[Show abstract][Hide abstract] ABSTRACT: We present the design, analysis, and experimental validation of a variable stiffness device based on annular dielectric electroactive polymer (EAP) actuators. The device is based on a diaphragm geometry, which partially linearizes the viscoelastic response of acrylic dielectrics, providing voltage-controlled stiffness without high damping losses. Multiple diaphragms can be connected in a single device to increase stiffness or provide custom stiffness profiles. The geometry is analyzed to determine the relationship among force, displacement and voltage. A single-layer diaphragm was constructed and tested to validate the concept, demonstrating up to 10x change in stiffness.
Full-text · Article · May 2012 · Proceedings - IEEE International Conference on Robotics and Automation
[Show abstract][Hide abstract] ABSTRACT: This paper presents a variable impedance suspen- sion system based on electroactive polymer (EAP) actuators, leveraging their inherent compliance and damping, light weight, and low power requirements. We describe the manufacturing process used to create a small, lightweight EAP suspension and a novel control circuit used to vary its properties. Next, we model the electromechanical coupling by which impedance values are changed, and experimentally verify its behavior. Of particular interest is the transient response, for example, as encountered when a robot touches down after jumping or gliding. We conclude with a discussion of the changes in performance that are possible when applying a variable impedance EAP suspension to a small flying and perching robot. I. INTRODUCTION
[Show abstract][Hide abstract] ABSTRACT: Prior research in biology and mechanics has shown the importance of hierarchy to the performance of dry adhesive systems on rough surfaces. The gecko utilizes several levels of hierarchy that operate on length scales from millimeters to 100s of nanometers in order to maneuver on smooth and rough vertical surfaces ranging from glass to rock. The gecko's hierarchical system serves two main purposes: it permits conformation to the surface for a large effective area of contact, and it distributes the load evenly among contacting elements. We present a new two-tiered directional adhesive system that provides these capabilities for a gecko-inspired climbing robot. The distal features consist of wedge-shaped structures with a base width of 50 mum and a height of approximately 180 mum. The wedges are mounted atop angled cylindrical features, 380 mum in diameter by approximately 1 mm long. Together, the proximal and distal features bend preferentially in the direction of inclination when loaded with a tangential force, achieving a combination of directional adhesion and conformation to rough surfaces. Using this system, a four legged robot that was previously restricted to climbing smooth surfaces is able to climb vertical surfaces such as a wood panels, painted metals, and plastics. On rougher surfaces, the two-tiered system improves adhesion by a factor of five compared to the wedge features alone. The hierarchical system also improved alignment and performance for large patch sizes.