Signal & Image Processing

Optical Tracking System for Rotor Blade Motion

Precise measurements of modal oscillations and vibrations in the rotorcraft are necessary for understanding the vibration modes. An innovative and inexpensive optical imaging system has been designed for non-contact measurements of all the components in-plane, components out-of-plane, and torsional distortions. This system utilizes structured light projected into the helicopter rotor blades. The imaging system employs 3-D profile gauging techniques and can provide real-time information. It thus maps amplitude, phase, and temporal evolution of modal oscillations throughout the complete helicopter blade. The measurements may be performed while the helicopter is in flight. The system can be accurate to 0.01 of an inch. During Phase I, we have performed numerical simulation and laboratory experiments, where the feasibility and the attainable precision have been demonstrated. A prototype system is planned for Phase II.

Current Status

Analysis performed with fixed images and optical projection.
Both numerical simulation and experimental observations have been made.
Image acquisition system set up.
Analysis software developed.
Image processing environment developed.
Various image processing tools.
Histogram, threshold, noise removal, interference removal, grid removal, trace identification, ridge detection, thinning, clustering.
Expert system.
Flexible, menu-driven development tool.
Fourier Transform technique, Moiré technique and subpixel analysis techniques used to measure deformations. Both numerical simulation and imaging of simulated rotor blade analyzed.
Two candidate techniques, Fourier Transform and Moiré technique, found to provide excellent resolutions, equivalent to about 0.01" displacement over a 20’ span.
Time sequence of rotating images acquired and analyzed.
Overall, demonstration of the measurement’s precision as well as the concept measuring time sequence images to obtain the modal information.

Innocations

Use of optical projection
Use of Fourier Technique to obtain flapping, bending, and TOR
Use of Moiré fringe to obtain deformations and vibrations
Optimization of illumination pattern with desired modal parameters.

Features

Extremely precise measurements of modal parameters (better than 0.01 of an inch)
Non-intrusive, easily mountable on the rotorcraft
In-flight measurements doable during actual flight
Choice of illumination and analysis adaptable to specific modes and modal

Parameters