Hot air balloon | EPFL Graph Search

A hot air balloon is a lighter-than-air aircraft consisting of a bag, called an envelope, which contains heated air. Suspended beneath is a gondola or wicker basket (in some long-distance or high-altitude balloons, a capsule), which carries passengers and a source of heat, in most cases an open flame caused by burning liquid propane. The heated air inside the envelope makes it buoyant, since it has a lower density than the colder air outside the envelope. As with all aircraft, hot air balloons cannot fly beyond the atmosphere. The envelope does not have to be sealed at the bottom, since the air inside the envelope is at about the same pressure as the surrounding air. In modern sport balloons the envelope is generally made from nylon fabric, and the inlet of the balloon (closest to the burner flame) is made from a fire-resistant material such as Nomex. Modern balloons have been made in many shapes, such as rocket ships and the shapes of various commercial products, though the tradit

A low-cost, autonomous mobile platform for limnological investigations, supported by high-resolution mesoscale airborne imagery

David Andrew Barry, Jérôme Béguin, Beat Marcel Geissmann, Nawaaz Sidharth Gujja Shaik, Abolfazl Irani Rahaghi, Anton Ivanov, Pascal Klaus, Ulrich Lemmin, Jean-Luc Liardon, Philippe Olivier Paccaud, Stepan Tulyakov, Htet Kyi Wynn, Ludovic Zulliger

Two complementary measurement systems – built upon an autonomous floating craft and a tethered balloon – for lake research and monitoring are presented. The autonomous vehicle was assembled on a catamaran for stability, and is capable of handling a variety of instrumentation for in situ and near-surface measurements. The catamaran hulls, each equipped with a small electric motor, support rigid decks for arranging equipment. An electric generator provides full autonomy for about 8 h. The modular power supply and instrumentation data management systems are housed in two boxes, which enable rapid setup. Due to legal restrictions in Switzerland (where the craft is routinely used), the platform must be observed from an accompanying boat while in operation. Nevertheless, the control system permits fully autonomous operation, with motion controlled by speed settings and waypoints, as well as obstacle detection. On-board instrumentation is connected to a central hub for data storage, with real-time monitoring of measurements from the accompanying boat. Measurements from the floating platform are complemented by mesoscale imaging from an instrument package attached to a He-filled balloon. The aerial package records thermal and RGB imagery, and transmits it in real-time to a ground station. The balloon can be tethered to the autonomous catamaran or to the accompanying boat. Missions can be modified according to imagery and/or catamaran measurements. Illustrative results showing the surface thermal variations of Lake Geneva demonstrate the versatility of the combined floating platform/balloon imagery system setup for limnological investigations.

2019

PyroMEMS: Improved Fabrication Methods and Ignition Reliability

David de Koninck

Generating large force/displacement actuators at the millimeter and sub-millimeter scales remains an important challenge for microsystems engineers. One promising solution is to integrate high-energy density solid propellant fuels in microsystems (pyroMEMS) to generate high-pressure, high-temperature combustion gases. However, integrating combustible materials within microsystems is non-trivial: solid propellant fuels are generally integrated manually into the device during back-end processing leading to large variability in the device performance. The goal of this thesis was to improve pyroMEMS reliability and performance. Reliability is particularly important for single-use devices –such as pyroMEMS– that cannot be tested before use. This was accomplished by simplifying their fabrication process and developing experimentally-validated models to improve device performance. First, a solid propellant fuel –and associated deposition technique– was specifically formulated for use in pyroMEMS devices. The fuel used was a mixture of potassium 4,6-dinitrobenzofuroxan (K-DNBF) and binder. The propellant combustion was modeled using a chemical equilibrium code and validated experimentally by measuring the in situ pressure and temperature inside a pyroMEMS test device. We recorded combustion temperatures of 1300±160 °C and overpressures of up to 60±5 bar. These results were in good agreement with the values obtained from simulations. This represents the first such measurements ever carried out in pyroMEMS devices. Two complementary pyroMEMS igniters were developed in this thesis: a drop-coated bottom-side igniter and a top-side shadow-mask evaporated igniter. The bottom-side igniter concept was based on the peripheral heating and ignition of fuel droplets to obtain smooth, steady combustion without fuel peeling or ejection. The overall fabrication process was highly simplified and extremely robust –over 350 igniters were successfully fabricated and tested. An investigation of igniter performance based on substrate material, igniter layout, fuel binder content and input power was performed. Semi-analytical models were developed and successfully predicted the ignition behavior of the igniters. The top-side pyroMEMS igniter was fabricated by direct deposition of a metal igniter on the fuel surface via offset shadow mask evaporation. In this way, reliable ignition was ensured by the intimate thermal contact between the fuel and igniter. The ignition concept was successfully demonstrated on fuel drops and over top full fuel chambers without fuel degradation or ignition. Lastly, pyroMEMS balloon actuators for use in automated drug delivery systems and microfluidic actuators were designed, fabricated and tested. A foil-level fabrication technique using low-cost polymer materials and additive fabrication techniques was developed. The fabrication was compatible with cleanroom-free processing, thus facilitating solid propellant fuel integration. Balloon actuators were successfully inflated yielding membranes displacements of between 5 and 7.5 mm (for an initial membrane diameter of 5 mm). A semi-analytical model was developed that successfully predicted the balloon displacement. This work represents an important step in developing simple, large-scale fabrication techniques that minimize manual back-end processing in order to improve device reliability.

EPFL2012

Haptic instrumentation for an interventional radiology simulator

Dejan Ilic

Low trauma, reduced costs and fast recovery are only a few factors why minimally invasive surgery (MIS) is taking over classical surgical methods. Interventional Radiology (IR) is a minimally invasive procedure where thin tubular instruments are steered through the patient's vascular system under X-ray imaging. In order to perform these procedures, a radiologist has to be trained to master hand-eye coordination, instrument manipulation and procedure protocols. The importance of training IR procedures rises with the increasing variety and sophistication of the procedures performed using this approach. Apart from the traditional "see one, do one, teach one" model, radiologists have only had few mock devices with limitations in practical use. Training on animals is an alternative, but its use is hindered by high costs and ethical issues. The existing simulation systems all have major drawbacks: the requirement to use modified instruments, high inertia of the haptic feedback that creates a noticeably degraded dynamic behavior, or excessive friction that is not properly compensated. In this thesis we propose a quality training environment dedicated to IR. The system is composed of a virtual reality (VR) simulation of the patients anatomy linked to a robotic interface providing haptic force feedback. This thesis focuses on the requirements, design and prototyping of a specific haptic interface for the manipulation of catheters and guide wires. Translational tracking and force feedback on the catheter are provided by two cylinders forming a friction drive arrangement. The complete friction drive can be set in rotation with an additional motor providing torque feedback. A force and a torque sensor are integrated in the cylinders for direct measurement on the catheter enabling disturbance cancellation with a closed-loop force control strategy. One of the specific requirements during a simulated intervention is to measure the position of the tip of a guide wire inside a catheter. This is a so called "tube in tube" problem. The guide wire is detected at the entrance of the simulator and then grasped by a micro-gripper. Forces and movements of the guidewire moving inside the catheter are then transmitted through a gripper and along a rod to an external unit. This thesis also reports a study of several micro-gripper designs developed and tested on a haptic force feedback interface developed at the LSRO-EPFL. A virtual reality environment has been developed to provide real-time visualisation and force feedback. Several different software routines are integrated in the system. During an IR procedure the tip of an employed instrument interacts with a wall of blood vessels and a repulsive force is transmitted to the user. Force feedback helps radiologist to orient and navigate the inserted instrument in the vessel. This thesis presents a novel method for measurement of internal constraints during an IR procedure. The measurements help to determine the maximum interaction forces between the catheter and the wall of the blood vessel and to observe the shape of dynamic interaction during manipulation. In order to recreate a realistic simulation environment it is necessary to derive the elastic properties and behavior of arteries when contact with an instrument occurs. A novel method for measurement of mechanical properties of blood vessels is proposed in this work. Information derived with this method is also very useful to determine coherent boundary conditions for hemodynamic simulations. Measurements of the modulus of elasticity of an artery are carried out by measuring the deformations due to the inflation of an angioplasty balloon catheter used for IR procedures. A test bench, consisting of an angioplasty balloon, a PVA model and an actuator used to inflate the balloon, is developed for realization of experiments. The pressure-volume curve during the inflation of the balloon is observed. The Young's modulus is derived with an analytical model of the measurement system. The results are then analyzed and compared to existing data from literature.

EPFL2005