JP5087464B2 - Developer supply device and image forming apparatus - Google Patents

Description

  The present invention relates to a developer replenishing device and an image forming apparatus that replenish a developing device with a two-component developer composed of toner and a carrier.

  In image forming apparatuses such as printers, facsimiles, copiers, and multifunction devices having at least two of these functions, development of toner or the like on an electrostatic latent image carried on a photosensitive member which is a latent image carrier. Visible image processing is performed using the agent. As the visible image processing, a two-component developing system using a two-component developer composed of a toner and a carrier is widely used from the viewpoint of transferability, halftone reproducibility, temperature / humidity stability, and the like. In the case of a developing method using a two-component developer, it is necessary to replenish the toner consumed by being used for visible image processing and to keep the developer concentration constant. New toner or the like is supplied to the developing device from a toner container such as a tank or a toner hopper. On the other hand, the carrier is often used as it is regardless of the supply of new toner.

  For this reason, there is a deterioration due to an increase in the stirring frequency as a change with time of the carrier. The deterioration of the carrier is related to the toner consumption amount. When the toner consumption amount is small, that is, when the image area ratio is small, deterioration of the resistance reduction due to wear of the carrier coat layer occurs. Further, when the toner consumption is large, that is, when the image area ratio is large, the deterioration of the low charge is likely to occur due to toner filming in which the toner is fused to the surface. When the resistance is lowered, carrier adhesion to the solid portion occurs. On the other hand, when the charge is lowered, background stains and toner scattering occur due to insufficient charging. In order to prevent such low resistance and low charging due to carrier deterioration, the developer that has become excessive by supplying the carrier separately from the toner supply is discharged from the developing tank to remove the deteriorated carrier. Patent Document 1 and the like propose a developer exchange system referred to as a premix development system in which a developer that is included is replaced with a new developer.

  The image forming apparatus described in Patent Document 2 has a sub hopper inside the machine. In this type of apparatus, as shown in FIG. 1, the toner is transported from the toner bottle to the sub hopper, and the toner is supplied from the sub hopper to the developing device. Has been put to practical use.

  By having the sub hopper inside the machine in this way, even if the toner in the toner bottle to be replaced by the user runs out, printing can be performed with the toner in the sub hopper for a while. Therefore, even if the toner bottle runs out of toner and it becomes necessary to replace the toner bottle, printing can be performed for a certain period of time, and the toner bottle can be replaced at a free time, thus reducing machine downtime. It has a big effect. Further, the sub hopper installed inside the machine can easily supply the toner to the developing device with higher accuracy than replenishing the developing device directly from the toner bottle.

  On the other hand, when there is no sub hopper, there are restrictions on the arrangement of the toner bottle and the developing device, and it is difficult to reduce the size of the machine for layout reasons, and it is necessary to devise a method for supplying toner to the developing device with high accuracy. .

  By the way, in the case of the premix system in which the toner and the carrier are mixed and replenished to the developing device, the difference in specific gravity between the toner and the carrier is large, so the ratio of the carrier contained in the toner supplied from the toner bottle fluctuates. The proportion of carriers increases in the second half of the toner bottle.

  On the other hand, the toner replenished from the sub hopper to the developing device changes depending on the carrier ratio, and the toner supply amount per unit time decreases as the carrier ratio increases. Although the cause of such a phenomenon has not been completely investigated, it is presumed that the toner replenished from the sub hopper is tightened to some extent and the fluidity is retreated. Normally, when toner is supplied to the developing device, a necessary toner amount is calculated, and toner is supplied from the sub hopper to the developing device for a time corresponding to the amount. As a result, the amount of toner that is actually replenished with respect to the target toner amount required by the developing device fluctuates depending on the ratio of the carrier, causing a deviation in toner density adjustment in the developing device, resulting in density fluctuations in the printed image and background contamination. There are problems that cause adverse effects such as toner scattering and carrier adhesion.

JP 2004-29306 A Japanese Patent No. 4006215

  An object of the present invention is to provide a developer replenishing device and an image forming apparatus capable of solving the above-described conventional problems and replenishing a developer in which toner and a carrier are mixed with accuracy through a sub hopper.

  To achieve the above object, the present invention provides a replaceable developer container for storing a two-component developer composed of toner and a carrier, and a developer transport means for transporting the developer stored in the developer container. A developer replenishing device comprising: a sub hopper for temporarily storing the developer conveyed through the developer conveying means; and a developer replenishing means for replenishing the developer stored in the sub hopper to the developing device. Proposing a developer replenishing device that calculates the weight ratio of carrier to toner in the sub hopper and adjusts the operating time of the developer replenishing means according to the calculated weight ratio of carrier to toner in the sub hopper To do.

In the present invention, it is advantageous that the weight ratio of the carrier to the toner in the sub hopper is calculated based on the remaining amount of the developer in the developer container.
Further, the present invention is an apparatus in which the developer conveying means conveys using a pressure difference by a pump, and the developer replenishing means replenishes by rotation of a spiral member, and the developer conveying means and the It is advantageous to calculate the weight ratio of the carrier to the toner in the sub hopper from the difference in operating time for a certain amount of toner with the developer replenishing means.

Furthermore, in the present invention, it is advantageous that the comparison between the developer conveying means and the developer replenishing means is performed using an average of the nearest fixed time.
Furthermore, in the present invention, it is advantageous that the developer conveying means is a uniaxial eccentric screw pump.

Furthermore, in the present invention, it is advantageous that the developer supply means is a screw.
In order to achieve the above object, the present invention proposes an image forming apparatus using the developer supply device according to any one of claims 1 to 6.

  According to the present invention, in toner replenishment from the sub hopper to the developing device, it is possible to accurately supply the toner amount required by the developing device even in the premix system by adjusting the replenishment time in consideration of the carrier ratio. This makes it possible to stabilize the density of printed matter and prevent abnormal images.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing a main part of a color laser printer showing an example of an image forming apparatus using a developing replenishing device according to an embodiment of the present invention. This printer includes four photoreceptors 1Y, 1C, 1M, and 1K for forming toner images of respective colors of yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K). A transfer device 5 is provided below the photoreceptors 1Y, 1C, 1M, and 1K arranged in the horizontal direction.

  Each color image forming unit provided with the photoreceptors 1Y, 1C, 1M, and 1K has substantially the same configuration except that the color of the toner to be formed is different. In this case, in order to form a Y toner image. The Y image forming unit will be described.

  The Y image forming unit includes a uniform charging device 2Y, an optical writing unit 3Y, a developing device 4Y, a cleaning device 5Y, and the like around a drum-shaped photoconductor 1Y that is driven to rotate counterclockwise in the drawing. These are held by a common casing and are integrally attached to and detached from the printer main body. The photoreceptor 1 </ b> Y is obtained by coating an organic photosensitive layer on an element tube such as aluminum.

The uniform charging device 2Y uniformly charges, for example, a negative polarity on the surface of the photoreceptor 1Y that is rotationally driven in the direction of arrow A (counterclockwise direction) in the drawing.
The optical writing unit 3Y has a light source composed of a laser diode or the like, a regular hexahedral polygon mirror, a polygon motor for rotationally driving the mirror, an fθ lens, a lens, a reflection mirror, and the like. A laser beam L emitted from a light source driven based on image information sent from a personal computer (not shown) or the like is reflected by the polygon mirror surface and deflected as the polygon mirror rotates, so that the photosensitive member 1Y. To reach. As a result, the surface of the photoreceptor 1Y is optically scanned, and an electrostatic latent image for Y is formed on the surface of the photoreceptor 1Y.

  The developing device 4Y for Y has a first developing roll 41Y and a second developing roll 42Y that expose a part of the peripheral surface from an opening provided in the casing. Each of these developing rolls has a developing sleeve formed of a non-magnetic pipe that is driven to rotate by a driving means (not shown), and a magnet roller (not shown) that is included so as not to be rotated. In the developing device 4Y, a Y developer (not shown) including a magnetic carrier and a negatively chargeable Y toner is included. The Y developer is agitated and conveyed by three conveying screws (not shown), and while the Y toner is triboelectrically charged, it is carried on the developing sleeves of these developing rolls and used for development.

  In the developing region where the developing sleeve and the photoreceptor 1Y face each other, a negative polarity is provided between the developing sleeve to which a negative developing bias output from a power source (not shown) is applied and the electrostatic latent image on the photoreceptor 1Y. The developing potential for electrostatically moving the Y toner from the sleeve side to the latent image side acts. In addition, a non-developing potential for electrostatically moving the negative M toner from the background side to the sleeve side acts between the developing sleeve and the uniformly charged portion (background portion) of the photoreceptor 1Y. The Y toner in the Y developer on the developing sleeve is separated from the sleeve by the action of the developing potential and is transferred onto the electrostatic latent image on the photoreceptor 1Y. By this transfer, the electrostatic latent image on the photoreceptor 1Y is developed into a Y toner image. The Y toner image on the photoreceptor 1Y is transferred onto an intermediate transfer belt 7 that runs in the direction of arrow B by a transfer device 5 described later.

  The developing device 4Y has a toner concentration sensor as a magnetic permeability sensor (shown in FIG. 2) that outputs a voltage having a value corresponding to the magnetic permeability of the stored Y developer. Output the voltage of the corresponding value. This output voltage value is sent to a supply control unit (not shown). The replenishment control unit includes a storage unit such as a RAM, in which M Vtref, which is a target value of the output voltage from the Y toner density sensor, and a toner density sensor mounted on another developing device. Vtref data for C, M, and K, which are target values of the output voltage from. For the Y developing device 4Y, the value of the output voltage from the Y toner density sensor is compared with the Y Vtref, and the developer replenishing device 10 described later is driven for a time corresponding to the comparison result. Thus, the replenishing Y developer is replenished to the developing device 4Y. By controlling in this way, an appropriate amount of Y developer is replenished to the Y developer whose Y toner concentration has been reduced with development, and the Y toner concentration of the Y developer in the developing device 4Y is within a predetermined range. Maintained. The same replenishment control is performed for the developing devices 4C, M, and K.

  The Y toner image developed on the photoreceptor 1Y is transferred to the front surface of an intermediate transfer belt 7 described later. Untransferred toner that has not been transferred onto the intermediate transfer belt 7 adheres to the surface of the photoreceptor 1Y that has undergone the transfer process. This transfer residual toner is removed by the cleaning device 5Y. The surface of the photoreceptor 1Y from which the transfer residual toner has been removed in this manner is discharged by a discharging lamp (not shown), and then uniformly charged by the uniform charging device 2Y.

  Although the Y image forming unit has been described in detail, C, M, and K toner images are formed on the surfaces of the photoreceptors 1C, M, and K by the same process in the image forming units for other colors.

  The transfer device 5 is disposed in the loop of the endless intermediate transfer belt 7 below the photoreceptors 1Y, 1C, 1M, and 1K in the drawing. The Y, C, M, and K toner images formed on the photosensitive members 1Y, 1C, 1M, and 1K of the respective colors are sequentially superimposed and transferred onto the intermediate transfer belt 7 by the transfer device 5. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 7.

  One of the rollers around which the intermediate transfer belt 7 is wound, in this example, the lowermost roller is configured as a secondary transfer bias roller 71, and the secondary transfer bias roller 71 includes a power source and wiring (not shown). A secondary transfer bias is applied by the voltage applying means.

  The printer includes a paper feeding cassette (not shown), and accommodates a recording paper bundle in which a plurality of recording papers 8 are stacked therein. Then, the uppermost recording paper 8 is sent out to the paper feed path at a predetermined timing. The sent recording paper 8 is sent out at a timing that can be synchronized with the four-color toner image on the intermediate transfer belt 7 through a pair of registration rollers (not shown) disposed at the end of the paper feeding path. By the action of the transfer bias roller 71, the image is secondarily transferred onto the recording paper 8. The recording paper 8 on which the full-color image is formed in this way is discharged from the secondary transfer nip, and then sent to a fixing device (not shown) to fix the full-color image.

FIG. 2 is a schematic diagram illustrating a configuration example of the developer supply device 10.
In FIG. 2, the developer supply device 10 includes a developer bottle 11 as a replaceable developer container for storing a premix developer composed of toner and carrier, and a premix developer stored in the developer bottle 11. A transport pump 12 as a developer transport means for transporting, a sub hopper 13 for temporarily storing the developer transported via the transport pump 12, and a development for supplying the developer stored in the sub hopper 13 to the developing device. It has a conveying screw 14 as a medicine replenishing means.

  The developer replenishing device 10 replenishes the toner consumed by the printing operation from the sub hopper 13 to the developing device 4 via the conveying screw 14. The sub hopper 13 is provided with a sensor 15. When the developer stored in the sub hopper 13 is reduced, the developer is transported from the developer bottle 11 via the transport pump 12. The amount of developer up to the detection position where 15 is attached is controlled so that it always exists.

  Since the developer replenishing device 10 configured in this manner replenishes the premix developer composed of toner and carrier, it can prevent the image quality from being deteriorated due to carrier deterioration, and further includes the sub hopper 13. Even if the developer becomes empty and the bottle needs to be replaced, printing can be performed for a certain period of time, so that the bottle can be replaced when the developer is free. Furthermore, since the developer is replenished from the sub hopper 13 using the conveying screw 14, it is easy to supply the developer to the developing device with high accuracy.

  As described above, the developer replenishing device 10 has various advantages. However, since the specific gravity of the carrier is much larger than that of the toner, the premix developer is difficult to be discharged from the developer bottle 11. FIG. 3 shows the relationship between the amount of toner present in the developer bottle 11 and the weight ratio of the carrier of the toner discharged from the developer bottle 11. Here, the toner and the carrier initially charged in the developer bottle 11 were 1840 g and 160 g, respectively, and the ratio of the carrier was 8% by weight. From the graph of FIG. 3, it can be seen that almost no carrier appears in the first half.

  FIG. 4 is a graph showing the toner weight per hour supplied from the sub hopper 13 to the developing device 4 using the conveying screw 14. The broken line indicates the total toner and carrier, and the solid line indicates the toner weight excluding the carrier. It has been converted. From this result, it can be seen that the toner replenishment amount per hour decreases as the carrier ratio increases in the replenishment of the conveying screw 14. Therefore, when the carrier rate increases, the amount of toner to be replenished decreases even if the conveying screw 14 is operated for the calculated time. The cause of this problem has not been completely clarified, but is presumed to be related to the degree of toner aggregation. As described above, as described above, the target toner amount is not replenished to the developing device 4 and the toner density becomes unstable, which may cause deterioration in image quality.

Therefore, the developer supply device 10 of this embodiment is controlled by the supply control unit according to the flowchart shown in FIG.
In FIG. 5, the amount of toner to be replenished to the developing device 4 is calculated from the image area of the printed image, the value of the toner density sensor, etc. (step 1), and the carrier rate is calculated from the remaining amount of the developer bottle 11 based on the graph of FIG. Is calculated (step 2). Based on the calculated carrier rate, the replenishment time is calculated based on the graph of FIG. 4 (step 3), and the conveying screw 14 is operated for the calculated replenishment time (step 4). Specifically, correction is performed so that the replenishment time is increased as the carrier ratio increases with respect to the required toner time. For example, in FIG. 4, the toner replenishment amount when the carrier rate is 40% is 0%. Since it is 0.775 times, when the carrier rate is 40%, the actual replenishment time is set to 1.29 (= 1 / 0.775) times from the target calculated value.

  With this configuration, the toner amount replenished to the developing device 4 becomes a necessary toner amount, and the toner density of the developing device 4 becomes stable. In this control, it is necessary to grasp the amount of the developer present in the developer bottle 11, and for this reason, the control is performed based on the flowchart as shown in FIG. 6, and the remaining amount in the developer bottle 11 is recognized. Yes.

  By the way, in the above embodiment, as shown in FIG. 2, a transport pump 12 that transports toner by generating a negative pressure is used as the developer transport means. As shown in FIG. 6, this conveying pump 12 is a suction type uniaxial eccentric powder pump, commonly called a MONO pump, and its configuration is made into a screw shape eccentric with a material having rigidity such as metal. The rotor 20, a stator 21 made of an elastic body such as rubber, and a stator 21 made of a double screw, and a case 22 made of a resin material that encloses the stator 21. The stator 21 is fixed to the case 22. Installed. The rotor 20 is rotationally driven via a supply clutch 23 that is drivingly connected to a drive source (not shown) and a shaft joint 24.

  In the transport pump 12 configured as described above, when the replenishing clutch 23 is turned on and the rotor 20 is rotated, a strong self-suction force is generated in the pump, and the developer is sucked from the suction portion at the tip of the case 22 and sucked in the developer. The agent can be sent to the sub hopper 13 from a discharge portion (not shown) in the vicinity of the shaft joint 24. Furthermore, since the silicon tube 16 is used for the conveyance path from the developer bottle 11 to the conveyance pump 12, it is easier to roll inside the machine as compared with the case where a screw is used for conveyance. As a result, the degree of freedom in layout increases and it becomes easy to realize downsizing of the machine. In addition, the screw stresses the toner and deteriorates the quality when the conveying path becomes long, whereas in the case of conveying by the conveying pump 12, the influence of the length of the conveying path is hardly seen. Furthermore, since the uniaxial eccentric powder pump has a substantially constant conveyance amount per unit time, the remaining amount of the developer bottle 11 can be known from the operation time.

  FIG. 7 shows the relationship between the carrier ratio and the conveyance capacity when the developer is conveyed by the conveyance pump 12. When the developer is transported using the pressure difference, the transport capacity is determined by the amount of developer that passes through the pump. For this reason, the conveyance capacity per time is constant in volume. Here, since the specific gravity of the toner is smaller and the volume is larger than that of the carrier, the amount of toner conveyed per time is substantially constant unlike the replenishment amount from the sub hopper 13 to the developing device 4.

  Further, as shown in FIG. 2, the toner in the sub hopper is controlled so as to be positioned at the sensor 15 of the sub hopper 13, and the same amount of toner as the toner replenished from the sub hopper 13 to the developing device 4 is contained in the developer bottle. 11 is conveyed.

  Therefore, by comparing the transport time from the developer bottle 11 to the sub hopper 13 and the replenishment time from the sub hopper 13 to the developing device 4, it is possible to estimate the ratio of carriers in the sub hopper, and from the result, the carrier The toner replenishment time is determined according to the ratio.

FIG. 8 is a flowchart showing the control of the developer supply device 10 by the supply control unit of the present embodiment.
In FIG. 8, the amount of toner replenished to the developing device 4 within a certain period is calculated (step 1), and the time for transporting to the sub hopper 13 within the certain period is calculated (step 2). At this time, since the amount of toner in the sub hopper 13 is substantially constant, the amount of toner conveyed from the developer bottle 11 and the amount of toner replenished to the developing machine can be regarded as the same amount. The fixed period corresponds to a sufficiently long time with respect to the variation in the toner amount of the sub hopper 13, for example, the amount of toner conveyed is several tens of grams or more.

  Next, the carrier rate is estimated from the ratio of the amount of toner conveyed to the sub hopper 13 and time (step 3), and the replenishment time is calculated in the same manner as in the flowchart of FIG. 5 (step 4). Then, toner supply for the calculated supply time is performed (step 5).

  By controlling in this way, the amount of toner required by the developing device 4 can be accurately supplied. In this control, since the toner is powder, the amount of toner in the sub hopper 13 varies. Therefore, in the comparison of the transport capability from the developer bottle 11 to the sub hopper 13 and the replenishment capability from the sub hopper 13 to the developing device 4. Is performed at an average over a certain time, and the toner replenishment time is determined according to the carrier ratio obtained from the result. Furthermore, accurate control can be obtained by setting the certain period to the nearest certain time. Furthermore, in order to always maintain a certain amount of toner in the sub hopper 13, there is a time difference between the time when the toner is transported from the developer bottle 11 to the sub hopper 13 and the time when the toner is supplied from the sub hopper 13 to the developing device 4. Arise. Therefore, in the comparison of the conveyance capability from the developer bottle 11 to the sub hopper 13 and the replenishment capability from the sub hopper 13 to the developing device 4, a time difference corresponding to the toner amount of the sub hopper 13 is provided, and the carrier ratio is more accurately determined. calculate. That is, in the flowchart of FIG. 8, the time difference is given to the fixed time by the amount corresponding to the amount of the sub hopper 13.

  Further, the uniaxial eccentric screw pump used for the transport pump 12 is functionally suitable because it has a high replenishment resolution and can shorten the minimum replenishment time. This pump increases the resolution of the toner conveyance amount and enables toner supply with little variation in the conveyance amount.

  Furthermore, the conveyance from the developer bottle 11 to the sub hopper 13 is not affected even if there is some variation, but the toner to be replenished to the developing device 4 is to maintain the toner density in the developing device 4 appropriately. High resolution is required. Therefore, toner can be replenished with high resolution by using the conveying screw 14 for replenishment from the sub hopper 13 to the developing device 4.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus using a developer supply device according to the present invention. It is explanatory drawing which shows the structure of the developer supply apparatus which concerns on this invention. 6 is a graph showing the relationship between the remaining amount of toner in a bottle and the carrier rate. 6 is a graph showing a relationship between a carrier rate and a toner replenishment amount when replenishing a developing device from a sub hopper. 3 is a flowchart of supply control showing an embodiment of a developer supply device. It is explanatory drawing which shows an example of a conveyance pump. 7 is a graph showing a relationship between a carrier rate and a toner replenishment amount when replenishing from a developer bottle to a sub hopper. It is a flowchart of replenishment control which shows other embodiment of a developer replenishment apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 4 Developing apparatus 11 Developer bottle 12 Conveyance pump 13 Sub hopper 14 Conveying screw

Claims (7)

A replaceable developer container for storing a two-component developer composed of toner and carrier, a developer transport means for transporting the developer stored in the developer container, and transported via the developer transport means In a developer replenishing device having a sub hopper for temporarily storing the developer, and a developer replenishing means for replenishing the developer stored in the sub hopper to the developing device,
A developer replenishing device that calculates a weight ratio of the carrier to the toner in the sub hopper and adjusts an operation time of the developer replenishing means according to the calculated weight ratio of the carrier to the toner in the sub hopper.   2. The developer replenishing apparatus according to claim 1, wherein the weight ratio of the carrier to the toner in the sub hopper is calculated based on the remaining amount of the developer in the developer container.   The developer replenishing device according to claim 1, wherein the developer transporting unit transports using a pressure difference by a pump, and the developer replenishing unit replenishes by rotation of a spiral member, A developer replenishing apparatus, wherein a weight ratio of a carrier to toner in the sub hopper is calculated from a difference in operating time for a certain amount of toner in the developer conveying means and the developer replenishing means.   4. The developer replenishing apparatus according to claim 3, wherein the comparison between the developer conveying means and the developer replenishing means is performed using an average of a nearest fixed time.   5. The developer replenishing device according to claim 1, wherein the developer conveying means is a uniaxial eccentric screw pump.   5. The developer replenishing apparatus according to claim 1, wherein the developer replenishing means is a screw.   An image forming apparatus using the developer replenishing device according to claim 1.

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