Abstract:
A recording apparatus for effecting recording on a material by a recording unit, the apparatus having a carriage for reciprocal movement while carrying the recording unit; a platen for support of the recording material at a position opposed to the recording unit; a feeding roller for feeding the recording material; a pinch roller driven by the feeding roller; a sheet feeding unit for feeding the recording material to the position opposed to the recording unit; a base unit supporting the recording unit, the platen, the feeding roller and the sheet feeding unit at respective positions.

Description:
FIELD OF THE INVENTION AND RELATED ART 
   The present invention relates to a recording apparatus which records images with the use of a recording means which is moved relative to recording medium in the direction intersectional to the direction in which recording medium is conveyed by recording medium conveyance rollers. 
   A recording apparatus such as a printer, a copying machine, a facsimileing machine, etc., is structured so that recording is made on recording medium with the use of a recording means such as a recording head. As one of the various forms of a recording apparatus, there is a recording apparatus of the serial type, which forms images on recording medium with the use of a recording means mounted on a carriage which is moved in the primary scan direction relative to the recording medium which is conveyed by a recording medium conveyance mechanism in the secondary scan direction. As the recording medium for a recording apparatus of the serial type, it is possible to use a sheet of various media, for example, recording paper, thin plate of plastic, OHP sheet, fabric, etc. As the recording method employed by the recording means employed by a recording apparatus of the serial type, various recording methods have been known, for example, the thermal method, thermal transfer method, ink jet method, laser beam method, wire-dot method, etc. Among the recording apparatuses which employ one of the abovementioned recording methods, an ink jet recording apparatus, that is, a recording apparatus employing the ink jet recording method, which records images by ejecting ink onto recording medium from its recording means enjoys various advantages in that it is higher in recording speed, and lower in recording noise, while being lower in operational cost. Further, it is easy to reduce in size, and also, easy to use for color recording. 
     FIG. 14  is a side view of a typical recording apparatus in accordance with the prior art, and  FIG. 15  is a side view of the typical recording apparatus in accordance with the prior art. In the following description of any of the recording apparatuses in accordance with the prior art as well as the present invention, the portion of the recording apparatus having a sheet delivery tray is referred to as front side, and the left side of the recording apparatus as seen from the front side is referred to as left side of the recording apparatus. In  FIGS. 14 and 15 , the printer unit  520  (recording unit) is provided with a bottom case  519 , and a chassis  501  which is U-shaped overall. 
   The chassis  501  is formed of a piece of plate, and has a virtually vertical rear wall, and a pair of lateral walls perpendicular to the rear wall. The chassis  501  is solidly fixed to the bottom case  519 . Between the pair of lateral walls of the chassis  501 , a guide shaft  504  is supported, to the left and right ends of which an unshown pair of shaft cams  540  are solidly fixed. The guide shaft  504  is supported by the chassis  501  with the interposition of this pair of shaft cams  540 . 
   The carriage  506 , which is carrying the recording head  508 , is supported by the guide shaft  504  so that it can be reciprocally moved along the guide shaft  504 . The shaft cams are supported by the chassis  501  so that they can be rotated relative to the chassis  501  to vertically move the guide shaft  504 . The distance between the recording head  508  and recording medium can be adjusted by changing the vertical position of the recording head  508  by vertically moving the guide shaft  504 . 
   The carriage  506  is supported by the guide shaft  504  and the guiding portion of the chassis  501 , so that the carriage  506  is guided by the guide shaft  504  and guiding portion. The guide shaft  504  and the guiding portion of the chassis  501  are disposed in parallel to each other. The carriage  506  can be reciprocally moved by the drive belt  510 , by driving the unshown carriage motor. The recording head  508  is mounted on the carriage  506  so that the surface of the recording head  508  having the ejection orifices is positioned below the bottom surface of the carriage  506 . To the rear surface of the carriage  506 , the substrate  534  for controlling the recording head  508  is solidly attached. To the front surface of the rear wall of the chassis  501 , an encoder  507  is attached. The position of the carriage  506  is detected as the sensor of the carriage  506  reads the encoder  507 . The signals which indicate the position of the carriage  506  are used for controlling the carriage  506  and recording head  508 . 
   On the bottom case  519 , an automatic sheet feeding portion  517  is disposed, which is provided with a pressure plate  526  and a feeder tray  527 , which are tilted relative to the bottom case  519 . Against the combination of the pressure plate  526  and feeder tray  527 , a plurality of recording mediums  524  are placed in layers. The pressure plate  526  is rotatably attached by its top edge portion to the ASF base  525 , with which the bottom case  519  is provided. The pressure plate  526  is kept pressured frontward by the force from springs which press on the bottom portion of the pressure plate  526 . Thus, as the recording mediums  524  are placed in the feeder tray  527 , the bottom portion of each recording mediums  524  can be pressed against a feed roller  528  by the pressure plate  526 . 
   The feed roller  528  is rotatably supported by the ASF base, by its shaft. Opposing the feed roller  528  is the separation roller  529  for separating the recording mediums  524 . The feed roller  528  feeds the recording mediums  524  into the main assembly of the recording apparatus by being driven by an unshown driving force source as a recording operation begins. The movement of the pressure plate  526  is tied to that of the feed roller  528  by an unshown cam, so that when one of the recording mediums  524  needs to be fed into the main assembly, the pressure plate  526  presses the recording mediums  524  against the feed roller  528 , whereas when the recording apparatus is kept on standby, the pressure plate  526  is kept in the rearward position (it is forced to retract rearward and remain there). Therefore, when the recording apparatus is on standby, the recording mediums  524  can be placed on the pressure plate in the feeder tray  527 , or removed from the feeder tray  527 . When a recording medium  524  is in the feeder tray, its bottom end is in contact with the ribs with which the ASF base  525  is provided. 
   As for the function of the separation roller  529 , even if a plurality of recording mediums  524  happen to enter the nip between the separation roller  529  and feed roller  528  while the recording mediums  524  are fed into the main assembly of the image forming apparatus, the separation roller  529  prevents the recording mediums  524  on the separation roller side from advancing further into the main assembly. With the employment of this structural arrangement, the recording mediums  524  in the automatic sheet feeding portion  517  are fed into the main assembly while being separated one by one. After being fed into the main assembly, each recording medium  524  is sent into the nip between a conveyance roller  502  and a pinch roller  503 , which are disposed upstream of the recording area. The conveyance roller  502  is borne by its shaft, and a pair of bearings  512  with which the pair of lateral walls of the chassis  501  are provided one for one. The pinch roller  503  is rotatably supported by the ends of its shaft, being kept pressed upon the conveyance roller  502  by springs. 
   The conveyance roller  502  is rotationally driven by an unshown LF motor. Each recording medium  524  is conveyed by the rotation of the conveyance roller  509  in the secondary scan direction, that is, the direction intersectional to the primary direction in which the carriage  506  is moved to cause the recording head  508  to scan the recording medium  524 . The recording apparatus is provided with a platen  516 , which is supported between the pair of lateral walls of the chassis  501 , directly facing the surface of the recording head  508 , at which the ejection orifices open. Recording is made on the recording medium  524  supported by the platen  516 . On the front side of the platen  516 , a sheet discharging roller  511  is disposed, upon which a rowel-like wheel  514  is kept pressed by springs. The sheet discharging roller  511  is supported by its shaft and the platen  516 , and is driven by the LF motor in synchronism with the driving of the conveyance roller  502 . Thus, the recording medium  524  is discharged by the sheet discharging roller  511  and rowel-like wheel  514  into a sheet delivery tray  518  attached to the front of the recording apparatus. The sheet delivery tray  518  extends diagonally up and frontward to a level equal to the level of the top surface of the platen  516  along which the recording medium  524  is conveyed. 
   In terms of the direction in which the carriage  506  is moved, the left end of the carriage track is the home position of the carriage  506 , and the mechanism  515  for recovering the performance of the recording head  508  is disposed below this home position of the carriage  506 . The recording head performance recovery mechanism  515  (which hereinafter will be referred to simply as recovery mechanism) is the mechanism for maintaining the performance of the recording head  508 , in terms of ink ejection, above a predetermined level, by restoring the performance of the recording head  508 . The recovery mechanism  515  has a suction-based performance recovery means which comprises a cap for covering the ejection orifices of the recording head  508  and a vacuum pump for generating negative pressure within the cap. The suction-based recovery means is for unplugging the ejection orifices by removing the debris having entered the ejection orifices, body of ink having increased in viscosity due to the evaporation of its liquid components, bubbles, and the like, from the recording head by suctioning ink, by a predetermined amount, from the recording head through the ejection orifices. The suction-based performance recovery means is also used for completely filling the ejection orifices with ink. The recovery mechanism  515  is also provided with a wiping means for wiping away such unwanted substances such as debris and ink having adhered to the surface of the recording head  508  having the ejection orifices. 
   The recording unit  520  which supports the carriage  506  in the recording apparatus structured as described above is solidly attached to the bottom case  519 , being thereby accurately positioned relative thereto. The automatic sheet feeding portion  517  is solidly attached to the recording unit  520 , being thereby precisely positioned relative to the recording unit  520 . Also, the platen  516  which supports the conveyance roller  502  and sheet discharging roller  511  is solidly attached to the recording unit  520 , being thereby precisely positioned relative thereto. 
   In the case of the recording apparatus structure in accordance with the prior art, most of the structural components of the recording mechanism, recording medium conveyance mechanism, and recording sheet discharging mechanism are attached to the recording unit  520 . Therefore, the chassis  501  of the recording unit  520  is subjected to a large amount of load, since it supports the abovementioned structural components. Thus, insufficiency in the strength and rigidity of the chassis  501  will affect the positional relationship between the recording head  508  and recording medium  524 , possibly having an ill effect upon the level of quality at which images are formed. Thus, the chassis  510  needs to be structured so that it is given a substantial amount of strength and rigidity, and this need is one of the causes of the increase in the cost of the recording apparatus. 
   SUMMARY OF THE INVENTION 
   The primary object of the present invention is to provide a recording apparatus which is substantially higher in image quality, and lower in cost, than a recording apparatus in accordance with the prior art, by precisely positioning and supporting each of the structural components of a recording apparatus, and reducing thereby the amount of load borne by the chassis of the recording apparatus. 
   According to an aspect of the present invention, there is provided a recording apparatus for effecting recording on a recording material by recording means, said apparatus comprising a carriage for reciprocal movement while carrying said recording means; a platen for support the recording material at a position opposed to said recording means; feeding roller for feeding the recording material; a pinch roller driven by said feeding roller; a sheet feeding unit for feeding the recording material to the position opposed to the recording means; a recording unit for supporting said carriage and said pinch roller; a base unit supporting said recording unit, said platen, said feeding roller and said sheet feeding unit at respective positions. 
   These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of the recording unit, sheet feeding unit, and base unit of the recording apparatus in the first embodiment of the present invention, which have been attached to each other. 
       FIG. 2  is a perspective view of the recording unit and base unit of the recording apparatus in the first embodiment of the present invention, shown in  FIG. 1 , with the recording unit separated from the base units. 
       FIG. 3  is a side view of the recording apparatus in the first embodiment of the present invention. 
       FIG. 4  is a perspective view of the base unit and sheet feeding unit of the recording apparatus in the first embodiment, which have been attached to each other, as seen from the rear side of the apparatus. 
       FIG. 5  is a perspective view of the base unit and sheet feeding unit shown in  FIG. 4 , which have been attached to each other, as seen from the front side of the apparatus. 
       FIG. 6  is a perspective view of the base unit, conveyance roller, and platen of the recording apparatus in the first embodiment of the present invention, which have been attached to each other. 
       FIG. 7  is a plan view of the base unit, conveyance roller, and platen of the recording apparatus, shown in  FIG. 6 , which have been attached to each other. 
       FIG. 8  is a perspective view of the recording unit, base unit, and main case unit of the recording apparatus in the first embodiment of the present invention, which have been attached to each other. 
       FIG. 9  is a perspective view of the recording unit, base unit, and main case unit of the recording apparatus shown in  FIG. 8 , with the main case unit separated from the other two. 
       FIG. 10  is a perspective view of the left end portion of the recording apparatus shown in  FIG. 1 , in which the carriage, which is holding the recording head and an ink container, is in its home position. 
       FIG. 11  is a perspective view of the recording gap adjustment mechanism of the recording unit of the recording apparatus shown in  FIG. 1 . 
       FIG. 12  is a perspective view of the recording performance recovery mechanism portion of the recording apparatus shown in  FIG. 1 , showing the structure thereof. 
       FIG. 13  is a perspective view of the driving system for driving the sheet conveyance mechanism and performance recovery mechanism of the recording apparatus in the first embodiment of the present invention. 
       FIG. 14  is a side view of a typical recording apparatus in accordance with the prior art. 
       FIG. 15  is a perspective view of the typical recording apparatus in accordance with the prior art. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, one of the preferred embodiments of the present invention will be described in detail with reference to the appended drawings. If the referential symbol of a given component in a drawing is identical to that of a component in another drawing, the two components are identical or correspondent to each other. The following embodiment of the present invention will be described with reference to a case in which the recording apparatus is an ink jet recording apparatus.  FIG. 1  is a perspective view of the recording unit, sheet feeding unit, and base unit of the recording apparatus in the preferred embodiment of the present invention, which have been attached to each other, and  FIG. 2  is a perspective view of the recording unit, sheet feeding unit, and base unit of the recording apparatus in the preferred embodiment of the present invention, which are separated from each other.  FIG. 3  is a side view of the recording apparatus in the preferred embodiment of the present invention, and  FIG. 4  is a perspective view of the base unit and sheet feeding unit of the recording apparatus in the preferred embodiment, which have been attached to each other, as seen from the rear side of the apparatus.  FIG. 5  is a perspective view of the base unit and sheet feeding unit shown in  FIG. 4 , which have been attached to each other, as seen from the front side of the apparatus.  FIG. 6  is a perspective view of the base unit, conveyance roller, and platen of the recording apparatus in the preferred embodiment of the present invention, which have been attached to each other.  FIG. 7  is a plan view of the base unit, conveyance roller, and platen shown in  FIG. 6 , which have been attached to each other. 
     FIG. 8  is a perspective view of the recording unit, base unit, and main case unit of the recording apparatus in the preferred embodiment of the present invention, which are attached to each other, and  FIG. 9  is a perspective view of the recording unit, base unit and main case unit of the recording apparatus, shown in  FIG. 8 , with the recording unit and base unit attached to each other, and the main case unit separated from the preceding two units.  FIG. 10  is a perspective view of the left end portion of the recording apparatus shown in  FIG. 1 , in which the carriage, which is holding the recording means and an ink container, is in its home position, and  FIG. 11  is a perspective view of the recording gap adjustment mechanism of the recording unit of the recording apparatus shown in  FIG. 1 .  FIG. 12  is a schematic perspective view of the recording performance recovery mechanism portion of the recording apparatus shown in  FIG. 1 , showing the structure thereof, and  FIG. 13  is a perspective view of the driving system for driving the sheet conveyance mechanism and performance recovery mechanism of the recording apparatus in the preferred embodiment of the present invention. 
   Referring to  FIGS. 1-13 , the recording apparatus in the preferred embodiment of the present invention essentially comprises a recording unit  20 , a base unit  21 , a sheet feeding unit  49 , and a main case unit  22 . These structural components are attached to each other, being thereby precisely positioned relative to each other, with the use of connective means such as small screws, and positioning means as shafts and holes for precisely positioning them relative to each other.  FIG. 1  shows the recording unit  20 , sheet feeding unit  49 , and base unit  21 , which have been attached to each other, whereas  FIG. 2  shows the recording unit  20 , and base unit  21 , which have been separated from each other.  FIG. 3  is a side view of the recording apparatus shown in  FIG. 2 , showing the structure thereof. In the following description of the preferred embodiment of the present invention, the portion of the recording apparatus having a sheet delivery tray  18  is referred to as front side, and the left side of the apparatus as seen from the front side will be referred to as left side of the apparatus. 
   Referring to  FIG. 2 , the recording unit  20  is provided with a chassis  1 , which is formed of a piece of plate, and has the rear wall portion, which is vertical. The chassis  1  has the top wall portion, left wall portion, and right wall portion, which perpendicularly extend frontward from the rear wall portion, giving the chassis  1  a boxy shape. The recording unit  20  is provided with a rail  50 , which is attached to one of the bottom edges of the chassis  1 , and is roughly L-shaped in cross section, being positioned so that its portion corresponding to the bottom stroke of L becomes horizontal. The rail  50  is solidly attached to the predetermined portion of the recording unit  20  with the use of small screws or the like, although it can be vertically moved by loosening the small screws or the like. The top edge portion of the chassis  1 , and the bottom side of the rail  50 , that is, the horizontal portion of the rail  50 , constitute the guide portions  4  and  51 , respectively, which guide the carriage  6 . More specifically, the carriage  6  is provided with engaging portions  52  and  53 , which are attached to the top and bottom ends of the carriage  6 , and engage with the guide portions  4  and  51 , respectively. Thus, the carriage  6  is supported by the guide portions  4  and  51 , so that the carriage  6  is allowed to slide on the guide portions  4  and  51  in both the right and left directions, with the engaging portions  52  and  53  remaining engaged with the guide portions  4  and  51 , respectively. 
   The carriage  6  is capable of holding the recording head  8  as a recording means. The distance (recording gap) between the surface of the recording head  8 , at which the ejection orifices open, and the recording surface of the recording medium, can be set to a desired value by moving the rail  50  in the direction roughly perpendicular to recording surface of the recording medium, so that the distance becomes the desired value, before tightening the aforementioned small screws or the like means for fastening the rail  50 . The smaller the recording gap, the more stable the relationship between a point of the recording surface of the recording medium, on which a given droplet of ink is expected to land, and the actual point on which the given droplet of ink lands, and therefore, the higher the level of quality at which recording is made. However, if the recording gap is smaller than a certain value, the recording head sometimes rubs against the recording medium, resulting in the formation of an image soiled with ink. In other words, it is necessary to control the recording gap in order to yield high quality images. 
   The rail  50  is movable by placing an unshown pair of eccentric cams as rail moving means in contact with the left and right cam follower portions  68  of the rail  50 . For example, as the pair of eccentric cams are rotated in the clockwise direction, the rail  50  is moved away from the recording surface of the recording medium, whereas as the pair of eccentric cams are rotated in the counterclockwise direction, the rail  50  is moved toward the recording surface of the recording medium. In other words, the rail  50  is vertically movable relative to the recording medium while remaining in the same position in terms of the direction parallel to the direction in which the carriage  6  is reciprocally movable. Incidentally, an experienced operator may be allowed to manually move the handhold portions  70  located at the left and right ends of the rail  50 , one for one, in order to adjust the recording gap. 
   To the carriage  6 , an endless driving belt  10  is connected, which is stretched around the pair of pulleys rotatably supported by their shafts, by the left and right end portions of the front side of the rear wall of the chassis  1 . The pulleys and driving belt  10  are toothed so that their teeth mesh with each other. The pulley on the right-hand side is kept pressured rightward so that the driving belt  10  will be provided with a predetermined amount of tension. The pulley on the left-hand side is solidly fixed to the output shaft of the carriage motor  104 . Thus, as the carriage motor  104  is driven, the driving force from the motor  104  is transmitted to the carriage  6  through the pulleys and driving belt  10 , causing the carriage  6  to reciprocally move. 
   On the left side of the left pulley, a belt stopper  32  is disposed, which surrounds the peripheral surface of the left pulley, with the presence of a predetermined distance between the peripheral surface of the left pulley and belt stopper  32 . The belt stopper  32  extends frontward from the chassis  1 , and prevents the jumping of the driving belt  10 , that is, the phenomenon (problem) that when the carriage  6  is overloaded, the teeth of the driving belt  10  are disengaged from the teeth of one or both of the pulleys in the radius direction of the pulleys, and slips. This belt stopper  32  is structured so that as the carriage  6  overruns leftward, the belt stopper  32  comes into contact with a part of the carriage  6 . In other words, the belt stopper  32  functions also as a stopper for preventing the carriage  6  from moving out of the predetermined primary scan range. 
     FIG. 10  is a perspective view of the right-hand end portion of the of the recording apparatus shown in  FIG. 1 , in which the carriage is in its home position. The recording head  8  is mounted on the carriage  6 . The recording head  8  has a plurality of electro-thermal transducing members as the elements for generating thermal energy, and a plurality of liquid passages (nozzles) which lead to the plurality of liquid ejection orifices, and in which the electro-thermal transducing elements are disposed one for one. Thus, as thermal energy is generated by the electro-thermal transducing element in any of the liquid passages, bubbles are generated in the liquid (liquid is boiled in the so-called film boiling fashion) in the liquid passage. As the bubbles grow and contract, the resultant changes in the internal pressure of the liquid passage causes the liquid in the liquid passage to eject through the liquid ejection orifices. 
   In this embodiment, the home position of the carriage  6  is located in the right-hand end of the recording apparatus. To the recording head  8 , a black (BK) ink container  9 BK, and a color (CL) ink container  9 CL are attached. The ink container which is farther from the recording area when the carriage  6  is in its home position is the black ink container  9 BK. 
   The recording head  8  is provided with a set of wires and connectors which are connected to the plurality of electro-thermal transducing elements, one for one. The wires are connected to the carriage  6  through these connectors, establishing thereby electrical connection between the recording head  8  and the main assembly of the recording apparatus. On the rear surface of the carriage  6 , a substrate  34 , which holds the circuit for controlling the operation of the recording head  8 , is attached, being connected to the main assembly of the recording apparatus through a flexible cable. 
   Disposed on the front surface of the rear wall  1 A of the chassis  1  is an encoder  7 , which is used, in combination with the sensor disposed on the substrate  34  of the carriage  6 , to detect the position of the carriage  6 . The signals which indicate the position of the carriage  6  detected as described above are used for controlling the movements of the carriage  6  and operation of the recording head  8 . The encoder  7  is kept pressured leftward. In the bottom portion of the chassis  1 , a pinch roller holder  13 , which rotatably supports a pinch roller  3  by the shaft of the pinch roller, by one end, is supported by the other end of the pinch roller holder  13 , by the chassis  1 . The pinch roller  13  is kept pressured downward. 
   The base unit  21  has a base member  19 . The surface of the recording apparatus, by which the recording apparatus is supported when the recording apparatus is normally position on a desk or the like, is the bottom surface of the base member  19 . On the rear edge portion of the base member  19 , the sheet feeding unit  49  is disposed, being precisely positioned relative to the main assembly of the recording apparatus. The sheet feeding unit  49  is provided with an ASF unit  54  as the primary sheet feeding unit, and a PF unit  55  as the secondary sheet feeding unit. The ASF unit  54  and PF unit  55  are precisely positioned relative to the main assembly by the pair of lateral plates of the chassis  1 , that is, the L lateral plate  56  and R lateral plate  57  of the chassis  1 , with the shafts engaged into the holes. Further, the shafts of the base member  19  are fitted one for one in the holes of the PF base  65  of the PF unit  55 , positioning thereby the sheet feeding unit  49  in parallel to the conveyance roller  2 . Here, that the sheet feeding unit  49  is parallel to the conveyance roller  2  means that the sheet feeding unit  49  is perpendicular to the recording medium conveyance direction. 
   To the left surface of the ASF unit  54  and the left surface of the PF unit  55 , the L lateral portion  56  of the chassis  1  is solidly attached with the use of small screws, being thereby precisely positioned relative to the PF base  65 . The ASF base  25  is precisely positioned relative to the L lateral portion  56  of the chassis  1 . The ASF base  25  is not solidly attached to the L lateral portion  56  (it is not attached with small screws). To the right surface of the ASF unit  54  and the right surface of the PF unit  55 , the R lateral portion  57  of the chassis  1  is solidly attached with the use of small screws, being thereby precisely positioned relative to the PF base  65 . The ASF base  25  is attached to the R lateral portion  57  of the chassis  1  also with the use of small screws. 
   Referring to  FIG. 4 , the bottom surface of the PF base  65  is provided with a hole  601  and an elongated hole  602 , which are used for precisely positioning the PF base  65  relative to the base  19 . Next, referring to  FIG. 5 , the base  19  is provided with bosses  603  and  604 , which are positioned so that the straight line B connecting the centers of the two bosses  603  and  604  becomes perpendicular to the recording medium conveyance direction. Referring to  FIG. 7 , the level of parallelism between the straight line B which coincides with the centers of the bosses  603  and  604  (axial line of PF base  65 ), and the axial line G of the conveyance roller  2 , which will be described later, is controlled to be no more than 0.1 degrees. Referring again to  FIGS. 4 and 5 , a first intermediate roller  58 , a second intermediate roller  605 , and a PF roller  64  are rotatably supported by their shafts, by the PF base  65 . The level of parallelism between the axial line B of the PF base  65  and the axial line N of the second intermediate roller  605 , the level of parallelism between the axial line N of the second intermediate roller  605  and the axial line D of the first intermediate roller  58 , and the level of parallelism between the axial line N of the second intermediate roller  605  and the axial line E of the PF roller  64 , are controlled to be no more than 0.1 degrees. 
   The level of perpendicularity of the rotational axis of the PF base  65  relative to the recording medium conveyance direction, and the level of perpendicularity of the rotational axis of the ASF base  25  relative to the recording medium conveyance direction, are controlled with the use of the L and R lateral portions  56  and  57 , respectively, of the chassis  1 . The level of parallelism between the rotational axis B of the PF base  65  and the axial line F of an ASF roller  28  supported by its shaft and the ASF base  25 , is controlled to fall within a predetermined range. The ASF unit  54  is provided with an ASF pressure plate  26  and ASF tray  27 , which are disposed so that they extend up and rearward. Against the combination of the ASF pressure plate  26  and ASF tray  27 , a plurality of recording mediums  24  are rested in layers. The ASF pressure plate  26  is attached to the ASF base  25  so that the ASF pressure plate  26  can be pivoted about the top edge portion of the ASF pressure plate  26 . The bottom edge portion of the ASF pressure plate  26  is kept pressured frontward (clockwise direction in  FIG. 3 ) by unshown springs. 
   The first feed roller  28  is (ASF roller) positioned so that the bottom portions of the recording mediums  24  resting against the ASF pressure plate  26  are pressed against the first feed roller  28  by the ASF pressure plate  26 , which is kept pressured by the unshown springs as described above. The ASF roller  28  is supported by the lengthwise ends of its shaft, by the first base  25  (ASF base). The ASF roller  28  is provided with an ASF roller gear  30  ( FIG. 2 ), which is attached to one of the lengthwise ends of the shafts of the ASF roller  28 . The ASF roller gear  30  is connected to the rotational shaft of the first intermediate roller  58  (which will be described later), with the interposition of gears or the like, and is rotationally driven by the PF motor  59  for driving the first intermediate roller  58 . An ASF separation roller  29  ( FIG. 3 ) is positioned so that it opposes the ASF roller  28 , being kept pressured upon the ASF roller  28  by unshown pressure generating means. 
   As a recording operation is started, the ASF roller  28  is rotationally driven to convey the recording medium  24 . The ASF portion is structured so that the ASF pressure roller  26  is moved, in coordination with the rotation of the ASF roller  28 , by the unshown control cam (unshown) supported by its shaft and the ASF base  25 . With the provision of this structural arrangement, when it is the time to feed the main assembly of the recording apparatus with the recording medium  24 , the ASF pressure plate  26  is moved to press the recording medium  24  upon the ASF roller  28 , whereas when it is unnecessary to feed the main assembly with the recording medium  24 , the ASF pressure plate  26  is pivoted against the pressure from the abovementioned springs so that the bottom portion thereof will be moved rearward, away from the recording medium  24  (it is moved back into standby position). Thus, when the ASF pressure plate  26  is in the standby position, the recording medium  24  can be easily placed on, or removed from, the ASF pressure plate  26 . When the recording medium  24  is in the ASF tray  27 , the leading edge of the recording medium  24  remains in contact with the ribs with which the ASF base  25  is provided. 
   Regarding the function of the ASF separation roller  29 , if a plurality of recording mediums  24  happen to enter the nip between the ASF separation roller  29  and ASF roller  28  while the recording mediums  24  are fed into the main assembly of the image forming apparatus, the ASF separation roller  29  prevents the recording mediums  24  on the ASF separation roller side from advancing further into the main assembly. With the employment of this structural arrangement, the recording mediums  24  are fed into the main assembly while being separated one by one. The ASF base  25 , ASF pressure plate  26 , ASF roller  28 , ASF separation roller  29 , etc., make up the ASF unit  54  as the first sheet feeding unit. 
   Next, referring primarily to  FIG. 3 , the PF unit  55  as the second sheet feeding unit will be described. To the base unit  21 , the PF pressure plate  61  and PF tray  62  are attached, being thereby positioned roughly parallel to the bottom surface of the base unit  21 . It is on the combination of the PF pressure plate  61  and PF feeder tray  62  that a plurality of recording mediums  63  are placed. The PF pressure plate  61  is attached to the base  19 , being enabled to pivot about the front edge portion of the PF pressure plate  61 , with the rear end portion of the PF pressure plate  61  being kept pressured upward (counterclockwise direction in  FIG. 3 ) by the unshown springs. The PF roller  64  as the second sheet feeding roller is positioned so that the leading edge portion of the top recording medium  63  in the PF feeder tray  62  is pressed on the PF roller  64  by the PF pressure plate  61 , which is kept pivotally pressured as described above. 
   The PF roller  64  is supported at the lengthwise ends of its shaft, by the second base  65  (PF base). The PF roller  64  is provided with a PF roller gear  66 , which is attached to one of the lengthwise ends of the shafts of the PF roller  64 . The PF roller gear  66  is connected to the rotational shaft of the first intermediate roller  58  located downstream of the PF roller  64  in terms of the recording medium conveyance direction, with the interposition of gears or the like, and is rotationally driven by the PF motor  59  for driving the first intermediate roller  58 . On the downstream side of the first intermediate roller  58  in terms of the recording medium conveyance direction, the second intermediate roller  605  is disposed. Within the PF unit  55 , a U-turn conveyance passage is provided, which not only places the recording medium  63  upside down, but also, reverses the recording medium  63  in terms of the conveyance direction. 
   The PF unit is provided with a PF separation roller  67 , which is disposed in a manner to oppose the PF roller  64 . The PF separation roller  67  is kept pressed upon the PF roller  64  by the unshown pressing means. As a recording operation is started, the PF roller is rotationally driven, conveying thereby the recording medium  63 . The PF pressure plate  61  is supported by its shaft and the PF base  65 , and its pivotal movement is controlled by the unshown control cam in coordination with the rotation of the PF roller  64 . With the provision of this structural arrangement, when it is necessary for the recording medium  63  to be fed, the PF pressure plate  61  is caused to press the recording medium  63  upon the PF roller  64 , whereas when it is unnecessary for the PF pressure plate  61  to press the recording medium  64 , the PF pressure plate  61  is pivoted against the pressure from the abovementioned springs so that its bottom portion is moved downward (the PF pressure plate  61  is pushed back into the standby position). 
   Thus, when the PF pressure plate  61  is in the standby position, the recording medium  63  can be easily placed on, or removed from, the PF pressure plate  61 . When the recording medium  63  is in the PF tray  62 , its leading edge remains in contact with the ribs with which the PF base  65  is provided. If a plurality of recording mediums  63  happen to enter the nip between the PF separation roller  67  and PF roller  64  while the recording mediums  24  are fed into the main assembly of the image forming apparatus, the PF separation roller  67  prevents the recording mediums  63  on the PF separation roller side from advancing further into the main assembly. The PF base  65 , PF roller  64 , PF pressure plate  61 , PF separation roller  67 , first and second intermediate rollers  58  and  608 , respectively, etc., make up the PF unit  55  as the second sheet feeding unit. 
   The conveyance roller  2  is positioned so that, as the recording medium  24  or  63  is fed into the main assembly of the recording apparatus by the ASF unit  54  or PF unit  55 , respectively, the leading edge of the recording medium  24  or  63  reaches the conveyance roller  2 . The conveyance roller  2  is rotatably supported by its shaft, and the LF chassis  60 , one end of which is supported by its shaft and the base  19 , and the other end of which is solidly fixed to the base  19 , being thereby precisely positioned relative to the base  19 . The conveyance roller  2  is provided with an LF gear  36 , which is attached to one of the lengthwise ends of the conveyance roller  2 . The conveyance roller  2  is rotationally driven by an LF motor  35  (conveyance motor), through this LF gear  36 . The conveyance roller  2  is supported by the LF chassis  60 , which is precisely positioned relative to the base unit  21  in order to ensure the abovementioned structural components are positioned in parallel, and the portions of the LF chassis  60 , which support the conveyance roller  2 , the portions of the LF chassis  60 , to which the base unit  21  is attached, and the portions of the base unit  21 , which support the conveyance roller  2 , are aligned in the direction perpendicular to the recording conveyance direction. 
   The pinch roller  3  attached to the bottom edge portion of the chassis  1  is placed in contact with the conveyance roller  2 . After the recording medium  24  or  63  is fed into the main assembly of the recording apparatus, its leading edge portion is pinched between the conveyance roller  2  and pinch roller  3 . In the main assembly, the recording head  8  is on the reciprocally movable carriage  6 , and the platen  16  is disposed so that it directly faces the surface of the recording head  8 , at which the ejection orifices open. On the downstream side of the platen  16 , the sheet discharging roller  11  is disposed. The sheet discharging roller  11  is rotatably supported by the platen  16  and LF chassis  60 ; one end of the shaft of the sheet discharging roller  11  is supported by the platen  16 , and the other end is supported by the LF chassis  60 . Referring to  FIGS. 8 and 9 , the rowel-like wheel  14  kept pressed on the sheet discharging roller  11  is supported by its shaft and the main case unit  22 . 
   The sheet discharging roller  11 , the one end of which is supported by the LF chassis  60 , and the other end of which is supported by the platen  16 , is connected to the shaft of the conveyance roller  2 , with the interposition of the idler gear  23  ( FIG. 2 ), and is rotationally driven by the rotation of the conveyance roller  2 . The unshown mechanical power source for driving the conveyance roller  2 , idler gear  23 , and sheet discharging roller  11  is precisely supported by the LF chassis  60 , which is one of the lateral portions of a single piece of plate. This unshown mechanical power source is a part of the conveyance chassis unit. The above described structural arrangement contributes to the improvement of the level of accuracy at which the recording mediums are conveyed. 
   The platen  16  is provided with a sheet pressing plate  606  for preventing the portion of the recording medium located next to the referential portion for aligning (precisely positioning) the recording mediums, from rising away from the platen  16 . The sheet pressing plate  606  is roughly L-shaped in cross section, and is attached to one of the lateral walls of the platen  16 , which is perpendicular to the sheet pressing surface of the sheet pressing plate  606 . The sheet pressing plate  606  is precisely positioned by being attached to the lateral wall of the platen  16 . The sheet pressing plate  606  is desired to be formed of elastic substance for the following reason. That is, if a recording medium jams the recording apparatus, or the like incidence occurs, a user sometimes forcefully lifts the sheet pressing portion of the sheet pressing plate  606 , causing thereby the sheet pressing plate  606  to bend, in order to remove the recording medium. However, with the sheet pressing member  606  formed of elastic substance, it restores itself into the original shape and position. With the sheet pressing plate  606  precisely positioned relative to the lateral portion of the platen  16  as described above, a sufficient amount of distance is secured for providing the actual pressing portion of the sheet pressing plate  606  with a proper amount of elasticity. 
   After being pinched by the peripheral surface of the sheet discharging roller  11  and the toothed portion of the rowel-like wheel  14 , the recording medium is discharged from the main assembly of the recording apparatus by the rotation of the sheet discharging roller  11 . The recording apparatus is provided with the sheet delivery tray  18 , which is attached to the base  19 . The base unit  21  is provided with a recovery mechanism  15  for maintaining at a predetermined level the performance of the recording head  8  in terms of ink ejection. This recording head performance recovery mechanism  15  is located below the home position of the carriage  6 . 
   Referring to  FIG. 12 , the recording head performance recovery mechanism  15  is provided with a cap slider  123 , the movement of which is tied to the movement of the carriage  6 . To the cap slider  123 , a cap holder  122  is attached, by which caps  112  and  113  are held so that their openings face upward. The caps  112  and  113  are molded of rubber-like elastic substance. Also to the cap slider  123 , a pair of wipers  118  and  119  for wiping the surface of the recording head  8  having the ejection orifices are attached so that they are raised upward from the cap slider  123 . The substance of which the blades of the wipers  118  and  119  are molded is also a rubber-like substance. 
   The cap slider  123  is kept pressed down and leftward of the drawing, by an unshown pressing means to assure that the cap slider  123  comes into contact with the functional surface of each of the four cam portions  124 , which are differentiated in lift in gradual steps so that the right-hand most cam portion  124  is highest in lift. The right-hand end of the cap slider  123  is provided with a bump  125 , with which the carriage  6  comes into contact as the carriage  6  is moved into the home position. Thus, as the carriage  6  is moved rightward to be moved into the home position, the cap slider  123  is also moved rightward because its movement is tied to the movement of the carriage  6 . During this movement of the carriage  6 , the cap slider  123  is moved upward by the movement of the carriage  6  while sliding the functional surface of each of the cam portions  124 . Also with this movement of the carriage  6 , the surface of the recording head  8  at which the ejection orifices open is wiped by the wipers  118  and  119 . 
   The wiper  118 , the one on the left side, is for the recording head surface having the ejection orifices for color inks, and the wiper  119 , the one on the right-hand side, is for the recording head surface having the ejection orifices for black ink. In other words, the wipers  118  and  119  are attached to the cap slider  123  so that they are precisely positioned to wipe the adjacencies of the column(s) of the black ink ejecting orifices and the columns of color ink ejecting orifices of the recording head  8  as the cap slider  123  is moved. That is, the above described structural arrangement ensures that the wipers  118  and  119  come into contact with the recording head surface having the ejection orifices, so that the wipers  118  and  119  contact the recording head surface having the ejection orifices, by a predetermined amount, in terms of the apparent amount by which the wipers  118  and  119  enter the recording head surface having the ejection orifices, at a predetermined angle, and with a predetermined amount of contact pressure. 
   As the carriage  6  is moved into the home position, the caps  112  and  113  are placed in contact with the surface of the recording head  8  having the ejection orifices, covering thereby the ejection orifices. Regarding this covering of the ejection orifices by the caps  112  and  113 , the cap slider  123  is pivotally supported by the cap holder  122 , and also, is kept pressured upward, being thereby allowed to pivot within a predetermined range, to ensure that the caps  112  and  113  evenly and airtightly contact the surface of the recording head  8  having the ejection orifices. The cap  112 , the one on the left side, is for the cap for covering the ejection orifices for color inks, and the cap  113 , the one on the right side, is for covering the ejection orifices for black ink. The caps  112  and  113  are connected to a negative pressure generating means such as a vacuum pump through a tube or the like. 
   The main case unit  22  ( FIGS. 8 and 9 ) is provided with a main case  33  which covers the above described recording unit  20  and base unit  21 , from the top and lateral directions. The main case  33  is removably attached to the recording unit and base unit with the use of small screws or the like. The aforementioned rowel-like wheel  14  is supported by its axle and the main case  33 , being positioned so that as the main case  33  is attached to the recording unit and base unit, it opposes the sheet discharging roller  11 . The rowel-like wheel  14  is kept pressed on the sheet discharging roller  11  by an unshown pressing means. 
   The main case  33  is immovably attached to the base  19  with the use of hooks and small screws. Further, the adjacencies of the right-hand end  613  ( FIG. 9 ) of the guide portion  4  (rail portion, that is, top edge portion of chasses  1 ) is sandwiched by the ribs of the main case  33 , with the presence of a certain amount of play, in terms of the recording medium conveyance direction, being thereby restricted in width. This play is desired to be roughly 0.5 mm. Referring to  FIGS. 9 and 11 , the left end portion of the chassis  1  is bent rearward, and the top portion of this rearwardly bent portion is inwardly bent and provided with two round holes  612 , which correspond in position to the two bosses with which the main case  33  is provided. The relationship in terms of size between the round holes  612  and bosses of the main case  33  are set so that a certain amount of play is provided between the main case  33  and chassis  1 , in terms of the direction parallel to the surface having the holes  612  (surface having bosses). This play is desired to be roughly 0.5 mm. 
   The top end portion of the R lateral portion  57  of the chassis  1 , which is located at the right end portion of the sheet feeding unit  49  located in the rear portion of the chassis  1  is bent inward, and provided with two round holes  614  ( FIG. 9 ), which correspond in position to the two bosses with which the main case  33  is provided. The relationship in terms of size between the round holes  614  and corresponding bosses of the main case  33  are set so that a certain amount of play is provided between the main case  33  and chassis  1 , in terms of the direction parallel to the surface having the holes  614  (surface having bosses). This play is desired to be roughly 0.5 mm. The main case  33  is immovably attached to the base  19 , while providing a certain amount of play between the chassis  1  of the recording unit  20  and the R lateral portion  57  of the sheet feeding unit  59 . Therefore, the recording apparatus in this embodiment is substantially greater in the overall rigidity than a recording apparatus in accordance with the prior art. 
   As for the usage of the ink jet recording apparatus in this embodiment, this recording apparatus is connected to a host computer, for example, to record images by receiving recording commands and image formation data from the host computer. As a recording command is received, the plurality of recording mediums  24  in the ASF tray  27  are fed into the main assembly of the ink jet recording apparatus while being separated one by one, by the ASF unit  54 . Then, each recording medium  24  is conveyed by the conveyance roller  2  to the predetermined recording position. Then, the carriage  6  is reciprocally moved, while the recording head  8  is driven according to the image formation data (ink is ejected from ejection orifices selected according to image formation data). As a result, an image is formed on the recording medium. 
   When no image is formed, the carriage  6  is moved into the home position, and kept therein. During this movement of the carriage  6  into the home position, the surface of the recording head having the ejection orifices is wiped by the wipers  118  and  119 . As a result, the ink and debris having adhered to the recording head surface having the ejection orifices are removed. Further, the ejection orifices of the recording head  8  are capped with the caps  112  and  113 , preventing thereby the bodies of ink in the ejection orifices from evaporating or increasing in viscosity due to the evaporation of liquid components therefrom. Further, a pumping unit  120  is driven as necessary, with the ejection orifices capped with the caps  112  and  113 . As a result, the ink is suctioned out of the ejection orifices, removing thereby the body of ink having increased in viscosity, residual bubbles, debris, etc. 
   In the recording apparatus in this embodiment of the present invention described above, the recording unit  20 , conveyance roller  2 , platen  16 , sheet feeding unit  49  (first and second sheet feeding units  54  and  55 ) are precisely positioned relative to the base unit  21  and fixed thereto, being thereby supported by the base unit  21 , so that they are disposed relative to each other at a high level of parallelism. Thus, the amount of load borne by the chassis of this recording apparatus is substantially smaller than the amount of load borne by the chassis of a recording apparatus in accordance with the prior art, in which the conveyance unit, recording unit, and sheet feeding unit are supported by the chassis. Further, the recording apparatus in this embodiment is substantially stronger and more rigid, in spite of being less expensive, being therefore capable of always yielding images of higher quality, than a recording apparatus in accordance with the prior art. 
   Also in this embodiment described above, the recording apparatus is structured so that the sheet feeding unit  49  is provided with the first sheet feeding unit which conveys the recording medium  24  to the recording unit  20  from the rear side of the recording unit  20 , and the second sheet feeding unit which conveys the recording medium  63  to the recording unit  20  from the bottom side of the recording unit  20  through the U-turn sheet passage. With the employment of this structural arrangement, the recording unit  20 , conveyance roller  2 , first sheet feeding unit  54 , and second sheet feeding unit  55  can all be precisely positioned to the base unit  21 , and be fixed thereto, making it possible to substantially reduce the amount of load borne by the chassis, compared to a recording apparatus structured in accordance with the prior art, in which the platen unit, recording unit, sheet feeding unit are supported by the chassis. 
   In other words, according to this embodiment of the present invention, the recording apparatus is provided with a base which is capable of precisely supporting each of the units, which make up the recording apparatus, while being simple in structure and inexpensive. Therefore, each unit of the recording apparatus is made to precisely operate, and therefore, the image forming apparatus is enabled to form image at a high level of precision. This kind of characteristic is one of the most important characteristics, in technical terms, required of an ink jet recording apparatus which forms images by ejecting ink onto recording medium from its recording head(s). In other words, while the present invention is applicable to recording apparatuses of various types, it is most remarkable when applied to an ink jet recording apparatus in order to solve the above described technical problems of various recording apparatuses. 
   Further, not only is the present invention applicable to a monochromatic recording apparatus, but also, a color recording apparatus which records color images with the use of a plurality of inks different in color and a single or plurality of recording heads, a recording apparatus capable of recording images with the use of a plurality of inks identical in color, but different in density, and a single or plurality of recording heads, and combination of the preceding recording apparatuses. 
   According to the present invention, it is possible to improve a recording apparatus in terms of the level of quality at which it produces images, by precisely positioning and supporting each of the structural components of the recording apparatus. Further, it is possible to reduce the amount of the load borne by the chassis, making it possible to provide a recording apparatus substantially lower in cost than a recording apparatus in accordance with the prior art. 
   While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
   This application claims priority from Japanese Patent Application No. 174967/2004 filed Jun. 14, 2004 which is hereby incorporated by reference.