GB2046522A - Bi-stable inertia switch - Google Patents

Abstract

Apparatus for indicating that an acceleration greater than a predetermined acceleration has occurred; has a housing 41 with a liquid reservoir 47 and an adjacent gas region 43 having contacts 49, 51 therein; the liquid gas interface resisting deformation by interfacial tension, the arrangement of electrical contacts 49, 51 in the gas reservoir and the liquid reservoir being such that the liquid has at least a portion moved to establish electrical continuity between the electrical contacts upon the occurrence of a predetermined acceleration. The structure and arrangement of the contacts and gas and liquid reservoirs are such that a greater negative acceleration is necessary to restore the shock-switch to its "off" condition after it is moved to its "on" condition. The switch is, however, resettable by imparting a negative acceleration of sufficient magnitude. The switch may also be operated by lateral accelerations. <IMAGE>

Description

SPECIFICATION Bi-stable, resettable shockswitch This invention relates to apparatus for detecting shock, or acceleration; and, more particularly, it relates to apparatus for indicating remotely when a shock of a predetermined magnitude has been received by an apparatus on which a switch is mounted.

In the prior art there are a wide variety of electronic, mechanical and electro-mechanical apparatus to measure shock or acceleration. Most of these devices are large and complex and provide a constant output showing the present value of acceleration. There is a need however for small simple devices that can indicate merely whether a shock greater than a particular value has been received.

Such devices are useful when used with mechanical or electronic instruments, such as computer discs, scientific instruments and the like, that can be damaged if a shock is given them. It is often not possible with these instruments to otherwise determine if damage has taken place.

One such simple acceleration detector is described in U.S. Patent Specification No.4068613 which provides a hollow tube containing a reservoir of liquid and an adjoining plug of gas. If a large enough acceleration occurs, the liquid-gas interfacial barrier is broken to provide a visual indication that the acceleration has been received. It would be desirable, however, to have a remote indication that the acceleration has occurred United States Patent Specification No.3846,748 discloses a freely movable drop of mercury in an apparatus having pairs of contacts at ends to indicate when a vehicle is accelerating, decelerating, or moving at a constant velocity.United States Patent Specification No.4 138 600 disclosed apparatus in which, in response to forces such as gravity, inertia or the like, a conductive liquid is moved between four contacts in an upper chamber, six contacts in a central tube and four contacts in a lower chamber, providing an elaborate force response analysis capability. United States Patent Specification No. 3 869 588 discloses a switch having a conductive liquid for mounting in an automobile to distinguish the conditions of acceleration of the automobile. There is disclosed parallel and switch series arrays. United States Patent Specification No. 2679819 shows a shock indicating device such as a steel ball held in a bifurcated prong.

United States Patent Specification No.3623449 shows a recording instrument that will produce visual and electrical signals when a preset acceleration has been experienced, using a movable body.

United States Patent Specification No. 3739 191 shows a T-shaped structure having a central electrode and employed as vehicular deceleration or acceleration sensor employing cavitation phenomena in the electrically conductive liquid.

From a consideration of the foregoing prior art, it can be seen that there is a need for a simple, inexpensive sensor to indicate by an on off condition and a bi-stable mode of operation that a predetermined acceleration, or shock, has been received. Moreover, the prior art has been deficient in providing a reset able apparatus that is bi-stable.

In summary, what is desirable, but not provided by the prior art, is a simple inexpensive switch that is also: (1) bi-stable; (2) resettable by a greater negative acceleration; (3) remaining in an "on" condition once set unless acted upon by a greater negative acceleration; (4) settable buy a lateral impact that would trigger it but not be resettable by a lateral impact of the same magnitude.

It is accordingly an object of the present invention in meeting substantially all these requirements, to provide an improved apparatus that is simple and economical, yet will indicate remotely receipt of a predetermined shock, or acceleration; the improved apparatus of operating in a bi-stable mode.

It is the further object of the present invention to provide a simple, economical, remotely indicating apparatus that is bi-stable; that remains "on", once acted upon by the predetermined acceleration, requiring a greater negative acceleration to reset it once it is triggered into its on condition; that is resettable by imparting a negative acceleration of sufficient magnitude; and that can be moved into its "on" condition by lateral impact but that can not be moved into its "off" condition by lateral impact of the same mangitude.

These and other objects of this invention will become apparent from the descriptive matter hereinafter, particularly, when taken in conjunction with the appended drawings.

In accordance with the present invention, there is provided an apparatus for indicating that an acceleration greater than a predetermined acceleration has occurred, the apparatus being of the type wherein a deformable reservoir of an electrically conductive liquid is contained adjacent a non-conductive fluid in a suitable way such that the surface, or interfacial, tension of the liquid prevents the liquid from entering the area occupied by non-conductive fluid until an acceleration largerthan the predetermined acceleration causes disruption of the interfacial barrier defined between the conductive liquid and the nonconductive fluid. An electrical circuit is activated into the "on" mode if the acceleration is received. In the apparatus, the arrangement of completing or breaking electrical continuity can be employed for the "on" condition.A simple embodiment comprises a pair of electrical contacts located in the gas plug in a cylindrical bore having a liquid dropletthereacross such that the contacts are electrically bridged by the liquid when the above mentioned rupture occurs. A particularly preferred embodiment is one that provides an arrangement of contacts and conductive liquid reservoir where the latter is moved as an entity to establish electrical continuity upon receipt of the predetermined acceleration; that resists movement of the liquid back into the "off" condition until there is received an acceleration force greater than that which moved it into the "on" condition; that is resettable by imparting a negative acceleration of sufficient magnitude; and that has the property of being moved to the "on" position by lateral impact but that will not be reset by lateral impact of the same magnitude.

As indicated, means are provided for electrically communicating to a remote indicator or the like that the electrical continuity has been formed.

Fig. is a side view of the present invention.

Fig. 2 is an enlarged section taken along the line Il-Il, Fig. 1.

Fig. 3 is a cross sectional view of a partially assembled switch in accordance with one embodiment of this invention.

Fig. 4 is a cross-sectional view of the contact and plug already inserted in the embodiment of Fig. 3.

Fig. 5 is a side view, including a schematic of the electrical circuit, of the switch of Fig. 3 in the "off" condition.

Fig. 6 shows the partial movement of the liquid reservoir in being moved forward the "on" condition.

Fig. 7 shows the final stages of movement following deformation great enough to effect movement into the "on" condition.

Fig. 8 is a side elevational view of the switch in the "on" position where it resist movement back into the off position.

It should be borne in mind that this invention may be practiced by several embodiments, but only one will be described in detail. For example, it is immaterial whether an electrical circuit be completed or broken to establish an "on" mode, indicating that at least the predetermined acceleration has been received. Moreover, a variety of methods of holding a deformable reservoir of conductive liquid adjacent a non-conductive fluid, such as a gas, can be employed. Thus, specific embodiments could comprise the contacts of an electrical circuit being in the liquid reservoir so asto break the electrical continuity if the predetermined shock effected rupture of the interfacial barrier or movement of the liquid; or the contacts being in the gas phase such that the rupture and conductive liquid being moved between the contacts would complete the electrical circuit.Also specifically, the conductive liquid reservoir can be held between or within discontinuous coils or other configurations such that the rupture of the interfacial barrier will render the circuit discontinuous. When the term "rupture of the interfacial barrier" is employed herein, it includes the concept of moving a part or the entire reservoir such that the liquid is positioned intermediate the contacts to allow the electrically conductive liquid to bridge the gap. The simplest and preferred embodiment, however, is illustrated and described hereinafter.

Referring to Fig. 1, a glass tube 11 containing a reservoir of liquid 13 and a plug of gas 15 are shown in a side view. The gas and liquid meet defining an interfacial barrier 17. Due to surface tension, the interfacial barrier 17 resists deformation such that liquid 13 does not enter the area occupied by gas 15.

However, if an acceleration greaterthan a predetermined acceleration occurs then interfacial barrier 17 is ruptured and liquid moves into the area occupied by gas 15. The principles of this rupture and liquid movement are described in more detail in U.S.

Patent No.4,068,613; the descriptive matter of which is hereby incorporated by reference for details omitted herein.

Disposed at the end of the gas plug opposite the reservoir of liquid 13, is a metal annular tube 19 and a metal wire 21 separated by an insulator 23. A cross-section of glass tube 11 metal tube 19, wire 21, and insulator 23 is shown is Fig. 2. Metal tube 19 fits snuggly within glass tube 11 and is sealed therto by a ring of epoxy resin 25. Wire 21 and insu;ator 23 fit snugly within metal tube 19 to completely seal the end of glass tube 11. A ring of glue 27 holds insulator 23 to tube 19. A second wire 29 is soldered to metal tube 19 at a location outside of glass tube 11. Wire 29 is covered by insulation 31 except at the point of soldering. Thus, it can be seen that two separate and insulated electrical pathways are provided into the area of gas plug 15.These pathways are electrically bridged only when liquid 13 moves into the gas region because of a rupture of intervacial barrier 17.

As indicated hereinbefore, the detector, peruse, can be employed in almost any conventional circuit to afford a remote indication of receipt of the predetermined physical shock, or acceleration. As shown schematically, in Fig. 1, the wires 29 and 21 are attached to a voltage source 33 and a communication device such as a bell or light 35 in order to warn an observer of the occurrence of physical shock, or acceleration, greater than the predetermined accelerations. Specifically, the relay 37 is energized when the interfacial barrier 17 is ruptured and the liquid bridges the two contacts, wire 21 and metal tube 19.

In order to electrically bridge the two contact areas provided by tube 19 and wire 21, the liquid 13 must be electrical conductor. In addition, the liquid must have a suitable surface tension in order to resist rupture of the interfacial barrier 17 prior to receiving an acceleration greater than the predetermined acceleration. Any of the conductive liquids; such as, those described in U.S. 4,068,613; can be employed. For example, aqueous solutions of inorganic salts can be employed. Mercury has been employed satisfactorily in operating devices, both for its surface tension and conductivity. An aqueous solution of 30% ethylene glycol has been found satisfactory for surface tension tension; and has adequate conductivity, particularly with ionic additives, such as NaCI or LION, for most purposes.This solution has the further advantage of a relatively low freezing point, since ethylene glycol is an antifreeze.

In operation, glass tube 11 is attached to a location where shocks are to be monitored. The voltage source 33 and communication device 35 (i.e. lights or bells) can be remotely located if necessary, since the lengths of wires 29 and 21 are adjustable. Until a shock greater than the predetermined acceleration occurs, the reservoir of liquid 13 cannot come into contact with metal tube 19 or wire 21. However, when an acceleration greater than the predetermined acceleration occurs, then at least a portion of the liquid 13 escapes from the reservoir and electrically bridges the gap between metal tube 19 and wire 21. This closes the circuit and the communication device 35 is activated.

Another embodiment is illustrated in Figs. 38.

Therein, a housing 41 hastherewithin a chamber 43.

There is included a body of gas 45, Fig. 5, and a deformable reservoir of an electrically conductive liquid 47 adjacent the gas so as to define an interfacial barrier therebetween. The apparatus 11 includes first and second electrical contacts 49 and 51. The apparatus also includes means 53 for conducting electricity intermediate the first and second contacts for electrically communicating that the bridge has been formed and that predetermined acceleration has been received.

The housing 41, Fig. 3, may comprise any suitable structure. As illustrated, it comprises a glass tube having the bore 43 of substantially uniform diameter penetrating longitudinally therethrough. The contact 51 is connected, physically and electrically with its electrical lead, or conductor 55. The electrical conductor 55 is, in turn, sealingly connected with its end plug 57. The interconnection between the peripheral surface of electrical conductor 55 and the end plug 57 may be chemically, as by polyepoxy bonding resin; thermally, as by fusing the two surfaces; or any other suitable method.Preferably, the electrical conductor 55, Fig. 4, is formed of a conductive metal that has the contact 51 formed of Kovar or other alloy that will not amalgamate with mercury or otherwise interact with the liquid when liquid is moved to close the gap between it and the other contact 49. The first plug 57 is likewise sealingly connected with the housing 41, as by chemically or thermally bonding the contiguous walls together.

Thereafter, the switch is ready to be assembled by inserting the second contact 49 liquid reservoir 47, and end plug 59. Similarly as discussed with respect to the contact 51, the other contact 49 is preferably formed of Kovar or other alloy that will not react with the fluid into which in comes in contact; for example, will not amalgamate with the mercury when the mercury is the liquid.

An electrical conductor 61 is connected with the contact 49 and sealingly passes through-its end plug 59, similarly as described hereinbefore with respect to the electrical conductor 55 and its end plug 57.

The liquid is emplaced about the electrical conductor 61 on the exterior side of the contact 49, forming a doughnut shaped deformable reservoir of liquid back of the contact 49. The liquid is same liquid described hereinbefore, such as the mercury, or the aqueous solution containing sufficient electrolyte and antifreeze to be viable, and yet have a sufficient surface tension to remain as an entity and move as an entity with respect to the gas.

The gas 45 that is employed in chamber 43 adjacent the deformable reservoir of liquid 47 may comprise any of the satisfactory gases. Preferably the gas is an inert gas; such as, nitrogen, argon, helium, hydrogen or the like. By inert means that it does not react with liquid or with the electrical contacts 49, 51.

The gaseous hydrogen forms a superior arc suppressant, and hence is preferablyforthis reason. It is, however, more dangerous to work with because of its flammability and explosiveness. Thus from the point of view of safety the chemically inert gases, like argon, helium, nitrogen, are preferable. With the gas emplaced in the chamber 43, the end plug 59 with its contact and liquid, is sealingly inserted and connected with the housing 41 at the other end 63 of the bore. Of course, as indicated hereinbefore, the doughnut shaped deformable reservoir of the liquid 47 is emplaced behind the first contact 49 and the end 59, as can be seen in Fig. 5.

The electrical circuit, or means, 53 is the same as that described hereinbefore with respect to the battery 33, the alarm or light 35, and the relay 37 of Fig.

1.

The operation can be understood completely by referring to Fig. 58. Referring to Fig. 5, the switch is in its "off" condition without having received the predetermined acceleration. In Fig. 6, an acceleration has been received such the the deformable reservoir of liquid 47 will have been moved to violate the interfacial barrier it had previously had defining it. As can be seen, the annular aperture 65 through which the liquid is moved also has an annular aperture 65a that allows movement of the gas without having significant compression of the gas. In the position illustrated by Fig. 6, the liquid reservoir 47 will return and will not be moved into the "on" position. This is the type behaviour that is experienced to a greater or lesser degree by a shock less than the predetermined shock.

Referring to Fig. 7, on the other hand, a greater predetermined shock, such as the predetermined shock effects movement of the liquid reservoir to such an extent that it is irreversible and the liquid reservoir will move into the "on" position shown in Fig. 8 with the entire liquid reservoir intermediate the respective contacts 49, 51 and creating electrical continuity.

Once moved into the "on" position shown in Fig.

8, the liquid reservoir can not be returned to the "off" position of Fig. 5 in the absence of a negative acceleration greater than the predetermined acceleration. This is because the liquid now exists as an entity intermediate the respective contacts 49, 51; whereas, before it existed as a doughnut shaped reservoir that was more mobile. Thus the switch operates as a bi-stable switch that remains in the "off" position or the "on" position; and does not readily change with a small accelerational forces.

Moreover, the liquid reservoir will not be returned to the "off" position than the positive acceleration to move it into its "on" position.

It is noteworthy, however, that the switch can be reset by a negative acceleration of sufficient mag nitude. Expressed otherwise, a negative acceleration greater than the predetermined acceleration can be employed to return the liquid reservoir to its dough nut shaped "off" condition. In the "off" condition, of course, the liquid reservoir exsists between the contact 49 and its end plug 59. Moreover, since the reservoir exists in the "off" position in a doughnut shape, a lateral impact of the predetermined accel eration force will trigger it, or move it to the "on" position. On the other hand, since the reservoir exists as an entity in its "on" position, the same negative lateral impact will not reset it. In fact, a lat eral impact even larger than the predetermined acceleration will not effect movement of the switch liquid into its "off" position. A negative acceleration along the longitudinal axis, when largerthan the predetermined acceleration and depending upon the design of the switch, will, however, effect resetting of the switch so that it can be used repeatedly.

As discussed hereinbefore, the operation is simple and straightforward in that once the electrical continuity is made, the relay 37 is energized to effect energizing of the alarm, such as the light 35. Once the acceleration has been received, the switch remains in its "on" position to maintain the indication that the acceleration force has been received.

This is the usual operation.

From the foregoing, it can be seen that this invention provides all of the features delineated hereinbefore as desirable and not heretofore provided. It is specifically noteworthy that the small bi-stable switches are economical and are small; for example, on the order of diameter of the number 6 wire or less with a length of less than one-half inch. Consequently they are unobtrusive and readly attached to any container, object or the like. The electrical conductors are also small wires that do not add to the bulk or mass, so the whole apparatus is unobstrusive.

Although the invention has been described with a certain degree of particularity, it is understood that the present disclosure is made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention, reference for the latter being had to the appended claims.

Claims (8)

1. Apparatus for completing an electrical circuit and thereby indicating that an acceleration greater than a predetermined acceleration has occurred, comprising: a. a housing having therewithin a chamber; b. a body of gas contained in said chamber; c. a deformable reservoir of electrically conductive liquid contained in said chamber adjacent said body of gas so as to define an interfacial barriertherebet- ween; said reservoir of liquid being contained such that respective interfacial tensions and interfacial barriers are defined such that an acceleration greater than a predetermined acceleration effects movement of at least a sufficient portion of said liquid to establish electrical continuity between two contacts; d. first and second electrical contacts disposed in said gas in said chamber and adjacent each other with a gap therebetween such that on electrical circuit is not possible therethrough until said liquid bridges said gap; said first and second contacts and said liquid and gas being so conformed that said apparatus forms a bi-stable switch that is in a first electrical state such as electrically nonconductive, and referred to as "off" until acted upon said acceleration and is movable to a second electrical state such as electrically conductive, and referred to "on", when acted upon by said acceleration and remains "on" until acted upon by a greater negative acceleration, that is resettable from an "on" condition by imparting sufficient negative acceleration to move it to said "off' condition, that is turned on by lateral imparting of substantially said predetermined acceleration force and is not turned off by lateral imparting of a force of the same magnitude; and e. means for conducting electricity connected to said first contact and connected to second contact for electrically communicating that the bridge has been formed when connected in an electrical circuit and that said predetermined acceleration has been received.

2. The apparatus of Claims 1 wherein said chamber has sidewall and first and second ends, said liquid is disposed in a first said end and said gas is disposed in a second said end; a first contact having its first electrical lead extending through said liquid reservoir and said first end with said first contact adjacent said liquid; an annular aperture intermediate said first contact and said side wall such that said liquid can be moved through said aperture by said predetermined acceleration; said second contact being disposed in said chamber so closely adjacent said first contact that electrical continuity is provided when said liquid is moved from said first end by said acceleration; said annular aperture also being sufficiently large to allow movement of said gas concommitantly with movement of said liquid without significant compression of said gas; said second contact has its second electrical lead seal inglythrough and extending exteriorly of said housing.

3. The apparatus of Claim 2 wherein said liquid is mercury that moves as a deformable entity, is normally doughnut shaped and disposed about said first electrical lead in said "off" position and is an entity contacting said two contacts in its "on" position.

4. The apparatus of Claim 3 wherein said housing is tubular having a longitudinally extending bore and having plugs sealingly disposed at each end of said bore defining said chambertherebetween; said plugs having respectively said electrical leads extending longitudinallytherethrough.

5. The apparatus of Claim 4 wherein said first contact has sufficient room between it and a first one of said plugs for said mercury and said second contact is closely adjacent said second of said plugs.

6. The apparatus of Claim 1 wherein said means for conducting electricity do not interact with-said liquid.

7. The apparatus of Claim 6 wherein said liquid is mercury and said means for conducting electricity includes contacts of a metal that does not amalgamate in the appreciable extent with said mercury.

8. Shock detector and indicator apparatus substantially as hereinbefore described with reference to the accompanying drawings.