Miniature omnidirectional instantly responsive impact switch

This miniature omnidirectional impact switch has a generally cylindrical electrically conductive mass held by coil spring bias in abutment with a conductive header wall at one end of a cylindrical housing. The mass has a blind bore in one end. The mass is held axially tilted by contact between a free end of a wire conductor and an end wall of the bore. A closed circuit is defined between a second conductor contacting the header wall and the first conductor, via the mass and header wall. The switch is responsive to an impact applied to the other end of the housing or to a side thereof within 200 microseconds after impact to open the closed circuit by separating the mass from the header wall and the end of the first conductor against the spring bias. A movement of the mass of 0.001 of an inch is sufficient to open the closed circuit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the art of electrical acceleration switches of 
the type having a mass movable in a housing against a spring bias in 
response to an applied force, and more particularly concerns a miniature 
omnidirectional switch instantly responsive to an impact of sufficient 
magnitude to open normally closed contacts in the switch. 
2. Description of the Art 
A typical miniature acceleration switch of a type described in prior U.S. 
Pat. Nos. 4,746,774, and 4,789,762 has a cylindrical shell or housing 
closed by a header at one end. In the shell is a cylindrical mass movable 
axially or tiltable laterally against spring bias in response to forces of 
acceleration applied to the housing and mass. The displaced electrically 
conductive mass closes a normally open electric circuit between spaced 
electrically conductive terminals. 
The prior miniature acceleration switches have been found to respond too 
slowly to an applied impact in applications where the switch must respond 
to an impact in less than 200 microseconds. In the prior switches the 
electrical contacts are normally open and are spaced apart sufficiently so 
that externally applied random vibrations do not cause the switch contacts 
to close. The time required for the mass to move to close the open 
contacts upon application of an actuating force is several milliseconds or 
longer. The switch cannot respond fast enough where the response time must 
be 0.2 of a millisecond or less. Another disadvantage of the prior 
switches is that they are normally open and are not useable in 
applications where the switch contacts must be normally closed. Some of 
the prior switches are limited to respond to forces directed only axially 
of the housings in which the masses move. Other switches are limited to 
respond only to forces directed laterally or angularly to the axes of the 
housings. 
SUMMARY OF THE INVENTION 
The present invention is directed at overcoming the disadvantages specified 
above and other difficulties and disadvantages of the miniature 
acceleration switches heretofore known. A principal object of the 
invention is to provide an instantly acting miniature acceleration switch 
which will respond to an axial, lateral, or angular impact of sufficient 
magnitude in less than 200 microseconds to open contacts in the switch for 
50 microseconds or more. This open time is sufficient to actuate an 
associated external circuit. No known prior acceleration switch is 
sufficiently sensitive to meet these omnidirectional instant response 
requirements. 
According to the invention there is provided a miniature omnidirectional 
instant acting impact switch assembly having a cylindrical shell or 
housing in which is a generally cylindrical mass movable axially and 
tiltable angularly in response to a force of impact applied in any 
direction, with respect to the axis of the housing, to open the switch 
contacts. The range of movement of the mass is very small, being limited 
to not more than 0.001 of an inch, which distance the mass can instantly 
traverse in less than 200 microseconds. The mass normally bridges two 
spaced contacts electrically. A coil spring in the housing holds the mass 
in a fixed position with such static force that it requires 25 an impact 
of 500 G or more where G is a unit of acceleration applied in any 
direction to the switch housing to open the switch contacts. The inertia 
of the mass is such that the switch contacts will respond to the impact to 
open the switch contacts in less than 200 microseconds and will keep the 
switch contacts open for 50 microseconds or more, to allow the external 
circuitry time to recognize the open condition of the switch and to react 
accordingly. 
These and other objects and many of the attendant advantages of this 
invention will be readily appreciated as the same becomes better 
understood by reference to the following detailed description when 
considered in connection with the accompanying drawings in which:

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings wherein like reference characters designate 
like or corresponding parts throughout, there is illustrated in FIGS. 1-6, 
a miniature impact switch generally designated by reference numeral 10, 
embodying the invention. The new switch 10 has an electrically conductive 
cylindrical housing or shell 12 made of a metal such as nickel. The shell 
is closed at one end by a circular wall 14 and is open at the other end 
with an outwardly turned annular radial flange 16. Fitted into the open 
end of the housing 12 is a header 20 having an electrically conductive 
cylindrical skirt 22 terminating in a flat circular end wall 24 having a 
central aperture 25. The header 20 terminates at its outer end in a radial 
flange 23 abutting the annular flange 16 and welded thereto to secure and 
seal the header 20 permanently to the housing or shell 12. The header 20 
contains an insulative plug or filling 26 made of glass, ceramic, plastic, 
or other suitable insulative material. Extending axially through the 
center of the cylindrical plug 26 and bonded thereto is an electrically 
conductive lead wire 28 and terminating at an end 30 with an end surface 
31. The wire 32 is bonded to the inner side of the end wall 24 in direct 
electrical contact therewith. 
Disposed in the housing 12 is a cylindrical mass 36 made of a suitable 
metal such as brass which is highly conductive electrically. The mass 36 
extends axially almost the full length of the interior cavity 38 in the 
housing 12. A flat end wall 40 of the mass 36 is normally spaced from the 
end wall 14 a short distance exceeding the maximum distance the mass 36 
can travel axially upon longitudinal impact applied the switch 10. The 
mass 36 has a short central axial bore 42 with an end wall 45 at a mass 
end 44. The bore 42 is larger in diameter than that of the wire end 30. In 
actual practice the wire end 30 is about 0.020 inches in diameter. 
The mass 36 has a radial annular flange 46 at the end 44 which is held in 
contact with the outer side 24' of the end wall 24 at all times by an 
axially compressed coil spring 48 seated on a shoulder 47 of the flange 46 
at one end, and the other end of the spring 48 bears against the end wall 
14 of the housing 12. The flange 46 has a sharp circular rim 36' around 
the end wall 44. A side wall 50 of the flange 46 is slightly tapered or 
frustoconical in shape for reasons explained below. In addition a side 
wall 52 of the conical mass 36 is tapered slightly from its wider end at 
the shoulder 47 of the flange 46 to narrower end wall 40. The widest 
diameter of the side wall 52 at the flange 46 is substantially equal to 
the internal diameter of coil spring 48. At the end wall 40 of the mass 36 
the inside diameter of the spring 48 is larger than the diameter of the 
end wall 40 to permit the mass 36 to tilt angularly with respect to the 
axis of the housing 12 when an angular or lateral impact is imparted to 
the housing. The center of gravity 54 of the mass 36 is located on the 
longitudinal axis of the mass 36 and at a point between the shoulder 47 
and the end wall 40. 
The length of the wire end portion 30 is about 0.001 of an inch longer than 
the axial length of the bore 42 so that the mass 36 is very slightly 
tilted at an angle to the axis of the housing 12. The coil spring 48 tilts 
and holds the mass 36 in this tilted position with one of portion of rim 
36' of the flange 46 in firm contact with the outer end wall 24' of the 
header; see FIG. 3. The rim 36' is about 0.001 of an inch smaller in 
diameter than the diameter of the housing 12 at an internal wall 12'. This 
allows about 0.0005 of an inch clearance between the rim 36' and the wall 
12' to permit the mass 36 to tilt about 0.001 of an inch to separate the 
bore wall 45 from the wire end 31 to open the switch contacts. At all 
times, in the absence of an applied force of impact, the lead wires 28 and 
32 are in direct electrical contact or closed circuit via the mass 36. The 
electrical contact between the mass 36 and the header wall 24 is less than 
500 ohms. When an impact force is applied laterally, longitudinally or 
angularly, it is only necessary for the mass 36 to move from 0.0005 to 
0.001 of an inch to open the circuit between the wires 28 and 32 as the 
inner wall 45 of the bore 42 moves away from the end 30 of the wire 28. 
When a longitudinal impact is applied to the housing end wall 14 the mass 
36 moves axially against the spring bias. When a lateral or angular impact 
is applied to the mass 36 it tilts angularly at a point on the diameter of 
the rim 36' without binding or jamming at the housing 12 or at the spring 
48. In order to facilitate tilting movement of the mass 36, the largest 
diameter of the mass at the rim 36' of the mass wall 44 is substantially 
equal to the internal diameter of the housing wall 12'. From there, the 
flange wall 50 tapers inwardly radially as best shown in FIGS. 6 and 7. 
This construction permits the mass to tilt rather than rotate when an 
angular impact is applied to the housing 12. 
The impact switch 10 is constructed to respond within 200 microseconds when 
an external impact in excess of about 500 G is applied in any direction to 
the housing 12 which would open the switch contacts. The spring 48 applies 
sufficient circuit closure pressure or bias to the mass 36 so that it is 
held in tilted position and cannot be displaced by operational or random 
vibrations which normally do not exceed 20 G. For operational stability 
the space or chamber 38 in the housing 12 can be evacuated of air and 
filled with an inert gas such as helium, argon, etc., after which the 
housing is hermetically sealed and closed by welding the header 20 to the 
shell 12. To insure long shelf life, the housing 12 can be made of 
noncorrosive metal such as nickel. The mass can be made of brass plated 
with gold or other noncorroding metal. The conductors 28 and 32 are 
typically made of a nickel alloy such as Kovar.RTM.. The mass 36 and the 
header 20 are typically gold or silver plated for electrical conductivity. 
The overall length of the housing 12 will not be more than about one half 
inch and the diameter of the cylindrical body of the housing 12 will not 
be more than about a quarter of an inch. The leads 28 and 32 may be about 
one half an inch in length. The total weight of the switch 10 will be 
about one gram. Thus the impact switch assembly is truly miniature in 
size. It can be used in applications requiring response to an impact of 
sufficient magnitude such as 500 G or more, in less than 200 microseconds 
and the inertia of the mass 36 will be such as to keep the switch 10 open 
circuited for at least 50 microseconds. Prior acceleration switches cannot 
respond in such an extremely short time with omnidirectional sensitivity. 
The impact sensed by the switch assembly 10 can be a grazing impact of an 
object lasting only a few microseconds. Nevertheless, if the impact 
exceeds the 500 G threshold or bias, the switch 10 will respond within 200 
microseconds to open circuit the wires or leads 28, and 32, as the mass 36 
separates by as little as 0.001 of an inch from the outer end wall 24' and 
the wire end 31. The conductor lead wires 28 and 32 are close circuited by 
the spring bias on the mass 36. The mass is normally held in axially 
tilted position by the spring bias and because the conductor end 31 is 
axially longer than the axial length of the blind bore 42 in the end of 
the mass 36 by about 0.001 of 10 an inch. Since the mass 36 is held tilted 
only a small portion of the end 44 of the mass 36 contacts the header wall 
24, so only a small movement of the mass 36 is sufficient to open circuit 
the closed circuit members. 
It should be understood that the foregoing relates to only a preferred 
embodiment of the invention which has been by way of example only, and 
that it is intended to cover all changes and modifications of the examples 
of the invention herein chosen for the purpose of the disclosure, which do 
not constitute departures from the spirit and scope of the invention.