The plastic, polyurethane, is used in the DIELASTAR research project (dielectric elastomers for control actuators) combined with graphite to make a new drive element (actuator). An actuator turns electrical signals into mechanical movements, for example to open and close a valve. In classic valves the actuator is an electromagnet. Dielectric elastomer actuators (DEA) can be used, for example, in valves instead of solenoids.
Festo uses the DEA in the research project as active elements in valves to control the air flow in pneumatic installations. A DEA of this type is made up of 300 wafer-thin polyurethane layers stacked on top of each other. One layer is approx. 0.05 millimetres, in other words around half as thick as a human hair. The stacked layers result in a small cuboid the size of a sugar cube.
Ultra-thin electrodes made of graphite are sprayed on between the polyurethane layers. These electrodes are arranged alternately so that an electric field can build up in the elastomer when an electric voltage is present. The attractive force generated by the electrical field causes the flexible polyurethane layers to move towards each other. This causes the whole actuator to shorten and opens the valve.
Unlike with solenoid operated valves, no heat is generated during this process, because the current only flows briefly to charge the electrodes. However, a high electrical voltage of around 2,000 volts is currently necessary to activate the DEA. This is therefore still around 80 times as high as the operating voltage of 24 volts required for standard industrial components. One of the main focuses in the research activities is therefore on the reduction of the electrical voltage.
Aims of the project
New actuators are developed in the research project. In classic valves the actuator is an electromagnet. Dielectric elastomers can be used in valves instead of solenoids.
These provide several benefits: by controlling or regulating the electrical voltage applied to the DEA, the air flow in the pneumatic valve can be changed. This means that positions between ‘open’ and ‘closed’ are also possible (proportional operation). Conventional valves with solenoid actuators, in contrast, can only be either completely opened or closed. DEAs are also cost-effective due to the low materials costs for polyurethane and graphite. As a DEA-controlled valve does not need any current to hold its position (holding current), valves fitted with DEAs work very energy-efficiently.
Research projects study to what extent the operating voltage of DEAs can be reduced, for example by a reduction to the thickness of the layers in the elastomer. The higher field strengths made possible by this lead to higher forces or lifts. The performance of the DEAs can be further increased by mixing nano particles in the elastomer material.
The studies so far show that polyurethane is well suited as an elastomer for constructing DEAs in principle, although the material has mechanically damping properties that restrict the dynamics of the fast-switching actuator. Better dynamic properties are promised for the future if silicone is used as an elastomer.
A demonstrator of the research project makes the positive properties clear: it shows the proportional DEA drive and its energy efficient consumption compared to a conventional valve with solenoid drive.
The DEA valve was constructed on the basis of a MHE2 valve housing, in which the solenoid drive was removed and replaced by a module with a thin DEA and a high voltage DC static converter. The operating voltage of the DEA valve, at 24 volts, is identical to that of the MHE2 valve. When the operating voltage is reduced, the 2/2-way proportional function of the DEA valve becomes clear.
In another demonstrator, DEAs are used as drive components for an energy-efficient small-parts gripper.
Other project partners
From the field of science
- OWL University of Applied Sciences
- Fraunhofer IAP
Aus der Industrie
- ABB AG research centre, Germany
The project DIELASTAR is funded by the German ministry of education and research (BMBF) (funding reference number 13X4011C).