Soft prismatic joint

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 47).This thesis documents the design and analysis of a soft prismatic joint for use in soft robotics. While this joint can be utilized in any soft robot, its immediate application is for Squishbot, a soft robot developed for the DARPA Chembot challenge. For the Squishbot application, the joint must fit within a cylindrical envelope 4cm long and 1cm in diameter, compress 1.2cm axially without buckling, and be soft such that it can undergo large deformations without plastically deforming. After considering a wide range of design concepts, a screw design was chosen. This design concept was selected because it has a high axial to bending compliance ratio and does not expand radially when compressed axially. A model was developed to describe this design as a function of its design parameters. A metric was also developed to predict based on a single-cell sample whether a full-scale model would be able to fulfill the design requirements. The model was validated with respect to the parameter of blade thickness by testing 3D printed, TangoPlus cell-pairs. The results show that the model is correct to within a factor of three over blade thickness but needs further modifications to better predict trends in joint behavior. The design still needs to be tested over other parameters such as cell height. Preliminary work was also conducted on designing a locking mechanism for the joint, but more work is needed in this area. Overall, the design presented in this thesis fulfills the project's design requirements and the model that was developed describes the joint's behavior to first order.S.B

An experimental and analytical exploration of the effects of manufacturing parameters on ceramic pot filter performance

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 163-165).Ceramic pot filters (CPF) are a promising low-cost option for household water treatment, providing a barrier of protection against-microbiological contaminants for households with or without reliable piped water supplies. The goal of this thesis is to provide CPF manufacturers with tools to increase their ability to reach performance objectives for CPF flow rate, bacteria removal and strength. This is achieved by experimentally determining relationships between these three aspects of performance and three manufacturing values: percentage rice husk, rice husk size and wall thickness. These relationships are used to run a series of optimizations that result in design recommendations including the recommendation to increase wall thickness to improve bacteria removal and to tightly control rice husk size to maintain consistent flow rates. In addition to the experimental relationships, this author seeks a theoretical explanation of filter performance. Through this process, the author determined that hydraulic head can be increased without decreasing bacteria removal and that incomplete combustion should not be of primary concern to manufacturers. While the results in this study are preliminary, the systematic approach to the CPF design shown here can be used in future studies to further analyze and improve the CPF design.by Amelia Tepper Servi.S.M

Desalination by Membrane Distillation using Electrospun Polyamide Fiber Membranes with Surface Fluorination by Chemical Vapor Deposition

Fibrous membranes of poly(trimethyl hexamethylene terephthalamide) (PA6(3)T) were fabricated by electrospinning and rendered hydrophobic by applying a conformal coating of poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) using initiated chemical vapor deposition (iCVD). A set of iCVD-treated electrospun PA6(3)T fiber membranes with fiber diameters ranging from 0.25 to 1.8 μm were tested for desalination using the air gap membrane distillation configuration. Permeate fluxes of 2–11 kg/m²/h were observed for temperature differentials of 20–45 °C between the feed stream and condenser plate, with rejections in excess of 99.98%. The liquid entry pressure was observed to increase dramatically, from 15 to 373 kPa with reduction in fiber diameter. Contrary to expectation, for a given feed temperature the permeate flux was observed to increase for membranes of decreasing fiber diameter. The results for permeate flux and salt rejection show that it is possible to construct membranes for membrane distillation even from intrinsically hydrophilic materials after surface modification by iCVD and that the fiber diameter is shown to play an important role on the membrane distillation performance in terms of permeate flux, salt rejection, and liquid entry pressure

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

The Combined Effect of Air Layers and Membrane Superhydrophobicity on Biofouling in Membrane Distillation

Previous studies of membrane distillation (MD) have shown that superhydrophobic membranes experience dramatically less inorganic and particulate fouling. However, little explanation for this improved performance has been given in the literature. Furthermore, studies comparing membrane superhydrophobicity and biofouling are lacking, though superhydrophobic surfaces are known to be more vulnerable to biofouling than other types. In non-membrane surfaces, visible air layers on superhydrophobic surfaces have been correlated with significant decreases in biofouling. Therefore, it was proposed here to use superhydrophobic MD membranes with periodic introduction of air to maintain an air layer on the membrane surface. Superhydrophobic membranes were created with initiated chemical vapor deposition (iCVD) of a fluorinated compound, perfluorodecyl acrylate (PFDA). The substrate membrane was PVDF. To test MD fouling, an MD membrane was placed on top of a fouling solution, with a heater and stirrer to caus e evaporation of water through the membrane. Results were analyzed with foulant mass measurements. Alginate gel fouling was examined, as this compound is a common proxy for biological fouling in ocean w ater. The introduction of air layers was found to dramatically decrease foulant adhesion to the membrane, by 95-97%. Membrane superhydrophobicity made a much smaller impact in reducing fouling. Keywords membrane distillation, superhydrophobic surfaces, alginate, air layers, anti-foulin

The effects of iCVD film thickness and conformality on the permeability and wetting of MD membranes

Membranes possessing high permeability to water vapor and high liquid entry pressure (LEP) are necessary for efficient membrane distillation (MD) desalination. A common technique to prepare specialized MD membranes consists of coating a hydrophilic or hydrophobic base membrane with a low surface-energy material. This increases its liquid entry pressure, making the membrane suitable for MD. However, in addition to increasing LEP, the surface-coating may also decrease permeability of the membrane by reducing its average pore size. In this study, we quantify the effects of initiated chemical vapor deposition (iCVD) polymer coatings on membrane permeability and LEP. We consider whether the iCVD films should have minimized thickness or maximized non-conformality, in order to maximize the permeability achieved for a given value of LEP. We determined theoretically that permeability of a single pore is maximized with a highly non-conformal iCVD coating. However, the overall permeability of a membrane consisting of many pores is maximized when iCVD film thickness is minimized. We applied the findings experimentally, preparing an iCVD-treated track-etched polycarbonate (PCTE) membrane and testing it in a permeate gap membrane distillation (PCMD) system. This study focuses on membranes with clearly defined, cylindrical pores. However, we believe that the principles we discuss will extend to membranes with more complex pore architectures. Overall, this work indicates that the focus of surface-coating development should be on minimizing film thickness, not on increasing their non-conformality.MIT & Masdar Institute Cooperative Program (02/MI/MI/CP/11/07633/GEN/G/00)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (W911NF-13-d-0001

OUTCOMES OF ELDERLY PATIENTS WITH ST-ELEVATION OR NON-ST-ELEVATION ACUTE CORONARY SYNDROME UNDERGOING PERCUTANEOUS CORONARY INTERVENTION

Acute coronary syndromes have been classified according to the finding of ST-segment elevation on the presenting ECG, with different treatment strategies and practice guidelines. However, a comparative description of the clinical characteristics and outcomes of acute coronary syndrome elderly patients undergoing percutaneous coronary intervention during index admission has not been published so far

Advancing hydrophobic desalination membranes using initiated chemical vapor deposition (iCVD) v/

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.Includes bibliographical references.Hydrophobic membranes are the central component of membrane distillation (MD) desalination systems. Optimizing their design is crucial for efficient desalination. There are many requirements on MD membranes. These include high liquid entry pressure (LEP) and high permeability to water vapor. There are many available manufacturing methods for producing hydrophobic membranes. An important subset of these methods use surface modification to prepare hydrophobic composite membranes. The many options for MD membrane design results in lack of consensus about how to achieve optimal performance. In this thesis we use initiated chemical vapor deposition (iCVD) to study how surface modification parameters and membrane morphology contribute to MD membrane performance. We introduce new models and analysis methods to support experimental results. This work informs hydrophobic MD membrane design by clarifying the roles of different membrane elements. By advancing MD technology, we increase capacity to produce fresh water for society.by Amelia Tepper Servi.Ph. D

Integrated Oxygen Flow Meter / Heat Exchanger for Portable Life Support Systems

Michael Izenson, Creare LLCAmelia Servi, Creare LLCScott Phillips, Creare LLCSheldon Stokes, Creare LLCColin Campbell, NASA Lyndon B. Johnson Space CenterICES402: Extravehicular Activity: PLSS SystemsThe 48th International Conference on Environmental Systems was held in Albuquerque, New Mexico, USA on 08 July 2018 through 12 July 2018.Space suits for future exploration missions will have multi-mission goals with new and challenging requirements for the portable life support system (PLSS). In particular, the space suit ventilation loop requires cooling and flow measurement components that must meet specifications that go well beyond the capabilities of the components used for the existing Extravehicular Mobility Unit. The flow meter must provide high measurement accuracy over a wide flow range, compatibility with pure oxygen, low pressure losses, and very compact size. The heat exchanger that cools the ventilation loop must be built from materials that are compatible with the liquid cooling loop, and it must provide efficient gas cooling in a small package across conditions ranging from normal suit pressure to elevated pressure. This paper describes the development of a novel device that combines the flow measurement and cooling functions in a single, compact flow meter / heat exchanger (FMHX). We have developed design methods that enable us to assess trade-offs, optimize performance, and specify the design of an FMHX that meets the requirements and constraints for operation in future PLSSs. We used computational fluid dynamics analysis to validate the pressure drop and heat transfer characteristics of the FMHX design. Data from tests of a proof-of-concept FMHX show that the system meets all design requirements. We used the results from these tests to refine the design parameters and predict performance of an optimized, prototype FMHX

High-Accuracy Oxygen Flow Meter for the Exploration Portable Life Support System

Michael Izenson, Creare LLC, USAmelia Servi, Creare LLC, USSheldon Stokes, Creare LLC, USTheodore Beach, Creare LLC, USCarl Kirkconnell, West Coast Solutions, USLeon Huynh, West Coast Solutions, USTessa Rundle, National Aeronautics and Space Administration (NASA) Lyndon B. Johnson Space Center, USSteven Lee, Renesas, USICES402: Extravehicular Activity: PLSS SystemsThe proceedings for the 2020 International Conference on Environmental Systems were published from July 31, 2020. The technical papers were not presented in person due to the inability to hold the event as scheduled in Lisbon, Portugal because of the COVID-19 global pandemic."The xEMU’s portable life support system (xPLSS) requires a high accuracy instrument to measure the rate of oxygen flow in the ventilation system. The sensor must produce accurate readings across a wide range of flow conditions while consuming very little volume or power and introducing very little pressure loss to the ventilation loop. We have developed an innovative flow sensor built around a commercial, off-the-shelf MEMS flow-sensing chip that is designed for oxygen service. We have developed a custom flow sensor housing to channel gas flow over the MEMS sensing elements and custom electronics to control the sensor and generate signals compatible with xEMU requirements. The flow sensor operates in parallel with the ventilation loop heat exchanger, so introduces no additional pressure loss to the ventilation system. The unit meets size and shape requirements for service in the xPLSS and is replaceable in space if necessary. Data from separate-effects tests and tests of the integrated xPLSS heat exchanger / flow meter system show that the flow meter achieves high accuracy requirements across the range of specified operating conditions. We built and tested a proof-of-feasibility prototype in mid-2019, followed by a “rapid turn” demonstration sensor that meets form, fit and function requirements in late 2019. Fully-qualified DVT units are scheduled for delivery in mid-2020.