Ph.D. Thesis Summary


Harry Douglas Garner, Jr.

May 2001

In many nonlinear systems such as multiple degree of freedom wrist-like actuators, absolute measurement of the orientation is essential to control such devices. In this thesis a real-time vision based absolute orientation sensor has been developed to measure the absolute orientation of a spherical body for use in real-time control. This sensor has the significant advantage over those using multiple single-axis encoders by providing a non-contact means of absolute orientation measurement, which has the potential to simplify the overall system dynamics and give improved performance. The specific objectives of this thesis are the development of a technique for recovering the absolute orientation of a spherical body through analysis of a specially designed grid pattern on the body, and a means of modeling such vision based measurement systems.

These objectives have been accomplished by the following tasks. First, a new optimized grid pattern design suitable for direct application to the rotor of the VR spherical motor has been developed along with more practical techniques for transferring such a pattern onto a spherical surface. The expected resolution limits using such a grid pattern with a vision based measurement technique have also been investigated. To aid in this design and other important aspects related to the vision based absolute orientation sensor, an OpenGL based grid pattern image modeling environment has been developed. Efficient image processing techniques more suitable for real-time machine vision have also been developed for analysis of the grid pattern images. These image processing results have also been used in a mathematically sound procedure for recovery of the absolute orientation that utilizes camera calibration and a closed form orientation recovery technique well suited for real-time applications. Finally, experimental tests and an OpenGL based grid pattern modeling environment have been used to verify the capability of the absolute orientation measurement system to make simultaneous high-resolution measurements of multiple degrees-of-freedom. It is expected that this thesis will extend the use of vision based measurement systems to real-time control applications that require absolute measurements.