JPH11133800A - Fixing unit and image forming device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing unit capable of preventing the cracking of a heating body by suppressing the rising of the temp. of the end part of the heating body as low as possible, even if small-sized sheets of paper are consecutively fixed and further, obtaining excellent fixability by preventing a temperature difference from being made in both end parts of the heating body, and a copying device provided with the fixing unit. SOLUTION: In the fixing unit provided with the heating body and a film which comes into contact with the heating body and is moved together with sheets of paper, to heat/fix a toner image on the paper by the heating body, with the film, the heating body consists of a main heating body H1 and a subheading body H2 and the main heating body H1 is formed such a size that sheets of paper having a maximum size in the axial direction of the heating body can be thermally fixed. Then, a central part temperature detecting means 51 is provided in the central part and an end part temperature detecting means 52 is provided in the end part. On the other hand, the subheating body H2 consists of a nondivided single body and a subheating body temperature detecting means 53 is provided in the central part. Then, the subheating body H2 is arranged on the upstream side in the carrying direction of the paper and the main heating body H1 is arranged on the downstream side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device (surf fixing device) having a heating element and a film which comes into contact with the heating element and moves together with the sheet, and heat-fixes a toner image on the sheet via the film. ) And an image forming apparatus provided with the surf fixing device.

[0002]

2. Description of the Related Art As shown in FIG. 8, a fixing unit 20, which is called a surf fixing device, includes a heating structure 31, an endless film 35 which comes into contact with the heating structure 31 and moves together with a sheet P. Film transport rollers 33 and 34 for driving the film 35 and a pressure roller 3 for pressing the paper P against the heating structure 31 via the film 35
6 is provided. The nip portion N is formed at a position where the pressure roller 36 comes into pressure contact with the heating structure portion 31 via the film 35, and is a portion that thermally fixes the paper P. Heating structure 31
Has a heating element 41 and a temperature detecting means 45 such as a thermistor. The temperature detecting means 45 is for detecting the temperature of the nip N.

[0003] As one of conventional examples of the heating element 41, the one shown in FIG. 9 is known. This heating element 41
Consists of one single body. The temperature detecting means 45 provided on the heating body 41 is for controlling the heating body 41 to a predetermined fixing temperature. However, the heating element 41 is a sheet P having a small size in the width direction of the heating element 41 as illustrated.
Is continuously fixed, the end of the heating body 41 that does not touch the sheet (non-sheet passing portion N2) does not lose heat by the sheet, so that the temperature increases. Non-paper passing section N2 and paper passing section N
If the temperature difference between them is too large, cracks occur in the heating element 41 due to thermal stress. For this reason, conventionally, a heating element that does not break even with a large temperature difference is taken, or measures are taken to improve the heat conduction of the heating element so that a temperature difference does not occur. However, when the heating element has such a special structure, there is a problem that manufacturing cost is increased.

[0004] To solve this problem,
A heating element as shown in FIG. 10 has been proposed and is known. This heating element is composed of a central heating element 41A disposed at the center and a pair of end heating elements 41 separately disposed so as to extend outside both ends of the central heating element 41A.
B. The nip width of the central heating body 41A and the nip width of the end heating body 41B are combined to form a nip portion capable of handling a sheet of the maximum size. The central heating body 41A and the end heating body 41B are provided with temperature detecting means 51 and 52, respectively, so that the temperature is controlled separately. According to this heating body, in the case of a large-sized sheet, both the center heating body 41A and the end heating body 41B are temperature-controlled. On the other hand, in the case of small-size paper (as shown), only the central heating body 41A is temperature controlled. This prevents the heating element from cracking during continuous fixing of small-size paper.

[0005]

However, the heating element shown in FIG. 10, that is, the heating element in which two end heating elements 41B are arranged at both ends of the central heating element 41A, is not provided. However, there are the following problems. Although the resistance of the heating element has the same standard, the actual resistance value actually has a relatively large variation in manufacturing, even if the standard is the same. Therefore, the two end heaters 41 which are separately disposed at both ends are provided.
B has a problem that a relatively large temperature difference is easily generated between B and the fixing state is deviated left and right, thereby causing a fixing failure. In short, the heating element shown in FIG. 10 can prevent cracking, but has a problem in that fixing performance is sacrificed.

SUMMARY OF THE INVENTION It is an object of the present invention to minimize the temperature rise at the end of a heating element even when small-sized paper is continuously fixed, thereby preventing the heating element from cracking. An object of the present invention is to provide a fixing device capable of achieving a good fixing property by preventing a temperature difference from occurring, and an image forming apparatus provided with the fixing device.

[0007]

According to a first aspect of the present invention, an object of the present invention is to provide a toner image having a heating element and a film which comes into contact with the heating element and moves together with the sheet. In a fixing device that heat-fixes a sheet through a film, the heating element is composed of a main heating element and a sub-heating element, and the main heating element is formed in a length capable of thermally fixing a sheet of the maximum size in the axial direction of the heating element, and The central part is provided with a central part temperature detecting means, the end part is provided with an end temperature detecting means, and the sub-heating body is formed of an undivided unitary body and the heating part is formed shorter than the heating part of the main heating body. This is achieved by providing a sub-heating body temperature detecting means in the center, the sub-heating body is arranged on the upstream side in the sheet conveying direction, and the main heating body is arranged on the downstream side.

[0008] According to a second aspect of the present invention,
The above object is achieved by the first aspect of the invention in which the main heating element is provided with the end temperature detecting means disposed on the extension of the boundary between the heating section and the conductor section of the sub-heating element in the paper transport direction. .

According to the third aspect of the present invention,
The above object is achieved by the sub-heating body of the first invention, wherein the length of the heating unit is longer in the axial direction of the heating body than the paper width of the minimum size paper.

According to a fourth aspect of the present invention,
An object of the present invention is to provide a fixing device according to any one of the first to third aspects of the present invention, wherein a main heating element driving means for energizing a main heating element and a sub-heating element driving means for energizing a sub-heating element. And a temperature control unit. The temperature control unit controls the main heating unit driving unit to set the main heating unit at the fixing temperature T00 based on the temperature detected by the central temperature detection unit after the start of image formation. When the temperature difference between the end portion and the center portion of the main heating body reaches a predetermined value T1 based on the respective detected temperatures of the central temperature detecting portion and the end portion temperature detecting portion, the detection is performed by the sub-heating body temperature detecting portion. Based on the temperature, the sub-heater driving means starts the temperature control of the sub-heater at the fixing temperature T00, and the temperature difference between the end portion and the center portion of the main heater becomes equal to or more than a predetermined value T2 (T2> T1). Sometimes the temperature at the center is detected from the temperature at the center. And temperature control of the main heater is switched to the detection means, the temperature of the end portion of the subsequent main heating body fixing temperature T
This is attained by setting the temperature control of the sub-heating member to be stopped when the temperature reaches 00, and the main heating member is again controlled at the fixing temperature T00 based on the temperature detected by the central temperature detecting means.

According to a fifth aspect of the present invention,
An object of the present invention is to provide a fixing device according to any one of the first to third aspects of the present invention, wherein a main heating element driving means for energizing a main heating element and a sub-heating element driving means for energizing a sub-heating element. And a temperature control unit. The temperature control unit controls the main heating unit driving unit to set the main heating unit at the fixing temperature T00 based on the temperature detected by the central temperature detection unit after the start of image formation. When the temperature difference between the end portion and the center portion of the main heating body reaches a predetermined value T1 based on the respective detected temperatures of the central temperature detecting portion and the end portion temperature detecting portion, the detection is performed by the sub-heating body temperature detecting portion. Based on the temperature, the sub-heating unit drives the sub-heating unit to a fixing temperature T01 (T01>
T00), the temperature control is started, and when the temperature difference between the end portion and the center portion of the main heating body becomes equal to or more than a predetermined value T2 (T2> T1), the temperature is switched from the center portion temperature detection portion to the end portion temperature detection portion. Then, when the temperature of the end of the main heating body reaches the fixing temperature T00, the temperature control of the sub-heating body is stopped, and the main heating body is controlled based on the temperature detected by the central temperature detecting means. This is achieved by setting the temperature to be controlled again at the fixing temperature T00.

According to a sixth aspect of the present invention,
An object of the present invention is to provide a fixing device according to any one of the first to third aspects of the present invention, wherein a main heating element driving means for energizing a main heating element and a sub-heating element driving means for energizing a sub-heating element. And a temperature control unit. The temperature control unit controls the main heating unit driving unit to set the main heating unit at the fixing temperature T00 based on the temperature detected by the central temperature detection unit after the start of image formation. When the temperature difference between the end portion and the center portion of the main heating body reaches a predetermined value T1 based on the respective detected temperatures of the central temperature detecting portion and the end portion temperature detecting portion, the detection is performed by the sub-heating body temperature detecting portion. Based on the temperature, the sub-heater driving means starts the temperature control of the sub-heater at the fixing temperature T00, and the temperature difference between the end portion and the center portion of the main heater becomes equal to or more than a predetermined value T2 (T2> T1). Sometimes the temperature control of the main heating element is stopped and Later, when the temperature of the end of the main heating body reaches the fixing temperature T00, the temperature control of the sub-heating body is stopped, and the temperature of the main heating body is controlled again at the fixing temperature T00 based on the temperature detected by the central temperature detecting means. Achieved by being set.

According to a seventh aspect of the present invention,
An object of the present invention is to provide a fixing device according to any one of the first to third aspects of the present invention, wherein a main heating element driving means for energizing a main heating element and a sub-heating element driving means for energizing a sub-heating element. And a temperature control unit. The temperature control unit controls the main heating unit driving unit to set the main heating unit at the fixing temperature T00 based on the temperature detected by the central temperature detection unit after the start of image formation. When the temperature difference between the end portion and the center portion of the main heating body reaches a predetermined value T1 based on the respective detected temperatures of the central temperature detecting portion and the end portion temperature detecting portion, the detection is performed by the sub-heating body temperature detecting portion. Based on the temperature, the sub-heating unit drives the sub-heating unit to a fixing temperature T01 (T01>
T00), the temperature control is started, and when the temperature difference between the end portion and the central portion of the main heating body becomes equal to or more than a predetermined value T2 (T2> T1), the temperature control of the main heating body is stopped. When the temperature of the end of the body reaches the fixing temperature T00, the temperature control of the sub-heating body is stopped, and the temperature of the main heating body is controlled again at the fixing temperature T00 based on the temperature detected by the central temperature detecting means. This is achieved by:

That is, in the first invention according to the present application, in order to reduce the temperature rise of the non-sheet passing portion at the end of the main heating body,
When the amount of heat generated by the main heating body is suppressed or stopped, heat is supplied from the sub-heating body to the paper passing portion of the main heating body so that the fixing temperature of the main heating body can be maintained. Therefore,
Even if small-sized paper is continuously fixed, the temperature rise at the end of the heating element is suppressed as much as possible. Further, since the sub-heating body is formed of an undivided single body, there is no variation in the temperature difference between both ends of the heating body.

Further, in the second invention according to the present application, the end temperature detecting means is disposed at a position of the main heating element on an extension of a boundary between the heating section of the sub-heating element and the conductor section. ing.
For this reason, the temperature detected at the end by the end temperature detecting means drops relatively quickly to the fixing temperature, so that the process shifts to the normal temperature control of the main heating element in a short time. Due to the heat generated by the main heating element itself, the paper passing part of the main heating element that is not replenished by the sub-heating element
The fixing temperature is maintained.

Further, in the third invention according to the present application, the length of the heating portion of the sub-heating body is longer than the width of the paper having the minimum size. Therefore, the sub-heating member replenishes the amount of heat necessary for fixing the sheet of the minimum size to the sheet passing portion of the main heating member.

Further, in the fourth invention according to the present application, first, the main heating element is fixed at the fixing temperature T00 by detecting the temperature at the center.
Then, when the temperature difference between the end portion and the center portion of the main heating member becomes T1, the sub-heating member starts temperature control at the fixing temperature T00, and then the temperature difference between the end portion and the center portion of the main heating member. When the temperature reaches T2, the temperature is switched from the central temperature detection to the edge temperature detection to control the temperature of the main heating body, thereby reducing the amount of heat of the main heating body to lower the temperature at the edge, and passing paper from the sub-heating body to the main heating body. When the end temperature reaches the fixing temperature, the temperature control of the sub-heating body is stopped, and the control returns to the normal control. Therefore, even if small-sized paper is continuously fixed, the temperature rise at the end of the main heating body is suppressed as much as possible.

In the fifth invention according to the present application, first, the main heating body is fixed at the fixing temperature T00 by detecting the temperature at the center.
Then, when the temperature difference between the end portion and the center portion of the main heating member becomes T1, the fixing temperature T01 (T01> T) is applied to the sub-heating member.
00) to start the temperature control, and when the temperature difference between the end and the center of the main heating element reaches the value of T2, the temperature is switched from the center temperature detection to the end temperature detection to control the temperature of the main heating element and the main heating. While reducing the amount of heat of the body and lowering the temperature of the end, heat is replenished from the sub-heating body to the paper passing part of the main heating body, and then when the end temperature reaches the fixing temperature, the temperature control of the sub-heating body is stopped. Return to control. Therefore, even if small-sized paper is continuously fixed, the temperature rise at the end of the main heating body is suppressed as much as possible. Further, since the temperature control of the sub-heating body is performed at T01 higher than the fixing temperature T00, even if there is a thermal resistance due to a gap between the two heating bodies,
Sufficient heat is supplied from the sub-heating body to the paper passing portion of the main heating body.

According to the sixth aspect of the present invention, first, the main heating element is fixed at the fixing temperature T00 by detecting the temperature at the center.
Then, when the temperature difference between the end portion and the center portion of the main heating member becomes T1, the sub-heating member starts temperature control at the fixing temperature T00, and then the temperature difference between the end portion and the center portion of the main heating member. When the temperature reaches T2, the temperature control of the main heating body is stopped to lower the temperature of the end portion, while the auxiliary heating body replenishes heat to the paper passing portion of the main heating body. Is stopped and the control returns to the normal control. That is, even if small-sized paper is continuously fixed, the temperature rise at the end of the main heating body is suppressed as much as possible.

In the seventh invention according to the present application, first, the main heating element is fixed to the fixing temperature T00 by detecting the temperature at the center.
Then, when the temperature difference between the end portion and the center portion of the main heating member becomes T1, the fixing temperature T01 (T01> T) is applied to the sub-heating member.
00), and when the temperature difference between the end portion and the center portion of the main heating body becomes T2, the temperature control of the main heating body is stopped to lower the temperature of the end portion, while the main heating body is started from the sub-heating body. Heat is replenished to the paper passing portion of the heating element, and when the end temperature reaches the fixing temperature, the temperature control of the sub-heating element is stopped, and the control returns to the normal control. Therefore, even if small-sized paper is continuously fixed, the temperature rise at the end of the main heating body is suppressed as much as possible. Further, since the temperature control of the sub-heating body is performed at T01 higher than the fixing temperature T00, even if there is a thermal resistance due to a gap between the two heating bodies, a sufficient amount of the sub-heating body to the paper passing portion of the main heating body. Heat is replenished.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to FIGS.

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 2 shows the entire image forming apparatus of the present embodiment. The image forming apparatus includes an optical system 3a to 3h for reading an original on the original glass table 1, and an optical system 3a to 3h.
h, a photosensitive drum 4 on which an electrostatic latent image is formed by exposure,
A developing device 6 for forming a visible toner image on the photosensitive drum 4, a transfer charger 14 for transferring the toner image on the photosensitive drum 4 to a sheet P, a transport belt 19 for transporting the transferred sheet, A fixing unit (surf fixing device) 20 for fixing the toner image on the paper P by heating and pressing. The main body driving unit M1 is a motor that drives each unit used for paper conveyance and image formation. Further, the optical system driving means M
Reference numeral 2 denotes a motor that drives the optical systems 3a to 3h.

The configuration of the fixing unit 20 is basically the same as that described with reference to FIG. The feature of this embodiment is that the heating elements H1 and H2 as shown in FIG. 1 are provided in the heating structure 31 of the fixing unit 20 shown in FIG. That is, the main heating element H1 is provided in the heating structure,
The sub-heating body H2 is arranged side by side in parallel with the vertical direction of the sheet conveyance direction. The sub-heating body H is located on the upstream side in the paper transport direction.
2. The main heating element H1 is disposed downstream. this is,
This is because the sub-heating member H2 has a function of replenishing the heat of the main heating member H1.

The main heating element H1 is provided with a heating element (a heating element) having a length for heating the entire nip portion, that is, a sheet of the maximum size (in this example, the length of A4 sheet in the longitudinal direction). (A portion indicated by a halftone in the figure). Further, the sub-heating body H2 has a heating unit 60 (portion indicated by a halftone in the drawing) provided with a resistor that heats a width shorter than the main heating body H1 (A5 short width in this example). I have. In this figure, white portions near both ends of the sub-heating body H2 indicate the conductor portions 61 that do not generate heat. Both heating elements H1, H2
Are provided with terminal connecting portions 54 at both ends, and can be electrically connected to the main heating element driving means 102 and the sub-heating element driving means 103 shown in FIG. In addition, both heating elements H1, H2
Is the upper surface (the side opposite to the contact surface with the film 35 in FIG. 8)
Provided with a temperature detecting means such as a thermistor,
It is used for temperature control. In other words, the main heating element H1 has a central temperature detecting means 51 at the center and an end temperature detecting means 52 at the end.
2 has a sub-heating body temperature detecting means 53 in the center.

FIG. 3 shows a control system in the image forming apparatus. In FIG. 3, solid-line arrows indicate input and output of electric signals, and broken-line arrows indicate the action of heat of the heating elements H1 and H2.

This control system includes a control unit 1 such as a CPU for controlling a unit 105 used for an image forming operation in accordance with an operation of the operation unit 101 or a signal from each detection unit 104.
00, a main heating element driving means 102 receiving a command from the control means 100, and a sub-heating element driving means 103 receiving a command from the control means 100 as well. Further, the control means 100 inputs the detected temperatures of the central portion and the end portion of the main heating element H1 from the temperature detecting means 51 and 52, and inputs the detected temperatures of the sub-heating element H2 from the sub-heating element temperature detecting means 53. After calculating based on the detected temperature, a command to drive the heating element driving units 102 and 103 is output. The control unit 100 has a function as a temperature control unit as one of its functions.

The main heating element driving means 102 and the sub-heating element driving means 103 are composed of a transistor or a triac, and energize the main heating element H1 and the sub-heating element H2 to generate heat as instructed by the control means 100. is there. Further, in the present embodiment, an AC power supply is used as a power supply for the heating elements H1 and H2, and power is supplied by phase control that controls supplied power based on the phase of the AC wave.

Next, a series of operations of the image forming apparatus will be described with reference to FIGS.
This will be described with reference to FIG.

First, when an image forming mode such as the number of images to be formed is set by the user using the operation unit 101 and the start key is pressed, the control unit 100 controls the image forming operation according to the selected mode. .

First, when the control means 100 knows that the start key has been pressed, it performs the following preparatory operations simultaneously in parallel. The main body driving means M1 is driven to rotate a group of rollers in the paper conveyance path, and preparations are made to start an image forming operation. Further, for the original reading operation, the position of the scanner is moved to the home position using the optical system driving means M2, and the optical system for preparing for the image forming operation is prepared. Further, it causes the fixing unit 20 to perform temperature control.

Next, the paper is fed from the cassette 7 onto the transport path, and waits immediately before the photosensitive drum 4. Next, the optical system starts reading, and further forms a visible toner image from the electrostatic latent image on the photosensitive drum 4 using the developing device 6, and then transfers the toner image on the photosensitive drum 4 in the transfer unit 14. Is transferred to paper. Further, the sheet is carried to the fixing unit 20 by the transport belt 19.

Next, the temperature control of the fixing unit 20 having the heating elements H1 and H2 shown in FIG. 1 will be described mainly with reference to FIGS. As described above, immediately after the copy key is pressed, the control unit 100 starts the main heating unit driving unit 10.
2, the main heating element H1 and the central temperature detecting means 52 are used to control the temperature so that the nip becomes the fixing temperature. In FIG. 4, the hatched portions of the heating elements H1 and H2 are as follows.
It is a heating section, and shows a range in which heating is possible (the conductor section of the sub-heating body H2 is omitted). The nip portion of the main heating element H1 has a nip portion N11 in the center region and a nip portion N in the end region.
It is 21.

In the image forming apparatus, the length of the nip portion (N11 + N21) of the main heating body H1 is determined according to the width of the sheet of the maximum size in the axial direction of the heating body. As shown, small-sized paper P has a nip portion N11 in the central region.
, The heat of the nip portion N11 is removed by the paper P. The temperature of the nip N11 is determined by the central temperature detecting means 51.
Is detected, and the control means 100 which inputs the detected temperature signal
However, the main heating element is energized to H1 to control the temperature so that the temperature of the nip portion N11 does not drop below the fixing temperature. On the other hand, since the paper P does not pass through the nip portion N21 in the end region, the temperature gradually increases. In such a state, if temperature control is performed with only one heating element as in the related art (see FIG. 9), the temperature difference between the central part and the end part increases, and the main heating element H1 is cracked. May occur.

Therefore, in order to eliminate this problem, in addition to the main heating element H1 for heating the entire nip (N11 + N21), heating at a central portion of the entire nip (N11 + N21) with a shorter width than the main heating element H1. Is installed. As shown in FIG. 4, when the small-sized paper P is fed, the main heating body H1 uses the central temperature detecting means 51.
The temperature of the nip portion N11 and the temperature of the nip portion N21 are detected by the and the end temperature detecting means 52, respectively, and the temperature difference between the nip portion N11 and the nip portion N21 is calculated and monitored.

The control means 100 includes, as temperature control means,
The temperature is set so as to minimize the temperature rise at the end of the main heating element H1 as follows.

First, the control means 100 controls the temperature of the main heating element H1 by the central temperature detecting means 51 at a predetermined value T00 which is the fixing temperature. Further, the control means 100 inputs temperature signals of the nip portion N11 and the nip portion N21 of the main heating element H1 detected by the central temperature detecting means 51 and the end temperature detecting means 52, respectively.

The small-size paper P is placed in the nip portion N in the central area.
11 (paper passing portion), the heat of the nip portion N11 is taken away by the paper, but the control means 100, which has input the detected temperature of the central temperature detecting means 51, makes up the main heating element H1 so as to compensate for the taken heat. Supply power. Therefore, the nip portion N11
Is maintained at a predetermined value T00 as the fixing temperature. on the other hand,
Since the sheet P does not pass through the nip portion N21 (non-sheet passing portion) in the end region, the temperature gradually increases. Thereby, a temperature difference occurs between the nip portion N11 and the nip portion N21.
The control means 100 controls the nip portion N1 of the main heating element H1 inputted from the central temperature detecting means 51 and the end temperature detecting means 52.
The temperature difference between the temperature signal of the nip portion N21 and the temperature signal of the nip portion N21 is obtained, and the temperature difference is monitored.

When the temperature difference between the central portion and the end portion of the main heating member H1 reaches a predetermined value T1, the control means 100 starts the temperature control of the sub-heating member H2 at a predetermined value T00. When the calorific value of the main heating body H1 is reduced later, the sub-heating body H1 is used to feed the paper at the central portion of the main heating body H1 (the nip portion N2).
The temperature is controlled to replenish heat in 1).

Next, when the temperature difference further increases and reaches T2 (T2> T1), the control means 100 changes the temperature from the central temperature detecting means 51 to the end temperature detecting means 52 to perform temperature control. The temperature of the nip N21 in the end region is
Naturally, it is higher than T00. Therefore, the control means 1 which has input the detected temperature signal from the end temperature detecting means 52
00 is energized so as to reduce the amount of heat generated by the main heating element H1 in order to reduce the temperature at the end. As described above, since the heating value of the main heating member H1 is reduced, if the heat is not applied to the main heating member H1 from the outside, the temperature of the nip portion N11 in the central region where the heat is taken away by the paper P becomes a predetermined value. It has to be lower than T00. However, as described above, since the temperature of the sub-heating member H2 is already controlled at the predetermined value T00, the nip portion N11 (paper passing portion) of the main heating member H1 from the sub-heating member H2.
And the nip portion N11 can be maintained at the predetermined value T00.

When the temperature of the end (N21) of the main heating element H1 drops to a predetermined value T00, the control means 100 stops the temperature control of the sub-heating element H2, returns to the beginning, and returns again.
The temperature control (normal temperature control) of the main heating element H1 by the central temperature detecting means 51 is started. Then, the above-described predetermined control is repeated until the set number of image formation is completed.

When the fixing unit 20 and the control means 100 configured as in this embodiment are used, the paper passing portion (nip portion 11) and the non-paper passing portion (nip portion 21) of the main heating member H1 are used. Can be suppressed to T2 at the maximum. The temperature difference T2 is, of course, set to a temperature that will not damage the ordinary heating elements H1 and H2.

The above control flow will be described next with reference to the flowchart of FIG. 5 and FIGS.

When the control means 100 knows that the start key has been pressed (step 1), it drives the paper transport system and the optical system, and starts the temperature control of the main heating element H1 of the fixing unit. Then, an image forming operation is prepared (step 2). Then, when the preparation of the optical system and the alignment of the paper are completed, the control unit 100 starts the image forming operation (step 3). The control means 100 monitors the temperature difference T between the end portion and the central portion of the main heating element H1. If the temperature difference T is T ≦ 0, the central heating element H1 is detected by the central temperature detecting section 51. , But the temperature control of the sub-heating member H2 is stopped (step 4). When the temperature difference becomes T ≧ T1, the temperature control of the sub-heating body H2 is started at a predetermined value T00 by the sub-heating body temperature detecting means 53 in addition to the main heating body H1 (step 5). Next, when the temperature difference becomes T ≧ T2, the temperature of the main heating body H1 is changed from the central temperature detecting means 51 to the end temperature detecting means 52 to perform temperature control to lower the temperature of the end. (Step 6). Thereafter, the temperature of the main heating element H1 is controlled by the central temperature detecting means 51, and the control of the above-described steps is repeated until the last sheet of the set number of sheets (step 7).

In the above description, in order to suppress the temperature rise at the end of the main heating element H1, the temperature of the main heating element H1 is changed from the temperature detection at the center to the temperature detection at the end to reduce the amount of generated heat. As described above, for the same purpose, the temperature control itself of the main heating body H1 may be stopped (see () in step 6 in the flowchart of FIG. 5).

(Second Embodiment) In the above-described first embodiment, the temperature of the sub-heating member H2 is controlled at the fixing temperature T00.
In the second embodiment, the temperature is controlled at a temperature T01 higher than the temperature T00.

Referring to FIG. 4, the distance between the main heating element H1 and the sub-heating element 2 is often not zero due to design. These two heating elements H1,
The gap present between H2 creates a thermal resistance. Therefore, the sub-heating body 2 is located at the center nip portion N1 of the main heating body H1.
1 may not be given a sufficient amount of heat. In order to solve this problem, in the present embodiment, the control means 100 is set so as to control the temperature of the sub-heating body H2 at T01 (T01> T00).

That is, according to the present embodiment, even if there is a gap between the two heating members 1 and 2, that is, a thermal resistance, the sub-heating member H2 and the nip portion N21 (paper passing portion) of the main heating member H1 are sufficient. Heat can be supplied, and more stable fixing properties can be realized.

(Third Embodiment) In the present embodiment, as shown in FIG. 6, the end temperature detecting means 52 of the main heating body H1 is connected to the boundary between the heating part 60 and the conductor part 61 of the sub-heating body H2. It is arranged on an extension in the paper transport direction.

When a sheet of a size larger than the sub-heater is continuously fixed, the area of the main heater corresponding to the area between the end of the nip portion of the sub-heater and the end of the sheet (D in FIG. 7) (See the area indicated by.) Becomes a part of the paper passing portion. The area of the main heating body H1 is not replenished with heat irrespective of being a part of the sheet passing portion (this area is referred to as a non-replenishment area).

If the end temperature detecting means is arranged completely within the non-sheet passing portion of the main heating element, the temperature of the main heating element is changed to the end temperature detecting means after switching from the central temperature detecting means to the end temperature detecting means. It takes a relatively long time to drop to T00. This is because the temperature of the region completely entering the paper passing portion is extremely high. Until the end of the main heating body drops to the temperature T00, the non-replenishment area is not only replenished with heat from the sub-heating body but also suppresses heat generation by the main heating body itself.
The temperature is lower than the fixing temperature T00 irrespective of being a part of the paper passing portion.

In order to solve such a problem, in the present embodiment, as shown in FIG. 6, the end temperature detecting means 52 is connected to the boundary line between the heating portion 60 of the sub-heating member H2 and the conductor portion 61. Are arranged on the extension of the paper transport direction. FIG. 7 shows the operation of the heating element. When switching from the central temperature detecting means 51 to the end temperature detecting means 52, the end temperature detecting means 52 is located in the paper passing portion.
The temperature does not rise so much, and therefore falls relatively quickly to the predetermined value T00, and as a result, the control shifts to the temperature control of the main heating element H1 in a short time. Therefore, the temperature of the non-replenishment area D, which is a part of the sheet passing portion, can be suppressed as low as possible from being equal to or lower than the predetermined value T00 which is the fixing temperature. Needless to say, the end temperature detecting means 52 also exhibits the original function expected of the end temperature detecting means, that is, monitoring of the temperature difference between the center and the end of the main heating element H1.

(Fourth Embodiment) The fourth embodiment will be described with reference to FIG. 4. As described above, the sub-heating member H2 replenishes heat to the nip portion N11 at the center of the main heating member H1. Has the function of maintaining the fixing temperature. Therefore, it is desirable that the sub-heating member H2 be formed to have a length equal to or greater than the paper passing width of the minimum-size paper.

[0054]

According to the first aspect of the present invention, when the temperature of the non-sheet passing portion at the end of the main heating body is reduced, the amount of heat generated by the main heating body is reduced or stopped. Heat was replenished from the sub-heating body to the paper passing portion of the main heating body so that the fixing temperature of the main heating body could be maintained. Therefore, even if small-sized paper is continuously fixed, the temperature rise at the end of the heating element can be suppressed as much as possible, and cracking of the heating element can be prevented. Further, since the sub-heating body is formed of an undivided single body, there is no variation in the temperature difference between both ends of the heating body.

According to the second invention of the present application,
The end temperature detecting means is disposed at a position of the main heating element on the extension of the boundary between the heating section of the sub-heating element and the conductor section in the sheet conveying direction. Therefore, the temperature detected at the end portion by the end portion temperature detecting means drops relatively quickly to the fixing temperature, so that the process shifts to the temperature control of the main heating element in a short time. Therefore, the area of the main heating body that is not replenished with heat from the sub-heating body can be maintained at the fixing temperature by the heat generated by the main heating body itself.

According to the third aspect of the present invention,
The sub-heating body has a heating unit whose length is longer than the paper width of the minimum-size paper. Therefore, the sub-heating body can replenish the amount of heat necessary for fixing the minimum size to the sheet passing portion of the main heating body.

According to the fourth invention of the present application,
First, the temperature of the main heating element is controlled at the fixing temperature T00 by detecting the temperature at the center, and then, when the temperature difference between the end and the center of the main heating element reaches T1, the sub-heating element starts temperature control at the fixing temperature T00. Then, the temperature difference between the end and the center of the main heating element is T
When the temperature becomes 2, the temperature of the main heating element is controlled by switching from the temperature detection of the central portion to the temperature detection of the edge portion, and the amount of heat of the main heating member is reduced to lower the temperature of the edge portion. When the end temperature reaches the fixing temperature, the temperature control of the sub-heating member is stopped, and the control returns to the normal control. Therefore, even if small-size paper is continuously fixed, the temperature rise at the end of the main heating body can be suppressed as much as possible, and cracking of the heating body can be prevented.

According to the fifth aspect of the present invention,
First, the temperature of the main heating body is controlled at the fixing temperature T00 by detecting the temperature at the center, and then the temperature difference between the end and the center of the main heating body is T.
When it becomes 1, the fixing temperature T01 (T01> T0)
0), the temperature control is started, and when the temperature difference between the end portion and the center portion of the main heating body becomes T2, the temperature is switched from the center portion temperature detection to the end portion temperature detection to control the temperature of the main heating body, and While reducing the amount of heat and lowering the temperature at the end, heat is replenished from the sub-heating body to the paper passing section of the main heating body, and then when the end temperature reaches the fixing temperature, the temperature control of the sub-heating body is stopped, and normal control is performed. Return. Therefore, even if small-sized paper is continuously fixed, the temperature rise at the end of the main heating body can be suppressed as much as possible, and cracking of the heating body can be prevented. Further, since the temperature control of the sub-heating body is performed at T01 higher than the fixing temperature T00, even if there is a thermal resistance due to a gap between the two heating bodies, a sufficient amount of the sub-heating body to the paper passing portion of the main heating body. Heat can be replenished and stable fixability can be realized.

According to the sixth invention of the present application,
First, the temperature of the main heating body is controlled at the fixing temperature T00 by detecting the temperature at the center, and then, when the temperature difference between the end and the center of the main heating body reaches a certain value, the sub-heating body starts temperature control at the fixing temperature T00. Then, when the temperature difference between the end portion and the central portion of the main heating body becomes larger than that, the temperature control of the main heating body is stopped to lower the temperature of the end portion, while the paper is passed from the sub-heating body to the main heating body. When the end temperature reaches the fixing temperature, the temperature control of the sub-heating body is stopped, and the control returns to the normal control. Therefore, even if small-sized paper is continuously fixed, the temperature rise at the end of the main heating body can be suppressed as much as possible, and cracking of the heating body can be prevented.

According to the seventh aspect of the present invention,
First, the temperature of the main heating body is controlled at the fixing temperature T00 by detecting the temperature at the center, and then, when the temperature difference between the end and the center of the main heating body reaches a certain value, the fixing temperature T01 (T01> T0) is applied to the sub-heating body.
In step 0), the temperature control is started, and when the temperature difference between the end and the center of the main heating element becomes larger than that, the temperature control of the main heating element is stopped to lower the temperature of the end while the sub-heating is performed. The body replenishes heat to the paper passing portion of the main heating body, and then when the end temperature reaches the fixing temperature, the temperature control of the sub-heating body is stopped, and the control returns to the normal control. Therefore, even if small-sized paper is continuously fixed, the temperature rise at the end of the main heating body can be suppressed as much as possible, and cracking of the heating body can be prevented. Further, since the temperature control of the sub-heating body is performed at T01 higher than the fixing temperature T00, even if there is a thermal resistance between the two heating bodies, sufficient heat is supplied from the sub-heating body to the paper passing portion of the main heating body. It can be replenished and can achieve stable fixability.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an embodiment of a fixing device of the present invention.

FIG. 2 is a schematic configuration diagram illustrating an entire image forming apparatus including the fixing device of FIG. 1;

FIG. 3 is a block diagram illustrating an electric control circuit of the image forming apparatus of FIG. 2;

FIG. 4 is an operation state diagram of the fixing device of FIG. 1;

FIG. 5 is a flowchart for explaining the operation flow of the image forming apparatus of FIG. 2 and the fixing device of FIG. 1;

FIG. 6 is a schematic plan view showing another embodiment of the fixing device of the present invention.

FIG. 7 is an operation state diagram of the fixing device of FIG. 6;

FIG. 8 is a side view showing a conventional surf fixing device.

FIG. 9 is an operation state diagram of an example of a heating body of a conventional fixing device.

FIG. 10 is an operation state diagram of another example of the conventional heating element.

[Explanation of symbols]

 H1 Main heating element H2 Sub-heating element 20 Fixing unit (fixing device) 30 Pressure roller 31 Heating structure 35 Film 51 Center temperature detecting means 52 End temperature detecting means 53 Sub-heating element temperature detecting means 60 Heating section 61 Conductor section REFERENCE SIGNS LIST 100 temperature control means 102 main heating element driving means 103 sub-heating element driving means P paper

Claims (7)

[Claims] 1. A fixing device having a heating element and a film which comes into contact with the heating element and moves together with the sheet, wherein the heating element heats and fixes a toner image on the sheet via the film. The main heating body is formed to have a length capable of thermally fixing a sheet of a maximum size in the axial direction of the heating body, and a center temperature detecting means is provided at a center portion, and an end portion is provided at an end portion. The sub-heating body is formed of an undivided unitary body, the heating section is formed shorter than the heating section of the main heating body, and the sub-heating body temperature detection means is provided in the center, and the sub-heating body is provided. A fixing device is provided on the upstream side in the paper transport direction, and the main heating body is provided on the downstream side. 2. The main heating element according to claim 1, wherein the end temperature detecting means is arranged on an extension of a boundary line between the heating section of the sub-heating element and the conductor in the sheet conveying direction. Fixer. 3. The fixing device according to claim 1, wherein a length of the heating portion of the sub-heating member is longer than a width of a sheet having a minimum size in the axial direction of the heating member. 4. A main heating element driving means for energizing a main heating element and a sub-heating element driving means for energizing a sub-heating element, comprising the fixing device according to any one of claims 1 to 3. The image forming apparatus further includes a temperature control unit. The temperature control unit controls the temperature of the main heating body to the main heating body driving unit at the fixing temperature T00 based on the temperature detected by the central temperature detection unit after the start of image formation. When the temperature difference between the end portion and the central portion of the main heating element reaches a predetermined value T1 based on the respective detected temperatures of the central temperature detecting section and the end temperature detecting section, the temperature detected by the sub-heating element temperature detecting section When the temperature difference between the end portion and the central portion of the main heating member is equal to or more than a predetermined value T2 (T2> T1), the sub-heating member driving means starts the temperature control of the sub-heating member at the fixing temperature T00 based on At the end from the center temperature detection means The temperature of the main heating body is controlled by switching to the informing means, and thereafter, the temperature of the end of the main heating body becomes the fixing temperature T0.
When the temperature becomes 0, the control of the temperature of the sub-heating member is stopped, and the main heating member is fixed at the fixing temperature T based on the temperature detected by the central temperature detecting means.
The image forming apparatus is set so that the temperature is controlled again at 00. 5. A fixing device according to claim 1, wherein the main heating element driving means for supplying electricity to the main heating element and the sub-heating element driving means for supplying electricity to the sub-heating element are provided. The image forming apparatus further includes a temperature control unit. The temperature control unit controls the temperature of the main heating body to the main heating body driving unit at the fixing temperature T00 based on the temperature detected by the central temperature detection unit after the start of image formation. When the temperature difference between the end portion and the central portion of the main heating element reaches a predetermined value T1 based on the respective detected temperatures of the central temperature detecting section and the end temperature detecting section, the temperature detected by the sub-heating element temperature detecting section The sub-heating element is driven by the sub-heating element driving means based on the fixing temperature T01 (T01> T
00), the temperature control is switched from the central temperature detecting means to the end temperature detecting means when the temperature difference between the end portion and the central portion of the main heating element becomes equal to or more than a predetermined value T2 (T2> T1). The temperature of the main heating element is controlled, and when the temperature of the end of the main heating element reaches the fixing temperature T00, the temperature control of the sub-heating element is stopped, and the temperature of the main heating element is detected based on the temperature detected by the central temperature detecting means. Wherein the temperature is set again at the fixing temperature T00. 6. A fixing device according to claim 1, wherein the main heating element driving means for energizing the main heating element and the sub-heating element driving means for energizing the sub-heating element are provided. The image forming apparatus further includes a temperature control unit. The temperature control unit controls the temperature of the main heating body to the main heating body driving unit at the fixing temperature T00 based on the temperature detected by the central temperature detection unit after the start of image formation. When the temperature difference between the end portion and the central portion of the main heating element reaches a predetermined value T1 based on the respective detected temperatures of the central temperature detecting section and the end temperature detecting section, the temperature detected by the sub-heating element temperature detecting section When the temperature difference between the end portion and the central portion of the main heating member is equal to or more than a predetermined value T2 (T2> T1), the sub-heating member driving means starts the temperature control of the sub-heating member at the fixing temperature T00 based on The temperature control of the main heating element is stopped at When the temperature of the end of the main heating body reaches the fixing temperature T00, the temperature control of the sub-heating body is stopped, and the temperature of the main heating body is controlled again at the fixing temperature T00 based on the temperature detected by the central temperature detecting means. An image forming apparatus characterized by being set. 7. A fixing device according to claim 1, wherein a main heating element driving means for energizing the main heating element and a sub-heating element driving means for energizing the sub-heating element are provided. The image forming apparatus further includes a temperature control unit. The temperature control unit controls the temperature of the main heating body to the main heating body driving unit at the fixing temperature T00 based on the temperature detected by the central temperature detection unit after the start of image formation. When the temperature difference between the end portion and the central portion of the main heating element reaches a predetermined value T1 based on the respective detected temperatures of the central temperature detecting section and the end temperature detecting section, the temperature detected by the sub-heating element temperature detecting section The sub-heating element is driven by the sub-heating element driving means based on the fixing temperature T01 (T01> T
00), the temperature control of the main heating element is stopped when the temperature difference between the end part and the central part of the main heating element becomes equal to or more than a predetermined value T2 (T2> T1). When the temperature of the end of the body reaches the fixing temperature T00, the temperature control of the sub-heating body is stopped, and the temperature of the main heating body is controlled again at the fixing temperature T00 based on the temperature detected by the central temperature detecting means. An image forming apparatus comprising: