Measuring and testing – Speed – velocity – or acceleration – With output transmitting mechanism
Reexamination Certificate
2000-06-07
2002-09-24
Kwok, Helen (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
With output transmitting mechanism
Reexamination Certificate
active
06453746
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to devices to discriminate between competing modes of acceleration, and more particularly to micromechanical devices therefor.
BACKGROUND OF THE INVENTION
There are numerous circumstances in which a certain action is to be taken if and only if a particular acceleration-time history is experienced. Perhaps the most common such circumstance involves the decision to trigger the inflation of an air bag in a moving vehicle.
It is now clear that undesired air bag inflation is an event often associated with serious injury of direct and indirect origin. As a result, whereas it is important that an air bag inflate properly when conditions require (i.e., during a crash), it is perhaps more important that it not inflate under non-threatening acceleration exposures, such as driving over a curb, or panic braking. In fact, safety statistics suggest that it is safer if air bags do not inflate in minor collisions.
To address this problem, it is first necessary to properly characterize the loading pattern associated with serious automobile crashes. For the purposes of this specification such details are not important, as the devices described herein have broader applicability. However, it is not difficult to understand that different types of collisions and other loading events will have quite different signatures. Dropping a wheel in a pothole will have an acceleration limited by the response rate of the shock absorbers. A fender bender will exhibit little more acceleration than an abrupt stop. A more serious collision, however, will show accelerations associated with the strength of the automobile's crumple zones and the relative velocity of the collision. Such accelerations, sustained for a period indicating a serious collision, should trigger the airbags. Otherwise, one is safer to depend on passive safety equipment. Similar considerations apply to transverse loading, as in side collisions.
However, simple and reliable sensors for a combined acceleration-time profile are few and far between. It is relatively easy to provide a sensor which will not produce a signal until a certain acceleration threshold is passed, but to include the additional requirement that the acceleration continue for at least a minimum length of time has required electronic circuitry to integrate sensor measurements, or complex and tricky hydraulic damping mechanisms to postpone sensor operation.
There is thus a need for a simple, robust, and reliable mechanism for discrimination of combined acceleration-time exposures. We address this need through introduction of a new type of micromechanical acceleration sensor.
SUMMARY OF THE INVENTION
The invention is of an acceleration history discriminator, in which a sense mass shuttle responds to external acceleration by moving as directed by a shuttle motion guide. The speed at which the sense mass shuttle moves is limited by a motion damper, which controls the shuttle speed to a level roughly proportional to the applied acceleration. When exposed to a predetermined acceleration-time history, these discriminators can produce a simple or coded signal which can direct a useful action, such as triggering an automotive airbag.
REFERENCES:
patent: 2641457 (1953-06-01), Carleton
patent: 2653019 (1953-09-01), Dreisbach
patent: 4825697 (1989-05-01), Huber
patent: 5239866 (1993-08-01), Froidevaux
patent: 11-151831 (1999-06-01), None
Plummer David W.
Polosky Marc A.
Dodson Brian W.
Kwok Helen
Sandia Corporation
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