Abstract:
An indexable gravity flow shelving system provides resilient comb members along the front and rear rails of each inclined shelf to removably and releasably secure track members to the inclined shelf. Each resilient comb includes a row of downwardly-extending tangs that define slots therebetween to receive elongated flow ribs extending the length of the upper surface of each track member. The tangs contact the sides of the elongated flow ribs and prevent transverse movement of the track members. The spacing of the tangs allow for the shelving system to be used effectively with track members besides track members having elongated flow ribs. The resilient comb members deform and rebound to readily allow for rearrangement of track members within each inclined shelf. The resilient comb members can cooperate with price tag moldings along the front and rear rails of the inclined shelf. The price tag moldings provide means for mounting labeling indicia in close proximity to columns of product units stored on the shelf, as well as means for receiving stop plates along the front and, if desired, the rear of the shelf to prevent unwanted spillage of product units. A desirable alternate embodiment utilizes adapter means to allow retrofitting an existing cantilevered gondola-type shelf with resilient comb members to form front and rear track interface means and convert the existing shelf into an indexable gravity flow shelf.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to gravity flow shelving units and, more specifically, to inclined shelves having adjustable track members for ready manipulation of horizontal spacing and location of track members in gravity flow shelves to accommodate product of various shapes and sizes, so as to maximize use of retail shelf space. 
     2. Description of the Related Art 
     In order to increase inventory turnover and maximize efficient use of shelf space, retailers increasingly utilize gravity flow shelving systems, wherein inclined shelves are used to stock merchandise. In such shelf systems, consumers are presented with an array of merchandise arranged in parallel tracks on each shelf, generally with only the front-most (or “first-up”) unit of merchandise in each individual track being easily accessible. Upon removing this front-most unit of merchandise, the remaining units of like-merchandise in that given track advance, i.e. slide down, toward the front of the shelf, so that the next-successive unit in line becomes the new front-most unit in that track. 
     Since conventional flat merchandise shelves, e.g., cantilevered or so-called “gondola”-type shelves, allow users to rearrange product on the shelves, such as to find product with later expiration dates, these inclined gravity flow shelving systems help ensure that oldest product is sold first. By making rearrangement of product more difficult, it is found that inventory waste is reduced. The inclined arrangement of the gravity flow shelves also allows greater shelf-space on a given footprint of valuable floor space for the retailer, which is a particular advantage in relatively costly refrigerated aisles and wall units where gravity shelving systems are becoming the industry standard. 
     In order to further maximize the use of shelf space, various attempts have been made to provide adjustable or indexable shelving, wherein individual track members are horizontally adjustable relative to a shelf frame, so that track members can be placed by a retailer at different customized desired horizontal locations to accommodate merchandise of varying size, i.e. width, and shape on a single inclined shelf. 
     The general concept of indexable shelf tracks for display shelves started as early as the late 1950&#39;s, where Bromberg, U.S. Pat. No. 2,915,193, showed the use of horizontally-spaced, upwardly- and inwardly-open slots along the front and rear of a flat shelf to accommodate vertical wall members at various desired spaced locations along the width of the shelf to form several compartments of desired sizes within the shelf. A shortcoming of such a shelf with variable width spacings, when utilizing upwardly-open slots to receive vertical wall members, is that the wall members can be easily removed by consumers, thereby easily circumventing the purpose of the vertical wall members. 
     Indexable shelf tracks have also been used in inclined gravity flow racks, such as in U.S. Pat. No. 4,383,614, which shows a plurality of teeth defining inwardly-open notches along the front and rear rails of an inclined shelf to securely receive individual roller track members to facilitate sliding of products on the track members. Each of the roller track members has an inverted generally U-shaped cross-section, with a flat top web having downwardly-projecting straight legs and inwardly-bent runners. The runners slidably receive a plastic clip member to lock the track member in place within a pair of the inwardly-open notches. Such clip members must be separately manufactured, increasing time and cost of production, as well as providing many additional parts for assembly (and possibly inadvertent loss of smaller parts) by the retailer. 
     In another previous attempt at an indexable gravity flow shelving system, shown in Highsmith, U.S. Pat. No. 4,909,402, longitudinal dividers having resilient legs are received between pegs having upright and transverse portions that define upwardly-open notches. In localized regions, the resilient legs of the longitudinal dividers are biased together by a clip in order to pass the longitudinal divider between desired adjacent pegs, and then the clip is removed to lock the longitudinal dividers in place. Again, a clip member is necessary to assemble the indexable shelf member. In this instance, since the clip is only used at the time of assembly or removal of a longitudinal divider, the clip may again inadvertently become lost, rendering rearrangement of the longitudinal dividers difficult. Furthermore, additional track members to support merchandise are required. 
     Most all conventional indexable gravity flow shelf systems require the use of track members specially adapted with legs or flanges on the underside thereof to be received in the indexing slots provided along the front and rear rails of the shelf. These legs or flanges are integral parts of the track members, such as shown in German Patent No. 196 09 432, requiring costly machine operations to form the track members having the required shape. As indicated in that German patent, gravity flow shelf tracks can utilize elongated grooved channels along the length of the track members order to reduce friction between merchandise and the upper flat surface of the track. Alternatively, as shown in Spamer, U.S. Pat. No. 5,022,535, elongated, upwardly-extending flow ribs or runners can be provided along the upper flat surface of the track members, which similarly serve to reduce friction between merchandise and the track members. Spamer discloses using adhesive to mount the shelf tracks to the front and rear rails of the inclined shelf, which can undesirably deteriorate over time. 
     It would be desirable for an indexable gravity flow shelf system to have the ability to utilize the existing flow ribs or slide runners on the upper surface of the track members to lock track members in desired locations along inclined shelves, because such use would eliminate the need for additional legs or flanges on the underside of the track members. However, there is no known prior gravity flow shelving system that uses the friction-reducing flow ribs on the upper surface of the tracks for securely installing the track members. 
     Another drawback of conventional indexable shelf systems is that the horizontal adjustability of the individual shelf tracks is limited by relatively wide spacing of the slots or apertures heretofore provided on front and rear rails to receive portions of the tracks. A typical center-to-center distance of about {fraction (5/16)}″ separates inwardly-open notches between the teeth members along the front and rear rails of finite horizontally-adjustable (i.e., indexable) gravity flow rack systems found in the prior art. However, it would be desirable for an indexable gravity flow shelf system to provide a greater number of shelf track interface points that are spaced more closely together than in such prior art indexable shelf systems, in order to achieve greater finite horizontal adjustability of track members. 
     It would also be useful to have an indexable gravity flow shelf system that is easy to assemble and for which the individual shelf tracks can be easily rearranged by the retailer, yet still be securely mounted in place once arranged to avoid inadvertent shelf track slippage or dislocation. It would be further desirable if such a shelf track system required no additional clip parts to lock shelf tracks in place or to install (or remove) shelf tracks in (from) desired locations along the width of the shelf. An additional desirable feature would be the ability to retrofit an existing shelf with components that allow the shelf to act as an indexable gravity flow shelf that does not suffer from the drawbacks described above. The manner in which these objectives are accomplished by the present invention is described in the following Brief Summary of the Invention, the Detailed Description of the Invention, and the drawings. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention utilizes a row of generally downwardly-extending resilient tangs that forms a resilient comb member along both the front and rear rails of each inclined shelf in a gravity flow shelving system. In general, when installing certain types of track members, a region of at least one of these rows of resilient tangs flexes outwardly while an individual track member is being installed, and then snaps closed, i.e. springs back or returns to its original position, once a flat surface of the track member passes beneath the selected series of tangs. Advantageously, the elongated, upwardly-extending flow ribs or slide runners which are provided along the upper flat surface of each of these certain types of track members are received in slots or gaps between pairs of the downwardly-extending resilient tangs to prevent unwanted lateral, i.e. transverse, movement of the track members, once arranged in a shelf. 
     Various shapes of track members having the upwardly-extending ribs can be utilized, such as flat track members, inverted T-shaped track members, L-shaped track members, and even others. The elongated body of the inverted T-shaped track members provides an integral vertical divider portion used to separate adjacent tracks of the shelf, keeping merchandise in its respective track. The L-shaped track member is used for the outside tracks of a given shelf, and provides the vertical divider portion for keeping merchandise in an outer end (i.e., left-most or right-most) column. It is the vertical divider portion of the inverted T-shaped track members and the L-shaped track members that causes the outward deformation of a region of one of the front and rear rows of resilient tangs during insertion or removal of the track members. 
     The exposed leading front (or rear) edge of the vertical divider portion of these track members engages a peak of a gap between a pair of the resilient tangs and deforms a region of the associated row of tangs that is wide enough to provide clearance for the flat runner portion of the track member to pass beneath the row of tangs, at which time the deformed region of the row of resilient tangs snaps back to its original position and the track member can be slid toward the opposite rail to be locked in position at that same end of the shelf. 
     In a preferred method of using the indexable shelf system of the present invention, a rear end of a track member is placed in a desired horizontal location against the row of resilient tangs along the rear rail of an inclined shelf, so that the upwardly-extending ribs on the upper flat surface of the track member are aligned with slots between pairs of the resilient tangs along the rear rail. Pressure is then applied longitudinally along the track member to rearwardly bias the region of resilient tangs in the vicinity of the vertical divider portion at the rear end of the track member, until the rear end of the track member passes below the resilient tangs adjacent to the rear end of the track member. At this time, this bent region of resilient tangs springs back to its original orientation. Finally, the track member is slid forwardly along the inclined plane of the shelf until the front end of the track member passes under the tangs along the front rail of the inclined shelf, or the front end of the track member is simply snapped downwardly into tangs at the front rail of the inclined shelf, to be releasably locked at that desired location within the shelf. 
     Advantageously, to remove the track member, the process is readily reversible, in that the track member is slid in a rearward direction, applying adequate force to bias the region of the row of resilient tangs adjacent the rear rail of the shelf rearwardly until the front end of the track member is clear of the resilient tangs along the front rail of the inclined shelf. The track member is then withdrawn from underneath the resilient tangs along the rear rail of the shelf. It will be understood that the track members can alternatively be installed or removed in the opposite directions to those just described. 
     Preferably, each of the front and rear rails of the indexable shelf of the present invention cooperates with a price tag molding having a horizontal channel that is generally U-shaped in cross-section to receive and retain a stop plate or filler piece in a position generally perpendicular to the plane of the inclined shelf. The front end stop plate is an acrylic, preferably transparent plate that is inserted in the U-shaped channel of the front price tag molding, and extends above the front price tag molding in order to prevent merchandise from falling of the shelf at the front end of each track member. Because of the height of the rear rail and angle of incline of the indexable shelf, a stop plate at the rear of the shelf is not necessary to prevent a rear-most (or “last-up”) product unit in a given column of product units from being pushed off the rear side of the shelf system when pressure is applied to the first-up product unit in that column of units from the front of the shelf system, for example if the shelves are front-loaded. 
     However, the use of an elongated filler piece, preferably plastic, in the U-shaped channel of the rear price tag molding is necessary to keep the resilient adjustment tangs of the rear of the shelf at a distance above the rear rail that is approximately the same as the distance of the tangs of the front of the shelf above the front rail. The front resilient adjustment tangs may be provided as integral downwardly and rearwardly-extending tooth-like projections of the front price tag molding or, more preferably, as downwardly and rearwardly-exending tooth-like projections that are part of a separate resilient comb member having a means for interlocking with the front price tag molding. 
     In either case, the gaps between the tangs of each comb member preferably have a center-to-center distance of 0.2″, which is shorter than the {fraction (5/16)}″ center-to-center spacing of many of the track-receiving gaps found in indexable shelving in the prior art. This closer spacing of the gaps between the tangs vastly increases the horizontal adjustability of the track members, so that the system can be better customized by retailers for their use with products of various widths. 
     Advantageously, a price plate receiving channel at the forward leading edge of the price tag molding can receive labeling indicia therein, such as product names, flavors, and prices, at positions associated with, i.e. immediately forwardly and below, each track member of the shelf for the benefit of consumers. 
     The resilient adjustment tangs along the rear rail are aligned with the resilient adjustment tangs of the front rail to assure proper alignment of the track members, and are formed as forwardly-extending tooth-like projections of either a rear price tag molding or, more preferably, a separate resilient comb-like member that interlocks with the rear price tag molding. Indicia may be provided on the individual tangs associated with the front rail, with corresponding indicia on the tangs associated with the rear rail, to further facilitate quick proper alignment of the track members. For example, a colored marking can be provided on every fifth tang along both the front and rear rails so that a retailer can easily align each track member at a desired horizontal location within the shelf. The price tag molding on the rear rail may also include a price plate receiving channel to receive rearwardly-facing indicia therein, such as product codes, product names, and flavors, to assist stock-keeping personnel in stocking items from the rear of the shelf. Again, these indicia may be provided in close proximity to associated track members. 
     More generally, it is recognized that the flexible track interface means of the shelf frame of the present invention can be used to secure various other types, i.e. designs, of track members, including those that do not have the upwardly-extending flow ribs. For example, the spacing of the tangs along each comb member are preferably such that the shelf frame can accommodate elongated roller track members found in the prior art, preferably having an inverted generally U-shaped cross-section including a flat top web having downwardly-projecting vertical side legs. Such elongated roller track members further include inwardly-bent flanges along the bottom of each side leg. 
     The vertical side legs serve the same function as the vertical divider portion of the L track member and inverted T track member described above. Each vertical side leg contacts the peak of a gap between two adjacent tangs, and when pressure is applied longitudinally along the length of the roller track member, a region of the corresponding comb member deforms outwardly so that the opposite end of the roller track member can be snapped in place along the opposite rail of the shelf frame. The length of the roller track member is such that when installed, i.e. snapped in place, between opposing tangs of the front and rear comb members, the roller track member is securely restrained against transverse movement. 
     In an alternate embodiment of the present invention, an existing cantilevered, so-called “gondola”-type shelf is retrofitted with components to convert the shelf into an indexable gravity flow shelf. The components include front and rear flexible track interface means of the type described above. Advantageously, mounting arms located on the rear of the gondola-type shelf can be used to mount the shelf at an incline, leaving space at the rear of the shelf for one or more generally J-shaped hooks to clip the front and rear flexible track interface means to the flat shelf surface. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a perspective view of an indexable gravity flow shelf system of the present invention; 
     FIG. 2 is an enlarged front perspective view, broken away, of a preferred vertical support for the gravity flow shelf system shown in FIG. 1, with shelf mounting clamps. 
     FIG. 3 is a front perspective view of a single indexable gravity flow shelf of the present invention; 
     FIG. 4 is a left, rear perspective view of a single indexable gravity flow shelf of the present invention; 
     FIG. 5 is a left side view of the front rail of the shelf shown in FIG. 3, taken along lines  5 — 5  of FIG. 3; 
     FIG. 6 is a perspective view, broken away, of an interface of an inverted T-shaped track member and the front track interface means of the shelf shown in FIG. 4, taken along line  6  of FIG. 4; 
     FIG. 7 is a perspective view, broken away, of an interface of an L-shaped track member and the rear track interface means of the shelf shown in FIG. 3, taken along line  7  of FIG. 3; 
     FIG. 8 is a front perspective view, broken away, of a flat track member for use with the indexable shelf of the present invention; 
     FIG. 9 is a front perspective view of an inverted T-shaped track member, partially broken away, for use with the indexable shelf of the present invention; 
     FIG. 10 is a front perspective view of an L-shaped track member for use with an indexable shelf of the present invention; 
     FIG. 11 is a rear perspective view of a conventional cantilevered gondola-type shelf equipped with a retrofit version of the indexable gravity flow shelf assembly of the present invention; 
     FIG. 12 is an enlarged front perspective view, broken away, of the connection of the shelf and retrofit indexable gravity flow shelf assembly of FIG. 11; 
     FIG. 13 is an enlarged left side view of the connection of the conventional cantilevered shelf of FIG. 11, taken along lines  13 — 13  of FIG. 12; 
     FIG. 14 is a front perspective view, broken away, of an indexable gravity flow shelf of the present invention in conjunction with roller track members; 
     FIG. 15 is a rear perspective view taken along lines  15 — 15  of FIG. 14, with the front end of a roller track member partially broken away for clarity, showing the interface between the roller track member and the front track interface means; and 
     FIG. 16 is a perspective view, broken away, of an interface of a roller track member and the front track interface means of the shelf shown in FIG. 14, taken along line  16  of FIG.  14 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIGS. 1-4, an indexable gravity flow shelf system  10  includes three inclined shelf frames  12 ,  14 ,  16  mounted on four vertical shelf rack support legs  18 ,  20 ,  22 ,  24 . Fewer or more inclined shelf frames may be utilized in the shelf system  10 , as desired, and as allowed by the height of both the vertical shelf rack support legs  18 - 24  and the height of product stored on the shelf frames. Each shelf frame  12 ,  14 ,  16  includes a pair of side rails  26 ,  28 , a front rail  30 , and a rear rail  32 . The front, rear, and side rails may be L-shaped in cross section, as described in more detail below. A center rail  34  is also preferably provided in each shelf frame for extra support of the track members. Additional intermediate lateral cross rails (not shown) may be provided horizontally across the width of the shelf  12  to provide additional support. The side rails  26 ,  28  are each provided with a plurality of downwardly-directed, inclined U-shaped mounting grooves  36  that are selectively hooked onto clamps fastened to the rear vertical support legs  18 ,  20  in order to adjust the angle of incline of the shelf frame  12 . Mounting grooves  36  may also be used to adjust how far the shelf frame  12  extends forwardly of the front vertical support legs  22 ,  24 . 
     Vertical Support Legs 
     Keyhole slots  38  that receive the clamps  39  (or similar fasteners as will be appreciated by those of ordinary skill in the art) are preferably provided along substantially the entire length of each of the vertical support legs  18 ,  20 ,  22 ,  24  to provide maximum adjustability for shelf height, number of shelves, and angle of incline of each shelf frame  12 ,  14 ,  16 . As shown in FIG. 2, each clamp  39  may be in the form of a generally cylindrical member having a pair of spaced annular grooves therein. A relatively wide entry/exit portion  38   a  of the keyhole slot  38  receives a complementarily-shaped support lock end  39   a  of the clamp  39 , and an adjacent annular groove of the clamp  39  slides into a relatively narrow channel  38   b  of the keyhole slot. The other annular groove of the clamp  39  receives a portion of one of the side rails  26 ,  28  of the shelf frame, or permits coupling of the clamp  39  with one of the U-shaped mounting grooves  36 . 
     Gravity retains the clamp  39  in a secure position. Preferably, each vertical support leg  18 ,  20 ,  22 ,  24  is generally U-shaped in cross section, with a solid, imperforate central web portion  55  flanked by two side walls  54 ,  56 . The keyhole slots  38  preferably extend along both of the sidewalls  54 ,  56  of the vertical support legs  18 - 24 , which permits front and rear vertical support legs to be shared by adjacent shelf rack systems  10 , thus facilitating the forming of an aisle of multiple, cooperating, side-by-side gravity flow shelf rack systems. 
     Advantageously, each of the vertical support legs  18 ,  20 ,  22 ,  24  is preferably generally U-shaped in cross-section, with a central web  17  and side legs  19 ,  21 . The keyhole slots  38  are preferably provided along both vertical side legs  19 ,  21 , so that a single vertical support leg may be used cooperatively for two adjacent shelf systems, and an entire row of shelf systems may thus be interlinked. For cosmetic reasons, the central web  17  of each vertical support leg  18 ,  20 ,  22 ,  24  faces the front of the shelf system  10 , to obscure the keyhole slots  38  and clamps  39  from view. While this type of vertical support leg, keyhole slot, and clamp system has been used in gravity flow shelving systems prior to the present invention, this structure is disclosed as one preferred exemplary environment for the shelf frame of the present invention. 
     “Price Tag” Moldings 
     Turning to FIGS. 5-7, a flat portion  30   a  of the front rail  30  lies in the plane of the shelf frame  12 , and an upstanding portion  30   b  of the front rail  30  interfaces with a specially adapted elongated price tag molding  40  that extends substantially the width of the shelf frame  12 . The price tag molding  40  derives its name because its leading portion  42 , which is the portion visible to the consumer, includes opposing lower and upper channels  44 ,  46  to receive labeling indicia therein, such as pricing information, product identification, and inventory control numbers. Most preferably, the price tag molding  40  is made of Acrylonitrile Butandiene Styrene (ABS), which is available from Bayer Corp., Rosemont, Ill. The leading portion  42  is integrally joined just rearwardly of the upper channel  46  to a secondary portion  48  of the price tag molding  40 . 
     Secondary portion  48  is preferably L-shaped in cross-section, in that it includes a wall member  50  that is substantially perpendicular to the inclined plane of the shelf frame  12  and a relatively short, flat, rearwardly-directed extension  52  that lies in the same inclined plane as the shelf frame  12  to lock the price tag molding  40  in place on the L-shaped front rail  30 . A short gap separates the second portion  48  from a tertiary portion  58  of the price tag molding  40 , consisting of a first wall  60 , a second wall  62  parallel to the first wall  60 , and a floor segment  64  separating the first wall  60  and the second wall  62 . The first wall  60 , second wall  62 , and floor segment  64  define generally U-shaped groove that can receive and retain a front stop plate  66  in an orientation generally perpendicular to the plane of the shelf frame  12 . The front stop plate  66  is preferably a transparent acrylic plate that extends above the top of the front price tag molding so that the first-up product stored in each column on shelf tracks  82 ,  84 ,  86  (which are described in more detail below) is visible to consumers, while being prevented from falling over the leading portion  42  of the price tag molding  40 . The front stop plate  66  is preferably easily removable from the tertiary portion  58  to facilitate cleaning of the front stop plate  66 . 
     The first wall  60  and floor segment  64  of the tertiary portion  58  cooperate with the wall member  50  and short, flat, rearwardly-directed extension  52  of the secondary portion  48  to securely receive the upstanding portion  30   b  of the front rail  30  and lock the price tag molding  40  in place on the front rail  30 . 
     Because the side rails  26 ,  28  are connected to the underside of the flat portion  30   a  of the front rail  30 , it is recognized that a portion of the rearwardly-directed extension  52  of the secondary portion  48  may need to be removed at each side of the front rail  30  to accommodate the width of the flat portion  26   a ,  28   a  of each of the respective side rails  26 ,  28  that lies in the plane of the shelf frame  12  (see FIGS. 2,  3 ). The side rails  26 ,  28  are also preferably L-shaped, with an integral downwardly-extending portion  26   b ,  28   b  from which the generally U-shaped mounting grooves  36  depend. 
     Immediately rearward of the tertiary portion  58  of the price tag molding  40  is support means for a front track interface means  68 . In the most preferred embodiment, this support means for the front track interface means includes closely-spaced opposing upper and lower channels  70 ,  72  located along the second wall  62  of the tertiary portion  58 . These opposing channels  70 ,  72  form a C-shaped (in cross-section) passageway that slidingly receives a corresponding T-shaped (in cross-section) extension  74  of the front track interface means  68 . Although the front track interface means  68  and the price tag molding  40  are designed to securely interlock with one another without the need for any bonding agents or welds, those of ordinary skill in the art will appreciate that, once assembled, these components can also be crimped together by the manufacturer for added integrity. Alternatively, the front track interface means  68  may be formed integral with the price tag molding  40 , and connected to the tertiary portion  58 , for example by a thin-sectioned, living hinge member (not shown). 
     The front track interface means  68  takes the form of a resilient comb member  69  having a concave curved cross-section and a plurality of downwardly, inwardly open tangs  76 . Each pair of tangs  76  defines a generally inverted U-shaped gap  78  therebetween. Each gap  78  has a peak  80  at its highest point. The gaps  78  between the tangs  76  are separated by a center-to-center distance of 0.2″ intervals, which is closer than the {fraction (5/16)}″ spacing of adjustable track supports found in the prior art. This closer spacing of the gaps  78  between the tangs  76  results in greater adjustability in horizontal placement of shelf tracks. The tangs  76  are formed as individual struck-out members with the bottom of each tang advantageously spaced a distance C above the flat portion  30   a  of the front rail  30  when the tangs  76  are in their resting position. This is done in order to provide clearance for the flat track strip portion of each shelf track between the bottoms of the tangs  76  and the front rail  30 . In an exemplary embodiment, the flat track strip portion has a thickness of preferably about 0.1″. The raised flow ribs  90  of the track members  82 ,  84 ,  86 , each has a height of about 0.063″, which gives the shelf track a total thickness of 0.163″ at the raised flow ribs  90 . Most preferably, distance C is approximately 0.135″±0.01″, so that the raised flow ribs  90  are retained within the gaps  78  between associated tangs  76  to prevent transverse movement of the track members. It is recognized, however, that track members having thicker flat track strips may be desirable, e.g., for use with particularly heavy products stocked on the shelving. In such applications, the distance C may have to be greater to accommodate such thicker track members. 
     A similar specially-adapted elongated price tag molding  41  extends along and securely interfaces with the rear rail  32 , extending substantially the width of the shelf frame  12 . Because of the height and incline of the rear price tag molding  41 , it need not include a raised rear stop plate to prevent last-up product from falling over the rear of the shelf. However, a plastic filler piece  67  (not shown in FIGS. 1-4, but see FIG. 7) is considered necessary in the tertiary portion of the rear price tag molding  41  to ensure that the resilient tangs of the rear price tag molding  41  extend the same dimension C above the flat portion of the rear rail  32 . Also, it is desirable for the rear price tag molding  41  to still include an indicia receiving means to assist stockkeeping personnel working from behind the shelf system  10  in identifying where to place product, particularly in rear-loaded gravity flow shelving systems. 
     Track Members 
     Turning now to FIGS. 8-10 three exemplary shelf track members  82 ,  84 ,  86  are shown. Each track member  82 ,  84 ,  86  is most preferably made of high impact polystyrene, available from Huntsman Chemical Co. of Chesapeake, Va., as well as Dow Corning Co. in Freeland, Mich. The high impact polystyrene may further include an additive, known as Dow Corning #MB25-504. Flat track member  82 , shown in FIG. 8, includes a generally flat track strip  88 , and a plurality of elongated slide runners or flow ribs  90  extending the length of the upper surface of the track strip  88 . The flow ribs  90  reduce the friction between the track strip  88  and product resting on the track member, so that when a first-up unit of product, i.e. a product at the forward- or lower-most position in a column of product units, is removed by a consumer, the remaining product units in the column move, i.e. slide downward, under the force of gravity until the next unit of product in line becomes the new first-up unit by reaching the front stop plate  66 . 
     Unlike the inverted T track member  84  shown in FIG.  9  and the L track member shown in FIG. 10, the flat track member  82  preferably includes at least two downwardly-depending support ridges  92 . Each of the support ridges  92  terminates at a front end  94  that is rearward of the front end  96  of the flat track member  82 , and terminates at a rear end  98  that is forward of the rear end of the flat track member  82 . This is done to provide clearance for the flat track strip  88  to lie flush against the flat portion  30   a  of the front rail  30 . Similarly, a central gap  100  is preferably provided in each of the ridges  92  so that the flat track strip  88  lies flush against the center rail  34 . Additional gaps (not shown) may be provided in the ridges  92  if the shelf frame  12  requires additional intermediate cross support rails. The ridges  92  advantageously add rigidity to the flat track member  82 . 
     The inverted T track member  84  similarly has a flat track strip  88  and a plurality of flow ribs  90  extending the length of the upper surface thereof. This track member  84  further includes a vertical divider wall member  102 , which separates adjacent columns of product units from one another. The L track member  86  also has a flat track strip  88  and flow ribs  90 , as well as an outer vertical divider wall member  104 . As seen in FIG. 1, an inverted T track member  84  can be used in conjunction with other inverted T track members to define a plurality of track columns for relatively narrow products, and also in conjunction with L track members  86  to define an outer track column for a given shelf frame  12 . For relatively wide products, flat track members  82  are used in conjunction with either or both of the other two types of track members to widen the track columns. 
     Mode of Operation 
     In order to install an inverted T track member  84  into a given shelf frame  12 , the front portion of the inverted T track member  84  is placed into contact with the front track interface means  68  at a desired location. Preferably, a leading edge  104  of the vertical divider wall member  102  is placed in contact with a peak  80  of one of the gaps  78  between tangs  76 . Pressure is applied longitudinally (by the person installing the track member) to the inverted T track member  84  in a downward and forward direction, i.e. toward the lower forward end of the shelf, which causes at least a region of the resilient comb member  69  of the front track interface means  68 , which is curved in cross-section, to flex forwardly, thereby allowing the flat track strip  88  to pass underneath the tangs  76 . Once the flat track strip  88  passes beneath the tangs  76 , the flexed region of the resilient comb member  69  snaps back to its original position, as demonstrated by the directional arrows in FIG.  5 . The track member  84  is then slid rearwardly until the opposite end of the track member is secured by the tangs of a similar rear track interface means  106 , or alternatively, snapped into a rear comb member  108  of the rear track interface means  106 . The upwardly-extending flow ribs  90  are advantageously located in the gaps  78  of the resilient comb members  69 ,  108 , thus the tangs  76  prevent the inverted T track member  84  from making any unwanted transverse, i.e. horizontal movement. 
     Installation of the L track member  86  is similar to the installation of the inverted T track member  84 , in that a leading edge  104  of the vertical divider wall member  102  of the L track member  86  is first placed in contact with one of the peaks  80  between the tangs  76 . Next, longitudinal pressure is applied on the L track member  86  in a direction toward the lower forward end of the shelf until a region of the resilient comb member  69  of the front track interface means  68  flexes forwardly. Then, the flat track strip  88  passes beneath the tangs  76  and that flexed region of the resilient comb member  69  snaps back to its original position as the L track member  86  is pushed rearwardly toward the rear track interface means  106 , or alternatively, snapped into the rear comb member  108  of the rear track interface means  106 . Again, the tangs  76  prevent unwanted transverse movement of the given L track member  86  by releasably trapping the upwardly-extending flow ribs  90  therebetween. 
     Advantageously, the rear track interface means  106  can function just as the front track interface means  68 . Thus, installation of either the inverted T track member  84  or the L track member  86  can be reversed, so that a rear leading edge  110  of the vertical divider wall member  102  of the given track member is first applied to the rear track interface means  106  until a region of the resilient comb member  108  of the rear track interface means  106  flexes. Then, the flat track strip  88  passes beneath the tangs  76 , and the region of the resilient comb member  108  of the rear track interface means  106  snaps back to its original position, as the given track member is slid downwardly toward the front track interface means  68  or alternatively, snapped into the comb member  69  of the front track interface means  68 . 
     Regardless of the direction in which the given inverted T track member  84  or L track member  86  is installed, removal, e.g., for horizontal adjustment purposes, of the given track member is a similar process. The given track member is again pushed in the direction of the resilient comb  69 ,  108  of either the front track interface means  68  or rear track interface means  106  until a leading edge  104 ,  110  of the vertical wall member  102  applies sufficient pressure to the peak  80  between two tangs  76  and the resilient comb flexes again to provide enough room for an opposite end of the flat track strip  88  of the given track member to be removed from the shelf frame  12 . 
     Because the flat track member  82  lacks a vertical divider wall member, installation of this track member is somewhat different than the inverted T track member  84  and the L track member  86 . The flat track member  82  is preferably about ½″ longer than the inverted T track member  84  and L track member  86 , and as a result, the longer length of the flat track strip  88  of the flat track member  82  is sufficient to temporarily flex the resilient comb member of the front and/or rear track interface means  68 ,  106  to allow for insertion of the flat track member  82  at a desired location. As before, the tangs  76  prevent transverse movement of the flat track member  82  by trapping the upwardly-directed flow ribs  90  therebetween. 
     The vertical divider wall member  102  aids in the retention of the L track member  86  and inverted T track member  84  in the gaps  80  between the tangs  76 . Since the flat track member  82  does not have the vertical divider wall member, the ½″ longer length of the flat track member  82  means the flat track member  82  extends an additional ¼″ past the tangs  76  of each of the front and rear track interface means  68 ,  106 , which helps retain the flat track member  82  in the gaps  80 . The flat track member  82  is preferably sufficiently flexible, even with the support ridges  92 , to be removed from the shelf frame  12  without having to flex the front and/or rear resilient comb members  69 ,  108  again. 
     In addition to the flat track member  82 , the inverted-T track member  84 , and L track member  86 , various other track shapes are considered to be within the scope of the present invention. Virtually any track shape that has a flat track strip with a plurality of elongated flow ribs on the upper surface can be used in the gravity flow shelf system  10 , so long as the track member is able to cause a region of the front and/or rear track interface means  68 ,  106  to flex outwardly so that the track member may be received and retained in the shelf frame  12 . For example, a track member with two vertical divider walls bounding a central flat track strip with elongated flow ribs, i.e. forming a U-shaped track defining a shelf column of fixed width is feasible. Similarly, a track member may have more vertical divider walls, such as a W-shaped track member with two parallel, fixed-width shelf columns. With such U-shaped and W-shaped track members (not shown), it is foreseeable that product to be dispensed on the gravity flow shelf system  10  could advantageously be shipped to retailers together with the track members as shrink-wrapped, ready-to-dispense columns of product units that are simply unwrapped, and the associated pre-loaded track member snapped in place into a shelf frame  12  of the present invention. 
     In addition, it is found that track members that do not have upstanding flow ribs on an upper surface can also be releasably secured within the shelf frame  12 . For example, as shown in FIGS. 14-16, it is found that roller track members  112  having an upper elongated surface  114  with side support legs  116  can be used in the shelf frame  12  of the present invention. The preferred 0.2″ center-to-center spacing of the gaps  78  between the tangs  76  permit the side support legs  116  of the roller track members  112  to act in substantially the same manner as the vertical divider wall members  102  described above. When the front (or rear) edges of the side support legs  116  of the roller track member are placed against the peaks  80  of two gaps  78  between tangs  76 , and pressure is applied longitudinally to the roller track member  112 , the associated front (or rear) track interface means deforms so that the opposite end of the roller track member  112  can be snapped into the opposite end of the shelf frame  12 . 
     Retrofit Version for Existing Cantilevered Gondola-Type Shelving 
     It will be further appreciated that the indexable shelf of the present invention is not limited to use with new shelf systems having vertical shelf supports  18 ,  20 ,  22 ,  24  as shown in FIG.  1 . Instead, the present invention may be used as a retrofit for existing shelving systems. For example, existing cantilevered, or so-called “gondola”-type retail shelving can be set on an incline, if so desired, and adapted to include the resilient front and rear track interface means of the present invention. Track members may then be installed at desired transverse locations and easily removed and repositioned to adjust the track column width for the gondola-type shelving. 
     As shown in FIGS. 11-13, an existing conventional cantilevered gondola-type shelf  120  has a shelf surface  122  with a front edge  124  and a rear edge  126 . An elongated rear flange  128  extends downwardly from the rear edge  126  a short distance, spanning the entire rear of the shelf  120 . The shelf  120  includes two side legs  130 ,  132 , having rear ends  134 ,  136 , respectively. A plurality of integral adjustable mounting brackets  138 ,  140 ,  142 ,  144  extend rearwardly of the rear ends  134 ,  136 , each including several teeth  146  used to latch the shelf  120  onto a pair of grooved mounting rails  148  mounted on a wall for conventional height-adjustable shelving. 
     Normally, the shelf  120  is mounted by directly aligning the teeth  146  of each mounting bracket  138 - 144  placed in the grooves of the mounting rails  148 , to ensure the shelf surface  22  lies in a horizontal plane. However, by intentionally staggering the teeth  146  of the mounting brackets, as shown in FIGS. 12 and 13, i.e., by using more rearwardly-disposed teeth on the upper adjustable mounting brackets  138 ,  140  and closer (i.e., more-forward) teeth on the lower adjustable mounting brackets  142 ,  144 , the shelf  120  can advantageously be securely mounted with the shelf surface  122  lying in an inclined plane, making an angle a with the horizontal. 
     Advantageously, the inclined mounting of the shelf  120  provides a gap  150  between the rear edge  126  of the shelf surface  122  and the vertical wall to which the grooved mounting rails  148  are fixed. This gap  150  allows for the insertion of an adapter means including one or more J-shaped hooks  152  at the rear edge  126  of the shelf surface  122  to grasp the rear flange  128 . The J-shaped hooks  152  are associated with front and rear track interface means  154 ,  156 . For example, the J-shaped hooks  152  may be integral extensions of elongated flat bar members  158  that are secured to, and extend between, L-shaped (in cross-section) front and rear rails  160 ,  162 . 
     Front and rear track interface means  154 ,  156  mount to the front and rear rails  160 ,  162  just as in the shelf frame  12  described previously. Each of the front and rear track interface means  154 ,  156  includes a curved resilient comb member  164 . The remaining details of the components and mode of operation of this retrofit version of our indexable gravity flow shelf are identical to the front and rear track interface means  68 ,  106  of the shelf frame  12  as described previously, and reference is made thereto. 
     While the present invention has been described with respect to particular preferred and alternate embodiments thereof, it is not intended to be limited thereto. Those of ordinary skill in the art will understand that variations can be made that are still within the scope of the following appended claims.