Position measurement system and method using cone math calibration

• US 20020154294A1
• Filed: 10/30/2001
• Published: 10/24/2002
• Est. Priority Date: 10/30/2000
• Status: Active Grant

• Current Assignee: 7D Kinematic Metrology Inc.
• Original Assignee: Arc Second, Inc. (Nikon Corporation)
• Inventors: Takagi, Hiro, Sobel, Michael J., Pratt, Timothy, Hedges, Thomas M.
• Granted Patent: US 6,535,282 B2
• Time in Patent Office: Days
• US Class Current: 356/141.4
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 5/16 using electromagnetic waves other than radio waves

Abstract

An improved three-dimensional position detector and measurement system includes one or more transmitters that each transmit planar light beams and a strobe pulse and a receiver that responds to illumination from the beams and the strobe. The receiver in the system includes calibration logic for executing a quadratic mathematical algorithm to uniquely characterize said planar beams of each of said optical transmitters active in said measurement field. In one embodiment, the quadratic mathematical algorithm uses cones to represent the scan path of the planar beams.

Claims

1. An improved position measurement system, comprising:

at least one optical transmitter positioned within a position measurement field to generate a pair of planar light beams and a strobe pulse to illuminate said measurement field;

at least one selectively positionable receiver within said position measurement field to generate position measurement data in response to said illumination from said planar beams and said strobe pulse; and

calibration logic associated with said light detector receiver for executing a quadratic mathematical algorithm to uniquely characterize said planar beams of each of said optical transmitters active in said measurement field.

2. The improved position measurement system of claim 1, wherein said quadratic mathematical algorithm uses a cone shape to describe a scan of each planar beam.

3. The improved position measurement system of claim 2, wherein the cone shape is selected from a group consisting of an elliptic cone shape, a parabolic cone shape, or hyperbolic cone shape.

4. The improved position measurement system of claim 2, wherein each cone shape has a cone surface corresponding to one planar beam.

5. The improved position measurement system of claim 4, wherein the calibration logic executes the quadratic mathematical algorithm by:

moving the cone surface to be tangential to a first axis;

rotating the cone surface about the first axis by a first angle to generate a second cone surface;

rotating the second cone surface about a second angle representing a scan angle of one of said planar beams at a given time; and

calculating a vector expression corresponding to a point at which said one of said planar beams intersects the receiver.

6. The improved position measurement system of claim 1, additionally including a plurality of base stations selectively located within said measurement field for monitoring calibration data uniquely associated with each optical transmitter active in said measurement field.

7. The improved position measurement system of claim 6, wherein each base station additionally includes recalibration logic for monitoring and recalculating transmitter calibration data for each active transmitter within said system in response to detection of any change in one or more of a plurality of transmitter parameters which would induce errors in said transmitter calibration data.

8. The improved position measurement system of claim 1, wherein said quadratic mathematical model is determined by a plurality of measurements of planar beam shapes for each optical transmitter and wherein the transmitter includes a lookup table to store parameters corresponding to the relative positions of the planar beams for each transmitter.

9. The improved position measurement system of claim 1, wherein the receiver includes a reference pulse stabilization loop.

10. The improved position measurement system of claim 9, wherein the reference pulse stabilization loop includes:

a period filter that produces a stable average reference period; and

a feedback loop that predicts a subsequent reference pulse time based on a previous predicted pulse time, the stable average reference period, and a loop error.

11. In a position measurement system which includes an optical transmitter for generating a pair of spaced apart planar light beams and a periodic strobe pulse and a selectively positionable detector having at least two spaced apart optical detectors wherein said transmitter and detector are positioned in a measurement field, an improvement comprising:

means to continuously monitor and calculate a pulse width of said beams;

means to characterize said planar beams using a quadratic mathematical algorithm, wherein a range distance from said transmitter position to said detector position is estimated based on the pulse width and the quadratic mathematical algorithm; and

means to display said estimated range to a user.

12. The improved position measurement system of claim 11, additionally including means to permit said user to set an error bounds as a linear measurement.

13. The improved position measurement system of claim 12, additionally including means to convert a selected error bound and estimated range data into a determined angular error.

14. The improved position measurement system of claim 13, additionally including means to signal the user when measurements are either within or outside an established error bound.

15. The improved position measurement system of claim 11, wherein said quadratic mathematical algorithm uses a cone shape to describe a scan of each planar beam.

16. The improved position measurement system of claim 15, wherein the cone shape is selected from a group consisting of an elliptic cone shape, a parabolic cone shape, or hyperbolic cone shape.

17. The improved position measurement system of claim 15, wherein each cone shape has a cone surface corresponding to one planar beam.

18. The improved position measurement system of claim 17, wherein the calibration logic executes the quadratic mathematical algorithm by:

moving the cone surface to be tangential to a first axis;

rotating the cone surface about the first axis by a first angle to generate a second cone surface;

rotating the second cone surface about a second angle representing a scan angle of one of said planar beams at a given time; and

calculating a vector expression corresponding to a point at which said one of said planar beams intersects the detector.

19. The improved position measurement system of claim 11, wherein the receiver includes a reference pulse stabilization loop.

20. The improved position measurement system of claim 19, wherein the reference pulse stabilization loop includes:

a period filter that produces a stable average reference period; and

a feedback loop that predicts a subsequent reference pulse time based on a previous predicted pulse time, the stable average reference period, and a loop error.

21. An improved position measurement method, comprising:

positioning at least one optical transmitter within a position measurement field to generate a pair of planar laser beams and a strobe pulse to illuminate said measurement field;

placing at least one selectively positionable light detector receiver within said position measurement field to generate position management data in response to said illumination from said planar beams and said strobe pulse; and

executing a quadratic mathematical algorithm using calibration logic associated with said light detector receiver to uniquely characterize said planar beams of each of said optical transmitters active in said measurement field.

22. The improved position measurement method of claim 21, wherein the quadratic mathematical algorithm in the executing act uses a cone shape to describe a scan of each planar beam, wherein the cone shape has a cone surface corresponding to one shaped beam.

23. The improved position measurement method of claim 22, wherein the cone shape is selected from a group consisting of an elliptic cone shape, a parabolic cone shape, or hyperbolic cone shape.

24. The improved position measurement method of claim 21, wherein executing the quadratic mathematical algorithm includes:

moving the cone surface to be tangential to a first axis;

rotating the cone surface about the first axis by a first angle to generate a second cone surface;

rotating the second cone surface about a second angle representing a scan angle of one of said planar beams at a given time; and

calculating a vector expression corresponding to a point at which said one of said planar beams intersects the light detector receiver.

25. The improved position measurement method of claim 24, further comprising positioning a plurality of base stations selectively located within said measurement field for monitoring calibration data uniquely associated with each optical transmitter active in said measurement field.

26. The improved position measurement method of claim 25, wherein each base station conducts monitoring and recalculating transmitter calibration data for each active transmitter within said system in response to detect any change in one or more of a plurality of transmitter parameters which would induce errors in said transmitter calibration data.

27. The improved position measurement method of claim 21, wherein said quadratic mathematical algorithm is determined by a plurality of measurements of the shaped beams for each optical transmitter and wherein the method further includes the act of storing parameters corresponding to the relative positions of the shaped beams for each transmitter in a lookup table.

28. The improved position measurement method of claim 21, further comprising:

calculating a stable average reference period; and

predicting a subsequent reference pulse time based on a previous stable average reference period, the stable average reference period from the calculating step, and a loop error.

30. The receiver of claim 29, wherein the receiver is selectively positionable within the position measurement field.

31. The receiver of claim 29, wherein the quadratic mathematical algorithm in said calibration logic uses a cone shape to describe a scan of each planar beam.

32. The receiver of claim 31, wherein the cone shape is selected from a group consisting of an elliptic cone shape, a parabolic cone shape, or hyperbolic cone shape.

33. The receiver of claim 32, wherein each cone shape has a cone surface corresponding to one planar beam.

34. The receiver of claim 33, wherein the calibration logic executes the quadratic mathematical algorithm by:

moving the cone surface to be tangential to a first axis;

rotating the cone surface about the first axis by a first angle to generate a second cone surface;

rotating the second cone surface about a second angle representing a scan angle of one of said planar beams at a given time; and

calculating a vector expression corresponding to a point at which said one of said planar beams intersects the receiver.

35. The receiver of claim 29, wherein said quadratic mathematical model is determined by a plurality of measurements of planar beam shapes for each optical transmitter and wherein the transmitter includes a lookup table to store parameters corresponding to the relative positions of the planar beams for each transmitter.

36. The receiver of claim 29, wherein the receiver includes a reference pulse stabilization loop.

37. The receiver of claim 36, wherein the reference pulse stabilization loop includes:

a period filter that produces a stable average reference period; and

a feedback loop that predicts a subsequent reference pulse time based on a previous predicted pulse time, the stable average reference period, and a loop error.

29. A receiver for an improved position measurement system having at least one optical transmitter positioned within a position measurement field that generates a pair of planar light beams and a strobe pulse to illuminate the position measurement field, the receiver comprising:

a data generator for generating position measurement data in response to illumination of the receiver from said planar beams and said strobe pulse; and

calibration logic associated with the receiver for executing a quadratic mathematical algorithm to uniquely characterize said planar beams of each of said optical transmitters active in said measurement field.