The invention relates to base structures capable of supporting a mass over a support surface, and more particularly to adaptive tension-compression base structures capable of holding a preferred orientation over irregular terrain.
The term “tensegrity” was originally coined by futurist designer and inventor R. Buckminster Fuller in the 1960s to describe systems of tension elements (e.g., ropes, cables, or cords) and compression elements (e.g. bars, rods, tubes, or other rigid strut-type components) held in a state of static pre-stressed equilibrium to define a three-dimensional frame structure, wherein the compression elements generally do not touch each other. The pulling forces applied by the tension elements are resisted by the rigid compression elements, and a tensegrity system remains stable even against externally applied forces. The word “tensegrity” itself combines “tension” and “structural integrity.” Fuller's U.S. Pat. No. 3,063,521 (filed in 1959 and issued in 1962) covers various basic tensegrity concepts, and Fuller and others have patented many variations since then.
When properly designed and constructed, tensegrity structures have proven to be robust and durable. Pioneering sculptor Kenneth Snelson's well-known “Needle Tower” sculpture, constructed of metal tubes and wire, has stood outdoors at the Hirshhorn Museum in Washington, D.C. for decades. Tensegrity structures can be suitable for furniture as well. A line of tensegrity sitting stools named after Snelson is offered by designer Sam Weller (samweller.co.uk).
The tensegrity concept has been well developed and used frequently in the decades since the 1960s (and even before then, as some structures—including the London Skylon tower dating from 1951—employed some tensegrity principles even before the term was coined). Tensegrity is capable of enabling lightweight but robust structures combined with artful design; there are many designs for furniture, bridges, buildings, sports stadiums, toys, and other structures—large and small—that employ tensegrity principles.
But for all their benefits, most tensegrity structures remain rigid and poorly adapted to use upon irregular surfaces. The pre-stressed balance between tension and compression provides little freedom for movement. Because of this, tensegrity furniture is not often suitable for use outdoors. The Snelson stools referenced above, for example, remain flat and balanced only on a flat floor; on an inclined surface the entire structure including the seating surface will also be inclined and vulnerable to tipping over, and on an irregular surface the legs of the stool will wobble. This, unfortunately, also holds true for many other pieces of tensegrity furniture.
Accordingly, there is a need for an adaptive tension-compression structure based on tensegrity principles but more capable of being used on inclined and irregular surfaces. Such a structure would be easily adjustable to various support surfaces and yet remain strong and stable as furniture or as a base for equipment or other objects.
An adaptive tension-compression structure according to Applicant's invention addresses some of the shortcomings of prior tensegrity structures described above.
Like many of these prior structures, the basic form of a tension-compression structure according to the invention is a tensegrity prism—in its simplest form, three compression elements held together with tension elements in a shape that resembles a twisted triangular prism. However, the present tension-compression structure includes a slidably adjustable path for the tension elements holding the compression elements together. The sliding adjustability of the tension elements provides additional compliance (in the circumferential direction) for the structure while maintaining its basic geometry, thereby providing a stable base for furniture or any other suitable structure—including but not limited to equipment that may be desirably held in a preferred orientation over a variable or irregular surface.
A tension-compression structure according to the invention may also be employed as a base for “active seating” furniture on a level surface or an irregular surface. The slidably adjustable tension elements allows a structure according to the invention to rock somewhat, subject to the user's control, encouraging some muscle activity to keep the structure (such as a stool) in a preferred position.
In an embodiment of a tension-compression structure according to the invention, the compression elements are hollow tubes that serve as pathways for the tension elements. However, in an alternative embodiment, the tension elements may also be provided with pathways adjacent to the compression elements.
In several possible embodiments of the invention the tension-compression structure is collapsible for storage or transportation. In one embodiment, one of the compression elements is axially collapsible via a spring-biased detent (or another suitable locking mechanism), thereby releasing the pre-stress on the system and enabling the structure to be broken down into a bundle of parallel legs (with some flexible parts folded therein). In another embodiment, a connector integrated into a tension element may be disconnected, thereby once again enabling the structure to be collapsed into a bundle.
With the present tension-compression structure in an uncollapsed state, when weight is applied, constraints applied by an upper platform and a lower set of tension segments prevent the structure from losing its integrity, while the sliding tensegrity tension elements accommodate surface irregularities until a stable position is reached.
Accordingly, then, a number of disadvantages of other known tensegrity support structures—particularly their shortcomings on irregular terrain and their inability to be collapsed for storage or portability—are addressed by the tension-compression structures of the invention.
These and other objects, features, and advantages of the invention will become apparent from the detailed description below and the accompanying drawings, in which:
The invention is described below, with reference to detailed illustrative embodiments. It will be apparent that a tension-compression base structure according to the invention may be embodied in a wide variety of forms. Consequently, the specific structural and functional details disclosed herein are representative and do not limit the scope of the invention.
The stool 110 of
In the illustrated embodiment, the compression elements, or legs 112, 114, and 116, are fabricated from tubes of a suitably strong metal, such as steel, though other materials may of course be used. This tubular construction enables a lightweight structure. Feet may be provided at the lower ends of the legs to provide good frictional contact with the terrain; such feet may optionally be pivoting.
When tubes are used as the compression elements 112, 114, and 116, the tension elements 118 extending between the upper portions of each leg and the lower portion of adjacent legs may be formed from a single loop of rope or cable; this configuration will be discussed further in connection with
The tension-compression structure disclosed herein further includes a lower end constraint 134, which as illustrated includes a plurality of tension segments 136 (preferably flexible) fixably attached to the lower portion 126, 128, and 130 of each of the legs 112, 114, and 116 and joined at a junction 138 at a midpoint. Other embodiments of constraints are possible here; the lower end constraint 134 might take a triangular configuration (like the platform 132) or may be rigid in nature.
As shown in
When weight is applied, the legs 112, 114, and 116 of a tension-compression structure 110 according to the invention move outward at both top and bottom against the constraints (the upper platform 132 and the lower constraint segments 134), and individually move down and/or outward to meet the terrain. Once the legs 112, 114, and 116 are in position, the upper platform 132 can be adjusted to suit the user's needs or comfort.
The irregularity shown in
An article of furniture according to the invention, such as a stool, may also be employed for “active seating” on any suitable surface. The sliding adjustability of the tension elements in a structure according to the invention allows the structure to move and comply with shifts in a user's position or center of gravity, thereby encouraging some continuous use of the user's core muscles to maintain a desired position. Some users may find this desirable, particularly in an office setting or other circumstance that would otherwise be primarily sedentary.
As illustrated, one of the compression elements or legs 612, 614, and 616, is a telescoping leg 614 formed from two segments, an upper segment and a 640 lower segment 642. The upper segment 640 is slightly smaller in diameter than the lower segment 642, and hence, the upper segment 640 is capable of sliding axially into and out of the lower segment 642. To maintain the telescoping leg in its fully extended position, the upper segment is provided with a spring-biased pushbutton protrusion 644 at the lower end of the upper segment 640, configured to lock with a mating hole at an upper end of the lower segment 642. When the two segments 640 and 642 are so engaged, the protrusion extends through the hole in the lower segment and the two segments are kept in an extended configuration. To collapse the telescoping leg 614, the pushbutton 644 is depressed to disengage it from the hole, and the two segments 640 and 642 may then be slid together. This releases the tension on the tension elements 618, and allows the stool 610 of
The disconnectable tension element, in an embodiment of the invention, may take the form of a carabiner (on one end of the tension element 818) and loop (on the other end), or alternatively one of many different kinds of release mechanisms, including but not limited to plastic quick-disconnect clips, magnetic mechanisms, hooks, and many other possibilities. In an embodiment of the invention, the tension element 818 is not fully disconnected to collapse the structure, but is loosened sufficiently to allow the legs 812, 814, and 816 to move into a collapsed bundle 910 (
As discussed above in connection with
As shown in
As noted above, the tension elements traverse the structure inside each of the legs 112, 114, and 116 and outside the legs (and between adjacent legs). As the tension elements transition between inside and outside of the legs, it is considered advantageous to provide a smooth and non-abrasive surface for them to slide over. Accordingly, the legs may be provided with saddle structures 1030, either internal to the legs or at the openings where the tension elements enter or exit the tubular legs. Such saddle structures 1030 provide the ability for the tension elements 118 and compression elements 112, 114, and 116 to move with respect to each other, while ensuring the tension elements 118 do not tend to fray over the course of time. The saddle structures 1030 also provide sufficient friction to ensure the tension-compression structure remains in a desired orientation and position without undue adjustment while it is being used. A practitioner of ordinary skill will recognize, of course, that the saddle structures may be replaced with pulleys, wheels, or simply flanged entry/exit holes or lips as desired; there are many other possibilities.
It should be observed that while the present invention has been described as primarily a sitting stool, a tension-compression structure according to the invention may be used for numerous other applications other than stools. Other types of furniture (including broader chairs, tables, etc.), tables and other platforms, and equipment bases (substituting for a tripod, for example) may also be made according to the invention.
It should be observed that while the foregoing detailed description of various embodiments of the present invention is set forth in some detail, the invention is not limited to those details and a tension-compression structure made according to the invention can differ from the disclosed embodiments in numerous ways. In particular, it will be appreciated that embodiments of the present invention may be employed in differing applications and may be configured in various manners that may depart in some details from the exemplary details set forth above. It should be further noted that functional distinctions are made above for purposes of explanation and clarity; specific structural distinctions in an apparatus according to the invention may not be drawn along the same boundaries. Hence, the appropriate scope hereof is deemed to be in accordance with the claims as set forth below.
Number | Date | Country | |
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62009912 | Jun 2014 | US |