CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of prior U.S. patent application Ser. No. 12/492,578, filed Jun. 26, 2009, which is hereby incorporated herein by reference in its entirety. 
         [0002]    This application was co-filed with and has related subject matter to U.S. patent application Ser. No. 12/492,496, filed Jun. 26, 2009. The above-identified patent application is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0003]    This invention relates generally to the field of carriage printers, and more particularly to an apparatus for adjustment of the spacing between the printhead and the recording medium in the print zone. 
       BACKGROUND OF THE INVENTION 
       [0004]    In a conventional carriage-style printer, the paper (or other recording medium) is successively advanced such that a portion of the paper is located within a print zone. While the paper is held stationary, a printhead is moved along a carriage scan direction that is substantially perpendicular to the paper advance direction, and marks are made by the printhead on the paper in the print zone as the printhead moves past. 
         [0005]    An example of such a carriage style printer is an inkjet printer, where the printhead includes an array of nozzles arranged in an array direction that is substantially parallel to the paper advance direction. The print zone within which printing may be done corresponds to the region between the two endmost nozzles in the array. The printhead and at least a portion of the ink supply for the printhead are typically located on a carriage which moves back and forth along a carriage guide rail. For good image quality, it is important to position the nozzles within a predetermined range of acceptable distances from the paper in the print zone. If the nozzles and the corresponding printhead face are positioned too close to the media support that holds the recording medium, the printhead can undesirably strike a sheet of recording medium in the print zone, particularly if the recording medium is thicker than anticipated, or if the recording medium is cockled, dog-eared, or otherwise not held flatly against the media support. On the other hand, if the nozzles and the corresponding printhead face are positioned too far from the media support, jets that are misdirected land further out of position on the recording medium than they would if the nozzles were closer to the recording medium. The resulting misaligned spots result in objectionable image artifacts. 
         [0006]    In many carriage-style printers, the carriage guide rail is a round rod, and the carriage includes a corresponding rounded recess or bushing which slides along the round rod. The carriage guide rail bears the weight of the carriage and is primarily responsible for the accurate travel of the carriage. A second rail, i.e., the anti-rotation rail is used to make contact with an extension of the carriage in order to fix the carriage rotational orientation about the carriage guide rail axis. The anti-rotation rail can be a second round rod, but it can typically be made more cost effectively out of sheet metal as shown in, for example, U.S. Pat. No. 5,368,403. 
         [0007]    One method used in the prior art to adjust the spacing between the printhead nozzle face and the paper is to adjust the interface between the extension of the carriage and the anti-rotation rail, such that the carriage is allowed to rotate forward about the carriage guide rail to position the printhead nozzle face closer to the media support, or is caused to rotate backward about the carriage guide rail to position the printhead nozzle face farther from the media support. Typically such carriage rotation positions are not locked into place. In some cases this allows for the user changing the spacing between the printhead and the recording medium during a printing job or between printing jobs. However, the adjustment mechanisms to enable such spacing changes can be complex. 
         [0008]    What is needed is a simple adjustment mechanism and method for setting a spacing between the printhead and the media support after the printer has been assembled in the factory, and locking the setting in place. 
       SUMMARY OF THE INVENTION 
       [0009]    A printing system is provided for setting a distance between a printhead and a media support within a preselected acceptable range. The printing system includes a carriage for moving the printhead, a guide rail for supporting the carriage, and an anti-rotation rail for limiting an amount of rotation of the carriage around the guide rail. The apparatus includes a lockable adjustment mechanism for setting the printhead distance using a rotatable variable spacer that can be locked into place. The spacer includes several faces at selected distances from a center of the spacer. These faces can be brought into contact with an anti-rotation rail for securing the rotatable spacer in place. A distance between the printhead and the media support is different when a second face is in contact with the anti-rotation rail as compared to when the first face is in contact with the anti-rotation rail. Notches contained in the spacer mate with a locking tab for locking the spacer in position. 
         [0010]    Another preferred embodiment of the present inventions includes a printer that comprises a printhead attached to a carriage and the carriage attached to a guide rail for supporting the carriage and for moving the carriage along the guide rail and defining a carriage scan axis by the movement. An anti-rotation rail is also connected to the carriage for preventing excessive rotation of the carriage around the guide rail. A lockable rotatable spacer is coupled to the carriage for engaging the anti-rotation rail and for fixing one of a plurality of different angles of the carriage with respect to the guide rail. The lockable rotatable spacer comprises a rotation axis, a plurality of contact points, and is rotatable for disposing one of the plurality of contact points into engagement with the anti-rotation rail. Each contact point is located at a different distance from the rotation axis and permits selectably fixing the carriage at a variety of angles with respect to the guide rail. The distance between the media support and the printhead, or the printhead support, corresponds to a distance between each contact point and the rotation axis. The contact points can be shaped as discrete planar faces formed on the rotatable spacer. 
         [0011]    A feature of one preferred embodiment of the present invention is a rotatable spacer that is locked into place in order to prevent unintentional or accidental rotation of the spacer. One preferred embodiment for achieving that function comprises forming a locking tab in the carriage and a plurality of catches in the spacer each for engaging the locking tab and preventing unintentional rotation of the rotatable spacer. Each of the catches corresponds to one of the contact points and when the locking tab engages one of the catches, it disposes one of the contact points into engagement with the anti-rotation rail. This fixes the angle of the carriage on the guide rail. Another preferred embodiment of the present invention is a screw that is coupled to the spacer for rotating the spacer. 
         [0012]    These, and other, aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. The figures below are not intended to be drawn to any precise scale with respect to relative size, angular relationship, or relative position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic representation of an inkjet printer system; 
           [0014]      FIG. 2  is a perspective view of a portion of a printhead chassis; 
           [0015]      FIG. 3  is a perspective view of a portion of a carriage printer; 
           [0016]      FIG. 4  is a schematic side view of an exemplary paper path in a carriage printer; 
           [0017]      FIG. 5  is a perspective view of a portion of a printing system according to an embodiment of the present invention; 
           [0018]      FIG. 6  is an exploded view of a portion of a printing system according to an embodiment of the present invention; 
           [0019]      FIG. 7  is an end view of a portion of a printing system according to an embodiment of the present invention; 
           [0020]      FIG. 8  is a cross-sectional view of the embodiment shown in  FIGS. 5 through 7 ; 
           [0021]      FIG. 9  is a close-up of the view shown in  FIG. 8 ; 
           [0022]      FIG. 10  shows a top view of a rotatable spacer according to an embodiment of the present invention; 
           [0023]      FIG. 11  shows a top perspective view of a rotatable spacer according to an embodiment of the present invention; 
           [0024]      FIG. 12  shows a top perspective view of a first contact face of a rotatable spacer locked into position according to an embodiment of the present invention; 
           [0025]      FIG. 13  shows the embodiment of  FIG. 12  after a spring-loaded screw has been loosened; 
           [0026]      FIG. 14  shows the embodiment of  FIG. 13  after the spring-loaded screw has been pushed downward; 
           [0027]      FIG. 15  shows the embodiment of  FIG. 14  after the rotatable spacer has been rotated to place a different contact face into position; 
           [0028]      FIG. 16  shows the embodiment of  FIG. 15  after the hold-down force on the spring-loaded screw has been released; and 
           [0029]      FIG. 17  shows the embodiment of  FIG. 16  after the spring-loaded screw has been tightened. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    Referring to  FIG. 1 , a schematic representation of an inkjet printer system  10  is shown for its usefulness with the present invention and is fully described in U.S. Pat. No. 7,350,902, which is incorporated by reference herein in its entirety. Inkjet printer system  10  includes an image data source  12 , which provides data signals that are interpreted by a controller  14  as being commands to eject drops. Controller  14  includes an image processing unit  15  for rendering images for printing, and outputs signals to an electrical pulse source  16  of electrical energy pulses that are inputted to an inkjet printhead  100 , which includes at least one inkjet printhead die  110 . 
         [0031]    In the example shown in  FIG. 1 , there are two nozzle arrays in the printhead. Nozzles  121  in the first nozzle array  120  have a larger opening area than nozzles  131  in the second nozzle array  130 . In this example, each of the two nozzle arrays has two staggered rows of nozzles, each row having a nozzle density of 600 per inch. The effective nozzle density then in each array is 1200 per inch (i.e. d= 1/1200 inch in  FIG. 1 ). If pixels on the recording medium  20  were sequentially numbered along the paper advance direction, the nozzles from one row of an array would print the odd numbered pixels, while the nozzles from the other row of the array would print the even numbered pixels. 
         [0032]    In fluid communication with each nozzle array is a corresponding ink delivery pathway. Ink delivery pathway  122  is in fluid communication with the first nozzle array  120 , and ink delivery pathway  132  is in fluid communication with the second nozzle array  130 . Portions of ink delivery pathways  122  and  132  are shown in  FIG. 1  as openings through printhead die substrate  111 . Other arrangements and designs of nozzles and ink delivery channels may be used together with the present invention and are not considered critical to the scope of the present invention, as will be explained more fully below. More than one inkjet printhead die  110  can be included in inkjet printhead  100 , but for greater clarity only one inkjet printhead die  110  is shown in  FIG. 1 . The printhead dies are arranged on a support member as discussed below relative to  FIG. 2 . In  FIG. 1 , first fluid source  18  supplies ink to first nozzle array  120  via ink delivery pathway  122 , and second fluid source  19  supplies ink to second nozzle array  130  via ink delivery pathway  132 . Although distinct fluid sources  18  and  19  are shown, in some applications it may be beneficial to have a single fluid source supplying ink to both the first nozzle array  120  and the second nozzle array  130  via ink delivery pathways  122  and  132  respectively. Also, in some embodiments, fewer than two or more than two nozzle arrays can be included on printhead die  110 . In some embodiments, all nozzles on inkjet printhead die  110  can be the same size, rather than having multiple sized nozzles on inkjet printhead die  110 . 
         [0033]    Not shown in  FIG. 1 , are the drop forming mechanisms associated with the nozzles. Drop forming mechanisms can be of a variety of types, some of which include a heating element to vaporize a portion of ink and thereby cause ejection of a droplet, or a piezoelectric transducer to constrict the volume of a fluid chamber and thereby cause ejection, or an actuator which is made to move (for example, by heating a bi-layer element) and thereby cause ejection. In any case, electrical pulses from electrical pulse source  16  are sent to the various drop ejectors according to the desired deposition pattern. In the example of  FIG. 1 , droplets  181  ejected from the first nozzle array  120  are larger than droplets  182  ejected from the second nozzle array  130 , due to the larger nozzle opening area. Typically other aspects of the drop forming mechanisms (not shown) associated respectively with nozzle arrays  120  and  130  are also sized differently in order to optimize the drop ejection process for the different sized drops. During operation, droplets of ink are deposited on a recording medium  20 . 
         [0034]      FIG. 2  shows a perspective view of a portion of a printhead chassis  250 , which is an example of a chassis for implementing an inkjet printhead  100 . Printhead chassis  250  includes three printhead die  251  (similar to printhead die  110  in  FIG. 1 ), each printhead die  251 , containing two nozzle arrays  253 , so that printhead chassis  250 , contains six nozzle arrays  253  altogether. The face of any printhead die  251 , containing nozzle arrays  253  (or collectively all such faces on individual printhead die  251 ) is referred to herein as the printhead nozzle face  252 . The six nozzle arrays  253  in this example can each be connected to separate ink sources (not shown in  FIG. 2 ); such as cyan, magenta, yellow, text black, photo black, and a colorless protective printing fluid. Each of the six nozzle arrays  253  is disposed along nozzle array direction  254 , and the length of each nozzle array along the nozzle array direction  254  is typically on the order of 1 inch or less. Typical lengths of recording media are 6 inches for photographic prints (4 inches by 6 inches) or 11 inches for paper (8.5 inches by 11 inches). Thus, in order to print a full image, a number of swaths are successively printed while moving printhead chassis  250  across the recording medium  20 . Following the printing of a swath, the recording medium  20  is advanced along a media advance direction that is substantially parallel to nozzle array direction  254 . 
         [0035]    Also shown in  FIG. 2  is a flex circuit  257  to which the printhead die  251  are electrically interconnected, for example, by wire bonding or tape-automated bonding (TAB). The interconnections are covered by an encapsulant  256  to protect them. Flex circuit  257  bends around the side of printhead chassis  250  and connects to connector board  258 . When printhead chassis  250  is mounted into the carriage  200  (see  FIG. 3 ), connector board  258  is electrically connected to a connector (not shown) on the carriage  200 , so that electrical signals can be transmitted to the printhead die  251 . 
         [0036]      FIG. 3  shows a portion of a desktop carriage printer. Some of the parts of the printer have been hidden in the view shown in  FIG. 3  so that other parts can be more clearly seen. Printer chassis  300  has a print region  303  across which carriage  200  is moved back and forth along carriage scan direction  305 , between the right side  306  and the left side  307  of printer chassis  300 , while drops are ejected from printhead die  251  (not shown in  FIG. 3 ) on printhead chassis  250  that is mounted on carriage  200 . A media support  301  helps to hold the recording medium flat in print region  303 . Carnage motor  380  moves belt  384  to move carriage  200  along carriage guide rail  382 . An encoder sensor (not shown) is mounted on carriage  200  and indicates carriage location relative to an encoder fence  385 . 
         [0037]    Printhead chassis  250  is mounted in carriage  200 , and multi-chamber ink supply  262  and single-chamber ink supply  264  are mounted in the printhead chassis  250 . The mounting orientation of printhead chassis  250 , as shown in  FIG. 3 , is rotated relative to the view in  FIG. 2 , so that the printhead die  251  are located at the bottom side of printhead chassis  250 , the droplets of ink being ejected downward onto the recording medium in print region  303  (i.e. the print zone) in the view of  FIG. 3 . Multi-chamber ink supply  262 , in this example, contains five ink sources: cyan, magenta, yellow, photo black, and colorless protective fluid; while single-chamber ink supply  264  contains the ink source for text black. Paper or other recording medium (sometimes generically referred to as paper or media herein) is loaded along paper load entry direction  302  toward the front of printer chassis  308 . 
         [0038]    A variety of rollers are used to advance the medium through the printer as shown schematically in the side view of  FIG. 4 . In this example, a pick-up roller  320  moves the top piece or sheet  371  of a stack  370  of paper or other recording medium in the direction of the arrow showing paper load entry direction  302 . A turn roller  322  acts to move the paper around a C-shaped path (in cooperation with a curved rear wall surface of the printer, not shown) so that the paper continues to advance along media advance direction  304  from the rear of the printer chassis  309  (with reference also to  FIG. 3 ). The paper is then moved by feed roller  312  and idler roller(s)  323  to advance across print region  303 , and from there to a discharge roller  324  and star wheel(s)  325  so that printed paper exits along media advance direction  304 . When the paper is held by both feed roller  312  and star wheel(s)  325 , media support  301  helps to keep the paper flat in the print region (zone)  303 . Feed roller  312  includes a feed roller shaft along its axis, and feed roller gear  311  is mounted on the feed roller shaft. Feed roller  312  can include a separate roller mounted on the feed roller shaft, or can include a thin high friction coating on the feed roller shaft. A rotary encoder (not shown) can be coaxially mounted on the feed roller shaft in order to monitor the angular rotation of the feed roller. 
         [0039]    The motor that powers the paper advance rollers is not shown in  FIG. 3 , but the hole  310  at the right side of the printer chassis  306  is where the motor gear (not shown) protrudes through in order to engage feed roller gear  311 , as well as the gear for the discharge roller (not shown). For normal paper pick-up and feeding, it is desired that all rollers rotate in forward rotation direction  313 . Toward the left side of the printer chassis  307 , in the example of  FIG. 3 , is the maintenance station  330 . 
         [0040]    Toward the rear of the printer chassis  309 , in this example, is located the printer electronics board  390 , which includes cable connectors  392  for communicating via cables (not shown) to the printhead carriage  200  and from there to the printhead chassis  250 . Also on the printer electronics board  390  are typically mounted motor controllers for the carriage motor  380  and for the paper advance motor, a processor and/or other control electronics (shown schematically as controller  14  and image processing unit  15  in  FIG. 1 ) for controlling the printing process, and an optional connector for a cable to a host computer. 
         [0041]      FIG. 5  is a perspective view and  FIG. 6  is an exploded view of a portion of a printing system according to one preferred embodiment of the present invention. Carriage  200  is movable along carriage guide rail  382  disposed along carriage scan direction (axis)  305 . Carriage guide rail  382  is typically a round rod, but is not limited to such a geometry. One or more carriage bushings  205  can provide a mechanical contact surface between the carriage  200  and the carriage guide rail  382 . Particularly when the printhead  250  is loaded into the carriage, the center of mass of the carriage  200  is forward of the carriage guide rail  382 , so that the carriage tends to rotate about the carriage guide rail  382  in the carriage rotation direction  210 . A rotatable spacer  410  is provided to contact anti-rotation rail  383  in order to limit the amount of rotation of the carriage  200  in carriage rotation direction  210 . Rotatable spacer  410  has an axis of rotation  431 . In the embodiment shown in  FIG. 5 , axis of rotation  431  is substantially perpendicular to carriage scan axis  305 . Rotatable spacer  410  has a plurality of contact faces or contact points (described below in more detail) that are at different spacings from the axis of rotation  431 . Depending upon which contact face is selected to be contact with anti-rotation rail  383 , the center of rotatable spacer  410  moves closer to, or further from, the anti-rotation rail  383  along direction  432 . To move the center of rotatable spacer  410  closer to the anti-rotation rail  383 , the carriage  200  must rotate along carriage rotation direction  210 . To move the center of rotatable spacer  410  further from the anti-rotation rail  383 , the carriage  200  must rotate in the opposite direction from carriage rotation direction  210 . Rotatable member  420  is coupled to rotatable spacer  410 . In one preferred embodiment, rotatable member  420  is a screw and rotatable spacer  410  has a threaded hole to accept the screw end  426  that is opposite the screw head  424 . A compression spring  422  can be provided to surround screw end  426  and to bias screw head  424  in a bias direction  425  pointing away from rotatable spacer  410  along rotation axis  431 . 
         [0042]      FIG. 7  is an end view of the embodiment shown in  FIGS. 5 and 6 . A first contact face  412  of rotatable spacer  410  is in contact with anti-rotation rail  383 . The distance that first contact face  412  is from the rotation axis  431 , determines how much carriage  200  can rotate in carriage rotation direction  210  around carriage guide rail  382 . Printhead nozzle face  252  is located near the bottom of carriage  200 . A distance D between printhead nozzle face  252  and media support  301  is determined by the amount of rotation of carriage  200  around carriage guide rail  382 . Let x be the distance between the center of rotatable spacer  410  and anti-rotation rail  383 . If the center of rotatable spacer  410  moves in the direction  432  with respect to anti-rotation rail  383  by a distance Ax, the change in distance D between media support  301  and a point on the printhead nozzle face  252  that is located a distance Y from the center of carriage guide rail  382  is ΔD˜YΔx/Z, where Z is the distance of the point of contact above the center of the carriage guide rail  382 . 
         [0043]      FIG. 8  is a cross-sectional view of the embodiment of  FIGS. 5 through 7  showing rotatable spacer  410  separately from spring-biased rotatable member (screw)  420 , and  FIG. 9  is a close-up view of  FIG. 8 . Compression spring  422  is held against a ledge  434  around the inside of hole  438  in an extension  436  of carriage  200 . Screw end  426  of screw  420  also can be passed through hole  438  to screw into threaded hole  411  of rotatable spacer  410 . Compression spring  422  is compressed between ledge  434  and screw head  424  to provide a biasing force on screw head  424  in bias direction  425 . Rotatable spacer  410  includes a plurality of contact faces, including first contact face  412 . Rotatable spacer  410  also includes a rim  440  that has a plurality of notches to be described below. Although the figures show discrete planar contact faces, the rotatable spacer could be designed with a continuous eccentric surface or with other structures, such as a series of contact bumps, for providing a variable distance between the central axis of the rotatable spacer and the anti-rotation rail. 
         [0044]      FIG. 10  shows a top view and  FIG. 11  shows a top perspective view of rotatable spacer  410 . In the embodiment shown in  FIG. 10  and  FIG. 11 , rotatable spacer  410  includes first contact face  412 , second contact face  413 , and third contact face  414 . The distance of the first contact face  412  to the rotation axis  431  of rotatable spacer  410  is a first distance, such as 5.0 mm. The distance of the second contact face  413  to rotation axis  431  is a second distance, such as 5.18 mm, which is greater than the first distance. The distance of the third contact face  414  to rotation axis  431  is a third distance, such as 4.82 mm, which is less than the first distance. First contact face  412  corresponds to a nominal spacing adjustment for the spacing D between the printhead nozzle face  252  and the media support  301  (with reference to  FIG. 7 ). Second contact face  413  moves the center of rotatable spacer  410  further away from anti-rotation rail  383  if it is in contact, so that the spacing D between printhead nozzle face  252  and media support  301  will be greater than if the first contact face were in contact with the anti-rotation rail. Similarly, third contact face  414  allows the center of rotatable spacer  410  to move closer to anti-rotation rail  383  if it is in contact, so that the spacing D between printhead nozzle face  252  and media support  301  will be less than if the first contact face  412  were in contact with the anti-rotation rail  383 . Again with reference to  FIG. 7 , if Y/Z=1.2, for example, the change in D when rotating rotatable spacer  410  from a nominal position where the first contact face  412  is in contact with anti-rotation rail  383 , for the exemplary dimensions of rotatable spacer  410  given above, is ΔD˜+0.2 mm if the second contact faced  413  is rotated into contact position, or ΔD˜−0.2 mm if the third contact face  414  is rotated into contact position. 
         [0045]    Directly opposite each contact face is a corresponding notch in rim  440  of rotatable spacer  410 . The notches serve as catches in a locking mechanism to hold a selected contact face against anti-rotation rail  383  (with reference to  FIG. 7 ) as will be described below. First notch  442  corresponds to first contact face  412 . Second notch  443  corresponds to second contact face  413 . Third notch  444  corresponds to third contact face  414 . Second notch  443  is 90 degrees of angular rotation away from first notch  442 , and third notch  444  is also 90 degrees away from first notch  442 , but second notch  443  is 180 degrees away from third notch  444 . Similarly, second contact face  413  is 90 degrees of angular rotation away from first contact face  412 , and third contact face  414  is also 90 degrees away from first contact face  412 , but second contact face  413  is 180 degrees away from third contact face  414 . In this configuration it is straightforward to increase the nominal spacing adjustment between the printhead nozzle face  252  and media support  301  by rotating rotatable spacer  410  in one direction by 90 degrees to place the second contact face  413  into contact with anti-rotation rail  383 , or to decrease the nominal spacing adjustment between the printhead nozzle face  252  and media support  301  by rotating rotatable spacer  410  in the opposite direction by  90  degrees to place the third contact face  414  into contact with anti-rotation rail  383 . 
         [0046]      FIG. 11  shows that rim  440  of rotatable spacer  410  has a first height near first contact face  412 , but has a lower height near second contact face  413 , and third contact face  414 . As a result, second notch  443  and third notch  444  each have one tall wall and one short wall  449 , while first notch  442  has two short walls  449 . In this embodiment, the tall wall of second notch  443  serves as a first stopper  447  that prohibits rotation of rotatable spacer  410  beyond the second notch  443 , as will be described below. Similarly, the tall wall of third notch  444  serves as a second stopper  448  that prohibits rotation of rotatable spacer  410  beyond the third notch  444 . 
         [0047]      FIGS. 12 through 17  show perspective views of a portion of carriage  200  and a lockable adjustment mechanism  450  for locking a selected contact face into position in order to adjust a distance D between the printhead nozzle face  252  and media support  301  (with reference to  FIG. 7 ) according to an embodiment of the present invention. Lockable adjustment mechanism  450  engages with a locking tab  435 , and includes rotatable spacer  410 , a first contact face  412 , a second contact face  413 , a first catch (first notch  442 ), a second catch (second notch  443  with reference to  FIG. 11 ), and a third catch (third notch  444 ). In this embodiment, locking tab  435  is part of carriage  200 , and more particularly is located on the outside of extension  436 . For clarity, anti-rotation rail  383  is not shown in  FIGS. 12 through 17 . 
         [0048]      FIG. 12  shows the nominal configuration of the lockable adjustment mechanism  450  with first contact face  412  locked into position to contact anti-rotation rail  383 . The nominal configuration is the configuration that the lockable adjustment mechanism  450  is set to when the printers are initially assembled at the factory. In the nominal configuration, locking tab  435  is engaged with the first catch (i.e., locking tab  435  is captured within first notch  442 ), so that rotatable spacer  410  cannot be rotated. It has been found that spacing D between the printhead nozzle face  252  and the media support  301  (with reference to  FIG. 7 ) is within an acceptable range for many printers when the lockable adjustment mechanism  450  is in its nominal configuration. Further, it has been found that substantially all of the rest of the printers can have spacing D adjusted (e.g., at the factory) into the acceptable range by either rotating the second contact face  413  or the third contact face  414  into position to contact the anti-rotation rail  383 . In the locked configuration shown in  FIG. 12 , rotatable screw  420  (with reference to  FIG. 7 ) is tightened so that the bottom surface of screw head  424  is in contact with collar  433 , and screw end  426  extends through the bottom of rotatable spacer  410 . 
         [0049]    After the printer has been assembled, the spacing D between the printhead nozzle face  252  and the media support  301  is measured directly and the appropriate contact face to be in contact with anti-rotation rail  383  is selected. In another embodiment, the spacing D can be determined indirectly prior to installing the printhead on a printhead support formed in the carriage. In this embodiment, a spacing D′ is measured as between the printhead support and the media support. This distance D′ indicates what the spacing D would be when the printhead is attached to the printhead support with prior knowledge of the mounting configuration of the printhead. If spacing D is within an acceptable range, then first contact face  412  is kept in contact with anti-rotation rail  383 . If spacing D is not within an acceptable range, the lockable adjustment mechanism  450  is subsequently unlocked. The rotatable spacer  410  is then rotated in a first rotational direction such that second contact face  413  is moved into position to contact anti-rotation rail  383  if the measured spacing is less than the acceptable range, or the rotatable spacer  410  is rotated in a rotational direction that is opposite the first rotational direction, such that third contact face  414  is moved into position to contact anti-rotation rail  383  if the measured spacing is greater than the acceptable range. 
         [0050]      FIG. 13  shows a first operation for unlocking the lockable adjustment mechanism  450 . Rotatable member (screw)  420  (with reference to  FIG. 9 ) is loosened so that compression spring  422  pushes screw head  424  up so that the bottom surface of screw head  424  is a spacing S from collar  433 . This extra spacing S is provided by withdrawing screw end  426  (with reference to  FIG. 12 ) upward into threaded hole  411  of rotatable spacer  410  by partially unscrewing rotatable member (screw)  420 . At this stage, locking tab  435  is still engaged with first notch  442 , and first contact face  412  is still in position to contact anti-rotation rail  383 . Rotational member (screw)  420  includes threads proximate to screw end  426  which engage threads interior to (threaded) hole  411  sufficient to operate the screw and the rotatable spacer  410  as described herein. The threads are not shown in the figures. 
         [0051]      FIG. 14  shows a second operation for unlocking the lockable adjustment mechanism  450 . Screw head  424  is pushed down along rotation axis  431  toward collar  433 . With reference to  FIG. 13 , screw head  424  can be pushed down by a first travel distance X which can be as large as the spacing S provided by loosening (rotatable member) screw  420 , and typically X=S. Because the threads of screw end  426  are still engaged with threaded hole  411 , rotatable spacer  410  is thereby pushed downward by the first travel distance X along rotation axis  431 , moving first notch  442  away from locking tab  435 . Comparing  FIG. 14  with  FIG. 13  it can also be seen that pushing screw head  424  down has opened up a gap between the bottom of extension  436  and the top of rim  440 . First travel distance X is sufficient so that short walls  449  (with reference to  FIG. 11 ) are below locking tab  435 , so that locking tab  435  is released from the first catch (i.e., from first notch  442 ) and rotatable spacer  410  can be freely rotated either to second catch (notch  443 ) or third catch (notch  444 ). In other words, when the rotatable spacer  410  is located at the first travel distance X along rotation axis  431 , there are no stoppers in a region that is located between the first stopper  447  and the second stopper  448 . However, first travel distance X does not provide clearance of locking tab  435  relative to stoppers  447  and  448 . As a result, if rotatable spacer  410  is rotated toward second notch  443 , its rotation is limited by an interference of locking tab  435  with first stopper  447 , so that tactile feedback is provided to the adjuster to indicate that locking tab  435  is aligned with second notch  443 . Similarly, if rotatable spacer  410  is rotated in the opposite direction toward third notch  444 , its rotation is limited by an interference of locking tab  435  with second stopper  448 , so that tactile feedback is provided to the adjuster to indicate that locking tab  435  is aligned with third notch  444 . In  FIG. 14 , however, rotation of rotatable spacer  410  has not yet occurred, so that first contact face  412  is still in position to contact anti-rotation rail  383 .  FIG. 14  also indicates that locking tab  435  has a lengthwise dimension L that is oriented substantially parallel to rotation axis  431 . Lengthwise dimension L is typically longer than first travel distance X, so that locking tab  435  will hit stoppers  447  or  448  if rotatable spacer  410  is rotated to place the second contact face  413  or the third contact face  414  respectively in position to contact the anti-rotation rail  383 . 
         [0052]    With the locking tab  435  released from the first catch (first notch  442 ) as a result of the operation shown in  FIG. 14 , rotatable spacer  410  can now be rotated as shown in  FIG. 15 . While still holding screw head  424  down, friction between the threads of screw end  426  and threaded hole  411  causes rotatable spacer  410  to rotate when the screw head  424  is rotated about rotation axis  431 . During the rotation of rotatable spacer  410 , it is not in contact with anti-rotation rail  383 , so it is free to rotate. For example, with reference to  FIG. 7 , rotatable spacer  410  can be moved out of contact with anti-rotation rail  383 , by rocking carriage  200  backward around carriage guide rail  382  in a direction that is opposite to carriage rotation direction  210 . In  FIG. 15 , rotatable spacer  410  has been rotated in direction  428  until locking tab  435  hit second stopper  448 , indicating that rotatable spacer is in position for locking tab  435  to engage with a third catch (third notch  444 , in this case). As a result, first contact face  412  is no longer in position to contact anti-rotation rail  383 . Rather, third contact face  414  is in position to contact anti-rotation rail  383 , thereby allowing the spacing D between the printhead nozzle face  252  and media support  301  to decrease. 
         [0053]      FIG. 16  shows the result of releasing the hold-down force on screw head  424 . Compression spring  422  pushes screw head  424  up, which also pulls rotatable spacer  410  upward until the gap (corresponding to first travel distance X) between the bottom of extension  436  and the top of rim  440  that existed in  FIGS. 14 and 15  is closed. Locking tab  435  is now engaged with third notch  444 . 
         [0054]    Rotatable member (screw)  420  is next tightened, without exerting sufficient hold-down force on screw head  424  to disengage locking tab  435  from the catch that it is currently in (third notch  444 , in this case).  FIG. 17  shows the result of tightening rotatable member (screw)  420 . Screw head  424  is held against collar  433 . Screw end  426  extends past rotatable spacer  410 . Locking tab  435  is firmly engaged in third notch  444 . The tightened screw  420  keeps locking tab  435  from being disengaged. Adjustment of spacing D between printhead nozzle face  252  and media support  301  is now completed and locked in, such that D is now within the acceptable range of spacings. 
         [0055]    Thus, a simple adjustment mechanism and method has been provided for setting a spacing between the printhead and the media support after the printer has been assembled in the factory, and for locking the setting in place. 
         [0056]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
       Parts List  
       [0057]      10  Inkjet printer system 
         [0058]      12  Image data source 
         [0059]      14  Controller 
         [0060]      15  Image processing unit 
         [0061]      16  Electrical pulse source 
         [0062]      18  First fluid source 
         [0063]      19  Second fluid source 
         [0064]      20  Recording medium 
         [0065]      100  Inkjet printhead 
         [0066]      110  Inkjet printhead die 
         [0067]      111  Substrate 
         [0068]      120  First nozzle array 
         [0069]      121  Nozzle(s) 
         [0070]      122  Ink delivery pathway (for first nozzle array) 
         [0071]      130  Second nozzle array 
         [0072]      131  Nozzle(s) 
         [0073]      132  Ink delivery pathway (for second nozzle array) 
         [0074]      181  Droplet(s) (ejected from first nozzle array) 
         [0075]      182  Droplet(s) (ejected from second nozzle array) 
         [0076]      200  Carriage 
         [0077]      205  Carriage bushing(s) 
         [0078]      210  Carriage rotation direction 
         [0079]      250  Printhead chassis 
         [0080]      251  Printhead die 
         [0081]      252  Printhead nozzle face 
         [0082]      253  Nozzle array(s) 
         [0083]      254  Nozzle array direction 
         [0084]      256  Encapsulant 
         [0085]      257  Flex circuit 
         [0086]      258  Connector board 
         [0087]      262  Multi-chamber ink supply 
         [0088]      264  Single-chamber ink supply 
         [0089]      300  Printer chassis 
         [0090]      301  Media support 
         [0091]      302  Paper load entry direction 
         [0092]      303  Print region 
         [0093]      304  Media advance direction 
         [0094]      305  Carriage scan direction 
         [0095]      306  Right side of printer chassis 
         [0096]      307  Left side of printer chassis 
         [0097]      308  Front of printer chassis 
         [0098]      309  Rear of printer chassis 
         [0099]      310  Hole (for paper advance motor drive gear) 
         [0100]      311  Feed roller gear 
         [0101]      312  Feed roller 
         [0102]      313  Forward rotation direction (of feed roller) 
         [0103]      320  Pick-up roller 
         [0104]      322  Turn roller 
         [0105]      323  Idler roller(s) 
         [0106]      324  Discharge roller 
         [0107]      325  Star wheel(s) 
         [0108]      330  Maintenance station 
         [0109]      370  Stack of media 
         [0110]      371  Top piece of medium 
         [0111]      380  Carriage motor 
         [0112]      382  Carriage guide rail 
         [0113]      383  Anti-rotation rail 
         [0114]      385  Encoder fence 
         [0115]      384  Belt 
         [0116]      390  Printer electronics board 
         [0117]      392  Cable connectors 
         [0118]      410  Rotatable spacer 
         [0119]      411  Threaded hole 
         [0120]      412  First contact face 
         [0121]      413  Second contact face 
         [0122]      414  Third contact face 
         [0123]      420  Rotatable member (screw) 
         [0124]      422  Compression spring 
         [0125]      424  Screw head 
         [0126]      425  Bias direction 
         [0127]      426  Screw end 
         [0128]      428  Rotation direction 
         [0129]      431  Rotation axis (axis of rotation) 
         [0130]      432  Direction from rotation axis to anti-rotation rail 
         [0131]      433  Collar 
         [0132]      434  Ledge 
         [0133]      435  Locking tab 
         [0134]      436  Extension 
         [0135]      438  Hole 
         [0136]      440  Rim 
         [0137]      442  First notch 
         [0138]      443  Second notch 
         [0139]      444  Third notch 
         [0140]      447  First stopper 
         [0141]      448  Second stopper 
         [0142]      449  Short wall(s) 
         [0143]      450  Lockable adjustment mechanism
A printing system with adjustable spacing between a portion of a printhead and a portion of a media support. The spacing is easily adjustable at the time of manufacture for locking a printhead into a selected distance from the media support. A rotatable variable spacer is abutted against an anti-rotation rail to lock the selected distance.