US3508667A - Antipendulation crane with damped sheave on bight of hoist rope - Google Patents

Description

Aprrxl 28, 1970 s. COMMORA 3,503,667

ANTIPENDULATION CRANE WITH DAMPED SHEAVE ON EIGHT OF HOIST ROPE Filed June 5, 1968 elm emor United States Patent 3,508,667 ANTIPENDULATION CRANE WITH DAMPED SHEAVE 0N BIGHT 0F HOIST ROPE Lawrence S. Commora, Duluth, Minn., assignor to Lake Shore, lnc., Iron Mountain, Mich., a corporation of Michigan Filed June 3, 1968, Ser. No. 733,998 Int. Cl. B66c 23/06 US. Cl. 212-58 Claims ABSTRACT OF THE DISCLOSURE The crane damps pendulation of the load as a consequence of slewing of the crane by supporting the load from a frictionally damped sheave rolling on the bight of the rope between the spaced boom ends.

BACKGROUND OF THE INVENTION Field of the invention As a boom type crane is slewed the load tends to pendulate tangential to the arc of the boom end. This results in time loss waiting for the load to stop swinging. In the interest of speeding up the crane duty cycle it is desirable to reduce this pendulation.

Description of the prior art Prior solutions have centered on supporting the load hook on the dead ends of two hoist ropes reeved over spaced sheaves on the boom end so the ropes converged on the hook. This requires simultaneous hoisting or lowering of both ropes to keep the load centeredand this is not easily achieved in practice. Some of the art adds a tag line to restrain outward movement of the load. This involves additional problems to keep the tag line properly tensioned. None of the prior approaches has met with commercial success. Without the tag line the load merely tends to pendulate at about 45 to the tangent and with the tag line the tensioning problems result in too costly mechanism.

SUMMARY OF THE INVENTION By imposing a frictional drag on the rolling of a load block on the bight of a hoist line reeved over spaced sheaves on the boom end the load is free to move in the tangential direction but with restraint which rapidly damps the oscillation of the load. Both ends of the rope are taken in or paid out so the block only rolls on the bight to accommodate any differences in the rate of each end. By rolling the block always centers and the load on the rope is uniform.

FIG. 1 is a schematic perspective view of the crane;

FIG. 2 is a detailed vertical section of the damped block; and

FIG. 3 is an end view showing how the block can roll on the bight of the line.

The drawings illustrate, in schematic form, a deck crane having a base mounted on the fixed pylon 12 for rotation about a vertical axis (this motion being known as slewing) and carrying a boom 14 comprised of spaced booms 14a and 14b pivoted at 16 for raising and lowering the boom (lufling). Wire rope 18 is reeved 3,508,667 Patented Apr. 28, 1970 "ice over a suitable winch drum to control the luffing the details of this being unimportant to the present invention.

Both ends on the hoist rope 20 are dead ended on the hoist winch drum 22 and the rope is reeved over sheaves 24a, 2412 at the top of the base structure and then over sheaves 26a, 261) at the ends of booms 14a, 14b. Block 28 rides on the bight of the line between sheaves 26a and 26b. In practice rope 20 is made in two pieces spliced at 30 so the lay of the rope can be opposite for each side of the hoist system to thereby minimize rope twist effects in the Way of block rotation as the block is loaded and unloaded. The splice is offset enough to not interfere with the rolling of block 28 on the bight of the line. The load hook 32 is supported from clevis 34 carried by the block. Since the sheaves 36 of block 28 rides or rolls on the bight of the rope it will tend to center itself between the boom ends but when the boom is slewed inertia will cause the sheave to roll towards the following boom. This will then tend to set up pendulation of the load after the slewing is stopped. If the load were hung from the two lines without the block it would still attempt to pendulate causing sharp increases in the loading of the leading line when accelerating, and in the following line when decelerating. Under conditions of too rapid speed change by the operator, the load will even transfer entirely to one cable and then come back onto the other with a jerk as pendulating does actually occur. Also on conditions of list or trim the load may increase sharply or transfer entirely to one cable. The present block, however, allows the load to remain somewhat equally supported by both lines regardless of pendulating list or trim. At the same time pendulation is rapidly damped out through the nominal resistance to rolling deliberately built into the block.

The block sheave 36 is keyed to shaft or axle 38 journaled. in friction liners 40 (or brake lining material) in the block cheeks 42. Therefore, rolling of the sheave 36 (and the block 28) along the bight of rope 20 is frictionally resisted and the pendulation induced by slewing is rapidly damped. Since the load on the friction liners 40 increases with increasing load carried on the hook 32 the frictional resistance is proportional to the load which is a desirable feature. Shaft 38 is centered in the block by nylon plugs or pads 44 carried by cover plates 46. For this usage the plugs are adequate and act as thrust hearings to the slight extent required.

I claim:

1. A crane comprising,

a base rotatable about a vertical axis,

a boom mounted on the base,

laterally spaced sheaves on the free end of the boom,

a hoist winch mounted on the base,

a rope leading from the winch over both sheaves and back to the winch so both ends are taken in or paid out simultaneously,

a block carried on the bight of the rope between the sheaves for rolling on the rope,

means damping rolling of the block on the bight of the rope, and

load support means carried by the block.

2. A crane according to claim 1 in which the damping means exerts an increased restraint with an increased load carried by the load support means.

- 4 3. A crane according to claim 2 in which the damping References Cited means acts between the block sheave and the block.

4. A crane according to claim 3 in which the block UNITED STATES PATENTS 297,128 4/1884 Garrett 254192 sheave is fixed on an axle journaled in the checks of the block and the damping means comprises a friction 5 liner between the axle and the cheeks and serves as the 3,062,383 11/1962 Claesson. 3,191,779 6/1965 Thomson.

bearing for the axle.

5. A crane according to claim 1 in which the rope is HARVEY HORNSBYPnmary Exammer made in two parts spliced near the block and having US. Cl. X.R.

opposite lay to minimize rope twist. 10 l8883; 254-192

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