Absolute diameter measurement arm
First Claim
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1. A method of determining absolute diameter of an object on a rotary table, comprising:
- on an assembly formed of (i) a rotary table on a base, and (ii) a support tower on the base and carrying a horizontal measurement arm,calibrating the horizontal measurement arm including determining (a) a measurement error of the horizontal measurement arm at a reference height, (b) a displacement factor bCAL of the support tower, and (c) a displacement factor α
CAL of a laser path aligned relative to a centerline of rotation of the rotary table;
using the calibrated horizontal measurement arm, measuring a plurality of points around a circumference of a subject object on the rotary table with sufficient accuracy to compute absolute diameter of the subject object instead of a relative measurement, by (i) measuring each point with the horizontal measurement arm at a height equal to or greater than the reference height, (ii) measuring temperature of the horizontal measurement arm for each measured point and determining a respective thermal expansion factor of the measured point, and (iii) for each measured point, determining a respective corrected point by applying the respective thermal expansion factor, the determined measurement error and a compensation factor to the measured point, the compensation factor being determined as a function of α
CAL, bCAL and height of the horizontal measurement arm relative to the reference height, wherein sum of α
CAL and bCAL is a constant value; and
applying the determined corrected points in a multi-point polygon model and determining absolute diameter of the subject object.
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Abstract
A measurement apparatus calibrated to measure an absolute diameter of a part in a shop floor environment. The measurement apparatus includes a calibration that includes compensation factors for thermal expansion, shifting of measurement parts (arm, support tower, and related laser), and variances of these parts. The resulting measurements report an absolute diameter of a part to a higher degree of accuracy than previously possible. Also, the calculated compensation factor eliminate the need for an isolated, climate-controlled measurement room.
47 Citations
23 Claims
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1. A method of determining absolute diameter of an object on a rotary table, comprising:
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on an assembly formed of (i) a rotary table on a base, and (ii) a support tower on the base and carrying a horizontal measurement arm, calibrating the horizontal measurement arm including determining (a) a measurement error of the horizontal measurement arm at a reference height, (b) a displacement factor bCAL of the support tower, and (c) a displacement factor α
CAL of a laser path aligned relative to a centerline of rotation of the rotary table;using the calibrated horizontal measurement arm, measuring a plurality of points around a circumference of a subject object on the rotary table with sufficient accuracy to compute absolute diameter of the subject object instead of a relative measurement, by (i) measuring each point with the horizontal measurement arm at a height equal to or greater than the reference height, (ii) measuring temperature of the horizontal measurement arm for each measured point and determining a respective thermal expansion factor of the measured point, and (iii) for each measured point, determining a respective corrected point by applying the respective thermal expansion factor, the determined measurement error and a compensation factor to the measured point, the compensation factor being determined as a function of α
CAL, bCAL and height of the horizontal measurement arm relative to the reference height, wherein sum of α
CAL and bCAL is a constant value; andapplying the determined corrected points in a multi-point polygon model and determining absolute diameter of the subject object. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method of calibrating measurements by a horizontal measurement arm, comprising:
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(a) given a high precision rotary table on a base, a support tower on the base carrying a horizontal measurement arm, and a laser device configured to indicate change in orientation of the horizontal measurement arm with respect to a centerline of rotation of the high precision rotary table, the laser device having a laser path aligned relative to the centerline of rotation of the rotary table; (b) determining a measurement error by; determining a first compensation factor for measurement error of a horizontal measurement arm; determining a second compensation factor for lean of a support tower carrying the horizontal measurement arm as a function of height above a reference height; determining a third compensation factor for variation of the support tower as a function of height above the reference height; determining a fourth compensation factor for thermal expansion of the horizontal measurement arm as a function of temperature; and (c) using the determined measurement error to effectively obtain a calibrated measurement of each point in a plurality of points around a circumference of an object on a rotary table with sufficient accuracy to compute absolute diameter of the object instead of a relative measurement of roundness, by (i) measuring each point with the horizontal measurement arm at a height equal to or greater than the reference height, and (ii) determining a plurality of corrected points around the circumference by applying the first compensation factor, second compensation factor, third compensation factor, and fourth compensation factor to each of the measured points;
such that an absolute radius of the object is able to be determined by applying the plurality of corrected points in a multi-point polygon model. - View Dependent Claims (11, 12, 13, 14, 15, 16)
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17. An apparatus for measuring absolute diameter of an object on a rotary table, comprising:
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a support tower mounted to a flat surface of a stable base, the support tower substantially perpendicular to the flat surface, the stable base including vibration-isolating mounts to isolate the stable base from ambient vibrations; a horizontal measurement arm mounted to the support tower substantially parallel to the flat surface and configured to move towards and away from a centerline of rotation of a precision rotary table mounted to the flat surface of the stable base, the horizontal measurement arm configured to measure a distance of a precision gauge head on an end of the horizontal measurement arm from the centerline of rotation; a thermocouple mounted to the horizontal measurement arm configured to measure the temperature of the horizontal measurement arm; a laser mounted to a base of the support tower and pointed substantially parallel to the centerline of rotation of the rotary table, laser light from the laser aimed at a housing of the horizontal measurement arm; and a computer controller configured to; (i) determine a first compensation factor for measurement error of the horizontal measurement arm; (ii) determine a second compensation factor for lean of the support tower as a function of height above a reference height; (iii) determine a third compensation factor for variation of the support tower as a function of height above the reference height; (iv) determine a fourth compensation factor for thermal expansion of the horizontal measurement arm as a function of temperature; (v) obtain a calibrated measurement of each point in a plurality of points around a circumference of an object on the rotary table with sufficient accuracy to compute absolute diameter of the object instead of a relative measurement of roundness, by (a) measuring each point with the horizontal measurement arm at a height equal to or greater than the reference height and (b) determining a plurality of corrected points around the circumference by applying the first compensation factor, second compensation factor, third compensation factor, and fourth compensation factor to each of the measured points; and (vi) determine an absolute radius of the object by applying the plurality of corrected points in a multi-point polygon model. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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Specification