SUPPORT STRUCTURES

Abstract: In a co-ordinate measuring machine a guideway base is formed from tubular components (10-14) of a lightweight material. An electrically heated strip (16) is located centrally of the tubular elements and fans (18) are also provided within the base. The strip (16) and the fans (18) can maintain the temperature of the base structure at a constant level at or above the ambient temperature so that changes in the latter do not result in any thermal expansion of the material of the base structure.

Description: Support Structures This invention relates to apparatus for supporting components and is particularly but not exclusively conc¬ erned with support structures for use with high accuracy measuring and checking machines. Heretofore for purposes of accuracy, it has been necessary to construct co-ordinate measuring machines using heavyweight material such as granite, i.e. material which remains as stable as possible with variations in temperature. It has not been practical to use lightweight base structures where thermal expansion of the material could lead to distortion and loss of accuracy. According to the present invention there is provided support apparatus comprising elongate means having a through passage, heating means provided in the passage, and means for controlling the heating means whereby to be capable of maintaining the temperature of the apparatus at a level at or above the ambient temperature. Preferably the heating means comprises one or more electrically heated strips which can be located centrally in the passage. Preferably also the elongate means comprises a plurality of linear tubular elements connected together in a rectangular configuration, particularly to form a base guideway of a measuring machine. The elongate means may be formed of a lightweight material such as steel or a granite composite material, and external insulation may be provided. Fan means may be provided within the elongate tubular means to move air therethrough and thereby assist in providing an even distribution of temperature throughout the apparatus. An embodiment of the present invention will now be described by way of example only with reference to the single figure of the accompanying drawings, in which:- Fig. 1 is a diagrammatic perspective view of an apparatus according to the invention; Fig. 2 is an enlarged section on AAAA of Fig. 1; and Fig. 3 is a section on B-B of Fig. 2. Referring to the drawing, a guideway base for use in a three axis co-ordinate measuring machine comprises a first pair of elongate tubular components 10 interconnected at their respective ends by a pair of tubular components 12 of reduced length whereby to define a rectangular configur¬ ation with a continuous passage therethrough. To reinforce the base an arrangement of elongate tubular struts 14 ext¬ end between inwardly facing external walls of the elements 10,12 in any suitable arrangement. The elements 10,12 and the struts 14 are formed of a lightweight material, prefer¬ ably steel or a granite composite material comprising granite chippings and epoxy. To heat the base, a strip 16 incorporating one or more resistance wires is located within the elements 10,12 and the- struts 14 to extend around the base. The strip 16 is preferably located centrally of the elements 10,12 by being suspended by arms 17 from side walls thereof, so as to avoid creating temperature gradients in the walls of the elements 10,12. The strip 16 is appropriately connected in an electrical circuit (not shown) for heating of the strip and thereby the base. Additional heating strips may be used as necessary and in a modification the strip 16 may not extend around the whole base. Within the base in the through passage there is prov¬ ided a plurality of electrically operated fans 18. These effect circulation of the heated air throughout the base and thereby assist in providing a substantially uniform temperature throughout. External insulation is provided for the elements 10,12 in order to avoid a temperature gradient across the walls. The insulation may be in a spaced relation with the external walls of the elements 10,12 to provide an air layer and it is envisaged that there may be provision for air to exit from the passage in the base into the spacing between the external walls and the insulation layer. In use, the heating circuit controls the heating strip such that the temperature of the base structure is maintained at a constant level, at or above the ambient temperature. In this way changes in the ambient tempera¬ ture do not result in any thermal expansion of the material of the base structure and therefore distortion and loss of measuring accuracy can be avoided. Various modifications may be made without departing from the invention. For example the configuration of the base structure may differ from that described and shown and other suitable heating means may be provided internally of the elements. Also the structure may be formed of any other suitable. material, and may be other than a machine base. For example the structure may take the form of a column and/or bridge of a co-ordinate measuring machine. It is particularly suitable to use such a lightweight base structure with a support as described in our co-pending U.K. Application No. 8808282 entitled "Support Assemblies", a lightweight structure for the other components of the machine as described in our co-pending U.K. Application No. 8808280 entitled "Machine Structure", and a linear guideway as described in our co-pending U.K. Application No. 8808279 entitled "Linear Guiding Apparatus".

Claims: Claims : - 1. Support apparatus comprising elongate means having a through passage, heating means provided in the passage, and means for controlling the heating means whereby to be capable of maintaining the temperature of the apparatus at a level at or above the ambient temperature. 2. Apparatus according to Claim 1, wherein the heating means comprises one or more electrically heated strips. 3. Apparatus according to Claim 2, wherein the heated strips are located centrally in the passage. 4. Apparatus according to any of Claims 1 to 3, wherein the elongate means comprises a plurality of linear tubular elements connected together in a rectangular configuration. 5. Apparatus according to any of the preceding Claims, wherein the elongate means is formed of a lightweight material. 6. Apparatus according to Claim 5, wherein the material is steel. x . 7. Apparatus according to Claim 5, wherein the material is a granite composite material. 8. Apparatus according to any of the preceding Claims, wherein external insulation is provided. 9. Apparatus according to any of the preceding Claims, wherein fan means is provided within the elongate tubular means to move air therethrough and thereby assist in providing an even distribution of temperature throughout the apparatus. 10. Support apparatus substantially as hereinbefore described with reference to the accompanying drawings. 11. Any novel subject matter or combination including novel subject matter herein disclosed in the foregoing Specification or Claims and/or shown in the drawings, whether or not within the scope of or relating to the same invention as any of the preceding Claims.

Inventors: BURY JAMES, BURY, JAMES
Applicants: LK TOOL CO LTD, L.K. TOOL COMPANY LIMITED
Application year: 1989
Main classification: G01B5
IPC codes: B23Q11, G01B5