Abstract:
An adaptive method for handling media is provided for an inkjet printing mechanism having a printhead that prints on media in a printzone. A drive motor, a spacing adjuster, a controller storing a tolerance adjust value, and a media support member are provided, with the support member defining a printhead-to-media spacing in the printzone. The tolerance value is summed with a value selected for the type of media or image to determine a total motor drive value. In a coupling step, the motor is operatively coupled to the support member using the spacing adjuster. Following the coupling step, in an adjusting step, the printhead-to-media spacing is selectively adjusted by the driving spacing adjuster with the motor for the total drive value. A method is provided of accommodating manufacturing tolerance variations accumulated during assembly of an inkjet printing mechanism having a printhead that prints on media in a printzone.

Description:
This is a continuation of copending application Ser. No. 08/652,720, filed May 30, 1996 now U.S. Pat. No. 6,102,509. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to printing mechanisms, and more particularly to an adaptive method for handling inkjet printing media to accurately move and print upon individual sheets of media in a printzone of an inkjet printing mechanism. 
     BACKGROUND OF THE INVENTION 
     Inkjet printing mechanisms use cartridges, often called “pens,” which shoot drops of liquid colorant, referred to generally herein as “ink,” onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text). 
     To clean and protect the printhead, typically a “service station” mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which hermetically seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as “spitting,” with the waste ink being collected in a “spittoon” reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead. 
     To print an image, the printhead is scanned back and forth across a printzone above the sheet, with the pen shooting drops of ink as it moves. By selectively energizing the resistors as the printhead moves across the sheet, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text). The nozzles are typically arranged in one or more linear arrays. If more than one, the two linear arrays are usually located side-by-side on the printhead, parallel to one another, and perpendicular to the scanning direction. Thus, the length of the nozzle arrays defines a print swath or band. That is, if all the nozzles of one array were continually fired as the printhead made one complete traverse through the printzone, a band or swath of ink would appear on the sheet. The width of this band is known as the “swath width” of the pen, the maximum pattern of ink which can be laid down in a single pass. Any variation in the media-to-printhead spacing along the length of the nozzle array may yield visually acceptable deviations in print quality. There are a variety of different problems that make it difficult to always achieve consistent and accurate media-to-printhead spacing. 
     As a preliminary matter, there is a term of art used by inventors skilled in this art that will speed the reading if used herein, and it is “pen-to-paper spacing,” often abbreviated as “PPS” or “PPS spacing.” In the English language of the inventor, “pen-to-paper spacing” or “PPS” is easier to pronounce than the more technically explicit term “media-to-printhead spacing,” and for this reason “pen-to-paper spacing” or “PPS” are used herein. During prototype testing and development, inventors use vast amounts of media, so the most plentiful and economical media, plain paper is used. Indeed, the short-hand term “pen-to-paper spacing” is a logical selection of terminology, although it must be understood that as used herein, this term encompasses all different types of media, unless specified otherwise in describing a particular type of media. Thus, “pen-to-paper spacing” (PPS) defines the spacing between the inkjet cartridge printhead and the printing surface of the media, which may be any type of media, such as plain paper, specialty paper, card-stock, fabric, transparencies, foils, mylar, etc. Having dispensed with preliminary matters, the discussion of the problems encountered in this art in maintaining an accurate PPS now continues. 
     First, there is a tendency for some graphic and photographic type images to saturate the media with ink, causing an undesirable effect known in the art as “cockle.” The term “cockle” refers to the tendency of media, such as paper, to uncontrollably bend or buckle as the wet ink saturates the fibers of the media and causes them to expand. This buckling or cockling causes the media to uncontrollably bend either downwardly away from the printhead, or upwardly toward the printhead, with either motion undesirably changing the PPS spacing and leading to poor print quality. Moreover, upward buckling may be extreme enough to cause the media to actually contact the printhead, which may clog a nozzle and/or smear ink on the media, damaging the image. 
     Second, there are variations in the thickness of the print media which also affect the PPS spacing. For example, envelopes, poster board and fabric are typically thicker than plain paper or a transparency. The thicker media decreases the spacing from the printhead to the printing surface, and as with cockle, in the worst case, this reduced spacing could lead to contact of the printhead with the media, possibly damaging either the printhead or the image. Furthermore, these various media thicknesses also offer challenges to an automatic feed system, which must pick the top sheet from a stack of media, and then accurately feed it into the print zone. 
     One earlier media handling system tried to accommodate thicker envelopes, using a width sensor that detected media narrower than about 12 cm (4.5 in). Upon detecting this narrow media, a mechanical arm opened an inlet port on the media handling system to a much wider gap than normal to prevent ink smear on the envelope. Unfortunately, the assumption envelope was being printed just because the media width was narrow completely ignored the printing of postcards by a user. Thus, when printing postcards the print quality was severely degraded by the greater PPS spacing. Moreover, there was no provision for the user to defeat this mechanical widening of the gap when postcards where printed. 
     The earlier media handling systems lacked any ability to adjust the PPS spacing, other than adjustments made during initial assembly at the factory. Manufacturing adjustments are required to accommodate the large number of parts whose various tolerances accumulate and lead to a large degree of variability around the nominal spacing value. One earlier method involved the rotation of a helical cam, and the tightening of an adjustment screw to fasten the cam in place. Unfortunately, errors may occur during manufacturing, for example, from human error in reading a dial indicator measuring device or other display. Furthermore, the act of tightening the adjustment screw caused various mechanical stresses on the component parts. Additionally, physical access to the adjustment cam and screw had to be provided for in the mechanical design of the printer. Furthermore, this manual adjustment may occur when the printing mechanism was only partially assembled, so the addition of other parts to the printer mechanism could warp the spacing adjustment. Any of these inaccuracies in the PPS spacing occurring during manufacture could result in degraded print quality for the entire life of the printer. 
     Beyond the PPS spacing issue, the earlier media handling systems have suffered a variety of other disadvantages. Many of these earlier systems required a multitude of separate parts, for picking sheets of media from a stack, feeding the media through the print zone, and then depositing the printed sheet in an output tray. For example, one earlier design required 15-17 separate parts, which contributed significantly to the overall complexity and cost of the printing mechanism, not only in the actual cost of the parts themselves, but also in labor time required for their assembly. Additionally, many of these earlier media handling systems used spring loaded parts, which at some point during printing would snap the parts back into place; a noisy operation indeed. Most customers in the home or office environment want quieter printers, so this noise from return springs and the associated noise of the parts colliding with one another in the earlier designs was undesirable. 
     Given the criticality of the pen-to-paper spacing, the desire for higher print quality, which typically implies a closer spacing, as well as the ability to handle different types of media (e.g., envelopes, plain paper, card stock, etc.) and different images (e.g., text vs. graphic vs. photographic), it would be desirable to adjust the PPS spacing automatically during use. Such an automatic adjustment would also aid manufacturing, particularly if it could be implemented in a media handling system having fewer and quieter components. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, an adaptive method of printing using an inkjet printing mechanism having a printhead that prints on media in a printzone is provided as including the step of providing a drive motor and a spacing adjuster. Also in the providing step, a media support member is provided, with the support member defining a printhead-to-media spacing in the printzone between the printhead and media when supported thereby. In a coupling step, the motor is operatively coupled to the support member using the spacing adjuster. Following the coupling step, in an adjusting step, the printhead-to-media spacing is selectively adjusted by the driving spacing adjuster with the motor. 
     According to another aspect of the invention, a method is provided of accommodating manufacturing tolerance variations accumulated during assembly of an inkjet printing mechanism having a printhead that prints on media in a printzone. The method includes the step of assembling a media handling system for an inkjet printing mechanism from plural components each having unique dimensions ranging between maximum and minimum limits. These components include a printhead, a drive motor, a spacing adjuster, a media support member that defines a printhead-to-media spacing in the printzone between the printhead and media when supported thereby. When assembled, the system has a manufactured printhead-to-media spacing. In a measuring step, the manufactured printhead-to-media spacing is measured, then compared in a comparing step, with a nominal value for printhead-to-media spacing to determine a spacing difference therebetween. In a determining step, the amount to drive the motor that corresponds to the determined spacing difference is determined, for instance, by referring to a look-up table correlating these values. In a coupling step, the motor is operatively coupled to the support member using the spacing adjuster. Following the coupling step, in an adjusting step, the printhead-to-media spacing is selectively adjusted by the driving spacing adjuster with the motor for the determined amount to arrive at an adjusted spacing. 
     According to a further aspect of the invention, an adaptive method of printing using an inkjet printing mechanism having a printhead that prints on media in a printzone is provided as including the step of providing a drive motor and a spacing adjuster. Also in the providing step, a media support member is provided, with the support member defining a printhead-to-media spacing in the printzone between the printhead and media when supported thereby. The providing step also includes providing a controller having a memory portion with a tolerance adjust value stored therein. In a selecting step, a desired printhead-to-media spacing is selected, along with an amount to drive the motor that corresponds to the desired printhead-to-media spacing. In a summing step, the tolerance adjust value and the selected amount to drive the motor are summed together to arrive at a total motor drive value. In a coupling step, the motor is operatively coupled to the support member using the spacing adjuster. Following the coupling step, in an adjusting step, the printhead-to-media spacing is selectively adjusted by the driving spacing adjuster with the motor for the total motor drive value. 
     An overall goal of the present invention is to provide an adaptive method for handling media to accurately move individual sheets of media and envelopes through a printzone of an inkjet printing mechanism, as well as long Z-folded strips of banner media. 
     Another goal of the present invention is to provide an adaptive method of adjusting printhead-to media spacing that may be automatically implemented, not only during initial assembly, but also during operation to meet the printing needs of different types of media and images. 
     A further goal of the present invention is to provide an economical method of operating an inkjet printing mechanism which optimizes the print quality of an image and which operates quietly, with minimal user intervention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmented perspective view of one form of an inkjet printing mechanism employing one form of an adaptive media handling system of the present invention. 
     FIG. 2 is a fragmented perspective view of the adaptive media handling system of FIG. 1, shown removed from the casing of the printing mechanism. 
     FIG. 3 is a fragmented, enlarged perspective view taken along line  3 — 3  of FIG. 2, showing the out-board side of one form of a media drive mechanism of the present invention. 
     FIG. 4 is a fragmented, enlarged perspective view taken along line  4 — 4  of FIG. 2, showing the in-board side of one form of a media drive mechanism of the present invention. 
     FIG. 5 is an enlarged perspective, partially exploded view of a portion of the in-board side of the media drive mechanism, with one component ( 100 ) shown reduced in size and rotated in the view around a vertical axis to better illustrate its coupling with the other components. 
     FIG. 6 is a fragmented, enlarged front elevational view taken along line  6 — 6  of FIG. 2, also showing a portion of the printhead carriage engaging a shift lever member of the media drive mechanism. 
     FIGS. 7-14 are out-board side elevational views, taken generally along line  7 — 7  of FIG. 6, but with the shift lever, drive motor and several of the drive gears removed for clarity, and more specifically: 
     FIG. 7 shows the drive mechanism in a kick position for ejecting media, which also corresponds to a rest position and a start position for picking fresh media; 
     FIG. 8 shows a transition portion of operation of the drive mechanism, where the printhead carriage engages the shift lever (not shown) to begin the media pick routine; 
     FIG. 9 shows the drive mechanism beginning to pick a sheet of media; 
     FIG. 10 shows the drive mechanism during an intermediate stage of picking the sheet; 
     FIG. 11 shows the drive mechanism during a final stage of picking the sheet, prior to transitioning to the initial position of FIG. 7; 
     FIG. 12 shows the drive mechanism in an initial position for beginning normal printing, for instance on plain paper; 
     FIG. 13 shows the drive mechanism during a media to printhead spacing adjustment portion of operation; and 
     FIG. 14 shows a transition portion of operation of the drive mechanism. 
     FIG. 15 is a flow chart illustrating one manner of adjusting the adaptive media handling system of FIG. 1 during initial assembly of the printing mechanism at the manufacturing facility. 
     FIGS. 16-19 are portions of a flow chart illustrating one manner of operating the adaptive media handling system of FIG. 1, including a media pick routine (FIG.  16 ), a PPS adjust routine (FIG.  17 ), a printing routine and media discharge routine (FIGS.  18  and  19 ). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an embodiment of an inkjet printing mechanism, here shown as an inkjet printer  20 , constructed in accordance with the present invention, which may be used for printing for business reports, correspondence, desktop publishing, and the like, in an industrial, office, home or other environment. A variety of inkjet printing mechanisms are commercially available. For instance, some of the printing mechanisms that may embody the present invention include plotters, portable printing units, copiers, cameras, video printers, and facsimile machines, to name a few. For convenience the concepts of the present invention are illustrated in the environment of an inkjet printer  20 . 
     While it is apparent that the printer components may vary from model to model, the typical inkjet printer  20  includes a chassis  22  surrounded by a housing or casing enclosure  24 , typically of a plastic material. Sheets of print media are fed through a print zone  25  by an adaptive print media handling system  26 , constructed in accordance with the present invention. The print media may be any type of suitable sheet material, such as paper, card-stock, transparencies, mylar, and the like, but for convenience, the illustrated embodiment is described using paper as the print medium. The print media handling system  26  has a feed tray  28  for storing sheets of paper before printing. A series of motor-driven paper drive rollers described in detail below (FIGS. 2-13) may be used to move the print media from tray  28  into the print zone  25  for printing. After printing, the sheet then lands on a pair of retractable output drying wing members  30 , shown extended to receive a the printed sheet. The wings  30  momentarily hold the newly printed sheet above any previously printed sheets still drying in an output tray portion  32  before retracting to the sides to drop the newly printed sheet into the output tray  32 . The media handling system  26  may include a series of adjustment mechanisms for accommodating different sizes of print media, including letter, legal, A4, envelopes, etc., such as a sliding length adjustment lever  34 , and an envelope feed slot  35 . 
     The printer  20  also has a printer controller, illustrated schematically as a microprocessor  36 , that receives instructions from a host device, typically a computer, such as a personal computer (not shown). Indeed, many of the printer controller functions may be performed by the host computer, by the electronics on board the printer, or by interactions therebetween. As used herein, the term “printer controller  36 ” encompasses these functions, whether performed by the host computer, the printer, an intermediary device therebetween, or by a combined interaction of such elements. The printer controller  36  may also operate in response to user inputs provided through a key pad (not shown) located on the exterior of the casing  24 . A monitor coupled to the computer host may be used to display visual information to an operator, such as the printer status or a particular program being run on the host computer. Personal computers, their input devices, such as a keyboard and/or a mouse device, and monitors are all well known to those skilled in the art. 
     A carriage guide rod  38  is supported by the chassis  22  to slideably support an inkjet carriage  40  for travel back and forth across the print zone  25  along a scanning axis  42  defined by the guide rod  38 . One suitable type of carriage support system is shown in U.S. Pat. No. 5,366,305, assigned to Hewlett-Packard Company, the assignee of the present invention. A conventional carriage propulsion system may be used to drive carriage  40 , including a position feedback system, which communicates carriage position signals to the controller  36 . For instance, a carriage drive gear and DC motor assembly may be coupled to drive an endless belt secured in a conventional manner to the pen carriage  40 , with the motor operating in response to control signals received from the printer controller  36 . To provide carriage positional feedback information to printer controller  36 , an optical encoder reader may be mounted to carriage  40  to read an encoder strip extending along the path of carriage travel. 
     The carriage  40  is also propelled along guide rod  38  into a servicing region, as indicated generally by arrow  44 , located within the interior of the casing  24 . The servicing region  44  houses a service station  45 , which may provide various conventional printhead servicing functions. For example, a service station frame  46  may hold a conventional or other mechanism that has caps to seal the printheads during periods of inactivity, wipers to clean the nozzle orifice plates, and primers to prime the printheads after periods of inactivity. Such caps, wipers, and primers are well known to those skilled in the art. A variety of different mechanisms may be used to selectively bring the caps, wipers and primers (if used) into contact with the printheads, such as translating or rotary devices, which may be motor driven, or operated through engagement with the carriage  40 . For instance, suitable translating or floating sled types of service station operating mechanisms are shown in U.S. Pat. Nos. 4,853,717 and 5,155,497, both assigned to the present assignee, Hewlett-Packard Company. A rotary type of servicing mechanism is commercially available in the DeskJet® 850C and 855C color inkjet printers, sold by Hewlett-Packard Company, the present assignee. In FIG. 1 a spittoon portion  48  of the service station is shown as being defined, at least in part, by the service station frame  46 . 
     In the print zone  25 , the media sheet receives ink from an inkjet cartridge, such as a black ink cartridge  50  and/or a color ink cartridge  52 . The cartridges  50  and  52  are also often called “pens” by those in the art. The illustrated color pen  52  is a tri-color pen, although in some embodiments, a set of discrete monochrome pens may be used. While the color pen  52  may contain a pigment based ink, for the purposes of illustration, pen  52  is described as containing three dye based ink colors, such as cyan, yellow and magenta. The black ink pen  50  is illustrated herein as containing a pigment based ink. It is apparent that other types of inks may also be used in pens  50 ,  52 , such as paraffin based inks, as well as hybrid or composite inks having both dye and pigment characteristics. 
     The illustrated pens  50 ,  52  each include reservoirs for storing a supply of ink. The pens  50 ,  52  have printheads  54 ,  56  respectively, each of which have an orifice plate with a plurality of nozzles formed therethrough in a manner well known to those skilled in the art. The illustrated printheads  54 ,  56  are thermal inkjet printheads, although other types of printheads may be used, such as piezo-electric printheads. The printheads  54 ,  56  typically include substrate layer having a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubble of gas is formed to eject a droplet of ink from the nozzle and onto media in the print zone  25 . The printhead resistors are selectively energized in response to enabling or firing command control signals, which may be delivered by a conventional multi-conductor strip (not shown) from the controller  36  to the printhead carriage  40 , and through conventional interconnects between the carriage and pens  50 ,  52  to the printheads  54 ,  56 . 
     Adaptive Media 
     Handling System 
     FIG. 2 shows an adaptive media transport system  60 , constructed in accordance with the present invention, which forms a portion of the print media handling system  26 . The adaptive transport system  60  pulls a sheet of print media from the feed tray  28 , delivers it to the print zone  25 , and after printing deposits the sheet on the output drying wings  30 , shown in FIG.  1 . The adaptive system  60  includes several components attached to the chassis  22 , including a pressure plate  62  which is pivoted along a front edge to the chassis  22  by a hinge member  64 . A rear edge of the pressure plate  62  is upwardly biased away from the chassis  22  by a compression spring member  65 . One or more compression springs  65  may be used between the pressure plate  62  and the chassis  22 , although for the purposes of illustration only one such spring is shown. Moreover, it is apparent that leaf springs or other biasing devices may be used to urge the rear edge of the pressure plate  62  upwardly and away from the lower portion of chassis  22 . 
     The chassis  22  has two opposing upright walls  66  and  68 . The transport system  60  includes a media advance or drive roller system  70  suspended by an axle  72  between the chassis walls  66  and  68 . The roller system  70  preferably includes three elastomeric drive rollers or tires  74 ,  75  and  76 . Two of the drive tires  75 ,  76  are clustered together along one edge of the print zone, adjacent the envelope feed slot  35  (FIG. 1) to evenly pull a business-sized envelope through the feed slot and into the print zone  25 . 
     In a preferred embodiment, the drive roller system  70  also includes a pick tire  78 , which is preferably of a softer durometer elastomer, and of a slightly smaller diameter than the drive tires  74 - 76 . The drive tires  74 - 76  and the pick tire  78  may be of the same or different type of elastomer, such as of a rubber or equivalent material known to those skilled in the art, with one preferred elastomer being ethylene polypropylene diene monomer (EPDM) for both drive and pick tires  74 - 78 . The durometer of the drive tires  74 - 76  may be selected from the range of 45-70, or more preferably 55-65, with a preferred nominal value being 60, all measured on the Shore A scale. The softer durometer of the pick tire  78  may be selected from the range of 25-45, or more preferably 30-40, with a preferred nominal value being about 35, also measured on the Shore A scale. Use of a softer durometer pick tire  78  allows for more frictional forces to be developed between the media and the outer periphery of the pick tire  78 , with these additional frictional forces assisting in pulling the media into the transport system  60 . By locating the pick tire  78  between the envelope drive rollers  75 ,  76 , the pick tire assists not only in picking sheets of paper from the input tray  28 , but also in picking and feeding envelopes received through slot  35 . 
     Also suspended in part from the chassis side wall  68 , and running parallel to the drive system axle  72 , is a media support member or pivot  80 . The pivot  80  has a leading media support edge  82 , which is adjustable in height as indicated by the double-headed arrow Z in a manner described further below. Extending outwardly from the left side of pivot  80  (as seen in FIG. 2) are two cam follower members, such as, a pick cam follower pin  84 , and a media spacing adjust cam follower or PPS adjust pin  86 . 
     A drive motor  88  is attached to an outboard side of the chassis upright wall  66 . As shown in FIGS. 2-6, the motor  88  forms a portion of a drive system or mechanism  90 . The drive mechanism  90  powers the drive roller system  70 , the pressure plate  62 , and the pivoting media support  80 , all of which form portions of the adaptive media transport system  60 . The motor  88  has an output shaft  91  that supports a pinion gear  92 . The pinion gear  92  engages and drives a roller gear  94 , which is coupled to the drive roller axle  72 . An intermediate or transfer gear  96  is also coupled to the axle  72 . As described further below, the transfer gear  96  may be selectively placed in engagement with a cam drive gear  98  to drive an adaptive spacing adjust member, such as a dual sided cam member  100 . A cam support  102  extends upwardly from the chassis  22  to support a cam axle  104 . Both the cam  100  and the cam gear  98  ride on axle  104 . 
     The cam gear  98  is designed to drive the cam  100  during paper pick, discharge, and pen-to-paper (PPS) spacing adjustment portions of operation. As shown in detail in FIG. 5, the cam gear  98  has a large outer rim having teeth  105  around the majority of its periphery. A raised land  106  is substantially concentric with the toothed outer rim  105  and extends inboardly therefrom. In the view of FIG. 5, to better illustrate the interaction of the cam gear  98  and cam  100 , cam  100  is shown removed from shaft  104 , as indicated by the line of alternating long and short dashes. Moreover, the cam  100  is shown rotated counterclockwise from its position in operation, as indicated by the curved arrow  108 , with this rotation being around a vertical axis  109 . For convenience, the cam  100  is shown reduced in size by approximately 50-60% with respect to the remaining components in FIG. 5, but is clearly shown in uniform relative proportions in all of the other figures. 
     The adaptor cam  100  has a series of splines  110  extending outwardly from a boss or sleeve portion  112 . The sleeve  112  and splines  110  fit within a bore  114  having a series of grooves  116  formed along the interior of the cam gear  98 . The sleeve  112  has a bore  118  which rides along axle  104 . A compression spring  120  is coiled around the raised land  106  of cam gear  98  and rides in part against a land portion  122  of cam  100 . 
     Two guide ribs  124  and  126  are located along the interior surface of the chassis wall  66 . As shown in FIG. 5, a pair of pivot pins, such as pin  128 , extend inwardly from the ribs  124  and  126  to support a shift lever  130 . As shown in FIG. 3, the outboard side of the cam gear  98  includes a raised disk portion  132 , which is received within a U-shaped channel  134  defined by a lower extremity  136  of the shift lever  130 . FIG. 6 shows an upper portion  138  of lever  130  being selectively engaged by a portion of the printhead carriage  40 , to move the lever from the dashed line position to the solid line position (also shown in FIG.  4 ). The upper and lower portions  136 ,  138  of lever  130  are not coplanar, but instead are joined together at an obtuse angle, for instance, such as shown in FIG.  6 . Thus, when the lever upper portion  138  is moved to the left in the views, the lever  130  pivots at pins  128  to force the lever lower portion  136  against the cam gear  98 . Pushing the cam gear  98  toward the cam  100  compresses spring  120 , and causes full engagement of the total width of teeth  105  with the teeth of the transfer gear  96 . As the carriage  40  moves away from lever  130 , for instance to print or to service the printheads  54 ,  56 , the tension between the teeth of gears  96  and  105  maintains compression of the spring and full engagement of the gears as shown in solid lines in FIG.  6 . 
     As shown in FIG. 5, a chordal cut has been made through a portion of the cam gear teeth  105 , leaving a lost motion land  140  and a narrow track of teeth  142  adjacent thereto, having a width A as indicated in FIG.  5 . The frictional forces between the narrow teeth  142  and the teeth of transfer gear  96  are not sufficient to maintain compression of spring  120 . Without assistance by lever  130 , the force of spring  120  pushes the cam gear  98  axially in an outboard direction, to the position indicated by dashed lines in FIG. 6, so the teeth of gear  96  rotate over the lost motion land region  140  and the cam gear  98  remains in a fixed rotational position. Thus, in this lost motion region, the cam gear  98  and cam  100  are uncoupled from the drive motor  88 . To rotate the cam  100  in this lost motion region, the carriage  40  must push lever  130  to engage the narrow teeth  142  with the transfer gear. Thus, the total travel of the cam gear  98  when pushed away from cam  100  by spring  120  is slightly greater than the width A of teeth  142 . Use of this lost motion region and the narrow band of teeth  142  are described in greater detail below. 
     The relative tooth length of the spline gear  110  and the spline gear receiving grooves  116  are selected with respect to the width A of teeth  142 , so that when the cam gear  98  is held in a fixed position, the cam  100  is also held in the same relative fixed position. When the transfer gear  96  is rotating above the lost motion land  140 , the spring  120  provides an outwardly biasing force against the lever lower portion  136 , to normally bias the lever in the dashed line position shown in FIGS. 4 and 6. It is apparent that other methods may be used to engage the cam gear  98  with cam  100 . For instance, rather than the carriage actuated lever  130 , a servo mechanism could be used to engage gear teeth  105 ,  142  with the transfer gear  96 . For that matter, other mechanisms could be used to provide incremental rotation to the cam  100 . 
     As shown in FIGS. 3 and 5, the dual sided adaptor cam  100  has an outboard surface  146 . A land  148  extends from the outboard surface  146 , with the land  148  having a periphery that defines a pick cam surface  150 . As shown in FIGS. 2 and 4, the cam  100  also has an inboard land surface  152 , which has a pick channel  154  and a pen-to-paper spacing (“PPS”) channel  156  formed therein. In operation, the pick pin  84  on pivot  80  travels through the pick channel  154 , whereas the PPS pin  86  travels through the PPS channel  156  during operation. Before discussing the operation of the adaptive media transport system  60 , one additional facet remains to be discussed. 
     Referring to FIGS. 2 and 3, pivoted to chassis  22  by a pair of pivot pins, such as pin  158 , is a plate lifter cam follower member  160 , which activates a plate lifter member  162 . The plate lifter member  162  extends along at least a portion of the underside of the pressure plate  62 . The plate lifter  162  has a pair of pins, such as pin  161  (FIG.  2 ), which ride within slots, such as slot  163  formed within the lower surface of the pressure plate  62 . Pivoting action of the lifter  162  raises and lowers the rear edge of the lifter plate  62 . As mentioned earlier, the pressure plate  62  is biased upwardly by spring  65  (FIG. 2) into contact with the drive tires  74 - 76 . Lifting the pressure plate  62  upwardly brings the media into contact with the pick tire  78  and drive tires  74 - 76 , while lowering the pressure plate moves the media away from the tires  74 - 78 . FIG. 4 shows an optional media guide  164 , located adjacent the rear edge of the pressure plate  62 . The media guide  164  is arcuate in nature to bend the media upwardly and around the exterior of the drive rollers  74 - 76  to assist in guiding print media around the periphery of the drive rollers. The media handling system may also include two or more pinch rollers, mounted on axles parallel to the drive axle  72 , and having outer surfaces which may be elastomeric in nature to grip a sheet of media between the pinch rollers and the drive rollers  74 - 76  For the purposes of illustration, two typical pinch rollers  165 ,  166  are shown in their approximate locations in cross section in FIGS. 7-14. For clarity, the pinch rollers  165 ,  166  have been omitted from the views of FIGS. 2-6. 
     In operation, the adaptive transport system  60  not only feeds media from the input tray  28  to the output tray drying wings  30 , but it also allows for adjustment of the pen-to-paper (PPS) spacing via a software routine which may be stored in the printer control  36 , the host computer, or some combination thereof. Merely for the purposes of illustration, this software routine is described herein as occurring within the printer controller  36 . First, the operation of the components of the transport system  60  will be described with respect to FIGS. 7-14, followed by a description of the software steps which control the action in FIGS. 15-19. 
     FIGS. 7-14 illustrate the interaction of the components of the adaptive media transport system  60 . The views in FIGS. 7-14 show the outboard side  146  of the adaptor cam gear  100 . FIGS. 7-14 show the interactions of the adaptor cam  100  with: (1) the pressure plate  62 , via the plate lifter cam follower  160 ; and (2) the pivot  80 , via the interaction of the pick and PPS pins  84 ,  86  with the pick and PPS cam tracks  154 ,  156 , respectively. For clarity, the various drive gears  92 - 98 , the shift lever  130 , the chassis  22 , chassis wall  66 , and motor  88  are omitted from FIGS. 7-14. 
     FIG. 7 shows the initial position of the drive mechanism  90 . This position may be referred to as a rest or start position, and it is also the position from which media may be ejected or kicked from the drive mechanism to be totally supported by wings  30 , prior to being dropped into the output tray  32 . To begin the media pick cycle, the drive system begins a transition, shown in FIG. 8, as motor  88  and the drive mechanism  90  rotates cam  100  counterclockwise in the views, as shown by arrow  168 . Before beginning the pick cycle, at rest in FIG. 7 the pick pin  84  is approximately midway along the pick track  154 , resting in a slightly dipped portion  170  of the track. The PPS pin  86  is located in a central open region  172  of the PPS track  156 . In these positions, the pins  84 ,  86  have drawn the pivot leading edge  82  downwardly, which assists in ejecting media from the drive mechanism. In FIG. 7, the pick pressure plate cam  150  is shown holding cam follower  160  and the lifter plate  62  in lowered positions, which leaves the spring  65  (FIG. 2) in a compressed state. 
     FIG. 8 shows the drive system in transition from rest (FIG. 7) to begin the media pick cycle as motor  88  and the drive gears  92 - 98  rotate the adaptor cam  100  counterclockwise, as shown by arrow  168 . In this transition stage, a raising nose portion  173  the pressure plate cam  150  is at the final position where it holds the plate lifter cam follower  160  in a lowered position. The PPS pin  86  is adjacent the wall of the PPS cam track  156 , while the pick pin  84  is transitioning through cam track  154  toward an exit end  174 , but the relative position of the pivot  80  has not yet changed from the rest position of FIG.  7 . 
     FIG. 9 shows the beginning of the media pick operation, where the pressure plate cam follower  160  is no longer held in a lowered position by the pressure plate cam  150 . This allows the pressure plate spring  65  to push the pressure plate  62  upwardly, into a maximum position where it is engaged with the drive rollers  74 - 76 . The pick pin  84  continues to travel through the pick track  154  toward the exit end  174 , but the PPS pin  86  has left track  156 . The PPS pin  86  is advantageously constructed to be shorter than the pick pin  84 , which allows the PPS pin  86  to actually travel over a recessed portion  175  of the land surface  152 , located between tracks  154  and  156 . As the pressure plate  62  raises, the upper sheet of media resting thereon is drawn into the media feed path, preferably using the softer durometer pick tire  78 , assisted by the drive tires  74 ,  76 , when rotated in the direction indicated by arrow  176 . 
     FIG. 10 shows a further continuation of the pick operation, where the pressure plate cam follower  160  is no longer held in a lowered position by the cam surface  150 . Indeed, while the cam surface  150  may be configured for continuous contact with follower  160 , the preferred design allows for different media thicknesses to be accommodated by the degree of compression of the pressure plate spring  65 . That is, the spring may be allowed to compress to different degrees to accommodate different thicknesses of media, such that the upward travel is not limited by the contact of the cam follower  160  with cam  150 . During this continuing of the pick operation, the PPS pin  86  is now back in contact with the PPS track  156  after traversing the recessed land  175 , while the pick pin  84  is now closer to the exit  174  of track  154 . 
     Upon completion of a successful pick routine, FIG. 11 shows the beginning of a transition, where the pressure plate  62  is lowered. In FIG. 11, the further rotation of cam  100  in the direction of arrow  168  causes a lowering nose portion  178  of the cam  150  to force the follower  160  down. Downward motion of follower  160  allows the plate lifter member  162  to pull the pressure plate  62  downward into a print position. The pivot  80  has now been raised to a more upright, near-print position in FIG.  11 . The pick pin  84  has now exited the pick track  150 , and the PPS pin  84  has begun to enter a PPS adjust portion  180  of track  156 . In transitioning from FIG. 11 to FIG. 12, it can be seen that the pressure plate  62  is lowered, which compresses spring  65  as the pressure plate cam  150  holds the follower  160  in a lowered position. 
     FIG. 12 shows the end of the media pick routine, and the beginning position of the PPS adjust routine. Briefly referring back to FIG. 5, it can be seen that the cam drive gear grooves  116 , which receive the splines  110  of cam  100 , are in a position of approximate engagement when located as shown in FIGS. 5 and 12. As noted before, in this region of travel, the cam spring  120  pushes the cam gear  98  toward the outboard side of the chassis  22 , and away from cam  100 . This action allows the teeth of the transfer gear  96  to ride within the lost motion region  140  of the cam gear teeth  105 . In this manner, the cam  100  is disengaged from being driven while the motor  80  continues to turn the drive tires  74 - 76  and incrementally advance media through the printzone  25 . Thus, the pivot  80  is decoupled from the media drive function so the pivot leading edge  82  is held in a position to accurately support media at a desired pen-to-paper spacing away from the printheads  54 ,  56  during printing. 
     FIGS. 12 and 13 illustrate the PPS adjustment routine, with FIG. 12 showing the beginning of the routine, where the pen-to-paper spacing is at a minimum, while FIG. 13 shows the maximum PPS adjust position. To engage the cam gear  98  with the cam  100  during the PPS adjust routine, the printhead carriage  40  travels to the far left of the printer  20 , to engage the shift lever  130  (see FIG.  6 ). The lower portion of the shift lever  130  forces the PPS adjust teeth  142  of cam gear  98  into engagement with the transfer gear  96 . The drive motor  88  then rotates a selected number of steps to advance the cam gear to position corresponding to a selected PPS spacing, either at the minimum position of FIG. 12, the maximum position of FIG. 13, or any other location therebetween in track  180 . 
     In rotating from the minimum position of FIG. 12, through the PPS adjustment portion  180  of track  156 , the cam  100  rotates through a total angle θ, shown in FIG.  12 . In rotating from the minimum to the maximum position, the pivot leading edge  82  can be seen to have been lowered, by a distance of ΔZ shown in FIG. 13, where the minimum PPS adjust position of the pivot from FIG. 12 is shown in dashed lines. Upon reaching the desired location for the PPS pin  86  within the PPS adjustment track  180 , the printhead carriage  40  then moves away from the shift lever  130 . Without pressure from the lever  130 , the spring  120  pushes cam gear  98  toward the outboard side of the printer  20 , so teeth  142  are no longer engaged with the teeth of the transfer gear  96 , and instead, rotate within the cam gear lost motion portion  140 . Thus, at the proper PPS adjustment, with the adaptor cam  100  decoupled from motor  88 , the pivot  80  is held at a fixed elevation, and printing may commence. It is apparent that during operation, if the type of media should change or some adjustment in print quality be desired, that the carriage  40  can engage the shift lever  130 , and the PPS spacing may be adjusted by further cam rotation, either counterclockwise or clockwise, to locate pin  86  in a different portion of the PPS adjust track  180 . The usefulness of the PPS adjustment capability is discussed further below, with respect to the software system illustrated in FIGS. 15-19. 
     Upon completion of printing, FIG. 14 shows a transition from the PPS adjust and print position (FIGS. 12 and 13) to the start position shown in FIG.  7 . During this FIG. 14 transition, the pick pin  84  enters an entrance portion  182  of the pick track  154 . The PPS pin  86  now enters the free region  172  of the PPS track  156 . In making this transition, the pivot leading edge  82  begins to lower, to the rest position shown in FIG.  7 . During this transition, the pressure plate  62  is held in a lowered position by engagement of cam follower  160  with the pressure plate cam  150 . 
     To initiate the transition of FIG. 14, the printhead carriage  140  engages the shift lever  130 , compressing spring  120  (FIG.  6 ), which engages the narrow cam gear teeth  142  with the transfer gear  96 . Rotation of the cam gear past the band of narrow teeth  142  allows the full width of the cam gear teeth  105  to engage the transfer gear  96 . The frictional forces of this full tooth width engagement overcomes the axial force of spring  120 , so the gears  96  and  98  remain engaged even when the shift lever pressure is removed. Thus, when rotated past the lost motion region  140  and teeth  142 , the carriage  40  is free to return the pens  50 ,  52  to the service station for servicing. Continued rotation of cam  100  discharges the printed media onto the drying wings  30 , and brings the drive mechanism back to the rest position of FIG.  7 . When at rest, the cam gear  98  is held in a fixed position through engagement with the transfer gear  96 . As the pivot  80  pivots downwardly to the rest position of FIG. 7, the output tray wings  30  advantageously raise upwardly into a retracted position for storage, as shown by arrows  184  in FIG.  1 . The operation of the wings  30  may occur in conjunction with, or independently from, the operation of the adaptive media transport system  60  illustrated herein. 
     Method of Operation 
     FIGS. 15-19 are flow charts showing the various steps of engagement illustrated in FIGS. 7-14. To accommodate for manufacturing tolerance accumulations of the various parts used to construct the media transport system  60 , the initial adjustment of the PPS spacing may occur at the factory, as illustrated in the factory PPS tolerance adjust flow chart  200  in FIG.  15 . For instance, for a particular printer assume that the optimal adjust is determined to occur at an angle of 10° for θ (FIG.  12 ). This 10° rotation value may be easily translated in to a particular number of steps which motor  88  turns. This particular step value corresponding to θ=10° then may be permanently stored in a read only memory (ROM) portion of the printer controller  36  and recalled for a nominal adjustment prior to printing. 
     The process of FIG. 15 starts at an operator initiated step  202 , which generates a start command  202 . In response to the start command, the actual pen-to-paper spacing is measured in a measure manufactured PPS step  206  using gauges or optical means, for example, and a signal  208  corresponding to measured manufactured PPS is supplied to a comparator portion  210 . The comparator  210  compares the magnitude of the measured manufactured PPS signal  208  with a nominal PPS value, and if they match, emits a YES signal  212 . The YES signal  212  indicates a perfect nominally toleranced system  60  requiring zero factory adjustment. This YES signal  212  is sent to a factory PPS tolerance storage routine  214  where the PPS tolerance adjust steps are stored in memory, such as in a ROM (read only memory) portion of the printer controller  36 . The YES signal  212  corresponds to a PPS tolerance adjust steps of zero, since the printer is at the nominal design PPS spacing. Following the storage step  214 , a completion signal  216  is emitted and an end factory PPS tolerance adjust step  218  is performed, perhaps by giving an assembly worker a visual signal, or by automatically allowing the printer to proceed down the assembly line. 
     A more likely scenario is that the comparator  210  finds that the magnitude of the measured manufactured PPS signal  208  does not match a nominal PPS value, so a NO signal  220  is transmitted to step  222 . In step  222 , the PPS difference between the measured PPS and nominal PPS values is determined, and a difference signal  224  is supplied to a look-up routine  226 . The routine  226  looks-up the number of motor steps encoder counts, or encoder positions required to adjust for the PPS difference, then emits a signal  228  to a move carriage step  230 . The look-up routine  226  also stores this retrieved value for later recall until a new printer is tested. 
     Having determined the number of motor steps required to adjust the PPS pin  86  to a location in the adjustment portion  180  of track  156 , the system will now verify that this adjustment will indeed bring the PPS spacing ΔZ (FIG. 13) to the nominal value. In response to signal  228 , in step  230  the printer controller  36  moves the carriage  40  in a conventional manner to engage the shift lever  130 , which couples the adaptor cam  100  to motor  88 . When the controller  36  receives conventional positional feed back that the carriage has engaged lever  130 , the controller then issues a drive motor signal  232 . The extent to which motor  88  rotates is controlled by step  234  to be the number of steps looked-up in step  226  to locate the pivot leading edge  82  at what is thought to be the nominal PPS spacing. At the conclusion of this repositioning, a signal  236  is supplied to another measurement step  238 , where the adjusted PPS is measured, and a measured adjusted PPS signal  240  is generated. 
     Once again, the magnitude of the adjusted PPS signal  240  is compared to the nominal PPS value by a second comparator  242 . If the adjustment was unsuccessful, a NO signal  244  is supplied back to the determine difference step  222 . The steps  222  through  242  may be repeated as necessary until the adjustment to the nominal PPS is successful and a YES signal  246  is generated. During any successive iterations of steps  222  through  242 , the values retrieved in step  226  are all stored. In response to receiving the YES signal  246 , step  248  sums together the values stored at step  226  to arrive at a total number of PPS tolerance adjust steps, represented by signal  250 . The summation of these tolerance adjust steps is stored in a memory portion of the controller  36  in step  214  as described above, and the factory adjust routine terminates at step  218 . 
     It is apparent that the majority of the factory adjust process  200  may be automated at the factory, rather that requiring extensive operator involvement, manual adjustments, tightening of set screws to hold the adjustment, etc. This is especially true if the measurement device is some type of transducer, such as an optic device that generates the measurement signals  208  and  240  and provides them as input signals to the printer controller  36 . In this manner, a smart self-testing printer  20  is provided. Alternatively, the process in flow chart  200  may be performed in part by an auxiliary computer or other processor communicating with the printer controller  36 . This system may also be advantageously used by personnel servicing a printer. In either implementation, human error is virtually eliminated from the process. The tolerance adjust value is stored in ROM in the printer controller, where it is accessed prior to each printing job (described further below). Thus, the printer cannot be jostled out of a mechanical adjustment during shipping. 
     Moving from the manufacturing context, flow chart  300  in FIGS. 16-19 shows a printing operation having several routines comprising several steps each, such as the pick routine  302  in FIG.  16 . The pick begins with step  304 , where the controller  36  issues a start pick signal  306  indicating that a sheet is to be printed. In response to the start pick signal  306 , from the rest position of FIG. 7, in step  308  the motor  88  rotates the adaptor cam  100  to raise the lifter plate  62  to touch the drive and pick rollers  74 - 78 , as shown in transitioning through FIG. 8 to the FIG. 9 position. Upon accomplishing step  308 , the controller  36  generates a continue rotation signal  310  which continues rotation of the drive and pick rollers  74 - 48  to pick media from the input tray  28  in step  312 , while simultaneously raising the media support pivot  80  in step  314 . The operation of steps  312  and  314  is shown by the transition of the drive mechanism  90  from FIG.  9  through FIGS. 10 and 11, after which signal  316  is then generated. 
     Upon receiving signal  316 , rotation of the adaptor cam  100  continues in step  318  to lower the lifter plate  62  to the end feed position of FIG.  12 . Upon reaching the FIG. 12 position, signal  320  is generated by controller  36  and rotation of the cam  100  is stopped. In this position, the transfer gear  96  engages only the narrow teeth  142 , and spring  120  pushes the cam gear  98  out of engagement with the transfer gear, uncoupling the cam  100  form the motor  88  in step  322 . At this point signal  324  is generated to indicate that the pick routine  302  has concluded at step  326 , and an end pick signal  328  is generated. 
     In FIG. 17, a PPS adjust routine  330  of the process  300  is shown receiving the end pick signal  328 . In response to signal  328 , a begin PPS adjust routine step  332  generates a start signal  334 , which is received by a determine media thickness step  336 . The determine thickness step  336  also receives another input signal  338 , which may be generated by one or a combination of a host computer  340 , an operator activated input mechanism  342 , and a sensor input  344 . The input signal  338  carries information as to what the media thickness may be. The manner in which the printer controller  36  determines that an envelope is being feed to the printer rather than plain paper or other media, may be accomplished in a variety of ways. For example, it could be input by the user from a keypad on the printer exterior, or through user input from the host computer  340 . The host computer  340  may automatically generate signal  338  based upon the type of document being printed, without further user input. Alternatively, a media thickness sensor  344  could be installed adjacent to chassis wall  68 , for example, to sense the thickness of an upcoming sheet of media. 
     Once step  336  determines the media thickness, signal  346  is supplied to a look-up step  348 . Step  348  correlates the media thickness from the information in signal  346  with the number of motor steps required to for an ideal PPS media adjustment, and generates a media adjust signal  350 . Upon receiving the media adjust signal  350 , or simultaneously with the looking-up in step  348 , step  352  looks-up the motor steps for PPS tolerance adjust stored at the factory in the controller memory in step  214  of FIG. 15. A PPS tolerance adjust signal  354  is supplied to a totaling step  356 , and the media adjust signal  350  is also delivered to the step  356 , shown here as passing through block  352 . In step  356 , a total PPS adjust signal  358  is generated by sum the number of motor steps required for the PPS media adjust from step  348  and the PPS tolerance adjust from step  214  (FIG.  15 ). For instance, an envelope or other thick media may, for instance, take an additional 10° of rotation for angle θ to increase the ΔZ PPS spacing. When the controller  36  is made aware that an envelope is being printed, the controller can direct motor  88  to step not only the initial 10° required to accommodate the particular printer tolerances, but an additional 10° to increase the PPS spacing to accommodate the envelope. 
     Upon determining the number of motor steps required to adjust the PPS, in step  360  the controller then moves the carriage  40  to engage shift lever  130  to couple the adaptor cam  100  to motor  88 , as described above with respect to step  230  of FIG. 15, and upon completion signal  362  is generated. In response to receiving signal  362 , step  364  drives the motor  88  for number of steps for total PPS adjust of signal  358  to move the pivot  80  to the selected PPS print position, somewhere at or between the minimum position of FIG.  12  and the maximum position of FIG.  13 . When in the selected PPS print position, a signal  366  is generated to indicate that step  368  may now let the controller  36  move the carriage  40  away from the shift lever  130  to uncouple the adaptor cam  100  from motor  88 , as described for step  332  of FIG.  16 . Upon completion of step  368 , a signal  370  is supplied to an end PPS adjust routine step  372  which then generates an end PPS adjust routine signal  374 . 
     In FIG. 18, a print routine  380  of the process  300  is shown receiving the end PPS adjust routine signal  374 . In response to signal  374 , a begin printing routine step  382  generates a start signal  384 , which is received by a uniform media thickness query step  386 . The uniform media thickness query step  386  looks for changes in the media thickness or effective thickness due to ink saturation causing cockle (described in the Background portion above), and when found, supplies a NO signal  338  to the determine thickness step  336  of FIG. 17 where further adjustments are made by the PPS adjust routine  330 . 
     Thus, the PPS adjustment may be made during printing to accommodate different media thicknesses. Note, this PPS adjust not only need occur at the beginning of printing a sheet, but may also occur during the printing of the sheet. For example, a new type of paper has recently become available upon which to print banners, for instance, one that would say “Happy Birthday” and would be displayed on a wall. This banner paper is supplied in Z-fold stack, for instance of letter sized paper, joined by perforated portions along the top and bottom edges. The earlier printers were vulnerable to damage when using banner-type paper. Since the perforations usually have paper fibers extending therefrom, there is the increased damage that paper fibers could be jammed into the nozzles, causing permanent damage. Moreover, even if the nozzles are not damaged, contact of the perforations with the nozzle plate could smear ink on the pen face, dirtying the printhead and damaging the image in the region of the perforation. This adaptive system  60  of printing on perforated paper avoids the risk of the upwardly projecting tents at a perforation hitting the orifice plates of printheads  54 ,  56  during printing. 
     When feeding through the printer  20 , the major portion of the perforated paper is the thickness of plain paper. However, as the perforation approaches the print zone there is an increase in the apparent thickness of the media, due to the perforation raising up toward the printheads  54 ,  56 . Thus, as a perforation is approached (the approach of which may be determined by counting the number of steps motor  88  has advanced since printing of the banner began) carriage  40  could engage lever  30  and cam  100  could be advanced to increase the PPS spacing ΔZ in the region of the perforation. Then following printing at the perforation, the PPS spacing could be readjusted back to the nominal position as the carriage again engages lever  130 . 
     Besides adjusting the pen-to-paper spacing for the type of media, the controller  36  may also adjust the pen-to-paper spacing based on the type of image being printed. For example, an image having a large amount of ink, such as a photographic type image or graphics, may saturate the media during printing, causing the media fibers to expand, causing media cockle. Thus, for these heavily saturated images, the controller  36  may interpret the incoming data stream from the host computer as being a saturated image, and increase the pen-to-paper spacing as described above with respect to FIGS. 12 and 13. Also from the host computer  340 , the user may make a selection that a postcard, rather than an envelope, is being printed. In this case, the pen-to-paper spacing may be adjusted for a postcard thickness, rather than an envelope thickness, allowing the postcards to be printed at a much closer pen-to-paper spacing gap, resulting in a higher quality image on the postcard. A smaller pen-to-paper spacing is believed to increase print quality, because there is less distance for the ink droplets to travel, and a lesser chance of over-spray occurring which would blur the image. Indeed, in a humid environment, it may be desirable to increase the pen-to-paper spacing to account for humidity absorbed by normal media, which may cause it to thicken somewhat, requiring a larger gap. 
     Returning to FIG. 18, when the media thickness is uniform, step  386  generates a YES signal  390 , which is transmitted to a hold pivot position step  392  until printing of the sheet is complete, indicated by signal  394 . Upon receiving the printing complete signal  394 , a finish printing routine step  396  concludes the routine  380  by issuing a finished printing signal  398 . After printing is complete, a discharge media routine  400  portion of the overall process  300  initiates media discharge from the media transport system  60 . In response to the finished printing signal  398 , a begin media discharge step  402  generates a start signal  404 , which in turn causes the carriage  40  to engage the shift lever  130  to couple the adaptor cam  100  to motor  88  in step  406 , in the same manner as described above for the steps  230  and  360 . After sufficient movement has occurred to mesh the full width of the cam gear teeth  105  with the transfer gear  96 , indicated by signal  408 , the carriage  40  may be returned to the service station  45  in step  409 . 
     Upon completion of step  406  and step  409 , if this optional step is performed, a signal  410  indicates that rotation of the drive tires  74 - 76  may continue in step  412 , and that cam  100  should continue to rotate to lower the pivot  80  to the rest position in step  414 . The illustrated simultaneous occurrence of step  412  and  414  is shown by the transition of the drive mechanism  90  from the printing position of FIGS. 12 and 13. through the view of FIG. 14, and to conclude with the mechanism  90  in the rest position of FIG. 7, at which point signal  416  is generated. As shown in FIG. 19, in response to signal  416 , an end media discharge step  418  issues a media discharge complete signal  420 . 
     After printing and discharging the printed sheet, it may be helpful to determine whether there are additional sheets to be printed. In FIG. 19, in response to signal  420  this question is asked in an end print job query step  422 . If additional sheets remain to be printed, a NO signal  424  is issued to a return to the begin pick routine step  426 , which starts again at step  304  of FIG.  16 . If the print job is complete, then step  422  issues a YES signal  428  to a finish print job step  430 , in response to which the printer  20  remains at idle, awaiting the next print job. 
     It is apparent that the factory tolerance adjust routine  200  and the printing routine  300  are discussed herein by way of example only, and may be varied in their individual steps or sequencing an still fall within the scope of the claims below. For example, in FIG. 18, when transitioning between the end of the print routine  380  and the beginning of the discharge routine  400 , steps  396  and  402  may be combined or totally omitted. Indeed, the speed of data processing and printing would likely be improved and thus preferred if the information freely flowed from one portion of the process to the next with minimal impediments. The use of the begin routine and finish routine steps, among others, in the flow chart is primarily for clarity in helping the reader better understand the entire process by breaking it down into smaller segments. Such streamlining modifications to the illustrated information flow process are apparent to those skilled in the art, and clearly fall within the scope of the claims below. Thus, practice of the claimed invention is not limited to the embodiments illustrated herein. 
     Conclusion 
     For simplicity, and minimization of parts, the illustrated embodiment of the adaptive transport system  60  is preferred. Moreover, the fewer number of parts used in transport system  60 , here, approximately seven moving gear parts as opposed to seventeen parts in the earlier designs, necessarily provides a quieter operating mechanism due to less interaction of gears and components. Furthermore, the lesser number of components in system  60  renders this system more economical to produce, as a fewer number of parts need to be procured, and then less labor time is required to assembled the parts. Moreover, the PPS adjust routine advantageously provides for automatable factory or service calibration of the PPS adjustment without requiring clumsy access panels, and which remains secure during shipping. 
     It is apparent that while the illustrated embodiment has been shown with respect to a replaceable inkjet cartridge, the principles of the adaptive transport system  60  may be applied to what is known in the art as an “off-axis” ink delivery system, where the main ink reservoir is stored at a stationary location for delivery to the reciprocating printhead, via flexible conduits or tubing, for instance. It is also apparent that the principles of the adaptive transport system  60  may be applied to what is known in the art as a “page-wide” printhead array, where the printhead extends over the entire width of the page, so reciprocation is unnecessary. In such a page-wide array printing mechanism, the clutch mechanism may be operated by a small solenoid, or through cooperation with one of the service station components. 
     Advantageously, operation of the adaptive transport system  60  allows for automatic adjustment of pen-to-paper spacing in response to the type and thickness of media being used to provide the best print quality. As a further advantage, the pen-to-paper spacing may also be adapted in response to the type of image being printed. For text or other minimal fill images, the spacing may be close to provide a crisper, cleaner image. For heavily filled images, such as charts, graphics or photographic images, that saturate the media with ink, the spacing may be increased to accommodate paper cockle, avoiding collision between the media and the printhead.