location is disclosed in, for example, “Patent Document 3”, wherein a plurality of toner density sensors are arranged at a location away from the developer circulation path. For example, “Patent Document 4” discloses a technique for detecting the density fluctuation of each.

  Further, by utilizing the fact that the sensitivity shift of the toner density sensor occurs due to the influence of the air layer contained in the developer, the density detection accuracy is improved by correcting the toner density sensor according to the rotation speed of the transport unit. A technique for stabilizing the image density and preventing the occurrence of background contamination is disclosed in, for example, “Patent Document 5”.

JP-A-11-95537 JP-A-5-333697 Japanese Patent Publication No. 7-38092 Japanese Patent Laid-Open No. 7-168437 JP-A-8-87168

  In the techniques disclosed in “Patent Document 1” to “Patent Document 4”, a plurality of toner density sensors are provided in order to reduce toner density fluctuation in the developing device, and density control is performed so that the output of each sensor is constant. However, in this configuration, the sensitivity shift of the toner density sensor occurs due to the influence of the air layer contained in the developer described above, thereby stabilizing the image density and preventing the occurrence of background stains. Can not. Further, the technique disclosed in “Patent Document 5” has a problem that driving means becomes expensive to control the rotation speed, and a problem that density detection shift due to developer deterioration is not taken into consideration. is there.

  The present invention solves the above-described problems, and provides a developing device capable of supplying toner while suppressing an increase in cost and considering a shift in density detection due to deterioration of the developer, and an image forming apparatus including the developing device. Objective.

According to the first aspect of the present invention, there is provided a developer carrying member for holding a two-component developer on a surface, a developer carrying member for carrying the two-component developer, and a toner concentration for detecting a toner ratio of the two-component developer. In the image forming apparatus including a developing device having a sensor, the developer transport member has two portions where the transport speeds of the two-component developer are different from each other, and the toner density sensor is located at the two portions. The ratio of the toner density at the place where the transport speed is slow and the toner density at the place where the transport speed is fast is preset in the initial toner density detection result after the start of operation of the developing device. When the value is smaller than a predetermined value smaller than 1, the toner consumption operation is performed .

According to a second aspect of the present invention, there is provided a developer carrying member for holding a two-component developer on a surface, a developer carrying member for carrying the two-component developer, and a toner concentration for detecting a toner ratio of the two-component developer. In the image forming apparatus including a developing device having a sensor , the developer transport member has two portions where the transport speeds of the two-component developer are different from each other, and the toner density sensor is located at the two portions. The ratio of the toner density at the place where the transport speed is slow and the toner density at the place where the transport speed is fast is preset in the initial toner density detection result after the start of operation of the developing device. When the value is larger than a predetermined value greater than 1, the developer conveying member is idled for a predetermined time .

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the developer conveying member further includes two or more conveying screws, and one of the toner density sensors corresponds to one conveying screw. The other toner density sensor is disposed at a position corresponding to the two-component developer delivery portion located between the respective transport screws .

According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect , the developer conveying member further includes a conveying screw having a screw portion and a non-screw portion in which the developer portion is not formed. A toner concentration sensor is disposed at a portion corresponding to the screw portion, and the other toner concentration sensor is disposed at a portion corresponding to the non-screw portion .

  According to the present invention, by measuring the toner density of the two-component developer at two locations in the developing device having different conveyance speeds by the two toner density sensors, not only the density deviation in the developing device but also two-component development. A developing device capable of determining the state of the agent and the like, suppressing the increase in cost, and capable of replenishing toner while considering a shift in density detection due to deterioration of the two-component developer, and an image forming apparatus including the same A developing device capable of performing density detection for providing a stable image to a user, an image forming apparatus provided with the same, and detecting when a problem occurs. Thus, it is possible to provide a developing device capable of determining whether maintenance is necessary and an image forming apparatus including the developing device.

  FIG. 1 shows an image forming apparatus employing one embodiment of the present invention. The image forming apparatus 1 has a latent image carrier 2 composed of a drum-like rotating body at substantially the center thereof, and the latent image carrier 2 is charged around the latent image carrier 2 in a direction indicated by an arrow in the figure. A charging device 3 composed of a roller, an optical scanning device 4 serving as optical writing means, a developing device 5 that is a characteristic part of the present invention, a transfer conveying belt 7 that holds and conveys a sheet-like medium 6, and the circumference of the latent image carrier 2 A cleaning device 9 having a blade 8 slidably contacting the surface is disposed. The latent image carrier 2, the charging device 3, the developing device 5, the cleaning device 9, and the like are disposed on an apparatus main body (not shown) of the image forming apparatus 1 so as to be fixed or detachable.

  A light beam Lb is irradiated from the optical scanning device 4 to a position between the charging device 3 and the developing device 5 on the peripheral surface of the latent image carrier 2, and the light beam Lb is emitted from the latent image carrier. Scanning is performed in the main scanning direction, which is the axial direction of two. The exposure unit 10 is configured at the irradiation position of the light beam Lb.

  The transfer / conveying belt 7 formed of an endless belt is supported by two support rollers 11 and 12 and is driven to rotate counterclockwise by a driving unit (not shown). The transfer conveyance belt 7 is disposed so that the upper surface thereof and the lower surface of the latent image carrier 2 are in contact with each other, and the transfer portion 13 is configured at this contact portion. A transfer roller 14 for applying a transfer bias is disposed on the back side of the transfer conveyance belt 7 in the transfer unit 13.

  A registration roller pair 15 is disposed on the right side of the transfer conveyance belt 7, and a sheet feeding tray (not shown) that stores the sheet-like medium 6 is disposed below the pair of registration rollers 15. The sheet medium 6 is sent out by a paper feed roller 16 disposed above a paper feed tray (not shown), and is conveyed toward the registration roller pair 15 by a conveyance guide (not shown).

  Above the support roller 12 via the transfer conveyance belt 7, a brush roller 17 that is in contact with the transfer conveyance belt 7 and is rotatable in the direction of the arrow is disposed. The brush roller 17 is configured such that a potential for applying a bias current having a polarity for attracting the sheet-like medium 6 to the transfer conveyance belt 7 is applied from a bias applying unit (not shown). A fixing device 18 having a fixing roller 18 a and a pressure roller 18 b is disposed on the left side of the transfer conveyance belt 7.

  A developing device 5 is disposed on the right side of the latent image carrier 2 and above the brush roller 17. The developing device 5 includes a casing 19, a developing roller 20 as a developer carrying member, a first conveying screw 21 and a second conveying screw 22 as a developer conveying member, a toner supply screw 23, a toner bottle 24, a toner concentration sensor 25, and the like. have.

  The casing 19 is fixed to or detachable from an apparatus main body (not shown) of the image forming apparatus 1 and supports the developing roller 20, the conveying screws 21 and 22, and the toner supply screw 23 in a rotatable manner. Yes. Inside the casing 19, a two-component developer 26 composed of toner and carrier is stored.

  A developing roller 20 is disposed on the left side of the middle stage of the casing 19. The developing roller 20 having a well-known configuration having a magnet roller fixedly disposed on the immovable member and a developing sleeve rotatably disposed around the magnet roller is connected to a gear train (not illustrated) from a main motor (not illustrated) of the image forming apparatus 1. The driving force is transmitted through the driving force transmitting means, and is rotated in the counterclockwise direction in the drawing. A developing bias voltage from a high voltage power source (not shown) is applied to the developing roller 20 via a conductive coupling and a roller driving shaft (not shown).

  As shown in FIG. 2, the first conveying screw 21 disposed on the lower right side of the developing roller 20 and the second conveying screw 22 disposed adjacent thereto are provided with a rotational driving force from a driving means (not shown). It is transmitted by the driving force transmission means 27 comprising a row and is driven to rotate in synchronization with the directions indicated by the arrows in FIG. Each transport screw 21, 22 has screw parts 21 a, 22 a for transporting the two-component developer 26, and the two-component developer 26 rotates with the rotation of each transport screw 21, 22. 21a and 22a are circularly moved in the directions indicated by arrows a and b in FIG. Further, the second transport screw 22 is provided with a non-screw portion 22b in which the screw portion 22a is not formed in the vicinity of the upstream end portion in the toner transport direction.

  On the upper part of the casing 19 positioned above the second conveying screw 22, a toner conveying screw 23 that is rotationally driven by a driving means (not shown) is disposed. The toner conveying screw 23 is rotationally driven when the toner is supplied from the toner bottle 24 disposed above the toner conveying screw 23, and uniformly supplies the toner into the casing 19. The toner bottle 24 is configured in the same manner as that disclosed in, for example, Japanese Patent Laid-Open No. Hei 8-152783, and is rotated by toner bottle driving means (not shown) so that the toner stored therein is opened. Discharge more.

  A toner concentration sensor 25 is disposed at the bottom of the casing 19 located below the second conveying screw 22. The toner density sensor 25 used in the present embodiment is of a type that detects the magnetic permeability of the two-component developer 26, and two toner density sensors 25 are arranged along the axial direction of the second conveying screw 22. Of the two toner density sensors 25, one is disposed below the no-screw part 22b corresponding to the no-screw part 22b, and the other is the screw part 22a near the downstream end in the toner transport direction. Are arranged below the screw part 22a which is a corresponding part. An output signal from each toner density sensor 25 is input to a control unit (not shown) of the image forming apparatus 1.

  With the above-described configuration, the two-component developer 26 is transported inside the casing 19 as indicated by an arrow in FIG. 3, but the transport speed of the two-component developer 26 in the second transport screw 22 is less than that of the screw portion 22a. It becomes slow in the screw part 22b. In the present invention, an experiment was performed in which the toner concentrations of the two-component developer 26 in different states are measured by the two toner concentration sensors 25 at two locations where the conveyance speeds are different from each other. The output of each toner density sensor 25 is shown in FIGS.

  FIG. 4 shows an initial toner density detection result in 10 sec to 1 min after the developing device 5 is operated. In this graph, the horizontal axis indicates the detected density at a location where the two-component developer conveyance speed is fast (the position corresponding to the screw portion 22a), and the vertical axis indicates the location where the conveyance speed is slow (corresponding to the non-screw portion 22b). The detected density at each position is taken. Here, if there is no problem with the charging characteristics of the two-component developer 26 being conveyed, the detection result plot becomes a value near the central 1: 1 line segment in about 10 seconds.

  However, when the two-component developer 26 which has been left for a long time or the two-component developer 26 which is moist (humidified) is used, the flow of the two-component developer is remarkably stagnated in a place where the conveyance speed is slow. 4 is a value in the vicinity of point A in FIG. Therefore, when such a detection result is measured in an actual machine, the charge amount of the toner is decreased. Therefore, the image forming operation is performed without supplying the toner for a certain period of time, or the toner is forcibly consumed. This is improved by supplying toner that is not conditioned.

  Further, when a two-component developer whose supplied toner is insufficiently dispersed is used, the value is in the vicinity of the point B in FIG. When such a detection result is measured in an actual machine, the toner is insufficiently dispersed. Therefore, idling is performed for a certain time to stabilize the density.

  FIG. 5 shows the toner density detection result over time after 5 minutes of operation of the developing device 5. Also in this graph, the horizontal axis represents the detected density at a location where the transport speed of the two-component developer is fast, and the vertical axis represents the detected density at a location where the transport speed is slow. Again, if there is no problem with the charging characteristics of the two-component developer 26 being conveyed, the detection result plot is a value in the vicinity of the central 1: 1 line segment in about 10 seconds.

  However, when a deteriorated two-component developer is used, the value is in the vicinity of point C in FIG. Therefore, even if the agitation and conveyance are performed for a certain time, if the value in the vicinity of the point C in FIG. 5 is taken, it can be determined that the two-component developer 26 has deteriorated and it is determined that the two-component developer 26 needs to be replaced.

  Further, when the value is in the vicinity of the point D in FIG. 5, it is determined that the toner is convection in the vicinity of the toner concentration sensor 25 in the developing device 5 or the toner concentration sensor 25 is malfunctioning, and maintenance is performed. It is judged necessary.

  As described above, the toner density of the two-component developer 26 is measured by the two toner density sensors 25 at two locations in the developing device 5 having different conveyance speeds, so that not only the density deviation in the developing device 5 is detected. The developing device 5 that can determine the state of the two-component developer 26 and the like, suppress the cost increase, and perform toner replenishment while considering the shift of density detection due to deterioration of the two-component developer 26, and the like The image forming apparatus 1 can be provided, and the developing device 5 capable of performing density detection for providing a stable image to the user, and the image forming apparatus 1 provided with the developing device 5 can be used. It is possible to provide the developing device 5 that can detect the above and determine whether or not the maintenance is necessary, and the image forming apparatus 1 including the developing device 5.

  In the above-described embodiment, when the two image sensors 25 are arranged at a location where the transport speed of the two-component developer is fast and a location where the transport speed is slow, a position corresponding to the screw portion 22a is taken as a location where the transport speed is fast. Although the position corresponding to the non-screw portion 22b is set as the slow part, the two-component developer 26 positioned between the transport screws 21 and 22 shown by the reference symbol c or reference numeral d in FIG. A configuration may be adopted in which the position is set in a position corresponding to the delivery section. In the case of adopting this configuration, the second transport screw that does not have a screw-free portion is used like the first transport screw 21.

1 is a schematic front view of an image forming apparatus employing an embodiment of the present invention. It is a schematic perspective view of the 1st conveyance screw used for one embodiment of the present invention, and the 2nd conveyance screw. FIG. 2 is a schematic diagram illustrating the inside of a developing device and the flow of a two-component developer used in an embodiment of the present invention. It is a graph which shows the initial output result of each toner concentration sensor used for one Embodiment of this invention. It is a graph which shows the time-dependent output result of each toner density | concentration sensor used for one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 5 Developing apparatus 20 Developer carrier (developing roller)
21 Developer conveying member (first conveying screw)
21a Screw part 22 Developer conveyance member (2nd conveyance screw)
22a Screw part 22b No screw part 25 Toner density sensor 26 Two-component developer c, d delivery part

Claims (4)

A developing device having a developer carrying member for holding a two-component developer on a surface; a developer carrying member for carrying the two-component developer; and a toner concentration sensor for detecting a toner ratio of the two-component developer. In the image forming apparatus,
The developer conveying member has two portions where the conveying speeds of the two-component developer are different from each other, and the toner density sensor is disposed at each of the two portions, and the initial state after the start of operation of the developing device When the ratio of the toner density at a place where the transport speed is slow and the toner density at a place where the transport speed is fast is smaller than a predetermined value smaller than 1, which is a preset toner density detection result An image forming apparatus that performs an operation of consuming toner . A developing device having a developer carrying member for holding a two-component developer on a surface; a developer carrying member for carrying the two-component developer; and a toner concentration sensor for detecting a toner ratio of the two-component developer. In the image forming apparatus,
The developer conveying member has two portions where the conveying speeds of the two-component developer are different from each other, and the toner density sensor is disposed at each of the two portions, and the initial state after the start of operation of the developing device When the ratio of the toner density at a place where the transport speed is slow and the toner density at a place where the transport speed is fast is larger than a preset predetermined value larger than 1, in a typical toner density detection result An image forming apparatus , wherein the developer conveying member is idled for a predetermined time . The image forming apparatus according to claim 1 or 2 ,
The developer conveying member has two or more conveying screws, one of the toner density sensors is disposed at a position corresponding to one of the conveying screws, and the other toner density sensor is located between the conveying screws. An image forming apparatus, wherein the image forming apparatus is disposed at a position corresponding to the delivery portion of the two-component developer . The image forming apparatus according to claim 1 or 2 ,
The developer conveying member has a conveying screw having a screw part and a non-screw part in which the developer conveying part is not formed, one of the toner density sensors is disposed at a position corresponding to the screw part, and the other toner density sensor Is disposed in a portion corresponding to the screw-free portion .

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