Identification of robotic manipulators' inverse dynamics coefficients via model-based adaptive networks

The values of a given manipulator's dynamics coefficients need to be accurately identified in order to employ model-based algorithms in the control of its motion. This thesis details the development of a novel form of adaptive network which is capable of accurately learning the coefficients of systems, such as manipulator inverse dynamics, where the algebraic form is known but the coefficients' values are not. Empirical motion data from a pair of PUMA 560s has been processed by the Context-Sensitive Linear Combiner (CSLC) network developed, and the coefficients of their inverse dynamics identified. The resultant precision of control is shown to be superior to that achieved from employing dynamics coefficients derived from direct measurement. As part of the development of the CSLC network, the process of network learning is examined. This analysis reveals that current network architectures for processing analogue output systems with high input order are highly unlikely to produce solutions that are good estimates throughout the entire problem space. In contrast, the CSLC network is shown to generalise intrinsically as a result of its structure, whilst its training is greatly simplified by the presence of only one minima in the network's error hypersurface. Furthermore, a fine-tuning algorithm for network training is presented which takes advantage of the CSLC network's single adaptive layer structure and does not rely upon gradient descent of the network error hypersurface, which commonly slows the later stages of network training

08291 Abstracts Collection -- Statistical and Geometrical Approaches to Visual Motion Analysis

From 13.07.2008 to 18.07.2008, the Dagstuhl Seminar 08291 ``Statistical and Geometrical Approaches to Visual Motion Analysis\u27\u27 was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, several participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar as well as abstracts of seminar results and ideas are put together in this paper. The first section describes the seminar topics and goals in general

Registration of 3D Point Clouds and Meshes: A Survey From Rigid to Non-Rigid

Three-dimensional surface registration transforms multiple three-dimensional data sets into the same coordinate system so as to align overlapping components of these sets. Recent surveys have covered different aspects of either rigid or nonrigid registration, but seldom discuss them as a whole. Our study serves two purposes: 1) To give a comprehensive survey of both types of registration, focusing on three-dimensional point clouds and meshes and 2) to provide a better understanding of registration from the perspective of data fitting. Registration is closely related to data fitting in which it comprises three core interwoven components: model selection, correspondences and constraints, and optimization. Study of these components 1) provides a basis for comparison of the novelties of different techniques, 2) reveals the similarity of rigid and nonrigid registration in terms of problem representations, and 3) shows how overfitting arises in nonrigid registration and the reasons for increasing interest in intrinsic techniques. We further summarize some practical issues of registration which include initializations and evaluations, and discuss some of our own observations, insights and foreseeable research trends

Performance analysis of a GPS Interferometric attitude determination system for a gravity gradient stabilized spacecraft

The performance of an unaided attitude determination system based on GPS interferometry is examined using linear covariance analysis. The modelled system includes four GPS antennae onboard a gravity gradient stabilized spacecraft, specifically the Air Force's RADCAL satellite. The principal error sources are identified and modelled. The optimal system's sensitivities to these error sources are examined through an error budget and by varying system parameters. The effects of two satellite selection algorithms, Geometric and Attitude Dilution of Precision (GDOP and ADOP, respectively) are examined. The attitude performance of two optimal-suboptimal filters is also presented. Based on this analysis, the limiting factors in attitude accuracy are the knowledge of the relative antenna locations, the electrical path lengths from the antennae to the receiver, and the multipath environment. The performance of the system is found to be fairly insensitive to torque errors, orbital inclination, and the two satellite geometry figures-of-merit tested

Source radiation analysis based on spatial transformation of acoustic fields

Source radiation analysis frequently involves characterization or identification of sound sources and fields. In order to effectively perform source radiation analysis, an integrated acoustical imaging system including software and hardware was developed based on spatial transformation. This system utilizes measurements of the complex sound field over a two-dimensional hologram surface with the one-microphone sequential sampling method. Four spatial transformation techniques, i.e. direct convolution, two-dimensional fast Fourier transform, Gauss-Hermite decomposition, and singular value decomposition, were implemented to project the hologram data to desired locations in the three-dimensional space. In addition, four new approaches based on feedback iteration concepts, with the variations of optimization and constraints, were developed to deal particularly with the ill-posed nature encountered in the backward reconstruction of source images;The theoretical background, numerical or experimental investigations, and applicational considerations of the previously mentioned aspects are thoroughly discussed in the dissertation. The conclusions detail the significance of the research results and the future prospects for radiation analysis based on spatial transformation. The technical aspects of the experimental implementation such as a computerized data acquisition system are also included in the appendix

Theoretical and experimental explorations in atomic force microscopy

Nanotechnology is the capability to build by controlling the arrangement of individual atoms and molecules. Such a technology would be founded on the ability to control, manipulate and investigate matter at the atomic scale. The invention of atomic force microscope (AFM) and the advances in micro-cantilever based scanning probe technology have significantly enhanced the experimental capability to probe and modify matter at the nanoscale. However, it is still severely limited in achieving the necessary bandwidth, sensitivity and resolution. To further the advances in this field an in-depth understanding of the nature and effects of the tip-sample interactions is imperative. A complementary approach involving theoretical investigations and experimental advances is best suited to overcome the current limitations of this technology.;This thesis investigates the atomistic phenomena associated with material modification at the tip-sample contact theoretically because such information is inaccessible to experimental observation. Molecular dynamics studies of nanoindentation of crystalline silicon and gold, representative of semiconductor and metallic substrates, shed light on the mechanics of plastic deformation and defect formation. Silicon undergoes a densification transformation to amorphous phase in the deformed region via the formation of interstitials. In gold a pyramidal defect structure is formed via a three step mechanism consisting of nucleation, glide and reaction of dislocations. This mechanism dictates the dependence of defect structure on the crystallography of the indented surface as observed in experimental studies performed by other researchers.;The experimental studies develop a new small amplitude non-contact AFM technique. In this frequency modulation method, changes in the cantilever\u27s resonance induced by the tip-sample interactions are detected from its thermal noise response. By eliminating the need for positive feedback it enables maintaining an extremely small tip-sample separation for extended periods of time at room temperatures. Consequently, this technique is particularly suited for studying highly localized slowly evolving atomic or molecular scale phenomena at ambient temperatures. The experiments performed in ambient room conditions have achieved tip-sample separations less than 2 nm for time periods in excess of 30 min. At such small separations a narrowband signal at 250 Hz is imaged with a force sensitivity of 14 fN in a bandwidth of 0.4 Hz