Study on core free rolled actuator based on soft dielectric EAP

The rolled actuator represents a design where the pre-stretched EAP film is wrapped many times around a spring core in order to form a multilayer actuator system with unidirectional actuation. The freestanding rolled configuration enables the use of the DE film for muscle like linear actuators with a broad application potential. The stress state of the pre-strained acrylic film in the rolled configuration and the required stiff core can cause several serious problems concerning lifetime, size and efficiency of the actuator. In order to obtain an acceptable specific actuator performance and lifetime the pre-stretching stress has to be essentially reduced or even eliminated. This can be achieved by the interpenetrating polymer network (IPN) process newly developed at the UCLA. Thereby a trifunctional methacrylate monomers is introduced into the highly pre-strained acrylic films and subsequently curing the monomers to form an interpenetrating elastomeric network. The as obtained interpenetrating polymer network (IPN) can effectively support the pre-strain of the acrylic film and consequently eliminate the need for external pre-strain-supporting structures. In this study a new rolled actuator design is presented based on the IPN post treated VHB material. Due to the stress free state of the wrapped film no spring core is necessary. As a result a significantly longer lifetime and better specific volume efficiency of the actuator has been achieved at lower unidirectional elongation when activated. Introductorily, the specific problems on conventional rolled actuators are discussed and the aims for core free rolled actuators are specified. Then some structural design parameters are addressed in order to achieve a slight shape and reliable working principle. In the main part of the study the manufacturing process of the actuators and some measurement results and experiences are discussed in detail.