JP2018106211A - Fixation device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device capable of intensively and stably heating a paper passing area to achieve the improvement of fixation quality and the energy saving.SOLUTION: A fixation device of an embodiment of the present invention includes: determination means for determining the size of a medium having a toner image formed thereon; a rotor having an endless shape; a plurality of heat generating members which have the same length in the medium conveyance direction, are separated into various lengths in the direction perpendicular to the conveyance direction, are adjusted so as to have an even temperature rise rate with respect to the same applied voltage, and are disposed to contact with the inside of the rotor; and a switching part for individually switching the electrification of these heat generating members. The fixation device comprises: heating means for heating a medium; pressure means that comes into pressure contact with the heating means at the positions of the plurality of heat generating members to form a nip, and holds and conveys together with the heating means the medium in the conveyance direction; and heating control means for selecting by the switching part a heat generating member among the plurality of heat generating members, corresponding to a position where a medium passes, and electrifying the heat generating member to control the heating.SELECTED DRAWING: Figure 9

Description

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

  As a heat source of a fixing device mounted in an image forming apparatus, a lamp emitting infrared rays such as a halogen lamp or a method of heating with Joule heat by electromagnetic induction has been put into practical use.

  Generally, a fixing device is composed of a pair of a heating roller (or a fixing belt stretched between a plurality of rollers) and a press roller. In order to maximize the thermal efficiency of the fixing device, the heat capacity of the components is reduced as much as possible. In addition, it is required to concentrate the heating region.

Japanese Patent No. 2629980

  In the above heating method, since the heating width is wide, it is difficult to concentrate the heat energy dispersed over a wide range only on the nip portion, and it is difficult to optimize the thermal efficiency. Also, in the electrophotographic fixing device, if uneven heat generation occurs in a direction perpendicular to the paper conveyance direction, the fixing quality is affected. In particular, in the case of color printing, there may be a difference in color development and gloss.

  Further, in a fixing device with an extremely reduced heat capacity, the temperature of the portion where the paper does not pass rises extremely, which may cause problems such as heater warpage, belt deterioration, and speed unevenness due to expansion of the conveying roller. It was. In addition, it is not preferable to heat the portion through which the paper does not pass from the viewpoint of energy saving. Concentrated heating of only the portion through which the paper passes is an important technical issue from the viewpoint of environmental friendliness.

  For this reason, it has been proposed to divide and control the heat generating area. However, when the heat generating area is divided, there is a problem in that the temperature rise rate varies between the areas and causes temperature unevenness. Arise.

  SUMMARY OF THE INVENTION In view of the above-described problems of the prior art, an object of the present invention is to enable concentrated and stable heating of a sheet passing area, and to improve fixing quality and save energy.

  In the fixing device according to the embodiment, the determination unit that determines the size of the medium on which the toner image is formed, the endless rotating body, and the length in the conveyance direction of the medium are the same, and the conveyance direction And a plurality of heat generating members arranged in contact with the inside of the rotating body, wherein the temperature rise rate with respect to the same applied voltage is uniformly adjusted, and the heat generation thereof. A switching unit that individually switches energization to the member, and a heating unit that heats the medium, and press-contacts the heating unit at the positions of the plurality of heating members to form a nip, and the medium together with the heating unit The switching unit selects and applies power to a pressure member that is nipped and conveyed in the conveying direction and a heat generating member corresponding to a position through which the medium passes among the plurality of heat generating members. Characterized in that it comprises a heating control means for controlling the.

1 is a diagram illustrating a configuration example of an image forming apparatus in which a fixing device according to an embodiment is mounted. FIG. 2 is a configuration diagram illustrating an enlarged part of an image forming unit according to an embodiment. FIG. 2 is a block diagram illustrating a configuration example of a control system of the MFP according to an embodiment. 1 is a diagram illustrating a configuration example of a fixing device according to an embodiment. FIG. FIG. 3 is a layout view of a heat generating member group in one embodiment. Sectional drawing of the heat generating member group in the broken line X shown in FIG. The figure which shows the connection state of the heat generating member group and its drive circuit in one Embodiment. 6 is a flowchart illustrating a specific example of an MFP control operation according to an embodiment. The figure which shows the connection state of the heat generating member group in the modification of one Embodiment, and its drive circuit. The figure which shows the shape pattern of the heat generating member group in the modification of one Embodiment.

  Hereinafter, a fixing device according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating a configuration example of an image forming apparatus in which a fixing device according to the present embodiment is mounted. In FIG. 1, an image forming apparatus 10 is, for example, an MFP (Multi-Function Peripherals), a printer, a copier, or the like, which is a multifunction peripheral. In the following description, an MFP will be described as an example.

  A transparent glass platen 12 is provided above the main body 11 of the MFP 10, and an automatic document feeder (ADF) 13 is provided on the platen 12 so as to be freely opened and closed. An operation unit 14 is provided on the upper portion of the main body 11. The operation unit 14 includes various keys and a touch panel display.

  A scanner unit 15 serving as a reading device is provided below the ADF 13 in the main body 11. The scanner unit 15 generates image data by reading a document sent by the ADF 13 or a document placed on a document table, and includes a contact image sensor 16 (hereinafter simply referred to as an image sensor). The image sensor 16 is arranged in the main scanning direction (the depth direction in FIG. 1).

  When reading the image of the document placed on the document table 12, the image sensor 16 reads the document image line by line while moving along the document table 12. This is executed over the entire document size, and one page of document is read. Further, when reading an image of a document sent by the ADF 13, the image sensor 16 is in a fixed position (position shown in the drawing).

  Further, a printer unit 17 is provided at the center of the main body 11, and a plurality of paper feed cassettes 18 for storing various sizes of paper P are provided at the bottom of the main body 11.

  The printer unit 17 processes image data read by the scanner unit 15 or image data created by a personal computer or the like to form an image on a sheet. The printer unit 17 is a tandem color laser printer, for example, and includes image forming units 20Y, 20M, 20C, and 20K for each color of yellow (Y), magenta (M), cyan (C), and black (K). The image forming units 20Y, 20M, 20C, and 20K are arranged below the intermediate transfer belt 21 in parallel from upstream to downstream. The laser exposure unit (scanning head) 19 also has a plurality of laser exposure units 19Y, 19M, 19C, and 19K corresponding to the image forming units 20Y, 20M, 20C, and 20K.

  FIG. 2 is an enlarged configuration diagram illustrating the image forming unit 20K among the image forming units 20Y, 20M, 20C, and 20K. In the following description, since the image forming units 20Y, 20M, 20C, and 20K have the same configuration, the image forming unit 20K will be described as an example.

    The image forming unit 20K includes a photosensitive drum 22K that is an image carrier. Around the photosensitive drum 22K, a charger (charging charger) 23K, a developing device 24K, a primary transfer roller (transfer device) 25K, a cleaner 26K, a blade 27K, and the like are arranged along the rotation direction t. The exposure position of the photosensitive drum 22K is irradiated with light from the laser exposure device 19K, and an electrostatic latent image is formed on the photosensitive drum 22K.

    The charger 23K of the image forming unit 20K uniformly charges the surface of the photosensitive drum 22K. The developing device 24K supplies a two-component developer containing black toner and a carrier to the photosensitive drum 22K by a developing roller 24a to which a developing bias is applied, and develops the electrostatic latent image. The cleaner 26K removes residual toner on the surface of the photosensitive drum 22K using the blade 27K.

    As shown in FIG. 1, a toner cartridge 28 that supplies toner to the developing devices 24Y to 24K is provided above the image forming units 20Y to 20K. The toner cartridge 28 includes toner cartridges of yellow (Y), magenta (M), cyan (C), and black (K).

    The intermediate transfer belt 21 moves cyclically. The intermediate transfer belt 21 is stretched around a driving roller 31 and a driven roller 32. The intermediate transfer belt 21 is in contact with the photosensitive drums 22Y to 22K. A primary transfer voltage is applied to the position of the intermediate transfer belt 21 facing the photosensitive drum 22K by the primary transfer roller 25K, and the toner image on the photosensitive drum 22K is primarily transferred to the intermediate transfer belt 21.

    A secondary transfer roller 33 is disposed opposite to the drive roller 31 that stretches the intermediate transfer belt 21. When the paper P passes between the drive roller 31 and the secondary transfer roller 33, a secondary transfer voltage is applied by the secondary transfer roller 33. Then, the toner image on the intermediate transfer belt 21 is secondarily transferred to the paper P. A belt cleaner 34 is provided near the driven roller 32 of the intermediate transfer belt 21.

    Further, as shown in FIG. 1, a paper feed roller 35 for conveying the paper P taken out from the paper feed cassette 18 is provided between the paper feed cassette 18 and the secondary transfer roller 33. Further, a fixing device 36 is provided downstream of the secondary transfer roller 33. Further, a conveyance roller 37 is provided downstream of the fixing device 36. The conveyance roller 37 discharges the paper P to the paper discharge unit 38. Further, a reverse conveyance path 39 is provided downstream of the fixing device 36. The reverse conveyance path 39 reverses the paper P and guides it in the direction of the secondary transfer roller 33, and is used when performing duplex printing. 1 and 2 show examples of the configuration of the MFP 10, and the structure of the image forming apparatus other than the fixing device 36 is not limited. The structure of a known electrophotographic image forming apparatus can be used.

  FIG. 3 is a block diagram illustrating a configuration example of the control system 50 of the MFP 10 in the present embodiment. The control system 50 includes, for example, a CPU 100 that controls the entire MFP 10, a read only memory (ROM) 120, a random access memory (RAM) 121, an interface (I / F) 122, an input / output control circuit 123, a paper feed / conveyance control circuit. 130, an image formation control circuit 140, and a fixing control circuit 150.

    The CPU 100 realizes a processing function for image formation by executing a program stored in the ROM 120 or the RAM 121. The ROM 120 stores a control program and control data for performing basic operations of the image forming process. The RAM 121 is a working memory. The ROM 120 (or RAM 121) stores, for example, control programs such as the image forming unit 20 and the fixing device 36 and various control data used by the control programs. As a specific example of the control data in the present embodiment, there is a correspondence relationship between the sheet passing area and the size of the printing area in the sheet (width in the main scanning direction) and the heating member to be energized.

  The fixing temperature control program of the fixing device 36 includes a determination logic for determining the size of the image forming area in the paper on which the toner image is formed, and the paper passing area of the paper before the paper is conveyed into the fixing device 36. And a heating control logic for selecting and switching the corresponding switching element of the heat generating member and controlling the heating in the heating means.

    The I / F 122 performs communication with various apparatuses such as a user terminal and a facsimile. The input / output control circuit 123 controls the operation panel 123 a and the display unit 123 b that constitute the operation unit 14. The paper feed / conveyance control circuit 130 controls a group of motors 130a that drive the paper feed roller 35 or the conveyance roller 37 in the conveyance path. The paper feed / conveyance control circuit 130 controls the motor group 130a and the like in consideration of detection results of various sensors 130b in the vicinity of the paper feed cassette 18 or on the conveyance path based on a control signal from the CPU 100. The image formation control circuit 140 controls the photosensitive drum 22, the charger 23, the laser exposure device 19, the developing device 24, and the transfer device 25 based on a control signal from the CPU 100. The fixing control circuit 150 controls the driving motor 360 of the fixing device 36, the heating member 361, and the temperature detection member 362 such as the thermistor based on the control signal from the CPU 100. In the present embodiment, the control program and control data of the fixing device 36 are stored in the storage device of the MFP 10 and executed by the CPU 100. However, the arithmetic processing device and the storage device are separately provided exclusively for the fixing device 36. May be.

  FIG. 4 is a diagram illustrating a configuration example of the fixing device 36. Here, the fixing device 36 is formed with a plate-like heating member 361, an elastic layer, an endless belt 363 suspended from a plurality of rollers, a belt conveying roller 364 for driving the endless belt 363, and an endless belt 363. A tension roller 365 and a press roller 366 having an elastic layer formed on the surface thereof are provided. The heating member 361 is in contact with the inside of the endless belt 363 on the heat generating portion side and is pressed in the direction of the press roller 366, thereby forming a fixing nip having a predetermined width with the press roller 366. Since the heating member 361 heats while forming the nip region, the responsiveness at the time of energization is higher than in the case of the heating method using a halogen lamp.

  The endless belt 363 has, for example, a silicon rubber layer having a thickness of 200 μm formed on the outer surface of a polyimide that is a 50 μm thick SUS base material or a 70 μm heat-resistant resin, and the outermost periphery is covered with a surface protective layer such as PFA. . In the press roller 366, for example, a silicon sponge layer having a thickness of 5 mm is formed on the surface of an iron rod having a diameter of 10 mm, and the outermost periphery is covered with a surface protective layer such as PFA.

Further, the heating member 361 has a glaze layer and a heating resistance layer laminated on a ceramic substrate. In order to release excess heat to the opposite side and prevent the substrate from warping, the heating resistance layer is formed of a known material such as TaSiO ₂ and is divided into a predetermined length and number in the main scanning direction.

The method for forming the heat generating resistance layer is the same as a known method (for example, a method for producing a thermal head), and a masking layer is formed of aluminum on the heat generating resistance layer. An aluminum layer is formed in a pattern that insulates adjacent heating members and exposes heating resistors (heating members) in the paper transport direction. To energize the heat generating member 361a, wiring is connected from the aluminum layers (electrodes) at both ends, and each is connected to the switching element of the switching driver IC. Furthermore, a protective layer is formed on the top so as to cover all of the heating resistor, the aluminum layer, the wiring, and the like. The protective layer is formed of, for example, Si ₃ N ₄ or the like.

  FIG. 5 is a layout view of the heat generating member group in the present embodiment. As shown in the figure, on the ceramic substrate 361c, a plurality of types of heat generating members 361a in the horizontal direction shown in the figure are arranged side by side, and both end portions of the heat generating member 361a in the paper transport direction (the vertical direction shown in the drawing). An electrode 361b is formed on the substrate. In order to make the heating time (paper passing time) by each heat generating member 361a constant, the length of the heat generating member 361a in the paper transport direction is uniform.

  As shown in FIG. 5, in the present embodiment, the heat generation pattern of the heating member 361 is configured by a plurality of types of heat generation members 361 a having a length in the horizontal direction in the drawing. Specifically, a plurality of lengths of heat generating members corresponding to postcard size (100 × 148 mm), CD jacket size (121 × 121 mm), B5R size (182 × 257 mm), A4R size (210 × 297 mm) ( Heating element) 361a. The heat generating member group composed of the adjacent heat generating members 361a has a margin of about 5% or about 10 mm with respect to the heating area in consideration of the conveyance accuracy of the conveyed paper, skew and escape of heat to the non-heated portion. So that it is energized.

  For example, in order to correspond to a postcard size width of 100 mm, which is the minimum size, a first heating member group is provided at the center in the main scanning direction (the left-right direction in the figure), and the width is 105 mm. In order to correspond to the next largest size of 121 mm and 148 mm, a second heat generating member group having a width of 50 mm is provided outside the first heat generating member group (in the left-right direction in the figure) to cover a width of 148 mm + 5% up to 155 mm. In order to correspond to the larger sizes 182 mm and 210 mm, a third heat generating member group having a width of 65 mm is provided on the outer side of the second heat generating member group to cover a width of 210 mm + 5% up to 220 mm. . In addition, the division | segmentation number and each width | variety of a heat generating member group are mentioned as an example, and are not limited to this. For example, when the MFP 10 supports five medium sizes, the heat generating member group may be divided into five according to each medium size.

  In the present embodiment, it is assumed that a line sensor (not shown) is arranged in the sheet passing area so that the size and position of the passing sheet can be determined in real time. A configuration may be adopted in which the paper size is determined from the image data or information in the paper feed cassette 18 in which the paper in the MFP 10 is stored at the start of the printing operation.

  Further, as shown in FIG. 5, when energizing all of the plurality of heat generating members 361a under the same conditions, the heat generation amount ( Power consumption) may be different and it is difficult to heat uniformly.

  Therefore, in the present embodiment, at least one of (1) the thickness of each heat generating member 361a, (2) the length between the power supply portions (electrodes 361b) of the heat generating pattern, and (3) the specific resistance of the heat generating member 361a. Is optimally adjusted so that the amount of heat generated is uniform. You may combine the adjustment by (1)-(3) suitably. For example, the length of the heat generating member 361a in the paper transport direction is made the same, and the output W of the heat generating member 361a is proportional to the divided length in the direction perpendicular to the paper transport direction.

The output W of the divided heating member 361a is (supply voltage V) ² = W × (electric resistance value R of the heating member 361a). The relationship between the supply voltage V and the current I is V = I × R. ^Therefore, W = V 2 / relationship R ^{= I} 2 / R to adjust the electric resistance value R of the heat generating member 361a to stand. Even when the specific resistances of the heat generating members 361a are the same, the electric resistance value R can be adjusted by changing the length and thickness.

For example, in order to increase the electrical resistance value R, the cross-sectional area is reduced or the current flow path is extended. When the voltage is constant, increasing the electric resistance value R decreases the current I. On the contrary, when the electric resistance value R is doubled, the current I becomes 1/2. In this case, the amount of heat generated by the heater is (1/2) ² × 2, resulting in ¼. Moreover, when the thickness of each heat generating member 361a is the same, heat dissipation can be prevented by changing the size in the longitudinal direction. Specifically, heat generation can be promoted by increasing the size in the longitudinal direction. When the heat generating members 361a have the same thickness, the heat generation amount per unit area is the same. However, if the heat (radiation) of the heat in the horizontal direction of each heater is the same, the larger the area, the more advantageous the temperature rise. It will be a thing. In the example of FIG. 5, if the thickness is the same, the temperature rise of the central heating member 361a is the fastest. On the other hand, the specific resistance can be changed by selecting the material of the heat generating member 361a.

  6 is a cross-sectional view of the heat generating member group taken along broken line X shown in FIG. Here, a case is shown in which the heat generation amount of each heat generating member 361a is uniformly adjusted by changing the thickness of each heat generating member 361a. Since the heat generating member 361a disposed in the center is relatively long in the horizontal direction in the drawing, it is considered that heat is most easily generated when the thickness and voltage V conditions are the same as described above. For this reason, it is formed so that the thickness D1 of the heat generating member 361a in the central portion is thinner than the thicknesses D2 to D4 of the other adjacent heat generating members 361a. By reducing the cross-sectional area and increasing the electric resistance value R, the value of the output W of the heat generating member 361a is adjusted.

  FIG. 7 is a diagram showing a connection state of the heat generating member group and its drive circuit. As shown in the figure, energization of each of the heat generating members 361a is individually controlled by the corresponding driving IC 151. The heat generating members 361a are connected in parallel so that the same potential is applied to each of the heat generating members 361a. Specific examples of the drive IC 151 that is a switching unit for energizing each heat generating member 361a include a switching element, FET, triax, and switching IC. Although FIG. 7 shows a configuration example in which a voltage is applied to each heat generating member 361a with an alternating current to generate heat, it may be a direct current. In the present embodiment, when the paper P is transported in the paper transport direction indicated by the arrow A, only the heat generating member 361a corresponding to the paper passing area of the paper P is selectively energized, and only the paper P passing area. Shall be heated intensively.

  For example, when the paper P is the minimum size (postcard size), only the switching element of the first heat generating member arranged at the center is turned on and heated. As the size of the paper P increases, the switching elements of the second heat generating member group and the third heat generating member group are controlled so as to be sequentially turned on. The electrical resistance value is adjusted so that the first to third heat generating member groups have a uniform temperature increase rate.

  Hereinafter, the printing operation of the MFP 10 configured as described above will be described with reference to the drawings. FIG. 8 is a flowchart illustrating a specific example of control of the MFP 10 in the present embodiment.

  First, when the scanner unit 15 reads image data (Act 101), the image forming control program in the image forming unit 20 and the fixing temperature control program in the fixing device 36 are executed in parallel.

  When the image forming process is started, the read image data is processed (Act 102), an electrostatic latent image is written on the surface of the photosensitive drum 22 (Act 103), and the developing unit 24 develops the electrostatic latent image. (Act 104), the process proceeds to Act 114.

  When the fixing temperature control process is started, the paper size is determined based on, for example, a detection signal from a line sensor (not shown) and paper selection information by the operation unit 14 (Act 105), and a position (passage of paper P) passes through. A group of heat generating members arranged in the paper area is selected as a heat generation target (Act 106).

  Next, when the temperature control start signal for the selected heat generating member group is turned ON (Act 107), the selected heat generating member group is energized, and the surface temperature of the heat generating member group rises. That is, when the heating region is determined, all the selected heat generating members 361a are operated under the same control. At this time, the energized heat generating member 361a generates heat at a uniform temperature increase rate.

  Next, when the surface temperature of the heat generating member group is detected by a temperature detecting member (not shown) disposed inside or outside the endless belt 363 (Act 108), whether the surface temperature of the heat generating member group is within a predetermined temperature range. It is determined whether or not (Act 109). If it is determined that the surface temperature of the heat generating member group is within the predetermined temperature range (Act109: Yes), the process proceeds to Act110. On the other hand, when it is determined that the surface temperature of the heat generating member group is not within the predetermined temperature range (Act 109: No), the process proceeds to Act 111.

  In Act 111, it is determined whether or not the surface temperature of the heat generating member group exceeds a predetermined temperature upper limit value. Here, when it is determined that the surface temperature of the heat generating member group exceeds the predetermined temperature upper limit value (Act 111: Yes), the power supply to the heat generating member group selected in Act 106 is turned off (Act 112). Return to Act108. On the other hand, when it is determined that the surface temperature of the heating member group does not exceed the predetermined temperature upper limit value (Act111: No), the surface temperature is less than the predetermined temperature lower limit value based on the determination result of Act109. Therefore, the energization of the heat generating member group is maintained in the ON state or is turned ON again (Act 113), and the process returns to Act 108.

  Next, when the sheet P is transported to the transfer section in a state where the surface temperature of the heat generating member group is within a predetermined temperature range (Act 110), after the toner image is transferred to the sheet P (Act 114), the sheet P is fixed to the fixing device. It is conveyed into 36.

  Next, when the toner image is fixed on the paper P in the fixing device 36 (Act 115), it is determined whether or not the printing process of the image data is finished (Act 116). If it is determined that the printing process is to be terminated (Act 116: Yes), the power supply to all the heat generating member groups is turned off (Act 117), and the process is terminated. On the other hand, if it is determined that the image data printing process has not yet ended (Act 116: No), that is, if there remains image data to be printed, the process returns to Act 101, and the same process is repeated until the end. .

  As described above, according to the present embodiment, not only can the abnormal heat generation in the non-sheet passing portion be prevented by switching the heat generating member group to be heated based on the group to which the paper size to be used belongs, but also non-sheet passing Unnecessary heating of the part can be suppressed. For this reason, the heat energy consumed by the fixing device 36 can be significantly reduced. Further, since the electric resistance value is adjusted in advance so that the divided heat generating member 361a has a uniform temperature increase rate, even when the heat generating member 361a has a plurality of types of lengths, the sheet passes through the position. It can be heated uniformly regardless.

<Modification>
Hereinafter, some modified examples of the embodiment will be described in detail with reference to the drawings. FIG. 9 is a diagram illustrating a connection state between a heat generating member group and a drive circuit thereof in a modification of the above embodiment. Here, similar to the case of FIG. 5, the same type of heat generating member 361 a is arranged equally on the left and right with respect to the heat generating member 361 a in the central portion. However, unlike the above embodiment, each heating member 361a has the same temperature increase rate in a no-load state (no paper or pressing member is in contact) when the same voltage is applied to the electrodes 361b at both ends. Thus, the distance between the electrodes 361b is adjusted by making the shape of the heat generating member 361a arranged next to the central portion meander in the vertical direction in the figure. That is, even when the heat generating member 361a is formed of the same specific resistance material and the same thickness, the heat generating member 361a having a large heat generating surface is formed in a meandering shape so that the current flow path ( The amount of heat generated in the central portion is kept small by increasing the distance between the power supply portions of the heat generating member and increasing the electric resistance value.

  Further, the pair of heat generating members 361a located at symmetrical positions with respect to the central portion are connected in series and are driven and controlled by the same switching element 151. For this reason, the number of switching elements can be reduced, and the apparatus size and manufacturing cost can be suppressed.

  FIG. 10 is a diagram showing a shape pattern of the heat generating member group in a modification of the present embodiment. In FIG. 10A, since the heating members 361a having a U-shape and the same size are arranged in the same direction and aligned in the vertical direction (the left-right direction in the drawing) with respect to the paper transport direction A, The electrode portions 361b are all arranged on the lower side in the figure. In this case, there is an advantage that all the wiring can be concentrated on one side. In FIG. 10, all of the heat generating members 361a have the same length. However, in the same manner as in the above embodiment, a plurality of types of lengths can be combined in consideration of the temperature increase rate. In FIG. 10B, the heat generating member 361a is formed in a meandering shape in the direction perpendicular to the paper transport direction A (the left-right direction in the drawing). Although the meandering direction of the heat generating member 361a differs by 90 degrees from the case of FIG. 9, it can be appropriately selected according to the wiring structure of the apparatus.

  Furthermore, in the above embodiment, the size of the paper passing area of the paper P is determined based on the paper setting information before the paper P is conveyed into the fixing device 36. Instead, it is possible to determine the position through which the printing area (image forming area) passes and heat it. As a method for determining the size of the print area of the paper P, a method using an analysis result of image data, a method based on print format information such as margin setting for the paper P, and a method for determining based on a detection result of an optical sensor Etc. In this case, only the portion that needs fixing can be heated in a limited manner, so that the energy saving efficiency can be further improved.

  As mentioned above, although embodiment of this invention was described, this embodiment is shown as an example and is not intending limiting the range of invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. This embodiment and its modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

36. Fixing device 150 ... Fixing device control circuit 151 ... Driving IC
361 ... heating member 361a ... heating member 361b ... electrode 363 ... endless belt 366 ... pressure roller

In the fixing device according to the embodiment, the determination unit that determines the size of the medium on which the toner image is formed, the endless rotating body, and the length in the conveyance direction of the medium are the same, and the conveyance direction The heating is composed of a plurality of heating members that are divided into a plurality of lengths in the direction perpendicular to the temperature, the temperature increase rate with respect to the same applied voltage is uniformly adjusted, and are arranged in contact with the inside of the rotating body. A member and a switching unit that individually switches energization to these heat generating members, and the pair of heat generating members among the plurality of heat generating members are connected in series, and these are provided in common. the energization by the switching unit is controlled, a heating means for heating the medium, said pressure contact at the position of the plurality of heating members to form a nip to the heating means, the said medium with said heating means And pressing means for nipping and conveying the feeding direction, on the basis of the magnitude of the determined said medium by determining means, among the plurality of heat-generating members, the heat-generating member corresponding to the position where the medium passes through the switching unit select energized simultaneously by, and a heating control means for controlling the heating in the heating means, said heating control means, the temperature range surface temperature of the predetermined heat generating member corresponding to the position where the medium passes determines whether it is, when the surface temperature is higher than the predetermined temperature range is the current in the OFF state, the to Rukoto the oN state current when the surface temperature is lower than the predetermined temperature range Features.

Claims (6)

Determining means for determining the size of the medium on which the toner image is formed;
The endless-shaped rotating body and the length in the transport direction of the medium are the same, and are divided into a plurality of types in the direction perpendicular to the transport direction, and the temperature increase rate with respect to the same applied voltage is uniform. A plurality of heat generating members that are adjusted and arranged in contact with the inside of the rotating body, and a switching unit that individually switches energization to these heat generating members, and heating means for heating the medium;
A pressure unit that press-contacts the heating unit at the positions of the plurality of heat generating members to form a nip, and holds the medium in the transport direction together with the heating unit; and
A heating control means for controlling heating in the heating means by selecting a heat generating member corresponding to a position through which the medium passes among the plurality of heat generating members by the switching unit and energizing;
A fixing device comprising:   The temperature increase rate is adjusted by changing at least one of a thickness of the heat generating member, a length between power feeding portions of the heat generating member, and a specific resistance of the heat generating member. Item 4. The fixing device according to Item 1.   Of the plurality of heat generating members, a pair of heat generating members arranged symmetrically with respect to the center line of the heating member are connected in series, and these are energized by the switching unit provided in common. The fixing device according to claim 1, wherein the fixing device is controlled. A transfer belt that moves in one direction;
A photoconductor disposed along the moving direction of the transfer belt and holding an electrostatic latent image on the surface;
A developing device disposed opposite to the photosensitive member and attaching the discharged toner to the electrostatic latent image to form a toner image on the photosensitive member;
A transfer member that presses against the photoconductor via the transfer belt based on supply of a transfer voltage, and transfers the toner image formed on the photoconductor onto the transfer belt;
A fixing device for fixing the toner image on the transfer belt to a medium by pressurization and heating;
With
The fixing device includes:
Determination means for determining the size of the medium on which the toner image is formed;
The endless-shaped rotating body and the length in the transport direction of the medium are the same, and are divided into a plurality of types in the direction perpendicular to the transport direction, and the temperature increase rate with respect to the same applied voltage is uniform. A plurality of heat generating members that are adjusted and arranged in contact with the inside of the rotating body, and a switching unit that individually switches energization to these heat generating members, and heating means for heating the medium;
A pressure unit that press-contacts the heating unit at the positions of the plurality of heat generating members to form a nip, and holds the medium in the transport direction together with the heating unit; and
A heating control means for controlling heating in the heating means by selecting a heat generating member corresponding to a position through which the medium passes among the plurality of heat generating members by the switching unit and energizing;
An image forming apparatus comprising:   The temperature increase rate is adjusted by changing at least one of a thickness of the heat generating member, a length between power feeding portions of the heat generating member, and a specific resistance of the heat generating member. Item 5. The image forming apparatus according to Item 4.   Among the plurality of heating members, a pair of heating members arranged symmetrically with respect to the center line of the heating member are connected in series, and these are electrically energized by the switching unit provided in common. 6. The image forming apparatus according to claim 4, wherein the image forming apparatus is controlled.

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