JP2008007277A - Paper transport device, image forming device, and document reading device - Google Patents

Abstract

Provided is a paper transport device that does not cause variations in the paper transport position when rotation of a registration roller is started even if the rigidity of the paper is not constant.
In a manuscript paper transport unit 101, an amount of deflection of a manuscript paper is detected upstream of a registration roller 65 by a deflection amount detection sensor 71, and the leading edge of the manuscript paper is brought into contact with a resist roller 65 in a stopped state. The rotation timing of the registration roller 65 is controlled according to the detected amount of deflection of the original paper when the rotation of the registration roller 65 is started after the original paper is bent in contact with the original paper. Even if the thickness and material of the paper are not constant and the rigidity changes depending on the type of the original paper, the leading edge of the original paper can reach the original reading window 102a at a prescribed timing.
[Selection] Figure 2

Description

  The present invention relates to a sheet conveying apparatus that conveys a recording sheet or an original sheet in a copying machine, a facsimile, a printer, or the like, an image forming apparatus including the same, and an original reading apparatus including the same.

  In a copying machine, a facsimile, a printer, and the like, an image is transferred to a recording sheet or an image on a document sheet is read while conveying the recording sheet or the document. When the image is transferred or read, if the recording paper or the original paper is skewed, the image is recorded obliquely on the recording paper or the original paper image is read obliquely.

  For this reason, a registration roller is provided in the paper conveyance path, the recording paper or the original paper in the middle of conveyance is brought into contact with the registration roller in the stopped state, and the recording paper or the original paper is bent. The skew of the sheet is corrected by aligning the leading end of the sheet in parallel with the registration roller by the elasticity of the sheet. Thereafter, the registration roller is rotated to resume the conveyance of the recording paper or the original paper.

Further, in Patent Document 1, since the load applied to the paper changes depending on the length of the paper feed path, the amount of paper deflection is adjusted according to the length of the paper feed path to reliably prevent the skew of the paper. Like.
JP-A-7-14496

  In recent years, it has been required to improve the accuracy of the image recording position on the recording paper and the image reading position on the original paper. However, if the recording paper or the original paper is bent when the front end of the paper is brought into contact with the registration roller to make the front end of the paper parallel to the registration roller as described above, the rigidity of the paper is not constant. For this reason, when the rotation of the registration roller is started and the conveyance of the paper is resumed, the paper conveyance position varies. This is because the paper is urged in the transport direction by the elastic force of the bent paper. If the rigidity of the paper is not constant, the elastic force of the bent paper is not constant and is not constant. This is because the amount of movement of the paper urged by the elastic force of the paper varies.

  For example, when the paper has high rigidity, the elastic force of the bent paper is large, and therefore when the registration roller starts rotating and the paper conveyance is resumed, the paper is also conveyed by the large elastic force of the paper. The paper transport position is shifted downstream in the transport direction. In addition, when the rigidity of the paper is low, the elastic force of the bent paper is small, so when the rotation of the registration roller is started and the paper conveyance is resumed, the paper is caused to move in the conveyance direction by the elastic force of the paper. Almost no movement is made, and the conveyance position of the sheet is shifted to the upstream side in the conveyance direction.

  That is, since the rigidity of the paper is not constant, the paper is transported when the leading edge of the paper is brought into contact with the registration roller, the paper is bent, the rotation of the registration roller is started, and the paper transportation is resumed. Variations in position occurred.

  For this reason, it has been impossible to improve the accuracy of the image recording position on the recording paper and the image reading position on the original paper.

  Therefore, the present invention has been made in view of the above-described conventional problems, and even if the rigidity of the sheet is not constant, the sheet conveying apparatus does not cause variations in the sheet conveying position when the rotation of the registration roller is started. An object of the present invention is to provide an image forming apparatus including the same and a document reading apparatus including the same.

  In order to solve the above-described problem, the paper transport device of the present invention is provided with a registration roller in the paper transport path, and the front end of the paper being transported is brought into contact with the stopped registration roller, and then the registration roller is rotated. In the sheet conveying apparatus that conveys the sheet by the registration roller, the sheet rigidity detecting unit that detects the rigidity of the sheet upstream of the registration roller in the sheet conveying direction, and the sheet rigidity detected by the sheet rigidity unit And a control unit for controlling the leading edge feeding operation of the sheet by the registration roller.

  Further, the rigidity detecting means detects the amount of bending of the paper corresponding to the rigidity of the paper.

  Further, the control means slows the speed of the leading edge feeding operation of the paper by the registration roller when the paper rigidity detected by the paper rigidity means is high.

  The control means delays the start of the leading edge feeding operation of the sheet by the registration roller when the rigidity of the sheet detected by the sheet rigidity means is high.

  Next, an image forming apparatus according to the present invention includes the above-described sheet conveying device according to the present invention.

  A document reading apparatus according to the present invention includes the paper conveying apparatus according to the present invention.

  According to such a sheet conveying apparatus of the present invention, the rigidity of the sheet is detected on the upstream side of the registration roller, and the leading edge feeding operation of the sheet by the registration roller is controlled according to the detected rigidity of the sheet. . For this reason, the rigidity of the paper is not constant, and even if the elastic force of the bent paper is large or small, the leading edge feeding operation by the registration roller is made faster or slower depending on the elastic force of the bent paper. can do. As a result, it is possible to absorb variations in the amount of movement of the sheet due to non-constant sheet elastic force, and to suppress variations in the sheet conveyance position.

  For example, the stiffness detecting means detects the amount of deflection of the paper corresponding to the stiffness of the paper. When the rigidity of the paper is high, the amount of bending of the paper is small, and when the rigidity of the paper is low, the amount of bending of the paper is large. That is, the rigidity of the paper corresponds to the amount of bending. For this reason, instead of directly detecting the rigidity of the sheet, the amount of bending of the sheet may be detected.

  In addition, when the rigidity of the sheet is high, the speed of the leading edge feeding operation of the sheet by the registration roller is slowed, or the start of the leading edge feeding operation of the sheet by the registration roller is delayed. When the rigidity of the paper is high, the elastic force of the bent paper is large. Therefore, when the rotation of the registration roller is started and the conveyance of the paper is resumed, the paper is greatly increased in the conveyance direction by the large elasticity of the paper. The leading edge of the sheet is shifted downstream in the transport direction. Therefore, the speed of the leading edge feeding operation by the registration rollers is slowed or the start of the leading edge feeding operation is slowed to delay the feeding of the paper and correct the deviation in the downstream direction of the feeding direction.

  On the other hand, since the image forming apparatus of the present invention includes the paper transport device of the present invention, the same operations and effects as the paper transport device of the present invention can be achieved.

  In addition, since the document reading apparatus of the present invention includes the paper transport device of the present invention, the same operations and effects as the paper transport device of the present invention can be achieved.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus to which an embodiment of a paper conveying apparatus of the present invention is applied. The image forming apparatus 100 acquires image data read from a document sheet, or acquires image data received from the outside, and forms a monochrome image indicated by the image data on a recording sheet. The configuration is roughly divided into an original paper transport unit (ADF) 101, an image reading unit 102, a printing unit 103, a recording paper transport unit 104, and a paper feed unit 105.

  As will be described in detail later, the paper transport device of the present embodiment is applied to a document paper transport unit (ADF) 101 and a recording paper transport unit 104. In the document paper transport unit 101, a document according to the rigidity of the document paper. Controls the leading edge feeding operation of the paper to suppress variations in the transport position of the original paper, and the recording paper transport unit 104 controls the leading edge feeding operation of the recording paper according to the rigidity of the recording paper to transport the recording paper. The position variation is suppressed.

  When at least one document sheet is set on the document set tray 11 in the document sheet transport unit 101, the document sheet is pulled out from the document set tray 11 and transported one by one. The original paper is guided to the original reading window 102a and passed therethrough, and the original paper is discharged to the paper discharge tray 12.

  A CIS (Contact Image Sensor) 13 is disposed above the document reading window 102a. The CIS 13 repeatedly reads an image on the back side of the original paper in the main scanning direction when the original paper passes through the original reading window 102a, and outputs image data indicating the image on the back side of the original paper.

  Details of the document sheet conveying unit 101 will be described later with reference to FIG.

  The image reading unit 102 exposes the surface of the original paper by the lamp of the first scanning unit 15 when the original paper passes through the original reading window 102a, and the original by the mirrors of the first and second scanning units 15 and 16. Reflected light from the paper surface is guided to the imaging lens 17, and an image on the surface of the original paper is formed on a CCD (Charge Coupled Device) 18 by the imaging lens 17. The CCD 18 repeatedly reads an image on the surface of the original paper in the main scanning direction, and outputs image data indicating the image on the surface of the original paper.

  Further, when the original paper is placed on the platen glass on the upper surface of the image reading unit 102, the first and second scanning units 15 and 16 are moved while maintaining a predetermined speed relationship with each other, so that the first scanning unit 15 The surface of the original paper on the platen glass is exposed by the first and second scanning units 15 and 16, and the reflected light from the original paper surface is guided to the imaging lens 17. An image is formed on the CCD 18.

  The image data output from the CIS 13 or the CCD 18 is subjected to various image processing by a control circuit such as a microcomputer and then output to the printing unit 103.

  The printing unit 103 records a document indicated by image data on a sheet, and includes a photosensitive drum 21, a charger 22, an optical writing unit 23, a developing unit 24, a transfer unit 25, a cleaning unit 26, and a fixing unit. 27 etc.

  The photosensitive drum 21 rotates in one direction, and after the surface is cleaned by the cleaning unit 26, the surface is uniformly charged by the charger 22. The charger 22 may be of a charger type or of a roller type or a brush type that contacts the photosensitive drum 21.

  The optical writing unit 23 is a laser scanning unit (LSU) including two laser irradiation units 28a and 28b and two mirror groups 29a and 29b. In the optical writing unit 23, image data is input, laser light corresponding to the image data is emitted from the laser irradiation units 28a and 28b, and the laser light is transmitted through the mirror groups 29a and 29b. The drum 21 is irradiated to expose the uniformly charged surface of the photosensitive drum 21 to form an electrostatic latent image on the surface of the photosensitive drum 21.

  The optical writing unit 23 employs a two-beam method including two laser irradiation units 28a and 28b in order to cope with high-speed printing processing, thereby reducing the burden associated with increasing the irradiation timing.

  As the optical writing unit 23, an EL writing head or an LED writing head in which light emitting elements are arranged in an array can be used instead of the laser scanning unit.

  The developing device 24 supplies toner to the surface of the photosensitive drum 21 to develop the electrostatic latent image, and forms a toner image on the surface of the photosensitive drum 21. The transfer unit 25 transfers the toner image on the surface of the photosensitive drum 21 onto the recording paper conveyed by the paper conveyance unit 104. The fixing unit 27 heats and pressurizes the recording paper to fix the toner image on the recording paper. Thereafter, the recording sheet is further conveyed to the sheet discharge tray 47 by the sheet conveying unit 104 and discharged. The cleaning unit 26 removes and collects the toner remaining on the surface of the photosensitive drum 21 after development and transfer.

Here, the transfer unit 25 includes a transfer belt 31, a drive roller 32, a driven roller 33, an elastic conductive roller 34, and the like, and the transfer belt 31 is stretched between the rollers 32 to 34 and other rollers. Is rotating. The transfer belt 31 has a predetermined resistance value (for example, 1 × 10 ⁹ to 1 × 10 ¹³ Ω / cm), and conveys the recording paper placed on the surface thereof. The elastic conductive roller 34 is pressed against the surface of the photosensitive drum 21 via the transfer belt 31, and presses the recording paper on the transfer belt 31 against the surface of the photosensitive drum 21. An electric field having a polarity opposite to the charge of the toner image on the surface of the photosensitive drum 21 is applied to the elastic conductive roller 34, and the toner image on the surface of the photosensitive drum 21 is transferred onto the transfer belt 31 by the electric field having the opposite polarity. Is transferred onto the recording paper. For example, when the toner image has a charge of (−) polarity, the polarity of the electric field applied to the elastic conductive roller 34 is set to (+) polarity.

  The fixing unit 27 includes a heating roller 35 and a pressure roller 36. A heat source for setting the surface of the heating roller 35 to a predetermined temperature (fixing temperature: approximately 160 to 200 ° C.) is provided inside the heating roller 35. In addition, pressure members (not shown) are arranged at both ends of the pressure roller 36 so that the pressure roller 36 is pressed against the heating roller 35 with a predetermined pressure. When the recording paper is conveyed to a pressure contact portion (referred to as a fixing nip portion) between the heating roller 35 and the pressure roller 36, the recording paper is conveyed by the rollers 35 and 36 and is not fixed on the recording paper. The toner image is heated and melted and pressed to fix the toner image on the recording paper.

  The paper transport unit 104 includes a plurality of pairs of transport rollers 41, a pair of registration rollers 42, a transport path 43, a reverse transport path 44, a plurality of branching claws 45, a pair of paper discharge rollers 46, and the like for transporting recording paper. I have.

  In the conveyance path 43, the recording paper is received from the paper supply unit 105, and the recording paper is conveyed until the leading edge of the recording paper reaches the registration roller 42. At this time, since the registration roller 42 is temporarily stopped, the leading edge of the recording paper reaches and contacts the registration roller 42, and the recording paper is bent. The leading edge of the recording sheet is aligned parallel to the registration roller 42 by the elastic force of the bent recording sheet. Thereafter, the rotation of the registration roller 42 is started, the recording paper is conveyed to the transfer unit 25 of the printing unit 103 by the registration roller 42, and the recording paper is further conveyed to the paper discharge tray 47 by the paper discharge roller 46.

  The registration roller 42 is stopped and rotated by switching on and off the clutch between the registration roller 42 and the drive shaft, or by switching on and off the motor that is the drive source of the registration roller 42.

  When recording an image on the back side of the recording paper, the plurality of branching claws 45 are rotated to switch the branch path between the transport path 43 and the reverse transport path 44, and the reverse side of the recording paper is reversed by the reverse transport path 44. After that, the recording sheet is returned to the registration roller 42 in the conveyance path 43 through the reverse conveyance path 44. As a result, an image is also recorded on the back surface of the recording paper.

  In the transport path 43 and the reverse transport path 44, sensors for detecting the position of the recording paper are arranged in various places, and the transport roller and the registration roller are driven and controlled based on the position of the recording paper detected by each sensor. The recording paper is conveyed and positioned.

  The paper feed unit 105 includes a plurality of paper feed trays 51. Each paper feed tray 51 is a tray for accumulating recording paper, and is provided below the image forming apparatus 100. Each paper feed tray 51 is provided with a pick-up roller or the like for pulling out recording sheets one by one, and sends out the pulled recording sheets to the transport path 43 of the paper transport unit 104.

  Since the image forming apparatus 100 of the present embodiment is intended for high-speed printing processing, each paper feed tray 51 has a capacity capable of storing 500 to 1500 standard-size recording sheets.

  Further, on the side surface of the image forming apparatus 100, a large-capacity paper feed cassette (LCC) 52 capable of storing a large amount of a plurality of types of recording papers and a manual feed tray 53 for mainly supplying irregular-size recording papers are provided. ing.

  The paper discharge tray 47 is disposed on the side surface opposite to the manual feed tray 53. In place of the paper discharge tray 47, a post-processing device for paper discharge (such as stapling and punching) and a plurality of paper discharge trays can be arranged as options.

  Next, the document sheet conveying unit 101 to which the sheet conveying apparatus of this embodiment is applied will be described. FIG. 2 is a schematic diagram illustrating the configuration of the document sheet conveyance unit 101.

  As shown in FIG. 2, the manuscript paper transport unit 101 includes a manuscript set tray 11 on which a manuscript paper bundle is placed and accommodated, a pickup roller 61 that feeds manuscript paper from the manuscript paper bundle to the manuscript transport path S1, and a manuscript transport path S1. A pair of pairs of paper feed rollers 62 and separating rollers 63 for conveying the original paper fed to the downstream side of the original conveying path S1 while separating the original paper one by one, and a plurality of pairs for conveying the original paper along the paper conveying path S1. A conveying roller 64, a pair of registration rollers 65 for feeding the original paper to the original reading window 102a at a predetermined timing, a pair of paper discharge rollers 66 for discharging the original paper whose image has been read to the paper discharge tray 12, and an original It is mainly composed of a CIS 13 which is arranged above the reading window 102a and reads an image on the back side of the original paper.

  The document set tray 11 can be moved in the vertical direction. When a bundle of document sheets is placed on the document set tray 11, a sensor (not shown) detects it and a print request is made from the user. Then, the document set tray 11 is moved upward, and the pickup roller 61 feeds the document sheet bundle from the uppermost document sheet to the sheet conveyance path S1.

  Normally, even when the original paper is overlapped and sent to the paper transport path S1, the double feed state is canceled by the separation roller 63, and one sheet is fed downstream of the paper transport path S1 by the paper feed roller 62. It is conveyed one by one.

  However, since the manuscript paper is conveyed at a high speed so as to correspond to the high-speed printing process, the possibility of double feeding cannot be denied even if the separation roller 63 is provided. Therefore, the document sheet conveyance unit 101 is provided with a double feed detection sensor (not shown) in the vicinity of the conveyance roller 64 arranged on the downstream side of the paper feed roller 62 and the separation roller 63. This double feed detection sensor includes a transmitter that transmits ultrasonic waves and a receiver that receives the ultrasonic waves transmitted from the transmitter, and detects a double feed of a document. In response to the detection output of the double feed detection sensor, the feeding of the original paper is interrupted to prevent the original paper from being conveyed while being double fed.

  In the paper conveyance path S1, the original paper is conveyed until the leading edge of the original paper comes into contact with the registration roller 65 while the registration roller 65 is temporarily stopped, and the original paper is bent. Then, after the leading edge of the original paper is aligned in parallel with the registration roller 65 by the elastic force of the bent original paper, the registration roller 65 is started to rotate, and the original paper is re-conveyed by the registration roller 65. Then, the original paper is guided through the original reading window 102 a of the image reading unit 102, and the original is discharged to the paper discharge tray 12 by the paper discharge roller 66.

  The registration roller 65 is stopped and rotated by switching on and off the clutch between the registration roller 65 and the drive shaft, or by switching on and off the motor that is the drive source of the registration roller 65.

  In the paper transport path S1, sensors for detecting the position of the original paper are arranged at various locations, and the transport rollers and the registration rollers are driven and controlled based on the position of the original paper detected by each sensor, thereby transporting the original paper. And positioning.

  By the way, in the document sheet transport unit 101 having such a configuration, the leading edge of the document sheet is brought into contact with the resist roller 65 in a stopped state, and the leading edge of the document sheet is aligned with the registration roller 65 by the elasticity of the bent document sheet. After aligning them in parallel, the rotation of the registration roller 65 is started, the conveyance of the original paper is resumed, and the original paper is conveyed to the original reading window 102a. The rigidity changes depending on the type of paper, and the elastic force of the bent original paper also changes. For this reason, when the conveyance of the original paper is resumed, a variation occurs in the amount of movement of the original paper that is urged in the conveyance direction by a non-constant elastic force of the original paper. The position of the original paper is shifted downstream of 65, which causes a reduction in the accuracy of the reading position of the original paper image.

  Therefore, in the document sheet conveying unit 101 of the present embodiment, a deflection amount detection sensor for detecting a deflection amount of the document sheet corresponding to the rigidity of the document sheet upstream of the registration rollers 65 in the document sheet conveyance direction. 71, and controls the rotation start timing of the registration roller 65 according to the detection output of the deflection amount detection sensor 71 to absorb the variation in the movement amount of the original paper due to the non-constant elastic force of the original paper, Variations in the transport position at the front end of the original paper are suppressed.

  FIG. 3 is a block diagram showing a control system for controlling the rotation start timing of such a registration roller 65. Here, a deflection amount detection sensor 71 for detecting the deflection amount of the original sheet, and comparators 72-1, 72-2, 72- for comparing the detection output of the deflection amount detection sensor 71 with the respective threshold values vth1, vth2, vth3. 3 and the output of each of the comparators 72-1, 72-2, 72-3, the amount of deflection of the original paper is determined, and the timing of starting the rotation of the registration roller 65 is determined according to the determined amount of deflection of the original paper. A control unit 73 is provided.

  The control unit 73 controls not only the rotation start timing of the registration roller 65 but also the paper feed roller 62, the separation roller 63, the conveyance roller 64, and the like to control the conveyance of the original paper. As described above, with the registration roller 65 temporarily stopped, the original paper is conveyed until the leading edge of the original paper contacts the registration roller 65, and the original paper is bent. The rotation of the registration roller 65 is started after the leading edge of the original paper is aligned in parallel with the registration roller 65 by the elastic force of.

  In the sheet conveyance path S1, a recess 74 that is recessed downward is provided on the upstream side of the registration roller 65 in the conveyance direction, and a deflection amount detection sensor 71 is disposed above the recess 74. The original sheet is conveyed by the conveying roller 64, and when the leading end reaches the recess 74, the leading end of the original sheet bends downward. At this time, the deflection amount detection sensor 71 detects the downward deflection amount of the leading end portion of the document sheet.

  The control unit 73 drives and controls the paper feed roller 62, the separation roller 63, the conveyance roller 64, and the like, and conveys the original paper when the leading end portion of the original paper reaches the recess 74 of the paper conveyance path S1. Stop for a while or reduce the conveyance speed to set a grace period when the leading edge of the original paper is bent downward, and then resume the conveyance of the original paper.

  Therefore, when the original paper is pulled out from the original set tray 11 and conveyed, and the leading end of the original paper reaches the recess 74 of the paper conveyance path S1, the conveyance of the original paper is temporarily stopped or the conveyance speed is reduced. After the deflection amount detection sensor 71 detects the deflection amount of the leading end portion of the document sheet, the conveyance of the document sheet is restored, and the leading end comes into contact with the registration roller 65 to bend the document sheet. After the leading edge of the original paper is aligned parallel to the registration roller 65 due to the elastic force, the rotation of the registration roller 65 is started and the original paper is conveyed to the original reading window 102a.

  FIG. 4 is a circuit diagram showing the deflection amount detection sensor 71 and its peripheral circuits. The deflection amount detection sensor 71 includes a light emitting element 71 a that emits light in the direction of the recess 74 and a light receiving element 71 b that receives light from the direction of the recess 74. The light emitting element 71a is, for example, a light emitting diode, and a driving current control transistor 81 and a resistor 82 are connected in series to the light emitting element 71a. A driving current i of the light emitting element 71a flows through the light emitting element 71a, the transistor 81, and the resistor 82, and a voltage v2 corresponding to the driving current i is generated in the resistor 82. The operational amplifier 83 inputs a voltage v1 indicating the light emission level of the light emitting element 71a to its non-inverting input terminal, and inputs a voltage v2 corresponding to the drive current i to its inverting input terminal, and the difference between the voltages v1 and v2 Is applied to the base of the transistor 81. As a result, the light emitting element 71a is driven at a constant current and emits light with a substantially constant light emission intensity.

  The light receiving element 71b is a phototransistor, for example, and outputs a detection current is corresponding to the light reception level, and a voltage vs corresponding to the detection current is is generated in the resistor 84. The operation amplifier 85 amplifies the voltage vs and outputs a detection voltage vd corresponding to the detection current is, that is, a detection voltage vd corresponding to the light receiving level of the light receiving element 71b. This detection voltage vd is input to each of the comparators 72-1 to 72-3 in FIG.

  Here, when there is no original paper in the recess 74 of the sheet transport path S1, the light of the light emitting element 71a is irregularly reflected on the surface of the recess 74, and a part of the reflected light is received by the light receiving element 71b, and the light receiving element 71b. The received light level is maintained constant, and the detection voltage vd corresponding to the received light level is also maintained at a constant level. Therefore, when there is no original paper, the operation amplifier 85 outputs a detection voltage vd at a certain level.

  Next, when the leading edge of the original paper reaches the recess 74 of the paper transport path S1, the light from the light emitting element 71a is diffusely reflected on the surface of the original paper, and a part of the reflected light is received by the light receiving element 71b. At this time, since the surface of the original paper is closer to the light emitting element 71a and the light receiving element 71b than the surface of the recess 74 of the paper transport path S1, the light reception level that is irregularly reflected on the surface of the original paper and received by the light receiving element 71b is the paper transport path. The detection level vd also rises because the light receiving level is irregularly reflected on the surface of the recess 74 of S1 and received by the light receiving element 71b.

  Further, the higher the rigidity of the original paper, the smaller the amount of downward deflection of the leading edge of the original paper in the recess 74, and the original paper surface approaches the light emitting element 71a and the light receiving element 71b. The light reception level received by the light receiving element 71b is irregularly reflected and increases. For example, as shown in FIG. 5, when the rigidity of the original paper Pa is low and the leading end portion of the original paper Pa bends to a large deflection amount L3, the light reception level received by the light receiving element 71b is that when there is no original paper Pa. A little higher than the light reception level. Further, when the rigidity of the original paper Pa is average and the leading end portion of the original paper Pa bends to the average deflection amount L2, the light receiving level received by the light receiving element 71b becomes higher. Furthermore, when the original paper Pa has high rigidity and the leading end portion of the original paper Pa is bent slightly to the bending amount L1, the light receiving level received by the light receiving element 71b is further increased.

  Therefore, when the leading edge of the original paper reaches the recess 74, the higher the rigidity of the original paper, the higher the detection voltage vd corresponding to the light receiving level of the light receiving element 71b.

  On the other hand, the threshold value vth1 of the comparator 72-1 is set slightly higher than the detection voltage vd of a certain level corresponding to the light receiving level of the light receiving element 71b when there is no original paper in the recess 74, and when the original paper is present. It is set smaller than the detection voltage vd corresponding to the light receiving level of the light receiving element 71b. The comparator 72-1 compares the detection voltage vd corresponding to the light receiving level of the light receiving element 71b with the threshold value vth1, outputs a low level signal when the detection voltage vd is lower than the threshold value vth1, and the detection voltage vd is the threshold value. A high level signal is output when vth1 or higher.

  Therefore, when the low level signal is output from the comparator 72-1, there is no original paper, and when the high level signal is output from the comparator 72-1, there is original paper.

  The threshold value vth2 of the comparator 72-2 is set to be slightly larger than the detection voltage vd corresponding to the light receiving level of the light receiving element 71b when the leading end portion of the original paper is bent at the recess 74 with a large deflection amount L3. ing. The comparator 72-1 compares the detection voltage vd indicating the light reception level of the light receiving element 71b with the threshold value vth2, and outputs a low level signal when the detection voltage vd is lower than the threshold value vth2, and the detection voltage vd is the threshold value vth2. When this happens, a high level signal is output.

  Therefore, when the high level signal is output from the comparator 72-1 and the low level signal is output from the comparator 72-2, the leading end portion of the document sheet is bent with a large deflection amount L3.

  Further, the threshold value vth3 of the comparator 72-3 is slightly larger than the detection voltage vd corresponding to the light receiving level of the light receiving element 71b when the leading end portion of the original paper is bent at the recess 74 by the average bending amount L2. Is set. The comparator 72-3 compares the detection voltage vd indicating the light reception level of the light receiving element 71b with the threshold value vth3, and outputs a low level signal when the detection voltage vd is lower than the threshold value vth3. The detection voltage vd is the threshold value vth3. When this happens, a high level signal is output.

  Therefore, when a high level signal is output from each of the comparators 72-1 and 72-2 and a low level signal is output from the comparator 72-3, the leading end portion of the original paper is bent with an average deflection amount L2. Will be.

  Further, when a high level signal is output from any of the comparators 72-1, 72-2, 72-3, the leading end portion of the original paper is bent with a slight deflection amount L1.

  The outputs of the comparators 72-1, 72-2, 72-3 are applied to the control unit 73. The control unit 73 determines the amount of deflection of the original paper based on the outputs of the comparators 72-1, 72-2, and 72-3, and controls the rotation start timing of the registration roller 65 according to the amount of deflection of the original paper. To do.

  Here, the smaller the amount of bending of the original paper in contact with the resist roller 65 in the stopped state (the higher the rigidity of the original paper), the greater the elastic force of the bent original paper, and the downstream of the registration roller 65. The amount of movement of the original paper on the side increases. Therefore, the amount of movement of the original paper according to the amount of deflection of the original paper occurs.

  Therefore, the control unit 73 controls the rotation start timing of the registration roller 65 in accordance with the amount of deflection of the document sheet, and even if the amount of movement of the document sheet in accordance with the amount of deflection of the document sheet occurs, At the timing, the leading edge of the document sheet reaches the document reading window 102a on the downstream side of the registration roller 65.

  For example, when the amount of deflection of the original paper is small and the amount of movement of the original paper due to the large elastic force of the original paper is large, the control unit 73 delays the rotation start timing of the registration roller 65 and causes the registration roller 65 to The conveyance of the original paper is delayed so that the leading edge of the original paper reaches the original reading window 102a at a specified timing.

  Further, when the amount of deflection of the original paper is large and the amount of movement of the original paper due to the small elastic force of the original paper is small, the control unit 73 advances the rotation start timing of the registration roller 65 to convey the original paper. The leading edge of the original paper reaches the original reading window 102a at a specified timing.

  Further, when the amount of deflection of the original paper is average and the amount of movement of the original paper due to the elasticity of the original paper is average, the control unit 73 sets the rotation start timing of the registration roller 65 as usual. The leading edge of the original paper reaches the original reading window 102a at a specified timing.

  The graph of FIG. 6 is a graph showing the relationship between the amount of deflection Lp (mm) of the original paper and the timing for starting the rotation of the registration roller 65. As is apparent from this graph, when the rotation start timing of the registration roller 65 when the deflection amount of the original paper is average is used as a reference (represented by 0), the registration roller 65 when the deflection amount of the original paper is small. The rotation start timing of the registration roller 65 is changed to the + side and delayed, and when the amount of deflection of the original paper is large, the rotation start timing of the registration roller 65 is changed to the-side and accelerated.

  As described above, in the document sheet transport unit 101, the deflection amount of the document sheet is detected by the deflection amount detection sensor 71 upstream of the registration roller 65, and the leading edge of the document sheet is brought into contact with the stopped registration roller 65. Thus, when the rotation of the registration roller 65 is started after the document sheet is bent, the timing of starting the rotation of the registration roller 65 is controlled according to the detected amount of deflection of the document sheet. Even if the thickness and material of the document are not constant and the rigidity changes depending on the type of document paper, the leading edge of the document paper can reach the document reading window 102a at a specified timing.

  Next, the recording paper transport unit 104 to which the paper transport device of this embodiment is applied will be described.

  In the recording paper transport unit 104, the front end of the recording paper is brought into contact with the registration roller 42 in a stopped state, and the front end of the recording paper is aligned in parallel with the registration roller 42 by the elasticity of the bent recording paper. The rotation of the roller 42 is started and the conveyance of the recording paper is resumed. For this reason, for the same reason as the original paper in the original paper transport unit 101, the amount of movement of the recording paper urged in the transport direction by the elastic force of the recording paper varies, and if this variation is left as it is, The recording paper is displaced on the downstream side of the registration roller 42, and this causes a reduction in the accuracy of the image transfer position with respect to the recording paper.

  Therefore, in the recording sheet conveyance unit 104 of the present embodiment, as shown in an enlarged view in FIG. 7, a deflection amount detection sensor for detecting the deflection amount of the recording sheet upstream of the registration rollers 42 in the recording sheet conveyance direction. 91 is provided to control the rotation start timing of the registration roller 42 according to the detection output of the deflection amount detection sensor 91 to absorb the variation in the moving amount of the recording paper due to the elastic force of the recording paper. The variation in the transfer position is suppressed.

  FIG. 8 is a block diagram showing a control system for controlling the registration rollers 42 and the transport rollers 41 in the transport path 43. This control system has substantially the same configuration as that shown in FIG. 3, and each of the comparators 92-1 compares the deflection amount detection sensor 91 and the detection output of the deflection amount detection sensor 91 with the respective threshold values vth1, vth2, and vth3. , 92-2, 92-3 and the outputs of the respective comparators 92-1, 92-2, 92-3 to determine the amount of deflection of the recording paper, and the registration rollers according to the determined amount of deflection of the recording paper. And a control unit 93 that controls the timing of the rotation start of 42.

  The deflection amount detection sensor 91 has the same configuration as the deflection amount detection sensor 71 of the document sheet conveyance unit 101. In the transport path 43, a recess 94 that is recessed downward is provided upstream of the registration rollers 42 in the transport direction, and a deflection amount detection sensor 91 is disposed above the recess 94. When the recording paper Pb is conveyed by the conveying roller 41 and the leading end of the recording paper Pb reaches the recess 94, the leading end of the recording paper Pb bends downward, and the bending amount detection sensor 91 causes the leading end of the recording paper Pb. The amount of bending downward is detected.

  The control unit 73 controls the conveyance of the recording paper by driving and controlling the conveyance roller 41 and the like. As a result, when the recording paper is pulled out from the paper supply unit 105 and conveyed, and the leading end of the recording paper reaches the recess 94 of the conveyance path 43, the conveyance of the recording paper is temporarily stopped or the conveyance speed is reduced. After the deflection amount detection sensor 91 detects the deflection amount of the leading end portion of the recording sheet, the recording sheet is transported again, the leading end comes into contact with the registration roller 42, the recording sheet bends, and the bent recording sheet. After the leading edge of the recording paper is aligned in parallel with the registration roller 42 by the elastic force, the rotational driving of the registration roller 42 is started and the recording paper is conveyed to the transfer site.

  In addition, when the rotation of the registration roller 42 is started, the control unit 93 controls the timing of starting the rotation of the registration roller 42 according to the amount of deflection of the recording paper, and the recording paper is moved by the elastic force of the bent recording paper. Even if the amount changes, the leading edge of the recording paper reaches the image transfer site on the downstream side of the registration roller 42 at a specified timing.

  For example, when the amount of deflection of the recording sheet is small and the amount of movement of the recording sheet due to the large elastic force of the recording sheet is large, the control unit 93 delays the rotation start timing of the registration roller 42 and causes the registration roller 42 to The conveyance of the recording paper is delayed so that the leading edge of the recording paper reaches the image transfer portion at a specified timing.

  In addition, when the amount of deflection of the recording sheet is large and the amount of movement of the recording sheet due to the small elastic force of the recording sheet is small, the control unit 93 advances the rotation start timing of the registration roller 42 to convey the recording sheet. The leading edge of the recording sheet reaches the image transfer portion at a specified timing.

  Further, when the amount of deflection of the recording paper is average and the amount of movement of the recording paper due to the elastic force of the recording paper is average, the control unit 93 sets the rotation start timing of the registration roller 42 as usual. Is set so that the leading edge of the recording paper reaches the transfer portion of the image at a prescribed timing.

  As described above, in the recording paper transport unit 104, the deflection amount of the recording paper is detected by the deflection amount detection sensor 91 on the upstream side of the registration roller 42, and the leading edge of the recording paper comes into contact with the stopped registration roller 42. When the rotation of the registration roller 42 is started after the recording sheet is bent, the timing of starting the rotation of the registration roller 42 is controlled according to the detected amount of bending of the recording sheet. Even if the thickness and material of the recording sheet are not constant and the rigidity varies depending on the type of recording paper, the leading edge of the recording paper can reach the image transfer site at a prescribed timing.

  In addition, this invention is not limited to the said embodiment, It can deform | transform variously. For example, the detection output of the deflection amount detection sensor is input to a plurality of comparators, and the deflection amount of the paper is determined by the comparison result of each comparator. Instead, the detection output of the deflection amount detection sensor is sent to the CPU or the like. It may be input and the CPU may directly determine the amount of bending of the paper.

  Moreover, although the deflection amount detection sensor provided with the light emitting element and the light receiving element is used, instead of this, a plurality of contact sensors are provided on the surface of the recess for bending the paper downward, and the sensor is bent downward. The amount of deflection of the sheet may be determined based on which of the contact sensors the sheet has contacted. Alternatively, a distance measuring sensor that measures the separation distance by ultrasonic waves, light, or the like is provided above the recess, and the distance to the sheet that is bent downward is measured by the distance measurement sensor. Based on this distance Then, the amount of deflection of the paper may be determined. Alternatively, instead of detecting the amount of bending of the paper, the rigidity of the paper may be directly detected. For example, the thickness of the paper may be directly detected and the thickness of the paper may be regarded as rigidity.

  Further, although the timing for starting the rotation of the registration roller is controlled, instead of this, the rotational speed of the registration roller may be controlled to adjust the sheet conveyance position on the downstream side of the registration roller. More specifically, instead of delaying or speeding up the rotation start timing of the registration roller, the rotation speed of the registration roller is decreased or increased. Alternatively, both the rotation start timing and the rotation speed of the registration roller may be controlled.

  In addition, the sheet conveying apparatus of the present invention can be applied not only to an image forming apparatus but also to a document or recording sheet conveying system in a facsimile or printer.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus to which an embodiment of a sheet conveying device of the present invention is applied. FIG. 2 is a schematic diagram illustrating a configuration of a document sheet conveyance unit in the image forming apparatus of FIG. 1. FIG. 3 is a block diagram illustrating a control system of a document sheet conveyance unit in FIG. 2. FIG. 3 is a circuit diagram illustrating a deflection amount detection sensor and its peripheral circuits in the document sheet conveyance section of FIG. 2. FIG. 3 is a diagram illustrating a deflection amount of a document sheet in a recess of a sheet transport path in the document sheet transport unit of FIG. 2. 6 is a graph showing the relationship between the amount of deflection Lp of the original paper and the timing of starting rotation of the registration rollers. FIG. 2 is a schematic diagram illustrating a partially enlarged recording paper conveyance unit in the image forming apparatus of FIG. 1. It is a block diagram which shows the control system of the recording paper conveyance part of FIG.

Explanation of symbols

41 Conveying Roller 42 Registration Roller 61 Pickup Roller 62 Feeding Roller 63 Separation Roller 64 Conveying Roller 65 Registration Roller 66 Discharge Roller 71, 91 Deflection Detection Sensors 72-1, 72-2, 72-3, 92-1, 92 -2, 92-3 Comparators 73, 93 Control unit 100 Image forming apparatus 101 Document paper transport unit 102 Image reading unit 103 Printing unit 104 Recording paper transport unit 105 Paper feed unit

Claims (6)

In a paper conveyance device that provides a registration roller in a paper conveyance path, contacts the leading edge of the paper in the middle of conveyance with the registration roller in a stopped state, rotates the registration roller, and conveys the paper by the registration roller.
A sheet rigidity detecting means for detecting the rigidity of the sheet on the upstream side of the registration roller in the sheet conveying direction;
And a control unit configured to control a leading edge feeding operation of the sheet by the registration roller in accordance with the sheet rigidity detected by the sheet rigidity unit.   The paper conveyance device according to claim 1, wherein the rigidity detection unit detects a deflection amount of the paper corresponding to a rigidity of the paper.   2. The sheet conveying apparatus according to claim 1, wherein the control unit slows down the speed of the sheet leading edge feeding operation by the registration roller when the sheet rigidity detected by the sheet rigidity unit is high.   2. The sheet conveying apparatus according to claim 1, wherein the control unit delays the start of the leading edge feeding operation of the sheet by the registration roller when the sheet rigidity detected by the sheet rigidity unit is high.   An image forming apparatus comprising the sheet conveying device according to claim 1.   An original reading apparatus comprising the paper conveying device according to claim 1.

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