JP2011064837A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that reduces the size of the apparatus by simplifying its structure. <P>SOLUTION: When a first-side printed medium on which an image is formed by an image forming section 9, turns on the detection signal of an ejection sensor 19, counting of time t1 is started using a timer. When the counted time t1 does not fall within a preset time range S or when the ejection sensor 19 remains on even when the time elapses beyond the time range S, a determination is made that a jam has occurred. When the counted time t1 falls within the time range S, counting of time t2 is started using another timer. When the counted time t2 does not fall in a preset time range T or when a paper feed sensor 6 is not turned on even when the time elapses beyond the time range T, it is determined that a jam has occurred in the middle of conveyance of the first-side printed medium in the direction of return. When the first-side printed medium passes through a conveyance path 30 within the time range T and the paper feed sensor 6 is turned on, printing on the second side of the first-side printed medium is controlled. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a conveyed medium.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer, a copier, a facsimile machine, or a multi-function machine including a printer unit and a scanner unit, after printing on one side of a print medium, the print medium is reversed and printed on the other side. Some print on both sides.
When performing double-sided printing in an image forming apparatus, an image is formed on the first surface of a printing medium such as paper in an image forming unit that forms an image, and then the conveyance direction of the medium is reversed to print the medium on both sides. A technique is disclosed in which an image is formed on a second surface again by an image forming unit (for example, see Patent Document 1).

  Therefore, it is necessary to determine the medium conveyance state in the medium conveyance path toward the return direction. In the medium conveyance path toward the return direction, the sensor lever that tilts by contacting the medium and the operation of the sensor lever By using a sensor that detects the presence of a medium, a medium detection unit that can detect the presence or absence of the medium has been provided.

Japanese Patent Laid-Open No. 2002-60091

  However, the above-described method requires a tilting amount of the sensor lever and a space for installing the sensor, and the structure of the double-sided printing apparatus or image forming apparatus in which such a medium detection unit is installed is complicated and the accompanying apparatus volume. There is a problem that the size of the apparatus cannot be reduced due to the increase in the number of devices.

  An object of the present invention is to provide an image forming apparatus capable of simplifying the structure and reducing the size of the apparatus in order to solve the above-described problems.

  In order to achieve the above object, an image forming apparatus according to one aspect of the present invention is an image forming apparatus that forms an image on a medium, and is fed by a sheet feeding unit that feeds the medium and the sheet feeding unit. An image forming unit that forms an image on a recording medium, a transport direction of the medium on which the image is formed by the image forming unit, a discharge direction in which the image is formed from the main body of the image forming apparatus, and a reflux direction that is different from the discharge direction. A direction reversing mechanism for switching, a first medium detecting unit provided in a conveying path upstream of the medium reversing direction from the direction reversing mechanism, and a second medium provided in a conveying path of the medium conveyed in the return direction When the medium conveyance direction is switched to the return direction by the detection unit and the direction reversal mechanism, the second medium detection unit detects the medium on which the image is formed by the image forming unit and then the second medium detection unit. The medium detection unit detects the medium. Characterized by comprising a determination section for conveying state of the medium on the basis of the time until the knowledge.

  According to another aspect of the present invention, there is provided an image forming apparatus for forming an image on a medium, wherein the image forming apparatus forms an image on a sheet fed by the sheet feeding unit and a sheet fed by the sheet feeding unit. And a direction reversing mechanism that switches the conveyance of the medium on which the image is formed by the image forming unit between a discharge direction for discharging from the main body of the image forming apparatus and a return direction for conveying to the paper feeding unit. A first medium detection unit provided in a conveyance path upstream of the direction reversing mechanism in the medium conveyance direction, and a second medium for detecting that the medium conveyed in the reflux direction has been conveyed to the paper feeding unit. When the medium conveyance direction is switched to the return direction by the medium detection unit and the direction reversing mechanism, the second medium detection unit detects the medium after the first medium detection unit detects the medium. Media transport based on the time to Characterized by comprising a determination unit for determining status.

  According to the present invention, it is possible to provide an image forming apparatus capable of simplifying the structure and reducing the size of the apparatus.

1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram illustrating a schematic configuration of a control unit that controls the image forming apparatus according to the first embodiment. It is a figure which shows schematic structure of a rotation direction reverse rotation mechanism. It is a figure which shows schematic structure of a rotation direction reverse rotation mechanism. It is a timing chart of each sensor at the time of conveying the 1st page printed medium. 6 is a flowchart for explaining a printing operation of the image forming apparatus. It is a flowchart for demonstrating the control operation | movement which conveys a 1st surface printed medium to an image formation part. It is sectional drawing which shows schematic structure of the image forming apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows schematic structure of the control part which controls the image forming apparatus which concerns on a 2nd Example. It is a timing chart of each sensor at the time of conveying the 1st page printed medium. 4 is a flowchart for explaining a printing operation of the image forming apparatus. It is a flowchart for demonstrating the control operation | movement which conveys the 1st surface printed medium to a paper feed cassette.

Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.
(First embodiment)
In describing the first embodiment of the present invention, first, the configuration of an image forming apparatus represented by a printer will be described with reference to FIG.
FIG. 1 is a cross-sectional view illustrating an overall configuration and a schematic configuration of main components of an image forming apparatus 1 according to the first embodiment of the present invention.

The image forming apparatus 1 includes a paper feed cassette 2 for setting a medium (paper for printing) and a paper feed roller for feeding the medium one by one in pairs with a separation piece 3 provided in the paper feed cassette 2. 4 is provided. A medium feeding path 5 provided downstream of the sheet feeding roller 4 is provided with a sheet feeding sensor 6 that detects that the medium has been fed.
Downstream of the paper feed sensor 6, a registration roller 7 and a pressure roller 8 for correcting the skew of the medium, a transfer roller 10 for transferring a toner image to the medium in a pair with a removable image forming unit 9, and a static based on the print data. A print head 11 for forming an electrostatic latent image and a passage sensor 12 for detecting timing for starting the formation of a toner image are provided.

The image forming unit 9 includes a photosensitive drum 13 that forms a toner image, a charging roller 14 that negatively charges the photosensitive drum 13, and a developing roller 15 that develops the electrostatic latent image into a toner image. .
The image forming apparatus 1 includes a fixing unit 18 having a heat roller 16 and a backup roller 17 for performing a high-temperature and high-pressure fixing process on a toner image transferred onto a medium, and a discharge for detecting a medium to be discharged after the high-temperature and high-pressure fixing process. A sensor 19, a face-up discharge roller 21 and a driven roller 22 that convey the medium to the discharge conveyance path 20, and a discharge roller 24 and a driven roller 25 that discharge the medium to a discharge stacker 23 provided in the upper part of the image forming apparatus 1 are provided. A discharge unit 26 is provided.

In addition, although mentioned later in detail, the discharge roller 24 and the driven roller 25 can switch the rotation direction.
The discharge conveyance path 20 also serves as a return path during double-sided printing, that is, a medium path for re-conveying to the image forming unit 9 in order to perform printing on the second side of the medium on which printing on the first side has been completed. Yes.
At the time of duplex printing, the medium on which the toner image formed on the first surface is fixed by the fixing unit 18 passes through the discharge conveyance path 20 and is discharged halfway by the discharge roller 24 and the driven roller 25. The medium is conveyed in the direction opposite to the discharge direction (return direction) by reversing the rotation of the discharge roller 24 from the middle. A duplex printing unit 27 is provided at the tip (downstream direction) in the opposite direction.

The duplex printing unit 27 is provided with conveyance rollers 28 and 29 and a conveyance path 30 for re-conveying the medium to the image forming unit 9.
Here, the discharge sensor 19 is a first medium detection unit in the duplex printing operation, and is disposed on the upstream side in the transport direction when the medium is discharged from the discharge unit 26. The discharge sensor 19 can detect completion of fixing of the toner image on the medium and discharge of the medium from the fixing unit 18.

On the other hand, as shown in FIG. 1, the paper feed sensor 6 is transported from the paper feed cassette 2 via the medium transport path 5 and a new medium transported from the duplex printing unit 27 via the transport path 30. The first surface printed medium can be detected. That is, the paper feed sensor 6 is a second medium detection unit disposed on the image forming unit side with respect to the junction of the conveyance paths (5, 30) of both media (new medium, first-side printed medium). It is.
Note that the transport path in the return direction of the first surface printed medium in the first embodiment is a duplex printing unit 27 including a discharge unit 26, a discharge transport path 20 (opposite to the discharge direction), and transport rollers 28 and 29. The transport path 30 is provided.

FIG. 2 is a block diagram illustrating a schematic configuration of the central processing unit 50 that functions as a control unit that controls the image forming apparatus 1 illustrated in FIG. 1.
The central processing unit 50 (hereinafter referred to as CPU 50) includes a memory 52, an input / output port 53, timers 61 and 62, and a determination unit 63.
The CPU 50 is connected to the paper feed sensor 5, the passage sensor 12, the discharge sensor 19, the drive circuit 54, and the host device 60 via the input / output port 53.

The host device 60 creates a print command and print data, and transmits the created print command and print data to the image forming apparatus 1 via a communication line such as a network.
Timers 61 and 62 are further connected to the input / output port 53. When determining the transport state of the first side printed medium during duplex printing, the timer 61 starts after the first side printed medium after the leading edge of the transported first side printed medium reaches the discharge sensor 19. The time t1 until the end of the end of passing over the discharge sensor 19 is measured. On the other hand, the timer 62 measures the time t2 from when the trailing edge of the first side printed medium has passed over the discharge sensor 19 to when the first side printed medium reaches the paper feed sensor 6. The timers 61 and 62 output the respective timing results to the determination unit 63. The determination unit 63 determines the conveyance state of the first-side printed medium at the time of duplex printing from the timing results of the timers 61 and 62.

The CPU 50 forwards the first side printed medium from the fixing unit 18 to the discharge conveyance path 20 at time t1, and reversely feeds the first side printed medium from the discharge unit 26 to the discharge conveyance path 20 at time t2. To control. Switching of the conveyance direction under the control of the CPU 50 is performed by a rotation direction reversing mechanism which will be described later.
The determination unit 63 includes a time range S required from the time when the leading edge of the first side printed medium reaches the discharge sensor 19 to the time when the trailing end of the medium finishes passing through the discharge sensor 19, and the first side printed A time range T necessary for the medium to reach the paper feed sensor 6 after the rear end of the medium has passed through the discharge sensor 19 is set in advance.
The time ranges S and T are determined in advance based on the medium conveyance speed in the image forming apparatus 1 and are stored in the memory 52 in the CPU 50.

A main motor 55, a paper feed motor 56, a registration motor 57, and a solenoid 58 are connected to the drive circuit 54.
The main motor 55 includes the photosensitive drum 13, the charging roller 14, the developing roller 15, the transfer roller 10, the heat roller 16, the backup roller 17, the face-up discharge roller 21, the driven roller 22, the discharge roller 24, and the image forming unit 9. The driven roller 25 is rotated.

  The paper feed motor 56 rotates the paper feed roller 4 of the paper feed cassette 2. The registration motor 57 rotates the registration roller 7 and the pressure roller 8 that remove the skew of the medium (paper) fed from the paper feed cassette 2. The solenoid 58 drives a rotation direction reverse mechanism (described later) provided to be connected to the discharge roller 24.

<Description of rotation direction reversal mechanism>
3 and 4 are diagrams showing a schematic configuration of a rotation direction reversing mechanism 70 provided to be connected to the discharge roller 24. FIG.
The rotation direction reversing mechanism 70 has a driving gear 71 coupled to the main motor 55 (see FIG. 2), idle gears 72 and 73 that receive the driving force meshed with the driving gear 71, and the idle gear 73 as the sun gear. The planetary gear 74 and the discharge roller 24 (illustrated by a two-dot chain line in FIGS. 3 and 4) are connected to rotate the discharge roller 24, the reverse gear 76 meshed with the moved planetary gear 74, and the reverse gear 76. , And idle gears 77 and 78 to which driving force is transmitted.

Further, the rotation direction reversing mechanism 70 is rotatably held at one end about the rotation shaft of the idle gear 73 and is connected to the pin 58a of the solenoid 58 by holding the planetary gear 74 rotatably at the other end. A switch arm 79 and a spring 80 for urging the switch arm 79 in a predetermined direction.
With such a configuration, when the solenoid 58 drives the pin 58a when the current is turned on (electromagnetically attracted), the switch arm 79 rotates and the planetary gear 74 meshes with the reverse gear 76 (see FIG. 4). When the solenoid 58 releases the drive of the pin 58a by turning off the current, the switch arm 79 is rotated by the pullback force of the spring 80, and the planetary gear 74 is engaged with the discharge roller gear 75 (see FIG. 3).

The mechanism operation of the rotation direction reversing mechanism 70 will be described in more detail.
The drive gear 71 is connected to the main motor 55 via a drive mechanism (not shown), and is rotated in one direction of an arrow A shown in FIG. When the solenoid 58 is turned off, the planetary gear 74 meshes with the discharge roller gear 75, and the discharge roller 24 connected to the discharge roller gear 75 conveys the medium in the forward direction, that is, in the direction of arrow B shown in FIG. A rotating driving force is transmitted.

  On the other hand, when the solenoid 58 is turned on and the pin 58a moves (drives) in the direction of arrow D shown in FIG. 4, the switch arm 79 rotates in the direction of arrow E, and the planetary gear 74 meshes with the reverse gear 76. The discharge roller gear 75 rotates in the reverse direction through the reverse gear 76 and the idle gears 77 and 78 and rotates in the direction of arrow F shown in FIG. As a result, the discharge roller 24 connected to the discharge roller gear 75 is rotated in the direction (arrow F direction) in which the discharge roller 24 is conveyed to the duplex printing unit 27 opposite to the normal direction in which the medium is discharged.

<Discharge roller and rotation direction reverse mechanism>
Next, the control operation of the discharge roller 24 and the rotation direction reverse mechanism 70 will be described with reference to FIGS.
FIG. 3 shows a gear train when the discharge roller 24 rotates in the direction of discharging the medium.

The drive gear 71 receives power through the main motor 55 and a drive mechanism (not shown), rotates counterclockwise (direction A), and transmits power to the planetary gear 74 through the idle gears 72 and 73. .
Since the planetary gear 74 meshes with the discharge roller gear 75, the discharge roller gear 75 rotates counterclockwise (direction B), and the discharge roller 24 connected to the discharge roller gear 75 rotates in the direction of discharging the medium. It is done. The engagement of the planetary gear 74 with the discharge roller gear 75 is held by the spring 80 pulling the switch arm 79 connected to the pin 58a of the solenoid 58.

FIG. 4 shows the gear train when the discharge roller 24 rotates in the reverse direction (the direction in which the medium is conveyed to the duplex unit 27) opposite to the direction in which the medium is discharged.
When performing duplex printing, the medium printed on the first surface is not discharged, but the discharge roller 24 is rotated in the middle of discharging the medium to transport the medium in the direction opposite to the discharge direction. At that time, the rotation direction reversing mechanism 70 is used.

  First, when the discharge sensor 19 detects the trailing edge of the first-side printed medium, the solenoid 58 is turned on at a timing described later to drive the pin 58a. When the pin 58 a is driven, the switch arm 79 is rotated, and the planetary gear 74 provided on the switch arm 79 is engaged with the reverse gear 76. As a result, the power is transmitted to the discharge roller gear 75 via the reverse gear 76 and the idle gears 77 and 78, and rotates clockwise (F direction). As a result, the discharge roller 24 connected to the discharge roller gear 75 rotates to convey the first surface printed medium in the reflux direction opposite to the discharge direction (F direction).

  The solenoid 58 is kept on until the medium passes between the discharge roller 24 and the driven roller 25, and then turned off. When the solenoid 58 is turned off, the planetary gear 74 is pulled back to the position shown in FIG. 3 by the spring 80 connected to the switch arm 79 and meshes with the discharge roller gear 75. As a result, the discharge roller 24 connected to the discharge roller gear 75 returns to the forward rotation for discharging the medium (direction B shown in FIG. 3).

  FIG. 5 is a diagram illustrating a timing chart of each sensor when the first-side printed medium is conveyed during duplex printing. When the first side printed medium reaches the discharge sensor 19, the timer 61 waits for a time t <b> 1 from when the leading edge of the medium reaches the discharge sensor 19 until the trailing edge of the medium finishes passing through the discharge sensor 19. Start timing. When the trailing edge of the medium finishes passing the discharge sensor 19, the timer 62 waits for a time t <b> 2 from when the trailing edge of the medium finishes passing the discharge sensor 19 until the medium reaches the paper feed sensor 6. Start timing.

  When the time t3 has elapsed since the trailing edge of the first-side printed medium has passed through the discharge sensor 19, the solenoid 58 is turned on and the drive of the pin 58a is started. The time t3 is the time from when the trailing edge of the first-side printed medium has passed through the discharge sensor 19 to when the trailing edge of the medium reaches the discharge conveyance path 20.

The solenoid 58 is in a current-on state, so that a time t <b> 4 from when the current-on state starts driving the pin 58 a until the medium passes between the discharge roller 24 and the driven roller 25 has elapsed. Until it is done. When the time t4 has elapsed, the solenoid 58 is turned off.
Note that the times t3 and t4 are determined in advance based on the conveyance speed of the medium in the image forming apparatus 1 and stored in the memory 52 in the CPU 50.

<Description of printing operation>
Next, the printing operation on the medium P in the image forming apparatus 1 in such a configuration will be described with reference to the flowchart of FIG.
When a power switch (not shown) is turned on, the CPU 50 initializes and then warms up (S1), and waits for a print command from the host device 60 (S2).

When the CPU 50 receives a print command and print data from the host device 60 (S2: Yes), the CPU 50 stores the print data in the memory 52, and drives the main motor 55 via the drive circuit 54 to start the print operation ( S3).
The CPU 50 drives the paper feed motor 56 via the drive circuit 54 to rotate the paper feed roller 4, and feeds the medium P placed on the paper feed cassette 2 by the separation piece 3 and the paper feed roller 4. Paper is made (S4).

When one medium P fed in step S4 reaches the paper feed sensor 6 (detection signal ON), the CPU 50 controls printing (first surface) on the fed medium P (S5).
First, the registration motor 57 is driven to rotate the registration roller 7 and the pressure roller 8, and the conveyed medium P contacts the registration roller 7 to remove the skew. Subsequently, when the conveyed medium P passes through the passage sensor 12 (detection signal is turned on), toner image formation in the image forming unit 9 is started.

  The toner image is formed in the image forming unit 9 as follows. First, the surface of the rotating photosensitive drum 13 is negatively charged by the charging roller 14. When a negatively charged portion of the surface of the photosensitive drum 13 comes under the print head 11, the print head 11 exposes the surface of the photosensitive drum 13 based on the print data stored in the memory 52. In this way, an electrostatic latent image is formed on the exposed portion of the surface of the photosensitive drum 13. This electrostatic latent image is developed by the developing roller 15 and a toner image is formed on the surface of the photosensitive drum 13.

The CPU 50 applies a voltage to the transfer roller 10 and transfers the toner image on the photosensitive drum 13 onto the medium P conveyed by the transfer roller 10.
Then, the CPU 50 performs a high-temperature and high-pressure fixing process on the toner image on the medium P conveyed using the heat roller 16 and the backup roller 17 of the fixing unit 18. Thereby, printing on the medium P (first surface) is completed.
When the medium P on which the toner image is fixed by the fixing unit 18 is detected by the discharge sensor 19 (detection signal ON), the CPU 50 discharges along the discharge conveyance path 20 using the face-up discharge roller 21 and the driven roller 22. The medium P is conveyed in the direction of the unit 26.

When single-sided printing is performed by the print command of the host device 60 (S6: Yes), the CPU 50 discharges the medium P to the discharge stacker 23 using the discharge roller 24 and the driven roller 25 (S7).
If the print command of the host device 60 includes a command to execute printing continuously (S8: Yes), the CPU 50 moves the process to step S4 and continues print control. Further, when the print command of the host device 60 includes a command to end printing (S8: No), the CPU 50 ends the print control.

When double-sided printing is executed in step S6 according to the print command of the host device 60 (S6: No), the CPU 50 describes the medium P printed on the first side (hereinafter referred to as the first side printed medium P). ) Is executed to invert the first side printed medium P and convey it to the image forming unit 9 (S9).
When the first side printed medium P reaches the paper feed sensor 6 (detection signal is turned on) in the transport control in step S9, the CPU 50 controls printing on the second side of the first side printed medium P (S10). ). Note that the printing control in step S10 is the same as the printing control in step S5, and thus description thereof is omitted.

When the printing control in step S10 is completed and the double-sided printed medium P on which the first side and the second side have been printed is detected by the discharge sensor 19 (detection signal on), the CPU 50 and the face-up discharge roller 21 are driven. The double-side printed medium P is conveyed along the discharge conveyance path 20 using the roller 22 in the direction of the discharge unit 26, and the double-side printed medium P is discharged to the discharge stacker 23 using the discharge roller 24 and the driven roller 25. (S7).
If the print command of the host device 60 includes a command to execute printing continuously (S8: Yes), the CPU 50 moves the process to step S4 and continues print control. Further, when the print command of the host device 60 includes a command to end printing (S8: No), the CPU 50 ends the print control.

Next, in step S9, the control operation of the CPU 50 for transporting the first side printed medium P to the image forming unit 9 will be described with reference to the flowchart of FIG.
First, the CPU 50 checks (detects) whether or not the first-side printed medium P has reached the discharge sensor 19 (S11). When the first-side printed medium P has not reached the discharge sensor 19 (S11: No), the CPU 50 continues the detection state of the medium arrival by the discharge sensor 19. When the first-side printed medium P reaches the discharge sensor 19 (detection signal ON) (S11: Yes), the CPU 50 starts measuring time t1 using the timer 61 (S12).
During this time, the first-side printed medium P is transported to the discharge unit 26 along the discharge transport path 20.

  When the time t1 counted in step S12 is not within the preset time range S, or when the time exceeding the time range S elapses, the trailing edge of the first-side printed medium P passes through the discharge sensor 19. If not finished (the detection signal of the discharge sensor 19 remains on. S13: No), the determination unit 63 determines that a jam has occurred in the discharge unit 26. When the determination unit 63 determines that a jam has occurred in the discharge unit 26, the CPU 50 performs control to display “discharge jam” on a display unit (not shown) (S14), and interrupts the print control.

When the measured time t1 is within the time range S (S13: Yes), the CPU 50 starts measuring the time t2 using the timer 62 (S15).
At the same time, when the trailing edge of the first-side printed medium P has passed through the discharge sensor 19, that is, when the detection signal of the discharge sensor 19 is turned off, the CPU 50 stores the time previously stored in the memory 52. The timing of t3 is started with a built-in timer (not shown), and when the time t3 has elapsed, the solenoid 58 is turned on. As a result, the discharge unit 26 starts reverse rotation in the middle of discharging the first-side printed medium P by the rotation direction reversing mechanism 70. The first-side printed medium P that has been discharged halfway by the discharge unit 26 is conveyed in the reverse conveyance path 20 and further conveyed to the conveyance path 30 via the duplex printing unit 27.

In addition, after the elapse of time t3, the CPU 50 starts counting the time t4 stored in the memory 52 in advance with an internal timer (not shown), and turns off the solenoid 58 when the time t4 elapses. . As a result, the discharge unit 26 rotates in the forward direction (discharge direction).
If the time t2 counted in step S15 is not within the preset time range T, or the time exceeding the time range T has elapsed, the leading edge of the first-side printed medium P reaches the paper feed sensor 6. When the detection signal is not turned on (S16: No), the determination unit 63 determines that the first-side printed medium P is in a jam occurrence state during conveyance in the reflux direction. When the determination unit 63 determines that a jam has occurred in the middle of conveyance in the return direction, the CPU 50 performs control to display “jam in the return direction” on the display unit (not shown) (S17), and interrupts the print control. .

  When the first side printed medium P reaches the paper feed sensor 6 via the conveyance path 30 within the time range T (detection signal ON) (S16: Yes), the CPU 50 determines the first side printed medium P. Control printing on the second side (shift to step S10).

  As described above, according to the first embodiment of the present invention, when performing double-sided printing, the discharge sensor 19 and the paper feed sensor 6 used when performing single-sided (first side) printing are used. In addition, it is possible to detect the occurrence of a jam while the first side printed medium is being conveyed in the reflux direction, and it is not necessary to provide a medium detection unit for double-sided printing in the medium conveyance path toward the reflux direction. The internal structure can be simplified. Therefore, the image forming apparatus can be downsized.

  In the description of the first embodiment, double-sided printing is executed for each medium. However, when double-sided printing is continuously performed on a plurality of media, printing of the first side of the first sheet is performed. It is also possible to carry out control so that the medium after the transfer is conveyed to the duplex printing unit and at the same time the second new medium is conveyed to the image forming unit. As a result, it is possible to shorten the entire printing time in the double-sided printing of a plurality of sheets. However, it is necessary to automatically discharge the paper in the duplex printing unit during the warm-up operation after releasing the jam. The CPU 50 functioning as a control unit can manage which medium is the first-side printed medium or the new medium by managing the printing order. For example, when performing double-sided printing, the CPU 50 realizes such management by recognizing a medium that is undergoing single-sided printing as a new medium and a medium that is undergoing double-sided printing as a first-side printed medium. it can.

(Second Embodiment)
FIG. 8 is a cross-sectional view showing an overall configuration and a schematic configuration of main components of an image forming apparatus 1A according to the second embodiment of the present invention. The same parts as those of the image forming apparatus 1 shown in FIG. The image forming apparatus 1A also includes a rotation direction reversing mechanism 70 shown in FIGS.
The image forming apparatus 1 </ b> A includes an auxiliary paper feed roller 81, a retard roller 82, a conveyance path 83 for returning a single-sided (first side) printed medium to the paper feed cassette 2 when performing double-sided printing, and the paper feed cassette 2. A sensor 84 is provided above the paper feed cassette 2 as a second medium detection unit for detecting the returned medium.

  In the second embodiment, the paper feed roller 4 uses a retard system having an auxiliary paper feed roller 81 and a retard roller 82. The paper feed roller 4 in the first embodiment is a separation piece system using the separation piece 3, but in this system, if the frictional force between the media placed in the paper feed cassette 2 is not constant, double feeding is performed.・ Non-feed may occur frequently. In the second embodiment, as will be described in detail later, since the first-side printed media having different frictional force states are fed, the frictional force between the media placed in the paper feed cassette 2 is constant. The retard method allows normal feeding even without it.

  A re-feed roller 85 is provided above the paper feed cassette 2 so as to be movable up and down. The re-feed roller 85 is a roller that moves from the upper side to the lower side and feeds the one-side printed medium conveyed to the uppermost surface of the medium placed in the paper feed cassette 2 toward the auxiliary paper feed roller 81. . The refeed roller 85 is configured to include a torque limiter and the like so that the moving mechanism is idled when a load is applied during the downward movement.

The medium conveyance path in the reflux direction in the second embodiment includes the discharge unit 26, the conveyance path 83, the paper feed cassette 2, the auxiliary paper feed roller 81, the retard roller 82, and the paper feed roller 4. .
The sensor 84 is attached to detect that the single-sided printed medium has returned to the paper feed cassette 2, but is placed in the paper feed cassette 2 using the paper feed mechanism of the paper feed cassette 2. A part of the sensor that detects the medium being used may be used.

FIG. 9 is a diagram showing a schematic configuration of a central processing unit 50A that controls the image forming apparatus 1A shown in FIG. The same parts as those in the central processing unit 50 shown in FIG.
Central processing unit 50A (hereinafter referred to as CPU 50A) includes memory 52A, input / output port 53A, timers 61 and 62, and determination unit 63.
The CPU 50A receives the detection signal of the sensor 84 via the input / output port 53A, and further controls the operations of the auxiliary paper feed roller 81, the retard roller 82, the paper feed roller 4, and the refeed roller 85.

  FIG. 10 shows a timing chart of each sensor when the first-side printed medium is conveyed during double-sided printing. When the first side printed medium reaches the discharge sensor 19, the timer 61 waits for a time t <b> 1 from when the leading edge of the medium reaches the discharge sensor 19 until the trailing edge of the medium finishes passing through the discharge sensor 19. Start timing. When the trailing edge of the medium finishes passing the discharge sensor 19, the timer 62 counts the time t <b> 5 until the medium reaches the sensor 84 after the trailing edge of the medium finishes passing the discharge sensor 19. Start.

When the time t3 has elapsed after the trailing edge of the first-surface printed medium has passed through the discharge sensor 19, the solenoid 58 is turned on and the drive of the pin 58a is started. The time t3 is the time from when the trailing edge of the first-side printed medium has passed through the discharge sensor 19 to when the trailing edge of the medium reaches the discharge conveyance path 20.
The solenoid 58 is in a current-on state, so that a time t <b> 4 from when the current-on state starts driving the pin 58 a until the medium passes between the discharge roller 24 and the driven roller 25 has elapsed. Until it is done. When the time t4 has elapsed, the solenoid 58 is turned off.

The determination unit 63 includes a time range S required from the time when the leading edge of the first surface printed medium reaches the discharge sensor 19 to the time when the trailing edge of the first surface printed medium finishes passing through the discharge sensor 19, A time range U necessary for the first side printed medium to reach the sensor 84 after the trailing edge of the first side printed medium has passed through the discharge sensor 19 is set in advance.
The times t3 and t4 and the time ranges S and U are determined in advance based on the medium conveyance speed in the image forming apparatus 1A and are stored in the memory 52A in the CPU 50A.

<Description of printing operation>
Next, the printing operation on the medium P in the image forming apparatus 1A in such a configuration will be described with reference to the flowchart of FIG. The control operations of steps S1 to S8 by the CPU 50A are the same as those in the flowchart of FIG.
In step S6, when double-sided printing is executed according to the print command of the host device 60 (S6: No), the CPU 50A prints the medium P printed on the first side (hereinafter referred to as first-side printed medium P). In order to execute the printing on the second side, the first side printed medium P is reversed and conveyed to the paper feed cassette 2 (S21).

  In step S <b> 21, the CPU 50 </ b> A transports the first-side printed medium P transported again to the paper feed cassette 2 to the detection position of the sensor 84 in the paper feed cassette 2 using the refeed roller 85. The operation start timing of the re-feed roller 85 is also determined in advance from the medium conveyance speed in the image forming apparatus 1A, and is stored in the memory 52A in the CPU 50A. When the first-side printed medium P is transported to the refeed roller 85 and reaches the sensor 84 (detection signal is turned on), the CPU 50A stops the transport of the refeed roller 85.

Subsequently, the CPU 50 </ b> A feeds the first-side printed medium P conveyed to the uppermost stage of the paper feed cassette 2 to the image forming unit 9 using the auxiliary paper feed roller 81, the paper feed roller 4, and the retard roller 82. Then, the printing on the second surface of the first surface printed medium P is controlled (S22). Note that the paper feed printing control in step S22 is the same as the paper feed printing control in steps S4 and S5, and a description thereof will be omitted.
When the print control in step S23 is completed and the double-sided printed medium P on which the first and second sides have been printed is detected by the discharge sensor 19 (detection signal is turned on), the CPU 50A follows the face-up discharge roller 21 The double-side printed medium P is conveyed along the discharge conveyance path 20 using the roller 22 in the direction of the discharge unit 26, and the double-side printed medium P is discharged to the discharge stacker 23 using the discharge roller 24 and the driven roller 25. (S7).

  If the print command of the host device 60 includes a command to execute printing continuously (S8: Yes), the CPU 50A shifts the process to step S4 and continues print control. Further, when the print command of the host device 60 includes a command to end printing (S8: No), the CPU 50A ends the print control.

Next, the control operation of the CPU 50A for transporting the first side printed medium P to the paper feed cassette 2 in step S21 will be described with reference to the flowchart of FIG.
First, the CPU 50A confirms (detects) whether or not the first-side printed medium P has reached the discharge sensor 19 (S31). When the first-side printed medium P has not reached the discharge sensor 19 (S31: No), the CPU 50A continues the detection state of the medium arrival by the discharge sensor 19. When the first side printed medium P reaches the discharge sensor 19 (detection signal ON) (S31: Yes), the CPU 50A starts measuring the time t1 using the timer 61 (S32).
During this time, the first-side printed medium P is transported to the discharge unit 26 along the discharge transport path 20.

  When the time t1 measured in step S32 is not within the preset time range S, or when the time exceeding the time range S has elapsed, the trailing edge of the first-side printed medium P passes through the discharge sensor 19. If not finished (the detection signal of the discharge sensor 19 remains on. S33: No), the determination unit 63 determines that a jam has occurred in the discharge unit 26. When the determination unit 63 determines that a jam has occurred in the discharge unit 26, the CPU 50A performs control to display “discharge jam” on a display unit (not shown) (S34), and interrupts print control.

When the measured time t1 is within the time range S (S33: Yes), the CPU 50A starts measuring the time t5 using the timer 62 (S35).
At the same time, when the trailing edge of the first-side printed medium P has passed through the discharge sensor 19, that is, when the detection signal of the discharge sensor 19 is turned off, the CPU 50A stores the time previously stored in the memory 52A. The timing of t3 is started with a built-in timer (not shown), and when the time t3 has elapsed, the solenoid 58 is turned on. As a result, the discharge unit 26 starts reverse rotation in the middle of discharging the first-side printed medium P by the rotation direction reversing mechanism 70. The first-side printed medium P that has been discharged halfway by the discharge unit 26 is conveyed in the reverse direction on the discharge conveyance path 20 and further conveyed to the paper feed cassette 2 via the conveyance path 83.

In addition, after the elapse of time t3, the CPU 50A starts the time t4 stored in the memory 52A in advance with a built-in timer (not shown) and turns off the solenoid 58 when the time t4 elapses. . As a result, the discharge unit 26 rotates in the forward direction (discharge direction).
When the time t5 measured in step S35 is not within the preset time range U, or even when the time exceeding the time range U has elapsed, the leading edge of the first surface printed medium P reaches the sensor 84 (detection). When the signal is not turned on (S36: No), the determination unit 63 determines that the first-side printed medium P is in a jam occurrence state during conveyance in the reflux direction. When the determination unit 63 determines that a jam has occurred during the conveyance in the return direction, the CPU 50A performs control to display “jam in the return direction” on the display unit (not shown) (S37), and interrupts the print control. .

When the first-surface printed medium P reaches the sensor 84 via the conveyance path 83 within the time range U (detection signal on) (S36: Yes), the CPU 50A performs the second printing on the first-surface printed medium P. The start of printing on the surface is controlled (the process proceeds to step S22).
In this second embodiment, the medium is transported in the return direction toward the paper feed roller 3 using the refeed roller 85 and the auxiliary paper feed roller 81, but is fed via the transport path 83. When the first-side printed medium transported to the paper cassette 2 can be sufficiently brought into contact with the paper feed roller 4, for example, when the paper feed roller 4 and the transport path exit in the reflux direction are close to each other, or If it is larger, the first-side printed medium can be directly conveyed by the paper feed roller 4, so that the refeed roller 85, the auxiliary paper feed roller 81, or both can be deleted.

As described above, according to the second embodiment of the present invention, it is not necessary to provide a double-sided printing unit and a dedicated conveyance path for conveying the first-side printed medium. The structure in the image forming apparatus 1A can be simplified. Therefore, the image forming apparatus can be further downsized.
In the first and second embodiments of the present invention, an example applied to a printer has been described. However, an image forming apparatus such as a copier, a facsimile machine, and a multifunction machine including a printer unit and a scanner unit having the same configuration may be used. Applicable.

1,1A Image forming apparatus 2 Paper feed cassette (paper feed unit)
4 Paper feed roller 5 Medium transport path 6 Paper feed sensor (second medium detector)
9 Image forming unit 18 Fixing unit 19 Ejection sensor (first medium detection unit)
DESCRIPTION OF SYMBOLS 20 Discharge conveyance path 23 Discharge stacker 24 Discharge roller 25 Driven roller 26 Discharge part 27 Duplex printing unit 30,83 Conveyance path 50,50A Central processing unit (CPU)
52, 52A Memory 53, 53A I / O port 54 Drive circuit 55 Main motor 56 Paper feed motor 57 Registration motor 58 Solenoid 61, 62 Timer 63 Judgment unit 70 Rotation direction reverse rotation mechanism (direction reverse rotation mechanism)
81 Auxiliary paper feed roller (medium transport mechanism)
82 retard roller (medium transport mechanism)
84 sensor (second medium detection unit)
85 Re-feed roller (medium transport mechanism)

Claims (14)

In an image forming apparatus for forming an image on a medium,
A paper feeding unit for feeding the medium;
An image forming unit that forms an image on a medium fed by the paper feeding unit;
A direction reversing mechanism that switches the conveyance of the medium on which the image is formed by the image forming unit between a discharge direction of discharging from the main body of the image forming apparatus and a reflux direction different from the discharge direction;
A first medium detector provided in a transport path upstream of the direction reversing mechanism in the medium transport direction;
A second medium detection unit provided in a conveyance path of the medium conveyed in the reflux direction;
When the medium conveyance direction is switched to the return direction by the direction reversing mechanism, the second medium detection unit detects the medium on which the image is formed by the first medium detection unit. A determination unit that determines a conveyance state of the medium based on a time until the medium is detected;
An image forming apparatus comprising:   The second medium detection unit is provided on the image forming unit side from a merging point between a conveyance path of a medium conveyed in the reflux direction and a conveyance path of a medium fed from the sheet feeding unit. The image forming apparatus according to claim 1.   The determination unit includes a period of time from when the first medium detection unit detects the trailing edge of the medium on which the image is formed by the image forming unit to when the second medium detection unit detects the leading edge of the medium. 2. The image forming apparatus according to claim 1, wherein when the time exceeds a preset time, it is determined that a jam has occurred in the conveyance path in the return direction. The second medium detection unit is a paper feed sensor that detects the medium fed to the image forming unit,
The time is a time from when the first medium detection unit detects the trailing edge of the medium on which the image is formed by the image forming unit to when the second medium detection unit detects the leading edge of the medium. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided. The second medium detection unit is
The image forming apparatus according to claim 1, wherein the image forming apparatus is provided above the sheet feeding unit. The transport path in the reflux direction is the paper feeding unit,
The image forming apparatus according to claim 1, wherein the second detection unit detects that the medium has been conveyed to the sheet feeding unit. The second medium detection unit is
The image forming apparatus according to claim 6, wherein the image forming apparatus is a sensor that detects the medium placed in the paper feeding unit. In an image forming apparatus for forming an image on a medium,
A paper feeding unit for feeding the medium;
An image forming unit that forms an image on a medium fed by the paper feeding unit;
A direction reversing mechanism for switching the conveyance of the medium on which the image is formed by the image forming unit between a discharge direction of discharging from the main body of the image forming apparatus and a return direction of conveying to the paper feeding unit;
A first medium detector provided in a transport path upstream of the direction reversing mechanism in the medium transport direction;
A second medium detection unit that detects that the medium conveyed in the reflux direction is conveyed to the sheet feeding unit;
Based on the time from when the first medium detection unit detects the medium to when the second medium detection unit detects the medium when the medium conveyance direction is switched to the return direction by the direction reversal mechanism. A determination unit for determining a medium conveyance state;
An image forming apparatus comprising:   9. The time according to claim 8, wherein the time is a time from when the first medium detection unit detects the trailing edge of the medium to when the second medium detection unit detects the leading edge of the medium. The image forming apparatus described. The image forming apparatus further includes:
A conveyance path for conveying the medium on which the image is formed by the image forming unit conveyed in the reflux direction by the direction reversing mechanism to the paper feeding unit;
A medium conveying mechanism that re-feeds the medium on which the image is formed by the image forming unit conveyed to the paper feeding unit;
The image forming apparatus according to claim 8, further comprising:   In the determination unit, the time from when the first medium detection unit detects the trailing edge of the medium to when the second medium detection unit detects the leading edge of the medium exceeds a preset time. The image forming apparatus according to claim 8, wherein the image forming apparatus determines that a jam has occurred in the conveyance path in the return direction.   In the determination unit, the time from when the first medium detection unit detects the leading edge of the medium on which the image is formed by the image forming unit until the trailing edge is detected exceeds a preset time. 12. The image forming apparatus according to claim 1, wherein the image forming apparatus determines that a jam has occurred in the conveyance path in the discharge direction. The image forming apparatus further includes:
2. The apparatus according to claim 1, further comprising: a control unit that performs control to form an image on the second surface of the medium on which the image is formed on the first surface by the image forming unit in accordance with a determination result of the determination unit. The image forming apparatus according to claim 12. The first medium detection unit includes:
The image forming apparatus according to claim 1, wherein the image forming apparatus is a discharge sensor that detects the medium discharged from a main body of the image forming apparatus.

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