The Artificial Muscle area within the Robotics Lab is a multidisciplinary collaboration between researchers at the Department of System Engineering and Automation and the Department of material science at Carlos III University of Madrid

Aims

We are conducting an oriented research effort resulting in a novel class of electrically controlled intelligent actuators based on polymer materials. For this purpose we are developing electroactive polymers (EAP) and studying their actuation properties and limitations for integration into a device. Due to the properties of EAP, we expect to obtain an extremely light, soundless, flexible, and very efficient actuator, with built-in mechanical sensing, matching and even besting human muscles. We name this goal “Artificial Muscles”.

Scope

Throughout history, new materials have played a key role revolutionizing many engineering disciplines. Light and strong materials have become enabling technologies in many industrial sectors. But engines, motors, actuators, and in general all the actual motion technologies haven’t evolved significantly in the past decades, becoming very often the performance barrier.

The proposed actuator offers certain advantages over contemporary motor technologies. As with real muscle, an artificial muscle could offer a transduction efficiency far superior to that of electric motors, or shape memory alloys powered by battery or fuel cell. Although high powers can be achieved from gasoline engines, stealth quietness cannot

The development of the proposed new technology will influence many technical aspects of society. Due to the enormous range of possibilities we will proceed to analyze the commercial applications by sectors:

Bio-inspired robotics

: Again reducing the actuator’s weight becomes a key role for this industry. For robots to be introduced fully into society, experts agree that a technology revolution in actuators would be required. Artificial muscles would mimic natural muscles in flexibility and efficiency and would mean a change in design philosophy that would allow integration of sensing, moving, suspension, and even control systems in a single device: the actuator. Due to this enhanced maneouverability robots could then be introduced into new sectors depending on the engineer’s needs and imagination.Gas powered autonomous robots are noisy and cumbersome. Humanoids and other biomimetics initiatives so far suffer from inflexibility. Consumer Applications: The materials under study could cost as little as one euro per kilogram to mass produce. This is why is interesting to look at consumer applications like toys (moving action figures), cosmetic or toothpaste dispensers. Anything that requires motion is fair game, and could be on the market in one to two years.

Aerospace

: The weight-performance ratio is closely watched in this sector, especially in the aerospace field. Artificial muscle technology could enhance considerably this figure and replace existing actuator technologies in the aeronautical sector. The flexible nature of artificial muscles would also allow development of highly efficient active suspension systems also useful to the automotive industry. A new commercial field still to be fully developed called Smart Structures could also benefit from this technology. As preliminary experiments show (further in this document), artificial muscles could be integrated into the structure of a plane enabling a shape-changeable and therefore self-repairable structure. Some other innovative possibilities are the design of anti-G suits for pilots, or the design of extremely small flying machines.

Biomedical

: The possibilities in this sector are unlimited. Prosthetics (highly weight sensitive), massage systems to prevent venous thrombosis for people who are at risk due to long periods of immobility, artificial urinary sphincters, cardio wraparounds, and stearable catheters are some of the ideas to start with, but there are probably many others only constrained to a doctor’s imagination.

Naval applications

: a fish’s swimming motion is highly efficient and could be copied with the help of artificial muscles. As the demonstration videos show, the movement of the muscles could be used as a flipper for nautical motion. The demonstrated performance in water would help to accelerate this research. Fabrication Processes: The deformation of this material with an electrical stimuli can be seen as a highly accurate shape fabrication procedure. For example, the fabrication of small steel devices could be enhanced with a moving mold that we can control electronically. Again, this new technology could solve many fabrication problems depending on the industry needs.

Military applications

: Most of the above applications could be military oriented. The materials involved in the device’s design so far are predicted to be valid for operation in the military temperature range.

Lines of work

We are focusing on ionic EAP materials, in particular Ionic Polymer Conductor Composites (IPCC). The reason is that this material is a low voltage intelligent material. It requires very low voltage in order to behave as actuator (3 V), and also works as a mechanical transducer. The activation mechanism of this group of materials is a relocation of the ions inside the structure due to a change in the electrical charge of the material. The movement of the ions and water molecules inside the material induces a change in the material’s volume, which can be used to produce electrically controlled actuation. The opposite effect is observed when used as a mechanical transducer. We manufacture the material at our labs, and after a tedious work, We have engineered several types of specimens, varying different aspects of their manufacturing (electrodes, doping ions, ion-conducting medium and coating.)

In parallel with the chemical work on these materials we are currently working on the final mechanism design and control. The size and design of the actuator will depend on the application, but the fundamental will be unique. Encapsulation requirements, mechanical design, control, speed, and scalability are some of the problems that must be solved to ensure a reliable prototype.

A specific line of research is focused on the characterization of Electroactive Polymer materials as intelligent materials. Both transducer and actuating properties of these materials are being fully characterized employing novel procedures and equipment. A specific Unit Tester for Electroactive Polymer actuators is being developed, and a project to adapt the equipment to the environmental testing of the materials is on the way.

Research challenges

The material needs to be humid in order to move, although not necessarily with water. Other polar solvents have proved feasible. Controllability of the material and long time operation stability seem to be extremely related to the loss of solvent, either by prolonged operation, or by electrolysis. Novel solvents and special silicones are being tested in order to overcome such limitation.

Preliminary experiments show the material can lift 100 times its own weight, but there is not a clear idea of the circumstances under which it will be able to sustain the required force. We plan to conduct a environmental testing of the material in order to evaluate the feasibility of using the material in a very harsh environment such as space.

Characterising the materials is a difficult task. There is a lack of instrumentation for the characterisation of intelligent materials. We are currently developing our own Unit Tester for the characterization of Electroactive Polymer materials.