Patent Publication Number: US-7725063-B2

Title: Image-forming device with interlockingly movable two paper guide members

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority from Japanese Patent Application No. 2006-305856 filed Nov. 10, 2006. The entire content of this priority application is incorporated herein by reference. 
   TECHNICAL FIELD 
   The present invention relates to an image-forming device such as a laser printer, and a process cartridge mounted in the image-forming device. 
   BACKGROUND 
   Normally, a process cartridge is detachably mounted in image-forming devices such as laser printers. The process cartridge includes a photosensitive drum functioning to carry an electrostatic latent image, which is developed into a toner image by developer. The photosensitive drum is disposed in confrontation with and in contact with a transfer roller. The toner image carried on the photosensitive drum is transferred onto paper passing through a nip position between the photosensitive drum and the transfer roller by a transfer bias applied to the transfer roller. In this construction, a guide member is typically provided near the photosensitive drum upstream of the nip position in the paper-conveying direction for guiding the paper to the nip position. 
   Japanese unexamined patent application publication No. HEI-5-53449, for example, discloses a transfer unit provided with the following type of guide member. The guide member includes a paper conveying guide, an eccentric cam for pivoting the paper conveying guide, and a photosensor. When the photosensor detects the leading edge of the paper, the eccentric cam is rotated to place the paper conveying guide near the photosensitive drum. When the photosensor detects the trailing edge of the paper, the eccentric cam is rotated to separate the paper conveying guide from the photosensitive drum. 
   However, the transfer unit described in Japanese unexamined patent application publication No. HEI-5-53449 requires a photosensor and eccentric cam for placing the downstream portion of the guide member near to the photosensitive drum and separating the same portion from the photosensitive drum. Moreover, the transfer unit requires a motor for rotating the eccentric cam, and a control unit for driving the motor at a prescribed timing based on signals received from the photosensor, thereby requiring a larger number of parts and a more complex construction. This construction may also be less reliable because electronic units, such as the control circuit board on which the photosensor and control unit are provided, are susceptible to electrical malfunctions. 
   SUMMARY 
   Therefore, it is an object of the present invention to provide an image-forming device and a process cartridge having a simple construction for moving a guide portion of a guide member on the downstream side relative to the paper-conveying direction toward and away from a photosensitive member. 
   The above objects and others will be attained by an image-forming device that includes a casing, an image-carrying member, a transfer member, a first guide member, and a second guide member. The image-carrying member carries a developer image. The transfer member is disposed in confrontation with the image-carrying member and transfers the developer image from the image-carrying member to a recording medium at a transfer point of contact with the image-carrying member. The first guide member is disposed in a predetermined position upstream of the transfer point in a conveying direction of the recording medium. The first guide member is selectively movable between a first position and a second position. The second guide member disposed between the first guide member and the transfer point along the conveying direction of the recording medium. The second guide member is selectively movable between a third position and a fourth position farther from the image-carrying member than the third position. The second guide member is movable in association with the movement of the first guide member in such a manner that when the first guide member is disposed in the first position, the second guide member is disposed in the third position for guiding the recording medium received from the first guide member to move toward the image-carrying member. 
   When the image-carrying member is a photosensitive drum, this photosensitive drum may be provided in a process cartridge that is detachably mounted in the image-forming device. In this case, the second guide member may also be provided in the process cartridge. 
   By the second guide member moving in association with the first guide member, the image-forming device can guide recording medium toward the image-carrying member without a complex structure for guiding the recording medium toward the image-carrying member, such as a motor, a sensor for detecting the leading edge of paper, and CPU for moving the motor based on the signal from the sensor, and complex control. Therefore, it can reduce the number of required parts and simplify the construction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
       FIG. 1  is a side cross-sectional view showing a laser printer according to a preferred embodiment of the present invention; 
       FIG. 2  is a side cross-sectional view of a process cartridge that detachably mounts in the laser printer; 
       FIG. 3  is a side cross-sectional view of a drum cartridge and a paper-guiding plate (not during the transfer operation); 
       FIG. 4  is a side cross-sectional view of the drum cartridge and the paper-guiding plate (during the transfer operation); 
       FIG. 5  is a perspective view from the plan view side of the paper-guiding plate (not during the transfer operation); 
       FIG. 6  is a perspective view from the plan view side of the paper-guiding plate (during the transfer operation); 
       FIG. 7  is a perspective view from the plan view side of the paper-guiding plate (during the transfer operation); 
       FIG. 8  is a perspective view from the bottom side of the paper-guiding plate (during the transfer operation); 
       FIG. 9  is a side view illustrating a transfer point guiding mechanism (not during the transfer operation); 
       FIG. 10  is a side view illustrating the transfer point guiding mechanism (during the transfer operation); and 
       FIG. 11  is a side view illustrating another transfer point guiding mechanism (not during the transfer operation). 
   

   DETAILED DESCRIPTION 
   An image-forming device according to preferred embodiments of the present invention will be described while referring to the accompanying drawings.  FIG. 1  is a side cross-sectional view showing the relevant construction of a laser printer serving as a preferred embodiment of the image-forming device according to the present invention. 
   As shown in  FIG. 1 , a laser printer  1  includes a main casing  2 , and, within the main casing  2 , a feeder unit  4  for feeding a paper  3 , an image-forming unit  5  for forming images on the paper  3  supplied from the feeder unit  4 , and the like. 
   The laser printer  1  also includes an access opening  6  formed in one side wall of the main casing  2  for inserting and removing a process cartridge  16  described later, and a front cover  7  capable of opening and closing over the access opening  6 . The front cover  7  is rotatably supported by a cover shaft (not shown) inserted through a bottom end of the front cover  7 . Accordingly, when the front cover  7  is rotated closed about the cover shaft, the front cover  7  covers the access opening  6 . When the cover is rotated open about the cover shaft, the access opening  6  is exposed, enabling the process cartridge  16  to be mounted into or removed from the main casing  2  via the access opening  6 . A control panel (not shown), including operating keys and an LED display unit, is embedded in the front cover  7 . 
   Hereinafter, the side of the laser printer  1  and the process cartridge  16  on which the front cover  7  is provided will be referred to as the “front side” and the opposite side as the “rear side”. The side of the laser printer  1  and the process cartridge  16  on which the feeder unit  4  is provided will be referred to as the “below side” and the opposite side as the “above side”. 
   The feeder unit  4  includes a paper supply tray  8  that is detachably mounted in a lower section of the main casing  2 , a feeding roller  9  and separating pad  10  disposed above the front end of the paper supply tray  8 , a pickup roller  11  disposed on the rear side of the feeding roller  9 , a pinch roller  12  disposed in opposition to the feeding roller  9  on the lower front side thereof, and a pair of registration rollers  13  disposed on the above rear side of the feeding roller  9 . 
   A paper pressing plate  14  is provided inside the paper supply tray  8  for supporting the paper  3  in a stacked state. The paper pressing plate  14  is pivotably supported on the rear end thereof, so that the front end can move vertically. When the front end of the paper pressing plate  14  is lifted, the topmost sheet of the paper  3  stacked on the paper pressing plate  14  is pressed against the pickup roller  11 . The pickup roller  11  rotates to begin conveying the topmost sheet of the paper  3  between the feeding roller  9  and separating pad  10 . The registration rollers  13  convey the sheet of the paper  3  to a transfer point in the image-forming unit  5 . The transfer point is a position between a photosensitive drum  23  and a transfer roller  26 . The photosensitive drum  23  and the transfer roller  26  are described later. 
   A paper-guiding plate  55  is provided in the main casing  2  along a conveying path of the paper  3  extends from the registration rollers  13 , through the image-forming unit  5 , to a fixing unit  17  described later. The paper-guiding plate  55  is formed in a flat plate-shape and disposed above the paper tray  8 . 
   The paper-guiding plate  55  is configured of a recessed part  56 , a front guiding plate  57 , and a rear guiding plate  58 . The recessed part  56  is formed in a center portion of the paper-guiding plate  55  relative to the front-to-rear direction. The front guiding plate  57  extends from the front end of the paper-guiding plate  55  to the recessed part  56  for conveying the paper  3  from the registration rollers  13  to the transfer point. The front guiding plate  57  slopes downward toward the rear side. A device-side slit  59  (see  FIG. 7 ) is formed in a left-to-right center of the front guiding plate  57 . The side of the laser printer  1  and the process cartridge  16  on which a photosensor  75  (as described later) is provided will be referred to as the “left side”, and the opposite side as the “right side” in  FIG. 5 . The device-side slit  59  is substantially rectangular in shape and extends in the front-to-rear direction into the recessed part  56 . 
   The rear guiding plate  58  extends from the recessed part  56  to the rear edge of the paper-guiding plate  55  for conveying the paper  3  from the transfer point to the fixing unit  17 . The rear guiding plate  58  slopes upward toward the rear side. 
   The image-forming unit  5  includes a scanning unit  15 , the process cartridge  16 , the fixing unit  17 , and the like. 
   The scanning unit  15  is disposed in the top section of the main casing  2  and includes a laser light source (not shown), a polygon mirror  18  that can be driven to rotate, fθ lenses  19 , reflecting mirrors  20 , and the like. The laser light source emits a laser beam based on image data. As illustrated by a dotted line in  FIG. 1 , the laser beam is deflected by the polygon mirror  18 , passes through the fθ lens  19 , and is reflected rearward by the reflecting mirror  20 . After passing through the fθ lenses  19 , the laser beam is reflected downward by the reflecting mirrors  20  and irradiated on the surface of the photosensitive drum  23  described later in the process cartridge  16 . 
   The process cartridge  16  is detachably mounted in the main casing  2  below the scanning unit  15 . 
     FIG. 2  is a cross-sectional side view of the process cartridge  16 . As shown in  FIG. 2 , the process cartridge  16  includes a drum cartridge  21 , and a developer cartridge  32  that is detachably mounted on the drum cartridge  21 . The drum cartridge  21  includes a drum frame  22 , a photosensitive drum  23 , a scorotron charger  24 , a cleaning brush  25 , and a transfer roller  26 . 
   As shown in  FIG. 5 , the drum frame  22  extends in the front-to-rear direction and is partitioned into a front part and a rear part. The front part is a developer-cartridge-accommodating section  27  for accommodating the developer cartridge  32  (see  FIG. 2 ), while the rear part is a photosensitive-drum-accommodating section  28  for accommodating the photosensitive drum  23  (see  FIG. 2 ). A transfer-roller-accommodating section  29  is provided in the drum frame  22  below the photosensitive-drum-accommodating section  28  for accommodating the transfer roller  26  (see  FIG. 2 ). 
   As shown in  FIG. 2 , a charger-supporting section  31  is provided in the drum frame  22  above the rear side of the photosensitive-drum-accommodating section  28  for supporting the scorotron charger  24 . A plate-shaped chute  30  is also provided in the drum frame  22  for guiding the paper  3  to the transfer point. 
   The chute  30  forms the bottom wall on the rear part of the developer-cartridge-accommodating section  27 . The chute  30  is separated a prescribed distance from the front end of the transfer-roller-accommodating section  29  and slopes downward toward the front. The chute  30  is formed a step lower than the bottom wall on the front part of the developer-cartridge-accommodating section  27 . A paper inlet  46  is formed between the front end of the chute  30  and the bottom wall on the front part of the developer-cartridge-accommodating section  27  for introducing the paper  3  into the drum cartridge  21 . 
   As shown in  FIG. 5 , a drum-side slit  53  is formed in a portion of the chute  30  opposing the device-side slit  59  (see  FIG. 7 ). The drum-side slit  53  is substantially rectangular in shape and disposed in the left-to-right center (widthwise center) of the chute  30 . 
   As shown in  FIG. 2 , a paper outlet  47  is formed in the rear end of the transfer-roller-accommodating section  29  for guiding the paper  3  out of the drum cartridge  21 . 
   When the drum frame  22  is mounted in the main casing  2 , as shown in  FIG. 1 , the transfer-roller-accommodating section  29  and chute  30  are accommodated in the recessed part  56  of the paper-guiding plate  55 . At this time, the front part of the bottom wall of the developer-cartridge-accommodating section  27  opposes the front guiding plate  57  of the paper-guiding plate  55  and is separated slightly therefrom in the vertical direction. 
   As shown in  FIG. 2 , the photosensitive drum  23  is accommodated in the photosensitive-drum-accommodating section  28 . The photosensitive drum  23  includes a main drum body  33  that is cylindrical in shape and has a positively charged photosensitive layer on its outer surface, and a metal drum shaft  34  extending along the axial center of the main drum body  33  in the longitudinal direction thereof. The drum shaft  34  can be rotatably supported in both side plates of photosensitive-drum-accommodating section  28 , while the main drum body  33  is rotatably supported on the drum shaft  34 . 
   The scorotron charger  24  is mounted on the charger-mounting unit  31  diagonally above and rearward of the photosensitive drum  23 . The scorotron charger  24  is disposed in opposition to but separated a prescribed distance from the photosensitive drum  23  so as not to contact the same. The scorotron charger  24  is a positively charging scorotron charger that generates a corona discharge from a wire formed of tungsten or the like, and can form a uniform charge of positive polarity over the surface of the photosensitive drum  23 . 
   The cleaning brush  25  is mounted on the rear side of the photosensitive drum  23 . The cleaning brush  25  is disposed so that a tip of the cleaning brush  25  is in contact with the surface of the main drum body  33  of the photosensitive drum  23 . 
   The transfer roller  26  is rotatably supported on both side plates of the drum cartridge  21  and contacts the photosensitive drum  23  in the above-to-below direction from the bottom thereof. The transfer roller  26  is configured of a metal roller shaft  36  that is covered with a roller  35  formed of a conductive rubber material. During a transfer operation, a transfer bias is applied to the transfer roller  26 . 
   When the laser printer  1  is printing, the drive force from a motor (not shown) is transmitted to the roller shaft  36  for driving the transfer roller  26  to rotate together with the roller shaft  36 . 
   The developer cartridge  32  is formed in a box shape that is open on the rear side. Within the developer cartridge  32  are provided a developer frame  37 , an agitator  38  accommodated in the developer frame  37 , a supply roller  39 , a developing roller  40 , and a layer-thickness regulating blade  41 . 
   The developer frame  37  is formed in a box shape open on the rear side. A partition  42  is provided for partitioning the developer frame  37  into a toner-accommodating chamber  43  on the front side, and a developing chamber  44  on the rear side. A passage  45  is formed in the partition  42  for providing communication between the toner-accommodating chamber  43  and developing chamber  44 . The toner-accommodating chamber  43  accommodates toner. 
   The agitator  38  is provided in the toner-accommodating chamber  43 . The supply roller  39  is disposed rearward of the passage  45  in the developing chamber  44 . The developing roller  40  is disposed rearward of the supply roller  39  in the developing chamber  44  and contacts the supply roller  39  so that both are compressed by the force. 
   The layer-thickness regulating blade  41  is provided above the developing roller  40  in the developing chamber  44  and contacts the surface of the developing roller  40  with pressure. 
   With this construction, the agitator  38  stirs toner in the toner accommodating chamber  43 , discharging toner toward the developing chamber  44 . Discharged toner is supplied onto the developing roller  40  by the rotating supply roller  39 . At this time, the toner is positively tribocharged between the supply roller  39  and developing roller  40 . As the developing roller  40  rotates, toner supplied to the surface of the developing roller  40  passes between the developing roller  40  and the layer-thickness regulating blade  41 , thereby maintaining a uniform thickness of toner layer on the surface of the developing roller  40 . 
   As the photosensitive drum  23  rotates, the scorotron charger  24  charges the surface of the photosensitive drum  23  with a uniform positive polarity. Subsequently, a laser beam emitted from the scanning unit  19  (see  FIG. 1 ) is scanned at a high speed over the surface of the photosensitive drum  23 , forming an electrostatic latent image corresponding to an image that will be formed on the paper  3 . 
   Next, positively charged toner carried on the surface of the developing roller  40  comes into contact with the photosensitive drum  23  as the developing roller  40  rotates and is supplied to areas on the surface of the positively charged photosensitive drum  23  that were exposed to the laser beam and, therefore, have a lower potential. In this way, the latent images on the photosensitive drum  23  are transformed into visible images so that a reverse toner image is carried on the surface of the photosensitive drum  23 . 
   As shown in  FIG. 1 , when the registration rollers  13  convey the paper  3  to a transfer point between the photosensitive drum  23  and transfer roller  26 , the toner image carried on the surface of the photosensitive drum  23  is transferred onto the paper  3  by a transfer bias applied to the transfer roller  26 . After the toner image is transferred, the paper  3  is conveyed to the fixing unit  17 . Toner remaining on the photosensitive drum  23  after the transfer operation is recovered by the developing roller  40 . Further, paper dust deposited on the photosensitive drum  23  from the paper  3  is recovered by the cleaning brush  25  after the transfer operation. 
   The fixing unit  17  is disposed on the rear side of the process cartridge  16  and includes a heating roller  48  and a pressure roller  49 . The pressure roller  49  is disposed below and contacts the heating roller  48  with pressure. 
   In the fixing unit  17 , toner transferred onto the paper  3  at the transfer point is fixed to the paper  3  by heat as the paper  3  passes between the heating roller  48  and pressure roller  49 . After the fixing process, the paper  3  is conveyed along a discharge path  50  that leads up to the top surface of the main casing  2 . Discharge rollers  51  provided at the top of the discharge path  50  discharge the paper  3  onto a discharge tray  52  formed on the top surface of the main casing  2 . 
   Next, a transfer position guiding mechanism  61  (see  FIG. 9 ) for guiding the paper  3  to the transfer point will be described with reference to  FIGS. 3 through 10 . As shown in  FIG. 3 , the transfer position guiding mechanism  61  includes a first pivoting member  62  and a second pivoting member  63 . 
   The first pivoting member  62  is disposed in a predetermined position upstream (on the front side) of the transfer point. The first pivoting member  62  pivotably is supported on the paper-guiding plate  55  of the main casing  2 . In other words, the first pivoting member  62  is selectively movable between a non-passing position and a passing position. The non-passing position and passing position are described later. The first pivoting member  62  functions to guide the paper  3  toward the second pivoting member  63 . 
   The first pivoting member  62  is integrally configured of a first rotational shaft  64 , a paper contact part  65 , a first contact part  66 , a sensor arm  67  (see  FIG. 5 ), and a pivot-restricting protrusion  68 . 
     FIG. 8  is a perspective view from the bottom side of the paper-guiding plate (during the transfer operation). As shown in  FIG. 8 , the first rotational shaft  64  extends in the left-to-right direction below the front guiding plate  57 . More specifically, a right bearing part  69  is provided on the bottom surface of the paper-guiding plate  55  in a left-to-right center region thereof, on the right side of the device-side slit  59 . A side plate  80  is provided on the left end of the paper-guiding plate  55  extending downward. A left bearing part  70  is provided on the side plate  80  at a position along a plane passing through the right bearing part  69  in the left-to-right direction. 
   The first rotational shaft  64  is inserted into and rotatably supported by the right bearing part  69  and left bearing part  70 . More specifically, the first rotational shaft  64  is supported in the right bearing part  69  and left bearing part  70  with a midpoint of the first rotational shaft  64  in the left bearing part  70  and the left end of the first rotational shaft  64  protruding leftward from the left bearing part  70 . Thereby, the first rotational shaft  64  can rotate about an axial center of the first rotational shaft  64 . The first rotational shaft  64  is also disposed to intersect the device-side slit  59  in the left-to-right direction. 
   As shown in  FIG. 3 , the paper contact part  65  protrudes radially outward from the first rotational shaft  64 . The paper contact part  65  is formed of a slender plate piece slightly narrower than the device-side slit  59  and is disposed opposite the device-side slit  59 . The paper contact part  65  is configured to protrude through the device-side slit  59  farther than the top surface of the front guiding plate  57 . 
     FIG. 9  is a side view of the transfer position guiding mechanism  61 . As shown in  FIGS. 3 and 9 , the first contact part  66  protrudes radially outward from the first rotational shaft  64  in a different direction from the paper contact part  65  and, more specifically, forms an obtuse angle (100-130°, for example) with the paper contact part  65 . The first contact part  66  is formed of a slender plate piece having substantially the same width as the paper contact part  65 , and is also disposed in a position on the first rotational shaft  64  corresponding to the device-side slit  59 , i.e. the same left-to-right position as the paper contact part  65 . 
   As shown in  FIGS. 8 and 9 , the first contact part  66  is formed substantially in the shape of the letter J in a side view. More specifically, the first contact part  66  includes a protruding rod  71  that protrudes radially outward from the first rotational shaft  64 , and an engaging piece  72  that protrudes further from the protruding portion. The engaging piece  72  bents from the free end of the protruding rod  71  toward a second contact part  83  described later at an acute angle (30-60°, for example). The engaging piece  72  is shorter than the protruding rod  71 , and the distal end of the engaging piece  72  is rounded into a circular shape when viewed from the side. 
   As shown in  FIGS. 8 and 9 , the sensor arm  67  is formed substantially in an L-shape having an arm part  73  disposed on the left end of the first rotational shaft  64 , and a light-interrupting piece  74  provided on the distal end of the arm part  73 . 
   The arm part  73  protrudes radially outward from the left end of the first rotational shaft  64  in a different direction from the paper contact part  65  when viewed from the side, and more specifically forms an acute angle (5-45°, for example) with the paper contact part  65 . 
   As shown in  FIGS. 5 and 9 , the light-interrupting piece  74  projects slightly leftward from the distal end of the arm part  73 , then extends from the left end of the projected part in a circumferential direction around the first rotational shaft  64 , forming an arc shape that is curved in the front-to-rear direction. As shown in  FIGS. 5 ,  6 ,  9  and  10 , the light-interrupting piece  74  pivots in the circumferential direction about the center of the first rotational shaft  64  when the first rotational shaft  64  rotates. 
   The photosensor  75  is also provided in the main casing  2 . As shown in  FIGS. 5 and 6 , the photosensor  75  is disposed in the same position as the light-interrupting piece  74  relative to the left-to-right direction and is positioned in the front-to-rear direction for allowing the light-interrupting piece  74  to be interposed therein and retracted therefrom as the first rotational shaft  64  rotates. The photosensor  75  is shaped substantially like three sides of a rectangle and includes a light-emitting element  76  and a light-receiving element  77  that are separated but confront each other vertically. A detection position P shown in  FIGS. 9 and 10  is a position at which the photosensor  75  detects a detection light transmitted between the light-emitting element  76  and light-receiving element  77 . 
   Through rotation of the first rotational shaft  64 , the light-interrupting piece  74  pivots between a retracted position shown in  FIGS. 5 and 9 , when the light-interrupting piece  74  is retracted from the light-emitting element  76  and light-receiving element  77 , and an advanced position shown in  FIGS. 6 and 10 , when the light-interrupting piece  74  is interposed between the light-emitting element  76  and light-receiving element  77 . 
   When the light-interrupting piece  74  is in the retracted position shown in  FIGS. 5 and 9 , the light-interrupting piece  74  is separated from the detection position P, allowing the light-receiving element  77  to receive detection light emitted from the light-emitting element  76 . 
   When the light-interrupting piece  74  is in the advanced position shown in  FIGS. 6 and 10 , the light-interrupting piece  74  overlaps the detection position P, thereby blocking the detection light emitted from the light-emitting element  76  and preventing the light-receiving element  77  from receiving this detection light. 
   As shown in  FIG. 8 , the pivot-restricting protrusion  68  has a substantially rectangular plate shape and is provided near the right side of the left bearing part  70 . As shown in  FIGS. 9 and 10 , the pivot-restricting protrusion  68  protrudes radially outward from the first rotational shaft  64  in a different direction than the paper contact part  65 , and more specifically in a direction forming an obtuse angle (120-180°, for example) with the paper contact part  65 . 
   As shown in  FIG. 8 , a stopper  78  is provided on the bottom surface of the paper-guiding plate  55  near the right side of the left bearing part  70  so as to be capable of contacting the pivot-restricting protrusion  68 . The stopper  78  is substantially rectangular in shape and extends in the front-to-rear direction. As shown in  FIG. 9 , the stopper  78  is disposed on the bottom surface of the paper-guiding plate  55  at an angle for contacting the pivot-restricting protrusion  68  when the first rotational shaft  64  rotates so that the paper contact part  65  is erected vertically. Hereafter, the first pivoting member  62  is said to be in a “non-passing position” when the paper contact part  65  is erected vertically. 
   As shown in  FIGS. 8 and 10 , a spring  79  is also connected to the first pivoting member  62  for positioning the first pivoting member  62  in the non-passing position. More specifically, the spring  79  urges the pivot-restricting protrusion  68  so that the first pivoting member  62  moves from the passing position toward the non-passing position. The spring  79  is configured of a coil spring (tension spring) and extends in the front-to-rear direction between the side plate  80  (see  FIG. 8 ) on the left end of the paper-guiding plate  55  and the stopper  78 . One end of the spring  79  is engaged in a spring-engaging part (not shown) protruding from the first rotational shaft  64  in substantially the same radially direction as the pivot-restricting protrusion  68 , while the other end is engaged with the side plate  80 . 
   The urging force of the spring  79  urges the first pivoting member  62  in a direction for rotating the first rotational shaft  64  clockwise in  FIG. 9 . Hence, when no external forces are applied, the first rotational shaft  64  rotates clockwise until the pivot-restricting protrusion  68  contacts the stopper  78 , placing the first pivoting member  62  in the non-passing position. By contacting the stopper  78 , the pivot-restricting protrusion  68  restricts the first rotational shaft  64  from rotating past the non-passing position in the clockwise direction. In other words, the first pivoting member  62  can pivot from the passing position to the non-passing position in the clockwise direction without overrunning the non-passing position. 
   When the first pivoting member  62  is disposed in the non-passing position, the paper contact part  65  is in the erect state shown in  FIGS. 3 and 5 , protruding upward from the front guiding plate  57  through the device-side slit  59 , and is received in the drum-side slit  53  on the drum side (see  FIG. 5 ). Further, the first contact part  66  is arranged so that the protruding rod  71  extends rearward, while the sensor arm  67  is arranged with the light-interrupting piece  74  in the retracted position shown in  FIG. 9 . 
   As shown in  FIG. 3 , the second pivoting member  63  is disposed between the first pivoting member  62  and the transfer point along the conveying direction of paper  3  (front-to-rear direction). The second pivoting member  63  guides a sheet of paper  3  received from the first pivoting member  62  to the photosensitive drum  23 . The second pivoting member  63  is pivotably supported by the chute  30  of the process cartridge  16  (see  FIG. 2 ). More specifically, the second pivoting member  63  is selectively movable between a separated position and a proximal position. The separated position is farther from the photosensitive drum  23  than the proximal position, described later. 
   As shown in  FIGS. 3 and 5 , the second pivoting member  63  is integrally configured of a second rotational shaft  81 , a transfer guide part  82 , and the second contact part  83 . 
   As shown in  FIG. 3 , the transfer guide part  82  and second contact part  83  form an inverted V-shape over the second rotational shaft  81 . The transfer guide part  82  and the second contact part  83  protrude forward from the second rotational shaft  81 . 
   Shaft-supporting parts  84  are provided on the rear end of the chute  30  for rotatably supporting the second rotational shaft  81 . As shown in  FIG. 5 , the second rotational shaft  81  is formed slightly longer than the drum-side slit  53  in the left-to-right direction. The second rotational shaft  81  is inserted through the shaft-supporting parts  84  and rotates about its axial center, serving as a second support point. 
   The shaft-supporting parts  84  are formed in the left-to-right center of the chute  30  on the rear end of the drum-side slit  53  so that the drum-side slit  53  is interposed between the shaft-supporting parts  84  in the left-to-right direction. 
   As shown in  FIGS. 5 and 9 , the transfer guide part  82  includes a guide-supporting part  85  protruding from the second rotational shaft  81  toward the transfer point, and film members  86  extending from the rear edge of the guide-supporting part  85  toward the transfer point. 
   As shown in  FIG. 9 , the guide-supporting part  85  is formed in a flat plate-shape extending in the left-to-right direction and is disposed on the rear side of the chute  30  (see  FIG. 5 ). The center of the front edge on the guide-supporting part  85  is fixed to the second rotational shaft  81  via a mounting plate  87 . The rear edge of the guide-supporting part  85  extends to a point between the second rotational shaft  81  and photosensitive drum  23  and confronts the photosensitive drum  23  with a gap formed therebetween. 
   As shown in  FIG. 5 , two of the film members  86  are disposed adjacent to each other in the left-to-right direction with a gap formed therebetween in the left-to-right center of the guide-supporting part  85 . The film members  86  are flexible film formed of a synthetic resin or the like in a substantially rectangular shape. The film members  86  are affixed to the top surface of the guide-supporting part  85 , extending in the left-to-right direction along the rear edge thereof. The rear edges of the film members  86  extend from the guide-supporting part  85  of the second pivoting member  63 . 
   As shown in  FIG. 5 , the second contact part  83  is formed in a substantially rectangular shape slightly narrower than the drum-side slit  53 , and extends in the front-to-rear direction. The second contact part  83  is disposed inside the drum-side slit  53 , with the rear end of the second contact part  83  affixed to the second rotational shaft  81  via the mounting plate  87  (see  FIG. 9 ). As shown in  FIG. 9 , the second contact part  83  protrudes from the second rotational shaft  81  toward the first contact part  66  of the first pivoting member  62  such that the distal end of the second contact part  83  can contact the engaging piece  72  from above. 
   The second pivoting member  63  is formed to satisfy the equation L 1 ·F 1 &lt;L 2 ·F 2 , where L 1  is the distance from the second rotational shaft  81  to the rear end of the guide-supporting part  85 , F 1  is the force that the weight of the transfer guide part  82  generates at the rear end of the guide-supporting part  85 , L 2  is the distance from the second rotational shaft  81  to the front end of the second contact part  83 , and F 2  is the force that the weight of the second contact part  83  generates at the front edge of the second contact part  83 . 
   Hence, the second pivoting member  63  is urged by its own weight to pivot so that the transfer guide part  82  pivots upward and the second contact part  83  pivots downward. Specifically, the second pivoting member  63  is urged to rotate clockwise in  FIG. 9  about the second rotational shaft  81 . Thereby, the second contact part  83  is moved in interlocking relation with the engaging piece  72  of first contact part  66 . 
   However, since the first pivoting member  62  is disposed in the non-passing position shown in  FIG. 9  by the urging force of the spring  79 , as described above, the first contact part  66  is oriented with the protruding rod  71  extending rearward and the engaging piece  72  protruding upward. 
   Accordingly, the second pivoting member  63  is disposed in the separated position when the first pivoting member  62  is disposed in the non-passing position. The separated position is the state of the second pivoting member  63  when the film members  86  are separated from the photosensitive drum  23 . In other words, the film members  86  are oriented farther from the photosensitive drum  23  when the second pivoting member  63  is moved to the non-passing position. When the second pivoting member  63  is in the separated position, the transfer guide part  82  protrudes rearward and slightly downward from the second rotational shaft  81 . At this time, the rear edges of the film members  86  are positioned toward the transfer roller  26  and separated from the photosensitive drum  23 . Further, the second contact part  83  protrudes forward from the second rotational shaft  81 , and the front-to-rear center portion of the second contact part  83  contacts the top of the engaging piece  72 . 
   As described above, the first pivoting member  62  is in the non-passing position and the second pivoting member  63  is in the separated position when the paper  3  is not passing over the first pivoting member  62 . When the paper  3  is conveyed from the registration rollers  13  so that the leading edge of the paper  3  in the conveying direction (hereinafter simply referred to as “leading edge”) contacts the paper contact part  65  positioned in the conveying path, as shown in  FIG. 9 , the pressure applied to the paper contact part  65  by the paper  3  causes the paper contact part  65  to rotate rearward, and the first rotational shaft  64  rotates counterclockwise against the urging force of the spring  79 . 
   When the paper contact part  65  rotates rearward about the center of the first rotational shaft  64 , as shown in  FIG. 10 , the paper  3  is conveyed over the paper contact part  65  toward the photosensitive drum  23 . In other words, abutting the paper  3  conveyed against the paper contact part  65  rotates the paper contact part  65  to move the first pivoting member  62  to the passing position from the non-passing position. The passing position is the orientation of the first pivoting member  62  when the paper contact part  65  is laid downward toward the rear. 
   The first pivoting member  62  remains in the passing position while the paper  3  passes over the paper contact part  65 . While the first pivoting member  62  is in the passing position and the paper contact part  65  is angled rearward, a gap is formed above the paper contact part  65  for allowing passage of the paper  3 , as shown in  FIGS. 4 and 10 . At this time, the first contact part  66  is arranged with the protruding rod  71  extending downward, and the sensor arm  67  is oriented with the light-interrupting piece  74  in the advanced position. 
   When in the advanced position, the light-interrupting piece  74  overlaps the detection position P in the optical path of the detection light, thereby preventing the light-receiving element  77  from receiving the detection light. The photosensor  75  inputs a light-interruption signal to a CPU (not shown) provided in the main casing  2  to indicate that the light-receiving element  77  is not receiving light. This light-interruption signal is inputted into the CPU while the paper  3  is in contact with the paper contact part  65 . 
   Based on the timing that the light-interruption signal is inputted, the CPU controls the scanning unit  15  to begin scanning a laser beam at high speed. Accordingly, before the paper  3  comes into contact with the photosensitive drum  23 , the scanning unit  15  forms an electrostatic latent image on the photosensitive drum  23  that is subsequently developed into a toner image. 
   In the meantime, since the second contact part  83  contacts the engaging piece  72  due to its own weight when the paper  3  presses against and rotates the paper contact part  65 , rotating the first contact part  66  downward, the second contact part  83  pivots downward by its own weight following the engaging piece  72  of the light-emitting element  76 . Since the second rotational shaft  81  rotates clockwise at this time, the second pivoting member  63  pivots from the separated position to the proximal position in association with the pivoting of the first pivoting member  62  as shown in  FIG. 10 . 
   In other words, the second pivoting member  63  is disposed in the proximal position while the paper  3  passes over the paper contact part  65 . The proximal position denotes the orientation of the second pivoting member  63  when the rear edges of the film members  86  are disposed in proximity to the photosensitive drum  23 . In other words, the film members  86  are oriented toward photosensitive drum  23  when the second pivoting member  63  is moved to the passing position. When the second pivoting member  63  is in the proximal position, the transfer guide part  82  protrudes rearward and upward from the second rotational shaft  81 , as shown in  FIGS. 4 and 10 . At this time, the second contact part  83  slopes downward toward the front from the second rotational shaft  81  with the front end of the second contact part  83  contacting the top of the engaging piece  72 . 
   Accordingly, after the leading edge of the paper  3  passes over the paper contact part  65 , the film members  86  guides the paper  3  so that the leading edge of the paper  3  contacts the photosensitive drum  23  upstream of the transfer point. As a result, instead of a gap being formed between the paper  3  and photosensitive drum  23  on the upstream side of the transfer point, the paper  3  is conveyed to the transfer point in close contact with the photosensitive drum  23 . 
   When the trailing edge of the paper  3  in the conveying direction (hereinafter simply referred to as the “trailing edge”) subsequently passes over the paper contact part  65 , the paper  3  no longer applies a force to the paper contact part  65 . At this time, the urging force of the spring  79  rotates the first rotational shaft  64  clockwise so that the first pivoting member  62  pivots from the passing position to the non-passing position. Hence, the first pivoting member  62  once again returns to the non-passing position shown in  FIG. 3 . 
   Further, as the protruding rod  71  pivots upward together with the pivoting of the first pivoting member  62 , the engaging piece  72  pivots upward while sliding rearward along the second contact part  83  of the second pivoting member  63 . The force with which the engaging piece  72  presses against the second contact part  83  causes the second contact part  83  to pivot upward against its own weight. Since the second rotational shaft  81  rotates counterclockwise at this time, the second pivoting member  63  pivots from the proximal position to the separated position along with the pivoting of the first pivoting member  62 . Hence, the second pivoting member  63  is again placed in the separated position shown in  FIGS. 3 and 9 . 
   When the second pivoting member  63  is in the separated position, the light-interrupting piece  74  is in the retracted position. Since the light-interrupting piece  74  is separated from the detection position P at this time, the light-receiving element  77  can receive the detection light. Hence, the photosensor  75  inputs a light-transmission signal to the CPU in the main casing  2  indicating that the light-receiving element  77  is receiving the detection light. The photosensor  75  inputs this light-transmission signal into the CPU as long as the paper  3  is not contacting the paper contact part  65 . 
   Hence, the light-transmission signal is inputted into the CPU while the paper  3  is not contacting the paper contact part  65 , and a light-interruption signal is inputted into the CPU when the light contacts the paper contact part  65 . 
   When the second pivoting member  63  is disposed in the separated position, the film members  86  are separated from the photosensitive drum  23 , with the rear edges of the film members  86  disposed near the transfer roller  26  side. 
   The image-forming device having the construction described above can obtain the following effects. 
   (1) When the paper  3  is conveyed by the registration rollers  13  toward the transfer position guiding mechanism  61 , the leading edge of the paper  3  first contacts the paper contact part  65  and begins to pass over the paper contact part  65 . When the paper  3  passes over the paper contact part  65 , the first pivoting member  62  pivots about the first rotational shaft  64  into the passing position. 
   Next, the paper  3  passes over the film members  86 . At this time, the second pivoting member  63  is disposed in the proximal position having pivoted about the second rotational shaft  81  together with the pivoting of the first pivoting member  62 . Hence, the paper  3  is guided along the film members  86  while being conveyed to the photosensitive drum  23 . 
   After the paper  3  has passed over the paper contact part  65 , the first pivoting member  62  pivots about the first rotational shaft  64  and returns to the non-passing position, and the second pivoting member  63  pivots about the second rotational shaft  81  in association with the pivoting of the first pivoting member  62  and returns to the separated position separated from the photosensitive drum  23 . When the trailing edge of the paper  3  has passed the paper contact part  65 , the film members  86  are brought into the separated position, so that the second pivoting member  63  guides the recording medium without the paper  3  pressing the film members  86  downward. Hence, when the trailing edge of the paper  3  separates from the film members  86 , it is prevented that the film members  86  generate abnormal noise. 
   Further, since the transfer position guiding mechanism  61  is configured to pivot the first pivoting member  62  and the second pivoting member  63  based only on passing or non-passing of the paper  3 , there is no need to provide a complex structure for placing the guide member near and separating from the photosensitive drum, such as a sensor for detecting the leading edge of paper, motor, and CPU for moving the motor based on the signal from the sensor, and complex control, thereby reducing the number of required parts and simplifying the construction. 
   (2) Further, when the paper  3  contacts the paper contact part  65  extending into the paper-conveying path above the front guiding plate  57 , the first rotational shaft  64  rotates about its axial center, pivoting the first contact part  66  into the passing position. As the first contact part  66  pivots, the second contact part  83  of the second pivoting member  63  slides along the engaging piece  72 . At this time, the second rotational shaft  81  rotates about its axial center, pivoting the transfer guide part  82  and placing the second pivoting member  63  in the proximal position, with the film members  86  of the transfer guide part  82  in proximity to the photosensitive drum  23 . 
   After the paper  3  passes over the paper contact part  65 , removing contact between the paper  3  and paper contact part  65 , the first rotational shaft  64  rotates about its axial center, pivoting the first contact part  66  and placing the first pivoting member  62  in the non-passing position. 
   As the first contact part  66  pivots, the second contact part  83  of the second pivoting member  63  slides along the engaging piece  72 . At this time, the second rotational shaft  81  rotates about its axial center, pivoting the transfer guide part  82  and placing the second pivoting member  63  in the separated position in which the film members  86  of the transfer guide part  82  are separated from the photosensitive drum  23 . 
   Hence, this construction can achieve reliable operations through simple formation of the first pivoting member  62  and the second pivoting member  63 . 
   (3) When the paper  3  is conveyed through the transfer position guiding mechanism  61  toward the photosensitive drum  23 , the paper  3  passes over the film members  86  on the transfer guide part  82 . Therefore, the transfer position guiding mechanism  61  can reliably place the paper  3  in contact with the photosensitive drum  23 . 
   (4) When the paper  3  does not contact the paper contact part  65 , the second pivoting member  63  is disposed in the separated position by the weight of the second contact part  83 , since the second contact part  83  always contacts the engaging piece  72  by its own weight in the transfer position guiding mechanism  61  described above. However, when the paper  3  contacts the paper contact part  65 , the first pivoting member  62  is moved to the passing position. Hence, the engaging piece  72  is rotated downward so that the second pivoting member  63  moves to the proximal position allowing the second contact part  83  to pivot down. Accordingly, through a simple construction that eliminates the need for a coupling member for coupling the first contact part  66  and the second contact part  83 , it is possible to pivot the second pivoting member  63  into the proximal position or the separated position in association with pivoting of the first pivoting member  62 . 
   (5) In the transfer position guiding mechanism  61  described above, the second pivoting member  63  is formed to satisfy the equation L 1 ·F 1 &lt;L 2 ·F 2 , where L 1  is the distance from the second rotational shaft  81  to the rear end of the guide-supporting part  85 , F 1  is the force that the weight of the transfer guide part  82  generates at the rear end of the guide-supporting part  85 , L 2  is the distance from the second rotational shaft  81  to the front end of the second contact part  83 , and F 2  is the force that the weight of the second contact part  83  generates at the front edge of the second contact part  83 . Hence, the second pivoting member  63  can be reliably placed in contact with the first contact part  66  at all times through the weight of the second contact part  83 . 
   (6) Further, after the paper  3  passes over the paper contact part  65 , removing contact between the paper contact part  65  and paper  3 , the first pivoting member  62  pivots about the axial center of the first rotational shaft  64  until the pivot-restricting protrusion  68  contacts the stopper  78 , placing the first pivoting member  62  in the non-passing position. In this way, the first pivoting member  62  can be placed in a prescribed non-passing position while the second pivoting member  63  can be placed in prescribed separated position. 
   (7) In the transfer position guiding mechanism  61  described above, the light-interrupting piece  74  of the sensor arm  67  pivots between the passing position and non-passing position through rotation of the first rotational shaft  64  so that the light-interrupting piece  74  overlaps or separates from the detection position P. The photosensor  75  detects whether the light-interrupting piece  74  is in an overlapped state or separated state relative to the detection position P and inputs the detected state into the CPU as a light-interruption signal or a light-transmission signal. Accordingly, the CPU can detect the timing for beginning to write an image on the photosensitive drum  23  based on the timing of the inputted light-interruption signal. By controlling the scanning unit  15  to begin scanning a laser beam at a high speed based on the inputted timing of the light-interruption signal, the CPU can reliably transfer a toner image onto the paper  3 . As a result, through the pivoting of the first pivoting member  62 , this construction can simultaneously guide the paper  3  to the photosensitive drum  23  by the pivoting of the second pivoting member  63  and detect a timing to begin writing an image on the photosensitive drum  23 . 
   (8) In the laser printer  1  of the preferred embodiment, the drum cartridge  21  is detachably mounted in the main casing  2 . This construction can simplify operations for removing paper jams and for replacing the drum cartridge  21 . 
   (9) Since the first pivoting member  62  is provided in the main casing  2  rather than in the drum cartridge  21 , which is a consumable product, this construction reduces the cost of the drum cartridge  21 . Further, if the first pivoting member  62  were provided in the drum cartridge  21 , the first pivoting member  62  could be damaged when mounting or removing the drum cartridge  21 . However, such damage can be avoided by providing the first pivoting member  62  in the main casing  2 . 
   (10) On the other hand, the second pivoting member  63  is provided in the drum cartridge  21 . This construction can improve the accuracy for placing the second pivoting member  63  in a proximal position and separated position relative to the photosensitive drum  23 , making it possible to reliably transfer a toner image onto the paper  3 . 
   In the preferred embodiment described above, the second contact part  83  contacts the engaging piece  72  of the first contact part  66  by its own weight. However, the second contact part  83  may be slidably engaged with the first contact part  66 , as shown in  FIG. 11 . In  FIG. 11 , like parts and components to those in the preferred embodiment described above are designated with the same reference numerals to avoid duplicating description. 
   As shown in  FIG. 11 , the first contact part  66  is formed substantially in the shape of the letter J in a side view, and is configured of a protruding rod  91  that protrudes along a straight line radially outward from the first rotational shaft  64 , and an engaging piece  92  that is bent from the free end of the protruding rod  91  at a prescribed angle (45-135°, for example) toward the second contact part  83 . The engaging piece  92  is shorter than the protruding rod  91 . Both widthwise edges on the distal end of the engaging piece  92  protrude slightly outward in the width direction. 
   The second contact part  83  includes an engaging piece  93  that is substantially rectangular in a plan view. The engaging piece  93  extends in the front-to-rear direction and is slightly narrower than the drum-side slit  53 . An elongated groove  94  is formed at a midpoint in the engaging piece  93  relative to the longitudinal direction and extends along the conveying direction of the paper  3  (the longitudinal direction) and receives the engaging piece  92  to slide therewithin. 
   The elongated groove  94  is formed with a front-to-rear length corresponding to the range in which the first pivoting member  62  pivots between the non-passing position and the passing position. The distal end of the engaging piece  92  penetrates and engages with the elongated groove  94 . Through this construction, the engaging piece  92  is slidably fitted into the elongated groove  94  and is allowed to slide within the elongated groove  94  a distance corresponding to the range in which the first pivoting member  62  pivots between the non-passing position and the passing position. 
   When the paper  3  passes over the paper contact part  65  causing the first rotational shaft  64  to rotate about its axial center in the transfer position guiding mechanism  61 , the engaging piece  92  of the first contact part  66  slides rearward relative to the elongated groove  94  of the second contact part  83 . Hence, the second pivoting member  63  rotates about the axial center of the second rotational shaft  81  into the proximal position. 
   After the paper  3  passes over the paper contact part  65 , the first rotational shaft  64  rotates about its axial center, sliding the engaging piece  92  of the first contact part  66  forward relative to the elongated groove  94  of the second contact part  83 . At this time, the second pivoting member  63  rotates about the axial center of the second rotational shaft  81  back to the separated position. 
   In the transfer position guiding mechanism  61  shown in  FIG. 11 , the elongated groove  94  has a length in the front-to-rear direction corresponding to the range in which the first pivoting member  62  pivots between the non-passing position and the passing position. Hence, when the engaging piece  92  slides rearward in the elongated groove  94  and contacts the rear edge of the elongated groove  94 , the second pivoting member  63  is disposed in the proximal position. When the engaging piece  92  slides forward in the elongated groove  94  and contacts the front edge of the elongated groove  94 , the second pivoting member  63  is disposed in the separated position. 
   Through the simple construction of the preferred embodiment described above, the first pivoting member  62  can be reliably placed in the non-passing position or passing position and the second pivoting member  63  can be reliably placed in the proximal position or separated position through contact between the pivot-restricting protrusion  68  and stopper  78 , rather than requiring special positioning. 
   Although the present invention has been described with respect to specific embodiments, it will be appreciated by one skilled in the art that a variety of changes may be made without departing from the scope of the invention. For example, although the embodiment has been described so that the first and second members  62  and  63  are pivotally movable about their own rotational shafts  64  and  81 , these two members may be arranged to move differently, e.g., vertically. Further, in the above-described embodiment, the first pivoting member  62  has been described to have the paper contact part  65  and the first contact part  66  both protruding radially outward from angularly displaced positions on the same portion in the axial direction of the first rotational shaft  64 . However, the paper contact part  65  and the first contact part  66  may be provided on different portions in the axial direction of the first rotational shaft  64  with the paper contact part  65  being disposed in the paper conveying path. The first contact part  66  may be disposed in a position offset from the paper conveying path.