Servo displacement transducers

The material requirements for these classes of devices are somewhat different, and certain compounds will be better suited to particular applications. The ultrasonic motor, for instance, requires a very hard piezoelectric with a high mechanical quality factor Qm, to suppress heat generation. Driving the motor at the antiresonance frequency, rather than at resonance, is also an intriguing technique to reduce the load on the piezoceramic and the power supply [42]. The servo displacement transducer suffers most from strain hysteresis and, therefore, a PMN electrostrictor is used for this purpose. The pulse drive motor requires a low permittivity material aimed at quick response with a certain power supply rather than a small hysteresis, so soft PZT piezoelectrics are preferred rather than the high-permittivity PMN for this application. 

Another apparatus for general biaxial extension testing, illustrated in Fig. 8, was built at our laboratory27). A square sheet of rubber, 11.5 cm long and 1 mm thick, is clamped at the edges by several pieces of movable chucks and stretched biaxially by means of the two bars that can be displaced separately bade and forth by a servo-meachnism. Tensile forces acting on the sheet in the stretching directions are transmitted to the bars and measured by two transducers mounted at the ends of each bar. After many modifications and improvements on the mechanical and electric parts,... 

The whole aim behind present ERF developments is to provide a means of control/adaptronics (that is easy to apply and economical) to a mechanism that has to be by its nature flexible in force, displacement or speed and hydraulically operated. Electronic solid-state semiconductor devices and computers are powerful, inexpensive and adequate for many applications in control, and yet their interface with hydraulic machines usually involves a bulky solenoid or an expensive servo-valve, often with a pilot stage and a power su > ply. The aim of ER research is to be able to influence a hydraulic mechanism directly with a current low enough to allow the integration of a system made up of electronic transducing and signal-conditioning equipment, computer processors and feedback monitoring, solid-state controllable field-excitation... 

Variable gap transducers are often used in feedback systems, like force-balance accelerometers, since the mass displacement is held very smaU - within the linear zone - by the servo control. 

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