Patent Publication Number: US-6986574-B2

Title: Recording apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a recording apparatus for recording a character, an image, and/or the like by discharging ink onto a recording medium such as a recording sheet, and more particularly, it relates to a recording apparatus including guide members for guiding a recording medium to a discharge roller. 
   2. Description of the Related Art 
   Commercially available recording apparatuses performing a recording operation on a recording medium such as a recording sheet or a sheet for an overhead projector (OHP) have a variety of recording heads mounted thereon, including those of a wire dot type, a thermal type, a thermal transfer type, and an inkjet type. In particular, a recording head of an inkjet type is known as a recording component whose operational cost is inexpensive and which operates with a relatively low noise level since it directly discharges ink onto a recording medium. 
     FIG. 20  is a perspective view of a known inkjet printer (hereinafter, referred to simply as a printer). For the sake of easy understanding, a part of an outer casing of the printer is omitted. Also,  FIG. 21  is a sectional view of the known printer, while a part thereof unnecessary for explanation is omitted. 
   As shown in  FIGS. 20 and 21 , the known printer includes a recording unit  100 , including a carriage  101  having a recording head mounted thereon, for recording an image and/or the like on a recording medium; an automatic feed unit  102  for feeding a recording medium; a transport unit  103  for transporting the recording medium to the recording unit  100  in the arrow T direction indicated in  FIGS. 20 and 21 ; and a discharge unit  105  for discharging the recording medium having a recording operation performed thereon by the recording unit  100 . 
   When the printer receives a recording signal, a plurality of recording media stacked in the automatic feed unit  102  are individually separated by separation means (not shown) and are transported sheet by sheet. 
   At the transport unit  103 , a recording medium is transported by a transport roller  106  and a transport pinch roller  107 . When the transport unit  103  transports a recording medium by a length corresponding to a recording width of the recording head, the printer causes the carriage  101  to sweep and sequentially performs a recording operation on the recording surface of the recording medium by driving and controlling the recording head in accordance with a recording signal. The recording unit has a platen for guiding the other side of the recording surface of the recording medium. After completion of the recording operation, the recording medium is transported to the discharge unit  105 . 
   As shown in  FIG. 21 , the transport unit  103  includes the transport roller  106  and the transport pinch roller  107 . The transport roller  106  has a coating material containing ceramic particles applied on the surface thereof and transports a recording medium with a friction generated between the recording medium and the transport roller  106  by pressing the recording medium with the transport pinch roller  107 . The transport roller  106  has a platen  112  disposed downstream therefrom for guiding a part of the recording medium facing the recording head mounted on the carriage  101 . 
   The platen  112  has a set of a first discharge roller  108  and a first discharge pinch roller  109  and a set of a second discharge roller  110  and a second discharge pinch roller  111 , all disposed in the downstream region thereof along the arrow T direction serving as a transport direction of the recording medium. The transport surface of each of the first and second discharge rollers  108  and  110  is composed of a high-friction material such as rubber having a relatively large coefficient of friction. The first and second discharge pinch rollers  109  and  111  are disposed so as to be pressed towards the first and second discharge rollers  108  and  110 , respectively. 
     FIG. 22  is a partial sectional view of the printer, illustrating a state in which a recording medium  113  is traveling in the vicinity of the first discharge roller  108 . A relative position between the platen  112  and the first discharge roller  108  in the height or vertical direction is set such that the top part of the peripheral surface of the first discharge roller  108  lies slightly higher than the recording-medium guiding-surface of the platen  112 . When the platen  112  lies higher than the top part of the first discharge roller  108 , a pressing force of the first discharge pinch roller  109  decreases due to elasticity of a recording medium, thereby deteriorating a discharge performance. Since the relative position between the platen  112  and the first discharge roller  108  in the height direction is set such that the top part of the peripheral surface of the first discharge roller  108  lies slightly higher than the recording-medium guiding-surface of the platen  112 , the recording medium  113  guided by the platen  112  abuts first against the first discharge roller  108 . 
   The transport speed of the first discharge roller  108  is arranged so as to rotate at nearly the same speed as that of the transport roller  106 . When the transport speed of the first discharge roller  108  is lower than that of the transport roller  106 , a recording sheet is sometimes deformed at the recording unit. As a countermeasure against this problem, taking tolerances and other characteristics of the discharge roller and the transport roller into account, in general, the former is often designed so as to rotate slightly higher than the latter. Here, the circumferential speed of the peripheral surface of the first discharge roller  108  is defined as VA. As shown in  FIG. 22 , when the leading edge of the recording medium  113  abuts against the first discharge roller  108 , the speed of the recording medium  113  in the horizontal transport direction becomes VB, thereby resulting in being slightly lower than the original design speed VA. 
   Hence, during a transitional period of the leading edge of the recording medium  113  being introduced to the first discharge roller  108 , the traveling speed of the recording medium  113  is sometimes slightly altered. 
   Since the recording head of an inkjet type is used performing a recording operation by ejecting ink droplets onto the recording surface of a recording medium, the recording operation is performed in a non-contact state between the recording medium and the recording head. A decrease in speed of an ink droplet due to an air drag and the like during ejection toward the recording medium sometimes causes the ink droplet to fly in a different direction from the originally designed one. In order to solve this problem, it is preferable that the recording medium and the recording head lie close to each other, and hence the distance therebetween is generally set in the range from 0.5 mm to 1.5 mm. 
   Meanwhile, a variety of recording media including from a sheet of relatively thin normal paper to a relatively thick envelope are used. When a relatively thick recording medium is used, it is expected that the recording head and the recording medium come into contact with each other. In order to avoid such a contact, many printers have a structure in which an operator can adjust the distance between the platen for supporting the recording medium and the recording head in accordance with the thickness of a recording medium. A carriage moving method and a platen moving method are known methods for adjusting the distance between the platen and the recording head. 
   As shown in  FIG. 22 , when the platen moving method is employed, since the abutment position between the leading edge of the recording medium  113  and the first discharge roller  108  lies below the top of the peripheral surface of the first discharge roller  108 , the speed VB of the recording medium becomes lower than VA, thereby leading to an increase in so-called printing irregularity. 
   SUMMARY OF THE INVENTION 
   The present invention can provide a recording apparatus having a relatively simple structure for easily, reliably, and stably transporting a recording medium toward a discharge roller. 
   A recording apparatus according to the present invention can include a recording head performing a recording operation by discharging ink; a platen for guiding the recording medium, disposed so as to face the recording head; a discharge roller for discharging the recording medium, disposed downstream of the platen and comprising at least two first roller portions and at least one second roller portion having a smaller diameter than the first roller portions; and at least two discharge guides for guiding the recording medium from the platen to the discharge roller. One end of each of the discharge guides is rotatably supported by the platen, and the other end thereof abuts against the second roller portion of the discharge roller. 
   The recording apparatus having the above structure according to the present invention can be equipped with the guide members, each having one end rotatably supported by the platen and the other end abutting against the second roller portion of the discharge roller, thereby eliminating so-called recording irregularity occurring upon abutment of the recording medium against the first roller portions of the discharge roller and thus achieving an accurate recording operation without decreasing the transport capacity of the discharge roller. Accordingly, the recording apparatus according to the present invention has a simple structure and also easily, reliably, and stably guides and transports a recording medium from the platen toward the discharge roller. 
   Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an inkjet printer housed in an outer casing, according to an embodiment of the present invention. 
       FIG. 2  is a perspective view of the printer, illustrating an operational state thereof. 
       FIG. 3  is a perspective view of the internal structure of the printer. 
       FIG. 4  is a perspective view of a platen and other components in the vicinity thereof. 
       FIG. 5  is a partial perspective view of the printer, illustrating a state in which the platen is being fixed to a chassis. 
       FIG. 6  is a partial perspective view of the printer, illustrating a sheet-distance adjusting method by rotating the platen. 
       FIG. 7  is a perspective view of a sheet-distance adjusting lever. 
       FIG. 8  is a partial side view of the printer, illustrating a detailed operation of the platen with the sheet-distance adjusting lever. 
       FIG. 9  is a partial side view of the printer, illustrating the detailed operation of the platen with the sheet-distance adjusting lever. 
       FIG. 10  is a partial side view of the printer, illustrating the detailed operation of the platen with the sheet-distance adjusting lever. 
       FIG. 11  is a partial side view of the printer, illustrating the detailed operation of the platen with the sheet-distance adjusting lever. 
       FIG. 12  is a perspective view of the platen. 
       FIG. 13  is a perspective view of a leaf spring and an ink absorber. 
       FIG. 14  is a partial perspective view of the printer, illustrating an operation of discharge guides. 
       FIG. 15  is a partial sectional view of the printer, illustrating the operation of one of the discharge guides. 
       FIG. 16  is a partial perspective view of the printer, illustrating the operation of the discharge guides. 
       FIG. 17  is a partial sectional view of the printer, illustrating the operation of one of the discharge guides. 
       FIG. 18  is a partial sectional view of the printer, illustrating the operation of the discharge guide. 
       FIG. 19  is a partial sectional view of the printer, illustrating the operation of the discharge guide. 
       FIG. 20  is a perspective view of a known inkjet printer. 
       FIG. 21  is a sectional view of the known inkjet printer. 
       FIG. 22  is a partial sectional view of the known inkjet printer, illustrating a discharge roller and other components in the vicinity thereof. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of the present invention will be described with reference to the attached drawings. 
     FIG. 1  is a perspective view of an inkjet printer according to the present embodiment, illustrating a non-operational state in which it is housed in an outer casing or being carried, for example. 
   As shown in  FIG. 1 , an inkjet printer  1  (hereinafter, referred to simply as a printer  1 ) includes an upper cover  2  and a discharge cover  3 , both serving as a part of the outer casing. 
     FIG. 2  illustrates an operational state of the printer  1 . As shown in  FIG. 2 , the printer  1  further includes a feed inlet  5  and an operation panel  4 , which become usable by lifting the upper cover  2 , and also includes a discharge outlet  6 , which becomes usable as well by lowering the discharge cover  3 . 
     FIG. 3  is a perspective view of the printer  1  from which the outer casing is removed for illustrating the internal structure thereof.  FIG. 15  is a partial sectional view of the printer  1 . The feed inlet  5  has an automatic feed unit for feeding a recording medium disposed therein so as to individually separate stacked recording media and transport them sheet by sheet to a recording unit. A transport roller  8  (transporting means) has a coating material containing ceramic particles applied on the peripheral surface thereof for transporting a recording medium. The transport roller  8  has a plurality of transport pinch rollers  9  disposed so as to be pressed toward the transport roller  8  by springs (not shown). Since pressing forces of the transport pinch rollers  9  cause the transport roller  8  and a recording medium to have a friction produced therebetween, the printer  1  transports the recording medium in the arrow A direction indicated in  FIG. 3  by rotating the transport roller  8 . Although not shown in the figure, the transport roller  8  is driven to rotate by a transport motor via a line-feed (LF) gear train. While being guided by a platen  11 , when the recording medium is transported to a position where it faces an inkjet recording head, it is temporarily halted there. 
   The inkjet recording head (hereinafter, referred to simply as recording head) is mounted on a carriage (holding means)  7 . The carriage  7  is supported so as to be movable along a guide shaft  12  and a guide rail  13 , both built in a chassis  16 , in main sweeping or scanning directions shown by the arrows B 1  and B 2  indicated in  FIG. 3  and is constrained by the guide rail  13  so as not to rotate about the guide shaft  12 . In other words, the carriage  7  is guided by the guide shaft  12  and the guide rail  13  and is driven by a transfer motor (not shown) in the main sweeping directions. 
   The printer  1  causes the carriage  7  to sweep in accordance with a recording signal so as to perform a recording operation on a recording medium. The transport roller  8  is rotated by a certain angular amount for every performance of a recording operation, and again the printer  1  causes the carriage  7  to sweep in accordance with another recording signal so as to perform another recording operation on the recording medium. This operation is repeated one after another so as to perform plural recording operations on the recording medium. After the recording operations are finished, the recording medium is discharged outside the mechanical body of the printer  1  by a discharge roller (transport roller)  10  and a discharge pinch roller  21 . 
     FIG. 4  is a perspective view of the platen  11  and other components in the vicinity thereof.  FIG. 5  is a partial perspective view of the printer  1 , illustrating a state in which the platen  11  is being fixed to the chassis  16 . 
   The platen  11  is journaled to the chassis  16  at two points thereof and has a plurality of discharge guides (guide members)  17  rotatably fixed thereto for guiding a recording medium from the platen  11  to the discharge roller  10 . 
   As shown in  FIGS. 4 and 5 , the platen  11  has shaft portions  11   a  and  11   b  integrally formed therewith, which are inserted into and rotatably supported by support holes  16   a  and  16   b  of the chassis  16 , respectively. The platen  11  also has an elastically deformable portion  11   c  integrally formed therewith, which is elastically deformable when the shaft portion  11   a  of the platen  11  is inserted into the support hole  16   a  of the chassis  16 . 
   The platen  11  is formed of a resin material such as an acrylonitrile-butadiene-styrene (ABS) plastic, and the elastically deformable portion  11   c  is formed so as to have example dimensions of about 2 mm thick, 7 mm wide, and 20 mm long. When the platen  11  is to be assembled into the chassis  16 , the shaft portion  11   a  of the platen  11  is inserted into the support hole  16   a  of the chassis  16  by elastically deforming the elastically deformable portion  11   c  and is then released from the elastic deformation. Thus, the platen  11  is rotatably fixed to the chassis  16  via the shaft portions  11   a  and  11   b.    
   The platen  11  further has bosses  11   d  and  11   e  disposed thereon so as to face the guide rail  13 , for regulating its rotation about the shaft portions  11   a  and  11   b , respectively. Accordingly, the platen  11  is rotatable between a first position where the bosses  11   d  and  11   e  abut against the guide rail  13  and a second position where the bosses  11   d  and  11   e  lie remote from the guide rail  13 . 
   An adjusting method for adjusting the distance between a recording medium and the recording head by rotating the platen  11  having the above-mentioned structure between the first and second positions will be described with reference to  FIG. 6  illustrating a partial perspective view of the printer  1 . 
   Since the recording head is used for performing a recording operation by ejecting ink droplets onto the recording surface of the recording medium, the recording operation is performed in a non-contact state between the recording medium and the recording head. A decrease in speed of an ink droplet due to air drag and the like during ejection toward the recording medium sometimes causes the ink droplet to fly in a different direction from the originally designed direction. In order to solve this problem, it is preferable that the recording medium and the recording head lie close to each other, and hence the distance therebetween is generally set in the range from 0.5 mm to 1.5 mm. 
   Meanwhile, a variety of recording media, ranging from relatively thin normal paper to relatively thick envelopes, is used. When a relatively thick recording medium is used, it is expected that the recording head and the recording medium come into contact with each other. In order to avoid this contact, many printers have a structure in which an operator can adjust the distance between the platen and the recording head in accordance with the thickness of a recording medium. A carriage moving method and a platen moving method are known adjusting methods for adjusting the distance between the platen and the recording head. In the present embodiment, the platen moving method is employed. Hereinafter, the distance between a recording medium (recording sheet) guided by the platen and the recording head is referred to simply as the sheet distance. 
   The chassis  16  has sheet-distance adjusting lever  18  slidably fixed thereto, for adjusting the sheet distance. 
     FIG. 7  is a perspective view of the sheet-distance adjusting lever  18 . As shown in  FIG. 7 , the sheet-distance adjusting lever  18  has linear grooves  18   c  and  18   d  disposed along the longitudinal direction thereof, and the widths of the grooves  18   c  and  18   d  are set so as to allow bent portions (not shown) of the chassis  16  to be inserted thereinto. Since the bent portions of the chassis  16  are engaged in the grooves  18   c  and  18   d , the sheet-distance adjusting lever  18  is guided along the arrow B 1  and B 2  directions indicated in  FIG. 6  with respect to the chassis  16 . 
   The sheet-distance adjusting lever  18  also has cams  18   a  and  18   b , each having a sloped surface, disposed adjacent to ends of the grooves  18   c  and  18   d , respectively. 
     FIGS. 12 and 13  are perspective views of the rear side of the platen  11  and components fixed to the platen  11 , respectively. 
   As shown in  FIGS. 12 and 13 , the platen  11  further has a depression  11   f  disposed in the rear surface thereof so as to face a region where the recording head is movable. The depression  11   f  has an ink absorber  20  disposed therein for collecting ink which does not land within the peripheries of a recording medium on which a marginless recording operation is performed. The ink absorber  20  is composed of, for example, a sufficiently-absorbent porous material. 
   By performing the recording operation over a part of the depression  11   f  extending slightly out from the edge of the recording medium, the printer  1  allows the recording medium to be recorded without leaving a margin along the edge thereof. Taking a degree of cutting accuracy of recording media at the time of manufacturing and a degree of transporting accuracy of the printer  1  into account, a distance of the part of the depression  11   f  extending out from the edge of the recording medium is set in a range from about 1 mm to 5 mm. 
   The platen  11  further has a leaf spring  19  fixed to the rear surface thereof such that the leaf spring  19  and the ink absorber  20  are disposed on opposite sides of the platen  11 . The leaf spring  19  has partially bent and raised spring portions  19   a  and  19   b  formed therein. Each of the spring portions  19   a  and  19   b  has dimensions of about 6 mm wide and 20 mm long, and the front thereof is bent so as to have a curved shape. The leaf spring  19  is composed of a spring-use stainless steel plate or the like and is subjected to low-temperature annealing after the bending process so as to remove residual stress during the bending process. 
   With a general molding method of a plastic component, the plastic component is completed in accordance with the steps of putting a resin material in a melted state at high temperatures, pouring it into a metal mold, cooling it down for solidification, and then releasing it from the metal mold. A resin material contracts by about 0.1% to 1% when it is cooled down for solidification. Hence, when the resin material is molded so as to provide a molded component having a non-uniform shape or an uneven thickness, it contracts unevenly, thereby sometimes causing a deformation such as a warp. 
   Since the platen  11  according to the present embodiment has a shape close to a flat plate, it is likely warped when molded. As a countermeasure against this problem, the leaf spring  19  has a substantially uniform width along the longitudinal direction of the platen  11  and engages with the platen  11  so as to be integrally fixed to the same. The leaf spring  19  also has a plurality of engaging holes  19   f  disposed at a certain spacing along the longitudinal direction thereof so as to engage with the platen  11 . Also, the platen  11  further has a plurality of engaging claws  11   g  integrally formed therewith on the rear side thereof so as to engage with the corresponding engaging holes  19   f  of the leaf spring  19 . 
   The leaf spring  19  further has bent portions  19   c  and  19   d  formed along both side ends thereof extending parallel to the longitudinal direction thereof so as to have a large mechanical strength by increasing a modulus of section. The leaf spring  19  is afforded its necessary mechanical strength by bending a part of a flat plate, thereby making it lighter than a flat plate that achieves its necessary mechanical strength by an increase in thickness. 
   Also, the leaf spring  19  acts as a reinforcement member of the platen  11 . As described above, by integrally fixing the leaf spring  19  to the platen  11 , even when the platen  11  is formed by molding, a warp of the platen  11  is straightened by an urging force of the leaf spring  19 . In addition, by integrally fixing the leaf spring  19  to the platen  11 , the platen  11  is not required to attain the increased mechanical strength by itself, thereby making the platen  11  thinner. As a result, the platen  11  has a necessary mechanical strength without increasing the number of components, thereby achieving a compact and light structure of the overall printer  1  and reducing a manufacturing cost thereof. 
   A detailed operation of the platen  11  with the sheet-distance adjusting lever  18  will be described with reference to  FIGS. 8 to 11 , partial sectional views of the printer  1 , each illustrating either of the cams  18   a  and  18   b  of the sheet-distance adjusting lever  18  and other components in the vicinity thereof. 
     FIGS. 8 and 9  are the partial sectional views of the printer  1 , illustrating a proximal state in which the sheet distance is set small. In the proximate state, the cam  18   b  of the sheet-distance adjusting lever  18  causes the spring portion  19   b  of the leaf spring  19  to be elastically deformed and compressed. The leaf spring  19  pushes up the platen  11  with an urging force of the spring portion  19   b , thus causing the platen  11  to rotate about the shaft portions  11   a  and  11   b.    
   As shown in  FIG. 8 , as the platen  11  rotates about the shaft portions  11   a  and  11   b , the boss  11   d  abuts against the guide rail  13 , whereby the rotation of the platen  11  is stopped at the first position. Since the guide rail  13  is a support member for supporting the carriage  7 , a relative position between the carriage  7  and the platen  11  in the thickness direction of a recording medium is determined with only a single component of the guide rail  13  interposed therebetween, thereby accurately determining the sheet distance, that is, the distance between the recording medium guided by the platen  11  and the recording head mounted on the carriage  7 . 
   Likewise, the cam  18   a  of the sheet-distance adjusting lever  18  causes the spring portion  19   a  of the leaf spring  19  to be compressed. The leaf spring  19  pushes up the platen  11  with its elastic force, thus causing the platen  11  to rotate about the shaft portions  11   a  and  11   b . When the boss  11   e  abuts against the guide rail  13 , the rotation of the platen  11  is stopped at the first position. 
   The leaf spring  19  is constructed such that urging forces of the spring portions  19   a  and  19   b  are greater than a load of the total weight of the platen  11 , the leaf spring  19 , a recording medium guided by the platen  11 , the ink absorber  20  for achieving a recording operation without leaving a margin, and ink absorbed in the ink absorber  20 , a repulsive force due to elasticity of the recording medium, and so forth so as to make the platen  11  rotatable. 
     FIGS. 10 and 11  illustrate a remote state in which the sheet distance is set large. As the sheet-distance adjusting lever  18  is moved in the arrow B 1  direction indicated in  FIG. 6 , the cam  18   b  is moved from directly underneath the spring portion  19   b , and likewise the cam  18   a  is also moved from directly underneath the spring portion  19   a . Since the platen  11  has no upward urging force of the spring portions  19   a  and  19   b  exerted thereon, it rotates downward due to its own weight about the shaft portions  11   a  and  11   b  and the rotation thereof is stopped at the second position when its stopper (not shown) abuts against the chassis  16 . As a result, the platen  11  causes the recording head and the recording medium to be remote from each other so as to provide a large sheet distance. 
   An operation of the discharge guides  17  will be described with reference to  FIGS. 14 to 17 . 
     FIG. 14  is a partial perspective view of the printer  1 , illustrating the proximal state in which the sheet distance is set small. As shown in  FIG. 14 , the discharge roller  10  has pluralities of first and second roll or roller portions  10   a  and  10   b  alternately disposed at certain intervals along the axial direction thereof, and the second roll portions  10   b  are formed so as to have a smaller diameter than the first roll portions  10   a.    
   The second roll portions  10   b  are formed by applying, for example, a nickel plating on the peripheral surface of a rotating shaft composed of a metal material and serve as “low-friction portions” having a smaller coefficient of friction than that of the first roll portions  10   a . The first roll portions  10   a  are composed of an elastic material such as a rubber material, are disposed around the periphery of the rotating shaft, and serve as “high-friction portions” having a larger coefficient of friction than that of the second roll portions  10   b . An example of the rubber material forming the first roll portions  10   a  is an ethylene-propylene diene monomer (EPDM), preferably having a rubber hardness of about 50° to 90°. Alternatively, the first roll portions  10   a  may be formed of a material having, for example, a urethane-base elastomer or a urethane coating material applied thereon, or a material such as a sponge having a relatively large coefficient of friction. 
   Each of the discharge guides  17  is composed of a resin material such as polyoxymethylene (POM) so as to provide a flat shape and has a support shaft (an upstream positioning portion or an upstream supporting portion)  17   a  integrally formed therewith at the rear end thereof in the transport direction of a recording medium so as to be rotatably supported by the platen  11 . The discharge guide  17  also has an abutment (a downstream positioning portion or a downstream supporting portion)  17   b  formed at the front end thereof in the transport direction of the recording medium so as to abut against the peripheral surface of the corresponding second roll portion  10   b  of the discharge roller  10 . Thus, when the discharge guide  17  causes the abutment  17   b  to abut against the corresponding second roll portion  10   b  of the discharge roller  10  due to its own weight, the rotation of the support shaft  17   a  about its axis is stopped. 
   Each of the first roll portions  10   a  of the discharge roller  10  has the discharge guides  17  disposed at both sides thereof in the axial direction thereof so as to be adjacent to each other. When the leading edge of a recording medium is not introduced into both side edges of the cylindrical first roll portion  10   a , the transport speed of the recording medium is especially apt to be slightly disturbed. This is because, when the leading edge of the recording medium abuts strongly against both side edges of the first roll portion  10   a , the leading edge of the recording medium is likely crushed. 
   Since each of the discharge guides  17  is composed of a low-friction resin material such as POM, having a relatively small coefficient of friction, even when it abuts against the corresponding second roll portion  10   b  of the discharge roller  10 , it does not exert an increased rotational load on the discharge roller  10 . 
   Also, as shown in  FIG. 19 , the discharge guide  17  is formed such that the thickness t of the abutment  17   b  abutting against the second roll portion  10   b  is smaller than a difference Ar in the radii between the first roll portion  10   a  and the second roll portion  10   b  of the discharge roller  10 . Thus, the first roll portions  10   a  of the discharge roller  10  protrude slightly from the principal surfaces of the corresponding discharge guides  17  toward a transport path (sheet path) of a recording medium formed by the discharge guides  17 . 
     FIGS. 15 and 17  are partial perspective sectional views of the printer  1 , illustrating the proximal and remote states in which the sheet distance is set small and large, respectively. The operation of the discharge guide  17  is easily understood by comparing  FIGS. 15 and 17 . 
   As shown in  FIGS. 15 and 17 , while the support shaft  17   a  of the discharge guide  17  moves as the platen  11  rotates, the abutment  17   b  lying on the opposite side of the support shaft  17   a  is maintained in a state of abutting against and being supported by the second roll portion  10   b  of the discharge roller  10 . 
   Meanwhile, each of spurs (rotors)  21  has needle-shaped edges or spokes formed around the periphery thereof by using a thin metal plate having a thickness of, for example, about 0.1 mm to 0.3 mm. Since ink on the recording surface of a recording medium does not fully dry immediately after a recording operation, by providing the spurs  21  each with the needle-shaped edges around the periphery thereof, a contact area between the recording medium and each periphery is reduced so that the ink is prevented from being transferred. 
     FIGS. 18 and 19  are magnified partial sectional views of the printer  1 , illustrating a state in which the abutment  17   b  of the discharge guide  17  lying on the opposite side of the support shaft  17   a  of the same abuts against the corresponding second roll portion  10   b  of the discharge roller  10 .  FIGS. 18 and 19  respectively illustrate the proximal and remote states in which the sheet distance is set small and large. 
   Each of the discharge guides  17  has a guide surface so as to guide a recording medium to the contact position between the corresponding spur  21  and first roll portion  10   a  of the discharge roller  10 . It is important that the first roll portion  10   a  of the discharge roller  10  is constructed so as to slightly protrude from the sheet path of the recording medium. More particularly, the guide surface of the discharge guide  17  is positioned by the corresponding second roll portion  10   b  so as to lie below the nip between the corresponding spur  21  and first roll portion  10   a.    
   When the first roll portions  10   a  of the discharge roller  10  do not protrude from the sheet path, the transport capacity of the discharge roller  10  decreases drastically. On the other hand, when an amount of protrusion of the first roll portions  10  of the discharge roller  10  is great, printing irregularity occurs upon abutment of a recording medium against the first roll portions  10   a . In addition, when the amount of protrusion of the first roll portions  10   a  is great, the orientation of a recording medium is likely disturbed upon abutment of recording medium against the first roll portions  10   a , thereby sometimes causing a risk that the recording medium is elevated from the platen  11  and abuts against the recording head. Since the recording head has a large number of fine discharge ports for ejecting ink droplets, when the recording medium abuts against it, some of the discharge ports may be clogged, damaged, or broken in the worst case. 
   Also, since ink on the recording surface of a recording medium immediately after a recording operation does not fully dry, the recording medium having absorbed moisture has a reduced stiffness, whereby the above-mentioned phenomena become more pronounced. The above-mentioned reduction in stiffness due to moisture is pronounced when a recording medium such as a sheet of normal paper composed of pulpwood is used. 
   Since the amount of protrusion of the first roll portions  10   a  is determined by making the discharge guides  17  abut against the second roll portions  10   b  of the discharge roller  10 , the amount of protrusion can be accurately controlled by controlling the dimensions of the discharge roller  10  and the discharge guides  17 . Although each of the discharge guides  17  is a molded component, it can be formed within a dimensional tolerance of about ±0.03 mm. Also, with respect to the discharge roller  10 , since each of the second roll portions  10   b  is formed by grinding the corresponding first roll portion  10   a , the step between the second roll portion  10   b  and the first roll portion  10   a  can be formed within a dimensional tolerance of about ±0.01 mm. 
   On the other hand, if the discharge guides  17  are affixed to the platen  11  in an upside down orientation, the foregoing amount of protrusion of the first roll portions  10   a  of the discharge roller  10  protruding from the sheet path is different from a design value, whereby the foregoing effect is not achieved. As a countermeasure against this problem, each of the discharge guides  17  has a projection  17   c  integrally formed on the other surface of the principal surface thereof in order to prevent the platen  11  from being fixed upside down during assembly. That is, the discharge guide  17  has a substantially flat principal surface for guiding a recording medium and the other surface having the projection  17   c  formed thereon. 
   By providing the discharge guide  17  with the projection  17   c , its front and rear surfaces can be easily recognized at a glance during the manufacturing process of the printer  1 , and also, even when it is fixed upside down by mistake, a recording medium is caught on the projection  17   c  and is not discharged during the inspection process of the printer  1 , whereby faulty assembly can be easily detected. 
   During the manufacturing process of the printer  1 , the platen  11 , the discharge guides  17 , and the discharge roller  10  are assembled, and then the guide rail  13  is built so as to lie vertically above them. Thus, even when the overall printer  1  is turned upside down after assembly, the discharge guides  17  abut against the guide rail  13  and the turning thereof is accordingly stopped. 
   In the present embodiment, each of the first roll portions  10   a  of the discharge roller  10  has the discharge guides  17  disposed at both sides thereof and fourteen units of the discharge guides  17  are disposed in total in the printer  1 . Although the discharge guides  17  could be integrally connected all together, when the flatness of the platen  11  and the straightness of the discharge roller  10  are taken into account, it is preferable that the discharge guides  17  operate independently of each other. 
   As described above, the printer  1  having the above structure is equipped with the discharge guides  17 , each having one end rotatably supported by the platen  11  and the other end abutting against the corresponding second roll portion  10   b  of the discharge roller  10 , thereby eliminating so-called printing irregularity occurring upon abutment of a recording medium against the first roll portions  10   a  of the discharge roller  10  and thus achieving an accurate recording operation without decreasing the transport capacity of the discharge roller  10 . Accordingly, with the structure of the printer  1 , the discharge guides  17  having a relatively simple structure allow a recording medium to be easily, reliably, and stably transported to the discharge roller  10 . 
   The printer  1  according to the present invention is suitable for use in a recording apparatus in which a sheet-distance adjustment is needed, especially for use in a recording apparatus in which a sheet distance is adjusted by moving a platen. 
   Meanwhile, the printer  1  according to the present embodiment is mainly aimed at a portable use. Since the longitudinal length of a general flat palm of a human hand is about 70 mm to 120 mm, when ease of holding an apparatus is taken into account, the apparatus having a thickness of 60 mm or less is excellent in portability. Also, many of office desks commercially available in Europe and the United States are equipped with drawers having an inner width of 310 mm or greater, considering that letter-sized files are stored in the drawers. In view of these circumstances, the size of the printer  1  is determined so as to provide dimensions of about 51.8 mm in thickness, 310 mm in width, and 174 mm in depth, whereby it can be easily held by hand and also be stored in a drawer of an office desk. 
   While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.