JP2008127159A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing erroneous paper feed. <P>SOLUTION: When an image formation is indicated (S11: YES), this image forming apparatus specifies a paper feed source (S12) and the specified paper feed source determines whether paper reverse is specified or not (S13). When determining that the paper reverse is specified (S13: YES), this apparatus applies an electric field of the same polarity with that of toner to a transfer roller (S14) and suppresses the transfer of a toner image. After increasing a fixing temperature, this apparatus controls the conveyance path (S 15 and S16), sets a route for reversing paper sheets and starts feeding the paper sheets (S17). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that prevents feeding errors.

  Some image forming apparatuses such as printers and digital multifunction peripherals are provided with a plurality of paper feed cassettes. Depending on the path from the paper feed cassette to the image forming unit, when setting recording paper (hereinafter simply referred to as paper) to the paper feed cassette, the paper is set with the recording surface facing up, and the recording surface is facing down. If you do.

  However, there are few users who set paper in consideration of the transport path, and there is a high tendency to set paper in the same direction even in different paper feed cassettes. Therefore, when the used paper that has been printed on one side is reused, there is a problem in that an image is formed again on the printed surface unless it is set properly.

Therefore, conventionally, an image forming apparatus that detects whether or not a sheet has been used on one side before performing image formation, and forms an image on an unused side of the sheet based on the detection result has been proposed (for example, , See Patent Document 1).
JP 2001-230900 A

  In the image forming apparatus described in Patent Document 1, the first and second image forming units are selectively driven according to the detection result of whether or not the paper is used on one side. That is, although two transfer rollers are in contact with one photoconductor, it is unclear whether or not a good toner image can be formed in such a configuration. Further, in order to form a toner image on the photosensitive member, in addition to the transfer roller, an exposure unit for forming an electrostatic latent image, a developing unit for developing the electrostatic latent image, and a method for removing residual toner. However, there is no description of how these devices are arranged, and it is unclear what process forms the image. Therefore, there is a problem that it may not function as a realistic image forming apparatus.

  The present invention has been made in view of such circumstances, and accepts selection of a sheet storage unit that stores a sheet to be reversed, and reverses the sheet when conveying the sheet from the selected sheet storage unit to the image forming unit. By switching to the first conveyance path that leads to the image forming means, it is possible to prevent image formation on the used surface even when two transfer rollers (image forming portions) are not provided. An object of the present invention is to provide an image forming apparatus that can avoid paper feeding errors.

  Another object of the present invention is to detect whether or not an image is formed on one side of the sheet when the sheet stored in any of the sheet storing means is conveyed, and the image is formed. If this is detected, the used surface is reversed even when two transfer rollers (image forming units) are not provided by switching to the first conveyance path that reverses the sheet and leads it to the image forming unit. It is an object of the present invention to provide an image forming apparatus that can prevent image formation and avoid paper feeding errors.

  An image forming apparatus according to the present invention includes: an image forming unit that forms an image on a sheet; a plurality of sheet storing units that store sheets; and a sheet stored in any of the sheet storing units by inverting the sheet An image comprising a first conveyance path for conveying to the image forming means, a second conveyance path for conveying the sheet to the image forming means without inverting the sheet, and a switching means for switching between the first and second conveyance paths. In the forming apparatus, when the sheet is transported from the sheet storing unit selected by the unit to the image forming unit, the first transport is performed on the transport path. And a means for controlling the switching means to switch to a road.

  In the present invention, when the selection of the sheet storage unit that stores the sheet to be reversed is received and the sheet is conveyed from the selected sheet storage unit to the image forming unit, the sheet is reversed and guided to the image forming unit. Since the sheet is switched to one conveyance path, the direction (front and back) of the sheets stored in the sheet storage unit can be unified, and a paper feeding error is avoided.

  An image forming apparatus according to the present invention includes: an image forming unit that forms an image on a sheet; a plurality of sheet storing units that store sheets; and a sheet stored in any of the sheet storing units by inverting the sheet An image comprising a first conveyance path for conveying to the image forming means, a second conveyance path for conveying the sheet to the image forming means without inverting the sheet, and a switching means for switching between the first and second conveyance paths. In the forming apparatus, when conveying a sheet stored in any of the sheet storing means, a detecting means for detecting whether or not an image is formed on one surface side of the sheet, and an image are formed Control means for controlling the switching means so as to switch the transport path to the first transport path.

  In the present invention, when conveying a sheet stored in any of the sheet storing means, it is detected whether an image is formed on one side of the sheet, and an image is formed. Is detected, the sheet is reversed and switched to the first conveyance path that leads to the image forming unit. Therefore, the image is used on the used surface regardless of the orientation (front and back) of the sheet stored in the sheet storing unit. It will not be formed.

  In the image forming apparatus according to the present invention, the first transport path is provided on the downstream side in the paper transport direction with respect to the image forming unit. When the sheet is transported to the first transport path, the image forming unit The apparatus further comprises means for stopping image formation.

  In the present invention, the first conveying path is provided on the downstream side in the sheet conveying direction with respect to the image forming unit, and when the sheet is conveyed to the first conveying path, the sheet is reversed to stop the image formation. When transporting to the first transport path for performing, image formation can be stopped and image formation on the use surface is prevented.

  In the image forming apparatus according to the present invention, the image forming unit includes a photosensitive member that generates an image using a charged developer, a transfer member that transfers an image generated on the photosensitive member onto the sheet, and an image. A means for applying a voltage having a polarity different from that of the developer to the transfer body when forming, and applying a voltage of the same polarity as the developer to the transfer body when stopping image formation; Features.

  In the present invention, when image formation is performed, a voltage having a polarity different from that of the developer is applied to the transfer member, and when image formation is stopped, a voltage having the same polarity as that of the developer is applied to the transfer member. When reversing, image formation on the surface to be used is prevented only by changing the polarity.

  The image forming apparatus according to the present invention is characterized in that the detecting means detects whether or not an image is formed in the entire area on the one surface side.

  In the present invention, since it is detected whether an image is formed on the entire area on one side of the sheet, detection is possible even when only a part of the sheet is used. It is detected well whether or not.

  The image forming apparatus according to the present invention is characterized in that the detecting means detects whether or not an image is formed in a partial area on the one surface side.

  In the present invention, since it is detected whether an image is formed on a partial area on one side of the sheet, it is possible to detect whether the sheet is a used sheet with a simple configuration. .

  An image forming apparatus according to the present invention forms an image on a sheet conveyed by the first conveying path, and a fixing unit that heats the sheet on which the image has been formed by the image forming unit and fixes the image on the sheet. In the case of performing, it further comprises means for raising the heating temperature by the fixing means.

  In the present invention, when the sheet is transported through the first transport path to form an image, the heating temperature of the fixing unit is increased, so that the fixing temperature is prevented from decreasing during the transport of the sheet. .

  In the present invention, when the selection of the sheet storage unit that stores the sheet to be reversed is received and the sheet is conveyed from the selected sheet storage unit to the image forming unit, the sheet is reversed and guided to the image forming unit. Switching to one transport path is made. Therefore, it is possible to unify the orientation (front and back) of the sheets stored in the sheet storing means, and avoid paper feeding errors.

  In the present invention, when conveying a sheet stored in any of the sheet storing means, it is detected whether an image is formed on one side of the sheet, and an image is formed. Is detected, the sheet is reversed and switched to the first conveyance path that leads to the image forming means. Therefore, even when two transfer units are not provided, an image can be formed on an unused surface regardless of the orientation (front and back) of the sheet stored in the sheet storage unit.

  In the present invention, the first conveying path is provided on the downstream side in the sheet conveying direction with respect to the image forming unit, and when the sheet is conveyed to the first conveying path, the sheet is reversed to stop the image formation. When transporting to the first transport path for performing, image formation can be stopped and image formation on the use surface can be prevented.

  In the present invention, when image formation is performed, a voltage having a polarity different from that of the developer is applied to the transfer member, and when image formation is stopped, a voltage having the same polarity as that of the developer is applied to the transfer member. When reversing, image formation on the surface to be used can be prevented only by changing the polarity.

  In the present invention, since it is detected whether an image is formed on the entire area on one side of the sheet, detection is possible even when only a part of the sheet is used. It can be detected satisfactorily.

  In the present invention, since it is detected whether an image is formed on a partial area on one side of the sheet, it is possible to realize detection of whether the sheet is a used sheet with a simple configuration. it can.

  In the present invention, when the sheet is transported through the first transport path and image formation is performed, the heating temperature of the fixing unit is increased, so that the fixing temperature is prevented from decreasing during the transport of the sheet. Can do.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
Embodiment 1 FIG.
FIG. 1 is a schematic diagram showing the overall configuration of an image forming apparatus according to the present invention. The image forming apparatus is specifically a printer apparatus or a digital multi-function peripheral, and includes a printer unit 1A that forms an image on a sheet (paper), a paper feeding unit 2 that supplies paper to the printer unit 1A, and a document. A scanner unit 3 that generates image data by optically reading an image is provided.

  The printer unit 1A includes an exposure unit 13, a developing unit 15, a photosensitive drum 17, a charger 19, a cleaner unit 21, a fixing unit 23, and the like as an image forming unit of an electrophotographic system, and an image generated by the scanner unit 3. A monochrome image is formed on a sheet conveyed from the sheet feeding unit 2 based on the data or data acquired by a communication unit described later.

  The charger 19 is a charging means for uniformly charging the surface of the photosensitive drum 17 to a predetermined potential. In the present embodiment, a charger type charger is used. In addition to the charger type charger, a contact type roller type or brush type charger may be used.

  The exposure unit 13 may be a technique using an EL or LED writing head in which light emitting elements are arranged in an array, in addition to a technique using a laser scanning unit (LSU) including a laser irradiation unit and a reflection mirror. Furthermore, this image forming apparatus employs a technique of using a plurality of laser beams to reduce the speed of irradiation timing and adopting a two-beam technique in order to perform high-speed printing processing. Then, the photosensitive drum 17 uniformly charged by the charger 19 is exposed according to the input image data, thereby forming an electrostatic latent image corresponding to the image data on the surface of the photosensitive drum 17.

  The developing device 15 visualizes the electrostatic latent image formed on the photosensitive drum 17 with toner as a developer. The cleaner unit 21 removes and collects toner remaining on the surface of the photosensitive drum 17 after development and image transfer.

  The toner visualized on the photosensitive drum 17 as described above is transferred onto the sheet conveyed from the sheet feeding unit 2. The transfer unit 39 for this purpose is a mechanism for applying an electric field having a polarity opposite to that of the toner to transfer the toner image onto the paper. For example, when the electrostatic latent image has a negative charge, the polarity applied to the transfer unit 39 is positive.

The transfer unit 39 of the image forming apparatus includes a transfer belt 45 that is constructed by rollers such as a driving roller and a driven roller and has a predetermined resistance value (range of 1 × 10 ⁹ to 1 × 10 ¹³ Ω · cm). A transfer roller 49 capable of applying a transfer electric field is disposed at a contact portion between the photosensitive drum 17 and the transfer belt 45. The transfer roller 49 has conductivity and elasticity. By the transfer roller 49, the photosensitive drum 17 and the transfer belt 45 are not in line contact but in surface contact with each other with a predetermined width (transfer nip). As a result, the transfer efficiency to the conveyed paper can be improved.

  Further, on the downstream side of the transfer area of the transfer belt 45, a static eliminating roller is disposed to neutralize the sheet charged by the voltage applied when passing through the contact portion described above, and smoothly carry it to the next process. Has been. The neutralizing roller is disposed on the back surface of the transfer belt 45.

  The transfer unit 39 is provided with a cleaning unit and a charge removal mechanism for removing toner from the transfer belt 45 and discharging the transfer belt 45. As the static elimination mechanism, there is a method of contacting through an apparatus or a method of positively applying a polarity opposite to the polarity of the transfer electric field. The sheet on which the toner image is transferred by the transfer unit 39 is conveyed to the fixing unit 23 provided on the downstream side.

  The fixing unit 23 includes a heating roller 57 and a pressure roller 59, and a sheet peeling claw, a roller surface temperature detector (thermistor), and a roller surface cleaning member are disposed on the outer periphery of the heating roller 57. In addition, a heat source for heating the roller surface to a predetermined temperature (approximately 160 to 200 ° C.) is disposed inside the heating roller 57.

  On the other hand, pressure members that can be pressed against the heating roller 57 with a predetermined pressure are disposed at both ends of the pressure roller 59. Similar to the outer periphery, a sheet peeling claw and a roller surface cleaning member are arranged.

  The fixing unit 23 heats and melts the unfixed toner on the conveyed paper at the pressure contact portion (fixing nip) between the heating roller 57 and the pressure roller 59 at the surface temperature of the heating roller 57. The unfixed toner on the paper is fixed on the paper by a throwing action by the pressure contact force.

  The paper feed cassettes 25a to 25d are trays for storing paper used for image formation, and are provided on the side wall of the apparatus below the printer unit 1A. Since this image forming apparatus is intended to perform high-speed printing processing, as a paper feed cassette disposed below the printer unit 1A, a plurality of paper feeds capable of storing 500 to 1500 standard sizes in each tray. Cassettes 25a to 25d are arranged. Further, on the side of the apparatus, a large-capacity paper feed cassette 26 capable of storing a large amount of a plurality of paper types and a manual feed tray 27 mainly used for printing of an irregular size are disposed.

  The paper discharge tray 33 is disposed on the side surface opposite to the manual feed tray 27 of the apparatus. However, instead of the paper discharge tray 33, a post-processing device (such as a stapling device or a punch processing device) for discharged paper is provided. It is also possible to arrange a plurality of trays as an option.

  Next, the paper conveyance process at the time of image formation will be described in detail. The paper suitable for the user's print request is selected from the aforementioned paper feed cassettes 25a to 25d, the large capacity paper feed cassette 26, and the manual feed tray 27, and is registered by the action of the transport roller provided along a predetermined path. It is conveyed to the roller 29. Then, the paper that has reached the registration roller 29 is temporarily stopped under the control of the control unit 101 (see FIG. 3) described later. The control unit 101 re-rotates the registration roller 29 at the timing when the leading edge of the stopped paper and the toner image on the photosensitive drum 17 are matched, and conveys the paper to the transfer unit 39. After the toner image on the photosensitive drum 17 is transferred onto the paper by the transfer unit 39, the paper is guided to the fixing unit 23, and the toner image is fixed on the paper. The sheet on which the toner image is fixed is discharged to the discharge tray 33 by the action of the discharge roller 95.

  As described above, the image forming apparatus is configured to convey a sheet stored in any one of the sheet feeding cassettes 25a to 25d, the large-capacity sheet feeding cassette 26, and the manual feed tray 27 to the image forming unit without being reversed. Second transport path). The image forming apparatus further includes a transport path (first transport path) that reverses the paper stored in any of the trays and transports the paper to the image forming unit. The control unit 101 switches between the first transport path and the second transport path. Note that a partially overlapped path is used for the first transport path and the second transport path.

  FIG. 2 is an explanatory diagram for explaining the switching of the conveyance path. The switching of the conveyance path is controlled by branch claws 77, 83, 85, 89, 92 provided on the path. The branching claw 77 switches between a conveyance path 79 that leads the paper to the paper discharge tray 33 and a conveyance path 81 that leads the switchback path 90 or the registration roller 29. The control unit 101 switches the position of the branch claw 77 by the driving force of the solenoid 77a (see FIG. 3). Further, the branch claw 83 is configured to be urged by an elastic member such as a spring arranged on a branch claw holding shaft (not shown) to shield the conveyance path 81. The sheet that has entered the conveyance path 81 from the conveyance roller 93 side can pass through the branch claw 83 by the waist of the sheet and the conveyance force. However, it is possible to prevent the sheet from entering the conveyance path 81 from the branching claw 83 side. The branch claw 85 is switched to any one of a conveyance path 84 that leads the sheet to the registration roller 29, a conveyance path 90 that leads to the switchback path 90, and a conveyance path 87 that leads the sheet from the switchback path 90 to the paper discharge tray 33. It is. The branching claw 89 switches between the conveyance path 91 and the conveyance path 84 that guide the sheet to the switchback path 90. The control unit 101 drives the solenoids 85a and 89a corresponding to the branch claws 85 and 89, respectively, and switches the positions of the branch claws 85 and 89 independently. The branching claw 92 is fixed.

  Hereinafter, an operation when the conveyance path is switched according to the application will be described. When performing face-up discharge in single-sided printing, the control unit 101 opens the conveyance path 79 and blocks the conveyance path 81 at a timing immediately before the sheet that has passed through the fixing unit 23 subsequently passes the conveyance roller 93. The position of the branch claw 77 is switched. The leading edge of the conveyed paper is guided by the branching claw 77, passes through the conveyance path 79, and is discharged to the paper discharge tray 33 through the paper discharge roller 95. By default, this transport path is selected, and when used for other purposes, the transport path is switched by switching the positions of the branch claws 77, 85, and 89.

  When performing face-down discharge in single-sided printing, the control unit 101 opens the conveyance path 81 and blocks the conveyance path 79 immediately before the sheet that has passed through the fixing unit 23 passes the conveyance roller 93. Switch the position of. Further, the position of the branch claw 85 is switched to open the conveyance path 84 and shield the conveyance path 88. The leading edge of the conveyed paper is guided by the branching claw 77 and passes through the conveyance path 81, and then passes through the branching claw 83 and reaches the branching claw 85 by the waist and the conveyance force of the leading edge of the paper. Thereafter, the leading edge of the sheet is guided by the branching claw 85 and guided to the conveyance path 84. When the trailing edge of the paper reaches the position of the branching claw 92, the control unit 101 temporarily stops the conveyance of the paper. Then, the control unit 101 switches the position of the branch claw 85 to open the transport path 87 and shield the transport path 88. As described above, the branch claw 83 is urged by the elastic member to shield the conveyance path 81. After switching the position of the branch claw 85, the control unit 101 reversely rotates the reverse conveyance roller 94 to convey the paper in the direction opposite to the entering direction. The sheet passes through the conveyance path 87 with the rear end when entering the conveyance path 84 being the leading end, and is discharged to the discharge tray 33 through the discharge roller 95.

  When performing double-sided printing, the control unit 101 switches the position of the branching claw 77 immediately before the printing on the first surface (front surface) is finished and the paper that has passed through the fixing unit 23 passes through the conveyance roller 93. 81 is opened and the conveyance path 79 is shielded. Further, the position of the branch claw 85 is switched to open the transport path 88 and shield the transport path 84. In addition, the position of the branch claw 89 is switched to open the conveyance path 91. The leading edge of the conveyed paper is guided by the branching claw 77 and passes through the conveyance path 81. After passing through the branching claw 83 by the waist and the conveyance force of the leading edge of the paper, it is guided by the branching claw 85 and passes through the conveyance path 88. Passes and is guided to the subsequent conveyance path 91. The control unit 101 temporarily stops the conveyance of the sheet when the trailing edge of the sheet reaches the conveyance path 91. Then, the position of the branch claw 89 is switched to shield the conveyance path 88 and the conveyance path 84 is opened. Thereafter, the control unit 101 reversely rotates the switchback roller 96 to convey the sheet in the direction opposite to that when entering the switchback path 90. The sheet passes through the branching claw 89 with the trailing end when entering the conveyance path 91 as the leading edge, and is guided to the conveyance path 84. Thereafter, the sheet is conveyed to a registration roller 29 disposed on the upstream side of the image forming unit such as the transfer unit 39 and is conveyed onto the transfer belt 45 in synchronization with the image. When the image formation on the second surface (back surface) is completed and the sheet passes through the fixing unit 23, the control unit 101 switches the position of the branching claw 77 to guide the sheet to the conveyance path 79 and discharge it to the sheet discharge tray 33. To do.

  In the present embodiment, when a sheet is supplied from a preselected sheet storage unit (for example, the large-capacity paper feed cassette 26), the sheet is reversed in the same manner as when double-sided printing is performed. Then, the image is formed by being conveyed to an image forming unit 39. By adopting such a configuration, it is possible to unify the orientation (front and back) of sheets to be stored in a plurality of sheet storage units (paper feed cassettes 25a to 25d, large capacity paper feed cassette 26, manual feed tray 27). That is, when an image is formed on the paper stored in the four paper feed cassettes 25a to 25d, the image is normally formed on the lower surface side of the stored paper. On the other hand, when an image is formed on the paper stored in the large-capacity paper feed cassette 26, an image is usually formed on the upper surface side of the stored paper. Therefore, when image formation is performed using the paper stored in the large-capacity paper feed cassette 26, first, the paper is reversed using the switchback path 90 and the like, and then the image is formed by performing image formation. Can be unified. It should be noted that the selection of the sheet storage means to be reversed can be set on an operation panel 102 (see FIG. 3) described later.

  Next, the configuration of the control system of the image forming apparatus will be described. FIG. 3 is a block diagram showing the configuration of the control system of the image forming apparatus. The image forming apparatus includes a control unit 101, an operation panel 102, and a communication IF 103 in addition to the above-described printer unit 1A, paper feed unit 2, and scanner unit 3, and the control unit 101 includes the printer unit 1A, paper feed unit 2, and scanner. By controlling the unit 3, the operation panel 102, and the communication IF 103, the entire apparatus is operated as an image forming apparatus according to the present invention.

  The control unit 101 includes a ROM in which control programs for controlling the various hardware described above are stored in advance, a RAM that provides a work area for work, a CPU that executes the control programs stored in the ROM, and the like. The operation panel 102 includes a touch panel provided with receiving means for receiving various operations by the user and display means for displaying information to be notified to the user. The communication IF 103 includes an interface for connecting an information processing apparatus such as a personal computer, receives data such as a print job from the connected information processing apparatus, and transmits information to be notified to the information processing apparatus.

  The control unit 101 controls the transfer electric field application unit 48 and the energization unit 56 in order to control the operations of the transfer roller 49 and the heating roller 57 provided in the printer unit 1A. That is, the control unit 101 controls the transfer electric field application unit 48 in order to control the intensity and polarity of the electric field applied to the transfer roller 49, and controls the heat source inside the heating roller 57 to adjust the surface temperature of the heating roller 57. Energization control is performed. Further, the control unit 101 controls the operations of the solenoids 77a, 85a, and 89a in order to switch the positions of the branch claws 77, 85, and 89 described above.

  FIG. 4 is a schematic diagram showing a setting screen for selecting a paper feed cassette for paper reversal. On the setting screen, the necessity of the printer function, copy function, and reversal function can be set for each of the paper feed cassettes 25a to 25d, 26 and the manual feed tray 27. That is, necessity switching is performed by pressing a check box provided for each function as an operation button of the touch panel. In the setting screen shown in FIG. 4A, settings are made for the paper feed cassettes 25a to 25c (cassette 1 to cassette 3). In the example shown in FIG. 4A, the use of the printer function and the copy function is set, but the use of the inversion function is set to be unnecessary. In the setting screen shown in FIG. 4B, settings are made for the paper feed cassette 25d (cassette 4), the large-capacity paper feed cassette 26 (cassette 5), and the manual feed tray 27 (manual feed). In the example shown in FIG. 4B, the printer function and the copy function are set to be used, but the reverse function is set to be used only for the large-capacity paper feed cassette 26 (cassette 5). .

  FIG. 5 is a flowchart for explaining the operation of the image forming apparatus according to the first embodiment. First, the control unit 101 of the image forming apparatus determines whether there is an instruction to form an image (step S11). When the communication IF 103 receives a print job from an external information processing apparatus or when an instruction to copy a document is given based on image data captured through the scanner unit 3, it is determined that there is an instruction for image formation (S11: YES), the paper supply source for image formation is specified (step S12). The paper supply source is the default paper supply cassette (for example, the large-capacity paper supply cassette 26), unless specified by the information processing apparatus or the operation panel 102. If it is determined in step S11 that there is no instruction for image formation (S11: NO), the process waits until there is an instruction for image formation.

  Next, the control unit 101 determines whether or not the paper supply source specified in step S12 is designated for paper reversal (step S13). If it is determined that paper reversal is designated (S13: YES), the control unit 101 controls the transfer electric field applying unit 48 to apply an electric field having the same polarity as the toner to the transfer roller 49 (step S14). By controlling the energization unit 56, the surface temperature (fixing temperature) of the heating roller 57 is increased by, for example, 5 ° C. to 10 ° C. (step S15). In other words, when paper reversal is designated, since the paper reversal is performed by temporarily passing between the transfer unit 39 and the photosensitive drum 17 without image formation, the transfer roller 49 has the same polarity as the toner. An electric field is applied to prevent transfer of the toner image. In addition, since the paper conveyance path becomes longer than when paper reversal is not performed, the fixing temperature is raised so that the surface temperature of the heating roller 57 does not decrease during conveyance.

  After raising the fixing temperature, the control unit 101 controls the transport path (step S16). Specifically, as in the case of performing double-sided printing, the positions of the branch claws 77, 85, and 89 are switched to open the conveyance paths 81, 88, and 91. When the paper supply is started in this state (step S17), the paper that has passed between the photosensitive drum 17 and the transfer unit 39 passes through the conveyance paths 81, 88, and 91 by the control of the conveyance path described above, and is switched. It is conveyed to the back path 90. When the trailing edge of the sheet comes to the conveyance path 91, the control unit 101 rotates the switchback roller 96 in the reverse direction and conveys it in the direction opposite to that when entering the switchback path 90. At this time, the control unit 101 switches the position of the branch claw 89 and shields the conveyance path 88 to guide the reversed sheet to the conveyance path 88 and convey it again to the registration roller 29. Then, image formation is performed when the photosensitive drum 17 and the transfer unit 39 are passed again, and the position of the branch claw 77 is switched to guide the sheet on which the image is formed to the conveyance path 79, and the discharge roller. The sheet is discharged onto the sheet discharge tray 33 by the action of 95.

  If it is determined in step S13 that paper reversal is not designated (S13: NO), the paper supply is started (S17), and image formation is performed when passing between the photosensitive drum 17 and the transfer unit 39. I do. Then, the paper is guided to the conveyance path 79 and discharged onto the paper discharge tray 33 by the action of the paper discharge roller 95.

  In this embodiment, the case where an image is formed on a sheet is described. However, when an OHP film is used, the image may be reversed by mirror image reversal without performing sheet reversal. That is, the image forming apparatus is provided with a mechanism for reversing the sheet immediately before the sheet ejection and ejecting the sheet in a face-down state. However, when an OHP film is used, the inversion is often prohibited. There is a problem that paper can only be discharged face up. When printing on a plurality of OHP films under such circumstances, the page order is discharged differently, but it is possible to arrange the page order by discharging in a state where a mirror image is reversed. It becomes possible.

Embodiment 2. FIG.
In the first embodiment, a description has been given of a mode in which the necessity of paper reversal is set in advance. However, it is detected whether an image has already been formed on the surface on which an image is to be formed, and the image has already been formed. If it is detected that the sheet is detected, the sheet may be reversed. In the present embodiment, a configuration for performing sheet reversal according to a detection result will be described.

  FIG. 6 is a block diagram illustrating a configuration of a control system of the image forming apparatus according to the second embodiment. The image forming apparatus according to the second embodiment includes a printer unit 1B, a paper feed unit 2, and a scanner unit 3, and the control unit 101 controls these units, the operation panel 102, the communication IF 103, and the like, whereby the apparatus The whole is operated as an image forming apparatus according to the present invention.

  The printer unit 1B includes a document surface detector 30 in addition to the configuration described in the first embodiment. The document surface detector 30 is provided at an appropriate position on the downstream side of the registration roller 29 and is disposed so as to face the surface on which an image is to be formed.

  FIG. 7 is a schematic diagram showing the manuscript surface detector 30. As the document surface detector 30, for example, an optical sensor can be used. In other words, the optical detector includes an irradiation unit that irradiates light onto a surface on which an image is to be formed, and a light receiving unit that receives reflected light from the irradiation surface, and is based on the amount of received light. It is detected whether or not an image is formed. In the manuscript surface detector 30 shown in FIG. 7A, the irradiation unit and the light receiving unit are arranged so as to detect the approximate center of the paper width direction (direction perpendicular to the paper transport direction). With this configuration, it is possible to detect the presence or absence of image formation even with a simple configuration. In the original surface detector 30 shown in FIG. 7B, a plurality of irradiation units and light receiving units arranged in a one-dimensional manner in the width direction of the paper are arranged. With such a configuration, the presence or absence of an image can be detected over substantially the entire surface of the paper.

  FIG. 8 is a flowchart for explaining the operation of the image forming apparatus according to the second embodiment. First, the control unit 101 of the image forming apparatus determines whether there is an instruction for image formation (step S21). When the communication IF 103 receives a print job from an external information processing apparatus or when an instruction to copy a document is given based on image data captured through the scanner unit 3, it is determined that there is an instruction for image formation (S21: YES), the paper supply source for image formation is specified (step S22). Then, the paper supply is started from the specified paper supply source (step S23). At this time, if it is instructed to form an image on a plurality of sheets, the sheets are sequentially supplied from the specified supply source. If it is determined that there is no instruction for image formation (S21: NO), the process waits until there is an instruction for image formation.

  Next, the control unit 101 determines based on the detection result of the document surface detector 30 whether the surface on which image formation is to be performed is a surface on which image formation has already been performed (step S24). If it is determined that the surface has already been subjected to image formation (S24: YES), the control unit 101 controls the transfer electric field applying unit 48 to apply an electric field having the same polarity as the toner to the transfer roller 49 (step S25). ), The surface temperature (fixing temperature) of the heating roller 57 is increased by, for example, 5 ° C. to 10 ° C. by controlling the energization unit 56 (step S26).

  After raising the fixing temperature, the control unit 101 controls the transport path (step S27). Specifically, as in the case of performing double-sided printing, the positions of the branch claws 77, 85, and 89 are switched to open the conveyance paths 81, 88, and 91. At this time, the paper that has passed between the photosensitive drum 17 and the transfer unit 39 is transported to the switchback path 90 through the transport paths 81, 88, 91 by the control of the transport path described above. When the trailing edge of the sheet comes to the conveyance path 91, the control unit 101 rotates the switchback roller 96 in the reverse direction and conveys it in the direction opposite to that when entering the switchback path 90. At this time, the control unit 101 switches the position of the branch claw 89 and shields the conveyance path 88 to guide the reversed sheet to the conveyance path 88 and convey it again to the registration roller 29. Then, image formation is performed when the photosensitive drum 17 and the transfer unit 39 are passed again, and the position of the branch claw 77 is switched to guide the sheet on which the image is formed to the conveyance path 79, and the discharge roller. The sheet is discharged onto the sheet discharge tray 33 by the action of 95.

  If it is determined in step S27 that no image is formed on the surface on which image formation is to be performed (S24: NO), the toner image formed on the photosensitive drum 17 is transferred to the paper supply source by the action of the transfer unit 39. Then, the image is transferred onto the paper conveyed from the printer and passed through the fixing unit 23 to fix the image. Then, the paper is guided to the conveyance path 79 and discharged onto the paper discharge tray 33 by the action of the paper discharge roller 95.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus according to the present invention. It is explanatory drawing explaining switching of a conveyance path. 2 is a block diagram illustrating a configuration of a control system of the image forming apparatus. FIG. FIG. 10 is a schematic diagram illustrating a setting screen for selecting a paper feed cassette for paper reversal. 3 is a flowchart for explaining the operation of the image forming apparatus according to the first embodiment. 5 is a block diagram illustrating a configuration of a control system of an image forming apparatus according to Embodiment 2. FIG. It is a schematic diagram showing a manuscript surface detector. 10 is a flowchart for explaining the operation of the image forming apparatus according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer unit 2 Paper feed unit 3 Scanner unit 25a-25b Paper feed cassette 26 Large capacity paper feed cassette 27 Manual feed tray 101 Control part 102 Operation panel 103 Communication IF

Claims (7)

Image forming means for forming an image on a sheet, a plurality of sheet storing means for storing sheets, and a first transport for inverting and transporting a sheet stored in any of the sheet storing means to the image forming means An image forming apparatus comprising: a path; a second transport path that transports the sheet to the image forming unit without inverting the sheet; and a switching unit that switches between the first and second transport paths.
A means for receiving selection of a sheet storage means for storing a sheet to be reversed; and a sheet transporting means from the sheet storage means selected by the means to the image forming means to switch the transport path to the first transport path An image forming apparatus comprising: means for controlling the switching means. Image forming means for forming an image on a sheet, a plurality of sheet storing means for storing sheets, and a first transport for inverting and transporting a sheet stored in any of the sheet storing means to the image forming means An image forming apparatus comprising: a path; a second transport path that transports the sheet to the image forming unit without inverting the sheet; and a switching unit that switches between the first and second transport paths.
Detecting means for detecting whether an image is formed on one side of the sheet when conveying a sheet stored in any one of the sheet storing means, and the detecting means that an image is formed An image forming apparatus comprising: a control unit that controls the switching unit to switch the conveyance path to the first conveyance path.   The first conveying path is provided on the downstream side in the paper conveying direction with respect to the image forming means, and further includes means for stopping image formation by the image forming means when conveying the sheet to the first conveying path. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming means includes a photosensitive member that generates an image using a charged developer, a transfer member that transfers the image generated on the photosensitive member onto the sheet, and the developer when image formation is performed. The apparatus according to claim 3, further comprising a unit that applies a voltage having the same polarity as that of the developer to the transfer body when an image having a different polarity is applied to the transfer body to stop image formation. Image forming apparatus.   5. The image forming apparatus according to claim 2, wherein the detection unit is configured to detect whether or not an image is formed in the entire area on the one surface side. 6. .   The image according to any one of claims 2 to 4, wherein the detection means detects whether or not an image is formed on a partial area on the one surface side. Forming equipment.   A heating unit that heats a sheet on which an image has been formed by the image forming unit and fixes the image on the sheet, and a heating temperature by the fixing unit when performing image formation on the sheet that is conveyed by the first conveyance path The image forming apparatus according to claim 1, further comprising a unit that raises the image quality.

Images