JP4333490B2 - Paper feeding device and image forming apparatus - Google Patents

Description

  The present invention relates to a sheet feeding apparatus that separates and conveys sheets one by one and an image forming apparatus equipped with the sheet feeding apparatus.

2. Description of the Related Art Image forming apparatuses such as copying machines and printers are provided with a sheet feeding device that takes out sheets one by one from a stack of stacked sheets and supplies them to an image forming unit. In this type of paper feeding device, it is necessary to appropriately adjust control parameters such as the pressure contact force and separation torque of the separation roller in order to prevent double feeding. Conventionally, there are two types of adjustment techniques. One is to detect the occurrence of double feeding and change the control parameter before transporting subsequent sheets, and is disclosed in, for example, Patent Documents 1 to 3. The other is to extract appropriate control parameters from a look-up table based on information such as the sheet thickness, the number of sheets before the separation unit, temperature, and humidity, and apply it to conveyance control. Here, as a technique for changing the separation torque by inputting the sheet thickness in advance, Patent Document 4 discloses at least one of the separation torque or the pressure contact force between the sheet feeding roller and the separation roller according to the number of inserted sheets, temperature, and humidity. A technique for increasing / decreasing control is disclosed in Patent Document 5.
JP 2001-213540 A Japanese Patent Laid-Open No. 10-095547 JP 05-032356 A Japanese Patent Laid-Open No. 08-217290 JP 2000-264489 A

  However, although the above-described conventional adjustment technique has an effect of reducing the number of occurrences of double feeding, it does not eliminate the double feeding that has occurred, and cannot eliminate double feeding.

  The present invention has been made in view of the circumstances described above, and an object of the present invention is to provide a paper feeding device that can effectively eliminate the double feeding that has occurred and an image forming apparatus using the same. It is said.

According to the present invention, a conveyance roller that conveys a sheet, and the conveyance roller that faces the conveyance roller are sandwiched. When two or more sheets are conveyed by the conveyance roller, the conveyance roller can rotate in a direction opposite to the conveyance direction. A separation roller, a sheet number sensor that detects the number of sheets at or downstream of the nip portion between the conveying roller and the separation roller, and a leading edge position of the sheet that is in contact with the separation roller and is located downstream from the nip portion A sheet position sensor for detecting the pressure, a pressing force generating means for generating pressure to press the separating roller against the conveying roller, and a separating torque generating means for applying a separating torque for returning the sheet in a direction opposite to the conveying direction to the separating roller. When the sheet number detection sensor detects two sheets, the second sheet position sensor detects the sheet number. And a control device for controlling at least one of the pressure generated by the pressing force generation means or the separation torque generated by the separation torque generation means so that the tip position of the head becomes a target value. To do.
According to this invention, when the two sheets pass through the nip portion, the upper first sheet is conveyed while performing the feedback control for holding the lower second sheet. It is possible to effectively eliminate existing double feeds.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<First Embodiment>
FIG. 1 shows the configuration of a sheet feeding device according to the first embodiment of the present invention. The sheet feeding device is provided in an image forming apparatus such as a copying machine, a facsimile machine, or a printer. A sheet fed by the sheet feeding device is supplied to an image forming unit of the image forming apparatus.

  In FIG. 1, a sheet feeding roller 1 is pressed against a sheet stacked on a tray and rotates to feed the sheet to a nip portion between a conveyance roller 2 and a separation roller 3. When the sheet reaches the nip portion, the sheet is conveyed by the conveyance roller 2. During this time, the paper feed roller 1 is disconnected from its rotational drive system and is in a free state, and rotates with the conveyed sheet. The separation roller 3 is rotatably held by a holding member 9 at its rotating shaft. The holding member 9 is rotatably supported at the fulcrum 4. FIG. 2 shows a configuration of the separation roller 3 as viewed from below. Similarly to the holding member 9, the drive shaft 5 is rotatably supported at the fulcrum 4. The drive shaft 5 transmits torque to the separation roller 3 via gears 5a and 3a. Further, the drive shaft 5 is connected to the rotation shaft of the motor 7 via the electromagnetic clutch 6. The motor 7 is, for example, a stepping motor, which transmits torque to the separation roller 3 via the drive shaft 5 and gears 5a and 3a, and rotationally drives the separation roller 3 in a direction to push the sheet back to the tray side. The torque transmitted from the motor 7 to the separation roller 3 is determined by the transmission torque set in the electromagnetic clutch 6. This transmission torque can be adjusted by a current flowing through the electromagnetic clutch 6. The torque generated in the separation roller 3 by the action of the motor 7 and the electromagnetic clutch 6 becomes the separation torque for separating the sheet on the separation roller 3 side from the plurality of sheets to be multi-fed and returning them to the tray side. . When only one sheet is passing through the nip portion, no separation torque is required. In this case, the electromagnetic clutch 6 is disconnected, and the separation roller 3 rotates according to the conveying roller 2.

  In FIG. 1, an arm 10 is fixed to the rotating shaft of the motor 8, and the tip of the arm 10 is engaged with the holding member 9 of the separation roller 3. When the motor 8 turns the arm 10 counterclockwise, the holding member 9 turns clockwise about the fulcrum 4 by the turning motion of the arm 10, and presses the separation roller 3 against the transport roller 2. Therefore, by adjusting the torque generated by the motor 8, the pressure when the separation roller 3 is pressed against the transport roller 2 can be adjusted.

  A sheet position sensor 12 is disposed in the vicinity of the nip where the conveying roller 2 and the separation roller 3 are in contact with each other. The sheet position sensor 12 includes a small roller provided in the sheet conveyance path and an encoder that detects the rotation amount of the roller. Here, the roller starts to rotate when the leading edge of the sheet arrives, and rotates according to the subsequent movement of the sheet. In this embodiment, the rotation amount of the roller is obtained by an encoder, and the leading end position of the sheet is obtained based on the rotation amount.

  A sheet detection sensor 13 that detects the presence / absence of a sheet is disposed downstream of the sheet position sensor 12. The sheet detection sensor 13 determines the timing at which the leading edge of the sheet passes.

  In the vicinity of the separation part slightly downstream of the nip part, there is a sheet number sensor 14 for detecting the number of sheets in the separation part. The number sensor 14 includes various types such as an ultrasonic type (see JP 2000-95390 A) and a capacitance type (see JP 11-301895 A). Does not matter. For example, the number sensor 14 may be as shown in FIGS. In the example shown in FIG. 3, the number sensor is constituted by a displacement meter 141 that measures the displacement of the holding member 9 in the thickness direction of the nip portion, that is, the thicknesses of all the sheets sandwiched between the nip portions. The control device 15 obtains the number of sheets in the nip portion from the sheet thickness measured by the displacement meter 141. In the example shown in FIG. 4, contact rollers 142 and 143 are provided on the upper and lower sides of the sheet conveyance path downstream of the nip portion. Here, the lower contact roller 143 is supported at the tip of the arm 144, and the arm 144 can rotate around a fulcrum 145. In addition, an appropriate pressure that presses the contact roller 143 against the contact roller 142 is applied to the arm 144. The displacement meter 146 measures the displacement of the arm 144 in the thickness direction of the nip portion, that is, the thickness of all sheets sandwiched between the contact rollers 142 and 143. The control device 15 obtains the number of sheets at a position downstream of the nip portion from the sheet thickness measured by the displacement meter 146. In the example shown in FIG. 5, an encoder 147 that measures the rotation angle of the arm 144 is provided instead of the displacement meter 146 in FIG. 4. The control device 15 obtains the number of sheets at the position downstream of the nip portion from the rotation angle measured by the encoder 147.

  The control device 15 determines the application current of the electromagnetic clutch 6 and the motor based on the passage timing of the leading edge of the sheet detected by the sheet detection sensor 13, the number of sheets detected by the sheet sensor 14, and the sheet position detected by the sheet position sensor 12. 8 is controlled to control the separation torque and the pressure for pressing the separation roller 3 against the conveying roller 2 (hereinafter referred to as a pressure load).

  In the present embodiment, the action of separating the sheet on the separation roller 3 side from the plurality of sheets that are about to be fed and returning it to the tray side is called the separation action. This separation action depends on control parameters such as separation torque and pressure load. That is, when the separation torque is increased, the separation action of the separation roller 3 becomes stronger and it becomes difficult for double feeding to occur. Further, when the pressure load is increased, the separating action is weakened. In order to control the separation action, one of the separation torque and the pressure load may be controlled, or both may be controlled.

  In the present embodiment, the control device 15 stores a set of control parameters for obtaining a relatively weak separation action and a set of control parameters for obtaining a relatively strong separation action. Hereinafter, the mode using the former control parameter set is referred to as “mode 1”, and the mode using the latter control parameter set is referred to as “mode 2”.

  Next, separation conveyance performed in this embodiment will be described. FIG. 6 shows the transition of the leading edge position of each sheet when two sheets are fed to the nip portion by the sheet feeding roller 1. When performing sheet conveyance, the control device 15 starts conveyance using a control parameter of “mode 1” as an initial state, that is, a control parameter that provides a relatively weak separation action. After the start of conveyance, the control device 15 monitors the output signal of the sheet detection sensor 13, and when the leading edge of the first sheet is detected by the sheet detection sensor 13, the sheet number sensor 14 is passing through the nip portion. The number of sheets is detected. As shown in this example, when two sheets pass through the nip portion and the number of sheets “2” is detected by the number sensor, the control device 15 moves the leading edge of the second sheet to a predetermined downstream of the nip portion. Control D for stopping at the target position is performed. FIG. 7 shows the contents of the control D. As shown in the figure, in the control D, a feedback control is performed in which the difference between the sheet position of the second sheet detected by the sheet position sensor 12 and the target position is obtained and the control parameter is adjusted so that the difference converges to zero. Do. This feedback control system includes, for example, a PID controller as a controller. The control parameter to be adjusted is a separation torque as shown in the figure, may be a pressure contact load, or may be both a separation torque and a pressure contact load.

  The control device 15 continues this control D until the trailing edge of the first sheet passes through the nip position. Then, the control device 15 starts sheet conveyance when the next sheet conveyance instruction is given. At this time, the previous second sheet has already come out of the nip portion, and the second sheet is conveyed to the subsequent stage by the conveying roller 2. During this time, the third sheet is taken out of the tray by the paper feed roller 1 and passes through the nip portion. When the control device 15 detects the leading edge of the third sheet by the sheet detection sensor 13, the third sheet is detected. The control D is executed to keep the at the target position.

  FIG. 8 is a flowchart of a program executed by the control device 15 in order to perform the separation and conveyance as described above. The control device 15 executes this program when a conveyance instruction is given. Before the transfer instruction is given, the operation mode of the control device 15 is mode 1. Therefore, when the conveyance instruction is given, the control device 15 starts conveyance of the sheet using the control parameter corresponding to mode 1, that is, the control parameter that provides a relatively weak separation action. After the start of sheet conveyance, the control device 15 determines the output signal of the sheet detection sensor 13 (step S1). When the leading edge of the first sheet is detected by the sheet detection sensor 13, the sheet sensor 14 detects the nip portion. It is determined whether or not the number of sheets passing through is one (step S2). If the determination result is “YES”, the control device 15 sets the operation mode to mode 1 (step S3), and then determines whether the number of sheets detected by the number sensor 14 is two (step S3). S4). When the determination result is “NO”, the control device 15 determines whether or not the number of sheets detected by the number sensor 14 is three or more (step S5). When the determination result is “NO”, the control device 15 determines whether or not the conveyance of the sheet is completed (step S6). If the determination result is “NO”, the process returns to step S2. Therefore, during the period when the number of sheets detected by the number sensor 14 is one, steps S2, S3, S4, S5, and S6 are repeated, and mode 1 sheet conveyance using a control parameter that provides a relatively weak separation action. Is done. When the conveyance is completed, the determination result in step S6 is “YES”, and the control device 15 determines whether or not the number of sheets detected by the number sensor 14 is three or more (step S7). When the determination result is “NO”, the control device 15 ends the processing for sheet conveyance.

  Next, the operation when two sheets are supplied to the nip portion as shown in FIG. 6 will be described. In this case, when the leading edge of the first sheet is detected by the sheet detection sensor 13, two sheets passing through the nip portion are detected by the number sensor 14, and therefore the determination result in step S <b> 2 is “NO”. Thus, the control device 15 performs the determination in step S4. Here, since the number of sheets is two, the determination result in step S4 is “YES”, and the control device 15 executes the above-described control D (step S8). With this control D, the leading edge of the lower second sheet of the two sheets that have passed through the nip portion is held at the target position downstream of the sheet detection sensor 13.

  Next, the control device 15 determines whether or not the number of sheets detected by the number sensor 14 is 1 (step S9). If the determination result is “NO”, the control is detected by the number sensor 14. It is determined whether the number of existing sheets is three or more (step S10). If the determination result is “NO”, it is determined whether or not the sheet conveyance has ended (step S11). If not, the process returns to step S9. Thereafter, steps S9 to S11 are repeated on condition that the number of sheets at the position of the number sensor 14 is two. During this time, the first sheet is conveyed downstream by the conveying roller 2 with the leading edge of the second sheet held at the target position. Then, when the trailing edge of the first sheet passes the position of the number sensor 14, the number of sheets detected by the number sensor 14 becomes 1, and the determination result in step S9 is “YES”. Thereby, the process of the control apparatus 15 progresses to step S4 via step S3. Then, steps S2 to S6 are repeated on condition that the number of sheets is one. When the conveyance of the first sheet is completed and the determination result in step S6 is “YES”, the control device 15 ends the process for conveyance after performing the determination in step S7.

  After that, when a conveyance instruction is generated, after the leading edge of the third sheet is detected in step S1, the process of the control device 15 proceeds to step S8 via steps S2 and S4. Thereafter, the second sheet is conveyed with the leading edge of the third sheet held at the target position (step S8).

  When Steps S9 to S11 are repeated in a state where the first sheet and the second sheet pass through the nip portion and the tip of the second sheet is held at the target position, depending on the length of the sheet, Before the trailing edge of the first sheet passes the position of the sheet number sensor 14, the leading edge of the first sheet is received by a device subsequent to the sheet feeding device, and conveyance may end. In that case, the result of determination in step S11 is “YES” when the conveyance ends, and the control device 15 sets the operation mode to “mode 1” (step S12), and ends the process for conveyance.

  Now, when steps S9 to S10 are repeated and the first sheet is being conveyed by the conveyance roller 2 with the leading edge of the second sheet held at the target position, a new conveyance instruction is given, A situation may occur in which the third sheet passes through the nip portion. In this case, since the three sheets are detected by the number sensor 14, the determination result in step S10 is “YES”. Accordingly, the control device 15 sets the operation mode to “mode 2”, switches to sheet conveyance using a control parameter that can obtain a relatively strong separation action, and returns the third sheet to the nip side (step S13). Thereafter, when the processing of the control device 15 proceeds to step S4 via steps S6 and S2, if the number of sheets is two, the determination result in step S4 is “YES”, and the control device 15 A control D for holding the first sheet at the target position is executed (step S8), and steps S9 to S11 are repeated. During this time, the first sheet is conveyed by the conveying roller 2. When the trailing edge of the first sheet passes the position of the number sensor 14 and the determination result in step S9 is “YES”, the control device 15 returns the operation mode to mode 1 (step S3) and is relatively weak. Switch to sheet conveyance based on control parameters that provide separation. The same applies to the case where the conveyance of the first sheet is completed while repeating steps S9 to S11, and the control device 15 sets the operation mode to mode 1 (step S12) and ends the conveyance process.

  Depending on the situation, when the conveyance is started in accordance with the conveyance instruction, three or more sheets may be supplied to the nip portion at a time. In this case, when the process of the control device 15 proceeds to step S5 via steps S1, S2, and S4 according to the conveyance instruction, the determination result is “YES”. Thereby, the control device 15 sets the operation mode to “mode 2” and returns the third and subsequent sheets to the nip portion. Then, steps S2 to S6 are repeated until the conveyance is completed or the detection result of the sheet number sensor 14 is two or less. The processing when the detection result of the number sensor 14 becomes 1 sheet during this period or when it becomes 2 sheets is as already described.

  After the end of conveyance is detected in step S6, three or more sheets may be detected in step S7. This means that a double feed that cannot be resolved in this embodiment has occurred. Accordingly, the control device 15 performs error processing such as stopping the machine and notifying the user.

  As described above, according to this embodiment, when the two sheets pass through the nip portion, the upper first sheet is controlled while controlling the control parameter for fastening the lower second sheet. Therefore, the generated double feed can be effectively eliminated.

The present embodiment has the following modifications.
(1) For example, in the embodiment, the electromagnetic clutch 6 is used for variable control of the separation torque, but instead, a DC motor 16 may be used as shown in FIG. When the separation torque for returning the sheet to the nip portion side is applied to the separation roller 3, the direction of the drive current passed through the DC motor 16 so that the rotational torque corresponding to the separation torque is generated in the same direction as the motor 7 in FIG. Adjust the size. In the present modification, the magnitude and direction of the torque applied to the separation roller 3 can be switched by adjusting the current flowing through the DC motor 16, so that the electromagnetic clutch 6 in FIG. 2 is unnecessary.

(2) Instead of the sheet position sensor 12, an encoder 11 for detecting the rotation of the separation roller 3 may be installed as shown in FIG. When the second sheet is in the nip portion, the movements of the outer periphery of the second sheet and the separation roller 3 are substantially the same. Therefore, in the present modification, the control device 15 processes the position on the outer periphery of the separation roller 3 calculated from the rotation angle of the separation roller 3 as the leading edge position of the second sheet.

Second Embodiment
As described in the first embodiment, when the sheet reaches the nip portion, the sheet is conveyed by the conveying roller 2. During this time, the paper feed roller 1 is disconnected from its rotational drive system and is in a free state, and rotates with the conveyed sheet. In this state, when the separation torque by the separation roller 3 acts on the sheet, the sheet conveyance speed decreases. In the present embodiment, the decrease in the sheet conveyance speed is suppressed, and the sheet conveyance is stabilized. FIG. 11 is a diagram illustrating a configuration of the sheet feeding device according to the present embodiment. This sheet feeding device is provided with a sheet speed sensor 17 for detecting the speed of the conveyed sheet at a position downstream of the sheet feeding roller 1. In addition to the function of performing the control D in the first embodiment, the control device 15 has a function of performing the control S shown in FIG. In this control S, feedback control is performed to obtain a difference between the sheet speed detected by the sheet speed sensor 17 and a predetermined target speed, and adjust the pressure contact load so that the sheet speed becomes equal to or higher than the target speed. As in the first embodiment, the control system for feedback control includes a PID controller.

  FIG. 13 shows a period during which the control S and the control D are performed. The period during which the control D is performed is the same as that in the first embodiment. The control S is performed only during a period from when the leading edge of the sheet is detected by the sheet detection sensor 13 until the leading edge of the sheet reaches a subsequent conveyance roller (not shown) and the conveyance is shifted to that. This control S is performed in parallel with the control D.

  FIG. 14 is a flowchart showing a process for performing the above control. As shown in the figure, after the conveyance instruction is generated, the control device 15 detects the leading edge of the sheet by the sheet detection sensor 13, and when the determination result in step S21 is "YES", the control device 15 Control S is executed until the arrival at the conveyance roller is detected (steps S22 and S23). On the other hand, in parallel with this, the control device 15 executes the processing after step S2 of FIG. 8 related to the first embodiment. In this process, switching between modes 1 and 2 is performed depending on whether or not the number of sheets detected by the number sensor 14 is two or less. At that time, only the separation torque is switched as a control parameter, and the pressure load is switched. Do not do. This is because the pressing load is a control target of the control S in step S22 executed in parallel with step S24. When both steps S23 and S24 are finished, the overall conveyance control is finished (step S25), and the process is finished. According to the present embodiment, in addition to the effect of the first embodiment, an effect that the sheet is conveyed at a stable speed is obtained. Note that a modification similar to that of the first embodiment can also be applied to this embodiment.

It is a figure which shows the structure of the paper feeder which is 1st Embodiment of this invention. It is a figure which shows the structure of the separation roller and its drive system in the embodiment. It is a figure which shows the structural example of the number sensor in the same embodiment. It is a figure which shows the structural example of the number sensor in the same embodiment. It is a figure which shows the structural example of the number sensor in the same embodiment. 6 is a time chart showing the behavior of the sheet leading edge in the embodiment. It is a figure showing control D in the embodiment. It is a flowchart which shows operation | movement of the embodiment. It is a figure which shows the structure of the separation roller and its drive system in the modification of the embodiment. It is a figure which shows the structure of the separation roller and its drive system in the modification of the embodiment. It is a figure which shows the structure of the paper feeder which is 2nd Embodiment of this invention. It is a figure showing control S in the embodiment. 6 is a time chart showing the behavior of the sheet leading edge in the embodiment. It is a flowchart which shows operation | movement of the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Paper feed roller, 2 ... Conveyance roller, 3 ... Separation roller, 4 ... Supporting point, 5 ... Drive shaft, 6 ... Electromagnetic clutch, 7, 8 ... Motor, 9 ... Holding member, 10 ...... Arm, 11 ... Encoder, 12 ... Seat position sensor, 13 ... Seat detection sensor, 14 ... Number sensor, 15 ... Control device, 16 ... DC motor, 17 ... Encoder, 141, 146 ... ... displacement meter, 144 ... arm, 145 ... fulcrum, 147 ... encoder, 142, 143 ... contact roller.

Claims (5)

A transport roller for transporting the sheet;
A separation roller that is opposed to the conveying roller with the sheet to be conveyed interposed therebetween and is capable of rotating in the direction opposite to the conveying direction when two or more sheets are conveyed by the conveying roller;
A sheet number sensor for detecting the number of sheets in the nip portion or downstream thereof between the transport roller and the separation roller;
A sheet position sensor that detects the leading edge position of the sheet that is in contact with the separation roller and is located downstream from the nip portion;
A pressing force generating means for generating pressure to press the separation roller against the conveying roller;
Separation torque generating means for applying a separation torque to the separation roller for returning the sheet in a direction opposite to the conveyance direction;
When two sheets are detected as the number of sheets by the sheet number detection sensor, the pressure generated by the pressing force generation means so that the leading edge position of the sheet detected by the second sheet position sensor becomes a target value or And a control device that controls at least one of the separation torques generated by the separation torque generating means. A transport roller for transporting the sheet;
A separation roller that is opposed to the conveying roller with the sheet to be conveyed interposed therebetween and is capable of rotating in the direction opposite to the conveying direction when two or more sheets are conveyed by the conveying roller;
A sheet number sensor for detecting the number of sheets in the nip portion or downstream thereof between the transport roller and the separation roller;
A sheet position sensor that detects the leading edge position of the sheet that is in contact with the separation roller and is located downstream from the nip portion;
A sheet speed sensor for detecting the speed of the conveyed sheet;
A pressing force generating means for generating pressure to press the separation roller against the conveying roller;
Separation torque generating means for applying a separation torque to the separation roller for returning the sheet in a direction opposite to the conveyance direction;
When controlling the pressure generated by the pressing force generating means so that the sheet speed detected by the sheet speed sensor becomes a predetermined value or more, and when two sheets are detected as the number of sheets by the sheet number detection sensor, And a control device that controls the separation torque generated by the separation torque generating means so that the leading edge position of the sheet detected by the second sheet position sensor becomes a target value. The control device uses a first set value for obtaining a weak separating action and a second set value for obtaining a strong separating action as set values of conveyance control parameters that influence the degree of sheet separating action by the separating roller. Remember
When one sheet is detected by the sheet number sensor, the conveyance control using the first set value is performed,
The sheet feeding device according to claim 1 or 2, wherein when the number of sheets sensor detects three or more sheets, the conveyance control using the second set value is performed.   The feeding according to any one of claims 1 to 3, wherein the sheet position sensor includes an encoder that detects a rotation angle of the separation roller, and calculates a position of the second sheet based on the rotation angle. Paper device. A paper feeding device according to any one of claims 1 to 4,
An image forming apparatus comprising: an image forming unit that forms an image on a sheet supplied from the sheet feeding device.

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