Abstract:
A set of ink sticks includes multiple ink sticks, each adapted to be inserted in an insertion direction into one of the feed channels of a phase change ink jet printer. Each ink stick has a keyed surface substantially aligned with the insertion direction, and each of the keyed surfaces has a key feature having a position relative to the keyed surface that corresponds to the position of the feed channel relative to an aspect of the printer. A method of inserting an ink stick into the delivery system of a phase change ink jet printer includes orienting the ink stick with a keyed surface facing a particular direction and identifying the position of the key feature relative to the remainder of the keyed surface. An ink feed channel of the feed system having a coinciding position in the ink delivery system is identified, and the ink stick is inserted into the identified ink feed channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned copending U.S. patent application Ser. No. 11/593,972, filed concurrently herewith, entitled “SOLID INK STICKS WITH CORNER GUIDES,” by Brent R. Jones et al., commonly-assigned copending U.S. patent application Ser. No. 11/593,973, filed concurrently herewith, entitled “INDEPENDENT KEYING AND GUIDANCE FOR SOLID INK STICKS”, by Brent R. Jones, and commonly-assigned copending U.S. patent application Ser. No. 11/593,971, filed concurrently herewith, entitled “ONE-WAY COMPATIBILITY KEYING FOR SOLID INK STICKS”, by Brent R. Jones et al., the disclosures of which are all incorporated herein by reference. 
     TECHNICAL FIELD 
     This disclosure relates generally to ink printers, the ink sticks used in such ink printers, and the devices and methods used to provide ink to such printers. 
     BACKGROUND 
     Solid ink or phase change ink printers conventionally receive ink in a solid form, as pellets or ink sticks. The solid ink pellets or ink sticks are placed in a feed chute and a feed mechanism delivers the solid ink to a heater assembly. Solid ink sticks are either gravity fed or urged by a spring through the feed chute toward a melt plate in the heater assembly. The melt plate melts the solid ink impinging on the plate into a liquid that is delivered to a print head for jetting onto a recording medium. Ink sticks for phase change ink printers have historically included bottom and side keying surfaces by which corresponding chutes and feed mechanisms (i.e., “ink loaders”) of the printers guide or coax the ink sticks into optimal feed/melt positions. In horizontal or near horizontal ink loaders, gravity influences the ink stick positions as the ink sticks lean against chute walls or special side-rails. Special guides have even been incorporated into the bottoms of some ink sticks to facilitate their movement over corresponding bottom-rails of some horizontal feed ink loaders. Such guides, coupled with gravity, have typically worked reasonably well to properly position and orient the ink sticks for feeding to the heater plates. In such situations, the sides of the keying features have typically included the ink surfaces contacting the guides. Such guide and key integration has undesirably limited the keying features in that insertion exclusivity has not been the only function that the keying features have been relied upon to provide. In many cases, size, placement, and configuration of keying features has been as much a function of guidance requirements as keying considerations. Keying for insertion is typically intended to allow differentiation between colors and different product models, which can include marketing programs such as contractual or retail pricing of the ink, thus aside from guiding and support functions, the keying offers opportunity to exclude inappropriate colors or models of ink from being inserted in a given ink loader. 
     Meanwhile, conventional keying and guide features have been even less effective in vertical ink loaders as the ink sticks have been somewhat position/orientation influenced but in most cases have not been sufficiently constrained to properly feed to the heat plates. Some vertical ink loader guidance systems have even allowed their ink sticks to misalign to extents that they have rotated and jammed. Consequently, most phase change ink printers accommodating multiple ink sticks of each of various colors and incorporating heat plates have used horizontal rather than vertical ink loader systems. 
     Keying features for use in many horizontal ink loader systems have been focused on a two vector interface with the ink loader: one surface for insertion and another for feed, with the former surface typically transverse to the latter. In addition to relying on gravity, such sticks are typically made more complex in shape due to color and product series (model or model range) key features running in one direction and guidance elements or surfaces running in another. The large amount of stick geography devoted to color keying in historical ink stick designs has undesirably limited the flexibility and extensibility in product series key features. As with the ink loaders, making design changes to the complex shapes of such ink sticks can introduce undesirable risks of ink stick failure from stress fracturing and variations in cooling deformation, can undesirably increase tooling cost/complexity, and/or can undesirably increase product development times. 
     Thus, guidance in the afore-noted cases has relied primarily on combinations of ink stick surfaces including keying surfaces not designed or intended solely for guidance. Another shortcoming of conventional loaders is that insertion keying, including model or series keying, changes from product to product to ensure marketing, operational parameter, or formulation differentiation. Parts internal to the loader, such as push blocks, change in addition to the external key plates. As a result of the historical lack of uniformity in keying schemes and the integration of guidance and keying systems, each new phase change ink printer model has typically needed a new loader configuration, which has undesirably increased ink delivery costs and product development times. 
     Orienting an ink loader vertically could potentially improve usability and lower cost. A vertical loader could provide the benefit of using gravity as the primary force to move or feed the ink stick. While guides in horizontal loaders typically emphasize load bearing support, such load bearing would not be required by a vertical loader. However, as noted above, conventional ink shapes are not compatible with vertical loading. Conventional ink shapes are also not compatible with an insertion direction that is in-line with or parallel to the feed direction. Ink sticks used in loaders with independent insertion and feed directions, irrespective of loader orientation or ink feed to gravity, suffer from a lack of simplified extensibility in creating independence between color, model, support, guidance and feed keying. 
     Thus, there is a need for phase change ink printer ink sticks having independent guidance and keying features such that the flexibility and extensibility of the keying features may be better optimized, and there is a further need for ink sticks having keying features that can be compatible with parallel insertion and feed to facilitate vertical loading or alternative loaders with feed orientation that may range from horizontal to vertical whether or not insertion is in the feed direction. 
     SUMMARY 
     For insertion into a phase change ink jet printer having first, second, third, and fourth ink feed channels that have first, second, third, and fourth channel positions, a set of ink sticks that includes a first ink stick having a first key feature at a first position on an ink stick corresponding to the position of the first feed channel, a second ink stick having a second key feature at a second position on the ink stick corresponding to the position of the second feed channel, a third ink stick having a third key feature at a third position on the ink stick corresponding to the position of the third feed channel, and a fourth ink stick having a fourth key feature at a fourth position on the ink stick corresponding to the position of the fourth feed channel. In examples the position of each ink stick key feature relative to the remainder of the ink stick corresponds progressively to the position of the feed channel relative to the remainder of the printer. 
     In accordance with another aspect of the described apparatus and method, a set of ink sticks were inserted into a phase change ink jet printer having a plurality of feed channels, includes a plurality of ink sticks, in which each of the ink sticks is adapted to be inserted in an insertion direction into one of the feed channels of the phase change ink jet printer. Each ink stick has a keyed surface substantially aligned with the insertion direction. Each of the keyed surfaces has a key feature having a position relative to the keyed surface, and the position of the key feature relative to the keyed surface corresponds to the progressive position of the feed channel relative to an aspect of the printer. 
     In accordance with a further apparatus of the invention, an ink delivery system for a phase change ink jet printer includes a plurality of ink feed channels for receiving solid ink sticks inserted in an insertion direction, and a plurality of ink sticks, each adapted for insertion in the insertion direction into one of the feed channels of the printer. Each of the ink sticks has a key element positioned on the ink stick in a progressive position to correspond to the relative progressive position of the feed channel for which the ink stick is adapted. 
     In accordance with a method described, inserting an ink stick into a delivery system of a phase change ink jet printer includes orienting the ink stick with a keyed surface facing a first direction, identifying the position of the key feature relative to the remainder of the keyed surface, identifying an ink feed channel of the feed system having a position in the ink delivery system corresponding to the position of the key feature relative to the remainder of the keyed surface, and inserting the ink stick into the identified ink feed channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary phase change ink printer. 
         FIG. 2  is a partial top perspective view of the rear section of the phase change ink printer of  FIG. 1  with its ink access cover open. 
         FIG. 3  is a side sectional view of a feed channel of the solid ink feed system of the phase change ink printer taken along lines  3 - 3  of  FIG. 2 . 
         FIG. 4  is a perspective view of the phase change ink printer of  FIG. 1  with its ink access cover open showing an alternate ink loader configuration. 
         FIG. 5  is a side sectional view of a feed channel of the solid ink feed system of the phase change ink printer of  FIG. 4 . 
         FIG. 6  is a perspective view of one embodiment of a solid ink stick. 
         FIG. 7  is a top view of the solid ink stick of  FIG. 6 . 
         FIG. 8  is a sectional view of a feed channel showing corner guide members and the ink stick of  FIG. 7  with complementary corner guide elements. 
         FIG. 9  is a top view of an alternate ink stick configuration with inset corner guide elements. 
         FIG. 10  is a sectional view of a feed channel showing alternative corner guide members and the ink stick of  FIG. 9  with complementary corner guide elements. 
         FIG. 11  is a top view of an embodiment of a solid ink stick with a corner guide having an orientation feature. 
         FIG. 12  is diagrammatical illustration of a multi-color set of ink sticks with progressive color key element, series keying and corresponding key plate. 
         FIG. 13  is diagrammatical illustration of an embodiment of parallel progressive color keying. 
         FIG. 14  is diagrammatical illustration of an embodiment of perpendicular progressive color keying. 
         FIG. 15  is a diagrammatical illustration of an embodiment of one way series compatibility keying for two platforms. 
         FIG. 16  is another diagrammatical illustration of an embodiment of one way series compatibility keying for two platforms. 
         FIG. 17  is a diagrammatical illustration of yet another embodiment of one way series compatibility keying for three platforms. 
         FIG. 18  is a diagrammatical illustration of yet another embodiment of one way series compatibility keying for two platforms. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of an exemplary phase change ink printer  10 . Printer  10  includes an outer housing having a top surface  12  and side surfaces  14 . A user interface display, such as a front panel display screen  16 , displays information concerning the status of the printer, and user instructions. Buttons  18  or other control elements for controlling operation of the printer are adjacent the user interface window, or may be at other locations on the printer. An ink jet printing mechanism (not shown) is contained inside the housing. The printer includes an access cover  20  that opens (see  FIG. 2 ) to provide the user access to an ink feed system (see  FIG. 3 ) contained under the top surface of the printer housing that delivers ink to the printing mechanism. 
       FIG. 2  is a partial top/front perspective view of the phase change ink printer  10  with its ink access cover  20  open. As seen in  FIG. 2 , opening the ink access cover  20  reveals a key plate  26  having keyed openings  24 . Each keyed opening  24 A,  24 B,  24 C,  24 D provides access to an insertion end of one of several individual feed channels  28 A,  28 B,  28 C,  28 D of the solid ink feed system (see  FIG. 3 ). A color printer typically uses four colors of ink (black, cyan, magenta, and yellow). Each color corresponds to one of the feed channels. In the illustrated embodiment, the key plate has four keyed openings  24 A,  24 B,  24 C, and  24 D. Each keyed opening  24 A,  24 B,  24 C,  24 D of the key plate  26  has a unique shape. The ink sticks  30  of the color for that feed channel have a shape corresponding to the shape of the keyed opening  24 A,  24 B,  24 C,  24 D. For example, the lateral sides of the key plate openings and the lateral sides of the ink sticks may have corresponding shapes. The keyed openings and corresponding ink stick shapes are designed to ensure that only ink sticks of the proper color are inserted into each ink stick feed channel. 
     Referring to  FIG. 3 , each feed channel, such as representative feed channel  28 A is a vertically oriented feed channel designed to deliver ink sticks  30  of a particular color to a corresponding melt plate  32 . The vertical orientation of the ink loader simplifies the ink loader by eliminating the need for complex mechanisms designed to urge an ink stick along a horizontally oriented feed channel, where support friction inhibits movement. The vertical orientation may be any orientation that is sufficiently vertical so that gravity provides the primary motive force to feed the ink sticks along the feed channel and to hold the ink sticks against the melt plate  32  as they are melted. 
     The feed channel receives ink sticks inserted in an insertion direction L at the insertion end through keyed opening  24 A. In the embodiment of  FIGS. 2 and 3 , the insertion and feed directions L, F are substantially parallel. Thus, the key plate  26  and keyed openings  24 A-D are oriented substantially perpendicular to the insertion and feed directions to provide access to the feed channels such that ink sticks are inserted in the feed direction F of the feed channel. In an alternative embodiment as shown in  FIGS. 4 and 5 , the insertion direction L may be different from the feed direction F. For example, as in the embodiment of  FIGS. 4 and 5 , the key plate  26  and keyed openings  24 A-D may be oriented substantially perpendicular to the insertion direction L and substantially parallel to the feed direction F of the feed channel such that ink sticks may be inserted in the insertion direction L and then moved along the feed channel in the feed direction F. 
     Referring now to  FIGS. 3 and 5 , the feed channel has sufficient longitudinal length that multiple ink sticks may be inserted into the feed channel. Each feed channel delivers ink sticks along the longitudinal length or feed direction F of the channel to the corresponding melt plate  32  at the melt end of the feed channel. The melt end of the feed channel is adjacent the melt plate  32 . The melt plate  32  melts the solid ink stick into a liquid form. The melted ink typically drips or flows through a gap  33  between the melt end of the feed channel and the melt plate, and into a liquid ink reservoir (not shown). 
     An exemplary solid ink stick  30  for use in the feed system is illustrated in  FIGS. 6 and 7 . The ink stick is formed of a three dimensional ink stick body. A substantially cubic ink stick body is illustrated in  FIG. 6 . The ink stick body illustrated has a bottom, represented by a general bottom surface  52 , and a top, represented by a general top surface  54 . The top and bottom surfaces are shown substantially parallel one another. The ink stick body also has a plurality of side extremities, such as side surfaces  55 ,  56 ,  61 ,  62 . The side surfaces  55 ,  56  are substantially parallel one another, and are substantially perpendicular to the top and bottom surfaces  52 ,  54 . The side surfaces  61 ,  62  are also substantially parallel one another, and substantially perpendicular to the top and bottom surfaces, and to the lateral side surfaces. 
     The respective surfaces of the ink stick body need not be substantially flat, nor need they be substantially parallel or perpendicular to one another. Other shapes of the side and end surfaces are also possible, including curved surfaces. The aspect ratios of the ink stick length to height to width could be substantially different. Some ink sticks may be quite long relative to their width, as example. The ink stick can be generally elongated lengthwise, widthwise or even in height or be altered in form in other ways. The lateral side surfaces can also be segmented or stepped, so that one portion of the ink stick body is narrower than another. Nevertheless, the present descriptions should aid the reader in visualizing, even though the surfaces may have three dimensional topographies, or be angled with respect to one another. The ink stick body may be formed by pour molding, injection molding, compression molding, or other known techniques. 
     The ink stick  30  includes side surfaces  55 ,  56 ,  61 ,  62  that are oriented substantially parallel to the feed direction F of the feed channel  28 . The bottom surface  52  is a leading end surface which is intended to contact the melt plate of a feed channel first, and the top surface  54  is a trailing end surface. In one embodiment, the ink stick  30  includes corner guide elements  80  for interacting with guide members  104  (See  FIG. 8 ) of a feed channel to maintain the orientation and alignment of the ink stick in the feed channel as gravity feeds the ink stick along the feed channel. This interaction of the corner guide elements  80  limit the movement of the ink stick  30  in the feed channel in directions that are perpendicular to the feed direction F. Limiting the relative movement of the ink sticks in directions other than the feed direction prevents rotational movement and skewing of the ink stick which may cause jams and/or improper alignment with the melt plate. Additionally, the use of guides at the extreme corners of an ink stick ensures that the larger surface/perimeter areas of the general sides of an ink stick have room to incorporate an extensible range of color and series keying features. Corner guide elements will be described as extending along the corner edge from the leading face to the trailing face of an ink stick and this description is intended to include non straight line topography and full or partial and segmented lengths of any length which can be intermediate or extending outward from the front and rear faces. 
     In one embodiment, the corner guide elements  80  comprise protrusions that extend at least partially along the corner edges of the ink stick parallel to the feed direction. In the embodiment of  FIGS. 6 and 7 , there is shown a corner guide element  80  at each corner, although corner guide elements  80  may be used at one, two or three corners. When using only two guide elements, they would ideally be positioned at opposite diagonal corners of the ink stick, though they could be on opposite sides so the term opposite corner is intended to encompass both relationships. Thus, contact between the ink stick  30  and feed channel  28  may be controlled and distributed more evenly thereby permitting low damping friction forces and reducing the effects of dimension intolerances between the feed channel and ink stick. Therefore, the ink stick body does not become skewed with respect to the feed channel. With the ink stick properly aligned with the feed channel, the ink stick meets the melt plate  32  with the intended attitude and alignment. Proper alignment between the ink stick and the melt plate enhances even melting of the ink stick. Even melting reduces the formation of unmelted slivers at the trailing end of each ink stick. Such unmelted slivers may slip through the gap  33  between the melt plate and the end of the feed channel. Such slivers may interfere with the proper functioning of certain portions of the printer or be introduced into different color reservoirs causing color mixing. 
       FIG. 8  shows a cross sectional view of the vertical feed channel  28  of  FIGS. 3 and 5 . As mentioned above, in a vertical or somewhat vertical loader, gravity may be relied upon to provide the force for moving the ink stick along the channel from the insertion end to the melt end. A gravity ink feed system may be augmented with a further nudging means, such as vibration, small abrupt motion, air blast or any other reasonable means to ensure feed reliability in view of variable exposure or environments (off angle product orientation, dropping the product during relocation, elevated temperatures, damaged ink sticks and the like). References to gravity feed therefore include the possibility of such augmentation but in these cases gravity is the primary motive force and under optimal conditions is all that is necessary to feed the ink. The feed channel includes guide members  104  for constraining movement to the feed direction by interacting with the guide elements  80  of an ink stick  30 . In the embodiment of  FIG. 8 , the feed channel guide members comprise corner protrusions that extend the length of the feed channel substantially parallel to the feed direction F. A pair of guide members  104  is provided for each corner guide element  80  of the ink stick  30 . Each pair of guide rails or members  104  for each corner guide element  80  define a space that is substantially complementary to the corner guide element  80 . The complementary shape of the space formed by the corner guide members  104  of the feed channel allow the corner guide elements  80  of the ink stick body to slidingly engage the feed channel guide members  40  of the ink stick feed channel  28  to allow the passage of the ink stick  30  along the feed channel while limiting lateral and rotational movement of the ink stick. The corner guide members  104  of the feed channel may be formed integrally as part of the feed channel body. Many other ink loader guide shapes are contemplated, such as “V” rails, arced, contoured or segmented rails and so forth. 
     Although the corner guide elements  80  of an ink stick have been described as protrusions, other forms of corner guide elements are contemplated. For instance, as shown in  FIG. 9 , corner guide elements  80 ′ may comprise an inset portion that extends along the corners of an ink stick  30 ′. The shape, placement and number of guide elements would be matched with complementary guide rails or members in the ink loader.  FIG. 10  also shows an embodiment of a feed channel for guiding ink sticks having guide members  104 ′ extending from the corners of the feed channel to slidingly engage the inset corner guides in order to maintain the alignment of the ink stick in the feed channel. Still other forms of ink stick corner guides are also envisioned, such as truncated or flattened surfaces that interface with complementary guide features in the loader. A single, predominantly corner positioned (may be asymmetrical) guide element with a shape that is conducive to adequately restraining excess off axis free play of the ink shape is contemplated, though it may not be optimal, it offers an alternative that may be a desirable option. 
     The corner guide elements  80  may be mutually independent from any keying features that may be incorporated in the ink stick. For example, the corner guide elements may be unchanging and present on ink sticks intended for printers across multiple platforms and models. The guide shapes used may be accommodated in all keyed openings of ink loaders for the different printers. The use of corner guide elements that are the same across the various platforms enables the feed system to be substantially the same on all units. Independent color and series keying (explained in more detail below) allows the modification or omission of the keying elements without affecting the basic loader configuration. A modification in the keying scheme of the ink sticks requires a change in the key plate configuration to accommodate the keying scheme and not a change to the parts internal to the ink loader, such as feed channel configuration. Due to size or fabrication limitations with some ink sticks, it may be desirable to have a side color or model keying feature extend fully or partially into a corner guide feature. In this case both features could exist and function independently but happen to be adjacent one another. 
     To prevent erroneous ink insertion when the corner guides and/or key element patterns (size and position) are symmetrical, the ink stick may include an orientation feature  84  as shown in  FIG. 11 . The orientation feature  84  illustrated comprises a modified corner guide element of the ink stick. A corner guide element may be modified in any suitable manner to facilitate proper insertion of the ink stick into the correct feed channel. For instance, in the embodiment of  FIG. 11 , the orientation feature  84  comprises a corner guide element having a greater width than the other corner guide elements  80 . The key plate includes a complementary shaped portion that allows the insertion of the unique corner guide element so that the ink stick is oriented correctly prior to insertion. Thus, the orientation feature provides further mechanisms for prohibiting incorrect insertion of the ink stick  30  into a feed channel. Those skilled in the art will identify numerous other modifications and configurations of the corner guide elements to facilitate proper orientation of the ink stick for insertion. For example, the orientation feature can be provided by the relative positioning of the color and/or series key elements  70 . Two corner guide elements on corners of opposite sides but not diagonally opposed can also be used to provide orientation and can be configured to do so with or without assistance from features used for keying. With respect to insertion keying, the ink loader or feed system keyed opening may be in a plate or may be incorporated into other elements of the ink loader, such as the channel or chute walls or one or more inserts that separately or in conjunction with the channel or other structure, make up a keyed opening. It is to be understood that a separate plate is not necessary and may not be present. Ink may be inserted into a loader body or receiving area transverse to the feed direction but the actual channel insertion keying may occur after the ink placement as the ink enters the feed channel. Orientation keying, such as truncating one side of one end, can be employed to prevent insertion of the ink into the receiving area unless it is in an orientation complementary to passage of the ink stick through the insertion keying en route to the feed channel. If a nominally incorrect ink stick were placed in this fashion, it would not proceed through the keyed opening and so could be retrieved so a correct stick could be inserted. Additional feed keying may be employed at any point in the feed channel beyond this feed direction insertion keyed opening. Feed key effectiveness in blocking inappropriate ink sticks is a nominal function, that is, undersize sticks may fit through. 
     The ink stick may include keying elements  88  for interacting with the keyed openings  24 A,  24 B,  24 C,  24 D of the key plate  26  to ensure that only ink sticks intended for a specific feed channel are inserted into the feed channel. The key elements  88  comprise a feature of a particular predetermined size, shape, and location on the outer perimeter of the ink stick body that extend at least partially the length of a side surface generally parallel to the insertion direction L of an ink loader. In the particular example illustrated in which the insertion direction L and feed direction F are substantially parallel, the ink stick key element  88  comprises a protrusion or ridge that extends from the top to bottom surface of the ink stick substantially parallel to the feed direction F of the ink loader. Key elements, however, may comprise inset features as well, such as, for example, recesses and notches. The key element  88  is shaped and positioned to match a complimentary key  90  formed in the perimeter of the keyed opening  24  in the key plate. 
     Each color for a printer may have a unique arrangement of one or more key elements in the outer perimeter of the ink stick to form a unique cross-sectional shape for that particular color ink stick. The combination of the keyed openings  24  in the key plate  26  and the keyed shapes of the ink sticks  30  (formed by the key elements  70 ) insure that only ink sticks of the proper color are inserted into each feed channel. A set of ink sticks is formed of an ink stick of each color, with a unique key arrangement for ink sticks of each color. In one embodiment, key elements  88  for differentiating between colors of an ink stick may be placed on a single side of each ink stick of a multi-color set of ink sticks. The positioning of the key elements along a perimeter segment of an ink stick may progressively correspond to the progressive position of the keyed opening (and associated feed channel) relative to the other keyed openings in the ink loader mechanism. 
     Referring to  FIG. 12 , there is shown an embodiment of the progressive keying scheme implemented in a set of ink sticks intended for the ink loader of  FIGS. 2 and 3  in which the insertion direction L and feed directions are substantially parallel. In this embodiment, the progressive orientation of the key elements  88 A-D is parallel to the orientation of the feed channels. Thus, the ink stick  30 A intended for the first feed channel  28 A includes a key element  88 A that is positioned the farthest to the left with respect to the other key elements  88 B-D of the ink sticks  30 B-D. The ink stick  30 B intended for the second feed channel  28 B includes a key element  88 B that is positioned the second farthest to the left, etc.  FIG. 13  shows an embodiment of the progressive keying scheme for the ink loader of  FIGS. 4 and 5 . In this embodiment, the insertion direction L is different than the feed direction F. The key elements comprise inset grooves that extend along the top surface  54  substantially parallel to the insertion direction L. Similar to the embodiment of  FIG. 12 , the ink stick  30 A intended for the first feed channel  28 A includes a key element  88 A that is positioned the farthest to the left with respect to the other key elements  88 B-D of the ink sticks  30 B-D. The ink stick  30 B intended for the second feed channel  28 B includes a key element  88 B that is positioned the second farthest to the left, etc. 
     Although the key elements  88 A-D are shown as being on a perimeter segment that is substantially parallel to the orientation of the feed channels, the progressive keying scheme of  FIG. 10  may be implemented on any side of the ink stick that is substantially aligned with insertion direction L. For example,  FIG. 14  shows an embodiment of the progressive keying scheme in which the keying elements have a perpendicular progressive orientation. In the perpendicular progressive orientation, the keying elements may be sequentially positioned along a perimeter segment or surface that is oriented substantially perpendicularly to the left to right orientation of the feed channels. For instance, as shown in  FIG. 14 , the keying elements are sequentially positioned along a side surface with each sequential position of the keying elements  88  corresponding to the sequential left to right positioning of the feed channels. The perpendicular progressive orientation may be useful in situations in which the perimeter segments of an ink stick that are parallel to the orientation of the feed channels are narrow, thereby precluding a practical implementation of the progressive keying scheme shown in  FIGS. 12 and 13 . 
     The single side placement of the keying elements  88  as well as sequential positioning of the key elements has the added benefit of promoting user familiarity with the keying scheme to further ensure that an ink stick is loaded in the proper feed channel. For instance, a printer operator can associate an ink stick with a particular feed channel of the printer by correlating the position of the key element with the correspondingly positioned keyed opening in the key plate. 
     In a manner similar to the color keying scheme, one or more series key elements  94  may be incorporated to provide series differentiation in order to ensure that only ink sticks intended for a particular printer are able to be inserted in the printer as shown in  FIG. 12 . Thus, a set of ink sticks intended for a particular printer may have one or more key elements  94  formed in the same position on each ink stick of the set as shown in  FIG. 12 . A set of ink sticks intended for a different printer may have one or more key elements formed in a particular position on each ink stick of the set that is the same position for each ink stick of the set but at a different position than ink sticks intended for other printers. In embodiments incorporating common side color keying, ink sticks may have up to three sides for incorporating series keying elements, thus, allowing for a wide range of differentiation between printer platforms and models. Additionally, the color key elements  88  and the series key elements  94  may be mutually independent in that the color key elements may be changed or omitted without affecting the configuration or operation of the series key elements and the series key elements may be changed or omitted without affecting the configuration or operation of the color key elements. Thus, ink sticks that are the same color but intended for different printers may have the same color key configuration but different series key configurations. Conversely, ink sticks that are intended for the same printer but are different colors may have the same series key configuration but different color key configurations. 
     In another embodiment, the series keying scheme may include “one way” or compatibility keying features in order to accommodate progressive product differentiation. For example, world markets with various marketing approaches, pricing, color table preferences, etc. have created a situation where multiple ink types or formulations may exist in the market simultaneously. Thus, ink sticks may appear to be substantially the same but, in fact, may be intended for different phase change printing systems due to factors such as, for example, date or location of manufacture; geographic variation including chemical or color composition based on regulations or traditions or special market requirements, such as “sold” ink vs. contractual ink supply, North American pricing vs. low cost markets, European color die loading vs. Asian color die loading, etc. A series keying scheme including compatibility keying may be implemented to ensure that ink stick configurations that are intended to be used with one or more phase change ink platforms, based on marketing approaches, ink formulations, geographic regulations, etc., are used only with those platforms. As an example, an ink formulation for one printer series may be compatible with a second printer series, but ink formulated specifically for the second printer series may not be compatible with the first printer series. Similarly, ink sticks intended for North American markets may be compatible with all printing platforms while ink sticks intended for low cost markets may not be compatible with North American printing platforms. This flexibility in one way keying accommodation allows for the intended multiple product use of some ink while appropriately preventing unintended alternate model use, such as convenience of accepting higher market price ink in a later model while preventing the lower market price ink of the later model from fitting into an earlier model. One way or compatibility keying configurations are defined by same color ink stick shapes that are very similar but differ to the extent that corresponding key plate insertion openings can be somewhat different so that alternate but similar shapes may be admitted or selectively excluded based on the size or configuration difference providing the compatibility keying. Though one way keying is facilitated by opportunities with corner guide ink stick configurations and single side color keying, the concept is intended to be extensible to any ink stick form and any ink loader configuration or orientation relative to gravity. One way or compatibility keying is not used for admitting or excluding different colors but rather same color sticks that would be used in different models or model variations. 
     Compatibility keying may be incorporated by varying a characteristic of the series key and accommodating the variation of the series key in the keyed openings of respective key plates. Ink stick shapes, including guide features and key elements, may otherwise be identical except for this variation in the series key. Take, for example, the case of two platform differentiation in which ink sticks for a first platform may be used with a second platform, but ink sticks for the second platform may not be used with the first platform. As shown in  FIG. 15 , a first series key feature  94 E may be included on both types of ink sticks  30 E,  30 F that is of the same size, shape and location. A second series key  94 F is included on ink stick  30 F that is not included on ink stick  30 E. Referring to the corresponding keyed openings  24 E,  24 F, the series key  94 F has been accommodated in key plate  24 F by incorporating a complementary keyed shape  94 F in opening  24 F such that both ink sticks  30 E and  30 F may be inserted through the keyed opening  24 F. Conversely, ink stick  30 F may not be inserted through the keyed opening  24 E because it does not include a complementary shape  98 F for accommodating the second key feature  94 F of ink stick  30 F. In the embodiment of  FIG. 15  and other example figures, the key features comprise protrusions although any suitable feature may be utilized including inset features. 
     In another embodiment, compatibility keying may be incorporated by varying a geometric characteristic of a series key element such as, for example, in the case of a protruding element, a width of the element. The more restricted ink sticks may have a wider or larger key feature, and less restricted ink sticks may have a smaller similarly shaped feature or one that would be enveloped by the larger in the same location. The passage of ink sticks through a keyed opening of the key plate may be controlled by varying the size of a complementary shape in the keyed opening of the key plate. For example, as shown in  FIG. 16 , ink sticks  30 G and  30 H include a key feature  94  in the same location On each ink stick. The key feature  94 H on ink stick  30 H is wider than the key feature  94 G on ink stick  30 G. Referring now to the corresponding key plates  26  of  FIG. 16 , key plate  26 G includes a keyed opening  24 G including a narrow shape  98 G that is configured to allow the passage of ink stick  30 G but not ink stick  30 H. Key plate  26 H includes a keyed opening  24 H including a wide shape  98 H that is configured to allow the passage of both ink sticks  30 G and  30 H. The configuration of an ink stick keying feature and the corresponding key feature in a key plate may have a dimension that is greater than these elements in a second configuration such that the first and second configuration ink stick fits through the key plate opening of the first configuration but only the second ink stick configuration fits through the key plate opening of the second configuration. Since the key feature can be an inset or a protrusion, the reference to a greater dimension defines one element of the ink stick dimension influencing the key feature so that when that dimension is greater, accomplishes the one way exclusion. As example, the greater dimension could apply to the width of the key feature itself in a protruding key configuration or an area adjacent to the key feature in an inset key configuration, the latter resulting in a narrower inset key width. 
     Compatibility keying may be incorporated by varying the number of key features and/or varying a geometric characteristic of the key features or varying one or more dimensions of the ink stick or any combination. In addition, in embodiments in which color keying is incorporated on a single side of the ink stick, up to three sides may be used to incorporate compatibility keying. By varying the number and/or characteristics of key features compatibility keying may be extended beyond two platform differentiation. Therefore, many combinations of one way compatibility keying are possible across a wide range of acceptance and exclusion sets. Other dimensional variations can be employed to accomplish one way keying, as example, the length dimension of an ink stick perpendicular to insertion where two sticks might be identical except for a small but exclusionary increase in the length of stick two relative to stick one. As shown in  FIG. 18 , for instance, the ink stick  30 M and ink stick  30 N are substantially similarly shaped except the dimension X of ink stick  30 M is smaller than the dimension X′ of ink stick  30 N. Thus, ink stick  30 M may be inserted through the keyed openings  24 M and  24 N. Ink stick  30 N may be inserted through keyed opening  24 N, but, due to the larger dimension X′, ink stick  30  is excluded from insertion through opening  24 M. 
       FIG. 17  is a diagrammatical illustration of an embodiment of a compatibility keying scheme for three platform differentiating incorporating geometric and number variations in the series compatibility keying. As can be seen, ink sticks  30 J,  30 K and  30 L may be inserted into key plate  26 L. Ink sticks  30 J and  30 K may be inserted into key plate  26 K, and only ink stick  30 J may be inserted into key plate  26 J. It can be appreciated that by varying the number, placement, shape of key features formed on up to three sides of an ink stick, the possible combinations of compatibility keying configurations is extensive. 
     The exemplary embodiments of the series and compatibility keying schemes depicted in  FIGS. 15 and 17  are shown as incorporated into embodiments of ink sticks intended for the ink loader of  FIGS. 2 and 3  in which the insertion direction L and feed directions F are substantially parallel. Thus, the keying features are shown as extending longitudinally along a surface of the ink stick in a direction parallel to the insertion and feed directions. These schemes, however, may be implemented in a similar manner for the ink loader of  FIGS. 4 and 5  in which the insertion directions and feed directions are different as long as the keying features extend along a surface of the ink stick in a direction that is generally the same as the insertion direction of the ink loader. 
     Those skilled in the art will recognize that numerous modifications can be made to the specific implementations described above. It should be appreciated that the various male-female implementations of the various key features may be suitably reversed. Additionally, those skilled in the art will recognize that the guide elements located at the ink stick corners, intermediate the corners or in the bottom surface of the ink stick body, and guide rails or members in complementary locations may have numerous shapes other than the particular shapes illustrated. In addition, numerous other configurations of the feed channel, key plate, and other components of the ink feed system can be constructed. Therefore, the following claims are not to be limited to the specific embodiments illustrated and described above. The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.