JP6107055B2 - Image forming apparatus and secondary transfer separation timing control method - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine, a facsimile, and a printer, and a secondary transfer separation timing control method.

  2. Description of the Related Art In recent years, regarding a color image forming apparatus using an electrophotographic method, there is a so-called tandem color image forming apparatus that realizes high speed image formation. In the tandem system, toner images are formed on a plurality of photoconductors, the toner images are superimposed on an intermediate transfer belt, and the superimposed toner images of a plurality of colors are collectively transferred to a sheet on a secondary transfer unit. Is to do.

  In a tandem color image forming apparatus, depending on the arrangement of the machine configuration, the distance from the image formation start position of the toner color that starts image formation first, for example, the yellow color, to the secondary transfer portion is the paper feed. In some cases, the distance from the paper feed tray to the secondary transfer portion becomes longer.

  In the case of such a mechanical configuration, image formation has already been started at the time when the paper supply in the paper supply tray is started. At that time, even if the image formation is stopped after detecting the paper out of the paper feed tray, the image formation has already started, so the toner image developed on the photosensitive member or the intermediate transfer member is not on the paper. In some cases, the toner remains on the intermediate transfer member without being transferred to the toner. Further, such residual toner on the intermediate transfer member is transferred to a secondary transfer roller that is in contact with the intermediate transfer member, and the transferred toner is retransferred to the back side of the paper, causing problems such as backside contamination. It was.

  If the remaining number of sheets in the paper feed tray can be accurately detected and the timing for running out of paper can be accurately determined, image formation is interrupted at that timing to avoid the generation of residual toner. Can do. However, it is difficult to accurately detect the remaining number in reality.

  In order to cope with the above-described problem, Patent Document 1 discloses that when the remaining amount of paper is equal to or less than a predetermined value, the paper feeding timing is delayed and it is confirmed that the paper is not out of paper before feeding and image formation. A copier is disclosed that starts the process. Similarly, in Patent Document 2, when it is detected that the remaining amount of recording paper in the paper feed tray has become a predetermined amount or less, the distance between papers during continuous paper feeding is made longer than usual. An invention relating to an image forming apparatus that makes it possible to recognize that recording paper has run out before starting exposure to a photoreceptor is disclosed.

  Further, Patent Document 3 discloses an image for controlling the cleaning operation of the secondary transfer according to the residual toner amount as a means for preventing the secondary transfer member from being soiled by the residual toner generated when the paper in the paper feed tray runs out. A forming apparatus is disclosed.

  However, in the copiers disclosed in Patent Document 1 and Patent Document 2, when the remaining amount of paper is equal to or less than a predetermined value, the paper feed interval is widened, and productivity is extremely reduced. There's a problem. Further, in the image forming apparatus described in Patent Document 3, there is a problem that even if residual toner that has contacted the secondary transfer member is cleaned, the resistance increases and the margin of dirt on the back of the paper decreases over time. . Further, since the time required for the cleaning operation increases in proportion to the data amount of the image data, there is a problem that productivity is lowered.

  The present invention has been made in view of such circumstances, and provides an image forming apparatus that prevents a decrease in productivity by avoiding a problem due to the influence of residual toner that occurs when a sheet runs out. Objective.

  In order to solve the above problems, an image forming apparatus of the present invention includes an image carrier, an exposure unit that forms an electrostatic latent image by exposing the image carrier on the basis of image data, and the image carrier. A developing means for supplying toner to the developed electrostatic latent image to develop it as a toner image, an intermediate transfer body for primary transfer of the toner image developed on the image carrier, a paper transport means, and an intermediate transfer body And a secondary transfer unit that secondary-transfers the toner image primarily transferred to the sheet conveyed from the paper feed tray to the sheet conveyed by the sheet conveying unit, and the secondary transfer unit contacts the intermediate transfer member. And a contact / separation mechanism that separates the contact transfer unit from the intermediate transfer member, and further includes a paper detection unit that detects the presence or absence of paper in the paper feed tray, and is fed by the paper detection unit. If it is detected that there is no paper in the tray, The timing at which the contact transfer unit is separated from the intermediate transfer member is controlled based on the comparison result between the toner image non-transfer time during which toner is not transferred and the separation time required for separation of the contact transfer unit from the intermediate transfer member. And

  According to the present invention, it is possible to prevent a decrease in productivity by avoiding problems due to the influence of residual toner due to running out of paper.

1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. It is the schematic of the secondary transfer part 9 and transfer member cleaning means of embodiment of this invention. 3 is a block diagram illustrating a control relationship of the image forming apparatus according to the exemplary embodiment of the present invention. FIG. It is explanatory drawing showing the relationship between distance L1, distance L2, and each machine structure. FIG. 6 is an explanatory diagram illustrating a size relationship between each selection condition of an image forming mode and a paper feed tray and a distance L1 and a distance L2. FIG. 6 is a schematic diagram illustrating a sheet, a toner image, and a time between sheets when a sheet break occurs. It is a flowchart which shows the process after detecting a paper out in embodiment of this invention. It is a flowchart which shows the process after detecting a paper out in another embodiment of this invention.

  An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the present embodiment as long as the gist of the present invention is not exceeded. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified thru | or abbreviate | omitted suitably.

  FIG. 1 is a schematic diagram of an image forming apparatus A according to the present embodiment. The image forming apparatus A is called a tandem type color image forming apparatus. A plurality of sets of image forming means 10Y (yellow), 10M (magenta), 10C (cyan), 10K (black), an intermediate transfer belt 6, A secondary transfer unit 9, a paper feeding unit 20, a fixing device 40, and the like are included.

  The paper feed unit 20 is composed of a plurality of paper feed trays 21a and 21b, and the paper S stored in the paper feed tray 21 is transported by a transport means 30 comprising a plurality of transport rollers 31, 32, 33, and the like. .

  The image forming means 10 for each color includes a photoreceptor 1 as an image carrier, a charging unit 2, an exposure unit 3, a developing unit 4, a cleaning unit 5, a primary transfer unit 7, and the like, and an image forming unit for each color. Since the mechanical configuration of 10 is the same, in the figure, only the Y (yellow) series configuration is given a reference symbol, and the other components of M (magenta), C (cyan), and K (black) are shown. The reference numerals are omitted.

  The developing unit 4 receives a one-component developer or two-component developer of each color of yellow (Y), magenta (M), cyan (C), or black (K) charged to the same polarity as that of the photosensitive member 1. Accommodate each. For example, a developing roller 4a which is a developer carrying member formed of a cylindrical nonmagnetic stainless steel or aluminum material having a thickness of 0.5 to 1 mm and an outer diameter of 15 to 25 mm is provided.

  The developing roller 4a is maintained in a non-contact manner with a predetermined gap, for example, 100 to 1000 μm, by a butting roller (not shown), and rotates in the same direction as the rotation direction of the photosensitive member 1. Yes.

  At the time of development, an exposure area on the photosensitive member 1 is applied to the developing roller 4a by applying a developing bias voltage that superimposes an AC voltage on a DC voltage or a DC voltage having the same polarity as the toner, for example, a negative polarity in this embodiment. Is subjected to reversal development. As the toner used for the reversal development, a styrene acrylic polymerization toner or a polyester polymerization toner having a small particle diameter is used.

The intermediate transfer belt 6 is an endless belt having a volume resistance of 10 ⁶ to 10 ¹² Ω · cm. For example, polycarbonate (PC), polyimide (PI), polyamideimide (PAI), polyvinylidene fluoride (PVDF), and etrafluoro A resin material such as ethylene-ethylene copolymer (ETFE), or a rubber material such as EPDM, NBR, CR, polyurethane, etc., in which a conductive filler such as carbon is dispersed or an ionic conductive material is contained. Used. The thickness of the intermediate transfer belt 6 is preferably set to about 50 to 200 μm in the case of a resin material and about 300 to 700 μm in the case of a rubber material.

[Image forming process]
The image forming process of this embodiment will be described. First, simultaneously with the start signal of image recording, the photosensitive member drive motor (not shown) is started to rotate the Y photosensitive member 1Y in the counterclockwise direction indicated by the arrow, and at the same time, a potential is applied to the photosensitive member 1Y by the charging action of the charging unit 2Y. Is started.

  After the potential is applied to the photoconductor 1Y, writing of an image corresponding to the Y image data is started by the exposure unit 3Y, and an electrostatic latent image corresponding to the Y image of the original image is formed on the surface of the photoconductor 1Y. Is done.

  The electrostatic latent image is reversely developed in a non-contact state by the developing unit 4Y, and a Y toner image is formed on the photoreceptor 1Y according to the rotation of the photoreceptor 1Y. The Y toner image formed on the photoreceptor 1Y is primarily transferred onto the intermediate transfer belt 6 by the action of the primary transfer portion 7Y. Thereafter, the photoreceptor 1Y is cleaned of residual toner by the photoreceptor cleaning section 5, and enters the next image forming cycle.

  Next, the exposure unit 3M writes an image corresponding to an M (magenta) color signal, that is, M image data, and an electrostatic latent image corresponding to the M image of the original image is formed on the surface of the photoreceptor 1M. . The electrostatic latent image becomes an M toner image on the photoreceptor 1M by the developing unit 4M, and is synchronized with the Y toner image on the intermediate transfer belt 6 in the primary transfer unit 7M. It is superimposed on the image.

  By a similar process, the Y and M superimposed toner images are synchronized, and the C (cyan) toner image is superimposed on the Y and M superimposed toner images in the primary transfer portion 7C. Next, the Y, M, and C superimposed toner images that have already been formed are synchronized, and the K (black) toner image is transferred to the Y, M, and C superimposed toners in the primary transfer portion 7K. Overlaid on the image, a superimposed toner image of Y, M, C and K is formed.

  The intermediate transfer belt 6 carrying the superimposed toner image is fed in the clockwise direction as indicated by an arrow. Further, the paper S accommodated in the paper feed tray 21b of the paper feed unit 20 is fed by the paper feed means 22b as the first paper feed unit, and transport rollers 31 and 32, and the resist as the second paper feed unit. It is conveyed to a secondary transfer unit 9 as a secondary transfer unit through a roller 33 and the like. The superimposed toner images are collectively transferred onto the sheet S conveyed to the secondary transfer unit 9.

  Thereafter, the intermediate transfer belt 6 travels, residual toner after transfer on the intermediate transfer belt 6 is cleaned by the belt cleaning unit 8, and the next image forming cycle starts.

  The sheet S on which the superimposed toner image is transferred is further sent to the fixing device 40, and is sandwiched and pressed between the heating roller and the pressure roller to be fixed. The sheet S on which the toner image is fixed is transported out of the apparatus by the transport roller 34 and placed on the paper discharge tray 28.

  The double-sided conveyance path 301 includes an introduction conveyance path r1, a switchback conveyance path sb, and a merging conveyance path r3. At the time of double-sided image formation, the sheet on which the image is formed on one side is switched back by the double-sided conveyance path 301 and turned upside down and joined again to the single-sided conveyance path by the registration roller 33. Then, the image is transferred to the back surface of the sheet S by the secondary transfer unit 9 and conveyed outside the apparatus via the fixing device 40 and the conveyance roller 34.

  The paper feed tray 21 is provided with an upper surface detection sensor (not shown) that detects the upper surface of the stored paper bundle. Based on the detection by the upper surface detection sensor, the height of the storage table 25a on which the paper S is placed is adjusted by driving a drive motor (not shown) so that the upper surface of the paper comes into contact with the paper feeding means 22a. The paper presence / absence detection sensor 26 detects the out of paper of the paper stored in the paper feed tray 21 by an optical sensor.

[Secondary transfer portion and transfer member cleaning means]
FIG. 2 is a schematic diagram of the secondary transfer unit 9 and the transfer member cleaning unit, and shows an enlarged view of the periphery of the secondary transfer unit 9 in FIG. The secondary transfer unit 9 includes a secondary transfer roller 9a and a high voltage power source HV1. The secondary transfer roller 9a functions as a “contact transfer unit that contacts the intermediate transfer member”.

  The secondary transfer roller 9a is rotatably supported at the tip of the drive rod 9c. The secondary transfer roller 9a is pressed against the intermediate transfer belt 6 at the time of image formation by a drive rod 9c driven by a secondary transfer roller contact / separation drive unit 9b as a contact / separation mechanism, and when the secondary transfer roller 9a is cleaned. Is driven away from the intermediate transfer belt 6 at a predetermined timing. The secondary transfer roller contact / separation drive unit 9b drives the drive rod 9c under the control of a control unit (not shown). The secondary transfer roller contact / separation drive unit 9b is, for example, a solenoid or a DC motor, but is not limited thereto, and an eccentric cam can be used, for example.

The secondary transfer roller 9a is formed by dispersing a conductive filler such as carbon in a rubber material such as polyurethane, EPDM, or silicone on the peripheral surface of a conductive metal core such as stainless steel having an outer diameter of 8 mm, for example. It is formed by coating a semiconductive elastic rubber containing a material. This semiconductive elastic rubber is in a solid state or foamed sponge state with a volume resistance of about 10 ⁵ to 10 ⁹ Ω · cm, a thickness of 5 mm, and a rubber hardness of about 20 to 70 degrees (Asker-C). Since the toner contacts the secondary transfer roller 9a, the surface thereof is covered with a material having good releasability such as semiconductive fluorine resin or urethane resin.

  The backup roller 62 has a peripheral surface of a conductive metal core such as stainless steel, a conductive filler such as carbon dispersed in a rubber or resin material such as polyurethane, EPDM, or silicone, or an ionic conductive material. It is formed by coating the semiconductive material. The thickness of the semiconductive material to be coated is about 0.05 to 0.5 mm.

  The secondary transfer roller 9a is disposed in pressure contact with the backup roller 62 with a predetermined pressing force against the elasticity of the elastic layer. In this embodiment, a transfer nip portion having a width of several mm, for example, 3 mm, is formed between the two.

  In the high voltage power supply HV1, a transfer voltage having a polarity opposite to the polarity of the toner is applied to the conductive core metal of the secondary transfer roller 9a. In this embodiment, since the toner polarity is a negative polarity, the high voltage power supply HV1 supplies a positive polarity high voltage power supply. The high voltage power supply HV2 applies a cleaning voltage having the same polarity as that of the toner to the secondary transfer roller 9a. By applying an alternating voltage to the secondary transfer roller 9a by the high voltage power supply HV1 and the high voltage power supply HV2, the high voltage power supplies HV1 and HV2 also function as “transfer member cleaning means”, that is, a cleaning voltage.

  In this embodiment, the backup roller is grounded and high voltage power is supplied to the secondary transfer roller. However, the secondary transfer roller may be grounded and high voltage power is supplied to the backup roller. . In this case, a high-voltage power supply having the same polarity as the toner, that is, a negative polarity is supplied to the backup roller.

  In this embodiment, the example in which the transfer roller is used as the contact transfer member has been described. However, the present invention is not limited to this, and a transfer belt may be used. In this case, the cleaning means may be a mode in which a cleaning brush is used together with a high voltage power source.

  FIG. 3 is a block diagram showing the control relationship of the image forming apparatus A of the present embodiment. In the drawing, the periphery of the portion necessary for the description of the operation of the present embodiment is mainly described, and description of other known portions as the image forming apparatus is omitted.

  The image forming apparatus A includes a control unit A1 that performs various controls, a reading unit A2 that reads a document with a CCD, a display unit that includes an LCD that performs various displays of the apparatus, an operation unit A3 that inputs various operations, and a network. An I / F (interface) A4 as communication means for performing communication via the image forming means 10, an image forming means 10, a paper feed unit 20, and a transfer member cleaning unit 95.

  In the figure, the control unit A1 includes a CPU (A11) that controls each unit, a system memory A12 as various recording units, a nonvolatile memory A13, an image memory A14, a residual toner amount calculation unit A15, and a cleaning control unit A16.

  Various controls are performed by the CPU (A11) executing a program stored in advance in the system memory A12. In the non-volatile memory A13, the distance between the paper feeding unit, the secondary transfer unit, the fixing unit, and the exposure position as the paper size of the standard paper and the path lengths between the respective components of the apparatus in advance, the toner per pixel The toner mass or the like as an adhesion amount is recorded. The image memory A14 records image data input via the reading unit A2 or the I / F (A4).

  Various input operations by the user are performed from the operation unit A3, and based on the input contents, a document is recorded in the image memory A14 by the reading unit A2, and image formation is performed by the image forming unit 10 based on the recorded image data. Made. In the input operation, the selection of the paper feed tray 21 for feeding paper and the output mode, for example, color, monochrome, etc., are performed.

  In the transfer member cleaning control unit A16, the separation timing and cleaning operation of the secondary transfer roller are controlled by the image data recorded in the image memory, the distance between the components, and the residual toner calculated by the residual toner amount calculation unit A15. To do. The control operation of the cleaning control unit A16 will be described later.

[Calculation of distance L1 and distance L2]
Here, a method of calculating the image formation path length distance L1 relating to image formation and the conveyance path length distance L2 relating to paper conveyance will be described. FIG. 4 is an explanatory diagram showing the relationship between the distance L1, the distance L2, and each machine configuration. FIG. 1 is a conceptual diagram in which the path of the image forming apparatus A shown in FIG. 1 is developed on a straight line along the flow of image formation and paper conveyance.

  FIG. 4A is an explanatory diagram illustrating a method of calculating the distance L1 related to the path length of image formation. In the drawing, L 11 is the distance of the outer peripheral surface of the photosensitive member 1 from the exposure position by the exposure unit 3 on the photosensitive member 1 to the primary transfer unit 7. L12 is the distance of the outer peripheral surface of the intermediate transfer belt 6 from the primary transfer portion 7 to the secondary transfer portion 9. The distance L1 is the sum of L11 and L12.

  FIG. 4B is an explanatory diagram illustrating a method of calculating the distance L2 related to the sheet conveyance path length. The distance L <b> 2 is a distance from the leading edge of the paper stored in the paper feed tray 21 to the secondary transfer unit 9. The distance L1 varies depending on the image forming mode, and the distance L2 varies depending on the position of the selected paper feed tray. L1 and L2 are both different depending on the distance between the constituent parts. That is, the magnitude relationship between the two differs depending on the layout between the components, the image forming mode, and the selection of the paper feed tray.

  FIG. 5A shows the magnitude relationship between the distances L1 and L2 under the condition that the image forming mode is the full color mode and the selected paper feed tray is the first paper feed tray 21a. The reference numerals shown in the figure correspond to the image forming apparatus A in FIG.

  In the case of the full color mode, the exposure position on the photoconductor 1Y by the yellow exposure unit 3Y having the longest distance from the secondary transfer unit 9 among the plurality of exposure units 3 passes through the primary transfer unit 7Y. A distance L1 to the secondary transfer unit 9 is calculated. The distance L2 is a distance from the paper feed tray 21a to the secondary transfer unit 9.

  Under the conditions of this embodiment, the relationship of L1> L2 is established as shown in the figure, and image formation is performed at the timing prior to the start of paper conveyance from the paper feed tray 21a, that is, the exposure unit 3Y for the photoreceptor 1Y. The exposure by is started.

  That is, at the time when the sheet presence / absence detecting sensor 26 detects that the sheet in the sheet feeding tray 21a is out of paper, image formation in the area corresponding to the difference distance Ld obtained by subtracting L2 from L1 has already been started. The toner corresponding to the area of the difference distance Ld is not transferred to the sheet, but is all “residual toner”.

  FIG. 5B shows the magnitude relationship between the distances L1 and L2 under the condition that the image forming mode is the monochrome mode and the selected paper feed tray is the second paper feed tray 21b.

  In the monochrome mode, the distance L1 is the distance from the exposure position on the photoreceptor 1K by the exposure unit 3K to the secondary transfer unit 9 via the primary transfer unit 7K. Compared to L12Y shown in FIG. 5A, the distance of L12K becomes shorter, so the distance of L1 becomes shorter. The distance L2 is a distance from the paper feed tray 21b to the secondary transfer unit 9.

  Under such conditions, as shown in the figure, a relationship of L1 ≦ L2 is established, and after conveying the paper from the paper feed tray 21b, that is, after confirming that there is paper in the paper feed tray 21b, Image formation can be started. In such a case, “residual toner” does not occur.

  The distances between these machine configurations are stored in advance in the nonvolatile memory A13. By referring to these, the distance L1 and the distance L2 are calculated by the CPU (A11) of the control unit A1.

  Under the condition of L1> L2 as shown in FIG. 5A described above, when the paper presence / absence detection sensor 26 detects that the paper is out during image formation, “residual toner” that is not transferred onto the paper is generated. The residual toner amount calculation unit A15 of the control unit A1 calculates the residual toner amount.

  “Residual toner amount” refers to the amount of toner that has already been imaged and is not transferred to the paper. The residual toner does not completely contaminate the secondary transfer roller. If the secondary transfer roller 9a can be separated before the residual toner reaches the secondary transfer portion, the secondary transfer roller 9a will not be contaminated. Therefore, in the present embodiment, when it is detected that the paper feed tray is out of paper, the cleaning control unit 16A controls the separation operation timing of the secondary transfer roller 9a and the subsequent cleaning operation.

"Method for determining secondary transfer roller separation operation timing"
Before describing the method for determining the separation operation timing of the secondary transfer roller 9a in this embodiment, FIG. 6 will be described. FIG. 6 is a schematic diagram illustrating a sheet, a toner image, and a sheet interval time when a sheet break occurs. Note that the inter-sheet time refers to, for example, a conveyance time lag between a sheet conveyed first from the paper feeding unit and a sheet conveyed later.

  Specifically, in FIG. 6, when the right side of the drawing is the paper transport direction, the paper D transported first and the paper E transported later transport with a transport time lag of the inter-paper time T2. It is a schematic diagram which shows the state performed. It is assumed that the toner image d is transferred to the paper D and the toner image e is transferred to the paper E. In addition, here, processing after detection of out of paper will be described. For this reason, a virtual paper E as a paper cut target conveyed after the paper D is represented by a broken line.

  Further, a portion where the toner image between the rear end of the toner image d opposite to the paper transport direction and the rear end of the paper D opposite to the paper transport direction is not transferred is defined as a toner non-transfer portion Ld. A portion where the toner image from the start end in the paper transport direction to the start end of the toner image e in the paper transport direction is not transferred is defined as a toner non-transfer portion Le. The toner non-transferred portion Le is a margin that is intentionally set when, for example, a text is printed.

  Based on the description of FIG. 6 described above, a method of determining the secondary transfer roller separation operation timing of the present embodiment will be described. First, the image forming process on the sheet is interrupted when the sheet presence / absence detection sensor 26 detects that the sheet has run out. Then, the residual toner amount calculation unit A15 determines whether the toner image e is transferred as residual toner between the exposure position of the intermediate transfer roller 6 and the secondary transfer position.

  When the residual toner amount calculation unit A15 determines that the toner image e is not transferred between the exposure position of the intermediate transfer roller 6 and the secondary transfer position, the secondary transfer unit is not soiled, and therefore the secondary transfer unit is not stained. The separation operation process and the cleaning operation process of the transfer roller 9a are not performed.

  On the other hand, if the residual toner amount calculation unit A15 determines that the toner image e is transferred between the exposure position of the intermediate transfer roller 6 and the secondary transfer position, the secondary transfer roller 9a of the present embodiment. The separation operation process is performed. The start timing of the separation operation processing of the secondary transfer roller 9a is after the transfer of the toner image d onto the paper D, which is the final paper before the paper runs out, that is, the paper that is finally conveyed from the paper feed tray.

  Conventionally, the secondary transfer roller is separated after the completion of the secondary transfer, that is, after the trailing edge of the paper D has passed the secondary transfer position. However, when the separation time T1 as the time required for the separation operation processing is longer than the inter-paper time T2, the separation operation processing is completed even if the separation operation processing is started after the paper D passes the secondary transfer position. Residual toner reaches the secondary transfer position before.

  Therefore, in this embodiment, the separation operation process of the secondary transfer roller 9a is started earlier by the distance of the toner non-transfer portion Ld described above, and the completion time of the separation operation process is advanced. That is, the cleaning control unit A16 performs control so that the timing at which the secondary transfer roller 9a is separated from the intermediate transfer belt 6 is advanced. As a result, the residual toner adhesion amount on the secondary transfer roller 9a is substantially eliminated or reduced. As a result, it is possible to prevent the residual toner from adhering to the secondary transfer roller 9a and becoming dirty due to the residual toner reaching the secondary transfer position.

  When the toner non-transferred portion Le is present, the time until the toner image e reaches the secondary transfer position with the paper transport speed V1 is the time when the leading edge of the paper E is scheduled to reach the secondary transfer position. It is later than Le / V 1 minute. For this reason, in the present embodiment, when determining the separation operation processing start timing of the secondary transfer roller 9a, not only the toner non-transfer portion Ld but also the toner non-transfer portion Le is considered. In the present invention, for example, the toner image non-transfer portions Lb and Le and the paper interval time T2 are set as a toner image non-transfer time during which the toner image is not transferred onto the paper.

  As described above, in this embodiment, the timing at which the secondary transfer roller 9a is separated from the intermediate transfer belt 6 is controlled based on the comparison result between the toner image non-transfer time and the separation time. For example, as described above, when the toner image non-transfer time such as the toner image non-transfer portion Lb is longer than the separation time T1, the separation operation processing of the secondary transfer roller 9a is started earlier by the distance of the toner non-transfer portion Ld. To do. Thereby, the amount of residual toner attached to the secondary transfer roller 9a can be eliminated or reduced.

  Further, when the separation operation process of the secondary transfer roller 9a is started earlier by the distance of the toner non-transfer portion Ld, the cleaning control unit 16A does not perform the cleaning process of the secondary transfer roller 9a by the transfer member cleaning unit 95. To control. As a result, the time required for the cleaning process can be saved, and the process can proceed to the next image forming process without reducing the productivity in image forming while preventing the secondary transfer roller 9a from being stained.

“Calculation method of secondary transfer roller separation operation start timing”
A method of calculating the secondary transfer roller separation operation start timing according to this embodiment will be described with reference to the flowchart of FIG. First, the paper presence / absence detection sensor 26 detects that the paper has run out (step S1). Then, the transfer member cleaning control unit A16 compares the distance of the untransferred portion Ld with the distance “L0−Lf” obtained by subtracting the distance Lf from the transfer nip position center to the fixing nip center from the length L0 of the paper D. (Step S2).

  When the transfer member cleaning control unit A16 determines that a distance obtained by subtracting the distance Lf from the transfer nip position center to the fixing nip center from the length L0 of the paper D is longer than the untransferred part Ld (YES in step S2). Thus, the leading end portion of the paper D surely passes through the fixing nip. That is, the conveyance of the paper D is controlled by the driving force of the fixing roller or the like that forms the fixing nip. For this reason, even if the secondary transfer roller 9a is separated at this timing, paper jam does not occur and the paper conveyance performance is not impaired.

  In this case, the transfer member cleaning control unit A16 transfers the secondary transfer roller 9a to the secondary transfer roller 9a at a timing after the toner image d passes the secondary transfer position and before the time indicated by the following expression 1 elapses. Control to move away from the position.

          (Ld + Le) / V1 + T2-T1 (Formula 1)

  However, when the time represented by the above formula 1 is negative, that is, the separation time T1 required for the separation operation processing of the secondary transfer roller 9a is the toner image non-transferred as the conveyance time of the paper portion where the toner image is not transferred. When the time {(Ld + Le) / V1 + T2} is exceeded, the secondary transfer roller 9a is soiled by the toner image e that becomes residual toner. Therefore, the transfer member cleaning control unit A16 determines whether or not to move the secondary transfer roller 9a away from the secondary transfer position based on the following formula 2 (step S3).

          T1 <(Ld + Le) / V1 + T2 (Equation 2)

  When the transfer member cleaning control unit A16 determines that the separation time T1 does not exceed the toner image non-transfer time {(Ld + Le) / V1 + T2} based on the above formula 2 (step S3, YES). Operation control for separating the secondary transfer roller 9a from the secondary transfer position is started at a timing before the time indicated by the above formula 1 elapses (step S4). In this case, the transfer member cleaning control unit A16 does not perform cleaning process control. The timing before the time shown in Formula 1 elapses is the timing within the time obtained by subtracting the separation time from the toner image non-transfer time.

  On the other hand, when the transfer member cleaning control unit A16 determines that the separation time T1 exceeds the toner image non-transfer time {(Ld + Le) / V1 + T2} based on the above formula 2 (step S3, NO). The secondary transfer roller 9a is not separated from the secondary transfer position, and the cleaning process control is performed on the secondary transfer roller 9a after the toner image e has passed the secondary transfer position (step S5).

  On the other hand, in step S2, when the transfer member cleaning control unit A16 determines that the distance obtained by subtracting the distance Lf from the transfer nip position center to the fixing nip center from the length L0 of the sheet D is shorter than the untransferred part Ld ( In step S2, NO), the leading end portion of the paper D does not reach the fixing nip of the fixing unit. That is, the conveyance of the paper D is controlled by the driving force of the secondary transfer roller 9a.

  For this reason, if the secondary transfer roller 9a is separated at this timing, the conveyance of the sheet is impaired, and when the sheet subsequently passes through the fixing nip, the sheet is jammed, a sheet jam or a skew occurs. Therefore, in consideration of this point, it is necessary to calculate the timing for starting the separation operation process of the secondary transfer roller 9a. That is, the transfer member cleaning control unit A16 controls the secondary transfer roller 9a not to be separated from the intermediate transfer belt 6 until the sheet reaches the fixing nip.

  In other words, the transfer member cleaning control unit A16 determines that the separation of the secondary transfer roller 9a is completed until the toner image e reaches the secondary transfer position after the leading end portion of the paper D reaches the fixing nip. The timing for starting the separation control of the next transfer roller 9a is adjusted. That is, the transfer member cleaning control unit A16 performs control to separate the secondary transfer roller 9a before the time represented by the following Expression 3 after the leading end portion of the paper D reaches the fixing nip.

          (L0-Lf + Le) / V1 + T2-T1 (Equation 3)

  However, in the same manner as in the above-described expression 2, the separation time T1 is equal to the distance “L0−Lf”, the time during which the sheet is conveyed in the untransferred portion Le, and the total time {(L0−Lf + Le). ) / V1 + T2}, the secondary transfer roller 9a is soiled by the toner image e that becomes residual toner. Therefore, the transfer member cleaning control unit A16 determines whether or not to move the secondary transfer roller 9a away from the secondary transfer position based on the following equation (4) (step S13). Here, the time during which the paper is conveyed in the non-transfer portion Le and the paper interval time T2 are the toner image non-transfer time.

          T1 <(Ld + Le) / V1 + T2 (Equation 4)

  When the transfer member cleaning control unit A16 determines that the separation time T1 does not exceed the total time {(L0−Lf + Le) / V1 + T2} based on the above equation 4 (YES in step S13). Then, the operation control for separating the secondary transfer roller 9a from the secondary transfer position is started at a timing before the time indicated by the above expression 3 passes (step S14). In this case, the transfer member cleaning control unit A16 does not perform cleaning process control.

  On the other hand, when the transfer member cleaning control unit A16 determines that the separation time T1 exceeds the total time {(L0−Lf + Le) / V1 + T2} based on the above equation 4 (NO in step S13). The secondary transfer roller 9a is not separated from the secondary transfer position, and the cleaning process control is performed on the secondary transfer roller 9a after the toner image e has passed the secondary transfer position (step S15).

  Next, a method of calculating the secondary transfer roller separation operation start timing according to another embodiment of the present invention will be described with reference to FIG. Note that description of the same processing as in FIG. 7 is omitted. That is, in another embodiment, the control when the time T1 required for the separation operation processing in step S3 and step S13 in the above-described embodiment exceeds the time {(Ld + Le) / V1 + T2} during which the toner image is not transferred. Is different.

  As described in the present embodiment, for example, when the separation time T1 exceeds the toner image non-transfer time {(Ld + Le) / V1 + T2}, the separation processing from the secondary transfer position of the secondary transfer roller 9a. Did not do. This is because the separation operation of the secondary transfer roller 9a is not in time until the next toner image e reaches the secondary transfer position, and in this case, the separation control of the secondary transfer roller 9a is not performed. This is because it is rather efficient to clean the roller 9a.

  However, even if the separation operation process of the secondary transfer roller 9a is not in time until the next toner image reaches the secondary transfer position, it may be better to perform the separation operation control of the secondary transfer roller 9a. . This is because, when the compatibility between the material of the surface of the secondary transfer roller 9a and the toner is poor, it may be difficult to remove the residual toner attached to the secondary transfer roller 9a by cleaning. In this case, it is desirable to control the separation operation of the secondary transfer roller 9a rather than cleaning to prevent any residual toner from adhering to the secondary transfer roller 9a.

  In another embodiment of the present invention, unlike the above-described embodiment, when the separation time T1 exceeds the toner image non-transfer time {(Ld + Le) / V1 + T2} (step S31, NO), transfer member cleaning control is performed. The part A16 starts the separation control of the secondary transfer roller 9a after the position G (see FIG. 6) of {L0-Ld} from the leading edge of the paper D passes the secondary transfer position. Then, after the toner image e has passed the secondary transfer position, the transfer member cleaning control unit A16 contacts the secondary transfer roller 9a to the secondary transfer position, and then performs a cleaning operation (step S51).

  In another embodiment of the present invention, unlike the above-described embodiment, when it is determined that the separation time T1 exceeds the total time {(L0−Lf + Le) / V1 + T2} (NO in step S131). The transfer member cleaning control unit A16 starts the separation control of the secondary transfer roller 9a when the leading end of the paper D reaches the fixing nip. Then, after the toner image e has passed the secondary transfer position, the transfer member cleaning control unit A16 performs contact control of the secondary transfer roller 9a to the secondary transfer position, and then performs a cleaning operation (step S151). ).

  According to another embodiment of the present invention described above, it is possible to reduce the amount of toner that contacts the secondary transfer roller, and it is possible to reduce contamination of the secondary transfer roller over time.

  Note that the above-described cleaning control unit A16 of the present embodiment may control the high-voltage power supply HV1 and the like so as not to apply a voltage during the separation operation time of the secondary transfer roller 9a. By not supplying voltage during the separation operation of the secondary transfer roller 9a, no electrical noise is generated, so that the secondary transfer roller 9a can be separated from the intermediate transfer belt 6 without causing an abnormal image or abnormal operation. .

  Further, the above-described cleaning control unit A16 of the present embodiment applies a high-voltage power supply H1 so as to apply a voltage having a polarity opposite to that when the toner is transferred to the secondary transfer roller 9a after the separation operation of the secondary transfer roller 9a. Etc. may be controlled. By doing so, it is possible to reduce the amount of toner that is scattered due to repulsive force between the toners, air resistance, and the like, and it is possible to further reduce the contamination of the secondary transfer roller 9a.

A Image forming apparatus A1 Control unit A11 CPU
A15 Residual toner amount calculation unit A16 Cleaning control unit 1 Photoconductor 2 Charging unit 3 Exposure unit 4 Development unit 5 Photoconductor cleaning unit 6 Intermediate transfer belt 7 Primary transfer unit 9 Secondary transfer unit 9a Secondary transfer roller 9b Secondary transfer Roller contact / separation drive unit 9c Drive rod 20 Paper feed unit 21 Paper feed tray 26 Paper presence / absence detection sensor (paper presence / absence detection unit)
HV1, HV2 High voltage power supply 62 Backup roller

JP-A 61-277536 JP 2002-323839 A JP 2008-191214 A

Claims (8)

An image carrier;
Exposure means for exposing on the image carrier based on image data to form an electrostatic latent image;
Developing means for supplying toner to the electrostatic latent image carried on the image carrier and developing it as a toner image;
An intermediate transfer member on which a toner image developed on the image carrier is primarily transferred;
Paper transport means;
Secondary transfer means for secondary transfer of the toner image primarily transferred to the intermediate transfer member from the paper feed tray onto the paper transported by the paper transport means;
The secondary transfer unit is an image forming apparatus including a contact transfer unit that contacts the intermediate transfer member, and a contact / separation mechanism that separates the contact transfer unit from the intermediate transfer member,
Paper detection means for detecting the presence or absence of paper in the paper feed tray,
When the paper detection unit detects that there is no paper in the paper feed tray, a toner image non-transfer time during which no toner image is transferred to the paper, and a separation time required for the contact transfer unit to separate from the intermediate transfer body And controlling the timing of separating the contact transfer unit from the intermediate transfer member based on the result of the comparison.   2. The image forming apparatus according to claim 1, wherein when the toner image non-transfer time exceeds the separation time, the timing for separating the contact transfer unit from the intermediate transfer member is advanced. A transfer member cleaning means for cleaning the toner adhering to the contact transfer portion;
The image forming apparatus according to claim 2, wherein when the timing of separating the contact transfer unit from the intermediate transfer member is advanced, a cleaning process by the transfer member cleaning unit is not performed. 4. The toner image non-transfer time includes at least a conveyance time of a paper portion on which a toner image is not transferred and a conveyance time lag between sheets conveyed by the paper conveyance unit. the image forming equipment according to claim. The image forming apparatus according to any one of claims 1 to 4, characterized in that no spacing the contact transfer unit from said intermediate transfer member to the tip of the paper reaches the fixing unit. The transfer member cleaning means has a high voltage power supply unit that applies a cleaning voltage to the contact transfer unit,
The image forming apparatus according to any one of 5 the voltage during separation time of the contact transfer section from claim 1, characterized in that not applied to the contact transfer unit. The image forming apparatus according to claim 6 , wherein after the contact transfer unit is separated, a voltage having a polarity opposite to a voltage when toner is transferred to the contact transfer unit is applied. The image carrier is exposed based on image data to form an electrostatic latent image, toner is supplied to the electrostatic latent image carried on the image carrier and developed as a toner image, and the image carrier After the toner image developed above is primarily transferred to an intermediate transfer member, it is secondarily transferred onto a sheet conveyed from a paper feed tray by the action of a transfer voltage applied to a contact transfer portion that contacts the intermediate transfer member. A secondary transfer separation timing control method executed by an image forming apparatus including an image forming unit and a cleaning unit that applies a cleaning voltage to the contact transfer unit and cleans toner adhering to the contact transfer unit. There,
A step of comparing a toner image non-transfer time during which a toner image is not transferred to the paper and a separation time required for separation of the contact transfer unit from the intermediate transfer body when there is no paper in the paper feed tray;
When the toner image non-transfer time exceeds the separation time, controlling to advance the timing of separating the contact transfer portion from the intermediate transfer body;
A secondary transfer separation timing control method, comprising: a step of controlling so as not to perform a cleaning process by the cleaning means when the timing of separating the contact transfer portion from the intermediate transfer member is advanced.

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