Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF INVENTION:
Field of Invention
The present invention relates to an inertia
switch for sensing shock or vibrations imparted to an
object to which the switch is secured, and wherein the
switch consists essentially of a pair of spaced-apart,
electrically-conductive contact plates, each having at
least one cavity therein in opposed aligned relationship
with a metal ball loosely captive between the pair of
cavities and in contact therewith to establish an electri-
-~ cal conductive path through the ball, and wherein the ball
engages each of the cavities at at least two contact
points.
Description of Prior Art
Inertia switches having metal balls which are
displaceable by shocks or vibrations to effectuate a
switch function to inditate a disturbance are known.
There are many known types of such switches and some of
these utilize magnets or other means to retain the metal
ball at a predetermined position. Once the ball is
displaced the switch requires mechanical or electrical
resetting. A major disadvantage of inertia switches is
that many of these must be mounted in a precisely oriented
manner in order to operate. Accordingly, such switches
have found limited utility. A still further disadvantage
of inertia switches which utilize balls is that often the
electrical contact between the ball and the contact
element is serious affected by the infiltration of dust
particles or other foreign matter within the switch
casing.
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The improved inertia of the present invention
is an improvement over the shock and vibration sensitive
switch as disclosed in U.S. patent No. 4,467,153. In that
patent there is described a switch construction in which
two E-shaped electrodes are mounted in a frame member in
planar alignment, one on opposite sides, and define dual
cavities between the arms of the electrode. Two cylin-
drical conductive members are retained loosely captive
between the two cavities formed between the E-shaped elec-
trodes. The circumference of the cylindrical element is
such as to contact two arms of the electrodes to establish
a contact thereacross. Accordingly four contacts are
established by the two conductive cylinders and the elec-
trodes. A major disadvantage of this switch construction
is that it can only operate effectively when positioned
vertically along its longitudinal axis. Therefore, it can
operate either right side up or up side down. If the
housing is mounted at a slight angle from its axis, its
sensitivity is minimized and may produce false switch
closures and alarms. U.S. patent 4,185,180 also discloses
an inertia switch which utilizes two plates having a
through bore therein with an ondulated rim and a conduc-
tive rod element is captive between the aligned cavities
or through bores. Such switch also has a disadvantage of
having to be mounted at a precise orientation in order to
work. Thls type of unit has a shorter period of disconti-
nuity when vibrated.
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SUMMARY OF INVENTION:
It is a feature of the present invention to
provide an inertia switch for sensing shock or vibrations
imparted to an object and wherein the switch can be
oriented to any angle along a 360 arc.
Another feature of the present invention is to
provide an inertia switch for sensing shock or vibrations
imparted to an object, and wherein the switch includes a
pair of spaced-apart, electrically-conductive contact
plates having aligned facial cavities and retaining there-
between one or two metal balls providing four or eight
conductive contact points thereby providing better consis-
tency and less chance of false or unwarranted alarms as
compared with the prior art switches hereinabove
described.
Another feature of the present invention is to
provide an inertia switch for sensing shock or vibrations
imparted to an object, and wherein the switch may be used
in a burglar alarm system for detecting abnormalities of
vibration in machines, or in many other applications where
it is necessary to detect a shock or abnormal vibrations
such as with a washing machine, an automated milling or
lathe machine, etc.
The use of vibration sensors has long been
established as an effective way to monitor shocks and
vibrations. In order for the switch to be effective,
great care must be taken to ensure that the internal
switching components of the switch are free from moisture
or dust particles that can settle between the contact
points thereby rendering the switch ineffective. It is
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therefore another feature of the present invention to
provide an inertia switch wherein the switch contacts and
the metal ball operate in a dust and moisture-free
environment by locating same in a sealed housing.
According to the above features, from a broad
aspect, the present invention provides an inertia switch
for sensing shock or vibrations imparted to an objected.
The switch comprises a pair of spaced-apart,
electrically-conductive contact plates. Each plate has at
least one cavity therein. The plates are held in fixed,
spaced, parallel facial relationship to one another with ~;
the cavities facing and aligned with each other to consti-
tute at least one opposed pair of cavities. A metal ball
is loosely captive between the at least one opposed pair
of cavities so that the ball, when in a condition fo rest,
establishes four conductive contact points, two with each
of the plates.
BRIEF DESCRIPTION OF DRAWINGS:
A preferred embodiment of the present invention
will now be described with reference to the accompanying
drawings, in which:
FIGURE 1 is a fragmented perspective view of
the inertia switch of the present invention;
FIGURE 2 is a plan view of the construction of
the contact plates;
FIGURE 3 is a top view of the switch housing;
FIGURE 4 is an end view of the switch housing
as seen from the open side thereof;
FIGURES 5A, 5B and 5C are illustrations showing
the different orientations of the switch housing; and
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FIGURES 6A and 6B are fragmented plan views of
a prior art inertia swtich.
DESCRIPTION OF PREFERRED EMBODIMENTS:
Referring to the drawings, and more particu-
larly to Figures 1 to 4, there will be described the
construction and operation of the inertia switch 10 of the
present invention. As shown in Figure 1, the inertia
swith 10 is comprised of a housing 11 in which is retained
a pair of spaced-apart, electrically-conductive contact
plates 12 and 12'. The construction of these plates is
better illustrated in Figure 2, and as herein shown, they
are flat rectangular plates each having an integral
contact arm 13 and 13' respectively extending from a top
end edge 14 thereof. A palr of diamond-shaped cavities 15
are formed in each of the plates. These cavities are
herein shown as being through bores of rectangular or
diamond-shaped outline. However, it is within the ambit
of the present invention to cover other shapes of cavities
to achieve the desired result of the present invention as
described herein. It is also within the ambit of the
present invention to provide a single cavity in each of
the plates to constitute a single switching element, but
in order to achieve more sensitivity, it is desirable to
have two or more pairs of these cavities, each having a
contact metal ball 16 loosely captive by each pair.
The metal ball 16 is retained loosely captive
between each opposed pair of cavities 15, as shown in
Figure 1, and constitutes an electrically-conductive path
between the pairs of contact plates 12 and 12'. With the
diamond-shaped cavities, there is established two contact
points between the balls 16 and a pair of adjacent walls
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17 of the cavities 15. Accordingly, as shown in Figure 1,
the ball 16 has two contact points with the plate 12 and
two further contact points with the plate 12'. The ball
16' similarly has four contact points. Accordingly, there
is a total of eight contact points formed between the two
contact plates and the two balls. This provides for a
switch in which the occurance of false switch closures are
very unlikely due to the many contact points.
The contact plates and balls are retained
within a switch housing 11 which is comprised of a rectan-
gular casing having f langes 18 provided with screw
receiving holes therein for mounting the housing at a
desired position on an object to be monitored. The casing
has a cavity 20 with aligned slots 22 on opposed sides
thereof to precisely locate the contact plates in facial
parallel aligned relationship. When the plates are
disposed within the cavity 20 the contact arms 13 protrude
from the housing end wall 21. A cover 23 is then press-
fitted or otherwise welded by ultrasound, etc. in the top
opening of the cavity so that only the contact arms
protrude therefrom with the remaining part of the plates
and balls being substantially hermetically sealed to
prevent the ingress of dust particles or moisture. It can
be appreciated that the switch of the present invention is
easy to assemble in such a housing structure while
achieving precision in the disposition of the contact
plates and the balls. As can be seen, the diamond-shaped
cavities 15 have their apexes disposed transverse to the
opposed end and side edges of the plates 12, as is clearly
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shown in Figure 2. It is still further pointed out that
the contact plates, or at least the area surrounding the
cavities 15 and the balls, may be gold-plated to provide
corrosion-resistant contact paths.
An important advantage of the construction of
this inertia switch is its sensitivity making it respon-
sive to both high and low level shocks thus making it
appropriate for numerous applications. With particular
reference to Figures 5A to 5C, it can be seen that the
switch can be mounted sideways along the horizontal axis,
as shown in Figure 5A, and positioned at any angle in the
horizontal plane, as shown by arrow 24. The switch can
also be rotated on its longitudinal axis 25, as shown in
Figure 5B, or placed at any angle within a 360-circum-
ference of its transverse axis along a vertical plane, as
shown in Figure 5C. Accordingly, the switch construction
of the present invention permits its mounting and effec-
tive functioning at numerous positions thereby further
increasing its applications. For example, the switch
could be used as a built-in safety or override switch
which would detect abnormalities of vibration in an
operating machine to signal a control unit which can
initiate partial or total shut down of the machine.
The switch of the present invention is a
normally closed inertia switch particularly, but not
exclusively, developed for use in a burglar alarm system,
with the switch housing at various locations, such as on
windows, ceilings, floors and fences, just to name a few
applications, to detect vibrations imparted by an unwanted
intruder. The switch can also be mounted on a washing
machine, or any industrial machine, such as a milling or
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lathe machine, to initiate an alarm signal when the
machine or the appliance exceeds a predetermined amplitude
of oscillation. The switch would initiate a signal to
cause a shut down. -
Figures 6A and 6B illustrate one of the prior
art switches as previously described wherein two E-shaped
electrodes 30 and 31 are mounted facing one another in
spaced planar relationship to align the cavities 32 formed
between the ends of the arms 33. A pair of metal discs 34
are held between an opposed pair of arms to establish a
contact point with each of said arms, as illustrated by
reference numeral 35. Accordingly, four contact points
would be established between the pair of discs and opposed
electrodes 30 and 31. A disadvantage of such switch, as
previously mentioned, is that having only four contact
points it is susceptible to fault and error.
Also, and more limiting is the fact that this
switch cannot operate when disposed at an acute angle or
on its side, as shown in Figure 6B. When disposed on its
side only one of the electrodes would be contacted by the
disc. Therefore, this type of switch housing has limited
applications, and was designed to be oriented specifically
along its vertical axis, as shown in Figure 6A.
It is within the ambit of the present invention
to cover any obvious modifications of the preferred
embodiment described herein, provided such modifications
fall within the scope of the appended claims.
