An evaluation of materials and processes suitable for manufacturing micro HASEL-actuators

Sammanfattning: HASEL-actuators use dielectric liquids and compliant shells as their media. This type of actuatorwould suit the actuators used as fins for soft milli robots (SOMIRO). These robots are going tobe used in aquaponic crops for studying its impact on the environment to help the farmersimprove their crops. The robots have to be soft and compliant, so the materials used for theHASEL-actuator should have the same properties. First, an automatic manufacturing method isinvestigated to find a proper way to produce these actuators. It was concluded that a processcalled the “two-layered actuator” had the most potential, where a PU film, PET film andDUALBOND glue was used to produce a well-defined HASEL-actuator by creating a cavitywithin the PU film by using a suction flask and fill the cavity with coconut oil. The cavity'sshape was two domes (3 mm in diameter) connected with a middle channel (1 mm in diameterand a length of 3 mm). The actuator had electrodes made of a curable silver paste or Galinstanwhere their potential difference is used for powering the actuation. The aim for the neededvoltage when actuating the actuators was to be below 1kV. This means that the actuators have tobe as thin and have a low Young’s modulus as possible. The silver electrodes made the actuatortoo stiff to actuate at that low voltage, so the other potential materials would be Galinstan as theelectrode and PDMS and PU film which could replace the PU and PET respectively. Dependingon the pressure used on the suction flask for fabrication of the two-layered actuator, differentheights of the cavity could be achieved. By changing the pressure to 1 kPa, it was found out thatthe lowest height of 260 µm could be achieved. Different compositions of paraffin oils wereevaluated to find a suitable dielectric liquid with the right melting temperature since the actuatoronly works when the media is in its liquid state. The sample showing highest potential had amixture of 4.4 g of a liquid paraffin oil and 1.17 g of a soft paraffin wax. The starting meltingpoint was concluded to be at 5 °C. During the voltage test of the actuators, no sign of movementcould be seen for any of the produced actuators when reaching the highest voltage of 1 kV. Thisindicates that the actuators are still too thick and stiff and needs to be improved in the future