JP2013047722A - Image forming apparatus and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which solves problems of a hue variation, fogging or the like caused by agitation defects of supplied toner and is capable of forming a good image, without increasing the size of the image forming apparatus body and cost.SOLUTION: An image forming apparatus 100 comprises: a developing sleeve 11 which carries and conveys a two component developer and is rotatable; an agitation screw 17b for agitating and mixing the two component developer in the inside of a second chamber 16 of a developing device 4; a supply device 200 for supplying the toner to the developing device 4; a detection device 52 for detecting a rotational phase of the agitation screw 17b; and a controller 22 for controlling a timing for supplying the toner by the supply device 200 toward concave portions formed with the screw shape of the agitation screw 17b on the basis of a detection result detected by the detection device 52.

Description

  The present invention relates to an image forming apparatus and a process cartridge including a developing device and a replenishing device that replenishes toner to the developing device.

  In recent years, image forming apparatuses have been reduced in size and speed. Under such circumstances, various problems relating to charging failure of the replenishment toner have occurred for the reasons described below. For example, with the miniaturization of the image forming apparatus, the length of the stirring chamber of the developing device in the thrust direction has been shortened. As a result, the distance at which the replenished toner is agitated with the carrier is shortened, and sufficient agitation is not performed, making it impossible to charge the toner to a desired charge.

  Further, as the speed of the image forming apparatus increases, the amount of toner consumed per unit time from the surface of the developing sleeve of the developing device increases. As a result, the toner replenished to the upstream side of the stirring screw needs to be transported to the developing sleeve in a short time, and the toner may not be charged to a desired charge due to insufficient stirring time. there were.

  In these cases, development is performed in a state where toners having different charge amounts are mixed. Therefore, toners having different charge amounts are charged with respect to the electrostatic image formed on the surface of the photosensitive drum. The applied amount corresponding to the amount is developed. As a result, the toner density may be different for the same electrostatic image, causing color variation, and when the toner charge amount is small, it may be output as a fog image. As an invention for solving such a problem, an invention relating to an image forming apparatus described in Patent Document 1 is disclosed.

  Patent Document 1 discloses an image forming apparatus that includes a developing device having a stirring screw and a preliminary stirring chamber that is disposed on the side of the developing device and has stirring blades.

  Further, a technique for improving the toner stirring effect by reducing the amount of developer inside the developing container can be applied to the invention described in Patent Document 1. For example, when the developer surface becomes higher than the upper edge (highest part) of the stirring screw inside the stirring chamber of the developing device, the toner replenished from the replenishing port is conveyed so as to float on the upper surface of the developer surface. It becomes difficult to be mixed with the developer present in the stirring chamber in advance. In order to avoid this, by reducing the amount of the developer, the developer surface is lowered below the stirring screw inside the stirring chamber to improve the stirring ability and mixing ability.

Japanese Patent Laid-Open No. 10-003219

  However, in the invention described in Patent Document 1, a preliminary stirring chamber must be provided in order to charge uncharged toner, resulting in an increase in the size and cost of the developing device.

  Further, when the developer surface is lowered below the upper edge of the stirring screw 17b inside the stirring chamber, the fluctuation of the toner carrier ratio of the two-component developer increases with respect to the amount of toner consumed.

  This phenomenon will be described in detail below. When the same amount of toner as the toner consumption is replenished, there is no fluctuation in the overall toner carrier ratio in the developing container, but the developer near the developing sleeve is temporarily removed when the toner consumption is repeated. The toner density is lowered. As a result, when high density images are continuously printed, the toner density is inclined in the thrust area of the developing sleeve (the toner density on the downstream side in the developer conveying direction by the stirring screw tends to decrease), and the image density is uneven in the thrust direction. Occurs. For these reasons, it is difficult to improve the stirring efficiency by reducing the amount of developer inside the developing container unnecessarily.

  In view of the above circumstances, the present invention eliminates problems such as color fluctuations and fogging due to poor stirring of replenished toner without causing an increase in the size and cost of the main body of the image forming apparatus, and provides a good image. An object of the present invention is to provide an image forming apparatus capable of forming an image.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a rotatable developer carrying member carrying and carrying a two-component developer having toner and a carrier, and a two-component inside a stirring chamber of the developing device. A screw-shaped stirring member that mixes the developer while stirring, a replenishing unit that replenishes toner to the developing device, a detecting unit that detects a phase in which the stirring member rotates, and a detection result detected by the detecting unit. Based on this, the replenishing means includes a controller for controlling the timing of replenishing the toner toward the concave portion formed in the screw shape of the stirring member.

  According to the present invention, without causing an increase in the size and cost of the main body of the image forming apparatus, problems such as color fluctuations and fogging due to poor stirring of the replenished toner can be solved, and a good image can be formed. Can do.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to Embodiment 1 of the present invention. It is sectional drawing which follows the AA line of FIG. FIG. 3 is a cross-sectional view illustrating an internal configuration of a toner storage container. It is sectional drawing which follows the BB line of FIG. It is a top view which shows the structure of a stirring screw, a flag, and a photo interrupter. It is an expansion schematic diagram which shows the positional relationship of the blade | wing of a stirring screw and a replenishment port when a flag interrupts | blocks a photo interrupter. It is a block diagram of a controller and its peripheral devices. It is a flowchart which shows the control process of a controller. 6 is a timing chart illustrating a replenishment timing when a replenishing device replenishes toner. It is a conceptual diagram which shows the relationship between a stirring screw and a developer surface. 7 is a graph showing a result of analyzing a toner charge amount distribution in a developer by randomly extracting the developer from the inside of a developing container after performing 100 sheets of continuous printing with a solid image. It is a graph which shows the relationship between the output value of an inductance sensor, and time. 6 is a timing chart illustrating a replenishment timing when a replenishing device replenishes toner.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, since the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions, there is no specific description. As long as the scope of the invention is not limited to these, it is not intended.

  FIG. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus 100 according to Embodiment 1 of the present invention. The image forming apparatus 100 is an image forming apparatus using an electrophotographic image forming process. As shown in FIG. 1, the image forming apparatus 100 includes an image forming apparatus main body (hereinafter simply referred to as “apparatus main body”) 100A, and an image forming unit 55 for forming an image is provided inside the apparatus main body 100A. Provided. The image forming unit 55 includes a photosensitive drum 1 that is an “image carrier”, a transfer roller 5 that is a “transfer device”, and the like. The photosensitive drum 1, the developing device 4, and the storage container 18 may be configured so that all or a part thereof is included in the process cartridge and is incorporated into the apparatus main body 100A as a process cartridge.

  The image forming apparatus 100 includes a charging roller 2, an exposure device 3, a developing device 4, a transfer roller 5, and a cleaning device 6 around a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 1. A fixing device 7 is disposed downstream of the transfer nip N between the photosensitive drum 1 and the transfer roller 5 in the transfer material transport direction Z.

  The photosensitive drum 1 is a negatively charged organic photosensitive member in the present embodiment, and has a photosensitive layer (not shown) on an aluminum drum base (not shown) having a diameter of 30 mm. The photosensitive drum 1 is rotationally driven in a direction indicated by an arrow (clockwise) at a predetermined peripheral speed (for example, 105 mm / sec), and is negatively charged uniformly by a charging roller 2 that contacts in the rotation process.

  A charging roller 2 as a charging unit is rotatably contacted with the surface of the photosensitive drum 1 and uniformly charges the photosensitive drum 1 to a predetermined polarity and potential by a charging bias applied from a charging bias power source (not shown). To do. The exposure apparatus 3 includes a laser driver (not shown), a laser diode, a polygon mirror, and the like. A laser beam modulated in accordance with a time-series electric digital image signal of image information input to a laser driver is output from a laser diode, and the laser beam is scanned by a polygon mirror that rotates at high speed, and a reflection mirror (not shown). Then, the surface of the photosensitive drum 1 is subjected to image exposure R. As a result, an electrostatic image corresponding to the image information is formed.

  The developing device 4 is a two-component developing device that performs development with a two-component developer (developer t) containing a non-magnetic toner and a magnetic carrier (details of the developing device 4 in the present embodiment will be described later). To do).

  A transfer roller 5 serving as a transfer unit contacts the surface of the photosensitive drum 1 with a predetermined pressing force to form a transfer nip portion N. The transfer roller 5 transfers a toner image on the surface of the photosensitive drum 1 at a transfer nip N between the photosensitive drum 1 and the transfer roller 5 by a transfer bias applied from a transfer bias power source (not shown). Transcript to. The cleaning device 6 has a cleaning blade 6a, and removes transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer by the cleaning blade 6a. The fixing device 7 includes a rotatable fixing roller 7a and a pressure roller 7b, and the transfer material P is nipped and conveyed at a fixing nip between the fixing roller 7a and the pressure roller 7b, and the surface of the transfer material P is fixed. The toner image transferred to is heat-pressed and heat-fixed.

  Next, an image forming operation by the image forming apparatus 100 will be described. At the time of image formation, the photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (for example, 105 mm / sec) in the direction of the arrow by a driving unit (not shown), and the surface is uniformly charged by the charging roller 2.

  Then, an image exposure R is given by the exposure device 3 on the charged photosensitive drum 1, and an electrostatic image (electrostatic latent image) corresponding to the input image information is formed. The charging polarity of the photosensitive drum 1 is applied by the developing sleeve 11 of the developing device 4 in which a developing bias having the same polarity as the charging polarity (negative polarity) on the photosensitive drum 1 is applied to the electrostatic image on the photosensitive drum 1. A toner charged with the same polarity as that of (negative polarity) is attached to make a toner image visible.

  When the toner image on the photosensitive drum 1 reaches the transfer nip N between the photosensitive drum 1 and the transfer roller 5, the transfer material P such as paper is transferred to the transfer nip by a registration roller (not shown) at this timing. It is conveyed to part N. The transfer roller 5 to which a transfer bias having a polarity opposite to that of the toner (positive polarity) is applied causes an electrostatic force generated between the photosensitive drum 1 and the transfer roller 5 on the transfer material P conveyed to the transfer nip N. Then, the toner image on the photosensitive drum 1 is transferred.

  The transfer material P onto which the toner image has been transferred is conveyed to the fixing device 7, where the toner image is heated and pressed on the transfer material P at the fixing nip between the fixing roller 7a and the pressure roller 7b, and then externally fixed. A series of image forming operations is completed. Further, the transfer residual toner remaining on the surface of the photosensitive drum 1 after the toner image transfer is removed and collected by the cleaning blade 6a of the cleaning device 6.

  Next, details of the developing device 4 according to the first embodiment will be described. The developing device 4 includes a developing container 10 containing a developer t containing a nonmagnetic toner and a magnetic carrier. An opening 4 a is formed in the upper part of the developing container 10, and a developing sleeve 11 made of a nonmagnetic material such as SUS as a developer carrier rotates in the opening 4 a so as to face the photosensitive drum 1. Arranged freely. The developing sleeve 11 that is a “developer carrying member” is a rotatable one that carries and conveys a two-component developer having toner and carrier. Inside the developing sleeve 11, a magnet roller 13 as a magnetic field generating means is fixedly disposed, and the magnet roller 13 has a plurality of magnetic poles.

  A regulating blade 12 is attached to the opening 4 a of the developing container 10 so as to be close to the developing sleeve 11. The regulating blade 12 regulates the layer thickness of the developer t carried on the surface of the developing sleeve 11.

  As the non-magnetic toner, a known toner obtained by adding a colorant, a charge control agent or the like to a binder resin can be used. In this embodiment, a toner having a volume average particle diameter of 5 to 15 μm is used. Also, as the magnetic carrier, a ferrite carrier, a resin-coated one, etc. can be suitably used. In the present embodiment, one having an average particle diameter of 5 to 70 μm was used.

  In addition, the inside of the developing container 10 that is a “developing apparatus body” is partitioned by a partition wall 14 into a first chamber 15 that is a “stirring chamber” and a second chamber 16 that is a “stirring chamber”. A stirring screw 17 a is disposed inside the first chamber 15, and a stirring screw 17 b is disposed inside the second chamber 16. The stirring screw 17a, which is the “stirring member”, mixes the two-component developer with stirring inside the first chamber 15, and the stirring screw 17b, which is the “stirring member”, develops the two-component developer inside the second chamber 16. The agent is mixed with stirring.

  These agitating screws 17a and 17b function as an agitating member and also as a conveying member for conveying the developer. The first chamber 15 and the second chamber 16 communicate with each other, and the developer t circulates in the first chamber 15 and the second chamber 16 by the rotation of the stirring screws 17a and 17b.

  In the upper part of the second chamber 16 of the developing container 10, a replenishing device 200 that is a “replenishing unit” for replenishing toner to the developing container 10 is disposed. The replenishing device 200 includes a storage container 18 that stores toner. A supply screw 21 is provided inside the storage container 18. The supply screw 21 causes the toner inside the storage container 18 to fall from the supply port 20 to the second chamber 16 while rotating.

  Further, an inductance sensor 19 that is a “detection device” that detects the magnetic permeability of the two-component developer t inside the developing container 10 is disposed on the side of the second chamber 16 of the developing container 10. The inductance sensor 19 detects the concentration of the two-component developer by detecting the magnetic permeability of the two-component developer t. The supply screw 21 and the inductance sensor 19 are connected to the controller 22.

  Here, the process of moving the developer t inside the developing device 4 will be described. The developer t inside the developing container 10 is transported from the second chamber 16 to the first chamber 15 by the rotation of the stirring screw 17b, and further transported while being stirred by the stirring screw 17a. At this time, a part of the developer t is pumped up by the pumping pole (N2 pole) of the magnet roller 13. The developer t pumped up by the pumping pole (N2 pole) is regulated to a predetermined layer thickness by the regulating blade 12 and attached to the surface of the developing sleeve 11. As the developing sleeve 11 rotates, the developer t whose thickness is regulated on the surface of the developing sleeve 11 is conveyed to the vicinity of the developing portion where the developing pole (S1 pole) of the magnet roller 13 is located, and the photosensitive drum 1 Develop the electrostatic image above.

  The developer remaining without contributing to the development falls into the first chamber 15 in the developing container 10 by the repulsive magnetic field due to the magnetic poles (N3 pole and N2 pole) of the magnet roller 13 as the developing sleeve 11 rotates. To do. The developer that has dropped into the first chamber 15 is conveyed to the second chamber 16 by the rotation of the stirring screw 17a and contributes to the next development.

  2 is a cross-sectional view taken along line AA in FIG. As shown in FIG. 2, the replenishment port 20 is positioned vertically above the axis of the agitation screw 17b (surface direction of the paper surface of FIG. 2), and in order to obtain the agitation time of replenishment toner and developer. The two chambers 16 are disposed upstream of the developer transport direction L1 (L). The length of the replenishing port 20 in the thrust direction is 10 mm. The distance between the replenishing port 20 and the upper edge (outermost partition surface) of the stirring screw 17b is set to 5 mm (see FIG. 1).

  The stirring screw 17b has a shaft 17b1 and a blade 17b2 that is a “blade portion” protruding from the shaft 17b1, and the stirring screw 17a is a shaft 17a1 and a “blade portion” protruding from the shaft 17a1. Blades 17a2.

  FIG. 3 is a cross-sectional view showing an internal configuration of the storage container 18. 4 is a cross-sectional view taken along line BB in FIG. As shown in FIGS. 3 and 4, the storage container 18 has a stirring screw 23 that stirs the toner in the storage container 18, and further replenishes the toner into the developing container 10 through the supply port 20. The screw 21 is provided integrally. The storage container 18 having the replenishing screw 21 is integrally formed as a cartridge and is detachable from the developing container 10 of the developing device 4. The supply screw 21 includes a shaft 21x and a blade 21y formed around the shaft 21x.

  Here, the replenishing screw 21 rotates at a screw outer diameter of 13 mm, a screw inner diameter of 8 mm, a screw pitch of 8 mm, and 5 rotations / second, and the clearance between the inner wall of the storage container 18 and the outer diameter of the replenishing screw 21 is 1 mm. It is. Further, as the replenishment motor M of the replenishment screw 21, a pulse motor that can be driven and stopped in minute time units is adopted. In addition, a flag and a photo interrupter (not shown) for counting the number of rotations of the supply screw 21 are provided. By counting the number of rotations of the replenishing screw 21 by using the flag and the photo interrupter, the toner for one pitch (block) can be conveyed by one rotation.

  In general, since the blade 21y of the replenishment screw 21 moves forward or pulls in the toner conveyance direction while the replenishment screw 21 rotates once, the replenishment amount of the toner conveyed while the replenishment screw 21 rotates once. Repeatedly pulsates. Here, the period during which the replenishment screw 21 rotates once is handled as one unit. This is because, for example, even when the amount of toner replenished when the replenishing screw 21 rotates once is 100, the amount of toner replenished when the replenishing screw 21 rotates 1/2 is not necessarily 50. It is taken into account that there are things.

  In order to make it less susceptible to the influence of toner pulsation, the replenishment screw 21 is always rotated in units of one rotation so that the position of the blade 21y of the replenishment screw 21 with respect to the replenishment port 20 is constant. Here, since the supply motor M is rotated at a speed of 5 rotations / second, the time required for the supply screw 21 to supply one block is 200 ms.

  The toner density measurement information input from the inductance sensor 19 is input to the controller 22 (see FIG. 1). Then, the controller 22 controls the rotation of the replenishing screw 21 based on the input density measurement information, and replenishes an appropriate amount of toner into the developing container 10 in time (details will be described later). The controller 22 is provided in the apparatus main body 100A. Here, the agitation screws 17a and 17b are set so that the outer diameter of the screw is 20 mm, the inner diameter of the screw is 14 mm, the screw pitch is 40 mm, and rotates at 2 rotations per second.

  FIG. 5 is a plan view showing the configuration of the stirring screw 17b, the flag 50, and the photo interrupter 51. The detection device 52 includes a flag 50 and a photo interrupter 51. Such a detection device 52 is provided in the stirring screw 17b.

  The detection device 52 that is “detection means” is a device that detects a phase in which the stirring screw 17 b rotates. The detection device 52 includes a flag 50 that is a “convex portion” provided on the shaft 17 b 1 and a photointerrupter 51 that is a “sensor” that detects the rotation of the flag 50. Since the stirring screw 17b rotates at 2 rotations per second, the output signal obtained by the photo interrupter 51 is obtained at a cycle of 500 ms. The controller 22 calculates the phase in which the stirring screw 17b rotates from the detection result detected by the detection device 52. Then, based on the calculation result, the controller 22 controls the timing at which the replenishing device 200 replenishes toner toward a recess (between adjacent blades 17b2 and 17b2) formed in the screw shape of the stirring screw 17b. .

  FIG. 6 is an enlarged schematic diagram showing the positional relationship between the blade 17 b 2 of the stirring screw 17 b and the replenishing port 20 when the flag 50 blocks the photo interrupter 51. The timing at which the toner is replenished from the replenishing device 200 to the second chamber 16 is the timing at which the central positions of the pitches of the blades 17b2 and 17b2 of the adjacent agitating screw 17b are located vertically below the replenishing port 20 of the replenishing device 200. is there. In other words, when the replenishing device 200 replenishes toner, the replenishment position where the replenishing device 200 replenishes and the intermediate position S of the pitch of the blades 17b2 overlap the stirring screw 17b in the developer transport direction L1 (L). It is timing. The replenishing device 200 has a replenishing port 20 for replenishing toner. The length J of the replenishing port 20 in the developer transport direction L1 (L) is shorter than the pitch K of the blades 17b2.

  It should be noted that the intermediate position S of the pitch between the adjacent blades 17b2 and 17b2 is not necessarily limited to the position immediately below the supply port 20. That is, it is considered that there may be a case where any part of the concave portion formed by the adjacent blade 17b2 and the blade 17b2 may be disposed directly below the supply port 20.

  FIG. 7 is a block diagram of the controller 22. The controller 22 (toner supply control device) includes a comparison circuit 31, a density standard value information unit 30, a supply toner amount calculation unit 34, a supply toner amount integration unit 35, a comparison circuit 32, and a drive control unit 33. An inductance sensor 19 is connected to the controller 22. In addition, a replenishment motor M and a replenishment screw 21 are sequentially connected to the controller 22 in series. The controller 22 is provided in the apparatus main body 100A.

  Specifically, the connection state is as follows. The comparison circuit 31 is connected to the inductance sensor 19, the density standard value information unit 30, and the replenishment toner amount calculation unit 34. Further, a replenishment toner amount calculation unit 34, a replenishment toner amount integration unit 35, a comparison circuit 32, and a drive control unit 33 are connected in series in order. Further, a replenishment motor M is connected to the drive control unit 33, and a replenishment screw 21 is connected to the replenishment motor M. In the following description, as an example, the amount of toner to be replenished when the replenishment screw 21 makes one revolution (planned toner amount c) is 100 mg, and the amount of toner necessary for each sheet of transfer material P (supplementary toner) The amount a) is 10 mg.

  First, the comparison circuit 31 receives detection information on the magnetic permeability of the developer detected by the inductance sensor 19 that detects the toner concentration inside the second chamber 16 of the developing container 10. For example, the comparison circuit 31 receives the output value (density measurement value) of the magnetic permeability of the developer necessary for each sheet of the transfer material P detected by the inductance sensor 19. The comparison circuit 31 receives an output value (concentration standard value) of the magnetic permeability of the developer necessary for one sheet of the transfer material P held by the density standard value information unit 30. For example, the density standard value information is an average value or the like of the output value of the magnetic permeability of the developer necessary for one sheet of the transfer material P (toner density information), and such information is received.

  The comparison circuit 31 compares the measured density value of the inductance sensor 19 and the density standard value held by the density standard value information unit 30. For example, assume that the toner consumption per sheet of transfer material P is 10 mg. For example, in this case, the comparison circuit 31 compares the density measurement value (magnetic permeability information corresponding to the toner amount of 10 mg) and the density standard value (magnetic permeability information corresponding to the toner amount of 10 mg).

  The replenishment toner amount calculation unit 34 receives the comparison information (comparison data) of the comparison circuit 31 and calculates the replenishment toner amount a (toner amount 10 mg) to be replenished. Further, the replenishment toner amount integration unit 35 sequentially integrates the replenishment toner amount a to derive the integration toner amount b (toner amount 100 mg).

  The comparison circuit 32 holds a predetermined toner amount c to be supplied from the supply port 20 to the second chamber 16 when the supply screw 21 makes one rotation. The scheduled toner amount c can also be said to be a unit rotation replenishment amount that the replenishment screw 21 makes one revolution. Then, the comparison circuit 32 compares the accumulated toner amount b and the scheduled toner amount c. The drive control unit 33 controls whether or not the replenishment motor 21 is driven by driving the replenishment motor M based on the information of the comparison circuit 32.

  In this case, the comparison circuit 32 determines that the accumulated toner amount b (10 mg × 10 sheets = 100 mg) accumulated by the replenishment toner amount integrating unit 35 as 10 sheets of the transfer material P is larger than the planned toner amount c (100 mg). Judge whether it is large or not.

  FIG. 8 is a flowchart showing the control process of the controller 22. That is, the toner supply operation during image formation in the developing device 4 is shown. The controller 22 starts the developing operation by rotating the developing sleeve 11. At the same time, the controller 22 starts stirring of the developer t by rotating the stirring screws 17a and 17b inside the developing container 10 (S1). At this time, the inductance sensor 19 measures the toner density by detecting the magnetic permeability of the toner inside the second chamber 16 of the developing container 10, and outputs the information to the controller 22 (comparing circuit 31) (S2). ).

  The controller 22 (comparison circuit 31), when controlling the toner density during the image forming operation, measures the toner density measurement value information (density measurement value) from the inductance sensor 19 and the toner density held by the density standard value information section 30. Standard value information (concentration standard value) is compared (S3). Then, the controller 22 (replenishment toner amount calculation unit 34) determines how much the density measurement value is deviated from the density standard value, and calculates a replenishment toner amount a corresponding to the consumed toner amount (S3). .

  The controller 22 (replenishment toner amount integration unit 35) integrates the replenishment toner amount a. Here, the controller 22 (comparison circuit 32) stores in advance a planned toner amount c to be conveyed when the replenishment screw 21 makes one rotation.

  The controller 22 (comparison circuit 32) determines whether or not the integrated toner amount b is larger than a predetermined toner amount c (S4). If the result of the determination in S4 is YES, the controller 22 determines whether or not a replenishment possible timing, which will be described later, is reached (S5), and if NO, it is determined whether or not printing is complete (S7). Note that the determination in S4 is based on the phase of the stirring screw 17b detected by the flag 50 and the photo interrupter 51 in the first embodiment. Further, in Example 2 described later, this is based on the phase of the stirring screw 17b detected by the photo interrupter 51.

  If the result of determination in S5 is YES, the controller 22 determines whether or not printing has ended after turning on the replenishment operation (S6) (S7). It is determined whether or not (S7). If the result of determination in S7 is YES, the controller 22 ends the developing operation, and if NO, the controller 22 starts the developing operation again.

  As described above, when the cumulative toner amount b exceeds the scheduled toner amount c (S4), and when it is time to replenish (S5), the drive control unit 33 rotates the replenishment screw 21 once (one block). ) Is driven for replenishment (S6). The controller 22 performs the following when the amount of toner required for the replenishing device 200 exceeds the amount of toner that can be replenished when the replenishing device 200 replenishes toner. That is, the controller 22 temporarily stops the toner supply operation, and then supplies the toner again at the timing when the supply device 200 supplies the toner.

  FIG. 9A is a graph showing the timing at which the photo interrupter 51 detects the flag 50 of the stirring screw 17b. FIG. 9B is a graph showing the timing for driving the supply motor M of the supply screw 21. FIG. 9C is a graph showing the timing for transmitting a trigger for starting the driving of the supply motor M of the supply screw 21. Here, the timing at which the replenishment toner falls on the stirring screw 17b of the second chamber 16 by the rotation of the replenishing screw 21 is determined to be an intermediate position S between the adjacent blades 17b2 and 17b2. .

  As shown in FIG. 9A, when one cycle of the stirring screw 17b is 500 ms, the timing when the flag 50 blocks the photo interrupter 51 is every 500 ms. As described above, the timing at which the flag 50 blocks the photo interrupter 51 is set to the timing at which the intermediate position between the blades 17b2 of the stirring screw 17b comes below the supply port 20.

  As shown in FIG. 9B, the timing at which the replenishment screw 21 can be driven is synchronized with the timing at which the flag 50 is turned on. Here, the 125 ms region before and after the timing when the output of the flag 50 is turned ON is set as a drivable region (supplementary region) where the replenishment motor M is driven. That is, the replenishment motor M is driven 125 ms before the flag 50 is turned on, and the replenishment motor M is stopped 125 ms after the flag 50 is turned on.

  As shown in FIG. 9C, the trigger timing for starting the driving of the supply screw 21 is the timing of the first 50 ms in the drivable region in which the supply motor M is driven. This is because the time required for one rotation of the replenishment screw 21 is 200 ms, and in order to end the replenishment operation within the drivable region of the replenishment motor M, a replenishment operation signal within 50 ms minus 200 ms. By having to send.

  In the timing chart of FIG. 9, the drop time during which the toner falls from the replenishing port 20 to the stirring screw 17 b is expressed as zero for easy understanding. Actually, it is necessary to take this into consideration when the toner drops from the replenishing port 20 to the stirring screw 17b. In the positional relationship shown in FIG. 1, the dropping time takes about 30 ms. Accordingly, the driveable area of the replenishment motor M in FIG. 9B and the transmission possible area of the replenishment start trigger of the replenishment motor M in FIG. 9C are at a timing shifted to the left by about 30 ms.

  Next, the effect by the structure of Example 1 is described. In the first exemplary embodiment, the replenishment control causes the replenishment toner to fall to the middle position S of the screw interval of the agitating screw 17b, thereby increasing the chance of contact with the developer and efficiently replenishing the replenishment toner with friction. Yes. This will be described in detail below.

  FIG. 10 is a conceptual diagram showing the relationship between the stirring screw 17b and the developer surface J. When the stirring screw 17b is driven, the surface of the blade 17b2 of the stirring screw 17b moves in the developer transport direction L and the developer is pushed in the developer transport direction L. For this reason, the developer level distribution of the developer while the stirring screw 17b is driven becomes a wave shape following the phase of the stirring screw 17b.

  Therefore, the “intermediate position S between the blade 17b2 and the blade 17b2 adjacent to the stirring screw 17b”, which is the position where the replenishing toner is dropped in the first embodiment, is the developer surface distribution (hereinafter referred to as “developer surface wave”). The developer surface E corresponds to a phase portion with a low period. Since the toner replenished to a position where the developer surface J is low is easily contacted and mixed with the surrounding developer as the stirring screw 17b rotates, the toner is efficiently triboelectrically charged.

  On the other hand, in the conventional replenishment control, since toner is replenished at an arbitrary timing, the replenished toner may naturally be replenished at a high position on the developer surface J. In this case, the replenished toner is transported so as to float on the upper surface of the developer surface J, and is difficult to be mixed with the developer present in the second chamber 16 in advance.

  FIG. 11 shows a result of analyzing the toner charge amount distribution in the developer by randomly extracting the developer from the inside of the developing container 10 after performing 100-sheet continuous printing with a solid image and performing a durability test. It is a graph. In the test, the amount of charged toner of 3000 toners in the developer was analyzed using an E-spurt analyzer manufactured by Hosokawa Micron. The vertical axis represents the number, and the horizontal axis represents the charge density (Charge Density (μC / g)).

  A solid line A indicates a toner charge amount distribution of the developer that is completely stirred and mixed. A solid line B indicates a toner charge amount distribution of the developer of the image forming apparatus to which the present invention is not applied. A dotted line C indicates a toner charge amount distribution of the developer of the image forming apparatus 100 to which the present invention is applied.

  As shown by the solid line B, in the image forming apparatus to which the present invention is not applied, the number of toners that are not sufficiently charged is increased compared with the initial toner charge amount distribution of the developer, and the agitation / mixing of the replenishment toner is poor. Is happening. In contrast, as indicated by the dotted line C, it can be seen that in the image forming apparatus 100 to which the present invention is applied, the toner charge amount distribution of the developer is almost the same as that of the initial developer and is completely stirred and mixed.

  Next, the configuration of the developing device of Example 2 will be described. Regarding the same configuration and effects as those of the developing device 4 of the first embodiment in the developing device of the second embodiment, the same reference numerals are used and the description thereof is omitted as appropriate. Since the second embodiment can be applied to the same image forming apparatus as that of the first embodiment, the description of the image forming apparatus is omitted. In particular, the configuration and control other than those relating to the phase detection of the stirring screw 17b are the same as in the first embodiment. The developing device of the second embodiment is different from the developing device 4 of the first embodiment in the following points.

  In Example 1, the phase of the stirring screw 17b was detected by the flag 50 and the photo interrupter 51 provided on the shaft 17b1. In the second embodiment, the controller 22 calculates the phase in which the stirring screw 17b rotates based on the detection result of the inductance sensor 19. That is, the phase of the stirring screw 17b is calculated based on the detection result of the increase / decrease in the output value of the inductance sensor 19 that occurs as the stirring screw 17b is driven.

  As is well known, the inductance sensor calculates the mixing ratio of toner and magnetic carrier by detecting the magnetic permeability of the developer. The magnetic permeability of the developer varies depending on the bulk density of the developer in addition to the toner mixing ratio. For example, when the bulk density is high, the magnetic carrier density is high even at the same toner mixing ratio, so that the magnetic permeability is detected high. The developer being driven by the agitating screw 17b is pushed close to the screw surface on the developer conveying direction L side, and hence the developer has a high bulk density. On the other hand, the developer on the screw surface in the direction opposite to the developer conveying direction. Developer bulk density tends to be low.

  FIG. 12 is a graph showing the relationship between the output value of the inductance sensor 19 and the time. When the agitating screw 17b is driven, the output value of the inductance sensor 19 installed in the developing container 10 is proportional to the phase of the blade 17b2 and changes with time as shown in FIG. In the second embodiment, by utilizing this phenomenon, the screw phase of the stirring screw 17b can be detected.

  As shown in FIG. 2, in Example 1, the position of the inductance sensor 19 attached to the second chamber 16 and the position of the supply port 20 are different. Therefore, it is necessary to adjust the amplitude timing of the magnetic permeability and the phase timing of the stirring screw 17b at the position of the replenishing port 20.

  On the other hand, in the second embodiment, the timing for detecting the maximum value of the permeability amplitude in FIG. 12 is aligned with the intermediate position S (center position) between the blades 17b2 shown in FIG. The position of the inductance sensor 19 is determined. Therefore, in the second embodiment, the replenishment timing is determined according to the timing chart of FIG.

  FIG. 13A is a graph showing the timing at which the inductance sensor 19 detects the maximum value of the magnetic permeability of the developer inside the second chamber 16. FIG. 13B is a graph showing the timing for driving the supply motor M of the supply screw 21. FIG. 13C is a graph showing the timing for transmitting a trigger for starting the driving of the supply motor M of the supply screw 21. Here, the timing at which the replenishment toner falls on the stirring screw 17b of the second chamber 16 by the rotation of the replenishing screw 21 is determined to be an intermediate position S between the adjacent blades 17b2 and 17b2. . In the second embodiment, the timing of detecting the phase of the stirring screw 17b is executed at the same replenishment timing as in the first embodiment except that the maximum value of the magnetic permeability of the inductance sensor 19 is used. .

  According to the configuration of the first or second embodiment, the toner is selectively replenished to a region where the height of the developer surface J of the developer conveyed by the stirring screw 17b is low in the developing container 10. As a result, the toner replenished by the replenishing device 200 and the two-component developer inside the developing container 10 are improved in agitation and mixing properties. As a result, without causing an increase in the size of the apparatus main body 100A and an increase in cost, it is possible to eliminate problems such as color fluctuations and fogging due to poor agitation of the replenished toner and form a good image. Further, since the replenishing device 200 replenishes the toner toward the region where the height of the developer conveyed by the stirring screw 17b is low, the developer inside the developing container 10 and the toner replenished by the replenishing device 200 are the same. , Stirrability and mixing properties are improved.

  According to the configuration of the second embodiment, the inductance sensor 19 provided inside the developing container 10 detects the phase of the stirring screw 17b. For this reason, it is possible to replenish toner selectively in the central region between the blades 17b2 as in the first embodiment, and the same effect can be obtained.

  In the first embodiment, the block replenishment method in which the replenishment screw 21 is always rotated by one rotation unit so as to be hardly affected by the pulsation of the replenishment toner has been described. However, the present invention is not limited to this. For example, even if the replenishing device does not replenish the toner by rotating the replenishing screw 21 in units of one rotation, and the replenishing device has a constant toner replenishing amount per unit time, the toner moves toward the position between the blades 17b2 of the stirring screw 17b. If replenished, the same effect can be obtained.

  Further, although an inductance sensor is used for toner density control in the first embodiment, the present invention is not limited to this, and a method of detecting the developer density with an optical sensor or the like may be used.

4 Developing device 10 Developing container (Developing device body)
11 Development sleeve (developer carrier)
16 Second chamber (stirring chamber)
17b Stir screw (stirring member)
22 controller 52 detection device (detection means)
100 Image forming apparatus 200 Replenishment device (replenishment means)

Claims (7)

A rotatable developer carrying member for carrying a two-component developer having toner and carrier,
A screw-shaped stirring member that mixes while stirring the two-component developer inside the stirring chamber of the developing device;
Replenishment means for replenishing toner to the developing device;
Detecting means for detecting a phase in which the stirring member rotates;
A controller that controls the timing at which the replenishing means replenishes toner toward the recess formed in the screw shape of the stirring member based on the detection result detected by the detecting means;
An image forming apparatus comprising: The stirring member has a shaft and a blade portion protruding from the shaft,
The timing at which the replenishing unit replenishes toner is a timing at which the replenishing position at which the replenishing unit replenishes and the center position of the pitch of the blade portions overlap the stirring member in the developer transport direction. The image forming apparatus according to 1. The detection means is a sensor that detects the rotation of the convex part provided on the shaft and the convex part,
The image forming apparatus according to claim 2, wherein the controller calculates a phase in which the stirring member rotates based on a detection result of the sensor. The detection means is a detection device that detects the magnetic permeability of the two-component developer inside the development device,
The image forming apparatus according to claim 2, wherein the controller calculates a phase in which the stirring member rotates based on a detection result of the detection device. The supply means has a supply port for supplying toner,
The image forming apparatus according to claim 2, wherein a length of the replenishing port in a developer transport direction is shorter than a pitch of the blades.   The controller temporarily stops the toner replenishment operation when the amount of toner required for the replenishing unit exceeds the amount of toner that can be replenished when the replenishing unit replenishes the toner. The image forming apparatus according to claim 1, wherein the replenishing unit replenishes the toner again at a timing when the toner is replenished. An image forming unit for forming an image;
A rotatable developer carrying member for carrying a two-component developer having toner and carrier,
A screw-shaped stirring member that mixes while stirring the two-component developer inside the stirring chamber of the developing device;
Replenishment means for replenishing toner to the developing device;
Detecting means for detecting a phase in which the stirring member rotates,
A process detachably attachable to the main body of the image forming apparatus having a controller for controlling the timing at which the replenishing means replenishes toner toward the recess formed in the screw shape of the stirring member based on the detection result detected by the detecting means. cartridge.

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