Performing measurement or calibration on positioning machines

Abstract

Apparatus which can be used to calibrate, or provide measurement data on, a machine. The apparatus comprises two structures each with three spherical supports spaced in a triangular array thereon. The supports may be balls or sockets. The structures are interconnected by six members and each support has the ends of two members connected to it. The members are passive extensible measuring bars and the structures are respectively connected to fixed and movable parts of a machine so that movement of the machine parts causes relative movement between the structures and varies the lengths of the measuring bars. From measurements of the lengths of the measuring bars the actual movement of the machine part can be determined. Calibration of the spherical supports is carried out using a measuring bar which is pre-calibrated in a Zerodur jig.

1 . Apparatus comprising a first structure having at least one spherical or part-spherical support thereon, a second structure which has three spherical or part-spherical supports spaced in a triangular pattern thereon, and at least three members interconnecting the two structures while allowing relative movements between the two structures.  
     
     
         2 . Apparatus according to    claim 1    and wherein the apparatus is a calibration device for attachment between moving and fixed parts of a machine, and the members comprise measuring bars for determining the distances between the supports on the two structures to which the measuring bars are connected.  
     
     
         3 . Apparatus according to    claim 1    and wherein the apparatus is itself a machine and the members comprise powered struts for manipulating one of the structures relative to the other.  
     
     
         4 . Apparatus according to    claim 2    and wherein the powered struts additionally include measuring devices for determining the distances between the supports to which the struts are connected.  
     
     
         5 . Apparatus according to    claim 1    and wherein both structures include three spherical or part-spherical supports and six members are provided, each support on both structures having the ends of two members connected thereto.  
     
     
         6 . Apparatus according to    claim 1    and in which the members are extensible and are connected between the supports on each structure.  
     
     
         7 . Apparatus according to    claim 1    and wherein the members are of fixed length and pass through the supports on at least one of the structures.  
     
     
         8 . Apparatus according to    claim 1    and wherein the axes of the struts, or extensions thereof pass through the centres of the supports.  
     
     
         9 . Apparatus according to    claim 1    and wherein the connections of the members to the supports on the struts are made by co-operating spherical or part-spherical surfaces held in place by magnetic forces.  
     
     
         10 . Apparatus according to    claim 1    and wherein the members include measuring transducers which measure the distances between the centres of the supports to which the members are connected.  
     
     
         11 . Apparatus according to    claim 10    and wherein the measuring transducers carried by a member comprises a scale which is read by a readhead connected to the structure.  
     
     
         12 . Apparatus according to    claim 11    and wherein the scale is aligned with the centre of the support on the structure to which the member is attached.  
     
     
         13 . Apparatus according to    claim 1    and wherein the structure comprises a triangular frame with spherical supports mounted at its apices.  
     
     
         14 . Apparatus according to    claim 1    and wherein the structure comprises three sockets spaced in a triangular array and having part-spherical surfaces, and in which are supported ball bearings to which the members are connected.  
     
     
         15 . A method of using the apparatus of    claim 1    for calibrating a machine wherein a first one of the structures is connected to a movable part of the machine, a second one of the structures is connected to a static part of the machine, and the machine is driven through a calibration routine which causes relative movement between the structures, the measuring transducers associated with the members providing measurements of the lengths of the members whereby the spatial positions of each of the supports can be determined.