Bidirectional Operating Actuator (BOA)

Marshall Space Flight Center, Alabama

A generic actuator has been designed to amplify the piezoelectric effect. The Bidirectional Operating Actuator (BOA) amplifies the stroke of a piezoelectric element and reorients it through a kinematic linkage.

Piezoelectric transducers are typically capable of low-strain and high-force output. The strain of a piezoelectric device is less than 0.1 percent. The force output per unit area of a piezoelectric device can be as high as 40 MPa. Piezoelectric actuators are desirable because of their direct conversion of electric potential to mechanical work. Typically, piezoelectric actuators are used in situations that require high-precision micromotion.

The Bidirectional Operating Actuator is a device for increasing the stroke output of a piezoelectric transducer.

A longer piezoelectric stroke is often needed. The stroke can be increased using a variety of methods. The most common method of piezoelectric stroke amplification is to use a bender element. In this case, a piezoelectric wafer is bonded to a substrate to form an "active" bimetallic strip. When a voltage is applied, the extension or contraction of the piezoelectric is converted to bending of the beam. Actuators used in this configuration are usually high-stroke, low-force devices.

Another method of increasing the stroke of a piezoelectric is to use a kinematic mechanism. The mechanisms can be simple lever arms or four-bar-type linkages. The most important factor in the design of a kinematic linkage is the use of flexure hinges - joints cut into a solid piece of material. The thin section of the joint is compliant in one direction, stiff in other directions.

Another significant consideration with piezoelectric transducers is the type of load on the material. Since piezoelectric is a ceramic material, it is not able to withstand large tensile or bending loads. The best way to avoid tensile loads is to apply a preload to the transducer, which allows the piezoelectric to operate in compression only. With a preload, the piezoelectric provides extension while the preload provides the return force. Preloading insures firm mechanical mating between the piezoelectric and the surrounding mechanism.

This work was done by David V. Newton and Ephrahim Garcia of Garman Systems Incorporated, for Marshall Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Mechanics category, or circle no. 152 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).

Inquiries concerning rights for the commercial use of this invention should be addressed to