US2203709A - Limit switch - Google Patents

Description

June 11, 1940. M. E. WEEKS 2,203,709

LIMIT SWITCH Filed Feb. 27, 1939 3 Sheets-Sheet 1 4 Fig. 1.

1r r /2 5/ 44 45 X O 24 INVENTOR Fig. 2 MARION E. WEEKS /K ATTORNEY M. E. WEEKS June 11, 1940.

mm swrrcn Filed Feb. 27, 1939 3 Sheets-Sheet 2 INVENTOR MARION E WEEKS W ATTORNEY M. E. WEEKS June 11, 1940.

LIMIT SWITCH Filed Feb. 27, 1959 3 Sheets-Sheet 5 R O N E V N MARlON E. WEEKS ATTORNEY /r-/ Patented June 11, 1940 UNITED STATES PATENT OFFICE 4 Claims.

(Granted under the act of March 3, 1883, as

This invention relates to a limit switch,'and has for an object to provide an improved limit switch especially intended for use on such equipment was cranes, hoists and conveyers, signal yard extensions, turretand gun training, gun elevating, steering gear, airplane elevators, shop equipment, etc.

A further object of this invention is the provision of a limit switch wherein spare parts and complete units are interchangeable, eifecting appreciable savings in cost and weight of spares.

A further object of this invention is to provide a limit switch which may be assembled so .as to be either a quick-make or a quick-break limit switch and with slight modification may be made as both a quick-make and a quick-break limit switch, depending upon the use to which it is to be placed.

With the foregoing and other objects in view, the invention consists in the construction, combination and arrangement of parts hereinafter described and illustrated in the drawings, in which,

Fig. 1 is a plan view of one form of limit switch in finished form of this invention, with the cover omitted.

Fig. 2 is a sectional view on line 2-2 of Fig. 1.

Fig, 3 is a fragmentary elevational view of the outside of the switch box, looking in the direction of arrow 3 at Fig. 4.

Fig. 4 is a sectional view on line 4-4 of Fig. 1.

F g. 5 is a diagrammatic view of another form of limit switch, and

Jlg. 6 is a diagrammatic view form of Fig. 5.

There is shown at II a switch box of suitable material provided with a cover having an edge l2 for cooperating with a gasket |3 countersunk in the top of box II. An opening I at one end of the box I! permits the introduction of conductors l5 and I5 which are connected by means of bolts and nuts I! to contact blocks l3 and l 3, each provided with contacts 2| adapted to be bridged by a contact spring bar 2| to complete the circuit therebetween. The contact blocks la and I! are each secured by means of the same bolts and nuts II to insulating base 22 which, in turn, is secured by stud screws 23 to bosses 24 extending from the bottom of the box ll. Another boss 25 has a condenser 25 secured thereon by a stud screw 21 and is electrically connected by conductors 23 to the bolts H to thereby prevent arcing and pitting oi the contacts 2| with the spring contact bar 2| when the circuit therethrough is 55 broken.

of a modified amended April 30, 1928; 370 O. G. 757) The spring contact bar 2| forms the head of a T-shaped spring bar whose leaf spring stem is secured to the bight of a rocker 3| by a securing means 32, an insulating sheet 33 and molded insulation 34 so separating the rocker and T- stem and surrounding the securing means 32 that there is no electrical connection between the leaf stem spring 30 and the rocker 3|. This rocker" 3| is U-shaped in cross-section, the legs 35 thereof being apertured so as to be journaled on a pivoting pin 35 therethrough, this pin 36 also passing through aligned apertures in upstanding arms 3'! of a bracket 38 secured to a boss 0 on the floor of the box III by nuts or stud screws 4|.

As will be observed, the rocker 3| is iulcrumed on the journal pin 36 at a point closely adjacent the end 42 of the rocker, the distance between the fulcrum pin 36 and the rocker end 42 being approximately one-fourth the distance between the same fulcrum journal pin 36 and the T-head contact bar 2| extending from the other side of the rocker. A double coil spring 43 is wound around the pivot pin 36 and has one end 44 anchored against cotter pin 45 inserted across the bracket arms 31 and has its other end 46 resting against the bight of the rocker 3| adjacent the rocker end 42, tending to raise the T-head contact bar 2| to the position 2| (1.

Extending under the rocker end 42 is a lifter cam 41 and a breaker cam 48 which are generally circular except where the litter cam 41 is provided with an angled wall 5!) cutting a chord across the circular cam, while the breaker cam I3 is provided wtih a right angular notch 5|, one side of which extends radially and the other side of which intersects a chord wall 52 thereon. The lifter cam and breaker cam are secured by a pin 53 in one of them cooperating with an arcuate slot 54 in the other of them so as to permit only limited relative angular movement between the cams and to cause simultaneous movement of the cams when the limit of relative movement has been reached. The breaker cam 43 is provided with a friction brake 55 extending part way around its periphery in the form of a leaf spring anchored as at 56 to a side wall of box Ill. The cam 41 is provided wtih an extending hub 51 through which is passed a shaft 58 in turn extending through a gland 60 and gland cover 6|, on the side of box Ill. The cam hub 51 is secured to the shaft 58 by means of a bolt and nut 52 which also serves as an anchor for one end of a coil spring 63, coiled about the hub 51 and anchored at its other end to a spring clip 54 secured by stud screw to a boss 66 on the ll box floor, and tending to rotate the lifter cam hub 51 and lifter cam 41 in a clockwise direction, as viewed in Fig. 2.

The breaker cam 48 is journaled on the same shaft 58, being caused to rotate on the shaft 58 within the limits permitted by the pin 58 and slot' 54 by the friction brake 55, above described. A sleeve 61 between the breaker cam 48 and the side of the box I8 holds the breaker cam 48 in position adjacent the lifter cam 41, the sleeve 81 being pinned to the shaft 58 by a bolt and nut 88, one end of which serves as an .anchor for a coil spring 18, whose other end is secured to a clip 1| secured in position by a stud screw 12, assisting the spring 68 in rotating the shaft 58, it being intended that either spring 88 or 18 may be strong enough alone to cause this rotation.

A stop lever 18 keyed on the shaft 88 exteriorlly voi! the box I8 abuts against an. abutment 14 forniins part of a cover holding means 15. This cover holding means 15 cooperates with a bolt 18 extending through an apertured projection of the cover N, there being four such cover holding means provided, one at each corner of the box.

A screw 18 and lock nut 88 provide means for adjusting the stopping position of the lever 18, thus adjusting the limit of rotation of the shaft 58. On the end of the shaft 58 is aflixed a lever arm 8| having a bifurcated end 82 and carrying an axle 88 for a roller 84.

In operation, the limiting switch just described is set to act as a quick breaker switch for a mechanism such as an elevator, for instance.

The switch box I8 with its assembled mechanism' is placed in such a position that the roller 84 is in the path of some part of the elevator just as it reaches the end of its permitted path of travel, the current for operating the elevator motor in that direction being routed through the conductor I5, contacts .28, contact bar 2|, and conductor I8. As the elevator rises and contacts the roller 84 it urges the lever 8| in a counter-clockwisedirection. This causes rotation of the shaft 58, carrying with it the lever cam 41. The breaker cam 48 is held stationary by thefriction brake with the rocker end 42 pressing on the periphery of breaker cam 48, while the lifter cam 41 rotates a distance therebeyond slightly less than the length of the slot 54. As the rotation continues the pin 58 contacts the end of slot54, thereby causing the breaker cam 48 to likewise move in a counterclockwise direction, and rotating the periphery of breaker cam 48 until the angle notch 5| comes thereunder. Immediately that this happens, the

double coil spring 48 pressing against the rockerend 42 rotates the rocker arm 8|, and instantly moves .the contact bar 2| to the position 2Ia, making a quick break of the circuit through conductors I5 and I8, arcing being prevented by the presence of the condenser 26 in the usual manner. The circuit is thus instantly broken, and the elevator operated thereby will naturally cease moving. When the elevator is operated intion the breaker cam 48 is held against rotation while the angle wall 58 of the lifter cam 41 presses against the rocker end 42, causing the rocker end 42 to ride thereon until it is supported by the periphery of the lifter cam 41, rotating the rocker 8| about its pivot 88 and moving the contact bar in position Ila to circuit-completing position 2| across the contacts 28. As soon as the rocker end 42 has ridden up upon the periphery of lifter cam 41, the pin 58 comes into con-' tact with the other end of slot 54 and causes the breaker cam 48 to rotate suiiiciently to bring its periphery under the rocker end 42, thus placing the cams in position to commence another cycle of operation when the elevator again strikes the roller 84. p

The structure just described has been assembled for use as a quick-break switch where the circuit is normally complete between contacts 28. By reversing the springs 88 and 18 so that they will tend to rotate the shaft 58 in the oppo-' site direction and likewise reversing the stop lever 18, the switch will be assembled to maintain. the circuit normally broken, rather thannormally complete, while by omitting the springs altogether the switch may be brought to circuitcompleting or circuit-breaking position and remain in either position until the lever is moved to bring it to the opposite direction.

In the form shown in Fig. 5, the same principles are shown diagrammatically as applied to a switch consisting of straight levers and straight cams, rather than the circular cams in the forms shown in Figs. 1 to 4. In this form the rocker 8| pivoted on the fulcrum 88 is lifted by cam arm 41 by movement of the operating lever 8| around the fulcrum I8I, thereby causing the bar I82 to force the latch 5| under the lifted end 42 of rocker 8|, thus holding the rocker 3| in the position shown in full lines with the contact bar 2| completing the circuit between contacts 28'. Movement of the lever 8| in the opposite direction first lowers the cam 41', then causes bar I82 to move the latch 5| from under the lifted end 42 of rocker 3|, whereupon spring 43 forces rocker 8| to quickly raise contact bar 2| from the contact pins 28, thus breaking the electric circuit. I

I If desired, additional contact pins 128' may be provided at the other end of the movement of the bar 2| so that a circuit may be completed to contacts I28, after the circuit to contacts 28 isbroken. Thus when used with an elevator. for instance, the cireuitfor raising the elevator may be routed through contacts 28, while the circuit for reversing the elevator may be routed through contacts I28. Spring 88' when placed in the full line position will normally hold the contact bar in circuit-completing position through the contacts 28. If placed in the dotted line position I88 it will hold the contact bar 2| in normally circuit-breaking position for the contacts 28, while, if omitted altogether, the switch will remain in either position until changed by moving the lever 8|.

In the form shown in Fig. 6, the switch has the switch to break the circuit quickly, the same 7 5 as in Fig. 5. In broken-circuit position in Fig. 6 the spring Hi4 causes pawl Hi3 to engage in notch I05.

Upon movement of the bar 8| back to the full line position, cam bar I41 is retained by pawl I03 until the projection I08 strikes it, causing it to release pawl I03, whereupon the tension of spring I09 causes the bar ill to move the rocker 3i quickly to the circuit-completing position shown in full lines.

Other modifications andchanges in the proportionsand arrangements of the parts may be made by those skilled in the art without departing from the nature of the invention, within the scope of what is hereinafter claimed.

The invention described herein may be manufactured and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

Having thus set forth and disclosed the nature of this invention, what is claimed is:

1. A limit switch mechanism comprising terminal contact means, a switch member adapted position, yieldable means urging said rocker toward circuit-breaking position on operation of said cam means in the opposite direction, said cam means including a cam member for gradually rocking said rocker toward circuit-completing position, and a second cam member supporting said rocker in circuit-completing position after said first cam member is initially withdrawn, said second cam member including means to abruptly release said rocker to circuit-break ing position.

2.A limit switch mechanism comprising terminal contact means, a switch member adapted to be moved into and out of engagement with said contact means, a rocker means, yieldable means insulatably supporting said switch member on said rocker means, cam means operable in one direction to rock said rocker toward circuit-completing position and then hold it in such position, yieldable means urging said rocker toward circuit-breaking position on operation of said cam means in theopposite direction, said cam means including a cam member for holding saidrocker in circuit-completing position, a secll ond cam member supporting said rocker in circuit-completing position after said first cam member is initially withdrawn, said second cam member including means to abruptly release said rocker to circuit-breaking position, yieldable means normally urging said cam means in one direction, and a lever operable by a mechanism to be controlled operating said cam means in the opposite direction.

3. A limit switch mechanism comprising terminal contact means, a switch member adapted to be moved into and out of engagement with said contact means, a rocker means, yieldable means insulatably supporting said switch member on said rocker means, cam means operable in one direction to rock said rocker toward circult-completing position, yieldable means urging said rocker toward circuit-breaking position on operation of said cam means in the opposite direction, said cam means including a first cam member for moving said rocker to circuit-completing position and holding it in said circuitcompleting position, and a second cam member supporting said rocker against rocking operation, lost' motion means connecting said cam members together to cause said second cam member to follow said first cam member after said first cam member is initially operated, said second cam member including means to abruptly release said rocker for operation to circuit-changing position.

4. A limit switch mechanism comprising terminal contact means, a switch member adapted to be moved into and out of engagement with said contact means, a rocker means, yieldable means insulatably supporting said switch member on said rocker means, cam means operable in one direction to rock said rocker toward circuit-completing position and then hold it in such position, yieldable means urging said rocker toward circuit-breaking position. on operation 0! said cam means in the opposite direction, said cam means including a litter cam member for rocking said rocker toward circuitscompleting position and for holding said rocker in circuitcompleting position, and a breaker-cam member, lost motion means connecting said cam members together to cause said breaker cam member to follow said lifter cam member after said lifter cam member is operated, said breaker cam member including means toalso support said rocker in circuit-completing position until after said lifter cam is initially operated and to then abruptly release said rocker to circuit-breaking position.

MARION E. WEEKS.

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