Interferometer system for controlling non-rectilinear movement of an object

• US 4,621,926 A
• Filed: 04/30/1985
• Issued: 11/11/1986
• Est. Priority Date: 04/30/1985
• Status: Expired due to Term

• Current Assignee: Faro Laser Trackers, LLC (Faro Technologies Incorporated)
• Original Assignee: Lasercon Corporation
• Inventors: Brown, Lawrence B., Merry, J. Bradford
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): MIS, DAVID C
• Application Number:
  US06/729,106
• Time in Patent Office: 560 Days
• Field of Search: 356/4.5, 356/345, 356/363, 356/356, 356/358, 33/125 R, 33/125 A, 33/125 W, 33/503, 250/550
• US Class Current: 356/508
• CPC Class Codes: G01B 11/005 coordinate measuring machines
• CPC Class Codes: G05B 19/25 for continuous-path control
• CPC Class Codes: G05B 2219/37275 Laser, interferometer
• CPC Class Codes: G05B 2219/37288 Tracking lasers follow object, reflection gives 3-D position

Abstract

A system for accurately controlling the movement of an object through a predetermined non-rectilinear path in a predetermined volume having X, Y and Z axes. The system uses three tracking laser interferometers rigidly positioned relative to the volume and a single retroreflector rigidly coupled to the object to control movement of the object non-rectilinearly through the volume along a predetermined path. Using two more tracking laser interferometers and an additional retroreflector rigidly coupled to the object, the system controls angular orientation of the object about one of the axes. Adding a sixth tracking laser interferometer and a third retroreflector to the object, the system can also control angular orientation about the other two axes. Each tracking laser interferometer comprises an interferometer and a tracking mirror which is pivoted to maintain the interferometer output beam on its associated retroreflector.

Claims

1. An apparatus for controlling the movement of an object through a predetermined non-rectilinear path in a predetermined volume having X, Y and Z axes, the combination comprising:

a support;

a first means, coupled to said support and the object, for moving the object simultaneously along the X, Y and Z axes;

a retroreflector rigidly coupled to the object;

a housing rigidly coupled to the support and in a fixed position relative to the predetermined volume;

first, second and third laser interferometers rigidly coupled to said housing, and having first, second and third laser output beams, and first, second and third output signals;

first, second and third tracking mirrors, each associated with one of said laser interferometers for directing the associated laser output beam incident on the center of said retroreflector;

second means for pivotally coupling each of said tracking mirrors to said housing for pivotal movement about two perpendicular axes;

motive means, coupled to each of said tracking mirrors and said housing, for moving each tracking mirror to maintain each of said output beams incident on the center of said retroreflector; and

control means, containing the X, Y and Z spacial coordinates of the predetermined path, coupled to said first means and said motive means and receiving said interferometer output signals, for

(a) repeatedly determining the actual location of the object based on said interferometer output signals,

(b) repeatedly comparing the actual location with the desired location along the predetermined path,

(c) actuating said first means to move the object from its actual location to the next desired location along the predetermined path, and

(d) actuating said motive means to pivot said tracking mirrors to maintain said laser output beams incident on the center of said retroreflector.

2. An apparatus according to claim 1, and further comprising

a second retroreflector rigidly coupled to the object a fixed and known distance from said retroreflector and vertically spaced therefrom,

fourth and fifth laser interferometers rigidly coupled to said housing and having fourth and fifth laser output beams, and fourth and fifth output signals,

fourth and fifth tracking mirrors, each associated with one of said fourth and fifth laser interferometers for directing the associated fourth and fifth laser output beams incident on the center of said second retroreflector,

third means for pivotally coupling each of said fourth and fifth tracking mirrors to said housing for pivotal movement about two perpendicular axes;

said motive means being coupled to each of said fourth and fifth tracking mirrors and said housing for moving said fourth and fifth tracking mirrors to maintain each of said fourth and fifth output beams incident on the center of said second retroreflector,

said first means including means for varying the angular orientation of the object about a horizontal axis parallel to the X axis,

said control means containing the desired angular orientation coordinates of the object about the X axis along the predetermined path, the distance between said reflector and second reflector, and receiving said fourth and fifth output signals, for

(a) repeatedly determining the actual angular orientation of the object about the X axis based on said fourth and fifth output signals,

(b) repeatedly comparing the actual angular orientation about the X axis with the desired angular orientation along the predetermined path,

(c) actuating said means for varying the angular orientation of the object to move the object from its actual orientation to the next desired orientation along the predetermined path, and

(d) actuating said motive means to pivot said fourth and fifth tracking mirrors to maintain said fourth and fifth laser output beams incident on the center of said second retroreflector.

3. An apparatus according to claim 2, and further comprising

a third retroreflector rigidly coupled to the object at fixed and known distances from said retroreflector and second retroreflector and spaced from a line intersecting said retroreflector and second retroreflector,

a sixth laser interferometer rigidly coupled to said housing and having a sixth laser output beam and a sixth output signal,

a sixth tracking mirror associated with said sixth laser interferometer for directing the associated sixth laser output beam incident on the center of said third retroreflector,

fourth means for pivotally coupling said sixth tracking mirror to said housing for pivotal movement about two perpendicular axes,

said motive means being coupled to said sixth tracking mirror and said housing for moving said sixth tracking mirror to maintain said sixth output beam incident on the center of said third retroreflector,

said first means including means for varying the angular orientation of the object about a horizontal axis parallel to the Y axis and about a vertical axis parallel to the Z axis,

said control means containing the desired angular orientation coordinates of the object about the Y and Z axes along the predetermined path, the distances between said third retroreflector and said reflector and second reflector, and receiving said sixth output signal, for

(a) repeatedly determining the actual angular orientation of the object about the Y and Z axes based on said fourth, fifth and sixth output signals,

(b) repeatedly comparing the actual angular orientation about the Y and Z axes with the desired angular orientation along the predetermined path,

(c) actuating said means for varying the angular orientation of the object about the Y and Z axes to move the object from its actual orientation to the next desired orientation along the predetermined path, and

(d) actuating said motive means to pivot said sixth tracking mirror to maintain said sixth laser output beam incident on the center of said third retroreflector.

4. An apparatus according to claim 1, and further comprising

a second retroreflector rigidly coupled to the object a fixed and known distance from said retroreflector and spaced therefrom,

fourth and fifth laser interferometers rigidly coupled to said housing and having fourth and fifth laser output beams, and fourth and fifth output signals,

fourth and fifth tracking mirrors, each associated with one of said fourth and fifth laser interferometers for directing the associated fourth and fifth laser output beams incident on the center of said second retroreflector,

third means for pivotally coupling each of said fourth and fifth tracking mirrors to said housing for pivotal movement about two perpendicular axes;

said motive means being coupled to each of said fourth and fifth tracking mirrors and said housing for moving said fourth and fifth tracking mirrors to maintain each of said fourth and fifth output beams incident on the center of said second retroreflector,

said first means including means for varying the angular orientation of the object about a horizontal axis parallel to one of the X and Y axes,

said control means containing the desired angular orientation coordinates of the object about one of the X and Y axes along the predetermined path, the distance between said reflector and second reflector, and receiving said fourth and fifth output signals, for

(a) repeatedly determining the actual angular orientation of the object about the horizontal axis based on said fourth and fifth output signals,

(b) repeatedly comparing the actual angular orientation with the desired angular orientation along the predetermined path,

(c) actuating said means for varying the angular orientation of the object to move the object from its actual orientation to the next desired orientation along the predetermined path, and

(d) actuating said motive means to pivot said fourth and fifth tracking mirrors to maintain said fourth and fifth laser output beams incident on the center of said second retroreflector.

5. An apparatus according to claim 1, wherein

said motive means comprises a piezoelectric actuator.

6. An apparatus according to claim 1, wherein

said control means comprises a laser beam position sensitive photodetector means for detecting the displacement of the laser beam from the center of said retroreflector.

7. An apparatus according to claim 6, wherein

said photodetector means comprises a quadrant detector.

11. A method according to claim 7, and further comprising the steps of

storing predetermined angular orientation coordinates of the object about a horizontal axis parallel to one of the X and Y axes,

rigidly coupling a second retroreflector a known distance from the retroreflector and spaced therefrom,

directing fourth and fifth laser beams incident on the center of the second retroreflector from fourth and fifth laser interferometers rigidly positioned relative to one another, the first three interferometers and the predetermined volume,

generating a second output signal from the outputs of the fourth and fifth laser interferometers, the distance between the retroreflector and the second retroreflector, and the output signal from the first three laser interferometers representing the actual angular orientation of the object about one of the X and Y axes,

comparing the actual angular orientation of the object with the desired angular orientation along the predetermined path,

varying the angular orientation of the object from its actual orientation to the next desired orientation along the predetermined path,

redirecting the fourth and fifth laser beams incident on the center of the retroreflector, and

continuously repeating the generating, comparing, varying and redirecting steps until the object has traversed the entire predetermined path.

8. A method for controlling the movement of an object through a predetermined non-rectilinear path in a predetermined volume having X, Y and Z axes, comprising the steps of

storing the predetermined X, Y and Z spacial coordinates of the predetermined path,

positioning the object in the predetermined volume with a retroreflector rigidly coupled thereto,

directing three laser beams incident on the center of the retroreflector from three laser interferometers rigidly positioned relative to one another and to the predetermined volume,

generating an output signal from the laser interferometers representing the actual location of the retroreflector and object,

comparing the actual location of the retroreflector and object with the desired location along the predetermined path,

moving the object from its actual location to the next desired location along the predetermined path,

redirecting the three laser beams incident on the center of the retroreflector, and

continuously repeating the generating, comparing, moving and redirecting steps until the object has traversed the entire predetermined path.

9. A method according to claim 8, and further comprising the steps of

storing predetermined angular orientation coordinates of the object about a horizontal axis parallel to the X axis,

rigidly coupling a second retroreflector a known distance from the retroreflector and vertically spaced therefrom,

directing fourth and fifth laser beams incident on the center of the second retroreflector from fourth and fifth laser interferometers rigidly positioned relative to one another, the first three interferometers and the predetermined volume,

generating a second output signal from the outputs of the fourth and fifth laser interferometers, the distance between the retroreflector and the second retroreflector, and the output signal from the first three laser interferometers representing the actual angular orientation of the object about the horizontal axis,

comparing the actual angular orientation of the object with the desired angular orientation along the predetermined path,

varying the angular orientation of the object from its actual orientation to the next desired orientation along the predetermined path,

redirecting the fourth and fifth laser beams incident on the center of the retroreflector, and

continuously repeating the generating, comparing, varying and redirecting steps until the object has traversed the entire predetermined path.

10. A method according to claim 9, and further comprising the steps of

storing predetermined angular orientation coordinates of the object about a horizontal axis parallel to the Y axis and a vertical axis parallel to the Z axis,

rigidly coupling a third retroreflector at known distances from the retroreflector and second retroreflector and spaced from a line intersecting the retroreflector and second retroreflector,

directing a sixth laser beam incident on the center of the third retroreflector from a sixth laser interferometer rigidly positioned relative to the other five interferometers and the predetermined volume,

generating third and fourth output signals from the output of the sixth laser interferometer, the second output signal from the outputs of the fourth and fifth laser interferometers, the distances between the third retroreflector and the retroreflector and second retroreflector, and the output signal from the first three laser interferometers representing the actual angular orientation of the object about the Y and Z axes,

comparing the actual angular orientations of the object about the Y and Z axes with the desired angular orientation along the predetermined path,

varying the angular orientations of the object from its actual orientations to the next desired orientations along the predetermined path,

redirecting the sixth laser beam incident on the center of the third retroreflector, and

continuously repeating the generating, comparing, varying and redirecting steps until the object has traversed the entire predetermined path.