The Thin Films Used in Robotics

By Benedette Cuffari, M.Sc.Oct 23 2018

Image Credits: Josh McCann/shutterstock.com

Thin films are unique materials that exhibit a thickness within the sub-nanometer to several micrometer ranges. These materials are typically utilized for a wide variety of coatings including those for decorative, optical, protective and electrically operating applications, as well as for energy storage in both photovoltaic cells (PVC) and batteries¹. As researchers continue to devote their time to enhancing the way in which thin films are produced, the potential applications of this material subsequently have grown as well. For example, during the last decade, there has been a growing interest in the potential incorporation of thin films into certain robotic devices.  

Thin Films in Biologically Inspired Microrobots

One of the earliest published articles that demonstrated the ability of thin films to be incorporated into autonomously-functioning microrobots was a result of a research collaboration between Oak Ridge Associated Universities in Tennessee and the United States Army Research Laboratory. In an effort to improve the mobility of microrobotic systems, which are typically smaller than 20 millimeters (mm) in size, the researchers focused on improving the actuators that were responsible for the locomotion of these robots². Microrobots are sought-after electronic systems, particularly within defense industries, as a result of their ability to access otherwise inaccessible environments while simultaneously transporting loads to and from their destination in the process.

Previous actuators that were utilized for powering the movement of these types of microrobots included shape-memory alloys, elastomers, ion-exchange polymers, and piezoelectric ceramics; however, these alternatives are limited in their ability to support certain constraints on the system. In their study, the researchers designed a bio-inspired terrestrial microrobot that was powered by a thin-film piezoelectric microactuator. With forces that reached as high as approximately 8 mN and strokes of almost 1 µm in a 500 µm by 100 µm footprint², this group of researchers was able to achieve actuation forces that significantly exceeded other commonly used MEMS actuators. This study confirmed that compact, high-force and low-power thin-film piezoelectric actuators showed great potential as an enabling technology for insect-like microrobotic systems.

Since this study has emerged, various other thin-film electrostatic actuator technologies have been developed, some of which include:

• Film slider
• Parallel plate/stackable
• Zipper
• Scratch drive
• Dielectric elastomer³

Moreover, several MEMS-scale electrostatic technologies have also incorporated thin-films into their designs. For example:

• Distributed electrostatic (DEMA)
• Integrated force arrays
• Repulsive-force electrostatic actuators³

Thin-Films in High-Voltage Robotics

A recent study conducted by graduate student Ethan Schaler at the University of California Berkeley involved the utilization of thin-film electrostatic actuators and adhesives and their application within high-voltage robotics. In his design, Schaler developed both repulsive-force electrostatic actuators (RFAs) and a novel bidirectional repulsive/attractive-force electrostatic actuator (RAFA) that were incorporated into dexterous robotic arms to evaluate their effectiveness³. Robotic arms that are currently used by organizations such as NASA and DARPA perform a wide variety of specific jobs such as cutting lock wire, soft goods such as multi-layer (MLI) insulation blankets, removing fuel caps and transferring fuel or cryogen fluids.  While the function of actuators in robotic arms allow for controllable limp power, the electrostatic adhesives allow for robots to grasp a wide variety of objects in a controlled manner.

During the course of Schaler’s study, the flexible and electrostatic adhesive gripper was found to generate electrostatic attractive forces that reached up to 3.5 N 90.75 kPA) when mounted onto a robotic arm. Furthermore, individual gripper fingers that were covered with electrostatic/hybrid adhesives generated shear pressures that were as high as 5.04 kPA/47.6 kPA, respectively³. While further development is needed to increase the flexibility of the gripper fingers, Schaler is hopeful that the future integration of force/torque sensors into the grippers will enable these powerful grasping forces to one day function autonomously.  

References

1. “How to Characterize Thin Films”
2. Oldham, K., Pulskamp, J., Polcawich, R., Ranade, P., & Dubey, M. (2010). Thin-film piezoelectric actuators for bio-inspired micro-robotic applications. Integrated Ferroelectrics 95(1); 54-65. DOI: 10.1080/10584580701756482.
3. “Thin-Film Electrostatic Actuators and Adhesives for High-Voltage Robotics” – UC Berkeley

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