Patent Publication Number: US-7581830-B2

Title: Image forming apparatus having urging member for urging feeding roller toward recording medium

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority from Japanese Patent Application No. 2005-370242 filed Dec. 22, 2005. The entire content of the priority application is incorporated herein by reference. 
   TECHNICAL FIELD 
   The disclosure relates to an image forming apparatus for forming an image on a sheet-like recording medium. 
   BACKGROUND 
   Conventionally, some image forming apparatuses, such as printers, are configured so as to have a recording-medium accommodating section (for example, a so-called sheet feed cassette and a sheet feed tray) for accommodating recording mediums such as sheets therein and convey the recording medium accommodated in the recording-medium accommodating section to an image forming position (a position at which an image is formed on a recording medium). Specifically, the image forming apparatuses generally has a configuration including a feeding roller for feeding the recording medium accommodated in the recording-medium accommodating section to a conveying path. 
   For example, Japanese Patent Application Publication No. 2005-246907 discloses an image recording apparatus having an arm member provided so as to swing about a swing axis which is parallel to a rotational axis of a sheet feeding roller (feeding roller) and which is located above a sheet accommodated in a sheet feeding cassette and on an upstream side in a sheet feeding direction relative to the rotational axis of the sheet feeding roller. In the image recording apparatus, the sheet feeding roller is rotatably supported by a free end of the arm member, and by urging the arm member downward by a torsion spring, the sheet feeding roller comes into contact with the sheet accommodated in the sheet feeding cassette. 
   SUMMARY 
   However, in the configuration described in Japanese Patent Application Publication No. 2005-246907, when an orientation of the arm member is close to a horizontal state (an orientation parallel to the surface of the sheet), a conveying force of the sheet by the sheet feeding roller becomes smaller. The reason is explained as follows. When the feeding roller is rotatingly driven, a force that makes the feeding roller rollingly move on the sheet is applied to the arm member. A component of this force acts as a force for pressing the sheet feeding roller toward the sheet. As the orientation of the arm member is closer to the orientation parallel to the surface of the sheet (the horizontal state), the component force becomes smaller. However, if an urging force by the torsion spring is set so large that a sufficient pressing force can be obtained when the orientation of the arm member is nearly horizontal, an excessive pressing force is applied to the sheet when the arm member is swung downward. As a result, it is likely to occur that a plurality of sheets is erroneously fed. 
   In view of the foregoing, it is an object of the invention to provide an image forming apparatus that prevents that a conveying force of a feeding roller for conveying a recording medium becomes insufficient due to a position of the feeding roller about a swing axis. 
   In order to attain the above and other objects, the invention provides an image forming apparatus. The image forming apparatus includes a main body, a recording-medium accommodating section, a feeding roller, a supporting member, a first urging member, and a second urging member. The recording-medium accommodating section is provided at the main body and is configured to accommodate a recording medium having a surface. The feeding roller is rotatable about an imaginary rotational axis extending in an axial direction and is configured to be rotatingly driven in a rotational direction for feeding the recording medium to a conveying path. The supporting member has a first end that is swingably supported at the main body and a second end that is opposite to the first end and rotatably supports the feeding roller. The supporting member is swingable about an imaginary swing axis that is parallel to the imaginary rotational axis. The imaginary swing axis is located above the recording medium accommodated in the recording-medium accommodating section and is located upstream in a feeding direction of the recording medium with respect to the imaginary rotational axis. The first urging member is configured to apply an urging force to the support member in such a manner that the feeding roller contacts the recording medium accommodated in the recording-medium accommodating section. The second urging member is configured to urge the second end in a direction that increases the urging force of the first urging member when an angle between the surface of the recording medium accommodated in the recording-medium accommodating section and a plane containing both the imaginary rotational axis and the imaginary swing axis is smaller than a predetermined angle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Illustrative aspects in accordance with the invention will be described in detail with reference to the following figures wherein: 
       FIG. 1  is a perspective view showing an exterior of an image forming apparatus according to illustrative aspects of the invention; 
       FIG. 2  is a cross-sectional view of a configuration housed in a main casing of the image forming apparatus; 
       FIG. 3  is a perspective view of a sheet feeding tray and a sheet feeding unit in a state where a second tray is not mounted; 
       FIG. 4  is a perspective view of the sheet feeding tray and the sheet feeding unit in a state where the second tray is mounted; 
       FIG. 5  is a plan view (when viewed from above) of the sheet feeding tray and sheet feeding unit in the state where the second tray is not mounted; 
       FIG. 6A  is a cross-sectional view taken along a line VI-VI in  FIG. 5 , particularly showing that a feeding roller is not immediately rotated in a reverse direction after switching of rotational direction of a drive gear, due to a play provided in the drive gear; 
       FIG. 6B  is a cross-sectional view taken along the line VI-VI in  FIG. 5 , particularly showing that the feeding roller starts rotating in the reverse direction after a delay for the play; 
       FIG. 7A  is a cross-sectional view taken along a line VII-VII in  FIG. 5 , where a shaft part (rotational shaft) is in a reference state; 
       FIG. 7B  is a cross-sectional view taken along the line VII-VII in  FIG. 5 , where the shaft part (rotational shaft) is inclined at a maximum angle from the reference state shown in  FIG. 7A  (maximum inclined state); 
       FIG. 8  is a cross-sectional view taken along a line VIII-VIII in  FIG. 5 ; 
       FIG. 9  is a plan view (when viewed from above) of the sheet feeding tray, the sheet feeding unit, and a frame in the state where the second tray is not mounted; 
       FIG. 10A  is a cross-sectional view taken along a line X-X in  FIG. 9 , where an arm member is positioned on a bottom surface of the sheet feeding tray; 
       FIG. 10B  is a cross-sectional view taken along the line X-X in  FIG. 9 , where the arm member is positioned on a bottom surface of a second tray; 
       FIG. 10C  is a cross-sectional view taken along the line X-X in  FIG. 9 , where the arm member is positioned on an uppermost recording medium when recording mediums are accommodated in the second tray to full capacity; 
       FIG. 11  is a perspective view of a configuration shown in  FIG. 10C , when viewed from obliquely below the frame; 
       FIG. 12  is a perspective view of an image recording unit of the image forming apparatus without a platen and a carriage; 
       FIG. 13A  is a side cross-sectional view of the image recording unit; 
       FIG. 13B  is a plan view of the image recording unit with the platen and the carriage; 
       FIG. 14  is a side view of the image recording unit; 
       FIG. 15A  is a schematic view of a power transmission switch mechanism when viewed from above; 
       FIG. 15B  is a perspective view of the power transmission switch mechanism; 
       FIG. 15C  shows how a switch gear, a first block, and a second block are arranged on a sliding shaft in the power transmission switch mechanism of  FIG. 15B ; 
       FIG. 16A  is a front view showing the power transmission switch mechanism switched to each mode; 
       FIG. 16B  is a plan view showing the power transmission switch mechanism switched to each mode; 
       FIG. 17A  is a schematic view fox illustrating a transmission route of a rotational driving force in an intermittent feed mode, where an uppermost recording medium which contacts the feeding roller is separated and fed to a conveying path; 
       FIG. 17B  is a schematic view for illustrating the transmission route of the rotational driving force in the intermittent feed mode, where the recording medium is positioned at a nip part between the conveying roller and a follow roller; 
       FIG. 18A  is a schematic view for illustrating a transmission route of a rotational driving force in a continuous feed mode, where the uppermost recording medium is separated and conveyed to the conveying path; 
       FIG. 18B  is a schematic view for illustrating the transmission route of the rotational driving force in the continuous feed mode, where the recording medium is nipped at the nip part between the conveying roller and the follow roller and is also in contact with the feeding roller; 
       FIG. 18C  is a schematic view for illustrating the transmission route of the rotational driving force in the continuous feed mode, where a previous recording medium (previous page) is discharged and next recording medium is continuously conveyed to a recording start position; 
       FIG. 19A  is a schematic view for illustrating a transmission route of a rotational driving force in a subsequent medium process, where a leading end of a subsequent recording medium has not reached a position of a registration sensor; 
       FIG. 19B  is a schematic view for illustrating the transmission route of the rotational driving force in the subsequent medium process, where a recording medium subjected to slant correction is discharged and the subsequent recording medium is returned to the sheet feeding tray; 
       FIG. 20  is a block diagram showing a schematic configuration of a control system of the image forming apparatus; 
       FIG. 21  is a flow chart of an image recording process; 
       FIG. 22  is a flow chart of the subsequent medium process; 
       FIG. 23A  is an explanatory diagram showing a force applied to the feeding roller and the arm member when the feeding roller is rotatingly driven in the forward direction; 
       FIG. 23B  is an explanatory diagram showing a force applied to the feeding roller and the arm member when the feeding roller is rotatingly driven in the reverse direction; 
       FIG. 23C  is an explanatory diagram showing a force applied to the feeding roller and the arm member when the feeding roller is pulled by the recording medium in a rearward direction; 
       FIG. 24  is a block diagram showing the transmission route of the rotational driving force from an LF motor to the feeding roller; and 
       FIG. 25  is a table showing rotational directions (forward/reverse) of the LF motor, conveying roller, and feeding roller in the intermittent feed mode and in the continuous feed mode. 
   

   DETAILED DESCRIPTION 
   An image forming apparatus according to some aspects of the invention will be described while referring to the accompanying drawings. In the following description, the expressions “front.”, “rear”, “upper”, “lower”, “right”, “left”, and “vertical direction” are used to define the various parts when an image forming apparatus  1  is disposed in an orientation in which it is intended to be used (the state shown in  FIG. 1 ). The front side (near side) is defined as the side on which an operation panel  10  described later is provided. The left and right sides are both sides of the image forming apparatus  1  when viewed from the front side. 
   [1. Description of Configuration] 
   The image forming apparatus  1  in the illustrative aspects is a so-called multifunction apparatus having a scanning function, a color-copying function, a facsimile function, in addition to a printing function. As shown in  FIG. 1 , the exterior of the image forming apparatus  1  is formed of a main casing  2  which is a resin-made rectangular box shaped member. 
   An operation panel  10  having an operation part  11  on which various operation buttons for input operations are disposed and a display part  12  (for example, a liquid crystal display) for displaying an image such as a message thereon are provided in the front portion on the upper surface of the main casing  2 . A scanner unit  20  for reading an image from an original is provided in the rear of the operation panel  10 . The scanner unit  20  is used for the scanning function, the color-copying function, and the facsimile function. 
   As shown in  FIG. 2 , a sheet feeding tray  30  which can accommodate a plurality of sheet-like recording mediums such as paper and plastic sheets in a horizontally piled (stacked) state therein is provided in the lower portion of the main casing  2 . The sheet feeding tray  30  can be removed by being horizontally pulled out frontward from an opening  2   a  (refer to  FIG. 1 ) formed on the front surface of the main casing  2 . The sheet feeding tray  30  can be mounted by being horizontally inserted into the opening  2   a  of the main casing  2 . 
   A metal box-like frame  4  which is long in the left-right direction (refer to  FIG. 9  and  FIG. 11 ) are provided at the rear portion in the main casing  2  and above the sheet feeding tray  30 . A sheet feeding unit  50  having a feeding roller  60  for feeding (conveying) recording mediums accommodated in the sheet feeding tray  30  one sheet at a time to a conveying path  5  is supported by the frame  4  so as to be disposed above the rear end of the sheet feeding tray  30 . That is, the conveying path  5  for guiding the recording medium conveyed rearward from the sheet feeding tray  30  toward the front by turning around the recording medium upward is formed at the rear end of the main casing  2 . An image recording unit  70  for recording (printing) an image on the recording medium conveyed while being guided through the conveying path  5  is disposed above the sheet feeding unit  50 . The recording medium on which the image is recorded by the image recording unit  70  is discharged to the front portion on the upper surface of the sheet feeding tray  30 . 
   Next, configuration of each part will be described in detail 
   [1-1. Configuration of Sheet Feeding Tray] 
   As shown in  FIG. 3  and  FIG. 5 , the sheet feeding tray  30  is a resin-made thin rectangular tray member of approximately A4 size when viewed from above and is configured so as to accommodate a plurality of recording mediums in a stacked state therein. The sheet feeding tray  30  has a pair of side end guides  31  and  32  at the left and right side ends, respectively, and serves to position the recording medium so that position of the center line in the left-right direction (width direction) may be constant irrespective of the size of accommodated recording medium. That is, mounting plates  31   a  and  32   a  which mount the recording medium thereon and side plates  31   b  and  32   b  which are erected upward from the outer ends of the mounting plates  31   a  and  32   a  in the left-right direction are provided on the side end guides  31  and  32 , respectively. Linear guide bars  31   c  and  32   c  extend from the bottom surfaces of the mounting plates  31   a  and  32   a  toward the other side end guides  31  and  32 , respectively. The linear guide bars  31   c  and  32   c  are disposed in parallel with a predetermined distance therebetween in the front-rear direction and engaged into grooves  33   a  and  33   b  formed on a bottom plate  33  of the sheet feeding tray  30  in the left-right direction. The side end guides  31  and  32  can be displaced in the left-right direction by sliding the linear guide bars  31   c  and  32   c  along the grooves  33   a  and  33   b , respectively. A rack gear is formed on each of opposing sides of the linear guide bars  31   c  and  32   c . Each rack gear engages with a pinion gear rotatably provided at the center of the bottom plate  33  in the width direction. In other words, the side end guides  31  and  32  are coupled to each other through the rack gears and the pinion gear and operate together so that the distance between the side plate  31   b  and the center line of the sheet feeding tray  30  in the left-right direction may be equal to the distance between the side plate  32   b  and the center line (that is, symmetrically) at all times. As a result, the recording medium can be positioned so that position of its center line may be constant. Here, regions of the side plates  31   b  and  32   b  which contact against the end of the recording medium in the left-right direction are each shaped like a flat surface along the front-rear direction (the direction of conveying the recording medium). For this reason, the recording medium accommodated in the sheet feeding tray  30  in the state where it is positioned by the side end guides  31  and  32  is prevented from moving (displacing) in the left-right direction (the rotational axis direction of the feeding roller  60 ) and conveyed in the constant direction. 
   The sheet feeding tray  30  has a guide plate  34  at the rear end. A metal separation member  34   a  is provided at the center of the guide plate  34  in the left-right direction. The separation member  34   a  has a plurality of teeth which are arranged at regular intervals in the vertical direction. The front end of each tooth slightly protrudes from the front surface of the guide plate  34 . Thus, a plurality of recording mediums pushed rearward by the feeding roller  60  of the sheet feeding unit  50  come into contact with the front ends of these teeth and the uppermost recording medium is separated. 
   As shown in  FIG. 4 , the sheet feeding tray  30  is configured so that a second tray  40  which can accommodate thick and small-sized recording mediums such as postcards and envelopes at the center in the left-right direction can be mounted/removed from above. The second tray  40  is a resin thin rectangular tray member which is the almost same as the sheet feeding tray  30  in size in the left-right direction and slightly smaller than the sheet feeding tray  30  in the front-rear direction. The second tray  40  can accommodate a plurality of recording mediums in a vertically stacked arrangement. Like the sheet feeding tray  30 , the second tray  40  has a pair of side end guides  41  and  42  and serves to position the recording medium so that position of the center line in the left-right direction (width direction) may be constant irrespective of the size of accommodated recording mediums. In the state where the second tray  40  is mounted at a predetermined position in the rear portion on the upper side of the sheet feeding tray  30  (a position shown in  FIG. 4 ), the recording medium accommodated in the second tray  40  is located so that the feeding roller  60  may be prevented from moving toward the sheet feeding tray  30  (downward). For this reason, the feeding roller  60  of the sheet feeding unit  50  comes into contact with the recording medium accommodated in the second tray  40 , not the recording medium accommodated in the sheet feeding tray  30  and thus, the recording medium accommodated in the second tray  40  is supplied to the conveying path  5 . 
   [1-2. Configuration of Sheet Feeding Unit] 
   As shown in  FIG. 3 through 5 ,  9 , and  11 , the sheet feeding unit  50  has a support shaft,  51  supported by the frame  4  so as to be disposed from the center to the right end of the sheet feeding tray  30  in the left-right direction. A large gear  53  is fixed at the right end of the support shaft  51  and a small gear  54  having the same diameter as the support shaft  51  is fixed at the vicinity of the left end of the support shaft  51 . The sheet feeding unit  50  is supported by the support shaft  51  and has an arm member  52  configured to be swingable about the support shaft  51  so as to extend obliquely downward toward its free end (rear end). The feeding roller  60  is supported at the rear end (swinging end) of the arm member  52  so as to be rotatable about the rotational axis along the left-right direction. That is, the arm member  52  can swing about a swing axis which is parallel to the rotational axis of the feeding roller  60  and which is located above the recording medium accommodated in the sheet feeding tray  30  and located on an upstream side (front side) in a feeding direction of the recording medium (front to rear) with respect to the rotational axis of the feeding roller  60 . 
   As shown in  FIGS. 7A and 7B , the feeding roller  60  has a resin main body member  61  and two rubber roller members  62  and  62  fixed at right and left ends of the main body member  61 . The roller members  62  and  62  are fixed on the outer circumference of cylindrical roller supporting parts  63  and  64 , respectively. The roller supporting parts  63  and  64  are formed at the both ends of the main body member  61 . A bar-like shaft part  65  connecting the right and left roller supporting parts  63  and  64  to each other is formed at the center in the rotational axis direction As shown in  FIG. 8 , the shaft part  65  is formed to have a cross-shaped cross section (cross-shaped cross section parts  65   c  in  FIG. 7A ), except for a gear contact part  65   a  formed at the center of the shaft part  65  in the axial direction and arm contact parts  65   b  and  65   b  formed on the both sides of the gear contact part  65   a  in the rotational axis direction. On the other hand, as shown in  FIGS. 6A and 6B , the gear contact part  65   a  is configured to have a cross section formed of: a circle having a size containing the cross-shaped cross section (i.e., a circle having a diameter larger than a height and width of the cross-shape); and a pair of protrusions  65   p  formed at opposing positions on the outer circumference of the circle. Each of the arm contact parts  65   b  and  65   b  has a cross section of a circle having a size containing the cross-shaped cross section (i.e., a circle having a diameter larger than a height and width of the cross-shape). 
   In the feeding roller  60 , the shaft part  65  of the main body member  61  is rotatably supported at the free end (rear end) of the arm member  52 . Specifically, as shown in  FIGS. 7A and 7B , two axial support parts  55  are provided at the free end of the arm member  52  along the left-right direction, so as to sandwich a drive gear  66  that transmits a rotational driving force to the feeding roller  60 . Each of the two axial support parts  55  is formed with a through-hole  55   a  having a circular cross section. 
   The feeding roller  60  is rotatably supported in a state where the shaft part  65  of the main body member  61  is inserted into the through-hole  55   a  of each axial support part  55 . In this state, each arm contact part  65   b  of the shaft part  65  is located in confrontation with the end on the central side in the left-right direction in the through-hole  55   a . That is, a narrowest part NP ( FIG. 7A ) of a gap between the shaft part  65  and the through-hole  55   a  is provided at the central side in the left-right direction (the direction parallel to the rotational axis of the feeding roller  60 ). The feeding roller  60  is rotatably supported at the free end of the arm member  52  in the central region in the rotational axis direction. With such configuration, by suppressing degree of freedom in position (unsteadiness of the drive gear  66 ) in the central region of the shaft part  65  in the left-right direction, the rotational driving force from the LF motor  6  is reliably transmitted and degree of freedom in position at the both ends of the shaft part  65  in the left-right direction (degree of freedom of the rotational axis in angle) is made larger. In this manner, the arm member  52  supports the feeding roller  60  such that an angle of the rotational axis has certain flexibility. Specifically,  FIG. 7A  shows a state where the shaft part  65  (rotational shaft) is in a reference state.  FIG. 7B  shows a state where the shaft part  65  (rotational shaft) is inclined at a maximum angle of 3 degrees, for example, from the reference state (maximum inclined state). 
   In the feeding roller  60 , the shaft part  65  of the main body member  61  is inserted into a through-hole  66   a  formed on the drive gear  66 . As shown in  FIGS. 6A and 6B , the through-hole  66   a  is formed of a circular portion corresponding to the circular portion of the gear contact part  65   a  of the shaft part  65  and a pair of fan-shaped notched parts formed at opposing positions on the outer circumference of the circular portion. Here, the fan-shaped notched parts of the through-hole  66   a  are formed so that the length in the circumferential direction is larger than that of the protrusions  65   p  of the gear contact part  65   a . In this manner, a predetermined play in the rotational direction (for example, the angle of 60 degrees) is given to the feeding roller  60  with respect to the drive gear  66 . 
   As shown in  FIGS. 6A ,  6 B, and  8 , four power transmission gears  56  connecting the small gear  54  fixed at the support shaft  51  to the drive gear  66  into which the shaft part  65  is inserted are serially provided in the arm member  52  along the extending direction of the arm member  52 . 
   The arm member  52  can swing about the support shaft  51  from a downward inclined position where the rotational axis of the feeding roller  60  is lower than the support shaft  51  to a horizontal position where the rotational axis of the feeding roller  60  is located at an approximately same level as an axial center of the support shaft  51 . 
   As shown in  FIGS. 3 and 4 , a first torsion coil spring  57  is provided at a base end (on a swing-axis-side end) of the arm member  52 . The first torsion coil spring  57  is configured of a single wire (or other materials) having a coiled part  57 A and a straight part  57 B. The coiled part  57 A is wound around the swing-axis-side end of the arm member  52 . The straight part  57 B has an end that is bent at a substantially right angle and that is in contact with a bottom surface of the sheet feeding tray  30 . With this configuration, the first torsion coil spring  57  urges the arm member  52  downward (in a direction for bringing the feeding roller  60  into contact with the recording medium accommodated in the sheet feeding tray  30 ) in an entire swinging range. Thus, the feeding roller  60  is disposed so as to be in contact with the uppermost recording medium accommodated in the sheet feeding tray  30  (refer to  FIG. 10A ). 
   As shown in  FIGS. 3 ,  5 , and  8 , a second torsion coil spring  58  is provided at the free end of the arm member  52 . The second torsion coil spring  58  is configured of a single wire (or other materials) having two coiled parts  58 A and a squared U shape part  58 B. The coiled parts  58 A are wound around the axial support parts  55  of the arm member  52  ( FIG. 7A ). The squared U shape part  58 B is provided between the two coiled parts  58 A and is bent at two positions at substantially right angles. The squared U shape part  58 B is contactable with a contact piece  4   a  (restricting member) described below. With this configuration, the second torsion coil spring  58  urges the arm member  52  downward (in a direction for increasing an urging force of the first torsion coil spring  57 ) only in a state where the arm member  52  is located close to the horizontal position. In other words, the second torsion coil spring  58  urges the arm member  52  downward only when an angle between a plane of the recording medium and a plane containing the rotational axis of the feeding roller  60  and the swing axis of the arm member  52  is smaller than a predetermined angle. 
   More specifically, as shown in  FIGS. 10A through 10C , the frame  4  has the contact piece  4   a  provided in a swinging range of the arm member  52 . The second torsion coil spring  58  urges the arm member  52  by contacting the contact piece  4   a  and by being elastically deformed. As shown in  FIGS. 10B ,  10 C, and  11 , when the arm member  52  is located so that the feeding roller  60  contacts the recording medium accommodated in the second tray  40 , the free part  58 B of the second torsion coil spring  58  comes into contact with the contact piece  4   a , thereby urging the arm member  52  downward. Note that a single-dot chain line in  FIG. 10B  represents the position of a bottom surface of the second tray  40  (in other words, the level of the recording medium when only one recording medium is placed in the second tray  40 ). A single-dot chain line in  FIG. 10C  represents the level of the uppermost recording medium when the recording mediums are accommodated in the second tray  40  to maximum capacity. 
   [1-3. Configuration of Image Recording Unit] 
   Next, configuration of the image recording unit  70  will be described. 
   As shown in  FIGS. 2 ,  12 ,  13 A, and  13 B, the image recording unit  70  has a conveying roller  71  supported by the side plate of the flame  4  so as to be rotatable about the rotational axis along the left-right direction at a position on the conveying path  5  where a recording medium is conveyed from the sheet feeding tray  30  in a U-turn manner. The image recording unit  70  also has a follow roller  72  which is provided below the conveying roller  71  so as to be rotatable about the rotational axis parallel to the conveying roller  71  and rotates following the conveying roller  71  (that is, the conveying roller  71  and the follow roller  72  form a pair of rollers). 
   As shown in  FIGS. 13A and 13B , a registration sensor  73  which can detect position of a leading edge and a trailing edge of a recording medium conveyed from the sheet feeding tray  30  is provided in the rear of the conveying roller  71  (on the upstream side in the conveying direction of the recording medium). 
   On the other hand, the image recording unit  70  has a platen  74  which supports the recording medium from below and a carriage  75  which can move above the platen  74  in the left-right direction (main scanning direction), A recording head  76  capable of ejecting ink of a plurality of colors for recording a color image is mounted on the carriage  75 . The image is recorded by ejecting ink to the recording medium on the platen  74  from the recording head  76  while moving the carriage  75  in the main scanning direction. The image recording unit  70  has a discharge roller  77  supported by side plates  4 L and  4 R of the frame  4  ( FIG. 12 ) so as to be rotatable about the rotational axis along the left-right direction in front of the platen  74  (on the downstream side in the conveying direction of the recording medium). 
   As shown in  FIG. 12 , in the image recording unit  70 , an ink receiving part  78  and a maintenance section  79  are provided on the left side and the right side, respectively, outside of the conveyed recording medium in the left-right direction (width direction). The recording head  76  regularly ejects ink for preventing clogging of a nozzle at a flushing position on the ink receiving part  78  during the recording operation. 
   [2. Description of Driving System] 
   Next, a driving system of the image forming apparatus  1  in the illustrative aspects will be described. 
   As shown in  FIG. 12  and  FIG. 14 , the image forming apparatus  1  has the LF motor  6  capable of generating the rotational driving force both in the forward and reverse directions. As shown in  FIG. 24 , the rotational driving force generated by the LF motor  6  is transmitted to the conveying roller  71  and the discharge roller  77  through a gear transmission mechanism  80 . 
   Specifically, the gear transmission mechanism  80  includes a pinion  81  fixed to a driving shaft of the LF motor  6 , a driving gear  82 , and an intermediate gear  83  which engage with the right and left sides of the pinion  81 , respectively, and a driving gear  84  engaging with the intermediate gear  83 . As shown in  FIG. 12 , the driving gear  82  is fixed at the left end of the conveying roller  71 , and the driving gear  84  is fixed at the left end of the discharge roller  77 . A rotary encoder  85  for detecting a conveyed distance of a recording medium is provided at a part of the gear transmission mechanism  80 . 
   As shown in  FIG. 15A , the rotational driving force generated by the LF motor  6  is selectively transmitted to the feeding roller  60  and a maintenance mechanism (not shown in detail) from the left end of the conveying roller  71  via a power transmission switch mechanism  90  disposed above the maintenance section  79 . 
   In other words, the power transmission switch mechanism  90  is configured so as to switch the transmission state of the rotational driving force transmitted from the LF motor  6  through the conveying roller  71  between: a maintenance-mode transmission state for transmitting the rotational driving force to only the maintenance section  79 ; and a conveying transmission state for transmitting the rotational driving force to only the feeding roller  60  of the sheet feeding unit  50 . The conveying transmission state is configured so as to switch between: an intermittent-feed-mode transmission state for transmitting the rotational driving force so as to rotate one of the conveying roller  71  and the feeding roller  60  in the forward direction and the other roller in the reverse direction (the direction opposite to the forward direction) and a continuous-feed-mode transmission state for transmitting the rotational driving force so as to rotate both the conveying roller  71  and the feeding roller  60  in the forward direction. The image forming apparatus  1  is configured so that a conveying speed of a recording medium by the conveying roller  71  is higher than a conveying speed of the recording medium by the feeding roller  60 . The forward direction of the rollers  60 ,  71 , and  77  is a rotational direction for conveying a recording medium from the supply side to the discharge side. Specifically, the forward direction of the feeding roller  60  and the conveying roller  71  is a rotational direction for conveying the recording medium to an image forming position at which the image recording unit  70  forms an image. The forward direction of the discharge roller  77  is a rotational direction for conveying the recording medium from the image forming position to the discharge position. 
   Specific configuration of the power transmission switch mechanism  90  will be described below. 
   As shown in  FIGS. 15A through 15C , the power transmission switch mechanism  90  has a drive gear  91  which extends in the axial direction and is fixed at the right end of the conveying roller  71  and a switch gear  93  which can slide along a sliding shaft  92  disposed in parallel to the rotational axis of the conveying roller  71  and is constantly engaged with the drive gear  91 . Although teeth are shown only on a part of the periphery of the switch gear  93  in  FIG. 15B  and  FIG. 15C , teeth are formed on the entire periphery of the switch gear  93 . 
   The power transmission switch mechanism  90  have a first block  94  which is slidably and rotatably provided with respect to the sliding shaft  92  and includes a contact piece  94   a  extending upward and a second block  95  which is slidably provided with respect to the sliding shaft  92  and disposed adjacent to the first block  94 . The first block  94  can be separated from the switch gear  93 . 
   The power transmission switch mechanism  90  has a first urging spring  96  which is fitted to the sliding shaft  92  and urges the second block  95  in the direction of an arrow C in  FIG. 15A  and a second urging spring  97  which is fitted to the sliding shaft  92  and urges the switch gear  93  in the direction of an arrow E in  FIG. 15A . In addition, the power transmission switch mechanism  90  has an intermittent feed driving gear  111 , a continuous feed driving gear  112 , and a maintenance driving gear  113  which are selectively engaged with the switch gear  93  depending on a sliding position of the switch gear  93 . Although teeth are shown only on a part of the entire periphery of each gear  111 ,  112 , and  113  in  FIG. 15B , teeth are formed on the entire periphery of each gear  111 ,  112 , and  113 . 
   As shown in  FIGS. 13A and 13B , a first engaging stepped part  75   a  protrudes rearwardly from the rear surface of the carriage  75 . A second engaging stepped part  75   b  protrudes rearwardly from the rear surface of the first engaging stepped part  75   a . When the carriage  75  is positioned on the right-side end of the image forming apparatus  1  and above the maintenance section  79  as shown in  FIG. 13B , the first and second engaging stepped parts  75   a  and  75   b  are located above a plate-shaped guide block  100  of the power transmission switch mechanism  90 . 
   With this configuration, when the carriage  75  is positioned on the right-side end of the image forming apparatus  1  and above the maintenance section  79 , as shown in  FIG. 16B , the carriage  75  receives, on either the first engaging stepped part  75   a  or the second engaging stepped part  75   b , the contact piece  94   a  of the first block  94  that protrudes upwardly through the guide through-hole  101  of the plate-shaped guiding block  100 . Thus, as the carriage  75  moves in the left-to-right direction, the contact piece  94   a  slides within the guide through-hole  101  in the leftward direction or in the rightward direction. As a result, the first block  94 , the switch gear  93 , and the second block  95  slide over the sliding shaft  92  in the leftward direction or in the rightward direction as the carriage  75  moves in the leftward direction or in the rightward direction (the direction of the arrow C or the arrow E). As shown in  FIG. 15C , an end face cam part  94   b  and an end face cam part  95   a  are formed on the opposing surfaces of the first block  94  and second block  95 , respectively. The end face cam part  95   a  is slanted relative to the axis of the sliding shaft  92 . With this configuration, when the second block  95  presses the first block  94  in the leftward direction C, the first block  94  with the contact piece  94   a  rotates in a frontward direction D indicated in  FIGS. 15B and 15C . 
   As shown in  FIGS. 15B ,  16 A, and  16 B, the plate-shaped guide block  100  is provided above the first block  94 . A guide through-hole  101  is formed in the guide block  100 . A distal end of the contact piece  94   a  is vertically inserted in the guide through-hole  101  and is slidable in the left-right direction in the guide through-hole  101 . As shown in  FIG. 16A  (plan view), the guide through-hole  101  has a straight groove part  101   a  which extends in the direction of the arrow C, E and a wide groove part  101   b  communicating with the left end of the straight groove part  101   a.    
   As shown in  FIG. 15B , the guide block  100  has a restricting piece  102 . The restricting piece  102  has: a rising part  102   a  rising up from the rear edge of the guide block  100  on the rear side of the wide groove part  101   b ; a forwardly-extending part  102   b  extending forwardly from the top end of the rising part  102   a  toward the position above the center region of the wide groove part  101   b ; and a downwardly-extending part  102   c  extending downwardly from the front edge of the forwardly-extending part  102   b . The downwardly-protruding part  102   c  extends downward as opposing the center region of the wide groove part  101   b  ( FIG. 16B ). As shown in  FIG. 16B , the rear surface of the downwardly-extending part  102   c  is in line with the front side edge of the straight groove part  101   a.    
   A step-like first setting part  101   c  and a step-like second setting part  101   d  are provided on the front part of the wide groove part  101   b . The guide block  100  has a front-right-side sloped edge  101   e  on the front-right side edge of the wide groove part  101   b  in continuation with the front edge of the straight groove part  101   a , and a rear-left side sloped edge  101   f  on the rear-left side edge of the wide groove part  101   b.    
   Thus, as shown in  FIG. 16A , when the carriage  75  largely moves from the maintenance section  79  ( FIG. 12 ) leftward (in the direction of the arrow C) and is located in a recording area of a recording medium, the second block  95  is pushed leftward by the first urging spring  96 , thereby pressing the first block  94  and the switch gear  93  to move along the sliding shaft  92 . At this time, the contact piece  94   a  of the first block  94  is located at the first setting part  101   c  (hereinafter, this position is referred to as a “first position PO 1 ”. At this position, the switch gear  93  engages with the intermittent feed driving gear  111 . 
   When the carriage  75  moves from the first position PO 1  rightward (in the direction of the arrow E), the contact piece  94   a  is pushed by the first engaging stepped part  75   a  of the carriage  75  and arrives at the second setting part  101   d  (hereinafter, this position is referred to as a “second position PO 2 ”. In this state, the switch gear  93  engages with the continuous feed driving gear  112 . 
   When the carriage  75  further moves from the second position PO 2  rightward (in the direction of the arrow E), the contact piece  94   a  is pushed by the first engaging stepped part  75   a  and slides along the front-right-side sloped edge  101   e . Then, the contact piece  94   a  arrives at a left-end position (an entrance position) of the straight groove part  101   a  (hereinafter, the position is referred to as a “third position PO 3 ”. In this state, the contact piece  94   a  is in contact with the second engaging stepped part  75   b  of the carriage  75 . 
   When the carriage  75  further moves from the third position PO 3  rightward (in the direction of the arrow E), the contact piece  94   a  is pushed by the second engaging stepped part  75   b  of the carriage  75  and is located at the right end of the straight groove part  101   a  (hereinafter, the position is referred to as a “fourth position PO 4 ”. The fourth position PO 4  serves as a home position (starting position). At this time, a side surface  93   s  of the switch gear  93  comes into contact with a bevel gear part  113   a  of the maintenance driving gear  113 , thereby preventing the switch gear  93  from moving rightward (in the direction of the arrow E). As a result, the switch gear  93  is separated from the first block  94  and keeps its engaged state with the maintenance driving gear  113 . 
   On the contrary, when the carriage  75  moves from the fourth position PO 4  leftward (in the direction of the arrow C) and the contact piece  94   a  moves from the straight groove part  101   a  to the wide groove part  101   b , since the contact piece  94   a  is received by the first engaging stepped part  75   a , the contact piece  94   a  does not enter to the front-right-side sloped edge  101   e . Thus, the contact piece  94   a  slides along the downwardly-extending part  102   c  and then moves along the rear-left side sloped edge  101   f  of the wide groove part  101   b . In this way, the contact piece  94   a  arrives at the first setting part  101   c.    
   Among the above-described four positions PO 1 -PO 4 , the third position PO 3  is a maintenance position also serving as a waiting position. At this position, as shown in  FIG. 12 , a cap part  79   a  of the maintenance section  79  covers a nozzle surface of the recording head  76  from below. At the time of maintenance, the LF motor  6  drives a suction pump (not shown) to perform recovery processing of selectively sucking ink from nozzles, removing air bubbles in a buffer tank (not shown) on the recording head  76  and the other similar operations. When the carriage  75  moves from the maintenance section  79  to the image forming region in the leftward direction, the nozzle surface is wiped by a cleaner (wiper blade)  79   b  and ink adhered to the nozzle surface is removed. When the image forming apparatus  1  is switched off, the carriage  75  stops at a position above the maintenance section  79  (the third position PO 3 ) and the nozzle surface of the recording head  76  is covered with the cap part  79   a.    
   As shown in  FIGS. 17A ,  17 B, and  19 B, when the switch gear  93  engages with the intermittent feed driving gear  111  at the first position PO 1 , a rotational driving force is transmitted to the support shaft  51  ( FIG. 3 ) via two intermediate gears  129   a  and  129   b  and the rotational driving force is transmitted to the drive gear  66  via the power transmission gears  56 . 
   On the other hand, as shown in  FIGS. 18A through 18C  and  19 A, when the switch gear  93  engages with the continuous feed driving gear  112  at the second position PO 2 , a rotational driving force is transmitted to the support shaft  51  via an intermediate gear  130  and the rotational driving force is transmitted to the drive gear  66  through the power transmission gears  56 . 
   [3. Description of Control System] 
   Next, a control system of the image forming apparatus  1  according to the illustrative aspects will be described. 
     FIG. 20  is a block diagram showing schematic configuration of the control system of the image forming apparatus  1 . 
   As shown in  FIG. 20 , the image forming apparatus  1  has a CPU  201 , a ROM  202 , a RAM  203 , and an EEPROM  204 . These components are connected to an ASIC (Application Specific Integrated Circuit)  206  through a bus  205 . 
   The ROM  202  stores a program for controlling various operations of the image forming apparatus  1  and the like. The RAM  203  is used as a storage area (operation area) where various data used when the CPU  201  executes the program is temporarily stored. 
   An NCU (Network Control Unit)  207  is connected to the ASIC  206 . A communication signal input from a public line through the NCU  207  is demodulated by a MODEM  208  and the demodulated communication signal is input to the ASIC  206 . When the ASIC  206  transmits image data to the outside by facsimile communication or a similar means, the image data is modulated to a communication signal by the MODEM  208  and the modulated communication signal is output to the public line through the NCU  207 . 
   According to an instruction by the CPU  201 , the ASIC  206  generates a phase excitation signal which applies power to the LF motor  6  and other signals, sends these signals to a driving circuit  209  of the LF motor  6  and a driving circuit  211  of a CR motor (a motor for driving the carriage  75 )  210 . Then, the ASIC  206  passes driving signals to the LF motor  6  and the CR motor  210  through the driving circuit  209  and the driving circuit  211 , respectively, to control forward and reverse rotation and stoppage of the LF motor  6  and the CR motor  210 . 
   A CIS (Contact Image Sensor)  212  serving as the image reading device in the scanner unit  20 , the operation panel  10  having the operation part  11  and the display part  12 , and a parallel interface  213 , and a USB interface  214  for transmitting/receiving data to/from an external information processing device such as a personal computer via a parallel cable and a USB cable are connected to the ASIC  206 . 
   Furthermore, the registration sensor  73 , the rotary encoder  85 , and a linear encoder  215  are connected to the ASIC  206 . The linear encoder  215  (also shown in  FIG. 13B ) detects the position of the carriage  75  in the main scanning direction. 
   The driving circuit  216  allows the recording head  76  to selectively eject ink to a recording medium at a predetermined timing and controls driving of the recording head  76  in response to the signal generated and outputted by the ASIC  206  on the basis of a driving control procedure outputted from the CPU  201 . 
   Next, an image recording process performed by the CPU  201  will be described with reference to a flow chart of  FIG. 21 . The image recording process is started when an image recording instruction is inputted from an external information processing device (for example, a personal computer). Note that a transmission route for a rotational driving force from the LF motor  6  to the feeding roller  60  is shown in the block diagram of  FIG. 24 , and that the rotational directions (forward/reverse) of the LF motor  6 , conveying roller  71 , and feeding roller  60  in intermittent and continuous feed modes (described later) is shown in the table of  FIG. 25 . 
   When the image recording process is started, in S 101 , the CPU  201  determines a feed mode that is currently set. In other words, the image forming apparatus  1  in the illustrative aspects is configured so that the user can select the feed mode from an intermittent feed mode and a continuous feed mode, in recording images on a plurality of recording mediums. The intermittent feed mode is a feed mode for conveying a recording medium fed from the sheet feeding tray  30  to the image recording unit  70  after slant correction by the conveying roller  71  (i.e., a feed mode that puts priority on image recording accuracy or image recording quality). The continuous feed mode is a feed mode for conveying a recording medium fed from the sheet feeding tray  30  to the image recording unit  70  without slant correction by the conveying roller  71  (i.e., a feed mode that puts priority on image recording speed). 
   If in S 101  the CPU  201  determines that the currently-set feed mode is the intermittent feed mode, the CPU  201  proceeds to S 102  and sets the power transmission switch mechanism  90  to the intermittent-feed-mode transmission state. Specifically, when the carriage  75  waiting at the waiting position (the third position PO 3 ) is largely moved leftward to the image recording area (in the direction of the arrow C in  FIG. 16A ), the first block  94  being pressed by the first urging spring  96  moves along the downwardly-extending part  102   c  leftward. When the carriage  75  further moves leftward beyond the wide groove part  101   b , the contact piece  94   a  of the first block  94  is received by the first setting part  101   c  and the position of the contact piece  94   a  (the first block  94 ) is maintained (the first position PO 1 ). At the first position PO 1 , the switch gear  93  engages with the intermittent feed driving gear  111  and a rotational driving force is transmitted to the support shaft  51  of the sheet feeding unit  50  via the two intermediate gears  129   a  and  129   b  shown in FIG.,  17 A. 
   In S 103  the recording medium is fed from the sheet feeding tray  30  to the image recording unit  70 . Specifically, the CPU  201  controls the LF motor  6  to rotate in the reverse direction, thereby driving the conveying roller  71  to rotate in the reverse direction (the counterclockwise direction in  FIG. 17A ) and driving the feeding roller  60  to rotate in the forward direction (the counterclockwise direction in  FIG. 17A ). Thus, a plurality of recording mediums accommodated in the sheet feeding tray  30  hits against the guide plate  34  provided at the rear end of the sheet feeding tray  30  and only the uppermost recording medium which contacts the feeding roller  60  is separated and fed (conveyed) to the conveying path  5 . At this time, since the conveying roller  71  is rotatingly driven in the reverse direction, the leading end of the recording medium hits against a nip part between the conveying roller  71  and the follow roller  72  (that is, passage of the recording medium is prevented), thereby correcting slant of the recording medium. 
   In S 104  the CPU  201  switches the rotational direction of the rotational driving force generated by the LF motor  6 . Specifically, the CPU  201  switches the rotational direction from the reverse direction to the forward direction, when the recording medium is conveyed a predetermined distance after the leading end of the recording medium is detected by the registration sensor  73  (i.e., when the leading end of the recording medium reaches the conveying roller  71 ) Thus, as shown in  FIG. 17B , by rotatingly driving the conveying roller  71  in the forward direction (in the clockwise direction in  FIG. 17B ), the recording medium is positioned at the nip part between the conveying roller  71  and the follow roller  72 . At this time, the feeding roller  60  is rotatingly driven in the reverse direction (in the clockwise direction in  FIG. 17B ). 
   Since a certain play is given to the feeding roller  60  in the rotational direction, even when the LF motor  6  switches from the reverse direction to the forward direction, the feeding roller  60  is not immediately rotated in the reverse direction (the state in  FIG. 6A ) and, after a delay for the play, the feeding roller  60  is rotated ( FIG. 6B ). For this reason, it is prevented that pinching the recording medium between the conveying roller  71  and the follow roller  72  is prevented by the feeding roller  60 . After the delay for the play, the feeding roller  60  is rotatingly driven in the reverse direction to convey the recording medium in the direction counter to the rotating direction of the conveying roller  71  ( FIG. 7B ). However, since the conveying force of the conveying roller  71  in the forward direction is greater than that of the feeding roller  60  in the reverse direction, conveying of the recording medium by the conveying roller  71  is not prevented. As shown in  FIG. 23A , when the feeding roller  60  is rotatingly driven in the forward direction R 1 , a force F 1  that makes the feeding roller  60  rollingly move frontward on the recording medium is generated. More specifically, the force F 1  has a component force F 1   a  parallel to the arm member  52  and a component force F 1   b  perpendicular to the arm member  52 . When the feeding roller  60  is rotated in the forward direction R 1 , since the component force F 1   b  of the frontward force F 1  acts as a force for pressing the feeding roller  60  toward the recording medium (i.e., a force for pivoting the arm member  52  downward), the pressing force is increased, thereby making the conveying force larger. In contrast, as shown in  FIG. 23B , when the feeding roller  60  is rotated in the reverse direction R 2 , a force F 2  that makes the feeding roller  60  rollingly move rearward on the recording medium is generated. The force F 2  has a component force F 2   a  parallel to the arm member  52  and a component force F 2   b  perpendicular to the arm member  52 . Since the component force F 2   b  of the rearward force F 2  acts as a force for separating the feeding roller  60  from the recording medium (i.e., a force for swinging the arm member  52  upward), the pressing force is decreased, thereby making the conveying force smaller. Thus, even when the feeding roller  60  is rotated in the reverse direction, conveying of the recording medium by the conveying roller  71  is not prevented. 
   In S 105  the CPU  201  starts recording of an image on the recording medium. Specifically, the image is recorded by ejecting ink on the surface of the recording medium from the nozzles of the recording head  76  while intermittently moving the recording medium in the conveying direction and reciprocating the carriage  75  in the main scanning direction. 
   In S 106  the CPU  201  determines whether or not the recording of one page (one recording medium) is finished. When the CPU  201  determines that recording of one page is finished, the CPU  201  proceeds to S 107 . 
   In S 107 , the recording medium on which the image is recorded is discharged to the front portion on the upper surface of the sheet feeding tray  30  ( FIG. 2 ). Specifically, the LF motor  6  is rotated in the forward direction by the number of steps as necessary, and the conveying roller  71  and the discharge roller  77  are rotated in the forward direction by a predetermined amount. 
   In S 108  the CPU  201  determines whether or not image recording data of next page for a subsequent recording medium exists. If the CPU  201  determines that the image recording data of the next page exists, the CPU  201  returns to S 103  and the above-described process of  3103  through S 107  is repeated. If the CPU  201  determines that the image recording data of the next page does not exist, the image recording process ends. 
   If, in S 101 , the CPU  201  determines that the currently-set feed mode is not the intermittent feed mode but the continuous feed mode, in S 109  the CPU  201  sets the power transmission switch mechanism  90  to the continuous-feed-mode transmission state. Specifically, the carriage  75  stopped at the first position PO 1  is moved rightward (in the direction of the arrow E) by a predetermined distance and the contact piece  94   a  is pressed by the first engaging stepped part  75   a  of the carriage  75 . When the contact piece  94   a  is located at the second setting part  101   d  (the second position PO 2 ), the switch gear  93  engages with the continuous feed driving gear  112  and the rotational driving force is transmitted to the support shaft  51  via the intermediate gear  130  shown in  FIGS. 18A through 18C . After that, even when the carriage  75  is moved leftward to the image recording area, the contact piece  94   a  urged by the first urging spring  96  is maintained at the second setting part  101   d.    
   In S 110  the recording medium is fed from the sheet feeding tray  30  to the image recording unit  70 . Specifically, the CPU  201  controls the LF motor  6  to rotate in the forward direction, thereby driving the conveying roller  71  to rotate in the forward direction (in the clockwise direction in  FIG. 18A ) and driving the feeding roller  60  to rotate in the forward direction (in the counterclockwise direction in  FIG. 18A ). Thus, only the uppermost recording medium of a plurality of recording mediums accommodated in the sheet feeding tray  30  is separated and conveyed to the conveying path  5 . At this time, since the conveying roller  71  is rotated in the forward direction, when the leading end of the recording medium reaches the nip part between the conveying roller  71  and the follow roller  72 , the recording medium passes between the rollers  71  and  72  and is nipped at the nip part without being subject to registration function. Here, even when the recording medium is nipped at the nip part between the conveying roller  71  and the follow roller  72  and is also in contact with the feeding roller  60  as shown in  FIG. 18B  (the recording medium is located over both the rollers  60  and  71 ), conveying of the recording medium by the conveying roller  71  is not prevented. This is because, as described above, the conveying speed of the recording medium by the conveying roller  71  is faster than that of the recording medium by the feeding roller  60  and the feeding roller  60  is pulled by the recording medium. As shown in  FIG. 23C , when the feeding roller  60  is pulled by the recording medium R in a direction PL, the recording medium R applies a rearward force F 3  to the feeding roller  60 . The rearward force F 3  has a component force F 3   a  parallel to the arm member  52  and a component force F 3   b  perpendicular to the arm member  52 . The component force F 3   b  of the rearward force F 3  acts as a force for separating the feeding roller  60  from the recording medium R (i.e., a force for swinging the arm member  52  upward). As a result, the pressing force is decreased, thereby making the conveying force smaller. Thus, although the conveying speed of the recording medium by the feeding roller  60  is lower than that of the conveying roller  71 , conveying of the recording medium by the conveying roller  71  is not prevented and is performed smoothly. 
   In addition, in the image forming apparatus  1 , it is prevented that slant of the recording medium is continuously generated by such continuous conveying. As described above, the conveying speed by the conveying roller  71  is faster than the conveying speed by the feeding roller  60 . Thus, when the recording medium conveyed by the conveying roller  71  is also in contact with the feeding roller  60  (i.e., the recording medium is located over both the rollers  60  and  71 ), the feeding roller  60  is pulled by the recording medium and thus advances than the drive gear  66  by the above-described play in the rotational direction. In this state, when the trailing end of the recording medium conveyed by the conveying roller  71  is separated from the feeding roller  60 , the feeding roller  60  comes into contact with the next (uppermost) recording medium. However, since the feeding roller  60  is an advanced state than the drive gear  66  by the play, the feeding roller  60  is not immediately rotated in the forward direction and, after delay for the play, is rotated in the forward direction. Consequently, it is prevented that slant of the recording medium is continuously generated by the continuous conveying of the recording mediums, which is caused by rotating both the feeding roller  60  and the conveying roller  71  in the forward direction. 
   In S 111  the CPU  201  starts recording of an image on the recording medium. Specifically, the image is recorded by ejecting ink on the surface of the recording medium from the nozzles of the recording head  76  while intermittently moving the recording medium forward in the conveying direction and reciprocating the carriage  75  in the main scanning direction. 
   In S 112  the CPU  201  determines whether or not image recording data of the next page (subsequent recording medium) exists. In S 112 , if the CPU  201  determines that the image recording data of the next page does not exist, in S 113  the CPU  201  sets the power transmission switch mechanism  90  to the intermittent-feed-mode transmission state and proceeds to S 114 . If the CPU  201  determines that the image recording data of the next page exists, the CPU  201  proceeds to S 114 . 
   In S 114  the CPU  201  determines whether or not recording of one page (one recording medium) is finished. If the CPU  201  determines that recording of one page is finished, the CPU  201  proceeds to S 115 . 
   In S 115  the CPU  201  determines whether or not the power transmission switch mechanism  90  is in the continuous-feed-mode transmission state. 
   In S 115 , if the CPU  201  determines that the power transmission switch mechanism  90  is not in the continuous-feed-mode transmission state but in the intermittent-feed-mode transmission state, the CPU  201  proceeds to S 116 . After the CPU  201  executes a subsequent medium process in S 116 , the image recording process ends. Specific details of the subsequent medium process will be described later with reference to  FIG. 22 . 
   In S 115 , if the CPU  201  determines that the power transmission switch mechanism  90  is in the continuous-feed-mode transmission state (the image recording data of the next page exists), the CPU  201  proceeds to S 117 . 
   In S 117 , the recording medium on which the image is formed is discharged and the subsequent recording medium is conveyed, and then the CPU  201  returns to S 111 . Specifically, the LF motor  6  is continuously rotated in the forward direction, the previous recording medium (previous page) is discharged and the next recording medium is continuously conveyed to the recording start position (refer to  FIG. 18C ). In this manner, in the continuous feed mode, since a plurality of recording mediums are continuously conveyed without temporarily stopping conveyance of the recording medium by the conveying roller  71 , a high-speed recording operation can be achieved. 
   Next, the subsequent medium process executed in S 116  in the above-described image recording process ( FIG. 21 ) will be described with reference to a flow chart of  FIG. 22 . 
   When the subsequent medium process is started, in S 201  the CPU  201  determines whether or not the registration sensor  73  is turned on. That is, the CPU  201  determines whether or not the leading end of the recording medium subsequent to the recording medium on which the image has been formed exceeds the position of the registration sensor  73 . 
   In S 201 , if the CPU  201  determines that the registration sensor  73  is not turned on (is turned off), in S 202  the CPU  201  controls the LF motor  6  to rotate in the forward direction by the number of steps as necessary, thereby rotating the feeding roller  60  in the reverse direction by a predetermined amount. Then, the subsequent medium process ends. As shown in  FIG. 19A , when the leading end of the subsequent recording medium has not reached the position of the registration sensor  73 , the subsequent recording medium is returned to the sheet feeding tray  30 . The recording medium on which the image is recorded is discharged by rotation of the conveying roller  71  and the discharge roller  77  in the forward direction. 
   In S 201 , on the other hand, if the CPU  201  determines that the registration sensor  73  is turned on, the CPU  201  proceeds to S 203 . In S 203  the CPU  201  controls the LF motor  6  to rotate in the reverse direction by the number of steps as necessary, thereby rotating the feeding roller  60  in the forward direction by a predetermined amount. That is, when the leading end of the subsequent recording medium exceeds the position of the registration sensor  73 , the CPU  201  controls the feeding roller  60  to rotate in the forward direction, such that the leading end of the subsequent recording medium contacts the conveying roller  71  to perform slant correction. 
   In S 204  the CPU  201  controls the LF motor  6  to rotate in the forward direction by the number of steps as necessary, thereby rotating the conveying roller  71  and the discharge roller  7  in the forward direction by a predetermined amount and rotating the feeding roller  60  in the reverse direction by a predetermined amount. Thus, as shown in  FIG. 19B , the recording medium subjected to slant correction is discharged and the subsequent recording medium is returned to the sheet feeding tray  30 . After that, the subsequent medium process ends. 
   As described above, when the leading end of the subsequent recording medium exceeds the position of the registration sensor  73  and is located downstream in the conveying direction, the subsequent recording medium is conveyed to the discharge side. In contrast, when the leading end of the subsequent recording medium does not reach the position of the registration sensor  73 , the subsequent recording medium is returned to the sheet feeding tray  30 . 
   [4. Effects of the Illustrative Aspects] 
   The image forming apparatus  1  in the above-described illustrative aspects is configured such that, in the intermittent feed mode, the recording medium conveyed by rotation of the feeding roller  60  in the forward direction is prohibited its passage by the conveying roller  71  rotating in the reverse direction and is subjected to slant correction. At the timing when the recording medium is conveyed by the feeding roller  60  and reaches the conveying roller  71 , the forward or reverse direction of the rotational driving force generated by the LF motor  6  is switched (the CPU  201  which executes processing in S 104  functions as a rotational direction switch controller), the conveying roller  71  is rotated in the forward direction and the recording medium subjected to slant correction is conveyed so as to pass through the conveying roller  71 . On the other hand, since a certain play is given to the feeding roller  60  in the rotational direction, even when the forward or reverse direction of the rotational driving force generated by the LF motor  6  is switched, the feeding roller  60  is not immediately rotated in the reverse direction and after a delay for the play, the feeding roller  60  is rotated in the reverse direction. Thus, it is prevented that the recording medium is pulled back due to rotation of the feeding roller  60  in the reverse direction before the conveying roller  71  is ready to convey the recording medium. As a result, slant correction of the recording medium by the conveying roller  71  can be achieved without separating the feeding roller  60  from the recording medium or cutting off the transmission route for the rotational driving force to be in a free state. 
   In the above-described image forming apparatus  1 , when the feeding roller  60  is rotatingly driven, a force that makes the feeding roller  60  rollingly move on the recording medium is applied to the arm member  52 . More specifically, when the feeding roller  60  is rotatingly driven in the forward direction, a force that makes the feeding roller  60  rollingly move frontward on the recording medium is generated. Since a component force of the frontward force acts as a force for pressing the feeding roller  60  toward the recording medium, the pressing force is increased, thereby making the conveying force larger. In contrast, when the feeding roller  60  is rotated in the reverse direction, a force that makes the feeding roller  60  rollingly move rearward on the recording medium is generated. Since a component force of the rearward force acts as a force for separating the feeding roller  60  from the recording medium, the pressing force is decreased, thereby making the conveying force smaller. Consequently, when the feeding roller  60  is rotated in the forward direction, the image forming apparatus  1  can ensure a conveying force necessary for feeding the recording medium accommodated in the sheet feeding tray  30 . On the other hand, when the feeding roller  60  is rotated in the reverse direction, conveying of the recording medium by the conveying roller  71  is not prevented. 
   In the image forming apparatus  1  in the above-described illustrative aspects, the feeding roller  60  rotates by the rotational driving force generated by the LF motor  6 , thereby feeding (conveying) the recording medium accommodated in the sheet feeding tray  30  to the conveying path  5 . Here, since an angle of the rotational axis of the feeding roller  60  has a certain flexibility (i.e., the angle of the rotational axis can change by a predetermined amount), a guiding action of the side end guides  31  and  32  (an action of preventing movement of the recording medium in a direction parallel to the rotational axis) has stronger effects than an inclination of the feeding roller  60 , thereby making the conveying direction stable. That is, in a configuration in which the angle of the rotational axis of the feeding roller  60  does not have any flexibility (i.e., the angle of the rotational axis is fixed), when the feeding roller  60  contacts the recording medium accommodated in the recording-medium accommodating section in an inclined state, the recording medium tends to be conveyed in an inclined state due to factors such as such as dimension error and assembly error of the feeding roller  60  itself. Thus, even if the side end guides  31  and  32  are provided, the conveying direction of the recording medium by the feeding roller interferes with a guiding direction of the side end guides  31  and  32 . As a result, when the effect of the feeding roller is greater, the recording medium is conveyed in the inclined state. In contrast, in the image forming apparatus  1  in the illustrative aspects, the feeding roller  60  is automatically located so that the recording medium can be smoothly conveyed in a normal conveying direction without interference with the side end guides  31  and  32 , thereby stabilizing the conveying direction. 
   Further, in a configuration in which a rotational driving force generated by a driving unit is transmitted to an end of the feeding roller in the direction parallel to the rotational axis, providing flexibility in an angle of the rotational axis of the feeding roller worsens an inclination of the feeding roller. However, the image forming apparatus  1  in the illustrative aspects transmits the rotational driving force to a central part of the feeding roller in the direction parallel to the rotational axis, thereby preventing such worsening of the inclination of the feeding roller. 
   As described above, in the image forming apparatus  1  in the illustrative aspects, it is possible to effectively prevent a recording medium from being conveyed in an inclined state. Further, since the feeding roller  60  reliably contacts the recording medium, a sufficient conveying force can be obtained. In addition, since an inclined contact (non-uniform contact) of the feeding roller  60  with the recording medium can be prevented, durability of the feeding roller  60  can be improved. 
   In the image forming apparatus  1  in the above-described illustrative aspects, the feeding roller  60  is rotatably supported by the free end of the arm member  52  that is swingable about the swing axis, and is rotated in a certain direction in contact with a recording medium accommodated in the feeding tray  30 , thereby feeding (conveying) the recording medium to the conveying path  5 . Because the first torsion coil spring  57  is provided at the base end of the arm member  52 , the first torsion coil spring  57  can easily urge the arm member  52  downward in a wide swinging range (the entire swinging range), compared with a configuration in which the first torsion coil spring  57  is provided at the free end of the arm member  52 . As the angle between the plane containing the rotational axis and the swing axis between the surface of the recording medium accommodated in the feeding tray  30  becomes smaller, the conveying force of the feeding roller  60  for conveying the recording medium also becomes smaller. In the illustrative aspects, however, necessary conveying force can be obtained because the arm member  52  is urged by the second torsion coil spring  58  when the angle is small. 
   Especially, in the image forming apparatus  1 , the second torsion coil spring  58  urges the free end of the arm member  52 . Hence, in comparison with a configuration of urging the swing axis side of the arm member  52 , an urging force (elastic force) of the second torsion coil spring  58  can be made smaller. In addition, the angle at which the second torsion coil spring  58  starts applying its force can be set relatively accurately. 
   In addition, in the image forming apparatus  1 , with a simple configuration in which the second tray  40  is disposed above the feeding tray  30 , the recording medium accommodated in the second tray  40  (not the recording medium in the feeding tray  30 ) can be fed (conveyed) to the conveying path  5 . Further, since the second torsion coil spring  58  applies its urging force when the recording medium accommodated in the second tray  40  is conveyed, necessary conveying force can be obtained and thus, the recording medium can be reliably conveyed. Especially, in the image forming apparatus  1 , the recording medium accommodated in the second tray  40  is conveyed along the conveying path  5  with a smaller radius of rotation than the recording medium accommodated in the feeding tray  30 . In addition, since thick and small-sized recording mediums such as postcards and envelopes are accommodated in the second tray  40 , a larger conveying force is required in comparison with a case of conveying the recording medium accommodated in the feeding tray  30 . However, this requirement is satisfied by setting an appropriate pressing force (urging force) of the second torsion coil spring  58 . 
   According to the image forming apparatus  1  in the illustrative aspects, it is possible to set independently a pressing force for pressing the recording medium accommodated in the feeding tray  30  (a pressing force by the first torsion coil spring  57 ) and a pressing force for pressing the recording medium accommodated in the second tray  40  (a combined pressing force by the first torsion coil spring  57  and second torsion coil spring  58 ). Thus, a user can use the feeding tray  30  and the second tray  40  depending on recording mediums that require different conveying forces due to differences in a surface condition, thickness, or the like. 
   While the invention has been described in detail with reference to the above aspects thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention. 
   For example, in the above-described image forming apparatus  1 , a gap is formed between the shaft part  65  of the feeding roller  60  and the axial support part  55  of the arm member  52 , allowing flexibility in the angle of the rotational axis of the feeding roller  60 . However, means for giving flexibility is not limited to this configuration. For example, the free end (rear end) of the arm member  52  that supports the feeding roller  60  may be configured to move relative to the other part of the arm member  52 . In this configuration, the free end (rear end) of the arm member  52  can be moved relative to the other part of the arm member  52 , allowing the angle of the rotational axis of the feeding roller  60  to be changed relative to a reference position. Alternatively, the flexibility given to the angle of the rotational axis of the feeding roller  60  may be flexibility either on angles in all directions as in the above-described image forming apparatus  1  or on an angle in a certain direction. The angle in a certain direction includes an angle along a plane parallel to the recording medium (i.e., an angle in the front-rear direction) and an angle along a plane perpendicular to the recording medium (i.e., an angle in the vertical direction), for example. 
   Further, in the above-described image forming apparatus  1 , the second torsion coil spring  57  provided at a base end (front end) of the arm member  52  comes into contact with the frame  4  and elastically deforms, thereby urging the arm member  52 . However, the invention is not limited to this configuration. For example, a spring may be provided at the frame  4 , such that the spring contacts the arm member  52  and elastically deforms, thereby urging the arm member  52 . 
   Further, in the above-described illustrative aspects, the invention is applied to an image forming apparatus for recording an image by an inkjet method. However, the invention is not limited to this configuration and, for example, can be applied to an image forming apparatus for recording an image by a laser method.