JP2007101633A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus using a blade cleaning device, which prevents stripes or image blur from occurring because powder developer (toner) having small particle size and an additive or the like are pressed and stuck to an image carrier. <P>SOLUTION: The image forming apparatus has a means for predicting the amount of developer removed from the image carrier 1 by a cleaning means 6 in the midst of rotating operation of the image carrier 1, and performs a cleaning mode for a transfer material carrying and conveying means in accordance with the predicted collected amount of developer just before performing next image forming operation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus configured to remove a transfer residual developer of an image carrier on which a developer image is formed by using an electrophotographic technique, with a cleaning unit. The present invention also relates to an image forming apparatus configured to transfer a developer image (toner image) formed on an image carrier onto a transfer material conveyed by a transfer material carrying conveyance unit.

  Conventionally, various electrophotographic image forming apparatuses are known as cleaning apparatuses that remove (clean) transfer residual toner on a rotating image carrier. Among them, the blade cleaning device is most commonly used.

  The blade cleaning device has a flexible (rubber elasticity) cleaning blade as a cleaning member brought into contact with the image carrier in a predetermined pressure contact state and wipes the surface of the image carrier to transfer residual toner from the image carrier. Is removed by scraping.

  In order to improve the cleaning efficiency, the cleaning blade is generally arranged in contact with the counter in the rotational direction during image formation of the image carrier with respect to the image carrier.

  In the image forming apparatus using such a blade cleaning device, the fine particle developer (toner) having a small particle size and the external additive remaining in the cleaning blade contact area while the image carrier is stopped are transferred to the image carrier. There is a case where a phenomenon of pressure bonding occurs. Then, in the region where the external additive or the like has been crimped, the friction coefficient with the cleaning blade is lower than that of the other image carrier surface, that is, it tends to be slippery. In this state, when image formation is resumed, a phenomenon occurs in which the rotation speed of the image carrier increases at the moment when the region where the external additive or the like has been crimped passes through the contact portion with the cleaning blade. There is. As a result, when the speed fluctuates, streaks of the rotation period of the image carrier and image blurring (density fluctuation, etc.) occur at the position on the image carrier where uniform charging, latent image formation, development, or transfer has been performed. In some cases.

  Along with the rotation of the image carrier, the fine toner having a small particle diameter, the external additive and the like which are pressed onto the image carrier are gradually removed by an abutment against the image carrier such as a cleaning blade. It is possible to avoid the above-mentioned phenomenon such as streaking and image blurring by starting image formation after the image carrier is sufficiently rotated and the pressure-bonded product is removed. However, this causes problems such as an increase in first printout time and deterioration of consumables.

  As a means for solving streaks and image blurring without causing problems such as an increase in first printout time and deterioration of consumables, a method described in Patent Document 1 has been proposed.

  That is, in Patent Document 1, the image carrier is reversely rotated when the image carrier is stopped, so that the agglomerated toner and the external additive accumulated at the contact edge portion of the cleaning blade with the image carrier are removed from the edge portion of the cleaning blade. It is configured to be removed from.

  FIG. 12 is an enlarged schematic view of the edge portion of the cleaning blade for explaining this conventional example.

  In FIG. 12, the image carrier 1 is in contact with the rubber cleaning blade 61 at the contact portion W. FIG. 12A shows a contact state during image formation, and the image carrier 1 is driven to rotate in the direction of arrow a. The cleaning blade 61 is disposed such that the front edge 61E is brought into contact with the counter with a predetermined pressing force with respect to the image carrier 1 in the positive rotation direction when the image carrier 1 forms an image. The leading edge 61E of the cleaning blade 6 is distorted by being dragged in the forward rotation direction of the image carrier 1. The surface of the image carrier is wiped by the edge portion 61E of the cleaning blade 61 brought into contact, and the transfer residual toner is scraped off from the image carrier.

Then, immediately after the forward rotation driving of the image carrier 1 is stopped, the image carrier 1 is reversely rotated in the reverse direction b as shown in FIG. Then, the toner accumulated in front of the edge portion 61E of the cleaning blade 61 is removed from the edge portion 61E before it aggregates, and the image carrier 1 is stopped. As a result, it is possible to avoid a phenomenon in which fine toner particles, external additives, and the like having a small particle diameter are pressed against the image carrier 1. Hereinafter, this drive control is referred to as “reverse rotation stop control”.
JP 2005-62280 A

  It is an object of the present invention to generate streaks and image blur due to a fine powder developer (toner) having a small particle size or an external additive being pressed against an image carrier in an image forming apparatus using a blade cleaning device. It is an object of the present invention to provide an image forming apparatus capable of suppressing the above.

  Another object of the present invention is to provide an image forming apparatus capable of avoiding the occurrence of stains on the back side of the transfer material due to the developer (toner) slipping out when the image carrier is started.

The above object is achieved by the image forming apparatus according to the present invention. In summary, according to the first aspect of the present invention,
A rotatable image carrier on which an electrostatic latent image is formed;
Developing means comprising a developer carrier for carrying and transporting the developer to develop the electrostatic latent image formed on the image carrier to form a developer image;
Transfer material carrying and conveying means for carrying and carrying the transfer material for transferring the developer image on the image carrier to a transfer material;
Cleaning means for removing the developer on the image carrier;
Have
In the image forming apparatus having a transfer material carrying / conveying means cleaning mode for removing the developer attached to the transfer material carrying / conveying means,
Means for predicting the amount of developer removed from the image carrier by the cleaning means during the rotation of the image carrier;
In accordance with the estimated developer recovery amount, the transfer material carrying / conveying unit cleaning mode is performed immediately before the next image forming operation is performed.
An image forming apparatus is provided.

According to a second aspect of the invention,
A forward and reverse rotatable image carrier on which an electrostatic latent image is formed;
Developing means comprising a developer carrier for carrying and transporting the developer to develop the electrostatic latent image formed on the image carrier to form a developer image;
Transfer material carrying and conveying means for carrying and carrying the transfer material for transferring the developer image on the image carrier to a transfer material;
A cleaning blade for removing the developer by contacting the image carrier in the direction of a counter with respect to the positive rotation direction of the image carrier;
Have
In the image forming apparatus for performing image carrier stop control for stopping the image carrier by rotating in the reverse direction after stopping the forward rotation of the image carrier,
Means for predicting the amount of developer removed from the image carrier by the cleaning blade during the forward rotation of the image carrier;
In accordance with the estimated developer recovery amount, the image carrier stop control is performed so as to shorten the time for rotating the image carrier in the reverse direction.
An image forming apparatus is provided.

  According to the present invention, when it is predicted that the amount of collected toner removed from the image carrier by the cleaning unit during the rotation operation of the image carrier is predicted to be very large, the transfer material immediately before the next image forming operation is performed. The carrying / conveying means cleaning mode is carried out. As a result, even if toner slips out at the time of starting rotation of the image carrier, it can be prevented that the toner becomes soiled and becomes apparent.

  Further, according to the present invention, when the amount of developer recovered is larger, the control is performed so that the reverse rotation time immediately after the image carrier is stopped is shortened. As a result, fine powder developer (toner) having a small particle diameter, external additives, and the like do not cause adverse effects such as streaks, image blurring, and increased first printout due to pressure bonding to the image carrier. . Further, it is possible to prevent the developer (toner) from slipping out when the image carrier starts rotating.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 is a schematic sectional view of a color image forming apparatus using an electrophotographic process which is an embodiment of an image forming apparatus according to the present invention.

  In this embodiment, the color image forming apparatus 100 has four independent process cartridges 7 (7a, 7b, 7c, 7d) that are detachably attached to the apparatus main body 100A. In this embodiment, the process cartridges 7 (7a, 7b, 7c, 7d) respectively have image forming means for yellow (Y) toner, magenta (M) toner, cyan (C) toner, and black (Bk) toner. Constitute.

  Referring to FIG. 2, each of the process cartridges 7 (7a, 7b, 7c, 7d) is a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a “photosensitive drum”) 1 that is used repeatedly as an image carrier. 1a, 1b, 1c, 1d). Around each photosensitive drum 1, a charging device 2 (2a, 2b, 2c, 2d) as a charging unit, a developing device 4 (4a, 4b, 4c, 4d) as a developing unit, and a cleaning as a recovery unit Device 6 (6a, 6b, 6c, 6d) is arranged. As described above, in this embodiment, the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning device 6 are integrally formed into a cartridge to form a process cartridge 7 (7a, 7b, 7c, 7d). .

  Further, developer images (that is, toner images) of different colors formed by the process cartridge 7 are sequentially transferred to the transfer material P carried and conveyed by a transfer belt 11 as a transfer material carrying and conveying means. . As a result, a full-color image is formed on the transfer material P. The transfer belt 11 is wound around rollers 13, 14, 15, and 16 provided in the transfer material transport unit 5 and is rotatable in the arrow direction.

  The transfer material P is fed from the sheet feeding unit 17 at the lower part of the color image forming apparatus 100 and conveyed upward, and the full-color image is transferred as described above and fixed by the fixing device 20. The paper is discharged to the paper discharge tray 26.

  Hereinafter, the photosensitive drum 1 will be described in detail.

  The photosensitive drum 1 (1a, 1b, 1c, 1d) is configured, for example, by applying an organic photoconductor layer (OPC photosensitive member) to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm. Both ends of the photosensitive drum 1 are rotatably supported by support members.

  In this embodiment, the photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (process speed) by a rotational driving device (not shown). Further, the photosensitive drum 1 can rotate in both directions, with respect to the transfer direction of the transfer material P, the forward rotation is forward rotation, and the counter direction rotation is reverse rotation (a in FIG. 2 is forward rotation, b is This will be referred to as reverse rotation).

  As the charging device 2 (2a, 2b, 2c, 2d), a contact charging type can be used. In this embodiment, the charging member of the charging device 2 is a conductive roller formed in a roller shape. The roller 2 is brought into contact with the surface of the photosensitive drum 1 and a charging bias voltage is applied to the roller 2 to uniformly charge the surface of the photosensitive drum 1.

  That is, the photosensitive drum 1 is uniformly charged to a predetermined polarity / potential (minus in this embodiment) by a primary charging roller (primary charging device) 2 serving as a charging means in the forward rotation process.

  In this embodiment, the scanner unit 3 (3a, 3b, 3c, 3d), which is an exposure apparatus, is arranged at substantially the same level as the corresponding photosensitive drum 1 in the vertical direction. In the scanner unit 3, image light corresponding to an image signal is irradiated to a polygon mirror 9 (9 a, 9 b, 9 c, 9 d) rotated at high speed by a scanner motor (not shown) by a laser diode (not shown). The image light reflected by the polygon mirror 9 selectively exposes the surface of the charged photosensitive drum 1 through the imaging lens 10 (10a, 10b, 10c, 10d). Thus, the photosensitive drum 1 has a static image corresponding to the first, second, third, and fourth color component images of the color image, that is, yellow, magenta, cyan, and black component images in this embodiment. An electrostatic latent image is formed.

  Next, the electrostatic latent image is developed by the developing device 4 of each process cartridge 7 constituting the image forming unit.

  Here, the developing device 4 will be described with reference to FIG.

  Each of the developing devices 4 includes a developer storage unit that stores toner of each color of yellow, magenta, cyan, and black, that is, a toner container 41 (41a, 41b, 41c, and 41d), and a developing frame, that is, a developing unit. Container 45 (45a, 45b, 45c, 45d).

  That is, the yellow developing device 4a includes a toner container 41a that stores yellow toner, and the magenta developing device 4b includes a toner container 41b that stores magenta toner. The cyan developing device 4c includes a toner container 41c that stores cyan toner, and the black developing device 4d includes a toner container 41d that stores black toner.

  Further, in each developing container 45, a developing roller 40 (40a, 40b, 40c, 40d) as a developer carrying member carrying and carrying the developer is disposed facing the photosensitive drum 1. Further, a toner supply roller 43 (43 a, 43 b, 43 c, 43 d) that supplies toner to the developing roller 40 is provided in the developing container 45.

  In FIG. 2, the developer in the toner container 41, that is, the toner, is sent to the toner supply roller 43 by the toner conveyance stirring mechanism 42. Next, the toner is applied to the outer periphery of the developing roller 40 by the toner supply roller 43 and the developing blade 44 pressed against the outer periphery of the developing roller 40, and charges are applied to the toner. Then, by applying a developing bias to the developing roller 40, the latent image formed on the photosensitive drum 1 is developed into a toner image.

  That is, each developing roller 40 carrying toner in each developing device 4 is rotated by a rotation driving device (not shown) and is arranged to face the photosensitive drum 1 in the developing process. Each color toner that is negatively frictionally charged in each developing device and carried on each developing roller 40 is electrostatically developed on each photosensitive drum 1 to form a toner image of each color.

The transfer belt 11 is rotationally driven at substantially the same peripheral speed as that of the photosensitive drum 1 while being in contact with each photosensitive drum 1. The transfer belt 11 is composed of an endless film-like member having a volume resistivity of 10 ⁸ to 10 ¹² Ωcm and a thickness of about 50 to 150 μm.

  The volume resistivity is a value obtained by applying 100 V at a temperature of 23.5 ° C. and a relative humidity of 60% with a high resistance meter R8340 manufactured by ADVANTEST, using a measurement probe in accordance with JIS method K6911. It is.

  The transfer material P fed from the paper feed cassette 17 is fed toward the adsorbing roller 22 that is driven to rotate relative to the transfer belt 11 by a registration roller pair 19 that is driven and rotated at a predetermined timing. The transfer belt 11 is electrostatically adsorbed. At this time, in order to electrostatically attract the transfer material P to the transfer belt 11, a predetermined voltage is applied to the attracting roller 22. As a result, a charge is applied to the surface of the transfer material P, a mirroring force is generated between the transfer material 11 and the transfer material P is electrostatically attracted to the transfer belt 11.

The suction roller 22 is formed by molding a solid rubber on a core metal having a diameter of 6 mm, and is configured to apply a high-pressure bias for suction to the core metal. The suction roller 22 is a solid rubber roller having a diameter of 12 mm in which carbon black is dispersed in EPDM rubber for resistance adjustment. The resistance value is adjusted to about 10 ⁵ to 10 ⁶ Ω when a metal foil having a width of 1 cm is wound around the outer periphery of the roller and a voltage of 500 V is applied between the core and the metal core. In order to ensure releasability, a coating layer may be provided on the surface layer.

  The transfer material P adsorbed on the transfer belt 11 passes through each process cartridge (each image forming unit) 7. At this time, toner images of different colors are transferred from the photosensitive drum 1 to the transfer material P by the action of static electricity due to the high voltage applied to the transfer roller 12 disposed opposite to the photosensitive drum 1 with the transfer belt 11 interposed therebetween. The

The transfer roller 12 is formed by molding a solid rubber on a core metal having a diameter of 6 mm, and is configured to apply a high-voltage bias for transfer to the core metal. The transfer roller 12 is a solid rubber roller having a diameter of 12 mm in which carbon black is dispersed for resistance adjustment in epichlorohydrin rubber, and the resistance value is adjusted to about 2 × 10 ⁷ Ω by the measurement method described above.

  Then, the transfer material P separated from the transfer belt 11 by the curvature is fixed on the transfer material P by heat and pressure by the fixing device 20 and discharged outside the apparatus (outside of the image forming apparatus main body).

  On the other hand, after the toner image is transferred from the photosensitive drum 1 to the transfer material P on the transfer belt 11, the toner (transfer residual toner) remaining on the photosensitive drum 1 is removed by a cleaning blade of the cleaning device (collecting means) 6. 61 to remove and collect. The collected toner is accumulated in a waste toner chamber (tank) 62 in the cleaning device 6.

  FIG. 3 is an enlarged model view of a contact portion between the photosensitive drum 1 and the cleaning blade 61. As the cleaning blade 61, urethane rubber having a Wallace hardness of 70 degrees is used in this embodiment. The cleaning blade 61 is supported by a support member 63. The support member 63 is configured such that the leading edge 61E of the cleaning blade 61 abuts with a predetermined pressing force in the counter direction in the positive rotation direction a of the photosensitive drum 1. In this embodiment, the contact pressure between the cleaning blade 61 and the photosensitive drum 1 was 70 g / cm.

  Further, the cleaning device 6 is provided with a seal sheet (squeeze sheet) 64 for preventing the collected toner from being blown out, and is brought into contact with the photosensitive drum forward rotation direction a in the forward direction. The squeeze sheet 64 is a flexible sheet, and is, for example, a polyethylene terephthalate film having a thickness of 30 μm to 100 μm.

  As shown in FIG. 2, the toner collected by the cleaning blade 61 is gradually conveyed to a waste toner chamber (tank) 62 by the action of a conveying member 65 that operates in synchronization with the rotation of the photosensitive drum 1. .

  Next, a method for collecting the residual toner remaining on and attached to the transfer belt 11 used in this embodiment, that is, a transfer material carrying / conveying means cleaning mode (hereinafter referred to as “transfer belt cleaning mode”) will be described.

  In this embodiment, no cleaning device that directly scrapes off the toner adhering to the transfer belt 11 is provided. Instead, a special sequence called “transfer belt cleaning mode” is executed when it is predicted that there is a possibility that a large amount of toner is attached on the transfer belt 11 such as immediately after the occurrence of a jam. In the transfer belt cleaning mode, the toner adhering to the transfer belt 11 is electrostatically transferred to the plurality of photosensitive drums 1 and removed by the cleaning blade 61. The removed developer is collected in a waste toner chamber (tank) 62 of the process cartridge 7. When this method is used, there is no need to prepare a waste toner bottle for the transfer belt 11, which is advantageous in terms of downsizing the apparatus.

  When the “transfer belt cleaning mode” is executed, a negative bias is applied to the transfer rollers 12a and 12c and a positive bias is applied to the transfer rollers 12b and 12d while rotating the photosensitive drum 1 and the transfer belt 11 in the positive direction a. Applied. As a result, the negative polarity toner is recovered by the process cartridges 7a and 7c and the positive polarity toner is recovered by the process cartridges 7b and 7d by the action of the electrostatic electric field.

  In order to further improve the efficiency of toner collection, the charging biases of the primary charging rollers 2a, 2b, 2c, and 2d and the exposure operation by the image exposure units 3a, 3b, 3c, and 3d may be combined.

  It has also been found that if a peripheral speed difference is provided between the rotational speeds of the photosensitive drum 1 and the transfer belt 11, the toner recovery efficiency is further improved. This is because a mechanical scraping force from the transfer belt 11 is applied to the lower layer toner that has been held on the transfer belt by the van der Waals force.

  In this embodiment, exposure is performed by the image exposure means 3a and 3c, so that the photosensitive drums 1a and 1c have a potential of approximately 0V, and the photosensitive drums 1b and 1d have a potential of approximately −500V. An appropriate bias is applied to the rollers 2b and 2d. Further, −2 kV is applied to the transfer rollers 12a and 12c, and +1.5 kV is applied to the transfer rollers 12b and 12d. Then, the speed of the transfer belt 11 was set to 160% of the speed of the photosensitive drum 1.

  Next, the “toner forced discharge operation” performed in this embodiment will be described.

  The development process and the transfer process are easily affected by the charging characteristics of the toner. If the charging characteristics of the toner change as the apparatus is used, the development performance and transfer performance may change, resulting in color variations and image defects. In particular, when low-printing paper is continuously used, the toner coated on the developing roller 4 is not used and remains indefinitely, and the charging characteristics of the toner greatly change. In order to avoid this, in this embodiment, the “toner forced discharge operation” is executed at a predetermined timing.

  Specifically, in the non-image area, a certain amount of toner is forcibly developed from the developing roller 4 to the photosensitive drum 1, and the toner is collected by the cleaning blade 6 without being transferred. As a result, new toner is supplied to the developing roller, and the charging characteristics can always be stabilized.

Means for forcibly developing a fixed amount of toner from the developing roller 4 to the photosensitive drum 1 include a method of changing a bias such as charging and developing, or forming an electrostatic latent image by the image exposure means 3. Conceivable. In this embodiment, a method of forming an electrostatic latent image for 1 second on the photosensitive drum 1 rotating at 150 mm / sec was used. The toner consumption weight per unit area (cm ² ) was about 0.64 mg. Therefore, about 9.6 mg of toner per unit length (cm) is collected by the cleaning 6 at a time.

Next, the details of the “reverse rotation stop control” of the photosensitive drum 1 performed in this embodiment will be described. Control is performed according to the following flow.
(1) The forward rotation of the photosensitive drum 1 is stopped.
(2) Wait for 5 seconds.
(3) The reverse rotation of the photosensitive drum 1 is started and the rotation speed is 50 mm / sec.
(4) After 280 msec, the reverse rotation of the photosensitive drum 1 is stopped.

  In the control operation described above, there is a time lag from when the reverse rotation operation start signal is output until the photosensitive drum 1 actually starts reverse rotation in a state where the normal rotation of the photosensitive drum 1 is stopped. This corresponds to the time during which various play in the drive transmission mechanism shifts from the normal rotation state to the reverse rotation state. In this embodiment, the time is about 200 msec.

  Therefore, in this embodiment, the reverse rotational movement distance of the photosensitive drum 1 is actually about 4 mm (= 50 * (0.28−0.20)). When the edge portion of the cleaning blade 6 after the completion of the “reverse rotation stop control” is confirmed, as shown in FIG. 12B described in the conventional example, the distortion is completely relaxed.

  4 shows the state in the vicinity of the cleaning blade 61 immediately after the forward rotation of the photosensitive drum 1 is stopped (FIGS. 4A1 and 4A2) and after the “reverse rotation stop control” is executed (FIGS. 4B1 and 4B2). Is shown.

  FIGS. 4A1 and 4B1 are examples in which the amount of accumulated toner is small, and FIGS. 4A2 and 4B2 are examples in which the amount of accumulated toner is large.

  When the amount of accumulated toner is small, there is almost no toner in the vicinity of the cleaning blade 61 after executing the “reverse rotation stop control”, but when there is a large amount of accumulated toner, a certain amount remains. ing.

  FIG. 5 shows a state in which printing is resumed from the state of FIG. 4B2 and the photosensitive drum 1 starts to rotate forward, and distortion is re-formed at the leading edge 61E of the cleaning blade 61. It is a thing.

  FIG. 5A shows a state after “reverse rotation stop control”, FIG. 5F shows a state where distortion is formed, and FIGS. 5B to 5E show the process. It can be seen that distortion is formed while the toner in the vicinity of the edge portion 61E is wound together. Then, the entrained toner finally slips out of the cleaning blade 61. The slipped toner once transfers to the transfer belt 11 and then adheres to the transferred transfer material P, and becomes apparent as the back stain of the transfer material P.

In this embodiment, the following control is performed in order to prevent the transfer material P from being stained.
(1) When the forward rotation operation of the photosensitive drum 1 is started, the amount of toner accumulated in the cleaning blade 6 is predicted.
(2) When it is predicted that a large amount of toner has accumulated, the transfer belt cleaning mode is executed.
(3) When the transfer cleaning mode is completed, the transfer material is conveyed and a printing operation is performed.

  FIG. 6 is a flowchart showing more specific control according to the present embodiment.

  In this embodiment, when starting the normal rotation operation of the photosensitive drum 1, it is determined whether or not it is after the jam processing (step S1). If NO, it is next determined whether or not it is immediately after the forced toner discharge operation (step S2). If NO, the transfer material is conveyed (step S4) and a printing operation is performed.

  If YES in step S1, and if NO in step S1 and YES in step S2, it is predicted that a large amount of toner has accumulated on the cleaning blade 6, and the transfer belt cleaning mode is set. Execute (S3). These correspond to cases where a large amount of toner is conveyed to the cleaning blade 6 at a time. That is, when the “jam processing” or the “toner forced discharge operation” is performed immediately before the start of the forward rotation operation of the photosensitive drum 1, the transfer belt cleaning mode is executed (S3).

  Next, when the transfer cleaning mode is completed, the transfer material is conveyed (S4), and a printing operation is performed.

  As described above, the toner collected by the cleaning blade 6 is gradually conveyed to the waste toner chamber 62 by the action of the conveying member 65 that operates in synchronization with the rotation of the photosensitive drum 1. Therefore, during normal printing in which only the transfer residual toner is collected, an extremely large amount of toner does not collect near the cleaning blade 61.

  As described above, according to the present embodiment, when it is predicted that the toner collection amount removed from the image carrier by the cleaning unit during the rotation operation of the image carrier is predicted to be very large, the next image forming operation is performed. Immediately before the transfer, the transfer belt cleaning mode is performed. As a result, even if the toner slips through when the image carrier starts rotating, it can be prevented that the toner becomes soiled and becomes apparent.

Example 2
In the present embodiment, a means for preventing toner slipping after “reverse rotation stop control” will be described. The structure of the image forming apparatus is the same as that of the first embodiment.

  If the method of Example 1 is used, it is possible to prevent the transfer material from being stained at a considerable rate. However, when an image with a high printing rate is continuously passed, a certain amount of untransferred toner is collected by the cleaning blade 6 and there is a concern that the backside of the transfer material may be generated.

  Even in such a case, as shown in the first embodiment, the transfer belt cleaning mode is executed prior to the start of the next printing operation, so that it is possible to suppress the occurrence of back contamination of the transfer material. However, the printout time is extended and the usability for the user is deteriorated. Therefore, it is not preferable to frequently perform the transfer belt cleaning mode.

  In the second embodiment, in such a case, a means that can prevent the toner from slipping out after the “reverse rotation stop control” and suppress the occurrence of the back stain on the transfer material without extending the printout time will be described. .

Table 1 shows the relationship between the level of occurrence of back stain on the transfer material and the halftone image data to be printed. The procedure is as follows. Table 1 also shows the period stripe / image blur level of the photosensitive drum 1. In a 23 ° C./50% RH environment, plain paper (Canon sales color laser copier paper 80 g) was used as a transfer material.
(1) 10 continuous halftone images are continuously printed on the entire surface of A4 size paper.
(2) Implementation of “reverse rotation stop control” described in Example 1 (photosensitive drum reverse rotation 280 msec / equivalent to about 4 mm).
(3) Leave for 5 minutes.
(4) Print halftone of image data 25%: Check the level of back dirt.

  In Table 1, as a reference value, the image density on paper and the toner consumption per unit area (toner adhesion amount on the paper) measured by RD918 manufactured by Gretag Macbeth are listed.

  The respective levels of the back stain of the transfer material and the photosensitive drum cycle streak / image blur were visually determined as follows. ○ is not at all. △ appears slightly when you look closely. X is clearly visible.

  The photosensitive drum cycle streak / image blur level is determined by the first sample printed in the above (4). It can be seen that the photosensitive drum cycle streaking / image blur does not occur at all, while the backside smudge occurs when the image density increases.

Table 2 shows the results when “reverse rotation stop control” was not performed with respect to Table 1. The specific procedure is as follows.
(1) 10 continuous halftone images are continuously printed on the entire surface of A4 size paper.
(2) Stop the photosensitive drum (without performing “reverse rotation stop control”).
(3) Leave for 5 minutes.
(4) Print halftone of image data 25%: Check the level of back dirt.

  In this case, it can be seen that the level of the photosensitive drum cycle streak / image blur is improved after printing a halftone close to a solid density.

  In the conventional example, the finely powdered toner having a small particle diameter, the external additive and the like which are pressed onto the photosensitive drum 1 are gradually removed from the photosensitive drum 1 by the action of the cleaning blade 6 and the like as the photosensitive drum 1 rotates. Explained. At that time, if a large amount of toner is present in the vicinity of the cleaning blade 6, the toner acts to polish the photosensitive drum 1, so that the pressure-bonded product can be removed with less rotation of the photosensitive drum 1. Become. That is, when the image data in Table 2 is 90% or more, the level of the photosensitive drum periodic streak / image blur is improved by removing the pressure-bonded material to some extent during the pre-rotation of the above (4).

  Table 3 shows the results when the reverse rotation time in the “reverse rotation stop control” is 240 msec. In this case, the moving distance in the reverse rotation is about 2 mm. This is referred to as “shortened reverse rotation stop control”. Hereinafter, in order to prevent confusion, the “reverse rotation stop control” described in the first embodiment is referred to as “complete reverse rotation stop control”.

FIG. 7 shows a state in the vicinity of the edge portion 61E of the cleaning blade 6 after the “shortening type reverse rotation stop control” is performed in a form in contrast with FIG. Although the distortion of the edge portion 61E has not been completely eliminated, the amount of fine powder toner and external additives that have entered under the edge portion 61E has decreased.
(1) 10 continuous halftone images are continuously printed on the entire surface of A4 size paper.
(2) Implementation of “shortened reverse rotation stop control” (photosensitive drum reverse rotation 240 msec / equivalent to about 2 mm).
(3) Leave for 5 minutes.
(4) Print halftone of image data 25%: Check the level of back dirt.

  Compared with the example of Table 2, the level of the photosensitive drum cycle streak / image blur is improved by the amount of the fine powder toner and the external additive that have entered under the cleaning blade edge 61E. I understand. In particular, when the image data is 90% or more, it does not occur at all.

  In view of the above results, the following control is performed in the present embodiment.

  That is, when the photosensitive drum 1 is stopped, either “complete type reverse rotation stop control” or “shortened type reverse rotation stop control” is executed. Then, which one to select is determined according to the toner consumption amount in the print job. As a method for acquiring the toner consumption amount, for example, a toner remaining amount detection result in the developing device can be used. As a method for detecting the remaining amount of toner, for example, a detection method of electrostatic capacity of toner, a light transmission method, and the like have been put into practical use. Further, as another method for acquiring the toner consumption amount, it is also possible to use the accumulated information of the video count of the print image.

  Due to the mechanical characteristics of the toner remaining amount detection method, when a sufficient amount of toner remains in the developing device, the detection accuracy tends to be low or cannot be detected.

  Therefore, in this embodiment, a method of approximating the toner consumption amount using the integrated information of the video count of the print image is adopted.

  In other words, when the average printing rate of the image printed from the start to the stop of the photosensitive drum 1 is 80% or more, “shortened reverse rotation stop control” is performed. The type reverse rotation stop control ”is adopted. The average printing rate is calculated on the basis of video count integration information and transfer material size information.

  FIG. 8 is a flowchart showing more specific control according to this embodiment.

  In this embodiment, the photosensitive drum 1 is started to rotate forward, the printing operation is performed, and the transfer material is conveyed (step S1).

Each time one sheet is conveyed, the size (area) information Psize of the conveyed transfer material is acquired, and the accumulated total area TotalPsize of the conveyed transfer material is updated through a series of operations (step S2).
TotalPsize (latest) = TotalPsize + Psize

Every time one sheet is conveyed, (area) information Vsize of the video count of the print image printed on the transfer material P is acquired, and the accumulated total area TotalVsize of the print image is updated by a series of operations (step S3).
TotalVsize (latest) = TotalVsize + Vsize

  Here, the “series of operations” is an operation from when the photosensitive drum 1 starts a forward rotation operation until it stops, and the number of prints in the “series of operations” is the job size sent from the host. Depends on.

  It is confirmed whether or not the transferred transfer material is the last transfer material P in a series of operations (step S5). If it is not the last transfer material (last paper), the process returns to step S1 to transfer the transfer material. That is, the printing operation is continued.

If the determination in step S5 is YES, that is, if the last transfer material P has been transported, the average print rate of images printed from the start to the stop of the photosensitive drum 1 from the start to the stop is obtained by the following equation ( Step S6).
Average printing rate = TotalVsize / TotalPsize

  It is determined whether or not the average printing rate is 80% or more (step S6). If YES, "shortened reverse rotation stop control" is performed (step S7). If NO, that is, if the average printing rate is less than 80%, “complete reverse rotation stop control” is executed (step S8).

  To summarize the control of the present embodiment, the amount of toner collected per unit time is larger than the amount of toner per unit time that can be conveyed from the vicinity of the cleaning blade 6 to the waste toner chamber (tank) 62. . In this case, “shortened reverse rotation stop control” is executed to prevent the toner from slipping out.

  According to this embodiment, when the toner recovery amount is larger, control is performed so that the reverse rotation time immediately after the photosensitive drum stops is further shortened. As a result, fine toner particles, external additives, and the like having a small particle diameter do not cause adverse effects such as streaks, image blurring, and increased first printout due to pressure bonding to the photosensitive drum. Furthermore, it has become possible to prevent toner from slipping out when the photosensitive drum starts rotating.

Example 3
In the present embodiment, a description will be given of means that is performed based on the amount of residual toner collected by the cleaning blade 61. The structure of the image forming apparatus is all the same as in the first and second embodiments.

  In the method of Example 2, although the toner consumption amount in printing can be estimated, the toner actually collected by the cleaning blade 61, that is, the transfer residual toner was not known.

  When the toner image is transferred from the photosensitive drum 1 to the transfer material P, the transfer efficiency varies greatly depending on the type of the transfer material P. Generally, a smoother transfer material tends to improve transfer efficiency.

  Table 4 shows comparison data of transfer efficiency for each transfer material. In a 23 ° C./50% RH environment, glossy paper, plain paper, and rough paper were used, and a solid black image (image data 100%) was printed and compared. Glossy paper is “HP Color Laser Glossy Photo and Imaging Paper 32 #”, plain paper is “Canon Sales Color Laser Copier Paper 80 g”, and rough paper is “Fox River Bond 24 #”.

  In this embodiment, a difference in transfer efficiency depending on the transfer material is added to the control method of the second embodiment.

  Hereinafter, a method of detecting the type of transfer material P (hereinafter referred to as “media detection”) in the present embodiment will be described with reference to FIGS. 9 and 10.

  FIG. 9 is a schematic cross-sectional view showing a schematic configuration of an apparatus for detecting the surface smoothness of the transfer material P and the amount of reflected light or transmitted light, that is, the media detection sensor 200.

  The media detection sensor 200 is disposed between the registration roller 19 and the suction roller 22 in the transfer path of the transfer material P, although not shown in the image forming apparatus of FIG.

  The transfer material P fed from the paper feed cassette 17 is temporarily stopped immediately before entering the suction roller 22. Then, the type of the transfer material P is determined by the following method.

  As shown in FIG. 9, the media detection sensor 200 includes a reflection LED 201 that is a light irradiation unit, a CMOS area sensor 202 that is a reading unit, and a lens 203 that is an imaging lens.

  The light having the reflection LED 201 as a light source is applied to the surface of the transfer material P. The reflected light from the transfer material P is condensed through the lens 203 and imaged on the CMOS area sensor 202. Thereby, the surface image of the transfer material P is read.

  In the present embodiment, the LED 201 is arranged so that the LED light irradiates the surface of the transfer material P obliquely with a predetermined angle as shown in FIG.

  FIG. 10 is a diagram showing the relationship between the surface of the transfer material P read by the CMOS area sensor 202 of the media detection sensor 200 and an example in which the output from the CMOS area sensor 202 is digitally processed to 8 × 8 pixels.

  The digital processing is performed by converting the analog output from the CMOS area sensor 202 into 8-bit pixel data by A / D conversion (not shown) as conversion means.

  10A is a so-called enlarged image of the surface of the transfer material A of rough paper, in which the surface property of the transfer material P is relatively rough and the unevenness due to the fibers of the transfer material P is easy to distinguish. FIG. 10B is an enlarged image of the surface of a so-called plain paper transfer material B that is normally used in a general office. FIG. 10C is an enlarged image of the surface of the transfer material C of glossy paper in which the paper fibers are sufficiently compressed.

  The images shown in FIGS. 10A, 10B, and 10C read into the CMOS sensor 202 are digitally processed into the images shown in FIGS. 10D, 10E, and 10F.

  Thus, the image on the surface varies depending on the type of the transfer material P. This is a phenomenon that occurs mainly because the fiber state on the paper surface is different.

  At this time, the reflected light amount of the transfer material P is detected from the total or average value of the light input to each pixel. At this time, only the result of one light receiving pixel may be used.

  As described above, the image obtained by reading the surface of the transfer material P by the CMOS area sensor 202 and digitally processed can be discriminated based on the surface state of the paper fiber of the transfer material P and the amount of reflected light.

  In the image comparison calculation, the pixel Dmax having the maximum density and the pixel Dmin having the minimum density are derived from the result of reading the images of a plurality of locations on the surface of the transfer material P. This is executed for each read video and averaged.

  That is, when the paper fiber on the surface is rough like the transfer material A, many shadows of the fiber are generated. As a result, the difference between the bright part and the dark part is large, and Dmax−Dmin becomes large.

  On the other hand, on the surface such as the transfer material C, the shadow of the fiber is small and Dmax−Dmin is small.

  By this comparison, the roughness of the surface of the transfer material P is determined. In this embodiment, glossy paper, plain paper, and rough paper can be discriminated based on the detection result “Dmax−Dmin”.

  Next, with reference to FIG. 11, a selection method of “complete reverse rotation stop control” and “shortened reverse rotation stop control” when the photosensitive drum 1 is stopped in this embodiment will be described.

  First, for each page to be printed, the transfer residual toner amount (area conversion) is calculated. When the transfer efficiency is α, the transfer residual toner amount is obtained by multiplying the area information of the video count by (1−α). As the transfer efficiency α, an appropriate value is used according to the media detection result (see Table 4).

  Finally, the average toner recovery rate (calculated based on the transfer residual toner amount (area conversion) for each page and the size information of the transfer material) from the start to the stop of the photosensitive drum 1 is 8% or more. In this case, “shortened reverse rotation stop control” is performed. Further, when the average toner recovery rate is less than 8%, “complete reverse rotation stop control” is adopted.

  FIG. 11 is a flowchart showing more specific control of this embodiment.

  In this embodiment, the photosensitive drum 1 is started to rotate forward, the printing operation is performed, and the transfer material is conveyed (step S1).

Each time one sheet is conveyed, the size (area) information Psize of the conveyed transfer material is acquired, and the accumulated total area TotalPsize of the conveyed transfer material is updated through a series of operations (step S2).
TotalPsize (latest) = TotalPsize + Psize

  Each time one sheet is conveyed, the amount of reflected light from the transfer material P is detected using the CMOS area sensor 202, and it is determined from the result whether the conveyed transfer material P is glossy paper (step S3). If NO, it is determined whether or not the transfer material P is rough paper (step S4). In the case of NO, it is determined that the conveyed transfer material P is neither glossy paper nor rough paper, and is plain paper with a transfer efficiency α = 0.90 (step S5).

Next, (area) information Vsize of the video count of the print image printed on the transfer material P is acquired, and the cumulative value TotalCsize of the toner collection amount (area conversion) in a series of operations is updated (step S6).
TotalCsize (latest) = TotalCsize + Vsize * (1-α)

  If YES in step S3, that is, if the transferred transfer material P is glossy paper, the transfer efficiency α = 0.92, and in step S6, the cumulative value of the toner recovery amount (area conversion). Update TotalCsize. If YES in step S4, that is, if the transferred transfer material P is rough paper, similarly, the transfer efficiency α = 0.86 and the toner collection amount (area) in step S6. Update cumulative value of conversion.

  It is confirmed whether or not the transferred transfer material is the last transfer material P in a series of operations (step S9). If it is not the last transfer material (last paper), the process returns to step S1 to transfer the transfer material. That is, the printing operation is continued.

If the determination in step S9 is YES, that is, if the last transfer material P has been transported, the average toner recovery rate from the start to the stop of the photosensitive drum 1 is determined by the following equation (step 10).
Average toner recovery rate = TotalCsize / TotalPsize

  It is determined whether or not the average toner recovery rate is 8% or more (step S11). If YES, "shortened reverse rotation stop control" is performed (step S12). If NO, that is, if the average toner recovery rate is less than 8%, “complete reverse rotation stop control” is executed (step S13).

  The threshold 8% for the average toner recovery rate is a value obtained by multiplying “80% for the average printing rate” in Example 2 by 0.1 (= 1−0.9).

  Here, 0.9 is the transfer efficiency of plain paper (Canon sales: color laser copier paper 80 g) (see Table 4).

  In this embodiment, the control is executed based on the transfer material type information obtained by the media detection sensor 200. However, the transfer material type information is not limited to this means as long as the transfer material type information can be obtained. For example, the control may be performed based on the transfer material designation by the user on the printer driver.

  According to this embodiment, when the toner recovery amount is larger, control is performed so that the reverse rotation time immediately after the photosensitive drum stops is further shortened. As a result, fine toner particles, external additives, and the like having a small particle diameter do not cause adverse effects such as streaking, image blurring, and increased first printout due to pressure bonding to the photosensitive drum. Furthermore, it has become possible to prevent toner from slipping out when the photosensitive drum starts rotating.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. It is a schematic block diagram of one Example of a process cartridge. It is a schematic block diagram of the contact part of a photosensitive drum and a cleaning blade. It is a schematic block diagram for demonstrating the state of the cleaning blade front-end | tip part at the time of photosensitive drum drive stop. It is a schematic block diagram for demonstrating the state of the cleaning blade front-end | tip part at the time of photosensitive drum drive start. It is a flowchart for demonstrating control in the 1st Example according to this invention. It is the schematic for demonstrating the mode of the cleaning blade front-end | tip part after "shortening type reverse rotation stop control" in 2nd Example according to this invention. It is a flowchart for demonstrating the control in the 2nd Example according to this invention. It is a schematic block diagram of the media detection sensor in the 3rd Example according to this invention. It is a figure which shows the transcription | transfer material detection result of LED for reflection of the media detection sensor in the 3rd Example according to this invention. It is a flowchart for demonstrating control in the 3rd Example according to this invention. FIG. 10 is a schematic diagram for explaining a state of a cleaning blade tip portion in a conventional image forming apparatus.

Explanation of symbols

1 (1a, 1b, 1c, 1d) Photosensitive drum (image carrier)
2 (2a, 2b, 2c, 2d) Primary charging device (charging means)
3 (3a, 3b, 3c, 3d) Exposure apparatus (exposure means)
4 (4a, 4b, 4c, 4d) Developing device (developing means)
6 (6a, 6b, 6c, 6d) Cleaning device (cleaning means)
7 (7a, 7b, 7c, 7d) Process cartridge 11 Transfer belt (transfer material carrying / conveying means)
20 Fixing device 40 (40a, 40b, 40c, 40d) Developing roller (developer carrier)
61 (61a, 61b, 61c, 61d) Cleaning device (cleaning means)
61E Blade edge part 200 Media detection sensor P Transfer material

Claims (9)

A rotatable image carrier on which an electrostatic latent image is formed;
Developing means comprising a developer carrier for carrying and transporting the developer to develop the electrostatic latent image formed on the image carrier to form a developer image;
Transfer material carrying and conveying means for carrying and carrying the transfer material for transferring the developer image on the image carrier to a transfer material;
Cleaning means for removing the developer on the image carrier;
Have
In the image forming apparatus having a transfer material carrying / conveying means cleaning mode for removing the developer attached to the transfer material carrying / conveying means,
Means for predicting the amount of developer removed from the image carrier by the cleaning means during the rotation of the image carrier;
In accordance with the estimated developer recovery amount, the transfer material carrying / conveying unit cleaning mode is performed immediately before the next image forming operation is performed.
An image forming apparatus.   In the transfer material carrying / conveying means cleaning mode, the developer on the transfer material carrying / conveying means is electrostatically transferred to the image carrying body and removed from the image carrying body by the cleaning means. The image forming apparatus according to claim 1. A forward and reverse rotatable image carrier on which an electrostatic latent image is formed;
Developing means comprising a developer carrier for carrying and transporting the developer to develop the electrostatic latent image formed on the image carrier to form a developer image;
Transfer material carrying and conveying means for carrying and carrying the transfer material for transferring the developer image on the image carrier to a transfer material;
A cleaning blade for removing the developer by contacting the image carrier in the direction of a counter with respect to the positive rotation direction of the image carrier;
Have
In the image forming apparatus for performing image carrier stop control for stopping the image carrier by rotating in the reverse direction after stopping the forward rotation of the image carrier,
Means for predicting the amount of developer removed from the image carrier by the cleaning blade during the forward rotation of the image carrier;
In accordance with the estimated developer recovery amount, the image carrier stop control is performed so as to shorten the time for rotating the image carrier in the reverse direction.
An image forming apparatus.   The image forming apparatus has a developer discharge operation for discharging the developer from the developer carrier to the image carrier at the time of non-image formation, and the developer recovery amount is determined based on the implementation status of the developer discharge operation. The image forming apparatus according to claim 1, wherein the image forming apparatus predicts the image quality.   The image forming apparatus according to claim 1, wherein the developer recovery amount is predicted based on a jam occurrence state.   6. The image forming apparatus according to claim 1, wherein the developer recovery amount is predicted based on toner consumption amount information in image formation.   The image forming apparatus according to claim 6, wherein the toner consumption amount information is information calculated based on integration of video counts during image formation.   The image forming apparatus has a developer remaining amount detection function, and the toner consumption amount information is a difference in the remaining developer amount detected by the remaining developer detection during rotation of the image carrier. The image forming apparatus according to claim 6, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein the developer recovery amount is predicted based on transfer material information used at the time of image formation.