An Autonomous Programmable Actuator and Shape Reconfigurable Structures Using Bistability and Shape Memory Polymers [1]

[1] Chen, T., & Shea, K., (2018), 3D Printing and Additive Manufacturing, 5(2), Accepted for Publication. arxiv.org/abs/1711.00452

Table of Content : Abstract | Video | Description

Abstract

Autonomous deployment and shape reconfiguration of structures is a crucial field of research in space exploration with emerging applications in the automotive, building and biomedical industries. Challenges in achieving autonomy include: imprecise deployment, jamming of components, lack of structural capacity and heavy power supply components. Leveraging advances in the fields of shape memory polymers, bistability and 3D multi-material printing, we present a 3D printed programmable actuator that enables the autonomous deployment and shape reconfiguration of structures activated though temperature change. Using a shape memory polymer as the temperature controllable energy source and a bistable mechanism as the linear actuator and force amplifier, the structures achieve precise geometric activation and quantifiable load bearing capacity. The proposed unit actuator integrates these two components and is designed to be assembled into larger deployable and shape reconfigurable structures. First, we demonstrate that the activation of the unit actuator can be sequenced by tailoring each shape memory polymer to a different activation time. Next, by changing the configuration of the actuator, we present an initially flat surface that transforms into a pyramid or a hyperbolic paraboloid, thus demonstrating a multi-state structure. Load bearing capability is demonstrated for both during activation and in the operating state.

Video

Unit actuator

To autonomously deploy multi-stable structures under increased temperature, an actuator that combines bistability and shape memory effect is proposed. The embedded Shape Memory Strip (SMS) is activated and triggers the bistable mechanism when the temperature increases beyond the threshold (the Glass Transition Temperature TG of the polymer is approximately 30 to 40C). The different between the TG of polymers allow for some components to remain invariant during activation.
Mechanical characterization of the unit actuator, both in expansion (a, c, e) and contraction (b,d,f), including simulation (solid lines) and experimental (dashed lines) results in both the glassy and the rubbery regime. a,b) Parametric study of the influence of the SMS thickness and recovery direction on its activation force at a temperature load above TG. The range of the thickness studies is between 1.0 to 2.0mm in 0.25mm intervals. c,d) Shows the force displacement curves of the bistable mechanism and the chosen SMS. Activation is guaranteed when the SMS force is greater than the bistable force in region I. In region II, both SMS and bistability are acting in the same direction. Stable equilibrium is indicated at point III. e,f) These plots compare the overall behavior of the actuator at TG and at operating temperature of approximately 20C.
Sequenced activation of multiple actuators. (L) Schematic showing three expansion actuators connected in series (+) and the physical specimen in both initial and final state. (R) Video screen captures showing the sequenced activation of the actuators.