United States Patent 3731022

A motion sensor for sensing shocks, vibrations or the like utilizing a pair of contacts mounted on vibratory supports so that when the supports vibrate the contacts close, completing an electrical circuit. The vibratory supports and the contacts are such that the quiescent deflections of the two supports in response to constant forces move the two contacts by the same amount to maintain a constant quiescent spacing between the contacts and hence a constant sensitivity of the device to shocks, vibrations or other irregular motions. The sensitivity is therefore constant for a wide range of different quiescent orientations of the device.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
200/61.45R, 200/61.48, 200/61.51, 200/61.53, 200/276
International Classes:
B62H5/20; H01H35/14; (IPC1-7): H01H35/14
Field of Search:
View Patent Images:
US Patent References:
3527906CENTRIFUGAL SWITCH1970-09-08Schwab
3193628Multiple circuit controller switch with elongated flexible contact member1965-07-06Wanlass
3141936Conductive springs and ball acceleration switch1964-07-21Boyle et al.
3001039Omni-directional inertial switch1961-09-19Johnson
2947830Vehicle alarm switch1960-08-02Goss
2666822Stop switch1954-01-19Pelletier et al.
2662945Electric switch1953-12-15Cockram
2132111Signaling mail box1938-10-04Honegger
2076251Antitilting device1937-04-06Rockola

Foreign References:
Primary Examiner:
Scott J. R.
What is claimed is

1. A motion sensor, comprising:

2. The motion sensor of claim 1, in which said first and second spring systems are secured to said base at adjacent positions and extend therefrom in the same direction in substantially parallel relationship to each other.

3. The motion sensor of claim 2, in which each of said first and second spring means comprises a cantilever-mounted leaf spring.

4. The motion sensor of claim 1, in which said first and second spring means comprise first and second coaxial helical coil springs.

5. A motion sensor, comprising:


This invention relates to apparatus for sensing motion of an object, and particularly to such apparatus which is mountable upon an object to provide indications of changes in the net gravitational and inertial forces acting thereon. In a preferred form, the invention relates to improved electrical contacting means for operating a pair of contacts in response to changes in acceleration of the base on which the contacts are supported.

There are a variety of applications in which it is desired to detect and provide indications of changes in the acceleration or in the gravitational field acting on a body. One specific use of such devices is in the sensing of the disturbance of the position of an object, or in detecting mechanical vibrations transmitted into the object.

One example of a practical application of such a device is in the detection of unauthorized movement of a portable object such as a vehicle. For example, a motion sensor installed upon a bicycle or other vehicle left unattended may be used to provide indications of unauthorized disturbance of the position of the vehicle so as to sound an alarm. Another practical use for such a motion sensor comprises detecting the presence of a trespasser by mounting a motion sensor so that sudden deflections or vibrations due to the presence of the trespasser are transmitted to the motion sensor. Military applications include, for example, motion-sensing fuses for land mines or for booby traps, and explosion sensors.

There are a variety of devices known for performing one or more of the above-identified functions. For example, it is known to employ a pair of contact structures, one of which is spring-mounted so that its contacting relation with the other contact changes in response to certain changes in the inertial and gravitational forces applied thereto. One form of such device may comprise a resilient spring for supporting a contact normally spaced from another fixed contact in such manner that a change of acceleration of the base on which the spring is supported will cause the spring deflection to change and close the contacts. A voltage applied between the two contacts will then cause a current to flow, which may be used as an indication of the motion causing the contacts to close. More particularly, such a spring may have different predetermined deflections for different steady accelerations or for different steady values of gravitational forces acting thereon, and the fixed contact will then serve to detect the extent of this steady deflection and thereby provide an indication of the gravitational and inertial force existing at that time. If such a spring device is resilient but not vibratory, i.e., is so heavily damped or so "lossy" moves between two different deflection positions produced by two different values of forces acting thereon without performing substantial oscillation, then the force for which the contacts are closed depends entirely upon the quiescent deflection characteristics of the spring.

A greater sensitivity, and a greater responsiveness to changes in motion of brief duration, are obtained when a vibratory spring arrangement is utilized for one of the contacts. With such an arrangement, a sudden change in the forces acting on the spring element will excite it into vibrations on either side of its quiescent deflection position, and if the force applied thereto thereafter remains constant at the new value, the oscillations will die out in a time depending upon the effective mechanical "Q" of the resonant spring element. Since the excursions in position of the spring member during such oscillations extend beyond the quiescent deflection positions thereof, the fixed contact may be placed so as to be contacted by the vibrating contact when it swings beyond its quiescent deflection position; or, viewing the matter from another aspect, for a given spacing between the two contacts, relatively smaller changes in applied forces will accomplish at least an instantaneous or intermittent contacting between the two contact elements than if one were to rely entirely upon the quiescent or static deflection of the spring element.

With such a vibratory structure then, the response of the structure to a change from a first to a second level of forces acting thereon in a direction along which it is capable of deflection, comprises an initial transient oscillatory or vibratory phase beginning at the time of the change in applied force, plus a steady-state or quiescent deflection of the resilient spring, the oscillations or vibrations thereafter dying down while the quiescent deflection continues so long as the new value of applied force continues at a steady value. Usually a spring device will be both resilient in the sense that it tends to return to its original rest position when a deflecting force is applied and then removed, and also vibratory in that it will react to the change in applied force to execute transient oscillations or vibrations. However, a resilient spring device need not be vibratory, since if it is sufficiently severely damped it will return to its original position when a deflecting force is removed, but will not vibrate substantially past that rest position.

While a fixed contact and an adjacent resilient, vibratory contact structure may be used as a motion sensor, in certain types of applications such an arrangement will have substantial drawbacks or limitations. I have found that such limitations or drawbacks arise particularly in applications in which the change in contact spacing produced by the quiescent or steady-state deflection of the spring is unnecessary and undesirable for the particular purpose; such applications occur where one is not interested in measuring the values of steady forces acting on the spring member, but merely wishes to sense changes in such forces, and the steady force component thus merely tends to obscure, or render less reliable, reproducible or accurate, the desired sensing of force changes.

As an example, consider a contact mounted on a spring and adjacent a second fixed contact, so that upon sufficient deflection of the spring the contacts will be closed. Also assume that the spring is mass loaded near one end, so as to increase the amplitude of its oscillations. Such a device, when placed in a gravity field, typically will have a static or quiescent deflection due to the action of the gravity field on the mass secured to the spring, and the extent of its deflection will vary depending upon the orientation of the structure with respect to the direction of gravity because the magnitude of the component of gravity directed transverse to the spring will vary. As a result, the spacing between the two contacts will also vary depending upon the orientation of the assembly with respect to the direction of gravity, and the amplitude of oscillation required to close the contacts will therefore also vary depending upon the orientation. Accordingly, the sensitivity of the device to changes in forces such as shocks or vibrations, for example, will vary with its orientation. There are a variety of applications in which it is desired that the sensitivity of such an assembly remain substantially constant, and yet that it be capable of use under different conditions of orientation with respect to the direction of gravity.

In one particular application with specific reference to which the invention will be described, a motion sensor is secured to a vehicle such as a bicycle so that when the bicycle is left unattended the sensor contacts remain open until such time as an unauthorized person may move the bicycle, thereby setting a spring-mounted contact into oscillation so that, near one extreme of its vibration, it touches the other contact to close an electrical circuit and sound an alarm. However, because the bicycle may be left in a large variety of orientations, the sensor will also have different orientations at such times, the component of gravity tending to close the switch contacts will be different, and accordingly the quiescent spacing between the contacts when the bicycle is left unattended will depend upon the rest orientation of the bicycle. This means that the sensitivity to changes in force, due to later non-uniform motion of the bicycle during its unauthorized removal, will also be different for different orientations. If the spacing of the contacts has been set in manufacture at such a large value as to prevent closing upon any fixed orientation thereof, then the device will be relatively insensitive, while if it is originally set so as to exhibit the desired high degree of sensitivity in one orientation thereof, the contacts may close when it is placed in a different fixed orientation, giving a false alarm.

Accordingly, in such an application the quiescent deflection of the spring not only changes the contact spacing unnecessarily, but in fact introduces an undesirable variation in the sensitivity of the device. It is then desirable to eliminate the effect of steady forces on the spacing between the contacts, while retaining sensitivity to changes in such forces due for example to shocks, vibrations, or other rapid changes in accelerations.

Accordingly, it is an object of the invention to provide a new and useful motion sensor.

Another object is to provide such a motion sensor which responds to changes in the inertial and gravitational forces acting thereon, at least along certain sensitive directions thereof, and yet is relatively insensitive, within predetermined ranges, to different steady values of such forces.

A further object is to provide such a sensor which is simple, inexpensive, compact and reliable.

A further object is to provide such a sensor which is purely mechanical in nature and requires no sliding parts or complicated mechanisms.

Another object is to provide a new and useful motion sensor which responds with substantially constant sensitivity to changes in the inertial and gravitational forces acting thereon, at least along one or more directions therein, when placed in different fixed orientations.

A further object is to provide a motion sensor of the vibratory contact type which has a substantially constant sensitivity over a wide range of orientations with respect to a gravity field in which it is located.


These and other objects and features of the invention are accomplished by the provision of a motion sensor of the class comprising first contact means, first support means for said first contact means, second contact means positioned adjacent the said first contact means, and resilient vibratory means supporting said second contact means so as to change its state of contact with respect to said first contact means when said vibratory means vibrate, which sensor comprises the improvement whereby said first support means is also resilient so as to be deflected in the same sense as said vibratory support means in response to steady inertial and gravitational forces acting thereon. Preferably the quiescent deflection characteristics of the first support means and of the vibratory support means are such that the contact means are deflected by substantially the same amount and in the same sense in response to different steady values of the component of gravitational and inertial force applied along a sensitive direction of the sensor, so that the spacing between the first and second contact means remains substantially fixed in the quiescent state of the sensor. The amplitude of vibration of one or both of the support means required to cause contacting between them is then substantially independent of such steady forces applied thereto. Where the above-mentioned different values of the component of steady gravitational and inertial forces are due to different orientations of the motion sensor with respect to the direction of gravity, the quiescent contact spacing and the sensitivity of the device to changes in accelerations due to shock, vibration, or similar irregular movement, then remain substantially the same despite differences in the orientation of the sensor at different times.

Preferably the resilient first support means is also vibratory, and preferably it has a vibration period differing from that of the aforesaid vibratory means so that the possibility of their vibrating in phase, and out of contact with each other, for any appreciable period of time is eliminated.

The preferred form of the sensor means of the invention will therefore have a sensitivity to changes in acceleration which is substantially the same regardless of the orientation of the sensor over at least a range of orientations thereof. Accordingly it will preserve the same sensitivity when the object on which it is mounted is placed in different orientations, or when it is mounted in any of a variety of orientations on a fixed object. In applications of the latter type, substantial practical advantages result from the fact that the sensor may be installed without requiring special critical mounting procedures and without the need to provide special orientations of mounting surfaces.


These and other objects and features of the invention will be more readily understood from a consideration of the following detailed description, taken in connection with accompanying drawings, in which:

FIG. 1 is an elevational view illustrating one use of the motion sensor of the invention in a bicycle alarm;

FIG. 2 is a block diagram showing the electrical function of the motion sensor in an alarm system;

FIG. 3 is a vertical section through one form of motion sensor embodying the invention;

FIG. 4 is a view taken along lines 4--4 of FIG. 3;

FIG. 5 is a fragmentary sectional view of a portion of the sensor of FIG. 3 as it appears when making electrical contact during use;

FIGS. 6 and 7 are perspective views of the spring loading masses in the sensor of FIG. 3;

FIG. 8 is a vertical section of another form of sensor according to the invention;

FIG. 9 is a side view, partly in section, of another form of the invention using leaf springs;

FIG. 10 is a view taken along line 10--10 in FIG. 9;

FIGS. 11 thru 14 are schematic side views showing the contacting arrangements usable in the device of the invention;

FIG. 15 is a schematic side view of another form of the invention.

FIGS. 16 and 17 are vertical sections of another form of the invention, shown in two corresponding different orientations; and

FIG. 18 is a vertical sectional view of another form of the invention.


Referring now to the particular embodiments of the invention illustrated in the drawings by way of example only, FIG. 1 illustrates a bicycle 10 having an alarm system 12 mounted on the frame element 14 by means of a clamping arrangement 16. As represented in FIG. 2, the alarm system may comprise a suitable battery 18 supplying operating current to alarm apparatus 20 when the sensor switch 22 is closed, but not when it is open. The sensor switch 22 is part of the motion sensor 24 mounted within the outer casing of the alarm system 12 in FIG. 1. Suitable circuitry for the electrical system of FIG. 2 is shown and claimed, by way of example, in the copending application, Ser. No. 144,104 of I.F. Bash and R.W. Horn, filed May 17, 1971 and of common assignee herewith. In general, the bicycle is normally left in a fixed rest position by its owner with the sensor switch contacts open so that no alarm occurs, but if the sensor switch contacts are closed, even momentarily, the alarm will be sounded and will continue thereafter for a predetermined length of time. Since suitable electrical circuitry for operating an alarm in response to closing of the switch contacts are known, and described for example in the above-cited copending application, the details of such circuitry need not be set forth herein.

Referring now to the particular form of the motion sensor 24 which is illustrated in FIGS. 3-5, an electrically insulating base means 30 supports an outer cylindrical shell of electrically insulating material 32. Also mounted on the base means 30 inside of the outer casing 32 are two coil springs 34 and 36.

Coil spring 36 is mounted so that, in the absence of lateral deflecting forces, its longitudinal axis extends along the axis AA' of the outer casing 32. At its right-hand end spring 36 surrounds closely a cylindrical surface portion 38 of the base means 30, and is held fixed thereto by the slideable insulating ring 40 surrounding the outer cylindrical surface of the right-hand end of the spring. Ring 40 may be adjusted axially to adjust the length of spring 36 cantilevered to the left of ring 40, this being the portion of the spring which is then free to deflect laterally. The last turn 42 of spring 36 extends outwardly through an opening 44 in the outer casing 32 to an external contact 46 connecting with electrical lead 48.

The left hand end of spring 36 is provided with a loading mass 49 in the form of a centrally apertured ring of metal. The leftmost coil of the spring 36 fits tightly into the annular peripheral recess 49a in mass 49 to hold the latter mass to the spring.

The spring 34 is mounted on base means 30 by means of the bore 50 extending axially through base means 30, the spring 34 forming a close spring fit with the interior of bore 50 yet permitting sliding adjustment of the axial position of the spring so as to set the length of the spring which is cantilevered to the left of the inner end 52 of the base means 30. The right-most end of spring 34 has a reduced diameter portion terminating in a pigtail extension 54, to which electrical lead 55 is soldered or otherwise secured in a manner to provide electrical contact therewith.

Spring 34 extends axially through the center of the aperture in the center of mass 49, and is provided at its leftmost end with the loading mass 56, secured thereto by means of the annular depression 58 into which the last coil of spring 34 extends.

The motion sensor of FIG. 3 is such that if it is so oriented that the mass 56 hangs directed downwardly in a gravity field, the axis of both of springs 36 and 34 will extend along the axis AA' of the outer casing 32. The inner surface 60 of the mass 49 comprises one electrical contact of the sensor, and the adjacent outer surface of spring 34 constitutes the other contact, and when these two surfaces contact each other an electrical circuit is completed between the leads 48 and 55.

If the motion sensor FIG. 3 is thus oriented with weight 56 directed directly downwardly in a gravity field, the spacing between contact surface 60 of mass 49 and the adjacent outer surface of spring 34 will be substantially the same as is shown in FIG. 3 wherein the axis of the motion sensor is at right angles to gravity, i.e., horizontal. More particularly, in the orientation shown in FIG. 3, both of the springs 34 and 36 are deflected downwardly by the action of gravity on the respective masses 56 and 49. However, the weights of the masses and the free lengths and stiffnesses of the springs 34 and 36 are selected so that, in the quiescent steady state conditions in a gravity field, spring 34 still passes substantially through the center of the opening in mass 49 and the inter-contact spacing remains the same. Similarly for other angular orientations of the sensor of FIG. 3, this spacing is substantially constant after the sensor has been left steady for a short length of time.

However, if the base means 30 is subjected to a change in acceleration so as to change the inertial forces acting on the masses 56 and 49, or if the gravitational field should change substantially, both of the springs 34 and 36 will be set into oscillation transversely of their lengths and electrical contact will quickly occur as shown in FIG. 5, wherein the mass 49 has vibrated sufficiently upwardly relative to spring 34 that its contacting surface 60 is in electrical contact with the lower side of the exterior of spring 34, thereby to close the electrical circuit between leads 48 and 55 at such time.

Because the quiescent spacing between the contact surface 60 and the outer contact surface of the spring 34 is the same for a wide range of variation of the angle of the sensor, with respect to an axis perpendicular to the plane of the figures, the sensitivity of the sensor to vibration or shock also remains substantially constant in these different orientations.

It is also noted that in the embodiment of FIGS. 3-5 the annular contact surface 60 surrounds the circular outer surface of spring 34 to provide a symmetrical arrangement about the longitudinal axis of the sensor, such that the sensitivity thereof also remains substantially constant for different orientations thereof about its longitudinal axis.

In the preferred arrangement, the natural periods of vibration of the mass-loaded springs 36 and 34 differ from each other, so as to avoid the possible condition in which both springs might oscillate at the same frequency and in the same phase at least for substantial periods of times, so as to delay or possibly even prevent their coming into electrical contact, although in many applications such a condition is unlikely to arise because of differences in starting phases of the oscillations of the two springs.

Thus when the motion sensor of FIG. 3 is installed as shown at 24, FIG. 1, the bicycle may be left vertical or nearly vertical, or left lying on its side or at some intermediate angle, with the alarm system turned on. Normally the alarm would not be turned on until the transient vibrations of the springs have substantially disappeared; if the alarm is turned on too soon, and spring vibrations cause closing of the contacts and sounding of the alarm, the system may then be turned off for a short period by the operator to allow the vibrations to subside further. If one thereafter attempts to steal the bicycle, even very slight irregularities in motion of the bicycle during such unauthorized removal will set the springs into vibration, causing the contacts to close and the alarm to be sounded. The contacts may be set very close together for high sensitivity, since different angles at which the bicycle is left will produce different quiescent deflections of one of the springs but a corresponding quiescent deflection of the other spring, so as to maintain the contact spacing and sensor sensitivity the same for these different orientations, as desired.

Without thereby in any way limiting the scope of the invention, the following example of an embodiment of the form of the invention shown in FIG. 3 is provided in the interest of complete definiteness. Spring 36 may have a coil diameter of about three-eighths inch, and be composed of phosphor bronze wire of about 0.016 inch diameter and 40 turns per inch in its unstressed state. Mass 49 may have a weight of about 0.0025 pounds, and the free length of spring 36 between the right-hand side of mass 49 and the left-hand side of cylinder 40 may be about five-sixteenths inch. Spring 34 may have a coil diameter of about 0.110 inch, and be made of phosphor bronze wire about 0.012 inch in diameter with about 56 turns per inch in its unstressed state. The free length of spring 34 from the left-hand end 52 of base means 30 to the right-hand end of the mass 56 may be about five-eighths inch, and mass 56 may have a weight of about 0.001 pounds. The quiescent spacing between the contacting surface 60 and the outer contact surface of the spring 34 is typically about 0.010 inch.

FIG. 8 illustrates a variation of the motion sensor shown in FIG. 3, which may be like that shown in FIG. 3 except for the details of the arrangement of the loading masses and contacting surfaces, corresponding parts being represented by corresponding numerals with the suffix A. Here the mass 56A has been extended along and outside the center spring 34A to provide a continuous solid contact surface opposite the contacting surface 60A of mass 49A, the latter contacting surface 60A being extended forwardly of the latter weight. This not only provides a better contacting surface arrangement, but also illustrates another controllably variable parameter available to the designer, namely the position of the contacting surfaces with respect to the corresponding spring elements. Thus because the contacting surface 60A is positioned to the left of the end of the spring 36A, it will experience a greater static or quiescent deflection in response to steady forces, thereby enabling use of a shorter spring or lighter mass for the same deflection, and different resonant periods for the two spring assemblies. Among the principal factors in any design are the stiffnesses of the springs employed, their lengths, the masses used to load them, and the positions and mountings of the contacts with respect to their respective spring structures.

FIGS. 9-14 illustrate embodiments of the invention utilizing leaf springs as the resilient vibratory support means for the contacts. In the embodiment shown in FIGS. 9 and 10, a pair of leaf springs 70 and 72 in the form of rectangular strips of spring material are supported on a common support block 76. For convenience, block 76 may comprise a center portion 76A to opposite sides of which the leaf springs 70 and 72 are cemented, the outer surfaces of the leaf springs then being covered by cemented end blocks 78 and 80 to hold them firmly in place and define clearly the beginning of the free portion of each leaf spring. Leaf spring 70 is loaded by a mass 82 made up of three metal blocks cemented to each other and to the leaf spring, while leaf spring 72 is loaded by a mass 84 made up of two blocks cemented onto opposite sides of it. For convenience in positioning the leaf springs with respect to the supporting block 76 and the masses 82 and 84, the leaf springs, the masses and the block may be provided with appropriate positioning holes 88 whereby a pin inserted through the aligned holes during assembly will assure proper location of the various elements.

The right-hand ends of the two leaf springs extend beyond the block 76 at 90 and 92 to provide contact areas for connection to a source of electrical current. Leaf spring 70 extends beyond the mass 82, as shown at 94, to provide one switch contact surface for the motion sensor, and leaf spring 72 extends beyond mass 84 and is then bent into a reverted shape so as to provide the other contact surfact 96 at a position slightly toward block 76 from mass 84.

It will be appreciated that the two leaf springs 70 and 72 are deflected in the same sense and by substantially the same amount in response to steady forces acting thereon, such as the force of gravity, and therefore the spacing between the contact surfaces 94 and 96 remains the same for different steady orientations of the sensor. However, when the support block 76 is subjected to a change in its acceleration, as by the application of shock or vibration thereto, both leaf springs will be excited into vibration generally along a direction perpendicular to their length and width, with different vibrational periods, and contact between the surfaces 94 and 96 will promptly occur even for relatively small magnitutes of shocks and vibrations. In this embodiment the springs 70 and 72 exhibit little or no deflection in the direction of their widths either in response to steady forces or in response to shocks, because of their stiffnesses in that direction. However, where the device is used as a sensor of unauthorized removal of property or of the presence of trespassers, the irregular motion transmitted to the base 76 will in almost every case produce a component in the direction for setting the leaf springs into oscillation, thereby closing the contacts to enable an alarm. The principal design variables in this embodiment are the locations and magnitudes of the loading masses, the lengths of the cantilever arms by which the weights are supported from the support block, and the lengths and orientations of the contacts extending from the leaf springs.

FIGS. 11-14 show schematically several variations which may be made in the leaf-spring sensor of FIGS. 9 and 10, corresponding parts being designated by the same numerals with a corresponding suffix letter. FIG. 11 utilizes a conductive contact 100 in the form of a metal strip secured to the leaf spring 70B and positioned in line with the center of the mass 82B so as to contact the leaf spring 72B on the side of mass 84B toward support block 76B.

In FIG. 12, the contact 102 is positioned beyond and below the mass 82C and in alignment with the center of the mass 84C, which serves as the other contact.

In FIG. 13, the leaf spring 70D is weighted at its end and leaf springs 72D and 73 are symmetrically placed above and below it, the latter two leaf springs, the masses 82D and 83 and their corresponding contact arrangements being substantially identical with each other. In this embodiment, one external electrical contact is made to spring 70D and the other connection is made to both of the leaf springs 72D and 73, so that a circuit is completed when either of the opposed contacts 106 or 108 touches center leaf spring 70D.

In FIG. 14, the arrangement is generally the same as that in FIG. 13, except that the two separate loading masses of FIG. 13 are replaced by a common mass 110 extending between the upper and lower leaf springs 72E and 73E, mass 110 being centrally apertured to permit passage therethrough of the center leafspring 70E. Two opposed screw contacts 112 and 114 are mounted in the common mass 110 with their contact tips pointed toward directly opposite sides of the leaf spring 70E.

In each of the variants shown in FIGS. 11-14, the parameters of the springs, masses and contact arms are selected so that when the sensor is oriented differently than shown in the figure, so as to change the component of gravity tending to urge the contacts together, the quiescent or steady-state spacing between the contacts will remain substantially the same because the leaf springs are deflected similarly by the same gravity forces under steady-state conditions. Also in each case a vibration, shock or similar change in acceleration imparted to the supporting block 76 will cause the leaf springs to vibrate so as to close the contacts, provide an electrical circuit through them, and thus produce an electrical indication of the motion to be sensed.

FIG. 15 shows another dual leaf-spring embodiment in which the two spring-loading masses and their geometrical arrangements are identical with each other. While suitable for many purposes, this form of the invention introduces the possibility that the two leaf springs will vibrate in the same phase and with the same frequency for appreciable lengths of time without contacting each other and, if the vibrations die down sufficiently rapidly, in some circumstances it is possible that they might not contact each other at all in response to relatively weak shocks or vibrations.

FIGS. 16 and 17 show an embodiment of the invention in which extension of a coil spring is utilized to provide the vibratory motion, rather than lateral deflection thereof. Thus the two coil springs 120 and 122 are supported from a common base 124, and electrical connections 126 and 128, respectively, are provided at the fixed ends of the springs. Respective loading masses 132 and 134 are provided at the opposite ends of the springs, and respective contacts 136 and 138 are secured to weight 132 and to spring 122, both of which are here assumed to be electrically conductive also. The springs are such that, when unloaded, they have available a range of motion for both compressional and expansional motion. Springs 120 and 122 are also provided with respective guides 137 and 139. When the motion sensor is mounted as shown in FIG. 16, with the masses extending downwardly along the direction of gravity, both springs will be expanded and a certain spacing will exist between the contacts. Any shock or vibration imparted to the support 124 will cause the masses to oscillate up and down, thus brining the contacts into engagement with each other and completing the electrical circuit.

Now if the arrangement is turned horizontal, i.e., to the position shown in FIG. 17 for example, the masses 132 and 134 are completely supported by the guides 137 and 139, the interiors of which are preferably lubricated and provide a sliding fit with the weights. Accordingly, both springs contract to their neutral state in the steady state condition, the contacts 136 and 138 moving by the same amount so as to maintain the spacing between them the same as in FIG. 16. Again, when vibration is imparted to the support 124, the springs will cause the masses to oscillate in a horizontal direction, in turn causing the contacts to close at least momentarily, thereby completing the electrical circuit. The device may be placed in any of a large range of orientations without changing the spacing of the contacts under steady-state conditions, so that the sensitivity to shocks and vibrations remains substantially the same despite differences in orientation.

FIG. 18 shows an arrangement generally similar to that of FIGS. 16 and 17 with the exception that identical springs and masses have been utilized in a symmetrical arrangement, with the advantage that uniformity of contact spacing can be assured without any special design procedures, since the two identical structures will always operate in the same manner in response to steady forces. However, this form has the same possible disadvantage in some applications as does the arrangement of FIG. 15, since the two periods of vibration are the same.

As will be seen from the embodiment of FIG. 18, if the two spring-mounted contact structures are the same, the quiescent contact spacing is always the same, as are the resonant periods of the two structures. In general, if one then modifies one of the structures to produce a difference in resonant period for the two structures, the centers of mass of the two loading masses will move by different amounts for different steady forces applied thereto, and if the two contacts are mounted to move with the centers of mass of the loading masses the quiescent spacing between the contacts will also change. However, by mounting the contacts so that they move by different amounts than the centers of mass of their corresponding loading masses, as shown in the other figures, this tendency for the quiescent contact spacing to change can be overcome even though the resonant periods are different.

In other embodiments of the invention load masses are not required, the weight of the spring itself causing the desired quiescent deflection and the desired vibratory characteristics.

In the embodiments of the invention described herein in detail, the two contacts are normally open and are closed to produce output indications. However, the invention may be embodied in devices in which the contacts are normally spring-biased in the closed condition (preferably lightly) and are opened by vibratory spring motion to produce electrical indications by breaking of an electrical circuit through the contacts.

While the invention has been described with reference to specific embodiments in the interest of definiteness, it will be understood that it can be embodied in a variety of forms differing substantially from those shown and described, without departing from the spirit and scope of the invention as defined by the appended claims.