Global ETD Search

1	Collision Analysis of the Reversible Crankshaft Mechanism in a Convertible Refrigeration Compressor Cain, Jason James 07 July 2000 (has links) The purpose of this study is to analyze the behavior of a reversible two-cylinder refrigerant compressor manufactured by Bristol Compressor Incorporated. This compressor contains a specialized linkage that causes the compressor to transition from a two-cylinder compressor to a single-cylinder compressor when the direction of rotation of the crankshaft is reversed. The linkage accomplishes this by reducing the throw of one cylinder to zero. Of interest are the conditions to which this linkage is subjected when the direction of rotation is again reversed, causing the compressor to return to its two-cylinder functioning. When this reversal takes place, a collision occurs within the linkage. These repeated collisions are thought to be the cause of fatigue failure of the linkage in many of these compressors. To verify that this collision is the problem, an understanding of the stress state during the collision is needed. This thesis begins the work necessary to determine the dynamic stress state present within the system. A FORTRAN program was developed that modeled the kinematic behavior of the system under operating conditions. The program predicts the accelerations, velocities, positions, and internal forces present within the system during startup conditions. Also, a method has been developed to model rotary sliding contact between two cylindrical surfaces. This method is developed and investigated in hopes that it will facilitate the modeling of the behavior of the compressor linkage in a dynamic finite element analysis. / Master of Science revolute contact reversible compressor two-stage compressor
2	Compliant Mechanisms to Perform Bearing and Spring Function in High Precision Applications Cannon, Jesse R. 19 November 2004 (has links) (PDF) An increasing number of mechanical systems are being designed on the micro and meso scales. Assembly and maintenance become increasingly difficult as the size of mechanisms decrease, and the minimum size of traditional elements such as bearings and springs is limited. The backlash of bearings also limits their usefulness in applications where high precision and repeatability are needed. At small scales and for high precision applications, alternative, non-traditional elements are needed. The objective of this thesis is to develop reliable and scalable compliant components to replace bearings and helical springs. Components replacing springs must be able to produce specified torque/motion requirements. Components replacing bearings must permit sufficient motion about the axis of rotation, bear specified loads in the lateral directions, and fit within roughly the same design space as a bearing. Additionally, all components will be designed to be manufactured using in-plane fabrication processes. Practical application of the components will be demonstrated by their use in Sandia National Laboratory's Stronglink assembly. The concepts discussed in this thesis fall into three categories: mechanisms that replace 1) the helical spring, 2) the bearing, and 3) both the helical spring and the bearing. The serpentine flexure belongs to the first category, the compliant rolling-contact element (CORE), CORE bearing, and elliptical CORE bearing belong to the second, and the compliant contact-aided revolute (CCAR) joint belongs to the third category. compliant precision contact mechanism bearing spring revolute joint Mechanical Engineering
3	Achieving Complex Motion with Fundamental Components for Lamina Emergent Mechanisms Winder, 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. paper mechanism pop-up popup pop up mechanism linkage paper engineering paper crafts origami kinematics spatial mechanism planar mechanism bistable multi-stable spherical mechanism ortho-planar compliant PRBM pseudo-rigid-body model Lamina Emergent Mechanism LEM sheet goods planar layer complex joint elemental joint spatial joint degrees of freedom mechanism modeling mechanism design serial joint chain parallel series fundamental components complex motion revolute prismatic spherical cylindric universal half planar RSSR RCCC RSRC RTRT Altmann Bricard Bennett Goldberg 6R 4R joint axis angular offset paper joint V-fold circular arch figure-8 single slit double slit tube strap arch knee mechanism 45 degree fold solid shape floating layer tent Mechanical Engineering

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