Patent Application
20060186388
1. Field of the Invention
This invention pertains to hoisting systems and, more particularly, to safety systems for heavy-duty hoisting systems that are designed for handling critical loads.
2. Description of the Related Technology
Typically, hoist systems of the type to which this invention pertains include a rotating drum that driven by a motor, and a grapple or other mechanism that is attached to the drum by means of a cable that is wrapped around the drum. As the drum rotates in one direction, it will raise the grapple, and when it rotates in a second, opposite direction it will lower the grapple.
Occasionally, an emergency situation will arise, such as when an overspeed condition is sensed or when system power is lost, that will require swift stoppage of the hoist mechanism. For that reason, it is typical for heavy-duty hoist mechanisms, and particularly those hoist mechanisms that are designed for use with critical payloads, to incorporate emergency braking systems. Conventionally, emergency braking systems have been incorporated into the drive train of the hoist drum. While such conventional emergency braking systems have proven to be generally effective, rapid engagement of the emergency braking system places stress on the drive train, and the presence of the emergency braking system within the drive train adds complexity and bulk to the drive train.
While it is important that an emergency braking system engage quickly in the event of an emergency situation, it is also important that the drive system, the hoist drum, and other mechanical components such as bearings are insulated somewhat from the shock of the initial engagement of the emergency braking system. It is also important that a critical load being handled by the hoist system not be decelerated too quickly. A need exists in this field of technology for an improved emergency braking system for hoists that can be quickly engaged in the event of an emergency situation, is independent from the drive train of the hoist and provides a measure of mechanical shock insulation to the mechanical elements of the hoist and the payload when it engages.
Accordingly, it is an object of the invention to provide an improved emergency braking system for hoists that can be quickly engaged in the event of an emergency situation, is independent from the drive train of the hoist and provides a measure of mechanical shock insulation to the mechanical elements of the hoist and the payload when it engages.
In order to achieve the above and other objects of the invention a hoist assembly according to a first aspect of the invention includes a frame, a hoist drum that is mounted for rotation with respect to the frame, a first toothed wheel connected to the rotatable hoist drum so as to rotate therewith during normal hoist operation, an arresting system for engaging the first toothed wheel in order to arrest rotation of said toothed wheel during an emergency condition, and a frictional braking system mechanically interposed between the rotatable hoist drum and the first toothed wheel, whereby a limited amount of relative rotation is permitted between the rotatable drum and the first toothed wheel when the arresting system engages the first toothed wheel during an emergency condition.
According to a second aspect of the invention, a hoist assembly includes a frame, a hoist drum that is mounted for rotation with respect to the frame, a disc member that is mounted to rotate together with the hoist drum, a first toothed wheel connected to the rotatable hoist drum so as to rotate therewith during normal hoist operation, a second toothed wheel connected to the rotatable hoist drum so as to rotate therewith during normal hoist operation, a first frictional bearing member operably positioned between the first toothed wheel and a first side of the disc member, a second frictional bearing member operably positioned between the second toothed wheel and a second side of the disc member, a compressive biasing system for biasing the first and second toothed wheels toward each other, and an arresting system for engaging the first and second toothed wheels simultaneously in order to arrest rotation of the toothed wheels during an emergency condition, whereby a limited amount of relative rotation is permitted between the disc member and the first and second toothed wheels upon engagement of the arresting system as a result of controlled slippage involving the first and second frictional bearing members.
These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.
Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to
Referring now to
Looking to
The first and second frictional bearing members 28, 30 are further preferably identical in shape and in size and in the area of frictional engagement surfaces that are presented to the disc member 16 and to the respective toothed wheels 24, 26. Preferably, the respective first and second frictional bearing members 28, 30 are secured to one of the disc member 16 or the respective toothed wheel 24, 26 so that relative motion of the frictional bearing member 28, 30 is limited during an emergency braking condition. In the preferred embodiment, both frictional bearing members 28, 30 are secured so that they will rotate together with the disc member 16 both during normal operating conditions and in the event of an emergency braking condition.
A compressive biasing system 32 is provided for impressively biasing the first and second toothed wheels 24, 26 toward one another both during normal hoist operation and in emergency braking conditions. In the preferred embodiment, compressive biasing system 32 includes a plurality of bolt members 34 that extend through the first and second toothed wheels 24, 26 without contacting the disc member 16 and a corresponding plurality of nuts 36 that are threaded on to the distal end of the respective bolt members 34. Preferably, at least one spring washer 38 is provided in each bolt/nut coupling so as to permit a greater range of adjustment of the compressive clamping force that is exerted by each one of the bolt/nut couplings. This permits adjustment of the compressive biasing system 32, which changes the braking force that is applied between the disc member 16 and the first and second toothed wheels 24, 26 during an emergency braking situation.
Referring now to
The arresting system 40 preferably includes a pawl member 52 that is pivotally mounted with respect to the frame 12 by a pivot mount 54. A mechanical pawl biasing system embodied as a spring 56 is provided to continuously bias the pawl 52 toward engagement with the first and second toothed wheels 24, 26. During normal operation of the hoist system 10, an actuating system will be employed to displace the pawl member 52 away from the toothed wheels 24, 26 against the influence of the biasing that is provided by the spring 56. In the preferred embodiment, the actuating system includes a solenoid actuator 60 that is coupled to a lever arm extension 58 of the pawl member 52 that extends on the opposing side of the pivot mount 54.
Accordingly, in an emergency braking situation such as when an overspeed condition is sensed or when power ceases to be applied to the solenoid actuator 60 the pawl 52 will immediately engage the first side surface 44 of corresponding teeth 42 on both the first and second toothed wheels 24, 26, immediately halting movement of the toothed wheels 24, 26. The sudden arrest of the movement of the toothed wheels 24, 26 will impart considerable shock to the system, especially if the hoist system 10 is handling a heavy load. Much of the shock, however, will be absorbed by the braking effect that is created by the frictional engagement of the first and second frictional bearing members 28, 30 with the inner side surfaces of the first and second toothed wheels 24, 26. The amount of relative rotational movement that is permitted to occur between the toothed wheels 24, 26 and the hoist drum 14 depends upon the material from which the frictional bearing members 28, 30 are fabricated, the amount of compression that is being applied by the compressive biasing system 32 and the amount of force and speed of the hoist load and drive train to be absorbed. A considerable amount of the shock will be absorbed by the system, which will reduce the sudden deceleration of the load and reduce stress on the drive train of the hoist system 10.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
