JP2021056529A - Fixing device and image forming apparatus - Google Patents

Abstract

To improve fixing quality and save energy.SOLUTION: A fixing device according to an embodiment comprises: heating means; switching means; and heating control means. The heating means includes a first heating member that is formed in meandering shape, and a plurality of second heating members that are arranged on both sides of the first heating member in an orthogonal direction orthogonal to a medium conveyance direction and have a length in the orthogonal direction shorter than that of the first heating member. The switching means individually switches energization to the first heating member and the plurality of second heating members. The heating control means selects the first heating member and the plurality of second heating members corresponding to the medium passing through a nip and simultaneously energizes the heating members through the switching means.SELECTED DRAWING: Figure 9

Description

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

As a heat source for a fixing device mounted on an image forming apparatus, a lamp that emits 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, the fixing device is composed of a pair of a heating roller (or a fixing belt spanned by a plurality of rollers) and a press roller, but in order to maximize the thermal efficiency of the fixing device, the heat capacity of the component is reduced as much as possible. It is required to concentrate the heating area.

Japanese Patent No. 2629980

In the above-mentioned heating method, since the heating width is wide, it is difficult to intensively apply the heat energy dispersed over a wide range only to the nip portion, and it is difficult to optimize the thermal efficiency. Further, in an electrophotographic fixing device, if heat generation unevenness occurs in a direction perpendicular to the paper transport direction, the fixing quality is affected. In particular, in the case of color printing, there is a possibility that differences in color development and gloss may occur.

Furthermore, in a fixing device with an extremely reduced heat capacity, the temperature of the part through which the paper does not pass rises extremely, which may cause problems such as warpage of the heater, deterioration of the belt, and speed unevenness due to expansion of the transport roller. It was. Further, it is not preferable to heat the portion through which the paper does not pass from the viewpoint of energy saving. Intensive heating of only the part 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 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. Occurs.

Therefore, in view of the above-mentioned problems of the prior art, it is an object of the present invention to enable intensive and stable heating of the paper-passing area, and to achieve improvement of fixing quality and energy saving.

The fixing device according to the embodiment includes a determination means, an endless-shaped rotating body, a heating means, a switching means, a pressurizing means, and a heating control means.
The determination means determines the size of the medium on which the toner image is formed. The heating means are arranged on both sides of the first heat-generating member formed in a meandering shape and on both sides in the orthogonal direction orthogonal to the transport direction of the medium with respect to the first heat-generating member, and the length in the orthogonal direction is the first. Includes a plurality of second heat generating members, which are shorter than the heat generating member. The switching means individually switches the energization of the first heat generating member and the plurality of second heat generating members. The pressurizing means forms a nip by being pressed against 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 a first heat-generating member and a plurality of second heat-generating members corresponding to the medium passing through the nip based on the size of the medium determined by the determination means, and simultaneously via the switching means. Energize.

The figure which shows the structural example of the image forming apparatus which mounts the fixing apparatus which concerns on one Embodiment. The block diagram which shows the part of the image forming part in one embodiment enlarged. The block diagram which shows the structural example of the control system of the MFP in one Embodiment. The figure which shows the structural example of the fixing device which concerns on one Embodiment. The layout of the heat generating member group in one embodiment. The cross-sectional view 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. The flowchart which shows the 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.

Hereinafter, the fixing device according to the embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a configuration example of an image forming apparatus on which the fixing apparatus according to the present embodiment is mounted. In FIG. 1, the image forming apparatus 10 is, for example, an MFP (Multi-Function Peripherals) which is a multifunction device, a printer, a copying machine, or the like. In the following description, the 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 transport unit (ADF) 13 is provided on the platen 12 so as to be openable and closable. Further, an operation unit 14 is provided on the upper part of the main body 11. The operation unit 14 has various keys and a touch panel type display.

A scanner unit 15 which is 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 platen to generate image data, and includes a close contact type image sensor 16 (hereinafter, simply referred to as an image sensor). The image sensor 16 is arranged in the main scanning direction (depth direction in FIG. 1).

When the image sensor 16 reads the image of the original placed on the platen 12, the image sensor 16 reads the original image line by line while moving along the platen 12. This is executed over the entire document size to read one page of the document. Further, when reading the image of the original 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 in the central portion of the main body 11, and a plurality of paper feed cassettes 18 for accommodating various sizes of paper P are provided in the lower portion of the main body 11.

The printer unit 17 processes the image data read by the scanner unit 15 and the 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 of each color of yellow (Y), magenta (M), cyan (C), and black (K). The image forming portions 20Y, 20M, 20C, and 20K are arranged in parallel on the lower side of the intermediate transfer belt 21 from the upstream side to the downstream side. Further, the laser exposure device (scanning head) 19 also has a plurality of laser exposure devices 19Y, 19M, 19C, 19K corresponding to the image forming units 20Y, 20M, 20C, 20K.

FIG. 2 is a configuration diagram showing an enlarged 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 has a photoconductor drum 22K which is an image carrier. A charger (charging charger) 23K, a developing device 24K, a primary transfer roller (transferring device) 25K, a cleaner 26K, a blade 27K, and the like are arranged around the photoconductor drum 22K along the rotation direction t. The exposure position of the photoconductor drum 22K is irradiated with light from the laser exposure device 19K to form an electrostatic latent image on the photoconductor drum 22K.

The charger 23K of the image forming unit 20K uniformly charges the surface of the photoconductor drum 22K. The developer 24K supplies a two-component developer containing black toner and carriers to the photoconductor drum 22K by a developing roller 24a to which a development bias is applied to develop an electrostatic latent image. The cleaner 26K uses a blade 27K to remove residual toner on the surface of the photoconductor drum 22K.

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

The intermediate transfer belt 21 moves cyclically. The intermediate transfer belt 21 is stretched on the drive roller 31 and the driven roller 32. Further, the intermediate transfer belt 21 is in contact with the photoconductor drums 22Y to 22K so as to face each other. A primary transfer voltage is applied by the primary transfer roller 25K to the position of the intermediate transfer belt 21 facing the photoconductor drum 22K, and the toner image on the photoconductor drum 22K is primarily transferred to the intermediate transfer belt 21.

A secondary transfer roller 33 is arranged to face the drive roller 31 on which the intermediate transfer belt 21 is stretched. When the paper P passes between the drive roller 31 and the secondary transfer roller 33, the 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 in the vicinity of the driven roller 32 of the intermediate transfer belt 21.

Further, as shown in FIG. 1, a paper feed roller 35 for transporting 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. A transport roller 37 is provided downstream of the fixing device 36. The transport roller 37 discharges the paper P to the paper ejection unit 38. Further, a reversing transport path 39 is provided downstream of the fixing device 36. The reverse transfer path 39 reverses the paper P and guides it in the direction of the secondary transfer roller 33, and is used when performing double-sided printing. 1 and 2 show a configuration example of the MFP 10, and do not limit the structure of the image forming apparatus portion other than the fixing device 36, and a known electrophotographic image forming apparatus structure can be used.

FIG. 3 is a block diagram showing 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, and a paper feed / transport control circuit. It includes 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, control data, and the like that control the basic operation 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. Specific examples of the control data in the present embodiment include a correspondence relationship between the size (width in the main scanning direction) of the paper passing area and the printing area in the paper and the heat generating member to be energized.

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

The I / F 122 communicates with various devices such as a user terminal and a facsimile. The input / output control circuit 123 controls the operation panel 123a and the display 123b that constitute the operation unit 14. The paper feed / transport control circuit 130 controls the motor group 130a or the like that drives the paper feed roller 35 or the transport roller 37 of the transport path. The paper feed / transport control circuit 130 controls the motor group 130a and the like based on the control signal from the CPU 100 in consideration of the detection results of various sensors 130b in the vicinity of the paper feed cassette 18 or on the transport path. The image formation control circuit 140 controls the photoconductor drum 22, the charger 23, the laser exposure device 19, the developer 24, and the transfer device 25, respectively, based on the control signal from the CPU 100. The fixing control circuit 150 controls the drive motor 360 of the fixing device 36, the heating member 361, and the temperature detecting member 362 such as the thermistor, respectively, 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, a calculation processing device and a storage device are separately provided for the fixing device 36. You may.

FIG. 4 is a diagram showing a configuration example of the fixing device 36. Here, the fixing device 36 applies tension to the plate-shaped heating member 361, the elastic layer, the endless belt 363 suspended on a plurality of rollers, the belt transport roller 364 for driving the endless belt 363, and the endless belt 363. It includes a tension roller 365 and a press roller 366 having an elastic layer formed on the surface. In the heating member 361, the heat generating portion side comes into contact with the inside of the endless belt 363 and is pressed in the direction of the press roller 366 to form a fixing nip having a predetermined width between the heating member 361 and 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 that in the case of the heating method using a halogen lamp.

In the endless belt 363, for example, a silicon rubber layer having a thickness of 200 um is formed on the outer side of a SUS base material having a thickness of 50 um or a polyimide which is a heat resistant resin of 70 um, 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 thereof is covered with a surface protective layer such as PFA.

Further, in the heating member 361, a glaze layer and a heat generation resistance layer are laminated on a ceramic substrate. _{The heat generation 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 in order to release excess heat to the opposite side and prevent the substrate from warping.

The method for forming the heat generation resistance layer is the same as that of a known method (for example, a method for producing a thermal head), and a masking layer is formed of aluminum on the heat generation resistance layer. The aluminum layer is formed in a pattern in which adjacent heat generating members are insulated and the heat generating resistor (heat generating member) is exposed 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. Further, a protective layer is formed at the uppermost portion so as to cover all of the heat generating 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 diagram of the heat generating member group in the present embodiment. As shown in the figure, on the ceramic substrate 361c, heat-generating members 361a having a plurality of lengths in the left-right direction shown are arranged side by side, and both ends of the heat-generating member 361a in the paper transport direction (vertical direction shown). An electrode 361b is formed on the surface. In order to keep the heating time (paper passing time) of 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 composed of the heat generating members 361a having a plurality of types of lengths in the left and right directions shown in the drawing. Specifically, heat generating members having a plurality of lengths corresponding to postcard size (100 x 148 mm), CD jacket size (121 x 121 mm), B5R size (182 x 257 mm), and A4R size (210 x 297 mm) ( It is divided into a heat generating 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 heated region in consideration of the transfer accuracy of the conveyed paper, skew, and heat escape to the unheated portion. Is energized.

For example, in order to correspond to a width of 100 mm, which is the minimum size of a postcard, a first group of heat generating members is provided at the center in the main scanning direction (horizontal direction in the drawing), and the width is 105 mm. In order to correspond to the next largest sizes 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 drawing), and 148 mm + 5% covers a width of up to 155 mm. In order to correspond to the larger sizes of 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 up to 220 mm at 210 mm + 5%. .. The number of divisions of the heat generating member group and the width of each are given as an example, and are not limited thereto. For example, when the MFP 10 corresponds to five medium sizes, the heat generating member group may be divided into five according to each medium size.

Further, in the present embodiment, a line sensor (not shown) is arranged in the paper passing area, and 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 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 all of the plurality of heat generating members 361a are energized under the same conditions, the heat generation amount of each heat generating member 361a is increased because the lengths in the left and right directions shown in the drawing are different. (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 of the heat generating members 361a, (2) the length between the feeding portions (electrodes 361b) of the heat generating pattern, and (3) the specific resistance of the heat generating member 361a. Is optimally adjusted to make the calorific value uniform. The adjustments according to (1) to (3) may be combined as appropriate. 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 heat-generating member 361a is (supply voltage V) ² = W × (electrical resistance value R of the heat-generating member 361a). The relationship between the supply voltage V and the current I is V = I × R. Therefore, the electric resistance value R of each heat generating member 361a is adjusted so that the relationship of W = V ² / R = I ^{2 / R is established.} Even when the specific resistances of the heat generating members 361a are the same, the electrical resistance value R can be adjusted by changing the length and thickness.

For example, in order to increase the electric 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 reduces the current I. On the contrary, when the electric resistance value R is doubled, the current I is halved. In this case, the amount of heat generated by the heater is (1/2) ² × 2, and as a result, it becomes 1/4. Further, 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 each heat generating member 361a has the same thickness, the amount of heat generated per unit area is the same, but assuming that the heat (heat dissipation) that escapes in the left-right direction of each heater is the same, the larger the area, the more advantageous it is for temperature rise. It will be a thing. In the example of FIG. 5, if the thickness is the same, the temperature of the central heat generating member 361a rises fastest. 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 in the 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 of the heat generating members 361a. Since the heat generating member 361a arranged in the center has a relatively long length in the left-right direction shown in the drawing, it is considered that heat is most likely to be generated when the thickness and the voltage V conditions 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. The value of the output W of the heat generating member 361a is adjusted by reducing the cross-sectional area and increasing the electric resistance value R.

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 to be energized by the corresponding drive IC 151. Each heat generating member 361a is connected in parallel so that the same potential is applied to each. Specific examples of the drive 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 a voltage is applied to each of the heat generating members 361a by alternating current to generate heat, but direct current can also be used. In the present embodiment, when the paper P is conveyed in the paper conveying direction indicated by the arrow A, only the heat generating member 361a corresponding to the paper passing region of the paper P is selectively energized, and only the paper passing region of the paper P is energized. Is to be heated intensively.

For example, when the paper P has 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 also controlled to be turned ON in sequence. The electric resistance values of the first to third heat generating member groups are adjusted so that the temperature rise rate is uniform.

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

First, when the image data is read by the scanner unit 15 (Act101), the image formation 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 formation process is started, the read image data is processed (Act102), the electrostatic latent image is written on the surface of the photoconductor drum 22 (Act103), and the electrostatic latent image is developed by the developing device 24. (Act104), proceed to Act114.

When the fixing temperature control process is started, for example, the paper size is determined based on the detection signal of the line sensor (not shown) and the paper selection information by the operation unit 14 (Act105), and the position (passing) through which the paper P passes is determined. A group of heat generating members arranged in the paper region) is selected as a heat generating target (Act106).

Next, when the temperature control start signal for the selected heat generating member group is turned ON (Act107), the selected heat generating member group is energized and the surface temperature of the heat generating member group rises. That is, once 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 rise rate.

Next, when the surface temperature of the heat generating member group is detected by the temperature detecting member (not shown) arranged inside or outside the endless belt 363 (Act108), is the surface temperature of the heat generating member group within a predetermined temperature range? Whether or not it is determined (Act109). Here, if it is determined that the surface temperature of the heat generating member group is within a 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 (Act109: No), the process proceeds to Act111.

In Act111, 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 a predetermined temperature upper limit value (Act111: Yes), the energization of the heat generating member group selected in Act106 is turned off (Act112). Return to Act108. On the other hand, when it is determined that the surface temperature of the heat generating 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 (Act113), and the process returns to Act108.

Next, when the paper P is conveyed to the transfer unit (Act110) while the surface temperature of the heat generating member group is within a predetermined temperature range, the paper P is fixed after the toner image is transferred to the paper P (Act114). Transport within 36.

Next, when the toner image is fixed on the paper P in the fixing device 36 (Act115), it is determined whether or not to end the printing process of the image data (Act116). Here, when it is determined that the printing process is finished (Act116: Yes), the energization of all the heat generating member groups is turned off (Act117), and the process is finished. On the other hand, when it is determined that the printing process of the image data has not been completed (Act116: No), that is, when the image data to be printed remains, the process returns to Act101 and the same process is repeated until the process is completed. ..

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

<Modification example>
Hereinafter, some modifications of the above embodiment will be described in detail with reference to the drawings. FIG. 9 is a diagram showing a connection state of the heat generating member group and its drive circuit in the modified example of the above embodiment. Here, as in the case of FIG. 5, the same type of heat generating member 361a is evenly arranged on the left and right sides with respect to 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 state of no load (no contact between the paper and the pressing member) 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 the central portion meandering in the vertical direction shown in the drawing. That is, even when the heat generating member 361a is formed of the same material having the same resistivity and the same thickness, the shape of the heat generating member 361a having a large heat generating surface is formed in a meandering shape so that the current flow path ( By lengthening (between the feeding parts of the heat generating member) and increasing the electrical resistance value, the amount of heat generated in the central part is suppressed to a small value.

Further, the pair of heat generating members 361a located symmetrically with respect to the central portion are connected in series and are 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 group of heat generating members in a modified example of the present embodiment. In FIG. 10A, the heat generating members 361a formed in a U shape and having the same size are arranged side by side in the same direction and in the direction perpendicular to the paper transport direction A (horizontal direction in the drawing). All the electrodes 361b are arranged on the lower side in the drawing. In this case, there is an advantage that all the wiring can be concentrated on one side. Although all the heat generating members 361a have the same length in FIG. 10, a plurality of types of lengths can be combined in consideration of the temperature rise rate as in the above embodiment. In FIG. 10B, the heat generating member 361a is formed in a meandering shape in a direction perpendicular to the paper transport direction A (horizontal direction in the drawing). Although the meandering direction of the heat generating member 361a is 90 degrees different from that in the case of FIG. 9, it can be appropriately selected according to the wiring structure of the apparatus.

Further, 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. Alternatively, the position through which the print area (image forming area) passes can be determined and heated. As a method of determining the size of the print area of the paper P, a method of using the analysis result of the image data, a method based on print format information such as a margin setting for the paper P, and a method of determining based on the detection result of the optical sensor. And so on. In this case, since only the portion that needs to be fixed can be heated in a limited manner, the energy saving efficiency can be further improved.

Although the embodiments of the present invention have been described above, the present embodiments are presented as examples and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. The present 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 the equivalent scope thereof.

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

Claims (5)

A determination means for determining the size of the medium on which the toner image is formed, and
Endless shaped rotating body and
The first heat-generating member formed in a meandering shape and the first heat-generating member are arranged on both sides in an orthogonal direction orthogonal to the transport direction of the medium, and the length in the orthogonal direction is the first. A heating means including a plurality of second heat-generating members shorter than the heat-generating member, and
A switching means for individually switching the energization of the first heat generating member and the plurality of second heat generating members, and
A pressurizing means that forms a nip by being pressed by the first heat-generating member and the plurality of second heat-generating members via the rotating body to convey the medium in the conveying direction.
Based on the size of the medium determined by the determination 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 the switching means is used. And the heating control means that energizes at the same time
A fixing device equipped with. The temperature rise rate of the plurality of the second heat generating members with respect to the applied voltage is uniformly adjusted.
Each of the plurality of second heat generating members arranged on one side of the first heat generating member in the orthogonal direction and each of the plurality of second heat generating members arranged on the other side in the orthogonal direction are paired with each other. The pair of the second heat generating members are connected in series to each other.
The fixing device according to claim 1, wherein the switching means switches the energization of the pair of the second heat generating members. The fixing device according to claim 1 or 2, wherein the plurality of the second heat generating members include a heat generating member formed in a meandering shape. When the surface temperature of the selected first heat-generating member and the plurality of second heat-generating members is less than a predetermined temperature upper limit value, the heating control means selects the first heat-generating member and the plurality of the first heat-generating members. Energize the second heat generating member,
The fixing device according to any one of claims 1 to 3, wherein the energization is stopped when the surface temperature is equal to or higher than a predetermined temperature upper limit value. A transfer belt that moves in one direction,
A photoconductor that is placed adjacent to the transfer belt and has an electrostatic latent image formed on its surface.
A developing device that develops the electrostatic latent image and forms a toner image on the surface of the photoconductor.
A transfer device that press-contacts the photoconductor via the transfer belt and transfers the toner image formed on the surface of the photoconductor to the transfer belt.
The fixing device according to any one of claims 1 to 4, wherein the toner image transferred from the transfer belt to a medium is fixed to the medium.
An image forming apparatus comprising.

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