Various scenarios exist where it is desirable to delay the initiation of an event until some time after an initial shock or acceleration. By way of example, in order to prevent premature detonation, many munition rounds, such as artillery shells, go through a multi-stage arming sequence after being fired. It is required that the sequence commence only after the shell has been fired, and for this purpose a delay after firing is imposed in the procedure.
One way of providing the necessary delay is by the use of an accelerometer. One problem with the accelerometer, however, is that it requires not only a power supply but a signal processor as well. Such arrangement needs a significant volume to package the necessary components, which is impractical for various situations, including use in a munition round.
The delay may also be accomplished by an inertial delay mechanism, one of which is known as a falling leaf delay mechanism comprised of a plurality of interlocking masses wherein a subsequent mass is prevented from moving until the previous mass has moved out of the way. The typical falling leaf delay mechanism is comprised of a first series of masses rotatable about a first post and a second series of masses, interlocked with the first series, rotatable about a second post. Each mass, except for the first, occupies a plane above a previous mass. When the mechanism is subjected to a shock, a first mass of the first series is moved out of position allowing a first mass of the second series of masses to move out of position. That is, movement of a mass allows the next interconnected mass to move out of position. A last of the masses to move includes an activation member to activate some event, the activation occurring after a time delay imposed by movement of the totality of all the masses, subsequent to the initial shock.
Existing falling leaf designs require masses, which are individually machined, followed by an assembly process. The required assembly is either by hand, a time consuming process, or by expensive machine placement. In addition, present designs are relatively large for placement in munition rounds and do not respond to relatively low acceleration environments.
It is an object of the present invention to provide an inexpensive miniature inertial delay device which can respond to low accelerations and which is fabricated utilizing MEMS (micro electromechanical systems) techniques.
A MEMS inertial delay device is provided which includes a substrate, an intermediate layer on the substrate, and a device layer on the intermediate layer. The device layer includes first and second spaced-apart support members secured to the substrate by the intermediate layer, and a plurality of interlocked masses, each connected to one of the first or second support members by a spring arrangement. The interlocked masses and the spring arrangement are devoid of any underlying intermediate layer so that the interlocked masses and the spring arrangement are freely moveable. The principles of the present invention may be applied to a free-standing inertial delay device which includes first and second spaced-apart support members with a plurality of interlocked masses, each connected to one of the first or second support members by a spring arrangement. The masses are all in the same plane and are positioned between the first and second support members.
The invention will be better understood, and further objects, features and advantages thereof will become more apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings, in which:
In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals.
Although the present invention is applicable for use in a variety of situations, it will be described, by way of example, with respect to the arming of a munitions round, such as an artillery shell.
The slider 16 may move out of position to allow firing by means of an arm command 18, however the slider is constrained from movement by lock 20, and lock 21, acting as a back-up safety, engaging respective projections 23 and 24. Once lock 20 is moved out of position, lock 21 may thereafter may be moved out of position to allow slider 16 to move whereby detonation may subsequently take place. Lock 20 is moved out of position after a certain delay after the firing of the artillery shell, and the lock movement is accomplished by an inertial delay device of the present invention.
After lock 20 is moved out of the way, as illustrated in
Inertial delay device 44 is one of a multitude of identical inertial delay devices fabricated on the same wafer 36, with all of the inertial delay devices being separated after fabrication for use as individual inertial delay devices. As illustrated in
The last mass 57 includes an extension 62 which functions to move an activator 64 which is connected to the first lock 20 in
The etchant will, in a relatively short period of time, dissolve the insulation beneath the springs 60, since they are of small width, thus freeing them for movement. In order to shorten the time for dissolving the silicon dioxide under masses 50 to 57, they are provided with a series of apertures 66 which extend from the top surface down to the insulating layer 40, thereby allowing the etchant direct access to the undersurface of the masses. Although some of the etchant dissolves the insulation under the supports 47 and 48, the process of freeing the masses 50 to 57 and springs 60 is completed before the supports are completely freed so that they remain immovable.
In response to an initial shock in the direction of arrow 68, the first mass 50 will move out of position, in the direction of arrow 69. This movement frees the second mass 51 for movement and the process is repeated until all the masses 50 to 57 are unlocked, as in
In the absence of any shock, mass 74 remains immobile and prevents movement of the subsequent masses 75 to 77. If the device is subject to a shock in the direction of arrow 90, mass 74 will move in the direction of arrow 91, thus freeing the remaining masses for movement. The last mass 77 includes an activator 92 for operating a mechanism, such as the removal of a lock, as previously described. The unlatched condition of the inertial delay device 72 is illustrated in
It will be readily seen by one of ordinary skill in the art that the present invention fulfills the objects set forth herein. After reading the foregoing specification, one of ordinary skill in the art will be able to effect various changes, substitutions of equivalents and various other aspects of the present invention as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents. Having thus shown and described what is at present considered to be the preferred embodiment of the present invention, it should be noted that the same has been made by way of illustration and not limitation. Accordingly, all modifications, alterations and changes coming within the spirit and scope of the present invention are herein meant to be included.
The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor.
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