Hoist Drive Safety System

1. Technical Field

This invention pertains to heavy-duty hoisting equipment and, more particularly, to safety systems for such hoist equipment.

2. Background Art

U.S. Pat. Nos. 4,175,727 and 4,177,973 are directed to safety systems for automatically setting a drum brake or other type of emergency holding device directly on the drum or on a shaft driving or driven by the drum and in close proximity to the drum so that the system makes the hoist essentially single-failure-proof. This means that should a failure occur in any location in the input drive or should there be a load hang-up or two-blocking condition, that this hazard or failure would immediately be detected and set the brake. This type of system is intended to serve as a substitute for the conventional redundant drive systems utilized in critical load cranes.

In U.S. Pat. Nos. 4,175,727 and 4,177,973, various devices were described for detecting the hazard or failure condition and setting the brake. It is one purpose of this invention to provide an improved form of one of these earlier-described detection devices.

One embodiment covered by said earlier patents is an embodiment which uses compressed air to hold the brake open against a spring-applied force, and the detection of the failure or hazard condition electrically or electromechanically releases the air to allow the brake to be applied. In many installations, air supplies and electrical controls for setting valves are not readily available or desirable. Thus, while the earlier patents contemplated improved detectors and brake actuators, this application is also directed to an improved brake setting device.

It is an object of this invention to provide an improved apparatus for detecting a failure or other hazard on a hoisting device.

It is another object of this invention to provide a totally mechanical detector and brake-applying system for a hoisting device.

It is still another object of one form of the invention to provide a mechanical out-of-sync detector which generates its own force for applying the brake in an out-of-sync condition.

Basically, these objects are obtained in their broadest sense by providing a mechanical differential, out-of-sync detector, the output of which is generated when mechanical inputs from the motor shaft and from the drum or related shaft to be monitored change their relative velocities to one another, or when one of the drive line inputs to the detector is otherwise interrupted due to drive line component failure, system overspeed, or loss of electrical power, causing the differential output shaft to rotate via a differential gear set and trigger some form of brake-actuating device to apply the brake.

In one form of the invention, the out-of-sync detector itself provides the force or muscle necessary to apply the brake without intervening air or electrical elements. Since the air and electrical elements are frequently not available or are susceptible to failure themselves in the frequently dusty or dirty environment around a hoisting device, the benefit of a purely mechanical system is very advantageous. This system, in effect, stands alone such that any failure within the crane or any hazard condition, such as two-blocking or load hang-up, will immediately be sensed and directly converted to stopping the motor and setting the emergency brake to grab the drum before it reaches an appreciable dangerous velocity.

In another embodiment, the out-of-sync detector signals a triggering mechanism to release a cocked highforce spring to set the brake.

In a preferred embodiment, the drive train between the motor and the drum is provided with a torque-limiting device for dissipating high-speed kinetic energy of the system in the event of load hang-up, two-blocking or overload. A nulling device is employed in the out-of-sync detector of this embodiment to compensate for minor creep in the torque-limiting device and/or to compensate for variations between the gear reduction units on opposite sides of the out-of-sync detector.

Still further features involve the use of a load-sensitive declutching device for detecting motor overspeed which is demand-sensitive; that is, the overspeed limit will vary depending upon the load carried by the drum. Light loads will allow greater overspeed, for example, than will heavier loads.

Even if the out-of-sync detector is itself not used to generate the force to apply the brake but merely signals to another brake-actuating device, the benefit of a simple mechanical differential, out-of-sync detector provides a relatively inexpensive, low-maintenance, stand-alone detection device for energizing brake actuation in an emergency condition.

It should also be understood that while a total system and variations thereof will be illustrated and described, various components themselves are unique and have utility apart from a total system.

FIG. 1 is a schematic plan view of a hoisting mechanism employing the safety system of this invention.

FIG. 2 is a section along the line 2--2 of FIG. 1.

FIG. 3 is a fragmentary section take along line 3--3 of FIG. 1 of a differential detection system embodying the principles of the invention.

FIG. 3A is a schematic fragementary section of another embodiment of detection device employed in one form of safety system.

FIG. 4 is a side elevation of the hoisting device and safety system of FIG. 1.

FIG. 5 is a fragmentary section of an overspeed clutch forming a part of an embodiment of the invention.

FIG. 6 is a load-sensitive control for the over-speed clutch of FIG. 5.

FIG. 7 is a schematic elevation of another embodiment of brake-setting apparatus.

FIG. 8 is similar to FIG. 7 but illustrates a total mechanical brake-setting apparatus.

As best shown in FIG. 1, a hoist system includes an operating brake 2 coupled to a motor shaft 2a which is powered by a motor 3. As is well understood by those skilled in this art, the operating brake 2 is hydraulically or, more commonly, electrically energized open (that is, to allow rotation of the motor shaft), and is hydraulically or electrically de-energized to be set to hold the motor shaft from rotating. Also, as is conventional, the operating brake will be set to hold the shaft, either when it is intentionally de-energized by a switch, when the hoist system is shut down, or when it is unintentionally de-energized, as in the case of a power failure. A coupling 4 couples the motor to a conventional gear reduction unit 5, such as a 500:1 reduction, which has an output shaft 7 rotatably carried in a pillow block 8. A drum pinion 9 meshes with the drum gear 10.

Shaft 2a is generally considered the first high-speed load-carrying element of the system. This term is understood in the art as meaning the first or furthest element that carries the load such that if that element or any element between that first element and the drum failed, the load could be dropped. Similarly, there will be a last low-speed load-carrying element at the opposite end of the drive train driven from the drum. In the embodiment illustrated in FIG. 1, for example, this low-speed element is drum shaft 11a (to be described). Any drive component that fails in the drive train lower speed components adjacent the drum will be detected, because there will be a change in relative speed or direction between the first high-speed and last low-speed load-carrying elements.

A drum 11 is rotated by the drum gear on a shaft 11a which is rotatably supported in a pair of spaced pillow blocks 13. As described in earlier U.S. Pat. No. 4,175,727, a unique feature of the hoist system is that it is provided with a second brake, such as a band brake 14, wrapped on a brake drum 12. As will be described in more detail below, a brake-applying assembly or brake actuator 15 will set the brake in response to a detected failure or other hazard condition.

In the preferred embodiment of the invention, a torque limiter assembly 6 of the type shown in U.S. Pat. No. 4,175,727 is provided to limit the torque which would be imposed from high-speed rotational kinetic energy of the motor and high-speed drive elements of the gear reduction and motor drive if a load hang-up, overload or two-blocking occurs. It is to be understood that the inputs to the out-of-sync detector are to be coupled to the two most extreme load-supporting elements or points in the drive train.

It is a unique feature of this invention that a mechanical differential, out-of-sync detector 20 is provided for detecting the failure or hazard condition. In one embodiment, the detector also provides the mechanical force for applying the band brake 14. In preferred embodiments, the detector merely signals the out-of-sync detection and a separate brake actuator or brake-applying means sets the brake, as in FIGS. 7 and 8. The out-of-sync detector 20 includes an input shaft 30 which, in the embodiment illustrated, is coupled to the motor shaft 2a by a conventional right angle drive 19 having a gear reduction equivalent to that of the total gear reduction between the motor and the drum. A conventional right angle drive 18 also couples the drum shaft 11a to an input shaft 31 to the detector 20. The purpose of the gear reduction in right angle drive 19 is to bring the two input shafts entering the detector to approximately the same speed. Exact speed equality is desirable, but if suitable nulling is provided, as will be described, exact speed equality is not essential. Other forms of speed reduction can also be provided.

Each of the input shafts 30,31, as is best shown in FIG. 3, is keyed to a drive gear which meshes with a side gear 26. The side gears 26 are keyed to pinion gears 27 that mesh with a planetary gear 27a of a planet carrier 28. As is well understood, equal and opposite rotational velocities of the drum input shaft 30 and motor input shaft 31 will cause the pinion gears 27 to rotate the gear 27a about a planet carrier post 28a that is fixed by a pin 46 to an output shaft 29 carried in bearings 25. Should the rotational velocity on either of the input shafts vary, an angular velocity will be created in the output shaft 29, the speed of which will depend on the relative variation between the velocities of the two input shafts. Thus, for example, if one of the input shafts should stop completely, the rotational output of the output shaft 29 will immediately reach a maximum speed. It is this rotation of the output shaft which triggers the brake actuation and, in one embodiment, creates or generates the force necessary for applying the brake on the brake drum 12. In this regard, while the preferred location for the brake is directly on the drum, it should be understood that it is also possible to place this brake on a downstream pinion shaft in close proximity to the drum rather than directly on the drum. The purpose of this brake is to apply a stopping force on the drum as close to the drum as is practicable so that no substantial risk occurs from a failure of some drive element between the brake and the drum. Furthermore, the input shaft 31 to the detector could also be from any location in the drive train between the motor and drum, which location is at the desired point to be monitored. Preferably, this location, however, will be at or close to the drum.

One form of brake actuator mechanism is shown as 15 in FIG. 1 and includes a lever 16a keyed to an extension 29a of shaft 29. The lever is coupled to the free end of the brake band 14 such that rotation of the lever 16a in either direction will set the band brake in a conventional manner. The lever 16a is provided with a notch 16b in which is inserted a spring-centered cog 17. A conventional clutch 32 couples shaft 29 to its extension 29a. A clutch throw out bar 33 follows a cam 34 on the drum to decouple the shaft extension 29a once each rotation of the drum. If the shaft 29 rotates through some predetermined maximum angle, as, for example, because of differences in the speed reductions between the motor and drum and the speed reductions between the motor and drum and detector 20 or because of creep in the drive train, lever 16a will rotate toward the maximum angle, but the clutch 32 will decouple the lever 16a before it rotates far enough for the cog to leave the notch 16b. Thus each time the clutch is decoupled at each complete revolution of the drum, the lever is returned to its centered position by the cog 17. In the event of a failure or load hang-up, etc., however, the shaft 29 will rotate at a high velocity and the drum will be stopped directly by the pull from lever 16a before one or perhaps at the most two more revolutions of the drum are possible.

It should also be understood that in those instances where there is an exact match between the drum, motor, and detector speed reductions and no torque-limiting device such as 6 which could cause creep, a nulling device such as clutch 32 is not necessary.

The details of a torque-limiting device (such as 6) are best described in U.S. Pat. No. 4,175,727, which is incorporated herein by reference thereto. The torque-limiting device 6 generally has a driven gear 40 which is driven by one of the upper stages of the gear reduction in the gear case 5. The gear 40 is provided with clutch facing 39 which is splined, as at 41, to a shaft 42. A spring 37 pushes a pressure plate 38 against the clutch facing, thus releasably holding the gear 40 in driving engagement with the shaft 42. A pinion gear 44 is fixed to the shaft 42 by a key 45. As is well understood, by adjusting the position of the spring holder 36, a desired torque can be carried between the clutch facing and the driven gear 40. If an overload occurs, such as by excessive load, load hang-up, two-blocking, a jamming in the drive train, or the like, the high-speed kinetic energy upstream of the driven gear 50 will be dissipated as heat in the clutch facing and the downstream drive components from pinion gear 44 to the drum will be stopped. Because of this safety feature of the torque-limiting device, however, there may be a certain minimum amount of creep or relative rotational movement between the gear 40 and the shaft 36 so that there may be slight variations between the input shaft 30 and the drum input shaft 31 in the differential detector 20, as earlier described.

In the preferred embodiment, a centrifugal clutch 47 (FIG. 5) is provided to decouple input shaft 30 from motor shaft 2a when the motor shaft rotates at an overspeed above some predetermined percentage of its normal driven speed. That is, if some failure occurs which causes the motor to rotate beyond its set speed, the shaft 30 will become decoupled and stop, thus providing a variation between the relative velocities of shaft 30 and shaft 31 to provide a rotational output to output shaft 29 and set the brake. It is important in the differential assembly that the differential not back drive the input shafts, and thus, in a preferred embodiment, there are provided drag mechanisms on each of the input shafts to assure that the output shaft is rotated when one of the input shafts changes its velocity relative to the other to provide a variation between the relative velocities of the input shafts. Continuous friction drags could be provided on each of the shafts for this purpose, or the inputs could be through worm gear drives; but in the preferred embodiment, the shafts are broken into two sections, namely, an external section 31e and an internal section 31i and an external section 30e and an internal section 30i. The internal and external sections of each shaft are joined by a conventional one-way drag clutch or "NO BAK" clutching device 21 of the type manufactured by Ann Arbor Bearing and Manufacturing Company, Ann Arbor, Mich. These types of devices are well known, and in the invention here described, are uniquely positioned so that the external section 30e, when driving in either direction, will freely rotate the internal section 30i. Likewise, the clutch on the drum input shaft is positioned so that when external section 31e is providing a driving input, the internal section 31i will freely rotate. The converse is not true, however. That is, if at any time, one of the internal sections tries to drive the external section of that input shaft, the clutch will lock up so that the internal section cannot rotate. This provides a unique and more positive clutching or drag device for the input shafts to assure that when there is a change in velocity relative to the other input shaft, this change cannot be transmitted backwards to rotation of the other input shaft, but rather must be converted immediately and in all cases to a rotational output of the output shaft 29.

An overspeed clutch 47 is provided in a preferred embodiment. Any type of conventional overspeed device can be employed, but it is an advantageous feature of one embodiment of this invention to employ a mechanical clutch having a clutch friction plate 48 keyed to shaft 2a and an opposed friction and pressure plate 49 keyed to a separate stub shaft 50 which drives the right angle gear box 19. A spring 52 is compressed by centrifugal governor weights 54 to hold the friction plates in driving engagement. When shaft 2a rotates rapidly, as in an overspeed condition, the weights 54 swing outwardly and spring 52 is released, thereby allowing plates 48 and 49 to slip relative to one another. Once shaft 50 is released from shaft 2a, the detector signals the out-of-sync condition and the brake 14 is set.

Control systems for high-performance hoists are sometimes designed to sense the lifted load and to command motor 3 to operate at higher than full-load rated speed when handling a lighter load. This may be as high as 300 percent when operating under such no-load condition. Conventional overspeed drives are generally set in this no-load case to cut out at more than 300 percent full-load speed. This reduces the safety when handling a full load.

Thus, if desired, the clutch 47 can also be made load-sensitive. To release the friction discs 48 and 49 sooner or at a lower speed, a bell crank 56 is threaded in a nut 58 such that when screwed away from spring 52, the weights 54 will have less pressure on them and will open to release the discs 48 and 49 sooner or at a lower overspeed. If the bell crank is screwed in the opposite direction, higher overspeed can occur before the clutch plates are separated.

Motion of the bell crank 56 is provided by a line 60 coupled to a pivoted arm 62 that is balanced by a calibrated spring 64. The drum line 70 is reaved about a traveling block 72 and thence to a sheave 73 on arm 62. As the load is increased, arm 62 is lowered, thus moving bell crank 56.

While the detector 20 can signal an electrical shutoff or brake-setting device, it advantageously preferably signals or triggers a mechanical brake actuator. In the embodiment of FIG. 1, the detector can itself apply the brake. Two forms of triggering devices for setting the brake 14 are illustrated in FIGS. 7 and 8. It is common to both these triggering devices that a large spring force can be applied to set the brake, but a small trigger release force is all that is necessary to release the spring. This allows an inexpensive, trouble-free, manual or powered reset mechanism to again set the large spring force using a slower but highly leveraged resetting force.

In FIG. 7, the brake band 14 is set by a spring 74 having a large spring force, as is necessary for high-load capacity drums. A lever 75 is engaged by a trigger 76 which holds the spring in a cocked position. The trigger 76 is anchored or locked by a conventional trigger release cam 78. A solenoid 80 having an extendible arm 81 pivotally mounts one end of the cam 78. The cam is also pivoted at 83 and has an end 84 that abuts the trigger 76. A spring 89 urges the cam 78 into the phantom-line position to disengage from the trigger 76. When solenoid 80 is energized, the trigger release cam is in the solid-line position. The solenoid will be de-energized to set the brake when lever 16a moves sufficiently to signal a failure condition. In this embodiment, the electrical signal to de-energize the solenoid 80 can be by any conventional electrical switch actuated by the lever 16a. Thus it is apparent that the small, easily controlled spring 89 is all that must be overcome to hold the large spring 74 in the cocked position.

To reset the trigger and spring 74, a relatively slow-speed rotary screw drive 90 moves the trigger, solenoid, and trigger release to the left. The trigger strikes a cam 92 that rotates the trigger counterclockwise, and the solenoid is energized to again hold the trigger in the cocked position. Movement of the screw to shift the trigger to the right then reengages the lever 75 and recompresses the spring 74. Since the spring can be compressed slowly, the highly leveraged screw drive is easily able to overcome very large spring forces.

FIG. 8 illustrates a mechanical trigger release. In this embodiment, the crane can be electrically de-energized without having to set the brake 14, which is a disadvantage in the embodiment of FIG. 7. In this preferred embodiment, the lever 16a (FIG. 1), rather than being coupled directly to the brake band 14, is coupled to an elongated cable 94 that is connected to the trigger release cam 78 by a lost-motion slot 95. As the lever 16a rotates in an out-of-sync condition, the cable 94 is pulled, pivoting trigger release cam 78 into the phantom-line position to release trigger 76 in the same manner as in FIG. 7. Resetting of the spring 74, trigger 76, and cam 78 is similar to the above description of FIG. 7.

FIG. 3A illustrates a schematic modification of the detector 20 capable of providing a signal for setting a brake actuator. In this embodiment, the detector output shaft 29 is provided with a flyball governor 97 that meshes with a rack 98 slidably mounted in the shaft 29b. As the ball levers swing out from an out-of-sync condition, teeth on the levers meshing with the rack extend the rack. The rack engages a normally closed switch 99 to open the switch and de-energize solenoid 80, for example, to set the brake. The structure of FIG. 3A is in essence an electromechanical replacement for the structure 15 of FIG. 1. FIGS. 7 and 8 are each alternative systems. FIG. 7 uses the centrifugal electric switch operator of FIG. 3A described hereafter.

If desired, a normally energized electric clutch 100 can be added to any of the embodiments to decouple the motor shaft from the detector for setting the brake automatically if an electrical power failure occurs. Furthermore, this clutch or the overspeed clutch could also be placed on the drum side of the input to the differential detector.

The operation of the various embodiments of the safety system will now be described. During normal operation, such as with the motor shaft 2a being rotated at approximately 1200 rpm, the drum speed will be reduced to approximately 2.4 rpm at the drum shaft 11a. The motor shaft at its 1200 rpm is then coupled through the centrifugal clutch 47 and right angle/gear reducer drive 19 to the differential detector assembly 20 via the input shaft 30. Similarly, the 2.4 rpm rotation of the drum shaft is coupled via right angle drive 18 to provide the same rpm input to the input shaft 31. It should be understood that these gear reductions do not have to be exact so long as they are proportionate, and the gear reduction, which is approximately 2:1 within the differential drive assembly, is sized accordingly. The desired result is that shaft 31 and shaft 30, when the hoist is operating either in the lowering or hoisting mode, provide substantially the same angular velocities to the differential gear 27a so that output shaft 29 rotates not at all or perhaps rotates one way or another at a very low rate, depending on the amount of slippage, variance in gear reductions, or creep in the system. If there is an overload, a load hang-up, a two-blocking or any failure in a drive component such that the drum tries to stop, the torque-limiting device, if provided, will dissipate the high-speed kinetic energy in the motor and upstream drive components, and the input shaft 31 will slow down or stop immediately, thus providing a variation between the angular velocities of the input shaft 31 and the input shaft 30. The motor input shaft will then cause the output shaft 29 to rotate rapidly; for example, at about 600 rpm., since no slippage or back rotation can occur due to the clutch or drag 21 on the drum input shaft. Rotation of the output shaft 29 will immediately rotate the ball governor 97 or rotate the lever 16a, and the force applied by this rotation will be used either as a signaling device, as in FIGS. 7 and 8, to set the brake, or, in a totally mechanical system, as in FIG. 1, to directly tighten the band brake. Should the motor shaft 2a rotate above its rated speed, such as where the controller may fail and allow the motor to drive the hoist too rapidly, the clutch 47 will disengage the motor shaft from the detector, stopping the input shaft 30 and providing an out-of-sync rotation of shaft 29. Similarly, if either the input shaft 30 or the input shaft 31 of the differential assembly should fail or any component in these inputs to the differential assembly should fail, the shaft 29 again will be rotated to set the brake. There is in essence no type of single failure that is not detected and the brake actuated, resulting in an extremely safe, relatively inexpensive detection and brake-actuating system for the hoist mechanism. Furthermore, any combination of overspeed and electrical clutches, as described, can be used with the detector, depending upon the requirements for a particular hoist.

While the preferred embodiments of the invention have been illustrated and described, it should be understood that variations will be apparent to one skilled in the art without departing from the principles herein. Accordingly, the invention is not to be limited to the specific embodiment illustrated in the drawing.