Method of correcting measurement error of shape measuring apparatus, and shape measuring apparatus

Patent metadata

Field	Value
Publication number	US-2016018218-A1
Application number	US-201514732056-A
Country	US
Kind code	A1
Filing date	Jun 5, 2015
Priority date	Jul 18, 2014
Publication date	Jan 21, 2016
Grant date	—

Abstract

In a shape measuring apparatus having a scanning probe to perform scanning measurement using a tip ball provided at an end of a stylus with the tip ball being in contact with an object to be measured, a tip ball displacement detector detects a displacement of the tip ball of the scanning probe, a displacement of a moving mechanism that relatively moves the object to be measured and the scanning probe is detected, and an angle formed by a contact direction of the tip ball with the object to be measured and an axial direction of the stylus is calculated. The displacement of the tip ball that is detected by the tip ball displacement detector is corrected on the basis of the angle, and a corrected value of the displacement is outputted. The corrected value is added to the displacement of the moving mechanism to calculate a measurement value.

First claim

1 . A method of correcting a measurement error of a shape measuring apparatus, the shape measuring apparatus having a scanning probe for performing scanning measurement using a tip ball that is provided at an end of a stylus and is brought into contact with an object to be measured, the method comprising:
detecting a displacement of the tip ball of the scanning probe by a tip ball displacement detector; detecting a displacement of a moving mechanism for relatively moving the object to be measured and the scanning probe; calculating an angle formed by a contact direction of the tip ball with the object to be measured and an axial direction of the stylus; correcting, on the basis of the angle, the displacement of the tip ball that is detected by the tip ball displacement detector and outputting a corrected value of the displacement; and adding the corrected value and the displacement of the moving mechanism to calculate a measurement value.

2 . The method of correcting a measurement error of a shape measuring apparatus according to claim 1 , wherein
the correcting, on the basis of the angle, the displacement of the tip ball that is detected by the tip ball displacement detector and outputting a corrected value of the displacement includes: calculating a sinusoidal value of the angle; correcting the displacement of the tip ball, which is detected by the tip ball displacement detector, on the basis of an inverse of a frequency transfer characteristic from the tip ball to the tip ball displacement detector; and adding a product of the corrected displacement and the sinusoidal value to a product of a subtracted value of the sinusoidal value from 1 and the displacement of the tip ball, and outputting a result of the addition as the corrected value.

3 . The method of correcting a measurement error of a shape measuring apparatus according to claim 2 , wherein the inverse of the frequency transfer characteristic is an estimated value.

4 . The method of correcting a measurement error of a shape measuring apparatus according to claim 3 , wherein the inverse of the frequency transfer characteristic is estimated by experiment.

5 . The method of correcting a measurement error of a shape measuring apparatus according to claim 4 , wherein
a displacement generation mechanism for displacing the tip ball and a displacement sensor for measuring a displacement of the displacement generation mechanism are used, so that the displacement generation mechanism is caused to generate a periodic displacement and both of the tip ball displacement detector and the displacement sensor actually measure the displacement, an amplitude and a phase of an output of the displacement sensor, with respect to an amplitude and a phase of a scanning probe detection value detected by the tip ball displacement detector, are calculated, and processes described above are repeated while a frequency of the periodic displacement generated by the displacement generation mechanism is changed to obtain an actual measurement value of the inverse of the frequency transfer characteristic, whereby the estimated value of the frequency transfer characteristic is obtained.

6 . The method of correcting a measurement error of a shape measuring apparatus according to claim 3 , wherein the inverse of the frequency transfer characteristic is estimated by a theory using a physical model of the scanning probe.

7 . The method of correcting a measurement error of a shape measuring apparatus according to claim 1 , further comprising performing filtering processing to remove an unnecessary frequency component from any one of the corrected displacement and the measurement value.

8 . A shape measuring apparatus having a scanning probe for performing scanning measurement using a tip ball that is provided at an end of a stylus and is brought into contact with an object to be measured, the shape measuring apparatus comprising:
a tip ball displacement detector configured to detect a displacement of the tip ball of the scanning probe; a scale configured to detect a displacement of a moving mechanism for relatively moving the object to be measured and the scanning probe; a first calculator configured to calculate an angle formed by a contact direction of the tip ball with the object to be measured and an axial direction of the stylus; a first corrector configured to correct, on the basis of the angle, the displacement of the tip ball that is detected by the tip ball displacement detector and output a corrected value of the displacement; and a first adder configured to add the corrected value and the displacement of the moving mechanism detected by the scale to calculate a measurement value.

9 . The shape measuring apparatus according to claim 8 , wherein
the first corrector includes: a second calculator configured to calculate a sinusoidal value of the angle; a second corrector configured to correct the displacement of the tip ball, which is detected by the tip ball displacement detector, on the basis of an inverse of a frequency transfer characteristic from the tip ball to the tip ball displacement detector; and a second adder configured to add a product of the corrected displacement and the sinusoidal value to a product of a subtraction of the sinusoidal value from 1 and the displacement of the tip ball, and output a result of the addition as the corrected value.

10 . The shape measuring apparatus according to claim 9 , wherein the inverse of the frequency transfer characteristic is an estimated value.

11 . The shape measuring apparatus according to claim 10 , wherein the inverse of the frequency transfer characteristic is estimated by experiment.

12 . The shape measuring apparatus according to claim 11 , wherein
a displacement generation mechanism configured to displace the tip ball and a displacement sensor for measuring a displacement of the displacement generation mechanism are provided, and configured such that the displacement generation mechanism is caused to generate a periodic displacement and both of the tip ball displacement detector and the displacement sensor actually measure the displacement, an amplitude and a phase of an output of the displacement sensor, with respect to an amplitude and a phase of a scanning probe detection value detected by the tip ball displacement detector, are calculated, and processes described above are repeated while a frequency of the periodic displacement generated by the displacement generation mechanism is changed to obtain an actual measurement value of the inverse of the frequency transfer characteristic, whereby the estimated value of the frequency transfer characteristic is obtained.

13 . The shape measuring apparatus according to claim 10 , wherein the inverse of the frequency transfer characteristic is estimated by a theory using a physical model of the scanning probe.

14 . The shape measuring apparatus according to claim 8 , comprising a filter configured to perform a filtering process to remove an unnecessary frequency component from any one of the corrected displacement and the measurement value.

Assignees

• Mitutoyo Corp

Inventors

• Nakagawa Hideyuki
• Ishikawa Nobuhiro

Classifications

• G01B21/045 Primary

  Correction of measurements (G01B9/02055 takes precedence) · CPC title

• G01B5/008

  using coordinate measuring machines · CPC title