Inertial dimensional metrology

• US 9,557,157 B2
• Filed: 12/01/2014
• Issued: 01/31/2017
• Est. Priority Date: 12/01/2014
• Status: Active Grant

• Current Assignee: Advanced Theodolite Technology, Inc. (Sandvik AB)
• Original Assignee: Edward A. Ingham, Steven Eugene Ihlenfeldt
• Inventors: Ihlenfeldt, Steven Eugene, Ingham, Edward A.
• Primary Examiner(s): Bennett, G. Bradley
• Application Number:
  US14/556,301
• Publication Number:
  US 20160153767A1
• Time in Patent Office: 792 Days
• Field of Search: 335/02, 335/03
• US Class Current: 1/1
• CPC Class Codes: G01B 11/005 coordinate measuring machines
• CPC Class Codes: G01B 5/008 using coordinate measuring machines
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors

Abstract

A method of performing dimensional metrology of an object (12) includes incorporating an Inertial Measurement Unit (IMU-18) with an elongate probe (20) in a portable metroprobe (10). A tip (22) of the probe (20) has an offset length (L) from an origin (26) of a coordinate system in the IMU (18) and position (X,Y,Z) thereof is correlated based on attitude (A,B,C) measurement of the IMU (18). The metroprobe (10) is transported in sequence to a complement of survey points (Pn) on the object (12) for measuring corresponding coordinates (X,Y,Z) thereof based on measured attitude (A,B,C) of the IMU (18).

Claims

1. A method of performing dimensional metrology of an object comprising:

integrating an Inertial Measurement Unit (IMU) with an elongate probe in a portable metroprobe;

correlating position of a tip of said probe having a first offset length from an origin of a coordinate system in said IMU based on attitude measurement of said IMU; and

transporting said metroprobe to a plurality of survey points on said object for measuring corresponding coordinates thereof based on measured attitude of said IMU.

2. A method according to claim 1 wherein:

said IMU comprises a plurality of accelerometers and gyroscopes for correspondingly defining three orthogonal linear axes and three respective angular axes; and

linear position of said probe tip is correlated to said coordinate system origin based on angular attitude of said IMU as measured by said gyroscopes.

3. A method according to claim 2 further comprising transporting said metroprobe to a reference location to establish at said probe tip three linear reference coordinates relative to said three linear axes and three angular reference coordinates relative to said three angular axes.

4. A method according to claim 2 wherein said probe tip offset position is correlated to said coordinate system origin based on angular position of said probe relative to at least one of said three linear axes;

and said metroprobe is operable with attitudes ranging from horizontal to vertical.

5. A method according to claim 1 further comprising:

transporting said metroprobe in a sequential survey of said survey points;

measuring linear positions of said IMU at each of said survey points;

measuring attitude of said IMU to correlate therewith attitude of said probe; and

establishing corresponding linear coordinates of said probe tip in contact with said survey points correlated to said measured linear positions of said IMU.

6. A method according to claim 5 wherein:

said IMU comprises a plurality of accelerometers and gyroscopes for correspondingly defining three orthogonal linear axes and three respective angular axes;

said angular attitude of said IMU is measured by said gyroscopes in said IMU; and

said linear positions of said IMU are measured by both said accelerometers and said gyroscopes in said IMU.

7. A method according to claim 6 wherein said metroprobe is autonomous in performing said dimensional metrology of said object, and is operatively joined to a controller for establishing said linear coordinates of said probe tip at said survey points relative to said three orthogonal linear axes based on said measured linear position and attitude of said IMU.

8. A method according to claim 7 wherein said IMU is subject to drift errors, and said linear coordinates at said survey points are corrected to reduce said drift errors.

9. A method according to claim 7 further comprising:

transporting said metroprobe between two reference locations in surveying said survey points;

establishing a position error vector based on a difference in linear positions measured at said two reference locations; and

resolving said error vector to reduce corresponding errors in said linear coordinates at said survey points.

10. A method according to claim 9 wherein:

said IMU drift errors increase with time during transportation of said metroprobe during said measurement survey; and

said error vector is resolved to correspondingly reduce more error in said linear coordinates at subsequent survey points.

11. A method according to claim 8 further comprising:

placing said metroprobe in a stationary cradle at one of said survey points; and

introducing a zero velocity update in said IMU to reduce said drift errors in all three linear coordinates for subsequent survey points.

12. A method according to claim 5 further comprising:

measuring linear positions of said IMU by an independent coordinate measurement machine (CMM) having line-of-sight with said metroprobe; and

establishing said linear coordinates of said probe tip at said survey points correlated to said linear positions of said IMU measured by said CMM.

13. A method according to claim 12 wherein:

said CMM comprises a laser tracker having a variable horizontal and vertical field of view;

a cooperating target is integrated with said IMU and said probe in said metroprobe, and has a second offset length from said origin of said coordinate system in said IMU; and

position of said target as measured by said laser tracker is correlated to said coordinate system origin in said IMU based on said attitude measurement of said IMU for correspondingly establishing said linear position of said IMU; and

in turn establishing said linear coordinates of said probe tip at said survey points.

14. A method according to claim 13 wherein:

said target comprises a spherically mounted retro-reflector (SMR) affixed atop said IMU in said metroprobe; and

said IMU comprises a plurality of accelerometers and gyroscopes for correspondingly defining three orthogonal linear axes and three respective angular axes.

15. A method according to claim 14 further comprising:

measuring linear position of said target using said laser tracker having line-of-sight therewith to in turn establish said linear coordinates of said probe tip as correlated with said target through said IMU; and

measuring linear position of said IMU using said accelerometers therein when line-of-sight to said target is blocked to in turn establish said linear coordinates of said probe tip as correlated with said IMU.

16. A method according to claim 14 further comprising measuring attitude of said IMU using said gyroscopes therein to correlate with attitude of both said probe and said target having corresponding offset lengths to correlate said linear position of said probe tip to said coordinate system origin in said IMU.

17. A method according to claim 14 further comprising:

placing said metroprobe in a stationary cradle at one of said survey points when line-of-sight to said target is blocked; and

introducing a zero velocity update in said IMU to reduce drift errors in all three linear coordinates in sequential survey points in which line-of-sight to said target is also blocked.

18. A method according to claim 14 further comprising:

operatively joining said laser tracker and said IMU to a controller;

measuring linear position of said IMU using said accelerometers therein;

correlating position of said SMR target to said measured linear position of said IMU; and

controlling said laser tracker to follow movement of said target atop said metroprobe based on said measured linear position of said IMU.

19. A method according to claim 14 wherein:

said target comprises a multiaxis motorized SMR pivotally mounted atop said IMU in said metroprobe; and

said laser tracker, said SMR target, and said IMU are operatively joined to a controller for automatically tracking said laser tracker to said SMR target and automatically back-tracking said SMR target to said laser tracker in response to correlated position of said SMR relative to position and attitude of said IMU.

20. A method according to claim 14 further comprising:

integrating a second IMU with said laser tracker for measuring position and attitude of said second IMU;

conducting said survey using said laser tracker at two different reference locations having line-of-sight with a plurality of common survey points for measuring coordinates thereof; and

performing a least squares iterative optimization process using said position and attitude of said second IMU at said two different reference locations, and said measured coordinates at said common survey points to conform all measurements from said laser tracker to a common coordinate reference system.

21. A system for performing dimensional metrology of an object comprising:

a coordinate measurement machine laser tracker having a variable horizontal and vertical field of view;

a portable metroprobe including an inertial measurement unit integrated with both an elongate probe and a spherically mounted retro-reflector target;

a controller operatively joined to said laser tracker and said IMU for controlling operation thereof;

said controller being configured to correlate position and attitude of both said probe and said target to a reference coordinate system in said IMU; and

said laser tracker being configured in conjunction with said metroprobe for establishing coordinates at said probe at a plurality of survey locations on said object based on location of said target as measured by said laser tracker and based also on attitude of said IMU as measured by said IMU.