JP2009139703A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and inexpensively prevent excessive heating of a part of a heater in one-side paper passage in an image forming apparatus adapted to perform center-based carrying of paper P. <P>SOLUTION: The image forming apparatus includes: a paper carrying passage 6; an image forming part 7; a fixing part 8 including a heater containing a heating element H and a temperature detector provided at an end of the heater to detect its temperature; a width regulation guide 58 for regulating paper P on a center basis to perform center-based carrying of the paper P; a size detection part detecting a paper size corresponding to the space of the width regulation guide 58; a paper feed part 5 including a paper detector provided on a guide member 57b on the side where the temperature detector is not provided; and a control part 9 performing, in response to output of the temperature detector, current-carrying control to the heating element H. The control part 9 performs collation of the size of paper actually put in the paper feed part 5 in response to outputs of the size detecting part and the paper detector, and determines whether excessive heating of the heater occurs or not during image formation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a multifunction machine, a printer, and a facsimile machine that forms a toner image with toner and heats the toner image with a fixing device to form an image.

  2. Description of the Related Art Conventionally, there is an image forming apparatus that forms a toner image, transfers the toner image to a sheet, and forms the image by heating and pressing the transferred sheet with a fixing device (electrophotographic method). In these image forming apparatuses, a heating element formed over the sheet passing area in a direction perpendicular to the sheet conveying direction (hereinafter referred to as “width direction”) is provided in the fixing device for heating the sheet. The heat from the body is transmitted to a heating body such as a heating roller or an endless film, and the toner is fixed by the heat from the heating body. Further, a temperature sensor may be provided on the heating body in order to maintain an appropriate fixing temperature. In these fixing devices, at the time of fixing, heat is removed from the area where the heating element and the sheet are in contact (the part through which the sheet has passed), so that the heating element is energized to maintain the temperature.

  The length in the width direction of the heating body is often set so that A4 size, which is the most frequently used paper, can be printed. For example, postcards, envelopes, B5, A5, A6 paper, etc. If image formation is continuously performed on a sheet whose width in the width direction is shorter than that of the sheet, heat is not taken away in the non-contact area of the heating body with the sheet, and the temperature of the non-contact area excessively increases. Sometimes. This excessive temperature rise leads to fusion / breakage of the fixing device. Therefore, in the image formation of paper having a size smaller than A4, control is performed to prevent an excessive temperature rise by reducing the image formation speed.

In order to prevent such an excessive temperature rise of the heating body, an invention such as Patent Document 1 has been proposed. Specifically, Patent Document 1 discloses a heating body (film) provided in a direction crossing the moving direction of the recording material, a first temperature detection member for detecting the temperature of the heating body, and the first temperature detection member. And an energization control unit that controls energization to the heating body so that the detected temperature is constant. A second heating unit that is provided at a position different from the first temperature detection member in the longitudinal direction of the heating body. An image heating apparatus having a temperature detection member and a feeding interval control means for controlling the feeding interval of the recording material during continuous image heating based on the detection output of the second temperature detection member is described. With this configuration, an attempt is made to prevent damage due to excessive heating of the heating element. (See Patent Document 1: Claim 1, paragraphs 0010 and 0117, FIG. 3, etc.).
JP 05-080604 A

  Here, an image forming apparatus that conveys a sheet by matching a reference position arranged in the central portion of the sheet conveyance path in the width direction with a central axis in the sheet conveyance direction (hereinafter referred to as “center reference”). Exists. The central reference image formation may include a paper supply unit capable of supplying various sizes of paper such as a manual feed tray.

  However, among users, a pair of guide members that restrict the paper placed on the manual feed tray in the width direction is greatly expanded, and a paper having a width narrower than the width of the pair of guide members is used as one of the restriction members. There are people who form images at the same time. This is a so-called one-side paper passing method, and is not an appropriate paper feeding method in the central reference image forming apparatus. For example, since the image forming apparatus used by the user was a one-sided standard in which one-sided paper is used for normal paper conveyance, the user made one-sided paper after making his own regulating member. Examples have been reported.

  In the central reference image forming apparatus, it is assumed that the sheet is conveyed in the center of the sheet conveyance path, and a sensor and a temperature sensor for detecting the presence of the sheet are arranged, and control for preventing an excessive temperature rise of the heating body is provided. However, if one-sided paper feeding is performed continuously, the sensor or other member cannot function effectively, causing an excessive temperature rise in the heating body, resulting in damage to the heating body or the fixing device. There is a problem that there is. Even if no damage occurs, unevenness may occur in the temperature distribution of the heating element. For example, if an image is formed on a wide sheet after passing one side, unevenness of fixing occurs, resulting in a decrease in image quality. There is also a problem that there are cases.

  Here, looking at the invention described in Patent Document 1, the image forming apparatus described in Patent Document 1 is a one-side reference image forming apparatus (see Patent Document 1: Paragraph 0035), and this configuration is a central reference image forming apparatus. It cannot be directly applied to the problem of one-sided paper feeding. In the image forming apparatus described in Patent Document 1, two or more thermistors are provided for checking the temperature of the film (see Patent Document 1: FIGS. 3 and 7), so that overheating of the heating body can be detected to some extent. In some cases, the number of parts such as sensors and wiring is large, and there are problems in terms of cost, space, and the like. Also, it is necessary to monitor the output of the thermistor and perform complex control for each paper size in order to detect an excessive temperature rise of the heating element, which places a heavy processing load on the CPU, and the capacity of the ROM and RAM. There is also a problem that the burden of program development increases, leading to higher costs.

  The present invention has been made in view of the above-described problems of the prior art, and is an image forming apparatus that transports a sheet with a central reference. The purpose is to prevent overheating of the part.

  According to the first aspect of the present invention, a paper transport path for transporting paper inside the apparatus, an image forming unit for forming a toner image and transferring the toner image onto the paper, and heating the paper to fix the toner image on the paper. Therefore, a heating element with a built-in heating element, the heating element having an axial direction as the width direction of the sheet, which is perpendicular to the sheet conveying direction, and an axial end of the heating element are detected, and the temperature of the heating element is detected. In order to transport the paper with the fixing unit having a temperature detection body and the reference position arranged in the central portion of the paper transport path in the width direction being aligned with the central axis of the paper, the paper is transported symmetrically in the width direction. A width regulating guide composed of a pair of sliding guide members, a size detecting unit for detecting the size of the paper corresponding to the interval between the pair of guide members, and the side on which the temperature detecting body is not provided Provided in the guide member A sheet supply unit that supplies the sheet to the sheet conveyance path, and a control unit that controls the operation of the apparatus and that controls the energization of the heating element in response to the output of the temperature detection unit The control unit receives the outputs of the size detection unit and the paper detection body, collates the detected paper size with the paper size actually placed on the paper supply unit, and forms an image. When performing, it was decided to determine whether or not the heating body was overheated.

  According to this configuration, since the paper size detected by the size detection unit and the size of the actually placed paper are collated using the paper detection body, it is determined whether or not the user is going to pass the paper on one side. Can be judged. Based on this determination, it is possible to predict the occurrence of overheating of the heating body and the deterioration of the formed image quality. In addition, the size detection unit and the paper detection body for detecting the paper size can be used not only for detecting one-side paper passing but also for normal paper feeding. In addition, it is sufficient to provide one temperature detection body for detecting the temperature of the size detection section, the paper detection body, and the heating body, respectively. Cost reduction and space saving can be achieved.

  According to a second aspect of the present invention, in the first aspect of the invention, the control unit is configured such that, based on the output of the size detection unit, the paper size is within the temperature detection region of the heating body by the temperature detection body or the temperature. When the size of the sheet passes through a predetermined range from the detection area and the sheet detector does not detect the presence of the sheet, it is determined that overheating of the heating element occurs due to sheet passing on one side.

  This configuration specifically shows the case where it is determined that overheating of the heating body occurs, and the size of the paper detected by the size detection unit is the temperature detection area of the heating body by the temperature detection body or the temperature detection. If the size is within a predetermined range from the area and the paper detection body does not detect the presence of the paper, the control unit determines that overheating of the heating body occurs due to paper passing on one side. That is, in this case, the detected temperature based on the output of the temperature detector is the temperature at which heat is taken away by the passage of the paper, and based on the temperature detection result, the control unit energizes the heating element to maintain the fixing temperature. If it does, since it will hardly take heat at the edge part of the heating body in which the temperature detection body is not arranged, it can be predicted that the heating body will be heated excessively. Therefore, based on this determination, it is possible to take measures to prevent the fixing unit from being damaged by predicting the occurrence of overheating of the heating element and the deterioration of the formed image quality.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the control unit does not supply paper from the paper supply unit when it is determined that overheating of the heating body occurs.

  According to this configuration, since the control unit prohibits image formation that involves overheating of the heating body such that the heating body is damaged or welded, the fixing portion by completely passing the paper on one side in the central reference image forming apparatus. It is possible to prevent the occurrence of breakage, fusion, etc., and the deterioration of image quality. Further, in order to prevent damage, the control unit does not need complicated control for controlling the image forming speed, temperature monitoring, and the like, and the burden on the control unit can be reduced.

  The invention according to claim 4 has a display unit for displaying the state of the apparatus in the inventions of claims 1 to 3, and when the control unit determines that overheating of the heating body occurs, A warning message is displayed on the display.

  According to this configuration, it is inappropriate for the user to pass the paper on one side, the paper placement method is abnormal, and the heater may be damaged due to an excessive increase in the temperature of the heating element. You can communicate something.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, the control unit is configured such that, from the output of the size detection unit, the paper size is within the temperature detection region of the heating body by the temperature detection body, or When the paper detection body detects the presence of the paper and has a size that passes within a predetermined range from the temperature detection region, it is determined that the heating body does not overheat.

  According to this configuration, even if one-side paper is passed, the paper does not pass through the region detected by the temperature detection body in the heating body, so that the temperature detection body is overheated even if the heating body is overheated. Can be detected, and at least energization of the heating element to the extent that the heating element or the fixing device is damaged can be prevented.

  According to a sixth aspect of the present invention, in the first to fifth aspects of the invention, the control unit is configured such that, from the output of the size detection unit, the paper size is within a temperature detection region of the heating body by the temperature detection body, or When the size does not pass through a predetermined range from the temperature detection region, it is determined that the heating body does not overheat.

  According to this configuration, in this case, since it can be determined that the image formation is originally the same as that for narrow-width paper, the temperature detection body can detect the occurrence of overheating even if the heating body is overheated. In addition, since the control unit only has to perform energization control and image formation control of the heating element when forming an image on a narrow paper sheet, the control unit can determine that the heating body does not overheat.

  According to a seventh aspect of the present invention, in the first to sixth aspects of the invention, when the control unit determines that the heating body does not overheat, the control unit performs sheet formation from the sheet supply unit to form an image. It was decided.

  According to this configuration, if abnormal heating of the heating body does not occur, image formation may be performed. Therefore, image formation is performed even if paper is passed on one side, thereby improving user convenience. Can do.

  According to an eighth aspect of the present invention, in the first to seventh aspects of the invention, the temperature detection body is a contact type or non-contact type thermistor provided inside or outside the heating body.

  According to a ninth aspect of the present invention, in the first to eighth aspects of the invention, the size detection unit includes a variable resistor whose resistance value changes in conjunction with the sliding of the pair of guide members, and the control unit includes the control unit The paper size is recognized based on the voltage applied to the variable resistor or the flowing current.

  According to a tenth aspect of the present invention, in the first to ninth aspects of the invention, the sheet detector is an optical sensor.

  According to these configurations of claims 8 to 10, it is easy to obtain each of these members, and the sheet supply unit and the fixing unit can be configured at low cost.

  According to the present invention, it is possible to detect a one-sided sheet that causes damage to a heating element, a fixing unit, and the like and a decrease in image quality with an inexpensive and simple configuration, and it is possible to inhibit such sheet conveyance.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 9, taking a copying machine 1 (corresponding to an image forming apparatus) as an example. It should be noted that the elements such as the configuration and arrangement described in this embodiment do not limit the scope of the invention and are merely illustrative examples.

  First, an outline of the copying machine 1 according to the embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic cross-sectional view showing an example of a copying machine 1 according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of the configuration of the fixing unit 8.

  As shown in FIG. 1, the copying machine 1 according to the present embodiment is provided with an operation panel 2 (corresponding to a display unit) at the upper front of the copying machine 1, and with an automatic document feeder 3 at the top. An image reading unit 4, a paper supply unit 5, a paper conveyance path 6, an image forming unit 7, a fixing unit 8 and the like are provided in the main body of the lower copying machine 1.

  The operation panel 2 includes various input keys (not shown) such as a numeric keypad and a start key, and a touch panel type liquid crystal display unit 21 (see FIG. 3). The user can select various input keys and a menu displayed on the liquid crystal display unit 21 to input settings for the operation of the copying machine 1. In addition, characters and images can be displayed on the liquid crystal display unit 21 to display information for transmitting the status of the copier 1 to the user, such as an error display when a paper jam occurs.

  The automatic document feeder 3 automatically and continuously conveys the document toward the image reading unit 4 that reads the image data of the document. Specifically, the automatic document feeder 3 includes a document placing tray 31 on which a document to be read is placed, a document supply roller 32 that feeds the document one by one toward a reading position (feed reading contact glass 41b), a document Are provided with a plurality of document conveyance roller pairs 34 provided along a document conveyance path 33 and a document discharge tray 35 for receiving a document after reading. Note that the automatic document feeder 3 is provided with a fulcrum on the back side of the paper and can be lifted upward. For example, a document such as a book is placed on the placement reading contact glass 41a to read the document one by one. You can also.

  The image reading unit 4 reads a document and forms image data of the read document. In the image reading unit 4, optical system members such as an exposure lamp, a reflecting plate, a mirror, a lens, and a CCD sensor (not shown) are provided. The original is irradiated with light, the reflected light is subjected to photoelectric conversion, and a pixel is obtained. Convert the document to image data in units. Further, a contact glass 41 is provided on the upper surface of the image reading unit 4, and the image reading unit 4 is fed by a document placed on the placement reading contact glass 41 a or a feed reading contact glass 41 b by the automatic document feeder 3. The document conveyed while touching is read to generate image data.

  The paper supply unit 5 supplies the paper P to the image forming unit 7, and has one manual feed tray 51 and two cassettes 52 in the copying machine 1 of the present embodiment. The cassette 52 is provided in two stages in the copying machine 1 of the present embodiment, and includes a supply roller 53 that feeds the paper P one by one to the paper transport path 6. For example, when the user inputs from the operation panel 2 that the image formation is started (for example, the start button is pressed), the supply roller 53 is supplied to the cassette supply motor 54 (see FIG. 3) at a predetermined interval. , And the paper P is supplied one by one.

  On the other hand, the manual feed tray 51 provided in the paper supply unit 5 is a part particularly related to the present invention, and the user forms an image using the paper P placed on the manual feed tray 51 separately from the cassette 52. For. In general, the manual feed tray 51 uses not only A4 and B5 standard size copy paper but also small paper such as postcards, envelopes, etc., as well as paper of any size, and single-side printed paper as the backing paper. Various sizes of paper P are placed. A supply roller 56 that is rotationally driven by a manual feed motor 55 (see FIG. 3) is provided to send the placed paper P one by one to the paper transport path 6. Further, the manual feed tray 51 is provided with a width regulating guide 58 including a pair of guide members 57a and 57b for regulating the width direction of the paper and transporting the paper P based on the center. In this embodiment, a variable resistor R1 is provided to detect the width of the loaded paper (details will be described later).

  The paper transport path 6 transports the paper P supplied from the paper supply unit 5 to the discharge tray 61 through the image forming unit 7 and the fixing unit 8 inside the apparatus. The paper transport path 6 is provided with a plurality of transport roller pairs 62 and a registration roller pair 63 for temporarily waiting the transported paper P in front of the image forming unit 7 and feeding the paper P in accordance with the formation of the toner image. . The paper conveyance path 6 from the cassette 52 joins the paper conveyance path 6 from the manual feed tray 51 on the upstream side of the registration roller pair 63. Here, the copying machine 1 of the present embodiment conveys the sheet P by combining the central axis of the sheet P to be conveyed and the reference position A arranged at the center part of the width W3 of the sheet conveyance path 6. Perform standard paper transport.

  The image forming unit 7 forms a toner image and transfers the toner image onto the conveyed paper P. The image forming unit 7 includes a photosensitive drum 71 rotatably supported in an arrow direction shown in the figure, a charging device 72 disposed around the photosensitive drum 71, a developing device 73, an exposure device 74, and a transfer roller. 75 and a cleaning unit 76.

  The photosensitive drum 71 is provided at the approximate center of the image forming unit 7 and is driven to rotate in a predetermined direction. The charging device 72 is provided above the photosensitive drum 71 and uniformly charges the surface of the photosensitive drum 71 to a predetermined potential. The exposure device 74 is provided above the charging device 72 and based on image data formed by the image reading unit 4 and image data from the user terminal 100 (see FIG. 3) connected by a network (see FIG. 3). 1 is a laser scanning unit that outputs a scanning latent image on the surface of the photosensitive drum 71 to form an electrostatic latent image according to image information. The developing device 73 is provided on the right side of the photoconductive drum 71 and supplies the electrostatic latent image on the photoconductive drum 71 with charged toner for development.

  The transfer roller 75 provided below the photosensitive drum 71 is in pressure contact with the photosensitive drum 71 to form a nip. By causing the paper P to enter the nip and applying a predetermined voltage to the transfer roller 75, the toner image on the photosensitive drum 71 is transferred to the paper P. The cleaning unit 76 cleans the toner remaining on the surface of the photosensitive drum 71 after the transfer is completed.

  The fixing unit 8 fixes the toner image transferred to the paper P. In the present embodiment, the fixing unit 8 mainly includes a heating roller 81 (corresponding to a heating body) whose axial direction is the width direction of the sheet P, which is a direction perpendicular to the sheet conveyance direction, and a pressure roller 82 that is in pressure contact with the heating roller 81. And a temperature sensor 83 (corresponding to a temperature detection body) that is disposed at the end of the heating roller 81 in the axial direction and detects the temperature of the heating roller 81. The heating roller 81 incorporates a heating element H that extends in the axial direction of the heating roller 81 in order to heat the paper P (in the direction perpendicular to the plane of FIG. 1).

  The fixing unit 8 is provided with a fixing motor 8M (see FIG. 3) for rotating the heating roller 81 and the pressure roller 82, whereby the heating roller 81 and the pressure roller 82 are rotationally driven. The sheet on which the toner image has been transferred is heated and pressurized by passing through the nip between the heating roller 81 and the pressure roller 82 by the rotation of each roller, and the toner on the sheet is melted and heated. As described above, the copying machine 1 of the present embodiment fixes the toner image on the paper P.

  For example, the heating roller 81 may be made of metal in order to reduce the heat capacity. Further, because of the adhesiveness of the molten toner, a coating such as a fluororesin may be provided so that the paper P does not stick to the heating roller. The heating roller 81 has a length similar to the width W3 of the paper transport path 6 (width W in a direction perpendicular to the paper transport direction), and is slightly wider than the maximum paper width W1 capable of forming an image. (See FIG. 5). On the other hand, the pressure roller 82 has an elastic layer such as rubber on the roller shaft, has the same length as the heating roller 81, and its axial direction is parallel to the axial direction of the heating roller 81.

  For example, a halogen heater of about 1000 W is employed as the heating element H built in the heating roller 81. In addition, since the output of the heat generating body H can be set as appropriate and the heating roller 81 only needs to be heated, an energizing heat generating body other than the halogen heater may be used.

  As shown in FIG. 2, the fixing unit 8 includes three rollers, a heating roller 81 containing a heating element H, a fixing roller 84, and a pressure roller 82, and the heating roller 81 and the fixing roller 84 are made of resin. Alternatively, an endless film 85 made of metal or the like may be stretched, and a pressure roller 82 that presses against the endless film 85 may be disposed at a position facing the fixing roller 84. If the fixing unit 8 is configured in this manner, the endless film 85 is thin and can be quickly warmed, so that the warm-up time of the fixing unit 8 can be shortened.

  In any case, in order to heat the toner on the sheet, a heating element H, a heating element such as the heating roller 81 and the endless film 85, and a pressure element such as a pressure roller 82 for pressing the sheet P are used. Can be used as the fixing unit 8 of the copying machine 1 of the present embodiment.

  On the other hand, the temperature sensor 83 is composed of, for example, a thermistor, and is provided to detect the temperature of the heating roller 81. One temperature sensor 83 is provided at one end of the heating roller 81 in the axial direction, which will be described in detail later.

  Next, a hardware configuration of the copying machine 1 according to the present embodiment will be described with reference to FIG. FIG. 3 is a block diagram showing an example of the hardware configuration of the copying machine 1 according to the embodiment of the present invention.

  As shown in FIG. 3, the copying machine 1 of this embodiment has a control unit 9 provided on a control board or the like in the copying machine 1 in order to control the operation. The control unit 9 includes a CPU 91, a memory 92, and the like.

  The CPU 91 functions as a central processing unit, and controls the operation of each unit of the copying machine 1 based on data and programs stored in an HDD, a flash ROM, or the like as the memory 92. Since the copying machine 1 is generally multifunctional, it can be equipped with a large number of CPUs 91 for image processing, operation control, etc., but only one CPU 91 is shown in FIG. 3 for convenience.

  In the present invention, the CPU 91 controls the temperature of the fixing unit 8. Specifically, the output of the temperature sensor 83 of the fixing unit 8 is input to the CPU 91, and the CPU 91 grasps the current temperature of the fixing unit 8 (heating roller 81). Then, based on the program, data, and the like stored in the memory 92, when fixing the toner, an appropriate temperature of the heating roller 81 (for example, about 220 ° C., varies depending on the image forming apparatus depending on factors such as the toner used). ) To keep the heating element H energized. That is, the CPU 91 performs control to turn on / off the power to the heating element H and maintain the temperature of the heating roller 81 at a temperature at which the heat roller 81 can be fixed so that proper fixing can be performed. In other words, the control unit 9 controls the operation of the apparatus and controls the energization of the heating element H in response to the output of the temperature sensor 83.

  Further, regarding the present invention, the CPU 91 receives the output of the size detection unit using the variable resistor R <b> 1 provided in the manual feed tray 51 and recognizes the size of the paper P placed on the manual feed tray 51. In addition, it receives an output from a paper sensor 59 (corresponding to a paper detector) for confirming the presence or absence of the paper P on the manual feed tray 51. Details of the arrangement of the sheet sensor 59 will be described later. The CPU 91 of the control unit 9 receives the outputs of the size detection unit and the paper sensor 59, collates the detected paper size with the paper size actually placed on the paper supply unit 5, and performs image formation. If it is determined that the overheating of the heating roller 81 has occurred (details will be described later). The CPU 91 also controls the operation of the cassette supply motor 54 and the manual tray supply motor 55 provided in the paper supply unit 5 and also controls the supply of the paper P to the image forming unit 7.

  In addition, the control unit 9 is connected to the operation panel 2, the automatic document feeder 3, the image reading unit 4, the paper conveyance path 6, the image forming unit 7, and the power supply device 10. The control unit 9 controls the operation of each unit, such as receiving input and controlling display on the liquid crystal display unit 21. The power supply device 10 is a device that is connected to a commercial power supply, performs rectification and voltage conversion, and supplies power to each unit such as the control unit 9, the heating element H of the fixing unit 8, and the motor in the copying machine 1. is there.

  Further, the copying machine 1 can be communicably connected to a user terminal 100 that is an external computer via a network and an interface. Therefore, for example, the copying machine 1 can receive image data from the user terminal 100 and perform image formation based on the image data (printer function).

  Next, according to the present invention, in the central reference image forming apparatus as shown in the present embodiment, damage to the fixing unit 8 caused by the one-side passing of the paper P placed on the paper supply unit 5 such as the manual feed tray 51 is prevented. It is characterized in that it is prevented, and it is simple and inexpensive. Therefore, a configuration for exhibiting these features will be described below.

  First, the configuration of the manual feed tray 51 according to the embodiment of the present invention will be described with reference to FIG. FIG. 4A is a plan view of the inside of the manual feed tray 51 as viewed from below to show an example of the configuration of the manual feed tray 51, and FIG. 4B is based on the variable resistor R1 according to the embodiment of the present invention. It is a schematic diagram of a paper size detection configuration.

  As shown in FIG. 4A, a pair of guide members 57a and 57b (illustrated by broken lines in FIG. 4A) are provided on the upper surface of the manual feed tray 51 in order to regulate the paper P in the width direction. The pair of guide members 57a and 57b slide and move symmetrically in the width direction of the paper P in order to regulate the paper P with the center reference. As a configuration for that purpose, each of the pair of guide members 57a and 57b is provided with a rack 57c extending in the moving direction, and these racks 57c are meshed with a common pinion gear 57d. Further, in the copying machine 1 of the present embodiment, the installation position of the pinion gear 57d coincides with the reference position A in the paper conveyance, so that the paper is regulated and conveyed with the center reference. That is, the manual feed tray 51 is symmetrically interlocked in the width direction because the paper P is transported by aligning the reference position A arranged in the center portion of the paper transport path 6 in the width direction with the central axis of the paper P. A width regulating guide 58 constituted by a pair of guide members 57a and 57b that slide in a sliding manner is provided.

  A slide type variable resistor R1 is provided on the lower surface of the manual feed tray 51, and is connected to one rack 57c. Specifically, the slide bar R1a of the variable resistor R1 is connected to the rack 57c, and the slide bar R1a moves in accordance with the movement of the rack 57c. As a result, the resistance value of the variable resistor R1 varies. The variable resistor R1 has one end connected to the power supply V1, the other end connected to the resistor R2, and the resistor R2 connected to the ground. That is, the size detection unit includes a variable resistor R1 whose resistance value changes in conjunction with the sliding of the pair of guide members 57a and 57b, and the control unit 9 is based on a voltage applied to the variable resistor R1 or a flowing current. Thus, the size of the paper P corresponding to the distance between the pair of guide members 57a and 57b is recognized. The variable resistor R1 is not limited to a slide type, and may be a variable resistor that varies the resistance value by rotating a knob. Also in this case, the knob is rotated in conjunction with the slide of the pair of guide members 57a and 57b.

Here, detection of the paper size by the variable resistor R1 will be described with reference to FIG. As shown in FIG. 4B, a control unit 9 (CPU 91) is connected to measure a voltage value Vref at a point between the variable resistor R1 and the resistor R2. Note that the voltage Vref at this point is V1 if the applied voltage is V1.
Vref = (R2 / (R1 + R2)) × V1
It becomes. Since the resistance value of the variable resistor R1 is changed by the movement of the width regulation guide 58, and the value of Vref is also changed, the CPU 91 responds to the interval of the width regulation guide 58 by receiving this output. The paper size to be determined is determined. That is, the manual feed tray 51 includes a size detection unit configured by a variable resistor R1, a resistor R2, a power source, and the like in order to detect the size of the paper P corresponding to the distance between the pair of guide members 57a and 57b.

  Next, based on FIGS. 5 to 8, the reason for the occurrence of overheating of the paper conveyance and a part of the heating roller 81 and the overheating prevention according to the embodiment of the present invention will be described. FIG. 5 is a schematic diagram illustrating an example of a state of conveyance of a large-size sheet according to the embodiment of the present invention, and FIG. 6 is a pattern diagram illustrating an example of a state of conveyance of a small-size sheet according to the embodiment of the present invention. FIG. 7 and FIG. 8 are schematic views showing an example of one-side paper passing in the fixing unit 8 according to the embodiment of the present invention.

  As shown in FIGS. 5 to 8, the heating roller 81 is provided with a heating element H that generates heat when energized, and leads are connected to both ends of the heating element H so that electric power is supplied to the heating element H. Are connected, and the CPU 91 controls power supply to the heating element H. A temperature sensor 83 is provided on the outer side (or the inner side) of one end of the heating roller 81 (on the left side of the heating roller 81 in FIGS. 5 to 8). Although the temperature sensor 83 of the present embodiment is a contact type thermistor, a non-contact type or other temperature sensor 83 may be used. The temperature sensor 83 may be provided either inside or outside the heating roller 81.

  The output of the temperature sensor 83 is input to the CPU 91 of the control unit 9, and the CPU 91 obtains information on the current temperature of the heating roller 81. Specifically, since the heating roller 81 rotates, as shown in FIGS. 5 to 8, the temperature sensor 83 detects the temperature in the belt-shaped constant region (temperature detection region T1) in the circumferential direction of the heating roller 81. The CPU 91 obtains temperature information of the temperature detection region T1 (shown by hatching in FIGS. 5 to 8).

  As shown in FIGS. 5 to 8, the guide member 57b on the side where the temperature sensor 83 is not provided in the width direction of the paper P in the pair of guide members 57a and 57b is placed on the paper on the manual feed tray 51. A paper sensor 59 that detects the presence or absence of P is provided. That is, a paper sensor 59 is provided in the manual feed tray 51. For example, the paper sensor 59 can be an optical sensor having a light emitting part and a light receiving part. That is, the paper sensor 59 of this embodiment is an optical sensor.

  To describe an example of the configuration of this optical sensor, a light emitting part and a light receiving part (not shown) are arranged so that light emission and light reception are performed in the width direction of the paper P, and between the light emitting part and the light receiving part. The paper sensor 59 can be configured by providing, for example, a fan-shaped shielding plate having a rotation shaft that rotates in the paper conveyance direction. In this configuration, when the paper P is placed, the shielding plate is rotated, so that there is no shielding object in the optical path between the light emitting unit and the light receiving unit, and the light receiving state changes, whereby the output current (voltage) of the light receiving unit is changed. Change occurs, and the presence or absence of the paper P is determined from the change in the output current (voltage). The paper sensor 59 only needs to be able to detect the presence or absence of the paper P. For example, a light emitting unit and a light receiving unit are provided so as to sandwich the paper P in the vertical direction, and the paper P is placed in a light-shielding state. An optical sensor may be provided, or a sensor other than the optical sensor may be used.

  Further, the width W1 of the heating roller 81 in the copying machine 1 of the present embodiment is determined by the paper size that can be conveyed. The copying machine 1 of the present embodiment is based on A4 size paper P1, which is the most commonly used paper. Specifically, the width W1 of the heating roller 81 is slightly wider than the width W2 of the A4 paper P1 of this embodiment. In other words, the width W1 of the heating roller 81 of the present embodiment is determined by the width W2 of the A4 paper P1 being transported (there are two types of A4 portrait and A4 landscape), and transports the A4 paper in the longitudinal direction. When it is possible, it is about 297 mm or more, and when A4 paper is conveyed in the horizontal direction, it is 210 mm or more. Note that the width W3 in the width direction of the sheet transport path 6 is also longer than the A4 sheet 1. Note that the width W1 of the heating roller 81 and the width W3 of the paper conveyance path 6 may be determined so that letter-size printing often used in North America can be performed (as opposed to the A4 size of about 210 mm × about 297 mm). The letter size is about 216 x about 279 mm).

  FIG. 5 shows how the A4 paper P1 is fed from the manual feed tray 51 in the vertical or horizontal direction and passed through the fixing unit 8 to form an image on the paper P. Here, the width regulation guide 58 sandwiches the A4 paper P1 from both sides, and the paper P1 is conveyed based on the center.

  The temperature sensor 83 of the fixing unit 8 according to the present embodiment is disposed at a position where the end of the paper P1 is in contact with the temperature detection region T1 of the temperature sensor 83 when an image of the A4 paper P1 is formed. When the paper P passes through the heating roller 81, the heat of the heating roller 81 is taken away by the paper P, and the detection temperature is lowered. Therefore, the CPU 91 performs control to turn on / off the energization of the heating element H based on the temperature detected by the temperature sensor 83 and maintain the heating roller 81 at a fixable temperature. When an image is formed on the A4 paper P1, the A4 paper P1 is in contact with almost the entire width of the heating roller 81 (the contact area T3 is shown by hatching in FIG. 5). It is not necessary to consider some overheating, and image formation is performed without reducing the image formation speed except in special cases.

  Next, a case where a postcard paper P2 smaller than the A4 paper P1 is printed will be described with reference to FIG. The configuration of the fixing unit 8, the manual feed tray 51, and the sheet conveyance path 6 is the same (hereinafter, the same applies to FIGS. 7 and 8).

  As shown in FIG. 6, in the copying machine 1 of the present embodiment, the paper P is conveyed with a central reference, but the width of the heating roller 81 is used for small paper P such as postcard paper P2, various envelopes, A5, A6 paper, and the like. The width W4 of the postcard paper P2 is much narrower than W1. Accordingly, the temperature of the contact region T3 between the heating roller 81 and the postcard paper P2 is lowered during image formation. On the other hand, for example, in the non-contact area T2 (a white background portion of the heating roller 81 in FIG. 6; the same applies to the following) in the non-contact area T2 that is not in contact with the postcard paper P2, such as both ends of the heating roller 81, the natural heat dissipation and the contact area T3. The temperature does not drop except for heat conduction.

  Therefore, when the image forming speed similar to that of the A4 paper P1 and the energization control of the heating element H are performed, the temperature rises (for example, about 300 ° C.) in the non-contact region T2, and the heating roller 81 and the pressure roller 82 There is a case where damage due to fusion or the like occurs. Further, if image formation is continuously performed on the A4 paper P1 even before breakage occurs, the temperature of the non-contact area T2 is too high, causing troubles such as melting of the toner, and appropriate image formation cannot be performed. become.

  Therefore, when the copying machine 1 of the present embodiment continuously prints small paper P such as postcard paper P2, the distance between the temperature sensor 83 and the postcard paper P2 from the paper size detected by the variable resistor R1. In consideration of the number of images to be continuously formed, the temperature of the contact area T3 of the postcard paper P2 is predicted, the temperature of the contact area T3 is set to an appropriate temperature for fixing, and the temperature of the non-contact area T2 increases. The energization control and image formation control of the heating element H are performed so as not to be too much. For example, the image forming speed is decreased, heat is conducted from the non-contact area T2 to the contact area T3, and the temperature unevenness of the heating roller 81 is reduced. Note that the relationship between the temperature prediction of the contact region T3 and the image forming speed depends on various factors such as the material of each member of the fixing unit 8, the output of the heating element H, the environmental temperature, and the like. Data obtained empirically can be stored in the memory 92 in advance, and the image forming speed and the energization timing of the heating element H can be controlled based on the data.

  Further, since the temperature sensor 83 and the CPU 91 detect the temperature of the non-contact area T2, if the temperature in the non-contact area T2 rises to the extent that the fixing unit 8 is damaged, the CPU 91 supplies power to the heating element H. It is also possible to take measures to prevent damage to the fixing unit 8, such as cutting the image and stopping image formation.

  Next, based on FIGS. 7 and 8, a case where one-side paper feeding is performed will be described.

  First, as shown in FIGS. 7 and 8, the one-side paper passing means that the paper P is brought close to one end in the width direction of the heating roller 81 or the paper transport path 6 and the paper is transported. Some image forming apparatuses have a one-side reference type in which normal sheet conveyance is performed based on the one-side paper passing. However, since the copying machine 1 according to the present embodiment conveys paper based on the central reference, it can be said that the one-sided sheet passing in the copying machine 1 according to the present embodiment is an inappropriate sheet passing method.

  When the one-side paper passing is performed in the copying machine 1 of the present embodiment, as shown in FIGS. 7 and 8, the width regulation guide 58 is widened more than the width W5 of the actual paper P3 on which image formation is to be performed. In general, the width is expanded to about W1, which is the maximum sheet width of the copying machine 1 of the present embodiment. In addition, some users have reported an example in which a self-made guide G is provided on the manual feed tray 51 so that the sheet is properly conveyed by this one-side paper passing.

  Next, an adverse effect of the one-side paper passing in the central reference copying machine 1 will be described with reference to FIG.

  As shown in FIG. 7, when the actual paper P <b> 3 is brought closer to the side where the temperature sensor 83 is provided in one-side paper passing, the paper P passes through the temperature detection region T <b> 1 of the temperature sensor 83. If image formation is continuously performed in this state, the heat is taken away by the sheet P3, so that the detected temperature in the temperature detection region T1 of the temperature sensor 83 decreases. Therefore, the control unit 9 controls the energization of the heating element H so that the temperature of the heating roller 81 does not fall below the fixable temperature.

  However, when such sheet passing is continuously performed, the temperature continues to rise in the non-contact region T2 of the heating roller 81. In addition, since the width regulation guide 58 is widened to the maximum sheet passing width W1 such as the A4 sheet P1, for example, some image forming apparatuses mistakenly recognize that the A4 sheet is placed, and FIG. In some cases, the heating element 81 is energized and the heating roller 81 is heated as much as the temperature sensor 83 detects a decrease in temperature without reducing the image forming speed or predicting the temperature described in the above. is there. As a result, the temperature of the non-contact area T2 rises excessively and the risk of damage to the fixing unit 8 increases. In particular, a thick paper P having a large heat capacity, such as a postcard paper P2, requires a large amount of heat in order to warm it. Therefore, the energization time to the heating element H is lengthened and the amount of heat given to the heating roller 81 is increased. May appear and the risk of damage to the fixing unit 8 may increase.

  Since such one-sided paper should not be executed, the copying machine 1 of the present embodiment prohibits one-sided paper passing the paper 3 toward the temperature sensor 83 side. Specifically, the control unit 9 receives the output of the variable resistor R1, detects the paper size corresponding to the distance between the pair of guide members 57a and 57b, and guides on the side where the temperature sensor 83 is not provided. The paper sensor 59 provided on the member 57b detects the presence or absence of the paper P3. Then, the control unit 9 (CPU 91) collates the detection result of the paper size with the detection result of the presence or absence of the paper P3.

  Here, as shown in FIG. 7, when the paper sensor 59 cannot detect the paper P <b> 3 when the paper is fed to the temperature sensor 83 side, the paper P <b> 3 is placed near the temperature sensor 83. Judgment can be made.

  In the central reference copying machine 1, it is usual to provide a paper sensor 59 at the reference position A of the manual feed tray 51 on the assumption that the paper P is always conveyed with the central reference without considering one-side paper passing. is there. However, according to such an arrangement method of the paper sensor 59, depending on the size of the paper P3, as shown in FIG. 7, the presence of the paper P3 is detected, and one-sided paper cannot be detected. However, in the copying machine 1 of the present embodiment, since the paper sensor 59 is provided on the guide member 57b on the side where the temperature sensor 83 is not provided, it is possible to reliably detect dangerous one-sided paper passing.

  Here, not only when the paper P3 passes through the temperature detection region T1 by one-side paper passing but also when the guide member 57a is not widened up to the maximum paper passing width W3, that is, depending on how the guide member 57a is widened (regulatory position). Even when the paper P passes through the predetermined range T4 (shown by hatching in FIGS. 7 and 8) from the temperature detection region T1, the heating roller 81 may be overheated. That is, when the paper P passes near the temperature detection region T1, there is a case where the temperature of the temperature detection region T1 is lowered due to heat conduction under the influence of a temperature drop due to the paper P. As a result, overheating of the heating roller 81 can occur.

  The predetermined range T4 is a range that is greatly affected by a temperature drop due to contact between the heating roller 81 and the paper P3 in the temperature detection of the heating roller 81 based on the temperature sensor 83. In other words, if the sheet is passed in this range, it is the range in which overheating of the heating roller 81 occurs due to the influence of the temperature decrease due to the sheet contact and the detection temperature of the heating roller 81 decreasing. The predetermined range T4 may be set as appropriate in consideration of the thermal conductivity and material of the heating roller 81, the number of continuously formed images, and the like.

  When the paper size detected by the variable resistor R1 is outside the temperature detection region T1 or the predetermined range T4 of the heating roller 81, the temperature sensor 83 can detect abnormal heating of the heating roller 81, thereby Thus, it is possible to take countermeasures such as turning off the heating element H.

  As described above, the control unit 9 is configured such that the detected size of the paper P3 passes through the temperature detection region T1 of the heating roller 81 by the temperature sensor 83 or the predetermined range T4 from the temperature detection region T1. When the sheet sensor 59 does not detect the presence of the sheet P3, it is determined that the heating roller 81 is overheated by the one-side sheet passing. When the controller 9 determines that overheating of the heating roller 81 occurs, the controller 9 prohibits image formation on the assumption that dangerous image formation is performed on the fixing unit 8. That is, when the controller 9 determines that the heating roller 81 is overheated, the controller 9 does not supply paper from the manual feed tray 51.

  Further, after prohibiting image formation, for example, a warning message such as “I am trying to pass one side of paper. Please slide the guide and feed the paper in the center” is displayed on the liquid crystal display unit 21 of the operation panel 2, for example. It can be performed. That is, the control part 9 displays a warning message on a display part, when it judges that the overheating of a heating body generate | occur | produces. If a speaker for a beep sound or the like is provided, a warning sound or a warning guide voice may be generated.

  However, when one-side paper passing is performed as shown in FIG. 8, it is not necessary to prohibit image formation. That is, even when image formation is performed by passing the paper P3 toward the side where the paper sensor 59 is provided, the overheating of the heating roller 81 can be detected by the temperature sensor 83. This is because the heating roller 81 can be prevented from being overheated so that it is possible to take measures such as cutting the energization and damage the fixing unit 8. In such a one-sided sheet passing, it is possible to prevent the fixing unit 8 from being damaged, but the temperature unevenness of the heating roller 81 occurs, so that image formation may be prohibited. In the case of this prohibition, a warning display may be displayed on the liquid crystal display unit 21 or the like as in the case of FIG.

  Therefore, the size of the detected paper P3 as shown in FIG. 8 is a size that passes through the temperature detection region T1 of the heating roller 81 by the temperature sensor 83 or the predetermined range T4 from the temperature detection region T1. When the paper detector detects the presence of the paper P3, either the large-size paper P such as the A4 paper P1 has been set or the single-side paper is being passed. Even so, the control unit 9 can determine that the heating roller 81 is not overheated.

  That is, if the paper sensor 59 detects the presence of the paper P, whether or not the paper size detected based on the variable resistor R1 is within the predetermined range T4 from the temperature detection region T1 of the heating roller 81, By detecting the temperature by the temperature sensor 83, it is possible to prevent the fixing unit 8 from being damaged due to excessive heating of the heating roller 81. In other words, when the paper sensor 59 detects the presence of the paper P, the control unit 9 determines that the heating body is not overheated, and can supply the paper from the manual feed tray 51 to form an image. . In addition, failure and breakage prevention for an abnormal usage method of one-sided paper passing in the central reference is achieved only by a configuration of a size detection unit including a temperature sensor 83, a paper sensor 59, a variable resistor R1, and the like that are also used in normal image formation. can do.

  In addition, when the size of the detected paper P is a size that does not pass through the temperature detection region T1 of the heating roller 81 by the temperature sensor 83 or the predetermined range T4 from the temperature detection region T1, it is one-side paper passing. However, even if the paper is not passed on one side, the control similar to that of the small-size paper P described in FIG. 6 may be performed, and the temperature sensor 83 can detect the overheating of the heating roller 81. What is necessary is just to judge that the overheating of a heating body does not generate | occur | produce.

  Next, control of paper feed from the manual feed tray 51 according to the embodiment of the present invention will be described with reference to FIG. FIG. 9 is a flowchart showing an example of paper feed control from the manual feed tray 51 according to the embodiment of the present invention.

  First, the start is a stage where the paper P is placed on the manual feed tray 51 and an input is made from the operation panel 2 or the like to feed the paper from the manual feed tray 51 to form an image.

  When the image formation by feeding from the manual feed tray 51 is instructed, the control unit 9 (CPU 91) receives the output of the size detection unit such as the variable resistor R1 and corresponds to the interval between the pair of guide members 57a and 57b. The paper size is detected (step # 1). Next, the control unit 9 confirms from the detected size of the paper P whether the paper P contacts the heating roller 81 within the temperature detection region T1 of the temperature sensor 83 or within the predetermined range T4 from the temperature detection region T1. Is performed (step # 2).

  If the sheet P is in contact with the heating roller 81 within the temperature detection region T1 of the temperature sensor 83 or within a predetermined range T4 from within the temperature detection region T1 (Yes in step # 2), the control unit 9 then It is confirmed whether or not the sheet sensor 59 provided on one of the guide members 57a and 57b has detected the presence of the sheet P (step # 3). If the sheet sensor 59 has not confirmed the presence of the sheet P (Yes in step # 3), the control unit 9 determines that overheating of the heating body occurs due to the one-side sheet passing (step # 4), and the image Paper supply from the manual feed tray 51 for formation is prohibited (step # 5). Further, the control unit 9 transmits a warning message to the user by means of the liquid crystal display unit 21 and sound, such as one-side paper passing, and correction of the paper P placement method (step # 6).

  Then, the control unit 9 confirms whether the paper P placement method has been corrected to the central reference while receiving the output of the size detection unit and the output of the paper sensor 59 (step # 7). If it has not been corrected (No in Step # 7), the paper feed prohibition state from the manual feed tray 51 is continued (to Step # 5). If corrected, paper supply from the manual feed tray 51 is started. (Step # 8). Thereafter, the necessary number of sheets are fed, and the paper supply from the manual feed tray 51 is ended (END).

  On the other hand, if the paper P comes into contact with the heating roller 81 within the temperature detection region T1 of the temperature sensor 83 or within the predetermined range T4 from the temperature detection region T1, and the paper sensor 59 confirms the presence of the paper P (step # 3). No), for example, the control unit 9 determines that the maximum width W2 of the transportable paper P such as the A4 paper P1 or the paper P close to the maximum width W2 has been placed (step # 9). Then, the paper supply from the manual feed tray 51 is started (to step # 8).

  Further, when the control unit 9 determines that the sheet P does not contact the heating roller 81 within the temperature detection region T1 of the temperature sensor 83 or within the predetermined range T4 from the temperature detection region T1 (No in step # 2), the control unit No. 9 determines that a sheet P smaller than the width W1 of the A4 sheet P1, such as a postcard sheet P2, A5, A6, and B5, is placed on the manual feed tray 51 (step # 10). After performing settings for performing control to prevent overheating of the heating element such as reduction of the forming speed and suppression of energization of the heating element H (step # 11), supply of paper from the manual feed tray 51 is started (step # 8). What).

  As described above, according to the configuration of the present embodiment, the paper sensor 59 (paper detector) is used to determine the paper size detected by the variable resistor R1 (size detector) and the size of the paper P actually placed. Therefore, it is possible to determine whether or not the user is going to pass the paper on one side. Based on this determination, it is possible to predict the occurrence of overheating of the heating roller 81 (heating body) and the deterioration of the formed image quality. In addition, the size detection unit and the paper detection body for detecting the paper size can be used not only for detecting one-side paper passing but also for supplying the normal paper P. In addition, it is sufficient to provide one temperature sensor 83 (temperature detection body) for detecting the temperature of the size detection unit, the paper detection body, and the heating body, respectively, and even one-side paper can be detected with a minimum configuration. Cost reduction and space saving of the paper supply unit 5 can be achieved.

  The size of the paper P detected by the size detection unit is a size that passes through the temperature detection area T1 of the heating body by the temperature detection body or within a predetermined range T4 from the temperature detection area T1, and the paper detection body is the paper P In the case where the presence of the heating element is not detected, the control unit 9 determines that overheating of the heating body occurs due to one-sided paper passing. Based on this determination, occurrence of overheating of the heating body and deterioration of the formed image quality are predicted. By doing so, it is possible to take measures to prevent the fixing unit 8 from being damaged.

  Further, since the control unit 9 prohibits image formation accompanied by overheating of the heating body that causes breakage or welding of the heating body, completely by one-sided paper feeding in the central reference copying machine 1 (image forming apparatus). It is possible to prevent the fixing unit 8 from being damaged, fused, or the like and the deterioration of the image quality. Further, in order to prevent damage, the control unit 9 does not need complicated control for controlling the image forming speed, temperature monitoring, and the like, and the burden on the control unit 9 can be reduced.

  In addition, the operation panel 2 is not suitable for one-sided paper passing, the paper P is placed in an abnormal manner, and may be damaged due to an excessive rise in the temperature of the heating element due to the abnormality. Can be transmitted. Further, even if one-side paper is passed, the paper P does not pass through the temperature detection region T1 detected by the temperature detection body or the predetermined range T4 from the temperature detection region T1, so that even if the heating body is overheated, The temperature detection body can detect the occurrence of overheating, and can prevent energization to the heating element H at least enough to cause damage to the heating body and the fixing device. Furthermore, if abnormal heating of the heating body does not occur, image formation may be performed. Therefore, image formation can be performed even when paper is passed on one side, and user convenience can be improved. Further, the members used for the temperature detector, the size detector, and the paper detector are easily available, and the paper supply unit 5 and the fixing unit 8 can be configured at low cost.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  The present invention can be used in an image forming apparatus such as a copying machine, a multifunction machine, a printer, and a facsimile machine that forms an image by heating a toner image with a fixing device.

1 is a schematic cross-sectional view illustrating an example of a copying machine according to an embodiment of the present invention. 3 is a schematic cross-sectional view illustrating an example of a configuration of a fixing unit 8. FIG. 1 is a block diagram illustrating an example of a hardware configuration of a copier according to an embodiment of the present invention. (A) is a plan view of the inside of the manual feed tray as viewed from below to show an example of the configuration of the manual feed tray, and (b) is a paper size detection based on the variable resistor R1 according to the embodiment of the present invention. It is a schematic diagram of a structure. FIG. 6 is a schematic diagram illustrating an example of a state of conveying a large size sheet according to an embodiment of the present invention. FIG. 6 is a schematic diagram illustrating an example of a state of transporting a small-size sheet according to an embodiment of the present invention. FIG. 6 is a schematic diagram illustrating an example of one-side paper passing in a fixing unit according to an embodiment of the present invention. FIG. 6 is a schematic diagram illustrating an example of one-side paper passing in a fixing unit according to an embodiment of the present invention. 6 is a flowchart illustrating an example of sheet feeding control from a manual feed tray according to the embodiment of the present invention.

Explanation of symbols

1 Copier (image forming device) 2 Operation panel (display unit)
5 Paper supply unit 51 Manual feed tray (paper supply unit 5)
57a, 57b Guide member 58 Width regulation guide 59 Paper sensor (paper detection body) 6 Paper conveyance path 7 Image forming section 8 Fixing section 81 Heating roller (heating body) 83 Temperature sensor (temperature detection body)
9 Control unit 91 CPU
A Reference position H Heating element P Paper R1 Variable resistor

Claims (10)

A paper transport path for transporting paper inside the apparatus;
An image forming unit that forms a toner image and transfers the toner image to paper;
A heating element with a built-in heating element for fixing the toner image on the sheet by heating the sheet, the axis direction being the width direction of the sheet, which is a direction perpendicular to the sheet conveyance direction, and the axial end of the heating element And a fixing unit having a temperature detecting body for detecting the temperature of the heating body,
A pair of guide members that slide symmetrically in the width direction in order to convey a sheet by matching a reference position arranged in the central portion of the sheet conveyance path in the width direction with the center axis of the sheet. A width regulating guide, a size detecting unit for detecting the size of the paper corresponding to the distance between the pair of guide members, and a paper detector provided on the guide member on the side where the temperature detector is not provided. A paper supply unit for supplying paper to the paper transport path;
A control unit that controls the operation of the apparatus and that controls the energization of the heating element in response to the output of the temperature detection body,
When the control unit receives the outputs of the size detection unit and the paper detection body, collates the detected paper size with the paper size actually placed on the paper supply unit, and performs image formation An image forming apparatus for determining whether or not overheating of the heating body has occurred.   The control unit, based on the output of the size detection unit, is a size that allows the paper size to pass within a temperature detection region of the heating body by the temperature detection body or within a predetermined range from the temperature detection region, The image forming apparatus according to claim 1, wherein when the sheet detection body does not detect the presence of the sheet, it is determined that overheating of the heating body occurs due to one-side sheet passing.   3. The image forming apparatus according to claim 1, wherein the control unit does not supply a sheet from the sheet supply unit when it is determined that overheating of the heating body occurs. 4. Having a display for displaying the status of the device;
4. The image forming apparatus according to claim 1, wherein the control unit displays a warning message on the display unit when it is determined that overheating of the heating body occurs. 5.   The control unit, based on the output of the size detection unit, is a size that allows the paper size to pass within a temperature detection region of the heating body by the temperature detection body or within a predetermined range from the temperature detection region, 5. The image forming apparatus according to claim 1, wherein when the paper detection body detects the presence of the paper, it is determined that the overheating of the heating body does not occur. 6.   The control unit, from the output of the size detection unit, when the paper size is a size that does not pass through the temperature detection region of the heating body by the temperature detection body or within a predetermined range from the temperature detection region, 6. The image forming apparatus according to claim 1, wherein it is determined that overheating of the heating body does not occur.   The image forming apparatus according to claim 1, wherein the control unit performs image formation by supplying a sheet from the sheet supply unit when it is determined that the heating body is not overheated.   The image forming apparatus according to claim 1, wherein the temperature detection body is a contact type or non-contact type thermistor provided inside or outside the heating body.   The size detection unit includes a variable resistor whose resistance value is changed in conjunction with the sliding of the pair of guide members, and the control unit is configured to determine a sheet size based on a voltage applied to the variable resistor or a flowing current. The image forming apparatus according to claim 1, wherein the image forming apparatus recognizes the image.   The image forming apparatus according to claim 1, wherein the sheet detector is an optical sensor.

Images