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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 14:54:27 +0000Experimental Study of Unsteady Hydrodynamic Force Matrices on Whirling Centrifugal Pump Impellers
https://resolver.caltech.edu/CaltechETD:etd-03262007-130547
Authors: {'items': [{'id': 'Jery-Belgacem', 'name': {'family': 'Jery', 'given': 'Belgacem'}, 'show_email': 'NO'}]}
Year: 1987
DOI: 10.7907/cmn0-qk37
<p>An experimental facility was constructed and instrumented. A study was conducted on a set of centrifugal flow pumps whose impellers were made to follow a controlled circular whirl motion. The aim was to characterize the steady and unsteady fluid forces measured on the impeller under various pump operating conditions. The postulation was that the unsteady lateral forces result from interactions between the impeller and the surrounding diffuser and or volute (via the working fluid), and that under certain flow regimes these forces can drive unstable lateral motions of the pump rotor.</p>
<p>The lateral hydrodynamic forces were decomposed into their steady and unsteady parts, the latter being further expressed in terms of a generalized fluid stiffness matrix. A study of this matrix as a function of the whirl to pump speed ratio supported the following chief conclusions:</p>
<p>i) the common assumption of matrix skew-symmetry is justified;</p>
<p>ii) the magnitudes and signs of the matrix elements are such that rotor whirl can indeed be caused by the hydrodynamic forces, in pumps operated well above their first critical speed,</p>
<p>iii) as expected, the matrix is very sensitive to the value of the flow coefficient, especially at flow rates below the design;</p>
<p>iv) the commonly postulated quadratic variation of the matrix elements with the reduced whirl frequency, resulting in the so-called rotordynamic coefficients (stiffness, damping and inertia) is not justified for flow coefficients significantly below design; and</p>
<p>v) surprisingly, it was discovered that the presence, number and orientation of diffuser guide vanes have little effect on the forces.</p>
<p>Conclusions regarding the effect of impeller geometry could not be reached given the similarity of the tested designs. However, other results on phenomena such as skin friction and leakage flow are presented. Some of the findings are compared to experimental and theoretical data from other sources. Finally, the rotordynamic consequences of the results are discussed as the present data were applied by another author to the case of the Space Shuttle Main Engine's (SSME) High Pressure Oxidizer Turbopump (HPOTP).</p>https://thesis.library.caltech.edu/id/eprint/1144A method for the representation and manipulation of uncertainties in preliminary engineering design
https://resolver.caltech.edu/CaltechETD:etd-11152007-080746
Authors: {'items': [{'email': 'wood@mail.utexas.edu', 'id': 'Wood-K-L', 'name': {'family': 'Wood', 'given': 'Kristin Lee'}, 'show_email': 'NO'}]}
Year: 1990
DOI: 10.7907/g1hs-p655
Each stage of the engineering design process, and particularly the preliminary phase, includes imprecision, stochastic uncertainty, and possibilistic uncertainty. A technique is presented by which the various levels of imprecision (where imprecision is: "uncertainty in choosing among alternatives") in the description of design elements may be represented and manipulated. The calculus of Fuzzy Sets provides the foundation of the approach. An analogous method to representing and manipulating imprecision using probability calculus is presented and compared with the fuzzy calculus technique. Extended Hybrid Numbers are then introduced to combine the effects of imprecision with stochastic and possibilistic uncertainty. Using the results, a preliminary set of metrics is proposed by which a designer can make decisions among alternative configurations in preliminary design.
In general, the hypothesis underlying the techniques described above is that making more information available than conventional approaches will enhance the decision-making capability of the designer in preliminary design. A number of elemental concepts toward this hypothesis have been formulated during the evolution of this work:
• Imprecision is a hallmark of preliminary engineering design. To carry out decisions based on the information available to the designer and on basic engineering principles, the imprecise descriptions of possible solution technologies must be formalized and quantified in some way. The application of the fuzzy calculus along with a fundamental interpretation provides a new and straight-forward means by which imprecision can be represented and manipulated.
• Besides imprecision, other uncertainties, categorized as stochastic and possibilistic, are prevalent in design, even in the early stages of the design process. Providing a method by which these uncertainties can be represented in the context of the imprecision is an important and necessary step when considering the evaluation of a design's performance. Extended Hybrid Numbers have been introduced in this work in order to couple the stochastic and possibilistic components of uncertainty with imprecision such that no information is lost in the process.
• Because of the size, coupling, and complexity of the functional requirement space in any realistic design, it is difficult to make decisions with regard to the performance of a design, even with an Extended Hybrid Number representation. Defining and utilizing metrics (or figures of merit) in the evaluation of how well a design meets the functional requirements reduces the complexity of this process. Such metrics also have merit when we begin to think of languages of design and adding the necessary pragmatics of "will a generated or proposed design satisfy the performance requirements with respect to the ever-present and unavoidable uncertainties?". These concepts form the central focus of this work. The mathematical methods presented here were developed to support and formalize these ideas.https://thesis.library.caltech.edu/id/eprint/4581Theory and Applications of Hyper-Redundant Robotic Manipulators
https://resolver.caltech.edu/CaltechETD:etd-11082006-132210
Authors: {'items': [{'email': 'gregc@jhu.edu', 'id': 'Chirikjian-Gregory-Scott', 'name': {'family': 'Chirikjian', 'given': 'Gregory Scott'}, 'show_email': 'NO'}]}
Year: 1992
DOI: 10.7907/F12D-0X25
The term "hyper-redundant" refers to robotic manipulators and mobile robots with a very large, possibly infinite, number of actuatable degrees of freedom. These robots are analogous in morphology and operation to snakes, worms, elephant trunks, and tentacles. This thesis presents a novel kinematic framework for hyper-redundant manipulator motion planning and task implementation. The basis of this formulation is the use of a "backbone reference set" which captures the essential macroscopic geometric features of hyper-redundant robots. In the analytical part of this work, the backbone representation is developed and used to solve problems in obstacle avoidance, locomotion, grasping, and "optimal" end effector placement. The latter part of this thesis deals with the design and implementation of a thirty-degree-of-freedom planar hyper-redundant manipulator which is used to demonstrate these novel kinematic and motion planning techniques. Design issues such as robustness with respect to mechanical failure, and design for easy assembly and repair are also addressed. The analytical and design concepts are combined to illustrate tasks for which hyper-redundant robotic mechanisms are well suited.
https://thesis.library.caltech.edu/id/eprint/4458A formal representational theory for engineering design
https://resolver.caltech.edu/CaltechETD:etd-08132007-134534
Authors: {'items': [{'id': 'Otto-K-N', 'name': {'family': 'Otto', 'given': 'Kevin N.'}, 'show_email': 'NO'}]}
Year: 1992
DOI: 10.7907/tx29-f628
In the design of engineered artifacts, it is hypothesized that computations must be performed. Informal specifications must be converted into formal functional requirements and informal descriptions must be converted into formal parameterizations, so that performance can be computed. Such performance evaluations are developed for general set based mappings. The development includes, for example, functional relations, differential equations, simple experimentation, and even subjective questioning. When this level of formalization is complete, the design is not determined; it is only parameterized. A designer must specify levels of the various performances desired, and how the various performances should be simultaneously considered in an overall determination. An axiomatically based methodology is presented to formalize such decisions. Each decision variable is equipped with a preference specification, whose determination is made from techniques similar to utility theory. A design strategy for resolving these different aspects of a design is developed to produce an overall rating. For example, a designer may rate a design by the worst case performance. Alternatively, a designer may rate a design by a compensation among the goals. In addition to decision representation, other parameters in a formalization reflect phenomena which the designer cannot control. A methodology for accommodating confounding noise influences is developed. Random measurement noise is represented, as well as the possibility of other decision makers in a design process. Convolutions of these methods are developed. For example, designer decision-making is developed for a decision which must be made in light of random errors (such as manufacturing). Designer decision-making is further developed for the case when a manufacturing engineer can subsequently tune a design (a possibilistic uncertainty) to eliminate such random error effects. Ensuring against failure is also discussed, with respect to the measured noise. Given this development, a methodology is constructed in which a designer can incompletely specify performance requirements on a design. The incomplete specification can be induced across the design, to determine any restrictions imposed on the portions of the design where no specifications have been made. Thus, an iterative design process of specification, calculation, observation, and re-specification is given formal foundation.https://thesis.library.caltech.edu/id/eprint/3114High-resolution optoelectronic and photogrammetic 3-D surface geometry acquisition and analysis
https://resolver.caltech.edu/CaltechETD:etd-08292007-091850
Authors: {'items': [{'id': 'Hsueh-W', 'name': {'family': 'Hsueh', 'given': 'Wen-Jean'}, 'show_email': 'NO'}]}
Year: 1993
DOI: 10.7907/wn0s-6y22
A high-resolution, high-speed, automatic, and non-contact 3-D surface geometry measuring system has been developed. It is based on a photogrammetric and optoelectronic technique that adopts lateral-photoeffect diode detectors sensitive in the near-infrared range. Two cameras in stereo positions are both equipped with the large 2-axis analog detectors. A light beam is focused and scanned onto the surface of an object as a very small light spot. Excitations on detectors generated by the reflected light from the spot create photocurrents that are transformed into 2-D position signals in a very short time. A simple set of calculations is done to photogrammetrically triangulate two sets of 2-D coordinates from the detectors into the 3-D coordinates of the light spot. Because only one small light spot in the scene is illuminated at a time, the stereo-correspondence problem is solved in real time. The detectors are able to collect data at 10 KHz with 4,096x4,096 resolution based on a 12-bit A/D converter. The resolution and precision can be improved up to eight times by oversampling. The system is able to resolve, for example, less than 10 µm from 47 cm away with a nominal viewing volume of (22 cm)[superscript 3]. Its performance is better than contemporary coordinate measuring, range finding, shape digitizing, and machine vision systems, and is comparable to the best aspects of each existing system. The irregular 3-D data it generates can be regularized so that data processing algorithms designed for image systems may be applied. The system is designed for the acquisitions of general surface geometries, such as fabricated parts, machined surfaces, biological surfaces, and deformed parts. The system will be useful in solving a variety of 3-D surface geometry measuring problems in engineering design, manufacturing, inspection, robot kinematics measurement, and vision.
https://thesis.library.caltech.edu/id/eprint/3268MEMS design : the geometry of silicon micromachining
https://resolver.caltech.edu/CaltechETD:etd-09162005-134646
Authors: {'items': [{'email': 'ted.hubbard@dal.ca', 'id': 'Hubbard-T-J', 'name': {'family': 'Hubbard', 'given': 'Ted J.'}, 'show_email': 'NO'}]}
Year: 1994
DOI: 10.7907/TK4C-M144
The design of MEMS (Micro Electro Mechanical Systems) on the millimeter to micron length scales will be examined in this thesis.
A very broad base of knowledge has been developed concerning the etching processes commonly used in MEMS fabrication. The fundamental problem we have sent out to study is how to model the shape transformations that occur in MEMS fabrication. The ultimate goal is to determine the required input mask geometry for a desired output etched shape.
The body of work begins with the crystal structure of silicon and ends with etched shapes. The underlying crystal structure causes different rates for different directions; this behavior has been modeled to obtain rate models. The information in these rate models has then been used in a number of shape modelers. High level models like the Eshape model provide not only simulation but a framework for true design. Other models such as the Cellular Automata model take a different approach and provide flexible and robust simulators. The tools were used to develop real world MEMS applications such as compensation structures.
As important as the individual models, is the ability to integrate them together to a coherent design tool and allow information to flow between different parts. This synthesis allows a fuller understanding of the etching process from start to finish.
It is important to note that while this thesis deals with etching, the methods developed are very general and are applicable to many shape transformation processes.
https://thesis.library.caltech.edu/id/eprint/3565Theory and Applications of Modular Reconfigurable Robotic Systems
https://resolver.caltech.edu/CaltechETD:etd-10202005-090745
Authors: {'items': [{'email': 'michen@ntu.edu.sg', 'id': 'Chen-I-Ming', 'name': {'family': 'Chen', 'given': 'I-Ming'}, 'orcid': '0000-0002-4831-3781', 'show_email': 'YES'}]}
Year: 1994
DOI: 10.7907/2AAA-RY45
A modular reconfigurable robotic system consists of various link and joint units with standardized connecting interfaces that can be easily separated and reassembled into different configurations. Compared to a fixed configuration robot, which is usually a compromised design for a limited set of tasks, a modular robot can accomplish a large class of tasks through reconfiguration of a small inventory of modules. This thesis studies how to find an optimal module assembly configuration constructed from a given inventory of module components for a specific task. A set of generalized module models that bear features found in many real implementations is introduced. The modular robot assembly configuration is represented by a novel Assembly Incidence Matrix (AIM). Equivalence relations based on module geometry symmetries and graph isomorphisms are defined on the AIMs. An enumeration algorithm to generate non-isomorphic assembly configurations based on this equivalence relation is proposed. Examples demonstrate that this method is a significant improvement over a brute force enumeration process. Configuration independent kinematic models for modular robots are developed, and they are essential for solving the task-optimal configuration problem. A task-oriented objective function is defined on the set of non-isomorphic module assembly configurations. Task requirements and kinematic constraints on the robot assembly are treated as parameters to this objective function. The task-optimal configuration problem is formulated as a combinatorial optimization problem to which genetic algorithms are employed for solutions. Examples of finding task-optimal serial revolute-jointed robot configurations are demonstrated. In addition, the applications of modular robots to planning multifinger grasping and manipulation are developed. Planning two-finger grasps is done through finding antipodal point grasps on smooth shaped objects. Planning n-finger grasps is achieved by defining a qualitative force-closure test function on the n-finger grasps on an object. Applications of this test function to manipulation task and finger gaiting are illustrated.https://thesis.library.caltech.edu/id/eprint/4189Grammars for engineering design
https://resolver.caltech.edu/CaltechETD:etd-03212005-140711
Authors: {'items': [{'email': 'andrew.b.wells.89@alum.dartmouth.org', 'id': 'Wells-A-B', 'name': {'family': 'Wells', 'given': 'Andrew B.'}, 'show_email': 'YES'}]}
Year: 1994
DOI: 10.7907/QCMP-6T83
<p>Just as grammars for natural languages use rules to form grammatical sentences from a dictionary of words, grammars for engineering design use rules to make structures from a dictionary of shapes, properties, labels, and other elements. Engineering grammars may be used to help the designer generate and evaluate ideas and concepts during the conceptual phase of the design process.</p>
<p>A formal definition of a grammar is given and some properties of grammars are discussed. Natural language grammars, shape grammars, and engineering grammars are defined. Some group-theoretic properties of shapes and operations are derived. It is shown that some sets of shapes form Boolean algebras under the standard regularized set operations. Polygonal tracings, which are extensions of the outlines of two-dimensional polygons, form a ring under the shape union and convolution (or generalized Minkowski sum) operations. A subset of polygonal tracings which includes all convex tracings, along with the convolution and shape scaling operations, form a vector space over the real numbers. The implications for grammar rules which use these types of shapes and operations are discussed.</p>
<p>Grammars and expert systems are compared and contrasted. While the formalisms have similar definitions, some explicit differences exist. Furthermore, when the customary uses of the two systems are compared, large differences are evident. It is concluded that grammars are more well-suited to generating many alternative designs and searching large, unexplored design spaces, while expert systems function best in well-known domains when only one design is required.</p>
<p>The formation and modification of grammatical rules is discussed, focusing on the relationships between form and function in design. Several strategies which could be used for the search for optimal designs in a grammar's language are considered. The significance of transformations used to apply rules is discussed.</p>
<p>An extended example of grammars used to generate configurations of modular reconfigurable robot arms is presented. The grammars generate all non-isomorphic assembly configurations, while simultaneously calculating kinematic properties of the arms. Several methods of quickly searching for arms to satisfy various requirements are discussed.</p>https://thesis.library.caltech.edu/id/eprint/1042A Study of Tip Vortices and Cavitation on a Propeller in a Non-Uniform Flow Field
https://resolver.caltech.edu/CaltechETD:etd-03262007-131335
Authors: {'items': [{'email': 'mckenn1@earthlink.net', 'id': 'McKenney-Elizabeth-Anne', 'name': {'family': 'McKenney', 'given': 'Elizabeth Anne'}, 'show_email': 'NO'}]}
Year: 1995
DOI: 10.7907/7THC-NG74
Unsteady lifting surface flows are important subjects for study, both for the purposes of improving propulsive or lifting efficiency and also for mitigating the destructive effects and noise caused by cavitation. Some progress may be made by selecting a simple type of unsteadiness for closer study. In the present work, this tactic was implemented in two ways: the operation of a propeller at an angle of yaw to the freestream and the pitching oscillation of a finite-span hydrofoil.
A new facility was designed and constructed to set a propeller at an angle of yaw to the freestream, creating a fairly simple non-uniformity in the propeller inflow. Tip vortex cavitation inception measurements were made for a range of yaw angles and freestream velocities, and photographs of the cavitation were taken to illustrate the effects of the yaw angle.
The unsteady tip vortex flow field was measured on an oscillating finite aspect ratio hydrofoil using Particle Image Velocimetry (PIV), revealing how the circulation varied during a typical oscillation cycle. The results were compared with unsteady infinite-span theory, and also with recent measurements using LDV techniques on the same foil.
The hydrofoil was also the focus of a study of surface cavitation. High-speed motion pictures of the cavitation cycle helped to separate the process into its component stages, and variations with cavitation number and reduced frequency of oscillation were observed. The acoustic signals generated by the cavity collapse were correlated with the motion pictures, providing insights into the correspondence between the flow structures involved in the cavity collapse process and the sound generated by them.
The results from these studies provide valuable insights into the effects of unsteadiness in lifting surface flows.
https://thesis.library.caltech.edu/id/eprint/1145Silicon Micromachined Sensors and Actuators for Fluid Mechanics Applications
https://resolver.caltech.edu/CaltechETD:etd-01072008-151023
Authors: {'items': [{'id': 'Liu-Chang', 'name': {'family': 'Liu', 'given': 'Chang'}, 'show_email': 'NO'}]}
Year: 1996
DOI: 10.7907/k8pm-8g13
<p>The major contributions of this thesis are the developments of silicon micromachined flow shear-stress sensors and magnetic actuators, together with original studies on two fundamental issues of micro fabrication. Sensors and actuators applications in two fluid-mechanics projects have been successfully demonstrated.</p>
<p>Micro shear-stress sensors utilize boundary-layer thermal transfer principles. For the proposed fluid-mechanics applications these sensors must have higher sensitive compared with conventional sensors, among other requirements. This has been realized by implementing a unique vacuum-sealed cavity which greatly reduces heat loss to the substrate silicon.</p>
<p>Fluid applications present unique challenges to micromachined actuators: they must achieve large out-of-plane motion and withstand large forces. We have developed two types of magnetic actuators that fit these requirements. The first type is based on interaction between the magnetic dipole moment of a current-carrying coil and an external magnetic field. A second-type uses the torque generated by an electroplated Permalloy (Ni[subscript 80]Fe[subscript 20] plate inside an external magnetic field.</p>
<p>The two fundamental micro-fabrication issues are the reactive sealing of cavities and the magnetic-levitation assisted release of surface structures. We have conducted systematic experiments to determine the dependance of sealing performance on the test- structure geometric parameters, sealing materials and other factors. Release/drying of micro actuators, with their large surface areas, is especially challenging. The idea for magnetic-levitation assisted release is obtained while we were developing the Permalloy magnetic actuator. Magnetic forces counteract the surface tension forces during the drying to avoid structure stiction to the substrate. Original results from these fundamental studies add to the general micromachining knowledge base.</p>
<p>The applications of developed sensors and actuators are demonstrated in two fluid- mechanics projects. In the first, we explore a unique scheme for active drag reduction, which is possible only by using a Micro Electro Mechanical System (MEMS). The MEMS consists of an array of shear-stress sensors, actuators and embedded neural-network (NN) circuitry. The goal of the second project is to achieve enhanced maneuverability of delta-wings using MEMS devices. Shear-stress sensors are successfully applied to identify the flow separation lines along the delta-wing's leading edges. Permalloy magnetic actuators interact with the leading-edge flow for controlling the wing motion.</p>https://thesis.library.caltech.edu/id/eprint/60Evaluating imprecision in engineering design
https://resolver.caltech.edu/CaltechETD:etd-08152006-130539
Authors: {'items': [{'email': 'w_law@yahoo.com', 'id': 'Law-W-S', 'name': {'family': 'Law', 'given': 'William Sauway'}, 'show_email': 'NO'}]}
Year: 1996
DOI: 10.7907/y175-ae87
Imprecision is uncertainty that arises because of vague or incomplete information. Preliminary design information is characteristically imprecise: specifications and requirements are subject to change, and the design description is vague and incomplete. Yet many powerful evaluation tools, including finite element models, expect precisely specified data. Thus it is common for engineers to evaluate promising designs one by one. Alternatively, optimization may be used to search for the single "best" design. These approaches focus on individual, precisely specified points in the design space and provide limited information about the full range of acceptable designs.
An alternative approach would be to evaluate sets of designs. The method of imprecision uses the mathematics of fuzzy sets in order to represent imprecision as preferences among designs:
• Functional requirements model the customer's direct preference on performance variables based on performance considerations: the quantified aspects of design performance represented by performance variables.
• Design preferences model the customer's anticipated preference on design variables based on design considerations: the unquantified aspects of design performance not represented by performance variables.
Design preferences provide a formal structure for representing "soft" issues such as aesthetics and manufacturability and quantifying their consequences.
This thesis describes continuing work in bringing the method of imprecision closer to implementation as a decision-making methodology for engineering design. The two principal contributions of this work are a clearer interpretation of the elements that comprise the method and a more efficient computational implementation.
The proposed method for modeling design decisions in the presence of imprecision is defined in detail. The decision-maker is modeled as a hierarchy of preference aggregation operations. Axioms for rational design decision-making are used to define aggregation operations that are suitable for design. An electric vehicle design example illustrates the method. In particular, the process of determining preferences and a preference aggregation hierarchy is shown to be both feasible and informative. Efficient computational methods for performing preference calculations are introduced. These methods use experiment design to explore the design space and optimization assisted by linear approximation to map preferences. A user-specified fractional precision allows the number of function evaluations to be traded-off against the quality of the answer obtained. The computational methods developed are verified on design problems from aircraft engine development and automobile body design. Procedures for specifying preferences and group decisionmaking are described. These procedures provide not only a pragmatic interpretation of the method, but also an informal solution to the problem of bargaining: prerequisites for bringing the method to design problems in the real world.
https://thesis.library.caltech.edu/id/eprint/3132Sensor Based Motion Planning: The Hierarchical Generalized Voronoi Graph
https://resolver.caltech.edu/CaltechETD:etd-12182007-090504
Authors: {'items': [{'email': 'choset@andrew.cmu.edu', 'id': 'Choset-Howard-Marc', 'name': {'family': 'Choset', 'given': 'Howard Marc'}, 'orcid': '0000-0002-2266-8744', 'show_email': 'NO'}]}
Year: 1996
DOI: 10.7907/49ee-a204
Sensor based motion planning incorporates sensor information reflecting the state of a robot's environment into its planning process, whereas traditional approaches assume complete prior knowledge of the robot's environment. Recent research has focused on the development and incremental construction of the hierarchical generalized Voronoi graph (HGVG), which is a concise representation of a robot's environment. The HGVG is advantageous in that it lends itself to sensor based construction in a rigorous and provably correct manner. With this approach, a robot can enter an unknown environment, incrementally construct the HGVG, and then use the HGVG for future excursions in the environment. Simulations and experiments validate this approach.https://thesis.library.caltech.edu/id/eprint/5048Autonomous Reorientation of a Maneuver-Limited Spacecraft Under Simple Pointing Constraints
https://resolver.caltech.edu/CaltechETD:etd-01162008-152619
Authors: {'items': [{'id': 'Vanelli-Charles-Anthony', 'name': {'family': 'Vanelli', 'given': 'Charles Anthony'}, 'show_email': 'NO'}]}
Year: 1997
DOI: 10.7907/kap2-6n63
This report presents techniques for using discrete finite rotations to reorient a spacecraft from a given initial attitude to a final attitude which satisfies a specified aiming objective. The objective may be a fully specified final orientation or it may require that the spacecraft direct an instrument along a certain direction. Constraints are also imposed on the allowable intermediate orientations that the spacecraft may assume during the course of the maneuver, representing the operational requirements of onboard instrumentation. The algorithms presented consider solutions that will achieve the desired objective with only one or two slew maneuvers, although they may be easily extended to consider more complicated solutions requiring additional maneuvers.https://thesis.library.caltech.edu/id/eprint/206Mechanics and Planning of Workpiece Fixturing and Robotic Grasping
https://resolver.caltech.edu/CaltechETD:etd-01302008-111854
Authors: {'items': [{'id': 'Lin-Qiao', 'name': {'family': 'Lin', 'given': 'Qiao'}, 'show_email': 'NO'}]}
Year: 1998
DOI: 10.7907/1d4m-j065
<p>This thesis addresses several key issues in mechanics and automated planning of workpiece fixturing and robotic grasping, including accurate and efficient modelling of compliance, well-defined and practically useful quality measures, and well-defined kinematic metric functions for rigid bodies.</p>
<p>The accurate and efficient modelling of compliant fixtures and grasps is considered. A stiffness matrix formula is derived using the overlap compliance representation for quasi-rigid bodies. In contrast to existing approaches using the linear contact model, this formula is well-suited to automated planning algorithms since it can incorporate realistic nonlinear contact models (e.g., the classical Hertz model), and can be directly computed from CAD data on basic geometric and material properties of the bodies. The formula is then used as a basis for a systematic analysis of local curvature effects on fixture stability. This analysis shows that destabilizing effects of local curvatures are practically negligible, and that curvature effects can be used to stabilize, sometimes significantly, an otherwise unstable fixture. The stiffness matrix formula is also used to show that stability analysis in general depends on the choice of contact models, which offers additional evidence for the importance of using realistic contact models.</p>
<p>The stiffness and deflection quality measures are defined for compliant fixtures and grasps, and are applied to optimal planning. Unlike existing quality measures that rely on heuristic rules or depend on reference frame choices, the stiffness and deflection quality measures are theoretically sound. Equally important is that these quality measures accurately characterize functional performances which are important to practical fixturing applications, such as fixture stiffness and workpiece deflections. The stiffness and deflection quality measures are applied to optimal fixture and grasp planning, resulting in maximum-stiffness and minimum-deflection fixtures and grasps. The qualitative properties of optimal fixtures are characterized with respect to each quality measure, and efficient techniques are developed for finding such optimal fixtures.</p>
<p>The final key issue is concerned with formal well-definedness conditions and practical development methods for rigid body kinematic metric functions, such as norms, inner products, and distance metrics. Based on an intrinsic definition of the configuration space of a rigid body, the notion of objectivity is proposed to formalize the natural requirement that metric measurements be indifferent to the observers who perform the measurements. This notion is then used to clarify the fundamental physical implications of left, right and bi-invariant functions on SE(3), and is further shown to be equivalent to the notion of frame-invariance. Based on these clarifications, several frame-invariant norms of rigid body velocities and wrenches, which have interesting physical interpretations, are defined.</p>https://thesis.library.caltech.edu/id/eprint/411Control of stratified systems with robotic applications
https://resolver.caltech.edu/CaltechETD:etd-01232008-144001
Authors: {'items': [{'id': 'Goodwine-J-W', 'name': {'family': 'Goodwine', 'given': 'John William'}, 'show_email': 'NO'}]}
Year: 1998
DOI: 10.7907/49h9-q898
Many interesting and important control systems evolve on stratified configuration spaces. Roughly speaking, a configuration manifold is called "stratified" if it contains subspaces (submanifolds) upon which the system had different equations of motion. Robotic systems, in particular, are of this nature. For example, a legged robot has discontinuous equations of motion near points in the configuration space where each of its "feet" comes into contact with the ground. In such a case, when the system moves from one submanifold to another, the equations of motion change in a non-smooth, or even discontinuous manner. In such cases, traditional nonlinear control methodologies are inapplicable because they generally rely upon some form of differentiation. Yet, it is precisely the discontinuous nature of such systems that is often their most important characteristic.
This dissertation presents methods which consider the intrinsic physical geometric structure present in such problems to address nonlinear controllability and motion planning for stratified systems. For both problems, by exploiting this geometric structure of stratified systems, we can extend standard nonlinear control results and methodologies to the stratified case. A related problem addressed by this dissertation is that of controllability of systems where some control inputs are constrained to be non-negative. This problem arises in stratified systems which arise by way of physical contact because the normal force between contacting systems must be nonnegative. For all the results, a basic goal is to generate results which are general. For example, for robotics applications, these results are independent of a particular robot's number of legs, fingers or morphology.
https://thesis.library.caltech.edu/id/eprint/306Formalizing negotiation in engineering design
https://resolver.caltech.edu/CaltechETD:etd-02262008-145407
Authors: {'items': [{'id': 'Scott-Michael-Joseph', 'name': {'family': 'Scott', 'given': 'Michael Joseph'}, 'show_email': 'NO'}]}
Year: 1999
DOI: 10.7907/thvr-5v61
Negotiations are common in engineering design, especially on large projects, and are typically conducted informally. Often, negotiation is used to handle the imprecision or uncertainty that is inherent in the design process. Performance targets, initially specified as hard numerical constraints, are adjusted throughout the design process in negotiations between engineers and managers. Crucial unmeasured or unmeasurable aspects of performances, such as aesthetic concerns, are commonly negotiated. Negotiations settle conflicts between engineering groups over values of shared design variables and distribution of limited design resources.
In this thesis, a formal description of negotiation in engineering design is presented. This formal model builds on earlier work at Caltech in the modelling of imprecision in engineering design. Negotiation is modelled mathematically as the aggregation of preferences. A complete characterization of the aggregation problem and of the aggregation operators suitable for engineering design is given. This class of operators spans a range of rational decisions and allows for different possible levels of compensation among goals. Furthermore, the entire range of aggregation operators is necessary to capture all possible engineering design decisions. Techniques are presented for determining which aggregation operators are appropriate for particular problems.
As the aggregation of preference is also a component of other fields, notably decision theory applied to economics and social choice, various concerns raised in those fields about the legitimacy of preference aggregation are treated. A more comprehensive justification is presented here of the approach to modelling imprecision known as the Method of Imprecision, or MoI, than has previously been offered.
Although the decision model presented here is statically one of choice among given alternatives, refinement and redesign are crucial in the engineering design process. The consideration of information about entire sets of designs not only accrues computational benefits, but is a more natural model for how designers reason, and can be of significantly more use to designers in refinement and redesign, than information about individual point designs. Conditions under which the negotiation model can support set-based information and still yield consistent answers are here explored and presented.
Finally, an example of the application of these ideas to a preliminary vehicle structure design is presented. This example was undertaken as a demonstration of the method for research engineers at Volkswagen Wolfsburg, and serves to help introduce many of the ideas in a more concrete manner.
https://thesis.library.caltech.edu/id/eprint/774Modeling and Experiments for a Class of Robotic Endoscopes
https://resolver.caltech.edu/CaltechETD:etd-10112006-154843
Authors: {'items': [{'email': 'abslat88@hotmail.com', 'id': 'Slatkin-Andrew-Brett', 'name': {'family': 'Slatkin', 'given': 'Andrew Brett'}, 'show_email': 'YES'}]}
Year: 1999
DOI: 10.7907/NG6V-TD44
<p>Current developments in minimally invasive medical practice motivated this study of self-propelled, robotic endoscopes for deep penetration into curved physiological lumens. The conceptual design of such devices is applicable to endoscopy within a variety of lumens in the human body, e.g., blood vessels, but the initial objective of this technology is to provide access to the interior of the entire small intestine without surgical incisions. The small intestine presents several challenges to endoscopic penetration: it is extremely compliant to applied loading, internally lubricated, easily injured, and contains many tight curves along its length of approximately eighteen feet.</p>
<p>This thesis reports the basic design and locomotion concepts for one class of endoscopic robots that are intended to provide safe and reliable traversal of the small intestine via worm-like actuation. Five generations of proof-of-concept prototype robots have been built to validate the fundamental concepts. Furthermore, these miniaturized robots have incorporated the following features: redundant actuation with computer control, tool-free modular assembly, and on-board videoimaging capability. The prototypes have been tested in rubber tubing, the small intestines of deceased pigs, and in the small intestines of live, anaesthetized pigs.</p>
<p>At the onset of this research, little regarding the elastic properties of small intestine existed in the biomechanics literature that would be applicable to the design of these mechanisms. However, accurate prediction of the small intestine's response to robotic loadings would dramatically improve the research and development process of these machines. Thus, an investigation of the elastic behavior of the small intestine commenced. Finite deformation, nonlinear, anisotropic, incompressible, viscoelastic behavior of the small intestine was studied. This soft tissue biomechanical analysis and experimentation (on living and dissected intestinal specimens) culminated with a numerical model that simulates intestinal response to the actions of a prototypical robotic component. Experiments on living specimens were performed to determine the levels of applied loadings and internal stresses that are likely to injure these fragile tissues, and the biomechanics computer modeling incorporates three distinct measures for injury potential.</p>https://thesis.library.caltech.edu/id/eprint/4035Evolutionary techniques applied to mask-layout synthesis in micro-mechanical-electronic systems (MEMS)
https://resolver.caltech.edu/CaltechETD:etd-09092005-131242
Authors: {'items': [{'id': 'Li-H', 'name': {'family': 'Li', 'given': 'Hui'}, 'show_email': 'NO'}]}
Year: 1999
DOI: 10.7907/000q-7m05
This thesis reports an automatic method for synthesizing MEMS mask-layouts. This method incorporates a forward simulation of fabrication into a general evolutionary algorithm loop. An initial random population of mask-layouts is generated. The fabrication of each layout is simulated through a digital process simulator to produce a 3D fabricated shape, which is compared to a user-specified desired shape. Each evolutionary loop governs the stochastic searching behavior such that the mask-layouts whose simulated shapes are closer to the desired shape are more likely to survive. More importantly, the "better" masks are more likely to be evolved among those survived mask-layouts for the next loop. Through such evolutionary iterations, a near global "optimum" mask-layout is likely to be found. By using this evolutionary approach, we are able to take use of existing simulations of fabrication processes to achieve those mask-layout synthesis where reversing a fabrication process simulation (so that a 2D mask-layout might be produced) appears not to be possible. The general evolutionary loop mainly consists of a mask genetics module, an evolutionary technique module and a MEMS simulation module. The mask genetics module provides heuristic genetic operations on mask-layouts, which includes mask coding scheme, random mask generation, random crossovers and mutations. The evolutionary technique module contains stochastic selection schemes and genetic operation schemes to control the searching convergence. The MEMS simulation module is the user input module, which requires a MEMS fabrication simulation and user-specified desired shape. A test loop is constructed for the bulk wet etching mask synthesis by incorporating a 3D wet etching simulation. The obtained results demonstrate the feasibility of this approach to mask-layout synthesis.https://thesis.library.caltech.edu/id/eprint/3400Visual methods for three-dimensional modeling
https://resolver.caltech.edu/CaltechETD:etd-02072008-115723
Authors: {'items': [{'id': 'Bouguet-J', 'name': {'family': 'Bouguet', 'given': 'Jean-Yves'}, 'show_email': 'NO'}]}
Year: 1999
DOI: 10.7907/hc2c-sp47
Most animals use vision as a primary sensor to interact with their environment. Navigation or manipulation of objects are among the tasks that can be better achieved while understanding the three-dimensional structure of the scene.
In this thesis, we present a variety of computational techniques for estimating 3D shape from 2D images, based on both passive and active technologies.
The first proposed method is purely passive. In this technique, a single camera is moved in an unconstrained manner around the scene to model as it acquires a sequence of images. The reconstruction process consists then of retrieving the trajectory of the camera, as well as the 3D structure of the scene using only the information contained in the images.
The second method is based on active lighting technology. In the philosophy of standard 3D scanning methods, a projector is used to project light patterns in the scene. The shape of the scene is then inferred from the way the patterns deform on the objects. The main novelty of our scheme compared to traditional methods is in the nature of the patterns, and the type of image processing associated to them. Instead of using standard binary patterns made out of black and white stripes, our scheme uses a sequence of grayscale patterns with a sinusoidal profile in brightness intensity. This choice allows us to establish correspondence (between camera image, and projector image) in a dense fashion, leading to depth computation at (almost)
every pixel in the image.
The last reconstruction method that we propose in this thesis is an alternative 3D scanning scheme that does not require any other device besides a camera. The main idea is to substitute the projector by a standard light source (such as a desk lamp), and use a pencil (or any other object with a straight edge) to cast planar shadows in the scene. The 3D geometry of the scene is then inferred from the way the shadow naturally deforms on the objects in the scene. Since this technology is largely inspired from structured lighting techniques, we call it 'weakly structured lighting.'
https://thesis.library.caltech.edu/id/eprint/541Robust mask-layout and process synthesis in micro-electro-mechanical-systems (MEMS) using genetic algorithms
https://resolver.caltech.edu/CaltechETD:etd-08302005-131428
Authors: {'items': [{'id': 'Ma-L', 'name': {'family': 'Ma', 'given': 'Lin'}, 'show_email': 'NO'}]}
Year: 2001
DOI: 10.7907/e8hm-z754
This thesis reports a Genetic Algorithm approach for the mask-layout and process flow synthesis problem. For a given desired target shape, an optimal mask-layout and process flow can be automatically generated using the Genetic Algorithm synthesis approach. The Genetic Algorithm manipulates and evolves a population of candidate solutions (mask-layouts and process parameters) by utilizing a process simulation tool to evaluate the performance of the candidate solutions. For the mask-layout and process flow synthesis problem, encoding schemes, selection schemes, and genetic operations have been developed to effectively explore the solution space and control the evolution and convergence of the solutions.
The synthesis approach is tested for mask-layout and process synthesis for bulk wet etching. By integrating a bulk wet etching simulation tool into the Genetic Algorithm iterations, the algorithm can automatically generate proper mask-layout and process flow which can fabricate 3-D geometry close to the desired 3-D target shape. For structures with convex corners, complex compensation structures can be synthesized by the algorithm. More importantly, the process flow can also be synthesized. For multi-step wet etching processes, proper etchant sequence and etch times for each etch step can be synthesized automatically by the algorithm. When the choice of different process flows exists, the enlarged solution space makes the design problem more challenging. The ability to synthesize process flows makes the automatic design method more complete and more valuable.
The algorithm is further extended to achieve robust design. Since fabrication variations and modeling inaccuracy always exist, the synthesized solutions without considering these variations may not generate satisfactory results in actual fabrication. Robust design methods are developed to synthesize robust mask-layouts and process flows in "noisy" environment. Since the synthesis procedure considers the effect of variations in the fabrication procedures, the final synthesized solution will have high robustness to the variations, and will generate satisfactory results under a variety of fabrication conditions. The robust design approaches are implemented and tested for robust mask-layout design for mask misalignment and etch rate variations. Mask-layouts robust to mask misalignment noise and etch rate variations during the fabrication can be synthesized. The synthesized mask-layouts generally improve the yield significantly by exhibiting consistent performance under a variety of fabrication conditions.https://thesis.library.caltech.edu/id/eprint/3279Control of Multiple Model Systems
https://resolver.caltech.edu/CaltechETD:etd-07312002-091923
Authors: {'items': [{'id': 'Murphey-Todd-David', 'name': {'family': 'Murphey', 'given': 'Todd David'}, 'show_email': 'NO'}]}
Year: 2002
DOI: 10.7907/17Q7-Y019
This thesis considers the control of multiple model systems. These are systems for which only one model out of some finite set of models gives the system dynamics at any given time. In particular, the model that gives the system dynamics can change over time. This thesis covers some of the theoretical aspects of these systems, including controllability and stabilizability. As an application, ``overconstrained' mechanical systems are modeled as multiple model systems. Examples of such systems include distributed manipulation problems such as microelectromechanical systems and many wheeled vehicles such as the Sojourner vehicle of the Mars Pathfinder mission. Such systems are typified by having more Pfaffian constraints than degrees of freedom. Conventional classical motion planning and control theories do not directly apply to overconstrained systems. Control issues for two examples are specifically addressed. The first example is distributed manipulation. Distributed manipulation systems control an object's motion through contact with a high number of actuators. Stability results are shown for such systems and control schemes based on these results are implemented on a distributed manipulation test-bed. The second example is that of overconstrained vehicles, of which the Mars rover is an example. The nonlinear controllability test for multiple model systems is used to answer whether a kinematic model of the rover is or is not controllable.https://thesis.library.caltech.edu/id/eprint/2989Efficient Automatic Engineering Design Synthesis Via Evolutionary Exploration
https://resolver.caltech.edu/CaltechTHESIS:05032011-082523919
Authors: {'items': [{'id': 'Lee-Cin-Young', 'name': {'family': 'Lee', 'given': 'Cin-Young'}, 'show_email': 'NO'}]}
Year: 2002
DOI: 10.7907/5HRP-ND58
The evolution of designs in nature has been the inspiration for this thesis, which seeks to develop a framework for efficient automatic engineering design synthesis based on evolutionary methods.
The design synthesis process is equated to an evolutionary process. Because of this, the same formalization for evolution, the evolution algorithm, is used as a design synthesis formalism. Implementation of the evolution algorithm on a computer allows evolution of non-biological systems, and, hence, automatic engineering design synthesis. The early and canonical versions of such evolutionary computation are bare bones evolution tools that neglect several key aspects of evolutionary systems. Some universal aspects of good designs are identified, three of which are dealt with in this thesis. These are variable complexity, modularity, and speciation.
Framed in an evolutionary context, each of these characteristics are requisites for being able to evolve in correspondence with a dynamic environment. Those that are most evolvable will survive. After all, if a species cannot evolve quickly enough with changes in the environment, it will perish. In a design context, this indicates that the characteristics are vital for efficiency and shorter design cycles.
An integrated framework is developed to address all three aspects individually or in any combination thereof, which has not been done heretofore. Because of the poor theoretical foundations of evolutionary computation, the effectiveness of the developed approach is determined through computer experimentation on several test and design problems. Results are promising as all three
aspects were successfully achieved in comparison to canonical evolutionary computation.
https://thesis.library.caltech.edu/id/eprint/6369Set Mapping in the Method of Imprecision
https://resolver.caltech.edu/CaltechETD:etd-10032002-214953
Authors: {'items': [{'id': 'Wang-Xiaoou', 'name': {'family': 'Wang', 'given': 'Xiaoou'}, 'show_email': 'NO'}]}
Year: 2003
DOI: 10.7907/J0JH-M190
<p>The Method of Imprecision, or MoI, is a semi-automated set-based approach which uses mathematics of fuzzy sets to aid the designer making decisions with imprecise information in the preliminary design stage.</p>
<p>The Method of Imprecision uses preference to represent the imprecision in engineering design. The preferences are specified both in the design variable space (DVS) and the performance variable space (PVS). To reach the overall preference which is needed to evaluate designs, the mapping between the DVS and the PVS should be explored. Many engineering design tools can only produce precise results with precise specifications, and usually the cost is high. In the preliminary stage, the specifications are imprecise and resources are limited. Hence, it is not cost-effective nor necessary to use these engineering design tools directly to study the mapping between the DVS and the PVS. An interpolation model is introduced to the MoI to construct metamodels for the actual mapping function between the DVS and the PVS. Due to the nature of engineering design, multistage metamodels are needed. Experimental design is used to choose design points for the first metamodel. In order to find an efficient way to choose design points when a priori information is available, many sampling criteria are discussed and tested on two specific examples. The difference between different sampling criteria when the number of added design points is small, while more design points do improve the accuracy of the metamodel substantially.</p>
<p>The metamodels can be used to induce preferences in the DVS or the PVS according to the extension principle. The Level Interval Algorithm (LIA) is a discrete approximate implementation of the extension principle. The resulting preference by the LIA is presented as an alpha-cut, which is the set of designs or performances with a certain level of preference. There are some limitations of the LIA, especially for multidimensional DVS and PVS. A new extension of the LIA is proposed to compute alpha-cuts with more accuracy and less limitations. The designers have more control over the trade-off between the cost and accuracy of the computation with the new extension of the LIA.</p>
<p>The results of the Method of Imprecision should be the set of alternative designs in the DVS at a certain preference level, and the set of achievable performances in the PVS. The information about preferences in the DVS and the PVS is needed to transfer back and forth. Usually the mapping from the PVS to the DVS is unavailable, while it is needed to induce preference in the DVS from the PVS. A new method is constructed to compute the alpha-cuts in both spaces from preferences specified in the DVS and the PVS.</p>
<p>Finally, a new measure is proposed to find the most cost-effective sampling region of new design points for a metamodel. Also, the full implementation of the Method of Imprecision is listed in detail. Then it is applied to an example of the structure design of a passenger vehicle, and comparisons are made between the new results and previous results.</p>https://thesis.library.caltech.edu/id/eprint/3884Fluid Locomotion and Trajectory Planning for Shape-Changing Robots
https://resolver.caltech.edu/CaltechETD:etd-05292003-160843
Authors: {'items': [{'id': 'Mason-Richard-James', 'name': {'family': 'Mason', 'given': 'Richard James'}, 'show_email': 'YES'}]}
Year: 2003
DOI: 10.7907/MFM1-0866
Motivated by considerations of shape changing propulsion of underwater robotic vehicles, I analyze the mechanics of deformable bodies operating in an ideal fluid. I give particular attention to fishlike robots which may be considered as one or more flexing or oscillating hydrofoils. I then describe methods of planning trajectories for a fishlike robot or any other sort of robot whose locomotion has a periodic or quasi-periodic nature.https://thesis.library.caltech.edu/id/eprint/2235Propagating and Mitigating Uncertainty in the Design of Complex Multidisciplinary Systems
https://resolver.caltech.edu/CaltechETD:etd-01072005-162147
Authors: {'items': [{'id': 'Thunnissen-Daniel-Pierre', 'name': {'family': 'Thunnissen', 'given': 'Daniel Pierre'}, 'show_email': 'NO'}]}
Year: 2005
DOI: 10.7907/0FX2-AM50
<p>As humanity has developed increasingly ingenious and complicated systems, it has not been able to accurately predict the performance, development time, reliability, or cost of such systems. This inability to accurately predict parameters of interest in the design of complex multidisciplinary systems such as automobiles, aircraft, or spacecraft is due in great part to uncertainty. Uncertainty in complex multidisciplinary system design is currently mitigated through the use of heuristic margins. The use of these heuristic margins can result in a system being overdesigned during development or failing during operation.</p>
<p>This thesis proposes a formal method to propagate and mitigate uncertainty in the design of complex multidisciplinary systems. Specifically, applying the proposed method produces a rigorous foundation for determining design margins. The method comprises five distinct steps: identifying tradable parameters; generating analysis models; classifying and addressing uncertainties; quantifying interaction uncertainty; and determining margins, analyzing the design, and trading parameters. The five steps of the proposed method are defined in detail. Margins are now a function of risk tolerance and are measured relative to mean expected system performance, not variations in design parameters measured relative to heuristic values.</p>
<p>As an example, the proposed method is applied to the preliminary design of a spacecraft attitude determination and control system. In particular, the design of the attitude control system on the Mars Exploration Rover spacecraft cruise stage is used. Use of the proposed method for the example presented yields significant differences between the calculated design margins and the values assumed by the Mars Exploration Rover project.</p>
<p>In addition to providing a formal and rigorous method for determining design margins, this thesis provides three other principal contributions. The first is an uncertainty taxonomy for use in the design of complex multidisciplinary systems with detailed definitions for each uncertainty type. The second is the modification of two simulation techniques, the mean value method and subset simulation, that can significantly reduce the computational burden in applying the proposed method. The third is a set of diverse application examples and various simulation techniques that demonstrate the generality and benefit of the proposed method.</p>https://thesis.library.caltech.edu/id/eprint/53Tools and Algorithms for Mobile Robot Navigation with Uncertain Localization
https://resolver.caltech.edu/CaltechETD:etd-06012006-150109
Authors: {'items': [{'email': 'kristopher.l.kriechbaum@jpl.nasa.gov', 'id': 'Kriechbaum-Kristopher-Lars', 'name': {'family': 'Kriechbaum', 'given': 'Kristopher Lars'}, 'show_email': 'YES'}]}
Year: 2006
DOI: 10.7907/R6YB-NQ21
The ability for a mobile robot to localize itself is a basic requirement for reliable long range autonomous navigation. This thesis introduces new tools and algorithms to aid in robot localization and navigation. I introduce a new range scan matching method that incorporates realistic sensor noise models. This method can be thought of as an improved form of odometry. Results show an order of magnitude of improvement over typical mobile robot odometry. In addition, I have created a new sensor-based planning algorithm where the robot follows the locally optimal path to the goal without exception, regardless of whether or not the path moves towards or temporarily away from the goal. The cost of a path is defined as the path length. This new algorithm, which I call "Optim-Bug," is complete and correct. Finally, I developed a new on-line motion planning procedure that determines a path to a goal that optimally allows the robot to localize itself at the goal. This algorithm is called "Uncertain Bug." In particular, the covariance of the robot's pose estimate at the goal is minimized. This characteristic increases the likelihood that the robot will actually be able to reach the desired goal, even when uncertainty corrupts its localization during movement along the path. The robot's path is chosen so that it can use known features in the environment to improve its localization. This thesis is a first step towards bringing the tools of mobile robot localization and mapping together with ideas from sensor-based motion planning.https://thesis.library.caltech.edu/id/eprint/2363System Architectures and Environment Modeling for High-Speed Autonomous Navigation
https://resolver.caltech.edu/CaltechETD:etd-05242006-190748
Authors: {'items': [{'id': 'Cremean-Lars-Brör', 'name': {'family': 'Cremean', 'given': 'Lars Brör'}, 'show_email': 'NO'}]}
Year: 2006
DOI: 10.7907/8HT2-N165
<p>Successful high-speed autonomous navigation requires integration of tools from robotics, control theory, computer vision, and systems engineering. This thesis presents work that develops and combines these tools in the context of navigating desert terrain.</p>
<p>A comparative analysis of reactive, behavior-based, and deliberative control architectures provides important guidelines for design of robotic systems. These guidelines depend on the particular task and environment of the vehicle. Two important factors are identified which guide an effective choice between these architectures: dynamic feasibility for the vehicle, and predictability of the environment. This is demonstrated by parallels to control theory, illustrative examples, simulations, and analysis of Bob and Alice---Caltech's full-scale autonomous ground vehicle entries in the 2004 and 2005 Grand Challenge races, respectively.</p>
<p>Further, new model-based methods are developed for constructing and maintaining estimates of terrain elevation and road geometry. These are demonstrated in simulation and in fully autonomous operation of Alice, including accurate detection and tracking of the centerline of desert roads at speeds up to 5 m/s. Finally, Alice's navigation architecture is presented in full along with experimental results that demonstrate its capabilities.</p>https://thesis.library.caltech.edu/id/eprint/2014Algorithms for Mobile Robot Localization and Mapping, Incorporating Detailed Noise Modeling and Multi-scale Feature Extraction
https://resolver.caltech.edu/CaltechETD:etd-05262006-130209
Authors: {'items': [{'email': 'pfister@post.harvard.edu', 'id': 'Pfister-Samuel-Thomas', 'name': {'family': 'Pfister', 'given': 'Samuel Thomas'}, 'show_email': 'NO'}]}
Year: 2006
DOI: 10.7907/FN3J-M568
<p>Mobile robot localization and mapping in unknown environments is a fundamental requirement for effective autonomous navigation. Three different approaches to localization and mapping are presented. Each is based on data collected from a robot using a dense range scanner to generate a planar representation of the surrounding environment. This externally sensed range data is then overlayed and correlated to estimate the robot's position and build a map.</p>
<p>The three approaches differ in the choice of representation of the range data, but all achieve improvements over prior work using detailed sensor modeling and rigorous bookkeeping of the modeled uncertainty in the estimation processes. In the first approach, the raw range data points collected from two different positions are individually weighted and aligned to estimate the relative robot displacement. In the second approach, line segment features are extracted from the raw point data and are used as the basis for efficient and robust global map construction and localization. In the third approach, a new multi-scale data representation is introduced. New methods of localization and mapping are developed, taking advantage of this multi-scale representation to achieve significant improvements in computational complexity. A central focus of all three approaches is the determination of accurate and robust solutions to the data association problem, which is critical to the accuracy of any sensor-based localization and mapping method.</p>
<p>Experiments using data collected from a Sick LMS-200 laser scanner illustrate the effectiveness of the algorithms and improvements over prior work. All methods are capable of being run in real time on a mobile robot, and can be used to support fully autonomous navigation applications.</p>https://thesis.library.caltech.edu/id/eprint/2110Engineering Design Synthesis of Sensor and Control Systems for Intelligent Vehicles
https://resolver.caltech.edu/CaltechETD:etd-05252006-221412
Authors: {'items': [{'id': 'Zhang-Yizhen', 'name': {'family': 'Zhang', 'given': 'Yizhen'}, 'show_email': 'NO'}]}
Year: 2006
DOI: 10.7907/NB6H-S822
<p>This thesis investigates the application of formal engineering design synthesis methodologies to the development of sensor and control systems for intelligent vehicles.</p>
<p>A formal engineering design synthesis methodology based on evolutionary computation is presented, with special emphasis on dealing with modern engineering design challenges, such as high or variable complexity of design solutions, multiple conflicting design objectives, and noisy evaluation results, etc. The efficacy of the evolutionary design synthesis method is validated through multiple different case studies, where a variety of novel design solutions are generated to represent different engineering design trade-offs, and they have achieved performances comparable to, if not better than, that of hand-coded solutions in the same simplified environment. More importantly, this automatic design synthesis method shows great potential to handle more complex design problems, where a good hand-coded solution may be very difficult or even impossible to obtain. Moreover, the evolutionary design synthesis methodology appears promising to deal with uncertainty in the problem efficiently and adapt to the collective task nature well.</p>
<p>In addition, multiple levels of vehicle simulation models with different computational cost and fidelity as well as necessary driver behaviors are implemented for different types of simulation experiments conducted for different research purposes. Efforts are made to try to generate good candidate solutions efficiently with less computational time and human engineering effort.</p>
<p>Furthermore, a new threat assessment measure, time-to-last-second-braking (<i>T<sub>lsb</sub></i>), is proposed, which directly characterizes human natural judgment of the urgency and severity of threats in terms of time. Based on driver reaction time experimental results, new warning and overriding criteria are proposed in terms of the new <i>T<sub>lsb</sub></i> measure, and the performance is analyzed statistically in terms of two typical sample pre-crash traffic scenarios. Less affected by driver behavior variability, the new criteria characterize the current dynamic situations better than the previous ones, providing more appropriate warning and more effective overriding at the last moment. Finally, the possibility of frontal collision avoidance through steering (lane-changing) is discussed, and similarly the time-to-last-second-steering (<i>T<sub>lss</sub></i>) measure is proposed and compared with <i>T<sub>lsb</sub></i>.</p>https://thesis.library.caltech.edu/id/eprint/2062Fundamental Ion-Surface Interactions in Plasma Thrusters
https://resolver.caltech.edu/CaltechETD:etd-11222006-105854
Authors: {'items': [{'email': 'rkolas@gmail.com', 'id': 'Kolasinski-Robert-David', 'name': {'family': 'Kolasinski', 'given': 'Robert David'}, 'orcid': '0000-0002-9633-1845', 'show_email': 'NO'}]}
Year: 2007
DOI: 10.7907/XWSV-1E98
Ion thrusters offer the potential to enable many future interplanetary robotic missions presently under consideration by NASA. To realize the benefits offered by these low thrust devices, the sputtering mechanisms that are responsible for the degradation of thruster components over time must be well understood. Predictions of thruster life depend directly on the material removal rates from thruster electrodes such as the ion optics and hollow cathodes. To better understand the conditions encountered at these surfaces, this study includes an investigation of low energy sputtering at glancing incidence. Relevant ion–target combinations that were considered included Xe⁺ incident on Mo, C, and Cu, as well as Ar⁺ incident on W, C, and Cu.
To characterize the sputtering yield angular dependence experimentally, an ion beam was used to etch a coated quartz crystal microbalance. This required the development of techniques to accurately measure the incident low energy ion flux to the target and the use of surface diagnostics to investigate the properties of target materials. Measurements of C and Mo sputtering yields were obtained for Xe⁺ incidence angles up to 80° from the surface normal and for energies ranging from 80 eV–1 keV. In addition, existing transport theory models were used to examine projectile scattering within the different target media. The models also indicate that the sputtering behavior as a function of angle of incidence is not a strong function of energy, a conclusion that is supported by the experimental results. The surface roughness of the targets was investigated using atomic force microscopy to obtain local incidence angle distributions.
A surface layer activation technique served as an alternate method of evaluating the sputtering rates of thruster components for situations where the ion bombardment conditions are not well known. In this study, a radioactive tracer was produced in the surfaces of a number of laboratory model ion thruster cathode assemblies by high energy proton bombardment. The cathodes were tested in a 30 cm diameter xenon ion thruster to provide insight into the relevant wear mechanisms at different thruster operating points. Methods for combating cathode degradation are proposed based on the experimental results.https://thesis.library.caltech.edu/id/eprint/4641Intelligent Information-Gathering: Using Control for Sensing and Decision-Making
https://resolver.caltech.edu/CaltechETD:etd-05312007-024822
Authors: {'items': [{'id': 'Chung-Timothy-Hahn-Deut', 'name': {'family': 'Chung', 'given': 'Timothy Hahn Deut'}, 'show_email': 'NO'}]}
Year: 2007
DOI: 10.7907/V5S4-4197
Information is everywhere and evolving, which necessitates both deliberate and efficient processing to acquire a good understanding of the dynamic situation, environment, or system of interest. Intelligent agents such as autonomous mobile sensors can control the way they gather information and thereby take advantage of feedback to improve the quality of that information. This approach reflects a shift from traditional "sensing for control" notions to "control for sensing" methods for addressing information-based objectives. This thesis presents several algorithms for distributed sensing tasks in the context of a team of mobile sensing agents. Applications of these types of mobile sensor networks include target tracking, dynamic environment monitoring, and distributed classification. These methods point beyond the use of sensory data for control and toward a framework for using control to improve information-based decisions made by intelligent agents. The sequential decision-theoretic framework presented herein has relevant applications in engineered systems such as search and rescue using a robotic team, as well as potential connections to natural systems including search strategies in the human vision system.https://thesis.library.caltech.edu/id/eprint/2336Exploration into the Feasibility of Underwater Synthetic Jet Propulsion
https://resolver.caltech.edu/CaltechETD:etd-09252006-134742
Authors: {'items': [{'email': 'apthomas@stthomas.edu', 'id': 'Polsenberg-Thomas-AnnMarie', 'name': {'family': 'Polsenberg Thomas', 'given': 'AnnMarie'}, 'show_email': 'YES'}]}
Year: 2007
DOI: 10.7907/72SZ-T823
<p>This thesis explores the feasibility of using synthetic jet actuators for the propulsion of small underwater vehicles. This work was inspired by the widespread use of pusatile jet propulsion by sea creatures such as squid, salp, and jellyfish. The jets created by these animals utilize vortex rings for thrust production. A method for creating similar vortex ring-based jets is the use of synthetic, or zero net mass flux, jets. These jets, which form a jet structure through the alternating sucking and blowing of fluid through a single orifice, have previously been investigated for the utility in air flow control.</p>
<p>The design, construction, and testing of aquatic synthetic jet prototypes is presented. Force measurement and flow visualization experiments are performed on these jets to gain an understanding of the forces and flow structures produced. The flow visualizations confirm the outflow vortex ring observations reported previously in the literature and present the first images of vortex ring formation inside the synthetic jet chamber. A new phenomenon, that of self-induced coflow upstream of the jet orifice, is discussed. The force measurements present confirmation that a net thrust is produced by the jets and give insight to the relationship between jet forcing parameters (such as frequency) and the resulting thrust. An automated genetic algorithmic approach to optimizing the thrust for a given jet geometry is also presented and tested.</p>
<p>Using the results of these experiments I propose a model for synthetic jet thrust. This model asserts that there are three force producing components to the flow: orifice inflow, orifice outflow, and a self-induced coflow. The contribution of each of these components is derived and compared with experimental results.</p>
<p>Included at the end of this thesis is a preliminary study into possible vehicle architecture for the utilization of synthetic jet thrusters.</p>https://thesis.library.caltech.edu/id/eprint/3761Information-Theoretic Methods for Modularity in Engineering Design
https://resolver.caltech.edu/CaltechETD:etd-05282007-183612
Authors: {'items': [{'email': 'ewangbw@yahoo.com', 'id': 'Wang-Bingwen', 'name': {'family': 'Wang', 'given': 'Bingwen'}, 'show_email': 'NO'}]}
Year: 2007
DOI: 10.7907/ZBBK-JM82
<p>Due to their many advantages, modular structures commonly exist in artificial and natural systems, and the concept of modular product design has recently received extensive attention from the engineering research community. Although some work has been done on modularity, most of it is qualitative and exploratory in nature, and little is quantitative. One reason for this gap is the lack of a clear definition of modularity. This thesis begins with a detailed discussion on the concepts of “modularity” and “module.”</p>
<p>Based on the background presented here, a mutual information-based method is proposed to quantify modularity. The method is based on the view that coupling is information flow instead of real physical interactions. Information flow can be quantified by mutual information, which is based on randomness (or uncertainty). Since most engineering products can be modeled as stochastic systems and therefore have randomness, the mutual information-based method can be applied in very general cases, and it is shown that the commonly existing linkage counting modularity measure is a special case of the mutual information-based modularity measure.</p>
<p>The mutual information-based method is applicable to final design products. But at the early stage of the engineering design process, there are generally only function diagrams. To exploit the benefits of modularity as early as possible, a minimal description length principle-based modularity measure is proposed to determine the modularity of graph structures, which can represent function diagrams. The method is used as criteria to hierarchically decompose abstract graph structures and the real function structure of an HP printer by evolutionary computation. Due to the specialty of genome representations in evolutionary computation, new genetic operators are developed to determine optimal hierarchical decompositions.</p>
<p>This quantitative modularity measure has been developed to synthesize modular engineering products, especially by evolutionary design. There are many factors affecting evolving modular structures, such as genome representation, fitness function, learning, and task structure. The thesis preliminarily studies the effects of the modularity of tasks on the modularity of products in evolutionary computation. Using feed-forward neural networks as examples, the results show that the effects are task-dependent and rely on the amount of resources available for the tasks.</p>https://thesis.library.caltech.edu/id/eprint/2202Robotic Training for Motor Rehabilitation after Complete Spinal Cord Injury
https://resolver.caltech.edu/CaltechETD:etd-09202007-135027
Authors: {'items': [{'email': 'yliang@caltech.edu', 'id': 'Liang-Yongqiang', 'name': {'family': 'Liang', 'given': 'Yongqiang'}, 'show_email': 'NO'}]}
Year: 2008
DOI: 10.7907/T01R-P904
<p>The spinal cord circuits have a great degree of automaticity and plasticity. They are able to generate complex locomotor patterns such as stepping and scratching even without input from supraspinal nervous systems. When provided with ensembles of afferent sensory information input associated with a specific motor task, e.g., stepping, the spinal cord can "learn" to perform that task even if it is isolated from the supraspinal nervous systems.</p>
<p>The plasticity of the spinal cord led researchers to study the use of physical locomotor training, e.g., treadmill step training with body weight support, to rehabilitate locomotor function after spinal cord injury (SCI). With intensive training, the spinal-cord-injured subject can recover some level of stepping ability. Explorations were made in this thesis to find an optimal training paradigm. Novel assist-as-needed paradigms were developed to allow variability during training since it is an intrinsic feature of normal stepping. Comparative experiments were conducted against fixed-trajectory training. Results demonstrated that variability is an important factor to induce more improvement in step training.</p>
<p>Standing is another important function in one's daily life, though it received less research attention than stepping. A prototype stand platform with 6 degrees of freedom was developed as an experimental tool for stand and postural study. Analogous to step training, we tested the effect of daily training on extensor responses in the hind limbs of complete spinal rats. The results showed no significant effect of the training. This led to the conclusion that without tonic input, the spinal cord has very limited ability to generate enough extensor muscle tone and to respond to postural disturbance. Further studies in standing rehabilitation should combine other methods to provide tonic inputs to the spinal cord.</p>https://thesis.library.caltech.edu/id/eprint/3666Automated Design Synthesis of Structures using Growth Enhanced Evolution
https://resolver.caltech.edu/CaltechETD:etd-06102008-153834
Authors: {'items': [{'email': 'fabien.nicaise@alum.rpi.edu', 'id': 'Nicaise-Fabien', 'name': {'family': 'Nicaise', 'given': 'Fabien'}, 'show_email': 'YES'}]}
Year: 2008
DOI: 10.7907/28H7-E831
<p>Engineering design is a complex problem on generating and evaluating a variety of options. In traditional methods, this typically involves evaluating up to a dozen different point designs. The limit on the process is the amount of time to generate, refine, and evaluate the various concepts. Using a computer helps to speed up the process, but human involvement still remains the weakest link.</p>
<p>The natural extension of this process is to continually and rapid generate, refine, and evaluate concepts entirely automatically. Evolutionary Algorithms provide such a method, by emulating natural evolution. The computer maintains a population point design, each of which is represented by a gene string that is allowed to change (mutate) and combine with other genes (crossover). At each generation, every individual is modified then evaluated and the improved solutions proceed to the next generation.</p>
<p>This thesis will extend the biological model by introducing a growth process to each individual. This is akin to the concept of a multi-cellular organism developing in the womb. An encoding for discrete truss structures is described that provides for such an extension. The truss grows from a few basic elements. After showing several examples demonstrating the growth process, the method is applied to a couple simple examples using evolutionary algorithms.</p>https://thesis.library.caltech.edu/id/eprint/5231Flatland Photonics: Circumventing Diffraction with Planar Plasmonic Architectures
https://resolver.caltech.edu/CaltechETD:etd-10302008-115303
Authors: {'items': [{'email': 'jdionne@stanford.edu', 'id': 'Dionne-Jennifer-Anne', 'name': {'family': 'Dionne', 'given': 'Jennifer Anne'}, 'orcid': '0000-0001-5287-4357', 'show_email': 'YES'}]}
Year: 2009
DOI: 10.7907/3DCC-CZ57
<p>On subwavelength scales, photon-matter interactions are limited by diffraction. The diffraction limit restricts the size of optical devices and the resolution of conventional microscopes to wavelength-scale dimensions, severely hampering our ability to control and probe subwavelength-scale optical phenomena. Circumventing diffraction is now a principle focus of integrated nanophotonics. Surface plasmons provide a particularly promising approach to sub-diffraction-limited photonics. Surface plasmons are hybrid electron-photon modes confined to the interface between conductors and transparent materials. Combining the high localization of electronic waves with the propagation properties of optical waves, plasmons can achieve extremely small mode wavelengths and large local electromagnetic field intensities. Through their unique dispersion, surface plasmons provide access to an enormous phase space of refractive indices and propagation constants that can be readily tuned with material or geometry.</p>
<p>In this thesis, we explore both the theory and applications of dispersion in planar plasmonic architectures. Particular attention is given to the modes of metallic core and plasmon slot waveguides, which can span positive, near-zero, and even negative indices. We demonstrate how such basic plasmonic geometries can be used to develop a suite of passive and active plasmonic components, including subwavelength waveguides, color filters, negative index metamaterials, and optical MOS field effect modulators. Positive index modes are probed by near- and far-field techniques, revealing plasmon wavelengths as small as one-tenth of the excitation wavelength. Negative index modes are characterized through direct visualization of negative refraction. By fabricating prisms comprised of gold, silicon nitride, and silver multilayers, we achieve the first experimental demonstration of a negative index material at visible frequencies, with potential applications for sub-diffraction-limited microscopy and electromagnetic cloaking. We exploit this tunability of complex plasmon mode indices to create a compact metal-oxide-Si (MOS) field effect plasmonic modulator (or plasMOStor). By transforming the MOS gate oxide into an optical channel, amplitude modulation depths of 11.2 dB are achieved in device volumes as small as one one-fifth of a cubic wavelength. Our results indicate the accessibility of tunable refractive indices over a wide frequency band, facilitating design of a new materials class with extraordinary optical properties and applications.</p>
https://thesis.library.caltech.edu/id/eprint/5256Computational Evolutionary Embryogeny
https://resolver.caltech.edu/CaltechETD:etd-01162009-072031
Authors: {'items': [{'email': 'or@aug-wind.com', 'id': 'Yogev-Or', 'name': {'family': 'Yogev', 'given': 'Or'}, 'show_email': 'NO'}]}
Year: 2009
DOI: 10.7907/N4XG-F402
<p>Evolution and development (Evo-Devo), are the two main processes which produce all of the different kinds of phenotypes we see in nature. Evolutionary process is responsible for eliminating the genetic information of weak phenotypes through natural selection, and also for exploring novel genotypes through genetic operations; crossover, mutation. The development process is the process of using the set of rules (codons) written in a genome, to turn a single set (zygote) into a mature phenotype. In this thesis, evolutionary and developmental processes are used to evolve the configurations of three-dimensional structures in silico to achieve desired performances. Although natural systems utilize the combination of both evolution and development processes to produce remarkable performance and diversity, this approach has not yet been applied extensively to the design of continuous three-dimensional load-supporting structures. Beginning with a single artificial cell containing information analogous to a DNA sequence, a structure is grown according to the rules encoded in the sequence. Each artificial cell in the structure contains the same sequence of growth and development rules, and each artificial cell is an element in a finite element mesh representing the structure of the mature individual. Rule sequences are evolved over many generations through selection and survival of individuals in a population.</p>
<p>Modularity and symmetry are visible in nearly every natural and engineered structure. Understanding of the evolution and expression of symmetry and modularity is emerging from recent biological research. Initial evidence of these attributes is present in the phenotypes that are developed from the artificial evolution, although neither characteristic is imposed nor selected for directly.</p>
<p>The computational evolutionary development approach presented here shows promise for synthesizing novel configurations of high-performance systems. The approach may advance system design to a new paradigm, where current design strategies have difficulty producing useful solutions. In addition to a new design approach perse, this model gives us the ability to explore the development process, from the standpoint of complex systems analysis. The phenotypes in our system have been grown under a highly stochastic environment, which serves as a triggered mechanism for gene expression. Still, evolution was able to find solutions which are robust to these stochastic elements, both at the phenotype level (the phenotype ability to function under the environment) and the growth process itself. In addition we have also explored the effects of symmetric and nonsymmetric environment over the topology of the phenotypes; we have found strong evidence that indicates a high correlation between the two. Finally we have also established a tool which enables us to understand the relationship between the environment and the degree of modularity of the phenotype.</p>
https://thesis.library.caltech.edu/id/eprint/208Neuro-Evolution Using Recombinational Algorithms and Embryogenesis for Robotic Control
https://resolver.caltech.edu/CaltechTHESIS:06092010-140839602
Authors: {'items': [{'email': 'tonyroy46@yahoo.com', 'id': 'Roy-Anthony-Mathew', 'name': {'family': 'Roy', 'given': 'Anthony Mathew'}, 'show_email': 'NO'}]}
Year: 2010
DOI: 10.7907/YNED-VN66
Control tasks involving dramatic nonlinearities, such as decision making, can be challenging for classical design methods. However, autonomous, stochastic design methods such as evolutionary computation have proved effective. In particular, genetic algorithms that create designs via the application of recombinational rules are robust and highly scalable. Neuro-Evolution Using Recombinational Algorithms and Embryogenesis (NEURAE) is a genetic algorithm that creates C++ programs that in turn create neural networks which can function as logic gates. The neural networks created are scalable and robust enough to feature redundancies that allow the network to function despite internal failures. An analysis of NEURAE evinces how biologically inspired phenomena apply to simulated evolution. This allows for an optimization of NEURAE that enables it to create controllers for a simulated swarm of Khepera-inspired robots.https://thesis.library.caltech.edu/id/eprint/5944