US2553299A - Switch for precise operating limits - Google Patents

Description

' y 1 1 1 w. F. CARR 2 5 3,2 9

SWITCH FDR PRECISE OPERATING LIMITS Filed Feb. 2, 1950 IN V EN TOR.

Willzam f C'arr Patented May 15, 195 1 UNITED j STATES"? PATENT ()FFICIE;v

SWITCHFOR'PRECISE OPERATING LIMITS J William Carr; Grand Rapids,: Mich, assignor to Lear, Incorporated, Grand Rapids; Mich a-' corporation of Illinois This invention relates to electrical switch mechanism. More specifically the invention hasreference to such mechanism'in-which the switch 7 proper is of the over-center snap-actiontype;

Switches for making and breaking anelectricalcircuit and incorporating rapid opening'and closing of the contacts by virtue of over-center spring== action are well known; These may take any of several forms but all have one feature in common; namely the inclusion of a resilient element so arranged as to provide a toggle action, and by means of which a predetermined storage of energy in the spring is released for actuation of a movable contact upon'movement of the switch opcrating element past a dead center.

Such switches are characterized however by a dead zone. That is to say, a portion ofthe move ment of the operating element must be utilized to store energy in the spring so that it 'becomesimpossible to open or close thecontacts immediately" 29 upon the application of force to the element." In many applications of such switches. as a limit switch it is important that opening or closingof. the contacts be effected at that same position {of the switch operating mechanism at which the I contacts had formerly been closed or opened. For; example, if such mechanism were to rely upon a rotary cam for such actuation, movementof the switch from closed to open is desirably effected at the same angular position of the cam in order that a switch opened at say zero angular position of the cam shall be closed atsanotherangular position not more than'a maximum nume 1:" her of degrees fromf zero, say 1 1.

Heretofore operation of the foregoing accurate character has been unavailable, the best prior arrangement known to me requiring a rotation oi the cam on the order of 5 to 10 because-of the inherent dead zone or'backlash action of the best--' over-center snap-action switches available. 4

Accordingly a principal object of the invention is the provision of mechanism 'for actuating a switch of the over-center snap-action typewherein the above-noted undesirable efiects of dead:

. to cam shaft 1 i. Also keyed to shaft-l l is a pinion 2 which the invention may be embodied in practice:

Fig. 1 shows-a front elevation of the mechanism;

Fig. 2 shows a rear elevation thereof;

Fig. 3 is a cross-sectional view taken'along the v line 33 of-Fig; 1;

Figs. 4 and 5 are detail views showing the o eration; and

Fig; 6 is a diagrammatic view to assist in the explanation of the words dead zone as employed herein. 1

At the-outset it willbe understood that the-invention 'mechanismis capable of manifold ap i plications; By way of example the same will be described as deriving operation from a rotary cam, as maybe the case in certain types of electrio motor driven rotary actuators for aircraft'-=- components, andin which installations the cur-" rent to themotor is-to be interrupted'upon a pre determined angular positioning of the output shaft following motion in one'directionand reestablished'upon rotation of the'shaft in the 'opposite sense. -As noted, it is preferred-thatreclosing of'the switch be effected in asnearly the same angularjpositionoccupied by'the camat'th'e moment the switchwas opened. e

Referringfirst to Figs. -1 2 and 3; there is shown a suitable support, e. a-plate- I ii in which asha-ft II is journalled'for rotation. -At its forwardend shaft H has aswitch operating cam l2, sometimes herein referred" to as the main cam, secured thereto, as by a nut 53. be rotated by power means (not shown) which; may be by means of reduction gearing driven by an electric motor, and to be pointed out hereinafter. In any case it will be'underst'ood that main cam I2 isrotated at a relatively-low rate of speed,

as would be required for reliable actuation of a limit switch, in order to avoid errors of over 'trave1 incident upon operation 'at'to-o higha speed.

Also journalled for rotation in plate I0 is an other shaft it upon which is secured, as by a screw iii; an eccentric cam'lhsometimes' herein? referred to as the auxiliary cam. In accordance with the principles of the invention the cam H is adapted forrotation at a speed substantially higher than that of the cam [2, say 100 times as fast. Secured to a shaft ii'driven by the power source is a pinion 25 in mesh with gear 2! keyed 1 22. Increased speed for the eccentric I! is atin turn meshes with pinion secured to eccen-'- trio shaft 15.

Shaft H is adapted to-- The snap-action switch 3| may be of any wellknown type, and is shown exemplificatively as comprising an insulating support 32 in which a pair of rigid contact members 33 and 34, a movable resilient center contact 35, an actuating arm 36 and the U-shaped resilient toggle spring 3?. Such switch is of the type disclosed in U. S. Letters Patent No. 2,237,705, granted April 8, 1941, so that further elaboration of details of construction and functioning is deemed superfluous. The several switch elements are embedded or otherwise carried in support 32, which latter is secured to a pivoted or oscillable bracket 4| shortly to be described. It will be noted that switch arm 35 bears on the surface of cam I2 for joint operation by a rise portion 38 of the latter and by the cam l1, and in a manner to be pointed out.

Pivoted on a shoulder screw 43 set into the support plate I5 is the swingable mounting plate 44 comprising a body portion 45, and an outturned flange 46 which, for portions of its length, continues parallel to the body 45 to form a retaining lip 57 for the oscillable switch body 32 and a second outturned flange 48 providing, together with the body 45 parts having apertures for engagement over the screw 43. A nut 43 is swaged into the upper end of the flange 45 and receives an adjusting screw 5| passing through an aperture in an outstanding projection 52 of the plate iii. Thus by rotation of Screw 5| the plate 45 may be hinged about the pivot 43 thereby to move the bracket 4| and hence the switch 3i toward and away from the cam I2 for adjustment of the relationship therebetween. Such selected adjustment may be rendered semi-permanent by lock nut 54.

Bracket 4| is arranged for pivotal movement with respect to plate 45 by supporting the same on a pivot screw 56 secured in the plate 45 and passing through an aperture in the lip 4'1, a nut 51 in turn locking screw 56 in place. A bolt 6| is employed to attach the switch body 32 to the bracket 4|, the opposite end of the body 32 likewise being apertured for clearance of pivot screw 55. An outturned ear of the bracket 4| is adapted to serve as a follower 62 for the auxiliary cam H, and a spring 53 secured to follower 32 and to a post 54 in the plate i biases bracket 4| constantly in a counter-clockwise sense about its pivot B. Thus rotation of cam I1 is effective to rock the switch 3| to and fro about the pivot 56 at a rate proportional to the angular velocity of the cam l2 and as determined by the ratio of the speeds of the shafts l and I5.

Prior to describing the operation of the invention mechanism it is believed that the same will be clarified by reference to Fig. 6. Such schematic showing represents somewhat generally an overcenter snap-action switch l including parts as described in connection with Fig. 1, and having an actuating button 72, which latter may be regarded as being secured to the switch arm 36 within the casing. The free position of the button 12 is shown in full lines and represents one position of the several switch elements, for example, a set of contacts 33 and being then regarded as closed. Assuming pressure is applied to the button 12 energy is stored in the spring 3! until a position is reached whereat the movable switch element 35 trips to the right. The end face of the button is now at the dotted line designated tripped position. To reverse the position of the element 35 the button is now released. However due to the toggle action, the element 35 is not moved simultaneously with reverse movement or release of the button, such reverse movement of the element 35 not occurring until a button po-' sition designated Reset position is reached. The delay between tripping and reset is defined as the dead zone, and, if actuation of the switch arm 35 is the result of rotary cam action, such dead zone would correspond to several degrees of rotation of the cam, and consequent inability to open and close the switch at substantially the same angular position of the cam.

Referring now to Fig. 4 the switch 3| is shown with element 35 against contact 33 so that the circuit represented thereby is closed. In the absence of the improvement of this invention the cam rise, after effecting opening of the contacts 33 and 35, would have to be backed off or reversed from 5 to 10 before the contacts could close again, this angular distance representing the dead zone.

With the invention improvement operation is as follows: Assuming that rise portion 38 has arrived, say in a counter-clockwise sense, into first contact with arm 35. However, since a finite amount of rotation is required to trip the switch, corresponding to a change in the radially spaced points of the cam rise surface, the switch unit 3| is not maintained stationary, awaiting such amount of rotation, but is moved against the cam in what may be termed a feeling action. Such action is brought about by the auxiliary earn 5?.

Assuming a speed of main cam i2 of 1 R. P. M. the auxiliary It, in the example, will have a speed of R. P. M. Such rotation of cam i? will oscillate the entire switch 3| about the pivot and the switch arm 36 is seeking to contact the cam l2. It will be understood that both cams are rotated jointly, and that consequently the first contact of rise 38 with switch arm 33 will occur while the switch is being oscillated. Upon first contact of switch arm and cam the switch is not tripped because the dead zone still exceeds the movement of the switch arm corresponding to the eccentricity of the cam i'i. Upon the next revolution of the cam H the point of trip is ap proached more closely due to advance of the cam rise 38. After the foregoing cycle has been repeated several times the trip is realized and the switch is finally actuated since the eccentric 5? has been continuously oscillating, the switch bracket 4|, and the rise 38 on cam i2 has slowly advanced to a position whereat the dead zone has been overcome. Should the cam l2 now be reversed from the point at which switch closure had just been effected, the eccentric likewise reverses to move the switch arm with respect to the cam i2 to break the circuit at once.

Inasmuch as the speed ratio between cams l2 and I! is, in the example, 100 to 1, very little mo tion of the cam I2 is required to open the contacts. On the second reverse turn of the cam i l the contacts can not be re-closed since the cam l2 has reversed far enough to prevent a trip.

The setting of the mechanism for the amount of dead zone individual to a selected switch be effected by selection of the speed ratio between the cams l2 and H.

Assuming a ratio of 100 to 1 between the rotational velocities of the cams l2 and ii, one-half a revolution of the eccentric, i. e., from minimum radius to maximum radius, will correspond to 1.8 on the cam l2. Accordingly while cam I2 is rotating 1.8 the bracket 4| is being swung one complete reciprocation. The arrangement is such that with a predetermined relation of the cam rise (represented by line A) to the arm 36, one reciprocation of the bracket will trip the switch, and vice versa, one reciprocation will.

upon reverse movement of the cam i2, reset the switch. Thus, with the speed ratio herein assumed, dead zone is made not more than 1.8". It will be obvious that with ratios greater than 100 to 1, greater angular accuracy may be achieved.

While for completeness in the description the switch 3! has been depicted as of the single poledouble throw type, the operation has been described for only one side thereof. It will be obvious that with the arrangement shown opening of contacts 33 and 35 will result in closing of contacts 34 and 35 and vice versa, but, in either event, with the advantages of the invention mechanism. Moreover that a single cam I2 may actuate more than one switch provided that each is arranged for oscillatory action as described. For example a second switch assembly and bracket may be located to the right of the vertical center line of the cam I2 (as seen in Fig. 4), symmetrically with the eccentric i1, and actuated by that eccentric.

While I have shown a particular embodiment of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

l. Mechanism for actuating an electrical switch of the over-center snap-action type having an actuating element comprising a main cam, an auxiliary cam, means for rotating said cams jointly, said means being arranged to provide a speed for said auxiliary cam substantially higher than the speed of said main cam, a support for said cams, a bracket oscillatably carried on said support and including means for mounting the switch thereon, the actuating element of the switch being positioned for operation by said main cam, and a follower forming part of said bracket and in operative relation with said auxiliary cam.

2. Mechanism as recited in claim 1 in which said main cam includes at least one rise portion, and said auxiliary cam is a simple eccentric.

3. Mechanism as recited in claim 1 in which said cam rotating means includes a power source and gearing interconnecting said cams.

4. A switch mechanism comprising a support, a bracket oscillably carried on said support, an over-center, snap-action electrical switch having an actuating element and secured to said bracket, a rotatable main cam, said element being disposed in operative relation with said cam, a rotatable auxiliary cam, means for driving said cams jointly at different speeds, said support having a follower portion in operative relation with said auxliary cam, each said cam having at least one active rise portion, and said driving means being so arranged as to cause said auxiliary cam rise portion to oscillate said support at a rate substantially greater than the rate at which said main cam rise actuates said switch element.

5. Mechanism as recited in claim 4 in which said main cam is provided with a single rise and said auxiliary cam is a simple eccentric.

6. Mechanism as recited in claim 4 in which said cam driving means comprises a power source and gearing interconnecting said cams.

'7. A switch mechanism comprising a support, a bracket oscillably mounted on. said support, an over-center, snap-action switch secured to said support, said switch having an actuating element, a rotatable main cam having at least one rise, said element being adapted for contact with said cam, a rotatable auxiliary eccentric cam, means for rotating said cams jointly, said bracket having a follower portion in contact with said auxiliary cam, said rotating means being so arranged as to cause said auxiliary cam to oscillate said bracket a substantial number of cycles during the period when said main cam rise is rotated over substantially half its angularly active portion.

8. Mechanism as recited in claim 7 in which said cam rotating means comprises a power source and gearing interconnecting said cams.

9. A switch mechanism comprising a support, a bracket oscillably mounted on said support, an overcenter, snap-action switch secured to said support and including a actuating element, a rotatable main cam having a rise portion in operative relation with said element, a rotatable auxiliary cam comprising a simple eccentric configuration, said bracket having a follower in operative relation with said auxiliary cam, power means for rotating said cams jointly, and gearing operatively connected to said power means and cams for rotating said auxiliary cam at a speed substantially in excess of that of said main cam.

WILLIAM F. CARR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,235,038 Pearce et a1 Mar. 18, 1941 2,294,573 Potter Sept. 1, 1942 2,338,565 Thorp et al Jan. 4, 1944 2,503,082 Tuttle Apr. 4, 1950 2,503,521 Stover Apr. 11, 1950

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