A monolithic tunable symmetric bistable mechanism

Abstract

A tunable symmetric bistable micro-machined mechanism with monolithic structure is presented. The mechanism consists of two sets of pre-shaped beams of similar properties and dimensions; however with one set is curved opposite to the other. The bistability is induced by creating a negative stiffness behavior at the initial position of the moving part to break its stability. This is possible at a certain electrothermal axial loading of both beam sets. The active bistability is symmetric with respect to the initial position. The distance between stable positions is tunable with the applied electrothermal voltages. The mechanism can be used as a tunable bi-directional actuator with different applied voltages. The design and concept are demonstrated based on finite-element simulations and experimental measurements.

Bistable Structures for Advanced Functional Systems

“…Hussein et al created a tunable symmetric bistable actuator consisting of two opposite sets of preshaped curved beams with similar materials and dimensions that are connected to each other by a shuttle at their mid-points (Figure 4E). [59] The tunable bistability was realized by Joule heating of the two sets of conductive beams via applied voltages, which created a negative stiffness behavior at their initial position.…”

“…The feasibility of using SMA wires to trigger the snap-through of unsymmetric composite laminates was demonstrated by an approximate theory and supported with experiments. 59 Numerical models were also developed and may help solve the manufacturing problems such as a large number of SMA wires required and their distribution as well as the influence of laminates processing. [62,63] These designs used one-way shape memory effect, thus enabled only one-way snap-through.…”

“…Reproduced with permission. [ 59 ] Copyright 2020, IOP Publishing. F) The printed state and programmed state of an expanded SMS and two states of the bistable actuator after assembly of the SMS.…”

“…E) The tunable symmetric bistable device. Reproduced with permission [59]. Copyright 2020, IOP Publishing.…”

Accurate Sensorless Multistable Microsystem With a Single Actuator

“…Multistable devices are increasingly implemented in novel applications, such as surgery tools (Zanaty et al, 2019), drug delivery (Salem et al, 2018), space applications (Zirbel et al, 2016), metamaterials (Ramakrishnan and Frazier, 2020), robotics (Gorissen et al, 2020), energy harvesters (Hwang and Arrieta, 2018), sensors (Frangi et al, 2015), and actuators (Hussein et al, 2018). Bistability represents the simplest case of multistability, and thin beam bistable mechanisms, with curved or inclined forms, are the most commonly used types of bistable mechanisms in microsystems (Hussein et al, 2015;Hussein et al, 2019;Hussein et al, 2020c;Hussein et al, 2020b;Hussein and Younis, 2020;Cao et al, 2021). Multistable micro-mechanisms are based on the assembly of elementary mechanisms with a small degree of multistability, either in series (Gerson et al, 2012;Zhang et al, 2015) or parallel (Chalvet et al, 2013;Che et al, 2016;Hua et al, 2019;Mohand-Ousaid et al, 2021), or on a mobile part actuated based on stepping mechanisms (Arthur et al, 2011;Hussein et al, 2018).…”