JP4331075B2 - Paper feeding method in image forming apparatus - Google Patents

Description

  The present invention relates to a paper feeding method in an image forming apparatus using an intermediate transfer method, and in particular, when the number of requested prints is plural, the paper feeding timing from the paper storage unit is controlled and stored in the paper storage unit. The present invention relates to a paper feeding method capable of detecting the presence or absence of the next paper.

  In recent years, the printing processing speed of image forming apparatuses has been increased. In addition to conventional monochrome printing image forming apparatuses, development of color printing image forming apparatuses is in progress. As an example of an image forming apparatus for color printing, image information that has been color-separated into a plurality of colors (for example, four colors K, C, M, and Y) is obtained by using a plurality of electrostatic latent image carriers. A color image is obtained by transferring the image onto a sheet (paper) conveyed from a paper storage unit (for example, a paper feed cassette) after being transferred onto an intermediate transfer belt that contacts and rotates with a latent image carrier at a predetermined pressure. There is an image forming apparatus that uses an intermediate transfer method for forming the image on a sheet.

  In such an intermediate transfer type image forming apparatus, when printing is requested, paper is fed from a paper storage unit in which a specified size of paper is stored. However, if there is no paper in the paper cassette in the middle of continuous printing, and it is detected that there is no paper, the printing process for the next paper has already started on the intermediate transfer belt. For this reason, the image formed image and the unfixed developer are wasted, the load of the cleaning unit is increased, the load is applied to the electrostatic latent image carrier and the developing device, and the life characteristics are deteriorated. There was a problem.

  Therefore, in the image forming apparatus, a paper presence / absence sensor is arranged at the rear end portion of the paper storage unit so that the presence / absence of the next paper can be detected at the time of slightly picking up the previous paper even during continuous printing. A technique has been proposed (see, for example, Patent Document 1). In this technique, before the image is written on the photosensitive belt, the presence or absence of the next sheet can be detected. When there is no sheet, the writing of the image on the photosensitive belt is stopped. We are trying to solve the problem.

  Next, a paper feeding method in an image forming apparatus using a conventional intermediate transfer method will be described with reference to FIG. FIG. 7 is a timing chart showing a printing process and a paper feeding process when the required number of prints is plural in an image forming apparatus using a conventional intermediate transfer method. FIG. 7 shows the printing process and the paper feeding process for the first to third sheets, but the printing process and the paper feeding process for the fourth and subsequent sheets (the number of requested prints is 4 or more). In the case of (3), the same timing as the printing process and paper feeding process for the third sheet is performed.

  In the image forming apparatus using the intermediate transfer method, when there is a continuous print request, that is, when there are a plurality of print requests, first, pre-printing processing is performed. Note that the pre-printing process is performed regardless of whether the requested number of prints is only one or plural.

  After the pre-printing process, a printing process and a paper feeding process for the first sheet are performed. The printing process includes a printing process for each color (in this case, the first to fourth colors) and a batch transfer process. The printing process for the first color (for example, yellow) → the second color (for example, magenta) The printing process of the third color (for example, cyan), the printing process for the fourth color (for example, black), and the batch transfer process are performed in this order. The printing process for each color includes a main charging process for charging the electrostatic latent image carrier with a charger, and an image exposure process for exposing the electrostatic latent image carrier with an exposure unit and forming an electrostatic latent image on the surface thereof. The main charging process comprises a developing process for developing an electrostatic latent image with a developer (toner) and forming a toner image on the electrostatic latent image carrier, and a transfer process for transferring the toner image to an intermediate transfer belt. -> Image exposure step-> development step-> transfer step.

  The main charging process of the first color printing process in the printing process for the first sheet is performed after the pre-printing process. In the first to fourth color printing steps, the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt, whereby a color toner image (multicolor toner image) is transferred onto the intermediate transfer belt. Is formed. In the batch transfer process, the multi-color toner image on the intermediate transfer belt is batch transferred onto the transported paper in the secondary transfer portion.

  The main charging process of the first color printing process in the printing process for the second sheet starts at a timing halfway of the second color printing process in the printing process for the first sheet. The subsequent printing process for the second sheet is performed in the same order as the printing process for the first sheet. Then, the printing process for the third and subsequent sheets is performed at the same timing.

  On the other hand, in the paper feed process, a paper pick-up process that feeds the paper from the paper feed cassette to the paper transport path one by one, a first paper transport process that transports the paper from the paper feed cassette to the registration rollers, and rotation of the registration rollers And a second sheet conveying step of conveying the sheet from the registration roller to the secondary transfer unit.

  In the paper feeding process for the first sheet, the paper pick-up process is substantially the same timing (time t1) as the main charging process of the first color printing process in the printing process for the first sheet after the pre-printing process. The first sheet is supplied from the sheet feeding cassette to the sheet conveyance path. At the same timing (time t1) as this paper pick-up process, the first paper transport process to the registration rollers starts, and the first sheet is transported to the registration rollers along the paper transport path. Thereafter, at a timing (time t2) slightly before the start of the batch transfer process in the printing process for the first sheet (time t3), the registration roller starts to rotate, and the second paper conveyance process by the rotation of the registration roller is performed. Start. The second paper transport process starts at a timing such that the leading edge of the first sheet and the leading edge of the multicolor toner image on the intermediate transfer belt are aligned at the secondary transfer portion.

The paper pick-up process and the first paper transport process in the paper feeding process for the second paper are the timing (time) after the main charging process of the first color printing process in the printing process for the third paper is started. Start at t4). Then, at the same timing, the paper pick-up process and the first paper transport process in the paper feeding process for the third and subsequent sheets are started. In addition, the second paper transporting process in the paper feeding process for the second and subsequent sheets starts at the same timing (time t6) as the second paper transporting process in the paper feeding process for the first and subsequent papers.
JP 2000-109224 A

  However, the paper feeding method in the image forming apparatus using the conventional intermediate transfer system as described above has the following problems.

  As shown in FIG. 7, when the required number of prints is plural, the sheet pick-up process for the first sheet is the main charging process of the first color printing process for the first sheet after the pre-printing process. It started at substantially the same timing (time t1). For this reason, as shown in Patent Document 1, when a paper presence / absence sensor is disposed at the rear end portion of the paper feed cassette, the presence / absence of the second paper indicates the start of the printing process for the second paper. It was detected before.

  On the other hand, for the third and subsequent sheets, even if a sheet presence / absence sensor is arranged at the rear end of the sheet feeding cassette, the presence / absence of the sheet to be fed is determined by the start of the printing process for this sheet. It could not be detected before. For example, the detection of the presence or absence of the third sheet is performed after the start of the sheet pick-up process for the second sheet (time t4) (time t5). It started after a time T1 from the main charging process of the first color printing process for three sheets.

  For this reason, with respect to the third and subsequent sheets, there is a possibility that the sheets in the sheet feeding cassette may run out during the continuous printing, which may cause the problems described in the background art.

  In the image forming apparatus using the intermediate transfer method, the presence or absence of the next sheet fed from the sheet storage unit can be detected before the printing process for the sheet starts. An object of the present invention is to propose a paper feeding method that can solve the conventional problems that have occurred when paper runs out.

  In the present invention, means for solving the above-described problems are configured as follows. That is, a plurality of pieces of color-separated image information are transferred onto an intermediate transfer belt that rotates with contact with each electrostatic latent image carrier at a predetermined pressure using a plurality of electrostatic latent image carriers, and then stored in a sheet. A sheet feeding method in an image forming apparatus using an intermediate transfer method for forming a color image on a sheet by batch transfer onto a sheet conveyed from a section, wherein when the number of print requests is plural, the sheet storage section It is characterized in that the presence or absence of the paper stored in the paper storage unit is detected by changing the timing of performing the paper pick-up process for supplying the paper one by one to the paper transport path in accordance with the number of fed paper.

  According to such a paper feeding method, when the number of print request sheets is plural, the timing of performing the paper pick-up process is varied according to the number of paper feeds, so that not only the second paper but also the third paper With regard to subsequent sheets, the presence or absence of the next sheet to be fed can be detected before the printing process for the sheet starts. As a result, the conventional problem that has occurred when the paper in the paper storage section runs out during continuous printing, specifically, the image formed image and unfixed developer are wasted, and the load on the cleaning section It is possible to prevent the occurrence of problems such as an increase in load, a load on the electrostatic latent image carrier and the developing device, and a decrease in life characteristics.

  In the paper feeding method in the image forming apparatus of the present invention, the paper pick-up process is performed by dividing the paper pick-up process into two parts, a front pick-up and a rear pick-up.

  In this case, the conveyance distance of the paper by the front pickup is the distance that the leading edge of the paper reaches the double feed preventing member provided in the vicinity of the paper storage portion, and the trailing edge of the paper is at the minimum This is the distance that passes through the paper detection unit that detects the presence or absence of. Here, the paper detection unit is movably provided at the rear part of the paper storage unit.

  According to such a paper feeding method, when the previous pickup is performed, it is possible to detect whether or not the paper to be fed next is in the paper storage unit. As a result, the presence or absence of the next paper to be fed can be detected before the printing process for this paper starts, and the conventional case that occurs when the paper in the paper storage section runs out during the continuous printing is performed. The problem can be solved.

  In the sheet feeding method in the image forming apparatus according to the present invention, the front pickup is performed on the second and subsequent sheets.

  In the paper feeding method in the image forming apparatus according to the present invention, the timing at which the previous pickup for the second and subsequent sheets ends is set to be before the printing process for the next sheet starts. Here, the start of the printing process for the next sheet is performed by the main charger for the electrostatic latent image carrier that is farthest from the batch transfer portion that performs batch transfer among the plurality of electrostatic latent image carriers. It is the start of electric field application.

  According to such a sheet feeding method, when there are a plurality of print request sheets, the timing at which the pre-pickup for the second and subsequent sheets of the third and subsequent sheets ends is the same as that in the printing process for the next sheet. This is before the main charging process of the first color printing process starts. Thus, the presence / absence of the next paper to be fed can be detected before the printing process for the paper starts. If it is detected that there is no next paper in the paper storage unit, the printing process is performed. You can stop before it starts. As a result, the conventional problem that occurred when the paper in the paper storage section was exhausted during continuous printing, specifically, the image formed image and unfixed developer was wasted, and the load on the cleaning section It is possible to prevent the occurrence of problems such as an increase in load, a load on the electrostatic latent image carrier and the developing device, and a decrease in life characteristics.

  Since the present invention is a paper feeding method as described above, the presence or absence of a sheet is detected not only for the second sheet but also for the third and subsequent sheets at the timing before the printing process starts. Can do. As a result, it is possible to prevent a conventional problem that has occurred when the paper in the paper storage portion runs out during continuous printing.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not.

  First, the overall configuration of an image forming apparatus to which the present invention is applied will be described. As shown in FIG. 1, an image forming apparatus 100 includes an exposure unit 1, a developing device 2, a photosensitive drum (electrostatic latent image carrier) 3, a main charger 5, a cleaner unit 4, an intermediate transfer belt unit 8, a fixing unit. The unit 12 includes a paper transport path S, a paper feed cassette 10, a paper discharge tray 15, and the like. The image forming apparatus 100 forms a multicolor image on a predetermined sheet (paper) in accordance with image data transmitted from the outside.

  Then, as described below, the image forming apparatus 100 uses the plurality of (four in this example) photoconductor drums 3 as the image information separated into a plurality of colors (four in this example), respectively. A color image is formed on the sheet by transferring the sheet onto the intermediate transfer belt 7 that rotates in contact with the photosensitive drum 3 at a predetermined pressure and then collectively transferring the sheet onto a sheet conveyed from a sheet storage unit such as a sheet feeding cassette 10. The color image forming apparatus uses an intermediate transfer method.

  Note that image data handled in the image forming apparatus 100 corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, the developing device 2 (2a, 2b, 2c, 2d), the photosensitive drum 3 (3a, 3b, 3c, 3d), the main charger 5 (5a, 5b, 5c, 5d), and the cleaner unit 4 (4a, 4b). 4c and 3d) are provided so that four types of latent images corresponding to the respective colors (K, C, M, Y) are formed, and four image stations are provided in the image forming apparatus 100. (Image forming unit) is configured. Here, the constituent member of the subscript a corresponds to black, the constituent member of the subscript b corresponds to cyan, the constituent member of the subscript c corresponds to magenta, and the constituent member of the subscript d corresponds to yellow.

  The photosensitive drum 3 is disposed (mounted) on the upper part of the image forming apparatus 100. A main charger 5, a developing unit 2, a cleaner unit 4 and the like are disposed around each photosensitive drum 3.

  The main charger 5 charges the surface of the photosensitive drum 3 uniformly to a predetermined potential in the main charging step. In this example, a contact roller type charger is used. Note that a brush-type charger, a charger-type charger, or the like may be used.

  In the image exposure process, the exposure unit 1 exposes the photosensitive drum 3 charged by the main charger 5 according to the input image data, thereby forming an electrostatic latent image according to the image data on the surface. In this example, a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror is used. An EL or LED writing head in which light emitting elements are arranged in an array may be used.

  The developing unit 2 visualizes the electrostatic latent images formed on the respective photosensitive drums 3 with toners of respective colors (K, C, M, Y) in the developing process, and forms toner images of the respective colors. It is. After the development process, in the transfer process, as described later, the toner image on the photosensitive drum 3 is transferred to the intermediate transfer belt 7 (primary transfer).

  The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and transfer.

  The intermediate transfer belt unit 8 disposed above the photosensitive drum 3 forms a color image on a sheet by using an intermediate transfer method, and includes an intermediate transfer belt 7, an intermediate transfer belt driving roller 71, an intermediate transfer. A belt tension mechanism 73, an intermediate transfer belt driven roller 72, an intermediate transfer roller 6 (6a, 6b, 6c, 6d), and an intermediate transfer belt cleaning unit 9 are provided.

  The intermediate transfer belt 7 is stretched around an intermediate transfer belt drive roller 71, an intermediate transfer belt tension roller 74 of the intermediate transfer belt tension mechanism 73, an intermediate transfer roller 6, an intermediate transfer belt driven roller 72, and the like. Rotation drive. In this example, the intermediate transfer belt 7 is formed endlessly using a film having a thickness of about 100 μm to 150 μm. The intermediate transfer belt 7 is provided so as to be sandwiched between the respective photosensitive drums 3 and the intermediate transfer roller 6. The toner images formed on the respective photosensitive drums 3 are sequentially superimposed and transferred onto the intermediate transfer belt 7 to form a color toner image (multicolor toner image) on the intermediate transfer belt 7. The

  The transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 7 is performed by the intermediate transfer roller 6 that is in contact with the back side of the intermediate transfer belt 7. The intermediate transfer roller 6 is rotatably supported by the intermediate transfer roller mounting portion of the intermediate transfer belt tension mechanism 73. In order to transfer the toner image on the photosensitive drum 3 onto the intermediate transfer belt 7, a high voltage transfer bias (a high polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 6. Voltage) is applied.

  The intermediate transfer roller 6 is a roller having a shaft of a metal (for example, stainless steel) having a diameter of 8 to 10 mm as a base, and the surface thereof being covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the intermediate transfer belt 7. In this example, a roller-shaped transfer electrode is used, but a brush-shaped transfer electrode may be used.

  As described above, the input image information is visualized on the respective photosensitive drums 3 in accordance with the respective colors, and is further laminated and transferred onto the intermediate transfer belt 7. In the batch transfer process, the laminated image information is batch-transferred onto the sheet at the secondary transfer portion 70 where the intermediate transfer belt 7 and the secondary transfer roller 11 are in pressure contact with each other by the rotation of the intermediate transfer belt 7. (Secondary transfer).

  At this time, the intermediate transfer belt 7 and the secondary transfer roller 11 are in pressure contact with each other at a predetermined nip in the secondary transfer unit 70, and the multi-color toner stacked on the intermediate transfer belt 7 is attached to the secondary transfer roller 11. A voltage (a high voltage having a polarity (+) opposite to the charging polarity (−) of the toner) for transferring the image onto the sheet is applied. Of the secondary transfer roller 11 and the intermediate transfer belt drive roller 71, one is a hard material (for example, metal) roller and the other is a soft material (for example, rubber, foaming resin, etc.) elastic roller. The nip is constantly obtained.

  Of the toner adhering to the intermediate transfer belt 7 due to contact with the respective photosensitive drums 3, the toner that is not transferred onto the sheet by the secondary transfer roller 11 and remains on the intermediate transfer belt 7 is transferred to the toner in the next step. In order to cause color mixing, it is removed and collected by the intermediate transfer belt cleaning unit 9. The intermediate transfer belt cleaning unit 9 includes, for example, a cleaning blade as a cleaning member that contacts the intermediate transfer belt 7. The intermediate transfer belt 7 is supported by an intermediate transfer belt driven roller 72 from the back side at a position in contact with the cleaning blade.

  The paper feed cassette 10 is provided below the image forming unit and the exposure unit 1 of the image forming apparatus 100 as a paper storage unit for storing paper used for image formation. On the other hand, the paper discharge tray 15 is provided at the top of the image forming apparatus 100 in order to place printed paper face down.

  The fixing unit 12 includes a heat roller 31, a pressure roller 32, and the like, and the heat roller 31 and the pressure roller 32 rotate with a sheet interposed therebetween. The temperature of the heat roller 31 is controlled so as to reach a predetermined fixing temperature based on a signal from a temperature detector (not shown). The heat roller 31 and the pressure roller 33 melt, mix, and press the multicolor toner image transferred to the paper by thermocompression bonding of the paper. As a result, the multicolor toner image is thermally fixed on the paper. After fixing by the fixing unit 12, the paper is transported by transport rollers (25-2, 25-3) and discharged to the paper discharge tray 15 face down (with the multicolor toner image facing downward). The

  The image forming apparatus 100 is provided with a paper transport path S that transports paper from the paper feed cassette 10 to the paper discharge tray 15 via the secondary transfer unit 70 and the fixing unit 12. In the vicinity of the paper transport path S from the paper feed cassette 10 to the paper discharge tray 15, a pickup roller (paper transport roller) 16, a registration roller 14, a secondary transfer unit 70, a fixing unit 12, and a transport roller 25 for transporting the paper. Etc. are arranged. The paper transport path S is substantially vertical between the transport roller 25-1 disposed in the vicinity of the paper feed cassette 10 and the transport roller 25-3 disposed in the vicinity of the paper discharge tray 15. Is formed.

  The transport rollers 25 are small rollers for promoting and assisting the transport of paper, and a plurality of transport rollers 25 are provided along the paper transport path S. The pickup roller 16 is a pull-in roller that is provided at the front end of the paper feed cassette 10 and supplies the paper from the paper feed cassette 10 to the paper transport path S one by one. The registration roller 14 temporarily holds the sheet conveyed along the sheet conveying path S, and at the same time aligns the leading end of the sheet with the leading end of the multicolor toner image on the intermediate transfer belt 7. It is a roller that conveys to the transfer unit 70.

  In the paper transport path S, the paper fed from the paper feed cassette 10 is transported to the registration roller 14 by the transport roller 25-1, and the leading edge of the paper is aligned with the leading edge of the image information on the intermediate transfer belt 7. The image is conveyed to the secondary transfer unit 70 and image information is written on the paper by the secondary transfer unit. Thereafter, the unfixed toner on the sheet is melted and fixed by the fixing unit 12 and is conveyed by the conveying roller 25-2 and the conveying roller (discharge roller) 25-3. The sheet is discharged to the sheet discharge tray 15 (in the case of single-sided printing request).

  On the other hand, when the print request content is a double-sided print request, the single-sided printing is completed as described above, and the paper that has passed through the fixing unit 12 is discharged with its rear end chucked by the paper discharge roller 25-3. When the paper roller 25-3 rotates in the reverse direction, the paper roller 25-3 is guided to the reverse conveyance path S ′. In the reverse conveyance path S ′, after being conveyed by the conveyance rollers 25-7 and 25-8, the paper is again guided to the paper conveyance path S. Then, after passing through the registration rollers 14, printing on the back surface is performed, and then the paper is discharged to the paper discharge tray 15.

  In the image forming apparatus 100, together with the above-described paper feed cassette 10, a manual feed tray 20 is disposed so that the user does not have to open and close the paper feed cassette 10 when printing a small number of sheets. A pickup roller 21 is provided at the end of the manual feed tray 20 so that the paper in the manual feed tray 20 is guided to the paper transport path S one by one. The sheets loaded on the manual feed tray 20 are fed by the pickup roller 21 and are conveyed to the registration roller 14 through a plurality of conveyance rollers (25-6, 25-5, 25-4). Thereafter, the paper is discharged to the paper discharge tray 15 in the same manner as the paper fed from the paper feed cassette 10.

  Next, a paper feeding method in the image forming apparatus 100 will be described with reference to FIGS. In the paper feeding method of this example, when there are a plurality of print request sheets, the paper feeding timing for feeding paper from the paper storage unit such as the paper feed cassette 10 is varied according to the number of paper feeds, and the paper storage unit The presence or absence of the stored paper is detected.

  First, the paper feed cassette 10 will be described in detail with reference to FIGS. 2 and 4 to 6. As described above, the pickup roller 16 is disposed at the leading end of the paper feed cassette 10. In a paper pick-up process, which will be described later, the paper stored in the paper feed cassette 10 is supplied to the paper transport path S one by one by the operation of the pick-up roller 16. Further, in the vicinity of the paper feed cassette 10 in the paper transport path S, a separation roller (multifeed prevention member) 119 is provided to prevent double feed of paper.

  A paper front end pressing plate 113 and a paper rear end pressing plate 114 are provided at the front end portion and the rear portion of the paper feed cassette 10 so as to store paper with the front end and rear end of the paper being pressed. The paper front end pressing plate 113 is fixed to the front end portion of the paper feeding cassette 10, whereas the paper rear end pressing plate 114 is moved back and forth along the slide groove 117 formed on the bottom surface of the paper feeding cassette 10. It is attached to a slide plate 115 that slides. The slide plate 115 is formed with a slide gear 116 that engages with the slide groove 117. Thus, the leading edge of the paper is always adjusted to a predetermined position by sliding the paper trailing edge pressing plate 114 to a position corresponding to the size of the paper to be stored. A rotating plate 118 is provided so that the leading end side of the paper stored in the paper feed cassette 10 is lifted upward.

  A paper detection unit 110 for detecting the presence or absence of paper stored in the paper supply cassette 10 is provided at the rear of the paper supply cassette 10. The paper detection unit 110 includes a light emission sensor 111 and a light reception sensor 112. The light emission sensor 111 is attached to the rear end of the slide plate 115 and slides back and forth along with the paper rear end pressing plate 114 along the slide groove 117. On the other hand, the light receiving sensor 112 is attached to the apparatus frame 120 of the image forming apparatus 100 above the sheet feeding cassette 10. The light receiving sensor 112 is provided at least over the moving range of the light emitting sensor 111 that slides together with the sheet rear end pressing plate 114.

  An optical signal is sent from the light emitting sensor 111 toward the light receiving sensor 112. This optical signal is blocked by the trailing edge of the paper and does not reach the light receiving sensor 112 when there is paper in the paper feed cassette 10. Conversely, when there is no paper in the paper feed cassette 10, the optical signal from the light emission sensor 111 reaches the light reception sensor 112. That is, when the paper in the paper cassette 10 runs out, the light signal from the light emitting sensor 111 is received by the light receiving sensor 112. In this way, the presence or absence of paper in the paper feed cassette 10 is detected based on whether or not an optical signal has reached the light receiving sensor 112 from the light emitting sensor 111.

  In the image forming apparatus 100, the following two relational expressions (Expression 1) and (Expression 2) are established.

L1 / V1 ≦ (L2−L3) / V2 + L3 / V1 (Formula 1)
V1 × 1.0 <V2 <V 1 × 2.0 (Formula 2)
Here, as shown in FIG. 2, L1 is an electric field applying unit by the main charger 5d in the photosensitive drum 3 (the yellow photosensitive drum 3d in this example) that is disposed farthest from the secondary transfer unit 70. The distance (X) on the photosensitive drum 3d along the rotational direction of the photosensitive drum 3d from 50 to the primary transfer portion 60 where the toner image on the photosensitive drum 3d is transferred to the intermediate transfer belt 7, and this This is the sum of the distance (Y) on the intermediate transfer belt 7 along the rotation direction of the intermediate transfer belt 7 from the primary transfer unit 60 to the secondary transfer unit 70. L2 is a distance along the sheet conveyance direction from the sheet detection unit 110 to the secondary transfer unit 70 of the sheet feeding cassette 10, and L3 is from the registration roller 14 on the sheet conveyance path S to the secondary transfer unit 70. Distance. V1 is a driving speed of the intermediate transfer belt 7, and is a sheet conveyance speed from the registration roller 14 to the secondary transfer unit 70. V2 is the sheet conveyance speed up to the registration roller 14.

  Next, the timing of paper feeding in the image forming apparatus 100 will be described with reference to FIG. FIG. 3 is a timing chart showing a printing process and a paper feeding process when the number of print request sheets is plural. FIG. 3 shows the printing process and the paper feeding process for the first to third sheets, but the printing process and the paper feeding process for the fourth and subsequent sheets (required number of prints is 4 or more). In this case, the same timing as the printing process and the paper feeding process for the second and third sheets is performed.

  In the image forming apparatus 100, when there are a plurality of print requests (when there is a continuous print request), first, a pre-printing process is performed. After the pre-printing process, a printing process and a paper feeding process for the first sheet are performed.

  The printing process includes a printing process for the first color to the fourth color and a batch transfer process. After the printing process for the first color to the fourth color, the batch transfer process is performed. The printing process of the first color to the fourth color is performed in order from the printing process in the image station arranged far from the secondary transfer unit 70, and the printing process of the first color (in this example, yellow) → second. The printing process of the color (magenta in this example) → the printing process of the third color (cyan in this example) → the printing process of the fourth color (black in this example) is performed in this order. Each color printing step includes a main charging step of charging the photosensitive drum 3 by the main charger 5, an image exposure step of exposing the photosensitive drum 3 by the exposure unit 1 and forming an electrostatic latent image on the surface thereof, The electrostatic latent image is visualized by the toner of the developing device 2 to form a toner image on the photosensitive drum 3 and a transfer step of transferring the toner image to the intermediate transfer belt 7. It is performed in the order of exposure step → development step → transfer step.

  The main charging process of the first color printing process in the printing process for the first sheet is performed after the pre-printing process. In the first to fourth color printing processes, the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 7, whereby a color toner image (multicolor toner) is transferred onto the intermediate transfer belt 7. Image) is formed. In the batch transfer process, the multi-color toner image on the intermediate transfer belt 7 is batch transferred onto the transported paper in the secondary transfer unit 70.

  The main charging process of the first color printing process in the printing process for the second sheet starts at a timing (time t13) during the second color printing process in the printing process for the first sheet. The subsequent printing process for the second sheet is performed in the same order as the printing process for the first sheet. Then, the printing process for the third and subsequent sheets is performed at the same timing.

  On the other hand, in the paper feeding process, a paper pick-up process in which the paper stored in the paper feeding cassette 10 by the pickup roller 16 is supplied to the paper transport path S one by one, and the paper is transported from the paper feeding cassette 10 to the registration roller 14. A first paper transporting process, and a second paper transporting process of rotating the registration roller 14 to transport the paper from the registration roller 14 to the secondary transfer unit 70.

  Further, in the paper pickup process, a front pickup and a rear pickup are performed. In the front pick-up, the paper stored in the paper feed cassette 10 is picked up by the operation of the pick-up roller 16 and is transported in the transport direction (direction toward the paper transport path S for a predetermined time (T11, T21, T31 in FIG. 3)). ). The distance that the sheet is conveyed by the front pickup for the predetermined time is a distance that the rear end of the sheet passes immediately above the light emitting sensor 111, and the distance that the front end of the sheet reaches the separation roller 119 is the maximum. It is. That is, the transport distance of the sheet by the front pickup is longer than the distance from the sheet rear end pressing plate 114 to the position directly above the light emitting sensor 111 and shorter than the distance from the start end of the sheet transport path S to the separating roller 119. ing.

  When the previous pickup is completed, the pickup roller 16 is temporarily stopped, and the paper conveyance is temporarily stopped. At this time, the rear end of the paper passes immediately above the light emitting sensor 111, and thus when the paper runs out above the light emitting sensor 111, an optical signal from the light emitting sensor 111 reaches the light receiving sensor 112. Then, it is detected that there is no sheet to be fed next. As described above, the light emission sensor 111 is provided below the rear end of the slide plate 115, that is, below the rear end of the paper stored in the paper feed cassette 10. It is possible to detect whether the paper to be printed is in the paper feed cassette 10 or not.

  The rear pickup starts when a predetermined time (T12, T22, T32 in FIG. 3) elapses after the end of the front pickup. In the post-pickup, the sheet stopped before the separating roller 119 in the sheet conveyance path S is conveyed toward the registration roller 14 for a predetermined time (in FIG. 3, T13, T23, T33) by the re-operation of the pickup roller 16. To do. The rear end of the paper is sent out from the paper feed cassette 10 to the paper transport path S by the post pickup for the predetermined time.

In the paper feeding process for the first sheet, the pre-pickup in the paper pick-up process has substantially the same timing as the main charging process in the first color printing process in the printing process for the first sheet after the pre-printing process. Start at (time t11). This pre-pickup is performed only for time T11, whereby the first sheet is picked up and conveyed along the sheet conveyance path S to the front of the separating roller 119. After the end of the pre-pickup, the post-pickup starts after the elapse of time T12 (time t12). The rear pickup is performed only for time T13, whereby the trailing edge of the first sheet is sent out from the sheet feeding cassette 10 to the sheet conveyance path S. Thereafter, at the same timing (time t12) as when the pickup is started, the first sheet conveyance process to the registration roller 14 is started. As a result, the first sheet supplied to the sheet conveyance path S is conveyed along the sheet conveyance path S to the registration rollers 14.

  Thereafter, at a timing (time t18) slightly before the start of the batch transfer process in the printing process for the first sheet (time t17), the registration roller 14 starts to rotate, and the second sheet is conveyed by the rotation of the registration roller 14. The process begins. The second paper transporting process starts at a timing such that the leading edge of the first sheet and the leading edge of the multicolor toner image on the intermediate transfer belt 7 are aligned at the secondary transfer unit 70. The second paper transport process in the paper feeding process for the second and subsequent sheets starts at the same timing as the second paper transport process in the paper feeding process for the first and subsequent papers.

The pickup before the paper pickup process in the paper feeding process for the second sheet is a timing (time t14) before the main charging process of the first color printing process in the printing process for the third sheet starts (time t16). ) Is performed only for time T21. In other words, the timing at which the pre-pickup for the second sheet ends is before the start of the main charging process for the first color for the third sheet (time t16). After pre-pickup completion, the time T22 has elapsed, the rear pickup and the first sheet conveying step is started. Then, at the same timing, the pre-pickup and post-pickup of the paper pickup process in the paper supply process for the third and subsequent sheets and the first paper transport process are started.

  As described above, in the paper pick-up process in the image forming apparatus 100, the front pick-up and the rear pick-up are performed separately, and the front pick-up for the second and subsequent sheets ends when the number of print requests is plural. The timing is before the start of the main charging process of the first color printing process in the printing process for the next sheet. The next sheet means the next sheet with respect to the target sheet in the sheet feeding process.

  In the paper pickup process, the time T11, the time T21, and the time T31 coincide with each other for the time when the previous pickup is performed (T11 = T21 = T31). In addition, regarding the time when the subsequent pickup is performed, time T13, time T23, and time T33 coincide with each other (T13 = T23 = T33). On the other hand, as for the time between the front pickup and the rear pickup, the time T22 and the time T32 substantially coincide with each other and both are longer than the time T12 (T12 <T22≈T32). In this way, the time required for the paper pick-up process for the second and subsequent sheets is made longer than that for the first sheet. Thus, when the timing at which the paper pick-up process is completed (the timing at which the post-pickup is finished) is used as a reference, the timing at which the paper pick-up process is started (timing at which the pre-pickup is started) is greater than the paper pick-up process for the first sheet. However, the paper pick-up process for the second and subsequent sheets is faster. That is, the start timing of the paper feeding process is earlier for the second and subsequent sheets.

  In this example, when the required number of prints is plural, for the second sheet, the first pickup in the printing process for the first sheet after the pre-printing for the first sheet performs pre-printing processing. Since the printing process starts at substantially the same timing as the main charging process (time t11), as in the conventional case (see FIG. 7), before the printing process for the second sheet starts (time t13), The presence or absence of the second sheet can be detected.

  For the third and subsequent sheets, the timing at which the pre-pickup for the second and subsequent sheets ends is set before the main charging process of the first color printing process in the printing process for the next sheet. Therefore, the presence / absence of a sheet to be fed next can be detected before the printing process for the sheet starts, and can be detected earlier than in the conventional case (see FIG. 7).

  In this way, not only for the second sheet but also for the third and subsequent sheets, the timing before the start of the printing process (for example, the printing process starts for the third sheet (time t16). The presence or absence of a sheet can be detected at the previous timing (time t15), and if it is detected that there is no next sheet in the sheet feeding cassette 10, the printing process can be stopped before the start. As a result, the conventional problem that has occurred when the paper in the paper cassette 10 runs out during continuous printing, specifically, an image formed image or unfixed developer is wasted, or the cleaner unit 4 is used. It is possible to prevent the occurrence of problems such as an increase in the load and a load on the photosensitive drum 3 and the developing device 2 and a decrease in life characteristics.

  In the above description, as shown in FIG. 3, the example in which the paper pickup process for the first sheet is divided into the front pickup and the rear pickup as in the paper pickup process for the second and subsequent sheets has been described. As in the conventional case (see FIG. 7), the front pickup and the rear pickup can be performed separately. That is, at least for the second and subsequent sheets, the sheet pickup process may be performed separately for the front pickup and the rear pickup.

  In the above description, as illustrated in FIG. 3, an example in which a plurality of sheets are fed from the sheet feeding cassette 10 with a gap between sheets has been described. However, a plurality of sheets may be continuously fed without a gap between the sheets. it can. In this case, the front pickup for the second and subsequent sheets may be performed simultaneously with the rear pickup for the previous sheet. That is, it is only necessary to perform the front pickup of the next sheet while the previous sheet is being conveyed toward the registration rollers along the sheet conveyance path S by the rear pickup.

  Furthermore, in the above description, as illustrated in FIG. 1, an example is described in which the paper storage unit is applied to the image forming apparatus 100 provided with one paper feed cassette 10, but a plurality of paper feed cassettes are provided. It can also be applied to the case where paper is fed from the manual feed tray 20.

It is explanatory drawing which shows one Embodiment of the image forming apparatus to which this invention is applied. FIG. 3 is an explanatory diagram schematically showing an arrangement relationship inside the image forming apparatus. 6 is a timing chart showing a printing process and a paper feeding process when there are a plurality of print request sheets. It is a side view showing the inside of a paper feed cassette. FIG. 6 is a plan view showing a rear portion of a paper feed cassette. FIG. 6 is a side view showing a light emitting sensor and the like provided at the rear of the paper feed cassette. 6 is a timing chart showing a printing process and a paper feeding process when a required number of prints is plural in an image forming apparatus using a conventional intermediate transfer method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exposure unit 2 Developing device 3 Photosensitive drum 5 Main charger 6 Intermediate transfer roller 7 Intermediate transfer belt 10 Paper feed cassette 11 Secondary transfer roller 14 Registration roller 16 Pickup roller 70 Secondary transfer unit 100 Image forming apparatus 110 Paper detection unit S Paper transport path

Claims (8)

A plurality of electrostatic latent image carriers are used to laminate and transfer the image information separated into a plurality of colors onto an intermediate transfer belt that rotates in contact with each electrostatic latent image carrier at a predetermined pressure. A paper feeding method in an image forming apparatus using an intermediate transfer method for forming a color image on a paper by batch transfer onto a conveyed paper,
When print request number is plural, it has rows in two front pick-up and post-pick up paper pickup feeding from said sheet storing section to the sheet conveying path one sheet at a time,
The length of time during which the front pickup and the rear pickup are performed is matched for each of the front pickup and the rear pickup, and the time length between the front pickup and the rear pickup is substantially the same for the second and subsequent sheets. The time required for the paper pick-up process for the second and subsequent sheets is longer than that for the first sheet, and the start timing is earlier in the paper pick-up process for the second and subsequent sheets than in the paper pick-up process for the first sheet. A paper feeding method in an image forming unit, wherein the presence or absence of paper stored in a storage unit is detected. Conveying distance of the sheet by the pre-SL before pickup, maximum image according to claim 1, the leading end of the sheet is characterized in that the distance to reach the double feed preventing member provided in the vicinity of the sheet storing section Paper feeding method in the forming apparatus. Conveying distance of the sheet by the front pickup image according to claim 1 or claim 2, wherein the minimal, the end after the sheet is a distance that passes through the sheet detecting portion for detecting the presence or absence of paper Paper feeding method in the forming apparatus. Paper in an image forming apparatus according to claim 3, the pre-Symbol for paper detection unit, characterized in that movable in a rear portion of the sheet storing section. Paper in an image forming apparatus according to any one of claims 1 to 4, characterized in that the pre-pickup is performed for the second and subsequent sheets paper. The timing at which the front pick-up for the second and subsequent sheets is completed, according to any one of claims 1, characterized in that the before the next printing step of pairs in the sheet begins to 5 A paper feeding method in an image forming apparatus. The next and the start of Printout step against the paper, by the one of the plurality of latent electrostatic image bearing member, a main charger for the farthest of the electrostatic latent image bearing member from the batch transfer unit to perform the collective transfer The sheet feeding method in the image forming apparatus according to claim 6 , wherein an electric field application is started . The paper feeding method in the image forming apparatus according to claim 7.
L1 is the electrostatic latent image from the electric field applying portion by the main charger in the farthest electrostatic latent image carrier to the primary transfer portion where the toner image on the electrostatic latent image carrier is transferred to the intermediate transfer belt. The sum of the distance on the electrostatic latent image carrier along the rotation direction of the carrier and the distance on the intermediate transfer belt along the rotation direction of the intermediate transfer belt from the primary transfer portion to the batch transfer portion;
L2 is a distance along the paper conveyance direction from the paper detection unit to the batch transfer unit of the paper storage unit,
L3 is the distance from the registration roller arranged along the paper conveyance path to the batch transfer unit,
V1 is the driving speed of the intermediate transfer belt,
If V2 is the sheet conveyance speed up to the registration rollers in the sheet conveyance path, then the following two relational expressions:
L1 / V1 ≦ (L2-L3) / V2 + L3 / V1
V1 × 1.0 <V2 <V1 × 2.0
Paper in images forming device you characterized in that hold.

Images