JP2008003561A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently adjust a charge amount of developer supplied to a developing device, even if external conditions (conditions for use) change. <P>SOLUTION: In the developing device, a developing unit 10 that conducts development on a photoreceptor drum and a developer storage device 40 storing developer composed of two components, toner and carrier, are separately disposed. The developer circulates through the developing unit 10 and developer storage device 40. The developing device includes a blower 60 for supplying the developer from the developer storage device 40 to the developing unit 10 and for charging toner. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing device that develops a latent image formed on an image carrier with a two-component developer containing toner and a carrier, and an image forming apparatus including the developing device.

  In an electrophotographic image forming apparatus such as a copying machine, a printer, or a facsimile, a two-component developer composed of toner and a carrier is used to visualize, that is, develop an electrostatic latent image on the surface of an image carrier such as a photoreceptor. A developing device is used. In such a developing container containing the two-component developer of the developing device, the toner is consumed by the developing operation. Therefore, new toner is replenished to the developing device, and the toner is dispersed while being transported to the carrier. At that time, the toner and the carrier are triboelectrically charged to generate a charge in the developer, and as a result, the toner is charged. If the replenished toner is not sufficiently dispersed and charged before it is supplied to the developing roller, it causes scattering of the poorly charged toner from the developing device, and scumming occurs on the image.

In particular, in a high-speed machine, since the circulation speed of the developer in the developing device is fast, it is not possible to secure time for sufficiently charging the toner. Therefore, if the capacity of the developer is increased in order to sufficiently charge the toner, the replenishment toner is easily dispersed, but the developing device becomes large and the machine main body becomes large. From such a point, it has been proposed that in a developing device using a two-component developer, a developer agitating means is provided in the interior of the photosensitive drum, and the developer is circulated by connecting the developer with a pipe ( Patent Document 1). It has also been proposed to separate a developing unit and a developer stirring unit in a developing device and connect the developing unit and the developer stirring unit with a developer circulating means (Patent Document 2). Further, an example is also known in which a developing unit and a developer agitation unit in a gradual increase device are connected by a developer circulating means, and the developer is transferred by a screw pump (Patent Document 3).
Japanese Utility Model Publication No.5-21082 JP-A-4-1989966 Japanese Patent Laid-Open No. 7-225515

  The conventional technology aims to stir the toner and the carrier outside the developing device and adjust the charge amount to a desired value in advance. However, the charge amount of the toner varies depending on various factors, and the charge amount varies even under the same stirring condition. For example, the factors include the ambient tide environment (temperature and humidity), the charging performance of the carrier over time, the change in the toner charge amount depending on the output image area, that is, the difference in the charge amount depending on the toner residence time. Further, the amount of charge varies depending on the amount of toner newly supplied. This is because when the amount of toner is large, mixing and stirring takes time.

  Therefore, in the above-described conventional technology, the charge amount is not constant depending on conditions, and affects the image quality. As a method for solving such a problem, it is possible to obtain an appropriate charge amount by controlling the stirring force in a developer storage unit outside the developing device. However, the developer is stressed by stirring, and toner, carrier There is a risk of accelerating deterioration.

  The present invention has been made in view of the situation of the prior art as described above, and the problem to be solved by the present invention is that the charge amount of the developer supplied to the developing device is efficient regardless of disturbance conditions (use conditions). To be able to adjust to.

  In order to achieve the above object, the first means includes a developing unit that develops a latent image on the image carrier and a developer storage unit that stores a two-component developer of toner and carrier, and is provided separately. In the developing device in which the developer circulates between the developing unit and the developer storing unit, the developing unit includes a transfer unit that supplies the developer from the developer storing unit to the developing unit and generates charges in the developer. It is characterized by.

  The second means is characterized in that, in the first means, the transfer means transfers the developer by a flow of air.

  The third means is characterized in that in the second means, means for changing the speed of the air is provided.

  A fourth means is characterized in that, in any one of the first to third means, the developer storage section includes a stirring means for stirring the developer.

  A fifth means is characterized in that, in any one of the first to fourth means, the developer storage section comprises means for quantitatively discharging the developer.

  The sixth means is characterized in that in the third means, the transfer means includes means for adjusting a cross-sectional area of a path through which the air is supplied.

  The seventh means is characterized in that, in the sixth means, the means for adjusting the cross-sectional area comprises a throttle valve.

  The eighth means is characterized in that, in the third means, the speed of the air is determined from at least one of the replenishment amount of the toner, the temperature and humidity in the apparatus, the driving time of the developing device, and the area ratio of the output image. And

  A ninth means is characterized in that the image forming apparatus includes a developing device according to any one of the first to eighth means.

  In the embodiments described later, the image carrier is the photosensitive drum 117, the developing device is the reference numeral 10, the developer storage unit is the developer storage device 40, the transfer means is the blower 60, and the stirring means is the agitator. 46, the means for quantitative discharge corresponds to the feeder 50, and the means for adjustment corresponds to the throttle valve 56.

  According to the present invention, when the image is formed, the developer is supplied to the developing device and charged, so that it is possible to reliably obtain the charge amount of the developer supplied to the developing device, and the defectively charged toner Can be reduced or prevented.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 is a perspective view showing an embodiment of a developing device according to the present invention, FIG. 2 is a longitudinal front view of a portion of the developing device of FIG. 1, FIG. 3 is a longitudinal side view of a portion of the developing device of FIG. FIG. 2 is a secondary sectional view of a portion of the developer storage device of FIG. 1.

  The developing device includes a developing device 10 that is a unit for developing a toner image of an electrostatic latent image to form a toner image, a toner container 20 made of a metal and a synthetic resin, and a toner and a carrier. A developer storage device 40 for storing the developer to be developed, a feeder 50 for discharging the developer from the developer storage device 40, and a blower 60 for sending the developer from the feeder 50 to the developing device 10. . A toner image formed on a photoreceptor (not shown), which is an image carrier provided opposite to the developing device 10, is transferred onto a transfer sheet and is transferred onto the transfer sheet by a fixing device, as in a general electrophotographic process. The image is output after being fixed to the image.

  The developing device 10 is a so-called two-component developing device in which a developer in which toner and a carrier are mixed is stored. As shown in FIGS. 2 and 3, the developing device 10 is positioned so as to face a photoreceptor (not shown), and develops the latent image while holding the developer on the roller surface by a magnetic force to form a toner image. It is made of the developing roller 12, the first and second conveying screws 13a and 13b for transferring the developer, and the metal, the synthetic resin, the rubber, etc. connecting the developing device 10 and the developer storage device 40. And two pipe-shaped developer transfer members 30, 31. An auger 32 without a shaft for transferring the developer is disposed inside the developer transfer member 30, and one end of the auger 32 is connected to a drive shaft 33 that is rotationally driven by a motor (not shown). Reference numeral 15 denotes a doctor blade which is a developer regulating member. By this doctor blade 15, the developer supplied to the developing roller 12 is formed into a developer layer having an optimum thickness and is used for development. The developing device 10 develops the developer from the supply port 17a for supplying the developer from the developer transfer member 31 to the compartment of the first conveying screw 13a and the developer from the compartment of the second conveying screw 13b. A discharge port 17 b for sending out to the agent transfer member 30 is formed. Note that arrows A and B in FIG. 3 indicate the flow of the developer.

  The toner container 20 is connected to the developer storage device 40 by a pipe-shaped toner supply member 21. A coil screw (not shown) is provided inside the toner replenishing member 21 and is rotated by a motor 28 to replenish the developer storage device 40 with toner.

  As shown in FIG. 4, the developer storage device 40 is provided with a developer inlet 42 through which the developer from the developer transfer member 30 flows and a toner supply port 44 through which the toner from the toner supply member 21 flows. In addition, an outlet 43 for allowing the developer to flow out to the feeder 50 is provided at the bottom. Inside the developer storage device 40, an agitator 46 for stirring the developer is disposed substantially vertically and is driven to rotate by an external motor 45. The motor 45 is provided with a control circuit (not shown) for controlling (adjusting) the rotational speed of the motor. A plurality of stirring blades 41 are attached to the agitator 46 as shown in the figure, and the developer is stirred by the rotation of the stirring blades 41.

  The developer storage device 40 can be installed at an arbitrary position of the machine main body, and if the capacity is increased, a large amount of developer can be stored therein, resulting in a long life of the developer. Can do. The control circuit includes a CPU, a ROM, and a RAM. The CPU uses the RAM as a work area and executes a program stored in the ROM, thereby executing the operation in the present embodiment set by the program.

  The feeder 50 is a so-called rotary feeder having a rotor 52 provided with a plurality of blades inside a holder 53 made of metal, resin, or the like. It discharges to the opening in the vertical direction of the T-shaped receiving pipe member 54.

  The blower 60 is connected to one horizontal opening of the receiving pipe member 54 of the feeder 50 by a pipe-shaped air supply member 33. The air supply member 33 is provided with a throttle valve 55 that adjusts the flow rate of air. The developer transfer member 31 is connected to the other horizontal opening of the receiving pipe member 54.

  As shown in FIG. 4, the developer is stored in advance in the developer storage device 40. The internal developer falls from the outlet 43 to the feeder 50 by its own weight while being stirred by the agitator 46. At this time, the agitator 46 does not need to rotate at all times, and stirs the developer as necessary, such as when toner is supplied. The developer dropped on the feeder 50 falls on the receiving pipe member 54 by the rotation of the rotor 52. The dropped developer is conveyed through the developer transfer member 31 by the air supplied from the blower 60 and enters the developing device 10 through the supply port 17a. With this configuration, the developer is agitated in the developer storage device 40, and the toner and the carrier can be mixed in advance before air transportation. For this reason, air contributes to toner charging. That is, the developer slides or floats in the developer transfer member 31 and is sequentially transferred. At this time, the developer repeats contact between the developers and contact with the inner wall of the developer transfer member 31. The amount of charge increases. The developer transferred to the developing device 10 is supplied to the developing roller 12 while being conveyed in the direction of arrow B in FIG. 3 by the conveying screw 13a, and toner development is performed. The developed developer is collected by the conveying screw 13b and transferred in the direction of arrow A in FIG. Thereafter, the toner is transferred from the discharge port 17 b to the auger 32 of the developer transfer member 30 and conveyed to the developer storage device 40.

  In the present embodiment, the auger method that is generally used is used for transport from the developing device 10 to the developer storage device 40, but in the same manner as the transport method from the developer storage device 40 to the developing device 10. Air may be used. In the present embodiment, the developing device 10 is positioned above the developer storage device 40. In such a case, the auger method is not preferable for transporting the developer against gravity. In the auger method (same as the screw method with a shaft), if the developer is transported against the weight, the developer falls by its own weight (reverses flow), and the transport efficiency is extremely deteriorated. Further, the layout of the path of the developer conveying member is limited (the curvature cannot be increased). Further, the developer enters the gap between the inner wall of the developer conveying member and the auger, and the developer is easily damaged. Conversely, when transporting from the top to the bottom, since it can be transported using the weight together with the auger, it is efficient and it is possible to secure a certain amount of clearance between the path inner wall and the auger.

  Toner supply is performed as follows. When an image is formed by the developing device and the toner is consumed, the toner density of the developer decreases. This decrease in toner density is detected by a toner density sensor (not shown) provided in the developer transfer member 30 or the like. In order to replenish the reduced toner, the toner is supplied from the toner container 20 through the toner replenishing member 21 to the developer storage device 40. At this time, the agitator 46 has a function of mixing the replenished toner and the developer whose toner density is reduced. Such mixing by the agitator 46 is stressed by stirring and easily damages the developer. In particular, as in the present embodiment, when the developer is stored in the developer storage device 40 in advance, a large force is required to mix the developer. Therefore, mixing by the agitator 46 is desired to be minimized.

  In this embodiment, the toner is supplied to the developer storage device 40. However, if the developer is supplied into the developer transfer member 30 before the developer enters the developer storage device 40, the above problem can be reduced. . That is, the replenished toner is mixed to some extent while being transported with the developer flowing in the developer transfer member 30 (charging is not required to be sufficient), so that the agitator 46 of the developer storage device 40 This is because the stirring operation can be reduced (in this case, there is no need for an agitator).

  Here, the charge amount control, which is a feature of the present invention, will be described. The charge amount of the toner varies depending on the surrounding environment (temperature and humidity), the deterioration of the charge performance of the carrier over time, the output image area (difference in charge amount due to toner residence time), and the like. Therefore, in the developer circulation system described in Patent Document 3, it is difficult to control the charge amount to be constant.

  In the present invention, even when the external condition (error condition) as described above changes, the charge amount is kept constant (control), and the charge amount is adjusted by the following method.

  The developer is transferred by the air generated by the blower 60, and the charge amount increases during the transfer. However, the increasing charge amount can be controlled by changing the air flow rate. For example, when the ambient humidity is high, the toner charge amount decreases. Therefore, in order to obtain a good image, it is desired to increase the charge amount. Conventionally, process control (detecting the output image density and adjusting the toner density, development bias, and photosensitive member charging potential) is performed so that the desired image density is obtained as much as possible, but time is wasted. There are problems such as (increase in downtime), stress application to the developer by idling, wasteful toner consumption by test pattern development for image density detection. In the present invention, in order to increase the charge amount, the air speed is increased (the air flow rate is increased) to increase the charge amount. Conversely, if the air speed is decreased (the flow rate is reduced), the amount of increase in charging can be reduced.

  The principle is that the density of the developer varies depending on the air velocity. That is, when the air speed is low, the moving speed of the developer is also low. On the other hand, since the supply amount from the feeder 50 is constant, the developer moves in a high density state, and there is less chance of rubbing between the developers and rubbing with the inner wall of the path, increasing the charge amount. Is suppressed. On the other hand, when the air speed is high, the density of the developer during movement is low and the movement speed is also high, so that the contact opportunity of the developer increases and the charge amount increases.

  If the toner is charged during air transportation in this way, the developer is greatly stressed (a strong pressure is applied between the developers, and the toner is applied to the toner more than mechanically moving and stirring the developer as represented by a conventional stirrer. Is not damaged).

  As a means for controlling the speed of air, it is possible to adjust the amount of air by a method of changing the input voltage of the blower as an air supply source or by the throttle valve 54 in the air supply member 33.

  These controls may be performed by the CPU of the control circuit.

  When the developer is transported in the tube using air, the behavior is greatly influenced by the moving speed and is divided into several patterns. That is, when the velocity is sufficiently high, the powder is completely suspended in the air and uniformly dispersed and flows (this is referred to as (1)). When the speed is gradually reduced, the powder flows like a liquid while the powder slides in a collective manner on the tube bottom of the developer transfer member 30 together with the powder flow as in (1). (2)) The pattern is mixed. When the speed is further decreased, the entire pipe of the developer transfer member 30 flows as shown in (2) (this is referred to as (3)).

  As a result, the density of the developer in the tube increases in the order of (3)> (2)> (1). If the density is large, the movement between the individual developers is limited (the contact opportunity is small). The increase in quantity is small. On the contrary, if the density is small, the individual developer tends to move (increased contact opportunity), and the charge amount tends to increase.

  The present invention is effective when the toner replenishment amount is different as described below. That is, when the toner replenishment amount is large, it naturally takes time to mix with the existing developer and increase the charge amount. Therefore, by controlling the air speed according to the toner replenishment amount, the charge amount can be increased without taking time.

  The speed of air is determined by any value of the toner replenishment amount, in-machine temperature and humidity, the driving time of the developing device 10, the area ratio of the output image, or a combination thereof. As a result, an external factor that changes the charge amount of the toner is grasped to determine the air velocity, and the charge amount can be optimized more accurately.

  FIG. 5 is a flowchart showing a control procedure of air speed control by such a CPU. In the figure, in the air velocity control, first, a measured value of the toner concentration in the developer detected by the above-described toner concentration sensor (not shown) is acquired (step S101). Next, a change in the charge amount is predicted from at least one parameter among the toner replenishment amount, the in-machine temperature and humidity, the developing device drive time, and the area ratio of the output image (step S102), and the toner density measurement value acquired in step S101. Is corrected based on the prediction in step S102.

  After the correction, it is determined whether or not the corrected charge amount is too small (step S104). If the charge amount is too small, the input voltage of the blower is increased or the throttle valve is opened to open the air. Increase speed (increase flow). On the other hand, if the charge amount is not too small, it is determined whether the charge amount is too large (step S106). If the charge amount is too large, the input voltage of the blower is decreased, or The throttle valve is throttled to reduce the air speed (decrease the flow rate). If the condition is not excessive in step S106, the process exits from this loop.

  As described above, according to the present embodiment, the toner can be charged while the developer is transferred using air, and the charge amount can be controlled by arbitrarily changing the speed of the air. A constant charge amount is always ensured and a stable image can be obtained.

  FIG. 6 is a diagram showing a schematic system configuration of the entire image forming apparatus to which the developing device of the present invention is applied. This image forming apparatus is taken as an example of a complex machine having a copying function and other functions such as a printer function and a facsimile function. This multi-function machine can be selected by sequentially switching a copying function, a printer function, and a facsimile function with an application switching key of an operation unit (not shown). The copy mode is selected when the copy function is selected, the print mode is selected when the printer function is selected, and the facsimile mode is selected when the facsimile mode is selected.

  The image forming apparatus is for forming a monochrome image. The main body 100, a writing unit 118 installed on the upper part of the main body 100, an image reading device 106 installed on the writing unit 118, and further thereon. An automatic document feeder (hereinafter referred to as “ADF”) 101 is basically configured.

  In the copy mode, the operation is as follows. In the ADF 101, when a document bundle is placed on the document table 102 so that the image surface is on top, and a start key on an operation unit (not shown) is pressed, the lowermost document is fed to the feed roller 103 and the feed. The belt 104 is fed to a predetermined position on the contact glass 105. The ADF10l has a counting function that counts up the number of documents every time a document is fed. The document on the contact glass 105 is discharged onto a sheet discharge table 108 by a feeding belt 104 and a discharge roller 107 after image information is read by an image reading device 106 as an image input unit.

  When the document set detector 109 detects that the next document is present on the document table 102, the lowermost document on the document table 102 is similarly contacted by the feed roller 103 and the feed belt 104. It is fed to a predetermined position on the glass 105. The feed roller 103, the feed belt 104, and the discharge roller 107 are driven by a transport motor (not shown).

  The image reading device 106 performs line scanning on the image information of the document in the sub-scanning direction while irradiating with the two lamps 128 that irradiate the document on the contact glass 105, and uses the reflected light as image data for the first mirror 129 and the second mirror. A mirror 130, a third mirror 131, a lens unit 132 that reflects the image in a predetermined direction by the mirrors 129, 130, and 131 and reduces and forms an image, and an image that is reduced and formed by the lens unit 132 is read. It comprises a CCD image sensor 133 that performs photoelectric conversion.

  The image data read from the document by the image reading device 106 is modulated by an image processing unit (not shown), and optical writing is performed by the writing unit 118 to form an electrostatic latent image on the photosensitive drum 117. The writing unit 118 includes a laser light emitting device 134, an fθ lens 135, a reflection mirror 136, and the like. The exposure light source is a laser beam, but is not limited to this. For example, an LED array may be used.

  The main body 100 includes a photosensitive drum 117, a developing device 119, a fixing unit 121, a paper discharge unit 122, first to third paper feeding devices 110, 111, 112, a vertical conveyance unit 116, and the like. The photosensitive drum 117 is uniformly charged by a charger (not shown) and then exposed to light information from the writing unit 118 to form an electrostatic latent image. The electrostatic latent image on the photosensitive drum 117 is developed by the developing device 119 to become a toner image.

  A conveyor belt 120 is disposed below the photosensitive drum 117. The transfer belt 120 also serves as a transfer unit and transfer unit for transfer paper as a recording medium. A transfer bias is applied from a power source (not shown), and the transfer sheet from the vertical transfer unit 116 is transferred to the photosensitive drum 117 or the like. While being conveyed at high speed, the toner image on the photosensitive drum 117 is transferred onto a transfer sheet. The toner image on the transfer paper is fixed by the fixing unit 121 and discharged to the paper discharge tray 123 by the paper discharge unit 122. The photosensitive drum 117 is cleaned by a cleaning device (not shown) after the toner image is transferred. Here, the photosensitive drum 117, the charger, the writing unit 118, the developing unit 119, and the transfer unit constitute an image forming unit that forms an image on transfer paper based on the image data. The photosensitive drum 117 is rotationally driven at a constant speed by a main motor.

  The paper discharge unit 122 is provided with a double-sided conveyance path. That is, the reversing unit 125 fed by the transport roller pair 124 from the middle of the paper discharge unit 122, the image forming side transport path 126 for transporting the transfer paper reversed by the reversing unit 125 to the vertical transport unit 116 again, and the reversed transfer. A paper discharge conveyance path 127 for returning the paper to the paper discharge unit 122 again is arranged. Images can be formed on both sides of the transfer paper by this double-sided conveyance path, or discharged onto the paper discharge tray 123 with the image-formed side down.

  The first paper feeding device 110, the second paper feeding device 111, and the third paper feeding device 112 as paper feeding means were loaded on the first tray 113, the second tray 114, and the third tray 115, respectively, when selected. The transfer paper is fed, and the transfer paper is conveyed by the vertical conveyance unit 116 to a position where it contacts the photoconductor 117.

  In the print mode, image data from the outside is input to the writing unit 118 instead of image data from the image processing means, and an image is formed on the transfer paper by the image forming means. In the facsimile mode, the image data from the image reading device 106 is transmitted to the other party by a facsimile transmission / reception unit (not shown), and the image data from the other party is received by the facsimile transmission / reception unit, instead of the image data from the image processing means. By being input to the writing unit 118, an image is formed on the transfer paper by the image forming means.

1 is a perspective view showing an embodiment of a developing device according to the present invention. FIG. 2 is a longitudinal front view of a portion of the developing device in FIG. 1. FIG. 2 is a vertical side view of a part of the developing device of FIG. 1. FIG. 2 is a secondary sectional view of a portion of the developer storage device of FIG. 1. It is a flowchart which shows the control procedure of air speed control. 1 is a diagram illustrating a schematic system configuration of an entire image forming apparatus to which a developing device of the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Developing device 12 Developing roller 20 Toner container 21 Toner replenishing member 30, 31 Developer transfer member 33 Air supply member 40 Developer storage device 46 Agitator 50 Feeder 56 Throttle valve 60 Blower 100 Main body 106 Image reading device 117 Photosensitive drum 118 Writing Unit 121 fixing unit

Claims (9)

A developing unit for developing the latent image on the image carrier and a developer storing unit for storing a two-component developer of toner and carrier are provided separately, and the developing unit and the developer storing unit are connected to the developer. In a developing device in which
A developing apparatus comprising: a transport unit that supplies the developer from the developer storage unit to the developing unit and generates charges in the developer.   The developing device according to claim 1, wherein the transfer unit transfers the developer by an air flow.   3. The developing device according to claim 2, further comprising means for changing a speed of the air.   The developing device according to claim 1, wherein the developer storage unit includes a stirring unit that stirs the developer.   The developing device according to claim 1, wherein the developer storage unit includes a unit that discharges the developer in a fixed amount.   4. The developing device according to claim 3, wherein the transfer means includes means for adjusting a cross-sectional area of a path for supplying the air.   7. The developing device according to claim 6, wherein the means for adjusting the cross-sectional area comprises a throttle valve.   4. The developing device according to claim 3, wherein the speed of the air is determined from at least one of the replenishment amount of the toner, the temperature and humidity in the apparatus, the driving time of the developing device, and the area ratio of the output image.   An image forming apparatus comprising the developing device according to claim 1.

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