JP4929025B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, which is a transfer means for transferring an image formed on an image carrier and has a transfer means for contacting and separating from the image carrier. The present invention relates to the image forming method used.

  In an image forming apparatus provided with an image carrier such as a photoconductor in an image forming apparatus such as a copying machine, a facsimile machine, or a printer, a charging process is performed on the image carrier according to the movement of the image carrier by rotation or the like. Image formation is performed by performing an exposure process, a development process, a transfer process, and the like.

  In the charging step, the surface of the image carrier is charged. In the exposure process, an electrostatic latent image is formed on the image carrier whose surface is charged in the charging process. In the developing step, the charged toner particles are attached to the surface of the image carrier corresponding to the electrostatic latent image to form a visible image. In the transfer step, the visible image is transferred from the image carrier to a recording medium such as paper or an intermediate transfer member.

  These steps are started after the operator gives an instruction to start image formation by pressing the copy button or the like, and the movement of the image carrier starts. The start timing of each step is to improve the image formation. For example, in [Patent Document 1] and [Patent Document 2], a technique for optimizing the start timing is proposed.

  In each of these processes, for example, the charging means for performing the charging process and the developing process respectively, and the developing means starts applying the voltage required for performing the charging process and the developing process after the movement of the image carrier starts. It is supposed to be.

  Ideally, the voltage application start position by the charging unit and the voltage application start position by the development unit on the image carrier are the same, but the current situation is that these deviations cannot be avoided. This is because the charging process and the developing process are performed on the moving image carrier, and it is difficult to ensure extremely high accuracy for the voltage application start instruction control for the charging unit and the developing unit.

  When such a deviation occurs, the voltage application start position by the charging unit and the voltage application start position by the developing unit move back and forth at the rising time when a high voltage is applied to both the charging unit and the developing unit. Either carrier or toner adheres to the image carrier.

However, when the carrier adheres to the image carrier, the attached carrier deteriorates the image carrier. Therefore, conventionally, control is performed to intentionally shift the voltage application start position by the developing unit with respect to the voltage application start position by the charging unit so that the toner adheres on the image carrier.
Such control is necessary for suppressing deterioration of the image carrier.

JP 2000-75670 A JP 2005-258243 A

  However, when such control is performed, toner adheres to the image carrier and a toner band is formed in the width direction of the image carrier. This toner band may adhere to the transfer means that performs the transfer process, and the toner attached to the transfer means may adhere to a recording medium such as paper, resulting in contamination of the recording medium.

  The transfer means includes a roller type that applies a transfer bias, and a belt type that is formed for the purpose of conveying a recording medium or transferring an image to itself. In the former type, it is possible to prevent the adhesion of the toner band or reversely transfer the adhered toner band to the image carrier by controlling the bias, that is, applying a reverse bias. It is also possible. However, in the latter type, since the bias application is usually at a position shifted from the nip between the belt and the image carrier, it is difficult to prevent the recording medium from being soiled by controlling the bias. In particular, contamination of the recording medium in a low temperature / low humidity environment is a problem. However, even in the former case, it is difficult to completely prevent the recording medium from being stained.

  In general, the transfer means, particularly the latter type of transfer means, is provided with a cleaning means for removing foreign matter such as attached paper dust. However, such cleaning means originally removes foreign matter attached at a high concentration. This is not intended to be performed, and cannot be said to have sufficient performance for cleaning the belt-like toner. Further, since the belt provided in the latter type of transfer means is generally formed of rubber or the like, it is difficult to remove the toner adhering to the belt.

  Such a problem caused by the toner adhering to the image carrier adhering to the transfer means has been known in the past. However, since suppression of image carrier deterioration due to carrier adhesion has priority, for example, [Patent Document 1] There has been proposed a technique that includes a transfer unit that can come into contact with and separate from the image carrier, and that the transfer unit comes into contact with the image carrier after passing through the toner band attachment position of the image carrier.

  On the other hand, in an image forming apparatus provided with a transfer unit that can come into contact with and separate from an image carrier, there is a known problem that a formed image is disturbed by an impact when the transfer unit comes into contact with the image carrier.

  Therefore, for example, in [Patent Document 1], in order to prevent the electrostatic latent image formed in the exposure process from being disturbed by such an impact and thereby causing a disorder in the formed image, the transfer means is an image carrier. There has been proposed a technique for adjusting the timing of contact with the wafer and the timing of forming an electrostatic latent image in the exposure process.

  In addition, [Patent Document 2] proposes a technique in which the timing for applying the transfer bias is adjusted so that the toner on the image carrier is not transferred to the transfer means.

  However, as a result of intensive studies by the inventor, the problem that the image formed by the impact when the transfer means that can come into contact with and separate from the image carrier is in contact with the image carrier is not only in the exposure process but also charged. It was found that this could occur due to the process.

  There are two types of charging means: a type that is separated from the image carrier, such as a charging charger, and a type that is in contact with the image carrier, such as a charging roller. In the latter type, charging is not caused by such an impact. It has been found that, when uniformity or the like occurs and image formation is performed in this region, there is a problem that the formed image is disturbed.

  In addition, the timing for starting each of the above-described steps needs to be set so as to make the time required for image formation as short as possible, and when such time is determined in advance, it is necessary to satisfy this timing. It is also necessary to set.

  In the configuration in which the transfer unit is in contact with and separated from the image carrier, it is necessary to adjust the timing at which the transfer unit contacts the image carrier and the transfer start timing.

  The present invention comprises a transfer means for transferring an image formed on an image carrier in contact with and separating from the image carrier, wherein a toner band attached on the image carrier is attached to the transfer means. Prevent or suppress image disturbance caused by impact when the transfer unit contacts the image carrier, minimize the time required for image formation, timing when the transfer unit contacts the image carrier and start of transfer An object of the present invention is to provide an image forming apparatus such as a copying machine, a facsimile machine, a printer, or the like in consideration of at least one of the conditions such as adjusting the timing, and an image forming method using the image forming apparatus.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier that moves at a predetermined speed, a charging means that contacts the image carrier and charges the image carrier, and the charging means charges the image carrier. A writing unit that forms a latent image on the image carrier; a developing unit that develops the latent image formed by the writing unit; and a transfer unit that transfers the image developed by the developing unit. In an image forming apparatus for forming an image on a recording medium in which the means comes in contact with and separates from the image carrier, after the start of the movement of the image carrier, the charging means starts charging the image carrier. The time T1 until the transfer unit contacts the image carrier is T1> L1 / V (L1: the contact between the image carrier and the charging unit from the contact position of the image carrier and the transfer unit). Movement of the image carrier to the contact position Away, V: meet the linear velocity), the contact position between the image carrier and the transfer means, among the contact position, a moving direction upstream end portion of said image bearing member, After the start of the movement of the image carrier, a time T3 from when the transfer unit comes into contact with the image carrier until the writing unit starts forming a latent image on the image carrier is T3> L3 / V (L3: the moving distance of the image carrier from the contact position between the image carrier and the charging unit to the position where the writing unit writes a latent image on the image carrier, V: the same as above) ΔTD + L3 / V <ΔTB (ΔTB: time from the start of movement of the image carrier to the time when the writing means starts to form a latent image on the image carrier, ΔTD: after the start of movement of the image carrier, The time until the transfer unit contacts the image carrier) Both of the charging means include a charging roller that is in contact with the image carrier, and the transfer means includes a transfer conveyance member that conveys a recording medium, and the transfer conveyance member that contacts and separates from the image carrier. Contacting / separating means, and the contacting / separating means is positioned between the cam and the motor, and a motor as a drive source for driving the cam. A transfer clutch for switching whether or not to transmit to the cam, the ΔTD is a rise time after the transfer clutch is turned on, and the transfer conveying member is brought into contact with the image carrier after the transfer clutch is raised. And an operation time required for the operation .

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the transfer conveying member is an endless belt, and the transfer unit includes a transfer bias applying member disposed inside the belt. R <L3 (R: radius of the charging roller, L3: the same as above) .

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, a time T4 from the start of the movement of the image carrier until the writing unit starts forming a latent image on the image carrier. The predetermined time T5 is T4 <T5, T5 = Fst− (L4 + L5 + LP) / V (Fst: a recording medium on which an image is formed after the image carrier starts moving with respect to the recording medium having a predetermined length. L4: time until the image carrier is discharged from the image forming apparatus, L4: movement of the image carrier from a position where the writing unit writes a latent image on the image carrier to a contact position between the image carrier and the transfer unit L5: moving distance of the image carrier to the downstream end in the direction, L5: the recording medium is located outside the image forming apparatus from the downstream end in the moving direction of the image carrier at the contact position between the image carrier and the transfer means. The moving distance of the image to the position where it is ejected , LP: the length of the recording medium in the Fst, V: and satisfies a linear velocity).

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the transfer unit comes into contact with the image carrier after the start of the movement of the image carrier. The time T6 from when the writing unit starts forming a latent image on the image carrier to when the transfer unit starts applying a transfer bias for transferring the image is T6 <L6. / V (L6: moving distance of the image carrier from the position where the writing means writes a latent image on the image carrier to the contact position between the transfer means and the image carrier, V: process linear velocity) It is characterized by satisfying.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the time until the transfer unit comes into contact with the image carrier after the start of the movement of the image carrier is determined. It has a contact start time setting mode for setting arbitrarily.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, after the movement of the image carrier, the writing unit forms a latent image on the image carrier. It has a write start time setting mode for arbitrarily setting the time until the start.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the transfer unit is an intermediate transfer unit.

According to an eighth aspect of the present invention, there is provided an image forming method for forming an image using the image forming apparatus according to any one of the first to seventh aspects.

The present invention relates to an image carrier that moves at a predetermined speed, a charging unit that contacts the image carrier and charges the image carrier, and writing that forms a latent image on the image carrier charged by the charging unit. Means, developing means for developing the latent image formed by the writing means, and transfer means for transferring the image developed by the developing means, the transfer means being in contact with and separating from the image carrier. In an image forming apparatus for forming an image on a recording medium, after the start of the movement of the image carrier, the transfer unit contacts the image carrier after the charging unit starts to charge the image carrier. The time T1 until T1> L1 / V (L1: the moving distance of the image carrier from the contact position between the image carrier and the charging unit to the contact position between the image carrier and the transfer unit) , V: process linear velocity) to meet, before The contact position between the image carrier and the transfer means is an upstream end portion in the movement direction of the image carrier among the contact positions, and after the start of the movement of the image carrier, the transfer means The time T3 from the contact with the image carrier until the writing unit starts to form a latent image on the image carrier is T3> L3 / V (L3: the relationship between the image carrier and the charging unit). The moving distance of the image carrier from the contact position to the position where the writing means writes a latent image on the image carrier, V: same as above, is satisfied. At this time, ΔTD + L3 / V <ΔTB (ΔTB: the image carrier) The time until the writing means starts to form a latent image on the image carrier after the start of movement, ΔTD: After the movement of the image carrier starts, the transfer means comes into contact with the image carrier. Time) and the charging means is the image carrier. The transfer unit includes a transfer conveyance member that conveys the recording medium, and a contact / separation unit that brings the transfer conveyance member into and out of contact with the image carrier. The separating means includes a cam, a motor as a drive source for driving the cam, and a transfer clutch that is positioned between the cam and the motor and switches whether the driving force of the motor is transmitted to the cam. The ΔTD includes a rise time after the transfer clutch is turned on, and an operation time required to bring the transfer conveying member into contact with the image carrier after the transfer clutch is raised . Of the transfer nip formed by the contact between the image carrier and the transfer means, the end portion on the upstream side in the moving direction of the image carrier closest to the position where the toner band adheres to the image carrier is defined as the contact position. by image carrier Since the toner adhering can by the shortest time to prevent from adhering to the transfer means, the backside contamination of the recording medium due to the toner adhering to the transfer means from the image bearing member is moved to the back surface of the recording medium from the transfer means Can be prevented in the shortest time, and the disturbance of the latent image formed by the writing means and the charging disturbance when the image carrier is charged by the charging means, caused by the impact when the transfer means comes into contact with the image carrier. Therefore, it is possible to provide an image forming apparatus capable of preventing or suppressing image disturbance caused by the above and capable of performing good image formation .

  After the start of the movement of the image carrier, the time T4 until the writing means starts to form a latent image on the image carrier and the predetermined time T5 are T4 <T5, T5 = Fst− (L4 + L5 + LP) / V (Fst: For a recording medium having a predetermined length, after the start of the movement of the image carrier, the time until the recording medium on which the image is formed is discharged out of the image forming apparatus, L4: The moving distance of the image carrier from the position where the latent image is written to the image carrier to the downstream end of the moving direction of the image carrier at the contact position between the image carrier and the transfer means, L5: the image carrier The moving distance of the image from the downstream end in the moving direction of the image carrier at the contact position between the image forming unit and the transfer means to the position where the recording medium is discharged out of the image forming apparatus, LP: recording medium at the Fst Length, V: process line speed) As a result, the time required for image formation can be further reduced, and the required time for image formation can be satisfied, so that an image forming apparatus with excellent usability can be provided. .

  In addition to the above-described conditions, after the start of the movement of the image carrier, after the transfer unit comes into contact with the image carrier, the writing unit starts to form a latent image on the image carrier. T6 <L6 / V (L6: position at which the writing unit writes a latent image on the image carrier). T6 <L6 / V (L6: time from when the transfer unit starts applying a transfer bias for transferring the image by the transfer unit) If the transfer distance of the image carrier from the transfer means to the contact position of the image carrier is satisfied, V: process linear velocity), the timing at which the transfer means contacts the image carrier The relationship with the transfer start timing can be set so that the image on the image carrier can be reliably transferred, and an image forming apparatus capable of performing good image formation can be provided.

  In addition to the above-mentioned conditions, if it has a contact start time setting mode for arbitrarily setting the time until the transfer means contacts the image carrier after the start of movement of the image carrier, Furthermore, it is possible to set the time required in consideration of the state of image formation, etc., further reducing the time required for image formation, and preventing toner adhering on the image carrier from adhering to the transfer means. In consideration of preventing the occurrence of an abnormal image due to, for example, it is possible to set the time required according to the situation, and it is possible to provide an image forming apparatus with excellent usability.

  In addition to the above-described conditions, a writing start time setting mode for arbitrarily setting a time until the writing unit starts forming a latent image on the image carrier after the movement of the image carrier is started. In that case, it is possible to set the time required depending on the situation, such as the time required for image formation can be set and the time required for image formation can be further reduced. Therefore, it is possible to provide an image forming apparatus with excellent usability.

  In addition to the above-described conditions, if the transfer unit is an intermediate transfer unit, an image forming apparatus that can be configured as an apparatus capable of forming a color image can be provided.

Since the present invention is in an image forming method for forming an image using the image forming apparatus according to any one of claims 1 to 7 , an image forming method having the above-described effects can be provided.

  FIG. 1 shows an outline of an image forming apparatus to which the present invention is applied. The image forming apparatus 1 is a monochrome multifunction machine including a laser copying machine, a printer, and a facsimile machine, but is another type of copying machine such as a color machine, a facsimile machine, a printer, and these multifunction machines. May be. The image forming apparatus 1 performs image forming processing based on image data of a document read by the image forming apparatus 1 or an image signal corresponding to image information received from the outside. The image forming apparatus 1 can form an image using plain paper generally used for copying, OHP sheets, thick paper such as cards and postcards, and envelopes as sheet-like recording media. .

  The image forming apparatus 1 includes an image forming unit 4 disposed substantially at the center in the height direction of the housing 1A, and a paper discharge storage unit serving as a paper discharge unit disposed above the image forming unit 4. A document reading unit 3 serving as a reading unit for reading a document and positioned above the image forming unit 4 with the paper tray 2 and the paper discharge tray 2 interposed therebetween, and a paper feeding unit disposed below the image forming unit 4 The sheet feeding device 11, a control unit (not shown) that performs overall control of the image forming apparatus 1, and an operator (not shown) that can perform various operations such as an image formation start instruction by pressing a copy button or the like. And an operation panel.

  The image forming apparatus 1 is an in-body discharge type image forming apparatus that discharges paper within a housing 1 </ b> A, and a paper discharge tray 2 is a space between the image forming unit 4 and the document reading unit 3. The sheet P as a recording medium on which image formation has been performed is discharged and stored on the discharge tray 2.

  The image forming unit 4 includes a photosensitive drum 5 as an image carrier that is a drum-like latent image carrier. The photosensitive drum 5 is moved, that is, rotated at a predetermined speed, which will be described later, in a counterclockwise X direction in the drawing by a main motor (not shown) as a driving source.

  The image forming unit 4 is also arranged around the photosensitive drum 5 along the rotation direction X. The charging device 6 serves as a charging unit that performs charging processing on the surface of the photosensitive drum 5 and the image information. And a writing device 7 as writing means as an exposure device for irradiating a beam L for scanning the surface of the photosensitive drum 5 charged by the charging device 6, and a surface of the photosensitive drum 5 exposed by the beam L. A developing device 8 as developing means for developing and visualizing the electrostatic latent image as a latent image with toner, and a paper on which a toner image formed by developing the electrostatic latent image on the photosensitive drum 5 is a transfer target A transfer device 9 serving as a transfer conveyance unit as a transfer means for transferring to P, and an image carrier cleaning for removing and collecting toner remaining on the surface of the photosensitive drum 5 after the transfer by the transfer device 9 And a cleaning device 10 as a stage.

  The image forming unit 4 also includes a registration roller 14 disposed on the upstream side of the transfer device 9 from the upstream side in the transport direction Y in the transport direction Y of the paper P indicated by a two-dot chain line arrow, and the paper P A fixing device 12 serving as a fixing unit disposed downstream of the transfer device 9 and upstream of the paper discharge tray 2 in the transport direction Y and the passage of the trailing edge of the paper P after passing through the fixing device 12 are detected. A paper discharge sensor 25 for detecting the discharge of the paper P to the paper discharge tray 2 and a paper discharge roller as a paper discharge means for discharging the paper P onto the paper discharge tray 2 and discharging it out of the housing 1A. The paper discharge device 13 is provided in this order.

  The document reading unit 3 includes a contact glass 3E serving as a document placement table, and a light source 3A serving as a document illumination light source and an optical path changing reflecting mirror 3B for scanning the document G placed on the contact glass 3E. The reading traveling body 3F provided, the reading optical system 3C including a lens that transmits the reflected light from the original formed by the reading traveling body 3F, and the light transmitted through the reading optical system 3C are incident, and this is used as an image signal. And an optical element 3D such as a CCD for reading. The document image information read by the optical element 3D is output to the control unit, digitized, and subjected to image processing.

  Although not shown in the drawing, the writing device 7 forms an image of a semiconductor laser as a laser diode that performs irradiation in accordance with image information of the document input to the control unit, and an image of light emitted from the semiconductor laser. It has a reflecting mirror and an imaging lens forming an optical system, a polygon mirror as a deflecting means for scanning light from a semiconductor laser that has passed through the reflecting mirror and the imaging lens, and a driving means for the polygon mirror, and is scanned by the polygon mirror. The emitted light is used as a beam L and irradiated onto the photosensitive drum 5 to form an electrostatic latent image.

  The semiconductor laser is controlled to emit light based on the image signal from the control unit. In the control unit, not only the image information from the document reading unit 3 but also the print signal and the facsimile apparatus when used as a printer. The drive control of the semiconductor laser is performed by an image signal corresponding to the transmission signal when used as a semiconductor device. Thus, the image forming apparatus 1 has a character as a digital multi-function machine having functions as a printer and a facsimile machine as well as a copying machine.

  The paper feeding device 11 stacks the paper P and supplies the stacked paper P to the image forming unit 4. The paper feeding device 11 is loaded on the paper feeding tray 11 </ b> A having a well-known structure on which the paper P is stacked and the paper feeding tray 11 </ b> A. The sheet P is provided with a sheet feeding roller 11B as a feeding roller that feeds the uppermost sheet P of the sheets P toward the image forming unit 4, specifically, the registration roller 14. Another sheet feeding device can be added to the sheet feeding device 11 as necessary.

  The registration roller 14 is abutted against the leading edge of the paper P fed from the paper feeding device 11 to temporarily stop the conveyance, and the positional relationship between the leading edge of the toner image on the surface of the photosensitive drum 5 and the leading edge of the paper P. The rotation is started at a predetermined timing at which the two coincide.

The fixing device 12 includes a fixing roller 12A capable of interlocking rotation by contacting and facing each other so that the paper P can be nipped and conveyed, and a pressurizing member as a pressing member disposed facing the fixing roller 12A. The paper P having a roller 12B and having the toner image transferred to the surface by the transfer device 9 is passed between the fixing roller 12A and the pressure roller 12B, and heating and pressurization are performed at this time. The toner image is fused and fixed on the paper P.
The paper discharge device 13 discharges the paper P on which the toner image is fixed by the fixing device 12 onto the paper discharge tray 2.

  As shown in FIG. 2, the photosensitive drum 5, the charging device 6, the developing device 8, and the cleaning device 10 constitute a part of the process cartridge 15. In addition to the photosensitive drum 5, the charging device 6, the developing device 8, and the cleaning device 10, the process cartridge 15 includes a housing 15A that integrally supports them. The casing 15A is detachably provided on the main body of the image forming apparatus 1.

  Therefore, the process cartridge 15 is configured such that the photosensitive drum 5, the charging device 6, the developing device 8, and the cleaning device 10 are integrated with each other and can be attached to and detached from the main body of the image forming apparatus 1. As a result, workability such as maintenance and replacement of the photosensitive drum 5, the charging device 6, the developing device 8, and the cleaning device 10 is improved. Further, workability such as maintenance and replacement of the transfer device 9 exposed after the process cartridge 15 is detached from the main body of the image forming apparatus 1 is improved.

  The charging device 6 is disposed so as to face and contact the photosensitive drum 5, and removes a charging roller 16 as a charging member for charging the photosensitive drum 5, and toner, paper dust, and the like attached to the charging roller 16. And a cleaning device 21 as a charging roller cleaner for cleaning. The diameter of the charging roller 16 is φ14 mm.

  The cleaning device 21 rotates in contact with the charging roller 16 as a cleaning object, that is, a cleaning roller 22 that rotates as a driven member, and presses and biases the cleaning roller 22 toward the charging roller 16. And a spring 23 which is a compression spring as an urging member.

  The developing device 8 is a developing device that uses a two-component developer including toner and carrier, and includes a developing roller 24 that is in contact with the photosensitive drum 5. The developing roller 24 rotates in the same direction as the photosensitive drum 5 at a position facing the photosensitive drum 5. The developing roller 24 carries a two-component developer and supplies toner contained in the two-component developer to the photosensitive drum 5. Then, development corresponding to the electrostatic latent image is performed. The diameter of the developing roller 24 is φ19 mm. In order to perform high-quality development, such a developer contains spherical toner.

The cleaning device 11 has a known configuration having a cleaning blade and the like.
The beam L includes a position PA where the charging device 6, specifically the charging roller 16 contacts the photosensitive drum 5, and a position PC where the developing device 8, specifically the developing roller 24 contacts the photosensitive drum 5. The photosensitive drum 5 is irradiated at the position PB.

  The transfer device 9 is an endless drive roller 18 that is driven to rotate by a motor (not shown) as a drive source, and an endless position in which the position facing the photosensitive drum 5 is rotated around the drive roller 18 in the direction Y by the drive roller 18. And a driven roller 20 around which the belt 19 is wound together with the driving roller 18.

  The transfer device 9 also has a contact / separation device 17 as a contact / separation device for moving the belt 19 to and away from the photosensitive drum 5 by displacing the driven roller 20, and a belt 19 provided inside the belt 19 by the displacement device 17. And a transfer bias roller 9a as a transfer bias applying member displaced together with the driven roller 20, a belt cleaning device as a belt cleaning means (not shown) for cleaning the belt 19, and a sheet P electrostatically adsorbed to the belt 19. A belt charging unit (not shown) for charging the belt 19 is provided for stable conveyance.

  At least the surface of the belt 19 is formed of a rubber-based material such as CR, EPDM, and urethane, and a filler for satisfying various functions as the belt 19 such as imparting resistance is uniformly contained in the material. Added in a dispersed manner. An example of the filler is an ionic material.

  The belt cleaning device has a blade and a bias roller in contact with the belt 19, and removes foreign matters such as toner and paper dust attached to the belt 19 from the belt 19. The belt cleaning device may be configured to have only a blade.

  The contact / separation device 17 is located between the lever, which is not shown, a lever integrated with the driven roller 20, a cam engaged with the lever, a motor as a drive source for driving the cam, and the cam and the motor. It has a transfer clutch for switching whether or not to transmit the driving force of the motor to the cam, a filler provided coaxially with the cam, and a home position sensor fixedly fixed.

  In the contact / separation device 17, when the transfer clutch is turned on, the cam rotates halfway, and the belt 19 comes into contact with the photosensitive drum 5 due to the displacement of the lever. At this time, the filler is detected by the home position sensor, and it is detected that the belt 19 is in contact with the photosensitive drum 5. When the transfer clutch is turned on again, the cam rotates halfway, and the belt 19 is separated from the photosensitive drum 5 due to the displacement of the lever. At this time, the filler is not detected by the home position sensor, and it is detected that the belt 19 is separated from the photosensitive drum 5.

  As shown in FIG. 3, the operation time of the contact / separation device 17 by the on operation of the transfer clutch, that is, the time required for the operation for contacting and separating the belt 19 to and from the photosensitive drum 5 is 100 msec. The transfer clutch is turned on. In FIG. 3, the waveform from the OFF state to the ON state of the transfer clutch is vertical and does not include the rise time. There is a rise time before. This rise time is 50 msec.

  Other configurations for bringing the belt 19 into and out of contact with the photosensitive drum 5 include those using a motor without using a clutch, those using a solenoid, and the like. Is preferable from the viewpoint of responsiveness, that is, shortening of operation time.

  As shown in FIG. 2, the belt 19 contacts the photosensitive drum 5 at the position PD in a state where the belt 19 contacts the photosensitive drum 5. Since the belt 19 and the photosensitive drum 5 come into contact with each other to form a nip having a predetermined width in the X direction and the Y direction, the position PD has such a predetermined width.

  The transfer bias roller 9 a is in contact with the belt 19 at a position PE inside the belt 19. The position PE occupies a position downstream of the position PD in the X direction and the Y direction. The transfer bias roller 9 a applies a transfer voltage for forming a transfer bias for transferring the toner image formed on the photosensitive drum 5 to the paper P conveyed by the belt 19.

  A position PF located between the rollers of the paper discharge device 13 indicates a paper discharge position at which the paper P is discharged to the outside of the housing 1A when the rear end of the paper P passes through this position.

  FIG. 4 shows a state in which each of the positions PA, PB, PC, PD, PE, and PF described above is developed linearly along the direction X and the direction Y, and a state where the rear end of the paper P is at the position PF. . This figure is schematically shown, and the distance between each position PA, PB, PC, PD, PE, PF, the length LP of the paper P, and the ratio thereof do not necessarily match the actual ones. .

  The positions PA, PB, PC, PD, PE, and PF are also shown in FIG. 2, but the position PA is the charging position of the photosensitive drum 5 by the charging device 6, and the position PB is the photosensitive drum 5 by the writing device 7. The latent image writing position, in other words, the exposure position, position PC is the development position of the photosensitive drum 5 by the developing device 8, position PD is the contact position between the photosensitive drum 5 and the transfer device 9, and position PE is by the transfer bias roller 9a. The transfer voltage application position, position PF, indicates the paper discharge position of the paper P by the paper discharge device 13.

  As described above, the belt 19 and the photosensitive drum 5 are in contact with each other to form a nip having a predetermined width. Therefore, as shown in the figure, the upstream end portion and the downstream end portion of the position PD in the X direction and the Y direction are set as positions PD1 and PD2, respectively. Such a nip width is 4.51 mm in this embodiment.

  The distances indicated by reference numerals L1, L2, L3, L4, L5, L6, and L7 in FIG.

  The distance L1 is a distance from the position PA to the position PD1. That is, the distance L1 is a moving distance of the photosensitive drum 5 from a contact position between the photosensitive drum 5 and the charging device 6 to a contact position between the photosensitive drum 5 and the transfer device 9. The contact position between the photosensitive drum 5 and the transfer device 9 is particularly an upstream end portion of the position PD in the direction X and the direction Y. In this embodiment, the distance L1 is 92.56 mm.

  The distance L2 is a distance from the position PC to the position PD1. That is, the distance L2 is a moving distance of the photosensitive drum 5 from a contact position between the photosensitive drum 5 and the developing device 8 to a contact position between the photosensitive drum 5 and the transfer device 9. The contact position between the photosensitive drum 5 and the transfer device 9 is particularly an upstream end portion of the position PD in the direction X and the direction Y. In this embodiment, the distance L2 is 57.43 mm.

  The distance L3 is a distance from the position PA to the position PB. That is, the distance L3 is the moving distance of the photosensitive drum 5 from the contact position between the photosensitive drum 5 and the charging device 6 to the writing position of the latent image on the photosensitive drum 5 by the writing device 7. In this embodiment, the distance L3 is 15.06 mm.

  The distance L4 is a distance from the position PB to the position PD2. That is, the distance L4 is the moving distance of the photosensitive drum 5 from the position where the writing device 7 writes the latent image on the photosensitive drum 5 to the contact position between the photosensitive drum 5 and the transfer device 9. The contact position between the photosensitive drum 5 and the transfer device 9 is particularly the downstream end portion of the position PD in the direction X and the direction Y. In this embodiment, the distance L4 is 82.01 mm.

  The distance L5 is a distance from the position PD2 to the position PF. That is, the distance L5 is a moving distance of the sheet P from the contact position between the photosensitive drum 5 and the transfer device 9 to the discharge position of the sheet P to the outside of the image forming apparatus 1. The contact position between the photosensitive drum 5 and the transfer device 9 is particularly the downstream end portion of the position PD in the direction X and the direction Y. In this embodiment, the distance L5 is 213.63 mm.

  The distance L6 is a distance from the position PB to the position PD1. That is, the distance L6 is the moving distance of the photosensitive drum 5 from the position where the writing device 7 writes the latent image on the photosensitive drum 5 to the contact position between the photosensitive drum 5 and the transfer device 9. The contact position between the photosensitive drum 5 and the transfer device 9 is particularly an upstream end portion of the position PD in the direction X and the direction Y. In this embodiment, the distance L6 is 77.5 mm.

  The distance L7 is a distance from the position PA to the position PC. That is, the distance L7 is a moving distance of the photosensitive drum 5 from the contact position between the photosensitive drum 5 and the charging device 6 to the contact position between the photosensitive drum 5 and the developing device 8. In this embodiment, the distance L3 is 35.13 mm.

  In the figure, the symbol LP indicates the length of the paper P along the direction Y. In this embodiment, the paper P is A4 size and is conveyed in the horizontal direction, and the distance L3 is 210 mm.

  In the same figure, the code | symbol V has shown process linear velocity. The process linear velocity V is a moving speed of an image or the like for image formation, and is a moving speed of the photosensitive drum 5 around the photosensitive drum 5, in other words, a rotational speed. P transport speed. In this embodiment, it is assumed that the moving speed of the photosensitive drum 5 and the conveying speed of the paper P are always the same and the same. In this embodiment, the process linear velocity V is set to two speeds of 230 mm / sec for 45 sheets / min (A4 horizontal) and 180 mm / sec for 35 sheets / min (A4 horizontal).

  In FIG. 4 and FIG. 5, the timing indicated by the symbols TA, TB, TC, TD, TE, TM and the time indicated by the symbol Fst will be described.

  Timing TA is a start timing of charging of the photosensitive drum 5 by the charging device 6.

  The timing TB is a timing for forming a latent image on the photosensitive drum 5 by the writing device 7, in other words, an exposure start timing.

  Timing TC is a start timing of development of the latent image on the photosensitive drum 5 by the developing device 8.

  Timing TD is a timing of contact of the transfer device 9 with the photosensitive drum 5. The contact timing is 150 msec after the rise time of the transfer clutch and the rise time of 50 msec and the operation time of 100 msec.

  Timing TE is the start timing of application of the transfer voltage by the transfer bias roller 9a.

  The timing TM is a start timing of driving of the main motor due to an instruction to start image formation by the operator, in other words, a start timing of movement, that is, rotation by driving of the photosensitive drum 5.

  During the time Fst, the rear end of the first sheet P passes through the position PF after the operator gives an instruction to start image formation and the driving of the photosensitive drum 5 is started, and the sheet P is discharged out of the image forming apparatus 1. It is time until.

  In FIG. 5, the time indicated by the symbols ΔTA, ΔTB, ΔTC, ΔTD, ΔTE, and ΔTM will be described.

  Time ΔTA is a time interval from timing TM to timing TA. That is, it is the time from the drive start timing of the main motor to the charge start timing of the photosensitive drum 5 by the charging device 6.

  Time ΔTB is a time interval from timing TM to timing TB. That is, the time from the drive start timing of the main motor to the exposure start timing of the writing device 7.

  Time ΔTC is a time interval from timing TM to timing TC. That is, the time from the drive start timing of the main motor to the development start timing of the latent image on the photosensitive drum 5 by the developing device 8.

  Time ΔTD is a time interval from timing TM to timing TD. That is, it is the time from the drive start timing of the main motor to the contact timing of the transfer device 9 to the photosensitive drum 5.

  Time ΔTE is a time interval from timing TM to timing TE. That is, the time from the drive start timing of the main motor to the transfer voltage application start timing by the transfer bias roller 9a.

  In FIG. 5, the time indicated by the symbols T1, T2, T3, T4, T6, and T7 will be described.

  Time T1 is a time interval from timing TA to timing TD. That is, the time from the charging start timing of the photosensitive drum 5 by the charging device 6 to the contact timing of the transfer device 9 to the photosensitive drum 5. This time T1 can also be expressed by the difference of ΔTA from ΔTD.

  Time T2 is a time interval from timing TC to timing TD. That is, the time from the development start timing of the latent image on the photosensitive drum 5 by the developing device 8 to the contact timing of the transfer device 9 to the photosensitive drum 5. This time T2 can also be expressed by the difference of ΔTC from ΔTD.

  Time T3 is a time interval from timing TD to timing TB. That is, the time from the contact timing of the transfer device 9 to the photosensitive drum 5 to the exposure start timing of the writing device 7. This time T3 can also be expressed by the difference of ΔTD from ΔTB.

  Time T4 is a time interval from timing TM to timing TB. That is, the time from the drive start timing of the main motor to the exposure start timing of the writing device 7. This time T4 can also be represented by ΔTB.

  Time T6 is a time interval from timing TB to timing TE. That is, the time from the exposure start timing of the writing device 7 to the transfer voltage application start timing by the transfer bias roller 9a. This time T6 can also be expressed by the difference of ΔTB from ΔTE.

  Time T7 is a time interval from timing TA to timing TC. That is, the time from the charging start timing of the photosensitive drum 5 by the charging device 6 to the development start timing of the latent image on the photosensitive drum 5 by the developing device 8. This time T7 can also be expressed by the difference of ΔTA from ΔTC.

  As described above, the times ΔTA, ΔTB, ΔTC, ΔTD, ΔTE, ΔTM, T1, T2, T3, T4, and T6 are measured based on the driving start timing of the main motor, and the timings TA, TB, TC, and TD are measured. , TE, Fst, TM are measured based on the drive start timing of the main motor.

Here, at the time of rising when a high voltage is applied to both the charging device 6 and the developing device 8, the voltage application start position by the charging device 6 and the voltage application start position 8 by the developing device are on the photosensitive drum 5. Be identical, ie
T7 = L7 / V
Ideally, it is difficult to ensure this as already mentioned.

Therefore, in consideration of the pros and cons of either carrier or toner adhering to the photosensitive drum 5, the voltage generated by the developing device 8 at the start-up so that the toner intentionally adheres to the photosensitive drum 5. The control unit shifts the application start position from the voltage application start position by the charging device 8.
T7 <L7 / V
Control is performed.

  When such control is performed, a toner band is formed in the width direction of the photosensitive drum 5, in other words, in the main scanning direction. When the toner band adheres to the belt 19, the toner band attached to the belt 19 may adhere to the back surface of the paper P and the like, and the back side of the paper P may be stained. In particular, back contamination in a low temperature and low humidity environment becomes a problem. The toner band adhering to the belt 19 is difficult to prevent by controlling the transfer bias roller 9a because the transfer bias roller 9a is at a position shifted from the position PD.

  The transfer device 9 has a belt cleaning device, which is provided for removing low-concentration foreign matter such as paper dust adhering thereto, and adhered at a high concentration like a belt-like toner. Since it is not intended to remove the foreign matter, it cannot be said that it has sufficient performance for cleaning the belt-like toner. Further, the surface of the belt 19 is formed of a rubber material, which is why it is difficult to remove the toner adhering to the belt shape.

  Therefore, when the amount of the belt-like toner is large, when the performance of the belt cleaning device is deteriorated due to the lapse of time or the like, or when the environment is a low temperature and low humidity, not only the first sheet P but also two sheets The backside stains may also occur on the third and third sheets of paper P at the period of the circumference of the belt 19.

  However, since suppression of deterioration of the photosensitive drum 5 due to carrier adhesion has priority, the voltage application start position by the developing device 8 and the voltage application by the charging device 8 are set such that the toner adheres to the photosensitive drum 5 as described above. Intentional control is performed to deviate from the start position.

  In such an image forming apparatus 1, in order to prevent the toner from adhering to the belt 19, the belt 19 after the belt of toner on the photosensitive drum 5 passes the position PD as the photosensitive drum 5 rotates. May be brought into contact with the photosensitive drum 5.

  Then, the toner band is removed from the photosensitive drum 5 by the cleaning device 10 having excellent toner removal performance, so that image formation is performed while the belt 19 is kept in contact with the photosensitive drum 5. Even if the above is repeated, the belt 19 is not contaminated by the toner band.

Therefore, in the image forming apparatus 1, after the timing TM, that is, after the rotation of the photosensitive drum 5 starts, the charging device 6 starts charging the photosensitive drum 5 at the timing TA, and then the transfer device 9 contacts the photosensitive drum 5. The time T1 until the contact timing TD is determined by the control unit.
T1> L1 / V
It is controlled to satisfy.

In other words,
ΔTA + L1 / V <ΔTD
It is controlled to satisfy.

For the same reason, in the image forming apparatus 1, after the timing TM, that is, after the photosensitive drum 5 starts to rotate, the developing device 8 starts developing the latent image on the photosensitive drum 5 at the timing TC, and then the transfer device. The time T2 until the timing TD at which 9 is in contact with the photosensitive drum 5 is determined by the control unit.
T2> L2 / V
It is controlled to satisfy.

In other words,
ΔTC + L2 / V <ΔTD
It is controlled to satisfy.

  A similar technique is described in the above [Patent Document 1]. However, the charging device described in the document is a charging charger, and the charging device 6 is charged in a state in which the photosensitive drum is charged away from the photosensitive drum. The configuration of the image forming apparatus 1 is in contact with the photosensitive drum 5 and charges the photosensitive drum 5 in this state.

  Here, as already described, when the timing TD, that is, the contact timing of the transfer device 9 with respect to the photosensitive drum 5 is after the timing TB, that is, the exposure start timing of the writing device 7, the transfer device 9 operates as described above. Due to the impact at the time of contact with the drum 5, the formation of the latent image by the writing device 7 is disturbed, and due to this, the formed image is disturbed. When such a blur of the latent image occurs, an image disturbance appears in the width direction of the paper P, and appears as a lateral stripe-like abnormal image called writing banding.

  Further, as in this embodiment, the charging device 6 is in contact with the photosensitive drum 5, and the timing TD, that is, the contact timing of the transfer device 9 with respect to the photosensitive drum 5 is the timing TA, that is, the photosensitive drum by the charging device 6. 5 is later than the charging start timing of 5, the non-uniformity of the charging of the photosensitive drum 5 by the charging device 6 due to the impact when the transfer device 9 contacts the photosensitive drum 5 as described above. Such a charging failure may occur, and this may cause disturbance in the formed image. When such a charging failure occurs and an image is formed by writing on this portion, image disturbance appears in the width direction of the paper P, and appears as a horizontal stripe-like abnormal image.

  When these abnormal images appear on the paper P, the position is the leading edge of the paper P due to the cause of the occurrence, and the writing banding appears on the leading edge of the paper P, and both abnormal images The interval is the distance L3, that is, the distance between the charging position PA and the exposure position PB.

  These abnormal images are likely to occur when a high printing rate, in other words, a high image area rate and halftone image is formed at the leading edge. In the case of a blank image or an image with an image area ratio of about several percent, there is no effect on the image due to the latent image and charging disturbance. In the case of a solid image, the image disturbance caused by such disturbance is visually recognized. This is because it is difficult.

  In the writing banding and the horizontal white stripe, the writing banding is narrower and sharper than the horizontal white stripe.

  Table 1 shows an example of the relationship between the ON timing of the transfer clutch and the occurrence position of the abnormal image. The process linear velocity V is 230 mm / sec. The exposure start timing TB is 920 msec after the start of driving of the main motor. This example is an example where such an abnormal image occurs, and is not obtained as a result of the application of the present invention.

  When the set value of the transfer contact timing ΔTD is 1000 msec after the start of driving of the main motor, the actual measured value of the operation is 970 msec. This actually measured value is 50 msec after the writing start timing TB by the writing means 7.

  Since the process linear velocity V is 230 mm / sec, the generation position of the write banding is 11.5 mm from the front end of the image corresponding to the write start position by the writing means 7 in calculation. The horizontal white stripe is generated at a position 26.56 mm from the top of the image because the distance L3 between the charging position PA and the exposure position PB is 15.06 mm.

  On the actual machine, the writing banding was generated at a position of 10 to 11 mm from the front end of the image, and the horizontal white streak was generated at a position of 25 to 26 mm from the front end of the image.

When the set value of the transfer contact timing ΔTD is 920 msec after the start of driving of the main motor, the actual measured value of the operation is 890 msec. This measured value is 30 msec before the write start timing TB by the writing means 7.
Therefore, write banding does not occur.

  Since the process linear velocity V is 230 mm / sec, when the contact of the belt 19 with the photosensitive drum 5 is completed, the leading end position of the image corresponding to the writing start position by the writing unit 7 is calculated from the positions PD1 to 6. It is a position 9 mm before.

  Therefore, the generation position of the horizontal white stripe is a position of 8.16 mm from the leading edge of the image because the distance L3 between the charging position PA and the exposure position PB is 15.06 mm.

  On the actual machine, no writing banding occurred, and the horizontal white streak was generated at a position of 5 to 6 mm from the front end of the image, and thus showed the same tendency as the calculated value.

When the set value of the transfer contact timing ΔTD is 900 msec after starting the driving of the main motor, the actual measured value of the operation is 870 msec. This actual measurement value is 50 msec before the write start timing TB by the writing means 7.
Therefore, write banding does not occur.

  Since the process linear velocity V is 230 mm / sec, when the contact of the belt 19 with the photosensitive drum 5 is completed, the leading end position of the image corresponding to the writing start position by the writing unit 7 is calculated from the positions PD1 to 11. It is a position 5 mm before.

  Therefore, the horizontal white streak generation position is a position 3.56 mm from the front end of the image because the distance L3 between the charging position PA and the exposure position PB is 15.06 mm.

  On the actual machine, no writing banding occurred, and the horizontal white streak was generated at a position 2.5 mm from the front end of the image.

  From Table 1, it can be seen that the higher the contact timing TD of the belt 19 with respect to the photosensitive drum 5 is, the more effective it is for writing banding and horizontal white stripes. This is in contrast to the fact that the belt 19 adheres to the belt 19 with a toner band on the photosensitive drum 5 as the contact timing TD of the belt 19 with the photosensitive drum 5 is delayed.

In consideration of such circumstances, in order to prevent writing banding, in the image forming apparatus 1, the transfer unit 9 contacts the photosensitive drum 5 after the timing TM, that is, after the photosensitive drum 5 starts rotating, by the control unit. The contact timing TD is controlled to be before the timing TB at which the writing unit 7 starts to form a latent image on the photosensitive drum 5. That is, the timing TB at which the writing unit 7 starts to form a latent image on the photosensitive drum 5 is controlled to be after the timing TD at which the transfer device 9 contacts the photosensitive drum 5.

In other words,
ΔTD <ΔTB
It is controlled to satisfy.

  However, in the control that simply satisfies such a relationship, there is a possibility that a horizontal white stripe is generated by forming a latent image in a poorly charged portion caused by an impact when the transfer device 9 comes into contact with the photosensitive drum 5. . Therefore, in order to surely avoid the occurrence of horizontal white stripes, it is necessary to start the formation of a latent image on the photosensitive drum 5 by the writing means 7 after such a poorly charged portion has passed the position PB.

Therefore, in order to prevent both abnormal images, in the image forming apparatus 1, after the timing TM, that is, after the rotation of the photosensitive drum 5 starts, the writing unit 7 contacts the photosensitive drum 5 at the timing TD. A time T3 up to a timing TB at which formation of a latent image on the photosensitive drum 5 is started is determined by the control unit.
T3> L3 / V
It is controlled to satisfy.

In other words,
ΔTD + L3 / V <ΔTB
It is controlled to satisfy.

  In this embodiment, since the distance L3 is 15.06 mm, the calculation time T3 is longer than 63 msec and 83 sec for each of the process linear velocity V of 230 mm / sec and 180 mm / sec.

  As described above, in the image forming apparatus 1, in order to prevent the toner band on the photosensitive drum 5 from adhering to the belt 19, the horizontal white stripes generated when the contact timing of the belt 19 with respect to the photosensitive drum 5 is delayed. In order to prevent this, each timing is adjusted.

  That is, when the charging device is configured to be separated from the photosensitive drum like a charging charger, even if the timing when the transfer device comes into contact with the photosensitive drum is after the start of exposure, the horizontal white stripe does not cause a problem. Further, even when the charging device includes a charging roller as in the image forming apparatus 1 and the transfer device contacts and separates from the photosensitive drum, the transfer device contacts the photosensitive drum before exposure starts. In the configuration, horizontal white stripes do not become a problem. However, when the contact timing of the transfer device with respect to the photosensitive drum is delayed as in the image forming apparatus 1 in order to prevent the toner band on the photosensitive drum from adhering to the transfer device, horizontal white stripes may occur. .

  Under such circumstances, in the image forming apparatus 1, the contact timing of the transfer device 9 with respect to the photosensitive drum 5 is set to prevent the toner band on the photosensitive drum 5 from adhering to the transfer device 9. Each timing is adjusted in order to prevent horizontal white stripes caused by delay.

  6 and 7, when the process linear velocity V is 230 mm / sec and 180 mm / sec, respectively, a time ΔTB from when the photosensitive drum 5 starts to rotate until the writing device 7 starts exposure, Time ΔTD until the transfer device 9 comes into contact with the photosensitive drum 5, time T3 from when the transfer device 9 comes into contact with the photosensitive drum 5 until the writing device 7 starts exposure, the presence / absence of each abnormal image, and the first The relationship in the actual machine with the first print time Fst that is the copy time is shown.

  The set value of the time ΔTD is 770 msec in the former case and 900 msec in the latter case. From these figures, it can be seen that when the time ΔTB is changed, the write banding has a narrower generation range, and there is a margin in the setting range of the time ΔTB. This is consistent with the fact that in the case of examining Table 1, the write banding is more easily canceled when the time ΔTD is changed.

  6 and 7, the first print time Fst is an actual measurement value. The measurement was performed as follows. That is, a signal when the rear end of the paper P passes through the paper discharge sensor 25 after a signal indicating the image formation start instruction is input to the control unit with the polygon mirror in the activated state and constantly rotated by the driving unit. And the time between them is measured, and the time obtained by dividing the distance from the paper discharge sensor 25 to the position PF by the process linear velocity V is calculated. The timing at which the image forming start instruction signal is input to the control unit may be equated with the driving start timing TM of the photosensitive drum 5.

  In the case shown in FIG. 6, the time T3 on the actual machine is 203 msec. When the process linear velocity V is 230 mm / sec, the calculated time T3 is 63 msec as described above. The difference between them is 140 msec, which is related to the sum of the transfer clutch rising time 50 msec and the operation time 100 msec, which is 150 msec, which are almost the same. That is, the exposure is started after the contact of the transfer device 9 with the photosensitive drum 5 is almost certainly completed and the operation of the contact / separation device 17 is almost completed.

  In the case shown in FIG. 7, NO. 10, the actual time T3 is 248 msec. When the process linear velocity V is 180 mm / sec, the calculated time T3 is 83 msec as described above. The difference between them is 165 msec, which is related to the sum of the transfer clutch rising time 50 msec and the operation time 100 msec, which is 150 msec, and the sum is within the range of the difference. That is, exposure is started after the contact of the transfer device 9 with the photosensitive drum 5 is reliably completed and the operation of the contact / separation device 17 is completed.

  The time T3 is adjusted so that an abnormal image does not occur depending on the performance related to the rise time and operation time of the contact / separation device 17. That is, the time ΔTD is preferably a time including the rise time and the operation time.

  The operation time may be shortened as long as the rise time is not affected. This is because if the operation time is short, a margin can be provided in a range where no abnormal image occurs. In the contact / separation device 17, the belt 19 contacts and separates from the photosensitive drum 5 every half rotation of the cam. Therefore, it is necessary to extend the operation time so that the cam does not rotate once.

  It is effective to shorten the distance L3 between the position PA and the position PB in order to shorten the time Δ3 until the writing device 7 starts the exposure after the start of driving of the photosensitive drum 5 by shortening the time T3. If the distance L3 is shortened, the interval between the writing banding and the horizontal white stripe is shortened, and the occurrence range of the abnormal image in the Y direction can be suppressed. Therefore, the setting range of the time TB can be afforded, and the photosensitive drum 5 It is possible to shorten the time ΔTB until the writing device 7 starts exposure after the start of driving.

However, the beam L and the charging roller 16 should not interfere with each other, and the minimum value of the distance L3 needs to be larger than 7 mm, which is the radius R of the charging roller 16.
That is,
R <L3
Must be met.

If ΔTB can be shortened as described above, the time required for image formation can be shortened.
From the viewpoint of shortening the time required for image formation, that is, the time required from completion of image formation start instruction by the operator to completion of image formation, the first sheet P of paper P after the image formation start instruction is issued by the operator. It is effective to shorten the time Fst until the trailing edge passes the position PF and the paper P is discharged out of the image forming apparatus 1.

Therefore, in the image forming apparatus 1, after the timing TM, that is, after the start of rotation of the photosensitive drum 5, the time T 4 until the timing TB at which the writing unit 7 starts to form a latent image on the photosensitive drum 5 is determined by the control unit. ,
T4 <T5
T5 = Fst− (L4 + L5 + LP) / V
It is controlled to satisfy.

  If the time T4 is made smaller than the time T5, the specification of the target time Fst can be satisfied. The time Fst is a specification value and depends on the process linear velocity V. In addition, the time Fst also depends on the position of the paper feed tray 11A, that is, the stacking position of the paper P. When the paper feed trays 11A are arranged in multiple stages, the paper is usually fed from the uppermost paper feed tray 11A. The time when paper P is fed is shorter than the time when paper P is fed from the other paper feed tray 11A. However, this does not change as long as it is limited to the image forming area where the latent image is formed, that is, around the photosensitive drum 5.

  In this embodiment, assuming that the time Fst for the A4 landscape paper P when the process linear velocity V is 230 mm / sec is 3.5 seconds, the time T5 is 3.5− (213. 63 + 82.01 + 210) /230=1.301 sec. Therefore, in order to satisfy the time Fst, the writing means 7 must start forming a latent image on the photosensitive drum 5 by 1.301 sec after the photosensitive drum 5 starts rotating.

  Further, when the time Fst for the A4 landscape paper P when the process linear velocity V is 180 mm / sec is 4.1 seconds, the time T5 is calculated as 4.1- (213.63 + 82. 01 + 210) /180=1.290 sec. Therefore, in order to satisfy the time Fst, the writing unit 7 must start forming a latent image on the photosensitive drum 5 by 1.290 sec after the photosensitive drum 5 starts rotating.

  The above equation can also be used to examine how far the time Fst can be reduced by its parameters L4, L5, length LP, process linear velocity V, and time T4.

  In the image forming apparatus 1, since the transfer device 9 contacts and separates from the photosensitive drum 5, the transfer device 9 contacts the photosensitive drum 5 at the timing TD at the start timing TE of application of the transfer voltage by the transfer bias roller 9a. Must be later.

That is, in the image forming apparatus 1, the control unit
ΔTD <ΔTE
It is controlled to satisfy.

  This indicates the lower limit of the time ΔTE. At the time ΔTE, the timing TE is set at the upstream end portion in the X direction and the Y direction of the position PD where the toner image on the image carrier 5 is the nip position. There is a restriction that it must be done before reaching the position PD1.

That is, in the image forming apparatus 1, after the timing TM, that is, after the rotation of the photosensitive drum 5 is started, after the transfer device 9 comes into contact with the photosensitive drum 5 at the timing TD, the writing unit 7 is the photosensitive drum 5. The time T6 from the timing TB at which the latent image is formed to the time TE until the timing TE at which the transfer bias roller 9a starts applying the transfer voltage and starts the transfer of the toner image on the photosensitive drum 5 to the paper P is controlled. Depending on the part
T6 <L6 / V
It is controlled to satisfy.

Therefore,
ΔTB + L6 / V>ΔTE> ΔTD
It is controlled to satisfy.

For image formation, the magnitude relationship is reversed for the times ΔTE and ΔTD in the above equation.
ΔTE <ΔTD
It can be said that.

  That is, the transfer device 9 may contact the photosensitive drum 5 in a state where application of the transfer voltage by the transfer bias roller 9a is started. However, in this case, a high voltage higher than the normal applied voltage is applied to the belt 19. This voltage is dangerous when there is a limiter, and when there is no limiter, leakage to the photosensitive drum 5 occurs.

The case where there is a limiter will be described in more detail.
For example, when the limiter is set at 6.8 KV, a high voltage of the same level is applied to the belt 19, and charges are concentrated on a part of the belt 19, and there is a concern that a crack, that is, a crack is generated in that part.

  Cracks can occur for the following reasons. That is, as described above, the filler is added to the belt 19 in a uniformly dispersed state, but since a part thereof is in an aggregated state, a high voltage applied to the aggregated filler is applied. In this case, cracks are generated starting from the agglomerated portion. When an ionic material is used as the filler, the resistance becomes high in a low temperature and low humidity environment, so that there is a high possibility that such a high voltage is applied.

  Therefore, from the viewpoint of suppressing the risk of applying such a high voltage and extending the life of the belt 19, application of the transfer voltage by the transfer bias roller 9a starts after the transfer device 9 contacts the photosensitive drum 5. Is good.

  8 and 9 show examples of timing charts of the image forming apparatus 1 that satisfy all the above-described conditions when the process linear velocity V is 230 mm / sec and 180 mm / sec, respectively. According to such an image forming apparatus 1, the toner band on the photosensitive drum 5 is prevented from adhering to the belt 19, each abnormal image is prevented, the first print time Fst is secured or shortened, the good transfer performance, the transfer device All of the extension of service life is achieved.

  In the image forming apparatus 1, the operator can arbitrarily set a timing TB at which the writing unit 7 starts forming a latent image on the photosensitive drum 5 after the timing TM, that is, after the photosensitive drum 5 starts to rotate. And a write start time setting mode are prepared.

  This mode is a mode for giving the highest priority to shortening the first print time Fst. That is, as described above, an abnormal image such as writing banding is mainly a problem when a halftone image having a high image area ratio is formed on the leading edge of the paper P. Therefore, when forming an image other than such an image, the operator can set the time TB to be shortened and the time ΔTB to be shortened.

  Therefore, in this mode, the end user as the operator shortens the first print time Fst, rather than being prepared for adjusting the timing TB so that the service person as an operator does not generate such an abnormal image. The main purpose is to make it possible.

  The transition to the mode is performed by an instruction from an operator from an operation panel or other input means such as a computer terminal connected to the image forming apparatus 1. Here, the operation panel, input means, and the like function as write start time setting mode transition means or mode change means. After the transition to the mode, the timing TB and time ΔTB can be input and adjusted by the operation panel, the input means, and the like. Here, the operation panel, the input unit, and the like function as a writing start time input unit or a writing start time changing unit.

  Further, the transition to the mode may be performed as an internal process of the image forming apparatus 1. For example, the control unit determines whether an image with a high image area ratio is formed at the leading end of the sheet P and is a halftone image, and whether or not the above-described abnormal image can occur. If it occurs, it may be determined which part, and the timing TB or the like may be automatically set so that an abnormal image does not occur according to the determination situation. In this case, the control unit functions as a write start time setting mode transition unit or a mode change unit, and also as a write start time input unit or a write start time change unit.

  The image forming apparatus 1 also has a contact start time setting that allows the operator to arbitrarily set the timing TD at which the transfer device 9 contacts the photosensitive drum 5 after the timing TM, that is, after the photosensitive drum 5 starts rotating. A mode is available.

  This mode is provided as a serviceman mode that can be changed by a serviceman as an operator and other modes that can be changed by an end user as an operator, and an abnormal image including shortening of the first print time Fst and transfer of a toner band. This is for the purpose of avoiding the above.

  The transition to the mode is performed by an instruction from an operator from an operation panel or other input means such as a computer terminal connected to the image forming apparatus 1. Here, the operation panel, input means, and the like function as contact start time setting mode transition means or mode change means. After the transition to the mode, the timing TD and time ΔTD can be input and adjusted by the operation panel, the input means, and the like. Here, the operation panel, input means, and the like function as contact start time input means or contact start time changing means.

  Further, the transition to the mode may be performed as an internal process of the image forming apparatus 1. For example, the control unit may automatically set the timing TD or the like so that the abnormal image does not occur. In this case, the control unit functions as contact start time setting mode transition means or mode change means, and contact start time input means or contact start time change means.

  In addition, other timings, times, and the like described above may be similarly changed to a mode in which each is changed and set by the operator and the control unit. An image formation start instruction may also be given by such input means.

  Although the above has described the case where the image forming apparatus 1 is a monochrome machine, the present invention can be similarly applied to a color machine.

  FIG. 10 shows an image forming apparatus 1 which is a color machine to which the present invention is applied. The same components as those described for the monochrome machine are denoted by the same reference numerals and description thereof is omitted. Further, the description overlapping with the description of the monochrome machine is omitted, and different parts are mainly described.

  The reference numerals shown in FIG. 10 and suffixed with Y, M, C, and K are image forming systems for forming toner images of yellow, magenta, cyan, and black, and the image forming system. The Y-, M-, C-, and K-suffixes are added to the above-described symbols attached to the monochrome machine, and their actions, operations, positions, etc. are indicated by the corresponding symbols. This is the same as the configuration and position of the monochrome machine.

  In the image forming apparatus 1 that is a monochrome machine described above, the transfer device 9 is a transfer and conveyance unit that transfers a toner image onto the sheet P to be conveyed. However, in the tandem image forming apparatus 1 that is such a color machine, The transfer device 9 is an intermediate transfer device as an intermediate transfer unit, and is provided as a primary transfer device as a primary transfer unit, and for each color formed on the photosensitive drums 5Y, 5M, 5C, and 5K. The toner images are superimposed and transferred in the order of yellow, magenta, cyan, and black onto a belt 19 as an intermediate transfer member provided in the toner image. The transfer bias rollers 9aY, 9aM, 9aC, and 9aK each function as a primary transfer bias roller that performs such primary transfer.

  The toner images of the respective colors formed on the photosensitive drums 5Y, 5M, 5C, and 5K are superimposed and transferred to the belt 19, and the color toner image obtained by the superimposed transfer is a secondary transfer device as a secondary transfer unit. 26 is transferred onto the paper P. The secondary transfer device 26 includes a counter roller 27 around which the belt 19 is wound, and a secondary transfer bias roller 28 that applies a secondary transfer bias to the counter roller 27 across the belt 19.

  In the image forming apparatus 1 which is such a color machine, for example, the exposure timing and the like in each of the image forming systems for yellow, magenta, cyan and black centering on the photosensitive drums 5Y, 5M, 5C and 5K. The timing is adjusted to the same timing as the timing described above, and the relationship between the transfer device 9 and each of the image forming systems is also set to the timing similar to the timing described above for the contact / separation timing, for example. It has been adjusted.

  Accordingly, toner belts on the photosensitive drums 5Y, 5M, 5C, and 5K are prevented from adhering to the belt 19, each abnormal image is prevented, and the first print time Fst is secured or shortened. Prolonging the service life is appropriately achieved.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

For example, the image forming apparatus 1 is configured to vertically convey the paper P in the above-described monochrome machine. However, even in the monochrome machine, the image forming apparatus 1 horizontally conveys the paper P as shown in FIG. There may be. Even a color machine may be conveyed vertically. The transfer device is not necessarily required to have a belt, even roller shape has good.

  In the embodiment described above, each timing is based on the drive start timing of the main motor, but the timing reference may be another timing.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

1 is a schematic front view of an image forming apparatus to which the present invention is applied. FIG. 2 is a partially enlarged schematic view of the image forming apparatus shown in FIG. 1. 2 is a timing chart of contact and separation of a transfer unit provided in the image forming apparatus shown in FIG. 1 with respect to an image carrier. FIG. 2 is a development view along a path along which an image moves in the image forming apparatus illustrated in FIG. 1. 2 is a timing chart of the operation of each component provided in the image forming apparatus shown in FIG. 1. FIG. 5 is a correlation diagram showing a relationship in an actual machine among an exposure start timing, a contact timing of a transfer unit to an image carrier, presence / absence of each abnormal image, and first print time Fst when a process linear velocity is 230 mm / sec. . FIG. 6 is a correlation diagram showing a relationship in an actual machine among an exposure start timing, a contact timing of a transfer means to an image carrier, presence / absence of each abnormal image, and first print time Fst when a process linear velocity is 180 mm / sec. . 6 is an example of a timing chart of the operation of each component of the image forming apparatus to which the present invention is applied when the process linear velocity is 230 mm / sec. 6 is an example of a timing chart of the operation of each component of the image forming apparatus to which the present invention is applied when the process linear velocity is 180 mm / sec. It is the schematic of the image forming apparatus of the other structure to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 5, 5Y, 5M, 5C, 5BK Image carrier 6 Charging means 7 Writing means 8 Developing means 9 Transfer means L1 Contact of an image carrier and a transfer means from the contact position of an image carrier and a charging means Distance of movement of image carrier to contact position L2 Distance of movement of image carrier from contact position of image carrier and developing means to contact position of image carrier and transfer means L3 Image carrier and charging means The moving distance of the image carrier from the contact position to the position where the writing means writes the latent image on the image carrier L4 The contact position between the image carrier and the transfer means from the position where the writing means writes the latent image on the image carrier Distance of movement of image carrier to L5 Distance of movement of recording medium from contact position between image carrier and transfer means to position where recording medium is discharged out of image forming apparatus L6 Writing means is latent image on image carrier Transfer position and image from writing position Distance of movement of image carrier to contact position with holder LP Length of recording medium at Fst P Recording medium PA Contact position between image carrier and charging means PB Writing means displays latent image on image carrier Writing position PC Contact position between the image carrier and developing means PD Contact position between the image carrier and transfer means PD1 Out of the contact positions, the upstream end portion PD2 of the contact position among the contact positions PD1 , Downstream end portion in the moving direction of the image carrier PE Transfer voltage application position by the transfer means PF Paper discharge position at which the recording medium is discharged out of the image forming apparatus T1 After the movement of the image carrier starts, the charging means carries the image Time from the start of charging of the body until the transfer unit contacts the image carrier T2 After the start of the movement of the image carrier, the developing unit starts developing the image carrier and the transfer unit contacts the image carrier. Time to contact T3 Movement of image carrier After the start, the time from when the transfer means comes into contact with the image carrier until the writing means starts forming a latent image on the image carrier T4 After the start of the movement of the image carrier, the writing means Time until image formation is started T5 Predetermined time T6 After the start of movement of the image carrier, after the transfer means comes into contact with the image carrier, the writing means forms a latent image on the image carrier. Time from the start to the start of image transfer by the transfer means TA Start timing of charging of the image carrier by the charging means TB Start timing of formation of a latent image on the image carrier by the writing means TC Image by the developing means Development start timing of the carrier TD Contact timing of the transfer means to the image carrier TE Start timing of transfer of the image on the image carrier by the transfer means TF Start of movement of the image carrier for a recording medium of a predetermined length , The transport direction of the moving direction Y recording medium moving start timing V linear velocity X image carrier time TM image bearing member to the recording medium on which an image has been formed is discharged outside the image forming apparatus

Claims (8)

An image carrier that moves at a predetermined speed; a charging unit that contacts the image carrier and charges the image carrier; a writing unit that forms a latent image on the image carrier charged by the charging unit; A developing unit that develops the latent image formed by the writing unit; and a transfer unit that transfers the image developed by the developing unit. The transfer unit contacts and separates from the image carrier. In an image forming apparatus for forming an image,
After the start of the movement of the image carrier, a time T1 from when the charging unit starts to charge the image carrier to when the transfer unit contacts the image carrier is:
T1> L1 / V
L1: moving distance V of said image bearing member from the contact position between the image bearing member and said charging means to the contact position between the transfer means and the image bearing member: meets process linear velocity,
The contact position between the image carrier and the transfer unit is an upstream end portion in the moving direction of the image carrier among the contact positions.
After the start of the movement of the image carrier, a time T3 from when the transfer unit contacts the image carrier until the writing unit starts forming a latent image on the image carrier is:
T3> L3 / V
L3: a moving distance of the image carrier from a contact position between the image carrier and the charging unit to a position where the writing unit writes a latent image on the image carrier.
V: Same as above
At this time,
ΔTD + L3 / V <ΔTB
ΔTB: Time from the start of movement of the image carrier until the writing means starts to form a latent image on the image carrier
ΔTD: time from the start of the movement of the image carrier until the transfer means contacts the image carrier
And
The charging means has a charging roller in contact with the image carrier,
The transfer means includes a transfer conveyance member that conveys a recording medium, and contact / separation means that contacts and separates the transfer conveyance member with respect to the image carrier. The contact / separation means drives a cam and the cam. And a transfer clutch that is positioned between the cam and the motor and that switches whether or not to transmit the driving force of the motor to the cam.
The ΔTD includes a rise time after the transfer clutch is turned on, and an operation time required to bring the transfer conveying member into contact with the image carrier after the transfer clutch is raised. apparatus. The image forming apparatus according to claim 1 .
The transfer conveying member is an endless belt,
The transfer means has a transfer bias applying member disposed inside the belt,
R <L3
R: Radius of the charging roller
L3: An image forming apparatus that satisfies the above . The image forming apparatus according to claim 1 or 2,
After the start of the movement of the image carrier, a time T4 until the writing unit starts to form a latent image on the image carrier, and a predetermined time T5 are:
T4 <T5
T5 = Fst− (L4 + L5 + LP) / V
Fst: Time required for a recording medium having a predetermined length to be discharged out of the image forming apparatus after the start of movement of the image carrier.
L4: The movement of the image carrier from the position where the writing means writes a latent image on the image carrier to the downstream end in the movement direction of the image carrier at the contact position between the image carrier and the transfer means. distance
L5: the moving distance of the image from the downstream end in the moving direction of the image carrier at the contact position between the image carrier and the transfer unit to the position where the recording medium is discharged out of the image forming apparatus
LP: Length of the recording medium at the Fst
V: Same as above
An image forming apparatus characterized by satisfying the above. The image forming apparatus according to any one of claims 1 to 3 ,
After the start of the movement of the image carrier, after the transfer means comes into contact with the image carrier, and after the writing means starts forming a latent image on the image carrier, the transfer means The time T6 until the application of a transfer bias for transferring the image is started,
T6 <L6 / V
L6: a moving distance of the image carrier from a position where the writing unit writes a latent image on the image carrier to a contact position between the transfer unit and the image carrier
V: Same as above
An image forming apparatus characterized by satisfying the above. The image forming apparatus according to any one of claims 1 to 4 ,
An image forming apparatus comprising: a contact start time setting mode for arbitrarily setting a time until the transfer unit contacts the image carrier after the start of movement of the image carrier . The image forming apparatus according to any one of claims 1 to 5 ,
An image forming method comprising: a writing start time setting mode for arbitrarily setting a time from the start of the movement of the image carrier until the writing unit starts forming a latent image on the image carrier. apparatus. The image forming apparatus according to any one of claims 1 to 6 ,
An image forming apparatus, wherein the transfer unit is an intermediate transfer unit . An image forming method for forming an image using the image forming apparatus according to claim 1 .

Images