Patent Publication Number: US-6705693-B2

Title: Adjustable pen-to-paper spacing mechanism

Description:
BACKGROUND 
     This invention relates generally to inkjet printers, and in particular to techniques for adjusting a pen-to-paper spacing. 
     As shown in FIG. 1, in this application a pen-to-paper spacing (PPS) is defined as the distance between a cartridge  103  of an inkjet printer and a bottom surface  118  of a media sheet  117  which is in a print zone  116  and which is supported by a platen  120  for printing. The PPS and the thickness of the media sheet  117  determine the distance between the cartridge  103  and an upper surface  119  of the media sheet  117 . Maintaining a suitable distance between the cartridge  103  and the upper surface  119  is important to achieve the best image quality possible. 
     Normally, when the printer is manufactured, the PPS is set and fixed at a nominal value based upon a default medium having a default thickness. Nevertheless, the distance between the cartridge  103  and the upper surface  119  of the media sheet  117  may vary as media of various thicknesses are used. 
     Especially, when a medium thicker than the default medium is used, and if the PPS remains unchanged, the distance between the cartridge  103  and the upper surface  119  of the media sheet  117  can be relatively close. Thus, there is the possibility of the cartridge  103  contacting the upper surface  118  of the media sheet  117  during printing. This phenomenon may cause the media sheet  117  to be smeared. 
     However, when a medium thinner than the default medium is used and if the PPS remains unchanged, the distance between the cartridge  103  and the upper surface  119  of the media sheet  117  can be relatively far. This may affect the accurate placement of ink dots when ink drops are ejected onto the medium and consequently the printing quality as well. 
     Therefore, there is a need for adjusting the PPS distance in an inkjet printer. 
     SUMMARY 
     According to a first embodiment of the invention, an inkjet printer includes a printer frame structure, a carriage movable in the printer frame structure for movement across a print zone during printing operations, and at least one cartridge mounted on the carriage for printing on a medium in the print zone. The printer further includes means for driving the cartridge between a first position in which the printer prints at a first PPS measured from a bottom surface of the medium, and a second position in which the printer prints at a second PPS. 
     According to a second embodiment of the invention, an inkjet printer for printing on a medium in a print zone includes a printer frame structure, a first path and a second path defined in the printer frame structure, and a carriage movable in the printer frame structure for movement across the print zone during printing operations. The carriage has a first slider for moving along one of the first and the second paths. Further more, the printer prints at a first PPS distanced from a bottom surface of the medium as the first slider moves along the first path, while prints at a second PPS distanced from said bottom surface as the first slider moves along the second path. 
     In an aspect of the invention, the printer includes at least one cartridge mounted on the carriage. The printer also includes means located below the cartridge for driving the cartridge relative to the printer frame structure in a direction vertical to the medium from a first position in which the printer prints at the first PPS to a second position in which the printer prints at the second PPS. 
     According to a second embodiment of the invention, an inkjet printer for printing on a medium in a print zone includes a printer frame structure, a carriage movable in the printer frame structure for movement across the print zone during printing operations. The carriage includes a first slider and a second slider disposed at the front and back of the carriage respectively. The printer also includes a first rail mounted on the printer frame structure and disposed at the front of the carriage for the first slider to move along with. The first rail determines a first pen-to-paper spacing distanced from a bottom surface of the medium at which spacing the printer prints as the first slider moves along the first rail. The printer further has a second rail mounted on the printer frame structure and disposed at the back of the carriage for the second slider to move along with. The second rail determines a second pen-to-paper spacing distanced from said bottom surface at which spacing the printer prints as the second slider moves along the second rail 
     Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a cartridge printing on a medium having an upper surface and a bottom surface to define PPS in a printer; 
     FIG. 2 illustrates an embodiment of the invention in which a printer prints at a normal PPS; 
     FIG. 3 shows the printer of FIG. 2 when it prints at a larger PPS; and 
     FIG. 4 is a close-up view of the mechanism for adjusting the PPS according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 2 shows a part of an inkjet printer  100  according to an exemplary embodiment of the invention. The printer  100  has a printer frame structure  200  (partially shown), a platen  120  in a print zone  116  for supporting a media sheet  117  during printing, a carriage  101  sliding on a longitudinal guide rod  129 , a first guide preferably a rail  107  and a second guide preferably also a rail  111 . The guide rod  129 , the platen  120 , the first rail  107  and the second rail  111  are all mounted on the printer frame structure  200 . 
     In the embodiment shown in FIG. 2, a cartridge  103  is mounted on the carriage  101 . The carriage  101  slides on the longitudinal guide rod  129  and moves along a cartridge scan axis  206  (see FIG. 4) across the print zone  116  during printing operations such that the cartridge  103  can imprint images on the media sheet  117  advanced to the print zone  116 . 
     In FIGS. 2 and 4, a service station carrier  105  carrying a service station  135  for servicing the cartridge  103  is provided. The service station carrier  105  is movable along a media movement axis  202  (shown in FIG. 2) perpendicular to the cartridge scan axis  206 . When a servicing is desired, the service station carrier  105  moves to a servicing space and the carriage  101  moves to a servicing position above the servicing space such that the cartridge  103  can be serviced. 
     In FIGS. 3 and 4, a service station motor  125  mounted on the printer frame structure provides the driving force for the service station carrier  105  through a gear train  123 . Furthermore, movement of the service station carrier  105  is commanded by firmware in the printer  100  and controlled by an encoder disc  127  mounted on a shaft of the service station motor  125 . Such a control mechanism is well known in the art. 
     As shown in FIGS. 2 and 4, the first rail  107  and the second rail  111  extend horizontally and substantially parallel to the guide rod  129 . In addition, the two rails  107 ,  111  are located at different sides, i.e., the front and the back of the guide rod respectively. In this embodiment, both the first and second rails have an upper portion  151 ,  153 , a lower portion  155 ,  157 , and a web  159 ,  161  connecting the upper and lower portions, all extending horizontally. In addition, as shown in FIG. 4, the first rail  107  is positioned such that an opening  131  is created along a first rail  107  and is opposite to the servicing position. The opening  131  allows the first slider  109  to move upward from a position under the upper portion  151  of the first rail  107  to a position above the upper portion  151  when the carriage  101  is in the servicing position. 
     In FIG. 2, the first slider  109  and a second slider  113  are provided on the carriage for sliding along the first rail  107  and the second rail  111  respectively. While the printer  100  prints at a normal PPS as shown in FIG. 2, the first slider  109  slides along a first path defined by a space under the upper portion  151  of the first rail  107 . The second slider  113  has a spring  115  such that the second slider  113  is urged against and moves along the lower portion  157  of the second rail  111 . As the printer  100  prints at the normal PPS, the second slider  113  is in contact with an inner surface  165  of the upper portion  153  of the second rail  111  and moves along the inner surface  165 . The carriage  101  is thus prevented from further rotating in an anti-clockwise direction about the guide rod  129 , and the normal PPS can be maintained. In this application, a clockwise direction is defined as such a direction that when the carriage  101  rotates about the guide rod  129  in the clockwise direction, the cartridge  103  is driven upward. 
     In the embodiment of the invention, the printer  100  can adjust the PPS upon receiving a command from a printer driver installed in a computer (not shown) which is connected to the printer  100 . In this embodiment, for example, a user specifies the type of media sheet to be printed by clicking on a printer driver printing dialogue box on the computer (not shown). The printer driver then identifies whether the media type selected is a normal or thick print media. If a thick media is selected, the printer driver instructs the printer  100  in the command to increase the PPS accordingly. 
     As shown in FIG. 3, when a larger PPS is desired, the carriage  101  moves to the servicing position on receiving the command from the printer driver to increase the PPS. The servicing position is located at an end along the cartridge scan axis. 
     Next, driven by the service station motor  125 , the service station carrier  105  moves forward in a media movement direction  204  (see FIG. 4) toward the servicing space. An inclined ramp  122  of an actuator  119  mounted on the service station carrier  105  comes into contact with an extension rib  121  mounted on the carriage  101 . In this application, the media movement direction is defined as the direction in which the media sheet  117  in the print zone  116  is advanced during printing. From FIG. 3 it is noted that the actuator  119  is located behind the service station  135  in the media movement direction, while the extension rib  121  is located in front of the cartridge  103  in the media movement direction  204 . Thus, when a normal servicing is requested, the actuator  119  would not be in contact with the extension rib  121  and the PPS would not be changed. For the actuator  119  and the extension rib  121  to be in contact so as to push the cartridge  103  upward, the service station carrier  105  needs to move forward further in the media movement direction. Such a movement is controlled by the encoder disc  127 . 
     Controlled by the encoder disc  127 , the service station carrier  105  keeps moving forward in the media movement direction  204 . The inclined ramp  122  of the actuator  119  pushes the extension rib  121  upward, i.e., in a direction vertical to the media sheet  117 , and the carriage  101  consequently rotates about the guide rod  129  in the clockwise direction. In addition, along with the carriage  101 , the cartridge  103  is driven relative to the printer in a direction vertical to the medium from a first position in which the printer prints at the normal PPS to a second position in which the printer prints at the larger PPS. 
     Consequently, the first slider  109  moves upward through the opening  131  to a position above the upper portion  151  of the first rail  107 . On the other hand, the second slider  113  leaves the inner surface  165  of the upper portion  153  of the second rail  111  and the spring  115  is compressed. The second rail  111  prevents the carriage from rotating about the guide rod  129  to exceed a predetermined degree. 
     The carriage  101  then moves out from the servicing position. Now the first slider  109  rests atop the upper portion  151  of the first rail  107  and slides along a second path defined by an upper surface  163  of the upper portion  151  of the first rail  107  during the following printing session. The first rail  107  prevents the carriage  101  from rotating in the anti-clockwise direction, and the desired larger PPS is maintained. 
     When the printing job is completed, the carriage  101  moves to the servicing position. When the carriage  101  arrives at the servicing position, the first slider  109  leaves the first rail  107  and reaches the opening  131 . In addition, the service station carrier  105  retreats backward in the media movement direction  204 . Without the first rail  107  supporting the first slider  109 , the carriage  101  tends to rotate in the anti-clockwise direction by its own weight. As the service station carrier  105  retreats, the extension rib  121  and consequently the carriage  105  slides down the inclined ramp  122 . The cartridge  103  returns to its first position, i.e., the position in which the printer prints at the normal PPS, when the extension rib  121  is no longer in contact with the actuator  119 . The upper portion  153  of the second rail  111  comes into contact with the second slider  113  and prevents the carriage  101  from further anti-clockwise rotation about the guide rod  129 . 
     Alternatives can be made to the preceding embodiment. For example, instead of the actuator  119  on the service station carrier  105  and the extension rib on the carriage  101 , electromagnetic mechanism can be used to drive the carriage  101  to rotate in the clockwise direction when the larger PPS is desired. Besides, if the cartridge  103  is movable in a vertical direction relatively to the carriage  101 , the PPS can be adjusted by driving the cartridge directly instead of through a rotating carriage  101 . 
     In addition, the distance between the upper portion  151  and the lower portion  155  of the first rail  107  can be configured such that as the printer prints at the normal PPS, the first slider  109  rests atop and moves along the lower portion  155 . The upper portion  153  of the second rail  111  can be removed by horizontally extending the lower portion  155  to the opening  131  for supporting the first slider  109  as the cartridge returns to its normal PPS. 
     Furthermore, a mid-portion located between the upper portion  151  and the lower portion  153  can be added to the first rail  107 . By controlling the movement of the service station carrier  105 , the first slider  109  can be positioned atop the mid portion rather than on the upper portion  151  of the first rail  107 . Thereby, a printer adjustable between three PPS distances can be provided.