JP3092410B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to a method for forming an electrostatic latent image on an image carrier, and developing the electrostatic latent image with a developer containing a toner and a carrier. The present invention relates to an image forming apparatus for forming a toner image on a carrier.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, the surface of an image carrier is charged,
After the exposure to form an electrostatic latent image, the developing device develops the electrostatic latent image. In a developing device that performs development using a two-component developer containing a toner and a magnetic carrier, a sleeve disposed so that an outer peripheral surface thereof faces a surface of an image carrier at a predetermined distance, and an inner peripheral side of the sleeve. , And a developing roller composed of a permanent magnet disposed in the developing device, and the toner and the magnetic carrier are charged to different polarities by frictional charging inside the developing device. The carrier that has adsorbed the toner on the surface by being charged is adsorbed in a brush shape on the outer periphery of the sleeve by the permanent magnet, and is conveyed together with the toner to the vicinity of the surface of the image carrier by rotating the sleeve.

The toner conveyed to the vicinity of the surface of the image carrier is attracted to the electrostatic latent image on the image carrier by a developing bias voltage applied to the sleeve and a potential difference between the electrostatic latent image and the electrostatic latent image. It is developed to form a toner image. The carrier is collected in the developing device while being attracted to the sleeve by the magnetic force of the permanent magnet. On the other hand, the image forming apparatus contacts a transfer material on an image carrier on which a toner image has been formed by development by a developing device, and transfers the toner image to the transfer material. Next, the transfer material is peeled from the image carrier, and the transfer image is fixed by a fixing device to form an image on the transfer material.

[0004] By the way, particularly, the particle size of the carrier is small.
Alternatively, when the magnetic properties of the carrier are weakened due to deterioration or the like, the carrier may adhere to the surface of the image carrier during development. The carrier adhered to the image carrier reduces the adhesion of the transfer material to the image carrier at the time of transfer, resulting in a decrease in the quality of the transferred image such as so-called white spots. For this reason, the developing device is often provided with a carrier collecting roller downstream of the developing roller. As described in Japanese Patent Application Laid-Open No. 61-200561, etc., the carrier collection roller is simultaneously rotated by the same drive source when the sleeve of the developing roller is rotated, and adheres to the image carrier during development. The carrier is attracted to the surface by magnetic force. The carrier sucked on the roller surface is scraped off from the roller surface by a scraper or the like and collected in the developing device.

[0005] However, it is difficult to scrape off all the carrier sucked to the surface of the carrier collection roller from the roller surface, and a part of the toner adhering to the surface of the carrier is separated from the carrier to recover the carrier. Although it adheres to the surface of the roller, it is more difficult to scrape this toner. Therefore, the surface of the roller that has passed the portion where the scraper or the like is disposed may be covered with toner, or a small amount of carrier may remain on the roller surface. As described above, the carrier collection roller is rotated at the same time as the sleeve of the developing roller. Therefore, even when the portion of the image carrier on which the toner image is formed passes near the carrier collection roller, the carrier collection roller is not rotated. There has been a problem that the toner image is disturbed or stained by the carrier and toner remaining on the surface of the carrier collection roller while rotating.

In an image forming apparatus provided with a plurality of developing units having the same polarity, the polarity of the carrier of the developer used in each developing unit is the same. A very small amount of the carrier that could not be collected by the carrier collecting roller of the developing unit on the downstream side is sucked by the surfaces of the developing roller and the carrier collecting roller of the developing unit on the downstream side. Accordingly, when the state in which only the upstream developing device is operated and the operation of the downstream developing device is stopped is continued, the carrier is deposited on the surface of the developing roller and the collecting roller of the downstream developing device, and There is a possibility that a failure or the like occurs in the developing device, the toner image is disturbed as described above, and dirt adheres.

[0007] Further, the carrier deposited on the developing roll of the downstream developing unit may attract a part of the toner forming the toner image by electrostatic force. Generally, in an image forming apparatus provided with a plurality of developing units, each developing unit is loaded with a toner of a different color, so that the toner sucked into the carrier is combined with the toner of the developer loaded in the downstream developing unit. There is also a problem that the colors are different, and when the downstream developing device is operated in a state where the toners of different colors are sucked, color mixing occurs.

The present invention has been made in view of the above-mentioned facts, and has as its object to provide an image forming apparatus capable of preventing the occurrence of inconvenience caused by the adhesion of a carrier to an image carrier.

[0009]

According to a first aspect of the present invention, there is provided a latent image forming means for forming an electrostatic latent image on an image carrier, and a latent image forming means formed on the image carrier. A developing unit for developing the electrostatic latent image with a developer containing toner and a magnetic carrier to form a toner image on the image carrier; and a carrier arranged at a predetermined distance from the image carrier downstream of the developing unit. if the collecting roller, the developing unit is performing development of an electrostatic latent image, seen key of when the carrier collecting roller corresponds to the portion where the toner image is not formed on the image bearing member And a drive unit for rotating and driving the carrier collection roller.

According to a second aspect of the present invention, there is provided a latent image forming means for forming an electrostatic latent image on an image carrier, a first sleeve arranged at a predetermined distance from the image carrier, and a first sleeve. A first magnetic field generating unit disposed on the inner periphery of the first sleeve to generate a magnetic field, the first latent image formed on the image carrier including a toner and a magnetic carrier attached to the first sleeve. A first developing roller that develops with the first developer to form a toner image on the image carrier; and a second sleeve that is disposed at a predetermined distance from the image carrier downstream of the first developing roller. And a second magnetic field generating unit disposed on the inner periphery of the second sleeve for generating a magnetic field, wherein the electrostatic latent image formed on the image carrier is attached to the toner of the second sleeve. And a magnetic carrier having the same polarity as the first developer. And a second developing roller that develops with the developer to form a toner image on the image carrier and a toner image on the image carrier when the first developing roller develops an electrostatic latent image. And a driving means for rotating and driving the second developing roller only when the second developing roller corresponds to a portion not formed.

According to a second aspect of the present invention, when the second developing roller is rotationally driven, the driving means causes the toner adhered to the second sleeve of the second developing roller to adhere to the image carrier. Preferably, a bias voltage is applied to the second developing roller.

[0012]

According to the first aspect of the present invention, the electrostatic latent image formed on the image carrier is developed with a developer containing a toner and a magnetic carrier to form a toner image on the downstream side of a developing unit for forming a toner image. Carrier recovery rollers are arranged at predetermined intervals, and when the developing unit is developing an electrostatic latent image, the carrier recovery roller corresponds to a portion of the image carrier on which the toner image is not formed. only career collecting roller when you're driven to rotate. As described above, a small amount of carrier may adhere to the image carrier due to development in the developing unit, and the carrier on the image carrier adheres to the surface of the carrier collection roller disposed downstream of the developing unit. You.

Here, if the carrier recovery roller is driven during the development in the developing section as in the prior art, the carrier recovery roller is attracted to the surface of the carrier recovery roller and remains on the surface without being scraped off from the carrier recovery roller. The carrier and the accumulated residual toner are supplied one after another to a portion facing the image carrier, and the toner image is disturbed or stained by the carrier and the toner. On the other hand, according to the first aspect of the present invention, when the carrier collection roller corresponds to the portion of the image carrier on which the toner image is formed, the carrier collection roller is not driven to rotate, so that the toner remains on the surface of the carrier collection roller. There is no possibility that the toner image is disturbed or stained by the carrier or toner.

If the rotation of the carrier recovery roller is stopped while the developing unit is performing development, the carrier is deposited on the portion of the carrier recovery roller facing the image carrier. The toner image on the image carrier may be disturbed by the deposited carrier. On the other hand, according to the first aspect of the present invention, the carrier recovery roller is driven to rotate when the portion of the image carrier on which the toner image is not formed corresponds to the carrier recovery roller. The carrier is collected in a state where the carrier is accumulated, so that a large amount of carrier is prevented from accumulating on a part of the carrier collection roller, and the toner image is prevented from being disturbed.

In general, a member such as a scraper for scraping off the carrier adhered to the surface of the carrier collection roller is in contact with the outer periphery of the carrier collection roller. Since the carrier recovery roller is rotationally driven only when the portion where no is formed corresponds to the carrier recovery roller, the wear of the surface of the carrier recovery roller by the scraper or the like is also reduced.

As described above, according to the first aspect of the present invention, the carrier adheres to the image carrier by the development by the developing unit, and the carrier is further sucked by the collecting roller and remains or accumulates. Inconvenience such as adhesion can be prevented. The carrier collecting roller may be provided in a developing device provided with the developing unit, or may be provided in a developing device provided downstream of the developing device provided with the developing unit.

According to the second aspect of the present invention, the first developing roller and the second developing roller are provided. The first developing roller includes: a first sleeve disposed at a predetermined distance from the image carrier; and a first magnetic field generating unit disposed on an inner periphery of the first sleeve to generate a magnetic field. The electrostatic latent image formed on the body is developed with a first developer containing a toner and a magnetic carrier attached to the first sleeve to form a toner image on the image carrier. The second developing roller includes a second sleeve disposed downstream of the first developing roller at a predetermined distance from the image carrier, and a second sleeve disposed on an inner periphery of the second sleeve to generate a magnetic field. Two magnetic field generators;
And developing the electrostatic latent image formed on the image carrier with a second developer having the same polarity as the first developer and including a toner and a magnetic carrier attached to a second sleeve. A toner image is formed on the carrier.

As described above, since the second developer has the same polarity as the first developer, the carrier adhered on the image carrier by the development by the first developing roller is removed by the second developing roller. Is attracted to the surface of the second sleeve by the magnetic field generated by the second magnetic field generator. On the other hand, when the first developing roller is developing the electrostatic latent image,
The second developing roller is driven to rotate only when the second developing roller corresponds to a portion of the image carrier on which the toner image is not formed. Accordingly, similarly to the first aspect of the present invention, the carrier adheres to the image carrier by the development by the first developing roller, and the carrier is further attracted to the second developing roller and remains or accumulates, so that the toner image is disturbed. It is possible to prevent the occurrence of inconveniences such as dusting and adhesion of dirt.

According to the second aspect of the present invention, the driving means rotates the second developing roller so that the toner adhered to the second sleeve of the second developing roller adheres to the image carrier. It is preferable to apply a bias voltage to the developing roller No. 2. As a result, the toner adhering to the surface of the carrier or the like sucked by the second sleeve is again attached to the image carrier. The bias voltage is applied when the second developing roller is rotationally driven, that is, when the second developing roller corresponds to a portion of the image carrier on which the toner image is not formed. The toner is adhered to a portion of the body where the toner image is not formed, does not adversely affect the toner image formed on the image carrier, and the toner mixes with the toner of the second developer. Is prevented.

[0020]

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

[First Embodiment] FIG. 1 is a schematic configuration diagram of an image forming apparatus 10 according to the first embodiment. The image forming apparatus 10 includes a photosensitive drum 12 as an image carrier. The photosensitive drum 12 has an insulating photoconductive layer formed on the surface, and is rotated in the direction of arrow A in FIG. 1 by driving means (not shown). A charging corotron 14 is arranged at a predetermined position on the outer periphery of the photosensitive drum 12. An exposure unit 16 is formed on the downstream side of the charging corotron 14 along the rotation direction of the photoconductor drum 12, and an exposure device 18 is provided corresponding to the exposure unit 16.

A developing unit 20 is located downstream of the exposure unit 16.
Are arranged. The configuration of the developing device 20 will be described later. On the downstream side of the developing device 20, the photosensitive drum 12
A pre-transfer corotron 22, a transfer corotron 24, and a peel-off corotron 26 are arranged in this order at predetermined intervals from the surface. The image receiving material P is transported by a conveying means (not shown) as shown in FIG.
Is inserted between the transfer corotron 24 and the photosensitive drum 12 as shown by a two-dot chain line. On the downstream side of the peeling corotron 26, a peeling claw 28 is arranged so that the tip thereof contacts the surface of the photosensitive drum 12, and further on the downstream side, a cleaning device 30 and a static elimination corotron 32 are provided.

As shown in FIG. 2, the developing device 20 has a casing 40 for storing the developer D, and is arranged at an end of the casing 40 on the side of the photosensitive drum 12 at a predetermined distance from the photosensitive drum 12. Developing roller 42 and developing roller 42
, A carrier collecting roller 48 disposed opposite to the photosensitive drum 12 with a predetermined distance therebetween, and a lower side opposite to the photosensitive drum 12 with the developing roller 42 interposed therebetween (obliquely right below in FIG. 2)
And a cylindrical paddle 5 arranged in parallel with the developing roller 42.
4, a blender 56 disposed parallel to the paddle 54 on the opposite side to the developing roller 42 across the paddle 54, and a wobble 58 disposed parallel to the blender 56 on the opposite side of the paddle 54 across the blender 56. , Is provided.

The developing roller 42 includes a rotatable sleeve 44 made of a nonmagnetic material and having a bottomed cylindrical shape, and a permanent magnet 46 as a magnetic field generator fixedly disposed on the inner peripheral side of the sleeve 44. Have been. The permanent magnet 46 has an S ₁ magnetic pole formed at a portion facing the photosensitive drum 12,
Counterclockwise direction N ₁ pole in the FIG. 2 adjacent to the S ₁ pole, N ₂ poles are respectively formed on the clockwise side of FIG. 2, N
_An S ₂ magnetic pole and an N ₃ magnetic pole are formed in this order on the clockwise side of the _two magnetic poles. That is, except for the relationship between the N ₁ pole and N ₃ pole are formed alternately and S poles and N poles, and N
Interval of _one magnetic pole and N ₃ pole is greatest.

A blade 60 is provided at a predetermined distance from the sleeve 44 in parallel with the developing roller 42 near the portion where the S ₂ magnetic pole is formed on the outer peripheral side of the developing roller 42. Further, the sleeve 44 is connected to the high-voltage power supply 34, and a developing bias voltage is applied during development as described later.

As shown in FIG. 3, a sprocket 62 is disposed outside the casing 40. The sprocket 62 is coaxially connected to the bottom of the sleeve 44 of the developing roller 42. The sprocket 62 meshes with a sprocket 64 pivotally supported by the casing 40, and the sprocket 64 meshes with a sprocket 66 attached to a drive shaft of a motor 68 disposed outside the casing 40. Therefore, the developing roller 42
The sleeve 44 is rotated counterclockwise in FIG. 2 by transmitting the driving force of the motor 68 via the sprockets 62, 64, 66.

On the other hand, the carrier recovery roller 48 is made of a non-magnetic material and has a bottomed cylindrical rotatable sleeve 5.
0 and a permanent magnet 52 as a magnetic field generator fixedly arranged on the inner peripheral side of the sleeve 50. The permanent magnet 52 has an S magnetic pole formed at a portion facing the photosensitive drum 12, and an N magnetic pole is formed adjacent to the S magnetic pole on the counterclockwise and clockwise sides in FIG. Further, the casing 40 is provided on the outer peripheral side of the carrier collecting roller 48.
A scraper 70 is provided between the S magnetic pole and the N magnetic pole located on the inner side, so as to be in parallel with the carrier collection roller 48 and to have the leading end contact the carrier collection roller 48.

As shown in FIG. 3, a sprocket 72 is disposed outside the casing 40. The sprocket 72 is coaxially connected to the bottom of the sleeve 50 of the carrier collecting roller 48. The sprocket 72 meshes with a sprocket 74 pivotally supported by the casing 40.
0 is engaged with a sprocket 76 attached to a drive shaft of a motor 78 disposed outside the motor. Therefore, the sleeve 50 of the carrier collection roller 48 is attached to the sprockets 72 and 7.
The motor 78 is rotated clockwise in FIG. 2 by transmitting the driving force of the motor 78 via the motors 4 and 76.

As shown in FIG. 1, the motors 68, 78 are connected to the control device 36 via drivers 80, 82. The control device 36, the driver 82, the motor 78,
The sprockets 72, 74, 76 constitute the driving means of the first aspect of the present invention. The control device 36 includes the exposure device 18,
A high voltage power supply 34 and the like are also connected. The control device 36 includes a microcomputer or the like, and controls the operation of each unit of the image forming apparatus 10.

Next, as an operation of the first embodiment, first, an operation of recording an image on the image receiving material P by the image forming apparatus 10 will be described. In the developing device 20 of the image forming apparatus 10, the paddle 54 is rotated in the counterclockwise direction in FIG. 2 by the driving force of a motor (not shown), whereby the developer D accumulated below the casing 40 is transferred to the developing roller 42. The developer D is transported toward the developing roller 42 and supplied to the developing roller 42, and the developer D located on the carrier collection roller 48 side in the casing 40 is transported to the blender 56 side. Blender 56
2 is rotated clockwise in FIG. 2 by the driving force of a motor (not shown), whereby the developer D conveyed by the paddle 54, the developer D accumulated below in the casing 40, and the toner supply device (not shown) Vessel 20
The toner supplied into the casing 40 is mixed and stirred.

The wobble 58 is rotated counterclockwise in FIG. 2 by the driving force of a motor (not shown), whereby the developer D conveyed by the rotation of the blender 56 and the developer D are accumulated below the casing 40. The developer D is mixed and stirred. By the mixing and agitation by the blender 56 and the wobble 58, the carrier contained in the developer D is negatively charged, and the toner is positively charged. On the other hand, the developer D supplied to the developing roller 42 is attracted to the sleeve 44 in a magnetic brush state along the magnetic force lines generated by the carrier from the permanent magnet 46. Note that the toner adheres to the surface of the carrier by electrostatic force.

When the motor 68 is driven, the developer D adsorbed on the sleeve 44 in the form of a magnetic brush is conveyed together with the rotation of the sleeve 44, and is passed by the blade 60 when passing through the portion where the blade 60 is provided. After the height is made constant by blocking some passage, the photosensitive drum 12 reaches a portion facing the photosensitive drum 12.

On the other hand, the charging corotron 14 of the image forming apparatus 10 charges the surface of the photosensitive drum 12 by attaching ions generated by corona discharge to the surface of the photoconductive layer of the photosensitive drum 12. The exposure device 18 receives image data obtained by reading a document image by a reading device (not shown) from the control device 36. The exposure device 18 emits a laser beam modulated in accordance with the image data from the laser diode, and scans the laser beam with a scanning unit such as a polygon mirror to scan the surface of the photosensitive drum 12 located at the exposure unit 16. Irradiate.

Thus, the portion of the surface of the photosensitive drum 12 irradiated with the laser beam is discharged in accordance with the amount of the laser beam, and an electrostatic latent image corresponding to the image of the original is formed on the surface of the photosensitive drum 12. You. Incidentally, the operation of the exposure device 18 as shown in FIG. 4 (A) exposing a plurality of images across a predetermined dwell time t ₁ for every exposure of one image is continuously performed.

As shown in FIG. 4B, the control device 36 causes the developing device 20 to perform development at a timing delayed by a predetermined time t ₂ from the operation timing of the exposure device 18 in synchronization with the operation of the exposure device 18. . That is, the high-voltage power supply 34 is turned on to apply a developing bias voltage to the sleeve 44 of the developing roller 42, and the motor 68 is driven to rotate the sleeve 44. Note that the predetermined time t ₂ is the exposure unit 1
6 is the time required for the portion on which the electrostatic latent image is formed to reach the portion where the developing unit 20 is provided by the rotation of the photosensitive drum 12, and the portion on the photosensitive drum 12 where the electrostatic latent image is formed. Reaches the developing device 20, the development by the developing device 20 is started.

As described above, of the developer D attracted to the sleeve 44 and reaching the portion facing the photosensitive drum 12, only the positively charged toner is charged by the developing bias voltage applied to the sleeve 44 and the photosensitive member. The photosensitive drum 1 is driven by a potential difference from an electrostatic latent image formed on the drum 12.
It is attracted to the electrostatic latent image portion on the two surfaces. As a result, the electrostatic latent image is developed, and a toner image is formed on the surface of the photosensitive drum 12. On the other hand, wherein the time of development, the carrier is negatively charged, most have a state of being attracted to the sleeve 44 by the magnetic force of the developing bias voltage and the S ₁ pole, with the rotation of the sleeve 44 developing conveyed vessel 20 inside, away from the sleeve 44 between the little N ₁ pole and N ₃ pole magnetic force.

However, the magnetic force of the S ₁ magnetic pole does not sufficiently act on a small portion of the carriers whose magnetic performance has deteriorated due to the deterioration, and separates from the sleeve 44 and adheres to the surface of the photosensitive drum 12. The carrier adhered to the surface of the photoconductor drum 12 is attracted to the sleeve 50 of the carrier collection roller 48 by the magnetic force of the S magnetic pole of the permanent magnet 52 when the photoconductor drum 12 slightly rotates and corresponds to the carrier collection roller 48. You. The carrier adsorbed on the sleeve 50 is carried into the developing device 20 when the sleeve 50 is rotated, and is transferred to the scraper 7.
Although most is scraped off from the surface of the sleeve 50 by 0, a part remains on the surface of the sleeve 50, and is further conveyed to a portion facing the photosensitive drum 12 by further rotating the sleeve 50.

On the other hand, the controller 36 controls the developing roller 4
In consideration of the time t ₃ until the toner image formed at the second portion reaches the portion where the carrier collection roller 48 is provided, the carrier collection roller 48 is moved to the portion of the photosensitive drum 12 where the toner image is formed. It is determined whether or not it is compatible (see FIG. 4C). When the carrier collection roller 48 corresponds to the portion where the toner image on the photosensitive drum 12 is formed, the motor 78 is not driven. To sleeve 5
0, the motor 78 is driven for a predetermined time every time when the carrier collection roller 48 corresponds to an inter-image portion where no toner image is formed (portion B in FIG. 5) as shown in FIG. Then, the sleeve 50 is rotated (see FIG. 4D).

Accordingly, when the portion of the photosensitive drum 12 where the toner image is formed passes through the portion where the carrier collection roller 48 is provided, the rotation of the sleeve 50 is stopped, and the toner remains on the surface of the sleeve 50. In addition to preventing the toner image from being disturbed by the carrier, the toner remaining on the surface of the carrier or the surface of the sleeve 50 does not adhere to the toner image as dirt. Further, while the rotation of the sleeve 50 is stopped, the carrier is gradually deposited on the portion of the sleeve 50 facing the photosensitive drum 12, but the carrier collection roller 48 is moved to the portion where the toner image is not formed. Since the sleeve 50 is rotated during the operation, the carrier is collected with a small amount of carrier deposited on the surface of the sleeve 50, and a large amount of carrier is deposited on a part of the carrier collection roller. Is prevented, and the toner image is prevented from being disturbed.

On the other hand, the portion of the photosensitive drum 12 where the toner image has been formed is transferred to the portion where the pre-transfer corotron 22 is provided after the potential is changed by the discharge of the pre-transfer corotron 22 to facilitate the transfer. Move to the 24 installation site. Further, the image receiving material P is transported between the photosensitive drum 12 and the transfer corotron 24 by a transport means (not shown), is brought into contact with the surface of the photosensitive drum 12, and is negatively charged by the transfer corotron 24. As a result, each toner constituting the toner image formed on the photosensitive drum 12 is attracted to the image receiving material P, and the toner image is transferred to the image receiving material P.

The image receiving material P to which the toner image has been transferred is charged again by the peeling corotron 26, and
The toner image is discharged from the image forming apparatus 10 after being transported along a path indicated by a two-dot chain line in FIG. 1 by a transport means (not shown) and heated by a fixing device (not shown) to fix the transferred toner image. Is done. When the peeling of the image receiving material P by the peeling corotron 26 fails, the image receiving material P is removed together with the photosensitive drum 12 by the peeling claw 2.
After being transported to the eight locations, they are physically peeled by the peeling claw 28. The surface of the photosensitive drum 12 that has passed through the portion where the peeling claw 28 is provided is cleaned by the cleaning device 30 to remove toner and the like remaining on the surface. The neutralizing charge is neutralized.

In the above description, the motor 78 is driven for a predetermined time to rotate the sleeve 50 every time the carrier collecting roller 48 corresponds to an inter-image portion where no toner image is formed. It is not limited to this. As an example, as shown in FIG. 6, the time interval for rotating the carrier collection roller may be changed according to the image amount of the toner image (toner amount, that is, the density of the toner image).

FIG. 6A shows a case where the image amount is large, that is, the density of the toner image is high. In such a case, since the amount of the carrier adhering to the surface of the photosensitive drum 12 becomes relatively large, the sleeve 50 is rotated every time the carrier collecting roller 48 corresponds to the inter-image portion. On the other hand, FIG. 6B shows a case where the image amount is small, that is, the density of the toner image is low. In such a case, the amount of the carrier adhering to the surface of the photosensitive drum 12 is relatively small. The rotation of the sleeve 50 is performed at a rate of (number of times). Thereby, the rotation amount of the sleeve 50 can be suppressed to a necessary minimum, and the deterioration or the like of the scraper 70 in contact with the sleeve 50 can be suppressed. The magnitude of the image amount (density of the toner image) can be determined by referring to exposure data or the like output to the exposure device 18 in the control device 36.

Further, the rotation of the sleeve 50 of the carrier collecting roller 48 is not limited to the case where the inter-image portion corresponds to the carrier collecting roller 48 as described above, and as shown in FIG. The sleeve 50 is rotated for a predetermined period of time from when the recording of a plurality of images to P is instructed to when the portion where the toner image is formed reaches the portion where the carrier collection roller 48 is provided, to correspond to the plurality of images. The rotation of the sleeve 50 is stopped until the plurality of toner images pass through the portion where the carrier collection roller 48 is provided,
The sleeve 50 may be rotated again for a predetermined time after all of the plurality of toner images have passed the portion where the carrier collection roller 48 is provided.

Further, the rotation of the sleeve of the carrier collection roller 48 is not limited to the rotation of the sleeve by transmitting the driving force of the motor 78 via a sprocket or the like as shown in FIG. As an example, it is also possible to drive by the mechanism shown in FIG. In FIG. 8, the casing 4 is provided at the bottom of the sleeve 50 of the carrier collecting roller 48.
One end of the one-way clutch 86 arranged outside the zero is connected to the sleeve 50 coaxially. The one-way clutch 86 transmits the clockwise rotational force of FIG. 8 applied to the cam 88 at the other end to the sleeve 50 at one end, and the counterclockwise rotational force of FIG. In this case, this rotational force is not transmitted.

An oval cam 88 is attached to the other end of the one-way clutch 86. The cam 88 is attached so that its elliptical longitudinal end protrudes toward the outer periphery of the sleeve 50, and a hole is formed at the tip of the protruding portion. One end of the extension coil spring 90 is inserted into this hole. The wire 92 is hooked and one end of the wire 92 is locked. The other end of the extension coil spring 90 is locked by a bracket formed outside the casing 40. The wire 92 has an intermediate portion wound around a pulley 94 pivotally supported by the casing 40. The other end of the wire 92 is attached to a movable shaft 96A of a solenoid 96 fixed to the casing 40 by a bracket (not shown). I have.

The operation of this mechanism will be described. Solenoid 9
6 attracts the movable shaft 96A when the excitation coil is energized and moves it in the direction of arrow C in FIG. As a result, the wire 92 is also pulled in the direction of arrow C, and the cam 88 is pulled by the tension coil spring 90.
8 is rotated clockwise in FIG. 8 to a position D shown by an imaginary line in FIG. 8 around the axis of the sleeve 50 against the urging force generated by the pulling. The cam 88 at this time
Rotation of the sleeve 50 via the one-way clutch 86
The sleeve 50 is also rotated clockwise in FIG.

When the energization of the excitation coil of the solenoid 96 is stopped, the movable shaft 96A returns to the position shown in FIG. 8 by the urging force of a compression coil spring (not shown) accommodated in the solenoid 96, and the cam 88 is turned off. Extension coil spring 90
8 to the position shown by the solid line in FIG.
At this time, no rotational force is transmitted to the sleeve 50 by the one-way clutch 86. Therefore, the sleeve 50 can be rotated stepwise by a predetermined rotation angle by repeating the energization of the excitation coil of the solenoid 96 and the stop of the energization.

[Second Embodiment] Next, a second embodiment of the present invention will be described. The same portions as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG.
The image forming apparatus 100 according to the second embodiment includes a first developing device 20A and a second developing device 20B downstream of the first developing device 20A. The first developing device 20A and the second developing device 20B have substantially the same configuration as the developing device 20 described in the first embodiment, but the carrier collecting roller 48 is provided only in the second developing device 20B. Have been. A first developer used in the first developing device 20A;
The second developer used in the second developing device 20 is charged to the same polarity although the color of the toner is different.

First developing device 2 as first developing roller
The developing roller 42A of the first magnetic field includes a sleeve 44A as a first sleeve and a permanent magnet 4 as a first magnetic field generating unit.
6A, and the sleeve 44A is connected to the motor 68A via a driving force transmission mechanism composed of a plurality of sprockets as in the first embodiment. The motor 68A is connected to the control device 36 via a driver 80A. The developing roller 42B of the second developing device 20B as a second developing roller is a sleeve 44 as a second sleeve.
B, and a permanent magnet 46B as a second magnetic field generating unit.
8B, and a motor 68B is connected to a driver 80B.
Is connected to the control device 36 via the. Note that the control device 36, the driver 80B, the motor 68B, and the like constitute driving means according to the second aspect of the present invention.

Next, the operation of the second embodiment will be described. The control device 36 specifies the color of the image recorded on the transfer material P from outside, and causes one of the first developing device 20A and the second developing device 20B to perform development in accordance with the specified color. Regarding the carrier collection roller 48, the carrier collection roller 48 is connected to the photosensitive member regardless of whether the first developing device 20A is performing development or the second developing device 20B is performing development. When it does not correspond to the portion of the drum 12 where the toner image is formed, the motor 7
8 is driven to rotate the sleeve 50. This allows
As in the first embodiment, it is possible to prevent the carrier and the toner once adsorbed on the sleeve 50 of the carrier collection roller 48 from disturbing the toner image on the photosensitive drum 12 and attaching dirt.

Next, the operation when the first developing unit 20A is performing development will be described. Since the polarity of the developer D is the same between the first developing device 20A and the second developing device 20B, the polarity of the magnetic pole formed on the portion of the permanent magnet of the developing roller 42A facing the photosensitive drum 12 is the same. The polarity of the magnetic pole formed on the portion of the permanent magnet of the developing roller 42B facing the photosensitive drum 12 is the same. Therefore, the carrier of the first developer adhered to the surface of the photosensitive drum 12 when the first developing device 20A is performing the development is attracted to the outer periphery of the sleeve 44B of the second developing roller 42B. become. Further, the toner of the first developer slightly adheres to the surface of the carrier adsorbed on the sleeve 44B.

For this reason, the control device 36 controls the first developing device 2
Based on the timing at which the rotation of the sleeve 44A of the developing roller 42A of 0A is started (see FIG. 10A), the toner image formed at the portion where the developing roller 42A is provided is disposed on the developing roller 42B of the second developing device 20B. taking into account the time t ₄ to reach the site, the developing roller 42B photosensitive drum 1
The second developing roller 42B determines whether or not it corresponds to the portion where the second toner image is formed (see FIG. 10B).
Corresponds to the inter-image portion on the photosensitive drum 12 where the toner image is not formed.
B for a predetermined time to rotate the sleeve 44B (FIG. 1).
0 (C)), the high voltage power supply 34 is controlled to apply a developing bias voltage to the sleeve 44B in synchronization with the rotation of the sleeve 44B (see FIG. 10 (D)).

As a result, the toner adhering to the carrier adsorbed on the sleeve 44B of the developing roller 42B becomes
When the developing bias voltage is applied to the sleeve 44B, the developing bias voltage is attracted to the inter-image portion on the surface of the photosensitive drum 12. Accordingly, when the second developing device 20B is operated, color mixture occurs due to the first developer toner having a different color from the second developer toner remaining on the surface of the sleeve 44B of the developing roller 42B. Or developing device 2
It is possible to prevent the toner of the first developer from entering the inside of OB. Note that the toner adhered to the inter-image portion on the surface of the photosensitive drum 12 is removed by the cleaning device 30 without being transferred to the transfer material P.

The carrier adsorbed on the sleeve 44B is transferred to the second developing roller 42B by rotating the sleeve 44B when the second developing roller 42B corresponds to the inter-image portion on the photosensitive drum 12, as described above. Developing device 2
Since the toner image is collected inside the OB, the toner image is also prevented from being disturbed.

The timing of the rotation of the sleeve 44B of the developing roller 42B of the second developing device 20B and the application of the developing bias voltage when the first developing device 20A is performing development are the same as those shown in FIG. Not limited
As described in the first embodiment, the time interval between the rotation of the sleeve 44B and the application of the developing bias voltage may be changed according to the image amount of the toner image (toner amount, that is, the density of the toner image). (See FIG. 6). Also,
As shown in FIG. 7, from when the recording of a plurality of images on the transfer material P is instructed to when the toner image portion reaches the portion where the developing roller 42B is provided, and when all the plurality of toner images are provided at the portion where the developing roller 42B is provided. After passing through, the rotation of the sleeve 44B and the application of the developing bias voltage may be performed.

The configuration of the carrier collecting roller 48 is not limited to the above-described one. For example, an electromagnet can be used instead of a permanent magnet. It is also possible to use a general columnar roller instead of the sleeve, and to arrange the electromagnet or the permanent magnet at a position where a magnetic field is generated at a portion where the roller and the photosensitive drum face each other. Further, the developing roller is not limited to the developing roller having the configuration in which the permanent magnet is fixedly arranged and the sleeve arranged on the outer periphery of the permanent magnet is rotated as described in the above embodiment. A magnetic roller may be provided on the circumferential side as a magnetic field generating unit, and a developing roller configured to rotate the magnetic roller may be used. It is also possible to use a developing roller configured to rotate the sleeve and the magnetic field generator.

Further, in the above description, the drum-shaped photosensitive member has been described as an example of the image carrier, but a belt-shaped or film-shaped photosensitive member may be used. Further, in the above, the present invention has been described by taking the image forming apparatus 10 shown in FIG. 1 and the image forming apparatus 100 shown in FIG. 9 as examples, but the image forming apparatus to which the present invention can be applied is not limited to the above. For example, disclosed in JP-A-3-209276, which has two exposure devices and three developing devices, forms a negative latent image with a first exposure device, and performs reversal development with a first developing device. The present invention relates to an image forming apparatus and the like that forms a positive latent image with a second exposure device and performs positive development using toner of a different color from the first developing device in a second developing device and a third developing device. It goes without saying that it is possible to apply

[0059]

As described above, according to the first aspect of the present invention, when the developing unit is developing an electrostatic latent image, the carrier is collected in a portion where the toner image is not formed on the image carrier. since the rotation driving only career collecting roller when the roller is compatible, by the carrier adheres the carrier is further sucked into the collection roller remaining or deposited on the image bearing member by development with the developing unit It is possible to obtain an excellent effect that it is possible to prevent inconveniences such as disturbing the toner image and attaching dirt.

According to a second aspect of the present invention, when the first developing roller is developing an electrostatic latent image, the second developing roller is provided on a portion of the image carrier where no toner image is formed. Since the second developing roller is rotationally driven only when it is compatible, the carrier adheres to the image carrier by the development by the first developing roller, and the carrier is further sucked by the second developing roller and remains or accumulates. As a result, an excellent effect of preventing inconveniences such as disturbing the toner image and attaching dirt can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic configuration diagram of a developing device.

FIG. 3 is a schematic diagram illustrating a driving mechanism of a developing roller and a carrier collecting roller of the developing device.

FIGS. 4A to 4D are timing charts illustrating an example of a timing of rotating a carrier collection roll.

FIG. 5 is a conceptual diagram illustrating a state in which an inter-image portion on a photosensitive drum corresponds to a carrier collection roll.

FIGS. 6A and 6B are timing charts for explaining a case where the timing of rotating the carrier collection roll is changed according to the toner image density.

FIG. 7 is a timing chart illustrating another example of the timing of rotating the carrier collection roll.

FIG. 8 is a schematic view showing another example of a drive mechanism of the carrier collection roller.

FIG. 9 is a schematic configuration diagram of an image forming apparatus according to a second embodiment.

FIGS. 10A to 10D are timings for explaining a timing of operating a downstream developing device when an upstream developing device is operating and a timing of applying a bias voltage to the downstream developing device. It is a chart.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photoreceptor drum 20 Developing device 42 Developing roller 44 Sleeve 46 Permanent magnet 48 Carrier collection roller 50 Sleeve 52 Permanent magnet 100 Image forming apparatus

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-94083 (JP, A) JP-A-3-171167 (JP, A) Fully open 1986-116366 (JP, U) Really open 1983 100367 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/08-15/095 G03G 15/00 303

Claims (3)

(57) [Claims] A latent image forming means for forming an electrostatic latent image on the image carrier; developing the electrostatic latent image formed on the image carrier with a developer containing toner and a magnetic carrier; A developing unit for forming a toner image on a body; a carrier collecting roller disposed at a predetermined distance from the image carrier downstream of the developing unit; and the developing unit performs development of the electrostatic latent image. case, an image forming apparatus comprising, a driving means for rotating the saw career collecting roller when said carrier recovery roller to a portion where the toner image on the image bearing member is not formed corresponds. 2. A latent image forming means for forming an electrostatic latent image on an image carrier, a first sleeve disposed at a predetermined distance from the image carrier, and an inner periphery of the first sleeve. And a first magnetic field generator for generating a magnetic field, wherein the electrostatic latent image formed on the image carrier is formed by a first developer containing a toner and a magnetic carrier attached to the first sleeve. A first developing roller for developing to form a toner image on the image carrier; a second sleeve disposed at a predetermined distance from the image carrier downstream of the first developing roller; A second magnetic field generating unit disposed on the inner periphery of the sleeve to generate a magnetic field, comprising a toner and a magnetic carrier attached to the second sleeve, the electrostatic latent image formed on the image carrier; and The second developer having the same polarity as that of the first developer is used. A second developing roller for forming a toner image on the image carrier, and a portion where the toner image is not formed on the image carrier when the first developing roller is developing an electrostatic latent image. And a driving unit for rotating and driving the second developing roller only when the second developing roller corresponds to the image forming apparatus. 3. The driving device according to claim 2, wherein the driving unit rotates the second developing roller so that the toner adhered to the second sleeve of the second developing roller adheres to the image carrier. 3. The image forming apparatus according to claim 2, wherein a bias voltage is applied to the image forming apparatus.