WO1994022760A1

WO1994022760A1 - Hoist drum braking system

Info

Publication number: WO1994022760A1
Application number: PCT/US1994/000208
Authority: WO
Inventors: Tsi Kang Suez; John Patrick Truemper
Original assignee: Duff-Norton Company, Inc.
Priority date: 1993-04-04
Filing date: 1994-01-06
Publication date: 1994-10-13
Also published as: AU6084094A

Abstract

Brake apparatus for halting rotation of a hoist drum (10) including an elongated, flexible element (14) forming at least one convolution about the brake drum, and an actuator (36) for tightening the elongated, flexible element about the hoist drum to stop rotation of the hoist drum.

Description

HOIST DRUM BRAKING SYSTEM

TECHNICAL FIELD

This invention relates to hoist equipment incorporating a rotatable hoist drum. More particularly, the apparatus of the present invention includes brake apparatus cooperable with a hoist drum to brake the hoist drum and stop rotation thereof in a predetermined direction of rotation. The arrangement may, for example, be employed as a backup to a primary hoist motor brake and utilized to arrest movement of the drum and its suspended load.

BACKGROUND ART

Hoist safety brakes are known in the prior art and such mechanisms are generally characterized by their relative complexity and high expense.

U.S. Patent No. 4,216,848, issued August 12, 1980, discloses an auxiliary brake for hoists and the like which is activated by a centrifugal mechanism which senses over-speeding of the motor shaft. With such an arrangement there is an essentially uncontrolled lowering of the load and excessive drum speeds prior to activation of the safety brake. This can result in casualty loss and personal injury. Other arrangements exist in the prior art in which the load halt brake is activated when excessive drum speeds occur in the lowering direction.

A search directed to the invention disclosed in this application located the following U.S. Patents: U.S. Patent No. 4,636,962, issued January 13, 1987, U.S. Patent No. 3,807,697, issued April 30, 1974, U.S. Patent No. 4,493,479, issued January 15, 1985, U.S. Patent No. 2,928,505, issued March 15, 1960, U.S. Patent No. 4,257,497, issued March 24, 1981, U.S. Patent No. 2,558,517, issued June 26, 1951, U.S. Patent No. 4,177,973, issued December 11, 1979, U.S. Patent No. 2,273,328, issued February 17, 1942, U.S. Patent No. 4,047,311, issued September 13, 1977, and U.S. Patent No. 1,716,025, issued June 4, 1929.

U.S. Patents Nos. 4,493,479 and 4,257,497 are deemed worthy of special note. U.S. 4,493,479 discloses a hoist drive safety system which employs a band brake partially wrapped about a shaft to halt rotation thereof. U.S. 4,257,497 discloses a vehicle braking system incorporating a circular brake spring which engages the complete periphery of a hub. The invention disclosed and claimed herein provides a more positive and effective means of stopping a hoist drum than would the systems disclosed in the two patents just referenced and discussed.

DISCLOSURE OF INVENTION

The apparatus of the present invention incorporates a rotatable hoist drum for selectively winding and unwinding a hoist or lift line. The hoist drum has an outer surface of substantially circular cross-section.

Brake apparatus is cooperable with the hoist drum to brake the hoist drum and stop rotation thereof in a predetermined rotational direction. The brake apparatus includes an elongated, flexible element wrapped completely about the hoist drum and forming at least one complete convolution about the hoist drum outer surface.

Actuator means is operatively associated with the elongated, flexible element to pull the elongated, flexible element and move the elongated, flexible element relative to the hoist drum between a first position wherein the elongated, flexible element engages the hoist drum outer surface but does not exert substantial braking forces on the hoist drum when the hoist drum is rotated in the predetermined rotational direction and a second position wherein the elongated, flexible element is constricted tightly about the hoist drum outer surface with frictional engagement between the elongated, flexible element and the hoist drum outer surface stopping rotation of the hoist drum in the predetermined rotational direction.

The elongated, flexible element preferably is a wire rope forming a plurality of convolutions about the hoist drum outer surface.

The elongated, flexible element has first and second ends and the actuator means comprises a movable actuator element connected to the first elongated, flexible element end for exerting a pulling force on the elongated, flexible element to move the elongated, flexible element from the first position to the second position.

The apparatus additionally includes mounting means, the second end of the elongated, flexible element being mounted in the mounting means against substantial movement relative to the hoist drum. The actuator means additionally comprises biasing means continuously biasing the actuator element away from the hoist drum. The brake apparatus also includes solenoid means operatively associated with the actuator element to move the actuator element toward the hoist drum against the bias exerted on the actuator element by the biasing means.

Other features, advantages, and objects of the present invention will become apparent with reference to the following description and accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a somewhat diagrammatic, side view of apparatus constructed in accordance with the teachings of the present invention;

Fig. 2 is a view similar to Fig. 1, but illustrating an alternative embodiment of the apparatus; and

Fig. 3 is a view similar to Figs. 1 and 2, but illustrating another alternative embodiment of apparatus constructed in accordance with the teachings of the present invention. MODES FOR CARRYING OUT THE INVENTION

Referring now to Fig. 1, reference numeral 10 designates the rotatable hoist drum of a hoist employed to wind and unwind a hoist line. The remainder of the hoist, including the hoist line, is not illustrated but the hoist can be of any suitable conventional type incorporating a prime mover, a drive train connecting the prime mover to the drum, and a primary hoist motor brake used during normal operation of the hoist to brake the drum against rotation.

The brake apparatus 12 of the present invention serves as a backup to the primary hoist motor brake and is of a fail- safe type for the purpose of braking the hoist drum and stopping rotation thereof in a predetermined rotational direction in the event of failure or malfunction of the primary hoist motor brake.

The brake apparatus 12 includes an elongated, flexible element having an irregular or rough outer surface in the form of a wire rope 14. Wire rope 14 forms a plurality of convolutions about the smooth outer surface of the hoist drum 10, preferably at an end of the hoist drum. For practicing the present invention it has been found suitable to form two and one-half wraps of the wire rope 14 about the hoist drum. The thickness of the wire rope can vary depending upon the hoist and load size; however, the wire rope should have a diameter of at least one sixteenth of the diameter of the drum for most conventional hoist applications.

The lower end of the wire rope 14, as viewed in Fig. 1, is attached to and disposed within a fitting 16. Fitting 16 is threadedly engaged to an end of a control rod 18 slidably disposed within a bushing or guide 20. A lock nut 22 may be utilized in conjunction with the control rod 18 and fitting 16 to adjust the location of the fitting relative to the control rod.

The end of control rod 18 remote from fitting 16 is connected to a spherical link 24. A coil compression spring 26 is disposed about the control rod 18 between the spherical link 24 and guide 20 to exert a force on the control rod in a direction away from the hoist drum.

A housing 30 supports guide or bushing 20 and covers the bushing and other structure operatively associated therewith. An actuator lever 32 is pivotally mounted within housing 30 about a pivot pin 34 attached to the housing. The actuator lever 32 is pivotally movable between the solid line position shown in Fig. 1 to the dash line position shown in Fig. 1 about the pivot pin.

Spherical link 24 provides a connection between actuator lever 32 and control rod 18 whereby pivotal movement of the actuator level in a clockwise direction, as viewed in Fig. 1, will cause the control rod 18 to move to the right against the bias exerted thereon by coil compression spring 26. In like manner, a counter clockwise movement of actuator lever 32 will correspond with movement of the control rod 18 to the left under the influence of spring 26.

An actuator solenoid 36 is mounted within housing 30 and has an arm or plunger 38 connected to actuator lever 32 by link 40. When the solenoid 36 is energized, the arm or plunger 38 will retract into the solenoid housing and pull the actuator lever 32 to its solid line position as depicted in Fig. 1. When the solenoid is de-energized, spring 26 will pivot the actuator lever 32 to its dash line position.

The upper end of wire rope 14, as viewed in Fig. 1, is swaged or otherwise attached to a fitting 42. Fitting 42 and lock nut 44 operatively associated therewith are threadedly engaged with a reaction rod 46 slidable within a guide 48. The reaction rod 46 has an enlarged head 50. Head 50 engages a plate 52 slidably disposed within a cavity formed in guide 48. One or more bevel spring washers 54 are sandwiched between the movable plate 52 and the guide. The bevel spring washers will distort when reaction rod and plate 52 move to the right relative to the guide and exert a biasing force resisting such movement. A microswitch 56 is connected to the guide and will be tripped to a closed position when the reaction rod head 50 moves to the right to a predetermined extent. The microswitch 56 is operatively connected to a signal light 58 on the exterior of housing 30 so that actuation or closure of the switch will light the signal light 58.

When the hoist is in operation, drum 10 will rotate in either a clockwise or counter clockwise direction when hoisting or lowering a load. Brake apparatus 12 will not react with nor apply any meaningful braking forces to the hoist drum when the hoist is operating normally. The brake apparatus is of a fail¬ safe character in that the solenoid 36 is normally energized and the wire rope 14 is normally essentially loosely disposed about the outer periphery of the hoist drum. An external switch 60 is provided in operative association with the solenoid so that the hoist operator can connect the solenoid to a suitable source of electricity. Switch 60 is also operatively connected to microswitch 56 for the purpose to be described below.

Energization of the actuator solenoid 36 upon actuation by the operator of switch 60 moves the actuator lever 32 to its solid line position in Fig. 1 to maintain the wire rope 14 in slack condition. When, however, the solenoid 36 is de-energized upon opening of switch 60 by the operator, spring 26 will cause the actuator lever 32 to pivot counter clockwise and exert a pulling force on the lower end of the wire rope. If drum 10 is rotating in the direction of the arrow (i.e. in a clockwise direction as shown in Fig. 1) when the wire rope is tightened thereabout, a reaction force will occur to arrest rotation of the hoist drum due to the frictional engagement between the wire rope and the hoist drum. This action will cause the upper end of the wire rope to move slightly to the right, compressing bevel spring washers 54, tripping microswitch 56, and lighting signal light 58 to indicate to the operator that the brake apparatus has been triggered. A wire rope has considerably greater reactive and braking capabilities than smooth brake bands or other similar known brake elements.

Failure of the primary hoist motor brake to stop the drum can result from many causes ranging from minor brake lining wear to major catastrophic drive train failure which isolates the primary hoist motor brake from the hoist drum.

After braking by the emergency fail-safe brake of the present invention has taken place, the operator can, if desired, manually manipulate the actuator lever to gradually loosen the grip between the wire rope and the hoist drum so that the load carried by the hoist can be gradually lowered to a rest position. This is a substantial advantage over many prior art arrangements which allow a load to be safely lowered and removed only with great difficulty and expense.

The arrangement shown in Fig. 1 results in an actuator force being applied virtually instantaneously with the release of the solenoid, resulting in a relatively instantaneous reaction force and braking of the hoist drum. In the case of higher speed hoist drums, such instantaneous reaction force may manifest itself as a severe shock load on the reaction rod end of the wire rope as well as on the hoist suspension system.

Fig. 2 discloses an arrangement whereby the shock load is reduced by dampening or ramping the actuator force as a function of time. The form of apparatus shown in Fig. 2 is in many respects identical to that of Fig. 1. In the Fig. 2 embodiment, however, the upper end of actuator lever 32 is connected to a spring-extend, reverse-acting, pneumatic cylinder 66 with a port-mounted control valve 68 that allows free movement in the retract direction, i.e. when voltage is applied to the solenoid, and dampened or restricted movement in the extend direction when the actuator lever 32 is pivoted counter clockwise by spring 26. The rate or degree of such movement can be adjusted by adjusting the control valve 68. In the Fig. 2 configuration of the brake apparatus, the pneumatic cylinder decelerator allows quick release of the drum grip brake with unimpeded movement of the actuator lever 32 by the energized solenoid 36 but relatively slow setting with a de- energized solenoid as the actuator lever is allowed to move to its full-set position at a rate determined by the control valve setting.

Fig. 3 illustrates yet another embodiment of the invention. In this embodiment, which incorporates many of the structural components of the Fig. 2 embodiment, a reaction force limiter has been added to further deal with reaction forces which may possibly reach dangerous levels for a given actuator force in the case of high speed drums.

In the arrangement of Fig. 3, the reaction rod 46 having a head 50 passes through a stack of bevel spring washers 70 disposed in a canister shell 72. The washer stack is pre-tensioned to a force level equal to a maximum allowable reaction force. This is accomplished by tightening pre-tensional bolts 74 moving canister cap 76 relative to the stack. Whenever the reaction force exceeds the pre-tensioned level, the reaction rod 46 will move toward the hoist drum 10 with the deflection of the bevel spring washers proportionate to the excess force.

A reaction force limit switch 78 is affixed to the reaction rod as are an adjustable stop arm 80 and an adjustable stop screw 82 threadedly connected to the stop arm 80. That is, the reaction force limit switch 78, the adjustable stop arm 80, the adjustable stop screw 82, and the reaction rod 46 all move together as a unit.

Thus, with excessive reaction force, the adjustable stop screw 82 comes into contact with the actuator lever 32 and moves the actuator lever toward the hoist drum to reduce the actuator force, in turn reducing the reaction force between the wire rope and hoist drum. With the adjustable stop screw 82 in contact with the actuator lever 32, a mechanical interaction of the reaction and actuator forces develops and results in the two forces reaching dynamic equilibrium. In this mode the brake apparatus maintains a constant brake torque to arrest the rotation of hoist drum 10 without exceeding the safe working limits of the wire rope at the reaction rod end thereof.

Any suitable brake control circuitry may be employed to actuate the brake apparatus of the present invention. As indicated above, this may be accomplished merely by manual actuation of a switch. However, the brake apparatus may, if desired, cooperate with and be automatically triggered by suitable conventional sensor arrangements which sense a desired hoist condition such as drum speed. Furthermore, such sensor arrangement may include conventional circuitry which introduces a slight delay between sensing of the condition and actual actuation of the brake apparatus so that the primary or work-horse brake of the hoist has an opportunity to terminate drum movement on its own, if possible.

Claims

1. In combination: a rotatable hoist drum for selectively winding and unwinding a hoist line, said hoist drum having an outer surface of substantially circular cross-section; and brake apparatus cooperable with said hoist drum to brake said hoist drum and stop rotation thereof in a predetermined rotational direction, said brake apparatus including an elongated, flexible element wrapped completely about said hoist drum and forming at least one complete convolution about said hoist drum outer surface, and actuator means operatively associated with said elongated, flexible element to pull said elongated, flexible element and move said elongated, flexible element relative to said hoist drum between a first position wherein said elongated, flexible element engages said hoist drum outer surface but does not exert substantial braking forces on said hoist drum when said hoist drum is rotated in said predetermined rotational direction and a second position wherein said elongated, flexible element is constricted tightly about said hoist drum outer surface with frictional engagement between said elongated, flexible element and said hoist drum outer surface stopping rotation of said hoist drum in said predetermined rotational direction.

2. The combination according to Claim 1 wherein said elongated, flexible element is a wire rope forming a plurality of convolutions about said hoist drum outer surface.

3. The combination according to Claim 1 wherein said elongated, flexible element has first and second ends and wherein said actuator means comprises a movable actuator element connected to the first elongated, flexible element end for exerting a pulling force on said elongated, flexible element to move said elongated, flexible element from said first position to said second position.

4. The combination according to Claim 3 additionally comprising mounting means, the second end of said elongated, flexible element being mounted in said mounting means against substantial movement relative to said hoist drum.

5. The combination according to Claim 3 wherein said actuator means additionally comprises biasing means continuously biasing said actuator element away from said hoist drum.

6. The combination according to Claim 5 wherein said brake apparatus additionally includes solenoid means operatively associated with said actuator element to move said actuator element toward said hoist drum against the bias exerted on said actuator element by said biasing means.

7. The combination according to Claim 5 wherein said actuator element comprises a pivoted, manually graspable lever.

8. The combination according to claim 4 wherein said brake apparatus additionally includes switch means operatively associated with said second elongated, flexible element end and said mounting means, said switch means being actuated when said second elongated, flexible element end moves a predetermined distance relative to said mounting means, and signal means operatively associated with said switch means to signal to an operator that actuation of said switch means has occurred.

9. The combination according to Claim 1 including adjustment means for adjusting said elongated, flexible element relative to said hoist drum when said elongated, flexible element is in said first position.

10. The combination according to Claim 5 wherein said brake apparatus additionally includes damper means operatively associated with said actuator element for impeding movement of said actuator element away from said hoist drum by said biasing means.

11. The combination according to Claim 10 wherein said damper means comprises a pneumatic cylinder connected to said actuator element.

12. The combination according to Claim 4 additionally comprising control means operatively associated with said second end of said elongated, flexible element end and said actuator element for controlling movement of said actuator element relative to said hoist drum responsive to movement of the second end of said elongated, flexible element relative to said hoist drum.

13. The combination according to Claim 12 wherein said control means is affixed to the second end of said elongated, flexible element and is movable with the second end of said elongated, flexible element relative to both said mounting means and said actuator element, said control means being engageable with said actuator element to control movement of said actuator element relative to said hoist drum.