Abstract:
A structure includes a first frame including a slit portion; and a second frame including a plate portion configured to enter the slit portion. The slit portion includes an introducing portion, a first positioning portion, and a first tapered portion connecting the introducing portion and the first positioning portion. The plate portion includes a free end portion capable of entering the introducing portion, a second positioning portion determining a position of the plate portion with respect to a longitudinal direction of the slit portion, a third positioning portion determining a position of the plate portion with respect to an inserting direction into the slit portion, and a second tapered portion contactable to the first tapered portion and connecting the free end portion and the second positioning portion.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a structure and a structure detachably mountable to an image forming apparatus. As the image forming apparatus, it is possible to use a copying machine, a printer, a facsimile machine and a multi-function machine having a plurality of functions of these machines. 
         [0002]    The structure for OA (office-automation) equipment such as the copying machine, the facsimile machine or the printer is required to simultaneously have strength of the structure itself and positional accuracy in some cases. In order to realize the strength and the positional accuracy, there is a method in which a jig exclusively for assembling of the structure is used and a plurality of parts are combined and thus the structure is bonded by welding or fastening with a screw. The method is no problem in the case where the structure is assembled and ten is not be mounted. 
         [0003]    However, in the case of the OA equipment such as the copying machine, the facsimile machine or the printer, a unit is demounted from the structure as a main body in some cases during maintenance or periodical exchange of parts. Then, in some cases, an operation in which the unit itself is exchanged to a fresh (new) unit or a some part in the unit is exchanged and then the unit is mounted again to the structure as the main body is performed. 
         [0004]    When such an operation is performed, a person for performing the operation is a service person or a user himself (herself). An operation place is an office or the like in which the OA equipment such as the copying machine, the facsimile machine or the printer is actually placed. Therefore, an exclusive tool such as an assembling jig cannot be used, and in addition, ease of the operation itself is also required. 
         [0005]    Accordingly, the unit and the parts or the like of the copying machine or the like may desirably have a constitution of a structure capable of reproducing assembling accuracy before assembling without relying upon the assembling jig when the unit and the parts are disassembled and then are assembled again. 
         [0006]    Reference Example 1 having a constitution realizing the structure constitution is shown in  FIG. 13 . An upright metal plate frame X 1  is 0.2 mm in thickness and is provided with an irregular-shaped hole X 2 . On the other hand, a metal plate stay X 3  is 1.2 mm in thickness is provided so as to be combined and connected with the metal plate frame X 1 . The stay X 3  is provided with an irregular-shaped projection X 4 . 
         [0007]    In Reference Example 1, a dimension of the irregular-shaped hole X 2  is set so that a width B is 16 mm and a tolerance of the width B is a fit tolerance H 9  defined by JIS and so that a height H is 1.2 mm and a tolerance of the height H is +0.01-0 mm. A dimension of the projection X 4  of the stay X 3  is set so that a width L is 16 mm and a tolerance of the width L is a fit tolerance f 9  and so that a height is 1.2 mm (as a plate thickness) and a tolerance of the height is ±0.07 mm as a metal plate thickness tolerance. 
         [0008]    When the stay X 3  is assembled with the frame X 1 , the stay X 3  is moved in an arrow X 6  direction. The projection X 4  of the stay X 3  is inserted into the irregular-shaped hole of the frame X 1 . At this time, a dimensional relationship between the irregular-shaped hole X 2  and the projection X 4  is such that the hole X 2  and the projection X 4  are engaged with each other as described above and therefore positioning of the stay X 3  relative to the frame X 1  is made. Such engaging portions X 2  and X 4  are provided in a plurality of pairs (not shown, a loose widthwise relationship is established from a second pair and subsequent pairs). Connection (fixing) between the frame X 1  and the stay X 3  is made in such a manner that a bent portion X 7  is provided with a tap at an end portion of the stay X 3  and the frame X 1  is provided with a hole through with the tap is fixed with a screw. 
         [0009]    Further, there is a positioning method or the like disclosed in Japanese Laid-Open Patent Application (JP-A) H08-6342. 
         [0010]    However, in Reference Example 1, there is a liability as described below. In the case where exchange of parts or the like is periodically made during continuous operation of the copying machine or the like, various forms of the structure exist depending on its purpose (use). 
         [0011]      FIG. 14  shows a state in which a frame  1  and a frame  2  are combined with each other in Reference Example 2. Each of the frames  1  and  2  is formed of metal plate of 1.2 mm in thickness. The frame  1  includes a plurality of inserting portions Y 1  and Y 2  between which a large cut-away portion Y 3  exists. 
         [0012]    In such a case, a slight deviation can generate between the inserting portions Y 1  and Y 2  with respect to a thickness direction (arrow K direction). Originally, irregular-shaped holes Y 4  and Y 5  provided in the frame  2  are holes for regulating the frame  1  with respect to a plate thickness direction. For that reason, even when the slight deviation generated in the frame  1 , inserting portions of the frame  2  cannot engage with the inserting portions Y 1  and Y 2  of the frame  1  smoothly, so that an assembling operation property of the frame  2  with the frame  1  was lowered in some cases. 
         [0013]      FIG. 15  shows a state in which a frame  3  and a frame  4  are combined with each other in Reference Example 3. A difference from Reference Example 1 is that a frame  3  has a box-like shape including front and rear side plates  31  and  32  provided with unit inserting portions  33 ,  34  and  35 . 
         [0014]    Then, the unit inserting portions  33 ,  34  and  35  of the front and rear side plates  31  and  32  engage with engaging holes  41 ,  42  and  43 , respectively, provided in the frame  4 , and a distance between the front and rear side plates  31  and  32  is maintained by an interval Q between the engaging holes of the frame  4 . Thus, in the case where the unit inserting portions  33 ,  34  and  35  are disposed at positions spaced between the front side plate and the rear side plate, leaning of the front and rear side plates themselves generates, and therefore it becomes difficult to insert the front and rear side plates into positioning holes of the frame  4 . Therefore, operativity of an assemble operation was lowered. 
       SUMMARY OF THE INVENTION 
       [0015]    According to an aspect of the present invention, there is provided a structure comprising: a first frame including a slit portion; and a second frame including a plate portion configured to enter the slit portion to determine a position of the second frame relative to the first frame, wherein the slit portion includes an introducing portion having a width larger than a thickness of the plate portion, a first positioning portion configured to determine a position of the plate portion with respect to a widthwise direction of the slit portion, and a first tapered portion configured to connect the introducing portion and the first positioning portion, and wherein the plate portion includes a free end portion capable of entering the introducing portion, a second positioning portion configured to determine a position of the plate portion with respect to a longitudinal direction of the slit portion, a third positioning portion configured to determine a position of the plate portion with respect to an inserting direction into the slit portion, and a second tapered portion contactable to said first tapered portion and configured to connect the free end portion and the second positioning portion. 
         [0016]    According to another aspect of the present invention, there is provided a structure detachably mountable to an image forming apparatus, comprising: a rotatable member; a first frame including a slit portion; and a second frame including a groove portion configured to rotatably hold the rotatable member and a plate portion configured to enter the slit portion to determine a position of the second frame relative to the first frame, wherein the slit portion includes an introducing portion having a width larger than a thickness of the plate portion, a first positioning portion configured to determine a position of the plate portion with respect to a widthwise direction of the slit portion, and a first tapered portion configured to connect the introducing portion and the first positioning portion, and wherein the plate portion includes a free end portion capable of entering the introducing portion, a second positioning portion configured to determine a position of the plate portion with respect to a longitudinal direction of the slit portion, a third positioning portion configured to determine a position of the plate portion with respect to an inserting direction into the slit portion, and a second tapered portion contactable to said first tapered portion and configured to connect the free end portion and the second positioning portion. 
         [0017]    Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1A  is an illustration of a hole and an inserting portion of a positioning mechanism, and  FIG. 1B  is an illustration of a hole and an inserting portion of another positioning mechanism. 
           [0019]      FIG. 2  is a schematic structural view of an example of an image forming apparatus. 
           [0020]      FIG. 3  is a sectional view of a fixing device. 
           [0021]      FIG. 4  is a perspective view of a fixing film unit. 
           [0022]      FIG. 5  is a perspective view of a pressing roller unit. 
           [0023]      FIG. 6  is a perspective view of a fixing device frame unit. 
           [0024]      FIG. 7  is a perspective view of a shutter unit. 
           [0025]      FIG. 8  is a perspective view of a state in which the pressing roller unit is assembled with the fixing device frame unit. 
           [0026]      FIG. 9  is a perspective view of a state in which the fixing device frame unit is further assembled. 
           [0027]      FIG. 10  is a schematic view showing a mounting process of the shutter unit. 
           [0028]      FIG. 11  is a schematic view showing the mounting process of the shutter unit. 
           [0029]      FIG. 12  is a schematic view showing completion of the mounting process of the shutter unit. 
           [0030]      FIG. 13  is an illustration of Reference Example 1. 
           [0031]      FIG. 14  is an illustration of Reference Example 2. 
           [0032]      FIG. 15  is an illustration of Reference Example 3. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0033]    Embodiments of the present invention will be described with reference to the drawings. 
       First Embodiment 
     Image Forming Apparatus 
       [0034]      FIG. 2  is a schematic sectional view of an example of an image forming apparatus  1 . This image forming apparatus is a full-color electrophotographic printer of a tandem type and an intermediary transfer type and includes four image forming portions UY, UM, UC and UK for forming toner images of Y (yellow), M (magenta), C (cyan) and Bk (black), respectively. 
         [0035]    Each of the image forming portions includes a photosensitive drum  11 , a charger  12 , a laser scanner  13 , a developing device  14 , a primary transfer charger  15  and a drum cleaner  16 . Incidentally, for brevity, reference numerals of these devices in the image forming portions UM, UC and UBk other than the image forming portion UY are omitted from illustration. Further, an electrophotographic process and an image forming operation at these image forming portions are well-known and therefore will be omitted from description. 
         [0036]    The respective color toner images are primary-transferred from the drums  11  of the respective image forming portions onto an intermediary transfer belt  17  in a predetermined superposition manner. As a result, the four color toner images which are superposed are formed on the belt  17 . On the other hand, one sheet of a sheet-like recording material P is fed from a cassette  18  or  19  or from a manual-feeding tray  20  and then introduced through a feeding path  21  into a secondary transfer nip which is a press-contact portion between the belt  17  and a secondary transfer roller  22  at predetermined timing. As a result, the four-color superposed toner images are secondary-transferred altogether from the belt  17  onto the recording material P. The recording material P is introduced into a fixing device  40 , and the toner images are fixed on the recording material P. 
         [0037]    The recording material P coming out of the fixing device  40  is, in the case of an operation in a one-sided image forming mode, introduced into a feeding path  24  by control of a flapper  23  and then is discharged face down (with an image surface downward) onto a discharge tray  25 . Alternatively, the recording material P is introduced into a feeding path  26  and then is discharged face up (with the image surface upward) onto a discharge tray  27 . 
         [0038]    In the case of an operation in a double-sided image forming mode, the recording material P coming out of the fixing device  40  is once introduced into a feeding path  26  side by the control of the flapper  23  and thereafter is fed into a feeding path  28  for the double-sided image forming mode in a switch-back manner. Then, the recording material P is fed again into the secondary transfer nip through the feeding path  21  in a state in which the recording material P is turned upside down. Thereafter, similarly as in the case of the operation in the one-sided image forming mode, the recording material P is introduced into the fixing device  40  and then is discharged as a double-sided image-formed product onto the discharge tray  25  and  27 . 
       [Fixing Device] 
       [0039]      FIG. 3  shows a principal cross-section of the fixing device  40  mounted in the image forming apparatus  1 . This fixing device  4  is a fixing device of a film (belt) heating type and a pressing member driving type. A fixing device constitution and a fixing operation of the fixing device are well-known and therefore will be described briefly. 
         [0040]    The fixing device  40  roughly includes a fixing device frame unit  400 , a fixing film unit  200  as a heating member assembled with the fixing device frame unit  400 , a pressing roller unit  220  as a pressing member, and a shutter unit  300 . Further, the fixing device  40  includes a fixing device entrance guide  291 , a separation plate  251 , a feeding roller pair  261 , a feeding roller pair  271 , a pressing mechanism  415  ( FIG. 4 ), and a pressing mechanism  416  ( FIG. 4 ). Details of principal units will be described below. 
       (Fixing Film Unit  200 ) 
       [0041]      FIG. 6  is a perspective view of an outer appearance of the fixing film unit  200 . Referring to  FIGS. 3 and 6 , a fixing film  201  is a cylindrical heat-resistant member as a heating member for conducting heat to the recording material P. An inner diameter of the fixing film  201  is set at 30 mm, and an inner peripheral length is set at 102% of an outer peripheral length of members consisting of a ceramic heater  203 , a heater holder  204  and fixing flanges  206  and  207 , so that the fixing film  201  is externally fitted around the members somewhat loosely. The fixing film  201  is a composite length film obtained by coating an outer peripheral surface of a 50 μm-thick heat-resistant polyamideimide film with a PFA tube. The fixing film  201  may also be formed of metal. 
         [0042]    The ceramic heater  203  has a basic constitution in which a thin elongated ceramic substrate and an energization heat generating resistor length provided on a surface of the substrate are combined, and is a low-thermal capacity heater which increases in temperature with an abrupt rising characteristic as a whole. 
         [0043]    The ceramic heater  203  is fixed to the heater holder  204  with a heat-resistant adhesive. Downstream of the heater holder  204  with respect to a recording material feeding direction  a , a projection is provided for the purposes of enlargement of a fixing nip width and improvement in separation (property) of the recording material P from the fixing film  201 . 
         [0044]    A stay  205  is pressed against a surface of the heater holder  204 , formed of a liquid crystal polymer material, where there is no heater  203 , so that strength is imparted to the heater holder  204  and the heater  203  and a fixing nip N is ensured. In addition, the stay  205  is connected with the fixing flanges  206  and  207  and thus ensures strength of the fixing film unit  200 . As a material of the stay  203 , a 2.3 mm-thick electroplated zinc steel plate is used, and the stay  203  is molded in a U-shape in cross-section to ensure strength thereof and then is used. 
         [0045]    The fixing flanges  205  and  207  are engaged in both longitudinal ends of the stay  205 . The fixing flanges  206  and  207  slide with the inner peripheral surface of the fixing film  201  and determine a locus of the fixing film  201  with respect to a rotational direction of the fixing film  201 . In addition, the fixing flanges  206  and  207  abut against a front end portion (one end side) and a rear end portion (the other end side), respectively, of the fixing film  201  and thus determines a position of the fixing film  201  in the fixing device with respect to the longitudinal direction. As a material of the fixing flanges  206  and  207 , a liquid crystal polymer resin material having both of a heat-resistant property and a sliding property is used. The fixing flanges  206  and  207  are, as described later, engaged with and held by side plates of the fixing device frame unit  400  and are disposed at positions shown in  FIGS. 3 and 6 . 
         [0046]    In a space enclosed by the stay  205  and the heater holder  204 , a heater thermistor  208  and a film thermistor  209  are supported by a thermistor holder  210  in order to detect and control a temperature of the heater  203 . A controller (not shown) adjusts the ceramic heater temperature so that a temperature of the fixing film  201  is a temperature depending on each of recording materials P of various species by a temperature-control system including the thermistors  208  and  209 . 
       (Pressing Roller Unit  220 ) 
       [0047]      FIG. 5  is a perspective view of an outer appearance of the pressing roller unit  220 . The pressing roller unit  220  includes a pressing roller  221 . The pressing roller  221  is constituted by a core metal  221   a  formed of a mild (soft) steel, an elastic layer  221   b  which is molded concentrically integral with the core metal  221   a  and which is coated on an outer peripheral surface of the core metal  221   a  with a silicone rubber material, and a parting layer consisting of a PFA tube  221   c  as a surface layer. An outer diameter of the pressing roller  221  is 30 mm. The pressing roller  221  is, as described later, rotatably supported by the side plates of the fixing device frame unit  400  via bearings  222  and  223 . 
         [0048]    To a gear  224  mounted to the core metal  221   a , a driving force of a driving motor (not shown) controlled by the controller is transmitted. As a result, the pressing roller  221  is rotationally driven at a predetermined peripheral speed in the counterclockwise direction of an arrow R 221  in  FIG. 3 . A portion formed by press-contact between the pressing roller  221  and the fixing film  201  is referred to as the fixing nip N. The pressing roller  221  is rotationally driven as described above, whereby the fixing film  201  of the fixing film unit  200  is rotated in the clockwise direction of an arrow R 201  by the rotation of the pressing roller  221  while being slid in close contact with the heater  203  at an inner surface thereof. 
         [0049]    The recording material on which an unfixed toner image is placed enters the pressing nip N as shown by an arrow  a  in  FIG. 3  and then is nipped and fed. As a result, heating and pressing of the recording material are simultaneously effected in the fixing nip N, so that the toner image is fixed as a fixed image on the recording material. The recording material on which the toner image is fixed at the fixing nip N is separated from the fixing film  201  by the separation plate  251 , and then is discharged from the fixing device  40  by the feeding roller pairs  261  and  271 . 
       (Shutter Unit  300 ) 
       [0050]    A temperature of a part of the fixing film  201  is increased by continuously introducing (passing) a large number of sheets of the recording materials into (through) the fixing nip N in some cases. When such a situation continues, the image on the recording material as a product causes an abnormal image in some cases. In order to prevent the abnormal image, cooling air is blown onto the fixing film  201  for maintaining suitability for the temperature of the fixing film  201  in some cases. The shutter unit  300  is a unit for controlling the cooling air toward the fixing film  201 . 
         [0051]      FIG. 7  is a perspective view of an outer appearance of the shutter unit  300 . A shutter (not shown) provided in the shutter unit  300  is opened, so that the cooling air from a fan (not shown) in an image forming apparatus main assembly is taken into the fixing device  40  and thus the fixing film temperature is made suitable. Although details will be described later, when the shutter unit  300  is combined with the fixing device frame unit  400 , the shutter unit  300  functions also as a strength member for maintaining strength as the fixing device  40 . 
       (Periodical Exchange Parts (Components)) 
       [0052]    The fixing film  201  and the pressing roller  221  caused deterioration of the PFA layer as the surface layer and the rubber layer with repetition of heating and pressing of the recording material, and thus cannot satisfy an initial image performance, and therefore are set as periodical exchange parts. In the case of the fixing device in this embodiment, when as an integrated value, an about 300,000 sheets of A4-sized recording materials are introduced, exchange of the fixing film  201  and the pressing roller  221  is recommended. That is, in this embodiment, the fixing device  40  is a structure (unit) mounted in the main assembly of the image forming apparatus while holding the parts to be exchanged. 
         [0053]      FIG. 4  is a perspective view showing a state in which the shutter unit  300 , the fixing film unit  200  and the pressing roller unit  210  are demounted from the fixing device  40  and thus only the fixing device frame unit  400  is shown. 
         [0054]    The fixing device frame unit  400  includes a fixing device frame  401 , a front side plate (one end side plate)  402 , a rear side plate (the other end side plate)  403 , and an entrance guide supporting plate  404  which are parts for ensuring basic strength of the fixing device frame unit  400  and which are formed using a 1.2 mm-thick zin-coated steel plate. An arcuate portion  411  of the front side plate  402  and an arcuate portion  412  of the rear side plate  403  are places where the bearing  222  and  223  ( FIG. 5 ) of the pressing roller unit  210  are engaged, respectively. 
         [0055]    A cut-away portion  413  of the front side plate  402  and a cut-away portion  414  of the rear side plate  403  are positioning portions for the fixing film unit  200 . With the cut-away portions  413  and  414 , positioning portions of the fixing flanges  206  and  207  are engaged, so that the fixing film unit  200  move along the cut-away portion  413  of the front side plate  402  and the cut-away portion  414  of the rear side plate  403 . In order to facilitate a mounting and demounting operation of the fixing film unit  200  and the pressing roller unit  210  relative to the fixing device frame unit  400 , parts of the front and rear side plates  402  and  403  are cut away as openings. 
         [0056]    A front pressing mechanism  415  and a rear pressing mechanism  416  are mechanisms for engaging with top portions of the fixing flanges  206  and  207  ( FIG. 6 ), respectively, of the fixing film unit  200  to impart a predetermined pressure. During exchange of the fixing film unit  200  and the pressing roller unit  210 , the front pressing mechanism  415  and the rear pressing mechanism  416  are in an open state as shown in  FIG. 4 . 
         [0057]    The front side plate  402  is provided with positioning portions (inserting portions)  417  and  418  for positioning the shutter unit  300 , and the rear side plate  403  is provided with positioning portions (inserting portions)  419 ,  420  and  421  for positioning the shutter unit  300 . In order to improve an exchange operation property of the periodical exchange units, the front side plate  402  is provided with the cut-away portion  413 , and therefore, leaning of the positioning portions  417  and  418  of the front side plate  402  generates, so that positional deviation in a plate thickness direction generates in some cases. Similarly, also the rear side plate  403  is provided with the cut-away portion  414 , so that the positioning portions (members)  419 ,  420  and  421  cause the positional deviation in the plate thickness direction in some cases. 
         [0058]    Further, also between the front side plate  402  and the rear side plate  403 , leaning generates in an interval (spacing) between the front side plate  402  and the rear side plate  403  for the above-described reason. 
         [0059]    In order to not only suppress the leaning of the above-described portions (members) but also maintain the interval between the front and rear side plates  402  and  403  at a certain value, a strength member may desirably be used. In this embodiment, as the strength member, an upper fixing stay  601  ( FIG. 7 ) is provided, so that a degree of the leaning of the front and rear side plates and the interval between the front and rear side plates are maintained at certain levels. An assembling problem can generate, but a solution to the problem will be described later in detail. 
         [0060]    Referring to  FIG. 5  showing the pressing roller unit  220 , at both end portions of the pressing roller  221 , the bearings  222  and  223  are assembled so that the pressing roller  221  can be held rotatably relative to the fixing device frame unit  400 . Further, also the gear  224  for transmitting a rotational (driving) force to the pressing roller  221  is mounted. When the pressing roller unit  210  is mounted to the fixing device frame unit  400 , the bearings  222  and  223  are engaged with the arcuate portion  411  of the front side plate  402  and the arcuate portion  412  of the rear side plate  403 , respectively. 
         [0061]    Referring to  FIG. 6  showing the fixing film unit  200 , at both end portions of the fixing film  201 , the fixing flanges  206  and  207  are mounted. The fixing flange  206  is provided with an engaging portion  501  engageable with the cut-away portion  414  of the rear side plate  403 , so that the engaging portion  501  engages with the cut-away portion  414  in a translatable manner. The fixing flange  207  side is not illustrated in  FIG. 6 , but is constituted similarly as in the fixing flange  206  side. 
         [0062]    As shown in  FIGS. 4-6 , by providing the front and rear side plates  402  and  403  with the cut-away portions  413  and  414 , respectively, it is understood that exchange of the pressing roller unit  210  and the fixing film unit  200  relative to the fixing device frame unit  400  can be easily made. 
         [0063]    Referring to  FIG. 7  showing the shutter unit  300 , the shutter unit  300  includes the upper fixing stay  601  as a main strength member. A material of the upper fixing stay  601 , a 1.2 mm-thick zin-coated steel plate is used. Openings  602 ,  603  and  604  through which cooling air from a fan is taken into the fixing device  40  are provided, and are opened and closed by a shutter (not shown) provided with a rack movable to a pinion  605 . 
         [0064]    A rotating portion for rotating the pinion  605  is mounted in the main assembly side of the image forming apparatus and is not shown. Depending on a size of the recording material used (introduced), an opening area is intended to be changed, and therefore in that case, the opening area is changed using sensors  606  and  607 . 
         [0065]    The upper fixing stay  601  is provided with positioning holes  611  and  612  engageable with the positioning portions (inserting portions)  417  and  418  of the front side plate  402  of the fixing device frame unit  400 . Further, the upper fixing stay  601  is provided with positioning holes  613 ,  614  and  615  (of which the hole  615  is not shown) engageable with the positioning portions (inserting portions)  419 ,  420  and  421  of the rear side plate  403 . That is, the positioning holes  611 - 615  are provided so that two or more holes are linearly arranged in each of the longitudinal end portion sides. 
         [0066]      FIG. 8  shows a state in which the pressing roller unit  220  is mounted to the fixing device frame unit  400 . After the mounting of the pressing roller unit  220 , the entrance guide  291  is mounted. 
         [0067]      FIG. 9  shows a state in which the fixing film unit  200  is further mounted to the fixing device frame unit  400  put in the state of  FIG. 8 , and then the pressing mechanisms  415  and  416  are set. On a top of the fixing flange  206  of the fixing film unit  200 , a predetermined load is exerted by a pressing spring  801  of the pressing mechanism  416  through a pressing arm (pressing plate)  802 . As a result, a necessary pressure generates in the fixing nip N. Also on the fixing flange  207 , a load is exerted by the pressing mechanism  415  similarly. 
         [0068]      FIG. 10  shows a state in which the shutter unit  300  is further mounted to the fixing device frame unit  400  put in the state of  FIG. 9 . In the case of this embodiment, the five positioning holes  611 - 615  of the upper fixing stay  601  and the five positioning portions (inserting portions)  417 - 421  of the front and rear side plates  402  and  403  are provided. That is, a plurality of the positioning holes and a plurality of the positioning portions (inserting portions) are provided, but for convenience of explanation, in the following, the case of the positioning hole  613  and the positioning portion  419  will be described as a representative example. 
         [0069]    In  FIG. 1A , details of shapes of the positioning hole  613  which is a slit portion of the upper fixing stay (first member)  601  of the shutter unit  300  and the positioning portion (inserting portion)  419  which is a plate(-like) portion of the rear side plate (second member)  403  of the fixing device frame unit  400  are shown. 
         [0070]    The positioning hole  613  includes an introducing portion  613   c , a first tapered portion  613   a  and an engaging portion  613   b . The positioning portion (member)  419  includes a first inserting portion  419   b , a second tapered portion  419   a  and a second inserting portion  419   c . Incidentally, the tapered portions  613   a  and  419   a  which are in a relation such that they are induced (guided) by each other are not necessarily required to have a shape gradually changing in width, i.e., a linear shape. For example, the tapered portions  613   a  and  419   a  may also have a shape such that the width varies stepwisely within a range of a tolerance. Further, the tapered portions  613   a  and  419   a  may also have a shape partly including a portion having a curved shape within a range of tolerance. Thus, in this embodiment, the tapered portion can include the curved portion as described above. 
         [0071]    A length (U: 11.6 mm) which is the same of a length of the introducing portion  613   c  and a length of the first tapered portion  613   a  of the hole  613  with respect to a longitudinal direction is longer than a width (N: 10 mm) of the first inserting portion (free end portion)  419   b  of the positioning member  419 . Conversely, the width N of the first inserting portion  419   b  is set at a value shorter than the length obtained by the sum of the lengths of the introducing portion  613   c  and the first tapered portion  613   a  with respect to the longitudinal direction of the hole  613 . 
         [0072]    Further, a length (width Ma: 3.5 mm) of the introducing portion  613   c  with respect to a widthwise direction is sufficiently larger than a thickness (no reference symbol: 1.2 mm) of the positioning portion  419 . For that reason, a service person can easily insert the first inserting portion  419   b  of the positioning member  419  into the introducing portion  613   c . A free end portion of the first inserting portion  419   b  has an arcuate shape having a radius of curvature W: 5 mm), and therefore, the first inserting portion  419   b  can further easily be inserted into the introducing portion  613   c.    
         [0073]    When the positioning member  419  is inserted into the hole  613  by (P 1 -P 2 ) and then is further inserted, the first tapered portion  613   a  and the second tapered portion  419   b  contact each other at an intermediary position of the insertion. Incidentally, in this embodiment, P 1 =30 mm, P 2 =13 mm and P 3 =6.8 mm are set. 
         [0074]    When the positioning member  419  is further inserted, the second tapered portion  419   a  is guided toward the engaging portion  613   b  while sliding with the first tapered portion  613   a . Then, a longitudinal length (no reference symbol) exceeds the length U. 
         [0075]    Thus, the second inserting portion (positioning portion)  419   c  of the positioning member  419  starts engagement with the engaging portion  613   b  of the hole  613 . When the positioning member  419  is further inserted into the hole  613  by (P 1 -P 3 ), the second inserting portion  419   c  with a width (length) (R: 14 mm) engages with the engaging portion  613   b  with reliability. In this state, the fixing device frame unit  400  and the shutter unit can be fastened with screws with accuracy. 
         [0076]    Here, widthwise length of the engaging portion  613   b  is Mb=1.3 mm, and therefore a difference in thickness between the positioning member  419  and Mb is 0.1 mm. Thus, the hole  613  and the positioning member  419  are in such a loose fitting state between the engaging portion  613   b  and the second inserting portion  419   c . This difference may desirably be 0 mm or more and 0.12 mm or less, more desirably be 0 mm or more and 0.07 mm or less. 
         [0077]    The above-described positioning mechanism is summarized as follows. The positioning mechanism, the first member  601  is provided with the hole  613 , and the second member  403  different from the first member  601  is provided with the positioning member  419  to be inserted into the hole  613 , and then the hole  613  and the positioning member  419  are combined with each other to make positioning between the first and second members  601  and  403 . 
         [0078]    The hole  613  includes the introducing portion  613   c  having the width Ma larger than the thickness of the positioning member  419 , the engaging portion (positioning portion)  613   b  having the width Mb substantially equal to the thickness of the positioning member  419 , and the first tapered portion  613   a  connecting between the portions  613   c  and  613   b.    
         [0079]    The positioning member  419  includes the first inserting portion  419   b  having the width (length) N shorter than the length U which is the sum of the lengths of the introducing portion  613   c  and the first tapered portion  613   a  of the hole  613  with respect to the longitudinal direction of the hole  613 . The positioning member  419  further includes the second inserting portion  419   c  having the width (roller) R substantially equal to the length K of the hole  613 . Further, the positioning member  419  includes the second tapered portion  419   a  connecting between the first inserting portion  419   b  and the second inserting portion  419   c.    
         [0080]    Then, the insertion of the first inserting portion  419   b  into the introducing portion  613   c  progresses, and the first tapered portion  613   a  and the second tapered portion  419   a  contact each other, and thereafter the engaging portion  613   b  and the second inserting portion  419   c  engage with each other, so that positioning between the first and second members  601  and  403  is made. That is, a stopper portion  419   d  functioning as a positioning portion abut against a periphery of the hole  613 , so that relative position between the first and second members  601  and  403  is determined with respect to a direction in which the positioning member  419  is inserted into the hole  613 . As a result, with respect to each of three-dimensional directions, the relative position between the first and second members  601  and  403  are determined. 
         [0081]    By providing such a positioning mechanism, during an assembling operation of the shutter unit  300  including the upper fixing stay  601  with the fixing device frame unit  400 , there is no need to intentionally effect the positioning therebetween. That is, even in such an image that the shutter unit  300  is subconsciously moved downward to the fixing device frame unit  400 , the positioning member  419  can be inserted into a region defined by L and Ma of the hole  613 . 
         [0082]      FIG. 11  shows a state in which engagement between the positioning member  419  and the positioning hole  613  is further progressed from an initial engagement state (in which the first inserting portion  419   b  is inserted into the introducing portion  613   c ) between the positioning member  419  and the positioning hole  613  shown in  FIG. 10 . That is,  FIG. 11  is a schematic view showing a state in which the first tapered portion  613   a  provided as a part of the positioning hole  613  of the upper fixing stay  601  and the second tapered portion  419   a  provided as a part of the positioning member  419  of the rear side plate  403  engage with each other. As described above, by an inclination effect of the first and second tapered portions  613   a  and  419   a  provided as the parts of the positioning hole  613  and the positioning member  419 , respectively, the inclination of the positioning member (portion)  419  is corrected. 
         [0083]      FIG. 12  shows a state in which the shutter unit  300  is further moved toward the fixing device frame unit  400  side from the state of  FIG. 11  and thus is set to the fixing device frame unit  400  (i.e., a schematic view showing completion of mounting of the shutter unit  300 ). In this state, the region R of the positioning member  419 , i.e., a plate thickness portion of the second inserting portion  419   c  of the positioning member  419  engages with the engaging portion  613   b  (Mb) of the positioning hole  613 , so that positioning of the positioning member  419  with respect to a plate thickness direction is made. 
         [0084]    In the case where the shutter unit  300  is demounted from the fixing device frame unit  400 , an operation which is the reverse of the above-described operation is performed. An operation of eliminating the positioning from the state of the positioning of the positioning member  419  with respect to the plate thickness direction is performed, and therefore this operation does not constitute an obstacle to the demounting operation. 
         [0085]    Therefore, by providing the positioning mechanism as described above, an assembling operation and a disassembling operation of the structure can be smoothly performed. Accordingly, effects such that an exclusive assembling tool is not needed, that the number of assembling steps is reduced, and that operativity of the users or the service person is improved are obtained. 
         [0086]    As described above, the pressing mounts  415  and  416  includes the pressing arms  802 . Each of the pressing arms  802  rotates about a pressing shaft (no reference symbol). The pressing shaft is provided on the fixing device frame unit  400 . Further, the pressing arm  802  causes the pressing spring  801  to act between the shutter unit  300  and the fixing film unit  200 . On each of the pressing arms  802 , a force of 150 N is exerted, so that at both end portions of the fixing film unit  200 , a force of 300 N in total is applied to the pressing arms  802 . For that reason, by reaction of the force, a similar force is exerted between the fixing device frame unit  400  and the shutter unit  300 . 
         [0087]    Here, when assembling accuracy between the fixing device frame unit  400  and the shutter unit  300  is not high, it becomes difficult to properly press the fixing film unit  200 , so that generation of an image defect such as density non-uniformity is invited. Or, in the case where the fixing device frame unit  400  and the shutter unit  300  are mounted in a distorted state, there is a liability that the pressure of the pressing springs  801  acts on the fixing device frame unit  400  and the shutter unit  300  in an unexpected direction and thus the fixing device frame unit  400  and the shutter unit  300  are deformed. For this reason, the constitution of this embodiment in which the assembling can be made with high accuracy is desirable. 
         [0088]    In  FIG. 1A , the positioning hole  613  includes the engaging portion  613   b  via the first tapered portion  613   a  only in one end side of the introducing portion  613   c . The present invention is not limited thereto, but as shown in  FIG. 1B , it is also possible to employ a constitution in which in both end sides of the introducing portion  613   c , two engaging portions  613   b  are provided via first tapered portions  613   a . In this case, the positioning member  419  includes two second tapered portions  419   a  provided correspondingly to the two first tapered portions  613   a  provided in the both end sides the introducing portion  613   c.    
         [0089]    In the above-described embodiment, as the structure which holds the parts to be exchanged and which is to be mounted in the apparatus main assembly of the image forming apparatus, the fixing device is described as an example, but the structure is not limited to the fixing device. The positioning mechanism in the present invention applicable to the structure is not limited to the structure mounted in the apparatus main assembly of the image forming apparatus, but may also be widely be applicable as a positioning mechanism in the case where the first member and the second member which are demounted and mounted during exchange of the parts are positioned and connected with each other. 
         [0090]    While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
         [0091]    This application claims the benefit of Japanese Patent Application No. 2015-176440 filed on Sep. 8, 2015, which is hereby incorporated by reference herein in its entirety.