US2720561A - Cam-actuated electric switch - Google Patents

Description

Oct. 11, 1955 D. o. NELSON 2,720,561

CAM-ACTUATED ELECTRIC SWITCH Filed March 9, 1955 INVENTOR. D. 0. Nelson ATTORNEY United States Patent CAM-ACTUATED ELECTRIC SWITCH Donald 0. Nelson, Los Angeles, Calif., assignor to Bendix Aviation Corporation, North Hollywood, Calif., a corporation of Delaware Application March 9, 1953, Serial No. 341,259

6 Claims. (Cl. 20030) This invention relates to make and break switches adapted for rapid recurrent actuation by a tripping mechanism such as a continuously running cam.

An object of the invention is to provide a compact and and inexpensive switch.

Another object is to provide a switch requiring little force and power to operate.

Another object is to provide a switch having the aforelisted desirable characteristics that has a long service life.

The manner in which the foregoing objects, together with other more specific objects and features, are achieved will become apparent from the following description of a specific embodiment of the invention as disclosed in the drawing.

In the drawing:

Fig. 1 is a front elevational view of the switch; and

Fig. 2 is a horizontal section in the plane II-II of Fig. 1.

Referring to the drawing, the switch comprises a frame 9 consisting of a flat bottom wall member 10, and top and side walls 11 and 12 respectively which are formed from a single piece of sheet metal. Lugs 13 on the lower edges of the side walls 1212 are folded over the edges of the bottom wall to retain it.

Compressed within the frame 9 is a resilient vibration absorptive body 14 consisting of first, second and third layers 15, 16 and 17 respectively, of a suitable insulating material. One such material is Corprene, which is a mixture of cork and rubber. The first and third layers 15 and 17 are longer than the second layer 16 and opposite ends of the layers 15 and 17 respectively are folded over the adjacent ends of the layer 16 as shown in Fig. 1. The three layers are firmly compressed within the frame at the time of manufacture, and support therebetween the contact structure of the switch.

The contact structure comprises a movable contact member 19 and a fixed contact member 20. The fixed contact member consists of a plate 21 compressed between the layers 16 and 1'7 and having a contact lug 22 projecting beyond the body 9 at one end thereof and having a connection lug 23 extending beyond the body 9 at the the opposite end. A contact 24 is provided on the upper face of the lug 22 as shown in Fig. l. The large area of the plate 21 forms a solid anchorage for the contact lug 22 with respect to the frame 9.

The movable contact member 19 is formed from a piece of resilient wire or thin walled tubing and comprises a fixed end portion 26 which is positioned between the body layers 15 and 16 and projects therefrom at the same end as the lug 23 (Fig. 2). The fixed end portion 26 merges into a hairpin section 27 which extends first away from the body and then back into it and merges into a straight section 28 which extends clear through the body between the body layers 15 and 16 and a short distance beyond where it merges into a free end portion 29 which swings about the straight section 28 as an axis. As shown in Fig. 1 the outer tip of the free end portion 29 may be curved as indicated at 31) for periodic contact by a cam 31 on a rotating shaft or the like. Each time the cam 31 passes the tip 30 it lifts it, and, as the cam passes, the contact is restored to its normal position by its own elasticity.

As shown, the free end portion 29 contacts the fixed or stationary contact 24 in its normal position, and engagement of the tip 30 by the cam breaks the connection momentarily.

One of the desirable features of the present construction is that little force and power must be exerted by the cam to lift the free end portion 29 of the movable contact away from the fixed contact 22. This result is obtained by the construction of the movable contact member including the straight section 28 at right angles to the free end portion 29. When the tip 30 of the free end portion is lifted by the cam, there is very little bending in the relatively short free end portion 29, the major yielding movement being in the long straight section 28, which twists in torsion. The result is a light resiilent force returning the free end portion 29 against the fixed contact 24 after the cam has passed the tip 30. Any tendency of the movable contact to bounce upon contacting the fixed contact 24 is further inhibited by the fact that the twisting motion of the straight section 28 is damped by being clamped between the resilient vibration absorbing body layers 15 and 16.

It will be apparent that the first and second layers 15 and 16 respectively of the body 14 constitute a means for supporting the straight section 28 of the movable contact member 19 against lateral movement relative to the frame 9, whereby the straight section 28 twists in torsion in response to deflection of the free end portion 29 in a surface of revolution about the axis of the section 28. At the same time, the layers 15 and 16, by virtue of their vibration absorptive properties, damp the twisting movement of the straight section and diminish bouncing of the free end of the movable contact against the fixed contact 24.

As previously indicated, the movable contact member 19 may be either wire or tubing. Tubing is preferable where bouncing of the free portion 29 against the fixed contact 24 is to be minimized, because a vibratable member of tubing has a greater ratio of stiffness to mass than does a solid wire, and hence a higher natural frequency. It has been found that a high natural frequency reduces contact bouncing. Very fine stainless steel tubing such as is used for hypodermic needles is a satisfactory material for use in small switches of the type herein disclosed.

To effect electrical connection to the movable contact member 19 a lug 35 is provided, this lug extending alongside of the fixed end portion 26 of the movable member and having a hole 36 therein through which the fixed end portion 26 extends. Since both the lug 35 and the fixed end portion 26 of the movable contact are compressed between the first layer 15 and the second layer 16, the compressive force tends to straighten the inner end of the lug 35 where the hole 36 is located, thereby insuring good electrical contact between the lug and the movable contact member.

A screw 37 may be secured to the top wall 11 of the device, the top wall being countersunk as indicated at 38 to retain the head of the screw between the top wall 11 and the first resilient layer 15 of the body 14. The threaded portion of the screw can be extended through any suitable supporting structure 40 and locked thereto by means of nuts 41 and 42, as shown.

Although for the purpose of explaining the invention, a particular embodiment thereof has been shown and de scribed, obvious modifications will occur to a person skilled in the art, and I do not desire to be limited to the exact details shown and described.

I claim:

1. An electrical switch for periodic operation by a cam comprising: a frame; a resilient, elongated movable con- .tact member having a fixed end-.anchored-to said frame, a .free end-portion deflected .and released .by the .cam. for movement in asurface of revolution, and an intermediate .portion interconnecting. said fixedendto saidv free end ,portion, a section ofsaid intermediate portion next ad- .jacent said free .end portion .being straight and extending in the axis of said surface of revolution; means supporting. said straight. section ofsaid member against lateral .movernent..relative..to..said frame. whereby said section ,twists in torsion in response. to said. deflectionandre- .leaseof said :free endportion; and a stationary contact member in thepath of movement of..said. free'end por- .tion for makeandbreak contacttherewith; said means supporting-said-straight section comprising a resilient vibration-absorptive body; and means including said frame j.for.compressingsaid body about. saidsection.

2. Aswitch according to claim 1,in which said straight .,section extends throughsaid body,..said fixed end lies within. and is anchored tosaid frame .by said body, and theremainderofsaid intermediate portion. comprises a hairpin section extending between said firstmentioned section and saidfixed end.

3. A switch according to claim 2 in which said body comprises two separate layers between which said straight section and said fixed end are compressed" and a contact @lughaving one; end portion compressed between said layers andtheother end extendingtherefrom, said one end of .said. lug having ahole therein through which said fixed end of said movable contactmembenextends, said lug extending alongside the arm of saidhairpin section adjacent,v said fixed end.

4. A switch according to claim 3 including a third layer .ofsaid resilientabsorptive material in which said stationary contact element comprises a base ,portion'sand- .wiched-between and supported by said second and third layers.

' lateral movement relative to saidframe whereby-said section twists in torsion in response to said deflection and release of..said free end portion, said means comprising first and second layers of resilient vibration-absorptive material between 'which said section is sandwiched, and means including said frame for compressing said layers together; and a stationary contact member in the path of movement of said free end portion for make and break contact therewith.

6. An electrical switchfonperiodic operation by a cam comprising: a frame; a resilient elongated movable contact member comprising a tube having a fixed end anchored to said frame, a free end portion deflected and released by the cam for movement in a surface of revolution, and an intermediate portion interconnecting said fixed end to said ..:free endportion, a sectionof said intermediate portion next adjacentsaid free end portion being straight and .extendinginfthe axis of said surface of revolution; means .supportingsaid.straight section of said member against laterahmovement relative to said frame whereby said section twists in torsion in response to said deflection. and release of said free end portion; and a stationary contact memberin the-path of movement of "said free end por- .tion for make and break contact therewith.

FOREIGN PATENTS "458,460 Germany Apr. 12, 1928 "(Maw

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