JP7312303B2 - Fixing device and image forming device - Google Patents

Description

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

As a heat source for a fixing device mounted in an image forming apparatus, a lamp that emits infrared rays, typically a halogen lamp, or a heating system that uses Joule heat due to electromagnetic induction has been put to practical use. In general, a fixing device consists of a pair of a heating roller (or a fixing belt stretched over multiple rollers) and a press roller. It is required to reduce the temperature and concentrate the heating area.

Japanese Patent No. 2629980

In the above-described heating method, since the heating width is wide, it is difficult to concentrate the heat energy distributed over a wide area only to the nip portion, and it is difficult to optimize the thermal efficiency. Further, in a fixing device for electrophotography, if uneven heat generation occurs in the direction perpendicular to the paper conveying direction, the fixing quality is affected. In particular, in the case of color printing, there is a possibility that there will be differences in color development and gloss.

Furthermore, in a fixing device with an extremely reduced heat capacity, the temperature of the part where the paper does not pass rises extremely, which may cause problems such as warping of the heater, deterioration of the belt, and uneven speed due to expansion of the transport roller. rice field. Moreover, it is not preferable from the viewpoint of energy saving to heat the portion through which the paper does not pass. Intensive heating of only the portion through which the paper passes has become an important technical issue from the viewpoint of environmental measures.

For this reason, it has been proposed to control by dividing the heat generation region, but when the heat generation region is divided, there is a problem that the temperature rise rate differs between the regions, which causes temperature unevenness. occur.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to address the above problems of the prior art, and to enable intensive and stable heating of a paper-passing area, thereby improving fixing quality and saving energy.

A fixing device according to an embodiment includes a determination unit, an endless rotator, a heating unit, a switching unit, a pressure unit, and a heating control unit. The determining means determines the size of the medium on which the toner image is formed. The heating means includes a first heat generating member group including a plurality of U-shaped first heat generating members arranged in a direction orthogonal to the medium transport direction, and a medium heat generating member group of the first heat generating member group. a second heat-generating member group consisting of a plurality of U-shaped second heat-generating members arranged in a direction perpendicular to the conveying direction of the recording medium on both sides in the orthogonal direction perpendicular to the conveying direction of the recording medium; including. The switching means individually switches energization to the plurality of first heat generating members and the plurality of second heat generating members. The pressurizing means forms a nip by being pressed by the first heat-generating member and the plurality of second heat-generating members via the rotating body, and conveys the medium in the conveying direction. The heating control means selects the first heat generating member and the plurality of second heat generating members corresponding to the medium passing through the nip based on the size of the medium determined by the determining means, and simultaneously selects the heat generating members via the switching means. energize. Each of the U-shaped first heat-generating members and each of the second U-shaped heat-generating members are arranged such that the openings of the U-shaped members are aligned in the same direction as the medium conveying direction. be. The electrodes formed on both ends of each of the first heat generating member and the second heat generating member are arranged on the opening sides of the first heat generating member and the second heat generating member. The plurality of first heat generating members and the switching means, and the plurality of second heat generating members and the switching means are connected at the opening sides of the first heat generating members and the second heat generating members.

1 is a diagram showing a configuration example of an image forming apparatus equipped with a fixing device according to one embodiment; FIG. FIG. 2 is a configuration diagram showing an enlarged part of an image forming unit according to one embodiment; 1 is a block diagram showing a configuration example of a control system of an MFP according to one embodiment; FIG. FIG. 2 is a diagram showing a configuration example of a fixing device according to one embodiment; FIG. 4 is a layout diagram of a heat generating member group in one embodiment. FIG. 6 is a cross-sectional view of the heat generating member group along the broken line X shown in FIG. 5; FIG. 4 is a diagram showing a connection state between a heat generating member group and its drive circuit in one embodiment. 4 is a flow chart showing a specific example of the control operation of the MFP in one embodiment; The figure which shows the connection state of the heat-generating member group and its drive circuit in the modification of one Embodiment. The figure which shows the shape pattern of the heat-generating member group in the modification of one Embodiment.

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

A transparent glass platen 12 is provided on the upper part of a 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. Further, an operation section 14 is provided on the upper portion of the main body 11 . The operation unit 14 has various keys and a touch panel display.

A scanner unit 15 as a reading device is provided below the ADF 13 in the main body 11 . The scanner unit 15 reads a document sent by the ADF 13 or a document placed on a document table to generate image data, 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 platen 12 , the image sensor 16 moves along the document platen 12 and reads the document image line by line. This is executed over the entire document size to read one page of the document. Further, when reading an image of a document fed by the ADF 13, the image sensor 16 is at a fixed position (position shown in the drawing).

Further, the main body 11 has a printer section 17 in the central portion thereof, and a plurality of paper feed cassettes 18 for accommodating sheets P of various sizes in the lower portion 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 paper. The printer unit 17 is, for example, a tandem color laser printer, and includes image forming units 20Y, 20M, 20C, and 20K for yellow (Y), magenta (M), cyan (C), and black (K). The image forming units 20Y, 20M, 20C, and 20K are arranged in parallel under the intermediate transfer belt 21 from upstream to downstream. The laser exposure device (scanning head) 19 also has a plurality of laser exposure devices 19Y, 19M, 19C and 19K corresponding to the image forming units 20Y, 20M, 20C and 20K.

FIG. 2 is an enlarged configuration diagram showing the image forming section 20K among the image forming sections 20Y, 20M, 20C, and 20K. Since the image forming units 20Y, 20M, 20C, and 20K have the same configuration in the following explanation, the image forming unit 20K will be explained as an example.

The image forming section 20K has a photosensitive drum 22K as an image carrier. A charger (charger) 23K, a developer 24K, a primary transfer roller (transfer device) 25K, a cleaner 26K, a blade 27K, and the like are arranged along the rotation direction t around the photosensitive drum 22K. The exposure position of the photosensitive drum 22K is irradiated with light from the laser exposure device 19K to form an electrostatic latent image on the photosensitive drum 22K.

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

Further, as shown in FIG. 1, a toner cartridge 28 for supplying toner to the developing devices 24Y-24K is provided above the image forming units 20Y-20K. The toner cartridges 28 include yellow (Y), magenta (M), cyan (C), and black (K) toner cartridges.

The intermediate transfer belt 21 moves cyclically. The intermediate transfer belt 21 is stretched around a drive roller 31 and a driven roller 32 . Further, the intermediate transfer belt 21 faces and contacts the photosensitive drums 22Y to 22K. A primary transfer voltage is applied by a primary transfer roller 25K to a position of the intermediate transfer belt 21 facing the photoreceptor drum 22K to primarily transfer the toner image on the photoreceptor drum 22K to the intermediate transfer belt 21 .

A secondary transfer roller 33 is arranged to face the drive roller 31 around which the intermediate transfer belt 21 is stretched. A secondary transfer voltage is applied by the secondary transfer roller 33 when the paper P passes between the driving roller 31 and the secondary transfer roller 33 . Then, the toner image on the intermediate transfer belt 21 is secondarily transferred onto 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, between the paper feed cassette 18 and the secondary transfer roller 33, a paper feed roller 35 for conveying the paper P taken out from the paper feed cassette 18 is provided. Furthermore, a fixing device 36 is provided downstream of the secondary transfer roller 33 . A transport roller 37 is provided downstream of the fixing device 36 . The conveying rollers 37 discharge the paper P to the paper discharge section 38 . Furthermore, a reversing conveying path 39 is provided downstream of the fixing device 36 . The reverse transport path 39 reverses the paper P and guides it toward the secondary transfer roller 33, and is used when double-sided printing is performed. 1 and 2 show an example of the configuration of the MFP 10. The structure of the image forming apparatus other than the fixing device 36 is not limited, and the structure of a known electrophotographic image forming apparatus can be used.

FIG. 3 is a block diagram showing a configuration example of the control system 50 of the MFP 10 in this 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 forming control circuit 140 and a fixing control circuit 150 .

CPU 100 implements processing functions for image formation by executing programs stored in ROM 120 or RAM 121 . The ROM 120 stores control programs and control data that control basic operations of image forming processing. RAM 121 is a working memory. The ROM 120 (or RAM 121) stores, for example, control programs for the image forming section 20, the fixing device 36, etc., and various control data used by the control programs. Specific examples of the control data in the present embodiment include the relationship between the size of the paper passing area or the print area in the paper (the width in the main scanning direction) and the heat-generating member to be energized.

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

The I/F 122 communicates with various devices such as user terminals and facsimiles. The input/output control circuit 123 controls an operation panel 123a and a display device 123b that constitute the operation unit 14 . The paper feed/conveyance control circuit 130 controls a motor group 130a for driving the paper feed roller 35 or the conveying roller 37 of the conveying path. The paper feed/conveyance control circuit 130 controls the motor group 130a and the like based on the control signal from the CPU 100, taking into consideration the detection results of various sensors 130b near the paper feed cassette 18 or on the conveying path. The image forming control circuit 140 controls the photosensitive drum 22 , charger 23 , laser exposure device 19 , developing device 24 and transfer device 25 based on control signals from CPU 100 . The fixing control circuit 150 controls a driving motor 360 of the fixing device 36, a heating member 361, and a temperature detection member 362 such as a thermistor based on control signals from the CPU 100. FIG. In the present embodiment, the control program and control data for the fixing device 36 are stored in the storage device of the MFP 10 and executed by the CPU 100. However, an arithmetic processing device and a storage device are separately provided for the fixing device 36. may

FIG. 4 is a diagram showing a configuration example of the fixing device 36. As shown in FIG. Here, the fixing device 36 includes a plate-like heating member 361 , an endless belt 363 formed with an elastic layer and suspended by a plurality of rollers, a belt conveying roller 364 for driving the endless belt 363 , and applying tension to the endless belt 363 . A tension roller 365 and a press roller 366 having an elastic layer formed on the surface thereof are provided. The heat generating portion of the heating member 361 contacts the inner side of the endless belt 363 and is pressed toward the press roller 366 to form a fixing nip of a predetermined width with the press roller 366 . Since the heating member 361 heats while forming a 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 is formed of, for example, a 50 μm thick SUS base material or a 70 μm thick heat-resistant resin polyimide, on which a 200 μm thick silicone rubber layer is formed on the outside, and the outermost periphery is covered with a surface protective layer such as PFA. . The press roller 366 is formed of, for example, a φ10 mm iron bar with a silicon sponge layer of 5 mm thickness formed on the surface thereof, and the outermost circumference thereof is covered with a surface protective layer such as PFA.

Also, the heating member 361 has a glaze layer and a heating resistor layer laminated on a ceramic substrate. In order to allow excess heat to escape to the opposite side and prevent warping of the substrate, the heating resistor layer is made of a known material such as TaSiO ₂ , and is divided into predetermined lengths and numbers in the main scanning direction.

The method of forming the heat generating resistor layer is the same as a known method (for example, the method of manufacturing a thermal head), and forms a masking layer of aluminum on the heat generating resistor layer. Adjacent heat generating members are insulated from each other, and the aluminum layer is formed in such a pattern that the heat generating resistors (heat generating members) are exposed in the paper conveying direction. Electricity is supplied to the heat-generating member 361a by connecting wires from the aluminum layers (electrodes) at both ends and connecting them to the switching elements of the switching driver IC. Furthermore, a protective layer is formed on the top so as to cover all of the heating resistor, aluminum layer, wiring, and the like. The protective layer is made of, for example _{, Si3N4} .

FIG. 5 is a layout diagram of the heat generating member group in this embodiment. As shown in the figure, on a ceramic substrate 361c, heat generating members 361a having a plurality of different lengths in the horizontal direction are arranged side by side. is formed with an electrode 361b. It should be noted that the length of the heat generating members 361a in the paper conveying direction is made uniform in order to keep the heating time (the passage time of the paper) of each heat generating member 361a constant.

As shown in FIG. 5, in the present embodiment, the heat generating pattern of the heating member 361 is composed of heat generating members 361a having a plurality of types of lengths in the horizontal direction of the drawing. Specifically, a plurality of lengths of heat-generating members ( heating element) 361a. The heat-generating member group consisting 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 conveying accuracy and skew of conveyed paper and heat escape to non-heated portions. is energized.

For example, in order to correspond to the minimum postcard size width of 100 mm, the first heat generating member group is provided in the central portion in the main scanning direction (horizontal direction in the drawing), and the width is set to 105 mm. In order to accommodate the next largest sizes of 121 mm and 148 mm, a second heat generating member group with a width of 50 mm is provided outside the first heat generating member group (horizontal direction in the drawing) to cover the width up to 155 mm by 148 mm + 5%. To accommodate larger sizes of 182 mm and 210 mm, a third heat generating member group with a width of 65 mm for each heat generating member is provided further outside the second heat generating member group to cover the width up to 220 mm by 210 mm + 5%. . Note that the number of divisions of the heat-generating member group and the width of each are given as an example, and are not limited to this. For example, if the MFP 10 supports five medium sizes, the heat generating member group may be divided into five according to each medium size.

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

Further, as shown in FIG. 5, when all of the plurality of heat generating members 361a are energized under the same conditions, the lengths in the horizontal direction of the drawing are different, so the amount of heat generated by each of the heat generating members 361a ( power consumption) may differ, making it difficult to heat uniformly.

Therefore, in the present embodiment, at least one of (1) the thickness of each of the heat generating members 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 members 361a. shall be optimally adjusted to make the calorific value uniform. The adjustments of (1) to (3) may be combined as appropriate. For example, the length of the heat generating member 361a in the sheet conveying direction is made the same, and the output W of the heat generating member 361a is made proportional to the divided length in the direction perpendicular to the sheet conveying direction.

The divided output W of the heat generating member 361a is (supply voltage V) ² =W×(electric resistance value R of the heat generating member 361a). Also, the relationship between the supply voltage V and the current I is V=I×R. Therefore, the electrical resistance value R of each heat generating member 361a is adjusted so that the relationship W=V ² /R=I ² /R is established. Even if the specific resistance of each heat generating member 361a is the same, the electrical 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. If the voltage is constant, increasing the electrical resistance value R causes the current I to decrease. Conversely, if the electrical resistance value R is doubled, the current I will be halved. In this case, the amount of heat generated by the heater is (1/2) ² ×2, resulting in 1/4. Further, when the thickness of each heat generating member 361a is the same, heat radiation 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. If each heat generating member 361a has the same thickness, the amount of heat generated per unit area is the same, but if the heat (radiation) that escapes in the left and right direction of each heater is the same, the larger the area, the more advantageous the temperature rise. matter. In the example of FIG. 5, if the thicknesses are the same, the central heating member 361a has the fastest temperature rise. On the other hand, the specific resistance can be changed by selecting the material of the heat generating member 361a.

FIG. 6 is a cross-sectional view of the heat generating member group along the broken line X shown in FIG. Here, a case is shown in which the amount of heat generated by each heat generating member 361a is uniformly adjusted by changing the thickness of each of the heat generating members 361a. Since the heat-generating member 361a disposed in the center is relatively long in the left-right direction in the figure, it is considered that heat is generated most easily when the conditions of thickness and voltage V are the same as described above. Therefore, the thickness D1 of the heat generating member 361a in the central portion is formed to be thinner than the thicknesses D2 to D4 of the other adjacent heat generating members 361a. By reducing the cross-sectional area and increasing the electrical 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 between the heat generating member group and its drive circuit. As shown in the figure, each of the heat generating members 361a is individually controlled by the corresponding drive IC 151 to be energized. Each heat generating member 361a is connected in parallel so that the same potential is applied to each. Specific examples of the driving IC 151, which is a switching unit for energizing each heat generating member 361a, include switching elements, FETs, triaxes, switching ICs, and the like. FIG. 7 shows a configuration example in which alternating current voltage is applied to each of the heat generating members 361a to generate heat, but direct current may also be used. In this embodiment, when the paper P is transported in the paper transport direction indicated by the arrow A, only the heating member 361a corresponding to the paper passing area of the paper P is selectively energized, and only the paper passing area of the paper P is supplied with electricity. shall be intensively heated.

For example, when the paper P is the minimum size (postcard size), only the switching element of the first heat generating member arranged in 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 to be turned on sequentially. The electric resistance values of the first to third heat generating member groups are adjusted so that the temperature rise rate is uniform.

The operation of the MFP 10 configured as described above during printing will be described below with reference to the drawings. FIG. 8 is a flow chart showing a specific example of control of the MFP 10 in this embodiment.

First, when image data is read by the scanner section 15 (Act 101), an image formation control program in the image forming section 20 and a 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 electrostatic latent image is developed by the developing device 24. (Act104), proceed to Act114.

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

Next, when the temperature control start signal to 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 area 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 rise rate.

Next, when the surface temperature of the heat generating member group is detected by a temperature detecting member (not shown) arranged inside or outside the endless belt 363 (Act 108), it is determined whether the surface temperature of the heat generating member group is within a predetermined temperature range. It is determined whether or not (Act 109). Here, when 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, if it is determined that the surface temperature of the heat generating member group is not within the predetermined temperature range (Act109: No), the process proceeds to Act111.

In Act 111, it is determined whether or not the surface temperature of the heat generating member group exceeds a predetermined upper temperature limit. Here, if it is determined that the surface temperature of the heat-generating member group exceeds the predetermined temperature upper limit value (Act111: Yes), energization to the heat-generating member group selected in Act106 is turned off (Act112), Return to Act108. On the other hand, if it is determined that the surface temperature of the heat-generating member group does not exceed the predetermined upper temperature limit (Act 111: No), the determination result of Act 109 indicates that the surface temperature is less than the predetermined lower temperature limit. Therefore, the energization to the heat generating member group is maintained in the ON state or turned ON again (Act113), and the process returns to Act108.

Next, when the sheet P is conveyed to the transfer section while the surface temperature of the heat generating member group is within a predetermined temperature range (Act 110), the sheet P is transferred to the fixing device after the toner image is transferred to the sheet P (Act 114). 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). Here, if it is determined that the printing process should 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 is not finished yet (Act 116: No), that is, if image data to be printed remains, the process returns to Act 101, and repeats the same process until it is finished. .

As described above, according to the present embodiment, by switching the heat-generating member group to which heat is generated based on the group to which the paper size to be used belongs, it is possible not only to prevent abnormal heat generation in the non-passing portion, but also to Useless heating of parts can be suppressed. Therefore, the heat energy consumed by the fixing device 36 can be greatly reduced. Furthermore, since the electric resistance value of the divided heat-generating member 361a is adjusted in advance so that the rate of temperature rise is uniform, even if the heat-generating member 361a has a plurality of different lengths, it is possible for the paper to pass through. It can be heated evenly regardless.

<Modification>
Several modifications of the above embodiment will be described in detail below with reference to the drawings. FIG. 9 is a diagram showing a connection state between a heat generating member group and its drive circuit in a modification of the above embodiment. Here, as in the case of FIG. 5, heat-generating members 361a of the same type are evenly arranged on the left and right sides of the heat-generating member 361a in the central portion. However, unlike the above embodiment, each heat generating member 361a has the same temperature rise 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. The distance between the electrodes 361b is adjusted by making the shapes of the central portion and the heat generating member 361a arranged next to it meandering in the vertical direction of the figure. In other words, even if the heat generating member 361a is made of a material having the same specific resistance and the same thickness, the shape of the heat generating member 361a having a large heat generating surface is formed into a long and narrow meandering shape so that the current flow path ( By lengthening the distance between the power supply portions of the heat generating member and increasing the electrical resistance, the amount of heat generated in the central portion is kept small.

Furthermore, a pair of heat generating members 361 a located symmetrically with respect to the central portion are connected in series and driven and controlled by the same switching element 151 . Therefore, the number of switching elements can be reduced, and the device size and manufacturing cost can be suppressed.

FIG. 10 is a diagram showing a shape pattern of a heat generating member group in a modified example of this embodiment. In FIG. 10A, the U-shaped heat generating members 361a having the same size are arranged in the same direction in the direction perpendicular to the sheet conveying direction A (horizontal direction in the drawing). All the electrodes 361b are arranged on the lower side of the drawing. In this case, there is an advantage that all wiring can be concentrated on one side. Although all the heat generating members 361a have the same length in FIG. 10, they can be combined with different lengths in consideration of the rate of temperature rise as in the above embodiment. In FIG. 10B, the heat-generating member 361a is formed in a serpentine shape in a direction perpendicular to the sheet conveying direction A (horizontal direction in the drawing). The meandering direction of the heat generating member 361a is different from that in FIG. 9 by 90 degrees, but can be appropriately selected according to the wiring structure of the device.

Furthermore, in the above-described 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. Alternatively, the position through which the printing area (image forming area) passes can be determined and heated. As a method for determining the size of the print area of the paper P, there is a method using the analysis result of the image data, a method based on print format information such as margin setting for the paper P, and a method based on the detection result of the optical sensor. etc. In this case, only the portions requiring fixing can be heated in a limited manner, so energy saving efficiency can be further enhanced.

Although the embodiment of the present invention has been described above, the present embodiment is presented as an example and is not intended to limit the scope of the invention. This novel embodiment can be embodied in various other forms, and various omissions, replacements, and modifications 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 scope of the invention described in the claims and its equivalents.

36... Fixing device 150... Fixing device control circuit 151... Driving IC
361 Heating member 361a Heat generating member 361b Electrode 363 Endless belt 366 Pressure roller

Claims (3)

determining means for determining the size of the medium on which the toner image is formed;
an endless rotating body;
a first heat generating member group including a plurality of U-shaped first heat generating members arranged in a direction orthogonal to the medium transport direction; a second heat-generating member group comprising a plurality of U-shaped second heat-generating members arranged in the orthogonal direction orthogonal to the medium transport direction on both sides in the orthogonal direction orthogonal to the transport direction; a heating means comprising;
switching means for individually switching energization of the plurality of first heat generating members and the plurality of second heat generating members;
pressing means for forming a nip by being pressed between the first heat-generating member and the plurality of second heat-generating members via the rotating body and conveying the medium in the conveying direction;
Based on the size of the medium determined by the determining means, the first heat generating member and the plurality of second heat generating members corresponding to the medium passing through the nip are selected, and via the switching means a heating control means for simultaneously energizing the
with
Each of the first heat-generating members formed in a U-shape and each of the second heat-generating members formed in a U-shape are configured such that the openings of the members formed in the U-shape are oriented in the same direction with respect to the conveying direction of the medium. is placed in
electrodes formed at both ends of each of the first heat-generating member and the second heat-generating member are arranged on the opening side of the first heat-generating member and the second heat-generating member;
The plurality of first heat generating members and the switching means, and the plurality of second heat generating members and the switching means are connected at the opening sides of the first heat generating members and the second heat generating members. fusing device. When the surface temperatures of the selected first heat-generating member and the plurality of second heat-generating members are lower than a predetermined temperature upper limit, the heating control means controls the selected first heat-generating member and the plurality of the plurality of heat-generating members. energizing the second heat generating member;
2. The fixing device according to claim 1 , wherein the energization is stopped when the surface temperature is equal to or higher than a predetermined upper temperature limit. a transfer belt that moves in one direction;
a photoreceptor disposed adjacent to the transfer belt and having an electrostatic latent image formed on its surface;
a developing device that develops the electrostatic latent image to form a toner image on the surface of the photoreceptor;
a transfer device that presses against the photoreceptor via the transfer belt and transfers the toner image formed on the surface of the photoreceptor to the transfer belt;
The fixing device according to claim 1 or 2 , which fixes the toner image transferred from the transfer belt to the medium on the medium;
An image forming apparatus comprising:

Images