JP7336262B2 - image forming device - Google Patents

Description

The present invention provides a fixing device for thermally fixing an unfixed toner image formed on a recording material such as paper, or a gloss imparting device for improving the glossiness of a toner image by reheating a fixed toner image on the recording material. The present invention relates to an image forming apparatus having an image heating device such as a device.

2. Description of the Related Art In an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus, an image is formed by forming a toner image on a recording material such as a sheet and fixing it by heating and pressurizing it. As such a fixing device (image heating device), a film fixing system in which a film having an internal heater and a pressure roller are pressed against each other to form a fixing nip and fixation is conventionally employed. As a method of feeding and conveying the recording material, there is a center-based conveyance in which the widthwise center of the recording material is aligned with the center of the conveyance path, and a method in which the recording material is conveyed on the side of the conveyance path as in the image forming apparatus described in Japanese Patent Application Laid-Open No. 2002-200310. There are known two methods of one-side reference conveyance in which the recording material is conveyed so as to be pressed against the reference surface. One-side reference feeding has the advantage of improving the repetitive reproducibility of the paper position by conveying the recording material while pressing it against the reference plate, and the printing accuracy is greatly improved.
On the other hand, for the fixing device, when a small size width sheet is continuously conveyed in the one-sided standard conveyance, there is a non-passing area where the fixing roller does not pass, and the temperature of this area becomes very high. In this case, the diameter of the side of the pressure roller that has reached a high temperature increases due to thermal expansion, and a lateral difference occurs in the outer diameter of the pressure roller. This lateral difference in the diameter of the pressure roller causes the fixing film to bias in one direction. If the bias force becomes too large, there is a problem that the fixing film is damaged. In order to prevent the film from being destroyed by the bias force, the fixing device described in Patent Document 2 detects the bias direction of the film and increases the temperature of the non-sheet-passing area on the side opposite to the bias force to reduce the bias force. was doing

JP-A-4-164753 JP 2010-66689 A

However, in the above-described prior art, the temperature of the non-sheet-passing area is increased to move the film toward the side where the temperature is increased. It is necessary to provide a non-paper-passing area outside the maximum paper size. As a result, there is a concern that the width of the fixing device will increase. In addition, if this technique is applied to one-side reference conveyance, it is necessary to prepare a non-sheet-passing area extending outside the reference position as an area for generating a shift force. As a result, the longitudinal length of the heater is extended and the size of the fixing device is increased.

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique capable of extending the life of an apparatus by reducing the force applied to the film.

In order to achieve the above object, the image forming apparatus of the present invention includes:
an image forming unit that forms an image on a recording material;
A cylindrical film that rotates while being in contact with a recording material ; and a heater that is elongated in a direction orthogonal to the conveying direction of the recording material and that is arranged in an internal space of the film, and that includes a plurality of heat generating elements arranged in the longitudinal direction of the heater. and a pressure member forming a nip portion together with the heater through the film , the image heating portion heating the recording material while conveying it in the nip portion ;
a control unit that controls power supplied to each of the plurality of heating elements according to the size of the recording material passing through the nip ;
with
An image forming apparatus in which a recording material is conveyed along the conveying path such that one end in the longitudinal direction coincides with a reference position in the longitudinal direction of the conveying path of the recording material, regardless of the size of the recording material. ,
a plurality of temperature detection members for detecting respective temperatures in a plurality of regions of the pressure member corresponding to the plurality of heating regions of the nip heated by the plurality of heating elements;
The control section is characterized by controlling the electric power supplied to the plurality of heating elements so that a difference between the temperatures detected by the plurality of temperature detection members becomes small.

According to the present invention, it is possible to extend the life of the apparatus by reducing the biasing force on the film.

Schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention FIG. 2 is a cross-sectional view showing the essential parts of the fixing device in the embodiment of the present invention; FIG. 2 is a schematic side view showing main parts of the fixing device in Embodiment 1; Schematic configuration diagram of a heating element side of a heating element (heater) in Embodiment 1 Schematic configuration diagram of the surface of the heating element (heater) opposite to the heating element in Example 1. A diagram showing the control target temperature of each heating element in the first embodiment. A diagram showing the control target temperature of each heating element in the second embodiment. Schematic side view showing main parts of a fixing device in Embodiment 3 Schematic configuration diagram of a heating element side of a heating element (heater) in Embodiment 4 Schematic configuration diagram of a heating element side of a heating element (heater) in Example 5 Schematic diagram of the surface of the heating element (heater) opposite to the heating element in Example 5 Schematic side view showing main parts of a fixing device in Example 5 A diagram showing the control target temperature of each heating element in Example 5. Schematic diagram of the heating element side of the heating element (heater) in Embodiment 6 Schematic side view showing main parts of a fixing device in Embodiment 6 Schematic diagram of the surface opposite to the heating element of the heating element (heater) in Example 6 A diagram showing the control target temperature of each heating element in Example 6. FIG. 10 is a schematic side view showing a fixing device in which no temperature detection element is arranged in the area of W1; Heating element pattern with an overlapping part at the boundary of the divided heating element

BEST MODE FOR CARRYING OUT THE INVENTION A mode for carrying out the present invention will be exemplarily described in detail below based on an embodiment with reference to the drawings. However, the dimensions, materials, shapes and relative arrangement of the components described in this embodiment should be appropriately changed according to the configuration of the device to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

[Example 1]
FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the invention. Examples of image forming apparatuses to which the present invention can be applied include copiers and printers using an electrophotographic method or an electrostatic recording method. Here, an image is formed on a recording material P using an electrophotographic method. A case of application to a laser printer will be described.

The image forming apparatus 100 has a video controller 120 and a control section 113 . The video controller 120 serves as an acquisition unit for acquiring information about an image to be formed on a recording material and information such as the size and type of the recording material on which the image is to be formed. is received and processed. The image forming apparatus 100 also includes an operation panel 130 , and various information and print instructions may be sent to the control unit 113 by input from the operation panel 130 by the user. Control unit 113 is connected to video controller 120 and controls each unit of image forming apparatus 100 according to instructions from video controller 120 . When the video controller 120 receives a print instruction from an external device, image formation is performed by the following operations.

When a print signal is generated, the scanner unit 21 emits laser light modulated according to image information, and scans the photosensitive member (photosensitive drum) 19 charged to a predetermined polarity by the charging roller 16 . As a result, an electrostatic latent image is formed on the photoreceptor 19 . Toner is supplied from a developing device (developing roller) 17 to the electrostatic latent image, and a toner image (toner image) corresponding to image information is formed on a photosensitive member 19 as an image carrier. On the other hand, a recording material (recording paper) P stacked in a paper feed cassette (paper feeding unit) 11 is fed one by one by a pickup roller 12 and conveyed toward a registration roller pair 14 by a roller pair 13 . Further, the recording material P is conveyed from the registration roller pair 14 to the transfer position in time with the timing at which the toner image on the photoreceptor 19 reaches the transfer position formed by the photoreceptor 19 and the transfer roller 20 . The toner image on the photosensitive member 19 is transferred to the recording material P while the recording material P passes the transfer position. After that, the recording material P is heated by a fixing device (image heating device) 200 as a fixing section (image heating section), and the toner image is fixed on the recording material P by heating. The recording material P bearing the fixed toner image is discharged to a tray above the image forming apparatus 100 by the pair of conveying rollers 26 and 27 .

The drum cleaner 18 cleans the toner remaining on the photoreceptor 19 . A paper feed tray (manual feed tray) 28 having a pair of recording material regulating plates whose width can be adjusted according to the size of the recording material P is provided to accommodate recording materials P of sizes other than the standard size. A pickup roller 29 feeds the recording material P from a paper feed tray 28 . The image forming apparatus 100 has a motor 30 that drives the fixing device 200 and the like. A control circuit 400 as heater driving means connected to a commercial AC power supply 401 controls power supply to the fixing device 200 .

The photoreceptor 19, charging roller 16, scanner unit 21, developing device 17, and transfer roller 20 described above constitute an image forming section for forming an unfixed image on the recording material P. FIG. In this embodiment, a developing unit including the photosensitive member 19, the charging roller 16 and the developing device 17, and a cleaning unit including the drum cleaner 18 are detachably attached to the main body of the image forming apparatus 100 as the process cartridge 15. It is

(Printable paper size)
The laser printer 100 of this embodiment is compatible with a plurality of recording material sizes. LETTER paper (approximately 216 mm×279 mm) and Legal paper (approximately 216 mm×356 mm) can be set in the paper feed cassette 11 . Furthermore, A4 paper (210 mm x 297 mm), Executive paper (about 184 mm x 267 mm), JIS B5 paper (182 mm x 257 mm), A5 paper (148 mm x 210 mm), and A6 paper (105 mm x 148 mm) can be set.

(Paper transport based on one side)
This image forming apparatus can print on recording materials (sheet materials) of the above sizes. They are set according to the cassette reference surface, which is always the same. Regardless of the size of the recording material, after it is fed, it is subjected to image formation, heat-fixing, and is ejected out of the machine so that it follows the paper conveyance reference plane (the width direction of the recording material). While one end remains aligned with the reference position), it is conveyed through the machine. In one-sided reference transport, the reference surface is constant regardless of the size of the recording material, so it is possible to set the reference surface over the entire paper passing area. There is an advantage that the reproducibility is improved and the printing accuracy is greatly improved. Also, the size of the recording material set in the paper feed cassette 11 is detected by a size detection member (not shown), and the information can be used to control the fixing device, which will be described later.

(fixing device)
FIG. 2 is a schematic cross-sectional view of a fixing device 200 as an image heating device of this embodiment. The fixing device 200 includes a cylindrical film 202 as a heating rotating member, a heater 300 that contacts the inner surface of the film 202, and a pressure roller (pressure rotating member) 208 that contacts the outer surface of the film 202 as a pressure member. and have The pressure roller 208 forms a fixing nip portion N together with the heater 300 via the film 202 .
The film 202 is a multilayer heat-resistant film having flexibility and formed in a cylindrical shape, and the material of the base layer is a heat-resistant resin such as polyimide or a metal such as stainless steel. In addition, the film 202 may be provided with an elastic layer such as heat-resistant rubber. Furthermore, a release layer such as a fluorine resin may be provided thereon.
The pressure roller 208 has a metal core made of iron, aluminum, or the like, and an elastic layer made of silicone rubber or the like. Furthermore, a release layer formed of a fluororesin tube or coat may be provided thereon.
The heater 300 is held by a holding member 201 made of heat-resistant resin such as liquid crystal polymer. The holding member 201 also has a guide function of guiding the rotation of the film 202 .
The metal stay 204 is for applying pressure to the holding member 201 by a pressure member such as a spring (not shown), and also serves to reinforce the holding member 201 and the heater 300 .

(flange)
FIG. 3 is a schematic diagram showing the configuration of the fixing device 200 in Example 1 when viewed from a direction parallel to the conveying direction of the recording material (in a direction orthogonal to the conveying direction). The fixing film 202 may shift left or right in the longitudinal direction, and fixing flanges 213 (restricting members) are provided at both ends of the fixing film 202 to regulate the shift. When the fixing film 202 is skewed, the end surface of the fixing film moves and abuts against the end surface facing portion of the fixing flange 213, thereby restricting the skew. The fixing flange 213 also has an inner surface facing portion that faces the inner surface of the end portion of the fixing film 202 . A slight clearance is provided between the inner surface of the fixing film 202 and the inner surface facing portion, and the inner surface facing portion also has the function of guiding the inner surface of the fixing film 202 during rotation of the fixing film.

The pressure roller 208 receives a driving force from the motor 30 and rotates in the direction of the arrow in FIG. The rotation of the pressure roller 208 causes the film 202 to rotate. The recording material P carrying the unfixed toner image is heated while being conveyed and nipped in the fixing nip portion N to be fixed.

(heater)
FIG. 4 is a schematic diagram (schematic plan view of the surface on the fixing nip portion N side) showing the configuration of the heater 300 of this embodiment.
The image forming apparatus of the present embodiment is a one-sided reference transport apparatus that transports the recording material so that the left end of the recording material in the longitudinal direction (direction perpendicular to the transport direction) is aligned with the transport reference position X. FIG.
The heater 300 includes a substrate 305 made of ceramic, and a heating element (heating resistor) 302 that generates heat by supplying power to the surface (first surface) of the fixing nip portion N of the substrate 305 on the substrate 305 . have

The heating element 302 is divided into three blocks in the longitudinal direction of the substrate 305 (heating elements 302-1, 302-2, 302-3). The heating element 302-1 is provided so as to form a heating area in the nip portion for heating the area from the conveyance reference position X to the paper width edge position of the A5 size paper. The heating element 302-2 is provided so as to form a heating area in the nip portion for heating the area from the paper width end position of the A5 size paper to the paper width end position of the EXECTIVE size paper. The heating element 302-3 is provided so as to form a heating region in the nip portion for heating a region ranging from the EXECTIVE size end to the LETTER size end.
That is, in the present embodiment, the end surface positions of the heat generating elements farther from the transfer reference position X are 148 mm for the heat generating element 302-1, 185 mm for the heat generating element 302-2, and 216 mm for the heat generating element 302-3. An arrangement example is shown.

Conductive portions 301-G, 301-1, 301-2, and 301-3 for supplying power to the respective heating elements are connected to the heating elements 302-1, 302-2, and 302-3. It is Further, contacts C1 to C4 are provided near the ends in the longitudinal direction of the substrate 305, and the contacts C1 to C4 are electrically connected to the control circuit 400 through contacts (not shown).
Further, the contact C1 is connected to the conductive portion 301-G, the contact C2 is connected to the conductive portion 301-1, the contact C3 is connected to the conductive portion 301-2, and the contact C4 is connected to the conductive portion 301-3. .
That is, when heating the heating element 302-1, between the contacts C1 and C2, when heating the heating element 302-2, between the contacts C1 and C3, and when heating the heating element 302-3, , and power is supplied from the control circuit 400 by energizing between the contacts C1 and C4.
The heating element 302 and the conductive portion 301 on the heater 300 are covered with a glass layer 307 for the purpose of ensuring the slidability of the film 202 and insulating the heating element 302 and the conductive portion 301 .

FIG. 5 is a schematic diagram (a schematic plan view of the surface opposite to the fixing nip portion N side) showing the configuration of the heater 300 of this embodiment.
As shown in FIGS. 2 and 5, the surface of the heater 300 opposite to the surface on which the heating element 302 is provided with the heater substrate 305 therebetween is provided with temperature detection means (second temperature detection means). The thermistors TH1 to TH3 are in contact with each other. The thermistors TH1 to TH3 are arranged on the surface of the heater substrate 305 opposite to the surface on which the heat generating elements 302-1 to 302-3 are provided, and are approximately parallel to the longitudinal direction of the heat generating elements 302-1 to 302-3. They are in contact directly behind the central position. In this embodiment, the distances from the transfer reference position X are 74 mm for thermistor TH1, 167 mm for thermistor TH2, and 200 mm for thermistor TH3. An example of central placement is shown. Lead wires are connected to the thermistors TH1 to TH3, respectively, and are connected to the control circuit 400 of the image forming apparatus.

Temperature detection of heater 300 is performed by thermistors TH (TH1-1 to TH1-3). That is, the control circuit 400 calculates the electric power to be supplied by, for example, PI control (proportional integral control) based on the control target temperature TGT _i of each heating element 302 and the detected temperature of the thermistor TH, and the temperature of the thermistor TH is calculated. It is controlled so as to reach the control target temperature TGT _i .

(Temperature detection of pressure roller)
As shown in FIG. 3, in order to detect the temperature of the pressure roller near the surface of the pressure roller 208 and at a position where the longitudinal position substantially coincides with the thermistor position of each heating element, the temperature of the first temperature detection means is measured. Non-contact temperature sensing elements S1 to S3 are arranged as sensing members.
Temperature detection elements S1 to S3 can detect the temperature of pressure roller 208 in a non-contact manner by detecting infrared rays emitted from pressure roller 208 . The temperature detection elements S1 to S3 are also connected to the control circuit 400 by electric wiring (not shown), like the temperature detection thermistors TH1 to TH3 of the heater 300 .

(Control target temperature of each heating element)
Referring to FIG. 6, temperature control of heating elements 301-1 to 301-3 when printing (heating and fixing) recording materials of various sizes will be described. FIG. 6 is a table showing control target temperatures TGT _{1 ,} TGT ₂ , and TGT ₃ of heating elements 302-1 to 302-3 in the first embodiment.

(Passing A4 size paper / LETTER size paper)
When A4 size (210 mm width) paper and LETTER size (216 mm width) paper are passed through, the control target temperatures TGT _1, TGT ₂ , and TGT ₃ of the heating elements 301-1 to 301-3 control the fixability of the recording material. The same control temperature T0 that satisfies the conditions is set, and the electric power supplied to each heating element is controlled. That is, temperature control is performed on all the heating elements using the temperatures detected by the thermistors TH1 to TH3 for detecting the temperature of the heater 300. FIG. In this case, since the width of the recording material is substantially the same as the width of the heating element 302, both the fixing film 202 and the pressure roller 208 have a substantially uniform temperature along their length. In this case, since the amount of thermal expansion along the length of the pressure roller 208 is also substantially uniform, the outer diameter of the pressure roller 208 is also substantially uniform over the length. Therefore, the film-side force due to the difference in the outer diameter of the pressure roller 208 does not act, and the film-side force is suppressed within the permissible range of the proof stress of the film 202 .

(Passing B5 size paper/Executive size paper)
When B5 (width 182 mm)/executive size (width 185 mm) paper is passed, the control target temperatures TGT ₁ and TGT ₂ of the heating elements 302-1 and 302-2 are set to a predetermined temperature T0 that satisfies the fixability, and heat generation Electric power supplied to bodies 301-1 to 301-2 is controlled. On the other hand, the control temperature _TGT3 of the heating element 302-3 outside the width of the EXECTIVE size paper is TS1 (which changes with the passage of paper), which is set so that the temperature of the temperature detection element S3 becomes the same as the temperatures of the temperature detection elements S1 and S2. ) to control the power supply to the heating element 302-3. That is, for the heating element 302-3 that heats the non-sheet-passing heating area among the heating areas that heat the nip portion, the temperature detected by the thermistor TH3 for detecting the temperature of the heater 300 is not the temperature detected by the thermistor TH3 for detecting the temperature of the pressure roller 208. Temperature control is performed using the temperature detected by the temperature detection element S3. By controlling the temperature of the heating element as described above, the temperature of the pressure roller 208 regions W1 to W3 becomes substantially uniform, and the outer diameters of the pressure rollers in the regions W1 to W3 become substantially the same. 202 can suppress the force to one side.

(Passing of A5 size paper)
When A5 size paper (width 148 mm) is passed, the control target temperature TGT ₁ of the heating element 302-1 is the predetermined temperature T0 that satisfies the fixability of the heating paper, and the electric power to be supplied to the heating element 301-1 is set. Control. The control temperatures TGT ₂ and TGT ₃ of the heating elements 302-2 and 302-3 outside the A5 size paper width are set so that the temperatures of the temperature detection elements S2 and S3 are the same as the temperature of the temperature detection element S1. TS1 (which changes as the paper passes), and controls the power supply. By controlling the temperature of the heating element as described above, the temperature of the regions W1 to W3 of the pressure roller 208 becomes substantially uniform, and the outer diameter of the pressure roller in the regions W1 to W3 becomes substantially the same. A force that causes the film 202 to lean to one side can be suppressed.

As described above, by detecting the temperature of the pressure roller 208 and controlling the control target temperature TGT _i of the heating elements 301-1 to 301-3 based on the detected value, the temperature difference in the longitudinal direction of the pressure roller 208 is The power supplied to each heating element is controlled so that . As a result, even when recording materials of various sizes are passed through, the occurrence of lateral temperature difference in the longitudinal direction of the pressure roller 208 can be suppressed, and the difference in outer diameter between the left and right due to thermal expansion of the pressure roller 208 can be minimized. can be done. As a result, it is possible to minimize the film bias force caused by the difference in the outer diameter of the pressure roller 208, suppress the occurrence of film breakage, and extend the life of the fixing device.

[Embodiment 2] (Change the control of the paper interval)
Embodiment 2 of the present invention will be described with reference to FIG. In the second embodiment, descriptions of the configurations and the like that are common to the first embodiment are omitted. Matters not described here in the second embodiment are the same as in the first embodiment.
In Example 1, the heating element of the heater is divided into three, 301-1 to 301-3, and LETTER size paper and A4 size paper, and EXECTIVE size paper and B5 size paper are both controlled at the same target temperature. An example of controlling is shown.
However, A4 size paper is 6 mm smaller in width than LETTER size paper, and B5 size is 2 mm smaller than EXECTIVE size. Therefore, when A4 size paper is passed, the temperature of the pressure roller is locally higher than other regions in the range between 210 mm and 216 mm from the conveyance reference position X, and in the case of B5 paper, between 182 mm and 184 mm. tend to become In particular, when about 20 sheets or more are continuously passed, or when a recording material having a large heat capacity such as thick paper is passed, this tendency becomes remarkable.
Embodiment 2 shows an example of heater temperature control for suppressing these local increases in pressure roller temperature.

FIG. 7 is a table showing control target temperatures TGT _{1 ,} TGT ₂ , and TGT ₃ of heating elements 302-1 to 302-3 in the second embodiment.
When the recording materials are continuously passed, a predetermined distance (paper gap) is provided between the recording materials to be passed. That is, there is provided a period during which the recording materials do not pass through the fixing nip portion when a plurality of recording materials pass through the fixing nip portion continuously at predetermined intervals. FIG. 7 shows the control target temperatures TGT ₁ to TGT ₃ of the heating elements 302-1 to 302-3 when passing through the nip and between sheets for recording materials of each paper size.

For example, in the case of A4 size paper, the control target temperatures of the heating elements 302-1 to 302-3 are all T0 when the recording material passes through the fixing nip. A lower control target temperature T3 is set. By doing so, it is possible to make the temperature in the longitudinal direction of the pressure roller 208 more uniform than when A4 size paper is passed in the first embodiment. If the temperature control between sheets is kept lower than that during sheet feeding, there is almost no effect on the fixability of the toner image.

Similarly, in the case of B5 size paper, the control target temperatures of the heating elements 302-1 to 302-3 are all T0 when the recording material passes through the fixing nip, but only the heating element 302-2 is set to T0 between sheets. , to be a control target temperature T2 lower than T0. By doing so, it is possible to make the temperature in the longitudinal direction of the pressure roller 208 more uniform than when B5 size paper is passed in the first embodiment.

Similarly, when passing a recording material (A6 size paper, envelope, index card, etc.) narrower than A5 size paper (width 148 mm), the control target temperature of the heating element 302-1 is set to T0 A lower control target temperature T1 is set. By doing so, the temperature in the longitudinal direction of the pressure roller 208 can be made more uniform.

As described above, when a recording material such as A4, B5, or A6 size paper, which is narrower than the end position of the heating elements 302-1 to 302-3 on the far side from the conveyance reference position X, is passed, , the control target temperature between sheets is set low. By doing so, it is possible to further reduce the difference in outer diameter due to thermal expansion of the pressure roller 208 . As a result, it is possible to minimize the film bias force caused by the difference in the outer diameter of the pressure roller 208, suppress the occurrence of film breakage, and extend the life of the fixing device.

[Example 3] (Place the temperature detection element near the edge of the paper)
A third embodiment of the present invention will be described with reference to FIG. In the third embodiment, a repetitive description of the configuration and the like that are common to the first and second embodiments will be omitted. Matters not described here in the third embodiment are the same as in the first and second embodiments.
FIG. 8 is a schematic diagram showing the configuration of the fixing device 200 in Example 3 when viewed from a direction parallel to the conveying direction of the recording material (in a direction orthogonal to the conveying direction).
In Embodiments 1 and 2, the longitudinal positions of the non-contact temperature detecting elements S1 to S3 for detecting the temperature of the pressure roller 208 are substantially the same as the thermistor positions of the respective heating elements ( in the longitudinal direction, the heating element ) is shown. In the third embodiment, as shown in FIG. 8, each of the temperature detection elements S2 to S3 is positioned slightly inside (the other (near the edge of ).

For example, when A4 size paper (width 210 mm) is passed through, the temperature detection element S3 is arranged at a distance of 210 mm to 216 mm from the recording material reference surface X, and is outside the area through which the A4 size paper passes. be. Therefore, when A4 size paper is continuously fed, the temperature rises locally in a region between 210 mm and 216 mm from the conveyance reference position X of the pressure roller 208 . As shown in the second embodiment, by lowering the control target temperature of the heating element 302-3 between sheets, the local temperature rise of the pressure roller 208 can be suppressed. However, since the temperature detection element S3 is at the position shown in FIG. 8, the temperature in the region of the distance of 210 mm to 216 mm from the conveying reference position X of the pressure roller 208 does not drop to the same temperature as the other regions. It is assumed that In such a case, based on the temperature detected by the temperature detection element S3, the paper interval is increased (the interval between the recording materials is widened when a plurality of recording materials are continuously passed through the nip portion). The heat of the pressure roller heating portion can be diffused. This makes it possible to make the temperature distribution of the pressure roller 208 in the longitudinal direction more uniform. As a result, it is possible to further reduce the film bias force caused by the difference in the outer diameter of the pressure roller 208, suppress the occurrence of film breakage, and extend the life of the fixing device.

[Example 4] (Heater for A4 size)
Embodiment 4 of the present invention will be described with reference to FIG. In the fourth embodiment, the repetitive description of the configurations and the like that are common to the first to third embodiments will be omitted. Matters not described here in Example 4 are the same as in Examples 1-3.
FIG. 9 is a schematic diagram (schematic plan view of the surface on the fixing nip portion N side) showing the configuration of the heater 300 of this embodiment.
In Examples 1 to 3, the heating element of the heater extends approximately 216 mm from the transport reference position X so as to satisfy the fixability of LETTER size paper (width 216 mm), which is the maximum paper width. However, LETTER size and EXECTIVE size are used only in the North American market and limited regions. It is enough if the body can also cover A4 size. Therefore, heaters having different dimensions from the transfer reference position X to the end of the heat generating element and different positions of dividing the heat generating elements may be used for the North American market and for the other markets. In this embodiment, an example of a heater having a heating element with specifications that are optimal for A4/B5 size rather than LETTER/EXECTION size is shown (Fig. 9).

The difference from the heaters of Examples 1 to 3 is that the distance from the transfer reference position X of the heating element 302-3 to the end on the far side is 210 mm, which is almost the same as the A4 size, and that the heating element 302-2 and the heating element are different. The division position of the body 302-3 is 182 mm, which is equivalent to the width of B5 size paper.

By using the heater of Example 4, even when A4 or B5 recording material is printed, the distance from the conveyance reference position X is 210 mm to 216 mm and 182 mm to 185 mm compared to the case of Examples 1 to 3. There is no local temperature rise of the pressure roller 208 in the area of . As a result, it is possible to further reduce the film bias force caused by the difference in the outer diameter of the pressure roller 208, suppress the occurrence of film breakage, and extend the life of the fixing device.

[Example 5] (4 divisions)
Embodiment 5 of the present invention will be described with reference to FIGS. 10 to 13. FIG. In the fifth embodiment, the repetitive description of the configurations and the like that are common to the first to fourth embodiments will be omitted. Matters not described here in Example 5 are the same as in Examples 1-4.
Examples 1 to 4 show examples in which the heat generating portion of the heater 300 is divided into three and controlled to independent control target temperatures TGT ₁ to TGT ₃ respectively, but in Example 5, as shown in FIGS. 2 shows an example in which the heat generating element 302-1 is further divided into two parts, resulting in a total of four parts. The heating elements of Example 5 are the heating element 302-4 at 105 mm from the transfer reference position X, the heating element 302-5 at 105 mm to 148 mm, the heating element 302-6 at 148 mm to 185 mm, and 185 mm to 216.
mm heating element 302-7. Further, as in the first to fourth embodiments, thermistors TH-4 to TH-7 corresponding to the heat generating elements 302-4 to 302-7, and the pressure roller 208 also have temperature detection elements in the regions W1 to W4, respectively. S4 to S7 are arranged.

FIG. 13 shows the control target temperatures TGT ₄ to TGT ₇ of the heating elements 302-4 to 302-7 when passing through the nip and between sheets for recording materials of each paper size.
Here, the control target temperatures TGT5 to TGT7 of the heating elements 302-4 to 302-7 when printing each size of LETTER, A4, Executive, B5, and A5 are set in the same manner as TGT1 to TGT3 in Examples 1 to 4. Therefore, the explanation is omitted.

(When A6 size paper is fed)
When A6 size paper (width 105 mm), which is the minimum size paper supported in this embodiment, is passed through, the control target temperature _TGT4 of the heating element 302-4 is set to a predetermined temperature T0 that satisfies the fixability of the recording material. , controls the power supplied to the heating element 302-4. For the control temperatures TGT ₅ to TGT ₇ of the heating elements 302-5 to 305-7 outside the width of the A6 size paper, the temperatures of the temperature detection elements S5 to S7 are controlled so that the temperature of the temperature detection element S4 is the same as that of the temperature detection element S4. (changes as the paper passes), and controls the power supply.

By controlling the temperature of the heating element as described above, even when printing on a recording material with a narrow width such as A6 size paper, the temperature of the regions W1 to W4 of the pressure roller 208 becomes substantially uniform, and the temperature of the region W1 becomes uniform. The outer diameters of the pressure rollers of W4 to W4 are substantially the same. As a result, the force that causes the film 202 to lean to one side can be suppressed. Therefore, the damage to the film 202 can be further reduced, and the life of the fixing device can be further extended.
Moreover, since it is not necessary to widen the paper interval more than necessary even when printing on a narrow recording material, it is possible to increase the number of prints per unit time.

[Example 6] (divided into two)
Embodiment 6 of the present invention will be described with reference to FIGS. 14 to 17. FIG. In the sixth embodiment, a repetitive description of the configuration and the like that are common to the first to fifth embodiments will be omitted. Matters not described here in Example 6 are the same as in Examples 1-5.
Examples 1 to 5 show examples in which the heating portion of the heater 300 is divided into 3 to 4 parts and controlled to the control target temperatures TGT ₁ to TGT ₃ independently of each other. In the sixth embodiment, as shown in FIGS. 14 to 16, the heating element of the heater 300 is divided into only two heating elements 302-8 and 302-9. As for the divided heating element 301, an example is shown in which the heating element 302-8 is located 105 mm from the transfer reference position X, and the heating element 302-9 is located from 105 mm to 210 mm. Thermistors TH-8 to TH-9 are arranged on the opposite surface of the heater substrate 305 of each of the heating elements 302-8 to 302-9, as in the first to third embodiments. Further, temperature detection elements S8 and S9 are arranged in the regions W1 and W2 of the pressure roller, respectively.

Temperature control of the heating elements 302-8 to 302-9 when printing recording materials of each size will be described. FIG. 17 shows the control target temperatures TGT ₈ and TGT ₉ of the heating elements 302-8 to 302-9.

(Passing LETTER size paper)
When LETTER size (width 216 mm) paper is passed, the control target temperatures TGT _{8 and} TGT ₉ of the heating elements 302-8 to 302-9 are the same control temperature T0 that satisfies the fixability of the paper. 8 to 302-9 control the power supplied. In this case, since the width of the paper is substantially the same as the width of the heating element 302, both the fixing film 202 and the pressure roller 208 have a substantially uniform temperature along their length. In this case, since the amount of thermal expansion along the length of the pressure roller 208 is also substantially uniform, the outer diameter of the pressure roller 208 is also substantially uniform over the length. Therefore, the film-side force due to the difference in the outer diameter of the pressure roller 208 does not act, and the film-side force is suppressed within the permissible range of the proof stress of the film.

(Passing A4 size, B5 size paper, and EXECTIVE size paper)
When A4 size, B5 (width 182 mm)/executive size (width 185 mm) paper is passed, the control target temperatures of the heating elements 302-8 to 302-9 are all T0 when passing through the fixing nip of the recording material. During the sheet interval, only the heating element 302-9 is set to control target temperatures T4 to T6, which are lower than T0. As a result, the temperature in the longitudinal direction of the pressure roller 208 can be made nearly uniform.
Here, if the temperature cannot be lowered to the same level as the temperature in other areas simply by changing the control target temperature between the sheets, the temperature detected by the temperature detection element S2 is further increased to increase the distance between the sheets. Diffusion of the heat of the pressure roller heating part. This makes it possible to make the temperature distribution of the pressure roller 208 in the longitudinal direction more uniform.

(Passing of A5 size paper)
When A5 size paper (width 148 mm) is passed, the control target temperature _TGT8 of the heating element 302-8 is set to a predetermined temperature T0 that satisfies the fixability of the paper, and the power supplied to the heating element 302-8 is controlled. . Also, the control temperature _TGT9 of the heating element 302-9 outside the width of the A5 size paper is set to TS8 (changes with paper passing) so that the temperature of the temperature detection element S9 becomes the same as the temperature of the temperature detection element S8. It controls the power supplied to body 302-9.

By controlling the temperature of the heating element as described above, the temperature of the regions W1 to W3 of the pressure roller 208 becomes substantially uniform, and the outer diameter of the pressure roller in the regions W1 to W3 becomes substantially the same. It is possible to suppress the force of the film leaning to one side.
When paper narrower than A5 size paper is passed, the control temperature of the TGT8 between papers is set to T7, which is lower than T0. It becomes possible to make the temperature distribution in the longitudinal direction of the pressure roller 208 more uniform.
With the configuration shown in this embodiment, it is possible to provide a fixing device that is simpler and less expensive than the configurations shown in the first to fifth embodiments.

As described above, the heating element of the heater is divided into a plurality of blocks and independently controlled, and the temperature of the pressure roller 208 is detected to control the control target temperature TGT _i of the heating element based on the detected value.
By doing so, even when recording materials of various sizes are passed through, the occurrence of a temperature difference in the longitudinal direction of the pressure roller 208 can be suppressed, and the difference in outer diameter between the left and right due to thermal expansion of the pressure roller 208 can be minimized. can be suppressed. As a result, it is possible to minimize the film bias force caused by the difference in the outer diameter of the pressure roller 208, suppress the occurrence of film breakage, and extend the life of the fixing device.

Further, the heating member 300 of the fixing device 200 of this embodiment is first divided by a length substantially corresponding to the width of the recording material of the minimum size, and then divided to a length substantially corresponding to the width of the recording material of the maximum size. It is configured to be divided into at least two or more. Although the heating element 302 is divided into 2, 3, and 4 parts in the above embodiment, the structure is not limited to this example. For example, even if the heating element 302 is divided into five or more sections, the configuration of the apparatus becomes complicated, but it is possible to perform optimum control corresponding to other paper sizes. This is effective in minimizing the difference in outer diameter of the roller, and it is possible to further extend the life of the fixing device.

Further, the division position of the heating element 302 of the heating element 300 is not limited to the position shown in this embodiment, and the optimum division position may be selected according to the frequency of use of the size of the recording material to be printed. is possible.

In addition, in this embodiment, an example is shown in which the temperatures in the regions W2 to W4 are controlled to be equal by following transient changes in the temperature detection element arranged in the pressurization region W1. It is not limited to the configuration example. For example, as shown in FIG. 18, no temperature detection element is placed in the area W1, and the temperature in the area W2 to W4 is simply adjusted so that the temperature in the area W2 to W4 does not exceed a predetermined threshold value (for example, 150° C.). It may be configured to control the temperature of the heating element. Even in this case, there is a certain effect in equalizing the temperature of the pressure roller and minimizing the difference in outer diameter of the pressure roller.

Further, in the heater 300, as shown in FIG. 19, the boundary portions of the divided heating elements 301 may be obliquely overlapped in a pattern. In this case, since the heat distribution at the boundary of the heating element 302 becomes more uniform, the heat generation distribution of the entire heater 300 becomes more uniform, and image defects due to temperature unevenness are less likely to occur.

In this embodiment, the temperature detection element for detecting the temperature of the pressure roller detects the roller surface temperature in a non-contact manner, but a contact type element using a thermistor or thermocouple may be used. .

In this embodiment, an example of a laser printer that basically feeds paper longitudinally (transports so that the long side of the paper is parallel to the transport direction) and that is compatible with A4 size and LETTER size paper has been shown. The configuration is not limited. For example, the present invention can be similarly applied to a printer compatible with A3 size paper that feeds paper sideways.

Further, although the image forming apparatus of the present embodiment is described as a typical example of a monochrome laser printer using monochrome toner, the image forming apparatus is not limited to this. For example, the present invention can be applied to a tandem type color laser printer that forms an image by transferring two or more color toners onto a recording material via an intermediate transfer belt.

Each of the above embodiments can be combined with each other as much as possible.

DESCRIPTION OF SYMBOLS 100... Image forming apparatus P... Recording material 200... Fixing device (image heating device) 300... Heater (heating body) 301... Heating element 202... Fixing film (endless belt) 208... Pressure roller (heater) pressure member), 213... fixing flange (restriction member), TH1 to TH9... thermistor (
second temperature detection means), S1 to S9... temperature detection member (first temperature detection means), X... conveyance reference position

Claims (6)

an image forming unit that forms an image on a recording material;
A cylindrical film that rotates while being in contact with a recording material ; and a heater that is elongated in a direction orthogonal to the conveying direction of the recording material and that is arranged in an internal space of the film, and that includes a plurality of heat generating elements arranged in the longitudinal direction of the heater. and a pressure member forming a nip portion together with the heater through the film , the image heating portion heating the recording material while conveying it in the nip portion ;
a control unit that controls power supplied to each of the plurality of heating elements according to the size of the recording material passing through the nip ;
with
An image forming apparatus in which a recording material is conveyed along the conveying path such that one end in the longitudinal direction coincides with a reference position in the longitudinal direction of the conveying path of the recording material, regardless of the size of the recording material. ,
a plurality of temperature detection members for detecting respective temperatures in a plurality of regions of the pressure member corresponding to the plurality of heating regions of the nip heated by the plurality of heating elements;
The image forming apparatus, wherein the control unit controls power supplied to the plurality of heating elements so that a difference between the temperatures detected by the plurality of temperature detecting members becomes small. A control target temperature is determined for each of the plurality of heating elements,
A control target temperature of the heating element corresponding to the heating region in which the recording material does not pass in the nip portion is detected by the temperature detection member corresponding to the heating region in which the recording material passes in the nip portion. 2. The image forming apparatus according to claim 1, wherein the temperature is set based on a difference between a temperature and a temperature detected by the temperature detecting member corresponding to the heating area through which the recording material does not pass in the nip portion. . Among the plurality of heating regions , the temperature detecting member for detecting the temperature of the heating region other than the heating region through which the recording material always passes regardless of the size of the recording material is arranged in the longitudinal direction in the heating region. 2. The image forming apparatus according to claim 1, wherein the reference position in the direction is provided near the other end. The control unit always controls the recording material to pass through the plurality of heating areas regardless of the size of the recording material.
wherein the power supplied to the plurality of heating elements is controlled so that the temperatures detected by the temperature detection members corresponding to the heating regions other than the heating region do not exceed a predetermined threshold value. The image forming apparatus according to . When a plurality of recording materials pass through the nip continuously at predetermined intervals, the control unit controls the recording materials to pass through the nip during a period in which the recording materials do not pass through the nip. electric power supplied to a heating element for heating a heating region, out of the plurality of heating regions, through which the recording material does not pass, so as to maintain a second control target temperature lower than the control target temperature when the recording material is 3. The image forming apparatus according to claim 2 , wherein the image forming apparatus supplies . The plurality of heating elements are
are arranged so as to be divided in a direction orthogonal to the conveying direction according to the size of the recording material,
From the reference position, it is first divided by a length substantially corresponding to the width of the recording material of the minimum size, and then divided into at least two or more to a length substantially corresponding to the width of the recording material of the maximum size. The image forming apparatus according to any one of claims 1 to 5 , characterized by:

Images