Showing papers by "Nima Tolou published in 2013"

Bistable vibration energy harvesters: A review

Abstract: Powering electronics without depending on batteries is an open research field. Mechanical vibrations prove to be a reliable energy source, but low-frequency broadband vibrations cannot be harvested effectively using linear oscillators. This article discusses an alternative for harvesting such vibrations, with energy harvesters with two stable configurations. The challenges related to nonlinear dynamics are briefly discussed. Different existing designs of bistable energy harvesters are presented and classified, according to their feasibility for miniaturization. A general dynamic model for those designs is described. Finally, an extensive discussion on quantitative measures of evaluating the effectiveness of energy harvesters is accomplished, resulting in the proposition of a new dimensionless metric suited for a broadband analysis.

A compact low-stiffness six degrees of freedom compliant precision stage

Abstract: This paper presents a low stiffness six degrees of freedom (DoF) compliant precision stage. To deal with problems like backlash, friction and lubrication for performing ultra-precise positioning in a vacuum environment, a novel compliant structure is proposed. All six degrees of freedom are statically balanced (i.e. near zero stiffness) to neutralize the gravity force and cancel out the stiffness due to the compliant design of the structure. Cooperative action of post-buckling behaviour of bi-stable beams and constant stiffness of v-shaped beams, arranged in three units in a triangular configuration, are proposed for out-of-the-horizontal-plane motions. The in-plane motions are achieved by three flexible rods loaded near their buckling load. An investigation on adjusting the design parameters to minimize the residual actuation force is also performed. A demonstrator was manufactured and finite element modelling was performed to evaluate the concept. Experimental evaluation of the demonstrator showed that a gravity force of 34.4 N was balanced with a residual stiffness of 1.75 N/mm in a domain of 2 mm for the out-of-plane translation, while the out-of-plane rotational stiffness was less than 18.5 Nm/rad, caused by parasitic torsion of the bi-stable beams and v-shaped beams. The stiffness for in-plane translations and rotation was 0.4 N/mm and 2 Nm/rad, respectively. The novel mechanism or the principle may be applied in precision engineering or in other relevant fields, such as vibration isolation.