US 3288970 A
Description (OCR text may contain errors)
NOV. 29, v G. PEREZ BOUNCELESS SWITCH CONSTRUCTION Filed June 22, 1964 INVENTQR GUILLERMO PEREZ ATTORNEYS United States This invention relates to a bounceless switch construc tion; more particularly it relates to a switch construction characterized by compressed spring contacts to provide makes and breaks.
Bounceless electrical contacts are desirable in many applications and particularly where the time required for a contact to settle cannot be tolerated. Further desirable features sought for in switches are reliability, long life, high contact pressures, and a compact construction as well as one which is easily manufactured at minimum cost.
All of the enumerated desiderata are obtained in the present invention. In accordance with the invention a switch construction may incorporate a normally open, a normally closed switch, or both. These are generally known in the art as form A, B, and C switches. Contact makes are accomplished by a spring which is normally compressed between a first fixed and a movable boundary and which, when the movable boundary moves away from the first fixed boundary toward a second fixed boundary, is permitted to expand toward, but short of, its free or equilibrium state until it makes electrical contact with a switch terminal element constituting the second fixed boundary positioned to intercept the spring before it expands to its free length. Breaks are effected simply by forcing the spring away from the switch terminal element through movement of the movable boundary.-
An object of the invention is to provide a reliable, long lived, bounceless, high contact pressure switch construction.
Another object of the invention is in the provision of a switch employing compression springs as contact elements to achieve bounceless high contact pressure makes.
-A further object of the invention is to provide a switch of the make, break, or make-break type in which clean makes and breaks are achieved through the use of the terminal coil of a coiled spring as a wiping contact element which due to its low mass and to the fact that the coil spring is under compression at the time of a make exhibits no bounce.
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 like reference numerals designate like parts throughout the figures thereof and wherein:
FIGURE 1 is a cross sectional view of a switch construction of the make-break type in normal position.
FIGURE 2 is a partial elevational view more clearly showing the make and break contacts in the normal position.
FIGURE 3 is a cross sectional view familiar to FIG- URE 1 showing the switch in an active position.
FIGURE 4 is a view similar to FIGURE 2 showing the make and break contacts in active position.
Referring now to the drawings wherein like reference atent "ice characters designate like or corresponding elements throughout the several views and wherein a preferred embodiment only is illustrated there is shown in FIG- URE 1 a rectangular switch housing of electrical insulating material generally designated by reference numeral 10 comprising top, bottom, front and rear walls 11, 12, 13 and 14 respectively. The top and bottom walls are provided with aligned preferably circular openings 15 to slidably support a cylindrical plunger like element 16 of insulating material, of which, though only one is shown, there may be a plurality mounted in the same housing.
As shown in FIGURES l and 2, the plunger element is provided with an annular flange 17 whose upper and lower sides constitute movable boundaries 18 and 19 respectively, for a first coil spring and a second coil spring 21 and 22. As shown in FIGURE 1 the springs 21 and 22 surround the plunger element above and below the flange respectively. The plunger or movable boundary element 16 is provided in the area of and extending a predetermined distance to either side of the flange 17 with an opening or slot 23 through which a conductive rod-like switch terminal element 24 extends. URE 1 the spring 21 is confined respectively between the underside 25 of the top wall of the housing and the element 24; spring 22 is confined between the upper side 26 of the bottom Wall of the housing and the boundary 19. The terminal element 24 is suitably secured in the front and rear walls midway of the top and bottom boundaries 25 and 26 and constitutes a common fixed boundary. As is evident, the slot 23 permits plunger movement relative to element 24.
In accordance with the invention, the free lengths of each of the coil springs 21 and 22 employed are greater than the distances respectively between the fixed boundaries 25 and 26 defined by the top and bottom of the switch housing and the terminal element 24 which as hereinbefore noted constitutes a second fixed common boundary for the springs such that predetermined contact pressures are obtained between the lower coil 27 of spring 21 and contact elements 24 (FIGURE 1), and between the upper coil 28 of spring 22 and contact element 24 (FIGURE 3).
In the embodiment disclosed springs 21 and 22 have the same spring constant but are of different free lengths, spring 21 having a longer free length. When the springs are accommodated within the housing 10 as illustrated the longer spring 21 having a greater initial compression, though short of closed coil, causes a net downward pressure to be exerted on the plunger element such that the bottom coil 27 of the upper spring 21 encounters and bears against the rod 24 with a desired net contact pressure. In this position also, as viewed in FIGURES 1- and 2, the spring 21 acting against boundary 18 causes the top coil 28 of the spring 22 to be spaced from the contact element 24.
As shown in FIGURE 1 the top coil 31 of spring 21 and the bottom coil 32 of spring 22 are brought out to serve as switch terminals and as is evident the circuit from switch terminal 31 through the spring 21 and via the high pressure spring contact to terminal element 24 is complete, while the circuit between switch terminals 24 and 32 is open.
Making circuit 2432 and breaking circuit 2431 is effected by operating a keying element, generally desig- In FIG' 3 nated by 33, thereby, as shown in FIGURES 3 and 4, to force the plunger 16 upwardly until the top coil 28 of spring 22, which follows the plunger 16 encounters and bears against the'rod 24 with a contact pressure determined by the ratio of the fixed boundary length i.e. between 26 and 24 to the free length of the spring. As viewed in FIGURE 3, plunger movement continues and compresses spring 21 until the bottom coil of spring 21 is cleanly carried away from rod 24 by the movable boundary 18 defined by the plunger flange. Accordingly a circuit make and break is simultaneously effected. A release of the force exerted by the keying element 33 causes the return of the plunger 16 to the position of ,as they make contact assuring a good high pressure It will be appreciated that, depending wiping contact. on the nature of the application and the type of keying element either FIGURE 1 or FIGURE 3 may be considered normal.
Obviously when an A switch only is desired spring 21 will serve simply at a return spring. Where a B switch only is desired spring 22 may be dispensed with where space is at a premium, and the plunger will be accordingly shortened.
In a specific embodiment the distance between 25 and 24 and between 26 and 24 was .2715; the length of the flange was .040"; the rod diameter .020". The spring 21 had a free length of .500" and a K of .9 #/inch, and the spring 22 had a free length of .380" and'a K of .85 #/inch. Both springs (20 coils approximately) of .008" wire had an outside coil diameter of approximately .070" and were accommodated on Delrin pins 16 of .060" diameter with a .090" diameter flange. This specific construction provided approximately 1.5 oz. contact pressures between element 24 and coil 27 and between element 24 and coil 28.
Actual operating experience borne out by calculations indicate that the make and break of the spring coils 27 and 28 relative to rod 24 are bounceless in an application where the movement of the plunger was a uniformly decelerated motion. This was true for any spring whose free length was greater than the distance between fixed boundaries regardless of the degree of initial compression. The calculations showed that over an appreciable time interval contact pressure in pounds after a make varied only in the hundredths order. Obviously then a bounceless switch characterized by any desired contact pressure may be built in accordance with the invention.
While the spring ends adjacent the boundaries 25 and 26 are brought out to serve as terminals in the embodiment illustrated, it is to be understood that the boundaries 25 and 26 might carry printed conductors against which the spring ends could bear; circuit terminals being connected to the printed conductors. Also the boundaries 25 and 26 in another alternative construction might be conductive rod-like terminal elements similar to element 24 and extending in similar fashion through slots provided in pin 16.
It should be understood that the foregoing disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention.
The invention claimed is:
1. A bounceless switch comprising a housing having an interior Wall defining a first fixed boundary,
a conductor comprising a switch contact extending through said housing defining a second fixed boundary parallel to said first fixed boundary,
a plunger element mounted for movement within said housing defining a movable boundary, said plunger element having an enlongated slot adapted to receive said conductor whereby said movable boundary may move relative thereto,
a conductive coiled spring comprising a movable switch contact mounted about said plunger between said movable and first fixed boundary, said spring having a free length longer than the distance between said first and second fixed boundaries,
yieldable means acting on said plunger element to cause the movable boundary to compress said spring to a length shorter than the distance between said first and second fixed boundaries thereby to open a circuit through said spring,
and keying means operative on said plunger element and against said yieldable means whereby the distance between said movable and said first fixed boundary becomes greater than the distance between said first and second fixed boundaries thereby permitting said spring to contact said conductor completing a circuit through said spring.
2. A bounceless switch comprising a housing having an interior wall defining a first fixed spring boundary,
a plunger element mounted for movement within said housing, said plunger element having a flange defining a movable boundary, said plunger element having an elongated slot through the flanged portion thereof and extending beyond said flange portion parallel to the direction of movement of said plunger element,
a conductive element comprising a fixed switch contact defining a second fixed boundary secured to said housing and extending through said slot,
a conductive coiled spring comprising the movable contact of said switch mounted about said plunger element between said movable and first fixed boundary, said spring having a free length longer than the distance between said first and second fixed boundaries,
yieldable means normally acting on said plunger element to cause said flange to compress said spring to a length such that the end coil of said spring adjacent the movable boundary is moved by said movable boundary out of contact with said conductive element where said switch is opened,
and keying means operable to move said plunger element against said yieldable means whereby the distance between said first fixed and movable boundaries becomes greater than the distance between said first and second fixed boundaries thereby to permit said spring to expand between said first and second fixed boundaries into contact with said conductive element completing a circuit through said spring.
3. A bounceless switch comprising a housing opposite internal walls of which constitute first and second fixed boundaries,
a conductor comprising a switch contact extending through said housing defining a common fixed boundary parallel to and intermediate said first and second fixed boundaries,
a plunger element defining third and fourth movable boundaries, said plunger element having an elongated slot adapted to receive said conductor whereby said movable boundaries may move relative thereto,
coiled springs comprising switch contacts mounted about said plunger element between said first fixed and third movable boundaries and between said second fixed and fourth movable boundaries, said springs having free lengths greater than the distance between fixed and common boundaries, one of said springs having a free length longer than the other whereby itv acts against its associated movable boundary to eifect contact of its end coil with said conductor'completing a circuit through said longer spring, and thereby causing the movable boundary associated with the other spring to move the end coil thereof out of contact with said conductor; opening a circuit through said shorter spring,
5 6 and keying means operable to move said plunger elewith said conductor, completing a circuit through merit whereby the distance between the movable said shorter spring. and fixed boundaries associated with said longer spring becomes shorter than the distance between References Cited y the Examiner said fixed and common boundaries, opening a circuit 5 UNITED STATES PATENTS therethrough, and the distance between the movable and fixed boundaries associated with the other shorter 2927988 3/1960 Powell ZOO-159 spring becomes greater than the distance between said fixed and common boundaries to thereby per- ROBERT SCHAEFER P'mmry Examiner mit the expansion of said shorter spring into contact 10 H. HOHAUSER, Assistant Examiner.