Compliant quasi-kinematic couplings

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2000.Includes bibliographical references (p. 113-116).Better precision at lower costs is a major force in design and manufacturing. However, this is becoming increasingly difficult to achieve as the demands of many location applications are surpassing the practical performance limit (~ five microns) of low-cost couplings. The absence of a means to meet these requirement has motivated the development of the Quasi-Kinematic Coupling (QKC). This thesis covers the theoretical and practical considerations needed to model and design QKCs. In a QKC, one component is equipped with three spherical protrusions while the other contains three corresponding conical grooves. Whereas Kinematic Couplings rely on six points of contact, the six arcs of contact between the mated protrusions and grooves of QKCs result in a weakly over-constrained coupling, thus the name Quasi-Kinematic. QKCs are capable of sub-micron repeatability, permit sealing contact as needed in casting, and can be economically mass produced. The design and application of a QKC is demonstrated via a case study on the location of two engine components. Integration of the QKC has improved coupling precision from 5 to 0.7 microns. In addition, this QKC uses 60% fewer precision features, 60% fewer pieces, costs 40% less per engine, and allows feature placement tolerances which are twice as wide as those of the previous dowel-pin-type coupling.by Martin L. Culpepper.S.M

Design of debris cleaner with compound auger and vacuum pick up

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997.by Martin L. Culpepper.M.S

Thermomechanical Actuator-Based Three-Axis Optical Scanner for High-Speed Two-Photon Endomicroscope Imaging

This paper presents the design and characterization of a three-axis thermomechanical actuator-based endoscopic scanner for obtaining ex vivo two-photon images. The scanner consisted of two sub-systems: 1) an optical system (prism, gradient index lens, and optical fiber) that was used to deliver and collect light during imaging and 2) a small-scale silicon electromechanical scanner that could raster scan the focal point of the optics through a specimen. The scanner can be housed within a 7 mm Ø endoscope port and can scan at the speed of 3 kHz x 100 Hz × 30 Hz along three axes throughout a 125 × 125 × 100 μm[superscript 3] volume. The high-speed thermomechanical actuation was achieved through the use of geometric contouring, pulsing technique, and mechanical frequency multiplication (MFM), where MFM is a new method for increasing the device cycling speed by pairing actuators of unequal forward and returning stroke speeds. Sample cross-sectional images of 15-μm fluorescent beads are presented to demonstrate the resolution and optical cross-sectioning capability of the two-photon imaging system.National Institutes of Health (U.S.) (Grant 1-R21-CA118400-01)Chinese University of Hong Kong (Direct Grant 2050495)National Institutes of Health (U.S.) (Grant 9P41EB015871-26A1)National Institutes of Health (U.S.) (Grant 5R01EY017656-02)National Institutes of Health (U.S.) (Grant 5R01 NS051320)National Institutes of Health (U.S.) (Grant 4R44EB012415-02)National Science Foundation (U.S.) (Grant CBET-0939511)Singapore-MIT Alliance for Research and TechnologyMIT Skoltech InitiativeHamamatsu CorporationDavid H. Koch Institute for Integrative Cancer Research at MIT (Bridge Project Initiative

Modeling and implementation of solder-activated joints for single actuator, centimeter-scale robotic mechanisms

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 139-140).This thesis explains when, and why, solder-based phase change materials (PCMs) are best-suited as a means to modify a robotic mechanism's kinematic and elastomechanic behavior. The preceding refers to mechanisms that possess joints which may be thermally locked and unlocked via a material phase change within the joint. Different combinations of locked and unlocked joints yield different one-DOF mechanisms states. A single actuator is used to control motion allowed by the different states. By reducing the number of required actuators, solderlocking joints enable the creation of compliant centimeter-scale mechanisms that can perform a multiplicity of tasks. Herein, this thesis presents physics-based design insights that provide understanding of how solder-based material properties and joint design dominate joint performance characteristics. First order models are used to demonstrate selection of suitable PCMs and how to set initial joint geometry prior to fine tuning via detailed FEA models and experiments. The first order models result in order-of-magnitude estimates of the locking and unlocking times for the joints. The insights and models are discussed in the context of two case studies. Squishbot1 is a crawling robot that uses a single spooler motor and three solder-locking joints to crawl and steer. Squishbot 1 is able to reconfigure its joints in approximately 10 seconds. SquishTendons utilizes solder-locking joints to actuate a compliant structure with a single motor. The second robot used the complete set of models and rules to improve on the performance of Squishbotl. SquishTendons can unlock and lock its joints in less than 6 seconds.by Maria J. Telleria.S.M

Carbon nanotubes as piezoresistive microelectromechanical sensors: Theory and experiment

Carbon-nanotube (CNT) -based strain sensors have the potential to overcome some of the limitations in small-scale force/displacement sensing technologies due to their small size and high sensitivity to strain. A better understanding of the dominant and limiting causes of high strain sensitivity is needed to enable the design and manufacture of high-performance sensor systems. This paper presents the theoretical framework that makes it possible to predict the strain sensitivity of a carbon nanotube based on it chiral indices (n,m). This framework is extended to capture the behavior of sensors composed of multiple CNTs in a parallel resistor network. This framework has been used to predict that a parallel resistor network of more than 100 randomly selected CNTs should have a gauge factor of approximately 78.5±0.4. This is within the experimental error of the measured gauge factor of 75±5 for such CNT resistor networks

Design of a Catheter-Based Device for Performing Percutaneous Chordal- Procedures

available in PMC 2010 June 1.This paper focuses on the design and implementation of a percutaneous catheter-based device to provide physicians with an externally controlled tool capable of manipulating and cutting specific chordae tendinae within the heart to alleviate problems associated with some forms of mitral valve (MV) regurgitation. In the United States alone, approximately 500,000 people develop ischemic or functional mitral regurgitation per year. Many of these patients do not possess the required level of health necessary to survive open-heart surgery, and the development of a chordal cutting procedure and device is needed to allow these patients to receive treatment. A deterministic design process was used to generate several design concepts and then evaluate and compare each concept based on a set of functional requirements. A final concept to be alpha prototyped was then chosen, further developed, and fabricated. Experiments showed that the design was capable of locating and grabbing a chord and that ultrasound imaging is a viable method for navigating the device inside of the human body. Once contact between the chord and radio-frequency (RF) ablation tip was confirmed, the chord was successfully ablated.Center for Integration of Medicine and Innovative Technolog