CA1094023A - Vertical motion compensated crane apparatus - Google Patents
Vertical motion compensated crane apparatusInfo
- Publication number
- CA1094023A CA1094023A CA352,656A CA352656A CA1094023A CA 1094023 A CA1094023 A CA 1094023A CA 352656 A CA352656 A CA 352656A CA 1094023 A CA1094023 A CA 1094023A
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- boom
- platform
- crane
- sheave
- hook
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Abstract
"VERTICAL MOTION COMPENSATED CRANE APPARATUS"
ABSTRACT OF THE DISCLOSURE
A relative motion compensation apparatus is provided in a crane having two platforms vertically movable with respect to each other and employing a boom supported on the first platform, a cable depending from the boom and supporting a hook and a winch to move the cable. The relative motion apparatus uses a fluid cylinder and piston assembly secured to the crane boom. Sensing means generate a signal responsive to the relative vertical movement of the two platforms. The signal is used to control the position of the piston in the cylinder to thereby vary the vertical separation between the hook and the boom.
ABSTRACT OF THE DISCLOSURE
A relative motion compensation apparatus is provided in a crane having two platforms vertically movable with respect to each other and employing a boom supported on the first platform, a cable depending from the boom and supporting a hook and a winch to move the cable. The relative motion apparatus uses a fluid cylinder and piston assembly secured to the crane boom. Sensing means generate a signal responsive to the relative vertical movement of the two platforms. The signal is used to control the position of the piston in the cylinder to thereby vary the vertical separation between the hook and the boom.
Description
~)94023 This invention relates to apparatus and methods for transferring loads between two platforms which are vertically movable relative to each other. More particularly, it relates to load transfer apparatus mounted on one platform and adapted to land a load on or remove a load from another platform, which apparatus includes relative vertical motion compensation apparatus to substantially reduce or cancel the effect of relative vertical movement of the two platforms.
Many operations involve the transfer of a load suspended on a tensioned cable from a first platform to a second platform. Typically, the first and second platforms are fixed relative to each other and s-uch transfers may be accomplished with relative ease. However, i'n many situations such as marine operations or the li'ke, the first and second platforms may be vertically movable relative to each other and the relative verti-cal movement may not be predictable with exact certainty or uni-formity. For example, in transferring a load from a pier to a floating vessel or vice versa, the floating vessel may move vertically in response to waves, tides~ etc. while the pier remains fixed. Accordingly, relative vertical movement between the ship deck and a crane mounted on the pier may cause difficul-ty in gently landing a load on the deck. The problem becomes even more acute in offshore operations where loads may be trans-ferred between a floating barge and an offshore platform which is secured to the ocean floor. In such offshore operations, the wave action may be more severe and less predictable. Further-more, offshore operations must often be carried out in rough 1~94023 weather wherein the heavy sea action makes such transfers extremely difficult. To further complicate the problem, many such load transfer operations involve the transfer of extremely heavy equipment, on the order of 1,000 tons, which equipment is very expensive and shock sensitive and may be seriously damaged unless landed on the receiving platform very carefully. Off-loading from a ship or barge subject to vertical movement onto a fixed or floating platform on which the crane is mounted can also he extremely dangerous. If the hook i`s lowered to the deck of the barge for attaching to the load while the barge is at the bottom of a swell, the harge deck will rise as the swell rises and thus contact and raise the hook. The cable suspended from the crane then becomes slack and may loop or become entangled with other cargo, personnel, or structure of the barge. When the barge sinks into the next valley between the swells, the hook is lowered with the barge deck and the cable again drawn taut~ thus endangering other cargo1 personnel and the like with which the slack cable may have become entangled. To avoid this problem crane operators usually attempt to raise and lower the hook in synchronization with the pitching deck. However, attempts at manually coordinating hook movement with a pitching deck are notoriously ineffectiYe.
Similar problems exist in attempting to transfer loads between two floating platforms such as the decks of two floating ships, one of which carries the crane~ In this case both plat-forms mav move vertically with respect to each other and with respect to a fixed hori~ontal position~ thus rendering the transfer between such independently moving platforms extremely difficult. Various other marine operations~ such as laying pipe on the ocean floor from a floating barge or landing submerged equ;pment on the ocean floor or s.ubmerged platforms from a floating vess.el involve si.milar difficulties.
Prior attempts to overcome the di`fficulti`es involved rely mainly on means for maintaining a constant tension on the hoist load line. Such systems, however, suffer from ;nherent limitations. Conventi:onal line tensioning apparatus operates on the line between the winch and the crane boom. Therefore, when multi:ple-reeved tackle i:s employed between the load hook and the crane boom the length of li:ne between the crane boom sheave and the wi:nch (known as the 'fast line') whi:ch must be adjusted to maintain a cons.tant tension on the li'ne at the load is a multiple of the verti`cal distance which must 6e compensated. Furthermore, while such li:ne tensioning apparatus may aid i'n li:fting a load from a movi:ng platform with a crane positioned on a fi`xed platform, s.uch li:ne tensi:oning offers- no way to synchronize vertical movement of a load suspended from a crane on a fixed platform with vertical movement of a moving platform so that the load may b.e gently landed on the movi:ng platform. Accordingly, maintaining constant tens~ion on a load li.ne wi'll not prevent the load from hei.ng s.mashed i:nto a rapi:dly vertically rising deck.
Hook-mounted relative motion compensation apparatus whi.ch. adjusts the distance between the end of the crane boom and the load hook in response t~ vertical movement of the landin3 platform may be devised which overcome some of the difficulties involved. However, such motion compensation apparatus, in order to be sturdy enough to supp~rt the wei~ht of heavy loads~ must i.tself be quite heavy. Furthermore, where such hook-mounted motion compensation apparatus is employed, the hydraulic cylinder as.semblies as well as the motors and pumps necessary to drive the 3Q apparatus must also be carried in the motion compensation ~ ~94023 apparatus itself, thus further increasing the ~eight of the motion compensation apparatus-. Since such motion compensation apparatus must be supported by the load line, the lifting capacity of the crane is reduced. Furthermore, such motion compensation apparatus must be suspended at the end of the load li`ne near the hook so that the motion compensation apparatus wi`ll not substantially interfere with the he;ght capacity of the crane~ Large, bulky and heavy motion compensation apparatus suspended from the end of a load line may become d;ffi`cult to maneuver in rough seas because of the action of the wind thereon. Furthermore, in si`tuations where the crane is supported on a floating platform, oscillatory movement of the floating platform may be transferred to the suspended motion compensation apparatus and amplified~
thus causing the motion compensation apparatus to sway and oscillate horizontally. Because of the mass of the motion compensation apparatus suspended on the end of the cable, such oscillatory motion can be dangerous and difficult to control in certain situations.
While a hook-mounted motion compensation system offers
Many operations involve the transfer of a load suspended on a tensioned cable from a first platform to a second platform. Typically, the first and second platforms are fixed relative to each other and s-uch transfers may be accomplished with relative ease. However, i'n many situations such as marine operations or the li'ke, the first and second platforms may be vertically movable relative to each other and the relative verti-cal movement may not be predictable with exact certainty or uni-formity. For example, in transferring a load from a pier to a floating vessel or vice versa, the floating vessel may move vertically in response to waves, tides~ etc. while the pier remains fixed. Accordingly, relative vertical movement between the ship deck and a crane mounted on the pier may cause difficul-ty in gently landing a load on the deck. The problem becomes even more acute in offshore operations where loads may be trans-ferred between a floating barge and an offshore platform which is secured to the ocean floor. In such offshore operations, the wave action may be more severe and less predictable. Further-more, offshore operations must often be carried out in rough 1~94023 weather wherein the heavy sea action makes such transfers extremely difficult. To further complicate the problem, many such load transfer operations involve the transfer of extremely heavy equipment, on the order of 1,000 tons, which equipment is very expensive and shock sensitive and may be seriously damaged unless landed on the receiving platform very carefully. Off-loading from a ship or barge subject to vertical movement onto a fixed or floating platform on which the crane is mounted can also he extremely dangerous. If the hook i`s lowered to the deck of the barge for attaching to the load while the barge is at the bottom of a swell, the harge deck will rise as the swell rises and thus contact and raise the hook. The cable suspended from the crane then becomes slack and may loop or become entangled with other cargo, personnel, or structure of the barge. When the barge sinks into the next valley between the swells, the hook is lowered with the barge deck and the cable again drawn taut~ thus endangering other cargo1 personnel and the like with which the slack cable may have become entangled. To avoid this problem crane operators usually attempt to raise and lower the hook in synchronization with the pitching deck. However, attempts at manually coordinating hook movement with a pitching deck are notoriously ineffectiYe.
Similar problems exist in attempting to transfer loads between two floating platforms such as the decks of two floating ships, one of which carries the crane~ In this case both plat-forms mav move vertically with respect to each other and with respect to a fixed hori~ontal position~ thus rendering the transfer between such independently moving platforms extremely difficult. Various other marine operations~ such as laying pipe on the ocean floor from a floating barge or landing submerged equ;pment on the ocean floor or s.ubmerged platforms from a floating vess.el involve si.milar difficulties.
Prior attempts to overcome the di`fficulti`es involved rely mainly on means for maintaining a constant tension on the hoist load line. Such systems, however, suffer from ;nherent limitations. Conventi:onal line tensioning apparatus operates on the line between the winch and the crane boom. Therefore, when multi:ple-reeved tackle i:s employed between the load hook and the crane boom the length of li:ne between the crane boom sheave and the wi:nch (known as the 'fast line') whi:ch must be adjusted to maintain a cons.tant tension on the li'ne at the load is a multiple of the verti`cal distance which must 6e compensated. Furthermore, while such li:ne tensioning apparatus may aid i'n li:fting a load from a movi:ng platform with a crane positioned on a fi`xed platform, s.uch li:ne tensi:oning offers- no way to synchronize vertical movement of a load suspended from a crane on a fixed platform with vertical movement of a moving platform so that the load may b.e gently landed on the movi:ng platform. Accordingly, maintaining constant tens~ion on a load li.ne wi'll not prevent the load from hei.ng s.mashed i:nto a rapi:dly vertically rising deck.
Hook-mounted relative motion compensation apparatus whi.ch. adjusts the distance between the end of the crane boom and the load hook in response t~ vertical movement of the landin3 platform may be devised which overcome some of the difficulties involved. However, such motion compensation apparatus, in order to be sturdy enough to supp~rt the wei~ht of heavy loads~ must i.tself be quite heavy. Furthermore, where such hook-mounted motion compensation apparatus is employed, the hydraulic cylinder as.semblies as well as the motors and pumps necessary to drive the 3Q apparatus must also be carried in the motion compensation ~ ~94023 apparatus itself, thus further increasing the ~eight of the motion compensation apparatus-. Since such motion compensation apparatus must be supported by the load line, the lifting capacity of the crane is reduced. Furthermore, such motion compensation apparatus must be suspended at the end of the load li`ne near the hook so that the motion compensation apparatus wi`ll not substantially interfere with the he;ght capacity of the crane~ Large, bulky and heavy motion compensation apparatus suspended from the end of a load line may become d;ffi`cult to maneuver in rough seas because of the action of the wind thereon. Furthermore, in si`tuations where the crane is supported on a floating platform, oscillatory movement of the floating platform may be transferred to the suspended motion compensation apparatus and amplified~
thus causing the motion compensation apparatus to sway and oscillate horizontally. Because of the mass of the motion compensation apparatus suspended on the end of the cable, such oscillatory motion can be dangerous and difficult to control in certain situations.
While a hook-mounted motion compensation system offers
2~ some distinct advantages, it inherently incorporates its own unique disadvantages. Accordingly, it is desirable to provide motion compensation apparatus which avoids the disadvantages of the hook-mounted moti`on compensation de~ices.
In accordance with the present invention vertical motion compensation apparatus is provided which is attached to the crane boom and operates only on the load line between the boom and the load hook. Since the motion compensation apparatus is secured to the boom7 the pumps and motors necessary to activate the motion compensation apparatus may be carried on the crane platform and the high pressure fluid transferred to the motion ~94023 compensation cylinder by a pressure l;ne carried by the crane boom. Accordingly, the mass of the portion of the motion compensation apparatus carried by the boom is substantially reduced. Likewise, the physical size of the motion compensation apparatus carried by the boom is substantially reduced, thus the total lift capacity of the crane i`s not substantially impaired.
Furthermore, since the motion compensation apparatus is attached to the boom itself, it is not su6ject to excessive wi`nd loading problems or extreme oscillation caused by movement of the plat-form on which the crane is mounted.
The motion compensation cylinder of the invention may be attached between the end of the load line and the end of the crane boom. In this case, the load hook means is suspended from the cable looped between the crane boom and the motion compensation cylinder. The motion compensation apparatus must then support only one-half the wei`ght of the load and must move the end of the cable vertically only twice the vertical distance to be compensated.
Alternatively, the apparatus may include a sheaved travelling block (load sheavel carrying the load hook and a sheaved block carried by the motion compensation cylinder. In this arrangement, the motion compensation apparatus must support more of the weight of the load (depending upon the number of reeves) but only need to move vertically approximately the vertical distance to be compensated.
Since the entire reeved cable and both sheave blocks are supported by a piston in the motion compensation cylinder supported by the boom, vertical movement of the pis-ton in proportion to relative vertical movement of the second platform eliminates undesired relative mo~ement of the hook with respect to the landing platform. The load may thus be gently landed on a pitching plat-
In accordance with the present invention vertical motion compensation apparatus is provided which is attached to the crane boom and operates only on the load line between the boom and the load hook. Since the motion compensation apparatus is secured to the boom7 the pumps and motors necessary to activate the motion compensation apparatus may be carried on the crane platform and the high pressure fluid transferred to the motion ~94023 compensation cylinder by a pressure l;ne carried by the crane boom. Accordingly, the mass of the portion of the motion compensation apparatus carried by the boom is substantially reduced. Likewise, the physical size of the motion compensation apparatus carried by the boom is substantially reduced, thus the total lift capacity of the crane i`s not substantially impaired.
Furthermore, since the motion compensation apparatus is attached to the boom itself, it is not su6ject to excessive wi`nd loading problems or extreme oscillation caused by movement of the plat-form on which the crane is mounted.
The motion compensation cylinder of the invention may be attached between the end of the load line and the end of the crane boom. In this case, the load hook means is suspended from the cable looped between the crane boom and the motion compensation cylinder. The motion compensation apparatus must then support only one-half the wei`ght of the load and must move the end of the cable vertically only twice the vertical distance to be compensated.
Alternatively, the apparatus may include a sheaved travelling block (load sheavel carrying the load hook and a sheaved block carried by the motion compensation cylinder. In this arrangement, the motion compensation apparatus must support more of the weight of the load (depending upon the number of reeves) but only need to move vertically approximately the vertical distance to be compensated.
Since the entire reeved cable and both sheave blocks are supported by a piston in the motion compensation cylinder supported by the boom, vertical movement of the pis-ton in proportion to relative vertical movement of the second platform eliminates undesired relative mo~ement of the hook with respect to the landing platform. The load may thus be gently landed on a pitching plat-
3~ form by normal operation of the crane controls. Furthermore, in off-loading operations where a hook is lowered to be affixed \
~940Z3 to the cargo, a constant tensi`on i`s maintained on the load cable regardless of the relative vertical movement of the two platforms by maintaining the load hook a minimum distance from the moving deck regardless of relative verti`cal movement of the two platforms.
5. In yet another alternative embodiment, the vertical motion compens~ation cyli`nder may be mounted parallel wi`th the longitudinal axis of the boom and preferably within the structure of the boom itself. In thi`s embodiment a sheaved block carri`ed on the end of a piston rod extending from the cylinder engages the load line between the load hook and the boom sheave and draws the load line over an idler sheave and into the boom structure to raise the load hook with respect to the boom.
The motion compensation apparatus of the invention may be incorporated into existing cranes with minimum modification.
Furthermore, if the compensation cylinder i`s mounted vertically, it may be mounted partially-extending above the boom. According-ly, the heiyht capacity of the crane is virtually unaffected and the lift capaci'ty of the crane is not substantially reduced. If the cylinder is mounted horizontally (wi'thin the boom), height capacity is unaffected. When vertical motion compensation is not required~ the apparatus may be de-activated and the crane operated in the conventional manner unaffected by the compensation apparatus.
Broadly stated, the ;nvention is a relative motion compens.ati:on apparatus in a crane for transferring loads between a first platform and a second platform vertically movable with respect to each other and employing a boom supported by said first platfonm, a cable dependi:ng from said boom and supporting hook means, and winch means to move said cable. The apparatus comprises: (a? cylinder means supported by sai:d boom, (b) piston means mounted for vertical reciprocal movement i.n said cylinder, (c) first sheave means supported by said piston, (d) second sheaYe means supporting said hook means with said cable reeved between said first sheave means and said second sheave means, (e) sensing means for generating a signal proportional to relative vertical movement of said first platform and second platform, and (f) means responsive to said si:gnal for supplying fluid to and removing fluid from said cylinder, thereby to raise and lower said piston in response to said signal.
Other features and advantages of the invention will become more readily understood when taken in connection with the appended claims and attached drawings in which:
FIGURE 1 is a pictorial illustration of a crane employing one emb.odiment of the invention;
FIGURE 2 is an elevational view of the motion com-pensation apparatus of the ;nvention mounted on the end of a crane 1~94Q23 boom with the cylinder swivel mounted to remain vertical;
FIGURE 3 is an end view of the apparatus of FIGURE 2;
FI`GURE 4 is an elevat;onal view of an alternate embodiment of the compensation apparatus of the invention with the cylinder mounted between the end of the load l;ne and the boom;
FIGURE 5 i`s a schemati`c i`llustration of a control system for the motion compensation apparatus;
FIGURE 6 i:s a diagrammati:c illustration of a control sys.tem for the apparatus of the i:nventi`on where both platforms are vertically movable with respect to a fixed horizontal position;
and FIGURE 7 is. an elevational view of an alternative emb.odi.ment of the invention wherein the compensation cylinder is mounted within and parallel with the crane boom.
It should be appreciated that the principles of the i.nvention are applica~.le to any load transfer operation wherein a s.us.pended load ;`s transferred between two platforms, one of whi.ch is vertically movable with res-pect to the other. For 2Q purposes of illustration, the invention is described herein with respect to transferri:ng loads between a floating vessel, such as a ship ~r barge, and a fi:xed platform, such as an offshore drillin~ platform or a pier, and between two floating vessels.
Accordingly, the term "platform" is used herein to mean a surface to or from which a load i:s to be transferred and may encompass th.e surface of a pier, an offshore platform, the deck of a ship or barge, the ocean floor, or any other surface to or from which a load may be transferred. Likewise, the term "crane" is employed herein in its broadest sense to describe any structure 3Q from which a load line, such as a cable, is suspended to raise 199~023 or lower a load. It will be understood, therefore, that a crane may take many forms. Ordinari`ly, however, the crane employs a structure known as a boom which extends from the base of the crane to a point over the platform from or to which the load is to be transferred. A motor-driven winch carri'ed by the crane reels in or plays- out a cable passing through a boom sheave at the end of the boom to ra;`s-e or lower the load hook. Such cranes are well known in the art and the operation of s~ame wi`ll not ~e di`scussed in detai`l herein.
In accordance with the invention a vertical motion compensation apparatus- is incorporated into a crane to automati-cally adjust the di'stance bet~een the load hook and the boom directly above the load hDok in response to relative vertical movement of the crane and the platform to or from which a load 5 is to be transferred. One preferred embodiment of the invention is illustrated in FIGURES 1, 2, 3 and 5A As illustrated in FIGURE 1, a crane, generally i'ndicated at 10, i's mounted on an offshore platform 11. The offshore platform 11 may be any of various types of structures which are secured to the ocean floor 20 by legs 12 to supp~rt the platform 11 at a stable fixed elevation above the surface 13 of the ocean~ As illustrated in FIGURE 1, the crane 10 is employed to transfer a load 14 to or from the deck 15 of barge 16. The crane 10 is generally adapted to pro-vide horizontal movement of the load with respect to the deck 25 of the platform 11 so that loads lifted from the deck 15 of the barge may ~e placed on the deck of the platform 11 or vice versa.
To provide such horizontal movement the crane may be mounted on tracks or pivotally mounted so that it may be rotated in the horizontal plane of the deck of the platform. Various other 30 means may be employed to prov;de horizontal movement of the load 14.
_ ln _ ~ ~.094023 Crane 10 employs a boom 17 which extends therefrom so that the end of the boom 17 may be positioned over the barge 16.
The crane 10 includes a motor-driven winch (not illustrated) to haul in and play out a ca61e 18 which. passes over a sheave at the end of the boom and supports the load hook 19 to which the load 14 may be secured. rn simple conventional cranes, the sheave may be a single grooved pulley and the load hook 1~
secured to the end of the cable. However, heavier cranes employ a multiple-sheaved stati:onary block at or near the end of the boom and a. multi:ple-sheaved travelling 610ck 21 between which the cahle is reeved to obtain the mechanical advantage of multiple-reeved tackle. I:n sucfi cases, the load hook 19 i's secured to the traYelling block 21. In cranes- employing a multiple reeved block arrangement as descri'bed above, the portion of the cable between the boom sheave (stationary block~ and the w.inch i:s known as the 'fast li`ne' since the li'near distance this ~ection of the cable moves i's- a multi`ple of the vertical distance the hook moves.
It wi:ll be readily appreci`ated that little diffi:culty i.s encountered i:n trans:ferri.ng a load from the platform 11 to deck 15 of harge 16 when the s:ea i:s calm~ However, since the load 14 is sus:pended on a tensioned cable from a crane secured to a fi:xed platform, the load 14 moves vertically only as the fast line is operated by the wi:nch. Si:nce the barge 16 is floating on the surface of the ocean, the deck 15 will rise and fall wi.th respect to the fixed platform as the barge rises and falls wi.th ocean waves. Accordingly, unless the vertical move-ment of the load 14 i`s synchronized with the vertical movement of the deck 15~ the deck 15 may rise rapidly and contact the load 14 when the crane operator is attempting to lower the load l~g4~23 onto deck 15. Conversely, when the crane operator is attempting to remove a load from the deck 15, the vertical movement of the empty load hook must be synchronized with the vertical movement of the deck 15 in order to prevent the hook from resting on deck 15 and permitting the cable to become slack.
In accordance wi:th the invention, the crane 10 is provided with a vertical motion compensation apparatus secured to the boom and acting only on the cable between the boom and the load hook in response to vertical movement of the deck 15.
In the embodiment illustrated in FI`GURES 1, 2 and 3, the vertical motion compensati`on apparatus comprises a hydraulic piston and cylinder assembly supported by the boom which is activated by a hydraulic pump in response to the vertical movement of the barge deck 15. In the preferred embodiment, the vertical motion com-pensation apparatus comprises a hydraulic cylinder 22 positionedvertically and pivotally secured between the lateral members 23 and 24 of the boom 17. The pivot axis of the cylinder is coaxial with a boom sheave 20. Boom s-heave 20 is free to rotate indepen-dently of the cylinder and the cylinder may likewise rotate in the vertical plane i:ndependently of the boom sheave 20.
A piston is mounted for reci`procal movement within cylinder 22 and attached to the end of a piston rod 26 which extends through the bottom end of the cylinder 22. A multiple-sheaved stationary block 27 is secured to the free end of rod 26. The term "stationary block" is used herein in the normal sense to define a portion of a multiple reeved tackle arrange-ment which is stationary with respect to the travelling block.
As will be described herein, the stationary block is not in fact stationary since i:t will be moved vertically by the motion compensation apparatus. The cable 18 from the winch passes over boom sheave 20 to a multiple-sheaved travelling block 21 and i.s reeved about block 27 and travelling block 21 in the conventional manner. A load hook 19 depends from the travelling block 21.
It will thus be apparent that when the piston is held stati.onary with res:pect to the cylinder 22, the crane 10 may be operated i:n the conventi'onal manner. The fast line sheave 20 is physi:cally spaced from the stati`onary block 27 (whïch now operates as the boom sheavè~, 6ut i.n all respects- the crane ; functions are conventi~onal. However, îf the fast line is held s.tati:onary, the load hook may b.e moved vertically 6y moving the piston within the cyilihder 22. Accordingly, the cylinder and piston ass~em61y may operate independently of the fast line to Yary the verti.cal posi:ti'on of the hook relatiYe to the boom.
Likewi.se, the fast li.ne and the cyli`nder as-sem61y may be operated at the s.ame time to collecti`vely vary the position of the load hook. I:t should be:observed that the wei'ght of the load is sub.stanti:ally supported by the pis-ton rod 26. Accordingly, since the cyli.nder i:s pi'votally mounted the cylinder 22 w;ll be held in the vertical pos1tion by the wei`ght of the tackle blocks, cable and hsok irrespective of horizontal or vertical movement of the boom. Furthermore, si`nce a substantial portion of the length of the cylinder i's. pos-i:ti~oned above the pi'vot point, the pi.ston may be withdrawn into the cylinder to raise the block 27 near the end of the boom, thus- the li'ft he;'ght capacity of the crane is virtually unaffected 6y the motion compensation apparatus.
Unless. alternate means: are used to mai:ntai`n the cylinder in the vertical pos:iti.on, the pi.Yot point should be above the center of gravity of the cyli`nder and piston assembly when supporting an unloaded hook.
Contrnl apparatus for the motion compensation apparatus of FIGURE 1 is illustrated schematically in FIGURE 5. As dis-cussed above, the hydraulic cylinder 22 is mounted on the crane boom. The cylinder 22 carries a reciprocal piston 100 connected to rod 26 which supports the stationary block 27. Hydraulic fluid is suppli'ed to the chamber 101 below the piston by a high pressure line 102. The chamber 103 above the piston 100 is vented to atmosphere by vent 104. If desired, the vent 104 may communi-cate by conduit (not shown) wlth the hydraulic fluid reservoir to mai:ntain a constant pressure on the reservoir.
In the preferred embodiment, hydraulic fluid is supplied to high pressure line 102 by a reversible variable displacement pump 105. Such pumps are well known in the art as over-center pumps and adapted to pump hydraulic fluid in ei`ther direction between lines 102 and 106. The direction in which the fluid is pumped and the rate at whi'ch it is pumped i's determined by the capacity of the pump and the position of the control yoke. Thus, by positioning the yoke in one direction hydraulic fluid is pumped from reservoi'r la7 through line 106 and into chamber 101 through high pressure line 102. By reversing the control yoke, hydraulic fluid i:s pumped in the reverse direction. Accordingly, stationary block 27 is verti`cally raised or lowered by appro--~ priately positioning the control yoke.
According to the above-described embodiment of the invention, the stationary block 27 is raised or lowered in synchronization with vertical movement of the landing platform 15 when the boom is over the barge. Where the crane is mounted on a fixed platform and the landing platform is vertically movable relative thereto as in the situation depicted in FIGURE
1, a sensor is placed on the movable platform to detect vertical movement of the movable platform with respect to the fixed platform. In the preferred embodiment, an accelerometer 110 is placed on the movable platform to detect relative vertical movement of the platform 15. The slgnal generated by the accelerometer ;n response to vertical movement of the platfonm 15 indicates direction of movement and acceleration. This signal is transmitted to a signal processor 112 which integrates the si.gnal to determine the rate or average velocity of movement of the platform and generate an appropriate signal which is trans-mi.tted to a controller 113. Controller 113 operates ;n response to the signal received from the ihtegrator 112 to generate a signal which controls the posi:tion of the control yoke of pump 105. Accordi.ngly, when upward movement in the vertical direction is. detected by accelerometer 110, the accelerometer generates a signal which i:s transmi`tted to the integrator 112 which in turn transmits a signal to controller 113 and controller 113 causes the pump to be stroked in the forward direction. Pump 105 then pumps hydrauli.c fluid from reservoir 107 to chamber 101 to cause the hook 19 to rise. In similar fas.hion, when accelerometer 110 detects- vertical movement in the downward direction, the signal generated by accelerometer 110 is processed by the integrator 112 and controller 113 which causes the pump to be yoked in the opposite direction and pump fluid from chamber 101 to reservoir 107 and lower the hook 19.
From the foregoi`ng it will be apparent that when the crane is on a fixed platform the sensor 110 must be situated to detect relative vertical movement of the landing platform.
Accordingly, when an accelerometer is used as a sensor 110, the accelerometer is placed on the movable platform. Conversely, when the crane is on a movable platform and used to land or remove a load from a fixed platform, the sensor must determine ~40Z3 relative vertical movement of the crane. In this situation an accelerometer is most appropriately placed on the upper end of the crane boom as shown on llOb in FIGURE 2.
Where the crane is on a vertically movable platform and the landin~ platform is also vertically movable, as when the crane is mounted on a barge and attempting to land or off-load cargo from another barge, it i`s necessary that the relative vertical movement of the two platforms must be detected. Suit-able control apparatus for the motion compensation apparatus described is shown in FIGURE 6. Since both platforms A and B
are vertically movable, s~ensors, such as accelerometers llOa and llOb, are positioned on each platform. Ordinarily, one sensor would be placed on the landing platform and the other sensor would be placed on the crane boom near the boom sheave so that vertical movement of the boom sheave ;s detected. Si`gnals generated by the sensors llOa and llOb are transmitted to appropriate signal processors, such as integrators 112a and 112b , respectively. The signals generated by the integrators 112a and 112b are fed to a comparator 114 whi`ch determines the vertical movement of the platforms with respect to each other and sends an appropriate signal to controller 113 which then appropriately controls the position of the control yoke of pump 105.
If desired~ the sensor used for detecting movement of the crane platform may be mounted on the travelling block 21.
In this arrangement the motion compensation apparatus is activated only when it is desired to maintain the hook at a fixed position relative to the landing platform, as when a hook is lowered to a landing platform for attachment to the load. Once the crane operator has positioned the hook at the desired relative position the motion compensation apparatus is activated to maintain the ~g402~
hook at a fixed position relative to the landing platform irrespective of realtive movement betweèn the ~oom and the landing platform.
It should be noted that when the crane is mounted on one platform (such as a fixed platform) and is used to transfer loads from a moving platform to the fixed platform on which the crane is mounted, the motion compensation apparatus must be de-activated after the load has been lifted from the moving platform.
Otherwise, the load will continue to move vertically in response 0 to the pitching motion of the landing platform. Accordingly~
activation and deactivation controls should be available to the crane operator so that the crane operator can activate the compensation apparatus only when it is requ;red. Likewise, when the crane is mounted on one platform and used to transfer loads between second and third platforms, 60th of which are vertically movable with respect to the crane platform (as when a crane on a fixed platform is used to transfer loads between two floating vessels), the sensor used to detect vertical move-ment of the landing platform must be transferred between the two movable platforms or each movable platform provided with a separate sensor and means prov;ded by wh;ch the crane operator ~ay select between the sensors controlling the motion compensa-tion apparatus as required.
While the invention has been described with particular reference to the use of accelerometers for detecting relative vertical movement of the platforms, it will be readily appre-ciated that other sensing means suitable for detecting relative vertical movement may be employed. Various other sensing apparatus will be readily apparent to those skilled in the art and may be substituted for the accelerometer control systems 1~94023 described herein without departing from the spirit and scope of the invention. It should further be recognized that the elec-tronic signal processing required to convert a signal from the sensor to an appropriate signal to control the control yoke of the pump will be dependent upon the type of sensor used. Various control circuits for performing such operations may be readily devised by those skilled in the art.
When an accelerometer is used to detect relati`ve verti-cal movement of the platforms as described hereinabove, the accelerometer must be placed on the movi`ng platform. If the landing platform is stable and the platform supporting the crane is vertically movable, the sensor is placed on the platform on which the crane is mounted. In this case the accelerometer is conveniently placed on the crane boom near the boom sheave so that relative vertical movement of the crane directly above the landing platform is detected. However, when the crane is on a fixed platform and the landing platform is movable with respect thereto, the accelerometer must be placed on the landing platform.
In the preferred embodiment the si`gnal from the accelerometer is converted to an appropriate telemetry signal which may be trans-mitted by radio signal from antenna 130 on the sensing and signal-ing device 110 to a receiving antenna 125 mounted on the crane.
Alternatively, the signal from the accelerometer can be transmitted directly to signal processing equi`pment aboard the crane by a suitable electrically conductive cable suspended from the landing platform to the crane. Other means for transmitting the signal to the control apparatus will be apparent to those skilled in the art and may be adapted as required to accommodate other sensing means.
As described above, the motion compensation cylinder ~ 4Q23 supports the entire weight of the load except for that portion supported by the fast line. Accordingly, the cylinder should have the lift capacity required to handle any load to be lifted by the crane. The stroke of the cylinder, of course, should be sufficient to equal the verti`cal movement to be compensated.
The performance capacity of the pump or pumps necessary to raise the load will depend on the size of the cylinder, the anticipated load, and the anticipated rise rate. The size and capacity of pumps, cylinders and the li`ke necessary to produce the required lifting capacity, however, may be readily determined and matched with appropriate sensing and control apparatus to raise and lower the hook in direct relation to the signal received from the motion sensor selected.
Since the motion compensation cylinder acts only on the cable between the crane boom and the load, the distance which the p;ston moves is directly related to but not necessarily equal to the movement sensed. For example, if the fast line is held steady while the piston is raised in the embodiment illustrated in FIGURE 1, the distance the stationary block 27 is raised is not equal to the distance the hook block 21 is raised since the fast line is not moved with the stationary block. This variance, however, is directly related to the number of reeves and may be readily compensated for in the control circuits. As the number of reeves is increased the variance decreases.
~y supporting the motion compensation cylinder 22 between the lateral members 23 and 24 to pivot about the axis of the boom sheave 20 as illustrated in FIGURES 1~ 2 and 3. addition-al advantages are obtained. For example, hydraulic fluid may be conducted from the pump to the cylinder 22 through a fixed hard pressure line 133 secured to or forming part of the boom 17.
1~94~3 Furthermore, the fluid may be injected directly into the cylinder through the pivot pin 132 supporting the cylinder 22 through a swivel connector 134, thus totally eliminating the use of flexible pressure hoses in the hydraulic system.
An alternat;ve embodi`ment of the invention is illustrated in FIGURE 4. In this embodiment the cable 18 passes over the boom sheave 20 and through a single grooved travelling block 120.
The end of the cable i`s attached to the pi`ston rod 126.
It will thus be observed that in this embodiment only one-half of the weight of the load is supported by the cylinder 122.
However, the pi'ston must travel twice the distance that load hook 119 travels. In this embodiment the cylinder 122 is sus-pended directly from the pivot axi`s of the boom sheave ~0, thus the motion compensation cyli-nder, if excessi'vely long, may interfere with the lift height capacity of the crane. However, the embodiment illustrated in FIGURE 4 may be more readily adapted to the ex;sting crane equipment. It will be understood that the piston rod 126 may support a multiple-sheaved stationary hlock and a multiple-sheaved hook block as shown in FIGURE 1.
Furthermore, the cyli'nder need not depend from the axis of the boom sheave but may depend from some other portion of the boom.
It is not necessary that the pumps be capable of supplying sufficient pressure to lift the entire weight of the load if the motion compensation apparatus is only required to coordinate the movement of an empty load hook with the movement of a pitching deck as when attempting to remove cargo from a pitching deck with a fixed crane. For example~ the motion compensation apparatus need only be sufficient to raise and lowerthe load hook in synchronization with the pitching deck.
Accordingly, as the load i`s lifted, the weight on the piston may ~n ,023 overcome the pressure in the cylinder and cause the piston to rest on the bottom of the cylinder. In this case the motion compensa-tion apparatus acts merely as a line tensioning means to maintain constant tension on the cable supporting the empty load hook so that load hook movement may be coordi:nated with the movement of a pi:tching deck while attaching the load hook to a cargo to be lifted. Once the crane is operated to lift the cargo, the piston contacts. the bottom of the cyli`nder and the crane operates in its normal fashi:on.
For handli`ng light loads or when operating only as. a cab.le tensioni.ng apparatus, i.t is not necessary that the cyli:nder be operated with hydraulic fluid. Pneumatic cylinders may suffice for li.ght load operati.ons and offer quicker response than hydrau-lic sys.tems.
Another embodiment of the invention is illus.trated i:n FIGURE 7. I:n this embodiment the cylinder 22 is mounted wi:thin and parallel with the boom 17. The cable 18 i`s reeved in conven-tional manner around the boom sheave (stationary block) 20 and the travelling block 21 which s-upports the load hook 1~. The boom 17 i:s modi:fi:ed, however, to include an idler sheave 200, preferably b.elow ahd i:nboard from the boom sheave 20 as illustrated.
A piston rod 26 transversely moveable with respect to the boom 17 extends from the cylinder 22 and carries a compensa-ting sheave 201 on the free end thereof. The compensating sheave 201 i.s positioned to engage the inboard cable reeved between b.oom sheave 20 and travelli`ng block 21. Thus, as the piston rod26 i.s withdrawn into cylinder 22, the cable reeved between the hoom sheave 20 and travelling block 21 is drawn over the idler sheave 200 and boom sheave 20, effectively varying the distance between boom sheave 20 and travelli:~ng block 21 i`n direct propor-09~023 tion to the lateral movement of the compensation sheave 201.Since the compensation sheave 201 does not engage the fast line, the embodiment of FIGURE 7 is the mechanical equivalent of the embodiment of FIGURE 2 with regard to the effect of movement of the piston to raise and lower the hook. This embodiment, however, offers the additional advantages of requiring only minimum modification of the boom structure and, since the cylinder is mounted parallel with the boom and does not vary the location of the original boom sheave 20 of the crane, vertical lift capacity of the crane i`s completely unaffected by the modi-fication. Furthermore, s;nce the load is supported directly by the idler 200 and boom sheave 20, the piston rod and cylinder are isolated from side loads caused by horizontal movement of the boom or load. The boom must only be modified so that the idler 200 as well as the boom sheave 20 may support the anticipated load and to accommodate the cylinder within the boom.
Use of a fluid system to compensate for relative vertical movement as described herein provides a unique safety feature. In many instances a crane operator attempting to off-load a cargo package from a moving barge deck with a cranemounted on a fixed deck (or vice YerSa) may inadvertently hook onto the barge itself while the barge is riding the crest of a wave. As the wave subsides~ the barge is rapidly lowered with respect to the crane. If the hook has accidentally eng3ged the harge rather than the cargo7 the crane is subjected to the entire weight of the barge. This usually results in damage to the crane, the barge, or both. However5 the high pressure line 102 between the pump 105 and the cylinder may be provided with a pressure relief valve which vents to the reservoir when the weight on the hook exceeds a predetermined amount. Accordingly, if the 10~?4023 hook engages the barge and the hook is subjected to loads greater than the load capacity of the crane, the relief valve vents and the piston is permitted to be lowered with respect to the cylinder, thus permitting the hook to be lowered with the barge without overloading the crane.
From the foregoing it will be apparent that the princi-pales of the invention may be employed with various load transfer apparatus where compensation of relative vertical movement is desired. It will be understood~ therefore, that although the invention has been described with particular reference to specific embodi`ments thereof, the forms of the invention shown and described in detail are to be taken as preferred embodiments of same, and that vari`ous changes and modifications may be resorted to without departing from the spirit and scope of the invention as defined by the appended clai`ms.
~940Z3 to the cargo, a constant tensi`on i`s maintained on the load cable regardless of the relative vertical movement of the two platforms by maintaining the load hook a minimum distance from the moving deck regardless of relative verti`cal movement of the two platforms.
5. In yet another alternative embodiment, the vertical motion compens~ation cyli`nder may be mounted parallel wi`th the longitudinal axis of the boom and preferably within the structure of the boom itself. In thi`s embodiment a sheaved block carri`ed on the end of a piston rod extending from the cylinder engages the load line between the load hook and the boom sheave and draws the load line over an idler sheave and into the boom structure to raise the load hook with respect to the boom.
The motion compensation apparatus of the invention may be incorporated into existing cranes with minimum modification.
Furthermore, if the compensation cylinder i`s mounted vertically, it may be mounted partially-extending above the boom. According-ly, the heiyht capacity of the crane is virtually unaffected and the lift capaci'ty of the crane is not substantially reduced. If the cylinder is mounted horizontally (wi'thin the boom), height capacity is unaffected. When vertical motion compensation is not required~ the apparatus may be de-activated and the crane operated in the conventional manner unaffected by the compensation apparatus.
Broadly stated, the ;nvention is a relative motion compens.ati:on apparatus in a crane for transferring loads between a first platform and a second platform vertically movable with respect to each other and employing a boom supported by said first platfonm, a cable dependi:ng from said boom and supporting hook means, and winch means to move said cable. The apparatus comprises: (a? cylinder means supported by sai:d boom, (b) piston means mounted for vertical reciprocal movement i.n said cylinder, (c) first sheave means supported by said piston, (d) second sheaYe means supporting said hook means with said cable reeved between said first sheave means and said second sheave means, (e) sensing means for generating a signal proportional to relative vertical movement of said first platform and second platform, and (f) means responsive to said si:gnal for supplying fluid to and removing fluid from said cylinder, thereby to raise and lower said piston in response to said signal.
Other features and advantages of the invention will become more readily understood when taken in connection with the appended claims and attached drawings in which:
FIGURE 1 is a pictorial illustration of a crane employing one emb.odiment of the invention;
FIGURE 2 is an elevational view of the motion com-pensation apparatus of the ;nvention mounted on the end of a crane 1~94Q23 boom with the cylinder swivel mounted to remain vertical;
FIGURE 3 is an end view of the apparatus of FIGURE 2;
FI`GURE 4 is an elevat;onal view of an alternate embodiment of the compensation apparatus of the invention with the cylinder mounted between the end of the load l;ne and the boom;
FIGURE 5 i`s a schemati`c i`llustration of a control system for the motion compensation apparatus;
FIGURE 6 i:s a diagrammati:c illustration of a control sys.tem for the apparatus of the i:nventi`on where both platforms are vertically movable with respect to a fixed horizontal position;
and FIGURE 7 is. an elevational view of an alternative emb.odi.ment of the invention wherein the compensation cylinder is mounted within and parallel with the crane boom.
It should be appreciated that the principles of the i.nvention are applica~.le to any load transfer operation wherein a s.us.pended load ;`s transferred between two platforms, one of whi.ch is vertically movable with res-pect to the other. For 2Q purposes of illustration, the invention is described herein with respect to transferri:ng loads between a floating vessel, such as a ship ~r barge, and a fi:xed platform, such as an offshore drillin~ platform or a pier, and between two floating vessels.
Accordingly, the term "platform" is used herein to mean a surface to or from which a load i:s to be transferred and may encompass th.e surface of a pier, an offshore platform, the deck of a ship or barge, the ocean floor, or any other surface to or from which a load may be transferred. Likewise, the term "crane" is employed herein in its broadest sense to describe any structure 3Q from which a load line, such as a cable, is suspended to raise 199~023 or lower a load. It will be understood, therefore, that a crane may take many forms. Ordinari`ly, however, the crane employs a structure known as a boom which extends from the base of the crane to a point over the platform from or to which the load is to be transferred. A motor-driven winch carri'ed by the crane reels in or plays- out a cable passing through a boom sheave at the end of the boom to ra;`s-e or lower the load hook. Such cranes are well known in the art and the operation of s~ame wi`ll not ~e di`scussed in detai`l herein.
In accordance with the invention a vertical motion compensation apparatus- is incorporated into a crane to automati-cally adjust the di'stance bet~een the load hook and the boom directly above the load hDok in response to relative vertical movement of the crane and the platform to or from which a load 5 is to be transferred. One preferred embodiment of the invention is illustrated in FIGURES 1, 2, 3 and 5A As illustrated in FIGURE 1, a crane, generally i'ndicated at 10, i's mounted on an offshore platform 11. The offshore platform 11 may be any of various types of structures which are secured to the ocean floor 20 by legs 12 to supp~rt the platform 11 at a stable fixed elevation above the surface 13 of the ocean~ As illustrated in FIGURE 1, the crane 10 is employed to transfer a load 14 to or from the deck 15 of barge 16. The crane 10 is generally adapted to pro-vide horizontal movement of the load with respect to the deck 25 of the platform 11 so that loads lifted from the deck 15 of the barge may ~e placed on the deck of the platform 11 or vice versa.
To provide such horizontal movement the crane may be mounted on tracks or pivotally mounted so that it may be rotated in the horizontal plane of the deck of the platform. Various other 30 means may be employed to prov;de horizontal movement of the load 14.
_ ln _ ~ ~.094023 Crane 10 employs a boom 17 which extends therefrom so that the end of the boom 17 may be positioned over the barge 16.
The crane 10 includes a motor-driven winch (not illustrated) to haul in and play out a ca61e 18 which. passes over a sheave at the end of the boom and supports the load hook 19 to which the load 14 may be secured. rn simple conventional cranes, the sheave may be a single grooved pulley and the load hook 1~
secured to the end of the cable. However, heavier cranes employ a multiple-sheaved stati:onary block at or near the end of the boom and a. multi:ple-sheaved travelling 610ck 21 between which the cahle is reeved to obtain the mechanical advantage of multiple-reeved tackle. I:n sucfi cases, the load hook 19 i's secured to the traYelling block 21. In cranes- employing a multiple reeved block arrangement as descri'bed above, the portion of the cable between the boom sheave (stationary block~ and the w.inch i:s known as the 'fast li`ne' since the li'near distance this ~ection of the cable moves i's- a multi`ple of the vertical distance the hook moves.
It wi:ll be readily appreci`ated that little diffi:culty i.s encountered i:n trans:ferri.ng a load from the platform 11 to deck 15 of harge 16 when the s:ea i:s calm~ However, since the load 14 is sus:pended on a tensioned cable from a crane secured to a fi:xed platform, the load 14 moves vertically only as the fast line is operated by the wi:nch. Si:nce the barge 16 is floating on the surface of the ocean, the deck 15 will rise and fall wi.th respect to the fixed platform as the barge rises and falls wi.th ocean waves. Accordingly, unless the vertical move-ment of the load 14 i`s synchronized with the vertical movement of the deck 15~ the deck 15 may rise rapidly and contact the load 14 when the crane operator is attempting to lower the load l~g4~23 onto deck 15. Conversely, when the crane operator is attempting to remove a load from the deck 15, the vertical movement of the empty load hook must be synchronized with the vertical movement of the deck 15 in order to prevent the hook from resting on deck 15 and permitting the cable to become slack.
In accordance wi:th the invention, the crane 10 is provided with a vertical motion compensation apparatus secured to the boom and acting only on the cable between the boom and the load hook in response to vertical movement of the deck 15.
In the embodiment illustrated in FI`GURES 1, 2 and 3, the vertical motion compensati`on apparatus comprises a hydraulic piston and cylinder assembly supported by the boom which is activated by a hydraulic pump in response to the vertical movement of the barge deck 15. In the preferred embodiment, the vertical motion com-pensation apparatus comprises a hydraulic cylinder 22 positionedvertically and pivotally secured between the lateral members 23 and 24 of the boom 17. The pivot axis of the cylinder is coaxial with a boom sheave 20. Boom s-heave 20 is free to rotate indepen-dently of the cylinder and the cylinder may likewise rotate in the vertical plane i:ndependently of the boom sheave 20.
A piston is mounted for reci`procal movement within cylinder 22 and attached to the end of a piston rod 26 which extends through the bottom end of the cylinder 22. A multiple-sheaved stationary block 27 is secured to the free end of rod 26. The term "stationary block" is used herein in the normal sense to define a portion of a multiple reeved tackle arrange-ment which is stationary with respect to the travelling block.
As will be described herein, the stationary block is not in fact stationary since i:t will be moved vertically by the motion compensation apparatus. The cable 18 from the winch passes over boom sheave 20 to a multiple-sheaved travelling block 21 and i.s reeved about block 27 and travelling block 21 in the conventional manner. A load hook 19 depends from the travelling block 21.
It will thus be apparent that when the piston is held stati.onary with res:pect to the cylinder 22, the crane 10 may be operated i:n the conventi'onal manner. The fast line sheave 20 is physi:cally spaced from the stati`onary block 27 (whïch now operates as the boom sheavè~, 6ut i.n all respects- the crane ; functions are conventi~onal. However, îf the fast line is held s.tati:onary, the load hook may b.e moved vertically 6y moving the piston within the cyilihder 22. Accordingly, the cylinder and piston ass~em61y may operate independently of the fast line to Yary the verti.cal posi:ti'on of the hook relatiYe to the boom.
Likewi.se, the fast li.ne and the cyli`nder as-sem61y may be operated at the s.ame time to collecti`vely vary the position of the load hook. I:t should be:observed that the wei'ght of the load is sub.stanti:ally supported by the pis-ton rod 26. Accordingly, since the cyli.nder i:s pi'votally mounted the cylinder 22 w;ll be held in the vertical pos1tion by the wei`ght of the tackle blocks, cable and hsok irrespective of horizontal or vertical movement of the boom. Furthermore, si`nce a substantial portion of the length of the cylinder i's. pos-i:ti~oned above the pi'vot point, the pi.ston may be withdrawn into the cylinder to raise the block 27 near the end of the boom, thus- the li'ft he;'ght capacity of the crane is virtually unaffected 6y the motion compensation apparatus.
Unless. alternate means: are used to mai:ntai`n the cylinder in the vertical pos:iti.on, the pi.Yot point should be above the center of gravity of the cyli`nder and piston assembly when supporting an unloaded hook.
Contrnl apparatus for the motion compensation apparatus of FIGURE 1 is illustrated schematically in FIGURE 5. As dis-cussed above, the hydraulic cylinder 22 is mounted on the crane boom. The cylinder 22 carries a reciprocal piston 100 connected to rod 26 which supports the stationary block 27. Hydraulic fluid is suppli'ed to the chamber 101 below the piston by a high pressure line 102. The chamber 103 above the piston 100 is vented to atmosphere by vent 104. If desired, the vent 104 may communi-cate by conduit (not shown) wlth the hydraulic fluid reservoir to mai:ntain a constant pressure on the reservoir.
In the preferred embodiment, hydraulic fluid is supplied to high pressure line 102 by a reversible variable displacement pump 105. Such pumps are well known in the art as over-center pumps and adapted to pump hydraulic fluid in ei`ther direction between lines 102 and 106. The direction in which the fluid is pumped and the rate at whi'ch it is pumped i's determined by the capacity of the pump and the position of the control yoke. Thus, by positioning the yoke in one direction hydraulic fluid is pumped from reservoi'r la7 through line 106 and into chamber 101 through high pressure line 102. By reversing the control yoke, hydraulic fluid i:s pumped in the reverse direction. Accordingly, stationary block 27 is verti`cally raised or lowered by appro--~ priately positioning the control yoke.
According to the above-described embodiment of the invention, the stationary block 27 is raised or lowered in synchronization with vertical movement of the landing platform 15 when the boom is over the barge. Where the crane is mounted on a fixed platform and the landing platform is vertically movable relative thereto as in the situation depicted in FIGURE
1, a sensor is placed on the movable platform to detect vertical movement of the movable platform with respect to the fixed platform. In the preferred embodiment, an accelerometer 110 is placed on the movable platform to detect relative vertical movement of the platform 15. The slgnal generated by the accelerometer ;n response to vertical movement of the platfonm 15 indicates direction of movement and acceleration. This signal is transmitted to a signal processor 112 which integrates the si.gnal to determine the rate or average velocity of movement of the platform and generate an appropriate signal which is trans-mi.tted to a controller 113. Controller 113 operates ;n response to the signal received from the ihtegrator 112 to generate a signal which controls the posi:tion of the control yoke of pump 105. Accordi.ngly, when upward movement in the vertical direction is. detected by accelerometer 110, the accelerometer generates a signal which i:s transmi`tted to the integrator 112 which in turn transmits a signal to controller 113 and controller 113 causes the pump to be stroked in the forward direction. Pump 105 then pumps hydrauli.c fluid from reservoir 107 to chamber 101 to cause the hook 19 to rise. In similar fas.hion, when accelerometer 110 detects- vertical movement in the downward direction, the signal generated by accelerometer 110 is processed by the integrator 112 and controller 113 which causes the pump to be yoked in the opposite direction and pump fluid from chamber 101 to reservoir 107 and lower the hook 19.
From the foregoi`ng it will be apparent that when the crane is on a fixed platform the sensor 110 must be situated to detect relative vertical movement of the landing platform.
Accordingly, when an accelerometer is used as a sensor 110, the accelerometer is placed on the movable platform. Conversely, when the crane is on a movable platform and used to land or remove a load from a fixed platform, the sensor must determine ~40Z3 relative vertical movement of the crane. In this situation an accelerometer is most appropriately placed on the upper end of the crane boom as shown on llOb in FIGURE 2.
Where the crane is on a vertically movable platform and the landin~ platform is also vertically movable, as when the crane is mounted on a barge and attempting to land or off-load cargo from another barge, it i`s necessary that the relative vertical movement of the two platforms must be detected. Suit-able control apparatus for the motion compensation apparatus described is shown in FIGURE 6. Since both platforms A and B
are vertically movable, s~ensors, such as accelerometers llOa and llOb, are positioned on each platform. Ordinarily, one sensor would be placed on the landing platform and the other sensor would be placed on the crane boom near the boom sheave so that vertical movement of the boom sheave ;s detected. Si`gnals generated by the sensors llOa and llOb are transmitted to appropriate signal processors, such as integrators 112a and 112b , respectively. The signals generated by the integrators 112a and 112b are fed to a comparator 114 whi`ch determines the vertical movement of the platforms with respect to each other and sends an appropriate signal to controller 113 which then appropriately controls the position of the control yoke of pump 105.
If desired~ the sensor used for detecting movement of the crane platform may be mounted on the travelling block 21.
In this arrangement the motion compensation apparatus is activated only when it is desired to maintain the hook at a fixed position relative to the landing platform, as when a hook is lowered to a landing platform for attachment to the load. Once the crane operator has positioned the hook at the desired relative position the motion compensation apparatus is activated to maintain the ~g402~
hook at a fixed position relative to the landing platform irrespective of realtive movement betweèn the ~oom and the landing platform.
It should be noted that when the crane is mounted on one platform (such as a fixed platform) and is used to transfer loads from a moving platform to the fixed platform on which the crane is mounted, the motion compensation apparatus must be de-activated after the load has been lifted from the moving platform.
Otherwise, the load will continue to move vertically in response 0 to the pitching motion of the landing platform. Accordingly~
activation and deactivation controls should be available to the crane operator so that the crane operator can activate the compensation apparatus only when it is requ;red. Likewise, when the crane is mounted on one platform and used to transfer loads between second and third platforms, 60th of which are vertically movable with respect to the crane platform (as when a crane on a fixed platform is used to transfer loads between two floating vessels), the sensor used to detect vertical move-ment of the landing platform must be transferred between the two movable platforms or each movable platform provided with a separate sensor and means prov;ded by wh;ch the crane operator ~ay select between the sensors controlling the motion compensa-tion apparatus as required.
While the invention has been described with particular reference to the use of accelerometers for detecting relative vertical movement of the platforms, it will be readily appre-ciated that other sensing means suitable for detecting relative vertical movement may be employed. Various other sensing apparatus will be readily apparent to those skilled in the art and may be substituted for the accelerometer control systems 1~94023 described herein without departing from the spirit and scope of the invention. It should further be recognized that the elec-tronic signal processing required to convert a signal from the sensor to an appropriate signal to control the control yoke of the pump will be dependent upon the type of sensor used. Various control circuits for performing such operations may be readily devised by those skilled in the art.
When an accelerometer is used to detect relati`ve verti-cal movement of the platforms as described hereinabove, the accelerometer must be placed on the movi`ng platform. If the landing platform is stable and the platform supporting the crane is vertically movable, the sensor is placed on the platform on which the crane is mounted. In this case the accelerometer is conveniently placed on the crane boom near the boom sheave so that relative vertical movement of the crane directly above the landing platform is detected. However, when the crane is on a fixed platform and the landing platform is movable with respect thereto, the accelerometer must be placed on the landing platform.
In the preferred embodiment the si`gnal from the accelerometer is converted to an appropriate telemetry signal which may be trans-mitted by radio signal from antenna 130 on the sensing and signal-ing device 110 to a receiving antenna 125 mounted on the crane.
Alternatively, the signal from the accelerometer can be transmitted directly to signal processing equi`pment aboard the crane by a suitable electrically conductive cable suspended from the landing platform to the crane. Other means for transmitting the signal to the control apparatus will be apparent to those skilled in the art and may be adapted as required to accommodate other sensing means.
As described above, the motion compensation cylinder ~ 4Q23 supports the entire weight of the load except for that portion supported by the fast line. Accordingly, the cylinder should have the lift capacity required to handle any load to be lifted by the crane. The stroke of the cylinder, of course, should be sufficient to equal the verti`cal movement to be compensated.
The performance capacity of the pump or pumps necessary to raise the load will depend on the size of the cylinder, the anticipated load, and the anticipated rise rate. The size and capacity of pumps, cylinders and the li`ke necessary to produce the required lifting capacity, however, may be readily determined and matched with appropriate sensing and control apparatus to raise and lower the hook in direct relation to the signal received from the motion sensor selected.
Since the motion compensation cylinder acts only on the cable between the crane boom and the load, the distance which the p;ston moves is directly related to but not necessarily equal to the movement sensed. For example, if the fast line is held steady while the piston is raised in the embodiment illustrated in FIGURE 1, the distance the stationary block 27 is raised is not equal to the distance the hook block 21 is raised since the fast line is not moved with the stationary block. This variance, however, is directly related to the number of reeves and may be readily compensated for in the control circuits. As the number of reeves is increased the variance decreases.
~y supporting the motion compensation cylinder 22 between the lateral members 23 and 24 to pivot about the axis of the boom sheave 20 as illustrated in FIGURES 1~ 2 and 3. addition-al advantages are obtained. For example, hydraulic fluid may be conducted from the pump to the cylinder 22 through a fixed hard pressure line 133 secured to or forming part of the boom 17.
1~94~3 Furthermore, the fluid may be injected directly into the cylinder through the pivot pin 132 supporting the cylinder 22 through a swivel connector 134, thus totally eliminating the use of flexible pressure hoses in the hydraulic system.
An alternat;ve embodi`ment of the invention is illustrated in FIGURE 4. In this embodiment the cable 18 passes over the boom sheave 20 and through a single grooved travelling block 120.
The end of the cable i`s attached to the pi`ston rod 126.
It will thus be observed that in this embodiment only one-half of the weight of the load is supported by the cylinder 122.
However, the pi'ston must travel twice the distance that load hook 119 travels. In this embodiment the cylinder 122 is sus-pended directly from the pivot axi`s of the boom sheave ~0, thus the motion compensation cyli-nder, if excessi'vely long, may interfere with the lift height capacity of the crane. However, the embodiment illustrated in FIGURE 4 may be more readily adapted to the ex;sting crane equipment. It will be understood that the piston rod 126 may support a multiple-sheaved stationary hlock and a multiple-sheaved hook block as shown in FIGURE 1.
Furthermore, the cyli'nder need not depend from the axis of the boom sheave but may depend from some other portion of the boom.
It is not necessary that the pumps be capable of supplying sufficient pressure to lift the entire weight of the load if the motion compensation apparatus is only required to coordinate the movement of an empty load hook with the movement of a pitching deck as when attempting to remove cargo from a pitching deck with a fixed crane. For example~ the motion compensation apparatus need only be sufficient to raise and lowerthe load hook in synchronization with the pitching deck.
Accordingly, as the load i`s lifted, the weight on the piston may ~n ,023 overcome the pressure in the cylinder and cause the piston to rest on the bottom of the cylinder. In this case the motion compensa-tion apparatus acts merely as a line tensioning means to maintain constant tension on the cable supporting the empty load hook so that load hook movement may be coordi:nated with the movement of a pi:tching deck while attaching the load hook to a cargo to be lifted. Once the crane is operated to lift the cargo, the piston contacts. the bottom of the cyli`nder and the crane operates in its normal fashi:on.
For handli`ng light loads or when operating only as. a cab.le tensioni.ng apparatus, i.t is not necessary that the cyli:nder be operated with hydraulic fluid. Pneumatic cylinders may suffice for li.ght load operati.ons and offer quicker response than hydrau-lic sys.tems.
Another embodiment of the invention is illus.trated i:n FIGURE 7. I:n this embodiment the cylinder 22 is mounted wi:thin and parallel with the boom 17. The cable 18 i`s reeved in conven-tional manner around the boom sheave (stationary block) 20 and the travelling block 21 which s-upports the load hook 1~. The boom 17 i:s modi:fi:ed, however, to include an idler sheave 200, preferably b.elow ahd i:nboard from the boom sheave 20 as illustrated.
A piston rod 26 transversely moveable with respect to the boom 17 extends from the cylinder 22 and carries a compensa-ting sheave 201 on the free end thereof. The compensating sheave 201 i.s positioned to engage the inboard cable reeved between b.oom sheave 20 and travelli`ng block 21. Thus, as the piston rod26 i.s withdrawn into cylinder 22, the cable reeved between the hoom sheave 20 and travelling block 21 is drawn over the idler sheave 200 and boom sheave 20, effectively varying the distance between boom sheave 20 and travelli:~ng block 21 i`n direct propor-09~023 tion to the lateral movement of the compensation sheave 201.Since the compensation sheave 201 does not engage the fast line, the embodiment of FIGURE 7 is the mechanical equivalent of the embodiment of FIGURE 2 with regard to the effect of movement of the piston to raise and lower the hook. This embodiment, however, offers the additional advantages of requiring only minimum modification of the boom structure and, since the cylinder is mounted parallel with the boom and does not vary the location of the original boom sheave 20 of the crane, vertical lift capacity of the crane i`s completely unaffected by the modi-fication. Furthermore, s;nce the load is supported directly by the idler 200 and boom sheave 20, the piston rod and cylinder are isolated from side loads caused by horizontal movement of the boom or load. The boom must only be modified so that the idler 200 as well as the boom sheave 20 may support the anticipated load and to accommodate the cylinder within the boom.
Use of a fluid system to compensate for relative vertical movement as described herein provides a unique safety feature. In many instances a crane operator attempting to off-load a cargo package from a moving barge deck with a cranemounted on a fixed deck (or vice YerSa) may inadvertently hook onto the barge itself while the barge is riding the crest of a wave. As the wave subsides~ the barge is rapidly lowered with respect to the crane. If the hook has accidentally eng3ged the harge rather than the cargo7 the crane is subjected to the entire weight of the barge. This usually results in damage to the crane, the barge, or both. However5 the high pressure line 102 between the pump 105 and the cylinder may be provided with a pressure relief valve which vents to the reservoir when the weight on the hook exceeds a predetermined amount. Accordingly, if the 10~?4023 hook engages the barge and the hook is subjected to loads greater than the load capacity of the crane, the relief valve vents and the piston is permitted to be lowered with respect to the cylinder, thus permitting the hook to be lowered with the barge without overloading the crane.
From the foregoing it will be apparent that the princi-pales of the invention may be employed with various load transfer apparatus where compensation of relative vertical movement is desired. It will be understood~ therefore, that although the invention has been described with particular reference to specific embodi`ments thereof, the forms of the invention shown and described in detail are to be taken as preferred embodiments of same, and that vari`ous changes and modifications may be resorted to without departing from the spirit and scope of the invention as defined by the appended clai`ms.
Claims (2)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a crane for transferring loads between a first platform and a second platform vertically movable with respect to each other and employing a boom supported by said first platform, a cable depending from said boom and supporting hook means, and winch means to move said cable, relative motion compensation apparatus comprising:
(a) cylinder means supported by said boom, (b) piston means mounted for vertical reciprocal movement in said cylinder, (c) first sheave means supported by said piston, (d) second sheave means supporting said hook means with said cable reeved between said first sheave means and said second sheave means, (e) sensing means for generating a signal proportional to relative vertical movement of said first platform and second platform, and (f) means responsive to said signal for supplying fluid to and removing fluid from said cylinder, thereby to raise and lower said piston in response to said signal.
(a) cylinder means supported by said boom, (b) piston means mounted for vertical reciprocal movement in said cylinder, (c) first sheave means supported by said piston, (d) second sheave means supporting said hook means with said cable reeved between said first sheave means and said second sheave means, (e) sensing means for generating a signal proportional to relative vertical movement of said first platform and second platform, and (f) means responsive to said signal for supplying fluid to and removing fluid from said cylinder, thereby to raise and lower said piston in response to said signal.
2. In a crane for transferring loads between a first platform and a second platform vertically movable with respect to each other and employing a boom supported by said first platform, a cable depending from said boom and supporting hook means, and winch means to move said cable, relative motion compensation apparatus comprising:
(a) cylinder means mounted substantially parallel with said boom, (b) piston means mounted for reciprocal movement in said cylinder, (c) boom sheave means carried by said boom and over which said cable is drawn, (d) hook means supported by said cable depending from said boom sheave, (e) sheave means connected to said piston means and adapted to engage said cable between said boom sheave means and said hook means, (f) idler means carried by said boom to engage said cable between said hook means and said sheave means connected to said piston, (g) sensing means for generating a signal proportional to relative vertical movement of said first platform and second platform, and (h) means responsive to said signal for supplying fluid to and removing fluid from said cylinder, thereby to cause said piston means to move the piston connected sheave means and thereby move said hook means vertically with respect to said boom sheave in response to said signal.
(a) cylinder means mounted substantially parallel with said boom, (b) piston means mounted for reciprocal movement in said cylinder, (c) boom sheave means carried by said boom and over which said cable is drawn, (d) hook means supported by said cable depending from said boom sheave, (e) sheave means connected to said piston means and adapted to engage said cable between said boom sheave means and said hook means, (f) idler means carried by said boom to engage said cable between said hook means and said sheave means connected to said piston, (g) sensing means for generating a signal proportional to relative vertical movement of said first platform and second platform, and (h) means responsive to said signal for supplying fluid to and removing fluid from said cylinder, thereby to cause said piston means to move the piston connected sheave means and thereby move said hook means vertically with respect to said boom sheave in response to said signal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA352,656A CA1094023A (en) | 1977-07-14 | 1980-05-26 | Vertical motion compensated crane apparatus |
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US81552977A | 1977-07-14 | 1977-07-14 | |
| US815,529 | 1977-07-14 | ||
| US05/838,085 US4179233A (en) | 1977-07-14 | 1977-09-30 | Vertical motion compensated crane apparatus |
| US838,085 | 1977-09-30 | ||
| CA307,041A CA1088894A (en) | 1977-07-14 | 1978-07-10 | Vertical motion compensated crane apparatus |
| CA352,656A CA1094023A (en) | 1977-07-14 | 1980-05-26 | Vertical motion compensated crane apparatus |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1094023A true CA1094023A (en) | 1981-01-20 |
Family
ID=27426093
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA352,656A Expired CA1094023A (en) | 1977-07-14 | 1980-05-26 | Vertical motion compensated crane apparatus |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1094023A (en) |
-
1980
- 1980-05-26 CA CA352,656A patent/CA1094023A/en not_active Expired
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