US2667546A - Snap switch - Google Patents

Description

J. M. BRADY Jan. 26, 1954 SNAP SWITCH 5 Sheets-Sheet 1 Filed 001:. l, 1952 ill m m m m (/4425? M BRAQV ATTORNEY-Y J. M. BRADY Jan; 26,- 1954 SNAP SWITCH 3 Sheets-Sheet 2 Filed Oct. 1, 1952 [Him] INVENTOR. M44155 M. Away 74W pm ATTORNEY;

J. M. BRADY Jan. 26, 1954 SNAP SWITCH 3 Sheets-Sheet 5 Filed Oct. 1, 1952 INVENTOR. Mm/5s M 3/640 Y ATTORNEYS Patented Jan. 26, 1954 SNAP SWITCH Jaines M." Brady, 'WantaghfN. Yl; assignor i t Servomechanisms, Inc., a corporation of New York Application October 1, 1952, Serial No. 312,539

W 15' Claims.

1. s The, present invention relates to' switches for controlling-electric circuits and moreparticularly to small switchestof the type adapted to operate contact carrying arm which, is 'carriedby crossed" threads suchaswires or .ribb'onsthat are under longitudinal tension, the threads crossingat' pointsl'aterally spaced frof'm the arm; The" crossmg: of the..tensioned.threadsis 'suchthat the contact arm will pivot witha snap action from one position toanother about a. natural axis 'when buttslightrpressure is applied to a thread at or near a cross-over point or tothe contact arm or.to a part carriedthereby. The switch may also be actuated by relative movement of the ends of the threads, as by rotation of a wall or arm .to which the; ends are anchored under tension. The invention includes also a rapid action" sequential snap switch which isbuilt upirorh the above briefly described switch." In the sequential switch thecontact armsare all supported'by the tensioned threads, the threads crossing betwee'n each arm and'the pivotal movement'of an arm serving to actuate a succeeding arm.

For aibetter understanding of the new switch and the various features of novelty thereof, reference: maybe had to theaccompanyin'g drawings,

of'Whichv Fig, 1 is a perspective vview of a snap'switch embodying the invention arranged as a single pole, 'doublethrow switch;

Fig; 2 is a view similar to Fig; "1' but illustrating a, double pole, "double throw switch;

Fig.3 is a side view of a hermetically sealed switch representing the presently preferred embodiment of the invention;

Figs. '4 and 5 areivertica'landhorizontallonigi tudinal sections;respective1y;,o'f thew/itch *of Figgt; Figifi' being'aisection taken on the line 5 -5 of Fig; 4';

FigI'B israitransverse sectiontakfen on the line" 6-6 of Fig; 4,;

Fig. 71s a perspective view of aiswit'ch embodying the invention and representing a modification; and

Fig. 8 is a perspective 'view' of a. sequential switclr embodyingtheinventionr The principle of operation of the n w; switch: may best be understood by reference to the rel'a tively simpleconstru'ction "illustrated in Fig.'"'l. In this embodiment the switch comprises two longitudinal beams 2 and 4 connected at their ends by cross beams 5' and 8 to form a rectangular framework, a contac'tarm H] of conducting mate-3 rial, and tensioned wires I2 and I4 anchored'at' their ends to the beams 2 and 4 and floatingly supporting the arm Ill, An end of each of the wires i2 and I4 is welded or'otherwise's'ecured to the beam 2 undertension, the points of attachment of the ends of the wires tothe beam 2 being, near the ends of thebeam. The contactarm f0 has two transvers'e passa'ges l6 and 18 therethrough, spaced from the center'b'f the "arm. Wire [2 extends from" its point of attachment with the beam 2 through the passage 18 of'arm it and is secured asby'weldin'g' atjits other end to the beam 4 ate, point'spacedf from the crossbeam 5 by a distancesubstantially equal to that by which the pointofattachment'of the other end to the beam 2 is spaced'irom the cross-beam E5, the wire |2 thus beingdisposed in substantially V-form. Similarly, wire I' l is welded or otherwise securedunder tension to the beam 2 adjacent'the" cross-beam'8, passes through'th'e aperture IS in the contact arm l0, andis secured "at its :other end to the beam 4 adjacent theicross-beam '8, the stretch of wire M between'beam' 2" and contact arm In passing under thecorre'spondin'g'f stretch of wire l2 andf'in the stretchbetweenthe' contact arm [8 andthe beam 4*passin'gover the corresponding stretch of wire 12. The contact arm 10 is thus floatingly'supported by the wires i2 and I l. 'Mo'unted'onthecross-beam '6 adja cent "the'end of the contact arm are a pairfof' brackets 26 and 2 2'carryingadjustablefixed con;- tacts 24 and 26 respectively, positioned for engagementwith a contact 28'c'arried on theend' Of arm [0." Each'of the brackets and 2 2 is insulated from the frame by's'uitable insulation" 30 On the cross-beam a are mounted brackets 32 and34 carrying adjustable contacts 36 and38 respectively,- ior engagement with a contact '40 v on the adjacent end of thecontact arm Brackets 26 and 22 carry suitable:terminals-10f which only terminal:-42 on bracket n is visible" in' the drawingand bracket 32 carries aterminal 44 forconnection of an external lead thereto;

With the above 'described constru'ction-the tension in the wires l2 and |4-OI1'theSlde ofthe contaotarm cf bea'm 2 createsa coupletending to rotatethe arm in a} counter clockwi'se direction as viewed in Fig". 1; about an axis intermediate the 'wires l2 and I4 on the side of the contact arm of beam 4 creates a couple tending to rotate the arm about the same axis but in a clockwise direction. If the distances between the wires l2 and I4 at the cross-over points, indicated at A and B, were equal, these opposing couples would be equal, assuming equal tension in the wires, and the contact arm would be in unstable equilibrium. The slightest departure from such unstable position in either direction of rotation increases the couple tending to rotate the arm in such direction. Hence the arm will continue to rotate until stopped by the fixed contacts or stops carried by the framework; To reverse the position of the contact arm it is only necessary to reverse the relative spacing of the wires at the cross-over points, thereby relatively increasing the couple acting on the arm in the desired direction. Thus the switch may be actuated by pressure upon either end of the contact arm or by pressure upon a wire 12 or [4 at or near a crossing point. In the particular embodiment of the invention illustrated in the drawing, the actuating means is shown as a bifurcated member 46, the furcations 48 and 56 of which span the crossing point A of the wires l2 and I4 intermediate the beam 2 and the contact arm It. When the member 46 is moved downwardly, the spacing between wires [2 and I4 at point A is decreased, reducing the couple tending to cause counterclockwise rotation of the arm and permitting the couple exerted by the wires 12 and I4 on the far side of the arm to rotate the arm in a clockwise direction, bringing contact 28 into engagement with fixed contact 24 and contact 40 into engagement with fixed contact 38, the arm moving with a snap action upon passing through its equilibrium position. In this position of the contact arm a circuit will be closed from the external lead connected to terminal 44 to the external lead connected to the terminal 42 carried by bracket 2!]. Depending upon the initial relative spacing of the wires at the cross-over points A and B, the arm will either remain in the described position after the actuating member 46 has been raised or will snap back to its initial position.

If the spacing at point A is originally substantially greater than that at point B, arm ID will be biased into the position shown in the drawing,

that is, with contacts 28 and 26 in engagement and contacts 40 and 36 in engagement. Lowering of member 46 will cause arm 10 to reverse its position. Upon raising of the member 46 under this initial condition, the arm will return to its biased position unless the travel of the arm has been sufiicient to make the spacing at point B greater than at point A. In this latter case, as in the case when the original spacings at points A and B are about equal, the contact arm will stay in either position until positively actuated into the opposite position.

If the arm thus remains in the position to which it has been actuated by member 46 and it is desired to reverse its position, the actuating member may be moved to the dotted line position shown in Fig. 1 and depressed to engage and depress the wire I4 at the crossing point B. Decrease of the spacing at point B will cause counter-clockwise rotation of the contact arm and closing of the contacts 28 and 26. The same result could be obtained by depressing wire l4 at point A to increase the spacing at this point.

As will be apparent from the above descrip tion, the operation of the above described switch depends upon the'initial adjustment of the fixed contacts or stops and upon the initial spacing of the wires 12 and 14 at the cross-over points. Relatively minute pressure upon a cross wire is sufficient to disturb the equilibrium of the contact arm l0 and cause actuation of the switch. By suitably insulating the brackets 32 and34 and connection of external leads thereto, the single pole, double throw switch of Fig. 1 could be changed to a two-point make and break switch for two separate circuits, one circuit being from bracket 32 to bracket 22 and the other circuit being from bracket 34 to bracket 20.

The switch illustrated in Fig. 2 is of substantially the same construction as that described in connection with Fig. 1, and therefore similar parts have been identified with like reference numbers but with a prime annexed thereto. In Fig. 2, however, the framework comprising the longitudinal beams 2' and 4 and cross-beams '6' and 8 is of insulating material, as is also the contact carrying arm Hi. In this embodiment of the invention the contacts 28 and 46 carried at the ends of the contact arm ID are connected through fiexible leads 52 and 54 respectively to external circuits, as is each of the brackets 26, 22, 32' and 34'. With this arrangement the switch operates as a double pole, double throw switch. In one position of the arm l0 lead 54 is connected through contact 40' to bracket 34' and lead 52 is connected through contact 28' to bracket 20', whereas in the other position of the contact arm lead 54 is connected to bracket 32 and lead 52 is connected to bracket 22. No actuating means is illustrated in Fig. 2 but it will be apparent that a member such as the member 46 of Fig. 1 could be employed or a finger engaging contact arm III at a point remote from its center could be employed.

The preferred embodiment of the invention in a practical commercial form is illustrated in Figs. 3 to 6, to which reference may now be had. In this embodiment of the invention the entire switch is enclosed within a hermetically sealed container and actuated externally by an arm mounted for slight pivotal motion. The entire device can be made in a small size, for example within a casing 2 inches long by inch wide and under an inch high. A switch of such dimensions may be used to control circuits carrying up to about 20 amperes, with the voltage across open contacts of the order of volts. The external casing of the switch of Figs. 3 to 6 is indicated at 56, having a bottom plate 58 within which are insulatedly sealed terminals 66, 62 and 64, of which the terminals 60 and 64 carry contacts 66 and 68 respectively for cooperation with the contacts carried by the contact arm. The inner end of terminal 62 serves as a pivotal support for the contact arm and also as an electrical connection thereto. The terminal 62 is secured to the base of a U-shaped member 10, the upright arms 12 and 14 of which are extended longitudinally to serve as the tensioning support for the contact arm supporting and actuating means. In this embodiment of the invention, ribbons rather than wires are employed for support, and actuation of the contact arm, as ribbons have greater strength in relation to flexibility than do wires. Also, instead of passing through holes in the. contact arm 16, the crossed ribbons are secured, as by welding, to the contact arm and could therefore be formed of two parts rather than as a single piece. Two parts of one ribbon are identified by reference numerals 18a and 18b and the corresponding parts of the other ribbon are identified as 60d is 4 ,sp figlit-arm "125a nds f, these ts a esecumq o? i. ntact'a m. T fig h fpafi 11 orerlym at. he

a art' bi is cu e j h co tacta m i7 a a continuationpf Y part 18a and, similarly; one lend secured to t e "contact arm.

i'I Jbb np B b H 6; s a c n nu tion "Qt part 309, t e. oth en heip jlii and .8 1 b ing secu ed t s aced Point n.;t ei n :e d th th upright rm 1 an p i'flflb ov rlr neip rt Wh th ros io e ipo n in "Pi'e b ibbon re. a ached o t e atm'siby m ans oijbead oa mesa-p t t ns o "'i th'e r .t

ip d to actuat t abwe desc ibed w t While maintainingthe parts'withi'n a' hermetically aled n he ru ture. new t be. described mpl ye hin a ledrhosp orlbronze' t ie 8 1 sealed thi .an perturecflfiin h upper a o the s g "fifi'iand to th s tubing xn s r'i tawh h, ove t e asing, is twisted 'lof'the n f e i permi adju throughi90 and bcnt' through"90 'top1tovide a n t na e en livia- 1 armiao for a tu tion by. external means. Theftubing fl withinthe casing is flattened about the strip 88 and s'ealingvcement, indicated at 92, is provided between thejstiipj88,

and the walls ofthe tube atfthffl point offflattening; The flattened tube 84 serves, as. a sealed pivot for anarm, 94 withinthe casing. The arm' extends"longitudinally to ajpoint slightly beyond the transverse section" within which are disposed the cross over pointsiA andjB. An in-. verted'U- shaped mmberefi'issecured to the free end of theStIip 94 (see Figj'fil'landthe lowerfend of ithis'pi'ece 96' isibentback iponjits'elf to form a rounded end 98 for engagement withribbon section 8 91) adjacent the-cross-over point B. y .Ad jac'entthe tube 84 the strip 941s twisted through 90 toprovide a horizontal section! 0'0.and is then bent downwardly and 'upwardly to. provide a U-;shaped part'102 into, which the flattened end offthetube 84 is received and cemented. With.

the above described construction, when the free end of the arm 901s moved'toward thecasing by external actuating meansfthe flattened phosphor 7 Bland 84, Upon downwardpresspre on ribbon part wha point B, the. arm will'sna'p into position to close the'circuit'between terminalsBLand 60 but upon release olfthepressureonribbon part v 8th will snap I back to its biasedgposition,

For convenience of imounting an d supporting theswitch, the "side wens ofthecasingj'6 are connected lnear opposite 'ends'pf the device by tubing' 'lfl t" and I06, both ends of each Vpieceof tubing being hermetically sealed to thecasing.

The. above described construction provides a quick acting snap switchio'f sma11 s1ze and one in which an m ving'parts' are protected from the atmosphere orfrom l an dling, J Tnepe'emaicauy 1 e es a etel a ra gem-t-s ii e ie he e ds of t e The arm is thus biased into,

niadetotheparticular,structureillustra a; For

' f v rte j eti th the c tac ant i i ld. eg d d d f the pivotal support oflthe contactarm could be;

example, additional fixed contacts eliminated if deed d. "The pivotal ever, provides insurance'against vibra t b w:

and alsoinsuresfa positive sy cngg ia aeeo of' both contacts;

In Fig.7 a switch having features .in common with thefhermeti'cally sealed switch of j'Figs. 31m

1 s at m'tn 'smb 'qir entbrtn i we tion actuation is 'e'iiected by rotation it ;a part to 1 which the ends of the crossed wires' or ribbons are attached. The switch comprises-albaseplate' an 'endwaHii ll) to wh ch-onsets offribbbns] lzzz.

and Ma are m ssed funde'r "tension" Adjacent the op-positeed cofplate [08' 'banflji'ispivotally mounted and one end offribbons I'I 21)!and are attached. .under tension to tl i's bar- The other ends of the ribbonsgareconnected-asin the embodiment-of the inventionfillustrated in Figs. 3 to 6, to spaced' points of a contact arm ,8, In this particular construction the central pivotal support for the contact arm iisornittedi the eon? tact'arm being supported solely by the tension'ed" ribbons. Upper and lower fixedf contactsforjcooperation ,With contacts carried on the ends of the contact arm are mountedlon suitable' brackets secured to the plate I118, [5 is so. mounted that its axis of rotationpasses through the crossover points of thecribbons Upstanding'irom the base" 108 is a member I20 carrying" abearing within, which is ;rotatably mounteda rock shaft I22. Bar. I I t is fixed at 124st ne end of shaft; I22 and a,downwardl y depending arm lZE Qis fixed to the other endlof thefshaft Arm. lzefis biased, by a spring I31 against afixedstop I38 formed'integral with the 'b'a sej'1 8 or otherwise fixedly mounted with "respect thereto. Contact arm I I8 is biased by origin showninFig. 7, thatis withthe contact en" the lefthand end of the iarnifin engagement withthe lower fixed contact. Thusiwh en th e arin l26 is' engaged as by an operating fin r I39 and moved in the direction of the "arrowqbarj H 6 rocks "is a direction to cause clockwis rotation of the contact arm. Returnof the-arm I 26 to initial posi-" tion permits contact arm H 8 to rotate counterclockwise back to its biased "position Thus if leads 'l30, 132 I34 and [316are'connected to the fixed contacts with; 'leaids fliith and 134 being connected to the upperfcontac ts and leads I32 and I36 to the lower contacts; a-circuit is cl'osed be tween leads I30 and 136 in on position of the contact arm and between ieads I32 and I34 inthe' other position of the contact arm. If'leads'IM' and 136 are connected togtfiehlthe switch operates, like that of Fig. "1, as asingle throw,

double pole switch'with tvvicelthe, rate of contact break and twice the contact clearance'of ordinary single throw doublepole switches. Witli'the circuitjas shown, theswitch operatesto closeeither of 'two circuits, depending' upon theposition of the contact arm. Spring I31 insures: return of thefbar 1 Hi to initial pos j' ion upon releaserof s re onthe arm-l2 In Fig. 8 asequentialswitchembodying the in- 7 vent on' is more, or less d a rammat ca i fr trated,.. LThe switch comprise sna in b i r b-1 bons at the cross-over pomts intofthe position sides I40 and MI and transverse parallel sides I 42 and I44, together with four contact arms I46, I40, I50 and I52, all fioatingly suspended by a single tensioned wire I54. The wire is connected at its ends under tension to two spaced points on side I44, crosses and passes through spaced holes in contact arm I46, then crosses again and passes through spaced holes in contact arm I48 and similarly through spaced holes in contact arms I50 and I52 with crossings intermediate the contact arms. The central stretch of the wire extends along the outer surface of the side I42 after passing through spaced holes in that side. Between each of the contact arms the overlying section of wire extends downward to the right as viewed in Fig. 8.

Insulatedly mounted on the side I4I above the contacts carried on the ends of the contact arms I46 and I50 are fixed contact carrying members I56 and I60, and, similarly, insulatedly mounted on the side I4I below the contacts carried on the ends of the contact arms I48 and I52 are fixed contact carrying members I58 and I62. External leads I64, I66, I68 and I are respectively connected to the fixed contact carrying members I56, I58, I60 and I62. Fixed stops for the contact arms are mounted on the side I4I below the ends of contact carrying arms I46 and I50 and above the ends of contact carrying arms I48 and I52. On the side I40 fixed contact carrying members I12 and I16 are insulatedly mounted below the contacts carried on the ends of arms I46 and I50 respectively, and, similarly, fixed contact carrying members I14 and I18 are positioned on side I40 above the contacts carried in the ends of contact arms I48 and I52. Suitable stops are mounted on the side I40 above the ends of contact arms I 46 and I50 and below the ends of contact arms I48 and I52. External leads I80, I82, I84 and I86 are connected respectively with contact carrying members I12, I14, I16 and I18. With this arrangement if pressure is applied to the upper stretch of the wire I54 adjacent the cross-over point intermediate the contact arm I46 and the end wall I44 as indicated by the arrow I88, contact arm I46 is rocked in a direction to close the circuit between leads I64 and I80. Movement of the contact arm I46 to this position causes contact arm I48 to rock in the opposite direction to close the circuit between leads I66 and I82 and this movement of contact arm I46 correspondingly causes rocking of contact arm I50 into position to close its circuit, whereupon contact arm I52 is likewise rocked to close its circuit. Thus the single actuation by pressure at the point indicated by arrow I88 causes successive closure of the circuit connected to the contact arms. To reverse the order of closure of the circuits, it is only necessary to press on the upper stretch of the wire I54 adjacent the crossover point between contact arm I52 and end wall I42, as indicated by the arrow I90. Downward pressure at this point causes successive rockings of arms I52, I50, I48 and I46 to close their respective circuits. v

To open the circuits successively, pressure may be exerted on the lower stretch of the wire I54 either at the cross-over between arm I46 and wall I44 or at the cross-over between arm I 52 and wall I42 or downward pressure may be applied to the upper stretch of the wire at the cross-over between arms I 46 and I48 or between arms I50 and I52. If the stops associated with the contact arms were replaced with insulated contacts and external leads, 'the'switch would operate to 8110-" a position of unstable equilibrium.

-31 The snap action-device according to-claiml' cessively close circuits connected to these con-- tact instead of to merely open the circuits heretofore identified.

The invention has now been described with reference to various embodiments thereof. In each embodiment of the invention flexible crossed wires or ribbons under tension support one or more contact arms, and movement of the contact arm or arms is effected with a snap action upon relative change in spacing of the wires or ribbons at the'cross-over points, the change in spacing being effected in any one of a number of ways. In one embodiment of the invention the change in spacing is effected by rotation of the wall supporting the ends of the ribbons, whereas in other embodiments the change in spacing is effected by downward pressure upon the upper stretch of a wire or ribbon adjacent the crossover point.

It will be apparent from the foregoing description that the invention comprises a positive acting, snap action device which is of simple construction and which insures good separation of contacts for relatively minute movements of an actuating device. The switch lends itself for incorporation within a hermetically sealed enclosure with all the advantages inherent to such construction. A switch constructed, for example, like that illustrated in Figs. 3 to 6, will actuate upon an angular displacement of the operating lever of as little as .015 degree. A switch such as that illustrated in Figs. 1, 2 or 7 will operate upon displacement of the tension wire or ribbon of as little as .002 inch, and one of the constructions of Fig. 3 upon displacement of .010 inch. The dimensions of the switch are not critical nor is it essential that the parts be exactly symmetrical. Ready adjustment is afforded by means of the fixed contacts and stops to insure any desired normal position of the contact arm. Depending upon the geometry of the device and upon the positioning of the contacts and stops, the switch may be made to return to initial position. upon release of the actuating pressure or may be made to remain in actuated position upon release of the actuating pressure. Various changes in the particular construction illustrated will occur to those skilled in the art.

The following is claimed:

1. A snap action device comprising a movable arm, flexible threads engaging and at least partially supporting said arm at two spaced points, said threads extending outwardly from their points of engagement with said arm and crossing at points spaced laterally of said arm, means securing the ends of said threads under tension in spaced relation, one of said threads overlying the other at the cross-over point on one side of said arm and underlying the other at the crossover point at the other side of the arm whereby said arm tends to rotate in one direction or the other, depending upon the relative spacing between the threads at the cross-over points about an axis located between the points of engagement with said threads, fixed means positioned for engagement by said arm for limiting the extent of rotation thereof in each direction, and actuating means for varying the spacing between the threads at a cross-over point to cause rotation of said arm.

2. The snap action device according to claim 1 wherein said threads comprise the sole support of said arm during rotation thereof through a wherein said actuating means comprises a member adapted to engage and move one thread toward the other thread adjacent a cross-over point to decrease the spacing between the threads.

4. The snap action device according to claim 1 wherein said actuating means comprise a movable member to spaced points of which one end of each thread is secured under tension and means for movin said member in a direction to vary the spacing between the threads at a crossover point. 5. The snap action device according to claim 1 wherein the ends of said threads are secured to points so located that the spacing between the threads at the cross-over point on one side of said arm is larger than that at the cross-over point on the other side of said arm whereby said arm has a biased position to Which it returns upon release by said actuating means.

6. The snap action device according to claim 1 wherein said threads are ribbons and are fixedly secured to said arm.

7. The snap action device according to claim 1 including at least one other movable arm engaged and at least partially supported at spaced points by said threads, said arm being laterally spaced from said first arm with a cross-over point of said threads located between said arms, the threads extending beyond said second arm and crossing at a location spaced laterally therefrom with the thread that overlies the other at the cross-over point between the arms underlying the other thread at the cross-over point on the other side of the second arm whereby when the spacing between the threads at a cross-over point on the far side or either arm is varied said arms rock sequentially in opposite directions.

8. A snap action switch comprising a movable arm carrying contacts adjacent the ends thereof, flexible threads engaging and at least partially supporting said arm at two spaced points, said threads extending outwardly from their points of engagement with said arm and crossing at point spaced laterally of said arm, means securing the ends of said threads under tension in spaced relation, one of said threads overlying the other at the cross-over point on one side of said arm and underlying the other at the cross-over point at the other side of the arm whereby said arm tends to rotate in one direction or the other, depending upon the relative spacing between the threads at the cross-over points about an axis located between the points of engagement with said threads, at least one fixed contact positioned adjacent each end of said arm for engagement with the contacts carried thereby and for limiting the extent of rotation of the arm, and actuating means for varying the spacing between the threads at a cross-over point to cause rotation of said arm and operation of said contacts.

9. A sequential snap action switch comprising a series of generally parallel contact carrying arms at least partially supported by tensioned threads which engage each arm at spaced points and cross at locations intermediate the arms and at locations beyond the first and last arm of the series, the ends of said threads being secured under tension in spaced relation, one of said threads alternately overlying and underlying the other thread at the cross-over points, and fixed means associated with each arm for limiting the extent of rotation thereof about axes located between the points of engagement of the threads with the arms, said last mention means including fixed contacts for engagement by the contacts carried by the arms whereby, when the spacing between he threads at a cross-over point is varied in a direction to rock an adjacent arm, rocking of such arm, varies the spacing of the threads at the cross-over point on the other side of that arm and thereby causes the next arm to rock with consequent sequential operation of the arms and contacts associated therewith.

10. A snap action switch comprising a movable arm, fixed wall members disposed on opposite sides of said arm, two flexible threads secured at their ends under tension to spaced points of said wall members and adjacent their midpoints to spaced points of said arm, the threads crossing intermediate said arm and each wall with the thread overlying the other at one cross-over underlying the other at the other cross-over a combined stop and fixed contact positioned adjacent each end of said arm for engagement therewith in opposite angular positions of the arm, electrical connections to said fixed contacts and to said arm, an actuating lever mounted for pivotal movement about an axis generally perpendicular to the plane of rotation of said arm and having a finger at its other end adapted to engage a thread adjacent a cross-over, and means for moving said lever about its pivot to vary the spacing between the threads at that cross-over and thereby cause said arm to snap from one contact closing position to another.

11. The snap action switch according to claim 10 wherein said arm, threads, contacts and lever are mounted within a hermetically sealed casing and wherein the pivotal mounting of said lever comprises a thin walled elastic tube of impervious material hermetically sealed at one end in an aperture in the casing wall and extending into the casing, the tubing being flattened at its other end, an end of said lever being secured to the flattened end of said tubing, and said means for moving said lever comprising a member extending into said tubing and gripped by the flattened portion thereof, whereby movement of said member flexes said tubing and rocks said lever.

12. The snap action device according to claim 11 wherein said member is generally L-shaped with one part extending into said tubing and another part extending generally parallel to said lever and in the same direction from the pivot whereby said lever follows the movement of said last mentioned part of said L-shaped member.

13. The snap action switch according to claim 10 wherein said threads are narrow ribbons secured along their flat sides to said arm.

14. The snap action switch according to claim 10 wherein said electrical connection to said arm comprises a fixed member engaging the arm intermediate the points of attachment of said threads and serving also as a pivot for said arm. 15. The snap action switch according to claim 10 wherein said finger engages the overlying thread at a cross-over and the ends of said threads are secured to said walls at points so located that the spacing between the threads at the cross-over adjacent the finger of said lever is larger than that at the other cross-over, whereby said arm is biased into one contact closing position and returns to that position upon reduction in pressure of the finger on the thread engaged thereby.

JAMES M. BRADY.

No references cited.

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