Title:
DEVICE FOR ACHIEVING PERMANENT EQUILIBRATION IN TOWER CRANES
United States Patent 3642148
Abstract:
A device for obtaining permanent equilibration in tower cranes of the type including a load jib, over which a carriage fitted with a lifting hook travels, and a jib over which a carriage carrying a counterweight is adapted to be shifted, said device including in combination: means for measuring the moment resulting from the weight of the load, on the one hand, and from the position of the load carriage on the jib, on the other hand, means for shifting the counterweight carrier on the corresponding jib, and means for increasing the duration of the loading operation in order to enable the counterweight carrier to move only slowly and progressively as the load moment varies, without any disorderly motions.
US Patent References:
Crane
Faure et al. - January 1947 - 2413701
Load responsive counterbalancing crane
Leavesley - March 1966 - 3240353
Translating means for the counterbalancing carriages in tower cranes
Durand - May 1968 - 3381826
Crane
Faure et al. - January 1947 - 2413701
Load responsive counterbalancing crane
Leavesley - March 1966 - 3240353
Translating means for the counterbalancing carriages in tower cranes
Durand - May 1968 - 3381826
Application Number:
05/039241
Publication Date:
02/15/1972
Filing Date:
05/21/1970
View Patent Images:
Export Citation:
Assignee:
Societe Anonyme Richier (Paris, FR)
Primary Class:
Other Classes:
212/278, 212/198
International Classes:
B66C9/14; B66C23/72; B66C9/00; B66C23/00; B66C23/72
Field of Search:
212/48,49
Primary Examiner:
Hornsby, Harvey C.
Assistant Examiner:
Maffei, Merle F.
Claims:
What is claimed is
1. A device for obtaining permanent equilibration in tower cranes of the type including a load jib, a carriage fitted with a load-lifting hook, a winding hoist cable connected at its free end to said carriage for imparting movement to the latter over said jib, a second jib, a carriage supporting a counterweight adapted to be shifted over said second jib, comprising the combination of means for measuring the moment resulting from the weight of the load on the one hand, and from the position of the load carriage on the load jib on the other hand, means for shifting the counterweight-supporting carriage on said second jib, and means for increasing the duration of the loading operation to enable said last-mentioned carriage to move slowly and progressively only in response to variations in the load moment while eliminating sudden motions thereof, the increase in the duration of the loading operation being in response to an increase in the length of hoist cable unwound from its winding end, and a device for temporarily slackening the tension in said hoist cable.
2. A device as claimed in claim 1, wherein the device slackening the tension of the cable temporarily is hydraulic, and comprises a multistrand block interposed between the fixed point of the hoist cable and the lifting hook, the first set of sheaves of said block being fast, while the second set of sheaves is mounted on a movable support connected to the fast support of the first set of sheaves by a single action hydraulic jack, the working chamber of said jack being connected to at least one oleopneumatic accumulator adjusted to a given pressure, in order that, at the time of the loading operation, the tension of the cable causes first the shifting of the movable support of said second set of sheaves towards said first set of sheaves, and then, only when said support has completed its travel, the elevation of the load.
1. A device for obtaining permanent equilibration in tower cranes of the type including a load jib, a carriage fitted with a load-lifting hook, a winding hoist cable connected at its free end to said carriage for imparting movement to the latter over said jib, a second jib, a carriage supporting a counterweight adapted to be shifted over said second jib, comprising the combination of means for measuring the moment resulting from the weight of the load on the one hand, and from the position of the load carriage on the load jib on the other hand, means for shifting the counterweight-supporting carriage on said second jib, and means for increasing the duration of the loading operation to enable said last-mentioned carriage to move slowly and progressively only in response to variations in the load moment while eliminating sudden motions thereof, the increase in the duration of the loading operation being in response to an increase in the length of hoist cable unwound from its winding end, and a device for temporarily slackening the tension in said hoist cable.
2. A device as claimed in claim 1, wherein the device slackening the tension of the cable temporarily is hydraulic, and comprises a multistrand block interposed between the fixed point of the hoist cable and the lifting hook, the first set of sheaves of said block being fast, while the second set of sheaves is mounted on a movable support connected to the fast support of the first set of sheaves by a single action hydraulic jack, the working chamber of said jack being connected to at least one oleopneumatic accumulator adjusted to a given pressure, in order that, at the time of the loading operation, the tension of the cable causes first the shifting of the movable support of said second set of sheaves towards said first set of sheaves, and then, only when said support has completed its travel, the elevation of the load.
Description:
The present invention relates to a device for obtaining permanent equilibration in tower cranes.
For many years, attempts have been made for achieving this result by shifting the counterweights of such cranes.
Many methods and devices have been devised for the purpose, but all of them come up against the problem set by the load being loaded and lifted within a very short time, which operations correspond to extreme positions of the counterweight. Moreover, the balance position during the operation is disturbed by dynamic effects, the latter being amplified by the overall elasticity of the crane.
The present invention relates to a device enabling a permanent balance to be obtained, whatever the load hanging from the hook of the carriage and the position of said carriage on the jib may be, this result being achieved by causing the counterweight carrier to move over the corresponding jib.
Said device for balancing a tower crane permanently includes in combination: means for shifting the counterweight carrier along the corresponding jib, means for measuring the moment resulting from the weight of the load, on the one hand, and from the position of the load carriage on the jib, on the other hand, and means for increasing the duration of the loading operation in order to enable the counterweight carrier to move only slowly and progressively as the load moment varies, without any disorderly motions.
In one embodiment of the invention, the means for measuring the load moment are disposed on the tie connecting the load jib to the top of the tower, and in the most common cases they consist of extensometers or some other stress-measuring devices.
Furthermore, the means for shifting the counterweight carrier consist of a speed-reducing motor unit.
In a preferred embodiment of the invention, the increase in the duration of the loading operation is obtained by increasing the length of the fixed end of the hoist cable by means of various windings, on the one hand, and by using an arrangement temporarily slackening the tension of said cable, on the other hand.
This increase in the duration of the loading operation is very important, because it gives the counterweight the time to move to achieve the equilibration before the load is actually lifted or laid down.
Preferably, the arrangement for slackening the tension of the cable temporarily is hydraulic, and comprises a multistrand block interposed between the fixed point of the hoist cable and the lifting hook, wherein a first set of sheaves is fast, while a second set of sheaves is mounted on a movable support connected to the fast support of the first set by a single-action hydraulic jack, the working chamber of said jack being connected to at least one oleopneumatic accumulator adjusted to a given pressure, in order that, at the time of the loading operation, the tension of the cable causes first the shifting of the movable support of the second set of sheaves towards the first set of sheaves, and then, only when said support has reached a position wherein the pressure generated in the accumulators produces at the level of the cables the tension required for lifting the load, the elevation of said load.
The invention will now be described in further detail, with reference to the appended diagrammatic drawing, which illustrates, by way of nonlimiting example, the application of the device of the invention to a tower crane having a horizontal crab jib. In the drawing:
FIG. 1 is a side elevational view of said tower crane,
FIG. 2 is a side elevational view, on an enlarged scale, of the load-carrying jib, and shows the various sheaves returning the hoist cable,
FIG. 3 is a diagram illustrating the path of the hoist cable,
FIGS. 4 and 5 are a side elevational view and a top plan view, respectively, of the device for slackening the tension of the cable, as shown on an enlarged scale.
The tower crane illustrated in FIG. 1 consists, in a known manner, of a tower 2, at the upper part of which a tower head 3 is mounted, which head is integral with the load jib 4 and the counterweight jib 5. A carriage 6, which carries the lifting hook 7, is adapted to travel on the load jib 4. The counterweight jib 5 is likewise provided with a carriage 8, which carries a counterweight 9, which carriage is adapted to be shifted between two positions A and B through the agency of a winch 10 and a cable 12.
According to the invention, said crane is provided with a device ensuring the permanent equilibration thereof, whatever the load carried by the crane and the position of the carriage 6 on the jib 4, and, therefore, the moment of said load with respect to the vertical longitudinal axis of the crane, may be.
Said device is essentially constituted by three means:
an extensometer 13 interposed between the two parts of a tie 14 connecting the jib 4 to the tower head 3,
the above-mentioned winch 10,
a device 16 for slackening the tension of the hoist cable 15, which device acts at the time the load is being loaded.
On the other hand, the hoist cable 15 follows an especially long path, as shown in FIGS. 2 and 3. As a matter of fact, said cable starts from a winch 17 and passes over a sliding sheave 18, over two sheaves 19 disposed at the top of the tower head 3, and over a sheave 20 disposed at the fixed end of the jib 4, and then over the sheaves 22 of a block integral with the lifting hook 7. From said block, the cable 15 passes over a sheave 23 disposed at the free end of the jib 4, and then, after passing over guiding sheaves 24, reaches the slackening device 16 disposed downstream of the anchorage point for said cable.
Said slackening device 16 comprises an eight-strand block having its first set of sheaves 26 keyed to a fast support 27, and its second set of sheaves 28 mounted on a carriage 29 adapted to travel lengthwise over rails 30 integral with a frame 32. Said carriage 29 is connected to the fast support 27 by a single action hydraulic jack 33 provided with a compensation tank. The chamber of said jack is connected to two oleopneumatic accumulators 34 located on the frame 32, while a flow regulator (not shown) is interposed therebetween.
As a result of said arrangement, when the lifting hook 7 is hooked on to a load, and the winch 17 for the cable 15 is operated in a direction to hoist said load, the tension in said cable 15 causes first the second set of sheaves 28 of the eight-strand block to be shifted towards the first set of sheaves 26 under the control of the jack 33. As a matter of fact, during said shifting, the rod of the jack withdraws within the jack body, while the piston of the jack drives the oil in the working chamber of the latter towards the accumulators 34. As a function of both the resisting stress caused by the pressure adjustment in said accumulators and the force applied to the cable, the two sets of sheaves 26, 28 are brought nearer to each other to a corresponding extent, whereby the distance between their centers is increased. As the accumulators store oil from the jack, the pressure increases, and, as a consequence, so does the stress on the cable until said stress becomes equal to the stress created by the weight of the load, whereupon the motion of the slackening device stops, while the load is lifted.
During the event of reduction of the distance between the centers of the sets of sheaves, the cable 15 passing over the block unwinds itself thus by a certain amount which, at the beginning of such motion, is compensated by the other end of the cable winding itself on the winch 17.
As a result, the load is not lifted during said event. The increase in the duration of the loading operation is turned to account for controlling the shifting of the counterweight 9.
As a matter of fact, although the load is not lifted yet, the stress said load exerts on the jib 4 is sensed by the extensometer 13, together with the position of said stress with respect to the vertical longitudinal axis of the tower 2. The extensometer 13 determines thus the moment resulting from said load and from the position thereof, and sends the information to a mechanical, electrical, or the like relay which actuates the speed reducing motor unit 10. The latter shifts then the counterweight 9 by the amount required for ensuring an absolute equilibration of the crane.
As appears from the foregoing, the increase in the duration of the loading operation is of great importance, because it allows not only to shift the counterweight 9, but also to carry out said shifting operation slowly and progressively, so that there are no risks of disorderly movements like those which would occur, due to the inherent elasticity of the various component parts of the crane, in the event of the load being lifted quickly and immediately.
Thus, owing to the slackening device 16, at the time the load begins being lifted the counterweight 9 is in its optimum position, and remains therein as long as the load is not laid down.
Obviously, when the load is laid down, the reverse process takes place. The winch 17 unwinds the cable 15, while the slackening device 16 winds the other end of the cable under the action of the accumulators 34 which supply the pressure required for pushing back the rod of the jack 33 and moving away the second set of sheaves 28 from the first set of sheaves 26, that is, for increasing the distance between the centers of said two sets. The laying down time increased in this way is then long enough for enabling the counterweight 9 to be shifted slowly and progressively towards its initial equilibrating position corresponding to the own moment of the tower crane.
In certain applications, and although the pressure adjustment of the accumulators 34 enables the shifting of the carriage 29 of the device 16 to be limited as a function of the load, electric or mechanical safety devices 35, 36, are provided for stopping said shifting when the load is either insufficient for deserving a shifting of the counterweight, or definitely too high for the capacity of the slackening device.
In a modified embodiment of the present invention, the increase in the duration of the loading operation may be obtained by increasing the flexibility of the crane.
Obviously, the invention is not limited to the sole embodiment of said device just described hereinabove, but covers all modifications thereof within the scope of the appended claims, as well as applications to cranes of other types, such as tower cranes with hinged jibs, tower cranes with hinged jibs and crabs, tower cranes with retractable jibs, and tower cranes with telescopic jibs.
For many years, attempts have been made for achieving this result by shifting the counterweights of such cranes.
Many methods and devices have been devised for the purpose, but all of them come up against the problem set by the load being loaded and lifted within a very short time, which operations correspond to extreme positions of the counterweight. Moreover, the balance position during the operation is disturbed by dynamic effects, the latter being amplified by the overall elasticity of the crane.
The present invention relates to a device enabling a permanent balance to be obtained, whatever the load hanging from the hook of the carriage and the position of said carriage on the jib may be, this result being achieved by causing the counterweight carrier to move over the corresponding jib.
Said device for balancing a tower crane permanently includes in combination: means for shifting the counterweight carrier along the corresponding jib, means for measuring the moment resulting from the weight of the load, on the one hand, and from the position of the load carriage on the jib, on the other hand, and means for increasing the duration of the loading operation in order to enable the counterweight carrier to move only slowly and progressively as the load moment varies, without any disorderly motions.
In one embodiment of the invention, the means for measuring the load moment are disposed on the tie connecting the load jib to the top of the tower, and in the most common cases they consist of extensometers or some other stress-measuring devices.
Furthermore, the means for shifting the counterweight carrier consist of a speed-reducing motor unit.
In a preferred embodiment of the invention, the increase in the duration of the loading operation is obtained by increasing the length of the fixed end of the hoist cable by means of various windings, on the one hand, and by using an arrangement temporarily slackening the tension of said cable, on the other hand.
This increase in the duration of the loading operation is very important, because it gives the counterweight the time to move to achieve the equilibration before the load is actually lifted or laid down.
Preferably, the arrangement for slackening the tension of the cable temporarily is hydraulic, and comprises a multistrand block interposed between the fixed point of the hoist cable and the lifting hook, wherein a first set of sheaves is fast, while a second set of sheaves is mounted on a movable support connected to the fast support of the first set by a single-action hydraulic jack, the working chamber of said jack being connected to at least one oleopneumatic accumulator adjusted to a given pressure, in order that, at the time of the loading operation, the tension of the cable causes first the shifting of the movable support of the second set of sheaves towards the first set of sheaves, and then, only when said support has reached a position wherein the pressure generated in the accumulators produces at the level of the cables the tension required for lifting the load, the elevation of said load.
The invention will now be described in further detail, with reference to the appended diagrammatic drawing, which illustrates, by way of nonlimiting example, the application of the device of the invention to a tower crane having a horizontal crab jib. In the drawing:
FIG. 1 is a side elevational view of said tower crane,
FIG. 2 is a side elevational view, on an enlarged scale, of the load-carrying jib, and shows the various sheaves returning the hoist cable,
FIG. 3 is a diagram illustrating the path of the hoist cable,
FIGS. 4 and 5 are a side elevational view and a top plan view, respectively, of the device for slackening the tension of the cable, as shown on an enlarged scale.
The tower crane illustrated in FIG. 1 consists, in a known manner, of a tower 2, at the upper part of which a tower head 3 is mounted, which head is integral with the load jib 4 and the counterweight jib 5. A carriage 6, which carries the lifting hook 7, is adapted to travel on the load jib 4. The counterweight jib 5 is likewise provided with a carriage 8, which carries a counterweight 9, which carriage is adapted to be shifted between two positions A and B through the agency of a winch 10 and a cable 12.
According to the invention, said crane is provided with a device ensuring the permanent equilibration thereof, whatever the load carried by the crane and the position of the carriage 6 on the jib 4, and, therefore, the moment of said load with respect to the vertical longitudinal axis of the crane, may be.
Said device is essentially constituted by three means:
an extensometer 13 interposed between the two parts of a tie 14 connecting the jib 4 to the tower head 3,
the above-mentioned winch 10,
a device 16 for slackening the tension of the hoist cable 15, which device acts at the time the load is being loaded.
On the other hand, the hoist cable 15 follows an especially long path, as shown in FIGS. 2 and 3. As a matter of fact, said cable starts from a winch 17 and passes over a sliding sheave 18, over two sheaves 19 disposed at the top of the tower head 3, and over a sheave 20 disposed at the fixed end of the jib 4, and then over the sheaves 22 of a block integral with the lifting hook 7. From said block, the cable 15 passes over a sheave 23 disposed at the free end of the jib 4, and then, after passing over guiding sheaves 24, reaches the slackening device 16 disposed downstream of the anchorage point for said cable.
Said slackening device 16 comprises an eight-strand block having its first set of sheaves 26 keyed to a fast support 27, and its second set of sheaves 28 mounted on a carriage 29 adapted to travel lengthwise over rails 30 integral with a frame 32. Said carriage 29 is connected to the fast support 27 by a single action hydraulic jack 33 provided with a compensation tank. The chamber of said jack is connected to two oleopneumatic accumulators 34 located on the frame 32, while a flow regulator (not shown) is interposed therebetween.
As a result of said arrangement, when the lifting hook 7 is hooked on to a load, and the winch 17 for the cable 15 is operated in a direction to hoist said load, the tension in said cable 15 causes first the second set of sheaves 28 of the eight-strand block to be shifted towards the first set of sheaves 26 under the control of the jack 33. As a matter of fact, during said shifting, the rod of the jack withdraws within the jack body, while the piston of the jack drives the oil in the working chamber of the latter towards the accumulators 34. As a function of both the resisting stress caused by the pressure adjustment in said accumulators and the force applied to the cable, the two sets of sheaves 26, 28 are brought nearer to each other to a corresponding extent, whereby the distance between their centers is increased. As the accumulators store oil from the jack, the pressure increases, and, as a consequence, so does the stress on the cable until said stress becomes equal to the stress created by the weight of the load, whereupon the motion of the slackening device stops, while the load is lifted.
During the event of reduction of the distance between the centers of the sets of sheaves, the cable 15 passing over the block unwinds itself thus by a certain amount which, at the beginning of such motion, is compensated by the other end of the cable winding itself on the winch 17.
As a result, the load is not lifted during said event. The increase in the duration of the loading operation is turned to account for controlling the shifting of the counterweight 9.
As a matter of fact, although the load is not lifted yet, the stress said load exerts on the jib 4 is sensed by the extensometer 13, together with the position of said stress with respect to the vertical longitudinal axis of the tower 2. The extensometer 13 determines thus the moment resulting from said load and from the position thereof, and sends the information to a mechanical, electrical, or the like relay which actuates the speed reducing motor unit 10. The latter shifts then the counterweight 9 by the amount required for ensuring an absolute equilibration of the crane.
As appears from the foregoing, the increase in the duration of the loading operation is of great importance, because it allows not only to shift the counterweight 9, but also to carry out said shifting operation slowly and progressively, so that there are no risks of disorderly movements like those which would occur, due to the inherent elasticity of the various component parts of the crane, in the event of the load being lifted quickly and immediately.
Thus, owing to the slackening device 16, at the time the load begins being lifted the counterweight 9 is in its optimum position, and remains therein as long as the load is not laid down.
Obviously, when the load is laid down, the reverse process takes place. The winch 17 unwinds the cable 15, while the slackening device 16 winds the other end of the cable under the action of the accumulators 34 which supply the pressure required for pushing back the rod of the jack 33 and moving away the second set of sheaves 28 from the first set of sheaves 26, that is, for increasing the distance between the centers of said two sets. The laying down time increased in this way is then long enough for enabling the counterweight 9 to be shifted slowly and progressively towards its initial equilibrating position corresponding to the own moment of the tower crane.
In certain applications, and although the pressure adjustment of the accumulators 34 enables the shifting of the carriage 29 of the device 16 to be limited as a function of the load, electric or mechanical safety devices 35, 36, are provided for stopping said shifting when the load is either insufficient for deserving a shifting of the counterweight, or definitely too high for the capacity of the slackening device.
In a modified embodiment of the present invention, the increase in the duration of the loading operation may be obtained by increasing the flexibility of the crane.
Obviously, the invention is not limited to the sole embodiment of said device just described hereinabove, but covers all modifications thereof within the scope of the appended claims, as well as applications to cranes of other types, such as tower cranes with hinged jibs, tower cranes with hinged jibs and crabs, tower cranes with retractable jibs, and tower cranes with telescopic jibs.