Methods and systems for ultra-precise measurement and control of object motion in six degrees of freedom by projection and measurement of interference fringes

• US 20070013916A1
• Filed: 07/18/2006
• Published: 01/18/2007
• Est. Priority Date: 07/18/2005
• Status: Active Grant

• Current Assignee: Ohio State Innovation Foundation (Ohio State University)
• Original Assignee: Ohio State University
• Inventors: Menq, Chia-Hsiang, Kim, Jung
• Granted Patent: US 7,705,996 B2
• Time in Patent Office: Days
• US Class Current: 356/498
• CPC Class Codes: G01B 9/02067 by electronic control systems, i.e. using feedback acting on optics or light
• CPC Class Codes: G01B 9/02084 Processing in the Fourier or frequency domain when not imaged in the frequency domain
• CPC Class Codes: G01B 9/0209 Low-coherence interferometers
• CPC Class Codes: G01B 9/04 Measuring microscopes

Abstract

A system and method for active visual measurement and servo control using laterally sampled white light interferometry (L-SWLI) for real-time visual tracking of six-degree-of-freedom (6 DOF) rigid body motion with near-nanometer precision. The visual tracking system is integrated with a 6 DOF motion stage to realize an ultra precision six-axis visual servo control system. Use of L-SWLI obtains the complete pose of the target object from a single image frame to enable real-time tracking. Six-degree-of-freedom motions are obtained by measuring the fringe pattern on multiple surfaces of the object or from a single surface with additional information gained from conventional image processing techniques.

Claims

1. A system for active visual measurement techniques, laterally sampled white light interferometry, capable of real-time visual tracking of six-degree-of-freedom rigid body motion with near-nanometer precision, comprising:

a computer controlled six-axis magnetic suspension stage;

a white light interference microscope including at least one lens with an interferometer attachment, the lens being optically coupled to a CCD camera capable of capturing and transferring images to a computer programmed to calculate six-degree-of-freedom rigid body motion by conducting two-dimensional Fourier Transform fringe pattern analysis utilizing an inner control loop for controlling the six-axis magnetic suspension stage,

and an outer control loop for employing visual feedback from the laterally sampled white light interferometry measurement, the inner control loop operative to stabilize and govern the non-linear transient dynamics of the six-axis magnetic suspension stage, and the outer control loop operative to control the six-axis magnetic suspension stage with respect to a visual coordinate system.

2. A method of real-time visual tracking of 6 DOF rigid body motion with near-nanometer precision by use of:

a computer controlled six-axis magnetic suspension stage integrated with a white light interference microscope, containing at least one lens with an interferometer attachment, the lens being optically coupled to a CCD camera capable of capturing and transferring images to a computer programmed to calculate six-degree-of-freedom rigid body motion by conducting two-dimensional Fourier Transform fringe pattern analysis utilizing an inner control loop for controlling the six-axis magnetic suspension stage and an outer control loop for employing visual feedback from the laterally sampled white light interferometry measurement, the inner control loop operative to stabilize and govern the non-linear transient dynamics of the six-axis magnetic suspension stage, and the outer control loop operative to control the six-axis magnetic suspension stage with respect to a visual coordinate system.

3. A method of real-time measurement of object motion in six degrees of freedom by projection of L-SWLI interference fringes onto a target plane of the object, obtaining and images of the interferences fringes on the target plane of the object, and determining motion of the object in six degrees of freedom based upon the images of the interference fringes.