Analysis and Design of a Robust RF MEMS Switch

A MEMS RF switch is expected to undergo 10 billion switching cycles before failure. Until complete physical explanation for these failure modes that include contact adhesion, damping effects, stiction, increases in resistance with time, dielectric breakdown, and electron trapping is fully established, the technology’s numerous advantages cannot be harvested reliably and efficiently. This paper investigates prospective solutions to problems in switch designs by proposing a new design for the switch. We consider the new design from different perspectives: dynamic, electric, fluidic, etc. It is billed to overcome the difficulties and involves the implementation of liquid metal contact electrostatically actuated to ensure the same switching performance, with prolonged life span, and robust switching speed.

Effect of Changing Atmospheric and Operating Conditions on the Thermal Stresses in PV Modules

Photovoltaic (PV) technology provides a direct method to convert solar energy into electricity. In recent years, the use of PV systems has increased greatly with many applications of PV devices in systems as small as battery chargers to large scale electricity generation systems and satellite power systems. An important factor that influences the reliability of photovoltaic modules is their ability to withstand high thermal stresses which develop in PV modules due to the different coefficients of thermal expansion of the different module materials. PV modules also experience thermal cycles which can lead to failure of the module. In the present work, three dimensional numerical thermal and structural models of a PV module were developed and sequentially coupled together to calculate the temperature distribution in the PV module and the thermal stresses developing in it. The model is also capable of simulating PV module cooling. Using the model, a study was conducted to evaluate the thermal and structural performance of the module with and without cooling and the variation in thermal stress magnitudes with changing environmental conditions (solar radiation and ambient temperature) and operating conditions (heat exchanger inlet temperature and velocity).

Numerical Investigation of Natural Convection in a Mono-Span Greenhouse

In this paper, the use of computational fluid dynamics is evaluated as a design tool to investigate the indoor climate of a confined greenhouse. The finite volume method using polyhedral cells is used to solve the governing mass, momentum and energy equations. Natural convection in a cavity corresponding to a mono-span venlo-type greenhouse is numerically investigated using Computational Fluid Dynamics. The CFD model is designed so as to simulate the climate above a plant canopy in an actual multi-span greenhouse heated by solar radiation. The aim of this paper is to investigate the influence of various design parameters such as pitch angle and roof asymmetry and on the velocity and temperature patterns inside a confined single span greenhouse heated from below. In the study reported in this paper a two-dimensional CFD model was generated for the mono-span venlo-type greenhouse, and a mesh sensitivity analysis was conducted to determine the mesh independence of the solution. Similar two-dimensional flow patterns were observed in the obtained CFD results as the experimental results reported by Lamrani et al [2]. The CFD model was then modified and used to explore the effect of roof pitch angle and roof asymmetry at floor level on the development of the flow and temperature patterns inside the cavity for various Rayleigh numbers. Results are presented in the form of vector and contour plots. It was found that considerable temperature and velocity gradients were observed in the centre of the greenhouse for each case in the first 40mm above the ground, as well as in the last 24mm close to the roof. Results also indicated that the Rayleigh number did not have a significant impact on the flow and temperature patterns inside the greenhouse, although roof angle and asymmetry did. The current results demonstrate the importance of CFD as a design tool in the case of greenhouse design.

An Unified Design Procedure for Flying Machining Operations

“Flying machining” represents synchronization of an axis (slave) with a master axis in motion. One of the most important aspects of the design of “flying machining” operation is the choice of the proper law of motion of the slave axis. In literature, technical reports and papers can be found concerning this subject, but they deal with specific problems and the solutions or suggestions proposed are specific as well, suitable for those cases. In order to try to overcome this limitation, in this paper we analyze the subject of the flying machining operations from a wider point of view. We propose a unified design procedure with general validity, suitable for the choice of the slave axis’ law of motion for whatever “flying machining” operation. Furthermore methodologies for the selection of the drive system will be proposed. The procedure is described applying it on a cross sealing operation, typical of wrapping machine.

Experimental Study of Very Low Aspect Ratio Wings in Slender Bodies

The dynamics of very low aspect ratio wings (or strakes) vortices in slender bodies are complex due to the interaction of the shed vortex sheet and the body vortex. For missiles at supersonic speeds these interactions are not easily predicted using engineering level tools. To shed some new light onto this problem, an experimental study in a water channel for moderate Reynolds number (Re = 1000) was performed for a 19D body and strake configuration with strakes having a span to body diameter ratio of 1.25. Comparisons to numerical simulations in supersonic flow are also performed. Flow visualisation has been carried out to characterize the vortex dynamics at different angles of attack; these being 11°, 16°, 22° and 27°. The comparison between a slender body without strakes and the body-strake configuration has given some key indicators in relation to the vortex position of the core. Furthermore, unsteady wing-body interference has been observed at angles of attack above 20° for both experimental and numerical simulations. Consequently, the average position of the vortex core is located at larger distances from the missile in comparison to the body without strakes. The numerical simulations show good correlation with the experimental tests even though the dynamic convective interactions between the body vortex and strake vortex sheet are not predicted.

Modelling IR-Heating in Stretch-Blow Moulding and Thermoforming

The two-stage stretch-blow moulding process has been established for the large scale production of high quality PET containers with excellent mechanical and optical properties. Thermoforming is the process of choice for manufacturing thin-gauge or large-area parts for packaging or technical applications. Both processes allow lightweight thermoplastic parts to be produced rapidly and economically. In both processes thermoplastic semi-finished products are formed by pressurised air under the influence of heat. To enable forming of the thermoplastic materials, the semi-finished products need to be transferred into a thermoelastic state. IR-heating is widely used due to short heating times. From a cost perspective, about 7 % of the total production costs of a stretch-blow moulded bottle are spent for energy in order to heat and form the preform to the later bottle. Depending on machine, semi-finished product type and cycle time, energy costs in thermoforming account for around 1–5 % of the total production costs. Modern roll-fed automatic thermoforming machines use about 22 % of the energy consumption for the heating step and around 70 % for the production of pressurised air. Due to this significant share and due to increasing energy costs during recent years, the packaging industry is interested in increasing the energy efficiency of these processes. The most important quality criterion for both processes is a uniform wall thickness distribution. The production of high-quality parts requires optimised temperature profiles of the semi-finished product depending on the particular product geometry. Simulation is an approved tool for the prediction of the influence of the heater setting on the temperature profile. Over the last decade IKV has developed an integrative three-dimensional process simulation which models the complete path of a preform through a stretch-blow moulding machine. An essential first step is the heating simulation where the temperature profile of the preform is computed. Based on this data the temperature-dependent material behaviour of PET can be considered during the inflation simulation. This work shows the influence of a thoughtful temperature profile on the wall thickness distribution in stretch-blow moulding. The focus is on modelling the reheat phase of the stretch-blow moulding process in FEA. Beyond that, a purposeful heating offers the possibility to cut down energy waste.

Robust Analysis of a Wireless Bistable Micro-Actuator

Nowadays, the integration of micro-actuators in the micro-systems poses a significant problem due to the complex designs as well as due to the contact power supply systems (e.g., via micro-batteries or via wires). A way to overcome this problem is to provide remote power supply and control to the bistable micro-actuators. It is mainly done by RF (radio-frequency) or optical means. As a consequence, the stability of the two positions of this kind of micro-actuators and the switching time evolution between them have to be studied to determine the robustness of the contactless bistable micro-actuators. In this work, these system parameters were analysed by the ANOVA (Analysis Of Variance) method during a longlife test for 8 different configurations (Design of Experiments) of bistable micro-actuators controlled by laser. Transient and permanent regimes were observed for the stability of the positions, for the standard deviation around the positions and for the switching time as well. In each case, the transient regime represented only 3% of the total duration of the longlife test. A very good stabilisation was observed in the permanent regime whereas a decrease of the stroke was observed in the transient regime. As a consequence, during this regime, the switching time was reduced compared with the regular values (few seconds, optical power dependent). In the permanent regime, a progressive increase of this factor was noted that indicated the progressive fatigue of the bistable micro-actuator. A second indicator of the micro-actuator fatigue was given by the increase of the standard deviation of the stable position after cycle number 9000. Above this point, the micro-actuator was vibrating during the functioning even if the stability remained acceptable.

Workpiece Placement Optimization of Six-Revolute Industrial Serial Robots for Machining Operations

Roboticists are faced with new challenges in robotic-based manufacturing. Up to now manufacturing operations that require both high stiffness and accuracy have been mainly realized by using computer numerical control machine tools. This paper aims to show that manufacturing finishing tasks can be performed with robotic cells knowing the process cutting phenomena and the robot stiffness throughout its Cartesian workspace. It makes sense that the finishing task of large parts would be cheaper with robots. However, machining robots have not been adapted for such operations yet. As a consequence, this paper introduces a methodology that aims to determine the best placement of the workpiece to be machined knowing the cutting forces exerted on the tool and the elastostatic model of the robot. In this vein, a machining quality criterion is proposed and an optimization problem is formulated. The KUKA KR270-2 robot is used as an illustrative example throughout the paper.

Control Strategies for a Linear MR-Brake With Serpentine Flux Path for Haptics

In haptics applications actuators with compact volume and high force output are desired for stable and stiff interfaces. Magnetorheological (MR) brakes are viable options since they have large force-to-volume ratios. However, linear MR-brakes available on the market have limited stroke due to the piston-cylinder design and show viscous damping behavior where the force output highly depends on the velocity of the actuator resulting in a high off-state friction force. Another problem is the inherent magnetic hysteresis, which requires complex control systems. In this research, we focused on the development and control of a linear MR-brake with infinite stroke and minimal off-state friction. The common piston-cylinder arrangement was removed from the design to address the limited stroke and high off-state-friction issues. The serpentine flux path methodology was followed to achieve compact geometry. Three control strategies namely, open-loop control, force feedback control, and current feedback with Preisach model, were implemented on the developed prototype. The results using Preisach model showed that the hysteresis could be reduced significantly without the need for an expensive force sensor in the control loop. Our new device has a 3% ratio of the off-state friction force to the maximum force output in comparison to more than 10% for most MR-damper devices in the literature. At the same time, our prototype is about half the size of a commercially available product.