Calibration process for shape measurement

• US 6,199,024 B1
• Filed: 09/07/1999
• Issued: 03/06/2001
• Est. Priority Date: 09/07/1999
• Status: Expired due to Term

• Current Assignee: Nextec Technologies 2001 Ltd. (Han's Laser Technology Industry Group Co., Ltd.)
• Original Assignee: Nextel
• Inventors: Bunimovich, David, Horovitz, Gabi
• Primary Examiner(s): ASSOUAD, PATRICK J
• Application Number:
  US09/391,611
• Time in Patent Office: 546 Days
• Field of Search: 702/95, 702/152, 702/153, 702/168, 33/561
• US Class Current: 702/95
• CPC Class Codes: G01B 21/20 for measuring contours or curvatures, e.g. determining profile

Abstract

A calibration method for a shape measurement with a variable distance between the scanning probe datum point and the measuring point on the surface of a workpiece, is provided. Based on the measured distance between the scanning probe datum point and each of a plurality of measuring points on the surface of a calibration object, and on the position of a reference point on a motion system platform on which the scanning probe assembly is mounted, corresponding to the scanning probe being in a sensing position of each of the plurality of measuring points, the method provides the necessary data for calculating the coordinate of a measuring point of the workpiece from the measured distance between the scanning probe datum point and the measuring point, and from the position of the reference point corresponding to the to the scanning probe being in a sensing position of the measuring point.

Claims

1. In a shape measuring system for measuring a shape of a workpiece, the shape measuring system having a fixed coordinate frame with a fixed origin point, a method for calibrating a configuration of a scanning probe having a variable distance to the workpiece, the scanning probe being held by a scanning probe holder, the method comprising the steps of:

(a) providing a calibration object to serve as the workpiece, said calibration object including a calibration point;

(b) for each of a first plurality of points on a surface of said calibration object;

(i) measuring a distance from said each point to the scanning probe; and

(ii) measuring a position of a reference point, when the scanning probe is in a scanning position of said each point, thereby providing a first set of measured calibration data; and

(c) performing a first simultaneous fitting of both an inclination of the scanning probe and a position of said calibration point to said first set of measured calibration data, thereby providing a first set of inferred calibration data.

2. The method of claim 1, wherein said calibration object includes a calibration sphere, with a center of said calibration sphere serving as said calibration point.

3. The method of claim 1, wherein said inclination of the scanning probe is expressed in polar coordinates relative to the fixed coordinate frame.

4. The method of claim 1, wherein said position of said reference point is expressed relative to the fixed origin point.

5. The method of claim 1, wherein said position of said calibration point is expressed relative to the fixed origin point.

6. The method of claim 1, further comprising the steps of:

(d) using an inclination of the scanning probe holder as a first estimation of said inclination of the scanning probe for said first simultaneous fitting.

7. The method of claim 6, wherein said inclination of the scanning probe holder is expressed in polar coordinates relative to the fixed coordinate frame.

8. The method of claim 1, further comprising the steps of:

(d) using said first set of inferred calibration data for locating each of a second plurality of points on said surface of said calibration object;

(e) for each of said second plurality of points on said surface of said calibration object;

(i) measuring a distance from said each point to the scanning probe, and

(ii) measuring a position of said reference point, when the scanning probe is in a scanning position of said each point, thereby providing a second set of measured calibration data; and

(f) performing a second simultaneous fitting of both said inclination of the scanning probe and said position of said calibration point to said second set of measured calibration data, thereby providing a second set of inferred calibration data, wherein said first set of inferred calibration data is used as a first estimation of both said inclination of the scanning probe and said position of said calibration point.

9. In a shape measuring system for measuring a shape of a workpiece, a method for calibrating a plurality of configurations of at least one scanning probe having a variable distance to the workpiece, each at least one scanning probe having an offset from a reference point in each respective configuration thereof, the method comprising the steps of:

(a) providing a calibration object including a calibration point;

(b) calibrating each configuration separately, to provide a set of inferred calibration data for said each configuration including an inclination of a respective scanning probe of said each configuration and a position of said calibration point;

(c) designating one of the plurality of configurations as a master configuration; and

(d) calculating, for each configuration other than said master configuration, a difference between said offset of said respective scanning probe of said each configuration other than said master configuration, and said offset of said respective scanning probe of said master configuration.

10. The method of claim 9, wherein said separate calibrating includes the steps of, for said each configuration:

(i) for each of a plurality of points on a surface of said calibration object;

(A) measuring a distance from said each point to said respective scanning probe of said each configuration; and

(B) measuring a position of said reference point, when said respective scanning probe of said each configuration is in a scanning position of said each point,

thereby providing a set of measured calibration data for said each configuration; and

(ii) simultaneously fitting both said inclination of said respective scanning probe of said each configuration and said position of said calibration point to said set of measured calibration data for said each configuration, thereby providing said set of inferred calibration data for said each configuration.

11. A method for measuring a shape of a workpiece using a configuration of a scanning probe having a variable distance to the workpiece, the method comprising the steps of:

(a) providing a calibration object including a calibration point;

(b) calibrating the configuration to provide a set of inferred calibration data including an inclination of the scanning probe and a position of said calibration point;

(c) for each of a plurality of points on a surface of the workpiece;

(i) measuring a distance from said each point to the scanning probe; and

(ii) measuring a position of a reference point, when the scanning probe is in a scanning position of said each point, thereby providing a set of measured data for said each point;

(d) calculating coordinates for each of said plurality of points, using said set of measured data for said each point and said set of inferred calibration data; and

(e) determining the shape of the workpiece, using said coordinates of said plurality of points.

12. The method of claim 11, wherein said calibrating includes the steps of:

(i) for each of a plurality of points on a surface of said calibration object;

(A) measuring a distance from said each point to the scanning probe; and

(B) measuring a position of a reference point, when the scanning probe is in a scanning position of said each point,

thereby providing a set of measured calibration data; and

(ii) simultaneously fitting both said inclination of the scanning probe and said position of said calibration point to said set of measured calibration data, thereby providing said set of inferred calibration data.

13. A method for measuring a shape of a workpiece using at least one of a plurality of configurations of at least one scanning probe having a variable distance to the workpiece, each at least one scanning probe having an offset from a reference point in each respective configuration thereof, the method comprising the steps of:

(a) providing a calibration object including a calibration point;

(b) calibrating each configuration separately, to provide a set of inferred calibration data for said each configuration including an inclination of a respective scanning probe of said each configuration and a position of said calibration point;

(c) designating one of the plurality of configurations as a master configuration;

(d) calculating for each of the configurations other than said master configuration, a difference between said offset of said respective scanning probe of said each configuration other than said master configuration, and said offset of said respective scanning probe of said master configuration, thereby providing an offset difference for said each configuration other than said master configuration;

(e) for each of a plurality of points on a surface of the workpiece, scanning said each point using a respective one of said at least one scanning probe in a respective configuration thereof, thereby measuring, for said each point;

(i) a distance from said each point to said respective scanning probe; and

(ii) a position of the reference point, when said respective scanning probe is in a scanning position of said each point, thereby providing a set of measured data for said each point;

(f) calculating coordinates for each of said plurality of points, using both said set of measured data for said each point, and said set of inferred calibration data for said respective configuration of said each point, said calculating also using said offset difference of said respective configuration of said each point, if said respective configuration of said each point is a configuration other than said master configuration; and

(g) determining the shape of the workpiece, using said coordinates of said plurality of points.

14. The method of claim 13, wherein said separate calibrating includes the steps of, for said each configuration:

(i) for each of a plurality of points on a surface of said calibration object;

(A) measuring a distance from said each point to said respective scanning probe of said each configuration; and

(B) measuring a position of said reference point, when said respective scanning probe of said each configuration is in a scanning position of said each point,

thereby providing a set of measured calibration data for said each configuration; and

(ii) simultaneously fitting both said inclination of said respective scanning probe of said each configuration and said position of said calibration point to said set of measured calibration data for said each configuration, thereby providing said set of inferred calibration data for said each configuration.