Abstract:
An image forming apparatus includes: a fixing device that fixes the toner image onto the recording medium by applying heat and pressure; ejection rollers provided away from the fixing device for ejecting the recording medium; a guide provided on at least one part of a recording medium ejection path between the ejection rollers and the fixing device for guiding a conveyance of the recording medium; at least one spur provided on the guide, having a plurality of teeth on a circumference thereof; and a slit formed on the guide so that the plurality of teeth of the spur are protruded on a side of the recording medium ejection path through the slit, wherein the recording medium is conveyed from the fixing device by bringing the plurality of teeth of the spur into contact with a surface of the recording medium.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to an electrophotographic image forming apparatus such as copying machine, printer, facsimile, and so on of the electrophotographic type. Particularly, the invention relates to an image forming apparatus using toner that contains comparatively much wax.  
         [0002]     A conventional electrophotographic image forming apparatus forms an image on a recording medium by the steps of charging the surface of an image carrier such as a photosensitive body with electricity, applying a laser beam to the electrically-charged surface in a scanning manner to form a latent image thereon, applying toner to the latent image by a developer to make it visible, heating, melting, and pressing the toner image by a fixing device to fix the toner image to a recording medium, and then ejecting the recording medium to the outside of the apparatus. The toner on the recording medium can be cooled and fixed thereto until the recording medium is ejected from the fixing device to the outside of the apparatus.  
         [0003]     In case of forming a color image, toners of four colors (yellow, magenta, cyan, and black) are used. The image forming apparatus forms a toner image of each color on the related photosensitive body, transfers toner images of the colors onto an intermediate transfer body in a superposition manner, and further transfers the superimposed multi-color images to a recording medium. Therefore, a color image uses more toner than a black and white image. When the quantity of toner increases, the toner heated by the heating roller of the fixing device becomes harder to be separated from the heating roller. Then, wax is added to toner to make toners be separated from the heating roller easily. Wax in the toner can make color images glossy and consequently improve the image quality.  
         [0004]     Usually, wax is set to be molten more easily than toner. Thus, wax is lower in melting and solidifying points than toner. Consequently toner is solidified immediately after it goes out from the fixing device, but wax is slow to be solidified.  
         [0005]     The recording medium is carried by the ejection rollers to pass through an ejection path between the exit of the fixing device and the outside of the apparatus. This ejection path is not linear but curved with guide plates or the like so that the recording medium may travel a preset curved course before reaching the ejection roller.  
         [0006]     When the recording medium touches the guide plates while wax is not solidified yet, the molten wax on the contact area of the recording medium is quickly cooled by it and solidified. However, wax on the other recording medium area is slow to be solidified.  
         [0007]     Generally, wax contained in toner is glossy when the molten wax is cooled and solidified quickly but becomes dull when the molten wax is cooled gradually. Therefore, the wax on the contact area of the recording medium is immediately cooled and becomes glossy but the wax on the non-contact area of the recording medium is cooled slowly and becomes dull. The uneven glossiness on the recording medium reduces the image quality. To prevent this, the recording medium must be carried without being in contact with the guide plates or the like.  
         [0008]     Patent Document 1, which represents Japanese Non-examined Patent Publication 2001-175112, discloses a method of transferring a recording medium without making the recording medium touch the guide plate or the like. In the description of Patent Document 1, the recording medium (a transfer sheet) passing through a nip area between the heating roller and the pressing roller of the fixing device is separated from the heating roller by separation claws provided near the heating roller. The transfer sheet is separated by the tip of each separation claw, slides on the surface of the claw to the ejection rollers, and then carried into the ejection tray. In this case, paper dust of the transfer sheet may remove the Teflon (registered trademark) coated layer. In extreme cases, toner may be caught in the area from which Teflon coat is removed and may give unwanted lines to the image on the transfer sheet or damage the transfer sheet. Patent Document 1 provides a spur on each separation claw so that the transfer sheet passing through the nip area between the heating roller and the pressing roller may not be in contact with the separation claws. Specifically, the transfer sheet separated from the heating roller by the separation claws is supported by the edges of the spurs away from the separation claws and sent to the ejection rollers. This mechanism keeps the transfer sheet away from the separation claws, prevents the Teflon coat from being damaged, and consequently prevents unwanted lines on the transfer sheet and damages of the transfer sheet.  
         [0009]     Patent Document 2, which represents Japanese Non-examined Patent Publication H11-95489, as another prior art discloses a means provided in the ejection path between the image carrier and the fixing device. This means is to carry a transfer sheet having unfixed toner images on both sides. When the transfer sheet touches the guide plate or the like, the unfixed toner on the transfer sheet may be rubbed away by it. To prevent this, the invention provides spurs in the ejection path and supports the transfer sheet by a plurality of spur edges without carrying the transfer sheet on the guide plates. As the spurs rotate while the transfer sheet moves forward, the transfer sheet is supported by a plurality of spur edges and toner images on the transfer sheet will not be damaged.  
         [0010]     Naturally, there are many parts other than the guide plates and the like that touch the molten wax on the transfer sheet. The transfer sheet is fed from the sheet cassette, carried along a preset conveyance path through the image forming apparatus, and finally ejected to the ejection tray. A plurality of sensors are disposed along this conveyance path. If a sensor does not detects the transfer sheet within a preset time period after the preceding sensor detected the transfer sheet, it is assumed that a paper jam has occurred. These sensors are helpful in detecting a paper jam earlier and enable easy and quick removal of the jam.  
         [0011]     Each sensor has an actuator. When touching the leading edge of a transfer sheet, the actuator works to turn on the sensor to tell that the transfer sheet is detected. When the actuator touches molten wax on the transfer sheet, the wax is quickly cooled and solidified. This causes a glossy stripe on the transfer sheet.  
         [0012]     However, in the above well-known example, the recording medium is kept away from the guide plates or the like before fixing or immediately after fixing. Contrarily, the molten wax is solidified near the ejection roller which is a little away from the fixing device. Therefore, this prior art cannot solve the unevenness of gloss of wax by a sensor provided just after the fixing device.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention is devised from the above prior art and its object is to provide an image forming apparatus that can detect a recording medium which is wet with wax just after fixing, solidify the wax on the recording medium uniformly without causing any stripe of unevenness of wax gloss, and thus form images without unevenness.  
         [0014]     The above object can be attained by any one of the structures (1) to (9) below.  
         [0015]     Structure (1): An image forming apparatus comprising a fixing device that receives a recording medium having unfixed toner images, heats and presses the toner images formed on the recording medium, and fixes the toner images onto the recording medium, ejection rollers provided away from the fixing device, a sensor provided in the recording medium ejection path between the ejection rollers and the fixing device to detect the recording medium, an actuator of the sensor, and a spur having a plurality of teeth on its circumference that is provided on the tip of the actuator.  
         [0016]     Structure (2): The image forming apparatus of structure (1), wherein the sensor is an optical sensor having a light emitter and a light receiver, the actuator is equipped with a light-shielding lever that moves between the light emitter and the light receiver, a medium detection lever which is rotated by the movement of the recording medium, and a shaft which holds both levers pivotally, and the medium detection lever is equipped with the spur on its tip.  
         [0017]     Structure (3): The image forming apparatus of structure (1), wherein the rotary axis of the spur is located in the outer side of the ejection path through which the recording medium is carried.  
         [0018]     According to Structure (1), the following operations and effects are produced.  
         [0019]     The fixing device heats and melts toner on a recording medium to fix the toner to the recording medium and sends out the recording medium wet with the molten wax in the toner to the ejection path. In the ejection path, the recording medium reaches the actuator and touches the sharp edges of a spur provided on the tip of the actuator. The spur can rotate as the recording medium advances. Therefore, the spur supports the recording medium by points (sharp spur edges) and the molten wax is not cooled quickly. As the result, the molten wax on the recording medium can be solidified uniformly. Specifically, this structure has an excellent effect to prevent unevenness of gloss of wax that is formed because of differences in wax solidifying speeds.  
         [0020]     According to Structure (2), the sensor is an optical sensor having a light emitter and a light receiver, the actuator is equipped with a light-shielding lever that moves between the light emitter and the light receiver, a recording medium detection lever which is rotated by the advance of the recording medium, and a shaft which holds both levers pivotally, and the medium detection lever is equipped with the spur on its tip.  
         [0021]     Therefore, just when the recording medium touches and rotates the spur, the medium detection lever and the light shielding lever rotate. With this, the recording medium can be detected.  
         [0022]     According to Structure (3), the rotary axis of the spur is located in the outer side of the ejection path through which the recording medium is conveyed. Therefore, the rotational direction of the spur that is made by the advance of a recording medium is equal to that of the detection lever. This enables a smooth detection of a recording medium.  
         [0023]     Structure (4): An image forming apparatus comprising a fixing device that receives a recording medium having toner images, heats and presses the toner images formed on the recording medium, and fixes the toner images onto the recording medium, ejection rollers provided away from the fixing device to eject the recording medium, a guide means provided on at least one part of the recording medium ejection path between the ejection roller and the fixing device to guide the conveyance of the recording medium, one or more spurs having a plurality of teeth on its circumference that are provided on the tip of the guide means, and a slit formed on the guide means so that the plurality of teeth of the spur are protruded on a side of the recording medium ejection path through the slit, wherein the recording medium is conveyed from the fixing device toward the ejection rollers by bringing the plurality of teeth of the spur into contact with a surface of the recording medium.  
         [0024]     Structure (5): The image forming apparatus of structure (4), wherein plural spurs are provided at a preset interval on a shaft that extends perpendicular to the conveyance direction of the recording medium.  
         [0025]     Structure (6): The image forming apparatus of structure (5), wherein plural shafts are provided in parallel to each other along the conveyance direction.  
         [0026]     Structure (7): The image forming apparatus of structure (6), wherein some of the spurs are characterized in that each tooth is more than 0.1 mm to less than 0.5 mm high and the projection from the surface of said guide means is 0.5 to 2 mm high.  
         [0027]     Structure (8): The image forming apparatus of structure (7), wherein a plurality of spurs of a small projection are provided on an identical shaft.  
         [0028]     Structure (9): The image forming apparatus of structure (8), wherein the ejection path has a normal-speed ejection path that carries the recording medium at an ordinary linear speed and a high-speed ejection path that carries the recording medium at a higher linear speed, these two ejection paths merge before the ejection roller, and the spur of a small projection is provided in the ejection roller side relative to the merging point.  
         [0029]     According to Structure (4), the following operations and effects are produced.  
         [0030]     The fixing device heats and melts toner on a recording medium to fix the toner to the recording medium and sends out the recording medium wet with the molten wax in the toner to the ejection path. In the ejection path, the recording medium is supported and carried by teeth of spurs provided on the guide means. After the molten wax on the recording medium is fully solidified, the recording medium reaches the ejection rollers and is ejected to the ejection tray. In this way, as the recording medium does not touch the guide means or the like directly between the time at which the medium comes out of the fixing device and the time at which the wax on the medium is fully solidified, the wax can be solidified uniformly. Specifically, this structure has an excellent effect to prevent unevenness of gloss of wax that is formed because of differences in wax solidifying speeds.  
         [0031]     According to Structure (5), a plurality of such spurs are provided at a preset interval on a shaft that extends perpendicularly to the conveyance of the recording medium to support the recording medium at points across the conveyance of the recording medium and to prevent the recording medium from touching the guide means in places where no spurs are provided.  
         [0032]     According to Structure (6), a plurality of the parallel shafts provided perpendicularly to the conveyance of the recording medium prevent the recording medium from touching the guide means until the molten wax is completely solidified even when the molten wax is slow to be solidified.  
         [0033]     According to Structure (7), some of the spurs are characterized in that each tooth is more than 0.1 mm to less than 0.5 mm high and the projection from the surface of said means is 0.5 to 2 mm high. This can prevent the recording medium from being damaged even when the recording medium is transferred at a high speed.  
         [0034]     According to Structure (8), a plurality of small-projected spurs are provided on an identical shaft and prevent the recording medium from touching the guide means between spurs.  
         [0035]     According to Structure (9), the ejection path has a normal-speed ejection path that conveys the recording medium at an ordinary linear speed and a high-speed ejection path that conveys the recording medium at a higher linear speed, these two ejection paths merge before the ejection rollers, and the spur of a small projection is provided on the ejection roller side relative to the merging point.  
         [0036]     The recording medium can be supported by spurs fully until the molten wax is solidified and this can prevent the recording medium from being damaged even when the recording medium is transferred at a high speed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]      FIG. 1  shows the cross-sectional view of the configuration of a color image forming apparatus, which is an embodiment of the invention.  
         [0038]      FIG. 2  shows a magnified view of a section between the fixing device and the ejection rollers of  FIG. 1 .  
         [0039]      FIG. 3  shows a perspective view of the spur mechanism.  
         [0040]      FIG. 4 ( a ) shows a front view of a large-projection spur and  FIG. 4 ( b ) shows a sectional view taken on line  4 ( b )- 4 ( b ) in  FIG. 4 ( a ).  
         [0041]      FIG. 5 ( a ) shows a front view of a small-projection spur and  FIG. 5 ( b ) shows a sectional view taken on line  5 ( b )- 5 ( b ) in  FIG. 5 ( a ).  FIG. 5 ( c ) shows a magnified view of part of  FIG. 5 ( a ).  
         [0042]      FIG. 6  is an explanatory drawing of the mounting position of the spurs.  
         [0043]      FIG. 7  is an explanatory drawing of the mounting position of the spurs. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]     The fixing device and the image forming apparatus of the invention will be explained with reference to the accompanying drawings.  
         [0045]      FIG. 1  shows the cross-sectional view of the configuration of a color image forming apparatus which is an embodiment of the invention. Although  FIG. 1  is a view of a color image forming apparatus, the invention can be applied to all image forming apparatus that use toners containing wax. Naturally, the invention can also be applied to monochromatic image forming apparatus.  
         [0046]     The color image forming apparatus A of  FIG. 1  is a tandem type color image forming apparatus has an automatic document feeder  30 , an image reader  60 , image writers ( 3 Y,  3 M,  3 C, and  3 K), image carriers ( 1 Y,  1 M,  1 C, and  1 K), chargers ( 2 Y,  2 M,  2 C, and  2 K), developers ( 4 Y,  4 M,  4 C, and  4 K), a fixing device  24 , a belt-like intermediate transfer body  6 , paper feeding means ( 21 A,  21 B, and  21 C), and a paper conveyance system  22 . Toner supplying means ( 5 Y,  5 M,  5 C, and  5 K) respectively supply new toners to the corresponding developers ( 4 Y,  4 M,  4 C, and  4 K).  
         [0047]     The automatic document feeder  30  is a means to automatically feed single- or double-sided documents “d”. The image reader  60  reads image information by a moving optical system which scans the contents of a plurality of documents “d” fed from the document tray, reflects them by three moving mirrors  60 C, and focuses the reflections into an image pickup element  60 A made of CCDs by a condenser lens  60 B.  
         [0048]     The image forming section  10 Y to form a yellow image has a charger  2 Y, an image writer  3 Y, a developer  4 Y, and a cleaner  8 Y that are placed around the image carrier  1 Y. The image forming section  10 M to form a magenta image has an image carrier  1 M, a charger  2 M, an image writer  3 M, a developer  4 M, and a cleaner  8 M. The image forming section  10 C to form a magenta image has an image carrier  1 C, a charger  2 C, an image writer  3 C, a developer  4 C, and a cleaner  8 C. The image forming section  10 K to form a magenta image has an image carrier  1 K, a charger  2 K, an image writer  3 K, a developer  4 K, and a cleaner  8 K.  
         [0049]     Sets of charger  2  and image writer  3  ( 2 Y and  3 Y,  2 M and  3 M,  2 C and  3 C, and  2 K and  3 K) respectively form a latent image forming means.  
         [0050]     The intermediate transfer body  6  is an endless belt which is entrained about and supported to rotate by a plurality of rollers and driven by a motor (not shown in the drawing).  
         [0051]     A signal of information of an image focused on the image pickup element  60 A is sent to an image processor (not shown in the drawing). The image processor performs analog processing, A/D conversion, shading correction, and image compression on the signal and sends the processed signals by colors to the corresponding image writers ( 3 Y,  3 M,  3 C, and  3 K).  
         [0052]     Each of the image writers ( 3 Y,  3 M,  3 C, and  3 K) using a semiconductor laser as its laser source converts the laser beam from the semiconductor laser into a scanning laser beam by optical elements such as a polygon mirror according to the signals sent from the image processor and forms an electrostatic latent image of each color on the corresponding image carrier ( 1 Y,  1 M,  1 C, and  1 K).  
         [0053]     The images of colors formed by the image forming sections ( 10 Y,  10 M,  10 C, and  10 K) are transferred in sequence onto the moving intermediate transfer body  6  by the primary transfer devices ( 7 Y,  7 M,  7 C, and  7 K) to make a composite color image of them on the intermediate transfer body  6  (primary transferring). A transfer sheet PE as a recording medium is fed from the paper cassette ( 20 A,  20 B, or  20 C), carried through the conveyance system  22 , aligned by registration rollers  23 , fed to the transfer device  7 A which is a secondary transfer device, and receives a color image on it by transferring (secondary transferring). The transfer sheet PE having a transferred color image is fixed by the fixing device  24  and ejected by the ejection rollers  25  to the ejection tray  26  outside the image forming apparatus.  
         [0054]     After transferring a color image onto the transfer sheet PE by the transfer device  7 A and separating the transfer sheet PE, the intermediate transfer body  6  is cleaned by the cleaner  8 A.  
         [0055]      FIG. 2  shows a magnified view of a section between the fixing device  24  and the ejection rollers  25  of  FIG. 1 . The fixing device  24  has a heating roller  241  and a pressing roller  242  which presses the heating roller. The transfer sheet PE as a recording medium having a toner image on it passes through the nip area between the heating roller  241  and the pressing roller  242 , have its toner image molten and fixed to the sheet PE, and sent toward the ejection rollers  25  by the delivery rollers  243 .  
         [0056]     A paper ejection path is provided between the delivery rollers  243  and the ejection rollers  25 . This ejection path has a straight ejection path  271  and an inversion ejection path  272 . A path changeover lever  281  is provided near the delivery rollers  243 . One end of the lever  281  is pivotally supported by the guide block  282 .  
         [0057]     A guide member  283  is provided below the guide block  282 , which has a guide wall  284  in the left side. Inversion rollers  27  are provided below them.  
         [0058]     A guide plate  285  is provided above the guide block  282  and equipped with a plurality of spurs ( 291 ,  292 ,  293 , and  294 ), which are characterized by the invention. Spurs  291  and  292  have a large projection and the spur  293  has a small projection. The spur  294  constitutes part of the sensor  300 . These spurs ( 291 ,  292 ,  293 , and  294 ) will be explained referring to another drawings.  
         [0059]     The space between the guide block  282  and the guide plate  285  is used as a straight ejection path  271 . An auxiliary guide plate  286  is provided opposite the guide plate  285  over a point C at which the straight ejection path  271  and the inversion ejection path  272  merge. It is smoothly connected to the nip section of the ejection roller  25 .  
         [0060]     In the above configuration, a set of the guide block  282 , the guide member  283 , the guide wall  284 , the guide plate  285 , and the auxiliary guide plate  286  is called a guide means.  
         [0061]     The inversion ejection path  272  is composed of first, second, and third inversion ejection paths. The first inversion ejection path  272   a  is the space between the guide block  282  and the guide member  283 . The second inversion ejection path  272   b  is the space between the guide member  283  and the guide wall  284 . The third inversion ejection path  272   c  is the space between the guide block  282  and the guide wall  284 .  
         [0062]     When the changeover lever  281  is in the position indicated by a solid line, the transfer sheet PE sent from the delivery rollers  243  reaches the ejection rollers  25  through the straight ejection path  271  and directly ejected to the ejection tray  26 .  
         [0063]     When the changeover lever  281  is in the position indicated by a broken line, the transfer sheet PE sent from the delivery rollers  243  enters the first inversion ejection path  272   a  and the second inversion ejection path  272   b,  and then reaches the inversion rollers  27 . The transfer sheet PE is nipped by the inversion rollers  27  and sent downwards in the drawing. When the trailing edge of the transfer sheet PE reaches the second inversion ejection path  272   b  and is detected by the sensor, the inversion rollers  27  stop and rotate backward. The transfer sheet PE starts to move with its trailing edge as the new leading edge, and keeps on going through the third inversion ejection path  272   c,  the merging point C, and the spurs  293  and  294 . The transfer sheet PE is nipped by the ejection rollers  25  and ejected to the ejection tray  26 . In this case, the ejected transfer sheet PE is already turned over. In this case, if the transfer sheet PE with an image upward is conveyed through the straight ejection path  271 , the transfer sheet with the image downward is conveyed through the inversion ejection path  272  (upside down).  
         [0064]      FIG. 3  shows a perspective view of the spurs  291 ,  292 ,  293  and  294 , and their vicinities. As shown in this drawing, a plurality of spurs  291 ,  292  and  293  are respectively provided on shafts  295 ,  296  and  297 , which are perpendicular to the conveyance direction of the transfer sheet PE. Parts of the spurs are projected towards the straight ejection path  271  through the slits  287  made on the guide plate  285 .  
         [0065]     The sensor  300  is composed of a detector  301  made of a photocoupler, a light-shielding lever  302  that moves between the light emitter and the light receiver of the detector  301 , a shaft  303  that can hold the light-shielding lever  302  pivotally, a detection lever  304  projecting from this shaft  303 , and a spur  294  which is pivotally mounted on the front end of the detection lever  304 . In this configuration, a set of the light-shielding lever  302 , the shaft  303 , and the detection lever  304  constitutes an actuator. Therefore the spur  294  is on the front end of the actuator. This configuration can be substituted for a rod or plate member that can extend and shrink.  
         [0066]     In  FIG. 2 , when the leading edge of the transfer sheet PE hits the spur  294 , the spur  294  rotates. At the same time, the detection lever  304  rotates clockwise and the light-shielding lever is turned to let the front end go out of the detector  301 . With this, the light receiver detects light coming from the light emitter of the detector  301 . Then, the sensor  300  changes its status from OFF to ON to indicate that the transfer sheet PE is passing through.  
         [0067]      FIG. 4 ( a ) shows a front view of a large-projection spur having large height of teeth and  FIG. 4 ( b ) shows a sectional view taken on line  4 ( b )- 4 ( b ) in  FIG. 4 ( a ).  
         [0068]     Spurs  291 ,  292 , and  294  are large-projection spurs.  FIG. 4  uses a spur  291  as a representative. The other spurs  292  and  294  are the same in shape. As shown in FIGS.  4 ( a ) and  4 ( b ), the spur  291  has a boss in the center and the boss center has a mounting through-hole. The circular disk of the spur  291  has equally-spaced teeth  291   a  on its circumference. As shown in  FIG. 4 ( b ), each tooth  291   a  has a triangular section and its outer end is sharp to make the contact area between the tooth edge and the transfer sheet PE as small as possible. The spur  291  of FIGS.  4 ( a ) and  4 ( b ) is 20 mm in outer diameter and has 30 teeth each of which is 1.6 mm high. This is only an example. Various spur dimensions can be selected.  
         [0069]      FIG. 5 ( a ) shows a front view of a small-projection spur  293  having small height of teeth and  FIG. 5 ( b ) shows a sectional view taken on line  5 ( b )- 5 ( b ) in  FIG. 5 ( a ).  FIG. 5 ( c ) shows a magnified view of part of  FIG. 5 ( a ).  
         [0070]     This spur  293  is the same as the large-projection spur  291  in the outer diameter and the number of teeth, but its tooth is 0.24 mm, which is shorter than that of the spur  291 . Further, the shape of the spur tooth  293   a  as well as the spur tooth  291   a  is triangular and its end is sharp. To realize this configuration, the spur disk has a tapered area  293   b,  which is higher than the tooth  293   a  on the circumference. The spurs  291  and  293  can be made of various kinds of materials such as synthetic resins and metals.  
         [0071]     Next, the operations of the invention will be explained below.  
         [0072]     The transfer sheet PE having an unfixed toner image on it is sent to the fixing device  24 , and nipped by the heating roller  241  and the pressing roller  242  during which the toner is molten, pressed, and fixed to the transfer sheet PE. Then, the transfer sheet PE is sent to the changeover lever  281  from the delivery rollers  243 . The changeover lever  281  is in the position indicated by a solid line of  FIG. 2  and the transfer sheet PE is sent to the straight ejection path  271 .  
         [0073]     The toner molten by the heating roller  241  is solidified before the transfer sheet PE reaches the delivery rollers  243 , but the wax in the toner is still molten and soft. The transfer sheet PE passes through the straight ejection path  271  with the printed side faced up (in  FIG. 2 ) towards the spurs  291  according to the shape of the straight ejection path  271 . When the leading edge of the transfer sheet PE hits the root of a tooth  291   a  of the spur  291 , the spur  291  starts to rotate. As the spur  291  rotates, the leading edge of the transfer sheet PE moves up along the slope of the tooth  291   a  and reaches the top of the tooth  291   a.    
         [0074]     The spur  291  is designed to rotate smoothly. When the leading edge of the transfer sheet PE hits and pushes the tooth of the spur  291 , the spur rotates smoothly without slipping as the transfer sheet PE advances. Then the transfer sheet PE reaches the next spurs  292  and  293  without touching the guide plate  285  and the other guide means. Similarly, the next spur  292  and the next small-projection spur  293  rotate. Finally, the transfer sheet PE reaches the spur  294  of the sensor  300 .  
         [0075]     As the transfer sheet PE moves forward, the spur  294  of the sensor  300  rotates clockwise. This rotates the shaft  303 . As the result, the light-shielding lever  302  on the shaft  303  turns to go out of the detector  301 . With this, the light receiver detects light coming from the light emitter of the detector  301 . The sensor  300  changes its status from OFF to ON to indicate that the leading edge of the transfer sheet PE has come. The spur  294  of the sensor  300  can also rotate smoothly without slipping against the transfer sheet PE.  
         [0076]     As explained above, thanks to the spurs  291  through  294 , the transfer sheet PE is supported and sent by spur teeth to the ejection rollers  25  without touching any guide means such as the guide plate  285  and the detection lever  304 . Further, as the molten wax is solidified before the transfer sheet PE reaches the ejection rollers  25 , we can get images free from unevenness of wax gloss. In the succeeding steps, the transfer sheet PE passes through the nip area of the ejection rollers  25  and is ejected to the ejection tray  26 . In this case, the wax on the transfer sheet PE is already solidified and no gloss unevenness may take place.  
         [0077]     In the above description, the straight ejection path  271  is used. Below is explained how the inversion ejection path  272  is used.  
         [0078]     The image forming apparatus of the invention can eject paper with its sides turned over. To eject a transfer sheet with the print side faced down, set the changeover lever to the position indicated by a broken line of  FIG. 2 . The transfer sheet PE sent from the delivery rollers  243  enters the first inversion ejection path  272   a  and the second inversion ejection path  272   b,  and then goes downward (in  FIG. 2 ) by the inversion rollers  27 . When the trailing edge of the transfer sheet PE reaches the second inversion ejection path  272   b,  the inversion rollers  27  stop and rotate backward. The transfer sheet PE starts to move with its trailing edge as the new leading edge, and keeps on going through the third inversion ejection path  272   c,  the merging point C, and then to the ejection rollers  25 .  
         [0079]     The inversed ejection takes more time than the straight paper ejection because the inversed ejection route is longer than the straight ejection route  271  and the paper must change its moving direction. However, the image forming speed is always fixed. Therefore, the paper transfer speed must be increased in the inversed ejection.  
         [0080]     Further, the molten wax is still soft after the transfer sheet PE passes over the spurs  291  and  292 . Therefore, another spur  293  is required at a point after the merging point C. However, this spur  293  must not be a large-projection spur such as spurs  291  and  292 . The reason is explained below.  
         [0081]     The transfer sheet PE from the inversion ejection path  272  moves towards the spur  293  after the merging point C. When the fast transfer sheet PE from the inversion ejection path  272  hits the spur  293 , the leading edge of the transfer sheet PE may be bent or broken if the spur  293  has a large projection as well as the spurs  291  and  292 . However, without the spur  293 , the molten wax in the toner is still soft in the straight paper ejection. This causes unevenness of wax gloss.  
         [0082]     To improve this, the invention reduced the height “h” of the tooth  293   a  of the spur  293  and the projection height “H” above the guide plate  285  as shown in  FIG. 5 ( c ). After deliberate studies and experiments by changing “h” and “H” values, we found that the height of tooth  293   a  is not so much dependent upon the diameter of the spur and the preferred “h” value is in the range of more than 0.1 mm to less than 0.5 mm (or 0.1 mm&lt;h&lt;0.5 mm). The example of  FIG. 5 ( a ) to  FIG. 5 ( c ) uses “h” of 0.25 mm. If the “h” value is 0.1 mm or less, it is impossible to support the transfer sheet PE by points and a stripe of unevenness of gloss is formed. Contrarily, if the “h” value is 0.5 mm or greater, the leading edge of the transfer sheet PE is apt to be damaged.  
         [0083]     Further, we found that the preferred projection height “H” above the guide plate  285  is in the range of 0.5 to 2.0 mm (or 0.5 mm≦H≦2.0 mm). The example of  FIG. 5 ( a ) to  FIG. 5 ( c ) uses “H” of 2.0 mm. If the “H” value is less than 0.5 mm, the transfer sheet PE directly touches the guide plate between the spurs  292  and  293 . Contrarily, if the “H” value is more than 2 mm, the transfer sheet PE is apt to be damaged even when the tooth height is low.  
         [0084]     In the conventional image forming apparatus, the detection lever  304  of the sensor  300  has nothing or simply a roller on the front end. Therefore, in the straight paper ejection, the wax on the transfer sheet PE is still soft when the sensor  300  detects the leading edge of the transfer sheet PE. The detection lever  304  or the roller on the detection lever may touch this soft wax and cause unevenness of gloss.  
         [0085]     Contrarily, the invention provides a spur  294  on the front end of the detection lever  304 . In this configuration, even when the wax on the transfer sheet PE is soft, the transfer sheet PE is supported by tooth edges of the spur  294  and the unevenness of wax gloss can be suppressed.  
         [0086]      FIG. 6  and  FIG. 7  are explanatory drawings of the mounting position of the spur  294 . In  FIG. 6 , the central axis P of the spur  294  is projected a little from the end surface “a” of the spur  293 . In this configuration, when the transfer sheet PE moves along the end surface “a” and touches the spur  294 , the transfer sheet PE tries to rotate the spur  294  counterclockwise. Contrarily, the detection lever  304  having the spur  294  tries to rotate clockwise around the shaft  303 . Consequently, as these rotational directions are different, the spur  294  cannot rotate and a paper jam occurs.  
         [0087]     Contrarily, in  FIG. 7 , the central axis P of the spur  294  is retracted a little from the end surface “a” of the spur  293 . In this configuration, when the transfer sheet PE moves along the end surface “a” and touches the spur  294 , the transfer sheet tries to rotate the spur  294  clockwise. Simultaneously, the detection lever  304  having the spur  294  tries to rotate clockwise around the shaft  303 . As these rotational directions are the same, the spur  294  can rotate easily and the sensor  300  steadily detects the transfer sheet PE.  
         [0088]     If the spur  294  has a small projection as well as the spur  293 , the leading edge of the transfer sheet PE may be broken when it hits the spur. However, when the spur  294  has a large projection, the transfer sheet PE is not damaged. Therefore, the example indicated in the drawing uses a large-projection spur.  
         [0089]     In the above description, the embodiment provides spurs  291  to  293  on the guide plate  285 . This is because the guide means that the transfer sheet PE having molten wax may touch is the guide plate  285 . Therefore, the location of the spurs is not limited to the guide plate  285  as long as the guide means may touch the molten wax.  
         [0090]     Further, this embodiment uses three rows of spurs  291 ,  292 , and  293 . The number of rows is not limited to three as long as the wax is solidified quickly. The number of rows can be changed according to the properties of the wax.  
         [0091]     AS shown in  FIG. 3 , the number of small-projection spurs  293  mounted on the shaft is twice the number of large-projection spurs  291  and  292 . This is because its “H” value is smaller than that of the large-projection spurs  291  and  292  as explained in  FIG. 5 ( a ) to  FIG. 5 ( c ) and more spurs  293  are required to support the transfer sheet PE to prevent the transfer sheet PE from touching the guide plate  285 .