JP2012137570A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device that suppresses excessive unevenness in feeding speed in a fixing roller axial direction to suppress image failure.SOLUTION: A fixing roller 81 heats a recording material S. A pressure belt 821 comes into pressure-contact with the fixing roller 81 to form a fixing nip part N between the pressure belt 821 and the fixing roller 81. An inner central heater H1 and an inner end heater H2 are supplied with electrical power to heat each of a plurality of areas of the fixing roller 81 divided in the axial direction of the fixing roller 81. A heater driver 86 independently supplies electrical power to each of the inner central heater H1 and the inner end heater H2. A heater controller 87 controls the electrical power supply of the heater driver 86 to the inner central heater H1 and the inner end heater H2 based on the detection result of feeding speed detected at a plurality of positions corresponding to the plurality of areas mentioned above.

Description

  The present invention relates to a fixing device and an image forming apparatus.

  In general, as an electrophotographic image forming apparatus, a copying machine, a laser beam printer, a facsimile, a digital multifunction machine, or the like is known. In these image forming apparatuses, a recording material (paper) is passed through a fixing nip formed at a contact portion between a fixing roller and a pressure belt (or a pressure roller), and at that time, a toner image is formed on the recording material. Is equipped with a fixing device for fixing the recording material on the recording material by heating with pressure.

  In the fixing device, if the nip pressure or the nip width is not properly maintained and the moving speed (sheet passing speed) of the recording material differs between the central portion and the end portion in the fixing roller axial direction, a defect occurs in the image. . For example, when the paper passing speed at the center of the fixing roller is excessively faster than the paper passing speed at the end, “wrinkles”, “wrinkle-like gloss unevenness”, etc. occur on the recording material. On the other hand, when the sheet passing speed at the end of the heating roller is excessively high, “waving, loose”, “edge image shift, edge gloss unevenness” and the like occur in the recording material.

  Conventionally, in order not to cause such a problem, the nip pressure and the nip width are optimized by a technique such as a crown shape on the outer peripheral surface of the fixing roller. In recent years, since the appropriate ranges of the nip pressure and the nip width are narrowed due to the complexity of the nip structure, it is required to realize the above optimization by the accuracy of parts.

  Further, Japanese Patent Application Laid-Open No. H10-228561 discloses a fixing device that solves the above-described problems by controlling the surface temperature of the fixing roller. Patent Document 1 discloses a control of a heater (center heater) that mainly heats the axial center of the fixing roller, and a control of a heater (end heater) that mainly heats the axial end of the fixing roller. Describes a fixing device that individually performs the above operation based on the detected temperature of the surface of each part of the fixing roller.

  In this fixing device, during the sheet passing operation, the target temperature on the surface in the central portion in the axial direction is fixed to a predetermined value, and the central heater is controlled according to the target temperature. At this time, the target temperature of the axial end surface is variably set according to the detected temperature of the axial center surface, and the end heater is controlled according to the target temperature.

JP 2002-357777 A

  Here, in the fixing device, in general, with the operation of the image forming apparatus, aging of components such as a change in the hardness of an elastic material constituting the fixing roller or wear of a surface layer of the fixing roller occurs. As a result, the nip pressure or the nip width changes, and the sheet passing speed in the axial direction of the fixing roller may become excessively non-uniform.

  In addition, if the accuracy of parts in the fixing device varies, the nip pressure or the nip width may deviate from the design value, resulting in excessive non-uniformity of the sheet passing speed, which may cause a defect in the image.

  However, the fixing device described in Patent Document 1 does not take into account the aging and accuracy variations of parts. Therefore, correcting the nip pressure or nip width improper state caused by aging or accuracy variation of parts and suppressing the non-uniformity of the sheet passing speed in the width direction of the fixing roller is described in Patent Document 1. It is difficult with a fixing device.

  An object of the present invention is to provide a fixing device and an image forming apparatus that can suppress image defects by suppressing excessive non-uniformity of the sheet passing speed in the fixing roller axial direction.

The fixing device according to the present invention includes:
A heating rotator for heating the recording material;
A pressure rotator that presses against the heating rotator to form a fixing nip portion with the heating rotator; and
A plurality of heating units that receive power supply and heat the heating rotator for each of a plurality of regions divided in the axial direction of the heating rotator;
A drive unit that individually supplies power to each of the plurality of heating units;
A detection unit for detecting the moving speed of the recording material at a plurality of positions corresponding to the plurality of regions;
A control unit that controls power supply to each heating unit of the drive unit based on the detected moving speed of the recording material at the plurality of positions;
Have

An image forming apparatus according to the present invention includes:
An image forming unit for forming a toner image on a recording material;
The fixing device for fixing the formed toner image to the recording material;
Have

  According to the present invention, it is possible to suppress image defects by suppressing excessive non-uniformity of the sheet passing speed in the fixing roller axial direction.

1 schematically shows an entire configuration of an image forming apparatus according to Embodiment 1 of the present invention. FIG. The figure which shows the internal structure of the fixing | fixed part which concerns on Embodiment 1 of this invention. The figure for demonstrating the positional relationship and connection relationship inside the fixing | fixed part which concern on Embodiment 1 of this invention. FIG. 5 is a flowchart for explaining heater control during a sheet passing operation according to the first embodiment of the present invention. The figure for demonstrating the duty correction | amendment of the inner center heater performed by the heater control shown in FIG. The figure for demonstrating the duty correction | amendment of the inner side edge heater performed by the heater control shown in FIG. The figure which shows an example of the setting panel which concerns on Embodiment 2 of this invention The figure which shows the correction coefficient determination table which concerns on Embodiment 2 of this invention. The figure which shows the other example of the setting panel which concerns on Embodiment 2 of this invention. The figure which shows the internal structure of the fixing part which concerns on Embodiment 3 of this invention. FIG. 9 is a flowchart for explaining heater control during a sheet passing operation according to the third embodiment of the present invention.

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

(Embodiment 1)
FIG. 1 is a diagram schematically showing an overall configuration of an image forming apparatus according to Embodiment 1 of the present invention.

  An image forming apparatus A shown in FIG. 1 is an electrophotographic image forming apparatus, and includes an image forming apparatus main body A1 and an automatic document feeder A2.

  The image forming apparatus main body A1 includes a scanner unit 1, an operation display unit 2, a data processing unit 3, image forming units 4Y, 4M, 4C, and 4K, an intermediate transfer belt 4tb, a secondary transfer roller 4tr, a paper feed cassette 5, and a paper feed. A transport unit 6, a paper discharge unit 7, a fixing unit 8, and a paper discharge tray 10 are provided. The four sets of image forming units 4Y, 4M, 4C, and 4K correspond to different color components Y (yellow), M (magenta), C (cyan), and K (black). Each of 4M, 4C, and 4K mainly includes an image recording unit 40, a photosensitive drum 41, and a developing unit.

  The scanner unit 1 optically scans a document conveyed on the contact glass by the automatic document feeder A2 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). An image is formed on the light receiving surface of the sensor 1A and the original is read.

  The operation display unit 2 is a display device having a touch panel screen, and various instructions and input operations for setting performed by the user are performed via the touch panel screen. Therefore, the above-described original reading is performed in accordance with a user instruction input from the operation display unit 2.

  The data processing unit 3 mainly includes a circuit that performs analog-digital (A / D) conversion processing and a circuit that performs digital image processing. The data processing unit 3 generates digital image data (RGB signal) by A / D conversion processing from the analog image signal acquired by the CCD sensor 1A as a result of the above-described document reading. Further, the data processing unit 3 performs color conversion processing, correction processing according to initial settings or user settings, compression processing, and the like on the digital image data. The data processing unit 3 outputs the digital image data (YMCK signal) subjected to these processes to the image recording unit 40.

  The toner images formed by the image forming units 4Y, 4M, 4C, and 4K based on the digital image data sent to the image recording unit 40 are sequentially transferred to the intermediate transfer belt 4tb and further recorded by the secondary transfer roller 4tr. S is transferred to S and sent to the fixing unit 8. This series of image forming processes is roughly as follows.

  In the image forming unit 4Y, the photosensitive drum 41 is charged and then irradiated with laser light output in accordance with a Y signal from a semiconductor laser constituting the image recording unit 40. As a result, an electrostatic latent image of the Y component is formed on the surface of the photosensitive drum 41.

  A developing unit 42 that stores a Y component developer (for example, a two-component developer composed of a toner having a small particle diameter and a magnetic material) develops an electrostatic latent image using the developer, and a photosensitive drum 41. A Y component toner image is formed on the surface of the toner. The Y component toner image is transferred to the intermediate transfer belt 4tb at the pressure-bonding portion between the photosensitive drum 41 and the intermediate transfer belt 4tb (primary transfer). After the primary transfer, the photosensitive drum 41 is subjected to residual toner cleaning, charge removal, and charging in order to form the next electrostatic latent image.

  The same processing as that described above in the image forming unit 4Y is also performed for the other colors (M, C, K), that is, in the other image forming units 4M, 4C, 4K. The toner images of the M component, the C component, and the K component are transferred to the intermediate transfer belt 4tb at the pressure-bonding portion between the photosensitive drum 41 and the intermediate transfer belt 4tb (primary transfer), similarly to the Y component. A synthesized color toner image (synthetic toner image) is formed on the surface of the intermediate transfer belt 4tb.

  The combined toner image formed on the intermediate transfer belt 4tb is conveyed by the recording material S conveyed from the sheet feeding cassette 5 via the sheet feeding / conveying unit 6 at the pressure-bonding portion between the intermediate transfer belt 4tb and the secondary transfer roller 4tr. (Secondary transfer). The paper feed conveyance unit 6 includes a double-sided conveyance path 6a including a switchback path sb. The double-sided conveyance path 6a is used to convey the recording material S when performing image formation on both sides of the recording material S. Used.

  In this way, an unfixed toner image is formed on the recording material S.

  The unfixed toner image is fixed on the recording material S by the fixing unit 8. The fixing unit 8 has a configuration mainly including a fixing roller 81 and a pressure unit 82 accommodated in the frame body 80. In the present embodiment, the fixing unit 8 adopts a belt nip configuration, but the detailed configuration will be described later.

  The paper discharge unit 7 discharges the recording material S having the toner image fixed by the fixing unit 8 out of the apparatus and places it on the paper discharge tray 10.

  Hereinafter, the configuration of the fixing unit 8 according to the present embodiment will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is a diagram illustrating an internal configuration of the fixing unit 8, and FIG. 3 is a diagram for explaining a positional relationship and a connection relationship inside the fixing unit 8.

  As shown in FIG. 2, the fixing unit 8 includes a fixing roller 81, a pressure unit 82, a heat transfer unit 83, a temperature sensor 84, a paper passing sensor 85, a heater driver 86, a heater controller 87, an internal heater HI, and an external heater. Has HO. These internal components are appropriately supported by a support member (not shown) provided in the frame body 80 (FIG. 1), but here, for the sake of simplification of explanation, details of the support structure are provided. The detailed explanation is omitted.

  The fixing roller 81 as a heating rotator includes a cylindrical cored bar 811, an elastic layer 812, and a release layer 813, and is rotatably supported at both ends in the longitudinal direction (axial direction). An internal heater HI is accommodated in the fixing roller 81. In the present embodiment, the fixing roller 81 has a straight shape having a uniform outer diameter (for example, 65 mm), but may have a crown shape (including an inverted crown shape).

  The cylindrical cored bar 811 is a cylindrical body made of a metal such as aluminum. The thickness of the cylindrical cored bar 811 is, for example, 7 mm.

  The elastic layer 812 is a layer made of an elastic material such as HTV (high temperature vulcanization) silicone rubber having high heat resistance and covering the cylindrical cored bar 811. The layer thickness of the elastic layer 812 is, for example, 1.5 mm.

  The release layer 813 is a layer made of a resin such as PFA (perfluoroalkyl vinyl ether) or PTFE (polytetrafluoroethylene) that covers the elastic layer 812. The layer thickness of the release layer 813 is, for example, 50 μm.

  The internal heater HI has an inner central heater H1 disposed at the axial center and inner end heaters H2 disposed at both axial ends (see FIG. 3). Here, the central portion in the axial direction is a region located in the central portion when the fixing roller 81 is viewed from the upstream side in the recording material conveyance direction (hereinafter simply referred to as “upstream side”). In the present embodiment, the central portion in the axial direction is a region (A4 size paper width) that extends 105 mm from the center position of the axial length (corresponding to the center position of the recording material S being conveyed) to the left and right sides. The axial end portions include an axial left end portion and an axial right end portion, and are regions located at the left and right end portions when the fixing roller 81 is viewed from the upstream side. In this embodiment, the left end in the axial direction is a region from the center position of the axial length to the left from the position of 105 mm to the position of 175 mm, and the right end in the axial direction is the right side from the center position of the axial length. The region from the position of 105 mm to the position of 175 mm.

  The inner center heater H1 and the inner end heater H2 are both halogen heaters in the present embodiment. That is, each of the inner center heater H1 and the inner end heater H2 is driven by the power supplied from the heater driver 86 and lights up, and heat is generated accordingly. In the present embodiment, the power consumption of the inner central heater H1 in the fully lit state is 900 W, and the power consumption of the inner end heater H2 in the fully lit state is 600 W.

  The method for applying heat to the fixing roller 81 may not be a method using a halogen heater, and may be an induction heating method, for example.

  The inner center heater H1 mainly heats the region of the axially central portion surface of the fixing roller 81, and the inner end heater H2 mainly heats the region of the axially opposite end portions surface of the fixing roller 81.

  That is, the inner central heater H1 and the inner end heater H2 are a first heating unit and a second heating unit included in a plurality of heating units that apply heat for heating the recording material S to the fixing roller 81.

  Further, the inner central heater H1 and the inner end heater H2 constitute an internal heating unit that applies heat for heating the recording material S to the fixing roller 81 from the inside.

  Since the inner central heater H1 and the inner end heater H2 are disposed inside the fixing roller 81, heat radiation from the inner central heater H1 and the inner end heater H2 passes through the intermediate layer (elastic layer 812) of the fixing roller 81. Then, it is transmitted to the surface layer (release layer 813) of the fixing roller 81.

  The pressure unit 82 includes a pressure belt 821, an entrance roller 822, a separation roller 823, a steering roller 824, and a pressing pad 825.

  A pressure belt 821 as a pressure rotator is an endless belt, and a base material (for example, 100 μm in thickness) made of a heat-resistant and flexible resin such as polyimide is released from a resin such as PFA or PTFE. It is configured by coating with a layer (for example, 25 μm thick).

  In addition, the pressure belt 821 is rotatably spanned around the entrance roller 822, the separation roller 823, and the steering roller 824. Further, the pressure belt 821 is disposed so that at least a part of a portion extending between the entrance roller 822 and the separation roller 823 follows the outer peripheral shape of the fixing roller 81. With this arrangement, a fixing nip portion N having a long nip width (a length from the nip inlet a to the nip outlet b in the recording material conveyance direction) is formed between the fixing roller 81 and the fixing nip N.

  The entrance roller 822 is, for example, a cylindrical roller made of stainless steel that is fixedly disposed on the entrance side where the recording material S enters the fixing nip portion N. The entrance roller 822 is rotatably supported at both ends in the longitudinal direction (axial direction).

  The separation roller 823 is, for example, a stainless steel cylindrical roller (for example, an outer diameter of 23 mm) disposed on the exit side where the recording material S exits from the fixing nip portion N. The separation roller 823 is rotatably supported at both ends in the longitudinal direction (axial direction) and is disposed so as to be in pressure contact with the fixing roller 81 via the pressure belt 821. The separation roller 823 presses the recording material S against the fixing roller 81 via the pressure belt 821, and separates the recording material S from the outer peripheral surface of the fixing roller 81 when leaving the fixing nip portion N by curvature separation. The separation roller 823 is urged in the direction of the white arrow by an urging member (not shown) so as to press the recording material S with a load of 600 N, for example.

  The steering roller 824 is disposed apart from the conveyance path of the recording material S in order to apply a certain level of tension to the pressure belt 821, and is supported rotatably at both ends in the longitudinal direction (axial direction). Laura. The steering roller 824 can change the inclination of the shaft for stable rotation of the pressure belt 821 so that the position of the pressure belt 821 does not greatly deviate left and right with respect to the recording material conveyance direction.

  A pressing pad 825 as a pressing member is a member that is disposed at an intermediate position between the entrance roller 822 and the separation roller 823 and presses the pressure belt 821 against the fixing roller 81. The pressing pad 825 is urged in the direction of a white arrow by an urging member (not shown) so as to press the recording material S against the fixing roller 81 with a load of 500 N, for example, via the pressure belt 821. The nip width corresponding to the pressure contact portion between the pressing pad 825 and the fixing roller 81 is, for example, about 20 mm.

  In addition, in the press pad 825, it is preferable to perform surface processing for ensuring low friction on the surface (press surface) that is in sliding contact with the pressure belt 821. On the other hand, in the pressure belt 821, it is preferable to apply a lubricant for ensuring low friction on the surface (inner peripheral surface) that is in sliding contact with the pressing pad 825.

  The rotation of the fixing roller 81 and the pressure belt 821 is driven by a drive motor (not shown) mechanically connected to the fixing roller 81. This drive motor drives the fixing roller 81 to rotate, whereby the pressure belt 821 is driven to rotate. The drive torque of the drive motor is controlled so that the rotation speeds of the fixing roller 81 and the pressure belt 821 are kept constant.

  For the purpose of assisting the rotation of the pressure belt 821, another drive motor is mechanically connected to the separation roller 823, and the rotation of the separation roller 823 is appropriately driven by this drive motor. Good.

  Similar to the internal heater HI, the external heater HO is for applying heat for heating the recording material S to the fixing roller 81. However, unlike the internal heater HI, the external heater HO is disposed outside the fixing roller 81.

  The external heater HO has an outer center heater H3 disposed at the axial center and outer end heaters H4 disposed at both axial ends (see FIG. 3).

  The outer center heater H3 and the outer end heater H4 are both halogen heaters in the present embodiment. That is, each of the outer central heater H3 and the outer end heater H4 is driven by the power supplied from the heater driver 86 and lights up, and heat is generated accordingly. In the present embodiment, the power consumption of the outer central heater H3 in the fully lit state is 600 W, and the power consumption of the outer end heater H4 in the fully lit state is 450 W.

  The method for applying heat to the fixing roller 81 may not be a method using a halogen heater, and may be an induction heating method, for example.

  The outer center heater H3 mainly heats the area of the axially central surface of the fixing roller 81, and the outer edge heater H4 mainly heats the area of the axially opposite end surfaces of the fixing roller 81.

  That is, the outer central heater H3 and the outer edge heater H4 are a third heating unit and a fourth heating unit included in a plurality of heating units that apply heat for heating the recording material S to the fixing roller 81.

  The outer central heater H3 and the outer end heater H4 constitute an external heating unit that applies heat for heating the recording material S to the fixing roller 81 from the outside.

  Since the outer central heater H3 and the outer end heater H4 are accommodated in the heat transfer portion 83 disposed outside the fixing roller 81, the heat transfer from the outer central heater H3 and the outer end heater H4 is performed by the heat transfer portion 83. To the surface layer (release layer 813) of the fixing roller 81.

  The heat transfer unit 83 includes an external heating belt 831 and external heating rollers 832a and 832b.

  The external heating rollers 832a and 832b are straight cylindrical bodies made of metal such as aluminum, and are arranged so that the axial direction thereof is parallel to the fixing roller 81, and the external heating belt 831 is rotatably spanned thereon. Has been. The external heating rollers 832a and 832b press the external heating belt 831 against the fixing roller 81 by an urging member (not shown) or by its own weight. An external heater HO is accommodated in the external heating roller 832a.

  The external heating belt 831 is a member formed by subjecting an endless belt-shaped base body to, for example, nickel electroforming and further covering with a release layer made of a resin such as PFA.

  The external heating belt 831 has at least a part of a portion extending between the external heating rollers 832a and 832b so as to contact the surface layer (release layer 813) of the fixing roller 81 over a wide range along the outer peripheral shape of the fixing roller 81. Has been placed. Then, it rotates according to the rotation of the fixing roller 81. With this configuration, the heat transfer efficiency from the external heater HO to the fixing roller 81 can be improved.

  The temperature sensor 84 as the temperature detection unit includes three temperature detection elements 84L, 84C, and 84R each formed of, for example, a non-contact thermistor (see FIG. 3).

  The temperature detection element 84L is disposed close to the axial left end surface (hereinafter simply referred to as “left end surface”) 814L of the fixing roller 81 at the center position of the axial left end, and the axial end surface of the fixing roller 81 (Hereinafter, simply referred to as “end surface 814LR”). The temperature detection element 84L outputs a temperature detection signal corresponding to the temperature of the left end surface 814L. The temperature detection signal is subjected to predetermined signal processing by an analog signal processing circuit (not shown), and is input to the heater controller 87 as digital temperature detection data. This temperature detection data indicates the detection temperature of the left end surface 814L.

  The temperature detection element 84C is disposed close to the axially central surface (hereinafter simply referred to as “central surface”) 814C of the fixing roller 81 at the central position of the axially central portion, and is used to detect the temperature of the central surface 814C. The temperature detection element 84C outputs a temperature detection signal corresponding to the temperature of the central surface 814C. The temperature detection signal is subjected to predetermined signal processing by an analog signal processing circuit (not shown), and is input to the heater controller 87 as digital temperature detection data. This temperature detection data indicates the detection temperature of the center surface 814C.

  The temperature detecting element 84R is disposed close to the axially right end surface (hereinafter simply referred to as “right end surface”) 814R of the fixing roller 81 at the center position of the axially right end, and the end surface is similar to the temperature detecting element 84L. Used for temperature detection of 814LR. The temperature detection element 84R outputs a temperature detection signal corresponding to the temperature of the right end surface 814R. The temperature detection signal is subjected to predetermined signal processing by an analog signal processing circuit (not shown), and is input to the heater controller 87 as digital temperature detection data. This temperature detection data indicates the detection temperature of the right end surface 814R.

  Only one of the temperature detection elements 84L and 84R may be provided.

  A sheet passing sensor 85 as a sheet passing detecting unit is an optical sensor including a light emitting unit 851 and a light receiving unit 852. In the present embodiment, the sheet passing sensor 85 is disposed in the vicinity of the nip inlet a, but may be disposed in the vicinity of the nip outlet b, or may be disposed in both the vicinity of the nip inlet a and the vicinity of the nip outlet b. May be.

  The light emitting unit 851 has, for example, three light emitting elements 851L, 851C, and 851R each configured by a light emitting diode, and the light receiving unit 852 has three light receiving elements 852L, 852C, and 852R each configured by, for example, a phototransistor. (See FIG. 3).

  The light emitting element 851L and the light receiving element 852L are arranged so as to face each other across the conveyance path of the recording material S at the outer edge of the left end in the axial direction. The light emitting element 851L emits light toward the light receiving element 852L under the control of the heater controller 87, and the light receiving element 852L receives the light. While the recording material S passes between the light emitting element 851L and the light receiving element 852L, light is blocked. Thereby, the recording material S passing through the fixing nip portion N can be detected. The light detection data indicating the light reception result of the light receiving element 852L is input to the heater controller 87 for measuring the sheet passing speed at the left end in the axial direction. This light detection data indicates the passage timing of the leading edge and the trailing edge of the recording material S at the left end in the axial direction.

  The light emitting element 851C and the light receiving element 852C are arranged so as to face each other across the conveyance path of the recording material S at the center position in the central portion in the axial direction. The light emitting element 851C emits light toward the light receiving element 852C under the control of the heater controller 87, and the light receiving element 852C receives the light. While the recording material S passes between the light emitting element 851C and the light receiving element 852C, light is blocked. Thereby, the recording material S passing through the fixing nip portion N can be detected. The light detection data indicating the light reception result of the light receiving element 852C is input to the heater controller 87 for measuring the sheet passing speed at the central portion in the axial direction. This light detection data indicates the passage timing of the leading edge and the trailing edge of the recording material S at the central portion in the axial direction.

  The light emitting element 851R and the light receiving element 852R are arranged so as to face each other across the conveyance path of the recording material S at the outer edge at the right end in the axial direction. The light emitting element 851R emits light toward the light receiving element 852R under the control of the heater controller 87, and the light receiving element 852R receives the light. While the recording material S passes between the light emitting element 851R and the light receiving element 852R, light is blocked. Thereby, the recording material S passing through the fixing nip portion N can be detected. The light detection data indicating the light reception result of the light receiving element 852R is input to the heater controller 87 for measuring the sheet passing speed at the right end in the axial direction. This light detection data indicates the passage timing of the leading end and the trailing end of the recording material S at the right end in the axial direction.

  Only one of the light receiving elements 852L and 852R may be provided. Further, when the light receiving element 852L is not provided, it is not necessary to provide the light emitting element 851L. When the light receiving element 852R is not provided, it is not necessary to provide the light emitting element 851R.

  The heater driver 86 as a drive unit is a set of heater drivers 861, 862, 863, and 864 (see FIG. 3). The heater drivers 861 to 864 individually drive the inner central heater H1, the inner end heater H2, the outer central heater H3, and the outer end heater H4.

  The heater driver 861 is a circuit that drives the inner central heater H1 by performing on / off control of energization of the inner central heater H1.

  Specifically, the heater driver 861 has a triac connected to a power supply unit (not shown) that supplies AC power. The heater driver 861 drives the inner central heater H1 by supplying the AC power to the inner central heater H1 while the triac is constantly or temporarily in a conductive state during a period when the energization execution instruction is received from the heater controller 87. . Therefore, this period is a lighting period (energization period) of the inner center heater H1. Further, the heater driver 861 keeps the TRIAC in a non-conducting state at all times during the period when the heater controller 87 receives an instruction to turn off the power, stops the supply of AC power to the inner central heater H1, and turns off the inner central heater H1. Stop driving. Therefore, this period is a non-lighting period (non-energization period) of the inner center heater H1.

  During the lighting period of the inner central heater H1, the heater driver 861 turns on / off the duty ratio of the driving voltage of the inner central heater H1, in other words, the on / off duty ratio of the AC power supplied to the inner central heater H1 (hereinafter simply referred to as “duty”). "). This can be realized by phase control of AC power using a triac.

Specifically, heater driver 861 receives an instruction of timing (conduction timing) for switching the triac from the non-conductive state to the conductive state from heater controller 87 for each half-wave section of AC power. The heater driver 861 switches the triac to the conductive state at the specified conduction timing. This triac is switched to a non-conduction state by the electrical characteristics of the triac at the timing when the voltage polarity is inverted in the AC power from the power supply unit (zero cross timing). Therefore, temporarily a conductive state the triac in the lighting period, if the duty _{D 1} of the inner central heaters H1 to _{0 [%] <D 1 <} 100 [%] is obtained a desired duty _{D 1} by the control be able to. Then, dimming lighting of the inner central heater H1 can be realized, and the inner central heater H1 can be caused to generate heat in a state where the amount of heat generation is limited.

The phase control using triac in the heater driver 861, when the inner central heater H1 is switched to light up from non-lighting, or when vice versa, increasing or flicker prevention control is gradually decreased duty D ₁ of the inner central heaters H1 Can be used.

When the heater driver 861 receives an instruction from the heater controller 87 to keep the triac in a continuous state, the heater driver 861 maintains the triac in a conductive state in accordance with the instruction, and the triac is non-conductive even when the voltage polarity inversion timing comes. Make sure that it does not switch to a state. And it kept connected the triac in the lighting period, if the duty D ₁ of the inner central heaters H1 and D _{1 =} 100 [%] can be by the control obtain the desired duty D _1. Then, the inner central heater H1 can be fully turned on, and the inner central heater H1 can generate heat without limiting the amount of heat generated.

  The heater driver 861 has a zero cross detection circuit (not shown) connected to the power supply unit. The zero-cross detection circuit detects the zero-cross timing and notifies the heater controller 87 of this for each half-wave section of AC power from the power supply unit. The zero cross timing is a reference timing for determining the conduction timing of the triac in each of the heater drivers 861 to 864.

In this embodiment, the heater driver 861 realizes supply power control by phase control using a triac, but realizes supply power control by voltage control using a regulator circuit of variable output voltage type. You can also. In other words, in this embodiment, as the control parameter affecting the power supply, but utilizes a duty D ₁ of the inner central heater H1, it may also be used the peak value of the driving voltage of the inner central heater H1.

  The heater driver 862 is a circuit that drives the inner end heater H2 by performing on / off control of energization of the inner end heater H2.

  Specifically, the heater driver 862 has a triac connected to the power supply unit. During a period when the heater driver 862 receives an instruction to execute energization from the heater controller 87, the TRIAC is always or temporarily turned on to supply AC power to the inner end heater H2 so that the inner end heater H2 is turned on. To drive. Therefore, this period is a lighting period of the inner end heater H2. Further, the heater driver 862 keeps the TRIAC in a non-conducting state at all times during the period when the heater controller 87 receives an instruction to turn off the power, stops the supply of AC power to the inner end heater H2, and stops the inner end heater. Stop driving H2. Therefore, this period is a non-lighting period of the inner end heater H2.

  During the lighting period of the inner end heater H2, the heater driver 862 controls the duty of the AC power supplied to the inner end heater H2. This can be realized by phase control of AC power using a triac.

Specifically, the heater driver 862 receives an instruction of the TRIAC conduction timing from the heater controller 87 for each half-wave section of the AC power. The heater driver 862 switches the triac to the conducting state at the designated conduction timing. This triac is switched to a non-conduction state at the zero cross timing due to the electrical characteristics of the triac. Therefore, temporarily a conductive state the triac in the lighting period, if the duty _{D 2} of the inner end portion heater H2 to _{0 [%] <D 2 <} 100 [%] is the desired duty _{D 2} by the control Obtainable. Then, the dimming lighting of the inner end heater H2 can be realized, and the inner end heater H2 can be caused to generate heat while the amount of heat generation is limited.

Incidentally, the phase control using a triac in the heater driver 862, when the inner end heater H2 is switched to light up from non-lighting, or when vice versa, is gradually increased or gradually decreased duty D ₂ of the inner end portion heater H2 flicker It can be used for prevention control.

When the heater driver 862 receives an instruction from the heater controller 87 to keep the triac in a continuous state, the heater driver 862 maintains the triac in a conductive state according to the instruction, and the triac is non-conductive even when the voltage polarity reversal timing comes. Make sure that it does not switch to a state. And it kept connected the triac in the lighting period, if the duty D ₂ of the inner end portion heaters H2 and D _{2 =} 100 [%] can be by the control obtain the desired duty D _2. Then, the inner end heater H2 is fully turned on, and the inner center heater H2 can generate heat without limiting the amount of heat generated.

In this embodiment, the heater driver 862 realizes supply power control by phase control using a triac. However, the heater driver 862 realizes supply power control by voltage control using a variable output voltage regulator circuit. You can also. In other words, in this embodiment, as the control parameter affecting the power supply, but utilizes a duty D ₂ of the inner end heaters H2, also use the peak value of the driving voltage of the inner end portion heater H2 it can.

  The heater driver 863 is a circuit that drives the outer central heater H3 by performing on / off control of energization of the outer central heater H3. The heater driver 864 is a circuit that drives the outer end heater H4 by performing on / off control of energization of the outer end heater H4. As the circuit configuration of the heater drivers 863 and 864, a circuit configuration similar to that of the heater driver 862 can be adopted, and thus detailed description thereof is omitted.

  The heater controller 87 is configured by a CPU (Central Processing Unit). The heater controller 87 is a control unit that individually controls energization of the inner central heater H1, the inner end heater H2, the outer central heater H3, and the outer end heater H4.

  The heater controller 87 acquires light detection data from the paper passing sensor 85. Further, the heater controller 87 acquires data indicating the process speed and the recording material length, respectively. The heater controller 87 calculates the sheet passing speed at the end portion in the axial direction and the central portion in the axial direction based on the process speed, the recording material length, and the light detection data from the sheet passing sensor 85. That is, the combination of the sheet passing sensor 85 and the heater controller 87 constitutes a detection unit that detects the sheet passing speed at the axial end portion and the axial center portion.

  In addition, the heater controller 87 acquires temperature detection data from the temperature sensor 84. Further, a notification of zero cross timing is received from the heater driver 861. The heater controller 87 generates the above-described instruction used for driving each heater based on the detected sheet passing speed, the temperature detection data acquired from the temperature sensor 84, and the zero cross timing notified from the heater driver 861. These are output to the heater drivers 861 to 864.

  The heater control of the heater controller 87 is specifically described as follows. Here, the heater control during the sheet passing operation will be described as an example.

  FIG. 4 is a flowchart for explaining heater control during the sheet passing operation according to the present embodiment.

  When the start of printing is instructed, the heater controller 87 sets target temperatures for the center surface 814C and the end surface 814LR during the sheet passing operation (step S101). In this example, both are set to 170 ° C.

  Then, the heater controller 87 starts individual control of each heater (step S102).

At this time, the control of the inner center heater H1 is on / off control based on the detected temperature of the center surface 814C. That is, the heater controller 87 determines whether or not the detected temperature of the central surface 814C indicated as the temperature detection result of the temperature detection element 84C in the temperature detection data is equal to or higher than the target temperature 170 ° C. When the detected temperature of the central surface 814C is 170 ° C. or higher, the heater controller 87 causes the heater driver 861 to cut off the energization of the inner central heater H1 so that the inner central heater H1 is not lit. The heater controller 87 causes the heater driver 861 to energize the inner center heater H1 so that the inner center heater H1 is turned on when the detected temperature of the center surface 814C is lower than 170 ° C. In the lighting period of the inner central heaters H1, the heater controller 87 sets the duty D ₁ at 100% inside the middle heaters H1 to a full lighting state (normal control mode).

The control of the inner end heater H2 is on / off control based on the detected temperature of the end surface 814LR. That is, the heater controller 87 determines whether or not the detected temperature of the end surface 814LR is equal to or higher than the target temperature 170 ° C. Here, the heater controller 87 averages the detected temperatures of the left end surface 814L and the right end surface 814R, which are indicated in the temperature detection data as the temperature detection results of the temperature detection elements 84L, 84R, to thereby detect the end surface 814LR. Get the detected temperature. When the detected temperature of the end surface 814LR is 170 ° C. or higher, the heater controller 87 causes the heater driver 862 to cut off the energization of the inner end heater H2 so that the inner end heater H2 is not lit. Further, when the detected temperature of the end surface 814LR is lower than 170 ° C., the heater controller 87 causes the heater driver 862 to energize the inner end heater H2 so that the inner end heater H2 is turned on. In the inner end heater lighting periods H2, the heater controller 87 sets the duty D ₂ to 100% inner end heater H2 to the full lighting state (normal control mode).

The control of the outer central heater H3 is on / off control based on the detected temperature of the central surface 814C. That is, the heater controller 87 determines whether the detected temperature of the center surface 814C is equal to or higher than the target temperature 170 ° C. When the detected temperature of the central surface 814C is 170 ° C. or higher, the heater controller 87 causes the heater driver 863 to cut off the energization of the outer central heater H3 so that the outer central heater H3 is not lit. Further, the heater controller 87 causes the heater driver 863 to energize the outer central heater H3 so that the outer central heater H3 is turned on when the detected temperature of the central surface 814C is lower than 170 ° C. In the lighting period of the outer central heater H3, the heater controller 87 sets the duty D ₃ to the outer central heater H3 and full lighting state to 100% (normal control mode).

The control of the outer end heater H4 is on / off control based on the detected temperature of the end surface 814LR. That is, the heater controller 87 determines whether or not the detected temperature of the end surface 814LR is equal to or higher than the target temperature 170 ° C. When the detected temperature of the end surface 814LR is 170 ° C. or higher, the heater controller 87 causes the heater driver 864 to cut off the energization of the outer end heater H4 so that the outer end heater H4 is not lit. Further, when the detected temperature of the end surface 814LR is lower than 170 ° C., the heater controller 87 causes the heater driver 864 to energize the outer end heater H4 so that the outer end heater H4 is turned on. In the lighting period of the outer end heaters H4, the heater controller 87 sets the duty D ₄ 100% to the outer end heaters H4 and the full lighting state (normal control mode).

  Then, the heater controller 87 acquires the process speed and the recording material length (step S103). For example, the value of the rotational speed of the photosensitive drum 41 or a value obtained by converting the value by a predetermined formula can be used as the process speed. These values can be acquired from a speed sensor (not shown) of the photosensitive drum 41. The recording material length is the length of the recording material S in the recording material conveyance direction, and this value can be acquired from setting information or the like input from the user by the operation display unit 2.

  Then, the heater controller 87 detects the passage of the recording material S (step S104). That is, the heater controller 87 acquires the passage timings of the leading end and the trailing end of the recording material S at the left end in the axial direction indicated as the light reception result of the light receiving element 852L in the light detection data. Further, the heater controller 87 acquires the passage timings of the leading end and the trailing end of the recording material S at the central portion in the axial direction indicated as the light reception result of the light receiving element 852C in the light detection data. Further, the heater controller 87 acquires the passage timing of the leading end and the trailing end of the recording material S at the right end in the axial direction indicated as the light reception result of the light receiving element 852R in the light detection data.

  Then, the heater controller 87 calculates the sheet passing speed at the axial end and the axial center, and further calculates a speed difference coefficient indicating the difference between these speeds (step S105).

  Specifically, the heater controller 87 divides the value of the recording material length of the recording material S by the value of the time difference between the passage timings of the leading and trailing ends of the recording material S at the left end in the axial direction. The sheet passing speed at the left end in the direction is calculated. Further, the heater controller 87 divides the recording material length of the recording material S by the value of the time difference between the passage timings of the leading end and the trailing end of the recording material S at the right end in the axial direction. Calculate the sheet passing speed. Further, the heater controller 87 calculates the sheet passing speed at the axial end by averaging the sheet passing speed at both axial ends.

  Also, the heater controller 87 divides the recording material length of the recording material S by the value of the time difference between the passage timings of the leading end and the trailing end of the recording material S at the axial central portion, thereby Calculate the sheet passing speed.

  The heater controller 87 calculates the speed difference by subtracting the sheet passing speed at the axial center from the sheet passing speed at the axial end, and further divides the speed difference by the process speed. The speed difference coefficient is calculated. That is, this speed difference coefficient is an index representing the ratio of the sheet passing speed at the axial end to the sheet passing speed at the axial center, and the axial end is faster than the axial center. The speed difference coefficient increases as the time increases.

  Then, the heater controller 87 compares the calculated speed difference coefficient with an upper limit value of a predetermined allowable range (step S106). If the calculated speed difference coefficient is equal to or lower than the upper limit value (S106: YES), the heater controller 87 compares the calculated speed difference coefficient with a lower limit value of a predetermined allowable range (step S107). ).

  Here, an appropriate value can be arbitrarily set for the upper limit value and the lower limit value to be compared with the speed difference coefficient. For example, according to the following Table 1 based on experimental data, image shift or edge gloss unevenness occurs when the speed difference coefficient is 0.27 or more, and wrinkle-like when the speed difference coefficient is −0.15 or less. Uneven gloss or paper wrinkles occur. On the other hand, an image defect does not occur within the intermediate range. Therefore, for example, 0.25 can be selected as the upper limit value, and -0.10 can be selected as the lower limit value.

  If the calculated speed difference coefficient is greater than or equal to the lower limit value (S107: YES), the heater controller 87 determines whether or not to end printing (step S108). When the heater controller 87 finishes printing (S108: YES), the heater controller 87 terminates heater control by shutting off the energization of all heaters (step S109). When the printing is continued (S108: NO), the process of the heater controller 87 returns to step S104.

When the calculated speed difference coefficient exceeds the upper limit value (S106: NO), the heater controller 87 selects another control mode for the inner central heater H1 (step S110). The control mode for the heaters other than the inner central heater H1 is the normal control mode determined in step S102. The control selected for the inner center heater H1 is on / off control based on the detected temperature of the center surface 814C. However, the duty D ₁ in the lighting period of the inner central heater H1, is corrected to 90% of the duty D ₂ of the inner end portion heater H2 to the dimming lighting state inside the central heater H1.

Here, by controlling the inner central heaters H1 90% duty D ₂ of the inner end heaters H2, it will be described in detail with reference to the control example shown in FIG.

In this control example, all the heaters are energized at 100% duty D ₁ , D ₂ , D ₃ , D ₄ until the time t11 when the control mode of the inner center heater H1 is switched, and all the lighting states are on. . Since the heaters other than the inner center heater H1 are in the normal control mode after the time t11, the set values of the duties D ₂ , D ₃ , and D ₄ during the lighting period remain 100%.

On the other hand, the inner central heaters H1, is switched control mode to the time t11, the duty _{D 1} of the inner central heaters H1 to this time, 90% of the duty _{D 2 (= 100 [%]} ), i.e. _D 1 = 100 [%] × 0.9 = 90 [%] is set.

As a result, the power supplied to the inner end heater H2 is maintained at 600 [W], while the power supplied to the inner central heater H1 is reduced from 900 [W] by ΔP ₁ [W]. That is, in order to reduce the ratio of the power supplied to the inner central heater H1 to the power supplied to the inner end heater H2, control is performed to reduce the power supplied to the inner central heater H1.

In other words, the heater controller 87 reduces the supply power of the inner central heater H1 disposed in the axial central portion in response to the axial central portion being excessively slowed with respect to the axial end portion. Identified as a power heater. The heater controller 87, the duty D ₁ of the inner central heater H1, corrected to a value that reduces the supply power.

  When the power supplied to the inner central heater H1 is reduced, the amount of heat transmitted from the inner central heater H1 to the central portion in the axial direction of the fixing roller 81 is reduced. Thereby, the thermal expansion of the central portion in the axial direction of the elastic layer 812 that is an intermediate layer of the fixing roller 81 is reduced. Therefore, the diameter of the central portion in the axial direction of the fixing roller 81 can be reduced to reduce the nip pressure in the central portion in the axial direction, and the rotation of the pressure belt 821 in the central portion in the axial direction can be smoothly performed. It is possible to slightly accelerate the sheet passing speed at the center in the direction. Then, the axial distribution of the sheet passing speed can be returned to an appropriate state.

The correction coefficient k [%] duty _{D 1} relative to the duty _{D 2} is in this embodiment is 90 [%], may arbitrarily determined within a range satisfying 0 <k <100. For example, the correction coefficient k may be gradually decreased as the number of prints increases cumulatively.

  Further, according to this control example, in response to the difference between the sheet passing speed at the end in the axial direction and the sheet passing speed at the center in the axial direction being below a predetermined level and deviating from the normal range, The power supplied to H1 is selectively reduced, and the ratio to the power supplied to the inner end heater H2 is reduced. That is, the heater controller 87 identifies the axial central portion, which is excessively slow compared to the axial end portion, as a region to be accelerated, and allows the inner central heater H1 disposed in this region to pass through. In order to increase the paper speed, control is performed to reduce the power supply. Therefore, the speed difference can be returned to the normal range while suppressing power consumption.

Furthermore, according to this control example, the inner central heaters H1 are the subject reduced electric power, the control mode switching to lower the set value of the duty D ₁ in the lighting period are performed. Therefore, it is possible to surely reduce the power supplied to the inner central heater H1.

Furthermore, according to this control example, the control mode of the inner central heater H1, is switched to the control mode is set lower than the duty cycle D ₂ of the duty D ₁ inner end heater H2 of the inner central heater H1. As a result, the ratio of the amount of heat applied to the axial center of the fixing roller 81 to the amount of heat applied to the axial end of the fixing roller 81 during the period when both the inner central heater H1 and the inner end heater H2 are lit. Can be lowered. Therefore, it is possible to delay the temperature rise in the axial central portion compared to the axial end portion, and to delay the thermal expansion of the axial central portion compared to the axial end portion.

Note that a temperature difference may occur between the axial central portion and the axial end due to a reduction in power supplied to the inner central heater H1, but the temperature that can be generated by simultaneous heating from the outer central heater H3. The difference can be minimized. At this time, the duty D ₃ of outer central heater H3 is to be maintained with duty D ₄ of the outer end heater H4 100%, it is possible to perform the surface temperature uniform in the entire axial direction efficiently. Further, since the heat from outside the fixing roller 81 is transmitted to the surface layer (release layer 813) of the fixing roller 81 without passing through the intermediate layer (elastic layer 812) of the fixing roller 81, the thermal expansion of the fixing roller 81 is performed. This is advantageous in that the surface temperature can be controlled without undue influence on the surface.

In this control example, the inner end heater H2 and the outer end heater H4 are not lit because the detected temperature of the end surface 814LR reaches the target temperature 170 ° C. at time t12. However, the detection temperature of the central surface 814C because even after the time t12 does not reach the target temperature 170 ° C., the inner central heaters H1 can maintain the lighting state at 90% duty D _1. Similarly, the outer central heater H3 can maintain the lighting state of 100% duty D _3.

  After step S110, the process of the heater controller 87 returns to step S104.

When the calculated speed difference coefficient is below the lower limit (S107: NO), the heater controller 87 selects another control mode for the inner end heater H2 (step S111). The control mode of the heaters other than the inner end heater H2 is the normal control mode determined in step S102. The control selected for the inner end heater H2 is on / off control based on the detected temperature of the end surface 814LR. However, the duty D ₂ in the lighting period of the inner end portion heaters H2, it is corrected to 90% of the duty D ₁ of the inner central heaters H1 to a dimming lighting state inner end heater H2.

Here, by controlling the inner end heaters H2 at 90% duty D ₁ of the inner central heater H1, it will be described in detail with reference to the control example shown in FIG.

In this control example, all the heaters are energized at 100% duty D ₁ , D ₂ , D ₃ , D ₄ until the time t21 when the control mode of the inner end heater H2 is switched, and all the lighting states are set. Yes. Since the heaters other than the inner end heater H2 are in the normal control mode after the time t21, the set values of the duties D ₁ , D ₃ , and D ₄ in the lighting period remain 100%.

On the other hand, the inner end heaters H2, the control mode is switched to the time t21, the duty _{D 2} of the inner end portion heater H2 in this case is 90% duty _{D 1 (= 100 [%]} ), i.e. _{D 2} = 100 [%] x 0.9 = 90 [%].

As a result, the power supplied to the inner central heater H1 is maintained at 900 [W], while the power supplied to the inner end heater H2 is reduced from 600 [W] by ΔP ₂ [W]. That is, in order to reduce the ratio of the power supplied to the inner end heater H2 to the power supplied to the inner central heater H1, control is performed to reduce the power supplied to the inner end heater H2.

In other words, the heater controller 87 reduces the power supplied to the inner end heater H2 disposed at the axial end in response to the axial end being excessively slowed with respect to the axial central portion. It is specified as a heater to be used. The heater controller 87, the duty D ₂ of the inner end heaters H2, is corrected to a value to reduce the supply power.

  When the power supplied to the inner end heater H2 is reduced, the amount of heat transmitted from the inner end heater H2 to the axial end of the fixing roller 81 is reduced. As a result, the thermal expansion of the axial end of the elastic layer 812 that is the intermediate layer of the fixing roller 81 is reduced. Accordingly, the diameter of the axial end of the fixing roller 81 can be reduced to reduce the nip pressure at the axial end, and the rotation of the pressure belt 821 at the axial end can be facilitated. The sheet passing speed at the direction end can be slightly accelerated. Then, the axial distribution of the sheet passing speed can be returned to an appropriate state.

Note that the correction coefficient k [%] of the duty D _{2 based on} the duty D ₁ is 90 [%] in the present embodiment, but may be arbitrarily determined within a range satisfying 0 <k <100. For example, the correction coefficient k may be gradually decreased as the number of prints increases cumulatively.

  Further, according to this control example, in response to the difference between the sheet passing speed at the axial end and the sheet passing speed at the axial center being below a predetermined level and deviating from the normal range, the inner end The power supplied to the heater H2 is selectively reduced, and the ratio to the power supplied to the inner central heater H1 is reduced. That is, the heater controller 87 identifies the axial end portion that is excessively slow compared to the axial central portion as a region to be accelerated, and with respect to the inner end heater H2 arranged in this region, Control is performed to reduce the power supply to increase the paper passing speed. Therefore, the speed difference can be returned to the normal range while suppressing power consumption.

Furthermore, according to this control example, with respect to the inner end heaters are the subject reduced electric power H2, the control mode switching to lower the set value of the duty D ₂ in the lighting period are performed. Therefore, it is possible to reliably realize a reduction in power supply to the inner end heater H2.

Furthermore, according to this control example, the control mode of the inner end portion heaters H2, is switched to a control mode for setting lower the duty D ₂ of the inner end portion heater H2 than the duty D ₁ of the inner central heater H1. As a result, the ratio of the amount of heat applied to the axial end of the fixing roller 81 to the amount of heat applied to the axial central portion of the fixing roller 81 during the period when both the inner central heater H1 and the inner end heater H2 are lit. Can be lowered. Therefore, it is possible to delay the temperature rise at the axial end compared to the axial central portion, and to delay the thermal expansion of the axial end compared to the axial central portion.

A temperature difference may occur between the axial center and the axial end due to a reduction in power supplied to the inner end heater H2, but this occurs due to simultaneous heating from the outer end heater H4. The temperature difference to be obtained can be minimized. At this time, the duty D ₄ of the outer end heater H4 are to be maintained at 100% with the duty D ₃ of outer central heater H3, it is possible to perform the surface temperature uniform in the entire axial direction efficiently. Further, since the heat from outside the fixing roller 81 is transmitted to the surface layer (release layer 813) of the fixing roller 81 without passing through the intermediate layer (elastic layer 812) of the fixing roller 81, the thermal expansion of the fixing roller 81 is performed. This is advantageous in that the surface temperature can be controlled without undue influence on the surface.

  After step S111, the process of the heater controller 87 returns to step S104.

  In this way, the heater control during the sheet passing operation can be executed.

  In this embodiment, the speed difference coefficient is compared with a predetermined upper limit value (S106) to detect an abnormality in the speed difference, but the speed difference coefficient is referred to by referring to the calculation history of the speed difference coefficient. It may be determined whether or not has significantly increased compared to the past.

  In the present embodiment, the speed difference coefficient is compared with a predetermined lower limit value (S107) to detect the speed difference abnormality. The speed difference coefficient is referred to by referring to the calculation history of the speed difference coefficient. It may be determined whether or not has been significantly reduced compared to the past.

  Here, the result of examining the occurrence / non-existence of an image defect will be described.

  Table 2 below shows a comparison of the operation results in Example 1 and the operation results in Comparative Example 1. The configuration and operation conditions of Example 1 are the same as those described in this embodiment. It is assumed that the fixing roller 81 has a straight shape and has no design variation. The configuration and operation conditions of Comparative Example 1 differ from Example 1 only in that the duty correction of the lighting period is not performed.

  Here, it was confirmed that gloss unevenness occurs in Comparative Example 1 when the number of prints exceeds 300000 and the speed difference coefficient deviates from the normal range (exceeds the upper limit of 0.25). On the other hand, in Example 1, it was confirmed that due to the duty correction, the speed difference coefficient is returned to the normal range even if any change such as aging of parts occurs, and no image defect occurs.

  Table 3 below shows a comparison of the operation results in Example 2 and the operation results in Comparative Example 2. The configuration and operation conditions of Example 2 are the same as those described in this embodiment. It is assumed that the fixing roller 81 has a crown shape and has design variations. The configuration and operation conditions of Comparative Example 2 differ from Example 2 only in that the duty correction of the lighting period is not performed.

  Here, the speed difference coefficient has deviated from the normal range from the start of printing due to design variation (below the lower limit value −0.10). In Comparative Example 2, it was confirmed that uneven gloss occurred until the 150,000th print in which the speed difference coefficient returned to the normal range. On the other hand, in Example 2, it was confirmed that due to the duty correction, the speed difference coefficient was returned to the normal range in spite of design variations, and no image defect occurred.

  As described above, according to the present embodiment, the sheet passing speeds at the axial center and the axial end are acquired, and the inner center heater H1 and the inner end heater H2 are obtained according to these sheet passing speeds. The power supplied to the outer central heater H3 and the outer end heater H4 is individually controlled. Therefore, the thermal expansion of the fixing roller 81 can be changed according to the individual adjustment of the power supplied to each heater, the sheet passing speed can be corrected and the axial distribution thereof can be optimized, and the recording material passing through the fixing nip portion N can be obtained. The slackness of S can be prevented. As a result, it is possible to suppress the occurrence of various image defects related to recording material conveyance, such as paper wrinkles, undulations, ribs, gloss unevenness, and image misalignment. Since slackness during conveyance is a phenomenon that is likely to occur in thin paper having a relatively low tension, it is particularly effective to apply this embodiment to printing on thin paper.

(Embodiment 2)
The second embodiment of the present invention will be described below. The image forming apparatus according to the present embodiment has the same basic configuration as that described in the first embodiment. Therefore, the same components as those described in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. In the present embodiment, the description will focus on the parts that are different from the first embodiment.

  This embodiment is different from the first embodiment in that a setting panel for adjusting the heater power can be displayed on the screen of the operation display unit 2 as an operation unit.

  FIG. 7 is a diagram illustrating an example of a setting panel displayed on the screen of the operation display unit 2.

  A setting panel SP1 shown in FIG. 7 is a setting panel for user instruction input of the heater power adjustment level. The user touches the level indicator LI in the setting panel SP1 on the screen, or moves the pointer P in the setting panel SP1 on the screen by using an operation button provided on the operation display unit 2, thereby heating the heater. A power adjustment level can be specified. This user instruction data is input to the heater controller 87. As shown in FIG. 8, the heater controller 87 reads a correction coefficient k corresponding to a user-indicated number from a previously stored table TA. When the control for reducing the power supplied to any one of the heaters is necessary, the read correction coefficient k is used.

  FIG. 9 is a diagram illustrating another example of the setting panel displayed on the screen of the operation display unit 2.

A setting panel SP2 shown in FIG. 9 is a setting panel for user instruction input of the heater power adjustment level. The user can increase or decrease the value of the level indicator LI displayed for each heater in the setting panel SP2 on the screen using the up button UB and the down button DB. This user instruction data is input to the heater controller 87. The heater controller 87 controls the power supplied to each heater according to the specified value. The value specified here may be used as the duty D ₁ , D ₂ , D ₃ , D ₄ , or may be a value indicating the ratio of the supplied power to the rated power of each heater, It may be another value that can be used for supply power control.

  Thus, according to the present embodiment, the user can designate the heater power adjustment level using the setting panels SP1 and SP2. Therefore, the image correction by heater control can be performed by the user's intention, and the user's preference can be reflected in the image correction intensity and the like.

(Embodiment 3)
The third embodiment of the present invention will be described below. The image forming apparatus according to the present embodiment has the same basic configuration as that described in the first embodiment. Therefore, the same components as those described in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. In the present embodiment, the description will focus on the parts that are different from the first embodiment.

  The present embodiment is different from the first embodiment in that the fixing unit 8 has a configuration in which a fixing nip portion is formed by pressure contact of a roller pair.

  FIG. 10 is a diagram illustrating an internal configuration of the fixing unit 8 according to the present embodiment. In the fixing unit 8 shown in FIG. 10, the pressing unit 82 includes a pressing roller 826 that presses against the fixing roller 81 to form a fixing nip N.

  Similar to the fixing roller 81, the pressure roller 826 as a pressure rotator has a cylindrical cored bar 827, an elastic layer 828, and a release layer 829. The pressure roller 826 is rotatably supported at both ends in the longitudinal direction (axial direction) and is urged toward the fixing roller 81 by an urging member (not shown). The cylindrical cored bar 827 is a cylindrical body made of a metal such as aluminum. The elastic layer 828 is a layer made of an elastic material such as HTV silicone rubber having high heat resistance and covering the cylindrical cored bar 827. The release layer 829 is a layer made of a resin such as PFA or PTFE that covers the elastic layer 828.

  The positional relationship between the pressure roller 826 and the fixing roller 81 in the axial direction is the same as the positional relationship between the fixing roller 81 and the pressure belt 821 shown in FIG.

  FIG. 11 is a flowchart for explaining heater control during the sheet passing operation according to the present embodiment.

When the speed difference coefficient calculated in step S105 exceeds the upper limit value (S106: NO), the heater controller 87 selects another control mode for the inner end heater H2 (step S210). The control mode of the heaters other than the inner end heater H2 is the normal control mode determined in step S102. The control selected for the inner end heater H2 is on / off control based on the detected temperature of the end surface 814LR. However, the duty D ₂ in the lighting period of the inner end portion heaters H2, it is corrected to 90% of the duty D ₁ of the inner central heaters H1 to a dimming lighting state inner end heater H2.

The control example for controlling the inner end heaters H2 at 90% duty D ₁ of the inner central heater H1, shown in FIG. 6 described in the first embodiment.

In this control example, while the set values of the duties D ₁ , D ₃ and D ₄ are maintained at 100%, the duty D ₂ is 90% of the duty D ₁ (= 100 [%]), that is, D ₂ = 100 [%] × 0.9 = 90 [%] is set.

As a result, the power supplied to the inner central heater H1 is maintained at 900 [W], while the power supplied to the inner end heater H2 is reduced from 600 [W] by ΔP ₂ [W]. That is, in order to reduce the ratio of the power supplied to the inner end heater H2 to the power supplied to the inner central heater H1, control is performed to reduce the power supplied to the inner end heater H2.

In other words, the heater controller 87 reduces the power supplied to the inner end heater H2 disposed at the end in the axial direction in response to the excessive increase in the speed in the axial end with respect to the axial center. It is specified as a heater to be used. The heater controller 87, the duty D ₂ of the inner end heaters H2, is corrected to a value to reduce the supply power.

  When the power supplied to the inner end heater H2 is reduced, the amount of heat transmitted from the inner end heater H2 to the axial end of the fixing roller 81 is reduced. As a result, the thermal expansion of the axial end of the elastic layer 812 that is the intermediate layer of the fixing roller 81 is reduced. Accordingly, the axial end portion of the fixing roller 81 can be reduced in diameter to reduce the nip pressure at the axial end portion, and the force for sandwiching the recording material S between the fixing roller 81 and the pressure roller 826 can be suppressed. The sheet passing speed at the axial end can be slightly reduced. Then, the axial distribution of the sheet passing speed can be returned to an appropriate state.

Note that the correction coefficient k [%] of the duty D _{2 based on} the duty D ₁ is 90 [%] in the present embodiment, but may be arbitrarily determined within a range satisfying 0 <k <100. For example, the correction coefficient k may be gradually decreased as the number of prints increases cumulatively.

  Further, according to this control example, in response to the difference between the sheet passing speed at the axial end and the sheet passing speed at the axial center being below a predetermined level and deviating from the normal range, the inner end The power supplied to the heater H2 is selectively reduced, and the ratio to the power supplied to the inner central heater H1 is reduced. That is, the heater controller 87 identifies the axial end portion that is excessively faster than the axial central portion as a region to be decelerated, and with respect to the inner end heater H2 disposed in this region, Control is performed to reduce the power supply in order to reduce the sheet passing speed. Therefore, the speed difference can be returned to the normal range while suppressing power consumption.

Furthermore, according to this control example, with respect to the inner end heaters are the subject reduced electric power H2, the control mode switching to lower the set value of the duty D ₂ in the lighting period are performed. Therefore, it is possible to reliably realize a reduction in power supply to the inner end heater H2.

Furthermore, according to this control example, the control mode of the inner end portion heaters H2, is switched to a control mode for setting lower the duty D ₂ of the inner end portion heater H2 than the duty D ₁ of the inner central heater H1. As a result, the ratio of the amount of heat applied to the axial end of the fixing roller 81 to the amount of heat applied to the axial central portion of the fixing roller 81 during the period when both the inner central heater H1 and the inner end heater H2 are lit. Can be lowered. Therefore, it is possible to delay the temperature rise at the axial end compared to the axial central portion, and to delay the thermal expansion of the axial end compared to the axial central portion.

A temperature difference may occur between the axial center and the axial end due to a reduction in power supplied to the inner end heater H2, but this occurs due to simultaneous heating from the outer end heater H4. The temperature difference to be obtained can be minimized. At this time, the duty D ₄ of the outer end heater H4 are to be maintained at 100% with the duty D ₃ of outer central heater H3, it is possible to perform the surface temperature uniform in the entire axial direction efficiently. Further, since the heat from outside the fixing roller 81 is transmitted to the surface layer (release layer 813) of the fixing roller 81 without passing through the intermediate layer (elastic layer 812) of the fixing roller 81, the thermal expansion of the fixing roller 81 is performed. This is advantageous in that the surface temperature can be controlled without undue influence on the surface.

  After step S210, the process of the heater controller 87 returns to step S104.

When the speed difference coefficient calculated in step S105 is below the lower limit value (S107: NO), the heater controller 87 selects another control mode for the inner central heater H1 (step S211). The control mode for the heaters other than the inner central heater H1 is the normal control mode determined in step S102. The control selected for the inner center heater H1 is on / off control based on the detected temperature of the center surface 814C. However, the duty D ₁ in the lighting period of the inner central heater H1, is corrected to 90% of the duty D ₂ of the inner end portion heater H2 to the dimming lighting state inside the central heater H1.

The control example for controlling the inner central heaters H1 90% duty D ₂ of the inner end heaters H2, shown in Figure 5 described in the first embodiment.

In this control example, while the set values of the duties D ₂ , D ₃ , and D ₄ are maintained at 100%, the duty D ₁ is 90% of the duty D ₂ (= 100 [%]), that is, D ₁ = 100 [%] × 0.9 = 90 [%] is set.

As a result, the power supplied to the inner end heater H2 is maintained at 600 [W], while the power supplied to the inner central heater H1 is reduced from 900 [W] by ΔP ₁ [W]. That is, in order to reduce the ratio of the power supplied to the inner central heater H1 to the power supplied to the inner end heater H2, control is performed to reduce the power supplied to the inner central heater H1.

In other words, the heater controller 87 reduces the supply power of the inner central heater H1 disposed in the axial central portion in response to the excessive increase in the axial central portion with respect to the axial end portion. Identified as a power heater. The heater controller 87, the duty D ₁ of the inner central heater H1, corrected to a value that reduces the supply power.

  When the power supplied to the inner central heater H1 is reduced, the amount of heat transmitted from the inner central heater H1 to the central portion in the axial direction of the fixing roller 81 is reduced. Thereby, the thermal expansion of the central portion in the axial direction of the elastic layer 812 that is an intermediate layer of the fixing roller 81 is reduced. Accordingly, the diameter of the central portion in the axial direction of the fixing roller 81 can be reduced to reduce the nip pressure in the central portion in the axial direction, and the force for pinching the recording material S between the fixing roller 81 and the pressure roller 826 can be suppressed. Thus, the sheet passing speed in the central portion in the axial direction can be slightly reduced. Then, the axial distribution of the sheet passing speed can be returned to an appropriate state.

The correction coefficient k [%] duty _{D 1} relative to the duty _{D 2} is in this embodiment is 90 [%], may arbitrarily determined within a range satisfying 0 <k <100. For example, the correction coefficient k may be gradually decreased as the number of prints increases cumulatively.

  Further, according to this control example, in response to the difference between the sheet passing speed at the end in the axial direction and the sheet passing speed at the center in the axial direction being below a predetermined level and deviating from the normal range, The power supplied to H1 is selectively reduced, and the ratio to the power supplied to the inner end heater H2 is reduced. That is, the heater controller 87 identifies the axial central portion, which is excessively faster than the axial end portion, as a region to be decelerated, and allows the inner central heater H1 disposed in this region to pass through. In order to slow down the paper speed, control is performed to reduce the power supply. Therefore, the speed difference can be returned to the normal range while suppressing power consumption.

Furthermore, according to this control example, the inner central heaters H1 are the subject reduced electric power, the control mode switching to lower the set value of the duty D ₁ in the lighting period are performed. Therefore, it is possible to surely reduce the power supplied to the inner central heater H1.

Furthermore, according to this control example, the control mode of the inner central heater H1, is switched to the control mode is set lower than the duty cycle D ₂ of the duty D ₁ inner end heater H2 of the inner central heater H1. As a result, the ratio of the amount of heat applied to the axial center of the fixing roller 81 to the amount of heat applied to the axial end of the fixing roller 81 during the period when both the inner central heater H1 and the inner end heater H2 are lit. Can be lowered. Therefore, it is possible to delay the temperature rise in the axial central portion compared to the axial end portion, and to delay the thermal expansion of the axial central portion compared to the axial end portion.

Note that a temperature difference may occur between the axial central portion and the axial end due to a reduction in power supplied to the inner central heater H1, but the temperature that can be generated by simultaneous heating from the outer central heater H3. The difference can be minimized. At this time, the duty D ₃ of outer central heater H3 is to be maintained with duty D ₄ of the outer end heater H4 100%, it is possible to perform the surface temperature uniform in the entire axial direction efficiently. Further, since the heat from outside the fixing roller 81 is transmitted to the surface layer (release layer 813) of the fixing roller 81 without passing through the intermediate layer (elastic layer 812) of the fixing roller 81, the thermal expansion of the fixing roller 81 is performed. This is advantageous in that the surface temperature can be controlled without undue influence on the surface.

  After step S211, the process of the heater controller 87 returns to step S104.

  In this way, the heater control during the sheet passing operation can be executed.

  As described above, the configuration of the present embodiment is different from the configuration of the belt nip method (Embodiment 1) in that the fixing nip portion N is formed by the pressure contact between the fixing roller 81 and the pressure roller 826. . However, according to the heater control of the present embodiment, as in the first embodiment, the thermal expansion of the fixing roller 81 is changed in accordance with the individual control of the power supplied to each heater, and the sheet passing speed is corrected to correct its axial direction. The distribution can be optimized, and the slack of the recording material S passing through the fixing nip N can be prevented. As a result, it is possible to suppress the occurrence of various image defects related to recording material conveyance, such as paper wrinkles, undulations, ribs, gloss unevenness, and image misalignment.

  Note that this embodiment mode can be implemented in combination with Embodiment Mode 2.

  The embodiments of the present invention have been described above. The above description is an illustration of a preferred embodiment of the present invention, and the scope of the present invention is not limited to this. That is, the description of the configuration and operation of each of the above devices is an example, and it is obvious that various modifications and additions to these examples are possible within the scope of the present invention.

A Image forming apparatus HI Internal heater HO External heater H1 Inner center heater H2 Inner end heater H3 Outer center heater H4 Outer end heater 2 Operation display unit 4Y, 4M, 4C, 4K Image forming unit 8 Fixing unit 81 Fixing roller 82 Addition Pressure part 83 Heat transfer part 84 Temperature sensor 84L, 84C, 84R Temperature detection element 85 Paper passing sensor 86, 861 to 864 Heater driver 87 Heater controller 814L Left end surface 814C Central surface 814R Right end surface 821 Pressure belt 825 Press pad 826 Pressure roller 851 Light emitting part 851L, 851C, 851R Light emitting element 852 Light receiving part 852L, 852C, 852R Light receiving element

Claims (11)

A heating rotator for heating the recording material;
A pressure rotator that presses against the heating rotator to form a fixing nip portion with the heating rotator; and
A plurality of heating units that receive power supply and heat the heating rotator for each of a plurality of regions divided in the axial direction of the heating rotator;
A drive unit that individually supplies power to each of the plurality of heating units;
A detection unit for detecting the moving speed of the recording material at a plurality of positions corresponding to the plurality of regions;
A control unit that controls power supply to each heating unit of the drive unit based on the detected moving speed of the recording material at the plurality of positions;
A fixing device.   The control unit obtains a movement speed difference between the plurality of positions based on the detected movement speed of the recording material at the plurality of positions, and based on the obtained movement speed difference, the plurality of heating units. The fixing device according to claim 1, wherein a heating unit whose supply power is to be changed is specified.   The control unit performs control to reduce power supplied to the heating unit in a region corresponding to a position where the moving speed of the recording material is excessively low or excessive when the obtained moving speed difference is out of a predetermined range. The fixing device according to claim 2.   The fixing device according to claim 2, wherein the control unit corrects a control parameter that affects power supplied to the identified heating unit.   The fixing device according to claim 4, wherein the control parameter is a duty ratio or a peak value of a driving voltage. The pressure rotator includes an endless belt that is rotatably mounted and is pressed from a pressing member and presses against the heating rotator.
The control unit obtains a moving speed difference between the plurality of positions based on the detected moving speed of the recording material at the plurality of positions, and based on the obtained moving speed difference, The fixing device according to claim 1, wherein control is performed to accelerate the moving speed of the recording material at any position. The pressure rotator includes a roller in pressure contact with the heating rotator,
The control unit obtains a moving speed difference between the plurality of positions based on the detected moving speed of the recording material at the plurality of positions, and based on the obtained moving speed difference, The fixing device according to claim 1, wherein control is performed to reduce a moving speed of the recording material at any position.   The fixing device according to claim 1, wherein the detection unit detects a recording material passing through the fixing nip portion, and calculates a moving speed of the recording material at the plurality of positions based on the detection result. A temperature detection unit for detecting the surface temperature of the heating rotating body;
The plurality of heating units include an internal heating unit disposed inside the heating rotator, and an external heating unit disposed outside the heating rotator,
The control unit controls power supply to the internal heating unit based on the detected moving speed of the recording material while controlling the internal heating unit and the external heating unit based on the detected surface temperature. Item 4. The fixing device according to Item 1. An image forming unit for forming a toner image on a recording material;
The fixing device according to claim 1, wherein the formed toner image is fixed to a recording material;
An image forming apparatus. It further has an operation unit for performing an input operation of a user instruction,
The image forming apparatus according to claim 10, wherein the control unit performs control according to the acquired moving speed in accordance with a user instruction input by the operation unit.

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