US2030128A - Hoisting apparatus - Google Patents

Description

Feb. 11, 1936. WEBSTER 2,030,128

HOISTING APPARATUS Filed May 11, 1933 5 SheetsSheet l 15 1W 7; 3 *i i 2 INVENTOR WITNESSES:

Feb. M, 1936.

WITNESSES:

% KWM J. E. WEBSTER HOISTING APPARATUS Filed May 11, 1933 5 Sheets-Sheet 2 HHHHHH INVENTOR Feb. 11, 1936. J WEBSTER HOISTING APPARATUS Filed May 11, 1955' 5 Sheets-Sheet 3 Z -Z m? j Feb, 111, 1935. J E, WEBSTER 2,@3U,12

HOISTING APPARATUS Filed May 11, 1933 5 Sheets-Sheet 4 l 7 Q v L445 mun f T 7 T W x11 g 72/7/9 71o (aw/0758 7f 7! 35 a Z? 0 o Feb, 111, 1936. J E, E 2,030,128

HOI STING APPARATUS Patented Feb. 11, 1936 PATENT OFFICE HOISTING APPARATUS John E. Webster, Pittsburgh, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 11, 1933, Serial No. 670,454

7 Claims.

My invention relates, generally, to hoisting apparatus and it has particular relation to electrically-operated grabs for such apparatus.

When it is desired to pile up a large number of packing cases such as the cases in which electric refrigerators are stored or shipped, it has been customary in the past to employ at least three individuals for performing the piling operation. One of the individuals is used to operate the crane that is used for picking up the cases. A second individual is used for hooking on the customary grab to the packing case, while a third individual is employed on the pile of packing cases to unhook the grab and closely pile the packing cases in position.

The above operation is attended by the danger to the two individuals directly handling packing cases in that they may be injured by the grab itself by its being picked up too quickly before it has been properly secured to the packing case or by the grab slipping after it has been secured to the packing case. In addition, the individual working on the pile of packing cases is subject to the additional hazard that he may fall from this rather precarious position, since in many warehouses, the cases are piled to a considerable height. It will also be apparent that a pile of packing cases offers a rather unstable footing to an individual working thereon and further increases the liability of injury.

A further difficulty encountered in the hoisting devices of the prior art has been that it was necessary to unhook the grab from the packing case before the packing case was placed in the de sired final position. The individual on the pile of packing cases then must move the packing case into position manually, and oftentimes this is very difficult to do in a satisfactory and safe manner. This is especially true when it is desired to pile a packing case into a position in which at least two adjoining sides thereof have abutting cases against which the case is to be piled.

In view of the foregoing, the object of my invention, generally stated, is to provide an electrically operated grab for lifting packing cases and the like which shall be simple and efficient in operation and which may be readily and economically manufactured and installed.

A principal object of my invention is to provide for remotely controlling an electrically-operated grab to cause it to pick up and let go of an object to be moved.

Another principal object of my invention is to provide for remotely controlling the adjustment of an electrically-operated grab so that objects of different sizes and shapes may be readily picked up thereby.

Another object of my invention is to provide for increasing the effectiveness of each of the grab heads that are used in an electrically-operated grab so that an object may be more readily picked up.

A further object of my invention is to provide for stripping the screws of an electrically-operated grab from extraneous material that would otherwise remain attached thereto.

Still another object of my invention is to prevent the coasting of the operating members of an electrically-operated grab when the power is shut off therefrom.

Still another object of my invention is to provide for automatically arresting the functioning of an electrically-operated grab after the operated members have been moved to a predetermined position.

Still another object of my invention is to provide for permitting the remaining screws of a grab head to engage an object to be lifted while one of the screws encounters a relatively impenetrable portion of. the object.

A still further object of my invention is to provide for mounting a control cable for an electrically-operated grab with a minimum of distortion and opportunity of wear thereof.

Other objects of my invention will in part be obvious and in part appear hereinafter.

My invention, accordingly, is disclosed in the embodiment hereof shown in the accompanying drawings, and comprises the features of construction, combination of. elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the application of which will be indicated in the appended claims.

For a more complete understanding of the nature and. scope of my invention, reference may be had to the following detailed description, taken in connection with the accompanying drawings in which:

Figure 1 is a View in side elevation illustrating 45 the use of one embodiment of my invention,

Fig. 2 is a plan view of an electrically-operated grab constructed in accordance with my invention, certain parts having been omitted for the sake of clearness,

Fig. 3 is a view in side elevation of the grab illustrated in Fig. 2, showing in addition the supporting structure therefor,

Fig. 4; is an enlarged cross sectional view taken along the line IVIV of Fig. 5, showing certain details of construction,

Fig. 5 is a sectional View taken along the line VV of Fig. 4,

Fig. 6 is a view, partially in side elevation and partially in section, showing a modification of my invention,

Fig. '7 is a view in side elevation of the supporting apparatus used for carrying the electricallyoperated grab,

Fig. 8 is an enlarged cross-sectional view of one embodiment of a conductor cable which may be used in practicing my invention,

Fig. 9 is a diagrammatic View of the circuit connectiOns that may be used for operating my invention, and

Fig. 10 is a diagrammatic view of an alternate system for circuit connections that may be used for operating my invention.

Referring now particularly to Fig. l of the drawings, the reference character I 0 designates a packing box, case or crate constructed of wood or the like, a number of which are to be closely piled or stacked in a warehouse, as illustrated. The packing case I0 is picked up by means of an electrically-operated grab, shown generally at I I, which may be carried by means of an overhead travelling crane, the control cab of which only is shown generally at I2. It will be understood that cab I2 may be mounted on any suitable type of crane such as the customary overhead crane which is supported on a track having rails located at opposite sides of a building. It will also be undertood that the cab I2 itself and associated apparatus may be moved at right angles to the direction of movement of the entire crane.

Included in connection with the cab I2 is the hoisting apparatus shown generally at I3, the drum of which is shown, generally at I4, in Fig. 7 of the drawings. It will be readily understood that the drum I4 may be rotated by any suitable means to effect the raising and lowering of the grab I I. The movement of the crane may be controlled by an operator seated in the cab I2 by means of levers I5, while the control of the electrically-operated grab II may be accomplished from the control box I6 which may be arranged to control apparatus contained in a controller II, a description of which will be set forth hereinafter.

It will be readily understood that any suitable type of control apparatus may be used for controlling the operation of the crane to move the cab I2 both longitudinally and horizontally and also for controlling the operation of the drum I4. Therefore, a description of this control apparatus will be omitted from this specification, while a description of the control apparatus and circuits used for controlling the operation of the electrically-operated grab II will be set forth in detail hereinafter.

Since the cases in which refrigerators or the like are generally packed are constructed of wood or a similar material which may be penetrated readily by means of wood screws, I have provided a grab for hooking onto packing cases of this type by means of wood screws which may be operated either into or out of engagement with the packing case by means of electric motors.

Referring particularly to Figs. 2 .and 3 of the drawings, it will be observed that the electricallyoperated grab II comprises a rectangular frame shown generally at I8, having grab heads, illustrated generally at I9, at each of the corners thereof. A support structure, illustrated generally at 20, is provided and may be attached to the frame I8 by means of eye-bolts 2I secured thereto, as shown. At the ends of the frame I8 the grab heads I9 are joined together by means of tubular frame members 22, the ends of which may be secured to the heads I9 by means of set screws 23 or in any other suitable manner.

In order to: permit the use of the electricallyoperated grab II for packing cases of different sizes, it is desirable to provide some means for adjusting the frame I 8 to accommodate different sizes of packing cases. In order to provide for this adjustment, internally threaded tubular members 24 are secured, as illustrated, to the grab heads I9 by means of set screws 23. The corresponding tubular members 24 are connected by means of oppositely threaded shafts 25 which are arranged, when rotated in one direction, to contract the frame I8 and, when rotated in the other direction, to expand it.

In order to provide for rotating the shafts 25 to adjust the frame I8, an electric motor 23 of the polyphase, squirrel cage type may be mounted on a suitable frame 21 carried by the main frame I3 and arranged to drive the shafts 25 by means of a gear, sprocket and chain mechanism, shown generally at 28.

Each of the grab heads I9 comprises a frame or gear box 3I having a plurality of threaded members or screws 32 which may be rotated by means of a motor 33. The motors 33 which may also be of the polyphase, squirrel cage type are arranged to rotate the screws 32 in either direction so that they may be caused to engage or disengage a packing case or box as desired.

While the motors 26 and 33 are illustrated and described as being of the polyphase, squirrel-cage type, it will be understood that other types of a1- ternating-current motors may be used as well as motors of the direct-current type.

In order to prevent the screws 32 from being bent on coming in contact with objects, guards 34. are provided at one end of the frame I8 while at the other end of the frame I8, guide members 35 serve the same purpose. In addition, the guide members 35 are provided in order to permit the operator to readily position the grab I I on the top of a packing case or crate as will be readily understood.

In certain kinds of wood which may be encountered, hard portions such as knots or the like may be attached to the screws 32 after they have been withdrawn. Since this remaining material might prevent the screws 32 from engaging a second packing case, stripper plates 35 are provided and are mounted either on the guards 34 or on the guides 35, as illustrated, and underneath the screws 32. The stripper plates 36 are provided with openings 31 alined with the screws 32 and through which they may be moved into engagement with a packing case. The openings 37 are made only slightly larger than the largest diameter of the screw 32 so as to prevent any material which would otherwise be retained on the screws from remaining there when the screws are withdrawn.

Referring now particularly to Figs. 4 and 5 of the drawings, it will be observed that the construction of the mechanism for transmitting the power from the motor 33 to the screws 32 of the grab head I3 is more fully illustrated. It will be noted that the threaded members or screws 32 are removably secured to shafts 49 by means of nuts M. It will also be observed that the lower ends of the shafts 40 are provided with projections 42 which are arranged to engage the slotted heads of the screws 32 in the manner of a screwdriver. 7

The shafts 40 are journalled in the frame or gear case 3| in suitable bearings, as illustrated, and are arranged not only to rotate therein but also to move longitudinally thereof. In order to insure that the shafts 40 will move longitudinally to cause the screws 32 to engage or disengage a packing box or crate, the shafts 40 are provided with threaded portions 43 which are arranged to cooperate with threads 44 in the gear case 3|. f

Each of the shafts 40 has a gear wheel 45 secured thereto against rotation by any suitable means. The gear wheels 45 are arranged to mesh with an elongated pinion 46 which is mounted on a shaft 41 that may be rotated by means of the motor 33.

It will then be observed that, when the motor 33 is energized to cause the elongated pinion 46 to rotate, the gear wheels 45 will be rotated thereby which will cause 'the rotation of the shafts 40 and in turn the rotation of the screws 32 either into or out of engagement with a packing case or crate. It will be apparent that if the pinion 46 is rotated in a counter-clockwise direction, as viewed in Fig. 4 of the drawings, the shafts 40 will be caused to rotate in a clockwise direction, and at the same time they will be moved downwardly because of the interaction of the complementary threads 43 and 44. During this operation the gear wheels 45, while remaining in engagement with the pinion 46, will slide downwardly therealong. When the rotation of the pinion 46 is reversed, the gear wheels 45 will be rotated in a counter-clockwise direction to cause the shafts 40 to move upwardly.

In order to provide for the satisfactory operation of the gear mechanism enclosed in the frame or gear box 3 I, it is intended that the gear box 3| be oil or grease-tight so that the moving parts may rotate continually in a satisfactory lubricant. Packing 48 and packing glands 49 are provided near the lower ends of the shafts 40 in order to prevent the lubricant in the gear box 3| from flowing out past the shafts 40.

With a view to preventing the gear mechanism enclosed in the gear case 3| from coasting after the power is shut off from the motor 33, suitable disk springs are provided between the upper and lower sides of certain of the gear wheels 45 and the top of the gear case 3| respectively, as illustrated, to apply a retarding force to the mechanism for rapidly overcoming the inertia thereof after the power has been shut off from the motor 33.

Since only the weight of the electrically-operated grab II is utilized for forcing the screws 32 into threaded engagement with a packing case or crate, it is desirable to apply this force in such a manner that the screws may be readily started into lifting engagement. Therefore, one of the screws 53 of each of the grab heads I9 is provided slightly longer than the remaining three screws 32. It will then be apparent that all of the weight of the grab H is concentrated upon one screw of each grab head or a total of four screws rather than upon all the screws, which in this instance is sixteen and, as a result, the lifting engagement of the screws with the packing case may be more readily obtained. As soon as the screws 53 are started, the remaining screws of each of the grab heads I9 will be forced into lifting engagement with the packing case.

In order to provide for stopping the operation of the grab head after the shafts '40 have moved through a predetermined distance, a limit switch, illustrated generally at 54, is provided on one of the grab heads l9. One of the shafts 43 is provided with an extension 55 for operating the limit switch 54. The limit switch 54 is shown diagrammatically in Fig. 9 of the drawings and its operation is described in detail hereinafter.

While in the foregoing description and in the accompanying drawings a motor 33 individual to each of the grab heads I9 is described and illustrated, it will be readily apparent that a single motor may be provided common to the grab heads l9 at the ends of the frame l8 if it is found desirable to use this modified construction.

Referring now to Fig. 6 of the drawings, it will be observed that a modification of the arrangement of the shafts 40 in the frame or gear wheel 3| is provided. In the event that one of the screws 32 or 53 should engage a portion of a packing case which would be relatively impenetrable such as a knot, a nail, or the like, it is desirable to permit the remaining three screws to engage the packing case. For most practical purposes, the lifting force exerted by three of the lifting screws will be sufficient, and therefore the lack of the lifting force provided by the fourth screw will generally be unimportant.

With a View to permitting the remaining screws to engage packing case or move downwardly while one of them is prevented from further downward movement, each of the shafts 45 may be arranged to have its threaded portion 43 engage a nut 58 which may be slidably mounted in the frame or gear case 3|. In order to maintain the nut 58 in normal operating position under ordinary operating conditions, a coil spring 53 is provided between the nut 58 and a bracket 65, as illustrated. Thus, in operation if one of the screws 32 encounters a knot or a nail so that it cannot move further downwardly while the remaining screws may be moved downwardly, the continued rotation of the shaft All will cause the slidably mounted nut 58 to move upwardly against the force of the spring 53 thereby permitting the remaining screws to engage the packing box or crate. 'Itis thus apparent that the force necessary'to cause the screws 32 and 53 to engage the packing case under ordinary circumstances may be less than the force exerted by the spring 59 associated with each of the shafts 4!) driving the screws. When a force greater than that exerted by the spring 59 is required to force the screws 32 or 53 downwardly, the springs 59 will be compressed, and further downward movement of the screws will be prevented.

With a view to providing for supplying electric power for operating and controlling the motors 25 and 33 located on the grab H, a flexible multiple conductor cable may be provided, as is more clearly illustrated in Figs. '7 and 8 of the drawings. As shown, the supporting structure 20 is arranged to be raised and lowered by means of cables 63 and 54 that may be wound on the grooved drum E4 in the customary manner. In order to connect the control apparatus in the cab l2 of the crane with the motors 25 and 33 and the limit switch 54 located on the grab H, a multiple conductor cable 65 is provided having a sufilcient number of conductors for performing the desired control functions. Secured to the cable 65 is a resilient member 65 preferably in the form of a spring steel wire which has been previously formed into the shape of a spiral of relatively large diameter. The resilient member 66 may be secured firmly to the cable 65 by means of taps 61 or any other suitable means. While the resilient member 66 is illustrated as being disposed externally to the multiple conductor cable 65, it will be readily apparent that it may be formed internally therewith, if it be so desired.

With a View to guiding the cable 65 and maintaining it in proper position, a guide wire 68 is provided which may be connected to the support structure through a coil spring 69 and which may be wound at its upper end on the drum I4. The purpose of the spring 69 is to prevent the guide wire 68, which is customarily of relatively small diameter, from exerting any considerable tension of the support structure 20 for lifting the grab II as might otherwise occur if it were rigidly secured thereto.

While the guide wire 68 is illustrated for maintaining the cable 65 in the desired position, it will be apparent that one of the cables 63 or 64 may be used for performing the same function.

The cable 65 may be centered on the guide wire 68 by means of rings 10 which are attached by means of suitable connecting members II to spaced parts of the spirally formed cable 65, as illustrated. A container I2, carried by the supporting structure 20, is provided for collecting the cable 65 when the grab II is in the full up position. The upper end of the cable 65 may be secured by any suitable means to the cab I2.

It will be apparent that the spirally formed resilient member 66 serves not only to maintain the cable 65 in the spaced relation with respect to the guide wire 68, but that it also serves to keep the spirals formed thereby in proper spaced relation. As the grab II is lowered, it will be readily understood that the tension applied to the upper spiral will be greater than that applied to the succeeding spirals. However, the resilient member 66 may be of such mate-rial as to maintain these spirals of substantially constant length.

The control apparatus which may be located in the control boxes I6 and IT on the cab I2 is diagrammatically illustrated in Fig. 9 of the drawings. The adjusting motor 26 may be controlled by means of switches I5 and I6 which, in turn, may be controlled by means of push button switches TI and I8 respectively.

As illustrated, the motors 33 for operating the grab heads I9 may be connected in parallel and controlled by means of switches I9 and which, in turn, may be controlled by means of push button switches 8| and 82, respectively. In addition, a push button switch 83 is provided for stopping the operation of motors 33 in the event that it is desired to do so before the predetermined limit of travel of the motors is reached.

Power for operating the motors 26 and 33 may be obtained from a suitable three-phase source and connection may be had thereto by means of a three-pole knife switch 84. It will be observed that the multiple conductor cable 65 is shown diagrammatically in the drawings to illustrate the connection that is had between the cab I2 and the grab I I.

In operation, the switch 84 is closed thereby energizing conductors 85, 86 and 81. The conductor 81 is connected by means of a common conductor 88 to all of the motors 26 and 33, as illustrated.

It will be observed that the limit switch 54 is in the up position or in the position to which it is moved after the shafts 40 have been moved upwardly for the predetermined distance. The

limit switch 54 is arranged not only to open a circuit so that the power may be removed from the motors 33, but it is also arranged to set up a circuit so that these motors may be subsequently operated in the reverse direction.

It being desired to pick up a packing case I0, the operator moves the crane and the control cab I2 to an appropriate position and lowers the grab II until it is in proper position over the packing case I 0. In the event that the frame 20 is not sufiiciently expanded to accommodate the packing box which it is desired to pick up, the operator may depress the push button switch Il, thereby energizing switch I5 to connect the winding 90 of motor 26 to conductors and 86.

The circuit for energizing switch I5 may be traced from the energized conductor 86, through conductor 9I, contact members 92 of switch I I, conductor 93, winding of switch 15 and conductor 94 to the energized conductor 85.

It will be observed that the sections of the winding not connected to the common conductor 88 are connected through conductors 95 and 96 to conductors 91 and 98, respectively, which are connected to one side of the contact members of switches I5 and I6, as illustrated. When the switch I5 is operated, conductors 91 and 98 are connected by means of conductors 99 and I00, respectively, to conductors 85 and 86, respectively, thus causing the motor 26 to rotate to expand the frame 20. After the frame 20 has been expanded to the proper distance the operator releases the push button switch 11 thereby deenergizing switch I5 and opening the circuit from conductors 85 and 86 to the Winding 90 of the motor 26. Because of the relatively large amount of friction involved inherently in the construction of the apparatus, the motor 26 will be stopped substantially instantaneously.

If it is desired to contract the frame 20, the operator depresses the push button switch I8 thereby energizing the switch I6 over a circuit which may be traced from energized conductor 86 through conductor 9|, contact members IOI of switch 18, conductor I02, winding of switch I6 and conductor 94 to the energized conductor 85.

The operation of switch I6 serves to connect conductors 91 and 98 to conductors I03 and I04, respectively, and thereby to conductors 86 and 85, respectively. It will be observed that the operation of switch 16 reverses the connection of conductors 91 and 98 to the conductors 85 and 86 from that previously described in connection with the operation of switch I5. As a result, the motor 26 will be caused to operate in a reverse direction, as will be readily understood.

When the frame 20 has been contracted to the desired position, the operator releases the push button switch I8 and the motor 26 will come to a stop, as set forth hereinbefore, substantially instantaneously.

After the frame 20 has been properly adjusted, the operator depresses the push button 8I thereby energizing the switch 19 and applying power from conductors 85 and 86 through conductors I05 and I06, contact members of switch I9, conductors I0! and I08, I09 and H0 to the sections of windings III of motors 33 which are not connected to the common conductor 88.

The circuit for energizing switch I9 may be traced from the energized conductor 85 through conductor I I 5, contact members I I 6 of switch 8!, conductors II! and H8, winding of switch I9, conductor II9, contact members I20 of the limit switch 54, conductor I2I, contact members I22 of the stop switch 83 and conductor I23 to the energized conductor 86.

The operation of switch I9 causes power to be applied to the motors 33 over the conductors traced hereinbefore, thereby causing the rotation of the gear mechanism in the gear box 3I and the resultant rotation of the screws 53 and 32 to cause them to come into lifting engagement with the crate or box to be lifted.

The operation of switch I9 also completes a circuit for holding the switch I9 energized until it is deenergized through the operation of the limitswitch 54. Therefore it is not necessary for the operator to hold the push button switch 8| in the closed position any longer than is necessary for the energization for the switch I9.

The holding circuit for switch I9 is completed by means of contact members I24 which serve to complete an obvious shunt circuit around the contact members II6 of the push button switch 8I.

In the event that it is desired to stop the operation of the motors 33 before they have reached their limit of travel in either direction, the operator may depress push button switch 83, thereby opening the energizing circuit for the winding of switch I9.

After the motors 33 have been energized for a time sufiicient to move the shafts 40 downwardly and the screws 32 and 53 into engagement with the packing box or crate for the predetermined distance, the limit switch 54 is operated to open the contact members I20 and to move the limit switch to the dotted position thereby deenergizing the switch I9. The motors 33 are then stopped and a circuit is set up so that they may be reversed for the succeeding operation of removing the screws 32 and 53 from the packing box or crate. When such box or crate has been moved to the desired position by the crane, the operator depresses the push button switch 82 thereby energizing switch 80 and connecting conductors I01 and I08 through contact members of switch 80 to conductors I25 and I26, respectively and by these conductors to conductors 86 and 85, respectively. It will be observed that the operation of switch 80 causes the connection of con ductors I01 and I08 to conductors 85 and 86 to be reversed from that described previously and for this reason the motors 33 will be energized to rotate in a reverse direction to withdraw the screws 32 and 53 from engagement with the packing box or case.

The circuit for energizing switch 80 may be traced from the energized conductor 85 through conductor H5, contact members I28 of push button switch 82, conductor I29, winding of switch 80, conductor I30, contact members I3I of the limit switch 54, conductor I2I, contact members I22 of stop switch 83, and conductor I23 to energized conductor 86.

The operation of. switch 80 also completes a circuit by means of its contact members I32,

which are closed when it is energized, to complete an obvious shunt circuit for the contact members I28 of push button switch 82 so that this push button switch need only be held in the closed position for a time sufliciently long to permit the operation of switch 80 to the closed position.

The motors 33 continue in operation to withdraw the screws 32 and 53 from the packing box or crate until the limit switch 54 is operated to its former position and contact members I3I are opened to effect the deenergization of switch 80. The hereinbefore described operations may be repeated in lifting additional packing cases or boxes, as will be readily understood.

, In certain instances, it may be undesirable to control the stopping of the head motors 33 by means of the single limit switch 54, which is actuated in accordance with the functioning of only one of the grab heads I9. Therefore, the alternative circuit connections illustrated diagrammatically in Fig. of the drawings are provided.

Referring particularly to Fig. 10 of the drawings, it will be observed that a limit switch I40 is provided individual to each of the motors 33. In effect, the limit switch I40 is of the doublepole double-throw type, which has been suitably illustrated for operation as a limit switch in connection with the operation of the gear mechanism that is driven by the motor 33.

The limit switch I40 may be of any suitable type in which contacts are always closed in either of its two positions. In the position'illustrated in the drawings, the contact members of the limit switch I40 are in the up position, to which they have been actuated when the motor 33 has reached its predetermined upper limit of travel. In the position illustrated, the limit switch I40 is arranged to provide suitable connections for effecting the energization of the motor 33 to energize it for driving the gear mechanism downwardly as will be set forth in detail hereinafter.

The remaining control circuit and equipment for the motors 33 are substantially the same as that illustrated in Fig. 9 of the drawings. It will be observed, however, that the holding contact members I24 and I32 of the switches I9 and 80 have been omitted, and also that the stop push button 83 has been omitted. The control circuits and equipment for controlling the operation of the motor 26, which is used for adjusting the size of the frame I8, is identical with that illustrated in Fig. 9 of the drawings.

Since, in a certain sense, each of the motors 33, as well as the motor 26, are individually operable, it is desirable to provide some means for indicating to the operator whether any or all of these motors are energized. With a view to providing this indication, a signal lamp I M, connected in series circuit relation with a suitable resistor I42, may be connected across the terminals of two of the windings III. It will, therefore, be apparent that whenever the motor 26 or any of the motors 33 are energized, the indicating lamps I4I, individual to the motors that are energized, will be illuminated. Since the indicating lamps MI and the resistors I42 may be mounted at any suitable position on the grab II for the convenience of the operator in the cab I2, a detailed description of their mounting will not be set forth herein.

In operation, if the main switch 84 has been closed to apply energy to conductors 85, 86 and 81, and the frame I8 has been adjusted to the desired position by means of the motor 26, as set forth hereinbefore, the motors 33 may be energized to cause the grab II to attach itself to a crate which it is desired to pick up.

The operator depresses the down push button 8 I, thereby effecting the energization of switch I9 over a circuit which-may be traced from the energized conductor 86, throughconductor I43, contact members I I6 of switch 8|, conductor I44, winding of switch I9, and conductor I45 to the energized conductor 85.

The operation of switch I9 completes a circuit for energizing the motors33 which may be traced from the conductors 85 and 86 through conductors I41 and I48, respectively, the contact members of switch I0, conductors I49 and I50, respectively, and through the first and third contact members of the limit switches I40 to the windings III.

As long as the operator holds the push button switch 8| in the closed position, the motors 33 will continue to operate until they are deenergized through the operation of the limit switches I40 individual thereto. Meanwhile, the indicating lamps MI are lighted to inform the operator that the motors individual thereto are energized. When all of the indicating lamps I II are extinguished, the operator may release the push button switch 8|, thereby deenergizing the switch I9. When the screws 32 and 53 have been moved downwardly for a predetermined distance, the limit switches I40 will be moved to open the first and third contact members and to close the second and fourth contact members, as will be readily understood.

After the packing box or crate has been moved to the desired position, the grab II may be released therefrom by a subsequent energization of the motors 33 in the reverse direction which may be effected by the operator in depressing the push button switch 82, thereby effecting the energization of switch 80.

The circuit for energizing switch may be traced from the energized conductor 86 through conductor I43, contact members I28 of switch 82, conductor I5I, winding of switch 80, and conductor I45 to the energized conductor 85.

The operation of switch 80 serves to connect the conductors and 86 to the windings III over circuits which may be traced from conductors 85 and 86 through conductors I41 and I48, respectively, contact members of switch 80, conductors I53 and I54, respectively, and through the second and fourth contact members of the limit switches I40 to the windings III.

It will be observed that the connections between the conductors 85 and 86 and the windings II I are reversed when the switch 80 is energized from the connections that are completed when the switch I9 is energized.

The motors 33 continue in operation and the indicating lamps I4I individual thereto are illuminated until a predetermined position is reached, at which the limit switches I40 are individually actuated back to the position illustrated in the drawings. The circuits for energizing the motors 33 are then interrupted and subsequently circuits are set up to permit the subsequent energization and operation of the motors 33 in the forward direction to cause the screws 32 and 53 to again be moved downwardly to come into lifting engagement with another crate or packing box.

Since further changes may be made in the above construction, and different embodiments of the invention may be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A grab for use in lifting wooden crates or the like comprising, in combination, a main frame, and a plurality of grab heads carried by the main frame, each of the grab heads comprising a frame, a plurality of operating members rotatably mounted on the frame, threaded means on the operating members outside the frame for engaging the article to be lifted, and a motor for each grab head having driving connection with the operating members for rotating the threaded means into or out of engagement with the wooden crate.

2. A grab for use in lifting wooden crates or the like comprising, in combination, a main frame, a plurality of grab heads carried by the main frame, each of the grab heads comprising a frame, a plurality of operating members rotatably mounted on the: frame, threaded means on the operating members outside the frame for engaging the article to be lifted, and a motor for each grab head having driving connection with the operating members for rotating the threaded means into or out of engagement with the wooden crate, circuit means connecting said motors to a source of electrical energy, and a limit switch operable after a predetermined movement of an operating member of one of the grab heads to disconnect the motors from the source of electrical energy.

3. A grab for use in lifting wooden crates or the like comprising, in combination, a rectangular frame, and a grab: head mounted at each of the corners of the frame, each of the grab heads comprising a plurality of rotatable screws on the under side thereof for engaging the article to be lifted, a plurality of intermeshing gears operatively connected to the screws, and an electric motor for each grab head having driving connection with the gears for rotating the screws into or out of engagement with the wooden crate.

4. A grab for use in lifting Wooden crates or the like comprising, in combination, an adjustable frame, a motor having driving connection With the frame for extending or contracting the frame depending upon the direction of rotation of the motor, and a plurality of grab heads carried by the frame, each of the grab heads comprising a frame, a plurality of operating members rotatably mounted on the frame, threaded means on the operating members underneath the frame for engaging the article to be lifted, and a motor for each grab head having driving connection with the operating members for rotating the threaded means into or out of engagement with the wooden crate.

5. A grab head for use in lifting wooden crates or the like comprising, in combination, a gear box, a plurality of threaded members rotatably mounted on the underside of the gear box for engaging a wooden crate, a plurality of intermeshing gears mounted in the gear box and operatively connected to the threaded members, an electric motor having driving connection with the gears for rotating the threaded members into or out of engagement with the wooden crate, and resilient means interposed between the gears and the gear box to prevent the coasting thereof after power is removed fro-m the motor.

6. A grab head for use in lifting wooden crates or the like comprising, in combination, a gear box, a plurality of threaded members rotatably mounted on the underside of the gear box for engaging a Wooden crate, a plurality of intermeshing gears: mounted in the gear box and operatively connected to the threaded members, an

electric motor having driving connection with the gears for rotating the threaded members into or out of engagement with the wooden crate, and a stripper plate carried by the grab head and provided with openings aligned with said threaded members and through which the threaded motor for each grab head having driving connection with the operating members for rotating the threaded means into or out of engagement with the wooden crate, circuit means for connecting the motor to a source of electrical energy, and a limit switch operable after a predetermined movement of the operating members to disconnect the motor from the source of electrical energy.

JOHN E. WEBSTER.

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