The ceramic spar sets the length of travel, and the system has the advantage that when no motion is commanded, the fingers act as a brake and prevent stage motion. ![]() The piezo elements are parts of a high-Q, high-frequency, resonant LC tank circuit. The combination of extension and bending creates an elliptical motion of the tip, which can be used to impart motion to the stage. In this design, one or more ceramic fingers are preloaded against a ceramic spar, and piezo elements are used to drive the fingers in an oscillatory motion against the spar. ![]() Resonant piezo actuator offers extended travel (from millimeters to meters) with moderate resolution and is the most practical implementation of the piezo effect for travels beyond the range of stack actuators. In general, piezo stages with internal preload and closed loop position feedback can be useful positioners, but will provide limited travel, may be longer and more expensive than desired, and will be limited to moderate servo bandwidths unless the payload mass is quite small. The high Q of this resonance can complicate efforts to notch it out, and the end result is often that a lower than desired servo bandwidth must be accepted. The payload mass and the stiffness of the piezo stack produce a high Q resonance, the natural frequency of which can be surprisingly low for realistic tooling and part masses. When operated in closed loop mode, an additional concern arises. While the use of a linear position feedback transducer and a closed loop servo control can overcome hysteresis and drift, compared to the inherent simplicity of an open loop voltage commanded piezo stack, this comes at a considerable added cost and complexity. The motion in the piezo actuator continues to slowly creep after a position step. This can be as much as 15% of full travel.
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