JP2019123576A - Sheet feeding device - Google Patents

Abstract

To provide a sheet feeding device and an image forming device, capable of accurately correcting bias feed even when a load exerted on a feed rotating body is changed.SOLUTION: In a sheet feeding device, a control part drives a feeding motor to start feeding a sheet and sets a value (K*R1+α, K*R2+α) obtained by adding an addition value α to a value of a load detected by a load detection part as a threshold value; when the value of the load detected by the load detection part after driving the feeding motor to start feeding the sheet is reduced by a predetermined value or more in terms of an absolute value before reaching the threshold value, a value (K*R2+α) obtained by adding the addition value α to a value of a reduced load is set as the threshold value; the feeding motor is started driving after the value of the load detected by the load detection part reaches the threshold value.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a sheet feeding apparatus for feeding a sheet, which is provided in an image forming apparatus or the like.

  In an image forming apparatus such as a printer, a facsimile, or a multifunction peripheral, the front end of the sheet is abutted against the registration roller pair to form a loop, and when the predetermined loop amount is reached, the registration roller pair is driven to There has been proposed one that corrects the skew of (see Patent Document 1). In this patent document, a detection switch is disposed between the registration roller pair and the conveyance roller in the sheet conveyance path, and the loop amount is detected to determine the timing for driving the registration roller pair.

Japanese Patent Application Publication No. 2003-252485

  By the way, in the case of detecting the loop amount of the sheet by the detection switch, the detection switch must be disposed, which hinders an increase in the number of parts and a cost reduction. Therefore, it is conceivable to detect the change in torque of the drive motor of the roller located on the upstream side of the sheet conveyance path of the registration roller pair as a current value or a voltage value, and replace it with detection of the loop amount. However, for example, when the roller that detects a change in torque is a feeding roller, the conveyance resistance received from the separation roller or the like changes depending on whether one sheet is fed or a plurality of sheets are fed. Sometimes. If the drive load of the feed roller changes in this manner, an appropriate loop amount can not be formed, and there is a possibility that high-accuracy skew correction can not be performed.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a sheet feeding apparatus and an image forming apparatus capable of highly accurate skew correction even if the load generated on the feeding roller changes.

  In this sheet feeding apparatus, a plurality of sheets are fed by a sheet stacking unit that stacks sheets, a feeding rotating body that feeds sheets stacked on the sheet stacking unit, and the feeding rotating body A separating means for separating a plurality of sheets one by one, a conveying rotary body located downstream of the feeding rotary body and the separating means in the sheet conveying direction, and the feeding rotary body; A first drive unit for driving, a control unit for controlling the first drive unit, and a load detection unit for detecting a load generated on the feeding rotary member, the control unit including the first drive unit It is driven to start sheet feeding by the feed roller, and a value obtained by adding an addition value to the load value detected by the load detection means is set as a first threshold, and is detected by the load detection means. Load value is the first threshold value The driving of the first driving means is stopped based on the arrival, and the first driving means is driven to start the feeding of the sheet by the feeding rotating body, and the load of the load detected by the load detecting means When the value reaches the first threshold and the absolute value decreases by a predetermined value or more, a value obtained by adding the addition value to the value of the load after the decrease is set as the second threshold. The driving of the first driving means is stopped based on the fact that the value of the load detected by the load detecting means has reached the second threshold value.

  In this sheet feeding apparatus, a plurality of sheets are fed by a sheet stacking unit that stacks sheets, a feeding rotating body that feeds sheets stacked on the sheet stacking unit, and the feeding rotating body A separating means for separating a plurality of sheets one by one, a conveying rotary body located downstream of the feeding rotary body and the separating means in the sheet conveying direction, and the feeding rotary body; A first drive means for driving, a second drive means for driving the conveyance rotary body, a control means for controlling the first drive means and the second drive means, and a load generated on the feeding rotary body A load detection unit, wherein the control unit drives the first drive unit to start feeding the sheet by the feed rotating member, and adds the value to the load value detected by the load detection unit Set the value obtained by adding as the first threshold Driving of the second driving means is started based on the value of the load detected by the load detecting means reaching the first threshold value, and the first driving means is driven to drive the feeding rotary member. When the sheet feeding is started, and the load value detected by the load detecting means is before reaching the first threshold value and the absolute value is reduced by a predetermined value or more, A value obtained by adding the addition value to a value is set as a second threshold, and driving of the second driving means is started based on the value of the load detected by the load detecting means reaching the second threshold. It is characterized by

  In this sheet feeding apparatus, a plurality of sheets are fed by a sheet stacking unit that stacks sheets, a feeding rotating body that feeds sheets stacked on the sheet stacking unit, and the feeding rotating body A separating means for separating a plurality of sheets one by one, a conveying rotary body located downstream of the feeding rotary body and the separating means in the sheet conveying direction, and the feeding rotary body; A first drive means for driving, a second drive means for driving the conveyance rotary body, a control means for controlling the first drive means and the second drive means, and a load generated on the feeding rotary body A load detection unit, wherein the control unit drives the first drive unit to start feeding the sheet by the feed rotating body, and a state in which one sheet is fed to the separation unit Are detected by the load detection means Driving of the second driving means is started based on the load value reaching the first judgment value, and the first driving means is driven to start feeding of the sheet by the feeding rotary member, In a state in which a plurality of sheets are fed to the separating means, the second load value detected by the load detection means reaches a second decision value which is smaller than the first decision value as an absolute value. 2 Driving of the driving means is started, and the first driving means is driven to start feeding of the sheet by the feeding rotary body, and one sheet is fed to the separating means, and then the separating means And driving the second driving means based on the fact that the value of the load detected by the load detecting means has reached the second determination value in a state in which another sheet is also fed. Do.

  According to the sheet feeding apparatus according to the present invention, the threshold value (determination value) for determining the start of driving of the second driving means or the stopping of driving of the first driving means even if the load generated on the feeding rotating body changes. Can be set appropriately, and formation of an appropriate loop amount for the sheet can be performed, and high-accuracy skew correction can be performed.

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to a first embodiment. FIG. 2 is a view showing a schematic configuration of a manual sheet feeding unit according to the first embodiment. FIG. 2 is a block diagram showing a control unit according to the first embodiment. FIG. 2 is a block diagram showing drive control of a feed motor according to the first embodiment. FIG. 7A is a view showing a state in which a sheet is fed by a feed roller, and FIG. 7B is a view showing a state in which another sheet is fed to a retard roller while the sheet is fed by the feed roller. (A) is a figure which shows the load torque at the time of setting the 1st threshold value which concerns on 1st Embodiment, (b) shows the load torque at the time of setting the 2nd threshold value which concerns on 1st Embodiment. Figure. 6 is a flowchart showing control of sheet feeding processing according to the first embodiment. FIG. 8 is a view showing a schematic configuration of a manual sheet feeding unit according to a second embodiment. FIG. 7 is a block diagram showing a control unit according to a second embodiment. (A) is a figure which shows the load torque at the time of setting the 1st threshold value which concerns on 2nd Embodiment, (b) shows the load torque at the time of setting the 2nd threshold value which concerns on 2nd Embodiment. Figure. 10 is a flowchart showing control of sheet feeding processing according to the second embodiment. (A) is a figure which shows the load torque at the time of setting the 1st threshold value concerning 3rd Embodiment, (b) shows the load torque at the time of setting the 2nd threshold value concerning 3rd Embodiment. Figure. 14 is a flowchart showing control of sheet feeding processing according to a third embodiment.

First Embodiment
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. First, an image forming apparatus provided with the sheet feeding apparatus of the present invention will be described with reference to FIG. FIG. 1 is a view showing a schematic configuration of an image forming apparatus according to the first embodiment.

[Schematic Configuration of Image Forming Apparatus]
In FIG. 1, reference numeral 201 denotes an image forming apparatus, 201A an image forming apparatus main body, and 201B an image forming unit for forming an image on a sheet. An image reading apparatus 202 is installed substantially horizontally above the image forming apparatus main body 201A, and a sheet discharge discharge space S is formed between the image reading apparatus 202 and the image forming apparatus main body 201A. .

  The image forming unit 201B, which is an image forming unit, is a 4-drum full-color type, and has a laser scanner 210 and toner images of four colors of yellow (Y), magenta (M), cyan (C) and black (K). Are provided to form four process cartridges 211. Here, each process cartridge 211 includes a photosensitive drum 212, a charger 213 which is a charging unit, and a developing unit 214 which is a developing unit. The image forming unit 201 </ b> B also includes an intermediate transfer unit 201 </ b> C disposed above the process cartridge 211 and a fixing unit 220. Reference numeral 215 denotes a toner cartridge for supplying toner to the developing device 214.

  The intermediate transfer unit 201C includes an intermediate transfer belt 216 wound around a driving roller 216a and a tension roller 216b. A primary transfer roller 219 is provided on the inner side of the intermediate transfer belt 216 to be in contact with the intermediate transfer belt 216 at a position facing the photosensitive drum 212. Here, the intermediate transfer belt 216 is rotated in the arrow direction by a drive roller 216 a driven by a drive unit (not shown).

  Then, each color toner image having a negative polarity on the photosensitive drum is sequentially multiple-transferred onto the intermediate transfer belt 216 by the primary transfer roller 219. At a position facing the driving roller 216a of the intermediate transfer unit 201C, a secondary transfer roller 217 for transferring the color image formed on the intermediate transfer belt to the sheet P is provided. Further, the fixing unit 220 is disposed above the secondary transfer roller 217, and the first discharge roller pair 225a, the second discharge roller pair 225b, and the duplex reversing unit 201D are disposed at the upper left portion of the fixing unit 220. . The double-sided reversing unit 201D is provided with a reversing roller pair 222 capable of rotating in the forward and reverse directions and a re-conveying passage R for transporting the sheet having an image formed on one side to the image forming unit 201B again.

  A sheet feeding unit 230 for feeding the set sheet to the image forming unit is provided at the lower part of the image forming apparatus main body 201A. On the right side of the image forming apparatus main body 201A, there is provided a manual sheet feeding unit 300 as a sheet feeding device for feeding the set sheet to the image forming means.

  The sheet feeding unit 230 includes a feeding cassette 1 for storing sheets, and a pickup roller 8 for feeding sheets stored in the feeding cassette 1. Further, the sheet feeding unit 230 is provided with a separating unit including a feed roller 9 and a retard roller 10 for separating the sheet P fed from the pickup roller 8. Further, the sheet feeding unit 230 is provided with a drawing roller pair 11 provided downstream of the separating means. The manual sheet feeding unit 300 will be described later in detail.

  Next, the image forming operation of the image forming apparatus 201 will be described. First, when image information of a document is read by the image reading device 202, the image information is subjected to image processing, converted into an electric signal, and transmitted to the laser scanner 210 of the image forming unit 201B. In the image forming unit 201B, the surface of the photosensitive drum 212 whose surface is uniformly charged to a predetermined polarity and potential by the charger 213 is sequentially exposed by the laser light. Thereby, yellow, magenta, cyan and black electrostatic latent images are sequentially formed on the photosensitive drums of the process cartridges 211, respectively.

  Thereafter, the electrostatic latent image is developed with each color toner to be visualized, and each color toner image on each photosensitive drum is sequentially superimposed on the intermediate transfer belt 216 by the primary transfer bias applied to the primary transfer roller 219. Transfer together. Thus, a toner image is formed on the intermediate transfer belt 216.

  On the other hand, the sheet P fed by the feed roller 9 of the sheet feeding unit 230 or the feed roller 17 of the manual feeding unit 300 is a registration roller pair (hereinafter referred to as a registration roller pair) 240 consisting of a driving roller and a driven roller. Transported to At this time, the driving of the registration roller pair 240 is stopped, and the leading end of the sheet P is abutted against the registration roller pair 240. As a result, the leading end of the sheet P is made to follow the registration roller pair 240. Thereafter, the conveyance of the sheet P is continued by the feed roller 9 or the feed roller 17, so that a bend (loop) is formed on the sheet P, and the resist roller pair 240 is driven when the predetermined loop amount is reached. Thus, the skew feed of the sheet P is corrected by the registration roller pair 240, and the sheet P with the skew feed corrected is conveyed to the secondary transfer portion by the registration roller pair 240. Subsequently, in the secondary transfer portion, the toner images are collectively transferred onto the sheet P by the secondary transfer bias applied to the secondary transfer roller 217. Then, the sheet P to which the toner image has been transferred is conveyed to the fixing unit 220, and heat and pressure are applied to the fixing unit 220 so that the toners of the respective colors are melted and mixed, and the sheet P is fixed as a color image.

  Thereafter, the sheet P on which the image is fixed is discharged to the discharge space S by the first discharge roller pair 225a and the second discharge roller pair 225b provided downstream of the fixing unit 220, and is projected to the bottom of the discharge space S. The loading unit 223 is loaded. When forming an image on both sides of the sheet P, after the image is fixed, the sheet P is conveyed to the re-conveying path R by the reversing roller pair 222, and is again conveyed to the image forming unit 201B.

[Configuration of manual feeding unit]
Subsequently, the configuration of the manual feeding unit 300 will be described. FIG. 2 is a view for explaining the configuration of the manual sheet feeding unit 300 according to the first embodiment. The manual feeding unit 300 includes a tray 13 which is a sheet stacking unit capable of stacking sheets and capable of opening and closing, and a pickup roller 16 for picking up the uppermost sheet P of the sheets stacked on the tray. Further, the manual feeding unit 300 is provided with a feed roller 17 as a feeding roller which is a feeding rotating body for feeding the sheet P fed from the pickup roller 16. Further, the manual feeding unit 300 is provided with a retard roller 18 as a separation roller which is a separation unit that is in pressure contact with the feed roller 17 and separates the sheet from the feed roller 17. The manual feeding unit 300 is provided with a registration roller pair 240 which is located downstream of the feed roller 17 in the sheet conveying direction and conveys the sheet to the image forming unit 201B and is also a skew correction unit. There is.

  A plurality of sheets P can be stacked on the tray 13, and the sheets P are fed out by the pickup roller 16. When a plurality of sheets are fed out, they are separated one by one by a nip 19 consisting of a feed roller 17 and a retard roller 18 and conveyed to a pair of registration rollers 240 downstream. That is, the feed roller 17 and the retard roller 18 are in contact with each other by a spring (not shown), and a torque limiter (not shown) is provided coaxially on the retard roller 18 so that it spins when a predetermined load or more is applied. ing. Thereby, when a plurality of sheets are conveyed to the nip 19, the sheets are separated and conveyed one by one. The pickup roller 16 and the feed roller 17 are driven by a feed motor M1 (see FIG. 3) which is a first drive unit, and the drive roller of the registration roller pair 240 is a registration motor M2 (see FIG. 3) which is a second drive unit. Driven by

[Configuration of control unit]
Next, the configuration of the control unit 260 of the image forming apparatus 201 will be described. FIG. 3 is a block diagram showing a control unit according to the first embodiment. As shown in FIG. 3, the control unit 260 is configured to include a CPU 261, a RAM 262, a ROM 263, an HDD 264, and the like. Further, the control unit 260 is connected to a motor control unit 157 which is a driver of the stepping motor, and the motor control unit 157 is connected to a feed motor M1, a registration motor M2, and the like. The CPU 261 of the control unit 260 loads the program stored in the ROM 263 or the HDD 264 into the RAM 261 and executes the program to function as the position command generation unit 500 and the load detection unit 509. Drive control of M2. Instead of the HDD 104, a non-volatile memory may be provided in which data is not erased even when the power is turned off, and the data may be stored in the non-volatile memory.

[Feed motor drive control and load detection]
Next, methods of vector control and load detection which are drive control of the feed motor M1 will be described. FIG. 4 is a block diagram showing drive control of the feeding motor according to the first embodiment.

  The feed motor M1, which is a stepping motor, is driven and controlled by vector control by a drive control unit 516 of a stepping motor that functions in a motor control unit 157 according to a position command from a position command generation unit 500 of a control unit 260. The position command generation unit 500 generates a position command accompanying a time change with respect to the target position command. Position command generation unit 500 may have not only control unit 260 but also a function of motor control unit 157.

  Vector control is a method of controlling the phase and amplitude of the current so as to generate maximum torque in a rotational coordinate system in which the magnetic flux direction component is defined as d axis and the direction orthogonal to this as q axis. The basic configuration is a configuration of inverter control using coordinate conversion used in a brushless DC motor, an AC servomotor or the like. Specifically, a rotating coordinate system in which a stationary coordinate system representing a normal current vector flowing in the A phase and B phase of the stepping motor is defined as a rotor magnetic pole direction d axis and a direction 90 ° further as q axis Converted to This inverter control is roughly divided into three control loops of current control, speed control and position control.

  In the drive control unit 516 of the stepping motor, the position controller 501 sets the speed command ω_ref so that the deviation between the detected position θ of the output shaft of the stepping motor and the position command θ_ref from the position command generation unit 500 is reduced. Output The speed controller 502 outputs the current command iq_ref so that the deviation between the detected rotation speed of the stepping motor and the speed command ω_ref becomes small. Here, the current command iq_ref is a current command value after being converted from the αβ axis to the dq axis.

Current flowing to the stepping motor in the stationary coordinate system is ia = I × cos θ
ib = I × sin θ (1)
θ: the angle between the α axis of the stationary coordinate system and the composite vector of the phase currents ia / ib, the current value in the rotational coordinate system is
iq = cos θ × ia + sin θ × ib
id = −sin θ × ia + cos θ × ib (2)
It is expressed as By this conversion, the alternating current ia and the alternating current ib flowing to the A phase and the B phase become the direct current iq and the direct current id in the rotational coordinate system. Here, the d-axis current is a component capable of controlling the amount of magnetic flux and does not contribute to torque. On the other hand, the q-axis current is a component that governs the generated torque of the stepping motor.

  The current flowing in each phase of the motor is detected by the current detection unit 507 and the current detection unit 508, and the analog value is converted to a digital value by the A / D converter 510 so that it can be taken into a programming device such as a CPU or FPGA. It will be Then, the dq conversion of the equation (2) is performed in the coordinate conversion unit 511, and the q-axis current iq and the d-axis current id are obtained. A deviation between the obtained q-axis current and d-axis current, and the current command value iq_ref and the current command value id_ref output from the speed controller 502 is input to the current controller 503 and the current controller 504. In normal vector control, the d-axis current is controlled such that an id component that does not contribute to torque is zero. The current controller 503 and the current controller 504 constitute a proportional-integral compensator similarly to the speed controller 502, and after amplifying the amount of current deviation, the coordinate converter 505 calculates the q-axis current iq and the d-axis current id. Inverse transformation is performed to the current value iα and the current value iβ of the stationary coordinate system.

Also, the inverse transformation is calculated by the following equation.
iα = cos θ × iq−sin θ × id
iβ = sin θ × iq + cos θ × id (3)

  The converted current value iα and current value iβ are output as the drive voltage vα and the drive voltage vβ, and when these signals are input to the PWM inverter 506, the full bridge circuit for driving each phase winding is driven. The desired amount of current is controlled to flow in the winding.

  As described above, in the vector control, in order to perform position control and speed control, it is necessary to feed back position information and speed information of the stepping motor to the controller. Usually, in order to detect such information, a rotary encoder is attached to a stepping motor, position information is obtained based on the number of output pulses, and speed information is obtained based on an output pulse period. However, the addition of a rotary encoder, which is essentially unnecessary for driving the stepping motor, has the problem of increasing the cost and expanding the arrangement space. Therefore, sensorless control has been proposed which estimates position information and speed information of a stepping motor without using an encoder.

Here, the sensorless control will be described. First, the current value iα and the current value iβ converted to digital values by the A / D converter 510 and the drive voltage vα and the drive voltage vβ of the stepping motor are input to the induced voltage calculation unit 512. The induced voltage computing unit 512 computes the induced voltage Eα and the induced voltage Eβ of the stepping motor based on the following voltage equation using the input current and voltage value.
Eα = Vα-R × iα-L × diα / dt
Eβ = Vβ-R × iβ-L × diβ / dt (4)
R: Winding resistance, L: Winding reactance

The values of the winding resistance R and the winding reactance L are stored in advance in the ROM or the like. The calculated induced voltage Eα and the induced voltage Eβ are input to the position calculation unit 513. The position calculation unit 513 calculates the position θ of the stepping motor by the following equation.
θ = ATAN (−Eβ / Eα) (5)

The calculated position θ of the stepping motor is fed back to the position controller 501 as described above. At the same time, the calculated position θ of the stepping motor is also input to the speed calculator 514. The speed calculator 514 calculates the rotational speed ω of the stepping motor based on the following equation.
ω = dθ / dt (6)
The calculated ω is fed back to the speed controller 502 as described above.

  The load detection unit 509 of the CPU 261 can calculate the q-axis current that governs the generated torque of the stepping motor from the current value iα and the current value iβ obtained from the current detection unit 507 and the current detection unit 508 by the above method. The load can be detected. That is, in the present embodiment, the load detection unit is configured by the current detection unit 507 and the current detection unit 508 as the current detection unit, and the load detection unit 509.

[Payment state and load torque pattern]
Next, the feeding state during sheet feeding and the load of the feeding motor M1 in the feeding state will be described. FIG. 5A is a view showing a state in which the sheet is fed by the feed roller, and FIG. 5B is a state in which another sheet is fed to the retard roller while the sheet is fed by the feed roller. FIG. Further, FIG. 6A is a view showing a load torque when setting the first threshold, and FIG. 6B is a view showing a load torque when setting the second threshold.

As shown in FIG. 5A, this occurs when feeding (one-sheet conveying state) is performed in a state in which only one sheet is nipped by the nip 19 formed by the feed roller 17 and the retard roller 18. The carrying load (carrying resistance) being carried out is expressed by the following equation.
R1 = μp · Na + Ft + Fg
R1: transport load in the sheet transport state μp: coefficient of friction between sheets Na: contact force of pickup roller 16 against sheet Ft: blocking force generated by torque limiter Fg: resistance generated by friction between guide and sheet

On the other hand, as shown in FIG. 5B, the conveyance load in the state in which a plurality of sheets are held in the nip 19 (separation conveyance state) is expressed by the following equation.
R2 = μp · Na + μp · Nb + Fg
R2: Transport load in the separated transport state Nb: Contact force between feed roller 17 and retard roller 18

Also, when the separation operation is working, the following equation holds.
Ft> μp · Nb
Therefore, the following equation holds.
R1> R2
That is, it can be understood that the conveyance load is lower when a plurality of sheets are conveyed and the retard roller 18 separates the sheets, as compared to the case where the pickup roller 16 conveys only one sheet.

  Here, the load torque applied to the feed motor M1 is obtained by multiplying the transport load by a constant K determined by the gear train from the feed roller 17 to the feed motor M1, the diameter of the roller, and the like. From the above relationship, the relationship of torque from the start of pick-up to the skew correction by the registration roller pair 240 is classified into the following three patterns shown in FIGS. 6 (a) and 6 (b).

Pattern 1: A state in which only one sheet is fed to the nip 19 (see the solid line in FIG. 6A and the solid line in FIG. 6B)
In pattern 1, only one sheet is fed to the nip 19, in other words, only one sheet is fed by the pickup roller 16.

  As shown in FIG. 6A, when sheet feeding is started at time t0, the conveyance load increases. Thereafter, the sheet is conveyed to the registration roller pair 240 while the resistance Fg gradually increases due to the friction between the guide and the sheet. The load torque applied to the feed motor M1 at time t1 at an arbitrary timing before the sheet is abutted against the registration roller pair 240 is K · R1. Thereafter, when the sheet reaches the pair of registration rollers 240 at time t2 and a loop is formed on the sheet, the load torque increases, and when driving of the registration motor M2 is started at time t3, the load of the feed motor M1 The torque is decreasing.

Pattern 2: A plurality of sheets are fed to the nip 19 (see the broken line in FIG. 6A)
The pattern 2 is a state in which a plurality of sheets are fed to the nip 19, in other words, a state in which a plurality of sheets are fed in the nip 19. A plurality of sheets are in the state of.

  As shown in FIG. 6A, when sheet feeding is started at time t0, the conveyance load increases. Thereafter, the sheet is conveyed to the registration roller pair 240 while the resistance Fg gradually increases due to the friction between the guide and the sheet. The inclination changes in the middle because the sheet comes in contact with the guide of the bending path and the conveyance resistance increases. The load torque applied to the feed motor M1 at time t1 at an arbitrary timing before the sheet is abutted against the registration roller pair 240 is K · R2. That is, when a plurality of sheets are already in the nip 19 at the stage of time point t1, the load torque of the feeding motor M1 becomes smaller than the load torque at the time of single sheet conveyance as described above, K · R1> K · R2 Relationship. Thereafter, when the sheet reaches the pair of registration rollers 240 at time t2 and a loop is formed on the sheet, the load torque increases, and when driving of the registration motor M2 is started at time t3, the load of the feed motor M1 The torque is decreasing.

Pattern 3: A state in which a plurality of sheets are fed to the nip 19 halfway (see the broken line in FIG. 6B)
The pattern 3 is a state in which a plurality of sheets are fed to the nip 19 halfway. In other words, initially, only one sheet is picked up by the pickup roller 16 and only one sheet is fed to the nip 19, but the subsequent sheet reaches the nip 19 before the sheet reaches the registration roller pair 240. It is in the state of entering.

  As shown in FIG. 6B, when sheet feeding is started at time t0, the conveyance load increases. Thereafter, the sheet is conveyed to the registration roller pair 240 while the resistance Fg gradually increases due to the friction between the guide and the sheet. The load torque applied to the feed motor M1 at time t1 at an arbitrary timing before the sheet is abutted against the registration roller pair 240 is K · R1. Subsequently, when the subsequent sheet reaches the nip 19 at time t4 before the sheet front end reaches the registration roller pair 240, the load torque is a difference value of load torque ΔT which is a difference between K · R1 and K · R2. The minutes drop. That is, if there is only one sheet in the nip 19, the load Ft by the torque limiter of the retard roller 18 is generated on the feed roller 17 through the sheet. When the subsequent sheet reaches the nip 19, the frictional force between the first sheet and the subsequent sheet corresponds to the load μp · Nb described above. Therefore, the load torque decreases as the load torque fluctuation value ΔT. Thereafter, when the sheet reaches the pair of registration rollers 240 at time t2 and a loop is formed on the sheet, the load torque increases, and when driving of the registration motor M2 is started at time t3, the load of the feed motor M1 The torque is decreasing.

As described above, since there are three patterns 1 to 3 when feeding a sheet, even if it is attempted to control the drive timing of the registration motor M2 with, for example, a fixed threshold value corresponding to the paper type, it does not work well. Therefore, it is necessary to detect the arrival of the subsequent sheet on the registration roller pair 240 from the load torque. The fluctuation value ΔT of the load torque is K · (Ft−μp · Nb), and when the fluctuation value ΔT of the load torque decreases by the state judgment value C or more for determining the state of the nip, the resist roller pair 240 is It is possible to detect the arrival of subsequent sheets of The state determination value C is a value corresponding to the difference between the values of the load generated on the feeding motor M1 between the one-sheet conveyance state and the separation conveyance state. However, the difference needs to be smaller than the difference in torque (load) between the one-sheet conveyance state and the separated conveyance state, and this can be expressed by the following equation.
C <K · (Ft−μp · Nb)

[Sheet feeding process]
Next, control of sheet feeding processing including skew feeding correction processing using the detection of load torque of the feeding motor M1 according to the first embodiment will be described. FIG. 7 is a flowchart showing control of sheet feeding processing according to the first embodiment.

  When an instruction for a sheet feeding job by manual feeding unit 300 is input based on, for example, an operation of a print start button (not shown) or an input of a print job from a computer connected externally, control unit 260 The feeding process is started (S1). Then, first, driving of the feed motor M1 is started to start sheet feeding, counting of the predetermined time T1 is started (S2), and the process waits until the predetermined time T1 elapses (No in S3). The predetermined time T1 is appropriately set so as to be the timing before the sheet conveyed by the feed roller 17 contacts the registration roller pair 240. When predetermined time T1 passes and time t1 is reached (Yes in S3), a value obtained by adding the addition value α to the load torque of the feeding motor M1 is set as a threshold (K · R1 + α or K · R2) (first threshold) To do (S4). The addition value α is a value corresponding to the paper type, and the amount of bending (loop amount) when the sheet is bent between the feed roller 17 and the pair of registration rollers 240 is a predetermined amount, that is, according to the paper type Is a value that can form a loop of an appropriate size. In other words, the addition value α is a value corresponding to the load generated on the feed roller 17 when the amount of bending when the sheet is flexed between the feed roller 17 and the registration roller pair 240 becomes a predetermined amount. . Further, the first threshold value is “K · R1 + α” which is the first determination value in the pattern 1 (a state in which only one sheet is fed to the nip 19), and the pattern 2 (a plurality of sheets in the nip 19). In the state in which the sheet is fed), the second judgment value "K · R2 + α" is obtained.

  On the other hand, the load detection unit 509 of the control unit 260 continuously executes the detection of the load torque of the feeding motor M1 at any predetermined sampling interval, and stores the value of the load torque for a predetermined period in the RAM 262. The load torque value stored in the RAM 262 deletes the oldest value each time a new value is stored. Then, the fluctuation value ΔT of the minimum value and the maximum value of the load torque for the predetermined period is calculated. At any time, it is determined whether or not the fluctuation value ΔT has decreased by more than the state determination value C of the nip 19 (more than a predetermined value) (S5), and it is determined at any time from its threshold value. S7). If the load torque fluctuation value ΔT does not decrease by more than the condition judgment value C of the nip 19 (No in S5) and the load torque becomes more than the above threshold (Yes in S7), a loop with a suitable size for the sheet It is determined that the sheet has been formed, and the feed motor M1 is stopped (S8). As a result, the pickup roller 16 and the feed roller 17 are stopped, and furthermore, the pair of registration rollers 240 is also stopped, so the conveyance of the sheet is stopped while a loop of an appropriate size is formed on the sheet.

  On the other hand, in step S5, as shown at time t4, after setting the threshold value at time t1, if the variation value ΔT of the load torque decreases by the state determination value C or more of the nip 19 (Yes in S5) It is determined that the sheet has been fed. Then, the threshold value is overwritten on a value (K · R2 + α) (second threshold value) obtained by adding the predetermined value α to the minimum value among the load torques for the predetermined period (S6). That is, the threshold is reset (S6). Since the second threshold value set at this time is the pattern 3 (a state in which a plurality of sheets are fed to the nip 19 halfway), the second threshold value is “K · R2 + α” which is a second determination value. It is not necessary to add the predetermined value α at the time of resetting the threshold, and a value different from the predetermined value α may be added according to the paper type.

  Thereafter, similarly, when the load torque becomes equal to or more than the threshold value (Yes in S7), it is determined that a loop of an appropriate size is formed on the sheet, and the feed motor M1 is stopped (S8). As a result, the pickup roller 16 and the feed roller 17 are stopped, and furthermore, the pair of registration rollers 240 is also stopped, so the conveyance of the sheet is stopped while a loop of an appropriate size is formed on the sheet.

  In step S8, when the conveyance of the sheet is stopped, the control unit 260 determines whether it is the image formation start timing (S9). The image formation start timing is the timing at which the image formation on the sheet is started, and the timing at which the secondary transfer roller 217 starts to convey the sheet. Specifically, the image formation start timing is a predetermined time after the image forming unit 200B receives the image formation start signal and starts the formation of the toner image on the intermediate transfer belt 216. That is, with the feed motor M1 stopped and sheet conveyance stopped, the image formation start timing is awaited (No in S9), and when the image formation start timing comes (Yes in S9), the feed motor M1 and the registration motor The drive of M2 is started (S10). As a result, the pickup roller 16, the feed roller 17, and the registration roller pair 240 are driven, and conveyance of the sheet is started. That is, the secondary transfer roller 217 of the image forming unit 201 B is aligned with the timing when the toner image on the intermediate transfer belt 216 reaches the secondary transfer roller 217 in the state in which the skew feeding is corrected by the registration roller pair 240. Transported to

  As described above, when the conveyance of one sheet to the secondary transfer roller 217 is completed, it is determined whether the sheet feeding job is completed (S11). Here, if the feeding job is not completed (No in S11), the count of the predetermined time T1 is reset (S12), and the process returns to step S2 again to start feeding the next sheet. On the other hand, when the feeding job is completed (Yes in S11), the above sheet feeding process is completed (S13).

  In the present embodiment, although a description is given of one in which conveyance of the sheet is temporarily stopped when a loop having an appropriate size is formed in the sheet, the present invention is not limited to this. For example, in an image forming apparatus in which a monochrome photosensitive drum is directly transferred to a sheet, there are some which can match the timing of forming a toner image with the conveyance of the sheet. In this case, when a loop of an appropriate size is formed on the sheet, that is, based on the fact that the load torque of the feed motor M1 has become equal to or greater than the threshold (Yes in S7), drive of the registration motor M2 is started (S10). ), That is, conveyance of the sheet can be continued. Further, even in the full-color image forming apparatus as in the present embodiment, it is conceivable to adjust the conveyance speed by the registration roller pair 240 without temporarily stopping the conveyance of the sheet. Also in this case, driving of the registration motor M2 is started based on the fact that the load torque of the feeding motor M1 has become equal to or higher than the threshold (Yes in S7) (S10), and at the timing when the toner image reaches the secondary transfer roller 217. The sheet may be conveyed so as to reach it.

  Further, although it is desirable to set the predetermined time T1 described above to be immediately before the leading edge of the sheet reaches the pair of registration rollers 240, in practice the variation of the transport speed of the feed roller 17 or the sheet at the start of feeding There is a variation in position. Therefore, it is difficult to set just before the leading edge of the sheet reaches the registration roller pair 240, but in consideration of these variations, set the threshold at the position where the leading edge of the sheet is close to the registration roller pair 240 Is preferred.

  As described above, according to the manual feeding unit 300 according to the first embodiment, the threshold value (determination value) for determining the start of the driving of the registration motor M2 is appropriately determined even if the load generated on the feed roller 17 changes. It can be set. As a result, it is possible to form an appropriate amount of loop on the sheet, and skew correction can be performed with high accuracy.

Second Embodiment
Next, a second embodiment in which the first embodiment is partially modified will be described. In the above-described first embodiment, the description has been made of the case where the feeding correction is performed by forming a loop between the feed roller 17 and the retard roller 18 and the registration roller pair 240. In the second embodiment, a drawing roller pair 20 (see FIG. 8) is provided between the feed roller 17 and the retard roller 18 and the registration roller pair 240. Then, a loop is formed between the feed roller 17 and the drawing roller pair 20 to perform skew correction, and further, by performing the skew correction between the drawing roller pair 20 and the registration roller pair 240, higher accuracy can be achieved. The skew correction is performed.

  Generally, the pressing force of the spring for pressing the retard roller 18 against the feed roller 17 can not be set high for separation, so the sheet tends to slip, but the drawing roller pair 20 has a high pressing force for the spring to press. Since it can be set, it is difficult for the sheet to slip. Therefore, in the second embodiment, the registration sensor 21 (see FIG. 8) for detecting the front end of the sheet such as an optical sensor is provided between the drawing roller pair 20 and the registration roller pair 240 to detect the loop amount. Even in this configuration, the amount of conveyance from when the leading end of the sheet passes to when forming a loop of an appropriate size is not easily deviated, so that highly accurate skew correction can be performed.

  In the second embodiment, the guide portions 22 and 23 (see FIG. 8) from the feed roller 17 to the drawing roller pair 20 are disposed so as not to intersect in the direction of the tangent L19 of the nip 19, that is, a sheet The sheet conveying path in which the sheet is conveyed is not curved. Thus, the guide resistance force Fg due to the contact between the sheet and the guide portion can be made constant, so that the detection accuracy of the load torque of the feed motor M1 is improved.

[Configuration of manual feeding unit]
First, the configuration of the manual feeding unit 300 according to the second embodiment will be described. FIG. 8 is a view showing a schematic configuration of a manual sheet feeding unit according to the second embodiment. As shown in FIG. 8, in addition to the manual feeding unit 300 according to the first embodiment, the manual feeding unit 300 according to the second embodiment includes the feed roller 17, the retard roller 18, and the registration roller pair 240. And a drawing roller pair 20 is disposed therebetween. That is, the drawing roller pair 20 is positioned downstream of the feed roller 17 in the sheet conveying direction, and the registration roller pair 240 is positioned downstream of the drawing roller pair 20 in the sheet conveying direction. Further, guides 22 and 23 are disposed between the feed roller 17 and the retard roller 18 and the drawing roller pair 20, and constitute a sheet conveyance path for conveying the sheet. The tangent L19 at the nip 19 between the feed roller 17 and the retard roller 18 is configured not to overlap the guide portions 22 and 23 but to overlap the drawing roller pair 20. Further, a registration sensor 21 for detecting the front end of the sheet such as an optical sensor is disposed between the drawing roller pair 20 and the registration roller pair 240. The other configuration is the same as that of the first embodiment.

  The sheets P stacked on the tray 13 are fed out by the pickup roller 16 and separated one by one by a separation unit including the feed roller 17 and the retard roller 18. The separated sheet P is conveyed in the direction of the tangent L19 of the nip 19, passes between the guide portions 22 and 23, and is delivered to the drawing roller pair 20. Further, the sheet P conveyed by the drawing roller pair 20 is conveyed to the registration roller pair 240. The pickup roller 16 and the feed roller 17 are driven by a feed motor M1 (see FIG. 9). The driving roller of the drawing roller pair 20 is driven by the drawing motor M3 (see FIG. 9), and the driving roller of the registration roller pair 240 is driven by the registration motor M2 (see FIG. 9).

[Configuration of control unit]
Next, the configuration of the control unit 260 according to the second embodiment will be described. FIG. 9 is a block diagram showing a control unit according to the second embodiment. As compared with the first embodiment, the registration sensor 21 is electrically connected to the control unit 260 according to the second embodiment, and the drawing motor M3 is connected to the motor control unit 157. There is. The other configuration is the same as that of the first embodiment, and in particular, the feed motor M1 is driven and controlled by vector control as in the first embodiment.

[Payment state and load torque pattern]
Pattern 1: A state in which only one sheet is fed to the nip 19 (see the solid line in FIG. 10A and the solid line in FIG. 10B)
As shown in FIG. 10A, when sheet feeding is started at time t0, the conveyance load increases. Thereafter, the sheet is conveyed to the pair of drawing rollers 20 in a state in which the guide portions 22 and 23 do not disturb the sheet conveyance direction and the resistance Fg due to the friction between the guide portions 22 and 23 and the sheet becomes constant. To go. Although the inclination is not changed halfway as compared with FIG. 6, the conveyance path is straight, so that the sheet does not increase the conveyance resistance by coming into contact with the guide portion. The load torque applied to the feed motor M1 at time t1 at an arbitrary timing before the sheet is abutted against the drawing roller pair 20 is K · R1. Thereafter, when the sheet reaches the drawing roller pair 20 at time t2 and a loop is formed on the sheet, the load torque increases, and when driving of the drawing motor M3 is started at time t3, the feed motor M1 is Load torque is decreasing.

Pattern 2: A plurality of sheets are fed to the nip 19 (see the broken line in FIG. 10A)
As shown in FIG. 10A, when sheet feeding is started at time t0, the conveyance load increases. Thereafter, the sheet is conveyed to the pair of drawing rollers 20 in a state in which the guide portions 22 and 23 do not disturb the sheet conveyance direction and the resistance Fg due to the friction between the guide portions 22 and 23 and the sheet becomes constant. To go. The load torque applied to the feed motor M1 at time t1 at an arbitrary timing before the sheet is abutted against the drawing roller pair 20 is K · R2. Thereafter, when the sheet reaches the drawing roller pair 20 at time t2 and a loop is formed on the sheet, the load torque increases, and when driving of the drawing motor M3 is started at time t3, the feed motor M1 is Load torque is decreasing.

Pattern 3: A state in which a plurality of sheets are fed to the nip 19 halfway (see the broken line in FIG. 10B)
As shown in FIG. 10B, when sheet feeding is started at time t0, the conveyance load increases. Thereafter, the sheet is conveyed to the pair of registration rollers 240 in a state in which the guide portions 22 and 23 do not disturb the sheet conveyance direction and the resistance Fg due to the friction between the guide portions 22 and 23 and the sheet becomes constant. To go. The load torque applied to the feed motor M1 at time t1 at an arbitrary timing before the sheet is abutted against the drawing roller pair 20 is K · R1. Subsequently, when the subsequent sheet reaches the nip 19 at time t4 before the sheet leading edge reaches the drawing roller pair 20, the load torque is a difference between load values of load torque ΔT, which is a difference between K · R1 and K · R2. The minutes drop. Thereafter, when the sheet reaches the drawing roller pair 20 at time t2 and a loop is formed on the sheet, the load torque increases, and when driving of the drawing motor M3 is started at time t3, the feed motor M1 is Load torque is decreasing.

[Sheet feeding process]
Next, control of sheet feeding processing including skew feeding correction processing using detection of load torque of the feeding motor M1 according to the second embodiment will be described. FIG. 11 is a flowchart showing control of sheet feeding processing according to the second embodiment.

  As in the first embodiment, when an instruction for a sheet feeding job by the manual feeding unit 300 is received, the control unit 260 starts sheet feeding processing (S1). Then, first, driving of the feed motor M1 is started to start sheet feeding, counting of the predetermined time T1 is started (S2), and the process waits until the predetermined time T1 elapses (No in S3). The predetermined time T1 is appropriately set so as to be the timing before the sheet conveyed by the feed roller 17 contacts the drawing roller pair 20. When predetermined time T1 passes and time t1 is reached (Yes in S3), a value obtained by adding the addition value α to the load torque of the feeding motor M1 is set as a threshold (K · R1 + α or K · R2) (first threshold) To do (S4). The addition value α is a value that can form a loop of an appropriate size according to the paper type. Further, the first threshold value is “K · R1 + α” which is the first determination value in the pattern 1 (a state in which only one sheet is fed to the nip 19), and the pattern 2 (a plurality of sheets in the nip 19). In the state in which the sheet is fed), the second judgment value "K · R2 + α" is obtained.

  On the other hand, the load detection unit 509 of the control unit 260 continues to detect the load torque of the feed motor M1 as needed. Then, it is determined at any time whether or not the fluctuation value ΔT of the load torque has decreased by the state determination value C of the nip 19 or more (S5), and it is also determined at any time whether the load torque is equal to or more than the threshold value S7). If the load torque fluctuation value ΔT does not decrease by more than the condition judgment value C of the nip 19 (No in S5) and the load torque becomes more than the above threshold (Yes in S7), a loop with a suitable size for the sheet It is determined that it has been formed, and the drive of the drawing motor M3 is started (S28). As a result, the sheet in a state in which the skew feeding is corrected in the drawing roller pair 20 is started to be conveyed toward the registration roller pair 240.

  On the other hand, in step S5, as shown at time t4, after setting the threshold value at time t1, if the variation value ΔT of the load torque decreases by the state determination value C or more of the nip 19 (Yes in S5) It is determined that the sheet has been fed. Then, the threshold value is overwritten on the value (K · R2 + α) (second threshold value) obtained by adding the predetermined value α to the load torque of the current feed motor M1, that is, the threshold value is reset (S6). After that, similarly, when the load torque becomes equal to or more than the threshold value (Yes in S7), it is determined that a loop having an appropriate size is formed on the sheet, and the drive of the drawing motor M3 is started (S28). As a result, the sheet in a state in which the skew feeding is corrected in the drawing roller pair 20 is started to be conveyed toward the registration roller pair 240.

  Subsequently, it is determined whether or not the front end of the sheet is detected by the registration sensor 21 (S29), and the process waits until the front end of the sheet is detected (No in S29), and the front end of the sheet has reached (registration sensor ON) Is detected (Yes in S29), the process proceeds to step S30. When the leading edge of the sheet reaches the registration sensor 21, it is determined whether or not a predetermined time has elapsed (S30), the process waits until the predetermined time passes (No in S30), and when the predetermined time passes (Yes in S30), The drawing motor M3 is stopped (S31). As a result, since the drawing roller pair 20 is stopped and the registration roller pair 240 is also stopped, the conveyance of the sheet is stopped while a loop of an appropriate size is formed on the sheet.

  In step S31, when sheet conveyance is stopped, it is determined whether it is the image formation start timing (S32), and the process waits until the image formation start timing (No in S32). Then, at the image formation start timing (Yes in S32), driving of the drawing motor M3 and registration motor M2 is started (S33). As a result, the drawing roller pair 20 and the registration roller pair 240 are driven to start sheet conveyance. That is, the secondary transfer roller 217 of the image forming unit 201 B is aligned with the timing when the toner image on the intermediate transfer belt 216 reaches the secondary transfer roller 217 in the state in which the skew feeding is corrected by the registration roller pair 240. Transported to

  As described above, when the conveyance of one sheet to the secondary transfer roller 217 is completed, it is determined whether the sheet feeding job is completed (S11). Here, if the feeding job is not completed (No in S11), the count of the predetermined time T1 is reset (S12), and the process returns to step S2 again to start feeding the next sheet. On the other hand, when the feeding job is completed (Yes in S11), the above sheet feeding process is completed (S13).

  In the same manner, in the present embodiment, although a description has been given of one in which sheet conveyance is temporarily stopped when a loop of an appropriate size is formed in the sheet, the present invention is not limited to this. As described above, when it is possible to match the timing of forming the toner image to the conveyance of the sheet, the registration motor M2 is based on the passage of a predetermined time (Yes in S30) after the registration sensor 21 is turned on (Yes in S29). Drive (S33) can be started. Similarly, the conveyance speed by the registration roller pair 240 may be adjusted without temporarily stopping conveyance of the sheet. Also in this case, driving of the registration motor M2 is started based on the passage of the predetermined time (Yes in S30) (S33), and the sheet is conveyed so that the sheet reaches the timing when the toner image reaches the secondary transfer roller 217. Just do it.

  As described above, according to the manual feeding unit 300 according to the second embodiment, the threshold value (determination value) for determining the start of the drive of the drawing motor M3 is appropriately determined even if the load generated on the feed roller 17 changes. It can be set to As a result, it is possible to form an appropriate amount of loop on the sheet, and skew correction can be performed with high accuracy.

Third Embodiment
Next, a third embodiment in which the second embodiment is partially modified will be described with reference to FIGS. 12 and 13. FIG. FIG. 12 (a) shows a load torque when setting the first threshold according to the third embodiment, and FIG. 12 (b) shows when setting the second threshold according to the third embodiment. FIG. 13 is a flowchart showing load torque, and FIG. 13 is a flowchart showing control of sheet feeding processing according to the third embodiment.

  In the second embodiment, the threshold for turning on the drawing motor M3 is determined according to the load torque of the feed motor M1, and the amount of decrease in the load torque of the feed motor M1 is used to determine the nip state. Explained. In the third embodiment, a method of setting the threshold by determining the nip state using the state determination value corresponding to the paper type setting from the load torque of the feed motor M1 will be described. The configuration of the manual feeding unit and the configuration of the control unit are the same as those of the second embodiment, and thus the description thereof will be omitted.

In the third embodiment, as shown in FIGS. 12A and 12B, a state determination value D is used to determine the state of the nip. Here, the state determination value D is a value prepared for each paper type, which is set between the feed motor torque K · R1 in the single sheet transport state and the feed motor torque K · R2 in the separate transport state, which are measured in advance. And a value satisfying the following equation.
K · R1>D> K · R2

  As shown in FIG. 13, as in the second embodiment, the control unit 260 starts sheet feeding processing when a sheet feeding job instruction from the manual feeding unit 300 is input (S1). Then, first, driving of the feed motor M1 is started to start sheet feeding, counting of the predetermined time T1 is started (S2), and the process waits until the predetermined time T1 elapses (No in S3). The predetermined time T1 is appropriately set so as to be the timing before the sheet conveyed by the feed roller 17 contacts the drawing roller pair 20. When the predetermined time T1 has passed and it becomes time t1 in FIG. 12A (Yes in S3), the first determination value β1 is determined as the threshold according to the paper type setting (S44).

  On the other hand, the load detection unit 509 of the control unit 260 continues to detect the load torque of the feed motor M1 as needed. Then, it is determined at any time whether the value of the load torque is equal to or greater than the state determination value D (S45), and it is also determined at any time whether the load torque is equal to or greater than the threshold (S7). If the load torque value remains above the state determination value D (Yes in S45) and becomes equal to or above the threshold (Yes in S7), it is determined that a loop of an appropriate size is formed in the sheet in the pattern 1 above. The driving of the drawing motor M3 is started (S28). As a result, the sheet in a state in which the skew feeding is corrected in the drawing roller pair 20 is started to be conveyed toward the registration roller pair 240.

  On the other hand, when the value of the load torque is less than the state determination value D at time t1 in step S45 (No in S45), it is determined that the pattern 2 is the above. Further, as shown at time t4 in FIG. 12B, when the load torque value becomes less than the state determination value D after setting the threshold at time t1 (No in S45), the pattern 3 judge. Then, in these cases (No in S45), the threshold is overwritten on the second determination value β2, that is, the threshold is reset (S46). After that, similarly, when the load torque becomes equal to or more than the threshold value (Yes in S7), it is determined that a loop having an appropriate size is formed on the sheet, and the drive of the drawing motor M3 is started (S28). As a result, the sheet in a state in which the skew feeding is corrected in the drawing roller pair 20 is started to be conveyed toward the registration roller pair 240. The first determination value β1 and the second determination value β2 are values capable of forming a loop of an appropriate size according to the paper type. Also, since the control after step S28 is similar to that of the second embodiment, the description will be omitted.

  In the third embodiment, although the first determination value β1 is set at time t1, it is determined first whether or not the state determination value D is greater than time t1 (S45), Thereafter, the first determination value β1 or the second determination value β2 may be set as a threshold. In this case, only when the first determination value β1 is set as the threshold value, it may be determined at any time whether it becomes smaller than the state determination value D until the load torque reaches the first determination value β1.

  As described above, according to the manual feeding unit 300 according to the third embodiment, the threshold value (determination value) for determining the start of the drive of the drawing motor M3 is appropriately determined even if the load generated on the feed roller 17 changes. It can be set to As a result, it is possible to form an appropriate amount of loop on the sheet, and skew correction can be performed with high accuracy.

[Possibilities of Other Embodiments]
In the first, second, and third embodiments described above, the configuration for detecting and calculating the current value of the feed motor M1 as load detecting means for the load generated on the feed roller 17 has been described. It is not limited to this. For example, the load can be detected by calculating the current value from the detected voltage using a sensor that detects the voltage at the feed motor M1. Alternatively, for example, a torque meter (torque transducer) that directly detects the torque generated in the feed roller 17 may be used.

  In the first, second, and third embodiments, the load torque, the first threshold, the second threshold, the first determination value, the second determination value, the nip condition determination value C, and the like are positive values. Although what was calculated was described, it is not limited to this. That is, since the control unit 260 may calculate by reversing the positive and negative, that is, may calculate with a negative value, it may be a determination criterion whether or not the threshold value or the determination value is reached as an absolute value. In other words, reaching means that the value approaches from the side of 0, and the value becomes the threshold value or the judgment value, or exceeds in the direction away from 0.

  In the first, second and third embodiments, the drive of the feed roller 17 is started and the threshold value is set after the predetermined time T1 so that both the pattern 1 and the pattern 2 can be determined. The threshold is set, and in the case of pattern 3, the threshold is changed. However, the first judgment value (K · R1 + α) is set in the case of pattern 1 by discriminating the one-sheet conveyance state and the separated conveyance state from the load torque, and the second judgment value in the case of pattern 2 and pattern 3 (K · R 2 + α) may be set.

  In the first, second, and third embodiments, when the timing at which the toner image reaches the secondary transfer roller 217 and the timing at which the sheet is conveyed to the secondary transfer roller 217 do not match, the feed is performed. The one for stopping the roller 17 and the drawing roller pair 20 has been described. However, the invention is not limited thereto. For example, the driving of the feed roller 17 and the drawing roller pair 20 may be maintained, and the conveyance speed may be adjusted after the start of the driving of the registration roller pair 240.

  Further, in the first, second and third embodiments, the manual feeding unit 300 has been described as an example of the sheet feeding apparatus, but the present invention can be similarly applied to the sheet feeding unit 230 as well. That is, when forming a loop between the feed roller 9 and the drawing roller pair 11, the load of the feed roller 9 may be detected. When the drawing roller pair 11 is not provided, the load of the feed roller 9 may be detected when forming a loop between the feed roller 9 and the registration roller pair 240.

  The manual feeding unit 300 in the present embodiment corresponds to an example of a sheet feeding apparatus, and when the image forming unit is provided, the image forming apparatus 201 in the present embodiment corresponds to an example of a sheet feeding apparatus. It will be.

13: Sheet stacking means (tray): 17: feeding rotating body, feeding roller (feed roller): 18: separating means, separating roller (retard roller): 19: nip: 20: sheet conveying rotating body (drawing roller pair) 22: 23 Guide part: 201 Sheet feeding apparatus (image forming apparatus): 201 B Image forming means (image forming part): 240 Transport rotating body (pair of registration rollers): 260 Control means (control part) : 300 ... sheet feeding device (manual feeding unit): 507 ... load detection means, current detection means (current detection unit): 508 ... load detection means, current detection means (current detection unit): 509 ... load detection means (Load detection unit): L19: Tangent line in the nip: M1: first drive means, stepping motor (feed motor): M2: second drive means (registration motor): M3: second drive means Pull-out motor)

Claims (10)

Sheet stacking means for stacking sheets,
A feeding rotary member for feeding sheets stacked on the sheet stacking unit;
A separation unit that separates a plurality of sheets one by one when the plurality of sheets are fed by the feeding roller;
A conveying rotating body located downstream of the feeding rotational body and the separating unit in the sheet conveying direction, and conveying the sheet;
First driving means for driving the feeding rotary body;
Control means for controlling the first drive means;
Load detection means for detecting a load generated on the feed roller;
The control means
The first driving unit is driven to start sheet feeding by the feeding rotating body, and a value obtained by adding an addition value to the load value detected by the load detecting unit is set as a first threshold value, Driving of the first driving means is stopped based on the fact that the value of the load detected by the load detecting means has reached the first threshold value;
The first driving means is driven to start feeding of the sheet by the feeding rotary member, and the load value detected by the load detection means is before reaching the first threshold and is an absolute value. When there is a decrease equal to or more than a predetermined value, a value obtained by adding the addition value to the value of the load after the decrease is set as a second threshold, and the value of the load detected by the load detection means is the second threshold. Stopping the driving of the first driving means based on the arrival.
Sheet feeding apparatus characterized in that. A second drive unit for driving the transport rotating body;
After stopping the driving of the first driving unit, the control unit starts driving of the first driving unit and the second driving unit based on an image formation start timing.
The sheet feeding device according to claim 1, Sheet stacking means for stacking sheets,
A feeding rotary member for feeding sheets stacked on the sheet stacking unit;
A separation unit that separates a plurality of sheets one by one when the plurality of sheets are fed by the feeding roller;
A conveying rotating body located downstream of the feeding rotational body and the separating unit in the sheet conveying direction, and conveying the sheet;
First driving means for driving the feeding rotary body;
Second driving means for driving the conveyance rotating body;
Control means for controlling the first drive means and the second drive means;
Load detection means for detecting a load generated on the feed roller;
The control means
The first driving unit is driven to start sheet feeding by the feeding rotating body, and a value obtained by adding an addition value to the load value detected by the load detecting unit is set as a first threshold value, Starting driving the second driving means based on the fact that the value of the load detected by the load detection means has reached the first threshold value;
The first driving means is driven to start feeding of the sheet by the feeding rotary member, and the load value detected by the load detection means is before reaching the first threshold and is an absolute value. When there is a decrease equal to or more than a predetermined value, a value obtained by adding the addition value to the value of the decreased load is set as a second threshold, and the value of the load detected by the load detection means reaches the second threshold Start driving the second driving means based on
Sheet feeding apparatus characterized in that. The control means sets the first threshold after a predetermined time after driving the first drive means.
The sheet feeding apparatus according to any one of claims 1 to 3, wherein The addition value is a value corresponding to the load generated on the feeding rotating body when the amount of bending when the sheet is flexed between the feeding rotating body and the conveyance rotating body becomes a predetermined amount. is there,
The sheet feeding apparatus according to any one of claims 1 to 3, wherein The predetermined value may be a load value generated in the first driving unit when one sheet is fed to the separating unit, and the first value when a plurality of sheets are fed to the separating unit. It is a value corresponding to the difference between the value of the load generated in the drive means and
The sheet feeding apparatus according to any one of claims 1 to 5, wherein The first drive means is a stepping motor,
The load detection unit includes a current detection unit that detects a current flowing through the stepping motor, and detects a load based on the current detected by the current detection unit.
The sheet feeding apparatus according to any one of claims 1 to 6, wherein The feed roller is a feed roller,
The separation means is a separation roller that contacts the feed roller to form a nip,
A guide unit that forms a sheet conveyance path along which the sheet is conveyed from the feeding roller to the conveyance rotating body;
A tangent at the nip does not overlap with the guide portion but overlaps with the transport rotating body;
The sheet feeding device according to any one of claims 1 to 7, characterized in that: Sheet stacking means for stacking sheets,
A feeding rotary member for feeding sheets stacked on the sheet stacking unit;
A separation unit that separates a plurality of sheets one by one when the plurality of sheets are fed by the feeding roller;
A conveying rotating body located downstream of the feeding rotational body and the separating unit in the sheet conveying direction, and conveying the sheet;
First driving means for driving the feeding rotary body;
Second driving means for driving the conveyance rotating body;
Control means for controlling the first drive means and the second drive means;
Load detection means for detecting a load generated on the feed roller;
The control means
In the state where the first driving means is driven to start sheet feeding by the feeding rotary body, and one sheet is fed to the separating means, the value of the load detected by the load detecting means Starts driving the second driving means based on the fact that the first judgment value is reached,
When the first driving unit is driven to start sheet feeding by the feeding rotating body, and the plurality of sheets are fed to the separating unit, the value of the load detected by the load detecting unit is Driving of the second driving means is started based on reaching a second determination value which is smaller than the first determination value as an absolute value,
The first driving means is driven to start feeding of the sheet by the feeding rotating body, one sheet is fed to the separating means, and then another sheet is also fed to the separating means In the state, the drive of the second drive unit is started based on the value of the load detected by the load detection unit reaching the second determination value.
Sheet feeding apparatus characterized in that. Image forming means for forming an image on a sheet,
The sheet feeding apparatus according to any one of claims 1 to 9, wherein

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