Multilaminate piezoelectric PVDF actuators to enhance performance of soft micro robots

TL;DR

Multilaminate PVDF actuators address the need for compact, high-bandwidth, low-voltage actuation in soft microrobotics by stacking PVDF layers with parallel electrical drive. The paper develops and validates a unimorph beam model and demonstrates 4- and 8-layer devices whose performance scales with layer count and thickness, achieving free deflection greater than 3 mm, blocked force greater than 20 mN, and bandwidths exceeding 500 Hz at voltages around 150 V. A planar microrobot demonstration driven by resonant actuation shows robust locomotion and resilience to perturbations, illustrating practical integration potential. Collectively, the work provides design rules linking layer number, thickness, and stiffness to performance and offers scalable fabrication strategies to bridge the gap between brittle ceramic actuators and soft polymer actuators for soft microrobotics.

Abstract

Multilayer piezoelectric polyvinylidene fluoride (PVDF) actuators are a promising approach to enhance performance of soft microrobotic systems. In this work, we develop and characterize multilayer PVDF actuators with parallel voltage distribution across each layer, bridging a unique design space between brittle high-force PZT stacks and compliant but lower-bandwidth soft polymer actuators. We show the effects of layer thickness and number of layers in actuator performance and their agreement with a first principles model. By varying these parameters, we demonstrate actuators capable of >3 mm of free deflection, >20 mN of blocked force, and >=500 Hz, while operating at voltages as low as 150 volts. To illustrate their potential for robotic integration, we integrate our actuators into a planar, translating microrobot that leverages resonance to achieve locomotion with robustness to large perturbations.

Figures (8)

• Figure 1: PVDF actuators integrated into a robot
• Figure 2: Cross-sectional view of the unimorph piezoelectric actuator and its simplified beam model. $t_p$, $t_\ell$, and $t_s$ are the thicknesses of the piezostack, individual piezoelectric layers, and stiffening layer, respectively. $A_p$ is the cross-sectional area of the piezostack. $z_p$ and $z_n$ are the centroid of the piezostack and neutral axis. $E_p$ and $E_s$ are the Young’s moduli of the piezostack and stiffening layer. $V$ is the applied voltage across the piezostack, and $d_{31}$ is the transverse piezoelectric coefficient of the PVDF layers.
• Figure 3: Schematic of the asymmetric electrode layup used to prevent interlayer shorting in multilaminate PVDF actuators. All positive electrodes are routed to one side of the stack, and all negative electrodes to the other, enabling reliable electrical connection with silver epoxy.
• Figure 4: Actuator manufacturing process
• Figure 5: Comparison between theoretical and experimental displacement