JP2017109837A - Sheet feeding device, image formation apparatus, control method of sheet feeding device and control program of sheet feeding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet feeding device which can prevent the sheet deviation in a register roller part with a simple configuration.SOLUTION: A sheet feeding device 40 conveys a sheet P3 along a curved sheet passage path 45 by using a sheet feeding roller 42 and a register roller 44. The sheet feeding device 40 controls the sheet feeding roller 42, and performs sheet inclination correction by butting a sheet P3 against the stopped register roller 44. When the sheet inclination correction is performed and the register roller 44 is driven, the speed control of the sheet feeding roller 42 is performed so as to keep the sag amount of the sheet P3 in the sheet passage path 45. The speed control is performed in a preset mode corresponding to the type of the used sheet P3.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a sheet feeding device, an image forming apparatus, a sheet feeding device control method, and a sheet feeding device control program, and in particular, a predetermined amount of sag in a curved sheet passing path between a sheet feeding roller and a timing roller. The present invention relates to a sheet feeding device that conveys a sheet while holding the sheet, an image forming apparatus, a sheet feeding device control method, and a sheet feeding device control program.

  Examples of the image forming apparatus include an MFP (Multi Function Peripheral) having a scanner function, a facsimile function, a copying function, a function as a printer, a data communication function, and a server function, a facsimile apparatus, a copying machine, and a printer. In such an image forming apparatus, there is known an apparatus that conveys a sheet while maintaining a predetermined amount of slack in a curved sheet passing path between a sheet feeding roller and a timing roller.

  In Patent Document 1 below, in a sheet conveying apparatus, a paper loop amount is constant after correction of the leading edge inclination in order to prevent a loud sound from being generated when the paper is stretched between a paper feed roller and a timing roller. It is disclosed that when the amount is reached, the paper feed roller is started at a lower speed than the timing roller, and the speed of loop reduction is reduced. In this apparatus, a loop amount sensor is used to detect the amount of loop formed by the paper.

  Japanese Patent Application Laid-Open No. 2004-228561 describes that in a paper feeding device of an image forming apparatus, in order to prevent fluctuations in the load due to paper stretching between paper feeding and timing rollers from affecting the image. It is disclosed that a switch for detecting the slackness of the paper is disposed in the paper, and the paper feed roller is rotated to increase the slackness of the paper when the loop amount becomes a certain amount or less.

  In Patent Document 3 below, in the recording paper transport device of the image forming apparatus, the leading edge of the paper is detected between the paper feed roller and the timing roller, and the timing from when the paper feed is stopped until the paper feed stops is adjusted according to the length of the paper. Thus, it is disclosed that a constant loop amount is ensured regardless of the paper size.

JP 2012-126492 A Japanese Patent Laid-Open No. 01-281227 JP 2008-037635 A

  In a sheet feeding device used in the image forming apparatus as described above, the following operation is generally performed in order to correct the inclination of the leading edge of a sheet to be fed.

  First, one sheet is separated from a sheet feed tray on which sheets are stacked via a separation unit. The separated paper is conveyed by a paper feed roller. The conveyance is performed until the leading edge of the sheet is abutted against the nip of the stopped pair of registration rollers.

  A roller (such as a paper feed roller) used for loop formation installed on the upstream side of the paper transport path is continuously rotated. As a result, a paper loop is formed in the conveyance path to the registration roller. By forming a loop having a predetermined loop amount, the inclination generated during conveyance on the upstream side of the apparatus is corrected.

  The sheet whose inclination is corrected is sent to the image recording unit. An image is written on the sheet by a transfer roller that rotates at a constant speed. Generally, at this time, the driving of the paper feed roller is stopped. When the driving of the paper feed roller is stopped and the registration roller is driven, the paper is pulled between the paper feed roller and the registration roller, and then the paper is pulled out from the paper feed roller. At this time, a slip may be caused in the registration roller portion due to an impact when the paper is stretched, and the paper may be displaced. If a paper misalignment occurs in the registration roller unit, a misalignment also occurs in image writing on the paper in the downstream transfer unit, which may lead to a decrease in image quality.

  On the other hand, since the sheet feeding roller generally has a larger slip than the registration roller, the conveyance speed of the sheet feeding roller is set higher than that of the registration roller. Therefore, if the drive of the paper feed roller is not stopped, the amount of paper sag between the paper feed roller and the registration roller becomes too large. In addition, depending on the size of the paper, the paper may be pushed into the registration roller. If paper misalignment occurs due to paper pushing in the registration roller section, image quality may be degraded.

  Various countermeasures have been proposed in order to avoid the occurrence of sheet misalignment at the registration roller portion.

  For example, it is conceivable that by ensuring the conveying force of the registration rollers, it is possible to prevent the sheet deviation from occurring even if there is a load fluctuation caused by the sheet feeding roller. However, in order to ensure the conveyance force, it is necessary to increase the amount of pressure contact force. For this purpose, it is necessary to use a registration roller having a large diameter, and the size of the paper feeding device is increased. Further, if the amount of pressure contact force is large, the rotational load of the registration roller increases, so that it is necessary to increase the size of the motor and the power consumption of the sheet feeding device increases.

  Further, it is conceivable to hold the slack of the paper so that the paper is not stretched and is not excessively bent between the paper feed roller and the registration roller. In order to do this, for example, as described in the above-mentioned patent document, a sensor for detecting the position of the paper is provided, and the driving of the paper feed roller may be controlled based on a signal from the sensor. However, in order to arrange the sensor for detecting the slack of the sheet between the sheet feeding roller and the registration roller as described above, it is necessary to secure a wide sheet passing path. This increases the size of the paper feeder. Further, since it is necessary to provide a sensor for detecting slackness, the number of parts increases and the assembly process becomes complicated, and the manufacturing cost of the sheet feeding device increases.

  The present invention has been made to solve such a problem, and has a simple configuration capable of preventing sheet misalignment at the registration roller portion, an image forming apparatus, and a control method for the sheet feeding apparatus. And a control program for the sheet feeding device.

  In order to achieve the above object, according to one aspect of the present invention, a curved sheet passing path is provided between the paper feed roller and the registration roller by using the paper feed roller and a registration roller downstream of the paper feed roller. A sheet feeding device that conveys the sheet along the sheet feeding roller, controls the sheet feeding roller, abuts the sheet against the stopped registration roller, corrects the sheet tilt, and corrects the sheet tilt by the correction unit, A speed control means for controlling the speed of the paper feed roller so that the amount of slack of the paper in the paper passing path is maintained when the registration roller is driven, and the speed control means determines the type of paper to be used. Speed control is performed in a corresponding preset manner.

  Preferably, the speed control unit performs speed control by repeatedly rotating and stopping the paper feed roller at a speed higher than that of the registration roller.

  Preferably, the speed control unit changes the timing for starting the speed control in accordance with the sheet thickness of the sheet.

  Preferably, the speed control means feeds the paper when the paper thickness is thinner than when the paper thickness is thick, after the paper tilt correction is performed by the correction means and the paper feed roller and the registration roller are driven. The time until the speed control is started is shortened by stopping the paper roller.

  Preferably, the speed control means rotates the paper feed roller when the paper thickness is thinner than when the paper thickness is thick, after the paper tilt correction is performed by the correction means and the registration roller is driven. By starting, the timing for starting the speed control is delayed.

  Preferably, the speed control unit switches the speed of the paper feed roller between a high side faster than the speed of the registration roller and a low side slower than the speed of the registration roller when the speed control is executed.

  Preferably, at the start of the speed control, the speed control unit sets the speed of the paper feed roller to the high side when the paper thickness is equal to or greater than a predetermined thickness, and when the paper thickness is smaller than the predetermined thickness, The speed of the paper feed roller is set to the low side.

  Preferably, the speed control unit performs speed control so that the paper is in a slack state regardless of the size or type of the paper when the trailing edge of the paper passes through the paper feed roller.

  According to another aspect of the present invention, an image forming apparatus includes any of the above-described paper feeding devices that transport paper, and an image forming unit that forms an image on the paper transported by the paper feeding device.

  According to still another aspect of the present invention, a sheet is fed along a curved sheet passing path between the sheet feeding roller and the registration roller by using the sheet feeding roller and a registration roller downstream of the sheet feeding roller. The control method of the paper feeding device to be conveyed includes a correction step of controlling the paper feed roller to abut the paper against the stopped registration roller and correcting the paper inclination, and the paper inclination correction by the correction step is performed. A speed control step for controlling the speed of the paper feed roller so that the amount of slack in the paper passing path is maintained when the roller is driven, and the speed control step corresponds to the type of paper to be used. The speed control is performed in a preset manner.

  According to still another aspect of the present invention, a sheet is fed along a curved sheet passing path between the sheet feeding roller and the registration roller by using the sheet feeding roller and a registration roller downstream of the sheet feeding roller. The control program for the sheet feeding device that controls the sheet feeding roller controls the sheet feeding roller to abut the sheet against the stopped registration roller, corrects the sheet tilt, and performs the sheet tilt correction by the correction step. When the roller is driven, the computer executes a speed control step for controlling the speed of the paper feed roller so that the slack amount of the paper in the paper passing path is maintained. Speed control is performed in a preset manner corresponding to the type.

  According to these inventions, it is possible to provide a sheet feeding device, an image forming apparatus, a sheet feeding device control method, and a sheet feeding device control program having a simple configuration capable of preventing sheet misalignment at the registration roller unit. it can.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an exemplary embodiment. It is a figure which shows an image process part. It is a block diagram which shows the structure of a control part. FIG. 4 is a side view illustrating a configuration of a sheet feeding device. It is a figure explaining the tension of a paper. It is a figure explaining pushing in of a sheet. FIG. 10 is a diagram for describing conveyance of a sheet in the present embodiment. It is a figure explaining the relationship between the kind of paper and speed control. 6 is a flowchart for describing a sheet feeding operation performed by a sheet feeding device based on control by a control unit. It is a figure which shows the specific example of speed control. It is a figure which shows another specific example of speed control. It is a figure which shows the modification of speed control.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described.

  In this embodiment, the image forming apparatus is, for example, a tandem type color digital copying machine that forms an image on a sheet by an electrophotographic method.

  [Overall Configuration of Image Forming Apparatus 1]

  FIG. 1 is a diagram showing an overall configuration of an image forming apparatus 1 according to the present embodiment.

  As shown in FIG. 1, the image forming apparatus 1 reads an automatic document feeder 2 that automatically feeds a document, a document reading unit 10 that reads an image of the conveyed document, and the document reading unit 10. And an image forming unit 20 that prints and reproduces an image on a recording sheet.

  The automatic document feeder 2 includes a document feed tray 3 on which documents are set. The automatic document feeder 2 transports the documents placed on the document feed tray 3 one by one to the document reading position on the platen glass 11. The document reading unit 10 reads the conveyed document. The automatic document feeder 2 further conveys the document and discharges it onto the document discharge tray 4.

  The document reading unit 10 includes a scanner and a full-color CCD sensor 12 (shown in FIG. 3). The scanner exposes and scans the document conveyed on the platen glass 11. The CCD sensor 12 converts the reflected light of the document resulting from the scanner exposure into an electrical signal. When the document is exposed and scanned by the scanner, the CCD sensor 12 performs photoelectric conversion, and electric signals of red (r), green (g), and blue (b) components indicating images are sent to the control unit 100.

  The image data of each color component of red (r), green (g), and blue (b) is subjected to correction processing in the image signal processing unit 101 (shown in FIG. 3) of the control unit 100, and yellow (Y), magenta (M), cyan (C), and black (K) are converted to gradation data of each reproduction color. The gradation data is temporarily stored in the image memory 102 (shown in FIG. 3). Hereinafter, red, green, and blue color components may be simply represented as “r, g, b”, and yellow, magenta, cyan, and black reproduction colors are represented as “Y, M, C, and K”, respectively. Sometimes.

  The image forming unit 20 includes an image processing unit 30 and a paper feeding device 40 for feeding the paper S. The image forming unit 20 forms an image on a sheet S as a recording sheet by an electrophotographic method.

  FIG. 2 is a diagram illustrating the image processing unit 30.

  As shown in FIG. 2, the image processing unit 30 includes an image forming unit 20Y, 20M, 20C, and 20K corresponding to each of Y, M, C, and K reproduction colors, and an intermediate transfer that rotates in the arrow A direction. Belt 31. The image processing unit 30 forms an image corresponding to the gradation data of each reproduced color.

  The image forming units 20Y-20K are arranged in series at a predetermined interval from the upstream side in the rotation direction of the intermediate transfer belt 31 to the downstream side in the rotation direction so as to face the intermediate transfer belt 31. The image forming units 20Y-20K include photosensitive drums 21Y, 21M, 21C, and 21K, chargers 22Y, 22M, 22C, and 22K, exposure units 23Y, 23M, 23C, and 23K, and developers 24Y, 24M, and 24C, 24K, primary transfer rollers 25Y, 25M, 25C, and 25K facing the photosensitive drums 21Y-21K so as to sandwich the intermediate transfer belt 31, and cleaners 26Y, 26M, 26C, and 26K. The photosensitive drums 21Y-21K rotate in the arrow B direction. The charger 22Y-22K, the exposure unit 23Y-23K, the developer 24Y-24K, the primary transfer roller 25Y-25K, and the cleaner 26Y-26K rotate around the photoconductor drum 21Y-21K. They are arranged in this order from the upstream side. The image forming units 20Y-20K are configured to be detachable from the apparatus.

  The developing devices 24Y-24K contain developers of the respective reproduction colors. In the present embodiment, for example, toner by a one-component development method is accommodated. Each reproducible color toner contains a charge control agent such as silica. When the toner particles rub against each other due to stirring in the developing devices 24Y-24K, the toner is charged and used for development.

  The developing device 24Y includes a developing roller 241Y, a regulating plate 242Y, and a stirring roller pair 243Y. The developing roller 241Y faces the photosensitive drum 21Y. The developing roller 241Y rotates in the direction opposite to the rotation direction of the photosensitive drum 21Y with the Y-color toner carried on the surface, and supplies the carried toner to the photosensitive drum 21Y. The agitation roller pair 243Y rotates to send the toner to the developing roller 241Y while agitating the toner contained in the developing device 24Y. The regulating plate 242Y is arranged so that the tip thereof uniformly contacts the surface of the developing roller 241Y. The regulating plate 242Y regulates the toner sent to the developing roller 241Y by the stirring roller pair 243, and forms a uniform thin layer of toner on the surface of the developing roller 241Y. Such a configuration is the same for the other developing devices 24M, 24C, and 24K.

  The image forming units 20Y-20K are provided with a drive source such as a motor, and each image forming unit 20Y-20K can be driven independently. The forced toner consumption operation (forced discharge operation) can be executed individually for each reproduction color. The forced toner consumption operation is performed by creating a solid image on the photosensitive drum 21Y-21K and collecting it with a cleaner 26Y-26K without transferring it to a sheet.

  Returning to FIG. 1, the intermediate transfer belt 31 is stretched around a drive roller 34, a driven roller 33, and a tension roller 32.

  As will be described later, the paper feeding device 40 includes a paper feeding cassette 41 that stores paper S, a paper feeding roller 42, a pair of registration rollers 44, and the like. The paper feed roller 42 feeds the paper S in the paper feed cassette 41 one by one. The registration roller 44 takes a timing to send the paper S to the secondary transfer position T.

  When forming an image, the control unit 100 sequentially reads out the image data of each color of the corresponding page from the image memory 102 (shown in FIG. 3), and drives the laser diodes (not shown) of the exposure units 23Y-23K. A drive signal for generating is generated. The laser diodes of the exposure units 23Y-23K are modulated and driven by a drive signal from the control unit 100 and emit laser beams to expose the photosensitive drums 21Y-21K.

  The remaining toner on the surface of the photosensitive drums 21Y-21K is removed by a cleaner 26Y-26K, and an eraser lamp (not shown) is irradiated to eliminate the charge. Thereafter, the surface of the photosensitive drum 21Y-21K is uniformly charged by the chargers 22Y-22K. The photosensitive drum 21Y-21K is exposed to the laser beam of the exposure unit 23Y-23K in a state of being uniformly charged as described above. When exposed, an electrostatic latent image is formed on the surface of the photosensitive drum 21Y-21K.

  Each electrostatic latent image is developed by each color developer 24Y-24K. As a result, Y, M, C, and K color toner images are formed on the surface of the photosensitive drum 21Y-21K. Each color toner image is sequentially transferred onto the intermediate transfer belt 31 at the primary transfer position by the electrostatic action of the primary transfer rollers 25Y-25K. At this time, the image forming operation for each color is executed with the timing shifted from the upstream side to the downstream side so that the toner image is transferred to the same position on the intermediate transfer belt 31.

  The toner image formed by superimposing the respective colors on the intermediate transfer belt 31 moves to the secondary transfer position T as the intermediate transfer belt 31 rotates.

  The sheet S is fed through the registration roller 44 in accordance with the movement timing of the toner image on the intermediate transfer belt 31 to the secondary transfer position T. At the secondary transfer position T, the toner images of the respective colors on the intermediate transfer belt 31 are collectively transferred onto the sheet S by the electrostatic action of the secondary transfer roller 35.

  The sheet S on which the toner image of each color is transferred passes through the fixing unit 36. As a result, the toner image is thermally fixed on the paper S. The paper S is discharged onto the paper discharge tray 38 via the discharge roller pair 37. This completes the color image forming operation.

  [Configuration of Control Unit 100]

  FIG. 3 is a block diagram illustrating a configuration of the control unit 100.

  As shown in FIG. 3, the control unit 100 includes an image signal processing unit 101, an image memory 102, a determination unit 103, a laser diode (LD) driving unit 104, a ROM 105, a RAM 106, an image formation number storage unit 107, and a CPU 108. I have. The image memory 102 temporarily stores image data read by the document reading unit 10. The ROM 105 stores a program 105b necessary for controlling each function of the image forming apparatus 1. The RAM 106 is used as a work area when the program 105b is executed. The CPU 108 controls various functions of the image forming apparatus 1 by executing the program 105b.

  The image signal processing unit 101 performs correction processing such as shading correction on the r, g, and b image data sent from the CCD sensor 12 of the document reading unit 10. The image signal processing unit 101 converts the image data into image data of Y, M, C, and K reproduction colors, and stores the converted image data in the image memory 102.

  When an address is instructed from the CPU 108 and a read request is received, the image memory 102 receives the image data (pixel data) of each reproduction color stored at the address in units of pages, and the determination unit 103 and the laser diode driving unit 104. Send to.

  The determination unit 103 determines the execution timing (toner discharge timing) of the forced toner consumption operation in units of pages based on the image data sent from the image memory 102. The determination unit 103 sends the determination result to the CPU 108 as determination information. If the CPU 108 determines that the forced consumption operation is necessary based on the determination information, the CPU 108 executes the forced consumption operation and discharges the toner from the developing devices 24Y-24K.

  On the other hand, the laser diode driving unit 104 modulates and drives the laser diodes of the exposure units 23Y-23K based on the image data sent from the image memory 102 to expose the photosensitive drums 21Y-21K.

  The CPU 108 controls the operation of each unit such as the automatic document feeder 2, the document reading unit 10, and the image forming unit 20 based on the program 105b stored in the ROM 105, and executes a determination of a paper jam or the like. . Thereby, a color image forming operation can be smoothly performed.

  [Description of Paper Feeder 40]

  FIG. 4 is a side view showing the configuration of the paper feeding device 40.

  As shown in FIG. 4, the paper feeding device 40 includes a paper feeding cassette 41, a paper feeding roller 42, a separating roller 43, and a pair of registration rollers 44. A sheet passing path 45 is provided between the sheet feeding roller 42 and the registration roller 44.

  The paper feed roller 42 cooperates with the separation roller 43 and feeds the paper from the paper feed cassette 41 one by one. The sheet is fed out in a direction (paper feeding direction) which becomes the right side in FIG.

  The registration roller 44 is located downstream of the paper feed roller 42 in the paper transport direction (hereinafter, sometimes simply referred to as the downstream side). The registration roller 44 is used for paper inclination correction. Further, the registration roller 44 conveys the paper on which the paper inclination correction has been performed to the secondary transfer position T.

  The sheet passing path 45 is provided so as to connect from the sheet feeding roller 42 to the registration roller 44 thereabove. In the present embodiment, the sheet passing path 45 is curved so as to be convex in the sheet feeding direction. The sheet passing path 45 is arranged so as to be sandwiched between an outer guide 46 provided on the outer side that is curved and an inner guide 47 provided on the inner side. The distance between the outer guide 46 and the inner guide 47 is relatively wide so that the sheet can sag in this portion.

  A paper edge detection sensor 49 is disposed on the upstream side of the registration roller 44 in the paper passage path 45. The paper edge detection sensor 49 can detect the presence or absence of paper at the detection position of the paper passage path 45. That is, the paper edge detection sensor 49 detects that the leading edge of the paper has reached the detection position and that the trailing edge of the paper has reached the detection position.

  The conveyance of the sheet is started when the sheet feeding roller 42 is driven and the sheet on the sheet feeding cassette 41 is fed out. At this time, the presence of the separation roller 43 prevents double feeding of paper. When one sheet is fed out, the driving of the sheet feeding roller 42 is continued and the sheet is conveyed on the sheet passing path 45. At this time, the leading edge of the sheet is guided upward along the outer guide 46.

  When the leading edge of the paper transported on the paper passing path 45 reaches the detection position, this is detected by the paper edge detection sensor 49. Then, the sheet inclination correction using the registration roller 44 and the sheet feeding roller 42 is performed based on the timing.

  In the paper tilt correction, the paper feed roller 42 continues to convey the paper for a predetermined time (or distance) while the paper is abutted against the stopped registration roller 44, and the paper is slackened on the paper path 45. (To form a paper loop). After the sheet is slack, the registration roller 44 is driven, so that the sheet can be conveyed to the secondary transfer position after correcting the inclination of the sheet.

  [Description of paper misalignment]

  In general, when the registration roller 44 is driven after correcting the inclination of the sheet, a sheet shift may occur, which may be a problem. The paper misalignment may occur when the paper posture on the paper passing path is not maintained in an ideal state and the paper is stretched or pushed into the registration roller 44.

  FIG. 5 is a diagram for explaining sheet stretching.

  FIG. 5 shows a case where the registration roller 44 rotates (arrow R1) and the driving of the paper feed roller 42 is stopped after the paper tilt correction is performed during the conveyance of the paper P1. Even if the paper feed roller 42 is not driven by a mechanism such as a one-way clutch, the paper feed roller 42 rotates as the paper P1 is conveyed.

  When the paper feed roller 42 stops after the inclination correction and the registration roller 44 is driven, the paper loop formed at the time of the inclination correction is eliminated. Then, as shown in FIG. 5, when the paper P1 is stretched between the paper feed roller 42 and the registration roller 44, the driving of the registration roller 44 is continued so that the paper P1 is conveyed. As a result, the paper feed roller 42 rotates. At this time, although the paper feed roller 42 is rotatable by a mechanism such as a one-way clutch, the paper P1 is slightly dragged because it is sandwiched between the paper feed roller 42 and the separation roller 43. Further, since the sheet passing path 45 is curved, the conveyance of the sheet P1 is continued while the sheet P1 is in contact with the inner guide 47, and the frictional resistance is applied to the sheet P1. For this reason, a downward load (direction in which the conveyance of the paper P1 is hindered; arrow F1) is applied to the registration roller 44. As a result, a sheet shift occurs at the registration roller 44, and the conveyance amount of the sheet may be smaller than the intended amount.

  FIG. 6 is a diagram for explaining the pushing-in of the paper.

  FIG. 6 shows a case where the registration roller 44 is driven (arrow R1) and the paper feed roller 42 is also driven (arrow P1) after the paper tilt correction is performed during conveyance of the paper P2. Yes. Even after the driving of the registration roller 44 is started, the paper feed roller 42 is driven at a rotational speed higher than that of the registration roller 44 so as not to cause the above-described sheet tension.

  In such a case, since the paper feed roller 42 is driven together with the registration roller 44, the amount of the paper loop increases as time elapses compared to the time when the inclination is corrected. When the amount of the paper loop increases, the paper P2 sticks to the outer guide 46, and there is no space for the paper P2 beyond that to escape. Then, when the paper feed roller 42 is further driven and the paper P2 is stiff, a load (upward direction of the paper P2; arrow F2) is applied to the registration roller 44. As a result, a sheet shift occurs at the registration roller 44, and the registration roller 44 cannot carry the original sheet, and the sheet conveyance amount may become larger than the intended amount.

  [Description on Speed Control of Paper Feed Roller 42]

  In this embodiment, in order to prevent such sheet misalignment, when the registration roller 44 is driven immediately after the sheet inclination correction is performed, the amount of sheet sag in the sheet passing path 45 is maintained. Thus, the speed control of the paper feed roller 42 is performed. Such speed control is performed based on the control of the control unit 100.

  FIG. 7 is a diagram for explaining conveyance of a sheet in the present embodiment.

  FIG. 7 shows a scene in which the sheet P3 is conveyed from the registration roller 44 to the secondary transfer position T after the sheet inclination correction is performed. In the present embodiment, the sheet P3 is centered on a state (shown by a solid line in FIG. 7) that is substantially at the center of the sheet passing path 45 (a position that is not too close to either the inner guide 47 or the outer guide 46). The speed control of the paper feed roller 42 is performed so that the paper is conveyed within a range that approaches the both sides of the inner guide 47 and the outer guide 46 to a certain extent. As indicated by a broken line in FIG. 7, the inner guide 47 is not contacted when the loop amount of the paper P3 is the smallest, and the outer guide 46 is not contacted when the loop amount of the paper P3 is the largest. Thus, the speed control of the paper feed roller 42 is performed, and the loop amount of the paper P3 is maintained within a certain range.

  FIG. 8 is a diagram for explaining the relationship between the paper type and the speed control.

  FIG. 8 shows the case where the sheet inclination correction is performed for the sheet P10 having a relatively thin sheet thickness and the case where the sheet inclination correction is performed for the sheet P20 having a relatively large sheet thickness. As shown in FIG. 8, the posture immediately after the correction of the sheet inclination by the registration roller 44 is different between the sheet P10 and the sheet P20. That is, since the thin paper P10 is weak, the leading edge of the thin paper P10 is detected by the paper edge detection sensor 49 and is in a posture along the relatively outer guide 46 when being abutted against the registration roller 44. In other words, the loop amount of the thin paper P10 is relatively large when the inclination correction is performed. On the other hand, since the thick paper P20 is stiff, even when the leading edge is detected by the paper edge detection sensor 49 and abuts against the registration roller 44, the thick paper P20 is relatively away from the outer guide 46. In other words, the loop amount of the thick paper P20 is relatively small when the inclination correction is performed.

  Since there is a difference between the sheets P10 and P20 depending on the sheet thickness, in this embodiment, the speed control of the sheet feeding roller 42 performed after the sheet inclination correction is performed in accordance with the sheet thickness (an example of the sheet type). Done in That is, the speed control mode is used when the paper is relatively stiff, such as when the paper P20 is transported, and when the paper is stiff, such as when the paper P10 is transported. Is switched.

  Specifically, in the present embodiment, when the paper thickness is greater than or equal to a predetermined value (hereinafter sometimes referred to as “when thick paper”), and when the paper thickness is less than the predetermined value (hereinafter referred to as “thick paper”). In this case, the speed control of the paper feed roller 42 is performed in a different manner depending on which one of the two categories “sometimes thin paper” belongs.

  FIG. 9 is a flowchart for explaining a paper feeding operation performed by the paper feeding device 40 based on the control of the control unit 100.

  When printing on a sheet is performed in the image forming apparatus 1, a series of sheet feeding operations as shown in FIG. 9 is started. When the paper feeding operation is completed, the paper is conveyed to the secondary transfer position T.

  As shown in FIG. 9, in step S101, the paper thickness (paper thickness) of the paper to be transported is determined. The determination is made based on, for example, paper information registered in the image forming apparatus 1 in advance. In this case, the paper information may be registered by inputting information from the user in advance for the paper stored in the paper feed cassette 41. Note that the present invention is not limited to such a discriminating method, and for example, paper thickness information may be input from the user in accordance with an instruction to execute printing on paper.

  In step S <b> 102, the control unit 100 determines the timing for starting the speed control and the speed of the paper feed roller 42 during the speed control based on, for example, a control table stored in advance in the ROM 105 or the like. In the control table, for example, a condition relating to the sheet thickness (for example, whether the sheet is thick or thin) and a setting value relating to speed control applied to the sheet corresponding to the condition are associated with each other. It is remembered. As the set value, a value related to the timing at which the speed control is started (for example, the time from when the leading edge of the paper is detected by the paper edge detection sensor 49 to when the speed control is started) is stored. Further, values relating to the speed of the paper feed roller 42 during speed control (for example, rotation time and stop time when the rotation and stop of the paper feed roller 42 are repeated as will be described later) are stored as set values.

  In step S103, paper feeding is started. A sheet of paper is conveyed on the paper passage path 45 by the paper feed roller 42 and the separation roller 43.

  In step S <b> 104, the leading edge of the paper is detected by the paper edge detection sensor 49.

  When the leading edge of the paper is detected, paper inclination correction is performed in step S105.

  In step S106, the paper feed roller 42 and the registration roller 44 are driven at the timing and speed determined in step S102. The speed control is started at a timing determined with reference to the timing at which the paper is detected by the paper edge detection sensor 49 (that is, the timing at which the paper inclination correction is performed after the predetermined time). The speed control is performed, for example, by driving the paper feed roller 42 at a determined speed while driving the registration roller 44 at a predetermined speed.

  In step S107, the control unit 100 has transported the paper to the front end of the paper (the vicinity of the rear end of the paper has reached the paper feed roller 42, and the rear end of the paper has not passed the paper feed roller 42) Or not) is determined. Until it is determined, the speed control is continued. The determination is made based on the size information of the paper to be transported. The control unit 100 can acquire the size information in the same manner as the paper thickness, for example.

  If it is determined that the paper has been transported to the front end of the paper, the control unit 100 thereafter controls the speed by forcibly rotating the paper feed roller 42 as shown in step S108. That is, when the trailing edge of the paper passes through the paper feed roller 42, speed control is performed so that the paper is in a slack state. As a result, the sheet is separated from the sheet feed roller 42 in a state where the sheet feed roller 42 is rotating regardless of the sheet size and sheet type, so that the sheet is not subjected to the force of the sheet feed roller 42 being dragged. It can be surely prevented.

  When the trailing edge of the paper passes the paper feed roller 42, the speed control for the paper feed roller 42 ends. The sheet being conveyed is continuously conveyed to the secondary transfer position T by the registration roller 44.

  [Description of specific examples of speed control]

  In the present embodiment, the speed control of the paper feed roller 42 is mainly performed by repeatedly rotating the paper feed roller 42 at a speed faster than that of the registration roller 44 and stopping it. By changing the ratio (duty ratio) of the rotation time of the paper feed roller 42 per unit time, the apparent rotation speed of the paper feed roller 42 can be changed. By controlling the rotation time and stop time of the paper feed roller 42 in correspondence with the rotation speed of the registration roller 44, the amount of slack in the paper passage path 45 is maintained.

  FIG. 10 is a diagram illustrating a specific example of speed control.

  In FIG. 10, the horizontal axis indicates the passage of time. Registrar roller 44 is driven at the same rotational speed (system speed when performing image formation) regardless of whether the sheet is thick paper or thin paper. On the other hand, the speed control mode of the paper feed roller 42 is different between the thick paper indicated by the alternate long and short dash line and the thin paper indicated by the broken line in the drawing. When the sheet feeding roller 42 is rotated (when it is “rotated” in the drawing), it rotates at a rotational speed faster than the rotational speed of the registration roller 44.

  In the example shown in FIG. 10, the speed control mode is changed by changing the timing for starting the speed control according to the paper thickness of the paper. That is, in the case of thin paper than in the case of thick paper, control is performed so that the time from when the paper tilt correction is performed and the registration roller 44 is driven to when the speed control is started is shortened. As a result, when there is a difference in sheet posture as shown in FIG. 8 between thick paper and thin paper, it is possible to maintain the sheet passing position within a predetermined range after improving the difference.

  Time t0 is the time when the paper inclination correction is completed. Until time t0, the registration roller 44 is stopped and the paper feed roller 42 is driven, a paper loop is formed, and paper inclination correction is performed. At time t0, the paper feed roller 42 is also temporarily stopped.

  At time t1 when a predetermined time has elapsed from time t0, the conveyance of the sheet to the secondary transfer position T is started. At time t1, both the registration roller 44 and the paper feed roller 42 that have been stopped are driven. At this time, since the paper feed roller 42 is driven at a higher speed than the registration roller 44, the paper loop becomes larger as this driving state continues. In the control example shown in FIG. 10, the speed control is not started at this stage, and the paper feed roller 42 is merely rotating.

  When the conveyance of the sheet is started at time t1, speed control is started at a predetermined timing thereafter. That is, the paper feed roller 42 is stopped, and thereafter, the rotation and stop of the paper feed roller 42 are changed at a predetermined cycle. At the time of thin paper, the stop and rotation of the paper feed roller 42 are started repeatedly at time t2 when the first predetermined time has elapsed from time t1. When the paper is thick, the stop and rotation of the paper feed roller 42 is started repeatedly at time t3 when the second predetermined time longer than the first predetermined time elapses from time t1.

  The speed control may be performed so that the paper feed roller 42 is driven at a speed corresponding to the speed of the registration roller 44. That is, the paper feed roller 42 is stopped before the paper loop amount increases and the paper contacts the outer guide 46. Then, the paper loop amount is reduced, and the paper feed roller 42 is rotated before the paper contacts the inner guide 47. As described above, since the speed control is performed by repeatedly stopping and rotating the paper feed roller 42, the paper loop amount in the paper passage path 45 can be maintained within a certain range. It is possible to prevent the load fluctuation caused by the force caused by dragging the paper feed roller 42 or the force caused by the paper contacting the guides 46 and 47 acting on the registration roller 44. Therefore, it is possible to prevent occurrence of sheet misalignment in the registration roller 44 with a simple configuration without providing a sensor or the like for detecting sheet sagging. As a result, the image forming apparatus 1 can appropriately form an image.

  In this way, the stop timing (start timing of speed control) of the paper feed roller 42 with respect to the rotation start timing of the registration roller 44 and the paper feed roller 42 is changed between thick paper and thin paper. That is, as described with reference to FIG. 8, when the paper is thin, the paper is relatively close to the outer guide 46 when the paper inclination correction is performed. Therefore, at a timing earlier than that for thick paper, the paper feed roller 42 is stopped once to start speed control, so that the ideal position and loop amount such as the central portion of the paper passage path 45 can be obtained. . On the other hand, for thick paper, the paper is relatively close to the inner guide 47 when the paper tilt correction is performed. Therefore, from the time of thin paper, the paper feed roller 42 is stopped once and the timing for starting speed control is delayed to increase the paper loop amount. As a result, the subsequent speed control can be performed in a state where the sheet is in an ideal position and loop amount.

  The speed control start timing and the rotation time and stop time of the paper feed roller 42 depend on the shape of the paper passing path 45 of the paper feed device 40, the rotational speeds of the paper feed roller 42 and the registration roller 44, and the like. Different. These values may be obtained and set by experiments or the like for each sheet thickness range (for example, thin paper and thick paper) for switching the speed control mode. As described above, the set value is stored as a control table in association with the condition regarding the paper thickness, and used for subsequent speed control.

  FIG. 11 is a diagram illustrating another specific example of speed control.

  Also in FIG. 11, as in FIG. 10, the horizontal axis indicates the passage of time. Registrar rollers 44 are driven at the same rotational speed regardless of whether they are thick paper or thin paper. On the other hand, the speed control mode of the paper feed roller 42 is different between the thick paper indicated by the alternate long and short dash line and the thin paper indicated by the broken line in the drawing. When the sheet feeding roller 42 is rotated, the sheet feeding roller 42 rotates at a rotation speed faster than the rotation speed of the registration roller 44.

  Also in the example shown in FIG. 11, the speed control mode is changed by changing the timing for starting the speed control according to the sheet thickness of the sheet. In this example, when thin paper is used, the paper tilt correction is performed and the registration roller 44 is driven, and then the rotation of the paper feed roller 42 is started so that the timing for starting the speed control is delayed. The As a result, when there is a difference in sheet posture as shown in FIG. 8 between thick paper and thin paper, it is possible to maintain the sheet passing position within a predetermined range after improving the difference.

  When the paper inclination correction is completed at time t0, the registration roller 44 rotates at a time t11 when a predetermined time has elapsed from that time, and the conveyance of the paper to the secondary transfer position T is started. Here, in the modified example shown in FIG. 11, when the paper is thick, the speed control is started by driving the paper feed roller 42 at time t11. Thereafter, the rotation and the stop are repeated at the rotation time and the stop time corresponding to the rotation speed of the registration roller 44 as described above.

  On the other hand, at the time of thin paper, speed control is not started even at time t11, and the paper feed roller 42 is kept stopped. Then, at time t12 when a third predetermined time has elapsed from time t11, the paper feed roller 42 is driven to start speed control. Thereafter, the rotation and stop of the paper feed roller 42 are repeated with the same rotation time and stop time as those for thick paper.

  As shown in FIG. 11, the rotation start timing (speed control start timing) of the paper feed roller 42 with respect to the rotation start timing of the registration roller 44 is changed between thick paper and thin paper. Therefore, as described above, when the paper is close to the outer guide 46 at the time of paper inclination correction, the rotation of the paper feed roller 42 is started with the loop amount reduced by rotating the registration roller 44, and the speed is increased. Control begins. Therefore, as described above, in both the thin paper state and the thick paper state, the paper is set to the ideal position and the loop amount, and the subsequent speed control can be performed to prevent the occurrence of paper misalignment. .

  In the state shown in FIG. 11, in the case of thick paper, the speed control may be started by rotating the paper feed roller 42 at a timing earlier than the rotation start of the registration roller 44. In this case as well, similarly, the sheet can be prevented from being misaligned by performing the subsequent speed control in a state where the sheet is in an ideal position and loop amount.

  [Explanation of speed control variants]

  Note that the rotation speed of the paper feed roller 42 may be switched between a high side that is faster than the rotation speed of the registration roller 44 and a low side that is slower than the rotation speed of the registration roller 44. Even in this case, the apparent rotation speed of the paper feed roller 42 can be changed by changing the ratio of the rotation time on the high side of the paper feed roller 42 in the unit time. By controlling the high-side rotation time and the low-side stop time of the paper feed roller 42 in accordance with the rotation speed of the registration roller 44, the amount of sag of the paper in the paper passage path 45 is maintained.

  In this case, the speed control mode may be changed by switching the rotation speed of the paper feed roller 42 between the high side and the low side at the start of the speed control according to the paper thickness of the paper. That is, when the paper is thin, the paper feed roller 42 is controlled to rotate at the low speed at the start of speed control. On the other hand, for thick paper, the feed roller 42 is controlled to rotate at a high speed at the start of speed control. As a result, when there is a difference in sheet posture as shown in FIG. 8 between thick paper and thin paper, it is possible to maintain the sheet passing position within a predetermined range after improving the difference.

  FIG. 12 is a diagram illustrating a modified example of the speed control.

  Also in FIG. 12, as in FIG. 10, the horizontal axis indicates the passage of time. Registrar rollers 44 are driven at the same rotational speed regardless of whether they are thick paper or thin paper. On the other hand, the speed control mode of the paper feed roller 42 is different between the thick paper indicated by the alternate long and short dash line and the thin paper indicated by the broken line in the drawing.

  When the paper tilt correction is completed at time t0, the paper feed roller 42 is temporarily stopped. Then, at a time t21 when a predetermined time has elapsed, the registration roller 44 rotates and the conveyance of the sheet to the secondary transfer position T is started. In addition, whether the paper is thick or thin, the paper feed roller 42 is driven at time t21 to start speed control.

  Here, at the time of thick paper, at time t21 when the speed control is started, the paper feed roller 42 is driven at a high speed. Thereafter, the rotation speed of the paper feed roller 42 is switched between the high side and the low side according to the high side rotation time and the low side rotation time corresponding to the rotation speed of the registration roller 44.

  On the other hand, at the time of thin paper, at time t21 when the speed control is started, the paper feed roller 42 is driven at a low speed. Thereafter, the rotation speed of the paper feed roller 42 can be switched between the high side and the low side at a rotation time ratio corresponding to the rotation speed of the registration roller 44.

  In this way, when the paper is thick and the paper is close to the inner guide 47 during the paper tilt correction, the speed control of the paper feed roller 42 is started at the high speed. As a result, when the speed control is started, the paper feed roller 42 is driven so that the paper loop amount increases, and thereafter, the paper loop amount is maintained. On the other hand, when the paper is close to the outer guide 46 during the paper tilt correction, the speed control of the paper feed roller 42 is started at the low speed. Thus, at the start of speed control, the paper feed roller 42 is driven so that the paper loop amount decreases, and thereafter, the paper loop amount is maintained. Therefore, in the same manner as the other speed control examples described above, the paper is shifted to the ideal position and loop amount for both thin paper and thick paper, and the subsequent speed control is performed to make the paper misalignment. Can be prevented.

  [Effects of the embodiment]

  Since the speed control is performed by switching the speed of the paper feed roller 42, the loop amount of the paper in the paper passage path 45 can be maintained within a certain range. It is possible to prevent the load fluctuation caused by the force caused by dragging the paper feed roller 42 or the force caused by the paper contacting the guides 46 and 47 acting on the registration roller 44. Therefore, it is possible to prevent occurrence of sheet misalignment in the registration roller 44 with a simple configuration without providing a sensor or the like for detecting sheet sagging. Accordingly, it is possible to realize the image forming apparatus 1 that can appropriately form an image without increasing the size of the machine configuration and the complexity of the configuration.

  In this way, the stop timing (start timing of speed control) of the paper feed roller 42 with respect to the rotation start timing of the registration roller 44 and the paper feed roller 42 is changed between thick paper and thin paper. That is, as described with reference to FIG. 8, when the paper is thin, the paper is relatively close to the outer guide 46 when the paper inclination correction is performed. Therefore, at a timing earlier than that for thick paper, the paper feed roller 42 is stopped once to start speed control, so that the ideal position and loop amount such as the central portion of the paper passage path 45 can be obtained. . On the other hand, for thick paper, the paper is relatively close to the inner guide 47 when the paper tilt correction is performed. Therefore, from the time of thin paper, the paper feed roller 42 is stopped once and the timing for starting speed control is delayed to increase the paper loop amount. As a result, the subsequent speed control can be performed in a state where the sheet is in an ideal position and loop amount.

  The speed control start timing and the rotation time and stop time of the paper feed roller 42 depend on the shape of the paper passing path 45 of the paper feed device 40, the rotational speeds of the paper feed roller 42 and the registration roller 44, and the like. Different. These values may be obtained and set by experiments or the like for each sheet thickness range (for example, thin paper and thick paper) for switching the speed control mode. As described above, the set value is stored as a control table in association with the condition regarding the paper thickness, and used for subsequent speed control.

  [Others]

  In the above-described embodiment, an example in which the speed control mode is changed in two cases of thick paper and thin paper has been described. However, more categories are provided for the paper thickness, and each of these categories is supported. In an aspect, speed control may be performed.

  For example, by calculating a control parameter used when speed control is performed using a paper thickness value and a preset calculation method for determining a speed control mode, a mode according to the paper thickness is obtained. Speed control may be performed. In other words, the speed control may be performed in a predetermined manner so as to be determined according to the paper thickness corresponding to the paper thickness.

  The speed control of the paper feed roller only needs to be performed in a mode corresponding to the type of paper to be used (conveyed), and is not limited to the mode switching based on the difference in paper thickness. For example, the speed control mode may be changed in accordance with other paper quality (an example of paper type). Specifically, for example, when the paper is different due to a difference in surface treatment, the speed control mode may be changed according to the strength of the paper.

  The speed control of the paper feed roller is not limited to one that is performed by switching between rotation and stop, or by switching between two speeds. The speed of the paper feed roller may be changed in more stages.

  The image forming apparatus may be a monochrome / color copying machine, a printer, a facsimile machine, or a multifunction machine (MFP) thereof. Further, the image forming method is not limited to the one that forms an image by an electrophotographic method, and for example, the image may be formed by a so-called ink jet method.

  Further, the paper feeding device according to the present invention is not limited to that used in the image forming apparatus. For example, the present invention can be applied to a paper feeding device used in various devices such as a scanner device that reads image data.

  The processing in the above embodiment may be performed by software or by using a hardware circuit.

  A program for executing the processing in the above-described embodiment can be provided, or the program can be recorded on a recording medium such as a CD-ROM, a flexible disk, a hard disk, a ROM, a RAM, or a memory card and provided to the user. It may be. The program may be downloaded to the apparatus via a communication line such as the Internet. The processing described in the text in the above flowchart is executed by the CPU according to the program.

  The above embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Image forming part 40 Paper feeding apparatus 41 Paper feeding cassette 42 Paper feeding roller 44 Registration roller 45 Paper passing path 46 Outer guide 47 Inner guide 100 Control part 105b Program P1, P2, P3, P10, P20 Paper

Claims (11)

A sheet feeding device that conveys a sheet along a curved sheet passing path between the sheet feeding roller and the registration roller using a sheet feeding roller and a registration roller downstream of the sheet feeding roller. And
A correction unit that controls the paper feed roller to abut the paper against the stopped registration roller to correct the paper inclination;
Speed control means for controlling the speed of the paper feed roller so that the amount of slack of the paper in the paper passing path is maintained when the paper tilt correction is performed by the correction means and the registration roller is driven. With
The speed control unit is a paper feeding device that performs the speed control in a preset manner corresponding to the type of paper to be used.   The sheet feeding device according to claim 1, wherein the speed control unit performs the speed control by repeatedly rotating and stopping the sheet feeding roller at a speed higher than that of the registration roller.   The sheet feeding device according to claim 2, wherein the speed control unit changes a timing at which the speed control is started according to a sheet thickness of the sheet.   In the case where the paper thickness is thinner than the case where the paper thickness of the paper is thick, the speed control means performs the paper inclination correction by the correction means and drives the paper feed roller and the registration roller. The paper feeding device according to claim 2 or 3, wherein the time until the speed control is started is shortened by stopping the paper feeding roller.   The speed control unit rotates the paper feed roller when the paper thickness is thinner than when the paper is thick, after the correction of the paper is corrected by the correction unit and the registration roller is driven. The sheet feeding device according to claim 2 or 3, wherein the timing at which the speed control is started is delayed by starting the operation.   The speed control unit switches the speed of the paper feed roller between a high side faster than the speed of the registration roller and a low side slower than the speed of the registration roller when the speed control is executed. 5 to 5.   The speed control means sets the speed of the paper feed roller to the high side when the paper thickness is equal to or greater than a predetermined thickness at the start of the speed control, and the paper feed when the paper thickness is smaller than the predetermined thickness. The sheet feeding device according to claim 6, wherein a speed of a roller is set to the low side.   The speed control means performs the speed control so that when the rear end of the paper passes through the paper feed roller, the paper is in a slack state regardless of the paper size or paper type. 8. The sheet feeding device according to any one of items 7. A paper feeding device according to any one of claims 1 to 8, which conveys paper,
An image forming apparatus comprising: an image forming unit that forms an image on a sheet conveyed by the sheet feeding device. Control of a sheet feeding device that conveys a sheet along a curved sheet passing path between the sheet feeding roller and the registration roller using a sheet feeding roller and a registration roller downstream of the sheet feeding roller A method,
A correction step of controlling the paper feed roller to abut the paper against the stopped registration roller to correct the paper tilt;
A speed control step for controlling the speed of the paper feed roller so that the amount of slack of the paper in the paper passing path is maintained when the paper tilt correction is performed by the correction step and the registration roller is driven; With
The speed control step is a method for controlling a paper feeding device, wherein the speed control is performed in a preset manner corresponding to the type of paper to be used. Control of a sheet feeding device that conveys a sheet along a curved sheet passing path between the sheet feeding roller and the registration roller using a sheet feeding roller and a registration roller downstream of the sheet feeding roller A program,
A correction step of controlling the paper feed roller to abut the paper against the stopped registration roller to correct the paper tilt;
A speed control step for controlling the speed of the paper feed roller so that the amount of slack of the paper in the paper passing path is maintained when the paper tilt correction is performed by the correction step and the registration roller is driven; To the computer,
The speed control step is a control program for a paper feeding device that performs the speed control in a preset manner corresponding to the type of paper to be used.

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