JP2008065032A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing a failure of a fixing device from occurring without performing paper feeding operation even if paper is one-sidedly fed to a side where a second temperature detection means exists. <P>SOLUTION: The image forming apparatus in which a sheet material P is fed with the center as reference is configured by; arranging a paper-feed section thermistor 65 which detects the temperature of a heater 64, and a thermo-switch 67 which is a safety switch within a minimum width dimension 2L<SB>1</SB>at the position where the paper feed is assured in the longitudinal direction of the heater 64; arranging a paper detection lever 103 which operates a sheet material presence or absence sensor 48 on a side outer than the minimum width dimension 2L<SB>1</SB>; and arranging an end thermistor 66 which detects the end temperature rise of the heater 64 in a position L<SB>4</SB>on the side opposite to the paper detection lever 103 with respect to a paper-feed position standard C<SB>0</SB>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system, and relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

  FIG. 8 is a sectional view of the overall configuration of the main body of a laser printer that is a color image forming apparatus.

  The sheets P stacked on the middle plate 4 of the sheet feeding cassette 7 as sheet stacking means are separated one by one by the sheet feeding roller 41 and pass through the intermediate conveying roller pair 47 and the registration roller pair 44, and the secondary transfer section. It is fed to T2.

  In the color image forming process, an image is formed as follows. First, an image carrier having a plurality of developing devices 2 (2Y, 2M, 2C, 2Bk) corresponding to a plurality of color components by laser exposure irradiated from a plurality of exposure devices 1 (1Y, 1M, 1C, 1Bk). A latent image is formed on 21 (21Y, 21M, 21C, 21Bk). The latent image is developed on the image carrier 21 (21Y, 21M, 21C, 21Bk) (hereinafter simply referred to as the image carrier 21) by developing means, ie, toner, by the developing means included in the developing device 2. Developed as a component image. Toner images corresponding to a plurality of color component images formed on each color image carrier 21 are primary transfer portions T1 (T1Y, T1) sandwiched between the image carrier 21 and primary transfer rollers 34 (34Y, 34M, 34C, 34Bk). T1M, T1C, T1Bk) are sequentially superimposed and transferred. Then, a target full-color image is formed on the intermediate transfer belt 35. The full-color image on the intermediate transfer belt 35 is collectively transferred to a sheet P as a recording material at the secondary transfer portion T2 constituted by the secondary transfer roller 51 and the secondary transfer counter roller 32 to obtain an unfixed full-color image.

  The sheet P to which the unfixed image has been transferred is introduced into the fixing device 50 and fixed by heating. Thereafter, the sheet P is discharged to a discharge stacking unit 56 by a plurality of discharge roller pairs 53, 54 and 55.

  Conventionally, fixing of a toner image formed on a sheet in an electrophotographic apparatus uses a halogen lamp or the like as a heating element, and a heating roller and a pressure roller 62 that are temperature controlled within a predetermined temperature range. It is carried out by a heat roller method for nipping and transporting. In some cases, the film heating and fixing method shown in FIG. The fixing device of the film heat fixing system is a heater unit composed of a fixedly supported heating body (ceramic heater) and a heat-resistant film that is conveyed while being pressed against the heating body, and a sheet that is in close contact with the heater unit. A pressure member. Then, the heat of the heating body is applied through the fixing film to fix the toner image formed on the sheet.

  In the two typical fixing methods described above, in order to control the temperature of the heating member, at least one temperature detecting means for the heating body is disposed in contact with the heating body, and the output of the image forming apparatus is based on the output. Temperature control is performed on the heating element by the control means.

  The temperature control for the heating body is performed as follows. In other words, a sheet presence / absence sensor (hereinafter referred to as a paper sensor) composed of a photo sensor and a flapper is disposed in the conveyance path of the image forming apparatus to detect the leading and trailing edge positions of the sheet, and the sheet enters the fixing nip. The control temperature is changed depending on whether it is present or not. Alternatively, the control temperature is changed for a certain time according to the timing at which the sheet enters the fixing nip, or a paper jam warning is issued by detecting that the sheet remains in the fixing nip or the like in the conveyance path.

  Also, the fixing device has a thermoswitch, a thermal fuse, etc. that forcibly cuts off the power supply when there is a problem of abnormal heating of the heating element due to failure of thermistors, relays, etc. that are components of the power supply control circuit. The safety device is arranged close to or in contact with the heating element.

  For example, Patent Document 1 describes that two temperature detection elements are provided to perform temperature control of a fixing device, cooling operation of a non-sheet passing portion, and the like.

  Here, if the image forming apparatus is an apparatus that supports A3 size paper, in addition to the A3 size, B4, A4 horizontal, vertical, A5 horizontal, vertical, B5 horizontal, vertical, western envelope, postcard, etc. In general, it is possible to pass sheets of various sizes. In view of this, the paper sensor for detecting the leading and trailing edges of the sheet described above is located along the paper conveyance direction at a position where the paper with the minimum longitudinal width that guarantees the passage of paper passes through in the longitudinal position of the image forming apparatus. Generally, a plurality of them are arranged.

  The heating body temperature detecting means is disposed in an area where the paper having the smallest longitudinal width passes through the paper passing portion temperature detecting means for detecting the temperature of the paper passing portion of the heating body. In addition, when the narrow sheet is passed, the end temperature detecting means for preventing the fixing device from malfunctioning due to abnormal temperature rise at the end of the heating element has a minimum longitudinal width at the longitudinal position. The paper is disposed outside the region through which the paper passes and within the region through which the paper with the maximum longitudinal width passes. Generally, the sheet passing portion temperature detecting means and the end portion temperature detecting means are arranged in this way. Further, the safety device is also generally arranged in a region where the paper passes in the longitudinal position so as to operate only when the temperature control circuit runs out of control and cannot be normally controlled.

In other words, the three elements of the leading and trailing edge detection sensors of the paper, the paper passing portion temperature sensor of the heating body, and the safety device pass through the sheet with the minimum longitudinal width in which each image forming apparatus guarantees the passing of the longitudinal position. Placed in the area. Further, it is general that the end temperature sensor of the heating body is disposed outside the sheet having the smallest longitudinal width that guarantees the passage of paper and in the region through which the sheet having the largest longitudinal width that guarantees the passage of paper passes.
JP 2002-258645A

  When the image forming apparatus is an apparatus having a so-called multi-tray paper feed capable of arbitrarily changing the width regulating plate according to the size of the recording medium, there are the following problems. That is, even if the paper size to be passed is within the guaranteed range, for example, when the envelope or postcard is opened with the width regulating plate of the tray wider than the appropriate width than the paper width, the paper is moved to one side and passed. The paper passes through a position that deviates from the longitudinal position that the paper should originally pass through. For this reason, there has been a problem that the temperature of the recording medium cannot be controlled without passing through the temperature detecting means.

  In particular, when paper is passed close to the side on which the temperature detecting means is disposed, the temperature detected by the temperature detecting means becomes the temperature of the paper passing area, and the temperature of the non-paper passing area that should be detected becomes undetectable. .

  As a result, there has been a problem that the fixing device suffers from a thermal failure, and the safety device (thermo switch) disposed inside the fixing device operates, and thereafter the fixing device becomes unusable. .

  The present invention has been made to solve the above-described problem, and even if the paper is about to be fed to one side to the side where the second temperature detection means is present, the paper feeding operation is not performed and a problem of the fixing device occurs. An object of the present invention is to provide an image forming apparatus capable of preventing the above-described problem.

  In order to solve the above problems, an image forming apparatus according to the present invention has the following configuration.

  (1) Image formation comprising: an image forming unit that forms an image based on a central reference of the recording medium; and a fixing unit that fixes the image on the recording medium formed by the image forming unit by applying pressure, heating and melting. In the apparatus, the first temperature detecting means and the second temperature detecting means for detecting the temperature of the fixing means, the paper feeding means for supplying the recording medium, and the recording medium loaded on the paper feeding means Recording medium detecting means for detecting the presence or absence of the recording medium, wherein the first temperature detecting means is a minimum width recording among the recording media that can be conveyed in a longitudinal direction perpendicular to the direction in which the recording medium is conveyed. At least one or more second temperature detection means is arranged in any one of the outside of the sheet passing area of the minimum width recording medium in the longitudinal direction, and the recording medium detection means , In the longitudinal direction, front Image forming apparatus characterized by being arranged at least 1 or more on the side opposite to the relative center reference second temperature sensing means.

  (2) In the image forming apparatus according to (1), the image forming apparatus includes a recording medium regulating unit that is arranged in parallel with the transported direction and regulates the recording medium from both sides. An image forming apparatus, wherein the image forming apparatus is interlocked while maintaining a relative position with the recording medium regulating unit opposite to the second temperature detecting unit with respect to a reference.

  (3) Image formation comprising: an image forming unit that forms an image on one side of the recording medium; and a fixing unit that fixes the image on the recording medium formed by the image forming unit by applying pressure, heat and melting. In the apparatus, the first temperature detecting means and the second temperature detecting means for detecting the temperature of the fixing means, the paper feeding means for supplying the recording medium, and the recording medium loaded on the paper feeding means Recording medium detecting means for detecting the presence or absence of the recording medium, fixed first recording medium regulating means for defining the position of the recording medium, and movable second recording medium regulation for defining the position of the recording medium And the first temperature detecting means is disposed in a pass area of the smallest width recording medium among the transportable recording media in a longitudinal direction perpendicular to the direction in which the recording medium is transported, and the second temperature detecting means The temperature detection means of the longitudinal And at least one or more of the second recording medium restricting means positioned at the time of the maximum width recording medium among the recording media that can be conveyed, wherein the recording medium detecting means An image forming apparatus, wherein the image forming apparatus is disposed in the vicinity of one recording medium regulating unit.

  According to the present invention, even if the recording medium is about to be fed one side to the side where the second temperature detecting means is present, it is possible to prevent the fixing device from failing without performing the sheet feeding operation.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to examples.

[Overall Description of Image Forming Apparatus]
First, the overall configuration of the color image forming apparatus will be outlined.

  FIG. 1 is a cross-sectional view of the overall configuration of a laser printer which is an embodiment of a color image forming apparatus.

  The color laser printer first comprises an image forming unit comprising process cartridges 2Y, 2M, 2C, and 2Bk having an image carrier 21 that rotates at a constant speed for each color of Y, M, C, and Bk. Further, the image forming unit includes an intermediate transfer body 35 that holds the color image developed and transferred in a multiple transfer manner and further performs secondary transfer onto the sheet P fed from the feeding unit. The sheet P on which the color image is transferred is conveyed to the fixing unit 50 to fix the color image on the sheet P, and is discharged onto a discharge tray 56 on the upper surface of the apparatus by a pair of discharge rollers 53, 54, and 55. The four-color process cartridges 2 are individually detachable from the printer body.

  Next, the configuration of each part of the image forming apparatus will be sequentially described in detail.

[Image carrier]
The image carrier (photosensitive drum) 21 (21Y, 21M, 21C, 21Bk) is integrally formed with the container 24 (24Y, 24M, 24C, 24Bk) of the developing device. The process cartridge 2 (2Y, 2M, 2C, 2Bk) is detachably supported with respect to the printer main body, and is configured to be easily replaceable in accordance with the life of the image carrier 21. An image carrier (photosensitive drum) 21 according to this embodiment is configured by coating an organic photoconductor layer on the outside of an aluminum cylinder, and is rotatably supported by a container 24 of the image carrier 21. Further, by transmitting a driving force of a driving motor (not shown) to one rear end in the figure, the image carrier 21 is rotated counterclockwise in the drawing in accordance with an image forming operation.

[Charging means]
The charging means 23 (23Y, 23M, 23C, 23Bk) uses a roller charging method and uniformly charges an applied voltage on the surface of the image carrier 21 by a charging roller.

[Exposure means]
The image carrier 21 is exposed from the scanner unit 1 (1Y, 1M, 1C, 1Bk). When the image signal is given to the laser diode, the laser diode irradiates the polygon mirror 13 (13Y, 13M, 13C, 13Bk) with the laser 12 (12Y, 12M, 12C, 12Bk) corresponding to the image signal. The polygon mirror 13 is rotated at a high speed by a scanner motor (not shown), and the surface of the image carrier 21 on which the laser 12 reflected by the polygon mirror 13 rotates at a constant speed is selectively exposed. An electrostatic latent image is formed on the surface.

[Development means]
The developing means is composed of four process cartridges 2 that can develop each color of yellow, magenta, cyan, and black in order to visualize the electrostatic latent image. Each of the four color process cartridges 2 faces the image carrier 21 and is arranged at a position where the developing device 22 (22Y, 22M, 22C, 22Bk) contacts the image carrier 21 while rotating. A visible image is formed with toner.

[Intermediate transfer member]
The intermediate transfer member 35 rotates in the clockwise direction in synchronization with the outer peripheral speed of the image carrier 21 in order to multiplex-transfer the toner images on the image carrier 21 visualized by the developing units 22 during the color image forming operation. The toner image formed on the image carrier 21 is transferred to a primary transfer portion T1 (T1Y, T1M, T1C, T1Bk) that is a contact point with a primary transfer roller 34 (34Y, 34M, 34C, 34Bk) to which a voltage is applied. Multiple transfer is performed on the intermediate transfer member 35. The intermediate transfer member 35 that has received the multiple transfer simultaneously multiplexes each color toner image on the intermediate transfer member 35 onto the sheet P by sandwiching and conveying the sheet P by the secondary transfer roller 51 to which a voltage is applied in the secondary transfer portion T2. Transcript.

  The intermediate transfer member (intermediate transfer belt) 35 according to this embodiment is formed of a seamless belt, and is stretched around three axes of a drive roller 31, a secondary transfer counter roller 32, and a tension roller 33. Then, both ends of the tension roller 33 are loaded with springs, and even if the circumferential length of the intermediate transfer belt 35 changes due to temperature and humidity in the main body or changes with time, the amount of change can be absorbed.

  The intermediate transfer member 35 is supported by the image forming apparatus main body with the driving roller 31 as a fulcrum, and the driving force of a driving motor (not shown) is transmitted to one end of the driving roller 31 at the rear of the drawing, thereby causing the intermediate transfer member 31 to perform an image forming operation. In response to the rotation, it is rotated clockwise in the figure.

[Paper Feeder]
The sheet feeding unit feeds the sheet P to the image forming unit. The sheet feeding unit mainly includes a cassette 7 storing a plurality of sheets P, a sheet feeding roller 41, a separation pad 42, a sheet feeding guide 43, and a registration roller pair 44. Composed. At the time of image formation, the paper feed roller 41 is driven and rotated according to the image forming operation to separate and feed the sheets P in the cassette 7 one by one, and is guided by the paper feed guide 43 and passes through the intermediate transport roller pair 47. To the registration roller 44. During the image forming operation, the registration roller 44 performs a non-rotating operation for stationaryly waiting the sheet P and a rotating operation for transporting the sheet P toward the intermediate transfer body 35 in a predetermined sequence, and a transfer process as a next process. The position image and the sheet P are aligned.

[Secondary transfer section]
The secondary transfer unit includes a secondary transfer roller 51. The secondary transfer roller 51 has a metal shaft wound with a medium-resistance foamed elastic body, is movable in the vertical direction in the figure, and has a drive. The secondary transfer roller 51 is pressed against the intermediate transfer body 35 with a predetermined pressure via the sheet P in accordance with the timing of transferring the color image to the sheet P. At the same time, a bias is applied to the secondary transfer roller 51 and the toner image on the intermediate transfer member 35 is secondarily transferred to the sheet P. Here, the intermediate transfer member 35 is driven, and the secondary transfer roller 51 rotates following the intermediate transfer member 35. For this reason, the sheet P sandwiched between the two is transported at a predetermined speed in the left direction in the figure at the same time as the transfer process is performed, and is transported toward the fixing device 50 as the next process by the transport belt 52.

[Fixing part]
FIG. 2 is a cross-sectional view of the fixing device.

  In FIG. 2, reference numeral 64 denotes a heating element obtained by printing an energization heating element made of a silver alloy on a substrate made of alumina. Reference numeral 69 denotes a thermistor which is a temperature detecting element, and reference numeral 70 denotes a fixing film in which a silicon rubber layer is formed on the outer peripheral surface of a cylindrical metal sleeve, and a fluororesin layer made of PTFE, PFA or the like is formed as a silicifying layer.

  Reference numeral 71 denotes a film guide made of a heat-resistant resin such as PPS or liquid crystal polymer, and reference numeral 72 denotes a reinforcing sheet metal for suppressing bending deformation that occurs when the film guide is pressed by the pressure roller 62. A heater unit is formed from the above members.

  63 is a heater unit in which an elastic layer made of silicon rubber, fluorine rubber or the like is formed on a cored bar made of aluminum, iron or the like, and is driven to rotate by a driving means (not shown). The heater unit 63 and the pressure roller 62 are pressurized by a pressing means (not shown) to form a fixing nip portion, and when the sheet P passes through the fixing nip portion, an unfixed toner image on the sheet is fixed. The

[Image forming operation]
Next, an operation when image formation is performed by the image forming apparatus configured as described above will be described (see FIG. 1).

  First, the sheet feeding roller 41 is rotated to separate one sheet P in the sheet feeding cassette 7 and conveyed to the registration roller 44.

  On the other hand, the image carrier 21 and the intermediate transfer member 35 rotate in the direction indicated by the arrow at a predetermined outer peripheral speed V (hereinafter referred to as process speed).

  The image carrier 21 whose surface is uniformly charged by the charging means 23 is exposed to the laser 12 to form an image.

1: Formation of Yellow Image A yellow image is formed on the image carrier 21Y by irradiating the scanner unit 1Y with a laser 12Y of a yellow image. Simultaneously with the formation of the latent image, the yellow developing unit 22Y is driven to apply a voltage having the same polarity as the charged polarity of the image carrier 21Y so that yellow toner adheres to the latent image on the image carrier 21Y. Develop. At the same time, the yellow toner image on the image carrier 21Y is primarily transferred onto the outer periphery of the intermediate transfer member 35 at the first transfer position T1Y downstream of the developing unit. At this time, primary transfer is performed by applying a voltage having a reverse characteristic to that of the yellow toner to the intermediate transfer member 35.

2: Formation of magenta image Next, the laser unit 12M starts laser 12M irradiation of the magenta image so that the leading edge of the yellow image on the outer periphery of the intermediate transfer member 35 coincides with the latent image on the image carrier 21M in the same manner as yellow. Then, the magenta toner image is developed. Then, the magenta toner image on the image carrier 21M is transferred onto the intermediate transfer member 35 at the first transfer position T1M.

3: Formation of Cyan Image Next, the laser unit 12C starts the irradiation of the cyan image with the laser 12C so that the yellow and magenta images on the outer periphery of the intermediate transfer member 35 coincide with each other, and the latent image on the image carrier 21C is started in the same manner as magenta. A cyan toner image is developed on the image. Then, the cyan toner image on the image carrier 21C is transferred onto the intermediate transfer member 35 so as to overlap the yellow and magenta toner images at the first transfer position T1C.

4: Formation of Black Image Next, the laser 12Bk irradiation of the black image is started by the scanner unit 1Bk so that the front ends of the yellow / magenta / cyan image on the outer periphery of the intermediate transfer member 35 coincide with each other on the image carrier 21Bk. A black toner image is developed on the latent image. Then, the black toner image on the image carrier 21Bk is further transferred onto the intermediate transfer member 35 at the first transfer position T1Bk.

  As described above, latent image formation and development and toner transfer to the intermediate transfer member 35 are performed in the order of yellow, magenta, cyan, and black at the primary transfer positions T1Y, T1M, T1C, and T1Bk. Then, a full color image composed of four types of toners of yellow, magenta, cyan, and black is formed on the surface of the intermediate transfer member 35.

  The sheet P that has been kept on standby by the registration roller 44 before the image leading edge of the intermediate transfer body 35 that has completed the primary transfer of the fourth color black toner and formed a full-color image reaches the secondary transfer portion T2, Start conveyance at the same timing. At the time of forming an image of each color on the four-color intermediate transfer member 35, the secondary transfer roller 51, which is in a waiting state below and is not in contact with the intermediate transfer member 35, is simultaneously moved upward by a cam (not shown). The sheet P is moved and brought into pressure contact with the secondary transfer portion T2 of the intermediate transfer member 35. At the same time, a full color image on the intermediate transfer member 35 is simultaneously transferred to the sheet P by applying a bias having a reverse characteristic to the toner to the secondary transfer roller 51. The sheet P that has passed through the secondary transfer portion T2 is peeled off from the intermediate transfer member 35, conveyed to the fixing portion 50, and fixed with toner, and then transferred onto the discharge tray 56 at the top of the main body via the discharge roller pairs 53, 54, and 55. The image forming operation is completed.

  Next, the most characteristic first and second sheet material detection means, first and second temperature detection means, and the longitudinal configuration of the thermoswitch according to the first embodiment of the present invention will be described.

  FIG. 3 is a diagram showing the longitudinal positional relationship between each sensor and the flag when the side regulating plates 45 and 46 on the multi-tray 14 to which the first embodiment of the present invention is applied are operated.

  In the figure, 100 is an apparatus main body, 14 is a multi-tray, and 45 and 46 are side regulating plates serving as recording medium regulating means for regulating the sheet P feeding position from the left and right when feeding from the multi-tray 14. Reference numeral 48 denotes a sheet material presence / absence sensor for detecting the presence / absence of a sheet on the multi-tray.

  Reference numeral 64 denotes a heater, 65 denotes a paper passing portion thermistor for detecting the temperature of the paper passing region, and 66 denotes an end thermistor for detecting the temperature of the end of the heater 64. The sheet passing portion thermistor 65 and the end portion thermistor 66 are connected to a DC controller as a control circuit through conductive electrodes, and the temperature of the heater 64 is detected by detecting the resistance value. Reference numeral 67 denotes a thermoswitch as a safety device having an operating temperature of 250 ° C., which is disposed in contact with the back surface of the heater (see FIG. 4). In the present embodiment, the fact that the temperature of the contact region of the thermo switch 67 reaches 250 ° C. is a case where the temperature control circuit runs away and normal temperature control becomes impossible. At this time, the thermo switch 67 Detects 250 ° C and cuts off power.

When the left side restricting plate 45 is moved in the direction of arrow A, the sensor flag guide 104 is moved in the same direction, and the paper detection lever 103 is moved in the same manner. Then, the pinion gear 108 rotates in the direction of arrow D, and the right side regulating plate 46 interlocked with the rack 107 moves in the direction of arrow B. 101 is a sensor flag shaft. In this embodiment, the left side restricting plate 45 and the right side restricting plate 46 are configured to move in conjunction with each other in order to form an image based on the center. In FIG. 3, the center reference is a sheet position reference C ₀ .

  A detailed operation will be described here.

  FIG. 4 shows the longitudinal positions of the four elements of the heating element of the fixing device, the sheet passing portion temperature detecting means, the edge temperature detecting means, the safety device, and the sheet material detecting means in the first embodiment of the present invention and the recommended sheet. It is explanatory drawing which looked at the relationship with a conveyance area | region from the top. Here, the heating body of the fixing device is the heater 64, and the sheet passing section temperature detecting means for detecting the temperature of the sheet passing section of the heating body is the sheet passing section thermistor 65, which detects the temperature of the end of the heating body. The end temperature detecting means is an end thermistor 66. The safety device is a thermo switch 67. The sheet material presence / absence sensor 48 is a sheet material detection unit that operates when the paper detection lever 103 detects the sheet material P as shown in FIG. Normally, the left side regulating plate 45 and the right side regulating plate 46 are set so as to match the width of the sheet material P, and the sheet material P is set therebetween as shown in FIG. In this case, a normal printing operation is performed, and if the temperature of the end thermistor 66 reaches the upper limit, control is performed to limit the power and delay the paper feeding timing.

The sheet passing of the image forming apparatus according to the present invention is a center sheet passing reference with reference to the sheet passing position indicated by the center line (C _{0 in} FIG. 4), and the inner two-dot chain line C ₁ is a sheet for guaranteeing sheet passing. of size, represent the two ends passing position of the sheet material of the minimum width dimensions shown in the figure 2L _1.

Passing portion thermistor 65 and the top sensor 49 and the thermal switch 67 is arranged at a position inside than the minimum width position L ₁ from the paper feed position reference C _0. In addition, the sheet passing portion thermistor 65 and the top sensor 49 for detecting the image writing timing are arranged on the left side of the image printing surface. Sheet detection lever 103 for operating the sheet presence sensor 48 on the multi-tray 14 outside than the minimum width position L _1, and is disposed on the image printed surface left. Further, the end thermistor 66 is outwardly than the minimum width position L _1, and is disposed on the image printed surface right, the end thermistor 66 is placed from the paper feeding position reference C ₀ at the position of L _4.

That is, in the image forming apparatus Chuodori paper reference is a present embodiment, the sheet material P in size sheet passing warranty range, if they are properly positioned in the sheet feeding port, shown by two-dot chain line C ₁ It will pass through a minimum width L ₁ region. In this case, the leading and trailing ends of the sheet material P are first detected by the sheet material presence / absence detection sensor 48, and then detected by the top sensor 49 located upstream of the fixing unit. The temperature of the heater 64 in the sheet passing area of the sheet material P is detected by the sheet passing section thermistor 65, and the thermo switch 67 is in contact with the heater 64 in the sheet passing area of the sheet material P.

Further, the narrow sheet width, for example, even a sheet material having a width of 2L ₁ is sheet passing, the end thermistor 66 is capable of detecting the temperature of the end portion of the heater 64. This makes it possible to control the temperature of the fixing unit, and as a result, it is possible to avoid the fixing device from undergoing a thermal problem. In the drawing, C ₂ denotes the maximum width dimension that ensures sheet passing.

  FIG. 5 is a view showing a state in which the side regulating plates 45 and 46 on the multi-tray 14 are opened larger than the width of the sheet material P to be passed in the image forming apparatus of the present embodiment. FIG. 5 shows a longitudinal positional relationship between the sheet material passing area and each sensor when the operator feeds the sheet material P in a state where the sheet material P is moved to the right side of the image printing surface.

In this case, the sheet material P is not fed because it is not in a position to operate the sheet material presence / absence sensor 48 (that is, the paper detection lever 103). As a result, damage to the fixing device can be avoided. Here, L ₃ represents the width of the sheet material P, and L ₆ represents the distance between the top sensor 49 and the right side regulating plate 46.

  6 shows a state in which the side regulating plates 45 and 46 on the multi-tray 14 are opened larger than the width of the sheet material P to be passed through in the image forming apparatus of the present embodiment, as in FIG. FIG. However, in FIG. 6, unlike the case of FIG. 5, the longitudinal positional relationship between the sheet material passing area and each sensor when the operator feeds the sheet material P in a state where the sheet material P is moved to the left side of the image printing surface is shown. Yes.

  In this case, the sheet material P is fed because it is in a position where the sheet material presence / absence sensor 48 (that is, the paper detection lever 103) on the multi-tray 14 is operated.

  In this case, even if the printing operation is performed, when the end temperature rises by the end thermistor 66, the input power is limited to delay the paper feeding timing.

  Even if the sheet material presence / absence sensor 48 is arranged on the right side of the image printing surface and the end thermistor 66 is arranged on the left side of the image printing surface, the effects of the present invention are the same.

  In the image forming apparatus that forms an image based on the central reference as described above, the left side regulating plate 45 and the sheet material presence / absence sensor 48 are linked to each other as follows. First, when the left side restricting plate 45 and the right side restricting plate 46 are opened wide and a small size paper is passed along the right side restricting plate 46, the sheet feeding operation is not performed. Further, when the paper is passed along the left side regulating plate 45, the end thermistor 66 detects the temperature and performs control such as opening a gap between the sheets, so that the fixing device is prevented from receiving a thermal trouble. it can.

  In this embodiment, the ceramic heater has been described as an example. However, a roller fixing method using a halogen heater or electromagnetic heating can also be implemented. Regardless of the color printer, the same effect can be obtained with an image forming apparatus using electrophotographic technology such as a monochrome printer, a monochrome copying machine, a color copying machine, and a facsimile.

  The feature of this embodiment is that the reference position of the recording medium is changed from the center reference to the one-side reference in the printer of the first embodiment. Since other printer configurations are the same as those in the first embodiment, the description thereof will be omitted.

  FIG. 7 is a diagram showing the longitudinal positional relationship between each sensor and the flag when the side regulating plates 45 and 46 on the multi-tray 14 to which the second embodiment of the present invention is applied are operated.

Since the image is formed on the left side of the drawing (the sheet passing position reference E _{0 in the} drawing), the left side regulating plate 45 is fixed, and only the right side regulating plate 46 can move in the direction of arrow B. In this case, when there is no paper at the position of the paper detection lever 103, the paper feeding operation is not performed, so that the fixing device can be prevented from being damaged. Even if the sheet material P having the minimum width is set on the left side as viewed in the drawing and the printing operation is performed, if the end temperature rises by the end thermistor 66, the input power is limited to delay the feeding timing. Perform the action.

  In this way, the same effect can be obtained even in an image forming apparatus using electrophotographic technology such as a printer or facsimile that forms an image with a left reference, which is often used in monochrome printers.

1 is a schematic sectional view of a color image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional view of a fixing device according to a conventional example and an embodiment of the present invention. The figure which shows the longitudinal positional relationship of the side control board and each sensor on the multi-tray which concerns on 1st Example of this invention. The figure which shows the example at the time of normal paper passing based on 1st Example of this invention The figure which shows the example at the time of carrying out the one-sided paper feeding to the right side which concerns on 1st Example of this invention The figure which shows the example at the time of carrying out the one-sided paper feeding to the left side which concerns on 1st Example of this invention The figure which shows the longitudinal positional relationship of the side control board on each multi-tray and each sensor which concerns on 2nd Example of this invention. Schematic configuration cross-sectional view of a color image forming apparatus according to a conventional example

Explanation of symbols

14 Multi-tray 45 Left side regulating plate (corresponding to recording medium regulating means, first recording medium regulating means)
46 Right side regulating plate (equivalent to recording medium regulating means, second recording medium regulating means)
41 Feed roller 48 Sheet material presence / absence sensor (equivalent to recording medium detection means)
49 Top sensor 50 Fixing device (equivalent to fixing means)
62 Pressure roller 63 Heater unit 64 Heater 65 Paper passing portion thermistor (corresponding to first temperature detecting means)
66 end thermistor (equivalent to second temperature detection means)
67 Thermo switch 69 Thermistor 70 Fixing film 71 Film guide 72 Film guide reinforcing sheet metal 100 Image forming apparatus 103 Paper detection lever (corresponding to recording medium detection means)

Claims (3)

An image forming apparatus comprising: an image forming unit that forms an image with a central reference of a recording medium; and a fixing unit that fixes the image on the recording medium formed by the image forming unit by pressurizing, heating, and melting.
First temperature detecting means and second temperature detecting means for detecting the temperature of the fixing means;
Paper feeding means for supplying the recording medium;
A recording medium detecting means for detecting the presence or absence of the recording medium when the recording medium is loaded on the paper feeding means;
The first temperature detection means is disposed in a pass area of the smallest width recording medium among the transportable recording media in a longitudinal direction perpendicular to the direction in which the recording medium is transported,
At least one second temperature detecting means is disposed on the outer side of the sheet passing area of the minimum width recording medium in the longitudinal direction;
The image forming apparatus according to claim 1, wherein at least one recording medium detection unit is disposed on the opposite side of the central reference in the longitudinal direction from the second temperature detection unit. The image forming apparatus according to claim 1, further comprising: a recording medium regulating unit that is arranged in parallel with the transported direction and defines the recording medium from both sides.
The image forming apparatus according to claim 1, wherein the recording medium detecting unit is interlocked with the recording medium regulating unit on a side opposite to the second temperature detecting unit with respect to the central reference while maintaining a relative position. An image forming apparatus comprising: an image forming unit that forms an image on one side of a recording medium; and a fixing unit that fixes the image on the recording medium formed by the image forming unit by applying pressure, heating and melting.
First temperature detecting means and second temperature detecting means for detecting the temperature of the fixing means;
Paper feeding means for supplying the recording medium;
Recording medium detecting means for detecting the presence or absence of the recording medium when the recording medium is loaded on the paper feeding means;
A fixed first recording medium regulating means for defining a position of the recording medium;
Movable second recording medium regulating means for defining the position of the recording medium,
The first temperature detection means is disposed in a pass area of the smallest width recording medium among the transportable recording media in a longitudinal direction perpendicular to the direction in which the recording medium is transported,
At least one or more of the second temperature detection means is disposed in the longitudinal direction in the vicinity of the second recording medium regulating means positioned at the maximum width recording medium among the conveyance recording media.
The image forming apparatus according to claim 1, wherein the recording medium detecting unit is disposed in the vicinity of the first recording medium regulating unit in the longitudinal direction.

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