Optical: systems and elements – Lens – With support
Reexamination Certificate
2000-01-18
2001-11-20
Mack, Ricky (Department: 2873)
Optical: systems and elements
Lens
With support
Reexamination Certificate
active
06320707
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to lightweight optics, including micro-optics and fiber optics translation. More particularly, the invention relates to a piezoelectric translator having a bridge geometry and a relatively large translation length.
BACKGROUND OF THE INVENTION
Background Art
Modern day aircraft and spacecraft, and particularly modern day military platforms, typically make use of a large number of optical components. Due to the physical characteristics of light, most electro-optical applications require alignment between one or more optical components. For example, the most basic function of launching light into an optical fiber requires alignment of the fiber with the light source. Typically, the light source will be a laser and the application will require high accuracy beam pointing. Such a configuration is commonly used in applications such as optical scanners, laser designators or projector systems. Another type of application involves the positioning of microlens arrays, which typically need to be moved for tens to hundreds of microns in one or two dimensions. Movement in such small proportions is termed “translation” in the optics industry and is the subject of much attention. Other applications include laser communications, laser radar and optical steering for unmanned airborne vehicles.
Conventional approaches to translating optical elements have employed piezo rod actuators to provide the required displacement. Rod actuators, however, are heavy, large, non-planar and bulky. These limitations have hindered the development of optical systems for airborne and space applications as well as other electro-optical systems requiring compactness and a large translation length. Translation length is defined by the amount of displacement achievable for a given voltage and rod length. Thus, rod actuators require a relatively large rod length for very small translation lengths. Typically, translation lengths are on the order of one micron per millimeter of rod length for applied fields of about 20 kV/cm.
Translation length is also affected by the weight of the optical element being displaced. For example, a typical lens array can weigh as little as 80 grams. This relatively small weight does not require the force generated by rod actuators. It is therefore desirable to enable relatively large displacements of lightweight optical elements at higher speeds and in very compact actuation systems.
It would further be desirable to provide a method and device for providing relatively large displacement of a micro-optic element using a small voltage. It will be appreciated that power consumption is often just as critical to optical applications as size. Accordingly, a large translation length is needed.
It would also be highly desirable to provide a method and system having inherent mechanical amplification. Such a system would allow increased compactness and lower voltages. It would also be desirable to provide high accuracy feedback to increase the speed of actuation. Conventional rod actuators are sluggish due to their size, weight and feedback problems.
It will be understood that displacement on the order of tens of microns is significantly affected by environmental effects. For example, slight fluctuations in temperature can result in changes in material properties which cause a substantial amount of system noise. It is therefore highly desirable to provide a micro-optic translation system with temperature compensated designs and/or compact and effective environmental isolation.
SUMMARY OF THE INVENTION
The above and other objects are provided by a preferred piezoelectric translator and method for translating lightweight optical elements such as micro-optics, mini-optics, or fiber optics. The piezoelectric translator includes a platform supporting the optical element and a piezo bridge actuation system for displacing the platform. A position sensing system provides feedback to the actuation system regarding displacement of the platform. The actuation system includes a plurality of bridge actuators wherein each actuator includes a flat piezoelectric ribbon and a metal bridge, similar to a leaf spring, bonded to the ribbon, such that each actuator forms a piezoelectric bridge having a slender geometry. Single-, and double-span piezoelectric bridges can be constructed for effecting pure translation, pure rotation, or mixed translation and rotation. Moreover, double-sided piezoelectric bridges can be constructed which can substantially increase translation at a given applied voltage. Similarly, stacks of single and/or double-sided bridge actuators can be constructed to further increase the translation at relatively low voltages.
The method for translating a lightweight optical element includes the steps of supporting the optical element with a platform and displacing the platform with a piezo bridge actuation system. Feedback is provided to the actuation system based on displacement of the platform. Furthermore, a leaf spring cap is bonded to a flat piezoelectric ribbon and the combination forms a thin strip, nearly one-dimensional actuator in the form of a piezoelectric bridge. The actuator is disposed along a perimeter of the platform and actuated to provide positive linear displacement of the optical element along a first axis. A second bridge actuator may be used to provide push-pull actuation and a greater control of translation of the micro-optic element. An alternative method to push-pull actuation is to replace one of the bridge actuators with a spring mechanism. Similar actuators on adjacent sides will allow full two-dimensional actuation. Placement of bridge actuators between the frames that hold micro-optic arrays can allow three-dimensional actuation and add optical focus control. A specific arrangement of using two independent bridge actuators or a double-span bridge actuator on each side of the optical or micro-optical element will add the capability to control micro-rotations, in addition to pure translation.
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Khoshnevisan Mohsen
Motamedi Manouchehr E.
Nelson Jeffrey Glenn
Neurgaonkar Ratnakar R.
Harness & Dickey & Pierce P.L.C.
Mack Ricky
The Boeing Company
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