Renishaw Plc

Renishaw Transducer Systems Limited

Benjamin R Taylor

David R McMurtry

Geoffrey McFarland

Mark A Chapman

Mark Adrian Vincent Chapman

Roger M Badland

Jeffrey Graham

Marcus J Eales

A method of inspecting a series of workpieces using a coordinate measuring apparatus, comprising the steps of: measuring a calibrated artefact on a coordinate measuring apparatus at a fast speed; generating an error map corresponding to the difference between the calibrated artefact and the measured artefact; measuring subsequent workpieces at the same fast speedand correcting the measurements of the subsequent workpieces using the error map. The artefact may be one of the workpieces.

Dynamic artefact comparison

Apparatus for aligning an optical measuring system to a desired direction comprises two housings () attachable to two relatively movable parts of a machine. The housings () have engagement means () such that when they are engaged together the optics inside () are aligned. The first housing () may be provided with attachment means, such as a ball (), which may be located in a mount () on the machine table (). The position of this ball () is determined and the machine spindle housing () to be attached to the spindle () when the two housings () are joined and such that the apparatus is aligned with the desired direction. The engagement means () between the two housings () may be compliant along an axis of the apparatus.

Aligning optical components of an optical measuring system

In a method of calibrating the measuring performance and apparatus for a machine, the conventional physical length bar is simulated by moving a retro-reflector to various positions along a track. A laser beam of an interferometer is aligned with the track using the retro-reflector at two extreme positions in order to define a measurement axis for the calibration. The retro-reflector has a part-spherical surface on its rear face which is centered on the nodal point of the retro-reflector. By contacting the reference surface with a probe on the machine at several points, the center of the sphere at the two positions of the retro-reflector can be calculated and hence the measurement axis is defined in the machine frame of reference. Measurements are taken with the interferometer of the position of the retro-reflector at several points on the measurement axis, and at each point the measuring probe is brought into contact with the spherical surface of retro-reflector (preferably at the intersection of the measurement axis and the surface) to make a second measurement of the retro-reflector's position. The accurate measurement of the interferometer is compared to the machine's measurement to determine the machine error. Many different length bars can be easily simulated by this method, and bars of different materials can be simulated by using the coefficient of linear expansion of commonly used materials to convert the measured distance into a length measurement of a bar of that material corrected to standard temperature and pressure.

Method of and apparatus for calibrating machines including a measuring

Telescopic ball bar 24 has a male member provided by a sphere 22 at one end and a female member provided by a pair of forks 30 at the other. The ball bar is attached to the spindle 10 of a machine tool by a universal pivotal coupling between the sphere 22 and a magnetic socket 14 retained on the spindle 10. The ball bar 24 is attached to the table by a further universal pivotal coupling between a sphere 28 retained on the table 12 in a clamping device 40, and the forks 30. In use, the spindle is operated to move in a circular path about a center defined by the center of the sphere 28. Any deviation of the spindle movement from such a circular path will be detected by a transducer 36, provided in the bar 24, which bears against the surface of the sphere 28. The position of the center of the sphere 28 is determined by bringing the sphere 28 into engagement with the socket 14, and measuring the position of the spindle 10 at that point. Easy engagement between the sphere 28 and the socket 14 is facilitated by the clamping device 40, which enables the sphere 28 to move relative to the table to engage the socket 14. Once the sphere 28 has engaged the socket 14 (and the position of its center has been measured by measuring the position of the spindle 10), the sphere 28 may be clamped rigidly relative to the table 12 for a calibration operation.

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Trelleck, United Kingdom

Benjamin R Taylor