Conducting polymers are becoming viable engineering materials and are gradually being integrated into a wide range of
devices. Parallel efforts conducted to characterize their electromechanical behavior, understand the factors that affect
actuation performance, mechanically process films, and address the engineering obstacles that must be overcome to
generate the forces and displacements required in real-world applications have made it possible to begin using
conducting polymers in devices that cannot be made optimal using traditional actuators and materials. The use of
conducting polymers has allowed us to take better advantage of biological architectures for robotic applications and has
enabled us to pursue the development of novel sensors, motors, and medical diagnostic technologies. This paper uses the
application of conducting polymer actuators to a biorobotic fin for unmanned undersea vehicles (UUVs) as a vehicle for
discussing the efforts in our laboratory to develop conducting polymers into a suite of useful actuators and engineering
components.
Sylvain Martel, Lorenzo Cervera Olague, Juan Bautista Coves Ferrando, Stefen Riebel, Torsten Koker, Jeremy Suurkivi, Timothy Fofonoff, Mark Sherwood, Robert Dyer, Ian Hunter
The NanoWalker is a miniature wireless instrumented robot designed for high-speed autonomous operations down to the atomic scale. As such, it requires very advanced electro-mechanical specifications and complex embedded sub-systems. The locomotion is based on three piezo-ceramic legs that are modulated at high frequencies to achieve several thousand steps per second with computer-controlled step sizes ranging from a few tenths of nanometers to a few micrometers. Each robot has an onboard 48 MIPS computer based on a digital signal processor (DSP) and 4 Mb/s half-duplex infrared communication system. A special instrument interface has been embedded in order to allow positioning capability at the atomic scale and sub-atomic operations within a 200 nanometer surface area using a scanning tunneling microscope (STM) tip. The design allows 200,000 STM-based measurements per second. In this paper, we describe the many sub-systems and the approaches used to successfully integrate them onto such a miniature robot.
Amplitude modulated piezo-based locomotion requires one power amplifier for each quadrant electrode on the piezo-legs of miniature robots. Since each amplifier has a significant amount of quiescent current, several DC/DC converters must be embedded to source at least the total amount of quiescent current. In order to achieve a significant reduction in the overall size of the piezo-actuated robots, the number of DC/DC converters is reduced through frequency modulation. Using frequency modulation, the amplitudes of deflection or the step sizes are reduced by modulating the piezo-legs above the resonant frequency. Although the frequency modulated approach can result in much smaller robots than what can be achieved using the amplitude modulated technique, it has some drawbacks that the amplitude modulated approach does not have. First, the magnitudes of deflection of the piezo-legs using frequency modulation are typically more difficult to control. Secondly, for much smaller amplitudes of deflection, the onboard electronics must operate faster, yielding an increase in power consumption and an increase in temperature of the miniature robot, which in turn may affect sensitive embedded instruments. Furthermore, modulating the piezo-legs above the resonant frequency yields a reduction in efficiency, which translates into additional heat. When very small deflections are required, the risk of the temperature to rise beyond the Curie temperature of the piezo-material may also become an issue. All these factors must be considered carefully when frequency modulated piezo-based locomotion is used.
The Telemetric Electrode Array System (TEAS) is a surgically implantable device for the study of neural activity in the brain. An 8x8 array of electrodes collects intra-cortical neural signals and connects them to an analog front end. The front end amplifies and digitizes these microvolt-level signals with 12 bits of resolution and at 31KHz per channel. Peak detection is used to extract the information carrying features of these signals, which are transmitted over a Bluetooth-based radio link at 725 Kbit/sec. The electrode array is made up of 1mm tall, 60-micron square electrodes spaced 500 microns tip-to-tip. A flex circuit connector provides mechanical isolation between the brain and the electronics, which are mounted to the cranium. Power consumption and management is a critical aspect of the design. The entire system must operate off a surgically implantable battery. With this power source, the system must provide the functionality of a wireless, 64-channel oscilloscope for several hours. The system also provides a low-power sleep mode during which the battery can be inductively charged. Power dissipation and biocompatibility issues also affect the design of the electronics for the probe. The electronics system must fit between the skull and the skin of the test subject. Thus, circuit miniaturization and microassembly techniques are essential to construct the probe's electronics.
The NanoRunner is designed to be primarily used as an experimental wireless robot in order ot quickly test and validate several hardware/software issues and ideas prior to being implemented on the more expensive and complex wireless instrumented NanoWalker robot. As such, the NanoRunner, Like the NanoWalker is based on three piezo- actuated legs forming a pyramid with the apex pointing upward. Unlike the NanoWlaker, the NanoRunner has much simpler embedded electronics and is not capable of an accuracy and computational throughput comparable to the NanoWalker. Because of its lighter weight, it can move or run much faster. Furthermore, the NanoRunner does not have a fast infrared communication infrastructure for downloading executable code. Instead the NanoRunner is first pre-programmed with a specific behavior suitable for the tasks to be performed. Nonetheless, the NanoRunner has all the required electronics to be fully autonomous while performing its experimentation tasks. Although not as sophisticated as the NanoWalker, the NanoRunner offers a smaller and simpler robot implementation for less demanding tasks. Another major motivation for the NanoRunner is to validate various ideas in order to decrease the overall size of the robot. The size is critical since our goal is to allow more robots to work within the same area. In this paper, the NanoRunner is described. Aspects such as construction, assembly, and the method used for downloading executable code in order to pre-program the robot's behavior are also covered.
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