Electrical generator or motor structure – Non-dynamoelectric – Charge accumulating
Reexamination Certificate
2000-04-07
2002-10-15
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Charge accumulating
Reexamination Certificate
active
06465929
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to the field of microelectromechanical systems (MEMS) actuators.
2. Description of the Related Art
Electrically controlled actuators receive an electrical signal input and provide a mechanical output. The mechanical output provides power (force times displacement, per unit time) that can be used to move objects. Large, electrically controlled actuators are common in mechanical systems to control valves, pumps, switches and otherwise move objects.
Recent innovations require control of very small components that are formed on semiconductor substrates by conventional semiconductor fabrication processes. Groups of such components are known as microelectromechanical systems (MEMS). MEMS borrow design elements from their larger, conventional-size, functional equivalents, but must be adapted to semiconductor fabrication techniques and the dynamic effects of miniature size. An often essential part of MEMS are actuators that provide physical movement or force to other MEMS components in order to operate, or initiate, the MEMS device.
In U.S. Pat. No. 5,808,384 a photolithographic process is used to fabricate a MEMS having an actuator that controls switches, relays, and valves. This actuator consists of a coil and magnetic core to move a member. However, this actuator is capable of only a very small range of motion and is thus limited to particular applications in which a relatively small range of motion is required.
Certain MEMS devices include relatively large planar objects that require a means to position the planar object for operation. In so-called “billboard” applications, a planar object is formed flat against a supporting wafer and must be moved upright for use (i.e., oblique to the wafer)—similar to how a billboard is arranged relative to its supporting ground surface.
U.S. Pat. No. 5,867,297 discloses such a billboard application in relation to a prior art MEMS optical scanner in which a mirror is fabricated in the horizontal plane (i.e., parallel to the wafer upon which the mirror is formed) and then lifted into a substantially vertical arrangement. The 5,867,297 patent states that a comb drive may be used “to facilitate this process” without disclosing how a comb drive could do so.
Electrostatic comb drives use principals of electrical capacitance to provide power to move an object. Electrostatic comb drives are comprised of two comb-shaped portions (“combs”) that are arranged so that a set of fingers of one comb is interdigitated with a set of fingers of the other comb. When a voltage is applied across the two combs, a capacitance is created between fingers of the respective combs that creates an attractive force urging the combs to move toward one another.
Comb drives may be linear, such that each comb includes parallel fingers projecting from a straight backbone, or rotary, wherein the fingers project radially from a curvilinear backbone. Inherent disadvantages of comb drives are its small range of motion and the forces generated are small.
In contrast to the motion produced by a comb drive, raising a billboard requires a relatively large range of motion and may require a relatively large force to start the movement or to push the billboard into a jig. Other MEMS devices may also require a large range of motion, including adjustable optical systems that have a large focal length.
Prior art devices that use comb drives to move an object through a large motion must compensate for the comb drive's small range of motion. One method uses two comb drives arranged orthogonal to one another to rotate a round drive wheel of a ratchet mechanism whereby the comb drives provide sequential pulling forces on the drive wheel and a pawl acts on the drive to prevent reverse motion so that the drive wheel rotates in one direction only. The ratchet mechanism is coupled to the object, such as the billboard structure, to raise the object to its desired orientation. Problems with such mechanisms include the large number or moving parts, which creates multiple failure modes and increases fabrication complexity, and the large area on the substrate (a so-called “footprint”) that is necessary for the parts. In contrast, ideal MEMS actuators are simple, compact, and easily fabricated.
SUMMARY OF THE INVENTION
The present invention provides a wafer-mounted microelectromechanical systems (MEMS) actuator that receives electrical input and provides a mechanical output having a relatively large range of motion.
A preferred embodiment of a MEMS actuator of the present invention includes a drive mechanism coupled to a pallet, and a drive member that is slideably coupled to a substrate wafer. Operation of the drive mechanism moves the pallet in-and-out of contact with the drive member so as to incrementally move the drive member. Movement of the drive member may be used to move other objects, such as raising a billboard or moving a lens.
In preferred embodiments, the drive mechanism is a comb drive, although other types of drive mechanisms are also suitable.
The drive member includes opposed rows of drive teeth located on inner margins of a channel formed in the drive member. The pallet has opposite edges that each include a row of pallet teeth, and the pallet is located in the channel, between the rows of drive teeth. The pallet and drive member are arranged so that when the drive mechanism moves the pallet, the pallet teeth move into, and out of, engagement with respective rows of drive teeth on the drive member. As explained below, when the pallet teeth move into engagement with the drive teeth, the drive member is moved incrementally. Repeated engagements of the pallet teeth with the drive teeth cause the drive member to move a desired distance. In preferred embodiments, the drive member is elongate and slideably coupled to the substrate and constrained to move along a desired drive axis.
The pallet teeth and the drive teeth are shaped so that the pallet teeth can mesh with the drive teeth. A preferred tooth design is a sawtooth pattern wherein each tooth includes a leading side and a trailing side. As explained in greater detail below, the orientation and arrangement of the respective sides determine a direction of motion, motion increment size, force, and other properties.
The pallet and drive teeth may be shaped to accommodate a particular application. The pallet and drive teeth may be made symmetrical so that the drive member may be driven in two directions, e.g., forward and backward. The pallet and drive teeth may be shaped to provide a greater incremental motion upon each contact or the respective teeth may be shaped to provide less motion per increment, but more force. The shape of the teeth may be further arranged to provide other advantages as may be desired for a particular application.
In operation, the pallet oscillates between the legs of the drive member so that the pallet teeth push against the drive teeth. When the pallet teeth are aligned with the drive teeth, and the pallet is pushed against the drive member, the teeth simply mesh and the drive member does not move. However, when the pallet teeth are misaligned with the drive teeth, meaning that the respective teeth are not in meshing alignment, and the pallet is pushed against the drive member, the drive member moves, in response to the force from the pallet, until the teeth mesh.
Repeated oscillation of the drive mechanism is necessary to move the pallet into repeated engagement with the drive member so as to incrementally move the drive member through its full range of motion.
The several preferred embodiments of the present invention provide different means for the misalignment of pallet and drive teeth, referred to above. In a first embodiment, the opposing inner margins of the drive member have offset teeth and the pallet teeth on the two pallet margins are aligned with one another. Then, when the pallet contacts a first one of the two inner drive member margins, the pallet teeth and drive teeth are, or become, aligned. But, now the opposing pa
Levitan Jeremy A.
Sinclair Michael J.
Ipsolon LLP
Perez Guillermo
Ramirez Nestor
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