Folding Chair Frame

Abstract

A compactly foldable chair frame designed to receive a fabric, leather or similar cover-seat, comprising eight multiple-hinged rod elements and having an offset side-hinge feature which provides optimum geometry for comfortable upright seating at desks and tables, and a double bend feature at the upper hinged joints which permits a high degree of compactness when folded.

Description

Chairs of the type sometimes known as "butterfly chairs" constructed of rigid rods bent to shape, footed at four lower bends and having fabric or leather cover-seats pocketed to the rods at four upper bends have been available since the early 1950's. Later improvements in this type of chair incorporated hinged joints for some degree of foldability.

In general the butterfly-type chair places the user in somewhat of a reclining posture while seated and usually makes for some degree of awkwardness in the placement of the user's legs, if not for leg discomfort. Furthermore, greater space is required for butterfly chair seating than for conventional seating. For these reasons the butterfly chair is primarily in the catagory of casual furniture, suitable mainly for lounges, patios, etc., but not suitable for upright seating, such as at tables or desks.

Although foldability was considerately improved by the collapsible version of R. W. Boucher, U.S. Pat. No. 2,691,410, issued Oct. 12, 1954, some degree of compactness was still lacking.

Consequently, it is an object of this invention to provide an improved folding mechanism wherein the chair frame collapses very tightly making for the ultimate in compactness, so as to offer greater ease of transport and storage.

Another object of this invention is to provide a chair of the "butterfly" design but with improved upright seating geometry suitable for the use at desks and tables as well as for casual seating.

Another object is to provide a cloth seated chair that is more comfortable and less awkward to sit in, and which requires less floor area for seating.

Another object of this invention is to provide a chair that is attractive and suitable for use in a variety of indoor or outdoor environments.

Another object is to provide a chair that is light in weight, simple in construction and low in cost.

Other objects and advantages will become more apparent from the following description taken together with the drawings of a preferred embodiment, in which:

FIG. 1 is a perspective view of the entire chair frame.

FIG. 2 is a front view of the chair frame in a nearly folded condition.

FIG. 2a is a partial view of one upper hinged joint to illustrate tightness of foldability.

FIG. 3 is a partial auxiliary view of the front-right hinged foot of the frame, with phantom lines illustrating the folded condition.

FIG. 4 is a cross-sectional view of the hinge-foot of FIG. 3.

FIG. 5 is a bottom view of the hinge-foot.

FIG. 6 is a partial side view of the chair frame in the open and closed (phantom lines) conditions to illustrate geometrical requirements for tight folding.

Referring to FIG. 1, 2, and 2a, front rods 11 and 12 are hinged at intermediate pivot point 13 located at the crossing point of their respective centerlines. Side rods 14 and 15, and 16 and 17 are hinged at intermediate pivot points 18 and 19, respectively. Back rods 20 and 21 are hinged at intermediate pivot point 22 located at the crossing point of their respective centerlines.

Front rods 11 and 12 are also hinged at their upper ends to the upper ends of side rods 15 and 17, respectively, at pivot points 23 and 24, respectively. Back rods 20 and 21 are also hinged at their upper ends to the upper ends of side rods 14 and 16, respectively, at pivot points 25 and 26, respectively.

Front rods 11 and 12 are also connected and hinged at their lower ends to the lower ends of side rods 16 and 14, respectively, by means of hinge-feet 27 and 28, respectively. Back rods 20 and 21 are also connected and hinged at their lower ends to the lower ends of side rods 17 and 15, respectively, by means of hinge-feet 29 and 30, respectively.

FIG. 2 illustrates generally the mode of folding of the chair frame of this invention as it approaches the folded condition. Top hinges 23, 24, 25, and 26, intermediate hinges 13, 18, 19, and 22 and hinge feet 27, 28, 29, and 30 maintain the similarity of geometry while all of the eight rods become more parallel in their alignment, approaching the substantially parallel alignment of the fully closed frame.

In the particular embodiment illustrated, front rods 11 and 12 and their respective top-hinged side rods 15 and 17 are the four shorter rods of the eight rods comprising the chair frame elements. All eight rods have a double bend at their upper ends, for example, bent portions 16' and 21' at the upper ends of the rods 16 and 21, respectively. Portions 16' and 21' bend over to nearly the horizontal as they join at hinge 26. Dimension d.sub.1 of FIG. 1, which is the widest measurement across bends 16 and 21 at joint 26 with frame fully open, collapses to smaller dimension d.sub.2 (FIG. 2a ) when the frame is folded fully.

In the open condition, the double bend design presents a wide rod spread to distribute seat fabric loading. Yet in the folded condition, high compactness is achieved with rods 16 and 21 becoming substantially parallel. Note that the center of hinge 26 lies along a straight line parallel to and closely adjacent to rods 16 and 21, as shown in FIG. 2a.

Lugged clip 31 acts as a stop to limit the degree to which the frame may open. Cover-seat 32, shown in phantom lines, fits over the chair frame at hinged connections 23, 24, 25 and 26. Seat 32 may be made of fabric, leather, or other sheet material. It is shown here as a related part of the folding chair of this invention, but is not specified in detail herein since it is not directly a part of the frame.

Referring to FIG. 3, hinge-foot 28 (typical of all) has sockets 33 and 34 in which are anchored lower ends of front rod 12 and side rod 14, respectively. Phantom lines show the hinge-foot in folded condition. Web portion 35 joins sockets 33 and 34 together and acts as a flexure hinge, the essential element of this hinge-foot component. Flexibility of the web may be achieved by molding the hinge-feet of a material which has sufficient strength & stiffness to form a solid connection, yet which will bend repeatedly without cracking or breaking.

Many rubberoid and plastic materials are known to have such a resistance to stress-cracking. Materials which have this property to a superior degree are considered to be "self-hingeable." Two excellent examples are polypropylene and polyallomer, both readily molded thermoplastic materials. Accordingly either would be suitable for this hinge-foot.

The specific features of this hinge-foot are being claimed as part of my co-pending application Ser. No. 405,474, filed Oct. 11, 1973, but are not being directly claimed herein.

Referring to FIG. 6, pivot point 18 is spaced substantially to the rear (dimension "O") from side rods 14 and 15 by means of offset hinge plates 36 and 37, respectively, welded to the rods and thereby forming the right side hinged connection. The connection on the left side is similar in geometry and construction. Offset "O" is equal for both plate 36 and plate 37.

It has been determined that folding chair frames of this type will not have a tight-folding capability unless the side pivot points lie at the vertex of an isosceles triangle, with the two side feet located substantially at the ends of its base. Using FIG. 6 as an example, side pivot point 18 thus must coincide with vertex C of the isosceles triangle A-B-C, wherein A and B are located at feet 28 and 30, respectively, and A-C and B-C are the equal sides.

A second requirement for tight foldability is that the front and rear pivot points, 13 and 22, respectively, must lie at the crossing point of the respective centerlines of the crossing rod elements.

Moreover, it has been determined that if the side pivot point 18 is located at the point C of the isosceles triangle, but on the intersection of the centerlines of rods 14 and 15 rather than being offset, the dimension from point 23 to 24 (FIG. 1) will be to the dimension from point 25 to 26 in proportion as the length of the short rods is to the length of the long rods. Similarly the frame will have considerable backward lean. These characteristics are unobjectionable in the conventional butterfly design for lounge and casual furniture use, but render the frame design unsuitable for upright seating.

Thus, in addition to the isosceles triangle requirement for points 18, 28, and 30, a requirement of major significance in the design of the frame of this invention is that a substantial offset "O" to the rear be provided by means of hinge plates 36 and 37. Proper proportioning of offset "O" in relation to the other chair dimensions renders the frame of this invention suitable for upright seating, fullfilling an important object previously specified.

Other embodiments of this invention employing identical or basically similar principles may be devised within the scope of the claims. Those skilled in the art will readily see that a variety of other such embodiments can be devised without departure from the principles set forth. Thus it will be understood that this invention is not limited to the specific construction shown and described except as so provided in the following claims.

Claims

I claim:

1. In a folding frame of the type described having four pairs of rod elements in crossing relationship at the front, rear, right side, and left side of the frame respectively, and wherein the top end of each rod element is mutually hinged with another top end to form four upper hinged joints, and wherein the bottom end of each rod element is mutually hinged to another bottom end to form four lower hinged joints, the improvement comprising:

two pairs of offset arms, one pair for the right-side pair of crossing rod elements, and the other pair for the left-side pair of crossing rod elements;

each offset arm fastened to a different rod element adjacent to its respective region of crossing;

each pair of offset arms forming a pivotal connection between crossing rod elements;

the pivot centers of both of said pivotal connections spaced away from and to the rear of the respective region of crossing;

both said pivot centers located substantially at the vertex of an isosceles triangle coplanar with the respective pair of the crossing rod elements, and whose base extends substantially from the lower end of one rod element to the lower end of the other rod element of the pair;

pivotal connections for the front and rear pairs of crossing rod elements having pivot centers located substantially at the respective points of crossing of said pairs.

2. A frame according to claim 1 additionally comprising:

a gradual bend at the top of each rod element starting immediately adjacent to each upper hinged joint;

a second bend in the opposite direction to the first bend and adjacent to the first bend;

said bends both lying in the same plane with respect to each rod;

the sum of the two bends being such that the pivot point of each hinged joint lies along a straightline parallel to and closely adjacent to the centerline of each respective rod.

3. A frame according to claim 1 additionally comprising:

a separate stop means having abutments upon which a pair of said crossing rod elements seat when said rod elements are in a predetermined angular relation;

said stop means insertable between a pair of crossing rods whose pivot center is located substantially at the crossing point of said pair.