US2456908A

US2456908A - Crane control

Info

Publication number: US2456908A
Application number: US696568A
Authority: US
Inventors: Bollaert Remi
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1946-09-12
Filing date: 1946-09-12
Publication date: 1948-12-21
Anticipated expiration: 1965-12-21

Description

Patented Dec. 21, 1948 UNITED STATES PATENT OFFICE CRANE CONTROL Application September 12, 1946, Serial No. 696,568

Claims. 1

My invention relates to electric hoist control systems, preferably for bridge type cranes.

It has been proposed to suspend two hook assemblies from a single cable and to operate them selectively by having the motor-driven cable drum act on only one of the hook assemblies while the other is held idle in its top limit position. As a rule, one of the hook assemblies. serving for heavy duty operation, is heavy in weight as compared with the other and is locked in its top position whenever the light hook assembly is to operate, while th light hook bears against a stop under the cable pull exerted by the heavier hook when the latter is in operation.

It is an object of my invention to provide an electric control system which is capable of operating the two hook assemblies of hoists and cranes of the just-mentioned type with an optimum degree of safety and reliability of selective operation and which secures an automatic protection from faulty manipulations with the aid of simple electric devices and circuit connections.

In one of its more specific aspects, the invention aims at devisin a selective control system which limits the hoist motor to slow-speed lowtorque operation when either hook assembly is close to the uppermost abutment or latching position, thus preventing overstressing and damaging the stop and latching means and the appertaining electric switches, so that no exceptional skill or attention is required from the operator of such a hoist.

Another one of the more specific objects of the invention, in conjunction with the foregoing, is to devise a control system which inherently prevents abusing the stop or latch means of the hook assemblies by suspending unduly heavy loads from the hooks while the latter are held in their topmost limit position in which they are supposed to carry no appreciable hoisting load.

It is further an object of the invention to provide an electric control system of simple design which requires a relatively low number of trolley wires, as compared with the customary singlehook crane trolleys, so that the system according to the invention can readily be installed in existing single book trolleys in order to convert them for double-hook operation.

These and other objects, as well as the means provided by my invention for achieving them, will be apparent from the followin description of the embodiment exemplified by the drawing, in which:

Figure 1 shows the circuit diagram and scheme of the appertaining hoisting assemblies, while Fig. 2 represents schematically a double-hook trolley of a bridge type crane t be controlled by the system of Fig. 1,

Referring at first to Fig. 2, numeral l denotes the trolley whose wheels 2 rest on the rails 3 of a crane bridge. The propulsion motor and control equipment of the trolley is not relevant to the present invention and hence not indicated in Fig. 2. Mounted on the trolley is a drum 4 for a hoist cable 5 from which two hock assemblies, 2. heavy main assembly MH and a light-weight auxiliary assembly AH are suspended (Fig. 1 and 2). The cable 5 passes from the drum in several turns around a pulley journalled about the shaft 6 of a block I which carries the main hook 8 and a latch and switch control member 9. Thence the cable is led over an idler sheave l0 and passes over a pulley I l in the block [2 of the auxiliary assembly. Block H. carries the auxiliary hook l3 and is designed to abut against a stop structure [4 (Fig. 1) of the trolley frame when the assembly is in its illustrated top limit position. The end of cable 5 is secured to the trolley frame. This illustrated way of roping provides equal lifting speeds for the two hooks at any given reelin speed of the cable, but can be replaced by a roping and pulley arrangement for other desired speed ratios. For instance, by omitting the pulley H and attaching the cable end to the blocklZ, the auxiliary assembly AH can be given twice the speed and half the lift of the main hook; or by adding a stationarily journaled sheave and second pulley to the main assembly, twice the speed and one-quarter the lift of the main hook can be given to the auxiliary assembly. Hence, the illustrated roping should be understood to represent merely one of the designs applicable in conjunction with the invention. The main hook assembl MH is considerably heavier than the auxiliary assembly so that the latter is always pulled up against the stop 14 when the main hook is in operation.

The cable drum 4 is connected through a reduction gear l5 (Fig. 2) with the hoist motor M, which in the embodiment of Fig. 1 is shown as consisting of a wound-rotor motor with three primary terminals T1, T2, T3. The transmission between motor M and drum 4 includes a spring-set, friction brake B (Fig. 1) whose magnet coil It must be energized in order to release the drum. Coil I6 is connected across motor terminals T1 and T3 so that the brake B is set when the motor is deenergized and automatically released when power is applied to the motor. The secondary or rotor circuit of motor M includes two sets of resistor denoted by I! and 18 in Fig. 1.

A latching device [9, mounted on the trolley, has a spring-biased latch 20 (Fig. 1) to engage a latch opening of member 9. An electromagnetic device, such as a torque motor or thrustor T serves to withdraw the latch in order to release the main assembly for operation. Mounted on the trolley are further four limit switches S1, S2, S3, S4 (Figs. 1 and 2). Switches S1 and S2 are actuated by the member 9 of the main assembly and switches S3 and S4 cooperate with the auxiliary assembly in the manner described in a later place.

It is assumed that, as customary, the hoist motor is controlled from a cab that is mounted on the crane bridge separate from the trolley. The necessary connections between cab and trolley are formed by trolley wires and appertainin" or roller contacts. Only the trolley .s appertaining to motor M are shown in Fig. .L. They comprise three power supply wires 2|, H2 and 23 whose appertaining slide contacts are c-zc-nnocted to motor terminals Ti, T2 and T3 respectively. Three

power wires

2t, 25, 26 connect is secondary tcriininals of motor M with the resisters ll and i8 and with the master controller MC in the cab; and six further trolley wires, denoted by (ill through 3o, connect the limit switches and the thruster T with the control equip: ent of the cab.

The master controller, though here shown as a dru i c may consist of any suitable type control apparatus. As illustrated, the controlle" has a group of contact lingers, such as th are denoted by 3 to cooperate with a number contact segments such as those denoted by ill, 38 and 33. The exemplified controller, shown in developed form, has an off position, three hoisting positions, and three lowering positions. sooiatcd with the circuits controlled by the master controller four push button contacts BR, BS, EM and BA. Button BR. must be depre. ed to start the system or to reset it for rewooed operation after each tripping of the main co actor LV mentioned below. Button BS, when depressed, trips the main contactor and stops the motor; and buttons BM and BA serve to select the main hook or the auxiliary hook operation. The four buttons are installed in easy reach of the operator, with buttons and BA preferably located in the handle of the master controller MC so that they can be depr ssed While the motor controller is being actuated.

The main contractor LV, as here shown, de-

signed a low voltage protective relay of the type customarily used on cranes. It may be equipped for overload protection unless separate overload protection is desired. Another contactor, denoted by RH, serves as a hoisting relay and closes only when one of buttons BM and BA is depressed.

it. relay RT controls the thrustor T. The system includes further the relays marl-zed RL, R2, R4, Etl'tli and RA. Relay RL responds to the closi itch. Si or $3. Relays R2 and R4 by the limit switches S2 and S4 ctively, while relays RM and RA operate .1 control by the respective selector buttons HM and BA.

Details of design and performance of the above-mentioned system elements will be re- 4 i-erred to presently in conjunction with a description of the operation of the control system.

With assemblies MH and AH in the illustrated uppermost positions, limit switches Si and S3 are open and limit switches 52 and S4 are closed. When the master controller MC is in the oil position, as shown, the energization of the power supply bus-es Li, La, L3, by the closing of a main switch (not illustrated) does not as yet cause any operation of the hoist motor but has immediately the effect of adjusting the system as follows;

Relay RL picks up in circuit:

and opens its contact Eli.

Relay R2 picks up in circuit:

and opens contact 58 while closing contact 59.

Relay R l piclis up in circuit:

and opens its contact E2 while closing contact 5|. Due to the opening of contacts 58 in relay R2 and in relay Rd, coil 55 of the hoist relay RH is disconnected, and relay remains dropped out. Relays RA, RM and RT remain also deenergized.

After energizing the buses Ll, L2, L3, the operator depresses temporarily the button BR. This has the effect ol closing the coil circuit of the 10W voltage contactor LV:

L i -3 %l-BR-BS-4 5-3 9--L3 (4) Contactor L'V picks up and closes the main contacts M, 42, 43 while also closing a self-holding circuit at back contact M. Hence, contactor LV re iii/i115; picked up as long; as no voltage failure occurs unless it is tripped by the actuation of the sto contact If, after dropping out. of con- Lactor LV, the master controller is not in its of! position, the circuit of coil 45 in contact If? remains interrupted until the segment 38 is placed in the illutsrated position by returning the motor controller to the off position. "With both hooks in top position, the motor controls, of course, cannot be set ior hoisting operation. If the master controller. is nevertheless turned for hoisting, the holding circuit of coil 35'is interrupted segi'nent t9 so that contactor LV is tripped. Hence, with mains Ll, L2, L3 energized and tel. 'arily depressing the start button BR, the s, stem permits at first only lowering operations until the hook to be used has dcscended from the illustrated position.

If the main hool; to be used, the operator first depresses the main button BM momentarily. Due to the actuation of button BM, the circuit of coil Si is opened so that relay RL closes its contact 55 and thereby completes for coil of the main hool: relay RM the circuit:

Relay RM, by closing its contact 48, energizes the coil 61 of relay RT in circuit:

L3-8 l--59-6 l-48.--Li (6) Relay RT closes the self-sealing circuit L3-E l--59-5 6--Li 1'7 and hence stays picked up when shortly thereafter push button BM is released and interrupts the coil circuit of relay RM and causes the latter to drop out. As a result, relay RT remains picked up and, by closing its contacts 64 and B5, closes the circuit of thrust or motor T through trolley circuit of coil 60 in relay R2.

wires 3: and 33. Hence, latch 20 is withdrawn and hook MH is ready to be lowered. Then the master controller is turned in the lowering direction. In the first position for lowering, the master controller connects bus Ll through con tact 41 with trolley wire 2| and primary terminal Tl of motor M, and bus L3 through contact 43 and trolley wire 23 with motor terminal T3, while bus L2 is in connection with terminal T2 through contact 42. Thus the motor M is energized to run the cable drum 4 in the lowering direction with all secondary resistors l1 and 18 effective for minimum acceleration. Simultaneously, the brake coil 16 is energized and releases the brake B. Hook MH is lowered at slow speed so that first the limit switch S2 is opened and then the limit switch S1 closed as the member 8 leaves the location of the limit switch assembly.

The opening of limit switch S2 interrupts the This relay drops out and, at contact 59, opens the self-sealing circuit of relay RT which in turn deenergizes the thrustor T and resets the latch 20 for catching and holding performance.

The closing of limit switch SI interconnects conductors l3 and I6 and thereby the trolley wires 30 and 3| thus placin the conductor 15 in connection with bus L3. This establishes for coil 51 of relay RL the parallel circuit:

so that relay RL will stay picked up independently of the future condition of the push buttons BM or BA during the continuance of the lowering performance and thereby prevents energization of RM or RA.

The condition of the system thus reached re mains unchanged when the motor controller is further advanced to the second and third lowering positions except that in the second position the resistors H of the secondary motor circuit are shorted while in the third position all resistors l1 and I8 are shorted for corresponding increases in lowering speed.

When the main hook MH is in lowered position, i. e., with limit switch SI closed and limit switch S2 open, the actuation of the master controller in the hoisting direction initiates the following performance.

In the ofi position of the master controller, relay RL is picked up and maintains its contact 56 open due to the closing of limit switch SI, and relay R2 remains dropped ofi due to the opening of switch S2. Since relay R4 is energized through the limit switch S4 of hook AH, coil 55 of relay RH is deenergized so that contacts 5| and 53 remain open during hoisting of the main hook.

In the first position hoist of controller MC, the voltage contactor LV remains now energized in circuit;

The master controller now connects bus LI through contact 4| with trolley wire 23 and motor terminal T3, while bus L3 is connected through contact 43 and controller MC with trolley wire 2| and motor terminal TI. The connection of terminal T2 to bus L2 remains as before. Hence the motor is now energized to run reversed with all secondary resistors l1, 18 in. In the sec-- end position hoist, resistors I! are shorted by the master controller, and in the third hoisting position all secondary resistors l1, l8 are shorted for increased hoisting speed.

During operation of the main hook, the auxiliary hook is held in top limit position under the pull exerted by the overbalanced main hook and hook load. If, after using the main hook, it is desired to operate with the auxiliary hook, the main hook must first be lifted into its top limit position. When the raising hook trips the limit switch SI, this switch opens the circuit (8) of coil 51 in relay RL so that contact closes, and it also interrupts the coil circuit (9) of contactor LV, thus disconnecting the power supply at contacts 4|, 42, 43. Consequently, when the main hook reaches the limit switch SI, the drive is automatically stopped. The operator now indicates his intention to use the auxiliary hook by depressing the button BA. This causes the motor M to continue pulling up the main hook at slowest speed until the hook is caught by latch 20 and closes the limit switch S2. It is required, however, that the master controller be placed in off position and the contactor LV closed by actuation of button BR in order to permit this pulling-up operation. The circuit then completed at button BA includes coil 41 of relay RA and extends as follows:

Relay RA picks up and, by closin its contact 46, energizes the coil 55 of the hoist relay RH in circuit:

Ll-4658-55L3 (11) Relay RH closes the power supply circuit at contacts 5| and 53 and thus causes the motor M to run in the hoisting direction with all resistors l1, I8 inserted in the secondary motor circuit.

As soon as the main hook is locked by latch 20 and limit switch S2 closed, the circuit (2) of coil in relay R2 is closed so that the coil circuit (I I) of relay RI-I is opened at contact 58, thus interrupting the power supply at contacts 5! and 53 and again stopping the motor.

Then, when the operator turns the master controller in the lowering direction, the motor M will run accordingly. However, since now the relays RM and RT are deenergized, the thrustor T remains idle and the main hook latched. As a result, the auxiliary hook is now lowered.

During its initial downward travel, hook assembly AH opens first the limit switch S4 and then closes the limit switch S3. Switch S4 breaks the coil circuit (3) of relay R4 so that contact 62 closes in preparation of a still open circuit for coil 55 of the hoisting relay RH. Switch S3, by closing, energizes coil 51 of relay RL in circuit:

so that the contact 56 opens. During lowering of the auxiliary hook, the master controller in first, second, and third positions lowering controls the primary and secondary motor circuits in the same manner as described above with reference to main hook operation. The hoisting performance in the three hoist positions of the master controller is likewise substantially as described above except that, due to the latching of the main hook, the auxiliary hook is now in use.

When the auxiliary hook is lowered from its top limit position and it is desired to use the main hook, the operator first hoists the auxiliary hook until it trips the limit switch S3. This opens the coil circuit (l2) of relay RL whose .contact 56 closes, and interrupts. also the. holding circuit:

of the contactor LV. The power supply cut off at contacts ii, :33 of contactor LV, the motor stops. 'I--e operator then resets the system by turning t ster controller into off" position and He then sign-ls his intention to use the main hook by actua e button BM. This energizes the coil 59 of relay BM in circuit.

Contact 69 of relay RM closes for the hoist relay RH the coil circuit:

tactsifii and 0 speed with L circuit inserts upward until it clo relay R4 picks up in circuit:

: condary motor main hook to auxiliary RH, thus stopping the power only at int ct, log; contact 0! of rela The closbutton BM dccompletcs the which continues h circuit coil circu, holding (l) and c latch '1]. The latc' a switch S3! .larice as deand advantages of be recogn sed with ed embodiment.

...ll'l no main hook to auxiliary hook operation thus preventing over iaglng of the limit 13s, cable and amp '3 achieved by the he opera. at ed once the operating part of. travel Once the rais limit s tcli S2 or S3, tin

Tiger be used to pertaining equi fact that the ho.

tween the two mo hook the motor hi in the illustra troller is then trol ed only by n minimum one:

other hand, the system prey button control for causing the ho. t n creep at m imum hoisting speed for an or length of time. This prevention liner op :aticn is achieved. by the fact that the push button control. circuits receive BXCltELDlOll thro' :1 relay EL only after the hook has reached the limit switch Si or S3. In other words, nothing will happen to affect the crane performanc if the main or auxiliary control buttons BM, BA are pushed while the hook assemblies are not sufficiently close to their sing the resethutton BR. I

the available hoisting .vitch S New,

tion by said motor, relay means connc 8 top limit positions. Should the operator hoist a load up to the top limit and then try to hold it with the. latch on the main hook, or should he try to leave a load suspended on the auxiliary hook close to the top limit position, such an operation becomes impossible ii? the load has an appreciable weight. This will he recognized ir the fact that the motor can be operated only i all secondary resistors in circuit soon the limit switch Si or reached. Consequently torque too low for lif in. substantial loads above these limit switches hence, to hold such loads latched suspended in th uppermost positions.

tinguished by its econ The system is iurthe c. only oi equipment necessary for controlling the two hook assemblies. Only lour more uley wires are re .lrccl in comparison with the conventionai systems with only one hoe assembly. This facilitates inst l ing acco." ling to the ention on e: n? bridge type c with -rol cab mo .ited on the .dge.

' 'ght auxaiary hoe a snccd t hook assembly wi' in ti o electrical ca p" the present invention.

obvious to those skilled in the art enlboclyi my invention o ed and modified with respect to dc circuit el ents '"ld circuit connectio den from 9 objects and princ and w hill the scope oi l turcs set forth in clai i I claim as 21-, lVC. on: 1. A control system for a hoist having main hook assembly, a light auxilia sembly and a singl cable from w semhlies are suspended, and compr bination a hoist motor for operating said cable to selectively hoist and lower one of saic I blies, means for latching said main assen its top limit position, an electric device for leasing said latching means to permit lowcl said main assembly from position, 1' switch means disposed to actua by said auxiliary assembly when the la top limit position, operator--actuahle me 0012/ trol means connected to said motor for controlling its speed torque performance in hoisting and lowering direction, operator-actuable co means for selecting of said assemblies O1 said selector contacts and said maste: With said limit switch means and SELIJ. latch ieleasing evice so as to perm t releasing s id latch means, for subsequent lower 1;; of said in sembly from said top position, only when said auxiliary assembly is in its top position a master control means in or condition and to permit selecting said auxiliary assembly, for sub-- sequently lowering it from its top position, on 1 when said main assembly is latched and said of said a,-

ing said main assembly from said position, a first limit switch means disposed near the top position of said main assembly and having a lower limit switch and an upper limit switch, a second limit switch means disposed near the top position of said auxiliary assembly and having a lower limit switch and an upper limit switch, operator actuable master control means connected to said motor for controlling it to run in hoisting and lowering directions under selective speed torque conditions, operator-actuable contact means for selecting of said assemblies for operation by said motor, relay means connected with said master control means and said lower limit switches for limiting said motor to low speed operation when the selected assembly is raised up to the appertaining lower limit switch and relay means connected with said upper limit switches for stopping said motor when the raising assembly reaches the appertaining upper limit switch.

3. A control system for a hoist having a heavy main hook assembly, a light auxiliary hook assembly and a single cable from which said assemblies are suspended, and comprising in combination a hoist motor for operating said cable to selectively hoist and lower one of said assemblies, means for latching said main assembly in it's top limit position, an electric device for releasing said latching means to permit lowering b said main assembly from said position, first limit switch means disposed near the top position of said main assembly and having a lower limit switch and an upper limit switch, second limit switch means disposed near the top position of said auxiliary assembly and having a lower limit switch and an upper limit switch, operator actuable master control means connected to said motor for controlling it to run in hoisting and lowering directions under selective speed torque conditions, operator-actuable contact means for selecting of said assemblies for operation of said motor, relay means connected with said master control means and said lower limit switches for limiting said motor to low speed operation when the selected assembly is raised up to the appertaining lower limit switch, relay means connected with said upper limit switches for stopping said motor when the raising assembly reaches the appertaining upper limit switch, and a relay controlled by said second limit switch means and connected with said contact means so as to permit selecting said main assembly for operation and causing said device to release said latching means only when said auxiliary assembly is in its top position.

4. A control system for a hoist having a heavy main hook assembly, a light auxiliary hook assembly and a single cable from which said assemblies are suspended, and comprising in combination a hoist motor for operating said cable to selectively hoist and lower one of said assemblies, means for latching said main assembly in its top limit position, an electric device for releasing said latching means topermit lowering said main assembly from said position, first limit switch means disposed near the top position of said main assembly and having a lower limit switch and an upper limit switch, second limit switch means disposed near the top position of said auxiliary assembly and having a lower limit switch and an upper limit switch, operator actuable master control means connected to said motor for controlling it to run in hoisting and lower directions under selective speed torque conditions, operator-a ctuable contact means for selecting of said assemblies for operation of said motor, relay means connected with said master control means and said lower limit switches for limiting said motor to low speed operation when the selected assembly is raised up to the appertaining lower limit switch, relay means connected with said upper limit switches for stopping said motor when the raising assembly reaches the appertaining upper limit switch, and a relay controlled by said upper limit switch of said first limit switch means and connected with said contact means so as to permit selecting said auxiliary assembly for operation only when said main assembly is latched in its top position.

5. A control system for a hoist having a heavy main hook assembly, a light auxiliary hook assembly and .a single cable from which said assemblies are suspended, and comprising in combination a hoist motor for operating said cable to selectively hoist and lower one of said assemblies, means for latching said main assembly in its top limit position, an electric device for releasing said latching means to permit lowering said main assembly from said position, first limit switch means disposed near the top position of said main assembly and having a lower limit switch and an upper limit switch, second limit switch means disposed near the top position of said auxiliary assembly and having a lower limit switch and an upper limit switch, operator actuable master control means connected to said motor for controlling it to run in hoisting and lowering directions under selective speed torque conditions, operator-actuable contact means for selecting one of said assemblies for operation by said motor, relay means connected with said master control means and said lower limit switches for limiting said motor to low speed operation when the selected assembly is raised up to the appertaining lower limit switch, relay means connected with said upper limit switches for stopping said motor when the raising assembly reaches the appertaining upper limit switch, and a relay controlled by said upper limit switches and connected with said contact means so as to render said contact means operative, for selecting one of said assemblies for operation, only when both assemblies are in their respective top position.

6. A control system for a hoist having a heavy main hook assembly, a light auxiliary hook assembly and a single cable from which said assemblies are suspended, and comprising in combination a hoist motor for operating said cable to selectively hoist and lower one of said assemblies, means for latching said main assembly in its top limit position, an electric device for releasing said latching means to permit lowering said main assembly from said poistion, first limit switch means disposed near the top position of said main assembly and having a lower limit switch and an upper limit switch, second limit switch means disposed near the top position of said auxiliary assembly and having a lower limit switch and an upper limit switch, operator actuable master control means connected to said motor for controlling it to run in hoisting and lowering directions under selective speed torque conditions, operator-actuable contact means for selecting of said assemblies for operation by said motor, relay means connected with said master control means, and said lower limit switches for limiting said motor to low speed operation when the selected assembly is raised up to the appertaining lower limit switch, relay means connected with said upper limit switches for stopping said motor when the raisin assembly reaches the appertaining upper limit switch, a relay controlled by said upper limit switches and connected with said contact means so as to render said contact means operative, for selecting one of said assemblies for operation, only when both assemblies are in their respective top position, and a latch release relay disposed for controlling said device and connected with said second limit switch means, said selector contact means and said master control means so as to release said latching means upon selected actuation of said contact means only when said motor control means are in off condition.

7. A control system for a hoist having a heavy main hook assembly, a light auxiliary hook assembly and a single cable from which said assemblies are suspended, and comprising in combination a hoist motor for operating said cable to selectively hoist and lower one of said assemblies, means for latching said main ssembly in its top limit position, an electric device for releasing said latching means to permit lowering said main asembly from said position, first limit switch means disposed near the top position of said main assembly and having a lower limit switch and an upper limit switch, second limit switch mean disposed near the top position of said auxiliary assembly and having a lower limit switch and an upper limit switch, operator actuable master control means connected to said motor for controlling it to run in hoisting and lowering directions unde selective speed torque conditions, operator-actuable contact means for selecting one of said assemblies for operation by said motor, relay means connected with said master control means and said low-er limit switches for stopping said motor when one of said assemblies is raised up to the appertaining lower limit switch, a hoist relay controlled by said contact means and said limit switch means so as to energize said motor for slow-speed hoisting when said latter lower limit switch is actuated by said latter assembly and when thereafter said contact means are actuated by the operator to select said other assembly for subsequent operation, and relay means connected with said upper limit switches for stopping said motor when the raising assembly reaches the appertaining upper limit switch.

8. A control system for a hoist having a heavy main hook assembly, a light auxiliary hook assembly and a single cable from which said assemblies are suspended, and comprising in combination a hoist motor for operating said cable to selectively hoist and lower one of said assemblies, means for latching said main assembly in its top limit position, an electric device to releasing said latching means to permit lowering said main assembly from said position, first limit switch means disposed near the top position of said main assembly and having a lower limit switch and an upper limit switch, second limit switch means disposed near the top position of said auxiliary assembly and having a lower limit switch and an upper limit switch, operator actuable master control means connected to said motor for controlling it to run in hoisting and lowering directions under selective speed torque conditions, operator-actuable contact means for selecting one of said assemblies for operation by said motor, relay means connected with said master control means and said lower limit switches for stopping said motor when one of said assemblies is raised up to the appertaining lower limit switch, a hoist relay having a coil 12 circuit controlled by said contact means and said limit switch means so as to energize said motor for s1ow-speed hoisting when said la lower limit switch is actuated by said latter assembly and when thereafter said contact means are actuated by the operator to select said other a", bly for subsequent operation, and further relay neans connected with said upper limit switches for stopping said motor when the raising as," 4 ply reaches the appertaining upper limit A control system for a hoist having a be main hook. assembly, a light auxiliary nook sembly and single cable from which said aw semblies are suspended, and comprising in combination a hoist motor for operating said cable to selectively hoist and lower one of said ttSilGlllblies, means for latching said main assembl, in its top limit position, an electric device i leasing said latching means to permit lowerin said main assembly from said position, first in switch means disposed near the top position of said main assembly and having a lower switch and an upper limit switch, seco switch means disposed near the top p0 said auxiliary assembly and having a lo switch and an upper limit switch, operator actuable master control means connected to id motor for controlling it to run in hoisting and low or lg directions under selectivespccd torque conclitions, operator-actuable contact means for sclooting one of said assemblies for operation by said motor, relay means connected with said mas or control means and said lower limit switches for limiting said motor to low speed operation when the selected assembly is raisedup to the appertaining lower limit switch, relay means connected with said upper limit switches for stopping said motor when the raising assembly reaches the ap pertaining upper limit switch, a release relay connected to said device and having a coil c" controlled by said contact means and said i i limit switch means so as to cause said device release said latching means when said contact means are actuated :[or selection of said 1 assembly while said main assembly is in its position, said coil circuit having a seii-ho branch in interlock association with said i switch of said first limit switch means so said release relay and said device remain en gized upon actuation of said contact means as long as said main assembly is above said switch and are deenergized when said main as sembly is below said latter switch.

10. A control system for a hoist having her main hook assembly, a light auxiliary hool: sembly and a single cable from which said semblies are suspended, and comprising in combination a hoist motor for operating said to selectively hoist and lower one of said asscmblies, means for latching said main assembly in its top limit position, an electric device for releasing said latching means to permit lowei said main assembly from said position, first 1.. switch means disposed near the top position of said main assembly and having a lower limit switch and an upper limit switch, second liini .v switch means disposed near the top position oi said auxiliaryassembly and having a lower limit switch and an upper limit switch, operator actuable master control means connected to said motor for controlling it to run in hoisting lowering directions under selective speed conditions, operator-actuable contact selecting one of said assemblies for operation in said motor, arelay controlled by said upper limit 13 switches and connected with said contact means and being motor controlled so as to render said contact means operative for selection of one of said assemblies only when both assemblies are in their operative top position and said master control means are in Off condition, a latch release relay disposed for controlling said device and connected with said second limit switch means, said selector contact means and said master control means so as to release said latching means upon selected actuation of said contact means only when said master control means are in off condition, a hoist relay having a coil circuit controlled said contact means and said limit switch means so as to energize said motor for slow speed hoisting when said latter lower limit switch is actuated by said latter assembly and when thereafter said contact means are actuated by the operator to select said other assembly for subsequent operation, said reiay means having interlock contacts disposed in said coil circuit to pre- 14 vent said hoist relay from energizing said motor when one of said assemblies is lowered below said appertaining lower limit switch, relay means connected with said upper limit switches for stop ping said motor when the raising assembly reaches the appertaining upper limit switch.

REMI BOLLAERT.

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

UNITED STATES PATENTS