Patent Publication Number: US-6220689-B1

Title: Unitary capping system for multiple inkjet printheads

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to inkjet printing mechanisms, and more particularly to a unitary capping system for simultaneously sealing multiple inkjet printheads during periods of inactivity. 
     BACKGROUND OF THE INVENTION 
     Inkjet printing mechanisms use cartridges, often called “pens,” which eject 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, ejecting 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. 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 supported by 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 substantially 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. The wiping action is usually achieved through relative motion of the printhead and wiper, for instance by moving the printhead across the wiper, by moving the wiper across the printhead, or by moving both the printhead and the wiper. 
     To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment-based inks have been developed. These pigment-based inks have a higher solid content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to form high quality images on readily available and economical plain paper, as well as on recently developed specialty coated papers, transparencies, fabric and other media. 
     As the inkjet industry investigates new printhead designs, the tendency is toward using permanent or semi-permanent printheads in what is known in the industry as an “off-axis” printer. In an off-axis system, the printheads carry only a small ink supply across the printzone, with this supply being replenished through tubing that delivers ink from an “off-axis” stationary reservoir placed at a remote stationary location within the printer. Since these permanent or semi-permanent printheads carry only a small ink supply, they may be physically more narrow than their predecessors, the replaceable cartridges. Narrower printheads lead to a narrower printing mechanism, which has a smaller “footprint,” so less desktop space is needed to house the printing mechanism during use. Narrower printheads are usually smaller and lighter, so smaller carriages, bearings, and drive motors may be used, leading to a more economical printing unit for consumers. There are a variety of advantages associated with these off-axis printing systems, but the permanent or semi-permanent nature of the printheads requires special considerations for servicing. 
     The caps in these earlier service station mechanisms typically included an elastomeric sealing lip supported by a movable platform or sled. Typically, provisions were made for venting the sealing cavity as the cap lips are brought into contact with the printhead. Without a venting feature, air could be forced into the printhead nozzles during capping, which could deprime the nozzles. A variety of capillary passageway venting schemes are known to those skilled in the art, such as those shown in U.S. Pat. Nos. 5,027,134; 5,216,449; and 5,517,220, all assigned to the present assignee, the Hewlett-Packard Company. In the past, a separate vent path was used for each individual cap, often including a separate vent plug for each cap, which contributed to increasing the total part count for a printing mechanism, resulting in a more costly product in terms of both material and labor costs. Another vent system, first sold by the Hewlett-Packard Company in the DeskJet® 693C model color inkjet printer, provided a vent channel in a spring-biased cap base, over which an elastomeric cap was stretched into place. 
     For two-pen printers, earlier cap sleds were often produced using high temperature thermoplastic materials or thermoset plastic materials which allowed the elastomeric sealing lips to be onsert molded onto the sled. The elastomeric sealing lips were sometimes joined at their base to form a cup-like structure, whereas other cap lip designs projected upwardly from the sled, with the sled itself forming the bottom portion of the sealing cavity. Unfortunately, the systems which used a portion of the sled to define the sealing cavity often had leaks where the cap lips joined the sled. To seal these leaks at the lip/sled interface, higher capping forces were used to physically push the elastomeric lip into a tight seal with the sled. This solution was unfortunate because these higher capping forces may damage, unseat or misalign the printheads, or at the vary least require a more robust printhead design which is usually more costly. Moreover, while suitable for sealing two printheads using a single sled, the onsert molded designs were incapable of providing the wide deflection range required to use a single sled to seal more printheads, and in particular, four closely spaced printheads in an off-axis system. 
     A reliable capping system must accommodate for tolerance variations in the components of a printhead carriage, as well as variations in the fit of the pens when installed in the carriage. To properly align the pens for printing, each pen is constructed with a set of alignment datums which are tightly seated against a set of corresponding datums on the carriage. Even minor excursions from nominal values for these datums can impact the position of the printhead relative to the cap. Moreover, even if the datums are all within acceptable tolerance norms, occasionally a pen is not fully seated against a carriage datum, leading to tilted and/or twisted printhead orifice plates. A reliable capping system must be robust enough to adapt to these datum and pen seating variations. 
     Capping systems also need to provide an adequate seal while accommodating several different types of variations in individual printheads. For example, today&#39;s printhead orifice plates often have a waviness or ripple to their surface contour because commercially available orifice plates unfortunately are not perfectly planar. Besides waviness, these orifice plates may also be slightly bowed in a convex, concave or compound (both convex and concave) configuration. The waviness property may generate a height variation of up to 0.05-0.08 millimeters (2-3 mils; 0.002-0.003 inches). These orifice plates may also have some inherent surface roughness over which the cap must seal. 
     The typical way of coping with both the waviness problem and the surface roughness problem is through elastomer compliance, where a soft material is used for the cap lips. The soft cap lips compress and conform to seal over these irregularities in the orifice plate. Unfortunately, some printheads have widely varying maximum and minimum tolerances which mere elastomer compliance is unable to accommodate, so separate spring-biased gimballing cap sleds were required to seal each printhead, such as in the new off-axis style model 2000C inkjet printer produced by the Hewlett-Packard Company. These separate gimballing cap sleds increased the part count, as well as the labor time required to assemble the product, leading to more expensive printing mechanisms. 
     Rather than relying solely on elastomer compliance, where the elastomer is compressed to varying degrees during capping to ensure a tight seal, one earlier design used a suspended lip configuration, as shown in U.S. Pat. No. 5,448,270, assigned to the Hewlett-Packard Company, the present assignee. In this suspended lip design, a single sealing lip projected upwardly from a suspension-bridge like support. In this design, a hollow channel was formed along the underside of the cap to provide an air pocket down into which the “bridge” portion of the cap could be deflected when the lip required more compression to accommodate for manufacturing tolerance extremes than could be accommodated by mere elastomer compression. 
     In this suspended lip design, separate caps for each printhead were fit over four separate race or boss structures, sometimes referred to as a “chimneys,” all formed on a single cap sled. Each boss served to locate the associated cap in position for sealing a printhead. Each boss had a central channel to provide additional room for the bridge portion to deflect downwardly for maximum desired deflection. Unfortunately, the separate caps required for each printhead further increased the part count for the unit, while also increasing the assembly costs because each cap had to be separately stretched over its boss on the sled. This stretching was required so in a relaxed state, the cap would resiliently grip the boss to provide the desired levels of diffusion resistance and venting. Moreover, because each cap is stretched and press-fit over its boss, cap-to-sled locating accuracy was more difficult to maintain than with onsert molded caps discussed above. The use of the boss to support the caps was believed to be a necessary component of the suspended lip design to adequately support the lip during sealing and ensure proper sealing forces, as well as to properly locate the lip around the printhead nozzles. 
     Proper capping requires providing an adequate hermetic seal without applying excessive force which may damage the delicate printheads or unseat the pens from their locating datums in the carriage. Moreover, it would be desirable to provide such a capping system which is easier to manufacture than earlier capping systems to provide consumers with a more economical, high quality inkjet printing mechanism. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, a unitary capping system is provided for sealing ink-ejecting nozzles of an inkjet printhead in an inkjet printing mechanism during periods of printing inactivity. The unitary capping system has a base defining a chamber and a cap hole through the base. A sled is received within the base chamber. The sled has an upper planar surface, with the sled moving between a sealing position and a rest position. The unitary capping system also has an elastomeric printhead sealing structure which includes a planar web sandwiched between the sled and the base inside the chamber. The printhead sealing structure also has a hollow lip support surrounded by the web. The lip support has an upper surface extending through the cap hole to encircle the printhead nozzles, with a lip supported by the lip support upper surface to surround the nozzles when the sled is in the sealing position. The hollow lip support and the web each have a lower surface that rests against the upper planar surface of the sled. 
     According to another aspect of the present invention, a unitary capping system for sealing ink-ejecting nozzles of plural inkjet printheads in an inkjet printing mechanism is provided. The unitary capping system has a sled which is moveable between a sealing position and a rest position. The sled has a planar surface. An elastomeric printhead sealing structure is supported by the sled. The printhead sealing structure has plural lip supports each of which is associated with one of the plural inkjet printheads. Each lip support has opposing first and second surfaces with a sealing lip projecting from the first surface of each lip support. Each sealing lip is configured to surround the nozzles of an associated printhead when the sled is in the sealing position. The second surface of each lip support cooperates with the sled planar surface to define a deflection cavity between the sled and the lip support, so a portion of the lip support may collapse into the deflection cavity when sealing the associated printhead. 
     According to a further aspect of the present invention, an inkjet printing mechanism may be provided with a unitary printhead capping system as described above. 
     An overall goal of the present invention is to provide an inkjet printing mechanism which prints sharp vivid images over the life of the printhead and the printing mechanism, particularly when using fast drying pigment or dye-based inks, and preferably when dispensed from an off-axis system or other printing systems using permanent or semi-permanent printheads. 
     Another goal of the present invention is to provide a unitary capping system for an inkjet printing mechanism that prolongs printhead life. 
     Still another goal of the present invention is to provide a unitary capping system for sealing printheads in an inkjet printing mechanism, with the system having fewer parts that are easier to manufacture and assemble than earlier systems, and which thus provides consumers with a reliable, economical inkjet printing unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one form of an inkjet printing mechanism, here, an inkjet printer, including a printhead service station having one form of a unitary capping system of the present invention for simultaneously sealing multiple inkjet printheads. 
     FIG  2  is an enlarged, top perspective view of the unitary capping system of FIG.  1 . 
     FIG. 3 is an enlarged, exploded, top perspective view of the capping system of FIG.  2 . 
     FIG. 4 is an enlarged, exploded, bottom perspective view of the capping system FIG. 2 
     FIG. 5 is an enlarged, side elevational view of the capping system of FIG. 2, taken along lines  5 — 5  thereof, shown sealing one of the multiple printheads. 
     FIG. 6 is an enlarged, exploded, top perspective view of an alternate embodiment of the unitary capping system of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     FIG. 1 illustrates an embodiment of an inkjet printing mechanism, here shown as an “off-axis” 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, as well as various combination devices, such as a combination facsimile/printer. 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 frame or chassis  22  surrounded by a housing, casing or enclosure  24 , typically of a plastic material. Sheets of print media are fed through a printzone  25  by a media handling system  26 . The print media may be any type of suitable sheet material, such as paper, card-stock, transparencies, photographic paper, fabric, mylar, and the like, but for convenience, the illustrated embodiment is described using paper as the print medium. The media handling system  26  has a feed tray  28  for storing sheets of paper before printing. A series of conventional motor-driven paper drive rollers (not shown) may be used to move the print media from the input supply tray  28 , through the printzone  25 , and after printing, onto a pair of extended output drying wing members  30 , shown in a retracted or rest position in FIG.  1 . The wings  30  momentarily hold a newly printed sheet above any previously printed sheets still drying in an output tray portion  32 , then the wings  30  retract 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, A-4, envelopes, etc., such as a sliding length adjustment lever  34 , a sliding width adjustment lever  36 , and an envelope feed port  38 . 
     The printer  20  also has a printer controller, illustrated schematically as a microprocessor  40 , that receives instructions from a host device, typically a computer, such as a personal computer (not shown). The printer controller  40  may also operate in response to user inputs provided through a key pad  42  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  44  is supported by the chassis  22  to slideably support an off-axis inkjet pen carriage system  45  for travel back and forth across the printzone  25  along a scanning axis  46 . The carriage  45  is also propelled along guide rod  44  into a servicing region, as indicated generally by arrow  48 , located within the interior of the housing  24 . A conventional motor assembly may be coupled to drive an endless belt (not shown), which may be secured in a conventional manner to the carriage  45 , with the motor operating in response to control signals received from the controller  40  to incrementally advance the carriage  45  along guide rod  44 . To provide carriage positional feedback information to printer controller  40 , a conventional encoder strip may extend along the length of the printzone  25  and over the service station area  48 , with a conventional optical encoder reader being mounted on the back surface of printhead carriage  45  to read positional information provided by the encoder strip. The manner of providing positional feedback information via an encoder strip reader may be accomplished in a variety of different ways known to those skilled in the art. 
     In the printzone  25 , the media sheet  34  receives ink from an inkjet cartridge, such as a black ink cartridge  50  and three monochrome color ink cartridges  52 ,  54  and  56 , shown schematically in FIG.  2 . The cartridges  50 - 56  are also often called “pens” by those in the art. The black ink pen  50  is illustrated herein as containing a pigment-based ink. While the illustrated color pens  52 - 56  may contain pigment-based inks, for the purposes of illustration, color pens  52 - 56  are described as each containing a dye-based ink of the colors cyan, magenta and yellow, respectively. It is apparent that other types of inks may also be used in pens  50 - 56 , such as paraffin-based inks, as well as hybrid or composite inks having both dye and pigment characteristics. 
     The illustrated pens  50 - 56  each include small reservoirs for storing a supply of ink in what is known as an “off-axis” ink delivery system, which is in contrast to a replaceable cartridge system where each pen has a reservoir that carries the entire ink supply as the printhead reciprocates over the printzone  25  along the scan axis  46 . Hence, the replaceable cartridge system may be considered as an “on-axis” system, whereas systems which store the main ink supply at a stationary location remote from the printzone scanning axis are called “off-axis” systems. In the illustrated off-axis printer  20 , ink of each color for each printhead is delivered via a conduit or tubing system  58  from a group of main stationary reservoirs  60 ,  62 ,  64  and  66  to the on-board reservoirs of pens  50 ,  52 ,  54  and  56 , respectively. The stationary or main reservoirs  60 - 66  are replaceable ink supplies stored in a receptacle  68  supported by the printer chassis  22 . Each of pens  50 ,  52 ,  54  and  56  have printheads  70 ,  72 ,  74  and  76 , respectively, which selectively eject ink to form an image on a sheet of media in the printzone  25 . The printheads  70 ,  72 ,  74  and  76  each have an orifice plate with a plurality of nozzles formed therethrough in a manner well known to those skilled in the art. The nozzles of each printhead  70 - 76  are typically formed in at least one, but typically two linear arrays along the orifice plate. Thus, the term “linear” as used herein may be interpreted as “nearly linear” or substantially linear, and may include nozzle arrangements slightly offset from one another, for example, in a zigzag arrangement. Each linear array is typically aligned in a longitudinal direction perpendicular to the scanning axis  46 , with the length of each array determining the maximum image swath for a single pass of the printhead. The illustrated printheads  70 - 76  are thermal inkjet printheads, although other types of printheads may be used, such as piezoelectric printheads. The thermal printheads  70 - 76  typically include a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubble of gas is formed which ejects a droplet of ink from the nozzle and onto a sheet of paper in the printzone  25  under the nozzle. The printhead resistors are selectively energized in response to firing command control signals delivered by a multi-conductor strip  78  from the controller  40  to the printhead carriage  45 . 
     Unitary Capping System 
     FIGS. 2-5 illustrate one form of a unitary capping system  100  constructed in accordance with the present invention and installed in the servicing region  48  within the printer casing  24 . The unitary capping system  100  may be moved between a sealing position (FIG. 5) and a rest position by a variety of different mechanisms known to those skilled in the art. Indeed, many different approaches have been used to move printhead servicing implements into engagement with their respective printheads. For example, a dual (two) printhead servicing mechanism which moves the caps in a perpendicular direction toward the orifice plates of the printheads is shown in U.S. Pat. No. 5,155,497, assigned to the present assignee, Hewlett-Packard Company, of Palo Alto, Calif. Another dual printhead servicing mechanism uses the carriage to pull the caps laterally up a ramp and into contact with the printheads, as shown in U.S. Pat. No. 5,440,331, also assigned to the Hewlett-Packard Company. Examples of a quad (four) pen capping systems that use a translational motion are seen in several other commercially available printers produced by the Hewlett-Packard Company, including the DeskJet® 1200 and 1600 models. 
     Another earlier capping system using a translational (sliding) platform to support the cap sled to seal two printheads is commercially available in the DeskJet® 720C and 722C models of inkjet printers produced by the Hewlett-Packard Company, with a similar capping mechanism being used in the Hewlett-Packard Company&#39;s PhotoSmart® color inkjet printer. One other earlier capping system, using a tumbler to support the cap sled to seal two printheads, has been sold in several models of printers produced by the Hewlett-Packard Company, including the DeskJet® 850C, 855C, 820C, 870C, 890C and 895C model inkjet printers. In both the tumbler and sliding platform systems, the cap sled is attached to the tumbler and platform to rock upward into a printhead sealing position as the tumbler and platform move after a portion of the sled has contacted either the printhead or the printhead carriage. In both of these systems, a coil spring is inserted between the sled and the tumbler or platform to push the caps into contact with the printhead. This rocking motion to seal the printheads, using either a rotary or sliding platform, is one preferred manner of installing the unitary capping system  100  in printer  20 , while another preferred manner of installing the unitary capping system  100  is seen in the DeskJet® 2000C model color inkjet printer, an off-axis printer, which uses both rotary and translational motion to move printhead servicing implements between rest and servicing positions. Thus, it is apparent that a variety of different mechanisms and angles of approach may be used to physically move the caps into a sealing position of engagement with the printheads, as illustrated by arrow  201  in FIGS. 2-4. 
     Returning to the unitary capping system  100  of FIGS. 2-5, the system  100  includes a base member  102 , a combination sled and vent path member  104 , and a resilient, elastomeric printhead sealing structure or lip assembly  105 , which is onsert molded over the base  102 . The lip assembly  105  has a lower web portion  106  and an upper web portion  108 . Projecting upwardly from the upper web  108  are a series of four suspended lip cap structures  110 ,  112 ,  114  and  116 , each of which surround the nozzles and form a hermetic seal at the orifice plates of printheads  70 ,  72 ,  74  and  76 , respectively, when moved into a servicing position, as shown in FIG. 5 for lip  110  sealing printhead  70 . The base  102  defines a series of knit holes  117  therethrough, which are used during the onsert molding process to permanently attach the lip assembly  105  to the base. During molding, the elastomer material of the lip assembly  105  flows through the knit holes  117  to form a series of knit points  118  which join the lower and upper webs  106 ,  108  together with the base  102  sandwiched between webs  106 ,  108 . Preferably, the lip assembly  105  is constructed of a flexible, resilient, non-abrasive, elastomeric material, such as nitrile rubber, or more preferably, ethylene polypropylene diene monomer (EPDM), or other comparable materials known in the art. 
     The base  102  also defines a group of cap holes  120 ,  122 ,  124  and  126  therethrough. Each cap structure  110 ,  112 ,  114  and  116  also defines a central vent passageway or throat  130 ,  132 ,  134  and  136  which extends downwardly through the cap holes  120 ,  122 ,  124  and  126  in base  102 . The sled  104  has a lower surface  137  and an upper flat or planar surface  138 . As best shown in FIG. 3, the sled upper surface  138  defines a series of vent passageways or diffusion paths  140 ,  142 ,  144  and  146  which are in fluid communication with the cap vent throats  130 ,  132 ,  134  and  136 , respectively. While the sled vent paths  140 ,  142 ,  144  and  146  may be formed in different patterns, in the illustrated embodiment, the passageways  140 - 146  are constructed in substantially the same shape. The vent path  140  is coupled by an intermediate passageway  148  to a final T-shaped vent passageway  150  which includes a lateral passageway  152  having opposing ends that extend downwardly at the periphery of the sled  104  from the upper surface  138  to terminate at the sled lower surface  137  at outlet ports  156  and  158 . The cap sled  104  also defines a second T-shaped final vent passageway  160 , which may have the same construction as described for the final vent  150 , and which is preferably fluidically coupled with vent  150 . 
     In the past, each cap has had a separate vent to prevent any cross contamination of the ink colors, as well as to prevent plugging of the vent path from mutually coagulating, precipitating or otherwise incompatible inks. The illustrated venting scheme advantageously allows the caps to share a common vent path, here, with a pair of caps, such as caps  110  and  112 , sharing the final T-shaped vent paths  150  and  160 . The vent path  142  is coupled to the T-shaped paths  150  and  160  by an intermediate or linking passageway  162 . The cap sled  104  also defines an intermediate passageway  164  which links the vent path  144  to a pair of T-shaped final vent paths  165  and  166 , which may be constructed as described above for the T-shaped path  150 . The last cap vent  146  is linked to the T-shaped vent paths  165  and  166  by another intermediate passageway  168  to share the paths  165 ,  166  with cap vent  144 . 
     As shown in FIG. 4, underneath each cap lip  110 ,  112 ,  114  and  116  is an empty, open, hollow deflection channel  170 ,  172 ,  174  and  176 , respectively, each of which have substantially the same construction. When assembled with the cap assembly  105  resting against the sled  104 , deflection cavities are then defined between each channel  170 ,  172 ,  174  and  176  and the planar sled upper surface  138 , so no portion of the sled  104  extends into these deflection cavities. The upper surface of the lip assembly  105 , opposite each channel  170 ,  172 ,  174  and  176  defines a lip support structure, which is then hollow since no portion of the sled  104  extends into the channels  170 - 176 . As illustrated in FIG. 5 for the black cap structure  110 , the channel  170  is defined by a cap exterior or peripheral wall  177 , and an interior vent throat wall  178 , which also defined the vent throat  130 . The exterior wall  177  and the interior wall  178  form the upright supports of the bridge-like structure across which a suspension portion or bridge  180  of the cap is suspended. The sealing lip  110  projects upwardly from the bridge  180  to seal the printhead  70  when the cap  110  is moved in the direction of arrow  201  into a sealing position, as shown in FIG.  5 . 
     The base  102  has a recessed undersurface that defines a sled receiving chamber  182 . The sled chamber  182  is sized to receive the sled  104  with a press fit, although in some implementations, it may be preferable to include a mechanical fastener or latching mechanism, such as a snap fit, between the base  102  and the sled  104 . The undersurface of the base  102  that defines chamber  182  also serves to enclose the intermediate vent paths  148 ,  162 ,  164  and  168 , and the T-shaped final vent paths  150 ,  160 ,  165  and  166  when assembled, leaving the vent outlet ports, such as ports  156  and  158 , open to atmosphere. When assembled, the hollow deflection channel  170  straddles the rectangular periphery of the vent path  140 , with the lower surface of the vent throat wall  178  resting firmly against segments  184 ,  185 ,  186  and  188  of the sled upper surface  138  (see FIGS.  3  and  5 ). The bottom opening of the throat  130  sits over the intersection portion of vent path  140  which separates the segments  184 ,  185 ,  186  and  188  from one another. The length and area of the vents paths, from the printhead  70  to the outlet ports  156 ,  158  may be varied as know by those skilled in the art, depending on the particular printhead geometries, sealing characteristics, etc. desired. 
     As mentioned near the beginning of this section, a variety of different mechanisms may be used to move the cap in the direction of arrow  201  into a sealing position, or in the general direction opposite arrow  201  to a rest position out of engagement with the printhead  70 , such as during printing or other printhead servicing operations. The sled  104  may be secured to the operating mechanism by way of an attachment member  190  extending downwardly from the sled lower surface  137 , as best shown in FIG.  4 . 
     FIG. 5 shows cap  110  sealing printhead  70 , which is slightly misaligned with respect to a nominal printhead plane  192 , shown in dashed lines. Here, the left side of the black printhead  70  dips below the reference plane  192 , and is sealed without experiencing excessive capping forces as the suspension bridge portion  180  to the left of center of the cap structure is deflected into the empty channel  170 . The various reasons and causes for such printhead misalignment are discussed in the Background section above. 
     FIG. 6 shows an alternative embodiment of a unitary capping system  200  constructed in accordance with the present invention, which may be substituted for the capping system  100 . Rather than being an onsert molded design, system  200  uses the combination sled and vent path member  104  described above, in conjunction with a covering base member  202  and a flexible lip assembly  205  which is sandwiched between the sled  104  and cover  202 . The lip assembly  205  has a web  206  with an upper surface  208  from which project four suspended lip cap structures  210 ,  212 ,  214  and  216 . The cover base  202  also defines a group of cap holes  220 ,  222 ,  224  and  226  through which the cap lips  210 ,  212 ,  214  and  216  project. The cover base  202  has a recessed undersurface that defines a sled receiving chamber  218  that may be sized to receive the sled  104  with a press fit, with or without additional latches, hooks or other fitments, as discussed above with respect to base  102  and chamber  182 . Each cap structure  210 ,  212 ,  214  and  216  also defines a central vent passageway or throat  230 ,  232 ,  234  and  236  which extends downwardly through holes  220 ,  222 ,  224  and  226  in cover  202 . Each cap structure  210 - 216  may be substantially the same as described above for the caps  110 - 116 , including the hollow deflection channel  170 , and the fit of each cap with respect to the vent paths  140 - 146  defined by the sled  104 . 
     Conclusion 
     A variety of advantages are realized using the unitary capping systems  100  and  200  described herein, and several of these advantages have been noted above. For example, this unitary capping system  100 ,  200  has been found to reduce the sealing forces exerted on printheads  70 - 76 . Also, assembly costs are lowered compared to earlier systems due to the decreased part count and the elimination of the chimney. Moreover, if some designs favor the onsert molded design  100  over the press-fit design  200 , the sled  104  may be easily used with either design  100 ,  200 . Indeed, as further modifications of the press-fit design  200 , in one embodiment the covering base  202  may be eliminated by configuring the lip assembly web  206  to have a downwardly protruding gripping ridge around the periphery of the web, sized to define a sled-receiving chamber similar to chamber  218 , with the gripping ridge resiliently holding the sled  104  within this chamber. Alternatively, the sled  104  may have lip assembly retaining features, such as an upwardly extending gripping ridge extending around the periphery of the sled so web  206  may be press-fit under this gripping ridge and retained thereby along the upper planar surface of the sled. 
     As mentioned in the Background section above, U.S. Pat. No. 5,448,270, assigned to the Hewlett-Packard Company, the present assignee, disclosed a suspended lip cap design, with each cap being separately press-fit over a positioning race or boss, sometimes referred to as a “chimney.” Commercial embodiments of this suspended lip design were sold in the DeskJet® 1200 and 1600 model inkjet printers, by the Hewlett-Packard Company. In this earlier suspended lip cap design, with each cap was separately press-fit over a positioning race or boss, sometimes referred to as a “chimney,” which projected upwardly from the sled. In this earlier design, the boss used to support the caps was a necessary evil believed to be required to ensure proper printhead sealing forces, diffusion path resistance and venting, as well as to properly locate the lip around the printhead nozzles. 
     Given the difficulty of assembly, and resulting increased cost of the product, the inventor began a study of the sealing ability of the unitary cap systems  100 ,  200  described above, and compared their performance to that of the caps sold in the DeskJet® 1200, 1600 and 2000C model inkjet printers. Surprisingly, the web  106 ,  108  and  206  gave the caps  110 - 116 ,  210 - 216  lateral stability, while the smooth fit of the vent throat wall  178  against the segments  184 ,  185 ,  186  and  188  of the sled upper surface  138  provided good support for the throat wall  178 . The illustrated cap geometry for systems  100  and  200  offered a larger operating range to accommodate tolerance stack than a mere compressed elastomer, such as in the DeskJet® 2000C model inkjet printer which required each cap to be separately gimbaled. Moreover, it was discovered that the chimneyless unitary cap system  100 ,  200  performed comparably with the earlier chimney designs in the DeskJet® 1200 and 1600 model inkjet printers, with the illustrated geometry of the caps  110 - 118 ,  210 - 218  being more important to performance than the durometer (relative hardness) of the cap elastomer, or the type of materials selected. Thus, manufacturing costs are lower because the tolerances on the material durometer could now be increased without sacrificing performance.