JP4468186B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus configured to be able to perform double-sided printing on a sheet, and more particularly to an image forming apparatus improved so as to eliminate an image obstruction of a printed image on the back side that occurs during paper discharge.

  2. Description of the Related Art Conventionally, an image forming apparatus configured to be capable of duplex printing on a sheet is known. Such an image forming apparatus is configured to switch the transport path between the paper discharge transport path and the return transport path for the single-sided printing and the double-sided printing after the fixing process is performed.

  In the case of single-sided printing, a switching guide provided immediately downstream of the developing device is set on the discharge conveyance path side, so that the fixed paper is discharged to the outside through the discharge conveyance path. On the other hand, in the case of double-sided printing, first, the switching guide is set on the return conveyance path side, and after the sheet on which the fixing process on one side has been completed is introduced into this return conveyance path, the image is formed in a state where the paper is further turned upside down. Returned to the portion, the back surface is subjected to a transfer process. As a result, the paper on which double-sided printing has been completed is subjected to the fixing process on the back side by the fixing device, and is then discharged to the outside through the switching guide switched to the paper discharge conveyance path side.

  By the way, the paper discharge conveyance path and the return conveyance path are provided along a conveyance path formed in a curved state in a direction opposite to each other from a position past the switching guide. Therefore, in the case of single-sided printing, there is no particular problem because the non-printing surface on the back side of the paper is conveyed while being in sliding contact with the inner surface side of the curved conveyance path, but in the case of double-sided printing, the paper on which the front side is printed An image in which the printing surface on the front side is in sliding contact with the inner surface of the conveyance path in a state where it is introduced into the return conveyance path, so that the toner that has not yet been fixed is rubbed by the inner surface of the conveyance path, thereby blurring the printing surface Failure occurs.

An image forming apparatus described in Patent Document 1 has been proposed as a means for solving such an image failure. In this image forming apparatus, the rotation speed of a conveyance roller provided at the downstream end of the return conveyance path is increased from the normal speed so that the sheet conveyance speed in the return conveyance path reaches the return conveyance path from the image forming unit via the fixing device. The speed is higher than the paper transport speed in the transport path. By doing so, the paper introduced into the return conveyance path is pulled by the conveyance roller, so that the printing surface is separated from the inner surface of the curved conveyance path. Is eliminated from being rubbed by the inner surface of the conveyance path, and image obstruction does not occur on the printing surface.
JP 2000-109275 A

  By the way, in the image forming apparatus described in Patent Document 1, the image trouble on the printing surface when the paper on which one-side printing is completed is sent to the return conveyance path during double-sided printing is resolved. When discharging the paper after the printing on the back side is completed, a problem is raised that an image failure occurs even when the paper is carried out to the outside through the switching guide switched to the discharge conveyance path side. It is not done and therefore there is no suggestion of a solution.

  However, when the paper on which double-sided printing has been completed is led out to the discharge conveyance path via the switching guide, the front-side printing surface on which printing has been completed first comes into sliding contact with the switching guide, thereby There is a disadvantage that the toner is scraped off by the edge of the switching guide. When the toner on the printing surface is scraped off, the image on the printing surface is not only damaged, but the scraped toner accumulates on the edge of the switching guide, and the deposited toner adheres to the printing surface of the next sheet. As a result, there arises a problem that the printing surface is contaminated.

  The present invention has been made to solve such a problem, and prevents the occurrence of an image failure when a sheet on which double-sided printing processing has been performed is transported toward a paper discharge transport path via a switching guide. In addition, an object of the present invention is to provide an image forming apparatus capable of preventing contamination of the printing surface of the next sheet.

  According to the first aspect of the present invention, there is provided a paper discharge conveyance path for discharging the paper after the fixing process to the outside on the downstream side of the fixing unit that performs the fixing process on the paper on which the toner image is transferred by the image forming unit. A return conveyance path for returning the fixed sheet, which has been subjected to a transfer process on one side to perform double-sided printing, to the image forming unit, and a branching position of the discharge conveyance path and the return conveyance path. An image forming apparatus comprising switching means for switching a destination to one of a paper discharge conveyance path and a return conveyance path, and a control unit for controlling a switching operation of the switching means, wherein the switching means is a predetermined switching A first posture for guiding the paper to the paper discharge conveyance path by driving the mechanism, a second posture for guiding the paper to the return conveyance route, and a third posture for substantially eliminating the contact state with the conveyed paper. The posture can be changed between When the sheet is subjected to transfer processing on both sides, the section sets the switching unit to the first position, and then immediately after the sheet starts to be guided to the switching unit, Control for changing the posture is performed through the switching mechanism.

  According to such a configuration, the sheet led out from the fixing unit after the double-sided printing is performed is discharged by the switching unit whose leading end is set to the first posture by driving the switching mechanism under the control of the control unit. Immediately after being guided so as to move to the third position, the switching means is changed to the third posture in which the contact with the paper is substantially eliminated. It is directed to the paper discharge conveyance path via the posture switching means. Therefore, it is possible to reliably prevent the occurrence of inconvenience such that the switching means slides on the printing surface of the paper and causes an image failure on the printing surface, and the toner scraped off from the printing surface of the paper accumulates. It is possible to reliably prevent the occurrence of inconvenience that the accumulated toner adheres to the next paper and contaminates the paper surface.

  According to a second aspect of the present invention, in the first aspect of the invention, the control unit includes a single-side / double-side discrimination unit and a control signal output unit, and the single-side / double-side discrimination unit is a sheet after fixing processing. Is for single-sided printing or double-sided printing, and if it is for double-sided printing, it is determined whether or not printing has been performed on both sides, and the control signal When the paper is for single-sided printing, the output unit causes the switching unit to be set to the first posture, and when the paper is for double-sided printing and only single-sided printing is performed, the switching unit Is set to the second posture, and when double-sided printing is performed, a control signal for changing the posture to the third posture after setting the switching means to the first posture is directed to the switching mechanism. Also characterized by output It is.

  According to this configuration, when the single-side / double-side discriminating unit determines that the paper after the fixing process conveyed through the fixing unit is for single-sided printing, the control signal output unit receives the discrimination result. Since the control signal for setting the switching unit to the first posture is output to the switching mechanism, the sheet is guided by the switching unit set to the first posture and travels toward the paper discharge conveyance path.

  On the other hand, if the single-side / double-side discriminating unit discriminates that the paper is for double-sided printing, and it is discriminated that the paper derived from the developing device is still printed on only one side, this discrimination result is The received control signal output unit outputs a control signal for setting the switching unit to the second posture toward the switching mechanism, so that the sheet is guided by the second posture switching unit and heads toward the return conveyance path. Become. Thereafter, when the one-side / both-side discriminating unit discriminates that the printing process has already been performed on both sides of the sheet, the control signal output unit that has received the discrimination result first sets the switching means to the first posture toward the switching mechanism. In order to output the control signal for setting the posture, the sheet is guided to the switching means set to the first posture and can go to the discharge conveyance path. When the leading edge of the paper starts to be guided to the switching means, the control signal output unit outputs a control signal for changing the attitude of the switching means to the third posture, so that the paper avoids contact with the paper. Then, the paper is discharged to the outside through the paper discharge conveyance path via the switching guide in the state.

  As described above, the single-sided / double-sided discrimination unit for discriminating whether the paper after the fixing process is for single-sided printing or double-sided printing is provided, and the discrimination result of this single-sided / double-sided discrimination unit is And a control signal output unit that outputs a specific control signal to the switching guide based on the switching guide. It is possible to effectively prevent the occurrence of inconveniences such as image failure due to interference of the printing surface and contamination of the next sheet by toner adhering to the switching guide.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the switching means is pivotally supported so as to be rotatable around a support shaft extending in a paper width direction orthogonal to the paper transport direction by driving the switching mechanism. The switching guide is provided with a first guide surface for directing the paper toward the paper discharge conveyance path and a second guide surface for directing the paper toward the return conveyance path.

  According to such a configuration, the switching guide as the switching unit can change the posture by rotating forward and backward around the support shaft by driving the switching mechanism, and the first guide of the sheet in the state in which the posture is set to the first posture. While the sheet is directed to the paper discharge conveyance path through the surface, the sheet can be directed to the return conveyance path through the second guide surface in a state in which the posture is set to the second posture, and the first posture and the second posture are The third posture is realized by the intermediate posture.

  By adopting the switching means having such a structure, the switching means surely fulfills the function of the posture change after having a simple structure.

  According to a fourth aspect of the invention, in the third aspect of the invention, the switching guide restricts a rotation range between the first and second postures around the support shaft of the switching guide. The posture is set to the posture.

  According to this configuration, since the posture is set to the third posture by restricting the rotation range between the first and second postures around the support shaft of the switching guide, the third posture is switched according to a necessary situation. It is possible to set the switching guide to the third posture with a simple configuration such as inserting a predetermined regulating member for regulating the rotation of the guide into the rotation range.

  According to a fifth aspect of the present invention, in the third aspect of the present invention, the switching guide is configured such that the switching mechanism acts to change the operating point at which the switching mechanism acts to rotate the switching guide around the support shaft. The posture is set to the posture.

  According to such a configuration, the switching guide is configured to be set to the third posture by changing the action point at which the switching mechanism acts, for example, between the first posture and the second posture. A structure in which the distance between the action point and the fulcrum in the posture change between the first posture and the third posture is shorter than the distance between the action point and the fulcrum (axis of the support shaft) in the posture change Between the first posture and the third posture in which the switching guide is changed in position between the first posture and the second posture with the same driving range of the switching mechanism. A structure in which switching between the second mode in which the posture is changed is easily performed.

  According to the first aspect of the present invention, the sheet derived from the fixing unit after the double-sided printing is performed by the switching means whose leading edge is set to the first posture by driving the switching mechanism controlled by the control unit. Immediately after being guided to the discharge conveyance path, the switching means is changed to the third posture in which the contact with the paper is substantially eliminated, so that the paper hardly touches the switching means thereafter. Thus, it can be directed to the paper discharge conveyance path via the switching means of the third posture.

  Therefore, it is possible to reliably prevent the switching means from sliding in contact with the printing surface of the paper and causing an image failure on the printing surface, and to accumulate toner scraped from the printing surface of the paper by the switching means. In addition, it is possible to reliably prevent the occurrence of inconvenience that the accumulated toner adheres to the next paper and contaminates the paper surface.

  According to the second aspect of the present invention, the paper includes a single-side / double-side discriminating unit for discriminating whether the paper after the fixing process is for single-sided printing or double-sided printing, and this Since it is designed to be properly controlled by a control unit having a control signal output unit that outputs a specific control signal to the switching guide based on the determination result of the single-sided / double-sided discrimination unit, particularly double-sided printing It is possible to effectively prevent the occurrence of inconvenience that the printing surface at that time causes an image failure due to the interference of the printing surface with the switching guide or the next sheet is contaminated by the toner adhering to the switching guide.

  According to the third aspect of the present invention, the paper is transported on the paper discharge path which is pivotally supported around the support shaft extending in the paper width direction orthogonal to the paper transport direction by driving a predetermined switching mechanism as the switching means. A switching guide comprising a first guide surface that is directed toward the second side and a second guide surface that is directed toward the return conveyance path is employed. While contributing to the reduction, it is possible to reliably perform the function by changing the posture.

  According to the fourth aspect of the invention, since the posture is set to the third posture by restricting the rotation range between the first and second postures around the support shaft of the switching guide, the third posture is necessary. Accordingly, it is possible to set the switching guide to the third posture with a simple configuration such as inserting a predetermined regulating member for restricting the rotation of the switching guide in accordance with the rotation range, thereby reducing the apparatus cost. Can contribute.

  According to the fifth aspect of the present invention, the switching guide is configured to be set to the third posture by changing the action point at which the switching mechanism acts. Adopting a structure that shortens the distance between the action point and the fulcrum in the posture change between the first posture and the third posture than the distance between the action point and the fulcrum in the posture change between the two postures By changing the position of the switching mechanism between the first position and the third position, the switching guide is changed in position between the first position and the second position with the same driving range of the switching mechanism. Therefore, it is possible to easily obtain a structure capable of switching between the second mode and the second mode, thereby contributing to reduction of the apparatus cost.

  First, an outline of an image forming apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a front cross-sectional view for explaining an embodiment of the internal structure of the image forming apparatus. As shown in FIG. 1, an image forming apparatus 10 according to the present embodiment is used as a copying machine, and has an apparatus main body 11 that has a box shape in which various image forming devices are housed. The apparatus has a basic configuration including an image reading device 19 that is attached to the upper surface of the apparatus main body 11 and reads a document image.

  In the apparatus main body 11, an image forming unit 12 that forms an image based on image information of a document read by the image reading device 19, and a fixing process for an image formed by the image forming unit 12 and transferred to the paper P A fixing unit 13 for performing the transfer, a sheet storage unit 14 for storing the transfer sheet P, a sheet discharge unit 15 for receiving the discharged sheet P after the fixing process, and a single side for performing double-sided printing on the sheet P. A paper reversing unit 16 that performs a front / back reversing process on the paper P for which the printing process has been completed is provided.

  The image reading device 19 includes a document holder 191 provided on the upper surface of the apparatus main body 11 so as to be openable and closable, and an optical system unit 192 disposed in the apparatus main body 11 so as to face the document holder 191 through a contact glass 193. ing. The contact glass 193 includes a placed document contact glass 193a having a slightly smaller planar shape than the document presser 191 for reading the document surface of the placed document, and a longitudinal direction for reading the document surface of the automatically fed document. A long and narrow automatic feeding paper contact glass 193b is provided (in a direction orthogonal to the paper surface of FIG. 1).

  On the upper surface of the apparatus main body 11 on the front side (front side of the paper surface in FIG. 1) of the image reading apparatus 19, an operation panel 194 for inputting processing conditions relating to document reading and copying is provided. The operation panel 194 is disposed on the upper surface of the front portion of the processing apparatus main body 11, and is provided with a display panel, a numeric keypad, a start button, a mode switching key, and the like (not shown). The display panel displays various types of input information and output information on a liquid crystal display, or inputs information selected from the displayed processing conditions by a touch-in operation. The numeric keypad is mainly for setting quantity information such as the number of copies. The mode switching key is used to switch the mode of the image forming apparatus 10, and the image forming apparatus 10 can be used as a copying machine, a facsimile machine, or a printer by pressing the mode switching key. You can do that.

  The document presser 191 is attached to the apparatus main body 11 so as to be opened and closed by rotating forward and backward about a predetermined axis provided on one side of the upper surface of the apparatus main body. The document presser 191 has a two-stage structure, and includes a document tray 195 for placing a document provided in the upper stage, and a document discharge tray 196 provided in the lower stage for discharging a document whose image has been read. And have. On the left side of the document retainer 191, a document feeding unit 197 is provided between the document tray 195 and the document discharge tray 196. The document tray 195 is disposed by a document feeding mechanism (not shown) of the document feeding unit 197. The originals are picked up one by one from the original bundle placed thereon and supplied to the automatic paper supply contact glass 193b. The picked-up document is read by the optical system unit 192 through the automatic feeding contact glass 193b while moving. The document after the document image is read is discharged to a document discharge tray 196.

  The optical system unit 192 includes an unillustrated light source, a plurality of mirrors, a lens unit, and a CCD (charge coupled device). The light from the light source is reflected by the original surface, and the reflected light is input to the CCD as original information through the mirror and the lens unit. Document information as an analog amount input to the CCD is converted into a digital signal and stored in a predetermined storage device.

  The image forming unit 12 forms a toner image on the paper P fed from the paper storage unit 14, and in this embodiment, sequentially from the upstream side (the right side of the paper surface in FIG. 1) to the downstream side. It has a yellow unit 12Y, a magenta unit 12M, a cyan unit 12C, and a black unit 12K.

  Each unit 12Y, 12M, 12C, 12K is provided with a photosensitive drum 121 and a developing device 122, respectively. Each photoconductive drum 121 is supplied with toner from a corresponding developing device 122 while rotating clockwise in FIG.

  A charger 123 is provided at a position immediately above each photosensitive drum 121, and an exposure device 124 is provided at a right position. Each photosensitive drum 121 is uniformly charged at its peripheral surface by the charger 123, and a laser beam based on image data input by the image reading device 19 is charged from each exposure device 124 by the photosensitive drum. By irradiating the peripheral surface of 121, an electrostatic latent image is formed on the peripheral surface of each photosensitive drum 121. By supplying toner from the developing device 122 to the electrostatic latent image, a toner image is formed on the peripheral surface of the photosensitive drum 121.

  Further, a cleaning device 125 for removing residual toner on the peripheral surface of the photosensitive drum 121 and cleaning it is provided at the lower left position in FIG. 1 of each photosensitive drum 121. The peripheral surface of the photosensitive drum 121 cleaned by the cleaning device 125 is directed to the charger 123 for a new charging process.

  Below each photoconductor drum 121, a transport belt 126 is provided so that the transport surface faces the photoconductor drum 121. The conveyor belt 126 is wound around a driving roller provided slightly downstream of the black unit 12K and a driven roller provided slightly upstream of the yellow unit 12Y, and circulates by driving rotation of the driving roller. It is like that. Then, the paper P supplied from the paper storage unit 14 moves while being in contact with the peripheral surface of the photosensitive drum 121 while being guided by the circumference of the transport belt 126, and is subjected to a transfer process.

  The fixing unit 13 performs a fixing process on the toner image on the paper P transferred by the image forming unit 12, and includes a fixing roller 131 having an energization heating element serving as a heating source therein, and a lower portion thereof. The image forming apparatus includes a fixing roller 131 and a pressure roller 132 disposed to face the fixing roller 131. Then, the transfer-processed paper P led out from the image forming unit 12 by the rotation of the conveyance belt 126 is heated between the fixing roller 131 and the pressure roller 132 while being heated by the fixing roller 131. A stable color image that has been fixed and has undergone a fixing process is formed on the paper P.

  In the case of single-sided printing, the paper P with a color image that has undergone the fixing process passes through a paper discharge conveyance path 151 that extends upward via a switching guide (switching means) 20 provided immediately downstream of the fixing unit 13. The paper is discharged toward a paper discharge unit 15 formed between the optical system unit 192 and the image forming unit 12.

  The switching guide 20 is configured to be able to switch between an obliquely upper side, an obliquely lower side, and an intermediate position thereof toward the downstream side, and is particularly set to the intermediate position when the paper P is printed on both sides. As a result, the toner transferred to the back side of the paper P can be prevented from adhering to the switching guide 20.

  The paper storage unit 14 includes a plurality of paper trays 141 that are detachably attached to the apparatus main body 11. Each sheet tray 141 stores a sheet bundle. Then, the paper P is fed one by one from the paper bundle of the selected paper tray 141 by driving the pickup roller 142, and is introduced into the image forming unit 12 through the paper feed conveyance path 143.

  The paper discharge unit 15 is a so-called in-body discharge method, and includes an in-cylinder discharge tray 152 formed at a position directly above the image forming unit 12 in the apparatus main body 11. A laterally long opening formed along the in-body discharge tray 152 is provided on the front side of the apparatus main body 11, and the paper P discharged to the in-body discharge tray 152 is taken out from the horizontally long opening. It is like that.

  The paper reversing unit 16 is interposed between the image forming unit 12 and the paper storage unit 14 and is supported by the support plate 161 that supports the paper P having the image after the fixing process on one side, and the support plate 161. And a pair of reversing rollers 162 that continue to be nipped with respect to the sheet P.

  Then, the sheet P introduced into the support plate 161 through the return conveyance path 163 by the switching operation of the switching guide 20 via the reverse roller pair 162 is once supported by the support plate 161 while being sandwiched between the reverse roller pair 162. Then, the paper is discharged from the rear end side by the reverse rotation of the pair of reverse rollers 162 and is directed to the paper feed transport path 143 through the reverse transport path 164. The paper P that has been turned upside down and supplied to the paper feed conveyance path 143 is supplied to the image forming unit 12 again, whereby the back side is subjected to a transfer process.

  FIG. 2 is an enlarged explanatory view of a front sectional view showing the vicinity of the switching guide 20 in the apparatus main body 11. FIG. 3 is a partially cutaway perspective view showing the first embodiment of the switching mechanism for switching the destination of the paper P. FIG. In these figures, the XX direction is referred to as the left-right direction, the YY direction is referred to as the front-rear direction, and in particular, the -X direction is referred to as the left, the + X direction is referred to as the right, the -Y direction is referred to as the front, and the + Y direction is referred to as the rear. .

  First, as shown in FIG. 2, the peripheral surface of the fixing roller 131 and the peripheral surface of the pressure roller 132 in the fixing unit 13 are in contact with each other at the left position of the nip portion 133 that presses and holds the paper P. A guide plate 134 composed of an upper guide plate 135 and a lower guide plate 136 that are opposed to each other in the vertical direction is provided. The upper and lower guide plates 135 and 136 are arranged and set so that the distance between them is reduced toward the downstream side. The tape P-shaped guide plate 134 is interposed between the downstream end (left end) of the fixing unit 13 and the switching guide 20, so that the sheet P that has passed through the nip 133 between the fixing roller 131 and the pressure roller 132 is obtained. After being captured between the upper and lower guide plates 135 and 136, it is surely supplied toward the switching guide 20.

  The switching guide 20 rotates forward and backward about the rotation fulcrum 201 to guide the paper P to the paper discharge unit 15 via the paper discharge conveyance path 151 (indicated by a solid line in FIG. 2), A second posture H2 (indicated by a one-dot chain line in FIG. 2) for guiding the paper P to the paper reversing unit 16 through the return conveyance path 163, and a third posture that is an intermediate posture between the first posture H1 and the second posture. The posture can be changed between H3 (indicated by a two-dot chain line in FIG. 2).

  As shown in FIG. 3, the switching guide 20 includes a cross-shaped rod 21 having a substantially cross shape (see FIG. 2) in a longitudinal cross-sectional view in the front-rear direction, and a plurality of sheets mounted on the cross-shaped rod 21. The guide fin 24 is provided with a basic configuration. The switching guide 20 rotates integrally forward and backward around the rotation shaft 23 attached to the frame F, whereby the guide fin 24 can change its posture between the first to third postures H1 to H3. Yes.

  As shown in FIG. 2, the guide fin 24 is formed in a substantially isosceles triangle shape that is elongated in a front view, and has a mouth corner portion 241 that is tapered toward the right, and a left end of the mouth corner portion 241. An upper arc portion 242 that is convex upward and formed in an arc shape on the upper side, and a lower arc portion 243 that is convex downward and formed in an arc shape so as to face the upper arc portion 242 at the lower portion of the left end portion. And the shape is set. Between the skirt portion of the upper arc portion 242 and the right end portion of the mouth corner portion 241, an upper arc inclined edge surface (first guide surface) 244 that is concave and gently inclined is formed, while the lower arc portion A lower arc inclined edge surface (second guide surface) 245 that is concave and gently inclined is formed between the skirt portion of 243 and the right end portion of the corner portion 241.

  In such a state that the guide fin 24 is set in the first posture H1, the right end of the upper arc inclined edge surface 244 is more than the left end edge of the lower guide plate 136, as initially indicated by a solid line in FIG. The sheet P, which is located below and is supplied from the fixing unit 13 to the switching guide 20 via the guide plate 134, comes into contact with the upper arc inclined edge surface 244 of the guide fin 24 and contacts the upper arc inclined edge surface 244. It is guided and is surely directed to the paper discharge transport path 151.

  Further, the guide fin 24 is set in the second posture H2, and the right end of the lower arc inclined edge surface 245 is located above the left end edge of the upper guide plate 135, as shown by a one-dot chain line in FIG. Thus, the sheet P supplied from the fixing unit 13 to the switching guide 20 via the guide plate 134 abuts on the lower arc inclined edge surface 245 of the guide fin 24 and is guided to the lower arc inclined edge surface 245. , It can be surely directed to the return conveyance path 163.

  The upper arc portion 242 of the guide fin 24 is slightly protruded rightward from the left face plate 151a of the paper discharge conveyance path 151 only in the initial state in a state where the switching guide 20 is set to the first posture H1. Thus, the sheet P that is moved while being guided by the upper circular arc inclined edge surface 244 is surely directed to the paper discharge conveyance path 151 without interfering with the left surface plate 151a.

  Similarly, the downward arc portion 243 of the guide fin 24 is in a state of slightly protruding rightward from the left face plate 163a of the return conveyance path 163 in a state where the switching guide 20 is set to the second posture H2. The sheet P which is shaped and moved while being guided by the lower circular arc inclined edge surface 245 is surely directed to the return conveyance path 163 without interfering with the left surface plate 163a.

  In the state where the switching guide 20 is set in the third posture H3 indicated by a two-dot chain line in FIG. 2, the tip of the corner portion 241 of the guide fin 24 is substantially between the upper and lower guide plates 135 and 136 of the fixing portion 13. It is located in the middle so that a gap is formed between the tip of the corner 241 and the upper guide plate 135 and between the lower guide plate 136.

  In addition, in the state where the switching guide 20 is set to the third posture H3, the upper arc portion 242 of the guide fin 24 is located to the left of the left face plate 151a of the paper discharge conveyance path 151 and the lower arc portion 243. Is positioned to the left of the left face plate 163a of the return conveyance path 163.

  The switching guide 20 configured as described above is changed in posture by driving a switching mechanism 30 provided on at least one end side of the switching guide 20. Hereinafter, the first embodiment of the switching mechanism 30 will be described in detail with reference to FIG. As shown in FIG. 3, the switching mechanism 30 includes a first actuator 40 that rotates the switching guide 20 forward and backward about the rotation shaft 23, and an operation range of the rotation operation of the switching guide 20 by the first actuator 40. A second actuator 50 that is driven to be changed, and a switching mechanism 60 that enables the posture of the switching guide 20 to be changed to be set to the third posture H3 by driving the second actuator 50. Configured.

  The first and second actuators 40 and 50 are connected to a transmission rod 69 having a columnar shape. The transmission rod 69 is provided through all the guide fins 24 at the left position of the cross-shaped rod 21 of the switching guide 20, and by rotating the transmission rod 69 forward and backward around the rotation shaft 23, The switching guide 20 can be rotated forward and backward so that the guide fin 24 can change its posture.

  On the other hand, the frame F is provided with a vertically-rotating range restriction hole F1 in a vertical direction at a position corresponding to the transmission rod 69, and the transmission rod 69 passes through the rotation range restriction hole F1. The rotation range of the guide fin 24 around the rotation shaft 23 is restricted between the first posture H1 and the second posture H2.

  In the present embodiment, the first actuator 40 is connected to the transmission rod 69 to rotate the switching guide 20 around the rotation shaft 23 via the transmission rod 69, whereas the second actuator 50 is connected. Is connected to the transmission rod 69 via a switching mechanism 60 in order to adjust the rotation range of the switching guide 20. In the present embodiment, a so-called solenoid device that operates by passing a current through an electromagnetic coil is applied to the first and second actuators 40 and 50.

  The first actuator 40 is arranged vertically at a position below the switching guide 20 outside a predetermined frame F that supports the switching guide 20 (front in the example shown in FIG. 3). The first actuator 40 includes a solenoid main body 41 having an electromagnetic coil therein, and an iron core member that penetrates the solenoid main body 41 so as to penetrate the electromagnetic coil and protrudes upward from the solenoid main body 41 so as to be movable up and down. 42 and a connecting plate 43 that is pivotally supported around the connecting shaft 421 extending in the front-rear direction at the upper end portion of the iron core member 42.

  The upper end of the connecting plate 43 is externally fitted to a portion of the transmission rod 69 that protrudes outward from the rotation range restricting hole F <b> 1, so that the iron member 42 can be advanced and retracted relative to the solenoid body 41 by driving the first actuator 40. Thus, the transmission rod 69 is moved up and down to change the posture of the guide fin 24.

  On the other hand, the second actuator 50 is disposed horizontally on the inner position of the frame F (the rear position of the frame F in the example shown in FIG. 3) and slightly above the transmission rod 69. The second actuator 50 includes a solenoid body 51 similar to the solenoid body 41 of the first actuator 40 and an iron core similar to the iron core member 42 of the first actuator 40 protruding forward from the solenoid body 51. A member 52 is provided. The second actuator 50 is disposed such that the iron core member 52 faces the back surface side of the frame F (front surface side in FIG. 3), and the switching mechanism 60 is moved by the advancement / retraction of the iron core member 52 with respect to the solenoid body 51. The rotation range is switched.

  The switching mechanism 60 includes a rotation range setting member 61 that is externally fitted to the transmission rod 69 at a position below the iron core member 52, and a coil spring 65 that applies an urging force to the rotation range setting member 61. Has been. The rotation range setting member 61 is provided so as to project outward in a radial direction from a position close to the rear on the peripheral surface of the cylindrical base 62 and to be fitted over the transmission rod 69 in a sliding state. The protruding portion (regulating member) 63 is provided, and a collar portion 64 that is integrally connected to a position further forward of the protruding portion 63.

  The outer diameter of the cylindrical base 62 is set slightly smaller than the width of the rotation range restriction hole F1, and the inside of the rotation range restriction hole F1 is moved by raising and lowering the connecting plate 43 by driving the first actuator 40. It is designed to go up and down. Then, the guide fin 24 is set in the second posture H2 as shown in FIG. 3 while the cylindrical base 62 is in contact with the lower end edge of the rotation range regulating hole F1, while the cylindrical base 62 is set. The posture is set to the first posture H1 in a state where 62 is in contact with the upper edge of the rotation range regulating hole F1.

  The protruding portion 63 is configured to reduce the rising amount of the connecting plate 43 by driving the first actuator 40 in a state where the protruding portion 63 is fitted in the rotation range restriction hole F1 by the forward movement of the cylindrical base body 62. This restricts the amount of rotation of the rotation axis 23 of the guide fin 24 in the clockwise direction. The protruding portion 63 is positioned so that the upper end portion thereof is positioned at a substantially intermediate position above and below the rotation range restriction hole F1 in a state where the cylindrical base 62 is in contact with the lower end edge portion of the rotation range restriction hole F1. The projecting amount is set.

  Thus, in a state where the protruding portion 63 is fitted in the rotation range restriction hole F1, the elevation range of the cylindrical base body 62 is restricted to the substantially lower half in the rotation range restriction hole F1 due to the presence of the protrusion portion 63. Thus, the guide fin 24 can be changed in posture only between the first posture H1 and the third posture H3. Therefore, in the state in which the protruding portion 63 is fitted in the rotation range restriction hole F1, the guide fin 24 set in the first posture H1 is moved to the first position even when the connecting plate 43 is lifted by driving the first actuator 40. The posture can be changed only to the three postures H3.

  The flange portion 64 is generally sized larger than the rotation range restricting hole F1, and has a plate-like extension portion 641 extending upward from a portion corresponding to the protrusion portion 63. is doing. The extended portion 641 is provided with a long hole-like escape hole 642 extending in the vertical direction on the surface facing the frame F. The distal end portion of the iron core member 52 of the second actuator 50 is attached to the escape hole 642 so as to be relatively raised and lowered while being guided by the escape hole 642.

  Accordingly, when the iron core member 52 is advanced and retracted by the driving of the second actuator 50, the rotation range setting member 61 is advanced and retracted with respect to the rotation range restriction hole F1 by this advance and retreat, thereby causing the cylindrical base body 62 to move forward and backward. The state of the second actuator 50 is changed between the state in which the protruding portion 63 is fitted in the rotation range restriction hole F1 due to the reverse movement and the state in which the protruding portion 63 is pulled out rearward from the first posture H1. The iron core member 52 moves up and down relatively in the escape hole 642 by the raising and lowering of the transmission rod 69 driven by the first actuator 40, whereby the iron core member 52 interferes with the flange portion 64 in the vertical direction and causes the transmission rod 69 to move. Inconveniences that cannot be raised and lowered are prevented.

  In this embodiment, a flange 691 is provided at a position rearward of the flange portion 64 of the transmission rod 69, and the coil spring 65 is externally fitted to the transmission rod 69 in a compressed state between the flange 691 and the flange portion 64. Has been. Therefore, in a state where no current is supplied to the electromagnetic coil in the solenoid body 51 of the second actuator 50, the iron core member 52 is pressed forward by the urging force of the coil spring 65, thereby causing the projecting portion 63 to rotate. The iron core member 52 is pulled back into the solenoid main body 51 by the excitation of the electromagnetic coil in the solenoid main body 51 when the current is supplied to the electromagnetic coil while being fitted in the movement range regulating hole F1, and the rear of the flange portion 64 thereby. The projecting portion 63 comes off from the rotation range restricting hole F <b> 1 by the movement to.

  Hereinafter, the attitude control of the switching guide 20 will be described based on FIGS. 4 and 5 with reference to FIGS. FIG. 4 is a block diagram illustrating an embodiment of posture control of the switching guide 20 by the control unit 70. FIG. 5 is an operation diagram for explaining the operation of the switching guide 20 whose posture is set by control by the control unit 70. FIG. 5A is a state in which the switching guide 20 is set in the first posture H1. (B) shows a state where the switching guide 20 is set to the second posture H2, and (C) shows a state where the switching guide 20 is set to the third posture H3. In FIG. 5, the positional relationship between the rotation range setting member 61 and the rotation range restriction hole F1 in each state is shown in an enlarged manner in a circle.

  The control unit 70 is a so-called microcomputer, and includes a central processing unit (CPU) 71 as a central processing unit and a read only memory (ROM) 72 that is a read-only storage device attached to the CPU 71. A random access memory (RAM) 73, which is a free storage device, and a timer 74 are provided.

  The ROM 72 stores a program for controlling the attitude of the switching guide 20 and invariant data such as setting numerical values necessary for the control, while the RAM 73 stores control that occurs during the control by the CPU 71. In addition, temporarily necessary data and the like are stored.

  The CPU 71 is provided with a print mode discrimination unit (single side / double side discrimination unit) 711 and a control signal output unit 712. Based on the print mode information, copy number information, paper size information, and the like input from the operation panel 194, the print mode determination unit 711 determines whether the paper P that is currently being derived from the fixing unit 13 is for single-sided printing. It is discriminated whether the double-sided printing has been subjected to the transfer process on the front side or the double-sided printing has been subjected to the transfer process on the back side.

  That is, the operation panel 194 is provided with a print mode setting key for inputting whether single-sided printing or double-sided printing, a number setting key for setting the number of prints, a size setting key for setting the paper size, and the like. Then, after these key settings are completed, the transfer process for the paper P is executed by pressing the start key. However, the pressed content of these keys is output to the print mode determination unit 711. It has become.

  Then, the print mode determination unit 711 determines whether the sheet P derived from the fixing unit 13 based on these pieces of information is for single-sided printing, for double-sided printing, particularly for double-sided printing. Determines whether only the front side is printed, or whether the back side is printed in addition to the front side, and the determination result and the paper size are directed to the control signal output unit 712. It is designed to output.

  The control signal output unit 712 outputs a control signal to the first and second actuators 40 and 50 based on the determination result of the control signal output unit 712, and the sheet P led out from the fixing unit 13 is output. In the case of single-sided printing, a control signal for pulling back the iron core member 52 protruding forward by the biasing force of the coil spring 65 toward the second actuator 50 is output, and then the iron core member toward the first actuator 40. A signal for projecting 42 is output.

  The second actuator 50 to which the control signal is input pulls the iron core member 52 back to the solenoid body 51, so that the protruding portion 63 of the rotation range setting member 61 is removed from the rotation range restriction hole F1. In this state, since the first actuator 40 causes the iron core member 42 to protrude upward, the transmission rod 69 rotates the connecting plate 53 about the rotation shaft 23 in the clockwise direction. As shown in (a), the posture of the guide fin 24 is set to the first posture H <b> 1 in which the tip of the corner 241 of the guide fin 24 is positioned below the tip (left end) of the lower guide plate 136 of the fixing unit 13.

  In this state, the sheet P led out from the fixing unit 13 is supplied to the guide fins 24 set in the first posture H1 through the guide plate 134, and hence the upper arc inclined edge surface 244 of the guide fins 24 thereafter. Are directed to the paper discharge conveyance path 151. At this time, the back surface side of the sheet P is slidably contacted with the upper end of the upper arc portion 242 of the guide fin 24 which is moved to the right from the left surface plate 151a and is fitted in the discharge conveyance path 151. Since the back side of the paper P is not printed, there is no particular inconvenience.

  On the other hand, when the paper P derived from the fixing unit 13 is for double-sided printing and the front side printing process has been completed, the control signal output unit 712 is directed toward the first actuator 40. A signal for immersing the iron core member 42 is output.

  The first actuator 40 to which such a control signal is input moves the transmission rod 69 counterclockwise around the rotation shaft 23 in order to lower the iron core member 42, whereby the switching guide 20 is moved as shown in FIG. As shown in (b), the posture of the guide fin 24 is set to a second posture H2 in which the tip of the corner 241 of the guide fin 24 is positioned above the tip (left end) of the upper guide plate 135 of the fixing unit 13.

  In this state, the paper P led out from the fixing unit 13 is supplied to the guide fin 24 set in the second posture H2 via the guide plate 134, and hence the lower arc inclined edge surface 245 of the guide fin 24 is thereafter. To the return conveyance path 163 while being guided by the user. As described above, the sheet P introduced into the return conveyance path 163 is turned upside down by the sheet reversing unit 16, returned to the image forming unit 12, and subjected to printing processing on the back side, and then printed on the back side. Fixing processing is performed on the image by the fixing unit 13.

  When the sheet P derived from the fixing unit 13 is for double-sided printing and the printing process on the back side is completed, the control signal output unit 712 displays the iron core member of the second actuator 50. A control signal for projecting 52 is output (specifically, supply of current to the electromagnetic coil of the second actuator 50 is cut off). Then, since the rotation range setting member 61 is moved forward by the biasing force of the coil spring 65, the projecting portion 63 is fitted in the rotation range restriction hole F1, so that the transmission rod 69 rotates around the rotation shaft 23. At this time, the upper edge portion of the projecting portion 63 fitted into the rotation range restriction hole F1 comes into contact with the upper edge portion of the rotation range restriction hole F1, and the rotation is further performed. 5 is blocked, the tip of the corner 241 of the guide fin 24 is positioned at a substantially intermediate position between the upper guide plate 135 and the lower guide plate 136 of the fixing unit 13 as shown in FIG. At the same time, the upper arc portion 242 of the guide fin 24 is set to the third posture H3 that is located to the left of the left face plate 151a of the paper discharge conveyance path 151.

  When the guide fin 24 is set to the third posture H3, the printing surface on the back surface side of the paper P is prevented from coming into contact with the upper arc portion 242 of the guide fin 24. It is possible to reliably prevent the occurrence of inconvenience that the toner is peeled off by rubbing against the upper arc portion 242 and accumulated on the upper arc portion 242.

  That is, when the sheet P is guided to the upper arc inclined edge surface 244 of the guide fin 24 while the position of the guide fin 24 is set to the first position H1 as in the prior art, when the sheet P moves to the sheet discharge conveyance path 151, The toner on the printing surface on the back side is scraped off by the tip of the upper arc portion 242 of the guide fin 24, whereby toner accumulates on the upper arc portion 242, so that the accumulated toner adheres to the paper P to be discharged thereafter. In the first embodiment, there is a disadvantage that the image is contaminated, but the paper P that has been printed on the back surface is discharged in a state where there is no interference with the upper arc portion 242. Does not cause such inconvenience.

  In the first embodiment, the sheet sensor 75 is interposed between the image forming unit 12 and the fixing unit 13 in order to detect the timing at which the sheet P subjected to the fixing process by the fixing unit 13 reaches the switching guide 20. (FIG. 1) is provided, and the paper sensor 75 detects the leading edge of the paper P. The detection signal of the paper sensor 75 is input to the control signal output unit 712.

  When the detection signal of the paper sensor 75 indicating that the paper P has been detected is input to the control signal output unit 712, the time from the detection time until the leading edge of the paper P reaches the switching guide 20 (this time is the image forming apparatus). 10 is known by referring to the timer 74, and the predetermined control signal as described above is sent to the first and second actuators 40 and 50 immediately before this time comes. Is output.

  In particular, when the paper P has been printed on the back side, the guide fin 24 is moved to the first posture H <b> 1 from when the paper P reaches the guide fin 24 until the leading end reaches the upper arc portion 242. The predetermined control signal is output from the control signal output unit 712 toward the first and second actuators 40 and 50 so as to change the posture from the first to the third posture H3.

  Hereinafter, a second embodiment of the switching mechanism 30 will be described in detail with reference to FIG. FIG. 6 is a partially cutaway perspective view showing a second embodiment of the switching mechanism for switching the destination of the paper P. FIG. In addition, the direction display by X and Y in this figure is the same as that of the case of FIG. As shown in FIG. 6, the switching mechanism 30 includes a first actuator (switching mechanism) 40 that rotates the switching guide 20 around the rotation shaft 23 in the forward and reverse directions, and a rotation operation of the switching guide 20 by the first actuator 40. The second actuator (switching mechanism) 50 for changing the action point 202 of the first and second actuators 50 and 50 is connected to both the first and second actuators 40 and 50, and the drive of the actuators 40 and 50 is transmitted to the switching guide 20. A rod 69 is provided.

  The first actuator 40 is configured in the same manner as that of the first embodiment, whereas the second actuator 50 is laterally positioned to the left of the reinforcing plate 22 formed integrally with the end portion of the switching guide 20. The connecting plate 53 similar to the connecting plate 43 of the first actuator 40 is pivotally supported around the connecting shaft 521 extending in the front-rear direction at the tip of the iron core member 52. Is different from that of the first embodiment.

  The transmission rod 69 is connected to the reinforcing plate 22 of the switching guide 20 to rotate the reinforcing plate 22 forward and backward around the rotation shaft 23 (that is, to rotate the switching guide 20). The first actuator 40 has a cylindrical shape and is fixed to the upper portion of the connecting plate 43 of the first actuator 40. A connecting hole 531 drilled at the right end of the connecting plate 53 of the second actuator 50 is fitted in a portion of the transmitting rod 69 protruding forward from the connecting plate 43 in a sliding contact state. It can be turned around.

  On the other hand, the reinforcing plate 22 is provided with a guide long hole 221 elongated in the left-right direction slightly to the left of the rotation shaft 23, and the rear end of the transmission rod 69 extends laterally into the guide long hole 221. It is fitted to be movable. That is, the guide long hole 221 has a hole width dimension slightly larger than the diameter of the transmission rod 69, so that the transmission rod 69 can move in the guide long hole 221 in the left-right direction in a sliding state. It is like that. Further, the left and right ends of the guide long hole 221 are formed in an arc shape (semicircle) in which the radius of curvature is set slightly larger than the radius of the transmission rod 69.

  In this embodiment, the distance d1 between the axis X0 of the rotation shaft 23 and the curvature center line X1 of the right semicircular end of the guide long hole 221 is the right semicircular shape in the guide long hole 221. It is set to be the same as the distance d2 between the curvature center line X1 at the end and the curvature center line X2 at the left semicircular end. Accordingly, when the transmission rod 69 is positioned at the left end portion of the guide slot 221, the switching guide 20 rotates forward and backward about the axis X 0 of the rotation shaft 23 that is the rotation fulcrum by forward and reverse driving of the first actuator 40. The amount of rotation is normal around the axis X0 of the rotation shaft 23 where the switching guide 20 is a rotation fulcrum by forward and reverse driving of the first actuator 40 with the transmission rod 69 positioned at the right end of the guide long hole 221. 1/2 of the amount of reverse rotation.

  In the second embodiment, the first actuator 40 is driven in a state where the connecting plate 53 of the second actuator 50 is driven away from the solenoid body 51 and the transmission rod 69 is positioned at the right end of the guide long hole 221. The switching guide 20 is changed in posture between the first posture H1 and the second posture H2 by forward / reverse driving, while the connecting plate 53 of the second actuator 50 is driven in the direction approaching the solenoid body 51 to transmit the transmission rod 69. Is positioned at the left end of the long guide hole 221, and the switching guide 20 is changed between the first posture H1 and the third posture H3 by forward and reverse driving of the first actuator 40. Such a posture change is executed under the control of the control unit 70 provided at an appropriate position in the apparatus main body 11 of the image forming apparatus 10.

  Hereinafter, the attitude control of the switching guide 20 in the second embodiment will be described with reference to FIG. 4 and FIG. Incidentally, FIG. 4 is used when explaining the control of the first embodiment, but the components are the same as those of the first embodiment except that the functions of the components are different. FIG. 7 is an operation diagram for explaining the operation of the switching guide 20 whose posture is set by control by the control unit 70. FIG. 7A is a state in which the switching guide 20 is set in the first posture H1. (B) shows a state in which the switching guide 20 is set to the second posture H2, and (c) shows a state in which the switching guide 20 is set to the third posture H3.

  The print mode determination unit 711 determines whether the paper P derived from the fixing unit 13 based on the information on the operation panel 194 is for single-sided printing or double-sided printing, particularly for double-sided printing. In some cases, it is determined whether only the front side is printed, or whether the back side is printed in addition to the front side, and the control result output unit 712 determines the determination result and the paper size. This function is the same as in the case of the first embodiment.

  The control signal output unit 712 outputs a control signal to the first and second actuators 40 and 50 based on the determination result of the control signal output unit 712, and the sheet P led out from the fixing unit 13 is output. In the case of single-side printing, a control signal for projecting the iron core member 52 toward the second actuator 50 is output, and then a signal for causing the iron core member 42 to project toward the first actuator 40 is output.

  The second actuator 50 to which such a control signal is input causes the iron core member 52 to protrude rightward from the solenoid main body 51, whereby the transmission rod 69 moves to the right end of the guide long hole 221. In this state, the first actuator 40 causes the iron core member 42 to protrude upward, so that the transmission rod 69 rotates the connecting plate 53 about the rotation shaft 23 in the clockwise direction. As shown in (a), the posture of the guide fin 24 is set to the first posture H <b> 1 in which the tip of the corner 241 of the guide fin 24 is positioned below the tip (left end) of the lower guide plate 136 of the fixing unit 13.

  In this state, the sheet P led out from the fixing unit 13 is supplied to the guide fins 24 set in the first posture H1 through the guide plate 134, and hence the upper arc inclined edge surface 244 of the guide fins 24 thereafter. Are directed to the paper discharge conveyance path 151. At this time, the back surface side of the sheet P is slidably contacted with the upper end of the upper arc portion 242 of the guide fin 24 which is moved to the right from the left surface plate 151a and is fitted in the discharge conveyance path 151. Since the back side of the paper P is not printed, there is no particular inconvenience.

  On the other hand, when the paper P derived from the fixing unit 13 is for double-sided printing and the front side printing process has been completed, the control signal output unit 712 is directed toward the second actuator 50. After outputting a control signal for projecting the iron core member 52, a signal for immersing the iron core member 42 is output toward the first actuator 40.

  The second actuator 50 to which the control signal is input causes the transmission rod 69 to move to the right end of the guide long hole 221 through the connecting plate 53 by causing the iron core member 52 to protrude rightward from the solenoid body 51. In this state, since the first actuator 40 lowers the iron core member 42, the transmission rod 69 rotates the connecting plate 53 about the rotation shaft 23 in the counterclockwise direction. As shown in (b), the posture of the guide fin 24 is set to a second posture H2 in which the tip of the corner 241 of the guide fin 24 is positioned above the tip (left end) of the upper guide plate 135 of the fixing unit 13.

  In this state, the paper P led out from the fixing unit 13 is supplied to the guide fin 24 set in the second posture H2 via the guide plate 134, and hence the lower arc inclined edge surface 245 of the guide fin 24 is thereafter. To the return conveyance path 163 while being guided by the user. As described above, the sheet P introduced into the return conveyance path 163 is turned upside down by the sheet reversing unit 16, returned to the image forming unit 12, and subjected to printing processing on the back side, and then printed on the back side. Fixing processing is performed on the image by the fixing unit 13.

  On the other hand, when the sheet P derived from the fixing unit 13 is for double-sided printing and the printing process on the back side is completed, first, the control signal output unit 712 first displays the second actuator. While maintaining the protruding state of the 50 core members 52, the core member 42 of the first actuator 40 is protruded to temporarily set the guide fin 24 to the first posture H1, whereby the sheet P is inclined to the upper arc of the guide fin 24. After being guided by the edge surface 244, a control signal for pulling the iron core member 52 back toward the solenoid body 51 toward the second actuator 50 before the leading edge of the paper P reaches the upper arc portion 242 of the guide fin 24. Then, immediately after that, a control signal for projecting the iron core member 42 toward the first actuator 40 is output.

  The second actuator 50 to which such a control signal is input pulls the iron core member 52 back to the solenoid body 51, thereby moving the transmission rod 69 to the left end of the guide long hole 221 through the connecting plate 53. In this state, since the first actuator 40 raises the iron core member 42, the transmission rod 69 rotates the connecting plate 53 around the rotation shaft 23 in the clockwise direction. ), The tip end of the corner portion 241 of the guide fin 24 is positioned at a substantially middle position between the upper guide plate 135 and the lower guide plate 136 of the fixing unit 13 and the upper arc portion 242 of the guide fin 24 is conveyed and discharged. The posture is set to the third posture H3 located to the left of the left face plate 151a of the road 151.

  When the guide fin 24 is set to the third posture H3, the printing surface on the back surface side of the paper P is prevented from coming into contact with the upper arc portion 242 of the guide fin 24. It is possible to reliably prevent the occurrence of inconvenience that the toner is peeled off by rubbing against the upper arc portion 242 and accumulated on the upper arc portion 242.

  That is, when the sheet P is guided to the upper arc inclined edge surface 244 of the guide fin 24 while the position of the guide fin 24 is set to the first position H1 as in the prior art, when the sheet P moves to the sheet discharge conveyance path 151, The toner on the printing surface on the back side is scraped off by the tip of the upper arc portion 242 of the guide fin 24, whereby toner accumulates on the upper arc portion 242, so that the accumulated toner adheres to the paper P to be discharged thereafter. In the present invention, however, the image P is contaminated, but the sheet P that has undergone the printing process on the back side is discharged in a state in which no interference with the upper arc portion 242 occurs. Does not cause such inconvenience.

  In the second embodiment, a sheet sensor 75 is interposed between the image forming unit 12 and the fixing unit 13 in order to detect the timing at which the sheet P subjected to the fixing process by the fixing unit 13 reaches the switching guide 20. (FIG. 1) is provided, and the paper sensor 75 detects the leading edge of the paper P. The detection signal of the paper sensor 75 is input to the control signal output unit 712.

  When the detection signal of the paper sensor 75 indicating that the paper P has been detected is input to the control signal output unit 712, the time from the detection time until the leading edge of the paper P reaches the switching guide 20 (this time is the image forming apparatus). 10 is known by referring to the timer 74, and the predetermined control signal as described above is sent to the first and second actuators 40 and 50 immediately before this time comes. Is output.

  In particular, when the paper P has been printed on the back side, the guide fin 24 is moved to the first posture H <b> 1 from when the paper P reaches the guide fin 24 until the leading end reaches the upper arc portion 242. The predetermined control signal is output from the control signal output unit 712 toward the first and second actuators 40 and 50 so as to change the posture from the first posture to the third posture H3.

  As described above in detail, the image forming apparatus 10 according to the present invention has the sheet P after the fixing process downstream of the fixing unit 13 that performs the fixing process on the sheet P on which the toner image is transferred by the image forming unit 12. A discharge conveyance path 151 that discharges the paper toward the outside, a return conveyance path 163 that returns the fixing-processed paper P that has undergone transfer processing on one side to perform double-sided printing, and the discharge conveyance path 163. A switching guide 20 provided at a branch position of the paper transport path 151 and the return transport path 163 to switch the destination of the paper P to either the paper discharge transport path 151 or the return transport path 163, and the switching operation of the switching guide 20 is controlled. The switching guide 20 has a first posture H that guides the paper P to the paper discharge conveyance path 151 by driving predetermined first and second actuators 40 and 50. And a second posture H2 for guiding the paper P to the return conveyance path 163 and a third posture H3 in which the contact state with the conveyed paper P is substantially eliminated, and the control unit No. 70, when the sheet P is subjected to transfer processing on both sides, and after the switching guide 20 is set to the first position H1, the third is immediately after the sheet P starts to be guided to the switching guide 20. Control to change the posture to the posture H3 is performed via the first and second actuators 40 and 50.

  According to this configuration, the leading edge of the sheet P led out from the fixing unit 13 after the duplex printing is performed is brought into the first posture H <b> 1 by driving the first and second actuators 40 and 50 under the control of the control unit 70. Immediately after being guided by the switching guide 20 set in the posture toward the paper discharge conveyance path 151, the posture of the switching guide 20 is changed to the third posture H3 in which the contact with the paper P is substantially eliminated. Thereafter, the paper P is directed to the paper discharge conveyance path 151 through the switching guide 20 in the third posture H3 in a state where it hardly contacts the switching guide 20. Therefore, the occurrence of inconveniences such that the switching guide 20 is in sliding contact with the printing surface of the paper P and causes an image failure on the printing surface is reliably prevented, and the upper arc inclined edge surface 244 of the guide fin 24 is printed on the paper P. The toner scraped off from the surface accumulates on the upper circular arc inclined edge surface 244, and it is possible to reliably prevent the occurrence of inconvenience that the accumulated toner adheres to the next sheet P and contaminates the sheet.

  Further, the control unit 70 includes a print mode determination unit 711 and a control signal output unit 712. The print mode determination unit 711 determines whether the paper P after the fixing process is for single-sided printing or for double-sided printing. If it is for double-sided printing, the control signal output unit 712 determines whether the paper P is for single-sided printing. In some cases, the switching guide 20 is set to the first position H1, and when it is for double-sided printing and only single-sided printing is performed, the switching guide 20 is set to the second position H2, while When duplex printing has been performed, a control signal for changing the posture of the switching guide 20 to the first posture H1 and then changing the posture to the third posture H3 is output to the first and second actuators 40 and 50. I will do it It is configured.

  According to this configuration, when the print mode determination unit 711 determines that the paper P after the fixing process conveyed via the fixing unit 13 is for single-sided printing, the control signal output unit 712 determines that the determination is made. In response to the result, a control signal for setting the switching guide 20 to the first posture H1 is output to the switching guide 20, so that the paper P is guided by the switching guide 20 set to the first posture H1 and discharged. It goes to the paper transport path 151.

  On the other hand, if the print mode determination unit 711 determines that the paper P is for double-sided printing, and if it is determined that the paper P actually derived from the developing device is still printed on only one side, this determination is performed. The control signal output unit 712 that has received the result outputs a control signal for setting the posture to the second posture H2 toward the switching guide 20, so that the paper P is guided by the switching guide 20 in the second posture H2 and returned and conveyed. You will head to the road 163.

  After that, when the print mode determination unit 711 determines that the printing process has already been performed on both sides of the paper P, the control signal output unit 712 that has received the determination result is directed to the switching guide 20 first. Since the control signal for setting the posture to the first posture H1 is output, the paper P is guided to the switching guide 20 set to the first posture H1 and can go to the discharge conveyance path 151. When the leading edge of the paper P starts to be guided by the switching guide 20, the control signal output unit 712 outputs a control signal for changing the posture of the switching guide 20 to the third posture H3. The paper is discharged to the outside through the paper discharge conveyance path 151 through the switching guide in a state where contact with P is avoided.

  As described above, the printing mode determination unit 711 that determines whether the paper P after the fixing process is for single-sided printing or double-sided printing is provided, and the determination result of the printing mode determination unit 711 is provided. The control unit 70 including the control signal output unit 712 that outputs a specific control signal to the first and second actuators 40 and 50 based on the control signal is appropriately controlled. It effectively prevents the occurrence of inconveniences such that the printing surface during printing causes an image failure due to the interference of the printing surface with the switching guide 20 or the next paper P is contaminated by the toner adhering to the switching guide 20. be able to.

  In addition, the switching guide 20 discharges the paper P that is pivotally supported around the rotation shaft 23 that extends in the paper width direction orthogonal to the paper conveyance direction by driving the first and second actuators 40 and 50. Since the guide fin 24 is provided with the upper circular arc inclined edge surface 244 that directs toward the conveyance path 151 and the lower circular arc inclined edge surface 245 that directs the paper P toward the return conveyance path 163, a switching guide as switching means is provided. 20 can drive the first and second actuators 40, 50 to rotate forward and backward around the rotation shaft 23 to change the posture, and inclines the paper P in the upper arc with the posture set to the first posture H1. The paper P is directed to the return conveyance path 163 via the lower arc inclined edge surface 245 while being set to the second attitude H2 while being directed to the paper discharge conveyance path 151 via the edge surface 244. At the same time, there is no inconvenience that the toner on the printing screen printed on the back side of the paper P is scraped off at the intermediate position between the first posture H1 and the second posture H2 and the toner is deposited on the guide fins 24. The third posture H3 is assumed.

  In addition, by adopting the switching guide 20 having such a structure, the switching guide 20 can be made to have a simple structure and reliably perform the function by the posture change.

  That is, the switching guide 20 of the first embodiment regulates the rotation range between the first posture H1 and the second posture H2 around the rotation shaft 23 by the protruding portion 63 provided on the rotation range setting member 61. Since the posture is set to the third posture H3 according to this restriction, the third posture H3 is required, that is, according to the situation where the paper P that has been printed on the back side in duplex printing is discharged. Thus, it becomes possible to set the switching guide 20 to the third posture H3 by a simple operation of fitting the protruding portion 63 into the rotation range restricting hole F1, which can contribute to a reduction in apparatus cost.

  Further, the switching guide 20 of the second embodiment has a point of action (axial center of the transmission rod 69) on which the first and second actuators 40 and 50 act to rotate the switching guide 20 around the rotation shaft 23. Since the posture is set to the third posture H3 by changing, for example, the action point and the fulcrum in the posture change between the first posture H1 and the second posture H2 (the axis of the rotating shaft 23). By adopting such a structure that the distance between the action point and the fulcrum in the posture change between the first posture H1 and the third posture H3 is made shorter than the distance between The first switching mode for changing the posture of the switching guide 20 between the first posture H1 and the second posture H2, and the first for changing the posture between the first posture H1 and the third posture H3. Between two switching modes Structure for the Rikae is simplified.

  The present invention is not limited to the above embodiment, and includes the following contents.

  (1) In the above-described embodiment, the guide fin 24 is in the third posture only when the paper P on which the back side is printed in the double-sided printing is the target and the paper P is directed toward the paper discharge conveyance path 151. Although the posture is set to the posture H3, in addition to this, the posture of the guide fin 24 is temporarily set to the second when the sheet P on which the front side printing process has been completed is directed to the return conveyance path 163 in double-sided printing. After setting the posture H2, the guide fin 24 may be controlled to change to the third posture H3 until the leading edge of the paper P reaches the lower arc portion 243 of the guide fin 24. This prevents the toner on the printing surface on the front side of the paper P from being scraped off by the lower arc portion 243 of the guide fin 24 even when it is directed toward the return conveyance path 163.

  (2) In the above embodiment, the first actuator 40 rotates the switching guide 20 around the rotation shaft 23 via the transmission rod 69, and the second actuator 50 limits the rotation range. However, instead of doing this, the drive rod of the electric motor that can easily and accurately control the rotation angle of the step motor or the like on the transmission rod 69 is directly or decelerated. By connecting to the rotation shaft 23 via a mechanism and controlling the rotation angle of the electric motor, the switching guide 20 may be changed in posture between the first posture H1, the second posture H2, and the third posture H3. Good.

  (3) In the first embodiment described above, the coil spring 65 is employed in the switching mechanism 60, and the current of the coil spring 65 is not supplied to the electromagnetic coil built in the solenoid body 51 of the second actuator 50. The rotation range setting member 61 is urged toward the rotation range restriction hole F1 of the frame F by the urging force. However, the present invention is limited to the application of the coil spring 65 to the switching mechanism 60. Instead, the iron core member 52 may be advanced and retracted relative to the solenoid body 51 by switching the direction of the current supplied to the electromagnetic coil in the solenoid body 51.

  (3) In the first embodiment described above, the second actuator 50 is provided on the back surface side of the frame F, but it may be provided on the front surface side of the frame F instead.

  (4) In the second embodiment, the first and second actuators 40 and 50 using solenoids are employed. However, in the present invention, the first and second actuators 40 and 50 are solenoids. The first and second actuators 40 and 50 may be a cylinder device that operates by air pressure or hydraulic pressure, an electric motor, or the like.

  (5) In the second embodiment, the axial center X0 of the rotation shaft 23 and the axial center of the transmission rod 69 positioned at the right end of the guide slot 221 (the right semicircular end of the guide slot 221). Of the transmission rod 69 positioned at the right end of the guide elongated hole 221 (the curvature center line X1 of the right semicircular end) and the guide elongated hole 221. The distance d2 between the axial centers of the transmission rods 69 positioned at the left end (the center of curvature X2 of the left semicircular end of the guide slot 221) is set to be the same (d1 = d2). The present invention is not limited to d1 = d2, and the values of d1 and d2 can be appropriately set depending on the situation.

It is explanatory drawing of front sectional view for demonstrating one Embodiment of the internal structure of an image forming apparatus. It is an expansion explanatory view of the front view which shows the vicinity of the switching guide in an apparatus main body. It is a perspective view showing a first embodiment of a switching mechanism for switching the destination of paper. It is a block diagram which shows one Embodiment of the attitude | position control of the switching guide by a control part. It is an operation view for explaining the operation of the switching guide whose posture is set by control by the control unit. (A) is a state where the switching guide is set to the first posture H1, and (b) is a state where the switching guide is A state in which the posture is set to the second posture, (C) indicates a state in which the switching guide is set to the third posture. In addition, the inside of a circle is an enlarged view which shows the positional relationship of the rotation range setting member and rotation range control hole in each state. It is a partially cutaway perspective view showing a second embodiment of a switching mechanism for switching the destination of a sheet. It is an operation | movement figure for demonstrating the effect | action of the switching guide by which the attitude | position is set by control by a control part, (a) is the state in which the switching guide was set to the 1st attitude | position, (b) A state in which the posture is set to two postures, (c) indicates a state in which the switching guide is set to the third posture.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Apparatus main body 12 Image forming part 12Y Yellow unit 12M Magenta unit 12C Cyan unit 12K Black unit 121 Photosensitive drum 122 Developing device 123 Charger 124 Exposure device 125 Cleaning device 126 Conveying belt 13 Fixing unit 131 Fixing roller 132 Pressure roller 133 Nip part 134 Guide plate 135 Upper guide plate 136 Lower guide plate 14 Paper storage part 141 Paper tray 142 Pickup roller 143 Paper feed conveyance path 15 Paper discharge part 151 Paper discharge conveyance path 151a Left side plate 152 Inside the cylinder Discharge tray 16 Paper reversing unit 161 Support plate 161a Support plate 162 Reverse roller pair 163 Return conveyance path 164 Reverse conveyance path 19 Image reading device 191 Document presser 192 Optical system unit 193 Contact glass 193a placed document contact glass 193b automatic sheet contact glass 194 operating panel 195 the document tray 196 document discharge tray 197 document feeding unit 20 switching the guide (switching means)
201 Rotating fulcrum 202 Action point 21 Cross-shaped rod 22 Reinforcement plate 221 Guide long hole 23 Rotating shaft (support shaft)
24 guide fins 241 corner 242 upper arc portion 243 lower arc portion 244 upper arc inclined edge surface (first guide surface)
245 Lower circular arc inclined edge surface (second guide surface)
30 switching mechanism 40 first actuator (switching mechanism)
41 Solenoid body 42 Iron core member 421 Connection shaft 43 Connection plate 50 Second actuator (switching mechanism)
51 Solenoid body 52 Iron core member 521 Connection shaft 53 Connection plate 60 Switching mechanism 61 Rotation range setting member 62 Cylindrical base body 63 Projection part 64 Hook part 641 Extension part 642 Relief hole 65 Coil spring 69 Transmission rod 691 Flange 70 Control part 71 CPU
711 Print mode discriminator (single / double-side discriminator)
712 Control signal output unit 72 ROM
73 RAM 74 Timer 75 Paper sensor P Paper

Claims (5)

On the downstream side of the fixing unit for fixing the paper on which the toner image has been transferred in the image forming unit, a paper discharge conveyance path for discharging the paper after the fixing processing to the outside, and on one side for performing double-sided printing A return conveyance path for returning the fixing-processed paper subjected to the transfer process to the image forming unit, and a branching position of the paper discharge conveyance path and the return conveyance path so that the destination of the paper is disposed at the paper discharge conveyance path and the return path. An image forming apparatus comprising: a switching unit that switches to one of the conveyance paths; and a control unit that controls a switching operation of the switching unit,
The switching means has a first posture for guiding the paper to the paper discharge conveyance path by driving a predetermined switching mechanism, a second posture for guiding the paper to the return conveyance path, and a contact state of the conveyed paper. The posture can be changed between the third posture to be canceled,
The control unit sets the switching unit to the first posture when the sheet is subjected to transfer processing on both sides, and then immediately after the sheet starts to be guided to the switching unit, the third unit. An image forming apparatus characterized in that control for changing the posture to a posture is performed via the switching mechanism. The control unit includes a single side / double side determination unit and a control signal output unit,
The single-side / double-side discriminating unit discriminates whether the paper after the fixing process is for single-sided printing or double-sided printing, and if it is for double-sided printing, printing is performed on both sides. Is to determine whether or not
The control signal output unit, when the paper is for single-sided printing, when the switching means is set to the first posture, is for double-sided printing and is subjected to only single-sided printing, While the switching means is set to the second attitude, and when double-sided printing is performed, a control signal for changing the attitude to the third attitude after setting the switching means to the first attitude is sent to the switching mechanism. The image forming apparatus according to claim 1, wherein the image forming apparatus outputs the output toward the screen.   The switching means is a first guide surface that is pivotally supported around a support shaft extending in the paper width direction orthogonal to the paper transport direction by driving the switching mechanism, and directs the paper toward the paper discharge transport path. The image forming apparatus according to claim 1, wherein the image forming apparatus is a switching guide including a second guide surface that directs the sheet toward the return conveyance path.   The posture of the switching guide is set to the third posture by restricting a rotation range between the first and second postures around the support shaft of the switching guide. 3. The image forming apparatus according to 3.   The posture of the switching guide is set to the third posture by changing an action point at which the switching mechanism acts to rotate the switching guide around the support shaft. 3. The image forming apparatus according to 3.

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