US2279722A - Grab hoist - Google Patents

Description

April 14, 1942. .1. R. TAYLOR 2,279,722

GRAB HoIsT Filed March 18, 1939 5 Sheets-Sheet l D www! o omNnm, S. ma s u; @E @a @s @a ma MN; m?

\ April 14, 1942.

J. R. TAYLORv GRAB Hoi/ST Filed March 18, 1939 5 Sheets-Sheet 2 ab. .3 23 o 3d? N3 m3 m3 w3 EE m3 April 14', 1942. J. R. TAYLOR 2,279,722

- I GRAB HoIsT Filed March 18, 1939 3 Sheets-Sheet 3 LH LIZ Di EU DZ G1 Mi MZ G2 Patented Apr. 14, 1942 UNITED GRAB HOIST John Russell Taylor, Bedford, England, assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a

corporation of Delaware Application March 18, 1939, Serial No. 262,651 In Great Britain March 21, 1938 Claims.

This invention relates to grab hoists.

Grab hoists are known having two separate lines, viz. a holding line and a closing line, actuated by respective electric motors, the closing line, when in tension, closing the grab, and both lines, when in tension, operating to support the weight of the grab. When the grab is to be supported in an open condition the holding line must take the whole weight, the closing line remaining slack, but when the full grab is to be supported, the closing line must be tight to keep the grab closed and it serves to share the load with the holding line which is also tight.

The object of the invention is the provision of an improved grab hoist of this kind in which inter alia it will be easier to maintain the grab open or closed at all speeds and especially at low speeds where diiiiculty has been heretofore eX- perienced, and in which the control in general will be more smooth. The invention consists in the arrangement that the two motors are direct current motors fed from respective generators.

In order that the invention may be the more clearly understood a grab hoist in accordance therewith will now be described, reference being made to the accompanying drawings wherein:

Figure 1 is an across-the-line diagram of the power circuits of the holding motor;

Fig. 2 is a similar diagram of the power circuits for the closing motor;

Fig. 3 is an across-the-line diagram of a drum controller and its associated control circuits for controlling the power circuits of the holding motor;

Fig. 4 is an across-the-line diagram of a drum controller and its associated control circuits for controlling the power circuits of the closing motor;

Fig. 3a is a representation of the switches embodied in Figs. 1 and 3 with their coils and contact members disposed in horizontal alinement with their positions in the across-the-line diagrams;

Fig. 4a is a diagram similar to that shown in Fig. 3a of the switches embodied in Figs. 2 and 4, and

Fig. 5 is a schematic view illustrating the apparatus shown in Figs. 1 to 4 in connection with a grab bucket having a holding line and a closing line.

As shown in Fig. 5, two separate Winches are employed for the holding line and the Closing line respectively and said Winches are driven by direct current electric motors Ml (Figure 1) and M2 (Figure 2) respectively. The motors MI and M2 have independently excited fields MFI and MFZ and their armatures are connected in circuit with the armatures of respective generators Gl and G2. The generators also have independently excited elds GFI and GF2. The field and armature circuits of the two motor generator sets are identical. The speed and direction of each motor is determined primarily by the degree and direction of field excitation of the generator supplying it, and each motor, after it has received maximum armature current from its generator, is capable of being speeded up a final step by having a resistance section rl inserted in its eld circuit.

The two motor generator sets are controlled by means of respective small drum controllers Dl (Figure 3) and D2 (Figure 4), and these drum controllers are identical except that the iinal step of speed can be applied only in the hoist direction in the case of the holding line drum DI, and

only in the lowering direction in the case of the closing line drum D2.

More particularly, in the off position (illustrated) of the holding line drum DI, a main switch has its winding wl energised and its contact IcI closed, connecting the armature Gl of the holding line generator in circuit with the armature MI of the holding line motor. The energising circuit for said winding wl may be traced from line LI, drum contact I, drum contact 2, contacts c2 of overload relay w2, said winding wl, normally closed interlock 2cl on the main switch winding wl to line L2. This main switch upon closing, establishes a maintaining circuit for its winding wl, through normally open interlock 3cl which remains established at all the positions of the drum and can only be disestablished upon the occurrence of overload whereupon the overload winding w2 opens the contacts c2. The original energising circuit of said main switch is, however, only established, through drum contact 2, at the off position of the drum, so that, overload having occurred, the main switch can only be re-energised by returning the drum to the oil position. When main switch winding wl is energised, interlock 2cl opens, thereby throwing an economising resistance r2 into the circuit.

At the first hoisting notch hl of said holding line drum, a hoist switch has its winding w3 energised through drum contact 3, and its contacts lc3 closed thereby effecting energisation of the generator eld GFI through all of a number of sections of a resistance R, in the hoisting direction. Upon response of said hoist switch an auxiliary contact 2c3 thereon closes, thereby establishing two circuits in parallel with said energsing circuit of the hoist switch winding w3, one of said circuits energising the winding w4 of a normally open decelerating switch whose contacts c4 thereupon close and cut out a resistance section r3 from the eld circuit of the motor Ml to give a decreased speed during hoisting, and the other of said circuits energising the winding w5 of a relay having contacts |05 which close energising the winding Br of an electromagnetic brake for operating the same to its released position. All these three circuits established at the rst notch are completed through an interlock 40| on the main switch winding wl, so that they will all be de-energised upon the occurrence of overload.

The motor MI accordingly starts in the hoist direction at slow speed.

At the second hoisting notch h2, an energisingv an energising circuit is established through drum Y contact 6 for the winding w8 of the third resistance-removing contactor whose contacts |08 close, cutting out a third section of resistance R; and at the fth hoisting notch h5 an energising circuit is established through drum contact for winding w9 of the fourth resistance-removing contactor whose contacts |09 close, cutting out a fourth section of resistance R.. At said fifth hoisting notch an energising circuit is also established through drum contact 8, for the winding w|0 of' the fifth and last resistance-removing contactor whose contacts |0| [I close removing the fth and. last section of resistance R, but this must be. subsequently to the preceding circuit as will hereinafter appear. All the resistance is now cutout of the generator field GFI.

Finally at the sixth hoisting notch h6., an energising circuit is established through drum contact 9 for the winding w|| of a normally closed accelerating switch, whose contacts c|| open inserting resistance rl in the circuit of the motor eld MFI andthe motor still further speededv up.

At the second notch h2, an anxiliary contact 20E on. the winding wS of the first resistanceremoving contactor establishes, through the aforesaid auxiliary contact 203 `on the hoist switch, and independently of the drum DI, the three circuits (through windings w3, w4 and w5 respectively) which were established at the first notch. Atthe third notch h3. an auxiliary contact 201 on the winding w1 of the second resistance-removing contactor establishes, independently of the drurn DI, the circuit through the winding 'L05 which was established at the second notch. At the fourth notch 17A-an auxiliary contact 208 on the winding w8 of the third resistance-removing contactor establishes, independently of the drumV Dil, the circuit through the winding w1 which was established at the third notch. At the fth notch h5 an auxiliary contact 209. on the winding wS of the fourth resistance-removingv contactor establishes independently of the drum DI the circuit through the winding w8. which. waszestablished at the fourth notch. At the fifth notch also, an auxiliary contact 20| il on the winding will of the fifth resistance-removing contactor establishes, independently of the drurn DI, the circuit through the winding wg which was also established at the fifth notch. Finally at the sixth notch h6 an auxiliary cont'act 20|| on the winding wll of the said normally closed accelerating switch establishes, independently of the drum DI, the circuit through the winding will which was established at the fth notch. The provision of these auxiliary contacts 206 to 20H as will hereinafter appear, prevents insertion of the resistance sections too fast when the drum is returned to the normal position.

Throughout the whole of the preceding operation, if the handle of the drum DI is thrown right over, the circuit established at any notch after the first, can only be established a time interval after the circuit or circuits established at the preceding notch. Thus, each resistancerernoving contactor is provided with a hold-out coil Iw to Iwi in series with its closing coil w6 to wlll. The hold out coils Iw'l to |w|0 are respectively short circuited by normally open auxiliary contacts 305 to 309 on the preceding resistance-removing contactor. The first hold out coil lwS is short circuited by normally open contacts 205 on the winding of the brake controlling relay w5. If' the handle is thrown quickly over through the several notches, each hold out coil lw to Iwlll will receive current before the auX- iliary contact 205 or 306 to 309 on the preceding contactor has had time to short circuit it and, until the current in this hold-out coil has died away, the contactor cannot close. Any other forrn of timing means may be provided for this purpose.

It will be observed that the winding wil of the accelerating switch for inserting resistance in the motor held MFl cannot be energised until after closure of auxiliary contacts Scifi' on the winding will.

The aforesaid auxiliary contacts 20@ to 20H for preventing the sections of the resistance R from being inserted too fast when the drum DI is being returned to the normal position, operate, as will be understood, by causing the contactors lcl to |06 to open' consecutively in thereverse order toithat in whichA they closed; and, furthermore, each contactor takes a time interval to open as its winding wifi to wl is shunted by a resistance ri to T5, and its current. therefore takes a time to die away after its circuit is disestablished. This resistance should be suitably proportioned to the spring tension'l on the contactor to obtain the'necessary time intervals between the falling out of the contactors.

The operation of the holding-line drum D! in the lowering direction is the same as in the hoisting direction except that the generatoriield GFI is energised in the reverse direction and neither thevnormally open decelerating contacts c4 nor the normally closed accelerating contacts 0|| come into operation, so that the general speed is faster in the lowering direction but the nal increase in speed is dispensed with. Thus at the first notch H a lowering switch has its winding w|2 energised through drum Contact l), thereby closing contacts I'clg and effecting ener sation of the generator field GFl in the lowering instead of the hoisting direction, and the auxiliary contact 20H2 on. the lowering switch does not, as in the case of 203 on the hoisting switch. establish an energising circuit for the winding-1124 of the normally open decelerating contacts 04.

Said contacts 2cl2, however, function in analogous manner to the contacts 2c3 to maintain the circuits of the lowering switch winding wl2 and of the brake relay winding wi.

In all other respects, save that the sixth lowering notch is dispensed with, the operation in the lowering direction is precisely the same. through notches l2 to l5, as in the hoisting direction as will be clear from the drawing.

The closing line drum D2 is exactly the same as the holding line drum DI except that the sixth notch, at which the normally closed accelerating switch is energised, is dispensed with in the hoisting direction and is added in the lowering direction, and except that a jamming relay, whose operation will be described is provided, said jamming relay having normally closed contacts y'rc connected between the line L2 and all the contactor windings after w1 and having its winding jrw connected in the motor generator circuit. Thus, in the case of the closing line, the general speed as in the case of the holding line, is faster in the lowering direction, but contrariwise to the holding line, there may be a final increase in speed in the lowering direction but not in the hoisting direction.

It has therefore been deemed clearer not to append any further reference to Figure 4 save to show that there are six lowering notches Z1 to Z6 and only ve hoisting notches hl to h5. It is deemed that the operation of the drum D2 will be clear from the preceding description of that of DI.

In operation therefore, when it is desired to hoist with a full grab, making both motors MI and M2 share the load, both drums DI and D2 are moved together, notch by notch, in the hoisting direction, the sixth notch h6 on the holding line drum DI not being used. The motors MI and M2 will thus run at the same rate sharing the load equally.

For hoisting the open grab, the holding line drum DI, whose motor MI must take the whole of the load, is moved one notch in advance of the closing line drum D2 right up to the full speed position, the sixth notch h6 on said holding line drum accordingly coming into use. Thus, the holding line motor Ml, although under load, will move at least as fast as the closing line motor M2 which is running light, and there will be no danger of the closing line picking up the load and closing the grab.

When lowering the open grab, the closing line drum D2 is moved one notch in advance of the holding line drum DI, and this, although the holding line motor MI which must take the whole of the weight, will be pulled round at somewhat above its unloaded speed, the closing line motor M2 will move at least as fast as said holding line motor and there will be no danger of the closing line picking up the load and closing the grab. In this case the sixth notch Z6 of the closing line drum D2 in the lowering direction will come into use. Finally, for lowering the full grab both drums DI and D2 are moved together in the lowering direction, notch by notch, and the motors MI and M2 will rotate at the same rate, sharing the load. In this case the sixth notch Z6 of the closing line drum D2 in the lowering direction will not come into use.

The two drums DI and D2 are arranged as shown in Fig. 5, so that their handles may be grasped when necessary by one hand so as to facilitate moving them together.

Safety latches, controlled by windings wi and rwl4 respectively in parallel with the windings w3 and wl 2 of the hoisting and lowering switches, are provided for preventing reversal of the drum, While the hoisting or lowering switch, as the case may be, is closed.

The aforesaid jamming relay y'rw, jre is for the purpose of safeguarding the mechanical parts of the hoist. If for example the grab should close upon a fixed part, the closing line would become suiiiciently overloaded for the contacts :irc to open thereby ensuring de-energisation of all the contactor windings after wl. 'Ihus the pull on the holding line will exceed that on the closing line and the grab will open.

Each generator is provided with a so called suicide circuit. That is to say the generator eld is normally connected, through suitable resistances rl l and 1I2, across the generator armature, through normally closed auxiliary contacts 303 and 3cl2 on the windings w3 and wl2 of the hoist and lowering switches. During hoisting and lowering one or other of these auxiliary contacts will be open and the suicide circuit will therefore be interrupted, but, when the drum is returned to zero, said suicide circuit is established and the field is connected across the armature in such a sense as to be quickly demagnetised.

The lines Li, L2 may be supplied from any constant voltage direct current source such as a small exciter.

What I claim and desire to secure by Letters Patent is:

l. The combination with a grab bucket having a holding line and a closing line, of a motor for operating each of said lines, separate generators for supplying current to the armatures of said motors, separate controllers for controlling the elds of said generators to selectively control the direction of operation of said motors and also the speed thereof, said controllers being operable to subject the armatures of said motors to the full voltage of their associated generators for operation of said motors at corresponding speeds in hoisting or lowering direction with the weight of the grab bucket shared by said holding and closing lines and means associated with said controllers for selectively controlling the eld strength of said motors while subjecting the armatures of said motors to the full voltage of their associated generators to provide for operation of said motors in hoisting or in lowering direction at corresponding speeds with substantially the entire weight of the grab bucket supported by said holding line.

2. The combination with a grab bucket having a holding line and a closing line, of a motor for operating each of said lines, separate generators for supplying current to the armatures of said motors, separate controllers for controlling the fields of said generators to selectively control the direction of operation of said motors and also the speed thereof, said controllers being operable to subject the armatures of said motors to the full voltage of their associated generators for operation of said motors at corresponding speeds in hoisting or in lowering direction with the weight of the grab bucket shared by said holding and closing lines, means associated with the controller for said holding line generator for weakening the eld of the holding line motor while maintaining full generator voltage for operation of said holding line motor in hoisting direction, said means enabling hoisting operation of both of said motors at a corresponding high speed with substantially the entire weight of the grab bucket supported by said holding line.

3. The combination with a grab bucket having a holding line and a closing line, of a motor for operating each of said lines, separate generators for supplying current to the armatures of said motors, separate controllers for controlling the elds of said generators to selectively control the direction of operation of said motors and also the speed thereof, said controllers being operable to subject the armatures of said motors to the full voltage of their associated generators for operation of said motors at corresponding speeds in hoisting or in lowering direction with the weight of the grab bucket shared by said holding and closing lines and means associated with the controller for said closing line generator for weakening the field of the closing line motor while subjecting the armature of said closing line motor to full generator voltage for operation of said closing line motor in lowering direction, said means enabling lowering operation of both of said motors at a correspondingly high speed with substantially the entire weight of the grab bucket supported by said holding line.

4. The combination with a vgrab bucket having a holding line and a closing line, of a motor for operating each of said lines, separate generators for supplying current to the armatures of said motors, separate controllers for controlling the ields of said generators to selectively control the direction of operation of said motors and also the speed thereof, each of said controllers including a master switch movable in opposite directions out of an intermediate off position to select the direction and speed of operation of its associated motor and said master switches having corresponding hoisting and lowering positions wherein the armatures of said motors are subjected to the full voltage of said associated generators, eld weakening means for each of said motors and means associated with said master switches'for selectively controlling said eld weakening means while subjecting the armatures of said motors to the full voltage of their associated generators to provide for operation of said motors in hoisting or in lowering direction at corresponding speeds with substantially the entire weight of the grab bucket supported by said holding line.

5. The combination with a grab bucket having a holding line and a closing line, of a motor for operating each of said lines, separate generators for supplying current to the armatures of said motors, separate controllers for controlling the elds of said generators to selectively control the direction of operation of said motors and also the speed thereof, each of said controllers including a master switch movable in opposite directions out of an intermediate 01T position to select the direction and speed of operation of its associated motor and said master switches having corresponding hoisting and lowering positions for subjecting the armatures of said motors to the full Voltage of their associated generators, means associated with said master switches for selectively weakening the fields or said motors while subjecting the armatures of said motors to the full voltage of their associated generators to provide for operation of said motors in hoisting or in lowering direction at corresponding speeds with substantially the entire weight of the grab bucket supported by said holding line and a switch responsive to overload conditions in the armature circuit of the motor associated with said closing line for weakening the eld of the generator associated with said closing line motor.

J OHN RUSSELL TAYLOR.

Images