US2443028A - Control system - Google Patents

Description

June 8, 1948. EDWARDS 2,443,028

CONTROL SYSTEM Ofiginal Filed March 21, 1936 Inventor: Martin A. Edwards,

H is Attorneggderstand that the power shaft l9 driven by the motor 22 drives a variable stroke oil pump, which supplies a variable volume of oil to a fluid motor which drives the output shaft 2|. The amount of oil supplied to the fluid motor is determined by the position of the control element 20, which when rotated varies the stroke of the oil pump. Vhen no oil is supplied to the oil motor, the output shaft 2| is at rest, and when a maximum amount is supplied, the shaft 2| rotates at maximum speed. Similarly, for intermediate rates of oil supply, the shaft 2| rotates at corresponding speed. The direction of rotation of the output shaft 2| depends upon the direction in which the control shaft 20 is turned from its neutral position.

The control shaft 20 is actuated through suitable differential gearing 2'! whose input spider 21a is geared to the input shaft I8. One bevel gear 28 of the differential device is connected through gearing 29 to the output shaft 21 and another bevel gear 30 is connected as shown, through gearing connections to the control element 20. With the power input motor 22 driving the power shaft l9 at full speed and with the control element 20 in its neutral position, the pump will have zero stroke and under this condition, the output shaft 2| will be at rest. When the motor 24 first begins to turn, the input shaft l8 does not have sufficient torque to move the heavy load l3, so it turns the control shaft 2!! instead, thereby opening the throttle some definite amount. As a result of the rotation of the control shaft, the output shaft would begin to rotate and continue to rotate at a speed proportional to the number of rotations of the control shaft, if it were not for the fact that the output shaft is connected back through the differential device 21 to the control shaft, so that when the output shaft is rotated, it turns the control shaft backwards toward its initial neutral position. As the control shaft is turned backward, the speed of the output shaft is of course diminished and when the control shaft is returned to its initial position, the output shaft is stopped. Thus, it will be seen that with the differential gear 2'! connecting the output shaft and the control shaft, the transmission device [4 functions inherently as a follow-up device, and the number of rotations of the output shaft 2! correspond exactly to the number of rotations of the input shaft It in a proportion depending upon the ratio of the gearing 29. However, if the input shaft is is rotated continuously, the output shaft 2| will also rotate continuously and at a corresponding velocity, but it will la the input shaft by an amount proportional to the velocity of the output shaft.

The electric valve apparatus 26 comprises a pair of valves 26a for supplying current in one direction to the armature of the pilot motor 24 and a second pair of valves 26b for supplying direct current to the armature in the reverse direction. These valves are in turn. supplied from a suitable source of alternating voltage represented by the three supply lines 3| through a suitable supply transformer 32, the primary winding of which is connected to the upper and middle supply lines 3! and the secondary windings of which are connected to the anodes of the four valves as illustrated. Thus, each pair of valves is connected for full wave rectification.

Although the electric valves may be of any suitable type, they are preferably of the threeelectrode type having a small quantity of an inert gas introduced into the envelope after exhaust. This inert gas may be mercury vapor or any other suitable gas and it serves to convert the usual pure electronic discharge into an arc stream there by constituting the valve a grid controlled arc rectifier. The average value of the current flowing in the anode circuit of electric valves of this character can be controlled by varying the phase relationship between the voltages supplied to the grids and the anodes respectively. When the grid voltage is substantially in phase with the anode voltage, the current flowing'in the anode circuit is maximum and when the grid voltage is lagging with respect to the anode voltage by a predetermined amount, usually more than the current flowing in the anode circuit is a minimum or substantially zero. For intermediate values of phase relationship between these voltages, the current how has corresponding intermediate values.

Alternating voltage is supplied to the grids of electric valves 26a and 26b by means of grid transformers 33 and 34 respectively, whose primary windings are connected in series relationship with the secondary winding of a grid biasing transformer 35. One of the terminals of the primary winding of the grid biasing transformer is connected to an intermediate tap of the primary winding of the supply transformer 32 and the other terminal is connected to the lower supply line 3!. This connection of the primary winding of the biasing transformer serves to derive a voltage for the grid or input circuit of the electric valve apparatus which is more than 90 lagging with respect to the anode voltage so that both pairs of valves are normally held at out off and therefore supply no current to the armature of the motor 24.

For the purpose of varying the phase relationship between the grid and anode voltages, a component voltage is supplied to the grid or input circuit through a transformer 36, one of whose secondary winding terminals is connected to an intermediate point of the secondary winding of the biasing transformer 35 and whose opposite terminal is connected to the common point between the primary windings of the grid transformers 33 and 34. Whenever this component voltage is present, it is substantially in phase with the anode voltage of one of the pairs of valves and, therefore, substantially out of phase with the anode voltage of the other pair of valves. Thus, it will be seen that by varying the magnitude of this component voltage, the phase relationship of the resultant grid voltage, 1. e., the vectoral sum of the component voltage and the grid bias voltage, may be varied as desired with the result that the magnitude of the current supplied to the electric pilot motor 24 is correspondingly varied. It will also be seen that by reversing the polarity of this component.

voltage and varying its magnitude, the opposite pair of valves will be energized so as to supply a current in the opposite direction to the electric motor. This reverse current also has a value dependent upon the magnitude of the component voltage. For the purpose of varying the magnitude of the component voltage supplied to the grid circuit of the electric valve apparatus, suitable rotary induction apparatus is provided. This rotary induction apparatus comprises the control device I5 and a similar device '31.

The control device l5 comprises a rotor member I50, provided with a single circuit winding (not shown) and a stator member l5b provided ea fl tnibut delpolynzireuitawindinatelnet: therehazprod einen;cheneein the-te ionat t e rs showmlwhiohsis physical-lygxshnilamtoa thre pulleymm g-The glevioe-iJ providedrioi; com per-1, phaseminding; eThjessingleicircuituroton:winding:l satingziorythis g11angein;tensionomprisesa is connectedito the upper.amiimiddlesupply lines pulleyetiamounted engagement Wibh :thefCaib1-Bg 3|.1iTIfe? devices 31 is lin lall respects i idellticailmfi @so as tOTOtate-With theicalolewhen it is in motion; h with atheldeviceiiclfihitThel terminalssof :theistat-on' tog-etherza Worm 14 Mtfihfifid t r by f w windingsof bothadevicesvlfi and 3:! :nrelconnectedh movingathe' position of :the;.1:a segment Also together-by: means of aconductors-:38sandtthersineh as to :change. the;;tensio nsetting of the; spring; 43 gle oircuit-rotor winding of-thei:devices!:is co oflthel tension responsive devi-e.e .---;Oloyious1y,;the;- nected to the primary-winding of the transit l iiwormfli :might:bezdirectly'w ne tfiditov l ld lmsrformer iw- A reversingswitohing deviceo3931sl3lii desired. includedin v the connections for raversingthe An electromagnetically operated elinesswitoh All polarity of the componentvoltages-supplied to is provided for. establishingand interrupting the the grid circuit of the'-eleeteic 'va1ve" apparatus paware-connections for;the ,electric valveapparathereby providing for seleetive energization of 15a tus: e The energizing:circuitnof the line switch one or the other -ot-the pairscof valvesezliawand=-- M xis controlled \byua suitable switchingdevice 2 filwayruzl of course foroperationof the pilotemotor l; a, and-thedrivingmeamdfl in thexiesiredmtire'c To plaoethe system incondition for operation, t me 7 the handle of the control device I5 is turnedwto T p a y w d fl t e 7 zgthe constant tension tie position as indicatedby Vice 1 5, when energized eprodudes an alternating- A thepOi11teI -&9 and 00- operating dial 50.: c In this. magnetic field bymeansof whioh-avoltag-ee s i position, -the. .axis of the -.magnetic field produced duced 'inthe stator Windin ;-'t y g by- -the-=stator winding of the device -31 will. he

current to fl w in t e stato din sn f hwat rightangleswith-the axis of therotorHwinddevice 31; This current inturn produces an al- 25.5:ing of the device -3'I..when the rider rolllll i in ternating magneticflfiel'drby S"' a position corresponding-With the tension that voltage-is induced in the rotor-winding of device t is d i e t holds 31 when the relationship between -the axis Of" with; the foregoing understanding 9f the 3ptherotor, Winding-and the axis'of the maenetio paratus and; its -organization in the completedfieldis otherthan-90-e--Theretore when this-90 n ftem, the operation of the system itself will 1 r t s p b r p'volta eis d fl d iflihe readily ,be understood from thefollowingdetai-led a rotor winding andconsequently no component description t p l t0 t s i i t id e- Assumingthat thehook-lfi has previously been trio v lv pp conditionsrtheh lowered to-a position in which it can be inserted system is die-energized and-at-resta- 5am the eye of the seaplane,-the-directional switch fl 39is operatedto theupposition as indicatedancfpinionfll -'tot he cable tension'respfi 'd 't viously been actuated to its 'closedposition to Vice illustrated as a rider 1 p eyfiew complete, anenergi-zing circuit'for the operating i t en m h'fi b1e". byimfi i coil of the line'switoh M,"which is therefore closed a Sp 3:" "Therotor 10f the-devi t'l zeroed to complete-the power connection from the supplyso that'no-voltage-is induced in-thewotor windlin'e 3|;to the electric 'valve ap aratus ing When 'p y 421s ina p fedet Y ifl *P =I" The hook 1 0 is inserted in the-eye of -the--seasition such'asthatin which it-isillustra-ted.-- lrr plane, by one of the-members of the crew- Unthis position; ;-a raeksegment' 144'? which includes '1 th se is quite calm while thisis taking place; the-support-for the-spring-43iremains in-a fixed: the seaplane will be rising; and falling with' -the Position; Pulleyfi is d"-'into-:areuate13 m". waves, After thehconnection hasb-eenmade-a tact-with the--cable by -the -force-rof the sprin falling wavegmotion causes the seaplane to drop a d" this f r s b l nc y f nsi n to a lower position-andthis of course, willtend the cables" Whenpa seaplan'ero 't t s,fl to'increase thBtGIlSlOll in the'cable-causing the on-the surface of the'water; it s" fifi fied" y" riden-roll; 42 to'movetoward-the right toa posi-- th w v m t on ndii' "is ther re 3 66 5 3 28? tion in which the-horizontal component of the tentha't thvcfi lebe' l ia'nd" u d."fi'q *tt sion will balance the force Offiiliipiingi 4A's tlhe hoist h to take care 0f the? changein-positionw pider roll-QT-moyes tothgrig I 7 a rag a, so T e p nsive devicer43 is in t y moves to the right-causing- -the rotor of the. device calibrated-to'hoide tension--inthe caflole ll that-:1 31to-rotate.- Asa result of thisrotatiomtheaxis is less-tharrthe forceq -to =1ift-'*the-b0atof the rotor-wincling of the-device 3l=is--r0tatedorseapla from the esurface'ofzthewatelt The" out-of the QO -"reIationship with-theaxis 0f the rack and pinion dl are "so" designed that --t fieldof the-stator and-a voltage is induced in the rotor-member of the-device -31 can--0nly--be"'r0-" rotor-windingw This---voltageis ii'n-pressed asa tated through-a limited; ranger The reasonfor componentvoitageonthe-grid or input-circuit ofthis is to"permit"the-speed oontrol-devioe5-to' the-"electricvalveapparatus; The-polarityof this energizethe systemand-increasethatensiondn; voltage-is such-as toadvancethephase-of the thecable beyond; the'value which" the-constantgrid-vo1tage withrespectto the anode voltage of tenSiO pp s Set i' that 'b one-:of the pairs of valves-and toretard the-grid or seaplane can; -be--raised from-"the surface of-- voltage of the other pair of-valvesi- It-is assumedthe water. that the'polalityof thisoomponentvoltage is such Maintaining constant tension" in-the1 cable-at as to--advance thephase of the grid-voltageof the the point of engagement witnthepulley fliwilh pair of valves--26apcausing-this pairotvalvesitot not insure constanttension at the point-of eon supplywurrent-tothearmature of the pilot motor. nection of the cable with"the -seap1ane;--i. e., -at 24. As a result of this, the pilot motor24 is=enerthe. hook-i0. The difference between the highgiZ-ed-and-rotatesthe inputshaft l8 and the pilot and low. positions-of the seaplane is-frequently so; shaft 20 in-such a direction-that the variable-sr eed great that a considerable weight ofpableisreeled transmission :devicel4 drives the-drum 43: m -a on orofi the drum betweenthe'se two-positions direction-to-payoutcableandthenebyto reduoe decreased sufllciently to permit the spring 43 to restore the rider roll 42 to its original position in which the rotor winding of the rotary induction 3! is also restored to its original position in which no voltage is induced in the rotor winding. This, of course, de-energizes the electric valve apparatus as well as the pilot motor 24. The output shaft 2| continues to rotate only for the brief interval of time necessary for the connections 20, 28, 30 to restore the control element 20 to its neutral position.

When the wave motion causes the seaplane to rise to a higher position, the tension in the cable tends to decrease, allowing the spring 43 to move the rider roll 42 to the left, which in turn causes a voltage to be induced in the rotor windings of the induction device 31 of opposite polarity. As a result of this, the opposite pair of valves 26b is energized and current is supplied to motor 24 for rotation in the opposite direction, causing opposite rotation of the motor 24 and opposite rotation of the throttle shaft 20. As a result of this, the output shaft of the variable speed transmission device is driven in the opposite direction to reel in cable until the tension is increased tothe in-ital value. When the initial tension is restored, the rider roll 42 is returned to its initial position as is the rotor winding of the rotary induction device 31 as a result of which the electric valve apparatus and the motor 24 are again de-energized and the output shaft of the variable speed transmission device I4 is again brought to rest.

As pointed out in the foregoing, maintaining the tension constant at the point of engagement of the rider roll 42 will not insure constant tension at the hook because of the changing weight of the effective length of the cable as it is unwound from the reel. As the cable is paid out from the unwinding drum, the tension in the cable tends to increase owing to the increasing weight of the unwound cable. Since the tension responsive device is set to hold a constant value of tension at the point of engagement with the rider roll 42, it would function to reduce the cable tension which of course would result in reducing the tension at the hook I!) which is not desired. However, as the cable is paid out, the pulley 45 is rotated in a clockwise direction, an amount proportional to the amount of cable paid out. The rotation of pulley 45 causes segment 44 to move to the left to increase the tension setting of the spring 43. The tension responsive device will now function to hold a higher value of cable tension at the point of engagement of the cable with the rider roll 42 and this in turn functions to maintain substantially constant cable tension at the hook l0.

When the seaplane has finally been maneuvered into a position from which it can be raised from the surface, the handle of the speed control de vice I5 is rotated to a position for hoisting at a desired speed as indicated by the position of the needle on the calibrated dial 50. The tension responsive device, of course, always attempts to hold a constant cable tension, which is less than the force required to raise the seaplane from the surface. Therefore, in order to overcome the effect of the tension control so that the seaplane can be raised from the surface-the rotor of the speed control device I5 must be rotatable through a greater angle.

Rotation of the rotor of the speed control device l5 to a predetermined speed position energizes the pair of valves 2% which supplies current to the pilot motor 24 in such a direction that 8. the ensuing rotation moves the throttle shaft 20 in such a direction as to cause the drum l3 to hoist the seaplane. As long as the speed control device I5 is maintained in the set position, the pilot motor 24 will continue to rotate and the drum. l3 will be driven at a corresponding speed. In controlling the hoisting and lowering operations of the seaplane, the speed control device l5 may be preset for a desired speed and the actual raising and lowering operation (depending of course upon the position of the switch 39) can be initiated by operation of the switch 48 to complete the supply connections from the supply line 3| to the electric valve apparatus.

Although in accordance with the provisions of the patent statutes, this invention is explained as embodied in concrete form, it will be understood that the apparatus and connections shown are merely illustrative and that the invention is not limited thereto, since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of the invention or from the scope of the annexed claims,

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A control system for hoists and the like having a hoisting cable and a winding drum therefor comprising a tension regulator responsive to the tension in said cable at a point between said drum and. the attachment of said cable to its load, a device for setting said regulator to maintain a predetermined value of tension, and means for actuating said tension setting device in accordance with the efiective length of said cable thereby to vary the tension in said cable at said point so as to maintain substantially constant tension in said cable at the point of attachment to its load.

2. A control system for hoists and the like having a pulley, a winding drum and a hoisting cable passing about said pulley to said drum comprising driving means connected to said drum, a tension regulator responsive to the tension in said cable at a point between said winding drum and said pulley for controlling said driving means, a device for setting the tension to be maintained by said regulator, and means for actuating said setting device in accordance with the effective length of cable unwound from said drum thereby to control said driving means to vary the tension in said cable at said point so as to maintain substantially constant tension in said cable at the point of attachment to the load.

3. A control system for hoists and the like having a hoisting cable and a winding drum therefor comprising driving means connected to said drum, means responsive to the tension in said cable at a point between said drum and the attachment of said cable to a load for controlling said driving means, a device for setting said tension responsive means to maintain a predetermined value of tension in said cable, and means for actuating said tension setting device in accordance with the length of cable passing said tension responsive device thereby to vary the tension at said point between said drum and said load so as to maintain substantially constant tension in said cable at the point of attachment to said load.

4. In a control system for hoists and the like having a hoisting cable and a winding drum therefor, driving means for said drum comprising a motor and a variable speed transmission dc vice connected between said motor and said drum,

: -;fisai:d-.-=transmission -devicehav;ing a speed control- :-.;2ling .element, a. -.pilot motorz;- foractuating said speedmontrollingielement,.amanually presettable "deviceifor; controlling the speed ofrsaid pilot motor thereby to. :control --the :speed of: said-drum; and mmeans actuated-by: the "tension of -said-cablefor --actuatingsaid-pilot motor to wmaintainathescable etension substantially constant.

- 5-.@In a controt system-for .hoists and: the like -.-zhaving anhoisting cable-wand a winding-drum therefor; aw-motorwand a-zvariablewspeed:transmission; device connecting said motors-and said i drumr isaid transmission device having arlspeed controlling element, a? pilot motor-:for- "actuating saidw'element; means =forrmaintaining: substantiallyrrconstant cable-tension zcomprising :a-eride'r roll :actuated byrsaid :cable andtha-ving limited r range of movement: andia-rotaryinduction device 1; actuated by. said'rider-lroltfor-*controlling-the en- :grgization. of said pit":'.m0tOl':, :andmeans for, controllingrthe hoistingspeed of said-cable-eom rap-rising a manually pre'settabl-e .TOtfily-h induction device for controlling the speed ofesaid' pilot motor.

6. In a control system for hoists and the like having a -hoistingncablezland a winding drum rtherefor, drivingmeanghayingan output shaft connected to said drum, an input shaft,,a speed control element and a differential device connecting said output shaft, input shaft and control ele; mentso that the controlelement is actuated to wproduce a speed of said output shaft proportional to thexspeed of said input shaft, a pilotimotor for actuating. said speed controlling element; :means wrrlIQSPQDSiVE to the tension. ofvsaid cablerfor en ti eerg-izinglsaid pilot motorto actuate said driving nil-means to-maintain substantially constant cable ..=tension,..and means for efieoting operation of said :snpilottmotor at a selectedspeed thereby. to ef- -e fectoperation of said cablev at a corresponding \pspeed.

e. 7a In ,aacontrol system ,for. hoists andthe like Mhaving hoisting cable. and a winding drum .,therefor, driving means having an output shaft connected to said drum and a directional control element, wpilot motor --foractuating said element, a control devicerforsenergizing-saidapilot :rcmotor to elfect operation ot-said driving means in eithers'directi-on, andrmeanszresponsive to tensession in-;said cableaforeenergizing said: motor to control said driving means to maintain substantially constant cable tension.

8. In a control system for hoists and the like having a hoisting cable and a winding drum therefor, driving means for said drum having a 55 speed control element, an electric motor for actuating said speed control element, electric valve apparatus for supplying said motor, means responsive to tension of the cable for energizing said valve apparatus thereby to energize said pilot motor to control said driving means to maintain substantially constant cable tension, and additional means for energizing said valve apparatus to cause said motor to control said driving means to operate said drum in a selected direction.

9. In a control system for hoists and the like having a hoisting cable and a winding drum therefor, driving means for said drum, said driving means having a control element, a pilot motor for actuating said element, electric valve apparatus for supplying said motor, a device responsive to tension in the cable and a rotary induction device operable thereby through a limited range for energizing said valve apparatus, to con- 72 10 trolsaid :driv ing means to maintain substantially 1aconstant-cable+.tension, and a:ma n,ually preset- I :r stable, rotary. rinduction device aoperable through arelativelylarger rangetthanthe. range of. said 5 'first. mentioned. -induction devicetfor. controlling 5 E.saio'l; valve: apparatus torenergize ,lsaidnpilot: mot rll). In .a.lcolntrol-system-for hoistsnand the like whaving a-lioistingcable-sand a w inding drum therefor, driving meansfonsaid drumlhavin a -c0ntr01--element, .a pilot motor-aforactuating said el-element, means for. supplying.- said, motor .com-

pr-isingmelectric. valve lapparatusf-provided with man o.utput-circuit ..and-:with an inputcontroL-cirt-cult, -a-device-dor-controllingthe .voltage of. said 1;- i-nput circuit thereby to control .energization of -..-saidmotor andpperation of .said drivingmeans, wand. means for controlling the-.tension on said i :cabletcomprisinga-device:movab1e in. response to {variations in;- the -.tension, .and .avoltage. control t-device in circuit with said first mentionedlvolt- ;-;age.controldeviceand actuated by movement of aesaid.tensionresponsive device forcontrollinglthe -tvoltage of-said input circuit.

11.-. Inacontrol. system forlhoists andlthe like ehaving a shoist ings cableaand a winding drum therefor; driving emeansaconnected to said drum, -saiddrivin means-having :al-controlrelement, a pilot ImOtor, .--for (actuatingsaid. element, supply r meansafors said lmotori comprising. electric. valve -rapparatus. provided with a,---c0ntrol grid, ..ineans "for 1 controlling the tension ofsaid, .cablehcomrising ar-ider roll movable inresponse to changes in thetension ofs-ther-cable arrd agridwoltage acontrol -device -actuated-ather ebyrfort energizing :said valve-apparatus and motor and a manually =operable: grid. ivoltage control,- device in circuit with said-v first --mentioned grid voltage control device foreffectingenergization of said lvalveapparatus and saidmotor .thereby to :effect operation of saiddriv-ingmeans. a

i 1 12;. In at control systemfor=hoists--and-thelike ehav-ing a hoisting? cable.' and a: winding drum therefor, driving means connected to said-drum, .u saiddrivingemeans having anelement for con- -trolling-direction.and speed apilot IIlOtQIgfOI ac- -,-,t.uating:.said: element -means :zfor controlling 13116 direction-andspeed of said driving'meanstcom- A ,prisinglelectric -vaWaaDPmatuslprovidedwith an (1 anode; and a! control -grid,-;means. ion/supplying 5 alternating nvoltagesf to, said grid and lanode, a manually presettable device for varying the phase relationship between said grid and anode voltages thereby to energize said motor and effect operation of said driving means in a selected direction, and means for controlling the tension of said cable comprising a rider roll movable through a limited range and a phas shifting device actuated thereby and in series relationship with said first mentioned phase shifting device for controlling the energization of said valve apparatus.

13. In a control system for hoists and the like having a hoisting cable and a Winding drum therefor, driving means connected to said drum, said driving means having an element for controlling speed and direction, a pilot motor for actuating said control element, means for controlling the direction and speed of said motor comprising electric valve apparatus provided with an anode and with a control grid, means for sup- 7 plying alternating voltages to the grid and anode, and means for controlling the tension of said cable comprising a resiliently mounted rider roll movable through a limited range in response to tension changes and a rotary induction device actuated thereby for varying the phase relationship between said grid and anode voltages to effect energization of said motor and operation of said driving means, and means for efiecting operation of said driving means at a selected speed comprising a presettable rotary induction device connected in series relationship with said first mentioned rotary induction device and operable through a relatively larger range than said first mentioned device.

14. In a control system for hoists and the like having a hoisting cable and a reel therefor, driving means for said reel having a control element, 'a pilot motor for actuating said element, electric valve apparatus for supplying said motor, means for maintaining the tension of said cable substantially constant comprising a 'device movable in response to changes in tension of said cable and means actuated thereby for controlling said valve apparatus to control said driving means, and means for varying the setting of said movable tension responsive device in accordance with the amount of cable unwound from the drum thereby to maintain substantially constant cable tension at the point of attachment to the load.

15. In a control system for hoists and the like having a hoisting cable and a winding drum therefor, driving means connected to said drum, said driving means having a control element, a pilot motor for actuating said element, supply means for said motor comprising electric valve apparatus provided with an output circuit connected to said motor and with an input control circuit, means for controlling cable tension comprising a rider roll movable in response to tension changes in the cable and a device actuated thereby for controlling the voltage of said input circuit, said rider roll being provided with a spring for holding it in engagement with said cable, and means for compensating said tension device for the length of cable unwound from said drum comprising a roller actuated by the motion of said cable for varying the tension of said spring. I

16. A control system for hoists and the like having a hoisting cable and a winding drum therefor, controllable driving means for said drum, control means responsive to the tension in the cable at a point intermediate the drum and load for maintaining the tension in said cable at the point of attachment to its load substantially constant, and means for varying the setting of the tension responsive means in'ac'cordance with the length of cable unwound from the'drum.

17. A control system for hoistsand the like having a pulley, a winding drum and 'a hoistin cable passing about said pulley to said drum, controllable driving means for said drum, control means responsive to the tension in the cable at a point intermediate the drum and pulley for maintaining the tension in said cable at the point of attachment to its load substantially constant, and means for varying the setting of the tension responsive means in accordance with the length of cable unwound from the drum.

18. A control system for hoists and the like having a hoisting cable and a winding drum therefor, controllable drivin means for said drum, control means for maintaining the tension in said cable at the point of attachment to its load substantially constant, and means for varying the setting of the tension responsive means in accordance with the lengthof cable'unwound from the drum.

MARTIN A. EDWARDS.

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

UNITED STATES PATENTS Number Name Date 1,049,826 Dunlop Jan. 7, 1913 1,433,079 J ett Oct. 24, 1922 1,773,709 Daniels Aug. 19, 1930 1,804,945 Miller May 12, 1931 1,815,100 Francis July 21, 1931 1,832,430 Siebs Nov. 17, 1931 1,857,817 McCann May 10, 1932 1,902,972 Rouse Mar, 28, 1933 1,966,214 Palmer July 10, 1934 1,976,611 Gulliksen Oct. 9, 1934 2,024,708 Staege Dec. 17, 1935 2,032,176 Kovalsky Feb. 25, 1936 2,163,231 Smaltz et al. June 20, 1938 FOREIGN PATENTS Number Country Date 10,361 Great Britain 1915 176,324 Germany Oct. 11, 1906 300,064 Great Britain Nov. 8, 1928

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