JP7039375B2 - Image heating device and image forming device - Google Patents

Description

The present invention relates to an image heating device that heats a toner image on a recording material , and an image forming device such as an electrophotographic system provided with the image heating device .

In the electrophotographic image forming apparatus, an unfixed toner image is formed on the recording material. Then, the recording material on which the toner image is formed is conveyed to the fixing device (image heating device). In the fixing device, heat and pressure are applied to the unfixed toner image at the fixing nip portion, and the toner image is fixed on the recording material.

By the way, in an image forming apparatus, usually, the recording paper (recording material) loaded on a cassette or a feeder is taken out one by one by a paper feeding member and conveyed to an image forming unit. Here, depending on various circumstances such as variation and deterioration of the recording paper and the paper feed member, a phenomenon called “double feeding” in which a plurality of recording papers are simultaneously stacked may occur exceptionally.

For example, a film heating type fixing device for forming a fixing nip portion by a heating film (endless belt) and a pressure roller will be described. When the recording paper is conveyed to the fixing device in a double-feeding state in this fixing device, a gap is provided between the film and the pressure roller due to the thickness of the overlapping recording materials near the widthwise end of the double-feeding recording paper. Occurs. At that portion, the heat of the heater is less likely to be taken away by the pressurizing roller, and the fixing member or the heating member may become locally hot at the end portion in the longitudinal direction.

In Patent Document 1, a plurality of temperature detecting members for detecting the temperature of the fixing member or the heating member are arranged at different positions in the direction orthogonal to the feeding direction of the recording paper. Then, by detecting the detected temperature inclination ΔT of the fixing member or the heating member within a predetermined time while the recording paper is passing through the nip portion by at least one temperature detecting member, and comparing the detected temperature inclination ΔT with the reference value. , Detects double feeding of recording paper. A technique has been proposed in which the power supply to the heating member is immediately turned off or reduced when the double feed is detected.

That is, Patent Document 1 discloses a configuration in which the power supply to the heating member is immediately turned off or reduced when the detected temperature slope ΔT is equal to or higher than the reference value (that is, the occurrence of a steep temperature rise) regardless of the detected temperature. ing.

JP-A-2002-296962

However, even if a steep temperature rise is detected, the temperature does not necessarily rise to a temperature (error temperature) at which the fixing member or the heating member may be damaged or significantly deteriorated. Even in such a case, if the heater is immediately turned off by detecting a steep temperature rise as in Patent Document 1, the temperature of the nip portion may drop.

Further, even in a state where the recording materials are transported one by one without being double-fed, it is required to suppress the temperature rise to the error temperature. However, it is unlikely that the temperature will rise to the error temperature at once as compared with the case of double feeding. Therefore, it is required not to lower the temperature of the nip portion too much for fixability or productivity.

The present invention has been made in view of these, and an object thereof is to suppress the overheating of the heater or the endless belt, and to reduce the temperature of the nip portion in a range where it is difficult to reach the overheating. It is to suppress.

The image heating device according to the present invention is
An endless belt that heats the toner image on the recording material while transporting the recording material at the nip.
A rotating body that cooperates with the endless belt to form the nip portion,
A heater that has a heating element that generates heat when energized and heats the endless belt,
With respect to the longitudinal direction of the endless belt, the heating element in a region outside the minimum passage region, which is the region of the endless belt, through which the recording material having the smallest size in the longitudinal direction passes among the recording materials conveyed to the nip portion. With a detector that detects the temperature of
It has a control unit that controls the temperature at which the energization of the heater is turned off according to the temperature rise rate of the detection temperature per unit time by the detection unit.
When the temperature rise rate is the first rise rate, the control unit turns off the energization of the heater in response to the detection temperature reaching the first temperature, and the temperature rise rate is the first. When the rise rate is lower than the rise rate of 1, the control unit turns off the energization of the heater in response to the detection temperature reaching the second temperature higher than the first temperature. It is characterized by making it.
Further, the image forming apparatus according to the present invention is
An image forming part that forms a toner image on the recording material,
An endless belt that heats the toner image formed on the recording material by the image forming unit while transporting the recording material at the nip portion.
A rotating body that cooperates with the endless belt to form the nip portion,
A heater that has a heating element that generates heat when energized and heats the endless belt,
With respect to the longitudinal direction of the endless belt, the heating element in a region outside the minimum passage region, which is the region of the endless belt, through which the recording material having the smallest size in the longitudinal direction passes among the recording materials conveyed to the nip portion. With a sensor that detects the temperature of
A double feed detection unit that detects that a plurality of recording materials are being conveyed to the nip unit, and a double feed detection unit.
It has a control unit that controls the temperature at which the energization of the heater is turned off according to the detection result by the double feed detection unit.
When it is detected by the double feed detection unit that a plurality of recording materials are being conveyed to the nip unit, the control unit determines that the temperature detected by the sensor reaches the first temperature. When the energization of the heater is turned off and the double feed detection unit does not detect that a plurality of recording materials are being conveyed to the nip unit, the control unit has the detection temperature higher than the first temperature. It is characterized in that the energization of the heater is turned off when a high second temperature is reached.

According to the present invention, it is possible to suppress an excessive temperature rise of the heater or the endless belt, and to suppress a temperature decrease of the nip portion in a range where the excessive temperature rise is difficult to reach.

It is a figure which shows the flowchart of the control which concerns on Example 1. FIG. It is a schematic cross-sectional view which shows the schematic structure of the image forming apparatus which concerns on Example 1. FIG. It is a schematic cross-sectional view which shows the schematic structure of the main part of the fixing device which concerns on Example 1. FIG. (A) is a schematic view of a partially cutout surface of the heater, (b) is a schematic view of the back surface, and (c) is a schematic view of an enlarged cross section. It is a schematic block diagram which shows the power supply path from the commercial power source to a heater. It is a figure which shows the timing chart of the control which concerns on Example 1. FIG. It is a figure which shows the effect which concerns on Example 1. FIG. It is a figure which shows the flowchart of the control which concerns on Example 2. FIG. It is a figure which shows the timing chart of the control which concerns on Example 2. FIG. It is a schematic cross-sectional view which shows the schematic structure of the main part of the fixing device which concerns on a reference example. It is a schematic cross-sectional view which shows the position of the temperature detection element in a reference example. It is a figure which shows the flowchart of the control which concerns on a reference example. It is a figure which shows the timing chart of the control which concerns on a reference example. It is a figure which shows the flowchart of the control which concerns on Example 3. FIG. It is a figure which shows the timing chart of the control which concerns on Example 3. FIG.

<< Example 1 >>
[Image forming device]
FIG. 2 is a schematic cross-sectional view showing a schematic configuration of the image forming apparatus 100 in this embodiment. The image forming apparatus 100 is a laser beam printer using an electrophotographic process. The printer 100 executes a print operation (image formation operation) corresponding to a print job (provided information) input from a data output device 200 such as a host computer to the engine controller 114 to form an image in which a toner image is formed on the recording material P. Output things.

A print job is a print instruction to which print conditions such as image data, information on the type of recording material to be used, layout, number of sheets, number of copies, and post-processing are added. The recording material P is a sheet-shaped recording medium on which a toner image (developer image) can be formed by an image forming apparatus. For example, plain paper, resin sheet, glossy paper, leaflet, envelope, label, transfer material sheet, electrofax sheet, electrostatic recording paper, OHP sheet, printing paper, format paper and the like are included. Hereinafter, the recording material P will be referred to as recording paper or paper. The engine controller 114 comprehensively controls various image-drawing devices of the printer 100 to execute a printing operation.

In the printer 100, the image forming unit 100A that forms a toner image (toner image) on the recording paper P is a drum-type electrophotographic photosensitive member (hereinafter referred to as a drum) 101 as an image carrier for forming the toner image. Has. The drum 101 is rotationally driven at a predetermined peripheral speed (process speed) in the clockwise direction of the arrow A. Further, the image forming unit 100A has a charging roller 102 as an electrophotographic process device acting on the drum 101, an exposure device (laser scanner) 115, a developing device 104, a transfer roller 108, and a cleaning device 110.

In the exposure apparatus 115, 103 is a laser beam as an exposure light. In the developing apparatus 104, T is a toner as a developing agent, and 106 is a developing sleeve carrying the toner t. In the cleaning device 110, 109 is a cleaning blade. Since the operation for image formation of the image forming unit 100A is well known, detailed description thereof will be omitted.

The recording paper P stored (stored) in the paper feed cassette (recording material storage unit) 107 is taken out one by one by the paper feed roller 112, passes through the path B, and the tip is received by the resist roller pair 113 on the way and is slanted. The line is corrected. In the resist roller pair 113, the tip portion of the toner image formed on the drum surface and the tip portion of the recording paper in the transfer nip portion, which is the contact portion between the drum 101 and the transfer roller 108, synchronize the recording paper P in a predetermined manner. It is sent out toward the transfer nip portion at a predetermined control timing. As a result, the toner image on the drum 101 side is sequentially transferred to the recording paper P side by the electric action in the transfer nip portion.

The recording paper P that has passed through the transfer nip portion is separated from the drum surface, introduced into the fixing device (image heating device) 111, pressed and heated, and the unfixed toner image carried is on the recording paper (on the recording material). ) Is fixed as a fixed image. If face-up (FU) ejection is selected, the image-fixed recording paper P leaving the fixing device 111 passes through the path C and is ejected to the FU tray 116 with the printed surface facing up. If face-down (FD) paper ejection is selected, the paper is ejected to the FD tray 117 through the path D with the print surface facing down.

[Fixing device]
FIG. 3 is a schematic cross-sectional view showing a schematic configuration of a main part of the fixing device 111. In the following description, regarding the fixing device 111 and the members constituting the fixing device, the longitudinal direction is the direction orthogonal to the transporting direction of the recording paper on the transport road surface of the recording paper, and the lateral direction is the transport road surface of the recording paper. The direction is parallel to the transport direction of the recording paper. The width is a dimension in the lateral direction. With respect to the recording paper, the width is a dimension in the direction orthogonal to the transport direction of the recording paper on the surface of the recording paper. The upstream side and the downstream side are the upstream side and the downstream side in the recording paper transport direction.

This fixing device 111 is a film (belt) heating method in which the pressure roller (pressurizing member) 302 is rotationally driven and the fixing film (fixing belt: fixing member) 303 is rotated by the conveying force of the pressure roller 302. It is a so-called tensionless type device that is driven by a pressure roller.

The fixing device F is roughly classified into a pressure roller 302 which is a drive rotating body, a film unit 310 including a fixing film (endless belt: hereinafter referred to as a film) 303, and a device frame (which houses them). It has a device housing) 311. A nip portion (fixing nip portion) N is formed by pressure contact between the pressure roller 302 as a pair of rotating bodies and the film 302. The pressure roller 302 is a rotating body that cooperates with the film 302 to form a nip portion N.

The film 302 is a heat transfer member that heats by transferring heat of the heating member in contact with the unfixed toner image t formed on the recording paper P. The nip portion N is a portion that sandwiches and conveys the recording paper P carrying the unfixed toner image t and fixes the toner image t as a fixed image by heat and pressure. ta shows the toner image after fixing.

Reference numeral 307 is a recording paper sensor (sheet sensor: outlet sensor) arranged in the vicinity of the recording paper outlet portion of the nip portion N on the downstream side of the nip portion N, and the tip of the recording paper exiting the nip portion N. Detects arrival and also detects rear end passage. The detection signal is input to the control unit (CPU) 203. Based on the input signal, the control unit 203 detects that the recording paper P is sandwiched and conveyed by the nip unit N and that the recording paper P has passed through the nip unit N.

(1) Pressurized roller The pressurized roller 302 is an elastic roller, and the core metal 302a is provided with an elastic layer 302b made of silicone rubber, fluororubber, or the like to reduce the hardness. In order to improve the surface property and the mold releasability with respect to the toner t, a fluororesin layer such as PTFE, PFA or FEP may be provided on the outer peripheral surface of the elastic layer 302b.

In the pressure roller 302, one end and the other end of the core metal 302a are rotatably held between the side plates on one end side and the other end side in the longitudinal direction of the fixing frame 311 (side plates are not shown) via bearing members, respectively. Are arranged. The pressurizing roller 302 serves as a drive rotating body, and the driving force of the motor (drive source) M controlled by the control unit 203 is transmitted via the drive transmission mechanism unit (not shown) and is predetermined in the counterclockwise direction of the arrow Y. It is driven to rotate at the peripheral speed.

(2) Film unit The film unit 310 includes a film 303, a heater 305 as a heating member, a heater holder (hereinafter referred to as a holder) 304 as a heating member holding member, a support stay 308, and flange members on one end side and the other end side. (Not shown), etc.

As a heat transfer member, the film 303 has a thickness of 400 μm or less, preferably about 30 to 80 μm, and is endless containing PTFE, PFA, FEP, or the like as a heat-resistant material in order to reduce the heat capacity and improve quick startability. It is a band-shaped body (endless belt).

The film 303 may have a single-layer structure, a multi-layer structure, or the like. As a multi-layer structure, silicone having a thickness of 300 μm as an elastic layer is formed on the outer peripheral surface of an endless strip as a base layer mainly composed of a metal material such as polyimide, polyamideimide, PEEK, PES or PPS or SUS or nickel. Form a rubber layer. Further, on the elastic layer, there is a multi-layer structure in which a release layer having a thickness of about 20 μm is covered with an endless band as a release layer containing PTFE, PFA, FEP or the like as a main component.

In this embodiment, a cylindrical member made of a nickel alloy as a base layer having a thickness of about 30 μm is used. Further, a silicone rubber layer having a thickness of about 300 μm is formed on the base layer as an elastic layer, and a fluororesin tube having a thickness of about 20 μm is coated on the elastic layer as a release layer. An endless strip film having a thickness of 350 μm was used.

A ceramic heater is used as the heater 305. The heater 305 will be described in detail in section (4). A highly heat-resistant resin or the like is used for the holder 304. The holder 304 has a groove portion provided along the longitudinal direction in the central portion of the outer surface in the lateral direction, and the heater 305 is fitted and fixedly held in the groove portion.

The stay 308 is a reinforcing member arranged inside the holder 304 to back up the holder 304. That is, the stay 308 is a member that supports the heater 305 via the holder 304. It is desirable that the stay 308 is made of a material that does not easily bend even when a large load is applied, and in this embodiment, a SUS304 (stainless steel) mold material having a U-shaped cross section or a U-shaped cross section is used.

The heater 305, the holder 304, and the stay 308 are long members in the width (length) direction of the film 303, and the film 303 is loosely, that is, tension-free with respect to the assembly of the heater 305, the holder 304, and the stay 308. It is fitted outside. That is, the film 303 contains the heater 305.

Both ends of the stay 308 in the film 303 project outward from one end and the other end of the film 303, respectively. Flange members on one end side and the other end side of the film unit as terminal members are fitted to the outward protrusions on one end side and the other end side of the stay 308, respectively. These flange members regulate the movement (thrust movement) of the film 303 in the film unit 310 in the longitudinal direction and the shape in the circumferential direction. A heat-resistant resin or the like is used for the flange member, and PPS (polyphenylene sulfide) is used in this embodiment.

The film unit 310 is arranged substantially in parallel with the heater 305 facing the pressure roller 302, and flange members on one end side and the other end side are provided on the side plates on one end side and the other end side of the fixing frame 311, respectively. It is arranged so as to be engaged with the slide slit portion. Then, the flange members on one end side and the other end side are pressed toward the axial direction of the pressure roller by the urging force of the pressure spring of the pressure mechanism (not shown), respectively. As a result, the heater 305 is pressed against the pressure roller 302 with the film 304 sandwiched between the stay 308 and the holder 304 against the elasticity of the elastic layer 302b.

In this embodiment, the pressing force on the film unit 310 is about 156.8N (16kgf) on one end side, and the total pressing force is about 313.3N (32kgf). Due to the pressing force, a nip portion N having a predetermined width is formed between the film 303 and the pressurizing roller 302 with respect to the transport direction of the recording paper. In the standby state of the printer 100, the pressurizing mechanism is released from the pressing force by the pressure releasing mechanism (not shown), and the pressure contact between the heater 305 and the pressure roller 302 is released (or the pressure contact force is reduced). That is, the formation of the nip portion N is maintained in a substantially released state.

(3) Fixing operation The control unit 203 pressurizes the pressurizing mechanism in the pressure release state at a predetermined control timing in the print job execution sequence to form a nip portion N between the film 303 and the pressurizing roller 302. .. Then, the control unit 203 activates the motor M to rotate and drive the pressurizing roller 302 in the counterclockwise direction of the arrow Y at a predetermined peripheral speed.

When the pressure roller 302 is rotationally driven, a rotational force acts on the film 303 due to the frictional force between the surface of the pressure roller 302 and the surface of the film 303 at the nip portion N. Therefore, the inner peripheral surface of the film 303 slides in close contact with the heater 305, and the outer periphery of the holder 304 is driven and rotated clockwise at the arrow X at a peripheral speed substantially equal to the peripheral speed of the pressurizing roller 302. The holder 304 has a semi-circular cross section and has a function of regulating the rotation trajectory of the film 303.

Further, along with the rotational drive of the pressurizing roller 302, electric power is supplied to the heater 305 from the triac (feeding unit) 200 controlled by the control unit 203 via the feeding path (not shown). As a result, the temperature of the heater 305 rises sharply. As will be described later, the temperature of the heater 23 is raised to a predetermined target temperature (fixing temperature) and adjusted in temperature.

Then, in a state where the pressurizing roller 302 is rotationally driven and the heater 305 is raised to a predetermined target temperature to control the temperature, the recording paper P on which the unfixed toner image t is formed is formed from the image forming unit 100A side. It is sent to the fixing device 111 and introduced into the nip portion N. The heat of the heater 305 is applied to the recording paper P via the film 303 in the process of being sandwiched and conveyed by the nip portion N. The unfixed toner image t is melted by the heat of the heater 305, and is fixed as a fixed image ta on the recording paper P by the pressure applied to the nip portion N.

(4) Configuration of Heater and Power Supply Control FIG. 4 is an explanatory diagram of the configuration of the heater 305 in this embodiment. (A) is a schematic view of a partial notch on the front surface side of the heater, (b) is a schematic view on the back surface side, and (c) is a schematic view of an enlarged cross section of (c)-(c) line arrow in (b). Is. The heater 305 is a so-called ceramic heater, which is a horizontally long planar heating body having a low heat capacity and exhibiting a steep temperature rise characteristic when energized. The heater 305 has an elongated heater substrate 305a and a heating element 305c formed along its length on one side (front side: sliding surface side of the heater 305 with the film 303).

The heater substrate 305a is mainly composed of good heat conductive ceramics such as alumina (Al ₂ O ₃ ) and aluminum nitride (Al N). In this embodiment, the aluminum nitride (thermal conductivity: 100 W / (m · K) elongated plate material having a length of 350 mm, a width of 9 mm, and a thickness of 1 mm is used as a heater substrate (ceramic substrate) 305a.

The heating element 305c is a resistance heating element (current heating element) obtained by coating and firing an electric resistance material such as _{TaSiO 2} , AgPd, Ta 2N, RuO ₂ or nichrome by screen printing. In this embodiment, two parallel heating elements 305c having a length of 300 mm, a width of 2 mm, and a thickness of 20 μm are formed at an interval of 0.5 mm. One end of the two parallel heating elements 305c is electrically connected in series with the conductive material 305d printed on the surface of the heater substrate. Further, the other end side of the parallel two heating elements 305c is electrically conductive to the electrodes 305e and 305f of the conductive material printed on the surface of the heater substrate, respectively.

Further, on the one side of the heater substrate 305a, in order to protect it from sliding with the film 303, glass or fluororesin or the like is used to cover the heating element 305c and the conductive material 305d except for the electrodes 305e and 305f. It is coated with a protective layer 305b as a main component.

Further, on the other surface side (back surface side: the non-sliding surface side of the heater 305 with the film 303) of the heater substrate 305a, a temperature sensitive element 301 (temperature detector: hereinafter referred to as a thermistor) that detects the temperature of the heater 305). Has. In this embodiment, it has two thermistors 301a and 301b, a first and a second. The first thermistor 301a is arranged at a position corresponding to the longitudinal center portion of the heating element 305c as a temperature detector for controlling the temperature of the heater. The second thermistor 301a is arranged at a position 115 mm away from the first thermistor 301a on the other end side of the heater substrate 305a as a temperature detector for detecting double feeding of recording paper.

The heater 305 is fitted and fixed by fitting the heater 305 outward into a groove provided along the longitudinal direction in the center of the outer surface of the holder 304 in the lateral direction with the heater surface side (one side on which the heating element 305c of the heater substrate 305a is formed) facing outward. It is being held. The heating element 305c is supplied with electric power from the triac 200 via the electrodes 305e and 305f, so that the entire length region generates heat. The heat generated by the heating element 305c heats the heater portion corresponding to the entire length region of the heating element 305c.

In the printer 100 of this embodiment, the transport of the recording paper P is the so-called central reference transport. That is, recording paper of any width that can be used for the device is fed so that the central portion in the width direction passes through the central reference transport line (recording material transport center) of the device. In (a) of FIG. 3, O is the central reference carrier line (virtual line).

Wmax is the pass area width of the maximum width size recording paper used in the device. In this embodiment, the width of the passage region is A3 length (297 mm), and the length of 300 mm of the heating element 305c corresponds to this Wmax. Wmin is the pass area width (minimum pass area width) of the recording paper having the minimum width size that can be used in the apparatus. The first thermistor 301a substantially corresponds to the position of the central reference carrier line O.

The power supply control to the heater 305 will be described with reference to FIG. FIG. 5 is a schematic block diagram showing a power supply path from the commercial power supply 201 to the heating element 305c of the heater 305. The heating element 305c is to receive electric power from the commercial power source 201 via the triac 200, and the electric power supply from the commercial power source 201 to the heating element 305c is performed by the central processing unit 203 (power supply control means). Hereinafter, it is abbreviated as CPU).

The temperature information of the heater 305 due to the heat generated by the heating element 305c is the analog information by the first thermistor 301a arranged within the width of the passing region width Wmin of the recording paper of the minimum width size of the heater 305 by the A / D conversion circuit 202. Converted to digital information. The digital information is input to the CPU 203. The CPU 203 compares the input temperature information with a predetermined target temperature (fixing temperature). Then, from the difference, the power supplied from the commercial power source 201 to the heating element 305c is PID controlled via the triac 200, and the temperature of the paper passing region of the heater 305 is adjusted to a predetermined target temperature.

The CPU 203 monitors the temperature information of the heater 305 at predetermined cycles, and corrects the power supplied to the heating element 305c at each predetermined cycle. In this embodiment, wave number control for selecting whether or not to supply power from the commercial power supply 201 to the heating element 305c for each half wave of the AC power supply output from the commercial power supply 201 in a predetermined cycle period. Is adopted. In addition to wavenumber control, the adjustment of the amount of power supplied from the commercial power supply 201 to the heating element 305c over a predetermined period also includes phase control that determines the phase range for each half wave of the AC power supply output from the commercial power supply 201. ..

The first thermistor 301a is a temperature detector for controlling the temperature of the heater for maintaining the heater 305 at the target temperature in the image fixing step of the recording paper of the print job from the start (start-up) of the heat treatment of the fixing device 111. Therefore, the first thermistor 301a is positioned within the width of the passing region width Wmin of the recording paper having the minimum width size of the heater 305, and in this embodiment, it substantially corresponds to the position of the central reference transfer line O.

That is, the first thermistor 301a detects the temperature corresponding to the paper passing portion (passing portion region of the recording paper) in the nip portion N when the recording material is introduced into the fixing device 111. The control unit 203 controls the power supply from the triac 200 to the heater 305 so that the temperature of the paper passing unit in the nip unit N is maintained at a predetermined target temperature based on the temperature detected by the first thermistor 301a. do.

(5) Double feeding detection of recording paper and device control The second thermistor 301b is a temperature detector for detecting double feeding of recording paper, and the analog information by the second thermistor 301b is the A / D conversion circuit 202. Is converted into digital information and input to the CPU 203. The CPU 203 performs double feed detection control based on the input temperature information of the heater 305.

The second thermistor 301b is a temperature detector for detecting the detection temperature gradient ΔT (inclination (gradient) of the change over time of the detection temperature) of the heater 305 within a predetermined time while the recording paper P is passing through the nip portion N. be. Therefore, it is arranged outside the region of the passing region width Wmin of the recording paper having the minimum width size and in the heating region of the heating element 305c.

That is, the second thermistor 301b detects the temperature corresponding to the non-passing portion (non-passing portion region of the recording paper) in the nip portion N when the recording paper is introduced into the fixing device 111. In this embodiment, the control unit 203 stops the power supply from the triac 200 to the heater 305 according to the detection temperature detected by the second thermistor 301a and the slope of the change over time of the detection temperature. Control.

Specifically, as shown in the flowchart described later, the control unit 203 forces the heater 305 to be energized according to the detection temperature detected by the second thermistor 301a and the slope of the change over time of the detection temperature. Change (control) the temperature setting to be turned off. The slope (gradient) of the change over time of the detected temperature is, more specifically, the temperature rise rate of the detected temperature per unit time.

Then, until the temperature detected by the second thermistor 301a reaches the set temperature (forced OFF temperature), the heater 305 is allowed to be energized and the temperature is adjusted so as to reach the target temperature of the heater 305. When the temperature detected by the second thermistor 301a reaches the set temperature (forced OFF temperature), the energization of the heater 305 is turned off.

As described above, the analog information by the second thermistor 301b is converted into digital information by the A / D conversion circuit 202 and input to the CPU 203. Here, if the CPU 203 is configured to convert the digital information into analog information again and then calculate the detected temperature gradient ΔT based on the analog information, the error is smaller than that of the configuration that calculates the detected temperature gradient ΔT based on the digital information. This is because analog information and digital information are not in a proportional relationship.

Based on the detection temperature gradient ΔT detected by the second thermistor 301b and the detection temperature T, the CPU 203 determines that the paper is double-feeding and changes the control. That is, the CPU 203 functions as a double feed detection unit. An example of a specific detection method is as shown in the flowchart described later. When the CPU 203 changes the control, the CPU 203 changes the control based on the information stored in the memory 204. The control unit controls the temperature at which the energization of the heater 305 is turned off according to the detection result by the double feed detection unit.

This control will be described with reference to the flowchart of FIG. First, a print command is issued from the CPU 203 (step S01). The image forming apparatus that has received the print command feeds the recording paper P (step S02). Subsequently, each part of the main body operates as described above, and the toner image is transferred to the recording paper P fed from the resist roller 113 at the transfer nip part (step S03).

The recording paper P on which the transfer image is placed rushes into the fixing nip portion N of the fixing device 111 (step S04). In order for the CPU 203 to determine that the recording paper P has entered the fixing nip portion, if the fixing device 111 has an inlet sensor, the signal of the inlet sensor may be used. If the fixing device 111 does not have an inlet sensor, it can be determined that the recording paper P has entered the fixing nip portion by dividing the transfer distance by the transfer speed.

In this embodiment, the CPU 203 reads the temperature of the second thermistor 301b every 0.1 [s] after the recording paper P rushes into the nip portion N for fixing. The CPU 203 reads the temperature T0 of the second thermistor 301b when the recording paper P rushes into the fixing nip portion N (step S05). Then, after n [s] (that is, 0.1 sec after step S05), the CPU 203 reads the temperature Tn of the second thermistor 301b (step S06). Further, after n + 1 [s] (that is, 0.1 sec after step S06), the CPU 203 reads the temperature Tn + 1 of the second thermistor 301b (step S07).

Note that n and n + 1 are symbols, and the interval for reading the temperature of the second thermistor 301b is not limited to 1 sec.

Since the detection temperature gradient is detected, the CPU 203 calculates ΔTn + 1 = Tn + 1-Tn (step S08). Of course, the CPU 203 also calculates the initial temperature slope ΔT1 = T1-T0.

The CPU 203 determines whether the detected temperature slope (temperature difference) ΔTn + 1 is larger than α1 (predetermined first temperature difference threshold value) and the temperature Tn + 1 is higher than β1 (predetermined first temperature threshold value) (step S09). .. If the result of the determination is correct, the CPU 203 sets the heater forced OFF temperature to Toff1 [° C.] (step S10). If the judgment is not correct, the process proceeds to step 11.

The heater forced OFF temperature control is a control that makes the power input to the heater 305 zero when the second thermistor 301b detects the heater forced OFF temperature.

In step 11, the CPU 203 has a detected temperature slope (temperature difference) ΔTn + 1 larger than α2 (predetermined second temperature difference threshold value: α2 <α1), and the temperature Tn + 1 is β2 (predetermined second temperature threshold value: β2>. It is determined whether it is higher than β1) (step S11). If the result of the determination is correct, the CPU 203 sets the heater forced OFF temperature to Toff2 [° C.] (> Tofff1 [° C.]) (step S12). If the determination is incorrect, the CPU 203 sets the heater forced OFF temperature to Toff3 [° C.] (> Tofff2 [° C.]) (step S13).

Here, the heater forced OFF temperature set in any one of steps S11 to S12 is stored in a memory built in the CPU 203 (note that a memory different from the CPU 203 may be used).

Next, the CPU 203 determines whether the rear end of the recording paper P has passed through the fixing nip portion N (step S14).

While one sheet of recording paper P passes through the fixing nip portion N, the CPU 203 forcibly turns off the heater by setting the lowest temperature among the heater forced OFF temperatures set during that time as the actual heater forced OFF temperature. Judge whether or not.

That is, if the rear end of the recording paper P is not pulled out, the CPU 203 adopts the heater forced OFF temperature as follows. The lowest temperature among the heater forced OFF temperatures (Toff1, Toff2, Toff3) set between the time when the tip of the recording paper P rushes into the fixing nip portion N and the time when the determination in step S14 is performed is the actual temperature. It is adopted as the heater forced OFF temperature (step S15).

As shown in steps S05 to S15 and S18 to 20, the determination of the heater forced OFF temperature based on the detection temperature inclination is performed between the time when the tip of the recording paper P reaches the fixing nip portion N and the time when the rear end comes off. Is repeated. That is, the CPU 203 reads the second thermistor 301 every 0.1 seconds and sets the heater forced OFF temperature each time.

Then, for example, when the heater forced OFF temperatures Toff1 and Toff2 set in steps S09 to S13 during this period are set, the procedure is as follows. That is, the actual heater forced OFF temperature is continuously set to Toff1 (S10) by step S15 until the recording paper P passes through the fixing nip portion N (step S15).

Next, the CPU 203 determines whether or not the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 exceeds the actual heater forced OFF temperature set in the step S15 (step S18). If the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 exceeds the actual heater forced OFF temperature set in S15, the power input to the heater 305 is set to zero (heater forced OFF) (step S19), and step S20. Move to.

On the other hand, if the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 does not exceed the actual heater forced OFF temperature set in S15, the CPU 203 continues the temperature adjustment while applying power to the heater 305, and proceeds to step S20. Transition.

Then, the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 is set to Tn (step S20). Then, 0.1 seconds after the detection temperature of the second thermistor 301b is read in the immediately preceding step S07, the detection temperature Tn + 1 of the second thermistor 301b is read again (step S07). That is, the CPU 203 continues to detect the detection temperature gradient while reading the temperature of the second thermistor 301b every 0.1 sec.

If the rear end of the recording paper P has passed through the fixing nip portion N, the heater forced OFF temperature is set to the default Toff3 [° C.] (step S016). In step S17, the CPU 203 determines whether a plurality of print jobs (JOBs) are performed and the next recording paper P comes to the fixing nip portion N. If the next recording paper P comes to the fixing nip portion N, the process returns to step S04. That is, even when the energization of the heater 305 is turned off due to the forced OFF temperature being reached, the image forming operation is continued if the job is not completed.

Since the first sheet may be double-feeding and the next paper may not be double-feeding, the heater forced OFF temperature was returned to Toff3 [° C.] in step S16. If the job is completed in step S17, this control is terminated.

The parameters n, α1, α2, β1, β2, Toff1, Toff2, and Toff3 of this control are summarized in Table 1 below.

n = 0.1 [s], α1 = 7 [° C / 0.1s], α2 = 5 [° C / 0.1s], β1 = 240 [° C], β2 = 250 [° C], Toff1 = 260 [° C. ], Toff2 = 270 [° C.], Toff3 = 285 [° C.].

If the value of the detection temperature slope α is large, the heater forced OFF must be changed from the state where the detection temperature β is low, so the setting is made as described above.

The specific values described in this embodiment are merely examples, and the present invention is not limited thereto.

For example, the threshold value of the detection temperature gradient that activates this control may be changed on paper having a basis weight of 105 [g / m ^ 2] and 300 [g / m ^ 2]. The larger the basis weight, the easier it is for the end portion of the film unit 310 to float from the pressure roller 302 in the fixing nip portion N. Therefore, the larger the basis weight, the higher the detection temperature slope may be, and this control may be activated.

Further, the threshold value of the detection temperature may be changed according to the basis weight and the paper width.

Further, the threshold value of the detection temperature inclination may be changed according to the detection temperature when the tip of the recording paper passes through the fixing nip portion N. If the temperature at which the tip of the recording paper passes through the fixing nip portion N is high, the temperature difference until the error is issued is small, so that this control may be activated even if the detection temperature inclination is low.

This control will be described with reference to the timing chart shown in FIG. FIG. 6A is a fixed NIP-ON signal. When the recording paper P is in the fixing nip portion N, it is 1, and when it is not in the fixing nip portion N, it is 0. (B) is the detected temperature. This always detects the temperature of the second thermistor 301b. (C) is the detection temperature slope. As shown in the flowchart of FIG. 1, the detection temperature inclination is calculated only when the recording paper P is in the fixing nip portion. (D) is the heater forced OFF temperature. The default is 285 [° C] setting.

When the detection temperature slope of (c) is larger than 5 [° C./0.1s] and the detection temperature of (b) is higher than 250 [° C.], the heater forced OFF temperature is changed to 270 [° C.]. When the detection temperature slope of (c) is larger than 7 [° C./0.1s] and the detection temperature of (b) is higher than 240 [° C.], the heater forced OFF temperature is changed to 260 [° C.]. Further, every time the recording paper P passes through the fixing nip portion N, the heater forced OFF temperature is returned to the default 285 [° C.].

In this control, once the heater forced OFF condition is changed, the setting is continued until the recording paper passing through the paper passes through the fixing nip portion. This is because the detection temperature is prevented from continuing to rise until the double feed paper passes through the fixing nip portion.

In this embodiment, the setting of the heater forced OFF temperature is changed stepwise (for example, 285 [° C.] ⇒ 270 [° C.]) by dividing the detection temperature gradient stepwise, but the amount of the detection temperature gradient is changed. It may be changed continuously depending on the situation. For example, the heater forced OFF temperature may be lowered by 1 [° C] each time the detection temperature slope changes by 1 [° C / 0.1s].

Next, the effect of this embodiment will be described with reference to FIG. 7. In FIG. 7, a and b are arranged in a non-passing area when four sheets of LGL size (216 mm × 356 mm: vertical feed) and a basis weight of 105 [g / m ^ 2] are passed. It is a temperature transition of the second thermistor 301b. c is the temperature transition of the thermistor when one sheet of the above LGL size recording paper is passed through the normal paper. In addition, as a conventional example, a is an example in which the forced OFF temperature is uniformly set to 285 ° C. regardless of the detection temperature inclination. Here, the normal paper means a recording paper that is conveyed as a single sheet without being double-fed.

As shown in a, when the double feed paper is passed under the control of the conventional example, the heater forced OFF temperature is set to 285 [° C.], so that the thermistor detection temperature detects 285 [° C.] until it is detected. Continue to apply power to the heating element 305c. As a result, even if the thermistor detection temperature detects 285 [° C] and power is not applied to the heating element, the effect of the heat stored in the fixing device (thermistor, heating element, etc.) and the effect of the double paper feeding Therefore, the long end of the fixing nip portion floats. Therefore, the heat does not escape to the pressure roller 302 side, and the detection temperature of the second thermistor 301b rises to the error detection temperature of 297 [° C.], and an error is issued.

On the other hand, when the double feed paper is passed under the control of this embodiment as shown in b, the detection temperature inclination of the second thermistor 301b is 6 [° C./0.1s], so the heater forced OFF temperature is set to 270 [° C.]. ]. When the thermistor detection temperature exceeds the heater forced OFF temperature, the heater is turned off (the input power is set to 0).

Therefore, due to the influence of heat stored in the fixing device (thermistor, heating element, etc.) and the error detection temperature of 297 [℃] even for double-feeding paper, the thermistor detection temperature does not reach and an error is issued. There is no such thing.

Further, in the case of the normal paper shown in c, since the detection temperature slope is low, even if the heater forced OFF temperature is 285 [° C.], the error temperature of 297 [° C.] is not reached.

When normal paper is being poured, the detection temperature slope does not increase. When the double feed paper is flown, the longitudinal end portion of the fixing nip portion floats, so that the detection temperature inclination becomes high.

Further, when normal paper is being flown, the second thermistor 301b arranged in the non-passing portion region does not go to the vicinity of the error detection temperature.

Therefore, the control is changed according to the detection temperature inclination and the detection temperature. As a result, false detection can be prevented when the recording paper within the specifications is flown, and if it is difficult to raise the temperature to the error temperature at once, the heater 305 is forcibly energized until the temperature reaches a high temperature (for example, 285 ° C.). It never turns off. As a result, it is possible to prevent the temperature of the fixing nip portion from dropping during normal times.

In addition, by changing the control according to the detection temperature inclination and the detection temperature, when a recording paper with a thickness outside the specifications is flown, such as double feed paper, at an earlier stage (for example, 270 ° C.). The energization of the heater 305 can be forcibly turned off. This makes it possible to prevent the occurrence of an error.

As a result, it is possible to prevent the heater 305 from rising to an error temperature at which the constituent members of the fixing device may be damaged or deteriorated.

In this embodiment, the second thermistor 301b arranged in the non-passing paper region has been described, but the same control may be performed for the first thermistor 301a. With such a configuration, for example, even if the user sets the recording paper on one side and sets it to pass the paper, and the first thermistor 301a arranged in the center becomes the non-passing area, an error occurs. It is possible to prevent the detection and prevent the occurrence of a high temperature error when the double feed paper is flown.

Further, in the unlikely event that the temperature rises to the error temperature, the image forming apparatus stops due to a high temperature error, and the user cannot use the image forming apparatus until the state of the high temperature error is canceled by a serviceman or the like. That is, the error temperature is a temperature at which the execution of the image forming operation is prohibited by the control unit until the error is cleared by a serviceman or the like.

Therefore, this control can suppress the occurrence of high temperature errors. Therefore, it is possible to reduce the frequency with which the user makes a serviceman call to resolve the error due to the occurrence of the high temperature error. Therefore, it is possible to reduce the risk that the productivity of the user will be impaired.

In this embodiment, one heater is taken as an example, but a plurality of heaters may be used. For example, there is a case where a main heater (mainly heating the central portion of the longitudinal portion and heating the end portion weakly) and a sub heater (mainly heating the longitudinal end portion and heating the central portion weakly) are used. Even in such an example, the above-mentioned "heater forced OFF" means to turn off both the main heater and the sub heater.

The temperature corresponding to the non-passing portion (passing portion region) for controlling to stop the power supply from the triac 200 to the heater 305 depends on the detection temperature detected by the second thermistor 301b and the slope of the detection temperature. Multiple can be provided. Further, the set value of the slope of the detection temperature for the control of stopping the power supply from the Triatsk 200 to the heater 305 can be changed according to the paper type (type) of the recording paper used.

Further, detection for control to stop the power supply from the triatsk 200 to the heater 305 according to the detection temperature detected by the second thermistor 301b when the tip of the introduced recording paper passes through the nip portion N. The set value of the temperature gradient can be changed.

<< Example 2 >>
In this embodiment, in addition to the heater forced OFF control of the heater 305 of the first embodiment, a control for further reducing the maximum electric power supplied to the heater 305 is combined. As a result, it is possible to more reliably prevent the occurrence of an error when the double feed paper is flown.

[Image forming device and fixing device]
Since the configuration of the image forming apparatus and the configuration of the fixing apparatus in the second embodiment are the same as those of the image forming apparatus and the fixing apparatus in the first embodiment, the description thereof will be omitted again.

[Double feed detection of recording paper and device control]
The control in the second embodiment will be described with reference to the flowchart of FIG. In FIG. 8, the control of steps S01 to S9 is the same as the control of steps S01 to S9 in the flowchart of FIG. 1 in the first embodiment, and thus the description thereof will be omitted again.

In step S09, the CPU 203 determines whether the detected temperature slope (temperature difference) ΔTn + 1 is larger than α1 and the temperature Tn + 1 is higher than β1. If the result of the determination is correct, the CPU 203 sets the heater forced OFF temperature Toff1 and the maximum usable power value Wmax1 [w] (step S10). If the determination is not correct, the process proceeds to step S11.

As described in the first embodiment, the heater forced OFF temperature control is a control in which the power input is reduced to zero when the second thermistor 301b detects the heater forced OFF temperature.

In step S11, the CPU 203 determines whether the detected temperature slope (temperature difference) ΔTn + 1 is larger than α2 (<α1) and the temperature Tn + 1 is higher than β2 (> β1) (step S11). If the result of the determination is correct, the CPU 203 is set to the heater forced OFF temperature Toff2 (> Toff1) and the maximum usable power value Wmax2 [w] (> max1 [w]) (step S12). If the determination is not correct, the CPU 203 is set to the heater forced OFF temperature Toff3 (> Toff2) and the maximum usable power value Wmax3 [w] (> max2 [w]) (step S13).

Next, the CPU 203 determines whether the rear end of the recording paper P has passed through the fixing nip portion N (step S14).

While one sheet of recording paper P passes through the fixing nip portion N, the CPU 203 forcibly turns off the heater by setting the lowest temperature among the heater forced OFF temperatures set during that time as the actual heater forced OFF temperature. Judge whether or not. That is, if the rear end of the recording paper P is not pulled out, the CPU 203 adopts the heater forced OFF temperature as follows. Heater forced OFF temperature set between the time when the tip of the recording paper rushes into the nip portion N and the time when the determination of S14 is performed The lowest temperature among the heater forced OFF temperatures (Toff1, Toff2, Toff3) is the actual heater. It is adopted as the forced OFF temperature (step S15).

Further, the CPU 203 has the lowest maximum usable power value among the maximum usable power values set between the time when the tip of the recording paper P rushes into the fixing nip portion N and the time when the determination in step S14 is performed. Is set to the actual maximum usable power value (step S15).

While one sheet of recording paper P passes through the fixing nip portion N, the CPU 203 sets the lowest maximum usable power value among the maximum usable power values set during that period to the actual maximum usable power value. And. That is, if the rear end of the recording paper P is not removed, the CPU 203 adopts it as the maximum usable power value as follows. The lowest maximum usable power value (Wmax1, Wmax2, Wmax3) set between the time when the tip of the recording paper P rushes into the fixing nip portion N and the time when the determination in step S14 is performed. The power value is adopted as the actual maximum usable power value.

For example, if the maximum usable power values Wmax1 and Wmax2 set in S09 to S13 before the rear end of the recording paper P is pulled out, it is as follows. That is, the actual maximum usable power value is continuously set to Wmax1 (S10) by step S15 until the recording paper P passes through the fixing nip portion N (step S15). The CPU 203 controls the power supply to the halogen heater 305A within the range of the maximum usable power value set in step S15.

Next, the CPU 203 determines whether or not the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 exceeds the actual heater forced OFF temperature set in the step S15 (step S18). If the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 exceeds the actual heater forced OFF temperature set in S15, the power input to the heater 305 is set to zero (heater forced OFF) (step S19), and step S20. Move to.

On the other hand, if the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 does not exceed the actual heater forced OFF temperature set in S15, the CPU 203 continues to adjust the temperature of the heater 305 within the range of the maximum usable power, and the step. Move to S20.

Then, the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 is set to Tn (step S20). Then, 0.1 seconds after the detection temperature of the second thermistor 301b is read in the immediately preceding step S07, the detection temperature Tn + 1 of the second thermistor 301b is read again (step S07). That is, the CPU 203 continues to detect the detection temperature gradient while reading the temperature of the second thermistor 301b every 0.1 sec.

If the rear end of the recording paper P has passed through the fixing nip portion N, the heater forced OFF temperature is set to the default Toff3 [° C.] and the maximum usable power value is set to the default Wmax3 [W] (step S016). In step S17, the CPU 203 determines whether a plurality of print jobs (JOBs) are performed and the next recording paper comes to the fixing nip portion N. If the next recording paper comes to the fixing nip portion N, the process returns to step S04.

Since the first sheet may be double-feeding and the next paper may not be double-feeding, in step S16, the heater forced OFF temperature is set to the default Toff3 [° C] and the maximum usable power value is set to the default Wmax3. Returned to.

If the job is completed in step S17, this control is terminated.

The parameters n, α1, α2, β1, β2, Toff1, Toff2, Toff3, Wmax1, Wmax2, and Wmax3 of this control are summarized in Table 2 below.

n = 0.1 [s], α1 = 7 [° C / 0.1s], α2 = 5 [° C / 0.1s], β1 = 240 [° C], β2 = 250 [° C], Toff1 = 260 [° C. ], Toff2 = 270 [° C.], Toff3 = 285 [° C.]. Wmax1 = 700 [W], Wmax2 = 900 [W], and Wmax3 = 1200 [W].

If the value of the detection temperature slope α is large, the heater must be forcibly turned off and the maximum usable power value must be changed from the state where the detection temperature β is low, so the settings are made as described above.

Although the above parameters are used in this embodiment, the above variable meters may be appropriately changed depending on the product specifications.

For example, the threshold value of the detection temperature gradient that activates this control may be changed on paper having a basis weight of 105 [g / m ^ 2] and 300 [g / m ^ 2]. The larger the basis weight, the easier it is for the end of the film unit 310 to float at the end of the pressurizing roller 302 at the fixing nip portion N. Therefore, the larger the basis weight, the higher the detection temperature slope may be, and this control may be activated. Further, the threshold value of the detection temperature may be changed according to the basis weight and the paper width.

Further, the threshold value of the detection temperature inclination may be changed according to the detection temperature when the tip of the recording material passes through the fixing nip portion N. If the temperature at which the tip of the recording material passes through the fixing nip portion N is high, the temperature difference until the error is issued is small, so that this control may be activated even if the detection temperature inclination is low.

This control will be described with reference to the timing chart shown in FIG. Since (a), (b), and (c) of FIG. 9 are the same as (a), (b), and (c) in the timing chart of FIG. 6 of the first embodiment, the description thereof will be omitted again. (D) is the heater forced OFF temperature. The default is 285 [° C] setting. (E) is the maximum usable power value. The default is 1200 [w] setting.

When the detection temperature slope of (c) is larger than 5 [° C./0.1s] and the detection temperature of (b) is higher than 250 [° C.], the heater forced OFF temperature is set to 270 [° C.] and the maximum usable power value. Is changed to 900 [w]. When the detection temperature gradient of (c) is larger than 7 [° C./0.1s] and the detection temperature of (b) is higher than 240 [° C.], the heater forced OFF temperature is 260 [° C.] and the maximum usable power value. Is changed to 900 [w]. Further, each time the recording paper P passes through the fixing nip portion N, the heater forced OFF temperature is returned to 285 [° C.] and the maximum usable power value is returned to the default of 1200 [w].

That is, the control unit limits the upper limit of the power input to the heater until the energization of the heater is turned off according to the temperature rise rate. Alternatively, the control unit limits the upper limit of the power input to the heater until the energization of the heater is turned off, depending on the detected temperature and the temperature rise rate.

In this control, once the control is changed, the setting is continued until the passing recording paper passes through the fixing nip portion N. This is because the detection temperature is prevented from continuing to rise until the double feed paper passes through the fixing nip portion N.

In this fixing device, the heater is controlled by wave number control with 12 half waves as one cycle. Control is performed by switching the energization of the heater in half-wave units. For example, when the heater is turned on all the time for 12 half waves (the number of half waves is 12), the input power is 1200 [w].

In this embodiment, the wave number at which the heater can be turned on is controlled according to the detection temperature inclination and the detection temperature. For example, when the maximum usable power Wmax is 1200 [w], the maximum number of waves that can turn on the heater is 12. When the maximum usable power Wmax is 900 [w], the control is changed so that the maximum number of waves that can turn on the heater is nine. When the maximum usable power Wmax is 700 [w], the control is changed so that the maximum number of waves that can turn on the heater is 7.

In this embodiment, the heater forced OFF temperature and the maximum usable power Wmax are changed stepwise (285 [° C.] ⇒ 270 [° C.], 1200 [w] ⇒ 900 [w]) when predetermined conditions are met. However, the detection temperature inclination may be continuously changed according to the amount. For example, every time the detection temperature slope changes by 1 [° C./0.1s], the heater forced OFF temperature may be lowered by 1 [° C.] and the maximum usable power Wmax may be lowered by 100 [W].

By implementing this control, if it is determined that the paper is double-fed, the heater forced OFF temperature and the maximum usable power value are changed, so the thermistor detection temperature does not reach the error temperature of 297 [° C] and an error is issued. Will not be done. On the other hand, when normal paper is flown, a high temperature gradient is not detected in the high temperature region, so that there is no problem without activating this control.

By changing the control according to the detection temperature inclination and the detection temperature, the same effect as that of the first embodiment can be obtained. Specifically, it is possible to prevent erroneous detection when the recording paper within the specifications is flown and prevent the occurrence of an error when the double feed paper is flown.

As a result, it is possible to prevent the heater 305 from rising to an error temperature at which the constituent members of the fixing device 111 may be damaged or deteriorated.

In this embodiment, the second thermistor 301b arranged in the non-passing paper region has been described, but the same control may be performed for the first thermistor 301a. With such a configuration, for example, even if the user sets the recording paper on one side and sets it to pass the paper, and the first thermistor 301a arranged in the center becomes the non-passing area, an error occurs. It is possible to prevent the detection and prevent the occurrence of a high temperature error when the double feed paper is flown.

Further, in the unlikely event that the temperature rises to the error temperature, the image forming apparatus stops due to a high temperature error, and the user cannot use the image forming apparatus until the state of the high temperature error is canceled by a serviceman or the like. That is, the error temperature is a temperature at which the execution of the image forming operation is prohibited by the control unit until the error is cleared by a serviceman or the like.

Therefore, this control can suppress the occurrence of high temperature errors. Therefore, it is possible to reduce the frequency with which the user makes a serviceman call to resolve the error due to the occurrence of the high temperature error. Therefore, it is possible to reduce the risk that the productivity of the user will be impaired.

The temperature corresponding to the non-passing portion (non-passing portion region) for controlling to change the maximum value of the power supply from the triac 200 to the heater 305 is the detected temperature and the detected temperature detected by the second thermistor 301b. A plurality of them can be provided according to the inclination of the change with time. Further, the set value of the slope of the detection temperature for control for changing the maximum value of the power supply from the triac 200 to the heater 305 can be changed according to the paper type (type) of the recording paper used.

Further, the control that changes the maximum value of the power supply from the triac 200 to the heater 305 according to the detection temperature detected by the second thermistor 301b when the tip of the introduced recording paper passes through the nip portion N. It is possible to change the set value of the slope of the detection temperature for this purpose. Further, the maximum value of the power supply from the triac 200 to the heater 305 can be changed so that the slope of the detected temperature detected by the second thermistor 301b becomes a predetermined value or less.

<< Reference example >>
In this reference example, the control unit 203 changes the maximum value of the power supply from the triac 200 to the heater according to the detection temperature detected by the second thermistor 301b and the slope of the change over time of the detection temperature.

[Image forming device]
In this reference example, the configuration of the image forming apparatus is the same as that of the printer of FIG. 2 of the first embodiment, and therefore the description thereof will be omitted again.

[Fixing device]
(1) Device Configuration FIG. 10 is a schematic cross-sectional view showing a schematic configuration of a main part of the fixing device 111 in this reference example. Similar to the fixing device 111 in the first embodiment, this fixing device 111 is also a so-called tensionless type device of a film (belt) heating method and a pressure roller drive method. The difference from the fixing device 111 in the first embodiment is that a halogen heater (halogen lamp) 305A is used as a heating member, and the first and second thermistors 301a and 301b, which are temperature detecting elements, detect the inner surface temperature of the film 303. It is in. Hereinafter, these different constituent points will be mainly described, and the same reference numerals will be given to common constituent members and parts, and the description thereof will be omitted again.

In the film unit 310, a rod-shaped halogen heater 305A long in the film width direction is provided in the inner space of the cylindrical film 303, and one end side and the other end side thereof are one end side and the other end side of the film unit 310, respectively. It is supported and arranged between the flange members of the above. Further, a long radiant heat reflecting mirror 312 is fixedly arranged on the stay 308 along the length of the halogen heater 305A between the halogen heater 305A and the stay 308.

Reference numeral 313 is a nip forming member provided in the film unit 310, which is composed of a sliding member 313a and a holding member 313b. The sliding member 313a and the holding member 313b are members corresponding to the heater 303 and the holder 304 in the fixing device 111 of the first embodiment, respectively. The stay 308 is arranged inside the nip forming member 313 to back up the nip forming member 313. The sliding member 313a and the holding member 313b constituting the nip forming member 313 are heat insulating members such as heat resistant resin.

From the viewpoint of energy saving, it is desirable to use a material having less heat conduction to the stay 308, and for example, heat-resistant glass, polycarbonate, liquid crystal polymer, or other heat-resistant resin is used.

The sliding member 313a of the nip forming member 313 has a film inner surface in the nip portion N in a state where the film unit 310 is pressed by the pressurizing roller 302 to form a nip portion N between the film 303 and the pressurizing roller 302. It is located corresponding to. The first thermistor 310a, which is a temperature detector for temperature control that detects the temperature of the paper passing portion region of the film 303, and the second thermistor 301b, which is a temperature detector for detecting double feeding of recording paper, are referred to in this reference. In the example, it is arranged on the sliding member 313a of the nip forming member 313.

FIG. 11 shows the arrangement form. The sliding member 313a is formed with first and second notch holes 313c and 313d, respectively, at a central portion in the longitudinal direction thereof and at a position 115 mm away from the other end side of the sliding member 313a. The first thermistor 301a is fitted in the first notch hole 313c, and the second thermistor 301b is fitted in the second notch hole 313d. A spring (not shown) is interposed between the first thermistor 301a and the holding member 313b of the nip forming member 313 and between the second thermistor 301a and the holding member 313b of the nip forming member 313, respectively.

In a state where the film unit 310 is pressed by the pressure roller 302 by the pressure mechanism and a nip portion N is formed between the film 303 and the pressure roller 302, the first and second thermistors 301a and 301b are respectively. Receives the urging force of the spring. Therefore, the first and second thermistors 301a and 301b have a function of elastically contacting the inner surface of the film at the nip portion N and detecting the temperature of the inner surface of the belt 303, respectively.

(3) Fixing operation The control unit 203 pressurizes the film 303 and the pressurizing mechanism in the pressure release state at a predetermined control timing in the print job execution sequence, similarly to the fixing device 111 of the first embodiment. A nip portion N is formed between the roller 302 and the roller 302. Then, the control unit 203 activates the motor M to rotate and drive the pressurizing roller 302 in the counterclockwise direction of the arrow Y at a predetermined peripheral speed.

When the pressure roller 302 is rotationally driven, a rotational force acts on the film 303 due to the frictional force between the surface of the pressure roller 302 and the surface of the film 303 at the nip portion N. Therefore, the inner peripheral surface of the film 303 slides in close contact with the sliding member 313a of the nip forming member 313, and the outer circumference of the nip forming member 313 is rotated in the clockwise direction of the arrow X at substantially the same circumference as the peripheral speed of the pressurizing roller 302. It rotates driven by speed. The cross section of the nip forming member 313 has a semicircular arc shape, and has a function of regulating the rotation trajectory of the film 303.

Further, the pressurizing roller 302 is rotationally driven and power is supplied to the halogen heater 305A from the feeding unit 205 controlled by the control unit 203 via the feeding path (not shown). As a result, the halogen heater 305A lights up over the entire effective heat generation range. The direct light of the radiant heat generated by the halogen heater 305A and the reflected light reflected by the reflecting mirror 312 are irradiated to the inner surface of the film 303 mainly in the range of the angle α in the circumferential direction. As a result, the entire peripheral portion of the rotating film 303 is heated.

The heating temperature due to the radiant heat of the halogen heater 305A is detected by the first thermistor 301a arranged within the passing region width Wmin of the recording paper having the minimum width of the film 303, and the detected temperature information is input to the CPU 203. The CPU 203 adjusts the film inner surface temperature so that the film surface temperature becomes a predetermined target temperature (fixing temperature) based on the detection temperature information of the thermistor 301a. That is, the CPU 203 controls the power supply from the feeding unit 205 to the halogen heater 305A by wave number control so that the film surface temperature reaches a predetermined target temperature.

Then, the recording paper P on which the unfixed toner image t is formed in a state where the pressure roller 302 is rotationally driven and the surface temperature of the film 303 is raised to a predetermined target temperature by the halogen heater 305A to control the temperature. Is introduced into the nip portion N of the fixing device 111. The heat of the film 303 is applied to the recording paper P in the process of being sandwiched and conveyed by the nip portion N. The unfixed toner image t is melted by the heat of the film 303, and is fixed to the recording paper P as a fixed toner image by the pressure applied to the nip portion N.

(6) Double feed detection of recording paper and device control The control in this reference example will be described using the flowchart of FIG. In FIG. 12, the control of steps S01 to S09 is the same as the control of steps S01 to S09 in the flowchart of FIG. 1 in the first embodiment, and thus the description thereof will be omitted again.

In step S09, the CPU 203 determines whether the detected temperature slope (temperature difference) ΔTn + 1 is larger than α1 and the temperature Tn + 1 is higher than β1. If the result of the determination is correct, the CPU 203 is set to the maximum usable power value Wmax1 [w] (step S10). If the determination is not correct, the process proceeds to step S11.

In step S11, the CPU 203 determines whether the detected temperature slope (temperature difference) ΔTn + 1 is larger than α2 (<α1) and the temperature Tn + 1 is higher than β2 (> β2) (step S11). As a result of the determination, if it is correct, the CPU 203 sets the maximum usable power value Wmax2 [w] (> Wmax1) (step S12). If the determination is incorrect, the CPU 203 sets the maximum usable power value Wmax3 [w]] (> Wmax2) (step S13).

Next, the CPU 203 determines whether the rear end of the recording paper P has passed through the fixing nip portion N (step S14).

While one sheet of recording paper P passes through the fixing nip portion N, the CPU 203 sets the lowest maximum usable power value among the maximum usable power values set during that period to the actual maximum usable power value. And. That is, if the rear end of the recording paper P is not removed, the CPU 203 adopts it as the maximum usable power value as follows. The lowest maximum usable power value (Wmax1, Wmax2, Wmax3) set between the time when the tip of the recording paper P rushes into the fixing nip portion N and the time when the determination in step S14 is performed. The power value is adopted as the actual maximum usable power value.

For example, if the maximum usable power values Wmax1 and Wmax2 set in S09 to S13 before the rear end of the recording paper P is pulled out, it is as follows. That is, the actual maximum usable power value is continuously set to Wmax1 (S10) by step S15 until the recording paper P passes through the fixing nip portion N (step S15). The CPU 203 controls the power supply to the halogen heater 305A within the range of the maximum usable power value set in step S15.

Then, the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 is set as Tn (step S18). Then, 0.1 seconds after the detection temperature of the second thermistor 301b is read in the immediately preceding step S07, the detection temperature Tn + 1 of the second thermistor 301b is read again (step S07). That is, the CPU 203 continues to detect the detection temperature gradient while reading the temperature of the second thermistor 301b every 0.1 sec.

If the rear end of the recording paper P has passed through the fixing nip portion N, the maximum usable power value is set to the default Wmax3 [W] (step S16). In step S17, the CPU 203 determines whether a plurality of print jobs (JOBs) are performed and the next recording paper comes to the fixing nip portion N. If the next recording paper comes to the fixing nip portion N, the process returns to step S04.

Since the first sheet may be double-feeding and the next paper may not be double-feeding, the maximum usable power value was returned to the default Wmax3 in step S16.

If the job is completed in step S17, this control is terminated.

The parameters n, α1, α2, β1, β2, Wmax1, Wmax2, and Wmax3 of this control are summarized in Table 3 below.

n = 0.1 [s], α1 = 7 [° C / 0.1s], α2 = 5 [° C / 0.1s], β1 = 240 [° C], β2 = 250 [° C], Wmax1 = 700 [W] ], Wmax2 = 900 [W], Wmax3 = 1200 [W].

If the value of the detection temperature slope α is large, the maximum usable power value must be changed from the state where the detection temperature β is low, so the setting is made as described above.

Although the above parameters are used in this reference example, the above parameter may be changed as appropriate depending on the product specifications.

For example, the threshold value of the detection temperature gradient that activates this control may be changed on paper having a basis weight of 105 [g / m ^ 2] and 300 [g / m ^ 2].

The larger the basis weight, the easier it is for the end of the film unit 310 to float at the end of the pressurizing roller 302 at the fixing nip portion N. Therefore, the larger the basis weight, the higher the detection temperature slope may be, and this control may be activated. Further, the threshold value of the detection temperature may be changed according to the basis weight and the paper width.

Further, the threshold value of the detection temperature inclination may be changed according to the detection temperature when the tip of the recording material passes through the fixing nip portion N. If the temperature at which the tip of the recording material passes through the fixing nip portion N is high, the temperature difference until the error is issued is small, so that this control may be activated even if the detection temperature inclination is low.

This control will be described with reference to the timing chart shown in FIG. Since (a), (b), and (c) of FIG. 13 are the same as (a), (b), and (c) in the timing chart of FIG. 6 of the first embodiment, the description thereof will be omitted again. FIG. 13D is the maximum usable power value. The default is 1200 [w] setting.

If the detection temperature slope of (c) is larger than 5 [° C./0.1s] and the detection temperature of (b) is higher than 250 [° C.], the maximum usable power value is changed to 900 [w]. If the detection temperature slope of (c) is larger than 7 [° C./0.1s] and the detection temperature of (b) is higher than 240 [° C.], the maximum usable power value is changed to 900 [w]. Further, each time the recording paper P passes through the fixing nip portion N, the maximum usable power value is returned to the default 1200 [w].

In this control, once the maximum usable power value is changed, the setting is continued until the recording paper passing through the paper passes through the fixing nip portion N. This is because the detection temperature is prevented from continuing to rise until the double feed paper passes through the fixing nip portion N.

In this fixing device, the heater is controlled by wave number control with 12 half waves as one cycle. Control is performed by switching the energization of the heater in half-wave units. For example, when the heater is turned on all the time for 12 half waves (the number of half waves is 12), the input power is 1200 [w].

In this reference example, the wave number at which the heater can be turned on is controlled according to the detection temperature inclination and the detection temperature. For example, when the maximum usable power Wmax is 1200 [w], the maximum number of waves that can turn on the heater is 12. When the maximum usable power Wmax is 900 [w], the control is changed so that the maximum number of waves that can turn on the heater is nine. When the maximum usable power Wmax is 700 [w], the control is changed so that the maximum number of waves that can turn on the heater is 7.

In this reference example, the maximum usable power Wmax was changed stepwise (1200 [w] ⇒ 900 [w]) when a predetermined condition was satisfied, but the detection temperature slope was continuously changed according to the amount. You may change it to. For example, the maximum usable power Wmax may be lowered by 100 [W] each time the detection temperature slope changes by 1 [° C./0.1s]. By implementing this control, if it is determined that the paper is double-fed, the maximum usable power value is changed, so the thermistor detection temperature does not reach the error temperature of 297 [° C], and the frequency of error issuance is reduced. Can be made to.

Also in this reference example, it is possible to reduce the frequency of error issuance when double-feeding paper is conveyed, but when the heater is not turned off, for example, in order to raise the temperature of the paper-passing part, There is a risk that the heater will continue to be turned on at the maximum usable power. Therefore, the above-mentioned Examples 1 and 2 are more preferable configurations.

In this reference example, the second thermistor 301b arranged in the non-passing paper region has been described, but the same control may be performed for the first thermistor 301a. With such a configuration, for example, even if the user sets the recording paper on one side and sets the paper to pass the paper, and the first thermistor 301a arranged in the center becomes the non-passing paper area, the same applies. The effect of can be obtained.

The temperature corresponding to the non-passing portion (non-passing portion region) for controlling to change the maximum value of the power supply from the triac 200 to the heater 305A is the detected temperature and the detected temperature detected by the second thermistor 301b. A plurality of them can be provided according to the inclination of the change with time. Further, the set value of the slope of the detection temperature for control for changing the maximum value of the power supply from the Triac 200 to the heater 305A can be changed according to the paper type (type) of the recording paper used.

Further, the control for changing the maximum value of the power supply from the triac 200 to the heater 305A according to the detection temperature detected by the second thermistor 301b when the tip of the introduced recording paper passes through the nip portion N. It is possible to change the set value of the slope of the detection temperature for this purpose. Further, the maximum value of the power supply from the triac 200 to the heater 305A can be changed so that the slope of the detected temperature detected by the second thermistor 301b becomes a predetermined value or less.

<< Example 3 >>
The third embodiment is an embodiment in which the maximum usable power is changed so that the detected temperature gradient becomes constant.

[Image forming device and fixing device]
Since the configuration of the image forming apparatus and the configuration of the fixing device in the third embodiment are the same as those of the image forming apparatus and the fixing apparatus in the first embodiment, the description thereof will be omitted again.

[Double feed detection of recording paper and device control]
The control in the third embodiment will be described with reference to the flowchart of FIG. In FIG. 14, the control of steps S01 to S9 is the same as the control of steps S01 to S9 in the flowchart of FIG. 1 in the first embodiment, and thus the description thereof will be omitted again.

In step S09, the CPU 203 determines whether the detected temperature slope (temperature difference) ΔTn + 1 is larger than α1 and the temperature Tn + 1 is higher than β1. If the result of the determination is correct, the CPU 203 sets the maximum usable power value Wmax [n + 1] = Wmax [n] -50 [w] so that the detected temperature slope becomes α1 or less (step S10). If the judgment is not correct, the maximum usable power value Wmax [n + 1] is inherited from the previous maximum usable power value Wmax [n] (step 11).

Next, the CPU 203 determines whether the rear end of the recording paper P has passed through the fixing nip portion N (step S12). If the rear end of the recording paper is not pulled out, the thermistor detection temperature Tn + 1 read in the immediately preceding step S07 is set to Tn (step S15). Then, 0.1 seconds after the detection temperature of the second thermistor 301b is read in the immediately preceding step S07, the detection temperature Tn + 1 of the second thermistor 301b is read again (step S07). That is, the CPU 203 continues to detect the detection temperature gradient while reading the temperature of the second thermistor 301b every 0.1 sec.

If the rear end of the recording paper is missing, the maximum usable power value Wmax [0] is returned to the default setting of the maximum usable power Wmax (ini) (step S13).

In step S14, the CPU 203 determines whether the plurality of JOBs are and the next recording paper comes to the fixing nip portion N, and if the next recording paper comes to the fixing nip portion N, the process returns to step S04.

Since the first sheet may be double-feeding and the next paper may not be double-feeding, in step S13, the maximum usable power value Wmax [0] is set as the default setting and the maximum usable power Wmax (ini). Returned to.

If the job is completed in step S14, this control is terminated.

The parameters n, α1, β1, and Wmax (ini) of this control are as follows. n = 0.1 [s], α1 = 5 [° C / 0.1s], β1 = 250 [° C], Wmax (ini) = 1200 [W].

Although the above parameters are used in this embodiment, the above variable meters may be appropriately changed depending on the product specifications.

For example, the threshold value of the detection temperature gradient that activates this control may be changed on paper having a basis weight of 105 [g / m ^ 2] and 300 [g / m ^ 2]. The larger the basis weight, the easier it is for the end of the film unit 310 to float at the end of the pressurizing roller 302 at the fixing nip portion N. Therefore, the larger the basis weight, the higher the detection temperature slope may be, and this control may be activated. Further, the threshold value of the detection temperature may be changed according to the basis weight and the paper width.

Further, the threshold value of the detection temperature inclination may be changed according to the detection temperature when the tip of the recording material passes through the fixing nip portion N. If the temperature at which the tip of the recording material passes through the fixing nip portion N is high, the temperature difference until the error is issued is small, so that this control may be activated even if the detection temperature inclination is low.

This control will be described with reference to the timing chart shown in FIG. (A) is a fixed NIP-ON signal. When the recording paper P is in the fixing nip portion N, it is 1, and when it is not in the fixing nip portion N, it is 0. (B) is the detected temperature. This always detects the temperature of the second thermistor 301b. (C) is the detection temperature slope. As shown in the flowchart of FIG. 14, the detection temperature inclination is calculated only when the recording paper P is in the fixing nip portion N. (D) is the maximum usable power value. The default is 1200 [w] setting.

When the detection temperature slope of (c) is larger than 5 [° C./0.1s] and the detection temperature of (b) is higher than 250 [° C.], the maximum usable power value is changed from the default 1200 [w] to 50 [w]. It is lowered by [w] and changed so that the detection temperature slope becomes 5 [° C./0.1s] or less.

Each time the recording paper P passes through the fixing nip portion N, the maximum usable power value is returned to the default of 1200 [w].

In this embodiment, the maximum usable power Wmax is gradually decreased by 50 [w] when a predetermined condition is satisfied, but the detected temperature slope may be continuously changed according to the amount. By implementing this control, if it is determined that the paper is double-fed, the control is changed, so that the thermistor detection temperature does not reach the error temperature of 297 [° C.] and no error is issued. On the other hand, when normal paper is flown, a high temperature gradient is not detected in the high temperature region, so that there is no problem without activating this control.

By changing the control according to the detection temperature inclination and the detection temperature, the same effect as in other embodiments can be obtained. Specifically, it is possible to prevent erroneous detection when the recording paper within the specifications is flown and prevent the occurrence of an error when the double feed paper is flown.

As a result, it is possible to provide a device capable of reliably preventing damage or deterioration of the constituent members of the fixing device 111, or an image forming device provided with this device.

In this embodiment, the second thermistor 301b arranged in the non-passing paper region has been described. Even if the user sets the recording paper close to one side and sets it to pass the paper, and the first thermistor placed in the center becomes the non-passing area, the second thermistor placed in the non-passing area. Control is performed in the same manner as the thermistor 301b of. Therefore, it is possible to prevent erroneous detection and prevent the occurrence of a high temperature error when the double feed paper is flown.

Further, in the unlikely event that the temperature rises to the error temperature, the image forming apparatus stops due to a high temperature error, and the user cannot use the image forming apparatus until the state of the high temperature error is canceled by a serviceman or the like. That is, the error temperature is a temperature at which the execution of the image forming operation is prohibited by the control unit until the error is cleared by a serviceman or the like.

Therefore, this control can suppress the occurrence of high temperature errors. Therefore, it is possible to reduce the frequency with which the user makes a serviceman call to resolve the error due to the occurrence of the high temperature error. Therefore, it is possible to reduce the risk that the productivity of the user will be impaired.

<< Other Examples >>
(1) In Examples 1 and 2 above, the case where the heater forced OFF temperature setting is changed based on the detection temperature of the second thermistor 301b that detects the temperature of the heater 305 and the temperature rise rate per unit time thereof. Explained in the example.

However, in the longitudinal direction of the film 303, a temperature sensor (detection unit) for detecting the temperature of the film 303 is provided outside the pass region width Wmin of the minimum width size recording paper and inside the maximum pass region width Wmax. Then, the configuration may be such that the control of each of the above-described embodiments is performed based on the temperature of this sensor. This temperature sensor is, for example, a thermistor that abuts on the inner surface of the film 303.

(2) Although the embodiments of the present invention have been described above, the numerical values such as dimensions and conditions exemplified in each embodiment are merely examples and are not limited to these numerical values. Numerical values can be appropriately selected within the range to which the present invention can be applied. Further, the configuration described in the examples may be appropriately changed to the extent to which the present invention can be applied. For example, a roller fixing method or an IH fixing type fixing device may be used to perform the control as in the embodiment.

(3) The film 303 in the first embodiment is not limited to the configuration in which the inner surface thereof is supported by the heater 305 and driven by the pressure roller 302. For example, the film 303 may be a unit system that is spread over a plurality of rollers and driven by any one of the plurality of rollers. However, from the viewpoint of reducing the heat capacity, the configuration as in Examples 1 and 2 is desirable.

(4) What forms the film 303 and the nip portion N is not limited to the roller member such as the roller 302. For example, a pressure belt unit in which a belt is spanned over a plurality of rollers may be used.

(5) Although the device for heating and fixing the unfixed toner image t formed on the recording paper as the fixing device 111 has been described as an example, the present invention is not limited to this. For example, a device (also referred to as a fixing device) may be used to increase the gloss (glossiness) of the image by heating and re-fixing the toner image hypothesized on the recording paper. That is, for example, a device for fixing a semi-fixed toner image on the recording paper P or a device for heat-treating the fixed image may be used. Therefore, the fixing device 111 mounted on the image forming device may be, for example, a surface heating device that adjusts the gloss and surface properties of the image.

(6) The image forming apparatus described using the printer 1 as an example is not limited to the image forming apparatus for forming a monochrome image, and may be an image forming apparatus for forming a color image. Further, the image forming apparatus can be implemented in various applications such as a copying machine, a fax machine, and a multifunction device having a plurality of these functions, in addition to necessary equipment, equipment, and a housing structure.

(7) In the above description, for convenience, the handling of the recording material (sheet) P will be described using terms related to paper such as paper passing, paper feeding, paper ejection, paper passing portion, and non-passing portion. Is not limited to paper. The recording material P is a sheet-shaped recording medium (media) on which a toner image can be formed by an image forming apparatus. Examples thereof include standard or irregular plain paper, thin paper, thick paper, high-quality paper, coated paper, envelopes, leaflets, stickers, resin sheets, transparencies, printing papers, format papers and the like.

111 ... Fixing device, 303 ... First rotating body (fixing film), 302 ... Second rotating body ... Pressurized roller, N ... Nip part, P ... Recording material, t ... Toner image , 305 ・ 305A ・ ・ Heating member (ceramic heater, halogen heater), 200 ・ ・ Power supply unit (triac), 301a ・ ・ First temperature detector (thermistor), 301b ・ ・ Second temperature detector (thermistor) , 203 ... Control unit

Claims (15)

An endless belt that heats the toner image on the recording material while transporting the recording material at the nip.
A rotating body that cooperates with the endless belt to form the nip portion,
A heater that has a heating element that generates heat when energized and heats the endless belt,
With respect to the longitudinal direction of the endless belt, the heating element in a region outside the minimum passage region, which is the region of the endless belt, through which the recording material having the smallest size in the longitudinal direction passes among the recording materials conveyed to the nip portion. With a detector that detects the temperature of
It has a control unit that controls the temperature at which the energization of the heater is turned off according to the temperature rise rate of the detection temperature per unit time by the detection unit.
When the temperature rise rate is the first rise rate, the control unit turns off the energization of the heater in response to the detection temperature reaching the first temperature, and the temperature rise rate is the first. When the rise rate is lower than the rise rate of 1, the control unit turns off the energization of the heater in response to the detection temperature reaching the second temperature higher than the first temperature. An image heating device characterized by being. When the temperature rise rate is the first rise rate, the control unit allows the heater to be energized until the detected temperature reaches the first temperature, and the temperature rise rate is the second rise rate. The image heating device according to claim 1, wherein when the rate of increase is high, the control unit allows energization of the heater until the detected temperature reaches the second temperature. Further having an image forming portion for forming a toner image on the recording material,
When the temperature rise rate is the first rise rate, the control unit allows the image forming unit to continue the image forming operation in response to the detection temperature reaching the first temperature. When the energization of the heater is turned off and the temperature rise rate is the second rise rate, the control unit is operated by the image forming unit in response to the detection temperature reaching the second temperature. The image heating device according to claim 1 or 2, wherein the energization of the heater is turned off while the continuation of the image forming operation is allowed. Further having an image forming portion for forming a toner image on the recording material,
The image according to claim 1 or 2, wherein the first temperature and the second temperature are lower than a predetermined temperature at which execution of an image forming operation by the image forming unit is prohibited. Heating device. When the temperature rise rate is the first rise rate, the control unit sets the temperature at which the energization of the heater is turned off to the first temperature, and the temperature rise rate is the second rise . When the rate is high, the temperature at which the energization of the heater is turned off is set to the second temperature, and when the detection temperature reaches the set temperature, the energization of the heater is turned off.
When the temperature at which the energization of the heater is turned off is set to the first temperature while the recording material passes through the nip portion, the control unit has the nip portion at the rear end of the recording material. The image heating device according to any one of claims 1 to 4, wherein the temperature at which the energization of the heater is turned off in response to the disconnection is set to a temperature higher than the first temperature. The control unit controls the temperature at which the energization of the heater is turned off according to the detected temperature and the temperature rise rate.
When the detected temperature is the first detected temperature and the temperature rise rate is the first rise rate, the control unit sets the temperature at which the energization of the heater is turned off to the first temperature. Then, when the detection temperature is a second detection temperature lower than the first detection temperature and the temperature rise rate is the first rise rate, the control unit turns off the energization of the heater. The image heating device according to any one of claims 1 to 4, wherein the temperature is set to a third temperature higher than the first temperature. A recording material having a size in the longitudinal direction is the first size, and the first size is a size that does not come into contact with the endless belt at the position where the detection portion is provided in the longitudinal direction. In the case of being transported
The control unit
When the temperature rise rate is the first rise rate, the energization of the heater is turned off in response to the detection temperature reaching the first temperature.
Claims 1 to 6 are characterized in that when the temperature rise rate is the second rise rate, the energization of the heater is turned off in response to the detection temperature reaching the second temperature. The image heating device according to any one of the above items. The control unit according to any one of claims 1 to 7, wherein the control unit limits the upper limit value of the input power to the heater until the energization of the heater is turned off according to the temperature rise rate. The image heating device according to claim 1. The control unit is characterized in that, according to the detected temperature and the temperature rise rate, the upper limit value of the power input to the heater is limited until the energization of the heater is turned off. The image heating device according to any one of 7 to 7. An image forming part that forms a toner image on the recording material,
An endless belt that heats the toner image formed on the recording material by the image forming unit while transporting the recording material at the nip portion.
A rotating body that cooperates with the endless belt to form the nip portion,
A heater that has a heating element that generates heat when energized and heats the endless belt,
With respect to the longitudinal direction of the endless belt, the heating element in a region outside the minimum passage region, which is the region of the endless belt, through which the recording material having the smallest size in the longitudinal direction passes among the recording materials conveyed to the nip portion. With a sensor that detects the temperature of
A double feed detection unit that detects that a plurality of recording materials are being conveyed to the nip unit, and a double feed detection unit.
It has a control unit that controls the temperature at which the energization of the heater is turned off according to the detection result by the double feed detection unit.
When it is detected by the double feed detection unit that a plurality of recording materials are being conveyed to the nip unit, the control unit determines that the temperature detected by the sensor reaches the first temperature. When the energization of the heater is turned off and the double feed detection unit does not detect that a plurality of recording materials are being conveyed to the nip unit, the control unit has the detection temperature higher than the first temperature. An image forming apparatus comprising turning off the energization of the heater in response to reaching a high second temperature. When it is detected by the double feed detection unit that a plurality of recording materials are being conveyed to the nip unit, the control unit energizes the heater until the detection temperature reaches the first temperature. If it is permissible and the double feed detection unit does not detect that a plurality of recording materials are being conveyed to the nip unit, the control unit sends the heater to the heater until the detection temperature reaches the second temperature. The image forming apparatus according to claim 10, wherein energization is allowed. When it is detected by the double feed detection unit that a plurality of recording materials are being conveyed to the nip unit, the control unit determines that the detection temperature has reached the first temperature. When the energization of the heater is turned off while the image forming operation by the forming unit is allowed to continue, and the double feed detecting unit does not detect that a plurality of recording materials are being conveyed to the nip portion, the control is performed. The unit is characterized in that the energization of the heater is turned off in a state where the continuation of the image forming operation by the image forming unit is allowed in response to the detection temperature reaching the second temperature. 10. The image forming apparatus according to 10. The image according to claim 10 or 11, wherein the first temperature and the second temperature are lower than a predetermined temperature at which execution of an image forming operation by the image forming unit is prohibited. Forming device. The one according to any one of claims 10 to 13, wherein the double feed detecting unit detects that a plurality of recording materials are conveyed to the nip unit based on the output of the sensor. Image forming device. An endless belt that heats the toner image on the recording material while transporting the recording material at the nip.
A rotating body that cooperates with the endless belt to form the nip portion,
A heater that has a heating element that generates heat when energized and heats the endless belt,
With respect to the longitudinal direction of the endless belt, the endless belt in a region outside the minimum passage region, which is the region of the endless belt through which the recording material having the smallest size in the longitudinal direction passes among the recording materials conveyed to the nip portion. With a detector that detects the temperature of
It has a control unit that controls the temperature at which the energization of the heater is turned off according to the temperature rise rate of the detection temperature per unit time by the detection unit.
When the temperature rise rate is the first rise rate, the control unit turns off the energization of the heater in response to the detection temperature reaching the first temperature, and the temperature rise rate is the first. When the rise rate is lower than the rise rate of 1, the control unit turns off the energization of the heater in response to the detection temperature reaching the second temperature higher than the first temperature. An image heating device characterized by being.

Images