JP2013054106A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus which keeps a constant developer level in a circulation pathway along a developer carrier when the processing speed is switched, and generates no quality deterioration of an output image without additional member or mechanism.SOLUTION: An image forming part 1 is capable of executing image formations in a constant speed mode and in a half speed mode. When the half speed mode is switched to the constant speed mode, an image forming operation is interrupted, and a developing sleeve is made to rotate at a higher rotation speed than a second rotation speed to execute an idle rotation performance for discharging a developer from a discharge port 4g. Driving time of a screw member 4c in the idle rotation performance is changed according to a history related to a developer supply amount in the execution time of the executed half speed mode. The longer the execution time of the half speed mode is, the longer the driving time of the screw member 4c is set in the idle rotation performance.

Description

  The present invention relates to an image forming apparatus capable of developing a toner image at a plurality of process speeds using a developer in which toner and a carrier are mixed, and more particularly, to reduce the quality of an output image immediately after changing the process speed. It relates to control to prevent.

  The developing device transfers the toner image developed on the image carrier using a developer in which toner and carrier are mixed to the recording material directly or via an intermediate transfer member, and heats and pressurizes the recording material onto which the toner image has been transferred. Therefore, an image forming apparatus that fixes an image on a recording material is widely used. In the developing device, the toner is consumed as the image is formed, but the carrier is not consumed and continues to circulate in the developing device. Therefore, there is a problem that the charging performance of the carrier is lowered as the image formation is accumulated. Therefore, there is a developing device that replenishes the developing device with a replenishment developer in which a certain amount of carrier is mixed with replenishment toner, while overflowing the developer in the developing device that has become excessive due to replenishment through the discharge port. It has been put into practical use (Patent Document 1).

  By the way, an image forming apparatus capable of switching the rotation speed of the image carrier, that is, the so-called process speed, in a plurality of stages according to the type of recording material used has been put into practical use. In a developing device, generally, a developer carrying member that carries toner and develops an electrostatic image of an image carrier and a screw member that circulates the developer in the developing device are linked in a gear train at a constant speed. Rotating at a ratio. For this reason, when the process speed is switched from a high speed to a low speed and the rotation speed of the developer carrier is changed from the first rotation speed to the second rotation speed lower than the first rotation speed, the rotation speed of the screw member is also increased. And the developer level in the developing device is lowered. This is because the effect of the developer jumping up by the screw member is reduced and the apparent developer density in the developing device is increased.

  On the other hand, when the process speed is switched from a low speed to a high speed and the rotation speed of the developer carrier is changed from the second rotation speed to the first rotation speed, the rotation speed of the screw member is increased and the developer level in the developing device is increased. Rises. This is because the effect of the developer jumping up by the screw member is increased and the apparent developer density in the developing device is decreased.

  Patent Document 2 discloses a developing device in which a regulating member for keeping a developer level constant is disposed between a developer carrying member and a screw member. The developer level in the circulation path along the developer carrier is kept constant by the regulating member, and the developer delivery condition between the screw member and the developer carrier is kept constant.

JP 2008-70539 A JP 7-175304 A

  In recent years, developing devices that overflow the developer through the discharge port have been miniaturized, and the amount of developer to be filled has decreased to the first half of 300 g, while the developing device has been developed in order to increase productivity in response to a high process speed. On the contrary, the circulation speed of the developer is increasing. As a result, the change in the developer level when the process speed is switched is larger than in the conventional case.

  Under such circumstances, if the image forming apparatus finishes the low process speed image formation and then returns to the high process speed image formation, the density of the toner image developed by the developing apparatus tends to be partially reduced. There was found. As will be described later, when the developer level in the circulation path along the developer carrier exceeds a predetermined limit, the developer with a small amount of toner carried on the developer carrier and finished with development again becomes the developer carrier. It has been found that the ratio of being carried and involved in development is increased, and the development efficiency is reduced.

  Therefore, as shown in Patent Document 2, a regulating member is arranged in parallel with the developer carrier so that the developer level in the circulation path along the developer carrier can be kept constant even when the process speed changes. It was considered to be. However, the downsized developing device does not have a space for arranging a regulating member that can exhibit a sufficient effect. There is also a problem that the cost is increased by a sensor for detecting the developer level and a motor for driving the regulating member.

  In the present invention, the developer level in the circulation path along the developer carrying member when the process speed is switched is kept constant without adding members or mechanisms, and the output image quality is not deteriorated. An object of the present invention is to provide an image forming apparatus.

  The image forming apparatus of the present invention includes an image carrier, an electrostatic image forming unit that forms an electrostatic image on the image carrier, and a developer that carries a developer and develops the electrostatic image of the image carrier. A carrier, a circulation path through which the developer circulates along the developer carrier, a screw member that feeds the developer in the circulation path to the developer carrier, and a predetermined height of the circulation path A discharge port through which the developer is discharged, and a replenishing device for replenishing the developer to the circulation path, wherein the developer carrying member and the screw member rotate at a constant speed ratio, and the developer carrying The first image forming mode for setting the first rotation speed on the body and the second image forming mode for setting the second rotation speed lower than the first rotation speed on the developer carrying member can be executed. Then, when switching from the second image forming mode to the first image forming mode, the image forming operation is interrupted and the developer carrier is rotated at a rotational speed higher than the second rotational speed, so that the discharge port A control unit capable of executing a discharge mode for discharging the developer from the discharge mode, wherein the control unit determines the drive time of the screw member in the discharge mode and the developer time in the execution time of the executed second image forming mode. Change according to the history of the replenishment amount.

  In the image forming apparatus of the present invention, the discharge mode is executed and the second image forming mode is executed after waiting for the excess developer to be discharged from the discharge port. The developer level in the circulation path along the agent carrier is sufficiently lowered.

  Accordingly, the developer level in the circulation path along the developer carrying member when the process speed is switched can be kept constant without adding members and mechanisms, and the output image quality does not deteriorate. That's it.

1 is an explanatory diagram of a configuration of an image forming apparatus. It is explanatory drawing of a structure of an image formation part. FIG. 6 is an operation process diagram of the image forming apparatus. It is explanatory drawing of supply and discharge | emission of the developer with respect to a developing device. It is explanatory drawing of the drive system of a developing device. It is explanatory drawing of the dosage level height immediately after switching from normal image formation mode to OHT mode. It is explanatory drawing of the dosage level height immediately after switching from OHT mode to normal image formation mode. 3 is a time chart of discharge mode control according to the first embodiment. 3 is a flowchart of discharge mode control according to the first embodiment. FIG. 7 is an explanatory diagram of a relationship between idling time and developer discharge amount in a constant speed mode. 6 is a flowchart of discharge mode control according to the second embodiment. 10 is a flowchart of discharge mode control according to the third embodiment. FIG. 10 is an explanatory diagram of an example of discharge mode control according to the third embodiment. 10 is a flowchart of supply mode control according to a fourth embodiment. FIG. 6 is an explanatory diagram of developer discharge characteristics in a high productivity mode.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, as long as the developer level in the developer container is adjusted by executing the discharge mode or the replenishment mode when the process speed is switched, a part or all of the configuration of the embodiment is replaced with the alternative configuration. Other embodiments can also be implemented.

  Therefore, any developing device that uses a two-component developer to overflow excess developer from the discharge port can be implemented without distinction between a vertical stirring type / horizontal stirring type and a supply / recovery integrated type / function separation type. The image forming apparatus can be implemented without any distinction between a tandem type / 1 drum type, an intermediate transfer type / a recording material conveyance type / a direct transfer type, an electrostatic image formation method, and a transfer method. In the present embodiment, only main parts related to toner image formation / transfer will be described. However, the present invention includes a printer, various printing machines, a copier, a fax machine, a composite machine, in addition to necessary equipment, equipment, and a housing structure. It can be implemented in various applications such as a machine.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of the configuration of the image forming apparatus. FIG. 2 is an explanatory diagram of the configuration of the image forming unit.

  As shown in FIG. 1, the image forming apparatus 100 is a tandem intermediate transfer type full-color printer in which yellow, magenta, cyan, and black image forming units 1Y, 1M, 1C, and 1Bk are arranged along an intermediate transfer belt 16. is there. In the image forming unit 1Y, a yellow toner image is formed on the photosensitive drum 2Y and transferred to the intermediate transfer belt 16. In the image forming unit 1M, a magenta toner image is formed on the photosensitive drum 2M and transferred to the intermediate transfer belt 16. In the image forming units 1 </ b> C and 1 </ b> Bk, a cyan toner image and a black toner image are formed on the photosensitive drums 2 </ b> C and 2 </ b> Bk and transferred to the intermediate transfer belt 16.

  The secondary transfer roller 15 is in contact with the intermediate transfer belt 16 whose inner surface is supported by the opposing roller 10 to form a secondary transfer portion T2. The recording material P drawn from the recording material cassette 20 is separated one by one by the separation roller 21 and sent to the registration roller 14. The registration roller 14 sends the recording material P to the secondary transfer portion T2 in synchronization with the toner image on the intermediate transfer belt 16. A full color toner image is recorded from the intermediate transfer belt 16 by applying a positive DC voltage to the secondary transfer roller 15 in the process in which the recording material P is nipped and conveyed over the secondary transfer portion T2 while being superimposed on the toner image. Secondary transfer to the material P is performed. The untransferred toner remaining on the intermediate transfer belt 16 without being transferred is collected by the belt cleaning device 18.

  The four color toner images carried on the intermediate transfer belt 16 are conveyed to the secondary transfer portion T2 and are collectively secondary transferred to the recording material P. The recording material P on which the four-color toner images are secondarily transferred is separated from the intermediate transfer belt 16 by the curvature and sent to the fixing device 13. The fixing device 13 heats and presses the recording material P to melt the toner and fix the image on the surface. Thereafter, the recording material P is discharged out of the machine body.

  The image forming units 1Y, 1M, 1C, and 1Bk are configured substantially the same except that the color of toner used in each developing device is different from yellow, magenta, cyan, and black. Hereinafter, a toner image forming process for the general image forming unit 1 will be described with reference to FIG. 2, using reference numerals excluding Y, M, C, and Bk that distinguish the image forming units.

  As shown in FIG. 2, the image forming unit 1 includes a charging roller 3, an exposure device 7, a developing device 4, a transfer roller 5, and a drum cleaning device 6 around the photosensitive drum 2. The photosensitive drum 2 is an organic photoconductor (OPC) having a negative charging property, and rotates in the direction of the arrow R1 at a predetermined process speed around an outer diameter of 30 mm and a central support shaft.

  The charging roller 3 is in contact with the surface of the photosensitive drum 2 and is driven to rotate. An oscillating voltage in which a frequency of 1.3 kHz, a peak-to-peak voltage Vpp of 1.5 kV, and a sinusoidal AC voltage (Vac) are superimposed on a DC voltage (Vdc) of −500 V is applied to the charging roller 3. As a result, the surface of the photosensitive drum 2 is uniformly charged to −500 V (dark portion potential VD) which is the same as the DC voltage applied to the charging roller 3.

  The exposure device 7 scans the scanning line image data obtained by developing the one-color image of the image with a rotating mirror, and writes an electrostatic image of the image on the surface of the photosensitive drum 2. The developing device 4 develops the electrostatic image on the photosensitive drum 2 into a toner image using a two-component developer including toner and carrier.

  The transfer roller 5 is brought into contact with the inner surface of the intermediate transfer belt 16 supported by the photosensitive drum 2 with a predetermined pressing force to form a toner image transfer portion between the photosensitive drum 2 and the intermediate transfer belt 16. The power source S3 applies a DC voltage of +2 kV, which is opposite in polarity to the charging polarity of the toner, to the transfer roller 5. As a result, the toner image on the surface of the photosensitive drum 2 is electrostatically transferred to the surface of the intermediate transfer belt 16 sequentially. The drum cleaning device 6 rubs the photosensitive drum 2 with a cleaning blade to collect the transfer residual toner remaining on the photosensitive drum 2Y by escaping from the transfer.

<Operation Process of Image Forming Apparatus>
FIG. 3 is an operation process diagram of the image forming apparatus. As shown in FIG. 3, the pre-multi-rotation step a is a start (start) operation period (warming period) of the image forming apparatus. When the main power switch of the image forming apparatus 100 is turned on, the pre-multi-rotation process a is started, the main motor of the image forming apparatus 100 is started, and a preparation operation for required process equipment is executed.

  The standby b is a time for holding the image forming apparatus in a standby (standby) state until the drive of the main motor is stopped and a print job start signal is input after a predetermined start operation period ends.

  The pre-rotation process c is a period in which the main motor is re-driven based on the input of the print job start signal and the pre-print job operation of the required process equipment is executed. Specifically, 1. the image forming apparatus receives a print job start signal; 2. Expand the image with the formatter (the expansion time varies depending on the amount of image data and the processing speed of the formatter). The sequence of starting the pre-rotation process is executed. When the print job start signal is input during the previous multi-rotation process a, after the previous multi-rotation process a is completed, the process proceeds to the pre-rotation process c without standby.

  The print job execution d is a time during which the actual image forming process is executed after the predetermined pre-rotation process is completed, and an image-formed recording material is output. In the case of a continuous print job, the image forming process is repeated, and a predetermined number of image-formed recording materials are sequentially output.

  In the case of a continuous print job, the inter-sheet process e is an interval process between the trailing edge of one recording material P and the leading edge of the next recording material P, and is a non-sheet passing state period in the transfer unit and the fixing device. .

  In the post-rotation step f, in the case of a single print job, after the image-formed recording material is output, or in the case of a continuous print job, the last image-formed recording material of the continuous print job is output. After that, the main motor is continuously driven for a predetermined time. Thus, it is a period during which the post-print job operation of the required process device is executed.

  The standby g holds the image forming apparatus in a standby (standby) state until the drive of the main motor is stopped and the next print job start signal is input after a predetermined post-rotation process is completed.

  In the above operation process, the print job execution time d is an image formation time, the pre-multi-rotation process time a, the pre-rotation process time c, the sheet-to-paper process e, and the post-rotation process time f are non-image formation times. At the time of non-image formation, at least one of the pre-multi-rotation process a, the pre-rotation process c, the inter-sheet process e, and the post-rotation process f, and at least a predetermined time within the process It is.

<Developing device>
As shown in FIG. 2, a two-component development system is used in which toner and carrier are mixed and used as a developer. The developing device 4 employs a two-component contact development method in which development is performed while bringing a magnetic brush made of a two-component developer into contact with the photosensitive drum 2. The two-component development system has advantages such as stability of image quality and durability of the apparatus as compared with other currently proposed development systems.

  In the developing device 4, a nonmagnetic developing sleeve 4b is rotatably disposed in the developing container 4a. The developing sleeve 4 b is opposed to the photosensitive drum 2 by exposing a part of the outer peripheral surface to the outside of the developing device 4. In the developing sleeve 4b, a magnet roller 4w is inserted in a non-rotating manner.

  The developing container 4a contains a two-component developer that is mainly a mixture of toner (non-magnetic) and carrier (magnetic). The toner has colored resin particles containing a binder resin, a colorant, and other additives as necessary. The toner is a negatively chargeable polyester resin produced by a polymerization method, and the volume average particle diameter is preferably 5 μm or more and 8 μm or less. Here, the volume average particle diameter is 6.2 μm.

As the carrier, metals such as surface oxidized or unoxidized iron, nickel, cobalt, manganese, chromium, rare earth, alloys thereof, or oxide ferrite can be preferably used. The method for producing these magnetic particles is not particularly limited. The carrier has a weight average particle diameter of 20 to 50 μm, preferably 30 to 40 μm, and a resistivity of 10 ⁷ Ω · cm or more, preferably 10 ⁸ Ω · cm or more. Here, as the low specific gravity magnetic carrier, a resin magnetic carrier produced by mixing a phenolic binder resin with a magnetic metal oxide and a nonmagnetic metal oxide at a predetermined ratio and using a polymerization method was used. The resistivity is 10 ⁸ Ω · cm, the volume average particle diameter is 35 μm, the true density is 3.6 to 3.7 g / cm ³ , and the magnetization is 53 A · m ² / kg.

  A screw member 4c is disposed on the bottom side in the developing container 4a and rotates in the direction of the arrow. In the process in which the two-component developer in the developing container 4a is agitated by the screw member 4c, the toner is triboelectrically charged to the negative polarity by sliding with the carrier.

  The developing sleeve 4b is disposed to face the photosensitive drum 2 while maintaining the closest distance (S-Dgap) to the photosensitive drum 2 at 350 μm. The opposing portion between the photosensitive drum 2 and the developing sleeve 4b is an electrostatic image developing portion c. The developing sleeve 4b is driven to rotate in the direction opposite to the traveling direction of the photosensitive drum 2 in the developing unit c. The rotation speed of the developing sleeve 4b is always rotating at a constant speed ratio of 1.5 times the circumferential speed of the photosensitive drum 2.

  Due to the magnetic force of the magnet roller 4w in the developing sleeve 4b, a part of the two-component developer in the developing container 4a is attracted and held on the outer peripheral surface of the developing sleeve 4b as a magnetic brush layer. The magnetic brush layer is rotated and conveyed with the rotation of the developing sleeve 4b, and the tip of the developing unit c comes into contact with the surface of the photosensitive drum 2 to rub the surface of the photosensitive drum appropriately.

  The power source S2 applies a predetermined developing voltage to the developing sleeve 4b. The development voltage is an oscillating voltage obtained by superimposing a DC voltage (Vdc) and an AC voltage (Vac). Specifically, the development voltage is an oscillating voltage in which a DC voltage of −350 V, a frequency of 8.0 kHz, a peak-to-peak voltage of 1.8 kV, and a rectangular wave AC voltage are superimposed.

  The two-component developer is coated as a thin layer on the surface of the rotating developing sleeve 4b and is conveyed to the developing unit c to form a magnetic brush. The toner in the magnetic brush is selectively attached to the electrostatic image on the surface of the photosensitive drum 2 by the electric field of the developing voltage, and the electrostatic image is developed into the toner image. The developer on the developing sleeve 4b that has passed through the developing section c is collected in the developer reservoir in the developing container 4a with the subsequent rotation of the developing sleeve 4b.

<Automatic developer replacement method>
FIG. 4 is an explanatory diagram of supply and discharge of the developer to the developing device. FIG. 5 is an explanatory diagram of a drive system of the developing device. In FIG. 5, the developing device 4 of FIG. 2 is shown in a plan sectional view as viewed from above, while the toner replenishing device 32 is shown in a vertical sectional view along the rotational axis direction of the photosensitive drum 2.

  As shown in FIG. 4, the developing device 4 inevitably deteriorates the developer accompanying the accumulation of image formation, in particular, a decrease in the charging performance of the carrier. This eliminates the need for regular developer replacement or developing device replacement by a service person, and improves maintainability and reduces running costs. Such a system is generally called a developer automatic replacement system. When the carrier is not replaced, toner fragments and external additives are gradually accumulated on the surface of the carrier, and the net friction area against the toner is impaired, so that the charging performance is deteriorated. As a result, the toner charge amount Q / M decreases, and white background fog, toner scattering, and development quality decrease. Since the developing device 4 is configured so that the carriers in the developing container 4a are gradually replaced, there is an effect of prolonging the life of the developer. The interval at which the developing device 4 is replaced with a new one is set every 600,000 image formations.

  The developing device 4 replenishes the developer container 4a with the developer containing the toner consumed by the developing operation from the toner bottle 4d, and disposes the developer in the developing container 4a that has become excessive due to the replenishment to the outside of the developing device 4. The discharged developer collection tank 4e is discharged. Since the developing device 4 discharges the surplus developer almost simultaneously with the replenishment of the developer, it is possible to stabilize the characteristics of the entire developer without causing an increase in the size of the image forming apparatus 100 and an increase in cost. is there. In the developing device 4, the old and new developers are replaced.

  The toner bottle 4d replenishes the developing container 4a with a replenishing developer in which a small amount of carrier is mixed in the toner. A transport path 4h for transporting the developer cut out from the hopper 4i by the replenishing screw 4j is connected to the replenishing port 4f of the developing container 4a. The hopper 4i temporarily stores the developer taken out from the toner bottle 4d and transfers it to the replenishing screw 4j in the conveyance path 4h. An encoder 4k for detecting the rotation amount of the supply screw 4j is attached to the upstream end of the supply screw 4j.

  At the same time as the developer bottle 4d replenishes the developer, the discharge port 4g of the developer container 4a overflows the developer in the developer container 4a from the discharge port 4g and delivers it to the discharge screw 4n. When a new developer is replenished from the toner bottle 4d and the volume of the developer in the developing container 4a increases, the developer in the developing container 4a overflows from the discharge port 4g and the developer is automatically replaced. .

  A discharge pipe 4m for discharging the deteriorated developer is connected to the discharge port 4g. A developer recovery tank 4e is detachably attached to the lower end of the discharge pipe 4m. A discharge screw 4n is disposed in the discharge pipe 4m, and the discharge screw 4n conveys the discharged developer to the developer recovery tank 4e.

  A developer circulation path is formed in the developing container 4a (see FIG. 5). In the developer circulation path, the discharge port 4g is disposed downstream of the position where the developer is coated on the developing sleeve 4b. A replenishment developer supply port 4f is arranged downstream of the discharge port 4g so that the developer just supplied from the discharge port 4g is not discharged.

  In the developing device 4, as the amount of the carrier supplied to the developing container 4a per unit time is larger, the replacement of the circulating developer carrier becomes faster, and the charging performance of the developer is stably kept high. For that purpose, it is better that the amount of the carrier mixed in the replenishment developer accommodated in the toner bottle 4d is larger. However, since replenishment of developer is mainly toner, the carrier ratio of the replenishment developer is limited to 40 Wt% in terms of the amount of replenishment of toner. There is also a problem that the developer cost increases as the ratio of the carrier contained in the replenishment developer increases. For this reason, in the developing device 4, the carrier ratio of the developer for replenishment is 20 Wt%.

  As shown in FIG. 5, the exposure device 7 as an example of an electrostatic image forming unit forms an electrostatic image on a photosensitive drum 2 as an example of an image carrier. The developing sleeve 4b, which is an example of the developer carrying member, carries the developer and develops the electrostatic image on the photosensitive drum 2. In the circulation path, the developer circulates along the developing sleeve 4b. The developing screw 4cA supplies the developer in the circulation path to the developing sleeve 4b while conveying it. The developing sleeve 4b, the developing screw 4cA, and the stirring screw 4cB rotate at a constant speed ratio. The discharge port 4g discharges a developer having a predetermined height or more in the circulation path. A toner replenishing device 32, which is an example of a replenishing device, replenishes developer in the circulation path.

  The space in the developing container 4a is divided into a developing chamber 4u and a stirring chamber 4v by a partition wall 4k, and a developing screw 4cA is disposed in the developing chamber 4u as a screw member (4c), and the stirring screw 4cB is provided in the stirring chamber 4v. Is arranged. The developing chamber 4u and the stirring chamber 4v communicate with each other through openings 4p and 4q at both ends of the partition wall 4k to form a developer circulation path. As the developing screw 4cA and the stirring screw 4cB convey the developer in the opposite directions as indicated by arrows, the developer circulates in the developing container 4a.

  The developing sleeve 4b, the developing screw 4cA, and the stirring screw 4cB are connected by a gear train 54, and are driven by a motor 51 to rotate at a constant ratio determined by the gear ratio of the gear train 54 and a rotational speed in a constant direction. The rotation of the motor 51 is controlled to be turned ON / OFF and the rotation speed by the control unit 30 which is an example of a control unit.

  The developer replenished from the toner replenishing device 32 to the stirring chamber 4v is mixed with the two-component developer circulating in the developing container 4a as the stirring screw 4cB rotates. The supply screw 4 j of the toner supply device 32 is driven by a motor 53. In order to replenish the toner consumed by the image formation, a replenishment developer is accommodated in the toner bottle 4d. A toner concentration sensor 31 is disposed in the developing container 4a to detect the toner concentration of the two-component developer circulating in the developing container 4a. The toner concentration sensor 31 is an optical type that detects the reflectance of the developer, but may be a magnetic permeability sensor.

  A correspondence relationship between the rotation time of the motor 53 in a state where a predetermined amount of toner is accumulated in the hopper 4i and the amount of toner replenished into the developing container 4a by the replenishing screw 4j is obtained in advance by experiments or the like. As stored in the control unit 30. The control unit 30 sets the toner replenishment amount for the developing container 4 a by adjusting the rotation time of the motor 53.

  The control unit 30 controls the motor 53 based on the detection information of the toner concentration sensor 31 to operate the replenishing screw 4j, and the toner concentration (T / D ratio) of the developer circulating in the developing container 4a is 7%. The developer is supplied from the hopper 4i to the developing container 4a. As a result, the developer satisfying the required toner amount is supplied into the developing container 4a, and the toner concentration (T / D ratio) of the two-component developer in the developing container 4a is maintained within a certain range. However, the control target value of the toner density (T / D ratio) is appropriately set according to the toner charge amount, the carrier particle size, the configuration of the image forming apparatus, and the like, and is not necessarily 7%.

<Second image forming mode>
FIG. 6 is an explanatory diagram of the surface height immediately after switching from the normal image forming mode to the OHT mode. FIG. 7 is an explanatory diagram of the coating surface height immediately after switching from the OHT mode to the normal image forming mode. As shown in FIG. 1, the image forming apparatus 100 is designed so that various image forming modes can be used by utilizing the fact that images with different image quality are formed by changing the fixing processing speed. ing.

  In addition to a normal image forming mode for mainly forming characters and the like, an OHT mode for forming an image with high transparency on a transparent sheet for overhead projector (hereinafter referred to as OHT) can be executed. Further, in order to emphasize the vividness of the color, it is possible to execute a gloss mode for forming an image rich in gloss, a mode for forming a glossy feeling matched to the paper quality (gloss control mode), and the like.

  The OHT mode (second image forming mode) increases the solubility of the toner forming the image by increasing the heating time of the image fixing process, and is higher than the normal image forming mode (first image forming mode). Increases the transparency and gloss of the image. In the OHT mode, the time for the recording material P to pass through the fixing device 13 is lengthened by lowering the conveying speed of the recording material P conveyed to the fixing device 13 than in the normal image forming mode. Corresponding to lowering the conveyance speed of the recording material P, the rotation speeds of the intermediate transfer belt 16 and the photosensitive drums 2Y, 2M, 2C, and 2Bk are also lowered. That is, in the OHT mode (second image forming mode), a lower process speed is set than in the normal image forming mode (first image forming mode).

  Similarly, the gloss control mode for forming a glossy feeling that matches the gloss of the paper that is the recording material P and the gloss mode for increasing the gloss level each have a multi-stage process speed for generating the required gloss level. It will be.

  In addition, there is a case where it is desired to increase the productivity of image formation even when the gloss is lower than usual. To cope with such a case, the high productivity mode in which image formation is performed at a process speed close to the limit of the conveyance speed that can be fixed. It also has. In the high productivity mode, the image formation speed is higher than that in the constant speed mode, so that the glossiness of the image is reduced due to the reduction in fixing property. However, for image formation, such as a character image, which has few problems even with low glossiness, the user's stress can be alleviated by selecting the high productivity mode and shortening the job processing time.

  As shown in FIG. 2, the image forming unit 1 sets the developing sleeve 4 b to a constant speed mode that is an example of a first image forming mode for setting a first rotation speed, and a second rotation speed that is lower than the first rotation speed. It is possible to execute the 1/2 speed mode, which is an example of the second image forming mode for setting the.

  In the OHT mode, the gloss mode, the gloss control mode, and the high productivity mode, the rotation speed of the developing sleeve 4b and the rotation speed of the screw member 4c change with changes in the rotation speed of the photosensitive drum 2 and the conveyance speed of the recording material. To do. In the OHT mode (second image forming mode), the rotation speeds of the developing sleeve 4b and the screw member 4c change with the switching of the process speed.

  The rotational speed ratio between the photosensitive drum 2 and the developing sleeve 4b is fixed at a constant value by the driving configuration of the image forming apparatus (100: FIG. 1). The rotational speed ratio between the developing sleeve 4b and the screw members (4cA, 4cB) is fixed at a constant value by the driving configuration of the developing device 4 shown in FIG. Therefore, when the process speed is switched and the rotation speed of the photosensitive drum 2 is changed, the rotation speeds of the developing sleeve 4b and the screw member 4c are changed while keeping the rotation speed ratio constant. In the OHT mode in which the fixing speed is lowered and the toner is sufficiently melted to increase the glossiness than in the normal image forming mode (first image forming mode), the screw member is more than in the normal image forming mode (first image forming mode). The rotational speed of 4c decreases. On the contrary, in the high productivity mode in which the process speed is increased, the rotational speed of the screw member 4c is higher than that in the normal image forming mode (first image forming mode).

  As shown in FIG. 6, when the normal image forming mode (a) is changed to the OHT mode (b), the rotational speed of the stirring screw 4cB decreases as the process speed decreases, and the developer jumps up. Less. As a result, the developer surface in the agitating chamber 4v is lowered, and the discharge of the developer through the discharge port 4g is stopped. In this state, the developer is continuously replenished in the developer container. The developer in the container will increase considerably.

  As shown in FIG. 7, when the OHT mode in (a) is changed to the normal image forming mode in (b), the rotational speed of the stirring screw 4cB increases as the process speed increases, and the developer jumps. Increases. As a result, when the developer surface of the developing chamber 4u rises and comes into contact with the developing sleeve 4b, the low-concentration developer collected from the developer sleeve 4b to the developing chamber 4u is directly brought to the developer sleeve 4b. The ratio will increase.

  For this reason, immediately after the change from the OHT mode to the normal image forming mode, a portion having a low toner concentration is locally generated in a part of the developer carried on the developing sleeve, and the developed toner image has uneven density. May occur.

  After that, when image formation is continuously performed with the rotational speed of the stirring screw 4cB being increased, the developer is often splashed by the stirring screw 4cB. Since the discharge is promoted, the developer in the developing container is reduced.

  When the developer in the developing container is reduced, as shown in FIG. 6, when the normal image forming mode (a) is changed to the OHT mode (b), the developer in the developing container is immediately after the change. The surface height of the liquid drops sharply. When the developer surface height of the developer in the developer container is lowered, the developer sleeve 4b is not sufficiently coated with the developer, which may cause density unevenness in the developed toner image.

  As a result, in an image forming apparatus that continuously performs image formation by switching the process speed, a partial density decrease occurs in the developed toner image for a while after the process speed is switched, resulting in density unevenness. It tends to occur.

  Therefore, as shown in FIG. 2, it has been proposed that the screw member 4c continue to rotate at a constant speed even when the process speed is switched and the rotation speed of the developing sleeve 4b changes.

  However, when the screw member 4c continues to rotate at a high speed while the rotation speed of the developing sleeve 4b is low (a state where toner consumption is low), the deterioration of the developer proceeds rapidly. If the screw member 4c continues to rotate at a low speed while the rotation speed of the developing sleeve 4b is high (a state where toner consumption is high), density unevenness is generated in the developed toner image due to insufficient developer supplied to the developing sleeve 4b. Occur. For this reason, the developing sleeve 4b and the screw member 4c must be driven at a constant speed ratio. If the developing sleeve 4b and the screw member 4c are driven separately, there is a problem that the driving mechanism of the developing device 4 becomes complicated and it is difficult to reduce the size.

  Therefore, as disclosed in Patent Document 2, a developer level sensor for the developer is provided in the developer container, and it can be confirmed that the developer has reached a predetermined level after switching the process speed. Until now, control for waiting for image formation has been proposed.

  However, providing a detection sensor for the developer surface height of the developer is disadvantageous in terms of space including wiring space, and there is a problem that costs are increased.

  In the following embodiments, in an image forming apparatus that employs a developer replacement system, a developer discharging operation is performed at a predetermined timing in accordance with the paper type of the recording material that has been imaged and the history of the number of images formed. . As a result, even when the image forming speed is changed according to the paper type, the amount of developer in the developing device 4 can be kept appropriate, so that stable image formation can always be performed.

<Example 1>
FIG. 8 is a time chart of the discharge mode control of the first embodiment. FIG. 9 is a flowchart of the discharge mode control according to the first embodiment. FIG. 10 is an explanatory diagram of the relationship between the idling time and the developer discharge amount in the constant speed mode.

  In the first embodiment, in addition to the normal image forming mode in which the process speed is 300 mm / sec, an OHT mode and a gloss mode in which the process speed is 150 mm / sec are provided. Hereinafter, the normal image forming mode is referred to as “constant speed mode”, and the OHT mode and the gloss mode are referred to as “½ speed mode”.

  When the process speed changes from 300 mm / sec to 150 mm / sec, the rotation speed of the developing sleeve changes from 450 mm / sec to 225 mm / sec.

  First, as a preliminary experiment, the developing device 4 is placed on a weighing scale and operated in various modes, and the developer is gradually filled from the supply port 4f, and the developer begins to be discharged from the discharge port 4g. The amount of developer was measured.

  When the operation is performed in the constant speed mode, the discharge starts when the developer amount in the developing container is 200 g. Therefore, the maximum developer amount of the developing device 4 in the constant speed mode is 200 g. The appropriate developer amount that does not cause density unevenness in the output image in the constant speed mode is 200 g or less.

  When the operation is performed in the 1/2 speed mode, since the discharging starts when the developer amount in the developing container is 220 g, the maximum developer amount of the developing device 4 in the 1/2 speed mode is 220 g. The appropriate developer amount that does not cause density unevenness in the output image in the 1/2 speed mode is 220 g or more.

  As shown in FIG. 8, in Example 1, the developing sleeve 4b is rotated at a rotational speed higher than the second rotational speed every time a job in the 1/2 speed mode, which is an example of the second image forming mode, is completed. Then, an idling operation for discharging the developer from the discharge port 4g is executed. The idling operation, which is an example of the discharge mode, is executed by operating only the developing device 4 in a state where the photosensitive drum 2 is stopped after completion of the job in the 1/2 speed mode.

  The idling operation is started by starting the developing sleeve 4b after stopping the voltage applied to the developing sleeve 4b in a state where the rotation of the developing sleeve 4b is stopped. The next constant speed mode job is started by starting the developing sleeve 4b after applying the voltage to the developing sleeve 4b with the developing sleeve 4b stopped once after the idling operation is completed.

  That is, when image formation is performed in the 1/2 speed mode, the image forming operation is temporarily interrupted after the end of the job in the 1/2 speed mode every time. Subsequently, by performing idling of the developing device 4 at a rotation speed corresponding to the constant speed mode for 20 seconds, the developer discharge through the discharge port 4g is promoted.

  As shown in FIG. 9 with reference to FIG. 3, in the first embodiment, when image formation in the 1/2 speed mode is performed (YES in S12), the image forming operation is temporarily interrupted (S13), 20 sec, etc. The idling operation of the developing device 4 is performed in the speed mode (S14).

  After starting the copy, the control unit 30 acquires information related to the image forming mode (1/2 speed mode, constant speed mode) (S11).

  When the image formation is performed in the 1/2 speed mode (Y in S12), the control unit 30 once completes the image formation after the end of the copy job in the 1/2 speed mode (S13), and the developing device 4 is empty. A rotation operation is executed (S14).

  After executing the idling operation of the developing device 4 (S14), the control unit 30 acquires information about the constant speed mode (S11) when there is a constant speed mode job (S11), and the constant speed mode job. Is executed (S12).

  When the image formation is performed in the constant speed mode (N in S12), the control unit 30 does not execute the idling operation of the developing device 4 after the end of the copy job in the constant speed mode (S15).

  As shown in FIG. 10, the constant speed mode operation is performed with the developer amount in the developer container 4a at the end of the 1/2 speed mode being 220 g, and the cumulative amount of developer discharged through the discharge port 4g is calculated. Asked. After starting the operation in the constant speed mode, 20 g is discharged through the discharge port 4g by idling for 20 seconds, and the developer amount in the developing container 4a may be 200 g which is the appropriate developer amount in the constant speed mode. found.

  Therefore, when the image is formed in the 1/2 speed mode (Y in S12), the idling time is set to 20 seconds, so that the developer amount is 200 g in which the density unevenness does not occur in the constant speed mode (S14). ).

  In the first exemplary embodiment, in the image forming apparatus 100 adopting the developer replacement method, the developer discharging operation is performed by the idling operation of the developing device 4 according to the paper type of the recording material. As a result, even when the process speed is changed in accordance with the paper type, the amount of developer in the developing container 4a can be kept appropriate, so that stable image formation can be achieved over a long period of time.

  In the first exemplary embodiment, the image forming apparatus is not limited to the intermediate transfer type, and can be applied to an image forming apparatus of a direct transfer type in which a toner image is directly transferred from a photosensitive drum to a recording material. The dimensions, materials, shapes, relative positions, and the like of the components of the image forming apparatus described are not limited to these unless otherwise specified.

  In the first embodiment, after image formation is performed in the 1/2 speed mode, the developing device 4 is idled at a rotation speed corresponding to the constant speed mode. However, the rotational speed of the idling operation does not need to be equivalent to the constant speed mode, and the idling speed higher than that corresponding to the constant speed mode may be adopted to discharge the developer in a shorter time.

<Example 2>
FIG. 11 is a flowchart of the discharge mode control according to the second embodiment.

  In the first embodiment, at the end of the job in the 1/2 speed mode, the developing device 4 is idly rotated at a rotation speed corresponding to the constant speed mode for 20 seconds each time, and the developer amount in the developing container 4a is set to the constant speed mode. The developer amount was returned to an appropriate amount. That is, the discharge mode for a predetermined time is executed regardless of the toner consumption per image forming sheet and the number of image forming sheets in the 1/2 speed mode job.

  For this reason, when the toner is not consumed and the developer is not replenished in the 1/2 speed mode job, an extra idling operation is performed without increasing the amount of developer in the developer container 4a. There was a case.

  Therefore, in the second embodiment, the driving time of the screw member 4c in the idling operation is changed according to the history relating to the developer replenishment amount in the execution time of the executed 1/2 speed mode. The developer amount in the developer container 4a is predicted from the history of the developer replenishment amount in the completed 1/2 speed mode job, and the idling time of the developing device 4 is set according to the predicted value. A variable discharge mode duration is set according to the excess amount of developer in the developer container 4a determined from the developer replenishment amount in the completed 1/2 speed mode job.

  The controller 30 sets the drive time of the screw member 4c in the idling operation longer as the execution time of the 1/2 speed mode is longer. The controller 30 sets the drive time of the screw member 4c in the idling operation longer as the developer replenishment amount replenished during the 1/2 speed mode execution time increases. When the execution time of the 1/2 speed mode is longer than the predetermined time, the control unit 30 sets the drive time of the screw member 4c in the idling operation to a certain time. The control unit 30 sets the drive time of the screw member 4c in the idling operation to a certain time when the supply amount of the developer replenished during the execution time of the 1/2 speed mode is a predetermined amount or more.

  As shown in FIG. 11 with reference to FIG. 3, after starting the copy, the control unit 30 acquires information related to the image forming mode (1/2 speed mode, constant speed mode) (S21).

  When the image formation is performed in the 1/2 speed mode (Y in S22), the control unit 30 acquires the number of copies and the toner supply amount when the image formation is performed in the 1/2 speed mode (S23). The developer replenishment amount in one job in the 1/2 speed mode is obtained (S24).

  The control unit 30 variably sets the idling time of the developing device 4 according to the estimated value of the developer supply amount (S25).

  More specifically, the maximum developer amount in the developing container 4a in the constant speed mode is 200 g, and the maximum developer amount in the developing container 4a in the 1/2 speed mode is 220 g. As shown in FIG. 10, the control unit 30 reduces the developer amount of 220 g to 200 g by idling the developing device 4 for a maximum of 20 seconds. The control unit 30 sets the idling time in the range from 0 to 20 seconds according to the developer supply amount.

The amount of toner consumed per A4 size image forming sheet with the highest overall density is 400 mg. When 200 images of the A4 size full-surface maximum density are continuously formed in the 1/2 speed mode, toner of the following formula is consumed and replenished.
200 sheets x 400mg = 80g

As described above, since toner replenishment is performed using a replenishment developer having a carrier ratio of 20%, the amount of developer that is replenished to the developing container 4a and increased in the developing container 4a due to toner replenishment is as follows. It becomes the quantity of the formula.
80g × 0.2 / 0.8 = 20g

As a result, the developer amount in the developing container 4a at the end of the 1/2 speed mode is estimated as the following equation.
200g + 20g = 220g

  Based on the table of FIG. 10, the control unit 30 sets 20 seconds for idling corresponding to the constant speed mode in order to discharge the excess 20 g of developer (S25). After the job in the 1/2 speed mode is completed (S26), the control unit 30 idles the developing device 4 for 20 seconds at a rotation speed such as the constant speed mode phase (S26).

  In addition, when 100 images of the A4 size full-surface maximum density are continuously formed in the 1/2 speed mode, the same calculation is performed to calculate the toner supply amount of 40 g, and the developer supply amount is It is calculated as 10 g (S24).

As a result, the developer amount in the developing container 4a at the end of the 1/2 speed mode is estimated as the following equation.
200g + 10g = 210g

  Based on the table of FIG. 10, the control unit 30 sets 10 seconds for idling corresponding to the constant speed mode in order to discharge the excess 10 g of developer (S25). After the job in the 1/2 speed mode is completed (S26), the control unit 30 idles the developing device 4 for 10 seconds at a rotation speed such as the constant speed mode phase (S26).

  After executing the idling operation of the developing device 4 (S27), the control unit 30 obtains information about the constant speed mode (S21) when there is a constant speed mode job (N in S28). Is executed (S22).

  When the image forming is performed in the constant speed mode (N in S22), the control unit 30 does not execute the idling operation of the developing device after the end of the copy job in the constant speed mode (S28).

  In the second embodiment, in the image forming apparatus 100 adopting the developer replacement method, the developer amount in the developing container 4a is predicted from the history of the toner replenishment amount in the 1/2 speed mode, and the predicted developer amount is obtained. Accordingly, the idling time of the developing device 4 is determined. As a result, the constant speed mode can be started earlier by executing the idling operation of the developing device 4 in a shorter time than in the first embodiment.

<Example 3>
FIG. 12 is a flowchart of the discharge mode control according to the third embodiment. FIG. 13 is an explanatory diagram of an example of the discharge mode control of the third embodiment.

  In the third embodiment, image formation in the constant speed mode and image formation in the 1/2 speed mode are mixed in one job. Therefore, the developer amount in the developer container 4a is predicted from the history of developer replenishment amounts in the constant speed mode and the 1/2 speed mode in one completed job, and development is performed according to the predicted value. The idling time of the device 4 is set.

  In Example 3, the maximum developer amount of the developing device 4 in the constant speed mode is 200 g. The maximum developer amount of the developing device 4 in the 1/2 speed mode is 220 g. Then, the appropriate developer amount of the developing device 4 in the constant speed mode is set to 210 g or less. FIG. 10 shows developer discharge characteristics during idling equivalent to the constant speed mode.

  As shown in FIG. 12 with reference to FIG. 3, when the copy job starts, the control unit 30 acquires information regarding the image forming mode (1/2 speed mode, constant speed mode) (S31). The control unit 30 acquires the number of copies and the amount of toner replenished when image formation is performed in the constant speed mode and the 1/2 speed mode (S32), and estimates and calculates the amount of developer in the developing container 4a (S33). ).

As shown in FIG. 13, when 50 A4 full-size full-surface images are formed in the 1/2 speed mode, the toner replenishment amount per image formation is 400 mg. Is done.
50 sheets x 400mg = 20g

The amount of carrier replenished to the developing container 4a with replenishment of the replenishment developer for replenishing the toner 20g is expressed by the following equation because the carrier ratio in the replenishment developer is 20%.
20g × 0.2 / 0.8 = 5g

As a result, the developer amount is predicted as follows:
200g + 5g = 205g

Subsequently, when three A4 size images are output in the constant speed mode, the developing device 4 rotates for 5 seconds at the rotation speed in the constant speed mode. As a result, the developer amount is predicted from the following equation from FIG.
205g-3g = 202g

  As described above, the developer amount in the developing container 4a is predicted based on the image formation history information in the constant speed mode and the half speed mode (S33).

  Then, when the copying operation in the 1/2 speed mode is continued and it is determined that the developer amount is greater than 210 g (N in S34), the constant speed mode phase or the like is used to discharge the excess amount of developer. The minimum necessary idling operation is executed at the rotation speed of. In FIG. 13, since it is 220 g, idling for 10 seconds is executed in order to discharge 10 g of the excess developer.

  In Example 3, when the image formation in the 1/2 speed mode and the image formation in the constant speed mode are repeated, and the developer amount in the developing container 4a is estimated to be 210 g or less, the 1/2 speed The idle rotation operation of the developing device 4 is not executed at the end of the mode (Y in S34). For this reason, the idle rotation time of the developing device 4 can be set to be shorter than the discharge mode control of the first embodiment in which the idle rotation operation is executed every time the image formation in the 1/2 speed mode is completed.

  Only when it is estimated that the developer amount exceeds 210 g at the end of the 1/2 speed mode (N in S34), the idling time of the developing device 4 is determined (S35), and the control unit 30 (S36) and the idling operation is executed (S37). For this reason, at the end of the image formation in the 1/2 speed mode, the accumulation time of the idling of the developing device 4 is shorter than the discharge mode control of the first embodiment in which idling is performed for a certain time, and the developer is discharged. Deterioration can be delayed.

  After executing the idling operation of the developing device 4 (S37), the control unit 30 acquires information about the constant speed mode (S31) when there is a constant speed mode job (N in S38). Is executed (S32).

<Example 4>
FIG. 14 is a flowchart of supply mode control according to the fourth embodiment. FIG. 15 is an explanatory diagram of developer discharge characteristics in the high productivity mode.

  As shown in FIG. 2, when the image formation in the high productivity mode is finished and the mode is switched to the constant speed mode, a problem opposite to the case of switching from the ½ speed mode to the constant speed mode occurs. Immediately after changing the process speed, the developer surface height of the developer in the developing device 4 is reduced, and the developing sleeve 4b is not coated with sufficient developer, causing development unevenness.

  Therefore, in the fourth embodiment, after the job in the high production mode is completed, the image forming operation is temporarily interrupted. The image forming apparatus 100 is operated to replenish the replenishment developer from the toner replenishment device 32 and recover the developer amount reduced to 196 g to 200 g. At that time, since the toner contained in the replenishment developer becomes excessive in the developing container 4a, the excess toner is discharged to the photosensitive drum 2 as a toner band.

  In the fourth exemplary embodiment, the image forming apparatus 100 has a constant speed mode in which normal image formation is performed and a high productivity mode in which image formation is performed at a higher speed than normal image formation. The process speed in the constant speed mode in Example 4 is 300 mm / sec, which is equal to that in Example 1, whereas the process speed in the high productivity mode is 350 mm / sec. The image forming process is the same in the sleeve constant velocity mode and the high productivity mode except that the process speed is changed.

  First, as a preliminary experiment, the developing device 4 is placed on a weighing scale and is operated in the constant speed mode and the high productivity mode, and the developer is gradually charged from the supply port 4f, and the developer is discharged from the discharge port 4g. The developer amount in the developing container 4a to be started was measured.

  When the operation is performed in the constant speed mode, the discharge starts when the developer amount in the developing container is 200 g. Therefore, the maximum developer amount of the developing device 4 in the constant speed mode is 200 g. The appropriate developer amount that does not cause density unevenness in the output image in the constant speed mode is 200 g or less.

  When the operation is performed in the high productivity mode, the discharge is started when the developer amount in the developing container is 196 g. Therefore, the maximum developer amount of the developing device 4 in the high productivity mode is 196 g.

  When the image formation is continuously performed in the high productivity mode, the process speed is high, so that the rotational speed of the screw member 4c is also high, and the developer in the developing container 4a jumps up. Therefore, the apparent surface level of the developer in the developer container 4a is increased, and the developer discharge through the discharge port 4g is promoted, so that the developer amount in the developer container 4a is reduced to a maximum of 196 g.

  Then, when the developer amount is reduced to a maximum of 196 g and the mode is changed from the high productivity mode to the constant speed mode, the developer surface height of the developer decreases immediately after that and the coating on the developing sleeve 4b is uneven. The image density unevenness due to is likely to occur.

  As shown in FIG. 14 with reference to FIG. 3, in Example 4, when image formation in the high productivity mode is executed (Y in S <b> 42), the image forming operation is temporarily interrupted, and the replenishment developer is supplied. The developer amount in the developing container 4a is recovered to the proper developer amount in the constant speed mode (S47).

  When the controller 30 switches from the high productivity mode, which is an example of the first image forming mode, to the constant speed mode, which is an example of the second image forming mode, the control unit 30 interrupts the image forming operation and develops an example of the replenishment mode. The agent replenishment operation can be executed. In the developer replenishing operation, the developer is replenished from the toner replenishing device 32 while rotating the developing sleeve at a lower rotational speed than in the high productivity mode.

  When the copy job starts, the control unit 30 acquires information related to the image forming mode (high productivity mode, constant speed mode) (S31).

  When the image formation is performed in the high productivity mode (Y in S42), the control unit 30 acquires the number of copies and the toner replenishment amount when the image formation is performed in the high productivity mode (S43), and the development. The amount of developer in the container 4a is estimated and calculated (S44).

  The controller 30 calculates the replenishment amount of replenishment developer necessary to restore the developer amount in the developing container 4a to 200 g (S45), and once the image is formed after the copy job in the high productivity mode is completed. After completion (S46), a developer replenishing operation is executed (S47).

  When there is a job in the constant speed mode (N in S48), the control unit 30 acquires information related to the constant speed mode (S41) and executes the job in the constant speed mode (S42).

  When image formation is performed in the constant speed mode (N in S42), the control unit 30 does not execute the developer replenishment operation after the end of the constant speed mode copy job (S48).

  As shown in FIG. 15, in the high productivity mode, the developer discharge amount changes according to the number of copying operations, and the developer amount in the developer container 4a changes from 196 to 200 g. This graph is stored in advance as a table in the control unit 30, and is used for calculating the developer replenishment amount.

  For example, when five sheets of images are formed in the high production mode, the carrier ratio of the developer for replenishment is 20%. Therefore, in order to replenish 4 g of the developer (carrier), the high productivity mode After completion of the copy job, 20 g of replenishment developer is replenished. In parallel with the replenishment, excess 16 g of toner contained in the replenished developer is discharged as a toner image onto the photosensitive drum 2 by the image formation of the full-density entire surface image.

  In the fourth embodiment, in the image forming apparatus adopting the developer exchange method, when the image formation is performed in the high productivity image forming mode, the replenishment developer is replenished. Image formation in the constant speed mode can be started with the amount of the agent restored to an appropriate value. Therefore, development unevenness does not occur immediately after the start of the constant speed mode.

DESCRIPTION OF SYMBOLS 1 Image formation part, 2 Photosensitive drum, 3 Charging roller, 4 Developing apparatus 4a Developing container, 4b Developing sleeve, 4c Screw member 4d Toner bottle, 4w Magnet roller 5 Transfer roller 6 Drum cleaning apparatus, 7 Exposure apparatus, 16 Intermediate transfer belt 30 control unit, 31 toner density sensor, 32 toner supply device

Claims (9)

An image carrier, an electrostatic image forming unit that forms an electrostatic image on the image carrier, a developer carrier that carries a developer and develops an electrostatic image of the image carrier, and the developer carrier A circulation path through which the developer circulates along the body, a screw member that feeds the developer in the circulation path to the developer carrier, and a developer that is higher than a predetermined height in the circulation path is discharged. A discharge port, and a replenishing device for replenishing developer to the circulation path,
The developer carrier and the screw member rotate at a constant speed ratio, and a first image forming mode for setting a first rotation speed for the developer carrier and the first rotation speed for the developer carrier An image forming apparatus capable of executing a second image forming mode for setting a low second rotation speed,
When switching from the second image forming mode to the first image forming mode, the image forming operation is interrupted and the developer carrying member is rotated at a rotational speed higher than the second rotational speed to develop from the discharge port. A control means capable of executing a discharge mode for discharging the agent;
The control means changes the drive time of the screw member in the discharge mode according to a history relating to the amount of developer replenishment in the execution time of the executed second image forming mode. .   The image forming apparatus according to claim 1, wherein the control unit sets the drive time of the screw member in the discharge mode to be longer as the execution time of the second image formation mode is longer.   3. The image formation according to claim 2, wherein when the execution time of the second image formation mode is longer than a predetermined time, the control unit sets the drive time of the screw member in the discharge mode to a fixed time. apparatus. Detecting means for detecting information relating to the amount of developer replenished during the execution time of the second image forming mode;
The control unit sets the drive time of the screw member in the discharge mode to be longer as the amount of developer replenished during the execution time of the second image forming mode is larger based on the detection information of the detection unit. The image forming apparatus according to claim 1.   The control means drives the screw member in the discharge mode when the amount of developer replenished during the execution time of the second image forming mode is greater than or equal to a predetermined amount based on the detection information of the detection means. 5. The image forming apparatus according to claim 4, wherein the time is set to a fixed time.   When the control unit switches from the first image forming mode to the second image forming mode, the image forming operation is interrupted and the developer carrier is rotated at a rotation speed lower than the first rotation speed. The image forming apparatus according to claim 1, wherein a replenishment mode for replenishing the developer from the replenishment apparatus is executable. An image carrier, an electrostatic image forming unit that forms an electrostatic image on the image carrier, a developer carrier that carries a developer and develops an electrostatic image of the image carrier, and the developer carrier A circulation path through which the developer circulates along the body, a screw member that feeds the developer in the circulation path to the developer carrier, and a developer that is higher than a predetermined height in the circulation path is discharged. A discharge port, and a replenishing device for replenishing developer to the circulation path,
The developer carrier and the screw member rotate at a constant speed ratio, and a first image forming mode for setting a first rotation speed for the developer carrier and the first rotation speed for the developer carrier An image forming apparatus capable of executing a second image forming mode for setting a low second rotation speed,
Control means for executing a discharge mode for discharging the developer from the discharge port by rotating the developer carrying member at a rotation speed higher than the second rotation speed every time the second image forming mode ends. An image forming apparatus.   The discharge mode is started by starting the developer carrier after stopping the voltage applied to the developer carrier in a state where the developer carrier is stopped after the second image forming mode is finished. The image forming apparatus according to claim 7.   The second image forming mode is started by activating the developer carrier after applying a voltage to the developer carrier in a state where the developer carrier is stopped after completion of the discharge mode. The image forming apparatus according to claim 8.

Images