US2374652A - Control apparatus - Google Patents

Description

y 1, 1945- T. A. COHEN CONTROL APPARATUS Filed Dec. 31, 1942 4 Sheets-$119M, 1

77 ad re A 6:6 en mvEN'roR y 1, 1945- r T, A. :COHEN- 2,374,652

CONTROL APPARATUS Th ego/0 re A Men, mvENfog BYJM Z;

May '1, 1945.

' T. A. COHEN CONTROL APPARATUS Filed Dec. 31, 1942 v 4 Sh eetS -Sheet :5

,Z M My.

May 1, 1945.

Filed Dec. 31, 1942 T. A. COHEN CONTROL APPARATUS 4 Sheets-Sheet 4 FIGA 771 eodare A (a601, INVENTQI; B JM A M, Ah}. I

Patented May 1, 1945 UNITED STATES PATENT OFFICE I I l i 2,374,632 v v coN'monAm-Anmws Theodore A. Cohen, Chicago, 11]., assignor, by mesne:asslgnments, towheelco Instruments Company, Chicago, Ill., ,a corporation of Illinois Application December 31, 1942 Serial No. 470,916 18 Claims. (01. 205 16) This invention relates to control apparatus andmore particularly to a control apparatus for automatically stopping a 'wire drawing apparatus upon any defect or breakage of the wire being drawn.

One of the objects of my invention is to provide an apparatus for, efliciently controlling a wire drawing apparatus to sharply and effec-.

tively stop the same in event of the aforementioned contingency, energize alarms, and to provide an improved apparatus whereby a minute change in an impedance change device may control an oscillator circuit to effect such control.

Other and further objects of my invention will be apparent as the same becomes better understood from an examination of the specification and claims in conjunction with the accompanying drawings wherein:

Figure 1 represents a diagrammatic and schematic view of an apparatus embodying my invention;

Figure 2 is a perspective view of the mounting and housing containing the apparatus of Figure 1; a

Figure 3 is a view similar to Figure 2 showing a portion of the impedance change device housing cut away and the side of the oscillator circuit housing removed to show the manner of mounting said device and circuit in their respective housings; Figure 4 is a view similar to Figure 3 of a modified form of the mounting and housing for the apparatus;

Figure 5 is a detail fragmentary side elevational view of the mounting and housingfor the impedance change device of the apparatus.

Referring to the drawings more particularly, reference character I designates a drum of wire 2 to be drawn from a larger diameter to a smaller diameter. Wire 2 is adapted to be unwound from said drum l and drawn over a roller 3, through a die 4, through an impedance change device 5 hereinafter described, and over a roller 6 to a drum 1 which is driven by an electric motor 8. The motor 8 has a solenoid 9 the winding of .which is in parallel with the motor operating winding .(not shown) and both are connected to a source of current l through a switch ll, controlled by a relay I2 in the output circuit of the oscillator circuit l3 hereinafter described. Thus when the power supply to the motor 8 is cut off, the solenoid releases a brake arm permitting a spring to apply a brake Hi to the drum 1. Likewise operation of relay It also causes switch H to make contact 64 to energize alarmv pilot light 65 when the wire breaks. The impedance change device 5 comprises a housing l1, mounted as will be hereinafter described, provided with aligned openings I8 and IS in opposite vertical walls for the wire 2. Within housing I! there is mounted an oscillating circuit including an inductance or coil which surrounds the wire 2 and is in the nature of a variable inductance or impedance changedevice whose inductance varies with the condition of said Wire whereby any radical change therein such as breakage thereof will cause a substantial change in said inductance of coil 20. This impedance change device is adapted to control the oscillator circuit 13 as will be hereinafter described.

A grid tank circuit is mounted in the container IT. The details of mounting will be hereinafter described in conjunction with Figures 2 to 5 inclusive.

A conductor 2| connects one end of coil 20 to a coupling condenser 22 and the latter is con nected to a male terminal plug 23 on container 11. to another male tainer IT.

The male plugs 23 and 24 are adapted to connect with female connector elements 25 and 26, respectively, at one end of a concentric conductor cable 21 insulated from ground by an external rubber sheath'or cover (not shown). The cable 2! comprises an inner conductor 28, separators 29 and an outer conducting sheath 30. The end of the cable opposite to the connector 23-26 is provided with a connector similar thereto for connection to the input of an oscillator circuit hereinafter described,

terminal plug 24 on the con- The concentric co-axial conductor cable is constructed in well known mannerwith a core conductor fixedly and concentrically positioned within a conducting sheath which may be covered with insulation (not shown). By properly choosing the values of the capacitive and inductivecomponents of the oscillating circuit in enclosure H, the cable is properly terminated so that minimum radio frequency loss is obtained in the system due to the cable for any substan-,,

- tial length thereof. In this manner the remote control assembly just described may control an oscillator apparatus hereinafter described without fear of transmission losses which otherwise would reduce the sensitivity of the apparatus if not actually prevent its operation.

The oscillator circuit includes a vacuum tube 35 connected to a plate tanl; comprising-an in- The other end of the coil 20 is connected.

ductance 40, variable condenser 4| for tuningto resonance, as will hereinafter be described, and grid bias resistor or grid leak 52 for said tube.'

Alternating current voltages are obtained from 5 a multi-winding transformer having a primary winding 44, connected to a suitable source of alternating current l0, and having a plurality of secondary windings 45, 55, 5S and 51 arranged to suppiy suitable voltages to the tube i and switch H to stop driving motor 8' and apply circuits. The tube 35 and repeater tube 41, hereinafter described, are self rectifyingand therefore the operation will-be described only with respect to the positive half cycles of the alternating current voltages.

The output section ofthe tube 35 .may be traced from the left-hand terminal of the secondary winding 46 through the plate tank circuit 40, 4|, the anode or plate 31, the cathode 38, the secondary winding 55, conductor 56a,

a load impedance or resistor 53 and thence to the right hand terminal of secondary winding '46. By-pass condensers 42 and 54 are connected as shown and prevent the flow of high frequency oscillatory windings and through the load impedance 53. The total voltage impressed across the anode circuit of tube 35 is the sum of the voltages of the secondary windings 43 and 56.

The output circuit for the repeater or amplifier tube 41 may be traced from the left hand terminal of the secondary winding 55 to the anode or plate 49, the cathode 50, the secondary winding 53, the voltage of which is in phase with the voltage of the winding 55, the operating winding 12 of the relay 58 and to the right hand terminal of the winding 55. A condenser 3| is connected as shown across the relay winding 53 and prevents chatter of relay by supplying energy to relay during negative or non-conducting portion of A. C.

cycle. Transformer secondary winding 51 is connected to filaments 33 and 5| to heat cathodes 33 and 55, respectively, by wires 15-); not completed. The grid bias for effecting proper operation of the repeater tube 41 is obtained by connecting the grid or control electrode 43 to one end of the load resistor 53, the remaining portion of this circuit extending from the cathode 50 to the secondary transformer winding 56, the conductor 56a to the opposite end or the 10m re- 5 sister 53. It will be apparent that the voltage across the winding 56 is opposite to and thus .compensates for a portion of the voltage drop across theload impedance 53 and accordingly when the oscillator tube 35 is in oscillatory condition so 5 that a plate current of low value flows through the load impedance 53. A minimum negative bias equal to the diflerence between the voltage of the winding 56 and the voltage drop across the load impedance is impressed on the grid 43. Under these conditions, and with proper voltages, the tube constants, and the value of the load resist:

ance all so pre-chosen to providea low negative grid bias, a high repeater plate current is obtained 6 the oscillator tube 35 extends from the cathode 33, the transformer winding 55, the lower end of relay 7 winding I2, the tap 50 and the grid bias res stor or grid leak 52 to the grid 33.

A fixed grid bias is applied; by the above circuit, to the grid 33 which isequal to the voltage drop across the relay winding 53 to tap50 and is currents through the transformer 25 ther increases the voltage drop across the load resistor 53 and the negative bias upon the amso chosen that with maximum current flow 'in I the output circuit of the amplifier or repeater tube 41 the maximum desired negative bias is applied to the grid 36. g

The plate tank is tuned to predetermined resonance with condenser 4| so as to close relay l2 when wire 2 is at desired normal reduced condition. Should the wire 2 change from desired condition such as breaking, the inductance of coil 20 changes, causing eventual opening of relay l2 brake IE to drum 1.

When wire 3 breaks as it invariably will, if at all, beyond the die 4, changing inductance of coil age drop across the resistor 53, which correspondingly increases the negative bias upon the amplifiertube 41 with, a consequent drop in its plate current through the relay 59. The decrease in current through the relay 53 causes a decrease in the negative grid bias applied to the grid of the oscillator tube 35, which'tends to further increase the plate current ofthe oscillator tube 35. This increase in the oscillator plate current furplifier tube 41 with the consequent efiect of rapidly dropping the amplifle'r plate current to the cut-ofi point, which causes approximately zero level in plate current and opening of relay #3 to stop motor 3 and apply brake Hi. When wire 2 is rethreaded and restored the reverse occurs.

Circuit is retuned and oscillator plate current drops, decreasing the drop across resistor 53, which decreases the negative bias on the amplifier tube 41; the plate-current of the amplifier increases, increasing the drop across the relay 53, which increases the negative bias onthe grid of the oscillator 35, aiding in dropping the oscillator plate current, which further tends to decrease the bias upon the amplifier 41, etc., with the result that the final positioning of the plate current of amplifier 41 is at saturation. Bythe judicious choosing of load resistance 53, of the resistance of the relay winding 53 andthe proper apportioning of bias voltages as shown, the values of plate current between cut-off and saturation may be fixed at any desired value. The result is that large, abrupt, and rapid plate current changes are always obtained. The result obtainable is comparable to the triggering of! of a Thyratron" type hot cathode grid control rectifier without a the necessity of using gas-filled tubes.

Study of the circuit arrangement will also bring out that the system is self compensating for changes in line voltage which prevents shiftage of the control point if the line voltage should change. It is not necessary that the apparatus be limited to the use of separate vacuum tubes, each containing separate triode elements, since these separate tubes have been chosen only as a matter of convenience. Dual purpose tubes having trlode elements in a common envelope may be operated in the same manner. Direct current voltages may also be used.

It will be noted that the platesupply for tubes 35 and 41 are obtained from winding and 55,

respectively, in series with 53. Should the line voltage fall the supply voltage iron; 55 would reduce and therefore the plate current flow in plate circuit of tube 41 would tend to decrease. However, since winding supplies the plate circuit of tube 35 and since the negative bias on grid'43 ings l8 and I9 maybe aligned on essentia I same level as the axis of the wire being drawn.

isobtained from drop across resistor 03 due to plate current flow in plate circuit of tube 35, the

changes in line voltage. Aging of tubes is also compensated for in the same manner in conjunction with the regenerative connection between tap 80 and resistor 52.

In summary, the advantages of this circuit are manifest. inasmuch as a relay with a high throw,-

out percentage is not necessary, since the plate current changes through said relay are very rapid and very large; It is impossible to lose control of the oscillator, since, because of the fact that it is self-rectified, oscillations, no matter how minute. will always reoccur. Other variations of this circuit will readily occur to those versed in the art. such as the use of a common power supply,

with a self-rectified circuit, instead of separate voltages as shown. Such circuits have been designed and are entirely feasible. The one shown a work-responsive impedance change device in proximity to said work, anoscillator circuit spaceda substantial distance from said device away from said work, an oscillating circuit -mechanically' mounted in proximity to said device and operatively connected thereto for control thereby, a

concentric-conductor cable having its central conductor and shield connected between terminals of said, second circuit and the grid circuit of said first circuit and means controlled by said oscillator circuit for stopping the feed means when the work departs from predetermined conditions.

2. The combination with af machine tool provided with means for feeding the workthereto, of a work responsive impedance change device inproximity to said work, an oscillator circuit, an

oscillating circuit mechanically mounted in proximity to said'device and operatively connected thereto for control thereby, a concentric conductor cable having its central conductor and being one of a family of such circuits and being chosen as the most descriptive of the above-explained operation.

Referring to Figures 2 and 3, reference character I00 designates a pedestal having. base and upper flanges MI and I02. respectively. Bolted'to I the upper flange I02 is an upper pedestal section flan e I03 of upper pedestal section..l0l.

Section I04 'supportsa housing I05 for the oscillator circuit I3 which is substantial y vapor and moisture roof. The parts of said circuit as set forth in Fi ure 1 and the description thereof are mo nted in said housing I05 in suitable manner. The housin I05 has an upper extension "a which contains the-ali ned openings I}! 2'! aligned with said openings and the condenser 22 cooperating to form the grid tank oscillating circuit.- said wrid tank forming a self contained unit in said housin extension l'la.

shield connected 'between terminals of said sec-{ ond circuitand the grid circuit of said first circuit, said oscillating circuit adapted to be tuned to predetermined resonance with the oscillator platecircuit and adapted to change the tuning of the latter upon a change of impedance of said device and means controlled by said oscillator circuit for stopping the feed means when the wor departs from predetermined conditions.

3. The combination with a machine tool provided with means for feeding the work thereto of a work responsive impedance change device in pro-Trimity to said work, an oscillator circuit pro- 'vided with grid and plate tanks andspaced a substantial distance from-said device away from said work. the grid tank being mechanically I and I9 for the wire 2 and also contains the coil. I

In Figures 4 and 5 tl-e housing for the self con I -tained grid tank unit is designated II, has the grid tank terminal 23-426 as described in connection with Figure 1 and the concentric conductor In this embodiment the housing ll'together with its self contained impedancechange device there cable 21 connected as previously described to the oscillator circuit I3 in the housinq- I05a therefor.

mounted in proximity to'said device'and operatively. connected thereto for controlthereb'y, a

concentric conductor cable having its central conductor and sheath connected 'between terminals of said grid tankand thegrid circuit of saidoscillator circuit and means controlled by said;

oscillator circuit for stopping the feed means when the work departs from predetermined conditions. i

4. The combination with a machine tool pro-'- vided with means for feedingthewprk thereto of a work responsive impedance change device Y in proximity to said work, an oscillator circuit provided with a plurality of tanks and spaced, except for onepf' said tanks, 'a substantial distance from said device away from said work, one of in are verticaly adiusta'blerelatlveto the oscillator I3. The housina 105a of said oscillator) I0 v has. a vertical stem I00 mounted to extend upwardly from said housing. A siidable lbracket I01 and lock screw I08 is attached to the back of housing I! for holding the same in desired vertical-position on stem I06 so that the allgneitzpe the As shown inFigures 3 and 4 the external ad- .iustment for tuning to resonanceof the condenser M of Figure 1, is' at 41a. I 'I'he advantages of the aforedescribed apparatus will be apparent without further detail.

I am aware that many changes may be made without departing from the p f nqiples of my invention and I therefore do not wish .to be limited to the details shown or described.

I'claim: I

1. 'I'he combination with a machine tool prohaving its central conductor and sheath "connected between terminals of said one tank and the 4 rest of-said oscillator circuit whereby'the same said tanks being mounted in proximity to said device and operatively' connected thereto for control thereby, and a concentric conductor'cable may be controlled in accordance with predetermined conditions of said work.

5,. In a control system for controlling the 'operation of a machine tool upon work, thecombina tion of a vacuum tube oscillator having input and output circuits, a load impedance efiectively ineluded in said output circuit, a vacuum tube repeater having an input circuit coupled to'said load impedance to control the output circuit of said repeater in accordance with changes in the I voltage across said loadflmpedance, an electrorcspon-sive device having an operating winding. eflectively included in said repeateroutput circuit. and "a work responsive device for affecting thetuning of saidoscillator circuit to vary the vided with means for feeding the work thereto, of

' device in accordance with voltage across said load. impedancejwhereupon said repeater causes operation of said electroresponsiv'e device for controlling the operation of said tool.

6. In a. control system for controlling the operation of a machine tool upon work, the combinavacuum tube repeater having an input circuit I coupled to said load impedance for energization in accordance with the voltage across said imelectro-responsive device ha an operating efiectively included in said repeater output circuit for controlling the operation of said machine tool in response to variations in the energization of said winding and work piece re- 59 sponsive means connected to the oscillator circuit by a fixed impedance conductor to control the tuning of said oscillator circuit in accordance with physical changes in said work piece, whereby the bias voltage impressed on said repeater input 55 circuit varies 'from a desired minimum during resonant conditions to a desired maximum upon I r a Physical change in the work piece to cause. 1 acessation of oscillations; said variation in the bias voltage controlling the output of said re- 80 peater tube to operate said ,electro-responsive said work.

8. In a machine tool control system, the com-- tuned input and output circuits, a load impedance eiiectively included in said output circuit adapted to be traversed only by the nonpulsating cornponent of the current in said output circuit, 8.

a physical change in the condition of said work including avariable impedance device ina portion of said oscillator input circuit to change the tuning of said oscillator, whereby the voltage drop across said load impedance is varied to efiect operation of said relay to control a machine tool apparatus.

9. In a machine tool control system, the combination of an oscillator circuit including input and output circuits coupled with the input and output electrodes of an electron discharge device, means including a variable impedance device re sponsive to'the condition of work on said tool in, a portion of said oscillator circuit to change the tuning thereof, a load impedance effectively pedance, a repeater output circuit, an electroincluded in Said p t cuit 80 as t0 be responsive device connected to' said repeater outtraversed nly by the nonpul tin component put circuit, and means responsive to the condition 0f the output current, anlamplifier circuit ncludof the work being o erated on by said tool to be i put nd utput i cu s c upl d with the controlled by operation of said electro-responsive QP and h electrodes f a Second c o device includingaportion ofsaidoscillator input dlscharse v sa d p fl p t circuit circuit spaced from the rest of said oscillator cirbeing 50 p d W th said load impedance as to cult, and connected thereto by acoaxial conductor a j amplifier output current in accordance cable. for gin the tuning of said oscillator with changes in the voltage across said load imto thereby vary the voltage across said load impedance, and an electro-responsive device conpedance to efiect operation of said elective-re. t e by s p ifie output current for consponsive device and thereby controlpperation of 8 a l machine tool in accordance with t machine t V change in the condition of the work.

'L In ajnachjne tuol control ystem the com 7 10. combination, a vacuum Oscillator bination of an electron discharge" device, having having tuned input and output cui s and proinput and output circuits adapted to be tuned to so also with means r iv to he condipredetermined resonance to cause said device to tion of work in a machine tool for changing the operate as an oscillator,a load impedance eflectuning 0f Said circuits. 'lo d impedance eflectively included in said output circuit so as to -be j fively included i said output circuit, a vacuum traversed only by the non-pulsating component m f' having an input circuit ouple of the oscillator output current, whereby the voltfor fimergizatmn m accordance with the Wltage age across said impedance changes when the across f 3 111199113110? whereby 3 81 in oscillatory condition of said tube varies from said the We o saidoscillator are effective to conresonance, a repeater tube having input and outl said l' tcr, an, outputclrcuit for said re v put circuits, a-source of biasing potential, means pea-ten and resieneratlve 51 8 tween said connecting said load impedance and said sourc repeater output circuit and said oscillator input in series relation to said repeater input circuit cu'cult for effecting a Sharp Variation of the '8 with the voltage of said source in opposition to Beater 91111111111 urrent between saturation a and of less magnitude than the voltage when F- response to a change i the tunin of 7 said oscillator is in s'aid resonant condition, an 5 SSJdOSClllfltOr independently of the magnitude of condition of the work on said tool in a portion of said oscillatorjcircuit to change the tuning thereof, an amplifier circuit including input and output circuits coupled with the input and outvice, means coupling said amplifier input circuit with said oscillator output circuit whereby a change in the tuning of said oscillator circuit efiects a change in the output current of said amplifier an electro-responsive devicehaving an operating winding adapted to operate said device between two positions upon changes of predetermined magnitude in said amplifier output current, and a. regenerative coupling betweenlsa'id n t of a vacuum ub oscil ator; having fiowindinginsaid amplifier output circuit and said oscillator input circuit for effecting a. sharp vari ation of said amplifier output current between cutofl and saturation in response to an initial change in the tuning of said oscillator of suflicient magvacuu l r p at having an input m I0 nitude to effect a slightchange in said amplicoupled to said load impedance for enetion inaccordance with the'voltage drop acros saidimpedance, a repeater output circuit, a relay have ing an operating winding connected in said refler output current, whereby said electro-respom device regardless of themagnitude of Qpeater output circuit, and means responsive to ".saidchangel put electrodes of .a second electron discharge de-- 12. In a machine tool-control system, the combination of anielectron discharge device or tube having input and output circuits adapted to be' tuned to predetermined resonance to cause said tube to operate as an oscillator, a load impedance eflectively' included in said output circuit so as to be traversed only by the non-pulsating component of the oscillator'ou'tput current, whereby the voltage acrom said impedance changes when the oscillatory condition 01 said tube varies-from or toward resonance; a. repeater tube having tively included in'said repeater output circuit for controlling the operation of said machine tool I .to variations in the energisation of said winding and work piece re'eponsivemeans connected to the oscillator circuit to control the tuningof said oscillator circuit in accordance with physical cha'nges in said work piece, whereby I 25 being mounted in proximity-to said device and operatively connected thereto for control there-'.

by, and a concentricflconductor cable having its the bias voltage impressed on said .repeaterinput circuit varies from a desired minimum during resonant conditions to desired maximum upon a physical change in the workpiece to cause a' cessation of oscillationa'said variation in the v ,bias voltage controlling the output of said repeater tubeto operate said electro-responsive device in accordance with aphysical change in said work to thereby control a machinetool accordingly. 7

13 The combination with a wire drawing die and means for drawing wire therethrough, 01 a wire responsive impedance change device including an inductive coil surrounding said wire afterit leaves said die, an oscillator circuit spaced a substantial distance from saidsdevice away from atively connected thereto for control thereby a concentric conductor cable having its. central' conductor and shield connected between terminals of 'saidsecond circuit and the grid "circuit of said first circuit and'means controlled by said.

oscillator circuitior stopping said iirst means in the event of breakage of said wire.

14. In a control system for'controlling the op- .eration of a wire drawing apparatus, the combination of a vacuum. tube oscillator having input and output circuits, a load impedance eflecmay included in said output circuit, a vacuum tube repeater having aninput circuit coupled to said load impedance 'to control the'tube cir-'- cuit of said repeater inaccordance with changes in. the voltage across said load, impedance, an electro responsive device having an operating winding effectively included in said repeater outno put circuit and a device'including an inductive coil surrounding the wire beingdrawn for ect- -ing the tuning of said oscillatbr circu'it to vary the voltage across said load impedance where-r upon said repeater causes operation or said elec-' tro responsive device for stopping the operation of said apparatus upon the breakage oi'the wire.

' 15. In combination, a vacuum tube oscillator having tuned input. and output circuits and provided also with means including an inductive coll j ratus for changing the tuning of said circuits, a

load impedance eflectively includedin said output circuit, a vacuum tube-repeater having 'an input circuit coupling for energization in accordance with the voltage across said load impedance whereby changes in the tuning of said oscillator are effective to control said repeater, an

' output circuit for said repeater and a regenerative coupling between said repeater output circuit and said oscillator input circuit for eiiecting a sharp variation of the repeater output current between saturation and out-ofl' in response cc a change in the tuning of-said oscillator lndependentl'y-oif the magnitude or saidchanga. 16. The combination with-a'wire'drawing apparatus provided with means for drawing a wire through a die, of a wire responsive impedance change device including an inductive coil sur- .rounding the wire being drawn, an oscillator-circuit provided with a plurality of tanks andspaced, except for one of said ta'nks,'a"substan-" tial distance from said device," one. of said tanks central conductor and sheath'connected between terminals of said one tank and the rest of said oscillator circuit whereby the same maybe controlled in'accordance with predetermined conditions of the wire being drawn.

v 17. The combination with awire drawing apparatus provided with means for drawing a wire through a die, of a device responsive to the condition of the-wire including an inductive coil surrounding the wire being drawn, an oscillator circuit, a mount for vsaid oscillator circuit including a pedestal situated beneath said wire 6 'after the same has left the die, an oscillating said wire and oscillating circuit mechanism mounted in proximity to said device and oper circuit including said inductive coil, a vertically adjustable support for said'coil and oscillating circuit above said pedestal, a concentric conducand oscillating circuits and means controlled by said oscillator circuit for stopping the wire drawing means upon the breakage of the wire. v l 18. The combination with a wire drawing apparatus provided withmeans' for drawing wire a through adie, of a wire responsive impedance 7 change device including an inductive coil surrounding a wirelbeiug drawn and mounted in a suitable housing'apertured at oppositeends to 5 receive the wire, an oscillator circuit including a relay mechanism in its output circuit, ahousing for said oscillator circuit and relay mechanism, a .pedestal support for said housing, an oscillating circuit mounted in the first housing and operatively connected to said'inductive coil for control thereby, a concentric conductor cable having'its central conductor and shieldconnected between terminals of said oscillatorand oscillating circuits, means for vertically adjusting the position of the first housing relative to the sec? 0nd mentioned housing and means controlled by said relay mechanism for stopping the drawing of the wire in the event said wire should break.

' rn ggonoan a. come.

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