CA1036681A - Multi-stage switching apparatus - Google Patents

Abstract

MULTI-STAGE SWITCHING APPARATUS

ABSTRACT OF THE DISCLOSURE

A multi-stage switching apparatus adapted to make and break an electrical circuit comprises a first compress-ible body having a resistance which varies inversely accord-ing to its state of compression and a second compressible body having a substantially uniform resistance lower than that of the first body, the two bodies being so arranged that the first body is compressed prior to compression of the second body in response to making of the circuit and is decompressed following decompression of the first body in response to breaking of the circuit.

Description

1 This invention relates to electrical switching

2 apparatus and more particularly to a switch having at least two compressible, electrically conductive members which are 4 compressible and decompressible sequentially. The first mem-ber to be compressed has an electrical resistance which ~ varies inversely according to its state of compression, where-7 as the second body has a substantially uniform resistance 8 which is less than that of the first body. Sequential com-9 pression of the two members, therefore, establishes a first electrically conductive path through the first body of dimin-11 ishing resistance, followed by the establishment of a second 12 electrically conductive path through the second member and 13 by-passing of the first member. Upon decompression of the 14 members, the electrical path through the lower resistance member is broken first and an electrical path of increasing 1~ resistance is reestablished through the variable resistance 17 member.

19 In a resistive circuit such as that having incan-descent lamps controlled by a switch, closing of the switch 21 to complete a circuit to the lamps results in a momentary 22 high inrush current of extremely high peak value. In a cir-23 cuit of the kind having an inductive load controlled by a 24 switch, opening of the switch results in a momentary, ex-tremely high voltage peak. These characteristics of resis-26 tive and inductive circuits are objectionable for many ~7 well-known reasons. Although these objectionable character-~8 istics can be minimized by the utilization of rheostatic 2~ switches, such switches have disadvantages. For example, ~0 the resistance of a rheostatic switch depends upon a .. . . . ..

10;~6681 1 particular setting thereof. Unless considerable care is 2 exercised to assure precise setting of the switch in its operating mode, then the resistance of the circuit may be 4 either too little or too great. Another disadvantage of rheostatic switches is that they generate substantial heat ~ in operation. Provision must be made to dissipate such heat, 7 and the problems associated with heat dissipation are magni-8 fied in those instances in which precise adjustment of the 9 switch is not assured.
. ' 11 An object of this invention is to provide switch-12 ing apparatus which is highly effective in supressing cur-13 rent and voltage peaks attendant the making and breaking of 14 resistive and inductive circuits, respectively.

16 Another object of the invention is to provide 17 switching apparatus of the character described and which 18 comprises at least a pair of conductive members, one of 19 which has variable resistance characteristics and the other 20 of which has substantially constant resistance characteris- ~-21 tics, the two members being so arranged that the variable 22 resistance member is the first to become electrically con-23 ductive and the last to become non-conductive.

A further object of the invention is to provide ~6 a multi-stage switching apparatus which has the advantages ~7 of a rheostatic switch, but none of its disadvantages.
~8 ~ Other objects and advantages of the invention will ~
30 be pointed out specifically or will become apparent from the -1(~36681 1 following description when it is considered in conjunction 2 with the appended claims and the accompanying drawings, in which:
4 Figure 1 is a plan view of a switch incorporating apparatus constructed in accordance with one embodiment of ~ the invention;
7 Figure 2 is a sectional view taken on the line 8 2-2 of Figure 1 and illustrating the parts in circuit 9 closing condition;
Figure 3 is a view similar to Figure 2, but illus-11 trating the parts in open-circuit condition;
12 Figure 4 is a sectional view taken on the line 4-4 13 of Figure 2;
14 Figure 5 is a plan view of the switching member illustrated in Figures 2 and 3;
1~ Figure 6 is a sectional view taken on the line 6-6 17 of Figure 5;
18 Figure 7 is a view similar to Figure 6, but illus-19 trating the switching member interposed between a pair of conductors and subjected to compressive force;
21 Figure 8 is a view similar to Figure 6, but illus-22 trating a modification of the switching member; and 23 Figure 9 is a side elevational view of switching 24 apparatus incorporating switch members according to another embodiment of the invention.
2~
27 Apparatus constructed in accordance with the embodi-~8 ment of the invention shown in Figures 1 - 7 comprises a 2~ switch casing 1 having a base 2, a pair of upstanding, ~0 spaced apart side walls 3, and front and rear walls 4 and 5, :.................. .. . .

lV366~1 1 respectively. The casing also includes a cover 6 fixed to 2 the side, front, and rear walls in any suitable manner.
Slidably accommodated within the casing 1 is an actuator 7 4 having a blind bore 8 extending inwardly from its rearward end. At the forward end of the actuator 7 is an elongate 6 operating stem 9 that extends through a tubular guide 10 7 which projects forwardly from the front wall 4 of the cas-8 ing. Fitted into the bore 8 is a compression spring 11, 9 one end of which seats on the base of the bore and the oppo-site end of which bears against an abutment 12 that is fixed 11 to the bottom wall 2 of the casing. The spring 11 normally 12 biases the actuator to the position shown in Figure 2 in 13 which it abuts the front wall 4 of the casing and in which 14 position the free end of the operating stem 9 extends beyond the guide 10.
1~ ......
17 Within the casing 1 is a pair of electrical con-18 ductors 13 and 14 the forward ends of which are fitted into -19 notches 15 and 16, respectively, formed in the front wall 4 of the casing. The rear ends of the conductors 13 and 14 21 extend through openings formed in the rear wall 5 of the 22 casing to form terminals 18 and 19 which are provided with 23 reinforcing ribs 20 and 21, respectively. The terminal 18 ~4 may be connected to a source of energy, such as a battery B, and the terminal 19 may be connected to a load L.
~6 27 The conductor 14 bears against the top wall 6 of ~8 the casing to prevent upward deflection of the conductor. ~ -2~ The conductor 13 has a section 22 thereof which is spaced below the conductor 14 and terminates at its rearward end , . , ~,: : . . . ' - ~ . ' ~' .

10361i81 1 ¦ in a downwardly turned leg 23 which is joined to the termi-2 ¦ nal 18 so as to provide spacing between the terminals 18 5 ¦ and 19 and permit reciprocation of the actua~or 7 without 4 unwanted interference with the conductor 13.

The section 22 of the conductor 13 is pro~ided -:-7 along its opposite edges with a pair of downwardly extend-8 ing, V-shaped projections 24 which lie in the path of move-9 ment of cams 25 carried by the body 7 at that side of the latter which confronts the conductor section 22. The for-11 ward ends of the cams 25 terminate in upwardly and rearwardly 12 inclined surfaces 26.

14 At substantially the center of the conductor 14 is a pair of downwardly struck mounting ears 27, 28 by means 1~ of which a switching member 30 is supported on the conductor 17 14 and between the latter and the conductor 13.

19 The switching member 30 comprises two resiliently compressible bodies 31 and 32, the body 31 being annular 21 in configuration and having a peripheral flange 33. The 22 body 32 is disc-like and has a peripheral flange 34. The 23 body 31 encircles the body 32 and is thicker than the latter ~4 for a purpose presently to be explained. The body 32 may be retained frictionally within the body 31 or it may be a6 bonded to the latter.
a7 .
~8 The switching member 30 is secured to the con-ductor 14 by fitting the flange 33 of the body 31 between ~0 the ears 27, 28 and the main body portion of the conductor 1(3;~6681 1 14. Alternatively, the ears 27, 28 may be dispensed with 2 and the switching member 30 secured to the conductor 14 by : .

3 any one of a number of known conductive cements. ~:

5 In the operation of the apparatus thus far de- .. - .
~ scribed, movement of the actuator 7 by means of the operat- . .
7 ing stem 9 from the position shown in Figure 2 to the posi- :
8 tion shown in Figure 3 moves the cams 25 out of engagement .. .
3 with the projections 24 so as to enable the section 22 of the conductor 13 to assume a substantially horizontal posi-11 tion in which the conductor 13 is out of engagement with the 12 switching member 30. Upon return movement of the actuator 13 to the position shown in Figure 2, however, the cams 25 14 will engage the projections 24 and deflect the section 22 15 of the conductor 13 upwardly or toward the conductor 14. .- ~:
13 As the conductor 13 is deflected upwardly, it will engage 17 the body 31 and compress the latter. When the body 31 has .-18 been compressed an amount corresponding to the difference in 19 thickness between the bodies 31 and 32, further deflection .. ~ .
of the conductor 13 toward the.conductor 14 will effect . ::
21 compression of both of the bodies 31 and 32, as is shown 22 in Figure 7. Compression of the body 31, therefore, pre- ~-23 cedes compression of the body 32.
~4 Upon movement of the actuator 7 from the position 26 shown in Figure 2 to the position shown in Figure 3, the ~7 projections 24 will slide down the inclined surfaces 26 of ~8 the cams 25 so as to enable the section 22 of the conductor 2~ 23 to move away from the conductor 14. During such movement of the section 22, both of the bodies 31 and 32 will be de-. .

10~66~
1 compressed. Eventually, the body 32 will be fully decom-2 pressed, and full decompression of the body 32 precedes 3 full decompression of the body 31.

When the switching member 30 is utilized in the ~ manner described, the annular body 31 is the first to be 7 compressed and the last to be decompressed. Accordingly, 8 the body 31 should be so constructed as to have an electri-9 cal resistance which varies inversely according to the state of its compression. Preferably, the body 31 comprises a 11 molded member of resiliently compressible, non-conductive 12 material, such as silicone rubber, containing a quantity of 13 electrically resistive, conductive particles of such size 14 as to accommodate the currents and heat to be encountered in normal usage. The body 31 may be molded from either a 1~ thermosetting or room temperature vulcanization silicone 17 resin containing the appropriate catalyst and a quantity 18 of fine particulate material such as carbon, tungsten, 19 nickel-chromium, and the like. Excellent results have been obtained when a body 31 intended for use with a 14 21 volt, d.c. battery contained A.M.I. nichrome of 140 - 200 22 mesh size and in a weight ratio of about seven parts 23 nichrome to one part of silicone rubber. Although the ~4 body 31 may be normally conductive even when it is not subjected to compressive force, the resistance of the body 26 31 preferably approaches infinity in its normal, uncompressed ~7 state, and diminishes generally linearly as the body is ~8 compressed.

~O The body 32 also comprises a molded member of 103~681 1 resiliently compressible, non-conductive material, such as 2 silicone rubber, throughout which is dispersed a quantity 3 of electrically conductive particles of a size appropriate

4 to the voltage and current of the circuit in which it is to be used. As compared to the particles contained in the ~ body 31, the particles contained in the body 32 are of con-7 siderably less resistance. Stated differently, the body 32 8 is considerably more conductive than the body 31. This re-~ lationship can be obtained by utilizing silver or silver-coated copper particles in the body 32. Excellent results11 have been obtained with a body 32 for use with the afore-12 mentioned d.c. battery and containing silver-coated copper 13 particles of 25 - 50 mesh size in a weight ratio of about 14 ten parts of particles to one part of silicone rubber.

1~ If desired, the body 32 may be molded under 17 pressure so as to be conductive even in the absence of the 18 application of compressive force thereto. Alternatively, 19 the body 32 may be molded at atmospheric pressure so as to be non-conductive until compressed. In either event, the 21 electrical resistance of the body 32, when conductive, 22 corresponds substantially to the resistance of silver and 23 is substantially less than the resistance of the body 31 ~4 when the latter is in its compressed state and conductive.

26 It is desirable that both of the bodies 31 and 32 ~7 be compressible. Such a construction makes it possible for ~8 the member 30 to accommodate overtravel of the conductor 13 2~ toward the conductor 14, thereby assuring sufficient move-~0 ment of the conductor 13 to ensure compression of the body .' .' 103~681 1 32 without risking damage to the other parts of the switch 2 mechanism.

4 It also is desirable that the body 31 be more easily compressible than the body 32 so as to avoid the ~ necessity of having to use excessive force in the operation 7 of the switching member 30. Excellent results may be obtained 8 if the body 31 has a durometer rating of about half that of 9 the body 32.

11 When the switching member 30 is interposed between 12 the conductors 13 and 14 and the actuator 7 moves from the 13 position shown in Figure 3 toward the position shown in 14 Figure 2, deflection of the conductor section 22 toward the conductor 14 will cause the body 31 to be subjected to com-1~ pression, thereby enabling current to flow from the battery 17 B through the terminal 20 to the conductor 13, thence through 18 the body 31 to the conductor 14, and from the latter through 19 the terminal 19 to the load L which, in the illustrative case, comprises a filament f of an incandenscent lamp, 21 thereby providing a resistive load, but it will be understood 22 that the load could be either resistive or inductive.
23 :
24 If the battery B has a voltage of 14 volts, the voltage drop across the conductors 13 and 14 will diminish 26 substantially linearly as the body 31 is compressed inas-~7 much as the particles contained in the body are subjected to the compressive force. When the body 31 has been com-pressed an amount corresponding to the difference in thick-30 ness between the body 31 and 32 further movement of the ~-_ g _ ',-, ' ' ~' :. . . . ~ . ::

10366~1 ~

1 conductor 13 toward the conductor 14 will effect compression 2 of both of the bodies 31 and 32. Since the resistance of the 3 body 32 is substantially less than that of the body 31, the 4 establishment of a conductive path between the conductors 13 and 14 via the body 32 will cause the body 31 to be short ~ circuited or by-passed. The voltage drop between the con-7 ductors 13 and 14 thus will correspond to the voltage drop 8 across the conductive body 32. If the conductive particles ~ of the body 32 are silver, or silver-coated copper particles, 10 the resistance of the body 32 will be substantially constant - -11 and will correspond substantially to the resistance of a `~
12 silver or silver-coated conductor. -13 ~`
14 The utilization of the two-part switching member 30 enables full voltage to be applied to the load L in two 1~ stages, the first of which has a variable resistance and the 17 second of which has a substantially constant resistance. As 18 a consequence, the inrush current to which the load L is 19 subjected is substantially suppressed.

21 When the actuator 7 moves from the position shown 22 in Figure 2 toward the position shown in Figure 3, the con-23 ductor 13 moves away from the conductor 14, thereby reliev-~4 ing the compressive force on the member 30. Due to the dif-ference in thickness between the bodies 31 and 32, the body ~6 32 is fully decompressed while the body 31 still is subjected ~7 to compression. As a consequence, the conductive path 28 through the body 30 is transferred from the body 32 to the 2~ body 31 and the resistance of the body 31 increases as it is ~0 decompressed. In this manner the peak voltage transient ., - 10 - - ' lV36~;tl1 1 associated with the opening of an inductive load circuit is 2 substantially suppressed.
4 The rapidity of compression and decompression of the member 30 depends upon the speed of movement of the 8 actuator 7 and upon the length and inclination of the sur-7 faces 26 of the cams 25. The rate at which the member 30 8 is compressed and decompressed may vary within wide limits, ~ but care should be taken to avoid maintaining the current path through the resistive body 31 to such an extent that 11 heat generated by the electrical resistance is detrimental 12 to the silicone rubber.

14 To assist in the dissipation of whatever heat may be generated in the body 31, the latter preferably encircles 18 the more conductive body 32. Such an arrangement is not 17 essential, howeveru If desired, a switching member 30a 18 (see Figure 8) may be constructed in such manner that a 19 variable resistance body 31a is encircled by a more con-ductive body 32a, the bodies 31a and 32a corresponding in 21 construction to the bodies 31 and 32, respectively, with 22 the exception that the body 31a is thicker than the body 23 32a so as to be compressed prior to the body 32a and to 24 be decompressed following decompression of the body 32a.
~6 Although the disclosed switching members 30 and ~7 30a incorporate only two discrete bodies, it will be under-~8 stood that a greater number of discrete bodies may be in-2~ cluded in a single switching member. In such a construc-~O tion each body would contain particles having conductive 1036681 ~ ~ ~
1 properties different from those of the other bodies and the 2 thickness of each more resistive body would be greater than 3 that of a less resistive body.
4 ~

5 It is not essential that the discrete bodies of a ~ -

6 multi-stage switching member be concentric. As is indicated

7 in Figure 9, an insulating base 40 supports a pair of spaced

8 conductors 41 and 42 adapted to be bridged by a blade 43

9 swingable about a pivot 44. Mounted side by side on the conductor 41 is a pair of bodies 31b and 32b corresponding 11 in construction to the bodies 31 and 32, respectively, ex-12 cept for their configuration. The variable resistance body 13 31b is located in a position such that movement of the blade 14 in the direction of the arrow a from the full line position to the dotted line position b effects compression of the 1~ body 31b and establishment of a variable resistance path 17 between tha conductors 41 and 42 via the blade 43 and the 18 body 31b. Further movement of the blade in the direction 19 of the arrow a to the dotted line position c will effect compression of the more conductive body 32b, whereupon the 21 conductive path between the conductors 41 and 42 is via the 22 blade 43 and the body 32b. The effect of this arrangement 23 is the same as that which has been described earlier.
~4 Tests of switching members constructed in accord-ance with the invention have demonstrated remarkable uni-26 formity of the electrical characteristics of such switching 27 members. For example, a construction corresponding to the ~8 member 30 was subjected to several hundred thousand on-off ~ cycles with virtually no variation in the voltage drop across the member when the more conductive body 32 was conductive.
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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An electrical switching device comprising a first body composed of resiliently compressible, non-conductive material containing electrically conductive material having a resistance which varies inversely ac-cording to the compression of said first body; and a second body composed of resiliently compressible, non-conductive material containing electrically conductive particles having a substantially uniform resistance lower than that of said conductive material, one of said bodies having an opening extending therethrough and in which the other of said bodies is accommodated.

2. A device according to claim 1 wherein said first and second bodies are of different thickness.

3. A device according to claim 1 wherein said first body is thicker than said second body.

4. A device according to claim 1 wherein said first body is non-conductive in the absence of compressive force being applied thereto.

5. A device according to claim 1 wherein said second body is non-conductive in the absence of conductive force being applied thereto.

6. A device according to claim 1 wherein said second body is conductive in the absence of conductive force being applied thereto.

7. A device according to claim 1 wherein one of said bodies is non-conductive in the absence of conductive force being applied thereto and the other of said bodies is conductive in the absence of compressive force being applied thereto.

8. A device according to claim 1 wherein neither of said bodies is conductive in the absence of compressive force being applied thereto.

9. A device according to claim 1 including a pair of spaced conductors, means mounting said bodies in a position to bridge said conductors, and operating means for applying and releasing compressive force on said bodies while the latter bridge said conductors.

10. A device according to claim 9 wherein said bodies are interposed between said conductors.