![]() ![]() While there has been a learning curve as suppliers adjusted their products through successive generations of design based on accumulating service experience, the technology has achieved maturity. In both cases, problems have emerged with the need for costly maintenance involving cleaning or replacement.Ĭomposite insulators were developed about 50 years ago largely because of these deficiencies and introduced on an industrial scale during the 1980s. However, their performance has not always been satisfactory – notably under high pollution applications or in service areas prone to vandalism. In fact, rapid expansion of overhead networks would not have been possible were it not for their consistent, long-term insulation and mechanical properties. Porcelain and glass insulators have been used since the start and have had a good record of performance and reliability. Using recent developments in high quality piezoelectric film deposition and microfabrication techniques, TWUM can be made an order of magnitude smaller than currently possible.Three proven insulator technologies are deployed in delivery of electrical power. Traveling wave ultrasonic motors (TWUM) can provide micro-to milli-newton-meters of torque at low speeds and fill a necessary place within the millimeter-scale rotary motor landscape. Electrostatic micro-motors require approximately 100 V for operation and produce limited torque. Electromagnetic motors, which are effective at the macro-scale, become less practical at the millimeter-scale due to unfavorable scaling of energy density and complex fabrication. ![]() In order to drive large loads at speeds closer to 100 to 1000 RPM, gearing would be required, which drastically increases system complexity and size. Many current millimeter-scale motor technologies, such as electrostatic motors and electromagnetic motors, operate at high speeds (on the order of 10 5 RPM) but low torque, usually pico-or nano-newton-meters. Concepts Magn Reson 29B: 191–209, 2006.įor many small-scale systems, compact rotary actuators are highly attractive. A synthesis of characteristics and three comparative tables aid in the choice of an adequate actuation method for a given task or application. ![]() A good solution to a given application often involves a combination of several actuation principles. The results are completed with developments of other groups. Our analysis is based on a variety of actuation principles that we have tested both for MR compatibility and for the quality of force feedback that can be realized, including hydrostatic, belt, and cable transmissions as well as electrostatic and piezoelectric actuators. In the case of functional MRI, actuation is also required during imaging, whereas current MR-compatible interventional systems are typically moved between imaging phases. This article analyzes actuation methods for robotic systems to be used within a magnetic resonance environment, such as systems for diagnostic and interventional MRI, neuroscience studies during functional MRI, and diagnostic fMRI. This choice is particularly difficult for robotic systems working within a magnetic resonance (MR) environment because of the safety and compatibility constraints imposed by the high magnetic field, switching gradients, electromagnetic pulses, and sensitive measuring equipment involved. The choice of an adequate actuation method is a central issue in the development of any mechatronic device and strongly determines the dynamic performances of the system.
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