US2253253A - Hoisting apparatus - Google Patents

Description

Aug. 19, 1941. B. SOHN 2,253,253

HOISTING APPARATUS Filed June 26, 1939 3 Shooter-Sheet 1 Z5 ZZ INVENTOR. L50 5. 501m.

Aug. 19, 1941. I B SQHN 2,253,253

nors'rme APPARATUS Filed June 26, 1939 s Sheets-Sheet 2 I mvysmox 50 5. Jon/v.

' Q N N BY A1 EYE Patented Aug. 19, 1941 UiTE STATES PATENT trio HOISTING APPARATUS Leo B. Sohn, Bediord, Incl, assignor to Bedtord Foundry & Machine (20., Bedford, Ind, a cornotation Application June 26, 1939, Serial No. 281,070

whims. (cl. re-1'19) view thereof. Fig. 4. is a diagram of electrical connections by means of which the invention may be carried out. Hg. 5 is an electrical diagram showing in a conventional manner certain motor connections for slow speed operation and.

. Fig. 6 is a similar diagram for high speed opermotors are to he used, to gear the hoisting apparatus to the speed appropriate for the heaviest load to he carried. Lighter loads must then be lifted at the some slow speed and even the operation of raising and lowering an empty hook must be done equally slowly. To overcome the loss of time due to this slow operation it has been common proctice to furnish two complete hoisting units on one crane, one of which is geared for low speed and heavy loads and the other for higher speeds and light loads. The use of duplicate units does not cove the time consumed in the slow lowering oi the hook on the slow speed unit. Mechanical gear changing units have also been employed but the difficulties inherent in controlling such units on o. moving trolley from a control station mounted on the bridge oi the crane has been o factor in preventing their genere] use.

Que object of the present invention is to pro vide slow speed operation for heavy loads and high speed operation for light loads with single hoisting unit and without the use of gear changing mechanism. 1

Another object of the invention is to prevent the loss of time occasioned by lowering the hook at the some slow speed as the hoisting; is done.

Another object of the invention is to provide means by which the .change of speeds may be controlled conveniently and safely trons the usual control station on the crane bridge.

These and other objects are attained by the apparatus described in the following specification and the accompanying drawings in which the invention is illustrated in one of its preferred forms.

Other objects of the invention will understood from the accompanying drawings and the following description and claims:

Fig. 1 is an elevational view of an overhead crane illustrating the type of apparatus to which the invention may be applied. Fig. 2 is a plan view of the crane trolley. Fig. 3 is an elevational ation.

The crane shown in Fig. l is provided with the usual travelling bridge iii running on rails it supported by I-beams it. The I-beams it may be carried by the frame structure of a building or by suitable independent structure if the crane is to be used outside of a building. The crsne is provided with the usual operator's cage iii car ried by the bridge it. A trolley it running on rails l5 carried by the bridge is movable in a direction transverse to the movement of the bridge.

Referring now to Figs. 2 and 3, the trolley consists of a frame it on which there are mounted wheels ll running on the rails iii. A trolley motor l8 drives a shaft ii on which two of the wheels H are mounted. The drive is through a reduction gear unit 20. A hoist drum 2G is mounted on a. suitable shaft journaled you the frame it and is rotated by a hoist motor 22 through a reduction gear unit in to housing 23 and. driving a shaft M in turn operating the drum 2| through gears in a housing 25. The motor 22 is provided with a solenoid broke 227i operating on an extension 28 of the motor shaft and serving to prevent movement of the drum when the power to the motor is cut off. The drum it has wound thereon a cable 29, both ends oi which are fastened to the drum. 'The cable 29 leads from the drum 2'! downwardly about a sheave to car ried by e. hoisting block M, then upwardly about a sheave 32. carried by the frame iii, then downwardly about a second sheave in the block and back to the drum 2!. The block iii carries the usual hoisting hook 33.

The construction 30 for described is well known in the overhead crane art. The invention lies in the combination with this structure of the particular type of motor employed for the hoisting and the control apparatus by which the operation of said motor in governed.

The motor 22 is a slip ring induction motor having its stator windings and secondary windings so arranged that by reversal of current flow in certain of the stator windings, the number of rotating 'magnetic poles produced thereby is changed and thus the synchronous speed of the motor is changed. The arrangement is such that the horsepower available at both speeds is substantially the same. At the lower speed, a. heavy winding a.

load may be lifted relatively slowly while at the high speed a light load may be lifted with relatively greater velocity. In the lowering operation with an empty hook, the high speed may be used exclusively.

In the preferred form of the invention, three: phase alternating current is used and the stator windings of the motor are arranged as shown in Fig. 4 in which one-half of said windings are conventionally illustrated and are indicated by the legend Stator." The portion of the stator illustrated is provided with six windings a, b, c, d, e, and f. The portion of the stator not shown is similarly wound and the corresponding windings in the two halves may be connected either in series or in parallel and thus can be considered as parts of the same windings. The several; windings are permanently connected to terminals Tl, T2, T3, I'd TE- and T8 as indi cated in. the diagram. this arrangement, when line voltage is itllpiifiili to the terminals T4, T5 and T6 and terminals Ti, and "fit are connected together indicated diagrammatically in Fig. 5, the six windings are arranged in pairs in a double star connection. Considering the pair of windings a and d spaced 90 apart in the stator, the current at a certain instant may,

be considered as flowing from the terminal Tito the center point in both windings. An inspection of Fig. 4 shows that the current in the adjacent conductors 34 of the two windings flows in opposite directions. The same relation holds in the pairs of windings b and e, and c and f. The-pitch of a pole pair is then equal to the angular distance between the two windings of each pair or 90". Four pole pairs or eight poles are produced and the synchronous speed of the motor is 900 R; P. M. when 60-cycle current is used.

If the line conductors are connected to terminals Ti, T2 and T3 and the terminals T4, T5

and T8 are left open as indicated diagrammatically in Fig; 6, the connection becomes a delta connection in which the direction of current flow in one winding of each pair is reversed with respect to the direction of current flow in the other winding of the pair. For example, in the windings a and d the current in Fig. 6 may be considered as flowing from the terminal T4 in winding :1 but flows from the terminal Tl in windings a and d have their current flowing in the same direction and the pitch of a pole pair is equal to the distance between the winding a in one half of the stator and the winding a in the other half or 180. Thus only two pole pairs or four poles are produced and the syn chronous speed of the motor is 1800 R. P. M. for (SO-cycle current. Due to the change from double star to delta connection, the voltage applied to each phase is such that substantially the same horsepower is available under either operating condition.

The rotor windings indicated by the legend "Rotor" are similarly divided into six windings but are permanently connected in the star conneotion as shown in the diagram. Thus the rotor may have the same number of induced poles as there are poles in the stator under either slow or fast operation.

The electrical connections by which the motor is controlled are shown in Fig. 4 in which there are indicated by name a line switch, a controller, a bank of resistors, a pole changing switch, an overload relay, a reversing switch. a cutout switch, a limit switch and push button station's Thus adjacent conductors in the "an electromagnet ML. One of the contactors in said switehis provided with a normally open uninsulated interlock 36. The line switch is adapted to connect power mains Ml, M2 and M3 to line conductors Li, L2 and L3 respectively.

The controller may be the usual drum controller having an Oil position and a number of running positions indicated in the diagram by the numbers i to 8, inclusive, under the legends Lower and I-loist." In the several running positions, the resistors are connected. in the rotor circuit to control the starting and running torque of the motor in a well known manner.

Th reversing switch is illustrated a magnetic switch having a pair of eontactors 31 and Sit adapted to connect the line conductors L2 and L? to conductors N2 and Nil respectively when electromagnet MU is energised tor the hoisting operation. The reversing switch. is also provided with a pair of contactors 39 and 40 adapted to connect the line conductors L2 and L3 to conductors P2 and P3 respectively when an elcctrornagnet MD is energized for the lowering operation.

The cutout switch is provided with a pair of contactors 4| and 42 adapted respectively to connect conductor N2 to conductor P3 and conductor N3 to conductor P2 when an electromagnet MC is energized.

The pole changing switch is provided with a group of contactors 43, 44, 45, 4B, 41, 48 and 49 operated by anelectromagnet MS for slow speed operation. When said magnet is energized contactors fl, 44 and 45"c0nnect the conductors Ll, P2 and P3 respectively to conductors E4, E5 and E8 and contactors 46 and 4! connect together the three conductors El, E2 and E3. Contactor 48 is a normally open interlock closed when magnet MS is actuated and contact 49 is a normally closed interlock opened when magnet MS is energized. The pole changing switch is also provided with "a group of contactors 50, El, 52, 53 and 54 operated by an eleotromagnet MP for fast speed operation. In this group contactors 50, BI and 52 connect the conductors Ll, P2 and P3 to conductors El, E2.and E3 respectively. The connection to conductor El from contactor an leads through the energizing'magnet coil MO olthe overload relay. normally open and normally closed interlocks respectively. The conductors El to E5, inclusive, are connected respectively to the stator winding terminals Ti to T6, inclusive, through the usual trolley wires carried by the crane bridge and indicated by name in the diagram.

The overload relay is provided with a single normally closed contactor 55 which is open when the current in the magnet coil MO exceeds a predetermined value. The Start, Slow" and Fast" push buttons are normally open while the Stop" and Change" push buttons are normally closed. The limit switch is normally closed and is mechanically opened in a well known manner when the hook is hoisted to a predetermined upper limit or travel. The resistors are arranged in six banks, each of which is connected to one of the rotor windings by one of a group of conductors 58 leading through the trolley wires to the slip rings 51 of the motor. Other conductors The contactors 53 and 54 are" shown in the drawings will be referred to by reference number only in tracing the circuits ofwhich they form a part.

Operation In the idle condition of the apparatus, the

line switch is open and none of the control circuits are complete. The controller normally stands in the off position in which a connection net ML by the operation of the interlock 36 (Ml,

36, 64; 65, Stop, 62, ML, 53, M2). This circuit retains the line contactors in closed position unless the stop push button is pressed or the overload relay functions in response to an excessive current in the portion of the conductor El leading tothe contactor 50.

The next operation is to select the speed at.

which the hoist will operate by pressing either the Slow or Fast push button. Since the first operation is usually the lowering of the hook. it will be assumed that the "Fast push button is pressed. A circuit is thus completed for the magnet ME (MI, 60, 58, 59, 66, Fast, 61, 49, 68, MF, 69, Change, 70, L2, M2). The operation of magnet MP closes contactors 50, 5i and 52 to connect the stator windings to the line con ductors Ll, P2 and P3 with the proper connec-=. tions for fast operation. It will be noted that the circuit for magnet MF can only be completed when the controller is in the Off position. The operation of the magnet MF' also closes the interlock 53 and completes a hold-in circuit for said magnet (Ml, Ll, 53, 'H', 49, 68, MF, 8%, Change, "i6, L2, M2). This circuit is retained until the line switch is opened or until the change push button is pressed.

The selection of speed having been made, the controller may be thrown to the running positions on the Lower side thereof. In each of these positions appropriate resistors are connect ed with the-rotor circuit of the motor and in all of said positions a connection is made in the controller between a pair of terminals 12 and '13. The completion of this connection establishes a circuit for the magnet MD (ME, 14, i2, i3, 55,1VID, L2, M2). MD establishes the final connection between the power mains Mi, M2 and M3 and the stator windings of the motor and starts the motor to lower the hook. The winding 90 of the solenoid brake is connected across one of the stator wind (MI, I4, 12, I6, 11, MU, L2, M2). The operation of the magnet MU closes contactors 31 and 38 and completes acircuit for the magnet MC (Ml,

LI, 511, El, stator winding a, E4, 18, limit switch,

19, MC, N2, L2, M2). In this circuit the stator winding has much less resistance than the magnet MC so suflicient voltage is available to energize said magnet while the current in the stator winding is extremely small. The actuation of the magnet MC closes the two contactors 4i and 42 for the cutout switchand completes the circuits to the stator windings of the motor with the connections between conductors L2 and L3 1 and conductors P2 and P3 reversed so that the The operation of magnet ings and thus receives current for releasing the I brake. When the hook; is lowered to the proper level the motor is stopped by placing the controller in the off position and thus deenergizing the magnet MD to open the stator circuits. The solenoid brake operates to hold the load when the power has been shut oil.

11 it is desired to lift a light load at a high speed, it is now only necessary to move the controller to oneof the running positions on the Hoist side. In all of these positions a connec 'tion is made in the controller between the ter-' minal i2 and a terminal i6. This connection completes a circuit for the electro-magnet MU motor operates in the opposite direction and lifts the. load. In this operation, if the limit switch is opened at the upper limit of travel, the magnet MC is deenergized and the cutout switch is opened, stopping the motor. If an attempt is made to lift too heavy a load at the high speed, the overload relay operates to open the switch 55, deenergizes the magnet ML, open the line switches and stop the motor.

If it is desired to hoist at the slow speed, th Change push button is pressed, breaking the circuit to the magnet MF. The controller is then placed in the off position and the Slow push button is pressed, completing a circuit for the magnet MS (Mi, 60, 58, 59, 66, Slow, 80, 54, 8|, MS, 69, Change, 16, L2, M2). The operation of magnet MS closes the contactors 43, 44, 45, 46'

and 4'! to connect the stator windings to conductor LI, P2 and P3 in the proper manner for slow speed operation.

The operation of the interlock 48 completes a hold-in circuit to retain. the magnet MS,(Mi, Ll, 46, 80, 54, Si, MS, 69, Change, 16, L2, N2). The controller may then be moved to one of the hoist running positions and the reversing switch is operated as before to start the motor. In this operation, the circuit for the magnet MC is as follows: (Ml, Li, 43, E4, limit switch, 19, MC, N2, L2, M2). The limit switch operates in the same manner as on slow speed operation but it will be observed that the current path to the stator windings no longer passes through the overload relay. This relay thus functions to stop the motor only on high speed operation. The necessary current for lifting the heavier loads is thus available for slow speed operation.

The normally closed interlocks 49 and 54 in the circuits of the magnets MF and MS insure that only one of said mangets can be energized at one time. They thus prevent short circuiting the power mains which wouldlotherwise result from a simultaneous operation'of both push buttons. It

will also be seen that neither of these magnets can be operated unless the controller is in the off position in which the motor is stopped. Thus the pole changing switch is never called upon. to make the motor circuits and the change of speeds cannot be made on the fly. Sudden shocks to the led without departing from the scope of the invention as defined by the appended claims.

The invention claimed is:-

I. In apparatus of the class described, a multispeed induction motor, a speed changing switch, electrical conductors connecting said switch to a ,source of current, other conductors connecting said switch to said motor, the connection oi! said lastmentioned conductors being such as to complete a high speed current pathto said motor when said switch is'in one position and a low speed current path when said switch is in a ditierent position. and an overload protective device operable only by current flowing in said high speed current path.

2. In apparatus of the class described, a multispeed induction motor. a speed changing switch, electrical conductors connecting said switch to a source of current, other conductors connecting said switch to said motor, the connection of said last mentioned conductors being such as to complete a high speed current path to said motor when said switch is in one position and a low speed current path when said switch is in a ditierent position, and an overload relay adapted to break said connections and operated only by current ilowi ng in said high speed current path.

3. In apparatus oi the class described, a multi.

speed slip ring induction motor, a magnetic pole changing switch and associated electrical connections for selectively connecting the stator windings of said motor to a source of current for high and low speed operation, a controller having an on position and one or more running positions, said controller beingconnected to break the circuits to said stator windings when in the of! position, and a control circuit for operating said pole changing switch, said circuit being interlocked with said controller so as to be operative for operating said pole changing ,switch only when said controller is in the oil! position.

4. In apparatus of the class described, an induction motor having a pole changing stator winding in which the number of magnetic poles is changed by reversal of current in a portion of said winding to changethe synchronous speed oi said motor, a pair of magnetically operated switches, conductors connecting said switches to I a source of current, conductors connecting said switches to said stator windings, and arranged to provide current paths from one 0! said switches to the stator windings in proper relation for low speed operation and current paths from the other of said switches to said stator winding in proper relation for high speed operation, said last mentioned current paths having at least a portion independent or said first mentioned current paths. and an overload protective device connected in said independent portion and responsive only to current flow therein to break the power supply to saidmotor.

6. In apparatus of the class described, an induction motor having a pole changing stator winding in which the number of magnetic poles is changed by reversal 01' current in a portion of said winding to change the synchronous speed oi. said motor, a pair of magnetically operated switches, conductors connecting said switches to a source of current, conductors connecting said switches to said stator windings, and arranged to provide current paths from one 01' said switches to the stator windings in proper relation for low speed operation and current paths from the other 0! said switches to said stator winding in proper only to current flow therein to break the power supply to said motor, and said switcheshaving mutually exclusive electrical interlocks whereby only one of said switches may be energized at a given time.

6. In apparatus of the class described, an inductlon motor having a pole changing stator winding in which the number of magnetic poles is changed by reversal of current in a portion of said winding to change the synchronous speed of said motor, a pair of magnetically operated switches, conductors connecting said switches to a source of current, conductors connecting said switches to said stator windings, and arranged to provide current paths from one of said switches to the stator winding in proper relation for low speed operation and current paths from the other of said switches to said stator winding in proper relation for high speed operation, a master controller connected to control power supply to said motor and having an of! position and one or more running positions, an energizing circuit for each of said switches, interlocking means in said circuits operated by said master controller to permit said circuits to be completed only when said controller is in the of! position, retaining circuits operated by said switches and each adapted to maintain its associated switch in energized osition when once energized irrespective of the position of said master controller, and manually operated means for breaking said retaining circuits.

7. In apparatus of the class described, an induction motor having a pole changing stator winding in which the number of magnetic poles is changed by reversal of current in a portion of said winding to change the synchronous speed of said motor, a pair of magnetically operated switches, conductors connecting said switches to a source of current. conductors connecting said switches to said stator windings, and arranged to provide current paths from. one of said switches to the stator windings in proper relation for low speed operation and current paths from the other of said switches to said stator winding in proper relation for high speed operation, said last mentioned current paths having at least a portion independent of said first mentioned current paths, an overload protective device connected in said independent portion and responsive only to current flow therein tobreak the power supply in said motor, a master controller connected to control power supply to said motor and having an of! position and one or more running positions, an energizing circuit for each of said switches, interlocking means in said circuits operated by said master controller to permit said circuits to be completed only when said controller is in the of! position, retaining circuits operated by said switches and each adapted to maintain its associated switch in energized position when once energised irrespective of the position oi said master controller, and manually operated means for breaking said retaining circuits.

. a LEO B. SOHN.

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