US3009583A

US3009583A - Overhead traveling double-hook bridge crane

Info

Publication number: US3009583A
Application number: US42850A
Authority: US
Inventors: Edward D Pierson
Original assignee: MINER MACHINE CO
Current assignee: MINER MACHINE CO
Priority date: 1960-07-14
Filing date: 1960-07-14
Publication date: 1961-11-21
Anticipated expiration: 1978-11-21

Description

Nov. 21, 1961 E. D. PIERSON OVERHEAD TRAVELING DOUBLE-HOOK BRIDGE CRANE 5 Sheets-Sheet 1 Filed July 14, 1960 INVENTOR.

Wm XQ Q MR, Sw 5 ww w 50/1/A/P0 D P/EPSON w ATTORNEYS Nov. 21, 1961 E. D. PIERSON OVERHEAD TRAVELING DOUBLE-HOOK BRIDGE CRANE 5 Sheets-Sheet 2 Filed July 14, 1960 Nov. 21, 1961 E. D. PIERSON 3,009,583

OVERHEAD TRAVELING DOUBLE-HOOK BRIDGE CRANE Filed July 14, 1960 5 Sheets-Sheet 3 INVENTOR. E DNA/FD D. P/E/PS 0N ATTORN E YS Nov. 21, 1961 E. D. PIERSON 3,009,583 OVERHEAD TRAVELING DOUBLE-HOOK BRIDGE CRANE Filed July 14, 1960 5 Sheets-Sheet 4 INVENTOR.

EDWARD D. P/ERSON ATTORNEYS United States Patent 'Ofifice 3,009,583 Patented Nov. 21, 1 961 3,099,583 OVERHEAD TRAVELING DGUBLE-HGGK BRIDGE CRANE Edward D. Pierson, Denver, (3050., assignor to Miner Machine Company, Denver, Cole, a corporation of Colorado Filed July 14, 1960, Ser. No. 42,850 22 Claims. (Cl. 212-21) This invention relates to hoisting apparatus and, more specifically, to overhead traveling cranes of the doublehook type.

Overhead traveling cranes, even of the. double-hook a type are, of course, in wide useas hoisting apparatus es-'- pecially in warehousing operations when'heavy and elongated materials must be moved from place to place and stacked. Among the several limitations of the prior art devices for this purpose, perhaps the most serious is that few, if any, provide a mechanism whereby either hook may be positioned either laterally or vertically entirely independent of the other and of longitudinal movement of the bridge while including means for instantaneously establishing a positive mechanical interlock adapted to permit both transverse and vertical movement of'the two hooks simultaneously. This feature becomes of especial importance when handling long thin. loads, sheet materials, structural shapes, etc, that may vary considerably with respect to one another and even within the same load insofar .as uniform weight distribution is concerned. In other words, most hoisting mechanisms of thisgeneral type require that considerable ,care'be exercised by the operator in picking up the load so that the weight there- -of is rather evenly distributed between the two hooks. Also, in those cranes where each hook and Winch assembly functions completely independent of the other even when both are required on the same load, a great deal of skill is needed by the operator to accomplish simultaneous operation of the hooks; otherwise, the load may shift and even slip out of the slings or hooks with resultant damage thereto and possibly serious injury to personnel working in the area. a

Another significant disadvantage of thecommonly used double-hook hoists is the complex arrangement of levers and pedals that comprise the control system used to operate the device. Highly skilled operators are needed for this type of crane with the attendant increase in labor costs occasioned by this need.

Yet, another limitation of the known double-hook hoists is the problem of rigging the load preparatory to use of the crane. In most instances, the crane provides so little provision of a hoisting apparatus that is capable of hanoverall efficiency.

An additional object is to provide a control system for double-hook hoists in which the hooks can be positioned with such accuracy and speed even by an unskilled operator that time-consuming adjustments in the rigging of the load slings is largely eliminated.

Further objectives of the invention of the class disclosed herein are to provide a double-hook crane .unit which is less costly to operate than other units for this purpose, one that is adaptable for'use in a wide-variety of material-handling applications, a device that is rugged and'relativelyfree of service problems, and ,a hoist that is simple and easy to use, compact and efficient.

Other objects will be in part apparent and in part pointed out specificallyhereinafter.in connection with 1 the description of the drawings that follow, and in which: FIGURE 1 is a top plan view of the overhead traveling crane of the present invention showing the b i ge with carriages at each end thereof mounted for longitudinal control over the positioning of the hooks that final adjustments must be made in the slings that attach directly to the'load rather than with the crane. This is a timeconsuming and difficult hand operation .that effects a substantial reduction in the quantity of material that can .be handledin a:. given period of time, requires additional personnel and, as a result, lowers the overall efficiency ofhtheunit.

It is, therefore, one of the principal objects of the present invention to prom/idea novel and improveddoublehook overhead traveling hoist.

A second objective is 'the provision 0f ;.a crane of the type aforementioned in which means are :provided for operating the hooks, either entirely independent of.

one another or in unison as the particular occasion demands.

Another objectis to provide a double-hook overhead crane in which all control functions can be handled by a single unskilled operator at ground level with a single compact-push-button control .box.

Still another objective of the instant invention is the rolling movement alonglth'e supporting rails, the hooksupporting dollies mounted for transverse movement along the bridge, and the winch assembly for operating the hooks, portions of the bridge having been broken away to conserve space; Y v H FIGURE 2 is aside elevation of the unit showing the drive mechanisms by which the bridge is moved along the rails and one of the dollies is moved within "the bridge, portions of the bridge having again been broken away to, conserve space;

FIGURE 3 is a fragmentary top plan view to an enlarged scale showing one end of the bridge and associated supporting rails therefor with particular emphasis on the drive mechanisms for the carriages anddollies, portions having been broken away to conserve space and better reveal the interior construction; 7

FIGURE 4 is a section taken along line 4- 4 of FIG- URE 3; I

FIGURE 5 is a section further enlarged taken along line 5-5 of FIGURE 4; I

FIGURE 6 is a section to the same scale as FIGURE 5 taken along line 66 of FIGURE 4; I j FIGURE 7 is a fragmentary top plan View to an enlarged scale showing one of the dollies mounted on the bridge, the associated sprocket chains for accomplishing relative transverse movement therebetween, land the sheaves which are reeved to provide the operative con- 'nection between the winch and hook;

FIGURE Syis a section taken along line 8--8",0f

FIGURE 7; g

FIGURE '9 is a somewhat diagrammatic representation of the'hook and dollysheaves showing the manner in which these elements are reeved'together;

FIGURE 10 is a diagram illustrating 'thegmanner in "which each "dolly is connected to its associated drive mechanism for accomplishing movement 'thereof along the bridge, and the manner in which 1 each winch'Eis .eratively connected to its hook through one of :the'

dollies; and, 1

FIGURE 11 is a simplified gcirc'uit dia'gram illustrating the control circuit for operating the crane.

Referring now 'to the drawing for -a detailed description of the present invention, and in particular toFIG- by numeral 10 and whichv spans the space between a'pair of longitudinally extending parallel rails 12 ,on whichitds mountedjfor rolling movement .by means of carriagesfi located at opposite ends thereof; The bridge 10 comprises a pair of heavy beams 16 arranged in longitudinally spaced substantially parallel relation to one another defining a space 18 therebetween in which the first and

second books

20 and 22, respectively, are suspended from the

corresponding dollies

24 and 26 that are mounted for transverse rolling movement on rails 28 carried by the beams. A double-decked platform 30 is carried by the bridge intermediate the ends thereof for the purpose of supporting the hoist mechanism that has been indicated broadly by numeral 32 along with the bridge drive 34. Also, the first and second

dolly drive mechanisms

36 and 38 are carried by the bridge 10 at one end thereof as best shown in FIGURE 4.

In the particular form shown, the main or bridge-supporting rails 12 are attached to the underside of same overhead structure such as a Warehouse roof 40, and comprise steel I-beams having the conventional Web and upper and lower flanges. The carriages 14 at opposite ends of the bridge are suspended from the lower flanges of these main rails 12 for rolling movement in the direction of their length. The bridge drive mechanism 34 comprises a reversible electric motor 42 mounted on the lower deck 44 of platform 30 and connected to both of the carriages 14 by a drive shaft 46 extending the full length of the bridge in a manner which will be set forth in detail in connection with the description of FIGURES 3 through 6, inclusive.

Transverse movement of the

dollies

24 and 26 along the bridge is accomplished by means of separate

dolly drive mechanisms

36 and 38, each of which includes a reversible electric motor 48, a speed reducer 50 and a chain and sprocket assembly 52 forming an operative connection between the latter and one of the dollies. The construction of the bridge is such that both dollies can be moved independent of one another in either direction substantially the full length thereof. Also, a clutch mechanism 54 (FIGURE 4) provides means for opera tively interconnecting the

dolly drive mechanisms

36 and 38 together for accomplishing simultaneous movement of the dollies along the bridge irrespective of their spacmg or transverse position.

The upper deck 56 of platform 30 provides the support for the first and second motor-driven

winches

58 and 60 of the hoist assembly 32 that are connected respectively' to hooks and 22, through

dollies

24 and 26. Each of these winches is independently operable in either direction by means of reversible electric motor 62 to raise or lower the associated hook. In addition, means comprising a differential 64 and a clutch 66 together with an associated belt and pulley drive 68 enable the

winches

58 and 60 to be operatively interconnected so that the

books

20 and 22 can be raised or lowered simultaneously.

Now, with particular reference to FIGURES 3-6, inclusive, of the drawings, the carriages 14 located at opposite ends of the bridge 10 will now be described in detail. The main bridge beams 16 terminate in endplates 70 that are welded or otherwise permanently attached to the ends thereof and project in both directions beyond the sides of the bridge. A second substantially identical endplate 72 is attached to the first-mentioned endplate 70 by means of tieplates 74 and 7 6 that maintain a spaced parallel relation therebetween. Of course, other reinforcing members may be added as needed to insure a sound structural assembly, some of which have been illustrated but require no detailed description.

Each carriage 14 includes as a part thereof a pair of

trolleys

78 and 80 mounted at opposite ends thereof in supporting relation. In the particular form shown, both trolleys include a pair of double-walled generally-triangular sideplates 82 interconnected and maintained in spaced substantially parallel relation to one another by several studs 84 spanning the distance therebetween and passing through sleeve elements 86 fastened within the double walls thereof. Two of these stud and sleeve assemblies are positioned in the bottom of each trolley and are used to hold a block 88 in place between the sideplates thereof as best shown in FIGURE 5. This block 88 is attached to the tieplate 74 spanning the space between the

endplates

70 and 72 of the carriage by means of a vertical stud 90 having a loose fit within opening 92 provided in the tie-plate. Actually, the entire bridge assembly rests on and is supported by blocks 88 of the trolleys which, of course, are in turn suspended from the main bridge rails 12; thus, stud 9t) primarily functions as a means for maintaining the carriage in assembled relation.

The top of block 38 is preferably provided with a bearing element 94 that has a spherically convex upper surface 96 adapted to fit into and tilt within a complementary concave or dished surface 98 on the underside of a second bearing element 100 attached to the bottom of tie-plate 74. 'T he opening 102 in bearing element 100 is i 4 sized to loosely receive stud 90 which passes up through the center of element 94. Thus, the connection between elements 94 and of the carriage provides for relative tiltable movement of the bridge relative to the trolleys which is desirable to compensate for minor irregularities in the main bridge rails 12.

A pair of stub shafts 104 are mounted in opposed coaxial relation to one another at opposite ends of each trolley along the top edge thereof and a supporting roller 106 is journalled for rotation on each stub shaft. The spacing between adjacent ends of each pair of stub shafts is such that the web of the I-beam main bridge rails 12 will pass therebetween as indicated by dotted lines in FIGURE 5. The rollers 106, on the other hand, roll along the upper surface of the lower flanges of said I- beam bridge rails thus supporting the entire hoist. Suitable sleeve elements 108 fastened within the double walls of the trolley sideplates receive the stub shafts 104 nonrotatably. Additional roller assemblies 110 are attached in longitudinally spaced relation on the inside surfaces of each sideplate 82 in, position to ride along the edge of the lower flange of the I beam bridge rails 12 for the purpose of maintaining the trolleys more or less centrally-located thereon.

Trolleys

78 and 80 of each carriage assembly differ from one another in that trolley 80 includes a chain and sprocket drive mechanism which is used to move the hoist longitudinally along the main bridge rails. The double-ended drive shaft 46 from reversible motor 42 positioned intermediate the ends of the bridge 10 terminates inside the carriages 14 between

end plates

70 and 72 in a sprocket 112 as best shown in FIGURE 6. Shaft 46 is journalled for rotation within a shaft bearing 114 that is bolted or otherwise secured to the wall of endplate 70. One of the studs 84 interconnecting the double-walled sideplates 82 of trolley 80 is provided with a hollow shaft 116 journalled for rotation thereon and and which includes an intermediate sprocket 118 together with a pair of sprockets 120 mounted near the ends. Sprocket 118 is drivingly connected to sprocket 112 by means of sprocket chain 122; whereas, sprockets 120 are operatively connected by sprocket chains 124 to another pair of sprockets 126 which are, in turn, securely fastened to one of the opposed pairs of drive rollers 106d for conjoint rotation therewith. Thus, rotation of double-ended drive shaft 46 in response to energization of motor 42 of the bridge drive mechanism 34 in either direction causes rotation of the drive rollers 106d located within the trolleys 30 at both ends of the bridge by reason of the above-described chain and sprocket mechanism. Obviously, the drive rollers 106d which support much of the weight of the entire hoist unit and rest upon the bottom flange of the bridge rails, have sufficient frictional contact with the latter to move the bridge structure and associated carriages from end to end of the rails.

The

dollies

24 and 26 that carry the hooks and are mounted on rails 28 of the bridge for movement between the carriages along with the drive mechanism therefor can best be described in connection FIG- URES 3, 4 7 and 8 of the drawings to which reference will now be had. Each dolly has a generally rectangular open-bottomed frame 128 that includes sidewalls 130 and endwalls 132. The endwalls 132 are preferably shaped to provide a deep V-shaped notch 134 (FIG- URE 8) that allows the winch cables to pass freely over the ends of the dolly. The side and endwalls have inturned flanges 136 along their lower margins that provide support for a rectangular sheave frame 138 positioned in the bottom of the dolly that carries the several winch cable sheaves which Will be described in detail presently. Flanged wheels 140 are mounted for rotation on stub axles 142 attached to the corners of the dolly frame and are designed to roll along the dolly rails 23, as shown.

Movement of the dollies along the bridge is 'accom-' plished by means of a pair of

sprocket chains

144 and 146, connected respectively to

dollies

24 and 26. Chain 144 has one free end thereof connected to an end of dolly 24 (FIGURES 2,7 and on oneside of its longitudinal centerline from whence it passes along the bridge and over sprocket 148 attached to shaft 150 that is mounted for rotation within bearings 152 located on end-plate 7'9 of one of the carriages between the rails 28. After passing over sprocket 148, chain 144 extends the full length of thebridge and underneath both dollies, up over sprocket 154 (FIGURES 2 and 7) that is journalled for rotation on the carriage at the opposite end of the bridge, and back along the bridge to the other end of dolly 24 where the remaining free end thereof is attached. Another sprocket 156 is provided on shaft drums 182 extending in'a direction normal to the length 15th and is operatively connected to the output shaft 158 of reducer 50 by means of chain 160 and a third sprocket 162. Shaft 158 is journalled for rotation within shaft bearings 16dcarried by an endwall 166 of subplatform 16% mounted underneath one of thecarriages. The output shaft 170 of reversible electric motor 48 is connected into the reducer S ll and, when energized, functions to pull the dolly 24 along the bridge in either direction by reason of the chain and sprocket assembly 52 just described that includes sprockets 162,'1 56, 154 and 143 along with sprocket chains Mil-and 144. Sprocket chain 145 is utilized in an identical assembly to -accomplish movement of the other dolly 26, such assembly having been identified by the same reference numerals with the letter a appended thereto. j

Now, as has already been mentioned, both -o'f the dolly drive

mechanisms

36 and 38 located at the same end of the bridge and reducer output shafts 158 and in the of the bridge. The winch motors 62 are positioned onv opposite sides of the platform for convenience in operatively connecting same to axially aligned shaifts 184 and 186 by means of belt and pulley drives 68 and 68a.

I Both shafts 184 and 186 are journalled for rotation in suitable shaft bearings 188 and are operatively interconnected at their adjacent ends-by a differential 64 adapted to reverse the direction of rotation of one with respect to the other. In addition, one of said shafts 136is' divided into two sections selectively interconnectable for conjoint rotation by an electrically-operated clutch 66. With clutch 'fifi'de-energized, the power driven winches operate independently of one another to raise or lo-wer'their respective hooks depending upon the direction of rotation of the winch motors; whereas,

on the other hand, when clutch 66 is energized to conple the two sections of shaft 186 together and connect them through the differential to shaft 184, the winch drums are operatively associated such that they tum in opposite directions at the same speed and-either raise or lower both hooks in unison. Specifically, a free end :of the hoist cable -18!) is deadended and wound on the win-ch drum 182 from whence it is drawn along' the'bridge and-over fixed sheave 172, a then -bac'k along the bridge and over one pulley 190 of 1 fixed pulley blockl' ffle carried by the dolly, around the hook-carrying movable pulley block 178 and back up over a second pulley 192 of the fixed block, along the bridge to the opposite end thereof where it passes around the second fixed sheave 174 and finally back along the bridge again to the drum where it is woundtherearound same direction and dead-ended. Thus, rotation of the drum .in'onedirection pays out'cable and lowers the movable block; whereasjrotation thereof in the opposite 158a thereof are arranged in end-'to-end 'coaria-l rela tion with electrically-operated clutch 54 forming anoperative connection therebetween. Thus, with clutch 54 deenergized, either dolly drive mechanism can be operated independent of the other to varythe spacing beshown in FIGURES 1-4 and 7-10 o'fthe drawings and,

therefore, all of these figures will be used in the description of this assembly. As was the case with the dolly drive mechanisms just described, the specific components of the hoist mechanism that operatively connect winch 58 with hook 20 are identical to those associated with winch and hook 22; therefore, only one of these systems will be described in detail and the like components of the other will be identified by adding the letter a to the reference numerals; Basically, 'both of these sections of the complete hoist "systeminclude fixed sheaves 172 and 1'74 mounted atopposite endsof the bridge, a fixed pulley block 176 carried by the dolly,

their position along the direction takes on cable and raises the hook. Ofcourser the reeving arrangement just described is that which has been illustrated schematically in FIGURE 10 and which has been simplified to eliminate the conventional force-multiplying sheaves 194- and 196 of the fixed and movable pulley blocks that have been shown in other figures of the drawing. It is apparent, therefore, that the particular number and arrangement of sheaves within the fixed and movable blocks becomesa matter of choice depending "upon the desired balance between the hoisting speed and'the mechanical advantage to be realized. Also, it should 'benoted that *wheirthe dolliea are shifted from placeto place alongthe bridge, thehoist cables run through the fixed andmovablepnlley block's; however, if'the winches are inoperative during this operation, the pick-up hooks remain the same distance above "ground level.

Finally, with'reference'to FIGURE ll of the 'clrawings, the electrical system for controllingthe hoist mechanism 32 'andthe dolly drive

mechanisms

36 and 38 Willnow be described. The electrical circuitry for controlling the bridge drivernechanism 34', on the other hand, has not been illustrated and will, -therefore,-not be described in detail as it is purely conventional and comprises nothin'g more than a simples'witch and relay circuit adaptedto start, stop and motor 42.

Operation of the unit is commenced by closingthe normally-open main on-off switch 193 of'the controlcir- "cuit thath'a'sb-een indicated in a general Way by numeral 299. When switch 1-98 closes, relay 202 is energized through application of the control voltage thereto and force-niultiplyin g reverse the starting leads to bridge drive thus activated, the various operations of the unit are controlled by main function selector switch 208 which has three operative positions indicated by full lines, dotted lines and dot-dash lines in FIGURE 11.

Placing the function selector switch 208 in the first or full line position thereof impresses the control voltage across relay B which immediately closes all the B contacts B -B inclusive. Note that with the selector switch in first position, relay C is not energized and all the C contacts C -C inclusive, are still open. Now, when the operator closes normally'open up-switch 210 relay SSU is energized to actuate the electric motor 62 of winch 58 in a direction to raise hook 28 suspended from dolly 24 to which said relay is electrically connected. Relay 6llU, on the other hand, is not energized because the C and C contacts are still open with the selector switch in first position. Similarly, closing the normally-open down-switch 212 energizes relay 58D which is electrically connected to motor 62 of winch 53 in a manner to reverse the input leads thereto thus lowering hook 29. Here again, the relay 66D is not energized when switch 212 is closed because contacts C and C remain open. I

With the function selector switch 208 in first position, actuation of left-switch 214 to move the latter from the full line to the dotted line position of FIGURE 11 energizes relay 241.. which is electrically connected to motor 48 of the dolly drive mechanism in a manner to move dolly 24 to the left along the bridge as viewed in FIGURES l and 2. Conversely, actuation of right-switch 216 in a manner to move same from the full to dotted line position energizes relay 24R which is also electrically connected to motor 43 but me manner to reverse the direction of rotation thereof and move dolly 24 to the right along the bridge. As before, relays 26R and 26L cannot be energized with selector switch 26 8 in first position because contacts C C and C7 are open. Thus, With the selector switch in first position, the movements of dolly 24 either right or left along the bridge may be controlled and the hook 20 operatively associated therewith can be raised or lowered. The circuitry for controlling the movements of dolly 26 and hook 22 is, however, completely inactive.

Now, before proceeding with the description of the circuitry for controlling dolly 26 and hook 22, it would be advisable to point out that even though contacts B are closed, contacts C in series therewith are still open thus preventing both electrically-operated

clutches

54 and 66 from being actuated.

Movement of function selector switch 268 into its second or dotted line position, de-energizes relay B and all the B contacts associated therewith while energizing relay C to close all the C contacts C inclusive. As was the case with the B-relay circuit, closing 'up-switch 210 energizes relay 60U starting motor 62a of winch 60 in a direction to raise hook 22 suspended from dolly 26. Closing the downswitch 212 energizes relay 60D and lowers hook 22 by reversing the direction of rotation of winch motor 62a. Actuation of left-switch 214 to move same to its dotted line position energizes relay 26L which starts dolly drive motor 48:: to which it is electrically connected in a direction to shift the position of dolly 26 to the left along the bridge as viewed in FIGURES 1 and 2. Movement of right-switch 216 to the dotted line position energizes relay 26R which reverses the direction of rotation of motor 48a and moves dolly 26v to the right along the bridge. Accordingly, it can be seen that the C- relay circuit and associated contacts control the movements of dolly 26 and its hook 22. As before, even though contacts C are closed, B is open and neither clutch operates.

=Finally, movement of function selector switch 208 into its third or dot-dashed line position of FIGURE 11, closes both the B and C relays together with all the B and C contacts. With both B and C closed, clutch 66 is actuated to operatively interconnect winches 58 and 60 together by means of

common shafts

134 and 136. At the same time, clutch 54 is energized to operatively interconnect the

dolly drive assemblies

36 and 38 together through

shafts

158 and 158a. In addition, closing upswitch 210 energizes both relays 58V and MN, closing down-switch 212 energizes

relays

58D and 60D, actuating left-switch 214 energizes relays 24L and 26L, and actuating right-switch 216 energizes

relays

24R and 26R. In other words, when the function selector switch is in its third position, the B and C relay circuits are both operative such that actuation of any of the control switches causes the like components of both of the driven assemblies controlled thereby to move in unison in the same direction. The

clutches

54 and 56 perform a most important function in this connection, however, as the motor components of the two assemblies are usually not equally loaded. For example, if hook 2% is connected to the heavy end of a load and hook 22 to the light end, winch motor 62 may be developing five horsepower while motor 62a is only developing three horsepower. With clutch 66 interconnecting these two Winch assemblies, the net efiect is to balance the load between the two which motors such that each supplies approximately four horsepower to raise the load. The same is, of course, true of clutch 54 that interconnects the

dolly drive assemblies

36 and 38 in a manner to balance the load on motors 48 and 48a. While it is obvious it should perhaps be mentioned that elements 213 and 220 of the control circuit are merely bridge-type full wave rectifiers connected to supply direct current to the

clutches

66 and 54, respectively, from the alternating current control voltage sup ply thereto.

Having thus described the several useful and novel features of the double-hook overhead traveling bridge crane of the present invention it will be seen that the many worthwhile objectives for which it was designed have been achieved. Although but a single specific embodiment of the invention has been shown and explained in connection with the accompanying drawings, I realize that certain changes and modifications therein may well occur to those skilled in the art within the broad teaching hereof; hence, it is my intention that the scope of protection afforded hereby shall be limited only insofar as said limitations are expressly set forth in the appended claims.

What is claimed is:

1. An overhead crane of the type supported for longitudinal travel between a pair of transversely spaced parallel rails which comprises: a pair of trolley-forming carriages mounted for movement along the rails in the direction of the length thereof, each carriage including at least one trolley having at least one roller journalled for rotation therein and in rolling contact with the rail; a bridge spanning the space between the rails is substantially normal relation thereto and supported by the carriages attached at opposite ends thereof for rolling movement therewith; a bridge drive mechanism carried by the bridge for movement therewith including a reversible motor, a power transfer assembly connected to form a driving connection between a roller of one trolley on both carriages and the motor, the power transfer assembly being adapted upon actuation of the motor to turn the rollers and move both carriages along the rails in the same direction at substantially the same speed, and bridge drive control means connected to the motor and selectively operable upon actuation to turn the latter in either direction; first and second dollies mounted on the bridge for independent rolling movement in the direction of the length thereof; first and second dolly drive mechanisms movable with the bridge and operatively connected to the first and second dollies, respectively, for effecting independent movement of the latter along the bridge, each of the first and second dolly drive mechanisms including a reversible electric motor, a haulage assembly connecting the motor to both ends of the dolly by way of opposite ends of the bridge, the haulage assembly being adapted upon actuation of the motor to pull the dolly along the bridge, and a dolly drive control means connected to the motor and selectively operable upon actuation to turn the latter in either direction; first electrically-operated clutch forming means interconnecting the first and'second dolly drive mechanisms, the first clutch-forming means being operative upon actuation to interlock the motors of the first and second dolly drive mechanisms together for conjoint rotation at the same speed and in a direction to move the dollies simultaneously along the bridge maintaining a fixed spaced relation therebetween; first and second hoist assemblies carried by the bridge for movement therewith along the rails, each of the first and second hoist assemblies including a drum-type Winch, a reversible electric motor operatively connected to the winch for rotating the drum thereof in either direction, a pair of fixed sheaves mounted for rotation at opposite ends of the bridge about axes substantially parallel to the rails, a fixed pulley block carried by the corresponding dolly of "the first and second dollies for movement therewith along the bridge, the fixed pulley block including at least two pulleys mounted for rotation about parallel axes substantially parallel to the rails, a length of cable reeved with an intermediate section drawn down between the pulleys of the fixed pulley block to form a reverse bend and the end sections extended along the bridge-in opposite directions around the fixed sheaves at the ends the bridge to the winch drumon which they are wound several turns in the same direction and dead-ended, a

movable pulley block suspended beneath the fixed pulley block within the reverse bend in the cable, means depending from the movable pulley block for attaching a load, and which control means connected to" the motor and selectively operable upon actuation to raise or lower the movable pulley block; second electrically-operated clutchforming means interconnecting the first and secondhoist assemblies, the second clutch-forming means being operative upon actuation to interlock the winch motors of the first and second hoist assemblies together for conjoint rotation at the same speed and in a direction to raise or lower the movable pulley blocks simultaneously; and a master control system'electrically connected to the control means of both the first and second doll-y drive mechanisms, the control means of both the first and second hoist assemblies, and both the first and second clutch-forming means, the master control system being operative upon actuation in a first position thereof to simultaneously energize the control means of the first dolly drive mechanism and the first hoist assembly, in a second position thereof to simultaneously energize the control means of the second dolly drive mechanism and the second hoist assembly, and in a third position thereof to simultaneously energize the control means of both the first'a'nd second dolly drive mechanisms, the control means of both the first and second hoist assemblies, and both the first and second clutch-forming means.

2. The overhead crane as set forth in claim 1 in which, each trolley includes at least two longitudinally spaced pairs of rollers, the rollers of each pair being journalled for rotation in opposed substantially coaxial relation, and at least one pair of rollers on one trolley of each carriage being operatively connected to the power transfer assembly of the bridge drive mechanism.

3. The overhead crane as set forth in claim 2 in which,

each trolley includes at least two longitudinally spaced 1.

pairs of rollers mounted for rotation about substantially vertical axes and in position to roll along the sides of the rails maintaining the trolleys centered thereon.

4. The overhead crane as setforth in claim 1 in which, the bridge comprises a pair of longitudinally spaced substantially parallel beams, dolly-supporting rails are at-- tached atop each beam, and the dollies include an openbottomed wheel-supported frame adapted to roll along the dolly rails spanning the space thercbet-ween.

5. The overhead crane as set forth in claim 4 in which,

thereof and back alongthe fixed pulley blocks are mounted within the, opena first operative. position to move the bridge along the;

rails in one direction and in a second operative position to move the bridge in the opposite direction. v

9. The overhead crane asset forth in claim 8 in which, thecontrol means of the first dolly drive mechanism is operative uponactuat ion in a first position to move the first dolly along the bridgein one direction and a secondoperative position to move the first dolly in the opposite direction, and the control means of the second dolly drive mechanism is operatlve upon actuation in a first position to move the second dolly along the bridge in the same direction as the first dolly, when the control means there-for is actuated in first position, and in a second operative position to move the second dolly in the opposite direction. i -10. The overhead crane as set forth inclaim 8 in which, the control means of the first hoist assembly is operative upon actuation in a first position to raise the movable pulley block thereof and in a second position to lower same, and the control meansof the second hoist assembly is operative upon actuation in a first operative position to raise the movable pulley block thereof and in a second operative position to lower same;

11. The overhead crane asset forth'in claim 1 in which,

the control means of the first dolly drive mechanism is operative upon actuation in a first position to move the first dolly along the bridge in one direction and in a second operative position to move the first dolly in the opposite direction, and the control means of the second dolly drive mechanism is operative upon actuation-in a first position to move the second dolly along the bridge in the same direction as the first dolly when the control means therefor is actuated in first position, and in a second operative position to move the second dolly in the opposition to raise the movablepulley'block thereof and in a second operative position .to lower same.

13. The overhead crane as set forth in claim 1 in which, each carriage includes apair of. trolleys attached at opposite ends thereof in longitudinallyspaced relation for limited relative tiltable movement to accommodate irregularities in the rails.

14. The overhead crane as set forth. in claim 1 in which, the reversible motor of the bridge drive mechanism is of the electrically-operated gear type having a double-ended relatively low speed output shaft, and the power transfer assembly of the bridge drive mechanism comprises a pair of elongated drive shafts having their adjacent end connected to the output shaft'of the motor and their remote ends journalled for rotation withinthe carriages at opposite ends of the bridge, and a chain and sprocket assembly operativelyinterconnecting the remote ends of each drive shaft with at least one roller of on of the trolleys associated with the carriage, 15. The overhead crane as set forth in claim 1 in which, the haulage assembly of each dolly drive mechanism includes a speed reducer, a pair of sprockets mounted for rotation at opposite ends of the bridge about axes second position I substantially parallel to the rails, one of the sprockets being operatively connected to the speed reducer, and a sprocket chain extending the length of the bridge, around the pair of sprockets and back along the bridge to points of attachment to the dolly.

16. The overhead crane as set forth in claim 1 in which, the winches of the first and second hoist assemblies are located intermediate the ends of the bridge in transversely spaced relation with the axes of rotation of their drums parallel to one another and to the rails and the winch motors are located at opposite ends of their respective winches; means comprising a differential located between the winches, the differential including a pair of coaxial stub shafts extending outwardly therefrom in opposite directions and in spaced substantially parallel relation to the axes of rotation of the winch drums, the differential being operative to reverse the direction of rotation of one of the stub shafts in relation to the other; means operatively interconnecting one of the stub shafts of the differential to the adjacent winch motor; a third shaft journalled for independent rotation in end-to-end coaxial rotation to the other stub shaft of the differential to which it is operatively connected by the second electrically-operated clutch-forming means; and means operatively interconnecting the free end of the third shaft to the other of the winch motors whereby onactuation of the master control system in third position both winch drums will turn in the same direction to either raise or lower the movable pulley blocks.

17. The overhead crane as set forth in claim 1 in which, the fixed pulley blocks of both the first and second hoist assemblies contain the same number and arrangement of pulleys, the movable pulley blocks of both the first and second hoist assemblies contain the same number and arrangement of the pulleys in the fixed and movable pulley blocks are adapted to cooperate with one another and produce a force-multiplying system.

18. The overhead crane as set forth in claim 1 in which, the second electrically-operated clutch-forming means comprises a magnetic clutch.

19. The overhead crane as set forth in claim 1 in which, the control means of the first hoist assembly is operative upon actuation in a first position to raise the movable pulley block thereof and in a second position to lower same, and the control means of the second hoist assembly is operative upon actuation in a first operative position to raise the movable pulley block thereof and in a second operative position to lower same.

20. An overhead crane of the double hook type mounted between a pair of transversely spaced supports which comprises: a bridge spanning the space between the supports; first and second dollies mounited on the bridge for independent rolling movement in the direction of the length thereof; first and second dolly drive mechanisms movable with the bridge and operatively connected to the first and second dollies, respectively, for effecting independent movement of the latter along the bridge, each of the first and second dolly drive mechanisms including a reversible motor, a haulage assembly connecting the motor to both ends of the dolly by way of opposite ends of the bridge, the haulage assembly being adapted upon actuation of the motor to pull the dolly along the bridge, and a dolly drive control means connected to the motor and selectively operable upon actuation to turn the latter in either direction; first clutch-forming means interconnecting the first and second dolly drive mechanisms, the first clutch-forming means being operative upon actuation to interlock the motors of the first and second dolly drive mechanisms together for conjoint rotation at the same speed and in a direction to move the dollies simultaneously along the bridge maintaining a fixed spaced relation therebetween; first and second hoist assemblies carried by the bridge for movement therewith along the rails, each of the first and second hoist assemblies including a drum-type winch, a reversible motor operatively connected to the winch for rotating the drum thereof in either direction, a pair of fixed sheaves mounted for rotation at opposite ends of the bridge about axes substantially normal thereto, a fixed pulley block carried by the corresponding dolly of the first and second dollies for movement therewith along the bridge, the fixed pulley block including at least two pulleys mounted for rotation about parallel axes substantially parallel to the fixed sheave axes, a length of cable reeved with an intermediate section drawn down between the pulleys of the fixed pulley block to form a reverse bend and the end sections extended along the bridge in opposite directions around the fixed sheaves at the ends thereof and back along the bridge to the winch drum on which they are wound several turns in the same direction and dcadended, a movable pulley block suspended beneath the fixed pulley block within the reverse bend in the cable, means depending from the movable pulley block for attaching a load, and winch control means connected to the motor and selectively operable upon actuation to raise or lower the movable pulley block; second clutch-forming means interconnecting the first and second hoist assemblies, the second clutch-forming means being operative upon actuaation to interlock the winch motors of the first and second hoist assemblies together for conjoint rotation at the same speed and in a direction to raise or lower the movable pulley blocks simultaneously; and a master control system connectedvto the control means of both the first and second dolly drive mechanisms, the control means of both the first and second hoist assemblies, and both the first and second clutch-forming means, the master control system being operative upon actuation in a first position thereof to simultaneously energize the control means of the first dolly drive mechanism and the first hoist assembly, in a second position thereof to simultaneously energize the control means of the second dolly drive mechanism and the second hoist assembly, and in a third position thereof to simultaneously energize the control means of both the first and second dolly drive mechanisms, the control means of both the first and second hoist assemblies, and both the first and second clutch-forming means.

21. The overhead crane as set forth in claim 20 in which, the bridge supports comprise a pair of spaced substantially parallel rails, a pair of trolley-forming carriages are attached at opposite ends of the bridge for movement long the rails in the direction of the length thereof, each carriage including at least one trolley having at least one roller journalled for rotation therein and in rolling contact with the rail, and bridge drive means operatively connected on a roller of each trolley and adapted upon actuation to rotate same in either direction for purposes of moving the bridge along the rails.

22. The overhead crane as set forth in claim 21 in which the bridge drive means comprises a source of power, and a power transfer assembly connected to form a driving connection between one roller of a trolley on each carriage and the source of power, said power transfer assembly being adapted upon actuation of the source of power to turn the rollers and move both carriages along the rails in the same direction at substantially the same speed.

No references cited,