JP2018116232A - Image heating device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device that can reduce the occurrence of fixing failure while suppressing an increase in temperature of a non-paper feed part.SOLUTION: An image heating device comprises: an elongated heater, the heater capable of controlling the ratio of the calorific value at the ends to the calorific value at the center in the longitudinal direction of the heater; a first temperature detection element that detects the temperature at the center in the longitudinal direction of the heater; second temperature detection elements that detect the temperature at the ends in the longitudinal direction of the heater; and a control part that controls the heater so that the temperature detected by the first temperature detection element becomes a target temperature, and the image heating device heats an image formed on a recording material with heat from the heater. When the temperatures detected by the second temperature detection elements exceed a predetermined threshold, the control part controls the heater to reduce the above-mentioned ratio; the control part changes the threshold according to a state of heating of the image heating device.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic system or an electrostatic recording system. The present invention also relates to an image heating apparatus such as a fixing device mounted on an image forming apparatus and a gloss applying apparatus that improves the glossiness of a toner image by reheating a toner image fixed on a recording material.

  2. Description of the Related Art Image forming apparatuses such as printers and copiers are provided with a fixing device that is an image heating device as a fixing unit and heat-fixes an unfixed toner image carried on a recording material as a fixed image. Conventionally, various configurations such as a heat roller system, a belt heating system, and a film heating system are known for fixing devices. Here, in the film heating type fixing device, since the fixing film is thin and has a small heat capacity, there is a problem that heat conduction in the direction perpendicular to the recording material conveyance direction (hereinafter referred to as the longitudinal direction) is poor. . When a recording material having a narrow width relative to the length in the longitudinal direction of the fixing nip portion is passed, heat is taken away by the recording material by the recording material. On the other hand, since heat is not taken away from the non-sheet passing portion, the temperature of the non-sheet passing portion increases (hereinafter, this phenomenon is referred to as non-sheet passing portion temperature rise). The narrow-width recording material is a so-called small-size recording material. For example, in the case of an image forming apparatus of letter size and A4 size longitudinal conveyance, the recording material is A5 or B5 size width or less.

  Patent Document 5 discloses a fixing device that can change the heat generation distribution of a ceramic heater according to the size of a recording material in a conventional film heating type fixing device. The ceramic heater of the fixing device includes a first heating resistor having a resistance value at the center in the longitudinal direction larger than both ends on the ceramic substrate, and a second heating resistor having a resistance value at both ends greater than the center. In addition, energization to the two heating resistors can be individually controlled. In this case, the center in the longitudinal direction is a conveyance reference for the recording material through which recording materials of all sizes pass. By setting various energization ratios to the first heating resistor and the second heating resistor, the heat distribution of the ceramic heater can be set variously. In this way, even when a small-size recording material is passed, the temperature rise of the non-sheet passing portion can be suppressed.

JP 2006-47630 A

  In recent years, with the increase in the speed of image forming apparatuses and the large amount of continuous printing, there is a problem of temperature rise in the non-sheet passing portion when A4 size paper (paper width 210 mm) is passed through a letter size (paper width 216 mm) machine. . The difference between the letter size and the A4 size is 3 mm on one side, which is a small value compared to the difference between the letter size and the small size paper, for example. However, it is necessary to keep the heater temperature high by increasing the speed, and as a result, a large amount of heat is accumulated even in a small non-sheet passing portion.

Further, the position of the recording material in the longitudinal direction of the heater is not always constant. When a recording material is set in a paper feed port of a printer, the recording material is generally set at a predetermined position by a restriction plate or the like provided for position restriction. The restriction plate generally has a plurality of positions corresponding to the size of the recording material, and the position is moved by being slid by the user depending on the size of the recording material to be used. Since all of these procedures are performed by the user's hand, the recording material is not always set correctly. In particular, when an A4 size recording material is set, the paper width is very close to the letter size, so there is a possibility that the recording material is set at the paper feed port while the position of the restricting plate is set to the letter size position. is there. If the A4 size recording material is set in the paper feed slot while the position of the restricting plate is the letter size position, there is a possibility that printing is performed with the recording material brought close to the left or right restricting plate. .

  As described above, when a recording material set with a bias is continuously fed at the paper feed port, the paper is continuously biased to the right side with respect to the heater in the fixing device, or vice versa. In some cases, the paper is biased to the left side. When the paper is continuously passed in such a state, the paper passing area is shifted in the longitudinal direction with respect to the heater, and when the paper is passed to the left, the non-paper passing portion on the right side is widened. Conversely, when the paper is passed to the right side, a situation occurs in which the left non-paper passing portion becomes wider. In such a situation, the temperature rise of the non-sheet passing portion becomes very large as compared to when the recording material set at the normal position is passed. For this reason, it is necessary to reduce the temperature rise of the non-sheet passing portion by adjusting the heat generation distribution of the heater to reduce the heat generation at the heater end. However, since the recording material is unbalanced, the amount of heat is insufficient at the end of the recording material on the side opposite to the side where the non-sheet passing portion temperature rise has occurred. In other words, if the recording material is passed to either the left or right side, if the heat generation at the end is reduced to cope with the non-sheet passing portion temperature rise, the non-sheet passing portion temperature rise occurs. There is a possibility that the fixing property at the image end on the opposite side is impaired.

  An object of the present invention is to provide an image heating apparatus capable of suppressing the occurrence of fixing failure while suppressing the temperature rise of the non-sheet passing portion.

In order to achieve the above object, the image heating apparatus of the present invention comprises:
An elongate heater, the heater capable of controlling the ratio of the calorific value at the end to the calorific value at the center in the longitudinal direction of the heater;
A first temperature detection element for detecting a temperature in the center of the heater in the longitudinal direction;
A second temperature sensing element for sensing the temperature of the longitudinal end of the heater;
A control unit that controls the heater so that the detected temperature of the first temperature detecting element becomes a target temperature;
The image formed on the recording material is heated with the heat of the heater,
In the image heating apparatus in which the control unit controls the heater so that the ratio becomes small when the detection temperature of the second temperature detection element exceeds a predetermined threshold.
The control unit is characterized in that the threshold value is changed according to a warming condition of the image heating apparatus.
In order to achieve the above object, an image forming apparatus of the present invention includes:
An image forming unit for forming an image on a recording material;
The above-described image heating device as a fixing unit for fixing the image formed on the recording material to the recording material,
It is characterized by providing.

  According to the present invention, it is possible to suppress the occurrence of fixing failure while suppressing the temperature rise of the non-sheet passing portion.

Schematic configuration diagram of an image forming apparatus Schematic cross-sectional view of a film heating type heating device Cross section of fixing heater The figure which shows the surface side of the fixing heater and the figure which shows the calorific value per unit length Longitudinal component layout of fixing heater Table for energization ratio level Explanatory diagram of temperature transition of non-sheet passing part of sub thermistor and fixing film Table of thresholds for changing the energization ratio level according to the type of recording material and the number of sheets passed Explanatory drawing of thermistor temperature transition and energization ratio transition according to the type of recording material Explanatory drawing of the contents of the side-by-side paper in Example 1 Explanatory drawing of thermistor temperature transition and energization ratio transition during unaligned paper Table of threshold values for warm-up index and energization ratio level change in embodiment 2

  Embodiments of the present invention are illustrated below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the embodiments should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions. This is not intended to limit the scope to the following embodiments.

Example 1
(Image forming device)
FIG. 1 is a schematic configuration diagram showing a color image forming apparatus equipped with an image heating apparatus according to an embodiment of the present invention. This image forming apparatus is an electrophotographic tandem type full color printer. The configuration of the image forming apparatus includes four image forming units (image forming units), and these four image forming units are arranged in a line at regular intervals. The image forming unit forms an image forming unit 1Y that forms a yellow image, an image forming unit 1M that forms a magenta image, an image forming unit 1C that forms a cyan image, and a black image. The image forming unit 1Bk.

  Photosensitive drums 2a, 2b, 2c, and 2d are installed in the image forming units 1Y, 1M, 1C, and 1Bk, respectively. Around each photosensitive drum 2a, 2b, 2c, 2d, charging rollers 3a, 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d, drum cleaning device 6a, 6b, 6c, 6d are installed. Exposure devices 7a, 7b, 7c, and 7d are installed above the charging rollers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d, respectively. Each developing device 4a, 4b, 4c, 4d contains yellow toner, magenta toner, cyan toner, and black toner, respectively.

  An endless belt-shaped intermediate transfer member 40 as a transfer medium is in contact with each primary transfer portion N of each of the photosensitive drums 2a, 2b, 2c, and 2d of the image forming portions 1Y, 1M, 1C, and 1Bk. The intermediate transfer belt 40 is stretched between a drive roller 41, a support roller 42, and a secondary transfer counter roller 43, and is rotated (moved) in the arrow direction (clockwise) by the drive of the drive roller 41.

  The transfer rollers 5a, 5b, 5c, and 5d for primary transfer are in contact with the photosensitive drums 2a, 2b, 2c, and 2d via the intermediate transfer belt 40 at the primary transfer nip portions 27, respectively. The secondary transfer counter roller 43 is in contact with the secondary transfer roller 44 via the intermediate transfer belt 40 to form a secondary transfer portion M. A belt cleaning device 45 that removes and collects transfer residual toner remaining on the surface of the intermediate transfer belt 40 is installed in the vicinity of the drive roller 41 outside the intermediate transfer belt 40.

  A fixing device 12 is installed on the downstream side of the secondary transfer portion M in the conveyance direction of the recording material P. When an image forming operation start signal is issued, the photosensitive drums 2a, 2b, 2c, and 2d that are rotationally driven at a predetermined process speed are uniformly charged by the charging rollers 3a, 3b, 3c, and 3d, respectively (in this embodiment, Negative polarity).

  The exposure devices 7a, 7b, 7c, and 7d respectively convert input color-separated image signals into optical signals at a laser output unit (not shown). Laser light, which is a converted optical signal, is scanned and exposed on each of the charged photosensitive drums 2a, 2b, 2c, and 2d to form an electrostatic latent image.

  Then, yellow toner is charged on the surface of the photosensitive member by the developing device 4a in which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied on the photosensitive drum 2a on which the electrostatic latent image is formed. Electrostatic adsorption is performed according to the potential. By this electrostatic adsorption, the electrostatic latent image is visualized to be a developed image. This yellow toner image is primary transferred onto the rotating intermediate transfer belt 40 by the transfer roller 5a to which a primary transfer bias (polarity opposite to the toner (positive polarity)) is applied at the primary transfer portion N. Is done. The intermediate transfer belt 40 to which the yellow toner image has been transferred is rotated toward the image forming unit 1M.

  Also in the image forming unit 1M, the magenta toner image formed on the photosensitive drum 2b in the same manner as described above is superimposed on the yellow toner image on the intermediate transfer belt 40 and transferred by the primary transfer unit N. . In the same manner, cyan and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1C and 1Bk on the yellow and magenta toner images superimposed and transferred onto the intermediate transfer belt 40 in the same manner are respectively used as the primary. The images are sequentially overlapped at the transfer portion N. As a result, a full-color toner image is formed on the intermediate transfer belt 40. Then, the recording material (transfer material) P is conveyed to the secondary transfer portion M by the registration roller 46 in accordance with the timing when the front end of the full color toner image on the intermediate transfer belt 40 is moved to the secondary transfer portion M. Full-color toner images are collectively transferred to the recording material P by the secondary transfer roller 44 to which a secondary transfer bias (opposite polarity (positive polarity) from the toner) is applied.

  The recording material P on which a full-color toner image is formed is conveyed to a fixing device 12 as a fixing unit. The fixing device 12 heats and presses the full-color toner image at the fixing nip portion between the fixing sleeve 20 as a heating rotation member and the pressure roller 22 that is driven to rotate, and melts and fixes it on the surface of the recording material P. Thereafter, the image is discharged to the outside and becomes an output image of the image forming apparatus. Then, a series of image forming operations is completed.

  In the primary transfer described above, the primary transfer residual toner remaining on the photosensitive drums 2a, 2b, 2c, and 2d is removed and collected by the drum cleaning devices 6a, 6b, 6c, and 6d. Further, the secondary transfer residual toner remaining on the intermediate transfer belt 40 after the secondary transfer is removed and collected by the belt cleaning device 45.

(Image heating device)
FIG. 2 is a schematic configuration model diagram of the fixing device 12 as an image heating device. The fixing device 12 heats and fixes a toner image on a recording material, and includes a heater 16 as a heating body having an energized heat generating resistance layer and a fixing sleeve 20 as a first rotating body that moves together with the recording material. ing. The fixing sleeve 20 is provided so as to be rotatable and capable of being heated in a longitudinal direction intersecting the rotation direction. The fixing device 12 further includes a pressure roller 22 as a second rotating body that is in pressure contact with the fixing sleeve 20, and a toner image on the recording material at a fixing nip 27 formed by the fixing sleeve 20 and the pressure roller 22. Is configured to heat and fix.

  The fixing film 20 is a cylindrical (endless belt-shaped) member in which an elastic layer is provided on a belt-shaped member. Specifically, a polyimide rubber is used as a material, and a silicon rubber layer (elastic layer) having a thickness of about 250 μm is formed on an endless belt (belt base material) formed in a cylindrical shape having a thickness of 70 μm. Further, a PFA resin tube (outermost surface layer) having a thickness of 30 μm is coated on the silicon rubber layer.

  The heater 16 is held by a heater holder 17. The heater holder 17 is a heat resistant and rigid member having a substantially semicircular arc shape in cross section, and the heater 16 is disposed on the lower surface of the heater holder 17 along the longitudinal direction of the holder. The heater 16 and the heater holder 17 constitute a backup member. The fixing sleeve 20 is loosely fitted on the heater holder 17.

  Here, the fixing heater 16 as the heating body uses a ceramic heater in this embodiment, and the details of the configuration will be described later. The heater holder 17 is formed of a liquid crystal polymer resin having high heat resistance, holds the fixing heater 16, and plays a role of guiding the fixing film 20 that rotates while being in contact with the fixing heater 16.

  The pressure roller 22 is formed by forming a silicon rubber layer on a stainless steel core by injection molding and coating a PFA resin tube thereon. The pressure roller 22 is disposed such that both ends of the core bar are rotatably supported by bearings between a side plate (not shown) and a front side plate of the apparatus frame 24. On the upper side of the pressure roller 22, the fixing film unit composed of the heater 16, the heater holder 17, the fixing film 20 and the like is disposed in contact with the pressure roller 22 in parallel with the heater 16 facing downward.

  Both ends of the heater holder 17 are urged in the axial direction of the pressure roller 22 by a force of 12.5 kgf on one side and a total pressure of 25 kgf by a pressure mechanism (not shown). As a result, the downward surface (hereinafter referred to as the surface) of the fixing heater 16 is pressed against the elastic layer of the pressure roller 22 via the fixing film 20 with a predetermined pressing force against the elasticity of the elastic layer. . Thus, a fixing nip portion 27 having a predetermined width necessary for heat fixing is formed.

  In this embodiment, the main thermistor 18 and the sub-thermistors 19a and 19b are arranged at different positions in the direction (longitudinal direction) orthogonal to the conveying direction of the recording material P, and the temperature of the heater 16 is detected. Specifically, the main thermistor 18 as a first temperature detection element is located at the center position (center part) in the longitudinal direction in the nip portion, and the second temperature detection element is located near the end portion at a distance equal to the center position. Sub-thermistors 19a and 19b are arranged.

  In FIG. 2, only one main thermistor 18 and sub-thermistors 19a and 19b are on the same line of sight. These thermistors are in contact with the upward surface (hereinafter referred to as the back surface) in FIG. 3 and FIG. 4 of the fixing heater 16 that is a heat source, and detect the temperature of the back surface of the fixing heater at the end of the heating resistor layer. .

  In this embodiment, the main thermistor 18 and the sub-thermistors 19a and 19b are arranged so as to contact the back surface of the fixing heater 16, and the temperature of the back surface of the fixing heater 16 is detected. However, the present invention is not necessarily limited to this position. Absent. For example, it may be arranged so as to contact the back surface of the fixing film 20 and the temperature of the back surface of the fixing film 20 may be detected.

  The main thermistor 18 and the sub-thermistors 19a and 19b are connected to an energization control unit 21 as a heating control unit (control unit). The energization control means 21 determines the temperature control content of the fixing heater 16 based on the detection results of the main thermistor 18 and the sub-thermistors 19a and 19b. Details of the temperature control content will be described later.

  Reference numerals 23 and 26 in FIG. 2 denote an entrance guide and a fixing paper discharge roller assembled to the apparatus frame 24. The entrance guide 23 serves to guide the transfer material so that the recording material P that has passed through the secondary transfer nip is accurately guided to the fixing nip portion 27. The entrance guide 23 of the present embodiment is formed of polyphenylene sulfide (PPS) resin.

  The pressure roller 22 is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed by a driving unit (not shown). A rotational force acts on the cylindrical fixing film 20 by the pressure frictional force in the fixing nip portion 27 between the outer surface of the pressure roller 22 and the fixing film 20 by the rotational driving of the pressure roller 22. The fixing film 20 is rotated in the clockwise direction indicated by the arrow around the outer circumference of the heater holder 17 while the inner surface of the fixing film 20 is in close contact with the downward surface of the fixing heater 16 and slides. Grease is applied to the inner surface of the fixing film 20 to ensure slidability between the heater holder 17 and the inner surface of the fixing film 20.

  In this way, the pressure roller 22 is rotationally driven, and accordingly, the cylindrical fixing film 20 is driven and rotated, and the fixing heater 16 is energized. In a state where the temperature of the fixing heater 16 is raised and raised to a predetermined temperature, the recording material P carrying the unfixed toner image is guided and introduced along the entrance guide 23 into the fixing nip portion 27. . In the fixing nip portion 27, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the fixing film 20, and the fixing nip portion 27 is nipped and conveyed together with the fixing film 20.

  In this nipping and conveying process, heat from the fixing heater 16 is applied to the recording material P through the fixing film 20, and an unfixed toner image on the recording material P is heated and pressurized on the recording material P to be melted and fixed. . The recording material P that has passed through the fixing nip 27 is separated from the fixing film 20 by the curvature, and is discharged by the fixing discharge roller 26.

(Fixing heater 16)
FIG. 3 is a sectional view of the fixing heater 16. The fixing heater 16 includes the following [1] to [5].
[1] An aluminum nitride substrate 41 which is an elongated ceramic substrate in a laterally long longitudinal direction having a longitudinal direction in a conveyance direction of the recording material P, that is, a direction orthogonal to the paper passing direction.
[2] Resistive heating element layers 42 and 43 (43a, 43a, 43a, 43m) having a thickness of about 10 μm and a width of about 1 mm, coated on the surface side of the aluminum nitride substrate 41 of [1] by screen printing along the longitudinal direction. 43b). The resistance heating element layers 42 and 43 are obtained by printing a conductive paste containing a silver palladium (Ag / Pd) alloy on the aluminum nitride substrate 41.
[3] An electrode portion 44 (FIG. 4) in which a pattern is formed on the surface side of the aluminum nitride substrate 41 by screen printing of silver paste or the like as a power supply pattern for the resistance heating element layers 42 and 43 of [2].
[4] A thin glass coat 45 having a thickness of about 80 μm for ensuring the protection and insulation of the resistance heating element layers 42 and 43.
[5] A sliding layer 46 made of glass provided on the contact surface between the aluminum nitride substrate 41 and the fixing sleeve 20.

  FIG. 4A is a diagram showing the surface side of the fixing heater 16, and FIG. 4B is a graph of the heat generation amount per unit length of the fixing heater 16. As shown in FIG. 4, the resistance heating element layer includes three heating elements 43 (43 a, 43 b) and 42.

The heating element 43 is a first heating element (hereinafter referred to as a main heater 43), is a resistance heating element that is energized through the electrode 44, and has a length of 223 mm in the longitudinal direction. The main heater 43 continuously increases the pattern width from the longitudinal center to both ends, thereby reducing the heat generation amount per unit length in the longitudinal direction from the longitudinal center to both ends as shown in FIG. ing. The amount of heat generated per unit length of the main heater 43 when 120 V is applied is 4.9 W / mm at the longitudinal center, and 2.9 W / mm at positions ± 111.5 mm at both ends from the longitudinal center. That is, the heat generation amount per unit length is relatively large in the central portion in the longitudinal direction and small at the end portions, and the heat generation amount per unit length at both end portions is 0.6 times that in the central portion. The parabola distribution is as follows.

  The heating element 42 is a second heating element (hereinafter referred to as a sub-heater 42) having a resistance ratio per unit length of the end portion with respect to the central portion in the heater longitudinal direction that is larger than that of the main heater 43. The sub heater 42 continuously narrows the pattern from the longitudinal center to the end, thereby increasing the heat generation amount per unit length from the longitudinal center to both ends as shown in FIG. The amount of heat generated per unit length of the sub-heater 42 when 120 V is applied is 2.9 W / mm at the longitudinal center, and 4.9 W / mm at positions ± 111.5 mm at both ends from the longitudinal center. That is, the heat generation amount per unit length is relatively small in the central portion in the longitudinal direction and large at the end portions, and the heat generation amount per unit length at both end portions is 1.68 times that in the central portion. The parabola distribution is as follows.

  The total heat generation amount of the main heater 43 and the sub heater 42 is such that the gradient with respect to the longitudinal direction is zero, and the heat generation amount is uniform over the entire length.

  A power supply connector is attached to the electrode portion 44 of the fixing heater 16. Power is supplied from the heater drive circuit unit to the electrode unit 44 via the power supply connector, so that the main heater 43 and the sub-heater 42 generate heat and the fixing heater 16 quickly rises in temperature.

  In normal use, the rotation of the fixing film 20 starts as the pressure roller 22 starts rotating, and the temperature of the fixing film 20 increases as the temperature of the fixing heater 16 increases. The energization of the fixing heater 16 is controlled by PID control, and the input power is controlled so that the detected temperature of the main thermistor 18 disposed at the center on the back side of the fixing heater 16 maintains the target value (target temperature). .

  FIG. 5 shows the positional relationship between the fixing heater 16 and the thermistor. In this embodiment, sub-thermistors 19a and 19b are provided at both ends of the fixing heater 16 in order to detect the temperature rise of the non-sheet passing portion when a recording material having a width smaller than the maximum sheet passing width is passed. ing. The main thermistor 18 is disposed at the center of the longitudinal direction, and the sub-thermistors 19a and 19b are disposed at a position of 102 mm from the longitudinal center.

(Energization ratio control)
Next, the energization ratio control to the main heater 43 and the sub heater 42 during paper feeding will be described. When the sheet feeding is started, the temperature of the sub-thermistors 19a and 19b rises due to the temperature rise of the non-sheet feeding portion. The temperature of the sub-thermistor is monitored, and when a certain threshold value is exceeded, control for decreasing the energization ratio to the sub-heater 42 is performed. The energization ratio is a ratio of power supplied to the main heater 43 and the sub heater 42. Since the sub-heater 42 is a heating element that generates a large amount of heat at the end, the amount of heat generated at the end of the fixing heater 16 decreases when the energization ratio decreases. That is, in the heating area of the fixing heater 16 formed by a plurality of heating elements, the heat generation amount (first heat generation amount) in the central portion in the longitudinal direction orthogonal to the recording material conveyance direction, and the heat generation amount in the end portion in the longitudinal direction. The ratio of (second calorific value) can be controlled. As a result, the temperature rise of the non-sheet passing portion can be suppressed.

  The threshold for determining to decrease the energization ratio of the sub-heater 42 includes a sub-thermistor obtained by subtracting the detected temperature of the main thermistor 18 from the detected temperature of the sub-thermistor 19a or 19b, whichever is higher. Use the temperature difference of the main thermistor.

When the temperature of the sub-thermistor 19 becomes higher than the detected temperature of the main thermistor 18 and the temperature difference exceeds a predetermined threshold value, it is determined that the temperature rise of the non-sheet passing portion has occurred, and the main heater 43 and the sub-heater 42 are energized. The amount of heat generated by the sub-heater 42 is reduced by changing the ratio. For example, L
When the ETTER size paper is passed, if the higher temperature of the sub-thermistor 19 becomes 10 ° C. higher than the temperature of the main thermistor 18, the energization ratio of the sub-heater 42 is decreased by 10%, and the main heater 43: sub-heater 42 = 100: 90 ratio. change. As a result, the amount of heat generated by the sub-heater 42 is reduced, and the temperature rise of the non-sheet passing portion is mitigated.

  As shown in FIG. 6, in this embodiment, there are eight levels of this energization ratio. For each level, the energization ratio of the sub-heater 42 is decreased by 10% and finally decreased to 30%. In the Letter size, every time the temperature difference between the sub-thermistor and the main thermistor exceeds the threshold value of 10 ° C., the energization ratio level is advanced by 1 to decrease the heat generation amount of the sub-heater 42. In this way, damage to the apparatus is prevented by sequentially decreasing the amount of heat generated at the end in accordance with the temperature rise of the non-sheet passing portion.

(Power ratio control when printing A4 size paper)
In this embodiment, in the A4 size paper passing as the second recording material, the threshold value for changing the energization ratio level is different from the threshold value (first threshold value) in the letter size paper passing as the first recording material. (Second threshold) is set.

  As described above, with the increase in speed, there is a problem of non-sheet passing portion temperature rise when A4 size paper is continuously fed. Furthermore, since A4 size paper is narrower than Letter size paper, it may be set with a bias in the paper feed slot. When A4 size paper is passed to either the left or right side (hereinafter, this state is referred to as “one-sided”), if the heat generation at the end is reduced to cope with the temperature rise of the non-sheet passing portion, There is a possibility that the fixing property at the image edge portion on the opposite side to the side where the temperature of the paper passing portion is increased may be impaired. For this reason, it is necessary to perform energization ratio control different from that for Letter size paper for A4 size paper.

  Moreover, as a phenomenon associated with the increase in the speed of the printer, there is an increase in the difference between the temperature detected by the sub-thermistor and the temperature of the member that is desired to prevent melting. Of the members used in the film heating type heating device, the one having the lowest heat-resistant temperature is a rubber used for an elastic layer of a fixing film or a pressure roller. In particular, the rubber layer of the fixing film in contact with the image surface of the recording material has a higher temperature than the rubber layer of the pressure roller. Therefore, when the non-sheet-passing portion temperature rises, melting is more likely to occur.

  Since the sub-thermistor is in contact with the surface of the heater opposite to the contact surface with the fixing film, the heat transfer from the heater is fast and the temperature difference with the heater is small. On the other hand, the rubber layer of the fixing film transfers heat from the heater via contact heat resistance generated between the fixing film base layer, the heater and the rotating film, and sliding grease. Transmission is slow and the temperature difference with the heater increases. For this reason, there is a difference between the temperature detected by the sub-thermistor in the state where the temperature rise in the non-sheet passing portion and the temperature of the rubber layer of the fixing film, and the temperature detected by the sub-thermistor is higher.

  This temperature difference also varies depending on the warming condition of the heating device, and this temperature difference becomes large immediately after the start of printing, that is, in a state where the heating device is still cooled. This is because the heat of the heater is consumed to raise the temperature of the members such as the sliding grease, the fixing film base layer, and the heater holder that are not yet warmed, and the temperature rise of the rubber layer of the fixing film is delayed accordingly. .

FIG. 7 is a graph that records the temperature transition of the non-sheet passing portion of the sub-thermistor and the fixing film when energization of the heater is started from the state in which the heating device is cold, and A4 size paper is continuously fed. Indicates. Since the temperature rise of the fixing film is slower than the temperature rise of the sub thermistor, the temperature difference between the sub thermistor and the fixing film immediately after the start of energization is large. Thereafter, when the paper is advanced, the temperature difference between the sub-thermistor and the fixing film becomes small, and a steady state is maintained while maintaining a certain difference.

  Thus, the difference between the temperature of the sub-thermistor that detects the temperature of the non-sheet passing portion and the actual temperature of the fixing film is not always constant. For this reason, when the threshold value for changing the energization ratio control level is constant, the temperature of the non-sheet passing portion of the fixing film does not reach the heat resistant temperature when the fixing device is not yet warmed. There is a possibility that the energization ratio of the sub-heater 42 may be lowered.

  In a state where the fixing device is not yet warmed up, the fixing strength of toner at the end of the recording material is generally low. This is due to the fact that the temperature of the members of the fixing device is less likely to rise compared to the central portion because the end portion has a large heat dissipation. That is, when printing starts from a state where the fixing device is cold, the energization ratio of the sub-heater 42 can be lowered more than necessary even though the toner fixing strength tends to be low at the end of the recording material. There was sex.

Furthermore, as described above, there is a risk that the A4 size recording material is passed to either the left or right side. Therefore, if the heat generation at the end portion is reduced in order to cope with the temperature rise at the non-sheet passing portion, the fixability at the end portion of the paper may be more easily impaired than when the paper is passed at the normal position.
In view of the above, in this embodiment, the threshold value for changing the energization ratio level for A4 size paper is set to a value different from that for Letter size paper, and the threshold value is set and changed according to the number of sheets to be passed.

  FIG. 8 shows a table summarizing the threshold values for changing the energization ratio level of Letter size paper and A4 size paper and the number of sheets to be passed. The threshold for changing the energization ratio level of the LETTER size is constant regardless of the number of sheets to be passed. On the other hand, the threshold value for changing the energization ratio level of A4 size paper changes depending on the number of sheets to be passed. First, it is 25 ° C. for 1-5 sheets, 20 ° C. for 6-10 sheets, 15 ° C. for 31-30 sheets, 31 sheets Thereafter, the temperature was set to 10 ° C.

  FIG. 9 shows the temperature transition at the non-sheet passing portion of the fixing film and the temperature at the initial stage (1st to 60th sheets) of the sub-thermistor when the actual sheet is passed. In the experiment, letter-size and A4-size plain paper was continuously fed at a temperature adjustment temperature of 240 ° C. by the main thermistor, the temperature of the non-sheet passing portion of the fixing film and the temperature of the sub-thermistor, and the main heater 43 and sub heater 42. The energization ratio of was monitored. A sheet bundle of 500 sheets was set in a paper feed cassette, and paper was passed from the paper feed cassette. For A4 size paper, the paper was set in a regular position in the paper feed cassette. The sheet conveyance speed was set to 300 mm / second, and the sheet interval was set to 10 mm. In addition, the image drawn on the paper was obtained by superimposing the entire solid image of magenta toner and yellow toner, and it was also confirmed at the same time whether or not there was an image defect at both ends of the image.

  According to FIG. 9, the letter temperature of the sub-thermistor is 250 ° C. with respect to the temperature of the main thermistor which is 240 ° C. As described with reference to FIG. 8, during letter passing, when the temperature of the sub-thermistor becomes 10 ° C. higher than that of the main thermistor due to the temperature rise of the non-sheet passing portion, the energization ratio level is increased by one. Control is performed to lower by 10%. The energization ratio of the sub-heater 42 decreases with the sheet passing, and is reduced to 50% when the number of sheets to be passed is about 50. By this control, the sub-thermistor changes while maintaining a state approximately 10 ° C. higher than the main thermistor. Although the surface temperature of the fixing film has increased to 225 ° C., it can be said that the temperature is controlled within a range where there is no problem considering that the continuous usable temperature of the silicon rubber of the film elastic layer is 230 ° C. Further, there was no image chipping at both ends of the image, and there was no problem with the fixing strength of the toner to the paper.

In the graph during A4 paper feeding shown in FIG. 9, the temperature of the sub-thermistor is 260 until the 10th sheet.
It moved around ℃, then gradually decreased with the passage of paper, and it kept at 250 ℃ in the latter half of the graph. This is because the threshold for changing the energization ratio is changed depending on the number of sheets as described with reference to FIG. The temperature of the sub-thermistor is higher than when the Letter is passed, but the fixing film temperature is sufficiently low at the initial stage of passing the paper, and thus exceeds the continuous usable temperature of the silicon rubber of the film elastic layer of 230 ° C. There is nothing. Therefore, there is no problem even if a high sub-thermistor temperature is allowed.

  On the other hand, A4 size paper has a width of 3 mm on both sides smaller than Letter, so even if the energization ratio change threshold value is increased, the energization ratio of the sub-heater 42 decreases at a high speed with the passing of paper. According to the graph shown in FIG. 9, the energization ratio is 50% in the vicinity of the 30th sheet, and the energization ratio decreases faster than the letter is lowered. Further, the energization ratio of the sub-heater 42 decreased to 40% in the vicinity of the 38th sheet, but there was no chipping of images at both ends, and there was no problem in toner fixing strength.

  Next, in order to confirm the effect of the energization ratio control when printing A4 size paper in this embodiment, printing was performed with the A4 size paper being offset. In order to align A4 size paper, the position of the left and right restricting plates in the paper feed cassette was set to the Letter position, and the A4 size paper was pressed against the left restricting plate with respect to the paper traveling direction. Since the other sheet passing conditions are the same as the above-described conditions, description thereof is omitted.

  FIG. 10 shows the contents of A4 size paper passing in the justified state, and also shows the contents of a comparative example performed in order to confirm the effect of this embodiment. The threshold for changing the energization ratio level in the present embodiment is the same as that described with reference to FIG. 8, with 1-5 sheets being 25 ° C., 6-10 sheets being 20 ° C., 11-30 sheets being 15 ° C., 31 sheets Thereafter, the temperature was set to 10 ° C. On the other hand, in the comparative example, the threshold value for changing the energization ratio level is not changed depending on the number of sheets, and is kept constant at 10 ° C.

  FIG. 11 shows the results of monitoring the temperature of the non-sheet passing portion of the fixing film and the temperature of the sub-thermistor, and the energization ratios of the main heater 43 and the sub heater 42 in the control of the example and the comparative example during A4 one-sided feeding.

  In the example, since the sheet is shifted by one side, the temperature rise at the non-sheet passing portion is increased, and the temperature of the sub-thermistor is higher than before. Since the sub-thermistor temperature reached 265 ° C. with about 5 sheets passed, the difference between the main thermistor temperature (240 ° C.) and the sub-thermistor temperature (265 ° C.) became 25 ° C., and the energization ratio of the sub-heater 42 was lowered by 10%. Thereafter, the energization ratio of the sub-heater 42 decreased at an early timing, reaching 50% for about 25 sheets, 40% for about 30 sheets, and 30% for about 37 sheets. The temperature of the fixing film was about 225 ° C. around the 60th sheet, and there was no problem. Further, when the image chipping at the edge of the sheet on the side where the sheet was brought close was confirmed, there was no chipping and there was no problem with the fixing strength.

  In the comparative example, the threshold for changing the energization ratio level is constant at 10 ° C. from the initial stage of paper passing. For this reason, when the main thermistor temperature is constant at 240 ° C., the sub-thermistor is controlled to be about 250 ° C. through the sheet passing.

According to the sub-thermistor temperature of the embodiment shown in FIG. 11, the A4 sheet is passed in a state of being justified, so the temperature rise of the non-sheet passing portion becomes very high. The sub-thermistor temperature has risen to ℃. On the other hand, in the comparative example, when the temperature reaches 250 ° C., the energization ratio of the sub-heater 42 is decreased, so that the energization ratio of the sub-heater 42 is decreased at an earlier timing than in the embodiment. According to the monitoring result shown in FIG. 13, the energization ratio of the sub-heater 42 decreased with the passage of paper, decreased to 40% near the 17th sheet, and decreased to 30% near the 25th sheet. When it was confirmed that there was a missing image at the edge of the paper on the side where the paper was placed, 5
Fine white spots can be seen in solid images from the first image. This is a phenomenon that occurs due to the toner that could not be fixed on the paper being taken away by the fixing film, and occurs because the fixing strength of the toner to the paper is low. With the passage of paper, the number of white spots increased and increased, and in the vicinity of the fifteenth sheet, it was clearly visible as a missing image.

  According to the present embodiment, even if A4 size paper is not set at a regular position and is passed in a state where it is offset, the temperature of the fixing film member rises to a temperature at which there is a risk of breakage. It was possible to fix the toner firmly to the edge of the image while preventing it. Moreover, the temperature of the member of the heating apparatus could be reduced.

In this embodiment, the film heating type heating apparatus has been described, but the effect of the present invention is not limited to the film heating type heating apparatus. Even the above-described heat roller type fixing device, belt heating type fixing device, and fixing device having a nip plate inside the belt can implement the configuration described in this embodiment.
In this embodiment, a heater having a configuration in which a plurality of heating elements are arranged in the conveyance direction of the recording material is used. However, the configuration of the heater is not limited to this. For example, a heater having a configuration in which a plurality of heating elements are arranged side by side in the longitudinal direction orthogonal to the conveyance direction of the recording material (the heating elements are divided in the longitudinal direction) and the energization of the plurality of heating elements is individually controlled on and off. It may be used.

  As described above, according to the present embodiment, the energization ratio can be controlled in accordance with the warming condition of the fixing device, so that an appropriate energization ratio level change threshold value can be set. As a result, the non-sheet passing portion on one end side in the longitudinal direction is prevented from abnormally rising in temperature while satisfying the fixing property of the opposite end portion, that is, the image end portion due to insufficient fixing strength. While preventing chipping, it is possible to prevent the temperature of the member from rising to a dangerous temperature. Therefore, it is possible to perform image heating in large quantities at high speed, and it is possible to provide an image heating apparatus and an image forming apparatus that improve both the durability of the apparatus and the convenience of the user.

(Example 2)
In the control described in the first embodiment, the threshold value for changing the energization ratio level is changed according to the number of prints (the number of recording materials on which an image is heated). Since the fixing device warms up as the number of prints increases, the threshold for changing the energization ratio level is increased during the initial period when the fixing device is cold, and the threshold for changing the energization ratio level is decreased during the latter half of the time when the fixing device is warm. Yes. However, the warming condition of the fixing device at the start of printing is not necessarily the same. For example, if the time has not passed since the previous print job, there is a possibility that the fixing device is still warmed by the heat at the previous job. It is also considered that the warming condition of the fixing device is affected by the number of prints of the previous job. For this reason, if the warming condition of the fixing device at the start of printing can be grasped and taken into consideration, it is possible to perform energization ratio control that can cope with a wider range of situations.

  Therefore, in the second embodiment, a warm-up index indicating the warming condition of the fixing device is calculated and used for energization ratio control. The warm-up index is a variable value that correlates with the heat storage amount of the fixing device 12. The warm-up index is a count value that is counted up according to the number of prints and is counted down according to the time during which the prints are paused. The warming of structures in the fixing device 12 including the pressure roller 22 is warmed up. It is a variable value that digitizes the condition. For example, the initial value of the warm-up index is 0, and 1 is added to every three continuous prints as the number of times of heating when the image formed on the recording material is continuously heated, and heating is not performed. As the length of the period, 1 is subtracted every 3 minutes after the end of printing. The warm-up index is set in the range of 0-30.

The energization control means 21 always calculates the warm-up index during the printing operation and the printing pause period. Then, energization ratio control in passing A4 size paper is performed based on the threshold shown in FIG. When the warm-up index is 0 to 2, that is, when the heat storage amount of the fixing device 12 is low and not warmed, the threshold value for changing the energization ratio level is set to 25 ° C. When the warm-up index is 3 to 4, the energization ratio level change threshold is 20 ° C. When the warm-up index is 5 to 10, the energization ratio level change threshold is 15 ° C and the warm-up index is 11 or more. The threshold for changing the energization ratio level was 10 ° C. As described above, according to the method of changing the threshold value for changing the energization ratio level by the variable value indicating the warming condition of the fixing device, printing is performed at an appropriate energization ratio level regardless of the warming condition of the fixing device at the start of printing. It can be carried out. Therefore, it can respond to a wider usage situation.

  Also in this embodiment, the effect of the present invention is not limited to the heating device of the film heating system. Even the above-described heat roller type fixing device, belt heating type fixing device, and fixing device having a nip plate inside the belt can implement the configuration described in this embodiment. According to the above configuration, even if the fixing device is warmed up before the start of printing, a threshold value for changing the energization ratio level can be provided. Therefore, in a wider range of situations, it is possible to prevent the temperature of the member from rising to a dangerous temperature while preventing chipping of the image end due to insufficient fixing strength, improving the durability of the device and improving the convenience of the user. It becomes possible to provide a heating apparatus with both improved.

  P ... paper (recording material), 12 ... fixing device, 16 ... heater heater, 17 ... heater holder, 42 ... second heating element, 43 ... first heating element, 18 ... main thermistor, 19 ... sub-thermistor, 20 ... fixing film , 22 ... pressure roller, 23 ... inlet guide, 24 ... device frame, 26 ... fixing discharge roller, 27 ... fixing nip portion

Claims (10)

An elongate heater, the heater capable of controlling the ratio of the calorific value at the end to the calorific value at the center in the longitudinal direction of the heater;
A first temperature detection element for detecting a temperature in the center of the heater in the longitudinal direction;
A second temperature sensing element for sensing the temperature of the longitudinal end of the heater;
A control unit that controls the heater so that the detected temperature of the first temperature detecting element becomes a target temperature;
The image formed on the recording material is heated with the heat of the heater,
In the image heating apparatus in which the control unit controls the heater so that the ratio becomes small when the detection temperature of the second temperature detection element exceeds a predetermined threshold.
The image heating apparatus, wherein the control unit changes the threshold according to a warming condition of the image heating apparatus. The controller is
Judging the degree of warming based on the number of recording materials that heated the image,
The image heating apparatus according to claim 1, wherein the threshold value is set to a smaller value as the number of recording materials on which the image is heated increases. The controller is
The warming state is added to at least a count value that is added according to the number of times of heating when the image formed on the recording material is continuously heated, and subtracted according to the length of the period during which heating is not performed. Based on
The image heating apparatus according to claim 1, wherein the threshold value is set to a smaller value as the count value increases. The controller is
The threshold is
When heating an image formed on a first recording material having a size that passes through the end of the heating area, a constant first threshold value is set regardless of the warming condition of the image heating device,
When heating an image formed on a second recording material having a size that does not pass through the end of the heating area, the second threshold value is set according to the warming condition of the image heating apparatus. The image heating apparatus according to any one of claims 1 to 3.   The image heating apparatus according to claim 4, wherein a value initially set as the second threshold value is a value larger than the first threshold value. The heater is
A plurality of heating elements arranged in the recording material conveyance direction,
A first heating element having a heat generation amount per unit length in the longitudinal direction relatively large at the center in the longitudinal direction and small at the end;
A second heating element having a heat generation amount per unit length in the longitudinal direction that is relatively small in the center of the longitudinal direction and large at the end;
Have
The controller is
The image heating apparatus according to claim 1, wherein the ratio is controlled by controlling an energization ratio between the first heating element and the second heating element. The controller is
The image heating apparatus according to claim 6, wherein input power to the heater is controlled so that a temperature detected by the first temperature detection element maintains a target temperature. The controller is
Controlling the energization ratio so that the amount of heat generated by the second heating element is smaller than the amount of heat generated by the first heating element when the temperature detected by the second temperature detecting element exceeds a predetermined threshold value. The image heating apparatus according to claim 6 or 7, wherein: A cylindrical film that rotates while the inner surface is in contact with the heater;
The image heating apparatus according to claim 1, wherein an image formed on the recording material is heated through the film. An image forming unit for forming an image on a recording material;
The image heating apparatus according to any one of claims 1 to 9, as a fixing unit that fixes an image formed on a recording material to the recording material,
An image forming apparatus comprising:

Images