Patent Publication Number: US-11022918-B2

Title: Fixing device with detector for conveyance of recording medium

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Stage Application which claims the benefit under 35 U.S.C. § 371 of International Patent Application No. PCT/KR2018/012001 filed on Oct. 12, 2018, which claims foreign priority benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2017-210470 filed on Oct. 31, 2017, in the Japanese Intellectual Property Office, the contents of all of which are incorporated herein by reference. 
     BACKGROUND ART 
     Printers, copiers and facsimiles using an electrophotographic technology and multifunctional machines having these integrated therein are equipped with a fixing device for fixing toner on a recording medium such as paper by heat and pressure. A fixing device is provided with a heating rotation body for supplying heat for fusing toner to a recording medium, and a pressing rotation body for supplying a pressure for pressure bonding of toner to the recording medium. Toner that has been transferred onto the recording medium is fixed onto the recording medium while the recording medium is conveyed in a state where it is sandwiched at a nip portion, where the heating rotation body and the pressing rotation body are pressed against each other. At that time, in the fixing device, the recording medium to be conveyed varies its position and angle for entry to the nip portion depending on the use environment, and the kind (or type) and the state of the recording medium. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic front view showing an example image forming apparatus including a fixing device according to an example. 
         FIG. 2  is a schematic side view showing the example fixing device shown in  FIG. 1 . 
         FIG. 3  a schematic side view showing an imaging region of an upstream side in conveyance (inlet-side) in the example fixing device of  FIG. 2 . 
         FIG. 4  is a schematic side view showing a recording medium, which passes through an inlet-side imaging region while being deformed (curled) in the example fixing device of  FIG. 2 . 
         FIG. 5  is a schematic side view showing a recording medium, which passes through the inlet-side imaging region in a normal state in the example fixing device of  FIG. 2 . 
         FIG. 6  is a block diagram showing one example of a functional block in the example fixing device shown in  FIG. 2 . 
         FIG. 7  is a schematic side view showing a fixing device according another example. 
         FIG. 8  is a schematic side view showing an operation of an example deformation correcting device (for correcting an upward curl), in the example fixing device shown in  FIG. 7 . 
         FIG. 9  is a schematic side view showing an operation of the example deformation correcting device (for correcting a downward curl), in the example fixing device shown in  FIG. 7 . 
         FIG. 10  is a schematic side view showing an imaging region of a downstream side in conveyance (outlet-side) in the example fixing device shown in  FIG. 7 . 
         FIG. 11  is a block diagram of the example fixing device shown in  FIG. 7 . 
         FIG. 12  is a schematic side view showing a state of a normal operation at an outlet-side imaging region of a fixing device according to another example. 
         FIG. 13  is a schematic side view showing a state where a malfunction occurs at the outlet-side imaging region of the example fixing device shown in  FIG. 12 . 
         FIG. 14  is a block diagram of the example fixing device shown in  FIG. 12 . 
     
    
    
     MODE FOR INVENTION 
     In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted. 
       FIG. 1  illustrates a schematic configuration (side configuration) of an example image forming apparatus (for example, printer) including an example fixing device. 
     Example Configuration of the Image Forming Apparatus 
     An image forming apparatus  1  is an apparatus forming a color image by use of each of colors such as magenta, yellow, cyan and black. As shown in  FIG. 1 , the image forming apparatus  1  includes an image forming part  100  and forms an image on a paper P (recording medium). 
     The image forming part  100  has a recording medium conveyance unit  10  for conveying a paper P, a developing device  20  for developing an electrostatic latent image, a transfer unit  30  for secondary transfer of a toner image on the paper P, a photoreceptor drum  40  being an electrostatic latent image carrier having an image formed on a periphery thereof, and a fixing device  50  for fixing the toner image on the paper P. 
     The recording medium conveyance unit  10  conveys the paper P, on which the image will be formed, on a conveyance path R 1 . Paper sheets P are stacked and accommodated in a cassette K, and picked up and conveyed one-by-one by a paper feeding roller. 
     The developing device  20  is provided for each of four colors. Each developing device  20  has a developing roller  21 , which allows the photoreceptor drum  40  to carry toner. The developing device  20  makes such an adjustment that toner and a carrier are included at a desired mixing ratio, and further, they are mixed and stirred so that the toner is dispersed uniformly, thereby preparing a developer having an optimum charge amount imparted thereto. The developer is carried on the developing roller  21 . Subsequently, when the developer is carried by the rotation of the developing roller  21  to a region facing the photoreceptor drum  40 , toner of the developer carried by the developing roller  21  is moved onto an electrostatic latent image formed on the periphery of the photoreceptor drum  40  and the electrostatic latent image is developed. 
     The transfer unit  30  conveys a toner image formed by each developing device  20  to a secondary transfer region R 2  where secondary transfer of the toner image is performed onto the paper P. The transfer unit  30  has a transfer belt  31 , suspending rollers  31   a ,  31   b ,  31   c  and  31   d , which are suspending the transfer belt  31 , a primary transfer roller  32 , which holds the transfer belt  31  together with the photoreceptor drum  40 , and a secondary transfer roller  33 , which holds the transfer belt  31  together with the suspending belt  31   d . The transfer belt  31  is an endless belt, which moves in a circulating manner by the suspending rollers  31   a ,  31   b ,  31   c  and  31   d.    
     The photoreceptor drum  40  is provided for each of four colors. Each photoreceptor drum  40  is provided along a moving direction of the transfer belt  31 . The photoreceptor drum  40  has the developing device  20 , a charging roller  41 , an exposure unit  42  and a cleaning unit  43  provided thereon. 
     The charging roller  41  includes charging means that uniformly charges the surface of the photoreceptor drum  40  at a predetermined electric potential. The charging roller  41  moves while following the rotation of the photoreceptor drum  40 . The exposure unit  42  exposes, to light, the surface of the photoreceptor drum  40 , which has been charged by the charging roller  32 , according to an image to be formed on the paper P. This changes an electric potential of a portion of the surface of the photoreceptor drum  40 , which is exposed to light by the exposure unit  42 , thereby forming an electrostatic latent image. Each of four developing devices  20  receives toner fed from a tonner tank N of each color, provided opposite to each developing device  20 , and develops an electrostatic latent image formed on the photoreceptor drum  40  with the toner, thereby forming a toner image. After the toner image formed on the photoreceptor  40  is transferred to the transfer belt  31  through primary transfer, the cleaning unit  43  collects toner remaining on the photoreceptor drum  40 . 
     The fixing device  50  adheres and fixes the toner image, which is transferred from the transfer belt  31  to the paper P through secondary transfer, to the paper P. The fixing device  50  has a heating roller (or fixing roller, or heating body)  51  for heating the paper P, and a pressing roller (or pressing body)  52  for pressing against the heating roller  51 . The heating roller  51  is one example of a heating rotation body. The pressing roller  52  is one example of a pressing rotation body. The heating roller  51  and the pressing roller  52  are formed in a cylindrical shape or a rod-like shape. The heating roller  51  is sometimes provided with a heating source such as a halogen lamp or a heater in the interior thereof. There is provided a nip portion  51   a , which is a contact region between the heating roller  51  and the pressing roller  52 . The paper P is allowed to pass through the nip portion  51   a , and this enables the toner image to be fused and fixed onto the paper P. After the secondary transfer of the toner image onto the paper P, toner remaining on the transfer belt  31  is collected by a belt cleaning device. 
     The image forming device  1  is provided with discharge rollers  53 ,  54  for discharging the paper P having the toner image fixed thereon by the fixing device  50  to the outside of the image forming device. 
     In some fixing devices, the recording medium to be conveyed varies its position and angle for entry to the nip portion depending on the use environment, and the kind (or type) and the state of the recording medium. Thus, some abnormal operation (e.g. paper winkle, image distortion and/or stains on images) and/or paper jams may occur in various conveyance systems. Further, if a recording medium winds around the heating rotation body or the pressing rotation body when it is discharged from the nip portion, a paper jam may occur, and further affect the material (or structural) condition of the heating rotation body, the pressing rotation body and/or other member(s) (or components). 
     Some fixing devices are configured to detect a paper jam caused in or around the fixing device by a recording medium passage sensor provided near an inlet of the fixing device and a recording medium passage sensor provided near an outlet of the fixing device. A detection method in such configurations is based on a transit time of the recording medium from the inlet to the outlet, and thus, a detection timing occurs later than a timing when a paper jam occurs, e.g. the paper jam is detected after it has occurred. As a result, the recording medium may wind around the heating rotation body or the pressing rotation body, which may interfere with the winding removal function. Further, depending on a state of the paper jam, the material (or structural) condition of the heating rotation body, the pressing rotation body and/or other member(s) (or components) may be affected. 
     In other fixing devices, the recording medium passage sensor provided near the inlet is replaced with a sensor capable of measuring a displacement of a recording medium such that the sensor detects a passing position (a distance from a guide member) and provides feedback to a conveyance motor and a conveyance guide. However, in this case, since the sensor detects the recording medium only at a specific point, an abnormal operation may still occur, resulting in a deformed (warped) recording medium, for example, which may further cause a paper jam and/or otherwise interfere with the normal conveyance of the recording medium. 
     In other configurations, when a recording medium has passed through first paper detection means after a paper jam is detected, there is a possibility that the paper is stopped where winding on a fixing roller and a pressing roller has occurred. If the rollers are moved in a reverse direction, the material (or structural) condition of the rollers may be affected. 
     In other configurations, a sensor at a downstream end does not detect paper, although a sensor at an upstream end detects the paper, and a paper jam only within a predetermined area is detected, thus causing a delay of detection. Therefore, when paper winds around a roller of a conveyance system, the wound paper must be removed from the roller. 
     In other configurations, only an amount of loop (bending) is detected, such that a deformation or the like of a recording medium cannot be detected. 
     An example fixing device is configured, at an upstream side of a nip portion: to stop conveyance of a recording medium depending on the passing region, the angle and the degree of deformation from a direction a side face of a tip of the recording medium during conveyance; or to stabilize the entry of the recording medium to the nip portion; or to adjust a speed of a conveyance motor for driving a rotation body. 
     Another example fixing device is configured, at a downstream side of the nip portion, depending on the passing region, the angle and the degree of deformation from a direction a side face of a tip of the recording medium during conveyance: to stop conveyance of a recording medium; or to correct the deformation of the recording medium; or to adjust a speed of conveyance means for conveying the recording medium downstream. 
     Another example fixing device is configured to detect a rotation speed, an action and a deformation state of a heating rotation body and a pressing rotation body from a direction of a side face of these rotation bodies. 
     Configuration of the Fixing Device 
     Example fixing devices will be described with reference to the drawings. 
     An example fixing device  50  is shown in  FIGS. 2 to 6 .  FIG. 2  is a side view of the configuration of the fixing device  50 . As described above, the heating roller  51  has a cylindrical shape or a rod-like shape. 
     When the heating roller  51  is formed of, for example, an endless belt as shown in  FIG. 2 , it may be formed of a base layer, an intermediate layer and a surface layer, ordered from the inside. For the base layer, a metal such as stainless or nickel can be used. For the intermediate layer, silicone rubber, for example, can be used. For the surface layer, a fluoro-resin, for example, can be used. This fluoro-resin makes it difficult to cause the paper P or a recording medium to be stuck. Further, when the heating roller  51  includes an endless belt, a nip portion forming-member made of, for example, a metal is sometimes disposed for forming the nip portion  51   a . When the heating roller  51  is formed of a rod-like member, the heating roller  51  may be formed of, for example, a core metal at the inner portion thereof and an elastic body covering the outer periphery of the core metal. Further, when the heating roller  51  is a rod-like member, the heating source may have a form wherein a heating member using IH (induction heating) is a heat generation source or a form wherein heat is given indirectly from the outside. 
     The pressing roller  52  is provided so as to be in contact with the position where the nip portion  51   a  is formed on an outer periphery of the heating roller  51 . The pressing roller  52  may be formed of, for example, a core metal at the inner portion and an elastic body covering the outer periphery of the core metal. 
     As described above, the pressing roller  52  drives the heating roller while holding the paper at the nip portion  51   a  on the outer periphery of the heating roller  51 . At that time, the image electrostatically formed on the paper is fused and fixed by heat generated by the heating roller  51  and the pressure from the pressing roller  52  at the nip portion  51   a.    
     Further, at an upstream side of the nip portion  51   a  in conveyance, or an inlet, there is provided an inlet guide plate  61  for guiding the paper P to the nip portion  51   a . Likewise, at a downstream side of the nip portion  51   a  in conveyance, or an outlet, there is provided an outlet guide plate  62  for guiding the paper P to the downstream side in conveyance. The inlet guide plate (or guide member)  61  and the outlet guide plate (or guide member)  62  are examples of corrective devices in the example fixing device  50 . 
     In addition, the fixing device  50  has detection means or a detector, for example a camera  71 , which is provided at the inlet of the paper P at the nip portion  51   a , and detects at least one of a passing region of a tip of the paper P, an angle of the paper P, and a deformation degree of the paper P from a direction of a side face of the paper P. The camera  71  may be, for example, a camera having an image sensor composed of a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor) sensor. Further, the detection means is not limited to the camera  71 , but may be a two-dimensional laser displacement meter (two-dimensional laser displacement sensor) or may be other two-dimensional displacement sensor. 
     As shown in  FIG. 2 , the camera  71  can capture an image of an inlet-side imaging region  71   a  positioned at the inlet of the nip portion  51   a.    
     The example fixing device  50 , is configured to determine a predictable malfunction in a conveyance of the recording medium. The predictable malfunction may be determined based on a detection of a passing region of a tip of the recording medium, on an angle of the recording medium and/or on a degree of deformation of the recording medium from a direction of a side face of the recording medium. The fixing device  50  further includes one or more corrective devices to carry out a corrective operation associated with the conveyance of the recording medium, in response to the predictable malfunction determined, in order to prevent the predictable malfunction from occurring. 
     Method for Controlling the Fixing Device/Determination of a Paper Jam 
     Hereafter, for methods for controlling the example fixing device, judgement (or determination) on paper jam will be described by referring the drawings. FIG.  3  shows a control map of an inlet-side imaging region  71   a  of the fixing device  50 . The inlet-side imaging region  71   a  of  FIG. 3  corresponds to the inlet-side imaging region  71   a  shown in  FIG. 2 . 
     As shown in  FIG. 3 , the inlet-side imaging region  71   a  is divided into three regions: a first passing region A, a second passing region B and a third passing region C. 
     For example, when the tip of the paper P passes through the first passing region A along a trajectory ( 1 ), it is determined that the paper P is in a normal conveyance state. Therefore, the fixing device  50  does not make any particular control on the paper P such as the above during conveyance. 
     When the tip of the paper P passes through the second passing region B along a trajectory ( 2 ), a guide changing part  73  (see  FIG. 6 ) changes at least one of a height  61   a , a position  61   b  and an angle  61   c  of the inlet guide plate  61 . The guide changing part  73  may use an electric motor, an electromagnetic solenoid or the like as a driving device for driving the inlet guide plate  61 . The guide changing part (or guide changing device)  73  is one example of guide changing means, among examples of corrective devices. 
     Further, for the paper P conveyed over the surface of the inlet guide plate  61 , an entry stabilizing part (or entry stabilizing device)  74  (see  FIG. 6 ) may be provided, which enables easy insertion of the tip of the paper into the nip portion  51   a . In this case, the inlet guide plate  61  has a plurality of through holes provided in the front-back direction and air is sucked from under the inlet guide plate  61  at least during conveyance of the paper P. This allows the conveyed paper P to be pressed to the upper surface of the inlet guide plate  61 . The entry stabilizing part (or entry stabilizing device)  74  is one example of entry stabilizing means. 
     Accordingly, when the tip of the paper P passes through the second passing region B, the guide changing part  73  adjusts at least one of the height  61   a , the position  61   b  and the angle  61   c  of the tip of the paper P, and thereby, the tip of the paper P can be guided to the nip portion  51   a . At that time, pressing the paper P to the upper surface of the inlet guide plate  61  by operation of the entry stabilizing part  74  allows the tip of the paper P to be more easily guided to the nip portion  51   a.    
     It should be noted that the fixing device  50  does not necessarily have both of the guide changing part  73  and the entry stabilizing part  74 , and it is effective to have either one of them. 
     Further, the entry stabilizing part  74  sucks air from under the inlet guide plate  61 ; however, instead of this, the entry stabilizing part may be configured so that air is discharged from above the inlet guide plate  61  to press the paper P to the upper surface of the inlet guide plate  61 . In this case, the inlet guide plate  61  may be provided with through holes for air circulation, or not provided therewith. 
     When the tip of the paper P passes through the third passing region C along a trajectory ( 3 ), it is determined that the paper P cannot be conveyed; and a conveyance stopping part  72  (see  FIG. 6 ) stops a conveyance motor (not illustrated), which drives the heating roller  51  or the pressing roller  52 . A conveyance stopping part (or conveyance stopping device, also referred to herein as a roller stopping device)  72  is an example of a corrective device in the example fixing device  50 . 
     When the tip of the paper P first passes through the second passing region B, and thereafter returns to the first passing region A, an inlet-side speed adjusting part  75  (see  FIG. 6 ) increases a rotation speed of the conveyance motor to make up for a delay of feeding of the paper P. The inlet-side speed adjusting part (or speed adjusting device)  75  is an example of a corrective device in the example fixing device  50 . When the paper P has a simple curl as shown in  FIG. 4 , the position of the tip of the paper P reaches later than that of paper P 0 , which is flat and not curled as shown in  FIG. 5 . Therefore, if the rotation speed of the heating roller  51  and the pressing roller  52  is increased to correct the curl, the entire of the paper P is allowed to return to the first passing region A. 
     Even when the tip of the paper first passes through the second passing region B and then, returns to the first passing region A, the conveyance motor is stopped when it is determined that an event other than a simple deform (curl) has occurred, for example, a paper winkle generated on the paper P. 
     In some fixing devices, a recording medium passing sensor is provided near an inlet and an outlet of the device, but the determination of a paper jam is made by the recording medium passing sensor provided near the outlet. Accordingly, the fixing device is stopped after a paper jam has occurred in the fixing device. 
     In order to prevent the paper jam from occurring, the above-described fixing device  50  is enabled to stop conveying the paper P when it detects a state where occurrence of a paper jam of the conveyed paper P is predicted. In addition, when it is determined that the paper P that has not passed through a predetermined region can be inserted to the nip port ion  51   a  if it is corrected or remedied, it is possible to continue the operation of the fixing device  50 . 
     Method for Controlling the Fixing Device/Failure Determination 
     Concerning methods for controlling the example fixing device, judgement (or determination) on a failure will be described. 
     Inlet-side detection data obtained from the inlet-side imaging region  71   a  in  FIG. 3  is accumulated (or collected); and then, when the probability of a transition from the trajectory ( 1 ) to the trajectory ( 4 ) is increased (beyond a threshold, for example), an alarm is issued (or set off). Thereafter, even when an adjustment of the rotation speed of the conveyance motor does not enable passing of the first passing region A, it is determined that a failure occurs and the conveyance motor is stopped. 
     Further, when the behavior of conveyance of the paper P is not stable, for example, when the paper repeatedly moves between the first passing region A and the second passing region B or when the paper P has vibrations or flapping, it is determined that a failure occurs and the conveyance motor is stopped. 
       FIG. 6  shows one example of a functional block configuration in the example fixing device  50 . As shown in  FIG. 6 , each of the above-described constituent elements can be controlled by, for example, a MPU (Micro Processor Unit)  80 . 
     Another example fixing device will be described with reference to  FIGS. 7 to 11 . Identical signs (reference numbers) are given to the same constituent members and constituent elements as those described in the example fixing device shown in  FIG. 2 , and thus detailed explanations thereof are omitted. 
       FIG. 7  illustrates a side view of the configuration of the example fixing device. As shown in  FIG. 7 , the example fixing device  50  has detection means (or a detector), for example, a camera  71 , which is provided at the outlet of the paper P at the nip portion  51   a , and detects at least one of a passing region of a tip of the paper P, an angle of the paper P, and a deformation degree of the paper P from a direction of a side face of the paper P. The detect ion means is not limited to a camera, but may be a two-dimensional laser displacement meter (two-dimensional laser displacement sensor) or may be other two-dimensional displacement sensor. 
     As shown in  FIG. 7 , the camera  71  may capture an image of an outlet-side imaging region  71   b  positioned at the outlet of the nip portion  51   a.    
     Further, provided at the downstream side of the heating roller  51  and the pressing roller  52  is a conveyance roller pair  64  for conveying the paper P having passed through the nip portion  51   a  and completed the fixing process. The conveyance roller pair  64  may have a configuration wherein a roller core thereof is made of a metal or a resin material and the surface of the roller core is coated with an elastic body. The conveyance roller pair (or conveyance device)  64  is one example of conveying means and an example of a corrective device in the example fixing device  50 . 
     At the downstream side of the conveyance roller pair  64  in conveyance, a deformation correcting device (curl correcting device)  66  as deformation correcting means is provided. Applicable configurations for the deformation correcting device  66  include for example, a configuration using a conveyance roller pair, a configuration using three or more conveyance roller, and a configuration which suspends an endless belt. The deformation correcting device (curl correcting device)  66  is an example of a corrective device in the example fixing device  50 . 
       FIGS. 8 and 9  show examples of the deformation correcting device  66 , having a configuration including a pair of conveyance rollers. 
     The example deformation correcting device  66  of  FIG. 8  is composed of, for example, a first roller  66   a  having a higher modulus of elasticity (hard) and a second roller  66   b , which is in pressure contact with the first roller  66   a  and has a larger diameter and a lower modulus of elasticity (soft) than the first roller  66   a . Further, the deforming correcting device  66  is provided so as to be able to adjust a pressing force F of each of rollers  66   a  and  66   b  depending on the degree of deformation of the paper P. 
     When an upward curl (projecting upwardly) occurs in the paper P having passed through the nip portion  51   a  and the conveyance roller pair  64 , the pressing force F is controlled by an instruction from a correction instructing part  76  (see  FIG. 11 ). As the degree of deformation of the paper P is larger, a larger pressing force is applied to correct an upward curl (the right-hand side of  FIG. 8 ). The correction instructing part (correction instructing device)  76  is an example of a corrective device in the example fixing device  50 . 
     The deformation correcting device  66  of  FIG. 9  has the first roller  66   a  and the second roller  66   b , whose places are changed therebetween relative to the deformation correcting device  66  of  FIG. 8 . When a downward curl (projecting downwardly) occurs in the paper P having passed through the nip portion  51   a  and the conveyance roller pair  64 , this can correct the downward curl. In this case, as the degree of deformation of the paper P is larger, a larger pressing force is applied thereby to correct a downward curl (see the right-hand side of  FIG. 9 ). 
     Method for Controlling the Fixing Device/Judgement on Paper Jam 
     Hereafter, for methods for controlling the example fixing device, judgement (or determination) on paper jam will be described by referring to the drawings.  FIG. 10  shows a control map of an outlet-side imaging region  71   b  of the fixing device  50 . The outlet-side imaging region  71   b  of  FIG. 10  corresponds to the outlet-side imaging region  71   b  shown in  FIG. 7 . 
     As shown in  FIG. 10 , the outlet-side imaging region  71   b  is divided into three regions: a first passing region A, a second passing region B and a third passing region C. 
     For example, when the tip of the paper P passes through the first passing region A along a trajectory ( 5 ), it is determined that the paper P is in a normal conveyance state. Therefore, the fixing device  50  does not make any particular control on the paper P such as the above during conveyance. 
     When the tip of the paper P passes through the second passing region B along a trajectory ( 6 ), the speed of the conveyance roller pair  64  is increased by an instruction from an outlet-side speed adjusting part (see  FIG. 11 ). Further, a correction amount for a curl, which may include an adjustment amount of a pressing force at the roller pair  64  is instructed (fed back) to the above-described deforming correcting device  66 . The outlet-side speed adjusting part (or speed adjusting device) is an example of a corrective device in the example fixing device  50 . 
     When the tip of the paper P passes through the third passing region C along a trajectory ( 7 ), it is determined that the paper P cannot be conveyed; and a conveyance stopping part  72  stops a conveyance motor (not illustrated), which drives the heating roller  51  or the pressing roller  52 , and the conveyance roller pair  64 . The conveyance stopping part (or conveyance stopping device)  72  is an example of a corrective device in the example fixing device  50   
     In some fixing devices, a recording medium passing sensor near an outlet of the device is used to detect a paper jam, which occurs in and around the fixing device. 
     The above-described example fixing device  50  stops conveying the paper P when it detects that a paper jam is predicted on the paper P having passed through the nip portion  51   a . In addition, when it is determined that the paper P that has not passed through a predetermined region can be corrected or remedied, it is possible to continue the operation of the fixing device  50 . 
     Method for Controlling the Fixing Device/Failure Determination 
     Concerning methods for controlling the example fixing device, judgement (or determination) on a failure will be described. 
     Outlet-side detection data obtained from the outlet-side imaging region  71   b  in  FIG. 10  is accumulated (or collected); and then, when the probability for passage of the paper P through the third passing region C is increased (beyond a threshold, for example), it is determined that a failure occurs and the conveyance motor is stopped. 
     Further, when the behavior of conveyance of the paper P is not stable, for example, when the paper repeatedly moves between the first passing region A and the second passing region B or when the paper P has vibrations or flapping, it is determined that a failure occurs and the conveyance motor is stopped. 
       FIG. 11  shows one example of a functional block configuration in the fixing device  50 . As shown in  FIG. 11 , each of the above-described constituent elements can be controlled by, for example, a MPU (micro Processor Unit)  81 . 
     Further, in other examples, the fixing device may have the configuration shown in  FIG. 11  combined with the configuration of the example shown in  FIG. 6 . This provides a configuration that allows paper jam detect ion and failure detection simultaneously at the inlet-side and outlet-side of the nip portion  51   a.    
     An example fixing device will be described with reference to  FIGS. 12 to 14 . 
     In additional examples, reference is made to the configuration of the fixing device  50  shown in  FIG. 7 . However, for the example of  FIG. 12 , a camera  71  capable of image processing is suitable as detection means. 
       FIG. 12  illustrates an outlet-side imaging region  71   b  in the example fixing device. In  FIG. 12 , identical signs (or numeric references) are given to the same constituent members as those described in the example fixing device of  FIGS. 7 to 11 , and thus detailed explanations thereof are omitted. 
     As shown in  FIG. 12 , the heating roller  51  and the pressing roller  52  have detection marks  51   b  and  52   b  identifiable as side faces thereof given to circumferential portions of the side faces thereof. For example, the heating roller  51  and the pressing roller  52  have side faces that are marked with the detection marks  51   b  and  52   b  on circumferential portions of the side faces. These detection marks  51   b  and  52   b  may be formed by affixing a sealing material, painting or the like. 
     The camera  71  detects at least one of the rotation speed, the action and the deformation state of the heating roller  51  and the pressing roller  52 , and the conveyance speed of the paper P. 
     These items (rotation speed, action, deformation state and conveyance speed) can be detected by making calculation based on image data captured by means of the camera  71 . 
     Method for Controlling the Fixing Device/Failure Determination 
     Regarding a malfunction of the heating roller  51  and the pressing roller  52 , also referred to as a first failure judgement (or first failure determination), it is determined that a failure occurs when a difference between the rotation speed of the heating roller  51  and the rotation speed of the pressing roller  52  as shown in  FIG. 13 , is equal to or greater than a threshold (e.g. a predetermined value). When it is determined that a failure occurs, the conveyance motor (not illustrated), which drives the heating roller  51  or the pressing roller  52 , is stopped by an instruction from the conveyance stopping part  72  (see  FIG. 14 ). The conveyance stopping part  72  is one example of rotation body stopping means. In the above, when the heating roller  51  and the pressing roller  52  have a difference of rotation speed of, for example, about 10% or more, it may be determined that a failure occurs. 
     Further, regarding a second failure judgement (or second failure determination), it is determined that a failure occurs when a difference between the rotation speed of the heating roller  51  or the pressing roller  52 , and the conveyance speed of the paper P during conveyance is equal to or greater than a threshold (e.g. a predetermined value). When it is determined that a failure occurs, the conveyance motor, which drives the heating roller  51  or the pressing roller  52 , is stopped by an instruction from the conveyance stopping part  72 . For example, when the difference between the rotation speed of the heating roller  51  or the pressing roller  52 , and the conveyance speed of the paper P becomes, for example, 10% or more, it may be determined that a failure occurs. 
     Further, regarding a third failure judgement (or third failure determination), it is determined that a failure occurs when the rotational trajectories of the heating roller  51  and the pressing roller  52  are changed beyond a threshold, e.g. the trajectories are changed by a predetermined value or more. When it is determined that a failure occurs, the conveyance motor, which drives the heating roller  51  or the pressing roller  52 , is stopped by an instruction from the conveyance stopping part  72 . For example, when a displacement amount between the rotational trajectories of the heating roller  51  and the pressing roller  52  becomes about 5% or more of the diameter (radius) of each of the rollers  51  and  52 , it may be determined that a failure occurs. 
     The location of the configuration (detection mechanism) is not limited to the outlet-side of the nip portion  51   a , but it may be provided at the inlet-side of the nip portion  51   a.    
       FIG. 14  shows one example of a functional block configuration in the fixing device  50 . As shown in  FIG. 14 , each of the above-described constituent elements can be controlled by, for example, a MPU (Micro Processor Unit)  82 . Further, in some examples, the fixing device may have the configuration shown in  FIG. 14  combined with the configuration of the example shown in  FIG. 11 . 
     The example fixing device detects at least one of the rotation speed, the action and the deformation state of the heating roller  51  and the pressing roller  52 , and the conveyance speed of the paper P, thus enabling early and reliable detection of a failure caused by a malfunction of the heating roller  51  and the pressing roller  52 . 
     Accordingly, a predictable malfunction such as a paper jam or deformation of a recording medium being conveyed, for example may be predicted, in order to carry out a corrective operation such as stopping or correcting the conveyance of the recording medium, in order to prevent the predictable malfunction from occurring. The operation of the device may thus be stopped by predicting a paper jam in advance, thereby better protecting the material (or structural) condition of constituent members (or components) of the device. Further, when the degree of deformation of a recording medium is small, the deformation may be corrected or remedied, thereby making it unnecessary to stop the operation of the device. 
     Various examples of fixing devices will be described. 
     An example fixing device includes a heating rotation body (or heating body), a pressing rotation body (or pressing body), detection means, and conveyance stopping means. The heating rotation body is provided with heating means. The pressing rotation body conveys a recording medium at a nip portion formed by pressing a peripheral side of the heating rotation body and fixes an image formed on the recording medium with heating at the nip portion. Detection means are provided at an upstream side of the nip portion in conveyance of the recording medium, to detect at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. Conveyance stopping means are adapted for stopping conveyance of the recording medium when the detection means detects that the recording medium is deviated from a predetermined region at the upstream side in conveyance. 
     When the detection means detects that the recording medium is deviated from a predetermined region at the upstream side in conveyance, the tip of the recording medium is less likely to be sandwiched at the nip portion and a paper jam is likely to occur. However, this example fixing device stops conveyance of the recording medium, and the device can be stopped before the occurrence of a paper jam. As a result, the material (or structural) condition of the rotation bodies and/or other member(s) are better protected. 
     Another example fixing device includes a heating rotation body, a heating rotation body, a pressing rotation body, detection means, a guide member, and guide changing means. The heating rotation body is provided with heating means. The pressing rotation body conveys a recording medium at a nip portion formed by pressing a peripheral side of the heating rotation body and fixes an image formed on the recording medium with heating at the nip portion. Detection means are provided at an upstream side of the nip portion in conveyance of the recording medium, to detect at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. A guide member is provided at the upstream side of the nip portion in conveyance, to guide the recording medium to the nip portion. The guide changing means are adapted to change at least one of a height, a position and an angle at the guide member when the detection means detects an abnormality in at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium, or entry stabilizing means for stabilizing the entry of the recording medium to the nip portion. 
     Therefore, the guide changing means or the entry stabilizing means changes the position of the tip of the recording medium during conveyance to a position that allows the entry to the nip portion, thereby preventing a paper jam and reducing abnormal operation of the conveyance, and also making it unnecessary to stop the operation of the device. 
     Another example fixing device includes a heating rotation body, a pressing rotation body, detection means, and speed adjusting means. The heating rotation body is provided with heating means. The pressing rotation body conveys a recording medium at a nip portion formed by pressing a peripheral side of the heating rotation body and fixes an image formed on the recording medium with heating at the nip portion. The detection means are provided at an upstream side of the nip portion in conveyance of the recording medium, detect at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. The speed adjusting means are adapted to adjust a rotation speed of a conveyance motor when the detection means detects an abnormality in at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. 
     When it is assumed that a loop occurs due to a low conveyance speed of the tip of the recording medium (delayed arrival time to a predetermined position), an increase of rotation speed of the conveyance speed of the pressing rotation body can eliminate the loop of the recording medium after the passage through the nip portion. This can stabilize the behavior of the recording medium from the process prior to fixing and reduce abnormal operation of the conveyance, also making it unnecessary to stop the operation of the device. 
     Another example fixing device includes a heating rotation body, a pressing rotation body, detection means, and conveyance stopping means. The heating rotation body is provided with heating means. The pressing rotation body conveys a recording medium at a nip portion formed by pressing a peripheral side of the heating rotation body and fixes an image formed on the recording medium with heating at the nip portion. The detection means are provided at an upstream side of the nip portion in conveyance of the recording medium, to detect at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. The conveyance stopping means are adapted to stop conveyance of the recording medium when a conveyance region of the recording medium is within a predetermined region at the upstream side in conveyance and the detection means detects an abnormality in a conveyance speed of the recording medium. 
     Thus, the device can be stopped before the occurrence of a paper jam. As a result, the material (or structural) condition of the rotation bodies and/or other member(s) are better protected. 
     Another example fixing device includes a heating rotation body, a pressing rotation body, detection means, and conveyance stopping means. The heating rotation body provided with heating means. The pressing rotation body conveys a recording medium at a nip portion formed by pressing a peripheral side of the heating rotation body and fixes an image formed on the recording medium with heating at the nip portion. Detection means are provided at a downstream side of the nip portion in conveyance of the recording medium, to detect at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. Conveyance stopping means are adapted to stop conveyance of the recording medium when the detection means detects that the recording medium is deviated from a predetermined region at the downstream side in conveyance. 
     Therefore, when the detection means detects that the recording medium is deviated from a predetermined region at the downstream side in conveyance, the tip of the recording medium cannot be discharged from the fixing device and a paper jam is likely to occur. However, in this aspect, the conveyance stopping means stops conveyance of the recording medium, so the device can be stopped before the occurrence of a paper jam. As a result, the material (or structural) condition of the rotation bodies and/or other member(s) are better protected. 
     Another example fixing device includes a heating rotation body, a pressing rotation body, detection means, deformation correcting means, and correction instructing means. The heating rotation body is provided with heating means. The pressing rotation body conveys a recording medium at a nip portion formed by pressing a peripheral side of the heating rotation body and fixes an image formed on the recording medium with heating at the nip portion. The detection means are provided at a downstream side of the nip portion in conveyance of the recording medium, to detect at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. The deformation correcting means are provided at the downstream side of the nip portion in conveyance, to correct a deformation of the recording medium while conveying the recording medium downstream. The correction instructing means are adapted to instruct the deformation correcting means to correct a deformation of the recording medium when the detection means detects the deformation of the recording medium. 
     This allows the deformation correcting means to correct a deformation of a recording medium during conveyance, thereby preventing a paper jam and reducing abnormal operation of the conveyance, also making it unnecessary to stop the operation of the device. 
     Another example fixing device includes a heating rotation body, a pressing rotation body, detection means, conveyance means, and speed adjusting means. The heating rotation body is provided with heating means. The pressing rotation body conveys a recording medium at a nip portion formed by pressing a peripheral side of the heating rotation body and fixes an image formed on the recording medium with heating at the nip portion. The detection means are provided at a downstream side of the nip portion in conveyance of the recording medium, to detect at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. Conveyance means are provided at the downstream side of the nip portion in conveyance and conveys the recording medium downstream. The speed adjusting means are adapted to adjust a conveyance speed of the conveyance means when the detection means detects an abnormality in at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. 
     Accordingly, the behavior of the recording medium between the nip portion and the conveyance means at the downstream side thereof, may be stabilized, thereby reducing abnormal operation of the conveyance, and also making it unnecessary to stop the operation of the device. 
     Another example fixing device includes a heating rotation body, a pressing rotation body, detection means, and conveyance stopping means. The heating rotation body is provided with heating means. The pressing rotation body conveys a recording medium at a nip portion formed by pressing a peripheral side of the heating rotation body and fixes an image formed on the recording medium with heating at the nip portion. The detection means are provided at a downstream side of the nip portion in conveyance of the recording medium and detects at least one of a passing region of a tip of the recording medium, an angle of the recording medium and a degree of deformation of the recording medium from a direction of a side face of the recording medium. The conveyance stopping means are adapted to stop conveyance of the recording medium when a conveyance region of the recording medium is within a predetermined region at the downstream side in conveyance and the detection means detects an abnormality in a conveyance speed of the recording medium. 
     Accordingly, the fixing device can be stopped before the recording medium is discharged from the device. As a result, the rotation bodies and/or other member(s) are better protected, for example as to their material (or structural) condition. 
     Another example fixing device includes a heating rotation body, a pressing rotation body, and detection means. The heating rotation body is provided with heating means. The pressing rotation body conveys a recording medium at a nip port ion formed by pressing a peripheral side of the heating rotation body and fixes an image formed on the recording medium with heating at the nip portion. The detection means are provided at least a downstream side of the nip portion, of an upstream side and the downstream side thereof, in conveyance of the recording medium, to detect at least one of a rotation speed, an action and a deformation state of the heating rotation body and the pressing rotation body from a direction of a side face of the heating rotation body and the pressing rotation body. 
     Accordingly, when the detection means detects at least one of a rotation speed, an action and a deformation state of each rotation body, stoppage of the rotation body enables the device to be stopped before the occurrence of a paper jam. As a result, the rotation bodies and/or other member(s) are better protected, for example as to their material (or structural) condition. 
     The detection means may further have rotation body stopping means for stopping a conveyance motor when a difference of rotation speed between the heating rotation body and the pressing rotation body exceeds a predetermined value. 
     The detection means may further have rotation body stopping means for stopping a conveyance motor when a difference between a rotation speed of the heating rotation body and the pressing rotation body, and a speed of the recording medium exceeds a predetermined value. 
     The detection means may further have rotation body stopping means for stopping a conveyance motor when a rotation trajectory of at least one of the heating rotation body and the pressing rotation body is deviated from a predetermined trajectory. 
     It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail. An example fixing device will be described with reference to  FIGS. 1 to 6  of the drawings. 
     LIST OF REFERENCE NUMBERS 
       50  Fixing device;  51  Heating roller (heating rotation body or heating body);  51   a  Nip portion;  52  Pressing roller (pressing rotation body of pressing body);  61  Inlet guide plate (guide member);  62  Outlet guide plate (guide member);  64  Conveyance roller pair;  66  Deformation correcting device (deformation correcting means or device);  66   a  First roller;  66   b  Second roller;  71  Camera (detection means or detector);  71   a  Inlet-side imaging region;  71   b  Outlet-side imaging region;  72  Conveyance stopping part (conveyance stopping means or device, rotation body stopping means or roller stopping device);  73  Guide changing part (guide changing means or device);  74  Entry stabilizing part (entry stabilizing means or device);  75  Inlet-side speed adjusting part (speed adjusting means or device);  76  Correction instructing part (correction instructing means or device);  77  Outlet-side speed adjusting part (speed adjusting means or device); P Paper (recording medium).