JP2019055835A - Paper sheet conveying device, and image forming apparatus - Google Patents

Abstract

To be arranged to determine a diameter of a paper sheet feeding roll without using a dedicated sensor for measuring the diameter according to a paper sheet conveying device.SOLUTION: A paper sheet conveying device 10 comprises a paper sheet feeding roll 406; drive means 407 connected to the paper sheet feeding roll via a one-way clutch; detection means 409 for detecting presence/absence of a load to the drive means; a conveyance roll 413; calculation means 724 for calculating a conveyance speed of a paper sheet during conveyance from a rotational speed of the conveyance roll and a diameter of the conveyance roll; control means 721 for controlling to increase the rotational speed of the drive means from a rotational speed at which the load is not detected by the detection means to a rotational speed at which the load is detected, after starting the conveyance of the paper sheet with the conveyance roll; and estimation means 725 for estimating the diameter of the paper sheet feeding roll from the rotational speed of the drive means and the conveyance speed of the paper sheet calculated by the calculation means when the detection means detects the load.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a sheet conveying device and an image forming apparatus.

  In Patent Document 1, a detection mechanism that detects that a predetermined amount of deflection has occurred on a sheet by contacting the sheet between the photosensitive drum and the transfer roller and the fixing device, and a driving torque of the fixing roller pair are detected. A control unit that controls the conveyance speed of the sheet by the fixing roller pair based on detection of deflection or driving torque after the conveyance of the sheet is started, and the sheet is appropriately placed between the transfer roller and the fixing device. An image forming apparatus that maintains a bent state is disclosed.

JP 2011-128398 A

  The sheet feeding roll of the image forming apparatus is worn out during the sheet feeding process, and when it is worn, the frictional force is lowered and the ability to feed and transport is lowered. As a method for predicting the wear of the paper feed roll, there is a method of predicting the wear state according to the number of papers fed and transported. It does not always wear out. Although it is conceivable to provide a sensor for measuring the diameter of the paper feed roll, it may lead to an increase in manufacturing cost and the configuration of the paper feed device may be complicated.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a paper transport device and an image forming apparatus that can determine the diameter of a paper feed roll without using a dedicated sensor for measuring the diameter.

The present invention according to claim 1 is a paper feed roll for conveying paper;
Drive means connected to the paper feed roll via a one-way clutch;
Detecting means for detecting the presence or absence of a load on the driving means;
A transport roll disposed on the downstream side of the paper feed path in the paper transport direction in the paper transport path;
Calculating means for calculating the conveyance speed of the paper conveyed by the conveyance roll from the rotation speed of the conveyance roll and the diameter of the conveyance roll;
Control means for performing control to increase the rotation speed of the driving means from a rotation speed at which the detection means does not detect a load to a rotation speed at which the load is detected after the conveyance of the paper by the conveyance roll is started;
Estimating means for estimating the diameter of the paper feed roll from the rotational speed of the driving means when the detecting means detects a load and the paper conveyance speed calculated by the calculating means;
Is a sheet conveying apparatus.

  According to a second aspect of the present invention, the detecting unit detects a load while the sheet being conveyed passes through the sheet feeding roll after the control unit starts conveying the sheet by the conveying roll. The sheet conveying apparatus according to claim 1, wherein control is performed to increase the rotational speed of the driving unit from a rotational speed that is not performed to a rotational speed at which a load is detected.

  According to a third aspect of the present invention, when the control unit conveys a plurality of sheets, the detection unit detects a rotation speed of the driving unit after the conveyance of each sheet by the conveyance roll is started. The sheet conveying apparatus according to claim 1, wherein the sheet conveying device performs control to increase each time each sheet passes from a rotation speed that does not occur to a rotation speed that detects a load.

  According to a fourth aspect of the present invention, when the detecting means has a magnitude of torque that is greater than or equal to a preset value when the driving means drives the paper feed roll, The sheet conveying device according to claim 1, wherein it is determined that a load has occurred.

  According to a fifth aspect of the present invention, the drive means is a DC motor, and the detection means detects the magnitude of torque when the drive means drives the paper feed roll from the drive current of the drive means. 5. A sheet conveying apparatus according to claim 4.

  According to a sixth aspect of the present invention, the detection means determines that a load is generated on the driving means when the rotational speeds of the driving means and the paper feed roll are equal. A sheet conveying apparatus according to any one of the above.

  In the present invention according to claim 7, when the transport roll is disposed within a distance shorter than the paper length from the position of the paper feed roll on the transport path, and the transport of the paper by the transport roll is started, The paper conveying apparatus according to claim 1, wherein the paper being conveyed is configured to be pulled out from the paper feed roll.

  In the present invention according to claim 8, the control unit performs a normal operation mode in which the drive unit is not rotated after the conveyance of the sheet by the conveyance roll is started, and a control to change the rotation speed of the drive unit. The sheet conveying apparatus according to claim 1, further comprising an estimation mode for estimating a diameter of the sheet feeding roll.

  According to a ninth aspect of the present invention, in the eighth aspect of the present invention, the control unit controls the estimation mode to be executed every preset period or every time a preset amount of print processing is executed. This is a paper transport device.

  According to a tenth aspect of the present invention, when the control means supplies paper from the paper feed roll to the transport roll, the drive means controls the driving means according to the diameter of the paper feed roll estimated by the estimation means. The paper conveying apparatus according to any one of claims 1 to 9, wherein control for changing a rotation speed is performed.

  The present invention according to claim 11 is provided with notification means for notifying a warning when the diameter of the paper feed roll estimated by the estimation means becomes smaller than a preset value. 10 is a sheet conveying apparatus according to any one of the above.

  According to a twelfth aspect of the present invention, there is provided the sheet conveying apparatus according to any one of the first to eleventh aspects, wherein the control unit performs control to stop driving of the driving unit when the detecting unit detects a load. It is.

According to a thirteenth aspect of the present invention, there is provided a paper feed roll for conveying paper,
Drive means connected to the paper feed roll via a one-way clutch;
Detecting means for detecting the presence or absence of a load on the driving means;
A transport roll disposed on the downstream side of the paper feed path in the paper transport direction in the paper transport path;
Calculating means for calculating the conveyance speed of the paper conveyed by the conveyance roll from the rotation speed of the conveyance roll and the diameter of the conveyance roll;
Control means for performing control to increase the rotation speed of the driving means from a rotation speed at which the detection means does not detect a load to a rotation speed at which the load is detected after the conveyance of the paper by the conveyance roll is started;
Estimating means for estimating the diameter of the paper feed roll from the rotational speed of the driving means when the detecting means detects a load and the paper conveyance speed calculated by the calculating means;
A paper transport device comprising:
Image output means for outputting an image on a sheet conveyed by the sheet conveying apparatus;
An image forming apparatus.

  According to the first aspect of the present invention, it is possible to provide a paper transport device that can determine the diameter of the paper feed roll without using a dedicated sensor for measuring the diameter.

  According to the second aspect of the present invention, it is possible to obtain the diameter of the paper feed roll within a period during which a single paper is fed.

  According to the third aspect of the present invention, it is possible to obtain the diameter of the paper feed roll with higher accuracy than in the case of obtaining the diameter of the paper feed roll within a period during which a single sheet is fed. Become.

  According to the fourth aspect of the present invention, the diameter of the paper feed roll can be obtained according to the timing at which the driving torque is generated in the driving means.

  According to the fifth aspect of the present invention, it is possible to measure the torque required to obtain the diameter of the paper feed roll without using a complicated device such as a torque measuring device.

  According to the sixth aspect of the present invention, it is possible to detect the presence or absence of a load necessary for obtaining the diameter of the paper feed roll without using a device such as a torque measuring device.

  According to the seventh aspect of the present invention, it is possible to adopt a configuration in which a load is not generated in the driving device that drives the paper feed roll when the conveyance of the paper by the transport roll is started.

  According to the eighth aspect of the present invention, the estimation mode for estimating the diameter of the paper feed roll can be selectively executed as necessary.

  According to the ninth aspect of the present invention, the execution frequency of the estimation mode for estimating the diameter of the paper feed roll can be reduced.

  According to the tenth aspect of the present invention, paper can be supplied from the paper feed roll to the transport roll at a constant speed without being affected by the decrease in the diameter of the paper feed roll.

  According to the eleventh aspect of the present invention, the user can be notified of the replacement timing of the paper feed roll.

  According to the twelfth aspect of the present invention, unnecessary energy consumption can be suppressed as compared with the case where the driving means is continuously driven even after the load is detected.

  According to the thirteenth aspect of the present invention, it is possible to provide an image forming apparatus capable of obtaining the diameter of the paper feed roll without using a dedicated sensor for measuring the diameter.

1 is a cross-sectional view illustrating a structure of an image forming apparatus 10 according to an embodiment of the present invention. It is explanatory drawing which shows typically the structure of the paper feed unit 40A in one Embodiment of this invention. It is a figure which shows the hardware constitutions of the control unit 70 in one Embodiment of this invention. It is a figure which shows the function structure of the control unit 70 in one Embodiment of this invention. 6 is a flowchart showing a flow of processing in the control unit 70 when determining the amount of wear of the feed roll 406 in an embodiment of the present invention. FIG. 6 is a diagram showing a comparison of the speeds of each part of the paper feed unit 40A when determining the amount of wear of the feed roll 406 in an embodiment of the present invention. 10 is a flowchart showing a flow of processing in the control unit 70 in a modified example for obtaining the wear amount of the feed roll 406. FIG. 10 is a diagram showing a comparison of the speed of each part of the paper feed unit 40A in a modified example for obtaining the wear amount of the feed roll 406.

  An image forming apparatus 10 according to the present embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view showing the structure of the image forming apparatus 10 of the present embodiment. As shown in FIG. 1, the image forming apparatus 10 includes a document reading device 20, a user interface 30, a paper feeding device 40, an image output device 50, a paper discharge tray 60, and a control unit 70.

  The document reading device 20 includes a document feed tray 21, a document discharge tray 22, an automatic document feeder 23, a document table 24, and an image scanner 25.

  The documents placed on the document feed tray 21 are taken one by one by the automatic document feeder 23 in accordance with an instruction from the user via the user interface 30. At that time, the image of the document is image scanner 25. The scanned image information is output to the control unit 70. The document is discharged to the document discharge tray 22 after passing through the automatic document feeder 23.

  In addition, when no document is placed on the document feed tray 21, the document reading device 20 reads the document placed on the document table 24 in response to an instruction from the user via the user interface 30. The image information scanned by the image scanner 25 is output to the control unit 70.

  The user interface 30 includes a display device and an input device. For example, the display device is a liquid crystal display, and the input device is a touch panel disposed on the liquid crystal display. A user of the image forming apparatus 10 touches the touch panel while visually recognizing an image displayed on the liquid crystal display, thereby performing necessary operation inputs such as an instruction to start scanning a document, an instruction to start copying a document, and the like. In addition to the touch panel, the input device may be a button or a keyboard arranged around the liquid crystal display.

  The paper feeding device 40 is for taking in paper placed on a paper feeding tray, which will be described later, and transporting it to the image output device 50. In the image forming apparatus 10 shown in FIG. 1, three sheet feeding units 40 </ b> A to 40 </ b> C are stacked in the vertical direction to constitute the sheet feeding apparatus 40. Since the respective paper feeding units 40A to 40C have substantially the same structure, in the following description, only one paper feeding unit 40A will be described, and description of the other paper feeding units will be omitted.

  FIG. 2 is an explanatory diagram schematically showing the structure of the paper feed unit 40A in the present embodiment. As shown in FIG. 2, the paper feed unit 40A includes a paper feed tray 401, a paper placement plate 402, a push-up plate 403, a push-up motor 404, a pickup roll 405, a feed roll (paper feed roll) 406, and a feed motor (driving means). 407, a one-way clutch 408, a load detection unit 409, a retard roll 410, a feed sensor 411, a curved guide 412, a TA roll (Take Away Roll) 413, a TA motor 414, and a TA sensor 415.

  The paper feed tray 401 is attached to the main body of the image forming apparatus 10 so that it can be inserted and removed. The paper feed tray 401 has a box shape with the top opened, and a space is formed in the inside to accommodate a predetermined number of sheets in a stacked state. A plate-shaped paper placement plate 402 is provided at the bottom of the internal space of the paper feed tray 401.

  The paper placement plate 402 is disposed on the paper feed tray 401 so as to be moved up and down by a push-up plate 403 and a push-up motor 404. When the paper feed unit 40A takes in the paper from the paper tray 401, when the push-up motor 404 is activated, the push-up plate 403 pushes the paper placement plate 402 upward, and the paper placed on the paper placement plate 402 is picked up. Pressed against the roll 405, the upper surface of the uppermost sheet comes into contact with the pickup roll 405 with a pressing force applied.

  The pickup roll 405 is driven by a pickup motor (not shown) and takes in the paper placed on the push-up plate 403 of the paper feed tray 401. The pickup roll 405 feeds in order from the uppermost paper in the paper feed tray 401. Pass to role 406. When picking up the paper, the pick-up roll 405 contacts the top surface of the paper pushed upward by the push-up plate 403 with a predetermined pressing force, and rotates to feed the paper between the feed roll 406 and the retard roll 410. .

  The feed roll 406 and the retard roll 410 are arranged in the paper conveyance path, and in particular, are arranged downstream of the front wall 401A of the paper feed tray 401 in the paper conveyance direction. The feed roll 406 and the retard roll 410 feed (carry) the paper taken from the paper feed tray 401 by the pickup roll 405 along the conveyance path, that is, send it out and deliver it to the TA roll 413 described later. Specifically, the feed roll 406 is driven by the feed motor 407, contacts the upper surface of the paper taken in from the paper feed tray 401 by the pickup roll 405, and rotates in the clockwise direction in the figure to thereby remove the paper. Then, the sheet is fed toward the downstream in the sheet conveying direction while nipping with a retard roll 410 described later.

  The feed motor 407 is for driving the feed roll 406, and a DC motor is employed in this embodiment. The rotational speed of the feed motor 407 is controlled by a control unit 70 described later. The feed motor 407 is connected to the feed roll 406 via a one-way clutch 408.

  The one-way clutch 408 connects the drive shaft 407A of the feed motor and the rotation shaft 406A of the feed roll, and transmits the driving force to the rotation shaft 406A of the feed roll. After the paper is fed from the feed roll 406 to the TA roll 413, when the conveyance speed of the paper increases, or when the rotation speed of the feed motor 407 is reduced or stopped, the feed roll 406 passes the paper. Accordingly, the rotation speed of the rotation shaft 406A of the feed roll is faster than the rotation speed of the drive shaft 407A of the feed motor. At this time, the one-way clutch 408 enters a so-called overrun state.

  The load detection unit 409 detects the presence or absence of a load on the feed motor 407. Specifically, the load detection unit 409 detects the magnitude of torque when the feed motor 409 drives the feed roll 406 from the drive current of the feed motor 409, and the detected magnitude of the torque is a preset value. When the above is reached, it is determined that a load is generated on the feed motor 409. Alternatively, since the feed motor 407 is a direct current motor, the load detection unit 409 measures the value of the drive current of the feed motor 407, and based on that value, determines the magnitude of torque when the feed motor 409 drives the feed roll 406. It may be detected, or the presence or absence of a load may be detected directly from the value of the drive current without obtaining torque. The load detection unit 409 may be a torque sensor attached to the main body of the feed motor 407 or the drive shaft 407A of the feed motor. Information about the presence or absence of the torque detected by the torque sensor, that is, the presence or absence of the load is output to the control unit 70.

The retard roll 410 is disposed to face the feed roll 406, contacts the lower surface of the paper taken in between the feed roll 406 (nip position) by the pickup roll 405, and the lower surface (or lower surface side paper) of this paper. ) Is given an appropriate frictional resistance to suppress double feeding of the paper and roll the paper one by one. Specifically, the retard roll 410 is connected to a fixed shaft via a torque limiter (not shown), and is driven to rotate as the feed roll 406 rotates. By adjusting the value of the torque limiter and the value of the nip load between the feed roll 406 and the retard roll 410 so as to always be within the range of the following expression (1), only one sheet is transported by the sheet. To be sent to.
Feed force F _f > retard force F _r > paper friction force F _p (1)

here,
Feed force F _f = μ _fp N,
Retard force F _r = μ _rp N,
Friction force between paper F _p = μ _pp N
N: Nip pressure μ _fp : Friction coefficient between feed roll and paper μ _rp : Friction coefficient between retard roll and paper μ _pp : Friction coefficient between paper

  The feed sensor 411 is arranged in the paper transport path downstream and closest to the feed roll 406 and the retard roll 410 in the paper transport direction, the paper is nipped by the feed roll 406 and the retard roll 410, and the paper feed is started. Detect that.

  As the feed sensor 411, a paper passage sensor such as a reflection type photo sensor or a transmission type photo sensor can be used. When it is detected that the sheet has passed, the information is output to the control unit 70.

  The curved guide 412 is disposed downstream of the feed roll 406 in the paper transport direction. Specifically, the curved guide 412 is installed on the side of the feed roll 406 and the retard roll 410 and on the downstream side in the sheet conveyance direction (when the image output device 50 is provided on the upper side). It is a member for guiding a sheet, which has a curved surface curved toward the top. The sheet fed from between the feed roll 406 and the retard roll 410 is guided by coming into contact with the surface of the curved guide 412 and moves along the curved guide 412 while gradually changing the transport direction from the horizontal direction to the vertical direction. And it guides to TA roll 413 mentioned later.

  The TA roll 413 is arranged so that the sheet is conveyed in the vertical direction downstream of the feed roll 406, the retard roll 410, and the curved guide 412 in the sheet conveyance direction in the sheet conveyance path. The TA roll 413 includes at least a pair of opposed rolls disposed between the feed roll 406 and the retard roll 407 of the paper feed unit 40A and the image output device 50, and is driven by a TA motor 414. In FIG. 2, only the pair of TA rolls 413 closest to the feed roll 406 and the retard roll 410 are shown. The TA roll 413 pulls the paper fed along the curved guide 413 from the feed roll 406 and the retard roll 410, and transports the paper downstream in the transport direction so that the paper transport direction is the vertical direction.

  The TA roll 413 is disposed within a distance shorter than the paper length of the paper placed on the paper feed tray 401 from the position of the feed roll 406 on the conveyance path, and the conveyance of the paper by the TA roll 413 is started. Then, the sheet being conveyed is structured to be pulled out from the feed roll 406 by the TA roll 413.

  The TA motor 414 drives the TA roll 413. Normally, a pair of TA rolls 413 are provided facing each other, and the paper is conveyed between the TA rolls 413 facing each other. Therefore, the TA motor 414 drives only one of the opposed TA rolls 413 and the other TA roll 413 is driven to rotate. In addition, by appropriately changing the driving speed of the TA motor 414 by the control unit 70 described later and adjusting the rotational speed of the TA roll 413, the time for the paper being conveyed to reach the image output device 50 is adjusted, and the paper The timing at which image formation is performed is precisely matched.

  The TA sensor 415 is arranged in the paper transport path downstream and closest to the TA roll 413 in the paper transport direction, and detects that the transport of the paper by the TA roll 413 is started.

  As the TA sensor 415, a paper passage sensor such as a reflection type photo sensor or a transmission type photo sensor can be used. When it is detected that the sheet has passed, the information is output to the control unit 70.

  The image output device 50 is provided downstream in the transport direction of the paper transported by the paper feed device 40 and outputs an image on the paper transported by the paper feed device 40.

  As shown in FIG. 1, the image output device 50 includes yellow, magenta, cyan, and black photoconductors 51Y to 51K arranged in a line, and charging devices 52Y to 52Y arranged around the photoconductors 51Y to 51K, respectively. 52K, exposure devices 53Y to 53K, developing devices 54Y to 54K, primary transfer devices 55Y to 55K, and cleaning devices 56Y to 56K. Further, the image output device 50 includes an intermediate transfer belt 57, a secondary transfer device 58, and a fixing device 59.

  The photoreceptors 51Y to 51K are charged by the charging devices 52Y to 52K, respectively. Next, in response to an instruction from the control unit 70, the exposure devices 53Y to 53K irradiate a pattern of image data to be printed to form a latent image on the surface of the photoreceptors 51Y to 51K. Next, toner of each color is attached to the latent images formed on the surfaces of the photoreceptors 51Y to 51K by the developing devices 54Y to 54K, and transferred to the intermediate transfer belt 57 by the primary transfer devices 55Y to 55K. The toner remaining on the surfaces of the photoreceptors 51Y to 51K is removed by the cleaning devices 56Y to 56K.

  The toner image formed on the intermediate transfer belt 57 is transferred by the secondary transfer device 58 to the paper conveyed from the paper feeding device 40 via the TA roll 413, and then heated and pressurized by the fixing device 59. The image is fixed on the paper and an image is formed on the paper. The sheet on which the image is formed is discharged to the discharge tray 60.

  The paper discharge tray 60 is provided below the document reading device 20 and the user interface 30 and is a space for receiving and stacking the discharged paper on which images have been formed by the image output device 50.

  Next, the control unit 70 will be described with reference to FIGS. FIG. 3 is a diagram illustrating a hardware configuration of the control unit 70, and FIG. 4 is a diagram illustrating a functional configuration of the control unit 70.

  As shown in FIG. 3, the control unit 70 includes a control microprocessor 701, a memory 702, a storage device 703, and a communication interface 704, and each is connected to a control bus 705.

  The control microprocessor 701 controls the operation of each unit of the image forming apparatus 10 based on a control program stored in the storage device 703.

  The memory 702 temporarily stores print data received from a computer (not shown) connected to the image forming apparatus 10 via a network or the like and image data read by the document reading apparatus 20. In addition, data such as the rotational speed of the feed motor 407, information about the presence or absence of a load detected by the load detection unit 409, and the rotational speed of the TA motor 414 are temporarily stored.

  The storage device 703 is configured by a hard disk (HDD) or a solid state drive (SDD), firmware and a control program for controlling each part of the image forming apparatus 10, information on the diameter of the TA roll 413, and so far. Stores information such as the cumulative number of sheets that have passed through the TA roll 413.

  The communication interface 704 performs communication control when the image forming apparatus 10 is connected to a computer or the like via a network, receives a print instruction or print data from the computer, a print end notification or a print error notification. Etc.

  Next, the functional configuration of the control unit 70 will be described with reference to FIG. The control unit 70 executes a control program or firmware stored in the storage device 703 in the control microprocessor 701, as shown in FIG. 4, as shown in FIG. 4, a paper take-in control unit 721, a paper transport control unit 722, an image It functions as a processing control unit 723, a conveyance speed calculation unit 724, a wear state estimation unit 725, a warning notification unit 726, and an operation mode setting unit 727.

  When a print start instruction is received from the image forming apparatus 10, the paper take-in control unit 721 operates the push-up plate 403 by driving the push-up motor 404, raises the paper placement plate 402, and feeds the paper feed tray 401. The upper surface of the uppermost sheet accommodated in the paper is brought into contact with the pickup roll 405. At substantially the same time, the paper take-in control unit 721 rotates a pickup roll 405 by driving a pickup motor (not shown), thereby moving the uppermost paper stored in the paper feed tray 401 downstream in the paper transport direction. Taking in and guiding between the feed roll 405 and the retard roll 410.

  Further, the paper take-in control unit 721 rotates the feed roll 406 by starting the drive of the feed motor 407 almost simultaneously with the start of driving of the pickup motor that drives the pickup roll 405, and the feed roll 406 is rotated by the pickup roll 405. The paper taken in is fed out, that is, fed downstream in the paper conveyance direction in a state where it is nipped between the opposing retard rolls 410.

  Further, the paper take-in control unit 721 performs control to increase the rotation speed of the feed motor 407 from the rotation speed at which the load detection unit 409 does not detect the load to the rotation speed at which the load is detected after the TA roll 413 starts to convey the paper. Do.

  Further, when feeding paper from the feed roll 406 to the TA roll 413, the paper take-in control unit 721 determines the feed motor 407's diameter according to the value of the diameter of the feed roll 406 estimated by a wear state estimation unit 724 described later. Control is performed to change the rotation speed, and the feed roll 406 feeds the paper to the TA roll 413 at a desired speed. Specifically, control is performed so that the rotation speed of the feed roll increases as the diameter of the feed roll 406 decreases.

  The paper transport control unit 722 rotates the TA roll 413 by starting the driving of the TA motor 414 from the time when the feed sensor 411 detects the passage of the paper at almost the same time as the driving of the pickup motor or the feed motor 407 or at the latest. When the sheet is fed to the TA roll 413, the sheet is brought into a state where the sheet can be conveyed to the image output device 50. When the paper is transported by the TA roll 413, the TA roll 413 is transported at a desired speed by adjusting the rotational speed of the TA motor 414, and the time for the paper to reach the image output device 50 is adjusted. Make sure that the timing to output the image on the paper matches.

  The image processing control unit 723 processes the image data temporarily stored in the memory 702 to print data, rotates each of the photoconductors 51Y to 51K, and uses the charging devices 52Y to 52K to output the photoconductors 51Y to 51K. And the exposure devices 53Y to 53K are controlled to form a latent image corresponding to the printing data on the photoconductors 51Y to 51K. Further, the image processing control unit 723 controls the toners of the respective colors to be supplied to the photoreceptors 51Y to 51K by the developing devices 54Y to 54K, and the formed toner images are transferred to the intermediate transfer belt 57 by the primary transfer devices 55Y to 55K. I do. Further, the image processing control unit 723 transfers the toner image on the intermediate transfer belt 57 onto the paper conveyed by the TA roll 413 by the secondary transfer device 58 and fixes it on the paper by the fixing device 59. Control is performed to discharge the sheet on which the sheet is formed to the sheet discharge tray 60.

The transport speed calculation unit 724 calculates the transport speed of the paper transported by the TA roll 413 from the rotational speed of the TA roll 413 and the diameter information of the TA roll 413. The rotational speed of the TA roll 413 is obtained based on the rotational speed of the TA motor 414. Information on the diameter of the TA roll 413 is stored in the storage device 703, and the sheet conveyance speed is obtained by the following equation (2).

V = r _(TA) x ω _(TA) (2)

here,
V: Paper transport speed [mm]
r _(TA) : TA roll radius [mm]
ω _(TA) : TA roll angular velocity [rad / sec]

  Since the TA roll 413 wears slightly compared to the feed roll 406, it may be assumed that the TA roll 413 is constant and may be approximated by the value of the diameter stored in the storage device 703, or the paper that has passed through the TA roll 413. The diameter value at the present time may be estimated from the accumulated number of the diameters, and the corrected diameter value may be used.

  The wear state estimation unit 725 is configured such that after the paper conveyance by the TA roll 413 is started, the above-described paper take-in control unit 721 performs the feed motor 407 from a rotation speed at which the load detection unit 409 does not detect the load to a rotation speed at which the load is detected. When the control for increasing the rotation speed is performed, the feed roll is calculated based on the rotation speed of the feed motor 407 when the load detection unit 409 detects the load and the sheet conveyance speed calculated by the conveyance speed calculation unit 724 described above. The diameter of 406 is estimated.

Specifically, the wear state estimation unit 725 calculates the diameter of the feed roll 406 by the following equation (3), and uses the estimated value of the diameter of the feed roll 406.

r = V / ω (3)

here,
r: Feed roll radius [mm]
V: Paper transport speed [mm / sec]
ω: Feed roll rotation angular velocity [rad / sec]

The diameter value of the feed roll 406 estimated by the wear state estimation unit 725 is stored in the memory 702 or the storage device 703.

  The warning notification unit 726 notifies the user interface 30 of a warning when the diameter of the feed roll 406 estimated by the wear state estimation unit 725 becomes smaller than a preset value. This warning includes a warning message that prompts the user to replace the feed roll 406.

  The operation mode setting unit 727 performs a normal operation mode in which the feed motor 407 is not rotated after the paper conveyance by the TA roll 413 is started, and a control for changing the rotation speed of the feed motor 407 to thereby change the diameter of the feed roll 406. The sheet feeding device 40 is operated in any one of the estimation modes in which can be estimated.

  Next, an operation flow for estimating the wear amount of the feed roll 406 of the image forming apparatus 10 according to the present embodiment will be described with reference to FIGS. FIG. 5 is a flowchart showing the flow of processing in the control unit 70 when obtaining the wear amount, that is, the diameter of the feed roll 406. FIG. 6 shows a comparison of the speed of each part of the paper feed unit 40A when the diameter of the feed roll 406 is obtained.

  In step S <b> 801, the operation mode setting unit 727 sets the sheet feeding unit 40 </ b> A to operate in the wear amount estimation mode for estimating the wear amount of the feed roll 406. The operation mode setting unit 727 does not have to perform control so that the wear amount estimation mode is executed every time the paper feeding process from the paper feeding unit 40A is performed, and is performed for a preset period or a preset amount. Control is performed so that the wear amount estimation mode is executed every time the printing process is executed. For example, the operation mode setting unit 727 is configured to execute the wear amount estimation mode every preset time such as every 24 hours or every time the sheet is first fed from the sheet feeding unit 40A by the image forming apparatus 10 every day. Alternatively, control may be performed so that the wear amount estimation mode is executed each time a preset amount of paper feed processing such as 1000 sheets is executed in the paper feed unit 40A. In the following description, the paper feed process for the paper feed unit 40A is described, but the same applies to the processes of the other paper feed units 40B and 40C.

In step S802, the paper take-in control unit 721 starts rotation of the pickup roll 405 by driving a pickup motor (not shown). Further, the sheet take-in control unit 721 starts the rotation of the feed roll 406 by starting the drive of the feed motor 407. (Time T _{1 in} FIG. 6) Further, the sheet conveyance control unit 722 starts the rotation of the TA roll 413 by starting the driving of the TA motor 414. The rotational speed of the TA motor 414 is controlled so that the conveyance speed of the sheet conveyed by the TA roll 413 is higher than the sheet speed when the sheet is fed by the feed roll 406.

In step S <b> 803, the paper take-up control unit 721 drives the push-up motor 404 to operate the push-up plate 403 to raise the paper placement plate 402 upward. As a result, the paper placed on the paper placement plate 402 in the paper feed tray 401 is pushed upward and pressed against the pickup roll 405 with a predetermined pressing force. Since the pick-up roll 405 has already started rotating in the above-described step S802, the uppermost sheet in the paper feed tray 402 pressed against the pick-up roll 405 starts moving in the paper transport direction, Incorporation is started (time T _{2 in} FIG. 6).

In step S <b> 804, the sheet is taken between the feed roll 406 and the retard roll 407. Here, since the speed at which the feed roll 405 feeds the paper is set faster than the speed at which the paper is taken in by the pickup roll 405, when the paper is nipped between the feed roll 406 and the retard roll 407, The sheet is conveyed downstream in the sheet conveying direction mainly by the driving force of the feed roll 406, and the pickup roll 405 is in a driven state interlocked with the feed roll 405 (time T _{3 in} FIG. 6). At this time, a drive torque is generated in the feed motor 407 that drives the feed roll 406.

  When only one sheet is nipped between the feed roll 406 and the retard roll 407, the retard roll 407 is driven as the sheet moves. On the other hand, when there are two sheets of nipped paper, the retard force acting on the lower surface side of the paper nipped by the retard roll 407 is set to be larger than the inter-sheet friction force between the two sheets. Therefore, the upper sheet is fed downstream in the sheet conveyance direction by the feed force of the feed roll 406, while the lower sheet is fed with the feed roll 406 by the retard force exerted by the retard roll 407 on the lower surface side of the lower sheet. It stays between the retard rolls 407, prevents double feeding of the paper, and turns the paper. At this time, the retard roll 407 does not rotate following the feed roll 406.

In step S805, when the paper is fed from the feed roll 406 toward the downstream side in the paper conveyance direction, the leading edge of the paper reaches the TA roll 413 while being guided by the curved guide 412, and the conveyance of the paper by the TA roll 413 is started. (Time T _{4 in} FIG. 6). When the sheet is fed to the TA roll 413, the driving torque generated in the feed motor 407 is eliminated. As shown in FIG. 6, after the TA sensor 415 detects that the paper is fed to the TA roll 413, the rotation of the feed motor 407 may be temporarily stopped (time T _{5 in} FIG. 6). The TA roll 413 rotates at a rotational speed at which the paper transport speed is faster after the paper transport by the TA roll 413 is started than the paper speed immediately before the front end of the paper reaches the TA roll 413. The conveyance speed increases once. Thereafter, the paper conveyance control unit 722 slightly reduces the rotation speed of the TA roll 413 (time T _{6 in} FIG. ₆ ), and the time at which the paper reaches the image output device 50 coincides with the start time of image output. The rotation of the motor 414 is controlled. At this time, the front portion in the paper conveyance direction is conveyed by the TA roll 413, while the rear portion in the paper conveyance direction is nipped by the feed roll 406 and the retard roll 410.

Next, in step S806, the paper take-in control unit 721 performs control to increase the rotation speed of the feed motor 407 from the rotation speed at which the load detection unit 409 does not detect the load to the rotation speed at which the load is detected. Specifically, after the TA sensor 415 detects the passage of the leading edge of the sheet, that is, after the sheet conveyance by the TA roll is started, the rotation of the feed motor 407 is temporarily stopped (time T _{5 in} FIG. 6), and then the conveyance is performed. The rotation speed (speed ω _{1 in} FIG. 6) is such that the peripheral speed of the feed roll 406 is slower than the paper conveyance speed conveyed by the TA roll 413 while one of the sheets passes through the feed roll 406. The rotation of the feed motor 407 is restarted (time T _{7 in} FIG. 6), and control is performed to gradually increase the rotation speed of the feed motor 407.

In step S807, the load detection unit 409 detects the presence or absence of a load applied to the feed motor 407. Immediately after the rotation speed control of the feed roll 406 in step S806 is started (time T ₇ ), the feed roll 406 is driven and rotated by the movement of the rear part of the paper being conveyed. Since the rotation speed of the feed motor 407 is slower than the rotation speed of the feed roll 406, the one-way clutch 408 enters a so-called overrun state. Therefore, the feed motor 407 is in a no-load rotation state, and the load is not detected by the load detection unit 409. If no load is detected, the process returns to step S806 to further increase the rotational speed of the feed motor 407.

However, when the rotational speed of the feed motor 407 is further increased, the rotational speed of the feed motor 407 exceeds the rotational speed of the feed roll 406 at a certain point in time (that is, the rotational speed of the drive shaft 407A of the feed motor is overtake the rotation speed of the rotation shaft 406A), the load is generated in the feed motor 407 from that point, the load is detected by the load detection section 409 (time T ₈ in FIG. 6).

  As for the presence / absence of a load, the load detection unit 409 generates a load on the feed motor 407 when the magnitude of the torque when the feed motor 407 drives the feed roll 406 exceeds a preset value. Judge that Alternatively, the load detection unit 409 may determine that a load is generated on the feed motor 407 when the rotation speeds of the feed motor 407 and the feed roll 406 become equal.

If a load is detected, the process proceeds to step S808. In step S808, the paper take-in control unit 721 stores the rotation speed (speed ω _{2 in} FIG. 6) of the feed roll 406 when the load detection unit 409 detects the load in the memory 702, and the paper conveyance control unit 722. Stores the rotational speed of the TA roll 413 in the memory 702. The conveyance speed calculation unit 724 calculates the conveyance speed of the sheet conveyed by the TA roll 413 from the rotation speed of the TA roll 413 stored in the memory 702 and the diameter of the TA roll 413 stored in the storage device 703. Further, the paper take-in control unit 721 performs control to stop driving the feed motor 407 when the load detection unit 409 detects a load (time T _{9 in} FIG. 6).

Next, the wear state estimation unit 725 calculates the diameter of the feed roll 406 from the rotation speed of the feed motor 407 when the load detection unit 409 detects the load and the sheet conveyance speed calculated by the conveyance speed calculation unit 724. (The above-mentioned feed motor rotational speed ω ₂ is calculated as the feed roll rotational angular speed ω in the above-described equation (2)). The diameter value of the feed roll 406 estimated by the wear state estimation unit 725 is stored in the memory 702 or the storage device 703.

  Even after the rotation of the feed motor 407 is stopped, the feed roll 406 is rotated in accordance with the movement of the sheet by the action of the one-way clutch 408 until the trailing edge of the sheet finishes passing through the feed roll 406.

  In step S809, the wear state estimation unit 725 determines whether the estimated radius of the feed roll 406 is smaller than a predetermined value. When the radius of the feed roll 406 is smaller than the predetermined value, the process proceeds to step S810, and when it is equal to or larger than the predetermined value, the process proceeds to step S811.

  In step S810, the warning notification unit 726 notifies the user interface 30 of a message warning that the wear of the feed roll 406 is progressing, prompts the user to replace or maintain the feed roll 406, and proceeds to step S812. .

  In step S811, the paper take-in control unit 721 performs the feed roll estimated by the wear state estimation unit 725 in step S808 in the subsequent paper feed processing, that is, when feeding paper from the feed roll 406 to the TA roll 413. Control is performed to change the rotation speed of the feed motor 407 in accordance with the diameter of the 406 so that the paper is always fed to the TA roll 413 by the feed roll 406 at a constant speed. The changed speed setting value is stored in the storage device 703.

  In step S812, the operation mode setting unit 727 finishes the process in which the paper feeding device 40 operates in the wear amount estimation mode for estimating the wear amount of the feed roll 406, and changes the setting so that normal conveyance is performed in the subsequent print processing. Then, the process ends. In the subsequent printing process, the feed roll 406 rotates at the rotation speed set in step S811 described above.

[Modification]
In the above example, after the sheet take-up control unit 721 starts conveying the sheet by the TA roll 413, the load detection unit 409 detects the load while the sheet being conveyed passes the feed roll 406. The case where the control for increasing the rotation speed of the feed motor 407 from the rotation speed to the rotation speed at which the load is detected has been described. However, the present invention is not limited to the above example, and when the sheet take-in control unit 721 conveys a plurality of sheets, the rotation speed of the feed motor 407 after the start of conveyance of each sheet by the TA roll 413 is determined. The load detection unit 409 may be controlled to increase each time the sheet passes the feed roll 406 from a rotation speed at which the load is not detected to a rotation speed at which the load is detected.

  Hereinafter, referring to FIGS. 7 and 8, when transporting a plurality of sheets, the rotation speed of the feed motor 407 after the start of transport of each sheet by the TA roll 413 is determined every time each sheet passes through the feed roll 406. The flow of processing for estimating the diameter of the feed roll 406 by raising it to the following will be described. FIG. 7 is a flowchart showing the flow of processing in the control unit 70 in a modified example for obtaining the wear amount of the feed roll 406. FIG. 8 is a diagram showing a comparison of the speed of each part of the paper feed unit 40A in a modified example for obtaining the wear amount of the feed roll 406.

In step S901 in FIG. 7, the operation mode setting unit 727 sets the sheet feeding unit 40A to operate in the wear amount estimation mode for estimating the wear amount of the feed roll 406, as in step S801 in FIG. . Unlike the above-described embodiment, the feed motor 407 is used when the sheet take-up control unit 721 rotates the feed motor 406 in order to estimate the wear amount of the feed roll 406 after the TA roll 413 starts conveying the sheet. Set the initial value of the rotation speed ω _f of. The initial value is a rotation speed at which the load detection unit 409 does not detect a load.

  Since the processing in steps S902 to S905 is the same as the processing in steps S802 to S805 in FIG. 5 described above, a description thereof will be omitted, but through these series of processing, paper is taken from the paper feed tray 401 and the TA roll 413 is processed. Then, the conveyance of the sheet by the TA roll 413 is started.

Next, in step S906, the paper take-in control unit 721 rotates the feed motor 407 at a rotation speed ω _f set in step S901 or step S908 described later, for a preset period. The predetermined period may be until the trailing edge of the sheet has passed, or the trailing edge of the sheet passes if it is sufficient to determine whether or not the driving torque is generated in the feed motor 407. It may be a period shorter than finishing.

In step S <b> 907, the load detection unit 409 detects the presence or absence of a load applied to the feed motor 407. When the rotation speed ω _f of the feed motor 407 is slower than the rotation speed of the feed roll 406 that rotates following the conveyance of the paper, the one-way clutch 408 is in an overrun state, the feed motor 407 is in a no-load rotation state, and the load The load is not detected by the detection unit 409. If no load is detected, the process proceeds to step S908. On the other hand, when the rotation speed ω _f of the feed motor 407 is faster than the rotation speed of the feed roll 406 (that is, when the rotation speed of the drive shaft 407A of the feed motor is faster than the rotation speed of the rotation shaft 406A of the feed roll 406) A load is generated in the motor 407, and the load is detected by the load detection unit 409. If a load is detected, the process proceeds to step S909.

In step S <b> 908, the paper take-in control unit 721 prepares for the next paper feed process, and feeds the feed motor 407 when rotating the feed motor 407 in order to estimate the amount of wear of the feed roll 406 after the TA roll 413 starts transporting the paper. The value of the rotational speed ω _f of the motor 407 is changed. Specifically, the rotation speed ω _f of the feed motor 407 is set to be faster than the previous time, and the process returns to step S902, whether or not the next paper is fed, and whether or not the load is detected in the feed motor 407 at that time Determine.

In step S909, the paper take-in control unit 721 stores the rotational speed ω _f of the feed roll 406 when the load detection unit 409 detects the load, and the paper calculated by the rotational speed and the transport speed calculation unit 724. The diameter of the feed roll 406 is estimated from the conveyance speed.

  The subsequent processes in steps S910 to S913 are the same as the processes in steps S809 to S812 in FIG.

FIG. 8 shows a change in the rotational speed of the feed motor 407 and a change in the magnitude of the drive torque when estimating the diameter of the feed roll 406 during the paper feeding process for a plurality of sheets. In FIG. 8, when feeding the first sheet, the feed motor 407 is driven at a rotational speed ω from time T _{801 to} T ₈₀₂ to feed the sheet from the feed roll 406 to the TA roll 413. At this time, a driving torque τ for feeding paper is generated in the feed motor 407. When the first sheet reaches the TA roll 413, the feed motor 407 temporarily stops at time _T802 , after which the sheet is conveyed by the TA roll 413, and the feed roll 406 is conveyed by the conveyance of the sheet by the TA roll 413. When in the driven state, the feed motor 407 is driven at a rotational speed ω ₈₁ that does not cause a drive torque in the feed motor 407 for a predetermined time, that is, from time T ₈₀₃ to time T ₈₀₄ . At this time, since the feed roll 406 is in a driven rotational state as the paper is conveyed, almost no driving torque is generated in the feed motor 407.

Next, when the paper feeding process for the second sheet is performed, the feed motor 407 is driven at the rotational speed ω from time T _{805 to} T _{806 in the same} manner as the paper feeding process for the first sheet. Sheet is fed from the feed roll 406 to the TA roll 413. At this time, a driving torque τ for feeding the second sheet is generated in the feed motor 407. The driving torque at this time is substantially the same as the driving torque τ generated when the first sheet is fed. When the second sheet reaches the TA roll 413, the feed motor 407 temporarily stops at time _T806 , after which the sheet is conveyed by the TA roll 413, and the feed roll 406 is conveyed by the conveyance of the sheet by the TA roll 413. In the driven state, the feed motor 407 is driven from time T ₈₀₇ to time T ₈₀₈ at a speed ω ₈₂ that is faster than when processing the first sheet. At this time, if the rotational speed of the feed roll rotary shaft 406A is higher than the rotational speed of the feed motor rotary shaft 407A, almost no drive torque is generated in the feed motor 407.

Further, when feeding the third sheet, the same as the feeding process of the first and second sheets, but the feed motor 407 is driven at the rotational speed ω from time T _{809 to} T ₈₁₀ , 3 The first sheet is fed from the feed roll 406 to the TA roll 413. At this time, a driving torque τ for feeding the third sheet is generated in the feed motor 407. The driving torque at this time is substantially the same as the driving torque τ generated when the first and second sheets are fed. When the third sheet reaches the TA roll 413, the feed motor 407 temporarily stops at time _T810 , after which the sheet is conveyed by the TA roll 413, and the feed roll 406 is conveyed by the sheet conveyance by the TA roll 413. In the driven state, the feed motor 407 is driven from time T ₈₁₁ to time T ₈₁₂ at a speed ω ₈₃ that is faster than when processing the second sheet. At this time, since the rotation speed of the drive shaft 407A of the feed motor is faster than the rotation speed of the rotation shaft 406A of the feed roll 406, a drive torque τ ₃ for feeding paper is generated in the feed motor 407, and the load detection unit 409 Thus, the load is detected, and the diameter of the feed roll 406 is estimated using the rotational speed ω ₈₃ of the feed motor 407 at this time. The driving torque τ ₃ and the driving torque τ when the first to third sheets are fed to the TA roll 413 are approximately the same.

  In the above-described example, the case where the control is performed so that the wear amount estimation mode is executed every preset period or every time a preset amount of print processing is executed has been described. Is not limited to the above example, and the above-described wear amount estimation mode may be executed by the user operating the user interface 30 of the image forming apparatus 10.

  In the above example, the case where the retard roll 410 is provided facing the feed roll 406 and the retard roll 410 rotates following the feed roll 406 when feeding paper is described. However, the present invention is not limited thereto, and the retard roll 410 may be connected to a drive motor that drives the retard roll 410 via a torque limiter, and may be configured to rotate in a direction opposite to the feed roll 406. Further, a retard pad may be employed instead of the retard roll 410.

  Further, the image forming apparatus 10 is usually provided with a plurality of paper trays stacked in the vertical direction. The paper feeding units 40A to 40C described in the above embodiment are provided corresponding to the plurality of paper trays, and the diameter of the feed roll 406 of each of the paper feeding units 40A to 40C is obtained by the above-described method. When notifying the user according to the amount of wear, for example, a message such as “The feed roll in Tray 1 is worn. Make it possible for users to know if they should be replaced.

  In the above-described embodiment, the case where the amount of wear of the feed roll 406 of the paper feed units 40A to 40C is obtained has been described. Further, the present invention can be applied not only to the paper feeding device 40 but also to a document transport roll (not shown) which is one of the components of the automatic document transport device 23 of the document reading device 20.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 20 Document reader 21 Document feed tray 22 Document discharge tray 23 Automatic document feeder 24 Document table 25 Image scanner 30 User interface 40 Paper feed device 40A to 40C Paper feed unit 50 Image output device 51Y to 51K Photosensitive Body 52Y-52K Charging device 53Y-53K Exposure device 54Y-54K Development device 55Y-55K Primary transfer device 56Y-56K Cleaning device 57 Intermediate transfer belt 58 Secondary transfer device 59 Fixing device 60 Paper discharge tray 70 Control unit 401 Paper feed tray 402 Paper Loading Plate 403 Pushing Plate 404 Pushing Motor 405 Pickup Roll 406 Feed Roll 406A Feed Roll Rotating Shaft 407 Feed Motor 407A Feed Motor Drive Shaft 408 One-way Clutch 40 Load detection unit 410 retard roll 411 feed sensor 412 bending guide 413 TA roll 414 TA motor 415 TA sensor 701 control microprocessor 702 memory 703 storage device 704 communication interface 705 control bus 721 paper take-in control unit 722 paper transport control unit 723 Image processing control unit 724 Conveying speed calculation unit 725 Wear state estimation unit 726 Warning notification unit 727 Operation mode setting unit

Claims (13)

A paper feed roll that transports paper,
Drive means connected to the paper feed roll via a one-way clutch;
Detecting means for detecting the presence or absence of a load on the driving means;
A transport roll disposed on the downstream side of the paper feed path in the paper transport direction in the paper transport path;
Calculating means for calculating the conveyance speed of the paper conveyed by the conveyance roll from the rotation speed of the conveyance roll and the diameter of the conveyance roll;
Control means for performing control to increase the rotation speed of the driving means from a rotation speed at which the detection means does not detect a load to a rotation speed at which the load is detected after the conveyance of the paper by the conveyance roll is started;
Estimating means for estimating the diameter of the paper feed roll from the rotational speed of the driving means when the detecting means detects a load and the paper conveyance speed calculated by the calculating means;
A sheet conveying apparatus comprising:   The control means rotates after detecting the load from the rotation speed at which the detection means does not detect the load while one sheet being conveyed passes through the paper feed roll after the conveyance of the sheet by the conveyance roll is started. The paper conveying apparatus according to claim 1, wherein control is performed to increase a rotational speed of the driving unit to a speed.   The control means detects the load from the rotation speed at which the detection means does not detect a load, when the plurality of sheets are conveyed, the rotation speed of the drive means after the conveyance roll starts to convey each sheet. The sheet conveying apparatus according to claim 1, wherein control is performed to increase each time each sheet passes up to a speed.   The detection means determines that a load has occurred on the drive means when the magnitude of torque when the drive means drives the paper feed roll is equal to or greater than a preset value. The sheet conveying apparatus according to any one of 1 to 3.   5. The sheet conveying apparatus according to claim 4, wherein the driving unit is a DC motor, and the detection unit detects a magnitude of torque when the driving unit drives the paper feed roll from a driving current of the driving unit. .   4. The sheet conveying device according to claim 1, wherein the detecting unit determines that a load is generated on the driving unit when the rotation speeds of the driving unit and the paper feed roll are equal. 5. The transport roll is disposed within a distance shorter than the paper length from the position of the paper feed roll on the transport path,
The sheet conveying apparatus according to any one of claims 1 to 6, wherein the sheet being conveyed is pulled out of the sheet feeding roll when conveyance of the sheet by the conveyance roll is started.   The control means performs the normal operation mode in which the drive means is not rotated after the conveyance of the paper by the transport roll is started, and the control means for changing the rotation speed of the drive means, thereby reducing the diameter of the paper feed roll. The sheet conveyance device according to claim 1, further comprising an estimation mode for estimation.   The sheet conveying apparatus according to claim 8, wherein the control unit controls the estimation mode to be executed every preset period or every time a preset amount of printing processing is executed.   The control means performs control to change the rotation speed of the driving means according to the diameter of the paper feed roll estimated by the estimation means when the paper is supplied from the paper feed roll to the transport roll. The paper conveyance device according to claim 1.   11. The sheet conveying apparatus according to claim 1, further comprising a notifying unit that notifies a warning when the diameter of the sheet feeding roll estimated by the estimating unit is smaller than a preset value. .   The sheet conveying device according to any one of claims 1 to 11, wherein the control unit performs control to stop driving of the driving unit when the detecting unit detects a load. A paper feed roll that transports paper,
Drive means connected to the paper feed roll via a one-way clutch;
Detecting means for detecting the presence or absence of a load on the driving means;
A transport roll disposed on the downstream side of the paper feed path in the paper transport direction in the paper transport path;
Calculating means for calculating the conveyance speed of the paper conveyed by the conveyance roll from the rotation speed of the conveyance roll and the diameter of the conveyance roll;
Control means for performing control to increase the rotation speed of the driving means from a rotation speed at which the detection means does not detect a load to a rotation speed at which the load is detected after the conveyance of the paper by the conveyance roll is started;
Estimating means for estimating the diameter of the paper feed roll from the rotational speed of the driving means when the detecting means detects a load and the paper conveyance speed calculated by the calculating means;
A paper transport device comprising:
Image output means for outputting an image on a sheet conveyed by the sheet conveying apparatus;
An image forming apparatus comprising:

Images