JP2007033990A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of image defects such as fog due to the reduction in charge amount and fluidity of a developer left for a long period of time within a developing device and to shorten a time required for a desired charge amount for the first copy, for example, when an image forming apparatus is started first in the morning. <P>SOLUTION: In a configuration wherein the developer is circulated in the developing device by a developer conveying and agitating member, the developer conveying and agitating member is rotated in a forward direction during image formation and is rotated alternately forward and backward for a prescribed time periodically to give irregular changes to a developer shape, whereby a conveyed shape is changed largely more than normal to more effectively agitate the developer and an effect of loosening the developer and giving a charge is enhanced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a developing device used in an electrophotographic image forming process.

  Conventionally, in an image forming apparatus using an electrophotographic system, as shown in FIG. 1, the surface of a photosensitive member 1, which is generally drum-shaped as an image carrier, is uniformly charged by a charger 2 and charged. The exposed photoreceptor 1 is exposed according to image information by the exposure device 3 to form an electrostatic latent image on the photoreceptor 1. The electrostatic latent image formed on the photoreceptor 1 is visualized with a developer toner using the developing device 4. The visualized image is transferred to the recording medium S by the transfer device 5. Thereafter, the toner image transferred onto the recording medium S is fused and fixed to the recording medium S by heat and pressure by the fixing device 6. Then, the toner remaining on the photosensitive member 1 after the transfer process is removed by the cleaning device 7, and the charge remaining on the photosensitive drum 1 is removed by the charge removing device 8, so that the photosensitive member 1 is used for the next image forming process. Prepare.

  The developing device 4 uses a two-component developer including non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. In particular, color image forming apparatuses are widely used because the toner does not need to contain a magnetic material, and the color is good.

  For example, the developing device 4 using a two-component developer is generally configured as shown in FIGS. The developing device 4 includes a developing container 41 that stores a developer. The developing container 41 is divided into a developing chamber (developer conveying path) 41a and an agitating chamber (developer conveying path) 41b by a partition wall 41c extending in the vertical direction. The developing chamber 41a and the agitating chamber 41b include A first developer carrying and stirring member 42 and a second developer carrying and stirring member 43 are disposed respectively.

  In addition, delivery portions (developer transport paths) 41d and 41e that allow the developer to pass between the developing chamber 41a and the stirring chamber 41b are provided at the end in the longitudinal direction of the partition wall 41c. The first and second developer transport agitating members 42 and 43 transport the developer while stirring and circulate the developer container 41. A developing sleeve 44 as a developer carrying member is rotatably disposed at a position of the developing container 41 facing the photosensitive drum 1. The developing sleeve 44 incorporates a magnet 45 as a magnetic field generating means.

  The two-component developer conveyed while being agitated by the first and second developer conveying and agitating means 42 and 43 and having the toner adhered to the surface of the carrier due to frictional charging is developed by the magnetic field generated by the magnet 45. 44 is attracted and carried on the surface. Then, the developer passes through the developer layer thickness regulating means 46 by the rotation of the developing sleeve, is coated on the surface of the developing sleeve 44 as a thin layer, and is conveyed to a portion facing the photoreceptor 1. At the facing portion, the developer forms a chain-like magnetic spike by the magnetic field generated by the magnet 45. The magnetic spikes are close to or in contact with the photosensitive drum 1, and only the toner is transferred to the electrostatic latent image formed on the surface of the photosensitive member 1 by the developing bias applied to the developing sleeve 44, and electrostatically is applied to the surface of the photosensitive member 1. A toner image corresponding to the latent image is formed.

  In the above-described electrophotographic image forming apparatus, when the developer is left in the developing device 4 without being conveyed and stirred for a long time, the particles are arranged so as to reduce the bulk density due to its own weight or the like. It may change to a semi-aggregated state, resulting in a decrease in fluidity, or a loss of charge on the charged toner particles, resulting in insufficient charge to be used in the development process. appear. For this reason, there is a problem such as fogging that develops toner on a portion of the photoreceptor 1 where an electrostatic latent image is not drawn due to generation of insufficiently charged toner. In this way, when the developing device 4 is not operated for a long time and continues for a long time, when the next image formation is performed, the developer is sufficiently agitated so as to satisfy the developing conditions, and the charge application and flow You must improve your sex.

  Conventionally, as a method for conveying and stirring the developer after being left for a long time, an operation time (several tens of seconds to several minutes) in which sufficient charge can be applied as determined in advance is set, and the developer conveying and stirring members 42 and 43 are moved at a constant speed. There is a way to idle. However, the above method has the following problems.

  That is, in many cases, the developer transport agitating members 42 and 43 have a screw shape having a rotating shaft installed in the transport direction and spirally tapered blades around it. When the developer is conveyed by the screw-like blades, the developer is conveyed while forming the same conveyance shape for each pitch. For this reason, since the developer is stirred along the screw while maintaining a constant structure, it takes time as described above to obtain a desired stirring state.

  Further, in order to improve the stirring ability, the second developer transport stirring member 43 in the stirring chamber 41b has a stirring rib 43c protruding in the radial direction from the rotating shaft and having a predetermined width in the developer transport direction. is there. However, since the stirring rib 43c increases the height of the agent surface and slows the transport speed, it is difficult to install the stirring rib 43c in the developing chamber 41a in consideration of the transport speed at the time of image formation, and the stirring effect in the developing chamber 41a is improved. difficult.

Japanese Patent Laid-Open No. 2004-133867 discloses a developer agitation method for improving the agitation property, preventing toner scattering, and restoring the image quality after being left for normal transport within a predetermined time in the first operable state after being left for a long time. Disclosed is a configuration in which the developer transport stirring means is rotated at a speed slower than the stirring speed and the rotation direction of the stirring transport means is reversed to the predetermined rotation direction within a predetermined time in the first operable state after being left for a long time. Yes.
JP 2000-347486 A

  However, in the former case, depending on the amount of developer in the developing device, for example, when the amount of developer is such that the developer conveyance stirring means is hidden, the developer can be stirred within a desired time to give a sufficient charge amount to the developer. I am worried about whether or not. In the latter case, the developer conveying and stirring member is reversely rotated for a predetermined time until the image quality after the long-term stop is recovered, thereby solving the problem of poor charging of the developer before the first printing. It is difficult to perform the operation. Further, when the developer conveying and stirring member has a screw shape, even if the rotation direction is reversed in the middle, the conveying and stirring is performed for a certain time with a constant structure for each pitch of the screw. Even if it compares, it is thought that there is no big effect.

  Accordingly, an object of the present invention is to provide an image forming apparatus based on an electrophotographic method, after an image forming operation is not performed, the developer in the developing apparatus is left for a long time, and the charge amount and fluidity are lowered. It is an object of the present invention to provide an image forming apparatus including a developing device that can shorten the time from the first image formation to the first image formation and can give the developer a sufficient charge amount for the developing conditions.

In order to achieve the above object, the invention described in claim 1 includes at least two developer conveying agitating members for agitating and conveying the developer, and the developer conveying directions of the adjacent developer conveying and agitating members are opposite to each other. An image forming apparatus comprising: a developing device configured to convey the developer so that the developer circulates inside the developing device; and a determination unit that determines whether the developer has been left for a predetermined time without stirring.
When it is determined by the determination means that the developer has been left for a predetermined time, the agitating and conveying operation of the developer conveying and agitating member is alternately performed in a forward rotation and a reverse rotation with respect to the rotation direction during the image forming operation. It is characterized by comprising possible drive means and control means.

  According to a second aspect of the present invention, in the developing device according to the first aspect of the present invention, the rotation time in one rotation direction of the forward rotation and the reverse rotation of the developer transport stirring member is about several rotations to several tens of rotations. To do.

  According to a third aspect of the present invention, in the developing device according to the first aspect, the developer carrying member is rotated in the same direction as that during image formation while the developer carrying and stirring member is operating.

  According to a fourth aspect of the present invention, in the developing device according to the first aspect, in the developing device, the rotation speed of the developer transport stirring member is made faster than the stirring transport speed during normal image formation.

  A fifth aspect of the present invention is the invention according to any one of the first to fourth aspects, wherein the developer transport stirring member has a screw-like configuration including a rotation shaft and a spiral blade along the developer transport direction. In addition, the axial cross-sectional shape of the spiral blade is a shape in which the surface shapes in the forward direction and the reverse direction are different from each other.

  According to the present invention, it is possible to obtain an effect of unraveling and applying a charge in a short time for a developer that has been left for a long time and has a reduced charge amount and fluidity.

  One of the detailed functions and effects that can be achieved by the present invention is to change the developer conveyance shape in an approximately non-stationary state by alternately performing circulation in the forward direction and the reverse direction, so that a normal structure for each pitch is obtained. It is possible to obtain a larger stirring effect than in a transporting state having This is because it is possible to obtain a larger agitation effect than in a normal conveyance state by alternately performing circulation in the forward direction and the reverse direction to obtain a greater shear effect than usual when turning back. This is because when the conveyance direction is turned back, the developer conveyance direction transported up to that time and the rotation direction of the developer conveyance agitation member are reversed, so the speed difference from the developer conveyance agitation member surface to the inside of the developer is large. This is because the shearing force increases. This is because a large stirring effect can be obtained.

  Further, the moment when the developer conveying stirring member rotates and the moment when it stops, the developer surface shape is changing while the developer conveying shape becomes a steady shape, and the change in the conveying shape becomes large. When the torque of the rotating shaft is measured, a force greater than the torque at the time of steady rotation is applied in the initial stage of rotation, and the energy that acts on the shape change due to stirring and transport increases, and a large stirring effect can be obtained by appropriately changing the transport direction. Is obtained.

  Also, when the transport direction is switched, the developer on the upper side of the developer transport stirring member is thrown by inertia in the transport direction so far and moved, and the transport shape in the transport direction of the developer stirring transport member is also changed. A larger stirring effect is obtained because the stirring effect is different.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
[Overall Configuration and Operation of Image Forming Apparatus]
The overall configuration and operation of the image forming apparatus 100 used in this embodiment will be described.

  FIG. 2 schematically shows a cross-sectional view of the image forming apparatus according to the present embodiment.

  The image forming apparatus 100 includes a document reading device (scanner) connected to the image forming apparatus main body or a yellow (Y) according to image information from a communication terminal such as a host device and a personal computer connected to the image forming apparatus main body. ), Magenta (M), cyan (C), and black (Bk) full-color images can be formed on a recording medium (paper, plastic sheet, cloth, etc.) using an electrophotographic method.

  The image forming apparatus 100 according to the present embodiment is a quadruple tandem type image forming apparatus, and forms first, second, and third images that respectively form yellow, magenta, cyan, and black images as a plurality of image forming units. And fourth image forming units PY, PM, PC, and PBk. Then, while the intermediate transfer member 51 provided in the transfer device 5 moves in the direction of the arrow shown in the drawing and passes through each image forming unit, images of each color are superimposed on the intermediate transfer member 51 in each image forming unit. A recorded image is obtained by transferring the multiple toner images superimposed on the intermediate transfer member 51 to the recording medium S.

  In the present embodiment, the structure of each image forming process unit is substantially the same except that the development colors are different. Therefore, in the following, one of the image forming process units belongs to the image forming process unit unless particularly distinguished. The subscripts Y, M, C, and Bk given to the reference numerals to indicate that they are elements will be omitted, and will be described generally.

  The image forming process unit P has a drum-shaped photoconductor (photosensitive drum) 1 as an additional carrier. On the outer periphery of the photosensitive drum 1, there are a charging device 2 as a charging unit, an exposure device 3 as an exposure unit (a laser exposure optical system in the present embodiment), a developing device 4 as a developing unit, and a transfer device 5 as a transfer unit. A cleaning device 7 as a cleaning means and a static elimination device 8 as a static elimination means are provided. The transfer device 5 has an intermediate transfer belt 51 as an intermediate transfer member. The intermediate transfer belt is wound around a plurality of rollers and rotates in the direction of the arrow shown. A primary transfer member 52 is disposed at a position facing each photosensitive drum 1 via the intermediate transfer belt 51. Further, a secondary transfer member 53 is disposed at a position facing one of the rollers around which the intermediate transfer member 51 is wound.

  At the time of image formation, the surface of the photosensitive drum 1 rotated by the charging device 2 is first uniformly charged. Next, an electrostatic latent image is formed on the photosensitive drum 1 by scanning and exposing the surface of the charged photosensitive drum 1 with a laser according to an image signal by the exposure device 3. The electrostatic latent image formed on the photosensitive drum 1 is visualized as a toner image with the developer toner using the developing device 4. The toner image formed on the photosensitive drum 1 is transferred onto the intermediate transfer belt 51 by the action of the primary transfer bias applied to the primary transfer member 52 in the primary transfer portion where the intermediate transfer belt 51 and the photosensitive drum 1 abut. The For example, at the time of image formation of a four-color full-color image, toner images are transferred from the respective photosensitive drums 1 onto the intermediate transfer belt 51 sequentially from the first image forming process unit PY, and four colors are transferred onto the intermediate transfer belt 51. Multiple toner images are formed.

  On the other hand, the recording medium S accommodated in the paper feed tray 9 as the recording medium accommodating portion is brought into contact with the intermediate transfer belt 51 and the secondary transfer member 53 by recording medium conveying means such as a pickup roller, a conveying roller and a registration roller. The toner image is conveyed in synchronization with the position of the toner image on the intermediate transfer belt 51 to the secondary transfer portion in contact therewith. The multiple toner images on the intermediate transfer belt 51 are transferred onto the recording medium S by the action of the secondary transfer bias applied to the secondary transfer member 53 in the secondary transfer portion.

  Then, the recording medium S separated from the intermediate transfer belt 51 is conveyed to the fixing device 6. The multiple toner images transferred onto the recording medium S are heated and pressurized by the fixing device 6, melted and mixed, and fixed onto the recording medium S. Thereafter, the recording medium S is discharged to the discharge tray 10 of the image forming apparatus 100.

  In addition, deposits such as toner remaining on the photosensitive drum 1 after the completion of the primary transfer process are scraped off and collected by a cleaning blade 71 provided in the cleaning device 7. The electrostatic latent image remaining on the photosensitive drum 1 is erased by the static eliminator 8. Thereby, the photosensitive drum 1 is prepared for the next image forming process. Further, deposits remaining on the intermediate transfer belt 51 after the secondary transfer process are scraped off and collected by the intermediate transfer body cleaner 54.

Note that the image forming apparatus 100 according to the present exemplary embodiment forms a single-color or multi-color image using the image forming process unit P of a desired single color or some of four colors such as a black single-color image. Is possible.
[Developer]
Next, the developing device 4 will be described in detail with reference to FIGS.
The developing device 4 includes a developing container 41 that stores a two-component developer including toner and a carrier. In the developing container 41, a developing sleeve 44 as a developer carrying member, a magnet roll 45 as a magnetic field generating means fixedly disposed in the developing sleeve 44, and a coating layer of a developer on the surface of the developing sleeve 44 in a thin layer. The developer layer thickness defining means 46 and first and second developer transport agitating members 42 and 43 for stirring and transporting the developer in the developer container 41 are disposed.

  The interior of the developing container 41 is divided into a developing chamber (developer transport path) 41a and an agitating chamber (developer transport path) 41b by a partition wall 41c extending in the vertical direction. The first developer transport stirring member 42 is disposed in the developing chamber 41a, and the second developer transport stirring member 43 is disposed in the stirring chamber 41b. At both ends in the longitudinal direction of the partition wall 41c (see FIG. 3), delivery portions (developer transport paths) 41d and 41e that allow the developer to pass between the developing chamber 41a and the stirring chamber 41b are provided.

  In the present embodiment, the first and second developer conveying and stirring members 42 and 43 are both screw-shaped members (hereinafter referred to as “first screw” and “second screw”, respectively). In other words, in the present embodiment, the first and second screws 42 and 43 are formed by providing spiral blades 42b and 43b as conveying portions around the rotation shafts 42a and 43a of the magnetic body, respectively. Yes.

  In the present embodiment, in addition to the blades 43b, the second screw 43 also has a stirring rib 43c that protrudes in the radial direction from the shaft 43a and has a predetermined width in the developer transport direction. . The rib 43c stirs the developer as the rotating shaft 43a rotates. The first screw 42 agitates and conveys the developer in the developing chamber 41a. In addition, the second screw 43 calculates a change in the toner density of the developer from the magnetic toner detected by the automatic toner replenishing control (ATR: Auto Toner Replenisher) and the inductance sensor 47, and the replenishing toner amount is determined. Then, the toner is supplied from the toner replenishing port in the transport upstream portion of the second screw 43, and the developer already in the stirring chamber 41b is stirred and transported to uniformize the toner density. The toner concentration is a toner concentration expressed as a weight percentage of the two-component developer and the toner.

  The first and second screws 42 and 43 are arranged substantially in parallel along the rotation axis direction (screw longitudinal direction) of the developing sleeve 44. The first screw 42 and the second screw 43 transport the developer in the opposite directions along the rotation axis direction of the developing sleeve 44. In this way, the developer is circulated in the developing container 41 by the first and second screws 42 and 43 through the transfer portions 41d and 41e. That is, the developer in the developing chamber 41a, in which the toner is consumed in the developing process due to the conveying force of the first and second screws 42 and 43 and the toner concentration is reduced, is transferred into the stirring chamber 41b through the one transfer portion 41d. Move to. In addition, the developer in the agitating chamber 41b that has been replenished and agitated with toner moves to the developing chamber 41a via the other delivery portion 41e.

  The developing chamber 41a of the developing device 4 is opened at a position corresponding to the developing area facing the photosensitive drum 1, and the developing sleeve 44 is rotatably arranged so as to be partially exposed to the opening of the developing container 41. Has been. In the present embodiment, the developing sleeve 44 is made of a non-magnetic material and rotates in the direction of the arrow in the drawing during a developing operation. A magnet roll 45 having a plurality of magnetic poles is fixed inside the developing sleeve 44 along the circumferential direction as a magnetic field generating means.

  The developer in the developing chamber 41 a is supplied to the developing sleeve 44 by the first screw 42. The developer supplied to the developing sleeve 44 is carried on the developing sleeve 44 by a magnetic field generated by the magnet roll 45. As the developing sleeve 44 rotates, the two-component developer on the developing sleeve 44 is transported to the developing region facing the photosensitive drum 1 while the layer thickness is regulated by the regulating blade 46. In the developing region, the developer on the developing sleeve 44 forms a chain-like magnetic spike. In this embodiment, the electrostatic latent image on the photosensitive drum 1 is developed as a toner image by bringing the magnetic spike into contact with the photosensitive drum 1 and supplying the developer toner to the photosensitive drum 1.

In order to improve the developing efficiency, that is, the application rate of the toner to the electrostatic latent image, the developing sleeve 44 usually has a developing bias voltage obtained by superimposing a DC voltage and an AC voltage from a developing bias power source as a voltage applying means. Is applied. The developer on the developing sleeve 44 after supplying the toner to the photosensitive drum 1 returns to the developing chamber 41a as the developing sleeve further rotates.
[Developer transport stirring control means]
In the image forming apparatus 100 and the developing device 4, for example, when the image forming process is not operated for a long time as in the early morning, the developer in the developing container 41 is reduced in bulk density due to its own weight or the like. The fluidity is lowered by moving and adhering to each other. Also, until the final operation of the previous day, the charged and charged toner particles lose their charge and become unsuitable for the development conditions.

  In the present embodiment, the thermistor arranged to detect whether the state of the image forming apparatus 100 is the first in the morning, the power switch ON / OFF, and the temperature of the surface of the fixing roller 61 provided in the fixing device 6. Judgment is made based on whether the temperature detected by 62 is below a preset threshold value. Here, the threshold is set to 90 ° C.

  In the present embodiment, the developing device 4 has the following configuration in order to assist recovery from the above problem to normal image forming conditions and to shorten the startup time of the image forming apparatus 100 until first copy or first print. Have.

  The driving device for the first and second screws 42 and 43 constituting the developing device 4 and the driving device for the developing sleeve 44 are different from each other, and both the screw and the developing sleeve 44 are not interlocked mechanically. The developing sleeve 44, which is a developer carrying member, has an independent drive system, but rotates in a fixed direction at the same speed as the image forming holder while the screw is driven. Moreover, the drive device of the 1st, 2nd screws 42 and 43 is comprised with the gear and motor which are drive devices.

  The gear is configured such that the developer transport directions in which the first and second screws 42 and 43 are filled in the developer container 41 by the rotation of the motor are opposite to each other. Specifically, the motor is connected to a gear on the delivery portion 41d side of the first screw 42 and transmits a driving force. A gear is also provided at the end of the first screw 42 on the side of the transfer portion 41e, and the first and second screws 42, 43 are transmitted by transmitting a driving force to the gear of the adjacent second screw 43. Are driven in conjunction with each other. At this time, the rotating shafts 42a and 42b of the first and second screws 42 and 43 rotate in opposite directions, respectively. Then, the first and second screws 42 and 43 are installed so that the winding directions of the spiral blades 42b and 43b around the rotation shafts 42a and 42b are the same direction, and the developer is conveyed in the opposite direction by the respective screws. Then, the developer is circulated inside the developing container 41.

  In the present invention, the motor as a driving device connected to the gear of the first screw 42 provided in the developing device 4 is a motor that can rotate in both directions and transmit torque, and the rotation direction can be freely controlled. A control device is provided.

  In addition, the image forming apparatus 100 includes a CPU (Central Processing Unit) as a determination and calculation unit, a HDD (Hard Disk Drive) and a RAM (Random Access Memory) as storage units, and a communication capable of exchanging information with other devices. An arithmetic device including means is provided.

  When the power switch is turned on or the sleep mode is released, the image forming apparatus 100 transmits a power-on signal to the arithmetic device. The arithmetic unit detects the power ON signal and the surface temperature information of the fixing roller 6 monitored by the thermistor 62, and the temperature threshold of the morning judgment stored in the storage means in the arithmetic unit and the surface of the fixing roller 6 monitored. The temperature is compared, and it is determined whether or not the surface temperature is a threshold value (90 ° C. in this embodiment) or less. When the surface temperature of the fixing roller 6 is 90 ° C. or less, the arithmetic unit uses communication means so that the first and second screws 42 and 43 periodically repeat forward rotation and reverse rotation alternately. Send instructions to the control unit. The control device that has received the screw operation information creates rectangular wave data with the output information of the motor corresponding to the rotation speed at the time of image formation as the amplitude, and two cycles of forward rotation and reverse rotation as one cycle. The motor of the driving device is driven according to the rectangular wave information, and a driving force is applied to the first screw.

  In the developing device of the present embodiment, the first and second screws are about 5.5 [rps] and about 6.5 [rps], respectively. It has been confirmed that it is sufficient to rotate for about 0.5 seconds in a room temperature and low humidity environment, which is generally said to have poor fluidity, from the initial stage to the steady state. In consideration of shortening the time for the transport shape to form a steady state and operating in any environment, the transport stirring time on one side is set to 1 second, and the transport and stirring in the forward and reverse directions are set to one cycle. One cycle was 2 seconds, that is, one cycle of the rectangular wave was 2 seconds.

  Regarding the effect of this embodiment, the developer prepared at once is divided and filled in each developing device and left for 10 hours until image formation in the morning in a high-temperature and high-humidity environment where the toner is difficult to be charged. An example in which the amounts are compared is described below with reference to FIG.

  Further, the charge amount of the toner before being left is about 23 μC / g, and the charge amount of the toner after being left for 10 hours is about 18 μC / g.

  When the screw and the developing sleeve are idly rotated for 2 minutes in a fixed direction at a rotation speed at the time of normal image formation as in the prior art, the charge amount of the toner rises to about 20 μC / g. In addition, when the developer in the developer container 41 is transported in the forward and reverse directions along the developer transport path and stirred in the cycle of the second embodiment by the method of the present embodiment in a cycle of 2 seconds, When the above operation is performed 60 cycles) (the scanning is performed 60 cycles), the charge amount is increased to about 22 μC / g. Further, from the transition of the charge amount for 2 minutes, the method of the present invention can increase the charge amount about 20 to 30% faster than the conventional method. From the above effects, according to the present invention, the developer can be agitated more efficiently than the conventional method, the time until the first image forming operation can be shortened after the power is turned on in the morning, and the time until the first copy can be reduced. It has become possible to provide a short image forming apparatus.

<Embodiment 2>
Next, another embodiment of the present invention will be described.

  Since the basic configuration of the image forming apparatus of the present embodiment is the same as that of the image forming apparatus 100 of the first embodiment, the elements having substantially the same or corresponding functions and configurations as those of the first embodiment are the same. Detailed description will be omitted.

  In the present embodiment, the first and second screws 42 and 43 are alternately rotated in the forward and reverse directions to change the developer circulation direction at a constant cycle. By making the rotational speed of the second screws 42 and 43 higher than the speed during the image forming operation, the same stirring effect as that of the first embodiment can be obtained in a shorter time.

  In the state of being left unattended for a long time, a signal is transmitted to the arithmetic device when the power supply is turned on or when the power supply device is started up from the sleep mode, as in the first embodiment, and the arithmetic device that has received the signal sends the fixing roller 61 of the fixing device 6. The temperature of the surface is detected by the thermistor 62 and is determined by comparing with the information that the temperature threshold value is 90 ° C. or less stored in the storage means.

  In this embodiment, when a command is transmitted from the arithmetic unit to the control unit so that the circulation direction of the developer conveyance is alternately performed in the forward direction and the reverse direction, the motor rotation speed that is twice the screw rotation speed during image formation. Is used to create rectangular wave data with two cycles of forward rotation and reverse rotation as one cycle, the drive motor is driven according to the rectangular wave information, and the driving force is applied to the first screw. give. Here, when the rotational speed of the screw is 11 to 13 [rps], the number of rotations until the developer conveyance shape reaches a steady state increases, but the arrival time is almost the same, so the period of the rectangular wave is The same 2 seconds as in the first embodiment was used.

  The effect will be described below with reference to FIG.

  Similarly to the first embodiment, the developer is filled in the developing device, and in a high temperature and high humidity environment where the toner is difficult to be charged, the charge amount is measured by leaving it to stand for 10 hours until image formation in the morning. Compare with results. In the configuration of the present embodiment, the toner charge amount after operating for 2 minutes is about 22 μC / g as in the first embodiment, and when the change of the charge amount with respect to time is compared, stirring is performed by the conventional method. Compared to the case, the toner can be charged about 40% faster.

  From the above effects, according to the present invention, the developer can be agitated more efficiently than the conventional method, the time until the first image forming operation can be shortened after the power is turned on in the morning, and the time until the first copy can be reduced. It has become possible to provide a short image forming apparatus.

<Embodiment 3>
Next, another embodiment of the present invention will be described.

  Since the basic configuration of the image forming apparatus according to the present embodiment is the same as that of the image forming apparatus 100 according to the first and second embodiments, elements having functions and configurations that are substantially the same as or equivalent to those of the second embodiment. Are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, in addition to the configuration described in the second embodiment, as shown in FIG. 5, the longitudinal sectional shapes of the screw blades 42a and 43b before and after the conveying direction are made asymmetrical so that the order of image formation is improved. The conveyance shape was made different when the rotation direction was opposite to the direction. Thereby, the change in the state of the developer is further increased, and the stirring effect is improved by alternately repeating the circulation direction in the forward direction and the reverse direction. In addition, in consideration of the shape of the surface of the agent when moving to the image forming process, control is performed so that the agitation direction immediately before the agitation is stopped ends in a forward rotation.

  The effect will be described below with reference to FIG.

  As in the first and second embodiments, the developer is filled in the developing device, and in a high-temperature and high-humidity environment where the toner is difficult to be charged, the amount of charge is measured by standing for 10 hours until image formation in the morning. , 2 results are compared. In the configuration of the present embodiment, the toner charge amount after operating for 2 minutes is about 22 μC / g as in the first and third embodiments, and the transition of the charge amount with respect to time is compared. Compared to the case of stirring by a conventional method, the toner can be charged with about 40 to 50% faster.

  From the above effects, according to the present invention, the developer can be agitated more efficiently than the conventional method, the time until the first image forming operation can be shortened after the power is turned on in the morning, and the time until the first copy can be reduced. It has become possible to provide a short image forming apparatus.

1 is a schematic view of an electrophotographic image forming apparatus. 1 is a schematic sectional view of an image forming apparatus. It is a figure which shows a developing device and a control means. It is a schematic sectional drawing of a developing device. It is a longitudinal cross-sectional view of a screw. It is a figure which shows charge amount transition with respect to stirring and conveyance time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 1 Photosensitive drum 2 Charging apparatus 3 Exposure apparatus 4 Developing apparatus 5 Transfer apparatus 6 Fixing apparatus 7 Cleaning apparatus 8 Static elimination apparatus 9 Paper feed tray 10 Paper discharge tray 41 Developing container (a developing chamber, b stirring chamber, c partition) , D, e delivery part)
42, 43 First and second screw (a rotating shaft, b blade, c rib)
44 Developing sleeve 45 Magnet roll 46 Regulating blade

Claims (5)

At least two developer conveying agitating members for agitating and conveying the developer are provided, and the developer conveying agitating members adjacent to each other are conveyed in a reverse direction so that the developer circulates inside the developing device. In an image forming apparatus comprising a developing device having a configuration and a determination unit that determines whether or not the developer has been left for a predetermined time without stirring,
When it is determined by the determination means that the developer has been left for a predetermined time, the agitating and conveying operation of the developer conveying and agitating member is alternately performed in a forward rotation and a reverse rotation with respect to the rotation direction during the image forming operation. An image forming apparatus comprising a drive unit and a control unit.   2. The image forming apparatus according to claim 1, wherein in the developing device, the rotation time in one rotation direction of forward rotation and reverse rotation of the developer conveying stirring member is about several rotations to several tens of rotations.   3. The image forming apparatus according to claim 1, wherein in the developing device, the developer carrying member is rotated in the same direction as that during image formation while the developer conveying and stirring member is operating.   The image forming apparatus according to claim 1, wherein in the developing device, the rotation speed of the developer transport stirring member is made faster than the stirring transport speed during normal image formation.   The developer transport agitating member has a screw-like configuration with a rotation shaft and spiral blades along the developer transport direction, and the axial cross-sectional shape of the spiral blades is the surface in the forward and reverse directions. The image forming apparatus according to claim 1, wherein the shapes are different from each other.

Images