JP2008003305A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a fixing device from getting unusable because the thermo-protector of a heating member acts by user's misoperation. <P>SOLUTION: At least a part of a detecting member for detecting the presence or absence of recording material and at least a part of a thermosensitive member for interrupting power supply to a heat generating member in abnormal temperature rise are at the same position in a width direction orthogonal to the moving direction of the recording material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention forms an image on a recording material by an image forming process such as an electrophotographic process, an electrostatic recording process, and a magnetic recording process, and relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a word processor. . In particular, the present invention relates to an image forming apparatus having a fixing device that heat-fixes an unfixed image on a recording material.

  Conventionally, in an image forming apparatus, an unfixed image (toner image) is formed on a recording material such as paper by an electrophotographic process or the like by a transfer method or a direct method, and the unfixed image is formed on the recording material by a fixing unit. The image is fixed.

  The fixing unit sandwiches the recording material at the fixing nip with a heating roller including a halogen lamp that is a heating element for heating and controlled in a predetermined temperature range, and a pressure roller having an elastic layer. A heat roller system for carrying and heating and pressure fixing is widely used.

  A film heating method has been proposed and put into practical use from the viewpoint of energy saving and quick start. The film heating method includes a heating unit that includes a ceramic heater that is a heating body and includes a heat-resistant film that is conveyed while being pressed against the heating body, and a pressure member that causes the recording material to adhere to the heating unit. The film heating method is to fix the unfixed image formed on the recording material onto the recording material by applying the heat of the heating body to the recording material via the heat resistant film.

  In the above-described two typical fixing methods, at least one temperature detecting means is disposed in proximity to or in contact with the heating member in order to control the temperature of the heating member such as a heating roller and a heating body. Based on the output from the temperature detection means, the energization control, i.e. temperature control, is performed on the heating member (heating element, heating body) by the control means of the image forming apparatus.

  In the case of a copier or printer, a recording material presence / absence sensor (hereinafter referred to as a paper sensor) including a photo sensor and a sensor flag is appropriately disposed in the conveyance path of the image forming apparatus. Edge is detected.

  The temperature control for the heating member can be performed by changing the control temperature depending on whether the recording material is in the fixing nip or not, changing the control temperature for a certain time according to the timing when the recording material enters the fixing nip, The control temperature is changed depending on the type.

  In addition, due to the failure of triacs, thermistors, relays, etc., which are components of the energization control circuit, or the runaway of the CPU, the fixing unit is continuously over-energized to the heating member, causing the heating member to rise abnormally. A thermo protector is provided to prevent this.

  The thermo protector is a thermo switch, thermal fuse, etc., which is connected in series to the AC line for energization, and is placed close to or in contact with the heating member, forcibly shutting off the energization when an abnormal temperature rise occurs It is a safety measure.

  If the image forming apparatus supports A3 size paper, various sizes other than A3 are generally used, for example, B4, A4 horizontal, A4 vertical, A5 horizontal, A5 vertical, B5 horizontal, B5 vertical, Western Recording materials of various sizes such as envelopes and postcards can be passed. Therefore, a plurality of paper sensors are arranged along the transport direction at a position where the minimum width of the recording material that guarantees the passage of paper passes through in the width direction of the recording material (direction orthogonal to the recording material transport direction). Will be.

  Further, the temperature detection means of the heating member is also disposed in an area where the recording material with the minimum width passes through in order to detect the temperature of the paper passing portion of the heating member.

  In addition, the thermo protector is also arranged in the region through which the recording material passes in the width direction so that it operates only in a state where the temperature control circuit runs out of control and cannot be controlled normally.

Japanese Patent Application Laid-Open No. 2005-228561 describes that three elements of a paper sensor, a temperature detection unit, and a thermo protector are provided in an area in the width direction of a recording material having a minimum width guaranteed by the image forming apparatus to pass paper.
JP 2002-296965 A

  However, in recent years, image forming apparatuses such as copiers and printers have been increased in speed, color, image quality, and cost. Moreover, diversification of device users and device usage methods is also progressing.

  As the speed increases as described above, the heating temperature for fixing unfixed images rises, the difference between the thermoprotector operating temperature and the fixing temperature decreases, and temperature control with better response and less variation is required. It is said. As diversification progresses, image forming apparatuses are used in various usage forms. However, the thermo protector operates only when the temperature control circuit runs out of control and cannot be controlled normally. A configuration that does not fall into an unusable state is required.

  The apparatus shown in the above background art is intended to prevent the thermoprotector from operating when a narrow recording material is passed, and the thermoprotector is disposed between the paper sensor and the temperature detecting means. It is.

  By the way, in this type of apparatus, the user can perform the following cases.

  (1) When using a recording material having a size smaller than the guaranteed paper passing size.

(2) In an apparatus having a paper feed port provided with a width restricting plate that can arbitrarily set the width restriction according to the size of the recording material, the recording material is opened in a state where the width restricting plate is opened wider than the recording material width size. When passing through one side. (That is, when the recording material passes through a position that deviates from the position in the width direction that should normally pass.)
(3) When using an irregularly shaped recording material.

  In this way, although the recording material is detected by the paper sensor, the following inconvenience may occur when the recording material does not substantially pass through the thermoprotector.

  During continuous paper feeding, the temperature of the thermoprotector portion of the heating member and the pressure member in the opposite portion when the recording material passes through the thermoprotector region and when the recording material does not pass through are compared. Then, when the recording material passes, the temperature of the thermo protector portion of the heating member and the pressure member of the opposite portion is low, and when the recording material does not pass, the temperature of the thermo protector portion of the heating member and the pressure member of the opposite portion is Get higher.

  If it stops suddenly in this state, if the recording material passes through the thermo-protector area, heat is transferred to the pressurizing part side, but if it does not pass, heat is hardly transmitted and the thermo-protector may malfunction. There is.

  In particular, when a paper sensor detects a recording material, and there is a temperature detecting means in the paper passing area, and there is no thermo-protector in the paper passing area, when a different shape recording material is passed, the temperature detecting means section Since the heat is taken away, the heating member further generates heat. However, since the heat of the thermo protector unit is not deprived, the thermo protector operates erroneously as a result.

  In order to solve the above-described problems, the present invention includes a fixing unit that includes a heat generating member that generates heat when energized, and fixes an unfixed image on the recording material. In an image forming apparatus having a recording material detecting member for detecting the heat and a heat sensitive member for interrupting energization to the heat generating member when the fixing unit is abnormally heated, the width of the recording material orthogonal to the moving direction of the recording material With respect to the direction, at least a part of the recording material detection member and at least a part of the heat sensitive member are at the same position.

  According to the present invention, it is possible to prevent the heat-sensitive member from operating due to an erroneous operation by the user and making the fixing unit unusable.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 5 is a diagram showing an image forming apparatus according to the first embodiment of the present invention. First, a schematic configuration will be described along the flow of the recording material S.

  The apparatus body E forms an image by an electrophotographic method. The sheet material S, which is a recording material, is conveyed to the image forming unit by the sheet feeding and conveying unit, and the toner image is transferred onto the sheet material S there. Thereafter, the sheet material S is conveyed to a fixing unit, and an unfixed toner image is fixed on the sheet material S. Thereafter, the sheet material S is discharged to a discharge unit.

  Specifically, a cassette 111 for loading and storing the sheet material S is loaded in the lower part of the apparatus. The sheet material S stacked and stored in the cassette 111 in the sheet material feeding unit 1 is sequentially fed out from the uppermost sheet material by a sheet feeding roller 112 that rotates counterclockwise, and is conveyed by a pair of conveying rollers 113 and 114. The image is sent to the image forming unit 2.

  In the vicinity of the image forming unit 2, a sensor lever 115 and a photo interrupter 116, which are recording material detection members (sheet material detection members) for detecting the passage of the sheet material S, are provided. That is, the recording material detection member detects the presence or absence of the recording material on the upstream side of the fixing unit described later with respect to the moving direction of the recording material.

  The photo interrupter 116 is a light transmission type, and the light shielding portion of the sensor lever 115 is positioned between the light emitting side and the light receiving side, and the light shielding portion is retracted by rotating the sensor lever 115 and the sheet material S is retracted. Detect. Further, since the sensor lever 115 is biased by an elastic member (not shown), the sensor lever 115 returns to the initial position when the sheet material S finishes passing.

  After the passage of the sheet material S is detected, a laser beam corresponding to the image information is irradiated onto the photoconductor 151 rotating in the clockwise direction by the laser scanner 121 after a predetermined time has elapsed. An electrostatic latent image is formed. This electrostatic latent image is developed as a toner image with toner at a developing portion in the process cartridge P.

  The sheet material S on which the toner image is transferred by the transfer roller 124 in the image forming unit 2 carries the toner image (unfixed image) and is sent to the fixing device 3 as a fixing unit. The sheet material S that has passed through the fixing device 3 and has been subjected to the fixing process is conveyed by a pair of discharge conveyance rollers 133 and discharged to a discharge unit 134.

  Note that reference numeral 4 in FIG. 5 denotes an electrical component having a power supply unit of the apparatus and a control board for controlling the apparatus.

  Next, the front and back double-sided printing of the sheet material S will be described. When recording is performed on both sides of the sheet material S, the sheet material S that has passed through the fixing device 3 and has an image recorded on the front side is switched back by a pair of discharge paper transport rollers 133 and a transport roller 131 that are driven in reverse. The Then, the sheet material S is conveyed again to the image forming unit 2 by the conveying roller pair 141 and 142, image recording is performed on the back side of the sheet material S, and then discharged to the discharge unit 134.

  When paper is fed from the manual paper feed unit 5, the manual feed tray 151 is opened and the sheet material S is stacked on the manual feed tray 151. The sheet material S stacked on the manual sheet feeding tray 151 is sequentially fed out from the uppermost sheet material S by the manual sheet feeding roller 152 that rotates in the clockwise direction, and is sent to the image forming unit 2 by the conveying roller pair 114. After being sent to the image forming unit 2, it is omitted because it is the same as described above.

  FIG. 6 is a schematic sectional view of the fixing device. The fixing device 3 in this embodiment will be described in more detail with reference to FIG.

  Reference numeral 34 denotes a heater (heating member) which is a heat generating member. The heater 34 is a ceramic substrate made of alumina or aluminum nitride. The energization heating element is connected to an AC energization control circuit. That is, the fixing device 3 as fixing means includes a heater 34 as a heat generating member that generates heat when energized, and fixes an unfixed image on the recording material.

  A thermistor 35, which is a temperature detection member that detects the temperature of the heater 34, is attached on the heater 34.

  A thermo protector 36 such as a thermal fuse or a thermo switch is provided on the heater 34 (see FIG. 1), which is a heat sensitive member that cuts off the energization to the heater when the temperature of the fixing device is abnormally increased. Connected to an AC power source in series with the body.

  Reference numeral 31 denotes a fixing film in which a fluororesin is formed on a cylindrical polyimide resin or stainless steel. A film guide 32 is formed in the fixing film 31 from a heat-resistant resin such as PPS, PEEK, or a liquid crystal polymer and supports the heater 34. And the reinforcement board 33 is equipped internally. These fixing film 31, film guide 32, reinforcing plate 33, heater 34, and the like constitute a heater unit.

  The pressure roller 38 has a structure in which an elastic layer made of silicon rubber, fluorine rubber or the like is formed on a shaft made of aluminum, iron or the like.

  The heater unit and the pressure roller 38 are pressed by a pressing means (not shown) to form a fixing nip portion, and the sheet material S passes through the fixing nip portion, whereby an unfixed image on the sheet material S is formed. Is fixed on the sheet material S.

  Next, the relationship between the sensor position and the paper passing area of this embodiment will be described.

  FIG. 1 is a view of an image forming apparatus according to the present embodiment as viewed from above. In FIG. 1, a sheet passing region of the sheet material S during normal passing from the manual sheet feeding unit, and the width direction of each sensor (sheet material detecting member, temperature detecting member, thermo protector) (direction orthogonal to the recording material moving direction). ) It is a diagram schematically showing the positional relationship. FIG. 2 is a diagram schematically showing the relationship between the width direction position, the heater, and the pressure roller temperature.

  First, when the sheet is fed from the manual sheet feeding unit 5, the manual tray 151 is opened, and the width regulating plate 154 is moved and matched according to the width size of the sheet material S. The width restricting plate 154 is moved to the equidistant position from the central sheet passing reference by a synchronous movement mechanism (not shown). In the image forming apparatus according to the present embodiment, the sheet passing is center passing with reference to a sheet passing position (center passing reference) indicated by a one-dot chain line, and the chain line indicates both ends of the sheet material S having the minimum width dimension that guarantees the sheet passing. In the passing position, the area between the chain lines is the minimum area for guaranteeing paper passage.

  In the drawing, the thermistor 35 is arranged on the right side of the center sheet passing reference and on the center sheet passing reference side (left side) of the right end portion position of the minimum sheet passing guarantee region. Further, the sensor lever 115 is arranged on the left side of the center sheet passing reference and on the center sheet passing reference side (right side) from the left end portion position of the minimum sheet passing guarantee area. The thermo switch 36 as a thermo protector is disposed at the same position in the width direction, that is, at a position overlapping the sensor lever 115 when viewed in the moving direction of the recording material. In the present embodiment, as shown in FIG. 1, the center of the sensor lever 115 and the center of the thermo switch 36 are disposed at the same position in the width direction.

  As shown in FIG. 2A, in the image forming apparatus based on the central sheet passing according to the present embodiment, the width size is the sheet material S with the minimum sheet passing guarantee area, and the sheet material S is properly arranged in the sheet feeding unit. If so, the sheet material S passes through the minimum area for guaranteeing paper passage indicated by the chain line. In this case, the sheet material S is detected by the sensor lever 115, the temperature of the heater 34 in the sheet material passage region is detected by the thermistor 35, and the thermo switch 36 is in contact with the heater 34 in the sheet material passage region.

  At this time, as described above, the thermo switch 36 is disposed at the same position as the sensor lever 115 in the width direction. For this reason, when the sheet material S is detected by the sensor lever 115, the sheet material always passes through the portion of the heater 34 corresponding to the thermo switch 36, whereby the heat of the heater 34 is taken away by the sheet material S. Is called. The same applies to the heat on the surface of the pressure roller 38. Therefore, in this case, the thermo switch 36 does not operate erroneously.

  In the present embodiment, it is experimentally required that the heater temperature does not rapidly increase in the area A of about 5 to 10 mm from the end of the sheet material passing area to the outside of the sheet passing area. Therefore, as shown in FIG. 2B, if the thermo switch 36 and the sensor lever 115 are at least partially overlapped when viewed in the recording material moving direction, the sheet material S passes through the thermo switch 36. The temperature will be the same as that of the area in which it is, and the thermoswitch will not operate accidentally.

  FIG. 3 illustrates an image forming apparatus according to the present exemplary embodiment in which the user moves the sheet material in the sheet feeding direction in a state where the width regulating plate 154 on the manual feed tray 151 is opened larger than the width size of the sheet material to be used. It is a figure which shows the case where it approaches to the left side. At this time, the right end portion of the sheet material is a position that passes over the sensor lever 115. FIG. 4A is a diagram showing the temperature in the width direction of the heater 34 and the pressure roller 38 and the positional relationship in the sensor width direction when paper is passed in the state of FIG. .

  In this case, the thermo switch 36 is disposed at the same position as the sensor lever 115 in the width direction. For this reason, when the sheet material S is detected by the sensor lever 115, the sheet material always passes through the portion of the heater 34 corresponding to the thermo switch 36, whereby the heat of the heater 34 is taken away by the sheet material S. Is called. The same applies to the heat on the surface of the pressure roller 38. Therefore, in this case, the thermo switch 36 does not operate erroneously.

  In the present embodiment, it is experimentally required that the heater temperature does not rapidly increase in the area A of about 5 to 10 mm from the end of the sheet material passing area to the outside of the sheet passing area. Therefore, as shown in FIG. 4B, if the thermo switch 36 and the sensor lever 115 are at least partially overlapped when viewed in the recording material moving direction, the sheet material S passes through the thermo switch 36. The temperature will be the same as that of the area, and the thermoswitch will not operate by mistake.

  Further, even when an overshoot occurs when the heater temperature is controlled by the thermistor 35 during paper feeding, or when an overshoot occurs when the apparatus suddenly stops, the portion of the heater 34 corresponding to the thermo switch 36 has a relatively high temperature. Since it is low, the thermo switch 36 does not operate.

  In addition, since the temperature and time margin until the thermo switch 36 is operated are increased, the necessity for strict response of the thermistor is reduced, and the cost can be reduced.

  In addition, since the responsiveness of the thermo switch 36 can be further increased, safety is improved.

  Furthermore, even when an irregularly shaped sheet material is used, the thermo switch 36 does not operate because the thermo switch 36 is disposed in the region where the sheet material exists.

  Further, in the above configuration, the thermo switch 36 does not necessarily cause a problem in increasing the speed because the sheet material always passes or is equivalent thereto.

  When the sensor 115 is not passed, the thermoswitch 36 is not passed. In this case, jamming occurs, jamming is performed, the sheet material is placed at a predetermined position, and the paper is passed again. The thermo switch 36 does not operate.

  As described above, in the present embodiment, at least a part of the thermo switch and at least a part of the sensor lever are at the same position in the width direction, that is, the thermo switch and the sensor lever are at least one of them when viewed in the recording material moving direction. The part is in an overlapping position. Thereby, this embodiment can prevent the malfunction of a thermo switch.

  Next, a second embodiment of the present invention will be described. The basic device configuration is the same as the device configuration of the first embodiment shown in FIGS. 5 and 6, and the description of the same configuration and function as those of the first embodiment will be omitted, and different parts will be described.

  In the present embodiment, the present invention is applied to an image forming apparatus in which the sheet passing reference position of the sheet material S is set on one side in the width direction.

  FIG. 7 is a view of the image forming apparatus according to the present embodiment as viewed from above. The sheet passing area of the sheet material S and the positional relationship in the width direction of each sensor during normal sheet feeding from the manual sheet feeding unit are schematically illustrated. FIG.

  First, when the sheet is fed from the manual sheet feeding unit 5, the manual tray 151 is opened, and the width regulating plate 254 is adjusted according to the width size of the sheet material S. The sheet passing reference is a left-side one-side sheet passing reference (reference plate 255) as viewed in the moving direction of the recording material. As the width restriction, only the right width restriction plate 254 is movable, and the distance from the reference plate 255 which is the left reference portion can be arbitrarily changed.

  In this image forming apparatus, the sheet passing is a one-sided sheet passing reference based on the sheet passing position indicated by the one-dot chain line, and the chain line indicates the right end passing position of the sheet material S having the minimum width dimension that is guaranteed to pass. The thermistor 35 is arranged on the one-side paper passing reference side. In addition, the sensor lever 115 that detects the passage of the sheet material S is disposed on the one-side sheet-feeding reference side with respect to the right-side end position of the minimum sheet-passing guaranteed area. The thermal fuse 236 that is a thermo protector is disposed at the same position as the sensor lever 115 in the width direction, that is, at a position overlapping the sensor lever 115 when viewed in the moving direction of the recording material. In FIG. 7, the sensor lever 115 and the thermal fuse 236 are disposed at the same position in the width direction.

  As shown in FIG. 7, in the image forming apparatus based on one-side paper passing according to the present embodiment, if the width size is the sheet material S in the minimum sheet passing guaranteed area and the sheet material S is properly arranged in the paper feeding unit. The sheet material S passes through the minimum sheet passing guaranteed area indicated by the chain line. In this case, the sheet material S is detected by the sensor lever 115, the temperature of the heater 34 in the sheet material passing region is detected by the thermistor 35, and the temperature fuse 236 is located at the heater 34 portion in the sheet material passing region.

  At this time, as described above, the thermal fuse 236 is disposed at the same position as the sensor lever 115 in the width direction. For this reason, when the sheet material S is detected by the sensor lever 115, the sheet material S always passes through the portion of the heater 34 corresponding to the thermal fuse 236, so that the heat of the heater 34 is transferred to the sheet material S. Stolen. The heat on the surface of the pressure roller 38 is the same. Therefore, in this case, the thermo switch 36 does not operate erroneously.

  Further, in this configuration, it is experimentally required that the heater temperature does not increase rapidly in an area of about 5 to 10 mm from the end of the sheet material passing area to the outside of the sheet passing area. Therefore, as in the first embodiment, if the temperature fuse 236 and the sensor lever 115 are at least partially overlapped when viewed in the recording material moving direction, the sheet material S passes through the temperature fuse 236. The temperature will be the same as that of the area, and it will not be cut accidentally.

  FIG. 8 illustrates an image forming apparatus according to the present exemplary embodiment in which the user moves the sheet material in the paper feeding direction in a state where the width regulating plate 254 on the manual feed tray 151 is opened larger than the width size of the sheet material to be used. It is a figure which shows the case where it approaches to the right side (non-reference | standard side). At this time, the left end portion of the sheet material is a position that passes over the sensor lever 115. FIG. 9A is a diagram showing the temperature in the width direction of the heater 34 and the pressure roller 38 and the positional relationship in the width direction of each sensor when paper is passed in the state of FIG. .

  In this case, the thermal fuse 236 is disposed at the same position as the sensor lever 115 in the width direction. For this reason, when the sheet material S is detected by the sensor lever 115, the sheet material always passes through the portion of the heater 34 corresponding to the thermal fuse 236, so that the heat of the heater 34 is taken away by the sheet material S. Is called. The same applies to the heat on the surface of the pressure roller 38. Therefore, in this case, the thermal fuse 236 does not operate erroneously.

  In this configuration, it is experimentally required that the heater temperature does not increase rapidly in the region A of about 5 to 10 mm from the end of the sheet material passing region to the outside of the sheet passing region. Therefore, as shown in FIG. 9B, if the temperature fuse 236 and the sensor lever 115 are at least partially overlapped when viewed in the recording material moving direction, the sheet material S passes through the temperature fuse 236. The temperature will be the same as that of the area in which it is located, and the thermal fuse will not be accidentally blown.

  Further, even when an overshoot occurs when the heater temperature is controlled by the thermistor 35 during paper feeding or an overshoot occurs when the apparatus suddenly stops, the portion of the heater 34 corresponding to the thermal fuse 236 has a relatively high temperature. Since it is low, the thermal fuse 236 will not operate.

  Further, since the temperature and time margin until the operation of the thermal fuse 236 is increased, the necessity for strict response of the thermistor is reduced, and the cost can be reduced.

  In addition, the responsiveness of the thermal fuse 236 can be further accelerated, leading to an improvement in safety.

  Furthermore, even when an irregularly shaped sheet material is used, the thermal fuse 236 is not blown because the thermal fuse 236 is disposed in the region where the sheet material exists.

  Further, in the above configuration, since the sheet material always passes through or is equivalent to the portion of the thermal fuse 236, there is no problem in increasing the speed.

  When the sensor 115 does not pass, the thermal fuse 236 does not pass. In this case, jamming occurs, jamming is performed, the sheet material is placed at a predetermined position, and the paper is passed again. The thermal fuse 236 does not blow.

  Thus, in the present embodiment, at least a part of the thermal fuse and at least a part of the sensor lever are at the same position in the width direction, that is, the thermal fuse and the sensor lever are at least one of them when viewed in the recording material moving direction. The part is in an overlapping position. Thereby, this embodiment can prevent malfunction of a thermal fuse.

  In the above-described embodiment, the laser beam printer is exemplified as the electrophotographic image forming apparatus. However, any apparatus that forms an image on a recording material such as recording paper, an OHP sheet, or cloth using an electrophotographic image forming process. The present invention is applicable.

  Further, although the film heating method is exemplified as the fixing method, it is apparent that the present invention can be applied even if a fixing method such as a heat roller method or an external heating method is used.

  In addition, the paper detection sensor is exemplified by a type using a sensor lever and a transmissive photo interrupter. However, a method using a light transmissive type or a light reflective type sensor that detects the presence / absence of a sheet material without using the sensor lever, or mechanical It is clear that the present invention can be applied even if a switch is used.

The figure which shows the relationship between the width direction position of a sheet | seat material detection member, a temperature detection member, and a thermo protector, and a sheet | seat material paper passing area | region in a center paper passing reference | standard. (A) is a figure which shows the relationship between the sheet material passing area | region and the width direction position of three sensors, and a heater and pressure roller temperature, (b) is a figure which shows the heater and pressure roller temperature of a thermo protector vicinity. The figure which shows the relationship between the width direction position of three sensors at the time of passing a sheet material from an appropriate paper passing position, and a sheet material passing area. (A) is a diagram showing the relationship between the sheet material passing area and the width direction positions of the three sensors and the heater and pressure roller temperature when the sheet material is shifted from an appropriate sheet passing position, and (b). ) Is a diagram showing the temperature of the heater and pressure roller in the vicinity of the thermo protector. 1 is a diagram illustrating an image forming apparatus according to an embodiment of the present invention. The figure which shows the fixing device of the apparatus of FIG. The figure which shows the relationship between the width direction position of a sheet material detection member, a temperature detection member, and a thermo protector, and a sheet material paper passing area | region in the one-side paper passing reference | standard. The figure which shows the relationship between the width direction position of three sensors at the time of passing a sheet material from an appropriate paper passing position, and a sheet material passing area. (A) is a diagram showing the relationship between the sheet material passing area and the width direction positions of the three sensors, and the heater and pressure roller temperature when the sheet material is shifted from an appropriate sheet passing position, and (b). ) Is a diagram showing the temperature of the heater and pressure roller near the thermoprotector.

Explanation of symbols

34 Heater 35 Thermistor 36 Thermo switch 115 Sensor lever 116 Photo interrupter 151 Manual feed tray 154 Width regulating plate 236 Thermal fuse 254 Width regulating plate 255 Reference plate

Claims (2)

A heat generating member that generates heat when energized, a fixing unit that fixes an unfixed image on the recording material, a recording material detection member that detects the presence or absence of the recording material upstream of the fixing unit with respect to the moving direction of the recording material, and A heat-sensitive member that cuts off power to the heat-generating member when the fixing unit is abnormally heated;
An image forming apparatus, wherein at least a part of the recording material detection member and at least a part of the thermosensitive member are in the same position with respect to the width direction of the recording material orthogonal to the moving direction of the recording material.   The recording material detection member and the heat sensitive member are provided in a region through which a recording material of a minimum size that is guaranteed to move in the apparatus with respect to the width direction of the recording material perpendicular to the moving direction of the recording material. The image forming apparatus according to claim 1.

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