Boots – shoes – and leggings
Patent
1988-10-25
1991-04-09
Lall, Parshotam S.
Boots, shoes, and leggings
356358, 356363, 36416701, 36447435, G01B 1100
Patent
active
050070061
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method of, and apparatus for, the calibration of a machine system in which relative movement takes place between two parts of the machine. Examples of such machine systems are co-ordinate measuring machines and machine tools.
Such machines generally have parts movable along three mutually orthogonal axes generally designated x,y and z axes, by means of which tools, which term includes measuring devices such as touch trigger probes, are positioned with respect to a workpiece. The machines include measuring devices for example, scales, positioned along the three axes of the machine, and scale readers which provide a measure of the movement of the movable part of the machine, thus providing a determination of the position of the tool along all three axes. The scales themselves are calibrated during manufacture.
The movable machine parts run in tracks on the fixed parts and errors arise between the actual movement of the movable parts, and the movement indicated by reading the scales. These errors are due, inter alia, to pitch, roll and yaw movements of the machine parts caused for example, by mis-alignments or tolerances in the tracks. There may also be mis-alignment of the scale on its axis or between the scale and scale reader.
It is known from U.S. Pat. No. 3,654,446 to account for machine errors of the sort outlined above, by plotting an error map of the machine. This is achieved according to the patent specification, by moving the movable parts of the machine to a large number of positions within the working envelope of the machine and, at each position once the machine has stopped, recording the counts of the machine scale readers. The actual distances moved by the machine parts along the three orthogonal axes are then independently measured by another measuring device in the form of a laser interferometer. The laser interferometer includes a counter for counting interference fringes produced within the interferometer during movement of the movable parts of the machine. The difference between the measured movements of the movable part of the machine as indicated by the scale reader and the interferometer fringe counter along each axis, are then recorded in analogue or digital form on any suitable recording medium.
While this method can provide useful information for correcting many of the above-mentioned errors, workpieces are usually measured while the machine is in motion, and the above-described method will not take account of any other errors which may be introduced due to movement of the machine.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of, and apparatus for, dynamically calibrating a machine during relative movement of parts thereof.
In accordance with the invention as claimed in the appended claims there is provided in a machine having parts which are relatively movable in three orthogonal directions for positioning a tool relative to a workpiece and having measuring devices positioned between the relatively movable parts for measuring the movements of the parts in said directions, a method of dynamically calibrating the machine comprising the steps of: providing a measurement of a movement of a first machine part in at least one of said directions independently of, and in addition to, the measurement being made of said movement by the respective measuring device or devices of the machine, the recording of the measurements of said movement produced by both of the measuring apparatus and the respective measuring device or devices, difference between them. It is to be understood that the word tool in this context encompasses a measuring probe.
The initiation of the recording of the readings of the interferometric measuring apparatus and the measuring devices of the machine (usually scales and scale readers) may be caused by an independent pulse generator which sends simultaneous signals to the fringe counter of the interferometer and the scale reader at pre-determined intervals, to initia
REFERENCES:
patent: 3654446 (1972-04-01), Gordon et al.
patent: 4128794 (1978-12-01), Burleson
patent: 4195412 (1980-04-01), Llop et al.
patent: 4378160 (1983-03-01), Vlad et al.
patent: 4628441 (1986-12-01), Johnstone et al.
patent: 4710865 (1987-12-01), Higomura
patent: 4792228 (1988-12-01), Haffner
patent: 4819195 (1989-04-01), Bell et al.
Chapman Mark A. V.
Graham Jeffrey
Taylor Benjamin R.
Cosimano Edward R.
Lall Parshotam S.
Renishaw plc
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