JP2014191195A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of residual toner scattering from a developing unit to reduce deterioration of image quality without adding a new member.SOLUTION: An image forming apparatus includes an image carrier, a developer carrier that supplies a developer to the image carrier, and a control unit that applies an AC voltage to the developer carrier during image formation. The control unit has a toner discharge control mode to apply developing bias only with a DC voltage to discharge a toner from the developer carrier to the image carrier during non-image formation with the image carrier.

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser beam printer provided with a developing device that develops an electrostatic latent image formed on an image carrier into a toner image.

  In an electrophotographic image forming apparatus, residual toner that is not involved in development may be scattered from the developing opening of the developing apparatus and contaminate the image forming apparatus main body. For example, the residual toner may adhere to the image carrier or adhere to the sheet, which may reduce image quality. In addition, there is a possibility that the residual toner stains the periphery of the developing opening and adheres to the operator during maintenance.

  In particular, when the amount of toner contained in the developer is higher than the normal state in a high-temperature and high-humidity environment, the toner may be scattered from the developing device. This is because the charge amount of the toner is lowered in a high-temperature and high-humidity environment or when the amount of toner in the developer is large. The toner having a reduced charge amount has a factor such as being easily scattered because the adhesion to the carrier is reduced.

  Conventionally, there is a method for preventing the toner from jumping out of the developing unit by providing a member such as a sheet in a place where the toner is likely to scatter. Due to the presence of the sheet or the like, when the residual toner that has not been developed is taken into the developing device again, it becomes easier to return to the developing device than going out of the developing device.

  Further, in Patent Document 1, an anti-scattering bias application electrode for collecting scattered toner is disposed in an opening or the like sandwiched between a developing sleeve and a developing container, and a voltage is applied to this to form an image forming unit or Toner scattering outside the machine is prevented.

JP-A-11-174848

  However, in the countermeasure as in Patent Document 1, it is necessary to install a member for preventing scattering, a base, and the like in the developing device. For this reason, there existed a subject about space saving and cost reduction.

  An object of the present invention is to reduce the amount of scattering from the developing device and reduce the deterioration of image quality without adding a new member.

  In order to achieve the above object, a typical configuration of the present invention includes an image carrier, a developer carrier that supplies a developer to the image carrier, and an AC voltage applied to the developer carrier during image formation. An image forming apparatus including: a control unit configured to apply a developing bias only with a DC voltage to the image carrier by applying a development bias only when a non-image is formed by the image carrier. It has a toner discharge control mode for discharging toner.

  With the above configuration, it is possible to reduce the amount of scattering from the developing device and reduce the deterioration of the image quality without adding a new member.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. FIG. 3 is a schematic cross-sectional view of the developing device according to the first embodiment. FIG. 2 is a schematic view of the developing device of the first embodiment as viewed from above. The schematic explanatory drawing of the structure of scattering amount measurement. FIG. 3 is a diagram for explaining a waveform of a developing bias according to the first embodiment. 3 is a graph showing a development bias and a particle size distribution of developed toner according to the first embodiment. 6 is a graph showing the transition of the toner particle size distribution according to the durability of the first embodiment. 6 is a graph showing a change in the amount of scattered toner according to the durability of the first embodiment. The graph which shows the amount of scattering before and after DC discharge operation of 1st Embodiment. Explanatory drawing of the conversion table of a video count value and a toner consumption. FIG. 6 is an explanatory diagram of a conversion table for a difference in toner density and a necessary toner supply amount. The block diagram of the control part of 1st Embodiment. 5 is a flowchart of a DC toner discharging operation according to the first embodiment. FIG. 4 is a diagram illustrating a developing bias during image formation and discharging operation according to the first embodiment. The chart which shows the threshold value of the total number of printed sheets and integrated supply amount of 2nd Embodiment. 10 is a flowchart of a DC toner discharging operation according to the second embodiment.

[First Embodiment]
Hereinafter, an image forming apparatus of the present invention will be described according to an embodiment.

(Configuration of image forming apparatus)
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the first embodiment.

  As shown in FIG. 1, the image forming apparatus has four image forming stations each including a photosensitive drum 101 (101Y, 101M, 101C, 101K) as an image carrier. The diameters of the photosensitive drums 101 are all 30 mm.

  Each image forming station forms a toner image of each color of yellow Y, magenta M, cyan C, and black K. Since the configuration of each image forming station is the same, the subscripts Y, M, C, and K are omitted as appropriate in the following description.

  An intermediate transfer device 120 is disposed below each image forming station. In the intermediate transfer device 120, an intermediate transfer belt 121 (intermediate transfer member) is stretched around a roller 122, a roller 123, and an inner transfer roller 124. The intermediate transfer belt 121 is made of polyimide resin and is conveyed in the direction of the arrow.

  In the toner image forming process, the surface of the photosensitive drum 101 is charged by the primary charging device 102 (102Y, 102M, 102C, 102K). The primary charging device 102 is a corona charging method that is non-contact charging.

  The surface of the photosensitive drum 101 is exposed by a laser 103 (103Y, 103M, 103C, 103K) emitted by a laser driver (not shown). Thereby, an electrostatic latent image is formed on the photosensitive drum 101.

  To the electrostatic latent image, toner charged in the developing device 104 (104Y, 104M, 104C, 104K) is supplied. Then, the electrostatic latent image is developed, and yellow, magenta, cyan, and black toner images are formed on the photosensitive drum 101, respectively.

  The toner image formed at each image forming station is transferred and superimposed on the intermediate transfer belt 121 by a transfer bias applied to a transfer roller 105 (105Y, 105M, 105C, 105K) as a primary transfer member.

  The four-color toner images formed on the intermediate transfer belt 121 are secondarily transferred to the recording material P by a secondary transfer roller 125 (secondary transfer member) disposed to face the inner transfer roller 124.

  On the other hand, residual toner that is not transferred to the recording material P and remains on the intermediate transfer belt 121 is removed by the intermediate transfer belt cleaner 114b.

  The recording material P to which the toner image has been transferred is pressed / heated by a fixing device 130 including a fixing roller 131 and a fixing roller 132. Thereby, the recording material P obtains a permanent image of the toner image.

  Further, the primary transfer residual toner remaining on the photosensitive drum 101 after the primary transfer is removed by the cleaner 109 (109Y, 109M, 109C, 109K), and is prepared for the next image formation.

(Developer and toner container)
FIG. 2 is a schematic cross-sectional view of the developing device according to the first embodiment. FIG. 3 is a schematic view of the developing device of the first embodiment as viewed from above. 2 and 3 schematically illustrate the developing device 104 and the replenishing device 1 that replenishes the developing device 104 with toner. In the present embodiment, the developing device 104 and the toner container 8 have the same configuration in the image forming units for all colors (Y, M, C, K).

  The developing device 104 includes a developing container 3 that stores a developer. The developer accommodated in the developing container 3 is a two-component developer including non-magnetic toner particles and magnetic carrier particles as main components.

  In the developing container 3, a first stirring / conveying screw 4 a and a second stirring / conveying screw 4 b are disposed as developer stirring members.

  A portion of the developing container 3 that faces the photosensitive drum 101 is an opening that is partially open. Then, the developer carrier 5 is rotatably arranged so as to be partially exposed from the opening.

  A magnet roll (magnetic field generating member) is fixedly arranged inside the developer carrier 5. The magnet roll has a plurality of magnetic poles in the circumferential direction, and attracts the developer in the developer container 3 by magnetic force so that the developer is carried on the developer carrier 5. In addition, the magnet roll forms developer spikes (magnetic brushes) in the developing unit facing the photosensitive drum 101.

  As shown in FIG. 3, the developer carrying member 5, the first stirring and conveying screw 4a, and the second stirring and conveying screw 4b are arranged in parallel to each other. Further, the developer carrying member 5, the first stirring / conveying screw 4 a, and the second stirring / conveying screw 4 b are disposed in parallel to the axial direction of the photosensitive drum 101.

  The diameter of the developer carrier 5 is 20 mm. The first stirring and conveying screw 4a and the second stirring and conveying screw 4b each have a shaft diameter of 8 mm and a screw portion diameter of 16 mm.

  The interior of the developing container 3 is divided by a partition wall 3c into a stirring chamber 3a that is a first chamber and a developing chamber 3b that is a second chamber. The stirring chamber 3a and the developing chamber 3b communicate with each other at both ends in the longitudinal direction of the developing container 3 (left end and right end in FIG. 3). The first stirring and conveying screw 4a is disposed in the stirring chamber 3a, and the second stirring and conveying screw 4b is disposed in the developing chamber 3b.

  The first stirring and conveying screw 4a and the second stirring and conveying screw 4b are rotationally driven in the same direction by the rotation of the motor. By this rotation, the developer in the stirring chamber 3a moves to the left in FIG. 3 while being stirred by the first stirring and conveying screw 4a, and then moves into the developing chamber 3b through the communicating portion. Further, the developer in the developing chamber 3b moves to the right in FIG. 3 while being stirred by the second stirring and conveying screw 4b, and then moves into the stirring chamber 3a through the communicating portion.

  That is, the developer is circulated and conveyed in the developing container 3 while being agitated by two screws, the first agitating and conveying screw 4a and the second agitating and conveying screw 4b.

  The toner in the developer is charged by stirring and transporting as described above. In the present embodiment, the toner is replenished from the toner replenishing port 2 provided in the upper part on the upstream end side in the developer conveying direction in the stirring chamber 3a.

  In addition, an inductance detection sensor 6 is attached as a toner concentration detection means for detecting the toner concentration of the developer (mixing ratio of toner and carrier) in the stirring chamber 3a.

  The developer carrier 5 rotates in the direction of the arrow in FIG. By this rotation, the developer is pumped up from the pumping upper part 5a. The height of the developer thus pumped up is regulated by the regulating blade 7 and is formed in a layer on the surface of the photosensitive drum 101.

  The developer formed in a layer on the developer carrier 5 is conveyed to a developing unit facing the photosensitive drum 101. In the developing unit, the developer on the developer carrying member 5 is in a state of being spiked by the magnetic force of the magnet roll inside the developer carrying member 5, which is called a magnetic brush.

  Then, the magnetic brush on the developer carrier 5 contacts or approaches the surface of the photosensitive drum 101 in the developing unit. At this time, a developing bias in which an AC voltage and a DC voltage are superimposed is applied to the developer carrier 5 by a developing bias application power source.

  Then, the toner of the developer (two-component developer having toner and carrier) is supplied to the electrostatic latent image on the photosensitive drum 101. As a result, the toner selectively adheres to the image portion of the electrostatic latent image, and the electrostatic latent image is developed as a toner image.

  The residual toner that has not been developed passes through the developing unit and is taken into the developing container 3 from the taking-in unit 5b. The residual toner taken in from the take-in portion 5b returns to the developing chamber 3b of the developing container 3 and circulates again.

  Since the toner in the two-component developer is consumed by the developing operation as described above, the toner concentration of the developer in the developing container 3 gradually decreases. Then, in order to keep the toner density constant, it is necessary to replenish toner from the replenishing device 1 (toner replenishing unit) to the developing container 3.

  As shown in FIG. 3, the replenishing device 1 includes a toner container 8 that stores toner to be replenished to the developing device 104. A toner transport pipe 11 is provided at the lower portion of the toner container 8 in the figure. A pipe toner discharge port 9 is provided at the left end of the toner transport pipe 11 in the drawing. The pipe toner discharge port 9 is connected to the toner supply port 2 of the developing device 104. Further, the toner conveying pipe 11 is provided with a toner replenishing screw 10 (toner replenishing member) that conveys toner toward the pipe toner discharge port 9.

  The toner replenishing screw 10 is rotated by a motor 14 (drive unit). The number of rotations or the rotation time of the motor 14 is set according to the amount of toner requested by the developing device 104. When the set number of rotations or rotation time is reached, the rotation of the motor 14 stops. As a result, the developer container 3 is replenished with an amount of toner required by the developing device 104.

  At this time, according to the size of each toner replenishing screw 10, the toner conveyance amount per rotation or unit time is set in advance. For this reason, the control which calculates the frequency | count of rotation or rotation time according to request | requirement amount is attained.

  Here, the amount of toner transported by the toner supply screw 10 is proportional to the number of rotations of the toner supply screw 10. Therefore, in order to set the rotation time, it is assumed that the motor 14 of the toner supply screw 10 can always rotate the screw at a constant speed.

  Moreover, it is preferable if a counting means for counting the number of rotations of the screw is provided. This is because the rotational speed of the screw can be set by the number of rotations, whether it is constant or not.

  Furthermore, the amount of toner replenished by the toner replenishing screw 10 is more stable when the replenishing operation is performed in units of a certain amount, a few tens of mg to a few hundreds of mg, rather than a unit of mg.

  Further, since the replenishment toner is conveyed using the toner replenishment screw 10, the amount of toner replenishment with respect to the screw rotation angle varies depending on the phase of the toner replenishment screw 10. Therefore, in order to reduce the variation in the amount of replenished toner due to the phase position of the toner replenishing screw 10, the replenishment control is performed so that one rotation of the replenishing screw is used as a basic unit of toner replenishment.

  The toner replenishment in one rotation of the toner replenishment screw 10 is defined as a replenishment center value Tb. In the configuration of the present embodiment, the shape and arrangement of the toner supply screw 10 are controlled such that the rotation speed of the toner supply screw 10 is 120 rpm and the supply center value Tb is supplied to be about 0.1 g.

  As shown in FIG. 1, since the photosensitive drum 101 is in contact with the recording material P or the intermediate transfer belt 121, it always rotates. On the other hand, the first stirring and conveying screw 4a and the second stirring and conveying screw 4b in the developing device 104 are generally rotated only for a necessary time during the image forming operation in order to minimize the deterioration of the developer. is there.

  If the operation of replenishing toner from the toner container 8 to the developing device 104 is performed in a state where the first agitating / conveying screw 4a and the second agitating / conveying screw 4b shown in FIG. There may be a stagnation near the supply port 2. Then, clogging of toner and T / D non-uniformity in the developing device 104 are caused.

  In order to prevent this clogging phenomenon, an operation of replenishing toner from the toner container 8 to the developing device 104 is performed while the first stirring and conveying screw 4a and the second stirring and conveying screw 4b in the developing device 104 are rotating. There is a need. Therefore, the toner replenishment possible timing is only when the first agitating and conveying screw 4a and the second agitating and conveying screw 4b are driven.

  In this embodiment, 200 g of developer is contained in the developing container 3, and the amount of developer is maintained at approximately 200 g by replenishing the amount of toner used in image formation.

(Two-component developer)
The two-component developer composed of toner and carrier that is accommodated in the developing container 3 of the developing device 104 of the present embodiment will be described in detail.

  The toner includes colored resin particles containing a binder resin, a colorant, and, if necessary, other additives, and colored particles to which an external additive such as colloidal silica fine powder is externally added. The toner is a negatively chargeable polyester resin, and the volume average particle size is preferably 4 μm or more and 10 μm or less. More preferably, it is 8 μm or less. In this embodiment, it is assumed that the toner having a volume average particle diameter of 6 μm and a particle diameter of 8 μm or more is 10% of the whole, and that a toner having a particle diameter of 9 μm or more is 3% of the whole.

As the carrier, for example, surface-oxidized or non-oxidized iron, nickel, cobalt, manganese, chromium, rare earth and other metals, and their alloys, or oxide ferrite can be preferably used. The production method is not particularly limited. The carrier has a weight average particle diameter of 20 to 60 μm, preferably 30 to 50 μm, and a resistivity of 10 ⁷ Ωcm or more, preferably 10 ⁸ Ωcm or more. In this embodiment, 10 ⁸ Ωcm is used.

  Note that the volume average particle diameter of the toner used in this embodiment was measured by the following apparatus and method. As a measuring device, an SD-2000 sheath flow electric resistance type particle size distribution measuring device (manufactured by Sysmex Corporation) was used. The measuring method is as follows.

  That is, 0.1 ml of surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of 1% NaCl aqueous electrolytic solution prepared using primary sodium chloride, and 0.5 to 50 mg of a measurement sample is added. Add. The electrolytic aqueous solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes. Using the SD-2000 sheath flow electric resistance type particle size distribution measuring apparatus, the particle size distribution of 2 to 40 μm particles is measured using a 100 μm aperture as an aperture to obtain a volume average distribution. The volume average particle diameter is obtained from the volume average distribution thus obtained.

In addition, a sandwich type cell having a measurement electrode area of 4 cm ² and an interelectrode spacing of 0.4 cm was used as the carrier resistivity used in this embodiment. Measurement was performed by applying an applied voltage E (V / cm) between the two electrodes to one electrode under a pressure of 1 kg and obtaining the carrier resistivity from the current flowing in the circuit.

(Scattering amount measuring method)
With the above-described configuration, the developer moves back and forth inside and outside the developing unit 104 in the process of passing through the drawing upper part 5a and the intake part 5b. Here, there is a pressure difference between the inside and outside of the developing device 104, and a centrifugal force due to the rotation acts on the developer carrier 5. This pressure difference and centrifugal force can cause the developer to scatter.

  Next, a method for measuring the amount of scattering used in this embodiment will be described. APS (Air Partile Sizer) was used for the measurement of the amount of scattering. The APS sucks air, accelerates the particles therein, calculates the particle size from the velocity, and measures the particle size and number of particles present in the gas. The detectable particles are on the order of μm up to 20 μm and are suitable for detecting toner having a particle size distribution of 2 to 10 μm.

  FIG. 4 is a schematic explanatory diagram of the structure of the scattering amount measurement. When measuring the amount of toner scattered from the developing unit 104, as shown in FIG. 4, only the developing unit is set on a jig that can rotate, and the space where the developing unit rotates is covered. At this time, since the air passage hole is not covered, the air enters the inside, and the air taken in the inside stably flows through the fan installed inside.

  In this state, the developing unit is idled for a predetermined time. At the same time, the air outlet was continuously sucked with APS, and the amount and particle size of the toner scattered from the developing unit per unit time were measured. At this time, the measurement was continued until the suction amount of APS became almost zero even after the idling of the developing device was stopped to suck all scattered toner.

  Examining the relationship between the amount of scattering measured by this method and the stain around the developing unit, it was found that if the amount of scattering was about 2500 / min or less, the toner would not adhere even if the operator touched it.

(Applied voltage and toner particle size distribution during image formation)
Next, the voltage applied to the developer carrying member 5 and the photosensitive drum 101 during image formation in the present embodiment and the particle size of the toner to be developed will be described.

  During image formation, as shown in FIG. 2, a developing bias is applied to the developer carrier 5 from the developing bias power supply unit 22. The developing bias Vdc applied to the developer carrying member 5 is obtained by superimposing a DC voltage of −550V with an AC voltage of 1300 Hz, 1600 Vpp, and 50% duty.

  By superimposing the AC voltage on the DC voltage, the toner can be used for development with a particle size distribution of finer powder than that of the replenished toner. Then, the dot reproducibility of the image can be improved, and the reduction in charging performance due to the carrier adhesion of the fine toner can be suppressed.

  For reference, FIG. 5 shows a developing bias waveform when the AC voltage is not superimposed on the DC voltage. FIG. 5 is a diagram illustrating the waveform of the developing bias according to the first embodiment.

  The photosensitive drum 101 is charged to Vd = −700 V, and the fog removal bias Vback is set to −150 V. The photosensitive drum 101 is adjusted to a latent image contrast Vcont = 0 to +300 V by laser exposure, and the toner on the developer carrier 5 is developed on the photosensitive drum 101.

  FIG. 6 is a graph showing the development bias and the particle size distribution of the developed toner according to the first embodiment. Specifically, the particle size distribution of the toner developed on the photosensitive drum when the AC voltage is not superimposed on the developing bias Vdc is shown.

  The particle size of the toner on the photosensitive drum is determined by introducing the sample particles into a detection unit (measurement unit) that simultaneously forms an electric field and an acoustic field, and measuring the particle moving speed by the laser Doppler method. The amount was measured with an apparatus for measuring the amount.

  As shown in FIG. 6, the particle size of the toner developed on the photosensitive drum is larger when only the DC voltage is used as the developing bias Vdc. Specifically, the volume average particle diameter is 5.79 μm for AC + DC and 6.50 μm for DC. This is because the charge amount of the toner is inversely proportional to the particle size, so that the finer powder has a larger electrostatic adhesion between the toner and the carrier, and development is difficult with only the DC voltage.

  FIG. 7 is a graph showing the transition of the toner particle size distribution according to the durability of the first embodiment. Specifically, it is experimental data showing the transition of the particle size distribution of the toner in the developing device 104 when 200,000 images of 5% Duty are printed without performing the DC discharge operation (described later). As shown in FIG. 7, it can be seen that the particle size is shifted to the larger when it is durable.

  Next, the transition of the scattering amount at this time will be described. FIG. 8 is a graph showing the change in the amount of toner scattering due to the durability of the first embodiment. As shown in FIG. 8, the amount of scattering increases as the number of printed sheets increases. After the endurance of 200,000 sheets, about 12700 toners are scattered per minute.

  The scattering amount immediately after the DC discharge operation is executed from this state and the average particle size of the scattering toner will be described. FIG. 9 is a graph showing the amount of scattering before and after the DC discharge operation of the first embodiment.

  In the experiment shown in FIG. 9, the consumed toner amount was about 0.6 g, and the scattering amount was reduced to 7500 particles / min. The average particle size of the scattered toner is also reduced. In this way, the amount of scattering was reduced by selectively discharging the toner that easily scatters on the coarse powder side. From the ratio of the reduction amount, the discharge amount necessary to reduce the scattering amount to 2500 pieces / min or less is about 2 g. In the above experiment, about 3000 g of toner was consumed during printing 200,000 sheets, and it was found that about 0.07% of the toner was discharged, and the amount of scattering was effective.

(Toner supply control)
Next, toner replenishment control in this embodiment will be described. In the present embodiment, replenishment control is performed using both the video count method and the inductance method, which are the same as the conventional one.

  FIG. 10 is an explanatory diagram of a conversion table of video count values and toner consumption. Specifically, the relationship between the video count value and the toner consumption amount Tv is shown.

  As shown in FIG. 10, it can be seen that the toner consumption increases in proportion to the video count value. In the video count method, if there is a difference between the toner consumption calculated from the image ratio and the toner consumption actually consumed, the toner density in the developing device increases or decreases.

  FIG. 11 is an explanatory diagram of a conversion table for the difference in toner density and the necessary toner supply amount. Specifically, it is an explanatory diagram of a conversion table of toner density and necessary toner replenishment amount in the inductance method.

  As shown in FIG. 11, the difference between the target toner density and the detected toner density is ΔTD, and the conversion rate to the replenished toner amount, that is, the toner density feedback rate (FB rate) is α. Then, the toner replenishment amount Ttd in the inductance method is represented by Ttd = α × ΔTD.

  When the toner density is lower than the target value, the necessary toner amount is replenished. On the other hand, if the toner density is higher than the target value, it is considered that the toner is excessive, and is reduced from the replenishment amount.

  When there is a difference between the supply amount and the consumption amount, or when the predetermined supply amount cannot be supplied, the toner supply amount Ttd is carried over to the next supply.

  The replenishment operation in the present embodiment is performed based on the next replenishment unit. That is, a quotient obtained by dividing the sum of the toner consumption amount Tv and the toner replenishment amount Ttd (T = Tv + Ttd) by the basic unit of toner replenishment (replenishment amount per rotation of the replenishment screw: 0.1 g in this embodiment) is replenished. Unit.

(Control part)
FIG. 12 is a block diagram of the control unit of the first embodiment. As shown in FIG. 12, the control unit 20 includes a CPU 12, a toner supply amount calculation unit 15, a ROM 16, a RAM 17, an image ratio calculation unit 18, and a toner consumption amount calculation unit 19.

  First, the image ratio calculation unit 18 calculates the image ratio of each color from the image signal read by the external input terminal or the document reading apparatus. Then, the toner consumption amount calculation unit 19 calculates the toner consumption amount Tv based on the image ratio calculated by the image ratio calculation unit 18 and the detection density of the inductance detection sensor 6.

  The previous replenishment amount stored in the RAM 17 is insufficient, and the sum of the carried toner replenishment amount Ttd and the calculated toner consumption amount Tv reaches the replenishment amount per rotation of the replenishment screw stored in the ROM 16. In this case, control is performed as follows. In this embodiment, 0.1 g is set as one unit as a basic unit for toner supply. In the above case, the toner supply amount calculation unit 15 inputs a supply signal for supplying the necessary toner supply amount to the CPU 12.

  Next, the CPU 12 determines the order of the image forming stations to be replenished from the replenishment signal and the state of the drive gear train of the motor 14 at the end of the previous image formation stored in the RAM 17. Then, the replenishment operation is performed by driving the motor 14. The RAM 17 stores the state of the drive gear train of the motor 14 at the end of the previous supply, the difference between the previous consumption amount and the supply amount, and the integrated supply amount.

  In this embodiment, each time image formation is performed, replenishment is performed using both the video count method and the inductance method. In this way, image formation is performed while the toner density in the developing container 3 is kept constant.

(DC discharge operation)
The present embodiment has a toner discharge control mode in which a developing bias Vdc is applied only with a DC voltage during non-image formation, and coarse powder toner that easily scatters on the photosensitive drum 101 is selectively discharged. The more the toner is replaced due to consumption and replenishment, the more the particle size distribution of the toner in the developer in the developing device 104 becomes coarser than the replenished toner. For this reason, the time and timing of the DC discharge operation are controlled according to the toner replenishment amount.

  In the present embodiment, when a 100% duty image is printed on A4 paper, 0.3 g of toner is consumed. If about 0.07% of the replenished toner amount is discharged by the DC voltage, it is highly effective in reducing the amount of scattering. Assume that the cumulative supply amount is 0.015 g with a threshold value of 22.5 g, that is, a toner amount of 297 mm × 10 mm is discharged at 100% duty.

  The discharge amount is not limited to this value, and may be in the range of 0.01% to 10% of the supply amount. The larger the discharge amount, the more effective the reduction of scattering is. However, since the toner consumption increases, 0.01% to 1% is more preferable. Similarly, the threshold value of the replenishment integrated amount is not limited to the above-described value. That is, the replenishment integrated amount may be in the range of 10 g to 1000 g, and more preferably 10 g to 100 g.

  Next, details of the DC discharge operation in the present embodiment will be described. FIG. 13 is a flowchart of the DC toner discharging operation of the first embodiment.

  As shown in FIG. 13, the image forming operation is performed by superimposing the AC voltage on the DC voltage on the developing bias (S101). After completion of image formation (S102), the engine controller 21 confirms the integrated replenishment amount stored in the RAM 17 (S103). Here, when the integrated replenishment amount is 22.5 g or more, the toner discharge operation for 0.015 g is executed using the DC voltage (S104).

  At this time, the number obtained by subtracting 22.5 g from the accumulated replenishment amount stored in the RAM 17 is newly stored, and the process ends (S105). If the accumulated replenishment amount is less than 22.5 g in S103, the process ends as it is.

  FIG. 14 is a diagram illustrating the developing bias at the time of image formation and discharging operation according to the first embodiment. Specifically, the voltage applied to the developer carrier 5 and the photosensitive drum 101 when the toner discharging operation is executed is shown.

  As described above, in the image forming apparatus that forms an image on the developer carrier 5 using an AC voltage, the coarse powder toner that easily scatters in the developing device 104 is selectively discharged using a DC voltage during non-image formation. . As a result, the toner particle size distribution of the developer is kept uniform in the developing device 104, and at the same time, scattered toner is reduced. Accordingly, it is possible to prevent the image quality from being deteriorated due to contamination in the image forming apparatus main body, and to prevent the periphery of the developing opening from becoming dirty and adhering to the operator during maintenance.

[Second Embodiment]
The second embodiment will be described below. The basic configuration of the apparatus according to the present embodiment is also the same as that of the first embodiment, and thus redundant description is omitted. Here, a configuration different from that of the first embodiment will be described. Moreover, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above.

  In the first embodiment, toner discharge using a DC voltage is performed in accordance with the amount of toner replenished into the developing device 104, the toner particle size distribution is made uniform, and the amount of scattering is reduced. However, as shown in FIG. 8, the actual scattering amount increases rapidly when the number of printed sheets exceeds a predetermined value. This is because as the number of printed sheets increases, the toner charge amount due to carrier deterioration decreases and the electrostatic adhesion between the carrier and the toner becomes weak.

  Therefore, in the second embodiment, the frequency of the DC discharge operation is changed according to the number of printed sheets. Specifically, a threshold value of the integrated replenishment amount for executing DC discharge is determined from the total number of printed sheets, and the discharge operation is performed based on this threshold value. As a result, in a state where it is difficult to scatter, toner consumption due to the discharging operation can be suppressed.

  FIG. 15 is a chart showing the total number of printed sheets and the threshold value of the integrated replenishment amount according to the second embodiment. FIG. 16 is a flowchart of the DC toner discharging operation of the second embodiment.

  As shown in FIG. 15, every time the total number of printed sheets is reached, the threshold of the integrated replenishment amount for executing the DC discharge is decreased. The threshold value of the integrated replenishment amount in FIG. 15 is not necessarily limited to this value, but is determined because the amount of scattering greatly increases in proportion to the number of printed sheets from 100,000 or more. The engine controller 21 is connected to the ROM 16 that records the threshold values in the table of FIG.

  Next, the procedure will be described with reference to the flowchart of FIG. As shown in FIG. 16, the image forming operation is performed by superimposing the AC voltage on the development bias and the DC voltage (S201). After completion of image formation (S202), the threshold value X of the integrated replenishment amount is determined from the total number of printed sheets (S203).

  The engine controller 21 confirms the integrated replenishment amount stored in the RAM 17 (S204). When the integrated replenishment amount is Xg or more, the toner discharge operation for 0.015 g is executed using the DC voltage (S205). At this time, the number obtained by subtracting Xg from the accumulated replenishment amount stored in the RAM 17 is newly stored, and the process ends. (S206).

  On the other hand, if the integrated replenishment amount is less than Xg in S204, the processing is terminated as it is.

  By performing the operation as described above, even when the total number of printed sheets increases and the charge amount of the toner decreases and the toner easily scatters, the scattered toner can be reduced. Thereby, it is possible to prevent the image quality from being deteriorated due to contamination in the image forming apparatus main body, and to prevent the periphery of the developing opening from becoming dirty and adhering to the operator during maintenance.

DESCRIPTION OF SYMBOLS 1 ... Replenishment apparatus 2 ... Toner replenishment port 3 ... Developer container 5 ... Developer carrier 8 ... Toner container 12 ... CPU
15 ... Toner replenishment amount calculation unit 16 ... ROM
17 ... RAM
DESCRIPTION OF SYMBOLS 18 ... Image ratio calculation part 19 ... Toner consumption calculation part 20 ... Control part 21 ... Engine controller 22 ... Development bias power supply part 101 ... Photoconductor drum 104 ... Developer

Claims (5)

In an image forming apparatus comprising: an image carrier; a developer carrier that supplies a developer to the image carrier; and a controller that applies an AC voltage to the developer carrier during image formation.
The controller has a toner discharge control mode in which toner is discharged from the developer carrier to the image carrier by applying a development bias only with a DC voltage during non-image formation by the image carrier. An image forming apparatus. A developer for supplying toner to the developer carrier;
A toner container for storing toner to be replenished in the developing unit;
A toner replenishing unit for replenishing the toner contained in the toner container to the developing device,
2. The image according to claim 1, wherein the toner discharge control mode by the control unit is performed to control a consumption amount of coarse toner according to an amount of toner replenished from the toner container to the developing device. Forming equipment.   The image forming apparatus according to claim 1, wherein the toner discharge control mode by the control unit is performed when the number of printed sheets reaches a predetermined value.   4. The control unit according to claim 1, wherein the control unit applies an AC voltage superimposed on a DC voltage to the developer carrying member during the image formation. 5. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the developer is a two-component developer in which a nonmagnetic toner and a magnetic carrier are mixed.

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