Abstract:
A stepping mechanism comprising a motor, a motor gear connectable to the motor and rotatable by the motor, a first one-way clutch and a second one-way clutch when the motor rotates the gear in a first direction so as to operate the first one-way clutch in a first mode and the motor rotates the gear in the second direction so as to operate the second one-way clutch in a second mode, wherein the first and second one-way clutch do not operate at the same time.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    This invention relates to a fluid ejection printing apparatus.  
           [0003]    2. Description of Related Art  
           [0004]    Fluid ejection systems, such as ink jet printers, have at least one fluid ejection head that directs droplets of fluid towards a recording medium. Within the fluid ejection head, the fluid may be contained in a plurality of channels. Energy pulses are used to expel the droplets of fluid, as required, from orifices at the ends of the channels.  
           [0005]    In a thermal fluid ejection system, such as a thermal ink jet printer, the energy pulses are usually produced using resistors. Each resistor is located in a respective one of the channels, and is individually addressable by voltage and/or current pulses to heat and vaporize the fluid in the channels. As a vapor bubble grows in any one of the channels, fluid bulges from the channel orifice until the pulse has ceased and the bubble begins to collapse. At that stage, the fluid within the channel retracts and separates from the bulging fluid to form a droplet moving in a direction away from the channel and towards the receiving medium. The channel is then re-filled by capillary action, which in turn draws fluid from a supply container. Operation of a thermal ink jet printer is described in, for example, U.S. Pat. No. 4,849,774, incorporated herein by reference in its entirety.  
           [0006]    A carriage-type thermal ink jet printer is described in U.S. Pat. No. 4,638,337, incorporated herein by reference in its entirety. That thermal ink jet printer has a plurality of printheads, each with its own ink tank cartridge, mounted on a reciprocating carriage. The channel orifices in each printhead are aligned perpendicular to the line of movement of the carriage. A swath of information is printed on the stationary receiving medium as the carriage is moved in one direction. The receiving medium is then stepped, perpendicular to the line of carriage movement, by a distance equal to or less than the width of the printed swath. The carriage is then moved in the reverse direction to print another swath of information.  
         SUMMARY OF THE INVENTION  
         [0007]    Some fluid ejection systems, such as low cost ink jet printers, have paper advance subsystems that must operate on two opposing modes. The first mode is a high speed mode which maximizes the throughput of the receiving medium. The second mode is a high precision mode to accurately register the receiving medium.  
           [0008]    Typically, a single motor with a single clutch and a single gear train is used to implement both the high speed mode and the high precision mode. The single motor is connected to the clutch and the gear train. The clutch and the gear train are also connected to a shaft with rollers. When the motor is activated, the rotational force of the motor is transferred through the clutch to the gear train. The gear train then transfers the rotational force to the shaft and roller. As the rollers rotate, the rollers advance the receiving medium.  
           [0009]    However, a single clutch and a single gear train, when used to implement as both the high speed mode and the high precision mode, fail to accurately advance the paper. In particular, when a high precision mode is requested, the single clutch and gear train cannot accurately register the receiving medium.  
           [0010]    This invention provides a receiving medium advancing mechanism having both a high speed subsystem and a high precision subsystem implemented using a simple low cost motor.  
           [0011]    The invention separately provides two gear trains and two one-way clutches to provide two types of motion from a single motor.  
           [0012]    In various exemplary embodiments of systems and methods according to this invention, a receiving medium advancing mechanism comprises a motor, a gear, a first one-way clutch and a second one-way clutch. When the motor rotates the gear in a first direction, the first one-way clutch, but not the second one-way clutch, is operated to advance the receiving medium in a first mode. When the motor rotates the gear in a second direction, the second one-way clutch, but not the first one way clutch, is operated to advance the receiving medium in a second mode. The first mode is a high advance mode while the second mode is high precision mode.  
           [0013]    These and other features and advantages of this invention are described in or apparent from the detailed description of various exemplary embodiments of the systems and methods according to this invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Various exemplary embodiments of the invention will be described in detail with reference to the following figures, wherein like numerals represent like elements, and wherein:  
         [0015]    [0015]FIG. 1 is a schematic view of a fluid ejection system and a receiving medium advancing mechanism according to this invention;  
         [0016]    [0016]FIG. 2 is an exemplary embodiment of the receiving medium advancing mechanism according to this invention;  
         [0017]    [0017]FIG. 3 is a schematic diagram of the receiving medium advancing mechanism according to this invention that advances the receiving medium at a high speed; and  
         [0018]    [0018]FIG. 4 is a schematic diagram of the receiving medium advancing mechanism according to this invention that advances the receiving medium at a high precision. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0019]    The following detailed description of various exemplary embodiments of the fluid ejection systems according to this invention are directed to one specific type of fluid ejection system, an ink jet printer, for sake of clarity and familiarity. However, it should be appreciated that the principles of this invention, as outlined and/or discussed below, can be equally applied to any known or later-developed fluid ejection systems, beyond the ink jet printer specifically discussed herein.  
         [0020]    [0020]FIG. 1 illustrates a partial perspective view of an ink jet printer  10  having an ink jet printhead cartridge  12  mounted on a carriage  14  supported by a carriage rail  16 . The printhead cartridge  12  includes a housing  18  containing ink that is supplied to a thermal ink jet printhead  20 . The thermal ink jet printhead  20  selectively expels droplets of ink under control of electrical signals received from a controller of the printer  10  through an electrical cable  22 . The printhead  20  contains a plurality of ink channels which carry ink from the housing to respective ink ejectors, such as orifices or nozzles.  
         [0021]    When printing, the carriage  14  reciprocates or scans back and forth along the carriage rail  16  in a fast scan direction, as indicated by an arrow  24 . As the printhead cartridge  12  reciprocates back and forth across a receiving medium  26 , such as a sheet of paper or a transparency, in the fast scan direction  24 , droplets of ink are expelled from selected ones of the printhead nozzles toward the receiving medium  26 . The ink ejecting orifices or nozzles are typically arranged in a linear array perpendicular to the fast scan direction  24 .  
         [0022]    During each pass of the carriage  14 , the receiving medium  26  is held in a stationary position. At the end of each pass, however, the receiving medium  26  is stepped by a receiving medium advancing mechanism  100  under control of the controller in a process or slow scan direction, as indicated by an arrow  28 . The receiving medium advancing mechanism  100  rotates a shaft  110 , and a number of attached transport rollers  112 . The transport rollers  112  contact the receiving medium  26 , and move the receiving medium  26  in the direction of the arrow  28 .  
         [0023]    FIGS.  2 - 4  show one exemplary embodiment of the receiving medium advancing mechanism  100  according to this invention used to drive the shaft  110 . The receiving medium advancing mechanism  100  includes a motor  120 . The motor  120  bi-directionally drives a drive gear  122 . The drive gear  122  is engaged with a pitch gear  130 . As should be appreciated, the drive gear  122  and pitch gear  130  can have any given number of teeth. The drive gear  122  can rotate the pitch gear  130  in both a clockwise direction and a counterclockwise direction.  
         [0024]    As shown in FIG. 2, the pitch gear  130  is attached to a pitch pulley  132 . The pitch pulley  132  includes a front track  134  and a rear track  136 . A first drive belt  150  is engaged to the front track  134 . A second drive belt  200  is engaged to the rear track  136 . As should be appreciated, as the pitch gear  130  rotates the pitch pulley  132 , the front track  134  rotates drive belt  150  and the rear track  136  rotates drive belt  200 .  
         [0025]    [0025]FIG. 3 shows a first subsystem for moving the receiving medium  26  in a first mode. FIG. 4 shows a second subsystem for moving the receiving medium  26  in a second mode. In various exemplary embodiments, the first subsystem is used as the high speed advance subsystem while the second subsystem is used as the high precision subsystem. Thus, in this exemplary embodiment, the first mode is a high advance mode and the second mode is a high precision mode. However, it should be appreciated that the first subsystem can be the high precision subsystem and the second subsystem can be the high advance subsystem.  
         [0026]    As shown in FIGS. 2 and 3, as the drive belt  150  rotates in a first direction, the drive belt  150  drives a first one-way clutch  160 . The first one-way clutch  160  is designed to rotate only when the drive belt  150  is driven in a first direction. As shown in FIG. 3, the clutch  160  is connected to a gear  162 . In contrast, as shown in FIGS. 2 and 4 as the drive belt  200  rotates in the second direction, the drive belt  200  drives the gear  210 . As shown in FIG. 4, the gear  210  is connected to a second one-way clutch  230 . The second one-way clutch  230  is designed to rotate only when the gear  210  is driven in the second direction. The gear  210  is driven in the second direction only when the drive belt  200  is driven in the second direction.  
         [0027]    When the first one-way clutch  160  rotates in the first direction, the first one-way clutch  160  drivingly engages the gear  162 . In response, the gear  162  also rotates in the first direction and drives a gear  180 , which rotates in a second direction. The gear  180  is attached to the shaft  110 . As the gear  180  rotates in the second direction, the shaft  110  rotates in the second direction. As the shaft  110  rotates in the second direction, the rollers  112  also rotate in the second direction. The rollers  112  thus contact the receiving medium  26 , and move the receiving medium  26  in the direction of the arrow  28 .  
         [0028]    As should be appreciated, the receiving medium advancing mechanism  100  rotates the rollers  112  in the second direction when the receiving medium advancing mechanism  100  is located at the right hand side of the receiving medium  26  as shown in FIG. 1. However, the receiving medium advancing mechanism  100  needs to rotate the rollers  112  in the first direction when the receiving medium advancing mechanism is located at the left hand side of the receiving medium  26 . In this case, the rotational directions of the one-way clutch  160  and the gear  180  can be reversed or an additional gear added between the one-way clutch  160  and the shaft  110  or between the drive belt  150  and the one-way clutch  160 .  
         [0029]    As should be appreciated, as the drive gear  122  rotates in the first or second direction, the drive gear  122  rotates the pitch gear  130  in the second or first direction, respectively. As the pitch gear  130  rotates in the first or second direction, the front track  134  rotates the drive belt  150  in the first or second direction, respectively. As the drive belt  150  rotates in the first direction, the drive belt  150  drives the first one-way clutch  160  in the first direction. The first one-way clutch  160  then drivingly engages the gear  162  to rotate in the first direction, which in turn drives the gear  180  in the second direction. As the gear  180  rotates in the second direction, the shaft  110  rotates in the second direction. As the shaft  110  rotates in the second direction, the rollers  112  also rotate in the second direction. The rollers  112  thus contact the receiving medium  26 , and move the receiving medium  26  in the direction of the arrow  28 .  
         [0030]    In contrast, as the pitch gear  130  rotates in the second direction, the front track  130  rotates the drive belt  150  in the second direction. However, the first one-way clutch  160  is stopped from being driven by the drive belt  150  in the second direction by a stopper  170 . Thus, as should be appreciated, when the first one-way clutch  160  is stopped by the stopper  170 , the first one-way clutch  160  is disengaged from the drive belt  150  so that the drive belt  150  is stopped from driving the first one-way clutch  160 . The first one-way clutch  160  is also disengaged from the gear  162  so that the gear  162  rotates freely without being driven by the first one-way clutch  160 .  
         [0031]    As shown in FIG. 4, the clutch  230  is connected to the gear  232 . When the second one-way clutch  230  is driven by the gear  210  to rotate in the first direction, the second one-way clutch  230  drives the gear  232 . In response, the gear  232  drives a gear  240  in the second direction. The gear  240  is attached to the shaft  110 . As the gear  240  rotates in the second direction, the shaft  110  rotates in the second direction. As the shaft  110  rotates in the second direction, the rollers  112  also rotate in the second direction. The rollers  112  thus contact the receiving medium  26 , and move the receiving medium  26  in the direction of the arrow  28 .  
         [0032]    As should be appreciated, as the drive gear  122  rotates in the first or second direction, the drive gear  122  rotates the pitch gear  130  in the second or first direction, respectively. As the pitch gear  130  rotates in the second direction, the rear track  136  rotates the drive belt  200  in the second direction. As the drive belt  200  rotates in the second direction, the gear  210  rotates in the second direction. As the gear  210  rotates in the second direction, the gear  210  drivingly engages the second one-way clutch  230  to rotate in the first direction. The second one-way clutch  230  then drivingly engages the gear  232  to rotate in the first direction, which in turn drives the gear  240  in the second direction. As the gear  240  rotates in the second direction, the gear  240  rotates the shaft  110  in the second direction. As the shaft  110  rotates in the second direction, the rollers  112  also rotate in the second direction. The rollers  112  thus contact the receiving medium  26 , and move the receiving medium  26  in the direction of the arrow  28 .  
         [0033]    In contrast, as the pitch gear  130  rotates in the first direction, the rear track  136  rotates the drive belt  200  in the first direction. The drive belt  200  then rotates the gear  210  in the first direction. However, the second one-way clutch  230  is stopped from being driven by the gear  210  in the second direction by a stopper  250 . Thus, as should be appreciated when the second one-way clutch  230  is stopped by the stopper  250 , the second one-way clutch  230  is disengaged from the gear  210  so that the gear  210  is stopped from driving the second one-way clutch  230 . The clutch  230  is also disengaged from the gear  232 , so that the gear  232  rotates freely without being driven by the second one-way clutch  230 .  
         [0034]    Thus, as should be appreciated, when the drive gear  122  rotates in the second direction, the gear  180  drives the shaft  110  in the second direction and when the drive gear  122  rotates in the first direction, the gear  240  drives the shaft  110  in the second direction.  
         [0035]    When providing a high precision advance subsystem, a gear with a lower number of teeth than the gear which it drives is used to slowly advance the shaft  110 . Conversely, when providing a high speed advance subsystem, a gear with a higher number of teeth than the gear which it drives is used to rapidly advance the shaft  110 . Thus, as should be appreciated, either the gear  162  or the gear  232  can have a relatively higher number of teeth than the corresponding gear  180  or  240  in order to be used as the high speed advance system, while the other one of the gears  162  or  232  has a lower number of teeth than the corresponding gear  180  or  240  in order to be used as the high precision advance subsystem. In various exemplary embodiments, the gear  162  has a relatively higher number of teeth than the gear  150 , while the gear  232  has a relatively lower number of teeth than the gear  240 . As the receiving medium  26  approaches the printhead  20 , the motor drives the drive gear  122  in the second direction. Thus, the receiving medium  26  is moved rapidly in the direction of the arrow  28 . Then, the motor  120  drives the drive gear  122  in the first direction when printing occurs on the receiving medium  26 . Thus, the receiving medium  26  is slowly moved in the direction of the arrow  28  in order to accurately place the receiving medium  26  relative to the array of nozzles on the printhead  20 . Once all of the image data to be placed on the receiving medium  26  has been placed on the receiving medium  26 , the motor  120  drives the drive gear  122  in the second direction to rapidly move the receiving medium  26  in the direction of the arrow  28 .  
         [0036]    As should be appreciated, in various exemplary embodiments, various modifications to the receiving medium advancing system  100  of FIGS.  2 - 4  may be used. For example, in various exemplary embodiments, the drive gear  122  may directly engage both the first and second one-way clutches  160  and  230  to drivingly engage the first and second one-way clutches  160  and  230 . Alternatively, the drive belts  150  and  200  may be replaced by one or more gears. Thus, it should be appreciated that any combination of mechanical elements that are capable of transmitting rotational and/or translational force to the shaft  110  may be used with the drive gear  122  and first and second one-way clutches  160  and  230  in order to provide a high speed advance subsystem when the drive gear  122  is rotated in one of the first and second directions and a high precision advance subsystem when the drive gear  122  is rotated in the other of the first and second directions.  
         [0037]    While this invention has been described in conjunction with the exemplary embodiments described above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.