Membrane Support for Seating

Field of the Invention

This invention relates to an improved chair, and in particular to an improved frame for a "stretched membrane" type chair and to a method of manufacture of the same.

Background of the Invention

Until recently, most chairs/seating whether for office, commercial or domestic use, typically comprise a rigid frame on top of which a seat and backrest are supported and which are often upholstered for additional comfort. In the manufacturing process for such seating, the frame is typically constructed and assembled first as a rigid frame and the seat and back support are simply fixed to the rigid frame by bolting or other suitable fastening means. Such traditional seating has drawbacks in terms of weight, which is particularly important when providing commercial seating for transport applications. Also the foam fills of the upholstery are often highly toxic and flammable and are manufactured by environmentally unfriendly processes.

More recently, it has been common to manufacture seating in which instead of the frame simply supporting upholstery, as in traditional seating, the frame carries a stretched membrane under tension. In order to carry the membrane and retain it in a stretched condition, such frames have to have different attributes to a traditional seating frames. With improvements in membrane technology, and in particular in stretchable membranes, seating incorporating stretch membranes is becoming increasingly popular. One reason for this increased popularity is that such seating provides a considerable degree of comfort for the user, as the membranes tend to follow and support the body of the person on the seating whilst at the same time, being relatively cost effective to manufacture, particularly in terms of economic use of materials. Such seating can be manufactured with the membrane itself, providing the seat area on which a user sits and the integral back support, often with double or triple layers of membrane or other fabrics in the seat area. Although unnecessary, for additional comfort, a layer of padding/upholstery may be provided on top of the membrane, although typically this layer can be thinner than that used on traditional seating.

Such seating may be manufactured by attaching a cylindrical bead to both sides of a sheet of membrane which is to be stretched to form the seat's surface, pulling each cylindrical bead through a respective elongate generally tubular channel in each opposed side frame of the chair, stretching the side frames apart in order to tension the

membrane, and applying front and back cross-pieces to the ends of the side frame to complete the frame and maintain the fabric in a stretched condition.

The existing method has a number of drawbacks. In particular, in use, it is extremely difficult to pull the beads through the tubular channels in the side frames, particularly where the fabric includes an additional layer of material such as is commonly provided in the seat portion, which results in a double thickness of material passing around the bead, being fitted into a tubular channel sized for a thinner bead/membrane combination. Also, although it is possible to apply lateral stretch to the seat using this method, it is difficult to satisfactorily apply and longitudinal stretch from the front to the back of the chair. Further, at the corners where the cross pieces attach to the side frames, bunching of the membrane tends to occur which is untidy and this generally necessities the provision of a cover for the top and front of the chair, for ascetic reasons, which increases costs.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Summary of the Invention

In a first aspect, the present invention provides a method of making a seating structure comprising a frame and a membrane supported on the frame under tension, comprising the steps of: providing a pair of side frames, each side frame defining a front face, a rear face which defines at least one open channel, and a, preferably generally smooth curved, outer edge portion joining the front and rear faces; providing a sheet of membrane formed to define a tubular portion extending along each side edge wherein a bead formed from a plastics material is located in each tube defined along the opposed side edges of the sheet, the bead being slidable in the tube, wherein in cross-section, the beads are relatively longer in a first longitudinal dimension than a perpendicular transverse dimension; inserting the beads in the open channels along the rear face of both side frames frame and membrane with the longitudinal axis of the bead directed into the channel; and

moving the side frames apart to tension the membrane, the arrangement being such that tension in the membrane is prevented from causing the bead to come out from the open channel by the relative length of the bead and the shape of the channel.

Typically tension tends to cause the bead to rotate about the outer edge of the opening of the channel and a protrusion or other structure is define in the channel to resist such rotation.

Because of the shape of the bead and channel, and the fact that tension applied to the bead tends to cause the bead to rotate rather than be pulled out in the direction of the applied tension, the bead can be a relatively loose fit in the channel and this allows for ease of insertion of the bead in the channel even where several layers of membrane are used and wrapped around the bead.

The bead is preferably at least twice as long in cross section is its longitudinal dimension that in its lateral dimension.

In a preferred embodiment, the bead is heated before being inserted in the channel to allow it to deform sufficiently to match the contour of the side frame.

Typically the side frames are moved apart on a hydraulic jig.

Longitudinal tension may be applied to the membrane by proving beads extending along the front and rear edges of the membrane, inserting them in cross- pieces and turning the cross-pieces through 180°. The bead is preferably formed from a relatively rigid grade of PVC.

Typically, the bead has a rectangular cross-section.

The present invention also encompasses a chairs incorporating a seating structure made by the method of the present invention.

The present invention also encompasses an extrusion for forming a side frame or cross piece of a chair embodying the present invention.

Brief Description of the Drawings

A specific example of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Figure 1 is a cross section through an extruded aluminium alloy section which forms a side frame and cross-pieces of a frame for seating embodying the invention;

Figure 2 shows the section after a flat PVC bead has been inserted into a profiled slot in the section to secure a membrane to the frame;

Figure 3 is a schematic drawing illustrating the membrane tensioning process; Figure 4 illustrates a corner piece connection between a side frame and a cross- piece;

Figure 5 illustrates a cover for the corner piece connection; Figure 6 shows an assembled seat frame without the stretched membrane; and Figure 7 is a close up view of the top of a chair illustrating the application of longitudinal tension is applied to the membrane; and

Detailed Description of Preferred Embodiments.

Referring to the drawings, Figure 1 shows a cross section through an aluminium alloy extrusion/section used to form the side frame 12 and front and back cross-pieces of seating incorporating an elastomeric seat membrane 14. As shown in Figure 1 the extrusion defines a relatively wider first or outer edge portion 16 which forms a smooth curve. The extrusion tapers from the outer edge along two sides 18, 20 to a relatively narrower second or inner edge 22. The extrusion defines a closed channel 23, adjacent the inner edge 22 and two open channels 24 and 26 both defining openings in the same edge 20. One channel 24 is defined at the outer edge 16. The other channel 26 is located in between that channel 24 and the closed channel 23.

Channel 26 has a part-circular cross-section and an opening which is initially narrower than the diameter of the part-circular portion but which flares outwardly.

Channel 24 defines a semi circular portion 28 (having a radius of 7.5mm) adjacent the outer edge 16 and a corner 29 and a wall portion 30 which extends generally radially towards a centre of the semi- circular portion where a protruding rib 32 is defined. A second curved portion 34 (having a radius of 5.5mm) extends from the rib 32 to the opening of the channel. The width w of the opening of the channel is about 7.8mm. Figure 4 illustrates a corner piece 50 which used to connect a side frame 52 and a cross-piece 54 formed from extrusions as described above. The corner piece defines two perpendicular grommets 56, 58 for receiving self tapping screws 60 which locate in the channels 26 of the side frame and a cross-piece respectively for holding the frame components together. It is to be noted that the side wall of the corner piece includes an outer wall 61 which bends through 90° and includes a curved lowered portion 62 in the centre of the bend where the wall height is lower which assists in providing a neat finish to the seating as will be described later. Lowered portion 62 is also visible in Figure 5 which also shows a cover 64 for the corner piece. In order to achieve proper support, elastomeric seat membranes must be tensioned. As relatively high forces are required for this, hydraulic jigs are used. The

support frame must be relatively strong and resist lateral as well as longitudinal forces. The frame of the present invention is thus made from an aluminium alloy which can be bent to the desired seat profile suitable for forming the side frame of a seat without losing strength. The actual curve of the side frames 80 is not critical to the invention. Typically there will be a gently convex curved seat portion, a 90° bend, and a convex back portion, defining a lumbar support at the apex of the curve.

The application of a membrane between two side frames 80 will best be understood by reference to Figures 2 and 3, and 7. The method uses a length of flat rectangular PVC bead 100 measuring 4 x 13mm. A rectangular piece of membrane is cut to predetermined size taking account the size of the seat frame and the degree of stretch to be applied. The bead 100 is sewn into the side edges of the membrane with the membrane passing around the bead and being stitched to itself to form a tube 101 in which the bead locates to retain the bead along the edge of the membrane. The bead is substantially the same length as the side of the membrane and the side frame of the seat and extends along the entire side length of the membrane on both sides. The bead 100 is not fixed to the membrane but may slide along the tube 101. The bead is preferably made from a grade which is very close to rigid, although any grade from semi-rigid to rigid would typically work.

Different membranes may be used for different applications. One membrane which is particularly suitable for outdoor use in full sun is a membrane sold under the "Synthesis" "Aspire" name by Gale Pacific Limited of Braeside, Victoria, Australia. For indoor use an elastomeric membrane is preferred such as that made by Matrex (a division of Leggett & Platt) of 911 Northridge St Greensboro, NC 27403, USA.

A length of bead is also sewn into the top and bottom edges of the membrane in a similar manner to the side edges. The bead is first heated in a hot box to allow it to be deformed sufficiently to follow the contours of the curved side frame 80 (best seen in Figure 6). The front and rear beads do not have to be heated, as the cross-pieces 82, 84 are straight. The rectangular bead in simply inserted in the channel 26 as shown in Figures 2 and 3. Once the rectangular bead has been inserted into both of the side frames located in the hydraulic jig in a parallel spaced apart arrangement, the hydraulic jig moves the side frames apart, applying a force F typically stretching the membrane by around 5 to 7%. When this force is applied tension T is applied to the membrane, it tends to pull at the corner of the bead 100 illustrated by the arrow "A" shown in Figure 2. The tension force applied bead has the effect of causing the bead to tend to rotate in a clockwise direction about point "A" illustrated by the arrow "C" in Figure 2. However, it is prevented from doing so by the protrusion 32. Thus the bead remains

inside the channel 24. When the bead 100 cools to a normal temperature, it retains the shape of the side frame 80 and the fact that the bead is then curved to match the shape of the side frame, also assists in retaining the bead 100 inside the frame in the long term. The pre-heating of the bead allows the membrane to be sewn to the bead in a straight format, and the bead does not have to be pre-curved to match the shape of the side frame.

The fastening system with the relatively wide opening w also allows for the build up of a number of layers of fabric around the bead without creating an application problem in terms of inserting the bead into the aperture. In order for the method to function, it is important that the PVC is relatively hard and should be as close as possible to rigid grade without actually being rigid. The bead needs to be soft enough to deform to the contour of the side frame when heated but needs to be rigid enough to resist severe deformation when the force is applied at corner A when stretching the membrane. Once the side frames are in place on the hydraulic jig and under tension, the front 84 and rear 82 cross rails are applied using the corner pieces as described above and to form the finished seating frame 86 and membrane assembly. Figure 6 shows the frame without the membrane to better show the frame per se. In this step, with reference to Figure 5, in order to apply longitudinal tension in the membrane in addition to lateral tension, the beading is inserted into the front and rear cross-pieces 82 to corner pieces 50 are attached and the cross pieces rotated through 180° prior to being fixed using self tapping screws passing through a grommet 58 of the corner piece into the channels 26 of the side frame.

The channel 26 may also be used for fixing the seating frame assembly to a structural underframe.

With reference to Figure 3 the overall shape of the membrane support frame, where an angle α of the order of 5 to 15° is defined between the side 18 and the membrane allows the membrane to float away from the frame as soon as it comes around from the outside and over the rounded top of the frame. This floating affect achieves a longer free span and therefore increases the elastomeric qualities of the membrane without widening the seat.

With reference to Figures 4 and 5, the lowered portion 62 of the side wall of the corner piece allows the fabric to be tucked neatly into the corner piece without wrinkles. The seating of the present invention may be utilised in a wide variety of applications depending on the base attachment attached to the seat frame. For example,

the seats may be supported on floor or deck bolted beams, self stabilising beams, and side frames which may be either bolted to the floor or free standing on leg supports, wheels or any other type of suitable support and base attachment. Applications for this seating may include, but is not limited to, marine seating such as seats for fast ferries, marine seating for pleasure crafts, seating for airport lounges and terminals, coach and bus seating, office seating, railway seating, demounted auditorium and theatre seating, aircraft seating, seating for the healthcare industry, domestic outdoor or indoor seating.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. For example, the specific dimensions provided may be varied. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.