Bidirectional actuation of buckled bistable beam using twisted string actuator

Abstract

A new actuation mechanism using the twisted string concept to trigger the snap-through of a bistable buckled beam to produce an effective on/off bistable actuator is proposed. The twisted string concept combined with a pin utilizes actuation moment to actuate a bistable beam. The required actuation loads are analytically formulated using the Euler–Bernoulli beam model and solved with the proposed solution algorithm. The actuation mechanism is fabricated to meet the 24.3 N mm actuation requirements. A prototype of the actuator was built, and its performance was evaluated. In a unidirectional actuation, an actuator response time of 104 ms was achieved. The overall response time of the actuator is affected by the length of the string. The twisted string mechanism was also placed in an antagonistic configuration to enable bidirectional actuation. The shape of the input voltage signal also affected the bidirectional performance of the actuator. The actuator produced an actuation bandwidth of 2 and 5 Hz with sine and square input voltages, respectively, while generating 10 mm output displacement.

Analytical modeling for rapid design of bistable buckled beams

“…The enlarged error of w cr when the precompression rate is large is due to the violation of the small-deflection hypothesis assumed in our model. The error of w 0 , however, is bounded within 10% when r falls in the range [0, 0.08], which indicates that our model still greatly applies to most circumstances [10,16,24].…”

“…Still, off-center actuation possesses unique behavioral properties that make it suitable for many applications. For example, compared with center actuation, off-center actuation usually requires a smaller actuating force but a longer actuating stroke [23,24].…”

Bistable Structures for Advanced Functional Systems

“…Addo‐Akoto and Han proposed an actuation mechanism that utilized a twisted string and a pin driven by a DC motor to apply the bending moment and trigger the snap‐through of a bistable buckled beam (Figure 2B). [ 12 ] Their design is simple and cost‐effective but needs the parts to exert loading in a contact way, which increases the complexity of the entire system and hinders its miniaturization. Plates and shells are also employed in actuators driven by pneumatically or hydraulically pressure.…”

“…Reproduced with permission. [ 12 ] Copyright 2018, SAGE Publishing. C) Illustration of the assembly process of a pre‐stressed twisting bistable structure.…”

“…B) Schematic illustration of an actuation mechanism using a bistable beam, which consists of a twisted string, a DC motor, a pin, and a moment arm for snap-through actuation. Reproduced with permission [12]. Copyright 2018, SAGE Publishing.…”