Patent Publication Number: US-6209983-B1

Title: Multi-ridge capping system for inkjet printheads

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This is a continuation of application Ser. No. 08/382,473 filed on Jan. 31, 1995, now U.S. Pat. No. 5,712,668, issued on Jan. 27, 1998, which is a continuation-in-part of application Ser. No. 08/218,391, filed Mar. 25, 1994, now U.S. Pat. No. 5,617,124, issued on Apr. 1, 1997. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to inkjet printing mechanisms, and more particularly to an improved capping system for storing inkjet printheads therein during periods of inactivity, including a new multi-ridge printhead cap, a new rotary printhead servicing apparatus, and a new printhead sealing method. 
     BACKGROUND OF THE INVENTION 
     Inkjet printing mechanisms use 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 moves back and forth across the page shooting drops as it moves. To clean and protect the printhead, typically a service station is mounted within the printer chassis. For storage, or during non-printing periods, service stations usually include a capping system which humidically 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.” Typically, the waste ink is collected in a stationary reservoir portion of the service station, which is often referred to as a “spittoon.” 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 improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide faster, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solids 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 use plain paper. Unfortunately, the combination of small nozzles and quick drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solids within the new inks themselves. 
     Partially or completely blocked nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Thus, spitting to clear the nozzles becomes even more important when using pigment based inks, because the higher solids content contributes to the clogging problem more than the earlier dye based inks. Unfortunately, while stationary spittoons were suitable for the earlier dye based inks, they suffer a variety of drawbacks when used with newly developed pigment based inks. 
     For example, FIG. 8, is a vertical sectional view of a conventional prior art spittoon S which has been receiving waste ink of the newer variety for a period of time. The rapidly solidifying waste ink has gradually accumulated into a stalagmite I. The ink stalagmite I may eventually grow to contact the printhead H, which could interfere with printhead movement, print quality, and/or contribute to clogging the nozzles. Indeed, ink deposits along the sides of the spittoon often grow into stalagmites which can meet one another to form a bridge blocking the entrance to the spittoon. To avoid this phenomenon, conventional spittoons must be wide, often over 8 mm in width to handle these new pigment based inks. This extra width increases the overall printer width, resulting in additional cost being added to the printer, both in material and shipping costs. 
     This stalagmite problem is particularly acute for a polymer or a wax based ink, such as an ink based on carnauba wax, or a polyamide. In the past, inkjet printers using polyamide based inks have replaced the conventional spittoon of FIG. 8 with a sheet of flat plastic. The nozzles are periodically cleared by “spitting” the hot wax ink onto the plastic sheet. At regular intervals, an operator must remove this plastic sheet from the printer, flex the sheet over a trash can to remove the waste ink, and then replace the cleaned sheet in the printer. This cleaning step is particularly inconvenient for operators to perform on a regular basis, and is not suitable for the new pigment ink. In comparison to the wax or polymer based inks, these new inks leave a dirty, sticky residue, due to the high amount of solids used to improve the contrast and quality of the printed images. Thus, operator intervention to regularly clean a pigmented ink spittoon could lead to costly staining of clothing, carpeting, upholstery and the like. 
     In addition to increasing the solids content, mutually precipitating inks have been developed to enhance color contrast. For example, one type of color ink causes black ink to precipitate out of solution. This precipitation instantly fixes the black solids to the page, which prevents bleeding of the black solids into the color regions of the printed image. Unfortunately, if the mutually precipitating color and black inks are mixed together in a conventional spittoon, they do not flow toward a drain or absorbent material. Instead, once mixed, the black and color inks instantly coagulate into a gel, with some residual liquid being formed. 
     Thus, the mixed black and color inks have the drawbacks of hot-melt inks, which have an instant solid build-up, and the aqueous inks, which tend to run and “wick” (flow through capillary action) into undesirable locations. To resolve the mixing problem, two conventional stationary spittoons are required, one for the black ink and one for the color inks. As mentioned above, these conventional spittoons must be wide to avoid clogging from stalagmites growing inward from the spittoon sides. Moreover, using two spittoons further increases the overall width of the printer, which undesirably adds to the overall size of the inkjet printer, as well as its weight and material cost to build. 
     To maintain a high print quality in the hardcopy output, pens containing the new pigment based inks require new capping strategies. The pigment based inks have posed new challenges for efficiently capping the printheads. To maintain the desired ink characteristics, the area around the printhead nozzles must be kept clean and moist to prevent drying or decomposition of the ink during periods of printer inactivity. These principles are equally applicable to pens containing dye based inks. 
     In the past, a variety of different systems have been used to seal an inkjet printhead during periods of printer inactivity. These capping systems may be divided into three general categories based upon the direction of movement to engage the printheads, specifically, (1) linear caps, (2) vertical caps, and (3) rotary caps. The first group, linear caps, unfortunately require excessive carriage overtravel well beyond the print zone to seal the printheads. The mechanisms employed by these linear capping systems include an in-line four bar linkage mechanism, a ramp mounted sled, a four bar linkage including a spring mechanism, and combination ramp and spring mechanisms. Typically, these linear caps are pushed by the printhead in a direction parallel to the printhead scanning axis, and during this lateral motion, the caps are raised to seal the printhead nozzles. 
     Second, the vertical capping group of mechanisms move the caps upwardly to engage the printheads. One system uses a vertical rack and pinion mechanism, driven by a motor to move the caps upward to seal the printheads. Another vertical system uses a spring loaded vertical cam drive mechanism to cap the printheads. 
     The third capping system involves rotating the caps into position. One known rotary capping system rotates the caps about an axis which is perpendicular to the scanning axis of the printhead, and then cams the cap upward to engage the printhead. Another rotary system rotates a spring-biased lever to pivot the cap into a sealing position. This particular system gimbal-mounts the cap to the lever for limited angular tilting with respect to the printhead. 
     Unfortunately, each of these earlier capping systems has a variety of disadvantages. For example, many of them require extra carriage travel beyond the width required to mount the caps. This extra carriage travel results in a wider product with a large “footprint” (the work surface area occupied by the product). Some of these capping systems also have difficulty in sealing substantially irregular or nonplanar surfaces, such as those encountered when ink residue or other debris has accumulated on the printhead. These earlier systems also have difficulty in maintaining critical capping tolerances. Additionally, many of these earlier capping systems are sensitive to ink leakage from the pens, and accumulations of ink aerosol within the capping mechanism. The sticky aerosol and/or ink leakage build up may impede motion of critical components, leading to ineffective capping. Moreover, ink leakage from the capped pens often blocked or clogged vent ports within these earlier capping mechanisms. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a service station is provided for servicing an inkjet printhead of an inkjet printing mechanism, with the printhead having nozzles that selectively eject ink therethrough. The service station includes a tumbler that is rotatable around a first axis, and a platform pivoted to the tumbler for movement to a capping position. A printhead cap is supported by the platform to surround and seal the printhead nozzles when in the capping position. 
     In an illustrated embodiment, the platform has an arm portion that engages a printhead structure when the tumbler is rotated around the first axis. A dual pivot structure is used to cradle the platform within the tumbler. A biasing member urges the platform away from the tumbler. The platform cooperates with a resilient vent stopper member to define a non-clogging vent passageway which avoids depriming the inkjet pen during capping, as well as during any environmental changes in temperature, barometric pressure, etc., while capped. 
     According to another aspect of the present invention, a method is provided of sealing inkjet printhead nozzles of an inkjet printing mechanism. The method includes the step of supporting a printhead cap with a platform. The cap is configured to surround and seal the printhead nozzles when in a capping position. In a revolving step, the platform is revolved around a first axis. During the revolving step, a portion of the platform is engaged with a printhead structure. In a rocking step, the engaged platform is rocked into the capping position. 
     According to a further aspect of the present invention, a method is provided of sealing inkjet printhead nozzles of an inkjet printing mechanism which includes the step of providing a printhead cap configured to surround and seal the printhead nozzles when in a capping position. In a cradling step, the cap is cradled within a tumbler. In a traversing step, the cap is traversed along a non-linear path into the capping position by rotating the tumbler. 
     According to one aspect of the invention, a service station is provided for servicing an inkjet printhead of an inkjet printing mechanism, where the printhead has a face plate defining a group of ink ejecting nozzles extending therethrough. The service station has a platform moveable into a capping position. A printhead cap is supported by the platform. The cap has a sealing lip that surrounds the nozzles and engages the face plate when in the capping position. The lip has at least a portion with adjacent plural contact regions capable of sealing over surface irregularities on the face plate. 
     An overall object of the present invention is to provide an inkjet printing mechanism which prints sharp vivid images, and which preferably does so using a fast drying pigment based ink. 
     Another object of the present invention is to provide a service station for an inkjet printing mechanism which maintains pen health and occupies a relatively small physical space to provide a more compact product. 
     A further object of the present invention is to provide a method of sealing an inkjet printhead mounted in a printing mechanism during periods of inactivity to maintain ink composition integrity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one form of an inkjet printing mechanism of the present invention incorporating a first embodiment of a self-cleaning service station of the present invention. 
     FIG. 2 is a perspective view of the self-cleaning service station of FIG.  1 . 
     FIG. 3 is a front vertical elevational view taken along lines  3 — 3  of FIG.  2 . 
     FIG. 4 is a side elevational view taken along lines  4 — 4  of FIG.  3 . 
     FIG. 5 is a side elevational view of a second embodiment of a self-cleaning service station of the present invention. 
     FIG. 6 is a front elevational view taken along lines  6 — 6  of FIG.  5 . 
     FIG. 7 is a side elevational view of a third embodiment of a self-cleaning service station of the present invention. 
     FIG. 8 is a side elevational view of a conventional spittoon portion of a prior art service station. 
     FIG. 9 is a perspective view of an alternate embodiment of a rotary service station capping system of the present invention, shown in a capping position but removed from the service station frame. 
     FIG. 10 is a perspective view of a tumbler portion of the system of FIG.  9 . 
     FIG. 11 is a perspective view of a cap sled and connecting link of the system of FIG.  9 . 
     FIG. 12 is a fragmentary, side elevational, sectional view of the system of FIG. 9, shown prior to capping. 
     FIGS. 13A-13C and  14 A- 14 C are enlarged side elevational sectional views showing the relative positions of the system components of FIGS. 9-12, with 
     FIGS. 14A,  14 B, and  14 C being views taken along the respective lines A—A, B—B, and C—C of FIG. 9 shown capping, and FIGS. 13A-13C showing prior to capping. 
     FIGS. 15 and 16 are schematic side elevational views illustrating the capping operation of the rotary service station embodiment of FIG.  9 . 
     FIG. 17 is a side elevational sectional view of the multi-ridge cap taken along lines  17 — 17  of FIG.  11 . 
     FIG. 18 is an enlarged bottom plan view of the cap sled of FIGS. 9-10 and FIGS.  12 - 13 . 
    
    
     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  and a print medium handling system  24  for supplying sheets of print media to the printer  20 . The print media may be any type of suitable sheet material, such as paper, card-stock, transparencies, mylar, foils, and the like, but for convenience, the illustrated embodiment is described using paper as the print medium. The print medium handling system  24  moves the print media into a print zone  25  from a feed tray  26  to an output tray  28 , for instance using a series of conventional motor-driven rollers (not shown). 
     In the print zone  25 , the media sheets receive ink from an inkjet cartridge, such as a black ink cartridge  30  and/or a color ink cartridge  32 . The cartridges  30 ,  32  are also referred to as “pens” by those in the art. The illustrated color pen  32  is a tri-color pen, although in some embodiments, a group of discrete monochrome pens may be used, or a single monochrome black pen  30  may be used. While the color pen  32  may contain a pigment based ink, for the purposes of illustration, pen  32  is described as containing three dye based ink colors, such as cyan, yellow and magenta. The black ink pen  30  is illustrated herein as containing a pigment based ink. It is apparent that other types of inks may also be used in pens  30 ,  32 , such as paraffin based inks, as well as hybrid or composite inks having both dye and pigment characteristics. 
     The illustrated cartridges or pens  30 ,  32  each include reservoirs for storing a supply of ink therein, although other ink supply storage arrangements, such as those having reservoirs (not shown) mounted along the chassis may also be used. The cartridges  30 ,  32  have printheads  34 ,  36  respectively. Each printhead  34 ,  36  has bottom surface comprising an orifice plate with a plurality of nozzles formed therethrough (see FIG. 18) in a manner well known to those skilled in the art. The illustrated printheads  34 ,  36  are thermal inkjet printheads, although other types of printheads may be used, such as piezoelectric printheads. The printheads  34 ,  36  typically include a plurality of resistors which are associated with the nozzles. Upon energizing a selected resistor, a bubble of gas is formed ejecting a droplet of ink from the nozzle and onto a sheet of paper in the print zone  25  under the nozzle. 
     The cartridges or pens  30 .  32  are transported by a carriage  38  which may be driven by a conventional drive belt/pulley and motor arrangement (not shown) along a guide rod  40 . The guide rod  40  defines a scanning direction or scanning axis  41  along which the pens  30 ,  32  traverse over the print zone  25 . The pens  30 ,  32  selectively deposit one or more ink droplets on a print media page located in the print zone  25  in accordance with instructions received via a conductor strip  42  from a printer controller, such as a microprocessor which may be located within chassis  22  at the area indicated generally by arrow  44 . The controller  44  may receive an instruction signal from a host device, which is typically a computer, such as a personal computer. The printhead carriage motor and the paper handling system drive motor operate in response to the printer controller  44 , which may operate in a manner well known to those skilled in the art. The printer controller may also operate in response to user inputs provided through a key pad  46 . A monitor coupled to the host computer may be used to display visual information to an operator, such as the printer status or a particular program being run on the 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. 
     Referring also to FIGS. 2-4, the printer chassis  22  has a chamber  48 , configured to receive a service station  50 , located at one end of the travel path of carriage  38 . Preferably, the service station  50  is constructed as a replaceable modular device capable of being unitarily inserted into the printer  20 , to enhance ease of initial assembly, as well as maintenance and repair in the field. The illustrated service station  50  has a frame  52  which may be slidably received within chamber  48  the printer chassis  22 . However, it is apparent that the service station  50  may also be constructed with the station frame  52  integrally formed within the chassis  22 . 
     The service station  50  has a tumbler portion  54  mounted to frame  52  for rotation about a first axis or tumbler axis  55  with bearing surfaces  56 ,  58 . The tumbler axis  55  is substantially parallel to the printhead scanning axis  41 . The tumbler  54  may be driven by motor and gear or belt assembly (not shown), or through a separate motor (not shown) via a gear  60 . The tumbler  54  includes a main body  62  upon which may be mounted conventional inkjet pen caps, such as a color ink cap  64  and a black cap  65 . The body  62  also supports color and black ink wipers  66  and  68  for wiping the respective color and black printheads  36 ,  34 . Other functions may also be provided on the main body  62 , such as primers and the like, which are known to those skilled in the art. It is apparent that other arrangements may be used to index the pen capping, wiping, etc. functions rather than the tumbler main body  62 . For example gears or linkages (not shown) known to those skilled in the art may be used for selectively engaging the service station equipment  64 ,  65  and  66 ,  68  with the respective printheads  36 ,  34 . However, the tumbler concept illustrated in FIGS. 1-4 is preferred because of its ease of implementation and adaptability for modular use. 
     Self-Cleaning Service Station—First Embodiment 
     FIGS. 1-4 illustrate the first embodiment of the self-cleaning service station  50  as having a rotating annular trough or “ferris wheel” spittoon  70 . The spittoon  70  receives ink which is spit from the black ink and color pens  30 ,  32  when they are positioned above the spittoon. The spittoon  70  is driven by gear  60  via a roller, spindle or axle portion  72 , which extends from the main body  62 . The frame structure  52  has a bottom wall  73  and an intermediate wall  74 . The wall  74  separates the service station  50  into a spittoon chamber  75  and a main servicing chamber  76 . As shown in FIG. 3, the spittoon chamber  75  is located between wall  74  and an outer wall  78  of the frame  52 . 
     The ferris wheel spittoon  70  has a moveable platform provided by an annular trough or “ferris wheel”  80 . The wheel  80  has an annular bottom portion  82  and two side walls  84 ,  85 , and is mounted to the axle  72  for rotation about the tumbler axis  55 . The wheel  80  receives ink purged from the printheads  34  and  36  through an opening  86 . The opening  86  is defined by an upper wall or lid  88 , which may be a portion of, or pivoted at a hinge  89  to, the frame  52 . Preferably, the wheel  80  is of an elastomeric or other resilient and flexible material, such as neoprene. The use of an elastomeric material is preferred to facilitate sealing the area between the wheel side walls  84 ,  86  and the frame walls  74  and  78 , respectively. However, it is apparent that other types of material may also be used for wheel  80 , such as various plastics which are flexible and resilient to provide a positive seal between the wheel  80  and walls of frame  52 . 
     The spittoon  70  also has a scraper portion  90  for removing purged ink from the ferris wheel  80 , as shown in FIG.  3 . Adjacent the scraper  90 , the main servicing chamber  76  may be lined with a liquid absorbent diaper  91 , which may be of a felt, pressboard, sponge or other material. The diaper  91  absorbs liquids spit from the pens  30 ,  32 . When both black and color inks are deposited in the spittoon  70 , once mixed, these inks instantly coagulate into a gel, with some residual liquid being formed. This residual liquid may also be absorbed by the diaper  91 . 
     In the illustrated embodiment, the scraper  90  is of a substantially rigid plastic material. The scraper  90  may be molded unitarily with the remaining portion of frame  52  for convenience, although it is apparent that the scraper  90  may be separately assembled into frame  52 . The scraper portion  90  preferably has a scraping surface  92  conformed to roughly approximate the cross-sectional shape of the wheel  80 , as shown in FIG.  3 . 
     In operation, referring to FIGS. 3-4, recently spit ink  94  is collected along the wheel bottom surface  82 . The tumbler  54  is rotated via a gear assembly (not shown) in contact with gear  60  until the majority of the discharged ink  94  is removed from roller  80  by scraper  90 . An accumulation of recently removed ink  95  may accumulate adjacent the upper edge  92  of the scraper  90 . Eventually, this accumulated ink  94  will dry and fall from the scraper to form piles of dried ink solids  96  at the bottom of the spittoon chamber  75 . Ink may also accumulate along the rim surface of the ferris wheel side walls  84 ,  85 , such as ink accumulation  98  shown in FIG.  4 . Advantageously, by selecting a relatively close spacing between the lid  88  and the walls  84 ,  85 , the lid  88  scrapes the ink solids  98  from the wheel rims to prevent the solids  98  from touching the printheads  34 ,  36 . As mentioned in the background portion, if left unattended, such ink residue  98  could contact the nozzle plate, potentially damaging or clogging the orifices of the printheads  34 ,  36 . 
     Self-Cleaning Service Station—Second Embodiment 
     FIGS. 5 and 6 illustrate a second alternate embodiment of an inkjet spittoon  100  constructed in accordance with the present invention, which may be substituted for the ferris wheel spittoon  70  of FIGS. 1-4. The spittoon  100  comprises a multiroller spittoon having two or more rollers, here, having four rollers  102 ,  104 ,  106  and  108 . One of the rollers  102 - 108  may be driven by gear  60  and the remaining rollers may be mounted between walls  74  and  78  for free pivoting. The rollers  102 - 108  support an a moving platform comprising an endless belt  110 , which may be constructed of an elastomer, polymer, plastic, fabric, or other flexible material. 
     In the spittoon  100 , the mechanism for removing recently spit ink  112  from belt  110  comprises an ink removal device formed by the contours of rollers  102  and  106 , rather than through the use of a scraper  90 . In the illustrated embodiments, the roller  102  is positioned under opening  86  in the lid  88 . The roller  102  has a concave surface  114  which forms a trough  115  in belt  110  for receiving the ink  112 . To expel the ink  112  from belt  110 , the lower roller  106  has a convex surface  116  which flexes the belt  110  outwardly to dump the spent ink solids  112  into a refuse ink pile  118  along the lower surface of the spittoon chamber  75 . Rollers  104  and  108  may be cylindrical or have configurations which are either concave or convex, but as illustrated, roller  104  is concave and roller  108  is convex. Furthermore, it is apparent that a scraper mechanism, such as scraper  90 , may also be used in conjunction with the contoured rollers  102 ,  106  to remove ink deposits from the belt  110 . The rim of roller  102 , thickness and width of belt  110 , and the relative location of lid  88  to the edges of belt  110  may be selected to remove ink accumulations  120  from the belt edges, as described above with respect to FIG. 4 for the rim accumulation  98 . 
     Self-Cleaning Service Station—Third Embodiment 
     A third embodiment of a self-cleaning spittoon  150  is shown in cross-section in FIG.  7 . The spittoon  150  may include two or more rollers, such as roller  152  and  154  which are coupled together by an endless belt  155 . Preferably, roller  152  may be coupled to the tumbler portion  54  to be driven by gear  60 . In the illustrated embodiment, roller  152  is positioned below the frame lid opening (not shown) in the frame lid  88  to receive the ink  156  from printheads  34 ,  36 . The ink  156  travels along the upper surface of belt  155 , and around roller  154  where it encounters a scraper  158 , and is scraped off as ink solids  160 . Alternatively, the illustrated cylindrical rollers  152  and  152  may be replaced with concave and convex rollers, such as roller  102  and  106 , respectively of FIGS. 5 and 6. In such an embodiment, the scraper  160  may be used in conjunction with roller  154  having a convex shape, or the scraper  160  may be omitted in such a contoured roller embodiment. The belt  155  may be as described above with respect to belt  110  regarding flexing. 
     One advantage of the spittoon embodiment  150  is that it receives ink in one portion of the printer adjacent roller  152 , and expels the dried solids in a remote location adjacent roller  154 . While the belt  155  is illustrated as being a substantially flat belt, it is apparent that it may be flexible to conform to the contours of rollers as described above with respect to FIGS. 5-6, or it may have side walls similar to walls  84  and  86  (FIG.  3 ). 
     Method of Purging an Inkjet Pen 
     According to another aspect of the illustrated embodiment, a method is also provided for cleaning an inkjet pen, such as pen  30  or  32 , when mounted for use in an inkjet printer, such as printer  20 . The method includes the steps of positioning the pen  30  or  32  over a moveable platform surface of the service station  70 . This moveable platform may be provided by the ferris wheel  80 , or belts  110  or  155 . A portion of the ink is purged from the pen  30  or  32  onto the platform. The platform is then moved to a discharge location, illustrated here with the platforms being driven by rotating gear  60  or the at least one of the rollers  102 - 108  and  152 - 154 . The discharge location is illustrated as adjacent scraper  90  (FIGS.  3 - 4 ), adjacent roller  106  (FIGS.  5 - 6 ), and adjacent roller  154  and scraper  158 , if used (FIG.  7 ). 
     In a discharging step, the purged waste ink is discharged from the platform surface at the discharge location. As shown in FIGS. 3-4, the discharging is illustrated by scraper  90  scraping ink off of the ferris wheel  80 . In FIGS. 5-6, discharging is accomplished by flexing the belt  110  using the convex contour  116  of roller  106 . In FIG. 7, the scraper  158  provides the discharge mechanism, in addition to, or as an alternative to a convex profile for roller  154 . That is, the contoured roller concept may be combined with the scraper concept (not shown) by forming the scraper upper surface (item  92  in FIG. 3) with a concave contour to compliment the convex contour of roller  106 , for instance. 
     Advantages of the Self-Cleaning Service Station 
     Thus, a variety of advantages are achieved using the movable platform spittoon of the present invention, for example in the various embodiments as illustrated in FIGS. 1-7. For instance, ink no longer accumulates into a stalagmite I as shown in FIG. 8 for the earlier conventional spittoon S. Instead, the waste ink is transported from a receiving location to a discharge location where it is broken off in small pieces  96 ,  118 ,  160 . During periodic servicing of the printer  20 , these waste ink solids  96 ,  118 ,  160  may be easily removed, and they are more compact for disposal than the large stalagmites I encountered in the prior art (FIG.  8 ). Thus, the packing density of a pile of short stalagmites formed as shown in FIGS. 3-7 is much less than that for the large stalagmite I shown in FIG.  8 . 
     Furthermore, the use of a moveable platform spittoon allows for the accumulation of a greater number of ink solids than achieved with the stationary spittoon S of FIG.  8 . As a result, the printer  20  may be operated for longer periods of time between servicing to remove accumulated ink solids. Additionally, accumulation of the ink solids  95  will not inhibit printhead performance as would be the case for high ink solids using the earlier FIG. 8 stationary spittoon S. 
     Moreover, the illustrated spittoons of FIGS. 1-7 may have a very narrow width, e.g. narrow in the axial direction parallel with the tumbler axis  55 . Indeed, the width of the ferris wheel  80 , or the belt  110 ,  155  need only be as wide as the precision within which the ink may be spit into them, for instance, on the order of 2 mm, as opposed to 8 mm for spittoon S of FIG.  8 . Thus, a narrower service station may be achieved, which reduces the overall size of printer  20  to reduce material costs, shipping and packing costs, and to provide a more compact printer  20  for the consumer. 
     The use of an elastomeric or other resilient material for the ferris wheel  80  of FIGS. 1-4 provides additional advantages. For example, the aqueous residue from the expelled ink  94  tends to run downwardly under the force of gravity, and to wick along comers and edges of the spittoon chamber  75 . The elastomeric rims  84  and  86  of wheel  80  advantageously provide a liquid seal against walls  74  and  78 , respectively. Even if liquid is lifted from the bottom portion of the chamber  75  by the rims  84  and  85  upwardly toward the lid  88 , the rim seals will prevent this liquid from reaching the remaining service station equipment of the main body  62 . That is, the rim  84  seals the opening in wall  74  through which the shaft  72  passes. Advantageously, the caps  64  and  65 , the wipers  66  and  68 , and any other service station component mounted on the main body  62  are kept clean to maintain print quality. 
     Ink aerosol generation is another problem that is addressed by the ferris wheel spittoon system described herein. Spit ink droplets and particles of ink impact the ferris wheel and stick to it, rather than losing velocity and being carried to, and deposited on, sensitive portions of the printer. These captured satellites are then unable to damage printhead components through friction and corrosion, nor are they available to fog any optical encoder components and cause loss of carriage position information. Eliminating a sizable portion of the aerosol also decreases soiling of an operator&#39;s fingers, clothing or other nearby objects. 
     Rotary Capping System 
     Referring to FIGS. 9-12, an alternate embodiment of a rotary service station  200  constructed in accordance with the present invention is illustrated. The rotary service station  200  includes a tumbler body portion  202  which terminates at opposing axial ends with two wheel portions or rims  204  and  205 . The tumbler body  202  may be mounted pivotally at hubs  206  and  208  (also see FIG. 12) within the service station frame  52  by bearing assemblies, such as bearing  58  shown in FIG. 3, in place of tumbler  62 . In the illustrated embodiment, the hub  208  may engage the spindle portion  72  which extends through the ferris wheel  80 . Alternatively, the service station wall  74  may be equipped with a bearing member similar to bearings  56  or  58 , to receive hub  206 , with the spindle  72  then engaging hub  206  for providing rotation about the tumbler axis  55 . In either case, the outer periphery of the tumbler rim  204  preferably has gear teeth formed thereon to function as the drive gear  60 , but for clarity, the gear teeth have been omitted from FIGS. 9 and 10. Alternatively, it is apparent that the rotary service station  200  may also be used with a conventional spittoon comprising one, two or more fixed spittoon chambers instead of the ferris wheel service station  80  shown in FIGS. 1-4. 
     The rotary station  200  includes a printhead capping system  210 , constructed in accordance with the present invention, which includes the tumbler body  202 . FIG. 10 shows the tumbler body  202  as having a rest wall  212 , and a capping or stop wall  214 . A rocker pivot post  215  extends upwardly from the stop wall  214 . The tumbler rims  204  and  205  each define half-moon shaped recesses  216  and  218 , respectively. The capping system  210  also has a cap support platform or sled  220 , shown in detail in FIG.  11 . The sled  220  has two extending alignment or contact arms  222  and  224 , which maybe configured to engage a printhead structure, such as one of the pens  30 ,  32  or the printhead carriage  38 , to facilitate capping, as described further below. In the illustrated embodiment, the arms  222 ,  224  are located for cooperative adjacency to engage a printhead structure comprising a downwardly extending alignment member  225  of carriage  38  during a selected portion of the tumbler rotation. 
     The sled  220  also defines two cap vent or drain holes  226  and  228 . The capping assembly  210  has black and color ink printhead sealing caps  230  and  232  supported by sled  220 , which surround the respective vent holes  226  and  228 . The caps  230 ,  232  may be joined to the sled  220  by any conventional manner, such as by bonding with adhesives, sonic welding, or more preferably by oncert molding techniques. In the illustrated embodiment, the caps  230 ,  232  may be of a non-abrasive resilient material, such as an elastomer or plastic, a nitrile rubber or other rubber-like material, but more preferably, caps  230 ,  232  are of an ethylene polypropylene diene monomer (EPDM), or other comparable material known in the art. In the illustrated embodiment, the black ink cap  230  seals the black pen  30 , which contains a pigment based ink, and the color cap  232  seals the color pen  32 , which contains three dye based colored inks, such as cyan, magenta, and yellow. 
     Referring also to FIGS. 13A through 16, one method of coupling the sled  220  to the tumbler body  202  is illustrated as using a link or yoke member  240  (for simplicity, the yoke  240  has been omitted from the views in FIGS.  13 C and  14 C). The yoke  240  is a dual pivot structure, having two upright ear members  242  and  244  joined together by a bridge member  245 . Each ear  242 ,  244  has a lower rim pivot member which extends through the respective half-moon shaped slots  216 ,  218  of tumbler rims  204 ,  205 , such as the rim pivot member  246  which extends through slot  218  in the tumbler rim  205 . The half-moon shaped slots  216 ,  218 , each define pivot shoulders  247 ,  248 . The rim pivot members  246  engage and toggle about the pivot shoulders  248  during operation (compare FIG. 13A with FIG.  14 A), for pivotal motion around a second axis  249 , which is substantially parallel to the tumbler rotational axis  55 . A comparison of FIGS. 13B and 14B shows the toggling action of the yoke  240  around axis  249  as the tumbler body  202  is rotated while sled  220  is held by the engagement of arms  222 ,  224  with the carriage locator  225 . With respect to FIG. 13B, rotation of the sled  220  in a clockwise direction is limited by a triangular projecting portion of ears  242 ,  244  which engages an under surface of sled  220 . 
     The second portion of the dual pivot structure of yoke  240  is provided by two wedge-shaped pivot hooks along the upper inner surface of ears  242 ,  244 , such as pivot hook  250  on ear  244  (see FIGS.  13 B and  14 B). Each pivot hook  250  is captured by and received within a pocket  252  of sled  220 . Each pocket  252  is defined by a pair of rails  254 ,  255  and a lower rest surface  256 . As shown in FIG. 13B, the pivot hook  250  rests against the lower surface  256  when the capping assembly  210  is at rest. When in a capping position, the hook  250  rests against a loaded or capping pocket surface provided by rail  255 . Thus, the sled  220  pivots with respect to the yoke  240  around a third axis  257 . As the yoke  240  toggles between the rest and fully capped positions, the pivoting action of yoke  240  with respect to the tumbler body  202  around axis  249  is controlled by the lower rim pivot  246 , whereas the pivoting of the sled  220  with respect to yoke  240  around axis  257  is provided by the wedge-shaped hooks  250 . 
     As shown in FIGS. 13C and 14C, to bias the sled  220  in a rest position relative to the tumbler body  202 , the capping assembly  210  also includes a biasing member  258  which urges sled  220  away from the tumbler body  202 . To accomplish this, the biasing member  258  includes a rocking spring retainer or keeper member  260 , and a compression oil spring  262 . The retainer  260  has a rocker member  264  that rests upon the rocker pivot post  215 , which projects from the tumbler stop wall  214 . During assembly and disassembly, the spring  262  is secured to the sled  220  by the rocker arms  264  of the keeper  260 . 
     The keeper  260  has two projecting finger members  266  and  268 , which both terminate in latches that grasp a pivot pin or post member  270  of the sled  220 . The sled pivot post  270  is recessed within a roughly T-shaped slot  272  formed within the cap-supporting platform portion of sled  220 . The T-shaped slot  272  is sized to slidably receive therethrough the tips of the retainer fingers  266 ,  268 , for instance, as shown in FIG.  11 . Preferably, the spring  262  is under a slight compression to bias sled  220  away from the tumbler stop wall  214 , and toward the rest wall  212 . This biasing is also assisted by the relative lateral positioning of the post  270  and the yoke-to-sled pivot axis  257 . Preferably, the post  270  is located within sled  220  to be centered (front to back) on the black cap  230 , whereas the link pivot axis  257  is positioned slightly off-center toward arms  222 ,  224  (such as about 2 mm off center in the illustrated embodiment). 
     To provide a greater upward sealing force of the cap  230  against the black pen face  34  than provided by the color cap  232  against the color pen face  36 , the retainer  260  is mounted offset from the center line of the sled  220 . That is, the T-shaped slot  272  and the pivot post  270  are mounted at a distance D 1  from the edge of the sled platform adjacent the black cap  230 , and a distance D 2  from the opposite platform adjacent the color cap  232 . For example, in the illustrated embodiment, the distance D 1  is approximately 23 mm, whereas D 2  is approximately 28 mm. 
     The spring  262  presses against the rocker arms  264  a lower surface of the sled  220 , with the varying points of contact being shown in FIGS. 13C and 14C. In FIG. 13C, when at rest, the sled pivot post  270  has an angled bearing surface  274 , which rests against the inner surface of keeper finger  266 . In FIG. 14C, the sled pivot post  270  has an upright side  276 , which rests against the inner surface of the other keeper finger  268 . Note, that the first finger  266  is much wider than the second finger  268 , which aids in biasing the sled  220  toward the rest position (FIG.  13 C), while also providing substantially upright alignment for capping (FIG.  14 C). 
     Moreover, the keeper finger  266  and  268  form a slot  277  therebetween, which, in cooperation with the sled T-shaped slot  272 , allows the sled  220  to further compress spring  262  through downward force of the printheads  30 ,  32 . This stressing of spring  262  provides more secure sealing of the printhead nozzle plates  34 ,  36 . That is, while the upper portions of fingers  266  and  268  are shown as being flush with the upper cap-supporting surface of sled  220  in FIG. 14C, the upper surfaces of the fingers  266 ,  268  may extend above this surface due to compression of spring  262  if required for capping. 
     Note, that compression of spring  262  causes the wedge-shaped pivot hooks (see FIGS. 13B and 14B) to float upwardly in the sled pockets  252 , allowing the sled  220  to move with respect to the yoke  240 , as also indicated schematically in FIG.  16 . This floating of hooks  250  allows for tilting of the sled  220 , as indicated by arrow  278  in FIG.  9 . In this tilting motion, the hooks  250  may dip to different depths within the pockets  252  of yoke ears  242 ,  244 , for example, to accommodate for any variations in the sealing forces required for pens  30  and  32 . Furthermore, the hooks  250  are undersized with respect to the width of pockets  252 , as defined by the spacing of rails  254 ,  255 , which allows for some skewing of the sled  220  with respect to yoke  240 , as indicated by arrow  279  in FIG.  9 . 
     In operation, from the following discussion of the rotary capping system  200 , a method of sealing inkjet printhead nozzles is also illustrated. Reference to the schematic drawings of FIGS. 15 and 16 is helpful to illustrate the relative forces and positions of the capping assembly  210  in the rest and capping positions, respectively. The printer  20  may include a conventional stepper motor, which is coupled to drive the service station about the first axis  55 , via the drive gear  60  (FIGS. 1-4 illustrate the drive gear  60  as having gear teeth surrounding the tumbler rim  204 ). The tumbler body  202  is rotated in the direction indicated by the curved arrow  330  until the carriage engagement arms  222 ,  224  contact the carriage alignment member  225  (see FIGS. 12,  13 A,  13 C). Continued rotation of the tumbler body  202  in the direction indicated by arrow  330  causes the pivoting illustrated through a comparison of FIGS. 13A-13C with the respective FIGS. 14A-14C, as the capping assembly  210  transitions from a rest state to a sealing state. In FIGS. 13A-13C, the tumbler  202  is at a cap entry position, nominally defined here as a zero degree (0°) position, which also corresponds to a cap exit position for uncapping followed by other servicing (e.g. wiping or priming) or printing. In FIGS. 14A-14C, the tumbler  202  is at a fully capped, maximum bottomed out position, which is about 44° beyond the cap entry (0°) position. 
     FIGS. 13A and 14A illustrate the rotation of the yoke  240  with respect to the tumbler body  202 . FIGS. 13B and 14B illustrate the rotation of the tumbler body  202 , with respect to the yoke  240  and the sled  220 . In FIG. 13B, while the tumbler body rotates in the direction indicated by arrow  330 , the link  240  rotates around axis  249  in a direction indicated by arrow  332 , and the sled  220  rotates upwardly around axis  257  in the direction indicated by the arrow  334  to rock into the capping position of FIG.  14 B. FIG. 13C illustrates the rotation of the rocking spring keeper  260  with arrow  336 . 
     As shown in FIGS. 14B and 14C, the respective black and color pens  30 ,  32  are capped, and spring  262  is compressed. The compression force supplied by spring  262  upwardly from the tumbler stop wall  214  forces the sled  220  and caps  230 ,  232  to press against the pen faces  34 ,  36 . The gimbal mounting provided by the loose fit of the yoke wedge-shaped pivot hooks  250  within the sled pockets  252 , as well as the gimbaling action provided by mounting sled  220  to the retainer  260 , allows the sled  220  to tilt with respect to a plane defined by the pen faces  34 ,  36 . This tilting ray compensate for irregularities on the printhead face, such as ink build up or the black pen encapsulant beads  280 ,  282 , while maintaining a pressure tight seal adjacent the pen nozzles. 
     In the capping position shown in FIGS. 14A-14C, the spring force supplied by spring  262  maintains a controlled pressure against the pen faces, even when the printer unit  20  has been turned off. Positive energy provided by the stepper motor reversing the rotational direction of arrow  330  is required to disengage the capping assembly  210  from the pens  30 ,  32 . When the arms  222 ,  224  are no longer contacted by the printhead carriage member  225 , the slight at-rest compression of spring  262  biases sled  220  away from the tumbler stop wall  214 , which serves to retract the capping assembly  210  from the capped position back to the rest position The noncentering feature of the keeper  260  also forces the sled  220  against the rest wall  212 . Thus, this offcentering feature of biasing member  258  forces the cap sled into a rest position adjacent wall  212 , allowing the capping assembly  210  to be rotated in the direction opposite arrow  330  without contacting the printheads  30 ,  32 . This rest position or retracted state, allows the pens to freely travel over the service station  200  to the printzone  25 . 
     Multi-Ridge Capping Assembly 
     FIGS. 17 and 18 illustrate a preferred embodiment of a multi-ridge capping assembly  230  constructed in accordance with the present invention. To provide higher resolution hardcopy printed images, recent advances in printhead technology have focused on increasing the nozzle density, with levels now being on the order of 300 nozzles per printhead, aligned in two 150-nozzle linear arrays for the black pen  30 . These increases in nozzle density, current limitations in printhead silicon size, pen-to-paper spacing considerations, and media handling constraints have all limited the amount of room remaining on the pen face for capping. While the printhead and flex circuit may be conventional in nature, the increased nozzle density requires optimization of cap performance, including sealing in often uneven sealing areas. For example, referring to FIG. 12, the printhead nozzle surface  34  is bounded on each end by two beads  280 ,  282  of an encapsulant material, such as an epoxy or plastic material, which covers the connection between a conventional flex circuit and the printhead housing the ink firing chambers and nozzles. The protective end beads  280 ,  282  occupy such a large portion of the overall printhead area, that providing a positive, substantially moisture impervious seal around the printhead nozzles is difficult using a conventional single sealing ridge or lip, such as lip  284  of the color cap  232  (FIG.  11 ). 
     However, to seal across the uneven of the protective end beads  280 ,  282 , the black cap  230  preferably has a lip with at least a portion comprising adjacent plural or redundant contact regions. Preferably, each redundant contact region is capable of sealing over surface irregularities on the face plate by forming an air-tight seal in the flat areas adjacent the irregularities. In the illustrated embodiment, the two such redundant sealing portions of the lip are shown as multi-ridged capping zones  290  and  292 , which seal the printhead adjacent the end beads  280  and  282 , respectively. The multi-ridge cap areas  290 ,  292  may have adjacent plural contact regions illustrated as two or more substantially parallel ridges or crests, with the illustrated embodiment having three ridges  294 ,  295  and  296  separated by two troughs or valley portions  297 ,  298 . Along the longitudinal lip region parallel to the linear nozzle arrays, the black cap  230  has single-ridged sealing surfaces  286 ,  288  (see FIG.  11 ). 
     The sealing ability of the multi-ridge cap area  292  is shown in FIG. 17, sealing pen face  34  over the end bead  282  by compressing the intermediate crest  295  more than crests  294  and  296  are compressed. These wide sealing regions  290 ,  292  may advantageously seal over ink residue or other debris accumulated on the pen face. Additionally, while the adjacent plural contact regions are illustrated as mutually parallel ribs, it is apparent that other geometric patterns may also be used, such as interlinking ovals, circles, or a labyrinth pattern, for instance. 
     The capping assembly  210  also includes a black pen sealing chamber vent cap or stopper  300 , which sits within a recess  302  formed along the underside of the capping sled  220 . Preferably, the vent cap  300  is of a Santoprene® rubber sold by Monsanto Company, Inc., or other ink-phyllic resilient compound structurally equivalent thereto, as known to those skilled in the arm Preferably, the cap sled  200  is of a polysulfone plastic or other structurally equivalent plastic known to those skilled in the art. When sealed against the printhead surface, the ridges  286 ,  288 ,  294 - 296  define a main sealing chamber or cavity  304 , which is in fluid communication with the vent hole  226 . 
     The vent cap recess  302  includes an upper surface  305  which has a pressure equalization groove or channel  306  formed therein to provide a pressure equalizing vent passageway from the main sealing chamber  304  to atmosphere when the vent stopper  300  is installed. To aid in pressure damping during capping, the stopper  300  also defines a damping chamber  308  therein which is in communication with the passageway formed by the pressure equalization channel  306 . The pressure equalization channel  306  provides an escape passage way for air trapped between the printhead  34  and the cap  230  during capping. Also, when capped during extended periods of printer inactivity, the vent  306  advantageously maintains an equal pressure between the cap chamber  304  and the ambient conditions in the environment, even during changed in barometric pressure, temperature, and the like. Without such a vent, the air trapped within the main sealing chamber  304  could be forced into the printhead nozzles, causing depriming. Use of the vent passageway  306  advantageously prevents depriming. 
     The pressure equalization groove  306  continues along the upper surface  305  until intersecting a vertical surface  310  of recess  302 . The pressure equalization channel continues through a groove  312  defined by wall  310 . To assist in drawing ink through the pressure equalization channel  306 ,  312  the vent cap  300  includes a vent cap drain stick  314 , also formed of the same materials as the main body of stopper  300 . 
     Clogging of the vent channel  306  by ink accumulation is advantageously avoided by using a Santoprene® or other ink-phyllic compound for the vent stopper  300 . In the areas where the stopper  300  meets the sled  220 , small passageways are formed which pull any accumulated ink from the channel  306  through capillary action. Through capillary draw, the wicked ink fills the sharp corners and small spaces where the stopper  300  meets the sled  220 , such as along the recess upper surface  305  and then along the side walls of the recess  302 , such as at  316 . Preferably, the stopper  300  has rounded corners  316 , such as indicated by dashed lines  318  in FIG.  18 . 
     As shown in FIG. 18, the capping assembly also includes a color vent stopper  320 , which sits in a recess  322  beneath the color cap  232 . The recess  322  also has a pressure equalization groove or channel  323  formed along the upper and vertical surfaces to allow pressure to escape from a main sealing chamber  326  (see FIG. 11) defined by the color pen  32  when sealed by cap  232 . Venting through channel  323  allows pressure formed during capping to vent from the cap area to avoid depriming of pen  32 . To avoid clogging of the pressure equalization channel  323 , the capillary action interrelation of the color stopper  320  and recess  322  are the sane as described above for the black ink pen stopper  300  and recess  302 . Preferably, the color stopper  320  also has a drain stick  324  (FIG. 9) adjacent the exit port of the equalization channel  323 . 
     Preferably, the caps  230  and  232  are oncert molded to the sled  220 . In the illustrated embodiment, the sled  220  has a plurality of oncert molding holes, such as holes  325 , formed therethrough which are filled with a portion of the cap material in a plug form  326 , as shown in FIG.  17 . Preferably, the molding holes  325  are joined together along the upper cap-supporting surface of the sled  220  by a molding race  328 , which aids in adhering the caps  230 ,  232  to the sled  220 . It is believed that the present invention is the first use of oncert molding techniques in attaching pen caps to sleds, and it is particularly advantageous to maintain the close tolerances and sealing dimensions desired in providing a high quality printer  20 . 
     Advantages of the Rotary Multi-Ridge Capping System 
     As a first advantage, an improved pen alignment and registration of the caps  230 ,  232  with the pens  30 ,  32  is realized due to the engagement of the arms  222 ,  224  with the printhead carriage structure  225 . This method of aligning the caps with the pens avoids inadvertently covering the printhead nozzles with any portion of the cap lip or sealing ridges, which could otherwise allow leaking or drying of the ink within the pen, and/or result in clogging the nozzles. 
     Another advantage of the gimbaling action of sled  220 , provided by the loose fitting alignment of the yoke  240  and sled  220 , as well as that provided by the rocker  264  coupling sled  220  with the tumbler body  220 , allows for gimbaling or tilting action of the sled  220  with respect to the tumbler body  202 . Moreover, the loose fitting nature of these pivots renders them virtually immune to any ink contamination from pen leakage, which would otherwise bind the service station and prevent operation in a tight fitting service station system. This immunity to ink contamination is particularly important with respect to the newer pigment-based inks, which may increase friction on the sliding surfaces of various subsystems within the printer, a problem avoided by the rotary service station  200 . 
     A further advantage of the capping system  210  is the ability to be positively locked in place when capped (FIGS. 14A-14Q without using friction along sliding surface, as required by many earlier capping systems. As described above, long sliding surfaces are prone to ink contamination, which may impede the seal, or cause excessive friction to impede capping. Another advantage of the present system  200  is the ability to securely cap the black printhead  30 , including providing capping along the end cap beads of protective sealant  280 ,  282 , through the use of the multi-ridged surfaces  290 ,  292  of the black cap  230 . 
     An additional advantage of the capping assembly  210  is the use of a single coil spring  262  to apply differing forces to the pen faces. While an alternative manner of providing a pressure differential would be to make the black cap taller than the color cap, such a solution would pose a variety of practical problems including lack of the pen-to-paper (or print medium) spacing for optimum print quality. Instead, force differentials are advantageously applied to the pens by offsetting the location of the spring pivot post  270  with respect to the overall length of the sled platform  220 . Thus, by virtue of the shorter distance D 1  of the retainer  260  to the black cap  230 , a greater force is applied to the black pen face  34  during capping than that applied to the color face  36 .