Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1989-05-22
1991-05-07
Turner, Samuel
Optics: measuring and testing
By particle light scattering
With photocell detection
356358, G01B 902
Patent
active
050131524
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to optical devices for use in interferometric measuring systems.
The optical devices with which the invention is concerned are for example, linear and angular interferometers, retro-reflectors and beam splitters.
Interferometric measuring systems are used for measuring movements of parts of machines e.g. co-ordinate measuring machines and machine tools, for determining pitch, roll, yaw and linear errors of the movable machine parts as they move along the slide-ways of the machine.
In order to carry out the measurements a laser beam is directed towards the various optical devices disposed on the machine.
Depending on the machine type, the bed of the machine may be movable while the spindle remains fixed in position, or more generally the bed of the machine remains fixed while the spindle is capable of movement in three co-ordinate axes. Thus it can be seen that there is always relative movement between the spindle and the machine bed and it is this relative movement which is used to make the required measurements.
Since one of the optical components will always be mounted on the spindle there must always be a minimum clearance between the spindle-mounted optical component and the bed of the machine in order to enable the relative movement to take place.
In the conventional interferometric measuring systems the laser is mounted on a tripod and directs the laser beam across the bed of the machine at a height above the bed of the machine such as to provide adequate clearance between the spindle-mounted optical device and the bed of the machine. The optical device on the bed of the machine is mounted on a stand such that its centre is at an appropriate height to receive the laser beam after it has passed through the spindle-mounted optical device.
It would be an advantage to be able to mount the laser and some of the optical devices directly- on the machine bed without packing pieces or stands. This would avoid the need for a bulky and expensive tripod, and would minimise the amount of time spent in aligning the laser beam and optical devices. It would also enable the measuring system to be left permanently in position to make measurements during an actual operation of the machine.
Conventional optical devices are made with square or rectangular housings to be interchangeable between spindle-mounted and bed-mounted positions to avoid mounting on the spindle or on a stand mounted on the machine bed to avoid creating devices for mounting at each of the two different positions. Thus, in order to align the laser beam through a conventional spindle-mounted optical device when the laser and the optical device are attached directly to the bed of the machine, that is, no stand is provided for the bed-mounted optical device, the spindle-mounted optical device would also need to be in contact with the bed of the machine in order to be in correct alignment with the laser beam. No relative movement could then take place between the spindle and the bed of the machine
The present invention solves this problem in a simple and effective manner.
According to the present invention an optical device for use in an interferometric measuring system comprises a housing having two opposite sides and an optical component mounted within the housing characterised in that the geometric centre of the optical component is arranged to be closer to one of the sides of the housing than to the other.
Examples of the invention will now be more particularly described with reference to the accompanying drawings in which,
FIG. 1 illustrates diagramatically the components of a laser interferometer system of the present invention mounted on a machine bed,
FIG. 2 illustrates one example of an optical device for use with the interferometer of FIG. 1, and
FIG. 3 illustrates another example of an optical device for use with the interferometer of FIG. 1.
Referring now to the drawings in FIG. 1 there is shown part of a co-ordinate measuring machine 1 having a bed 2 on which a workpiece may be positioned and a spindle 3 mounted
REFERENCES:
patent: 2806293 (1957-09-01), James et al.
patent: 2880644 (1959-04-01), Brockway et al.
patent: 3409375 (1968-11-01), Hubbard
patent: 3486824 (1969-12-01), Cook et al.
patent: 3588254 (1971-06-01), Rhoades
patent: 3592549 (1971-07-01), Hoffman
Renishaw plc
Turner Samuel
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