Crane incorporating vertical motion apparatus

Abstract

A crane incorporating vertical movement compensation apparatus. A crane having a boom with suspended hoisting cable is adapted to support a load substantially independent of the vertical movement of the crane and associated apparatus. The hoisting cable is supported by a winch incorporating a continuously slipping clutch which maintains the load in a controlled tension mode. The winch shaft about which is secured the crane drum drives through an overrunning clutch to a braking device to permit the load to be moved in the in-haul direction without interference of the brake while precluding inadvertent downward movement of the load as a result of vertical displacement of the crane.

Parent Case Text

This application is a continuation-in-part of my application Ser. No. 823,894 filed May 12, 1969.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention crane apparatus is generally related to the field of hoisting devices and, in particular, to those devices incorporating apparatus for vertical movement compensation.

2. Prior Art

The need to equip marine vessels and other like structures with winches or cranes which are capable of compensating for the vertical motion of the vessel or supporting structure has long been recognized. The ability to vertically lift a load independent of the vertical movement of the crane or winch structure has been a problem which has heretofore not been totally resolved by the devices disclosed in the prior art. The requirements for a crane or winch intended for vertically lifting loads are considerably more complicated than systems designed for the horizontal movement of loads. These complications arise out of the need to institute safeguards to prevent inadvertent release of the loads in the event of power failure, vertical movement of the lifting mechanism or other similar occurrances.

One of the devices disclosed by the prior art is set forth in Applicant's U.S. Pat. No. 3,373,972. The device disclosed is a winch incorporating a continuously slipping clutch to permit movement of loads utilizing the controlled tension in the hoisting line of the winch. One of the problems left unresolved by this device concerns the inability to compensate for failures in the energy source for the winch or to provide improved methods for initiating movement of loads without encountering the complications inherent in the transition from a static to a dynamic condition.

Another device disclosed by the prior art constitutes an apparatus for horizontally transferring loads between displaced stations. This mechanism in no way encounters the problems of vertically displaced loads since the supporting stations fully provide stability for the hoisting line and the attached loads. The problems sought to be solved by the present invention are created where loads must be vertically lifted in a manner which will minimize disturbances of the load while concurrently eliminating the possibility of dropping the load as a result of power failures or other adverse conditions.

Another device disclosed by the prior art is used for the drilling of well bores, typically in an off-shore environment. The device utilizes a fluid coupling in the attempt to compensate for vertical motion of the floating support structure. A fluid coupling presents inherent problems with respect to response time, load capacity and control over a supporting load. In addition, the device disclosed by the prior are includes no means for insuring that the load will not be inadvertently dropped. In the particular application, a drill string is supported by a winch powered through the fluid coupling. A flaw in this system could easily result in damage to the drill string and attached drill bit, problems which are substantially resolved by the present invention.

The present invention crane substantially resolves the problems left unsolved by the devices disclosed in the prior art. The power source for the present invention crane is supplied through a continuously slipping clutch coupled to the drum shaft. In order to prevent unintended damage to the load as a result of inadvertent vertical displacement thereof, the drum shaft is coupled to a supplemental braking system through an overrunning or one-way clutch. In this manner, the load will be supported in an in-haul direction by free-wheeling against the brake, the out-haul movement of the hoisting line being subject to a supplemental braking system.

SUMMARY OF THE INVENTION

The present invention comprises a crane having means for compensating for vertical displacement of the crane supporting structure as well as incorporated apparatus for preventing inadvertent out-haul movement of the hoisting line. The present invention crane incorporates a boom supported by an adjustable block and tackle assembly or other like structure. The hoisting line is supported by a sheave at the top of the boom, the hoisting line being wound about and secured to the hoisting drum. The drum is securely mounted upon the drum shaft, the shaft being powered through a continuously slipping clutch. The housing of the clutch is driven in an over-speeded condition to insure that there is a predetermined speed differential between the driving and driven elements of the clutch. A tension measuring device is responsive to the tension in the hoisting line, the tension measuring device providing an output indicative of any adjustment to be made to the respect to the output torque of the continuously slipping clutch. The tension measuring device is coupled to the continuously slipping clutch to enable incremental changes in the output torque of the continuously slipping clutch to maintain a controlled tension in the hoisting line.

The driving element of the continuously slipping clutch rotates in the in-haul direction, the speed differential between the driving and driven elements of the clutch insuring adequate recovery rates for vertical displacement of the crane assembly. To prevent inadvertent vertical displacement of the load supported on the hoisting line, the drum shaft is run through a one-way clutch to a supplemental braking system. When the braking system is actuated, the drum clutch will rotate in the in-haul direction in a free-wheeling mode independent of the braking system, any out-haul movement of the clutch being subject to the action of the braking system. The present invention crane permits upward or downward movement of the load by the operation of the clutch in a continuously slipping mode, the movement being controlled by control over the output torque of the clutch. By driving the drum shaft through a one-way or overrunning clutch and allowing same to rotate in the in-haul direction in a free-wheeling manner, a load can be supported by the braking system yet in-haul movement initiated totally free of any inadvertent and adverse vertical displacement of the load.

It is therefore an object of the present invnetion to provide a crane incorporating vertical movement compensating apparatus.

It is another object of the present invention to provide an improved crane apparatus to prevent inadvertent vertical displacement of a supported load.

It is still another object of the present invention to provide a crane capable of compensating for vertical displacement of the crane as well as apparatus for eliminating the adverse affect resulting from the transition from static to dynamic movement of the load.

It is still yet another object of the present invention to provide a crane for initiating upward vertical displacement of a load from a static condition substantially eliminating perturbations of the load.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objectives and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only and is not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective view of a crane fabricated in accordance with the present invention.

FIG. 2 is a side, elevation, cross-sectional view of the continuously slipping clutch of FIG. 1 adapted to operate in accordance with the present invention.

FIG. 3 is a schematic view of the control system for the continuously slipping clutch of FIG. 1.

FIG. 4 is a schematic view of the drum, drum shaft, one-way clutch and braking system of the crane of FIG. 1 in accordance with the present invention.

FIG. 5 is a side elevation, partial cross-sectional view of the one-way clutch of FIG. 4 taken through line 5--5 of FIG. 4.

FIGS. 6a, 6b and 6c are schematic, partial cross-sectional views of a one-way clutch illustrating the mode of operation thereof.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT

An understanding of the structure of the present invention apparatus can be best gained by reference to FIG. 1 wherein a perspective view of a crane incorporating the elements of the invention is shown therein, the crane being generally designated by the reference numeral 1. Crane 1 is constructed upon platform 2, platform 2 being a portion of a floating or fixed structure. As stated, an object of the present invention is to provide a crane capable of vertical motion compensation as is typically encountered in off-shore applications. Although a preferred embodiment of the present invention is utilized upon a marine vessel or other floating support structure, the scope of the present invention encompasses the same with fixed structures. A hoisting assembly 3 is coupled to boom 4 for the purpose of orienting boom 4 in any desired position. Load 5 is supported by hoisting cable 6. To raise and lower boom 4, cable 7 is secured to the upper portion thereof, cable 7 being coupled to hoisting assembly 3 by block and tackle assembly 8. Although the scope of the present invention embodies the use of same with a gantry, A-frame derrick or similar structure, the preferred embodiment of the present invention utilizes the boom assembly as shown in FIG. 1.

Hoisting cable 6 is disposed over sheave 10, portion 9 of hoisting cable 6 being disposed for measurement of the tension therein as will be explained in detail below. Hoisting cable 6 is supported and disposed around drum 11, the winch assembly coupled thereto being powered by motor 12. Motor 12 is coupled to clutch 14, clutch 14 being coupled to shaft 15 which supports drum 11 and is coupled to brake assembly 13 as will be explained in detail below. The operation of motor 12, clutch 14, drum 11 and associated hoisting cable 6 are similar to that described in Applicant's U.S. Pat. No. 3,373,972.

The ability of the present invention to maintain constant tension in hoisting cable 6 irrespective of vertical displacement of platform 2 can be best understood by reference to FIG. 2 wherein a side elevation, cross-sectional view of clutch 14 is shown. Clutch 14 is one capable of one operating in a continuously slipping mode whereby a predetermined speed differential can be maintained between the driving and driven elements of clutch 14. Motor 12 is coupled to drive ring 16 which is concentrically disposed about and journeled upon shaft 15 by suitable bearings 17. Drive ring 16 is securely coupled to clutch housing 18. The preferred embodiment of the present invention utilizes a motor 12 having a substantially constant output torque which is imposed upon clutch housing 18 through drive ring 16. The driving elements of clutch 14 which are concentrically disposed within and adapted to rotate with housing 18 are friction elements 19 and 20. Friction elements 19 and 20 are disposed at axially opposed interior surfaces of housing 18, friction element 20 being axially moveable upon the introduction of actuating energy at expandable element 21. Driven friction disc 22 is concentrically disposed about and secured to clutch hub 23 by spline teeth or other suitable coupling means. Clutch 14 is suitable to allow a predetermined differential speed to be maintained between driving friction elements 19 and 20 and driven friction disc 22. In order to dissipate the heat horsepower generated at friction discs 19 and 20, annular channels 24 are disposed in clutch housing 18 adjacent friction elements 19 and 20 to appropriately dissipate the generated heat. Annular channels 24 and 25 are adapted to receive appropriate cooling liquid such as water. In order to provide for cooling of clutch 14 through the use of liquid coolant, roto-coupling 26 provides for coolant input and output lines 27 and 28, the connections between the coolant lines and annular channels 24 and 25 not shown.

As stated, friction elements 19 and 20 will frictionally engage friction disc 22 upon actuation of expandable element 21. Expandable element 21 is typically an air actuated element. Air is introduced at roto-coupling 29, the air line being designated by the reference numeral 30. Air is distributed at ring 31, the output line 32 being coupled to input line 33 of expandable elements 21. The coupling between output line 32 and input coupling 33 not being shown.

As stated, the output of motor 12 provides the driving torque on clutch housing 18 which is transmitted to friction disc 22 through friction elements 19 and 20. The output torque of clutch 14 appears at shaft 15 and is determined by the level of actuation at expandable element 21. Drive ring 16 and therefore clutch housing 18 constantly rotates in the in-haul direction, the output torque on shaft 15 being controlled to maintain a predetermined tension in hoisting cable 6 (FIG. 1). By maintaining a speed differential between clutch housing 18 and shaft 15, the tension in hoisting cable 6 will maintain load 5 in a dynamic condition whereby load 5 can be raised or lowered by adjusting the air pressure at expandable element 21. In addition, maintaining cable 6 in a controlled tension mode will permit accurate control over the in-haul/out-haul or stationary mode of hoisting cable 6 and load 5. Although it is within the scope of the present invention to implement clutch 14 by a number of conventional clutches, clutch 14 is preferably an air actuated, water cooled disc clutch capable of operating in a continuously slipping mode wherein there is a controlled differential speed between clutch hub 23 and housing 18 and therefore between friction disc 22 and friction elements 19 and 20.

An understanding of the apparatus used to control the tension in hoisting cable 6 can be best seen by reference to FIG. 3 wherein a schematic diagram of the regulating system, clutch 14, braking system 13 and a tension measuring device can be best seen, the regulating system being generally designated by the reference numeral 60. Load cell or tensiometer 61 is coupled to portion 9 of hoisting cable 6, load cell 61 being a conventional device adapted for sensing and measuring the tension line. Load cell 61 is responsive to the tension in hoisting cable 6, changing the hydraulic pressure in pressure line 34 in proportion to the tension in hoisting cable 6. Gauge 35 is coupled to pressure line 34 to visually illustrate the tension in hoisting cable 6.

As stated, the output of load cell 61 is coupled to regulator 60 by pressure line 34. One of the advantages of the present invention is to provide simplified control over operation of the present invention crane structure. As shown in FIG. 3, a single manual control 62 will permit full control over the operation of the tension regulating system as well as braking assembly 13. Air under pressure is input at pressure line 36 from a conventional pressure source not shown. Pressure line 36 conducts the pressurized air to the variable air pressure load control valve 37 and variable brake release valve 38. The variable air pressure valve 37 is actuated by manual control 62 as shown, the output of valve 37 being connected to the conventional selector valve 39. Pressure line 40 couples the output of variable brake release valve 38 to the spring set air release of braking assembly 13.

Regulator 60 includes bellows chamber 41 which is coupled to hydraulic pneumatic transducer 42 by pressure line 43. Although it was stated that load cell 61 produces a hydraulic or pneumatic pressure output, it is obvious that load cell 61 could be fabricated from any sensing device which is compatible with the selected transducer 42. The output of transducer 42 is coupled to regulator valve 44 through pressure line 45. Air is introduced to regulator valve 44 from pressure line 36 via pressure line 46. A conventional booster relay 47 is serially coupled in pressure line 36 and therefore to air line 30 of roto-coupling 29 via pressure line 48. Bellows chamber 49 receives pressurized air from reset rate adjustment valve 50, valve 50 receiving pressurized air from proportional valve 51 via pressure line 52. Proportional valve 51 is coupled to relay valve 53 by pressure line 54. Pressurized air is supplied to relay valve 53 and proportional valve 51 through pressure line 55 which extends from selector valve 39. As a result of the above-defined coupling, the elements of regulator 60 are pressurized and controllable from manual control 62.

In operation, when the output of load cell 61 increases the pressure in pressure line 34, this in turn will increase the pressure in bellows chamber 41 via the output transducer 42 and coupling pressure line 43. The increase in pressure in bellows chamber 41 will move plate 56 upwardly toward nozzle 57 to simultaneously increase the pressure at booster relay 47 and proportional valve 51 and therefore at the input to bellows chamber 49. The increase in pressure at bellows chamber 49 will halt the increase in pressure to booster relay 47. The pressure in the pressure line leading to bellows chamber 49 will slowly pass through reset rate adjustment valve 50 and will increase the pressure in the lower part of bellows chamber 49. This will cause plate 56 to move towards nozzle 57, again increasing the pressure throughout the system to booster relay 47 and the upper part of bellows 49. This build up in pressure will increase pressure through the reset rate adjustment valve 50 to the lower part of bellows chamber 49 and start another increase throughout the system and to booster relay 47. The increase in pressure in the system will continue until the pressure from load cell 61 and transducer 42 is decreased and the system is brought back to its predetermined set point as established at control valve 63.

The adjustment of the output torque of clutch 14 via regulator 60 will increase or decrease the output torque based upon the tension in hoisting cable 6. Where it is desired to maintain the stability of load 5 irrespective of the vertical displacement of platform 2, drum 11 and the coupled hoisting cable 6 will adapt to the changing vertical displacement of platform 2. As discussed, a predetermined differential speed is maintained between clutch housing 18 and coupled friction elements 19 and 20, and the driven friction disc 22 and coupled shaft 15. The differential speed between the pair of members will change to maintain controlled tension in hoisting cable 6. Where platform 2 is moving vertically downward, the tension in hoisting cable 6 will tend to increase and therefore drum 11 and hoisting cable 6 will move in the out-haul direction to compensate for the vertical displacement. When platform 2 is moving vertically upward, the tension in cable 6 would tend to decrease, drum 11 and hoising cable 6 being moved in the in-haul direction to compensate for this vertical displacement. The combination of load cell 61 and coupled regulator 60 maintains the tension in hoisting cable 6 at the preset level established at valve 63. When hoisting cable 6 and attached load 5 are to be vertically moved, operation of manual control 62 enables movement of hoisting cable 6 in the desired direction while maintaining proper compensation for vertical displacement of platform 2 and the crane elements.

As stated, an object of the present invention was to provide means for initiating the movement of load 5 when same was being held by braking assembly 13. In order to accomplish this, the present invention crane 6 provides the ability to initiate upward vertical displacement of load 5 negating the effect of braking assembly 13 while imposing the effects of braking assembly 13 to prevent inadvertent downward displacement of load 5. Referring now to FIG. 4, an understanding of the structure used to implement the safeguard apparatus can be best seen. Drum 11 is keyed to shaft 15, hoisting cable 6 being disposed thereon. Shaft 15 is extended to and coupled within overrunning or one-Way clutch 70. The outer race of overrunning clutch 70 is coupled to shaft 71 which is in axial alignment with shaft 15. Shaft 71 is coupled to and secured within hub 72 of brake assembly 13. Overrunning clutch 70 will be explained in detail below. Although the scope of the present invention is broad enough to permit brake assembly 13 to be fabricated by any number of conventional braking systems such as air actuated band brakes, brake assembly 13 is preferably an air actuated disc brake. Brake assembly 13 comprises outer housing 73 which is rotatably mounted about shaft 71 on suitable bearings 74. Friction elements 75 and 78 are concentrically disposed within brake housing 73 and can be caused to frictionally engage friction disc 76 upon the actuation of expandable elements 77 through roto-coupling 79. The coupling, roto-coupling 79 and expandable elements are not shown. Brake housing 73 is referenced to a fixed frame of reference such as platform 2. Friction disc 76 is concentrically disposed upon and secured to clutch hub 72 which in turn is keyed to shaft 71. The actuation of brake assembly 13 will cause the relative motion between shaft 71 and brake housing 73 to cease.

An understanding of overrunning clutch 70 can be best gained by reference to FIG. 5. FIG. 5 is a schematic, partial cross-sectional view of a cam-clutch utilized to implement overrunning clutch 70. It shall be understood that the terms cam-clutch, overrunning clutch or one-way clutch are synonomous with respect to the use within the present invention. Axially disposed on opposite ends of overrunning clutch 70 are cylindrical bores 80 and 81 for receiving shafts 71 and 15 respectively. Keys 82 and 83 are axially aligned with cylindrical bores 80 and 81 respectively and will prevent inadvertent rotation of shaft 71 or 15 with respect to overrunning clutch 70. Shaft 71 is secured to outer race 84 and drum shaft 15 is secured to inner race 85. Inner race 85 is rotatably disposed within outer race 84, inner race 85 being suitably journeled within outer race 84 by bearings 86. Cams 87 frictionally engage the inner cylindrical surface of outer race 84 and the outer cylindrical surface of inner race 85. The orientation of cams 87 is controlled by outer cage 88 and inner cage 89.

The operation of overrunning clutch 70 can be best seen by reference to FIG. 6a, FIG. 6b and FIG. 6c wherein schematic views of the operation of overrunning clutch 70 are shown. As stated, overrunning clutch 70 is used to allow drum shaft 15 to free-wheel with respect to shaft 71 when braking assembly 13 is engaged and it is desired to initiate movement of load 5 and hoisting cable 6 in the in-haul direction. Overrunning clutch 70 will effectively lock drum shaft 15 and shaft 71 when drum 11 is paying out hoisting cable 6 in the out-haul direction. When braking assembly 13 is engaged, hoisting cable 6 can be payed out only against the force of brake assembly 13.

Referring now to FIG. 6a, the free-wheeling mode of overrunning clutch 70 is illustrated therein. Inner race 85 and outer race 84 will be free-wheeling with respect to each other when the respective angular rotation is as shown. Inner race 85 is being rotated in a counterclockwise manner whereby hoisting cable 6 is being reeled in upon drum 11 through the action of clutch 14. Inner cage 89 and outer cage 88 are concentric with respect to each other, each transverse edge of each section of inner cage 89 and outer cage 88 contacting a point on cam 87. In this mode, inner cage 89 rotates counterclockwise with respect to outer cage 88 orienting cams 87 to allow inner race 85 to be in an overrunning condition with respect to outer race 84. Since the top and bottom surfaces of cams 87 are not forced against the respective radial surfaces of inner and outer races 85 and 84, the shafts coupled to inner and outer races 85 and 84 will be effectively disengaged from each other thereby precluding the transmission of torque from one shaft to the other. Springs 90 insure that cams 87 maintain contact with races 84 and 85.

Referring now to FIG. 6b, a mode of operation is illustrated whereby outer race 84 is rotated counterclockwise with respect to inner race 85 thereby effectively engaging overrunning clutch 70 and providing for the transmission of torque from shaft 71 to shaft 15. It will be recognized that this mode of operation is not encountered since brake assembly 13 does not initiate any rotational force. This mode would be utilized where brake assembly 13 was replaced by a clutch and power source used to counter the over-haul movement of drum 11 and attached hoisting cable 6. As can be seen by comparing FIG. 6b with FIG. 6a, outer cage 88 and inner cage 89 have rotated counterclockwise with respect to each other forcing cams 87 to rotate counterclockwise thereby loading overrunning clutch 70 and effectively locking shaft 71 and drum shaft 15. The loading of overrunning clutch 70 will provide for the transmission of torque from shaft 71 to drum shaft 15.

Referring now to FIG. 6c, overrunning clutch 70 is illustrated under the mode whereby inner race 85 is rotated clockwise with respect to outer race 84, this mode arising where hoisting cable 6 is being payed out and brake assembly 13 engaged. In this configuration, inner cage 89 will be rotated clockwise with respect to outer cage 84 thereby fully loading cams 87 and imposing the force of brake assembly 13 on the outhaul movement of drum 11. Where there is effective engagement between drum shaft 15 and shaft 71, brake assembly 13 will act as a braking system thereby providing for the safeguard needed to initiate upward vertical displacement of load 5 while load 5 is being held by braking assembly 13 as well as preventing inadvertent downward vertical displacement of load 5.

The present invention crane provides means for compensating for vertical displacement of the supporting platform as well as providing means for dynamically initiating the vertical movement of a load without the severe problems inherent in systems disclosed by the prior art. The ability to initiate the upward vertical movement of a suspended load without encountering deleterious perturbations yields a system which provides substantial advantages regarding economy, safety and ease of operation.

Claims

I claim:

1. A crane apparatus for use with a supported platform comprising:

a. a boom pivotally secured to the platform;

b. a first shaft;

c. a drum concentrically disposed about and secured to said first shaft;

d. a hoisting cable secured to said drum and moveably disposed over said boom;

e. a continuously slipping clutch having an outer housing and inner hub coupled to frictionally rotate with respect to each other and fluid means for dissipating the frictionally generated heat therein, said inner hub being securely coupled to said first shaft whereby said hoisting cable is maintained in a controlled tension mode;

f. a second shaft;

g. an overrunning clutch interposed between said first and second shafts having means for engaging said first and second shafts when said drum is paying out hoisting cable whereby said overrunning clutch is in a free-wheeling mode when said drum is rotating to reel in hoisting cable; and

h. a brake interposed between said second shaft and the platform whereby braking force is imposed on the hoisting cable when said drum is rotating to pay out hoisting cable.

2. A crane apparatus as defined in claim 1 wherein said continuously slipping clutch includes a friction disc secured to said inner hub, friction elements adapted to slidably engage and rotate with said outer housing, said fluid means for dissipating heat adjacent said friction elements, and air actuated expandable elements secured to said housing and adjacent said friction elements, whereby said friction elements frictionally engage said friction disc upon actuating said expandable elements.

3. A crane apparatus as defined in claim 2 including tension measuring means for measuring the tension in said hoisting cable and outputting indicia of same, said tension measuring means including tension transducing means for detecting the tension in said hoisting cable and outputting indicia of same, and pressure means for outputting a pressurized source responsive to the output of said tension transducing means, said tension transducing means being coupled to said hoisting cable, said pressure means being coupled intermediate said tension transudcing means and said expandable elements.

4. A crane apparatus as defined in claim 1 including a constant speed power source coupled to the housing of said continuously slipping clutch whereby said housing is rotated at a constant speed.

5. A crane apparatus for use with a supported platform comprising:

a. a boom pivotally secured to the platform;

b. a drum shaft;

c. a drum concentrically disposed upon and secured to drum shaft;

d. a hoisting cable disposed about said drum, a portion thereof suspended over said boom whereby a load is supported;

e. a constant speed power source;

f. a continuously slipping clutch having an inner hub and outer housing, a friction disc secured to said inner hub, friction elements adapted to slidably engage and rotate with said outer housing, fluid means for dissipating heat adjacent said friction elements, and air actuating, expandable elements secured to said housing and adjacent said friction elements whereby said friction elements frictionally engage said friction disc upon actuating said expandable elements maintaining a speed differential therebetween, said inner hub being concentrically disposed upon and secured to said drum shaft, said continuously slipping clutch keeping said hoisting cable in a controlled tension mode;

g. a brake shaft spaced from and in axial alignment with said drum shaft;

h. an overrunning clutch interposed between and secured to said drum shaft and said brake shaft, said overrunning clutch adapted to free-wheel said drum shaft with respect to said brake shaft and couple said shafts upon alternate rotational movement of said drum shaft whereby said shafts rotate together when said drum is rotating to pay out said hoisting cable;

i. tension measuring means for measuring the tension in said hoisting cable and producing a hydraulic pressure signal porportional to the tension in said hoisting cable, said tension means including a tension transducer and pressure output means for producing said hydraulic pressure signal, said tension transducer being in cooperative relationship with said hoisting cable and producing an output signal responsive to the tension in said hoisting cable, said pressure output means being coupled intermediate to said tension transducer and said expandable elements; and

j. a brake interposed between said brake shaft and the platform whereby braking force is imposed on said hoisting cable when said drum is rotating to pay out the hoisting cable.

6. In combination with a platform mounted crane including a pivotal boom and a power source for the poistioning of the boom, a vertical motion compensating apparatus comprising:

a. a drum shaft;

b. a drum concentrically disposed about and secured to said drum shaft;

c. a hoisting cable disposed about said drum, a portion thereof suspended over the boom whereby a load is supported;

d. a continuously slipping clutch having an inner hub and outer housing, and having a friction disc secured to said inner hub, friction elements adapted to slidably engage and rotate with said outer housing, fluid means for dissipating heat adjacent said friction elements, and air actuated, expandable elements secured to said housing and adjacent said friction elements, said inner hub being disposed about and secured to said drum shaft whereby a speed differential is maintained between said friction elements and said friction disc keeping said hoisting cable in a controlled tension mode;

e. a brake shaft, in spaced relation with and in axially alignment with said drum shaft;

f. an overrunning clutch interposed between and coupled to said drum shaft and said brake shaft, said overrunning clutch adapted to free-wheel said drum shaft with respect to said brake shaft and couple said shafts upon alternate rotational movement of said drum shaft whereby said shafts rotate together when said drum is rotating to pay out the hoisting cable; and

g. a brake interposed between said brake shaft and the platform whereby braking force is imposed on said hoisting cable when said drum is rotating to pay out the hoisting cable.

7. A vertical motion compensating apparatus as defined in claim 6 including tension measuring means for measuring the tension in said hoisting cable and outputting indicia of same, said tension measuring means including tension transducing means for detecting the tension in said hoisting cable and outputting indicia of same, and pressure means for outputting a pressurized source responsive to the output of said tension transducing means, said tension transducing means being coupled to said hoisting cable, said pressure means being coupled intermediate said tension transducing means and the expandable elements of said continuously slippint clutch.

8. A vertical motion compensating apparatus as defined in claim 7 wherein said pressurized source is hydraulic pressure proportional to the tension in said hoisting cable.

9. A vertical motion compensating apparatus as defined in claim 6 including a constant speed power source coupled to the housing of said continuously slipping clutch whereby said housing rotates at a constant speed.