Shannon Ridgeway

Fundamental Comparison of the Use of Serial and Parallel Kinematics for Machines Tools

Abstract Classical cartesian kinematics Machining Center (MC) structures are compared with parallel kinematics hexapods (HX) structures from the point of view of workspace, stiffness, accuracy, acceleration ability, and motion dynamics for use as high speed milling machines. Concrete stiffness values are used as achievable. It is concluded that variable strut length HX are fundamentally inferior to the MC and cannot practically be used as high speed milling machines. The constant strut length HX offer larger workspace and higher strut stiffness and may produce characteristics comparable to MC in particular designs.

Team CIMAR's NaviGator: An unmanned ground vehicle for the 2005 DARPA grand challenge

This paper describes the development of an autonomous vehicle system that participated in the 2005 DARPA Grand Challenge event. After a brief description of the event, the architecture, based on version 3.2 of the Department of Defense Joint Architecture for Unmanned Systems (JAUS), and the design of the system are presented in detail. In particular, the “smart sensor” concept is introduced which provided a standardized means for each sensor to present data for rapid integration and arbitration. Information about the vehicle design, system localization, perception sensors, and the dynamic planning algorithms that were used is then presented in detail. Subsequently, testing results and performance results are presented.

Team Gator Nation's Autonomous Vehicle Development for the 2007 DARPA Urban Challenge

This paper describes the system design developed for Team Gator Nation’s submission to the 2007 DARPA Urban Challenge. A hybrid Toyota Highlander has been automated and instrumented with pose estimation (GPS and inertial) and object detection (vision and ladar) sensors. The control architecture consists of four primary elements, i.e. Planning Element, Perception Element, Intelligence Element, and Control Element. The Intelligence Element implements the Adaptive Planning Framework developed by researchers at the University of Florida. This framework provides a means for situation assessment, behavior mode evaluation, and behavior selection and execution. The architecture is implemented on a system distributed over ten dual-core computers that intercommunicate via the Joint Architecture for Unmanned Systems (JAUS) version 3.2 protocol. This work’s primary contribution addresses the technical challenges of (a) the reconciliation of differences in estimated global pose, a priori data, and sensed information, (b) the determination of the appropriate behavior mode, and (c) the smooth transition of vehicle control between behavior modes. The processes that perform these tasks as well as the other necessary processes that perform perception, data integration, planning, and control are described in detail together with their design rationale. Finally, testing results accomplished to date are presented.

A Comparison of Stiffness Characteristics of Serial and Parallel Machine Tools

Abstract The stiffness characteristics of classical serial machine tools are compared with parallel kinematic, or hexapod, structures for high-speed milling applications. A structural stiffness requirement for this application is determined by the stiffness of current-generation high-speed spindles and the desire for stability against chatter. It is found that hexapod structures exhibit lower structural stiffness than can be achieved in serial machines using the same drive components. Furthermore, the stiffness varies widely across the workspace of hexapod machines, leading to difficulties in control and limiting achievable accuracy. Theoretically derived stiffnesses are compared with experimentally measured stiffnesses for two hexapod machines and are found to show good agreement.

Investigation of a special 6-6 parallel platform for contour milling

Recently, companies have been experimenting with parallel-mechanism based approaches for milling machines. This research presents an investigation into the development of a special 6-6 parallel mechanism for application to contour milling, The idea behind this approach is that existing non-CNC milling equipment can be augmented to increase its capability at a lower cost than purchasing traditional 5-axis machining centers. This paper presents the phase of research associated with developing a parametric kinestatic design methodology for a special 6-6 parallel mechanism (Kinestatic Platform, KP). This methodology was applied to the design specifications associated with 5-axis contour milling. The resulting kinestatic designs dynamics were evaluated to determine the actuation requirements of each connector. A prototype connector was built to allow the evaluation of actuator response under simulated loading conditions. Joint stiffness and control strategy were of primary concern in evaluating the performance of the prototype connector. The parametric kinestatic design and control strategy results are presented. Several observations are evidenced from the research. Joint deflection is an obvious critical issue and the most difficult to quantify. A scheme is proposed detailing the concept of using a separate metrology frame to overcome difficulties associated with accurate connector length determination.

A Forward Analysis of a Two Degree of Freedom Parallel Manipulator

The forward analysis of a parallel planar manipulator (PPM) with two degrees of freedom is developed. The two degree of freedom PPM has been applied to an articulated mobile robot and the forward analysis is one of the tools developed to aid in the design and control of the articulated mobile robot. The forward analysis is derived from the loop closure equation for a quadrilateral applied to two quadrilaterals that make up the PPM. One side and two angles are common between the two quadrilaterals. An input-output equation is derived that generates six closures for the mechanism. The forward analysis is applied to the geometry of the PPM utilized in the articulated mobile robot, and determines four real and two imaginary closures.

Development of an articulated transporter/manipulator system

The development of an articulated transporter/manipulator system was undertaken to meet the navigational and manipulation needs expected in confined areas associated with the nuclear power industry...

Mechanics of Materials Laboratory Course

This book is designed to provide lecture notes (theory) and experimental design of major concepts typically taught in most Mechanics of Materials courses in a sophomore- or junior-level Mechanical or Civil Engineering curriculum. Several essential concepts that engineers encounter in practice, such as statistical data treatment, uncertainty analysis, and Monte Carlo simulations, are incorporated into the experiments where applicable, and will become integral to each laboratory assignment. Use of common strain (stress) measurement techniques, such as strain gages, are emphasized. Application of basic electrical circuits, such as Wheatstone bridge for strain measurement, and use of load cells, accelerometers, etc., are employed in experiments. Stress analysis under commonly applied loads such as axial loading (compression and tension), shear loading, flexural loading (cantilever and four-point bending), impact loading, adhesive strength, creep, etc., are covered. LabVIEW software with relevant data acquisition (DAQ) system is used for all experiments. Two final projects each spanning 2‒3 weeks are included: (i) flexural loading with stress intensity factor determination and (ii) dynamic stress wave propagation in a slender rod and determination of the stress‒strain curves at high strain rates. The book provides theoretical concepts that are pertinent to each laboratory experiment and prelab assignment that a student should complete to prepare for the laboratory. Instructions for securing off-the-shelf components to design each experiment and their assembly (with figures) are provided. Calibration procedure is emphasized whenever students assemble components or design experiments. Detailed instructions for conducting experiments and table format for data gathering are provided. Each lab assignment has a set of questions to be answered upon completion of experiment and data analysis. Lecture notes provide detailed instructions on how to use LabVIEW software for data gathering during the experiment and conduct data analysis.

UNIVERSITY RESEARCH PROGRAMS IN ROBOTICS, TECHNOLOGIES FOR MICROELECTROMECHANICAL SYSTEMS IN DIRECTED STOCKPILE WORK RADIATION AND ENGINEERING CAMPAIGNS - 2005-06 FINAL ANNUAL REPORT

The research performed by the University of Florida (UF) is directed to the development of technologies that can be utilized at a micro-scale in varied environments. Work is focused on micro-scale energy systems, visualization, and mechanical devices. This work will impact the NNSA need related to micro-assembly operations. The URPR activities are executed in a University environment, yet many applications of the resulting technologies may be classified or highly restrictive in nature. The NNSA robotics technologists apply an NNSA needs focus to the URPR research, and actively work to transition relevant research into the deployment projects in which they are involved. This provides a “Research to Development to Application” structure within which innovative research has maximum opportunity for impact without requiring URPR researchers to be involved in specific NNSA projects. URPR researchers need to be aware of the NNSA applications in order to ensure the research being conducted has relevance, the URPR shall rely upon the NNSA sites for direction.

Design, fabrication, and control of a robotic wall-crawler for remote inspection operations

A prototype wall-crawler for remote inspection operation was designed and fabricated for use in a constrained hazardous environment. The transporter was designed to carry inspection sensors to detect weld flaws in reactor and containment vessels and had to withstand elevated temperature and radiation exposure. Other design parameter considerations included limitations on size and operation in an inert environment. The transporter was programmed using a language developed for several in-house robotic systems.