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

Patent metadata

Field	Value
Publication number	US-9683839-B2
Application number	US-201514732056-A
Country	US
Kind code	B2
Filing date	Jun 5, 2015
Priority date	Jul 18, 2014
Publication date	Jun 20, 2017
Grant date	Jun 20, 2017

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

The invention claimed is:

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 value of displacement of the tip ball of the scanning probe by a tip ball displacement detector;
detecting a value of displacement of a moving mechanism for relatively moving the object to be measured with respect to 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, based on the angle, the detected value of displacement of the tip ball;
outputting a corrected value of the displacement of the tip ball; and
adding the corrected value and the detected value of displacement of the moving mechanism to determine a calculated measurement value.

2. The method of correcting a measurement error of a shape measuring apparatus according to claim 1 , wherein
the correcting of the detected value of displacement of the tip ball and the outputting of the corrected value includes:
calculating a sinusoidal value of the angle;
correcting the detected value of displacement of the tip ball based on an inverse of a frequency transfer characteristic from the tip ball to the tip ball displacement detector; and
adding a product of the corrected value of the displacement of the tip ball and the sinusoidal value to a product of a subtracted value of the sinusoidal value from 1 and the detected value of 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
in the detecting of the value of displacement of the tip ball, a displacement generation mechanism for displacing the tip ball and a displacement sensor for measuring a displacement provided by 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 performs measuring of the periodic 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 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 value of the displacement and the calculated 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 value of displacement of the tip ball of the scanning probe;
a scale configured to detect a value of displacement of a moving mechanism for relatively moving the object to be measured with respect to 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, based on the angle, the detected value of displacement of the tip ball and output a corrected value of the displacement of the tip ball; and
a first adder configured to add the corrected value and the detected value of displacement of the moving mechanism to determine a calculated 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 detected value of displacement of the tip ball, based on 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 value of the displacement of the tip ball and the sinusoidal value to a product of a subtraction of the sinusoidal value from 1 and the detected value of 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 , further comprising:
a displacement generation mechanism configured to displace the tip ball; and
a displacement sensor configured to perform measuring of a displacement provided by the displacement generation mechanism are provided,
wherein the displacement generation mechanism is caused to generate a periodic displacement and both of the tip ball displacement detector and the displacement sensor perform measuring of the periodic 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 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 value of the displacement and the calculated measurement value.

Assignees

• Mitutoyo Corp

Inventors

• Nakagawa Hideyuki
• Ishikawa Nobuhiro

Classifications

• G01B5/008

  using coordinate measuring machines · CPC title

• G01B21/045 Primary

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