Patent Publication Number: US-8123211-B2

Title: Pickup roller lifting and lowering mechanism in paper feeding unit and image forming apparatus including the pickup roller lifting and lowering mechanism

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior the U.S. Patent Application No. 61/079,723, filed on 10 Jul., 2008, the prior the U.S. Patent Application No. 61/079,733, filed on 10 Jul., 2008, and the prior the U.S. Patent Application No. 61/081,683, filed on 17 Jul., 2008, the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a pickup roller lifting and lowering mechanism with improved lowering timing in a paper feeding unit and an image forming apparatus including the lifting and lowering mechanism. 
     BACKGROUND 
     In an image forming apparatus such as a copying machine, a MFP (Multifunction Peripheral), or a printer, recording media such as paper are stored in a paper feeding cassette. In image formation, the image forming apparatus extracts the recording media one by one from the paper feeding cassette. The image forming apparatus extracts the recording media from the paper feeding cassette using a pickup roller. 
     In an image forming apparatus in the past, a pickup roller falls as a paper feeding cassette is inserted into the image forming apparatus (e.g., JP-A-5-162870). 
     Therefore, when the paper feeding cassette is inserted into the image forming apparatus or drawn out from the image forming apparatus, the pickup roller may come into contact with recording media stacked in the paper feeding cassette. In order to avoid this contact, the size of an apparatus body in the vertical direction has to be set large. 
     SUMMARY 
     It is an object of the present invention to provide a pickup roller lifting and lowering mechanism of a paper feeding unit that can lower a pickup roller after a paper feeding cassette is completely inserted. 
     In an aspect of the present invention, a pickup roller lifting and lowering mechanism includes: 
     a lifting and lowering driving mechanism having a base disc, which is a disc perpendicular to a rotation axis, and a cam that is set in contact with the base disc, the lifting and lowering driving mechanism including a cam gear urged in a direction opposite to an inserting direction of a paper feeding cassette in which recording media are stacked and a push-back mechanism that urges the cam gear in a direction opposite to the paper feeding cassette and releases the urging of the cam gear in the inserting direction of the paper feeding cassette by being pressed by a pressing projection provided in the paper feeding cassette; 
     a rotation lever rotated by the cam and the base disc; 
     a pickup roller lifting and lowering shaft rotated by the rotation lever; and 
     a pickup roller lowered by the rotation of the pickup roller lifting and lowering shaft. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a schematic configuration of an image forming apparatus; 
         FIG. 2  is a perspective view of a main part of a paper feeding unit; 
         FIG. 3  is a front view of a cam gear; 
         FIG. 4  is a side view of the cam gear; 
         FIG. 5  is a rear perspective view of a lifting and lowering driving mechanism; 
         FIG. 6  is a front perspective view of the lifting and lowering driving mechanism; 
         FIG. 7  is a side view of the lifting and lowering driving mechanism immediately before a paper feeding cassette is inserted; 
         FIG. 8  is a side view of the lifting and lowering driving mechanism at the start of the insertion of the paper feeding cassette; 
         FIG. 9  is a side view of the lifting and lowering driving mechanism immediately after a cam gear thereof starts rotation; 
         FIG. 10  is a side view of the lifting and lowering driving mechanism during the rotation of the cam gear; 
         FIG. 11  is a side view of a state before a tray lift is driven; 
         FIG. 12  is a side view of a state after the tray lift is driven; 
         FIG. 13  is a diagram of an application example of a push-back mechanism; 
         FIG. 14  is a perspective view of a push-back arm at the time of the insertion of the paper feeding cassette; 
         FIG. 15  is a perspective view of a load actuator that is an actuator of a load sensor; 
         FIG. 16  is a perspective view of the load actuator and the load sensor; 
         FIG. 17  is a perspective view of a state immediately after recording media P are stacked in the paper feeding cassette and the paper feeding cassette is inserted; 
         FIG. 18  is a diagram of a load actuator including a screening projection for overload detection; 
         FIG. 19  is a side view of an empty state of the paper feeding cassette; 
         FIG. 20  is a perspective view of the empty state of the paper feeding cassette viewed from below; 
         FIG. 21  is a side view of a full state of the paper feeding cassette; 
         FIG. 22  is a perspective view of an overload state of the paper feeding cassette; 
         FIG. 23  is a front view of a cam gear with shaft; 
         FIG. 24  is a side view of the cam gear with shaft; 
         FIG. 25  is an enlarged side view of a fitting shaft; 
         FIG. 26  is an enlarged perspective view of a distal end portion of a tooth; 
         FIG. 27  is a perspective view of a state immediately after the start of the insertion of the paper feeding cassette; and 
         FIG. 28  is a perspective view of a state immediately after the completion of the insertion of the paper feeding cassette. 
     
    
    
     DETAILED DESCRIPTION 
     Throughout this description, the embodiments and examples shown should be considered as exemplars, rather than limitations on the apparatus and methods of the present invention. 
     A pickup roller lifting and lowering mechanism in a paper feeding unit and an image forming apparatus including the lifting and lowering mechanism according to an embodiment of the present invention are explained in detail below with reference to the accompanying drawings. 
     Overview of the Image Forming Apparatus 
     An image forming apparatus of an electrophotographic system is explained below as an example. An image forming system of the image forming apparatus may be an ink jet system or other image forming systems. 
       FIG. 1  is a schematic diagram of a configuration of the image forming apparatus of the electrophotographic system according to this embodiment. As shown in  FIG. 1 , an image forming apparatus  1  includes an auto document feeder  2 , an image reading unit  3 , an image forming unit  4 , a transfer mechanism  5 , a sheet conveying mechanism, paper feeding units  6 , a fixing unit  7 , a reverse conveying mechanism  8 , and a discharging mechanism  9 . 
     The auto document feeder  2  is openably and closably set in an upper part of a main body of the image forming apparatus  1 . The auto document feeder  2  includes a document conveying mechanism that extracts original documents from a document tray one by one and conveys the original document to a paper discharge tray. 
     The auto document feeder  2  conveys, with the document conveying mechanism, the original documents to a document reading unit of the image reading unit  3  one by one. It is also possible to open the auto document feeder  2  and place original documents on a document table of the image reading unit  3 . 
     The image reading unit  3  includes a carriage including an exposure lamp that exposes an original document to light and a reflecting mirror, plural reflecting mirrors set in a main body frame of the image forming apparatus  1 , a lens block, and a CCD (Charge Coupled Device) of an image reading sensor. 
     The carriage stands still in the document reading unit or reciprocatingly moves below the document table to reflect the light of the exposure lamp, which is reflected by the original document, to the lens block via the plural reflecting mirrors. The lens block magnifies this reflected light and outputs the reflected light to the CCD. The CCD converts the light made incident thereon into an electric signal and outputs the electric signal to the image forming unit  4  as an image signal. 
     The image forming unit  4  includes laser irradiating units, photoconductive drums, and toner supplying units. 
     The laser irradiating units irradiate laser beams on the photoconductive drums on the basis of the image signal and form electrostatic latent images on the photoconductive drums. The toner supplying units supply toner to the photoconductive drums and form toner images from the electrostatic latent images. 
     The paper feeding units  6  extract the recording media P from paper feeding cassettes  6   a  one by one and pass the recording medium P to the sheet conveying mechanism. The sheet conveying mechanism conveys the recording medium to the transfer mechanism  5 . The transfer mechanism  5  includes a transfer belt and transfer rollers. The transfer belt as an image bearing member receives the transfer of the toner images on the photoconductive drums and bears the toner images. The transfer rollers apply voltage to the toner images on the transfer belt and transfer the toner images onto the recording medium P conveyed thereto. 
     The fixing unit  7  heats and presses the toner images and fixes the toner images on the recording medium P. 
     In the case of a simplex printing mode, the recording medium P having the toner images fixed on one side thereof is discharged through the discharging mechanism  9 . In the case of a duplex printing mode, the recording medium P having the toner images fixed on one side thereof is conveyed to the image forming unit  4  via the reverse conveying mechanism  8  and toner images are formed in the same manner as explained above. Then, the recording medium P is discharged through the transfer mechanism  5 , the fixing unit  7 , and the discharging mechanism  9 . 
     On the other hand, an image forming apparatus of the ink jet system is the same as the image forming apparatus of the electrophotographic system except that an ink jet recording unit is built in an image forming unit and peculiar mechanical components such as an ink supplying mechanism are provided. 
     Paper Feeding Unit According to a First Embodiment 
       FIG. 2  is a perspective view of a main part of the paper feeding unit  6 . As shown in  FIG. 2 , the paper feeding unit  6  includes a pickup roller lifting and lowering mechanism  200  set in the main body of the image forming apparatus  1  and a lifting and lowering driving mechanism  100 . 
     The pickup roller lifting and lowering mechanism  200  includes a rotation lever  201 , a pickup roller lifting and lowering shaft  202  that rotates in association with the rotation lever  201 , and a pickup roller  203  that rises and falls according to the rotation of the pickup roller lifting and lowering shaft  202 . 
     The lifting and lowering driving mechanisms  100  includes a driving motor  102 , a deceleration gear  103  driven by the driving motor  102 , and a cam gear  101  driven by the deceleration gear  103 . 
     When the driving motor  102  rotates, the cam gear  101  rotates via the deceleration gear  103 . A cam of the cam gear  101  rotates the rotation lever  201 . When the rotation lever  201  rotates, the pickup roller lifting and lowering shaft  202  rotates and lowers the pickup roller  203 . 
       FIG. 3  is a front view of the cam gear  101 . As shown in  FIG. 3 , the cam gear  101  has a base disc  101 B, which is a disc perpendicular to a rotation axis, and a cam  101 A set in contact with the base disc  101 B. 
     The cam  101 A is formed such that the radius thereof increases as an angle increases toward a rotating direction. A minimum radius r 1  of the cam  101 A is the same as the radius of a center cylinder  101 C provided in the center of the cam gear  101 . A maximum radius r 2  of the cam  101 A is the same as a radius r 0  of the base disc  101 B. A central angle at which the radius of the cam  101 A is maximized is equal to or larger than 90° and equal to or smaller than 120°. An external shape of the cam  101 A smoothly continues from the portion of the minimum radius r 1  to the portion of the maximum radius  2   r.    
       FIG. 4  is a side view of the cam gear  101 . As shown in  FIG. 4 , the cam gear  101  has a pressing disc  101 G, a cylindrical section  101 F, a gear section  101 E, the base disc  101 B, the cam  101 A, the center cylinder  101 C, and a fitting section  101 D. 
     The pressing disc  101 G is made of a disc perpendicular to the rotation axis of the cam gear  101 . The diameter of the pressing disc  101 G is larger than that of the cylindrical section  101 F. 
     The diameter of the cylindrical section  101 F is smaller than those of the pressing disc  101 G and the gear section  101 E. The gear section  101 E has teeth of a toothed gear on the surface thereof. In  FIG. 4 , the teeth are not shown. The diameter of the gear section  101 E is larger than that of the cylindrical section  101 F and smaller than that of the base disc  101 B. 
     The diameter of the center cylinder  101 C is smaller than that of the base disc  101 B. The center cylinder  101 C has the fitting section  101 D at an end thereof. The fitting section  101 D includes plural teeth having tooth surfaces, one sides of which vertically rise up and the other sides of which incline. 
       FIG. 5  is a rear perspective view of the lifting and lowering driving mechanism  100 .  FIG. 6  is a front perspective view of the lifting and lowering driving mechanism  100 . As shown in  FIGS. 5 and 6 , the lifting and lowering driving mechanism  100  rotatably supports the cam gear  101  in a lifting and lowering driving mechanism frame  106 . 
     The lifting and lowering driving mechanism  100  pivotally supports a pair of push-back levers  104 , which are push-back mechanisms, in the lifting and lowering driving mechanism frame  106 . A space between the push-back levers  104  is narrower than the pressing disc  101 G. One ends of the push-back levers  104  are arranged between the gear section  101 E and the pressing disc  101 G to hold the cylindrical section  101 F. 
     Elastic members such as tension springs  105  are provided at the other ends of the push-back levers  104 . The tension springs  105  urge the push-back levers  104  in a direction in which the push-back levers  104  push the pressing disc  101 G. 
     An elastic member such as a compression spring (not shown) is provided in the inside of the cam gear  101 . The compression spring urges to push the cam gear  101  in the direction of the rotation lever  201 , i.e., a direction opposite to the inserting direction of the paper feeding cassette  6   a . The force of the tension springs  105  is stronger than the force of the compression spring. 
       FIG. 7  is a side view of the lifting and lowering driving mechanism  100  before the paper feeding cassette  6   a  is inserted. As shown in  FIG. 7 , the tension spring  105  pulls one end of the push-back lever  104  in an arrow X direction. The compression spring in the inside of the cam gear  101  pushes the cam gear  101  in an arrow Y direction. The force of the tension spring  105  for pulling the push-back lever  104  is stronger than the force of the compression spring for pushing the cam gear  101 . Therefore, the cam gear  101  is pushed to a position set in contact with the lifting and lowering driving mechanism frame  106  and is stopped. The cam gear  101  is separated from the rotation lever  201 . 
       FIG. 8  is a side view of the lifting and lowering driving mechanism  100  at the start of the insertion of the paper feeding cassette  6   a . As shown in  FIG. 8 , the distal end of a pressing projection  204  of the paper feeding cassette  6   a  pushes a pressure receiving section  104 A, which is one end to which the tension spring  105  of the push-back lever  104  is attached, in an arrow X 0  direction. At the same time, an insertion sensor (not shown) that detects the insertion of the paper feeding cassette  6   a  detects the insertion of the paper feeding cassette  6   a.    
     When the pressing projection  204  pushes the pressure receiving section  104 A, the push-back lever  104  separates from the pressing disc  101 G. When the push-back lever  104  separates from the pressing disc  101 G, the cam gear  101  is moved in the arrow Y direction by the compression spring. However, the cam  101 A comes into contact with the rotation lever  201 . The fitting section  101 D does not fit with a cassette-side fitting section  205 . 
       FIG. 9  is a side view of the lifting and lowering driving mechanism  100  immediately after the cam gear  101  starts rotation. As shown in  FIG. 9 , when the insertion sensor detects the insertion of the paper feeding cassette  6   a , the driving motor  102  is driven to rotate the cam gear  101 . 
     When the cam gear  101  rotates, the rotation lever  201  enters a portion where the radius of the cam  101 A is smaller than that of the base disc  101 B. The cam gear  101  moves in the direction of the rotation lever  201  by the thickness of the cam  101 A. The rotation lever  201  does not rotate yet. 
       FIG. 10  is a side view of the lifting and lowering driving mechanism  100  during the rotation of the cam gear  101 . As shown in  FIG. 10 , the cam  101 A rotates the rotation lever  201 . When the rotation lever  201  approaches a portion where the radius of the cam  101 A is equal to the radius of the base disc  101 B, the cam gear  101  further moves in the direction of the rotation lever  201 . The fitting section  101 D and the cassette-side fitting section  205  fit with each other. 
     When the fitting section  101 D and the cassette-side fitting section  205  fit with each other, the rotation lever  201  is pushed up to the circumference of the base disc  101 B by the rotation of the cam  101 A and rotates. The rotation lever  201  rotates the pickup roller lifting and lowering shaft  202 . The pickup roller lifting and lowering shaft  202  drives a driving belt  209 . The pickup roller  203  falls. 
     In a cassette side frame, a cassette-side fitting section  205  rotatably supported by the cassette side frame, a deceleration gear  206 , a semicircular gear  207 , and a tray-up shaft  208  are set. 
     The rotation of the cam gear  101  is transmitted to the cassette-side fitting section  205  via the fitting section  101 D. A rotation gear  205 A of the cassette-side fitting section  205  rotates the deceleration gear  206 . The deceleration gear  206  rotates the semicircular gear  207 . The semicircular gear  207  rotates the tray-up shaft  208 . The tray-up shaft  208  drives a tray lifting and lowering member (hereinafter referred to as tray lift  210 ) coupled thereto. 
       FIG. 11  is a side view of a state before the tray lift  210  is driven. As shown in  FIG. 11 , the tray lift  210  is coupled to the tray-up shaft  208  and pushed down by the weight of a stacking tray  211  in which recording media are stacked. 
       FIG. 12  is a side view of a state after the tray lift  210  is driven. As shown in  FIG. 12 , the deceleration gear  206  pivots the semicircular gear  207 . The semicircular gear  207  rotates the tray-up shaft  208 . 
     The tray-up shaft  208  drives the tray lift  210 . The tray lift  210  lifts the stacking tray  211 . 
       FIG. 13  is a diagram of an application example of the push-back mechanism. As shown in  FIG. 13 , a pair of push-back arms  104 B according to the application example of the push-back mechanism are arranged to hold the cylindrical section  101 F such that one ends thereof push the pressing disc  101 G in an arrow Y 1  direction. 
     The push-back arms  104 B are supported by a fulcrum Q to be pivotable in the lifting and lowering driving mechanism frame  106 . The push-back arms  104 B bend to the cam gear  101  side at the fulcrum Q. The push-back arms  104 B have push-up pins  104 C at the other ends thereof. 
     A hook  204 A as an application example of the pressing projection  204  is provided in a frame  213  on the paper feeding cassette  6   a  side. When the paper feeding cassette  6   a  is inserted, the hook  204 A pushes up the push-up pins  104 C in an arrow X 1  direction. 
     When the push-up pins  104 C are pushed up, the push-back arms  104 B pivot and press the pressing disc  101 G. The cam gear  101  moves in the arrow Y 1  direction. 
       FIG. 14  is a perspective view of the push-back arms  104 B at the time of the insertion of the paper feeding cassette  6   a . As shown in  FIG. 14 , the push-up pins  104 C fit in the hook  204 A when the paper feeding cassette  6   a  is inserted. When the push-up pins  104 C fit in the hook  204 A, one ends of the push-back arms  104 B move in an arrow X 2  direction. The other ends of the push-back arms  104 B move in an arrow Y 2  direction. The cam gear  101  is moved in the arrow Y 2  direction by the compression spring. 
     The cam gear  101  rotates and the cam  101 A rotates the rotation lever  201 . When the rotation lever  201  approaches a portion where the radius of the cam  101 A is equal to the radius of the base disc  101 B, the cam gear  101  further moves in the direction of the rotation lever  201 . The fitting section  101 D and the cassette-side fitting section  205  fit with each other. 
     Load Sensor 
       FIG. 15  is a perspective view of a load actuator  300  that is an actuator of a load sensor. As shown in  FIG. 15 , the load actuator  300  has an arrow-shaped load detecting section  301  at the distal end thereof and has a driving projection  302  and a first screening member (projection  303 ) for proper load detection in the center of an arm section. 
       FIG. 16  is a perspective view of the load actuator  300  and a load sensor  212 . As shown in  FIG. 16 , the load actuator  300  is pivotably attached to the pickup roller lifting and lowering shaft  202 . 
     The driving projection  302  is placed on a supporting projection  214 A provided in a pickup roller supporting arm  214 . The load sensor  212  is arranged in a position where the first screening projection  303  interrupts an optical path. 
       FIG. 17  is a perspective view of a state immediately after the recording media P are stacked in the paper feeding cassette  6   a  and the paper feeding cassette  6   a  is inserted. When a load of the recording media P is proper, the load detecting section  310  does not come into contact with the recording media P. Therefore, the first screening projection  303  turns off the load sensor  212 . A pickup roller detection sensor  203 A is turned on only when the pickup roller  203  passes. 
       FIG. 18  is a diagram of the load actuator  300  including a second screening member (projection  303 B) for overload detection. As shown in  FIG. 18 , the second screening projection  303 B is provided below the first screening projection  303  in the center of the arm section of the load actuator  300 . 
     A state in the case of a proper load of recording media is shown in  FIG. 18 . As shown in  FIG. 18 , the first screening projection  303  and the second screening projection  303 B do not interrupt the light of the load sensor  212 . The load sensor  212  is turned off. 
       FIG. 19  is a side view of an empty state of the paper feeding cassette  6   a . As shown in  FIG. 19 , even if the stacking tray  211  rises, the load detecting section  301  is not lifted. Therefore, the load sensor  212  is turned on by the first screening projection  303 .  FIG. 20  is a perspective view of the empty state of the paper feeding cassette  6   a  viewed from below. As shown in  FIG. 20 , in the stacking tray  211 , a no-sheet detection hole  213  is provided in a position where the load detecting section  301  falls. Therefore, when at least one recording medium P is present, the load detecting section  301  is lifted and the load sensor  212  is turned off. 
       FIG. 21  is a side view of a full state of the paper feeding cassette  6   a . As shown in  FIG. 21 , even if the pickup roller  203  falls, the pickup roller detection sensor  203 A is kept off. The load sensor  212  is turned on by screening projection  303 . 
       FIG. 22  is a perspective view of an overload state of the paper feeding cassette  6   a . As shown in  FIG. 22 , when the paper feeding cassette  6   a  is overloaded, the second screening projection  303 B turns on the load sensor  212 . 
     Control of a Tray-Up Operation 
     The driving motor  102  is controlled as explained below in order to perform tray-up operation that is operation for lifting the stacking tray  211 . 
     When an Overload is not Detected 
     (1) When the paper feeding cassette  6   a  is inserted in the main body of the image forming apparatus  1 , the insertion sensor is turned on. 
     (2) After several tens ms, when the pickup roller detection sensor  203 A is off (does not interrupt) and the load sensor  212  is off (does not interrupt), the driving motor  102  is driven. 
     (3) When the driving motor  102  is driven, the pickup roller  203  starts to fall from an uppermost position to turn on the pickup roller detection sensor  203 A shown in  FIG. 11  for an instance and turn off the pickup roller detection sensor  203 A again. When the pickup roller detection sensor  203 A is not turned off, processing at abnormal time such as error display is started. 
     When the pickup roller detection sensor  203 A is turned on, the driving motor  102  stops for a predetermined time. This predetermined time is time sufficient for the pickup roller  203  to fall and pass the pickup roller detection sensor  203 A. 
     After the predetermined time elapses, it is checked again whether the pickup roller detection sensor  203 A is on or off. When the insertion sensor is turned off, the processing at abnormal time is started. 
     (4) 
     (a) When the pickup roller detection sensor  203 A is off, the driving motor  102  is driven until the pickup roller detection sensor  203 A is turned on. 
     (b) When the pickup roller detection sensor  203 A is on, the tray-up operation is finished. 
     When an Overload is Detected 
     (1) When the paper feeding cassette  6   a  is inserted in the main body of the image forming apparatus  1 , the insertion sensor is turned on. 
     (2) After several tens ms, when the pickup roller detection sensor  203 A is off (does not interrupt) and the load sensor  212  is off (does not interrupt), the driving motor  102  is driven. 
     When the pickup roller detection sensor  203 A is off and the load sensor  212  is on, an alarm indicating an overload is emitted. The alarm is performed by means of voice, display on a control panel, or the like. 
     (3) When the driving motor  102  is driven, the pickup roller  203  starts to fall from the uppermost position to turn on the pickup roller detection sensor  203 A shown in  FIG. 11  for an instance and turn off the pickup roller detection sensor  203 A again. When the pickup roller detection sensor  203 A is not turned off, the processing at abnormal time is started. 
     When the pickup roller detection sensor  203 A is turned on, the driving motor  102  stops for a predetermined time. This predetermined time is time sufficient for the pickup roller  203  to fall and pass the pickup roller detection sensor  203 A. 
     After the predetermined time elapses, it is checked again whether the pickup roller detection sensor  203 A is on or off. When the insertion sensor is turned off, the processing at abnormal time is started. 
     (4) 
     (a) When the pickup roller detection sensor  203 A is off, the driving motor  102  is driven until the pickup roller detection sensor  203 A is turned on. 
     (b) When the pickup roller detection sensor  203 A is on, the tray-up operation is finished. 
     Effect of this Embodiment 
     As explained above, the pickup roller lifting and lowering mechanism and the image forming apparatus including the lifting and lowering mechanism according to this embodiment includes the lifting and lowering mechanism  100  including the cam gear  101 , which includes the cam  101 A, the base disc  101 B, the pressing disc  101 G, and the compression spring, and the push-back levers  104 , which includes the tension springs  105 , and the pickup roller lifting and lowering mechanism  200  including the pressing projection  204  and the rotation lever  201  that lowers the pickup roller  203 . 
     The pickup roller lifting and lowering mechanism and the image forming apparatus including the lifting and lowering mechanism according to this embodiment lift the stacking tray  211  awaiting the elapse of time from the time when the pickup roller  203  starts to fall until the pickup roller  203  completely falls. 
     Therefore, there is an effect that the pickup roller lifting and lowering mechanism and the image forming apparatus including the lifting and lowering mechanism according to this embodiment can lower the pickup roller  203  after the paper feeding cassette  6   a  is completely inserted and the height of the paper feeding cassette  6   a  can be set lower. 
     Paper Feeding Unit According to a Second Embodiment 
     The paper feeding unit  6  according to this embodiment is the same as the paper feeding unit  6  according to the first embodiment except that a cam gear with shaft  121  is used instead of the cam gear  101  and the frame  213  on the paper feeding cassette  6   a  side has a fitting hole (explained later) through which a fitting shaft (explained later) of the cam gear with shaft  121  is inserted. 
       FIG. 23  is a front view of the cam gear with shaft  121 . As shown in  FIG. 23 , the cam gear with shaft  121  includes the base disc  101 B, which is a disc perpendicular to a rotation axis, and the cam  101 A set in contact with the base disc  101 B. 
     The cam  101 A is formed such that the radius thereof increases as an angle increases toward a rotating direction. The minimum radius r 1  of the cam  101 A is the same as the radius of the center cylinder  101 C provided in the center of the cam gear with shaft  121 . The maximum radius r 2  of the cam  101 A is the same as the radius r 0  of the base disc  101 B. A central angle at which the radius of the cam  101 A is maximized is equal to or larger than 90° and equal to or smaller than 120°. 
       FIG. 24  is a side view of the can gear with shaft  121 . As shown in  FIG. 24 , the cam gear with shaft  121  includes the pressing disc  101 G, the cylindrical section  101 F, the gear section  101 E, the base disc  101 B, the cam  101 A, the center cylinder  101 C, and a fitting shaft  121 D. 
     The pressing disc  101 G is made of a disc perpendicular to the rotation axis of the cam gear with shaft  121 . The diameter of the pressing disc  101 G is larger than that of the cylindrical section  101 F. 
     The diameter of the cylindrical section  101 F is smaller than those of the pressing disc  101 G and the gear section  101 E. The gear section  101 E has teeth of a toothed gear on the surface thereof. In  FIG. 24 , the teeth are not shown. The diameter of the gear section  101 E is larger than that of the cylindrical section  101 F and smaller than that of the base disc  101 B. 
     The diameter of the center cylinder  101 C is smaller than that of the base disc  101 B. The center cylinder  101 C has the fitting shaft  121 D at an end thereof. The fitting shaft  121 D has teeth  121 D 1  of a toothed gear in a root section thereof and is formed to taper toward the distal end thereof. 
       FIG. 25  is an enlarged side view of the fitting shaft  121 D. As shown in  FIG. 25 , the fitting shaft  121 D has the teeth  121 D 1  of the toothed gear in the root section thereof. The teeth  121 D 1  are provided in parallel to a rotation axis of the fitting shaft  121 D. 
       FIG. 26  is an enlarged perspective view of the distal end portion of the tooth  121 D 1 . As shown in  FIG. 26 , the tooth  121 D 1  is chamfered such that the height thereof gradually decreases and the width thereof gradually decreases toward the distal end. The distal end portion may be chamfered in a streamline shape. 
       FIG. 27  is a perspective view of a state immediately after the start of the insertion of the paper feeding cassette  6   a . In an example shown in  FIG. 27 , the push-back arms  104 B are used. The push-back levers  104  can also be used. 
     The frame  213  on the paper feeding cassette  6   a  side has a fitting hole  211 H through which the fitting shaft  121 D of the cam gear with shaft  121  is inserted. 
       FIG. 28  is a perspective view of a state immediately after the completion of the insertion of the paper feeding cassette  6   a . As shown in  FIG. 28 , the fitting shaft  121 D is inserted into the fitting hole  211 H. The teeth  121 D 1  of the fitting shaft  121 D engage with teeth of the deceleration gear  206 . Therefore, when the cam gear with shaft  121  rotates, the deceleration gear  206  rotates. 
     The teeth  121 D 1  are chamfered as explained above. Therefore, when the paper feeding cassette  6   a  is inserted, the teeth  121 D 1  smoothly engage with the teeth of the deceleration gear  206 . Since the fitting shaft  121 D is inserted into the fitting hole  211 H, the teeth  121 D 1  and the teeth of the deceleration gear  206  that engage each other do not disengage. 
     The teeth  121 D 1  are provided in parallel to the rotation axis of the fitting shaft  121 D. Therefore, when the paper feeding cassette  6   a  is inserted and removed, the teeth  121 D 1  can be easily engaged with and disengaged from the teeth of the deceleration gear  206 . 
     Effect of this Embodiment 
     As explained above, in the pickup roller lifting and lowering mechanism and the image forming apparatus including the lifting and lowering mechanism according to this embodiment, the lifting and lowering driving mechanism  100  includes the cam gear with shaft  121  including the fitting shaft  121 D. The frame  213  on the paper feeding cassette  6   a  side has the fitting hole  211 H through which the fitting shaft  121 D of the cam gear with shaft  121  is inserted. Therefore, there is an effect that the number of components can be further reduced. 
     Although exemplary embodiments of the present invention have been shown and described, it will be apparent to those having ordinary skill in the art that a number of changes, modifications, or alterations to the invention as described herein may be made, none of which depart from the spirit of the present invention. All such changes, modifications, and alterations should therefore be seen as within the scope of the present invention.