Laboratory Introduction
Dr. Seiki Chiba
Executive Director,
The Advanced Automation Technology Center of SRI International
1. Introduction of AATC
The Advanced Automation Technology Center(AATC) of SRI International (SRI) focuses on thedesign, development, and transfer to its clients ofadvanced automation technologies. These technologies span a wide range of fields and include intelligent document understanding, 3-D machine vision, sensor placement, telerobotics, field robotics,
and new transducer technologies such as artificialmuscle. In the area of new transducer technologies, AATC works closely with other laboratories
within SRI, sharing a wide range of facilities andequipment within SRI. These laboratories maintain state-of-the-art design, analysis, and fabrication facilities including special and general measurement and test equipment, an environmental
chamber, a model shop, chemistry and spray fabrication facilities, and computer-aided design centers. AATC works closely with SRI’s Physical Electronics Laboratory, which maintains clean rooms
and other microfabrication facilities.
AATC has worked with a wide range of government and commercial clients in the US, Japan, andEurope. As a nonprofit institution, SRI transfers
the technologies developed at AATC to the sponsoring commercial clients, or licenses them tomanufacturing companies in the case of U.S. government-sponsored work.
AATC has worked on a wide range of robotic
and transducer technologies. In the area of robotics, for example, AATC developed a laboratory prototype of a pipeline inspection robot. The pipeline
robot used novel magnetic wheels that enabled it
to travel on the walls and ceilings of 15-cm natural-gas pipes. Other research and development focuses on basic transducers; In addition to work on
artificial muscle, AATC has developed novel levitated devices for applications such as sensors (flowmeters, accelerometers, etc.), micromotors, andclean-room automation. AATC demonstrated what
is believed to be theworld’s first passive self-levitated (no biasforces) magnetic structure at room temperature.
Another sensor area of interest to AATC is tonom-

4etry, a technique for measuring blood pressure
unobtrusively and continuously. For a number ofyears AATC has developed tonometry technology,
some of which is currently sold commercially.
2. Artificial Muscles
AATC has been investigating artificial muscleson the “Artificial Muscles in R&D of MicromachineTechnology, industrial Sciences and Technology
frontier Program” since 1992. The term artificialmuscle, analogous to natural muscle, describes any
actuator material that is substantially scale invariant in performance, where larger actuators canbe considered as a collection of mechanically linked
microactuators. For example, a single electromagnetic voice coil actuator is not an artificial muscle
because it is not scale invariant (it has poor performance on small scales), and it is not a collection of mechanically linked microactuators. By contrast, a piezoelectric material has substantiallyscale-invariant performance, and a large, multilayer piezoelectric actuator consists of a collectionof mechanically linked microactuators.
Our goal for the project is to identify and develop an artificial muscle with performance comparable to that of natural muscle. Such an artificial muscle would have overall performance greatly
exceeding that of existing artificial actuators andcould be used for small robots, inkjet printers, micro light scanners, micropumps, and a wide rangeof other microapplications. The artificial muscle
would be particularly applicable to microdevices,
for which existing actuator technologies are limited; but since it is scale invariant, it could also beused for a wide range of macro applications including robots, speakes, and motors.
The principle of operation of the electrostrictive
polymers investigated by SRI is shown in Figure
1. Unlike other electrostrictive polymers (EPs),
which work via molecular changes, SRI’s EP materials work via bulk electrostatic forces (Maxwell stress). As shown in Figure 1, a relatively softpolymer is sandwiched between two compliant
electrodes. When a voltage difference is appliedbetween the compliant electrodes, the electrostaticforces squeeze and stretch the polymer, thus providing a mechanism for actuation.

Fig. 1 Principle of Operation of Electrostrictive Polymers (Circular Black Areas in Bottom Photos
are Active Electrode Areas).

Figure 2 shows a comparison between artificial muscle and other high-speed actuator technologies. Note that the performance of artificial
muscle exceeds that of natural muscle.

Fig. 2 Comparison Between High-Speed Actuator
Technologies

Many polymer materials have been tested as
artificial muscle. All insulating polymers show
some response, Silicon and acrylic are dramatically
better than others. Note that the strain of theacrylic elastomer can exceed 200%, and its energy
density is higher than that of any known field-actuated material. The acrylic elastomer is a powerful material, but we note that silicone is faster, due
to higher viscoelastic losses in acrylic. Silicones

have a bandwidth greater than 1 kHz, while acrylic
elastomers are currently limited to below 100 Hz.
Research is now concentrating on ways to achieve
the high strain and energy density performanceof acrylics in operation at the speeds of silicones.
In addition to the polymer, SRI is investigating
various electrode materials. Metals such as gold
are typically too stiff and crack when actuated, but
we have found that by suitable patterning theycan elongate up to 80% while retaining their conductivity. For higher strains, particulate materials such as carbon black and carbon nanotubes ina binder generally work well.
We have developed a variety of ways to fabricate artificial muscle. Spin coating of polymers insolvents works well, and we have demonstrated
muscle as thin as 1 µm. Thinner films reduce theoperating voltage, which tends to be higher forelectrostrictive polymer artificial muscle than it
is for other electrostatically driven technologies.
We have designed and demonstrated a wide
range of artificial muscle actuators. Examples include artificial muscle bimorphs and unimorphs
capable of greater than 270 degrees of bending,
artificial muscle diaphragms that can actuate froma flat to a hemispherical shape, and a range ofsimple linear actuators. Application-level devices,such as micro light scanners and minipumps, havealso been demonstrated to show the wide applicability of the technology.
An interesting area for research and development has been the investigation of the unique actuation properties of artificial muscle and the design of actuators that can best exploit it. For example, uses a high prestrain in the polymer in one
direction, together with a flexure design, to enhance actuation in the low prestrain direction.
3. Summary
Research on artificial muscles at SRI’s AATC
has reached an application phase. Strain, pressure,energy density, and response time performance parameters have increased by factors of 5-30 in thelast 2 years. Technical progress continues in understanding the fundamental design of artificial
muscles at the material, fabrication, and actuator
levels. Thus, the near future of artificial muscle
research at SRI’s AATC will focus on both fundamental and application areas.

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