US2736413A - Multistation angular-movement actuator - Google Patents

Description

Feb. 28, 1956 c. E. BIEBER ET AL MULTISTATION ANGULAR-MOVEMENT ACTUATOR 4 Sheets-Sheet 1 Filed 001;. 6, 1954 5) er E 5 M N.6 0 E T m .5 n H S um v r 0 MR C Y B YN\ xfi Feb. 28, 1956 c. E. BIEBER ET AL MULTISTATION ANGULAR-MOVEMENT ACTUATOR 4 Sheets-Sheet 2 Filed 001;. 6, 1954 Feb. 28, 1956 c. E. BIEBER ETAL MULTISTATION ANGULAR-MOVEMENT ACTUATOR 4 Sheets-Sheet 3 Filed 001;. 5, 1954 Ji l.

:lllllll'l II I'll] I I lJllIllI INVENTORS. E. B46178?" Charles BY Robert S. (arr 1i TIWRNE'Y.

Feb. 28, 1956 c. E. BIEBER ET AL 2,736,413

MULTISTATION ANGULAR-MOVEMENT ACTUATOR Filed Oct. 6, 1954 4 Sheets-Sheet 4 INVENTORS'. Charles E. Bieher BY Haber? ,5. (arr 1? TTORIVEY United States Patent -MULTISTATION AN GULAR-MOVEMENT ACTUATOR Charles E. *Bieber, Elizabeth,randiRobert S. Carr, Summit,

NHL, :assignors to Airtron, Inc., Linden, N. 1., a corporation of New Jersey ApplicationOctober6, 1954, Serial No. 460,692

2 .Claims. ((21. .192-.-1-42 .This invention relates .to improved means for .imparting :angular movement :to :an element between imore than .two precise positions and, more:particularly,*to:such means which may more effectivelyaccomplishand precisely con- :trol 'such'movement.

.An important object of this invention, therefore, is to provide such means in the. form of a-devicewhich operates very rapidly, yet avoids Iharmful impact .effects at each terminus of angular movement.

Another important object is to provide such a device which is electrically controllable from a point :remote from (the .device.

The foregoing and other more or less obvious objects are accomplished by this invention which is disclosed herein, for illustrative purposes, as embodied in certain structures without, however, limiting the invention to the particular disclosed structures.

.In the accompanying drawings:

Figure 1 is an approximately central, axial, sectional view of a deviceaccording to this'invention, in association with an element to which .itimparts angular movement, the section being substantially =on their-regular line -11 of Fig. 3.

Fig. 2 is a reduced scale, .transverse, sectionalView substantially on the line 2-2 ofFigure 1.

Fig. 3 is a similarly reduced scale, transverse, sectional view substantially on .the line 3-3 of Fig. 1.

Fig. 4 is a fragmentary, sectional view substantially on the line 44 of Fig. 3.

Fig. 5 is a fragmentary, approximately-central, .axial, sectional view substantially on-the line 5-15 of Fig. 1.

Fig. 6 is a sectional view substantially .on :theline 6-6 of :Fig. 5.

Fig. 7 is a perspective view of a stop ring .employed to limit the angular movement imparted by :the device, with a fragmentary, sectionalized view, in exploded relationship to said ring, of apart which coacts :with .said ring ,for the mentioned purpose.

.Fig. .8 is .a fragmentary, phantom, perspective .view 10f parts which coact to absorb shock of impact .:at :the termini of angular movements.

,Fig. 9 .is an electric circuitdiagrarn illustrating .the.coaction of electrical components in the device.

Fig. 1 0 is a transverse, sectional view somewhat ,zlike Fig. '3, illustrating one of various possible modifications of this invention.

Referring to Big. 1, the device comprises an electric motor -which, through pinion 22, gear wheel 24;, worm '26, wormwheel 28 worm wheel shaft '30 and-transmission "link-32,.drivesadriven'shaft 34 0f -'a rotatable e'lement36 which is :the element to be angular'ly moved between several positions by the device.

Suitablesupport and :bearings, as :shown, are provided : fonthe parts 120, 22, 2.4, :26, .28 and 30 on amounting plate :38, asupported by ,studibolts A0 :(Eig 2r) which/rigidly secure plate .38 n spaced vrelationsh p t .an end :plate Eor purpose of;illustration, the elementififi, ttorbetturned ICC by the present inventive device, is shown 'as a generally cylindrical rotor of a wave-guide switch 44. The element 36 is rotatablysupported iby integral end journals 46 and 48 whichare carried respectively in bearing 50 in an outer end plate52 ofthe wave-guide switch and in bearing 54 in the end plate 42 which maybe considered as an inner end plate of said wave-guide switch. The wave-guide switch further comprises 'a generally cylindrical outer casing '56 to .oppositeends-of which theend .plates 42oand 52 are suitably fixed as, for example, :by screws 58 of which a suitable numberare provided.

The casing 56 of the wave-guide switch is .provided with plural flange connections :60, formed. similarly with radial passages 62 (only one being shown in Fig. 1) by which microwave energy from external wave guides (not shown), connected to .the .flangeconnections :60, maybe conducted to or from the interior of thecasing 56. The rotary switching element 36 may be formed with an arcuate passage 64 (or plural such passages if needed) to conduct microwave energy, interiorly of said switching element, between any selected two or more of passages '62. The function of the actuator, which embodies the presentinvention, is to rotate the rotary switching element 36 to any of several angular switching positions under remote control and thereby selectively establish conducting'connection through varcuate passage .(or passages) '64 between any selectedradialpassages '62. The motor and transmission means, already described, serve as means lfor turning the rotor 36 in the-casing 56, but afford no means for limiting the turning of said rotor to certain selected angular positions wherein-the passage 64 may register or align 'with certain passages 62 to establish microwave conduction therebetween. The further description herein relates chiefly to the means for controlling the turning I movement of the rotor 36.

The control of rotation of rotor.3 6.arises chiefly from the provision .ofa specially recessed -or ,notched stop -,-ring .66 -:(Eigs. 1 and 7) which is-disposed-within the -.wave- ;guide switch casing 56 and rigidly ifixed .by screws 68 (only .one shown to the inner .fiat :face of .rotor 36 ;in coaxial relation to the latter,,and a stop-plunger 70'which is controllably operated, by means ;hereinafter described, between ,anadvanced :or :stopping position in "which it ,coacts with notches A, .B gflI1d-C v in .the stop ring-66, as illustrated, to stop .therotationsof rotor-36 and a retracted or inactive position in which the plunger :70 is clear of ring 66 sothatthe latter and rotor.36.are free to ,bedriven .by ,the motor .20.

Itmay be well at this ,point .toenplain that transmission link .32 provides :means by which a spring gives initial .impetus to therotorfifiwtoassist the ,motor20 :in moving said ,rotor rapidly (from one -to another angular position. For this purpose, the .link.32 comprises ,a .fl-at spirahspring 7.3, ,the inner .end 3010f which .is suitably held within a diametral slot182 :formed inoneend .of .a nose piece 34 ('Figs. ,5 ,and 46),, which is ,coaxia'lly recessed -at,its .other endas 2186 to receive therewithin a ,reduced inner .end

impetus to rotor '36 in a manner hereinafter explained.

The mechanism :for operating the plunger comprises :a rot-aryssolendid 102 v suitablyafix'etl,121s by bolts 1051, upon fa :bracket 1 06 which :'in' turn is :secured by ebqlts'1108 t-to .rr l rr i'ngrplate.ealinas best eeenzin 4. :ZEhe solenoid .102 of 1a wellvknown ttypje has ;a estub shaft 1%1-0 which,

through a motion conversion device in the solenoid, is given limited rotary motion about its axis by an induction coil in the solenoid which, when energized, turns the stub shaft 110 to one limit of rotation against the action of a solenoid spring which, when the induction coil is not energized, yieldably urges the stub shaft 110 rotatively to its other limit of rotation. Said motion conversion device, induction coil and solenoid spring are not illustrated in the drawings because they are part of the solenoid 102 which, per se, is not the subject of the present invention. It is necessary for present purposes only to understand that shaft 110 is capable of about of rotation, more or less, being yieldably urged clockwisely, as viewed in Fig. 4, by the mentioned solenoid spring and being urged counterclockwisely by the mentioned induction coil of the solenoid when the latter is energized.

Rigidly fixed to the end of the shaft 110 is an arm 112 into one end of which is fixed a switch-actuating pin 114 which, when the arm 112 turns .clockwisely with the shaft 110, engages a lower leaf 116 of an electric switch 118 to separate a contact point 120 on the leaf 116 from a contact point 122 on an upper leaf 124 of said switch, the latter being fixed by bolts 126 to mounting plate 38. In this condition, the switch 118 may be said to be normally open inasmuch as it is thus held open when the arm 112 is in its normal spring-held position.

A link 128 is pivotally connected by a pivot pin 130 to the arm 112 intermediate pin 114 and the point at which said arm is rigidly secured to the end of shaft 110. The link 128 extends freely through an opening 132 in mounting plate 38 and is pivotally connected at its other end by a pivot pin 134 to the outer end of plunger '70. The plunger 70 extends through and receives longitudinal guidance from a guide sleeve 136 which is formed at the free end of a first arm 137 of a slightly oscillatable offset bell crank 138 having a hub portion 139 and a second arm 140 axially and angularly offset from said first arm. This bell crank is associated with a shock-absorbing assembly 141 hereinafter described. The sleeve 136 extends freely through an opening 142 in end plate 42 of the wave-guide switch 44; the opening 142 being enough larger than sleeve 136 that the latter may oscillate in said opening sufficiently to yield a shock-absorbing effect as hereinafter described.

The inner end of plunger 70 is reduced as at 144 and preferably hardened by suitable heat treatment, and this reduced inner end 144 is held by guide sleeve 136 in alignment with the outer marginal portion of stop ring 66 so that the plunger end 144 may be moved into any selected one of the notches A, B, C or withdrawn therefrom to control rotation of element 36. Thus, when the coil of solenoid 102 is in a deenergized condition, the spring of the solenoid causes the right end of arm 112 to be yieldably held in a lowered position as shown in full lines in Fig. 4, in which position the arm 112, through the link 128, holds the plunger 70 in its innermost longitudinal position with the end 144 of said plunger fully seated within one of the notches A, B, C, to hold the element 36 against rotation by the motor 20. However, when the coil of solenoid 102 is energized in a manner hereinafter described, arm 112 turns counterclockwisely to its broken-line posifion shown in Fig. 4 and, through link 128, plunger 70 is pulled outwardly so that its reduced end 144 is clear of the notched margin of the ring 66, and the latter and the element 36 are free to be driven by motor 20.

It may be well at this point to explain that the element 36 and with it the stop ring 66 are unidirectionally rotated by motor 20 in the direction indicated by the arrow in Fig. 7, which would be a clockwise direction of said stop ring is viewed from the left side as it appears in Fig. 1. Having this direction of rotation in mind, energizing of the coil of solenoid 102 may be caused to occur to retract the plunger from the notch in which it is then located and thereby permit commencement of a desired rotation of the element from one to another angular position; then, the solenoid coil is deenergized at a point in the motor-drive rotation of stop ring 66 when the plunger end 144 is in line with one of three intermediate surfaces 146, 148, 150 which are formed on a marginal portion of the face of the stop ring 66 adjacent, respectively, to notches A, B, C, said intermediate surfaces being in advance of the notches during rotary movement of the stop ring. The positions of said notches on ring 66 correspond to the several angular positions to which it might be desired to turn the rotor 36, and, of course, the just-mentioned deenergizing of the solenoid is timed to occur when the plunger 70 is in line with that one of said intermediate surfaces which is immediately in advance of the notch corresponding to the desired stopping position of rotor 36. When the solenoid 102 is deenergized, the plunger 70, urged by the solenoid spring, engages and slides on the adjacent one of said intermediate surfaces until the plunger engages the adjacent one of the notches A, B or C and is pushed into said notch by the solenoid spring, thereby stopping the rotor 36 in its desired angular position.

The shock-absorbing assembly 141 functions on the principle that the guide sleeve 136 is spring-urged normally to an eccentric position in the opening 142 and that, when the plunger end 144 is projected into one of the notches A, B, C, the guide sleeve 136 and the plunger end 144 may slightly yield sidewisely upon engaging a side wall of such a notch while the stop ring 66 and the element 36 are still being driven by motor 20 or are under momentum as a result of being so driven. This yielding action is possible because the plunger 70 may shift or oscillate slightly with its guide sleeve 136 from the latters said eccentric position in opening 142 to or toward its opposite eccentric position in said opening; this shifting, of course, occurring against the force of the spring means which holds the guide sleeve 136 normally in its firstmentioned eccentric position.

The shock-absorbing assembly 1411, designed to employ the principle just described, may best be understood by reference to Figs. 1, 2 and 8. A stud bolt 152, having one function, like bolts 40, for supporting the mounting plate 38, is threaded as at 154 into end plate 42 of the Wave-guide switch 44, and a screw 156, threaded into the outer end of stud bolt 152, maintains the latter in fixed relation to mounting plate 38. The bolt 152 extends through hub 139 of the bell crank 138 to serve as a shaft about which said bell crank may slightly turn, and a spacing sleeve 158, disposed on the stud bolt 152 outwardly of the bell crank 138, abuts the lat ter and retains it at the inner end of belt 152 with the bell cranks guide sleeve 136 extending into the opening 142 in end plate 42. A torque spring 160, coiled under tension about the spacing sleeve 158, has one end rigidly fixed under a clamp 162 fastened to the inner face of mounting plate 38 and its other end forcibly pressing angularly against a pin 164 fixed in the end of arm of the bell crank. The spring force thus applied angularly to hell crank 138 urges the guide sleeve 136 in that direction within opening 142 which is opposite to the direction of rotation of ring 66 so that when plunger 70 engages one of the notches A, B, C to stop said ring and the rotor 36, the plunger and guide sleeve 136 yield somewhat in the oversize opening 142 against the force of spring 160, thereby cushioning the stopping of rotation of the rotor 36.

As a part of electrical apparatus for controlling the operation of the device, the latter includes separate, similar microswitches A1, B1, C1 which are three in number in the illustrated device because the latter is illustrated as a three-position wave-guide switch. It should be understood, however, that the device must in- O .clude as many such vmicroswitchesias .the :number of nositions qt whichgthe rotor;36 is :to be turn-able.

The i switches ,A1, ;-B1, C 1 are suitably fixed :to .end plate 4.2 in :angular positions corresponding to the ganggula-rrpositions ;of;the inotches A, ,B,:C -on ring 166 which, in turn, correspond to the angular positions :to which the rotor 36 .is turnable. These. switches ,are normally closed but have operatingnrms 17,2, 174,17-6IeSpectively which may be :engagedxby ,a-cam surface .l7'8ton cam arm 9 6,.ofcollar 98.

The electrical apparatus ,also includes a remote .control switch 180 (Fig. 9) designed to establish as many different connections -,therethrough as the number of positions to which -;the motor -of the controlled waveguide .switch or equivalent rotor is .turnable. Thus, as illustrated, the control .switchhas three selective contact points A2 -B2, :C2 which, conveniently, may be angularly spaced, at similar radii, about a common central contact point X; and has, also, a ,shiftable connection element 182 whichis so arranged .thatit may be :manually .turned from anyone :to any other of "the selective contact points A2 :32, C2, preferably without engaging any intervening one of saidzselective contact points.

To understand 'the operation .of the-device, it is helpful to note that microswitch A1 vand contact ,;point A2 are operative in connection with turning-of th6'1OIOI'36 to its position corresponding with notch A; that microswitch -B1 and contact point B2 are operative vin iconnection with turning :of the rotor ,36 to ;its;p,osition corresponding with notch .B; and that microswitch C1 .and contact pointCZ ,are operative in connection with turning *of the rotor 36 to its position corresponding with notch C. Assuming that the rotor 36 -is.in'the position in which plunger 7.0 i-isin notch A and that .it is desired to shift the rotor to its position corresponding --to :notch C, the electrical controls at ffirst will :be in their .condition .as :indicated in Fig. 9.

To achieve the mentioned shift, the operator iturns connection element 182 of {remote control switch 180 from its engagement withcontact point A210 aposition in which it goes into engagement with contact point 1C2,

establishing arcircuit from voltage gsource lead plus through microswitch -C1, and thence through solenoid 102 to voltagesource lead minus Upon'solenoid 102 thus becoming energized, pin 114 .disengages the said motor.

Another effect of the energizing of solenoid "102 is that plunger 70 is withdrawn from notch A, thereby freeing rotor 36 to turn -in-response both to the tension stored up in spring 78 -at-the end =of a-previous-cycle of operation, in a manner which will be apparent from the description of the present cycle of operation, and to the action of motor 20. The mentioned spring action is immediate so' that the force of the spring has the effect of materially aiding the motor 20 in actuating the rotor 36 and also relieves said motor of a relatively heavy, instantaneous starting load that otherwise would be encountered.

When the rotor 36, turning in response to the combined spring and motor action just described, reaches a point at which the plunger 70 has just come into align ment with intermediate surface 150, the cam surface 178 of cam arm 96 engages operating arm 176 of microswitch C1 and opens the latter switch, thereby breaking the circuit previously established through said microswitch and through the solenoid 102.

Upon the breaking of said circuit, the solenoid spring urges plunger 70 toward ring 66 so that the end of said plunger slides on surface 150 until, upon reaching notch C, it falls into said notch to assure that the rotor 36 will stop in its desired angular position corresponding et notchC. While ,the plunger :wassliding .along surface l50srarm an associated with the solenoid hasmot been able 210 ",drop .suficiently vto .open motor-control .switch 118 but :as .soon .as the .plunger 70 .dropsLinto ,notch \C.-.that movement of course '.being accompanied by a complete downward movement of arm 112 as viewed .in Fig. 4 ..the .,pin 114=on ,the latter .engagesfhe bottom :leaf.11,6'.of, switch 118 and Opensthe latter switch, there- .by terminatingthe circuit through niotor20 to cause the latter .to stop.

There is .a very .slight lag .in the opening vof switch 118 following the point .at which the. plunger reaches notch Candthis .lag, together with the coasting cf the motor due to inertia, causes the spring 78 ,to wind up and store .tension therein which, in a later operation, will function .to assist motor 20 in starting rotation of rotor 3.6 .in .the same manneras has [just been described with reference to the present sequenceof operations. It will of .course be understood that, although the coasting .of .themotor-can wind up the spring, the reverse cannot oc- .curQbecause reverse motion cannot be transmitted back through worm wheel 28 and worm I26.

The .second embodiment illustrated in Fig. 110 differs from .the first-described embodiment chiefly in that means, other vthan/the described transmission link 32, are .providedfostore ,up ajforce .for aiding a motor 20a to ini .tiate .movement of ,an ejlement such .as 36 (of Fig. "1

to shift the latter from one toanother angular position.

In ,the structure illustrated in .Fig. 10, central shaft 21.6Iis-.11 nyielda'bl y constrained to turn with the element which is to be ,angularly moved by the subject actuator, and worm wheel 28a is rigidly fixed by setscrew 217 -uponsa'idsha'ft and thus the latter is constrained to turn with said worm Wheel. The latter is driven by motor 20;: through the latters ,pinion 22a, spur gear 24a which is ,1" idly fixed on shaft '202, and worm 26a which also 'is rigidly jfixefd -,to shaft 202. The structure of the second embodiment also includes a cam collar similar to .cam collar,9 8 (of Fig. 5) for switch operational purposes,.said

cam collaribeingrigidlyfixednn shaft 216.

The shaft "202 is sosupported at opposite endsin bearings,j204 and 206 as to be capable of axial movement from an extreme rightward position as shown in full lines in fig. 10 ,to an extreme fleftward position as shown in .idot-vandeiias'h lines in said lfigure. shifting of spur gear 24a also is shown in dot-and-dash lines, the .pihionfZZa being..sufiicientb'elongate to function with said spur gear regardless of such shifting =0'f the latter.

A coi1,sprin g208 extends about shaft 202 and is compressed between a spring-seat collar 210 which is on said "shaft, backed against the 'worm 26a, and 'a second spring seat collar which is on said shaft, :backed against "bearing 206. 'When shaft 202 is shifted leftwardly, collar 210 shifts with it but collar 212 does not shift as it is prevented by bearing 206 from doing so; and shaft 202 slides in the latter collar. Thus, spring 208 is compressed with energy stored therein when the shaft is in its leftward position and such energy may be utilized in a manner hereinafter described.

Instead of employing a motor-control switch such as is shown at 118 in Fig. 4, the second embodiment includes a microswitch 118a having an operating arm 214 with a roller 215 on its end in position to be engaged by the adjacent side face of spur gear 24a, when the latter is in its leftward position, to hold switch 118a in its open condition. When gear 24a moves to its rightward position, arm 214 is disengaged by said gear, thereby permitting switch 118a to close. The switch 118a is supported on a bracket 222 which is mounted upon plate 38 by bolts or screws 218 extending through elongate holes or slots 220 in said bracket which permit precise adjustment of the position of switch 118a so that the latter will coact properly with spur gear 24a as the latter shifts axially.

Corresponding axial The second embodiment also includes microswitches such as A1, B1, C1 of Fig. 2 and, indeed, all other parts hereinbefore described with reference to the first embodiment except as replaced by the described structure of Fig. 10. It also utilizes electric controls as shown in Fig. 9.

It may be assumed that, at the commencement of a cycle of operation, the device is in its condition as at the end of a preceding cycle of operation. Thus, for example, shaft 202 would be in its leftward position, spring 208 compressed, motor-control switch 118a held open by spur gear 24a, plunger 70 seated within notch A, microswitch A1 held open by cam surface 178 of cam collar 98 and shiftable element 182 of remote control switch 180 at contact point A2 of the latter switch.

To cause rotation of element 36 to an angular position in which plunger 70 will seat in notch C (for example), the operator shifts shiftable element 182 to contact C2 of remote control switch 180, thereby, through then-closed microswitch C1, energizing solenoid 102a to lift plunger 70 from notch A. Immediately upon plunger 70 clearing notch A to free ring 66 and element 36 to turn, the compressive force stored in spring 208, pushing against spring seat 210 and worm 26a, urges shaft 202 to its rightward position, causing the teeth of worm 26a to initiate rotation instantly of worm wheel 28a and shaft 216, ring 66, and rotor element 36, all of which are constrained to turn with the worm wheel.

Another effect of the described rightward shifting of shaft 202 is that spur gear 24a releases arm 214 of motorcontrol switch 118a to close the latter and start operation of motor 20a so that the latter assures further rotation of shafts 202 and 216. The turning of shaft 216 causes cam collar 98 thereon to disengage arm 172 of microswitch A1 to permit the latter to close and, although said cam collar will engage and then disengage arm 174 of microswitch B1, that will have no effect as element 182 is not in engagement with contact B2.

When cam collar 98 engages arm 176 of microswitch C1, the latter opens to deenergize solenoid 102, this occurring when plunger 70 is in alignment with surface 150 of notch ring 66 so that end 144 of said plunger, responsive to the force of the solenoid spring, engages surface 150 and slides therealong into notch C to stop element 36 with a shock-absorbing effect derived from shock-absorbing assembly 141 as already described.

At this point in operation, the worm wheel 28a cannot turn, but motor 20a is still operating, causing a reaction which is the reverse of driving coaction between Worm 26a and worm Wheel 2801. This reverse reaction causes worm 26a to thread its way leftwardly, carrying shaft 202 and spur gear 24a with it to cause the latter to open motor-control switch 11811 to stop motor 20a and to cause spring 208 to be compressed again in readiness for a further cycle of operation of the character just described.

It should be obvious that, in both described embodiments, the actuator is adapted to cause rapid and positive control of rotation of rotor element from any one to any other of several selected positions.

Although only two embodiments have been illustrated and described, it will be understood that the concept of this improvement may be utilized in various other possible embodiments without departing from the invention as set forth in the following claims.

We claim:

1. A multi-station angular-movement actuator comprising a coaxial, circular, notched portion of a rotor to be angularly moved having circumferentially spaced notches therein corresponding to points to which said rotor is to be turned, a motor drivingly connected to said rotor, a plunger adapted to coact with said notches to control rotation of said rotor by said motor, means for withdrawing said plunger from any one of said notches in which it may have been disposed to free the rotor to enable it to be turned by said motor, means for projecting said plunger into any selected one of said notches to terminate turning of said rotor, and shock-absorbing means associated with said plunger, restraining the latter yieldably against lateral movement in the direction of rotary movement of said notched portion, to cushion the stopping of said rotor when said plunger is projected into any of said notches, said shock-absorbing means comprising a pivotal member mounted for limited angular movement about an axis approximately parallel to the line of longitudinal movement of said plunger toward said notched portion and having an arm-constituting means for guiding said plunger in its said longitudinal movement to maintain the plunger in alignment with said notched portion, and means yieldably urging said arm and said plunger oppositely to the direction of rotation of said notched portion.

2. An actuator according to claim 1, said pivotal member being a bell crank having a second arm and said lastmentioned means comprising a spring coacting with said second arm to yieldably urge the bell crank angularly to cause said first arm and plunger to yieldably oppose and terminate rotation of the rotor by said motor when the plunger is engaged With one of said notches.

References Cited in the file of this patent UNITED STATES PATENTS 2,135,506 Hansch et a1 Nov. 8, 1938 2,174,552 Collins Oct. 2, 1939 2,646,152 Retz July 21, 1953 2,658,599 Luhn Nov. 10, 1953 2,702,609 Frazier et a1 Feb. 22, 1955

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