Method for calibrating the geometry of a multi-axis metrology system
First Claim
1. In a metrology system including a part-positioning means having a spindle axis and a wavefront-measuring gauge, a part-on-mount method for determining the misalignment of a test part with respect to the spindle axis, and the misalignment of the spindle axis with respect to the wavefront-measuring gauge, the method comprising the steps of:
- a) mounting said test part onto said spindle axis such that a surface of said test part is exposed to said gauge;
b) obtaining measurements of said test part surface with said gauge at a plurality of rotary positions of said spindle;
c) extracting tilt components from said surface measurements at each of said rotary positions;
d) fitting a circle to said tilt components and said rotary positions;
e) determining the center of said circle with respect to said spindle to provide said gauge-to-spindle misalignment; and
f) determining the radius coordinates of said circle with respect to said spindle to provide said spindle-to-part misalignment.
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Accused Products
Abstract
A method for calibrating and aligning a metrology system comprising a machine including multi-axis part-positioning means and a wavefront-measuring gauge embedded in the machine. The gauge is used in determining spatial relationships among the translational and rotational axes, between part surface coordinates and machine coordinates, and between machine coordinates embedded gauge coordinates; in calibrating various components of the machine and the embedded gauge; and in aligning itself to the machine. A complete method comprises the steps of coarsely aligning the machine rotary axes with their respective translational axes and setting nominal zero points for the rotary axes; aligning the embedded gauge mainframe to the machine axes; aligning the embedded gauge focal point onto a spindle axis; determining the spatial offsets between the rotary axes when so aligned; precisely aligning the machine rotary axes with their respective translational axes; and setting precise zero points for the rotary axes.
18 Citations
34 Claims
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1. In a metrology system including a part-positioning means having a spindle axis and a wavefront-measuring gauge, a part-on-mount method for determining the misalignment of a test part with respect to the spindle axis, and the misalignment of the spindle axis with respect to the wavefront-measuring gauge, the method comprising the steps of:
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a) mounting said test part onto said spindle axis such that a surface of said test part is exposed to said gauge; b) obtaining measurements of said test part surface with said gauge at a plurality of rotary positions of said spindle; c) extracting tilt components from said surface measurements at each of said rotary positions; d) fitting a circle to said tilt components and said rotary positions; e) determining the center of said circle with respect to said spindle to provide said gauge-to-spindle misalignment; and f) determining the radius coordinates of said circle with respect to said spindle to provide said spindle-to-part misalignment. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. In a metrology system including a part-positioning means having a spindle axis and a wavefront-measuring gauge, a part-on-mount method for determining the misalignment of a test part with respect to the spindle axis, assuming that the gauge-to-spindle misalignment values are known, the method comprising the steps of:
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a) mounting said test part onto said spindle axis such that a surface of said test part is exposed to said gauge; b) obtaining a measurement of said test part surface with said gauge at a rotary position of said spindle; c) extracting tilt components from said surface measurement; and d) subtracting said assumed known gauge-to-spindle misalignment values from said tilt components to determine said spindle-to-part misalignments.
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10. A method for employing an embedded gauge and test surface to determine geometrical constants of a mechanical positioning system including X, Y, and Z translational axes and A, B, and C rotational axes, wherein such constants may include lateral scale of the translational axes, spatial separations between the rotary axes, and axial position of a gauge focus with respect to a machine stage, the method comprising the steps of:
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a) providing said embedded gauge with a focusing element; b) mounting a test part having a test surface on said machine stage; c) setting the positions of said rotary axes to zero; d) moving said stage along at least one of said X and Y axes such that said A axis passes through the focus of said gauge; e) adjusting said translational axes such that said test surface is confocal with said embedded gauge; f) moving a one of said rotary axes to a new value; g) repositioning said test part at said confocal position by adjusting said translational axes; h) recording the positions of axes that achieve said confocal condition; i) repeating steps f) and g) for several different positions of said rotary axes; and j) performing a numerical fit to an analytical model of said machine geometry to provide said geometrical constants of said mechanical positioning system.
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11. A method for aligning a wavefront-measuring gauge to a mechanical positioning system having a spindle axis, comprising the steps of:
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a) mounting said gauge, with focusing element removed, onto said mechanical positioning system; b) adjusting mechanical axes of said mechanical positioning system to a desired work origin position; c) placing a test part having at least one flat surface on said spindle; d) using said gauge to measure angular misalignment between said spindle (A) axis and said gauge; and e) re-orienting said gauge mainframe with respect to said mechanical positioning system, based on said angular misalignment measurement, to align said mainframe with said spindle axis. - View Dependent Claims (12)
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13. A method for calibrating and aligning a metrology system including a multi-axis mechanical positioning system and an embedded wavefront-measuring gauge to determine accurately the spatial relationships among the translational and rotational axes of the system, the method comprising the steps of:
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a) coarsely aligning said mechanical positioning system rotary axes A, B, and C with said respective translational axes Z, Y, and X, and setting nominal zero points for said rotational axes; b) aligning the mainframe of said embedded gauge to said mechanical positioning system; c) aligning said embedded gauge onto said A rotational (spindle) axis; d) determining spatial offsets between said rotational axes when so aligned; and e) precisely aligning said machine rotational axes with said respective translational axes to set precise zero points for said rotational axes. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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20. In a metrology system including a multi-axis positioning machine and an embedded wavefront-measuring gauge in collimated mode, a method for determining the lateral misalignment of a machine spindle axis with respect to said embedded gauge'"'"'s coordinate system and the lateral misalignment of a test part with respect to said spindle axis, comprising the steps of:
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a) installing a test part having at least one flat surface on a spindle axis of said positioning machine exposed to said gauge wavefront, the aperture dimensions being fully contained in said gauge wavefront; b) measuring said part surface at a plurality of rotary positions of said spindle axis; c) extracting x-y coordinates in the gauge coordinate system from said measurements at each spindle position; d) fitting a circle to said x-y positions; and e) determining the center and radius coordinates of said circle to provide both said lateral misalignment of said spindle axis with respect to said embedded wavefront-measuring gauge coordinate system and said lateral misalignment of said test part with respect to said spindle axis, respectively.
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21. In a metrology system including a wavefront-measuring gauge and part-positioning means having at least one rotational axis and at least one translational axis, a method for aligning said one rotational axis and said one translational axis by calculating the misalignment angle between them, comprising the steps of:
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a) mounting a test part on said one rotational axis; b) obtaining gauge measurements of the surface of said test part at a plurality of positions of said one rotational axis; c) performing repeatedly steps a) and b) at a plurality of different positions of said one translational axis using at least one spherical part mounted confocally at said plurality of translational axis positions to generate a plurality of terms representing misalignment between said gauge and said rotational axis in a plane perpendicular to said one rotational axis; d) fitting line to said plurality of gauge misalignment terms plotted versus position along said one translational axis; and e) calculating said misalignment angle of said one rotational axis from said one translational axis in said plane, equal to the arctangent of the slope of said line fit. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29)
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30. A method for aligning an interferometer aperture converter to a mechanical positioning system having a spindle axis, comprising the steps of:
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a) mounting said aperture converter onto said interferometer that is already mounted and aligned to said mechanical positioning system; b) adjusting mechanical axes of said mechanical positioning system to a desired work origin position, preferably the one where the interferometer (without aperture converter) is aligned to; c) placing a corner cube having a measurable front surface on said spindle; d) using said interferometer to measure angular misalignment between said spindle (A) axis and said interferometer with aperture converter attached; and e) re-orienting said aperture converter with respect to said interferometer mainframe, based on said angular misalignment measurement, to align said aperture converter on said interferometer mainframe with said spindle axis. - View Dependent Claims (31)
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32. A method for aligning an interferometer aperture converter to a mechanical positioning system having a spindle axis, comprising the steps of:
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a) mounting said aperture converter onto said interferometer which has been previously mounted and aligned to said mechanical positioning system; b) adjusting mechanical axes of said mechanical positioning system to a desired work origin position wherein said interferometer (without aperture converter) is aligned thereto; c) placing a corner cube having a measurable front surface on said spindle; d) using said interferometer to measure angular misalignment between said spindle (A) axis and said interferometer with aperture converter attached; and e) re-orienting said aperture converter with respect to said interferometer mainframe, based on said angular misalignment measurement, to align said aperture converter on said interferometer mainframe with said spindle axis. - View Dependent Claims (33)
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34. A method for aligning a transmission sphere to an interferometer with partial spatial coherence, comprising the steps of:
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a) mounting and aligning a test part to, or near, its confocal position; b) introducing misalignment interference fringes with a distinct center (e.g. bull'"'"'s eye fringe pattern), such as would be observed by moving the test part along the axis of the interferometer; c) changing the focus position of the interferometer as necessary to observe a modulation envelope over the interference fringes; and d) adjusting the tip/tilt of the transmission sphere to make the modulation envelope pattern and the fringe pattern concentric.
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Specification