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Harmonic drives are special flexible gear systems widely used in space robots, the semiconductor industry, precision measuring devices, and military applications because of their advantages including near-zero backlash, high gear reduction, compact design, and light weight. On the other hand, they possess nonlinear transmission attributes including kinematic error, friction, flexibility, and hysteresis that are responsible for transmission performance degradation. Therefore, in-depth understanding, accurate modeling and control of transmission attributes are critical to the use of harmonic drives. There has been little research to date concerning these transmission attributes. This thesis characterizes harmonic drive transmission attributes and develops nonlinear control algorithms to enhance harmonic drive performance. The complete characterization of kinematic error in this research provides a new perspective to the understanding of the error. This thesis proposes an accurate hysteresis model in a differential equation form along with a constructive parameter identification scheme and extensive experimental validation. Furthermore, we extend a recently developed, accurate, dynamic friction model in a differential equation form to represent harmonic drive position dependent friction. Finally, several model-based nonlinear control algorithms are developed to improve harmonic drive performance. The most complex development compensates for kinematic error in presence of all other transmission attributes (flexibility, hysteresis and friction). Asymptotic stability with these algorithms is established using Lyapunov stability theory. The superior performance exhibited by these algorithms as compared to the traditional schemes is demonstrated using extensive simulation and experimental results. Thus, this thesis provides a solid foundation for performance improvement with harmonic drives as well as with other systems sharing one or more of the transmission attributes.

To investigate the mechanisms of human T-cell reconstitution following allogeneic haematopoietic stem cell transplantation (alloSCT), I analysed the clonal composition of human cytomegalovirus (HCMV)-specific and EBV-specific CD8+ T cells in 9 alloSCT recipients and their donors. All virus-specific CD8+ T-cell clones isolated from post-alloSCT recipients contained DNA of donor origin. Following transplantation from HCMV-seropositive donors into HCMV-seropositive recipients, immunodominant donor HCMV-specific clones underwent early expansion and were maintained long-term. In contrast, donor HCMV-specific clones were undetectable in two HCMV-seronegative EBV-seropositive recipients whereas transferred EBV-specific clones were maintained in the same recipients, suggesting that transferred clones require antigen for their maintenance. Following transplantation from seronegative donors into seropositive recipients, the delayed primary response of virus-specific CD8+ T-cells containing donor DNA suggested that new antigen-specific T-cells in the recipient arose from donor-derived progenitor cells. Two HCMV-seropositive recipients developed a different clonal composition from their HCMV-seropositive donors, with delayed persistent expansion of HCMV-specific clones that were undetectable in the donor or in the recipient during the first 5 months after transplantation; these may represent expansion of novel clones generated from donor-derived progenitor cells. I conclude that after alloSCT there is late diversification of the virus-specific CD8+ T-cell clonal repertoire in response to persistent viral antigen.

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Thesis (Ph.D.)--Auburn University, 2006. / Abstract. Vita.

Thesis (M.S.)--Southern Illinois University Carbondale, 2007. / "Department of Electrical and Computer Engineering." Includes bibliographical references (leaf 28). Also available online.

Thesis (M. Sc.)--University of Toronto, 2007. / Source: Masters Abstracts International, Volume: 45-06, page: 3028.