JP2005156977A - Fixing device and image forming apparatus using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device in which high-temperature offset or curling of recording paper, which are caused by a partial temperature increase of a heat roller after the passage of image formation paper of a small size, is prevented and power can be saved, and to provide an image forming apparatus using the fixing device. <P>SOLUTION: A main heater 391a and a sub-heater 391b are disposed in a heating roller. Control is exerted so as to shut off power supplied to the sub-heater, in the case of an instruction to print on recording paper of a large size after the passage of image formation paper P' of a small size in a paper passage range D narrower than a paper passage range F that corresponds to the heat distribution characteristics of the main heater in the axial middle section of the heating roller. Also, the control is exerted such that when the temperature of the axial middle section of the heating roller has become almost uniform, power is supplied to the sub-heater so that the axial middle section reaches a predetermined temperature for fixing. On the other hand, in the case of an instruction to successively print on image formation paper of a small size, the control is exerted so as to shut off power to the sub-heater. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fixing device that controls a heater lamp when fixing unfixed developer on B5 size or postcard size recording paper during standby in an energy saving mode, and an image forming apparatus using the same.

  In general, in a fixing device used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile, unfixed developer on a recording sheet is applied to a nip portion between a heating roller and a pressure roller. The roller is fixed by passing the sheet with reference to the axial center position of each roller. Two types of heater lamps having coiled filaments are provided inside the heating roller. Each of the filaments of these heater lamps has a light emitting part and a non-light emitting part. The light emitting part of the filament in one heater lamp is arranged to face the non-light emitting part of the filament in the second heater lamp. That is, the first heater lamp having the heat distribution characteristic corresponding to the central portion in the axial direction of the heating roller, and the heat distribution characteristic corresponding to the left and right axial portions of the heating roller not corresponding to the heat distribution characteristic of the first heater lamp. The 2nd heater lamp which has is provided (for example, refer to patent documents 1).

As another fixing device, the first heater lamp and the second heater are used to quickly heat-fix unfixed developer on recording papers of different sizes at a stable fixing temperature without causing hot offset. In some cases, the heater lamp is controlled by a control unit, and this control unit controls the heat generation density (in the first heat generation area of the first heater lamp facing the central portion in the axial direction of the heating roller with which the small-size recording paper contacts ( A1) and the heat generation density (B1) of the first heat generation area of the second heater lamp and the left and right sides of the heating roller in contact with the large size recording sheet at the left and right sides of the axial center of the heating roller. The heat generation density (A2) of the second heat generation area of the first heater lamp and the heat generation density (B2) of the second heat generation area of the second heater lamp are A1> A2 and B1 <B2. Further, A1 + B1 <A2 + B2 is set to be satisfied, and when fixing a large size recording paper, the first heater lamp is controlled to be always on, while the second heater lamp is controlled to be on / off. doing. In this case, when fixing the unfixed developer on the small size recording paper, the first heater lamp is turned on, and the second heater lamp is set to the upper fixing temperature (180 ° C.) and the lower fixing temperature (170). On / off control (Duty 50%) is performed during (C) (see, for example, Patent Document 2).
JP 2002-258646 A JP 2003-107956 A

  By the way, in the above-described conventional one, when fixing the unfixed developer on the A4 size recording paper conveyed by vertical feeding (direction in which the longitudinal direction of the recording paper is parallel to the paper conveying direction), the axis of the heating roller is fixed. The heat distribution characteristic (first heat generation region) by the first heater lamp corresponding to the central portion in the direction is dealt with, but the paper passing corresponding to the heat distribution characteristic of the first heater lamp in the central portion in the axial direction of the heating roller. Fix the unfixed developer on small size recording paper such as B5 size or postcard size in vertical feeding that is smaller than the range (for example, vertical paper feeding range of A4 size recording paper) Even in such a case, the heat distribution characteristic by the first heater lamp is used. However, as shown in FIG. 6 (a), the amount of heat captured by the small-size recording sheet p smaller than the sheet passing range corresponding to the heat distribution characteristic of the first heater lamp b is the first range. Since it is limited to the vicinity of the central portion d of the sheet passing range of the heating roller corresponding to the heat distribution characteristic of the heater lamp b, a small size recording sheet p corresponding to the heat distribution characteristic of the first heater lamp b is passed. The surface temperature in the vicinity of the left and right sides e, e (the non-passage range of the small size recording paper p) of the heating roller in the axial center is not fixed by the fixing set temperature TS without being taken by the passing of the small size recording paper p. It will be accumulated in the vicinity.

  In that case, when printing of a large size recording paper such as A3 size is instructed after passing the small size recording paper p, the surface temperature of the central portion in the axial direction of the heating roller is fixed by the heat distribution characteristic of the first heater lamp b. Of course, the surface temperature of the left and right side portions in the axial direction of the heating roller is raised to the fixing set temperature TS by the heat distribution characteristics of the second heater lamps c on both the left and right sides as well as the temperature TS. However, since there is a high temperature region in which the surface temperature is accumulated near the fixing set temperature TS due to the non-passage of the small size recording paper p on both the left and right sides of the central portion in the axial direction of the heating roller, FIG. When the heating roller is heated by the heat distribution characteristics of the first and second heater lamps b and c, as shown in FIG. The non-sheet passing area) is further heated, and when fixing the unfixed developer on the large size recording paper, the local temperature rise of the heating roller causes a high temperature offset such as adhesion of the developer to the heating roller due to overmelting of the developer. Or curl of the recording paper.

  Moreover, further heating of the high-temperature regions on both the left and right sides e and e of the central portion in the axial direction of the heating roller after passing the small-size recording paper p causes waste of electric power, which is contrary to energy saving.

  The present invention has been made in view of such a point, and an object of the present invention is to prevent a high temperature offset and a curling of the recording paper due to a local temperature rise of the heating roller after the small size recording paper is passed. Another object of the present invention is to provide a fixing device that can save power and an image forming apparatus using the same.

  In order to achieve the above object, in the present invention, the unfixed developer on the recording paper is passed through the nip portion between the heating roller and the pressure roller with reference to the center position in the axial direction of each roller and fixed. And a first heater lamp provided inside the heating roller and having heat distribution characteristics corresponding to the central portion in the axial direction, and heating rollers on both the left and right sides of the first heater lamp. When a print instruction is received when the second heater lamp having heat distribution characteristics corresponding to both the left and right sides in the axial direction and the first and second heater lamps are each waiting at a predetermined set temperature, the print instruction And a control means for controlling the first and second heater lamps according to the passing range of the recording paper. When the small-size recording sheet having a sheet passing range smaller than the sheet passing range corresponding to the heat distribution characteristic of the first heater lamp is passed through the control means in the axial center portion of the heating roller, The control of the second heater lamp is changed after the small-size recording paper is passed.

  Due to this specific matter, when a small size recording sheet having a sheet passing range smaller than the sheet passing range corresponding to the heat distribution characteristics of the first heater lamp is passed in the central portion in the axial direction of the heating roller, the small size recording sheet is passed. Since the control of the second heater lamp is changed after the passage of the sheet, when the print command for the large size recording sheet is issued after the passage of the small size recording sheet, the energization of the second heater lamp is cut off. By controlling, after passing the small size recording paper, it is accumulated near the fixing set temperature without being taken away by paper passing near the left and right sides of the central portion of the heating roller in the axial direction (non-passage range of the small size recording paper). The surface temperature (high temperature region) temporarily rises due to automatic energization by the first heater lamp for returning the surface temperature of the small size recording paper passing region to the fixing set temperature TS. However, heat is smoothly radiated to the left and right sides of the heating roller whose temperature drops due to interruption of energization of the second heater lamp, and the heat distribution characteristics of the first heater lamp become substantially equal, that is, the central portion in the axial direction of the heating roller. When the temperature in the vicinity of both the left and right sides (high temperature region) is lowered and the central portion in the axial direction of the heating roller (region corresponding to the heat distribution characteristics of the first heater lamp) reaches a substantially uniform temperature, the second heater lamp is turned on. By energizing and controlling to reach the fixing set temperature, it is possible to reliably prevent high temperature offsets such as adhesion of the developer to the heating roller due to overmelting and curling of the recording paper, as well as small size recording. It is also possible to save energy by preventing unnecessary consumption of electric power for further heating the high temperature regions on both the left and right sides of the central portion in the axial direction of the heating roller after the paper is passed.

  On the other hand, when there is a print command for the small size recording paper even after the small size recording paper is passed, the heating roller is controlled after the small size recording paper is passed by controlling the power supply to the second heater lamp to be cut off. The surface temperature (high temperature region) that is accumulated near the fixing set temperature without being taken by the paper passing near the left and right sides of the central portion in the axial direction of the sheet is the fixing set temperature TS. Although it temporarily rises due to automatic energization by the first heater lamp for returning to the normal temperature, heat is smoothly radiated to both the left and right sides of the heating roller, where the temperature decreases due to interruption of energization of the second heater lamp. Unfixed developer on small size recording paper is continuously fixed while suppressing the local surface temperature rise near the left and right sides of the central portion of the heating roller in the axial direction. Rukoto is possible.

  In addition, when a print instruction for a small size recording sheet is received while the first and second heater lamps are waiting in a non-energized state, the first heater lamp is controlled to reach a fixing set temperature at which fixing can be performed. In addition, when the second heater lamp is controlled to stand by at a predetermined set temperature, for example, a remaining heat standby temperature lower than the fixing set temperature, the central portion in the axial direction of the heating roller is passed after the small-size recording paper is passed. The surface temperature (high temperature region) that has been accumulated near the fixing set temperature without being taken away by the paper passing near the left and right sides is used to return the surface temperature of the small size recording paper passing region to the fixing set temperature TS. Although the temperature rises temporarily due to automatic energization by the first heater lamp, the temperature is increased by the second heater lamp that stands by at the remaining heat standby temperature lower than the fixing set temperature. Heat is dissipated to the left and right sides of the low heating roller, and the temperature near the left and right sides of the heating roller in the axial direction (high temperature region) decreases, contributing to energy savings by reducing unnecessary power consumption to the second heater lamp. It becomes possible. In addition, even if a large size recording paper is instructed to print after the small size recording paper has passed, the large size recording paper can be quickly printed without waiting for the surface temperature to drop near the left and right sides (high temperature area) of the central portion in the axial direction of the heating roller. The upper unfixed developer can be fixed.

  Then, when the first and second heater lamps are each waiting at a pre-set standby temperature lower than a predetermined set temperature, for example, the fixing set temperature, the heat distribution characteristics of the first heater lamp at the center in the axial direction of the heating roller. When the printing instruction for the large size recording paper in the paper passing range larger than the paper passing range corresponding to is received, the first and second heater lamps are controlled to reach the fixing set temperature. The first and second heater lamps quickly shift to the fixing set temperature, and the unfixed developer on the large size recording paper can be quickly fixed.

  In addition, when the heater lamp corresponding to the paper passing range of the recording paper instructed to print is controlled to start printing when the fixing set temperature is reached, the unfixed developer on the recording paper is stabilized. And can be fixed.

  Further, when the above-described fixing device is used in an image forming apparatus, high temperature offset and curling of the recording paper due to a local temperature rise of the heating roller after passing a small size recording paper are prevented, and power saving is achieved. It is possible to provide an image forming apparatus capable of achieving the above.

  As described above, the control of the second heater lamp is changed after passing a small size recording sheet having a sheet passing range smaller than the sheet passing range corresponding to the heat distribution characteristic of the first heater lamp at the center in the axial direction of the heating roller. Thus, if control is performed so that the second heater lamp is de-energized when there is a print command for the large size recording paper after the small size recording paper is passed, the axis of the heating roller after the small size recording paper is passed The surface temperature accumulated near the fixing set temperature without being taken away by paper passing near the left and right sides in the center of the direction is smoothly dissipated to the left and right sides of the heating roller, the temperature of which decreases when the second heater lamp is turned off. If the heat distribution characteristics of the first heater lamp are substantially uniform, the second heater lamp is energized and controlled so as to reach the fixing set temperature. Over can be reliably prevented, it is also possible to save energy by preventing wasteful consumption of power further heating the axial central portion right and left sides of the high-temperature region of the heating roller. On the other hand, if control is performed so that the second heater lamp is de-energized when there is a print command for the small size recording paper even after the small size recording paper is passed, the axial direction of the heating roller after the small size recording paper is passed The surface temperature accumulated near the fixing set temperature near the left and right sides of the center is smoothly radiated to the left and right sides of the heating roller, where the temperature drops due to the power-off of the second heater lamp. Thus, it is possible to continuously fix the unfixed developer on the small size recording paper while suppressing a local surface temperature increase near the left and right sides of the central portion in the axial direction of the heating roller.

  In addition, when receiving a print instruction for a small size recording sheet while the first and second heater lamps are waiting in a non-energized state, the first heater lamp is controlled to reach the fixing set temperature, 2 By controlling the heater lamp to stand by at the remaining heat standby temperature lower than the fixing temperature, after the small-size recording paper is passed, it is fixed without being taken away by passing the paper near the left and right sides of the central portion in the axial direction of the heating roller. The surface temperature accumulated near the set temperature is dissipated to the left and right sides of the low-temperature heating roller by the second heater lamp waiting at the remaining heat standby temperature, and the temperatures near the left and right sides of the central portion in the axial direction of the heating roller This can reduce the wasteful power consumption of the second heater lamp and contribute to energy saving. In addition, even if a large size recording paper is instructed to print after the small size recording paper is passed, it is quickly unfixed on the large size recording paper without waiting for the surface temperature to decrease near the left and right sides of the central portion in the axial direction of the heating roller. The developer can be fixed.

  Then, during standby at the remaining heat standby temperature of the first and second heater lamps, a large size of the sheet passing range that is larger than the sheet passing range corresponding to the heat distribution characteristics of the first heater lamp at the central portion in the axial direction of the heating roller. In response to the print instruction for the recording paper, the first and second heater lamps are controlled to reach the fixing set temperature, so that the first and second heater lamps can be promptly shifted to the fixing set temperature. The unfixed developer on the size recording sheet can be quickly fixed.

  In addition, by controlling to start printing when the heater lamp corresponding to the paper passing range of the recording paper instructed for printing reaches the fixing set temperature, the unfixed developer on the recording paper is stably fixed. Can be made.

  Furthermore, by using such a fixing device for an image forming apparatus, high temperature offset and curling of the recording paper due to a local temperature rise of the heating roller after passing a small size recording paper can be prevented, and power can be saved. An image forming apparatus that can be realized can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  In the present embodiment, a case will be described in which the present invention is applied to a multifunction machine as an image forming apparatus having a copy function, a print function, and a facsimile function.

-Description of overall configuration of MFP-
FIG. 1 shows an outline of the internal configuration of a multifunction machine 1 (image forming apparatus) according to this embodiment. As shown in FIG. 1, the multifunction machine 1 includes a scanner unit 2, a print unit 3, and an automatic document feeder 4. Hereinafter, each part will be described.

-Description of the scanner unit 2-
The scanner unit 2 reads image of a document placed on a document table 41 made of transparent glass or the like, or a document image fed one by one by the document automatic sheet feeding unit 4 to generate image data. It is. The scanner unit 2 includes an exposure light source 21, a plurality of reflecting mirrors 22, 23, 24, an imaging lens 25, and a photoelectric conversion device (CCD: Charge Coupled Device) 26.

  The exposure light source 21 emits light to a document placed on the document table 41 of the automatic document feeder 4 or a document conveyed through the automatic document feeder 4. Each reflecting mirror 22, 23, 24 reflects the reflected light from the document once in the left direction in the drawing, as shown by an alternate long and short dash line A in FIG. Reflected in the right direction in the figure so as to go to 25.

  As a document image reading operation, when a document is placed on the document table 41 (when used as a “sheet fixing method”), the exposure light source 21 and the reflecting mirrors 22, 23, 24 are connected to the document table 41. The image of the entire document is read by scanning in the horizontal direction. On the other hand, when reading a document conveyed by the automatic document feeder 4 (when used as a “sheet moving method”), the exposure light source 21 and the reflecting mirrors 22, 23, 24 are fixed at the positions shown in FIG. Then, the image is read when the document passes through a document reading unit 42 of the automatic document feeder 4 described later.

  The light reflected by the reflecting mirrors 22, 23, 24 and passing through the imaging lens 25 is guided to the photoelectric conversion element 26, and the reflected light is converted into an electric signal (original image data) by the photoelectric conversion element 26. It is like that.

-Description of the print unit 3-
The printing unit 3 includes an image forming system 31 and a paper transport system 32.

  The image forming system 31 includes a laser scanning unit 31a as an exposure unit and a photosensitive drum 31b as a drum-type electrostatic latent image carrier. The laser scanning unit 31a irradiates the surface of the photosensitive drum 31b with laser light based on the document image data converted by the photoelectric conversion element 26. The photosensitive drum 31b rotates in a direction indicated by an arrow in FIG. 1, and an electrostatic latent image is formed on the surface of the photosensitive drum 31b by being irradiated with laser light from the laser scanning unit 31a.

  In addition to the laser scanning unit 31a, a developing device 31c as a developing unit, a transfer roller 31d as a transfer unit, a cleaning device 31e, a static eliminator (not shown), and a charging unit are provided around the outer periphery of the photosensitive drum 31b. The charging rollers 31f are sequentially arranged in the circumferential direction. The developing device 31c develops the electrostatic latent image formed on the surface of the photosensitive drum 31b into a visible image with toner (developer). The transfer roller 31d transfers the toner image formed on the surface of the photosensitive drum 31b onto an image forming paper P (see FIG. 2) as a recording paper. The cleaning device 31e removes the toner remaining on the surface of the photosensitive drum 31b after the toner transfer. The static eliminator removes residual charges on the surface of the photosensitive drum 31b. As the charging roller 31f, a contact charging type that applies a DC voltage from a power source (not shown) by contact charging to the surface of the photosensitive drum 31b before the electrostatic latent image is formed is applied. Has been.

  Therefore, when an image is formed on the image forming paper P, the surface of the photosensitive drum 31b is charged to a predetermined potential by the contact of the charging roller 31f, and the laser scanning unit 31a emits laser light based on the document image data. Irradiate the surface of the photosensitive drum 31b. Thereafter, the developing device 31c develops a visible image with toner on the surface of the photosensitive drum 31b, and the toner image is transferred onto the image forming paper P by the transfer roller 31d. Further, after that, the toner remaining on the surface of the photosensitive drum 31b is removed by the cleaning device 31e, and the residual charge on the surface of the photosensitive drum 31b is removed by the static eliminator. Thereby, one cycle of the image forming operation (printing operation) on the image forming paper P is completed. By repeating this cycle, it is possible to continuously form images on a plurality of image forming sheets P.

  On the other hand, the paper transport system 32 transports the image forming paper P stored in the paper cassette 33 one by one to cause the image forming system 31 to perform image formation, and discharges the image formed paper P on which the image has been formed. The paper is discharged to the paper tray 35. In this case, as the image forming paper P accommodated in the paper cassette 33, A3 size paper that is passed by vertical feeding (direction in which the longitudinal direction of the paper is parallel to the paper transport direction) is a large image forming paper. In addition to large-size image forming paper such as A3 size that is passed by this vertical feed, normal size image forming paper P such as A4 size that is passed by vertical feed, A5 size image-forming paper, A small-size image forming sheet P ′ (shown in FIG. 4) such as a postcard is also accommodated.

  The paper transport system 32 includes a main transport path 36 and a reverse transport path 37. The main conveyance path 36 faces the discharge side of the paper cassette 33 and the other end faces the discharge tray 35. One end of the reverse conveyance path 37 is connected to the main conveyance path 36 on the upstream side (lower side in the figure) of the transfer roller 31d, and the other end is downstream of the transfer roller 31d. (Upper side in the figure) is connected to the main transport path 36.

  A pickup roller 36a having a semicircular cross section is disposed at the upstream end of the main conveyance path 36 (the part facing the discharge side of the paper cassette 33). Due to the rotation of the pickup roller 36a, the image forming paper P stored in the paper cassette 33 can be intermittently fed to the main transport path 36 one by one.

  Registration rollers 36d and 36d are disposed upstream of the position where the transfer roller 31d is disposed in the main conveyance path 36. The registration rollers 36d and 36d convey the image forming paper P while aligning the toner image on the surface of the photosensitive drum 31b with the image forming paper P. A fixing device 39 for fixing the toner image transferred to the image forming sheet P through the nip portion between the heating roller 391 and the pressure roller 392 on the downstream side of the arrangement position of the transfer roller 31 d in the main conveyance path 36. Is arranged. Further, a discharge roller 36 e for discharging the image forming paper P to the paper discharge tray 35 is disposed at the downstream end of the main transport path 36.

  A branching claw 38 is disposed at a connection position of the upstream end of the reverse conveyance path 37 with respect to the main conveyance path 36. The branch claw 38 is rotated about the horizontal axis between the first position indicated by the solid line in FIG. 1 and the second position that rotates counterclockwise from the first position to open the reverse conveyance path 37. It is free to rotate. When the branch claw 38 is at the first position, the image forming paper P is conveyed toward the paper discharge tray 35, and when it is at the second position, the image forming paper P can be supplied to the reverse conveying path 37. When the image forming paper P is supplied to the reverse conveying path 37 (when the image forming paper P is supplied to the reverse conveying path 37 by so-called switchback conveyance), a conveying roller 37a is disposed in the reverse conveying path 37. ), The image forming paper P is transported by the transport roller 37a, and the image forming paper P is reversed upstream of the registration roller 36d and transported again through the main transport path 36 toward the transfer roller 31d. ing. That is, an image can be formed on the back surface of the image forming paper P.

-Description of automatic document feeder 4-
Next, the automatic document feeder 4 will be described. The automatic document feeder 4 is configured as a so-called automatic duplex document feeder. The automatic document feeder 4 can be used as a sheet moving type, and includes a document tray 43 as an original placement unit, an intermediate tray 44, a document discharge tray 45 as a document discharge unit, and trays 43, 44, A document transport system 46 is provided for transporting a document between 45.

  The document transport system 46 includes a main transport path 47 for transporting a document placed on the document tray 43 to the intermediate tray 44 or the document discharge tray 45 via the document reading unit 42, and the document on the intermediate tray 44. And a sub-transport path 48 for supplying the main transport path 47 to the main transport path 47.

  A document pick-up roller 47a and a separating roller 47b are disposed at the upstream end of the main conveyance path 47 (a portion facing the discharge side of the document tray 43). A separation plate 47c is disposed below the separation roller 47b, and one of the documents on the document tray 43 is placed between the separation roller 47b and the separation plate 47c as the document pickup roller 47a rotates. Is fed to the main transport path 47. PS rollers 47e and 47e are disposed on the downstream side of the joining portion (B portion in the figure) of the main transport path 47 and the sub transport path 48. The PS rollers 47 e and 47 e adjust the leading edge of the document and the image reading timing of the scanner unit 2 and supply the document to the document reading unit 42. That is, the PS rollers 47e and 47e temporarily stop the conveyance of the document while the document is supplied, and adjust the timing to supply the document to the document reading unit 42.

  The document reading unit 42 includes a platen glass 42a and a document pressing plate 42b, and the exposure light source when the document supplied from the PS rollers 47e and 47e passes between the platen glass 42a and the document pressing plate 42b. The light from 21 passes through the platen glass 42a and is irradiated onto the document. At this time, the document image data is acquired by the scanner unit 2. A biasing force by a coil spring (not shown) is applied to the back surface (upper surface) of the document pressing plate 42b. Thereby, the document pressing plate 42b is in contact with the platen glass 42a with a predetermined pressing force, and prevents the document from floating from the platen glass 42a when passing the document reading unit 42.

  On the downstream side of the platen glass 42a, a conveyance roller 47f and a document discharge roller 47g are provided. The document that has passed over the platen glass 42a is discharged to the intermediate tray 44 or the document discharge tray 45 through the transport roller 47f and the document discharge roller 47g.

  An intermediate tray swinging plate 44 a is disposed between the document discharge roller 47 g and the intermediate tray 44. The intermediate tray swinging plate 44a swings between a position 1 indicated by a solid line in the figure and a position 2 that is flipped upward from the position 1 with the end on the intermediate tray 44 side being the center of swinging. It is possible. When the intermediate tray swinging plate 44 a is at position 2, the document discharged from the document discharge roller 47 g is collected to the document discharge tray 45. On the other hand, when the intermediate tray swinging plate 44a is at the position 1, the document discharged from the document discharge roller 47g is discharged to the intermediate tray 44. When the sheet is discharged onto the intermediate tray 44, the edge of the document is sandwiched between the document discharge rollers 47g and 47g. It is supplied to the transport path 48 and is sent again to the main transport path 47 via the sub-transport path 48. The reverse rotation operation of the document discharge roller 47g is performed by adjusting the document delivery to the main conveyance path 47 and the image reading timing. Thus, the image on the back side of the document is read by the document reading unit 42.

-Basic operation of MFP-
As an operation of the MFP 1 configured as described above, first, when the MFP 1 functions as a printer, it receives print data (image data or text data) transmitted from a host device such as a personal computer. The received print data (print data) is temporarily stored in a buffer (memory) (not shown). Along with storing the print data in the buffer, the print data is sequentially read from the buffer, and based on the read print data, an image is formed on the image forming paper P by the image forming operation of the print unit 3 described above. .

  When the multifunction machine 1 functions as a scanner, scanned image data of a document read by the scanner unit 2 is temporarily stored in a buffer. Along with storing the scan image data in the buffer, the scan image data is sequentially transmitted from the buffer to the host device, and the image is displayed on the display or the like of the host device.

  Further, when the multifunction machine 1 functions as a copying machine, an image is formed on the image forming paper P by the image forming operation of the printing unit 3 based on the original image data read by the scanner function.

  As a characteristic part of the present invention, as shown in FIG. 2, the fixing device 39 includes a fixing unit 390 that houses a heating roller 391 and a pressure roller 392. The fixing unit 390 includes a fixing upper frame 390a that accommodates the heating roller 391 and a fixing lower frame 390b that accommodates the pressure roller 392. The frames 390a and 390b are opened and closed via hinges (not shown). The heating roller 391 and the pressure roller 392 are arranged to face each other when the frames 390a and 390b are closed. As shown in FIG. 3, the heating roller 391 and the pressure roller 392 are rotatably supported by the frames 390a, 390b via bearings 393,. A driving gear 391g that meshes with the output gear 394g of the driving motor 394 is connected to one end (the right end in FIG. 3) of the heating roller 391 in a rotationally integrated manner. Further, a driven gear 392g meshing with the drive gear 391g is connected to one end (right end in FIG. 3) of the pressure roller 392 in a rotationally integrated manner, and the heating roller 391 and the pressure roller 392 are driven by the driving force of the drive motor 394. It is designed to rotate. In this case, the closed state of both frames 390a and 390b is held by lock levers (not shown) provided at both ends in the axial direction.

  Inside the heating roller 391, there are a main heater 391a as a first heater lamp in which a nichrome wire is tightly wound in accordance with the center reference of the image forming paper P at the center in the axial direction, and both sides of the main heater 391a in the axial direction. Two types of heaters, ie, a sub-heater 391b as a second heater lamp, in which nichrome wires are densely wound, are accommodated in the section. The main heater 391a and the sub heater 391b have heat distribution characteristics such that light is emitted with a predetermined heat distribution (a central portion in the axial direction of the heating roller 391 and both left and right side portions) when energized from a control unit (not shown). The inner peripheral surface of the heating roller 391 is heated by infrared radiation. The main heater 391a and the sub heater 391b are independently temperature controlled by the control unit.

  The heating roller 391 heats the heat distribution characteristics in the axial direction by energizing the main heater 391a and the sub heater 391b to 100% as a set temperature (here, 180 ° C.) as a set temperature. The image forming paper P passed through the nip portion of the fixing device 39 (the nip portion between the heating roller 391 and the pressure roller 392) is heated. In this case, in the main heater 391a, the central portion in the axial direction of the heating roller 391 serving as a sheet passing area for the image forming paper P of normal size (A4 size in the longitudinal feed in which the longitudinal direction is parallel to the paper transport direction). While the heat distribution characteristic is 100%, the heat distribution characteristic in the vicinity of both ends in the axial direction of the heating roller 391 that is a non-sheet passing region of the normal size image forming paper P is about 30%. In order to heat almost the entire area in the axial direction of 391, the sub-heater 391b is energized in the vicinity of both ends in the axial direction of the heating roller 391 so as to supplement the heat distribution characteristics in the vicinity of both ends in the axial direction of the heating roller 391 by the main heater 391a. The heat distribution characteristics are set to 100%. Further, as the image forming paper P that is passed through the nip portion of the fixing device 39, the A3 size image forming paper is vertically fed (the longitudinal direction of the image forming paper P is parallel to the paper transport direction). Paper.

  As shown in FIG. 2, the heating roller 391 is formed on the outer peripheral surface of the core metal 391c to prevent the core metal 391c as the main body and the toner T on the image forming paper P from being offset. And a release layer 391d.

  For the metal core 391c, for example, a metal such as iron, stainless steel, aluminum, copper, or an alloy thereof is used. In addition, as the core metal 391c of this embodiment, a thin one made of iron (STKM) having a diameter of 40 mm and a thickness of 0.25 mm is used.

  For the release layer 391d, fluororesins such as PFA (copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether) and PTFE (polytetrafluoroethylene), silicone rubber, fluororubber, and the like are suitable. A fluororesin is applied as the release layer 391d in this embodiment.

  The pressure roller 392 is configured to have a heat-resistant elastic material layer 392b such as silicone rubber on the outer surface of a cored bar 392a such as steel, stainless steel, or aluminum. On the surface of the heat-resistant elastic material layer 392b of the pressure roller 392, a release layer made of the same fluororesin as that of the heating roller 391 may be formed. The pressure roller 392 in this embodiment is provided with a heat-resistant elastic body layer 392b made of silicone rubber and a release layer 392c made of PFA tube having a diameter of 40 mm and heated by an elastic member such as a spring (not shown). The roller 391 is pressed against the roller 391 with a force of 200 N, whereby a nip portion having a width of about 6 mm is formed between the roller 391 and the heating roller 391.

  And the thermistor 395 (only one is shown in FIG. 2) which detects surface temperature in each location is provided in the axial direction center part of the said heating roller 391, the center part right-and-left both-sides position, and right-and-left both-sides edge part position. Yes. The surface temperature at the central portion in the axial direction of the heating roller 391 and the left and right both side positions and the left and right end positions detected by each thermistor 395 is output to the control unit, and the heating roller 391 in the control unit. The energization to the main heater 391a and the sub-heater 391b is controlled so that the surface temperature in the axial direction is maintained at the fixing set temperature TS.

  When the control unit receives a print instruction when the main heater 391a and the sub-heater 391b are each waiting at a preheat standby temperature YT lower than a predetermined set temperature, that is, the fixing set temperature TS, the image forming paper instructed to print is received. The main heater 391a and the sub heater 391b are controlled according to the sheet passing range. Specifically, as shown in FIG. 4A, when a small size image forming paper P ′ is instructed to be printed, the main heater 391a is energized and the central portion in the axial direction of the heating roller 391 is set to the fixing set temperature TS. After the transition, as shown in FIG. 4B, a small size that becomes a sheet passing range D smaller than the sheet passing range F corresponding to the heat distribution characteristics of the main heater 391a at the central portion in the axial direction of the heating roller 391. When the image forming paper P ′ is passed through the nip portion between the heating roller 391 and the pressure roller 392 of the fixing device 39, the sub heater 391b is controlled after the small size image forming paper P ′ is passed. To change. This is because the capture range of the amount of heat taken by the small size image forming paper P ′ smaller than the paper passing range F corresponding to the heat distribution characteristics of the main heater 391a is the central portion of the paper passing range F of the heating roller 391. Since it is limited to the nearby paper passing range D, the left and right sides E and E of the central portion in the axial direction of the heating roller 391 where the small size image forming paper P ′ is not passed (non-paper passing range of the small size image forming paper P ′ This is because the surface temperature in the vicinity of the image forming paper P ′ having a small size is not taken but is accumulated in the vicinity of the fixing set temperature TS even if the image forming paper P ′ is passed. In this case, the sub heater 391b is shifted to the fixing set temperature TS as shown in FIG. 4C after the energization of the sub heater 391b is interrupted after the small-size image forming paper P ′ is passed. When the heat distribution characteristics of the heater 391a are substantially equal, that is, after the surface temperature at the central portion in the axial direction of the heating roller 39 is detected to be substantially equal by the thermistor 395, the sub-heater 391b is detected after the detection by the thermistor 395. And may be controlled to reach the fixing set temperature TS.

  In addition, when the main heater 391a and the sub-heater 391b are each waiting in a non-energized state, the control unit energizes the main heater 391a and receives a heating roller when receiving a print instruction for the small-size image forming paper P ′. Control is performed so that the surface temperature of the central portion 39 in the axial direction reaches the fixing set temperature TS, and the sub heater 391b is controlled to stand by at the remaining heat standby temperature YT (predetermined set temperature). Then, the control unit determines from the sheet passing range D corresponding to the heat distribution characteristic of the main heater 391a at the central portion in the axial direction of the heating roller 391 when the main heater 391a and the sub heater 391b are each waiting at the remaining heat standby temperature YT. In response to a print instruction for a large-size image forming sheet (A3-sized image forming sheet in a longitudinal feed in which the longitudinal direction is parallel to the sheet conveying direction) having a larger sheet passing range G, the main heater 391a and the sub heater 391b are received. Is controlled so that the surface temperature of the central portion in the axial direction of the heating roller 39 and the left and right side portions reach the fixing set temperature TS. Further, the control unit energizes the main heater 391a and the sub heater 391b in accordance with the sheet passing range of the image forming sheet instructed to be printed, and the central portion in the axial direction of the heating roller corresponding to the main heater 391a and the sub heater 391b and both left and right sides Control is performed such that printing is started when the surface temperature of the portion reaches the fixing set temperature TS.

  Here, the flow of control by the control unit when a printing instruction is given after passing a small-sized image forming paper P ′ (such as B5 size or postcard size) to the fixing device 39 of the multifunction device 1 is a flowchart of FIG. It demonstrates along a figure.

  First, in step ST1 of the flowchart of FIG. 5, when the fixing device 39 is waiting in a non-energized state and there is a print instruction for image forming paper in step ST2, the print instruction is a small size in step ST3. It is determined whether or not the image forming paper P ′. If the determination in step ST3 is NO for large-size image forming paper, in step ST4, the main heater 391a is energized to move the vicinity of the central portion in the axial direction of the heating roller 39 to the fixing set temperature TS. Then, the sub-heater 391b is energized to shift both the left and right axial portions of the heating roller 39 to the fixing set temperature TS. In step ST5, the thermistor 395 indicates that the axial center and both left and right sides of the heating roller 39, that is, the entire area of the heating roller (the sheet passing range G of the large size image forming paper) has reached the fixing set temperature TS. When detected, in step ST6, printing is started, and then the process returns to step ST2.

  On the other hand, if the determination in step ST3 is YES for the small-sized image forming paper P ′, in step ST7, the main heater 391a is energized and the vicinity of the central portion in the axial direction of the heating roller 39 is set at the fixing set temperature TS. At the same time, the sub heater 391b is energized to shift both the left and right axial portions of the heating roller 39 to the remaining heat standby temperature YT. In step ST8, when the thermistor 395 detects that the vicinity of the central portion in the axial direction of the heating roller 39 has reached the fixing set temperature TS, printing is started in step ST9.

  Next, when it is detected in step ST10 that the small-size image forming paper P ′ has passed through the nip portion between the heating roller 391 and the pressure roller 392, that is, passed through the fixing device 39, step ST11. It is then determined whether there is a print instruction. If the determination in step ST11 is NO in which there is no print instruction, in step ST12, the energization of the main heater 391a is interrupted and the vicinity of the central portion in the axial direction of the heating roller 39 is shifted to the remaining heat standby temperature YT. The main heater 391a is controlled while maintaining the remaining heat standby temperature YT. Thereafter, when a timer (not shown) detects that the remaining heat standby temperature YT remains at a predetermined time, for example, about 30 minutes, at step ST13, the main heater 391a is de-energized at step ST14. At the same time, after the energization to the sub-heater 391b is cut off, the process returns to step ST1.

  On the other hand, if the determination in step ST11 is YES in which there is a print instruction, it is determined in step ST15 whether or not the image formation sheet that has been instructed to be printed is a small-size image formation sheet P ′. . If the determination in step ST15 is “YES” for the small-sized image forming paper P ′, the main heater 391a is energized in step ST16 and the vicinity of the central portion in the axial direction of the heating roller 39 is set to the fixing set temperature TS. At the same time, the energization of the sub-heater 391b is cut off, and the surface temperatures of the left and right sides of the heating roller 39 in the axial direction are lowered from the remaining heat standby temperature YT. In step ST17, when the thermistor 395 detects that the vicinity of the central portion in the axial direction of the heating roller 39 has reached the fixing set temperature TS, printing is started in step ST18, and then the process returns to step ST11.

  On the other hand, if the determination in step ST15 is NO, which is an instruction to print a large image forming sheet instead of the small image forming sheet P ′, the energization to the sub heater 391b is cut off in step ST19. Thus, the surface temperatures of the left and right side portions of the heating roller 39 in the axial direction are lowered from the remaining heat standby temperature YT. At this time, the main heater 391a is automatically energized so as to return the surface temperature of the central portion in the axial direction of the heating roller to the fixing set temperature TS. Thereafter, in step ST20, the process waits until the surface temperature of the central portion in the axial direction of the heating roller 39 becomes a substantially uniform fixing set temperature TS, and then in step ST21, the sub-heater 391b is energized to turn on the axis of the heating roller 39. The surface temperature on both the left and right sides of the direction is shifted to the fixing set temperature TS. Thereafter, in step ST22, when the thermistor 395 detects that the central portion in the axial direction of the heating roller 39 and both left and right side portions, that is, the entire area of the heating roller 39 has reached the fixing set temperature TS, printing is started in step ST23. The process returns to step ST11.

  As described above, in this embodiment, a small-sized image forming sheet P ′ having a sheet passing range D smaller than the sheet passing range F corresponding to the heat distribution characteristic of the main heater 391a passes through the central portion in the axial direction of the heating roller 391. Since the control of the sub-heater 391b is changed after the small-size image forming paper P ′ is passed when the paper is fed, printing of the large-size image forming paper after the small-size image forming paper P ′ is passed. When there is a command, the energization of the sub-heater 391b is controlled so as to cut off the small-size image forming paper P ′, so that the left and right sides E and E (small size The surface temperature (high temperature region) accumulated near the fixing set temperature TS without being taken away by the sheet passing in the vicinity of the non-sheet passing range of the image forming sheet P ′ is the small size image forming sheet P. Left and right sides of the heating roller 391, which temporarily rises due to automatic energization by the main heater 391a for returning the surface temperature of the sheet passing area D to the fixing set temperature TS, but decreases due to the energization interruption of the sub heater 391b. When the heat distribution characteristics of the main heater 391a become substantially uniform, that is, the temperature of the heating roller 391 is decreased by reducing the temperature in the vicinity of both the left and right sides E and E (high temperature region) of the heating roller 391. By controlling so that the sub-heater 391b is energized to reach the fixing set temperature TS when the axial center F (region corresponding to the heat distribution characteristics of the main heater 391a) reaches a substantially uniform temperature. To reliably prevent high temperature offset such as adhesion to the heating roller 391 due to overmelting of the toner and curling of the image forming paper P In addition, it is possible to save energy by preventing wasteful consumption of electric power for further heating the high-temperature regions E and E on both the left and right sides of the central portion in the axial direction of the heating roller 391 after passing the small-sized image forming paper P ′. .

  On the other hand, when there is a print command for the small-sized image forming paper P ′ even after the small-sized image forming paper P ′ is passed, the small heater is controlled so as to cut off the energization of the sub-heater 391b. The surface temperature (high temperature region) accumulated near the fixing set temperature TS without being taken away by the paper passing in the vicinity of both the left and right sides E and E of the central portion in the axial direction of the heating roller 391 after passing the forming paper P ′ is small. Although the surface temperature of the sheet passing area D of the image forming paper P 'of the size is temporarily increased by automatic energization by the main heater 391a for returning to the fixing set temperature TS, the temperature is decreased by deenergizing the sub heater 391b. Heat is smoothly radiated to the left and right side portions of the heating roller 391, and a small-size image forming paper P ′ is passed through the axial center portion of the heating roller 391. It can be fixed continuously unfixed toner local surface temperature rise on to while the image forming paper P of small size 'suppression in the vicinity of E.

  When the main heater 391a and the sub-heater 391b are each waiting in a non-energized state and receiving a print instruction for the small-size image forming paper P ′, the main heater 391a is energized to shift to the fixing set temperature TS. And the sub-heater 391b is controlled to wait at the remaining heat standby temperature YT. Therefore, in the vicinity of both the left and right sides E and E of the central portion in the axial direction of the heating roller 391 after passing the small-size image forming paper P ′. The surface temperature (high temperature region) accumulated without being taken by the sheet passing and staying in the vicinity of the fixing set temperature TS is changed to the fixing set temperature TS of the sheet passing region D of the small-sized image forming paper P ′ by the main heater 391a. The sub-heater 39 stands by at the remaining heat standby temperature YT lower than the fixing set temperature TS, although it temporarily rises due to re-energization The heat is smoothly radiated to both the left and right sides of the low-temperature heating roller 391 by b, and the temperature in the vicinity of both the left and right sides E and E in the axial center of the heating roller 391 (high temperature region) is reduced. It can contribute to energy saving by reducing consumption. In addition, even when a large-size image forming paper is instructed to be printed after the small-size image forming paper P ′ is passed, the surface temperature of the heating roller 391 near the left and right sides E and E (high temperature region) decreases. It is possible to quickly fix the unfixed toner on the large-sized image forming paper P without waiting.

  When the main heater 391a and the sub-heater 391b are each waiting at the remaining heat standby temperature YT, the sheet passing range F is larger than the sheet passing range F corresponding to the heat distribution characteristic of the main heater 391a at the center in the axial direction of the heating roller 391. When receiving a print instruction for large-sized image forming paper in the range, the main heater 391a and the sub heater 391b are controlled to reach the fixing set temperature TS, so that the main heater 391a and the sub heater 391b quickly reach the fixing set temperature TS. The unfixed toner on the large-size image forming paper can be quickly fixed.

  Further, since the main heater 391a and the sub heater 391b corresponding to the printing range of the image forming paper instructed to print are controlled to start printing when the fixing set temperature TS is reached, the indefinite state on the image forming paper is determined. The contact toner can be stably fixed.

  Further, by using such a fixing device 39 in the multi function device 1, high temperature offset and curling of the image forming paper due to a local temperature rise of the heating roller 391 after passing the small size image forming paper P ′ are prevented. It is possible to provide the multi-function device 1 that can prevent power saving.

  In addition, this invention is not limited to the said form, The other various modifications are included. For example, in the above embodiment, the thermistor 395 detects the surface temperature at two locations, the center position in the axial direction of the heating roller and the side end position, but the surface temperature is detected at three or more locations in the axial direction of the heating roller. You may do it.

  Further, in the above embodiment, after the small-size image forming paper P ′ is passed, the heat roller 391 is accumulated in the vicinity of the fixing set temperature TS without being taken away by the paper passing in the vicinity of both the left and right sides E and E of the central portion in the axial direction. The surface temperature (high temperature region) is temporarily raised by re-energization to the fixing set temperature TS of the sheet passing region D of the small-sized image forming paper P ′ by the main heater 391a, but the temperature is cut by turning off the energization of the sub heater 391b. Although the heat is smoothly radiated to both the left and right sides of the heating roller 391 that decreases, the fixing set temperature is not taken by the passing of paper in the vicinity of the left and right sides of the central portion in the axial direction of the heating roller after passing the small-size image forming paper. The surface temperature accumulated in the vicinity of TS (high-temperature region) is first applied to the left and right sides of the heating roller, where the temperature drops when the sub-heater is turned off. It was allowed heated, may be allowed to migrate paper passing area of the image forming sheet of a small size set fixing temperature by re-energizing the main heater.

  Furthermore, in the above embodiment, the case where the present invention is applied to the fixing device 39 of the multifunction machine 1 has been described. However, the present invention is applied to a fixing device of an image forming apparatus having a copy function, a print function, or a facsimile function. Of course.

FIG. 2 is a schematic diagram illustrating a schematic configuration of a multifunction machine including a fixing device according to the present invention. FIG. 3 is a cross-sectional view of the fixing device viewed from the side. FIG. 3 is a cross-sectional view of a fixing device showing a heating roller in a cross section. FIG. 6 is a characteristic diagram showing a change in the surface temperature of the heating roller by the sub-heater in the axial direction of the heating roller when a small-size image forming sheet is passed. FIG. 6 is a flowchart illustrating a control flow by a control unit when a printing instruction is issued after passing a small-size image forming sheet to the fixing device. FIG. 10 is a characteristic diagram showing a change in surface temperature in the axial direction of a heating roller when a small-size recording sheet according to a conventional example is passed.

Explanation of symbols

1 MFP (image forming device)
39 Fixing device 391 Heating roller 391a Main heater (first heater lamp)
391b Sub heater (second heater lamp)
392 Pressure roller D Paper passing range F smaller than the paper passing range corresponding to the heat distribution characteristic of the main heater F Paper passing range P corresponding to the heat distribution characteristic of the main heater Image forming paper (recording paper)
P 'Small size image forming paper T Toner (Developer)
TS Fixing set temperature YT Standby heat standby temperature (predetermined set temperature)

Claims (8)

In a fixing device in which unfixed developer on a recording sheet is passed through a nip portion between a heating roller and a pressure roller with reference to the center position in the axial direction of each roller and fixed.
A first heater lamp provided inside the heating roller and having a heat distribution characteristic corresponding to the central portion in the axial direction;
A second heater lamp having heat distribution characteristics corresponding to the left and right sides in the axial direction of the heating roller on both the left and right sides of the first heater lamp;
When a printing instruction is received while the first and second heater lamps are each waiting at a predetermined set temperature, the first and second heater lamps are controlled in accordance with the sheet passing range of the recording sheet instructed for printing. Control means for
When the small size recording sheet having a sheet passing range smaller than the sheet passing range corresponding to the heat distribution characteristic of the first heater lamp is passed at the central portion in the axial direction of the heating roller, the control means A fixing device characterized in that the control of the second heater lamp is changed after the recording paper is passed. In the fixing device according to claim 1,
When the control means receives a print instruction for a small-size recording sheet while the first and second heater lamps are each in a de-energized state, the control means reaches a fixing set temperature at which the first heater lamp can be fixed. And a fixing device that controls the second heater lamp to stand by at a predetermined set temperature. In the fixing device according to claim 1 or 2,
The fixing device is characterized in that the control means changes the control of the second heater lamp by cutting off the energization of the second heater lamp after the small size recording paper is passed. In the fixing device according to any one of claims 1 to 3,
When the first and second heater lamps are each waiting at a predetermined set temperature, the control means has a passage larger than the sheet passing range corresponding to the heat distribution characteristic of the first heater lamp at the central portion in the axial direction of the heating roller. A fixing device characterized by controlling the first and second heater lamps to reach a fixing set temperature upon receiving a print instruction for a large size recording paper in a paper range. In the fixing device according to claim 1, claim 2, or claim 4,
The fixing device is characterized in that the predetermined set temperature is a preheat standby temperature lower than the fixing set temperature. The fixing device according to any one of claims 1 to 5, wherein:
The fixing device controls the heater to start printing when a heater lamp corresponding to a sheet passing range of a recording sheet instructed for printing reaches a fixing set temperature. In the fixing device according to any one of claims 1 to 6,
The control means cuts off the energization of the second heater lamp after passing the small-size recording paper and causes the second heater lamp to reach the fixing set temperature when the heat distribution characteristics of the first heater lamp become substantially equal. The fixing device is characterized by being controlled.   An image forming apparatus using the fixing device according to any one of claims 1 to 7.

Images