JP6070372B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus employing an electrophotographic system.

  As an image forming apparatus, a printer that continuously prints on both sides of a plurality of sheets is known.

  As such a printer, the paper on which the image is formed on one side is re-conveyed (switchback conveyance) into the main casing by rotating the paper discharge roller in the reverse direction, and is also applied to the other side of the paper. A printer that forms an image has been proposed (see, for example, Patent Document 1).

  In such a printer, in order to carry out switchback conveyance, there are three states: a state where the paper discharge roller and the intermediate paper discharge roller are rotated in the forward rotation direction, a state where the discharge roller is rotated in the reverse direction, and a state where the roller is not rotated. Since a dedicated motor is provided to control the state, when the printer is activated, an initial mode of the dedicated motor is set and an image forming operation is executed.

JP 2011-048328 A

  However, in Patent Document 1, since dedicated motors are provided for each of the paper discharge unit, the image forming unit, and the transport unit, the drive sounds of a plurality of motors are generated, and the drive sound of the printer may increase. There is. In order to reduce the driving noise of the printer, it has been proposed to eliminate the dedicated motor. However, if the dedicated motor is eliminated, the initial mode cannot be set by the dedicated motor, and the switchback transport is performed when the printer is started. In order to set the initial mode of the mechanism for detecting the initial mode, a member for detecting the initial mode must be added.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of setting an initial mode as a reference for control while reducing costs and noise.

(1) In order to achieve the above object, an image forming apparatus according to the present invention switches a driving source that generates a rotational driving force to one side and a conveyance direction of a recording medium on which an image is formed by an image forming unit. In addition, the switchback roller whose rotation direction can be switched between the normal rotation direction and the reverse rotation direction, and the rotational driving force to one of the drive sources is transmitted to the switchback roller so that the rotation direction of the switchback roller is the normal rotation direction. The first gear train that rotates, the second gear train that transmits the rotational driving force to one of the drive sources to the switchback roller, and the rotation of the drive source to one so that the rotation direction of the switchback roller is the reverse direction. A first mode in which driving force is transmitted to the first gear train, a second mode in which rotational driving force to one of the driving sources is transmitted to the second gear train, and a rotational driving force to one of the driving sources in the first gear Row and second gear A switching mechanism configured to be switchable to a third mode that is not transmitted to either of the columns, a first state that allows the switching mechanism to switch to the first mode or the third mode, and a second mode of the switching mechanism. Switch means for selectively changing the state to a second state permitting switching, and control means for controlling the state change between the first state and the second state of the switch means. Is configured to be switchable only to the third mode, and the control means holds the first state for controlling the switch means so as to hold the first state for the first time, and holds the second state for the second time. Thus, the second control for controlling the switch means can be executed, and by executing the second control, the switching mechanism is switched to the second mode and then switched to the first control.

  According to such a configuration, in order to switch the rotation direction of the switchback roller, it is not necessary to switch the rotational driving force of the driving source in the forward and reverse directions. Therefore, the rotation that rotates the rotating body that rotates in one direction in the image forming apparatus. The drive source that generates the drive force and the drive source that generates the rotational drive force transmitted to the switchback roller can be used as the same drive source.

  In addition, the control means selectively changes the state between a first state that allows switching of the first mode or the third mode of the switching mechanism and a second state that allows switching of the second mode of the switching mechanism. The state change of the switch means between the first state and the second state is controlled by the control means.

  Since the switching mechanism can be switched only from the second mode to the third mode, when the control mechanism is controlled by the control means to execute the image forming operation, the switching mechanism is first set to the second mode, and then If the switching mechanism is switched from the second mode to the third mode, the control reference can be set for the switching timing.

As a result, the cost and noise can be reduced, and the image forming operation can be executed using the switching mechanism from the second mode to the third mode as a control criterion.
(2) In addition, the control unit may execute the second control from when the image forming apparatus is turned on until an image is formed on the recording medium.

According to such a configuration, the switching mechanism is switched from the second mode to the third mode between the time when the image forming apparatus is turned on and the image is formed on the recording medium, and the control reference is set. Can do.
(3) Further, the control means can execute a third control for controlling the switch means so as to hold the second state for a third time shorter than the second time, and the switching mechanism can perform a third control of the control means. Before and after the first mode, the first mode and the third mode may be interchanged.

  Note that the recording medium remaining in the image forming apparatus needs to be rotated in the forward rotation direction and discharged out of the image forming apparatus before the switchback roller is rotated in the reverse direction. However, it is not possible to determine whether the switching mechanism is in the first mode or the third mode simply by setting the switch means to the first state. Before the switch mechanism is set in the second mode and the switchback roller is rotated in the reverse direction, There is a problem that the recording medium cannot be discharged out of the image forming apparatus by rotating the switchback roller in the forward direction in the first mode.

  Therefore, according to such a configuration, it is possible to execute the third control for controlling the switch means so that the second state is held for a third time shorter than the second time.

  As a result, the first mode and the third mode can be switched by executing the third control on the switching mechanism that becomes the first mode or the third mode by the first control of the control means.

  Thus, if the first control and the third control are executed before the second control is executed, the first mode can be executed without fail in the second mode.

Therefore, the recording medium can be discharged by reliably setting the switching mechanism to the first mode before the second mode and rotating the switchback roller in the forward rotation direction.
(4) Also, a discharge port that can discharge the recording medium on which the image is formed and a sensor that is provided in the middle of conveyance from the image forming unit to the discharge port and that detects the recording medium are provided. May be longer than the conveyance time of the recording medium during conveyance from the sensor to the discharge port.

  When the sensor can detect whether or not the recording medium remains in the middle of conveyance from the image forming unit to the discharge port, the recording medium is not erroneously sent and the sensor can detect that the recording medium remains. In this case, it is possible to set the switching mechanism to the second mode by executing the second control after performing an appropriate discharge process of the recording medium.

  On the other hand, when the recording medium remains on the downstream side in the conveyance direction from the sensor in the middle of conveyance from the image forming unit to the discharge port, there is a problem that the presence or absence of the recording medium cannot be detected by the sensor.

  However, according to such a configuration, regardless of the detection of the recording medium by the sensor, before the second control, the first time, which is longer than the conveyance time of the recording medium during the conveyance from the sensor to the discharge port, One mode can be executed.

Therefore, the recording medium can be reliably discharged before the switching mechanism is set to the second mode.
(5) The switch means may be a solenoid switch in which one of the excited state and the non-excited state corresponds to the first state, and the other of the excited state and the non-excited state corresponds to the second state. Good.

  According to such a configuration, since a solenoid switch can be used as the switch means, the state of the switching mechanism can be selectively changed between the first state and the second state with a simple configuration.

Therefore, the switch means having a complicated configuration is not required, and the cost can be reduced.
(6) In the solenoid switch, the non-excitation state may correspond to the first state, and the excitation state may correspond to the second state.

  In the image forming apparatus, when an image is formed only on one side of the recording medium, it is not necessary to switch the switchback roller in the reverse direction. Therefore, the switching mechanism is not switched to the second mode, but only in the first mode. An image can be formed on a recording medium.

According to such a configuration, since the first state corresponding to the first mode corresponds to the non-excited state of the solenoid switch, the solenoid switch when an image is formed only on one side surface of the recording medium. Power consumption can be suppressed.
(7) The switching mechanism includes a first meshing position that meshes with the first gear train, a second meshing position that meshes with the second gear train, and non-meshing that does not mesh with either the first gear train or the second gear train. A pendulum gear that is selectively positioned at a position, a holder that supports the pendulum gear so as to be relatively rotatable, a cam that contacts the holder and moves the holder, and a drive gear that transmits rotational driving force from a drive source, A toothless portion having a toothed portion meshed with the drive gear and a toothless portion facing the drive gear in each of the first mode, the second mode, and the third mode, and the first mode and the second mode. And in each of the third modes, a lock means for maintaining a state where the tooth missing portion and the drive gear face each other, the lock means is rotatable in conjunction with the tooth missing gear, A regulating member having a convex part, and a convex part By combining, the first engagement portion and the second engagement portion are provided, the rotation of the toothless gear can be restricted, the first engagement portion engages with the convex portion, and the second engagement A first engagement position where the joint portion does not engage with the convex portion, and a second engagement where the second engagement portion engages with the convex portion, and the first engagement portion does not engage with the convex portion. An engaging member that can move between the first engaging portion and the second engaging portion; and the first engaging portion that engages with the first engaging portion. And a second convex portion that is not engaged with the second engaging portion, the engaging member is located at the first engaging position, and the first engaging portion and the first convex portion are engaged with each other. Thus, the first mode is established, the engaging member is located at the second engaging position, and the second engaging portion and the first convex portion are engaged, so that the first mode is changed to the second mode, and the engaging member is engaged. Is located at the first engaging position, and the first engaging portion and the second convex portion are engaged. Thus, the second mode is changed to the third mode, and the switch means positions the engagement member at the first engagement position in the first state, and sets the engagement member to the second mode in the second state. You may make it located in an engagement position.

  According to such a configuration, by controlling the control means so that the switch means is in the first state, the switching mechanism is switched to the first mode, and the control means is controlled so that the switch means is in the second state. Thus, the switching mechanism can be switched from the second mode to the third mode by switching the switching mechanism from the first mode to the second mode and controlling the control means so that the switch means is in the first state.

Therefore, the first mode, the second mode, and the third mode can be switched by a simple operation of controlling the control unit so that the switch unit is in the first state or the second state.
(8) An image forming unit disposed upstream of the switchback roller in the transport direction, and a transport roller disposed upstream of the image forming unit in the transport direction and to which a rotational driving force is input from the drive source. A sheet feeding unit on which the recording medium is placed, a primary conveying path configured so that the recording medium is supplied from the conveying roller, passes through the image forming unit, and reaches the switchback roller, and the recording medium is switched back. And a secondary conveyance path configured to merge upstream from the image forming unit of the primary conveyance path with respect to the conveyance direction, and the control unit performs double-sided image formation processing for forming an image on the recording medium. The double-sided image forming process is a process for forming images on both sides of two recording media, a first recording medium and a second recording medium, and the first recording medium is fed from a paper feed unit to a transport roller. By A first step for holding the first mode so that the first side is supplied to the primary conveyance path, one side surface of which is image-formed by the image forming unit, and conveyed to the switchback roller; A second step for holding the second mode so as to be conveyed, a third step for holding the third mode so as to stop the conveyance of the first recording medium in the secondary conveyance path, and the second recording medium, A fourth step for holding the first mode so as to be conveyed to the switchback roller, a fifth step for holding the second mode so that the second recording medium is conveyed to the secondary conveyance path, and the first recording The medium is discharged from the discharge port in the primary conveyance path, the second recording medium is supplied from the secondary conveyance path to the primary conveyance path by the conveyance roller, and the other side surface is image-formed by the image forming unit. It may comprise a sixth step of holding the first mode so as to be discharged from the discharge port.

  According to such a configuration, image formation on each of the one side surface and the other side surface of the second recording medium of the first recording medium is performed on one side surface of the first recording medium, one side surface of the second recording medium, and the first recording medium. It is executed in the order of the other side surface of the medium and the other side surface of the second recording medium.

  Therefore, the first recording can be performed in a shorter time than the step of forming an image on one side and the other side of the first recording medium and then forming an image on the one side and the other side of the second recording medium. An image can be formed on the medium and the second recording medium.

  As a result, it is possible to efficiently form an image on one side surface and the other side surface of a plurality of recording media while reducing costs and noise.

  In the image forming apparatus of the present invention, it is possible to set a reference for control while reducing costs and noise.

FIG. 1 is a central sectional view showing a printer according to an embodiment of the image forming apparatus of the present invention. 2 is a block diagram showing a drive transmission system in the printer shown in FIG. 1. FIG. 2A shows a block diagram of the main motor, and FIG. 2B shows a block diagram of the process motor. FIG. 3 is a rear view of the driving force transmission mechanism configured in the printer shown in FIG. 4 is a side view of the driving force transmission mechanism shown in FIG. 3 in the first mode. 5 is a cross-sectional view taken along line AA of the driving force transmission mechanism shown in FIG. 3 in the first mode. 6 is a BB cross-sectional view of the driving force transmission mechanism shown in FIG. 3 in the first mode. 7 is a missing gear, a lever, and a drive gear of the sector gear shown in FIG. 3 in the first mode. FIG. 7A is a CC cross section shown in FIG. 3, and FIG. 7B is seen from the rear upper side. It is a perspective view. 8 is a sector gear shown in FIG. 4, in which FIG. 8A is a right side view, FIG. 8B is a rear view, FIG. 8C is a left side view, and FIG. 8D is a view from the front upper side. FIG. In FIG. 8, for the sake of convenience, the posture of the sector gear in the forward rotation mode is used as a reference for the direction. FIG. 9 is a side view of the driving force transmission mechanism shown in FIG. 3 in the second mode. FIG. 10 is a cross-sectional view taken along line AA of the driving force transmission mechanism shown in FIG. 3 in the second mode. 11 is a BB cross-sectional view of the driving force transmission mechanism shown in FIG. 3 in the second mode. 12 is a missing gear, a lever, and a drive gear of the sector gear shown in FIG. 3 in the second mode, FIG. 7A is a DD cross section shown in FIG. 3, and FIG. 7B is seen from the rear upper side. It is a perspective view. FIG. 13 is a side view of the driving force transmission mechanism shown in FIG. 3 in the third mode. 14 is an AA cross-sectional view of the driving force transmission mechanism shown in FIG. 3 in the third mode. 16 is a BB cross-sectional view of the driving force transmission mechanism shown in FIG. 3 in the third mode. FIG. 16 is a missing gear, a lever and a drive gear of the sector gear shown in FIG. 3 in the third mode. FIG. 16A is a CC cross section shown in FIG. 3, and FIG. It is a perspective view. FIG. 17 is a block diagram showing a flow of control in the printer shown in FIG. FIG. 18 is a timing chart for explaining the operation of each unit immediately after power-on. FIG. 19 is a timing chart for explaining the double-sided image forming process. 20A and 20B are explanatory diagrams for explaining the conveyance of the paper in the double-sided image forming process. FIG. 20A corresponds to the timing A in FIG. 19, and FIG. 20B corresponds to the timing B in FIG. 20C corresponds to the timing C in FIG. 19, and FIG. 20D corresponds to the timing D in FIG. FIG. 21 is an explanatory diagram for explaining the sheet conveyance in the double-sided image forming process following FIG. 20. FIG. 21E corresponds to the timing E in FIG. 19, and FIG. 21F shows the timing in FIG. 21G corresponds to the timing G in FIG. 19, and FIG. 21H corresponds to the timing H in FIG. FIG. 22 is an explanatory diagram for explaining the sheet conveyance in the double-sided image forming process following FIG. 21. FIG. 22I corresponds to the timing I in FIG. 19 and FIG. 22J is the timing in FIG. 22K corresponds to the timing K in FIG. 19, and FIG. 22L corresponds to the timing L in FIG.

1. Overall Configuration of Printer As shown in FIG. 1, a printer 1 as an example of an image forming apparatus is a direct tandem color laser printer. The printer 1 includes a paper feeding unit 3 for feeding paper P as an example of a recording medium, an image forming unit 4 for forming an image on the fed paper P, and an image in a main casing 2. Is provided with a paper discharge unit 5 for discharging the paper P on which the image is formed, and a reverse conveyance unit 6 for conveying the paper P on which the image is formed to the image forming unit 4 again.

In the following description, when referring to the direction of the printer 1, the state in which the printer 1 is horizontally placed is used as the upper and lower reference. That is, the upper side of the drawing in FIG. 1 is the upper side, and the lower side of the drawing is the lower side. Further, the right side of FIG. 1 is the front, and the left side of FIG. 1 is the rear. In addition, when the printer 1 is viewed from the front, the left and right reference is used. That is, the front side of the page of FIG. 1 is the left side, and the back side of the page is the right side.
(1) Main Body Casing The main body casing 2 is formed in a box shape having a substantially rectangular shape in side view that accommodates the paper feeding unit 3, the image forming unit 4, the paper discharging unit 5, and the reverse conveying unit 6. The main casing 2 includes a front wall having a main body opening 9 and a front cover 10. The front cover 10 is configured to be swingable so as to open and close the main body opening 9 with its lower end as a fulcrum.
(2) Paper Feed Unit The paper feed unit 3 is configured to convey the paper P toward the image forming unit 4. The sheet feeding unit 3 includes a sheet feeding tray 12 as an example of a sheet feeding unit, a pickup roller 13, a sheet feeding roller 14, a sheet feeding pad 15, a conveyance roller 16, and a registration roller 17.

  The paper feed tray 12 places and accommodates paper P, and is detachably attached to the bottom of the main body casing 2. The paper P on the paper feed tray 12 is sent between the paper feed roller 14 and the paper feed pad 15 by the rotation of the pickup roller 13, and is fed one by one by the rotation of the paper feed roller 14.

  The transport roller 16 is located in a substantially U-shaped transport path from the paper feed roller 14 to the image forming unit 4, and transports the paper P transported from the paper feed roller 14 toward the registration roller 17.

The registration roller 17 is positioned downstream of the transport roller 16 in the transport direction of the paper P and upstream of the image forming unit 4 in the transport direction of the paper P, and abuts against the paper P transported from the transport roller 16. The skew of the paper P is corrected. Then, by rotating the registration roller 17 in the forward rotation direction, the paper P is conveyed at a predetermined timing between a photosensitive drum 28 described later in the image forming unit 4 and a conveying belt 39 described later.
(3) Image Forming Unit The image forming unit 4 includes a scanner unit 20, a drawer unit 21, a transfer unit 22, and a fixing unit 23.
(3-1) Scanner Unit The scanner unit 20 is disposed on the upper part of the main body casing 2. The scanner unit 20 emits a laser beam to each of a plurality of, that is, four photosensitive drums 28 described later, based on the image data, and exposes the photosensitive drums 28 described later.
(3-2) Drawer Unit The drawer unit 21 is arranged at the approximate center in the vertical direction of the main body casing 2 and below the scanner unit 20. The drawer unit 21 is slidable in the front-rear direction, and is configured to be drawn out of the main body casing 2 through the main body opening 9. The drawer unit 21 includes one process unit 27 and a plurality of, that is, four developing cartridges 30.

  The process unit 27 includes a plurality, that is, four photosensitive drums 28 and a plurality, that is, four scorotron chargers 29 corresponding to the respective colors.

  Each of the plurality of photosensitive drums 28 is arranged in parallel at intervals in the front-rear direction. Specifically, a black photosensitive drum 28K, a yellow photosensitive drum 28Y, a magenta photosensitive drum 28M, and a cyan photosensitive drum 28C are sequentially arranged from the front to the rear of the process unit 27.

  The photosensitive drum 28 is formed in a substantially cylindrical shape that is long in the left-right direction, and is rotatably supported at the lower end of the process unit 27 so as to be exposed from below.

  Each of the plurality of scorotron chargers 29 is provided corresponding to one of the plurality of photosensitive drums 28. The scorotron charger 29 is positioned above and behind the corresponding photosensitive drum 28 with a gap from the photosensitive drum 28.

  Each of the plurality of developing cartridges 30 is provided corresponding to one of the plurality of photosensitive drums 28. The developing cartridge 30 is detachably attached to the process unit 27 above the corresponding photosensitive drum 28. The developing cartridge 30 includes a developing roller 31, a supply roller 32, and a layer thickness regulating blade 33.

  Each of the developing rollers 31 of the plurality of developing cartridges 30 corresponds to each color of the plurality of photosensitive drums 28 from the front to the rear from the black developing roller 31K, the yellow developing roller 31Y, the magenta developing roller 31M, The cyan developing roller 31C is sequentially arranged.

  The developing roller 31 is formed in a substantially cylindrical shape that is long in the left-right direction, and is in contact with the front upper side of the photosensitive drum 28.

  The supply roller 32 is formed in a substantially cylindrical shape elongated in the left-right direction, and is in contact with the front upper side of the developing roller 31.

  The layer thickness regulating blade 33 is in contact with the upper side of the developing roller 31.

  Each of the plurality of developing cartridges 30 contains toner corresponding to each color in a space above them.

  The toner in the developing cartridge 30 is supplied to the supply roller 32 and further supplied to the developing roller 31, and is triboelectrically charged positively between the supply roller 32 and the developing roller 31.

  The toner supplied to the developing roller 31 is regulated by the layer thickness regulating blade 33 as the developing roller 31 rotates, and is carried on the surface of the developing roller 31 as a thin layer having a constant thickness.

  On the other hand, the surface of the photosensitive drum 28 is uniformly positively charged by the scorotron charger 29 as the photosensitive drum 28 rotates, and then exposed by high-speed scanning of the laser beam from the scanner unit 20. As a result, an electrostatic latent image corresponding to the image to be formed on the paper P is formed on the surface of the photosensitive drum 28.

The positively charged toner carried on the surface of the developing roller 31 is supplied to an electrostatic latent image formed on the surface of the photosensitive drum 28 when the photosensitive drum 28 further rotates. As a result, a toner image by reversal development is carried on the surface of the photosensitive drum 28.
(3-3) Transfer Unit The transfer unit 22 is disposed along the front-rear direction in the main body casing 2 above the paper feed unit 3 and below the drawer unit 21. The transfer unit 22 includes a driving roller 37 and a driven roller 38 that are spaced apart in the front-rear direction, a transport belt 39 wound around the driving roller 37 and the driven roller 38, and a plurality of photosensitive drums 28. On the other hand, a plurality of, that is, four transfer rollers 41 located across the upper portion of the transport belt 39 and a belt cleaning roller 42 facing the lower portion of the transport belt 39 are provided.

  The paper P fed from the paper feeding unit 3 is transported by the transport belt 39 from the front to the rear so as to sequentially pass through the transfer positions where the photosensitive drums 28 and the transfer rollers 41 face each other. The Further, the toner images of the respective colors carried on the respective photosensitive drums 28 are sequentially transferred onto the paper P while the paper P is being conveyed.

Further, the residual toner on the conveyor belt 39 is cleaned by the belt cleaning roller 42.
(3-4) Fixing Unit The fixing unit 23 includes a heating roller 43 and a pressure roller 44 that is in contact with the lower back of the heating roller 43 and is located behind the transfer unit 22. In the transfer unit 22, the color image transferred onto the paper P is heat-fixed on the paper P by being heated and pressed while the paper P passes between the heating roller 43 and the pressure roller 44. .
(4) Paper Discharge Unit The paper discharge unit 5 conveys the paper P on which an image has been formed in the image forming unit 4 to the outside of the main body casing 2, or reverses the paper P switched back by the switchback roller 50. It is configured to transport toward the transport unit 6. The paper discharge unit 5 includes a flapper 47, an intermediate paper discharge roller 48, a switchback roller 50, a discharge port 49, and a paper discharge tray 51.

  The intermediate paper discharge roller 48 is supported by the main casing 2 so that the rotation direction can be switched between the normal rotation direction and the reverse rotation direction at the rear portion of the main casing 2 at the substantially center in the vertical direction.

  The switchback roller 50 is supported by the main body casing 2 so that the rotation direction of the switchback roller 50 can be switched between the normal rotation direction and the reverse rotation direction in the upper and rear portions of the main body casing 2. More specifically, the switchback roller 50 forwards the paper P toward the paper discharge tray 51 via the discharge port 49 and the paper P transported toward the paper discharge tray 51. The rotation direction can be switched by a switching unit 83 to be described later in the reversing direction to be drawn in.

  The discharge port 49 is an opening through which the sheet P conveyed to the switchback roller 50 that rotates in the forward rotation direction after the image is formed by the image forming unit 4 is discharged out of the main casing 2.

  The paper discharge tray 51 is formed in a substantially V shape in a side view in the upper part of the main casing 2 so that the upper part is opened.

  The flapper 47 is configured to be switchable between a paper discharge position and a re-transport position on the downstream side of the fixing unit 23 in the transport direction of the paper P. The flapper 47 positioned at the paper discharge position guides the paper P thermally fixed in the fixing unit 23 toward the intermediate paper discharge roller 48. The flapper 47 positioned at the re-conveying position guides the paper P reversed by the switchback roller 50 toward the reverse conveying unit 6 formed below the paper discharge unit 5.

The path from the paper P fed to the paper feed roller 14 to the transport roller 16, passing through the image forming unit 4 and then transported to the switchback roller 50 of the paper discharge unit 5 is a primary transport route. 52.
(5) Reversal Transport Unit The reverse transport unit 6 is configured to transport the paper P from the rear side to the front side of the main casing 2. The reverse conveyance unit 6 passes from the lower side of the flapper 47 through the lower side of the paper feeding unit 3 to the upstream side of the image forming unit 4 in the primary conveyance path 52 in the conveyance direction of the paper P. Specifically, from the conveyance roller 16. Is also formed so as to merge upstream in the transport direction of the paper P. The reverse conveyance unit 6 includes a reverse conveyance roller 55.

  A plurality of reverse conveying rollers 55 are provided below the paper feeding unit 3, specifically, three in pairs in the front-rear direction.

  When images are formed on both sides of the paper P, the paper P passes through the fixing unit 23, passes through the flapper 47 whose rear end portion is located at the paper discharge position, and then is conveyed toward the paper discharge tray 51. After that, it is returned to the main casing 2. Then, the paper P passes through the flapper 47 positioned at the re-conveying position, and is conveyed from the rear to the front by the plurality of reverse conveying rollers 55 in the reverse conveying unit 6.

  Then, the paper P that has passed through the plurality of reverse conveyance rollers 55 is conveyed from the front to the top of the paper feed tray 12 and is conveyed to the primary conveyance path 52. The paper P transported to the primary transport path 52 is transported again toward the image forming unit 4 by the transport roller 16, and an image is formed on the surface where no image is formed, and is discharged onto the paper discharge tray 51. The

The paper P switched back by the switchback roller 50 is transported from the paper discharge unit 5 toward the reverse transport unit 6, and the transport route from the reverse transport unit 6 to the primary transport path 52 is a secondary transport route. 56.
2. Main Motor and Process Motor The printer 1 further includes a main motor 68 and a process motor 69 as examples of drive sources in the main body casing 2.

  The main motor 68 is located in the rear portion of the center of the main body casing 2 on the left side in the vertical direction. The main motor 68 is configured to generate a rotational driving force in one direction when driven. As shown in FIG. 2A, the main motor 68 includes an intermediate paper discharge roller 48, a switchback roller 50, a paper feed roller 14, a conveyance roller 16, a registration roller 17, a black developing roller 31K, a heating roller 43, and a reverse conveyance roller 55. Each is configured to transmit a rotational driving force. When the paper P is jammed in the main casing 2, the main motor 68 generates a rotational driving force to the other and rotates the transport roller 16, the registration roller 17, the reverse transport roller 55 and the like in the reverse direction. It is configured.

As shown in FIG. 1, the process motor 69 is located at a substantially central portion in the up-down front-rear direction on the left side of the main casing 2. The process motor 69 is configured to generate a rotational driving force in one direction when driven. As shown in FIG. 2B, the process motor 69 includes a black photosensitive drum 28K, a yellow photosensitive drum 28Y, a magenta photosensitive drum 28M, a cyan photosensitive drum 28C, a driving roller 37, a yellow developing roller 31Y, a magenta developing roller 31M, and a cyan developing roller 31C. The rotational driving force is transmitted to each of the belt cleaning rollers 42.
3. Configuration of Driving Force Transmission Mechanism In order to form images on both sides of the paper P, that is, on both one side and the other side of the paper P, the printer 1 has the rotation directions of the switchback roller 50 and the intermediate paper discharge roller 48 set to be normal. A driving force transmission mechanism 76 capable of switching between the rolling direction and the reversing direction is provided.

  Note that the forward rotation direction of the switchback roller 50 and the intermediate paper discharge roller 48 is a rotation direction in which the paper P is rotated toward the paper discharge tray 51 as described above. The reverse direction of the intermediate paper discharge roller 48 is a rotational direction in which the paper P rotates so as to transport the paper P from the discharge port 49 toward the reverse transport unit 6 as described above.

  More specifically, as shown in FIG. 4, the switchback roller 50 is a driving roller disposed outside the conveyance path, and the forward rotation direction of the switchback roller 50 is counterclockwise when viewed from the left side. That is. The intermediate paper discharge roller 48 is a driving roller disposed outside the conveyance path, and the forward rotation direction of the intermediate paper discharge roller 48 is clockwise when viewed from the left side. As shown in FIG. 9, the reverse direction of the switchback roller 50 is clockwise when viewed from the left side, and the reverse direction of the intermediate paper discharge roller 48 is counterclockwise when viewed from the left side. .

  In addition, the rotation direction of each gear in the forward rotation mode and the reverse rotation mode, which will be described later, is a direction indicated by an arrow shown in each drawing, and description thereof is omitted.

Although not shown, the driving force transmission mechanism 76 is located in the rear portion of the main casing 2 and includes an input gear 79, a rotation direction variable gear train 82, and a switching unit 83.
(1) Input Gear The input gear 79 constitutes a lower part of the driving force transmission mechanism 76 as shown in FIG.

  The input gear 79 is configured to receive a rotational driving force to one of the main motors 68 via a plurality of gears (not shown) in the main body casing 2 and rotate clockwise when viewed from the left side. The input gear 79 is a two-stage gear composed of a small-diameter gear and a large-diameter gear. The small-diameter gear meshes with a drive gear 98 described later, and the large-diameter gear is a plurality of unillustrated plural parts in the main casing 2. It meshes with one of the gears.

The rotational driving force generated from the main motor 68 is supplied through a plurality of gears (not shown) of the main body casing 2 to the paper feed roller 14, the transport roller 16, the registration roller 17, the black developing roller 31K, the heating roller 43, and the reverse transport. This is transmitted to gears provided at the left end portions of the rollers 55 to rotate the paper feed roller 14, the transport roller 16, the registration roller 17, the black developing roller 31 </ b> K, the heating roller 43, and the reverse transport roller 55.
(2) Rotation direction variable gear train The rotation direction variable gear train 82 constitutes the rear upper part of the driving force transmission mechanism 76 as shown in FIG. A rotational driving force to one of the main motors 68 is transmitted to the rotation direction variable gear train 82 via the input gear 79 and the switching unit 83. The rotational direction variable gear train 82 includes a switchback roller gear 86 positioned at the upper end of the rotational direction variable gear train 82, an intermediate discharge roller gear 87 positioned at the lower end of the rotational direction variable gear train 82, and a switchback roller gear. A first idle gear 91, a second idle gear 92, a third idle gear 93, a fourth idle gear 94, and a fifth idle gear 95 are provided between 86 and the intermediate paper discharge roller gear 87.

  As shown in FIG. 3, the switchback roller gear 86 is provided at the left end of the switchback roller 50 so as to rotate integrally with the switchback roller 50. The switchback roller gear 86 meshes with a first idle gear 91 described later.

  As shown in FIG. 4, the first idle gear 91 is positioned below the switchback roller gear 86 and is supported rotatably with respect to the left wall of the main casing 2. The first idle gear 91 meshes with the switchback roller gear 86 and a second idle gear 92 described later.

  The second idle gear 92 is positioned below the first idle gear 91 and is supported so as to be rotatable with respect to the left wall of the main casing 2. The second idle gear 92 is a two-stage gear composed of a small-diameter gear and a large-diameter gear. The small-diameter gear meshes with the first idle gear 91 and a third idle gear 93 described later, and the large-diameter gear. The gear meshes with a fifth idle gear 95 described later.

  The third idle gear 93 is positioned below the second idle gear 92 and is supported rotatably with respect to the left wall of the main casing 2. The third idle gear 93 is a two-stage gear composed of a small diameter gear and a large diameter gear. The small diameter gear meshes with the second idle gear 92, and the large diameter gear is a fourth idle gear 94 described later. Is engaged.

  The fourth idle gear 94 is positioned below the third idle gear 93 and above and in front of an intermediate paper discharge roller gear 87 described later, and is rotatably supported with respect to the left wall of the main casing 2. The fourth idle gear 94 meshes with the third idle gear 93 and an intermediate paper discharge roller gear 87 described later. Further, as will be described in detail later, the fourth idle gear 94 is configured such that the rotational driving force generated from the main motor 68 is transmitted via the switching unit 83.

  The fifth idle gear 95 is positioned in front of and below the second idle gear 92 and is supported rotatably with respect to the left wall of the main body casing 2. The fifth idle gear 95 meshes with the second idle gear 92. Further, as will be described in detail later, the fifth idle gear 95 is configured such that the rotational driving force generated from the main motor 68 is transmitted via the switching unit 83.

The intermediate paper discharge roller gear 87 is provided at the left end portion of the intermediate paper discharge roller 48 so as to rotate integrally with the intermediate paper discharge roller 48. The intermediate paper discharge roller gear 87 meshes with the fourth idle gear 94.
(3) Switching unit The switching unit 83 constitutes a portion between the input gear 79 and the rotation direction variable gear train 82 in the driving force transmission mechanism 76. The switching unit 83 includes a drive gear 98, a holder 99, a pendulum gear 100, a sector gear 101 as an example of a switching gear, a lever 103 as an example of an engaging member, and a solenoid switch 104 as an example of a switch means. It has.
(3-1) Drive Gear, Holder, and Pendulum Gear The drive gear 98 is positioned above the input gear 79 and its drive support shaft 108 is supported by the left wall of the main body casing 2, thereby On the other hand, it is rotatably supported. Further, the drive gear 98 supports the holder 99 rotatably by inserting the drive gear shaft 108 into a drive gear shaft insertion hole 113 of the holder 99 described later. The drive gear 98 meshes with the input gear 79 and a pendulum gear 100 described later.

  The holder 99 includes a gear support part 110 and a switching power receiving part 111. In the following description, the orientation of the holder 99 in the normal rotation mode is described as a reference for the direction, and specifically, the description is based on the direction shown in FIG.

  The gear support portion 110 constitutes a rear portion of the holder 99, and as shown in FIGS. 4 and 6, as shown in FIG. 4 and FIG. And it is formed in the flat plate shape of planar view substantially U shape. As shown in FIG. 4, the gear support portion 110 includes a drive gear shaft insertion hole 113 and a pendulum gear shaft insertion hole 114.

  The drive gear shaft insertion hole 113 is penetrated in the left-right direction so that the drive gear shaft 108 of the drive gear 98 can be inserted below the substantially central portion in the front-rear direction of the gear support portion 110.

  The pendulum gear shaft insertion hole 114 is penetrated in the left-right direction so that a pendulum gear shaft 120 of a pendulum gear 100 described later can be inserted in the rear upper end portion of the gear support portion 110.

  The switching power receiver 111 constitutes a front portion of the holder 99. The switching power receiving portion 111 includes a frame portion 116 and a lid portion 117.

  As shown in FIG. 5, the frame portion 116 has a substantially rectangular frame shape in side view that extends from the front end portion of the gear support portion 110 toward the front and penetrates in the left-right direction.

  As shown in FIG. 4, the lid portion 117 is formed in a thin plate shape that closes the left end portion of the frame portion 116. The lid portion 117 includes a long hole 118 and a hook 119.

  The elongated hole 118 extends in the left-right direction so as to follow an arc centered on the drive gear shaft insertion hole 113 of the gear support 110 from the rear upper end of the lid 117 in a side view to the lower end of the substantially central portion in the front-rear direction. It is penetrated by.

  The hook 119 is located in the front part of the long hole 118 in the lid part 117. As shown in FIG. 3, the hook 119 has a substantially hook shape that protrudes leftward from the left surface of the lid 117 and bends forward and downward.

  The pendulum gear 100 is supported rotatably with respect to the holder 99 by supporting the pendulum gear shaft 120 in the pendulum gear shaft insertion hole 114 of the holder 99. The pendulum gear 100 is always meshed with the drive gear 98. Further, the pendulum gear 100 is configured to be selectively meshed with the fourth idle gear 94 or the fifth idle gear 95 when the holder 99 swings around the drive gear shaft 108 as a fulcrum.

  Specifically, as shown in FIG. 4, the pendulum gear 100 is rotated relative to the fourth idle gear 94 by rotating the holder 99 counterclockwise as viewed from the left side with the drive gear shaft 108 as a fulcrum. , Located at the first meshing position meshing from the front. The rotational drive force to one side of the main motor 68 includes an input gear 79, a drive gear 98, a pendulum gear 100, a fourth idle gear 94, a third idle gear 93, a second idle gear 92, a first idle gear 91, a switchback. This is transmitted to the switchback roller 50 via the roller gear 86. As a result, the switchback roller 50 rotates in the forward rotation direction. Further, the rotational driving force to one side of the main motor 68 is transmitted to the intermediate paper discharge roller 48 via the input gear 79, the drive gear 98, the pendulum gear 100, the fourth idle gear 94, and the intermediate paper discharge roller gear 87. . As a result, the intermediate paper discharge roller 48 rotates in the forward rotation direction.

  A fourth idle gear 94, a third idle gear 93, which transmit a rotational driving force for rotating the switchback roller 50 from the pendulum gear 100 in the forward rotation direction when the holder 99 is rotated counterclockwise as viewed from the left side; The gear arrangement of the second idle gear 92, the first idle gear 91, and the switchback roller gear 86 is an example of the first gear train. The rotation driving force to one side of the main motor 68 is transmitted to the first gear train, so that the pendulum gear 100 of the switching unit 83 is in the first direction so that the switchback roller 50 and the intermediate paper discharge roller 48 rotate in the forward rotation direction. The state held at the first meshing position meshing with the gear train is defined as a normal rotation mode as an example of the first mode of the switching unit 83.

  As shown in FIG. 9, the pendulum gear 100 is engaged with the fifth idle gear 95 from below by rotating the holder 99 clockwise about the drive gear shaft 108 as a fulcrum. Located at the second meshing position. Thereby, the rotational driving force to one side of the main motor 68 is the input gear 79, the driving gear 98, the pendulum gear 100, the fifth idle gear 95, the second idle gear 92, the first idle gear 91, and the switchback roller gear 86. Is transmitted to the switchback roller 50. Thereby, the switchback roller 50 rotates in the reverse direction. The rotational driving force to one side of the main motor 68 includes an input gear 79, a driving gear 98, a pendulum gear 100, a fifth idle gear 95, a second idle gear 92, a third idle gear 93, a fourth idle gear 94, This is transmitted to the intermediate paper discharge roller 48 via the intermediate paper discharge roller gear 87. As a result, the intermediate paper discharge roller 48 rotates in the reverse direction.

  A fifth idle gear 95, a second idle gear 92, and a first idle gear that transmit a rotational driving force for rotating the switchback roller 50 in the reverse direction from the pendulum gear 100 when the holder 99 is rotated clockwise in the left side view. The gear arrangement of the gear 91 and the switchback roller gear 86 is an example of the second gear train. The rotation driving force to one side of the main motor 68 is transmitted to the second gear train, and the pendulum gear 100 of the switching unit 83 rotates the second gear so that the switchback roller 50 and the intermediate paper discharge roller 48 rotate in the reverse direction. The state held at the second meshing position meshing with the row is set as an inversion mode as an example of the second mode of the switching unit 83.

  Further, as shown in FIG. 13, the pendulum gear 100 is positioned at an intermediate position between the fourth idle gear 94 and the fifth idle gear 95 with the drive gear shaft 108 as a fulcrum. It is located at a non-meshing position where it does not mesh with any of the five idle gears 95. By this. The pendulum of the switching unit 83 prevents the rotational driving force to one of the main motors 68 from being transmitted to either the first gear train or the second gear train and the switchback roller 50 and the intermediate paper discharge roller 48 from rotating. The state in which the gear 100 is held at the non-engagement position where it does not mesh with either the first gear train or the second gear train is defined as a stack mode as an example of the third mode of the switching unit 83.

  In the main casing 2, the tension spring 121 is positioned so as to connect a hook (not shown) provided behind the hook 119 of the holder 99 and the hook 119 of the holder 99.

As a result, as shown in FIG. 4, the holder 99 is counterclockwise when viewed from the left side with the driving gear shaft 108 as a fulcrum, that is, the pendulum gear 100 meshes with the fourth idle gear 94 by the urging force of the tension spring 121. It is always biased so as to be located at the first meshing position.
(3-2) Sector Gear The sector gear 101 is positioned on the front upper side of the drive gear 98 and is supported to be rotatable with respect to the left wall of the main body casing 2. As shown in FIG. 8, the sector gear 101 includes a sector gear shaft 125, a first partition plate 126, a toothless gear 130, a cylindrical portion 131 as an example of a regulating member, and a V-shaped cam as an example of a second cam. 145, the second partition plate 127, and an I-shaped cam 146 as an example of the first cam. In the following description, the posture of the sector gear 101 in the forward rotation mode is described as a reference of the direction, and specifically, the description is based on the direction shown in FIG.

  The sector gear shaft 125 is a central portion of the sector gear 101 in a side view and is formed so as to extend in a substantially cylindrical shape in the left-right direction. As shown in FIG. 4, the sector gear shaft 125 has its left end inserted through a long hole 118 of the holder 99.

  As shown in FIG. 8, the first partition plate 126 has a substantially circular flat plate shape in a side view larger than the diameter of the sector gear shaft 125 at a substantially central portion in the left-right direction of the sector gear shaft 125.

  The toothless gear 130 has a substantially cylindrical shape extending from the right surface of the first partition plate 126 toward the right. The missing tooth gear 130 includes a missing tooth portion 133 and a toothed portion 134.

  The missing tooth portion 133 is clockwise from the first missing tooth portion 135 and the first missing tooth portion 135 where the gear teeth are not formed in the range of about 45 ° on the outer periphery of the rear lower portion of the missing gear 130 and the first missing tooth portion 135. There is provided a second missing tooth portion 136 in which gear teeth are not formed at a position shifted by approximately 90 °, that is, in a range of approximately 90 ° on the outer periphery of the front portion of the missing gear 130.

  The toothed portion 134 is a portion where gear teeth are formed excluding the portion of the missing tooth portion 133 of the missing tooth gear 130. Specifically, the toothed portion 134 is adjacent to the first missing tooth portion 135 in the clockwise direction of the right side view and adjacent to the second missing tooth portion 136 in the counterclockwise direction of the right side view. A toothed portion 137; and a second toothed portion 138 adjacent to the second missing tooth portion 136 in the clockwise direction of the right side view and adjacent to the first missing tooth portion 135 in the counterclockwise direction of the right side view. ing.

  The cylindrical portion 131 is formed in a substantially cylindrical shape extending from the right surface of the first partition plate 126 on the inner side of the missing gear 130 in the side view to the right. The cylindrical portion 131 has a diameter smaller than that of the toothless gear 130, and the right end portion thereof is positioned between the right end portion of the missing tooth gear 130 and the right end portion of the sector gear shaft 125. The cylindrical part 131 includes a convex part 140.

  The convex portion 140 protrudes radially outward at the first convex portion 141 protruding outward in the radial direction at the rear upper portion of the outer periphery of the cylindrical portion 131 and the lower portion of the outer periphery of the cylindrical portion 131. 2nd convex part 142 to be provided.

  The first convex portion 141 has a substantially triangular shape in a side view protruding from the outer peripheral surface of the cylindrical portion 131 toward the radially outer side of the cylindrical portion 131. A surface extending along the radial direction of the cylindrical portion 131 of the first convex portion 141 is partitioned as a first engagement surface 143. The first engagement surface 143 is a surface facing the counterclockwise direction when viewed from the right side in the circumferential direction of the cylindrical portion 131. The first convex portion 141 has a tip that overlaps with a portion where the second toothed portion 138 of the toothless gear 130 is formed in a side view, and is cylindrical from the right end portion of the toothless gear 130 in a front view. It is formed over the right end portion of the portion 131.

  The second convex portion 142 is located on the outer periphery of the cylindrical portion 131 at a position shifted by about 150 ° from the first convex portion 141 in the clockwise direction when viewed from the right, and the diameter of the cylindrical portion 131 from the outer peripheral surface of the cylindrical portion 131. It has a substantially triangular shape in side view protruding outward in the direction. A surface extending along the radial direction of the cylindrical portion 131 of the second convex portion 142 is partitioned as a second engagement surface 144. The second engagement surface 144 is a surface facing the counterclockwise direction when viewed from the right side in the circumferential direction of the cylindrical portion 131. The second protrusion 142 has a tip that overlaps with the portion of the missing gear 130 where the first toothed portion 137 is formed in a side view, and is missing from the right end of the missing gear 130 in a front view. It is formed over a range up to an intermediate position between the right end portion of the tooth gear 130 and the right end portion of the cylindrical portion 131. That is, the first convex portion 141 includes a portion that overlaps with the second convex portion 142 and a portion that does not overlap when the first convex portion 141 is projected in the circumferential direction of the cylindrical portion 131.

  The V-shaped cam 145 extends from the left surface of the first partition plate 126 toward the left. As shown in FIG. 6, the V-shaped cam 145 is formed in a substantially bowl shape having a substantially V shape in a side view extending radially from the outer peripheral surface of the sector gear shaft 125. Specifically, the V-shaped cam 145 has one end portion extending from the sector gear shaft 125 toward the second toothless portion 136, and the other end portion extending from the sector gear shaft 125 to the second toothed portion 138. It extends to head. The tips of the one end and the other end of the V-shaped cam 145 have a substantially circular shape when viewed from the side.

  The second partition plate 127 is located on the left side of the V-shaped cam 145 with a space leftward from the first partition plate 126, and its right surface is continuous with the V-shaped cam 145. The second partition plate 127 has a substantially flat plate shape larger than the diameter of the sector gear shaft 125. Specifically, the second partition plate 127 has a substantially triangular shape with the periphery of the sector gear shaft 125, one end of the V-shaped cam 145, and the other end of the V-shaped cam 145 as viewed from the side. ing. The second partition plate 127 has a substantially semicircular shape at each vertex in a side view. The second partition plate 127 is sized to fit inside the first partition plate 126 when projected in the left-right direction, and is sized to fit the V-shaped cam 145 inside.

  The I-shaped cam 146 is formed in a substantially bowl shape extending from the outer peripheral surface of the sector gear shaft 125 toward the radially outer side on the left side of the second partition plate 127. The right surface of the I-shaped cam 146 is continuous with the second partition plate 127. The I-shaped cam 146 extends toward the front upper vertex of the second partition plate 127. That is, the I-shaped cam 146 overlaps with one end portion of the V-shaped cam 145 extending toward the second missing tooth portion 136 when projected in the left-right direction. The I-shaped cam 146 extends in the direction of about 2 o'clock about the sector gear shaft 125 in the left side view in the normal rotation mode described later. Further, the tip of the I-shaped cam 146 has a substantially semicircular shape when viewed from the side.

In addition, the 2nd partition plate 127, the V-shaped cam 145, and the I-shaped cam 146 are comprised as the cam 147 as an example of a cam.
(3-3) Lever and Solenoid Switch As shown in FIG. 4, the lever 103 is located in front of the sector gear 101 and is supported so as to be swingable with respect to the left wall of the main body casing 2. As shown in FIG. 7, the lever 103 includes a lever shaft 151, a connection portion 152, a first engagement portion 153, and a second engagement portion 154. In the following description, the state of the lever 103 in the forward rotation mode will be described with reference to the direction, and specifically, the description will be made with reference to the direction shown in FIG.

  The lever shaft 151 is formed in a substantially cylindrical shape extending in the left-right direction.

  The connecting portion 152 is formed in a substantially bowl shape that protrudes rearward and upward from the outer peripheral surface of the upper portion of the lever shaft 151, and a hooking portion 165 of a solenoid switch 104 described later is fitted therein.

  The first engaging portion 153 has a shape protruding from the outer peripheral surface of the rear lower portion of the lever shaft 151 toward the rear lower portion. The first engagement portion 153 includes a first engagement claw 158.

  The first engagement claw 158 constitutes a rear lower end portion of the first engagement portion 153 and is formed in a substantially prismatic shape having a substantially rectangular shape in a side view. The first engaging claws 158 are arranged so as to overlap the first convex portion 141 and the second convex portion 142 in the axial direction of the cylindrical portion 131, that is, in the left-right direction. In other words, the first engaging claw 158 is disposed so as to overlap the first convex portion 141 and the second convex portion 142 when the cylindrical portion 131 is projected in the circumferential direction.

  The second engaging portion 154 is formed so as to protrude toward the front lower side from the outer peripheral surface of the front lower portion of the lever shaft 151. The second engagement portion 154 includes a second engagement claw 159.

  The second engagement claw 159 constitutes a front lower end portion of the second engagement portion 154 and is formed in a claw shape that bends rearward. The second engaging claw 159 is disposed so as not to overlap the second convex portion 142 but to the first convex portion 141 in the axial direction of the cylindrical portion 131, that is, in the left-right direction. In other words, when the cylindrical part 131 is projected in the circumferential direction, it is arranged so as not to overlap the second convex part 142 but to the first convex part 141.

  The lever 103 is swingably supported with respect to the left wall of the main casing 2 by inserting a support shaft (not shown) of the main casing 2 in front of the sector gear 101 into the lever shaft 151. As shown in FIGS. 7 and 16, the lever 103 has a first engagement claw 158 close to the cylindrical portion 131 of the sector gear 101 and a second engagement claw 159 spaced apart from the cylindrical portion 131 of the sector gear 101. As shown in FIG. 12, the first engaging claw 158 is relatively separated from the cylindrical portion 131 of the sector gear 101, and the second engaging claw 159 is relatively close to the cylindrical portion 131 of the sector gear 101. It can swing to the second engagement position.

  That is, in the lever 103, the first engaging portion 153 can be engaged with the first convex portion 141 and the second convex portion 142, and the second engaging portion 154 is engaged with the first convex portion 141 and the second convex portion 142. A first engagement position that is not engaged with the second protrusion, and the second engagement portion 154 is engageable with the first protrusion 141, and the first engagement portion 153 is the first protrusion 141 and the second protrusion 142. It can move to the 2nd engagement position which does not engage.

  The solenoid switch 104 is positioned above the lever 103 as shown in FIG. 4 in order to switch the lever 103 between the first engagement position shown in FIGS. 7 and 16 and the second engagement position shown in FIG. The main body casing 2 is fixed to the left wall. The solenoid switch 104 receives a signal from the CPU 72, which will be described later, and is switched between an excited state as an example of a second state in which a current flows and a non-excited state as an example of a first state in which no current flows. The solenoid switch 104 includes a main body portion 163 and an advance / retreat portion 164.

  The main body 163 is formed in a substantially box shape with the lower part opened, and includes an electromagnet (not shown) and a compression spring (not shown) on the inside thereof.

  The advance / retreat portion 164 is formed in a substantially cylindrical shape that protrudes downward from the open portion of the main body portion 163. The advance / retreat part 164 includes a hooking part 165.

  The hook portion 165 has a groove shape that is recessed from the peripheral surface of the advance / retreat portion 164 toward the center of the advance / retreat portion 164 at the lower end portion of the advance / retreat portion 164. The hook portion 165 is fitted to the connection portion 152 of the lever 103.

  Then, when the solenoid switch 104 is in a non-excited state, the advance / retreat portion 164 advances so that the hooking portion 165 moves relatively away from the main body portion 163 by the biasing force of a compression spring (not shown) in the main body portion 163. The lever 103 is held in the first engagement position shown in FIGS. Further, when the solenoid switch 104 is in an excited state, the advancing / retreating portion 164 is magnetized by a current flowing through an electromagnet (not shown) in the main body portion 163, and the upper portion of the advancing / retreating portion 164 is pulled upward by the magnetic force. Accordingly, the lever 103 is retracted so as to be relatively close to the main body 163 against the urging force of a compression spring (not shown) in the main body 163, so that the lever 103 is moved to the second engagement shown in FIG. Hold in position.

  As shown in FIG. 6, the switching unit 83 includes a torsion spring 148 as an example of a biasing unit that biases the V-shaped cam 145 of the sector gear 101 from the front upper side toward the rear lower side. Thereby, the torsion spring 148 urges the sector gear 101 to rotate clockwise as viewed from the left side by its urging force.

  On the other hand, the lever 103 and the solenoid switch 104 are configured such that the solenoid switch 104 is in a non-excited state or an excited state, the lever 103 is positioned at the first engagement position or the second engagement position, and the first engagement portion 153 By engaging the first engaging claw 158 or the second engaging claw 159 of the second engaging portion 154 with the convex portion 140 of the cylindrical portion 131, the sector gear 101 is viewed from the left side by the urging force of the torsion spring 148. Restricting attempts to rotate clockwise. When the rotation of the sector gear 101 is restricted, the missing tooth portion 133 (the first missing tooth portion 135 or the second missing tooth portion 136) of the missing gear 130 faces the drive gear 98.

  Thus, the sector gear 101 described above receives the rotational driving force to one side of the main motor 68 by meshing the toothed portion 134 of the toothless gear 130 with the driving gear 98 even when the driving gear 98 is always rotating. In this configuration, the missing tooth portion 133 of the missing gear 130 is opposed to the driving gear 98 so that the driving force generated from the main motor 68 is not transmitted.

  More specifically, in the forward rotation mode, the torsion spring 148 urges one end portion of the V-shaped cam 145 from the front upper side to the rear lower side as shown in FIG. On the other hand, the lever 103 and the solenoid switch 104 are biased to rotate clockwise as viewed from the left side, and as shown in FIG. 7, the solenoid switch 104 is de-energized and the lever 103 is positioned at the first engagement position. Then, by engaging the first engagement claw 158 of the first engagement portion 153 with the first engagement surface 143 of the first convex portion 141 of the cylindrical portion 131, as shown in FIG. The first missing tooth portion 135 of the missing gear 130 is held so as to face the drive gear 98 against the urging force of 148.

  Further, as shown in FIG. 11, the torsion spring 148 urges the other end portion of the V-shaped cam 145 from the front upper side to the rear lower side to rotate the sector gear 101 clockwise as viewed from the left side. On the other hand, the lever 103 and the solenoid switch 104 are urged to rotate, as shown in FIG. 12, the solenoid switch 104 is energized, the lever 103 is positioned at the second engagement position, and the second engagement is performed. By engaging the second engagement claw 159 of the portion 154 with the first engagement surface 143 of the first convex portion 141 of the cylindrical portion 131, the urging force of the torsion spring 148 is resisted as shown in FIG. Thus, the sector gear 101 is held such that the downstream side portion in the rotation direction of the second missing tooth portion 136 of the missing tooth gear 130 faces the drive gear 98.

  Further, in the stack mode, the torsion spring 148 urges the other end portion of the V-shaped cam 145 from the front upper side toward the rear lower side as shown in FIG. On the other hand, as shown in FIG. 16, the solenoid switch 104 is energized, the lever 103 is positioned at the first engagement position, and the first engagement claw 158 of the first engagement portion 153 is urged to rotate. Is engaged with the second engagement surface 144 of the second convex portion 142 of the cylindrical portion 131, so that the sector gear 101 is moved against the biasing force of the torsion spring 148 as shown in FIG. An upstream portion in the rotational direction of the 130 second missing tooth portion 136 is held so as to face the drive gear 98.

The lever 103, the solenoid switch 104, and the cylindrical portion 131 of the sector gear 101 are configured as an example of a locking unit.
4). As described above, the switching unit 83 is switched to the normal mode, the reverse mode, and the stack mode by switching the solenoid switch 104 between the excited state and the non-excited state.

In the following description, it is assumed that the main motor 68 is always driven and the input gear 79 is rotated in one direction.
(1) Switching operation from normal rotation mode to reverse mode Next, the switching operation from the normal rotation mode to the reverse mode will be described.

  To switch the switching unit 83 from the normal rotation mode to the reverse mode, as shown in FIG. 4, the solenoid switch 104 in the normal rotation mode is switched from the non-excitation state to the excitation state as shown in FIG.

  As a result, the lever 103 swings clockwise in a left side view and moves from the first engagement position to the second engagement position.

  Then, the contact between the first engagement claw 158 and the first engagement surface 143 of the first convex portion 141 is released, and the urging force of the torsion spring 148 against one end portion of the V-shaped cam 145 is shown in FIG. As shown, the sector gear 101 rotates clockwise in the left side view.

  When the sector gear 101 rotates, the first toothed portion 137 of the partial gear 130 moves to a position facing the drive gear 98. As a result, the first toothed portion 137 meshes with the drive gear 98, and the sector gear 101 rotates as the drive gear 98 rotates.

  At this time, the I-shaped cam 146 rotates in accordance with the rotation of the sector gear 101 as shown in FIG. The I-shaped cam 146 rotates clockwise in a left side view so that the first toothed portion 137 is brought into contact with the frame portion 116 of the holder 99 from above after the first toothed portion 137 is engaged with the drive gear 98. Since the sector gear 101 continues to rotate even after the I-shaped cam 146 and the frame portion 116 contact each other, the I-shaped cam 146 rotates while pressing the frame portion 116 downward.

  The holder 99 is rotated clockwise with the drive gear shaft 108 as a fulcrum when the frame portion 116 is pressed downward. As the holder 99 rotates, the pendulum gear 100 pivotally supported by the holder 99 moves from the first meshing position toward the second meshing position. When the pendulum gear 100 moves to the second meshing position, the I-shaped cam 146 extends in the direction of about 6 o'clock when viewed from the left side, and presses the frame portion 116 to the lowest side. .

  While the sector gear 101 rotates and the pendulum gear 100 moves to the second meshing position, the second toothless portion 136 faces the drive gear 98 as shown in FIG. At this time, the torsion spring 148 applies an urging force that rotates the sector gear 101 in the clockwise direction in the left side view to the other end of the V-shaped cam 145.

  When the sector gear 101 rotates due to the urging of the torsion spring 148 to the other end of the V-shaped cam 145, as shown in FIG. 12, the second engagement claw 159 of the lever 103 located at the second engagement position is It abuts on the first convex portion 141 of the sector gear 101.

As a result, the rotation of the sector gear 101 is restricted, and the switching unit 83 is switched from the normal rotation mode to the reverse mode.
(2) Switching Operation from Inversion Mode to Stack Mode Next, switching operation from the inversion mode to the stack mode will be described.

  In order to switch the switching unit 83 from the inversion mode to the stack mode, as shown in FIG. 9, the excitation state of the solenoid switch 104 in the inversion mode is switched to the non-excitation state as shown in FIG.

  Accordingly, the lever 103 swings counterclockwise as viewed from the left side, and moves from the second engagement position to the first engagement position.

  Then, the contact between the second engagement claw 159 and the first engagement surface 143 of the first convex portion 141 is released, and the urging force of the torsion spring 148 against the other end portion of the V-shaped cam 145 causes the FIG. As shown, the sector gear 101 rotates clockwise in the left side view.

  At this time, the I-shaped cam 146 rotates in accordance with the rotation of the sector gear 101. The I-shaped cam 146 rotates clockwise from the left side view from the approximately 6 o'clock position in the left side view. Since the position of pressing the frame portion 116 of the I-shaped cam 146 moves upward, the holder 99 is moved to the left side with the driving gear shaft 108 as a fulcrum by the upward biasing force of the tension spring 121 as shown in FIG. Rotate counterclockwise. As the holder 99 rotates, the pendulum gear 100 pivotally supported by the holder 99 moves from the second meshing position toward the first meshing position.

  Then, when the sector gear 101 is rotated by the urging force of the torsion spring 148, the first engagement claw 158 of the lever 103 located at the first engagement position is moved to the second convexity of the sector gear 101 as shown in FIG. The part 142 contacts the first engagement claw 158 from the rear.

  Thereby, the rotation of the sector gear 101 is restricted, and the rotation of the sector gear 101 by the urging force of the torsion spring 148 is restricted.

  At this time, as shown in FIG. 14, the I-shaped cam 146 of the sector gear 101 points in the direction of about 7 o'clock around the sector gear shaft 125 in the left side view. Since the sector gear 101 is restricted from rotating in a state where the I-shaped cam 146 presses the frame portion 116, the pendulum gear 100 is in a non-recessed position where it does not mesh with either the first gear train or the second gear train. Retained.

Thereby, the switching unit 83 is switched from the reverse mode to the stack mode.
(3) Switching operation from stack mode to forward rotation mode Switching operation from the stack mode to forward rotation mode will be described.

  In order to switch the switching unit 83 from the stack mode to the normal rotation mode, the solenoid switch 104 in the stack mode is switched from the non-excited state to the excited state, and immediately after that, is switched again to the non-excited state.

  As a result, the lever 103 is swung clockwise as viewed from the left side, and immediately after being moved from the first engagement position to the second engagement position, is swung counterclockwise as viewed from the left side. It moves from the second engagement position to the first engagement position.

  Then, the contact between the first engagement claw 158 and the second engagement surface 144 of the second protrusion 142 is released, and the biasing force of the torsion spring 148 against the other end of the V-shaped cam 145 is As shown in FIG. 6, the sector gear 101 rotates clockwise as viewed from the left side. The rotation of the sector gear 101 causes the second protrusion 142 to move from the position engaged with the first engagement claw 158, and then the first engagement claw 158 is moved again to the first engagement position.

  When the sector gear 101 rotates, the second toothed portion 138 of the missing gear 130 moves to a position facing the drive gear 98. As a result, the second toothed portion 138 meshes with the drive gear 98, and the sector gear 101 rotates as the drive gear 98 rotates.

  At this time, the I-shaped cam 146 rotates in accordance with the rotation of the sector gear 101. The I-shaped cam 146 is separated from the frame portion 116 by rotating counterclockwise in the left side view from the position of about 7 o'clock in the left side view. When the I-shaped cam 146 moves away from the frame portion 116, the holder 99 rotates counterclockwise as viewed from the left side with the drive gear shaft 108 as a fulcrum by the upward biasing force of the tension spring 121. As the holder 99 rotates, the pendulum gear 100 pivotally supported by the holder 99 moves from the non-meshing position toward the first meshing position.

  When the sector gear 101 rotates, the first missing tooth portion 135 faces the drive gear 98. At this time, the torsion spring 148 applies an urging force that rotates in the clockwise direction in the left side view to one end portion of the V-shaped cam 145.

  When the sector gear 101 rotates by urging the torsion spring 148 to one end of the V-shaped cam 145, as shown in FIG. 7, the first engagement claw 158 of the lever 103 located at the first engagement position is moved to the sector gear. 101 abuts on the first convex portion 141.

As a result, the rotation of the sector gear 101 is restricted, and the stack mode is switched to the forward rotation mode.
(4) Switching Operation from Stack Mode to Inversion Mode Next, switching operation from the stack mode to the inversion mode will be described.

  In order to switch the switching unit 83 from the stack mode to the reverse rotation mode, as shown in FIG. 13, the solenoid switch 104 in the stack mode is switched from the non-excited state to the excited state as shown in FIG. Holds the excited state.

  As a result, the lever 103 is swung clockwise as viewed from the left side and is held in a state of being moved from the first engagement position to the second engagement position.

  Then, the contact between the first engagement claw 158 and the second engagement surface 144 of the second convex portion 142 is released, and the urging force of the torsion spring 148 against the other end portion of the V-shaped cam 145 causes the FIG. As shown, the sector gear 101 rotates clockwise in the left side view.

  When the sector gear 101 rotates, the second toothed portion 138 of the toothless gear 130 meshes with the drive gear 98, and the sector gear 101 rotates as the drive gear 98 rotates.

  At this time, the I-shaped cam 146 rotates in accordance with the rotation of the sector gear 101 as shown in FIG. The I-shaped cam 146 is separated from the frame portion 116 by rotating counterclockwise in the left side view from the position of about 7 o'clock in the left side view. When the I-shaped cam 146 is separated from the frame portion 116, the holder 99 is rotated counterclockwise as viewed from the left side about the drive gear shaft 108 by the upward biasing force of the tension spring 121. As the holder 99 rotates, the pendulum gear 100 pivotally supported by the holder 99 moves from the non-engagement position toward the first engagement position.

  When the sector gear 101 rotates, the first missing tooth portion 135 faces the drive gear 98 as shown in FIG. At this time, the torsion spring 148 applies a biasing force in the clockwise direction on the left side to one end of the V-shaped cam 145.

  When the sector gear 101 is rotated by the urging force of the torsion spring 148 to one end of the V-shaped cam 145, the second convex portion of the sector gear 101 is moved to the second engagement claw 159 of the lever 103 located at the second engagement position. 142 is close. However, since the second engaging claw 159 and the second convex portion 142 are arranged at positions that do not overlap in the left-right direction that is the axial direction of the cylindrical portion 131, the second engaging claw 159 and the second convex portion 142 are engaged. The sector gear 101 continues to rotate without matching.

  Thereafter, the pendulum gear 100 is moved to the first meshing position by the rotation of the sector gear 101. However, since the first engagement claw 158 is separated from the cylindrical portion 131, the sector gear continues to rotate as it is.

  Therefore, the pendulum gear 100 is swung toward the second meshing position without being held at the first meshing position.

  In addition, after the pendulum gear 100 is swung from the first meshing position toward the second meshing position, the operation is the same as the switching operation from the normal rotation mode to the reverse rotation mode, and thus the description thereof is omitted.

As a result, the rotation of the sector gear 101 is restricted, and the stack mode is switched to the reverse mode.
5. Effects of Driving Force Transmission Mechanism (1) According to this printer 1, the switching unit 83 holds the pendulum gear 100 at the first meshing position where it meshes with the fourth idle gear 94 as shown in FIG. By transmitting the rotational driving force to one side of the motor 68 to the first gear train, the normal rotation mode in which the rotation direction of the switchback roller 50 and the intermediate paper discharge roller 48 is the normal rotation direction, as shown in FIG. The pendulum gear 100 is held at the second meshing position for meshing with the fifth idle gear 95, and the rotational driving force to one side of the main motor 68 is transmitted to the second gear train, so that the switchback roller 50 and the intermediate paper discharge As shown in FIG. 13, the pendulum gear 100 is held in the non-engagement position between the fourth idle gear 94 and the fifth idle gear 95 as shown in FIG. One rotary drive to the chromatography data 68 that does not even transmitted on either the first gear train and the second gear train, and a stack mode which does not rotate the switchback roller 50 and the intermediate discharge rollers 48.

  As a result, there is no need to switch or stop the rotational driving force of the main motor 68 in order to switch or stop the rotation direction of the switchback roller 50. The paper roller 14, the transport roller 16, the registration roller 17, the black developing roller 31K, the heating roller 43, and the reverse transport roller 55) are transmitted to a motor that generates a rotational driving force, and to the switchback roller 50 and the intermediate paper discharge roller 48. The main motor 68 can bear the motor that generates the rotational driving force.

As a result, an increase in the number of motors in the printer 1 can be prevented, and the rotation direction of the switchback roller 50 can be switched between the forward rotation direction and the reverse rotation direction while cost and noise can be reduced. Thus, it is possible to form images on both the one side surface and the other side surface of the paper P.
(2) According to the printer 1, as shown in FIGS. 5 and 10, in the pendulum gear 100 rotatably supported by the holder 99, the cam 147 presses the frame portion 116 of the holder 99, and the holder It is moved by swinging 99.

Therefore, the pendulum gear 100 can be moved by pressing the holder 99 with the cam 147, and the first meshing position, the second meshing position, and the non-meshing position of the pendulum gear 100 can be switched.
(3) According to the printer 1, as shown in FIGS. 5 and 10, when the drive gear 98 is rotating, the toothless gear 130 meshes the toothed portion 134 with the drive gear 98. Therefore, the pendulum gear 100 can be moved by pressing the holder 99 by moving the cam 147. Further, as shown in FIGS. 7 and 12, the missing tooth gear 130 rotates so that the missing tooth portion 133 is opposed to the driving gear 98 so as not to receive the rotational driving force from the main motor 68. The movement of the pendulum gear 100 can be stopped without stopping and pressing the holder 99.

For this reason, the missing gear 130 switches the pendulum gear 100 to the first meshing position, the second meshing position, and the non-meshing position by meshing and rotating the toothed portion 134 with the drive gear 98. By stopping the tooth portion 133 so as to face the drive gear 98, the pendulum gear 100 can be held at each meshing position, and the forward rotation mode, the reverse mode, and the stack mode can be maintained.
(4) Also, according to the printer 1, as shown in FIG. 7, the first missing tooth portion 135 is associated with the normal rotation mode in which the use frequency is relatively high, as shown in FIGS. As shown, the inversion mode and the stack mode, which are relatively less frequently used, can correspond to the missing tooth portion 133 in accordance with the usage frequency by making it correspond to the second missing tooth portion 136. The enlargement of the missing gear 130 can be efficiently suppressed.
(5) Also, according to this printer 1, as shown in FIGS. 6 and 11, the pendulum gear 100 is engaged with the drive gear 98, and the rotational driving force is always transmitted to one side while the holder 99 is swung. The first mesh position shown in FIG. 4 that meshes with the first gear train, the second mesh position shown in FIG. 9 that meshes with the second gear train, and the first gear train and the second gear train are not meshed by the movement. It moves to the non-meshing position shown in FIG.

That is, as shown in FIGS. 6 and 11, the pendulum gear 100 is always rotated in one direction, and is switched to the first meshing position, the second meshing position, and the non-meshing position, thereby causing the switchback roller 50 to move. It is possible to switch between rotation in the forward direction, rotation in the reverse direction, and non-rotation state.
(6) Further, according to the printer 1, as shown in FIGS. 6 and 11, the locking means (lever 103, solenoid switch 104) are resisted against the biasing force of the torsion spring 148 that biases the toothless gear 130. , And the cylindrical portion 131) of the sector gear 101, the missing tooth portion 133 of the missing tooth gear 130 in the normal rotation mode, the reverse mode and the stack mode and the drive gear 98 are opposed to each other. It is possible to prevent the driving force from being transmitted.

  Therefore, the forward rotation mode, the reverse mode, and the stack mode of the switching unit 83 can be reliably held.

On the other hand, when the state where the tooth missing portion 133 and the drive gear 98 are opposed to each other by the locking means is released, the tooth missing gear 130 is attached in the direction rotated by the drive gear 98 by the urging force of the torsion spring 148. Therefore, the rotational driving force from the main motor 68 can be reliably transmitted to the missing gear 130.
(7) According to the printer 1, as shown in FIGS. 5 and 6, in the cam 147, the I-shaped cam 146 that presses the holder 99 and the V-shaped cam 145 urged by the torsion spring 148 The mode of the switching unit 83 can be switched reliably.
(8) Further, according to this printer 1, as shown in FIG. 8, the cam 147 and the toothless gear 130 are integrally formed, so that the number of parts can be reduced.
(9) Further, according to the printer 1, as shown in FIGS. 7 and 12, the solenoid switch 104 switches between engagement and release of the lever 103 with respect to the convex portion 140 of the cylindrical portion 131, and The engagement of the part 140 restricts the rotation of the toothless gear 130, and the engagement of the lever 103 and the convex part 140 is released to rotate the toothless gear 130.

Therefore, the rotation restriction state and the rotation state of the missing gear 130 can be switched by switching the solenoid switch 104.
(10) According to the printer 1, as shown in FIGS. 7 and 12, the lever 103 is moved between the first engagement position and the second engagement position by switching the solenoid switch 104. The engagement of the first engaging portion 153 with respect to the first convex portion 141 is released and the toothless gear 130 rotates, but the second engaging portion 154 is engaged with the first convex portion 141 to The rotation of the tooth gear 130 is restricted. That is, since the engagement of the first engaging portion 153 with respect to the first convex portion 141 is released and until the second engaging portion 154 is engaged with the first convex portion 141, the missing gear 130 is It is rotating.

  The lever 103 is moved from the second engagement position to the first engagement position by switching the solenoid switch 104 as shown in FIGS. The engagement with the convex portion 141 is released, and the toothless gear 130 rotates. However, the first engaging portion 153 is engaged with the second convex portion 142 and the rotation of the toothless gear 130 is restricted. That is, since the engagement of the second engaging portion 154 with respect to the first convex portion 141 is released and until the first engaging portion 153 is engaged with the second convex portion 142, the missing gear 130 is It is rotating.

In this way, by switching between engagement and release of the lever 103 with respect to the convex portion 140 by the solenoid switch 104, the rotation restriction state and the rotation state of the missing gear 130 can be repeated.
(11) Further, according to the printer 1, as shown in FIG. 12, the missing gear 130 has a position where the first convex portion 141 and the first engaging portion 153 are engaged, as shown in FIG. 3, a position where the first protrusion 141 and the second engagement part 154 are engaged, and a position where the second protrusion 142 and the first engagement part 153 are engaged, as shown in FIG. 16. Its rotation is restricted at one position.

That is, by switching these three positions to the normal rotation mode, the reverse mode, and the stack mode, it is possible to switch to each mode.
(12) Also, according to this printer 1, as shown in FIGS. 12 and 16, the second convex portion 142 and the second engaging portion 154 are arranged in the axial direction of the cylindrical portion 131 formed in the sector gear 101. Since the second protrusions 142 and the second engagement portions 154 are engaged with each other, it is possible to reliably prevent the second protrusions 142 and the second engagement portions 154 from engaging with each other.
(13) According to the printer 1, as shown in FIGS. 10 and 14, the switching unit 83 is switched by switching the lever 103 between the first engagement position and the second engagement position by the solenoid switch 104. The normal mode can be switched to the reverse mode, and the reverse mode can be switched to the stack mode.
(14) Further, according to the printer 1, when the stack mode is directly switched to the reverse mode, the pendulum gear 100 moves from the non-engagement position shown in FIG. 13 to the first engagement position shown in FIG. By moving from the first meshing position to the second meshing position shown in FIG. 9, the stack mode is switched to the reverse mode.

However, during the direct switching from the stack mode to the reverse mode, the pendulum gear 100 is not held at the first meshing position and does not enter the normal rotation mode. You can switch to the mode reliably.
(15) According to the printer 1, as shown in FIG. 8, the missing gear 130, the cylindrical portion 131, and the cam 147 are integrally configured as the sector gear 101.

  Therefore, various members that switch between the normal rotation mode, the reverse mode, and the stack mode can be integrally configured as one sector gear 101.

As a result, the member configuration can be simplified while the number of parts can be reduced.
(16) Further, according to the printer 1, as shown in FIG. 2, the rotational driving force to one side of the main motor 68 is applied to the rotating body (the paper feeding roller 14, the conveying roller 16, the registration roller 17, the black developing roller). 31K, the heating roller 43 and the reverse conveying roller 55), and the switchback roller 50 and the intermediate paper discharge roller 48, respectively.

Then, while the rotating body can always rotate in one direction by the rotational driving force from the main motor 68 to one side, the rotation direction of the switchback roller 50 and the intermediate paper discharge roller 48 is switched between the normal rotation direction and the reverse rotation direction. Can do.
6). Initial Control of Switching Unit by CPU As shown in FIG. 17, the printer 1 includes a CPU 72 as an example of a control unit that controls the solenoid switch 104 to switch between the excited state and the non-excited state.

  The CPU 72 controls the solenoid switch 104 to be held in a non-excited state for a first time, the second control to control the solenoid switch 104 to be held in an excited state for a second time, and the solenoid switch 104. It is possible to execute the third control for controlling to maintain the excited state for the third time.

  Here, the first time is 0.12 sec or more, and the first engagement claw 158 and the first engagement surface are released after the contact between the first engagement claw 158 and the second engagement surface 144 is released. The first engagement claw 158 and the second engagement after the time when the sector gear 101 rotates until the position where the first engagement claw 143 contacts or the contact between the first engagement claw 158 and the first engagement surface 143 is released. This is a longer time than the longer time during which the sector gear 101 rotates to the position where the surface 144 abuts.

  The second time is 0.13 sec or more, and after the contact between the first engagement claw 158 and the second engagement surface 144 is released, the second engagement claw 159 and the first engagement surface 143 This time is longer than the time during which the sector gear 101 rotates to the contact position.

  The third time is 0.01 to 0.05 sec, which is longer than the time during which the contact between the first engagement claw 158 and the second engagement surface 144 can be reliably released. It is a time shorter than the time when the sector gear 101 rotates until the position where the first engagement claw 158 and the first engagement surface 143 come into contact after the contact with the second engagement surface 144 is released. That is, the third time is shorter than the second time.

In addition to the first control, the second control, and the third control, the CPU 72 executes a control for switching the solenoid switch 104 between the excited state and the non-excited state in order to execute the double-sided image forming process for the paper P.
(1) Discharge of paper remaining in the main casing when the power is turned on In the printer 1 immediately after the power is turned on, the solenoid switch 104 is controlled by the CPU 72 so as to be always in a non-excited state.

  After the printer 1 is powered on, first, the main motor 68 is driven.

  Thereby, the main motor 68 transmits a rotational driving force to one side to the input gear 79 via a plurality of gears (not shown) of the main casing 2.

  Then, the rotational driving force to one side transmitted to the input gear 79 is transmitted to the pendulum gear 100 via the driving gear 98.

  At this time, since the solenoid switch 104 is controlled so as to be in the non-excited state, the switching unit 83 is in the forward rotation mode in which the pendulum gear 100 is held at the first meshing position, or the pendulum gear 100 is in the non-meshing position. Is one of the stack modes held in

  As shown in FIG. 18, after the power supply to the printer 1 is turned on, the CPU 72 executes a first control for holding the solenoid switch 104 in a non-excited state for a first time. The first time in the first control after the power is turned on for the printer 1 is longer than the time during which the paper P is discharged from the post-fixing sensor 63 to the paper discharge tray 51. The first control of the present embodiment is an example of the first control in the claims, and the first control in the claims issues an instruction to keep the solenoid switch 104 in a non-excited state, or the solenoid switch 104 Control is also included unless an instruction is given to enter the excited state.

  Accordingly, when the switching unit 83 is in the normal rotation mode when the printer 1 is turned on, the intermediate paper discharge roller 48 and the switchback roller 50 rotate in the normal rotation direction, which will be described later in the main body casing 2. Even when the post-fixing sensor 63 and the paper discharge sensor 64 remain between the post-fixing sensor 63 and the paper discharge sensor 64, the paper P is discharged. As a case where the paper P is not detected, a case where the length of the paper P is shorter than the distance between the post-fixing sensor 63 and the paper discharge sensor 64 is assumed.

  Further, when the switching unit 83 is in the stack mode when the printer 1 is turned on, the intermediate paper discharge roller 48 and the switchback roller 50 do not rotate in either the forward rotation direction or the reverse rotation direction and cannot be detected. When a new sheet P remains, the sheet P is not conveyed anywhere and remains in the main casing 2 as it is.

  Next, the CPU 72 executes a third control for holding the solenoid switch 104 in an excited state for a third time.

  As a result, the engagement of the first engagement claw 158 of the lever 103 with the convex portion 140 is released, and the missing gear 130 rotates. More specifically, when the switching unit 83 is in the normal rotation mode when the printer 1 is turned on, as shown in FIG. 7, the first convex portion of the first engagement claw 158 of the lever 103 is used. The engagement of 141 with the first engagement surface 143 is released, and the sector gear 101 rotates. If the switching unit 83 is in the stack mode when the printer 1 is turned on, the second engagement of the second protrusion 142 of the first engagement claw 158 of the lever 103 is performed as shown in FIG. The engagement with the mating surface 144 is released, and the sector gear 101 rotates.

  Next, the CPU 72 executes a first control for holding the solenoid switch 104 in an excited state again for a first time.

  Since the third time of the third control is as short as 0.01 to 0.05 sec, as shown in FIGS. 7 and 16, when the pendulum gear 100 rotates in the left side view, the third engagement claw 158 is engaged. Immediately after the convex portion 140 that has been joined passes below the first engagement claw 158, the first engagement claw 158 is positioned again at the first engagement position.

  As a result, when the switching unit 83 immediately after power-on is in the stack mode, the sector gear 101 rotates approximately 210 °, and the first engagement claw 158 is brought into contact with the first engagement surface 143 of the first convex portion 141. Engage with each other to switch to the forward rotation mode.

  Then, the intermediate paper discharge roller 48 and the switchback roller 50 rotate in the forward direction, and the paper P that has not been discharged in the stack mode is discharged.

  Further, when the switching unit 83 immediately after the power is turned on is in the normal rotation mode, the sector gear 101 rotates approximately 150 °, and the first engagement claw 158 is brought into contact with the second engagement surface 144 of the second convex portion 142. Engage with each other and switch to stack mode. At this time, the paper P has already been discharged.

The CPU 72 executes a startup process of the printer 1.
(2) Mode Detection As described above, as shown in FIG. 18, when the printer 1 is turned on and / or after the discharge of the paper P remaining in the main body casing is executed, the switching unit 83 is in the normal rotation mode. In order to determine whether the mode is the stack mode, the CPU 72 performs mode detection of the switching unit 83.

  In order to execute the mode detection, the CPU 72 executes a second control for holding the solenoid switch 104 in an excited state for a second time after discharging the paper P remaining in the main casing 2 when the power is turned on.

  Accordingly, when the switching unit 83 is in the normal rotation mode immediately before executing the second control, the switching unit 83 is switched to the reverse mode.

  In addition, when the switching unit 83 is in the stack mode immediately before executing the second control, as shown in FIG. 16, the second convex portion 142 of the cylindrical portion 131 is forward-downward, specifically, the left side. When the sector gear 101 is rotated approximately 330 ° in the clockwise direction in the left side view from the state of facing the direction of about 4 o'clock in the plan view, the first engagement surface 143 of the first convex portion 141 is in the second engagement claw 159. Is switched to the reverse mode.

  When the switching unit 83 is switched from the stack mode to the reverse mode, the second convex portion 142 overlaps with the second engaging claw 159 of the lever 103 in the left side view while the sector gear 101 is rotating. Since the portion 142 and the second engagement claw 159 are displaced in the left-right direction so as not to overlap each other when viewed from the direction orthogonal to the rotation axis direction of the cylindrical portion 131, the second projection 142 and the second engagement claw 159 does not engage, and the sector gear 101 rotates by receiving the rotational driving force of the drive gear 98 as it is. In addition, the first convex portion 141 passes below the first engaging claw 158 in the left side view while the sector gear 101 is rotating. At this time, as shown in FIG. 5, the I-shaped cam 146 of the sector gear 101 points in the direction of about 3 o'clock with the sector gear shaft 125 as the center in the left side view, whereby the holder 99 biases the tension spring 121. Accordingly, the pendulum gear 100 is positioned at the first meshing position, and the intermediate paper discharge roller 48 and the switchback roller 50 are temporarily rotated in the normal rotation direction.

  After the switching unit 83 is switched to the reverse mode in this way, the switching unit 83 is switched to the stack mode by setting the solenoid switch 104 to the non-excited state by the CPU 72.

Thereby, the mode detection of the switching unit 83 by the CPU 72 is completed.
7). Operation and Effect by Control of CPU of Switching Unit (1) According to this printer 1, as shown in FIGS. 4 and 9, a main motor 68 is used to switch the rotation direction of the switchback roller 50 and the intermediate sheet discharge roller 48. Therefore, it is not necessary to switch the rotational driving force of the printer 1 in the forward and reverse directions. The main motor 68 can serve as a motor that generates a rotational driving force for rotating 55) and a motor that generates a rotational driving force transmitted to the switchback roller 50.

  On the other hand, according to the printer 1, the solenoid switch 104 is selected between a non-excitation state that allows the switching unit 83 to switch between the normal rotation mode and the stack mode and an excitation state that allows the switching unit 83 to switch between the reverse modes. The switching of the solenoid switch 104 between the non-excited state and the excited state is controlled by the CPU 72.

  Therefore, the CPU 72 cannot determine whether the switching unit 83 is in the normal rotation mode or the stack mode only by setting the solenoid switch 104 to the non-excited state, and sets the switching unit 83 in the reverse mode so that the switchback roller 50 is in the reverse direction. There is a problem in that the paper P cannot be discharged out of the printer 1 by rotating the switchback roller 50 in the normal rotation direction before the rotation.

  Therefore, in this printer 1, as shown in FIG. 18, the CPU 72 performs the first control for controlling the solenoid switch 104 so as to hold the non-excited state for the first time, and the solenoid so as to hold the excited state for the second time. The second control for controlling the switch 104 and the third control for controlling the solenoid switch 104 so as to hold the excitation state for a third time shorter than the second time can be executed.

  As a result, by performing the third control on the switching unit 83 that is in the normal rotation mode or the stack mode by the first control of the CPU 72, the normal rotation mode and the stack mode can be switched.

  Thus, if the first control and the third control are executed before the second control is executed, the forward rotation mode can always be executed before the reverse mode is executed.

Accordingly, the main motor 68 that generates a rotational driving force to one side for rotating the switchback roller 50 and the intermediate paper discharge roller 48 has a rotational driving force for rotating a rotating body that rotates to one side in the printer 1. By carrying the same main motor 68 as the main motor 68 that is generated, cost and noise can be reduced, but the switching unit 83 is surely set to the forward rotation mode before the reverse mode, and the switchback roller 50 and The paper P can be discharged by rotating the intermediate paper discharge roller 48 in the forward rotation direction.
(2) Also, according to this printer 1, as shown in FIG. 18, immediately after the printer 1 is turned on, the switching unit 83 is set to the normal rotation mode, and the switchback roller 50 is rotated in the normal rotation direction to P can be discharged.

Therefore, even if the paper P remains in the printer 1 immediately after the printer 1 is turned on, the paper P can be forcibly discharged.
(3) According to the printer 1, as shown in FIG. 1, when the post-fixing sensor 63 can detect whether or not the sheet P remains in the middle of conveyance from the image forming unit 4 to the discharge port 49. In other words, after the paper P is appropriately discharged, the second control can be executed to set the switching unit 83 to the reverse mode and execute the double-sided image forming process.

  On the other hand, if the paper P remains on the downstream side in the transport direction from the post-fixing sensor 63 during the transport from the image forming unit 4 to the discharge port 49 in the primary transport path 52, There is a problem that the presence or absence cannot be detected.

  However, in the printer 1, regardless of the detection of the paper P by the post-fixing sensor 63, the second time before the second control is longer than the transport time of the paper P while being transported from the post-fixing sensor 63 to the discharge port 49. The forward rotation mode can be executed for 1 hour.

Therefore, the paper P can be reliably discharged before the switching unit 83 is set to the reverse mode.
(4) Also, according to this printer 1, as shown in FIGS. 4 and 9, the solenoid switch 104 is used as the switch means, so that the switching unit 83 can be switched between the non-excited state and the excited state with a simple configuration. And can be switched selectively.

Therefore, the switch means having a complicated configuration is not required, and the cost can be reduced.
(5) Also, according to the printer 1, as shown in FIG. 1, in the printer 1, when an image is formed only on one side of the paper P, it is not necessary to switch the switchback roller 50 in the reverse direction. Therefore, an image can be formed on the paper P only in the normal rotation mode without switching the switching unit 83 to the reverse mode.

According to this printer 1, since the forward rotation mode corresponds to the non-excited state of the solenoid switch 104, the power consumed by the solenoid switch 104 when an image is formed only on one side of the paper P is consumed. Can be suppressed.
(6) Also, according to the printer 1, as shown in FIG. 17, the switching unit 83 is switched to the forward rotation mode by controlling the CPU 72 so that the solenoid switch 104 is in a non-excited state, and the solenoid switch 104 By switching the switching unit 83 from the normal rotation mode to the reversal mode by controlling the CPU 72 so as to be in the excited state, and reversing the switching unit 83 by controlling the CPU 72 so that the solenoid switch 104 is in the non-excited state. You can switch from mode to stack mode.

Therefore, the forward mode, the reverse mode, and the stack mode can be switched by a simple operation of controlling the CPU 72 so that the solenoid switch 104 is in a non-excited state or an excited state.
(7) According to this printer 1, as shown in FIGS. 4 and 9, there is no need to switch the rotational driving force of the main motor 68 forward and backward in order to switch the rotational direction of the switchback roller 50. A motor for generating a rotational driving force for rotating a rotating body (feed roller 14, transport roller 16, registration roller 17, black developing roller 31K, heating roller 43, and reverse transport roller 55) that rotates in one direction in 1; The motor that generates the rotational driving force transmitted to the back roller 50 can be carried by the main motor 68.

  Further, the CPU 72 selectively switches the solenoid switch 104 between a non-excitation state that allows the switching unit 83 to switch between the normal rotation mode and the stack mode, and an excitation state that allows the switching unit 83 to switch the reverse mode. Is controlling.

  As shown in FIG. 18, since the switching unit 83 can be switched only from the reverse mode to the stack mode, when the CPU 72 controls the switching unit 83 to execute the image forming operation, first, the switching unit 83 is used. If the switching unit 83 is switched from the inversion mode to the stack mode, the switching timing can be set to the initial mode as a reference for control.

As a result, the cost and noise can be reduced, and the image forming operation can be executed using the switching unit 83 from the inversion mode to the stack mode as a reference for control.
(8) According to the printer 1, as shown in FIG. 18, the switching unit 83 is switched from the reverse mode to the stack mode from when the printer 1 is turned on until an image is formed on the paper P. Thus, the control standard can be set.
8). Double-Sided Image Forming Process With reference to FIG. 19, the double-sided image forming process by the CPU 72 for a plurality of sheets P will be described.

  As shown in FIG. 1, the main casing 2 includes a paper feed sensor 60, a pre-registration sensor 61, a post-registration sensor 62, a post-fixing sensor 63, and a paper ejection sensor in the primary conveyance path 52. 64 and a reverse path sensor 65 in the secondary transport path 56.

  The paper feed sensor 60 is located near the paper feed roller 14 in the main body casing 2.

  The pre-registration sensor 61 is positioned in the primary conveyance path 52 of the main body casing 2 on the downstream side in the conveyance direction of the paper P with respect to the conveyance roller 16 and on the upstream side in the conveyance direction of the paper P with respect to the registration roller 17. Yes.

  The post-registration sensor 62 is located on the primary conveyance path 52 of the main body casing 2 on the downstream side in the conveyance direction of the paper P with respect to the registration roller 17 and on the front of the photosensitive drum 28 and the conveyance belt 39. It is located upstream in the conveyance direction of P.

  The post-fixing sensor 63 is positioned downstream of the fixing unit 23 in the transport direction of the paper P in the primary transport path 52 of the main casing 2 and upstream of the intermediate paper discharge roller 48 in the transport direction of the paper P. Has been.

  The paper discharge sensor 64 is positioned in the vicinity of the switchback roller 50 upstream of the switchback roller 50 in the conveyance direction of the paper P in the primary conveyance path 52 of the main casing 2.

  The reverse path sensor 65 is located in the vicinity of the rearmost reverse conveyance roller 55 in the main body casing 2.

  Each of the paper feed sensor 60, the pre-registration sensor 61, the post-registration sensor 62, the post-fixing sensor 63, the paper discharge sensor 64, and the reverse path sensor 65 includes a swingable actuator, and the paper P is in contact therewith. Thus, the actuator is tilted and turned on, and the paper P is separated, so that the actuator is turned off. This ON / OFF detection signal is configured to be transmitted to the CPU 72.

  The double-sided image forming process by the CPU 72 for a plurality of sheets P is executed with two sheets as one set.

  Of the one set of two sheets P, a sheet P on which an image is formed on the first sheet is a preceding sheet P1 as an example of the first recording medium, and a sheet P on which an image is formed on the second sheet is the first sheet P. 2 is a subsequent sheet P2 as an example of a recording medium.

  Further, in the preceding paper P1 and the succeeding paper P2, a surface on which an image is formed first is defined as one side surface, and a surface on which an image is formed later is defined as the other side surface.

  The CPU 72 corrects the preceding sheet P 1 so that the preceding sheet P 1 is supplied from the sheet feeding unit 3 to the primary conveyance path 52 by the conveyance roller 16, and one side surface of the preceding sheet P 1 is formed by the image forming unit 4 and conveyed to the switchback roller 50. The first step of maintaining the rotation mode is executed.

  Specifically, to execute the first step, the process motor 69 is driven after the mode detection is completed and the startup process is completed.

  Next, the CPU 72 controls the switching unit 83 to be held in the normal rotation mode.

  Then, as shown in FIG. 20A, the preceding paper P1 on the paper feed tray 12 of the paper feed unit 3 is transported between the photosensitive drum 28 and the transport belt 39 as described above.

  The succeeding paper P2 is stacked on the paper feed tray 12 of the paper feed unit 3.

  As a result, as shown at timing A in FIG. 19, the paper feed sensor 60, the pre-registration sensor 61, and the post-registration sensor 62 are turned on.

  Next, when the preceding sheet P1 is conveyed along the primary conveyance path 52, as shown in FIG. 20B, the preceding sheet P1 is formed with an image on one side surface thereof by the image forming unit 4 as described above. After passing through the fixing unit 23, the intermediate paper discharge roller 48 and the switchback roller 50 are transported so that the front ends (upstream end portions in the transport direction in the primary transport path 52) are positioned in the vicinity of the discharge port 49.

  The succeeding paper P2 is stacked on the paper feed tray 12 of the paper feed unit 3.

  As a result, as shown at timing B in FIG. 19, the paper feed sensor 60, the pre-registration sensor 61, and the post-registration sensor 62 are turned off, and the post-fixing sensor 63 and the paper discharge sensor 64 are turned on.

  Next, as shown in FIG. 20C, the preceding paper P <b> 1 is transported to a position where the rear end (the downstream end in the transport direction in the primary transport path 52) is near the discharge port 49.

  The succeeding paper P2 is stacked on the paper feed tray 12 of the paper feed unit 3.

  At this time, as indicated by timing C in FIG. 19, the paper discharge sensor 64 remains ON, and the post-fixing sensor 63 is OFF.

  Then, based on the ON of the paper discharge sensor 64 for the preceding paper P1, the CPU 72 executes a second step for holding the reverse mode so that the preceding paper P1 is transported to the secondary transport path 56 after a predetermined time has elapsed. .

  Specifically, in order to execute the second step, the switching unit 83 is switched from the normal rotation mode to the reverse rotation mode under the control of the CPU 72 when the sheet discharge sensor 64 is turned on and 1.00 sec elapses.

  As a result, the preceding paper P <b> 1 is reversed and conveyed toward the secondary conveyance path 56.

  Then, as shown in FIG. 20D, the preceding paper P1 is transported such that the leading end (the downstream end in the transport direction in the secondary transport path 56) is positioned in the vicinity of the rearmost reverse transport roller 55.

  The CPU 72 drives the paper feed roller 14 a predetermined time after switching the switching unit 83 from the normal rotation mode to the reverse mode. As a result, the succeeding paper P2 is transported between the photosensitive drum 28 and the transport belt 39 after a predetermined time has elapsed.

  Then, as shown at timing D in FIG. 19, the paper discharge sensor 64 is turned off, and the paper feed sensor 60, the pre-registration sensor 61, and the post-registration sensor 62 are turned on.

  In addition, the CPU 72 sets the stack mode so that the preceding sheet P1 stays on the secondary conveyance path 56 so that the preceding sheet P1 conveyed on the secondary conveyance path 56 cannot catch up with the subsequent sheet P2 during the second step. The third step of holding is executed.

  Specifically, the switching unit 83 is in the reverse mode in the second step, but switches to the stack mode until the predetermined time has elapsed after the succeeding sheet P2 passes the post-registration sensor 62, and the preceding sheet P1. In the secondary transfer path 56. The CPU 72 switches the switching unit 83 from the stack mode to the reverse mode after a predetermined time has elapsed since the post-registration sensor 62 for the succeeding paper P2 is turned on.

  Then, after a predetermined time has elapsed since the post-registration sensor 62 for the succeeding sheet P2 is turned on, the CPU 72 executes a fourth step for maintaining the normal rotation mode so that the succeeding sheet P2 is conveyed to the switchback roller 50.

  Specifically, to execute the fourth step, when the preceding sheet P1 is conveyed toward the secondary conveying path 56 and the reverse path sensor 65 is turned on and a predetermined time has elapsed, the preceding sheet P1 Since the entirety is in the secondary conveyance path 56 and passes through the intermediate paper discharge roller 48, the switching unit 83 is switched from the reverse mode to the normal mode via the stack mode under the control of the CPU 72. .

  As a result, the succeeding paper P2 forms an image on one side surface thereof, and is conveyed toward the discharge port 49 by the intermediate paper discharge roller 48 that rotates in the forward rotation direction.

  Then, as shown in FIG. 21E, the preceding paper P1 is transported to a position where the rear end (the upstream end in the transport direction in the secondary transport path 56) exceeds the reverse reverse transport roller 55.

  The succeeding sheet P2 is conveyed to a position where the leading end (the downstream end in the conveying direction in the primary conveying path 52) is near the discharge port 49 by the intermediate sheet discharge roller 48 and the switchback roller 50 that rotate in the forward direction. The

  Then, as shown at timing E in FIG. 19, the reverse path sensor 65 is turned off, and the post-fixing sensor 63 and the paper discharge sensor 64 are turned on.

  Next, as shown in FIG. 21F, the preceding paper P1 is transported such that the leading end (the downstream end in the transport direction in the secondary transport path 56) is positioned in the vicinity of the transport roller 16.

  The succeeding paper P2 is transported so that the rear end (the downstream end in the transport direction in the primary transport path 52) is positioned in the vicinity of the discharge port 49.

  At this time, as indicated by timing F in FIG. 19, the paper discharge sensor 64 remains ON, and the post-fixing sensor 63 is OFF.

  Next, the CPU 72 executes a fifth step in which the reverse mode is maintained so that the subsequent sheet P2 is transported to the secondary transport path 56.

  Specifically, in order to execute the fifth step, the switching unit 83 is switched from the forward rotation mode to the reverse rotation mode under the control of the CPU 72 when the sheet discharge sensor 64 is turned on and 1.00 sec elapses.

  As a result, the succeeding paper P <b> 2 is reversed and conveyed toward the secondary conveyance path 56.

  Then, as shown in FIG. 21G, the succeeding paper P2 is transported such that the leading end (the downstream end in the transport direction in the secondary transport path 56) is positioned in the vicinity of the rearmost reverse transport roller 55.

  The preceding paper P <b> 1 is transported again into the primary transport path 52 by the rotation of the transport roller 16 and transported between the photosensitive drum 28 and the transport belt 39.

  As a result, as shown at timing G in FIG. 19, the paper discharge sensor 64 is turned off, and the reverse path sensor 65 and the post-registration sensor 62 are turned on.

  Then, based on the reverse path sensor 65 being turned on by the succeeding paper P2, the CPU 72 executes a sixth step of maintaining the normal rotation mode after a predetermined time has elapsed. The preceding paper P1 is discharged from the main casing 2 through the discharge port 49 in the primary transport path 52, and the subsequent paper P2 is transported from the secondary transport path 56 to the primary transport path 52 by the transport rollers 16. The other side surface is image-formed by the image forming unit 4 and is discharged from the main body casing 2 through the discharge port 49.

  Specifically, to execute the sixth step, the succeeding sheet P2 is transported toward the secondary transport path 56, and when the reverse path sensor 65 is turned on and a predetermined time has elapsed, the succeeding sheet P2 Since the entirety is in the secondary conveyance path 56 and passes through the intermediate paper discharge roller 48, the switching unit 83 is switched from the reverse mode to the normal mode via the stack mode under the control of the CPU 72. .

  As a result, the preceding sheet P1 conveyed to the sheet discharge unit 5 forms an image on the other side surface, and is conveyed toward the discharge port 49 by the intermediate sheet discharge roller 48 that rotates in the normal rotation direction.

  Then, as shown in FIG. 21H, the leading sheet P1 has its leading end (downstream in the transport direction in the primary transport path 52) at the discharge port 49 by the intermediate discharge roller 48 and the switchback roller 50 that rotate in the forward rotation direction. It is transported to a nearby position.

  The succeeding paper P2 is transported to a position where the rear end (upstream side in the transport direction in the secondary transport path 56) exceeds the reverse reverse transport roller 55.

  Then, as shown at timing H in FIG. 19, the reverse path sensor 65 is turned off, and the post-fixing sensor 63 and the paper discharge sensor 64 are turned on.

  Next, as shown in FIG. 22I, the preceding paper P <b> 1 is transported so that the rear end (the downstream end in the transport direction in the primary transport path 52) is positioned in the vicinity of the discharge port 49.

  The succeeding paper P2 is transported so that the leading end (the downstream end in the transport direction in the secondary transport path 56) is positioned in the vicinity of the transport roller 16.

  At this time, as indicated by timing I in FIG. 19, the paper discharge sensor 64 remains ON, and the post-fixing sensor 63 is OFF.

  Next, as shown in FIG. 22J, the preceding sheet P1 is discharged from the discharge port 49 to the discharge tray 51.

  The succeeding paper P2 is transported again into the primary transport path 52 by the rotation of the transport roller 16, and is transported between the foremost photosensitive drum 28 and the transport belt 39.

  At this time, as indicated by timing J in FIG. 19, the paper discharge sensor 64 is OFF, and the pre-registration sensor 61 and the post-registration sensor 62 are ON.

  Next, as shown in FIG. 22K, the preceding paper P1 is placed on the paper discharge tray 51.

  The succeeding sheet P2 is conveyed by the intermediate sheet discharge roller 48 and the switchback roller 50 that rotate in the forward direction so that the leading end (downstream in the conveyance direction in the primary conveyance path 52) is positioned in the vicinity of the discharge port 49. .

  As a result, as shown at timing K in FIG. 19, the post-fixing sensor 63 and the paper discharge sensor 64 are turned on.

  Next, as shown in FIG. 22L, the preceding paper P1 is placed on the paper discharge tray 51.

  The subsequent sheet P2 is discharged from the discharge port 49 to the discharge tray 51 so as to be placed on the preceding sheet P1.

  As a result, as shown at timing L in FIG. 19, the post-fixing sensor 63 and the paper discharge sensor 64 are turned off.

  Thus, the double-sided image forming process for the first set of two sheets of paper P is completed.

  When the double-sided image forming process is subsequently performed on the second and subsequent sets of paper P, the second set of preceding paper P1 is fed to the paper feed tray 12 at the timing K in FIG. 19 as shown in FIG. 20A. From the photosensitive drum 28 to the conveyor belt 39.

  Then, when the first set of the preceding paper P1 and the succeeding paper P2 are placed on the discharge tray 51 as shown in FIG. 22L, the second set of the preceding paper P1 is displayed as shown in FIG. 20B. An image is formed on one side surface of the forming unit 4, passes through the fixing unit 23, and the front end (upstream end portion in the transport direction in the primary transport path 52) of the intermediate discharge roller 48 and the switchback roller 50. Then, it is conveyed so as to be positioned in the vicinity of the discharge port 49.

  Thereafter, an image is formed on the paper P by a process similar to the double-sided image forming process for the first set of the preceding paper P1 and the succeeding paper P2.

  If the plurality of sheets P is an odd number, an image is formed on one side of the sheet P for the last sheet P, and then the trailing edge of the sheet P is fed to the sheet discharge sensor 64. The switching unit 83 is switched from the normal rotation mode to the reverse mode at the timing at which (the upstream end in the conveyance direction in the primary conveyance path 52) arrives, and is conveyed toward the secondary conveyance path 56.

  Then, at the timing when the leading end of the paper P (the upstream end in the transport direction in the secondary transport path 56) reaches the reverse reverse transport roller 55 and the reverse path sensor 65 is turned on and a predetermined time has elapsed, the switching unit. 83 is a stack mode.

  Then, the paper P is transported again to the primary transport path 52, an image is formed on the other side surface, and the switching unit 83 is switched from the stack mode to the normal rotation mode before reaching the fixing unit 23.

  Then, the sheet is discharged onto the discharge tray 51 via the discharge port 49 by the intermediate discharge roller 48 and the switchback roller 50 that rotate in the forward direction.

Thereby, the image forming process for both surfaces of the plurality of sheets P is completed.
9. Effects of Double-sided Image Forming Process According to this printer 1, as shown in FIGS. 21, 22 and 23, image formation on each one side surface and the other side surface of the succeeding sheet P2 of the preceding sheet P1 is performed on the preceding sheet. The process is executed in the order of one side surface of P1, one side surface of the following paper P2, the other side surface of the preceding paper P1, and the other side surface of the following paper P2.

  Therefore, compared to the process of forming an image on one side surface and the other side surface of the preceding paper P1, and then forming an image on the one side surface and the other side surface of the subsequent paper P2, the preceding paper P1 and the subsequent paper are completed in a short time. An image can be formed on the paper P2.

As a result, it is possible to efficiently form an image on one side surface and the other side surface of the plurality of sheets P, while reducing costs and noise.
10. Other Embodiments As an example of the switchback roller, the switchback roller 50 that conveys the paper P toward the paper discharge tray 51 is illustrated. However, the present invention is not limited to this, and the paper in the main body casing 2 is not limited thereto. The intermediate paper discharge roller 48 that switches the transport direction of P may be an example of a switchback roller.

  At that time, the gear arrangement of the fourth idle gear 94 and the intermediate paper discharge roller gear 87 that transmits the rotational driving force for rotating the intermediate paper discharge roller 48 in the forward rotation direction is an example of the first gear train, The gear arrangement of the fifth idle gear 95, the second idle gear 92, the third idle gear 93, the fourth idle gear 94 and the intermediate discharge roller gear 87 for transmitting the rotational driving force for rotating the paper roller 48 in the reverse direction is the second. It may be an example of a gear train.

DESCRIPTION OF SYMBOLS 1 Printer 3 Paper feed part 4 Image forming part 16 Conveyance roller 49 Ejection port 50 Switchback roller 52 Primary conveyance path 56 Secondary conveyance path 63 Post-fixing sensor 68 Main motor 72 CPU
82 Rotational direction variable gear train 83 Switching unit 86 Switchback roller gear 87 Intermediate paper discharge roller gear 91 First idle gear 92 Second idle gear 93 Third idle gear 94 Fourth idle gear 95 Fifth idle gear 98 Drive gear 99 Holder 100 Pendulum gear 103 Lever 104 Solenoid switch 130 Toothless gear 131 Cylindrical part 133 Toothed part 134 Toothed part 140 Convex part 141 First convex part 142 Second convex part 147 Cam 153 First engaging part 154 Second engaging part

Claims (9)

A drive source that generates rotational drive force to one side;
A switchback roller whose rotation direction is switched between a forward rotation direction and a reverse rotation direction in order to switch the conveyance direction of the recording medium on which the image is formed by the image forming unit;
A first gear train that transmits a rotational driving force to the one of the drive sources to the switchback roller so that the rotation direction of the switchback roller is the forward rotation direction;
A second gear train for transmitting a rotational driving force to the one of the driving sources to the switchback roller so that the rotational direction of the switchback roller is the reverse direction;
A first mode for transmitting a rotational driving force to the one of the driving sources to the first gear train; a second mode for transmitting a rotational driving force to the one of the driving sources to the second gear train; A switching mechanism configured to be switchable to a third mode in which the rotational driving force to the one of the drive sources is not transmitted to either the first gear train or the second gear train;
Switch means for selectively changing the state between a first state allowing the switching mechanism to switch to the first mode or the third mode and a second state allowing the switching mechanism to switch to the second mode. When,
Control means for controlling a state change between the first state and the second state of the switch means;
The switching mechanism is configured to be switchable only from the second mode to the third mode,
The control means includes
A first control for controlling the switch means to maintain the first state for a first time;
A second control for controlling the switch means so as to hold the second state for a second time, and
An image forming apparatus comprising: switching the switching mechanism to the third mode after setting the switching mechanism to the second mode by executing the second control.   The image forming apparatus according to claim 1, wherein the control unit executes the second control during a period from when the image forming apparatus is powered on until an image is formed on a recording medium. The control means includes
A third control for controlling the switch means to hold the second state for a third time shorter than the second time can be performed;
The switching mechanism is
The image forming apparatus according to claim 1, wherein the first mode and the third mode are interchanged before and after the third control of the control unit. A discharge port capable of discharging the recording medium on which the image is formed;
Provided in the middle of conveyance from the image forming unit to the discharge port, and provided with a sensor for detecting the recording medium,
4. The image forming apparatus according to claim 3, wherein the first time of the first control is a time longer than a conveyance time of the recording medium during conveyance from the sensor to the discharge port. . The switch means is a solenoid switch in which one of an excited state and a non-excited state corresponds to the first state, and one of the excited state and the non-excited state corresponds to the second state. The image forming apparatus according to any one of claims 1 to 4.   The image forming apparatus according to claim 5, wherein the solenoid switch has a non-excitation state corresponding to the first state and an excitation state corresponding to the second state. The switching mechanism is
Selective to a first meshing position that meshes with the first gear train, a second meshing position that meshes with the second gear train, and a non-meshing position that meshes with neither the first gear train nor the second gear train A pendulum gear located at
A holder for supporting the pendulum gear in a relatively rotatable manner;
A cam that contacts the holder and moves the holder;
A driving gear to which the rotational driving force from the driving source is transmitted;
A toothless portion that meshes with the drive gear, and a toothless gear that has a toothless portion that faces the drive gear in each of the first mode, the second mode, and the third mode;
In each of the first mode, the second mode, and the third mode, a lock means for maintaining a state in which the toothless portion and the drive gear face each other,
The locking means is
A regulating member that can rotate in conjunction with the toothless gear and has a convex portion on the outer periphery thereof;
By engaging with the convex part, a first engaging part and a second engaging part are provided, and the rotation of the partial gear can be restricted, and the first engaging part is in relation to the convex part. A first engagement position where the second engagement portion does not engage with the convex portion, and the second engagement portion engages with the convex portion, and the first engagement. An engagement member movable between a second engagement position at which the portion does not engage with the convex portion,
The convex portion is
A first convex portion engageable with the first engaging portion and the second engaging portion;
A second protrusion that is engageable with the first engagement portion and does not engage with the second engagement portion;
The engagement member is located at the first engagement position, and the first mode is achieved by the engagement of the first engagement portion and the first convex portion,
When the engaging member is located at the second engaging position and the second engaging portion and the first convex portion are engaged, the first mode is changed to the second mode,
When the engaging member is located at the first engaging position and the first engaging portion and the second convex portion are engaged, the second mode is changed to the third mode,
The switch means includes
When in the first state, the engagement member is positioned at the first engagement position,
The image forming apparatus according to claim 3, wherein the engagement member is positioned at the second engagement position in the second state. The image forming unit disposed upstream of the switchback roller in the transport direction;
A transport roller disposed upstream of the image forming unit in the transport direction and to which the rotational driving force from the drive source is input;
A paper feeding unit on which the recording medium is placed;
A primary conveyance path configured such that the recording medium is supplied from the conveyance roller, passes through the image forming unit, and reaches the switchback roller;
A secondary conveyance path configured to join the recording medium from the switchback roller to the upstream side in the conveyance direction with respect to the image forming unit of the primary conveyance path;
The control means can execute double-sided image formation processing for forming an image on the recording medium,
The double-sided image forming process is a process of forming images on both sides of two recording media, a first recording medium and a second recording medium,
The first recording medium is supplied from the paper feeding unit to the primary conveyance path by the conveyance roller, and one side surface of the first recording medium is formed by the image forming unit and conveyed to the switchback roller. A first step of maintaining one mode;
A second step of maintaining the second mode so that the first recording medium is transported to the secondary transport path;
A third step of maintaining the third mode so as to stop the conveyance of the first recording medium in the secondary conveyance path;
A fourth step of maintaining the first mode so that the second recording medium is conveyed to the switchback roller;
A fifth step of maintaining the second mode so that the second recording medium is transported to the secondary transport path;
The first recording medium is discharged from the discharge port in the primary transport path, and the second recording medium is supplied from the secondary transport path to the primary transport path by the transport roller, and the other way 5. The image forming apparatus according to claim 4, further comprising: a sixth step of holding the first mode so that a side surface is image-formed by the image forming unit and is discharged from the discharge port. 6. .   The image forming unit disposed upstream of the switchback roller in the transport direction;
  A transport roller disposed upstream of the image forming unit in the transport direction and to which the rotational driving force from the drive source is input;
  A paper feeding unit on which the recording medium is placed;
  A primary conveyance path configured such that the recording medium is supplied from the conveyance roller, passes through the image forming unit, and reaches the switchback roller;
  A secondary conveyance path configured such that the recording medium merges from the switchback roller to the upstream side in the conveyance direction with respect to the image forming unit of the primary conveyance path;
  A discharge port capable of discharging the recording medium;
With
  The control means can execute double-sided image formation processing for forming an image on the recording medium,
  The double-sided image forming process is a process of forming images on both sides of two recording media, a first recording medium and a second recording medium,
  The first recording medium is supplied from the paper feeding unit to the primary conveyance path by the conveyance roller, and one side surface of the first recording medium is formed by the image forming unit and conveyed to the switchback roller. A first step of maintaining one mode;
  A second step of maintaining the second mode so that the first recording medium is transported to the secondary transport path;
  A third step of maintaining the third mode so as to stop the conveyance of the first recording medium in the secondary conveyance path;
  A fourth step of maintaining the first mode so that the second recording medium is conveyed to the switchback roller;
  A fifth step of maintaining the second mode so that the second recording medium is transported to the secondary transport path;
  The first recording medium is discharged from the discharge port in the primary transport path, and the second recording medium is supplied from the secondary transport path to the primary transport path by the transport roller, and the other way A sixth step of holding the first mode so that a side surface is imaged by the image forming unit and is discharged from the discharge port;
The image forming apparatus according to claim 1, further comprising:

Images