Optimal design of compliant mechanisms using topology optimization

The report discussed the issues on optimal design of compliant mechanisms using topology optimization.Master of Engineering (MPE

Ink-Jet Printing of Micro-Electro-Mechanical Systems (MEMS)

Beyond printing text on paper, inkjet printing methods have recently been applied to print passive electrical and optical microparts, such as conductors, resistors, solder bumps and polymeric micro lenses. They are also useful to print micro-electro-mechanical systems (MEMS) as sub-millimeter sensor and actuator arrays, such as multifunctional skins applicable to robotic application and ambient monitoring. This paper presents the latest review of a few successful cases of printable MEMS devices. This review shows that inkjet printing is good for printing two-dimensional or surface MEMS devices from a small unit to an array over a large area. In the future, three-dimensional printing of multi-materials, from metal, plastic, to ceramic, will open the possibility of realizing more variety and function of a large-areal MEMS array, for a mobile electro-mechanical systems.Published versio

Tunable window device based on micro-wrinkling of nanometric zinc-oxide thin film on elastomer

This Letter presents a tunable window device based on microscopic wrinkling of a transparent elastomeric surface. “Crack-free” microscopic wrinkling of a 50-nm ZnO thin film is possible on a highly adhesive acrylic elastomer membrane (VHB 4910) upon partial release from a large radial pre-stretch of membrane. This ZnO-based tunable window device demonstrates reversible tunability between transparent and translucent states. At zero compression with a flat surface, the device is transparent with a 93% in-line transmittance at 550-nm wavelength. At 14% radial compression with wrinkled surface, the device appears translucent with a 3% in-line transmittance. Analysis shows that a large amplitude and a small wavelength of transparent micro-wrinkles are good for refracting light diffusely. This method and material system are promising to make a low-cost, high-performance smart window

The effect of folds in thin metal film electrodes used in dielectric elastomer actuators

Due to high electrical conductivity, metals have been the traditional material for electrodes. However, as metal films have low fracture strains, they are not commonly used as compliant electrodes in the field of dielectric elastomer actuators and generators. We have recently demonstrated that the use of metal films as electrodes can in fact allow dielectric elastomer actuators to have large actuated area strains of more than 100%. The metal film electrodes used have a network of crumples that unfolds as it is subjected to in-plane strains. This mechanism enables the metal electrodes to have a relatively low stiffening effect on the soft dielectric elastomer and to be able to retain its low resistance despite being highly strained; the latter characteristic would facilitate in the reduction of parasitic losses in dielectric elastomer generator applications. By metalizing a highly bi-axially pre-stretched dielectric elastomer that was subsequently partially relaxed, a bi-axial compressive force was introduced into the metal films, thereby causing a network of folds to form. In this paper, we study the change in the topography of the crumpled metal electrodes as the metal films are subjected to varying extents of bi-axial compression. It was also found that the way in which the metal films fold does in fact alter the electrodes’ stretchability, as manifested in the performance of the dielectric elastomer actuators using these crumpled metal films as electrodes.Published versio

Very high breakdown field strength for dielectric elastomer actuators quenched in dielectric liquid bath

Dielectric elastomer actuators (DEAs) are prone to failure by pull-in instability. However, this work showed that DEAs, which were immersed in a silicone oil bath (Dow Corning Fluid 200 50cSt), can survive the pull-instability and operates beyond the pull-in voltage. Membrane DEAs (VHB 4905), which were pre-stretched bi-axially at 200% strain and immersed in the oil bath, survived a very high eld strength (>800 MV/m) and demonstrated areal strains up to 140%. The dielectric strength, achieved in the immersion, is approximately two times larger than that in the air (450 MV/m). This is achieved because the dielectric liquid bath helps to quench the localized electrical breakdown, which would have discharged sparks and burnt the dielectric lm in the air .Published versio

“Clicking” compliant mechanism for flapping-wing micro aerial vehicle

This paper presented a click mechanism, which is inspired by a Dipteran insect, for use in flapping-wing micro aerial vehicle. The clicking mechanism is integrated in a thorax-like compliant mechanism, which buckles and consequently produces a large wing stroke when driven by an electric motor. The thorax-like compliant mechanism can store elastic energy in flexible hinges and is good for storing kinetic energy expended during wing reversal. This work showed that clicking compliant mechanism produces more thrust per input power than a conventional non-clicking rigid-body mechanism. The clicking prototype weighs 3.58g, has 115° wing stroke, and is able to achieve hovering at 15.8Hz flapping frequency. The non-clicking prototype is lighter at 3.35g with a wingstroke of 100°, but could not achieve hover but could not achieve hovering even though driven by the same motor at a faster flapping frequency (16.2Hz) under the same driving voltage (4.9 V). The clicking prototype produces a thrust-to-power ratio of 2.17g/W, higher than 1.15g/W of the nonclicking counterpart

Very high dielectric strength for dielectric elastomer actuators in liquid dielectric immersion

This letter reported that a dielectric elastomer actuator (3M VHB), which is immersed in a liquid dielectric bath, is enhanced tremendously in dielectric strength up to 800 MV/m, as compared to 450 MV/m for the actuator operated in air. The bath consists of silicone oil (Dow Corning Fluid 200 50cSt), which is 6.5 times more thermally conductive than air, and it is found able to maintain the actuator at a stable temperature. As a result, the oil-immersed dielectric elastomer actuator is prevented from local thermal runaway, which causes loss of electrical insulation, and consequently avoids the damage by electromechanical instabilityPublished versio

Is clicking mechanism good for flapping wing micro aerial vehicle?

In this paper, we examine the effect of non-sinusoidal flapping motion caused by click mechanism and compared it to a sinusoidal flapping motion. Many had observed and described the click mechanism through insect’s anatomy. Through theoretical models and numerical studies, some dismissed its effect on flapping efficiency, while others predicted better thrust generation with it. Without concrete experimental proof, the argument is hypothetical. This work showed the benefits of the click mechanism by experiment, with its simple compliant thorax designed using carbon fiber and polyimide film. The click mechanism system is designed like a thin elastic plate which was compressed until bent, with its center point stable at either the top most extreme or the bottom most extreme positions. ‘Clicking’ occurs when the plate center is moved forcibly from one extreme to the other. Before it passes the midpoint, the plate center moves slowly as it tends to return to the original extreme and resist the displacement. When moved passed the midpoint, it now tends to move to the other extreme, together with the external force, resulting in a fast, snapping ‘click’ to the other extreme. Hence, the clicking prototype showed a sudden high increase in wing flap speed when it is moved beyond midpoint towards the other end. It also showed quick wing reversal and is able to produce consistent large wing stroke (~115°). The clicking prototype, which weighs 3.78g, produces a higher thrust of 2.9g at a flapping frequency of 19Hz. In comparison, a 3.26g prototype of sinusoidal flapping motion with similar design configuration produces only 2.2g of thrust at 19Hz.Published versio