Browsing by Author "Dr. Edward Grant, Committee Co-Chair"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    Development of Millimeter Scale Motors for Miniature Direct Drive Robots
    (2002-09-30) Palmer, Jeremy Andrew; Dr. Edward Grant, Committee Co-Chair; Dr. Jeffrey Eischen, Committee Co-Chair
    The twentieth century marked a period of rapid expansion of technology associated with miniaturization of engineering systems. A recent theme in this trend is the development of miniature, distributed robots that mimic insect behavior and locomotion. This research addresses the need for millimeter-scale, direct drive, high force/torque motors to support these platforms. Among the technologies currently available, scalable motors based on piezoelectric transducers are the focus. The specific contributions of this work are as follows. (1.) The design, analysis, and characterization of a macro-scale linear piezomotor constructed with a parallel arrangement of stressed unimorph piezoelectric transducers are presented. The prototype demonstrates a novel application of passive mechanical latches to produce inchworm motion while eliminating the need for multiple control signals. (2.) A dimensional analysis is conducted to reveal scale factors that govern the relationship between stressed unimorph performance parameters and size. The results support a millimeter-scale version of the linear piezomotor that incorporates transducers with alternative annular geometry for improved stiffness. (3.) The development of a miniature mode conversion rotary ultrasonic motor based on a piezoelectric stack transducer is reported. Results of a dynamic analysis lead to scale factors for static torque and rotor velocity. Lastly, the linear and rotary piezomotor systems are compared in the context of scalability to determine the most effective system for miniature direct drive robotics. Blocked force performance of the miniature linear piezomotor was limited to 0.25 N by back slip in the passive latches, and transducer displacement losses leading to greater compliance in the assembly. Since displacement of the annular stressed unimorph transducer decreases with the square of the outside radius, precision engineering is required to avoid these losses. The rotary ultrasonic motor proved to be a more effective choice for driving the robotic locomotion system. Dimensional analysis results indicate that static torque scales with the square of the rotor contact radius. Using alternative designs, a static torque density of 0.37 Nm/kg was measured in the prototype.
  • No Thumbnail Available
    Reconstruction of Lambertian Surfaces from Photometric Stereo
    (2005-06-13) Sethuram, Amrutha Shree; Dr. Edward Grant, Committee Co-Chair; Dr. David Lalush, Committee Co-Chair; Dr. Wesley E. Snyder, Committee Chair
    The objective of this thesis is to implement and compare two algorithms to reconstruct the shape of an object from photometric stereo. Photometric stereo is a practical technique for determining an object's shape and surface reflectance properties at a distance. The implementation proposes the use of three images of an object, recorded from the same viewpoint but with different illumination. The first algorithm employs the Fourier transform method to solve the minimization problem. The gradient data is obtained by incorporating photometric stereo method on image triplets. The Fourier transform of the unknown surface is then expressed as a function of the Fourier transform of the gradients. The relative depth values are then obtained by applying an inverse Fourier transform of the function. The second algorithm is based on iterative reconstruction which minimizes the cost function by gradient descent and annealing. Both these algorithms are implemented to reconstruct both real and synthetic surfaces and the results are compared. It is also shown that better reconstruction results are obtained by adopting the second algorithm in the presence of discontinuities in the image. Noise sensitivity of the frequency-domain method is also evaluated. An experimental setup to obtain real world images is also presented.