An inertial switch is a switch that can change its state, e.g., from open to closed, in response to acceleration and/or deceleration. For example, when the absolute value of acceleration along a particular direction exceeds a certain threshold value, the inertial switch changes its state, which change can then be used to trigger an electrical circuit controlled by the inertial switch. Inertial switches are employed in a wide variety of applications such as automobile airbag deployment systems, vibration alarm systems, detonators for artillery projectiles, and motion-activated light-flashing footwear.
A conventional inertial switch is a relatively complex, mechanical device assembled using several separately manufactured components such as screws, pins, balls, springs, and other elements machined with relatively tight tolerance. As such, conventional inertial switches are relatively large (e.g., several centimeters) in size and relatively expensive to manufacture and assemble. In addition, conventional inertial switches are often prone to mechanical failure.
One acceleration switch is manufactured using a layered wafer and has a movable electrode supported on a substrate layer of the wafer and a stationary electrode attached to that substrate layer. The movable electrode is adapted to move with respect to the substrate layer in response to an inertial force such that, when the inertial force per unit mass reaches or exceeds a contact threshold value, the movable electrode is brought into contact with the stationary electrode, thereby changing the state of the inertial switch from open to closed. The MEMS device is a substantially planar device, designed such that, when the inertial force is parallel to the device plane, the displacement amplitude of the movable electrode from a zero-force position is substantially the same for all force directions.
There is a need for a low-G MEMS acceleration switch. There is a further need for a MEMS acceleration switch that is insensitive to transverse loads. There is a further need for a MEMS acceleration switch that does not have the current flow through the entire device and provides for lower resistance in the closed state.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.
The device is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” or “some” embodiment(s) in this disclosure are not necessarily to the same embodiment, and such references mean at least one.
A motion-sensitive low-G MEMS acceleration switch, which is a MEMS switch that closes at low-g acceleration (e.g., sensitive to no more than 10 Gs), is proposed. Specifically, the low-G MEMS acceleration switch has a base, a sensor wafer with one or more proofmasses, an open circuit that includes two fixed electrodes, and a contact plate. During acceleration, one or more of the proofmasses move towards the base and connects the two fixed electrodes together, resulting in a closing of the circuit that detects the acceleration. Sensitivity to low-G acceleration is achieved by proper dimensioning of the proofmasses and one or more springs used to support the proofmasses in the switch. In addition to high sensitivity in the direction of interest, the proposed switch is insensitive to transverse loads during acceleration and does not have the current flow through the entire device thereby providing for lower resistance in the closed circuit state.
In various other embodiments, the low-G MEMS acceleration switch 10 for activation at a load less than 10 G may be dimensioned for a lower G activation load that does not exceed 5 G, 3 G, 2 G and the like.
In some embodiments, the MEMS acceleration switch 10 is substantially insensitive to transverse load, which is a load applied in a direction perpendicular to the intended axis of measurement (sensitive axis), with zero or minimum displacement along the sensitive axis when the transverse load is applied, e.g., a given transverse load results in less than 1% of displacement along the sensitive axis than if the same axial load is applied along the sensitive axis, i.e., the axis of measurement. As such, the MEMS acceleration switch 10 provides a displacement along the sensitive axis that is substantially independent of the transverse load. In addition, a transverse load as high as 10 times (or more) than the nominal range (e.g., anywhere between 1 and 10 Gs) does not result in closure of the switch.
In the example of
In some embodiment and as illustrated by the example depicted in
While the invention has been described and illustrated with reference to certain particular embodiments thereof, those skilled in the art will appreciate that various adaptations, changes, modifications, substitutions, deletions, or additions of procedures and protocols may be made without departing from the spirit and scope of the invention.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the appended claims.
This application claims priority to U.S. Provisional Patent Application No. 61/410,211, filed Nov. 4, 2010, and entitled “Low-G MEMS Acceleration Switch,” and is hereby incorporated herein by reference.
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Number | Date | Country |
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2005216552 | Aug 2005 | JP |
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Translation of JP 2005216552 A, downloaded Nov. 18, 2013. |
Number | Date | Country | |
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20120111703 A1 | May 2012 | US |
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61410211 | Nov 2010 | US |