US3625373A

US3625373A - Fail-safe accessory for hoisting equipment

Info

Publication number: US3625373A
Application number: US101A
Authority: US
Inventors: Ralph E Hull
Original assignee: RALPH E HULL
Current assignee: RALPH E HULL
Priority date: 1970-01-02
Filing date: 1970-01-02
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07

Abstract

A safety accessory attachable to existing hoist equipment to provide fail-safe operation of the winch-braking means for the hoisting cable. The accessory comprises spring-powered linkage means connectable to the winch brake and held in armed position so long as the hoist engine is operating and control means for the accessory is held cocked. The control means for the armed spring preferably includes a deadman control operable by the hoist operator, as well as remote control means operable by an observer having a good view of the operating end of the hoist cable. The accessory may and preferably does include failsafe means attachable to the operating linkage for the clutch connecting the hoist engine to the cable winch and effective and operable to disengage the clutch automatically and hold it disengaged under unsafe hoisting conditions.

Description

United States Patent Primary Examiner- Duane A. Reger Attorney-Sellers and Brace ABSTRACT: A safety accessory attachable to existing hoist equipment to provide fail-safe operation of the winch-braking means for the hoisting cablel The accessory comprises springpowered linkage means connectable to the winch brake and held in armed position so long as the hoist engine is operating and control means for the accessory is held cocked. The control means for the armed spring preferably includes a dead man control operable by the hoist operator. as well as remote control means operable by an observer having a good view of the operating end of the hoist cable. The accessory may and preferably does include failsafe means attachable to the operating linkage for the clutch connecting the hoist engine to the cable winch and effective and operable to disengage the clutch automatically and hold it disengaged under unsafe hoisting conditions.

weave/165p (91/6/1660 PATENIEnnic 7197:

Mm vmmmm mm QM INVENTOR & mm mm Arrow/6V5 FAIL-SAFE ACCESSORY lFOlR lhlOISTllNG EQUIPMENT This invention relates to heavy-duty hoisting equipment and more particularly to a fail-safe accessory designed for installation on and removal from existing brake and clutch control connections of such equipment thereby to convert the same to fail-safe operation without need for disassembly of connections or the substitution of different components.

There are in operation today, large numbers of cranes, power booms and hoisting equipment of a wide variety lacking fail-safe components operable automatically to lock powerdriven components against operation in an emergency or under unsafe conditions. In consequence, such equipment is unacceptable and incapable of complying with applicable safety requirements and code provisions. In many instances, suitable fail-safe auxiliaries are not available for use on the hoisting equipment and it cannot be used. In other cases, such auxiliaries are available but are excessively costly, complex and necessitate expensive dismantling and reassembly of the original equipment in order to incorporate needed safety subunits. In certain instances the hoisting equipment required for a particular operation is so specialized and costly that it commonly is obtained temporarily on a lease basis and returned to the owner upon completion of the work. In such cases, owing to the high cost of the fail-safe safety auxiliaries, these must be removed and the original components reassembled and checked for operativeness prior to returning the equipment to the lessor. The additional rental charge for the time required to install the safety equipment and later to remove it is a further major item of expense.

To avoid the foregoing and other shortcomings of hoisting equipment, there is provided by this invention a simple, rugged, inexpensive, self-powered, fail-safe accessory especially designed for addition to existing hoist equipment with a minimum of expense and installation time and on either a permanent or temporary basis. One part of the accessory serves to set the winch brake whereas another component operates to disengage the power clutch interconnecting the engine and winch. Both of these subcomponents are highly versatile and adapted to be connected to brake and clutch mechanisms of a wide variety of types, sized and constructions, including those having either mechanically or hydraulically actuated braking mechanisms.

The invention fail-safe accessory includes mechanical spring means sufiiciently strong not only to set the brake and disengage the clutch but to resist releasing the set brake or rcengaging the clutch manually. A separate spring for each mechanism is normally held in armed condition using either vacuum or pressurized air supplied by the hoist engine so long as the engine is operating and controls are held in a predetermined position. These controls preferably include a deadman control on the hoist-operating lever as well as a manually operated remote control on a service cable extending to an observer station near the working end of the hoist cable. If any one of these controls is permitted to move from its restrained position the armed fail-safe spring operates to set the brake and to disengage the clutch thereby locking the hoist cable instantly and powerfully against movement.

Accordingly the primary object of the present invention is to provide a fail-safe accessory adapted to be readily superimposed upon the operating means of both brake and clutch mechanisms and including self-powered means for setting the brake and disengaging the clutch under emergency or unsafe conditions.

Another object of the invention is the provision of simple, rugged, self-powered means readily attachable to a hoist cable winch brake without interfering with the operation of that brake and operable automatically upon the occurrence of an emergency to set the winch brake.

Another object of the invention is the provision of fail-safe accessory means readily installable on and disassembled from conventional operating means for hoisting equipment and effective to set and maintain the brake set should the hoist engine fail or upon the occurrence of a dangerous operating condition.

Another object of the invention is the provision of fail-safe brake control accessory adapted to be installed on existing mechanisms of either the mechanically or hydraulically actuated type.

Another object of the invention is the provision of a fail-safe accessory adapted to be installed on either existing or original hoisting equipment and enabling a roving observer carrying a remote control to set the winch brake substantially instantly and independently of an operator stationed on the hoisting equipment.

These and other more specific objects will appear upon reading the following specification and claims and upon considering in connection therewith the attached drawing to which they relate.

Referring now to the drawing in which a preferred embodiment of the invention is illustrated:

FIG. 1 is a generally schematic view of a preferred embodiment of the invention fail-safe accessory and essential cooperating components of typical hoisting equipment operatively associated therewith;

FIG. 2 is a fragmentary cross-sectional view on an enlarged scale taken along line 2-2 on FIG. 1.

Referring more particularly to FIG. 1, there is shown an illustrative embodiment of the invention fail-safe accessory, designated generally 10, operatively connected to typical crane hoisting equipment. The latter equipment includes a main frame 11 pivotally supporting a boom 12 on pivot pin 13. A hoist cable 14 extends over suitable pulleys represented generally at 15 to a cable winch I8 having a drive shaft 19 coupled to a driving engine 20 through any suitable clutch mechanism 21.

Cable winch 18 is equipped with a heavy-duty brake 24 of any suitable mechanical or hydraulic type. The brake herein shown is of the latter type and includes a hydraulic brake cylinder 25 having its ends connected between the opposite ends of the brake band 26 through operating levers 28, 29 pivotally connected to one another by pin 30. Lever 28 also includes a pivot 31, it being understood that either or both of the

pivots

30 and 31 may be suitably supported by the crane frame or the like. Spring 33 is effective to relax the brake band whereas the extension of the hydraulic cylinder 25 by pressurized fluid supplied from master cylinder 34 through hose 35 is effective to pivot the outer ends of levers 28, 29 away from one another and set the brake band against the brakedrum of winch 18. Master cylinder 34 is pressurized by a suitable brake pedal 37 pivoted to main frame 11 on pivot pin 38.

The fail-safe accessory 10 includes a self-contained brake operating mechanism, designated generally 40, having a rigid main frame 41 weldable or otherwise securable to hoist frame 1 1. As herein shown, main frame 41 is formed from a length of angle iron. Independently pivoted crosswise of one end of frame 41 on a pivot pin 43 is a bellcrank 44 and two independent

short arms

45, 46. Initially and during installation, each of the

members

44, 45 and 46 can pivot independently of the others about pin 43. However during installation of unit 40 on a particular piece of hoisting equipment arm 45 is welded, at 47 (FIG. I), to a selected area of bellcrank 44 so that thereafter arm 45 is rigid with and pivots with bellcrank 44. The controlling conditions for weld 47 will be described more fully presently.

Welded to the right hand edge of lever 45, as viewed in FIG. 1, is a lug 48 the outer free end of which is positioned to engage the lower lateral edge of arm 46 as bell crank 44 pivots clockwise about pin 43. It will be understood that the bellcrank can pivot freely counterclockwise away from arm 46 whereas, upon clockwise movement, it engages arm 46 and rotates the latter clockwise along therewith.

The outer end of arm 46 is coupled to the outer ends of the brake operation levers 28, 29 by linkage means including

links

51, 52 and 53. As will be apparent from FIG. 1, clockwise movement of arms 46 pulls link 53 upwardly, pivoting link 52 about fulcrum 55 causing the outer ends of brake levers 28, 29

to pivot away from one another thereby contracting the brakeshoe 26 against its drum.

Links

51 and 53 are adjustable in length and the pivotal connection 55 between

links

51 and 52 may be adjusted by inserting pin 55 in a different one of the openings distributed along link 52.

Connected to the outer end of arm 45 is a threaded rod 55 slidably supported from main frame 41 in a slide bracket 56. Rod 55 is encircled by a powerful compression spring 57 having one end abutting bracket 56 and the other bearing against an adjustable nut 58.

As shown in FIG. 1, spring 57 is retained in its armed or highly stressed condition by either one of the pressure differential power sources 60, 61. Typically and by way of example, devices 60, 61 comprise air-operated boosters of the type commonly employed on pneumatic vehicle brakes featuring a pair of cup-shaped housing supporting a flexible diaphragm therebetween. Devices 60 and 61 are secured to main frame 41 of the fail safe accessory by brackets 60a, 61a, respectively. A common operating rod 63 serves to connect the diaphragm of each device with the outer end of bellcrank 44. Normally only one of the devices 60, 61 would be employed to operate bellcrank 44 but, for maximum safety and protection, both may be employed in parallel, the one providing a backup for the other in case of malfunctioning. It will be understood that either is effective to hold spring 57 armed.

The differential power source for device 60 comprises a vacuum hose 65 connected to the intake manifold, not shown, of engine 20 and connected to the upper side of the diaphragm in device 60 via a solenoid-operated valve 66 and a conduit 67. When valve 66 is deenergized the upper side of the diaphragm is vented to the atmosphere through conduit 68. The lower side of the diaphragm is always in communication with the atmosphere through vent port 69. Accordingly, if valve 66 is deenergized, the pressure on both sides of the diaphragm is atmospheric and device 60 is incapable of restraining the powerful spring 57. Consequently the spring expands pivoting bellcrank 44 and arm 45 clockwise, rotating projection 48 clockwise to pivot arm 46 clockwise thereby operating

links

51, 52, 53 to set brake 24 and lock the winch 18 against movement in either direction.

A similar operation takes place at device 61 having the lower side of its flexible diaphragm connected via conduit 65 to a source of pressurized air, not shown but understood as provided in any well-known manner by engine 20 only so long as the latter is operating, it being pointed out that the air pressure collapses immediately that the engine stops. Solenoid valve 66' is similar to valve 66 described above and, when energized, supplies pressurized air to the lower side of the diaphragm of unit 61 to hold the same in the dotted line position shown in FIG. 1 and thereby hold spring 57 compressed and in armed position. However, if valve 66' is deenergized it immediately closes and vents the pressurized air from the lower side of the diaphragm through tube 68' thereby allowing spring 57 to set brake 24.

Various means may be employed to control the

solenoid valves

66, 66 including the deadman control 72 mounted at the handgrip 73 of a conventional hoist manipulating lever 74. Other control devices include a boom limit control 75 and a remote control 76 adapted to be carried by an observer to any conveniently located observation post adjacent the load carrying end 77 of hoist cable 14. As herein shown, controls 72, 75, 76 will be understood as connected in series with a suitable source of power and with

solenoid valve

66, 66.

Deadman control 72 is mounted directly on the operating handle 74 and includes a normally open switch 78 herein shown held closed by its operating lever 79 so long as the operator grasps handle 73. Likewise the remote control switch 76 is of the normally open type here shown held forcibly closed by an observer in position to view the load handle by hook 77. It will be understood that switch 76 may include a manual detent for holding the same closed until released by the operator in charge of this switch.

Boom limit switch 75 is of the normally closed type and has an operating button positioned to be contacted by the boom if the latter pivots to a dangerous position, such as that indicated by the dot-and-dash line to the right of the boom proper.

The fail-safe operating device provided for disengaging clutch 21 in an emergency includes a main frame 81 bolted, welded or otherwise rigidly secured to hoist frame 11 in a position closely adjacent the clutch operating rod 82. This rod is supported for reciprocable movement with one end connected to the clutch-operating lever 83 and the other end connected to a clutch-operating lever 84 pivoted to a fixed support by pin 85. Supported on frame 81 is a pressure differential device 86 similar in construction to devices 60, 61 described above, and having its diaphragm connected to a reciprocable rod 87. Surrounding and anchored to the outer end of rod 87 is a powerful compression spring 88 having one end bearing against an upturned tang of frame 81. A yoke 90 forming part of rod 87 straddles the upper end of a one-way clutch lever pivoted at 92 to a bracket 93 securable by welding 94 or otherwise to the clutch-operating rod 82. The lower right hand corner of clutch 91 as viewed in FIG. 1 is rounded and pivots freely without interference from bracket 93. However, its nonrounded left hand corner 95 abuts bracket 93 to limit counterclockwise pivotal movement past the upright position shown in full lines in FIG. 1.

As shown in FIG. 1, differential pressure device 86 is connected to a source of vacuum via line 96 so long as solenoid valve 66 is energized. Under these conditions atmospheric pressure acting on the left-hand side of the diaphragm of device 86 holds the diaphragm projected to the right thereby holding spring 88 in its compressed armed position. The operator may then manipulate the clutch control lever 84 to engage and disengage the clutch driving winch 18 without interference from its associated fail

safe device

86, 88. As he does so, one way clutch 91 pivots freely about pin 92 and within the slot of yoke 90. However, should the vacuum in line 96 cease, armed spring 88 immediately moves rod 87 to the left. In so doing, yoke 90 engages clutch member 91 and forcibly carries clutch operating rod 82 to the left shifting the engine clutch 21 to its fully disengaged position.

OPERATION The installation and operation of the described fail-safe accessory will be readily apparent from the foregoing detailed description of the structure and its relationship to typical conventional parts of power-operated hoisting equipment. Main frames 41 and 81, respectively, of the brake and clutch operating accessories are preferably welded to suitable portions of the hoisting equipment frame and conveniently located relative to the respective brake and clutch mechanisms. Any welding mechanic can complete simple welding operations found most appropriate for the particular hoisting equipment being serviced with these safety auxilia ries.

Links

51, 52, 53 are then connected to the outer ends of the brake-operating levers 28, 29 and suitably adjusted for the most effective operation for the powerful spring 57. At this time bellcrank 44 and arm 45 are not welded together by welding 47. Thus operation is preferably performed on the site and with the parts positioned most advantageously for that particular installation. Welding 47 is applied while spring 57 is held in armed position and while abutment 48 is so positioned relative to arm 46 as to permit normal full relaxation of the brake 24 on that particular hoist. This position having been found, welding 47 is applied thereby providing full assurance that the parts cannot become loose or get out of proper adjustment. By this simple technique, each fail-safe device is tailored on the job for the most effective operation.

The clutch operation portion of the fail-safe device is likewise welded to the hoist frame closely parallel to clutch rod 82. While device 86 is operated to hold spring 88 in armed position, bracket 93 supporting the one-way clutch 91 is applied against rod 82 and welded in place while the clutch is engaged and with parts 91, 92 in the full line position shown. it is then known that the clutch can be engaged and disengaged without interference from the fail-safe mechanism.

The equipment is now ready for operation in the usual manner, proper precautions being taken to first ascertain that control switches 72, 75 and 76 are in closed position to complete an energizing circuit to solenoids 66, 66'. So long as engine is operating each of the springs57, 88 of the respective fail-safe devices is held fully armed in the manner described by the associated

difierential pressure devices

60, 61, 86 and the operator has full normal control of the hoist brake as well as the driving clutch for the winch. Likewise both the operator stationed on the equipment beside brake pedal 37 and

control lever

73, 74 and the observer stationed opposite the work being lifted will have independent and emergency control of the hoisting equipment. Either operator can lock the hoist against operation at any time merely by allowing his own emergency switch 72 or 76 to open. This deenergizes the solenoid valves thereby equalizing the pressure on the opposite sides of the booster diaphragm and instantly releasing the energy in the armed spring to lock the winch brake as well as to disengage and hold the engine clutch disengaged.

After the hoist equipment has completed a precarious operation and the fail-safe accessories are no longer deemed essential, these safety components are easily detached using torch equipment or like with the result that the hoist is restored to its original condition without need for disassembly of or change in its original brake and clutch control equipment.

While the particular fail-safe accessory for hoisting equipment herein shown and disclosed in detail is fully capable of attaining the objects and providing the advantages hereinbefore started, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention.

lclaim:

1. ln hoisting equipment having a cable winch controlled by manually operated brake means and powered by an internal combustion engine, that improvement which comprises: a failsafe accessory attachable to said equipment without interfering with the existing braking equipment or the normal operation thereof, said accessory having a main frame, linkage means movably supported on said main frame, including a lost motion means, connectable to said winch brake means, powerful spring means normally urging said linkage means to a position holding said linkage means retracted and ineffective to interfere with normal manual operation of said winch brake means but in armed position and in readiness to set said brake means if released, pressure operated booster means operatively connected to said linkage means and to said engine operable to hold said spring means in armed position so long as said engine is operating, and deadman control means operatively connected to said booster means and effective when manually held in one position thereof to render said engine-responsive booster means operable to hold said spring means in armed position and operable when not so forcibly held to deactivate said booster means and allow said spring means to operate said linkage means to set said winch brake means under emergency braking pressure.

2. The combination defined in claim 1 characterized in that said pressure-operated booster means includes diaphragm means having one side thereof exposed to atmospheric pressure and the other side connected to means operative when said engine is operating to maintain a pressure differential across said diaphragm adequate of hold said spring means in armed position.

3. The combination defined in claim 2 characterized in that said booster means is connected to a source of vacuum maintained by said engine only while operating.

4. The combination defined in claim 2 characterized in that deadman control means includes valve means between said booster means and said engine operable to deactivate said booster means and render the same ineffective to hold said spring means in armed position upon release of said dead man means.

5. The combination defined in claim 1 characterized in that said winch brake means includes manually controlled hydraulic means for controlling the normal manual operation thereof, and said linkage means including mechanical means connected in parallel with said hydraulic means and operable to set said brake means independently of said hydraulic means selectively upon release of said deadman control means and upon stopping said engine.

6. The combination defined in claim 1 characterized in the provision of operator-controlled clutch means connecting said engine to said hoist cable winch means, and fail-safe means including spring-operated means normally held in armed position and ineffective to interfere with the manual operation of said clutch means so long as the operator maintains a grasp of said deadman control means, and said last mentioned fail-safe means being operable to disengage said clutch means and hold the same positively disengaged upon release of said deadman control means.

7. The combination defined in claim 1 characterized in that said deadman control means includes a plurality of independent controls connected in series and each required to be maintained closed to render said booster means effective to hold said spring means in armed position.

8. The combination defined in claim 7 characterized in that one of said plurality of deadman control means comprises normally open switch means located remotely from the deadman control for said brake-operating means and effective to control setting of said winch brake means from a remote observation station remote from the operator for said winch-braking means and enabling an operator in position to observe the working end of the hoist cable to operate said winch brake means.

9. The combination defined in claim 6 characterized in the provision of means positioned to be operated by movement of the hoisting means to a predetermined position to deactivate said booster means and render the same ineffective to hold said spring means in armed position.

10. The combination defined in claim 6 characterized in that said hoisting equipment includes pivoting boom means supporting said hoisting cable, and means positioned in the path of movement of said boom means effective when said boom means reaches an undesirable position to deactivate said booster means and release said spring means from the armed position thereof.

11. The combination defined in claim 1 characterized in that said manually operable winch brake means remains intact and in full operating condition upon disassembly of means connecting said linkage means to said winch brake means whereby said hoisting equipment can be restored to the original operating condition thereof without disassembly of any part of its normal winch brake means.

12. A fail-safe converter accessory adapted to be installed on and removed from hoisting equipment of the type having an engine driving manually braked hoisting cable winch means comprising: a main frame fixedly securable to the hoisting equipment, linkage means mounted on said main frame and connectable to said winch-braking means, spring means connected to said linkage means effective when released to operate said linkage and set said winch brake means, booster means connected to said linkage means and to said engine operable to hold said spring means in armed position, control means for said booster means for operatively deactivating said booster means and releasing said spring means while the engine continues in operation, and lost motion means in said linkage means permitting the operator to manipulate said winch-braking means so long as said booster means is holding said spring means in armed position.

13. A fail-safe converter accessory as defined in claim 12 characterized in that said booster control means comprises electrical switch means remote from but connected to the control means for said booster means and operable by an observer stationed to view work being performed by the working end of the hoisting cable thereby to control the activation and deactivation of said booster means and to set the winch-braking means independently of an operator stationed in the hoisting equipment.

14. A fail safe converter accessory as defined in claim 12 characterized in that said control means for said booster means includes dcadman switch means located on the manual control for said winch-braking means and connected to said booster control means and operable to deactivate said booster means when not forcibly held in cocked position by the hoisting equipment operator.

is. A safety control accessory for use in setting the winchbraking means for the cable of hoisting equipment from any vantage point selected by a safety observer of the working end of the hoisting cable, said safety control accessory having spring driven linkage means connectable to the winch-braking means, power means operable when activated to hold said linkage means in armed position with the winch-braking means free for normal operation, and manually manipulatable remote control means for controlling the activation and deactivation of said power means from a vantage point close to the working end of the hoisting cable enabling the operator of said remote control means to set and release the winch-braking means at will, and said spring driven linkage means including means permitting an operator to operate the winch-braking means freely so long as said power means is activated.

16. A safety control accessory as defined in claim 14 characterized in that said accessory is attached to previously assembled winch-braking means without need for replacing or substituting other components therein.

17. The combination defined in claim 1 characterized in that said booster means is connected to a source of pressurized air maintained by said engine only so long as said engine is operating 18 The combination defined in claim 1 characterized in that said booster means includes a pair of booster means operating in parallel and either of which is effective to hold said spring means in armed position so long as the engine is operating, whereby the failure of one to function leaves the other available to hold the spring means armed while the engine is operatmg.

l9. Pivoting boom hoisting equipment of the type having operator-controlled brake-setting means for power-driven winch means for a load-handling cable trained over pulley means carried by said boom and which winch means includes a manipulating control lever, said hoisting equipment being readily convertible between fail-safe operation and nonfailsafe operation by a converter accessory readily attachable to and detachable from said brake-setting means, said converter accessory comprising: a main frame fixedly securable to a stationary part of said hoisting equipment, linkage means mounted on said main frame and having means for connecting the same to said winch-braking means, spring means connected to said linkage means effective when released to operate said linkage and set said winch brake means, booster means connected to said linkage means and to the power means driving said winch means operable to hold said spring means in an armed energized position, control means for said booster means for operatively deactivating said booster means and releasing said spring means while the power means for said winch means continues in operation, lost motion means in said linkage means permitting the operator to manipulate said winch-braking means so long as said booster means is holding said spring means in armed position, and dcadman control means located adjacent the manual control for said winchbreaking means and connected to said booster control means and operable to deactivate said booster means when not forcibly held in a predetermined position by the hoisting equipment operator.

20. Hoisting equipment as defined in claim 19 characterized in that the installed presence of said fail-safe converter accessory leaves the normal winch brake control means free to operate In the normal manner so long as the operator holds said deadman control in said predetermined position and, when not so held, being automatically effective to release said spring means to set the winch brake means and hold the brake set.

21. Hoisting equipment as defined in claim 19 characterized in that said power drive means for said winch means comprises an internal combustion engine, and means responsive to the nonoperating condition of said engine to release said spring means independently and irrespective of the position of said dcadman control means.

Claims

1. In hoisting equipment having a cable winch controlled by manually operated brake means and powered by an internal combustion engine, that improvement which comprises: a fail-safe accessory attachable to said equipment without interfering with the existing braking equipment or the normal operation thereof, said accessory having a main frame, linkage means movably supported on said main frame, including a lost motion means, connectable to said winch brake means, powerful spring means normally urging said linkage means to a position holding said linkage means retracted and ineffective to interfere with normal manual operation of said winch brake means but in armed position and in readiness to set said brake means if released, pressure operated booster means operatively connected to said linkage means and to said engine operable to hold said spring means in armed position so long as said engine is operating, and deadman control means operatively connected to said booster means and effective when manually held in one position thereof to render said engine-responsive booster means operable to hold said spring means in armed position and operable when not so forcibly held to deactivate said booster means and allow said spring means to operate said linkage means to set said winch brake means under emergency braking pressure.

2. The combination defined in claim 1 characterized in that said pressure-operated booster means includes diaphragm means having one side thereof exposed to atmospheric pressure and the other side connected to means operative when said engine is operating to maintain a pressure differential across said diaphragm adequate to hold said spring means in armed position.

14. A fail safe converter accessory as defined in claim 12 characterized in that said control means for said booster means includes deadman switch means located on the manual control for said winch-braking means and connected to said booster control means and operable to deactivate said booster means when not forcibly held in cocked position by the hoisting equipment operator.

15. A safety control accessory for use in setting the winch-braking means for the cable of hoisting equipment from any vantage point selected by a safety observer of the working end of the hoisting cable, said safety control accessory having spring driven linkage means connectable to the winch-braking means, power means operable when activated to hold said linkage means in armed position with the winch-braking means free for normal operation, and manually manipulatable remote control means for controlling the activation and deactivation of said power means from a vantage point close to the working end of the hoisting cable enabling the operator of said remote control means to set and release the winch-braking means at will, and said spring driven linkage means including means permitting an operator to operate the winch-braking means freely so long as said power means is activated.

17. The combination defined in claim 1 Characterized in that said booster means is connected to a source of pressurized air maintained by said engine only so long as said engine is operating.

18. The combination defined in claim 1 characterized in that said booster means includes a pair of booster means operating in parallel and either of which is effective to hold said spring means in armed position so long as the engine is operating, whereby the failure of one to function leaves the other available to hold the spring means armed while the engine is operating.

19. Pivoting boom hoisting equipment of the type having operator-controlled brake-setting means for power-driven winch means for a load-handling cable trained over pulley means carried by said boom and which winch means includes a manipulating control lever, said hoisting equipment being readily convertible between fail-safe operation and nonfail-safe operation by a converter accessory readily attachable to and detachable from said brake-setting means, said converter accessory comprising: a main frame fixedly securable to a stationary part of said hoisting equipment, linkage means mounted on said main frame and having means for connecting the same to said winch-braking means, spring means connected to said linkage means effective when released to operate said linkage and set said winch brake means, booster means connected to said linkage means and to the power means driving said winch means operable to hold said spring means in an armed energized position, control means for said booster means for operatively deactivating said booster means and releasing said spring means while the power means for said winch means continues in operation, lost motion means in said linkage means permitting the operator to manipulate said winch-braking means so long as said booster means is holding said spring means in armed position, and deadman control means located adjacent the manual control for said winch-breaking means and connected to said booster control means and operable to deactivate said booster means when not forcibly held in a predetermined position by the hoisting equipment operator.

21. Hoisting equipment as defined in claim 19 characterized in that said power drive means for said winch means comprises an internal combustion engine, and means responsive to the nonoperating condition of said engine to release said spring means independently and irrespective of the position of said deadman control means.