JP7414485B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunctional device having multiple functions thereof.

In an image forming apparatus, the toner image is fixed to the recording material by heating the recording material on which the toner image is formed in a fixing device. Such a fixing device includes an endless belt, a roller that forms a nip portion that heats the toner image on the recording material while nipping and conveying the recording material between the endless belt, and a heater that heats the endless belt. Such a configuration has been known for a long time.

In such a fixing device, when double feeding occurs in which a plurality of recording materials are conveyed in an overlapping state at the nip portion, a gap is created between the endless belt and the roller depending on the thickness of the recording materials. Since the heat of the heater is not absorbed by the roller in the area where this gap is created, the endless belt and the heater locally become hot.

For this reason, a configuration has been proposed that detects the temperature of the heater and lowers the heater-off temperature, which turns off the power to the heater when the rate of temperature rise is high, to prevent the endless belt and heater from rising in temperature excessively. (Patent Document 1). In the configuration described in Patent Document 1, after the recording material passes through the nip portion, the heater-off temperature is returned to the original temperature.

JP2018-205698A

Here, for example, double feeding does not necessarily occur only once in one image forming job. In the case of the configuration described in Patent Document 1, after the recording material passes through the nip portion, the heater-off temperature is returned to the original temperature, so if double feeding occurs multiple times in one image forming job, the endless belt There is a possibility that excessive temperature rise of the heater cannot be sufficiently suppressed. On the other hand, if an image forming job is continued with the heater-off temperature kept low, the temperature at the nip portion may drop, resulting in poor fixation of the toner image onto the recording material.

SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration capable of suppressing excessive temperature rise of the endless belt and heater and suppressing the occurrence of fixing failure.

In the image forming apparatus of the present invention, between an image forming section that forms a toner image on a recording material, a rotatable endless belt, and the endless belt, the recording material on which the toner image is formed in the image forming section is transferred. a nip part forming member that forms a nip part that heats the toner image on the recording material while being held and conveyed; a heater that heats the endless belt, and a heater in a region outside in the longitudinal direction of a minimum passing region through which a recording material having the smallest size in the longitudinal direction among the recording materials that can pass through the nip portion passes. A detection section that detects temperature; and a control section that controls productivity, which is the number of recording materials that pass through the nip section per unit time, and the control section controls the temperature of the detection section per unit time. When the rate of increase is a first rate of increase, the productivity is the first productivity, and when the rate of increase in temperature is a second rate of increase, which is lower than the first rate of increase, the productivity is the first productivity is smaller than the second productivity; When the productivity is set to the first productivity, the productivity is set to the first productivity until the last recording material of the image forming job finishes passing through the nip portion, regardless of a change in the temperature increase rate. It is characterized by making the productivity less than or equal to 1.

Further, in the image forming apparatus of the present invention, between an image forming section that forms a toner image on a recording material, a rotatable endless belt, and the endless belt, the image forming apparatus includes a recording medium in which a toner image is formed in the image forming section. a nip part forming member that forms a nip part that heats the toner image on the recording material while nipping and conveying the material; a heater that generates heat to heat the endless belt; and a heater that generates heat to heat the endless belt; and a heater that generates heat to heat the endless belt; A detection section that detects the temperature of the endless belt; and a control section that controls productivity, which is the number of recording materials that pass through the nip section per unit time; When the temperature increase rate per unit is a first increase rate, the productivity is the first productivity, and when the temperature increase rate is a second increase rate lower than the first increase rate, the productivity is a second productivity, the first productivity is smaller than the second productivity, and the control unit executes an image forming job for forming images on a predetermined number of recording materials. When the productivity is set to the first productivity when the productivity is set to the first productivity, the productivity is maintained until the last recording material of the image forming job finishes passing through the nip portion, regardless of the change in the temperature increase rate. is characterized in that the productivity is set to be less than or equal to the first productivity .

According to the present invention, it is possible to suppress excessive temperature rise of the endless belt and heater and to suppress the occurrence of fixing failure.

1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment; FIG. FIG. 1 is a schematic cross-sectional view of a fixing device according to a first embodiment. (a) A partially cutaway plan view as seen from the front side, (b) a plan view as seen from the back side, and (c) an AA sectional view of the heater according to the first embodiment. . The figure which shows the power supply circuit from a commercial power supply to a heater. 5 is a flowchart of controlling heater-off temperature and productivity according to the first embodiment. 5 is a timing chart showing an example of control of heater-off temperature and productivity according to the first embodiment. FIG. A graph showing temperature changes of the thermistors at the center and ends in Examples and Comparative Examples. 7 is a flowchart of controlling heater-off temperature and productivity according to the second embodiment. FIG. 7 is a schematic cross-sectional view of a fixing device according to a third embodiment.

<First embodiment>
A first embodiment will be described using FIGS. 1 to 7. First, the schematic configuration of the image forming apparatus of this embodiment will be described using FIG. 1.

[Image forming device]
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of an image forming apparatus 100 in this embodiment. This image forming apparatus 100 is a laser beam printer using an electrophotographic process. The image forming apparatus 100 executes a print operation (image forming operation) corresponding to an image forming job input to the engine controller 114 from an external device such as a host computer or a data output device 120 such as a document reading device. Then, an image formed product in which a toner image is formed on a recording material P corresponding to the image forming job is output.

An image forming job (also referred to as a print job in this embodiment) is a series of operations as described below that are performed based on an image forming command signal (print command signal in this embodiment). That is, after starting a preliminary operation (so-called pre-rotation operation) necessary for performing image formation, through the image forming process, a preliminary operation (so-called post-rotation) necessary for completing image formation is completed. This refers to the series of actions that lead up to this point. Such an image forming job includes image data, information regarding the type of recording material to be used, and image forming conditions such as layout, number of sheets, number of copies, and post-processing.

Also, if another image forming job is entered consecutively after one image forming job, the post-rotation of the previous image forming job and the pre-rotation of the subsequent image forming job are omitted, and these images are May run formation jobs. In this embodiment, even in such a case, the previous image forming job and the subsequent image forming job are each regarded as one image forming job. However, these consecutive image forming jobs may be regarded as one image forming job.

Further, the recording material P is, for example, a sheet-like recording medium on which a toner image (developer image) can be formed by the image forming apparatus 100. Examples of such recording materials include plain paper, cardboard, thin paper, resin sheets, glossy paper, postcards, envelopes, labels, transfer material sheets, electrofax sheets, electrostatic recording paper, OHP sheets, printing paper, and format paper. etc. are included. The engine controller 114 centrally controls various image forming devices of the image forming apparatus 100 to execute a printing operation.

The image forming apparatus 100 includes an image forming section 100A that forms a toner image on a recording material P. The image forming section 100A includes a photosensitive drum 101 that is a drum-shaped electrophotographic photosensitive member that serves as an image carrier for forming a toner image. The photosensitive drum 101 is rotationally driven in the clockwise direction of arrow A at a predetermined circumferential speed (process speed). The image forming section 100A further includes a charging roller 102 as an electrophotographic process device that acts on the photosensitive drum 101, an exposure device (laser scanner in this embodiment) 115, a developing device 104, a transfer roller 108, and a cleaning device 110.

When forming a toner image on the photosensitive drum 101, first, the surface of the photosensitive drum 101 is uniformly charged by the charging roller 102. Next, the exposure device 115 irradiates the charged photosensitive drum 101 with laser light 103 as exposure light based on the image data input to the engine controller 114 to form an electrostatic latent image on the photosensitive drum 101. . Then, the developing device 104 develops the electrostatic latent image formed on the photosensitive drum 101 with toner T to form a toner image. The developing device 104 contains toner T as a developer therein, and this toner T is carried on a developing sleeve 106 disposed facing the photosensitive drum 101 . Then, the electrostatic latent image on the photosensitive drum 101 is developed by the toner carried on the developing sleeve 106.

Note that the developer may be a one-component developer containing a non-magnetic toner or a magnetic toner, or a two-component developer containing a non-magnetic toner and a magnetic carrier.

The toner image formed on the photosensitive drum 101 is transferred to a recording material fed from a feeding cassette 107 at a transfer portion formed by the photosensitive drum 101 and a transfer roller 108, as described later. Transfer residual toner remaining on the photosensitive drum 101 after the transfer is removed by a cleaning device 110. The cleaning device 110 includes a cleaning blade 109 that comes into contact with the photosensitive drum 101 to remove toner, paper powder, etc. on the photosensitive drum 101.

A feeding cassette 107 serving as a recording material storage section stores recording materials P. The recording materials P accommodated in the feeding cassette 107 are fed one by one by a feeding roller 112 serving as a feeding section. That is, the feeding roller 112 can feed the recording material to the image forming section 100A. The fed recording material P passes through the path B, and along the way, the leading end is received by a pair of registration rollers 113, and the skew is corrected. The registration roller pair 113 feeds the recording material P toward the transfer section at a predetermined timing so that the leading edge of the toner image on the photosensitive drum 101 and the leading edge of the recording material are synchronized in the transfer section. As a result, in the transfer section, the toner images on the photosensitive drum 101 side are sequentially transferred onto the recording material P side by electrical action.

The recording material P that has passed through the transfer section is separated from the photosensitive drum 101 and introduced into a fixing device 111 as an image heating device. As will be described in detail later, the fixing device 111 applies pressure and heat to the introduced recording material P so that the unfixed toner image carried on the recording material P is fixed as a fixed image on the recording material P. . If face-up (FU) ejection is selected, the recording material P on which the image has been fixed after leaving the fixing device 111 passes through a path C and is ejected to the FU tray 116 with the image side facing up. Further, if face-down (FD) ejection is selected, the FD passes through path D and is ejected to the FD tray 117 with the image side facing down.

[Fusing device]
Next, a schematic configuration of the fixing device 111 will be described using FIG. 2. In the following description, regarding the fixing device 111 and the members constituting the fixing device, the longitudinal direction is the direction perpendicular to the recording material conveyance direction on the recording material conveyance path surface, and the transversal direction is the direction in which the recording material is conveyed. This is a direction parallel to the conveyance direction of the recording material on the road surface. Width is the dimension in the transverse direction. Further, regarding a recording material, the width is a dimension in a direction perpendicular to the conveying direction of the recording material on the surface of the recording material. The upstream side and the downstream side are the upstream side and the downstream side with respect to the recording material conveyance direction.

The fixing device 111 is a so-called tensionless type device of a film heating type and a pressure roller driving type, in which a pressure roller 302 is rotationally driven and a fixing film 303 is rotated by the conveyance force of the pressure roller 302.

Such a fixing device 111 includes a fixing film 303 as a rotatable endless belt, a pressure roller 302 as a nip forming member and a pressure member, a heater 305, a first thermistor 301a, a second thermistor 301b, etc. Be prepared. Further, the fixing device 111 can be roughly divided into a pressure roller 302 which is also a driving rotating body, a film unit 310 including a fixing film 303, and a device frame (device housing) 311 that houses these. . 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 fixing film 303. The pressure roller 302 is a rotating body that forms a nip portion N in cooperation with the fixing film 303.

The fixing film 303 is also a heat transfer member that comes into contact with the unfixed toner image t formed on the recording material P and heats it by transferring heat from the heater 305 as a heating member. The nip portion N is a portion that heats the toner image t on the recording material while nipping and conveying the recording material P carrying the unfixed toner image t. The toner image t on the recording material is fixed onto the recording material as a fixed image by heat and pressure in the nip portion N, and after fixing, it is discharged from the nip portion as a toner image ta.

A recording material sensor (also referred to as an exit sensor) 307 is disposed downstream of the nip portion N and near the recording material exit portion of the nip portion N. The recording material sensor 307 detects that the leading edge of the recording material that has left the nip portion N has arrived, and also detects the trailing edge of the recording material that has passed. The detection signal is input to a CPU (Central Processing Unit) 203 as a control unit. Based on the input signal, the CPU 203 detects that the recording material P is being held and conveyed in the nip portion N and that the recording material P has passed through the nip portion N.

Note that the CPU 203 may be a CPU that is included in the engine controller 114 and controls the entire image forming apparatus, or may be provided separately for the fixing device 111. In any case, a control device including such a CPU 203 has a ROM (Read Only Memory) and a RAM (Random Access Memory). The CPU 203 controls each unit while reading a program corresponding to a control procedure stored in the ROM. Further, the RAM stores work data and input data, and the CPU performs control by referring to the data stored in the RAM based on the aforementioned program and the like.

[Pressure roller]
The pressure roller 302 is an elastic roller, and has a core metal 302a provided with an elastic layer 302b made of silicone rubber, fluororubber, or the like to reduce hardness. In order to improve surface properties and releasability against toner, a fluororesin layer such as PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxyalkane), FEP (perfluoroethylene-propene copolymer), etc. is provided on the outer peripheral surface of the elastic layer 302b. may be provided.

The pressure roller 302 is rotatably held at one end and the other end of a core metal 302a between side plates (the side plates are not shown) at one end and the other end in the longitudinal direction of the fixing frame 311 via bearing members, respectively. It has been arranged. The pressure roller 302 is a driving rotating body, and the driving force of a motor (drive source) M controlled by the CPU 203 is transmitted to the pressure roller 302 through a drive transmission mechanism (not shown), and the pressure roller 302 rotates around a predetermined circumference in the counterclockwise direction of an arrow Y. Rotationally driven at high speed.

[Film unit]
The film unit 310 is an assembly including a fixing film 303, a heater 305 as a heating member, a holder 304 as a heater holding member, a stay 308, flange members (not shown) at one longitudinal end and the other end, and the like.

The fixing film 303 is mainly made of a heat-resistant material such as PTFE, PFA, or FEP and has a film thickness of 400 μm or less, preferably about 30 to 80 μm, in order to reduce the heat capacity as a heat transfer member and improve quick start performance. It is an endless strip.

The fixing film 303 can have a single layer structure or a multilayer structure. As for the multilayer structure, a silicone rubber layer having a thickness of 300 μm is formed as an elastic layer on the outer peripheral surface of an endless band-like body as a base layer mainly composed of resin or metal. Examples of the resin for the base layer include polyimide, polyamideimide, PEEK (polyetheretherketone), PES (polyethersulfone), and PPS (polyphenylene sulfide). Moreover, examples of the metal of the base layer include SUS (stainless steel), nickel, and the like. Furthermore, a release layer having a thickness of about 20 μm, for example, may be provided on the elastic layer. Examples of the release layer include fluororesins such as PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer), or FEP (tetrafluoroethylene/hexafluoropropylene copolymer).

The fixing film 303 of this embodiment uses a cylindrical member made of a nickel alloy and having a thickness of about 30 μm as a base layer. Further, a silicone rubber layer with a thickness of about 300 μm is formed as an elastic layer on the base layer, and a fluororesin tube with a thickness of about 20 μm is coated on the elastic layer as a release layer. The fixing film 303 is formed into an endless strip having a diameter of 25 mm and a total thickness of 350 μm.

The heater 305 uses a ceramic heater. A detailed explanation of this heater 305 will be given later. The holder 304 is made of highly heat resistant resin or the like. The holder 304 has a groove provided along the longitudinal direction in the center of the outer surface in the transverse direction, and the heater 305 is fitted into this groove and fixedly held.

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

The heater 305, the holder 304, and the stay 308 are members that are long in the longitudinal direction of the fixing film 303, which intersects with the rotation direction of the fixing film 303. Note that in this embodiment, the longitudinal direction of the fixing film 303 is the same as the direction perpendicular to the recording material conveyance direction on the recording material conveyance path surface described above. The fixing film 303 is loosely fitted to the assembly of the heater 305, holder 304, and stay 308, that is, without tension. Therefore, the fixing film 303 includes the heater 305.

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

The film unit 310 is arranged substantially parallel to the pressure roller 302 with the heater 305 side facing the pressure roller 302, and the flange members on one end side and the other end side are connected to 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 section provided in the. The flange members at one end and the other end are each pressed in the axial direction of the pressure roller 302 by the urging force of a pressure spring of a pressure mechanism (not shown). As a result, the heater 305 is pressed against the pressure roller 302 via the stay 308 and the holder 304 with the fixing film 303 in between, against the elasticity of the elastic layer 302b.

In this embodiment, the pressing force applied to the film unit 310 is approximately 156.8 N (16 kgf) on one end side, and the total pressing force is approximately 313.3 N (32 kgf). Due to the pressure, a nip portion N having a predetermined width is formed between the fixing film 303 and the pressure roller 302 in the recording material conveyance direction. When the image forming apparatus 100 is on standby, the pressure force of the pressure mechanism is released by a pressure release 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). ing. That is, the formation of the nip portion N is maintained in a state where it is substantially released.

[Fusing operation]
Next, the fixing operation in the fixing device 111 will be explained. At a predetermined control timing in the print job execution sequence, the CPU 203 causes the pressure mechanism in the pressure-released state to pressurize, thereby forming a nip portion N between the fixing film 303 and the pressure roller 302. Then, the CPU 203 starts the motor M to rotate the pressure roller 302 in the counterclockwise direction of the arrow Y at a predetermined circumferential speed.

When the pressure roller 302 is rotationally driven, a rotational force acts on the fixing film 303 due to the frictional force between the surface of the pressure roller 302 and the surface of the fixing film 303 at the nip portion N. Therefore, the fixing film 303 is driven to rotate around the outer periphery of the holder 304 in the clockwise direction of arrow X at a circumferential speed that is substantially the same as the circumferential speed of the pressure roller 302 while the inner circumferential surface of the fixing film 303 slides in close contact with the heater 305 . The holder 304 has a semicircular cross section and has a function of regulating the rotational trajectory of the fixing film 303.

Further, along with the rotation of the pressure roller 302, power is supplied to the heater 305 from a triac (power supply section) 200 controlled by the CPU 203 via a power supply path (not shown). This causes the temperature of the heater 305 to rise rapidly. The temperature of the heater 305 is raised to a predetermined target temperature (fixing temperature) and regulated as described later.

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

[Heater configuration and power supply control]
Next, the configuration of the heater 305 and control of power supply to the heater 305 will be described using FIGS. 3(a) to 3(c) and FIG. 4. As described above, the heater 305 is a ceramic heater, and is a longitudinally long planar heating body with a low heat capacity that exhibits a steep temperature rise characteristic when energized. The heater 305 includes an elongated heater substrate 305a and a heating element 305c formed along the longitudinal direction on one side (front side: the sliding surface side of the heater 305 with the fixing film 303).

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

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

Further, the above-mentioned one side of the heater substrate 305a is coated with a protective layer 305b whose main component is glass or fluororesin. The protective layer 305b covers the heating element 305c and the conductive material 305d, except for the electrodes 305e and 305f, in order to protect them from sliding on the fixing film 303.

In addition, on the other side of the heater substrate 305a (back side: the side of the heater 305 that does not slide with the fixing film 303), a first thermistor 301a and a second thermistor 301a as a detection unit that detects the temperature of the heater 305 are installed. A thermistor 301b is provided. The first thermistor 301a is arranged as a detection part for heater temperature control at a position corresponding to the longitudinal center of the heating element 305c. The second thermistor 301b serves as a detection unit for detecting double feeding of recording materials and is disposed 115 mm away from the first thermistor 301a toward the other end in the longitudinal direction of the heater board 305a.

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

In the image forming apparatus 100 of this embodiment, the recording material P is conveyed by so-called central reference conveyance. That is, recording materials of any size and width that can be used in the apparatus are fed so that the center portion in the width direction passes through the center reference conveyance line (center of recording material conveyance) of the apparatus. In FIG. 3(a), "O" is the central reference conveyance line (imaginary line).

Wmax is the passage area width of a recording material of maximum width size used in the apparatus. In other words, it is the width of the maximum passage area through which the recording material with the largest longitudinal size among the recording materials that can pass through the nip portion N passes. In this embodiment, the width of the passage area is A3 length (297 mm), and the length of the heating element 305c of 300 mm corresponds to this Wmax.

Wmin is the width of the passage area of the recording material of the minimum width size usable in the apparatus. In other words, it is the width of the minimum passage area through which the recording material with the smallest length in the longitudinal direction among the recording materials that can pass through the nip portion N passes. The first thermistor 301a is arranged at a position substantially corresponding to the position of the central reference conveyance line O. That is, the first thermistor 301a is placed within the minimum passage area and detects the temperature of the heater 305 in the minimum passage area. On the other hand, the second thermistor 301b is arranged outside the minimum passage area in the longitudinal direction and within the maximum passage area, and detects the temperature of the heater 305 in the area outside the minimum passage area.

Control of power supply to the heater 305 will be explained based on FIG. 4. FIG. 4 is a schematic block diagram showing a power supply path from the commercial power source 201 to the heating element 305c of the heater 305. The heating element 305c receives power from the commercial power source 201 via the triac 200, and the power supply from the commercial power source 201 to the heating element 305c is controlled by the CPU 203.

The temperature information of the heater 305 due to the heat generated by the heating element 305c is converted to analog information by the first thermistor 301a disposed within the width Wmin of the recording material passage area of the minimum width size of the heater 305. This is digital information converted by The digital information is input to CPU 203. The CPU 203 compares this input temperature information with a predetermined target temperature (fixing temperature). Then, based on the difference, the power supplied from the commercial power source 201 to the heating element 305c is controlled by PID via the triac 200, and the temperature of the passage area of the heater 305 is adjusted to a predetermined target temperature.

The CPU 203 monitors the temperature information of the heater 305 at predetermined intervals, and corrects the power supplied to the heating element 305c at every predetermined interval. In the present embodiment, wave number control is performed to select whether or not to supply power from the commercial power source 201 to the heating element 305c for each half wave of the AC power output from the commercial power source 201 during a predetermined cycle period. is adopted. The amount of power supplied from the commercial power source 201 to the heating element 305c over a predetermined period can be adjusted by not only wave number control but also phase control that determines the phase range for each half wave of the AC power output from the commercial power source 201. .

The first thermistor 301a is a temperature detection unit for controlling the temperature of the heater 305 to maintain the heater 305 at a target temperature from the start of the heating process (startup) of the fixing device 111 to the image fixing process of the recording material of the print job. Therefore, the first thermistor 301a is located within the width Wmin of the passage area width Wmin of the recording material having the minimum width size of the heater 305, and in this embodiment, it is located at a position approximately corresponding to the position of the central reference conveyance line O. It is placed.

That is, the first thermistor 301a detects the temperature corresponding to the area through which the recording material passes in the nip portion N when the recording material is introduced into the fixing device 111. The CPU 203 controls the power supply from the triac 200 to the heater 305 so that the temperature of the recording material passage area in the nip portion N is maintained at a predetermined target temperature based on the temperature detected by the first thermistor 301a. do.

[Detection of double feeding of recording materials and device control]
Next, detection of double feeding of recording materials and control of the apparatus based on this detection of double feeding will be explained. The second thermistor 301b is a temperature detection unit for detecting double feeding of recording materials, and the analog information from the second thermistor 301b is converted into digital information by the A/D conversion circuit 202 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 detection unit for detecting the detected temperature gradient ΔT (gradient of the detected temperature change over time) of the heater 305 within a predetermined time while the recording material P is passing through the nip portion N. be. Therefore, it is arranged outside the area of the passing area width Wmin of the recording material having the minimum width size and within the heat generating area of the heat generating element 305c.

That is, the second thermistor 301b detects the temperature corresponding to the region through which the recording material does not pass in the nip portion N when the recording material is introduced into the fixing device 111. In this embodiment, the CPU 203 controls the heater 305 to stop power supply from the triac 200 to the heater 305 according to the detected temperature detected by the second thermistor 301b and the slope of the detected temperature change over time. 305 is controlled.

Specifically, as shown in FIG. 5, which will be described later, the CPU 203 forces the heater 305 to be energized according to the detected temperature detected by the second thermistor 301b and the slope of the change over time of the detected temperature. Change the temperature setting to turn it off. More specifically, the inclination (gradient) of the temporal change in the detected temperature is the rate of increase in the detected temperature per unit time. Further, the temperature at which the power supply to the heater 305 is forcibly turned off is defined as a heater-off temperature (referred to as a heater forced-off temperature in this embodiment).

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

As described above, analog information from 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 to analog information again and then calculate the detected temperature slope ΔT using the analog information, the error will be smaller than the configuration where the detected temperature slope ΔT is calculated using the digital information. This is because analog information and digital information are not in a proportional relationship.

In this embodiment, the CPU 203 determines that double feeding has occurred based on the detected temperature gradient ΔT (ie, temperature increase rate) detected by the second thermistor 301b and the detected temperature T, and changes the control. That is, the CPU 203 functions as a double feed detection section. A specific example of the detection method is as shown in the flowchart of FIG. 5, which will be described later. When the CPU 203 changes the control, the CPU 203 changes the control based on the information stored in the memory 204. Then, the CPU 203 controls a heater forced OFF temperature at which the power supply to the heater 305 is turned off (heater forced OFF temperature control) according to the detection result by the double feed detection unit. Heater forced OFF temperature control is a control in which when the second thermistor 301b detects the heater forced OFF temperature, the power input to the heater 305 is reduced to zero.

Here, double feeding does not necessarily occur only once for one print job. Even if it is possible to suppress excessive temperature rise by changing the heater forced OFF temperature, which turns off the power supply to the heater when a sudden temperature rise is detected, the heater may become overheated if double feeding is performed again. You may end up doing this. In particular, in recent years there has been a need to be compatible with a variety of media, including those with good surface properties, those coated with coating agents, and those with multiple perforations. , all of them tend to cause double feeding when being fed from the feeding section.

On the other hand, if a print job is continued with the heater forced OFF temperature kept low, the temperature of the nip portion may drop and the fixation of the toner image onto the recording material may occur. Therefore, in this embodiment, the heater forced OFF temperature is changed based on the detected temperature gradient ΔT detected by the second thermistor 301b, and the feeding interval of the recording material from the feeding cassette 107 is also changed. .

That is, when the temperature increase rate per unit time of the detected temperature of the second thermistor 301b (that is, the detected temperature slope ΔT) is the first increase rate, the CPU 203 sets the heater forced OFF temperature to the first temperature. Set to . On the other hand, when the detected temperature gradient ΔT is a second rate of increase that is lower than the first rate of increase, the CPU 203 sets the forced heater OFF temperature to a second temperature that is higher than the first temperature. In addition, the CPU 203 sets the recording material feeding interval when the detected temperature slope ΔT is the first rate of increase as the first feeding interval, and when the detected temperature slope ΔT is the second rate of increase. The recording material feeding interval is defined as the second feeding interval. At this time, the first feeding interval is made wider than the second feeding interval. For this purpose, the CPU 203 controls the feeding roller 112 so that the recording material feeding interval can be changed.

In other words, in this embodiment, when the rate of temperature increase in the area where the recording material does not pass in the nip portion N is high, the heater forced OFF temperature is lowered. If the recording material continues to pass through the nip portion N when the heater forced OFF temperature is lowered, the temperature of the nip portion N may drop and the temperature for fixing the toner image may not be maintained. For this reason, when the heater forced OFF temperature is lowered, the recording material feeding interval is widened to suppress a drop in temperature at the nip portion. A detailed explanation will be given below using the flowchart shown in FIG.

First, the CPU 203 receives a print command to execute a print job for forming images on a predetermined number of recording materials, for example (S1). The image forming apparatus 100 that has received the print command sets initial productivity as the recording material feeding interval (S2), and feeds the recording material P (S3). In this embodiment, the initial productivity is, for example, 30 cpm (copy/minute). That is, the recording material feeding interval is set to an interval at which 30 recording materials are output per minute.

Subsequently, each part of the image forming apparatus 100 operates as described above, and the toner image is transferred at the transfer section onto the recording material P fed from the pair of registration rollers 113 (S4). The recording material P carrying the transferred image enters the nip portion N of the fixing device 111 (S5). In order for the CPU 203 to determine that the recording material P has entered the nip portion N, if the fixing device 111 is equipped with an entrance sensor, a signal from the entrance sensor may be used. If the fixing device 111 is not equipped with an entrance sensor, it can be determined that the recording material P has entered the nip portion N by dividing the transport distance by the transport speed.

The CPU 203 reads the temperature T0 of the second thermistor 301b when the recording material P enters the nip portion N (S6). In this embodiment, the CPU 203 reads the temperature of the second thermistor 301b every 0.1 [s] after the recording material P enters the nip portion N. Then, after n [s] (that is, 0.1 sec after S6), the CPU 203 reads the temperature Tn of the second thermistor 301b (S7). After further n+1 [s] (that is, 0.1 sec after S7), the CPU 203 reads the temperature Tn+1 of the second thermistor 301b (S8). Note that n and n+1 are signs, and the interval for reading the temperature of the second thermistor 301b is not limited to 1 sec.

Next, the CPU 203 calculates the detected temperature gradient ΔTn+1=Tn+1−Tn (S9). Of course, the CPU 203 also calculates the initial temperature gradient ΔT1=T1−T0.

The CPU 203 determines whether the detected temperature gradient (temperature difference) ΔTn+1 is larger than α1 (first threshold temperature difference) and whether the temperature Tn+1 is higher than β1 (first threshold temperature) (S10). That is, the CPU 203 determines that the detected temperature slope ΔTn+1 as a temperature increase rate per unit time is the first increase rate, and the detected temperature Tn+1 detected by the second thermistor 301b when the recording material passes through the nip portion N. is higher than β1.

If ΔTn+1>α1 and Tn+1>β1 are satisfied in S10 (Yes in S10), the CPU 203 sets the heater forced OFF temperature to Toff1 [° C.] as the first temperature (S11). Further, the CPU 203 sets the recording material feeding interval to "productivity 1", which is a first feeding interval that is wider than the initial productivity (in other words, productivity is lowered) (S12). Here, for example, it is assumed that α1=7 [°C/0.1s], β1=240 [°C], and Toff1=260 [°C]. Further, productivity 1 is, for example, 25 cpm.

On the other hand, if the requirements in S10 are not satisfied (No in S10), the CPU 203 moves to S13. Specifically, the CPU 203 determines that the detected temperature gradient (temperature difference) ΔTn+1 is larger than α2 (second threshold temperature difference: α2<α1), and the temperature Tn+1 is β2 (second threshold temperature: β2>β1). It is determined whether it is higher (S13). That is, the CPU 203 determines that the detected temperature slope ΔTn+1 as a temperature increase rate per unit time is the second increase rate, and the detected temperature Tn+1 detected by the second thermistor 301b when the recording material passes through the nip portion N. is higher than β2. Here, the second rate of increase is lower than the first rate of increase. That is, the second threshold temperature difference α2 is lower than the first threshold temperature difference α1. Further, the second threshold temperature β2 is higher than the first threshold temperature β1.

If ΔTn+1>α2 and Tn+1>β2 are satisfied in S13 (Yes in S13), the CPU 203 sets the heater forced OFF temperature to Toff2 [° C.] as the second temperature (S14). Furthermore, the CPU 203 sets the recording material feeding interval to "productivity 2", which is a second feeding interval that is wider than the initial productivity (in other words, productivity is lowered) (S15). In productivity 2, the feeding interval is narrower than in productivity 1. That is, productivity 2 is a setting that lowers productivity than the initial productivity, but does not lower productivity as much as productivity 1. Here, for example, α2=5[°C/0.1s], β2=250[°C], and Toff1=270[°C]. Further, productivity 2 is, for example, 27 cpm.

On the other hand, if the requirements in S13 are not satisfied (No in S13), the CPU 203 sets the heater forced OFF temperature to the initial set temperature (predetermined temperature) Toff3 [°C] (>Toff2 [°C]) (S16) . Toff3 is higher than Toff1 as the first temperature and Toff2 as the second temperature. Further, for example, Toff3=285 [° C.].

Note that the heater forced OFF temperature and productivity set in any of S10 to S16 are stored in the memory of the control device in which the CPU 203 is built, as tables such as those shown in Tables 1 and 2, which will be described later. has been done.

Next, the CPU 203 adopts the heater forced OFF temperature and productivity as follows (S17). First, the heater forced OFF temperature is the lowest temperature among the heater forced OFF temperatures (Toff1, Toff2, Toff3) set between S10 and S16 after the leading edge of the recording material P enters the nip portion N. Adopted as the actual heater forced OFF temperature. Next, the productivity is also the highest among the productivity (productivity 1, productivity 2, initial productivity) set between S10 and S16 after the leading edge of the recording material P enters the nip portion N. Adopt low productivity. Note that the case where the initial productivity is adopted is the case where "No" is obtained in each of S10 and S13.

Here, in this embodiment, there is no temperature lower than Toff1 as the heater forced OFF temperature. Therefore, when the CPU 203 sets the heater forced OFF temperature to Toff1 while executing a print job, the last recording material of the print job finishes passing through the nip portion N regardless of the change in the detected temperature slope. The heater forced OFF temperature remains at Toff1 until Note that if Toff1 is not set after Toff2 is set as the heater forced OFF temperature, Toff2 is continued until the last recording material of the print job. Further, if Toff1 or Toff2 is not set during a print job, the initial set temperature Toff3 is continued until the last recording material of the print job.

Similarly, there is no productivity lower than productivity 1. Therefore, if the CPU 203 sets the productivity to productivity 1 while executing a print job, the last recording material of the print job will finish passing through the nip portion N regardless of the change in the detected temperature gradient. Productivity remains at productivity 1 until Note that, if productivity is not set to productivity 1 after productivity is set to 2, productivity 2 continues until the last recording material of the print job. Further, unless productivity 1 or productivity 2 is set during a print job, the initial productivity continues until the last recording material of the print job.

Next, it is determined whether the thermistor detection temperature Tn+1 read in the immediately preceding S8 exceeds the heater forced OFF temperature (any one of Toff1, Toff2, or Toff3) set in the above-mentioned S17 (S18). If the thermistor detection temperature Tn+1 exceeds the heater forced OFF temperature (Yes in S18), the power input to the heater 305 is set to zero (heater forced OFF, S19). Then, the thermistor detection temperature Tn+1 read in S8 is set as Tn (S20).

On the other hand, in S18, if the thermistor detection temperature Tn+1 does not exceed the heater forced OFF temperature (No in S18), the CPU 203 continues temperature adjustment while supplying power to the heater 305, and proceeds to S20.

Next, the CPU 203 determines whether the rear end of the recording material P has passed through the nip portion N (S21). If the rear end of the recording material P has not passed through the nip portion N, that is, if the recording material P has still passed through the nip portion N (No in S21), the process returns to S8. That is, the CPU 203 reads the detected temperature Tn+1 of the second thermistor 301b every 0.1 seconds until the recording material P passes through the nip portion N (S8), and calculates the detected temperature gradient ΔTn+1=Tn+1−Tn. (S9). Then, S10 to S20 are executed, and the heater forced OFF temperature control is performed using the heater forced OFF temperature set here.

In S21, if the recording material P has passed through the nip N (Yes in S21), the CPU 203 determines whether the recording material P that has passed through the nip N is the last recording material of the print job. (S22). If it is not the last recording material in S22 (No in S22), the process returns to S5 and the print job is continued. At this time, as described above, the print job is continued with the heater forced OFF temperature and productivity set in S17.

On the other hand, if it is the last recording material in S22 (Yes in S22), the heater forced OFF temperature is set to the initial setting temperature Toff3 [°C] (S23), and the productivity is set to the initial productivity (S24). ). That is, at the end of the print job, the heater forced OFF temperature and productivity are returned to their initial values. Then, the print job is ended (S25). Note that the timing for returning the heater forced OFF temperature and productivity to their initial values may be at the start of the next print job.

As shown in S6 to S22 and S18 to S20 of the above-described flowchart, until the last recording material passes through the nip portion N, determination of the heater forced OFF temperature based on the detected temperature gradient is repeatedly performed. That is, the CPU 203 reads the second thermistor 301b every 0.1 seconds and sets the heater forced OFF temperature each time. Also, productivity is set based on the detected temperature gradient. During a print job, if a low temperature is set as the heater forced OFF temperature, that temperature continues to be set unless a lower temperature is set. Furthermore, if a low productivity is set, that productivity continues to be set unless a lower productivity is set.

The parameters n, α1, α2, β1, β2, Toff1, Toff2, Toff3, productivity 1, productivity 2, and initial productivity of this control explained above are summarized as follows.
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]. Productivity 1 = 25 [cpm], Productivity 2 = 27 [cpm], Initial productivity = 30 [cpm].

Note that if the value of the detected temperature gradient α is large, it is necessary to change the heater forced OFF from a state where the detected temperature β is low, so the setting is made as described above.

Further, Table 1 shows an example of a table of heater forced OFF temperatures set based on the detected temperature gradient and the detected temperature.

Further, Table 2 shows an example of a productivity table set based on the detected temperature slope and the detected temperature.

The specific numerical values described in this embodiment are merely examples, and these numerical values can be set as appropriate depending on the configuration and specifications of the device. For example, the smaller the size of the recording material, the higher the temperature of the non-passage area in the nip portion N. Therefore, the productivity after the heater forced OFF temperature change may be lowered depending on the distance from the second thermistor 301b to the widthwise end (edge) of the recording material. In this case, even if the non-passing region is wide and the recording material rises in temperature while passing through the nip portion N, productivity is lowered, so that the recording material that is continuously conveyed to the nip portion N and the recording material are The temperature can be lowered sufficiently by the interval (so-called paper interval).

Further, the productivity after changing the heater forced OFF temperature may be changed depending on the temperature detected when the leading edge of the recording material passes through the nip portion N. If the temperature of the leading edge of the recording material is high when it passes through the nip N, it takes time to turn the heater on again after the heater is turned off, resulting in a significant drop in the temperature of the nip. Therefore, when the detected temperature is high, productivity may be lowered and the paper interval may be increased to make it easier to restore the temperature of the nip portion.

[Example of this control]
An example of this control is shown in the timing chart of FIG. The (a) fixing NIP-ON signal in FIG. 6 becomes 1 when the recording material P is in the nip portion N, and becomes 0 when it is not in the nip portion N. (b) The detected temperature is the temperature detected by the second thermistor 301b, and continues to be detected regardless of whether the recording material is in the nip portion N or not. (c) The detected temperature gradient is calculated only when the recording material P is in the nip portion, as shown in the flowchart of FIG. (d) Heater forced OFF temperature and (e) productivity are as explained in the flowchart of FIG. 5, and defaults are set to 285 [° C.] and 30 [cpm], respectively.

Hereinafter, the process will be explained along the time chart of FIG. 6 while referring to the flow chart of FIG. First, if (c) the detected temperature slope ΔTn+1 is larger than 5 [°C/0.1 s] (α2), and (b) the detected temperature Tn+1 is higher than 250 [°C] (β2), then S13 and 14 in FIG. Based on (d) change the heater forced OFF temperature to 270 [° C.] (Toff2). At this time, (e) productivity is changed to 27 [cpm] (productivity 2) based on S15 of FIG.

Next, if (c) the detected temperature gradient ΔTn+1 is larger than 7 [°C/0.1 s] (α1), and (b) the detected temperature Tn+1 is higher than 240 [°C] (β1), then S10 in FIG. 11, (d) change the heater forced OFF temperature to 260 [° C.] (Toff1). At this time, (e) productivity is changed to 25 [cpm] (productivity 1) based on S12 of FIG.

Thereafter, even when the recording material P passes through the nip portion N, the heater forced OFF temperature remains set at 260 [° C.] and the productivity remains set at 25 [cpm]. In this control, once the heater forced OFF condition is changed, the setting is continued until the last recording material of the job passes through the nip portion. This is to prevent double feeding from occurring again in a state where the temperatures of the ends of the fixing film 303 and the heater 305 have increased after double feeding occurs, thereby preventing an excessive temperature rise error from occurring. Further, once the productivity conditions are changed, the settings are continued until the last recording material of the job passes through the nip. This is because if the job is continued without lowering the productivity with the heater forced OFF temperature lowered, the nip temperature will not recover and a fixing failure will occur. Therefore, by lowering productivity, the temperature of the nip portion is restored and the occurrence of fixing failures is suppressed.

In the above explanation, the setting of the heater forced OFF temperature was changed in stages (for example, from 285 [°C] to 270 [°C]) by dividing the detected temperature gradient into stages. However, the heater forced OFF temperature may be changed continuously depending on the amount of the detected temperature gradient. For example, the heater forced OFF temperature may be lowered by 1 [°C] every time the detected temperature gradient changes by 1 [°C/0.1 s].

[Example]
Next, an experiment conducted to examine the effects of this embodiment will be described using FIG. 7. The experiment was conducted using the image forming apparatus 100 shown in FIG. 1 in a case where the control according to the above-described embodiment was performed (example) and a case where the control according to the present embodiment was not performed (comparative example). occurred multiple times. Conditions other than the heater forced OFF temperature and productivity control are the same in Examples and Comparative Examples 1 and 2. Figure 7 shows the experimental results.

In FIG. 7, A, B, and C are non-passing areas when four sheets of LGL size (216 mm x 356 mm: vertical feeding) and grammage 105 [g/m ² ] are passed through the nip portion N. This is the temperature transition of the second thermistor 301b placed in the figure. D and E show the temperature changes of the first thermistor 301a disposed in the passage area when four sheets of the LGL size recording material are fed.

In Comparative Example 1, as described in the above-mentioned Patent Document 1, the heater forced OFF temperature is lowered according to the temperature increase rate, and after the recording material passes through the nip portion N, the heater forced OFF temperature is set to the initial value. The temperature was returned to the set temperature. Furthermore, productivity remained unchanged regardless of the rate of temperature rise.

Further, in Comparative Example 2, when the heater forced OFF temperature was lowered as in the present embodiment, this setting was continued until the last recording material of the print job. However, even if the heater forced OFF temperature was lowered, the productivity did not change.

As shown in A to C in Figure 7, when the first sheet of a job is double-fed, the detected temperature slope is 7 [°C/0.1s], so the heater forced OFF temperature is 260 [°C]. When the temperature detected by the thermistor detected 260 [°C], the power to the heater was turned off. As a result, even under the influence of heat stored in the fixing device (thermistor, heating element, etc.) or when multiple sheets are being fed, the thermistor detection temperature can reach up to the error temperature of 297 [°C]. However, the error did not cause the issue to be issued. Note that the error temperature is a temperature at which execution of the image forming operation is prohibited by the CPU until the error is cleared by a service person or the like.

However, in Comparative Example 1 of A, the heater forced OFF temperature setting was returned to 285 [° C.], so heat was accumulated in the fixing device (thermistor, heating element, etc.). Therefore, when multiple sheets are fed in the latter half of the job, the heater forced OFF temperature is set to 260 [°C] when the detected temperature slope is 7 [°C/0.1 s], and the power to the heater is turned off. However, the thermistor detected temperature rose to an error temperature of 297 [°C]. And then an error occurred.

On the other hand, in Example B, the heater forced OFF temperature of 260°C, which was set when the first double-feed sheet was passed, is maintained, so the heat accumulated in the fixing device (thermistor, heating element, etc.) is suppressed. Ta. Therefore, even if multiple sheets are fed again in the latter half of the job, the temperature detected by the second thermistor 301b will not rise to the error temperature of 297 [°C], just like the first sheet, and an error will not be issued. There was no.

Next, in Comparative Example 2 of C, when LGL size sheets continue to be fed after the double feeding, the temperature detected by the second thermistor 301b, which is a non-passage area, rises again. However, since productivity has not been changed, if the heater forced OFF temperature continues to be set at 260°C, the detected temperature will immediately exceed 260°C. For this reason, the heater is forced to be turned off frequently. As a result, as shown by E, the temperature detected by the first thermistor 301a decreases, making it impossible to maintain a temperature sufficient to fix the toner image on the recording material, resulting in a fixing failure. .

On the other hand, in the case of the example, when the first double feed occurs, the heater forced OFF temperature is changed, the productivity is changed, and the subsequent feeding interval is widened, so there is no problem between sheets. The temperature of the passage area decreased. Also, during that time, the temperature of the passage area rose. As a result, normal paper feeding continued after the double feeding, and even if the temperature at the end increased, it became difficult to reach the heater forced OFF temperature of 260°C. As a result, power is continuously supplied to the heater, so the temperature detected by the first thermistor 301a does not drop, and a temperature sufficient to fix the toner image on the recording material can be maintained, suppressing the occurrence of fixing defects. Ta.

In this manner, in the case of the present embodiment, it is possible to suppress excessive temperature rise of the fixing film 303 and the heater 305 and to suppress the occurrence of fixing failures. In addition, by maintaining the change in the heater forced OFF temperature and widening the feeding interval after double feeding is detected, even if thick recording materials outside the specifications are fed to the nip part N, such as with double feeding, for example, , it is possible to prevent the occurrence of errors and maintain image quality above a certain level.

Furthermore, in the case of this embodiment, even if double feeding occurs multiple times in one print job, the temperature of the heater 305 can be suppressed from rising to an error temperature that may cause damage or deterioration of the constituent members of the fixing device. . Then, even if the job continues thereafter, it is possible to prevent the temperature from rising to the error temperature again and maintain image quality.

If the temperature rises to the error temperature, the image forming apparatus will stop due to a high temperature error, and the user will not be able to use the image forming apparatus until the high temperature error is cleared by a service person or the like. Therefore, by suppressing the occurrence of high temperature errors through this control, it is possible to reduce the frequency at which the user calls a service person to resolve the errors. Therefore, it is possible to reduce the possibility that the user's productivity will be impaired.

In the above explanation, the productivity was set to three stages: initial productivity, productivity 1, and productivity 2. However, the productivity may be set to two stages, or four stages, as long as the feeding intervals are different from each other. The process may be performed in multiple stages. Similarly, the heater forced OFF temperature may be set in two stages, or may be set in multiple stages of four or more stages. In addition, changes in the heater forced OFF temperature and productivity may be determined based only on ΔTn+1, but as mentioned above, it is better to consider Tn+1 as well to suppress excessive temperature rises in the fixing film and heater, and The occurrence of defects can be suppressed with higher precision.

<Another example of the first embodiment>
In the above-described embodiment, the detected temperature gradient is calculated based on the detected temperature of the second thermistor 301b arranged in the non-passage region, and the above-described heater forced-off temperature and productivity are changed. However, such control may be similarly performed on the first thermistor 301a. That is, although the above-described embodiment uses central reference conveyance, for example, the user may set the recording material to one side in the width direction and perform image formation. In this case, the first thermistor 301a located at the center may become a non-passage region. Even in such a case, the same effect can be obtained by calculating the detected temperature gradient using the detected temperature of the first thermistor 301a and changing the above-described heater forced-off temperature and productivity.

<Second embodiment>
The second embodiment will be described using FIG. 8 while referring to FIGS. 1 to 4. In the first embodiment described above, the heater forced OFF temperature and productivity are changed based on the detected temperature gradient ΔTn+1 and the detected temperature Tn+1 detected by the second thermistor 301b. On the other hand, in this embodiment, the heater forced OFF temperature is changed based on the detected temperature gradient ΔTn+1 detected by the second thermistor 301b, and the productivity is changed according to the detected temperature detected by the first thermistor 301a. That's what I do. Other configurations and operations are the same as those in the first embodiment, so illustrations and descriptions of similar configurations will be omitted or simplified, and the following will focus on the differences from the first embodiment.

In this embodiment, in addition to the forced heater OFF control of the heater 305 described in the first embodiment, the type of recording material to be used (for example, paper setting) and the detection of the passing area after the heater forced OFF control are performed. Change the productivity after double feeding depending on the temperature. Thereby, it is possible to more reliably suppress the occurrence of errors when double-feeding sheets are shed, and to suppress unnecessary productivity decline.

That is, in the case of this embodiment as well, as in the first embodiment, the CPU 203 determines that the detected temperature Tn+1 as the first detected temperature detected by the second thermistor 301b as the first detection unit is the heater forced OFF temperature. When the threshold is reached, power to the heater 305 is turned off. Further, the CPU 203 sets the heater forced OFF temperature to the first temperature when the detected temperature gradient ΔTn+1 as the rate of temperature increase per unit time of the first detected temperature is the first rate of increase. On the other hand, if the detected temperature gradient ΔTn+1 is a second rate of increase that is lower than the first rate of increase, the CPU 203 sets the forced heater OFF temperature to a second temperature that is higher than the first temperature.

In addition, in this embodiment, when the recording material is passing through the nip portion N, the CPU 203 controls the temperature of the recording material according to the second detected temperature detected by the first thermistor 301a as the second detection section. The feeding interval, that is, the productivity is changed. Specifically, the CPU 203 can set the target temperature in the minimum passage area through which the recording material with the smallest longitudinal size passes, depending on the type of recording material. Then, the feeding interval of the recording material when the temperature difference between the target temperature and the second detected temperature is a first temperature difference is set as a first feeding interval, and a second feeding interval in which this temperature difference is smaller than the first temperature difference is set. The recording material feeding interval when there is a temperature difference is defined as a second feeding interval. At this time, the first feeding interval is made wider than the second feeding interval. That is, the larger the temperature difference between the target temperature and the detected temperature of the recording material passage area, the wider the feeding interval, that is, the lower the productivity.

For example, the optimum temperature at the nip portion for fixing the toner image on the recording material varies depending on the basis weight of the recording material, whether or not it is coated, and so on. Therefore, the CPU 203 sets the above-mentioned target temperature in accordance with information about the type of recording material input by the user through an input unit (not shown). Here, if the detected temperature gradient ΔTn+1 increases due to double feeding of recording materials and the heater forced OFF temperature is set low, if the recording materials are passed through the nip portion N without reducing productivity, the nip portion The temperature of N will drop. If the temperature in the passing region falls too much from the target temperature, there is a risk that a fixing failure will occur. For this reason, in this embodiment, when the difference between the target temperature and the temperature in the passage area becomes large, productivity is reduced to suppress fixing failure.

On the other hand, as in the first embodiment, when the heater forced OFF temperature is lowered and the productivity is uniformly lowered, in reality, even if the temperature at the nip part N is not so low, the productivity is lowered. may have been dropped. In this case, fixing failure may not occur even if productivity is not reduced. For this reason, in this embodiment, the temperature is actually detected in the passage area, and when the temperature difference between the detected temperature and the target temperature becomes large, the productivity is reduced, resulting in an unnecessary decrease in productivity. I'm trying to suppress it.

A detailed explanation will be given below using the flowchart of FIG. Note that S101 to S109 in FIG. 8 are the same as S1 to S9 in FIG. 6, respectively, and therefore the description thereof will be omitted.

The CPU 203 determines whether the detected temperature gradient (temperature difference) ΔTn+1 calculated in S109 is larger than α1 (first threshold temperature difference) and whether the temperature Tn+1 is higher than β1 (first threshold temperature) (S110). . That is, the CPU 203 determines that the detected temperature slope ΔTn+1 as a temperature increase rate per unit time is the first increase rate, and the detected temperature Tn+1 detected by the second thermistor 301b when the recording material passes through the nip portion N. is higher than β1.

If ΔTn+1>α1 and Tn+1>β1 are satisfied in S110 (Yes in S110), the CPU 203 sets the heater forced OFF temperature to Toff1 [° C.] as the first temperature (S111). Here, for example, it is assumed that α1=7 [°C/0.1s], β1=240 [°C], and Toff1=260 [°C].

On the other hand, if the requirements in S110 are not satisfied (No in S110), the CPU 203 moves to S112. Specifically, the CPU 203 determines that the detected temperature gradient (temperature difference) ΔTn+1 is larger than α2 (second threshold temperature difference: α2<α1), and the temperature Tn+1 is β2 (second threshold temperature: β2>β1). It is determined whether it is higher (S112). That is, the CPU 203 determines that the detected temperature slope ΔTn+1 as a temperature increase rate per unit time is the second increase rate, and the detected temperature Tn+1 detected by the second thermistor 301b when the recording material passes through the nip portion N. is higher than β2. Here, the second rate of increase is lower than the first rate of increase. That is, the second threshold temperature difference α2 is lower than the first threshold temperature difference α1. Further, the second threshold temperature β2 is higher than the first threshold temperature β1.

If ΔTn+1>α2 and Tn+1>β2 are satisfied in S112 (Yes in S112), the CPU 203 sets the heater forced OFF temperature to Toff2 [° C.] as the second temperature (S113). Here, for example, α2=5[°C/0.1s], β2=250[°C], and Toff1=270[°C].

On the other hand, if the requirements in S112 are not satisfied (No in S112), the CPU 203 sets the heater forced OFF temperature to the initial set temperature (predetermined temperature) Toff3 [°C] (>Toff2 [°C]) (S114) . Toff3 is higher than Toff1 as the first temperature and Toff2 as the second temperature. Further, for example, Toff3=285 [° C.].

Next, the CPU 203 adopts the heater forced OFF temperature as follows (S115). That is, the heater forced OFF temperature is the lowest temperature among the heater forced OFF temperatures (Toff1, Toff2, Toff3) set between S110 and S114 after the leading edge of the recording material P enters the nip portion N. Adopted as the actual heater forced OFF temperature.

Next, it is determined whether the thermistor detection temperature Tn+1 read in the immediately preceding S108 exceeds the heater forced OFF temperature (any one of Toff1, Toff2, or Toff3) set in the above-mentioned S115 (S116). If the thermistor detection temperature Tn+1 exceeds the heater forced OFF temperature (Yes in S116), the power input to the heater 305 is set to zero (heater forced OFF, S117). Then, the thermistor detection temperature Tn+1 read in S108 is set as Tn (S118).

On the other hand, in S116, if the thermistor detection temperature Tn+1 does not exceed the heater forced OFF temperature (No in S116), the CPU 203 continues temperature adjustment while supplying power to the heater 305, and proceeds to S118. The flow from setting the forced heater OFF temperature to controlling the forced heater OFF temperature is the same as that shown in FIG. 5 of the first embodiment.

Next, the CPU 203 determines a decrease in the temperature detected by the passing area thermistor when the heater is forced off, that is, the temperature detected by the first thermistor 301a. First, while the recording material is passing through the nip portion N, the first thermistor 301a detects a second detected temperature (referred to as passing area thermistor temperature in this embodiment) (S119). Then, the CPU 203 compares the temperature difference ΔT between the detected passage area thermistor temperature and the target temperature set for each type of recording material with γ1, which is a threshold value of the first passage area temperature difference (S120). That is, it is determined whether ΔT is greater than or equal to γ1.

In S120, if ΔT is γ1 or more, that is, the passing area thermistor temperature is lower than the target temperature by γ1 or more (Yes in S120), the CPU 203 sets the productivity to "productivity 1". (S121). In this embodiment, when ΔT is greater than or equal to γ1, it is assumed that ΔT is the first temperature difference. Productivity 1 is the first feeding interval in which the recording material feeding interval is wider than the initial productivity (for example, 30 cpm) (in other words, the productivity is lowered), as in the first embodiment. In this embodiment, for example, it is set to 15 cpm.

On the other hand, if the requirements in S120 are not satisfied (No in S120), the CPU 203 calculates the temperature difference ΔT between the passing area thermistor temperature detected in S119 and the target temperature set for each type of recording material and the second passing area temperature. The difference threshold value γ2 is compared (S122). That is, it is determined whether ΔT is greater than or equal to γ2.

In S122, if ΔT is γ2 or more, that is, the passing area thermistor temperature is lower than the target temperature by γ2 or more (Yes in S122), the CPU 203 sets the productivity to "productivity 2". (S123). γ2 is smaller than γ1. In this embodiment, when ΔT is less than γ1 and greater than or equal to γ2, ΔT is considered to be the second temperature difference. Productivity 2 is a second feeding interval in which the recording material feeding interval is wider than the initial productivity (in other words, productivity is lowered), as in the first embodiment. Further, in productivity 2, the feeding interval is narrower than in productivity 1. That is, productivity 2 is a setting that lowers productivity than the initial productivity, but does not lower productivity as much as productivity 1, and in this embodiment, it is set to 20 cpm, for example.

On the other hand, if the requirements in S122 are not satisfied (No in S122), the CPU 203 calculates the temperature difference ΔT between the passing area thermistor temperature detected in S119 and the target temperature set for each type of recording material and the third passing area temperature. The difference threshold value γ3 is compared (S124). That is, it is determined whether ΔT is greater than or equal to γ3.

In S124, if ΔT is γ3 or more, that is, the passing area thermistor temperature is lower than the target temperature by γ3 or more (Yes in S124), the CPU 203 sets the productivity to "productivity 3". (S125). γ3 is smaller than γ2. In the present embodiment, when ΔT is less than γ2 and greater than or equal to γ3, it is assumed that ΔT is the third temperature difference.

Productivity 3 is a third feeding interval in which the recording material feeding interval is wider than the initial productivity (in other words, productivity is lowered). Further, in productivity 3, the feeding interval is narrower than in productivity 2. That is, productivity 3 is a setting that lowers productivity than the initial productivity, but does not lower productivity as much as productivity 2, and in this embodiment, it is set to 25 cpm, for example. Note that if the CPU 203 does not satisfy the requirements in S124 (No in S124), the productivity remains the initial productivity.

Next, the CPU 203 employs productivity as follows (S126). The productivity is one of the productivity (productivity 1, productivity 2, productivity 3, initial productivity) set between S120 and S125 after the leading edge of the recording material P enters the nip portion N. Adopt the lowest productivity.

Here, also in the case of this embodiment, there is no productivity lower than productivity 1. Therefore, if the CPU 203 sets the productivity to productivity 1 while executing a print job, the last recording material of the print job will finish passing through the nip portion N regardless of the change in the detected temperature gradient. Productivity remains at productivity 1 until Note that, if productivity is not set to productivity 1 after productivity is set to 2, productivity 2 continues until the last recording material of the print job. Similarly, after the productivity is set to productivity 3, unless it is set to productivity 1 or productivity 2, productivity 3 continues until the last recording material of the print job. Further, unless the productivity is set to 1 to 3 during a print job, the initial productivity continues until the last recording material of the print job.

The subsequent steps S127 to S131 are the same as S21 to S25 in FIG. 5, and after the last recording material passes through the nip N, the heater forced OFF temperature and productivity are returned to their initial values, and the print job is resumed. end.

The parameters n, α1, α2, β1, β2, γ1, γ2, γ3, Toff1, Toff2, Toff3, productivity 1, productivity 2, productivity 3, and initial productivity of this control explained above are summarized as follows. It becomes like this.
n=0.1[s], α1=7[℃/0.1s], α2=5[℃/0.1s], β1=240[℃], β2=250[℃], γ1=130, γ2 = 100, γ3 = 70, Toff1 = 260 [°C], Toff2 = 270 [°C], Toff3 = 285 [°C]. Productivity 1 = 15 [cpm], Productivity 2 = 20 [cpm], Productivity 3 = 25 [cpm], and initial productivity = 30 [cpm].

Table 3 shows an example of a productivity table set based on the range of ΔT, which is the temperature difference between the detected passing area thermistor temperature and the target temperature set for each type of recording material, and is the passing area detected temperature drop. Shown below.

In the case of this embodiment as described above, the larger the temperature drop in the nip portion N, the longer it takes for the temperature to return from forced OFF of the heater. It is possible to suppress the occurrence of fixing failure after feeding. Furthermore, since the temperature of the passage area to maintain image quality is not necessarily maintained at the minimum necessary level, if the temperature drop is small, the recording material can be passed through the nip N without changing productivity.

Note that if the recording material is a recording material with a low basis weight such as thin paper, it may be determined not to change the productivity as described above. For example, if the recording material is thin paper, the previously determined productivity may be maintained without performing steps S120 to S125 in FIG.

Further, in this embodiment, productivity is determined based on the width of temperature decrease, but productivity may be determined based on the type of recording material (paper settings). In other words, the larger the basis weight of the recording material, the higher the passing area temperature to maintain the image quality. Therefore, recording materials with a large basis weight will greatly reduce productivity after double feeding, and recording materials with a small basis weight will decrease productivity. Try not to lower it too much.

For example, in S12 and S15 of FIG. 5 of the first embodiment, the productivity is set using the detected temperature gradient ΔTn+1, etc., but at this time, the productivity may also be set taking into account the type of recording material. good. Specifically, productivity 1 and productivity 2 may each have a plurality of productivity values depending on the type of recording material. For example, for productivity 1, if the recording material is plain paper, the productivity is set to 25 [cpm], if the recording material is thick paper, the productivity is further reduced to, for example, 23 [cpm], and if the recording material is thin paper, the productivity is set to 25 [cpm]. For example, it is set to 26 [cpm] without reducing productivity too much. That is, the productivity may be set depending on the temperature rise rate of the non-passage area and the type of recording material.

Also, in the case of this embodiment, as in the other example of the first embodiment, the detection of the first thermistor 301a takes into consideration the case where the recording material is set to one side in the width direction and image formation is performed. The heater forced OFF temperature may be changed based on the temperature. In this case, productivity is set based on the temperature detected by the second thermistor 301b. That is, the first thermistor 301a may be used as the first detection section, and the second thermistor 301b may be used as the second detection section.

<Third embodiment>
A third embodiment will be described using FIG. 9. Note that this embodiment includes a film thermistor 309 as a detection unit that detects the temperature of the fixing film 303, and the temperature detected by the film thermistor 309 is used to change the heater forced OFF temperature and productivity. Other configurations and operations are the same as those in the first embodiment or the second embodiment described above, so similar configurations are given the same reference numerals and explanations and illustrations are omitted or simplified. 1. Points that are different from the second embodiment will be mainly explained.

A film thermistor 309 serving as a detection unit is supported by the stay 308 and comes into contact with the inner peripheral surface of the fixing film 303 to detect the temperature of the fixing film 303. In the case of this embodiment, the film thermistor 309 is arranged at the same position as the second thermistor 301b shown in FIG. 3 with respect to the longitudinal direction of the fixing film 303. That is, the film thermistor 309 detects the temperature of the fixing film 303 in a region outside in the longitudinal direction of the minimum passage region through which the recording material having the smallest longitudinal size passes.

Specifically, in the longitudinal direction of the fixing film 303, a film thermistor 309 for detecting the temperature of the fixing film 303 is provided outside the passing area width Wmin of the recording material of the minimum width size and inside the maximum passing area width Wmax. . Based on the temperature of this sensor, each of the above-described embodiments is controlled.

That is, the CPU 203 changes the heater forced OFF temperature and productivity based on the temperature detected by the film thermistor 309, similar to the first embodiment. In other words, in this embodiment, the second thermistor 301b in the first embodiment is replaced with a film thermistor 309. In this way, even if the temperature of the fixing film 303 is detected, the same effects as in the first embodiment can be obtained.

<Another example of the third embodiment>
Furthermore, when the configuration of FIG. 9 described above is applied to the second embodiment, the first detection section corresponds to the film thermistor 309, and the second detection section corresponds to the first thermistor 301a as in the second embodiment. handle. Even in this case, the same effects as in the second embodiment can be obtained.

Furthermore, two or more film thermistors 309 may be provided, one in the same position as the second thermistor 301b in FIG. 3 and one in the same position as the first thermistor 301a in FIG. In this case, the film thermistor 309 placed outside the minimum passage area corresponds to the first detection section, and the film thermistor 309 placed inside the minimum passage area corresponds to the second detection section. Even in this case, the same effects as in the second embodiment can be obtained.

<Other embodiments>
In each of the above embodiments, one heater is used as an example, but there may be a plurality of heaters. For example, when using a main heater (mainly heats the longitudinal center part and heats the ends weakly) and a sub-heater (mainly heats the longitudinal ends and heats the central part weakly). Also in such an example, the above-mentioned "heater forced OFF" refers to turning off both the main heater and the sub-heater.

Furthermore, in each of the embodiments described above, control was performed to stop the power supply from the triac 200 to the heater 305 in accordance with the detected temperature detected by the second thermistor 301b and the slope of the detected temperature. However, depending on the type of recording material used, the set value of the slope of the detected temperature for controlling the stopping of power supply from the triac 200 to the heater 305 may be changed.

Further, detection for controlling the power supply from the triac 200 to the heater 305 is stopped according to the detected temperature detected by the second thermistor 301b when the leading edge of the introduced recording material passes through the nip portion N. The set value of the temperature slope may be changed. Further, the productivity setting value may be changed depending on the usage environment and the number of images formed up to that point.

Further, productivity may be restored during the job depending on the recovery status of the passage area temperature. In other words, in this embodiment, once the productivity has been reduced, the productivity is maintained until the end of the job, but if the temperature at the nip has not decreased significantly, the productivity may be reduced, for example. You may return to the initial productivity or increase it by one level.

Furthermore, the heater forced OFF temperature may be returned to the initial setting value or one level higher setting value if the temperature increase rate becomes low. In short, when the heater forced OFF temperature or productivity is lowered, this may not be continued until the end of the job.

Further, in each of the embodiments described above, productivity is set using a table, but it may be set using calculation. For example, a new productivity setting value may be obtained by subtracting the temperature drop in the passage area when the heater is forced off multiplied by the productivity reduction rate from the previous productivity. Specifically, it is assumed that the initial productivity is 30 cpm, the productivity down rate is 5% at 10°C (5%/10°C), and the temperature decrease is 20°C. In this case,
30×(1-((0.05/10)×20))=27[cpm]
Set to .

Furthermore, in each of the embodiments described above, when the present invention is applied to a fixing device that includes a fixing film as an endless belt, a heater that heats the fixing film, and a roller that forms a nip portion between the fixing film and the fixing film. explained. However, the fixing device to which the present invention can be applied is not limited to this configuration. For example, an IH type configuration may be used in which the endless belt is heated by electromagnetic induction heating. Further, the heater may be of other configurations such as a halogen heater in addition to the above-mentioned ceramic heater.

In addition to the above-mentioned film, the endless belt may be stretched by a plurality of stretching rollers. Furthermore, the nip portion may be formed by a pair of endless belts. That is, the nip portion forming member may also be an endless belt. Further, the endless belt may be configured to be rotationally driven by using one of the rollers stretched thereon as a driving roller.

Further, as an image heating device, a fixing device that heats and fixes an unfixed toner image t formed on a recording material has been described as an example. However, the image heating device is, for example, a device (in this case also referred to as a fixing device) that increases the gloss (glossiness) of the image by heating and re-fixing the toner image temporarily attached to the recording material. There may be. That is, for example, it may be an apparatus that fixes a semi-fixed toner image onto the recording material P, or an apparatus that performs heat treatment on a fixed image. Therefore, the fixing device installed in the image forming apparatus may be, for example, a surface heating device that adjusts the gloss and surface properties of the image.

Furthermore, in each of the embodiments described above, a monochrome printer was used as an example of the image forming apparatus. However, the image forming apparatus is not limited to an image forming apparatus that forms monochrome images, but may be an image forming apparatus that forms color images. Further, the image forming apparatus may be a printer, a copying machine, a fax machine, a multifunction machine having multiple of these functions, or the like.

100...Image forming apparatus/100A...Image forming unit/111...Fixing device/112...Feeding roller (feeding unit)/203...CPU (control unit)/303... Fixing film (endless belt) / 301a... First thermistor (detection section, second detection section) / 301b... Second thermistor (detection section, first detection section) / 302... Pressure roller (Nip part forming member)/305...Heater

Claims (12)

an image forming section that forms a toner image on a recording material ;
A rotatable endless belt,
a nip portion forming member that forms a nip portion between the endless belt and the recording material on which the toner image has been formed in the image forming section, which heats the toner image on the recording material while nipping and conveying the recording material;
a heater that is arranged along a longitudinal direction of the endless belt that intersects with a rotational direction of the endless belt, and that generates heat when energized to heat the endless belt;
a detection unit that detects the temperature of the heater in a region outside in the longitudinal direction of a minimum passing region through which a recording material having the smallest length in the longitudinal direction among the recording materials that can pass through the nip portion;
a control unit that controls productivity, which is the number of recording materials passing through the nip portion per unit time ;
The control unit includes:
When the temperature increase rate per unit time of the detection unit is a first increase rate , the productivity is the first productivity , and the temperature increase rate is a second increase rate lower than the first increase rate. If the productivity is a second productivity ,
the first productivity is smaller than the second productivity ,
When the control unit sets the productivity to the first productivity while executing an image forming job for forming images on a predetermined number of recording materials, the control unit may set the productivity to the first productivity regardless of the change in the temperature increase rate. , the productivity is set to be equal to or lower than the first productivity until the last recording material of the image forming job finishes passing through the nip portion;
An image forming apparatus characterized by: When the rate of temperature increase per unit time of the detection unit is the first rate of increase, a heater-off temperature at which electricity is turned off to the heater is set to the first temperature, and the rate of temperature increase is set to the first temperature. If the second rate of increase is lower than the first rate of increase, the heater-off temperature is set to a second temperature higher than the first temperature;
The image forming apparatus according to claim 1, characterized in that: a feeding section that feeds a recording material to the image forming section;
The control unit controls the productivity by changing the feeding interval of the recording material fed by the feeding unit,
A recording material feeding interval when the temperature increase rate is the first increase rate is a first feeding interval, and a recording material feeding interval when the temperature increase rate is the second increase rate. the interval is a second feeding interval,
the first feeding interval is wider than the second feeding interval;
The image forming apparatus according to claim 2, characterized in that: The control unit includes:
When the temperature increase rate is the first increase rate and the temperature detected by the detection unit is higher than the first threshold temperature, the heater-off temperature is set to the first temperature, and the recording material Let the feeding interval be the first feeding interval,
When the temperature increase rate is the second increase rate and the detected temperature is higher than a second threshold temperature that is higher than the first threshold temperature, the heater-off temperature is set to the second temperature. setting, and setting the recording material feeding interval to the second feeding interval;
The image forming apparatus according to claim 3 , characterized in that: When the controller sets the heater-off temperature to the first temperature while executing an image forming job for forming images on a predetermined number of recording materials, the heater-off temperature remains at the first temperature until the last recording material of the image forming job finishes passing through the nip portion;
The image forming apparatus according to claim 3 or 4 , characterized in that: a second detection unit that detects the temperature of the heater in the minimum passage area;
The image forming apparatus according to any one of claims 1 to 5, characterized in that: an image forming section that forms a toner image on a recording material ;
A rotatable endless belt,
a nip portion forming member that forms a nip portion between the endless belt and the recording material on which the toner image has been formed in the image forming section, which heats the toner image on the recording material while nipping and conveying the recording material;
a heater that is arranged along a longitudinal direction of the endless belt that intersects with a rotational direction of the endless belt, and that generates heat when energized to heat the endless belt;
a detection unit that detects the temperature of the endless belt in a region outside the longitudinal direction of the minimum passing region through which a recording material having the smallest length in the longitudinal direction among the recording materials that can pass through the nip portion;
a control unit that controls productivity, which is the number of recording materials passing through the nip portion per unit time ;
The control unit includes:
When the temperature increase rate per unit time of the detection unit is a first increase rate , the productivity is the first productivity, and the temperature increase rate is a second increase rate lower than the first increase rate. If the productivity is a second productivity ,
the first productivity is smaller than the second productivity ,
When the control unit sets the productivity to the first productivity while executing an image forming job for forming images on a predetermined number of recording materials, the control unit may set the productivity to the first productivity regardless of the change in the temperature increase rate. , the productivity is set to be equal to or lower than the first productivity until the last recording material of the image forming job finishes passing through the nip portion;
An image forming apparatus characterized by: When the rate of temperature increase per unit time of the detection unit is the first rate of increase, a heater-off temperature at which electricity is turned off to the heater is set to the first temperature, and the rate of temperature increase is set to the first temperature. If the second rate of increase is lower than the first rate of increase, the heater-off temperature is set to a second temperature higher than the first temperature;
The image forming apparatus according to claim 7, characterized in that: a feeding section that feeds a recording material to the image forming section;
The control unit controls the productivity by changing the feeding interval of the recording material fed by the feeding unit,
A recording material feeding interval when the temperature increase rate is the first increase rate is a first feeding interval, and a recording material feeding interval when the temperature increase rate is the second increase rate. the interval is a second feeding interval,
the first feeding interval is wider than the second feeding interval;
The image forming apparatus according to claim 8. The control unit includes:
When the temperature increase rate is the first increase rate and the temperature detected by the detection unit is higher than the first threshold temperature, the heater-off temperature is set to the first temperature, and the recording material Let the feeding interval be the first feeding interval,
When the temperature increase rate is the second increase rate and the detected temperature is higher than a second threshold temperature that is higher than the first threshold temperature, the heater-off temperature is set to the second temperature. setting, and setting the recording material feeding interval to the second feeding interval;
The image forming apparatus according to claim 9, characterized in that: When the controller sets the heater-off temperature to the first temperature while executing an image forming job for forming images on a predetermined number of recording materials, the heater-off temperature remains at the first temperature until the last recording material of the image forming job finishes passing through the nip portion;
The image forming apparatus according to claim 9 or 10, characterized in that: a second detection unit that detects the temperature of the heater in the minimum passage area;
The image forming apparatus according to any one of claims 7 to 11.

Images