A lifting system for a vertically-elevating cab, the lifting system includes a frame assembly having a first and a second support column, first and a second lift screws which are attached to the, respective, first and second support columns, a cab-lifting beam that has a first and a second end attached to the, respective, first and second lift screws. A vertically-elevating cab is mounted on the cab-lifting beam in such a manner that a center of gravity of the cab is not aligned with a center of the cab-lifting beam. A plurality of rollers are located on each end of the lifting beam. Each one of the plurality of rollers is in contact with a guide bar on each of the respective first and second support columns, and a first and a second power system is connected to the, respective, first and second lift screw.

FIELD OF THE INVENTION

This invention pertains to gantry cranes and, more particularly, to elevating cabs employed on gantry cranes.

BACKGROUND OF THE INVENTION

It is common practice for cranes to be used to lift heavy objects in order to reposition them from one place to another. Known cranes come in various sizes and shapes and are designed to ensure the safe handling of a load while it is in transit. While it is always important that a crane operator be able to see the object he is lifting, depending on what is being lifted, and the purpose for the lift, a crane operator may need the ability to reposition himself vertically with respect to the object being lifted in order to ensure that the object is placed gently and safely in the desired location.

For example, a crane operator who is lifting debris left over from a demolition or construction project may safely operate a crane from a ground or near ground position as he most likely only needs to have enough visibility to see that the object being lifted does not impact anything as it is moved from one position to the next. This is especially true if the operator is handling debris as there is less concern about the integrity of the object being lifted as it is dropped in its new position. If however, the crane operator is operating an intermodal crane or other material handling machine that is lifting a container filled with finished goods that are to be shipped to a store or final customer, the operator may desire the ability to adjust his position to various eye levels with respect to the load so as to be able to see both above and below the load to, for example, look down over the side rail of a ship or on top of a rail car so as to be able to gently reposition the container in an exact spot.

In order to allow a crane operator to be able to adjust his position vertically with respect to a load, vertically-elevating operator cabs have been employed on cranes such as gantry cranes and the like. Traditionally, these vertically-elevating cabs have relied on lift systems comprised of wire ropes or chains to raise or lower the cab from one position to another. Various problems are associated with such lift systems including the fact that the ropes or chains may fray or break. Furthermore, such lift systems are rather complex and may not always prevent a repositioned cab from sliding back down toward the ground once it has been raised to a desired level. For these and various other reasons, a lifting system for a vertically-elevating cab used with a crane would be an important improvement in the art.

BRIEF SUMMARY OF THE INVENTION

Disclosed is a lifting system for a vertically-elevating cab used in conjunction with intermodal cranes or other material handling machines. The lifting system is comprised of a frame assembly having a first and a second support column. First and second lift screws are attached to the, respective, first and second support columns. A cab-lifting beam has a first and a second end attached to the, respective, first and second lift screws. A vertically-elevating cab is mounted on the cab-lifting beam in such a manner that a center of gravity of the cab is not aligned with a center of the cab-lifting beam. A plurality of rollers are located on each end of the lifting beam. Each one of the plurality of rollers is in contact with a guide bar on each of the respective first and second support columns. A first and a second power system is connected to the, respective, first and second lift screw.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion illustrates the disclosed lifting system10in conjunction with a rubber tired intermodal gantry crane used for handling container and trailers but, of course, should not be construed as in any way limiting the scope of the invention when applied to other devices where elevation of an operator's cab may be required.

Disclosed is a lifting system10for a vertically elevating cab12used in conjunction with intermodal cranes or other material handling machines. As shown inFIGS. 1 and 4, the lifting system10is comprised of a frame assembly14having a first16and a second18support column. These support columns16,18may themselves be part of the frame14of the crane or material handling machine. A first20and a second22lift screw are attached to the, respective, first and second support columns16,18. A cab-lifting beam24, as shown inFIG. 6, that has a first26and a second28end is attached to the, respective, first and second lift screws20,22. As shown inFIGS. 1 and 4, the vertically elevating cab12is mounted on the cab-lifting beam24in such a manner that a center of gravity of the cab12is not aligned with a center of the cab-lifting beam24. As shown inFIGS. 6 and 7, a plurality of rollers30are located on each side of end of the lifting beam26,28. Each one of the plurality of rollers30is in contact with a guide bar, as partially shown for clarity inFIG. 6, on each of the respective first and second support columns16,18. A first34and a second36power system is connected to the, respective, first and second lift screw20,22, as shown inFIGS. 1,2,2A and2B.

In an embodiment, the lifting screws20,22may be Acme screws, however, any suitable-like screws may be used without departing from the spirit and scope of the invention. In a more specific embodiment, the screw pitch is such that the screws20,22are non-backdriving. A first56and a second58bearing support may also be attached at a respective first and second end of each of the lift screw20,22.

As shown inFIGS. 3,5and5A, a nut assembly38may be used to secure the cab-lifting beam24to the lift screw20,22. The nut assembly38may include a load-supporting nut40, a safety nut42which is displaced a first distance L1from the load-supporting nut40, a first grease seal44located on a first side of the load-supporting nut40, and a second grease seal46located on a second side of the load-supporting nut40between the load-supporting nut40and the safety nut42.

Any suitable form of power system34,36may be used to rotate the lift screws20,22including, but not limited to, a first and second motor which may be electrical, hydraulic, or pneumatic power systems. The electrical motors may also be controlled by variable frequency drives50.

The first and second power systems may34,36also be equipped with encoders, as shown inFIG. 8, these encoders are capable of, among other things, controlling the speed and position of the vertically-elevating cab12. The encoders may also synchronizes a rotation of the lifting screws20,22such that the cab12remains level through an entire range of cab motion.

When in operation, the two power systems34,36supply power to their respective lift screws20,22, causing those screws20,22to rotate. Depending on the direction of rotation, the vertically-elevating cab12is either raised or lowered as the screw threads engage the nut assembly38, thereby causing the nut assembly38to advance along the length of the screw20,22. The pitch of the screw20,22is such so that the screw20,22is non-backdriving and the force of the load acting on the screw20,22will not cause screw rotation, thereby providing maximum safety and reliability to the cab operator. Although a motor brake is not required to hold the load, one may be used to provide a redundant system for holding the vertically-elevating cab12at any desired position.

The load-supporting nut40of the nut assembly bears38the weight of the cab-lifting beam24and the vertically-elevating cab12as it travels along the length of the screw20,22. As shown inFIGS. 5 and 5A, the first44and second46grease seals retain grease on the Acme nut40to maintain lubrication on the nut40and screw20,22.

The load-supporting Acme nut40will wear with continued use and will eventually require replacement. The safety nut42, which is displaced a first distance L1from the load-supporting nut40in the assembly38, will support the load in the event of failure of the load-supporting nut40. This displacement distance L1is used to indicate the amount of wear on the load-bearing nut40as measurement of the change in the first distance L1between the two nuts40,42will indicate the amount of wear on the load-supporting nut40.

As the lift screws20,22rotate, the mounting arrangement of the cab12on the cab-lifting beam24, as shown inFIGS. 1 and 4, causes a turning moment on the cab lifting-beam24because the center of gravity of the cab12is not in line with the center of gravity of the cab-lifting beam24. The rollers30on both the first26and second28ends of the cab-lifting beam24provide a reaction to the turning moment on the cab-lifting beam24, thereby stabilizing the beam throughout its movement.

In an embodiment, the electric motors34,36that drive the lifting screws20,22are controlled by variable frequency drives (VFD)50, as shown inFIG. 8. These VFDs50provide speed control to the vertically-elevating cab12. In another embodiment, as shown inFIG. 8, the drive motors34,36are equipped with encoders. In such an embodiment, the software of the computer54onboard the vertically-elevating cab12uses the encoder data to control the speed and position of the cab12by means of the VFDs50that control the power systems34,36associated with each respective lift screw20,22. This control system synchronizes the lift screws20,22, thereby assuring that the vertically-elevating cab12remains level throughout the entire range of motion of the cab12. The system can also provide for reduce speed zones at the top or bottom of the cab's range of travel or anywhere within such range. A reduced speed performance option may also be used to allow for very fine positioning of the cab12in a particular spot.