Chair accessory
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to chair accessories and in particular to an assembly for attaching a tray to a chair such as a lawn chair. 
     2. Description of Related Art 
     At a buffet party people may sit in a chair and eat and drink without a table. Consequently, eating and drinking becomes difficult without a free hand. This problem is especially acute at a lawn party where guests may be seated on a lawn chair. Therefore an accessory tray that can be attached to a chair is greatly needed. 
     Adaptability is an important design consideration for a tray accessory for a chair. Chairs, especially lawn chairs, can come in various sizes and may have a variety of interfering structure. An adaptable design can work around these variations. 
     U.S. Pat. No. 4,715,652 shows a stadium chair that clips onto a bench. This known seat has a pair of parallel runners with grooves that hold a sliding tray. This design is not adapted, however, to be mounted on 30 various types of chairs such as lawn chairs. 
     U.S. Pat. No. 4,556,250 shows a case that is secured to a seat by means of a sleeve. While the case 1 has a sliding tray, the sleeve is not useful for attaching the tray to a variety of chairs. For example, a lawn chair may have struts that connect from the side of the chair to an arm. That structure may prevent the sleeve from slipping around the chair. Moreover, this sleeve interferes with the seating surface and may require an additional cushion. 
     U.S. Pat. No. 2,755,845 shows a bracket for attaching a tray to a chair, but this structure requires a special type of chair seat which is not ordinarily present in familiar chairs as lawn chairs. 
     U.S. Pat. Nos. 2,244,459; 5,035,464 and 5,129,702 show various assemblies for attaching a tray to a chair. These assemblies, however, are either not adaptable and may be dedicated to a specific chair. See also U.S. Pat. Nos. 4,341,418 and 5,096,249. 
     SUMMARY OF THE INVENTION 
     In accordance with the illustrative embodiments demonstrating features and advantages of the present invention, there is provided an accessory for a seat of a chair. The accessory has an assembly with a pair of opposing grippers. The assembly is arranged for attachment underneath the seat of the chair. The grippers have an expandable separation to accommodate size variations in the seat of the chair. A tray is slidably mounted at the assembly for retracting underneath and extending beyond the seat of the chair. 
     By employing such structure, an improved chair accessory is achieved. In a preferred embodiment, two frames are slidably interconnected for adjusting the width of the assembly. By adjusting the width of the assembly, hooks mounted atop the assembly can be attached to various sizes of chairs. In the preferred embodiment, an elastic band or spring is attached between the two frames to urge them together to clamp the hooks onto the edges of the chair seat. 
     In this preferred embodiment, the two frames each have a support panel supporting a pair of channels having C-shaped cross-sections. The channels of the two frames slide together for adjusting the width of the 15 assembly. A tray is slidably mounted between the channels. In one constructed embodiment, the tray slides through a slot in one of the support panels and enters the groove of a smaller channel. With this nesting arrangement the tray fits a smaller channel and the smaller channel fits inside the larger channel. 
     Hooks are mounted on the two support panels. The top edge of the support panels are then canted so that the tray will remain horizontal even though the support panels are hooked onto the edge of a slanted chair seat. After the assembly is attached to the chair seat, the tray can be either extended or retracted, depending on whether the user needs the tray to hold food or drink. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above brief description, as well as other objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred, but nonetheless illustrative embodiments in accordance with the present invention, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is an axonometric view of a chair accessory in accordance with the principles of the present invention; 
     FIG. 2 is a view of a support for the accessory, taken along line 2--2 of FIG. 1; 
     FIG. 3 is an elevational view of another support for the accessory, taken along line 3--3 of FIG. 1; 
     FIG. 4 is a cross-sectional view of the accessory taken along line 4--4 FIG. 2; 
     FIG. 5 is detailed, exploded view of the joint at the lower left corner of FIG. 2 between the support and channel; 
     FIG. 6 is a detailed, sectional view of the channels, tray and strut, taken along line 6--6 of FIG. 1; 
     FIG. 7 is a detailed axonometric view of the joint between the channels in the accessory of FIG. 1; 
     FIG. 8 is an axonometric view showing the accessory of FIG. 1 attached to the seat of a chair. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-7, an accessory is shown having a first frame, comprising a first support 10 and primary braces 12 and 14. First support 10 may be a molded plastic panel that is 9 inches (22.9 cm) wide and with a height that varies from 2 to 2 3/4 inches (5 to 7 cm). It will be appreciated that the panel can be made of other materials and can be sized differently in other embodiments. Slot 16 is shown parallel to the bottom edge of support 10. 
     Braces 12 and 14 are shown as channels having C-shaped cross-sections. A brace having other than a C-shape may be considered a channel. For example, an H-shaped brace or other brace having a longitudinal concavity or track may be considered a channel. FIG. 5 shows the outside end of channel 14 fitting into a mortise 18 that communicates with slot 16. Channels 12 and 14 are secured to support 10 by gluing, heat sealing, or by other fastening means. The height of the opening 15 of channel 14 matches the height of the opening of slot 16. Accordingly, tray 16 can slide through slot 16 and into openings 13 and 15 of channels 12 and 14. Channels 12 and 14 are 3/4 inch (1.9 cm) tall and 1/2 inch (1.3 cm) wide. The openings 13 and 15 are about 1/4 inch (0.6 cm) tall. In other embodiments these dimensions can differ significantly. 
     Grippers in the form of hooks 26 and 28 are shown mounted at the top edge of support 10. Because the height of support 10 varies from end to end, the elevation of hooks 26 and 28 vary likewise. Hooks 26 and 28 may be metal stampings having a cylindrical upper end and planar lower end. The hooks 26 and 28 may be attached by gluing, riveting or by other fastening means. 
     A second frame is shown with a second support 20. Again, support 20 can be a molded plastic panel 9 with a length and height similar to support 10. The top edges of supports 10 and 20 are tilted in the same direction. Again, grippers, shown as hooks 30 and 32, are mounted to the top edge of support 20. Hooks 30 and 32 are fabricated and attached in the same way as previously mentioned hooks 26 and 28. 
     The lower corners on the inside face of support 20 are mortised to receive the outside ends of secondary braces, shown as channels 22 and 24. Channels 22 and 24 are 1 inch (2.5 cm) tall and 3/4 inch (1.9 cm) wide, although these dimensions can vary in other embodiments. 
     Channel 14 is shown slidably mounted inside channel 24. Similarly, channel 12 is slidably mounted inside channel 22. The spacing between channels 22 and 24 is fixed by strut 34, which is mounted atop the inside ends of those channels. In a similar fashion strut 35 is mounted in channels 12 and 14 at their inside ends. Struts 34 and 35 may be secured by gluing, nailing or other fastening means, as well as by being integrally molded. 
     Tray 36 is slidably mounted through slot 16 and into the openings 13 and 15 of channels 12 and 14. Tray 36 may be of various sizes but is shown here about 16 inches (40.6) long, 8 inches (20.3 cm) wide, and 1/4  inch (0.6 cm) thick. Tray 36 has a cup holder in the form of a hole 38 sized to receive a beverage glass, coffee container, or similar article. In some embodiments hole 38 may be replaced with a recess or an annular ridge designed to hold a cup without the need for an opening in the tray. 
     Tray 36 has a cantilever tab 40 pointing upwardly and toward support 10. Tab 40 is much like a section of material that has been peeled from the surface of tray 36. Tab 40 acts as a flexible locking device. Thus when tray 36 is passing through slot 16, tab 40 is depressed, but will spring back to the illustrated position when emerged from the slot. Once through slot 16, tab 40 prevents tray 36 from being pulled out again through slot 16. In some embodiments several reinforcing ribs (not shown) underlie and run the length of tray 36. In that case slot 16 will have matching slots to accommodate passage of the ribs. 
     The minimum spacing between supports 10 and 20 is about 16 inches (40.6 cm) when channels 12 and 14 are fully retracted into channels 22 and 24. The supports 10 and 20 can be pulled apart to expand this support to support spacing by about 7 inches (17.8 cm), although in some embodiments the range of expansion can be different. 
     Referring to FIGS. 6 and 7, previously illustrated channels 14 and 24 are shown telescopically interconnected. The outside vertical face of channel 14 is shown with a longitudinal, semicylindrical track 42. The inside vertical face of channel 24 is shown with a longitudinal, semicylindrical track 44. Tracks 42 and 44 together form a slender cylindrical cavity between channels 14 and 24 (although the tracks may be rectangular or shaped otherwise). 
     A yielding means is shown mounted inside cavity 46. Specifically, an elastic band 48 is stretched between pin 50 mounted in track 42 of channel 14 and pin 52 mounted in track 44 of channel 24. Consequently, elastic band 48 can draw channels 14 and 24 together to reduce the support to support spacing. A similarly set of tracks and elastic band is mounted in a cylindrical cavity between channels 12 and 22. In other embodiments, band 48 can be replaced with a spring. Alternatively, a spring may be connected directly between supports 10 and 20 or elsewhere. 
     In some embodiments channel 14 can be reversed with its opening facing the opening of channel 24. In this case the openings of both channels provide ample clearance for the retracting band 48 (or a retracting spring). Tray 36 can then be slidably mounted in a groove formed between two parallel ridges formed on the inside face of modified channel 14. 
     To facilitate an understanding of the principles associated with the foregoing apparatus, its operation will now be briefly described, in connection with FIG. 8 and the other Figures. The accessory of FIG. 1 can be grasped at supports 10 and 20 and pulled apart, to increase the spacing between the hooks 26, 28 and hooks 30, 32. With the hooks sufficiently separated, the accessory can be positioned underneath the seat S of chair C. The hooks are positioned at the right and left edges of seat S and then the supports 10 and 20 are released. 
     The tension in bands 48 (FIGS. 6 and 7) partially collapses channels 14 and 24, as well as channels 12 and 22. Consequently, supports 10 and 20 are drawn together so that hooks 26 and 28 are clamped securely to one edge of seat S while hooks 30 and 32 are clamped securely to the opposite edge. 
     If tray 36 is in the fully extended position shown in FIG. 8, the tray can hold dishes of food. Also, a glass or cup G can be inserted into cup holder 38. Because the upper edges of supports 10 and 20 are canted, the chair seat S may be tilted but the tray 36 will remain horizontal. 
     If tray 36 is not needed and glass G is removed, tray 36 can be pushed inwardly. Consequently, tray 36 slides through slot 16 and through the openings 13 and 15 of channels 12 and 14. Tray 36 cannot be pulled completely pulled out of support 10, however, because cantilever tab 40 hits the inside face of support 10 to prevent full removal (without special manipulation). 
     It is to be appreciated that various modifications may be implemented with respect to the above described, preferred embodiments. For example, the illustrated supports may be integral with the channels. In some embodiments, the channels will be bent to have a U-shaped longitudinal axis, with the hooks mounted directly onto the transverse length of the channel. Moreover, spring loaded gripping jaws may be used instead of hooks. Alternatively, the illustrated hooks may be replaced with gripping grooves formed directly on the supports. Also, in some embodiments the channels may be replaced with two boards that are held together with appropriate fasteners and slots to allow longitudinal expansion. Furthermore, in some embodiments the elastic band may be eliminated and the width of the accessory held by set screws or other clamping devices. While the illustrated embodiment employs primarily molded plastic parts, in other embodiments, metals, ceramics, wood or other materials may be used instead. Furthermore, the various dimensions may be altered depending upon the size of the intended chair or the desired size of the tray. 
     Obviously, certain modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.