The goal of this project is to generate novel actuators, sensors and materials to enable the creation of future soft robots. These technologies must be able to function under the demanding requirements imposed by highly deformable systems. This includes being able to generate, sense and/or withstand large deformations and forces without breaking. Some of our innovative solutions are discussed below.
Dielectric Elastomer Actuators
We are exploring the creation of new types of soft actuators based on Dielectric Elastomer Actuators (DEAs). DEAs are a type of artificial muscle actuator that exploits electrostatic forces by combining a soft flexible dielectric with stretchable electrodes.
Variable Stiffness Actuator
Controllable stiffness can be an important function for soft robots to exert large forces to environments, and to withstand external loads while keeping their shape. We developed a variable stiffness actuator using DEA and low-melting-point-alloy (LMPA) embedded silicone substrate. The actuator which we call variable stiffness dielectric elastomer actuator (VSDEA) exhibits a bending actuation and a high rigidity change (~90x) between the soft state and the rigid state.
Variable stiffness dielectric elastomer actuator (VSDEA)
The result will be presented at the 2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Hamburg, Germany.
This work has been done as a collaboration work with the EPFL-LMTS.
Foldable Antagonistic Actuator
We developed an actuator based on DEA that is capable of antagonistic actuation and passive folding. The actuator enables foldability in robots, and gives robustness to external shocks and overload by its compliance.
Concept of the actuator
We also developed a micro air vehicle (MAV), in which the actuator was used as an elevon to demonstrate its usefulness. The MAV performed fully controlled flights by only the actuators via a remote transmitter with a human pilot.
(left) The elevon actuator, and (right) the folded state of the actuator
Soft Grippers based on DEMES
Dielectric Elastomer Minimum Energy Structures (DEMES) are a special type of DEA based on the balance between mechanical and electrical energy. A DEMES device can be fabricated by bonding a stretched DEA to a flexible frame. This composite structure folds up into a minimum energy configuration shown below. When a voltage is applied to the DEA, it expands, returning whole device to the flattened state.
We developed and characterized a prototype of DEMES using silicone type elastomer. Based on the result, two and four-finger gripper are developed.
Variable Stiffness Materials
Soft robots are exciting to many applications because they can deform, allowing them to conform to many different surfaces or readily change their shape. However, because they are soft, they can have difficulty holding their position or shape under high external loads. This is why we are interested in developing materials that can controllably change from very soft and flexible to rigid and strong.
One solution that we have developed is a composite material composed of a rigid low-melting-point-alloy (LMPA) microstructure embedded in soft poly(dimethylsiloxane) (PDMS). This material can transition between rigid and soft states by controlling the phase of the LMPA (Tm = 47°C) through efficient, direct Joule-heating of the LMPA microstructure. This composite material demonstrates a relative stiffness change of >25x (elastic modulus is 40 MPa when LMPA is solid and 1.5 MPa when LMPA is liquid) and a fast transition from rigid to soft states (<1 s) at low power (<500 mW). Additionally, the material possesses inherent state (soft and rigid) and strain sensing (Gauge Factor = 0.8) based on resistance changes.