Machine element or mechanism – Rotary member or shaft indexing – e.g. – tool or work turret – Preselected indexed position
Patent
1993-04-13
1994-08-30
Luong, Vinh T.
Machine element or mechanism
Rotary member or shaft indexing, e.g., tool or work turret
Preselected indexed position
74813R, 74816, 74826, B23B 2924, B23Q 1600
Patent
active
053417020
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the calibration of angular displacement of an object about a rotary axis, such as a rotary table.
2. Description of Related Art
It is known to calibrate a rotary table using an angular interferometer together with an indexing table which is mounted co-axially with the rotary table, and which may rotate relative to the rotary table in equi-angular and accurately known indexable increments which are mechanically defined by the construction of the table. Angular displacement of the rotary table may be measured by the angular interferometer by detecting rotation of a pair of retroreflectors mounted on the indexing table (when the indexing table rotates with the rotary table). The angular interferometer may detect rotary displacement over a range of about .+-.15.degree. from a datum position (which is the position at which the plane of the two retroreflectors lies exactly perpendicular to the incident of beams of the angular interferometer).
The calibration operation using this apparatus is performed by coupling the indexing table to the rotary table (and therefore coupling the retroreflectors of the angular interferometer to the rotary table); rotating the rotary table to a predetermined target angular displacement; decoupling the indexing table and counter-rotating the indexing table by a number of indexing positions which is approximately equal to the target angular displacement of the rotary table; and interpolating with the interferometer any net angular displacement of the retroreflectors from the datum position. The counter-angular displacement of the indexing table (which is accurately known from the indexed construction of the indexing table), is then summed with the net angular displacement measured by the interferometer and compared with the predetermined target angular displacement of the rotary table. A difference between these two values represents the error in the rotary table at the predetermined target angular displacement.
One problem with such a table occurs when the target angle of the rotary table exceeds the maximum angular displacement which the interferometer may continuously measure (typically .+-.15.degree.). One proposed solution to this problem has been to prevent rotation of the indexing table relative to the datum during rotation of the rotary table; i.e. the indexing and rotary tables are uncoupled during rotation of the rotary table to its target angle and the indexing table is mechanically retained at a position which lies within a few degrees of the datum, so that the indexing table effectively simultaneously counter-rotates relative to the rotary table. This method is inconvenient for the user.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for measuring angular displacement of a rotary table using an angular interferometer, having a pair of retroreflectors mounted on the rotary table via an intermediate indexing table, in which: a control system is provided to monitor the angular interferometer readings to measure rotation of the indexing table, so that when, during rotation of the rotary table to a target angle, rotation of the retroreflectors exceeds a predetermined threshold, a motor is actuated to counter-rotate the indexing table and thus maintain the retroreflectors within the requisite range of angular displacement.
A first aspect of the present invention provides an apparatus for measuring angular displacement of a rotatable support of a rotary table, the support being mounted to a base for rotation relative thereto about an axis, the apparatus comprising: support of the rotary table, and a rotor rotatable relative to the stator between a plurality of mechanically defined descrete indexed angular rest positions; of said indexing table; control signal; rotor in dependence upon the rotation of said rotor relative to said base, wherein said control comprises: means for receiving a value of angular displacement from said interferometer and for determi
REFERENCES:
patent: 3277789 (1966-10-01), Graham
patent: 3518899 (1970-07-01), Greenberg et al.
patent: 3543609 (1970-12-01), Borodin
patent: 3572175 (1971-03-01), Deprez
patent: 3593597 (1971-07-01), Jennings
patent: 3653282 (1972-04-01), Bouffiou et al.
patent: 3782226 (1974-01-01), Boyd et al.
patent: 4189963 (1980-02-01), Sano et al.
Hewlett Packard Journal, Apr. 1983, R. R. Baldwin et al.: "Laser Optical Components for Machine Tool and Other Calibrations: Angular Optics" pp. 14-16.
Measurement Techniques, vol. 27, No. 11, Nov. 1984 (New York, US), Yu. P. Darmenko: "Calibrating Circular Angle Digitizers" pp. 982-985.
Measurement Techniques, vol. 20, No. 7, Jul. 1977, (New York US), B. E. Blanter: "Experiment Study of Accuracy of Magnetic Angle Converters" pp. 990-994.
Measurement Techniques, vol. 23, No. 5, May 1980, (New York, US), V. P. Petrov et al.: "Method of Mutual Compensation for the Errors of Angle Transducers", pp. 399-400.
Chaney Raymond J.
Graham Jeffrey
Luong Vinh T.
Renishaw Transducer Systems Limited
LandOfFree
Apparatus for calibration of an angular displacement does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for calibration of an angular displacement, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for calibration of an angular displacement will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-23936