JP2009145677A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form an image, without reducing an image forming speed, while enhancing convenience of a user, when the image is formed on a narrow width paper sheet. <P>SOLUTION: An image forming apparatus includes: a fixing section 7 having a heating element H and a heating body; a paper sheet supply section 4 supplying at least two or more of sizes of paper sheets P of a narrow width paper sheet P1 and a wide width paper sheet P2; a paper feed path 5; a both-side printing section 8; and a control section 9. When the image is formed on the narrow width paper sheet P1, the control section 9 makes the paper sheet supply section 4 separately supply the wide width paper sheet P2 for preventing overheating of the heating body as an overheating prevention paper sheet P3 and conveys the overheating prevention paper sheet P3 after passing through the fixing section 7 to the both-side printing section 8 to make the narrow width paper sheet P1 and the overheating prevention paper sheet P3 alternately pass through the fixing section 7, during the image is formed on the narrow width paper sheet P1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a double-sided printing function in a printer, a multifunction machine, a copying machine, a facsimile machine, or the like.

  2. Description of the Related Art Conventionally, there is an image forming apparatus (so-called electrophotographic system) that forms a toner image, transfers the toner image to a sheet, and fixes the image by heating and pressing to form an image. Specifically, in such an image forming apparatus, a toner image is heated by bringing a heating body such as a heating roller including a heating element such as a heater into contact therewith. When the sheet and the heating element come into contact with each other, heat is taken away from the heating element by the sheet, so that the heating element generates heat and the temperature of the heating element is maintained at a fixable temperature. In general, the heating element is provided over the axial direction of the heating body so that the entire heating body is heated substantially uniformly.

  However, when a sheet having a width smaller than the maximum sheet passing width of the heating body is passed, heat is taken away from the sheet only by the contact portion. Accordingly, when image formation of small-sized paper is continuously performed, the non-contact portion of the heating body with the paper is hardly deprived of heat, so the temperature becomes high and the high temperature of each member constituting the fixing unit is high. There is a problem that damage and short-lived life can be caused. In addition, when image formation is performed on a wide sheet in a state where temperature unevenness in the axial direction of the heating element is significant, contact between the high temperature portion of the heating element and a part of the wide sheet causes, for example, Insufficient fixing of toner due to a part of the temperature being too high, melted toner adhering to the surface of the heated body, paper jam due to the adhesive force of the toner, uneven glossiness of the formed image, moisture contained in the paper There may be a problem in fixing such as generation of paper wrinkles due to a difference in evaporation amount.

Then, the invention of patent document 1 is proposed with respect to the problem of the remarkable temperature difference in the axial direction of a heating body. Specifically, in Patent Document 1, in the image forming unit, the first image formation for forming an image on a recording sheet whose width in the direction orthogonal to the sheet passing direction is the first width, and orthogonal to the sheet passing direction. And the second image formation for forming an image on the recording sheet having a second width larger than the first width in the direction in which the image is formed, and the recording sheet on which the image is formed is heated. An image forming apparatus including a fixing roller for fixing, a receiving unit that receives a plurality of print jobs, a determination unit that determines whether a temperature difference in an axial direction of the fixing roller exceeds a predetermined range, and the determination If the temperature difference in the axial direction of the fixing roller exceeds the predetermined range by the means, and there is a print job for executing the second image formation among the print jobs accepted by the acceptance means Describes an image forming apparatus including a control unit that selects at least one of the print jobs and then controls the image forming unit to execute the print job (Patent Document 1: Claim). (Refer item 1 etc.).
JP 2001-356647 A

  Here, when image formation is continuously performed on paper having a width smaller than the maximum paper passing width of an image forming apparatus such as a postcard or an envelope, the image forming speed is generally reduced in order to eliminate temperature unevenness in the axial direction of the heating element. Control is made. Thereby, the interval of paper conveyance is expanded, temperature unevenness is reduced by heat conduction of the heating element, and overheating of the non-contact portion with the paper is prevented. However, when such control is performed, there is a problem that the image forming speed is reduced.

  Thus, when viewing the image forming apparatus described in Patent Document 1, it is true that according to the invention of Patent Document 1, the temperature difference in the axial direction of the fixing roller does not exceed a predetermined range without decreasing the image forming speed. There is a case. However, the invention described in Patent Document 1 is special in that each job of the first image formation with a narrow paper width and the second image formation with a paper width wider than the first image formation are accepted simultaneously. Conditions are necessary.

  In this regard, Patent Document 1 describes that it is generally considered that a large-size job is accepted during the formation of a small-size image (Patent Document 1: Paragraph 0033). It cannot be said that a state in which the apparatus continuously receives jobs is common. Therefore, as long as there is no input of a second image forming job, the invention described in Patent Document 1 has a problem that the image forming speed must be reduced. Moreover, the printed trays after the first image formation and the second image formation are mixed in the discharge tray after the printing is completed, and the user must sort the printed materials, which is inconvenient. There is also a problem.

  In continuous printing of narrow paper, narrow paper and wide paper that is not subjected to image formation may be alternately fed one by one to form an image, thereby improving the image forming speed. However, when such sheet feeding control is performed, there is a problem that wide sheets are wasted. Further, since the discharge tray has a mixture of a narrow paper and a wide paper, it needs to be separated and is not convenient. Further, even if a wide sheet on which no image is formed can be reused, it is troublesome to return the wide sheet to the paper feed cassette or the like each time.

  The present invention has been made in view of the above-described problems of the prior art. When performing image formation on narrow paper, image formation can be performed without reducing the image formation speed as much as possible while improving user convenience. The task is to do.

  According to a first aspect of the present invention, an image forming apparatus forms a toner image and transfers the image to a sheet, a heating element, and the toner image transferred to the sheet by heat from the heating element to fix the image. At least two types of a fixing unit having a heating body, a narrow paper whose width in the direction perpendicular to the paper conveyance direction is narrower than a predetermined width, and a wide paper whose width is wider than the narrow paper A sheet supply unit capable of supplying a sheet of a size, a sheet conveyance path for conveying the sheet in the order of the image forming unit, and the fixing unit, and the front and back of the sheet that has passed through the fixing unit are reversed. A double-sided printing unit for transporting the paper to the front of the printer and printing on both sides of the paper, and a control unit for controlling the operation of each part of the apparatus, and forming images continuously on the narrow paper When performing, the control unit removes the wide paper The sheet is supplied separately to the sheet supply unit as an overheating prevention sheet of a thermal body, and during the image formation of the narrow sheet, the overheating prevention sheet after passing through the fixing unit is conveyed to the double-sided printing unit, and the narrow sheet and the The overheat prevention paper is merged between narrow sheets, and the overheat prevention paper is repeatedly passed through the fixing unit.

  According to this configuration, during the image formation of narrow paper, the axial direction of the heating element that does not contact the narrow paper, such as by alternately passing the wide paper and the narrow paper through the fixing unit by utilizing the double-sided printing unit Can be prevented from being overheated. As a result, even if a wide paper image is formed after a narrow paper image is formed, there is a problem in fixing, and it is possible to avoid damage to the fixing portion and shortening of life due to a part of the heating body becoming high temperature. Can do.

  Further, conventionally, in order to reduce the image forming speed on the narrow paper, a waiting time is provided for feeding the narrow paper. However, since this waiting time can be reduced, the narrow paper is compared with the conventional paper. The image forming speed can be improved. Further, only one wide sheet is used during the image formation of the narrow sheet, and the sheet is not wasted. In addition, unlike the prior art, the paper discharged to the discharge tray is not mixed with narrow paper and wide paper, so there is no need to separate the paper, and wide paper is accommodated for reuse. Since it does not need to be redone, the convenience for the user is enhanced.

  According to a second aspect of the present invention, in the first aspect of the present invention, the apparatus according to the first aspect further includes a storage unit that stores the state of the apparatus, and after the image formation of the narrow paper is completed, the storage unit The control unit stores that the overheat prevention paper remains in the double-sided printing unit, and the control unit does not supply the wide paper from the paper supply unit when continuously forming images on the narrow paper. The overheat preventing paper remaining in the double-sided printing unit is used to repeatedly pass the overheat preventing paper through the fixing unit during image formation of the narrow paper.

  According to this configuration, when the image formation on the narrow paper is continuously performed, the overheat preventing paper remaining in the double-sided printing unit is used, so that wasteful consumption of the wide paper can be further reduced.

  According to a third aspect of the present invention, in the first or second aspect of the invention, when the control unit forms an image of a paper having the same size as the overheat-preventing paper remaining in the double-sided printing unit, the double-sided Image formation was performed using the overheat-preventing paper remaining in the printing section.

  According to this configuration, since the image formation is performed by feeding the overheat prevention paper from the double-sided printing unit, the overheat prevention paper is also finally used for image formation, thereby eliminating unnecessary paper consumption. be able to.

  According to a fourth aspect of the present invention, in the invention according to the first to third aspects, the control unit performs the double-sided printing on the paper different in size from the overheat preventing paper remaining in the double-sided printing unit. The overheat-preventing paper is left in the duplex printing section.

  According to this configuration, since the overheat prevention paper is left until the double-side printing, the overheat prevention paper does not interfere with the double-side printing during the double-side printing. For example, the overheat prevention paper is discharged or used for image formation.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, the paper supply unit supplies a paper having a maximum paper width among the plurality of types of paper to be stored as the overheat prevention paper. It was decided.

  According to this configuration, the paper supply unit supplies the paper having the maximum paper width as the overheat prevention paper, so that the heating body and the paper can be brought into contact with each other more efficiently, and the heating body in the axial direction of the heating body can be efficiently provided. Temperature unevenness can be reduced.

  As described above, according to the present invention, the image forming speed on narrow paper such as postcards and envelopes is improved while improving the convenience for the user as compared with the prior art. In addition, since a part of the heating body that does not contact the narrow sheet in the axial direction is prevented from being overheated, it is possible to provide an image forming apparatus in which accurate fixing can be performed and the fixing unit has a long life.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. It should be noted that each element such as the configuration and arrangement described in the present embodiment does not limit the scope of the invention and is merely an illustrative example.

  First, the structure and image output operation of the electrophotographic copying machine 1 (corresponding to an image forming apparatus) in the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic front sectional view showing an example of a schematic configuration of a copying machine 1 according to an embodiment of the present invention. It should be noted that solid arrows in the figure indicate the transport path and direction of the paper P.

  As shown in FIG. 1, a copying machine 1 according to the present embodiment includes a document conveying device 2 at the top, and an image reading unit 3, a sheet feeding unit 4, a sheet conveying path 5, an image on the main body side below the copying machine. A forming unit 6, a fixing unit 7, a double-sided printing unit 8 and the like are provided. In addition, an operation panel 1a for operating / inputting the copying machine 1 is provided at an upper front position (illustrated by a broken line in FIG. 1).

  Various types and sizes of originals to be copied by the user are placed on the original conveying device 2. When copying is started by inputting printing conditions and the like to the operation panel 1a, the document conveying device 2 separates the documents one by one while reading by the image reading unit 3 provided below the document conveying device 2. Transport toward position 31. The image reading unit 3 optically reads a document passing through the reading position 31 and obtains image data. The document conveying device 2 has a fulcrum on the back side of the paper surface of FIG. 1 and can be lifted. The document conveying device 2 reads the document by placing the documents one by one on the contact glass 32 on the upper surface of the image reading unit 3. It is also possible.

  The paper supply unit 4 mainly includes cassettes 41 and 42 provided in the lower part of the copying machine 1 and a manual feed tray 43 provided on the right side surface of the copying machine 1. The cassettes 41 and 42 can accommodate standard size paper (for example, A4, A3, B4, B5, etc.) and have partition plates 41a and 42a for regulating the position of the paper P to be accommodated. The cassettes 41 and 42 are provided with one or more sheet size detection sensors 41b and 42b (see FIG. 5) for confirming the size of the sheet P to be stored depending on the positions of the partition plates 41a and 42a and the storage position of the sheet P. A plurality can be provided. Further, the uppermost sheet P among the sheets P stored in the cassettes 41 and 42 abuts on supply rollers 41c and 42c that are rotationally driven by the sheet feeding motor M1, and the sheets P enter the sheet transport path 5 one by one. Sent out.

  On the other hand, on the manual feed tray 43, a plurality of papers of a size that the cassettes 41 and 42 do not correspond, a special paper such as an OHP sheet, a small paper such as a postcard or an envelope can be placed. The supply roller 44 is also provided in the manual feed tray 43. The uppermost paper P among the papers P placed on the manual feed tray 43 contacts the supply roller 44, and the paper P is sent out one by one.

  As described above, by combining the cassettes 41 and 42 and the manual feed tray 43, the paper supply unit 4 allows the paper width in the direction perpendicular to the paper transport direction to be narrower than a predetermined width (details will be described later), and the width. It is possible to supply at least two types of paper P having a width wider than that of a narrow paper (three types in this embodiment). In addition, if an optional device having a paper feed function such as a feeder (not shown) is installed separately, paper of a plurality of sizes can be further fed.

  The paper transport path 5 transports the paper P in the order of the image forming unit 6 and the fixing unit 7, and transports the paper P supplied from the paper supply unit 4 within the apparatus. The paper transport path 5 is provided with a plurality of guides 51 and transport roller pairs 52, and the transport roller pairs 52 are rotated by driving from the transport motor M2 or the like (see FIG. 5) to transport the paper P. . Specifically, the paper P sent out from the cassettes 41 and 42 is first transported vertically upward along the right side surface of the copying machine 1 through the paper transport path 5. On the other hand, the paper P sent out from the manual feed tray 43 is conveyed substantially horizontally to the left. The paper transport path 5 from the cassettes 41 and 42 and the paper transport path 5 from the manual feed tray 43 merge, and then the paper P is transported toward the image forming unit 6 and the fixing unit 7.

  Note that a pair of registration rollers 53 is disposed on the sheet conveyance path 5 immediately upstream of the image forming unit 6. The registration roller pair 53 corrects the oblique feeding of the paper P, synchronizes with the toner image formed by the image forming unit 6, and feeds the paper P to the nip between the transfer roller 65 and the photosensitive drum 61.

  The image forming unit 6 is disposed below the image reading unit 3 on the downstream side of the registration roller pair 53 in the sheet conveying direction. The image forming unit 6 forms a toner image based on the image data read by the image reading unit 3 and transfers the toner image onto the paper P that has been sent. Specifically, the image forming unit 6 includes a photosensitive drum 61, a charging device 62, an exposure device 63, a developing device 64, a transfer roller 65, a cleaning device 66, and the like.

  The photosensitive drum 61 extends in the width direction of the paper P (perpendicular to the paper surface in FIG. 1) perpendicular to the paper transport direction in the copying machine 1 and is arranged with its axis direction horizontal. The photosensitive drum 61 has a photosensitive layer on the outside of a conductive roller-shaped substrate made of aluminum or the like. The photosensitive drum 61 is rotated by a driving device (not shown) such as a motor so that the peripheral speed thereof is the same as the paper conveyance speed (the direction of rotation is indicated by an arrow).

  The charging device 62 is provided above the photosensitive drum 61 and extends in the width direction of the paper P along the axial direction of the photosensitive drum 61 while facing the photosensitive drum 61. Then, the opposing portions of the photosensitive drum 61 are charged to a constant potential by corona discharge or the like. In addition, a method of charging by contacting a roller or a brush may be used.

  The exposure device 63 is provided further above the charging device 62 and scans and exposes the charged photosensitive drum 61 with a laser beam to form an electrostatic latent image corresponding to the image data of the image to be formed. . Instead of the laser light, an LED unit using a plurality of LEDs may be used as the exposure apparatus. In FIG. 1, the developing device 64 is provided on the right side of the photosensitive drum 61, accommodates toner and is charged to a predetermined potential, and supplies the toner to the electrostatic latent image on the photosensitive drum 61. Thereby, the electrostatic latent image is developed as a toner image.

  The transfer roller 65 is provided in a transfer conveyance belt 67 that conveys the paper P below the photosensitive drum 61. The transfer roller 65 and the transfer conveyance belt 67 are rotated counterclockwise in FIG. 1 by a driving device (not shown) such as a motor so as to be equal to the peripheral speed of the photosensitive drum 61. The transfer conveyance belt 67 is sandwiched between the transfer roller 65 and the photosensitive drum 61, and the transfer roller 65 is pressed against the transfer conveyance belt 67 from below. The sheet P enters the transfer nip between the photosensitive drum 61 and the transfer conveyance belt 67 in synchronization with the toner image. By applying a predetermined voltage to the transfer roller 65 when the sheet enters the transfer nip, the toner image is transferred to the sheet.

  The fixing unit 7 is provided downstream of the image forming unit 6 in the sheet conveying direction. The fixing unit 7 mainly includes a heating roller 71 (corresponding to a heating body) that incorporates a heating element H and a pressure roller 72 that presses against the heating roller 71. The heating roller 71 and the pressure roller 72 are rotatably supported while the axial directions are parallel to each other. Then, the driving force from the fixing motor M3 (see FIG. 5) is transmitted to the heating roller 71 or the pressure roller 72 to rotate.

  For example, the heating roller 71 is made of metal in order to improve thermal conductivity. On the other hand, the pressure roller 72 is provided with an elastic layer (for example, sponge rubber) on the peripheral surface thereof in order to apply pressure evenly to the paper P. Then, the paper P carrying the unfixed toner image after the primary transfer is sent to the fixing unit 7 and enters the nip between the heating roller 71 and the heating roller 71, whereby the toner image is heated and pressurized, It is fixed. In other words, the fixing unit 7 performs fixing by the heating element that heats and heats the toner image transferred to the paper P with heat from the heating element H and the heating element H.

  A branching portion 54 is provided on the downstream side of the fixing portion 7 and in the vicinity of the left side surface of the main body. The branching portion 54 is provided with a switching guide 55 that rotates to switch the transport direction of the paper P. When duplex printing is not performed, the switching guide 55 of the branch unit 54 guides the paper P discharged from the fixing unit 7 toward the discharge tray 56.

  The double-sided printing unit 8 is a part for inverting the front and back of the paper P that has passed through the fixing unit 7 and carrying the paper P to the front of the image forming unit 6 again to perform double-sided printing. Provided between the cassettes 41. The double-sided printing unit 8 appropriately includes a guide 81, a double-sided conveyance roller pair 82, a reverse conveyance path 83, a rejoining conveyance path 84, and the like for conveying the paper P.

  When performing duplex printing, the sheet P discharged from the fixing unit 7 after completion of image formation on one side is guided downward in FIG. 1 by the switching guide 55 of the branching unit 54. Specifically, the paper P guided to the duplex printing unit 8 is guided to the reverse conveyance path 83 in order to reverse the front and back of the paper P. A switchback roller 85 is provided at the entrance of the reverse conveyance path 83 to be driven to rotate forward and backward by a duplex printing motor M4 (see FIG. 5). The switchback roller 85 causes the paper P to enter the reverse conveyance path 83 to some extent, and then the rotation direction is reversed.

  As a result, the sheet P is reversed and is guided to the rejoining conveyance path 84. Here, the rejoining conveyance path 84 is a conveyance path provided between the reverse conveyance path 83 and the cassette 41, and connects the reverse conveyance path 83 to the sheet conveyance path 5 on the upstream side of the registration roller pair 53. Then, the sheet P for duplex printing is rejoined on the upstream side of the registration roller pair 53 and sent to the image forming unit 6. Note that a switching guide 87 that rotates and switches the transport direction of the paper P is provided at a connection portion 86 between the reverse transport path 83 and the re-merging transport path 84.

  Further, a discharge conveyance path 88 is provided which extends upward from a connection portion 86 between the reverse conveyance path 83 and the re-merging conveyance path 84 and is connected to the paper conveyance path 5 between the branching portion 54 and the discharge tray 56. With this discharge conveyance path 88, when discharging the paper P that remains in the rejoining conveyance path 84, the discharge can be performed without passing the image forming unit 6 again.

  Next, overheating that occurs in the fixing unit 7 due to the relationship between the size of the paper P that can be used in the copying machine 1 and the paper P that is used will be described. FIG. 2 is a perspective view of the manual feed tray 43 of the copying machine 1 according to the embodiment of the present invention. FIG. 3 is a schematic diagram for explaining overheating of the fixing unit 7 according to the embodiment of the present invention.

  As shown in FIG. 2, the copying machine 1 of the present embodiment is provided with a manual feed tray 43 as a paper supply unit 4 on the right side surface. Normally, a small size paper P such as a postcard or envelope that the cassettes 41 and 42 do not correspond to is placed on the manual feed tray 43. Note that it is possible to place paper P of various standard sizes on the manual feed tray 43.

  The manual feed tray 43 is provided with a pair of regulation guides 43a that regulates in the direction perpendicular to the paper conveyance direction (illustrated by white arrows in FIG. 2), that is, in the width direction of the paper P. Each of the pair of regulation guides 43 a is provided with a rack 43 b extending in the width direction of the paper P inside the manual feed tray 43, and each rack 43 b is provided at a central portion of the manual feed tray 43 in the width direction of the paper P. It is connected to the pinion 43c (in FIG. 2, each rack and pinion are shown by broken lines). As a result, the pair of regulation guides 43a are interlocked so that the center in the width direction of the paper P coincides with the center of the manual feed tray 43 (so-called paper transport based on the center).

  Specifically, in the copying machine 1 of the present embodiment, when the pair of restriction guides 43a are widened to the maximum, the width of the paper is A4 size paper P in the vertical direction (about 29.7 cm) (= A3 horizontal direction). Can be placed. On the other hand, as the pair of regulating guides 43a narrows, B6 length (128mm x 182mm), postcard (100mm x 148mm), Western type 2 (162mm x 114mm), 5.5 "x 8.5" (about 140mm) It is possible to regulate various small size papers P that are about half or less than half the maximum sheet passing width such as × 216 mm).

  As described above, the manual feed tray 43 has various sizes of paper P that can be placed. In order to check the width of the paper P placed on the manual feed tray 43, the variable resistor 43 d is provided inside the manual feed tray 43. Is provided. The resistance value of the variable resistor 43d changes according to the sliding amount of the regulation guide 43a. Then, by appropriately applying a voltage to the variable resistor and detecting the reference voltage based on the voltage applied to the variable resistor and the current flowing through the variable resistor, the current width of the regulation guide 43a is detected, and the sheet P The width information is output to the control unit 9 (see FIG. 5).

  In addition, the size of the paper P placed on the manual feed tray 43 may be set by inputting to the operation panel 1a by the user. Further, even if one or a plurality of paper sensors 43e, for example, are provided in the manual feed tray 43 along the paper transport direction, the length of the paper P placed on the manual feed tray 43 in the paper transport direction is detected. Good.

  As described above, in the copying machine 1 according to the present embodiment, it is possible to use A3 size paper P to small size paper P such as postcard and envelope. However, small size paper P such as postcard and envelope is continuously used. A problem when the image is formed will be described with reference to FIG.

  As shown in FIG. 3, in the fixing unit 7 of the present embodiment, a heating roller 71 and a pressure roller 72 are rotatably supported in parallel to form a fixing nip. The sheet after transfer of the toner image enters the fixing nip.

  Here, the length in the width direction of the sheet P of the heating roller 71 and the pressure roller 72 has a margin slightly more than the sheet width of the maximum sheet P that can be passed (hereinafter referred to as “maximum sheet passing width W1”). The length is assumed to be. The maximum sheet passing width W1 is different for each image forming apparatus, but is often based on the most commonly used A4 sheet. Therefore, the maximum sheet passing width W1 of the copying machine 1 according to the present embodiment will be described below assuming that A4 sheets have a length corresponding to the vertical direction (the horizontal direction for A3 sheets).

  A rod-like heating element H (for example, a halogen heater) that generates heat when energized is incorporated in the heating roller 71 having a length corresponding to the maximum sheet passing width W1. The heating element H extends in the axial direction of the heating roller 71 and uniformly heats the entire peripheral surface of the heating roller 71 from the inner surface.

  Here, the copying machine 1 according to the present embodiment passes a sheet based on a so-called central reference, but a sheet P having a width smaller than a predetermined width such as a postcard or an envelope (hereinafter referred to as “narrow sheet P1”). If image formation is performed without taking any means, there is a problem that temperature unevenness occurs in the axial direction of the heating roller 71.

  The predetermined width is appropriately determined for each image forming apparatus in consideration of the maximum sheet passing width W1 in the image forming apparatus, the thermal conductivity of the heating body, and the like. As a guideline, if the paper P having a width smaller than a predetermined width is continuously formed, the width W2 of the paper P that causes temperature irregularity of the heating body that causes fixing failure, breakage of the fixing unit 7, and the like. (For example, postcard, envelope).

  More specifically, as shown in FIG. 3, the passage width W2 of the narrow sheet P1 is shorter than the maximum sheet passing width W1, and the contact portion 71a in contact with the narrow sheet P1 in the heating roller 71 is heated. Is taken away and the temperature drops. Therefore, in order to keep the fixing temperature of the heating roller 71, the heating element H must be energized to compensate for the temperature drop of the contact portion 71a at the heating roller 71. However, the non-contact portion 71b (shown by hatching in FIG. 3) that does not contact the narrow paper P1 in the heating roller 71 is hardly deprived of heat, and the heating element H is in the axial direction of the heating roller 71. Therefore, the temperature increases as image formation is continuously performed on the narrow paper P1.

  Such temperature unevenness of the heating roller 71 may damage the member of the fixing unit 7 due to fusion of the pressure roller 72 to the heating roller 71 or the like. When an image is formed on a paper P having a width wider than P1, there is a possibility that a fixing failure may occur.

  Therefore, in order to alleviate the temperature unevenness of the heating roller 71 accompanied by various adverse effects, generally, in the image formation of the narrow paper P1, the image forming speed is reduced, and the temperature unevenness is eliminated by the heat propagation in the heating roller 71. Is made. However, this greatly reduces the image forming speed. Therefore, the copying machine 1 according to the present embodiment is characterized in that the unevenness of temperature is solved at low cost by using the duplex printing unit 8 and the image forming speed of the narrow paper P1 is improved.

  Hereinafter, this point will be outlined with reference to FIG. 4A to 4D are schematic cross-sectional views showing sheet conveyance in image formation of the narrow sheet P1 of the copying machine 1 according to the embodiment of the present invention.

  First, in FIG. 4A, in the case of continuously forming images of narrow paper P1 (for example, several tens of sheets or more), the first narrow paper P1 passes through the fixing unit 7 and is discharged to the discharge tray. 56 shows a state of being discharged.

  At this time, a paper P that is already wider than the narrow paper P1 accommodated in the cassette 41 or the cassette 42 (see FIG. 1) (hereinafter referred to as “wide paper P2”) is supplied and directed toward the fixing unit 7. In this state, it is being conveyed. Here, in the copying machine 1 of the present embodiment, the sizes accommodated in the cassette 41 and the cassette 42 can be different. However, in order to eliminate the temperature unevenness in the axial direction of the heating roller 71, the sheet width should be as small as possible. Wide paper P is desirable. Accordingly, the wide paper P2 supplied at this time may be automatically selected from among the stored paper P having the widest paper width. Alternatively, the wide paper P2 supplied by the user from the operation panel 1a may be selected.

  In the following description, the wide paper P2 (hereinafter referred to as “overheating”) supplied from the cassette 41 or the cassette 42 to prevent partial heating of the heating roller 71 when continuously forming images on the narrow paper P1. The prevention paper P3 ") will be described as being A3 paper. The overheat prevention paper P3 may be A4 paper, and has an effect of reducing the temperature unevenness of the heating roller 71 if the paper width is at least wider than the narrow paper P1.

  Then, as shown in FIG. 4B, after the image formation of the first narrow sheet P1 is completed, the A3 sheet supplied as the overheat prevention sheet P3 is not subjected to image formation at all. The sheet passes through the unit 6 and the fixing unit 7 and is further guided to the reverse conveyance path 83 of the duplex printing unit 8.

  Thereafter, as shown in FIG. 4C, the overheat prevention paper P3 is switched back and conveyed in the re-merging conveyance path 84. At this time, an image is formed on the second narrow sheet P1, and FIG. 4C shows a state in which the second narrow sheet P1 passes through the fixing unit 7.

  Before the image formation of the third narrow paper P1, the overheat prevention paper P3 passes through the fixing unit 7 again, as shown in FIG. 4B, and the overheat prevention paper P3 is again double-sided. Guided to the printing unit 8. Thus, as long as the image formation on the narrow paper P1 continues, the narrow paper P1 and the overheat prevention paper P3 alternately pass through the fixing unit 7. In other words, the states of FIG. 4B and FIG. 4C are repeated. That is, when image formation is continuously performed on the narrow paper P1, the wide paper P2 is separately supplied to the cassettes 41 and 42 as the overheat-preventing paper P3 of the heating roller 71, and during the image formation of the narrow paper P1, the fixing unit 7 The overheat prevention sheet P3 after passing through the sheet is conveyed to the duplex printing unit 8 to join the overheat prevention sheet P3 between the narrow sheet P1 and the narrow sheet P1, and the overheat prevention sheet P3 is repeatedly passed through the fixing unit 7.

  When the image formation on all the narrow sheets P1 is completed, the overheat preventing sheet P3 remains in the rejoining conveyance path 84. This state is stored in the storage unit 92 (see FIG. 5). Thus, since the overheat prevention paper P3 and the narrow paper P1 are alternately passed through the fixing unit 7, the heat of the non-contact portion 71b of the heating roller 71 with the narrow paper P1 can be transmitted to the overheat prevention paper P3. . In other words, the temperature of the non-contact part 71b can be lowered. Accordingly, it is possible to reduce the waiting time in the image formation of the narrow paper P1 as compared with the conventional case. For example, if the copying machine 1 has a printing speed of 32 PPM (Pages per minute) on A4 paper, it was conventionally about 10 PPM on the narrow paper P1, but according to the present embodiment, 15 to 20 PPM (conventional). Even when image formation is performed at a ratio of 1.5 to 2 times, temperature unevenness of the heating roller 71 that causes damage to the fixing unit 7 and appropriate fixing can be prevented.

  Further, after the overheat prevention paper P3 passes through the fixing unit 7, the overheat prevention paper P3 is guided to the rejoining conveyance path 84. At this time, the overheat prevention paper P3 is cooled, and the overheat prevention paper P3 itself does not become abnormally high temperature. . Therefore, the effect of preventing overheating of the heating roller 71 is stable.

  Next, the control unit 9 that performs image formation of the paper P and paper conveyance control in the continuous image formation of the narrow paper P1 will be described with reference to FIG. FIG. 5 is a block diagram showing an example of the hardware configuration of the copying machine 1 according to the embodiment of the present invention.

  As shown in FIG. 5, the control unit 9 for controlling the operation of each unit of the copier 1 of this embodiment includes a CPU 91 (central processing unit), an I / O (input / output) port (not shown), a storage. A unit 92, a time measuring unit 93, and the like are provided, which are connected by a signal bus.

  The CPU 91 functions as a central processing unit, performs various calculations based on programs and data stored in or input to the storage unit 92, and controls each unit of the copier 1. The storage unit 92 includes a memory such as a RAM, a ROM, an HDD, and a flash ROM, for example. The RAM is used when a control program or control data is temporarily expanded in a volatile memory, or when image data is temporarily stored. ROM, HDD, and flash ROM are non-volatile storage devices, and are used for storing device status, control programs, image data, and setting information of the copier 1 by the user. .

  In order to carry out the present invention, the information relating to the sheet conveyance at the time of image formation of the narrow paper P1, and the residual information of the overheat prevention paper P3 in the double-sided printing unit 8 after the image formation of the narrow paper P1 is completed The data is stored in the storage unit 92 such as the HDD or flash ROM. The time measuring unit 93 counts various times such as the time required for confirming the size of the paper P from the timing of paper conveyance / merging in double-sided printing and the like, the output state from various sensors and the paper conveyance speed.

  The control unit 9 (CPU 91) is connected to the document conveying device 2, the image reading unit 3, the image forming unit 6, the operation panel 1a through an I / O (input / output) port, and controls the operation of each unit. .

  The control unit 9 is also connected to the paper supply unit 4, and a plurality of paper supply motors M1 are provided to rotate the supply rollers 41c, 42c, and 44 in the cassettes 41 and 42 and the manual feed tray 43 of the paper supply unit 4. Drive control is performed (only one is shown in FIG. 5 for convenience). Under the control of the paper feed motor M1, the control unit 9 supplies paper at the time of image formation based on a user instruction input from the operation panel 1a or the like or by automatically selecting paper P to be fed. Is done.

  Then, the control unit 9 receives the output from the variable resistor 43 d provided on the manual feed tray 43 and the paper sensor 43 e and determines the size of the paper P placed on the manual feed tray 43. Thereby, it is confirmed whether or not the paper P placed on the manual feed tray 43 is a narrow paper P1 such as a postcard or an envelope. Further, the size of the paper P may be confirmed by setting input of the paper P placed by the user. Similarly, in the cassettes 41 and 42, the control unit confirms the paper size to be accommodated by receiving the output of the paper size detection sensor.

  The control unit 9 is also connected to the fixing unit 7 and controls the driving of a fixing motor M3 provided to rotate the heating roller 71 and the pressure roller 72. The control unit 9 controls the fixing motor M3 to rotate the heating roller 71 and the pressure roller 72 during image formation. Then, the control unit 9 performs energization control to the heating element H so that the temperature of the heating roller 71 maintains the fixing possible temperature during continuous image formation. As a result, the heating roller 71 is kept at a fixable temperature, and an appropriate image is formed.

  The control unit 9 is also connected to one or a plurality of conveyance motors M2 for rotating the conveyance roller pair 52 that conveys the paper P in the paper conveyance path 5 (only one is shown in FIG. 5 for convenience). The conveyance control of the paper P is performed. By controlling the conveyance motor M2 by the control unit 9, the paper P is fed into the image forming unit 6 in synchronization with the toner image formed by the image forming unit 6, or the narrow paper P1 and the wide paper P2 are alternately fixed. The paper is conveyed through the section 7. The control unit 9 controls the rotation of the switching guide 55 and controls the conveyance direction of the paper P in the branching unit 54.

  The controller 9 receives the output of a plurality of sensors 57 provided as appropriate along the paper transport path 5 in order to detect arrival and passage of the paper P. A sensor 57 for detecting the arrival and passage of the paper P is also provided in the duplex printing unit 8. With these sensors 57, the control unit 9 confirms at which position and in what size paper P is being transported in the paper transport path 5 and the duplex printing unit 8.

  In addition, the control unit 9 rotates the switchback roller 85 forward and backward in the double-sided printing unit 8, and also transports the paper P in the reverse conveyance path 83, the rejoining conveyance path 84, and the discharge conveyance path 88. One or a plurality of double-sided printing motors M4 provided for rotating the roller pair 82 are also connected (only one is shown in FIG. 5 for convenience), and the conveyance control of the paper P in the double-sided printing unit 8 is performed. Under the control of the double-sided printing motor M4, the paper P led to the double-sided printing unit 8 is reversed, and the overheat-preventing paper P3 and the single-sided printed paper P are rejoined upstream of the image forming unit 6. The control unit 9 controls the rotation of the switching guide 87 and controls the transport direction of the paper P.

  In this way, the control unit 9 controls each unit to control the conveyance of the paper P, so that when the narrow paper P1 is continuously printed, the double-sided printing unit 8 is used to narrow the width at the fixing unit 7. The alternate passage of the paper P1 and the overheat prevention paper P3 (wide paper P2) is realized.

  The copying machine 1 can be connected to a user terminal 100 as an external computer via an interface (not shown) via a network or the like. Accordingly, the copying machine 1 can receive image data and print setting data from the user terminal 100 and perform image formation (printer function).

  Next, an example of the flow of image formation control of the copying machine 1 according to the embodiment of the present invention will be described with reference to FIG. FIG. 6 is a flowchart showing an example of image formation control of the copying machine 1 according to the embodiment of the present invention.

  First, at the start of this flowchart, the paper size can be set and received by the paper size setting on the operation panel 1a, the paper size detection sensors 41b and 42b of the cassettes 41 and 42, the variable resistor 43d of the manual feed tray 43, and the like. The size of the correct paper P has already been confirmed by the control unit 9. Then, in this state, an input for image formation is made, and the time point when job data including image data to be formed and print setting data is input to the control unit 9 is started.

  When this image formation is started, the control unit 9 confirms whether or not the paper P having a size corresponding to the paper P specified in the job is stored and placed in the cassettes 41 and 42 or the manual feed tray 43. Perform (step # 1). If the designated paper P is not accommodated and placed in the copying machine 1 (No in Step # 1), for example, it stops as an error (Step # 2), and this control is terminated.

  On the other hand, if the designated paper P is received and placed in the copying machine 1 (Yes in step # 1), the control unit 9 performs continuous printing in which the designated job continuously performs a plurality of papers P. (Step # 3). In other words, for the instructed job, confirmation is made as to whether the image data extends over a plurality of pages, or whether printing of a plurality of copies of image data over a plurality of pages is instructed.

  Here, just because a plurality of sheets are printed, it is not always necessary to determine that the printing is continuous. For example, when the narrow paper P1 is continuously formed, each part of the heating roller 71 is subjected to printing. Whether or not continuous printing is performed can be determined from one viewpoint whether or not the number of sheets (for example, several tens of sheets) at which the temperature difference is equal to or greater than a predetermined temperature difference. Note that the number of sheets that should be recognized as continuous printing depends on factors such as the output of the heating element H and the thermal conductivity of the heating roller 71, and may be set as appropriate based on experimental data. As an extreme example, if a large number of destinations and texts stored in the database are printed at once for printing such as New Year's cards and summer greetings, it is determined that continuous printing is performed.

  If it is confirmed that the job content is continuous printing (Yes in step # 3), the control unit 9 confirms whether or not the paper size specified in the job is the narrow paper P1. (Step # 4). This confirmation may be performed by confirming the selection of the paper to be used on the operation panel 1a or the selected paper size in the print setting data from the user terminal 100. If it is not continuous printing (No in step # 3), the process proceeds to step # 15 described later.

  If the paper size designated in the job is the narrow paper P1 (Yes in step # 4), the control unit 9 overheats the narrow paper P1 used during the previous continuous printing of the narrow paper P1. It is confirmed whether the prevention sheet P3 remains in the duplex printing unit 8 (step # 5). For example, the confirmation is performed by checking the storage unit 92 based on the presence / absence of a flag indicating a state in which the overheat prevention sheet P3 stored in the storage unit 92 remains at the end of the previous continuous printing of the narrow sheet P1. be able to. In addition, when performing continuous image formation on the narrow paper P1, this confirmation is performed by using the overheat prevention paper P3 remaining in the duplex printing unit 8 without supplying the wide paper P2 from the cassettes 41 and 42. This is performed to repeatedly pass the overheat prevention paper P3 through the fixing unit 7 during the image formation of P1.

  On the other hand, if the overheat prevention paper P3 does not remain in the duplex printing unit 8 (Yes in Step # 5), the control unit 9 places the wide paper P2 such as A4 portrait or A3 in any of the cassette 41, the cassette 42, and the like. Is checked (step # 6). If the wide paper P2 is not accommodated (No in step # 6), the control unit 9 increases the conveyance interval between the narrow paper P1 and the narrow paper P1 to prevent a part of the heating roller 71 from overheating. Thus, image formation is performed at a reduced image formation speed (step # 7).

  If the wide paper P2 is stored (Yes in Step # 6) or if the overheat prevention paper P3 remains in the duplex printing unit 8 (No in Step # 5), first, the control unit 9 The narrow paper P1 is fed, and an image is formed on one narrow paper P1 (step # 8). Next, the control unit 9 feeds wide paper P2 (= overheat prevention paper P3) from the paper supply unit 4 or the double-sided printing unit 8 and passes the paper through the fixing unit 7 (step # 9). At this time, the paper supply unit 4 may automatically supply the wide paper P2 having the maximum width of the paper P among the plural types of paper P to be stored as the overheat prevention paper P3. The overheat prevention sheet P3 after passing through the fixing unit 7 is conveyed to the re-merging conveyance path 84 of the duplex printing unit 8 (step # 10). Then, after the overheat prevention sheet P3 passes through the fixing unit 7, the control unit 9 checks whether all jobs to be executed are completed (step # 11). If image formation has not been completed for all the narrow sheets P1, the process returns to step # 8 (No in step # 11).

  When image formation is completed for all narrow sheets P1 (Yes in step # 11), the overheat prevention sheet P3 remains in the duplex printing unit 8 and the sheet size of the overheat prevention sheet P3 is stored in the storage unit 92. Then (step # 12), the image formation is completed.

  Here, if the paper size designated in the job is not the narrow paper P1 (No in Step # 4), the control unit 9 confirms whether or not the overheat prevention paper P3 remains in the double-sided printing unit 8 ( Step # 13). If the overheating prevention paper P3 remains in the duplex printing unit 8 (Yes in Step # 13), the control unit 9 then prevents the overheating remaining in the duplex printing unit 8 and the paper size specified in the job. It is checked whether or not the size of the paper P3 is the same (step # 14). In this confirmation, if the image formation is performed on the paper P having the same size as the overheating prevention paper P3 remaining in the double-sided printing unit 8, the image formation is performed using the overheating prevention paper P3 remaining in the double-sided printing unit 8. Made to do. On the other hand, if the overheat prevention paper P3 does not remain in the duplex printing unit 8 (No in Step # 13), normal image formation is performed as it is (Step # 15).

  If the paper size specified in the job and the size of the overheating prevention paper P3 remaining in the double-sided printing unit 8 are the same (Yes in step # 14), the control unit 9 sets the double-sided paper P as the first paper P. The overheat prevention paper P3 is supplied from the printing unit 8 to perform image formation (step # 16). Thereafter, a normal print job as set is executed (step # 15).

  On the other hand, if the paper size specified in the job and the size of the overheat prevention paper P3 remaining in the duplex printing unit 8 are different (No in step # 14), the control unit 9 confirms whether the job is a duplex printing job. (Step # 17). If the job is double-sided printing (Yes in step # 17), the overheat prevention paper P3 remaining in the double-sided printing unit 8 is discharged from the discharge conveyance path 88 (step # 18), and then normal printing as set is performed. The job is executed (step # 15). On the other hand, if the job is single-sided printing (No in step # 17), a normal single-sided printing job is executed as set without discharging the overheat prevention paper P3 (step # 15). That is, the control unit 9 keeps the overheating prevention paper P3 in the double-sided printing unit 8 until the double-sided printing is performed on the paper P having a different size from the overheating prevention paper P3 remaining in the double-sided printing unit 8.

  After the normal print job is executed, the presence or absence of the overheat prevention paper P3 in the double-sided printing unit 8 is stored in the storage unit 92 (step # 19), and the series of image forming operations ends.

  In this way, according to the configuration of the present embodiment, during the image formation of the narrow paper P1, the double-sided printing unit 8 is used to overheat the wide paper P2 between the narrow paper P1 and the narrow paper P1. Since the prevention paper P3 is passed through the fixing unit 7, it is possible to prevent a part of the heating roller 71 (heating body) that does not contact the narrow paper P1 in the axial direction from being overheated. As a result, even if the image formation on the wide paper P2 is performed after the image formation on the narrow paper P1, problems in fixing occur, damage to the fixing unit 7 due to the high temperature of part of the heating body, and shortening of life. It can be avoided.

  Further, conventionally, a waiting time is provided for feeding the narrow paper P1 in order to reduce the image forming speed on the narrow paper P1, but this waiting time can be reduced. The image forming speed on the narrow paper P1 can be improved. Further, only one wide sheet P2 is used during the image formation of the narrow sheet P1, and the sheet P is not wasted. Further, unlike the prior art, the paper P discharged to the discharge tray 56 is not mixed with the narrow paper P and the wide paper P, so there is no need to separate them. Since the wide paper P is not accommodated again, the convenience for the user is enhanced.

  Further, when the image formation of the narrow paper P1 is continuously performed again, the waste heat consumption of the wide paper P2 can be further reduced because the overheat prevention paper P3 remaining in the double-sided printing unit 8 is used. In addition, since the image formation is performed by feeding the overheat prevention paper P3 from the double-sided printing unit 8, the overheat prevention paper P3 is also finally used for image formation, so that unnecessary consumption of the paper P is eliminated at all. be able to. Further, since the overheat prevention paper P3 is left until the double-sided printing, the overheat prevention paper P3 does not interfere with the double-sided printing during the double-sided printing. For example, the overheat prevention sheet P3 is discharged or used for image formation. Further, since the paper supply unit 4 supplies the paper P having the maximum width as the overheat prevention paper P3, the heating body and the paper P can be brought into more contact with each other, and the axial direction of the heating body can be efficiently performed. Temperature unevenness can be reduced.

  Embodiments other than the above embodiment will be described. In the above embodiment, the narrow paper P1 and the overheat prevention paper P3 are alternately passed during the continuous printing of the narrow paper P1, but a plurality of widths are considered in consideration of the size of the narrow paper P1 and the number of prints. After printing the narrow paper P1, the overheat prevention paper P3 may be passed, and this may be repeated until the job is completed. In the above-described embodiment, the maximum sheet passing width W1 in the fixing unit 7 and the sheet transport path 5 is described as corresponding to A4 length. However, the present invention is not limited to this, and letter sizes often used in North America and other sheet sizes are used. The maximum sheet passing width W1 may be set according to.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  The present invention can be used for an image forming apparatus having a double-sided printing function.

1 is a schematic front sectional view showing an example of a schematic configuration of a copier according to an embodiment. FIG. 3 is a perspective view of a manual feed tray of the copying machine according to the embodiment. FIG. 6 is a schematic diagram for explaining overheating of the fixing unit according to the embodiment. FIG. 4 is a schematic cross-sectional view illustrating paper conveyance in image formation of narrow paper in the copying machine according to the embodiment. 1 is a block diagram illustrating an example of a hardware configuration of a copier according to an embodiment. 3 is a flowchart illustrating an example of image formation control of the copier according to the embodiment.

Explanation of symbols

1 Copier (image forming apparatus) 4 Paper supply unit 41, 42 Cassette (part of paper supply unit 4)
43 Bypass tray (part of paper supply unit 4)
5 Paper transport path 6 Image forming unit 7 Fixing unit 71 Heating roller (heating body)
8 Double-sided printing unit 9 Control unit 92 Storage unit H Heating element P Paper P1 Narrow paper P2 Wide paper P3 Overheat prevention paper

Claims (5)

An image forming unit that forms a toner image and transfers the toner image to a sheet;
A fixing unit having a heating element and a heating element for fixing the toner image transferred to the paper by heat from the heating element;
Paper supply capable of supplying paper of at least two types of sizes, a narrow paper whose width in a direction perpendicular to the paper transport direction is narrower than a predetermined width and a wide paper whose width is wider than the narrow paper. And
A paper transport path for transporting paper in the order of the image forming section and the fixing section;
A double-sided printing unit for reversing the front and back of the paper that has passed through the fixing unit, and again transporting the paper to the front of the image forming unit and printing on both sides of the paper;
A control unit for controlling the operation of each unit of the device,
When performing image formation continuously on the narrow paper, the control unit separately supplies the wide paper to the paper supply unit as an overheating prevention paper of the heating body, and during the image formation of the narrow paper, The overheat prevention paper after passing through the fixing unit is conveyed to the duplex printing unit, the overheat prevention paper is merged between the narrow paper and the narrow paper, and the overheat prevention paper is repeatedly passed through the fixing unit. An image forming apparatus. A storage unit for storing the state of the device;
After the image formation of the narrow paper is completed, the storage unit stores that the overheat prevention paper from the previous image formation remains in the double-sided printing unit,
When the image is continuously formed on the narrow paper, the control unit does not supply the wide paper from the paper supply unit, and uses the overheat prevention paper remaining in the double-sided printing unit to The image forming apparatus according to claim 1, wherein the overheat prevention sheet is repeatedly passed through the fixing unit during image formation of narrow sheets.   The control unit performs image formation using the overheat preventing paper remaining in the double-sided printing unit when forming an image of the same size paper as the overheat preventing paper remaining in the double-sided printing unit. The image forming apparatus according to claim 1 or 2.   The control unit leaves the overheating prevention paper in the double-sided printing unit until the double-sided printing is performed on a sheet having a different size from the overheating prevention paper remaining in the double-sided printing unit. The image forming apparatus according to any one of 1 to 3.   5. The image forming apparatus according to claim 1, wherein the sheet supply unit supplies a sheet having a maximum sheet width among the plurality of types of sheets stored therein as the overheat prevention sheet. apparatus.

Images