US 3551614 A
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United States Patent  Inventor Otto Babler Chicago, Ill.  Appl. No. 845,369  Filed July 28, 1969  Patented Dec. 29, 1970  Assignee Illinois Tool Works Inc.
Chicago, Ill. a corporation of Delaware  SWITCH ACTUATOR ASSEMBLY 8 Claims, 5 Drawing Figs.
[521 US. Cl 200/16, 200/77, 200/78, ZOO/153, 200/159, 200/166  Int. Cl HOIh 15/18  Field of Search 200/166SD, 153.10, 159, 16.1, 77,68
 References Cited UNITED STATES PATENTS 951,347 3/1910 Stevens 200/77 2,064,656 12/1936 Goff 200/77 2,692,920 10/1954 Brown 200/159X FORElGN PATENTS 577,928 6/1946 Great Britain 200/l6.1(UX) Primary ExaminerDavid Smith, Jr. Attorney-Robert W. Beart, Michael Kovac, Barry L. Clark and Jack R. Halvorsen ABSTRACT: Actuator assembly for electric switch provides high initial resistance to switch actuation to insure positive feel and to assure quick follow through so as to actuate the switch with a minimum of arcing. In its preferred embodiment, the actuator comprises a conical cam surface which is interrupted by a reduced diameter section so as to form an abrupt corner. A tensioned garter spring surrounds the actuator member and in the unactuated position of the actuator is positioned in the interrupted area with a point on the side of its innermost semicircular cross section in engagement with the abrupt corner. Due to the changes which take place in the angle at which force is applied to the garter spring during actuation as it is moved past the abrupt corner and onto the cam surface, the switch actuating force required to axially move the actuator decreases significantly as soon as the garter spring is on the cam surface and thus facilitates the further movement of the actuator to cause a positive, substantially unteasible switching action. A spring biased shorting plate mounted on the actuator member and adapted to connect a plurality of contacts permits a limited degree of overtravel of the actuator without damaging the contacts.
l SWITCH ACTUATOR ASSEMBLY BACKGROUND OF THE INVENTION member which carries and guides the garter spring travels in an axial direction opposite to the direction in which the cam moves after the garter spring has snapped over the enlarged portion of the cam. In US. Pat. No. 1,479,520 to J. A. Ter- I 'beclt, the cam follower or spring members 22 are fixed against axial movement and cooperate with a somewhat spherically surfaced axially moving cam surface mounted on an actuator to assist in the continued axial movement of the actuator after the largest part of the cam has moved past the springs. The patent notes that the particular action would effectively break the current and prevent the formation of arcs.
Although angled cam surface and spring type cam followers provide a particularly desirable means to bias an actuator to a predetermined position, they have the disadvantage when used for making a momentary contact that the operator experiences a feel" during operation which is so small that it makes him wonder whether the switch actuation has taken place. Another disadvantage is that they'permit arcing and stewardess call systems but wherein the passengers are accustomed to the maintained contact type of switch which has an inherent fcel". Without somedegree of feel in a momentary switch as compared to the maintained contact switch which'passengers are used to, a passenger may have doubts as to whether or. not he has actuated a signal somewhere.
SUMMARY It is anobject of this invention to provide a'switch actuating assembly which provides a positive feel even when actuated over only a short distance to make a momentary contact.
It is a further object of this invention to provide an actuating assembly for an electrical switch which requires a significantly greater force to initiate the switch operation than to continue it and thus insures that electrical contact will be made quickly and firmly so as to prevent problems caused by arcing.
An additional object of this invention is to provide an actuator assembly having a contact shorting plate or member which is mounted on the actuator so as to permit overtravel of the actuator beyond the point'at which the shorting member first contacts the contact members.
These objects are obtained by the switch actuator assembly of the present invention which preferablyincludes a housing member for mounting an actuator member for movement between an unactuated and an actuated position. The housing termost portion of the cam follower is positioned in the area of the interrupted portion and radially inwardly of the cam surface.
Preferably, the cam member and actuator member are integrally formed such that the cam surface is formed as a frustum which has its smaller end defined by its intersection with one of the sidewalls of a groove in the actuator into which a cam follower in the form of a garter spring is moved by its own spring force when no actuating force is applied to the actuator. The garter spring is mounted for radial movement relative to the axis of the actuator or cam member when an actuating force is applied to move the actuator. The dimension of the groove in which the garter spring rests in its unactuated position and the cross-sectional dimension of the garter spring are chosen so that when the actuator is in its unactuated position, the diameter of the smaller end of the frustum which defines the cam surface'will be less than the mean diameter of the garter spring and greater than the minor diameter thereof. Since the cross-sectional configuration of the garter spring is circular,.it can be readily seen that the acute angle formed in a plane containing the axis of the cam merhber and the tangent to the garter spring at the point at which it contacts the abrupt corner of the cam surface will be greater than the acute angle formed between the axis of the cam member and the tangent to the garter spring after it has moved onto the cam surface.
Because of this variation in angle during actuation, it is a necessity that a considerable force be applied to initiate the actuation of the switch, which force can be shown to be several times greater than that force required to expand the spring to complete the actuation of the switch. Obviously, once the garter spring is in contact with the conical surface of the cam, it is necessary that ever increasing forces be applied to the actuator to continue expanding the spring until the switch is actuated. However, the increase in force requirements as the spring moves along'the cam surface is of little or no significance to the overall actuation of the switch since it is virtually impossible when one considers the short travel of the actuator and the large mass of the operators fingers and arm which engage it, for the operator to reduce the force which he applies after he initiates the actuation. Thus, the initial force exerted will be continued by its own momentum to a point where the switch is actuated. Although a gradual incremental application of force to the actuator would permit the switch to be teased, it is virtually impossible for a person to apply force gradually with his fingers, and thus the switch can be considered teaseproof in'normal use. i
In order to maintain good contact pressure over the life of the switch and permit a limited degree of overtravel, the actuator includes a shorting bar carried between a pair of spring washers.
The foregoing and other objects, features and advantages will be apparent from the following more particular description of a preferred embodiment thereof, as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 isa side sectional view of a switch incorporating the improved actuator assembly taken on the line 1-1 of FIG. 3 showing the actuator in its actuated position;
FIG. 2 is a fragmentary side sectional view similar to FIG. 1 except that it shows the actuator assembly in its unactuated position;
FIG. 3 is a bottom view of the switch shown in FIG. 1;
FIG. 4 is a diagrammatical showing of the forces on the garter spring at the initiation of movement of the actuator and at the completion of such movement; and
FIG. 5 is a diagrammatical perspective view showing the relationship between the shorting bar and the switch terminals.
DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 the improved actuator assembly is illustrated in connection with a push-pull momentary type of switch device indicated generally at 10. The switch device 10 includes an outer housing 11 preferably of aluminum which may be af fixed to a panel member (not shpwn) by a nut member 12 threadingly engaged therewith which is-adapted to hold the panel in firmcontact with the shoulder portion 14 of housing ll. Positioned within the housing 11 is an actuator member 16 formed of an insulating material such as polycarbonate and having a constant cross section through any axial plane. The
actuatormember 16 includes an outwardly extending handle portion 18 which may be either pressed inwardly so as to momentar ily assume the position shown in FlG. or pulledoutwardly momentarily from the normal position shown in FIG.
2. A pair of generally frustoconical cam surfaces 20, 22 are formed on the actuator 16. The cam surfaces 20, 22 are spaced from ,each other by a groove 24 having a bottom 26 and a pair of sidewalls 28,30 which cooperate'withthe, cam surfaces 20, 22 so as to form abrupt corner edges 32, 34 respectively. The angled cam surfaces 20,22 cooperate with a tensioned garter spring 36 to cause the actuator 16 to be moved to the position shown in FIG. 2 whenever handle porkjtion is released. The garter spring 36is, guided for movemerit perpendicular to th'e'axis of theactuator by a pair of washer members 38, 4?) which should be made of some.relatively strong and wear-resistant material such as stainless steel. The lower washer 40 is held in place bya-plurality of-projections 44 formed on a terminal supporting member 46 which may bemade of an insulating material such as plastic. The terminal support member 46 is held in position relative to the housing 11 by means such as epoxy placed in the opening 48 at the end of the housing. ,7
The vertical limits of movement of the actuator 16 are determined by the stop member 50'which'projects radially therefrom and is capable of contacting either the top of the washer member 38 or the shoulder portion 52 on the housing 11. At the'lower end oftheactu ator 16,'a stud portion 56 is in-" tegrally formed. The s'tud portion 56 carries a contact shorting plate 58 which may be made of copper and is capable of undergoing a limited degree of axial movement due to the fact that it is mounted between a pair of spring washers 60, 62 which are held on the stud 56 by a fastener ring 64. The spring mounting of the contact shorting plate 58 permits the actuator to have a limited degree of overtravel between the respective positions in which the shorting plate 58 contacts the contacts 68 and 70 as the siop member 50 bottoms on the washer 38 or the spring 36 assumes at the end of an actuating stroke is indicated by dotted lines. It can be mathematically proved in av relatively lengthy-derivation that the plunger force F (assumed to be constant) applied to the actuator will have a radial component D at the end of the actuating stroke which is several time'shigher than the radial force component D at the startof a stroke..lt can also be shown that the force component D is several times higher than the force exerted by the spring which I must be overcome in order to stretch the spring sufficiently to enable the actuator to reach the end of its actuating stroke. That force component D is greater than D' is obvious from the fact that D tan aF. Since the plunger force F can be assumed constant due to the mass'of the operator's fingers and arm pressing or-pulling on theactuator one can readily see that for the angle a 30 as shown in the drawing D will be equal to .57735F whereas for the angle a 66 (for a cam surface having a slope of 24), .D will be equal to 2.2460F. One will readily see that for the relative sizes of spring and cam surface shown, the value of D is approximately four times as great as D". Obviously, in choosing the dimensions for the parts the diameter of the inner surface 26 of groove 24 must .be less than the mean diameter of the garter spring 36 since the tanof the switch as can be seen ingentdrawn at the point of contact at which the garter ,spring engages the abrupt corner 32 must be atasufficient angle to the sidewall 28 in order for the plunger force F to have a radial. component D which will be large enough to cause the garter spring to be tensioned and moved'radially outwardly of the groove. Obviously,"the position of the point.
80 on the circumference of the garter spring'36 which will engage. the abrupt corner 32 of the cam surface 20 in 'the unactuated position of the actuator can 1;.be varied by-appropriately sizing'the garter spring and the gro'ove 24. Theoretically, the
. angle a"can be varied over asubsta'ntial' range which is greater than zero and less than a. Obviouslythough, as a. becomes smallerfand-smaller, the. plunger fo rceF requiredto radially move the garter spring 36 approaches infinity. in like manner,
the plunger force F necessary to radially move the garter spring 36 would decrease as the angle a is increased. Although, as a practical matter, a can be varied between 201- -50, it has been found that by choosing the-garter spring and groove depth so that the angle a is approximately30 the actuator assembly will provide a good sense of feel due to the sudden lessening of the'force required to move the garter spring 36 radially as the garter spring starts to roll over the abrupt corner 32 and engages the cam surface 20 atpoint 82 on its periphery. Although an angle of cam surface 20 relative to the axis of the actuator equal to 24 has'been found satisfactory, this angle can be"varied over arangeof 0-4Sinorder to permit variations in the spring force available for return and thus the time'which it takes'the actuator to' return to its unactuated position when released. The cam surface angle could also be negative if a momentary action was hot required.
In, FIG. 5, the contactshorting plate 58 is shown in perspective relative to its various contacts. When theshortingplate 58 is .in its lower position inenga'gement with contact 68, it will carry current through contact88 and terminal 74. When the shorting plate 58 is in its upper position itwill carry current from contact 70 through contact 90cm terminal member 76.
'The elements 92 and 94 on terminal members 74 and 76 respectively are dummy contacts made of insulating materials.
By providing such dummyco'ntacts it is possible to provide a three point support'for the shorting plate 58 in either of its opposed positions of actuation. 1 w
Although the actuator mechanism hasbeen illustrated in connection with push-pull type of momentary switch,- itis obvious that the invention would also be applicable to other .types of switches byappropriate'modificationsaFor example,
it if was desired to have only a push type momentary switch, the lower cam surface 22 could be eliminated. Furthermore, if a maintained contact type of switch were desired, the actuator could-be formed so that the amount of relative movement possible between the garter spring and-cam surface would be sufficient to permit the garter spring to move beyond the cam surface 20 and-into a detent which would hold the members until released.
lclaim: lI-An actuator assembly for an electric .switch comprising a housing,,an actuatormembermovablymounted in said housing for axial relative movement between a first unactuated positionandasecond actuated position, a. cam member and a cam follower member mounted in said housing, an angled cam surface on the outer periphery of said'cam member which is .of increasingradial distance from the axis of the cam member between a first point at the end of the cam surface engaged by the cam follower memberv when the switch is unactuated, and a second point on 'the'cam surface which is engaged by the cam follower in the actuated position of the switch, a relieved surface on said actuator extending'substantially radially inwardly toward saidraxis from a line of intersection with said angled cam surface which includes said first point, said camsurface and said relieved surface forming an abrupt corner at said line of intersection, resilient biasing means for biasing said cam follower member radially toward the axis of said actuator, a curved cam contacting surface on said cam follower member, a first side point on said curved surface beingbiased against said abrupt corner when said actuator member is in its unactuated position while the inner endpoint os said curved surface is positioned radially inwardly of said corner and said angled cam surface, the curvature of said curved surface being such that an acute angle in a plane containing the axis of the actuator exists between a tangent to such curved surface at said first side point of contact with said abrupt corner and said axis, said acute angle being greater than the angle as measured in the same plane between said angled cam surface and said axis, said acute angle being effective to cause the amount of force necessary to initiate movement of said actuator member to be substantially higher than the force necessary to continue the movement of the actuator member towards its actuated position, means on one of said cam member or actuator member for limiting said axial movement to said angled cam surface. y
2. The actuator assembly as described in claim 1 wherein said cam follower member comprises a garter spring which surrounds said cam member, said garter spring having a free diameter which is less than any diameter which it assumes when it is in surrounding engagement with said cam follower member.
3. The actuator assembly as described in claim 2, wherein said peripheral cam surface defines a circle in any plane passing through it which is normal to the axis of said cam member, the diameter of said circle in such a plane of said cam surface which inciudes said first point at the end of the cam surface being less than the mean diameter of said garter spring when in its unactuated position and greater than the minor diameter of said garter spring in the same position.
4. The actuator assembly as defined in claim 1, wherein said actuator member and said cam member are integrally formed and wherein guide means are provided for restraining said cam follower member from axial movement relative to said housing while permitting radial movement thereof relative to the axis of said cam surface.
5. The actuator assembly as defined in claim 4, wherein said guide means comprise a pair of metal washer members and said cam follower member is a garter spring positioned for radial movement between said washer members.
6. The actuator assembly as defined in claim 1, and further including a plurality of electrical contacts in said housing and a contact shorting member mounted on said actuator member together with a spring member which is adapted to be compressed by overtravel movement of said actuator once said shorting member contacts at least some of said electrical contacts.
7. The actuator assembly as defined in claim 5, wherein at least two electrical contacts and at least one abutment member are arranged in a plane positioned normal to the axis of said actuator in spaced relationship to said shorting member when said actuator is in its unactuated position, said pair of electrical contact members and said abutment member being substantially equally spaced about said axis so as to prevent tilting of said shorting member relative to said actuator during actuation.
8. The actuator assembly as defined in claim 6 wherein angled cam surfaces extend generally axially in opposite directions from each side of said interrupted portion of said cam member and said plurality of electrical contacts are ar ranged in a pair of spaced planes normal to said axis, said shorting member being positioned between said pair of spaced planes and supported on said actuator between a pair of springs so as to permit said actuator to be either pushed or pulled from its unactuated position to an actuated position wherein said shorting bar may be held in selective engagement with the electrical contacts in either of said spaced planes.