SPACE FRAME CONSTRUCTION SYSTEM

Abstract: The invention relates to a space frame construction system for three-dimensional positioning of reference points (1). The frame system comprises struts (3) in the form of tubular elements and nodes (2) in the form of spherical elements with a larger diameter than the diameter of the tubular elements, for joining struts. Each node is directly connected via struts to at least three other nodes and the struts (3) are connected to the nodes (2) by means of an adhesive. Each reference point (1) is mounted upon at least one respective node (2).

Description: TITLE Space frame construction system TECHNICAL FIELD The present invention relates to a space frame construction system for three-dimensional positioning of reference points, which frame comprises struts in the form of tubular elements and nodes in the form of spherical elements with a larger diameter than the diameter of the tubular elements, for joining struts. Also, the invention relates to a method for producing such a frame system. STATE OF THE ART Space frames for positioning reference points are used for example within the engineering industry for making fixtures. Such a use is for example measuring jig fixtures for measuring elastic (slender) details. One example of such details may be compression molded sheet metal pieces, which for instance are used within the automotive industry. Such a fixture forms a support for the sheet metal piece during measuring, which is often performed by a robot arm, to form a part of the quality control in an usually largely automatic manufacturing process. Because of this, high demands for precision and function are put on these fixtures, which means that they usually are expensive to manufacture. Fixtures are often manufactured by means of aluminum profiles, which are joined together by means of screw joints. This results in the possible presence of angle faults and inner strain in the construction. Normal temperature variations occurring through day and night may lead to that a measuring jig fixture is deformed so much that the quality of a product is affected. OBJECT OF THE INVENTION One object of the present invention is therefore to provide a space frame construction system and a method for producing it, which enables building the space frame rapidly and efficiently with a high degree of precision. Another object of the invention is that the space frame should not be appreciable affected by temperature variations. THE SOLUTION For this object, the space frame according to the invention is characterized in that each node is directly connected via struts to at least three other nodes, that the struts are connected to the nodes by means of an adhesive, and that each reference point is mounted upon at least one respective node. By this design of the space frame system a rigid construction is provided which can be easily erected. At the same time, each reference point will be completely integrated in the construction. Preferably, four adjacent nodes form a tetrahedron. In that case, a main tetrahedron may form a support structure for a number of smaller tetrahedrons. The adhesive may preferably consist of an epoxy resin. This solution results in bonds with a very high degree of strength. The tubular elements are preferably manufactured from a laminate of fiber reinforced thermosetting resin and the spherical elements may be manufactured from a plastic material. By this design of the space frame system according to the invention, it is not appreciable affected by temperature variations in the surroundings, or by the objects that will be carried by the space frame . A method for manufacturing a space frame according to the invention, for three-dimensional positioning of reference points, wherein a number of struts and nodes are joined, is characterized by cutting struts into exact lengths, mounting a base comprising three nodes and three struts at a distance from the reference points, assembling a base comprising three nodes and three strut elements at a distance from the reference points, and mounting additional nodes and strut elements, which bridge the distance between the base and the reference points, in such a way that each node is connected via beams to at least three other nodes, wherein the strut elements are connected to the nodes by gluing. According to this method, the space frame assembled easily and efficiently without a risk for the final result deviating from the intended. BRIEF DESCRIPTION OF THE DRAWINGS The invention will in the following be further described in a non- limiting way under reference to the accompanying drawing which shows a space frame system designed in accordance with the invention. DETAILED DESCRIPTION OF THE INVENTION The space frame shown in the figure forms an attachment for a number of at mutual distances from each other arranged reference points 1, each of which is mounted on a respective node 2 and is especially designed for cooperation with a not shown workpiece . Each node 2 is connected to at least three other nodes 2 via struts 3. The struts consist of tubular elements, while the nodes consist of spherical elements with a larger diameter than the diameter of the tubular elements. It is simple to establish the actual cut length a tubular element need to have in order for the center points of two spherical elements, which will be mounted at the two ends of the tubular element, to end up at a predetermined exact distance. Thus, the cut length L of the tubular element corresponds to the total distance D between the two spherical elements, subtracted by the radius R from the respective spherical element, and added by a trimming allowance M for each tube end, i.e. L = D - 2R + 2M. This trimming allowance depends upon the relationship between the inner diameter of the tubular element and the outer diameter of the sphere . It is a simple thing to design a three-dimensional model of the space frame by means of CAD-drawing with a computer. As soon as the trimming allowance M is known, it is simple to produce a list of the actual cut length of each tubular element 3 which is a part of the space frame. During the design of the three-dimensional computer model, regard is paid to the weight of the workpiece which will be carried by the fixture, so that no tubular element will be overloaded. The basic principle element of the design is a regular triangle or an unequal-sided triangle which is built up from three spherical elements 2 and three tubular elements 3. All relative distances and angles are decided by the lengths of the tubular elements. This basic triangle may then be built upon with further triangle elements, in the form of tetrahedrons, in any optional direction until the desired space frame has been achieved. In the example shown in the drawing, the different reference points 1 have first been established and they have been provided with nodes 2. Then these points have been interconnected in a suitable manner to form tetrahedrons via struts 3 and additional nodes, until each node is connected to at least three other nodes. In principle, the frame now forms a "space structure" which carries all the reference points 1. In the drawing, half the number of reference points have been omitted, in order to illustrate the space frame system more clearly. Finally, this "space structure" is connected in a suitable manner tetrahedronically with a base which is formed by a triangle, and which positions the reference points at the desirable height, for example above a floor. Various kinds of prior art anchoring means may be used to anchor the base triangle rigidly to the floor. The frame apparatus is built up rapidly and easily, by gluing the spherical elements to the ends of the tubular elements. The adhesive may be an epoxy resin type glue, which exhibits a very high strength and a short setting time. The building work follows a simple assembly instruction, without time time-consuming fine adjustment and positioning of single building elements. As soon as the setting time has been achieved for one node, it will be possible to use this point to build the next part of the frame. It has proven that it is possible to achieve the desired precision in the completed frame structure in this manner. A frame structure which does not exhibit any inner stress is obtained by means of the tetrahedron shaped basic design and the method of gluing. A very light and resistant frame structure is obtained by the use of a plastic material for the spherical elements and a fiber reinforced laminate of thermosetting resin for the tube elements, e.g. so called carbon fiber tubes. The invention is not limited to the above described embodiment, but several variants are imaginable within the scope of the following claims. For example, the struts do not have to be cylindrical. Other areas of use than measuring jig fixtures are imaginable for the space frame system, e.g. assembly fixtures.

Claims: CLAIMS 1. A space frame construction system for three-dimensional positioning of reference points (1) , which frame comprises struts (3) in the form of tubular elements and nodes (2) in the form of spherical elements with a larger diameter than the diameter of the tubular elements, for joining struts, c h a r a c t e r i z e d in that each node (2) is directly connected via struts to at least three other nodes, that the struts (3) are connected to the nodes (2) by means of an adhesive, and that each reference point (1) is mounted upon at least one respective node (2) . 2. A frame system according to claim 1, c h a r a c t e r i z e d in that four adjacent nodes (2) form a tetrahedron. 3. A frame system according to claim 2 , c h a r a c t e r i z e d in that a main tetrahedron forms a structural support for a number of smaller tetrahedrons. 4. A frame system according to any one of the preceding claims, c h a r a c t e r i z e d in that the adhesive consists of an epoxy resin. 5. A frame system according to any one of the preceding claims, c h a r a c t e r i z e d in that tubular elements (3) are manufactured from a laminate of fiber reinforced thermosetting resin. 6. A frame system according to any one of the preceding claims, c h a r a c t e r i z e d in that the spherical elements (2) are manufactured from a plastic material. 7. A method for producing a space frame for three-dimensional positioning of reference points (1) , wherein a number of strut members (3) and nodes (2) are joined together, c h a r a c t e r i z e d in the steps of cutting struts (3) into exact lengths, assembling a base comprising three nodes (2) and three struts (3) at a distance from the reference points (1), mounting additional nodes (2) and strut elements (3) , which bridge the distance between the base and the reference points, in such a way that each node is connected via beams to at least three other nodes, wherein the strut elements (3) are connected to the nodes (2) by gluing.

Inventors: OLSSON BERTIL, OLSSON, BERTIL
Applicants: OLSSON BERTIL, OLSSON, BERTIL
Application year: 1999
Main classification: E04B1
IPC codes: E04B1, F16M13