US3731020A - Inertia switch with manually adjustable conductive spring arm assembly - Google Patents

Abstract

An inertia switch capable of detecting the arrival of stress waves from any direction in the plane of the mounting surface is disclosed. In a preferred embodiment, a plurality of conductive spheres are held in a plurality of corresponding recesses by spring arms. A pair of interconnected conductors on each recess surface form, with the conductive spheres, an electrical circuit which is broken if any of the spheres is moved outwardly of its recess against the spring by any impact or stress wave in the structure. Provisions are included for adjusting the switch sensitivity by adjusting the spring preload on the spheres.

Description

United States Patent 1 1 1111 3,73m20 York 1451 May 1, 1973 [54] INERTIA SWITCH WITH MANUALLY 2,921,999 1/1960 Ziegler, Jr. ..200/61.52

ADJUSTABLE CONDUCTIVE SPRING ARM ASSEMBLY Primary Examiner-J. R. Scott [75] Inventor: Kenneth C. York, Pomona, Calif. Attorney-Edward Johnson [73] Assignee: General Dynamics Corporation, [57] ABSTRACT Pomona Cahf' An inertia switch capable of detecting the arrival of [22] Filed: Jan. 17, 1972 stress waves from any direction in the plane of the mounting surface is disclosed. in a preferred embodi- [21] Appl' 218329 ment, a plurality of conductive spheres are held in a plurality of corresponding recesses by spring arms. A [52] US. Cl.....200/6l.45 R, ZOO/61.52, 200/ 166 BE pair of interconnected conductors on each recess sur- [51] Int. Cl. ..l-l01h 35/02 face form, with the conductive spheres, an electrical [58] Field of Search ..200/61.45 R, 61.53, circuit which is broken if any of the spheres is moved ZOO/61.11, 166 BE, 835, 835 A outwardly of its recess against the spring by any impact or stress wave in the structure. Provisions are in- [56] References Cited eluded for adjusting the switch sensitivity by' adjusting th 1 (1 th h UNITED STATES PATENTS Spmg pre 6 Sp ms 2,741,674 4/1956 Richard ..200/61.45 R 15 Claims 8 Drawmg Fgures 2,912,534 11/1959 Rowell et a1. ..200/61.45 R X 0, 54 l I b 1 1 12 14 a 36 1 34 2 I2 33 32 I I 4 4.

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I Patented May 1, 19 73 4 Sheets-Sheet 5 98 I4 90 I6 FIG. 4

FIG.5

INERTIA SWITCII WITH MANUALLY ADJUSTABLE CONDUCTIVE SPRING ARM ASSEMBLY BACKGROUND OF THE INVENTION Inertia switches are useful in a number of applications. Such a switch will respond instantly to a sudden acceleration or deceleration of a predetermined magnitude. A typical application is as a contact fuze for mortar or artillery shells. Inertia switches may also be used as safety devices, for example, to deenergize the electrical system of an automobile or aircraft in the event of a collision, or to shut down pumps, etc., in the event of an earthquake or nearby explosion. Inertia switches may also be used to activate an impact recorder in shipping containers for delicate instruments to show that permitted impact levels have been exceeded.

Many different types of inertia or impact switches have been developed for these various purposes. However, these designs still have several deficiencies. Simple switches tend to be responsive to inertial forces applied from only a single direction. Omnidirectional switches tend to be complex and unreliable.

The sensitivity of most prior inertia switches is low and generally no sensitivity adjustment is provided.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide an inertia switch of improved simplicity and reliability.

Another object of this invention is to provide an inertia switch capable of detectingstress waves from any direction in the plane of its supporting surface.

Still another object of this invention is to provide an inertia switch having adjustable sensitivity.

The above objects, and others, are accomplished in accordance with this invention by an inertia switch in which a plurality of recesses are formed in a support member, each of which has two spaced conductors on the recess wall, and conductive members, such as spheres, are positioned in the recesses in contact with the conductors. The conductors in the several recesses are interconnected so that with the members in place a single complete electrical circuit is formed through all of the conductors and members. This electrical circuit is broken by movement of any member outwardly of its recess. Thus, this assembly operates as a normallyclosed switch. A spring member mounted on the support has a plurality of spring arms which engage the members and bias them into the recesses. When the switch is subjected to acceleration or deceleration forces, inertial forces on some members will force them outwardly from the recesses against the spring force to open the circuit. Means are provided to adjust the spring force holding the members in place, to adjust the sensitivity to stress waves. Preferably, the recesses are formed around the support axis facing outwardly in a single plane parallel to the mounting plane of the switch, so that the switch will react to any stress waves traveling in that plane from any direction. While two spaced recess-and-member assemblies are often sufficient, for best multi-directional sensitivity four evenly spaced assemblies are preferred.

, The spring force adjusting means may be arranged so that all spring arms are adjusted simultaneously, or individual adjustment of each arm may be provided. If

operated at temperatures as high as l800 F. The simplicity of this switch permits substantial miniaturization; if desired, the maximum dimension may be as little as 0.4 inch.

BRIEF DESCRIPTION OF THE DRAWING Details of the invention, and of a preferred embodiment, will be further understood upon reference to a drawing, wherein:

FIG. 1 is a prospective exploded view of the switch;

FIG. 2 is a horizontal sectional view of the switch taken on line 2-2 in FIG. 3;

FIG. 3 is a vertical sectional view of the switch taken on line 3-3 in FIG. 2;

FIG. 4 is a horizontal sectional view of an alternative embodiment of the switch taken on line 4-4 in FIG. 5;

FIG. 5 is a vertical sectional view through the switch embodiment of FIG. 4, taken on line 5-5 in FIG. 4;

FIG. 6 is schematic horizontal section through the switch of FIG. 4 taken on line 66 in FIG. 5, together with schematic side views of the recess conductor arrangement; and

FIGS. 7 and 8 are vertical sectional views through a portion of a switch illustrating alternative spring adjustment means.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, there is seen an exploded view illustrating the component parts of the switch according to this invention. The switch is contained within a housing 10 which has a pair of ears 12 extending outwardly at the opposite sides of the housing base.

Housing 10 includes a cavity 14 which is cylindrical near the top and becomes inwardly-narrowing frustoconical in shape near the base, as seen in FIG. 3.

An insulating body generally designated 16, which may be formed from a ceramic or other dielectric material, is shaped to conform to cavity 14. Upper cylincrical portion 18 fits loosely within the cylindrical portion of cavity 14, while tapered lower portion 20 of body 16 matches the lower frusto-conical portion of cavity 16 (as seen in FIG. 3). Thus, as body 15 is pressed downwardly into cavity 14, the body is wedged tightly and securely in place through the full range of temperature change.

Body 14 also has a pair of generally rectangular cutouts 22 and 23 on opposite sides and a dished upper surface 24. Generally U-shaped spring member 26 fits within cutouts 22 and 23, with the center portion 28 bridging dished surface 24. As spring 26 is pressed downwardly, center portion 28 rests on ridges 30 bounding dished surface 24.

A pair of inwardly extending conical recesses 32 and 33 are provided at the lower ends of cutouts 22 and 23 (not seen in FIG. 1, but shown in FIGS. 2 and 3). A pair of conductive spheres 34 and 36 are positioned within recesses 32 and 33, respectively. As described below, spheres 34 and 36 normally bridge spaced conductors within recesses 32 and 33 to function as normallyclosed switches. A pair of insulating pads 38 and 40 on spring 26 press against spheres 34 and 36 to bias them into their respective recesses while insulating them from spring 26.

The open upper end of cavity 14 is closed with cover 42 which is preferably welded to housing 10. Belleville spring-washer 44 is compressed between cover 42 and shoulder 46 of body 16 to hold body 16 firmly in place within cavity 14.

An adjusting screw 48 is threaded through an opening in cover 42 to bear against center portion 28 of spring 26. As best seen in FIG. 3, as screw 48 is moved downwardly, center portion 28 of spring 26 is moved downwardly, slightly spreading the spring legs 'to decrease spring pressure on spheres 34 and 36. Thus, the force needed to move spheres 34 and 36 outwardly against spring 26 can be adjusted by screw 48.

External electrical connections to the switch are made through a conventional electrical connector 50 which is electrically connected to a pair of roll pins 52 and 54 embedded in openings in body 16. As is discussed below, roll pins 52 and 54 are electrically connected to conductors in contact with spheres 34 and 36 to make up the switch mechanism.

The internal switch structure will become more apparent upon reference to FIGS. 2 and 3, taken together. The conductive strips 56 and 58 are formed, such as by vapor deposition, from roll pins 52 and 54 down into conical recesses 33 and 32, respectively. A second pair of strips, 60 and 62, are similarly formed on the lower portions of recesses 33 and 32, respectively. Strips 60 and 62 are in electrical contact through a small conductive bead 64 pressed into a small opening between conical recesses 32 and 33. The resulting electrical circuit with spheres 34 and 36 in place then extends from roll pin 52 through strip 56, sphere 36, strip 60, head 64, strip 62, sphere 34, strip 58 to roll pin 54. This circuit is opened any time inertial forces move either sphere 34 or 36 out of the corresponding recesses against the restraining force of spring 26.

In order that the switch open when a selected inertial impact is received, it is important that the switch be firmly mounted with no looseness slack. Therefore, the switch base is provided with a downwardly extending frusto-conical portion 66 which wedges tightly into correspondingly tapered opening 68 in mounting plate 70. The force holding the switch in place is provided by a pair of straps 72 and 74 which engage ears 12. Straps 72 and 74 are in the nature of leaf springs to maintain tightness despite differential thermal expansion of the parts. Bolts 76 and 78 engage strap 72 and bolts 80 and 82 engage strap 74 to urge ears 12 downwardly.

The switch embodiment shown in FIG. 1-3 is primarily capable of responding to inertial forces from either direction along a single line, that line passing through the centers of spheres 34 and 36. Of course, the switch will respond to forces from other directions approximately in the direction of this line. An alternative embodiment of the switch which will respond to forces from any direction in the plane parallel to plate 70 is shown in FIGS. 4 and 5.

In this embodiment, as seen in FIGS. 4 and taken together, housing is substantially identical to that shown in FIG. 1-3. Hold-down ears 12 are provided and tapered lower portion 66 fits into tapered opening 68 to hold the switch in place.

Body 88, however, has four equally spaced cutouts 90, 92, 94 and 96 within which four arms of spring 98 fit. Each arm ends with an insulating pad 100 which, typically, presses a sphere 102 into a corresponding conical recess 104 (FIG. 5) as in the embodiment previously described. The spring pressure on the spheres is adjusted by means of adjusting screw 48. Again, body 88 is held in place within housing 10 by a Belleville spring washer 44.

Conductive strips formed on body 88 electrically connect the roll pins (one of which, pin 54, is shown) to the spheres and the spheres to each other. A schematic illustration of a typical conductor pattern is shown in FIG. 6. A conductive strip 106 extends downward from roll pin 54 (not shown) and across a portion of recess 104. Another conductive strip 108 is formed on recess 104, spaced from strip 106. When sphere 102 is in place in recess 104 it is in electrical contact with both strips 106 and 108. A conductive pin 110 extends through body 88 to connect strip 108 to a similar strip 112 on the surface of adjacent recess 114. When sphere 118 is in place in recess 114, it connects strips 112 and 116. A pin 120 connects strip 116 through body 88 to a similarstrip 122 on the opposite recess 124. Another strip 126 is formed on recess 124, spaced from strip 122. When sphere 128 is seated in recess 124, strips 122 and 126 are electrically connected. A pin 130 through body 88 electrically connects strip 126 to a similar conductive strip 132 on adjacent recess 134. Another conductive strip 136 is formed on the surface of recess 134, spaced from strip 132. Strip 136 extends upwardly to a second roll pin, not shown. When sphere 138 is seated in recess 134, it electrically connects strips 132 and 136. Thus, with all spheres in place, theelectrical path is as follows: from roll pin 54 through strip 106, sphere 102, strip 108, pin 110, strip 112, sphere 118, strip 116, pin 120, strip 122, sphere 128, strip 126, pin 130, strip 132, sphere 138, strip 136 and finally to the second roll pin. Movement of any of the four spheres away from its recess will interrupt this circuit.

Two alternative embodiments of the spring pressure adjusting means are shown in FIGS. 7 and 8. While each is shown used with the four-sphere switch, each is equally useful with the two-sphere switch embodiment.

FIG. 7 shows a means for independently adjusting each spring arm. Spring 140 rests on body 16 within housing 10 as in the previously described embodiment. Here, however, the center of spring 140 is supported on a pin 142. An adjusting screw means 144 is provided in cover 42 above each arm of spring 140. Downward movement of each screw decreases the pressure applied on the corresponding sphere by the corresponding spring arm. Thus, the pressure on all of the spheres may be exactly equalized, or the switch may be-made more or less sensitive to impact from a selected direction by varying the spring pressure on any one sphere.

An embodiment featuring positive switch sealing is shown in FIG. 8. While the previously described embodiments can be sealed by covering the adjustment screw switch with solder, an epoxy resin, etc., only the embodiment of FIG. 8 features both positive sealing and continued adjustability. As with the previously described switches, a spring 98 is supported on body 16 within housing 10. A cover 148 closes the open end of housing 10. A Belleville spring washer between cover 148 and body 16 keeps body 16 in place. In this embodiment, cover 148 has an enlarged center portion 150 which bears on spring 98. This center portion 150 is connected to the edges of cover 148 by a thin web or diaphragm 152. A bar 154 across cover 148 carries a central block 156 in which an adjustment screw 158 is threaded. Upward and downward movement of screw 158 moves portion 150 due to the flexible nature of web 152, thus increasing or decreasing pressure on the central portion of spring 98.

While specific propositions, sizes and arrangements of component parts have been shown in the above illustrations of preferred embodiments, these may be varied, where suitable, within the scope of this invention. For example, any desired number of sphere-andrecess sets may be used, as desired.

Other variations, ramifications and applications of the present inventions will occur to those skilled in the art upon reading this disclosure. These are intended to be included within the scope of the invention, as defined in the appended claims.

I claim:

1. An inertia switch comprising:

a. a body having a plurality of recesses formed therein;

b. a plurality of conductive members adapted to removably seat in corresponding recesses;

c. a first and a second fixed conductor secured along the walls of each recess so that a member seated in the recess completes a circuit from the first conductor through the seated member to the second conductor;

. said fixed conductors and conductive members arranged in series to provide an electrical circuit through all'of said fixed conductors and members seated in recesses which circuit is broken upon movement of any of said members away from a recess;

e. a spring means comprising a plurality of spring arms extending from a common base, each arm positioned adjacent to one of said members and biasing that member toward said corresponding recess; and

f. means to adjust the spring force applied to said members.

2. The switch according to claim 1 wherein said plurality of recesses includes two conical recesses on opposite sides of said body extending inwardly toward each other and said conductive members are spherical.

3. The switch according to claim 1 wherein said plurality of recesses includes four conical recesses arranged in one plane around said body, all of which extend inwardly toward a common point.

4. The switch according to claim 1 wherein said body is mounted within a housing, said body and housing having corresponding tapered portions, and a biasing means engages said body to force said tapered portions into intimate contact.

5. The switch according to claim 4 wherein said housing includes an outwardly extending frusto-conical portion adapted to be received in a correspondingly configured opening in a plate to which said housing is to be mounted and mounted means adapted to urge said housing toward said plate.

6. The switch according to claim I wherein said common base extends across one end of said body with said sprin arms extending from said base along the sides of said ody and terminating ad acent to eac conductive 8. The switch according to claim 7 wherein a single adjusting screw presses on the center of said common base, whereby the spring force of all of said spring arms may be adjusted simultaneously.

9. The switch according to claim 7 wherein the center of said common. base is supported by a pin mounted on said body, and an adjusting screw is positioned to bear on said base between said pin and each spring arm, whereby the spring force of each arm may be independently adjusted. 1

10. The switch according to claim 7 wherein said body is mounted within a sealed housing, the end of said housing adjacent to said common base being closed by a flexible diaphragm having a center portion bearing on said common base, and an adjusting screw external of said housing adapted to force said center portion toward said common base, whereby the force of said spring arms may be adjusted while maintaining seal integrity.

1 1. An inertia switch comprising:

a. a housing;

b. a body mounted within said housing;

c. said body and housing having corresponding tapered portions so that said body seats securely in said housing;

d. first spring means urging said tapered portions into contact;

at least one conductive inertial member located in a corresponding recess in said body;

f. second spring means adjacent to each inertial member biasing said member toward said recess;

. electrical current means disposed within and structurally attached to the surface of said recess adapted to complete an electrical circuit when said member is seated in said recess and open said circuit upon movement of said member from said recess.

12. The switch according to claim 11 further including means to adjust the pressure applied by each said second spring means to said members.

13. The switch according to claim 11 wherein said housing includes an outwardly extending frusto-conical portion adapted to be received in a correspondingly configured opening in a plate to which said housing is to be mounted and mounted means adapted to urge said housing toward said plate.

14. The switch according to claim 11 wherein said inertial members are spherical and seat in generally conical recesses.

15. The switch according to claim 14 wherein said recesses include four conical recesses arranged in one plane around said body, all of which extend inwardly toward a common point.

Claims (15)

1. An inertia switch comprising: a. a body having a plurality of recesses formed therein; b. a plurality of conductive members adapted to removably seat in corresponding recesses; c. a first and a second fixed conductor secured along the walls of each recess so that a member seated in the recess completes a circuit from the first conductor through the seated member to the second conductor; d. said fixed conductors and conductive members arranged in series to provide an electrical circuit through all of said fixed conductors and members seated in recesses which circuit is broken upon movement of any of sAid members away from a recess; e. a spring means comprising a plurality of spring arms extending from a common base, each arm positioned adjacent to one of said members and biasing that member toward said corresponding recess; and f. means to adjust the spring force applied to said members.

2. The switch according to claim 1 wherein said plurality of recesses includes two conical recesses on opposite sides of said body extending inwardly toward each other and said conductive members are spherical.

3. The switch according to claim 1 wherein said plurality of recesses includes four conical recesses arranged in one plane around said body, all of which extend inwardly toward a common point.

4. The switch according to claim 1 wherein said body is mounted within a housing, said body and housing having corresponding tapered portions, and a biasing means engages said body to force said tapered portions into intimate contact.

5. The switch according to claim 4 wherein said housing includes an outwardly extending frusto-conical portion adapted to be received in a correspondingly configured opening in a plate to which said housing is to be mounted and mounted means adapted to urge said housing toward said plate.

6. The switch according to claim 1 wherein said common base extends across one end of said body with said spring arms extending from said base along the sides of said body and terminating adjacent to each conductive member, and said body is depressed adjacent to the center of said common base, said common base supported on ridges on said body adjacent to said depression.

7. The switch according to claim 6 wherein an adjusting screw means is positioned to press on said common base adjacent to said depression, whereby the spring force of said spring arms may be adjusted by adjusting the pressure on said common base.

8. The switch according to claim 7 wherein a single adjusting screw presses on the center of said common base, whereby the spring force of all of said spring arms may be adjusted simultaneously.

9. The switch according to claim 7 wherein the center of said common base is supported by a pin mounted on said body, and an adjusting screw is positioned to bear on said base between said pin and each spring arm, whereby the spring force of each arm may be independently adjusted.

10. The switch according to claim 7 wherein said body is mounted within a sealed housing, the end of said housing adjacent to said common base being closed by a flexible diaphragm having a center portion bearing on said common base, and an adjusting screw external of said housing adapted to force said center portion toward said common base, whereby the force of said spring arms may be adjusted while maintaining seal integrity.

11. An inertia switch comprising: a. a housing; b. a body mounted within said housing; c. said body and housing having corresponding tapered portions so that said body seats securely in said housing; d. first spring means urging said tapered portions into contact; e. at least one conductive inertial member located in a corresponding recess in said body; f. second spring means adjacent to each inertial member biasing said member toward said recess; g. electrical current means disposed within and structurally attached to the surface of said recess adapted to complete an electrical circuit when said member is seated in said recess and open said circuit upon movement of said member from said recess.

12. The switch according to claim 11 further including means to adjust the pressure applied by each said second spring means to said members.

13. The switch according to claim 11 wherein said housing includes an outwardly extending frusto-conical portion adapted to be received in a correspondingly configured opening in a plate to which said housing is to be mounted and mounted means adapted to urge said housing toward said plate.

14. The switch according to claim 11 wherein said inertial members Are spherical and seat in generally conical recesses.

15. The switch according to claim 14 wherein said recesses include four conical recesses arranged in one plane around said body, all of which extend inwardly toward a common point.

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