Electrical generator or motor structure – Non-dynamoelectric – Charge accumulating
Reexamination Certificate
2000-03-29
2001-12-11
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Charge accumulating
Reexamination Certificate
active
06329738
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to microelectromechanical systems (MEMs), and more particularly relates to electrostatically-actuated structures for MEMs.
MEMs are increasingly being employed for a wide range of applications, in part due to the ability to batch fabricate such microscale systems with a variety of highly complex features and functions. Microscale sensing and actuation applications are particularly well-addressed by MEMs For many MEMs applications, electrostatically-actuated structures are particularly effective as analog positioning and tuning components within complex Microsystems. Electrostatic actuation provides a combination of advantages for the microscale size regime of MEMs, including the ability to produce high energy densities and large force generation, as well as the general ease of electrostatic actuator fabrication, and high operational speed due to relatively small mass. Indeed, for many MEMs applications, electrostatic actuation is preferred.
Electrostatic actuation of a structure is typically accomplished by applying a voltage between an electrode on the structure and an electrode separated from the structure. The resulting attractive electrostatic force between the electrodes enables actuation of the structure toward the separated electrode. This applied electrostatic force is opposed by a characteristic mechanical restoring force that is a function of the structure's geometric and materials properties. Control of the structure's position during actuation requires balancing the applied electrostatic force and inherent mechanical restoring force.
The electrostatic force is a nonlinear function of distance; as the structure moves toward the separated electrode, such that the electrodes' separation distance decreases, the electrostatic force between the electrodes typically increases superlinearly. In contrast, the mechanical restoring force of the structure typically is a linear function of distance. Due to this disparate dependence on distance, not all positions between the electrodes are stable. Specifically, at electrode separations less than some minimum stable separation characteristic of the structure, the structure position is unstable and causes uncontrollable travel of the structure through the remaining distance to the separated electrode. This instability condition, known generally as “pull-in,” is a fundamental phenomenon resulting from the interaction of the nonlinear electrostatic force with the linear, elastic restoring force of the structure being actuated. Generally characteristic of a electrostatically-actuated structures, pull-in instability is well-known to severely limit the fraction of an electrode separation gap through which such a structure can be stably positioned.
A separate but related limitation of electrostatically-actuated structures is the relatively high voltage level typically required to position such a structure through a relatively large stable actuation range. As a result of this limitation, in combination with the electrostatic pull-in limitation, electrostatically-actuated structures typically are not well-suited to produce a large range of actuation motion. But for many microscale positioning and tuning systems, such as optical systems, large ranges of travel, and analog tuning of position, can both be critically required. There thus remains a need for electrostatic actuation techniques that enable large ranges of travel and further that are optimized for actuator operation at the lowest possible operational voltage.
SUMMARY OF THE INVENTION
The invention provides electrostatic actuator configurations and actuation mechanisms that enable stable, large range-of-motion electrostatic actuation, achievable with relatively low actuation voltages.
In a first electrostatically-controllable actuator in accordance with the invention there is provided a stationary electrode, with an actuating element separated from the stationary electrode by an actuation gap. The actuating element includes a mechanically constrained support region, a deflection region free to be deflected through the actuation gap, and a conducting actuation region extending from about the support region to the deflection region. A commonality in area between the actuation region and the stationary electrode is selected to produce controlled and stable displacement of the deflection region over a displacement range, e.g., extending to a specified point in the actuation gap, when an actuation voltage is applied between the actuation region and the stationary electrode. This range of stable displacement, which can be stable bending, can extend to a point greater than about ⅓ of the actuation gap, or even through the full actuation gap. As a result, the invention overcomes the limitation of ⅓ gap actuation of conventional electrostatic actuation configurations.
In embodiments provided by the invention, the actuation region of the actuating element can be provided as a conducting region of the element. Alternatively, the actuating element can be insulating, with the conducting actuation region provided as a conducting layer disposed on the element. The stationary electrode can be provided as a conducting layer.
In accordance with the invention, the support region of the actuating element can extend from the actuating element to a plane that is coincident with the stationary electrode. For example, the actuating element can be suspended by the support region over a substrate on which the stationary electrode is disposed, to vertically separate the actuation region from the stationary electrode. The support region can be provided as, for example, a support post, with the actuating element provided as, e.g., a cantilever beam, a doubly-supported beam, a plate suspended by a central support post, or a plate suspended by a peripheral support post.
In a further electrostatically-controllable actuator in accordance with the invention there is provided a stationary electrode and an actuation element separated from the stationary electrode by an actuation gap. The actuation element includes a mechanically constrained actuation support region and a conducting actuation region connected to the actuation support region and free to be deflected through the actuation gap. An auxiliary element is provided, separated from the actuation element by an auxiliary gap. The auxiliary element includes a mechanically constrained auxiliary support region connected to the actuation element, and a deflection region connected to the auxiliary support region and free to be deflected through the auxiliary gap. The auxiliary gap is less than the actuation gap and is selected to produce controlled and stable displacement of the actuation region over a displacement range extending to a specified point in the actuation gap when an actuation voltage is applied between the actuation region and the stationary electrode. With this configuration, the displacement range of the actuation region, which can undergo bending through this displacement range, can extend to a point greater than about ⅓ of the actuation gap.
In embodiments provided by the invention, the thickness of the actuation element and the auxiliary element are further selected to produce the specified controlled and stable displacement of the actuation region. The auxiliary gap can further be selected to produce planarity of the auxiliary element deflection region during stable displacement of the actuation region. As with the first configuration above, the actuation region of the actuating element can be provided as a conducting region of the element. Alternatively the actuating element can be insulating, with the conducting actuation region provided as a conducting layer disposed on the element. The stationary electrode can be provided as a conducting layer.
In further embodiments, the auxiliary gap can be selected in conjunction with actuation region thickness, actuation region residual stress and actuation region Young's modulus to produce controlled and stable di
Deutsch Erik R.
Hung Elmer S.
Senturia Stephen D.
Addison Karen
Lober Theresa A.
Massachusetts Institute of Technology
Ramirez Nestor
LandOfFree
Precision electrostatic actuation and positioning does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Precision electrostatic actuation and positioning, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Precision electrostatic actuation and positioning will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2596644