JP2015000789A - Sheet conveying device, image reading apparatus, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet conveying device which adjusts connection timing of a clutch to be connected for driving a conveyance roller on an upstream side of a conveyance path and drive start timing of a stepping motor which drives a conveyance roller on a downstream side of the conveyance path, an image reading apparatus, an image forming apparatus.SOLUTION: Drive of a resist roller 61 on a downstream side is started after elapse of delay time TA after connecting a clutch 66 for transmitting driving force to a conveyance roller 71 on an upstream side of a conveyance path 30, electromotive force Vr to be generated in a first excitation coil 81 of a stepping motor 64 which drives the resist roller 61 is compared with a predetermined setting value, and the timing for connecting the clutch 66 is adjusted according to its comparison result.

Description

  The present invention relates to a sheet conveying apparatus including a plurality of types of drive motors for driving a conveying roller, an image reading apparatus including the sheet conveying apparatus, and an image forming apparatus including the sheet conveying apparatus.

An image reading apparatus that reads an image on a sheet or an image forming apparatus that forms an image on a sheet includes a sheet conveying apparatus that conveys the sheet. The sheet conveying apparatus is equipped with a plurality of types of motors as the driving source of the conveying roller according to the realization of cost reduction and the specifications required at the place where the conveying roller is used. For example, a stepping motor is applied to a driving source of a conveyance roller used in a place where high positioning accuracy is required. In addition, a high torque motor such as a DC motor or an induction motor is applied as a driving source of a conveyance roller used in a place where high positioning accuracy is not required or a place where a high load is applied. The drive transmission path between the high torque motor and the conveyance roller is configured to be connectable by a clutch, and the driving force of the high torque motor is transmitted to the conveyance roller by controlling the clutch.
In such a sheet conveying apparatus, a conveying roller driven by a high torque motor and a clutch is provided upstream of the sheet conveying path, and a conveying roller driven by a stepping motor is provided downstream of the sheet conveying path. . In this configuration, if the clutch connection timing and the stepping motor drive start timing are deviated, a problem occurs when the sheet is conveyed. Specifically, if the clutch connection timing is too early than the driving start timing of the stepping motor, the sheet hits the downstream conveyance roller and the sheet bends, and the contact sound is heard when the bent sheet hits the conveyance guide surface. Will occur. On the other hand, if the clutch connection timing is too late than the stepping motor drive start timing, the sheet cannot be transported by the downstream transport roller alone, and a high load is applied to the stepping motor, causing a problem of stepping out. . In addition, the sheet may be pulled and damaged.
In general, because clutch manufacturing and variation over time are large, it is not possible to uniformly determine clutch connection timing and stepping motor drive start timing at the design and manufacturing stages. It is necessary to adjust to.
For this reason, in a general sheet conveying apparatus, the clutch connection timing and the stepping motor drive start timing are aligned after the product is manufactured. In Patent Document 1 and Patent Document 2, the step-out motor is detected by detecting the output voltage or output current of the stepping motor, increasing the supply current amount based on the detection result, and increasing the torque of the stepping motor. A stepping motor control device and a media transport control device to prevent are described.

JP-A-6-133593 JP-A-9-295722

However, timing adjustment after product manufacture can adjust timing deviation due to manufacturing variation, but timing adjustment due to secular change cannot be adjusted. Further, in the methods disclosed in Patent Document 1 and Patent Document 2, it is possible to prevent the stepping motor on the downstream side from stepping out, but it is possible to adjust the clutch connection timing and the driving start timing of the stepping motor. Can not.
Accordingly, the present invention has been made in view of the above circumstances, and the object of the present invention is to convey the drive start timing of the second motor that drives the conveyance roller on the downstream side in the conveyance direction of the conveyance path. An object of the present invention is to provide a sheet conveying apparatus, an image reading apparatus, and an image forming apparatus capable of adjusting the connection timing of the connecting means of the first conveying roller on the upstream side in the conveying direction of the path.

The sheet conveying apparatus according to the present invention includes a first conveying roller, a first driving motor, a connecting unit, a second conveying roller, a second driving motor, a detecting unit, and a timing changing unit. The first transport roller is provided in a sheet transport path. The first drive motor supplies a driving force to the first transport roller. The connecting means connects the drive transmission path between the first drive motor and the first transport roller at a predetermined reference timing. The second transport roller is provided downstream of the first transport roller in the sheet transport direction in the transport path. The second drive motor is driven in synchronization with an input drive signal to rotate the second transport roller. The detection means detects a load value of a load applied to the second drive motor being driven. In the timing change, the load value detected by the detection means is compared with a preset value related to the load of the second drive motor, and the reference timing of the connecting means is changed according to the comparison result. To do. According to the configuration of the sheet conveying apparatus of the present invention, it is possible to adjust the driving start timing of the first conveying roller and the driving start timing of the second conveying roller.
An image reading apparatus according to the present invention includes the sheet conveying device and an image reading unit. The image reading unit reads an image of a sheet conveyed by the sheet conveying apparatus.
An image forming apparatus according to the present invention includes the sheet conveying device and an image forming unit. The image reading unit forms an image on a sheet conveyed by the sheet conveying apparatus.

  According to the present invention, it is possible to adjust the coupling timing of the clutch that is coupled to drive the transport roller on the upstream side of the transport path and the drive start timing of the stepping motor that drives the transport roller on the downstream side of the transport path. it can.

FIG. 2 is a cross-sectional view schematically illustrating a schematic configuration of the multifunction peripheral according to the embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing a schematic configuration near a registration roller of an image forming unit. FIG. 3 is a block diagram showing a configuration of a control system in the paper transport apparatus 70. The block diagram which shows schematic structure of a stepping motor control apparatus. The flowchart which shows an example of the procedure of the electromotive force acquisition process performed by the control part. The timing chart which shows an example which detects a load with a stepping motor control apparatus. The timing chart which shows the relationship between the clutch connection by a control part, and a stepping motor drive start. The flowchart which shows an example of the clutch connection timing adjustment process by a control part. The flowchart which shows the other example of the clutch connection timing adjustment process by a control part.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. The embodiment described below is an example embodying the present invention, and does not limit the technical scope of the present invention.

[Embodiment]
<Schematic configuration of MFP 100>
First, a schematic configuration of the MFP 100 according to the embodiment of the present invention will be described.
As shown in FIG. 1, the MFP 100 includes an image reading unit 1, an ADF (Automatic Document Feeder) 2, an image forming unit 3 (an example of an image forming apparatus), a paper feeding unit 4, and a control unit 5 (FIG. 3). And an operation display unit 6 and the like. The operation display unit 6 is a touch panel or the like that displays various types of information in accordance with control instructions from the control unit 5 and inputs various types of information to the control unit 5 in response to user operations. Here, FIG. 1A is a front view of the multifunction peripheral 100, and FIG. 1B is a plan view of the image reading unit 1.
A combination of the image reading unit 1 and the ADF 2 is an example of the image reading apparatus of the present invention. The MFP 100 is only an example of an image reading apparatus and an image forming apparatus according to the present invention. For example, the present invention may be a printer, a fax machine, a copying machine, or the like.

The image reading unit 1 acquires image data from the paper P. The image reading unit 1 is an image reading unit including a paper cover 2A, a contact glass 11, a reading unit 12, a mirror 13, a mirror 14, an optical lens 15, a CCD (Charge Coupled Device) 16, and the like. The contact glass 11 is provided on the upper surface of the image reading unit 1 and is a transparent paper base on which the paper P to be read by the multifunction machine 100 is placed.
The paper cover 2A covers the contact glass 11 as necessary. Then, the image reading unit 1 reads image data from the paper P placed on the contact glass 11 under the control of the control unit 5.
The reading unit 12 includes an LED light source 121 and a mirror 122, and is configured to be movable in the sub-scanning direction (left-right direction 9 in FIG. 1) by a moving mechanism (not shown) such as a stepping motor. When the reading unit 12 is moved in the sub-scanning direction by the moving mechanism, the light emitted from the LED light source 121 toward the contact glass 11 is scanned in the sub-scanning direction.
The LED light source 121 includes a large number of white LEDs arranged along the main scanning direction (front-rear direction 8 in FIG. 1) of the multi-function device 100. The LED light source 121 emits white light for one line toward the paper P at the reading position 12A on the contact glass 11. The reading position 12A moves in the sub scanning direction as the reading unit 12 moves in the sub scanning direction.
The mirror 122 reflects reflected light toward the mirror 13 when light is emitted from the LED light source 121 to the paper P at the reading position 12A. The light reflected by the mirror 122 is guided to the optical lens 15 by the mirror 13 and the mirror 14. The optical lens 15 collects incident light and makes it incident on the CCD 16.
The CCD 16 is a photoelectric conversion element that converts received light into an electrical signal (voltage) corresponding to the amount of light and outputs it to the control unit 5. Specifically, the CCD 16 generates image data based on an electrical signal corresponding to an image on the paper P based on light reflected from the paper P when light is emitted from the LED light source 121.

The ADF 2 is provided on the paper cover 2A. The ADF 2 is an automatic document feeder provided with a paper tray 21, a feeding mechanism 22, a plurality of transport rollers 23, a paper press 24, a paper discharge unit 25, and the like.
The ADF 2 causes the paper P set on the paper tray 21 to pass through the reading position 12A on the contact glass 11 by driving each of the feeding mechanism 22 and the transport roller 23 with a stepping motor (not shown). Then, it is conveyed to the paper discharge unit 25. At this time, the image reading unit 1 reads an image of the paper P passing through the reading position 12A.
The sheet presser 24 is provided at a position on the contact glass 11 above the reading position 12 </ b> A with an interval through which the sheet P can pass. The sheet presser 24 is formed in an elongated shape in the main scanning direction, and a white sheet is attached to the lower surface (the surface on the contact glass 11 side). In the MFP 100, the image data of the white sheet is read as white reference data. The white reference data is used in known shading correction or the like.

The image forming unit 3 performs an image forming process (printing process) based on image data read by the image reading unit 1 or image data input from an information processing apparatus such as an external personal computer. This is an image forming unit of the type.
The image forming unit 3 includes a photosensitive drum 31, a charging device 32, an LSU (Laser Scanner Unit) 33, a developing device 34, a transfer roller 35, a static eliminating device 36, a fixing roller 37, a pressure roller 38, and the like. . The image forming unit 3 includes a sheet conveying device 70 (an example of a sheet conveying device) that conveys the sheet S fed from the sheet feeding unit 4 to the sheet discharge tray 40, and the sheet S (sheet In one example, an image is formed by the following procedure.
Specifically, first, the photosensitive drum 31 is uniformly charged to a predetermined potential by the charging device 32. Next, the LSU 33 irradiates the surface of the photosensitive drum 31 with light based on image data. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 31. The electrostatic latent image on the photosensitive drum 31 is developed (visualized) as a toner image by the developing device 34. Subsequently, the toner image formed on the photosensitive drum 31 is transferred onto the paper S by the transfer roller 35. Thereafter, the toner image transferred to the paper S is heated by the fixing roller 37 and melted and fixed to the paper S when the paper S passes between the fixing roller 37 and the pressure roller 38 and is discharged. To do. The electric potential of the photosensitive drum 31 is neutralized by the neutralization device 36.
The details of the sheet conveying device 70 will be described later.

  The paper feeding unit 4 feeds the paper S on which an image is formed in the image forming unit 3. The paper feeding unit 4 feeds a plurality of sheets S placed in a paper feeding cassette (not shown) mounted in a cassette mounting unit (not shown) one by one to the image forming unit 3.

The general function of the control unit 5 will be described. As shown in FIG. 3, the controller 5 includes a CPU 51, a ROM 52, a RAM 53, an EEPROM 54, and the like. The control unit 5 controls the multifunction peripheral 100 in an integrated manner by executing a predetermined control program stored in the ROM 52 by the CPU 51. Specifically, the ROM 52 stores in advance an image forming sheet conveyance control program for conveying the paper S when forming an image. The CPU 51 causes the image forming unit 3 to convey the paper S by operating according to the image forming sheet conveyance control program. The RAM 53 is a volatile storage means, and the EEPROM 54 is a non-volatile storage means, and is used as a temporary storage memory for various processes executed by the CPU 51.
The control unit 5 may be configured by an electronic circuit such as an integrated circuit (ASIC, DSP) or the like, and may be a control unit provided separately from a main control unit that controls the multifunction peripheral 100 in an integrated manner. .

<Configuration of Paper Conveying Device 70>
Next, the details of the sheet conveying device 70 will be described with reference to FIGS. 1 to 3. FIG. 2 is a cross-sectional view schematically showing a schematic configuration in the vicinity of the registration roller 61 (an example of a second transport roller) of the image forming unit 3. FIG. 3 is a block diagram illustrating a configuration of a control system in the sheet conveying device 70.
As shown in FIG. 1, the paper transport device 70 has a mechanism for transporting the paper S, the registration roller 61 (an example of a second transport roller), a plurality of transport rollers 71 to 73, a paper discharge roller 74, a tip end. A detection sensor 67 is provided. The conveyance roller 71 is an example of a first conveyance roller.
Further, as shown in FIG. 3, the paper transport device 70 includes a stepping motor 64 (an example of a second driving motor), a stepping motor control unit 10, a gear 63, a DC motor 65 (an example of a first driving motor), A clutch 66 (an example of a connecting means) is provided.

A conveyance path 30 for conveying the paper S by a conveyance guide (not shown) is formed inside the image forming unit 3. The conveyance path 30 is formed in a curved shape from the sheet feeding unit 4 to the sheet discharge tray 40 provided obliquely above the sheet feeding unit 4. Along the conveyance path 30, the registration roller 61, the plurality of conveyance rollers 71 to 73, the photosensitive drum 31, the fixing roller 37, the pressure roller 38, and the paper discharge roller 74 are arranged. .
The conveyance path 30 includes a curved path 30A that curves upward from the sheet feed roller 41 of the sheet feeding unit 4 and an intermediate path 30B that extends rearward from the end of the curved path 30A to reach the registration roller 61. And a straight path 30 </ b> C from the registration roller 61 to the photosensitive drum 31. The transport roller 71 and the registration roller 61 are rotatably provided so that the outer peripheral surface is exposed in the transport path 30.

The transport roller 71 transports the paper S transported from the transport roller 72 to the registration roller 61 on the downstream side of the transport path 30.
As shown in FIG. 2, the transport roller 71 is disposed inside the curved path 30 </ b> A. The conveyance roller 71 is a roller pair constituted by a pair of driving rollers 71A and a driven roller 71B. The driven roller 71B is disposed to face the driving roller 71A and is in contact with the driving roller 71A.

The drive roller 71 </ b> A is connected to the DC motor 65 through the clutch 66. When the clutch 66 is in a connected state, the driving roller 71A is rotated by driving the DC motor 65. When the clutch 66 is in the off state, the driving roller 71A does not rotate even if the DC motor 65 is driven. The driven roller 71B rotates according to the rotation of the driving roller.
The DC motor 65 is connected to the control unit 5 and is driven in accordance with a control signal output from the control unit 5.
The clutch 66 is an electromagnetic clutch provided on the rotation shaft of the transport roller 71, for example. The clutch 66 is connected to the controller 5 and is connected or disconnected according to a switching signal (ON signal or OFF signal) output from the controller 5. As a result, the drive transmission path from the DC motor 65 to the transport roller 71 is cut off or connected at the output timing of the switching signal. In other words, the clutch 66 connects the drive transmission path between the shaft of the drive roller 71A and the shaft of the DC motor 65 at a predetermined reference timing. When the clutch 66 is turned on or off by the control unit 5, transmission and non-transmission of the driving force of the DC motor 65 are switched, and the rotation driving of the transport roller 71 is controlled.
Each of the other transport rollers 72, the transport roller 73, and the paper discharge roller 74 has the same configuration as the transport roller 71 and is driven by the DC motor 65 via the clutch 66.

The registration roller 61 is connected to the stepping motor 64 through the gear 63. When the stepping motor 64 is driven and the driving force is transmitted, the registration roller 61 is rotationally driven. As a result, the sheet S that has reached the registration roller 61 can be transported downstream in the transport direction of the transport path 30.
The registration roller 61 is a roller pair including a pair of driving rollers 61A and a driven roller 62B. The driven roller 62B is disposed to face the driving roller 61A and is in contact with the driving roller 61A. The drive roller 61 </ b> A is connected to the stepping motor 64 through the gear 63 and is rotated by driving the stepping motor 64. The driven roller 61B rotates according to the rotation of the driving roller 61A.
The stepping motor 64 is a 1-2 phase excitation type, and is connected to the registration roller 61 via the gear 63, and a pulse signal (an example of a drive signal) input from the stepping motor control unit 10 described later. The registration roller 61 is driven in synchronism with the above. The stepping motor 64 is not limited to a 1-2 phase excitation type stepping motor. In other words, the stepping motor 64 only needs to be capable of switching between transmission and non-transmission of driving force to the registration roller 61 by driving and stopping driving.

  The stepping motor control unit 10 is connected to the control unit 5, and the stepping motor control unit 10 controls the stepping motor 64 based on the control signal sent from the control unit 5. The configuration of the stepping motor control unit 10 will be described later.

The tip detection sensor 67 is provided in the intermediate path 30B.
The tip detection sensor 67 is provided on the upstream side of the conveyance path 30 with respect to the registration roller 61. The leading edge detection sensor 67 is for detecting the leading edge of the sheet S conveyed toward the registration roller 61 from the upstream side of the conveyance path 30 (the end on the downstream side of the conveyance path 30). The tip detection sensor 67 is used for a purpose of determining the timing for rotationally driving the registration roller 61. In other words, it is used for determining a set time (hereinafter referred to as “registration time”) that is a time required for a registration operation performed on the paper S by the registration roller 61. The leading edge detection sensor 67 is, for example, a reflective phototransistor that can detect the paper S passing through the intermediate path 30B. Alternatively, a detector that is displaced according to the passage of the paper S and a transmission type phototransistor whose optical path is blocked or transmitted according to the displacement of the detector may be combined. It should be noted that any configuration may be used as long as it can detect the passing position of the leading edge of the sheet S conveyed through the intermediate path 30B.

<Driving start timing of registration roller 61 and transport roller 71>
Next, the drive start timing of the registration roller 61 and the transport roller 71 will be described with reference to FIG. FIG. 7 is a timing chart showing the relationship between the coupling of the clutch 66 by the controller 5 and the start of driving of the stepping motor 64.

In the paper conveyance device 70, the registration roller 61 for performing a registration operation (also referred to as registration) on the paper S is provided. Here, the registration operation means that the sheet S is conveyed by the conveying roller 71 or the like, and the leading edge of the sheet S is abutted against the nip portion of the registration roller 61 that is stopped. It is an operation for applying a conveyance force. By performing this registration operation, the skew of the sheet S being conveyed is corrected. Further, it is possible to align the image forming position on the paper S and the transfer position of the image transferred to the paper S.
When the registration operation is performed, the sheet S is bent before the registration roller 61. When the sheet S is bent by a predetermined amount, the driving of the transport roller 71 is stopped. Specifically, the clutch 66 is disconnected and the rotational driving force of the DC motor 65 is not transmitted. In the paper conveying device 70, the clutch 66 is disconnected at a timing at which this bending does not become excessively large. After the registration operation, the registration roller 61 and the conveyance roller 71 are rotated at a predetermined timing, and the sheet S is conveyed to the downstream side of the conveyance path 30.
Here, after the registration operation is performed, an appropriate interval between the drive start timing of the upstream conveying roller 71 and the drive start timing of the downstream registration roller 61 is defined as a time ts. The time ts is a time during which the paper S is not pulled or bent excessively.
If the interval from when the upstream conveying roller 71 starts driving to when the downstream registration roller 61 starts driving is longer than the time ts (time ta), the sheet S Deflection becomes excessively large. In this case, the bent portion of the paper S collides with the guide surface of the transport path 30 and a collision sound is generated that makes the user feel uncomfortable.
Conversely, when the interval from when the upstream conveying roller 71 starts driving to when the downstream registration roller 61 starts driving is shorter than the time ts (time tb), the sheet S The pulling force becomes excessively large. In this case, the load during conveyance of the paper S temporarily increases, and the paper S may be damaged or the registration roller 61 may step out.
Therefore, in the paper transport device 70, the control unit 5 performs a timing adjustment process described later in order to set the drive start timing of the registration roller 61 and the drive timing of the transport roller 71 to the time ts. .

<Schematic configuration of stepping motor control unit 10>
Next, the general function of the stepping motor control unit 10 will be described with reference to FIG. FIG. 4 is a block diagram showing a configuration of the stepping motor control unit 10.
The stepping motor control unit 10 includes a drive circuit 55, a voltage detection circuit 56, a comparison unit 57, an ASIC 59, and the like, and controls the stepping motor 64. The stepping motor control unit 10 is connected to the control unit 5, and the stepping motor control unit 10 controls the stepping motor 64 based on a control signal sent from the control unit 5.
The image reading sheet conveyance control program stored in the ROM 52 of the control unit 5 executes a current setting process and a stepping motor control process, which will be described later, executed by the control unit 5 and the stepping motor control unit 10. A stepping motor control program (see FIG. 5) is included. The ASIC 59 is a circuit for converting an analog signal and a digital signal. Specifically, the ASIC 59 converts the digital drive control signal ref_sig output from the control unit 5 into an analog signal (voltage signal) drive signal RefIn and outputs the converted signal to the drive circuit 55. The ASIC 59 converts the comparison result signal CmpOut of the analog signal output from the comparison unit 57 into a comparison signal cmp_sig of a digital signal, and outputs it to the control unit 5. The drive signal RefIn and the comparison result signal CmpOut will be described later.

  The drive circuit 55 sequentially outputs and excites a pulse signal to the excitation coils (first excitation coil 81 and second excitation coil 82) of each phase of the stepping motor 64 according to the control of the control unit 5. The stepping motor 64 is driven. Specifically, an external enable signal ENB_sig, a clock CLK_sig, and the drive signal RefIn are input to the drive circuit 55, and the stepping motor 64 is controlled based on these signals. The drive circuit 55 changes the amount of current supplied to the stepping motor 64 according to the voltage level of the drive signal RefIn input from the ASIC 59. That is, the drive signal RefIn is a voltage signal for setting (changing) the amount of current that the drive circuit 55 supplies to the stepping motor 64. The amount of current supplied to the stepping motor 64 is determined by the voltage level of the drive signal RefIn. Hereinafter, the voltage level of the drive signal RefIn set by the controller 5 is referred to as a set voltage value Vc. The amount of current supplied from the drive circuit 55 to the stepping motor 64 when the drive signal RefIn is input is referred to as a set current amount Ic.

  In this embodiment, when the voltage level of the drive signal RefIn is a voltage level corresponding to a drive torque required when the stepping motor 64 is in a steady state to be described later, the stepping motor 55 outputs the stepping signal. The amount of current supplied to the motor 64 is defined as a first current amount Is (see FIG. 6). That is, at this time, the voltage level of the drive signal RefIn is set so that the set current amount Ic becomes the first current amount Is. Here, the steady state is a driving that generates a driving torque having a necessary and sufficient magnitude with respect to the transport load when the stepping motor 64 transports the paper P while maintaining a predetermined rotational speed. It is a state. In the present embodiment, in order to suppress the power consumption of the stepping motor 64 as much as possible, the current amount obtained by multiplying the average current amount (average current amount) required when transporting the paper P by the safety coefficient is the first amount. The steady state of the stepping motor 64 is realized by supplying the first current amount Is to the stepping motor 64. In the present embodiment, when a load (overload) that cannot maintain the steady state is applied to the stepping motor 64, the control unit 5 detects the load value of the overload in a current setting process described later. Then, the control unit 5 changes the set current amount Ic supplied to the stepping motor 64 from the first current amount Is to a current amount that generates a driving torque larger than the overload.

  The voltage level of the drive signal RefIn is switched by the CPU 51 at a predetermined timing. Specifically, every time a 3-bit internal counter (see FIG. 6) provided in the CPU 51 counts the rising edge of the clock CLK_sig eight times, the CPU 51 switches the drive control signal ref_sig for a period of one clock. As described above, the drive control signal ref_sig is converted into the drive signal RefIn by the ASIC 59. Therefore, in the present embodiment, as shown in FIG. 6, the CPU 51 sets the timing at which the drive control signal ref_sig is switched without supplying current to the first excitation coil 81 of the stepping motor 64. The internal counter is set so as to coincide with the timing at which current is supplied only to the exciting coil 82. Specifically, in the timing chart of the switching timing in FIG. 6, the drive control signal ref_sig is switched at switching timings T51, T52, T53,. In FIG. 6, when the rising edge of the clock CLK_sig is repeatedly counted from 1 to 8, it is switched to Low when the count value of the internal counter is 1 and switched to High when the count value is 2 to 8. The timing chart of timing is shown.

  Further, during the period in which the drive signal RefIn is switched (period in which the switching timing in FIG. 6 is Low), the control unit 5 executes a current setting process described later in order to detect a load applied to the stepping motor 64. In the current setting process, the control unit 5 detects an electromotive force Vr generated in the first excitation coil 81 using a period in which no current is supplied to the first excitation coil 81 of the stepping motor 64. The load applied to the stepping motor 64 is detected based on the electromotive force Vr. As described above, when detecting the load applied to the stepping motor 64, the control unit 5 detects the control mode of the stepping motor 64 by the stepping motor control unit 10 so that the load applied to the stepping motor 64 can be detected. Switch to mode. In the present embodiment, during the detection mode, the drive signal RefIn having a voltage level corresponding to the detection mode is output to the drive circuit 55. Hereinafter, the voltage level set by the drive signal RefIn output to the drive circuit 55 in the detection mode is referred to as a detection voltage value Vd. That is, the set voltage value Vc is set to the detected voltage value Vd by the control unit 5 in the detection mode. Further, when the voltage level of the drive signal RefIn is the detected voltage value Vd, the amount of current supplied from the drive circuit 55 to the stepping motor 64 is defined as a detected current amount Id. That is, at this time, the voltage level of the drive signal RefIn is set to the detected voltage value Vd so that the set current amount Ic becomes the detected current amount Id. The detected voltage value Vd is a voltage level equal to or lower than the set voltage value Vc in a period in which the drive signal RefIn is not switched (period in which the switching timing in FIG. 6 is High), and the detected current amount Id is The current value is equal to or less than the set current amount Ic. That is, in the period in which the drive signal RefIn is switched, the control unit 5 supplies the detected current amount Id that is equal to or less than the current amount of the set current amount Ic when the switching timing is High to the stepping motor 64. The

  In the detection mode, since no current is supplied to the first excitation coil 81 of the stepping motor 64, no drive voltage is applied from the drive circuit 55 to the first excitation coil 81. However, a current is supplied to the second exciting coil 82 of the stepping motor 64. Therefore, the electromotive force Vr is generated in the first exciting coil 81 by the rotational driving of the stepping motor 64.

The clock CLK_sig is a pulse waveform signal having a frequency of 1 kHz to 3 kHz. The clock CLK_sig is input to the CPU 51, the ASIC 59, and the driving circuit 55, and is used to synchronize processing timings by the CPU 51, the ASIC 59, and the driving circuit 55, that is, to synchronize. Signal. The clock CLK_sig is used as a timing signal for counting up the internal counter.
The external enable signal ENB_sig is input to the CPU 51, the ASIC 59, and the drive circuit 55 when the entire MFP 100 is activated. Here, the activation of the multifunction peripheral 100 is when the main power is turned on or when the MFP 100 returns from the sleep mode. By inputting the external enable signal ENB_sig, the current value set by the drive signal RefIn is changed to the first current amount Is that is an initial value. That is, when the MFP 100 is activated, the first current amount Is is set as an initial value of the amount of current supplied to the stepping motor 64 regardless of the load state of the stepping motor 64.

  The drive circuit 55 has a current output terminal OUT1A and a current output terminal OUT1B, and these terminals are connected to the first excitation coil 81 of the stepping motor 64. A current is supplied from the current output terminal OUT1A and the current output terminal OUT1B to the first excitation coil 81 of the stepping motor 64. Similarly, the drive circuit 55 has a current output terminal OUT2A and a current output terminal OUT2B, and these terminals are connected to the second excitation coil 82 of the stepping motor 64. A current is supplied to the second exciting coil 82 of the stepping motor 64 from the current output terminal OUT2A and the current output terminal OUT2B.

  As shown in FIG. 6, the current supplied to the first excitation coil 81 and the current supplied to the second excitation coil 82 are currents having the same amplitude and period, although the timing is different. Specifically, at a certain timing, a current is supplied to both the first excitation coil 81 and the second excitation coil 82, and at another timing, which of the first excitation coil 81 and the second excitation coil 82 is selected. Current is supplied to only one of them. As described above, in the detection mode, the detection current amount Id lower than the set current amount Ic set corresponding to the load is supplied to the stepping motor 64. In the present embodiment, a period in which the drive signal RefIn is switched (a period in which the switching timing is Low) is a period in which current is supplied only to the second excitation coil 82. That is, the drive circuit 55 supplies the detected current amount Id only to the second excitation coil 82 during the period when the switching timing is Low. During the period when the switching timing is Low, no current is supplied to the first excitation coil 81. Therefore, if the voltage of the first excitation coil 81 is detected, the first excitation coil caused by the load applied to the stepping motor 64 is detected. An electromotive force generated in the coil 81 can be obtained. In the detection mode, by setting the detection current amount Id to be a current amount lower than the set current amount Ic, an electromotive force caused by a load lower than an electromotive force caused by a load corresponding to the set current amount Ic. Electric power can be obtained.

  The voltage detection circuit 56 detects the voltage value Vin of the current output terminal OUT1A of the stepping motor 64 and outputs the detected voltage value Vin to the comparison unit 57. The voltage value Vin detected by the voltage detection circuit 56 is a voltage between both ends of the first exciting coil 81, that is, a voltage between the current output terminal OUT1A and the current output terminal OUT1B. The voltage value Vin detected by the voltage detection circuit 56 includes two voltages. Specifically, when a drive voltage is applied to the first excitation coil 81, the drive voltage is included in the voltage value Vin, and the stepping motor 64 is loaded to apply the load. When the electromotive force Vr is generated in the first excitation coil 81, the electromotive force Vr is included in the voltage value Vin. However, as described above, since the first excitation coil 81 is not excited during the period when the switching timing is Low, the load generated in the first excitation coil 81 when the stepping motor 64 is loaded. Only the electromotive force Vr is detected as the voltage value Vin. In this embodiment, paying attention to the fact that the electromotive force Vr increases as the load applied to the stepping motor 64 increases, and the electromotive force Vr decreases as the load decreases, the period when the switching timing is Low. The control unit 5 determines the change in the load value applied to the stepping motor 64 based on the change in the voltage value Vin (that is, the electromotive force Vr). The voltage detection circuit 56 implements the detection means of the present invention.

  The comparison unit 57 compares the voltage value Vin detected by the voltage detection circuit 56 with a predetermined set value electromotive force Vrc (an example of a threshold value) and a detection electromotive force Vrd (an example of a threshold value). It is. The comparison unit 57 can be realized by, for example, a plurality of operational amplifiers and logic elements. Here, the set value electromotive force Vrc is the first excitation coil 81 when a load equivalent to the driving torque of the stepping motor 64 when the set current amount Ic is supplied is applied to the stepping motor 64. Is a voltage value corresponding to the electromotive force generated in step (b). The detection electromotive force Vrd is an electromotive force generated in the first excitation coil 81 of the stepping motor 64 by setting the set current amount Ic supplied to the stepping motor 64 to the detected current amount Id. It was obtained by measuring in advance.

  The set value electromotive force Vrc is a voltage value that is higher by one or more steps than the detection-time electromotive force Vrd. In the present embodiment, as specific examples of the set value electromotive force Vrc and the detection-time electromotive force Vrd, a plurality of threshold values determined in advance as a first voltage value Vs, a voltage value V1, a voltage value V2, and The voltage value V3 is used. Among these threshold values, the smallest threshold value is the first voltage value Vs, which is set to a larger voltage value in the order of the voltage value V1, the voltage value V2, and the voltage value V3. Each threshold value (each voltage value) is set so that the voltage difference becomes equal. In the following, for convenience of explanation, changing from a low threshold value to the next higher threshold value is referred to as raising one step, and changing from a higher threshold value to the next lower threshold value is referred to as lowering one step. In other words, increasing the level by one means changing the threshold value from the first voltage value to the voltage value V1, for example. To lower by one step means to change the threshold value from the voltage value V3 to the voltage value V2, for example.

  In the comparison unit 57 shown in FIG. 4, voltage values V1 to V1 corresponding to the current amount supplied to the stepping motor 64 by the drive circuit 55 from the first voltage value Vs corresponding to the first current amount Is. It compares with the value to voltage value V3. The comparison unit 57 outputs the comparison result signal CmpOut to the ASIC 59 as a comparison result between the voltage value Vin and the detected electromotive force Vrd (each of the first voltage value Vs to the voltage value V3). The ASIC 59 converts the comparison result signal CmpOut, which is an analog signal, into the comparison signal cmp_sig, which is a digital signal, and outputs it to the control unit 5. Specifically, four signal lines corresponding to the detected electromotive force Vrd (each of the first voltage value Vs to the voltage value V3) are allocated to the comparison result signal CmpOut. The comparison unit 57 compares the voltage value Vin with each of the first voltage value Vs to the voltage value V3. When the voltage value Vin is large, the corresponding signal line is set to High, and the voltage value Vin Is low, the corresponding signal line is set to Low. The ASIC 59 converts the comparison result signal CmpOut to the comparison signal cmp_sig that is a binary digital signal and outputs the comparison signal cmp_sig to the control unit 5. Here, the first voltage value Vs corresponds to the driving torque of the stepping motor 64 when the first current amount Is is supplied in the steady state. Specifically, the first voltage value Vs is the electromotive force generated in the first excitation coil 81 when a load equivalent to the driving torque of the stepping motor 64 in the steady state is applied to the stepping motor 64. It is set to a value corresponding to Vr. The load when the set value electromotive force Vrc is the voltage value V1 is a load equivalent to the driving torque when the amount of current supplied to the stepping motor 64 is the current amount I1. Similarly, the load when the set value electromotive force Vrc is the voltage value V2 is a load equivalent to the driving torque when the amount of current supplied to the stepping motor 64 is the current amount I2. The load when the set value electromotive force Vrc is the voltage value V3 is a load equivalent to the driving torque when the amount of current supplied to the stepping motor 64 is the amount of current I3.

<Electromotive force acquisition process>
The electromotive force acquisition process executed in step S6 of the timing adjustment process described later will be described.
Hereinafter, the electromotive force acquisition process executed by the control unit 5 will be described with reference to the flowchart of FIG. 5 and the timing chart of FIG. FIG. 5 is a flowchart showing an example of the procedure of the electromotive force acquisition process executed by the control unit 5.
This electromotive force acquisition process is a process executed when the control unit 5 executes the timing adjustment process in the paper transport apparatus 70. In the flowchart of FIG. 5, steps S21, S22,... Represent processing procedure (step) numbers. FIG. 6 is a timing chart illustrating the timing at which the control unit 5 changes the amount of current supplied to the stepping motor 64 in response to a change in load.
Further, in the following description, as shown in FIG. 6, counting from the rising clock at the timing when the current value to the first exciting coil 81 becomes zero (see switching timings T51, T52... In FIG. 6). The stepping motor control process is executed periodically every control cycle, with 8 clocks as one cycle (hereinafter referred to as “control cycle”). In the following description, the low period of the switching timing corresponds to one clock of the timing when the current value to the first exciting coil 81 becomes zero (see switching timings T51, T52,... In FIG. 6). It is assumed that it is set to.

(Step S21)
First, in step S21, the control unit 5 determines whether it is a switching timing based on the count value output from the internal counter. The control unit 5 continues to wait until the switching timing is reached (NO side of S21). If it determines with it being the said switch timing, the said control part 5 will transfer a process to step S2 (YES side of S21). In the present embodiment, the switching timing is the timing of the eighth clock from the first clock in the control cycle (see switching timings T51, T52, T53... In FIG. 6).

  As described above, the control unit 5 executes the current setting process only for a period of one clock within a period of eight clocks of the clock CLK_sig. If an overload exceeding the steady state has occurred, the drive circuit 55 supplies the set current amount Ic to obtain a drive torque that can withstand the overload. However, due to the influence of the drive torque, It cannot be detected that the load has returned to the steady state load. Therefore, the control unit 5 switches the voltage level of the drive signal RefIn and switches the current amount from the set current amount Ic to the detected current amount Id for a period of one clock of the clock CLK_sig when the switching timing becomes Low. Change to In a short period of one clock, even if the detection current amount Id that is insufficient for that period is supplied when an overload occurs, the operation of the stepping motor 64 is not greatly affected, and the rotation speed is reduced. Nothing happens. Even if the detected current amount Id is continuously supplied, a driving torque that can withstand the overload cannot be obtained.

(Step S22)
Next, in step S22, the control unit 5 changes the drive control signal ref_sig to switch the voltage level of the drive signal RefIn output from the ASIC 59 from the set voltage value Vc to the detected voltage value Vd. Specifically, the control unit 5 performs the above operation at the rising timing (see T51, T51, T52,... In FIG. 6) of the eighth clock from the first clock in the control cycle. The drive control signal ref_sig is changed to change the voltage level of the drive signal RefIn from the set voltage value Vc to the detected voltage value Vd. In the present embodiment, the control unit 5 shifts to the detection mode only for a period of one clock of the clock CLK_sig. As described above, the detection mode is a period in which no current flows between the current output terminal OUT1A and the current output terminal OUT1B of the drive circuit 55, and the drive circuit 55 is connected to the stepping motor 64. The amount of current supplied to the second exciting coil 82 is changed to the detected current amount Id that is one step lower than the set current amount Ic.

(Step S23)
In step S <b> 23, the control unit 5 detects the comparison signal cmp_sig that is a comparison result of the comparison unit 57 input from the ASIC 59. At this time, the control unit 5 acquires information on whether or not the load applied to the stepping motor 64 can be withheld by the detected current amount Id that is one step lower than the set current amount Ic. Accordingly, the control unit 5 can detect the electromotive force Vr having a voltage value equal to or higher than the detection-time electromotive force Vrd generated by the detected current amount Id that is lower by one or more steps than the set current amount Ic. . The control unit 5 detects when the output of the comparison signal cmp_sig is stable in order to prevent erroneous detection.
In step S23, the control unit 5 extracts only the comparison signal cmp_sig in the detection mode, and the voltage value Vin (that is, the electromotive force Vr) in the detection mode according to the comparison signal cmp_sig in the period. Is determined.
Here, the steps S22 and S23 correspond to an example of detection means for detecting the electromotive force Vr of the load applied to the stepping motor 64 being driven.

  In this manner, the amount of current supplied to the second excitation coil 82 of the stepping motor 64 is changed to the detected current amount Id during a period in which no current is supplied to the first excitation coil 81 of the stepping motor 64. The electromotive force Vr is detected. Since the electromotive force Vr varies depending on the load applied to the stepping motor 64, the control unit can be compared with the electromotive force Vr without affecting the driving torque of the stepping motor 64. 5 can detect the fluctuation of the load with high accuracy.

<Timing chart of stepping motor control unit 10>
Next, referring to FIG. 6, the control unit 5 changes the electromotive force Vr according to the comparison signal cmp_sig that is the comparison result of the comparison unit 57, that is, the load applied to the stepping motor 64. The fluctuation will be described.

First, as shown in FIG. 6, during the period when the switching timing is Low, no current flows between the current output terminal OUT1A and the current output terminal OUT1B of the drive circuit 55, and the current output terminal This is a period in which current flows only through OUT2A and the current output terminal OUT2B. During this period, drive torque is generated only by the excitation of the second excitation coil 82 of the stepping motor 64.
In FIG. 6, the electromotive force Vr can be measured by detecting the voltage value Vin during a period when the switching timing is Low. Therefore, only the electromotive force Vr in the period is shown in the timing chart.
Further, the voltage value Vin when the switching timing is High is for supplying a current value by the voltage value due to the electromotive force Vr generated in the first exciting coil 81 and the current output terminal OUT1A and the current output terminal OUT1B. Is a voltage value that is combined with the voltage value applied to, and fluctuates periodically. In the present embodiment, for convenience of explanation, the voltage value Vin and the electromotive force Vr during the period when the switching timing is High are not shown in the timing chart. In the timing chart of FIG. 6, periods t01, t02,... Represent the numbers of periods in which the value of the switching timing is low.

(Period t01)
In the period t01, the stepping motor 64 is overloaded. At this time, the electromotive force Vr generated at the current output terminal OUT1A is the same as the voltage value V2, and is detected by the voltage detection circuit 56 and input to the comparison unit 57. The comparison unit 57 compares the set value voltage value Vc (the first voltage value Vs) and the detected electromotive force Vrd (the first voltage value Vs) with the electromotive force Vr (the voltage value V2). The result signal CmpOut is output to the ASIC 59. The ASIC 59 converts the comparison result signal CmpOut to the comparison signal cmp_sig and outputs it to the control unit 5. Thereby, the control unit 5 includes the electromotive force Vr (the voltage value V2), the set value voltage value Vc (the first voltage value Vs), and the detection electromotive force Vrd (the first voltage value Vs). Can be determined. In the period t01, the control unit 5 overloads the stepping motor 64 because the electromotive force Vr (the voltage value V2) is larger than the set value voltage value Vc (the first voltage value Vs). It is determined that That is, the control unit 5 can recognize that the paper S sandwiched between the registration roller 61 and the transport roller 71 is pulled. In this case, in order to eliminate the tension, the control unit 5 determines that the reference timing needs to be delayed according to the comparison signal cmp_sig. Further, the control unit 5 changes the amount of current that the drive circuit 55 supplies to the stepping motor 64 to the amount of current I2. Thereby, the control unit 5 prevents the stepping motor 64 from stepping out.

(Period t02)
In the period t02, as in the period t01, the stepping motor 64 is overloaded. The electromotive force Vr generated at the current output terminal OUT1A is the same as the voltage value V2, and is detected by the voltage detection circuit 56 and input to the comparison unit 57. The comparison unit 57 compares the electromotive force Vr (the voltage value V2) with the set value voltage value Vc (the first voltage value Vs) and the detected electromotive force Vrd (the first voltage value Vs). The result signal CmpOut is output to the ASIC 59. The ASIC 59 converts the comparison result signal CmpOut to the comparison signal cmp_sig and outputs it to the control unit 5. In the period t02, the controller 5 determines that the stepping motor 64 is overloaded because the electromotive force Vr (the voltage value V2) is larger than the first voltage value Vs in the steady state. To do. The controller 5 determines that the reference timing needs to be delayed according to the comparison signal cmp_sig. Further, the control unit 5 maintains the amount of current supplied to the stepping motor 64 as the amount of current I2.

(Period t03)
In the period t03, the stepping motor 64 is overloaded lower than the period t2. The electromotive force Vr generated at the current output terminal OUT1A is the same as the voltage value V1, and is detected by the voltage detection circuit 56 and input to the comparison unit 57. The comparison unit 57 outputs the set value electromotive force Vrc (the voltage value V2) and the comparison result signal CmpOut of the detected electromotive force Vrd (the voltage value V1) and the electromotive force Vr to the ASIC 59. The ASIC 59 converts the comparison result signal CmpOut to the comparison signal cmp_sig and outputs it to the control unit 5. In the period t03, the control unit 5 determines that the stepping motor 64 is overloaded because the electromotive force Vr (the voltage value V1) is larger than the first voltage value Vs in the steady state. To do. The controller 5 determines that the reference timing needs to be delayed according to the comparison signal cmp_sig. The control unit 5 changes the amount of current that the drive circuit 55 supplies to the stepping motor 64 to the amount of current I1.

(Period t04)
In the period t04, the steady load Ts is applied to the stepping motor 64. The electromotive force Vr generated at the current output terminal OUT1A is the same as the first voltage value Vs, and is detected by the voltage detection circuit 56 and input to the comparison unit 57. The comparison unit 57 outputs to the ASIC 59 the comparison result signal CmpOut of the set value electromotive force Vrc (the voltage value V1) and the detected electromotive force Vrd (the first voltage value Vs) and the electromotive force Vr. To do. The ASIC 59 converts the comparison result signal CmpOut to the comparison signal cmp_sig and outputs it to the control unit 5. Thereby, the control unit 5 can determine the magnitude relationship between the electromotive force Vr and the first voltage value Vs. In the period t04, the control unit 5 determines that the steady state load is applied to the stepping motor 64 because the voltage value Vr is equal to the first voltage value Vs. That is, the control unit 5 can recognize that no tension or the like has occurred in the paper S sandwiched between the registration roller 61 and the transport roller 71. The controller 5 determines that the reference timing needs to be maintained according to the comparison signal cmp_sig. The controller 5 changes the amount of current that the drive circuit 55 supplies to the stepping motor 64 to the first amount of current Is.

<Consolidation timing adjustment processing>
Hereinafter, the procedure of the connection timing adjustment process executed by the control unit 5 will be described with reference to the flowchart of FIG. FIG. 8 is a flowchart showing an example of the connection timing adjustment process of the clutch 66 executed by the control unit 5. In the flowchart of FIG. 8, steps S1, S2,... Represent processing procedure (step) numbers.
Here, the control unit 5 when executing the connection timing adjustment processing corresponds to the timing changing means according to the present invention. The connection timing adjustment process is executed when an adjustment instruction is input from the operation display unit 6, when a predetermined time has elapsed, and when a predetermined number of sheets S are conveyed.
The connection timing adjustment process is an adjustment method in which the load is reduced (the delay time is increased) from the state in which the paper S is pulled.

(Step S1)
First, in step S1, the control unit 5 sets a delay time TA. The delay time TA is an interval time from when the clutch control signal for controlling connection / disconnection of the clutch 66 is turned ON to when the stepping motor 64 is started to be driven. The delay time TA is a time that is determined so that the paper S sandwiched between the registration roller 61 and the transport roller 71 is pulled, and is determined in consideration of variations in the characteristics of the clutch 66.

(Step S2)
In step S <b> 2, the control unit 5 performs a preprocess for performing the connection timing adjustment process. In the preprocessing, the control unit 5 transports only one sheet S, performs the registration operation, and keeps the leading edge of the sheet S against the nip portion of the registration roller 61 that is stopped. At S, the driving of the DC motor 65 is stopped and the clutch 66 is disengaged.

(Step S3)
Next, in step S3, the controller 5 turns on the clutch control signal for controlling the clutch 66 after the DC motor 65 is driven. When the clutch control signal is turned on, the driving force of the DC motor 65 is transmitted to the transport roller 71. Due to the characteristics of the clutch 66, after the clutch control signal is turned on, the transport roller 71 until the driving force is transmitted to the DC motor 65.

(Step S4)
In step S4, the control unit 5 determines whether or not the delay time TA has elapsed. The control unit 5 continues to wait until the delay time TA has elapsed (NO side of S4).
On the other hand, if it determines with the said delay time TA having passed, the said control part 5 will transfer a process to step S5 (YES side of S4). As described above, the delay time TA is adjusted by the control unit 5 so that the paper S is not pulled.

(Step S5)
Next, in step S5, the controller 5 drives the stepping motor 64. As a result, the sheet S sandwiched between the registration roller 61 and the transport roller 71 is transported to the downstream side of the transport path 30.

(Step S6)
In step S6, the control unit 5 acquires the electromotive force Vr generated in the stepping motor 64 from the stepping motor control unit 10 by the electromotive force acquisition process. As described above, the voltage level of the electromotive force Vr changes according to the load applied to the registration roller 61. Therefore, the control unit 5 can determine whether or not a load is applied to the registration roller 61 based on the electromotive force Vr.

(Step S7)
In step S7, the control unit 5 determines whether or not the electromotive force Vr generated in the stepping motor 64 by the stepping motor control unit 10 is larger than a predetermined second threshold value (an example of a second load). . If it determines with the said electromotive force Vr being below the said 2nd threshold value, the said control part 5 will transfer a process to step S8 (NO side of S7).
On the other hand, if it determines with the said electromotive force Vr being larger than the said 2nd threshold value, the said control part 5 will transfer a process to step S71 (YES side of S7).
An appropriate load setting value (an example of a setting value) corresponding to the driving torque of the stepping motor 64 to which a predetermined amount of current is supplied is determined. The second threshold value is an upper limit value of the set value, and the control unit 5 adjusts the timing to be longer so that the load is lighter than the second threshold value.

(Step S8)
Next, in step S8, the control unit 5 adds a margin time tm to the delay time TA. The margin time tm is a time determined so that the paper S sandwiched between the registration roller 61 and the transport roller 71 is not excessively bent or pulled. By adding the margin time tm to the delay time TA, it is possible to prevent the paper S from being pulled or bent due to a change in the timing at which the paper S is transported or a load.

(Step S9)
Next, in step S9, the control unit 5 maintains the driving of the registration roller 61 and the transport roller 71, discharges the sandwiched paper S to the paper discharge tray 40, and ends the processing. . The control unit 5 prepares for a normal image forming process in a state where there is no sheet S in the transport path 30.

(Step S71)
If it is determined in step S7 that the electromotive force Vr is greater than or equal to the second threshold value (YES side of S7), in step S71, the control unit 5 adds the unit delay time td to the delay time TA. Is added. The unit delay time td is a unit time for increasing the delay time TA, and is about 5 to 10 percent of the delay time TA.
Here, the control unit 5 and the stepping motor control unit 10 that execute the processing of each procedure according to the step S7 and the step S71, the electromotive force Vr detected by the stepping motor control unit 10 and the stepping motor 64. This corresponds to an example of a control unit that compares the predetermined second threshold with respect to the second threshold and changes the timing at which the clutch 66 is engaged according to the comparison result. In other words, the control unit 5 quickly changes the timing at which the clutch 66 is engaged when the electromotive force Vr detected by the stepping motor control unit 10 is smaller than the second threshold value. In this way, the delay time TA is increased by the unit delay time td, and the timing is adjusted so that proper deflection occurs in the paper S sandwiched between the registration roller 61 and the transport roller 71.

(Step S72)
In step S72, as in step S9, the control unit 5 maintains the driving of the registration roller 61 and the transport roller 71 and discharges the sandwiched paper S to the paper discharge tray 40. The process proceeds to step S2. The control unit 5 prepares for the connection timing adjustment process again in a state where there is no sheet S in the transport path 30.

<Effect of embodiment>
As described above, according to the paper transport device 70 of the present invention, the connection timing of the clutch 66 that is connected to drive the transport roller 71 on the upstream side of the transport path 30 and the downstream of the transport path 30. The drive start timing of the registration roller 61 on the side can be adjusted to an appropriate timing. That is, it is possible to adjust the clutch 66 to be connected at a timing that does not cause pulling by the registration roller 61 or excessive bending due to excessive conveyance of the conveyance roller 71.

<Modification of Embodiment>
In the description of the embodiment, the delay time TA is adjusted in the direction of increasing, but the present invention is not limited to this.
For example, it is conceivable to determine a standard delay time TS and adjust the timing so that the delay time TS is increased or decreased.
Here, what is different from the embodiment is a processing procedure (see FIG. 9) for controlling the control unit 5. Since other parts are common to the configuration and processing of the first embodiment, only different parts will be described here, and description of the common parts will be omitted. In the modification of the embodiment, the stepping motor control unit 10 has a function of detecting a difference between the electromotive force Vr and a set value.

<Timing adjustment processing>
Hereinafter, the procedure of the second connection timing adjustment process executed by the control unit 5 will be described with reference to the flowchart of FIG. FIG. 9 is a flowchart illustrating an example of the second connection timing adjustment process of the clutch 66 executed by the control unit 5. In the flowchart of FIG. 9, steps S11, S12,... Represent processing procedure (step) numbers.
Here, the control unit 5 when executing the second connection timing adjustment processing corresponds to the control means according to the present invention. The connection timing adjustment process is executed in response to an adjustment instruction input from the operation display unit 6.
The second connection timing adjustment process is an adjustment method in which the delay time is increased or decreased depending on the load applied to the paper S.

(Step S11)
First, in step S11, the control unit 5 sets a delay time TS. The delay time TS is an interval time from when a clutch control signal for controlling connection and disconnection of the clutch 66 is turned on to when driving of the stepping motor 64 is started. The delay time TS is an average time during which the sheet S sandwiched between the registration roller 61 and the transport roller 71 can be appropriately bent.

(Step S12)
In step S12, the control unit 5 performs a pre-process for performing the second connection timing adjustment process in the same manner as in step S2. In the preprocessing, the control unit 5 transports only one sheet S, performs the registration operation, and keeps the leading edge of the sheet S against the nip portion of the registration roller 61 that is stopped. At S, the driving of the DC motor 65 is stopped and the clutch 66 is disengaged.

(Step S13)
Next, in step S13, the control unit 5 turns on the clutch control signal for controlling the clutch 66 after the DC motor 65 is driven.

(Step S14)
In step S14, the control unit 5 determines whether or not the delay time TS has elapsed. The control unit 5 continues to wait until the delay time TS has elapsed (NO side of S14).
On the other hand, if it determines with the said delay time TS having passed, the said control part 5 will transfer a process to step S15 (YES side of S14).

(Step S15)
Next, in step S <b> 15, the control unit 5 drives the stepping motor 64. As a result, the sheet S sandwiched between the registration roller 61 and the transport roller 71 is transported to the downstream side of the transport path 30.

(Step S16)
In step S16, the control unit 5 acquires the electromotive force Vr generated in the stepping motor 64 from the stepping motor control unit 10 by the electromotive force acquisition process.

(Step S17)
In step S17, the control unit 5 determines whether or not the electromotive force Vr generated in the stepping motor 64 by the stepping motor control unit 10 is smaller than a predetermined first threshold value (an example of a first threshold value). judge. If it determines with the said electromotive force Vr being smaller than the said 1st threshold value, the said control part 5 will transfer a process to step S18 (YES side of S17).
On the other hand, if it determines with the said electromotive force Vr not being smaller than the said 1st threshold value, the said control part 5 will transfer a process to step S73 (NO side of S17).
The first threshold value is a lower limit value of the installation value, and the control unit 5 adjusts the timing so that the load becomes heavier than the first threshold value.

(Step S18)
In step S18, the control unit 5 corrects the delay time TS so as to shorten it, and shifts the processing to step S19.
For example, contrary to the first embodiment, the control unit 5 subtracts the unit delay time td from the delay time TS until the appropriate deflection occurs, from Step S11 to Step S18 and later described. Step S19 is repeated. In other words, the control unit 5 quickly changes the timing at which the clutch 66 is engaged when the electromotive force Vr detected by the stepping motor control unit 10 is smaller than the first threshold value. That is, the timing can be adjusted in the opposite direction to the first embodiment.
Further, the electromotive force Vr detected by the stepping motor control unit 10 is compared with the appropriate time electromotive force Vrs when appropriate deflection occurs due to the sheet S sandwiched between the stepping motors 64. The control unit 5 changes the delay time TS connected to the clutch 66 to be short according to the difference between the electromotive force Vr and the appropriate time electromotive force Vrs. In this case, the control unit 5 measures the relationship between the length of the delay time based on the difference between the electromotive force Vr and the appropriate time electromotive force Vrs, and stores it in the ROM 52 in advance.
Thereby, the sheet conveying device 70 can finish the second connection timing adjustment process in a short time.

(Step S73)
If it is determined in step S17 that the electromotive force Vr is greater than or equal to the first threshold value (NO side of S17), in step S73, the control unit 5 causes the stepping motor control unit 10 to perform the stepping. It is determined whether or not the electromotive force Vr generated in the motor 64 is larger than the predetermined second threshold value. If it determines with the said electromotive force Vr being larger than the said 2nd threshold value, the said control part 5 will transfer a process to step S74 (YES side of S73).
On the other hand, if it determines with the said electromotive force Vr not being larger than the said 2nd threshold value, the said control part 5 will transfer a process to step S19 (NO side of S73). The control unit 5 is in a state where the coupling timing of the clutch 66 and the driving timing of the stepping motor 64 are adjusted within an appropriate range.

(Step S74)
In step S74, the control unit 5 corrects the delay time TS in the direction of increasing the time, and shifts the process to step S19.
For example, as in the first embodiment, the control unit 5 subtracts the unit delay time td from the delay time TS until the appropriate deflection occurs, from Step S11 to Step S17, Step S73. And Step S74 is repeated.
Further, the electromotive force Vr detected by the stepping motor control unit 10 is compared with the appropriate time electromotive force Vrs when an appropriate deflection is caused by the sheet S sandwiched between the stepping motors 64. The control unit 5 changes the delay time TS connected to the clutch 66 longer according to the difference between the electromotive force Vr and the appropriate time electromotive force Vrs. Thereby, the sheet conveying device 70 can finish the second connection timing adjustment process in a short time.

(Step S19)
In step S19, the control unit 5 maintains the driving of the registration roller 61 and the transport roller 71, discharges the sandwiched paper S to the paper discharge tray 40, and ends the processing. The control unit 5 prepares for a normal image forming process in a state where there is no sheet S in the transport path 30.

  As described above, according to the modified sheet conveying apparatus 70, the adjustment time can be shortened by starting the delay time for starting the timing adjustment from the average delay time TS.

<Other application examples>
In the description of the first embodiment, the image forming unit 3 including the paper transport device 70 has been described. However, the present invention is not limited to this example. For example, the paper transport device 70 can be applied to the ADF 2. In this case, the image reading unit 1 reads the image of the sheet P conveyed by the ADF 2.

As shown in FIG. 1, the ADF 2 includes the feeding mechanism 22, the registration roller 23 </ b> A (an example of a second transport roller), the plurality of transport rollers 23 </ b> B to 23 </ b> D, the paper discharge roller 23 </ b> E, and the like. Of the inside. In addition, a transport path 20 for transporting the paper P by a transport guide (not shown) is formed inside the ADF 2. The transport path 20 is formed by the feeding mechanism 22, the registration rollers 23A, the plurality of transport rollers 23B to 23D, and the paper discharge rollers 23E from the paper tray 21 to the paper discharge unit 25 provided below the paper tray 21. It is formed to bend in a horizontal U shape.
The feeding mechanism 22 includes a pickup roller 22A (an example of the first transport roller), a driving roller 22B, a driven roller 22C, the paper feeding belt 22D, and the separation roller 22E.
The control unit 5 adjusts the connection timing of a clutch (not shown) coupled to the pickup roller 22A and the drive start timing of the registration roller 23A.
As described above, the sheet conveying device 70 can be applied to the ADF 2.

In the description of the embodiment of the present invention, the sheet conveying device 70 directly detects the load value of the stepping motor 64, but the present invention is not limited to this.
For example, the paper transport device 70 is provided with an encoder that detects a step-out in the registration roller 61, and the control unit 5 determines whether or not the step-out occurs in the registration roller 61.
Then, the control unit 5 always sets the delay time set at the start of the connection timing adjustment process to a time when step-out occurs. The control unit 5 increases the delay time by the connection timing adjustment process, and sets the delay time at which the step-out does not occur until the stepping motor 64 is driven after the clutch 66 is connected. It can be considered.

100: MFP 1: Image reading unit 2: ADF
3: Image forming unit 4: Paper feeding unit 5: Control unit 6: Operation display unit 10: Stepping motor control unit 30: Transport path 31: Photoconductor drum 32: Charging device 33: LSU
34: Development device 35: Transfer roller 36: Static elimination device 37: Fixing roller 38: Pressure roller 51: CPU
52: ROM
53: RAM
54: EEPROM
55: Drive circuit 56: Voltage detection circuit 57: Comparison unit 59: ASIC
61: Registration roller 63: Gear 64: Stepping motor 65: DC motor 66: Clutch 67: Tip detection sensor 70: Paper transport devices 71 to 73: Transport roller 74: Paper discharge roller P, S: Paper

Claims (7)

A first conveying roller provided in a sheet conveying path;
A first drive motor for supplying a driving force to the first transport roller;
Connecting means for connecting the drive transmission path between the first drive motor and the first transport roller at a predetermined reference timing;
A second transport roller provided on the downstream side of the sheet transport direction in the transport path from the first transport roller;
A second drive motor for driving the second transport roller to rotate by being driven in synchronization with an input drive signal;
Detecting means for detecting a load value of a load applied to the second drive motor being driven;
Timing changing means for comparing the load value detected by the detecting means with a preset value for the load of the second drive motor and changing the reference timing of the connecting means according to the comparison result; ,
A sheet conveying apparatus comprising:   The sheet conveying apparatus according to claim 1, wherein the control unit changes the reference timing of the coupling unit according to a difference between the load value detected by the detection unit and the set value.   The sheet conveying apparatus according to claim 1, wherein the set value corresponds to a driving torque of the second driving motor supplied with a predetermined amount of current. The set value has a lower limit value and an upper limit value larger than the lower limit value,
The control means advances the reference timing of the connecting means when the load value detected by the detection means is smaller than the lower limit value, and the load value detected by the detection means exceeds the upper limit value. The sheet conveying apparatus according to claim 3, wherein the reference timing of the connecting unit is delayed when the value is larger. An instruction means for receiving an input of an adjustment instruction for adjusting the timing of connection by the connecting means;
5. The sheet conveying apparatus according to claim 1, wherein the timing changing unit changes the reference timing of the connecting unit in response to an input of the adjustment instruction to the instruction unit. A sheet conveying device according to any one of claims 1 to 5,
Image reading means for reading an image of a sheet conveyed by the sheet conveying device;
An image reading apparatus comprising: A sheet conveying device according to any one of claims 1 to 5,
Image forming means for forming an image on a sheet conveyed by the sheet conveying device;
An image forming apparatus comprising:

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