U.S. patent number 3,731,022 [Application Number 05/198,219] was granted by the patent office on 1973-05-01 for inertia type switch with coaxial conductive springs.
This patent grant is currently assigned to Alcotronics Corporation. Invention is credited to Peter J. Loftus.
United States Patent |
3,731,022 |
Loftus |
May 1, 1973 |
INERTIA TYPE SWITCH WITH COAXIAL CONDUCTIVE SPRINGS
Abstract
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.
Inventors: |
Loftus; Peter J. (Middletown,
PA) |
Assignee: |
Alcotronics Corporation (Mt.
Laurel Township, NJ)
|
Family
ID: |
22732482 |
Appl.
No.: |
05/198,219 |
Filed: |
November 12, 1971 |
Current U.S.
Class: |
200/61.49;
200/61.45R; 200/61.53; 200/61.48; 200/61.51; 200/276 |
Current CPC
Class: |
B62H
5/20 (20130101); H01H 35/144 (20130101) |
Current International
Class: |
B62H
5/00 (20060101); B62H 5/20 (20060101); H01H
35/14 (20060101); H01h 035/14 () |
Field of
Search: |
;200/61.48,61.49,61.50,61.51,61.52,61.53,61.74,61.78,166BA,166J,61.45R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Scott; J. R.
Claims
What is claimed is:
1. A motion sensor, comprising:
a supporting base;
a first spring system secured to said base so as to turn with said
base, said first spring system comprising first spring means
supported at one end on said base, a first spring-loading mass
supported on said first spring means at a position spaced along
said first spring means from said base so as to deflect said first
spring means, and first electrical contact means on said first
spring means at a first point spaced along said spring means from
said base;
a second spring system secured to said base so as to turn with said
base, said second spring system comprising second spring means
supported at one end on said base, a second spring-loading mass
supported on said second spring means at a position spaced along
said second spring means from said base so as to deflect said
second spring means, and second electrical contact means on said
second spring system at a second point spaced along said spring
means from said base;
said first spring-loading mass being spaced further along said
first spring system than is said second spring-loading means to
produce different periods of free vibration for said first and
second spring systems and different static displacements of those
ends of said first and second spring means adjacent said first and
second spring-loading means, respectively;
said first and second electrical contacts being positioned so as to
be spaced apart when said first and second spring systems are
quiescent, and aligned so that the contact surfaces thereof are
closed to each other when said first and second spring systems are
deflected sufficiently in opposite directions;
said first and second spring systems differing from each other with
respect to the values of at least one of the parameters of loading
mass and spring stiffness, so that the static deflections of said
contact surfaces are substantially the same for different values of
gravitational and inertial forces acting on said spring-loading
masses.
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:
first coil spring means;
means mounting said first coil spring means to permit steady
lateral deflection and lateral vibratory motion thereof;
second coil spring means;
means mounting said second coil spring means to permit lateral
steady deflection and lateral vibratory motion thereof;
said first and second coil spring means having respective first and
second contact surfaces thereon positioned so that said contact
surfaces are spaced from each other by substantially a fixed
distance when said sensor is oriented in different quiescent
positions but contact each other when said first and second coil
spring means are set into vibration;
said first and second coil spring means being helical and coaxial,
and said first coil spring means being positioned inside said
second coil spring means.
Description
BACKGROUND OF INVENTION
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.
SUMMARY OF THE INVENTION
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.
BRIEF DESCRIPTION OF FIGURES
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.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
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.
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