JP6532578B2 - Image forming device - Google Patents

Description

  The present invention relates to an image forming apparatus employing an electrophotographic method or an electrostatic recording method.

  In an image forming apparatus such as a copying machine using an electrophotographic method or an electrostatic recording method, a printer, a facsimile, or a multifunction machine having a plurality of functions among them, electrostatic formed on an image carrier such as a photosensitive drum A developer is attached to the latent image to make it visible (developed). As a developing device used for such development, a device using a two-component developer (hereinafter referred to as a developer) consisting of toner of nonmagnetic particles and carrier of magnetic particles is known.

  In such a developing device, the developer is carried on the surface of the developing sleeve, and the developer is conveyed by rotation of the developing sleeve. The amount of developer (layer thickness) of the developer is regulated by a regulating blade as a developer regulating member disposed in the vicinity of the developing sleeve, and the developer is conveyed to the developing region facing the photosensitive drum. Then, the electrostatic latent image formed on the photosensitive drum is developed with the toner in the developer.

  Here, a so-called function-separated configuration has a supply chamber (first chamber) for supplying the developer to the developing sleeve and a collection chamber (second chamber) for collecting the developer from the development sleeve as the developing device. Are known. In addition, since the carrier is deteriorated by use and the charging performance is lowered, a so-called carrier refresh configuration is also known in which a new developer is replenished and an excess developer is discharged from the discharge port. As a function separation type developing device having such a carrier refresh configuration, a configuration that performs the following control is known.

  For example, in order to remove the toner layer generated upstream of the regulating blade, the ratio between the rotational speed Vsc of the transport screw for circulating the developer in the supply chamber and the recovery chamber and the rotational speed Vsl of the developing sleeve is reduced. It is proposed (patent document 1). That is, when image formation is continuously performed, toner is deposited upstream of the regulating blade to form a toner layer. The toner layer narrows the gap (gap) between the developing sleeve and the regulating blade, which causes a transport failure that inhibits the supply of the developer to the developing sleeve. Therefore, in Patent Document 1, when the image formation is continuously performed, the toner layer is removed by temporarily interrupting the image formation and performing the above-described control (control for preventing developer conveyance failure). I have to.

JP, 2011-53451, A

  However, in the control (mode) described in Patent Document 1 described above, depending on the configuration of the developing device, it may not be sufficient to suppress the generation of the immobile layer. Further, when the control (mode) described in Patent Document 1 described above is executed, there is a risk that the developer conveyed by the developing sleeve may overflow. That is, in the case of the functional separation type developing device, the developer is not only circulated and conveyed through the supply chamber and the collection chamber by the conveyance screw, but also conveyed from the supply chamber to the collection chamber by the developing sleeve. Therefore, if there is no space in the collection chamber for storing the developer, the developer conveyed by the developing sleeve overflows without being collected in the collection chamber.

  The present invention has been made in view of the above problems, and in the case of executing a mode requiring a space capable of containing the developer conveyed by the developing sleeve in the collection chamber, the developer is not stored in the collection chamber but is out It is an object of the present invention to provide an image forming apparatus capable of preventing overflow.

  According to the present invention, an image carrier, a developer carrier that rotatably supports a developer including a toner and a carrier and transports the developer to a development area facing the image carrier, the development A control portion disposed opposite to the developer carrier, for regulating the amount of developer carried on the developer carrier, a first chamber for supplying the developer to the developer carrier, and the developer And a second chamber disposed opposite to the carrier and recovering the developer having passed through the developing region from the developer carrier, and a partition separating the first chamber and the second chamber. A developer container configured to store the developer and configured to circulate the stored developer between the first chamber and the second chamber; and a developer container disposed in the first chamber; A first conveying screw for conveying the developer in a first direction, and the second chamber disposed in the second chamber An image forming unit having a second conveying screw that conveys the developer in a second direction opposite to the first direction; and a first drive that rotationally drives the first conveying screw and the second conveying screw Unit, a second drive unit for driving the developer carrier to rotate, and the first drive unit to rotate the first transport screw and the second transport screw to rotate the developer carrier. A control unit configured to control the second drive unit to drive the image forming apparatus, wherein the control unit controls the developer support when the developer support is rotationally driven by the second drive unit. The first conveying screw and the second conveying disk when the first conveying screw and the second conveying screw are rotationally driven by the first driving unit with respect to the rotational speed (Vsl) of With respect to the rotational speed ratio (Vsc / Vsl) which is the ratio of the rotational speed (Vsc) of the image forming apparatus, the image forming operation is more than the rotational speed ratio in the image forming period in which the image forming operation is performed The first drive unit and the second drive unit are controlled such that the rotational speed ratio in the first period of the non-image formation period which is not executed becomes larger, and the rotation in the image formation period is performed. A mode in which the first drive unit and the second drive unit are controlled such that the rotational speed ratio in the second period subsequent to the first period in the non-image forming period is smaller than the speed ratio. It is characterized in that it is feasible.

  According to the present invention, the developer can be prevented from overflowing without being accommodated in the second chamber.

FIG. 1 is a schematic configuration view showing a configuration of an image forming apparatus to which a developing device according to a first embodiment of the present invention is applied. FIG. 2 is a cross-sectional view showing the configuration of the developing device as viewed in a cross-section perpendicular to the axis. FIG. 2 is a cross-sectional view showing the configuration of the developing device as viewed in a vertical cross section including the axial direction. 5 is a flowchart of an image forming job according to the first embodiment. 5 is a timing chart illustrating control of an image forming job according to the first embodiment. It is a timing chart for explaining developer overflow prevention control of a 2nd embodiment of the present invention. It is a flowchart of the image formation job of the 3rd Embodiment of this invention. It is a timing chart which shows each control of the image formation job of a 3rd embodiment. It is sectional drawing which shows the structure of the image development apparatus which concerns on the 4th Embodiment of this invention.

First Embodiment
Hereinafter, the first embodiment of the present invention will be described in detail with reference to FIGS. 1 to 5. The developing device according to the present embodiment is applied to the image forming apparatus described below, but is not limited to this, and can be applied to other image forming apparatuses. That is, as long as the image forming apparatus is used, it can be implemented without distinction between the tandem type / one drum type and the intermediate transfer type / direct transfer type. In the present embodiment, only the main parts relating to the formation / transfer of the toner image will be described. However, the present invention adds the necessary equipment, equipment, and housing structure to the printer, various printing machines, copiers, fax machines, It can be implemented in various applications such as multi-function machines.

[Image forming apparatus]
First, a schematic configuration of an image forming apparatus to which a developing device according to the present embodiment is applied will be described with reference to FIG. FIG. 1 is a schematic configuration view showing a configuration of an image forming apparatus to which a developing device according to the present embodiment is applied. The image forming apparatus 1 shown in FIG. 1 is a full-color printer of a tandem intermediate transfer system in which the image forming units UY, UM, UC, and UK are arranged along the intermediate transfer belt 121.

  In the image forming unit UY, a yellow toner image is formed on the photosensitive drum 101Y and transferred to the intermediate transfer belt 121. In the image forming unit UM, a magenta toner image is formed on the photosensitive drum 101M and transferred to the intermediate transfer belt 121. In the image forming units UC and UK, a cyan toner image and a black toner image are formed on the photosensitive drums 101C and 101K, respectively, and are transferred to the intermediate transfer belt 121. The four color toner images transferred to the intermediate transfer belt 121 are conveyed to the secondary transfer portion T2 and collectively secondarily transferred to the recording material P (paper, sheet material such as OHP sheet, etc.).

  The image forming units UY, UM, UC, and UK have substantially the same configuration except that toner colors used in the developing devices 104Y, 104M, 104C, and 104K are different from yellow, magenta, cyan, and black. In the following, the configuration members and the operations of the image forming unit U are summarized by attaching to the constituent members a code in which Y, M, C and K at the end of the code representing the image forming unit UY, UM, UC and UK are omitted. Explain to.

  The image forming unit U includes a primary charger 102, an exposure device 103, a developing device 104, a transfer charger 105, and a drum cleaning device 109 so as to surround the photosensitive drum 101 as an image carrier. The photosensitive drum 101 has a photosensitive layer formed on the outer peripheral surface of an aluminum cylinder, and rotates in the direction of the arrow R1 at a predetermined process speed.

  The primary charger 102 irradiates, for example, charged particles associated with corona discharge to charge the photosensitive drum 101 to a uniform negative dark potential. The exposure device 103 scans, with a rotating mirror, a laser beam obtained by on-off modulating scanning line image data obtained by developing separated color images of respective colors, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 101. The developing device 104 supplies toner to the photosensitive drum 101 to develop an electrostatic image into a toner image.

  The transfer charger 105 is disposed opposite to the photosensitive drum 101 with the intermediate transfer belt 121 interposed therebetween, and forms a primary transfer portion T1 of the toner image between the photosensitive drum 101 and the intermediate transfer belt 121. At the primary transfer portion T 1, a transfer bias is applied to the transfer charger 105, whereby the toner image is primarily transferred from the photosensitive drum 101 to the intermediate transfer belt 121. The drum cleaning device 109 rubs the cleaning blade against the photosensitive drum 101 to collect transfer residual toner slightly remaining on the photosensitive drum 101 after the primary transfer.

  The intermediate transfer belt 121 is bridged and supported by rollers such as the drive roller 122, the tension roller 123, and the secondary transfer inner roller 124, and is driven by the drive roller 122 to rotate in the direction of arrow R2 in the drawing. The secondary transfer portion T2 is a toner image transfer nip portion to the recording material P formed by bringing the secondary transfer outer roller 125 into contact with the intermediate transfer belt 121 stretched around the secondary transfer inner roller 124. In the secondary transfer portion T2, a secondary transfer bias is applied to the secondary transfer outer roller 125, whereby the toner image is secondarily transferred onto the recording material P conveyed from the intermediate transfer belt 121 to the secondary transfer portion T2. Ru. The transfer residual toner remaining attached to the intermediate transfer belt 121 after the secondary transfer is collected by the belt cleaning device 114 rubbing the intermediate transfer belt 121.

  The recording material P on which the four color toner images are secondarily transferred by the secondary transfer portion T2 is conveyed to the fixing device 130. In the fixing device 130, the fixing rollers 131 and 132 are in contact with each other to form a fixing nip T3, and the toner image is fixed on the recording material P while the recording material P is conveyed at the fixing nip T3. In the fixing device 130, the fixing roller 132 is brought into pressure contact with the fixing roller 131, which is internally heated by a lamp heater or the like (not shown), by a biasing mechanism (not shown), thereby forming the fixing nip T3. The recording material P is heated and pressed by being nipped and conveyed by the fixing nip T3, and the toner image is fixed on the recording material P. The recording material P on which the toner image is fixed by the fixing device 130 is discharged out of the machine.

  Here, after primary transfer of toner images of the respective colors from the photosensitive drums 101 of the respective colors onto the intermediate transfer belt 121, the image forming apparatus 1 configured to collectively and secondarily transfer composite toner images of the respective colors onto the recording material P is used. Although explained, it does not restrict to this. For example, the image forming apparatus may be a direct transfer system in which the photosensitive drum 101 directly transfers the recording material P which is carried and conveyed by the transfer material conveyance belt. The photosensitive drum 101 is not limited to the drum-like photosensitive member, and may be a belt-like photosensitive member. Furthermore, the charging method, the transfer method, the cleaning method, and the fixing method are not limited to the above-described methods.

<Two-component developer>
In the developing device 104 shown in FIG. 1, as the developer, a two-component developer including a toner (nonmagnetic) of negative charging characteristics and a carrier of positive charging characteristics is used. The toner may be a binder resin such as a styrene resin or a polyester resin, a coloring agent such as carbon black, a dye, or a pigment, and further, if necessary, colored resin particles including other additives and colloidal silica fine powder. And an external additive is added to the toner. The volume average particle diameter of the toner is preferably 4 μm to 10 μm, because when the particle diameter is too small, it becomes difficult to control the charge amount because it becomes difficult to rub with the carrier and when too large it becomes impossible to form a fine toner image. As an example, it is a polyester resin having a negative charge characteristic, and a toner having a volume average particle diameter of 7.0 μm is used.

  On the other hand, as the carrier, for example, surface oxidized or unoxidized iron, metals such as nickel, cobalt, manganese, chromium, rare earths and their alloys, oxide ferrites, etc. can be suitably used. If the volume average particle size of the carrier is too small, the carrier may adhere to the photosensitive drum 101 during development, and if too large, the carrier may disturb the toner image during development. As an example, a ferrite carrier having a volume average particle size of 40 μm is used. In addition, a two-component developer having an initial weight ratio of toner and carrier of 1: 9 is used.

[Developer]
Next, the configuration of the developing device 104 will be described using FIGS. 2 and 3. The developing device 104 shown in FIG. 2 is a vertical agitation type developing device in which a supply chamber 401 and a recovery chamber 403 described later are disposed vertically. The developing device 104 includes a developing container 2 forming a housing, a developing sleeve 6 as a developer carrier, and a regulating blade 5 as a regulating member. The developing sleeve 6 is partially exposed from an opening 2 a of the developing container 2 provided at a position opposed to the photosensitive drum 101 and is rotatably disposed in the developing container 2. The developing sleeve 6 rotates in the direction of the arrow R3 in the drawing while carrying the developer D whose layer thickness is regulated by the regulating blade 5, and conveys the developer to the opposing photosensitive drum 101. The transported developer D rubs the photosensitive drum 101. As a result, toner is supplied to the electrostatic image formed on the photosensitive drum 101, and the electrostatic image is developed into a toner image. The diameter of the developing sleeve 6 is, for example, 20 mm, and the diameter of the photosensitive drum 101 is, for example, 80 mm.

  Here, the transportability of the developer D due to the difference in the surface shape of the developing sleeve 6 will be described. When the surface of the developing sleeve 6 has a smooth shape, such as a mirror surface, for example, the frictional force generated between the developer D and the surface of the developing sleeve 6 is extremely small. Therefore, in the case of the developing sleeve 6 having a smooth surface, the developer D is hardly transported even when the developing sleeve 6 rotates.

  On the other hand, when the surface of the developing sleeve 6 has an uneven shape, the frictional force generated between the developer D and the surface of the developing sleeve 6 is greater than when the surface is smooth. Therefore, in the case of the developing sleeve 6 having an uneven shape on the surface, the developer D is easily transported following the rotation of the developing sleeve 6. In view of this, on the surface of the developing sleeve 6, for example, irregularities having a surface roughness of about 15 μ are formed. In order to form asperities on the surface of the developing sleeve 6, blasting is performed. The blasting treatment is a processing treatment that gives unevenness by spraying particles such as abrasive powder and glass beads having a predetermined particle size distribution under high pressure. Considering that the developer D is transported in the blasted uneven region, the uneven region is formed in a range slightly larger than the maximum region in which the image can be formed on the photosensitive drum 101.

<Magnet roller>
The developing sleeve 6 is formed in a cylindrical shape of a nonmagnetic material such as aluminum or stainless steel, and a magnet roller 6m as a magnetic field generating means is fixedly disposed therein. The magnet roller 6m has a developing pole S1 and magnetic poles S2, N1, N2 and N3 for carrying and transporting the developer D. As shown in FIG. 2, the developing pole S1 is disposed to face the photosensitive drum 101 in the developing area A, and the magnetic pole S2 is disposed facing the regulating blade 5 as shown in FIG. A magnetic pole N1 is disposed between the magnetic poles S1 and S2, a magnetic pole N2 is disposed upstream of the magnetic pole S2 in the developing sleeve rotation direction, and a magnetic pole N3 is disposed downstream of the magnetic pole S1 in the developing sleeve rotation direction. A magnetic brush (or magnetic brush) of the developer D is formed on the surface of the developing sleeve 6 by the magnetic force of each of the magnetic poles. However, since the magnetic pole N2 having the same polarity and the magnetic pole N3 are disposed adjacent to each other, a repulsive magnetic field is formed between these poles. The developer D is separated from the surface of the developing sleeve 6 by the repulsive magnetic field, and the separated developer D is collected into the collection chamber 403.

<Regulation blade>
As described above, a magnetic brush of the developer D is formed on the surface of the developing sleeve 6. The thickness of the magnetic brush is regulated by the regulating blade 5 and is sent to the developing area A. The regulating blade 5 is a plate-like member made of a nonmagnetic material such as aluminum, and is disposed along the longitudinal direction of the developing sleeve 6 on the upstream side of the photosensitive sleeve 101 in the rotational direction of the developing sleeve 6. . Further, the regulating blade 5 is disposed so as to face the developing sleeve 6 so that the tip thereof faces the rotation center of the developing sleeve 6. By adjusting the gap (gap) between the tip of the regulation blade 5 and the surface of the developing sleeve 6, the amount of cutting of the magnetic brush formed on the surface of the developing sleeve 6 is regulated and conveyed to the development area A The developer amount is adjusted.

If the gap between the regulating blade 5 and the developing sleeve 6 is too narrow, aggregates of foreign matters and toner are easily clogged, which is not preferable. If the amount of developer D conveyed by the developing sleeve 6 is too large, the developer D may be clogged in the vicinity of the closest position (specifically, the developing area A) between the photosensitive drum 101 and the developing sleeve 6 or Problems such as the carrier adhering to the photosensitive drum 101 may occur. On the other hand, if the amount of the developer D conveyed by the developing sleeve 6 is too small, problems such as the toner image may not be developed by a desired toner amount may occur. As these problems do not occur, by setting the distance between the closest position between the regulating blade 5 developing sleeve 6 for example, 400 [mu] m, the amount, for example 30 mg / cm ² of about developer D being conveyed by the developing sleeve 6 It was adjusted.

  The developing sleeve 6 rotates in the same direction (the direction of the arrow R3) as the opposing photosensitive drum 101 while supporting the developer whose layer thickness is regulated by cutting of the magnetic brush by the regulating blade 5 and carries the developer. Transport to the development area A. For example, the peripheral speed of the photosensitive drum 101 is 300 mm / s, and the peripheral speed of the developing sleeve 6 is 450 mm / s. The peripheral speed ratio of the developing sleeve 6 to the photosensitive drum 101 is usually set between 1.0 and 2.0. The larger the circumferential speed ratio, the higher the development efficiency. However, if it is too large, problems such as toner scattering and developer deterioration tend to occur, so the circumferential speed ratio should be set within the above 1.0 to 2.0 times range. preferable.

  In the development area A, the tip of the magnetic brush formed by the development pole S1 rubs the photosensitive drum 101, supplies toner to the electrostatic latent image formed on the photosensitive drum 101, and develops the electrostatic latent image into a toner image Do. At this time, in order to improve the developing efficiency, that is, the application rate of toner to the electrostatic latent image, a developing bias voltage obtained by superimposing an AC voltage on a DC voltage is applied to the developing sleeve 6 from a power supply (not shown). For example, an oscillating voltage is applied to an AC voltage of -500 V, peak-to-peak voltage of 1800 V, frequency of 12 kHz, and waveform of rectangular wave. Of course, the DC voltage value, the AC voltage value and the waveform are not limited to this.

<Developer container>
The developing container 2 contains, for example, 300 g of a two-component developer D containing nonmagnetic toner and magnetic carrier. The inside of the developing container 2 for containing the developer D is divided into an upper supply chamber 401 and a lower collection chamber 403 by a partition 300 extending in the vertical direction of FIG. As shown in FIG. 3, the supply chamber 401 and the recovery chamber 403 communicate with each other in the vertical direction through the openings 404 provided at both ends, and form a circulation path of the developer. The developing device 104 according to the present embodiment has a so-called function-separated configuration including a supply chamber 401 for supplying the developer to the developing sleeve 6 and a collection chamber 403 for collecting the developer from the developing sleeve 6.

  In the supply chamber 401 as the first chamber and the collection chamber 403 as the second chamber, the developing screw 31 as the first conveying means and the stirring screw 32 as the second conveying means are rotatably disposed. As shown in FIG. 3, at one end (left end in FIG. 3) of the developing screw 31, the stirring screw 32, and the developing sleeve 6, a developing screw gear 503, a stirring screw gear 504, and a developing sleeve gear (not shown) are provided. ing. The developing sleeve gear rotates the developing sleeve 6 under the driving force from the developing sleeve driving unit 501 (see FIG. 2). The developing screw gear 503 rotates the developing screw 31 by receiving a driving force from the developing screw drive unit 502 (see FIG. 2). At the same time, the driving force from the developing screw drive unit 502 is also transmitted to the agitating screw gear 504 to rotate the agitating screw 32 simultaneously with the developing screw 31.

  The developing screw 31 and the stirring screw 32 have a screw structure in which a stirring blade made of nonmagnetic material is provided in a spiral shape around the rotation axis. Therefore, as the developing screw 31 and the stirring screw 32 rotate, the developer is circulated and conveyed in the developing container 2 while being stirred. As the developer is agitated, the toner is negatively charged and the carrier is positively charged. The developing screw 31 is disposed substantially parallel along the rotation axis of the developing sleeve 6 in the supply chamber 401, and the stirring screw 32 is disposed substantially parallel to the developing screw 31 in the collection chamber 403. When the developing screw 31 rotates, the developer in the supply chamber 401 is conveyed in one direction from left to right in FIG. 3 along the rotation axis of the developing screw 31. The developer transported to the downstream side of the developer transport direction of the supply chamber 401 falls from the opening 404 to the recovery chamber 403 according to gravity. On the other hand, when the stirring screw 32 rotates, the developer in the collection chamber 403 is unidirectionally from right to left in FIG. 3 along the rotation axis of the stirring screw 24, that is, opposite to the developer in the supply chamber 401. It is transported in the direction. The developer conveyed to the downstream side of the developer conveyance direction of the collection chamber 403 is scraped by the stirring screw 32 from the opening 404 to the supply chamber 401 against gravity. Thus, the developer conveyed by the rotation of the developing screw 31 and the stirring screw 32 passes through the openings 404 provided at both ends of the partition 300, in the direction indicated by the arrow R4, with the supply chamber 401 and the collection chamber 403. Between the

  As described above, in the developing device 104, the developer is transported along the first transport path (circulation path) circulating through the supply chamber 401 and the recovery chamber 403 through the opening 404. Further, in the developing device 104, the developer is also transported in the second transport path. That is, in the developing device 104, the developer is supplied from the supply chamber 401 to the developing sleeve 6, and the developer supplied to the developing sleeve 6 is involved in the development. In other words, the first conveyance path is a circulation path that does not contribute to development, and the second conveyance path is a path that contributes to development. The developer involved in development on the developing sleeve 6 and having a reduced toner concentration is collected exclusively in the collection chamber 403. The recovered developer is sufficiently mixed with the replenishing developer in the recovery chamber 403 to recover the toner concentration, and then returned to the supply chamber 401, again carried on the developing sleeve 6 and used for development. As a result, the toner concentration of the developer carried on the developing sleeve 6 is kept constant. The toner concentration of the developer is detected by a toner concentration sensor (not shown) provided at an opening 404 communicating the supply chamber 401 with the recovery chamber 403. The toner concentration sensor is a sensor that detects the permeability of the developer. Further, in the collection chamber 403, a developer temperature detection sensor 601 as a developer temperature detection unit is provided in order to detect the temperature of the developer.

<Countermeasures against toner change>
By the way, the toner in the developing container 2 is loaded with the image formation, and the shape and the surface property are changed to change the toner characteristics. The change of the toner characteristics depends on the time when the toner is loaded in the developing container 2, but the change of the toner characteristics is remarkable particularly when the image formation with a small consumption of toner is continued. In the case of the image forming apparatus 1 provided with a plurality of developing devices 104 shown in FIG. 1, there may be a developing device 104 that does not consume toner at the time of image formation. In such a developing device 104, processing is usually performed to maintain toner characteristics. Specifically, the minimum consumption of toner is determined for each number of recording materials on which an image has been formed and the number of rotations of the developing sleeve 6, and if it is less than this, development is performed outside the image forming area or during image forming. After consuming the toner, control is performed to replace the toner by supplying new toner.

For example, the minimum toner consumption amount is set to 1% of the maximum toner consumption amount consumed when the full-area maximum density image is output based on the A4 size. Specifically, if the toner consumption amount at the maximum density is 0.5 mg / cm ² , the maximum toner consumption amount consumed at the time of image formation on the A4 size recording material is 0.31 g. In that case, if the average toner consumption per number of sheets (predetermined number of sheets) of recording material on which an image is formed is less than 1% of the maximum toner consumption, control is performed such that the average toner consumption becomes 1%. It will be. As such, the change in toner properties is greatest during continuous imaging with 1% toner consumption. However, it is necessary to pass approximately 10,000 sheets until the average time when the toner in the developing container 2 is loaded becomes a predetermined value. This can be calculated from the amount of toner consumption and the amount of toner in the developer.

<Developer supply>
In the developing device 104, a developer for replenishment (hereinafter, referred to as a replenishment agent) is replenished from the developer replenishment device 12 as a replenishment unit. A replenishing port 11 is provided at an upper portion on the upstream side of the developer conveyance direction of the collection chamber 403, and the developer replenishing device 12 is connected to the replenishing port 11 via a replenishing path (not shown). The replenishing agent is supplied from the developer replenishing device 12 through the replenishing port 11 to the recovery chamber 403, and the replenishing agent supplied to the recovery chamber 403 is transported downstream by the stirring screw 32 in the transport direction. The developer replenishing device 12 adjusts the replenishment amount of the replenishing agent so that the toner concentration becomes about 10% by weight ratio, based on the ratio of the toner and the carrier calculated according to the detection value of the toner concentration sensor (not shown). As a result, substantially the same amount of toner as that consumed at the time of image formation is replenished.

<Reagent>
The replenisher includes both toner and carrier. For example, the replenishment agent is a mixture of toner and carrier in a weight ratio of 9: 1. The use of a replenisher containing not only toner but also carrier is to prevent the deterioration of the chargeability of the carrier during the image formation. That is, by charging a new carrier, the chargeability of the carrier is maintained, thereby maintaining the charge amount of the toner within an appropriate range. The developer replenishing apparatus 12 may separately replenish the toner replenishing agent and the carrier replenishing agent.

<Discharger>
At a predetermined height position of a side wall on the downstream side of the developer conveyance path of the supply chamber 401, a discharge port 13 as a discharge unit is provided in order to perform developer exchange by the trickle method. In the trickle method, the excess developer is spilled out (discharged) from the discharge port 13 as the replenishment agent is replenished. That is, when the agent surface of the developer becomes higher than the discharge port 13, the developer of the increased amount overflows from the discharge port 13 and is discharged to the outside of the developing container 2. That is, also in this embodiment, since the carrier is deteriorated by use and the charging performance is lowered, a so-called carrier refresh configuration is adopted in which a new developer is replenished and an excess developer is discharged from the discharge port. Generally, the height position of the discharge port 13 is determined in accordance with the height of the developer surface when the developer surface of the developer at the time of image formation is stabilized (steady state). As shown by the dotted line in FIG. 3, in the steady state, the developer surface height gradually decreases in the supply chamber 401 from the upstream to the downstream in the developer conveyance direction, and the developer conveyance direction in the collection chamber 403 The downstream level is higher than the upstream of the

<Control unit>
Further, as shown in FIG. 2, the developing device 104 includes a control unit 500 as a control unit, a developing sleeve driving unit 501, and a developing screw driving unit 502. The control unit 500 controls the driving of the developing sleeve 6 by the developing sleeve driving unit 501 and the driving of the developing screw 31 and the stirring screw 32 by the developing screw driving unit 502. The developing sleeve driving unit 501 and the developing screw driving unit 502 are driving sources such as a motor. The driving force of the developing sleeve driving unit 501 is transmitted to the developing sleeve gear (not shown), whereby the developing sleeve 6 is rotated. The driving force of the developing screw drive unit 502 is transmitted to the developing screw gear 503 and the stirring screw gear 504 (see FIG. 3), whereby the developing screw 31 and the stirring screw 32 rotate. The control unit 500 can control the developing sleeve driving unit 501 and the developing screw driving unit 502 to change the driving speeds (rotational speed as an example) of the developing sleeve 6, the developing screw 31 and the stirring screw 32.

  The control unit 500 executes an image forming job (print job). The image forming job will be described with reference to FIGS. 4 and 5. FIG. 4 is a flowchart of an image forming job according to the present embodiment. FIG. 5 is a timing chart showing each control of the image forming job of this embodiment.

  The control unit 500 starts image formation control for forming an image on a recording material of a predetermined number of prints and printing out the image (S1). The control unit 500 controls the screw rotation speed Vsc of the developing screw 31 and the stirring screw 32 to be 800 rpm and the sleeve rotation speed Vsl of the developing sleeve 6 to be 600 rpm in synchronization with the start of image formation control.

  The control unit 500 counts the total number of recording materials already printed out from the start of the image formation control to the present time, and the number of recording materials printed out since the developer overflow prevention control was last performed ( Hereinafter, the integrated number is called) (S2). As shown in FIG. 5, during continuous print output (during image formation), the screw rotation speed Vsc is maintained at 800 rpm, and the sleeve rotation speed Vsl is maintained at 600 rpm.

  The control unit 500 determines whether or not the total number of recording materials already printed out has reached a predetermined number of prints (S3). If it is determined that the total number of recording materials already printed out has reached the predetermined number of prints (YES in S3), the image formation control is ended (S4). That is, control is performed to stop the developing screw 31, the stirring screw 32, and the developing sleeve 6 by setting the screw rotation speed and the sleeve rotation speed to 0 rpm.

  If it is determined that the total number of recording materials already printed out has not reached the predetermined number of prints (NO in S3), image formation is performed, and the total number and the cumulative number are updated. The control unit 500 determines whether “developer overflow prevention control” is to be executed (S5). Whether or not the developer overflow prevention control is to be executed is, for example, whether or not the integrated number (denoted as N in the figure) has reached a predetermined number (for example, 5000), in other words whether the integrated number is equal to or greater than a threshold It is good to judge by whether or not. Alternatively, it may be determined based on whether or not the image formation time has reached a predetermined time (whether or not it is equal to or more than a threshold). Furthermore, it may be determined based on whether or not the number of revolutions of the developing sleeve 6 has reached a predetermined number. When the integrated number reaches a predetermined number (or when the image forming time reaches a predetermined time, or when the number of rotations of the developing sleeve 6 reaches a predetermined number), the control unit 500 executes developer overflow prevention control. judge.

  If it is determined that the developer overflow prevention control is not to be executed (NO in S5), the control unit 500 returns to the process of S2 and continues the process. In this case, the screw rotation speed is maintained at 800 rpm, the sleeve rotation speed is maintained at 600 rpm, and image formation control is continuously performed.

  On the other hand, when it is determined that the developer overflow prevention control is to be executed (YES in S5), the control unit 500 suspends the image formation control and executes the developer overflow prevention control (S6). That is, as shown in FIG. 5, in the developer overflow prevention control, the screw rotation speed (Vsc) and the sleeve rotation speed (Vsl) are temporarily set to 0 rpm, that is, driving of the developing screw 31 and the stirring screw 32 and the developing sleeve 6 is performed. Stop. Then, while the developing sleeve 6 is stopped, the developing screw 31 and the stirring screw 32 are driven for 2 seconds at the same screw rotation speed of 800 rpm as at the time of image formation. That is, in the developer overflow prevention control, the developing screw 31, the stirring screw 32, and the developing sleeve 6 are controlled so as to increase the rotational speed ratio (Vsc / Vsl) at the time of non-image formation as compared with at the time of image formation. When the developer overflow prevention control is executed, the integrated number is cleared.

  After the developer overflow prevention control, the control unit 500 executes developer conveyance defect prevention control (S7). As shown in FIG. 5, in the developer conveyance defect prevention control (hereinafter simply referred to as conveyance defect prevention control), the screw rotation speed is set to 0 rpm, and the driving of the developing screw 31 and the stirring screw 32 is stopped. Then, while the developing screw 31 and the stirring screw 32 are stopped, only the developing sleeve 6 is driven for 1 second at the same sleeve rotational speed 600 rpm as at the time of image formation. That is, in the conveyance failure prevention control, the developing screw 31, the stirring screw 32, and the developing sleeve 6 are controlled so as to make the rotational speed ratio (Vsc / Vsl) smaller at the time of non-image formation than at the time of image formation.

  As described above, when image formation is continuously performed in the developing device 104, toner released from the developer is deposited on the back of the control blade 5 (upstream in the rotational direction of the developing sleeve 6, see FIG. 2). A toner layer is formed. The toner layer narrows the gap (gap) between the developing sleeve and the regulating blade, thereby inhibiting the supply of the developer to the developing sleeve 6 and causing a conveyance failure. Therefore, the control unit 500 is configured to prevent the developer conveyance failure caused by the toner layer by removing the toner layer by executing the above-described "conveyance failure prevention control". However, in the function separation type developing device, when the conveyance failure prevention control is executed, the developer conveyed from the supply chamber 401 to the collection chamber 403 by the developing sleeve 6 overflows into the collection chamber 403 without being collected. There was a thing. This is because in the conveyance failure prevention control, the rotational speed ratio (Vsc / Vsl) is made smaller than at the time of image formation, so the developer collected from the developing sleeve 6 is collected in the collection chamber 403 and the developer is stored in the collection chamber 403 It is because there is not enough space available.

  Therefore, by executing the mode in which the developer overflow prevention control is performed before the above-described transport failure prevention control, a space sufficient to accommodate the developer in the collection chamber 403 is secured in advance. When the developing screw 31 and the stirring screw 32 are driven, the developer is circulated and conveyed in the supply chamber 401 and the collection chamber 403. At the same time, if the developing sleeve 6 is driven to increase the rotational speed ratio (Vsc / Vsl) compared to that at the time of image formation, in particular if the developing sleeve 6 is stopped, the developer in the supply chamber 401 increases. The developer in the collection chamber 403 is reduced. That is, while the relative amount of developer circulated and conveyed in the supply chamber 401 and the recovery chamber 403 by the developing screw 31 and the stirring screw 32 does not change, it is transported from the supply chamber 401 to the recovery chamber 403 by the developing sleeve 6 Amount of developer decreases. Therefore, the developer in the supply chamber 401 increases and the developer in the collection chamber 403 decreases. As the amount of developer in the collection chamber 403 decreases, the space capable of containing the developer is expanded.

  Returning to FIG. 4, after the conveyance failure prevention control (S7), the control unit 500 returns to the process of S2 and continues the process. As shown in FIG. 5, the control unit 500 temporarily stops driving the developing screw 31, the stirring screw 32 and the developing sleeve 6. Then, when restarting the image formation control that has been temporarily stopped, the developing screw 31, the stirring screw 32, and the developing sleeve 6 are driven so that the screw rotation speed is 800 rpm and the sleeve rotation speed is 600 rpm.

Comparative Example 1
Contained in collection chamber 403 at the start of image formation when developer overflow prevention control is executed before transport failure prevention control (when present) and when developer overflow prevention control is not executed before conveyance failure prevention control (none) Table 1 shows the results of experiments in which the amount of developer that overflowed without being measured was measured. As can be understood from Table 1, when the developer overflow prevention control was executed before the transport failure prevention control, the developer overflow did not occur.

  As described above, the developer overflow prevention control is executed before the conveyance failure prevention control. Specifically, after non-image formation, control is performed to increase the rotational speed ratio (Vsc / Vsl) compared to that during image formation (developer overflow prevention control), and then the rotational speed ratio (Vsc / Vsl) is image-formed. Control to make it smaller than the time (conveyance failure prevention control). By executing the developer overflow prevention control, the developer in the supply chamber 401 is increased while the developer in the collection chamber 403 is decreased. That is, it is possible to secure in advance a region for collecting the developer conveyed by the developing sleeve 6 in the collection chamber 403. In this way, when the toner layer is removed by the transport failure prevention control, the developer is not overflowed outside without being accommodated in the collection chamber 403.

Second Embodiment
A second embodiment of the present invention will be described using FIG. 6 with reference to FIG. 2 and FIG. In the first embodiment described above, the discharge of the developer from the discharge port 13 is not particularly considered when executing the developer overflow prevention control before the conveyance failure prevention control. On the other hand, in the present embodiment, when the developer overflow prevention control is performed, the control in consideration of preventing the developer from being excessively discharged from the discharge port 13 is performed.

  As described above, the developing device 104 is a function-separated developing device having a carrier refresh configuration, and is capable of discharging the old carrier with reduced charging performance from the discharge port 13 together with the developer. Then, by charging a new carrier with the replenishment of the replenishment agent from the developer replenishment device 12, it is possible to maintain the charging performance of the carrier in the developing container 2 and thus the toner charge amount. In this configuration, if the amount of the carrier discharged with respect to the carrier to be filled is large, the developer in the developing container 2 is gradually reduced, and there is a risk that the developing function can not be eventually performed if it continues. That is, when the developer is excessively discharged and the developer in the developing container 2 runs short, the developer can not be appropriately supplied to a part of the developing sleeve 6, and an image defect such as a part of the toner image is generated. obtain. This problem may also occur when developer overflow prevention control is performed to forcibly transport the developer to the supply chamber 401. Therefore, when performing developer overflow prevention control, it is necessary to consider that the developer is not excessively discharged from the discharge port 13.

  As shown in FIG. 6, in the present embodiment, since each control other than developer overflow prevention control is the same as that in the first embodiment, the description here is omitted. In this embodiment, when executing developer overflow prevention control to increase the rotational speed ratio (Vsc / Vsl) compared to that at the time of image formation, the developing screw 31 and the stirring screw 32 are rotated while the developing sleeve 6 is stopped. Drive for 4 seconds at a speed of 400 rpm. That is, the screw rotation speed is changed from 800 to 400 rpm, and the driving time is changed from 2 seconds to 4 seconds, as compared with the case where the excessive discharge of the developer is not considered.

Comparative Example 2
Here, Table 2 shows experimental results of measuring the amount of the developer discharged when the developer overflow prevention control is performed by changing the screw rotation speed and the driving time, and the presence or absence of the occurrence of the overflow. As can be understood from Table 2, when the screw rotation speed is driven at 800 rpm for 2 seconds in consideration of only the overflow of the developer, the overflow does not occur. However, the amount of developer discharged (discharge amount) is 6 g. On the other hand, when the screw rotation speed is driven at 400 rpm for 4 seconds in consideration of not only the developer overflow but also the excess discharge of the developer, not only overflow does not occur but the amount of developer discharged (discharge amount ) Is reduced to 2g. That is, the developer discharged at the time of execution of the developer overflow prevention control can be reduced by decreasing the screw rotation speed. However, when the screw rotation speed is reduced, if the drive time is not changed, as shown in Table 2, although the discharge amount decreases, overflow occurs (2 seconds at 400 rpm). This is because the amount of developer transported from the supply chamber 401 to the recovery chamber 403 decreases when the screw rotation speed is reduced, and the developer can be accommodated without reducing the developer in the recovery chamber 403. It is because the space can not be secured.

  As described above, the developer overflow preventing control is executed by setting the screw rotation speed to a low speed as compared with that at the time of image formation, and correspondingly increasing the driving time. Thereby, in addition to the fact that the developer overflow can be prevented, the excessive discharge of the developer can be suppressed.

Third Embodiment
By the way, in the transport failure prevention control, only the developing sleeve 6 is driven, so the developer is only transported from the supply chamber 401 to the recovery chamber 403. As a result, the developer distribution is more accommodated in the collection chamber 403 than in the supply chamber 401 unlike in the image formation. Further, in the supply chamber 401 and the recovery chamber 403, the developer amount is biased and a portion where the agent surface is raised is partially generated. That is, the amount of developer in the portion facing the developing sleeve 6 in the supply chamber 401 is small, and the amount of developer in the portion facing the developing sleeve 6 in the collection chamber 403 is large. This is because the developer is conveyed only by the developing sleeve 6, and only the amount of developer in the portion facing the developing sleeve 6 fluctuates.

  When the image formation is performed after the conveyance failure prevention control as described above (see S6 and S7 in FIG. 4), the developer may be excessively discharged and the developer in the developing container 2 may run short. This is because when the rotational speeds of the developing screw 31 and the stirring screw 32 are 800 rpm and the rotational speed of the developing sleeve 6 is 600 rpm for image formation, they are different from the normal developer distribution. . In this case, the developer in a portion with a large amount of developer formed in the collection chamber 403 with the execution of the transport failure prevention control is transported to the discharge port 13 with the image formation control and discharged from the discharge port 13 It is because. In order to prevent this, control may be performed to drive the developing screw 31, the stirring screw 32, and the developing sleeve 6 at a lower speed than at the time of image formation, at least for a time when the developer circulates around the developing container 2 about half. . Hereinafter, a third embodiment of the present invention will be described using FIGS. 7 and 8.

  FIG. 7 is a flowchart of an image forming job according to this embodiment. However, since the processes of S1 to S7 are the same as the process shown in FIG. 4 described above, the description here is omitted. As shown in FIG. 7, the control unit 500 executes developer surface break-in control after execution of the conveyance failure prevention control (S8). In developer surface break-in control, as shown in FIG. 8, the developing screw 31 and the stirring screw 32 are simultaneously driven at a screw rotational speed of 400 rpm and the developing sleeve 6 at a sleeve rotational speed of 200 rpm for 10 seconds simultaneously. The screw rotational speed 400 rpm and the sleeve rotational speed 200 rpm at this time are lower than the screw rotational speed 800 rpm at the time of image formation and the sleeve rotational speed 600 rpm. Here, the driving time of 10 seconds corresponds to the time for which the developer is circulated and conveyed so as to make about one rotation of the circulation path in the developing container 2. However, since this driving time may be at least only a time for the developer to make a half cycle of the circulation path in the developing container 2, it may not be 10 seconds and may be 5 seconds or more.

  When the screw rotation speed is reduced, the moving amount of the developer per unit time (in other words, the moving speed) in the circulation path in the developing container 2 becomes smaller than that at the time of image formation. If the moving amount of the developer is small, it takes time until the developer at a portion where the amount of the developer is large is transported to the discharge port 13 as compared with the steady state as shown in FIG. In addition, since the developer collapses when being transported at a slow moving speed, a portion with a large amount of developer is eliminated as compared with the steady state. The driving time for the developer to make a half cycle of the circulation path in the developing container 2 is equal to the length in the longitudinal direction of the developing container 2 (more specifically, the supply chamber 401). It is obtained by dividing by the moving speed of the agent. That is, the driving time changes depending on the screw rotation speed and the length of the developing container 2 in the longitudinal direction. For example, the driving time may be calculated by dividing the distance of one circulation cycle or half cycle of the circulation path by the average speed of the developer conveyed by the screw rotation speed. In addition, for example, the length of the developing screw 31 and the stirring screw 32 in the rotational axis direction between the central portions of the opening portions 404 at both ends is set to the rotation shaft of the developing screw 31 and the stirring screw 32. The distance between the two may be doubled.

  Then, by driving the developing sleeve 6 simultaneously, a state in which the surface of the developer gradually lowers as in the steady state at the time of image formation is created, and excessive discharge from the discharge port 13 is prevented. At this time, by setting the rotational speed of the sleeve to be lower than that at the time of image formation and driving the developing sleeve 6, a large amount of developer is not stored in either the supply chamber 401 or the recovery chamber 403. The amount of movement of the developer amount is adjusted. For example, if the rotational speed of the sleeve is the same 600 rpm as during image formation, a large amount of developer is contained in the collection chamber 403, and if the rotational speed of the sleeve is extremely low (for example, 50 rpm), the large amount of developer is contained in the supply chamber 401. Therefore, they have a developer distribution different from that at the time of image formation. That is, the sleeve rotational speed is determined by the screw rotational speed. In developer surface break-in control, the screw rotation speed is preferably 500 to 300 rpm, and the sleeve rotation speed is preferably 300 to 100 rpm. The screw rotation speed is at least a speed capable of generating a force for scraping the developer from the recovery chamber 403 to the supply chamber 401 against the gravity at least, and it goes without saying that the driving time changes depending on the screw rotation speed. .

  Referring back to FIG. 7, after developer surface break-in control (S8), the control unit 500 returns to the process of S2 and continues the process. As shown in FIG. 8, the driving of the developing screw 31, the stirring screw 32, and the developing sleeve 6 is temporarily stopped. Then, when restarting the image formation control that has been temporarily stopped, the developing screw 31 and the stirring screw 32 and the developing sleeve 6 are driven with the screw rotating speed being 800 rpm and the sleeve rotating speed being 600 rpm. Resume the paused image formation control. When image formation is performed after developer surface break-in control (S8), the rotational speeds thereof are 400 to 800 rpm and 200 to 600 rpm without temporarily stopping the driving of the developing screw 31, the stirring screw 32, and the developing sleeve 6. It may be changed to

Comparative Example 3
Here, Table 3 shows experimental results of measuring the amount of the developer discharged at the start of image formation when the developer surface break-in control is performed and when the developer surface break-in control is not performed. When 300 g of the developer is stored in the developing container 2 and the image formation is performed after executing the developer surface break-in control, the amount (discharge amount) of the developer discharged out of the developing container 2 is “1 .2g ". On the other hand, when the image formation was performed without executing the developer surface break-in control, the amount (discharge amount) of the developer discharged out of the developing container 2 was “2.0 g”. As described above, if the developer surface break-in control is executed after the conveyance failure prevention control, the developer discharged at the start of image formation can be reduced as compared with the case where the developer surface break-in control is not performed.

  As described above, the developer surface break-in control is executed after the conveyance failure prevention control. In the developer surface break-in control, the developing screw 31 and the stirring screw 32 are driven at a lower speed than at the time of image formation. As a result, the developer moves in the developing container 2 at a slower moving speed than at the time of image formation. Further, the developing sleeve 6 is driven at a lower speed than at the time of image formation. Thus, the distribution of the developer is adjusted, and the developer is not biased and stored in either the supply chamber 401 or the recovery chamber 403. With the execution of the developer surface break-in control, even if the transport failure prevention control is executed, the developer is adjusted to a state suitable for image formation and distributed in the developing container 2. Therefore, when the image formation is started, the developer is not excessively discharged.

Fourth Embodiment
Next, a fourth embodiment of the present invention will be described using FIG. In the first embodiment described above, the developing device 104 does not include a backup member. On the other hand, in the present embodiment, the developing device 104 is configured to include the backup member, and performs control such that the ratio of the developer occupied in the buffer unit, which will be described later, is 50% or less. I have to. The other configurations and functions are the same as those of the first embodiment, and thus the description and illustration overlapping with the first embodiment will be omitted or simplified, and the same reference numerals will be given to the same configurations as the first embodiment. Hereinafter, parts different from the first embodiment will be mainly described. FIG. 9 is a cross-sectional view showing the configuration of a developing device provided with a backup member.

  As shown in FIG. 9, the backup member 600 is integrally formed with the partition 300 that divides the supply chamber 401 and the recovery chamber 403 so as to be provided on the upstream side of the regulating blade 5 in the rotational direction of the developing sleeve 6. . By providing the backup member 600, the developer from the developing screw 31 is temporarily stored in the buffer portion 602 surrounded by the regulating blade 5 and the backup member 600 on the upstream side of the regulating sleeve 5 in the rotational direction of the developing sleeve 6. Be done. By temporarily storing the developer in the buffer unit 602 and then supplying the developer to the developing sleeve 6, periodical supply unevenness of the developer caused by the developer being directly supplied from the developing screw 31 to the developing sleeve 6 is It can be prevented.

  Also in the developing device 104 provided with the backup member 600, a toner layer is formed upstream of the regulating blade 5 with the image formation. This toner layer may interfere with the supply of developer as described above. Further, the toner layer may be broken, conveyed by the developing sleeve 6 and attached to the photosensitive drum 101, which may cause an image defect called toner contamination or the like. Therefore, it is necessary to remove the toner layer.

  The developer contained in the buffer portion 602 can be reduced by rotating only the developing sleeve 6. Therefore, at the time of conveyance failure prevention control (see S7 in FIG. 4 and FIG. 7), the control unit 500 performs control to stop the developing screw 31 and the stirring screw 32 and drive the developing sleeve 6 at a sleeve rotation speed of 600 rpm for 2 seconds. . The driving time of 2 seconds here is a sufficient time for the developing sleeve 6 to rotate 20 times from the stopped state, and the toner layer can be removed by rotating the developing sleeve 6 20 times. As described later, if the ratio of the developer occupied in the buffer portion 602 is, for example, 50% or less (indicated by a dotted line in FIG. 9), the toner layer can be removed. For example, the developer amount corresponding to at least 50% of the volume of the buffer portion 602 is transported from the supply chamber 401 to the recovery chamber 403 by the developing sleeve 6. In this case, since the amount of the developer conveyed from the supply chamber 401 to the collection chamber 403 is limited by the developing sleeve 6, overflow of the developer can be prevented. In this case, the developing screw 31 and the stirring screw 32 need not necessarily be stopped, and may be rotated as long as the developer is not supplied from the developing screw 31 to the buffer section 602. The ratio of the developer occupied in the buffer portion 602 is defined as 100% of the space surrounded by the horizontal surface passing through the top of the backup member 600, the backup member 600, the developing sleeve 6, and the regulating blade 5. In the conveyance failure prevention control of the present embodiment, the rotation time of the developing sleeve 6 is set to a time corresponding to the time when all the developer amount in the buffer unit 602 (the area corresponding to 100%) is conveyed. Note that, in consideration of the case where the developer amount is accumulated above the horizontal plane passing the top of backup member 600, the time during which the rotation time of developing sleeve 6 can transport a toner amount larger than the 100% toner amount occupying the buffer portion It may be set to That is, the developer amount corresponding to the volume integral of the buffer unit 602 may be transported by the developing sleeve 6.

Comparative Example 4
Here, Table 4 shows the presence or absence of toner contamination at the time of image formation when the proportion of the developer occupied in the buffer portion 602 is 50% or less and 50% or less by the conveyance defect prevention control. As can be understood from Table 4, in the case of 50% or less, no toner contamination occurred. On the other hand, when the content was not 50% or less, toner contamination occurred.

  As described above, in the developing device 104 including the backup member 600, the developer contained in the buffer unit 602 is transported from the supply chamber 401 to the recovery chamber 403, thereby collapsing the toner layer and transporting it. It is possible to prevent the occurrence of toner contamination. Specifically, the developer may be transported from the supply chamber 401 to the collection chamber 403 by the developing sleeve 6 until the ratio of the developer occupied in the buffer portion 602 becomes at least 50% or less. In addition, since the amount of developer transported from the supply chamber 401 to the recovery chamber 403 is limited, the space of the recovery chamber 403 always has a margin as compared with the case where it is not limited. Therefore, at the time of execution of the transport failure prevention control, the developer transported to the developing sleeve 6 does not overflow outside without being collected in the collection chamber. As described above, when the ratio of the developer occupied in the buffer portion 602 is at least 50% or less, the toner layer is eliminated, so that the toner contamination caused by the toner layer is also less likely to occur.

Other Embodiments
Although the developer overflow prevention control is executed before the conveyance failure prevention control, the execution timing is determined based on the integrated number of sheets as described above (see S5 in FIGS. 4 and 7). This is because it is necessary to execute transport failure prevention control before the toner layer narrows the gap (gap) between the developing sleeve 6 and the regulating blade 5 to inhibit the supply of the developer. By the way, the time taken for the toner to be accumulated to such an extent that it obstructs the vicinity of the regulation blade 5, that is, the time taken for forming the toner layer which inhibits the supply of the developer, It depends on the amount of consumption. As a result of actual measurement, the toner layer was accumulated until the toner inhibited the supply of the developer at a toner consumption rate of 1% and the temperature in the developing container 2 was raised to 45 ° C. This corresponds to the time taken to continuously print out a recording material equivalent to 5000 to 5500 sheets in A4 size. Therefore, in each of the above-described embodiments, the threshold value of the execution timing of the developer overflow prevention control is set to 5000 sheets, and when the integrated number reaches 5000 sheets, the developer overflow prevention control is executed, and the transport defect prevention control is continued. I am trying to run it.

  However, the time taken to form the toner layer that inhibits the supply of the developer varies depending on the state of the developer in the developer container 2. For example, when the temperature of the developer in the developer container 2 is high, the toner layer is formed in a shorter time than when the temperature is low until the supply of the developer is inhibited. Further, when the average toner staying time is long, that is, when the developer in the developing container 2 is heavily loaded to change the toner characteristics and the image formation with a low average printing rate continues for a long time, the average toner staying time The toner layer is formed in less time as compared with the case where. Therefore, at the execution timing based on the accumulated number of 5000 sheets described above, there is a possibility that the transport failure prevention control is executed at a timing earlier than necessary than the actual supply of the developer is inhibited. Then, the conveyance failure prevention control is executed many times at the time of the image forming job, and the downtime is increased. Therefore, it is necessary to optimize the execution timing of the developer overflow prevention control, that is, the conveyance failure prevention control according to the state of the developer.

  One way to optimize execution timing is shown below. The method accumulates an index determined by the temperature at the time of image formation, the average printing ratio (average image ratio), the size of the recording material, etc., as the number of output sheets for each image formation when updating the integrated number, and comparing this with the threshold Do. Table 5 shows the cumulative indices. In view of the fact that the time it takes to form a toner layer that inhibits the supply of developer varies depending on the toner characteristics and the temperature of the developer, the indexes shown in Table 5 are weighted according to the temperature of the developer and the average printing rate It is an index. This is obtained by estimating the change in toner characteristics based on the average printing rate of a plurality of (for example, 1000) recording materials printed and output in the past. As shown in Table 5, for example, when the temperature of the developer is 48 ° C. and the average printing rate is 1%, “1.0” is added as the integrated number. When the temperature of the developer is 42 ° C. and the average printing rate is 3%, “0.8” sheets are added as the cumulative number. When the temperature of the developer is 38 ° C. and the average printing rate is 10%, “0.5” sheets are added as the cumulative number.

  The control unit 500 calculates an average printing rate as a change in toner characteristics. For example, the number of dots of the electrostatic image formed on the photosensitive drum 101 is detected by an image dot counting unit (not shown), and the average printing rate is calculated based on the detection result. Of course, it is not limited to this. The control unit 500 acquires the temperature of the developer from the developer temperature detection sensor 601 (see FIG. 2) provided in the developing container 2 (more specifically, the collection chamber 403). The control unit 500 refers to the index table (data) corresponding to Table 5 stored in a memory (not shown) or the like according to the calculated average printing rate and the acquired developer temperature, and adds the corresponding weighting index. Calculate the cumulative number. The control unit 500 determines whether or not “developer overflow prevention control” is to be performed based on the calculated integration sheet number (see S5 in FIGS. 4 and 7).

  As described above, the control unit 500 determines whether or not the developer overflow prevention control is to be performed, for example, based on whether or not the integrated number has reached a predetermined number (for example, 5000). When the weighted index is added to obtain the integrated number, the determination is made based on the obtained integrated number. That is, for example, when the temperature of the developer is 48 ° C. and the average printing rate is 1%, when the image forming job is repeated 5000 times, the integrated number obtained by adding the weighting index is 5000 sheets (1 × 5000). Become. Therefore, in this case, the control unit 500 executes developer overflow prevention control every time the image forming job is repeated 5000 times.

  On the other hand, when the temperature of the developer is 42 ° C. and the average printing rate is 3%, when the image forming job is repeated 5000 times, the integrated number obtained by adding the weighting index is 4000 sheets (0.8 × 5000). It becomes. That is, in this case, even if the image forming job is repeated 5000 times, the integrated number does not reach the threshold. In this case, when the image forming job is repeated 6250 times, the integrated number reaches 5000 (0.8 × 6250) which is a threshold value. Therefore, in this case, the control unit 500 executes developer overflow prevention control every time the image forming job is repeated 6250 times. Table 6 shows the execution timing of the developer overflow prevention control according to the conditions (combination of the temperature of the developer and the average printing rate) corresponding to Table 5. In this way, the execution timing of the developer overflow prevention control, that is, the conveyance failure prevention control is made appropriate according to the state of the developer.

  In each embodiment described above, an example is shown in which the stirring screw 32 is also driven when the developing screw 31 is driven. However, the present invention is not limited to this, and the developing screw 31 and the stirring screw 32 can be separately driven. It is also good. Also in this case, the developing screw 31 and the stirring screw 32 are driven at the same speed.

  In each embodiment described above, the vertical stirring type developing device in which the developing container 2 is divided into the supply chamber 401 and the collection chamber 403 is described as an example, but the present invention is not limited to this configuration. That is, the present invention also relates to a configuration in which the supply chamber 401 and the recovery chamber 403 are partitioned in the horizontal direction, and the function is divided into a chamber for supplying the developer to the developing sleeve 6 and a chamber for recovering the developer from the developing sleeve 6. It is possible to apply

  In each of the above-described embodiments, the case where the conveyance failure prevention control is performed for each predetermined number of sheets has been described as an example. This can reduce downtime.

  In addition, when it is time to execute the conveyance failure prevention control in one of the developing devices of each color, it is not the timing to execute the conveyance failure prevention control of the other color development devices, but at the execution timing. If they are close, they may be simultaneously performed.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Developer container, 6 ... Development sleeve, 12 ... Developer replenishment apparatus,
13 ... discharge port, 31 ... developing screw, 32 ... stirring screw,
101: photosensitive drum, 104: developing device, 401: supply chamber, 403: collection chamber,
500: control unit, 501: developing sleeve driving unit, 502: developing screw driving unit,
600 ... backup member, 601 ... developer temperature detection sensor, 602 ... buffer unit,
D: Developer, P: Recording material

Claims (16)

An image carrier,
A developer carrier that is rotatably provided and carries a developer including toner and carrier and transports the developer to a development area facing the image carrier;
A regulating unit disposed opposite to the developer carrier and regulating the amount of developer carried on the developer carrier;
A first chamber for supplying the developer to the developer carrier, and a second chamber disposed opposite to the developer carrier for recovering the developer having passed through the developing region from the developer carrier And a partition separating the first chamber and the second chamber, the developer is accommodated, and the accommodated developer is configured to be circulated between the first chamber and the second chamber. The developer container, and
A first conveying screw disposed in the first chamber for conveying the developer in the first chamber in a first direction;
A second conveying screw disposed in the second chamber for conveying the developer in the second chamber in a second direction opposite to the first direction;
An image forming unit having
A first drive unit that rotationally drives the first conveyance screw and the second conveyance screw;
A second drive unit that rotationally drives the developer carrier;
A control unit that controls the first drive unit to rotationally drive the first transport screw and the second transport screw, and controls the second drive unit to rotationally drive the developer carrier;
In an image forming apparatus provided with
The control unit
The first drive unit rotationally drives the first conveyance screw and the second conveyance screw with respect to the rotational speed (Vsl) of the developer carrier when the developer carrier is rotationally driven by the second drive unit With respect to a rotational speed ratio (Vsc / Vsl) which is a ratio of rotational speeds (Vsc) of the first and second conveying screws at the time of image formation, an image forming period in which the image forming operation is performed by the image forming unit The first drive unit and the second drive unit are configured such that the rotation speed ratio in the first period of the non-image forming period in which the image forming operation is not performed is larger than the rotation speed ratio in And controlling the rotational speed ratio in the image formation period, in the second period subsequent to the first period in the non-image formation period. Serial feasible mode for controlling the first driver and the second driver so it is smaller the rotation speed ratio,
An image forming apparatus characterized by When the control unit executes the mode, the first drive is performed such that a rotational speed of the first transport screw in the first period is slower than a rotational speed of the first transport screw in the image forming period. Controlling the first drive unit such that the rotational speed of the second conveying screw in the first period is slower than the rotational speed of the second conveying screw in the image forming period;
The image forming apparatus according to claim 1, When the control unit executes the mode, the rotational speed of the first conveyance screw in a third period following the second period of the non-image formation period is the first conveyance in the image formation period. The first drive unit is controlled to be slower than the rotational speed of the screw, and the rotational speed of the second conveying screw in the third period is greater than the rotational speed of the second conveying screw in the image forming period. Control the first drive so as to be too slow,
The image forming apparatus according to claim 1 or 2, wherein When the control unit executes the mode, the rotation speed of the developer carrier in a third period following the second period in the non-image formation period is the developer carrier in the image formation period. Control the second drive to be slower than the rotational speed of the body,
The image forming apparatus according to any one of claims 1 to 3, wherein When the control unit executes the mode, the rotational speed of the first transport screw in the second period is zero, and the rotational speed of the second transport screw in the second period is zero.
The image forming apparatus according to any one of claims 1 to 4, characterized in that: The control unit can execute the mode each time the image forming operation is performed on a predetermined number of recording materials.
The image forming apparatus according to any one of claims 1 to 5, wherein The image processing apparatus further includes an acquisition unit that acquires information on the temperature of the developer contained in the developing container.
The control unit determines the predetermined number of sheets based on the information on the temperature of the developer acquired by the acquisition unit, and the mode is set every time the image forming operation is performed on the determined predetermined number of recording materials. Is feasible,
The image forming apparatus according to claim 6, The image processing apparatus further includes an acquisition unit that acquires information on the amount of toner consumed as the image forming operation is performed on a plurality of recording materials.
The control unit determines the predetermined number of sheets based on the information on the toner amount acquired by the acquisition unit, and can execute the mode each time the image forming operation is performed on the determined predetermined number of recording materials Is
The image forming apparatus according to claim 6, A first acquisition unit configured to acquire information on the temperature of the developer contained in the developer container;
A second acquisition unit that acquires information on the amount of toner consumed as the image forming operation is performed on a plurality of recording materials;
And further
The control unit determines the predetermined number of sheets based on the information on the temperature of the developer acquired by the first acquisition unit and the information on the toner amount acquired by the second acquisition unit. The mode can be performed each time the image forming operation is performed on a recording material.
The image forming apparatus according to claim 6, The control unit can execute the mode each time the image forming operation is performed for a predetermined time.
The image forming apparatus according to any one of claims 1 to 5, wherein The control unit is capable of executing the mode each time the developer carrier is rotated a predetermined number of times.
The image forming apparatus according to any one of claims 1 to 5, wherein The first drive unit is a motor for rotationally driving the first conveyance screw and the second conveyance screw.
The second drive unit is a motor for rotationally driving the developer carrier.
The image forming apparatus according to any one of claims 1 to 11, wherein A developer supply unit for supplying the developer to the developing container;
A developer discharge unit for discharging a part of the developer as the developer is supplied by the developer supply unit;
Further comprising
The image forming apparatus according to any one of claims 1 to 12, wherein The restricting portion is vertically above the rotation center of the developer carrier.
The image forming apparatus according to any one of claims 1 to 13, wherein The rotation center of the first conveyance screw is vertically above the rotation center of the developer carrier.
The image forming apparatus according to any one of claims 1 to 14, characterized in that: The bottom of the first chamber is vertically above the bottom of the second chamber,
An image forming apparatus according to any one of claims 1 to 15, characterized in that.

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