JP5903365B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus provided with a developing device employing a developer containing toner.

  An image forming apparatus such as a copying machine, a printer, or a facsimile using an electrophotographic system supplies a developer to an electrostatic latent image formed on an image carrier (for example, a photosensitive drum or a transfer belt) and supplies the developer. By developing the electrostatic latent image, a toner image is formed on the image carrier. As one of the developing methods, a touch-down developing method using a two-component developer containing a non-magnetic toner and a magnetic carrier is known. In this case, a two-component developer layer (so-called magnetic brush layer) is carried on the magnetic roller, and the toner is moved from the two-component developer layer on the development roller to carry the toner layer. Further, the electrostatic latent image is visualized by supplying toner from the toner layer to the image carrier.

  Patent Document 1 discloses a technique in which a developing bias in which an AC bias is superimposed on a DC bias is applied to a developing roller during a developing operation and a non-developing operation in which the developing operation is not performed.

JP-A-7-92804

  When a DC bias and an AC bias are applied to the developing roller as in the technique described in Patent Document 1, the external additive added to the toner is separated from the toner by the AC bias and moved to the image carrier side. There was. Examples of such external additives include titanium oxide added mainly for the purpose of maintaining the chargeability of the toner and promoting the polishing action on the surface of the image carrier. The external additive is not only consumed on the image carrier side with the toner during the developing operation, but also in the non-developing operation, the external additive may be consumed alone on the image carrier side by the AC bias. Further, during the developing operation, when the toner image printing rate is low, the external additive is easily consumed from the developing device alone. On the other hand, when the printing rate is high, the external additive is supplied together with new toner to the developing device, so that the amount of the external additive in the developing device is relatively increased. Further, there has been a problem that the change in the amount of the external additive in the developing device changes the chargeability of the toner, resulting in density fluctuations and toner fogging.

  When the developing device is mounted on the image forming apparatus, if the developer stored in the developing device is new, the amount of the external additive as described above may be significantly changed. That is, a new developer contains a relatively large amount of external additives. For this reason, many external additives are contained in the developing device at the initial stage where the developing device is used. Further, when the developing roller mounted on the developing device is a new one, there is a problem that the external additive tends to adhere to the peripheral surface of the developing roller and the density fluctuation of the toner image is likely to occur.

  The present invention has been made to solve the above-described problems, and even when a new developer is introduced into the developing device or when a new developing device is attached to the apparatus main body, An object of the present invention is to provide an image forming apparatus in which the amount of the specific component of the developer in the developing device is stably maintained.

An image forming apparatus according to one aspect of the present invention includes an apparatus main body, an image carrier that forms an electrostatic latent image on a surface thereof, and carries a toner image, and is attached to the apparatus main body, to which an external additive is added. A developer housing for storing a developer containing toner; a toner carrier disposed in the developer housing, driven to rotate, carrying the toner layer made of toner, and supplying the toner to the image carrier; and the toner A bias applying unit configured to apply a bias in which an AC bias is superimposed on a DC bias to form a predetermined potential difference between the image carrier and the toner carrier; and the toner image on the image carrier. A first developing bias is applied to the bias applying means during a developing operation, and a second developing bias is applied to the bias applying means during a non-developing operation different from the developing operation. That the bias control means, the first condition the developer housing is mounted containing the toner carrier unused to the apparatus main body, or the second to the developer unused in the developing housing is stored corresponding to the condition, have a, and the external additive consumption means for consuming said image bearing member the external additive from the toner carrier in the developer, the external additive consumption means, the bias The external developing agent is consumed by controlling the control means to change the second development bias, and the amplitude of the AC bias in the first development bias is greater than the amplitude value of the AC bias. In the duty ratio of the AC bias, the amplitude value of the AC bias is set to be large, or the polarity of the AC bias on the side where the toner moves from the toner carrier to the image carrier. By setting the duty ratio of the second developing bias smaller than the duty ratio of the image bias, the polarity of the second developing bias on the side where the toner moves from the toner carrier to the image carrier is increased. A potential difference between the maximum peak value of the AC bias and the surface potential of the image carrier is changed .

According to this configuration, even when a developing housing including an unused toner carrier is attached to the apparatus main body (first condition), or when unused developer is stored in the developing housing. even (second condition), the external additive consumption means, to consume the image carrier external additives in the developer from the toner carrying member. Therefore, a predetermined period of time, compared to the developer used, also include a number of external additive in the unused developer stably the amount of external additive in the developer housing Can be maintained. Further, it is preferable to prevent a large amount of external additives from adhering to the unused toner carrier. In addition, according to this configuration, the amount of the external additive in the development housing is stabilized even when many external additives are contained in the unused developer as compared with the used developer. Can be maintained. Further, it is preferable to prevent a large amount of external additives from adhering to the unused toner carrier. Further, according to this configuration, the external additive is suitably consumed by changing the second development bias during a non-development operation different from the development operation. For this reason, the amount of the external additive in the developing housing can be stably maintained without affecting the developing operation. Further, according to this configuration, during the non-development operation, the amount of movement of the external additive toward the image carrier is suitably changed by changing the potential difference between the maximum peak value of the AC bias and the image carrier. Is done. Furthermore, according to this configuration, the potential difference between the maximum peak value of the AC bias and the image carrier is preferably increased by increasing the amplitude value of the AC bias in the second developing bias or reducing the duty ratio. For this reason, the movement of the external additive from the toner carrier to the image carrier is promoted.

  In the above configuration, the external additive is preferably titanium oxide.

  According to this configuration, the amount of titanium oxide in the developing housing can be stably maintained.

In the above-described configuration, the image carrier and the toner carrier are the same in regions facing each other during a development operation in which the toner image is formed on the image carrier and a non-development operation different from the development operation. has a rotation driving means for rotationally driving direction, the external additive consumption means, wherein during the non-development operation, by increasing the rotational speed ratio of the toner carrying member to said image bearing member, the external additive It is desirable to consume.

According to this configuration, during the non-development operation, the rotation speed ratio of the toner carrier to the image carrier is increased. For this reason, the contact time for the toner layer to contact the image carrier is increased, and the movement of the external additive from the toner carrier to the image carrier is promoted.

In the above configuration, the image forming apparatus further includes an image quality adjusting unit that performs image quality adjustment of the toner image, and the external additive consuming unit performs the first condition or before the image quality adjusting unit performs the image quality adjustment. It is desirable to consume the external additive corresponding to the second condition.

According to this configuration, even when the amount of the external additive in the developing housing affects the chargeability of the toner, the image quality adjustment is performed after the amount of the external additive is adjusted. For this reason, the image quality adjustment is realized stably.

In the above configuration, the external additive consumption means, before the start of the developing operation of the toner image is formed on said image bearing member, a predetermined time, it is desirable to consume the external additive.

According to this configuration, the amount of the external additive is concentrated and adjusted before the development operation is started. For this reason, the developing operation is started with the amount of the external additive in the developing housing being suitably adjusted.

In the above configuration, the external additive consuming unit is in a non-development operation different from a development operation in which the toner image is formed on the image carrier, and when an image is formed on a plurality of sheets. It is desirable to consume the external additive between the sheets between one sheet and the subsequent sheet.

According to this configuration, the external additive is consumed between the sheets of the plurality of sheets. For this reason, it is possible to start the developing operation earlier than when the external additive is consumed for a predetermined time before the developing operation is started.

  In the above configuration, the developer in the developing housing is received while rotating in a predetermined direction, and the developer carrying member carrying the developer layer and the developing member while rotating in contact with the developer layer. It is desirable to have the toner carrier that receives the toner from the agent layer and carries the toner layer.

According to this configuration, the amount of the external additive in the developing housing is stably maintained in the image forming apparatus provided with the touch-down type developing technique in which the developer carrier and the toner carrier are disposed.

  According to the present invention, the amount of the specific component of the developer in the developing device is stabilized even when a new developer is introduced into the developing device or when a new developing device is installed in the apparatus main body. Thus, an image forming apparatus is provided that suppresses density fluctuations and toner fog generation.

1 is a cross-sectional view illustrating an internal structure of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view of a developing device according to an embodiment of the present invention. 1 is a diagram illustrating a structure inside a developing device according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating an electrical configuration of a developing device according to an embodiment of the present invention. It is the schematic diagram which showed the image development operation | movement which concerns on embodiment of this invention. 5 is a graph showing a relationship between a potential difference between a developing roller and a photosensitive drum and a flying amount of an external additive. It is a flowchart of the external additive consumption operation | movement which concerns on the 1st Embodiment of this invention. FIG. 6 is a diagram schematically showing a waveform of an AC bias constituting a developing bias. It is a schematic diagram for demonstrating the effect | action of the alternating current bias at the time of a non-development operation. It is a flowchart of the external additive consumption operation | movement which concerns on the 2nd Embodiment of this invention. It is the schematic diagram which showed the structure of the developing device which concerns on deformation | transformation embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an internal structure of an image forming apparatus 1 according to an embodiment of the present invention. Here, as the image forming apparatus 1, a multi-function machine having a printer function and a copying function is illustrated, but the image forming apparatus may be a printer, a copier, or a facsimile machine.

<Description of Image Forming Apparatus>
The image forming apparatus 1 includes an apparatus main body 10 having a substantially rectangular parallelepiped housing structure, and an automatic document feeder 20 disposed on the apparatus main body 10. In the apparatus main body 10, a reading unit 25 that optically reads a document image to be copied, an image forming unit 30 that forms a toner image on a sheet, a fixing unit 60 that fixes the toner image on a sheet, and image formation A sheet feeding unit 40 for storing sheets conveyed to the unit 30, and a conveyance path 50 for conveying the sheet from the sheet feeding unit 40 or the sheet feeding tray 46 to the sheet discharge port 10E via the image forming unit 30 and the fixing unit 60. And a conveyance unit 55 having therein a sheet conveyance path constituting a part of the conveyance path 50 is accommodated.

  An automatic document feeder (ADF) 20 is rotatably attached to the upper surface of the apparatus body 10. The ADF 20 automatically feeds a document sheet to be copied toward a predetermined document reading position in the apparatus main body 10. On the other hand, when the user manually places the document sheet on a predetermined document reading position, the ADF 20 is opened upward. The ADF 20 includes a document tray 21 on which a document sheet is placed, a document transport unit 22 that transports a document sheet via an automatic document reading position, and a document discharge tray 23 that discharges a document sheet after reading. .

  The reading unit 25 optically reads an image of a document sheet automatically fed from the ADF 20 on the upper surface of the apparatus main body 10 or a manually placed document sheet. In the reading unit 25, a scanning mechanism including a light source, a movable carriage, a reflection mirror, and the like, and an image sensor are accommodated (not shown). The scanning mechanism irradiates the original sheet with light and guides the reflected light to the image sensor. The image sensor photoelectrically converts the reflected light into an analog electric signal. The analog electric signal is converted into a digital electric signal by an A / D conversion circuit and then input to the image forming unit 30.

  The image forming unit 30 performs a process of generating a full-color toner image and transferring it onto a sheet. Yellow (Y), magenta (M), cyan (C), and black (Bk) arranged in tandem. An image forming unit 32 including four units 32Y, 32M, 32C, and 32Bk for forming the respective toner images, an intermediate transfer unit 33 disposed adjacent to the image forming unit 32, and an intermediate transfer unit 33. And a toner replenishing section 34 disposed in the.

  Each of the image forming units 32Y, 32M, 32C, and 32Bk includes a photosensitive drum 321 (image carrier) and a charger 322, an exposure unit 323, a developing device 324, and a primary transfer arranged around the photosensitive drum 321. A roller 325 and a cleaning device 326.

  The photosensitive drum 321 rotates about its axis, and an electrostatic latent image and a toner image are formed on its peripheral surface. As the photosensitive drum 321, a photosensitive drum using an amorphous silicon (a-Si) material can be used. The charger 322 uniformly charges the surface of the photosensitive drum 321. The exposure device 323 includes a laser light source and optical system devices such as a mirror and a lens, and forms an electrostatic latent image by irradiating the peripheral surface of the photosensitive drum 321 with light based on image data of a document image. .

  The developing device 324 supplies toner to the peripheral surface of the photosensitive drum 321 in order to develop the electrostatic latent image formed on the photosensitive drum 321. The developing device 324 is for a two-component developer and includes a screw feeder, a magnetic roller, and a developing roller. The details of the developing device 324 will be described in detail later.

  The primary transfer roller 325 forms a nip portion with the photosensitive drum 321 across the intermediate transfer belt 331 provided in the intermediate transfer unit 33, and the toner image on the photosensitive drum 321 is primary transferred onto the intermediate transfer belt 331. To do. The cleaning device 326 includes a cleaning roller and the like, and cleans the peripheral surface of the photosensitive drum 321 after the toner image is transferred.

  The intermediate transfer unit 33 includes an intermediate transfer belt 331, a driving roller 332, and a driven roller 333. The intermediate transfer belt 331 is an endless belt that is stretched around a driving roller 332 and a driven roller 333, and toner images from a plurality of photosensitive drums 321 are superimposed on the same portion on the outer peripheral surface of the intermediate transfer belt 331. Is transcribed. The intermediate transfer unit 33 is rotated counterclockwise in FIG.

  A secondary transfer roller 35 (transfer means) is disposed facing the peripheral surface of the drive roller 332. A nip portion between the driving roller 332 and the secondary transfer roller 35 serves as a secondary transfer portion that transfers a full-color toner image overcoated on the intermediate transfer belt 331 to a sheet. A secondary transfer bias potential having a polarity opposite to that of the toner image is applied to one of the driving roller 332 and the secondary transfer roller 35, and the other roller is grounded. In addition, the density sensor 35 </ b> A is disposed opposite to the circumferential surface of the intermediate transfer belt 331 at a position upstream of the drive roller 332 in the rotation direction of the intermediate transfer belt 331. The density sensor 35A outputs an electrical signal corresponding to the density of the image formed on the intermediate transfer belt 331.

  The toner supply unit 34 includes a yellow toner container 34Y, a magenta toner container 34M, a cyan toner container 34C, and a black toner container 34Bk. These toner containers 34Y, 34C, 34M, and 34Bk respectively store toner of each color, and are supplied to the developing devices 324 of the image forming units 32Y, 32M, 32C, and 32Bk corresponding to each color of YMCBk through a supply path (not shown). Supply toner of each color.

  The paper feed unit 40 includes two-stage paper feed cassettes 40A and 40B that accommodate sheets subjected to image forming processing. These paper feed cassettes 40A and 40B can be pulled out from the front of the apparatus body 10 toward the front.

  The fixing unit 60 is an induction heating type fixing device that performs a fixing process for fixing a toner image on a sheet, and includes a heating roller 61, a fixing roller 62, a pressure roller 63, a fixing belt 64, and an induction heating unit 65. A pressure roller 63 is pressed against the fixing roller 62 to form a fixing nip portion. The heating roller 61 and the fixing belt 64 are induction-heated by an induction heating unit 65, and give the heat to the fixing nip portion. As the sheet passes through the fixing nip portion, the toner image transferred to the sheet is fixed to the sheet.

<Configuration of developing device>
Next, the developing device 324 will be described in detail. 2 is a cross-sectional view in the vertical and horizontal directions schematically showing the internal structure of the developing device 324, and FIG. 3 is a cross-sectional view in the front and back and horizontal directions of the developing device 324. The developing device 324 includes a developing housing 80 that defines an internal space of the developing device 324. The developing housing 80 is provided with a developer storing portion 81 for storing a developer containing a non-magnetic toner and a magnetic carrier. Further, inside the developing housing 80, a magnetic roller 82 (developer carrying member) disposed above the developer reservoir 81, and a developing roller disposed opposite to the magnetic roller 82 at a position obliquely above the magnetic roller 82. 83 (toner carrier) and a developer regulating blade 84 disposed opposite to the magnetic roller 82 are disposed. Note that the developing housing 80 including these members is detachable from the apparatus main body 10.

  The developer storage unit 81 includes two adjacent developer storage chambers 81 a and 81 b extending in the longitudinal direction of the developing device 324. The developer storage chambers 81a and 81b are separated from each other by a partition plate 801 that is formed integrally with the developing housing 80 and extends in the longitudinal direction. However, as shown in FIG. 3, the communication paths 803 and 804 are formed at both ends in the longitudinal direction. Are in communication with each other. The developer storage chambers 81a and 81b accommodate screw feeders 85 and 86 that agitate and convey the developer by rotating around the axis. The screw feeders 85 and 86 are rotationally driven by a drive unit 962 described later, and their rotational directions are set in opposite directions. As a result, the developer is circulated and conveyed between the developer storage chamber 81a and the developer storage chamber 81b as shown by the arrows in FIG. By this stirring, the nonmagnetic toner and the carrier are mixed, and the nonmagnetic toner is charged positively, for example. In this embodiment, the nonmagnetic toner has an average particle size of 6.8 μm, and the carrier has an average particle size of 35 μm. Further, the toner concentration in the developing housing 80 (average weight ratio T / C between toner and carrier) is set to 11%.

  The nonmagnetic toner in this embodiment is composed of a binder resin, a colorant, and the like. Examples of the binder resin include polystyrene resins, acrylic resins, styrene-acrylic copolymers, polyethylene resins, polypropylene resins, polyvinyl chloride resins, polyester resins, polyamide resins, polyurethane resins, and polyvinyl resins. It is preferable to use a thermoplastic resin such as an alcohol resin, vinyl ether resin, N-vinyl resin, or styrene-butadiene resin.

  The colorant is not particularly limited, and examples thereof include black, magenta, cyan and yellow pigments. These colorants are usually blended in an amount of 2 to 20 parts by mass, preferably 5 to 15 parts by mass with respect to 100 parts by mass of the binder resin.

  Other additives may be added to the toner as long as the effects of the exemplary embodiment are not impaired. Examples of such additives include charge control agents and waxes. A known charge control agent can be used as the charge control agent. As the positively chargeable charge control agent, for example, a nigrosine dye, a fatty acid-modified nigrosine dye, a carboxyl group-containing fatty acid-modified nigrosine dye, a quaternary ammonium salt, an amine compound, an organometallic compound, or the like can be used.

  The wax is not particularly limited, and examples thereof include carnauba wax and Fischer-Tropsch (hereinafter sometimes referred to as “FT”) wax having ester in the side chain, synthetic hydrocarbon wax such as polyethylene wax, polypropylene wax, and the like. It is done. Among these, from the viewpoint of dispersibility, use of FT wax or polyethylene wax having ester in the side chain is recommended.

  In addition, inorganic oxide fine particles are externally added to the nonmagnetic toner as necessary. As such an external additive, fine particles such as silica fine particles, alumina, titanium oxide, zinc oxide, magnesium oxide, and strontium titanate can be used. Further, if necessary, an organic external additive such as resin fine particles can also be used. The volume average diameter of the external additive is 0.001 to 1.0 μm, preferably 0.005 to 0.3 μm. The addition amount of the external additive is preferably in the range of 0.1 to 2.0 parts by mass with respect to 100 parts by mass of the toner.

  Here, the silica fine particles are mainly used as a fluidizing agent. Titanium oxide, alumina, resin fine particles, and the like are used as toner charge control agents. Titanium oxide or the like is suitably used as an abrasive for the surface of the photoreceptor. When titanium oxide is used alone, it has a characteristic of being charged with a polarity opposite to that of the toner body.

  The magnetic roller 82 is disposed along the longitudinal direction of the developing device 324 and can be rotated clockwise in FIG. In the present embodiment, the magnetic roller 82 has a diameter of 20 mm. A fixed so-called magnet roll (not shown) is arranged inside the magnetic roller 82. The magnet roll has a plurality of magnetic poles. In this embodiment, the magnet roll has a drawing pole 821, a regulation pole 822, and a main pole 823. The scooping pole 821 faces the developer storage section 81, the regulation pole 822 faces the developer regulation blade 84, and the main pole 823 faces the developing roller 83.

  The magnetic roller 82 magnetically pumps (receives) the developer from the developer reservoir 81 onto its peripheral surface 82A by the magnetic force of the pumping pole 821. The developer drawn up is magnetically held as a developer layer (magnetic brush layer) on the peripheral surface 82A of the magnetic roller 82, and is conveyed toward the developer regulating blade 84 as the magnetic roller 82 rotates. .

  The developer regulating blade 84 is disposed on the upstream side of the developing roller 83 when viewed from the rotation direction of the magnetic roller 82, and regulates the layer thickness of the developer layer magnetically attached to the peripheral surface 82 </ b> A of the magnetic roller 82. The developer regulating blade 84 is a plate member made of a magnetic material extending along the longitudinal direction of the magnetic roller 82, and is supported by a predetermined support member 841 fixed at a proper position of the developing housing 80. Further, the developer regulating blade 84 has a regulating surface 842 (that is, the leading end surface of the developer regulating blade 84) that forms a regulating gap G having a predetermined size with the peripheral surface 82A of the magnetic roller 82.

  The developer regulating blade 84 formed from a magnetic material is magnetized by the regulating pole 822 of the magnetic roller 82. As a result, a magnetic path is formed between the regulating surface 842 of the developer regulating blade 84 and the regulating pole 822, that is, in the regulating gap G. When the developer layer adhering to the peripheral surface 82A of the magnetic roller 82 by the drawing pole 821 is conveyed into the regulation gap G as the magnetic roller 82 rotates, the layer thickness of the developer layer is regulated in the regulation gap G. Is done. Thereby, a uniform developer layer having a predetermined thickness is formed on the peripheral surface 82A.

  The developing roller 83 is disposed so as to extend along the longitudinal direction of the developing device 324 and in parallel with the magnetic roller 82, and can rotate clockwise in FIG. The developing roller 83 has a peripheral surface 83A that receives toner from the developer layer and carries the toner layer while rotating in contact with the developer layer held on the peripheral surface 82A of the magnetic roller 82. During the development in which the development operation is performed, the toner in the toner layer is supplied to the peripheral surface of the photosensitive drum 321. In the present embodiment, the developing roller 83 includes a urethane rubber layer on the surface. In the present embodiment, the developing roller 83 has a diameter of 20 mm.

  The developing roller 83 and the magnetic roller 82 are rotationally driven by a driving unit 962 (rotational driving means). A gap S having a predetermined dimension is formed between the peripheral surface 83A of the developing roller 83 and the peripheral surface 82A of the magnetic roller 82. The gap S is set to about 250 μm, for example. The developing roller 83 is disposed so as to face the photosensitive drum 321 through an opening formed in the developing housing 80, and a gap having a predetermined dimension is also formed between the peripheral surface 83A and the peripheral surface of the photosensitive drum 321. Yes. In the present embodiment, the gap is set to 100 μm.

<Electrical configuration, block diagram>
Next, the main electrical configuration of the image forming apparatus 1 will be described. The image forming apparatus 1 includes a control unit 90 that comprehensively controls the operation of each unit of the image forming apparatus 1. FIG. 4 is a functional block diagram of the control unit 90. The control unit 90 includes a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores a control program, a RAM (Random Access Memory) that is used as a work area of the CPU, and the like. In addition to the image forming unit 30 described above, the control unit 90 includes a first application unit 88 (bias application unit), a second application unit 89 (bias application unit), an operation unit 961, and a drive unit 962 (rotation drive unit). ), An image memory 963, an I / F 964, a developing device detector 965, and the like are electrically connected.

  The first application unit 88 includes a DC power source and an AC power source, and applies a bias to the magnetic roller 82 in the developing device 324 based on a control signal from the bias control unit 92 (bias control unit). Similarly, the second application unit 89 includes a DC power source and an AC power source, and applies a bias to the developing roller 83 in the developing device 324 based on a control signal from the bias control unit 92.

  The operation unit 961 is disposed in the apparatus main body 10 of the image forming apparatus 1. The operation unit 961 includes a touch panel (not shown), operation buttons, and the like. The user can input usage conditions of the image forming apparatus 1 from the operation unit 961. In the present embodiment, the operation unit 961 is used when an operator inputs a work history during maintenance of the image forming apparatus 1. When the operator takes out the old developer in the developing device 324 and inserts a new developer into the developing device 324, the operator inputs “new developer charging information” from the operation unit 961. In another embodiment, when the operator removes the old developing device 324 from the apparatus main body 10 and attaches a new developing device 324 to the apparatus main body, the operator supplies “new developing device attachment information” from the operation unit 961. input.

  The drive unit 962 includes a motor and a gear mechanism that transmits torque thereof, and in accordance with a control signal from the control unit 90, a developing roller 83 and a magnetic roller 82 in the developing device 324 are described during a developing operation and a non-developing operation described later. Further, the screw feeders 85 and 86 are driven to rotate. In the present embodiment, the developing roller 83, the magnetic roller 82, and the screw feeders 85 and 86 are rotationally driven in synchronization by the drive unit 962. The driving unit 962 drives the photosensitive drum 321 to rotate during the developing operation and the non-developing operation. In the present embodiment, the photosensitive drum 321 and the developing roller 83 are rotationally driven in the same direction at portions facing each other. The drive unit 962 receives a control signal output from the drive control unit 91 described later, and changes the rotation speed ratio (S / D) of the developing roller 83 with respect to the photosensitive drum 321.

  The image memory 963 temporarily stores image data for printing given from an external device such as a personal computer when the image forming apparatus 1 functions as a printer. The image memory 963 temporarily stores image data optically read by the ADF 20 when the image forming apparatus 1 functions as a copying machine.

  The I / F 964 is an interface circuit for realizing data communication with an external device. For example, the I / F 964 creates a communication signal in accordance with a network communication protocol for connecting the image forming apparatus 1 and the external device, and from the network side. Are converted into data in a format that can be processed by the image forming apparatus 1. A print instruction signal transmitted from a personal computer or the like is given to the control unit 90 via the I / F 964, and image data is stored in the image memory 963 via the I / F 964.

  When the image forming apparatus 1 is turned on, the developing device detection unit 965 confirms new / old information of the developing device 324 attached to the apparatus main body 10. Specifically, the developing device detection unit 965 detects old and new information stored in a wireless memory (not shown) attached to the developing housing 80. The usage time of the developing housing 80 in the apparatus main body 10 is overwritten in the wireless memory. In other words, in the case of a new development housing 80, the new / old information is zero.

  The control unit 90 executes a control program stored in the ROM by the CPU, so that a drive control unit 91, a bias control unit 92 (bias control unit), an image quality adjustment unit 93 (image quality adjustment unit), and a consumption condition change unit. It functions so as to include 94 (specific component consumption means).

  The drive control unit 91 controls the drive unit 962 to rotationally drive the developing roller 83, the magnetic roller 82, and the screw feeders 85 and 86. In addition, the drive control unit 91 controls the drive unit 962 to drive the photosensitive drum 321 to rotate. In the present embodiment, the drive control unit 91 rotationally drives the above members in the developing operation and the non-developing operation. Further, the drive control unit 91 receives a control signal from the consumption condition changing unit 94 and changes the rotation speed ratio of the developing roller 83 with respect to the photosensitive drum 321.

  The bias control unit 92 (bias control means) determines the bias setting values for the developing roller 83 and the magnetic roller 82 when executing the developing operation, and controls the first applying unit 88 and the second applying unit 89 to perform the first operation. 1 development bias Bd is applied. In addition, the bias control unit 92 determines a bias setting value for the developing roller 83 and the magnetic roller 82 and controls the first application unit 88 and the second application unit 89 during the non-development operation when the development operation is not performed. Then, the second developing bias Bp is applied.

  The image quality adjustment unit 93 includes a density sensor 35A that detects the density of the toner image on the intermediate transfer belt 331 described above. The image quality adjustment unit 93 is applied to the toner density in the developing device 324, the potential of the electrostatic latent image on the photosensitive drum 321 or the primary transfer roller 325 and the secondary transfer roller 35 according to the density of the toner image. Various image quality such as the density of the toner image is adjusted. The image quality adjustment unit 93 performs image quality adjustment using the case where the power source of the image forming apparatus 1 is turned on or the case where a predetermined time has passed while the power source is turned on as a trigger. The image quality adjustment unit 93 may perform image quality adjustment when temperature / humidity data detected by an environmental sensor (not shown) attached to the apparatus main body 10 changes abruptly.

  The consumption condition changing unit 94 stores the unused developer (new developer) in the first condition in which the developing housing 80 including the unused developing roller 83 is mounted on the apparatus main body 10 or in the developing housing 80. Corresponding to the second condition, a specific component in the developer is consumed from the developing roller 83 to the photosensitive drum 321. In this embodiment, the specific component is made of titanium oxide externally added to the toner. The consumption condition changing unit 94 controls the bias control unit 92 to change the second development bias Bp described later during the non-development operation, thereby consuming the specific component. At this time, the consumption condition changing unit 94 includes the maximum peak value Vpp-MAX of the AC bias having the polarity on the side where the toner moves from the developing roller 83 to the photosensitive drum 321 in the second developing bias Bp, and the photosensitive member. The potential difference from the surface potential of the drum 321 is changed. Specifically, the consumption condition changing unit 94 controls the bias control unit 92 so that the amplitude value of the AC bias at the second development bias Bp is relatively relative to the amplitude value of the AC bias at the first development bias Bd described later. To enlarge. Further, the consumption condition changing unit 94 controls the bias control unit 92 so that the duty ratio of the first developing bias Bd is the duty ratio of the AC bias having the polarity where the toner moves from the developing roller 83 to the photosensitive drum 321. On the other hand, the duty ratio of the second developing bias Bp is relatively reduced. Further, the consumption condition changing unit 94 consumes the specific component by increasing the rotation speed ratio of the developing roller 83 with respect to the photosensitive drum 321 during the non-developing operation.

<Application of development bias and development operation>
Next, with reference to FIG. 5, a configuration for bias application of the developing device 324 and a developing operation will be described. The developing device 324 includes the first applying unit 88, the second applying unit 89, and the control unit 90 described above in order to control the developing operation. As shown in the figure, the first application unit 88 has a DC voltage source 881 and an AC voltage source 882 connected in series, and is connected to the magnetic roller 82. A voltage obtained by superimposing the AC bias output from the AC voltage source 882 on the DC bias output from the DC voltage source 881 is applied to the magnetic roller 82. The second application unit 89 includes a DC voltage source 891 and an AC voltage source 892 connected in series, and is connected to the developing roller 83. A voltage obtained by superimposing the AC bias output from the AC voltage source 892 on the DC bias output from the DC voltage source 891 is applied to the developing roller 83.

  The values of the direct current bias and the alternating current bias applied to the magnetic roller 82 and the developing roller 83 are determined when the developing device 324 supplies toner onto the peripheral surface of the photosensitive drum 321 (develops the electrostatic latent image). It is changed according to the charging property of the supplied toner. Further, in the non-development operation, different bias values are applied to the magnetic roller 82 and the development roller 83.

  Next, the developing mechanism of the electrostatic latent image on the photosensitive drum 321 in the developing operation will be described. The magnetic brush layer on the peripheral surface 82 </ b> A of the magnetic roller 82 is transported toward the developing roller 83 as the magnetic roller 82 rotates after the layer thickness is uniformly regulated by the developer regulating blade 84. Thereafter, in the region of the gap S (FIG. 2), a large number of magnetic brushes DB in the magnetic brush layer come into contact with the peripheral surface 83A of the rotating developing roller 83.

  At this time, the bias control unit 92 controls the first application unit 88 and the second application unit 89 to apply predetermined DC bias and AC bias to the magnetic roller 82 and the developing roller 83, respectively. As a result, a predetermined potential difference (developing potential difference) is generated between the peripheral surface 82A of the magnetic roller 82 and the peripheral surface 83A of the developing roller 83. Due to this potential difference, only the toner T moves from the magnetic brush DB to the peripheral surface 83A at a position where the peripheral surface 82A and the peripheral surface 83A face each other (at a position where the main pole 823 (FIG. 2) faces the peripheral surface 83A). The carrier C of the magnetic brush DB and a part of the remaining toner remain on the peripheral surface 82A. At this time, the toner T is supplied from the peripheral surface 82A of the magnetic roller 82 to the peripheral surface 83A of the developing roller 83. Accordingly, the toner layer TL having a predetermined thickness is carried on the peripheral surface 83A of the developing roller 83.

  The toner layer TL on the circumferential surface 83A is conveyed toward the circumferential surface of the photosensitive drum 321 as the developing roller 83 rotates. A superimposed voltage of a DC voltage and an AC voltage is applied to the developing roller 83. Therefore, a predetermined potential difference is generated between the peripheral surface of the photosensitive drum 321 having a potential on the surface according to the electrostatic latent image and the peripheral surface 83A of the developing roller 83. Due to this potential difference, the toner T in the toner layer TL moves to the peripheral surface of the photosensitive drum 321. Thereby, the electrostatic latent image on the peripheral surface of the photosensitive drum 321 is developed, and a toner image is formed.

  In the present embodiment, the bias controller 92 controls the first application unit 88 and the second application unit 89 during the development operation, and an example of the first development bias Bd applied to the magnetic roller 82 and the development roller 83. And other conditions are as follows.

<First Development Bias Bd1 and Other Conditions>
DC bias Vmag_dc of magnetic roller 82; 200V
DC bias Vslv_dc of developing roller 83; 50V
AC roller bias (Vpp) Vmag_ac of magnetic roller 82; 300V (4.0 kHz)
AC bias of developing roller 83 (Vpp) Vslv_ac; 1700 V (4.0 kHz)
Duty ratio of the bias between the photosensitive drum 321 and the developing roller 83 (Duty 1); 43%
Duty ratio of bias between developing roller 83 and magnetic roller 82 (Duty 2); 57%
Linear speed of photosensitive drum 321; 200 mm / sec
Surface potential of photosensitive drum 321; background portion (dark potential) 230V, image portion (bright potential) 20V
Rotational speed ratio of developing roller 83 to photosensitive drum 321 (S / D); 1.5
Toner chargeability Q / m; 20 μC / g

<Description of non-development operation>
Next, the non-developing operation in the developing device 324 in this embodiment will be described. This non-development operation is a timing at which the previous development operation is not performed, for example, before and after the image forming operation in which an image is formed on a sheet, or after one sheet when an image is formed on a plurality of sheets and thereafter The process is executed corresponding to the interval between the sheets between successive sheets.

  In the non-development operation, as in the development operation, each member of the developing device 324 including the developing roller 83 is rotated in addition to the photosensitive drum 321. Then, by applying the second developing bias Bp to the developing roller 83 and the magnetic roller 82, a toner layer is formed on the developing roller 83 in preparation for the developing operation. In the non-development operation, the toner is preliminarily formed on the development roller 83 to cope with the rapid consumption of the toner from the development roller 83 toward the photosensitive drum 321 when the development operation is started. Can do. In addition, in a non-development operation performed between sheets or after image formation, a part of the toner carried on the development roller 83 during the development operation is moved to the magnetic roller 82 side, so that The toner is preferably replaced, and the charging property of the toner on the developing roller 83 is stably maintained.

<Specific components of developer>
In developing and non-developing operations, toner carried on the developing roller 83 by an AC bias electric field formed between the magnetic roller 82 and the developing roller 83 or between the developing roller 83 and the photosensitive drum 321. In some cases, the external additive (specific component) is detached from the photosensitive drum 321 and moved to the photosensitive drum 321 side. 6 shows the maximum peak value Vpp-MAX of the AC bias in the polarity on the side where the toner moves from the developing roller 83 to the photosensitive drum 321 among the developing bias applied to the developing roller 83 and the dark potential of the photosensitive drum 321. 3 is a graph showing the amount of the external additive flying to the photosensitive drum 321 when the potential difference between and is changed. As described above, the external additive is consumed independently from the developing device 324 to the photosensitive drum 321 according to the AC bias component applied to the developing roller 83.

  The external additive is not only consumed with the toner during the developing operation, but is also consumed by the AC bias alone on the image carrier side during the non-developing operation. Further, when the printing rate of the toner image is low during the developing operation, the external additive is consumed by itself on the background potential portion of the photosensitive drum 321. On the other hand, when the printing rate is high, external additive is supplied from the toner supply unit 34 to the developing device 324 together with new toner. For this reason, the amount of the external additive in the developing device 324 is relatively increased. Further, the change in the amount of the external additive in the developing device 324 causes a change in toner chargeability, resulting in a density change and a toner fog on the image. That is, when the amount of the external additive is excessive, toner fog occurs, and when the amount of the external additive is excessive, the density is lowered due to poor chargeability of the toner.

  Further, when the developing device 324 is mounted on the apparatus main body 10 of the image forming apparatus 1 and the developer (toner) stored in the developing device 324 is new, the amount of the external additive as described above is used. Fluctuations can occur significantly. That is, a new developer contains a relatively large amount of external additives. For this reason, many external additives are included in the developing device 324 at the initial stage where the new developing device 324 starts to be used. In addition, such a phenomenon of excessive external additives occurs when the developer stored in the interior is replaced with a new developer without being replaced with the developing device 324 (developing housing 80). ) Can also occur. Further, when the developing roller 83 attached to the developing device 324 is new, there is a problem that the external additive tends to adhere to the peripheral surface of the developing roller 83 made of urethane rubber, and the density fluctuation of the toner image easily occurs.

  In the present embodiment, in order to solve the above-described problems, the first condition in which the developing device 324 including the unused developing roller 83 is mounted on the apparatus main body 10 or the unused developer on the developing housing 80 is used. Corresponding to the stored second condition, the consumption condition changing unit 94 causes the external additive to be consumed from the developing roller 83 to the photosensitive drum 321. Hereinafter, a first embodiment of the external additive consuming operation of the present invention will be described with reference to FIG.

  FIG. 7 is a first flowchart when the consumption condition changing unit 94 consumes the external additive in the present embodiment. In the present embodiment, the consumption condition changing unit 94 transfers the external additive from the developing roller 83 to the photosensitive drum corresponding to the first condition in which the developing device 324 including the unused developing roller 83 is attached to the apparatus main body 10. 321 is consumed.

  In the present embodiment, the first developing bias Bd is referred to as a first developing bias Bd11. Referring to FIG. 7, when the image forming apparatus 1 is powered on (step S001), the developing device detection unit 965 determines whether the developing device 324 is new or old (step S002). When the developing device detection unit 965 detects zero as new / old information stored in the wireless memory of the installed developing device 324, the developing device detection unit 965 determines that the developing device 324 is new (in step S002). YES). In this case, the consumption condition changing unit 94 determines that the consumption operation of the external additive is necessary (step S003). First, the consumption condition changing unit 94 determines whether or not the number of printed sheets has reached 100 in the image forming apparatus 1 whose power is turned on (step S004). If the number of printed sheets has not reached 100 after the power is turned on (YES in step S004), the consumption condition changing unit 94 sets the second developing bias Bp in the interval between sheets being printed (non-developing operation) to the second developing. The bias Bp12 is set. In other words, the consumption condition changing unit 94 increases the Vpp of the second development bias Bp12 as compared with the first development bias Bd11 during the development operation. Further, the consumption condition changing unit 94 reduces the duty ratio of the second developing bias Bp12 as compared with the developing bias Bd11.

  Further, in the present embodiment, when the second developing bias Bp12 is selected in step S005, the photosensitive drum 321 and the developing roller 83 are rotationally driven at a rotational speed ratio different from that during the developing operation. In this case, the consumption condition changing unit 94 controls the drive control unit 91 to increase the rotation speed of the developing roller 83 as compared with the developing operation. As a result, the rotation speed ratio (S / D) of the developing roller 83 with respect to the photosensitive drum 321 is increased.

  On the other hand, if it is determined in step S004 that the number of printed sheets has exceeded 100 after the power is turned on (NO in step S004), the consumption condition changing unit 94 sets the second developing bias Bp between sheets. Then, the second developing bias Bp11 is set (step S006). In other words, the consumption condition changing unit 94 sets the same Vpp as the first developing bias Bd11 during the developing operation as the Vpp of the second developing bias Bp11. Further, the consumption condition changing unit 94 slightly reduces the duty ratio of the second developing bias Bp11 as compared with the developing bias Bd11. Further, the consumption condition changing unit 94 slightly increases the rotation speed of the developing roller 83 than during the developing operation. As a result, the photosensitive drum 321 and the developing roller 83 are rotationally driven with a slightly higher rotational speed ratio than during the developing operation. As described above, when the number of printed sheets exceeds 100, the consumption of the external additive is suppressed as compared with the case where the number of printed sheets is less than 100. On the other hand, even in this case, the consumption of the external additive during the non-development operation (between sheets) is promoted compared to the development operation. This is because the external additive is consumed little by little in response to the supply of the external additive together with the toner from the toner replenishing section 34 to the developing housing 80 in accordance with the formation of the toner image during the developing operation. .

  FIG. 8 is a schematic diagram showing a waveform of one cycle of the AC bias when a developing bias having a different duty ratio is applied to the developing roller 83. In addition to the effect of reducing the duty ratio in the change from the first developing bias Bd11 to the second developing bias Bp12, the duty ratio is 37% in the order of FIGS. 8A, 8B, and 8C, respectively. 40% and 43% are set. In this case, Vpp-MAX (A)> Vpp-MAX (B)> Vpp with respect to the maximum peak value (Vpp-MAX) of the AC bias in the polarity on the side where the toner is moved from the developing roller 83 to the photosensitive drum 321 side. -Changed to MAX (C). Therefore, the potential difference between the dark potential on the surface of the photosensitive drum 321 during the non-development operation and the Vpp-MAX is increased as the duty ratio is reduced. As a result, the reduction of the duty ratio promotes the consumption of the external additive from the developing roller 83 to the photosensitive drum 321. Similarly, in the change from the first developing bias Bd11 to the second developing bias Bp12, the potential difference is increased by increasing Vpp, and thus the consumption of the external additive is further promoted. When the rotation speed ratio of the developing roller 83 to the photosensitive drum 321 is increased with the selection of the second developing bias Bp12, the toner layer on the developing roller 83 is applied to the surface of the photosensitive drum 321. The contact time for contact is increased. For this reason, consumption of said external additive is further accelerated | stimulated.

  Here, an example of the second developing bias Bp and the driving condition set by the bias control unit 92 and the drive control unit 91 for the non-development operation by the control signal of the consumption condition changing unit 94 is as follows. During the developing operation, various conditions including the first developing bias Bd1 are set.

<Normal Second Development Bias Bp11 (100 or More Prints)>
DC bias Vmag_dc of magnetic roller 82; 200V
DC bias Vslv_dc of developing roller 83; 50V
AC roller bias (Vpp) Vmag_ac of magnetic roller 82; 300V (4.0 kHz)
AC bias of developing roller 83 (Vpp) Vslv_ac; 1700 V (4.0 kHz)
Duty ratio of duty between photosensitive drum 321 and developing roller 83 (Duty 1); 41%
Duty ratio of bias between developing roller 83 and magnetic roller 82 (Duty 2); 59%
Linear speed of photosensitive drum 321; 200 mm / sec
Surface potential of photosensitive drum 321; background portion (dark potential) 230V
Rotational speed ratio of developing roller 83 to photosensitive drum 321 (S / D); 1.7

<Second development bias Bp12 when promoting the consumption of external additives (less than 100 printed sheets)>
DC bias Vmag_dc of magnetic roller 82; 200V
DC bias Vslv_dc of developing roller 83; 50V
AC roller bias (Vpp) Vmag_ac of magnetic roller 82; 300V (4.0 kHz)
AC bias (Vpp) Vslv_ac of developing roller 83; 1900 V (4.0 kHz)
Duty ratio (Duty 1) of bias between the photosensitive drum 321 and the developing roller 83; 40%
Duty ratio of bias between developing roller 83 and magnetic roller 82 (Duty 2); 60%
Linear speed of photosensitive drum 321; 200 mm / sec
Surface potential of photosensitive drum 321; background portion (dark potential) 230V
Rotational speed ratio of developing roller 83 to photosensitive drum 321 (S / D); 1.8

  In the above setting example, as described above, the rotation speed ratio of the developing roller 83 to the photosensitive drum 321 is higher in the second developing bias Bp12 when the external additive consumption is promoted than in the first developing bias Bd11 during the developing operation. (S / D) is increased, the AC bias (Vpp) Vslv_ac of the developing roller 83 is increased, and the duty ratio of the bias between the photosensitive drum 321 and the developing roller 83 is reduced.

  Next, the case where the second developing bias Bp12 is applied during the non-developing operation will be described in detail with reference to FIG. FIG. 9 is a schematic diagram illustrating the relationship between the potentials of the photosensitive drum 321 and the developing roller 83 when images are formed on three sheets in the image forming apparatus 1. In FIG. 9, Vdrum indicates the time on the horizontal axis and the transition of the potential on the photosensitive drum 321 on the vertical axis. P1, P2, and P3 indicate development steps (development operations) in which toner images are formed on the first, second, and third sheets, respectively. A1 indicates a non-developing operation immediately before the developing operation for the first sheet, and A2 indicates a non-developing operation after the developing operation for the third sheet is completed. Further, B1 and B2 correspond to a so-called non-development operation between sheets, and correspond to between the sheets between the first sheet, the second sheet, the second sheet, and the third sheet, respectively.

  In the present embodiment, the photosensitive drum 321 is charged with a potential of the background portion to +250 V by the charger 322. That is, the photosensitive drum 321 is charged to +250 V corresponding to A1, P1, B1, P2, B2, P3, and A2 in FIG. Then, in the developing steps P1, P2, and P3 of each sheet, when the area corresponding to the maximum image density is exposed by the exposure unit 323, the surface potential is reduced to Vimg; + 20V. At this time, as described above, a DC bias Vslv_dc; 50 V is applied to the developing roller 83. Further, an AC bias (Vpp) Vslv_ac1; 1700 V (4.0 kHz) is applied to the developing roller 83 with a duty ratio of 43%. Further, the rotation speed ratio (S / D) of the developing roller 83 to the photosensitive drum 321 is set to 1.5. As a result, toner is supplied from the developing roller 83 to the + 20V image portion.

  On the other hand, in the non-development operations A1, B1, B2, and A2 where the above-described development operation is not performed, the photosensitive drum 321 is similarly charged to + 250V. Further, a DC bias Vslv_dc; 50V is applied to the developing roller 83 as the second developing bias Bp12, and an AC bias (Vpp) Vslv_ac2; 1900V (4.0 kHz) is applied with a duty ratio of 40%. Further, the rotation speed ratio (S / D) of the developing roller 83 to the photosensitive drum 321 is set to 1.8.

  In FIG. 9, as described above, the Vpp of the second development bias Bp12 is increased and the duty ratio is reduced in the gaps B1 and B2 as compared with the first development bias Bd11. As a result, compared to Vpp-MAX1 during the development operation (P1, P2, P3), the potential difference between the background portion potential (dark potential) Vback of the photosensitive drum 321 of Vpp-MAX2 during the non-development operation is set larger. The At this time, during the non-development operation, the image portion potential (bright potential) Vimg is not set on the photosensitive drum 321, so that an electrical leak occurs between the image portion potential Vimg and the enlarged Vpp-MAX 2. Is deterred.

  Next, a second embodiment of the external additive consuming operation will be described with reference to FIG.

  FIG. 10 is a second flowchart when the consumption condition changing unit 94 consumes the external additive. In the present embodiment, the consumption condition changing unit 94 causes the external additive to be consumed from the developing roller 83 to the photosensitive drum 321 in response to the second condition in which unused developer is stored in the developing housing 80.

  When the image forming apparatus 1 is powered on (step S011), the consumption condition changing unit 94 confirms information input by the operator from the operation unit 961 (step S012). Here, when the fact that the developer in the developing housing 80 of the developing device 324 has been replaced with a new one is input as “new developer charging information” by the operator, the consumption condition changing unit 94 is in the developing housing 80. Is determined to be replaced (YES in step S012). The consumption condition changing unit 94 determines that the external additive consumption mode needs to be executed prior to the subsequent image quality adjustment or image forming operation (development operation). (Step S013). The consumption condition changing unit 94 sets the second developing bias Bp12 described above as the second developing bias Bp, and increases the rotation speed ratio of the developing roller 83 with respect to the photosensitive drum 321 (step S014). Then, the consumption condition changing unit 94 controls the driving unit 962 in a state where the second developing bias Bp12 is applied, and rotates the developing roller 83 and the photosensitive drum 321 for 60 seconds. The driving of the developing roller 83 and the photosensitive drum 321 in the external additive consumption mode is not limited to 60 seconds, and may be rotated by 180 seconds or the like according to the amount of external additive mixed. The second developing bias Bp12 is applied to the developing roller 83, and the developing roller 83 and the photosensitive drum 321 are rotationally driven, whereby the external additive is consumed from the developing roller 83 to the photosensitive drum 321.

  When the external additive consumption mode ends, the consumption condition changing unit 94 controls the image quality adjustment unit 93 to execute the image quality adjustment of the toner image (step S015). At this time, since the amount of the external additive in the developing housing 80 of the developing device 324 is suitably adjusted, toner charging abnormality due to excessive external additive hardly occurs. For this reason, the image quality adjustment of the toner image is executed in a state where the chargeability of the toner is stably maintained.

  When the external additive consumption mode and the image quality adjustment are executed, the consumption condition changing unit 94 determines that a printing operation (development operation) is possible (step S016). Note that the first developing bias Bd11 described above may be applied to the developing roller 83 or the second developing bias Bp12 may be applied between the sheets during subsequent printing (non-developing operation). As described above, by intensively consuming the external additive as the developer in the developing housing 80 is replaced, a stable toner image can be obtained during subsequent printing. If it is not determined in step S012 that the developer in the developing housing 80 has been replaced (NO in step S012), the image quality adjustment is performed as usual without executing the external additive consumption mode.

  According to the above embodiment, even when the developing housing 80 including the unused developing roller 83 is attached to the apparatus main body 10 (first condition), the unused developer in the developing housing 80. Is stored (second condition), the consumption condition changing unit 94 causes the specific component in the developer to be consumed from the developing roller 83 to the photosensitive drum 321. For this reason, the amount of the specific component in the development housing 80 is stably maintained even when many specific components are contained in the unused developer as compared with the developer used for a predetermined period. can do. Further, it is preferable to prevent many specific components from adhering to the unused developing roller 83.

  Further, according to the above-described embodiment, the amount of the external additive in the development housing 80 can be increased even if the external developer is included in the unused developer as compared with the used developer. Can be maintained stably. Further, it is preferable to prevent a large amount of external additives from adhering to the unused developing roller 83. In particular, when titanium oxide is added as an external additive, the amount of titanium oxide in the developing housing 80 can be stably maintained. As a result, the charging property of the toner in the developing device 324 is stably maintained. Further, since the titanium oxide moved to the photosensitive drum 321 without excess or deficiency is interposed between the cleaning roller of the cleaning device 326 and the photosensitive drum 321, the surface of the photosensitive drum 321 is stably polished. .

  Further, according to the above embodiment, the specific component is preferably consumed by changing the second development bias Bp during the non-development operation different from the development operation. For this reason, the amount of the specific component in the developing housing 80 can be stably maintained without affecting the developing operation. In particular, during a non-development operation, the amount of movement of the specific component toward the photosensitive drum 321 is suitably changed by changing the potential difference between the maximum peak value Vpp-MAX of the AC bias and the photosensitive drum 321. The Specifically, the potential difference between the maximum peak value Vpp-MAX of the AC bias and the photosensitive drum 321 is preferably increased by increasing the amplitude value Vpp of the AC bias in the second developing bias Bp or reducing the duty ratio. For this reason, the movement of the specific component from the developing roller 83 to the photosensitive drum 321 is promoted.

  Further, according to the above-described embodiment, the rotation speed ratio of the developing roller 83 to the photosensitive drum 321 is increased during the non-developing operation. For this reason, the contact time for the toner layer to contact the photosensitive drum 321 is increased, and the movement of the specific component from the developing roller 83 to the photosensitive drum 321 is promoted.

  Further, according to the above-described embodiment, even when the amount of the specific component in the developing housing 80 affects the chargeability of the toner, the image quality adjustment is performed after the amount of the specific component is adjusted. . For this reason, the image quality adjustment is realized stably.

  Further, according to the above-described embodiment, the amount of the specific component is concentrated and adjusted in the consumption mode before the development operation is started. Therefore, the developing operation is started in a state where the amount of the specific component in the developing housing 80 is suitably adjusted.

  Further, according to the above-described embodiment, the specific component is consumed corresponding to the space between the sheets in the plurality of sheets. For this reason, it is possible to start the developing operation earlier than when the specific component is consumed for a predetermined time before the developing operation is started.

  Further, according to the above-described embodiment, in the image forming apparatus 1 including the touch-down type developing technique in which the magnetic roller 82 and the developing roller 83 are provided, the amount of the specific component in the developing housing 80 is stably maintained. Is done.

  The image forming apparatus 1 according to the embodiment of the present invention has been described above. However, the present invention is not limited to this, and for example, the following modified embodiment can be adopted.

  (1) In the above embodiment, the consumption conditions for the external additive to be consumed from the developing roller 83 to the photosensitive drum 321 side are the rotation speed ratio of the developing roller 83 to the photosensitive drum 321 and the Vpp at the second developing bias Bp. However, one of these conditions may be selected, or two of these conditions may be set by selectively combining them.

  (2) In the above embodiment, the toner external additive is used as the specific component contained in the developer. However, the present invention is not limited to this. The specific component may be powder, beads, or the like dispersed in the developer together with the toner, or may be a component added internally to the toner. Further, the external additive of the toner consumed as the specific component is not limited to titanium oxide, and other external additive may be consumed initially.

  (3) In the above embodiment, when the developing device 324 including the unused developing roller 83 is attached to the apparatus main body 10 (first condition), the consumption of the external additive is executed between the sheets. It explained in the aspect. Further, the description has been given of the mode in which the external additive consumption mode is executed prior to the developing operation when unused developer is stored in the developing housing 80 (second condition). The present invention is not limited to these. The external additive consumption mode may be executed when the first condition is satisfied, and the consumption of the external additive may be executed between the sheets when the condition of the second condition is satisfied. Further, both the external additive consumption mode and the consumption of the external additive between the sheets may be executed. Further, the mode in which it is detected that a new developing device 324 is mounted on the apparatus main body 10 is not limited to the mode detected by the developing device detection unit 965, but by an operator via the operation unit 961. Mounting information may be input.

  (4) Further, in the above-described embodiment, the development bias applied to the development roller 83 and the magnetic roller 82 has been described in the aspect shown in FIG. 5, but the present invention is not limited to this. FIG. 11 is a diagram schematically showing a third application unit 88A and a fourth application unit 89A for applying a developing bias to the developing roller 83 and the magnetic roller 82 in another modified embodiment. Unlike the first application unit 88 and the second application unit 89 in the previous embodiment, the third application unit 88A and the fourth application unit 89A are connected to the fourth application unit 89A without the third application unit 88A being grounded. It is characterized in that it is connected in parallel. Such a so-called dual development bias application method is characterized in that the duty ratio of the AC bias applied to the magnetic roller 82 and the development roller 83 can be individually changed. Even in such a dual development bias application method, as shown below, the second development bias Bp31, 32 is set with respect to the first development bias Bd13, so that the non-representation represented by the gap between the papers. It is possible to promote consumption of the external additive during the developing operation.

<First development bias Bd13 (during development operation)>
DC bias Vmag_dc of magnetic roller 82; 200V
DC bias Vslv_dc of developing roller 83; 50V
AC roller bias (Vpp) Vmag_ac of magnetic roller 82; 300V (4.0 kHz)
AC bias of developing roller 83 (Vpp) Vslv_ac; 1700 V (4.0 kHz)
Duty ratio of the bias between the photosensitive drum 321 and the developing roller 83 (Duty 1); 43%
Duty ratio of the bias between the developing roller 83 and the magnetic roller 82 (Duty 2); 70%
Linear speed of photosensitive drum 321; 200 mm / sec
Surface potential of photosensitive drum 321; background portion (dark potential) 230V
Rotational speed ratio of developing roller 83 to photosensitive drum 321 (S / D); 1.5

<Second development bias Bp31 (during normal non-development operation, between sheets)>
DC bias Vmag_dc of magnetic roller 82; 200V
DC bias Vslv_dc of developing roller 83; 50V
AC roller bias (Vpp) Vmag_ac of magnetic roller 82; 300V (4.0 kHz)
AC bias of developing roller 83 (Vpp) Vslv_ac; 1800 V (4.0 kHz)
Duty ratio of duty between photosensitive drum 321 and developing roller 83 (Duty 1); 41%
Duty ratio of the bias between the developing roller 83 and the magnetic roller 82 (Duty 2); 70%
Linear speed of photosensitive drum 321; 200 mm / sec
Surface potential of photosensitive drum 321; background portion (dark potential) 230V
Rotational speed ratio of developing roller 83 to photosensitive drum 321 (S / D); 1.7

<Second development bias Bp32 when promoting the consumption of external additives (less than 100 printed sheets)>
DC bias Vmag_dc of magnetic roller 82; 200V
DC bias Vslv_dc of developing roller 83; 50V
AC roller bias (Vpp) Vmag_ac of magnetic roller 82; 300V (4.0 kHz)
AC bias of developing roller 83 (Vpp) Vslv_ac; 2000 V (4.0 kHz)
Duty ratio (Duty 1) of bias between the photosensitive drum 321 and the developing roller 83; 40%
Duty ratio of the bias between the developing roller 83 and the magnetic roller 82 (Duty 2); 70%
Linear speed of photosensitive drum 321; 200 mm / sec
Surface potential of photosensitive drum 321; background portion (dark potential) 230V
Rotational speed ratio of developing roller 83 to photosensitive drum 321 (S / D); 1.8

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Apparatus main body 30 Image forming part 32 Image forming unit 33 Intermediate transfer unit 321
324 Developing device 80 Developing housing 81 Developer reservoir 82 Magnetic roller (Developer carrier)
821 Flush upper electrode 822 Regulating electrode 823 Main electrode 83 Developing roller (toner carrier)
84 Developer regulating blade 85 Screw feeder 86 Screw feeder 88 First application section (bias application means)
89 Second application section (bias application means)
90 control section 91 drive control section 92 bias control section (bias control means)
93 Image quality adjustment unit (image quality adjustment means)
94 Consumption change section (specific component consumption means)
961 Operation part 962 Drive part (rotation drive means)
963 Image memory 964 I / F
965 Developing device detector

Claims (11)

The device body;
An electrostatic latent image is formed on the surface, and an image carrier that carries a toner image;
A developing housing which is mounted on the apparatus main body and stores a developer containing toner to which an external additive is added ;
A toner carrier disposed in the developing housing, driven to rotate, carrying the toner layer made of toner, and supplying the toner to the image carrier;
A bias applying means for applying a bias in which an AC bias is superimposed on a DC bias to the toner carrier to form a predetermined potential difference between the image carrier and the toner carrier;
A first developing bias is applied to the bias applying unit during a developing operation in which the toner image is formed on the image carrier, and a second developing bias is applied to the bias applying unit during a non-developing operation different from the developing operation. Bias control means for applying,
Corresponding to a first condition in which the developing housing including the unused toner carrier is mounted on the apparatus main body, or a second condition in which the unused developer is stored in the developing housing, and an external additive consumption means for consuming said image bearing member the external additive in the developer from the toner carrying member,
I have a,
The external additive consuming means consumes the external additive by controlling the bias control means to change the second development bias, and the amplitude of the AC bias in the first development bias. The amplitude value of the AC bias in the second developing bias is set to be larger than the value, or the duty ratio of the AC bias of the polarity on the side where the toner moves from the toner carrier to the image carrier, By setting the duty ratio of the second development bias to be smaller than the duty ratio of the first development bias, the side of the second development bias where the toner moves from the toner carrier to the image carrier An image forming apparatus characterized by changing a potential difference between a maximum peak value of the AC bias having a polarity of 5 and a surface potential of the image carrier . The image forming apparatus according to claim 1 , wherein the external additive is titanium oxide. The image forming apparatus according to claim 1, wherein the toner carrier has a urethane rubber layer on a surface thereof. The potential of the background portion of the image carrier that is set according to the second development bias during the non-development operation is that of the background portion of the image carrier that is set according to the first development bias during the development operation. The image forming apparatus according to claim 1, wherein the image forming apparatus has the same potential. 5. The image forming apparatus according to claim 1, wherein the single external additive has a property of being charged with a polarity opposite to that of the main body of the toner. A cleaning device including a cleaning roller disposed to face the image carrier;
6. The surface of the image carrier is polished by the cleaning roller while the external additive consumed from the toner carrier is interposed by the external additive consuming means. The image forming apparatus according to claim 1. The image carrier and the toner carrier are rotated in the same direction in regions facing each other during a development operation in which the toner image is formed on the image carrier and a non-development operation different from the development operation. Having rotational drive means;
The external additive consumption means, wherein during the non-development operation, by increasing the rotational speed ratio of the toner carrying member to said image bearing member, 1 to claim, characterized in that to consume the external additive The image forming apparatus according to any one of 6. Further comprising image quality adjustment means for performing image quality adjustment of the toner image;
The external additive means consumes the external additive in accordance with the first condition or the second condition before the image quality adjusting means performs the image quality adjustment. Item 8. The image forming apparatus according to any one of Items 1 to 7. The external additive consumption means, before the start of the developing operation of the toner image is formed on said image bearing member, a predetermined time, any claim 1 to 3, characterized in that to consume the external additive The image forming apparatus according to claim 1. The external additive consuming means is a non-development operation different from a development operation in which the toner image is formed on the image carrier, and one sheet after the image is formed on a plurality of sheets, and thereafter 4. The image forming apparatus according to claim 1, wherein the external additive is consumed between paper sheets between successive sheets. 5. A developer carrying member that receives the developer in the developing housing while rotating in a predetermined direction and carries the developer layer;
The toner carrier that receives the toner from the developer layer and carries the toner layer while rotating in contact with the developer layer;
The image forming apparatus according to claim 1, further comprising:

Images