The Piezohydraulic Actuation Principle – Recent Advancements from Ultrafast to Long-Stroke Drives
W. Zoels, A. Goedecke, G. Bachmaier
Siemens AG, München, Germany
Piezoelectric actuation and (micro-) hydraulics has seen its successful marriage in a number of commercially successful piezohydraulic systems, from automotive piezo injectors to electro-hydrostatic actuators in the aerospace industry.
The piezoelectric stack actuator, with its high force and stiffness, is complemented surprisingly well by its combination with a micro-hydraulic transmission. Vibrations and resonances, which can lead to common failure modes of leveraged piezo actuators, are effectively suppressed by the excellent damping characteristics of the hydraulic system. By using the fluid pressure as a transportation medium, the displacement of the piezo crystal can be amplified, transformed, integrated and delivered to the point of action with negligible losses. The flexibility and robustness of this approach makes piezohydraulics an attractive actuation principle for many applications.
Moreover, in contrast to traditional hydraulic systems with a central pump and hydraulic pipes leading to comparatively simple hydraulic piston actuators, the power in piezohydraulic actuators is generated close to where it is needed. By replacing heavy and bulky hydraulic leads by light and flexible electric cables, a good power-toweight ratio can be achieved.
This presentation presents recent advances in the state of the art of piezohydraulic actuators as well as examples for successful commercial applications. An especially attractive application area for piezohydraulic actuators are harsh environments. Full encapsulation by means of metal bellows yields highly reliable piezohydraulic actuators. The metal encapsulation makes the devices virtually impervious to dust, aggressive chemicals or other airborne contaminants. In addition to that, by using the hydraulic leads as a thermal barrier, high temperature applications could be demonstrated. As a use case example, the application of a harsh environment piezohydraulic actuator in a
high-temperature environment will be shown.
Metal encapsulation also ensures that the hydraulic system has zero leakage, making the actuator clean enough to be used in systems where hydraulic systems were previously deemed too contaminating. A successful adaption of the piezohydraulic actuator principle to a clean-room manufacturing environment in the semiconductor industry will be shown.
However, the most promising applications are projected to be in the area of robotic drives and human-machine cooperation. By combining the high power density of the piezoelectric actuator with hydraulic stroke integration by means of check valves, fast long-stroke actuators can be built. The flexibility and versatility of hydraulic circuits makes it easy to built additional functionality like variable impedance or back-driveability directly into the actuator hardware. In contrast to traditional approaches utilizing closed control loops for the same purpose, the hardwareonly approach could potentially offer advantages in regard to safety, reliability and certification. To demonstrate the possibilities, prototypes of piezohydraulic artificial muscle-type actuators recently built in our lab will be shown.
ACTUATOR 2014 Manuscript A5.1
Publication date: 08/04/2015
Manuscript A5.1 published in Conference Proceedings ACTUATOR 2014
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