EP2574988B1 - Image forming apparatus with mechanism capable of moving transfer device with respect to toner image carrier - Google Patents
Image forming apparatus with mechanism capable of moving transfer device with respect to toner image carrier Download PDFInfo
- Publication number
- EP2574988B1 EP2574988B1 EP12182500.4A EP12182500A EP2574988B1 EP 2574988 B1 EP2574988 B1 EP 2574988B1 EP 12182500 A EP12182500 A EP 12182500A EP 2574988 B1 EP2574988 B1 EP 2574988B1
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- EP
- European Patent Office
- Prior art keywords
- toner
- transfer device
- secondary transfer
- toner image
- intermediate transfer
- Prior art date
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Images
Classifications
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/14—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base
- G03G15/16—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer
- G03G15/1605—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer using at least one intermediate support
- G03G15/161—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer using at least one intermediate support with means for handling the intermediate support, e.g. heating, cleaning, coating with a transfer agent
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/14—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base
- G03G15/16—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer
- G03G15/1665—Apparatus for electrographic processes using a charge pattern for transferring a pattern to a second base of a toner pattern, e.g. a powder pattern, e.g. magnetic transfer by introducing the second base in the nip formed by the recording member and at least one transfer member, e.g. in combination with bias or heat
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/50—Machine control of apparatus for electrographic processes using a charge pattern, e.g. regulating differents parts of the machine, multimode copiers, microprocessor control
- G03G15/5054—Machine control of apparatus for electrographic processes using a charge pattern, e.g. regulating differents parts of the machine, multimode copiers, microprocessor control by measuring the characteristics of an intermediate image carrying member or the characteristics of an image on an intermediate image carrying member, e.g. intermediate transfer belt or drum, conveyor belt
- G03G15/5058—Machine control of apparatus for electrographic processes using a charge pattern, e.g. regulating differents parts of the machine, multimode copiers, microprocessor control by measuring the characteristics of an intermediate image carrying member or the characteristics of an image on an intermediate image carrying member, e.g. intermediate transfer belt or drum, conveyor belt using a test patch
Definitions
- Exemplary aspects of the present invention relate to an image forming apparatus, and more particularly, to an image forming apparatus for forming a toner image by transferring the toner image onto a recording medium directly or indirectly via an intermediate transferor.
- a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is primarily transferred from the photoconductor onto an intermediate transfer belt and secondarily transferred from the intermediate transfer belt onto a recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
- a toner patch is formed on the photoconductor, which is transferred onto the intermediate transfer belt.
- An optical sensor disposed opposite the intermediate transfer belt detects the toner density of the toner patch based on which image forming conditions such as the toner density of the toner image, the charging bias, and the development bias are adjusted. For example, if the image forming apparatus receives a multiple print job for forming a toner image on a plurality of recording media, the toner patch is created in a gap between successive toner images formed on the intermediate transfer belt.
- the toner image primarily transferred from the photoconductor onto the intermediate transfer belt is secondarily transferred onto the recording medium conveyed through a secondary transfer region formed between the intermediate transfer belt and a secondary transfer device pressed against the intermediate transfer belt. Since the toner patch should not be transferred onto the recording medium, no recording medium is conveyed through the secondary transfer region as the toner patch passes through the secondary transfer region. Accordingly, the toner patch created on the intermediate transfer belt may contact the secondary transfer device as it is conveyed through the secondary transfer region due to absence of the recording medium and toner may move from the toner patch to the secondary transfer device. Hence, as a subsequent recording medium is conveyed through the secondary transfer region, the toner may further move from the secondary transfer device to the back side of the subsequent recording medium that contacts the secondary transfer device, staining the subsequent recording medium.
- a sensor disposed upstream from the secondary transfer region in a recording medium conveyance direction may detect absence of a recording medium conveyed toward the secondary transfer region. Whenever the sensor detects such absence of the recording medium, the secondary transfer device separates from the intermediate transfer belt so that the toner patch created on the intermediate transfer belt does not come into contact with the secondary transfer device as it is conveyed through the secondary transfer region, thus preventing adhesion of toner of the toner patch to the secondary transfer device.
- the secondary transfer device separates from the intermediate transfer belt whenever the sensor detects absence of the recording medium, the secondary transfer device comes into contact with and separates from the intermediate transfer belt repeatedly during the multiple print job for forming the toner image on the plurality of recording media. Since it takes time to bring the secondary transfer device into contact with and isolation from the intermediate transfer belt, an increased time may be consumed to finish the multiple print job, degrading productivity of the image forming apparatus.
- EP 1 202 125 A2 relates to an image forming apparatus comprising photoreceptors, around which is a charging section, an exposing section and a developing section, for forming a toner image; a rotatable intermediate transfer member; first transfer sections; a second transfer section, having a transfer roller; for transferring the toner image from the intermediate transfer member to a transfer material; and a controller to control the image forming condition based on the detected density of an image pattern formed on a non-image area of the photoreceptor; wherein the controller releases a pressure contact of the transfer roller of the second transfer section, before the image pattern arrives the second transfer section, and starts a next print cycle after again making the pressure contact.
- JP 2007-286176 A relates to an image forming apparatus, image formation control method, and program.
- An image forming apparatus regards a start signal as a trigger, and writes the positioning test pattern between papers when continuously writing a plurality of normal images, and reads the test pattern with a sensor on an intermediate transfer belt in order to regulate an image formation control condition to be fed back.
- the normal images on the intermediate transfer belt are transferred on a medium passing the papers in a secondary transfer, and the test pattern passes through the secondary transfer without passing the paper. Since a transfer roller is fouled, the secondary transfer and a transfer belt are separated and detached by a contact and separation mechanism while the test pattern written between the papers passes secondary transfer.
- US 2007/0217801 A1 relates to an image forming apparatus and method for detecting separated state of the transfer unit.
- An image forming apparatus has a structure in which a toner image formed in an electrophotographic process is transferred from an intermediate transfer belt to a member to be transferred.
- the apparatus includes a secondary transfer roller that becomes a pressure contact state with respect to the intermediate transfer belt to make it perform a transfer process and can move between the pressure contact state and a separated state, and a press and separation driving device for driving the secondary transfer roller to become the pressure contact state and the separated state.
- the pressure contact state or the separated state of the secondary transfer roller is detected in accordance with a variation of an output of an IDC sensor for detecting a state of a bare surface of the intermediate transfer belt.
- FIG. 1 an image forming apparatus 100 according to an exemplary embodiment of the present invention is explained.
- FIG. 1 is a schematic vertical sectional view of the image forming apparatus 100.
- the image forming apparatus 100 may be a copier, a facsimile machine, a printer, a multifunction printer having at least one of copying, printing, scanning, plotter, and facsimile functions, or the like.
- the image forming apparatus 100 is a tandem color copier for forming a color toner image on a recording medium by electrophotography.
- the image forming apparatus 100 employs an intermediate transfer method using an intermediate transfer belt 10 serving as a toner image carrier that carries a toner image to be transferred onto a recording medium.
- the image forming apparatus 100 is constructed of a paper storage 2 disposed in a lower portion thereof, a body 1 disposed above the paper storage 2, a scanner 3 disposed above the body 1, and an auto document feeder (ADF) 4 disposed above the scanner 3.
- ADF auto document feeder
- the body 1 includes a transfer unit 20 in substantially a center portion thereof.
- the transfer unit 20 incorporates the endless intermediate transfer belt 10 stretched over a driving roller 14 and support rollers 15 and 16.
- the driving roller 14 drives and rotates the intermediate transfer belt 10 clockwise in FIG. 1 in a rotation direction R1
- the support rollers 15 and 16 are driven and rotated in accordance with rotation of the intermediate transfer belt 10 by friction therebetween.
- Downstream from the support roller 16 in the rotation direction R1 of the intermediate transfer belt 10 is a belt cleaner 17 that removes residual toner remaining on an outer circumferential surface of the intermediate transfer belt 10 after a toner image is transferred from the intermediate transfer belt 10 onto a recording medium as described below, thus rendering the intermediate transfer belt 10 to be ready for the next transfer operation.
- the intermediate transfer belt 10 are four drum-shaped photoconductors 40Y, 40M, 40C, and 40K arranged along the rotation direction R1 of the intermediate transfer belt 10.
- the photoconductors 40Y, 40M, 40C, and 40K serve as electrostatic latent image carriers that carry electrostatic latent images and resultant yellow, magenta, cyan, and black toner images, respectively.
- the photoconductors 40Y, 40M, 40C, and 40K are rotatable counterclockwise in FIG.
- chargers 60Y, 60M, 60C, and 60K development devices 61Y, 61M, 61C, and 61K, primary transfer devices 62Y, 62M, 62C, and 62K, photoconductor cleaners 63Y, 63M, 63C, and 63K, and dischargers 64Y, 64M, 64C, and 64K, respectively.
- an exposure device 21 Above the photoconductors 40Y, 40M, 40C, and 40K is an exposure device 21.
- a secondary transfer device 22 serving as a transfer device or a secondary transferor.
- the secondary transfer device 22 is pressed against the support roller 16 via the intermediate transfer belt 10 to form a secondary transfer region N between the secondary transfer device 22 and the intermediate transfer belt 10.
- the secondary transfer device 22 secondarily transfers the yellow, magenta, cyan, and black toner images formed on the intermediate transfer belt 10 onto the recording medium collectively, thus forming a color toner image on the recording medium.
- the fixing device 25 Downstream from the secondary transfer device 22 in a recording medium conveyance direction is an endless conveyance belt 24 looped over a pair of rollers 23 that conveys the recording medium bearing the color toner image toward a fixing device 25 disposed downstream from the conveyance belt 24 in the recording medium conveyance direction.
- the fixing device 25 includes an endless fixing belt 26 and a pressing roller 27 pressed against the fixing belt 26 to form a fixing nip therebetween through which the recording medium is conveyed. As the recording medium is conveyed through the fixing nip, the fixing belt 26 and the pressing roller 27 apply heat and pressure to the recording medium, melting and fixing the color toner image on the recording medium.
- a reverse device 28 Below the secondary transfer device 22 is a reverse device 28 that reverses the recording medium conveyed from the fixing device 25 for duplex printing.
- the following describes a copying operation of the image forming apparatus 100 having the structure described above to form a color toner image on a recording medium.
- conveyance rollers of the ADF 4 automatically convey the original document onto an exposure glass 32 of the scanner 3 and the scanner 3 starts scanning the original document.
- the scanner 3 starts scanning the original document.
- a light source mounted on the first carriage 33 emits light onto the original document placed on the exposure glass 32.
- a mirror mounted on the first carriage 33 deflects light reflected by the original document toward the second carriage 34.
- a pair of mirrors mounted on the second carriage 34 deflects light by 180 degrees toward a reading sensor 36 through an image forming lens 35 so that the reading sensor 36 reads an image on the original document into image data.
- the intermediate transfer belt 10 starts rotating clockwise in FIG. 1 in the rotation direction R1 and at the same time the photoconductors 40Y, 40M, 40C, and 40K start rotating counterclockwise in FIG. 1 .
- the chargers 60Y, 60M, 60C, and 60K uniformly charge the photoconductors 40Y, 40M, 40C, and 40K; the exposure device 3 emits laser beams onto the charged photoconductors 40Y, 40M, 40C, and 40K according to image data sent from the scanner 3, thus forming electrostatic latent images thereon; and the development devices 61Y, 61M, 61C, and 61K develop the electrostatic latent images into yellow, magenta, cyan, and black toner images, respectively.
- the primary transfer devices 62Y, 62M, 62C, and 62K primarily transfer the yellow, magenta, cyan, and black toner images formed on the photoconductors 40Y, 40M, 40C, and 40K, respectively, onto the intermediate transfer belt 10 successively as the intermediate transfer belt 10 rotates in the rotation direction R1 so that the yellow, magenta, cyan, and black toner images are superimposed on a same position on the intermediate transfer belt 10, thus forming a color toner image thereon.
- one of a plurality of paper trays 44 situated inside a paper bank 43 of the paper storage 2 is selected according to a print job input by the user using the control panel. Accordingly, a pickup roller 42 corresponding to the selected paper tray 44 picks up and feeds an uppermost recording medium from a plurality of recording media loaded on the paper tray 44. A separation roller 45 separates the uppermost recording medium from other recording media and feeds the separated recording medium toward a conveyance path 46. Conveyance roller pairs 47 convey the recording medium through the conveyance path 46 toward a conveyance path 48 situated inside the body 1. As the recording medium comes into contact with a registration roller pair 49, the registration roller pair 49 halts the recording medium temporarily.
- a rotating pickup roller 50 picks up and feeds an uppermost recording medium toward a separation roller 52.
- the separation roller 52 separates the uppermost recording medium from other recording media and conveys the separated recording medium toward a conveyance path 53.
- the registration roller pair 49 halts the recording medium temporarily.
- the registration roller pair 49 resumes rotating at a time when the color toner image formed on the intermediate transfer belt 10 is transferred onto the recording medium conveyed through the secondary transfer region N formed between the intermediate transfer belt 10 and the secondary transfer device 22. Thereafter, the conveyance belt 24 conveys the recording medium bearing the color toner image to the fixing device 25 where the fixing belt 26 and the pressing roller 27 apply heat and pressure to the recording medium, fixing the color toner image on the recording medium. Then, a switch pawl 55 guides the recording medium toward an output roller pair 56 that discharges the recording medium onto an output tray 57 where the recording media bearing the fixed toner image are stacked.
- the switch pawl 55 guides the recording medium bearing the color toner image on a front side thereof toward the reverse device 28 that reverses and feeds the recording medium toward the secondary transfer region N formed between the secondary transfer device 22 and the intermediate transfer belt 10. As the recording medium is conveyed through the secondary transfer region N, another toner image is transferred from the intermediate transfer belt 10 onto a back side of the recording medium. After the recording medium is conveyed through the fixing device 25, the switch pawl 55 guides the recording medium toward the output roller pair 56 that discharges the recording medium onto the output tray 57.
- the support rollers 15 and 16 move to isolate the intermediate transfer belt 10 from the photoconductors 40Y, 40M, and 40C so that only the photoconductor 40K contacts the intermediate transfer belt 10 to allow the primary transfer device 62K to transfer the black toner image formed on the photoconductor 40K onto the intermediate transfer belt 10.
- the image forming apparatus 100 is a single drum image forming apparatus that incorporates a single photoconductor instead of a tandem image forming apparatus that incorporates the four photoconductors 40Y, 40M, 40C, and 40K shown in FIG.
- the image forming apparatus 100 forms a black toner image first to shorten a first print time required to output a recording medium bearing a toner image onto the output tray 57 after the image forming apparatus 100 receives a print job. Then, the image forming apparatus 100 forms yellow, magenta, and cyan toner images for a color print job.
- the registration roller pair 49 is grounded.
- the registration roller pair 49 may be applied with a bias to remove paper dust produced from the recording medium.
- a bias for example, if a conductive rubber roller having a diameter of 18 mm and a surface layer coated with a conductive nitrile-butadiene rubber (NBR) having a thickness of 1 mm is used as the registration roller pair 49 applied with a bias, since the conductive NBR has a volume resistivity of 10 9 ⁇ cm, the rubber roller contacting the front side of the recording medium bearing the toner image is applied with a voltage of -800 V and the rubber roller contacting the back side of the recording medium not bearing the toner image is applied with a voltage of +200 V.
- NBR conductive nitrile-butadiene rubber
- paper dust produced from the recording medium does not generally move to the photoconductors 40Y, 40M, 40C, and 40K. Accordingly, it is not necessary to take measures against paper dust that may be transferred onto the toner image. Consequently, the registration roller pair 49 can be grounded.
- the registration roller pair 49 is generally applied with a direct current bias.
- the registration roller pair 49 may be applied with an alternating current voltage having a direct current offset component to uniformly charge the recording medium. Accordingly, after the recording medium passes through the registration roller pair 49, the front side of the recording medium is negatively charged slightly. To address this circumstance, it may be necessary to set a secondary transfer condition different from that for the registration roller pair 49 applied with no voltage to secondarily transfer the color toner image from the intermediate transfer belt 10 onto the recording medium.
- toner sensor 5 disposed opposite the driving roller 14 via the intermediate transfer belt 10.
- the toner sensor 5 is disposed opposite the outer circumferential surface of the intermediate transfer belt 10 and serves as a toner detector that detects an amount of toner, that is, a density of toner, adhered to the outer circumferential surface of the intermediate transfer belt 10.
- the toner sensor 5 is constructed of an infrared-emitting diode used as a light emitting portion and a photodiode used as a diffuse reflection light receiving portion. The toner sensor 5 outputs voltage according to an amount of light received.
- FIG. 2 is a perspective view of the transfer unit 20.
- a toner patch TP is created on the outer circumferential surface of the intermediate transfer belt 10 to adjust the density of toner adhered to the intermediate transfer belt 10.
- a toner patch TP is formed on the respective photoconductors 40Y, 40M, 40C, and 40K and transferred onto the intermediate transfer belt 10 by the respective primary transfer devices 62Y, 62M, 62C, and 62K as the toner patch TP passes through a primary transfer nip formed between the respective photoconductors 40Y, 40M, 40C, and 40K and the intermediate transfer belt 10.
- the toner patch TP adheres to the intermediate transfer belt 10.
- a plurality of toner patches TP having different target densities is created for a plurality of colors of yellow, magenta, cyan, and black.
- the toner sensor 5 disposed opposite the intermediate transfer belt 10 detects the amount of toner, that is, the density of toner, of each toner patch TP.
- the toner sensor 5 detects the amount of toner of the toner patch TP in a process control mode, that is, a toner density adjustment mode, different from the image forming operation described above or during the image forming operation of forming a toner image on a plurality of recording media continuously by using a gap between successive toner images, that is, between successive recording media, on the intermediate transfer belt 10.
- FIG. 3 is a partially enlarged vertical sectional view of the photoconductor 40K and a toner density adjuster 95.
- a charging bias applicator 65 is connected to the charger 60K; a development bias applicator 66 is connected to the development device 61K; a toner supply unit 90K incorporating a toner supply motor 91K is connected to the development device 61K.
- the toner density adjuster 95 is operatively connected to the charging bias applicator 65, the development bias applicator 66, and the toner supply motor 91K of the toner supply unit 90K.
- the toner sensor 5 detects an amount of toner of the toner batch TP formed on the intermediate transfer belt 10. Based on the result detected by the toner sensor 5, the toner density adjuster 95 controls at least one of the charging bias applicator 65, the development bias applicator 66, and the toner supply motor 91K of the toner supply unit 90K to adjust the toner density of a toner image to be formed on the photoconductor 40K. For example, when adjusting the density of the toner image using the charging bias applicator 65, the toner density adjuster 95 controls the charging bias applicator 65 to adjust an amount of charging bias applied to the photoconductor 40K.
- the toner density adjuster 95 controls the toner supply motor 91K to adjust an amount of toner supplied to the development device 61K.
- the toner density adjuster 95 controls the development bias applicator 66 to adjust an amount of development bias applied to the photoconductor 40K.
- FIGS. 4A and 4B the following describes a configuration of a secondary transfer device separator 70 incorporated in the image forming apparatus 100 depicted in FIG. 1 according to a first exemplary embodiment.
- the secondary transfer device separator 70 moves the secondary transfer device 22 with respect to the intermediate transfer belt 10.
- FIG. 4A is a vertical sectional view of the intermediate transfer belt 10, the secondary transfer device 22, and the secondary transfer device separator 70 that brings the secondary transfer device 22 into contact with the intermediate transfer belt 10 at a contact position.
- FIG. 4B is a vertical sectional view of the intermediate transfer belt 10, the secondary transfer device 22, and the secondary transfer device separator 70 that isolates the secondary transfer device 22 from the intermediate transfer belt 10 at an isolation position.
- the secondary transfer device separator 70 includes a cam 71 having an outer circumferential face that contacts a contact point S of the secondary transfer device 22; a rotation shaft 71a supporting the cam 71; and a driver 72 (e.g., a motor) connected to and rotating the rotation shaft 71a.
- the driver 72 is operatively connected to a controller 73, that is, a central processing unit (CPU), provided with a random-access memory (RAM) and a read-only memory (ROM), for example.
- CPU central processing unit
- RAM random-access memory
- ROM read-only memory
- the secondary transfer device 22 keeps in contact with the outer circumferential face of the cam 71 by its weight. Accordingly, as the cam 71 rotates from the contact position shown in FIG. 4A to the isolation position shown in FIG. 4B , the secondary transfer device 22 rotates about a rotation shaft 22a clockwise in FIG. 4A from the contact position shown in FIG. 4A to the isolation position shown in FIG. 4B .
- FIG. 5 is a diagram illustrating a time when first to third recording media P1 to P3 bearing first to third toner images T1 to T3, respectively, and the toner patch TP formed on the intermediate transfer belt 10 pass through the secondary transfer region N and a time when the secondary transfer device 22 comes into contact with and isolation from the intermediate transfer belt 10.
- a toner patch TP is formed at a predetermined time in a gap between the successive toner images, that is, between the first toner image T1 and the second toner image T2, on the intermediate transfer belt 10.
- the toner patch TP detects the toner patch TP, performing process control, that is, toner density adjustment.
- process control that is, toner density adjustment.
- the toner patch TP formed on the intermediate transfer belt 10 passes through the secondary transfer region N, no recording medium is conveyed through the secondary transfer region N.
- the secondary transfer device 22 contacts the intermediate transfer belt 10 while the toner patch TP passes through the secondary transfer region N, the toner patch TP comes into contact with and adheres to the secondary transfer device 22. If the adhered toner patch TP is transferred from the secondary transfer device 22 onto a recording medium coming into the secondary transfer region N, the toner patch TP adheres to and stains the back side of the recording medium.
- the controller 73 controls the driver 72 to rotate the cam 71 as shown in FIG. 5 .
- the cam 71 isolates the secondary transfer device 22 from the intermediate transfer belt 10 at the isolation position shown in FIG. 4B .
- the controller 73 controls the driver 72 to start rotating the cam 71 at a time A shown in FIG. 5 . Specifically, the controller 73 determines the time A to start rotating the cam 71 so that half-turn of the cam 71 is completed and therefore the secondary transfer device 22 is isolated from the intermediate transfer belt 10 at the isolation position shown in FIG.
- the controller 73 controls the driver 72 to start rotating the cam 71 at a time C shown in FIG. 5 . Specifically, the controller 73 determines the time C to start rotating the cam 71 so that half-turn of the cam 71 is completed and therefore the secondary transfer device 22 comes into contact with the intermediate transfer belt 10 at the contact position shown in FIG. 4A at a time D shown in FIG. 5 before a leading edge of the second recording medium P2 enters the secondary transfer region N. That is, the cam 71 moves from the isolation position shown in FIG. 4B to the contact position shown in FIG. 4A within a shortened time M2, bringing the secondary transfer device 22 into contact with the intermediate transfer belt 10.
- the secondary transfer device 22 is isolated from the intermediate transfer belt 10. After the time D, the secondary transfer device 22 remains in contact with the intermediate transfer belt 10 while the second recording medium P2, a blank section S2 on the intermediate transfer belt 10 without the toner patch TP interposed between the second recording medium P2 and the third recording medium P3, and the third recording medium P3 are conveyed through the secondary transfer region N.
- FIGS. 6A, 6B, and 6C the following describes a configuration of a secondary transfer device separator 170 incorporated in the image forming apparatus 100 depicted in FIG. 1 according to a second exemplary embodiment.
- the secondary transfer device separator 170 moves the secondary transfer device 22 with respect to the intermediate transfer belt 10.
- FIG. 6A is a vertical sectional view of the intermediate transfer belt 10, the secondary transfer device 22, and the secondary transfer device separator 170 that brings the secondary transfer device 22 into contact with the intermediate transfer belt 10 at a contact position.
- FIG. 6B is a vertical sectional view of the intermediate transfer belt 10, the secondary transfer device 22, and the secondary transfer device separator 170 that isolates the secondary transfer device 22 from the intermediate transfer belt 10 at a first isolation position.
- FIG. 6C is a vertical sectional view of the intermediate transfer belt 10, the secondary transfer device 22, and the secondary transfer device separator 170 that isolates the secondary transfer device 22 from the intermediate transfer belt 10 at a second isolation position.
- the secondary transfer device separator 170 includes a cam 171 having an outer circumferential face that contacts the contact point S of the secondary transfer device 22; a rotation shaft 171a supporting the cam 171; and the driver 72 (e.g., a motor) connected to and rotating the rotation shaft 171a.
- the driver 72 is operatively connected to the controller 73. As the controller 73 drives the driver 72, the driver 72 rotates the rotation shaft 171a, thus rotating the cam 171.
- the secondary transfer device separator 170 includes the cam 171 that rotates and moves the secondary transfer device 22 with respect to the intermediate transfer belt 10.
- the secondary transfer device separator 170 isolates the secondary transfer device 22 from the intermediate transfer belt 10 at two positions, that is, the first isolation position shown in FIG. 6B where the secondary transfer device 22 is spaced apart from the intermediate transfer belt 10 with a first interval D1 therebetween and the second isolation position shown in FIG. 6C where the secondary transfer device 22 is spaced apart from the intermediate transfer belt 10 with a second interval D2 therebetween.
- the secondary transfer roller 22c of the secondary transfer device 22 comes into contact with the intermediate transfer belt 10 at the contact position shown in FIG. 6A .
- a length L1 from the rotation shaft 171a to the closer face 171c shown in FIG. 6B is greater than a length L2 from the rotation shaft 171a to the closest face 171d shown in FIG. 6C .
- the first interval D1 between the secondary transfer device 22 and the intermediate transfer belt 10 produced when the closer face 171c of the cam 171 contacts the contact point S of the secondary transfer device 22 is smaller than the second interval D2 between the secondary transfer device 22 and the intermediate transfer belt 10 produced when the closest face 171d of the cam 171 contacts the contact point S of the secondary transfer device 22.
- the cam 171 Since the cam 171 is rotatable clockwise and counterclockwise in FIG. 6A , the cam 171 moves the secondary transfer device 22 from any one of the contact position shown in FIG. 6A , the first isolation position shown in FIG. 6B , and the second isolation position shown in FIG. 6C to any other one of them.
- the cam 171 is shaped to have the farthest face 171b, the closer face 171c, and the closest face 171d. Accordingly, the cam 171 rotates clockwise or counterclockwise by 180 degrees from the contact position shown in FIG. 6A where the farthest face 171b contacts the secondary transfer device 22, thus moving to the first isolation position shown in FIG. 6B where the closer face 171c contacts the secondary transfer device 22.
- the cam 171 rotates clockwise or counterclockwise by 90 degrees from the contact position shown in FIG. 6A or the first isolation position shown in FIG. 6B , thus moving to the second isolation position shown in FIG. 6C where the closest face 171d contacts the secondary transfer device 22.
- the cam 171 may be shaped otherwise.
- FIGS. 7A, 7B, and 7C the following describes a configuration of a secondary transfer device separator 270 incorporated in the image forming apparatus 100 depicted in FIG. 1 according to a third exemplary embodiment.
- the secondary transfer device separator 270 moves the secondary transfer device 22 with respect to the intermediate transfer belt 10.
- FIG. 7A is a vertical sectional view of the intermediate transfer belt 10, the secondary transfer device 22, and the secondary transfer device separator 270 that brings the secondary transfer device 22 into contact with the intermediate transfer belt 10 at a contact position.
- FIG. 7B is a vertical sectional view of the intermediate transfer belt 10, the secondary transfer device 22, and the secondary transfer device separator 270 that isolates the secondary transfer device 22 from the intermediate transfer belt 10 at a first isolation position.
- FIG. 7C is a vertical sectional view of the intermediate transfer belt 10, the secondary transfer device 22, and the secondary transfer device separator 270 that isolates the secondary transfer device 22 from the intermediate transfer belt 10 at a second isolation position.
- the secondary transfer device separator 270 isolates the secondary transfer device 22 from the intermediate transfer belt 10 with the first interval D1 and the second interval D2 greater than the first interval D1 therebetween. However, unlike the secondary transfer device separator 170, the secondary transfer device separator 270 moves the secondary transfer device 22 by using two cams, that is, a first cam 271A and a second cam 271B.
- the secondary transfer device separator 270 is constructed of the first cam 271A, the second cam 271B, an arm 272, and a compressing spring 273.
- the first cam 271A presses against a free end 272b of the arm 272, that is, a left end in FIG. 7A disposed downstream from the secondary transfer roller 22c in a recording medium conveyance direction C1.
- the arm 272 is swingable about a swing shaft 272a mounted on a fixed end 272c of the arm 272, that is, a right end in FIG. 7A disposed upstream from the secondary transfer roller 22c in the recording medium conveyance direction C1.
- the first cam 271A rotates by 180 degrees from the contact position shown in FIG. 7A to the first isolation position shown in FIG. 7B and the second isolation position shown in FIG. 7C , the first cam 271A lowers the free end 272b of the arm 272 and therefore rotates the arm 272 about the swing shaft 272a. Accordingly, the arm 272 presses down the roller shaft 22b of the secondary transfer roller 22c, thus isolating the secondary transfer device 22 from the intermediate transfer belt 10.
- the second cam 271B contacts the compression spring 273 anchored to a lower face 22d of the secondary transfer device 22.
- the compression spring 273 constantly biases the secondary transfer device 22 upward. Accordingly, the roller shaft 22b of the secondary transfer roller 22c rotates the arm 272 to constantly move the free end 272b of the arm 272 upward, keeping the free end 272b of the arm 272 in contact with an outer circumferential face of the first cam 271A.
- a first driver 74 (e.g., a motor) is connected to the first cam 271A and a second driver 75 is connected to the second cam 271B.
- the first driver 74 and the second driver 75 are operatively connected to the controller 73.
- the controller 73 controls the first driver 74 to rotate the first cam 271A by 180 degrees from the contact position shown in FIG. 7A where the secondary transfer device 22 contacts the intermediate transfer belt 10
- the first cam 271A lowers the free end 272b of the arm 272 and the roller shaft 22b of the secondary transfer roller 22c, thus moving the secondary transfer device 22 to the first isolation position shown in FIG. 7B where the secondary transfer device 22 is isolated from the intermediate transfer belt 10 with the first interval D1 therebetween.
- first control method uses the secondary transfer device separator 170 shown in FIGS. 6A to 6C
- basic processes of the first control method are also applicable to the secondary transfer device separator 70 shown in FIGS. 4A and 4B , the secondary transfer device separator 270 shown in FIGS. 7A to 7C , and other secondary transfer device separators.
- FIG. 8 is a flowchart illustrating control processes of the first control method for moving the secondary transfer device 22 with respect to the intermediate transfer belt 10.
- step S1 the controller 73 receives a print job. If the controller 73 receives the print job (YES in step S1), the controller 73 controls the driver 72 to rotate the cam 171 clockwise in FIG. 6C by 90 degrees from the second isolation position shown in FIG. 6C to the contact position shown in FIG. 6A to bring the secondary transfer device 22 into contact with the intermediate transfer belt 10 before the first recording medium P1 enters the secondary transfer region N in step S2.
- step S3 the controller 73 starts printing, that is, the image forming operation described above, on the first recording medium P1.
- step S4 the controller 73 determines whether or not printing is finished, that is, whether or not there is a toner image to be transferred onto the intermediate transfer belt 10.
- step S4 the controller 73 determines whether or not a tailing edge of the first recording medium P1 has passed through the secondary transfer region N in step S10. If the controller 73 determines that the trailing edge of the first recording medium P1 has passed through the secondary transfer region N (YES in step S10), the controller 73 controls the driver 72 to rotate the cam 171 counterclockwise in FIG. 6A by 90 degrees from the contact position shown in FIG. 6A to the second isolation position shown in FIG. 6C , isolating the secondary transfer device 22 from the intermediate transfer belt 10 with the greater second interval D2 therebetween in step S11.
- the controller 73 determines whether or not to form a toner patch TP on the intermediate transfer belt 10 in the toner patch section S1 thereon interposed between the first toner image T1 transferred onto the first recording medium P1 and the subsequent, second toner image T2 to be transferred next onto the second recording medium P2 in step S5. If the controller 73 determines not to form the toner patch TP (NO in step S5), the controller 73 starts transferring the second toner image T2 onto the intermediate transfer belt 10 at a predetermined time.
- the secondary transfer device 22 remains in contact with the intermediate transfer belt 10 at the contact position shown in FIG. 6A . Accordingly, a passage time for which the blank section S2 of the intermediate transfer belt 10 passes through the secondary transfer region N is not restricted by a speed at which the secondary transfer device separator 170 isolates the secondary transfer device 22 from the intermediate transfer belt 10. Consequently, the passage time of the blank section S2 of the intermediate transfer belt 10 is shortened to a period of time that is available in the image forming apparatus 100.
- the controller 73 determines whether or not the tailing edge of the first recording medium P1 bearing the first toner image T1 has passed through the secondary transfer region N in step S6. If the controller 73 determines that the trailing edge of the first recording medium P1 has passed through the secondary transfer region N (YES in step S6), the controller 73 controls the driver 72 to rotate the cam 171 counterclockwise in FIG. 6A by 180 degrees from the contact position shown in FIG.
- step S8 the controller 73 determines whether or not a trailing edge of the toner patch TP has passed through the secondary transfer region N. If the controller 73 determines that the trailing edge of the toner patch TP has passed through the secondary transfer region N (YES in step S8), the controller 73 controls the driver 72 to rotate the cam 171 clockwise in FIG. 6B by 180 degrees from the first isolation position shown in FIG. 6B to the contact position shown in FIG. 6A within the shortened time M2, bringing the secondary transfer device 22 into contact with the intermediate transfer belt 10 in step S9 before the subsequent, second recording medium P2 enters the secondary transfer region N.
- the controller 73 starts transferring the second toner image T2 from the intermediate transfer belt 10 onto the second recording medium P2 at a predetermined time. While the toner patch TP formed in the toner patch section S1 on the intermediate transfer belt 10 interposed between the first toner image T1 transferred onto the first recording medium P1 and the subsequent, second toner image T2 passes through the secondary transfer region N, the secondary transfer device 22 remains in isolation from the intermediate transfer belt 10 at the first isolation position shown in FIG. 6B . Accordingly, the toner patch TP does not come into contact with the secondary transfer device 22 and therefore toner of the toner patch TP does not adhere to the secondary transfer device 22. Consequently, even if the subsequent, second recording medium P2 passes through the secondary transfer region N, toner of the toner patch TP does not adhere to and stain the back side of the second recording medium P2.
- control method described below is applicable to the secondary transfer device separator 70 shown in FIGS. 4A and 4B , the secondary transfer device separator 170 shown in FIGS. 6A to 6C , and the secondary transfer device separator 270 shown in FIGS. 7A to 7C .
- a secondary transfer bias applied at the secondary transfer region N is switched between a negative bias and a positive bias.
- a secondary transfer bias applicator 96 connected to the support roller 16 applies a secondary transfer bias to the support roller 16.
- the secondary transfer region N is applied with a positive secondary transfer bias opposite a negative secondary transfer bias applied while the secondary transfer device 22 contacts the intermediate transfer belt 10 to transfer the toner image formed on the intermediate transfer belt 10 onto the recording medium.
- FIG. 9 is a diagram of a control method according to the fourth exemplary embodiment illustrating a time when the first to third recording media P1 to P3 bearing the first to third toner images T1 to T3 and the toner patch TP formed on the intermediate transfer belt 10 pass through the secondary transfer region N and a time when the secondary transfer device 22 comes into contact with and isolation from the intermediate transfer belt 10.
- the toner image formed on the intermediate transfer belt 10 is transferred onto the recording medium by two bias application methods.
- a first method is to apply a secondary transfer bias having a polarity identical to a polarity of toner to the support roller 16 contacting an inner circumferential surface of the intermediate transfer belt 10.
- a second method is to apply a secondary transfer bias having a polarity opposite a polarity of toner to the secondary transfer device 22 contacting the back side of the recording medium.
- the first method of applying a negative secondary transfer bias identical to the negative polarity of toner to the support roller 16 is employed.
- the second method is also applicable.
- the secondary transfer device 22 is isolated from the intermediate transfer belt 10. After the time D, the secondary transfer device 22 remains in contact with the intermediate transfer belt 10 while the second recording medium P2, the blank section S2 on the intermediate transfer belt 10 without the toner patch TP interposed between the second recording medium P2 and the third recording medium P3, and the third recording medium P3 are conveyed through the secondary transfer region N.
- FIG. 10 is a flowchart illustrating control processes of the second control method for moving the secondary transfer device 22 with respect to the intermediate transfer belt 10.
- step S101 the controller 73 receives a print job. If the controller 73 receives the print job (YES in step S101), the controller 73 controls the driver 72 to rotate the cam 171 clockwise in FIG. 6C by 90 degrees from the second isolation position shown in FIG. 6C to the contact position shown in FIG. 6A to bring the secondary transfer device 22 into contact with the intermediate transfer belt 10 before the first recording medium P1 enters the secondary transfer region N in step S102.
- step S103 the controller 73 starts printing, that is, the image forming operation described above, on the first recording medium P1.
- step S104 the controller 73 determines whether or not printing is finished, that is, whether or not there is a toner image to be transferred onto the intermediate transfer belt 10.
- step S104 determines whether or not printing is finished (YES in step S104). If the controller 73 determines whether or not a tailing edge of the first recording medium P1 has passed through the secondary transfer region N in step S112. If the controller 73 determines that the trailing edge of the first recording medium P1 has passed through the secondary transfer region N (YES in step S112), the controller 73 controls the driver 72 to rotate the cam 171 counterclockwise in FIG. 6A by 90 degrees from the contact position shown in FIG. 6A to the second isolation position shown in FIG. 6C , isolating the secondary transfer device 22 from the intermediate transfer belt 10 with the greater second interval D2 therebetween in step S113.
- the controller 73 determines whether or not to form a toner patch TP on the intermediate transfer belt 10 in the toner patch section S1 thereon interposed between the first toner image T1 transferred onto the first recording medium P1 and the subsequent, second toner image T2 to be transferred next in step S105. If the controller 73 determines not to form the toner patch TP (NO in step S105), the controller 73 starts transferring the second toner image T2 onto the intermediate transfer belt 10 at a predetermined time.
- the secondary transfer device 22 remains in contact with the intermediate transfer belt 10 at the contact position shown in FIG. 6A . Accordingly, a passage time for which the blank section S2 of the intermediate transfer belt 10 passes through the secondary transfer region N is not restricted by a speed at which the secondary transfer device separator 170 isolates the secondary transfer device 22 from the intermediate transfer belt 10. Consequently, the passage time of the blank section S2 of the intermediate transfer belt 10 is shortened to a period of time that is available in the image forming apparatus 100.
- the controller 73 determines whether or not the tailing edge of the first recording medium P1 bearing the first toner image T1 has passed through the secondary transfer region N in step S106. If the controller 73 determines that the trailing edge of the first recording medium P1 has passed through the secondary transfer region N (YES in step S106), the controller 73 controls the driver 72 to rotate the cam 171 counterclockwise in FIG. 6A by 180 degrees from the contact position shown in FIG.
- the secondary transfer bias applicator 96 switches the secondary transfer bias applied to the support roller 16 from negative to positive in step S108.
- step S109 the controller 73 determines whether or not a trailing edge of the toner patch TP has passed through the secondary transfer region N. If the controller 73 determines that the trailing edge of the toner patch TP has passed through the secondary transfer region N (YES in step S109), the controller 73 controls the driver 72 to rotate the cam 171 clockwise in FIG. 6B by 180 degrees from the first isolation position shown in FIG. 6B to the contact position shown in FIG. 6A within the shortened time M2, bringing the secondary transfer device 22 into contact with the intermediate transfer belt 10 in step S110 before the subsequent, second recording medium P2 enters the secondary transfer region N. Simultaneously, the secondary transfer bias applicator 96 switches the secondary transfer bias applied to the support roller 16 from positive to negative in step S111.
- the controller 73 starts transferring the second toner image T2 from the intermediate transfer belt 10 onto the second recording medium P2 at a predetermined time. While the toner patch TP formed in the toner patch section S1 on the intermediate transfer belt 10 interposed between the first toner image T1 transferred onto the first recording medium P1 and the subsequent, second toner image T2 passes through the secondary transfer region N, the secondary transfer device 22 remains in isolation from the intermediate transfer belt 10 at the first isolation position shown in FIG. 6B . Accordingly, the toner patch TP does not come into contact with the secondary transfer device 22 and therefore toner of the toner patch TP does not adhere to the secondary transfer device 22. Consequently, even if the subsequent, second recording medium P2 passes through the secondary transfer region N, toner of the toner patch TP does not adhere to and stain the back side of the second recording medium P2.
- the following describes a comparative control method for turning the secondary transfer bias off while the secondary transfer device 22 is isolated from the intermediate transfer belt 10 instead of applying the positive secondary transfer bias as shown in FIG. 9 .
- FIG. 11 is a diagram of the comparative control method illustrating a time when the first to third recording media P1 to P3 bearing the first to third toner images T1 to T3 and the toner patch TP formed on the intermediate transfer belt 10 pass through the secondary transfer region N and a time when the secondary transfer device 22 comes into contact with and isolation from the intermediate transfer belt 10.
- the secondary transfer bias is switched off at a time A".
- the secondary transfer bias may not have reached zero.
- the secondary transfer bias is switched on.
- the secondary transfer bias has been turned negative.
- Switching off the secondary transfer bias according to the comparative control method shown in FIG. 11 may take longer to turn the secondary transfer bias to zero based on performance of a power supply compared to the fourth exemplary embodiment shown in FIG. 9 .
- the secondary transfer bias may not have reached zero at the time B" when the toner patch TP enters the secondary transfer region N.
- a potential difference between the intermediate transfer belt 10 and the secondary transfer device 22 may move and spatter toner onto the secondary transfer device 22, thus staining the secondary transfer device 22 with toner.
- the secondary transfer bias is switched to positive, that is, a polarity opposite the negative polarity of toner. Accordingly, an electric field is applied to the toner patch TP formed on the intermediate transfer belt 10 in a direction away from the secondary transfer device 22. Accordingly, toner does not spatter from the intermediate transfer belt 10 onto the secondary transfer device 22 and stain the secondary transfer device 22.
- the potential difference between the secondary transfer device 22 and the intermediate transfer belt 10 is turned to zero within a shortened time before the time B' shown in FIG. 9 compared to the comparative control method for turning the secondary transfer bias off as shown in FIG. 11 .
- the secondary transfer bias is under constant current control to retain a predetermined transfer electric field even if the resistance of the recording medium and the secondary transfer device 22 changes.
- the secondary transfer bias is switched from negative to positive while the secondary transfer device 22 is isolated from the intermediate transfer belt 10, such isolation may obstruct or hinder passage of an electric current.
- the positive secondary transfer bias applied while the secondary transfer device 22 is isolated from the intermediate transfer belt 10 is under constant current control, voltage is substantially increased for passage of a predetermined electric current. Consequently, the electric current may leak to an inappropriate location, degrading the toner image formed on the recording medium or damaging the components incorporated in the image forming apparatus 100.
- the positive secondary transfer bias applied while the secondary transfer device 22 is isolated from the intermediate transfer belt 10 is constant voltage controlled, preventing the above-described problem due to abnormal increase of voltage and spattering of toner from the intermediate transfer belt 10 onto the secondary transfer device 22.
- the image forming apparatus 100 includes the intermediate transfer belt 10 serving as a toner image carrier that carries a toner image formed thereon according to image data; the secondary transfer device 22 serving as a transfer device separatably contacting the intermediate transfer belt 10 to form the secondary transfer region N therebetween; the registration roller pair 49 serving as a recording medium feeder that feeds a recording medium to the secondary transfer region N; and the secondary transfer device separator 70, 170, or 270 serving as a transfer device separator that moves the secondary transfer device 22 with respect to the intermediate transfer belt 10, As the recording medium is conveyed through the secondary transfer region N formed between the intermediate transfer belt 10 and the secondary transfer device 22 by the secondary transfer device separator 70, 170, or 270 that brings the secondary transfer device 22 into contact with the intermediate transfer belt 10, the toner
- the image forming apparatus 100 receives a print job for forming a toner image on three or more recording media continuously, that is, a multiple print job, the image forming apparatus 100 forms a toner patch TP, that is, a non-transfer toner image not to be transferred onto a recording medium, on the intermediate transfer belt 10 at one of a plurality of gaps between successive toner images.
- the controller 73 controls the secondary transfer device separator 70, 170, or 270 to bring the secondary transfer device 22 into contact with the intermediate transfer belt 10 while the toner image formed on the intermediate transfer belt 10 is transferred onto the recording medium.
- the controller 73 controls the secondary transfer device separator 70, 170, or 270 to isolate the secondary transfer device 22 from the intermediate transfer belt 10 while the toner patch TP interposed between the first toner image T1 transferred onto the first recording medium P1 and the second toner image T2 to be transferred onto the second recording medium P2 passes through the secondary transfer region N. Accordingly, the toner patch TP does not come into contact with the secondary transfer device 22 and therefore toner of the toner patch TP does not stain the secondary transfer device 22. Consequently, even if the subsequent, second recording medium P2 passes through the secondary transfer region N, toner does not adhere to and stain the back side of the subsequent, second recording medium P2.
- the controller 73 controls the secondary transfer device separator 70, 170, or 270 to retain the secondary transfer device 22 in contact with the intermediate transfer belt 10 even during interval between a preceding transfer of transferring the second toner image T2 onto the second recording medium P2 and a subsequent transfer of transferring the third toner image T3 onto the third recording medium P3, not isolating the secondary transfer device 22 from the intermediate transfer belt 10.
- the gap between the successive toner images on the intermediate transfer belt 10 that carries no toner patch TP, that is, the blank section S2 interposed between the second toner image T2 and the third toner image T3, remains in contact with the secondary transfer device 22, eliminating a time required to isolate the secondary transfer device 22 from the intermediate transfer belt 10 and thus shortening a time for which the gap between the successive toner images, that is, the blank section S2 interposed between the second toner image T2 and the third toner image T3, passes through the secondary transfer region N regardless of the speed at which the secondary transfer device separator 70, 170, or 270 isolates the secondary transfer device 22 from the intermediate transfer belt 10.
- the image forming apparatus 100 shortens the time required to complete the multiple print job, improving productivity of the image forming apparatus 100.
- a passage time required for the gap between the successive toner images on the intermediate transfer belt 10 that carries no toner patch TP, that is, the blank section S2 interposed between the second toner image T2 and the third toner image T3, to pass through the secondary transfer region N in a state in which the secondary transfer device 22 contacts the intermediate transfer belt 10 is shorter than a passage time required for the gap between the successive toner images on the intermediate transfer belt 10 that carries the toner patch TP, that is, the toner patch section S1 interposed between the first toner image T1 and the second toner image T2, to pass through the secondary transfer region N in a state in which the secondary transfer device 22 is isolated from the intermediate transfer belt 10, thus shortening the time required to complete the multiple print job and improving productivity of the image forming apparatus 100.
- the secondary transfer device separators 170 and 270 isolate the secondary transfer device 22 from the intermediate transfer belt 10 with at least two switchable intervals therebetween, that is, the first interval D1 and the second interval D2 greater than the first interval D1.
- the controller 73 controls the secondary transfer device separators 70, 170, and 270 to move the secondary transfer device 22 with respect to the intermediate transfer belt 10 even at a predetermined time other than a multiple print job, for example, immediately after such multiple print job is finished.
- the controller 73 controls the secondary transfer device separator 70, 170, or 270 to isolate the secondary transfer device 22 from the intermediate transfer belt 10 with the first interval D1 smaller than the second interval D2 with which the secondary transfer device 22 is isolated from the intermediate transfer belt 10 immediately after a multiple print job is finished. Accordingly, control for isolating the secondary transfer device 22 from the intermediate transfer belt 10 while the toner patch TP passes through the secondary transfer region N shortens the time required to isolate the secondary transfer device 22 from the intermediate transfer belt 10 compared to control for isolating the secondary transfer device 22 from the intermediate transfer belt 10 immediately after a multiple print job is finished. Consequently, the time required to complete a multiple print job is shortened, improving productivity of the image forming apparatus 100.
- toner contained in the development devices 61Y, 61M, 61C, and 61K depicted in FIG. 1 is discharged to replace waste toner with fresh toner.
- the discharged waste toner is supplied from the development devices 61Y, 61M, 61C, and 61K onto the photoconductors 40Y, 40M, 40C, and 40K, respectively, and is further transferred from the photoconductors 40Y, 40M, 40C, and 40K onto the intermediate transfer belt 10.
- the belt cleaner 17 for cleaning the intermediate transfer belt 10 collects the transferred waste toner from the intermediate transfer belt 10.
- An amount of waste toner transferred onto the intermediate transfer belt 10 is substantially greater than an amount of toner of the toner patch TP.
- the secondary transfer device 22 is isolated from the intermediate transfer belt 10 with the smaller first interval D1 therebetween while the toner patch TP passes through the secondary transfer region N to prevent adhesion of toner of the toner patch TP to the secondary transfer device 22 and at the same time shorten the time to isolate the secondary transfer device 22 from the intermediate transfer belt 10.
- the secondary transfer device 22 is isolated from the intermediate transfer belt 10 with the smaller first interval D1 therebetween even while the waste toner discharged from the development devices 61Y, 61M, 61C, and 61K and transferred onto the intermediate transfer belt 10 passes through the secondary transfer region N, the waste toner of which amount is greater than the amount of toner of the toner patch TP may adhere to the secondary transfer device 22.
- the secondary transfer device separators 170 and 270 depicted in FIGS. 6A to 7C isolate the secondary transfer device 22 from the intermediate transfer belt 10 with the two switchable intervals, that is, the first interval D1 and the second interval D2 therebetween, thus minimizing adhesion of the waste toner to the secondary transfer device 22 immediately after a multiple print job is finished while preventing adhesion of toner of the toner patch TP to the secondary transfer device 22 and at the same time shortening the time to isolate the secondary transfer device 22 from the intermediate transfer belt 10.
- the secondary transfer device separators 170 and 270 move the secondary transfer device 22 from the first isolation position shown in FIGS. 6B and 7B or the second isolation position shown in FIGS. 6C and 7C to the contact position shown in FIGS. 6A and 7A and vise versa with a single motion, that is, a single movement of the cams 171, 271A, and 271B, with the simple configuration of the secondary transfer device separators 170 and 270. For example, as shown in FIGS.
- the secondary transfer device separator 170 includes the cam 171 having the farthest face 171b, the closer face 171c, and the closest face 171d that contact the contact point S on the secondary transfer device 22 and the driver 72 that rotates the cam 171 to the contact position, the first isolation position, and the second isolation position.
- the secondary transfer device separator 270 includes the first cam 271A and the second cam 271B that press against the secondary transfer device 22, the first driver 74 that rotates the first cam 271A, and the second driver 75 that rotates the second cam 271B.
- the secondary transfer device separators 170 and 270 are simplified.
- the controller 73 controls the driver 72, the first driver 74, and the second driver 75 to rotate the secondary transfer device separators 70, 170, and 270, thus isolating the secondary transfer device 22 from the intermediate transfer belt 10 at the first isolation position shown in FIGS. 4B , 6B , and 7B where the toner patch TP passes through the secondary transfer region N.
- the controller 73 controls the driver 72, the first driver 74, and the second driver 75 to rotate the secondary transfer device separators 70, 170, and 270, thus bringing the secondary transfer device 22 into contact with the intermediate transfer belt 10.
- the secondary transfer device separators 70, 170, and 270 isolate the secondary transfer device 22 from the intermediate transfer belt 10 as the thick recording medium enters the secondary transfer region N, preventing the leading edge of the thick recording medium from striking the secondary transfer device 22 at the entry to the secondary transfer region N. Accordingly, the thick recording medium does not vibrate the intermediate transfer belt 10, preventing formation of a faulty toner image due to vibration of the intermediate transfer belt 10.
- the toner patch TP created in the gap between the successive toner images, that is, the toner patch section S1 interposed between the first toner image T1 and the second toner image T2, on the intermediate transfer belt 10 during a multiple print job is a toner pattern used to adjust the density of toner of the toner images.
- the toner sensor 5 depicted in FIG. 1 serving as a toner detector detects an amount of toner of the toner pattern adhered to the intermediate transfer belt 10 so that adjustment of the density of the toner images, that is, a process control, is performed by the toner density adjuster 95 depicted in FIG. 3 based on the amount of toner of the toner pattern detected by the toner sensor 5.
- the toner pattern does not adhere to the secondary transfer device 22, preventing toner of the toner pattern from moving from the secondary transfer device 22 onto the back side of the subsequent, second recording medium P2 conveyed through the secondary transfer region N.
- the image forming apparatus 100 is a tandem color copier employing the intermediate transfer method.
- the image forming apparatus 100 includes the plurality of photoconductors 40Y, 40M, 40C, and 40K serving as electrostatic latent image carriers that carry electrostatic latent images and resultant yellow, magenta, cyan, and black toner images; and the intermediate transfer belt 10 serving as a toner image carrier or an intermediate transferor that carries the yellow, magenta, cyan, and black toner images transferred and superimposed on the intermediate transfer belt 10.
- the superimposed, yellow, magenta, cyan, and black toner images are formed into a color toner image and transferred onto a recording medium conveyed through the secondary transfer region N formed between the intermediate transfer belt 10 and the secondary transfer device 22.
- Yellow, magenta, cyan, and black toner patterns are created on the photoconductors 40Y, 40M, 40C, and 40K, respectively, and then transferred onto a single gap between successive toner images on the intermediate transfer belt 10, that is, the toner patch section S1 interposed between the first toner image T1 and the second toner image T2. Accordingly, the number of gaps between successive toner images where the toner pattern is created during a multiple print job decreases, and instead the number of gaps between successive toner images where no toner pattern is created increases, thus shortening passage time for which the gaps between the successive toner images where the toner pattern is created pass through the secondary transfer region N and improving productivity of the image forming apparatus 100 during a multiple print job.
- a plurality of toner sensors 5 may be provided to correspond to a plurality of toner patterns, that is, yellow, magenta, cyan, and black toner patterns, respectively.
- a single toner sensor 5 configured to detect a plurality of toner patterns, it is necessary to arrange the plurality of toner patterns in the rotation direction R1 of the intermediate transfer belt 10 in such a manner that the plurality of toner patterns travels under a detection region of the toner sensor 5 successively. In this case, it is necessary to lengthen the gap between the successive toner images where the plurality of toner patterns is created in the rotation direction R1 of the intermediate transfer belt 10, increasing the time for such longer gap to pass through the secondary transfer region N and thereby degrading productivity of the image forming apparatus 100.
- the plurality of toner sensors 5 allows the plurality of toner patterns to be arranged in a direction, that is, a width direction, orthogonal to the rotation direction R1 of the intermediate transfer belt 10 in such a manner that the plurality of toner patterns travels under the detection region of the plurality of toner sensors 5, respectively, at one time.
- the gap between the successive toner images where the plurality of toner patterns is created occupies a decreased length in the rotation direction R1 of the intermediate transfer belt 10 compared to the configuration in which the single toner sensor 5 detects the plurality of toner patterns, thus retaining productivity of the image forming apparatus 100.
- the secondary transfer bias is switched to positive opposite to the negative polarity of toner of the toner patch TP. Accordingly, toner of the toner patch TP does not spatter from the intermediate transfer belt 10 onto the secondary transfer device 22, preventing the toner from staining the secondary transfer device 22. Further, the positive secondary transfer bias applied while the secondary transfer device 22 is isolated from the intermediate transfer belt 10 is constant voltage controlled to prevent toner of the toner patch TP from spattering from the intermediate transfer belt 10 onto the secondary transfer device 22, minimizing abnormal voltage increase and resultant failures.
- the above-described exemplary embodiments are also applicable to an image forming apparatus employing a direct transfer method in which a toner image formed on a photoconductor is directly transferred onto a recording medium.
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Description
- Exemplary aspects of the present invention relate to an image forming apparatus, and more particularly, to an image forming apparatus for forming a toner image by transferring the toner image onto a recording medium directly or indirectly via an intermediate transferor.
- Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is primarily transferred from the photoconductor onto an intermediate transfer belt and secondarily transferred from the intermediate transfer belt onto a recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
- In order to form a toner image having a desired toner density, a toner patch is formed on the photoconductor, which is transferred onto the intermediate transfer belt. An optical sensor disposed opposite the intermediate transfer belt detects the toner density of the toner patch based on which image forming conditions such as the toner density of the toner image, the charging bias, and the development bias are adjusted. For example, if the image forming apparatus receives a multiple print job for forming a toner image on a plurality of recording media, the toner patch is created in a gap between successive toner images formed on the intermediate transfer belt. The toner image primarily transferred from the photoconductor onto the intermediate transfer belt is secondarily transferred onto the recording medium conveyed through a secondary transfer region formed between the intermediate transfer belt and a secondary transfer device pressed against the intermediate transfer belt. Since the toner patch should not be transferred onto the recording medium, no recording medium is conveyed through the secondary transfer region as the toner patch passes through the secondary transfer region. Accordingly, the toner patch created on the intermediate transfer belt may contact the secondary transfer device as it is conveyed through the secondary transfer region due to absence of the recording medium and toner may move from the toner patch to the secondary transfer device. Hence, as a subsequent recording medium is conveyed through the secondary transfer region, the toner may further move from the secondary transfer device to the back side of the subsequent recording medium that contacts the secondary transfer device, staining the subsequent recording medium.
- To address this problem, a sensor disposed upstream from the secondary transfer region in a recording medium conveyance direction may detect absence of a recording medium conveyed toward the secondary transfer region. Whenever the sensor detects such absence of the recording medium, the secondary transfer device separates from the intermediate transfer belt so that the toner patch created on the intermediate transfer belt does not come into contact with the secondary transfer device as it is conveyed through the secondary transfer region, thus preventing adhesion of toner of the toner patch to the secondary transfer device.
- However, since the secondary transfer device separates from the intermediate transfer belt whenever the sensor detects absence of the recording medium, the secondary transfer device comes into contact with and separates from the intermediate transfer belt repeatedly during the multiple print job for forming the toner image on the plurality of recording media. Since it takes time to bring the secondary transfer device into contact with and isolation from the intermediate transfer belt, an increased time may be consumed to finish the multiple print job, degrading productivity of the image forming apparatus.
- To address this problem, the secondary transfer device may move with respect to the intermediate transfer belt at an increased speed. However, the secondary transfer device moving at the increased speed may vibrate the intermediate transfer belt, degrading the toner image formed on the intermediate transfer belt.
EP 1 202 125 A2
JP 2007-286176 A
US 2007/0217801 A1 relates to an image forming apparatus and method for detecting separated state of the transfer unit. An image forming apparatus has a structure in which a toner image formed in an electrophotographic process is transferred from an intermediate transfer belt to a member to be transferred. The apparatus includes a secondary transfer roller that becomes a pressure contact state with respect to the intermediate transfer belt to make it perform a transfer process and can move between the pressure contact state and a separated state, and a press and separation driving device for driving the secondary transfer roller to become the pressure contact state and the separated state. The pressure contact state or the separated state of the secondary transfer roller is detected in accordance with a variation of an output of an IDC sensor for detecting a state of a bare surface of the intermediate transfer belt. - The invention is defined by the appended claims.
- A more complete appreciation of the invention and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
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FIG. 1 is a schematic vertical sectional view of an image forming apparatus according to an exemplary embodiment of the present invention; -
FIG. 2 is a perspective view of a transfer unit incorporated in the image forming apparatus shown inFIG. 1 ; -
FIG. 3 is a partially enlarged vertical sectional view of a photoconductor and a toner density adjuster incorporated in the image forming apparatus shown inFIG. 1 ; -
FIG. 4A is a vertical sectional view of an intermediate transfer belt, a secondary transfer device, and a secondary transfer device separator according to a first exemplary embodiment incorporated in the image forming apparatus shown inFIG. 1 in a state in which the secondary transfer device contacts the intermediate transfer belt; -
FIG. 4B is a vertical sectional view of the intermediate transfer belt, the secondary transfer device, and the secondary transfer device separator shown inFIG. 4A in a state in which the secondary transfer device is isolated from the intermediate transfer belt; -
FIG. 5 is a diagram illustrating a control method according to the first exemplary embodiment; -
FIG. 6A is a vertical sectional view of the intermediate transfer belt, the secondary transfer device, and a secondary transfer device separator according to a second exemplary embodiment incorporated in the image forming apparatus shown inFIG. 1 in a state in which the secondary transfer device contacts the intermediate transfer belt; -
FIG. 6B is a vertical sectional view of the intermediate transfer belt, the secondary transfer device, and the secondary transfer device separator shown inFIG. 6A in a state in which the secondary transfer device is isolated from the intermediate transfer belt at a first isolation position; -
FIG. 6C is a vertical sectional view of the intermediate transfer belt, the secondary transfer device, and the secondary transfer device separator shown inFIG. 6A in a state in which the secondary transfer device is isolated from the intermediate transfer belt at a second isolation position; -
FIG. 7A is a vertical sectional view of the intermediate transfer belt, the secondary transfer device, and a secondary transfer device separator according to a third exemplary embodiment incorporated in the image forming apparatus shown inFIG. 1 in a state in which the secondary transfer device contacts the intermediate transfer belt; -
FIG. 7B is a vertical sectional view of the intermediate transfer belt, the secondary transfer device, and the secondary transfer device separator shown inFIG. 7A in a state in which the secondary transfer device is isolated from the intermediate transfer belt at a first isolation position; -
FIG. 7C is a vertical sectional view of the intermediate transfer belt, the secondary transfer device, and the secondary transfer device separator shown inFIG. 7A in a state in which the secondary transfer device is isolated from the intermediate transfer belt at a second isolation position; -
FIG. 8 is a flowchart illustrating first control processes for moving the secondary transfer device shown inFIGS. 6A to 6C with respect to the intermediate transfer belt; -
FIG. 9 is a diagram of a control method according to a fourth exemplary embodiment; -
FIG. 10 is a flowchart illustrating second control processes for moving the secondary transfer device shown inFIGS. 6A to 6C with respect to the intermediate transfer belt; and -
FIG. 11 is a diagram of a comparative control method. - Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, in particular to
FIG. 1 , animage forming apparatus 100 according to an exemplary embodiment of the present invention is explained. -
FIG. 1 is a schematic vertical sectional view of theimage forming apparatus 100. Theimage forming apparatus 100 may be a copier, a facsimile machine, a printer, a multifunction printer having at least one of copying, printing, scanning, plotter, and facsimile functions, or the like. According to this exemplary embodiment, theimage forming apparatus 100 is a tandem color copier for forming a color toner image on a recording medium by electrophotography. Theimage forming apparatus 100 employs an intermediate transfer method using anintermediate transfer belt 10 serving as a toner image carrier that carries a toner image to be transferred onto a recording medium. Theimage forming apparatus 100 is constructed of apaper storage 2 disposed in a lower portion thereof, abody 1 disposed above thepaper storage 2, ascanner 3 disposed above thebody 1, and an auto document feeder (ADF) 4 disposed above thescanner 3. - The
body 1 includes atransfer unit 20 in substantially a center portion thereof. Thetransfer unit 20 incorporates the endlessintermediate transfer belt 10 stretched over a drivingroller 14 andsupport rollers roller 14 drives and rotates theintermediate transfer belt 10 clockwise inFIG. 1 in a rotation direction R1, thesupport rollers intermediate transfer belt 10 by friction therebetween. Downstream from thesupport roller 16 in the rotation direction R1 of theintermediate transfer belt 10 is abelt cleaner 17 that removes residual toner remaining on an outer circumferential surface of theintermediate transfer belt 10 after a toner image is transferred from theintermediate transfer belt 10 onto a recording medium as described below, thus rendering theintermediate transfer belt 10 to be ready for the next transfer operation. - Above the
intermediate transfer belt 10 are four drum-shapedphotoconductors intermediate transfer belt 10. Thephotoconductors photoconductors FIG. 1 and surrounded bychargers development devices primary transfer devices photoconductor cleaners dischargers 64Y, 64M, 64C, and 64K, respectively. Above thephotoconductors exposure device 21. - Below the
intermediate transfer belt 10 is asecondary transfer device 22 serving as a transfer device or a secondary transferor. Thesecondary transfer device 22 is pressed against thesupport roller 16 via theintermediate transfer belt 10 to form a secondary transfer region N between thesecondary transfer device 22 and theintermediate transfer belt 10. As a recording medium is conveyed through the secondary transfer region N, thesecondary transfer device 22 secondarily transfers the yellow, magenta, cyan, and black toner images formed on theintermediate transfer belt 10 onto the recording medium collectively, thus forming a color toner image on the recording medium. - Downstream from the
secondary transfer device 22 in a recording medium conveyance direction is anendless conveyance belt 24 looped over a pair ofrollers 23 that conveys the recording medium bearing the color toner image toward a fixingdevice 25 disposed downstream from theconveyance belt 24 in the recording medium conveyance direction. The fixingdevice 25 includes anendless fixing belt 26 and apressing roller 27 pressed against the fixingbelt 26 to form a fixing nip therebetween through which the recording medium is conveyed. As the recording medium is conveyed through the fixing nip, the fixingbelt 26 and thepressing roller 27 apply heat and pressure to the recording medium, melting and fixing the color toner image on the recording medium. Below thesecondary transfer device 22 is areverse device 28 that reverses the recording medium conveyed from the fixingdevice 25 for duplex printing. - The following describes a copying operation of the
image forming apparatus 100 having the structure described above to form a color toner image on a recording medium. - As a user places an original document on an
original document tray 30 of theADF 4 and presses a start button on a control panel disposed atop thebody 1, conveyance rollers of theADF 4 automatically convey the original document onto an exposure glass 32 of thescanner 3 and thescanner 3 starts scanning the original document. Alternatively, as the user lifts theADF 4, places an original document on the exposure glass 32 manually, lowers theADF 4 to press the original document against the exposure glass 32, and presses the start button on the control panel, thescanner 3 starts scanning the original document. For example, as afirst carriage 33 and asecond carriage 34 of thescanner 3 move, a light source mounted on thefirst carriage 33 emits light onto the original document placed on the exposure glass 32. A mirror mounted on thefirst carriage 33 deflects light reflected by the original document toward thesecond carriage 34. A pair of mirrors mounted on thesecond carriage 34 deflects light by 180 degrees toward a readingsensor 36 through animage forming lens 35 so that the readingsensor 36 reads an image on the original document into image data. - On the other hand, as the user presses the start button on the control panel, the
intermediate transfer belt 10 starts rotating clockwise inFIG. 1 in the rotation direction R1 and at the same time thephotoconductors FIG. 1 . As thephotoconductors chargers photoconductors exposure device 3 emits laser beams onto the charged photoconductors 40Y, 40M, 40C, and 40K according to image data sent from thescanner 3, thus forming electrostatic latent images thereon; and thedevelopment devices primary transfer devices photoconductors intermediate transfer belt 10 successively as theintermediate transfer belt 10 rotates in the rotation direction R1 so that the yellow, magenta, cyan, and black toner images are superimposed on a same position on theintermediate transfer belt 10, thus forming a color toner image thereon. - On the other hand, one of a plurality of
paper trays 44 situated inside apaper bank 43 of thepaper storage 2 is selected according to a print job input by the user using the control panel. Accordingly, apickup roller 42 corresponding to the selectedpaper tray 44 picks up and feeds an uppermost recording medium from a plurality of recording media loaded on thepaper tray 44. Aseparation roller 45 separates the uppermost recording medium from other recording media and feeds the separated recording medium toward aconveyance path 46. Conveyance roller pairs 47 convey the recording medium through theconveyance path 46 toward aconveyance path 48 situated inside thebody 1. As the recording medium comes into contact with aregistration roller pair 49, theregistration roller pair 49 halts the recording medium temporarily. Alternatively, if the user places a plurality of recording media onto abypass tray 51, arotating pickup roller 50 picks up and feeds an uppermost recording medium toward aseparation roller 52. Theseparation roller 52 separates the uppermost recording medium from other recording media and conveys the separated recording medium toward aconveyance path 53. As the recording medium comes into contact with theregistration roller pair 49, theregistration roller pair 49 halts the recording medium temporarily. - Whether the recording medium is sent from the
paper tray 44 or thebypass tray 51, theregistration roller pair 49 resumes rotating at a time when the color toner image formed on theintermediate transfer belt 10 is transferred onto the recording medium conveyed through the secondary transfer region N formed between theintermediate transfer belt 10 and thesecondary transfer device 22. Thereafter, theconveyance belt 24 conveys the recording medium bearing the color toner image to the fixingdevice 25 where the fixingbelt 26 and thepressing roller 27 apply heat and pressure to the recording medium, fixing the color toner image on the recording medium. Then, aswitch pawl 55 guides the recording medium toward anoutput roller pair 56 that discharges the recording medium onto anoutput tray 57 where the recording media bearing the fixed toner image are stacked. - If the user selects duplex printing, the
switch pawl 55 guides the recording medium bearing the color toner image on a front side thereof toward thereverse device 28 that reverses and feeds the recording medium toward the secondary transfer region N formed between thesecondary transfer device 22 and theintermediate transfer belt 10. As the recording medium is conveyed through the secondary transfer region N, another toner image is transferred from theintermediate transfer belt 10 onto a back side of the recording medium. After the recording medium is conveyed through the fixingdevice 25, theswitch pawl 55 guides the recording medium toward theoutput roller pair 56 that discharges the recording medium onto theoutput tray 57. If the user selects monochrome printing, thesupport rollers intermediate transfer belt 10 from thephotoconductors intermediate transfer belt 10 to allow theprimary transfer device 62K to transfer the black toner image formed on thephotoconductor 40K onto theintermediate transfer belt 10. If theimage forming apparatus 100 is a single drum image forming apparatus that incorporates a single photoconductor instead of a tandem image forming apparatus that incorporates the fourphotoconductors FIG. 1 , theimage forming apparatus 100 forms a black toner image first to shorten a first print time required to output a recording medium bearing a toner image onto theoutput tray 57 after theimage forming apparatus 100 receives a print job. Then, theimage forming apparatus 100 forms yellow, magenta, and cyan toner images for a color print job. - Generally, the
registration roller pair 49 is grounded. However, theregistration roller pair 49 may be applied with a bias to remove paper dust produced from the recording medium. For example, if a conductive rubber roller having a diameter of 18 mm and a surface layer coated with a conductive nitrile-butadiene rubber (NBR) having a thickness of 1 mm is used as theregistration roller pair 49 applied with a bias, since the conductive NBR has a volume resistivity of 109 Ω·cm, the rubber roller contacting the front side of the recording medium bearing the toner image is applied with a voltage of -800 V and the rubber roller contacting the back side of the recording medium not bearing the toner image is applied with a voltage of +200 V. In theimage forming apparatus 100 incorporating theintermediate transfer belt 10, paper dust produced from the recording medium does not generally move to thephotoconductors registration roller pair 49 can be grounded. - Further, the
registration roller pair 49 is generally applied with a direct current bias. Alternatively, theregistration roller pair 49 may be applied with an alternating current voltage having a direct current offset component to uniformly charge the recording medium. Accordingly, after the recording medium passes through theregistration roller pair 49, the front side of the recording medium is negatively charged slightly. To address this circumstance, it may be necessary to set a secondary transfer condition different from that for theregistration roller pair 49 applied with no voltage to secondarily transfer the color toner image from theintermediate transfer belt 10 onto the recording medium. - Referring to
FIGS. 1 and2 , the following describes atoner sensor 5 disposed opposite the drivingroller 14 via theintermediate transfer belt 10. - As shown in
FIG. 1 , thetoner sensor 5 is disposed opposite the outer circumferential surface of theintermediate transfer belt 10 and serves as a toner detector that detects an amount of toner, that is, a density of toner, adhered to the outer circumferential surface of theintermediate transfer belt 10. Thetoner sensor 5 is constructed of an infrared-emitting diode used as a light emitting portion and a photodiode used as a diffuse reflection light receiving portion. Thetoner sensor 5 outputs voltage according to an amount of light received. -
FIG. 2 is a perspective view of thetransfer unit 20. As shown inFIG. 2 , a toner patch TP is created on the outer circumferential surface of theintermediate transfer belt 10 to adjust the density of toner adhered to theintermediate transfer belt 10. Initially, a toner patch TP is formed on therespective photoconductors intermediate transfer belt 10 by the respectiveprimary transfer devices respective photoconductors intermediate transfer belt 10. Thus, the toner patch TP adheres to theintermediate transfer belt 10. Generally, a plurality of toner patches TP having different target densities is created for a plurality of colors of yellow, magenta, cyan, and black. Thetoner sensor 5 disposed opposite theintermediate transfer belt 10 detects the amount of toner, that is, the density of toner, of each toner patch TP. For example, thetoner sensor 5 detects the amount of toner of the toner patch TP in a process control mode, that is, a toner density adjustment mode, different from the image forming operation described above or during the image forming operation of forming a toner image on a plurality of recording media continuously by using a gap between successive toner images, that is, between successive recording media, on theintermediate transfer belt 10. - Referring to
FIG. 3 , a description is now given of adjustment of image density, also referred to as a toner density, for a black toner image, as a representative example of the adjustment of image density. - Although not illustrated, the density of toner for cyan, magenta, and yellow is adjusted in the same manner.
FIG. 3 is a partially enlarged vertical sectional view of thephotoconductor 40K and atoner density adjuster 95. - As shown in
FIG. 3 , a chargingbias applicator 65 is connected to thecharger 60K; adevelopment bias applicator 66 is connected to thedevelopment device 61K; atoner supply unit 90K incorporating atoner supply motor 91K is connected to thedevelopment device 61K. Thetoner density adjuster 95 is operatively connected to the chargingbias applicator 65, thedevelopment bias applicator 66, and thetoner supply motor 91K of thetoner supply unit 90K. - The
toner sensor 5 detects an amount of toner of the toner batch TP formed on theintermediate transfer belt 10. Based on the result detected by thetoner sensor 5, thetoner density adjuster 95 controls at least one of the chargingbias applicator 65, thedevelopment bias applicator 66, and thetoner supply motor 91K of thetoner supply unit 90K to adjust the toner density of a toner image to be formed on thephotoconductor 40K. For example, when adjusting the density of the toner image using the chargingbias applicator 65, thetoner density adjuster 95 controls the chargingbias applicator 65 to adjust an amount of charging bias applied to thephotoconductor 40K. When adjusting the density of the toner image using thetoner supply motor 91K, thetoner density adjuster 95 controls thetoner supply motor 91K to adjust an amount of toner supplied to thedevelopment device 61K. When adjusting the density of the toner image using thedevelopment bias applicator 66, thetoner density adjuster 95 controls thedevelopment bias applicator 66 to adjust an amount of development bias applied to thephotoconductor 40K. - Referring to
FIGS. 4A and 4B , the following describes a configuration of a secondarytransfer device separator 70 incorporated in theimage forming apparatus 100 depicted inFIG. 1 according to a first exemplary embodiment. - The secondary
transfer device separator 70 moves thesecondary transfer device 22 with respect to theintermediate transfer belt 10. - A detailed description is now given of a construction and an operation of the secondary
transfer device separator 70. -
FIG. 4A is a vertical sectional view of theintermediate transfer belt 10, thesecondary transfer device 22, and the secondarytransfer device separator 70 that brings thesecondary transfer device 22 into contact with theintermediate transfer belt 10 at a contact position.FIG. 4B is a vertical sectional view of theintermediate transfer belt 10, thesecondary transfer device 22, and the secondarytransfer device separator 70 that isolates thesecondary transfer device 22 from theintermediate transfer belt 10 at an isolation position. - As shown in
FIGS. 4A and 4B , the secondarytransfer device separator 70 includes acam 71 having an outer circumferential face that contacts a contact point S of thesecondary transfer device 22; arotation shaft 71a supporting thecam 71; and a driver 72 (e.g., a motor) connected to and rotating therotation shaft 71a. Thedriver 72 is operatively connected to acontroller 73, that is, a central processing unit (CPU), provided with a random-access memory (RAM) and a read-only memory (ROM), for example. As thecontroller 73 drives thedriver 72, thedriver 72 rotates therotation shaft 71a, thus rotating thecam 71. As afarthest face 71b of thecam 71 farthest from therotation shaft 71a comes into contact with the contact point S of thesecondary transfer device 22, asecondary transfer roller 22c of thesecondary transfer device 22 comes into contact with theintermediate transfer belt 10 at the contact position shown inFIG. 4A . Conversely, as thecam 71 rotates from the contact position shown inFIG. 4A by 180 degrees and thereby aclosest face 71c of thecam 71 closest to therotation shaft 71a comes into contact with the contact point S of thesecondary transfer device 22, thesecondary transfer roller 22c of thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 at the isolation position shown inFIG. 4B . - As the
cam 71 rotates from the contact position shown inFIG. 4A to the isolation position shown inFIG. 4B , thesecondary transfer device 22 keeps in contact with the outer circumferential face of thecam 71 by its weight. Accordingly, as thecam 71 rotates from the contact position shown inFIG. 4A to the isolation position shown inFIG. 4B , thesecondary transfer device 22 rotates about arotation shaft 22a clockwise inFIG. 4A from the contact position shown inFIG. 4A to the isolation position shown inFIG. 4B . - Referring to
FIG. 5 , the following describes a control method for moving thesecondary transfer device 22 with respect to theintermediate transfer belt 10. -
FIG. 5 is a diagram illustrating a time when first to third recording media P1 to P3 bearing first to third toner images T1 to T3, respectively, and the toner patch TP formed on theintermediate transfer belt 10 pass through the secondary transfer region N and a time when thesecondary transfer device 22 comes into contact with and isolation from theintermediate transfer belt 10. According to the first exemplary embodiment, during a print job for forming a toner image on a plurality of recording media continuously (hereinafter referred to as a multiple print job), a toner patch TP is formed at a predetermined time in a gap between the successive toner images, that is, between the first toner image T1 and the second toner image T2, on theintermediate transfer belt 10. Thetoner sensor 5 depicted inFIG. 1 detects the toner patch TP, performing process control, that is, toner density adjustment. As the toner patch TP formed on theintermediate transfer belt 10 passes through the secondary transfer region N, no recording medium is conveyed through the secondary transfer region N. Hence, if thesecondary transfer device 22 contacts theintermediate transfer belt 10 while the toner patch TP passes through the secondary transfer region N, the toner patch TP comes into contact with and adheres to thesecondary transfer device 22. If the adhered toner patch TP is transferred from thesecondary transfer device 22 onto a recording medium coming into the secondary transfer region N, the toner patch TP adheres to and stains the back side of the recording medium. - To address this problem, the
controller 73 controls thedriver 72 to rotate thecam 71 as shown inFIG. 5 . Thus, while the toner patch TP, that is, toner not to be transferred onto a recording medium, passes through the secondary transfer region N, thecam 71 isolates thesecondary transfer device 22 from theintermediate transfer belt 10 at the isolation position shown inFIG. 4B . - For example, in a state in which the
secondary transfer device 22 contacts theintermediate transfer belt 10 at the contact position shown inFIG. 4A , immediately before a toner patch TP is formed on theintermediate transfer belt 10, the first toner image T1 formed on theintermediate transfer belt 10 is secondarily transferred onto the first recording medium PI conveyed through the secondary transfer region N. After a trailing edge of the first recording medium P1 passes through the secondary transfer region N, thecontroller 73 controls thedriver 72 to start rotating thecam 71 at a time A shown inFIG. 5 . Specifically, thecontroller 73 determines the time A to start rotating thecam 71 so that half-turn of thecam 71 is completed and therefore thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 at the isolation position shown inFIG. 4B at a time B shown inFIG. 5 before a leading edge of the toner patch TP enters the secondary transfer region N. That is, thecam 71 moves from the contact position shown inFIG. 4A to the isolation position shown inFIG. 4B within a shortened time M1, thus isolating thesecondary transfer device 22 from theintermediate transfer belt 10 quickly. - After a trailing edge of the toner patch TP passes through the secondary transfer region N, the
controller 73 controls thedriver 72 to start rotating thecam 71 at a time C shown inFIG. 5 . Specifically, thecontroller 73 determines the time C to start rotating thecam 71 so that half-turn of thecam 71 is completed and therefore thesecondary transfer device 22 comes into contact with theintermediate transfer belt 10 at the contact position shown inFIG. 4A at a time D shown inFIG. 5 before a leading edge of the second recording medium P2 enters the secondary transfer region N. That is, thecam 71 moves from the isolation position shown inFIG. 4B to the contact position shown inFIG. 4A within a shortened time M2, bringing thesecondary transfer device 22 into contact with theintermediate transfer belt 10. - Accordingly, while a toner patch section S1 on the
intermediate transfer belt 10 defined as an interval between the time B and the time C passes through the secondary transfer region N, thesecondary transfer device 22 is isolated from theintermediate transfer belt 10. After the time D, thesecondary transfer device 22 remains in contact with theintermediate transfer belt 10 while the second recording medium P2, a blank section S2 on theintermediate transfer belt 10 without the toner patch TP interposed between the second recording medium P2 and the third recording medium P3, and the third recording medium P3 are conveyed through the secondary transfer region N. - Referring to
FIGS. 6A, 6B, and 6C , the following describes a configuration of a secondarytransfer device separator 170 incorporated in theimage forming apparatus 100 depicted inFIG. 1 according to a second exemplary embodiment. - The secondary
transfer device separator 170 moves thesecondary transfer device 22 with respect to theintermediate transfer belt 10. - A detailed description is now given of a construction and an operation of the secondary
transfer device separator 170. -
FIG. 6A is a vertical sectional view of theintermediate transfer belt 10, thesecondary transfer device 22, and the secondarytransfer device separator 170 that brings thesecondary transfer device 22 into contact with theintermediate transfer belt 10 at a contact position.FIG. 6B is a vertical sectional view of theintermediate transfer belt 10, thesecondary transfer device 22, and the secondarytransfer device separator 170 that isolates thesecondary transfer device 22 from theintermediate transfer belt 10 at a first isolation position.FIG. 6C is a vertical sectional view of theintermediate transfer belt 10, thesecondary transfer device 22, and the secondarytransfer device separator 170 that isolates thesecondary transfer device 22 from theintermediate transfer belt 10 at a second isolation position. - As shown in
FIGS. 6A to 6C , the secondarytransfer device separator 170 includes acam 171 having an outer circumferential face that contacts the contact point S of thesecondary transfer device 22; arotation shaft 171a supporting thecam 171; and the driver 72 (e.g., a motor) connected to and rotating therotation shaft 171a. Thedriver 72 is operatively connected to thecontroller 73. As thecontroller 73 drives thedriver 72, thedriver 72 rotates therotation shaft 171a, thus rotating thecam 171. Like the secondarytransfer device separator 70 depicted inFIGS. 4A and 4B , the secondarytransfer device separator 170 includes thecam 171 that rotates and moves thesecondary transfer device 22 with respect to theintermediate transfer belt 10. However, unlike the secondarytransfer device separator 70, the secondarytransfer device separator 170 isolates thesecondary transfer device 22 from theintermediate transfer belt 10 at two positions, that is, the first isolation position shown inFIG. 6B where thesecondary transfer device 22 is spaced apart from theintermediate transfer belt 10 with a first interval D1 therebetween and the second isolation position shown inFIG. 6C where thesecondary transfer device 22 is spaced apart from theintermediate transfer belt 10 with a second interval D2 therebetween. For example, as afarthest face 171b of thecam 171 farthest from therotation shaft 171a comes into contact with the contact point S of thesecondary transfer device 22, thesecondary transfer roller 22c of thesecondary transfer device 22 comes into contact with theintermediate transfer belt 10 at the contact position shown inFIG. 6A . - Conversely, as the
cam 171 rotates clockwise or counterclockwise inFIG. 6A by 180 degrees from the contact position shown inFIG. 6A and thereby acloser face 171c of thecam 171 closer to therotation shaft 171a than thefarthest face 171b comes into contact with the contact point S of thesecondary transfer device 22, thesecondary transfer roller 22c of thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 at the first isolation position shown inFIG. 6B where thesecondary transfer device 22 is spaced apart from theintermediate transfer belt 10 with the first interval D1 therebetween. As thecam 171 rotates counterclockwise inFIG. 6A by 90 degrees from the contact position shown inFIG. 6A and thereby aclosest face 171d of thecam 171 closest to therotation shaft 171a comes into contact with the contact point S of thesecondary transfer device 22, thesecondary transfer roller 22c of thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 at the second isolation position shown inFIG. 6C where thesecondary transfer device 22 is spaced apart from theintermediate transfer belt 10 with the second interval D2 greater than the first interval D1 therebetween. A length L1 from therotation shaft 171a to thecloser face 171c shown inFIG. 6B is greater than a length L2 from therotation shaft 171a to theclosest face 171d shown inFIG. 6C . Hence, the first interval D1 between thesecondary transfer device 22 and theintermediate transfer belt 10 produced when thecloser face 171c of thecam 171 contacts the contact point S of thesecondary transfer device 22 is smaller than the second interval D2 between thesecondary transfer device 22 and theintermediate transfer belt 10 produced when theclosest face 171d of thecam 171 contacts the contact point S of thesecondary transfer device 22. - Since the
cam 171 is rotatable clockwise and counterclockwise inFIG. 6A , thecam 171 moves thesecondary transfer device 22 from any one of the contact position shown inFIG. 6A , the first isolation position shown inFIG. 6B , and the second isolation position shown inFIG. 6C to any other one of them. According to the second exemplary embodiment, thecam 171 is shaped to have thefarthest face 171b, thecloser face 171c, and theclosest face 171d. Accordingly, thecam 171 rotates clockwise or counterclockwise by 180 degrees from the contact position shown inFIG. 6A where thefarthest face 171b contacts thesecondary transfer device 22, thus moving to the first isolation position shown inFIG. 6B where thecloser face 171c contacts thesecondary transfer device 22. Further, thecam 171 rotates clockwise or counterclockwise by 90 degrees from the contact position shown inFIG. 6A or the first isolation position shown inFIG. 6B , thus moving to the second isolation position shown inFIG. 6C where theclosest face 171d contacts thesecondary transfer device 22. Alternatively, thecam 171 may be shaped otherwise. - Referring to
FIGS. 7A, 7B, and 7C , the following describes a configuration of a secondarytransfer device separator 270 incorporated in theimage forming apparatus 100 depicted inFIG. 1 according to a third exemplary embodiment. - The secondary
transfer device separator 270 moves thesecondary transfer device 22 with respect to theintermediate transfer belt 10. - A detailed description is now given of a construction and an operation of the secondary
transfer device separator 270. -
FIG. 7A is a vertical sectional view of theintermediate transfer belt 10, thesecondary transfer device 22, and the secondarytransfer device separator 270 that brings thesecondary transfer device 22 into contact with theintermediate transfer belt 10 at a contact position.FIG. 7B is a vertical sectional view of theintermediate transfer belt 10, thesecondary transfer device 22, and the secondarytransfer device separator 270 that isolates thesecondary transfer device 22 from theintermediate transfer belt 10 at a first isolation position.FIG. 7C is a vertical sectional view of theintermediate transfer belt 10, thesecondary transfer device 22, and the secondarytransfer device separator 270 that isolates thesecondary transfer device 22 from theintermediate transfer belt 10 at a second isolation position. - Like the secondary
transfer device separator 170 depicted inFIGS. 6A to 6C , the secondarytransfer device separator 270 isolates thesecondary transfer device 22 from theintermediate transfer belt 10 with the first interval D1 and the second interval D2 greater than the first interval D1 therebetween. However, unlike the secondarytransfer device separator 170, the secondarytransfer device separator 270 moves thesecondary transfer device 22 by using two cams, that is, afirst cam 271A and asecond cam 271B. - For example, the secondary
transfer device separator 270 is constructed of thefirst cam 271A, thesecond cam 271B, anarm 272, and acompressing spring 273. Thefirst cam 271A presses against afree end 272b of thearm 272, that is, a left end inFIG. 7A disposed downstream from thesecondary transfer roller 22c in a recording medium conveyance direction C1. Thearm 272 is swingable about aswing shaft 272a mounted on afixed end 272c of thearm 272, that is, a right end inFIG. 7A disposed upstream from thesecondary transfer roller 22c in the recording medium conveyance direction C1. A substantial center of thearm 272 in the recording medium conveyance direction C1 contacts aroller shaft 22b of thesecondary transfer roller 22c at each axial end of thesecondary transfer roller 22c in an axial direction thereof. As thefirst cam 271A rotates by 180 degrees from the contact position shown inFIG. 7A to the first isolation position shown inFIG. 7B and the second isolation position shown inFIG. 7C , thefirst cam 271A lowers thefree end 272b of thearm 272 and therefore rotates thearm 272 about theswing shaft 272a. Accordingly, thearm 272 presses down theroller shaft 22b of thesecondary transfer roller 22c, thus isolating thesecondary transfer device 22 from theintermediate transfer belt 10. - The
second cam 271B contacts thecompression spring 273 anchored to alower face 22d of thesecondary transfer device 22. Thecompression spring 273 constantly biases thesecondary transfer device 22 upward. Accordingly, theroller shaft 22b of thesecondary transfer roller 22c rotates thearm 272 to constantly move thefree end 272b of thearm 272 upward, keeping thefree end 272b of thearm 272 in contact with an outer circumferential face of thefirst cam 271A. - As shown in
FIG. 7A , a first driver 74 (e.g., a motor) is connected to thefirst cam 271A and asecond driver 75 is connected to thesecond cam 271B. Thefirst driver 74 and thesecond driver 75 are operatively connected to thecontroller 73. As thecontroller 73 controls thefirst driver 74 to rotate thefirst cam 271A by 180 degrees from the contact position shown inFIG. 7A where thesecondary transfer device 22 contacts theintermediate transfer belt 10, thefirst cam 271A lowers thefree end 272b of thearm 272 and theroller shaft 22b of thesecondary transfer roller 22c, thus moving thesecondary transfer device 22 to the first isolation position shown inFIG. 7B where thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 with the first interval D1 therebetween. At the first isolation position, since thecompression spring 273 biases thesecondary transfer device 22 upward, theroller shaft 22b of thesecondary transfer roller 22c contacting thearm 272 retains thesecondary transfer roller 22c at the first isolation position shown inFIG. 7B where thesecondary transfer roller 22c is isolated from theintermediate transfer belt 10 with the first interval D1 therebetween. - Conversely, as the
controller 73 controls thesecond driver 75 to rotate thesecond cam 271B by 180 degrees from the first isolation position shown inFIG. 7B , a lower end of thecompression spring 273 lowers and decreases an amount of compression of thecompression spring 273, thus decreasing bias of the compressingspring 273 that biases thesecondary transfer device 22 upward. Accordingly, weight of thesecondary transfer device 22 lowers an upper end of thecompression spring 273, thus retaining thesecondary transfer device 22 at the second isolation position shown inFIG. 7C where weight of thesecondary transfer device 22 and bias of thecompression spring 273 are balanced. Consequently, thesecondary transfer device 22 moves to the second isolation position shown inFIG. 7C where thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 with the second interval D2 therebetween greater than the first interval D1 created at the first isolation position shown inFIG. 7B . - Referring to
FIG. 8 , the following describes an example of a first control method for moving thesecondary transfer device 22 with respect to theintermediate transfer belt 10. - It is to be noted that although the first control method below uses the secondary
transfer device separator 170 shown inFIGS. 6A to 6C , basic processes of the first control method are also applicable to the secondarytransfer device separator 70 shown inFIGS. 4A and 4B , the secondarytransfer device separator 270 shown inFIGS. 7A to 7C , and other secondary transfer device separators. -
FIG. 8 is a flowchart illustrating control processes of the first control method for moving thesecondary transfer device 22 with respect to theintermediate transfer belt 10. - In step S1, the
controller 73 receives a print job. If thecontroller 73 receives the print job (YES in step S1), thecontroller 73 controls thedriver 72 to rotate thecam 171 clockwise inFIG. 6C by 90 degrees from the second isolation position shown inFIG. 6C to the contact position shown inFIG. 6A to bring thesecondary transfer device 22 into contact with theintermediate transfer belt 10 before the first recording medium P1 enters the secondary transfer region N in step S2. In step S3, thecontroller 73 starts printing, that is, the image forming operation described above, on the first recording medium P1. In step S4, thecontroller 73 determines whether or not printing is finished, that is, whether or not there is a toner image to be transferred onto theintermediate transfer belt 10. If thecontroller 73 determines that printing is finished (YES in step S4), thecontroller 73 determines whether or not a tailing edge of the first recording medium P1 has passed through the secondary transfer region N in step S10. If thecontroller 73 determines that the trailing edge of the first recording medium P1 has passed through the secondary transfer region N (YES in step S10), thecontroller 73 controls thedriver 72 to rotate thecam 171 counterclockwise inFIG. 6A by 90 degrees from the contact position shown inFIG. 6A to the second isolation position shown inFIG. 6C , isolating thesecondary transfer device 22 from theintermediate transfer belt 10 with the greater second interval D2 therebetween in step S11. - On the other hand, if the
controller 73 determines that printing is not finished, that is, if thecontroller 73 determines that there is the subsequent, second toner image T2 to be transferred onto the intermediate transfer belt 10 (NO in step S4), thecontroller 73 determines whether or not to form a toner patch TP on theintermediate transfer belt 10 in the toner patch section S1 thereon interposed between the first toner image T1 transferred onto the first recording medium P1 and the subsequent, second toner image T2 to be transferred next onto the second recording medium P2 in step S5. If thecontroller 73 determines not to form the toner patch TP (NO in step S5), thecontroller 73 starts transferring the second toner image T2 onto theintermediate transfer belt 10 at a predetermined time. Even while the blank section S2, without the toner patch TP, on theintermediate transfer belt 10 interposed between the preceding, second toner image T2 transferred onto the second recording medium P2 and the subsequent, third toner image T3 passes through the secondary transfer region N, thesecondary transfer device 22 remains in contact with theintermediate transfer belt 10 at the contact position shown inFIG. 6A . Accordingly, a passage time for which the blank section S2 of theintermediate transfer belt 10 passes through the secondary transfer region N is not restricted by a speed at which the secondarytransfer device separator 170 isolates thesecondary transfer device 22 from theintermediate transfer belt 10. Consequently, the passage time of the blank section S2 of theintermediate transfer belt 10 is shortened to a period of time that is available in theimage forming apparatus 100. - If the
controller 73 determines to form the toner patch TP and therefore the toner patch TP is created on theintermediate transfer belt 10 in the toner patch section S1 between the first toner image T1 already transferred onto theintermediate transfer belt 10 and the second toner image T2 to be transferred onto the intermediate transfer belt 10 (YES in step S5), thecontroller 73 determines whether or not the tailing edge of the first recording medium P1 bearing the first toner image T1 has passed through the secondary transfer region N in step S6. If thecontroller 73 determines that the trailing edge of the first recording medium P1 has passed through the secondary transfer region N (YES in step S6), thecontroller 73 controls thedriver 72 to rotate thecam 171 counterclockwise inFIG. 6A by 180 degrees from the contact position shown inFIG. 6A to the first isolation position shown inFIG. 6B within the shortened time M1, isolating thesecondary transfer device 22 from theintermediate transfer belt 10 with the smaller first interval D1 therebetween in step S7 before the toner patch TP formed on theintermediate transfer belt 10 enters the secondary transfer region N. - In step S8, the
controller 73 determines whether or not a trailing edge of the toner patch TP has passed through the secondary transfer region N. If thecontroller 73 determines that the trailing edge of the toner patch TP has passed through the secondary transfer region N (YES in step S8), thecontroller 73 controls thedriver 72 to rotate thecam 171 clockwise inFIG. 6B by 180 degrees from the first isolation position shown inFIG. 6B to the contact position shown inFIG. 6A within the shortened time M2, bringing thesecondary transfer device 22 into contact with theintermediate transfer belt 10 in step S9 before the subsequent, second recording medium P2 enters the secondary transfer region N. Thereafter, thecontroller 73 starts transferring the second toner image T2 from theintermediate transfer belt 10 onto the second recording medium P2 at a predetermined time. While the toner patch TP formed in the toner patch section S1 on theintermediate transfer belt 10 interposed between the first toner image T1 transferred onto the first recording medium P1 and the subsequent, second toner image T2 passes through the secondary transfer region N, thesecondary transfer device 22 remains in isolation from theintermediate transfer belt 10 at the first isolation position shown inFIG. 6B . Accordingly, the toner patch TP does not come into contact with thesecondary transfer device 22 and therefore toner of the toner patch TP does not adhere to thesecondary transfer device 22. Consequently, even if the subsequent, second recording medium P2 passes through the secondary transfer region N, toner of the toner patch TP does not adhere to and stain the back side of the second recording medium P2. - Referring to
FIG. 9 , the following describes a control method for moving thesecondary transfer device 22 with respect to theintermediate transfer belt 10 according to a fourth exemplary embodiment. - It is to be noted that the control method described below is applicable to the secondary
transfer device separator 70 shown inFIGS. 4A and 4B , the secondarytransfer device separator 170 shown inFIGS. 6A to 6C , and the secondarytransfer device separator 270 shown inFIGS. 7A to 7C . - According to the fourth exemplary embodiment, a secondary transfer bias applied at the secondary transfer region N is switched between a negative bias and a positive bias. As shown in
FIGS. 4A, 4B ,6A to 6C , and7A to 7C , a secondarytransfer bias applicator 96 connected to thesupport roller 16 applies a secondary transfer bias to thesupport roller 16. For example, while thesecondary transfer device 22 is isolated from theintermediate transfer belt 10, the secondary transfer region N is applied with a positive secondary transfer bias opposite a negative secondary transfer bias applied while thesecondary transfer device 22 contacts theintermediate transfer belt 10 to transfer the toner image formed on theintermediate transfer belt 10 onto the recording medium.FIG. 9 is a diagram of a control method according to the fourth exemplary embodiment illustrating a time when the first to third recording media P1 to P3 bearing the first to third toner images T1 to T3 and the toner patch TP formed on theintermediate transfer belt 10 pass through the secondary transfer region N and a time when thesecondary transfer device 22 comes into contact with and isolation from theintermediate transfer belt 10. - Generally, the toner image formed on the
intermediate transfer belt 10 is transferred onto the recording medium by two bias application methods. A first method is to apply a secondary transfer bias having a polarity identical to a polarity of toner to thesupport roller 16 contacting an inner circumferential surface of theintermediate transfer belt 10. A second method is to apply a secondary transfer bias having a polarity opposite a polarity of toner to thesecondary transfer device 22 contacting the back side of the recording medium. According to the fourth exemplary embodiment, the first method of applying a negative secondary transfer bias identical to the negative polarity of toner to thesupport roller 16 is employed. However, the second method is also applicable. - As shown in
FIG. 9 , after the trailing edge of the preceding, first recording medium P1 passes through the secondary transfer region N formed between thesecondary transfer device 22 and theintermediate transfer belt 10, the secondary transfer bias applied from the secondarytransfer bias applicator 96 to thesupport roller 16 is switched from negative to positive at a time A'. Hence, by a time B' when the toner patch TP enters the secondary transfer region N, the secondary transfer bias has been turned positive. At a time C' when the toner patch TP has passed through the secondary transfer region N, the secondary transfer bias is switched from positive to negative. By a time D' before the leading edge of the subsequent, second recording medium P2 enters the secondary transfer region N, the secondary transfer bias has been turned negative. That is, while the toner patch section S1 on theintermediate transfer belt 10 defined as an interval between the time B and the time C passes through the secondary transfer region N, thesecondary transfer device 22 is isolated from theintermediate transfer belt 10. After the time D, thesecondary transfer device 22 remains in contact with theintermediate transfer belt 10 while the second recording medium P2, the blank section S2 on theintermediate transfer belt 10 without the toner patch TP interposed between the second recording medium P2 and the third recording medium P3, and the third recording medium P3 are conveyed through the secondary transfer region N. - Referring to
FIG. 10 , the following describes an example of a second control method for moving thesecondary transfer device 22 with respect to theintermediate transfer belt 10. - It is to be noted that although the second control method below uses the secondary
transfer device separator 170 shown inFIGS. 6A to 6C , basic processes of the second control method are also applicable to the secondarytransfer device separator 70 shown inFIGS. 4A and 4B , the secondarytransfer device separator 270 shown inFIGS. 7A to 7C , and other secondary transfer device separators. -
FIG. 10 is a flowchart illustrating control processes of the second control method for moving thesecondary transfer device 22 with respect to theintermediate transfer belt 10. - In step S101, the
controller 73 receives a print job. If thecontroller 73 receives the print job (YES in step S101), thecontroller 73 controls thedriver 72 to rotate thecam 171 clockwise inFIG. 6C by 90 degrees from the second isolation position shown inFIG. 6C to the contact position shown inFIG. 6A to bring thesecondary transfer device 22 into contact with theintermediate transfer belt 10 before the first recording medium P1 enters the secondary transfer region N in step S102. In step S103, thecontroller 73 starts printing, that is, the image forming operation described above, on the first recording medium P1. In step S104, thecontroller 73 determines whether or not printing is finished, that is, whether or not there is a toner image to be transferred onto theintermediate transfer belt 10. If thecontroller 73 determines that printing is finished (YES in step S104), thecontroller 73 determines whether or not a tailing edge of the first recording medium P1 has passed through the secondary transfer region N in step S112. If thecontroller 73 determines that the trailing edge of the first recording medium P1 has passed through the secondary transfer region N (YES in step S112), thecontroller 73 controls thedriver 72 to rotate thecam 171 counterclockwise inFIG. 6A by 90 degrees from the contact position shown inFIG. 6A to the second isolation position shown inFIG. 6C , isolating thesecondary transfer device 22 from theintermediate transfer belt 10 with the greater second interval D2 therebetween in step S113. - On the other hand, if the
controller 73 determines that printing is not finished, that is, if thecontroller 73 determines that there is the subsequent, second toner image T2 to be transferred onto the intermediate transfer belt 10 (NO in step S104), thecontroller 73 determines whether or not to form a toner patch TP on theintermediate transfer belt 10 in the toner patch section S1 thereon interposed between the first toner image T1 transferred onto the first recording medium P1 and the subsequent, second toner image T2 to be transferred next in step S105. If thecontroller 73 determines not to form the toner patch TP (NO in step S105), thecontroller 73 starts transferring the second toner image T2 onto theintermediate transfer belt 10 at a predetermined time. Even while the blank section S2, without the toner patch TP, on theintermediate transfer belt 10 interposed between the preceding, second toner image T2 transferred onto the second recording medium P2 and the subsequent, third toner image T3 passes through the secondary transfer region N, thesecondary transfer device 22 remains in contact with theintermediate transfer belt 10 at the contact position shown inFIG. 6A . Accordingly, a passage time for which the blank section S2 of theintermediate transfer belt 10 passes through the secondary transfer region N is not restricted by a speed at which the secondarytransfer device separator 170 isolates thesecondary transfer device 22 from theintermediate transfer belt 10. Consequently, the passage time of the blank section S2 of theintermediate transfer belt 10 is shortened to a period of time that is available in theimage forming apparatus 100. - If the
controller 73 determines to form the toner patch TP and therefore the toner patch TP is created on theintermediate transfer belt 10 in the toner patch section S1 between the first toner image T1 already transferred onto theintermediate transfer belt 10 and the second toner image T2 to be transferred onto the intermediate transfer belt 10 (YES in step S105), thecontroller 73 determines whether or not the tailing edge of the first recording medium P1 bearing the first toner image T1 has passed through the secondary transfer region N in step S106. If thecontroller 73 determines that the trailing edge of the first recording medium P1 has passed through the secondary transfer region N (YES in step S106), thecontroller 73 controls thedriver 72 to rotate thecam 171 counterclockwise inFIG. 6A by 180 degrees from the contact position shown inFIG. 6A to the first isolation position shown inFIG. 6B within the shortened time M1, isolating thesecondary transfer device 22 from theintermediate transfer belt 10 with the smaller first interval D1 therebetween in step S107 before the toner patch TP formed on theintermediate transfer belt 10 enters the secondary transfer region N. Simultaneously, the secondarytransfer bias applicator 96 switches the secondary transfer bias applied to thesupport roller 16 from negative to positive in step S108. - In step S109, the
controller 73 determines whether or not a trailing edge of the toner patch TP has passed through the secondary transfer region N. If thecontroller 73 determines that the trailing edge of the toner patch TP has passed through the secondary transfer region N (YES in step S109), thecontroller 73 controls thedriver 72 to rotate thecam 171 clockwise inFIG. 6B by 180 degrees from the first isolation position shown inFIG. 6B to the contact position shown inFIG. 6A within the shortened time M2, bringing thesecondary transfer device 22 into contact with theintermediate transfer belt 10 in step S110 before the subsequent, second recording medium P2 enters the secondary transfer region N. Simultaneously, the secondarytransfer bias applicator 96 switches the secondary transfer bias applied to thesupport roller 16 from positive to negative in step S111. - Thereafter, the
controller 73 starts transferring the second toner image T2 from theintermediate transfer belt 10 onto the second recording medium P2 at a predetermined time. While the toner patch TP formed in the toner patch section S1 on theintermediate transfer belt 10 interposed between the first toner image T1 transferred onto the first recording medium P1 and the subsequent, second toner image T2 passes through the secondary transfer region N, thesecondary transfer device 22 remains in isolation from theintermediate transfer belt 10 at the first isolation position shown inFIG. 6B . Accordingly, the toner patch TP does not come into contact with thesecondary transfer device 22 and therefore toner of the toner patch TP does not adhere to thesecondary transfer device 22. Consequently, even if the subsequent, second recording medium P2 passes through the secondary transfer region N, toner of the toner patch TP does not adhere to and stain the back side of the second recording medium P2. - Referring to
FIG. 11 , the following describes a comparative control method for turning the secondary transfer bias off while thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 instead of applying the positive secondary transfer bias as shown inFIG. 9 . -
FIG. 11 is a diagram of the comparative control method illustrating a time when the first to third recording media P1 to P3 bearing the first to third toner images T1 to T3 and the toner patch TP formed on theintermediate transfer belt 10 pass through the secondary transfer region N and a time when thesecondary transfer device 22 comes into contact with and isolation from theintermediate transfer belt 10. - As shown in
FIG. 11 , after the trailing edge of the preceding, first recording medium P1 passes through the secondary transfer region N formed between thesecondary transfer device 22 and theintermediate transfer belt 10, the secondary transfer bias is switched off at a time A". Hence, at a time B" when the toner patch TP enters the secondary transfer region N, the secondary transfer bias may not have reached zero. At a time C" when the toner patch TP has passed through the secondary transfer region N, the secondary transfer bias is switched on. By a time D" before the leading edge of the subsequent, second recording medium P2 enters the secondary transfer region N, the secondary transfer bias has been turned negative. - Switching off the secondary transfer bias according to the comparative control method shown in
FIG. 11 may take longer to turn the secondary transfer bias to zero based on performance of a power supply compared to the fourth exemplary embodiment shown inFIG. 9 . Further, the secondary transfer bias may not have reached zero at the time B" when the toner patch TP enters the secondary transfer region N. In this case, a potential difference between theintermediate transfer belt 10 and thesecondary transfer device 22 may move and spatter toner onto thesecondary transfer device 22, thus staining thesecondary transfer device 22 with toner. - To address this problem, according to the fourth exemplary embodiment shown in
FIG. 9 , while thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 after the trailing edge of the preceding, first recording medium P1 is discharged from the secondary transfer region N and before the leading edge of the subsequent, second recording medium P2 enters the secondary transfer region N, the secondary transfer bias is switched to positive, that is, a polarity opposite the negative polarity of toner. Accordingly, an electric field is applied to the toner patch TP formed on theintermediate transfer belt 10 in a direction away from thesecondary transfer device 22. Accordingly, toner does not spatter from theintermediate transfer belt 10 onto thesecondary transfer device 22 and stain thesecondary transfer device 22. Although it takes some time to switch the polarity of the secondary transfer bias based on performance of the power supply, the potential difference between thesecondary transfer device 22 and theintermediate transfer belt 10 is turned to zero within a shortened time before the time B' shown inFIG. 9 compared to the comparative control method for turning the secondary transfer bias off as shown inFIG. 11 . - Generally, the secondary transfer bias is under constant current control to retain a predetermined transfer electric field even if the resistance of the recording medium and the
secondary transfer device 22 changes. However, if the secondary transfer bias is switched from negative to positive while thesecondary transfer device 22 is isolated from theintermediate transfer belt 10, such isolation may obstruct or hinder passage of an electric current. Accordingly, if the positive secondary transfer bias applied while thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 is under constant current control, voltage is substantially increased for passage of a predetermined electric current. Consequently, the electric current may leak to an inappropriate location, degrading the toner image formed on the recording medium or damaging the components incorporated in theimage forming apparatus 100. - To address this problem, according to the fourth exemplary embodiment shown in
FIG. 9 , the positive secondary transfer bias applied while thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 is constant voltage controlled, preventing the above-described problem due to abnormal increase of voltage and spattering of toner from theintermediate transfer belt 10 onto thesecondary transfer device 22. - The following describes advantages of the secondary
transfer device separators FIGS. 1 ,4A ,4B ,6A, 6B, 6C ,7A, 7B, and 7C , theimage forming apparatus 100 includes theintermediate transfer belt 10 serving as a toner image carrier that carries a toner image formed thereon according to image data; thesecondary transfer device 22 serving as a transfer device separatably contacting theintermediate transfer belt 10 to form the secondary transfer region N therebetween; theregistration roller pair 49 serving as a recording medium feeder that feeds a recording medium to the secondary transfer region N; and the secondarytransfer device separator secondary transfer device 22 with respect to theintermediate transfer belt 10, As the recording medium is conveyed through the secondary transfer region N formed between theintermediate transfer belt 10 and thesecondary transfer device 22 by the secondarytransfer device separator secondary transfer device 22 into contact with theintermediate transfer belt 10, the toner image formed on theintermediate transfer belt 10 is transferred onto the recording medium, thus forming the toner image on the recording medium according to the image data. - If the
image forming apparatus 100 receives a print job for forming a toner image on three or more recording media continuously, that is, a multiple print job, theimage forming apparatus 100 forms a toner patch TP, that is, a non-transfer toner image not to be transferred onto a recording medium, on theintermediate transfer belt 10 at one of a plurality of gaps between successive toner images. Thecontroller 73 controls the secondarytransfer device separator secondary transfer device 22 into contact with theintermediate transfer belt 10 while the toner image formed on theintermediate transfer belt 10 is transferred onto the recording medium. Conversely, thecontroller 73 controls the secondarytransfer device separator secondary transfer device 22 from theintermediate transfer belt 10 while the toner patch TP interposed between the first toner image T1 transferred onto the first recording medium P1 and the second toner image T2 to be transferred onto the second recording medium P2 passes through the secondary transfer region N. Accordingly, the toner patch TP does not come into contact with thesecondary transfer device 22 and therefore toner of the toner patch TP does not stain thesecondary transfer device 22. Consequently, even if the subsequent, second recording medium P2 passes through the secondary transfer region N, toner does not adhere to and stain the back side of the subsequent, second recording medium P2. - When at least one gap between a preceding toner image and a subsequent toner image adjacent to the preceding toner image on the
intermediate transfer belt 10 where no toner patch TP is formed passes through the secondary transfer region N, that is, when the blank section S2 between the second recording medium P2 and the third recording medium P3 passes through the secondary transfer region N, thecontroller 73 controls the secondarytransfer device separator secondary transfer device 22 in contact with theintermediate transfer belt 10 even during interval between a preceding transfer of transferring the second toner image T2 onto the second recording medium P2 and a subsequent transfer of transferring the third toner image T3 onto the third recording medium P3, not isolating thesecondary transfer device 22 from theintermediate transfer belt 10. Accordingly, the gap between the successive toner images on theintermediate transfer belt 10 that carries no toner patch TP, that is, the blank section S2 interposed between the second toner image T2 and the third toner image T3, remains in contact with thesecondary transfer device 22, eliminating a time required to isolate thesecondary transfer device 22 from theintermediate transfer belt 10 and thus shortening a time for which the gap between the successive toner images, that is, the blank section S2 interposed between the second toner image T2 and the third toner image T3, passes through the secondary transfer region N regardless of the speed at which the secondarytransfer device separator secondary transfer device 22 from theintermediate transfer belt 10. - That is, compared to conventional image forming apparatuses in which all of the gaps between the successive toner images pass through the secondary transfer region N for an extended time increased by the speed at which the
secondary transfer device 22 is isolated from theintermediate transfer belt 10, theimage forming apparatus 100 shortens the time required to complete the multiple print job, improving productivity of theimage forming apparatus 100. For example, a passage time required for the gap between the successive toner images on theintermediate transfer belt 10 that carries no toner patch TP, that is, the blank section S2 interposed between the second toner image T2 and the third toner image T3, to pass through the secondary transfer region N in a state in which thesecondary transfer device 22 contacts theintermediate transfer belt 10 is shorter than a passage time required for the gap between the successive toner images on theintermediate transfer belt 10 that carries the toner patch TP, that is, the toner patch section S1 interposed between the first toner image T1 and the second toner image T2, to pass through the secondary transfer region N in a state in which thesecondary transfer device 22 is isolated from theintermediate transfer belt 10, thus shortening the time required to complete the multiple print job and improving productivity of theimage forming apparatus 100. - As shown in
FIGS. 6A to 7C , the secondarytransfer device separators secondary transfer device 22 from theintermediate transfer belt 10 with at least two switchable intervals therebetween, that is, the first interval D1 and the second interval D2 greater than the first interval D1. Thecontroller 73 controls the secondarytransfer device separators secondary transfer device 22 with respect to theintermediate transfer belt 10 even at a predetermined time other than a multiple print job, for example, immediately after such multiple print job is finished. - In order to isolate the
secondary transfer device 22 from theintermediate transfer belt 10 during passage of the toner patch TP through the secondary transfer region N, thecontroller 73 controls the secondarytransfer device separator secondary transfer device 22 from theintermediate transfer belt 10 with the first interval D1 smaller than the second interval D2 with which thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 immediately after a multiple print job is finished. Accordingly, control for isolating thesecondary transfer device 22 from theintermediate transfer belt 10 while the toner patch TP passes through the secondary transfer region N shortens the time required to isolate thesecondary transfer device 22 from theintermediate transfer belt 10 compared to control for isolating thesecondary transfer device 22 from theintermediate transfer belt 10 immediately after a multiple print job is finished. Consequently, the time required to complete a multiple print job is shortened, improving productivity of theimage forming apparatus 100. - According to the above-described exemplary embodiments, immediately after a multiple print job is finished, toner contained in the
development devices FIG. 1 is discharged to replace waste toner with fresh toner. The discharged waste toner is supplied from thedevelopment devices photoconductors photoconductors intermediate transfer belt 10. Then, thebelt cleaner 17 for cleaning theintermediate transfer belt 10 collects the transferred waste toner from theintermediate transfer belt 10. An amount of waste toner transferred onto theintermediate transfer belt 10 is substantially greater than an amount of toner of the toner patch TP. - As described above, the
secondary transfer device 22 is isolated from theintermediate transfer belt 10 with the smaller first interval D1 therebetween while the toner patch TP passes through the secondary transfer region N to prevent adhesion of toner of the toner patch TP to thesecondary transfer device 22 and at the same time shorten the time to isolate thesecondary transfer device 22 from theintermediate transfer belt 10. However, if thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 with the smaller first interval D1 therebetween even while the waste toner discharged from thedevelopment devices intermediate transfer belt 10 passes through the secondary transfer region N, the waste toner of which amount is greater than the amount of toner of the toner patch TP may adhere to thesecondary transfer device 22. - To address this problem, the secondary
transfer device separators FIGS. 6A to 7C isolate thesecondary transfer device 22 from theintermediate transfer belt 10 with the two switchable intervals, that is, the first interval D1 and the second interval D2 therebetween, thus minimizing adhesion of the waste toner to thesecondary transfer device 22 immediately after a multiple print job is finished while preventing adhesion of toner of the toner patch TP to thesecondary transfer device 22 and at the same time shortening the time to isolate thesecondary transfer device 22 from theintermediate transfer belt 10. - The secondary
transfer device separators secondary transfer device 22 from the first isolation position shown inFIGS. 6B and7B or the second isolation position shown inFIGS. 6C and7C to the contact position shown inFIGS. 6A and7A and vise versa with a single motion, that is, a single movement of thecams transfer device separators FIGS. 6A to 6C , the secondarytransfer device separator 170 includes thecam 171 having thefarthest face 171b, thecloser face 171c, and theclosest face 171d that contact the contact point S on thesecondary transfer device 22 and thedriver 72 that rotates thecam 171 to the contact position, the first isolation position, and the second isolation position. As shown inFIGS. 7A to 7C , the secondarytransfer device separator 270 includes thefirst cam 271A and thesecond cam 271B that press against thesecondary transfer device 22, thefirst driver 74 that rotates thefirst cam 271A, and thesecond driver 75 that rotates thesecond cam 271B. Thus, the secondarytransfer device separators - In order to form a toner image on a thick recording medium, before a leading edge of the thick recording medium enters the secondary transfer region N, the
controller 73 controls thedriver 72, thefirst driver 74, and thesecond driver 75 to rotate the secondarytransfer device separators secondary transfer device 22 from theintermediate transfer belt 10 at the first isolation position shown inFIGS. 4B ,6B , and7B where the toner patch TP passes through the secondary transfer region N. After the leading edge of the thick recording medium enters the secondary transfer region N, thecontroller 73 controls thedriver 72, thefirst driver 74, and thesecond driver 75 to rotate the secondarytransfer device separators secondary transfer device 22 into contact with theintermediate transfer belt 10. - As the rigid, thick recording medium enters the secondary transfer region N while the
secondary transfer device 22 contacts theintermediate transfer belt 10, the leading edge of the thick recording medium strikes theintermediate transfer device 22 at an entry to the secondary transfer region N with substantial vibration transmitted to theintermediate transfer belt 10, degrading the toner image formed on theintermediate transfer belt 10. To address this problem, the secondarytransfer device separators secondary transfer device 22 from theintermediate transfer belt 10 as the thick recording medium enters the secondary transfer region N, preventing the leading edge of the thick recording medium from striking thesecondary transfer device 22 at the entry to the secondary transfer region N. Accordingly, the thick recording medium does not vibrate theintermediate transfer belt 10, preventing formation of a faulty toner image due to vibration of theintermediate transfer belt 10. - The toner patch TP created in the gap between the successive toner images, that is, the toner patch section S1 interposed between the first toner image T1 and the second toner image T2, on the
intermediate transfer belt 10 during a multiple print job is a toner pattern used to adjust the density of toner of the toner images. Thetoner sensor 5 depicted inFIG. 1 serving as a toner detector detects an amount of toner of the toner pattern adhered to theintermediate transfer belt 10 so that adjustment of the density of the toner images, that is, a process control, is performed by thetoner density adjuster 95 depicted inFIG. 3 based on the amount of toner of the toner pattern detected by thetoner sensor 5. Thus, the density of the toner images is stabilized during a multiple print job. Further, the toner pattern does not adhere to thesecondary transfer device 22, preventing toner of the toner pattern from moving from thesecondary transfer device 22 onto the back side of the subsequent, second recording medium P2 conveyed through the secondary transfer region N. - As shown in
FIG. 1 , theimage forming apparatus 100 is a tandem color copier employing the intermediate transfer method. For example, theimage forming apparatus 100 includes the plurality of photoconductors 40Y, 40M, 40C, and 40K serving as electrostatic latent image carriers that carry electrostatic latent images and resultant yellow, magenta, cyan, and black toner images; and theintermediate transfer belt 10 serving as a toner image carrier or an intermediate transferor that carries the yellow, magenta, cyan, and black toner images transferred and superimposed on theintermediate transfer belt 10. The superimposed, yellow, magenta, cyan, and black toner images are formed into a color toner image and transferred onto a recording medium conveyed through the secondary transfer region N formed between theintermediate transfer belt 10 and thesecondary transfer device 22. - Yellow, magenta, cyan, and black toner patterns are created on the
photoconductors intermediate transfer belt 10, that is, the toner patch section S1 interposed between the first toner image T1 and the second toner image T2. Accordingly, the number of gaps between successive toner images where the toner pattern is created during a multiple print job decreases, and instead the number of gaps between successive toner images where no toner pattern is created increases, thus shortening passage time for which the gaps between the successive toner images where the toner pattern is created pass through the secondary transfer region N and improving productivity of theimage forming apparatus 100 during a multiple print job. - A plurality of
toner sensors 5 may be provided to correspond to a plurality of toner patterns, that is, yellow, magenta, cyan, and black toner patterns, respectively. With asingle toner sensor 5 configured to detect a plurality of toner patterns, it is necessary to arrange the plurality of toner patterns in the rotation direction R1 of theintermediate transfer belt 10 in such a manner that the plurality of toner patterns travels under a detection region of thetoner sensor 5 successively. In this case, it is necessary to lengthen the gap between the successive toner images where the plurality of toner patterns is created in the rotation direction R1 of theintermediate transfer belt 10, increasing the time for such longer gap to pass through the secondary transfer region N and thereby degrading productivity of theimage forming apparatus 100. - To address this problem, the plurality of
toner sensors 5 allows the plurality of toner patterns to be arranged in a direction, that is, a width direction, orthogonal to the rotation direction R1 of theintermediate transfer belt 10 in such a manner that the plurality of toner patterns travels under the detection region of the plurality oftoner sensors 5, respectively, at one time. Thus, the gap between the successive toner images where the plurality of toner patterns is created occupies a decreased length in the rotation direction R1 of theintermediate transfer belt 10 compared to the configuration in which thesingle toner sensor 5 detects the plurality of toner patterns, thus retaining productivity of theimage forming apparatus 100. - As shown in
FIG. 9 , while the toner patch TP created on theintermediate transfer belt 10 passes through the secondary transfer region N in a state in which thesecondary transfer device 22 is isolated from theintermediate transfer belt 10, the secondary transfer bias is switched to positive opposite to the negative polarity of toner of the toner patch TP. Accordingly, toner of the toner patch TP does not spatter from theintermediate transfer belt 10 onto thesecondary transfer device 22, preventing the toner from staining thesecondary transfer device 22. Further, the positive secondary transfer bias applied while thesecondary transfer device 22 is isolated from theintermediate transfer belt 10 is constant voltage controlled to prevent toner of the toner patch TP from spattering from theintermediate transfer belt 10 onto thesecondary transfer device 22, minimizing abnormal voltage increase and resultant failures. - The above-described exemplary embodiments are also applicable to an image forming apparatus employing a direct transfer method in which a toner image formed on a photoconductor is directly transferred onto a recording medium.
Claims (13)
- An image forming apparatus (100) comprising:a toner image carrier (10) rotatable in a predetermined direction of rotation (R1) and carrying at least three, first to third toner images (T1, T2, T3) created successively thereon in the direction of rotation (R1) thereof to be transferred onto at least three successive recording media (P1, P2, P3), respectively, as a print job, a toner patch section (S1) disposed between the first toner image (T1) and the second toner image (T2) and carrying a toner patch (TP), and a blank section (S2) interposed between the second toner image (T2) and the third toner image (T3); anda transfer device (22) separatably contacting the toner image carrier (10) to form a transfer region (N) therebetween through which the recording media (P1, P2, P3) are conveyed, wherein the image forming apparatus (100) further comprises:a transfer device separator (70; 170; 270) contacting and moving the transfer device (22) between a contact position and a first isolation position within a shortened time (M1; M2), the contact position where the transfer device (22) contacts the toner image carrier (10) and the first isolation position where the transfer device (22) is isolated from the toner image carrier (10) with a first interval (D1) therebetween; anda controller (73) operatively connected to the transfer device separator (70; 170; 270) to control the transfer device separator (70; 170; 270) to move the transfer device (22) to the contact position as the first to third toner images (T1, T2, T3) and the blank section (S2) of the toner image carrier (10) pass through the transfer region (N) and to the first isolation position as the toner patch section (S1) of the toner image carrier (10) passes through the transfer region (N),wherein the transfer device separator (170; 270) further includes:a cam (171; 271A; 271B) contacting the transfer device (22); anda driver (72; 74; 75) connected to and rotating the cam (171; 271A; 271B) to the contact position, the first isolation position, and a second isolation position, whereinthe transfer device separator (70; 170; 270) further moves the transfer device (22) to the second isolation position where the transfer device (22) is isolated from the toner image carrier (10) with a second interval (D2) therebetween greater than the first interval (D1).
- The image forming apparatus (100) according to claim 1, wherein the controller (73) retains the transfer device (22) in contact with the toner image carrier (10) as the blank section (S2) of the toner image carrier (10) passes through the transfer region (N) after the second toner image (T2) on the toner image carrier (10) passes through the transfer region (N) to cause a first time for which the blank section (S2) of the toner image carrier (10) passes through the transfer region (N) to be shorter than a second time for which the toner patch section (S1) of the toner image carrier (10) passes through the transfer region (N).
- The image forming apparatus (100) according to claim 1, wherein the controller (73) controls the transfer device separator (70; 170; 270) to move the transfer device (22) to the second isolation position when the print job is finished.
- The image forming apparatus (100) according to claim 1 or 3, wherein the controller (73) controls the transfer device separator (70; 170; 270) to move the transfer device (22) to the second isolation position when waste toner carried on the toner image carrier (10) passes through the transfer region (N).
- The image forming apparatus (100) according to claim 1, wherein the transfer device separator (170; 270) moves the transfer device (22) between the contact position, the first isolation position, and the second isolation position with a single movement of the cam (171; 271A; 271B).
- The image forming apparatus (100) according to any one of claims 1 to 5,
wherein the transfer device (22) includes a transfer roller (22c) separatably contacting the toner image carrier (10),
wherein the transfer device separator (270) includes:an arm (272) contacting the transfer roller (22c) of the transfer device (22);a first cam (271A) contacting the arm (272) and having a first farthest face (271Ab) with a greatest distance from a first rotation shaft (271Aa) thereof and a first closest face (271Ac) with a smallest distance from the first rotation shaft (271Aa);a compression spring (273) anchored to a lower face (22d) of the transfer device (22) to exert a bias to the transfer device (22);a second cam (271B) contacting the compression spring (273) and having a second farthest face (271Bb) with a greatest distance from a second rotation shaft (271Ba) thereof and a second closest face (271Bc) with a smallest distance from the second rotation shaft (271Ba);a first driver (74) connected to and rotating the first cam (271A); anda second driver (75) connected to and rotating the second cam (271B), andwherein as the first closest face (271Ac) of the first cam (271A) contacts the arm (272) and the second farthest face (271Bb) of the second cam (271B) contacts the compressing spring (273), the transfer roller (22c) contacts the toner image carrier (10), as the first farthest face (271Ab) of the first cam (271A) contacts the arm (272) and the second farthest face (271Bb) of the second cam (271B) contacts the compression spring (273), the transfer roller (22c) is isolated from the toner image carrier (10) with the first interval (D1) therebetween, and as the first farthest face (271Ab) of the first cam (271A) contacts the arm (272) and the second closest face (271Bc) of the second cam (271B) contacts the compression spring (273), the transfer roller (22c) is isolated from the toner image carrier (10) with the second interval (D2) therebetween. - The image forming apparatus (100) according to any one of claims 1 to 6, wherein the controller (73) controls the transfer device separator (70; 170; 270) to move the transfer device (22) to the first isolation position before a leading edge of a thick recording medium enters the transfer region (N) and to the contact position after the leading edge of the thick recording medium enters the transfer region (N).
- The image forming apparatus (100) according to any one of claims 1 to 7, further comprising:a toner detector (5) disposed opposite the toner image carrier (10) to detect an amount of toner of the toner patch (TP); anda toner density adjuster (95) connected to the toner detector (5) to adjust a density of toner of the second and third toner images (T2, T3) based on the amount of toner of the toner patch (TP) detected by the toner detector (5).
- The image forming apparatus (100) according to claim 8, further comprising a plurality of electrostatic latent image carriers (40Y, 40M, 40C, 40K) contacting the toner image carrier (10) and carrying a plurality of toner patches (TP), respectively, to be transferred onto the single toner patch section (S1) on the toner image carrier (10).
- The image forming apparatus (100) according to claim 9, wherein the toner detector (5) includes a plurality of toner sensors (5) to detect the plurality of toner patches (TP) on the toner image carrier (10), respectively.
- The image forming apparatus (100) according to any one of claims 1 to 10, further comprising a support roller (16) contacting the toner image carrier (10) and disposed opposite the transfer device (22) via the toner image carrier (10),
wherein the support roller (16) is applied with a transfer bias having a polarity opposite a polarity of toner of the toner patch (TP) as the transfer device separator (70; 170; 270) moves the transfer device (22) to the first isolation position when the toner patch section (S1) of the toner image carrier (10) passes through the transfer region (N). - The image forming apparatus (100) according to claim 11, wherein the transfer bias applied to the support roller (16) as the transfer device separator (70; 170; 270) moves the transfer device (22) to the first isolation position is constant voltage controlled.
- The image forming apparatus (100) according to any one of claims 1 to 12, wherein the toner image carrier (10) includes an endless intermediate transfer belt (10).
Applications Claiming Priority (1)
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JP2011212692A JP5888587B2 (en) | 2011-03-07 | 2011-09-28 | Image forming apparatus |
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EP2574988A3 EP2574988A3 (en) | 2017-01-25 |
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JP2002123052A (en) * | 2000-10-12 | 2002-04-26 | Konica Corp | Image forming apparatus |
JP4329775B2 (en) * | 2006-03-16 | 2009-09-09 | コニカミノルタビジネステクノロジーズ株式会社 | Image forming apparatus and method for detecting separation state of transfer member |
JP2007286176A (en) * | 2006-04-13 | 2007-11-01 | Ricoh Co Ltd | Image forming apparatus, image formation control method, and program |
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