Measuring and testing – Instrument proving or calibrating – Volume of flow – speed of flow – volume rate of flow – or mass...
Patent
1995-10-30
1997-10-28
Noland, Thomas P.
Measuring and testing
Instrument proving or calibrating
Volume of flow, speed of flow, volume rate of flow, or mass...
738659, 33502, G01B 2104, G01P 2100
Patent
active
056819811
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to machines in which one member is positioned relative to another. For example, it relates to coordinate measuring machines, machine tools, scanning machines and robots, in which a tool or probe is positioned relative to a workpiece.
More particularly, the invention relates to performing measurements or calibration on such machines.
In some aspects, the present invention is a development of the apparatus and methods described in our International Patent Application No. PCT/GB94/02593, published as WO95/14905 to which reference should be made. Reference is also directed to the apparatus and methods described in International Patent Applications Nos. WO91/03145 (Kearney & Trecker) and WO92/17313 (Geodetic Machines), and in European Patent Application No. 534585 (Ingersoll).
All the above applications show machines in which a tool, probe or other operator is mounted on one structure, for movement relative to another structure upon which a workpiece may be mounted. The tool, probe or other operator may be movable and the workpiece fixed, or vice versa. The relative movement is effected by six rams acting between the two structures. These rams can be controlled so as to produce any desired relative movement between the structure, with six degrees of freedom (three translational and three rotational). It is necessary to measure the movements of the rams, and one aspect of the present invention is concerned with such measurement.
A problem with the apparatus described in the various above-referenced patent applications is that of calibrating the movement of the machine. To achieve this, it is necessary to measure the relative position and orientation of the moving structure relative to the fixed structure, independently of the measurements of the extensions of the rams which produced that position and orientation. Another aspect of the present invention allows such calibration, both on the type of machine described in the above patent applications, and on more conventional machines.
SUMMARY OF THE INVENTION
According to one aspect of the present invention a method of calibrating a machine comprises the steps of attaching a first structure to one part of a machine, said structure having at least one spherical or part-spherical support thereon, having three spherical, or part-spherical supports thereon arranged in a triangular pattern, which is attached to one of the supports on each structure, causing relative movement between the two structures, determining the changes in the lengths of the measuring bars caused by the relative movement of the two structures, and structures.
According to one embodiment of the invention the first structure has three spherical or part-spherical supports thereon which are arranged in a triangular pattern, six measuring bars are provided, opposite ends of each bar being connected to one support on each structure. In such an embodiment, each support on both structures has the ends of two measuring bars connected to it.
According to another embodiment of the invention, the first structure comprises a single support disposed on the machine at the position which would normally be occupied by the tip of a tool or a measuring probe, three measuring bars are provided, opposite ends of each bar being connected to the single support on the first structure, and to one of the supports on the second structure.
According to another aspect of the invention there is provided 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.
The apparatus may be connected to a machine as a calibration device in which case the members may be passive measuring bars, or alternatively the members may be powered extensible struts capable of manipulating one of the structures relative to the other.
In one embodiment of the invention both of th
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Noland Thomas P.
Renishaw plc
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