JP2009192607A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device whose power consumption can be reduced by preventing an end of a heating rotary member from being heated. <P>SOLUTION: The fixing device includes a heating element roller 600 which form a fixing nip portion with a pressure roller 505 and has a plurality of heating elements (surface heaters 602) corresponding to a plurality of form widths and constituted in a plane shape. Further, the fixing device includes a control means (heating element roller position control unit 513) of controlling the position of the heating element roller 600. The control means controls the position of the heating element roller 600 so that a predetermined heating element moves to a predetermined position corresponding to the width of a form passing through the fixing nip portion. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a copying machine that forms an image on a transfer material (paper) using an electrophotographic method, a fixing device used in a printer, and the like, and an image forming apparatus such as a copying machine equipped with the fixing device and a printer. In particular, the present invention relates to a heat fixing type fixing device and an image forming apparatus that heat and fix unfixed toner formed and supported on a sheet.

  2. Description of the Related Art Conventionally, a fixing device of an electrophotographic image forming apparatus is generally a method of fixing a toner image by heating (heat fixing method) from the viewpoint of fixability, and in particular, a rotating body (heating) including a heating source. A system in which a toner image is directly brought into contact with a rotating member and fixed is widely used.

  Specifically, this fixing device passes a sheet through a fixing nip portion formed by a contact portion of a heating rotating member and a pressure rotating member, and fixes an unfixed toner image on the sheet.

  In recent years, there has been a demand for image forming apparatuses corresponding to various paper sizes, for example, from a relatively large size paper such as A3 size to a normally used small size paper such as A4R and B5 sizes. For this reason, it is necessary to configure the axial lengths of the heating rotary member and the pressure rotary member to correspond to a relatively large size such as A3 size, for example.

  However, when a small-size sheet such as A4R or B5 passes through the fixing device when the above configuration is adopted, as shown in FIG. 14, the effective fixing region (b) of the heating rotating member (a) is shown. In (-1), the non-sheet passing area (b-2) through which the sheet does not pass increases.

  When small-size paper is continuously copied, heat is not taken away by the paper from the surface of the heating rotating member (a) corresponding to the non-sheet passing area (b-2). The surface temperature of -2) becomes too high and hot offset occurs.

  In order to prevent an increase in the surface temperature of the non-sheet-passing area (b-2) when passing small-size paper as described above, a technique for cooling the non-sheet-passing area with cooling air has been proposed (for example, Patent Document 1). And 2).

Also, a fixing device including a plurality of heaters having different heating lengths depending on the sheet passing width of each sheet size with respect to the longitudinal direction of the fixing roller (heating rotating member) has been proposed (for example, see Patent Document 3). ).
Japanese Patent Application Laid-Open No. 60-136779 JP-A-5-181382 Japanese Patent No. 3445702

  In the techniques described in Patent Documents 1 and 2, energy that is consumed as power and converted as heat of the fixing roller is cooled by a cooling fan, so that the temperature rise of the non-sheet passing portion can be prevented, but energy is wasted. Is consumed. It can be said that there is double waste because energy is consumed to warm the unused area of the fixing device and energy for driving the fan for cooling it is consumed.

  In the technique described in Patent Document 3, it is necessary to provide a plurality of heaters for each paper size, and the heating device inside the fixing roller is increased in size. Further, in order to appropriately heat-fix the toner image on the paper, it is desirable to heat the vicinity of the fixing nip where the fixing roller and the pressure roller (pressure rotation member) are in pressure contact.

  However, as the number of heaters provided increases, the distance between the fixing nip portion and the heater becomes longer, and there is a concern that the vicinity of the fixing nip portion cannot be appropriately heated. When a ceramic heater or the like is used as the heater, these problems become more prominent because each heater takes a large space.

  An object of the present invention is to provide a fixing device and an image forming apparatus that can prevent the temperature rise at the end of the heating rotating member and reduce the energy consumption.

  In order to achieve the above object, the fixing device according to claim 1 includes a pressure roller and a fixing nip portion formed between the pressure roller and a plurality of heating elements corresponding to a plurality of paper widths. A heating element roller; and a control unit configured to control a position of the heating element roller, wherein the control unit generates heat corresponding to a length in a width direction of a sheet passing through the fixing nip portion among the plurality of heating elements. The position of the heating element roller is controlled so that the body is positioned at the fixing nip portion.

  An image forming apparatus according to a fifth aspect includes the fixing device according to the first aspect.

  According to the fixing device and the image forming apparatus of the present invention, it is possible to prevent the temperature rise at the end of the heating rotating member and reduce the energy consumption.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of an image forming apparatus (full color printer) according to an embodiment of the present invention.

  In FIG. 1, the image forming apparatus includes four image forming units (image forming units). That is, an image forming unit 1Y that forms a yellow image, an image forming unit 1M that forms a magenta image, an image forming unit 1C that forms a cyan image, and an image formation that forms a black image. Part 1Bk. These four image forming units 1Y, 1M, 1C, and 1Bk are arranged in a line at regular intervals.

  In each of the image forming units 1Y, 1M, 1C, and 1Bk, drum-type electrophotographic photosensitive members (hereinafter referred to as photosensitive drums) 2a, 2b, 2c, and 2d are installed.

  Around the photosensitive drums 2a, 2b, 2c and 2d, there are primary chargers 3a, 3b, 3c and 3d, developing devices 4a, 4b, 4c and 4d, transfer rollers 5a, 5b, 5c and 5d, a drum cleaner device 6a, 6b, 6c and 6d are respectively arranged.

  An exposure device 7 is installed below the primary chargers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d.

  The developing devices 4a, 4b, 4c, and 4d store yellow toner, cyan toner, magenta toner, and black toner, respectively.

  The photosensitive drums 2a, 2b, 2c, and 2d are negatively charged OPC photosensitive members having a photoconductive layer on an aluminum drum base, and are driven in a direction indicated by an arrow (clockwise in FIG. 1) by a driving device (not shown). ) Is rotated at a predetermined process speed.

  The primary chargers 3a, 3b, 3c, and 3d uniformly charge the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d to a predetermined negative potential by a charging bias applied from a charging bias power source (not shown).

  The developing devices 4a, 4b, 4c, and 4d contain toner, and each color latent image formed on the photosensitive drums 2a, 2b, 2c, and 2d is attached to each color toner and developed as a toner image (possible). Visualize).

  The transfer rollers 5a, 5b, 5c, and 5d are disposed so as to be in contact with the photosensitive drums 2a, 2b, 2c, and 2d via the intermediate transfer belt 8 in the primary transfer portions 32a to 32d.

  The drum cleaners 6 a, 6 b, 6 c, and 6 d have a cleaning blade or the like for removing the transfer residual toner remaining on the photosensitive drum 2 during the primary transfer from the photosensitive drum 2.

  The intermediate transfer belt 8 is disposed on the upper surface side of the photosensitive drums 2a, 2b, 2c, and 2d and is stretched between the secondary transfer counter roller 10 and the tension roller 11. The secondary transfer counter roller 10 is disposed in the secondary transfer portion 34 so as to be in contact with the secondary transfer roller 12 via the intermediate transfer belt 8. The intermediate transfer belt 8 is made of a dielectric resin such as polycarbonate, polyethylene terephthalate resin film, or polyvinylidene fluoride resin film.

  In addition, the intermediate transfer belt 8 has a primary transfer surface (lower flat surface) 8b formed on the surface facing the photosensitive drums 2a, 2b, 2c, and 2d inclined with the secondary transfer roller 12 side facing downward. It is.

  That is, the intermediate transfer belt 8 is movably disposed on the upper surfaces of the photosensitive drums 2a, 2b, 2c, and 2d, and the primary transfer surface 8b formed on the surface facing the photosensitive drum 2 is moved to the secondary transfer portion. It is inclined and arranged so that the 34 side is downward.

  Specifically, this inclination angle is set to about 15 °. The secondary transfer counter roller 10 is disposed on the secondary transfer unit 34 side and applies a driving force to the intermediate transfer belt 8. The tension roller 11 is disposed on the opposite side across the primary transfer portions 32 a to 32 d and applies tension to the intermediate transfer belt 8.

  The secondary transfer counter roller 10 is disposed so as to be in contact with the secondary transfer roller 12 via the intermediate transfer belt 8 at the secondary transfer unit 34. In addition, a belt cleaning device 13 that removes and collects transfer residual toner remaining on the surface of the intermediate transfer belt 8 is installed outside the endless intermediate transfer belt 8 and in the vicinity of the tension roller 11. Further, the fixing device 16 is installed in a vertical path configuration on the downstream side in the transport direction of the transfer material P from the secondary transfer unit 34.

  The exposure device 7 includes a laser light emitting unit that emits light corresponding to a time-series electric digital pixel signal of given image information, a polygon lens, a reflection mirror, and the like. The exposure device 7 exposes the photosensitive drums 2a, 2b, 2c, and 2d to image information on the surfaces of the photosensitive drums 2a, 2b, 2c, and 2d charged by the primary chargers 3a, 3b, 3c, and 3d. A corresponding electrostatic latent image of each color is formed.

  Other configurations of the image forming apparatus will be described together with the following image forming operations.

  When an image formation start signal is issued, the photosensitive drums 2a, 2b, 2c, and 2d of the image forming units 1Y, 1M, 1C, and 1Bk that are rotationally driven at a predetermined process speed are respectively connected to the primary chargers 3a, 3b, and 3c. 3d is uniformly charged to negative polarity. Then, the exposure device 7 irradiates an externally input color-separated image signal from the laser light-emitting element, and statically outputs each color on the photosensitive drums 2a, 2b, 2c, and 2d via a polygon lens, a reflection mirror, and the like. An electrostatic latent image is formed.

  First, yellow toner is adhered to the electrostatic latent image formed on the photosensitive drum 2a by the developing device 4a to which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied. Visualize as an image.

  This yellow toner image is driven by a transfer roller 5a to which a primary transfer bias (a reverse polarity (positive polarity) to toner) is applied in a primary transfer portion 32a between the photosensitive drum 2a and the transfer roller 5a. Primary transfer is performed on the intermediate transfer belt 8.

  The intermediate transfer belt 8 onto which the yellow toner image has been transferred is moved to the image forming unit 1M side. Also in the image forming unit 1M, the magenta toner image formed on the photosensitive drum 2b is superimposed on the yellow toner image on the intermediate transfer belt 8 in the same manner as described above, and the primary transfer unit 32b. Transcribed.

  At this time, the transfer residual toner remaining on the photosensitive drum 2 is scraped off and collected by a cleaner blade or the like provided in the drum cleaner devices 6a, 6b, 6c and 6d.

  Similarly, cyan and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1C and 1Bk on the yellow and magenta toner images superimposed and transferred on the intermediate transfer belt 8 are similarly transferred to the primary transfer unit. The images are sequentially overlapped at 32a to 32d. In this way, a full color toner image is formed on the intermediate transfer belt 8.

  Then, the front end of the full color toner image on the intermediate transfer belt 8 is moved to the secondary transfer portion 34 between the secondary transfer counter roller 10 and the secondary transfer roller 12. In accordance with this timing, the transfer material (paper) P selected from the paper feed cassette 17 or the manual feed tray 20 and fed through the transport path 18 is transported to the secondary transfer section 34 by the registration roller 19.

  A full-color toner image is collectively transferred to the transfer material P conveyed to the secondary transfer unit 34 by the secondary transfer roller 12 to which a secondary transfer bias (polarity opposite to the toner (positive polarity)) is applied. Is done.

  The transfer material P on which the full-color toner image is formed is conveyed to the fixing device 16, and after the full-color toner image is heated and pressurized and thermally fixed onto the surface of the transfer material P, the main body is discharged by the paper discharge roller 21. The sheet is discharged onto the upper discharge tray 22 and the series of image forming operations is completed. The secondary transfer residual toner and the like remaining on the intermediate transfer belt 8 are removed and collected by the belt cleaning device 13.

  The above is the image forming operation at the time of single-sided image formation.

  Subsequently, a double-sided image forming operation in the image forming apparatus will be described.

  Up to the point where the transfer material P is conveyed to the fixing device 16, the operation is the same as the one-sided image forming operation. After the full-color toner image is heated and pressurized and thermally fixed on the surface of the transfer material P, the transfer material P is mostly discharged onto the discharge tray 22 on the upper surface of the main body by the discharge roller 21. Then, the rotation of the paper discharge roller 21 is stopped. At that time, the paper discharge roller 21 is stopped so that the rear end position of the transfer material P reaches the reverse position 42.

  Subsequently, the sheet discharge roller 21 is normally rotated in order to feed the transfer material P, which has been stopped by stopping the rotation of the sheet discharge roller 21, to the double-sided path including the double-sided upper roller 40 and the double-sided lower roller 41. And reverse.

  By rotating the paper discharge roller 21 in the reverse direction, the rear end side of the transfer material P located at the reversal position 42 is set as the front end side and reaches the double-sided upper roller 40.

  Thereafter, the transfer material P is conveyed to the double-sided lower roller 41 by the double-sided upper roller 40, and the transfer material P is sequentially conveyed toward the registration roller 19 by the double-sided upper roller 40 and the double-sided lower roller 41.

  In the meantime, an image formation start signal is generated and the same operation as in the above-described single-sided image formation is performed. That is, the secondary transfer portion is moved by the registration roller 19 in accordance with the timing at which the front end of the full color toner image on the intermediate transfer belt 8 is moved to the secondary transfer portion 34 between the secondary transfer counter roller 10 and the secondary transfer roller 12. The transfer material P is moved to 34.

  After the toner image is transferred by aligning the leading edge of the toner image with the leading edge of the transfer material P in the secondary transfer unit 34, the image on the transfer material P is fixed by the fixing device 16 in the same manner as in the single-sided image forming operation. Let The transfer material P is again conveyed by the paper discharge roller 21 and finally discharged onto the paper discharge tray 22 to complete a series of image forming operations.

  FIG. 2 is a control block diagram of the image forming apparatus of FIG.

  In FIG. 2, a CPU 171 performs basic control of the image forming apparatus, and includes a ROM 174 in which a control program is written, a RAM (work RAM) 175 for performing processing, and an input / output port (I / O) 173. They are connected by an address bus and a data bus.

  The input / output port 173 is connected to various loads (not shown) such as a motor and a clutch for controlling the image forming apparatus, and an input (not shown) such as a sensor for detecting the position of the transfer material.

  The CPU 171 sequentially performs input / output control via the input / output port 173 in accordance with the contents of the ROM 174, and executes an image forming operation. An operation unit 172 is connected to the CPU 171 and controls display means and key input means of the operation unit 172.

  The operator instructs the CPU 171 to switch the image forming operation mode and display through the key input means, and the CPU 171 displays the state of the image forming apparatus and the operation mode setting by key input.

  The CPU 171 includes an image forming unit 1 that performs processing for exposing the line image data transferred from the image memory unit 300 to the exposure device 7, and an image memory unit 300 that performs image expansion processing, temporary storage processing, and the like. It is connected. The CPU 171 is connected to an external I / F processing unit 400 that transmits and receives image data, processing data, and the like from an external device such as a PC.

  FIG. 3 is a control block diagram of the image memory unit in FIG.

  In FIG. 3, the image memory unit 300 writes the image data received from the external I / F processing unit 400 via the memory controller unit 302 into the page memory 301 configured by a memory such as a DRAM. The image memory unit 300 performs image input / output access such as image reading to the image forming unit 1.

  The memory controller unit 302 determines whether the image data from the external device received from the external I / F processing unit 400 is compressed data. If it is determined that the image data is compressed data, the compressed data expansion processing unit The decompression process is performed using 303. Thereafter, a write process is performed on the page memory 301 via the memory controller unit 302.

  The memory controller unit 302 generates a DRAM refresh signal for the page memory 301, and arbitrates access to the page memory 301 for writing from the external I / F processing unit 400 and reading to the image forming unit 1.

  Further, the memory controller unit 302 controls a write address to the page memory 301, a read address from the page memory 301, a read direction, and the like according to an instruction from the CPU 171.

  FIG. 4 is a control block diagram of the external I / F processing unit in FIG.

  In FIG. 4, the external I / F processing unit 400 transmits image data and print command data transmitted from the external device 410 to any one of the USB I / F unit 401, the Centro I / F unit 402, and the network I / F unit 403. Receive via. Further, the external I / F processing unit 400 transmits the status information of the image forming apparatus determined by the CPU 171 to the external apparatus 410. Here, the external device 410 is a computer, a workstation, or the like.

  Print command data received from the external device 410 via any of the USB I / F unit 401, the Centro I / F unit 402, and the network I / F unit 403 is processed by the CPU 171. Then, the CPU 171 generates settings and timings for executing a printing operation using the image forming unit 1, the input / output port 173 in FIG.

  Image data received from the external device 410 via any of the USB I / F unit 401, the Centro I / F unit 402, and the network I / F unit 403 is transferred to the image memory unit 300 according to the timing based on the print command data. Sent. Then, processing is performed so that the image forming unit 1 forms an image in the image memory unit 300.

  FIG. 5 is an external perspective view of the fixing device in FIG.

  In FIG. 5, a fixing belt 500 is formed by molding a heat-resistant resin material such as polyimide into an endless belt shape. The fixing belt 500 is stretched by a fixing belt driving roller 501 and a heating element roller 600. The fixing belt driving roller 501 is driven by a fixing belt driving motor 504 to rotate the fixing belt 500. The heating element roller 600 will be described later with reference to FIG.

  The pressure roller 505 covers the core metal with an elastic layer such as silicon rubber, and further covers the surface with a fluorine coat layer as a release layer. The pressure roller 505 is rotated by a pressure roller drive motor 506.

  The fixing belt driving motor 504 and the pressure roller driving motor 506 are controlled by motor control units 514 and 515. The thermistors 507 and 508 detect the temperatures at the end and center of the surface of the fixing belt 500.

  The thermistors 507 and 508 send the detected temperatures to the temperature adjustment control units 509 and 510 as electric signals. The temperature adjustment control units 509 and 510 control the heating element roller 600 so that the surface temperature of the fixing belt 500 becomes a constant temperature.

  A flange 502 is press-fitted into the heating element roller 600. The heating element roller 600 is rotated by a heating element roller rotation motor 503. The heating element roller position control unit 513 controls the heating element roller 600 to move to a predetermined position by a sensor flag 511 and a position detection sensor 512 that are attached on the rotation shaft of the flange 502.

  In the present embodiment, the heating element roller rotation motor 503 is a stepping motor, and the heating element roller 600 is moved to a predetermined position using the change in the input of the position detection sensor 512 and the number of pulses output to the heating element roller rotation motor 503. Move to.

  FIG. 6 is a configuration diagram of the heating element roller in FIG. 5.

  In FIG. 6, the heating element roller 600 is made of aluminum, and planar heaters 602A, 602B, 602C, 602D, and 602E are attached thereto. That is, the heating element roller 600 has a plurality of heating elements (planar heaters 602) corresponding to a plurality of paper widths.

  The planar heaters 602A, 602B, 602C, 602D, and 602E are connected to the power control units 603A, 603B, 603C, 603D, and 603E through the connector 601 and are supplied with power. Here, the power supplied to the plurality of planar heaters 602 is different. In addition, power is individually supplied to the plurality of planar heaters 602.

  The power control units 603A, 603B, 603C, 603D, and 603E are controlled by the temperature adjustment control units 509 and 510 as necessary. Further, the heat generating roller 600 is pressed in the direction of the pressure roller 505 at the opposite position, and forms a fixing nip portion with the pressure roller 505.

  An arrow X represents the rotation direction of the fixing belt 500 (the heat generating roller 600), and an arrow Y represents the sheet passing direction with respect to the fixing belt 500.

  Next, the planar heater widths 604A, 604B, 604C, 604D, and 604E in the present embodiment will be described.

  In the present embodiment, the planar heaters 602A, 602B, 602C, 602D, and 602E are configured with different widths.

  The planar heater 602A has an A4 size width (297 mm + 5 mm), the planar heater 602B has an LTR size width (279 mm + 5 mm), and the planar heater 602C has a B4 size width (257 mm + 5 mm). The planar heater 602D has an LGL size width (216 mm + 5 mm), and the planar heater 602E has an A4R size width (210 mm + 5 mm).

  Here, FIG. 7 shows the relationship of power consumption for maintaining the planar heaters 602A, 602B, 602C, 602D, and 602E at 200 ° C. during continuous paper feeding.

  The planar heater 602 prevents the temperature unevenness in the planar heater 602 by providing a seamless structure in the width direction. If the sheet heater 602 is arranged by being divided in the paper width direction, density unevenness and gloss due to temperature unevenness (low temperature if there is a gap, high temperature if overlapped) at the joint of the sheet heater 602. There is concern about image defects such as unevenness.

  In the present embodiment, the sheet heaters 602 corresponding to the respective sheet widths are arranged in order on the heating roller 600 (by arranging the sheet heaters 602 in the sheet direction), thereby causing image defects due to temperature unevenness. It is possible to prevent.

  FIG. 8 is a cross-sectional view of the planar heater in FIG.

  In the planar heater 602, the heat generating portion 801 is configured by a resistor. The heat generating unit 801 generates heat when power is supplied from the power control unit 603. The heat generating portion 801 is sandwiched between the insulating portions 802 and 803.

  Next, the positional relationship between the position detection sensor 512 and the heating element roller 600 in this embodiment will be described with reference to FIG.

  The position where the heating element roller rotation motor 503 is rotated and the sensor flag 511 shields the position detection sensor 512 is the position where the planar heater 602A becomes the fixing nip portion. The position where 10 pulses are output to the heating element roller rotation motor 503 after light shielding is the position where the planar heater 602B becomes the fixing nip portion.

  Further, when the planar heater 602C is located in the fixing nip portion, the planar heater 602E is moved to the fixing nip portion by further outputting 20 pulses. On the contrary, when the planar heater 602A is moved to the fixing nip portion, the heating element roller rotation motor 503 outputs 20 pulses in the reverse rotation direction.

  As described above, the heating roller position control unit 513 manages the output pulse from the light shielding position of the position detection sensor 512, so that any planar heater 602 can be moved to the fixing nip portion.

  That is, the heating element roller position control unit 513 functions as a position control unit that controls the position of the heating element roller 600. Then, the position control unit controls the position of the heating element roller 600 so that the predetermined heating element (planar heater 602) moves to the predetermined position (fixing nip portion) corresponding to the width of the sheet passing through the nip portion. .

  FIG. 10 is a flowchart showing the procedure of the initial positioning process of the heating element roller of FIG. 6 executed by the image forming apparatus of FIG. FIG. 11 is a diagram showing the rotation direction of the heating roller in FIG.

  The processing in FIG. 10 is executed under the control of the CPU 171 in FIG.

  In the present embodiment, the heating element roller 600 is rotated by rotating the heating element roller rotation motor 503 with the direction of arrow A in FIG. 11 being forward rotation and the direction of arrow B being reverse rotation.

  In FIG. 10, the CPU 171 first confirms whether the position detection sensor 512 is shielded from light by the sensor flag 511 (S101). When the light is blocked, the CPU 171 rotates the heating element roller rotation motor 503 in the forward direction until the position detection sensor 512 transmits light (the sensor flag 511 is in a state where the position detection sensor 512 emits light and is out of the light receiving portion) (S102). ).

  Next, the CPU 171 waits until light is transmitted based on the output of the position detection sensor 512 (S103). When the light transmission is confirmed in step S103, the CPU 171 stops the heating element roller rotation motor 503 (S104), and proceeds to step S105. Similarly, when the position detection sensor 512 transmits light in step S101, the process proceeds to step S105.

  Next, the CPU 171 starts reverse rotation of the heating element roller rotation motor 503 (S105). Thereafter, the CPU 171 waits for the sensor flag 511 to shield the position detection sensor 512 (S106). When the light shielding is confirmed in step 106, the CPU 171 stops the heating element roller rotating motor 503 (S107), and the initial position setting process of the heating element roller 600 is ended.

  FIG. 12 is a flowchart showing the procedure of fixing control processing during image formation executed by the image forming apparatus of FIG.

  The processing in FIG. 12 is executed under the control of the CPU 171 in FIG.

  In FIG. 12, the CPU 171 first confirms whether or not the initial positioning of the heating element roller 600 has been completed (S201). If the initial positioning has not been completed, the CPU 171 performs the initial positioning process of FIG. 11 (S202).

  Next, when it is determined in step S201 that the initial positioning has been completed, the CPU 171 acquires the paper size (transfer material P) (S203). The paper size is included in the processing data notified from the external I / F processing unit 400. Then, the CPU 171 confirms whether or not the sheet heater 602 corresponding to the sheet size is positioned at the fixing nip (S204).

  The relationship between the paper size and the corresponding sheet heater is shown in FIG. If the corresponding planar heater 602 has already moved to the fixing nip portion, the process proceeds to step S210. When the different planar heater 602 has moved to the fixing nip portion, the CPU 171 once prohibits image formation (S205).

  Next, based on FIG. 9, the CPU 171 acquires the number of output pulses of the heating element roller rotation motor 503 necessary for moving the corresponding planar heater 602 (S206). Then, the CPU 171 starts driving the heating element roller rotation motor 503 by the number of pulses acquired in step S206 (S207). Next, the CPU 171 waits until a predetermined pulse is output (S208). After confirming that the predetermined pulse has been output, the CPU 171 stops driving the heating element roller rotation motor 503 (S209).

  Next, the CPU 171 determines the output power of the corresponding planar heater 602 based on FIG. 7 (S210), performs temperature adjustment (temperature adjustment) processing (S211), and permits image formation (S212).

  Then, the CPU 171 confirms whether all image formation has been completed (S213), and if not completed, returns to step S203. If it is determined that the image formation has been completed, an initial position finding process for the heating element roller 600 is executed (S214), and this process is terminated.

  As described above, by implementing the present invention, it is possible to optimally select a sheet heater suitable for the sheet size, and prevent the temperature rise at the end of the fixing device (the end of the heating element roller 600). be able to. As a result, it is not necessary to leave the paper interval more than necessary for the small size paper, and downtime can be reduced. In addition, energy saving can be achieved by supplying optimal power.

1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a control block diagram of the image forming apparatus in FIG. 1. FIG. 3 is a control block diagram of an image memory unit in FIG. 2. FIG. 3 is a control block diagram of an external I / F processing unit in FIG. 2. FIG. 2 is an external perspective view of the fixing device in FIG. 1. It is a block diagram of the heat generating roller in FIG. 6 is a chart relating to the planar heater in FIG. 5 (1). It is sectional drawing of the planar heater in FIG. It is a chart regarding the planar heater in FIG. 5 (2). FIG. 7 is a flowchart showing a procedure of initial positioning processing of the heating element roller of FIG. 6 executed by the image forming apparatus of FIG. 2. It is a figure which shows the rotation direction of the heat generating body roller in FIG. 3 is a flowchart showing a procedure of fixing control processing at the time of image formation executed by the image forming apparatus of FIG. 2. It is a chart regarding the planar heater in FIG. 5 (3). FIG. 4 is a diagram illustrating a relationship between an effective fixing region, a non-sheet passing region, and each sheet size of a heating rotation member in the fixing device.

Explanation of symbols

505 Pressure roller 513 Heating roller position control unit 600 Heating roller 602 Planar heater

Claims (5)

A pressure roller;
A heating element roller that forms a fixing nip portion with the pressure roller and has a plurality of heating elements corresponding to a plurality of paper widths;
Control means for controlling the position of the heating element roller,
The control means controls the position of the heating element roller such that a heating element corresponding to a length in a width direction of a sheet passing through the fixing nip portion among the plurality of heating elements is positioned in the fixing nip portion. A fixing device.   The fixing device according to claim 1, wherein electric power supplied to the plurality of heating elements is different.   The fixing device according to claim 1, wherein electric power is individually supplied to the plurality of heating elements.   The fixing device according to claim 1, wherein the plurality of heating elements are arranged side by side in a sheet passing direction.   An image forming apparatus equipped with the fixing device according to claim 1.

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