US 3265360 A
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2 Sheets-Sheet l JOHANN TAX ALSO KNOWN AS HANS TAX TOWER CRANE WITH AUXILIARY HOIST Aug. 9, 1966 Flled June 2 1964 2 Sheets-Sheet 2 Arr/mm J flflj .751 WW Q fig: '7"
JOHANN TAX ALSO KNOWN As HANS TAX TOWER CRANE WITH AUXILIARY HOIST Filed June a, 1964 United States Patent 3,265,360 TOWER CRANE WITH AUXILIARY HOEST Johann Tax, also known as Hans Tax, 3 Potsdamer Strasse, Munich 23, Germany Filed June 2, 1964, Ser. No. 372,064 Claims priority, application Belgium, June 5, 1963, 507,097, Patent 633,231 Claims. (Cl. 254-173) This invention relates to tower cranes of the type commonly employed in housing construction, and more particularly to a tower crane equipped with an auxiliary hoist.
It is known to increase the normal load lifting capacity of tower cranes by the provision of an auxiliarly hoist equipped to raise a load closely adjacent the vertical tower axis so as to reduce the torque exerted by the load to a value substantially smaller than the torque exerted by a similar load suspended from the jib of the crane. The auxiliary hoist permits the lifting of loads which would normally exert a greater torque than is consistent with the fiexural strength of the tower structure.
In view of the high tensions in the cables or ropes of the auxiliary hoists, defects in the hoist mechanism, including the cable, can have particularly serious consequences.
This invention is concerned with safety device for preventing or mitigating the consequences of such defects, and more particularly with a device which applies brakes to the hoist cables in the event of a defect.
In one of its aspects, the invention provides the top portion of a tower in a crane of the type described with pulleys. Two cables, ropes, or similar elongated tension members, hereinafter referred to as cable members are trained over the pulleys. Each cable has an end portion which is attached to a cable drum and another portion which depends from a pulley and is secured to a load supporting member which is common to the two cable members. Motors and brakes are provided for rotating the pulley drums and for arresting their rotation. The cable members are under tension when supporting a load, and a sensing device is provided for sensing the quantitative relationship of the tensions. Brake actuating means are operatively connected to the sensing device and to the brakes for actuating the latter, and for thereby arresting rotation of at least one brake drum in response to a predetermined sensed relationship of the cable tensions.
Other features and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which FIGURE 1 illustrates a tower crane equipped with the safety device of the invention in a fragmentary perspective view, and FIG- URE 2 illustrates the cable arrangement in a modified embodiment.
The crane 10 is illustrated only to the extent needed for an understanding of the invention, there being shown the upper portion of the tower 12 and the rotary head 14. The tower, as far as illustrated, has two telescopically engaged sections 16, 18 which may be moved relative to each other by means not illustrated to adapt the height of the tower to specific requirements. An annular bearing 20 on the tower section 18 supports a turntable 22 which forms the supporting platform for the rotatable crane superstructure. A pillar 24 extends axially upward from "ice the platform 22. The jib 28 and an arm 30 carrying a counterweight 32 extend in opposite, approximately horizontal directions from the pillar 24, and are suspended from the topmost portion 26 of the pillar by cables 34, 36, as is conventional. The hoisting mechanism associated with the jib has not been shown since it may be entirely conventional and is not in itself a part of this invention.
Two horizontal beams 38, 40 are attached to opposite vertical faces of the tower section 18 in such a manner that the two ends of each beam project slightly beyond the tower section in opposite directions. The beams constitute brackets the ends of which carry pairs of pulleys, the four ends of the two beams thus supporting eight pulleys 42, 44, 46, 48, 50, 52, 54, 56. The pulleys 66, 68 are jointly attached to a load 64.
Two cable drums 58, 60 are mounted on the base of the tower 12, not itself shown in the drawing. The cable drums are respectively connected to electric brake motors 88, 96 to constitute winches. One end of a steel cable 61 is wound on the drum 58. The free portion of the cable is trained in sequence over a pulley 56 on one end of the beam 40, a pulley 52 on the other end of the beam, the load supporting pulley 66, the other two pulleys 50, 54 on the beam 40, and downward toward a lever 71 mounted on the tower base by means of a pivot 72. The end of the cable 61 is attached to the arm 74 of the lever 71.
A second steel cable 62 is attached in a corresponding manner to the drum 60, and trained over the pulleys 42, 46 on the beam 38, the load supporting pulley 68, and the pulleys 48, 44 on the beam 38. The end of the cable 62 is attached to the arm of the lever 71. Pivotal movement of the lever 71 is opposed by two helical compression springs 76, 78. An extension rod on the lever arm 70 carries a cam 82 which engages the actuating pin 84 of a switch 86. The switch is arranged in circuit with the brake motors 88 and 90 as indicated by the conductors 92. It will be understood that the motors 88 and 90 are equipped with the usual starting and operating controls which are arranged in an operators cab, not shown. The circuit partly represented by the conductors 92 may include non-illustrated relays and similar circuit elements conventional in themselves and commonly employed in brake motor circuits.
The motors 88, 10 are synchronized, and the cable drums 58, 60 are of equal diameter and of suflicient axial length to accommodate the cables 61, 62 in a single layer when the load 64 is at the highest point to which it is intended to be raised. The cables are of equal diameter. Under all normal operating conditions, the tensions in the cables 61, 62 are closely similar or equal. Any small or temporary differences are absorbed by the springs 76, 78. The lever 71 maintains a fixed angular position on the pivot 72. I
The resultant of the downward forces in the cables 61, 62 is represented by a vector which approximately coincides with the vertical tower axis because of the symmetrical arrangement of the pulleys 4256 about that axis. The individual bending torque components associated with the cables 61, 62 normally balance each other.
In the event of a defect in one of the two hoist arrangements which are each constituted by a cable, pulleys, a drum, and a motor, the arms 70, 74 of the lever 71 are unequally loaded, and the imbalance, if significant to affect the safety of the tower, is also sufiicient to overcome the resistance of the springs 76, 78. The switch 86is thereby operated to actuate the brakes of the motors S3, 90. Because of the characteristics of a motor equipped with an internal electrically operated brake, the drums 58, 6d are not stopped abruptly. The brake arrangement has inherent damping properties.
When the imbalance of cable tension is due to increased friction. in a pulley hearing which lacks lubrication or is otherwise defective, damping of the brake action is not as vitally important as in the event of a cable break. Although it is standard practice to select cables having a collective carrying capacity of at least twice the greatest load to be lifted, the sudden transfer of the supported weight to one cable when the other one breaks would impose a dynamic stress on the intact cable which may lead to failure if the brake were not applied in a gradual manner.
The illustrated very simple mechanical sensing device mainly constituted by the lever 71 is preferred because it is well suited by its ruggedness to the conditions under which it operates. Other sensing devices, however. will readily suggest themselves to those skilled in the art. A signal indicative of the tension in each cable may be derived from the pressure exerted on a hearing by a pulley over which the cable is trained. A similar signal may be derived from the current flowing through each of the Winch motors 83, 9t) when the motor actuates rotation of the associated cable drum. Equipment commercially available may thus be employed for generating a cable tension signal, for comparing the signals, and for actuating cable drum brakes if the cable tensions do not maintain a desired quantitative relationship. The lever 71 and the associated illustrated elements of the invention operate in an analogous manner.
Because of the close proximity of the beams 38, 40 to the vertical tower axis, the bending stresses exerted by the load 64 on the tower 12 in the event of failure of one cable are relatively small. It is essential therefore that the vector which represents the vertical forces in each individual cable be as close to the tower axis as possible, and that its spacing from the axis be no more than a small fraction of the tower height, as is evident from the drawings.
FIGURE 2 shows a preferred cable arrangement. All parts besides the cable are the same as in the embodiment of FIG. 1 and are provided with the same reference numerals. A first steel cable N0 is coming from cable drum 60 and is trained in sequence over pulley 44 on beam 38, pulley 48 on beam 38, pulley 66 of load 64, pulley 50 of beam 40 and pulley 54 of beam 40. The free end of steel cable 62 is fixed to one of the arms 7 it, 74 of lever '71.
A second steel cable 102 is coming from cable drum 58 and is trained in sequence of .a pulley 56 on beam 40, pulley 52 on beam 40, pulley 68 of load 64, pulley 46 on beam 38 and pulley 42 on beam 38 to the other of said arms 70, 74 of the lever '71.
It is to be remarked that cable 1% runs over beam 38 as well as over beam 40 and that cable 102 runs over beam 4% as well as over beam 38; this means that in the event of rupture of one of the cables the symmetry of load distribution does not get lost.
It should be understood, of course, that the foregoing disclosure relates to only a preferred embodiment of the invention, and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.
What is claimed is:
1. A crane comprising, in combination:
(a) an elongated tower having a normally vertical longitudinal axis;
(b) two cable members having respective first longitudinal portions guided on a top portion of said tower,.
and respective second portions depending from said first portions;
(0) joint load supporting means attached to said second portions for transmitting the weight of a supported load to said cable members;
(d) Winch means operatively connected to said cable members for tensioning the same and for thereby raising a load supported on said second portions, said winch means including brake meansfor arresting movement of the connected cable members;
(e) sensing means for sensing the relationhip of the respective tensions in said cable members; and
(f) brake actuating means operatively connected to said sensing means and to said brake means, and responsive to a predetermined sensed relationship of said tensions for actuating said brake means.
2. A crane as set forth in claim 1, wherein the tensions in said two second cable members have a resultant vector which substantially coincides with said axis when a load is supported on said two cable members.
3. A crane as set forth in claim 1, wherein said winch means include two winches, said cable members having respective third portions attached to said winches, and said brake actuating means being operatively connected to said winches for arresting the same in response to said predetermined relationship.
4. A crane as set forth in claim 1, wherein said sensing means include a pivotally mounted two-armed lever, said cable members'being respectively attached to the arms of said lever, and said brake actuating means being responsive to pivoting movement of said lever.
5. A crane as set forth in claim 4, further comprising yieldably resilient means opposing said pivoting movement.
6. A crane as set forth in claim 1, wherein'said winch means include two rotatable cable drum means respectively attached to said cable members and said winch means and said brake means jointly include two brake motors respectively connected to said cable drum means for rotating the same and for arresting rotary motion of said cable drum means.
7. A crane as set forth in claim 1, wherein the tension of each of said cables defines a vertical vector closely adjacent said longitudinal axis, the horizontal spacing of said vector from said axis being not greater than a small fraction of the height of said tower.
8. A crane comprising, in combination:
(a) an elongated tower having a normally vertically extending longitudinal axis;
(b) pulley means on a top portion of said tower,
(c) two cable members;
(d) two rotatable cable drum means;
(e) load supporting means for transmitting the weight of a load to said cable members, said cable members each having 1) an end portion attached to a respective one of said cable drum means,
(2) an intermediate portion trained over said pulley means, and
(3) a dependent portion downwardly extending from said pulley means, said load supporting means including a load supporting member secured to the dependent portions of said two cable members; 7
(f) motor means for rotating each of said cable drum means, whereby said cable members are tensioned when supporting a load;
(g) brake means for arresting rotation of said cable drum means;
(h) sensing means for sensing the relationship of the respective tensions in said cable members; and
(i) brake actuating means operatively connected to said sensing means and to said brake means for actuating said brake means and for thereby arresting rotation of at least one of said cable drum means in response to a predetermined sensed relationship of said tensions.
9. A crane as set forth in claim 8, wherein said sensing means include a pivotally mounted two armed lever, said cable members having respective other end portions respectively attached to the arms of said lever, and said brake actuating means being responsive to pivoting movement of said lever.
10. A crane as set forth in claim 9, wherein said brake means and said motor means jointly constitute two electric brake motors in respective engagement with said cable References Cited by the Examiner UNITED STATES PATENTS 5/1941 Severson 254173 9/1954 Green 254-173 10 EVON C. BLUNK, Primary Examiner. H. HORNSBY, Assistant Examiner.