Abstract
This work reports a three-dimensional polymer interdigitated pillar electrostatic actuator that can produce force densities 5–10× higher than those of biological muscles. The theory of operation, scaling, and stability is investigated using analytical and FEM models. The actuator consists of two high-density arrays of interdigitated pillars that work against a restoring force generated by an integrated flexure spring. The actuator architecture enables linear actuation with higher displacements and pull-in free actuation to prevent the in-use stiction associated with other electrostatic actuators. The pillars and springs are 3D printed together in the same structure. The pillars are coated with a gold–palladium alloy layer to form conductive electrodes. The space between the pillars is filled with liquid dielectrics for higher breakdown voltages and larger electrostatic forces due to the increase in the dielectric constant. We demonstrated a prototype actuator that produced a maximum work density of 54.6 µJ/cc and an electrical-to-mechanical energy coupling factor of 32% when actuated at 4000 V. The device was operated for more than 100,000 cycles with no degradation in displacements. The flexible polymer body was robust, allowing the actuator to operate even after high mechanical force impact, which was demonstrated by operation after drop tests. As it is scaled further, the reported actuator will enable soft and flexible muscle-like actuators that can be stacked in series and parallel to scale the resulting forces. This work paves the way for high-energy density actuators for microrobotic applications.
Highlights
Micro-to-milli-scale robotic systems display numerous advantages in applications such as disaster recovery and high-risk environmental investigation
Structure and operation The polymer interdigitated pillar electrostatic (PIPE) actuator design is inspired by how skeletal muscles contract
Analytical model We develop an analytical model for the parametric dependence of the force and work density of PIPE actuators
Summary
Micro-to-milli-scale robotic systems display numerous advantages in applications such as disaster recovery and high-risk environmental investigation. To accomplish these tasks, robotic systems must produce high output forces with high efficiencies. Muscle-like work densities have been a goal of actuator engineers, especially in the context of winged flight systems for humans[1]. Over the past two decades, efforts have been made in insect-scale robot research programs with the goal of achieving a work density comparable to that of muscles while maintaining flexibility. One of the great challenges in biohybrid systems is achieving coupling between muscle tissues and microfabricated devices with sufficient force and power transmissions. A completely manmade high work density, flexible, and efficient actuator can enable robotics to more closely resemble biological systems
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