Chair base

Abstract: A chair base comprises a central hub (10) around which are arranged parallel pairs of quarter sine wave shaped steel straps (16) which radiate outwardly in an equally spaced apart configuration. A caster socket block (20) is interposed in the space between the two straps of each pair thereof at an outer end (18). The central hub (10) and the caster sockets (20) are covered by plastic shells (34), and the exposed steel straps (16) are coated.

Description: This invention relates to a chair base for office chairs and the like, according to the generic part of claim 1. Various chair bases of the kind having support legs radiating from a central column or pedestal have long been employed for the support of office chairs and other pieces of furniture suitable for office and home alike. Such bases are popular because of their aesthetic qualities and adaptability for use with various tilt and swivel mechanisms. In the highly competitive furniture industry, it is desirable to provide chair bases that are highly durable, yet light in weight and relatively inexpensive to produce. One common type of chair base assembly employs a plurality of tubular members arranged about a central hub. Examples can be found in US-A-4,005,841 and in US-A-2 470 397. While such tubular chair bases may be light in weight, they lack the necessary strength, particularly in a direction lateral to the tubular member, which may be required in a modern office environment. Other types of chair base assemblies common in the art include a plurality of tapered legs disposed radially around a central hub and secured to the hub by welding. One example of such a chair base is disclosed in US-A-3 281 105. The leg elements and the central column in such bases are necessarily made of relatively heavy gauge material in order to sustain normal stresses and to prevent flexure and deformation of the legs, particularly in the area of the welded joints. Flanges are also frequently used to provide additional strength to the legs to prevent deformation. Such bases are generally durable, but are nevertheless heavy, and require more material in their construction thus increasing their cost and weight. Other welded joints have been proposed in US-A-3 682 425 and US-A-4 084 776 which address the problem of weaknesses introduced by welding. The proposed expedients, however, do not solve the problem of obtaining a highly durable chair base, using steel, for example, and simultaneously maintaining a relatively light weight and simple construction. US-A-2 311 875 describes a tilting swivel chair which has a supporting base. The supporting base includes legs which have the shape of a first quadrant one-quarter sine wave. The invention is defined in claim 1. Advantageous embodiments are defined in the dependent claims. According to the invention, a chair base of the type which has a central hub or column, a plurality of legs extending radially from the central hub, and means for mounting casters at the outer ends of the legs, is provided in which each of the legs is formed from a pair of straps spaced apart in a parallel configuration open at the top and bottom thereof. Each of the straps has a shape conforming generally to a first quadrant one-quarter sine wave with one end of the strap secured to an upper portion of the column. The mounting of the straps at an upper portion of the hub provides greater stability and strength to the chair base than if the legs were mounted to a lower portion of the hub. The hub and the straps may be formed of ordinary carbon steel and welded together at the juncture thereof. The hub is preferably covered with a separate decorative plastic cover which is held in place by a C-clip. Further, the straps may be coated with a decorative coating, such as paint or a plastic material for protective purposes. The caster mounting means preferably comprise a socket block, typically made of metal and welded between each pair of straps. Desirably, a separate decorative cover is securely mounted to each of the socket blocks to provide a decorative and protective cover therefor. The chair base is of the type wherein the central hub is hollow and preferably cylindrical in configuration. A height-adjusting cylinder is preferably mounted within the hub and provided with a decorative cover. The invention provides a low-cost but very sturdy chair base, and one which is very attractive in appearance. The low cost and strength are derived from the use of ordinary steel which is joined by conventional welding techniques. The strength is further provided by mounting the straps to the upper portion of the hub without the use of bent tubing and the like. Rigid straps can be used for this purpose. The chair base is made decorative by the use of plastic coatings and coverings over the steel parts and weldments. The coatings and coverings are easily and inexpensively applied. Further, the coatings and covers can be of any color which has the advantage of complementing any color in the chair. Thus, the chair bases can be of various different colors as desired to complement the color of the upholstery or shell of the chair. The invention will now be described with reference to the accompanying drawings in which: Figure 1 is a partially exploded isometric view of a chair base according to the invention; Figure 2 is a top plan view of the chair base shown in Figure 1 with all but one of the decorative parts removed; Figure 3 is an elevational view of the chair base of Figures 1 and 2 taken along line 3-3 of Figure 2 with all but one of the legs removed for clarity; Figure 4 is a sectional view in elevation and taken through the central hub of the chair base of Figure 1 illustrating the interconnection of the parts; and Figure 5 is a sectional view in elevation and taken along line 5-5 of Figure 2. Referring first to Figure 1, the chair base comprises a steel hollow central hub 10 having an upper portion 12 and a lower end 14 around which are spaced a series of legs, each formed of a pair of steel straps 16. The hub is preferably cylindrical in shape, but may be any shape which is aesthetically pleasing to complement the entire chair design. The straps 16 are roughly shaped in the form of a quarter sine wave and are arranged in parallel pairs with each strap welded to the upper portion 12 of the central hub 10 such that the pairs extend radially outwardly in an equally spaced apart configuration. The straps 16 of each pair are thus not directly connected along their span, there being an open space between them. In the embodiment shown, they are arranged in five pairs to form five legs, but more or fewer pairs may be provided, depending upon the particular desired configuration of the chair base. As can be seen in Figure 3, the shape of the straps 16 is such that outer ends 18 of the straps 16 are lower than upper ends 19 thereof, and they extend downwardly below the plane of the lower end 14 of the central hub 10. Thus when weight is applied to the central hub, the force will be transferred laterally outwardly and downwardly through each pair of straps 16. Existing chair bases with straight legs radiating outwardly from a central hub tend to transfer the downward force in a shear direction transversely through the leg. The quarter sine wave shape of the straps 16 translates the downward force laterally across the span of the leg, thus permitting higher forces to be transmitted by a relatively thinner material. Further, the paired configuration tends to resist flexure of the straps, thus permitting the use of relatively thin straps and consequently lessening the cost of materials. Also, the chair base occupies less floor space to sustain a given load than existing chairs, and permits more space for freedom of foot movement underneath the chair. As shown in Figure 2, the outer end 18 of each pair of straps 16 mounts a caster socket block 20 interposed in the space between the two straps of each pair and preferably welded. A socket 22 in each caster socket block receives the spindle of a conventional caster, not shown. A smaller bore 23 parallels the socket 22 in each caster socket block, and is spaced inwardly of hole 22 with respect to the hub 10. An end plate 24 with a central aperture 26 covers the lower end 14 of the central hub 10. (See Figure 3.) Referring again to Figure 1, the central hub 10 may be internally dimensioned to receive, for example, a conventional pneumatic air cylinder mechanism 28 for height adjustment of a chair seat (not shown). Such chair seat forms no part of this invention. Alternatively, a conventional mechanical height adjustment mechanism (not shown) may be inserted into the central hub 10. The chair adjustment mechanism 28 further comprises a shaft 27 extending upwardly from the top thereof on which a chair seat may be mounted, and a stubshaft 29 extending from the bottom. A cap 30, preferably made of plastic, and having a central aperture 32 covers the top of the hub 10 and the shaft 27 of the chair adjustment mechanism 28 in order to protect the mechanism 28 and the hub 10 from abrasions and also to provide an aesthetic appearance. As shown in Figure 4, the cap 30 comprises a plug portion 31 dimensioned to fit snugly into the hollow interior of central hub 10. The central aperture 32 extending through the cap 30 is thus elongated, such that when the cap 30 is mounted on the hub 10, the shaft 27 of the chair adjustment mechanism 28 extends through the aperture 32 and is stabilized and supported thereby. The cap 30 also has an annular shoulder 33 which serves to limit movement of the cap 30 into the hub 10. An annular groove 40 on the shoulder 33 extends circumferentially around the cap, exterior to the hub 10, for a purpose to be described hereinafter. A cylindrical shell 34, also preferably of plastic, is open at an upper end thereof, and has a bottom 35 closing a lower end thereof to form a cup. A series of elongate slots 36 extends downwardly from the open end, through a longitudinal distance approximately equal to the length of the junction between each straps 16 and the hub 10. The shell 34 covers the central hub 10 from the bottom such that the straps 16 are received in slots 36, allowing the cylindrical shell 34 to cover the entire central hub 10 and to rest in juxtaposition to the cap 30. An upper rim 41 of the shell 34 is received in the groove 40 of the shoulder 33 to provide a secure connection between the cap 30 and the shell 34. The bottom 35 of the shell 34 has a centrally located aperture 37 through which the stubshaft 29 of the chair adjustment mechanism 28 extends. A fastener 38 such as a conventional C-clip mounts an annular groove 39 on the stubshaft 29 to retain the shell 34 on the hub 10, and also to secure the chair adjustment mechanism 28 in the hub 10. An annular rib 42 on the perimeter of the bottom 35 of the shell 34 extends downwardly and serves to conceal the C-clip 38 and contribute to the aesthetic appearance of the chair base. Caster socket covers 44, also preferably made of plastic, are dimensioned to cover the outer end 18 and caster socket 20 of each pair of straps 16 to provide protection from abrasions and also to enhance the appearance of the chair base. As can be seen in Figure 5, a finger 46 extends downwardly from the inside top of the caster socket cover 44 into the smaller hole 23 of the caster socket 20. A screw 48 inserted through hole 23 from the bottom and into the finger 46 secures the cover 44 in place. Covers 44 may be of any shape consistent with the overall appearance of the chair so long as each adequately covers the socket block 20. For example, the exterior of the cover may continue the lines of the straps 16. All decorative and protective plastic parts 30, 34, 44 may be colored to provide a pleasing and attractive appearance which will complement any chair seat mounted to the base. The steel straps 16 and the use of plastic covers 30, 34, 44 permit construction of the chair base at significantly less cost. The straps 16 may be stamped out and welded to the hub 10 without any secondary operations such as forming, coining, rounding, or similar finishing operations. The covers 30, 34, 44 conceal unsightly weldments. The straps 16 are also coated with a suitable protective coating such as paint or vinyl. Preferably, the straps 16 are dipped in plastisol to obtain a significant thickness of coating, greater than would be provided by with paint. The coating may be coloured to complement the overall color scheme of the chair. It can readily be seen that the invention described herein provides a highly durable chair base which is relatively light in weight while maintaining a high degree of stability and strength. The simple, conventional materials and simplified construction permit a substantial savings in material and labor costs, and also allow flexibility in choosing aesthetically pleasing and novel designs.

Claims: A chair base comprising a central hub (10), a plurality of legs (16) fixed to said central hub (10) and extending radially therefrom, and means (20) for mounting a caster at an outer end (18) of each of said legs (16), characterized in that each of said legs (16) are formed from a pair of straps (16) spaced apart in a parallel configuration, each of said legs (16) being open at top and bottom portions thereof, that each of said straps (16) has a shape conforming generally to a first quadrant one-quarter sine wave, an inner end (19) of said strap (16) being secured to an upper portion (12) of said hub (10) and that said legs (16) are welded to said central hub (10). A chair base according to claim 1, characterized in that said base further comprises a separate cover (34) enclosing said central hub (10), and means (38) for mounting said cover (34) to said hub (10). A chair base according to claim 2, characterized in that said cover (34) has a bottom (35) with an annular rib (42) at a perimeter thereof which extends downwardly to at least partially conceal said cover mounting means (38). A chair base according to any of claims 1 to 3, characterized in that each of said caster mounting means (20) comprises a socket block (20) secured between the two straps (16) of each pair of straps (16) at a lower end (18) thereof. A chair base according to claim 4, characterized in that each of said socket blocks (20) is welded between the two straps (16) of each pair of straps (16). A chair base according to claim 4 or 5, characterized in that said straps (16) are steel and each of said socket blocks (20) is welded to the two straps (16) of each pair of straps (16), said central hub (10) is steel and said straps (16) are welded to said central hub (10). A chair base according to any of the foregoing claims, characterized in that said straps (16) are steel, said caster mounting means (20) are steel socket blocks (20), one of which is welded between the two straps (16) of each pair of straps (16), said central hub (10) is steel and said straps (16) are welded to said central hub.

Inventors: EDWARDS THOMAS M, NAGELKIRK ROBERT A, EDWARDS, THOMAS M., NAGELKIRK, ROBERT A.
Applicants: MILLER HERMAN INC, HERMAN MILLER, INC.
Application year: 1989
Main classification: A47C7
IPC codes: A47C7