JP2018017838A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which can achieve reduction in the image defect that occurs after initial supply of a developer to an empty development device and reduction in the image defect that occurs in a case of continuously outputting images after initial supply.SOLUTION: A control unit executes initial supply control (S1). The amount of a supply agent is smaller than a prescribed storage amount. In this case, since the agent level height of the developer does not reach a gap part of two development sleeves, the developer having high fluidity is hardly supplied to the gap part. Therefore, it is impossible that the vertical stripe-shaped density unevenness occurs. The control unit executes stopgap supply control until the developer amount becomes equal to or greater than the prescribed storage amount after the initial supply control (S4). Since the amount of the supply agent is the amount obtained by adding an additional amount that fluctuates according to the printing ratio to the consumption amount consumed following image formation, the developer amount in the development container is increased by the additional amount for each execution of the image formation job at the stopgap supply. Consequently, even when images at the high printing ratio are continuously output after the initial supply, image defect like image missing hardly occurs.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus using electrophotographic technology such as a printer, a copying machine, a facsimile machine, or a multifunction machine.

  2. Description of the Related Art Conventionally, a developing device is provided that develops an electrostatic latent image formed on a photosensitive drum by developing a developer such as a one-component developer on two developing sleeves arranged to face each other with a gap. An image forming apparatus has been proposed (Patent Document 1). In the image forming apparatus, the developer is consumed as the image is formed. Therefore, when the developer in the developing device becomes less than a predetermined amount, the developer supply device supplies the developer for replenishment to the developing device.

  The developing device is detachably provided in the image forming apparatus main body, and the user can easily replace the developing device. However, a new developing device (or an unused image forming apparatus) does not contain a developer. Therefore, when a new developing device (or an unused image forming apparatus) is used for the first time, it is necessary to replenish the developer from the developer replenishing device. Conventionally, when the developing device is replaced, control for supplying a predetermined amount of developer from the developer replenishing device to the developing device (initial replenishment control) is executed (Patent Document 2). For example, a display on the operation panel or the like is displayed so as to prompt the user to execute the initial supply control, and the user is allowed to select.

JP 2004-29569 A JP 2002-258593 A

  However, in the case of the conventional image forming apparatus, for a while after the initial replenishment, an image defect such as density unevenness occurs along the vertical streaks along with the image formation. It was found that it was resolved. This is because the developer for replenishment has a high fluidity, and for a while after the initial replenishment, the proportion of the developer with high fluidity in the developing device is large. This is because a larger amount of developer is supplied to the gap between the two developing sleeves. Therefore, in order to make it difficult for the vertical stripe-shaped density unevenness to occur, it is conceivable to reduce the amount of developer replenished during initial replenishment to such an extent that it can be regulated by the gap between the two developing sleeves. However, if the amount of developer to be replenished during the initial replenishment is reduced, the developer becomes insufficient at a relatively early timing when image formation for continuously outputting images with a high printing rate is performed subsequently. Image defects such as missing images are likely to occur.

  In view of the above problems, the present invention reduces image defects such as density unevenness that are likely to occur after the initial supply of developer to an empty developing device, and an image that is likely to occur when an image with a high printing rate is continuously output after the initial supply. An object of the present invention is to provide an image forming apparatus capable of reducing both image defects such as omission.

  An image forming apparatus according to the present invention is rotatably provided in parallel with a rotating photosensitive member, a developing container containing a developer, and a position of the developing container facing the photosensitive member. A first developer carrying member and a second developer carrying member that carry and convey the developer and develop the electrostatic latent image formed on the photosensitive member with the developer, and a developer for replenishing the developer container A replenishing device for replenishing the developer, and the developer in the developer container is provided at a height position equal to or higher than the closest position between the first developer carrier and the second developer carrier in the developer container. A first mode for controlling the replenishing device to replenish the empty developer container with a first replenishment amount of the replenishment amount that is not detected by the detection means; and the first mode. If an image forming job is started later, at least the detection Until a second supply amount is added to the consumption amount of the developer that is consumed in the image formation until the detection amount is detected, plus a larger additional amount when the printing rate is lower than when the printing rate is high. And a control unit that executes a second mode for replenishing water.

  According to the present invention, image defects such as vertical streak-like density unevenness that is likely to occur after the initial supply of developer to an empty developing device are reduced, and an image with a high printing rate is continuously output after the initial supply. It is possible to achieve both reduction of image defects such as easy image omission.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. Sectional drawing which shows a developing device. Schematic which shows a developing agent replenishment apparatus. Sectional drawing which shows a developing agent replenishment apparatus. FIG. 3 is a control block diagram showing a developer supply control system. 7 is a flowchart showing developer supply control. The flowchart which shows splicing replenishment control. The figure which shows an example of a selection execution screen. The figure which shows transition of the developer amount in a developing container at the time of splicing replenishment control. The flowchart which shows normal replenishment control. 6 is a timing chart showing the transition of the developer amount in the developing container in the toner replenishment control of the embodiment. 6 is a timing chart showing a change in the amount of developer in a developing container in conventional toner replenishment control. The figure which shows an experimental result.

<Image forming apparatus>
Hereinafter, the present embodiment will be described with reference to the drawings. First, the configuration of the image forming apparatus of this embodiment will be described with reference to FIG. The image forming apparatus shown in FIG. 1 includes a charging device 1, an exposure device 2, a developing device 3, a pre-transfer charger 4, a transfer roller 5, a drum cleaning device 6, and a static elimination exposure device 7 so as to surround a photosensitive drum 10. Has been. A photosensitive drum 10 as a photosensitive member has a photosensitive layer mainly composed of amorphous silicon formed on the outer peripheral surface thereof, and rotates in a direction indicated by an arrow R1 in FIG. 1 at a predetermined process speed (for example, 500 mm / s). The photosensitive drum 10 has an outer diameter of, for example, 84 mm.

  The charging device 1 irradiates charged particles accompanying, for example, corona discharge to charge the photosensitive drum 10 to a uniform dark portion potential (for example, +500 V). On the surface of the charged photosensitive drum 10, image exposure is performed by a laser beam (indicated by an arrow L in FIG. 1) irradiated from the exposure device 2 and modulated based on an image signal, thereby forming an electrostatic latent image. The In the present embodiment, the surface of the photosensitive drum 10 is uniformly charged to a dark portion potential, the non-image portion (background portion) is exposed to discharge the light portion potential, and the toner is developed to the dark portion potential (charge portion). Partial exposure method is adopted. Therefore, the exposed surface of the photosensitive drum 10, that is, the background portion, is discharged to, for example, +120 to + 200V. The developing device 3 supplies toner charged to a polarity opposite to the charged polarity of the photosensitive drum 10 to the photosensitive drum 10 to develop the electrostatic latent image into a toner image. The developing device 3 will be described later (see FIG. 2).

  The pre-transfer charger 4 pre-transfer charges the surface of the photosensitive drum 10 on which the toner image is formed. The transfer roller 5 is disposed to face the photosensitive drum 10, and forms a toner image transfer portion T <b> 1 (transfer nip portion) between the transfer roller 5 and the photosensitive drum 10. The recording material S is conveyed to the transfer portion T1 by the registration roller 13 at a predetermined timing. In the transfer portion T1, a toner image is transferred from the photosensitive drum 10 to the recording material S by applying a transfer voltage to the transfer roller 5 by a high voltage power source (not shown), for example, with respect to the recording material S being conveyed. That is, when a transfer voltage having a polarity opposite to the toner charging polarity is applied to the transfer roller 5, the toner image on the photosensitive drum 10 is electrostatically attracted to the recording material S and transferred. The drum cleaning device 6 rubs the photosensitive drum 10 with a cleaning blade to remove toner slightly remaining on the photosensitive drum 10 after the transfer.

  On the upstream side in the rotation direction of the photosensitive drum 10 with respect to the charging device 1 and on the downstream side in the rotation direction of the photosensitive drum 10 with respect to the transfer roller 5, a static elimination exposure device 7 that performs static elimination exposure on the surface of the photosensitive drum 10 is disposed. The static elimination exposure apparatus 7 irradiates a laser beam having a different intensity from that of the exposure apparatus 2 to expose the surface of the photosensitive drum 10 to lower the surface potential to a predetermined potential (for example, 0 V).

  The recording material S to which the toner image is transferred is conveyed to the fixing device 11. The recording material S is pressed while being heated by the heating roller 111 and the pressure roller 112 of the fixing device 11. As a result, the toner image on the recording material S is fixed to the recording material S. The recording material S on which the toner image is fixed by the fixing device 11 is discharged out of the machine body. In the case of double-sided output, the recording material S is reversed after single-sided output and is conveyed again to the transfer unit T1. Then, after the toner image is fixed on the other surface of the recording material S, the recording material S is discharged out of the machine body.

  Connected to the developing device 3 is a developer replenishing device 12 for replenishing a replenishing developer (hereinafter referred to as a replenishing agent). The developer replenishing device 12 accommodates the replenishing agent and replenishes the developing device 3 with the replenishing agent as necessary. The developer supply device 12 will be described later (see FIGS. 3 and 4).

<Developing device>
The developing device 3 will be described with reference to FIG. As shown in FIG. 2, the developing device 3 includes a developing container 20, an upstream developing sleeve 21 as a first developer carrier, a downstream developing sleeve 22 as a second developer carrier, an agitation transport member 25, and the like. And a regulating blade 26. A developer amount detection sensor 30 is provided in the developing container 20 at a height position not less than the gap G between the upstream developing sleeve 21 and the downstream developing sleeve 22 (more than the closest position). A developer amount detection sensor 30 serving as a detection unit detects whether or not the developer stored in the developer container 20 is equal to or greater than a predetermined storage amount. That is, the developer amount detection sensor 30 determines that the developer is predetermined when the developer level of the developer contained in the developer container 20 is equal to or higher than a predetermined height (indicated by a broken line St in FIG. 2). A signal indicating that the amount is greater than or equal to the amount accommodated. In this specification, the predetermined storage amount is the minimum developer amount in the developer container 20 that can be detected by the developer amount detection sensor 30 as “developer present” (for example, 400 g). A high voltage power source 35 is electrically connected to the upstream developing sleeve 21 and the downstream developing sleeve 22.

<Developer>
The developing container 20 contains a one-component developer containing magnetic toner. In the case of this embodiment, the magnetic toner has negative charging characteristics. As for the one-component developer, the one-component developer contains a binder resin, an external additive and the like in addition to the magnetic iron oxide particles. As the binder resin, for example, a styrene copolymer resin, a polyester resin, a mixture of a polyester resin and a styrene copolymer resin, or a hybrid resin in which a polyester resin and a styrene copolymer resin are partially reacted are used. As an external additive, it is preferable to use a silica fine powder having a specific surface area of 3 m ² / g or more by nitrogen adsorption to improve the charging stability, developability, fluidity, and durability. The silica fine powder is added in an amount of 0.1 to 5 parts by mass to ensure fluidity as a developer. If the silica fine powder is less than this, it is difficult to ensure fluidity. However, the flowability of the developer does not change even if the amount of silica fine powder is larger than this, but if the amount of silica fine powder is increased, it will be released from the magnetic iron oxide particles and stain the inside of the image forming apparatus and the output image. It is easy to cause adverse effects.

For example, the magnetic toner preferably has a saturation magnetization of ² to 40 Am ² / kg or less at a magnetic field of 795.8 kA / m. Moreover, it is preferable that content of a magnetic iron oxide particle is 25-75 mass parts or less with respect to 100 mass parts of binder resin. Further, the weight average particle diameter of the toner is preferably 4 to 8 μm. The saturation magnetization was measured using a vibration magnetometer VSM-3S-15 (manufactured by Toei Industry Co., Ltd.).

  If necessary, external additives other than fine silica powder include fluidity imparting agents such as titanium oxide powder and aluminum oxide powder, or abrasives such as cerium oxide powder, silicon carbide powder, and strontium titanate powder. It may be added. For example, when 0.1 to 5% by mass of the above-described abrasive is added, the abrasive removes the developer attached to the surface of the photosensitive drum 10. Further, when the toner has a negative charge characteristic, the above-described abrasive improves the toner chargeability with rubbing.

<Upstream developing sleeve>
Returning to FIG. 2, the upstream developing sleeve 21 is partially exposed from the opening of the developing container 20 provided at a position facing the photosensitive drum 10, and is rotatable to the developing container 20 in the direction of arrow R <b> 2 in the drawing. Is provided. The upstream developing sleeve 21 is formed by coating a resin film on the surface of a cylindrical main body having an outer diameter of 20 mm, which is a nonmagnetic material such as aluminum or stainless steel.

  An upstream magnet roller 23 is fixedly disposed inside the upstream developing sleeve 21. On the upstream magnet roller 23, magnetic poles having different polarities are alternately arranged in the circumferential direction so as to form a magnetic field pattern (see N11, S11, N13, S13, N12, and S12 in the figure). In the developing device 3 shown in FIG. 2, the developing pole S <b> 11 is disposed facing the photosensitive drum 10 in the developing area A <b> 1, and the magnetic pole N <b> 11 is disposed facing the regulating blade 26. The regulating blade 26 is a plate-like member made of a nonmagnetic material such as aluminum, and is upstream of the photosensitive drum 10 in the rotational direction of the upstream developing sleeve 21 and in the rotational axis direction (longitudinal direction) of the upstream developing sleeve 21. It is provided along. A gap (gap) between the regulating blade 26 and the upstream developing sleeve 21 is set to about 0.23 mm, for example.

<Downstream development sleeve>
The downstream developing sleeve 22 is arranged in parallel with the lower side of the upstream developing sleeve 21 in the gravitational direction and opposed to both the upstream developing sleeve 21 and the photosensitive drum 10 in the direction of arrow R2 (that is, the same rotational direction as the upstream developing sleeve 21). The developer container 20 is rotatably provided. The downstream developing sleeve 22 may have the same diameter as the upstream developing sleeve 21. The distance between the position where the upstream developing sleeve 21 and the downstream developing sleeve 22 are closest (the closest position) may be 1 mm or less, and is set to about 0.22 mm, for example. Similarly to the upstream developing sleeve 21, the downstream developing sleeve 22 is formed by coating a resin film on the surface of a cylindrical body that is a nonmagnetic material, for example, an outer diameter of 20 mm.

  A downstream magnet roller 24 is fixedly disposed inside the downstream developing sleeve 22. On the downstream magnet roller 24, magnetic poles having different polarities are alternately arranged in the circumferential direction so as to form a magnetic field pattern (see N31, S31, N32, S33, and S32 in the figure). However, in the downstream magnet roller 24, unlike the upstream magnet roller 23, the magnetic pole S33 and the magnetic pole S32 having the same polarity are arranged adjacent to each other. Therefore, a repulsive magnetic field is formed between these poles. In the developing device 3 shown in FIG. 2, the developing pole S31 is disposed facing the photosensitive drum 10 in the developing region A2, and the magnetic pole N31 is disposed facing the upstream developing sleeve 21.

  Here, the flow of the developer in the developing device 3 will be described with reference to FIG. The developer in the developing container 20 is supplied to the developing sleeves 21 and 22 while being stirred by the stirring and conveying member 25. Then, magnetic spikes are formed on the surfaces of the developing sleeves 21 and 22 by the magnetic force of the magnet rollers 23 and 24. That is, the developer is carried on the developing sleeves 21 and 22. The developer carried on the upstream developing sleeve 21 is sent to the developing area A1 with the layer thickness regulated by the regulating blade 26. By adjusting the gap (gap) between the regulating blade 26 and the upstream developing sleeve 21, the amount of magnetic spikes formed on the upstream developing sleeve 21 is regulated, and the amount of developer conveyed to the developing area A1 is adjusted. Is done.

  On the other hand, the developer carried on the downstream developing sleeve 22 is sent to the developing area A2 with the layer thickness regulated by the upstream developing sleeve 21. In other words, the developer carried on the downstream developing sleeve 22 is controlled in the amount of spikes of the magnetic spikes by the gap G formed including the closest position between the upstream developing sleeve 21 and the downstream developing sleeve 22, and the developing region. The amount of developer conveyed to A2 is adjusted. In this way, the developing sleeves 21 and 22 rotate in the same direction as the opposing photosensitive drum 10 while carrying the developer whose layer thickness is regulated (see arrow R2 in the figure), and the developer is developed in the developing region A1. , A2 respectively.

  When the developing sleeves 21 and 22 convey the developer to the developing areas A1 and A2, the developing sleeves 21 and 22 supply the developer to the electrostatic latent image formed on the photosensitive drum 10 to develop the toner image. At this time, a developing bias voltage obtained by superimposing an AC voltage (for example, amplitude 1100 V, frequency 2800 Hz) on a DC voltage (for example, +600 V) is applied to the developing sleeves 21 and 22 from the high voltage power source 35. In response to this, the developer carried on the developing sleeves 21 and 22 flies to the photosensitive drum 10 side, and the electrostatic latent image on the photosensitive drum 10 is developed in a non-contact manner. The upstream developing sleeve 21 performs the first development on the electrostatic latent image on the photosensitive drum 10, and the downstream developing sleeve 22 performs the second development on the electrostatic latent image on the photosensitive drum 10 after passing through the development area A1.

  The developer carried on the upstream developing sleeve 21 is conveyed to the gap G while being carried on the upstream developing sleeve 21 unless it is used for image formation. A part of the gap G is returned into the developing container 20, and the rest moves from the upstream developing sleeve 21 to the downstream developing sleeve 22. On the other hand, of the developer carried on the downstream developing sleeve 22, the developer that has not been used for image formation is peeled off from the downstream developing sleeve 22 by the repulsive magnetic field formed by the magnetic pole S 33 and the magnetic pole S 32, and the developing container 20. Returned in.

In addition, as for the surface roughness of said developing sleeves 21 and 22, arithmetic mean roughness Ra is 0.6-0.9 micrometer, for example. The average charge amount of the developer on the upstream developing sleeve 21 in a normal temperature and normal humidity environment is −4 to −6 μC / g, and the coating amount is 0.4 to 0.6 mg / cm ² . On the other hand, the average charge amount of the developer on the downstream developing sleeve 22 in the normal temperature and normal humidity environment is −3 to −5 μC / g, and the coating amount is 0.3 to 0.6 mg / cm ² . The developing sleeves 21 and 22 are rotated at the same rotational speed (for example, 550 mm / s).

<Developer supply device>
Next, the developer supply device 12 will be described with reference to FIGS. 3 and 4. As shown in FIGS. 3 and 4, the developer supply device 12 can be roughly divided into a first supply device 17 and a second supply device 18. The first replenishing device 17 includes a first developer accommodating portion 170, a magnet roller 171, a discharge screw 172, a first agent amount detection sensor 173, a second agent amount detection sensor 174, a first drive motor 175, and an electromagnetic clutch 176. . On the other hand, the second supply device 18 includes a second developer accommodating portion 180, a second drive motor 181, and a hollow cylindrical toner bottle 19. The first supply device 17 and the second supply device 18 are formed on a receiving port (not shown) formed on the upper end surface of the first developer accommodating portion 170 and on a lower end surface of the second developer accommodating portion 180. It communicates with a discharge port (not shown) so that the replenisher can be delivered.

  The toner bottle 19 stores a replenisher and is detachably connected to the second developer storage unit 180. The toner bottle 19 is rotated by the second drive motor 181. In the second replenishing device 18, as the toner bottle 19 rotates, the replenisher in the toner bottle 19 moves to the second developer accommodating portion 180 side, and the replenisher is temporarily stored in the second developer accommodating portion 180. It is done. Finally, the replenisher is supplied to the first replenishing device 17 from the discharge port of the second developer accommodating unit 180.

  In the first replenishing device 17, the replenisher supplied from the second replenishing device 18 is supplied to the first replenishing device 18 in response to the discharge screw 172 provided in the first developer accommodating portion 170 being driven by the first drive motor 175. The developer container 170 is conveyed in one direction from one end side to the other end side. The first drive motor 175 continues to drive the discharge screw 172 when it is detected by the first agent amount detection sensor 173 that the replenisher is a predetermined amount or more. The first agent amount detection sensor 173 is disposed on the upstream side of the discharge screw 172 in the developer transport direction and at a predetermined height position on the wall surface of the first developer accommodating portion 170.

  The replenisher transported in one direction through the first developer container 170 as the container is developed by the developing device 3 (lower than the first developer container 170 in the gravitational direction by a magnet roller 171 that is rotated. Specifically, it is conveyed to the developing container 20). The magnet roller 171 as the conveying means is formed in a cylindrical shape by, for example, a magnet having an outer diameter of 18 mm in which S poles and N poles are alternately magnetized in total, and the first driving motor as driving means by the electromagnetic clutch 176. It rotates when the drive of 175 is transmitted. That is, as the electromagnetic clutch 176 is connected, the magnet roller 171 rotates, and the developer is supplied from the first developer container 170 to the developing device 3. The second drive motor 181, the first drive motor 175, and the electromagnetic clutch 176 are controlled according to the detection result of the second agent amount detection sensor 174. The second agent amount detection sensor 174 is disposed downstream of the discharge screw 172 in the developer transport direction and at a predetermined height position on the wall surface of the first developer accommodating portion 170.

<Control unit>
The image forming apparatus also includes a control unit 200 as shown in FIG. The control unit 200 will be described with reference to FIG. FIG. 5 is a control block diagram showing the developer supply control system. The control unit 200 can control each of the above-described units (see FIG. 1) other than those shown in FIG. 5, but the illustration and description thereof are omitted here because it is not the gist of the invention.

  The control unit 200 is, for example, a CPU (Central Processing Unit) that performs various controls such as an image forming job and replenishment agent replenishment. As shown in FIG. 5, a memory 201, an operation unit 202, a sensor unit 203, a developer supply device 12, and a high voltage power source 35 are connected to the control unit 200. The memory 201 is a storage unit such as a ROM, a RAM, or a hard disk device. The memory 201 stores various control programs and data for controlling the image forming apparatus. In the present embodiment, for example, various control programs such as an image forming job (not shown) and a developer replenishment process described later, various data such as the total number of image-recorded recording materials S, and the like are stored. In addition, the memory 201 can temporarily store calculation processing results and the like accompanying execution of various control programs.

  The operation unit 202 is, for example, an operation panel having a touch panel display or an external terminal that accepts execution instructions of various programs and various data inputs by a user. The control unit 200 displays an input screen (not shown) for various information related to image formation, a selection execution screen (see FIG. 8 described later) related to “developer supply control”, and the like on a display (not shown) of the operation unit 202. be able to.

  The control unit 200 can execute an image forming job stored in advance in the memory 201 based on an input of image information or the like by a user using an input screen (not shown) displayed on the operation unit 202. The control unit 200 controls the operation of the image forming apparatus as the image forming job is executed. The image forming job is a series of operations from the start of image formation to the completion of the image forming operation based on a print signal for forming an image on the recording material S. Specifically, it refers to the period from pre-rotation (preparation operation before image formation) after receiving a print signal to post-rotation (operation after image formation). Time).

  Further, the control unit 200 can execute a developer supply process stored in advance in the memory 201 based on an instruction input by the user using a selection execution screen (see FIG. 8 described later) displayed on the operation unit 202. . Based on the detection results of the sensor unit 203 (first agent amount detection sensor 173, second agent amount detection sensor 174, developer amount detection sensor 30), the control unit 200 performs developer replenishment processing based on the detection result of the sensor unit 203 (first agent amount detection sensor 173, second agent amount detection sensor 174, developer amount detection sensor 30). 35 can be operated to control the supply of the replenisher to the developing device 3.

<Developer supply control>
The developer replenishment control of this embodiment will be described with reference to FIGS. 6 and 12 with reference to FIGS. 4 and 5 as appropriate. FIG. 11 is a timing chart showing the transition of the developer amount in the developer container when the developer replenishment control of this embodiment is executed, and FIG. 12 is a timing chart showing the transition of the developer amount in the developer container when the conventional replenishment control is executed. 6 is a timing chart showing changes in the developer amount. Further, in FIGS. 11 and 12, the developer amount (W2) indicates the accommodation amount.

  As shown in FIG. 6, when receiving an instruction to execute the developer supply process from the operation unit 202, the control unit 200 executes “initial supply control” as the first mode (S1). In the “initial supply control”, the developer supply device 12 is operated based on the detection results of the first agent amount detection sensor 173 and the second agent amount detection sensor 174 as described above, and the supply agent is supplied to the developing device 3. The control unit 200 adjusts the replenisher supply amount by controlling the rotation time of the magnet roller 171. In the case of this embodiment, the amount of the replenisher supplied to the developing device 3 by the “initial replenishment control” is the first replenishment amount that is smaller than a predetermined accommodation amount (for example, 250 g). The first replenishment amount is an amount that is not detected by the developer amount detection sensor 30 as “developer present”, but the developer agent is located more than the gap G (closest position) between the upstream developing sleeve 21 and the downstream developing sleeve 22. The surface height is low. As can be understood by comparing FIG. 11 and FIG. 12, in the case of the present embodiment, the replenishment agent is not replenished up to the accommodation amount W2, so that the time required for replenishment is naturally shortened compared to the conventional case (first). Time t1s) until reaching one supply amount W0).

  The control unit 200 controls the high-voltage power supply 35 after supplying the first supply amount of supply agent, and applies a DC voltage of, for example, +600 V to the developing sleeves 21 and 22 (S2). Here, the DC voltage (+600 V) is applied to prevent the charged toner having a reversed polarity contained in a large amount in the replenisher from adhering to the developing sleeves 21 and 22, and the surface of the developing sleeves 21 and 22 is formed during image formation. This is because the charging of the toner can be optimized in a short time. Then, the control unit 200 determines whether or not a predetermined time (for example, 600 s) has elapsed after the start of the “initial supply control” (S3). As shown in FIG. 11, after reaching the first supply amount, the developer amount in the developer container 20 remains the first supply amount W0 and does not change until the joint supply control is started (time t1s to t1). .

  FIG. 8 shows an example of a selection execution screen displayed on the operation unit 202 at the time of initial replenishment. As shown in FIG. 8, the selection execution screen 161 displays a start operator for instructing the start of the developer supply process (START in FIG. 8), an end operator for instructing the forced end of the developer supply process, and the like. (ABORT in FIG. 8). The user can instruct to start or forcibly end the developer supply process by touching these pseudo-operation elements displayed on the display.

  The selection execution screen 161 displays the remaining time of the initial supply control. FIG. 8 shows the case where the remaining time is 779 seconds. This is to present to the user the time required to start the image forming job. In the initial replenishment control, replenishment agent replenishment is performed at a higher speed than the joint replenishment control (see FIG. 7) and normal replenishment control (see FIG. 10), which will be described later, and even after the first replenishment amount is replenished, the developing sleeves 21 and 22. And the stirring conveyance member 25 (refer FIG. 2) is rotated. As a result, the toner charge amount is optimized after the initial supply control is completed. In spite of the toner charge amount not being an appropriate value, an image defect is likely to occur when an image forming job is executed. Therefore, the user is prevented from starting the image forming job until the toner charge amount reaches an appropriate value.

  Returning to FIG. 6, when it is determined that the predetermined time has not elapsed (NO in S3), the control unit 200 returns to the process of S2. On the other hand, when it is determined that the predetermined time has elapsed (YES in S3), the control unit 200 can accept an instruction to start an image forming job from an input screen (not shown) or the like, "Is executed (S4). The “connection supply control” will be described later (see FIG. 7). The control unit 200 repeatedly executes “connection supply control” until the amount of developer in the developer container 20 becomes equal to or greater than a predetermined amount (NO in S5). When the amount of developer in the developing container 20 becomes equal to or greater than the predetermined amount (YES in S5), the controller 200 starts “normal replenishment control” as the third mode (S6). The “normal supply control” will be described later (see FIG. 10).

<Connection supply control>
“Connection supply control” (see S4 in FIG. 6) executed after the initial supply control (after the first mode) will be described with reference to FIG. As shown in FIG. 7, the control unit 200 determines whether an instruction to start an image forming job is received from an input screen (not shown) or the like (S11). When the image forming job start instruction has not been received (NO in S11), the control unit 200 ends the splicing supply control. In this case, the replenisher is not replenished from the developer replenishing device 12 to the developing device 3. Further, since no image is formed, the developer is not consumed. That is, the amount of developer in the developing container 20 does not decrease or increase.

  On the other hand, when it is determined that an instruction to start an image forming job has been received (YES in S11), the control unit 200 calculates the consumption amount of developer consumed in association with image formation (S12). The consumption amount of the developer is obtained according to the printing rate as shown in Equation 1 below.

  Developer consumption = 5.5 × printing ratio Equation 1

  Here, the printing rate refers to the area ratio of the printing portion with respect to the area where the image can be formed on the recording material S. For example, the solid white is 0%, and the solid black is 100%. The printing rate may be calculated for each image forming job. However, when the recording material S on which an image is formed exceeds, for example, 100 pages in A4 horizontal conversion, it is preferable to obtain the printing rate every 100 pages.

  The control unit 200 determines the additional amount (S13). The additional amount varies according to the printing rate. However, as described above, the consumption increases as the printing rate increases, and decreases as the printing rate decreases (see Equation 1 above). However, the additional amount decreases as the printing rate increases. If the rate is low, it will decrease. The control unit 200 obtains the additional amount according to a predetermined calculation formula, or determines the additional amount with reference to the additional amount table stored in the memory 201 in advance. In the additional amount table, a predetermined additional amount to be added to the consumption amount per page is set in advance for each predetermined printing rate range (for example, about 1 to 10%). For example, when the printing rate is 5%, the additional amount is set to 75 mg, and when the printing rate is 50%, the additional amount is set to 10 mg.

  FIG. 9 shows the transition of the developer amount in the developing container 20 during the connection replenishment control. A straight line J in FIG. 9 shows a case where an A4 horizontal image with a printing rate of 5% is formed, and a straight line K shows a case where an A4 horizontal image with a printing rate of 50% is formed. When forming an A4 landscape image with a printing rate of 5%, the amount of developer consumed per page is 27.5 mg. Therefore, 102.5 mg (27.5 + 75) of replenisher per page is used in splicing replenishment control. To be replenished. In this case, in order to replenish the replenisher from the developer amount after initial replenishment (for example, 250 g) to a predetermined storage amount (for example, 400 g), it is necessary to form an image on 2000 sheets of recording material S ([400 −250] / [75/1000]) = 2000). On the other hand, when forming an A4 landscape image with a printing rate of 50%, the consumption amount of the developer per page is 275 mg. Therefore, 285 mg (275 + 10) of the replenishment agent is supplied per page in the splicing replenishment control. In this case, in order to replenish the replenisher from the developer amount after initial replenishment (for example, 250 g) to a predetermined storage amount (for example, 400 g), it is necessary to form an image on 15,000 sheets of recording material S ([400 −250] / [10/1000]) = 15000).

  As described above, in the present embodiment, the additional amount when the printing rate is low is made larger than the additional amount when the printing rate is high. This is because, when the printing rate is high, if the additional amount is increased although the consumption amount is large, the proportion of the developer having high fluidity in the developing container 20 increases, and as a result, before the replenishment agent is replenished. This is because vertical streaks are more likely to occur. That is, at the time of joint replenishment control, a developer having a relatively low fluidity is consumed and replaced with a replenisher having a relatively high fluidity. When the printing rate is high, the ratio of the developer to be replaced in the developer in the developing container 20 increases as the replenishment agent is replenished as compared with the case where the printing rate is low. Nevertheless, if the additional amount is further increased when the printing rate is high, the fluidity of the developer in the developing container 20 becomes higher. Therefore, when the printing rate is high, it is better to reduce the additional amount as much as possible. However, if the additional amount remains small, as described above, it takes too much time to replenish the replenisher up to a predetermined accommodation amount (see FIG. 9). Therefore, when the printing rate is low, the additional amount is increased as compared with the case where the printing rate is high, so that the time required to replenish the replenishment agent to a predetermined capacity is reduced as much as possible.

  Returning to FIG. 7, the control unit 200 calculates the replenishment amount of the replenisher to be replenished by the developer replenishing device 12 (S14). The supply amount of the replenisher is obtained by adding the additional amount determined above to the consumption amount obtained above (supplementary agent replenishment amount = developer consumption amount + additional amount). In the case of the present embodiment, as described above, a replenishment amount (a second replenishment amount) of replenishment agent is replenished by adding a larger amount when the printing rate is lower than when the printing rate is high. As described above, the replenishment amount of the replenishment agent supplied to the developing device 3 in the “joint replenishment control” is the sum of the consumption amount of the developer consumed in association with the image formation and the additional amount that varies depending on the printing rate. Second supply amount. The control unit 200 starts the replenishment by controlling the developer replenishing device 12 so as to replenish the obtained replenishment amount (S15).

  Note that the controller 200 controls the rotational speed of the magnet roller 171 so that the amount of replenishment agent supplied per unit time is smaller at the time of replenishment than at the time of initial replenishment. That is, the control unit 200 performs control so that the drive speed of the first drive motor 175 when supplying the replenishment agent during connection replenishment is slower than that during initial replenishment.

  As shown in FIG. 11, at the time of replenishment, the amount of replenisher supplied is larger than the amount of developer consumed, so that the amount of developer in the developer container 20 increases by an additional amount each time an image forming job is executed. (W0 to W2 in the figure). Thereafter, when the amount of developer in the developing container 20 becomes equal to or greater than a predetermined capacity (time t2), normal replenishment is performed. On the other hand, in the conventional case, as shown in FIG. 12, normal replenishment is performed without interposing the replenishment control after the initial replenishment.

<Normal replenishment control>
Next, “normal replenishment control” will be described with reference to FIG. The normal replenishment control is executed at predetermined time intervals after the start of the “normal replenishment control” (see S6 in FIG. 6). As shown in FIG. 10, the control unit 200 determines whether an instruction to start an image forming job is received from an input screen (not shown) or the like (S21). If the image forming job start instruction has not been received (NO in S21), the control unit 200 waits until the image forming job start instruction is received without continuing the processing.

  When it is determined that the image forming job start instruction has been received (YES in S21), the control unit 200 determines whether or not the developer amount in the developing container 20 is less than a predetermined storage amount (S22). This determination is made based on whether or not the control unit 200 has received a signal from the developer amount detection sensor 30. That is, when the control unit 200 receives a signal from the developer amount detection sensor 30, the control unit 200 determines that the developer amount in the developer container 20 is equal to or greater than a predetermined accommodation amount. When it is determined that the amount of developer in the developing container 20 is equal to or greater than the predetermined amount (NO in S22), the control unit 200 normally replenishes that a sufficient amount of developer is stored in the developing container 20. End control. That is, in this case, the replenisher is not replenished from the developer replenishing device 12 to the developing device 3.

  On the other hand, when it is determined that the amount of developer in the developing container 20 is less than the predetermined storage amount (YES in S22), the control unit 200 calculates the amount of developer consumed in association with image formation (S23). The consumption amount of the developer is obtained according to the above formula 1. Then, the control unit 200 starts the replenishment by controlling the developer replenishing device 12 so as to replenish the determined amount of replenisher (S24). In this case, the replenishment agent is replenished from the developer replenishing device 12 to the developing device 3, but the replenishment amount is the same as the consumption amount of the developer. Accordingly, as shown in FIG. 11, the amount of developer in the developing container 20 does not decrease or increase. The normal replenishment control is the same in the conventional case as shown in FIG. However, in the conventional case, after initial replenishment (after time t1), it takes time until the developer amount in the developing container 20 is stabilized. On the other hand, as shown in FIG. 11, in the case of the present embodiment, it takes less time for the amount of developer in the developer container 20 to be stabilized after replenishment (after time t <b> 2) compared to the conventional case.

<Experimental result>
FIG. 13 shows experimental results comparing the present embodiment in which the above-described splicing replenishment control is performed with a conventional example that does not perform the splicing replenishment control described above and a comparative example. The conventional example and the comparative example differ in the replenishment amount of the replenisher to be replenished in the conventional initial replenishment control (first developer amount). The conventional example replenishes 400 ± 30 g of replenisher, while the comparative example replenishes 250 ± 30 g of replenisher. In the case of the embodiment, the first developer amount indicates the amount of developer in the developing container 20 after initial replenishment, and the second developer amount indicates the amount of developer in the developing container 20 after joint replenishment. In the case of the conventional example and the comparative example, the first developer amount indicates the developer amount in the developing container 20 after the initial replenishment, and the second developer amount forms an image on the 50 sheets of recording material S after the initial replenishment. The amount of developer in the developing container 20 after the job is performed is shown.

  In FIG. 13, as an experimental result, after completion of the initial replenishment control, an image forming job for outputting an image with a printing rate of 30% up to the tip 30 mm and the remaining solid white image on both sides of A4 horizontal plain paper was performed. In this case, the vertical stripes generated in the recording material S are shown in 10 levels. The vertical stripe level is a good result that the vertical stripe is not so conspicuous as the numerical value is large. If the level of the vertical stripe is 7 or less, most users can recognize the vertical stripe. Further, the number of recording materials S that can be continuously output when an image forming job for continuously outputting 1000 black images continuously on both sides of A4 horizontal plain paper during normal replenishment is shown.

  As shown in FIG. 13, with respect to the level of vertical stripes, the result of this embodiment is level 10, the conventional example is level 5, and the comparative example is level 3. That is, in the present embodiment, vertical stripes are less likely to occur than in the conventional example and the comparative example. This is because, in the case of this embodiment, the amount of developer after the initial replenishment is suppressed as compared with the conventional case. In the comparative example, the developer amount after the initial replenishment is suppressed as compared with the conventional example. However, vertical lines are more likely to occur in the comparative example than in the present embodiment because about 150 g of developer is replenished in a short time for image formation on 50 recording materials S, and the amount of developer increases rapidly. Because. On the other hand, in the case of the present embodiment, as described above, the time for forming an image on the recording material S of 2000 sheets (printing rate 5%) and 15000 sheets (printing rate 50%) to supply about 150 g of developer. As the amount of developer is gradually increased, vertical stripes are unlikely to occur.

  As described above, the control unit 200 executes the “initial supply control”, but sets the amount of the supply agent supplied to the developing device 3 in the “initial supply control” as the first supply amount that is smaller than the predetermined storage amount. In this case, since the developer level in the developer container 20 does not reach the gap G (closest position) between the upstream developing sleeve 21 and the downstream developing sleeve 22, development with high fluidity after the initial replenishment is performed. It is difficult for the agent to be supplied to the gap G between the two developing sleeves 21 and 22. If the developer with high fluidity is not supplied to the gap G between the two developing sleeves 21 and 22, the vertical stripe-shaped density unevenness cannot occur. Then, after the initial replenishment control, the control unit 200 executes “joint replenishment control” until the amount of developer in the developing container 20 becomes equal to or greater than a predetermined accommodation amount. The replenishment amount of the replenishment agent supplied to the developing device 3 by the “joint replenishment control” is a second replenishment amount obtained by adding an additional amount that varies depending on the printing rate to the consumption amount of the developer consumed in association with image formation. . Therefore, at the time of replenishment, the amount of developer in the developing container 20 increases by an additional amount every time an image forming job is executed. As a result, even when image formation is performed in which an image with a high printing rate is continuously output after the initial replenishment, there is no shortage of developer and image defects such as image omission do not occur.

<Other embodiments>
Note that the above Equation 1 is an example, and the coefficient (5.5) and the additional amount in Equation 1 are not limited to those described above. The coefficient and the additional amount described above may be different for each model in which the size and process speed of the photosensitive drum 10 or the sizes and rotation speeds of the developing sleeves 21 and 22 are different.

  In the above-described embodiment, the direct transfer type image forming apparatus that directly transfers the toner image from the photosensitive drum 10 to the recording material S has been described as an example, but the present invention is not limited thereto. For example, the present invention may also be applied to an intermediate transfer type image forming apparatus that primarily transfers a toner image from a photosensitive drum to an intermediate transfer belt, and then secondarily transfers the toner image from the intermediate transfer belt to a recording material.

  The developing device 3 may be a two-component developing device that performs development using a two-component developer including a non-magnetic toner having a negative charge characteristic and a carrier having a positive charge characteristic. A full-color machine uses a non-magnetic toner, and a two-component developing device is used to output a high-speed and stable image.

DESCRIPTION OF SYMBOLS 3 ... Developing device, 10 ... Photoconductor (photosensitive drum), 12 ... Replenisher (developer supply device), 20 ... Developer container, 21 ... First developer carrier (upstream developer sleeve), 22 ... Second developer Carrier (downstream developing sleeve), 30 ... detecting means (developer amount detecting sensor), 170 ... container (first developer accommodating portion), 171 ... conveying means (magnet roller), 175 ... driving means (first driving) Motor), 200 ... control unit, G ... closest position (gap)

Claims (6)

A rotating photoreceptor,
A developer container containing a developer;
The developer container is rotatably provided in parallel with a position facing the photoreceptor, and carries and transports the developer in the developer container, and the electrostatic latent image formed on the photoreceptor is developed by the developer. A first developer carrier and a second developer carrier to be developed;
A replenishing device for replenishing the developer container with a replenishing developer;
A detecting unit provided at a height position equal to or higher than a closest position between the first developer carrying member and the second developer carrying member in the developer container; and detecting the developer in the developer container;
A first mode in which the replenishing device is controlled to replenish the empty developer container with a first replenishment amount of replenishment developer that is not detected by the detection means, and an image forming job is started after the first mode. In this case, at least until it is detected by the detection means, a larger additional amount is added to the consumption amount of the developer consumed in association with the image formation when the printing rate is low than when the printing rate is high. A control unit that executes a second mode of supplying a second supply amount of developer for supply,
An image forming apparatus. The first replenishment amount is an amount in which the developer level of the developer is lower than the closest position,
The image forming apparatus according to claim 1. In the second mode, the replenishment amount of the replenishment developer per unit time is smaller than that in the first mode.
The image forming apparatus according to claim 1, wherein: The replenishing device includes a housing that contains a replenishing developer, a transporting unit that transports the replenishing developer from the housing to the developer container, and a driving unit that drives the transporting unit.
In the second mode, the driving speed of the driving means when replenishing the replenishment developer is slower than that in the first mode.
The image forming apparatus according to claim 3. The developer consumption is determined based on the printing rate.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The developer is a one-component developer containing magnetic toner.
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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