Six-Degree-of-Freedom Motion Tracking via Lateral White Light Interferometry
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Solution Overview
Problem
Current methods for real-time visual tracking of six-degree-of-freedom rigid body motion with high precision are limited by pre-calibration errors, thermal expansion, sensor drift, and the uncertainty of micro-domain mechanics, particularly in achieving accurate vertical resolution and overcoming mechanical scanning requirements.
Innovation Solution
The development of a novel method using Laterally Sampled White Light Interferometry (L-SWLI) that eliminates the need for mechanical scanning by analyzing interference fringes on an object's surface, enabling real-time measurement of six degrees of freedom with near-nanometer precision through fringe pattern analysis and two-dimensional Fourier Transform processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical scanning is used to achieve depth recovery in visual servoing, then depth information can be obtained, but real-time measurement capability is limited and system complexity increases
Solution Approach 1:
The patent replaces mechanical scanning systems with an optical interference-based measurement system. By using white light interferometry and analyzing interference fringes in a single lateral image, the system achieves nanometer-scale vertical resolution without moving parts or mechanical scanning, thereby eliminating the associated complexity and enabling real-time measurement.
Solution Approach 2:
The patent introduces interference fringes as an intermediary carrier of depth information. By projecting interference fringes onto the object surface and analyzing their distortion patterns, the system indirectly retrieves three-dimensional shape and depth information from a single two-dimensional image, avoiding the need for mechanical scanning while achieving high vertical resolution.
2Productivity
If pre-calibrated kinematic coordinate transformation is used for multi-degree-of-freedom actuation, then actuation can be achieved, but pre-calibration errors and time variance accumulate leading to reduced precision
Solution Approach 1:
The patent implements real-time visual feedback by continuously measuring the object's position and orientation using interference fringe analysis. This feedback directly compensates for pre-calibration errors and time-varying deviations, maintaining high positioning accuracy throughout multi-degree-of-freedom actuation operations without relying on pre-calibrated transformations.
Solution Approach 2:
Instead of using pre-calibrated forward kinematic transformations to predict object position from actuator commands, the patent inverts the approach by directly measuring the object's actual position and orientation through interference fringe analysis, then using this measured information to guide actuation, thereby eliminating accumulation of calibration errors.
3Measurement precision
If stereoscopic techniques or active illumination with triangulation are used for depth recovery, then the third degree-of-freedom can be recovered, but mechanical scanning or intensive computation is required limiting real-time capability
Solution Approach 1:
The patent replaces mechanical scanning methods with a static optical setup that captures all depth information simultaneously in a single lateral image. By using white light interferometry and analyzing interference fringe patterns, the system achieves nanometer-scale depth resolution without moving parts, enabling real-time measurement of the third degree-of-freedom.
Solution Approach 2:
The patent encodes three-dimensional depth information into two-dimensional interference fringe patterns that can be captured in a single lateral image. By analyzing the distortion and phase of these fringes, the system retrieves depth information without requiring mechanical scanning or intensive computation, achieving real-time depth recovery.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves real-time visual tracking of 6 DOF rigid body motion with ±10 nm precision, effectively compensating for time-varying errors and overcoming limitations in vertical resolution and mechanical scanning, demonstrating improved precision and stability in ultra-precision motion control.
Implementation Method 1
The white light source is amplitude divided at the beam splitter 2 into a reference arm and an object arm. The reference arm reflects off the reference plane 13 and the object arm reflects off the object 10. The two arms are recombined hence interfering with each other and the interference is detected at the CCD array 1.
Implementation Method 2
The white light source is amplitude divided at the beam splitter 2 into a reference arm and an object arm. The reference arm reflects off the reference plane 13
Data Source
AI summary
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.