- About
-
The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
provided by the
Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
Search results
Showing 21 to 22 of 22 (0.043 seconds)Spelling suggestions: "subject:"pseudofrigida body"" "subject:"freedomrigid body""
| 21 |
The modelling and optimal design of a three degree-of-freedom XYθz micro-motion stage.Handley, Daniel Charles January 2007 (has links)
This thesis presents an investigation of the modelling and optimal design of a particular 3-degree-of-freedom (DOF) XYθz micro-motion stage. This stage provides micron-scale motion in X and Y directions and a rotation about the Z-axis. Such a stage can be used for applications where positioning of components with micrometre, or even nanometre positioning accuracy is required. Some applications are; the positioning of samples in a scanning-electron-microscope; the positioning of masks in lithography; aligning fibre-optics and lasers; and manipulation of micro-scale objects in micro-biology or micro-systems assembly. The XYθz micro-motion stage investigated in this study uses a particular topology of monolithic compliant mechanism and three stack piezoelectric actuators. The compliant mechanism used is a 3RRR (three revolute-revolute-revolute) parallel compliant mechanism using flexure hinges. This parallel mechanism uses three RRR linkages. Each of the three RRR linkages uses three circular profile flexure hinges. Each flexure hinge provides predominantly rotational motion about one axis. This topology of mechanism has a symmetrical structure and provides numerous advantages that make it appropriate for use in a micro-motion stage. However, as yet this topology of compliant mechanism has only been investigated by a handful of researchers and it has not been used in any commercially developed systems. The design methodology of a stage using the 3RRR compliant mechanism has not been investigated in detail. In this thesis a study is presented that investigates different approaches to model the 3RRR compliant mechanism and also considers the piezo-actuator modelling, to give the complete XYθz micro-motion stage. Three models are presented and compared; the Pseudo-Rigid-Body Model (PRBM); a two-dimensional Finite-Element-Model (2-D FEM); and a third model is developed that is similar to the PRBM, but uses analytical equations to model the multiple degree-of-freedom compliance of the flexure hinges. The models developed are then used in parametric study so that the relationship between design parameters and output behaviour can be understood. An optimal design approach is then presented to develop an XYθz micro-motion stage for a particular application in a Scanning-Electron-Microscope (SEM). Finally experimental validation of the models is presented. The results of this study indicate which modelling approaches are accurate enough to prove useful for design, while also considering which models are computationally simple enough to be efficient and easy to use. The kinematic and dynamic behaviour of the 3RRR compliant mechanism and XYθz micro-motion stage is discussed in detail. This includes; a comprehensive description of the stage workspace, defining reachable and constant-rotation workspace areas; a discussion of actuator coupling; and in depth investigation of the modes of vibration. The results of the parametric study provide useful insight to aid the design of the XYz micro-motion stage and help simplify optimal design. The parametric study also highlights the difference in trends predicted by different modelling methods, which demonstrates the importance of using an appropriate model in design. The experimental validation demonstrates the accuracy of some modelling approaches while highlighting the limited accuracy of others. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1272186 / Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2007
|
| 22 |
Achieving Complex Motion with Fundamental Components for Lamina Emergent MechanismsWinder, Brian Geoffrey 01 March 2008 (has links) (PDF)
Designing mechanical products in a competitive environment can present unique challenges, and designers constantly search for innovative ways to increase efficiency. One way to save space and reduce cost is to use ortho-planar compliant mechanisms which can be made from sheets of material, or lamina emergent mechanisms (LEMs). This thesis presents principles which can be used for designing LEMs. Pop-up paper mechanisms use topologies similar to LEMs, so it is advantageous to study their kinematics. This thesis outlines the use of planar and spherical kinematics to model commonly used pop-up paper mechanisms. A survey of common joint types is given, as well as an overview of common monolithic and layered mechanisms. In addition, it is shown that more complex mechanisms may be created by combining simple mechanisms in various ways. The principles presented are applied to the creation of new pop-up joints and mechanisms, which also may be used for lamina emergent mechanisms. Models of the paper mechanisms presented in Chapter 2 of the thesis are found in the appendix, and the reader is encouraged to print, cut out and assemble them. One challenge associated with spherical and spatial LEM design is creating joints with the desired motion characteristics, especially where complex spatial mechanism topologies are required. Hence, in addition to a study of paper mechanisms, some important considerations for designing joints for LEMs are presented. A technique commonly used in robotics, using serial chains of revolute and prismatic joints to approximate the motion of complex joints, is presented for use in LEMs. Important considerations such as linkage configuration and mechanism prototyping are also discussed. Another challenge in designing LEMs is creating multi-stable mechanisms with the ability to have coplanar links. A method is presented for offsetting the joint axes of a spatial compliant mechanism to introduce multi-stability. A new bistable spatial compliant linkage that uses that technique is introduced. In the interest of facilitating LEM design, the final chapter of this thesis presents a preliminary design method. While similar to traditional methods, this method includes considerations for translating the mechanism topology into a suitable configuration for use with planar layers of material.
|
Page generated in 0.0485 seconds