Shock and vibration resistant electrical switch

First and second counterbalanced contact elements rotate about a common axis so that shock and vibration induced loads produce negligible moments on the contact elements with respect to their axis of rotation. Springs are included and arranged for snap opening and closing of the contact elements to minimize electrical arcing during opening and closing of the contacts.

The present invention relates to electrical switches and more particularly 
to an electrical switch which remains in the condition in which it is set, 
whether open or closed, even when subjected to mechanical shock or 
vibration. 
A conventional mechanically operated switch includes one or more fixed and 
one or more movable electrical contacts. When such a switch is subjected 
to mechanical shock, its movable contact(s), if initially engaged with its 
fixed contact(s), may be momentarily jarred open. This causes interruption 
of power through the switch which, of course, is undesired. To overcome 
this problem, the spring tension of switches has been increased but this 
increase of tension causes more severe contact bounce and stiffer switch 
operation. 
Another problem with ordinary switches is their relatively low switching 
speeds. When high currents are controlled, electrical arcs are generated 
during switch opening. This results in premature contact failure due to 
arc pitting. Stiffer springs have been used to increase the switching 
speed; however, as mentioned above, this increases contact bounce which is 
undesirable and also makes the switch more difficult to operate. 
A switch embodying the present invention has both contacts rotatably 
secured and balanced so that the axis of rotation passes through the mass 
center of gravity of each of the contacts. As a result, moments about the 
axis of rotation for each contact induced by mechanical shock loads are 
equal and therefore balanced.

In FIGS. 1 and 2, the movable elements of switch 2 are rotatable about axis 
22. These elements are pivotally secured to a support plate 4 which may 
comprise a housing of the apparatus to which the switch 2 is to be 
electrically connected or other supporting structure. Switch 2 includes 
two vane assemblies 6 and 8 which may be identical in construction. Vane 
assembly 6 includes a hub 10 having a shaft bearing aperture 12. A contact 
vane 14 is secured to the hub 10. A counterbalance vane 16 is secured to 
hub 10 diametrically opposite the vane 14. Vane 14 may comprise a sheet 
metal or other electrically conductive sheet material formed as a quadrant 
or other segment of a circular disc. Contact tab 18 may be part of the 
vane 14 and bent to be normal to the plane of the vane 14. The contact tab 
18 has a contact surface 20 on the far side. 
The counterbalance vane 16, which may be smaller in dimensions but of a 
thicker and heavier metal than the vane 14, in combination with the vane 
14 have a combined mass center located on the hub 10 axis of rotation 22. 
Vane 16 may also be a quadrant of a circular disc of metal, as shown. Vane 
assembly 8 being a mirror image of the vane assembly 6 has its elements 
which are similar to the elements of assembly 6 identified with the same 
numbers, but primed. Boss 24 is secured to plate 4 and includes a threaded 
aperture 26. Threaded shaft 28 has a bearing shaft 30 and an end cap 32 
and rotatably secures the vane assemblies 6 and 8 to the support plate 4 
via hubs 10, 10'. The bearing shaft 30 of the shaft 28 is passed through 
the apertures 12, 12' of the respective hubs 10, 10' and is threaded at 
threads 31 to the boss 24 threaded aperture 26. The cap 32 retains the 
hubs 10 and 10' on the bearing shaft 30. 
Actuating lever 34 is pivotally mounted to pin 36 which is secured to 
support plate 4. The lever 34 rotates about axis 38. Axis 38 is parallel 
to axis 22. Lever 34 comprises an arm 40 and two legs 42 and 44 extending 
in the same direction from arm 40. 
Leg 42 has an aperture 46; and leg 44 has an aperture 48. Vane 14 has an 
aperture 50 closely spaced to edge 52 of the vane. The vane 14' has an 
aperture 50' closely spaced to edge 52'. The position of the pin 36 with 
respect to the axis 22 and to the apertures 50, 50' and 46, 48 is such 
that when the switch is in one closed orientation, that is, with the 
contact surfaces 20, 20' in engagement, the axis 22, aperture 46, and 
aperture 50 lie on one radial line and the aperture 50', aperture 48, and 
the axis 22 lie on a second radial line as shown in FIG. 6. 
The vane assembly 6 is resiliently secured to the leg 42 by spring 54. 
Spring 54, formed of spring wire, includes a body portion 56 which is 
horseshoe shaped and slightly skewed in a somewhat spiral configuration. 
Leg 58 of spring 54 is at one end of the body portion 56 and a leg 60 is 
bent from the other end of the body portion 56. The leg 58 is in the 
aperture 50 and the leg 60 is in the aperture 46. Similarly, spring 54', 
which may be identical to spring 54, has a body portion 56' and two legs 
60' and 58' which are respectively in apertures 48 and 50'. 
Pin 62 is secured to the support plate 4 at a position adjacent edge 52' of 
contact vane 14'. The pins 36 and 62 act as stops, limiting the travel of 
the respective vanes 14, 14' when the vanes are rotated to an opened 
position, FIG. 3. 
Secured to hub 10 is an electrical connecting strap 64 which may be braided 
copper or similar material. Connected to hub 10' is a connecting strap 66 
of braided copper or similar material. Straps 64 and 66 electrically 
connect the contacts 18 and 18' to circuits (not shown) of which the 
switch 2 is part. It is to be understood that all of the parts included in 
the vane assemblies 6 and 8 are made of metal to provide good electrical 
conduction between the contacts 18, 18' and the respective conductor 
straps 64, 66. Pins 36 and 62, boss 24, and shaft 28 are electrical 
insulators. 
The masses of the vanes 14 and 14' are counterbalanced by the masses of the 
corresponding counterbalancing vanes 16 and 16' so that moments introduced 
by shocks and vibrations, that is, by rapid accelerations of the vane 
structures in response to shock and vibration loading are equal and 
opposite in direction about the axis 22 for each of the vane assemblies 6 
and 8. As a result, little or no rotary motion of the vane assemblies 6 
and 8 is induced by such shock and vibrations. This is an important 
feature in that whether the contacts 18, 18' are in the engaged closed 
position or the disengaged switch open position, no moments tending to 
reverse their position from a disengaged to an engaged state or from an 
engaged state to a disengaged state is induced by such shock and vibration 
accelerations. The springs 54, 54' need not be made of heavy duty material 
due to the absence of significant moments resulting from such shock loads. 
In FIGS. 3-6 counterbalance vanes 16, 16' (FIG. 1) are omitted for 
simplicity of explanation. It is to be understood that these 
counterbalance vanes, in practice, are present on the structure of FIGS. 
3-6. An important feature also present in the present embodiment is that 
the springs 54, 54', due to their relative position with respect to the 
lever arm 34 and the vanes 14 and 14', provide rapid switch action and 
perform as a snap action switch. This rapid switch action tends to 
minimize arcing between the contact surfaces 20 and 20', FIG. 1, when the 
switch contacts are opened or closed. 
FIGS. 3-6 show different positions of the switch as a function of the 
action of the lever arm 40, the lever arm 40 being pivoted about axis 38 
to operate the switch. For example, in FIG. 3 the lever arm has been 
rotated clockwise to open the switch. The contacts 18 and 18' are 
separated; the edge 52 of contact vane 14 rests on pin 36 and the edge 52' 
of contact vane 14' rests on pin 62. The pins 36, 62 act as stops limiting 
the distance traveled by the vanes 14 and 14' to their open position. 
To close the switch, lever 34 is rotated counterclockwise in direction 67 
about axis 38. In the orientation of FIG. 3, the leg 60 of spring 54 (FIG. 
1) is spaced above a radial line between axis 22 and leg 58 and leg 60' of 
spring 54' above a radial line between axis 22 and the other leg 58'. As 
the arm 40 is rotated counterclockwise the legs 60, 60' are moved 
downward. Relative to the movement of leg 60, the radial line between 22 
and 58 represents the dead center position of the switch. When the leg 60 
passes just beyond this radial line, the switch snaps into the position 
shown in FIG. 4. The movement of leg 60 of the spring to the position 
shown has caused the vane 14 to rotate counterclockwise, as indicated by 
arrow 70. The contact 18 now engages the contact 18'. The vane 14' remains 
in the same position as in FIG. 3 abutting pin 62 at edge 52'. At this 
point the leg 60, is below the radial line between axis 22 and leg 58 and 
leg 60' is above the radial line between axis 22 and leg 58'. 
Continuing to rotate the lever counterclockwise (direction 67) maintains 
the contacts closed and increases the torque created by the springs 54, 
54'. This is shown in FIG. 5. As the leg 60' of spring 54' is moved 
further down, the action of spring 54' tends to cause the leg 58' to move 
upward and to rotate the vane 14' clockwise (direction 70'). In response 
to the counterclockwise movement of arm 40, the leg 60 of spring 54 also 
moves down but not as far as the leg 60' of spring 54'. This downward 
movement tends to rotate vane 14 counterclockwise (direction 70); however, 
the counterclockwise torque on vane 14 is smaller than the clockwise 
torque on vane 14'. The overall result therefore is to rotate both vanes 
clockwise to the position shown in FIG. 5, while the two contacts 18, 18' 
remain in very firm engagement. Further, counterclockwise movement of 
lever arm 40 will cause the edge 52 of vane 14 to rest against pin 36 
which stops the movement of the vanes 14, 14' about axis 22. 
To open the contacts, the lever 34, arm 40, is rotated in the clockwise 
direction 71, FIG. 5, about axis 38. This tends to rotate the lever legs 
42, 44 in direction 71 until the legs 60, 60' of the respective springs 
54, 54' are aligned with the radial line passing through the axis 22 and 
the other ends of the springs at legs 58, 58'. When the two legs 60, 60' 
of the springs move just past this, the dead center position of the 
switch, then the switch snaps open and assumes the condition shown in FIG. 
3. In FIG. 6 the contacts 18, 18' are still closed but further rotation of 
the lever arm 40 in direction 71 from the position of FIG. 6 tends to snap 
the contacts 18, 18' open to the position of FIG. 3. 
While the above action has been described in a sequence of steps, it is to 
be understood that manual movement of the lever is relatively fast in the 
matter of a fraction of a second and that the action of the switch 
contacts in opening and closing is also in a fraction of a second, 
providing a snap action in opening and closing the contacts and therefore 
minimizing arcing which may result during the opening and closing. 
While the structure of the present embodiment is shown in the form of 
vanes, it should be understood that this is by way of example, as other 
counterbalanced contact elements may be readily constructed in other 
shapes and forms. An important consideration is that the contact elements 
be balanced with respect to their axis of rotation so that negligible 
moments are introduced as a result of acceleration induced forces in the 
presence of vibrations and shock induced loads. Because the contacts are 
balanced, they tend to remain in position whether open or closed and 
without the need for heavy duty springs.